Energy Technology Data Exchange (ETDEWEB)
Nassif, Nabil [Florida Solar Energy Center, A Research Institute of the University of Center Florida, 1679 Clearlake Road, Cocoa, FL 32922 (United States)
2010-07-15
HVAC systems and associated equipment consume a relatively large fraction of total building energy consumption, a significant portion of which is attributed to fan operation. The operation of economizer dampers when installed can cause high energy consumption in fans if they are not functioning in proper and optimal manner. This will mainly be due to the potential high pressure drops through those dampers and associated high total pressures that should be developed by supply and/or return fans. It is then necessary to ensure that a proper strategy to operate optimally the economizer dampers is implemented with minimum fan energy use. The paper examines several operation strategies of the economizer dampers and investigates their effects on the performance of both the supply and return fans in HVAC system. It also discusses a new operating strategy for economizer dampers that can lead to lower fan energy use. The strategies are evaluated by simulations for a typically existing HVAC system. Several factors such as the building locations, system characteristics, resistance in the duct where the dampers are installed, supply air temperature and economizer control, and minimum ventilation requirements are also considered during the evaluations. The results show that the way of the economizer dampers been controlled has a significant effect on fan performance and its energy use. The proposed strategy if properly implemented can provide fan energy saving in the range of 5-30%, depending mainly on the number of hours when the system operates in the free cooling mode, damper characteristics, and minimum outdoor air. (author)
The importance of damper drive performance for clean air
International Nuclear Information System (INIS)
Wistrom, K.
2002-01-01
Amendments to the U.S. Federal Clean Air Act require petroleum refineries and other industries to examine every aspects of their process heating operations in order to reduce cumulative nitrogen oxide emissions from their plants. It has been found that changing the final damper control elements to more reliable and accurate damper drives greatly improves the combustion of air and flue gases and reduces tramp air from entering furnaces. This paper discusses the increasing importance of precise damper drives in nitrogen oxides reduction efforts, and the challenges involved in effecting good damper control. It also provides some technical details about final control drives, manufactured by TYPE K Damper Drives, a division of Controls International Inc., that thrive in environments of extreme temperatures, heavy vibration and fly ash, while providing continuous duty service with smooth, accurate and repeatable damper positioning. Case history of an Ontario oil refinery installing several damper drives designed by TYPE K, indicating high level of nitrogen oxides reduction is described to illustrate the importance and the advantages of damper control drives designed by this firm. In addition to meeting regulatory requirements, additional benefits include improved product quality and safety levels, combined with lower maintenance expenses. photos
Directory of Open Access Journals (Sweden)
Bikić Siniša M.
2016-01-01
Full Text Available This paper is focused on the mathematical model of the Air Torque Position dampers. The mathematical model establishes a link between the velocity of air in front of the damper, position of the damper blade and the moment acting on the blade caused by the air flow. This research aims to experimentally verify the mathematical model for the damper type with non-cascading blades. Four different types of dampers with non-cascading blades were considered: single blade dampers, dampers with two cross-blades, dampers with two parallel blades and dampers with two blades of which one is a fixed blade in the horizontal position. The case of a damper with a straight pipeline positioned in front of and behind the damper was taken in consideration. Calibration and verification of the mathematical model was conducted experimentally. The experiment was conducted on the laboratory facility for testing dampers used for regulation of the air flow rate in heating, ventilation and air conditioning systems. The design and setup of the laboratory facility, as well as construction, adjustment and calibration of the laboratory damper are presented in this paper. The mathematical model was calibrated by using one set of data, while the verification of the mathematical model was conducted by using the second set of data. The mathematical model was successfully validated and it can be used for accurate measurement of the air velocity on dampers with non-cascading blades under different operating conditions. [Projekat Ministarstva nauke Republike Srbije, br. TR31058
Response of air cleaning system dampers and blowers to simulated tornado transients
International Nuclear Information System (INIS)
Gregory, W.; Idar, E.; Smith, P.; Hensel, E.; Smith, E.
1985-01-01
The effects of tornado-like pressure transients upon dampers and blowers in nuclear air cleaning systems were studied. For the dampers pressure drop as a function of flow rate was obtained and an empirical relationship developed. Transient response was examined for several types of dampers, as was structural integrity. Both centrifugal and axi-vane blowers were tested and transient characteristic curves were generated in outrunning and backflow situations. The transient characteristic curves do not necessarily match the quasi-steady characteristic curves
Sun, Xiaoqiang; Yuan, Chaochun; Cai, Yingfeng; Wang, Shaohua; Chen, Long
2017-09-01
This paper presents the hybrid modeling and the model predictive control of an air suspension system with damping multi-mode switching damper. Unlike traditional damper with continuously adjustable damping, in this study, a new damper with four discrete damping modes is applied to vehicle semi-active air suspension. The new damper can achieve different damping modes by just controlling the on-off statuses of two solenoid valves, which makes its damping adjustment more efficient and more reliable. However, since the damping mode switching induces different modes of operation, the air suspension system with the new damper poses challenging hybrid control problem. To model both the continuous/discrete dynamics and the switching between different damping modes, the framework of mixed logical dynamical (MLD) systems is used to establish the system hybrid model. Based on the resulting hybrid dynamical model, the system control problem is recast as a model predictive control (MPC) problem, which allows us to optimize the switching sequences of the damping modes by taking into account the suspension performance requirements. Numerical simulations results demonstrate the efficacy of the proposed control method finally.
Dynamic Analysis of a Rotor System Supported on Squeeze Film Damper with Air Entrainment
Zhang, Wei; Han, Bingbing; Zhang, Kunpeng; Ding, Qian
2017-12-01
Squeeze film dampers (SFDs) are widely used in compressors and turbines to suppress the vibration while traversing critical speeds. In practical applications, air ingestion from the outside environment and cavitation may lead to a foamy lubricant that weakens oil film damping and dynamic performance of rotor system. In this paper, a rigid rotor model is established considering both lateral and pitching vibration under different imbalance excitations to evaluate the effect of air entrainment on rotor system. Tests with three different imbalances are carried out on a rotor-SFD apparatus. Volume controlled air in mixture ranging from pure oil to all air are supplied to the SFD. The transient response of rotor is measured in the experiments. The results show that two-phase flow produces significant influence on the system stability and dynamical response. The damping properties are weakened by entrained air, such as the damping on high frequency components of rolling ball bearing. Super-harmonic resonance and bifurcation are observed, as well as the low frequency components due to air entrainment.
The effect of air entrapment on the performance of squeeze film dampers: Experiments and analysis
Diaz Briceno, Sergio Enrique
Squeeze film dampers (SFDs) are an effective means to introduce the required damping in rotor-bearing systems. They are a standard application in jet engines and are commonly used in industrial compressors. Yet, lack of understanding of their operation has confined the design of SFDs to a costly trial and error process based on prior experience. The main factor deterring the success of analytical models for the prediction of SFDs' performance lays on the modeling of the dynamic film rupture. Usually, the cavitation models developed for journal bearings are applied to SFDs. Yet, the characteristic motion of the SFD results in the entrapment of air into the oil film, thus producing a bubbly mixture that can not be represented by these models. In this work, an extensive experimental study establishes qualitatively and---for the first time---quantitatively the differences between operation with vapor cavitation and with air entrainment. The experiments show that most operating conditions lead to air entrainment and demonstrate the paramount effect it has on the performance of SFDs, evidencing the limitation of currently available models. Further experiments address the operation of SFDs with controlled bubbly mixtures. These experiments bolster the possibility of modeling air entrapment by representing the lubricant as a homogeneous mixture of air and oil and provide a reliable data base for benchmarking such a model. An analytical model is developed based on a homogeneous mixture assumption and where the bubbles are described by the Rayleigh-Plesset equation. Good agreement is obtained between this model and the measurements performed in the SFD operating with controlled mixtures. A complementary analytical model is devised to estimate the amount of air entrained from the balance of axial flows in the film. A combination of the analytical models for prediction of the air volume fraction and of the hydrodynamic pressures renders promising results for prediction of the
Energy Technology Data Exchange (ETDEWEB)
Jianping Jing; Zhengqi Li; Guangkui Liu; Zhichao Chen; Chunlong Liu [Harbin Institute of Technology, Harbin (China). School of Energy Science and Engineering
2009-07-15
Measurements were performed on a 200 MWe, wall-fired, lignite utility boiler. For different overfire air (OFA) damper openings, the gas temperature, gas species concentration, coal burnout, release rates of components (C, H, and N), furnace temperature, and heat flux and boiler efficiency were measured. Cold air experiments for a single burner were conducted in the laboratory. The double-swirl flow pulverized-coal burner has two ring recirculation zones starting in the secondary air region in the burner. As the secondary air flow increases, the axial velocity of air flow increases, the maxima of radial velocity, tangential velocity and turbulence intensity all increase, and the swirl intensity of air flow and the size of recirculation zones increase slightly. In the central region of the burner, as the OFA damper opening widens, the gas temperature and CO concentration increase, while the O{sub 2} concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and coal particles ignite earlier. In the secondary air region of the burner, the O{sub 2} concentration, NOx concentration, coal burnout, and release rates of components (C, H, and N) decrease, and the gas temperature and CO concentration vary slightly. In the sidewall region, the gas temperature, O{sub 2} concentration, and NOx concentration decrease, while the CO concentration increases and the gas temperature varies slightly. The furnace temperature and heat flux in the main burning region decrease appreciably, but increase slightly in the burnout region. The NOx emission decreases from 1203.6 mg/m{sup 3} (6% O{sub 2}) for a damper opening of 0% to 511.7 mg/m{sup 3} (6% O{sub 2}) for a damper opening of 80% and the boiler efficiency decreases from 92.59 to 91.9%. 15 refs., 17 figs., 3 tabs.
Electromagnetic dampers for cryogenic applications
Brown, Gerald V.; Dirusso, Eliseo
1988-01-01
Cryogenic turbomachinery of the type used to pump high-pressure liquid hydrogen at -423 F and liquid oxygen at -297 F to the main engines of the Space Shuttle are subjected to lateral rotor vibrations from unbalance forces and transient loads. Conventional dampers which utilize viscous fluids such as lubricating oil cannot be used in turbopumps because the bearing components are filled with either liquid hydrogen or liquid oxygen, which have viscosity comparable to air and, therefore, are not effective in viscous dampers. Electromagentic dampers are currently being explored as a means of providing damping in cryogenic turbopumps because their damping effectiveness increases as temperature decreases and because they are compatible with the liquid hydrogen or liquid oxygen in the turbopumps.
Improvements for rotary viscous dampers used in spacecraft deployment mechanisms
Stewart, Alphonso; Powers, Charles; Lyons, Ron
1998-01-01
During component level thermal-vacuum deployment testing of eight rotary viscous dampers for the Tropical Rainfall Measuring Mission (TRMM) satellite, all the dampers failed to provide damping during a region of the deployment. Radiographic examination showed that air in the damping fluid caused the undamped motion when the dampers were operated in a vacuum environment. Improvements in the procedure used to fill the dampers with damping fluid, the installation of a Viton vacuum seal in the damper cover, and improved screening techniques eliminated the problem.
Appleberry, W. T.
1983-01-01
Standard hydraulic shock absorber modified to form coulomb (linear friction) damper. Device damps very small velocities and is well suited for use with large masses mounted on soft springs. Damping force is easily adjusted for different loads. Dampers are more reliable than fluid dampers and also more economical to build and to maintain.
Directory of Open Access Journals (Sweden)
Loktev Aleksey Alekseevich
2013-01-01
Full Text Available The authors present their findings associated with their modeling of a dynamic load damper. According to the authors, the damper is to be installed onto a structure or its element that may be exposed to impact, vibration or any other dynamic loading. The damper is composed of paralleled or consecutively connected viscous and elastic elements. The authors study the influence of viscosity and elasticity parameters of the damper produced onto the regular displacement of points of the structure to be protected and onto the regular acceleration transmitted immediately from the damper to the elements positioned below it.
Directory of Open Access Journals (Sweden)
Radu BOGATEANU
2009-09-01
Full Text Available The low frequency damper is an autonomous equipment for damping vibrations with the 1-20Hz range.Its autonomy enables the equipment to be located in various mechanical systems, without requiring special hydraulic installations.The low frequency damper was designed for damping the low frequency oscillations occurring in the circuit controls of the upgraded IAR-99 Aircraft.The low frequency damper is a novelty in the aerospace field ,with applicability in several areas as it can be built up in an appropriate range of dimensions meeting the requirements of different beneficiaries. On this line an equipment able to damp an extended frequency range was performed for damping oscillations in the pipes of the nuclear power plants.This damper, tested in INCAS laboratories matched the requirements of the beneficiary.The low frequency damper is patented – the patent no. 114583C1/2000 is held by INCAS.
1978-01-01
The proposed magnetically anchored viscous fluid damper can maintain the Skylab in a gravity-gradient stabilized mode at the anticipated reboost altitudes. The parameters influencing damper performance (and thereby affecting the degree of risk) are: (1) amount of skylab pitch bias in the orbit plane which will result from aerodynamic trim conditions of the post-reboost configuration Skylab; (2) the lowest altitude to which the post-reboost Skylab will be allowed to decay prior to the next rendezvous; (3) maximum allowable weight and size of the proposed damper in order to match shuttle/TRS mission constraints; (4) the amount of magnetic materials expected to be in the vicinity of the damper.
Kinetic analysis of elastomeric lag damper for helicopter rotors
Liu, Yafang; Wang, Jidong; Tong, Yan
2018-02-01
The elastomeric lag dampers suppress the ground resonance and air resonance that play a significant role in the stability of the helicopter. In this paper, elastomeric lag damper which is made from silicone rubber is built. And a series of experiments are conducted on this elastomeric lag damper. The stress-strain curves of elastomeric lag dampers employed shear forces at different frequency are obtained. And a finite element model is established based on Burgers model. The result of simulation and tests shows that the simple, linear model will yield good predictions of damper energy dissipation and it is adequate for predicting the stress-strain hysteresis loop within the operating frequency and a small-amplitude oscillation.
2010-07-01
... used in return air outby the last open crosscut; maximum level of alternating or direct electric... other in return air outby the last open crosscut, shall not exceed one ampere as determined from the... Electrical Equipment-General § 75.524 Electric face equipment; electric equipment used in return air outby...
Magnetorheological dampers in shear mode
International Nuclear Information System (INIS)
Wereley, N M; Cho, J U; Choi, Y T; Choi, S B
2008-01-01
In this study, three types of shear mode damper using magnetorheological (MR) fluids are theoretically analyzed: linear, rotary drum, and rotary disk dampers. The damping performance of these shear mode MR dampers is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping at field-on status to the damping at field-off status. For these three types of shear mode MR damper, the damping coefficient or dynamic range is derived using three different constitutive models: the Bingham–plastic, biviscous, and Herschel–Bulkley models. The impact of constitutive behavior on shear mode MR dampers is theoretically presented and compared
Energy Technology Data Exchange (ETDEWEB)
Walker, Iain [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Stratton, Chris [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
2015-08-01
This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The study team prepared a draft test method through ASTM International to determine the uncertainty of air flow measurements at residential heating ventilation and air conditioning returns and other terminals. This test method, when finalized, can be used by the Energy Commission and other entities to specify required accuracy of measurement devices used to show compliance with standards.
Laboratory Evaluation of Air Flow Measurement Methods for Residential HVAC Returns
Energy Technology Data Exchange (ETDEWEB)
Walker, Iain; Stratton, Chris
2015-07-01
This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The series of tests performed measured air flow using a range of techniques and devices. The measured air flows were compared to reference air flow measurements using inline air flow meters built into the test apparatus. The experimental results showed that some devices had reasonable results (typical errors of 5 percent or less) but others had much bigger errors (up to 25 percent).
LABORATORY EVALUATION OF AIR FLOW MEASUREMENT METHODS FOR RESIDENTIAL HVAC RETURNS
Energy Technology Data Exchange (ETDEWEB)
Walker, Iain; Stratton, Chris
2015-02-01
This project improved the accuracy of air flow measurements used in commissioning California heating and air conditioning systems in Title 24 (Building and Appliance Efficiency Standards), thereby improving system performance and efficiency of California residences. The research team at Lawrence Berkeley National Laboratory addressed the issue that typical tools used by contractors in the field to test air flows may not be accurate enough to measure return flows used in Title 24 applications. The team developed guidance on performance of current diagnostics as well as a draft test method for use in future evaluations. The series of tests performed measured air flow using a range of techniques and devices. The measured air flows were compared to reference air flow measurements using inline air flow meters built into the test apparatus. The experimental results showed that some devices had reasonable results (typical errors of 5 percent or less) but others had much bigger errors (up to 25 percent). Because manufacturers’ accuracy estimates for their equipment do not include many of the sources of error found in actual field measurements (and replicated in the laboratory testing in this study) it is essential for a test method that could be used to determine the actual uncertainty in this specific application. The study team prepared a draft test method through ASTM International to determine the uncertainty of air flow measurements at residential heating ventilation and air conditioning returns and other terminals. This test method, when finalized, can be used by the Energy Commission and other entities to specify required accuracy of measurement devices used to show compliance with standards.
Seismic Applications of Energy Dampers
Shambhu Sinha
2004-01-01
Damping devices based on the operating principle of high velocity fluid flow through orifices have found numerous applications in the shock and vibration isolation of aerospace and defence systems. The study aims to investigate the feasibility of using energy dissipating fluid viscous dampers in structures to protect against seismic loads and to prove analytically and experimentally that fluid viscous dampers can improve the seismic capacity of a structure by reducing damage and displacement...
Multiphysics modeling of magnetorheological dampers
Directory of Open Access Journals (Sweden)
D Case
2016-09-01
Full Text Available The dynamics of a small scale magnetorheological damper were modeled and analyzed using multiphysics commercial finite element software to couple the electromagnetic field distribution with the non-Newtonian fluid flow. The magnetic flux lines and field intensity generated within the damper and cyclic fluid flow in the damper under harmonic motion were simulated with the AC/DC and CFD physics modules of COMSOL Multiphysics, respectively. Coupling of the physics is achieved through a modified Bingham plastic definition, relating the fluid's dynamic viscosity to the intensity of the induced magnetic field. Good agreement is confirmed between simulation results and experimentally observed resistance forces in the damper. This study was conducted to determine the feasibility of utilizing magnetorheological dampers in a medical orthosis for pathological tremor attenuation. The implemented models are thus dimensioned on a relatively small scale. The method used, however, is not specific to the damper's size or geometry and can be extended to larger-scale devices with little or no complication.
Study on eliminating fire dampers to maintain process confinement
International Nuclear Information System (INIS)
Walling, R.C.; Patel, J.B.; Strunk, A.J.
1991-01-01
The DOE General Design Criteria for the Defense Waste Processing Facility (DWPF) at the Westinghouse Savannah River Site (WSRS) requires the NFPA National Fire Codes to be incorporated into the design and simultaneously maintain process confinement integrity to prevent the release of radioactivity. Although the NFPA Standard for the Installation of Air Conditioning and Ventilation Systems, NFPA 90, requires fire dampers (FD) in HVAC duct penetrations of two hour rated fire barriers, closure of fire dampers at DWPF may compromise the integrity of the process confinement system. This leads to the need for an overall risk assessment to determine the value of 39 fire dampers that are identified later in the study as capable of a confinement system upset
Optimal damper placement research
Smirnov, Vladimir; Kuzhin, Bulat
2017-10-01
Nowadays increased noise and vibration pollution on technopark and research laboratories territories, which is negatively influencing on production of high-precision measuring instruments. The problem is actual for transport hubs, which experience influence of machines, vehicles, trains and planes. Energy efficiency is one of major functions in modern road transport development. The problem of environmental pollution, lack of energy resources and energy efficiency requires research, production and implementation of energy efficient materials that would be the foundation of environmentally sustainable transport infrastructure in road traffic. Improving the efficiency of energy use is a leading option to gain better energy security, improve industry profitability and competitiveness, and reduce the overall energy sector impacts on climate change. This paper has next indirect goals. Research impact of vibration on constructions, such as bus and train stations, terminals, which are mostly exposed to oscillation. Extend the buildings operation by decreasing the negative influence. Reduce expenses on maintenance and repair works. It is important not to forget about seismic protection, which is actual nowadays, when the safety stands first. Analysis of devastating earthquakes for last few years proves reasonableness of application such systems. The article is dedicated to learning dependence of damper location on natural frequency. As a model for analyze was simulated concrete construction with variable profile. We used program complex Patran for analyzing the model.
Analysis of air return alternatives for CRS-type open volumetric receiver
International Nuclear Information System (INIS)
Marcos, Ma. Jesus; Romero, Manuel; Palero, Silvia
2004-01-01
Even though air-cooled receivers provide substantial benefits, such as low inertia and quick sun-following dispatchability, and the volumetric effect leads to designs with aperture areas similar to those used in molten salt or water/steam receivers, some concern persists regarding absorber durability, reduction of radiation losses and improvement of the air return ratio (ARR). The paper focuses on this last issue, since the ARR is a source of significant receiver losses in current designs. Today's scaled-up receivers claim values between 45 and 70% for ARR, which means, in terms of energy loss, between 5 and 15%. As a consequence of ARR and the radiation loss stemming from high working temperatures, open volumetric receivers efficiencies below 75% are reported at temperatures usable by the power block. Those values may be acceptable for a first demonstration plant, but are categorically not competitive for commercial schemes in which receiver efficiency should approach 90%. This paper discusses the impact of several geometrical properties of the absorber and air injection system used. The study was performed by CFD with the FLUENT code. The assessment considered such alternatives as modularity of the air return system (HITREC receiver concept), outer ring injection with air curtain effect or cavity aperture (with and without secondary concentrator). A detailed analysis reveals that some parts of the receiver aperture achieve an ARR above 90% at well-selected operating conditions, but average values hardly surpass 70%. Therefore, a careful design should keep in mind important variables such as the effects of receiver edge and lateral wind, as well as air injection angle
2010-07-01
... points; outby the last open crosscut; return air; permissibility requirements. 75.507-1 Section 75.507-1... other than power-connection points; outby the last open crosscut; return air; permissibility... permit for noncompliance may be used in return air outby the last open crosscut for the duration of such...
Adaptive tuning of elasto-plastic damper
DEFF Research Database (Denmark)
Høgsberg, Jan Riess; Krenk, Steen
2007-01-01
the damper parameter(s) with respect to the magnitude of the damper motion. The procedure is demonstrated in terms of the bilinear elasto-plastic damper model, and optimality corresponds to maximum modal damping. A parametric solution for the damping ratio is obtained by a two-component system reduction...
Dampers for Stationary Labyrinth Seals
El-Aini, Yehia; Mitchell, William; Roberts, Lawrence; Montgomery, Stuart; Davis, Gary
2011-01-01
Vibration dampers have been invented that are incorporated as components within the stationary labyrinth seal assembly. These dampers are intended to supplement other vibration-suppressing features of labyrinth seals in order to reduce the incidence of high-cycle-fatigue failures, which have been known to occur in the severe vibratory environments of jet engines and turbopumps in which labyrinth seals are typically used. A vibration damper of this type includes several leaf springs and/or a number of metallic particles (shot) all held in an annular seal cavity by a retaining ring. The leaf springs are made of a spring steel alloy chosen, in conjunction with design parameters, to maintain sufficient preload to ensure effectiveness of damping at desired operating temperatures. The cavity is vented via a small radial gap between the retaining ring and seal housing. The damping mechanism is complex. In the case of leaf springs, the mechanism is mainly friction in the slippage between the seal housing and individual dampers. In the case of a damper that contains shot, the damping mechanism includes contributions from friction between individual particles, friction between particles and cavity walls, and dissipation of kinetic energy of impact. The basic concept of particle/shot vibration dampers has been published previously; what is new here is the use of such dampers to suppress traveling-wave vibrations in labyrinth seals. Damping effectiveness depends on many parameters, including, but not limited to, coefficient of friction, mode shape, and frequency and amplitude of vibrational modes. In tests, preloads of the order of 6 to 15 lb (2.72 to 6.8 kilograms) per spring damper were demonstrated to provide adequate damping levels. Effectiveness of shot damping of vibrations having amplitudes from 20 to 200 times normal terrestrial gravitational acceleration (196 to 1,960 meters per square second) and frequencies up to 12 kHz was demonstrated for shot sizes from 0.032 to
Reduction of magneto rheological dampers stiffness by incorporating of an eddy current damper
Asghar Maddah, Ali; Hojjat, Yousef; Reza Karafi, Mohammad; Reza Ashory, Mohammad
2017-05-01
In this paper, a hybrid damper is developed to achieve lower stiffness compared to magneto rheological dampers. The hybrid damper consists of an eddy current damper (ECD) and a Magneto Rheological Damper (MRD). The aim of this research is to reduce the stiffness of MRDs with equal damping forces. This work is done by adding an eddy current passive damper to a semi-active MRD. The ECDs are contactless dampers which show an almost viscous damping behavior without increasing the stiffness of a system. However, MRDs increase damping and stiffness of a system simultaneously, when a magnetic field is applied. Damping of each part is studied theoretically and experimentally. A semi-empirical model is developed to explain the viscoelastic behavior of the damper. The experimental results showed that the hybrid damper is able to dissipate energy as much as those of MRDs while its stiffness is 12% lower at a zero excitation current.
Improved Coulomb-Friction Damper
Campbell, G. E.
1985-01-01
Equal damping provided on forward and reverse strokes. Improved damper has springs and wedge rings symmetrically placed on both ends of piston wedge, so friction force same in both directions of travel. Unlike conventional automotive shock absorbers, they resemble on outside, both versions require no viscous liquid and operate over wide temperature range.
High-Temperature Vibration Damper
Clarke, Alan; Litwin, Joel; Krauss, Harold
1987-01-01
Device for damping vibrations functions at temperatures up to 400 degrees F. Dampens vibrational torque loads as high as 1,000 lb-in. but compact enough to be part of helicopter rotor hub. Rotary damper absorbs energy from vibrating rod, dissipating it in turbulent motion of viscous hydraulic fluid forced by moving vanes through small orifices.
Theoretical and experimental study on dynamic responses of piping systems with combined dampers
International Nuclear Information System (INIS)
Gershtein, M.; Fridman, Ya.; Perelmiter, A.
1996-01-01
Vibrations of pipelines transporting fluids, gases, and granular materials are excited by the air flow, internal pressure pulsation, or seismic ground motion. The susceptibility of oil and gas pipelines to seismic damage has been demonstrated in earthquakes everywhere around the world. Devices for above-ground pipelines and piping systems vibration suppression with combination of dry friction and viscous energy dissipation are developed by AVIBRA, Shear deformation of viscous-elastic material in these devices occurs prior to interfacial slip. The way to account this phenomenon is to model the damper as an elastic-viscous element in series with an ideal Coulomb dry friction element. The harmonic balance method was applied to obtain an equivalent viscous damping constant for a combined damper. Iteration process was used to predict a dynamic response of a piping system with combined dampers subjected to sinusoidal excitation. Every iteration step was based on ANSYS procedures. Time integration of systems with hysteretic friction models presents computational difficulties. Some examples of dynamic responses of piping systems were analyzed by a time integration procedure for finite-element models. Combined dry friction-viscous dissipation dampers were tested on a piping model under harmonic excitation. It was clarified that combined dampers are very effective to reduce dynamic response. The seismic response of the piping system with combined dampers was calculated using time history finite-element analysis. The excellent effectiveness of AVIBRA combined dampers for aseismic design and retrofitting of pipelines and piping systems was confirmed by the analysis
Design method for fluid viscous dampers
Energy Technology Data Exchange (ETDEWEB)
Jia, Jiuhong; Hua, Hongxing [Shanghai Jiaotong University, State Key Laboratory of Mechanical System and Vibration, Shanghai (China); Du, Jianye; Wang, Yu [Naval Arming Academy, Institute of Naval Vessels, Beijing (China)
2008-09-15
A basic design method of doubly acting fluid viscous dampers with double guide bars is presented. The flow of the viscoelastic fluid between two parallel plates, one of which is started suddenly and the other of which is still, is analyzed. According to this solution, the velocity and the shear stress of the fluid at the fringe of the piston are solved approximately. A mathematical model of viscous dampers is derived, and the shock test is carried out. From experimental results, the parameters of the mathematical model are determined. Consequently, a semi-empirical design equation is obtained. Applying this equation to a certain practical damper, the damping material is chosen and the physical dimensions of the damper are determined. Shock tests using this damper are performed. Theoretical results are in good agreement with experimental results, which validates the reliability of the calculated physical dimensions of the specimen damper and the validity of the basic design equation. (orig.)
Shallow Water Tuned Liquid Dampers
DEFF Research Database (Denmark)
Krabbenhøft, Jørgen
that for realistic roughness parameters the bottom friction has very limited effect on the liquid sloshing behavior and can be neglected. Herby the postulate is verified. Based on the mathematical model three dimensionless parameters are derived showing that the response of the damper depends solely on ratio......The use of sloshing liquid as a passive means of suppressing the rolling motion of ships was proposed already in the late 19th century. Some hundred years later the use of liquid sloshing devices, often termed Tuned Liquid Dampers (TLD), began to find use in the civil engineering community....... The TLDs studied in this thesis essentially consist of a rectangular container partially filled with liquid in the form of plain tap water. The frequency of the liquid sloshing motion, which is adjusted by varying the length of the tank and the depth of the wa- ter, is tuned to the structural frequency...
Magneto-Rheological Damper - An Experimental Study
Lozoya-Santos , Jorge De-Jesus; Morales-Menéndez , Rubén; Ramirez-Mendoza , Ricardo; Tudon-Martınez , Juan ,; Sename , Olivier; Dugard , Luc
2012-01-01
International audience; A Magneto-Rheological (MR) damper is evaluated under exhaustive experimental scenarios, generating a complete database. The obtained database includes classical tests and new proposals emphasizing the frequency contents. It also includes the impact of the electric current fluctuations. The variety of the performed experiments allows to study the MR damper force dynamics. A brief description of the damper behavior and a categorization of experiments based on driving con...
Control strategies for friction dampers: numerical assessment and experimental investigations.
Coelho H.T.; Santos M.B.; Lepore Neto F.P.; Mahfoud J.
2014-01-01
The use of friction dampers has been proposed in a wide variety of mechanical systems for which it is not possible to apply viscoelastic materials, fluid based dampers or others viscous dampers. An important example is the application of friction dampers in aircraft engines to reduce the blades vibration amplitudes. In most cases, friction dampers have been studied in a passive way, however, a significant improvement can be achieved by controlling the normal force in the dampers. The aim of t...
Magnetorheological Damper Working in Squeeze Mode
Directory of Open Access Journals (Sweden)
Xinglong Gong
2014-05-01
Full Text Available This research is focused on evaluation of the magnetorheological fluids (MRFs based damper which works in squeeze mode. The operation direction of this damper is parallel to the direction of the external magnetic field. Before testing, commercial software ANSYS was used to analyze the magnetic field distribution inside the damper generated by charging current in the coil. The performance of the damper was tested by using the MTS809 (produced by MTS Systems Corporation, USA. For simulation of this damper, a mathematical model was set up. Experimental results showed that the small squeezed MR damper could produce large damping force; for example, the maximum damping force is nearly 6 kN, while the amplitude is 1.2 mm, the frequency is 1.0 Hz, and the current is 2.0 A, and the damping force was controllable by changing the current in the coil. The damping force versus displacement curves are complex. We divide them into four regions for simulation. The maximum damper force increased quickly with the increasing of the current in coil. This kind of damper can be used in vibration isolation for precise equipment.
Hybrid viscous damper with filtered integral force feedback control
DEFF Research Database (Denmark)
Høgsberg, Jan; Brodersen, Mark L.
2016-01-01
In hybrid damper systems active control devices are usually introduced to enhance the performance of otherwise passive dampers. In the present paper a hybrid damper concept is comprised of a passive viscous damper placed in series with an active actuator and a force sensor. The actuator motion...... is controlled by a filtered integral force feedback strategy, where the main feature is the filter, which is designed to render a damper force that in a phase-plane representation operates in front of the corresponding damper velocity. It is demonstrated that in the specific parameter regime where the damper...
Assessment of semi-active friction dampers
dos Santos, Marcelo Braga; Coelho, Humberto Tronconi; Lepore Neto, Francisco Paulo; Mafhoud, Jarir
2017-09-01
The use of friction dampers has been widely proposed for a variety of mechanical systems for which applying viscoelastic materials, fluid based dampers or other viscous dampers is impossible. An important example is the application of friction dampers in aircraft engines to reduce the blades' vibration amplitudes. In most cases, friction dampers have been studied in a passive manner, but significant improvements can be achieved by controlling the normal force in the contact region. The aim of this paper is to present and study five control strategies for friction dampers based on three different hysteresis cycles by using the Harmonic Balance Method (HBM), a numerical and experimental analysis. The first control strategy uses the friction force as a resistance when the system is deviating from its equilibrium position. The second control strategy maximizes the energy removal in each harmonic oscillation cycle by calculating the optimal normal force based on the last displacement peak. The third control strategy combines the first strategy with the homogenous modulation of the friction force. Finally, the last two strategies attempt to predict the system's movement based on its velocity and acceleration and our knowledge of its physical properties. Numerical and experimental studies are performed with these five strategies, which define the performance metrics. The experimental testing rig is fully identified and its parameters are used for numerical simulations. The obtained results show the satisfactory performance of the friction damper and selected strategy and the suitable agreement between the numerical and experimental results.
Evaluation of shear mounted elastomeric damper
Zorzi, E.; Walton, J.
1982-01-01
Viton-70 elastomeric shear mounted damper was built and tested on a T-55 power turbine spool in the rotor's high speed balancing rig. This application of a shear mounted elastomeric damper demonstrated for the first time, the feasibility of using elastomers as the primary rotor damping source in production turbine engine hardware. The shear damper design was selected because it was compatible with actual gas turbine engine radial space constraints, could accommodate both the radial and axial thrust loads present in gas turbine engines, and was capable of controlled axial preload. The shear damper was interchangeable with the production T-55 power turbine roller bearing support so that a direct comparison between the shear damper and the production support structure could be made. Test results show that the Viton-70 elastomer damper operated successfully and provided excellent control of both synchronous and nonsynchronous vibrations through all phases of testing up to the maximum rotor speed of 16,000 rpm. Excellent correlation between the predicted and experienced critical speeds, mode shapes and log decrements for the power turbine rotor and elastomer damper assembly was also achieved.
Energy Technology Data Exchange (ETDEWEB)
Neto, Jose H.M.; Azevedo, Walter L. [Centro Federal de Educacao Tecnologica de Minas Gerais (CEFET), Belo Horizonte, MG (Brazil). Dept. de Engenharia Mecanica]. E-mail: henrique@daem.des.cefetmg.br
2000-07-01
This work presents an algorithm control strategy denominated enthalpy economizer. The objective of this algorithm strategy is to determine the adequate fractions of outside and return air flowrates entering a cooling coil based on the analysis of the outside, return and supply air enthalpies, rather than on the analysis of the dry bulb temperatures. The proposed algorithm predicts the actual opening position of the outside and return air dampers in order to provide the lower mixing air enthalpy. First, the psychometrics properties of the outside and return air are calculated from actual measurements of the dry and wet bulb temperatures. Then, three distinct cases are analyzed: the enthalpy of the outside air is lower than the enthalpy of the supply air (free cooling); the enthalpy of the outside air is higher than the enthalpy of the return air; the enthalpy of the outside air is lower than the enthalpy of the return air and higher than the temperature of the supply air. Different outside air conditions were selected in order to represent typical weather data of Brazilians cities, as well as typical return air conditions. It was found that the enthalpy control strategy could promote an opportunity for energy savings mainly during mild nights and wintertime periods as well as during warm afternoons and summertime periods, depending on the outside air relative humidity. The proposed algorithm works well and can be integrated in some commercial automation software to reduce energy consumption and electricity demand. (author)
Waveguide harmonic damper for klystron amplifier
International Nuclear Information System (INIS)
Kang, Y.
1998-01-01
A waveguide harmonic damper was designed for removing the harmonic frequency power from the klystron amplifiers of the APS linac. Straight coaxial probe antennas are used in a rectangular waveguide to form a damper. A linear array of the probe antennas is used on a narrow wall of the rectangular waveguide for damping klystron harmonics while decoupling the fundamental frequency in dominent TE 01 mode. The klystron harmonics can exist in the waveguide as waveguide higher-order modes above cutoff. Computer simulations are made to investigate the waveguide harmonic damping characteristics of the damper
A numerical investigation into the effect of windvent dampers on operating conditions
Energy Technology Data Exchange (ETDEWEB)
Hughes, Ben Richard; Abdul Ghani, S.A.A. [Faculty of Arts, Computing, Engineering and Sciences, Materials and Engineering Institute, Sheffield Hallam University, Sheffield, South Yorkshire S1 1WB (United Kingdom)
2009-02-15
The United Kingdom has made a commitment to reduce buildings carbon emissions, placing a greater onus on sustainable energy sources. Therefore, an anticipated increase of usage of zero carbon technologies in new and existing building has led to the emergence of passive ventilation devices as an alternative to mechanical ventilation and air conditioning. The windvent is a commercially available passive ventilation device. The device is constructed from sheet metal and works on the principle of pressure differential. Whereby air rises, creating a low pressure in the receiving room, which then draws in the fresh air. The ensuing air delivery velocity is controlled by the dampers, installed at the room entry interface. The dampers are actuator operated, and form the basis of the control system for the device. The purpose of this paper is to investigate the control mechanism for the device and ascertain an optimum operating range. Numerical analysis is carried out using a commercial computational fluid dynamics (CFD) code, to investigate the effect of various damper angles (range 0-90 ). The results show that optimum operating occurs at a damper angle range of 45-55 , at the UK average 4.5 m/s external wind speed. The operating range when considered in tandem with macro climatic influences is central to determining the overall control strategy for the fresh air supply. The results provide useful information for both engineers and architects when examining ways to reduce new and existing buildings running costs, and conform to new legislation. (author)
A new controllable damper with neuro controller
International Nuclear Information System (INIS)
Kobayashi, N.; Kobayashi, H.; Saito, O.; Yokoi, R.; Morishita, S.
1993-01-01
A new controllable damper is proposed for suppressing the vibration of the piping system for wide frequency range. Electro-Rheological fluid (ER fluid) is enclosed in the damper casing in place of oil, and the apparent viscosity of ER fluid can be varied by applying electric field strength (E.F.S.), which is controlled by an adaptive neural network controller. The shaking test is conducted about a simplified L-shaped piping model with a prototype controllable damper. The test results show the effectiveness of the presented controllable damper for suppressing very small amplitude vibration of the piping system. Furthermore an application of neural network is discussed to control E.F.S. of the electrode. (author)
Modelling and Control of Magnetorheological Damper
DEFF Research Database (Denmark)
Bhowmik, Subrata
, used as reference case for assessment of the proposed control methods with negative stiffness. Viscous damping with negative stiffness (VDNS) initially illustrates the effectiveness of the negative stiffness component in structural damping. In a linear control setting negative stiffness requires active...... damper is identified by both the standard parametric Bouc-Wen model and the non-parametric neural network model from an experimental data set generated by dynamic tests of the MR damper mounted in a hydraulic testing machine. The forward model represents the direct dynamics of the MR damper where...... are essential input parameters for the MR damper modelling. Thus, for proper training, the quality of the velocity data is very important. However, direct velocity measurement is not easy. From the displacement data or the acceleration data, velocity can be determined by using simple differentiation...
Dynamic characteristics of stay cables with inerter dampers
Shi, Xiang; Zhu, Songye
2018-06-01
This study systematically investigates the dynamic characteristics of a stay cable with an inerter damper installed close to one end of a cable. The interest in applying inerter dampers to stay cables is partially inspired by the superior damping performance of negative stiffness dampers in the same application. A comprehensive parametric study on two major parameters, namely, inertance and damping coefficients, are conducted using analytical and numerical approaches. An inerter damper can be optimized for one vibration mode of a stay cable by generating identical wave numbers in two adjacent modes. An optimal design approach is proposed for inerter dampers installed on stay cables. The corresponding optimal inertance and damping coefficients are summarized for different damper locations and interested modes. Inerter dampers can offer better damping performance than conventional viscous dampers for the target mode of a stay cable that requires optimization. However, additional damping ratios in other vibration modes through inerter damper are relatively limited.
Dampers, fluidics and the failsafe fallacy [fire protection
International Nuclear Information System (INIS)
Dann, M.; Hodgson, T.
1989-01-01
The fire protection practices adopted at nuclear power stations generally follow the well established principles used throughout industry. Unfortunately, there is one particular area - the interaction with heating, ventilation and air conditioning (HVAC) services - where nuclear power stations pose a seemingly insoluble conflict: that between the need to contain and the need to ventilate. Now, however, solid state fire dampers using power fluidics may promise a solution. One of the key characteristics of a fluidic device is that it is 'solid state', i.e. it has no moving parts. Because of this, its inherent reliability is orders of magnitude greater than a mechanical device. (U.K.)
Damper modules with adapted stiffness ratio
Energy Technology Data Exchange (ETDEWEB)
Sonnenburg, R.; Stretz, A. [ZF Sachs AG, Entwicklungszentrum, Schweinfurt (Germany)
2011-07-15
A mechanism for the excitation of piston rod vibrations in automotive damper modules is discussed by a simple model. An improved nonlinear model based on elasticity effects leads to good simulation results. It is shown theoretically and experimentally that the adaptation of the stiffness of the piston rod bushing to the ''stiffness'' of the damper force characteristic can eliminate the piston rod oscillations completely. (orig.)
Gas Turbine Blade Damper Optimization Methodology
R. K. Giridhar; P. V. Ramaiah; G. Krishnaiah; S. G. Barad
2012-01-01
The friction damping concept is widely used to reduce resonance stresses in gas turbines. A friction damper has been designed for high pressure turbine stage of a turbojet engine. The objective of this work is to find out effectiveness of the damper while minimizing resonant stresses for sixth and ninth engine order excitation of first flexure mode. This paper presents a methodology that combines three essential phases of friction damping optimization in turbo-machinery. The first phase is to...
Damper mechanism for nuclear reactor control elements
International Nuclear Information System (INIS)
Taft, W.E.
1976-01-01
A damper mechanism which provides a nuclear reactor control element decelerating function at the end of the scram stroke is described. The total damping function is produced by the combination of two assemblies, which operate in sequence. First, a tapered dashram assembly decelerates the control element to a lower velocity, after which a spring hydraulic damper assembly takes over to complete the final damping. 3 claims, 2 figures
Results from the AGS Booster transverse damper
International Nuclear Information System (INIS)
Russo, D.; Brennan, M.; Meth, M.; Roser, T.
1993-01-01
To reach the design intensity of 1.5 x 10 13 protons per pulse in the AGS Booster, transverse coupled bunch instabilities with an estimated growth rate of 1500s -1 have to be dampened. A prototype transverse damper has been tested successfully using a one turn digital delay and closed orbit suppression implemented in a programmable gate array. An updated damper, which includes an algorithm to optimize damping for a changing betatron rune, will also be presented
Gas Turbine Blade Damper Optimization Methodology
Directory of Open Access Journals (Sweden)
R. K. Giridhar
2012-01-01
Full Text Available The friction damping concept is widely used to reduce resonance stresses in gas turbines. A friction damper has been designed for high pressure turbine stage of a turbojet engine. The objective of this work is to find out effectiveness of the damper while minimizing resonant stresses for sixth and ninth engine order excitation of first flexure mode. This paper presents a methodology that combines three essential phases of friction damping optimization in turbo-machinery. The first phase is to develop an analytical model of blade damper system. The second phase is experimentation and model tuning necessary for response studies while the third phase is evaluating damper performance. The reduced model of blade is developed corresponding to the mode under investigation incorporating the friction damper then the simulations were carried out to arrive at an optimum design point of the damper. Bench tests were carried out in two phases. Phase-1 deals with characterization of the blade dynamically and the phase-2 deals with finding optimal normal load at which the blade resonating response is minimal for a given excitation. The test results are discussed, and are corroborated with simulated results, are in good agreement.
Leak testing of bubble-tight dampers using tracer gas techniques
Energy Technology Data Exchange (ETDEWEB)
Lagus, P.L. [Lagus Applied Technology, Inc., San Diego, CA (United States); DuBois, L.J. [Commonwealth Edison, Zion, IL (United States); Fleming, K.M. [NCS Corporation, Columbus, OH (United States)] [and others
1995-02-01
Recently tracer gas techniques have been applied to the problem of measuring the leakage across an installed bubble-tight damper. A significant advantage of using a tracer gas technique is that quantitative leakage data are obtained under actual operating differential pressure conditions. Another advantage is that leakage data can be obtained using relatively simple test setups that utilize inexpensive materials without the need to tear ducts apart, fabricate expensive blank-off plates, and install test connections. Also, a tracer gas technique can be used to provide an accurate field evaluation of the performance of installed bubble-tight dampers on a periodic basis. Actual leakage flowrates were obtained at Zion Generating Station on four installed bubble-tight dampers using a tracer gas technique. Measured leakage rates ranged from 0.01 CFM to 21 CFM. After adjustment and subsequent retesting, the 21 CFM damper leakage was reduced to a leakage of 3.8 CFM. In light of the current regulatory climate and the interest in Control Room Habitability issues, imprecise estimates of critical air boundary leakage rates--such as through bubble-tight dampers--are not acceptable. These imprecise estimates can skew radioactive dose assessments as well as chemical contaminant exposure calculations. Using a tracer gas technique, the actual leakage rate can be determined. This knowledge eliminates a significant source of uncertainty in both radioactive dose and/or chemical exposure assessments.
Free vibration analysis of linear particle chain impact damper
Gharib, Mohamed; Ghani, Saud
2013-11-01
Impact dampers have gained much research interest over the past decades that resulted in several analytical and experimental studies being conducted in that area. The main emphasis of such research was on developing and enhancing these popular passive control devices with an objective of decreasing the three parameters of contact forces, accelerations, and noise levels. To that end, the authors of this paper have developed a novel impact damper, called the Linear Particle Chain (LPC) impact damper, which mainly consists of a linear chain of spherical balls of varying sizes. The LPC impact damper was designed utilizing the kinetic energy of the primary system through placing, in the chain arrangement, a small-sized ball between each two large-sized balls. The concept of the LPC impact damper revolves around causing the small-sized ball to collide multiple times with the larger ones upon exciting the primary system. This action is believed to lead to the dissipation of part of the kinetic energy at each collision with the large balls. This paper focuses on the outcome of studying the free vibration of a single degree freedom system that is equipped with the LPC impact damper. The proposed LPC impact damper is validated by means of comparing the responses of a single unit conventional impact damper with those resulting from the LPC impact damper. The results indicated that the latter is considerably more efficient than the former impact damper. In order to further investigate the LPC impact damper effective number of balls and efficient geometry when used in a specific available space in the primary system, a parametric study was conducted and its result is also explained herein. Single unit impact damper [14-16]. Multiunit impact damper [17,18]. Bean bag impact damper [19,20]. Particle/granular impact damper [21,23,22]. Resilient impact damper [24]. Buffered impact damper [25-27]. Multiunit impact damper consists of multiple masses instead of a single mass. This
Development of semi-active hydraulic damper as active interaction ...
Indian Academy of Sciences (India)
Semi-auto controller; displacement semi-active hydraulic damper; ... 2000), and Magnetorheological Damper (Dyke et al 1998) were widely discussed or used. ... driving force provided by electrical motor causes the subordinate structure to ...
Experimental investigation of nonlinear characteristics of a smart fluid damper
Rahman, Mahmudur; Ong, Zhi Chao; Chong, Wen Tong; Julai, Sabariah; Ahamed, Raju
2018-05-01
Smart fluids, known as smart material, are used to form controllable dampers in vibration control applications. Magnetorheological(MR) fluid damper is a well-known smart fluid damper which has a reputation to provide high damping force with low-power input. However, the force/velocity of the MR damper is significantly nonlinear and proper characteristic analysis are required to be studied for optimal implementation in structural vibration control. In this study, an experimental investigation is carried out to test the damping characteristics of MR damper. Dynamic testing is performed with a long-stroke MR damper model no RD-80410-1 from Lord corporation on a universal testing machine(UTM). The force responses of MR damper are measured under different stroke lengths, velocities and current inputs and their performances are analyzed. This study will play a key role to implement MR damper in many structural vibration control applications.
An Experimental Study on Steel and Teflon Squeeze Film Dampers
Directory of Open Access Journals (Sweden)
Asad A. Khalid
2006-01-01
Full Text Available In this paper, the vibration analysis on Teflon and steel squeeze film dampers has been carried out. At different frequency ranges, vibration amplitude and the resonance frequency are measured. The eccentricity ratio at resonance speed has been determined. Results show that the vibration amplitude of the steel damper is 10% less at resonance compared with the Teflon damper. On the other hand, saving weight of 36% has been achieved by using the Teflon damper.
Modelling of Dampers and Damping in Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Riess
2006-01-01
and the maximum attainable damping are found by maximizing the expression for the damping ratio. The theory is formulated for linear damper models, but may also be applied for non-linear dampers in terms of equivalent linear parameters for stiffness and damping, respectively. The format of the expressions......, and thereby the damping, of flexible structures are generally described in terms of the dominant vibration modes. A system reduction technique, where the damped vibration mode is constructed as a linear combination of the undamped mode shape and the mode shape obtained by locking the damper, is applied....... This two-component representation leads to a simple solution for the modal damping representing the natural frequency and the associated damping ratio. It appears from numerical examples that this system reduction technique provides very accurate results. % Analytical expressions for the optimal tuning...
The transverse damper system for RHIC
International Nuclear Information System (INIS)
Xu, J.; Claus, J.; Raka, E.; Ruggiero, A.G.; Shea, T.J.
1991-01-01
If the beam is injected with errors x c , x' c (or y c , y' c ) with respect to the closed orbit or disturbed by transverse instabilities, it will execute coherent oscillations and will be diluted in betatron phase space within a time interval of about 1/Δν turns, even if it is properly matched to the focusing characteristics of the lattice, unless there is an effective damper system to prevent this. Here Δν is the tune spread in the beam. Such a damper will not prevent dilution due to mismatches. Without such a damper the emittance of the beam will ultimately develop to a properly centered matched ellipse with an area ε in phase space that is larger than that of the injected one ε 0 which is also matched but off-centered by x c and x' c
Nonlinear Squeeze Film Dampers without Centralized Springs
Directory of Open Access Journals (Sweden)
Zhu Changsheng
2000-01-01
Full Text Available In this paper, the bifurcation behavior of a flexible rotor supported on nonlinear squeeze film dampers without centralized springs is analyzed numerically by means of rotor trajectories, Poincar maps, bifurcation diagrams and power spectra, based on the short bearing and cavitated film assumptions. It is shown that there also exist two different operations (i.e., socalled bistable operations in some speed regions in the rotor system supported on the nonlinear squeeze film dampers without centralized springs. In the bistable operation speed regions, the rotor system exhibits synchronous, sub-synchronous, sub-super-synchronous and almost-periodic as well as nonperiodic motions. The periodic bifurcation behaviors of the rotor system supported on nonlinear squeeze film dampers without centralized springs are very complex and require further investigations.
Learning from Local Wisdom: Friction Damper in Traditional Building
Directory of Open Access Journals (Sweden)
Pudjisuryadi P.
2012-01-01
Full Text Available Indonesia is situated in the so called “Ring of Fire” where earthquake are very frequent. Despite of all the engineering effort, due to the March 28, 2005 strong earthquake (8.7 on Richter scale a lot of modern buildings in Nias collapsed, while the traditional Northern Nias house (omohada survived without any damage. Undoubtedly many other traditional buildings in other area in Indonesia have survived similar earthquake. Something in common of the traditional building are the columns which usually are not fixed on the ground, but rest on top of flat stones. In this paper some traditional building are subjected to non linear time history analysis to artificial earthquake equivalent to 500 years return period earthquake. This study shows that apparently the columns which rest on top of flat stone acts as friction damper or base isolation. The presence of sliding at the friction type support significantly reduces the internal forces in the structure.
Using magnetorheological fluids in an innovative hybrid bicycle damper
International Nuclear Information System (INIS)
Shiao, Y J; Nguyen, T S
2015-01-01
Magnetorheological fluids are capable of changing their viscosity quickly. This can provide good controllability and fast dynamic response. A conventional passive suspension system with air spring or hydraulic damper has simple design and financial benefit for bicycles, but its operation is uncontrollable and non-adaptive. This paper presented a semi-active hybrid bicycle suspension system which combines conventional air spring and a new magnetorheological damping brake together to reduce vibration of a bicycle. A multi-layer magnetorheological brake and linkage mechanism are connected to bike fork to form the adaptive damping part of the innovative hybrid suspension system. The simulation results proved that the semi-active suspension system can reduce bike vibration effectively. (paper)
Development of models of the magnetorheological fluid damper
Energy Technology Data Exchange (ETDEWEB)
Kazakov, Yu.B., E-mail: elmash@em.ispu.ru; Morozov, N.A.; Nesterov, S.A., E-mail: sergeinesterov37@gmail.com
2017-06-01
The algorithm for analytical calculation of a power characteristic of magnetorheological (MR) dampers taking into account the rheological properties of MR fluid is considered. The nonlinear magnetorheological characteristics are represented by piecewise linear approximation to MR fluid areas with different viscosities. The extended calculated power characteristics of a MR damper are received and they coincide with actual results. The finite element model of a MR damper is developed; it allows carrying out the analysis of a MR damper taking into account the mutual influence of electromagnetic, hydrodynamic and thermal fields. The results of finite element simulation coincide with analytical solutions that allows using them for design development of a MR damper. - Highlights: • Division of a MR fluid rheological curve into two sections with different viscosities. • Algorithm for calculation of a power characteristic of MR dampers is proposed. • Finite element model of a MR damper is developed. • Results of finite element simulation coincide with analytical solutions.
Friction dampers, the positive side of friction
Lopez Arteaga, I.; Nijmeijer, H.; Busturia, J.M.; Sas, P.; Munck, de M.
2004-01-01
Friction is frequently seen as an unwanted phenomenon whose influence has to be either minimised or controlled. In this work one of the positive sides of friction is investigated: friction damping. Friction dampers can be a cheap and efficient way to reduce the vibration levels of a wide range of
Nonlinear Study of Industrial Arc Spring Dampers
DEFF Research Database (Denmark)
Lahriri, Said; Santos, Ilmar; Hartmann, Henning
2011-01-01
acting on the SFD are presented. It is worth mentioning, that the maps and diagrams can be used as design guidance. Finally, a comparison between the numerical results and experimental result is facilitated in form of waterfall diagrams. For this, a full scale model of the arc-spring damper was designed...
Warm damper for a superconducting rotor
International Nuclear Information System (INIS)
Hooper, G.D.
1984-01-01
A warm damper for a superconducting rotor is described which uses a laminar assembly of a conductive tube and a plurality of support tubes. The conductive tube is soldered to axially adjacent support tubes and the resulting composite tube is explosively welded to two or more support tubes disposed adjacent to its radially inner and outer surfaces
Energy based optimization of viscous–friction dampers on cables
International Nuclear Information System (INIS)
Weber, F; Boston, C
2010-01-01
This investigation optimizes numerically a viscous–friction damper connected to a cable close to one cable anchor for fastest reduction of the total mechanical cable energy during a free vibration decay test. The optimization parameters are the viscous coefficient of the viscous part and the ratio between the friction force and displacement amplitude of the friction part of the transverse damper. Results demonstrate that an almost pure friction damper with negligibly small viscous damping generates fastest cable energy reduction over the entire decay. The ratio between the friction force and displacement amplitude of the optimal friction damper differs from that derived from the energy equivalent optimal viscous damper. The reason for this is that the nonlinearity of the friction damper causes energy spillover from the excited to higher modes of the order of 10%, i.e. cables with attached friction dampers vibrate at several frequencies. This explains why the energy equivalent approach does not yield the optimal friction damper. Analysis of the simulation data demonstrates that the optimally tuned friction damper dissipates the same energy per cycle as if each modal component of the cable were damped by its corresponding optimal linear viscous damper
Magnetorheological fluid dampers: a review of parametric modelling
International Nuclear Information System (INIS)
Wang, D H; Liao, W H
2011-01-01
Due to the inherent nonlinear nature of magnetorheological (MR) dampers, one of the challenging aspects for developing and utilizing these devices to achieve high performance is the development of models that can accurately describe their unique characteristics. In this review, the characteristics of MR dampers are summarized according to the measured responses under different conditions. On these bases, the considerations and methods of the parametric dynamic modelling for MR dampers are given and the state-of-the-art parametric dynamic modelling, identification and validation techniques for MR dampers are reviewed. In the past two decades, the models for MR dampers have been focused on how to improve the modelling accuracy. Although the force–displacement behaviour is well represented by most of the proposed dynamic models for MR dampers, no simple parametric models with high accuracy for MR dampers can be found. In addition, the parametric dynamic models for MR dampers with on-line updating ability and the inverse parametric models for MR dampers are scarcely explored. Moreover, whether one dynamic model for MR dampers can portray the force–displacement and force–velocity behaviour is not only determined by the dynamic model itself but also determined by the identification method. (topical review)
A fully dynamic magneto-rheological fluid damper model
International Nuclear Information System (INIS)
Jiang, Z; Christenson, R E
2012-01-01
Control devices can be used to dissipate the energy of a civil structure subjected to dynamic loading, thus reducing structural damage and preventing failure. Semiactive control devices have received significant attention in recent years. The magneto-rheological (MR) fluid damper is a promising type of semiactive device for civil structures due to its mechanical simplicity, inherent stability, high dynamic range, large temperature operating range, robust performance, and low power requirements. The MR damper is intrinsically nonlinear and rate-dependent, both as a function of the displacement across the MR damper and the command current being supplied to the MR damper. As such, to develop control algorithms that take maximum advantage of the unique features of the MR damper, accurate models must be developed to describe its behavior for both displacement and current. In this paper, a new MR damper model that includes a model of the pulse-width modulated (PWM) power amplifier providing current to the damper, a proposed model of the time varying inductance of the large-scale 200 kN MR dampers coils and surrounding MR fluid—a dynamic behavior that is not typically modeled—and a hyperbolic tangent model of the controllable force behavior of the MR damper is presented. Validation experimental tests are conducted with two 200 kN large-scale MR dampers located at the Smart Structures Technology Laboratory (SSTL) at the University of Illinois at Urbana-Champaign and the Lehigh University Network for Earthquake Engineering Simulation (NEES) facility. Comparison with experimental test results for both prescribed motion and current and real-time hybrid simulation of semiactive control of the MR damper shows that the proposed MR damper model can accurately predict the fully dynamic behavior of the large-scale 200 kN MR damper. (paper)
Digital active material processing platform effort (DAMPER), SBIR phase 2
Blackburn, John; Smith, Dennis
1992-11-01
Applied Technology Associates, Inc., (ATA) has demonstrated that inertial actuation can be employed effectively in digital, active vibration isolation systems. Inertial actuation involves the use of momentum exchange to produce corrective forces which act directly on the payload being actively isolated. In a typical active vibration isolation system, accelerometers are used to measure the inertial motion of the payload. The signals from the accelerometers are then used to calculate the corrective forces required to counteract, or 'cancel out' the payload motion. Active vibration isolation is common technology, but the use of inertial actuation in such systems is novel, and is the focus of the DAMPER project. A May 1991 report was completed which documented the successful demonstration of inertial actuation, employed in the control of vibration in a single axis. In the 1 degree-of-freedom (1DOF) experiment a set of air bearing rails was used to suspend the payload, simulating a microgravity environment in a single horizontal axis. Digital Signal Processor (DSP) technology was used to calculate in real time, the control law between the accelerometer signals and the inertial actuators. The data obtained from this experiment verified that as much as 20 dB of rejection could be realized by this type of system. A discussion is included of recent tests performed in which vibrations were actively controlled in three axes simultaneously. In the three degree-of-freedom (3DOF) system, the air bearings were designed in such a way that the payload is free to rotate about the azimuth axis, as well as translate in the two horizontal directions. The actuator developed for the DAMPER project has applications beyond payload isolation, including structural damping and source vibration isolation. This report includes a brief discussion of these applications, as well as a commercialization plan for the actuator.
Study on coupled shock absorber system using four electromagnetic dampers
International Nuclear Information System (INIS)
Fukumori, Y; Hayashi, R; Okano, H; Suda, Y; Nakano, K
2016-01-01
Recently, the electromagnetic damper, which is composed of an electric motor, a ball screw, and a nut, was proposed. The electromagnetic damper has high responsiveness, controllability, and energy saving performance. It has been reported that it improved ride comfort and drivability. In addition, the authors have proposed a coupling method of two electromagnetic dampers. The method enables the characteristics of bouncing and rolling or pitching motion of a vehicle to be tuned independently. In this study, the authors increase the number of coupling of electromagnetic dampers from two to four, and propose a method to couple four electromagnetic dampers. The proposed method enables the characteristics of bouncing, rolling and pitching motion of a vehicle to be tuned independently. Basic experiments using proposed circuit and motors and numerical simulations of an automobile equipped with the proposed coupling electromagnetic damper are carried out. The results indicate the proposed method is effective. (paper)
Performance of a viscous damper using electro-rheological fluid
International Nuclear Information System (INIS)
Otani, A.; Kobayashi, H.; Kobayashi, N.; Tadaishi, Y.
1994-01-01
A new damper has been developed that suppresses small-amplitude vibrations over a wide frequency range. The damper has been tested using both an electro-rheological fluid (ERF) and a highly viscous liquid, which are enclosed in the damper's casing (a metal bellows). The apparent viscosity of the ERF can be changed by varying the strength of the applied electrical field. Initially, a simple L-shaped piping model excited by a rotary-type exciter was used to investigate the performance of the damper, utilizing both fluids. The experimental results demonstrate the effectiveness of the passive damper. Based on the experimental results, application of the damper to an actual piping system with a big pump was carried out analytical
A Novel Double-Piston Magnetorheological Damper for Space Truss Structures Vibration Suppression
Qiang Wang; Mehdi Ahmadian; Zhaobo Chen
2014-01-01
The design, fabrication, and testing of a new double-piston MR damper for space applications are discussed. The design concept for the damper is described in detail. The electromagnetic analysis of the design and the fabrication of the MR damper are also presented. The design analysis shows that the damper meets the weight and size requirements for being included in a space truss structure. The prototype design is tested in a damper dynamometer. The test results show that the damper can provi...
The partially filled viscous ring damper.
Alfriend, K. T.
1973-01-01
The problem of a spinning satellite with a partially filled viscous ring damper is investigated. It is shown that there are two distinct modes of motion, the nutation-synchronous mode and spin-synchronous mode. From an approximate solution of the equations of motion a time constant is obtained for each mode. From a consideration of the fluid dynamics several methods are developed for determining the damping constant.
The LHC Transverse Damper (ADT) Performance Specification
Boussard, Daniel; Linnecar, Trevor Paul R; CERN. Geneva. SPS and LEP Division
1997-01-01
The appended document specifies the performance of the transverse damper (ADT) for the LHC. As Annex 1 of the Addendum No.1 to the Protocol of April 18, 1997; it forms part of the 1992 co-operation agreement between CERN and JINR (Dubna, Russia) concerning its participation in the LHC project. The current text is a reprint of the original version. Changes that have been agreed upon are inserted as footnotes.
BNL 56 MHz HOM Damper Prototype Fabrication at JLab
Energy Technology Data Exchange (ETDEWEB)
Huque, Naeem A. [Jefferson Lab., Newport News, VA (United States); Daly, Edward F. [Jefferson Lab., Newport News, VA (United States); Clemens, William A. [Jefferson Lab., Newport News, VA (United States); McIntyre, Gary T. [Brookhaven National Lab. (BNL), Upton, NY (United States); Wu, Qiong [Brookhaven National Lab. (BNL), Upton, NY (United States); Seberg, Scott [Brookhaven National Lab. (BNL), Upton, NY (United States); Bellavia, Steve [Brookhaven National Lab. (BNL), Upton, NY (United States)
2015-09-01
A prototype Higher-Order Mode (HOM) Damper was fabricated at JLab for the Relativistic Heavy-Ion Collider's (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL). Primarily constructed from high RRR Niobium and Sapphire, the coaxial damper presented significant challenges in electron-beam welding (EBW), brazing and machining via acid etching. The results of the prototype operation brought about changes in the damper design, due to overheating braze alloys and possible multi-pacting. Five production HOM dampers are currently being fabricated at JLab. This paper outlines the challenges faced in the fabrication process, and the solutions put in place.
Stochastic seismic response of building with super-elastic damper
Gur, Sourav; Mishra, Sudib Kumar; Roy, Koushik
2016-05-01
Hysteretic yield dampers are widely employed for seismic vibration control of buildings. An improved version of such damper has been proposed recently by exploiting the superelastic force-deformation characteristics of the Shape-Memory-Alloy (SMA). Although a number of studies have illustrated the performance of such damper, precise estimate of the optimal parameters and performances, along with the comparison with the conventional yield damper is lacking. Presently, the optimal parameters for the superelastic damper are proposed by conducting systematic design optimization, in which, the stochastic response serves as the objective function, evaluated through nonlinear random vibration analysis. These optimal parameters can be employed to establish an initial design for the SMA-damper. Further, a comparison among the optimal responses is also presented in order to assess the improvement that can be achieved by the superelastic damper over the yield damper. The consistency of the improvements is also checked by considering the anticipated variation in the system parameters as well as seismic loading condition. In spite of the improved performance of super-elastic damper, the available variant of SMA(s) is quite expensive to limit their applicability. However, recently developed ferrous SMA are expected to offer even superior performance along with improved cost effectiveness, that can be studied through a life cycle cost analysis in future work.
Cycle energy control of magnetorheological dampers on cables
International Nuclear Information System (INIS)
Weber, F; Feltrin, G; Motavalli, M; Distl, H
2009-01-01
The dissipated cycle energy of magnetorheological (MR) dampers operated at constant current results from controllable hysteretic damping and from almost current independent, small viscous damping. Thus, the emulation of Coulomb friction and linear viscous damping necessitates current modulation during one vibration cycle and therefore current drivers. To avoid this drawback, a cycle energy control (CEC) approach is presented which controls the hysteretic MR damper part such that the total MR damper energy equals the energy of optimal linear viscous damping by constant current during one cycle. The excited higher modes due to the hysteretic damping part are partially damped by the MR damper viscous part. Simulations show that CEC copes better with damper force dynamics and constraints than emulated linear viscous damping due to the slow control force dynamics of CEC which are given by cable amplitude dynamics. It is demonstrated that CEC of MR dampers with viscosity of approximately 4.65% of the optimal modal viscosity performs better than optimal linear viscous damping. The reason is that this damper viscosity represents an optimal compromise between maximum energy spillover to higher modes due to the controllable hysteretic part which produces more cable damping and maximum viscous damping of these higher modes. Damping tests on a cable with an MR damper validate the CEC approach
Modeling and control of magnetorheological fluid dampers using neural networks
Wang, D. H.; Liao, W. H.
2005-02-01
Due to the inherent nonlinear nature of magnetorheological (MR) fluid dampers, one of the challenging aspects for utilizing these devices to achieve high system performance is the development of accurate models and control algorithms that can take advantage of their unique characteristics. In this paper, the direct identification and inverse dynamic modeling for MR fluid dampers using feedforward and recurrent neural networks are studied. The trained direct identification neural network model can be used to predict the damping force of the MR fluid damper on line, on the basis of the dynamic responses across the MR fluid damper and the command voltage, and the inverse dynamic neural network model can be used to generate the command voltage according to the desired damping force through supervised learning. The architectures and the learning methods of the dynamic neural network models and inverse neural network models for MR fluid dampers are presented, and some simulation results are discussed. Finally, the trained neural network models are applied to predict and control the damping force of the MR fluid damper. Moreover, validation methods for the neural network models developed are proposed and used to evaluate their performance. Validation results with different data sets indicate that the proposed direct identification dynamic model using the recurrent neural network can be used to predict the damping force accurately and the inverse identification dynamic model using the recurrent neural network can act as a damper controller to generate the command voltage when the MR fluid damper is used in a semi-active mode.
Control strategies for friction dampers: numerical assessment and experimental investigations.
Directory of Open Access Journals (Sweden)
Coelho H.T.
2014-01-01
Full Text Available The use of friction dampers has been proposed in a wide variety of mechanical systems for which it is not possible to apply viscoelastic materials, fluid based dampers or others viscous dampers. An important example is the application of friction dampers in aircraft engines to reduce the blades vibration amplitudes. In most cases, friction dampers have been studied in a passive way, however, a significant improvement can be achieved by controlling the normal force in the dampers. The aim of this paper is to study three control strategies for friction dampers based on the hysteresis cycle. The first control strategy maximizes the energy removal in each harmonic oscillation cycle, by calculating the optimum normal force based on the last displacement peak. The second control strategy combines the first one with the maximum energy removal strategy used in the smart spring devices. Finally, is presented the strategy which homogenously modulates the friction force. Numerical studies were performed with these three strategies defining the performance metrics. The best control strategy was applied experimentally. The experimental test rig was fully identified and its parameters were used for the numerical simulations. The obtained results show the good performance for the friction damper and the selected strategy.
Broadband Liquid Dampers to Stabilize Flexible Spacecraft Structures
Kuiper, J.M.
2012-01-01
Mass-spring and liquid dampers enable structural vibration control to attenuate single, coupled lateral and torsional vibrations in diverse structures. Out of these, the passively tuned liquid damper (TLD) class is wanted due to its broad applicability, extreme reliability, robustness, long life
A design strategy for magnetorheological dampers using porous valves
International Nuclear Information System (INIS)
Hu, W; Robinson, R; Wereley, N M
2009-01-01
To design a porous-valve-based magnetorheological (MR) damper, essential design parameters are presented. The key elements affecting the damper performance are identified using flow analysis in porous media and an empirical magnetic field distribution in the porous valve. Based on a known MR fluid, the relationship between the controllable force of the damper and the porous valve characteristics, i.e. porosity and tortuosity, is developed. The effect of the porosity and tortuosity on the field-off damping force is exploited by using semi-empirical flow analysis. The critical flow rate for the onset of nonlinear viscous damping force is determined. Using the above design elements, an MR damper using by-pass porous valve is designed and tested. The experimental damper force and equivalent damping are compared with the predicted results to validate this design strategy.
Flow Mode Magnetorheological Dampers with an Eccentric Gap
Directory of Open Access Journals (Sweden)
Young-Tai Choi
2014-07-01
Full Text Available This paper analyzes flow mode magnetorheological (MR dampers with an eccentric annular gap (i.e., a nonuniform annular gap. To this end, an MR damper analysis for an eccentric annular gap is constructed based on approximating the eccentric annular gap using a rectangular duct with a variable gap, as well as a Bingham-plastic constitutive model of the MR fluid. Performance of flow mode MR dampers with an eccentric gap was assessed analytically using both field-dependent damping force and damping coefficient, which is the ratio of equivalent viscous field-on damping to field-off damping. In addition, damper capabilities of flow mode MR dampers with an eccentric gap were compared to a concentric gap (i.e., uniform annular gap.
A design strategy for magnetorheological dampers using porous valves
Energy Technology Data Exchange (ETDEWEB)
Hu, W; Robinson, R; Wereley, N M [Smart Structures Laboratory, Alfred Gessow Rotorcraft Center, Department of Aerospace Engineering, University of Maryland, College Park, MD 20742 (United States)], E-mail: wereley@umd.edu
2009-02-01
To design a porous-valve-based magnetorheological (MR) damper, essential design parameters are presented. The key elements affecting the damper performance are identified using flow analysis in porous media and an empirical magnetic field distribution in the porous valve. Based on a known MR fluid, the relationship between the controllable force of the damper and the porous valve characteristics, i.e. porosity and tortuosity, is developed. The effect of the porosity and tortuosity on the field-off damping force is exploited by using semi-empirical flow analysis. The critical flow rate for the onset of nonlinear viscous damping force is determined. Using the above design elements, an MR damper using by-pass porous valve is designed and tested. The experimental damper force and equivalent damping are compared with the predicted results to validate this design strategy.
International Nuclear Information System (INIS)
Weber, F; Boston, C; Maślanka, M
2011-01-01
This paper presents a new adaptive tuned mass damper (TMD) whose stiffness and damping can be tuned in real-time to changing frequencies of a target structure. The adaptive TMD consists of a tuned mass, a tuned passive spring and a magnetorheological (MR) damper. The MR damper is used to emulate controlled friction–viscous damping and controlled stiffness. The controlled positive or negative stiffness emulated by the MR damper works in parallel to the stiffness of the passive TMD spring. The resulting overall TMD stiffness can therefore be varied around the passive spring stiffness using the MR damper. Both the emulated stiffness and friction–viscous damping in the MR damper are controlled such that the resulting overall TMD stiffness and damping are adjusted according to Den Hartog's formulae. Simulations demonstrate that the adaptive TMD with a controlled MR damper provides the same reduction of steady state vibration amplitudes in the target structure as a passive TMD if the target structure vibrates at the nominal frequency. However, if the target structure vibrates at different frequencies, e.g. due to changed service loads, the adaptive TMD with a controlled MR damper outperforms the passive TMD by up to several 100% depending on the frequency change
The use of platform dampers to reduce turbine blade vibrations
Energy Technology Data Exchange (ETDEWEB)
Jareland, Martin H.
2001-07-01
Friction damping is commonly used in jet engines to reduce the vibration level of the blades and thereby increase the reliability of the engine. This thesis deals with a specific type of friction damper denoted platform damper, which is frequently used in turbine stages. A platform damper is a piece of metal located in a cavity underneath two adjacent blade platforms. It is pressed against the platforms by centrifugal force and friction forces arise in the contacts when a relative motion between the platforms occurs. In this thesis, a number of phenomena regarding platform dampers are investigated and discussed. This is performed both experimentally and theoretically. In the simulations, friction interface models valid for both macroslip and microslip are used. Macroslip means that slipping occurs in the whole contact interface and microslip means that slipping occurs in only part of the interface. The latter is most likely in the contacts between the platform damper and the blade platforms due to the high normal force and the small motions. The first paper deals with mistuning of bladed disks due to variations in the properties of the platform dampers and the closely related topic wear of the dampers. This study indicates that damper mistuning can greatly affect the blade vibrations and that damper and blade mistuning constitutes a more severe case than blade mistuning alone. It is also found that wear of the contact areas can lead either to an increase or decrease in the resonance amplitude of the blades in the studied configuration. In the second paper, so-called cottage-roof dampers are studied. Cottage-roof dampers are a type of platform damper with inclined contact surfaces. The inclination leads to a varying normal load, which complicates the analysis. A model including this effect is presented and simulations are performed both in the time and frequency domain. A parametric study is performed with the aim of finding the optimal damper design with respect to
DEFF Research Database (Denmark)
Bhowmik, Subrata
2011-01-01
This paper presents a neural network based semi-active control method for a rotary type magnetorheological (MR) damper. The characteristics of the MR damper are described by the classic Bouc-Wen model, and the performance of the proposed control method is evaluated in terms of a base exited shear...... to determine the damper current based on the derived optimal damper force. For that reason an inverse MR damper model is also designed based on the neural network identification of the particular rotary MR damper. The performance of the proposed controller is compared to that of an optimal pure viscous damper...
Study on the development of passive MR damper with displacement-dependent damping characteristics
International Nuclear Information System (INIS)
Murakami, Takahiro; Sakai, Michiya; Nakano, Masami
2010-01-01
In this paper, we propose a new concept of a magneto-rheological (MR) fluid damper, which is a passive MR fluid damper. The passive MR damper has no electrical devices, such as a sensor, power supply and controller, and hence, it has an advantage in reliability and cost compared with semi-active MR dampers. Moreover, the proposed MR damper can be designed to have a variable damping force in response to its displacement. In this paper, the dynamic performance of the passive MR damper is experimentally demonstrated. The prototype of the proposed damper has been manufactured in order to verify the dynamic performance. The displacement excitation test result of the damper demonstrates that the damping characteristics depend on its displacement amplitude, that is, the damper behaves as a linear viscous damper under small vibrations and develops much higher damping performance under large vibrations. (author)
The effect of friction in coulombian damper
Wahad, H. S.; Tudor, A.; Vlase, M.; Cerbu, N.; Subhi, K. A.
2017-02-01
The study aimed to analyze the damping phenomenon in a system with variable friction, Stribeck type. Shock absorbers with limit and dry friction, is called coulombian shock-absorbers. The physical damping vibration phenomenon, in equipment, is based on friction between the cushioning gasket and the output regulator of the shock-absorber. Friction between them can be dry, limit, mixture or fluid. The friction is depending on the contact pressure and lubricant presence. It is defined dimensionless form for the Striebeck curve (µ friction coefficient - sliding speed v). The friction may damp a vibratory movement or can maintain it (self-vibration), depending on the µ with v (it can increase / decrease or it can be relative constant). The solutions of differential equation of movement are obtained for some work condition of one damper for automatic washing machine. The friction force can transfer partial or total energy or generates excitation energy in damper. The damping efficiency is defined and is determined analytical for the constant friction coefficient and for the parabolic friction coefficient.
Advanced damper with negative structural stiffness elements
International Nuclear Information System (INIS)
Dong, Liang; Lakes, Roderic S
2012-01-01
Negative stiffness is understood as the occurrence of a force in the same direction as the imposed deformation. Structures and composites with negative stiffness elements enable a large amplification in damping. It is shown in this work, using an experimental approach, that when a flexible flat-ends column is aligned in a post-buckled condition, a negative structural stiffness and large hysteresis (i.e., high damping) can be achieved provided the ends of the column undergo tilting from flat to edge contact. Stable axial dampers with initial modulus equivalent to that of the parent material and with enhanced damping were designed and built using constrained negative stiffness effects entailed by post-buckled press-fit flat-ends columns. Effective damping of approximately 1 and an effective stiffness–damping product of approximately 1.3 GPa were achieved in such stable axial dampers consisting of PMMA columns. This is a considerable improvement for this figure of merit (i.e., the stiffness–damping product), which generally cannot exceed 0.6 GPa for currently used damping layers. (paper)
Londono, J.M.; Wagg, D.; Neild, S.A.
2014-01-01
Viscous fluid dampers have proved to be effective in suppressing unwanted vibrations in a range of engineering structures. When dampers are fitted in a structure, a brace is typically used to attach them to the main structure. The stiffness of this brace can significantly alter the effectiveness of the damper, and in structures with multiple dampers, this can be a complex scenario to model. In this paper, we demonstrate that the effects of the brace compliance on the damper performance can be...
Response of ventilation dampers to large airflow pulses
International Nuclear Information System (INIS)
Gregory, W.S.; Smith, P.R.
1985-04-01
The results of an experiment program to evaluate the response of ventilation system dampers to simulated tornado transients are reported. Relevant data, such as damper response time, flow rate and pressure drop, and flow/pressure vs blade angle, were obtained, and the response of one tornado protective damper to simulated tornado transients was evaluated. Empirical relationships that will allow the data to be integrated into flow dynamics codes were developed. These flow dynamics codes can be used by safety analysts to predict the response of nuclear facility ventilation systems to tornado depressurization. 3 refs., 21 figs., 6 tabs
Flow Mode Magnetorheological Dampers with an Eccentric Gap
Young-Tai Choi; Norman M. Wereley
2014-01-01
This paper analyzes flow mode magnetorheological (MR) dampers with an eccentric annular gap (i.e., a nonuniform annular gap). To this end, an MR damper analysis for an eccentric annular gap is constructed based on approximating the eccentric annular gap using a rectangular duct with a variable gap, as well as a Bingham-plastic constitutive model of the MR fluid. Performance of flow mode MR dampers with an eccentric gap was assessed analytically using both field-dependent damping force and dam...
Study on lead extrusion damper as a seismic support
International Nuclear Information System (INIS)
Nomura, T.; Kojima, N.; Fujita, K.; Ito, T.
1989-01-01
The fundamental characteristics of two types of lead extrusion dampers (cylinder type, rotary type) for use as the nuclear power plant piping support of the elasto-plastic of damper are clarified. As a result, these lead extrusion dampers are found to have the following dynamic characteristics: hysteresis loop is both rectangular shape and bi-linear shape; maximum reaction force is independent of velocity and frequency but it increases as displacement exceeds the specified value; and the dissipated energy is very large and is independent of velocity, frequency and initial displacement (i.e., thermal expansion of pipings) in the range of test
LHC Damper Beam commissioning in 2010
Höfle, W; Schokker, M; Valuch, D
2011-01-01
The LHC transverse dampers were commissioned in 2010 with beam and their use at injection energy of 450 GeV, during the ramp and in collisions at 3.5 TeV for Physics has become part of the standard operations pro- cedure. The system proved important to limit emittance blow-up at injection and to maintain smaller than nominal emittances throughout the accelerating cycle. We describe the commissioning of the system step-by-step as done in 2010 and summarize its performance as achieved for pro- ton as well as ion beams in 2010. Although its principle function is to keep transverse oscillations under control, the system has also been used as an exciter for abort gap clean- ing and tune measurement. The dedicated beam position measurement system with its low noise properties provides additional possibilities for diagnostics.
Optimization analysis of a new vane MRF damper
Energy Technology Data Exchange (ETDEWEB)
Zhang, J Q; Feng, Z Z; Jing, Q [Department of Technical Support Engineering, Academy of Armored Force Engineering, Beijing, 100072 (China)], E-mail: zhangjq63@yahoo.com.cn
2009-02-01
The primary purpose of this study was to provide the optimization analysis certain characteristics and benefits of a vane MRF damper. Based on the structure of conventional vane hydraulic damper for heavy vehicle, a narrow arc gap between clapboard and rotary vane axle, which one rotates relative to the other, was designed for MRF valve and the mathematical model of damping was deduced. Subsequently, the finite element analysis of electromagnetic circuit was done by ANSYS to perform the optimization process. Some ways were presented to augment the damping adjustable multiple under the condition of keeping initial damping forces and to increase fluid dwell time through the magnetic field. The results show that the method is useful in the design of MR dampers and the damping adjustable range of vane MRF damper can meet the requirement of heavy vehicle semi-active suspension system.
Simulation and experiemntal study on damper by accumulator
International Nuclear Information System (INIS)
Wang Xiaobin; Zhou Yong; Chen Wuxing; Hu Junhua
2010-01-01
In order to prevent stressing penstocks broken by earthquake or other shock waves, dampers are used widely in nuclear power plant or pipelines transporting radioactive material. A new-style damper by accumulator is introduced. Inside the damper an accumulator is installed, the outward corrugated tubes are added outside the piston rod. So it has advantages of small volume, no oil leakage. The simulation and experimental research show that if the clearance between the piston and cylinder, the spring stiffness of accumulator or the throttle valve size is varied, the dynamic performance of the impact displacement, resistance in low velocity and lock-up velocity of dampe would be influenced. The support of nuclear classified pipelines can be satisfied by using this new-style accumulator damper. (authors)
The Effective Design of Bean Bag as a Vibroimpact Damper
Directory of Open Access Journals (Sweden)
A.Q. Liu
2000-01-01
Full Text Available The technique of a bean bag damper has been effectively applied in many engineering fields to control the vibroimpact of a structural system. In this study, the basic parameters responsible for the design of an effective bean bag: the size of beans, the mass ratio of the bean bag to the structure to which it is attached, the clearance distance and the position of the bag, are studied by both theoretical and experimental analyses. These will provide a better understanding of the performance of the bean bag for optimisation of damper design. It was found that reducing the size of beans would increase the exchange of momentum in the system due to the increase in the effective contact areas. Within the range of mass ratios studied, the damping performance of the damper was found to improve with higher mass ratios. There was an optimum clearance for any specific damper whereby the maximum attenuation could be achieved. The position of the bag with respect to nodes and antipodes of the primary structure determined the magnitude of attenuation attainable. Furthermore, the limitations of bean bags have been identified and a general criteria for the design of a bean bag damper has been formulated based on the study undertaken. It was shown that an appropriately configured bean bag damper was capable of reducing the amplitude of vibration by 80% to 90%.
Energy Technology Data Exchange (ETDEWEB)
Hino, H; Hotta, M [Nippon Light Metal Co. Ltd., Tokyo (Japan); Maeda, Y; Shimizu, H [Fukoku Co. Ltd., Saitama (Japan)
1997-10-01
We have developed a welded aluminum viscous damper to improve the joining strength between the case and the cover of the conventional damper mechanically fastened by adhesion. The distortion of the welded damper was decreased to an acceptable level using the high speed MIG welding process. Sound quality and good appearance were obtained by optimizing the initial speed of the filler wire and by controlling the welding conditions at the starting part and in the lap part. The leakage load and the fatigue limit of the welded damper were 5 and 10 times those of the conventional damper, respectively. 3 refs., 15 figs.
International Nuclear Information System (INIS)
Savornin, J.; Laborde, J.C.
1989-10-01
In nuclear facilities, where unacceptable quantities of radioactive aerosols could be spread in the event of a fire, the ventilation system must be designed so that an underpressure is maintained under such circumstances. This is the reason why the extracting ventilation of the room in which the fire has broken out has generally to be kept going as long as possible. This prevents smoke and radioactive aerosols from spreading to accessways and adjacent rooms. Consequently, the various devices of the ventilation network need to have high fire resistance. Fire dampers can be applied to exhaust air to delay the heat build-up of a major fire. Specialized qualification testing is required for these dampers. The criteria we have used as a basis for specifying the required qualities of installations are defined. The tests that have been performed, or are now in progress, are described. The results obtained so far are given. Devices and arrangements are suggested
Modeling impact damper in building frames using GAP element
Directory of Open Access Journals (Sweden)
Seyed Mehdi Zahrai
2017-05-01
Full Text Available Main effective factor in impact dampers to control vibration is to create disruption in structural oscillation amplitude using small forces induced by auxiliary masses to reduce strong vibrations. So far, modeling of the impact damper has been conducted solely through MATLAB software. Naturally, the functional aspects of this software are limited in research and development aspects compared to the common programs such as SAP2000 and ETABS. In this paper, a Single Degree of Freedom System, SDOF, is first modeled under harmonic loading with maximum amplitude of 0.4g in SAP2000 program. Then, the results are compared with numerical model. In this way, the proposed model is validated and the SDOF system equipped with an impact damper is investigated under the Kobe and Northridge earthquake records using SAP2000 model. Based on obtained results, the system equipped with an impact damper under the Kobe and Northridge earthquakes for structures considered in this study would have better seismic performance in which maximum displacements are reduced 6% and 33% respectively. Finally, impact dampers are modeled in a 4-story building structure with concentric bracing leading to 12% reduction in story drifts.
Vibration power generator for a linear MR damper
International Nuclear Information System (INIS)
Sapiński, Bogdan
2010-01-01
The paper describes the structure and the results of numerical calculations and experimental tests of a newly developed vibration power generator for a linear magnetorheological (MR) damper. The generator consists of permanent magnets and coil with foil winding. The device produces electrical energy according to Faraday's law of electromagnetic induction. This energy is applied to vary the damping characteristics of the MR damper attached to the generator by the input current produced by the device. The objective of the numerical calculations was to determine the magnetic field distribution in the generator as well as the electric potential and current density in the generator's coil during the idle run and under the load applied to the MR damper control coil. The results of the calculations were used during the design and manufacturing stages of the device. The objective of the experimental tests carried out on a dynamic testing machine was to evaluate the generator's efficiency and to compare the experimental and predicted data. The experimental results demonstrate that the engineered device enables a change in the kinetic energy of the reciprocal motion of the MR damper which leads to variations in the damping characteristics. That is why the generator may be used to build up MR damper based vibration control systems which require no external power
A novel model of magnetorheological damper with hysteresis division
Yu, Jianqiang; Dong, Xiaomin; Zhang, Zonglun
2017-10-01
Due to the complex nonlinearity of magnetorheological (MR) behavior, the modeling of MR dampers is a challenge. A simple and effective model of MR damper remains a work in progress. A novel model of MR damper is proposed with force-velocity hysteresis division method in this study. A typical hysteresis loop of MR damper can be simply divided into two novel curves with the division idea. One is the backbone curve and the other is the branch curve. The exponential-family functions which capturing the characteristics of the two curves can simplify the model and improve the identification efficiency. To illustrate and validate the novel phenomenological model with hysteresis division idea, a dual-end MR damper is designed and tested. Based on the experimental data, the characteristics of the novel curves are investigated. To simplify the parameters identification and obtain the reversibility, the maximum force part, the non-dimensional backbone part and the non-dimensional branch part are derived from the two curves. The maximum force part and the non-dimensional part are in multiplication type add-rule. The maximum force part is dependent on the current and maximum velocity. The non-dominated sorting genetic algorithm II (NSGA II) based on the design of experiments (DOE) is employed to identify the parameters of the normalized shape functions. Comparative analysis is conducted based on the identification results. The analysis shows that the novel model with few identification parameters has higher accuracy and better predictive ability.
Experimental Study of Hysteretic Steel Damper for Energy Dissipation Capacity
Directory of Open Access Journals (Sweden)
Daniel R. Teruna
2015-01-01
Full Text Available This study aims to evaluate energy absorption capacity of hysteretic steel damper for earthquake protection of structures. These types of steel dampers are fabricated from mild steel plate with different geometrical shapes on the side part, namely, straight, concave, and convex shapes. The performance of the proposed device was verified experimentally by a series of tests under increasing in-plane cyclic load. The overall test results indicated that the proposed steel dampers have similar hysteretic curves, but the specimen with convex-shaped side not only showed stable hysteretic behavior but also showed excellent energy dissipation capabilities and ductility factor. Furthermore, the load-deformation relation of these steel dampers can be decomposed into three parts, namely, skeleton curve, Bauschinger part, and elastic unloading part. The skeleton curve is commonly used to obtain the main parameters, which describe the behavior of steel damper, namely, yield strength, elastic stiffness, and postyield stiffness ratio. Moreover, the effective stiffness, effective damping ratio, cumulative plastic strain energy, and cumulative ductility factor were also derived from the results. Finally, an approximation trilinear hysteretic model was developed based on skeleton curve obtained from experimental results.
Modeling and analysis of a novel planar eddy current damper
Zhang, He; Kou, Baoquan; Jin, Yinxi; Zhang, Lu; Zhang, Hailin; Li, Liyi
2014-05-01
In this paper, a novel 2-DOF permanent magnet planar eddy current damper is proposed, of which the stator is made of a copper plate and the mover is composed of two orthogonal 1-D permanent magnet arrays with a double sided structure. The main objective of the planar eddy current damper is to provide two orthogonal damping forces for dynamic systems like the 2-DOF high precision positioning system. Firstly, the basic structure and the operating principle of the planar damper are introduced. Secondly, the analytical model of the planar damper is established where the magnetic flux density distribution of the permanent magnet arrays is obtained by using the equivalent magnetic charge method and the image method. Then, the analytical expressions of the damping force and damping coefficient are derived. Lastly, to verify the analytical model, the finite element method (FEM) is adopted for calculating the flux density and a planar damper prototype is manufactured and thoroughly tested. The results from FEM and experiments are in good agreement with the ones from the analytical expressions indicating that the analytical model is reasonable and correct.
Optimizing of the higher order mode dampers in the 56MHz SRF cavity
International Nuclear Information System (INIS)
Wu, Q.; Ben-Zvi, I.
2010-01-01
Earlier, we reported that a 56 MHz cavity was designed for a luminosity upgrade of the RHIC, and presented the requirements for Higher Order Mode (HOM) damping, the design of the HOM dampers, along with measurements and simulations of the HOM dampers. In this report, we describe our optimization of the dampers performance, and the modifications we made to their original design. We also optimized the number of the HOM dampers, and tested different configurations of locations for them.
DEFF Research Database (Denmark)
Bhowmik, Subrata; Weber, Felix; Høgsberg, Jan Becker
2013-01-01
This paper presents a systematic design and training procedure for the feed-forward backpropagation neural network (NN) modeling of both forward and inverse behavior of a rotary magnetorheological (MR) damper based on experimental data. For the forward damper model, with damper force as output...
Darlow, M.; Zorzi, E.
1981-01-01
A comprehensive guide for the design of elastomer dampers for application in rotating machinery is presented. Theoretical discussions, a step by step procedure for the design of elastomer dampers, and detailed examples of actual elastomer damper applications are included. Dynamic and general physical properties of elastomers are discussed along with measurement techniques.
A nonlinear auxetic structural vibration damper with metal rubber particles
International Nuclear Information System (INIS)
Ma, Yanhong; Zhang, Dayi; Zhu, Bin; Chen, Lulu; Hong, Jie; Scarpa, Fabrizio
2013-01-01
The work describes the mechanical performance of a metal rubber particles (MRP) damper design based on an auxetic (negative Poisson’s ratio) cellular configuration. The auxetic damper configuration is constituted by an anti-tetrachiral honeycomb, where the cylinders are filled with the MRP material. The MRP samples have been subjected to quasi-static loading to measure the stiffness and loss factor from the static hysteresis curve. A parametric experimental analysis has been carried out to investigate the effect of relative density and filling percentage on the static performance of the MRP, and to identify design guidelines for best use of MRP devices. An experimental assessment of the integrated auxetic-MRP damper concept has been provided through static and dynamic force response techniques. (paper)
Evaluation of dampers using a resonance adhesion tester
Directory of Open Access Journals (Sweden)
Stanislav Koláček
2013-01-01
Full Text Available This paper describes the diagnostics of dampers using resonant adhesion tester. This kind of test is non-invasive and evaluation is based on the EUSAMA methodology. The main goals of this method were to practically measure and evaluate technical condition of the shock absorbers. However, this method does not measure only damper properties, but the whole axle, too. During measurements, one must take into account the fact that the results can be easily influenced by external factors. These include e.g. wrong tire pressure, different kind of shock absorbers, and tires. The actual testing revealed that the measurement results are also influenced by bad condition of the vehicle axles. If we eliminate all these draw-backs, dampers testing can be very accurate.
Force Feedback Control Method of Active Tuned Mass Damper
Directory of Open Access Journals (Sweden)
Xiuli Wang
2017-01-01
Full Text Available Active tuned mass dampers as vibration-control devices are widely used in many fields for their good stability and effectiveness. To improve the performance of such dampers, a control method based on force feedback is proposed. The method offers several advantages such as high-precision control and low-performance requirements for the actuator, as well as not needing additional compensators. The force feedback control strategy was designed based on direct-velocity feedback. The effectiveness of the method was verified in a single-degree-of-freedom system, and factors such as damping effect, required active force, actuator stroke, and power consumption of the damper were analyzed. Finally, a simulation study was performed by configuring a main complex elastic-vibration-damping system. The results show that the method provides effective control over modal resonances of multiple orders of the system and improves its dynamics performance.
DARHT-II Injector Transients and the Ferrite Damper
Energy Technology Data Exchange (ETDEWEB)
Waldron, Will; Reginato, Lou; Chow, Ken; Houck, Tim; Henestroza, Enrique; Yu, Simon; Kang, Michael; Briggs, Richard
2006-08-04
This report summarizes the transient response of the DARHT-II Injector and the design of the ferrite damper. Initial commissioning of the injector revealed a rise time excited 7.8 MHz oscillation on the diode voltage and stalk current leading to a 7.8 MHz modulation of the beam current, position, and energy. Commissioning also revealed that the use of the crowbar to decrease the voltage fall time excited a spectrum of radio frequency modes which caused concern that there might be significant transient RF electric field stresses imposed on the high voltage column insulators. Based on the experience of damping the induction cell RF modes with ferrite, the concept of a ferrite damper was developed to address the crowbar-excited oscillations as well as the rise-time-excited 7.8 MHz oscillations. After the Project decided to discontinue the use of the crowbar, further development of the concept focused exclusively on damping the oscillations excited by the rise time. The design was completed and the ferrite damper was installed in the DARHT-II Injector in February 2006. The organization of this report is as follows. The suite of injector diagnostics are described in Section 2. The data and modeling of the injector transients excited on the rise-time and also by the crowbar are discussed in Section 3; the objective is a concise summary of the present state of understanding. The design of the ferrite damper, and the small scale circuit simulations used to evaluate the ferrite material options and select the key design parameters like the cross sectional area and the optimum gap width, are presented in Section 4. The details of the mechanical design and the installation of the ferrite damper are covered in Section 5. A brief summary of the performance of the ferrite damper following its installation in the injector is presented in Section 6.
Graphene nanoribbon as an elastic damper
Evazzade, Iman; Lobzenko, Ivan P.; Saadatmand, Danial; Korznikova, Elena A.; Zhou, Kun; Liu, Bo; Dmitriev, Sergey V.
2018-05-01
Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.
Invention of a tunable damper for use with an acoustic waveguide in hostile environments
International Nuclear Information System (INIS)
Rogers, S.C.
1984-06-01
A damper was invented to remove undesirable stress pulses from an acoustic waveguide. Designed to be tunable, the damper was constructed to withstand a corrosive or otherwise hostile environment. It serves to simplify the design and enhance the performance of a water-level measurement system, of which the damper and acoustic waveguide are integral parts. An experimental damper was constructed and applied to an existing level probe and measurement system. The resulting damper, properly tuned, causes acoustic stress pulses that pass into it along the waveguide to be attenuated
Edgewise vibration control of wind turbine blades using roller and liquid dampers
DEFF Research Database (Denmark)
Zhang, Zili; Nielsen, Søren R.K.
2014-01-01
suppressing edgewise vibrations. The roller dampers are more volumetrically efficient due to the higher mass density of the steel comparing with the liquid. On the other hand, TLCDs have their advantage that it is easier to specify the optimum damping of the damper by changing the opening ratio of the orifice......This paper deals with the passive vibration control of edgewise vibrations by means of roller dampers and tuned liquid column dampers (TLCDs). For a rotating blade, the large centrifugal acceleration makes it possible to use roller dampers or TLCDs with rather small masses for effectively...
Alfriend, K. T.
1973-01-01
A ring partially filled with a viscous fluid has been analyzed as a nutation damper for a spinning satellite. The fluid has been modelled as a rigid slug of finite length moving in a tube and resisted by a linear viscous force. It is shown that there are two distinct modes of motion, called the spin synchronous mode and the nutation synchronous mode. Time constants for each mode are obtained for both the symmetric and asymmetric satellite. The effects of a stop in the tube and an offset of the ring from the spin axis are also investigated. An analysis of test results is also given including a determination of the effect of gravity on the time constants in the two modes.
Ventilation air conditioner for a reactor container
International Nuclear Information System (INIS)
Ikegame, Noboru; Nakagawa, Takeshi.
1980-01-01
Purpose: To suppress the variations in the internal pressure of a reactor container and smoothly ventilate the reactor container. Constitution: The air conditioner provides an air-flow-rate-control damper, a purge-air supply fan, and a filter device in the air-supply pipe of a reactor container. Furthermore, it provides a pressure difference detector at a part of the container. The air-flow-rate-control damper is connected electrically through a position-modulator-comparison amplifier to the pressure difference detector. When the filtration becomes insufficient by clogging of the filter device and the internal pressure increased abruptly in the container, the pressure-difference detector can detect it, and the damper is operated by a pressure regulator and the comparator so as to control the air flow to the container. Thus, the internal pressure variation is controlled so as to easily ventilate the container. (J.P.N.)
Feasibility study of a large-scale tuned mass damper with eddy current damping mechanism
Wang, Zhihao; Chen, Zhengqing; Wang, Jianhui
2012-09-01
Tuned mass dampers (TMDs) have been widely used in recent years to mitigate structural vibration. However, the damping mechanisms employed in the TMDs are mostly based on viscous dampers, which have several well-known disadvantages, such as oil leakage and difficult adjustment of damping ratio for an operating TMD. Alternatively, eddy current damping (ECD) that does not require any contact with the main structure is a potential solution. This paper discusses the design, analysis, manufacture and testing of a large-scale horizontal TMD based on ECD. First, the theoretical model of ECD is formulated, then one large-scale horizontal TMD using ECD is constructed, and finally performance tests of the TMD are conducted. The test results show that the proposed TMD has a very low intrinsic damping ratio, while the damping ratio due to ECD is the dominant damping source, which can be as large as 15% in a proper configuration. In addition, the damping ratios estimated with the theoretical model are roughly consistent with those identified from the test results, and the source of this error is investigated. Moreover, it is demonstrated that the damping ratio in the proposed TMD can be easily adjusted by varying the air gap between permanent magnets and conductive plates. In view of practical applications, possible improvements and feasibility considerations for the proposed TMD are then discussed. It is confirmed that the proposed TMD with ECD is reliable and feasible for use in structural vibration control.
Effect of nonlinearity of connecting dampers on vibration control of connected building structures
Directory of Open Access Journals (Sweden)
Masatoshi eKasagi
2016-01-01
Full Text Available The connection of two building structures with dampers is one of effective vibration control systems. In this vibration control system, both buildings have to possess different vibration properties in order to provide a higher vibration reduction performance. In addition to such condition of different vibration properties of both buildings, the connecting dampers also play an important role in the vibration control mechanism. In this paper, the effect of nonlinearity of connecting dampers on the vibration control of connected building structures is investigated in detail. A high-damping rubber damper and an oil damper with and without relief mechanism are treated. It is shown that, while the high-damping rubber damper is effective in a rather small deformation level, the linear oil damper is effective in a relatively large deformation level. It is further shown that, while the oil dampers reduce the response in the same phase as the case without dampers, the high-damping rubber dampers change the phase. The merit is that the high-damping rubber can reduce the damper deformation and keep the sufficient space between both buildings. This can mitigate the risk of building pounding.
Enhanced damping for bridge cables using a self-sensing MR damper
Chen, Z. H.; Lam, K. H.; Ni, Y. Q.
2016-08-01
This paper investigates enhanced damping for protecting bridge stay cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.
Optimal design of nuclear mechanical dampers with analytical hierarchy process
International Nuclear Information System (INIS)
Zou Yuehua; Wen Bo; Xu Hongxiang; Qin Yonglie
2000-01-01
An optimal design with analytical hierarchy process on nuclear mechanical dampers manufactured by authors' university was described. By using fuzzy judgement matrix the coincidence was automatically satisfied without the need of coincidence test. The results obtained by this method have been put into the production practices
A new adaptive hybrid electromagnetic damper: modelling, optimization, and experiment
International Nuclear Information System (INIS)
Asadi, Ehsan; Ribeiro, Roberto; Behrad Khamesee, Mir; Khajepour, Amir
2015-01-01
This paper presents the development of a new electromagnetic hybrid damper which provides regenerative adaptive damping force for various applications. Recently, the introduction of electromagnetic technologies to the damping systems has provided researchers with new opportunities for the realization of adaptive semi-active damping systems with the added benefit of energy recovery. In this research, a hybrid electromagnetic damper is proposed. The hybrid damper is configured to operate with viscous and electromagnetic subsystems. The viscous medium provides a bias and fail-safe damping force while the electromagnetic component adds adaptability and the capacity for regeneration to the hybrid design. The electromagnetic component is modeled and analyzed using analytical (lumped equivalent magnetic circuit) and electromagnetic finite element method (FEM) (COMSOL ® software package) approaches. By implementing both modeling approaches, an optimization for the geometric aspects of the electromagnetic subsystem is obtained. Based on the proposed electromagnetic hybrid damping concept and the preliminary optimization solution, a prototype is designed and fabricated. A good agreement is observed between the experimental and FEM results for the magnetic field distribution and electromagnetic damping forces. These results validate the accuracy of the modeling approach and the preliminary optimization solution. An analytical model is also presented for viscous damping force, and is compared with experimental results The results show that the damper is able to produce damping coefficients of 1300 and 0–238 N s m −1 through the viscous and electromagnetic components, respectively. (paper)
On the nonlinear design of industrial arc spring dampers
DEFF Research Database (Denmark)
Lahriri, Said; Santos, Ilmar; Hartmann, Henning
2011-01-01
The objective of this paper is to present a numerical approach for analyzing parameter excited vibrations on a gas compressor, induced by the nonlinear characteristic of the arc spring feature of certain designs of squeeze film dampers, SFDs. The behavior of the journal is studied in preparation...
A gun recoil system employing a magnetorheological fluid damper
International Nuclear Information System (INIS)
Li, Z C; Wang, J
2012-01-01
This research aims to design and control a full scale gun recoil buffering system which works under real firing impact loading conditions. A conventional gun recoil absorber is replaced with a controllable magnetorheological (MR) fluid damper. Through dynamic analysis of the gun recoil system, a theoretical model for optimal design and control of the MR fluid damper for impact loadings is derived. The optimal displacement, velocity and optimal design rules are obtained. By applying the optimal design theory to protect against impact loadings, an MR fluid damper for a full scale gun recoil system is designed and manufactured. An experimental study is carried out on a firing test rig which consists of a 30 mm caliber, multi-action automatic gun with an MR damper mounted to the fixed base through a sliding guide. Experimental buffering results under passive control and optimal control are obtained. By comparison, optimal control is better than passive control, because it produces smaller variation in the recoil force while achieving less displacement of the recoil body. The optimal control strategy presented in this paper is open-loop with no feedback system needed. This means that the control process is sensor-free. This is a great benefit for a buffering system under impact loading, especially for a gun recoil system which usually works in a harsh environment. (paper)
Modelling and Experimental Investigation of an Active Damper
Directory of Open Access Journals (Sweden)
Rafael Luís Teixeira
2006-01-01
Full Text Available This paper presents a validation methodology of the dynamic behavior of an active viscous damper. The damper has two flexible metallic bellows connected to a rigid reservoir filled with fluid. When one of the bellows is connected to a vibrating structure a periodic flow passes through a variable internal orifice and the damping effect is produced. The size of the orifice is adjusted by a controlled linear piezoelectric actuator that positions the conical core into a conical cavity. The device finite element structural model consists of the valve body and its conical core that are assumed rigid and the flexible bellows are represented by two pistons with elastic suspensions. The flow developed inside the damper is modeled considering the fluid-structure interation, using the Lagrangean-Eulerian formulation. To validate the proposed model a prototype was constructed and experimental tests and numerical simulations are accomplished in the time domain, applying harmonic excitations. The results are compared using curves that relate the damping coefficient with the orifice size and with the input velocity applied at the bellows face. However, for the proper control design and system operation, the direct use of the finite element model becomes unviable due to its high computational time. Then, a reduced second order discrete dynamic model for the damper was developed. The model parameters are identified by analysis in the frequency domain, using impulsive excitation force, for constant and variable orifice sizes. At low excitation frequencies, the damper prototype behaves like a single degree of freedom system which damping factor changes with the orifice size A fuzzy controller was designed and it generates the orifice reference size associated to the desired damping factor. The active system presented better performance when compared to the passive one.
A Novel Double-Piston Magnetorheological Damper for Space Truss Structures Vibration Suppression
Directory of Open Access Journals (Sweden)
Qiang Wang
2014-01-01
Full Text Available The design, fabrication, and testing of a new double-piston MR damper for space applications are discussed. The design concept for the damper is described in detail. The electromagnetic analysis of the design and the fabrication of the MR damper are also presented. The design analysis shows that the damper meets the weight and size requirements for being included in a space truss structure. The prototype design is tested in a damper dynamometer. The test results show that the damper can provide nearly 80 N of damping force at its maximum velocity and current. The test results also show that the seal drag could contribute significantly to the damping forces. Additionally, the test results indicate that both the work by the damper and damping force increase rapidly with increasing current at lower currents and taper off at higher currents as the damper starts to saturate. The damper force versus velocity plots show hysteresis in both pre- and postyield regions and asymmetric forces in jounce and rebound. A model is proposed for representing the force-displacement, force-velocity, and asymmetric forces observed in test results. A comparison of the modeling results and test data indicates that the model accurately represents the force characteristics of the damper.
Experimental Study of under-platform Damper Kinematics in Presence of Blade Dynamics
Botto, D.; Gastaldi, C.; Gola, M. M.; Umer, M.
2018-01-01
Among the different devices used in the aerospace industries under-platform dampers are widely used in turbo engines to mitigate the blade vibration. Nevertheless, the damper behaviour is not easy to simulate and engineers have been working in order to improve the accuracy with which theoretical contact models predict the damper behaviour. Majority of the experimental setups collect experimental data in terms of blade amplitude reduction which do not increase the knowledge about the damper dynamics and therefore the uncertainty on the damper behaviour remains a big issue. In this paper, a novel test rig has been purposely designed to accommodate a single blade and two under-platform dampers to deeply investigate the damper-blade interactions. In this test bench, a contact force measuring system was designed to extensively measure the damper contact forces. Damper kinematics is rebuilt by using the relative displacement measured between damper and blade. This paper describes the concept behind the new approach, shows the details of new test rig and discusses experimental results by comparing with previously measured results on an old experimental setup.
Hybrid magnetorheological fluid–elastomeric lag dampers for helicopter stability augmentation
International Nuclear Information System (INIS)
Hu Wei; Wereley, Norman M
2008-01-01
A laboratory demonstration of a hybrid magnetorheological fluid–elastomeric (MRFE) damper is investigated for adjustable or programmable lag mode damping in helicopters, so that damping requirements can be varied as a function of different flight conditions. The laboratory demonstration of this hybrid MRFE lag damper consists of a double lap shear elastomeric damper in parallel with two magnetorheological (MR) flow mode dampers. This is compared to a damper where only elastomeric materials are implemented, i.e., a double lap shear specimen. The relationship between the output force and the quasi-steady harmonic displacement input to a flow mode MR damper is exploited, where the output force can be adjusted as a function of applied magnetic field. Equivalent viscous damping is used to compare the damping characteristics of the hybrid damper to a conventional elastomeric damper under steady-state sinusoidal displacement excitation. To demonstrate feasibility, a hybrid MRFE damper test setup is designed, and single frequency (lag frequency or rotor in-plane bending frequency) and dual frequency (lag frequency and rotor frequency) tests are conducted under different magnetic fields. The hybrid MRFE damper exhibits amplitude-dependent damping behavior. However, with application of a magnetic field, the damping level is controlled to a specific damping level objective as a function of displacement amplitude. Similarly, under dual frequency conditions, damping degradation at the lag frequency, because of lag motion at the rotor frequency, can also be recovered by increasing magnetic field. A time-domain analysis is developed to study the nonlinear dynamic behavior of the hybrid MRFE damper. Using rate-dependent elasto-slides, the amplitude-dependent behavior of the hybrid MRFE damper is accurately reconstructed using both constant and current-dependent (i.e. controllable) parameters. The analysis is physically motivated and can be applied to the elastomer and MR fluid
An experimental artificial-neural-network-based modeling of magneto-rheological fluid dampers
International Nuclear Information System (INIS)
Tudón-Martínez, J C; Lozoya-Santos, J J; Morales-Menendez, R; Ramirez-Mendoza, R A
2012-01-01
A static model for a magneto-rheological (MR) damper based on artificial neural networks (ANNs) is proposed, and an intensive and experimental study is presented for designing the ANN structure. The ANN model does not require time delays in the input vector. Besides the electric current signal, only one additional sensor is used to achieve a reliable MR damper structure. The model is experimentally validated with two commercial MR dampers of different characteristics: MR 1 damper with continuous actuation and MR 2 damper with two levels of actuation. The error to signal ratio (ESR) index is used to measure the model accuracy; for both MR dampers, an average value of 6.03% of total error is obtained from different experiments, which are designed to explore the nonlinearities of the MR phenomenon at different frequencies by including the impact of the electric current fluctuations. The proposed ANN model is compared with other well known parametric models; the qualitative and quantitative comparison among the models highlights the advantages of the ANN for representing a commercial MR damper. The ESR index was reduced by the ANN-based model by up to 29% with respect to the parametric models for the MR 1 damper and up to 40% for the MR 2 damper. The force–velocity diagram is used to compare the modeling properties of each approach: (1) the Bingham model cannot describe the hysteresis of both MR dampers and the distribution function of the modeled force varies from the experimental data, (2) the algebraic models have complications in representing the nonlinear behavior of the asymmetric damper (MR 2 ) and, (3) the ANN-based MR damper can model the nonlinearities of both MR dampers and presents good scalability; the accuracy of the results supports the use of this model for the validation of semi-active suspension control systems for a vehicle, by using nonlinear simulations. (paper)
Directory of Open Access Journals (Sweden)
Polach P.
2008-11-01
Full Text Available Vertical dynamic properties of the ŠKODA 21 Tr low-floor trolleybus were investigated on an artificial test track when driving with a real vehicle and when simulating driving with a multibody model along a virtual test track. Driving along the artificial test track was aimed to determine vertical dynamic properties of the real trolleybus and on the basis of them to verify computer trolleybus models. Time histories and extreme values of the air springs relative deflections are the monitored quantities. Due to differences of the experiments and the computer simulations results the influences of the characteristics of the spring-damper structural elements of the axles suspension and the radial characteristics of the tires used in the trolleybus multibody model on the extreme values of the monitored quantities are evaluated.
Viscous-Fluid-Spring Damper Retrofit of a Steel Moment Frame Structure
International Nuclear Information System (INIS)
Hussain, Saif; Van Benschoten, Paul; Al Satari, Mohamed; Lin, Silian
2008-01-01
The subject building is a peculiar pre-Northridge steel moment resisting frame building. Upon investigating the existing lateral resisting system, numerous significant deficiencies were identified; inherent lack of redundancy, poor geometry and inadequate stiffness of the lateral resisting system. All of which resulted in an extremely soft 5-story structure with a primary torsional mode of vibration at T 1 = 5.46 s. Significant structural modifications were deemed necessary to meet the ''life-safety'' performance objective as outlined in rehabilitation standards such as ASCE 41. Both increased stiffness and damping were required to adequately retrofit the building. Furthermore, adjacent building separation as well as deformation compatibility issues needed to be addressed and resolved. A three-dimensional computer model of the building was created using ETABS mathematically simulating the building's dynamic characteristics in its current condition. Multiple seismic retrofit systems were investigated such as Buckling Restrained Braced Frames (BRBF's). However, based on the performance effectiveness and constructability of the retrofit schemes studied, the Viscous-Fluid-Spring Damper (VFSD) system was proposed as the ''optimum'' solution for the building. The VFSD, was chosen because it combines the relatively compact size and minimally invasive constructability with the required properties (an elastomeric spring in parallel with a nonlinear velocity dependent viscous damper). A site-specific response spectrum was developed for the Design Basis Earthquake (DBE, 475 year return period) event, and three pairs of representative earthquake horizontal ground motion time-histories were scaled to match this DBE. The proposed scheme reduced the building maximum inter-story drift ratio from 5.4% to about 1%. Similarly, the maximum roof displacement was reduced by about 70% (23'' to 7'')
A novel test rig to investigate under-platform damper dynamics
Botto, Daniele; Umer, Muhammad
2018-02-01
In the field of turbomachinery, vibration amplitude is often reduced by dissipating the kinetic energy of the blades with devices that utilize dry friction. Under-platform dampers, for example, are often placed in the underside of two consecutive turbine blades. Dampers are kept in contact with the under-platform of the respective blades by means of the centrifugal force. If the damper is well designed, vibration of blades instigate a relative motion between the under-platform and the damper. A friction force, that is a non-conservative force, arises in the contact and partly dissipates the vibration energy. Several contact models are available in the literature to simulate the contact between the damper and the under-platform. However, the actual dynamics of the blade-damper interaction have not fully understood yet. Several test rigs have been previously developed to experimentally investigate the performance of under-platform dampers. The majority of these experimental setups aim to evaluate the overall damper efficiency in terms of reduction in response amplitude of the blade for a given exciting force that simulates the aerodynamic loads. Unfortunately, the experimental data acquired on the blade dynamics do not provide enough information to understand the damper dynamics. Therefore, the uncertainty on the damper behavior remains a big issue. In this work, a novel experimental test rig has been developed to extensively investigate the damper dynamic behavior. A single replaceable blade is clamped in the rig with a specific clamping device. With this device the blade root is pressed against a groove machined in the test rig. The pushing force is controllable and measurable, to better simulate the actual centrifugal load acting on the blade. Two dampers, one on each side of the blade, are in contact with the blade under-platforms and with platforms on force measuring supports. These supports have been specifically designed to measure the contact forces on the
Damping of edgewise vibration in wind turbine blades by means of circular liquid dampers
DEFF Research Database (Denmark)
Basu, Biswajit; Zhang, Zili; Nielsen, Søren R.K.
2016-01-01
centrifugal acceleration. This centrifugal acceleration makes the use of this kind of oscillatory liquid damper feasible with a small mass ratio to effectively suppress edgewise vibrations. A reduced 2-DOF non-linear model is used for tuning the CLCD attached to a rotating wind turbine blade, ignoring......This paper proposes a new type of passive vibration control damper for controlling edgewise vibrations of wind turbine blades. The damper is a variant of the liquid column damper and is termed as a circular liquid column damper (CLCD). Rotating wind turbine blades generally experience a large...... the coupling between the blade and the tower. The performance of the damper is evaluated under various rotational speeds of the rotor. A special case in which the rotational speed is so small that the gravity dominates the motion of the liquid is also investigated. Further, the legitimacy of the decoupled...
Application of tuned mass dampers in high-rise construction
Teplyshev, Vyacheslav; Mylnik, Alexey; Pushkareva, Maria; Agakhanov, Murad; Burova, Olga
2018-03-01
The article considers the use of tuned mass dampers in high-rise construction for significant acceleration and amplitude of vibrations of the upper floors under dynamic wind influences. The susceptibility of people to accelerations in high-rise buildings and possible means of reducing wind-induced fluctuations in buildings are analyzed. The statistics of application of tuned mass dampers in high-rise construction all over the world is presented. The goal of the study is to identify an economically attractive solution that allows the fullest use of the potential of building structures in high-rise construction, abandoning the need to build massive frames leading to over-consumption of materials.
HOM Dampers or not in Superconducting RF Proton Linacs
Tückmantel, Joachim
2009-01-01
Circular machines are plagued by Coupled Bunch Instabilities, driven by impedance peaks, irrespectively of their frequency relation to machine lines; hence all cavity Higher Order Modes are possible drivers. This is the fundamental reason that all superconducting RF cavities in circular machines are equipped with HOM dampers. This raises the question if HOM damping would not be imperative also in high current proton linacs where a mechanism akin to CBI might exist. To clarify this question we have simulated the longitudinal bunched beam dynamics in linacs, allowing bunch-to-bunch variations in time-of-arrival. Simulations were executed for a generic proton linac with properties close to SNS or the planned SPL at CERN. It was found that for monopole HOMs with high Qext large beam scatter or even beam loss cannot be excluded. Therefore omitting HOM dampers on superconducting RF cavities in high current proton linacs, even pulsed ones, is a very risky decision.
HOM Dampers or not in SUPERCONDUCTING RF Proton Linacs
Tückmantel, Joachim
2009-01-01
Circular machines are plagued by Coupled Bunch Instabilities, driven by impedance peaks, irrespectively of their frequency relation to machine lines; hence all cavity Higher Order Modes are possible drivers. This is the fundamental reason that all superconducting RF cavities in circular machines are equipped with HOM dampers. This raises the question if HOM damping would not be imperative also in high current proton linacs where a mechanism akin to CBI might exist. To clarify this question we have simulated the longitudinal bunched beam dynamics in linacs, allowing bunch-to-bunch variations in time-of-arrival. Simulations were executed for a generic proton linac with properties close to SNS or the planned SPL at CERN. It was found that for monopole HOMs with high Qext large beam scatter or even beam loss cannot be excluded. Therefore omitting HOM dampers on superconducting RF cavities in high current proton linacs, even pulsed ones, is a very risky decision.
Stability of a dual-spin satellite with two dampers
Alfriend, K. T.; Hubert, C. H.
1974-01-01
The rotational stability of a dual-spin satellite consisting of a main body and a symmetric rotor, both spinning about a common axis, is investigated. The main body is equipped with a spring-mass damper, while a partially filled viscous ring damper is mounted on the rapidly spinning rotor. The effect of fluid motion on the rotational stability of the satellite is calculated, considering the fluid as a single particle moving in a tube with viscous damping. Time constants are obtained by solving approximate equations of motion for the nutation-synchronous and the spin-synchronous modes, and the results are found to agree well with the numerical integrations of the exact equations. A limit cycle may exist for some configurations; the nutation angle tends to increase in such cases.
The application of viscous dampers as pipe restraints
International Nuclear Information System (INIS)
Keowen, R.S.; Hueffmann, G.; Mays, B.; Rencher, D.
1993-01-01
Dynamic loading of power generation piping systems may result in nonpermissable deflections and stresses. Fatigue failure translate to increased maintenance costs and possible lost revenue. Undesirable loading can occur due to external events such as earthquakes and internal events such as water and steam hammer, two-phase flow and cavitation. Sway braces and snubbers have been employed to reduce the negative effects of piping motion in emergency cases, however, repetitive loading due to internal events has caused premature wear and failure. Visco elastic dampers, however, have proven to be piping response due to slugging, steam hammer and other repetitive loads. Functional and modeling aspects of visco elastic dampers are discussed, experimental evidence of their effectiveness in a steam hammer application is presented and examples of primary coolant loop restraint applications are illustrated
MEMS mass-spring-damper systems using an out-of-plane suspension scheme
Abdel Aziz, Ahmed Kamal Said; Sharaf, Abdel Hameed; Serry, Mohamed Yousef; Sedky, Sherif Salah
2014-01-01
MEMS mass-spring-damper systems (including MEMS gyroscopes and accelerometers) using an out-of-plane (or vertical) suspension scheme, wherein the suspensions are normal to the proof mass, are disclosed. Such out-of-plane suspension scheme helps such MEMS mass-spring-damper systems achieve inertial grade performance. Methods of fabricating out-of-plane suspensions in MEMS mass-spring-damper systems (including MEMS gyroscopes and accelerometers) are also disclosed.
MEMS mass-spring-damper systems using an out-of-plane suspension scheme
Abdel Aziz, Ahmed Kamal Said
2014-02-04
MEMS mass-spring-damper systems (including MEMS gyroscopes and accelerometers) using an out-of-plane (or vertical) suspension scheme, wherein the suspensions are normal to the proof mass, are disclosed. Such out-of-plane suspension scheme helps such MEMS mass-spring-damper systems achieve inertial grade performance. Methods of fabricating out-of-plane suspensions in MEMS mass-spring-damper systems (including MEMS gyroscopes and accelerometers) are also disclosed.
THE THEORETICAL FOUNDATIONS OF VIBRATION DAMPERS BY ROLLING FRICTION
Directory of Open Access Journals (Sweden)
L. M. Bondarenko
2015-06-01
Full Text Available Purpose. There are some unresolved issues in vibration damping – the lack of engineering calculations for the vibration dampers by rolling friction; the absence of evidence of their application appropriateness. Considering this fact, the authors suggest to prove that the dampers based on rolling friction, are similar in rate of oscillation damping by hydraulic shock absorbers. At the same time, they are easier for the hydraulic design, and easily amenable to manual adjustment, both in automatic and manual mode. Methodology. Fixed techniques of practice in order to determine amplitudes of the oscillations of a shock absorber led to a predetermined result and will apply this theory in the calculation of other vibration dampers. Findings. Analysis of the formulas and graphs leads to the following conclusions and recommendations: 1 the nature of the oscillation damping at vibration dampers by rolling friction is close to their decay in the viscous resistance; 2 when conducting the necessary experiments the shock absorber rolling can be recommended as alternatives to hydraulic ones. The research results of this task will help implement the new trend in reduction of dynamic loads in vehicles. Originality. With the help of theoretical curves to determine the coefficients of rolling friction the dependences for determining the amplitudes of the oscillations in the vertical movement of cargo were obtained. At the same time, the previously proposed analytical dependence for determining the coefficient of rolling friction contains only conventional mechanical constants of the contacting bodies and there geometrical dimensions. Practical value. Due to the existing well-known disadvantages of hydraulic shock absorbers it would be logical to apply shock absorbers that are technologically convenient in manufacturing and easy to adjust the damping rate. The proposed theory can be used in the design of shock absorbers rolling as an alternative to the hydraulic
Programmable high power beam damper for the Tevatron
International Nuclear Information System (INIS)
Crisp, J.; Goodwin, R.; Gerig, R.
1985-06-01
A bunch-by-bunch beam damper has been developed for the Fermilab Tevatron. The system reduces betatron oscillation amplitudes and incorporates some useful machine diagnostics. The device is programmable via look-up tables so the output is an arbitrary function, on a bunch-by-bunch basis, of the beam displacement. We are presently using this feature to measure the betatron tune throughout the acceleration cycle. 4 refs
Unsteady flow damping force prediction of MR dampers subjected to sinusoidal loading
Yu, M.; Wang, S. Q.; Fu, J.; Peng, Y. X.
2013-02-01
So far quasi-steady models are usually used to design magnetorheological (MR) dampers, but these models are not sufficient to describe the MR damper behavior under unsteady dynamic loading, for fluid inertia is neglected in quasi-steady models, which will bring more error between computer simulation and experimental results. Under unsteady flow model, the fluid inertia terms will bring error calculated upto 10%, so it is necessary to be considered in the governing equation. In this paper, force-stroke behavior of MR damper with flow mode due to sinusoidal loading excitation is mainly investigated, to simplify the analysis, the one-dimensional axisymmetric annular duct geometry of MR dampers is approximated as a rectangular duct. The rectangular duct can be divided into 3 regions for the velocity profile of the incompressible MR fluid flow, in each region, a partial differential equation is composed of by Navier-Stokes equations, boundary conditions and initial conditions to determine the velocity solution. In addition, in this work, not only Bingham plastic model but the Herschel—Bulkley model is adopted to analyze the MR damper performance. The damping force resulting from the pressure drop of unsteady MR dampers can be obtained and used to design or size MR dampers. Compared with the quasi-steady flow damping force, the damping force of unsteady MR dampers is more close to practice, particularly for the high-speed unsteady movement of MR dampers.
Unsteady flow damping force prediction of MR dampers subjected to sinusoidal loading
International Nuclear Information System (INIS)
Yu, M; Fu, J; Wang, S Q; Peng, Y X
2013-01-01
So far quasi-steady models are usually used to design magnetorheological (MR) dampers, but these models are not sufficient to describe the MR damper behavior under unsteady dynamic loading, for fluid inertia is neglected in quasi-steady models, which will bring more error between computer simulation and experimental results. Under unsteady flow model, the fluid inertia terms will bring error calculated upto 10%, so it is necessary to be considered in the governing equation. In this paper, force-stroke behavior of MR damper with flow mode due to sinusoidal loading excitation is mainly investigated, to simplify the analysis, the one-dimensional axisymmetric annular duct geometry of MR dampers is approximated as a rectangular duct. The rectangular duct can be divided into 3 regions for the velocity profile of the incompressible MR fluid flow, in each region, a partial differential equation is composed of by Navier-Stokes equations, boundary conditions and initial conditions to determine the velocity solution. In addition, in this work, not only Bingham plastic model but the Herschel—Bulkley model is adopted to analyze the MR damper performance. The damping force resulting from the pressure drop of unsteady MR dampers can be obtained and used to design or size MR dampers. Compared with the quasi-steady flow damping force, the damping force of unsteady MR dampers is more close to practice, particularly for the high-speed unsteady movement of MR dampers.
Fermilab 500 GeV main accelerator rf cavity 128 MHz mode damper
International Nuclear Information System (INIS)
Kerns, Q.A.; Miller, H.W.
1977-01-01
The Fermilab 500-GeV main accelerating system has been operating for a year now with the aid of 128-MHz mode dampers. Such dampers proved to be necessary to achieve stable operation and a reasonably smooth slow spill at intensities of approximately 2 x 10 13 protons per pulse, and furthermore are low-cost and reliable. The approach used to identify troublesome modes, the observed beam blow-up without dampers, and the steps taken to design and install suitable dampers on eighteen main ring cavities are discussed. Spectrum analyzer pictures help illustrate the performance
Edgewise vibration control of wind turbine blades using roller and liquid dampers
International Nuclear Information System (INIS)
Zhang, Z L; Nielsen, S R K
2014-01-01
This paper deals with the passive vibration control of edgewise vibrations by means of roller dampers and tuned liquid column dampers (TLCDs). For a rotating blade, the large centrifugal acceleration makes it possible to use roller dampers or TLCDs with rather small masses for effectively suppressing edgewise vibrations. The roller dampers are more volumetrically efficient due to the higher mass density of the steel comparing with the liquid. On the other hand, TLCDs have their advantage that it is easier to specify the optimum damping of the damper by changing the opening ratio of the orifice. In this paper, 2-DOF nonlinear models are suggested for tuning a roller damper or a TLCD attached to a rotating wind turbine blade, ignoring the coupling between the blade and the tower. The decoupled optimization is verified by incorporating the optimized damper into a more sophisticated 13- DOF wind turbine model with due consideration of the coupled blade-tower-drivetrain vibrations, quasi-static aeroelasticity as well as a collective pitch controller. Performances of the dampers are compared in terms of the control efficiency and the practical applications. The results indicate that roller dampers and TLCDs at optimal tuning can effectively suppress the dynamic response of wind turbine blades
Performance of a New Fine Particle Impact Damper
Directory of Open Access Journals (Sweden)
Yanchen Du
2008-01-01
Full Text Available The energy dissipation mechanisms of conventional impact damper (CID are mainly momentum exchange and friction. During the impact process, a lot of vibration energy cannot be exhausted but reverberated among the vibration partners. Besides, the CID may produce the additional vibration to the system or even amplify the response in the low-frequency vibration. To overcome these shortcomings, this paper proposes a new fine particle impact damper (FPID which for the first time introduces the fine particle plastic deformation as an irreversible energy sink. Then, the experiments of the cantilevered beam with the CID and that with the FPID are, respectively, carried out to investigate the behavior of FPID. The experimental results indicate that the FPID has a better performance in vibration damping than in the CID and the FPID works well in control of the vibration with frequency lower than 50 Hz, which is absent to the non-obstructive particle damper. Thus, the FPID has a bright and significant application future because most of the mechanical vibration falls in the range of low freqency.
Synthesis of lever-blade dampers with enhanced mechanical structure
Directory of Open Access Journals (Sweden)
Igor I. Sydorenko
2015-03-01
Full Text Available Since the torsion bar represents just an elastic element, the energy dissipation in suspensions problem is highly relevant for its application. Currently in quality of a dissipation device in torsion suspension are used the hydraulic dampers with movable members reciprocating translational motion respectively to the housing or lever-type hydraulic shock absorbers of piston and vane types, with the movable member’s rotational movement respectively to the housing. These dampers are implementing only throttle-valve performance type, associated with these devices’ functional capacities and depending on design constraints. The paper presents a synthesis of innovative lever-blade dampers, whose performance is not related to the value of working chambers inner pressure. Their essential peculiarity relates to the mechanical control loop presence in the structure that determines a close relationship between the performance and the value of the shock absorber movable element displacement relatively to the body. In the process of synthesis carried out tested are the appropriate methods, built on the basis of technical systems’ modeling with modified kinematic graphs. The synthesis results are shown in the form of two structurally implemented samples. Performed is a comparative analysis of the samples with their basic performance determining.
Special Fluid Viscous Dampers For The Messina Strait Bridge
International Nuclear Information System (INIS)
Colato, Gian Paolo; Infanti, Samuele; Castellano, Maria Gabriella
2008-01-01
The Messina Strait Bridge would be the world's longest suspension bridge, with a design earthquake characterised by a PGA value of 0.58 g and a distance between the ipocenter and the bridge of 15 km. Said critical structure of course would need a suitable restraint system for traffic braking loads, wind and seismic actions. Each type of load requires a specific behaviour of the restraint system, making its design a big challenge.The restraint system comprises special types of fluid viscous dampers, installed both in longitudinal and transverse direction, both at the towers and at the anchorages. In seismic conditions they behave as viscous dampers, to reduce the forces on the structural elements and the movements of the bridge deck. But in service dynamic conditions, e.g. under traffic or wind load, the devices shall behave like shock transmission units, thus preventing the longitudinal and transverse movements of the deck.FIP Industriale cooperated with the selected General Contractor, a consortium lead by Impregilo, in the design of said viscous dampers. This paper describes the main features of said devices
Optimization of location and forces of friction dampers
Directory of Open Access Journals (Sweden)
Sergio Pastor Ontiveros-Pérez
Full Text Available Abstract Damper optimization is a new area which has been investigated in recent years. There are various methods employed in optimization, among which are highlighted the classic and the most recent that are functioning with reliability, efficiency and speed for optimum results. This paper proposes a method for simultaneous optimization of placement and forces of friction dampers using the Firefly Algorithm, which is a recent meta-heuristic algorithm inspired in the behavior of fireflies. Herein, three different optimization objective are presented: i minimize the maximum displacement at the top of the structure; ii minimize the maximum inter-story drift; iii minimize the maximum acceleration at the top of the structure. The three objective functions were evaluated in two civil structures (a nine-story building and a sixteen-story building subjected to two real seismic records. The first seismic record is El Centro, which took place in the southeastern California on the boarder of the United States and Mexico in 1940. The second one is the earthquake that occurred in Caucete, province of San Juan, Argentina, in 1977. The results showed that the proposed method was able to optimize the friction dampers, reducing considerably the response of the structures.
Fabrication and testing of an energy-harvesting hydraulic damper
International Nuclear Information System (INIS)
Li, Chuan; Tse, Peter W
2013-01-01
Hydraulic dampers are widely used to dissipate energy during vibration damping. In this paper, an energy-harvesting hydraulic damper is proposed for collecting energy while simultaneously damping vibration. Under vibratory excitation, the flow of hydraulic oil inside the cylinder of the damper is converted into amplified rotation via a hydraulic motor, whose output shaft is connected to an electromagnetic generator capable of harvesting a large amount of energy. In this way, the vibration is damped by both oil viscosity and the operation of an electrical mechanism. An electromechanical model is presented to illustrate both the electrical and mechanical responses of the system. A three-stage identification approach is introduced to facilitate the model parameter identification using cycle-loading experiments. A prototype device is developed and characterized in a test rig. The maximum power harvested during the experiments was 435.1 W (m s −1 ) −1 , using a predefined harmonic excitation with an amplitude of 0.02 m, a frequency of 0.8 Hz, and an optimal resistance of 2 Ω. Comparison of the experimental and computational results confirmed the effectiveness of both the electromechanical model and the three-stage identification approach in realizing the proposed design. (paper)
An Experimental Design of Bypass Magneto-Rheological (MR) damper
Rashid, MM; Aziz, Mohammad Abdul; Raisuddin Khan, Md.
2017-11-01
The magnetorheological (MR) fluid bypass damper fluid flow through a bypass by utilizing an external channel which allows the controllability of MR fluid in the channel. The Bypass MR damper (BMRD) contains a rectangular bypass flow channel, current controlled movable piston shaft arrangement and MR fluid. The static piston coil case is winding by a coil which is used inside the piston head arrangement. The current controlled coil case provides a magnetic flux through the BMRD cylinder for controllability. The high strength of alloy steel materials are used for making piston shaft which allows magnetic flux propagation throughout the BMRD cylinder. Using the above design materials, a Bypass MR damper is designed and tested. An excitation of current is applied during the experiment which characterizes the BMRD controllability. It is shown that the BMRD with external flow channel allows a high controllable damping force using an excitation current. The experimental result of damping force-displacement characteristics with current excitation and without current excitation are compared in this research. The BMRD model is validated by the experimental result at various frequencies and applied excitation current.
Analysis of Train Suspension System Using MR dampers
RamaSastry, DVA; Ramana, K. V.; Mohan Rao, N.; Siva Kumar, SVR; Priyanka, T. G. L.
2016-09-01
This paper deals with introducing MR dampers to the Train Suspension System for improving the ride comfort of the passengers. This type of suspension system comes under Semi-active suspension system which utilizes the properties of MR fluid to damp the vibrations. In case of high speed trains, the coach body is subjected to vibrations due to vertical displacement, yaw and pitch movements. When the body receives these disturbances from the ground,the transmission of vibrations to the passenger increases which affect the ride comfort. In this work, the equations of motion of suspension system are developed for both conventional passive system and semi-active system and are modelled in Matlab/Simulink and analysis has been carried out. The passive suspension system analysis shows that it is taking more time to damp the vibrations and at the same time the transmissibility of vibrations is more.Introducing MR dampers,vertical and angular displacements of the body are computed and compared. The results show that the introduction of MR dampers into the train suspension system improves ride comfort.
A novel magnetorheological damper based parallel planar manipulator design
International Nuclear Information System (INIS)
Hoyle, A; Arzanpour, S; Shen, Y
2010-01-01
This paper presents a novel parallel planar robot design which is low cost and simple in structure. The design addresses some of the problems, such as concentration of excessive load on the links and joints, due to wrong commanding signals being given by the controller. In this application two of the conventional actuators are replaced by magnetorheological (MR) dampers, and only one actuator is used to generate motion. The design paradigm is based on the concept that a moving object 'intuitively' follows the path with minimum resistance to its motion. This implies that virtual adoptable constraints can be used effectively to define motion trajectories. In fact, motion generation and adaptive constraints are two elements essential to implementing this strategy. In this paper, MR dampers are used to provide adjustable constraints and to guide the platform that is moved by the linear motor. The model of the MR dampers is derived using the Bouc–Wen model. This model is then used for manipulator simulation and controller design. Two controllers are developed for this manipulator: (1) a closed loop on/off one and (2) a proportional–derivative controller. Also, three different trajectories are defined and used for both the simulations and experiments. The results indicate a good agreement between the simulations and experiments. The experimental results also demonstrate the capability of the manipulator for following sophisticated trajectories
Directory of Open Access Journals (Sweden)
Waleed F. Faris
2008-01-01
Full Text Available This work is devoted to the fabrication and investigation of the Squeeze Film Dampers (SFDs which are widely used in many applications. This include the fabrication of a test rig and several dampers with different sizes and two different materials which composite and non-composite. Composite dampers (Glass/epoxy, each consists of 30 layers, were fabricated by hand lay-up method. Outer and inner diameters of all the fabricated dampers were maintained as 60 and 40 mm respectively. Non-composite dampers (Steel were fabricated and tested using turning machine. Three dampers of different lengths were examined for both materials. A rotor-bearing system for the analysis has been designed and fabricated. The test rig consists of mild steel shaft, two supports, oil pressure system, and two self-alignment ball bearings were fixed on each end support. Two squeeze film dampers were used for the two support ends. Vibration amplitude has been examined for all the fabricated dampers at different shaft rotational speeds. The first resonance speed was examined for all the dampers tested. Results show that the vibration amplitude of the steel damper was lower than Glass/epoxy dampers with the same L/D ratio. On the other hand, a considerable weight saving has been achieved by using Glass/epoxy composite dampers. It has been found that the performance of squeeze film damper improved with increasing length/diameter ratio (L/D within the range tested.
An Evaluation of Magneto Rheological Dampers for Controlling Gun Recoil Dynamics
Directory of Open Access Journals (Sweden)
Mehdi Ahmadian
2001-01-01
Full Text Available The application of magneto rheological dampers for controlling recoil dynamics is examined, using a recoil demonstrator that includes a single-shot 50 caliber BMG rifle action and a MR damper. The demonstrator is selected such that it can adequately represent the velocities that commonly occur in weapons with a recoil system, and can be used for collecting data for analyzing the effects of MR dampers on recoil dynamics. The MR damper is designed so that it can work effectively at the large velocities commonly occurring in gun recoil, and also be easily adjusted to reasonably optimize the damper performance for the recoil demonstrator. The test results show that it is indeed possible to design and use MR dampers for recoil applications, which subject the damper to relative velocities far larger than the applications that such dampers have commonly been used for (i.e., vehicle applications. Further, the results indicate that the recoil force increases and the recoil stroke decreases nonlinearly with an increase in the damping force. Also of significance is the fact that the adjustability of MR dampers can be used in a closed-loop system such that the large recoil forces that commonly occur upon firing the gun are avoided and, simultaneously, the recoil stroke is reduced. This study points to the need for several areas of research including establishing the performance capabilities for MR dampers for gun recoil applications in an exact manner, and the potential use of such dampers for a fire out of battery recoil system.
International Nuclear Information System (INIS)
Nguyen, Quoc-Hung; Choi, Seung-Bok
2009-01-01
This paper presents an optimal design of a passenger vehicle magnetorheological (MR) damper based on finite element analysis. The MR damper is constrained in a specific volume and the optimization problem identifies the geometric dimensions of the damper that minimize an objective function. The objective function consists of the damping force, the dynamic range, and the inductive time constant of the damper. After describing the configuration of the MR damper, the damping force and dynamic range are obtained on the basis of the Bingham model of an MR fluid. Then, the control energy (power consumption of the damper coil) and the inductive time constant are derived. The objective function for the optimization problem is determined based on the solution of the magnetic circuit of the initial damper. Subsequently, the optimization procedure, using a golden-section algorithm and a local quadratic fitting technique, is constructed via commercial finite element method parametric design language. Using the developed optimization tool, optimal solutions of the MR damper, which are constrained in a specific cylindrical volume defined by its radius and height, are determined and a comparative work on damping force and inductive time constant between the initial and optimal design is undertaken
Evaluation of applicability of lead damper to 3-dimensional isolation system based on loading tests
International Nuclear Information System (INIS)
Matsuda, Akihiro
2003-01-01
To develop a damper for 3-dimensional base isolation system, horizontal and vertical mechanical properties, effect of loading frequency on vertical mechanical properties, coupled properties between horizontal and vertical directions, stability performance due to cyclic deformation are evaluated experimentally using scale models of lead damper originally developed for horizontal base isolation system. Loading test results are summarized as follows; 1) The lead damper has good vertical damping performance, in that the vertical yield load of the lead damper is three times as large as that for the horizontal direction, and the lead damper shows plastic behavior in the small deformation region. 2) The lead damper shows enough stability for static vertical displacement of ±40 mm. 3) the lead damper shows high stability performance for dynamic cyclic loading test using motions of isolation layer calculated by earthquake response analysis of FBR building subjected to S2-earthquake motion. Thus, applicability of the lead damper to 3-dimensional isolation system is shown from these results. (author)
Active tuned mass damper for damping of offshore wind turbine vibrations
DEFF Research Database (Denmark)
Brodersen, Mark Laier; Bjørke, Ann-Sofie; Høgsberg, Jan Becker
2017-01-01
An active tuned mass damper (ATMD) is employed for damping of tower vibrations of fixed offshore wind turbines, where the additional actuator force is controlled using feedback from the tower displacement and the relative velocity of the damper mass. An optimum tuning procedure equivalent to the ...
Development of Optimal Viscous Dampers for RC Structures in Near Field Ground Motions
International Nuclear Information System (INIS)
Puthanpurayil, Arun M.; Reynolds, Paul
2008-01-01
Recent researches show that more than 50% of the economic loss in earthquakes is due to damage of non-structural elements: $8 billion loss in the 1989 Loma Prieta earthquake and $18.5 billion in the 1994 Northridge earthquake. An approach to reduce the economic loss during a seismic event without compromising the structural safety aspect is to incorporate special mechanical devices like fluid viscous dampers in the parent structural system. A recent study carried out to assess the efficacy of viscous dampers in reducing nonstructural damage of low, medium and high rise structures shows that; linear dampers are well suited for low rise category whereas the medium and high rise category requires nonlinear dampers. In this paper an analytical approach is adopted to derive the optimal combination of damper design parameters for all the three categories of structure subjected to near field ground motion. Linear time history analysis by direct time integration was carried out for the linear viscous dampers, while the parameters of the nonlinear viscous dampers were obtained using nonlinear modal time history analysis (Fast Nonlinear analysis). The results of the study are presented in the form of a set of design curves which can be used for the initial selection of parameters for Damper design
Xie, Longhan; Li, Jiehong; Li, Xiaodong; Huang, Ledeng; Cai, Siqi
2018-01-01
Hydraulic dampers are used to decrease the vibration of a vehicle, where vibration energy is dissipated as heat. In addition to resulting in energy waste, the damping coefficient in hydraulic dampers cannot be changed during operation. In this paper, an energy-harvesting vehicle damper was proposed to replace traditional hydraulic dampers. The goal is not only to recover kinetic energy from suspension vibration but also to change the damping coefficient during operation according to road conditions. The energy-harvesting damper consists of multiple generators that are independently controlled by switches. One of these generators connects to a tunable resistor for fine tuning the damping coefficient, while the other generators are connected to a control and rectifying circuit, each of which both regenerates electricity and provides a constant damping coefficient. A mathematical model was built to investigate the performance of the energy-harvesting damper. By controlling the number of switched-on generators and adjusting the value of the external tunable resistor, the damping can be fine tuned according to the requirement. In addition to the capability of damping tuning, the multiple controlled generators can output a significant amount of electricity. A prototype was built to test the energy-harvesting damper design. Experiments on an MTS testing system were conducted, with results that validated the theoretical analysis. Experiments show that changing the number of switched-on generators can obviously tune the damping coefficient of the damper and simultaneously produce considerable electricity.
Unuh, M. H.; Muhamad, P.; Norfazrina, H. M. Y.; Ismail, M. A.; Tanasta, Z.
2018-01-01
The applications of semi-active damper employing magnetorheological (MR) fluids keep increasing in fulfilling the demand to control undesired vibration effect. The aim of this study is to introduce the new design of damper for Malaysian vehicle model as well to evaluate its effectiveness in promoting comfort. The vibration isolation performance of the OEM damper featuring MR fluid was analysed physically under real road profile excitation experimentally. An experiment using quarter car rig suspension and LMS SCADAS Mobile was conducted to demonstrate the influence of current in controlling the characteristics of MR fluid in alter the damping behaviour under 5 cm bump impact. Subsequently, the displacement values were measured with respect to time. The new design OEM damper featuring MR fluid was validated by comparing the data with original equipment manufacturer (OEM) passive damper results under the same approach of testing. Comparison of numerical data of the new design OEM damper shown that it can reduce the excitation amplitude up to 40% compared to those obtained by OEM passive damper. Finally, the new design OEM damper featuring MR fluid has effectively isolated the disturbance from the road profile and control the output force.
Novel design of a self powered and self sensing magneto-rheological damper
International Nuclear Information System (INIS)
Ferdaus, Mohammad Meftahul; Rashid, M M; Bhuiyan, M M I; Muthalif, Asan Gani Bin Abdul; Hasan, M R
2013-01-01
Magneto-rheological (MR) dampers are semi-active control devices and use MR fluids. Magneto-rheological dampers have successful applications in mechatronics engineering, civil engineering and numerous areas of engineering. At present, traditional MR damper systems, require a isolated power supply and dynamic sensor. This paper presents the achievability and accuracy of a self- powered and self-sensing magneto-rheological damper using harvested energy from the vibration and shock environment in which it is deployed and another important part of this paper is the increased yield stress of the Magneto rheological Fluids. Magneto rheological fluids using replacement of glass beads for Magnetic Particles to surge yield stress is implemented here. Clearly this shows better result on yield stress, viscosity, and settling rate. Also permanent magnet generator (PMG) is designed and attached to a MR damper. For evaluating the self-powered MR damper's vibration mitigating capacity, an Engine Mount System using the MR damper is simulated. The ideal stiffness of the PMG for the Engine Mount System (EMS) is calculated by numerical study. The vibration mitigating performance of the EMS employing the self-powered and self sensing MR damper is theoretically calculated and evaluated in the frequency domain
Neural Network modeling of forward and inverse behavior of rotary MR damper
DEFF Research Database (Denmark)
Bhowmik, Subrata; Høgsberg, Jan Becker; Weber, Felix
2010-01-01
of nonlinear problems. The present paper concerns the nonparametric neural network modeling of the dynamic behavior of a rotary MR damper. A rotary type MR damper consists of a rotating disk which is enclosed in a metallic housing filled with the MR fluid which is operated in shear mode. The dissipative torque...
A comparative analysis of the degree of stability and damper coefficient of an electric system
Energy Technology Data Exchange (ETDEWEB)
Gruzdev, I.A.; Shakhayeva, O.M.; Tin' , N.V.
1981-01-01
The problem is examined of optimization of parameters of strong action ARV. The technique is given for determining the damper coefficient from SG equations, and based on equivalent circuits. It is shown that use of the damper coefficient for estimating the length of transient processes is only possible for systems with low attenuation.
Novel design of a self powered and self sensing magneto-rheological damper
Meftahul Ferdaus, Mohammad; Rashid, M. M.; Bhuiyan, M. M. I.; Muthalif, Asan Gani Bin Abdul; Hasan, M. R.
2013-12-01
Magneto-rheological (MR) dampers are semi-active control devices and use MR fluids. Magneto-rheological dampers have successful applications in mechatronics engineering, civil engineering and numerous areas of engineering. At present, traditional MR damper systems, require a isolated power supply and dynamic sensor. This paper presents the achievability and accuracy of a self- powered and self-sensing magneto-rheological damper using harvested energy from the vibration and shock environment in which it is deployed and another important part of this paper is the increased yield stress of the Magneto rheological Fluids. Magneto rheological fluids using replacement of glass beads for Magnetic Particles to surge yield stress is implemented here. Clearly this shows better result on yield stress, viscosity, and settling rate. Also permanent magnet generator (PMG) is designed and attached to a MR damper. For evaluating the self-powered MR damper's vibration mitigating capacity, an Engine Mount System using the MR damper is simulated. The ideal stiffness of the PMG for the Engine Mount System (EMS) is calculated by numerical study. The vibration mitigating performance of the EMS employing the self-powered & self sensing MR damper is theoretically calculated and evaluated in the frequency domain.
Nonlinear modeling of adaptive magnetorheological landing gear dampers under impact conditions
Ahuré Powell, Louise A.; Choi, Young T.; Hu, Wei; Wereley, Norman M.
2016-11-01
Adaptive landing gear dampers that can continuously adjust their stroking load in response to various operating conditions have been investigated for improving the landing performance of a lightweight helicopter. In prior work, adaptive magnetorheological (MR) landing gear dampers that maintained a constant peak stroking force of 4000 lbf across sink rates ranging from 6 to 12 ft s-1 were designed, fabricated and successfully tested. In this follow-on effort, it is desired to expand the high end of the sink rate range to hold the peak stroking load constant for sink rates ranging from 6 to 26 ft s-1, thus extending the high end of the speed range from 12 (in the first study) to 26 ft s-1. To achieve this increase, a spring-based relief valve MR landing gear damper was developed. In order to better understand the MR landing gear damper behavior, a modified nonlinear Bingham Plastic model was formulated, and it incorporates Darcy friction, viscous forces across the MR and relief valves to better account for the damper force behavior at higher speeds. In addition, gas pressure inside the MR damper piston is considered so the total damper force includes a gas force. The MR landing gear damper performance is characterized using drop tests, and the experiments are used to validate model predictions data at low and high nominal impact speeds up to 26 ft s-1 (shaft velocity of 9.6 ft s-1).
A new magnetorheological damper with improved displacement differential self-induced ability
International Nuclear Information System (INIS)
Hu, Guoliang; Zhou, Wei; Li, Weihua
2015-01-01
This work is an extension of our previous study on the development of a linear variable differential sensor (LVDS)-based magnetorheological (MR) damper with self-sensing capability, where a new MR damper integrated with LVDS technology was developed and prototyped, then its self-induced performance under static and dynamic working conditions was experimentally evaluated. The results of the static and dynamic experiments indicated that the self-induced voltage was proportional to the displacement of the damper. Moreover, the damping performance of this new MR damper was also evaluated through an experimental study. Compared with our previous study, the new MR damper performed better in terms of its self-induced sensing ability and damping capacity. (technical note)
SEISMIC Analysis of high-rise buildings with composite metal damper
Directory of Open Access Journals (Sweden)
Chen Ruixue
2015-01-01
Full Text Available This paper mainly studies on the mechanical characteristics and application effect of composite metal damper in the high-rise buildings via the numerical simulation analysis. The research adopts the elastic and elastic-plastic dynamic approach and the displacement time history response and damper energy dissipation capacity and so on of the high-rise building are compared and analyzed before and after installation. The analysis found that the energy dissipation characteristic of metallic dampers is good. High-rise building story drift significantly is reduced and the extent of damage of the walls and coupling beams is decreased, achieved a good energy dissipation effect. Composite metal damper can effectively and economically improve the seismic performance of high-rise buildings, meet the requirement of the 3-level design for seismic resistance. The result has certain reference significance for the application of metallic damper in the high-rise buildings.
Coaxial higher-order mode damper employing a high-pass filter
International Nuclear Information System (INIS)
Kang, Y.W.; Jiang, X.
1997-01-01
Two different types of coaxial higher-order mode (HOM) dampers have been investigated for the Advanced Photon Source (APS) storage ring cavities: e-probe dampers and h-loop dampers. Realization of the h-loop dampers has been difficult because the loop antenna couples not only to the HOMs but also to the accelerating mode and results in loss of Q at the fundamental frequency. Previously, a first-order fundamental rejection filter was tested with unsatisfactory rejection characteristics. This problem can be overcome by using a higher-order high-pass filter between the loop and the matched load. Prototype dampers have been fabricated and tested in a storage ring single-cell cavity and the damping characteristic was analyzed
Dynamic modeling and simulation of sheave damper based on AMESim software
Directory of Open Access Journals (Sweden)
BI Ke
2017-10-01
Full Text Available [Objectives] Considering the shortcomings of the traditional sheave damper in buffer performance and the peak value of the greatest cable tension,[Methods] this paper presents a sheave damper with variable damping according to piston displacement as a replacement for the traditional sheave damper, and AMESim software is used for the modeling and simulation.[Results] The results show that the new sheave damper can significantly improve the arresting gear performance indicators, and has better adaptability for aircraft impact load. Compared with the traditional sheave damper, the new method can reduce cable tension by 25% and reduce the maximum deceleration of aircraft by 23%.[Conclusions] As such, the research in this paper can provide a theoretical reference for improving the performance of aircraft arresting gear.
LHC Abort Gap Cleaning with the Transverse Damper
Gianfelice-Wendt, E; Höfle, Wolfgang; Kain, V; Meddahi, M; Shaposhnikova, E; Koschik, A
2010-01-01
In the Large Hadron Collider, LHC, particles not captured by the RF system at injection or leaking out of the RF bucket may quench the superconducting magnets during beam abort. The problem, common to other superconducting machines, is particularly serious for the LHC due to the very large stored energy in the beam. For the LHC a way of removing the unbunched beam has been studied and it uses the existing damper kickers to excite resonantly the particles travelling along the abort gap. In this paper we describe the results of simulations performed with MAD X for various LHC optics configurations, including the estimated multipolar errors.
Investigation of earthquake factor for optimum tuned mass dampers
Nigdeli, Sinan Melih; Bekdaş, Gebrail
2012-09-01
In this study the optimum parameters of tuned mass dampers (TMD) are investigated under earthquake excitations. An optimization strategy was carried out by using the Harmony Search (HS) algorithm. HS is a metaheuristic method which is inspired from the nature of musical performances. In addition to the HS algorithm, the results of the optimization objective are compared with the results of the other documented method and the corresponding results are eliminated. In that case, the best optimum results are obtained. During the optimization, the optimum TMD parameters were searched for single degree of freedom (SDOF) structure models with different periods. The optimization was done for different earthquakes separately and the results were compared.
Energy Technology Data Exchange (ETDEWEB)
Takeda, T.; Yamanobe, S.; Niihara, Y. [Kajima Corp., Tokyo (Japan)
1994-10-31
It is important in designing a PC cable-stayed bridge to properly estimate the seismic response of the bridge for reduction of the response. In this paper, an improvement of the seismic resistance of PC cable-stayed bridges when dampers are installed between the deck and piers and lateral vibration of the deck is restricted is investigated using a time history response model. PC cable-stayed bridges with a span length of 400 m, particularly two types of bridges of harp and semi-harp are investigated and the following is found by analyzing the case where there are installed hysteresis type dampers (with 1 cm yield displacement and secondary rigidity assumed to be 1/10 times that of initial rigidity, the initial rigidity being parametrically changed.) or viscous type dampers (a damping factor is changed.) The result shows that the dampers can reduce the seismic response of a PC cable-stayed bridge and that a semi-harp configuration of stay cables where stay cable members are substantially vertically arranged is more effective than a harp configuration for the seismic performance of PC cable-stayed bridges. The damper partly bear inertial force of the bridge upon earthquake whereby tension of the stay cable members is reduced and bending moment of the deck is reduced. There is existing an optimum characteristic value of the damper concerning the bending moment of the piers. 5 refs., 7 figs., 2 tabs.
Robert J. Barro; Sanjay P. Misra
2013-01-01
From 1836 to 2011, the average real rate of price change for gold in the United States is 1.1% per year and the standard deviation is 13.1%, implying a one-standard-deviation confidence band for the mean of (0.1%, 2.1%). The covariances of gold's real rate of price change with consumption and GDP growth rates are small and statistically insignificantly different from zero. These negligible covariances suggest that gold's expected real rate of return--which includes an unobserved dividend yiel...
DEFF Research Database (Denmark)
Agergaard, Jytte; Brøgger, Ditte
2016-01-01
flows. By focusing on these educational migrants, this paper explores how they connect to their rural homes. Guided by a critical reading of the migration-development scholarship, the paper examines how migrants and their relatives make sense of educational migrants’ remitting and returning practices......, and by comparing three groups of educational migrants, the migrants’ reasons for staying connected and sending remittances are scrutinized. The paper finds that although educational migrants do not generate extensive economic remittances for local development in Nepal, they stay connected to their rural homes...
Earthquake response of adjacent structures with viscoelastic and friction dampers
Directory of Open Access Journals (Sweden)
Žigić Miodrag
2015-01-01
Full Text Available We study the seismic response of two adjacent structures connected with a dry friction damper. Each of them consists of a viscoelastic rod and a rigid block, which can slide without friction along the moving base. A simplified earthquake model is used for modeling the horizontal ground motion. Energy dissipation is taken by the presence of the friction damper, which is modeled by the set-valued Coulomb friction law. Deformation of viscoelastic rods during the relative motion of the blocks represents another way of energy dissipation. The constitutive equation of a viscoelastic body is described by the fractional Zener model, which includes fractional derivatives of stress and strain. The problem merges fractional derivatives as non-local operators and theory of set-valued functions as the non-smooth ones. Dynamical behaviour of the problem is governed by a pair of coupled multi-valued differential equations. The posed Cauchy problem is solved by use of the Grünwald-Letnikov numerical scheme. The behaviour of the system is analyzed for different values of system parameters.
Innovative design of viscoelastic dampers for seismic mitigation
International Nuclear Information System (INIS)
Tsai, C.S.
1993-01-01
In this paper, an advanced and more reliable design of viscoelastic dampers for seismic mitigation of high-rise buildings is presented. The innovative design of energy-absorbing devices has some advantages, compared to the classical design, as follows: One, the device is directly subjected to shear strains and forces due to story drifts; two, the device can support its own weight during normal operations, and maintain stable for large deformations during earthquakes; three, the device can reduce the responses of a structure to horizontal as well as vertical seismic loadings; and four, the device can also decrease the responses of the floor system of a building. In this study, a ten-story building is given as an example to express the merits obtained from the new system. Comparisons of the building equipped with classical and proposed devices of viscoelastic dampers are carefully studied. Numerical results show that the energy-absorbing capacity of the new device is superior to the classical one, especially for vertical vibrations. (orig.)
Jung, Ho-Yeon; Kim, In-Ho; Jung, Hyung-Jo
2017-10-31
Cable structure is a major component of long-span bridges, such as cable-stayed and suspension bridges, and it transfers the main loads of bridges to the pylons. As these cable structures are exposed to continuous external loads, such as vehicle and wind loads, vibration control and continuous monitoring of the cable are required. In this study, an electromagnetic (EM) damper was designed and fabricated for vibration control and monitoring of the cable structure. EM dampers, also called regenerative dampers, consist of permanent magnets and coils. The electromagnetic force due to the relative motion between the coil and the permanent magnet can be used to control the vibration of the structure. The electrical energy can be used as a power source for the monitoring system. The effects of the design parameters of the damper were numerically analyzed and the damper was fabricated. The characteristics of the damper were analyzed with various external load changes. Finally, the vibration-control and energy-harvesting performances of the cable structure were evaluated through a hybrid simulation. The vibration-control and energy-harvesting performances for various loads were analyzed and the applicability to the cable structure of the EM damper was evaluated.
International Nuclear Information System (INIS)
Li, Hui; Wang, Jian
2011-01-01
This paper reports the results of an experimental study conducted to demonstrate the feasibility and capability of magnetorheological (MR) dampers commanded by a decentralized control algorithm for seismic control of nonlinear civil structures considering soil-structure interaction (SSI). A two-story reinforced concrete (RC) frame resting in a laminar soil container is employed as the test specimen, and two MR dampers equipped in the first story are used to mitigate the response of this frame subjected to various intensity seismic excitations. A hyperbolic tangent function is used to represent the hysteretic behavior of the MR damper and a decentralized control approach for commanding MR dampers is proposed and implemented in the shaking table tests. Only the response of the first story is feedback for control command calculation of the MR dampers. The results indicate that the MR damper can effectively reduce the response of the soil-structure system, even when the soil-structure system presents complex nonlinear hysteretic behavior. The robustness of the proposed decentralized control algorithm is validated through the shaking table tests on the soil-structure system with large uncertainty. The most interesting findings in this paper are that MR dampers not only mitigate the superstructure response, but also reduce the soil response, pile response and earth pressure on the pile foundation
A mechanical energy harvested magnetorheological damper with linear-rotary motion converter
Chu, Ki Sum; Zou, Li; Liao, Wei-Hsin
2016-04-01
Magnetorheological (MR) dampers are promising to substitute traditional oil dampers because of adaptive properties of MR fluids. During vibration, significant energy is wasted due to the energy dissipation in the damper. Meanwhile, for conventional MR damping systems, extra power supply is needed. In this paper, a new energy harvester is designed in an MR damper that integrates controllable damping and energy harvesting functions into one device. The energy harvesting part of this MR damper has a unique mechanism converting linear motion to rotary motion that would be more stable and cost effective when compared to other mechanical transmissions. A Maxon motor is used as a power generator to convert the mechanical energy into electrical energy to supply power for the MR damping system. Compared to conventional approaches, there are several advantages in such an integrated device, including weight reduction, ease in installation with less maintenance. A mechanical energy harvested MR damper with linear-rotary motion converter and motion rectifier is designed, fabricated, and tested. Experimental studies on controllable damping force and harvested energy are performed with different transmissions. This energy harvesting MR damper would be suitable to vehicle suspensions, civil structures, and smart prostheses.
Analytical Model of Coil Spring Damper Based on the Loading Test
Energy Technology Data Exchange (ETDEWEB)
Cho, Sung Gook; Park, Woong Ki [INNOSE TECH Co. LTD, Incheon (Korea, Republic of); Furuya, Osamu [Tokyo City University, Tokyo (Japan); Kurabayashi, Hiroshi [Vibro-System, Tokyo (Japan)
2016-05-15
The one way of solving such problems is to enhance and to develop an improved damping element used in base-isolation and response control system. A cost reduction of damper for a large scale structure is another important task to upgrade the total response control abilities in the near future. This study has examined a response control device using elastoplastic hysteresis damping of metal material. The proposed damper is designed to be coil spring element shape for a uniform stress of metal and for a reduction of low cyclic fatigue in large deformation to upgrade a repetitive strength during the earthquake motions. By using the metal material of SS400 general structural rolled steel, the corresponding cost issues of the damping element will be effectively reduced. The analytical of elasto-plastic coil spring damper (CSD) is introduced, and basic mechanical properties evaluated experimentally and analytically. This study has been examined the response control damper using elasto-plastic hysteresis characteristics of metal material. The paper described the design method of elasto-plastic coil spring damper, basic mechanical properties evaluated from loading test, and analytical model of damper are summarized. It was confirmed that the damping force and mechanical characteristics of elasto-plastic coil spring damper are almost satisfied the design specifications.
Directory of Open Access Journals (Sweden)
Ho-Yeon Jung
2017-10-01
Full Text Available Cable structure is a major component of long-span bridges, such as cable-stayed and suspension bridges, and it transfers the main loads of bridges to the pylons. As these cable structures are exposed to continuous external loads, such as vehicle and wind loads, vibration control and continuous monitoring of the cable are required. In this study, an electromagnetic (EM damper was designed and fabricated for vibration control and monitoring of the cable structure. EM dampers, also called regenerative dampers, consist of permanent magnets and coils. The electromagnetic force due to the relative motion between the coil and the permanent magnet can be used to control the vibration of the structure. The electrical energy can be used as a power source for the monitoring system. The effects of the design parameters of the damper were numerically analyzed and the damper was fabricated. The characteristics of the damper were analyzed with various external load changes. Finally, the vibration-control and energy-harvesting performances of the cable structure were evaluated through a hybrid simulation. The vibration-control and energy-harvesting performances for various loads were analyzed and the applicability to the cable structure of the EM damper was evaluated.
Directory of Open Access Journals (Sweden)
Guerineau E.L.C.
2016-01-01
Full Text Available Auxiliary Mass Damper‘s (AMD performance is susceptible to changes in the frequency or in the excitation force’s nature. Therefore, to improve the robustness of the AMD it’s necessary to design new systems which are tunable and that could be used over large frequency range. In this work a friction damper, which is an association in series of a spring and a scratcher, is used to tune the AMD at the same time it dissipates the mechanical energy of the principal mass by changing the normal force on the scratcher. Three normal force control strategies, and two combinations of them, are studied: i The normal force is assumed constant; ii The normal force is obtained from the solution of the equation of motion assuming null displacement for the principal mass; iii The normal force is obtained based on the vibratory system’s state variables condition, guarantying that the direction of the friction force promotes the movement of the principal mass toward its static equilibrium position. The effectiveness of the proposed tunable AMD, where the adaptability is obtained by controlling the normal force on the smart friction damper, is evaluated based on mass and frequency ratios variations for each strategy.
Establishment of the technical basis to apply the viscous damper in nuclear power plant
Energy Technology Data Exchange (ETDEWEB)
Nakajima, J.; Suezono, N.; Higuchi, T. [Toshiba Corp., Isogo Nuclear Engineering Center, Isogo-ku, Yokohama (Japan); Katayama, H. [Toshiba Corp., Power and Industrial Systems Research and Development Center, Isogo-ku, Yokohama (Japan)
2014-07-01
In recent years, the technical development of the damper using viscous fluid (hereinafter called 'the viscous damper') for the structures, bridges and components in the general industrial field is remarkable, and the experiences of the application to mitigate influence in an earthquake is being gathered now. In this paper, purpose of the whole activity, schedule, the research and test results carried out so far, and future plan to establish the technical basis to apply the viscous damper in nuclear power plant are reported. (author)
Establishment of the technical basis to apply the viscous damper in nuclear power plant
International Nuclear Information System (INIS)
Nakajima, J.; Suezono, N.; Higuchi, T.; Katayama, H.
2014-01-01
In recent years, the technical development of the damper using viscous fluid (hereinafter called 'the viscous damper') for the structures, bridges and components in the general industrial field is remarkable, and the experiences of the application to mitigate influence in an earthquake is being gathered now. In this paper, purpose of the whole activity, schedule, the research and test results carried out so far, and future plan to establish the technical basis to apply the viscous damper in nuclear power plant are reported. (author)
Passivity enhancement by series LC filtered active damper with zero current reference
DEFF Research Database (Denmark)
Bai, Haofeng; Wang, Xiongfei; Blaabjerg, Frede
2016-01-01
can be improved by enhancing the passivity of the total admittance seen by the grid, which allows for a zero current reference and a much simpler current controller for the active damper. To show the performance of the active damper with zero reference, this paper first carries out the impedance based...... stability analysis of grid converters in the weak grid. Based on the impedance model of the series LC filtered active damper, the real part of its output admittance is investigated and shown to be able to enhance the passivity of the admittance of the converters seen by the grid. Finally, simulation...
Zorzi, E. S.; Burgess, G.; Cunningham, R.
1980-01-01
This paper describes the design and testing of an elastomer damper on a super-critical power transmission shaft. The elastomers were designed to provide acceptable operation through the fourth bending mode and to control synchronous as well as nonsynchronous vibration throughout the operating range. The design of the elastomer was such that it could be incorporated into the system as a replacement for a squeeze-film damper without a reassembly, which could have altered the imbalance of the shaft. This provided a direct comparison of the elastomer and squeeze-film dampers without having to assess the effect of shaft imbalance changes.
Linear and nonlinear analysis of fluid slosh dampers
Sayar, B. A.; Baumgarten, J. R.
1982-11-01
A vibrating structure and a container partially filled with fluid are considered coupled in a free vibration mode. To simplify the mathematical analysis, a pendulum model to duplicate the fluid motion and a mass-spring dashpot representing the vibrating structure are used. The equations of motion are derived by Lagrange's energy approach and expressed in parametric form. For a wide range of parametric values the logarithmic decrements of the main system are calculated from theoretical and experimental response curves in the linear analysis. However, for the nonlinear analysis the theoretical and experimental response curves of the main system are compared. Theoretical predictions are justified by experimental observations with excellent agreement. It is concluded finally that for a proper selection of design parameters, containers partially filled with viscous fluids serve as good vibration dampers.
Digital transverse beam dampers from the Brookhaven AGS
International Nuclear Information System (INIS)
Smith, G.A.; Castillo, V.; Roser, T.; Van Asselt, W.; Witkover, R.; Wong, V.
1995-01-01
A wide band, digital damper system has been developed and is in use at the Brookhaven Alternating Gradient Synchrotron (AGS). The system consists of vertical and horizontal capacitive pickups, analog and digital processing electronics, four 500 Watt wide band power amplifiers, and two pairs of strip line beam kickers. The system is currently used to damp transverse coherent instabilities and injection errors, in both planes, for protons and all species of heavy ions. This paper discusses the system design and operation, particularly with regard to stabilization of the high intensity proton beam. The analog and digital signal processing techniques used to achieve optimum results are discussed. Operational data showing the effect of the damping are presented
The damper for the transverse instabilities of the SPS
Bossart, Rudolf; Gareyte, Jacques; de Raad, Bastiaan; Rossi, V
1979-01-01
For beam intensities above 10/sup 12/ protons per pulse in the SPS, collective transverse beam instabilities develop with frequencies between 15 kHz and 3 MHz because of the resistive wall effect of the vacuum chamber. An active feedback system with an electrostatic deflector has been installed in the SPS for damping the resistive wall instabilities in both the vertical and horizontal planes. Measurements have been made to determine the threshold and growth rate of these instabilities. As a novel application, the damper can be used also for the excitation of small coherent betatron oscillations. A phase-locked loop tracks the beam oscillations and provides a continuous display of the betatron wave-number Q during the cycle. (4 refs).
Vibration Control of Novel Passive Multi-joints Rotational Friction Dampers
DEFF Research Database (Denmark)
Mualla, Imad H.; Koss, Holger
2017-01-01
that the damper performance is: - Independent of forcing frequency within applicable range - Linearly dependent on displacement amplitudes - Linearly dependent on normal forces - Very stable over many cycles Furthermore, a numerical model of the 4-joint damper has been developed based on an analytical derivation...... that are supplied by Damptech A/S have been installed in many projects in Japan, among them Japan tallest building and in other countries around the world. The paper provides a number of show cases demonstrating versatile application of rotational friction dampers (RFD)....... or strong winds. The damper is based on a rotational friction concept that was developed by Mualla, I.H. The devices have a stable energy dissipating behavior. They are flexible in the application, since they only need limited space. The devices can be installed easily. The damping capacity of the devices...
Site selection of active damper for stabilizing power electronics based power distribution system
DEFF Research Database (Denmark)
Yoon, Changwoo; Wang, Xiongfei; Bak, Claus Leth
2015-01-01
electronics based power device, which provides an adjustable damping capability to the power system where the voltage harmonic instability is measured. It can stabilize by adjusting the equivalent node impedance with its plug and play feature. This feature gives many degrees of freedom of its installation......Stability in the nowadays distribution power system is endangered by interaction problems that may arise from newly added power-electronics based power devices. Recently, a new concept to deal with this higher frequency instability, the active damper, has been proposed. The active damper is a power...... point when the system has many nodes. Therefore, this paper addresses the proper placement of an active damper in an unstable small-scale power distribution system. A time-domain model of the Cigre benchmark low-vltage network is used as a test field. The result shows the active damper location...
Elastomeric Dampers Derived From First-Principles-Based Analytical Simulation, Phase I
National Aeronautics and Space Administration — The lead-lag motions of rotor blades in a helicopter require damping to stabilize them. In practice, this has necessitated the use of external hydraulic dampers...
Czech Academy of Sciences Publication Activity Database
Zapoměl, Jaroslav; Kozánek, Jan; Ferfecki, Petr
2014-01-01
Roč. 21, č. 2 (2014), s. 75-81 ISSN 1802-1484 Institutional support: RVO:61388998 Keywords : rigid rotors * controllable damping * hybrid magnetorheological dampers * vibration stability Subject RIV: BI - Acoustics
Longitudinally Vibrating Elastic Rods with Locally and Non-Locally Reacting Viscous Dampers
Directory of Open Access Journals (Sweden)
Şefaatdin Yüksel
2005-01-01
Full Text Available Eigencharacteristics of a longitudinally vibrating elastic rod with locally and non-locally reacting damping are analyzed. The rod is considered as a continuous system and complex eigenfrequencies are determined as solution of a characteristic equation. The variation of the damping ratios with respect to damper locations and damping coefficients for the first four eigenfrequencies are obtained. It is shown that at any mode of locally or non-locally damped elastic rod, the variation of damping ratio with damper location is linearly proportional to absolute value of the mode shape of undamped system. It is seen that the increasing damping coefficient does not always increase the damping ratio and there are optimal values for the damping ratio. Optimal values for external damping coefficients of viscous dampers and locations of the dampers are presented.
Hybrid damper with stroke amplification for damping of offshore wind turbines
DEFF Research Database (Denmark)
Brodersen, Mark L.; Høgsberg, Jan
2016-01-01
tower. The proposed hybrid damper consists of a passive viscous dashpot placed in series with a load cell and an active actuator. By integrated force feedback control of the actuator motion, the associated displacement amplitude over the viscous damper can be increased compared with the passive viscous......The magnitude of tower vibrations of offshore wind turbines is a key design driver for the feasibility of the monopilesupport structure. A novel control concept for the damping of these tower vibrations is proposed, where viscous-type hybrid dampers are installed at the bottom of the wind turbine...... case, hereby significantly increasing the feasibility of viscous dampers acting at the bottom of the wind turbine tower. To avoid drift in the actuator displacement, a filtered time integration of the measured force signal is introduced. Numerical examples demonstrate that the filtered time integration...
Elastomeric Dampers derived from First-Principles-Based Analytical Simulation, Phase II
National Aeronautics and Space Administration — Lead-lag motions of rotor blades in helicopters require damping to stabilize them. In practice, this has necessitated the use of external hydraulic dampers which...
Seismic Responses of an Added-Story Frame Structure with Viscous Dampers
Cheng, Xuansheng; Jia, Chuansheng; Zhang, Yue
2014-01-01
The damping ratio of an added-story frame structure is established based on complex damping theory to determine the structure seismic response. The viscous dampers are selected and arranged through target function method. A significant damping effect is obtained when a small velocity index is selected. The seismic responses of a five-floor reinforced concrete frame structure with directly added light steel layers and light steel layers with viscous dampers are compared with the finite element...
Studies on Horizontal Axis Wind Turbine with Passive Teetered Brake & Damper Mechanism
SHIMIZU, Yukimaru; KAMADA, Yasunari; MAEDA, Takao
1998-01-01
In order to improve the reliability of megawatt wind turbines, the passive teetered brake & damper mechanism is applied. Its two unique effects, as its name implies, are braking and damping. The passive brake & damper mechanism is useful for variable speed control of the large wind turbine. It is comprised of teetering and feathering mechanisms. When the wind speed exceeds the rated wind speed, the blade is passively teetered in a downwind direction and, at the same time, a feathering mechani...
Experimental analysis of large capacity MR dampers with short- and long-stroke
International Nuclear Information System (INIS)
Zemp, René; De la Llera, Juan Carlos; Weber, Felix
2014-01-01
The purpose of this article is to study and characterize experimentally two magneto-rheological dampers with short- and long-stroke, denoted hereafter as MRD-S and MRD-L. The latter was designed to improve the Earthquake performance of a 21-story reinforced concrete building equipped with two 160 ton tuned pendular masses. The MRD-L has a nominal force capacity of 300 kN and a stroke of ±1 m; the MRD-S has a nominal force capacity of 150 kN, and a stroke of ±0.1 m. The MRD-S was tested with two different magneto-rheological and one viscous fluid. Due to the presence of Eddy currents, both dampers show a time lag between current intensity and damper force as the magnetization on the damper changes in time. Experimental results from the MRD-L show a force drop-off behavior. A decrease in active-mode forces due to temperature increase is also analyzed for the MRD-S and the different fluids. Moreover, the observed increase in internal damper pressure due to energy dissipation is evaluated for the different fluids in both dampers. An analytical model to predict internal pressure increase in the damper is proposed that includes as a parameter the concentration of magnetic particles inside the fluid. Analytical dynamic pressure results are validated using the experimental tests. Finally, an extended Bingham fluid model, which considers compressibility of the fluid, is also proposed and validated using damper tests. (paper)
Experimental analysis of large capacity MR dampers with short- and long-stroke
Zemp, René; de la Llera, Juan Carlos; Weber, Felix
2014-12-01
The purpose of this article is to study and characterize experimentally two magneto-rheological dampers with short- and long-stroke, denoted hereafter as MRD-S and MRD-L. The latter was designed to improve the Earthquake performance of a 21-story reinforced concrete building equipped with two 160 ton tuned pendular masses. The MRD-L has a nominal force capacity of 300 kN and a stroke of ±1 m; the MRD-S has a nominal force capacity of 150 kN, and a stroke of ±0.1 m. The MRD-S was tested with two different magneto-rheological and one viscous fluid. Due to the presence of Eddy currents, both dampers show a time lag between current intensity and damper force as the magnetization on the damper changes in time. Experimental results from the MRD-L show a force drop-off behavior. A decrease in active-mode forces due to temperature increase is also analyzed for the MRD-S and the different fluids. Moreover, the observed increase in internal damper pressure due to energy dissipation is evaluated for the different fluids in both dampers. An analytical model to predict internal pressure increase in the damper is proposed that includes as a parameter the concentration of magnetic particles inside the fluid. Analytical dynamic pressure results are validated using the experimental tests. Finally, an extended Bingham fluid model, which considers compressibility of the fluid, is also proposed and validated using damper tests.
Directory of Open Access Journals (Sweden)
S Saha Ray
2016-05-01
Full Text Available This article presents the formulation and a new approach to find analytic solutions for fractional continuously variable order dynamic models, namely, fractional continuously variable order mass–spring–damper systems. Here, we use the viscoelastic and viscous–viscoelastic dampers for describing the damping nature of the oscillating systems, where the order of fractional derivative varies continuously. Here, we handle the continuous changing nature of fractional order derivative for dynamic systems, which has not been studied yet. By successive recursive method, here we find the solution of fractional continuously variable order mass–spring–damper systems and then obtain closed-form solutions. We then present and discuss the solutions obtained in the cases with continuously variable order of damping for oscillator through graphical plots.
Design and testing of a MRF rotational damper for vehicle applications
International Nuclear Information System (INIS)
Giorgetti, A; Baldanzini, N; Citti, P; Biasiotto, M
2010-01-01
Adaptive dampers are an interesting solution for conjugating the necessity of controllable devices and low power consumption. Magneto-rheological fluids (MRF) can be profitably employed in adaptive dampers because of the significant variation of fluid parameters with magnetic field properties. This paper focuses on the design process of an innovative rotational MR damper specifically created to be placed in the front-wheel suspension of a compact car. The advantages of the rotational damper and the definition of the optimal design are described. The proposed damper significantly reduces several key problems associated with MR devices: the quantity of fluid required, the sedimentation of ferromagnetic particles in the suspension and the abrasion of the seals. In fact, with this solution, low average working pressure, low flow velocity through valves, a wide range of variable damping characteristics, and high durability of the damper can be achieved. Thanks to this innovative component, different new architectures for adaptive suspension systems can be developed to have a planar distribution of the suspension components with a consequent space optimization and size reduction in the vertical direction
Directory of Open Access Journals (Sweden)
Bo Chen
2015-01-01
Full Text Available The vibration control and performance evaluation on a transmission-tower line system by using friction dampers subjected to wind excitations are carried out in this study. The three-dimensional finite element (FE model of a transmission tower is firstly constructed. A two-dimensional lumped mass model of a transmission tower is developed for dynamic analysis. The analytical model of transmission tower-line system is proposed by taking the dynamic interaction between the tower and the transmission lines into consideration. The mechanical model of passive friction damper is presented by involving the effects of damper axial stiffness. The equation of motion of the transmission tower-line system incorporated with the friction dampers disturbed by wind excitations is established. A real transmission tower-line system is taken as an example to examine the feasibility and reliability of the proposed control approach. An extensive parameter study is carried out to find the optimal parameters of friction damper and to assess the effects of slipping force axial stiffness and hysteresis loop on control performance. The work on an example structure indicates that the application of friction dampers with optimal parameters could significantly reduce wind-induced responses of the transmission tower-line system.
DEFF Research Database (Denmark)
Zhou, Q.; Nielsen, Søren R.K.; Qu, W.L.
2007-01-01
amplitude is located in a certain range for the case OE2o1/3, the original zero out-of-plane vibration of the cable should be changed to the stable in-plane and out-of-plane coupled oscillation by using the optimal passive viscous damper or the MR damper with the SA-1 rule. It is also observed...... to the first in-plane eigenmode of the cable. The numerical results show that the MR damper with the SA-1 rule and the optimal viscous damper perform similarly to mitigate the vibration of the cable under axial periodic support motion, and, in some cases, the SA-2 rule is more favourable in suppressing...... the cable vibration compared with the SA-1 rule. In the final analysis, both the MR damper and the viscous damper can effectively mitigate the out-of-plane component of the cable, while having little effect on the reduction of the in-plane response in most cases. Furthermore, when the support motion...
Evaluation of the Reduction of Seismic Response of Adjacent Structures Using Viscous Damper Joint
Directory of Open Access Journals (Sweden)
Hamed Karbalay Malek
2017-09-01
Full Text Available This study examines the effect of common viscose damper on the behavior of adjacent reinforced concrete structures. For this purpose, three reinforced concrete 3, 5 and 7 floors buildings with a regular plan were selected and were compared in two cases without and with viscous dampers at the seams. They are designed based on discussions of Buildings Regulations 2800 and the 6 and 9 issues of Iranian National Building Regulations. Those buildings face under accelerograms of Bam, Mangil and El Centro, and then they are analyzed with nonlinear modal time history. This Accelerograms before applying to the structures, they are scaled based on the 2800 Regulations. Those buildings were modeled by SAP2000 finite element modeling software. Linear behavior of structural components of the structure and the non-linear behavior viscous damper were modeled. Finally, the seismic response of buildings includes the base shear force, up to a maximum lateral acceleration of seismic classes and classes for both with and without the viscous damper have been extracted and compared. The results showed the reduction in relative lateral displacement, maximum acceleration and base cut applied to structure in the presence of viscous dampers between two structures. This decline is not even in the direction that the viscous damper is viewed as significant.
Design and development of the Macpherson Proton Preve Magneto rheological damper with PID controller
Amiruddin, I. M.; Pauziah, M.; Aminudin, A.; Unuh, M. H.
2017-10-01
Since the creation of the first petrol-fuelled vehicle by Karl Benz in the late nineteenth century, car industry has grown considerably to meet the industrial demands. Luxurious looks and agreeable rides are the primary needs of drivers. The Magneto-rheological damper balanced their damping trademark progressively by applying the damping coefficient depending on the control system. In this research, the control calculations are assessed by utilizing the MR damper. The capacity and reliably of the target force for the damper speed is investigated from control algorithm. This is imperative to defeat the damper limitation. In this study, the simulation results of the semi-dynamic MR damper with the PID controller shows better performance in sprung mass acceleration, unsprung mass acceleration and suspension dislodging with permitting over the top tyre acceleration. The altered model of the MR damper is specially designed for Proton Preve specifications and semi-active PID control. The procedure for the advancement incorporates the numerical model to graphically recreate and break down the dynamic framework by utilizing Matlab.
Directory of Open Access Journals (Sweden)
Fitrian Imaduddin
2017-10-01
Full Text Available This paper presents the characterization and hysteresis modeling of magnetorheological (MR damper with meandering type valve. The meandering type MR valve, which employs the combination of multiple annular and radial flow passages, has been introduced as the new type of high performance MR valve with higher achievable pressure drop and controllable performance range than similar counterparts in its class. Since the performance of a damper is highly determined by the valve performance, the utilization of the meandering type MR valve in an MR damper could potentially improve the damper performance. The damping force characterization of the MR damper is conducted by measuring the damping force as a response to the variety of harmonic excitations. The hysteresis behavior of the damper is identified by plotting the damping force relationship to the excitation displacement and velocity. For the hysteresis modeling purpose, some parts of the data are taken as the training data source for the optimization parameters in the neuro-fuzzy model. The performance of the trained neuro-fuzzy model is assessed by validating the model output with the remaining measurement data and benchmarking the results with the output of the parametric hysteresis model. The validation results show that the neuro-fuzzy model is demonstrating good agreement with the measurement results indicated by the average relative error of only around 7%. The model also shows robustness with no tendency of growing error when the input values are changed.
Dynamic analysis of electro- and magneto-rheological fluid dampers using duct flow models
International Nuclear Information System (INIS)
Esteki, Kambiz; Bagchi, Ashutosh; Sedaghati, Ramin
2014-01-01
Magneto-rheological (MR) and electro-rheological (ER) fluid dampers provide a semi-active control mechanism for suppressing vibration responses of a structure. MR and ER fluids change their viscosity under the influence of magnetic and electrical fields, respectively, which facilitates automatic control when these fluids are used in damping devices. The existing models, namely the phenomenological models for simulating the behavior of MR and ER dampers, rely on various parameters determined experimentally by the manufacturers for each damper configuration. It is of interest to develop mechanistic models of these dampers which can be applied to various configurations so that their fundamental characteristics can be studied to develop flexible design solutions for smart structures. This paper presents a formulation for dynamic analysis of electro-rheological (ER) and magneto-rheological (MR) fluid dampers in flow and mix mode configurations under harmonic and random excitations. The procedure employs the vorticity transport equation and the regularization function to deal with the unsteady flow and nonlinear behavior of ER/MR fluid in general motion. The finite difference method has been used to solve the governing differential equations. Using the developed approach, the damping force of ER/MR dampers can be calculated under any type of excitation. (paper)
International Nuclear Information System (INIS)
Dong, Xiaomin
2016-01-01
An axial flux permanent magnet energy harvester (AFPMEH) is proposed and analyzed for a vehicle magneto-rheological (MR) damper. The relationship between the output voltage and the input excitations are analytically developed. Under different constant rotation speeds and sinusoidal excitations, the harvesting energy is numerically computed for different loads of pure resistance and coil in the MR damper. To check the performance of the proposed AFPMEH for the MR damper, the AFPMEH and MR damper are fabricated individually. Experiments are performed to measure the harvesting energy of the AFPMEH and the damping characteristics of the MR damper under different excited conditions. The excited conditions include three constant rotation speeds and sinusoidal inputs. Load inputs of the pure resistance and the coil of the MR damper are considered. The results show that the time history of the generated voltage of the AFPMEH in experiment is agreed well with that of the AFPMEH in simulation. Under constant rotation speeds, the root mean square (rms) of loaded voltage will increase with the increment of load, whereas the rms of power will be affected by the amplitude of load. The MR damper powered by the AFPMEH can almost obtain the similar damping characteristics of that external power supply. Under sinusoidal inputs, the rms of loaded voltage will increase with the increment of external loads, whereas the rms of power will be almost kept as a constant. The damping range of the MR damper can also be enlarged over 30% comparing to off-state damping force. A quarter car model with an MR damper powered by the AFPMEH is developed to investigate the control performance. The on–off skyhook control is adopted to tune the input current of the MR damper. The vibration performance of the MR suspension is investigated under different roads and vehicle speeds. The numerical results show that the MR suspension with the AFPMEH under on–off skyhook control can achieve better ride
Novikov, Dmitrii K.; Diligenskii, Dmitrii S.
2018-01-01
The article considers the work of some squeeze film damper with elastic rings parts. This type of damper is widely used in gas turbine engines supports. Nevertheless, modern analytical solutions have a number of limitations. The article considers the behavior of simple hydrodynamic damping systems. It describes the analysis of fluid-solid interaction simulation applicability for the defying properties of hydrodynamic damper with elastic rings (“allison ring”). There are some recommendations on the fluid structural interaction analysis of the hydrodynamic damper with elastic rings.
International Nuclear Information System (INIS)
Gugele, B.; Scheider, J.; Spangl, W.
2001-01-01
In recent years several regulations and standards for air quality and limits for air pollution were issued or are in preparation by the European Union, which have severe influence on the environmental monitoring and legislation in Austria. This chapter of the environmental control report of Austria gives an overview about the legal situation of air pollution control in the European Union and in specific the legal situation in Austria. It gives a comprehensive inventory of air pollution measurements for the whole area of Austria of total suspended particulates, ozone, volatile organic compounds, nitrogen oxides, sulfur dioxide, carbon monoxide, heavy metals, benzene, dioxin, polycyclic aromatic hydrocarbons and eutrophication. For each of these pollutants the measured emission values throughout Austria are given in tables and geographical charts, the environmental impact is discussed, statistical data and time series of the emission sources are given and legal regulations and measures for an effective environmental pollution control are discussed. In particular the impact of fossil-fuel power plants on the air pollution is analyzed. (a.n.)
Contributions to modeling functionality of a high frequency damper system
Sirbu, E. A.; Horga, S.; Vrabioiu, G.
2016-08-01
Due to the necessity of improving the handling performances of a motor vehicle, it is imperative to understand the suspensions properties that affects ride and directional respons.The construction of a fero-magnetic shock absorber is based on two bellows interconnected by a pipe-line. Through this pipe-line the fero-magnetic fluid is carried between the two bellows. The damping characteristic of the shock absorber is affected by the viscosity of the fero-magnetic fluid. The viscosity of the fluid, is controlled through a electric coil mounted on the bellows connecting pipe-line. Modifying the electrical field of the coil, the viscosity of the fluid will change, finally affecting the damping characteristic of the shock absorber. A recent system called „CCD Pothole Suspension” is implemented on Ford vehicles. By modifying the dampning characteristic of the shock absorbers, vehicle daynamics can be improved; also the risk of damaging the suspension will be decreased. The approach of this paper is to analyze the behaviour of the fero magnetic damper, thus determining how it will affect the performances of the vehicle suspensions. The experimental research will provide a better understanding of the behavior of the fero-magnetic shock absorber, and the possible advantages of using this system.
A magneto rheological hybrid damper for railway vehicles suspensions
Directory of Open Access Journals (Sweden)
Gheorghe GHITA
2012-09-01
Full Text Available High speed railway vehicles features a specific lateral oscillation resulting from the coupled lateral displacement and yaw of the wheelset which leads to a sinusoid movement of the wheelset along the track, transferred to the entire vehicle. The amplitude of this oscillation is strongly dependant on vehicle’s velocity. Over a certain value, namely the critical speed, the instability phenomenon so-called hunting occurs. To raise the vehicle’s critical speed different designs of the suspension all leading to a much stiffer vehicle can be envisaged. Different simulations prove that a stiffer central suspension will decrease the passenger’s comfort in terms of lateral accelerations of the carboy. The authors propose a semi-active magneto rheological suspension to improve the vehicle’s comfort at high speeds. The suspension has as executive elements hybrid magneto rheological dampers operating under sequential control strategy type balance logic. Using an original mathematical model for the lateral dynamics of the vehicle the responses of the system with passive and semi-active suspensions are simulated. It is shown that the semi-active suspension can improve the vehicle performances.
Re-tuning tuned mass dampers using ambient vibration measurements
International Nuclear Information System (INIS)
Hazra, B; Sadhu, A; Narasimhan, S; Lourenco, R
2010-01-01
Deterioration, accidental changes in the operating conditions, or incorrect estimates of the structure modal properties lead to de-tuning in tuned mass dampers (TMDs). To restore optimal performance, it is necessary to estimate the modal properties of the system, and re-tune the TMD to its optimal state. The presence of closely spaced modes and a relatively large amount of damping in the dominant modes renders the process of identification difficult. Furthermore, the process of estimating the modal properties of the bare structure using ambient vibration measurements of the structure with the TMD is challenging. In order to overcome these challenges, a novel identification and re-tuning algorithm is proposed. The process of identification consists of empirical mode decomposition to separate the closely spaced modes, followed by the blind identification of the remaining modes. Algorithms for estimating the fundamental frequency and the mode shape of the primary structure necessary for re-tuning the TMD are proposed. Experimental results from the application of the proposed algorithms to identify and re-tune a laboratory structure TMD system are presented
Dynamic characteristics of Non Newtonian fluid Squeeze film damper
Palaksha, C. P.; Shivaprakash, S.; Jagadish, H. P.
2016-09-01
The fluids which do not follow linear relationship between rate of strain and shear stress are termed as non-Newtonian fluid. The non-Newtonian fluids are usually categorized as those in which shear stress depends on the rates of shear only, fluids for which relation between shear stress and rate of shear depends on time and the visco inelastic fluids which possess both elastic and viscous properties. It is quite difficult to provide a single constitutive relation that can be used to define a non-Newtonian fluid due to a great diversity found in its physical structure. Non-Newtonian fluids can present a complex rheological behaviour involving shear-thinning, viscoelastic or thixotropic effects. The rheological characterization of complex fluids is an important issue in many areas. The paper analyses the damping and stiffness characteristics of non-Newtonian fluids (waxy crude oil) used in squeeze film dampers using the available literature for viscosity characterization. Damping and stiffness characteristic will be evaluated as a function of shear strain rate, temperature and percentage wax concentration etc.
Design of a Hydraulic Damper for Heavy Machinery
Directory of Open Access Journals (Sweden)
Emil Zaev
2011-09-01
Full Text Available A hydraulic unit consisting of an accumulator as energy storage element and an orifice providing friction was designed to damp oscillations of a machine during operation. In the first step, a model for the gas spring was developed from the ideal gas laws for the dimensioning the elements. To model the gas process with a graphical simulation tool it is necessary to find a form of the gas law which can be integrated with a numerical solver, such as Tustin, Runge-Kutta, or other. For simulating the working condition, the model was refined using the van der Waals equations for real gas. A unified model representation was found to be applied for any arbitrary state change. Verifications were made with the help of special state changes, adiabatic and isothermal. After determining the dimensional parameters, which are the accumulator capacity and the orifice size, the operational and the limiting parameters were to be found. The working process of a damper includes the gas pre-charging to a predefined pressure, the nearly isothermal static loading process, and the adiabatic change during the dynamic operation.
Modelling the nonlinear behaviour of an underplatform damper test rig for turbine applications
Pesaresi, L.; Salles, L.; Jones, A.; Green, J. S.; Schwingshackl, C. W.
2017-02-01
Underplatform dampers (UPD) are commonly used in aircraft engines to mitigate the risk of high-cycle fatigue failure of turbine blades. The energy dissipated at the friction contact interface of the damper reduces the vibration amplitude significantly, and the couplings of the blades can also lead to significant shifts of the resonance frequencies of the bladed disk. The highly nonlinear behaviour of bladed discs constrained by UPDs requires an advanced modelling approach to ensure that the correct damper geometry is selected during the design of the turbine, and that no unexpected resonance frequencies and amplitudes will occur in operation. Approaches based on an explicit model of the damper in combination with multi-harmonic balance solvers have emerged as a promising way to predict the nonlinear behaviour of UPDs correctly, however rigorous experimental validations are required before approaches of this type can be used with confidence. In this study, a nonlinear analysis based on an updated explicit damper model having different levels of detail is performed, and the results are evaluated against a newly-developed UPD test rig. Detailed linear finite element models are used as input for the nonlinear analysis, allowing the inclusion of damper flexibility and inertia effects. The nonlinear friction interface between the blades and the damper is described with a dense grid of 3D friction contact elements which allow accurate capturing of the underlying nonlinear mechanism that drives the global nonlinear behaviour. The introduced explicit damper model showed a great dependence on the correct contact pressure distribution. The use of an accurate, measurement based, distribution, better matched the nonlinear dynamic behaviour of the test rig. Good agreement with the measured frequency response data could only be reached when the zero harmonic term (constant term) was included in the multi-harmonic expansion of the nonlinear problem, highlighting its importance
Design, Analysis, and Experimental Evaluation of a Double Coil Magnetorheological Fluid Damper
Directory of Open Access Journals (Sweden)
Guoliang Hu
2016-01-01
Full Text Available A magnetorheological (MR damper is one of the most advanced devices used in a semiactive control system to mitigate unwanted vibration because the damping force can be controlled by changing the viscosity of the internal magnetorheological (MR fluids. This study proposes a typical double coil MR damper where the damping force and dynamic range were derived from a quasistatic model based on the Bingham model of MR fluid. A finite element model was built to study the performance of this double coil MR damper by investigating seven different piston configurations, including the numbers and shapes of their chamfered ends. The objective function of an optimization problem was proposed and then an optimization procedure was constructed using the ANSYS parametric design language (APDL to obtain the optimal damping performance of a double coil MR damper. Furthermore, experimental tests were also carried out, and the effects of the same direction and reverse direction of the currents on the damping forces were also analyzed. The relevant results of this analysis can easily be extended to the design of other types of MR dampers.
Establishment of the technical basis for applying viscous dampers to nuclear power plants
International Nuclear Information System (INIS)
Narahara, Yukiko; Higuchi, Tomokazu; Katayama, Hiroshi; Ito, Ryo; Hattori, Kiyoshi; Nakajima, Jun
2017-01-01
For the purpose of introducing viscous dampers to nuclear power plants, the damping characteristic of the viscous damper under specific conditions in nuclear power plants was examined. In particular the seismic response analysis method, the design evaluation method, and the maintenance and management guideline were studied. In the viscous dampers characteristic test, the damping characteristics under earthquake motion and the environmental condition of nuclear power plants have been examined. From the test results, if the parameters such as vibration amplitude, vibration frequency, repeated load, temperature, and radiation are considered, there is a possibility of viscous damper application to components in nuclear power plants. In order to evaluate the applicability of the complex modal analysis method using response spectrum, comparison with the time history response analysis result was performed using a PWR steam generator analysis model. The evaluation result from the complex modal analysis method was in good agreement with the time history response analysis result, and the availability of this method was confirmed. From the test results, considerations in design and maintenance in the case of applying viscous dampers to nuclear power plants were selected. The bases of the design evaluation method and the maintenance and management guideline were developed. (author)
Semi-active H∞ control of high-speed railway vehicle suspension with magnetorheological dampers
Zong, Lu-Hang; Gong, Xing-Long; Xuan, Shou-Hu; Guo, Chao-Yang
2013-05-01
In this paper, semi-active H∞ control with magnetorheological (MR) dampers for railway vehicle suspension systems to improve the lateral ride quality is investigated. The proposed semi-active controller is composed of a H∞ controller as the system controller and an adaptive neuro-fuzzy inference system (ANFIS) inverse MR damper model as the damper controller. First, a 17-degree-of-freedom model for a full-scale railway vehicle is developed and the random track irregularities are modelled. Then a modified Bouc-Wen model is built to characterise the forward dynamic characteristics of the MR damper and an inverse MR damper model is built with the ANFIS technique. Furthermore, a H∞ controller composed of a yaw motion controller and a rolling pendulum motion (lateral motion+roll motion) controller is established. By integrating the H∞ controller with the ANFIS inverse model, a semi-active H∞ controller for the railway vehicle is finally proposed. Simulation results indicate that the proposed semi-active suspension system possesses better attenuation ability for the vibrations of the car body than the passive suspension system.
Power turbine dynamics - An evaluation of a shear-mounted elastomeric damper
Zorzi, E. S.; Walton, J.; Cunningham, R.
1983-01-01
As an alternative to the more conventional squeeze-film bearing damper designs, a Viton-70 shear-mounted, elastomeric damper was built and tested in a T-55 power turbine high-speed balancing rig. This application demonstrated, for the first time, the feasibility of using elastomers as the primary rotor damping source in production turbine engine hardware. The shear-mounted damper design was selected because of its compatibility with actual gas turbine engine radial space constraints, its accommodation of both the radial and axial thrust loads present in gas turbine engines, and its capability of controlled axial preload. Test results showed that the Viton-70 elastomeric damper operated successfully and provided excellent control of both synchronous and nonsynchronous vibrations through all phases of testing to the maximum rotor speed of 1676 rad/s (16,000 rpm). Excellent correlation between the predicted and experienced critical speeds, mode shapes, and log decrements for the power turbine rotor and elastomer damper assembly was also achieved.
Optimal Control via Integrating the Dynamics of Magnetorheological Dampers and Structures
Directory of Open Access Journals (Sweden)
Amir Fayezioghani
2015-03-01
Full Text Available Magnetorheological (MR dampers have the advantage of being tuned by low voltages. This has attracted many researchers to develop semi-active control of structures in theory and practice. Most of the control strategies first obtain the desired forces of dampers without taking their dynamics into consideration and then determine the input voltages according to those forces. As a result, these strategies may face situations where the desired forces cannot be produced by the dampers. In this article, by integrating the equations of the dynamics of MR dampers and the structural motion, and solving them in one set, a more concise semi-active optimal control strategy is presented, so as to bypass the aforementioned drawback. Next, a strong database that can be utilized to form a controller for more realistic implementations is produced. As an illustrative example, the optimal voltages of the dampers of a six-storey shear building are obtained under the scaled El-Centro earthquake and used to train a set of integrated analysis-adaptive neuro-fuzzy inference systems (ANFISs as a controller. Results show that the overall performance of the proposed strategy is higher than most of the other conventional methods.
Madheswaran, C. K.; Prakash vel, J.; Sathishkumar, K.; Rao, G. V. Rama
2017-06-01
A three-storey half scale reinforced concrete (RC) building is fixed with X-shaped metallic damper at the ground floor level, is designed and fabricated to study its seismic response characteristics. Experimental studies are carried out using the (4 m × 4 m) tri-axial shake-table facility to evaluate the seismic response of a retrofitted RC building with open ground storey (OGS) structure using yielding type X-shaped metallic dampers (also called as Added Damping and Stiffness-ADAS elements) and repairing the damaged ground storey columns using geopolymer concrete composites. This elasto-plastic device is normally incorporated within the frame structure between adjacent floors through chevron bracing, so that they efficiently enhance the overall energy dissipation ability of the seismically deficient frame structure under earthquake loading. Free vibration tests on RC building without and with yielding type X-shaped metallic damper is carried out. The natural frequencies and mode shapes of RC building without and with yielding type X-shaped metallic damper are determined. The retrofitted reinforced concrete building is subjected to earthquake excitations and the response from the structure is recorded. This work discusses the preparation of test specimen, experimental set-up, instrumentation, method of testing of RC building and the response of the structure. The metallic damper reduces the time period of the structure and displacement demands on the OGS columns of the structure. Nonlinear time history analysis is performed using structural analysis package, SAP2000.
A semi-active control suspension system for railway vehicles with magnetorheological fluid dampers
Wei, Xiukun; Zhu, Ming; Jia, Limin
2016-07-01
The high-speed train has achieved great progress in the last decades. It is one of the most important modes of transportation between cities. With the rapid development of the high-speed train, its safety issue is paid much more attention than ever before. To improve the stability of the vehicle with high speed, extra dampers (i.e. anti-hunting damper) are used in the traditional bogies with passive suspension system. However, the curving performance of the vehicle is undermined due to the extra lateral force generated by the dampers. The active suspension systems proposed in the last decades attempt to solve the vehicle steering issue. However, the active suspension systems need extra actuators driven by electrical power or hydraulic power. There are some implementation and even safety issues which are not easy to be overcome. In this paper, an innovative semi-active controlled lateral suspension system for railway vehicles is proposed. Four magnetorheological fluid dampers are fixed to the primary suspension system of each bogie. They are controlled by online controllers for enhancing the running stability on the straight track line on the one hand and further improving the curving performance by controlling the damper force on the other hand. Two control strategies are proposed in the light of the pure rolling concept. The effectiveness of the proposed strategies is demonstrated by SIMPACK and Matlab co-simulation for a full railway vehicle with two conventional bogies.
Active Elastic Support/Dry Friction Damper with Piezoelectric Ceramic Actuator
Directory of Open Access Journals (Sweden)
Liao Mingfu
2014-01-01
Full Text Available The basic operation principle of elastic support/dry friction damper in rotor system was introduced and the unbalance response of the rotor with elastic support/dry friction damper was analyzed theoretically. Based on the previous structure using an electromagnet as actuator, an active elastic support/dry friction damper using piezoelectric ceramic actuator was designed and its effectiveness of reducing rotor vibration when rotor traverses its critical speed and blade-out event happened was experimentally verified. The experimental results show that the active elastic support/dry friction damper with piezoelectric ceramic actuator can significantly reduce vibration in rotor system; the vibration amplitude of the rotor in critical speed region decreased more than 2 times, and the active damper can protect the rotor when a blade-out event happened, so the rotor can traverse the critical speed and shut down smoothly. In addition, the structure is much simpler than the previous, the weight was reduced by half and the power consumption was only 5 W.
International Nuclear Information System (INIS)
Erkus, Baris; Johnson, Erik A
2011-01-01
This paper investigates the dissipativity and performance characteristics of the semiactive control of the base isolated benchmark structure with magnetorheological (MR) fluid dampers. Previously, the authors introduced the concepts of dissipativity and dissipativity indices in the semiactive control of structures with smart dampers and studied the dissipativity characteristics of simple structures with idealized dampers. To investigate the effects of semiactive controller dissipativity characteristics on the overall performance of the base isolated benchmark building, a clipped optimal control strategy with a linear quadratic Gaussian (LQG) controller and a 20 ton MR fluid damper model is used. A cumulative index is proposed for quantifying the overall dissipativity of a control system with multiple control devices. Two control designs with different dissipativity and performance characteristics are considered as the primary controller in clipped optimal control. Numerical simulations reveal that the dissipativity indices can be classified into two groups that exhibit distinct patterns. It is shown that the dissipativity indices identify primary controllers that are more suitable for application with MR dampers and provide useful information in the semiactive design process that complements other performance indices. The computational efficiency of the proposed dissipativity indices is verified by comparing computation times
International Nuclear Information System (INIS)
Cho, Sang Won; Koo, Jeong Hoi; Jo, Ji Seong
2007-01-01
This paper presents a novel electromagnetic induction (EMI) system integrated in magneto rheological (MR) dampers: The added EMI system converts reciprocal motions of MR damper into electiral energy (electromotive force or emf) according to the Faraday's law of electromagnetic induction. Maximum energy dissipation algorithm (MEDA) is employed to regulate the MR dampers because it strives to simplify a complex design process by employing the Lyapunov's direct approach. The emf signal, produced from the EMI, provides the necessary measurement information (i.e., realtive velocity across the damper) for the MEDA controller. Thus, the EMI acts as a sensor in the proposed MR-EMI system. In order to evaluate the performance and robustness of the MR-EMI sensor system with the MEDA control, this study performed an extensive simulation study using the first generation benchmark cable-stayed bridge. Moreover, it compared the performance and the robustness of proposed system with those of Clipped-Optimal Control (COC) and Sliding Mode Control (SMC), which were previously studied for the benchmark cable-stayed bridge. The results show that the MR-EMI system reduced the vibrations of the bridge structure more than those of COC and SMC and show more robust performance than that of SMC. These results suggest that EMIs can be used cost-effective sensing devices for MR damper control systems without compromising the performance of them
Bapat, V. A.; Prabhu, P.
1980-11-01
The problem of designing an optimum Lanchester damper for a viscously damped single degree of freedom system subjected to inertial harmonic excitation is investigated. Two criteria are used for optimizing the performance of the damper: (i) minimum motion transmissibility; (ii) minimum force transmissibility. Explicit expressions are developed for determining the absorber parameters.
DEFF Research Database (Denmark)
Zhou, Q.; Nielsen, Søren R.K.; Qu, W. L.
2006-01-01
Three-dimensional semi-active vibration control of an inclined sag cable with discrete magnetorheological (MR) dampers is investigated in this paper using the finite difference method (FDM). A modified Dahl model is used to describe the dynamic property of MR damper. The nonlinear equations...
DEFF Research Database (Denmark)
Lu, Dapeng; Wang, Xiongfei; Bai, Haofeng
2016-01-01
resistance through detection and resonant controller, the series active damper can suppress the resonance with its external damping character in closed-loop damping character are carried out. Simulation and experimental results are presented to verify the effectiveness of the proposed series active damper....
DEFF Research Database (Denmark)
Zhang, Zili; Nielsen, Søren R. K.; Basu, Biswajit
2015-01-01
Tuned liquid dampers (TLDs) utilize the sloshing motion of the fluid to suppress structural vibrations and become a natural candidate for damping vibrations in rotating wind turbine blades. The centrifugal acceleration at the tip of a wind turbine blade can reach a magnitude of 7–8g. This facilit......Tuned liquid dampers (TLDs) utilize the sloshing motion of the fluid to suppress structural vibrations and become a natural candidate for damping vibrations in rotating wind turbine blades. The centrifugal acceleration at the tip of a wind turbine blade can reach a magnitude of 7–8g...... free-surface elevation equally well, the one-mode model can still be utilized for the design of TLD. Parametric optimization of the TLD is carried out based on the one-mode model, and the optimized damper effectively improves the dynamic response of wind turbine blades....
Semiactive Control Using MR Dampers of a Frame Structure under Seismic Excitation
International Nuclear Information System (INIS)
Gattulli, Vincenzo; Lepidi, Marco; Potenza, Francesco; Carneiro, Rubia
2008-01-01
The paper approaches the multifaceted task of semiactively controlling the seismic response of a prototypal building model, through interstorey bracings embedding magnetorheological dampers. The control strategy is based on a synthetic discrete model, purposely formulated in a reduced space of significant dynamic variables, and consistently updated to match the modal properties identified from the experimental response of the modeled physical structure. The occurrence of a known eccentricity in the mass distribution, breaking the structural symmetry, is also considered. The dissipative action of two magnetorheological dampers is governed by a clipped-optimal control strategy. The dampers are positioned in order to deliver two eccentric and independent forces, acting on the first-storey displacements. This set-up allows the mitigation of the three-dimensional motion arising when monodirectional ground motion is imposed on the non-symmetric structure. Numerical investigations on the model response to natural accelerograms are presented. The effectiveness of the control strategy is discussed through synthetic performance indexes
Vibration isolation using nonlinear damping implemented by a feedback-controlled MR damper
International Nuclear Information System (INIS)
Ho, C; Lang, Z Q; Billings, S A; Sapiński, B
2013-01-01
The main problem of using a conventional linear damper on a vibration isolation system is that the reduction of the resonant peak in many cases inevitably results in the degradation of the high-frequency transmissibility. Instead of using active control methods which normally depend on the model of the controlled plant and where unmodelled dynamics may induce stability concerns, recent studies have revealed that optimal vibration isolation over a wide frequency range can be achieved by using nonlinear damping. The present study is concerned with the realization of the ideal nonlinear damping characteristic using a feedback-controlled MR damper. Both simulation and experimental studies are conducted to demonstrate the advantages of the simple but effective vibration control strategy. This research work has significant implications for the effective use of MR dampers in the vibration control of a wide range of engineering systems. (paper)
Controllable outrigger damping system for high rise building with MR dampers
Wang, Zhihao; Chang, Chia-Ming; Spencer, Billie F., Jr.; Chen, Zhengqing
2010-04-01
A novel energy dissipation system that can achieve the amplified damping ratio for a frame-core tube structures is explored, where vertical dampers are equipped between the outrigger and perimeter columns. The modal characteristics of the structural system with linear viscous dampers are theoretically analyzed from the simplified finite element model by parametric analysis. The result shows that modal damping ratios of the first several modes can increase a lot with this novel damping system. To improve the control performance of system, the semi-active control devices, magnetorheological (MR) dampers, are adopted to develop a controllable outrigger damping system. The clipped optimal control with the linear-quadratic Gaussian (LQG) acceleration feedback is adopted in this paper. The effectiveness of both passive and semi-active control outrigger damping systems is evaluated through the numerical simulation of a representative tall building subjected to two typical earthquake records.
International Nuclear Information System (INIS)
Ekkachai, Kittipong; Nilkhamhang, Itthisek; Tungpimolrut, Kanokvate
2013-01-01
An inverse controller is proposed for a magnetorheological (MR) damper that consists of a hysteresis model and a voltage controller. The force characteristics of the MR damper caused by excitation signals are represented by a feedforward neural network (FNN) with an elementary hysteresis model (EHM). The voltage controller is constructed using another FNN to calculate a suitable input signal that will allow the MR damper to produce the desired damping force. The performance of the proposed EHM-based FNN controller is experimentally compared to existing control methodologies, such as clipped-optimal control, signum function control, conventional FNN, and recurrent neural network with displacement or velocity inputs. The results show that the proposed controller, which does not require force feedback to implement, provides excellent accuracy, fast response time, and lower energy consumption. (paper)
Mathematical model of a novel small magnetorheological damper by using outer magnetic field
Directory of Open Access Journals (Sweden)
Liutian Huang
2017-03-01
Full Text Available In order to realize small loading and small damping, a mini Magneto-rheological fluid (MRF damper is suggested by using new method of outer coils, and its physical model is established firstly. It was found that the landing force is only 1.74∼8N, the landing force is the third-order function with the current by polynomial fitting of the experimental data, which shows a force-current model. The results of force-displacement and force-velocity indicate that it has nonlinear hysteretic damping characteristics. Based on the new mini-mode principle and the damping characteristics, an improved nonlinear dynamics model is proposed, and its parameter expressions are obtained by parameter identification and regression fitting. Model curves fit well with experimental curves, and the improved model has fully demonstrated the dynamic characteristics of the mini-MRF damper. It will provide scientific method and physical model for the small MRF damper development.
H∞ control of railway vehicle suspension with MR damper using scaled roller rig
International Nuclear Information System (INIS)
Shin, Yu-Jeong; You, Won-Hee; Hur, Hyun-Moo; Park, Joon-Hyuk
2014-01-01
In this paper, a magneto-rheological (MR) damper was applied to the secondary suspension to reduce the vibration of a car body. The control performance of the MR damper was verified by numerical analysis with a 1/5 scale railway vehicle model in accordance with the similarity law. The analysis results were then validated in tests. In particular, the objective of the study was to understand how the control performance affected the dynamic characteristics of a railway vehicle and to systematically analyze the relationship between control performance and dynamic characteristics depending on various running speeds. To achieve this, experimental results for the dynamic characteristics of the scaled MR damper designed for the 1/5 scale railway vehicle model were applied to the railway vehicle model. The H ∞ control method was applied to the controller. The means of designing the railway vehicle body vibration controller and the effectiveness of its results were studied. (paper)
A novel two-way-controllable magneto-rheological fluid damper
International Nuclear Information System (INIS)
Aydar, Gokhan; Wang, Xiaojie; Gordaninejad, Faramarz
2010-01-01
In this paper, a disc type, radial flow-mode magneto-rheological (MR) fluid damper comprising a permanent magnet and an electromagnet is designed, built and tested. The proposed MR fluid damper has an MR valve with which two-way controllability through cancellation or enhancement of the magnetic field is obtained. This added feature provides damping forces less than or greater than that of a passive viscous original equipment manufacturer damper. A three-dimensional electromagnetic finite element analysis has been performed to realize this unique function in the proposed design. Experimental and theoretical studies have been conducted in order to demonstrate that this new design can provide softer damping properties by cancelling the effect of the permanent magnet, while at the same time enhancing the field effect, resulting in a harder damping device. Softer and harder damping refer to decrease and increase in the damping, respectively
A Cable-Passive Damper System for Sway and Skew Motion Control of a Crane Spreader
Directory of Open Access Journals (Sweden)
La Duc Viet
2015-01-01
Full Text Available While the crane control problem is often approached by applying a certain active control command to some parts of the crane, this paper proposes a cable-passive damper system to reduce the vibration of a four-cable suspended crane spreader. The residual sway and skew motions of a crane spreader always produce the angle deflections between the crane cables and the crane spreader. The idea in this paper is to convert those deflections into energy dissipated by the viscous dampers, which connect the cables and the spreader. The proposed damper system is effective in reducing spreader sway and skew motions. Moreover, the optimal damping coefficient can be found analytically by minimizing the time integral of system energy. The numerical simulations show that the proposed passive system can assist the input shaping control of the trolley motion in reducing both sway and skew responses.
Design and analysis of a magneto-rheological damper for an all terrain vehicle
Krishnan Unni, R.; Tamilarasan, N.
2018-02-01
A shock absorber design intended to replace the existing conventional shock absorber with a controllable system using a Magneto-rheological damper is introduced for an All Terrain Vehicle (ATV) that was designed for Baja SAE competitions. Suspensions are a vital part of an All Terrain Vehicles as it endures various surfaces and requires utmost attention while designing. COMSOL multi-physics software is used for applications that have coupled physics problems and is a unique tool that is used for the designing and analysis phase of the Magneto-rheological damper for the considered application and the model is optimized based on Taguchi using DOE software. The magneto-rheological damper is designed to maximize the damping force with the measured geometric constraints for the All Terrain Vehicle.
Seismic Responses of an Added-Story Frame Structure with Viscous Dampers
Directory of Open Access Journals (Sweden)
Xuansheng Cheng
2014-01-01
Full Text Available The damping ratio of an added-story frame structure is established based on complex damping theory to determine the structure seismic response. The viscous dampers are selected and arranged through target function method. A significant damping effect is obtained when a small velocity index is selected. The seismic responses of a five-floor reinforced concrete frame structure with directly added light steel layers and light steel layers with viscous dampers are compared with the finite element software SAP2000. Calculation results show that, after adding the layers, the structure becomes flexible and the shear in the bottom layer decreases. However, the interlaminar shear of the other layers increases. The seismic response of the added layers is very significant and exhibits obvious whiplash effect. The interstory displacement angles of some layers do not meet the requirements. The seismic response of the structure decreases after the adoption of viscous dampers; thereby seismic requirements are satisfied.
Passivity Enhancement of Grid-Tied Converter by Series LC-Filtered Active Damper
DEFF Research Database (Denmark)
Bai, Haofeng; Wang, Xiongfei; Loh, Poh Chiang
2015-01-01
attention. Also, parasitic capacitance of the grid transmission line brings new challenge for the application of an active damper, which has not been discussed before. In order to fill these gaps, this paper first analyzes the stability of a grid-tied converter with the help of passivity. Based......Series LC-filtered active damper can be used to stabilize the grid-tied voltage source converter in a non-ideal grid. The operation principle of the active damper is to mimic a damping resistance at the resonance frequencies. However, the selection of the damping resistance has not received much...... on the passivity-based-stability analysis, a damping resistance selection method is proposed. Then, an admittance shaping method is developed to ensure the system stability in the presence of parasitic capacitance of the transmission line. Finally, experimental results are provided to show the validity...
Semi-active friction damper for buildings subject to seismic excitation
Mantilla, Juan S.; Solarte, Alexander; Gomez, Daniel; Marulanda, Johannio; Thomson, Peter
2016-04-01
Structural control systems are considered an effective alternative for reducing vibrations in civil structures and are classified according to their energy supply requirement: passive, semi-active, active and hybrid. Commonly used structural control systems in buildings are passive friction dampers, which add energy dissipation through damping mechanisms induced by sliding friction between their surfaces. Semi-Active Variable Friction Dampers (SAVFD) allow the optimum efficiency range of friction dampers to be enhanced by controlling the clamping force in real time. This paper describes the development and performance evaluation of a low-cost SAVFD for the reduction of vibrations of structures subject to earthquakes. The SAVFD and a benchmark structural control test structure were experimentally characterized and analytical models were developed and updated based on the dynamic characterization. Decentralized control algorithms were implemented and tested on a shaking table. Relative displacements and accelerations of the structure controlled with the SAVFD were 80% less than those of the uncontrolled structure
Magneto Rheological Semi-Active Damper with External By-pass Circuit in Modular Structure
Directory of Open Access Journals (Sweden)
Alexandru Boltoşi
2010-10-01
Full Text Available In order to perform experimentally studies, in the paper it is presented a simple method which was elaborated to realize reliable, at low cost and reproducible semi-active dampers with magnetorheological fluids, having external magnetic circuit. The main components are common constitutive elements of industrial hydraulic and pneumatic drivers, having the supplementary advantages being manufactured in a large scale of overall dimensions and demanding minimal modifications. As accumulator, a similar type of hydraulic or pneumatic cylinder was used. The work of the whole damper can be optimized by modifying the nitrogen pressure and interior volume of accumulator. Another important advantage of this conception is the possibility to realize a modular structure composed by the damper, accumulator and magnetic field generator, interconnected by flexible elements.
Vibration of a string against multiple spring-mass-damper stoppers
Shin, Ji-Hwan; Talib, Ezdiani; Kwak, Moon K.
2018-02-01
When a building sways due to strong wind or an earthquake, the elevator rope can undergo resonance, resulting in collision with the hoist-way wall. In this study, a hard stopper and a soft stopper comprised of a spring-mass-damper system installed along the hoist-way wall were considered to prevent the string from undergoing excessive vibrations. The collision of the string with multiple hard stoppers and multiple spring-mass-damper stoppers was investigated using an analytical method. The result revealed new formulas and computational algorithms that are suitable for simulating the vibration of the string against multiple stoppers. The numerical results show that the spring-mass-damper stopper is more effective in suppressing the vibrations of the string and reducing structural failure. The proposed algorithms were shown to be efficient to simulate the motion of the string against a vibration stopper.
Semi-active Control of Magneto-Rheological Dampers with Negative Stiffness
DEFF Research Database (Denmark)
Bhowmik, Subrata
2009-01-01
performance by introduction of apparent negative damper stiffness. The design of the control strategy aims at maximizing the damping ratio of the critical mode of the structure. Explicit solutions for the complex valued natural frequency of the damped structure and the associated damping ratio are obtained...... sufficiently accurate. This is done by letting the desired force be the input to an inverse Bingham model, which provides the corresponding desired voltage level of the MR damper. Numerical simulations are conducted to demonstrate the performance of the proposed semi-active control strategy with apparent......Effective damping of large and flexible structures by semi-active dampers relies greatly on the control strategy applied, which should combine the robustness of passive devices and the increased damping performance often available from active control. For structural control the Magneto...
A PSO Driven Intelligent Model Updating and Parameter Identification Scheme for Cable-Damper System
Directory of Open Access Journals (Sweden)
Danhui Dan
2015-01-01
Full Text Available The precise measurement of the cable force is very important for monitoring and evaluating the operation status of cable structures such as cable-stayed bridges. The cable system should be installed with lateral dampers to reduce the vibration, which affects the precise measurement of the cable force and other cable parameters. This paper suggests a cable model updating calculation scheme driven by the particle swarm optimization (PSO algorithm. By establishing a finite element model considering the static geometric nonlinearity and stress-stiffening effect firstly, an automatically finite element method model updating powered by PSO algorithm is proposed, with the aims to identify the cable force and relevant parameters of cable-damper system precisely. Both numerical case studies and full-scale cable tests indicated that, after two rounds of updating process, the algorithm can accurately identify the cable force, moment of inertia, and damping coefficient of the cable-damper system.
Wang, W. L.; Zhou, Z. R.; Yu, D. S.; Qin, Q. H.; Iwnicki, S.
2017-10-01
A full nonlinear physical 'in-service' model was built for a rail vehicle secondary suspension hydraulic damper with shim-pack-type valves. In the modelling process, a shim pack deflection theory with an equivalent-pressure correction factor was proposed, and a Finite Element Analysis (FEA) approach was applied. Bench test results validated the damper model over its full velocity range and thus also proved that the proposed shim pack deflection theory and the FEA-based parameter identification approach are effective. The validated full damper model was subsequently incorporated into a detailed vehicle dynamics simulation to study how its key in-service parameter variations influence the secondary-suspension-related vehicle system dynamics. The obtained nonlinear physical in-service damper model and the vehicle dynamic response characteristics in this study could be used in the product design optimization and nonlinear optimal specifications of high-speed rail hydraulic dampers.
Applications of tuned mass dampers to improve performance of large space mirrors
Yingling, Adam J.; Agrawal, Brij N.
2014-01-01
In order for future imaging spacecraft to meet higher resolution imaging capability, it will be necessary to build large space telescopes with primary mirror diameters that range from 10 m to 20 m and do so with nanometer surface accuracy. Due to launch vehicle mass and volume constraints, these mirrors have to be deployable and lightweight, such as segmented mirrors using active optics to correct mirror surfaces with closed loop control. As a part of this work, system identification tests revealed that dynamic disturbances inherent in a laboratory environment are significant enough to degrade the optical performance of the telescope. Research was performed at the Naval Postgraduate School to identify the vibration modes most affecting the optical performance and evaluate different techniques to increase damping of those modes. Based on this work, tuned mass dampers (TMDs) were selected because of their simplicity in implementation and effectiveness in targeting specific modes. The selected damping mechanism was an eddy current damper where the damping and frequency of the damper could be easily changed. System identification of segments was performed to derive TMD specifications. Several configurations of the damper were evaluated, including the number and placement of TMDs, damping constant, and targeted structural modes. The final configuration consisted of two dampers located at the edge of each segment and resulted in 80% reduction in vibrations. The WFE for the system without dampers was 1.5 waves, with one TMD the WFE was 0.9 waves, and with two TMDs the WFE was 0.25 waves. This paper provides details of some of the work done in this area and includes theoretical predictions for optimum damping which were experimentally verified on a large aperture segmented system.
Extended neural network-based scheme for real-time force tracking with magnetorheological dampers
DEFF Research Database (Denmark)
Weber, Felix; Bhowmik, Subrata; Høgsberg, Jan Becker
2014-01-01
This paper validates numerically and experimentally a new neural network-based real-time force tracking scheme for magnetorheological (MR) dampers on a five-storey shear frame with MR damper. The inverse model is trained with absolute values of measured velocity and force because the targeted...... the pre-yield to the post-yield region. A control-oriented approach is presented to compensate for these drawbacks. The resulting control force tracking scheme is validated for the emulation of viscous damping, clipped viscous damping with negative stiffness, and friction damping with negative stiffness...
Nie, Shida; Zhuang, Ye; Wang, Yong; Guo, Konghui
2018-01-01
The performance of velocity & displacement-dependent damper (VDD), inspired by the semi-active control, is analyzed. The main differences among passive, displacement-dependent and semi-active dampers are compared on their damping properties. Valve assemblies of VDD are modelled to get an insight into its working principle. The mechanical structure composed by four valve assemblies helps to enable VDD to approach the performance by those semi-active control dampers. The valve structure parameters are determined by the suggested two-step process. Hydraulic model of the damper is built with AMEsim. Simulation result of F-V curves, which is similar to those of semi-active control damper, demonstrates that VDD could achieve the similar performance of semi-active control damper. The performance of a quarter vehicle model employing VDD is analyzed and compared with semi-active suspension. Simulation results show that VDD could perform as good as a semi-active control damper. In addition, no add-on hardware or energy consumption is needed for VDD to achieve the remarkable performance.
International Nuclear Information System (INIS)
Yu, Miao; Peng, Youxiang; Wang, Siqi; Fu, Jie; Choi, S B
2014-01-01
Under extreme service conditions in vehicle suspension systems, some defects exist in the hardening, bodying, and poor temperature stability of magnetorheological (MR) fluid. These defects can cause weak and even invalid performance in the MR fluid damper (MR damper for short). To ensure the effective validity of the practical applicability of the MR damper, one must implement an online state-monitoring sensor to monitor several performance factors, such as acceleration. In this empirical work, we propose a new energy-harvesting device system for the wireless sensor system of an MR damper. The monitoring sensor system consists of several components, such as an energy-harvesting device, energy-management circuit, and wireless sensor node. The electrical energy harvested from the kinetic energy of the MR fluid that flows within the MR damper can be automatically charged and discharged with the help of an energy-management circuit for the wireless sensor node. After verifying good performance from each component, an experimental apparatus is built to evaluate the feasibility of the proposed self-powered wireless sensor system. The measured results of pressure, temperature, and acceleration data within the MR damper clearly demonstrate the practical applicability of monitoring the operating work states of the MR damper when it is subjected to sinusoidal excitation. (technical note)
Procedure for Balancing an Air Distribution System with Decentralised Fans
DEFF Research Database (Denmark)
Gunner, Amalie; Hultmark, Göran; Vorre, Anders
2015-01-01
flawed. This paper presents a new procedure for balancing of CAV systems in combination with decentralised fans. The new system was based on replacing the balancing dampers with decentralised fans. By replacing the balancing dampers with decentralised fans, airflows can be balanced by adjusting the speed...... of the fans. In conventional air distribution systems the fan provides the necessary pressure to overcome the resistance in the branch with the highest pressure resistance. This gives an unnecessary overpressure in the remaining branches that does not provide any useful purpose. In order to decrease the fan...... pressure requirements the fan was dimensioned for the branch with the least pressure resistance. The decentralised fans then provided sufficient pressure to overcome the exact resistance in the corresponding branch. The results show that by using decentralised fans in duct systems instead of dampers...
Egger, Philipp; Caracoglia, Luca
2015-09-01
Impact dampers are often used in the field of civil, mechanical and aerospace engineering for reducing structural vibrations. The behavior of this type of passive control device has been investigated for several decades. In this research a distributed-mass impact damper, similar to the "chain damper" used in wind engineering, has been examined and applied to the vibration reduction on a slender line-like structural element (stay-cable). This study is motivated by a practical problem and describes the derivation of a reduced-order model for explaining the behavior, observed during a field experiment on a prototype system. In its simplest form, the dynamics of the apparatus is modeled as a "resilient damper", composed of mass-spring-dashpot secondary elements, attached to the primary structure. Various sources of excitation are analyzed: free vibration, external harmonic force and random excitation. The proposed model is general and potentially applicable to the analysis of several structural systems. The study also shows that the model can adequately describe and explain the experimentally observed behavior.
Tuned liquid column dampers for mitigation of edgewise vibrations in rotating wind turbine blades
DEFF Research Database (Denmark)
Zhang, Zili; Basu, Biswajit; Nielsen, Søren R.K.
2015-01-01
are the mounting position, the mass ratio, the geometries, and the head loss coefficient of the damper. Based on a reduced 2-DOF nonlinear model developed by the authors, the optimization of these parameters are carried out by minimizing the standard deviation of the edgewise tip displacement...
Investigation of damping potential of strip damper on a real turbine blade
Afzal, M.; Lopez Arteaga, I.; Kari, L.; Kharyton, V.
2016-01-01
This paper investigates the damping potential of strip dampers on a real turbine bladed disk. A 3D numerical friction contact model is used to compute the contact forces by means of the Alternate Frequency Time domain method. The Jacobian matrix required during the iterative solution is computed in
Energy Technology Data Exchange (ETDEWEB)
Bai, Xian-Xu, E-mail: bai@hfut.edu.cn [Department of Vehicle Engineering, Hefei University of Technology, Hefei 230009 (China); Wereley, Norman M.; Hu, Wei [Department of Aerospace Engineering, University of Maryland, College Park, Maryland 20742 (United States)
2015-05-07
A single-degree-of-freedom (SDOF) semi-active vibration control system based on a magnetorheological (MR) damper with an inner bypass is investigated in this paper. The MR damper employing a pair of concentric tubes, between which the key structure, i.e., the inner bypass, is formed and MR fluids are energized, is designed to provide large dynamic range (i.e., ratio of field-on damping force to field-off damping force) and damping force range. The damping force performance of the MR damper is modeled using phenomenological model and verified by the experimental tests. In order to assess its feasibility and capability in vibration control systems, the mathematical model of a SDOF semi-active vibration control system based on the MR damper and skyhook control strategy is established. Using an MTS 244 hydraulic vibration exciter system and a dSPACE DS1103 real-time simulation system, experimental study for the SDOF semi-active vibration control system is also conducted. Simulation results are compared to experimental measurements.
Improving total-building seismic performance using linear fluid viscous dampers
Del Gobbo, GM; Blakeborough, A; Williams, MS
2018-01-01
Previous research has revealed that Eurocode-compliant structures can experience structural and nonstructural damage during earthquakes. Retrofitting buildings with fluid viscous dampers (FVDs) can improve interstorey drifts and floor accelerations, two structural parameters that characterize seismic demand. Previous research focusing on FVD applications for improving seismic performance has focused on structural performance. Structural parameters such as interstorey drifts and floor accelera...
A new vibration isolation bed stage with magnetorheological dampers for ambulance vehicles
International Nuclear Information System (INIS)
Chae, Hee Dong; Choi, Seung-Bok
2015-01-01
The vibration experienced in an ambulance can lead to secondary injury to a patient and discourage a paramedic from providing emergency care. In this study, with the goal of resolving this problem, a new vibration isolation bed stage associated with magnetorheological (MR) dampers is proposed to ensure ride quality as well as better care for the patient while he/she is being transported. The bed stage proposed in this work can isolate vibrations in the vertical, rolling and pitching directions to reflect the reality that occurs in the ambulance. Firstly, an appropriate-sized MR damper is designed based on the field-dependent rheological properties of MR fluid, and the damping force characteristics of a MR damper are evaluated as a function of the current. A mechanical model of the proposed vibration isolation bed stage is then established to derive the governing equations of motion. Subsequently, a sliding mode controller is formulated to control the vibrations caused from the imposed excitation signals; those signals are directly measured using a real ambulance subjected to bump-and-curve road conditions. Using the controller based on the dynamic motion of the bed stage, the vibration control performance is evaluated in both the vertical and pitch directions. It is demonstrated that the magnitude of the vibration in the patient compartment of the ambulance can be significantly reduced by applying an input current to the MR dampers installed for the new bed stage. (technical note)
Exploring Parallel Algorithms for Volumetric Mass-Spring-Damper Models in CUDA
DEFF Research Database (Denmark)
Rasmusson, Allan; Mosegaard, Jesper; Sørensen, Thomas Sangild
2008-01-01
) from Nvidia. This paper investigates multiple implementations of volumetric Mass-Spring-Damper systems in CUDA. The obtained performance is compared to previous implementations utilizing the GPU through the OpenGL graphics API. We find that both performance and optimization strategies differ widely...
A new neuro-fuzzy training algorithm for identifying dynamic characteristics of smart dampers
International Nuclear Information System (INIS)
Nguyen, Sy Dzung; Choi, Seung-Bok
2012-01-01
This paper proposes a new algorithm, named establishing neuro-fuzzy system (ENFS), to identify dynamic characteristics of smart dampers such as magnetorheological (MR) and electrorheological (ER) dampers. In the ENFS, data clustering is performed based on the proposed algorithm named partitioning data space (PDS). Firstly, the PDS builds data clusters in joint input–output data space with appropriate constraints. The role of these constraints is to create reasonable data distribution in clusters. The ENFS then uses these clusters to perform the following tasks. Firstly, the fuzzy sets expressing characteristics of data clusters are established. The structure of the fuzzy sets is adjusted to be suitable for features of the data set. Secondly, an appropriate structure of neuro-fuzzy (NF) expressed by an optimal number of labeled data clusters and the fuzzy-set groups is determined. After the ENFS is introduced, its effectiveness is evaluated by a prediction-error-comparative work between the proposed method and some other methods in identifying numerical data sets such as ‘daily data of stock A’, or in identifying a function. The ENFS is then applied to identify damping force characteristics of the smart dampers. In order to evaluate the effectiveness of the ENFS in identifying the damping forces of the smart dampers, the prediction errors are presented by comparing with experimental results. (paper)
A new neuro-fuzzy training algorithm for identifying dynamic characteristics of smart dampers
Dzung Nguyen, Sy; Choi, Seung-Bok
2012-08-01
This paper proposes a new algorithm, named establishing neuro-fuzzy system (ENFS), to identify dynamic characteristics of smart dampers such as magnetorheological (MR) and electrorheological (ER) dampers. In the ENFS, data clustering is performed based on the proposed algorithm named partitioning data space (PDS). Firstly, the PDS builds data clusters in joint input-output data space with appropriate constraints. The role of these constraints is to create reasonable data distribution in clusters. The ENFS then uses these clusters to perform the following tasks. Firstly, the fuzzy sets expressing characteristics of data clusters are established. The structure of the fuzzy sets is adjusted to be suitable for features of the data set. Secondly, an appropriate structure of neuro-fuzzy (NF) expressed by an optimal number of labeled data clusters and the fuzzy-set groups is determined. After the ENFS is introduced, its effectiveness is evaluated by a prediction-error-comparative work between the proposed method and some other methods in identifying numerical data sets such as ‘daily data of stock A’, or in identifying a function. The ENFS is then applied to identify damping force characteristics of the smart dampers. In order to evaluate the effectiveness of the ENFS in identifying the damping forces of the smart dampers, the prediction errors are presented by comparing with experimental results.
Retrofit of Ressalat jacket platform (Persian Gulf) using friction damper device
DEFF Research Database (Denmark)
Komachi, Y.; Tabeshpour, M. R.; Golafshani, A. A.
2011-01-01
A friction damper device (FDD) is used for vibration control of an existing steel jacket platform under seismic excitation. First, the damping is presented for vibration mitigation of structures located in seismically active zones. A new method for quick design of friction or yielding damping dev...
Transverse digital damper system for the Fermilab anti-proton recycler
International Nuclear Information System (INIS)
Eddy, N.; Crisp, J.; Fermilab
2006-01-01
A transverse damping system is used in the Recycler at Fermilab to damp beam instabilities which arise from large beam intensities with electron cooling. Initial tests of electron cooling demonstrated beam loss due to transverse beam motion when the beam was cooled past the beam density threshold. The transverse damper system consists of two horizontal and two vertical pickups whose signals are amplified and passed into an analog hybrid to generate a difference signal from each pickup. The difference signals are input to a custom digital damper board which digitizes the analog signals at 212mhz, performs digital processing of the signals inside a large Altera Stratix II FPGA, then provides analog output at 212mhz via digital to analog converters. The digital damper output is sent to amplifiers which drive one horizontal and one vertical kicker. An initial prototype digital damper board has been successfully used in the Recycler for over six months. Currently, work is underway to replace the prototype board with an upgraded VME version
Lu, Zheng; Chen, Xiaoyi; Zhou, Ying
2018-04-01
A particle tuned mass damper (PTMD) is a creative combination of a widely used tuned mass damper (TMD) and an efficient particle damper (PD) in the vibration control area. The performance of a one-storey steel frame attached with a PTMD is investigated through free vibration and shaking table tests. The influence of some key parameters (filling ratio of particles, auxiliary mass ratio, and particle density) on the vibration control effects is investigated, and it is shown that the attenuation level significantly depends on the filling ratio of particles. According to the experimental parametric study, some guidelines for optimization of the PTMD that mainly consider the filling ratio are proposed. Furthermore, an approximate analytical solution based on the concept of an equivalent single-particle damper is proposed, and it shows satisfied agreement between the simulation and experimental results. This simplified method is then used for the preliminary optimal design of a PTMD system, and a case study of a PTMD system attached to a five-storey steel structure following this optimization process is presented.
Passivity Enhancement of Grid-Tied Converters by Series LC-Filtered Active Damper
DEFF Research Database (Denmark)
Bai, Haofeng; Wang, Xiongfei; Loh, Poh Chiang
2017-01-01
in the literature. Its effect with parasitic capacitance present in the grid has also usually been ignored, even though it may bring new challenges to the active damper. To address these issues, passivity is applied to study the grid converter stability before the understanding gained is used for formulating...
A hysteretic model considering Stribeck effect for small-scale magnetorheological damper
Zhao, Yu-Liang; Xu, Zhao-Dong
2018-06-01
Magnetorheological (MR) damper is an ideal semi-active control device for vibration suppression. The mechanical properties of this type of devices show strong nonlinear characteristics, especially the performance of the small-scale dampers. Therefore, developing an ideal model that can accurately describe the nonlinearity of such device is crucial to control design. In this paper, the dynamic characteristics of a small-scale MR damper developed by our research group is tested, and the Stribeck effect is observed in the low velocity region. Then, an improved model based on sigmoid model is proposed to describe this Stribeck effect observed in the experiment. After that, the parameters of this model are identified by genetic algorithms, and the mathematical relationship between these parameters and the input current, excitation frequency and amplitude is regressed. Finally, the predicted forces of the proposed model are validated with the experimental data. The results show that this model can well predict the mechanical properties of the small-scale damper, especially the Stribeck effect in the low velocity region.
Modelling of magnetorheological squeeze film dampers for vibration suppression of rigid rotors
Czech Academy of Sciences Publication Activity Database
Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, Jan
2017-01-01
Roč. 127, Jul SI (2017), s. 191-197 ISSN 0020-7403 R&D Projects: GA ČR GA15-06621S Institutional support: RVO:61388998 Keywords : squeeze film damper * magnetorheological fluid * bilinear material * rigid rotor * frequency response Subject RIV: JR - Other Machinery OBOR OECD: Mechanical engineering Impact factor: 2.884, year: 2016
Studi Respon Seismik Penggunaan Steel Slit Damper (SSD pada Portal Baja
Directory of Open Access Journals (Sweden)
Lisa Ika Arumsari
2012-09-01
Full Text Available Salah satu metode yang dapat digunakan untuk mengurangi dampak dari beban gempa terhadap portal baja adalah menggunakan peredam. Steel Slit Damper (SSD adalah salah satu jenis peredam yang dibuat dari sejumlah pelat baja lunak berbentuk segi-4 yang dimodelkan sebagai pegas-pegas yang disusun secara seri. Energi akibat gempa disalurkan melalui strip-strip damper yang mudah meleleh ketika perangkat mengalami deformasi inelastis siklik. SSD mendisipasi energi melalui pembentukan sendi plastis atau pelelehan pelat damper. Pada penelitian ini dilakukan analisa respon seismik Steel Slit Damper (SSD pada portal baja 1 lantai yang menerima beban lateral berupa beban gempa, dengan membandingkan portal baja konvensional, portal baja inverted-v, dan portal baja dengan SSD. Hasil analisa menunjukkan bahwa gaya geser, gaya normal, dan momen yang dihasikan portal dengan SSD lebih kecil hingga 80,49% dari gaya-gaya yang dihasilkan portal konvensional, tetapi gaya-gaya tersebut masih lebih besar daripada yang dihasilkan portal inverted-V. Portal dengan SSD dapat memperkecil simpangan sebesar 94,12% pada portal konvensional dan sebesar 33,33% pada portal bracing inverted-v. Hasil penelitian juga menunjukkan bahwa portal SSD memiliki daktilitas 105,85% lebih tinggi dari portal konvensional dan 298,67% lebih tinggi dari portal bracing inverted-v
Wen, Mingfu; Yu, Miao; Fu, Jie; Wu, Zhengzhong
2015-02-01
This article describes the design and simulation of a novel multi-functional hinge equipped with a rotary magnetorheological damper for solar array deployment system, which is comprised of a hinge, an angular sensor, a positioning and locking mechanism and a rotary damper. In order to achieve the compact design in structure, some components were reused in different function modules. It's the first to use magnet-rheological fluid (MRF) to dissipate the energy in solar array deployment system. The main advantage in using MR rotary damper instead of a viscous fluid rotary damper is that the damping force of MR damper can be adjusted according to the external magnetic field environment excited. A mechanic model was built and the structure design was focused on the MR rotary damper, a damping force model of this damper is deduced based on hydromechanics with Bingham plastic constitutive model. A simulation of deployment motion was taken to validate the motion sequence of various components during the unfolding and locking process. It can be obtained that a constant damping coefficient can hardly balance the different performance of solar deployment system, then a simulation of the proposed deployment system equipped with rotary MR damper was carried out. According to the simulation, it can be obtained that the terminal velocity decreased by 75.81% and the deployment time decreased by 72.37% compared with a given constant damping coefficients. Therefore, the proposed new type of rotary damper can reach a compromise with different performance utilizing an on-off control strategy.
Energy Technology Data Exchange (ETDEWEB)
Yoneda, M. (Kawada Industries Inc., Tokyo (Japan)); Shimoda, I. (Oiles Corp., Tokyo (Japan))
1993-12-20
Oil dampers and viscous shearing dampers have been used to control wind-induced cable vibrations of cable-stayed bridges. The damping addition efficiency in the case where only damping force of the viscous shearing damper is considered was discussed in the previous paper. In this paper, more precise estimation is done by also considering the spring elasticity of the damper. Arranging the results of an indoor excitation test on viscous shearing dampers using SA-P viscous body, an experimental equation to express the spring rigidity is derived. The spring elasticity becomes smaller with increasing temperature of viscous body, decreasing frequency, and increasing amplitude. Then, the damping addition effect is measured by installing the viscous shearing damper on the actual bridge cable, and is compared with the theoretical value resulting from the complex-eigenvalue analysis. Consequently, it is shown that the theoretical value is almost correspondent with the measured result through the analysis using equivalent coefficient of viscosity and equivalent spring constant, which are arranged in the experimental equation. Moreover, application examples of damping estimation curves for designing cables with dampers are given. 15 refs., 13 figs., 10 tabs.
Oviedo, J. A. (Juan Andrés)
2011-01-01
This paper investigates the influence of the story stiffness of reinforced concrete (R/C) frame on the seismic response of R/C buildings with proportional hysteretic dampers. For this purpose, non-linear time-history analyses were conducted on a series of multi-degree-of-freedom system models that include a wide range of structural parameters and vertical distributions of story stiffnesses and strengths of R/C main frame and dampers. Although the basic purpose of damper installation is to red...
Gyr, Marcel; Klem, J T; Louwerse, R; Milstead, I
1995-01-01
The analogue noise signal produced by a WAVETEK function generator, which is used to excite one of the horizontal dampers BDH 21437 or BDH 21451 for blowing up the beam during the crystal extraction MDs, has been analysed to determine its r.m.s. value as a function of the selected attenuation. The input/output characteristics of damper NÂº 2 (BDH 21451) has been measured in order to calibrate the r.m.s. kicks (diffusion speed) which a particle experiences on its passage through the damper.
MR Damper Controlled Vibration Absorber for Enhanced Mitigation of Harmonic Vibrations
Directory of Open Access Journals (Sweden)
Felix Weber
2016-12-01
Full Text Available This paper describes a semi-active vibration absorber (SVA concept based on a real-time controlled magnetorheological damper (MR-SVA for the enhanced mitigation of structural vibrations due to harmonic disturbing forces. The force of the MR damper is controlled in real-time to generate the frequency and damping controls according to the behaviour of the undamped vibration absorber for the actual frequency of vibration. As stiffness and damping emulations in semi-active actuators are coupled quantities the control is formulated to prioritize the frequency control by the controlled stiffness. The control algorithm is augmented by a stiffness correction method ensuring precise frequency control when the desired control force is constrained by the semi-active restriction and residual force of the MR damper. The force tracking task is solved by a model-based feed forward with feedback correction. The MR-SVA is numerically and experimentally validated for the primary structure with nominal eigenfrequency and when de-tuning of −10%, −5%, +5% and +10% is present. Both validations demonstrate that the MR-SVA improves the vibration reduction in the primary structure by up to 55% compared to the passive tuned mass damper (TMD. Furthermore, it is shown that the MR-SVA with only 80% of tuned mass leads to approximately the same enhanced performance while the associated increased relative motion amplitude of the tuned mass is more than compensated be the reduced dimensions of the mass. Therefore, the MR-SVA is an appropriate solution for the mitigation of tall buildings where the pendulum mass can be up to several thousands of metric tonnes and space for the pendulum damper is limited.
The spectral analysis of an aero-engine assembly incorporating a squeeze-film damper
Holmes, R.; Dede, M. M.
1989-01-01
Aero-engine structures have very low inherent damping and so artificial damping is often introduced by pumping oil into annular gaps between the casings and the outer races of some or all of the rolling-element bearings supporting the rotors. The thin oil films so formed are called squeeze film dampers and they can be beneficial in reducing rotor vibration due to unbalance and keeping to reasonable limits the forces transmitted to the engine casing. However, squeeze-film dampers are notoriously non-linear and as a result can introduce into the assembly such phenomena as subharmonic oscillations, jumps and combination frequencies. The purpose of the research is to investigate such phenomena both theoretically and experimentally on a test facility reproducing the essential features of a medium-size aero engine. The forerunner of this work was published. It was concerned with the examination of a squeeze-film damper in series with housing flexibility when supporting a rotor. The structure represented to a limited extent the essentials of the projected Rolls Royce RB401 engine. That research demonstrated the ability to calculate the oil-film forces arising from the squeeze film from known motions of the bearing components and showed that the dynamics of a shaft fitted with a squeeze film bearing can be predicted reasonably accurately. An aero-engine will normally have at least two shafts and so in addition to the excitation forces which are synchronous with the rotation of one shaft, there will also be forces at other frequencies from other shafts operating on the squeeze-film damper. Theoretical and experimental work to consider severe loading of squeeze-film dampers and to include these additional effects are examined.
Sassi, Sadok; Cherif, Khaled; Mezghani, Lotfi; Thomas, Marc; Kotrane, Asma
2005-08-01
The development of a powerful new magnetorheological fluid (MRF), together with recent progress in the understanding of the behavior of such fluids, has convinced researchers and engineers that MRF dampers are among the most promising devices for semi-active automotive suspension vibration control, because of their large force capacity and their inherent ability to provide a simple, fast and robust interface between electronic controls and mechanical components. In this paper, theoretical and experimental studies are performed for the design, development and testing of a completely new MRF damper model that can be used for the semi-active control of automotive suspensions. The MR damper technology presented in this paper is based on a completely new approach where, in contrast to in the conventional solutions where the coil axis is usually superposed on the damper axis and where the inner cylindrical housing is part of the magnetic circuit, the coils are wound in a direction perpendicular to the damper axis. The paper investigates approaches to optimizing the dynamic response and provides experimental verification. Both experimental and theoretical results have shown that, if this particular model is filled with an 'MRF 336AG' MR fluid, it can provide large controllable damping forces that require only a small amount of energy. For a magnetizing system with four coils, the damping coefficient could be increased by up to three times for an excitation current of only 2 A. Such current could be reduced to less than 1 A if the magnetizing system used eight small cores. In this case, the magnetic field will be more powerful and more regularly distributed. In the presence of harmonic excitation, such a design will allow the optimum compromise between comfort and stability to be reached over different intervals of the excitation frequencies.
Predictability of Stock Returns
Directory of Open Access Journals (Sweden)
Ahmet Sekreter
2017-06-01
Full Text Available Predictability of stock returns has been shown by empirical studies over time. This article collects the most important theories on forecasting stock returns and investigates the factors that affecting behavior of the stocks’ prices and the market as a whole. Estimation of the factors and the way of estimation are the key issues of predictability of stock returns.
The Usefulness of Impact Dampers for Space Applications.
1983-03-01
5 ’DTIC ditfibutif’n is uni td . 14 1983 THDEPARTMENT OF THE AIR FORCER ’.’. AIR UNIVERSITY (ATC)FAIR FORCE INSTITUTE OF TECHNOLOGY TilES I W right...Laboratory with Important Parameters 88 -. . . . . . - 4.. X0 a >1 0 t 0.. 43 fqj 050i ONr 4*) flj $4 04 k5* 0 .0r 0V1: 5.4 0 4 (d P40 00 05 4.)v4 04
International Nuclear Information System (INIS)
Yamaguchi, Hiroshi; Zhang, Xin-Rong; Niu, Xiao-Dong
2010-01-01
The damping characteristics and flow behaviors of ER fluids inside a piston–cylinder viscous damper subjected to external electric fields are studied based on experiment, theoretical analysis and numerical simulation. The viscous damper is a closed system with an inner piston and an outer cylinder, which is designed and constructed in our laboratory. In the experiment, the test ER fluid is enclosed in the gap of a piston–cylinder system. To examine the damping characteristics of the test ER fluid, a piston sine vibration experiment is performed with accompanying theoretical analyses. In addition, in order to investigate the ER flow behaviors inside the damper, a numerical simulation is carried out. The present study discloses the damping characteristics and the fluid mechanism of the ER fluid in the piston–cylinder damper with an applied external electric field
Smart Novel Semi-Active Tuned Mass Damper for Fixed-Bottom and Floating Offshore Wind (Presentation)
Energy Technology Data Exchange (ETDEWEB)
Rodriguez Tsouroukdissian, Arturo [Alstom Renewable US LLC
2016-05-02
The intention of this paper is to present the results of a novel smart semi-active tuned mass damper (SA-TMD), which mitigates unwanted loads for both fixed-bottom and floating offshore wind systems. (Presentation Format).
National Aeronautics and Space Administration — Develop a rotary MR (magneto rheologic) Damper to integrate into exploration spacecraft crew seats to be used as an exercise device and launch/landing load isolation...
International Nuclear Information System (INIS)
Zhabitskij, V.M.; Korenev, I.L.; Yudin, L.A.
1991-01-01
The investigation of the direct alternating kicker current perturbation influence of the particle motion in synchrotron with the beam coherent transverse oscillation damper in feedback are obtained. It has been shown that for a some pick-up and kicker placements are impossible due to this reason. The resonance conditions and their dependences on feedback gain-transfer characteristic have been found. The numerical results are given for the damper systems in UNK-1 and LHC. 6 refs.; 5 figs
a Method for Preview Vibration Control of Systems Having Forcing Inputs and Rapidly-Switched Dampers
ElBeheiry, E. M.
1998-07-01
In a variety of applications, especially in large scale dynamic systems, the mechanization of different vibration control elements in different locations would be decided by limitations placed on the modal vibration of the system and the inherent dynamic coupling between its modes. Also, the quality of vibration control to the economy of producing the whole system would be another trade-off leading to a mix of passive, active and semi-active vibration control elements in one system. This termactiveis limited to externally powered vibration control inputs and the termsemi-activeis limited to rapidly switched dampers. In this article, an optimal preview control method is developed for application to dynamic systems having active and semi-active vibration control elements mechanized at different locations in one system. The system is then a piecewise (bilinear) controller in which two independent sets of control inputs appear additively and multiplicatively. Calculus of variations along with the Hamiltonian approach are employed for the derivation of this method. In essence, it requires the active elements to be ideal force generators and the switched dampers to have the property of on-line variation of the damping characteristics to pre-determined limits. As the dampers switch during operation the whole system's structure differs, and then values of the active forcing inputs are adapted to match these rapid changes. Strictly speaking, each rapidly switched damper has pre-known upper and lower damping levels and it can take on any in-between value. This in-between value is to be determined by the method as long as the damper tracks a pre-known fully active control demand. In every damping state of each semi-active damper the method provides the optimal matching values of the active forcing inputs. The method is shown to have the feature of solving simple standard matrix equations to obtain closed form solutions. A comprehensive 9-DOF tractor semi-trailer model is used
Directory of Open Access Journals (Sweden)
Jong Wan Hu
2018-01-01
Full Text Available With the aim of effectively reducing the structural damage caused by earthquake events, bracing systems equipped with retrofitting damper devices, which take advantage of the energy dissipation and impact absorption, have been widely used in practical construction sites. These bracing dampers, however, have been recognized as expendable supplies for easily replacing the damaged ones after a strong earthquake because they are commonly designed to undergo concentrated force and deformation for the purpose of protecting the main structural members such as the columns and beams. In this paper, the use of new superelastic shape memory alloy (SMA dampers that can partially recover their original configuration is proposed to decrease the repair cost. In addition, the conventional steel dampers used for improving the energy dissipation arising due to metallic yielding are additionally integrated into the bracing member. The behaviors of such bracing systems with the damper devices were reproduced in experimental tests with the cyclic loading history, and then their strength capacity and recentering capability were estimated based on the experiment results. Finally, additional experimental tests were performed by imposing cyclic loading histories with different loading speeds on the superelastic SMA and steel plate damper specimens.
Directory of Open Access Journals (Sweden)
Gurubasavaraju T. M.
2018-01-01
Full Text Available Magnetorheological fluids are smart materials, which are responsive to the external stimulus and changes their rheological properties. The damper performance (damping force is dependent on the magnetic flux density induced at the annular gap. Magnetic flux density developed at fluid flow gap of MR damper due to external applied current is also dependent on materials properties of components of MR damper (such as piston head, outer cylinder and piston rod. The present paper discus about the influence of different materials selected for components of the MR damper on magnetic effect using magnetostatic analysis. Different materials such as magnetic and low carbon steels are considered for piston head of the MR damper and magnetic flux density induced at fluid flow gap (filled with MR fluid is computed for different DC current applied to the electromagnetic coil. Developed magnetic flux is used for calculating the damper force using analytical method for each case. The low carbon steel has higher magnetic permeability hence maximum magnetic flux could pass through the piston head, which leads to higher value of magnetic effect induction at the annular gap. From the analysis results it is observed that the magnetic steel and low carbon steel piston head provided maximum magnetic flux density. Eventually the higher damping force can be observed for same case.
Predictable return distributions
DEFF Research Database (Denmark)
Pedersen, Thomas Quistgaard
trace out the entire distribution. A univariate quantile regression model is used to examine stock and bond return distributions individually, while a multivariate model is used to capture their joint distribution. An empirical analysis on US data shows that certain parts of the return distributions......-of-sample analyses show that the relative accuracy of the state variables in predicting future returns varies across the distribution. A portfolio study shows that an investor with power utility can obtain economic gains by applying the empirical return distribution in portfolio decisions instead of imposing...
Design Guidelines of a Spring-Damper System for Emergency Diesel Generator Sets
Energy Technology Data Exchange (ETDEWEB)
Kim, Min Kyu; Choun, Young Sun; Seo, Jeong Moon
2007-05-15
This guidelines described about the procedure of isolation system design for Emergency Diesel Generator (EDG) of Nuclear Power Plant (NPP). First of all, a vibration concept including the ground vibration was described and vibration control system and seismic isolation system were considered. The behavior characteristics and design consideration of coil spring-viscose damper system were summarized. The material properties of foundation of EDG system and the ground were considered. A design load and seismic load for isolation system design were described and an analysis method was explained. Finally, a design example for an EDG in Yonggwang Nuclear Unit 5 and 6 was attached of Appendix. First of all, this design guideline can apply to design of a vibration and seismic isolation system for EDG system and the design example present a design procedure practically. Moreover, this design guideline can be used for isolation design of other rotational machines and other isolation system except spring-damper system.
Virtual spring damper method for nonholonomic robotic swarm self-organization and leader following
Wiech, Jakub; Eremeyev, Victor A.; Giorgio, Ivan
2018-04-01
In this paper, we demonstrate a method for self-organization and leader following of nonholonomic robotic swarm based on spring damper mesh. By self-organization of swarm robots we mean the emergence of order in a swarm as the result of interactions among the single robots. In other words the self-organization of swarm robots mimics some natural behavior of social animals like ants among others. The dynamics of two-wheel robot is derived, and a relation between virtual forces and robot control inputs is defined in order to establish stable swarm formation. Two cases of swarm control are analyzed. In the first case the swarm cohesion is achieved by virtual spring damper mesh connecting nearest neighboring robots without designated leader. In the second case we introduce a swarm leader interacting with nearest and second neighbors allowing the swarm to follow the leader. The paper ends with numeric simulation for performance evaluation of the proposed control method.
Optimum Parameters of a Tuned Liquid Column Damper in a Wind Turbine Subject to Stochastic Load
Alkmim, M. H.; de Morais, M. V. G.; Fabro, A. T.
2017-12-01
Parameter optimization for tuned liquid column dampers (TLCD), a class of passive structural control, have been previously proposed in the literature for reducing vibration in wind turbines, and several other applications. However, most of the available work consider the wind excitation as either a deterministic harmonic load or random load with white noise spectra. In this paper, a global direct search optimization algorithm to reduce vibration of a tuned liquid column damper (TLCD), a class of passive structural control device, is presented. The objective is to find optimized parameters for the TLCD under stochastic load from different wind power spectral density. A verification is made considering the analytical solution of undamped primary system under white noise excitation by comparing with result from the literature. Finally, it is shown that different wind profiles can significantly affect the optimum TLCD parameters.
A Brief Discussion Regarding Types of Cavitation in Squeeze Film Dampers and Cavitation Effects
Directory of Open Access Journals (Sweden)
Laurentiu MORARU
2017-03-01
Full Text Available Squeeze film dampers (SFD are probably the most used shaft control devices in aircraft jet engines; SFDs consist in oil films, elastic elements and various antirotational devices that tune the stiffness and damping of the shafts’ supports and consequently adjust the lateral dynamics of the shaft. Fluid layers in SFDs are usually thin, hence the modeling can often be done using the Reynolds’ theory,; however, some of the main features of the film, namely the behavior of the fluid in the divergent, negative squeeze area, where discontinuities may appear in the liquid, are still subject to intense research. This paper will discuss some aspects regarding the types of cavitation that appear in squeeze film dampers and some of the effects of cavitation on the SFDs.
Nguyen, T. P.; Pham, D. T.; Ngo, K. T.
2018-04-01
Reducing vibration in structures under lateral load always attracts many researchers in during pastime, hence the mainly purpose of paper analyzes effectiveness of multiple-tuned liquid dampers for reducing dynamic responses of structures under ground acceleration of earthquakes. In this study, the multi-tuned liquid damper with slat screens (M-TLDWSS) is considered in detail for analyzing dynamic response of multi-degrees of freedom structure due to earthquake, which is more different previous studies. Then, the general equation of motion of the structure and M-TLDWSS under ground acceleration of earthquake is established based on dynamic balance of principle and solved by numerical method in the time domain. The effects of characteristic parameters of M-TLDWSS on dynamic response of the structure are investigated. The results obtained in this study demonstrate that the M-TLDWSS has significantly effectiveness for reducing dynamic response of the structure.
Force effects on rotor of squeeze film damper using Newtonian and non-Newtonian fluid
Dominik, Šedivý; Petr, Ferfecki; Simona, Fialová
2017-09-01
This article presents the evaluation of force effects on rotor of squeeze film damper. Rotor is eccentric placed and its motion is translate-circular. The amplitude of rotor motion is smaller than its initial eccentricity. The force effects are calculated from pressure and viscous forces which were gained by using computational modeling. Two types of fluid were considered as filling of damper. First type of fluid is Newtonian (has constant viscosity) and second type is magnetorheological fluid (does not have constant viscosity). Viscosity of non-Newtonian fluid is given using Bingham rheology model. Yield stress is a function of magnetic induction which is described by many variables. The most important variables of magnetic induction are electric current and gap width which is between rotor and stator. Comparison of application two given types of fluids is shown in results.
A broadband damper design inspired by cartilage-like relaxation mechanisms
Liu, Lejie; Usta, Ahmet D.; Eriten, Melih
2017-10-01
In this study, we introduce a broadband damper design inspired by the cartilage-like relaxation mechanisms. In particular, we study broadband (static to 10 kHz) dissipative properties of model cartilage systems by probe-based static and dynamic indentation, and validate that fractional Zener models can simulate the empirical data up to a desirable accuracy within the frequency range of interest. Utilizing these observations, we design a composite damper design where a poroelastic layer is sandwiched between two hard materials, and load transfer occurs across interfaces with multiple length scales. Modeling those interfaces with fractional Zener elements in parallel configuration, and manipulating the distribution of the Zener elements across different peak relaxation frequencies, we obtain a relatively constant loss factor within an unprecedented frequency range (3-3 kHz). We also discuss how these findings can be employed in a practical damping design.
DEFF Research Database (Denmark)
Zhou, Qiang; Nielsen, Søren R.K.; Qu, Weilian
2010-01-01
Considering the coupling between the in-plane and out-of-plane vibration, the stochastic response of an inclined shallow cable with linear viscous dampers subjected to Gaussian white noise excitation is investigated in this paper. Selecting the static deflection shape due to a concentrated force...... together with the C-type Gram-Charlier expansion with a fourth-order closure are applied to obtain statistical moments, power spectral density and probabilistic density function of the cable response, whose availability is verified by Monte Carlo method. Taking a typical cable as an example, the influence...... of several factors, which include excitation level and direction as well as damper size, on the dynamic response of the cable is extensively investigated. It is found that the sum of mean square in-plane and out-of-plane displacement is primarily independent of the load direction when the excitation level...
Beam stability in synchrotrons with digital filters in the feedback loop of a transverse damper
International Nuclear Information System (INIS)
Zhabitskij, V.M.
2009-01-01
The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. Solving the characteristic equation allows one to calculate the achievable damping rates as a function of instability growth rate, feedback gain and parameters of the signal processing. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital notch, Hilbert and all-pass filters are analyzed in comparison with those in an ideal feedback system
Energy Technology Data Exchange (ETDEWEB)
Anon.
2007-07-01
Three-Point Suspension: In wind turbines with stall and pitch systems of every size the three-point suspension with clamping bushings of ESM is very common. It is the task of the vibration isolation to suspend the gearbox elastically on the main frame at two mounting points. Four-Point Suspension: Particularly in wind turbines of the multi-megawatt-class the four-point suspension is a more and more spreading system. The rotor shaft is supported by one bearing which is able to take the yaw and nodding torques or by two rotor shaft bearings. So all the torques except the driving torque are directly transferred to the main frame by the rotor shaft support. The gearbox has only one degree of freedom left. To avoid horizontal constraint forces on the gearbox with the four-point suspension normally multi-sandwich mounts or a pendulum support is used as both have a very low horizontal stiffness. One problem persists anyway: Due to assembly tolerances and main frame deformations because of nodding torques the gearbox has to withstand huge vertical constriant forces. Especially for wind turbines with four-point suspension ESM has developed a hydraulic gearbox support. Generator Suspension: In wind turbines with a gearbox and a fast running generator the generator is mounted to the main frame with normally four elastomeric generator mounts. Tuned Mass Dampers: Tuned mass dampers are used to reduce single tone vibrations in machines, buildings and other facilities. The function of a tuned mass damper is based on an oscillating mass which moves contrary to the spurious vibration and reduces it thereby. ESM has developed easy adjustable tuned mass dampers, which may be installed to a wind turbine easily if a wind turbine has problems with single tone vibrations. (orig.)
Mathematical modelling of the mass-spring-damper system - A fractional calculus approach
Directory of Open Access Journals (Sweden)
Jesus Bernal Alvarado
2012-08-01
Full Text Available In this paper the fractional differential equation for the mass-spring-damper system in terms of the fractional time derivatives of the Caputo type is considered. In order to be consistent with the physical equation, a new parameter is introduced. This parameter characterizes the existence of fractional components in the system. A relation between the fractional order time derivative and the new parameter is found. Different particular cases are analyzed
Operational performance of a bunch by bunch digital damper in the Fermilab Main Injector
International Nuclear Information System (INIS)
Adamson, P.; Ashmanskas, W.J.; Foster, G.W.; Hansen, S.; Marchionni, A.; Nicklaus, D.; Semenov, A.; Wildman, D.; Kang, H.
2005-01-01
We have implemented a transverse and longitudinal bunch by bunch digital damper system in the Fermilab Main Injector, using a single digital board for all 3 coordinates. The system has been commissioned over the last year, and is now operational in all MI cycles, damping beam bunched at both 53MHz and 2.5MHz. We describe the performance of this system both for collider operations and high-intensity running for the NuMI project
Analysis and testing of an inner bypass magnetorheological damper for shock and vibration mitigation
Bai, Xian-Xu; Hu, Wei; Wereley, Norman M.
2013-04-01
Aiming at fundamentally improving the performance of MR dampers, including maximizing dynamic range (i.e., ratio of field-on to field-off damping force) while simultaneously minimizing field-off damping force, this study presents the principle of an inner bypass magnetorheological damper (IBMRD). The IBMRD is composed of a pair of twin tubes, i.e., the inner tube and outer concentric tube, a movable piston-shaft arrangement, and an annular MR fluid flow gap sandwiched between the concentric tubes. In the IBMRD, the inner tube serves simultaneously as the guide for the movable piston and the bobbin for the electromagnetic coil windings, and five active rings on the inner tube, annular MR fluid flow gap, and outer tube forms five closed magnetic circuits. The annular fluid flow gap is an inner bypass annular valve where the rheology of the MR fluids, and hence the damping force of the MR damper, is controlled. Based on the structural principle of the IBMRD, the IBMRD is configured and its finite element analysis (FEA) is implemented. After theoretically constructing the hydro-mechanical model for the IBMRD, its mathematical model is established using a Bingham-plastic nonlinear fluid model. The characteristics of the IBMRD are theoretically evaluated and compared to those of a conventional piston-bobbin MR damper with an identical active length and cylinder diameter. In order to validate the theoretical results predicted by the mathematical model, the prototype IBMRD is designed, fabricated, and tested. The servo-hydraulic testing machine (type: MTS 810) and rail-guided drop tower are used to provide sinusoidal displacement excitation and shock excitation to the IBMRD, respectively.
Suppression of Instabilities Generated by an Anti-Damper with a Nonlinear Magnetic Element in IOTA
Energy Technology Data Exchange (ETDEWEB)
Stern, E. [Fermilab
2018-04-01
The Integrable Optics Test Accelerator (IOTA) storage ring is being constructed at Fermilab as a testbed for new accelerator concepts. One important series of experiments tests the use of a novel nonlinear magnetic insert to damp coherent instabilities. To test the damping power of the element, an instability of desired strength may be intentionally excited with an anti-damper. We report on simulations of beam stabilization using the Synergia modeling framework over ranges of driving and damping strengths.
Directory of Open Access Journals (Sweden)
Junwon Seo
2015-07-01
Full Text Available Although the steel slit dampers commonly utilized for aseismic design approach can dissipate considerable energy created by the yielding of base materials, large residual deformation may happen in the entire frame structure. After strong external excitation, repair costs will be incurred in restoring a structure to its original condition and to replace broken components. For this reason, alternative recentering devices characterized by smart structures, which mitigate the damage for such steel energy dissipation slit dampers, are developed in this study. These devices, feasibly functioning as seismic restrainers, can be improved by implementing superelastic shape memory alloy (SMA bending bars in a parallel motion with the steel energy-dissipating damper. The bending bars fabricated with superelastic SMAs provide self-centering forces upon unloading, and accordingly contribute to reducing permanent deformation in the integrated slit damper system. The steel slit dampers combined with the superelastic SMA bending bars are evaluated with respect to inelastic behavior as simulated by refined finite element (FE analyses. The FE slit damper models subjected to cyclic loads are calibrated to existing test results in an effort to predict behavior accurately. The responses of the proposed slit damper systems are compared to those of the conventionally used slit damper systems. From the analysis results, it is concluded that innovative steel slit dampers combined with superelastic SMA bending bars generate remarkable performance improvements in terms of post-yield strength, energy dissipation, and recentering capability.
Moiseev, Yu B; Ignatovich, S N; Strakhov, A Yu
The article discusses anthropometric design of shockproof pilot seats for state-of-the-art helicopters. Object of the investigation was anthropometric parameters of the helicopter aviation personnel of the Russian interior troops. It was stated that the body parameters essential for designing helicopter seat dampers are mass of the body part that presses against the seat in the seating position, and eye level above the seat surface. An uncontrolled seat damper ensuring shockproof safety to 95 % helicopter crews must be designed for the body mass contacting the seat of 99.7 kg and eye level above the seat of 78.6 cm. To absorb.shock effectively, future dampers should be adjustable to pilot's body parameters. The optimal approach to anthropometric design of a helicopter seat is development of type pilot' body models with due account of pilot's the flight outfit and seat geometry. Principle criteria of type models are body mass and eye level. The authors propose a system of type body models facilitating specification of anthropometric data helicopter seat developers.
Lee, Tae-Hoon; Han, Chulhee; Choi, Seung-Bok
2018-01-01
This work proposes a novel type of tunable magnetorheological (MR) damper operated based solely on the location of a permanent magnet incorporated into the piston. To create a larger damping force variation in comparison with the previous model, a different design configuration of the permanent-magnet-based MR (PMMR) damper is introduced to provide magnetic flux dispersion in two magnetic circuits by utilizing two materials with different magnetic reluctance. After discussing the design configuration and some advantages of the newly designed mechanism, the magnetic dispersion principle is analyzed through both the formulated analytical model of the magnetic circuit and the computer simulation based on the magnetic finite element method. Sequentially, the principal design parameters of the damper are determined and fabricated. Then, experiments are conducted to evaluate the variation in damping force depending on the location of the magnet. It is demonstrated that the new design and magnetic dispersion concept are valid showing higher damping force than the previous model. In addition, a curved structure of the two materials is further fabricated and tested to realize the linearity of the damping force variation.
Dynamic Model of MR Dampers Based on a Hysteretic Magnetic Circuit
Directory of Open Access Journals (Sweden)
Pengfei Guo
2018-01-01
Full Text Available As a key to understand dynamic performances of MR dampers, a comprehensive dynamic magnetic circuit model is proposed in this work on the basis of Ampere’s and Gauss’s laws. It takes into account not only the magnetic saturation, which many existing studies have focused on, but also the magnetic hysteresis and eddy currents in a MR damper. The hysteresis of steel parts of MR dampers is described by Jiles-Atherton (J-A models, and the eddy current is included based on the field separation. Compared with the FEM results, the proposed model is validated in low- and high-frequency studies for the predictions of the magnetic saturation, the hysteresis, and the effect of eddy currents. A simple multiphysics model is developed to demonstrate how to combine the proposed magnetic circuit model with the commonly used Bingham fluid model. The damping force in the high-frequency case obviously lags behind the coil current, which exhibits a hysteresis loop in the current-force plane. The lag of damping force even exists in a low-frequency varying magnetic field and becomes more severe in the presence of eddy currents.
Bifurcations and chaos of a vibration isolation system with magneto-rheological damper
Energy Technology Data Exchange (ETDEWEB)
Zhang, Hailong [Magneto-electronics Lab, School of Physics and Technology, Nanjing Normal University, Nanjing 210046 (China); Vibration Control Lab, School of Electrical and Automation Engineering, Nanjing Normal University, Nanjing 210042 (China); Zhang, Ning [Magneto-electronics Lab, School of Physics and Technology, Nanjing Normal University, Nanjing 210046 (China); Min, Fuhong; Yan, Wei; Wang, Enrong, E-mail: erwang@njnu.edu.cn [Vibration Control Lab, School of Electrical and Automation Engineering, Nanjing Normal University, Nanjing 210042 (China)
2016-03-15
Magneto-rheological (MR) damper possesses inherent hysteretic characteristics. We investigate the resulting nonlinear behaviors of a two degree-of-freedom (2-DoF) MR vibration isolation system under harmonic external excitation. A MR damper is identified by employing the modified Bouc-wen hysteresis model. By numerical simulation, we characterize the nonlinear dynamic evolution of period-doubling, saddle node bifurcating and inverse period-doubling using bifurcation diagrams of variations in frequency with a fixed amplitude of the harmonic excitation. The strength of chaos is determined by the Lyapunov exponent (LE) spectrum. Semi-physical experiment on the 2-DoF MR vibration isolation system is proposed. We trace the time history and phase trajectory under certain values of frequency of the harmonic excitation to verify the nonlinear dynamical evolution of period-doubling bifurcations to chaos. The largest LEs computed with the experimental data are also presented, confirming the chaotic motion in the experiment. We validate the chaotic motion caused by the hysteresis of the MR damper, and show the transitions between distinct regimes of stable motion and chaotic motion of the 2-DoF MR vibration isolation system for variations in frequency of external excitation.
Bifurcations and chaos of a vibration isolation system with magneto-rheological damper
Directory of Open Access Journals (Sweden)
Hailong Zhang
2016-03-01
Full Text Available Magneto-rheological (MR damper possesses inherent hysteretic characteristics. We investigate the resulting nonlinear behaviors of a two degree-of-freedom (2-DoF MR vibration isolation system under harmonic external excitation. A MR damper is identified by employing the modified Bouc-wen hysteresis model. By numerical simulation, we characterize the nonlinear dynamic evolution of period-doubling, saddle node bifurcating and inverse period-doubling using bifurcation diagrams of variations in frequency with a fixed amplitude of the harmonic excitation. The strength of chaos is determined by the Lyapunov exponent (LE spectrum. Semi-physical experiment on the 2-DoF MR vibration isolation system is proposed. We trace the time history and phase trajectory under certain values of frequency of the harmonic excitation to verify the nonlinear dynamical evolution of period-doubling bifurcations to chaos. The largest LEs computed with the experimental data are also presented, confirming the chaotic motion in the experiment. We validate the chaotic motion caused by the hysteresis of the MR damper, and show the transitions between distinct regimes of stable motion and chaotic motion of the 2-DoF MR vibration isolation system for variations in frequency of external excitation.
Nonlinear modeling of a rotational MR damper via an enhanced Bouc–Wen model
International Nuclear Information System (INIS)
Miah, Mohammad S; Chatzi, Eleni N; Dertimanis, Vasilis K; Weber, Felix
2015-01-01
The coupling of magnetorheological (MR) dampers with semi-active control schemes has proven to be an effective and failsafe approach for vibration mitigation of low-damped structures. However, due to the nonlinearities inherently relating to such damping devices, the characterization of the associated nonlinear phenomena is still a challenging task. Herein, an enhanced phenomenological modeling approach is proposed for the description of a rotational-type MR damper, which comprises a modified Bouc–Wen model coupled with an appropriately selected sigmoid function. In a first step, parameter optimization is performed on the basis of individual models in an effort to approximate the experimentally observed response for varying current levels and actuator force characteristics. In a second step, based on the previously identified parameters, a generalized best-fit model is proposed by performing a regression analysis. Finally, model validation is carried out via implementation on different sets of experimental data. The proposed model indeed renders an improved representation of the actually observed nonlinear behavior of the tested rotational MR damper. (paper)
A novel self-powered MR damper: theoretical and experimental analysis
International Nuclear Information System (INIS)
Xinchun, Guan; Hui, Li; Jinping, Ou; Yonghu, Huang; Yi, Ru
2015-01-01
This paper presents a novel magnetorheological (MR) damper with a self-powered capability, which is proposed to have energy harvesting and MR damping technologies integrated into a single device. Vibration energy harvesting mechanisms were adopted, based on ball-screw mechanisms and a rotary permanent magnet dc generator, to convert the external vibration energy into electrical energy to power the MR damping unit. The configuration and operating principles of the proposed self-powered MR damper were presented. Considering the core loss effect on the magnetic field, a theoretical analysis of the proposed MR damper was carried out and a mechanical model was developed. Finally, a prototype with a capacity of 10 kN was fabricated and experimentally investigated in both the direct-supply mode and the supply-with-rectifier mode. The results indicated that the proposed configuration is feasible and that both modes can realize good self-adaptability of the MR damping force. However, the direct-supply mode has a sag effect in the force–displacement curve and provides a lower energy-dissipating capacity than the direct-supply mode does under the same conditions. (paper)
Lu, Lyan-Ywan; Lin, Tzu-Kang; Jheng, Rong-Jie; Wu, Hsin-Hsien
2018-01-01
A semi-active friction damper (SAFD) can be employed for the seismic protection of structural systems. The effectiveness of an SAFD in absorbing seismic energy is usually superior to that of its passive counterpart, since its slip force can be altered in real time according to structural response and excitation. Most existing SAFDs are controlled by adjusting the clamping force applied on the friction interface. Thus, the implementation of SAFDs in practice requires precision control of the clamping force, which is usually substantially larger than the slip force. This may increase the implementation complexity and cost of SAFDs. To avoid this problem, this study proposes a novel position-controlled SAFD, named the leverage-type controllable friction damper (LCFD). The LCFD system combines a traditional passive friction damper and a leverage mechanism with a movable central pivot. By simply controlling the pivot position, the damping force generated by the LCFD system can be adjusted in real time. In order to verify the feasibility of the proposed SAFD, a prototype LCFD was tested by using a shaking table. The test results demonstrate that the equivalent friction force and hysteresis loop of the LCFD can be regulated by controlling the pivot position. By considering 16 ground motions with two different intensities, the adaptive feature of the LCFD for seismic structural control is further demonstrated numerically.
Semi-active control of tracked vehicle suspension incorporating magnetorheological dampers
Ata, W. G.; Salem, A. M.
2017-05-01
In past years, the application of magnetorheological (MR) and electrorheological dampers in vehicle suspension has been widely studied, mainly for the purpose of vibration control. This paper presents theoretical study to identify an appropriate semi-active control method for MR-tracked vehicle suspension. Three representative control algorithms are simulated including the skyhook, hybrid and fuzzy-hybrid controllers. A seven degrees-of-freedom tracked vehicle suspension model incorporating MR dampers has been adopted for comparison between the performance of the three controllers. The model differential equations are derived based on Newton's second law of motion and the proposed control methods are developed. The performance of each control method under bump and sinusoidal road profiles for different vehicle speeds is simulated and compared with the performance of the conventional suspension system in time and frequency domains. The results show that the performance of tracked vehicle suspension with MR dampers is substantially improved. Moreover, the fuzzy-hybrid controller offers an excellent integrated performance in reducing the body accelerations as well as wheel bounce responses compared with the classical skyhook and hybrid controllers.
On the validity of the classical hydrodynamic lubrication theory applied to squeeze film dampers
International Nuclear Information System (INIS)
Danaila, S; Moraru, L
2010-01-01
Squeeze film dampers (SFD) are devices utilized to control vibrations of the shafts of high-speed rotating machinery. The SFD - squirrel cage combination is probably the most used system for tuning the stiffness and damping of the supports for rotors installed on ball bearings. Squeeze film dampers are essentially hydrodynamic bearings which contain the ball bearings housings of ball-bearings supported shafts. Consequently, the oil film within the SFD are influenced only by the precession and nutation of the shaft, that is the flow of the oil within the damper is not directly influenced by the spin of the rotor. However, in the classical theory, the flow in the thin film is also governed by the Reynolds equation. In this paper, some of the limits of the classical theory of the SFD are discussed and theoretical and experimental studies, which illustrate the ideas presented herein, are presented as well. The orbits of an unbalanced rotor that is supported by a ball-bearings-SFD-squirrel-cage assembly at one end and by rigidly mounted ball bearings at the other end are computed using the bearing forces provided by the classical short bearing theory. The numerical model also includes the properties of the squirrel cage. The parameters of the squirrel cage were measured, together with the effect of the friction within the assembly. Experimental unbalance responses were also collected for various rotation speeds and unbalances to validate the numerical simulations.
imulasi Numerik Aliran Tiga Dimensi Melalui Rectangular Duct dengan Variasi Bukaan Damper
Directory of Open Access Journals (Sweden)
Edo Edgar Santosa
2016-04-01
Full Text Available Dalam sistem saluran terdapat banyak penggunaan elbow dan assesoris lain yang akan menyebabkan terjadinya kerugian tekanan pada aliran. Hal tersebut disebabkan karena adanya perubahan arah aliran fluida yang melalui saluran tersebut. Nilai penurunan tekanan (pressure drop pada aliran yang melalui suattu saluran dipengaruhi oleh besarnya laju aliran pada inlet, serta radius kelengkungan dari elbow yang akan menyebabkan aliran sekunder kemudian timbul aliran vortex. Hal ini berakibat kerugian energi (headloss yang lebih besar. Peletakan bodi pengganggu dan pemasangan elbow dimaksudkan untuk melihat fenomena aliran di sekitar bodi pengganggu Model uji yang akan digunakan di dalam studi ini berupa rectangular duct yang pada bagian inlet terpasang elbow 90o dengan damper yang diletakkan pada jarak x/Dh=2. Fluida kerjanya adalah udara yang mengalir secara incompressible, viscous, steady dan mempunyai profil kecepatan uniform pada sisi inlet dengan dua variasi bilangan Reynolds yaitu 2.05 x 105 dan 8.2 x 105serta empat pengaturan sudut bodi pengganggu 0o, 10o, 20o, dan 30o Penelitian dilakukan secara numerik 3D menggunakan piranti lunak Computation Fluid Dynamics (CFD komersial dengan model turbulensi k-ε Realizable. Hasil studi ini diperoleh bahwa proses recovery aliran dipengaruhi oleh sudut bukaan damper, untuk variasi sudut bukaan damper 30°. Dengan sudut bukaan 30° terjadi percepatan aliran pada daerah dekat dinding yang berakibat bertambahnya momentum aliran sehingga mempercepat proses recovery aliran dan aliran sekunder pada daerah dekat dinding dapat teratasi.
Mixed Skyhook and FxLMS Control of a Half-Car Model with Magnetorheological Dampers
Directory of Open Access Journals (Sweden)
Piotr Krauze
2016-01-01
Full Text Available The problem of vibration attenuation in a semiactive vehicle suspension is considered. The proposed solution is based on usage of the information about the road roughness coming from the sensor installed on the front axle of the vehicle. It does not need any preview sensor to measure the road roughness as other preview control strategies do. Here, the well-known Skyhook algorithm is used for control of the front magnetorheological (MR damper. This algorithm is tuned to a quarter-car model of the front part of the vehicle. The rear MR damper is controlled by the FxLMS (Filtered-x LMS taking advantage of the information about the motion of the front vehicle axle. The goal of this algorithm is to minimize pitch of the vehicle body. The strategy is applied for a four-degree-of-freedom (4-DOF vehicle model equipped with magnetorheological dampers which were described using the Bouc-Wen model. The suspension model was subjected to the road-induced excitation in the form of a series of bumps within the frequency range 1.0–10 Hz. Different solutions are compared based on the transmissibility function and simulation results show the usefulness of the proposed solution.
Johnson, Erik A.; Elhaddad, Wael M.; Wojtkiewicz, Steven F.
2016-04-01
A variety of strategies have been developed over the past few decades to determine controllable damping device forces to mitigate the response of structures and mechanical systems to natural hazards and other excitations. These "smart" damping devices produce forces through passive means but have properties that can be controlled in real time, based on sensor measurements of response across the structure, to dramatically reduce structural motion by exploiting more than the local "information" that is available to purely passive devices. A common strategy is to design optimal damping forces using active control approaches and then try to reproduce those forces with the smart damper. However, these design forces, for some structures and performance objectives, may achieve high performance by selectively adding energy, which cannot be replicated by a controllable damping device, causing the smart damper performance to fall far short of what an active system would provide. The authors have recently demonstrated that a model predictive control strategy using hybrid system models, which utilize both continuous and binary states (the latter to capture the switching behavior between dissipative and non-dissipative forces), can provide reductions in structural response on the order of 50% relative to the conventional clipped-optimal design strategy. This paper explores the robustness of this newly proposed control strategy through evaluating controllable damper performance when the structure model differs from the nominal one used to design the damping strategy. Results from the application to a two-degree-of-freedom structure model confirms the robustness of the proposed strategy.
Directory of Open Access Journals (Sweden)
Y. M. Parulekar
2012-01-01
Full Text Available Recently, there has been increasing interest in using superelastic shape memory alloys for applications in seismic resistant-design. Shape memory alloys (SMAs have a unique property by which they can recover their original shape after experiencing large strains up to 8% either by heating (shape memory effect or removing stress (pseudoelastic effect. Many simplified shape memory alloy models are suggested in the past literature for capturing the pseudoelastic response of SMAs in passive vibration control of structures. Most of these models do not consider the cyclic effects of SMA's and resulting residual martensite deformation. Therefore, a suitable constitutive model of shape memory alloy damper which represents the nonlinear hysterical dynamic system appropriately is essential. In this paper a multilinear hysteretic model incorporating residual martensite strain effect of pseudoelastic shape memory alloy damper is developed and experimentally validated using SMA wire, based damper device. A sensitivity analysis is done using the proposed model along with three other simplified SMA models. The models are implemented on a steel frame representing an SDOF system and the comparison of seismic response of structure with all the models is made in the numerical study.
Directory of Open Access Journals (Sweden)
Tsubasa Tani
2017-10-01
Full Text Available A new structural control system using damper-installed shear walls in lower stories with reduced stiffness is proposed for vibration control of high-rise RC buildings. That system has some design variables, i.e., height of shear wall, degree of stiffness reduction at lower stories, and quantity of dampers. In this paper, some parametric studies on the shear-beam model with a stiff beam against two kinds of ground motion, a pulse-type sinusoidal wave and a resonant sinusoidal wave, are conducted to clarify the vibration characteristics of the proposed structural control system. It is shown that the optimal combination of design parameters depends on the input ground motion. It is also shown that it is possible to prevent from increasing the response under the one-cycle sinusoidal input resonant to the lowest mode and reduce the steady-state response under the harmonic input with the resonant fundamental period by reducing the stiffness in the lower structure and increasing the damper deformation.
Caterino, N.; Spizzuoco, M.; Occhiuzzi, A.
2018-06-01
The proposed work gives a response, based on the experimental evidence, to the issue of long-term magnetorheological (MR) dampers’ behavior, when they are applied for structural control of earthquake induced vibrations. MR control devices, designed for infrequent dynamic loads as earthquakes, might be dormant for most of their life until a seismic event hits the hosting controlled structure. Two prototype MR devices have been tested three times, first in 2008, then in 2013 after five years of absolute inactivity, and finally in 2017 after further four years of rest. The comparison between the results of the three experimental testing activities is made in terms of force-displacement loops, dissipated energy and maximum reacting force. It is shown that only the first stroke of the damper is characterized by an unexpected mechanical response. However, after this first movement, the damper comes back to behave similarly to what was before the rest, with only a slight not reversible decrease of the damping force. This reduction results to be more significant (about 5%) for larger currents, while less significant in the case of zero feeding current. From a civil engineering perspective, this performance decay is definitely acceptable, even if it is referred to a possible cause, deeply studied in literature, that could continue endangering the mechanical response of the devices over time. The paper shows the experimental results, but the possible causes of mechanical deterioration of the dampers will be discussed also.
Time delay effects on large-scale MR damper based semi-active control strategies
International Nuclear Information System (INIS)
Cha, Y-J; Agrawal, A K; Dyke, S J
2013-01-01
This paper presents a detailed investigation on the robustness of large-scale 200 kN MR damper based semi-active control strategies in the presence of time delays in the control system. Although the effects of time delay on stability and performance degradation of an actively controlled system have been investigated extensively by many researchers, degradation in the performance of semi-active systems due to time delay has yet to be investigated. Since semi-active systems are inherently stable, instability problems due to time delay are unlikely to arise. This paper investigates the effects of time delay on the performance of a building with a large-scale MR damper, using numerical simulations of near- and far-field earthquakes. The MR damper is considered to be controlled by four different semi-active control algorithms, namely (i) clipped-optimal control (COC), (ii) decentralized output feedback polynomial control (DOFPC), (iii) Lyapunov control, and (iv) simple-passive control (SPC). It is observed that all controllers except for the COC are significantly robust with respect to time delay. On the other hand, the clipped-optimal controller should be integrated with a compensator to improve the performance in the presence of time delay. (paper)
Characteristic analysis of the lower limb muscular strength training system applied with MR dampers.
Yu, Chang Ho; Piao, Young Jun; Kim, Kyung; Kwon, Tae Kyu
2014-01-01
A new training system that can adjust training intensity and indicate the center pressure of a subject was proposed by applying controlled electric current to the Magneto-Rheological damper. The experimental studying on the muscular activities were performed in lower extremities during maintaining and moving exercises, which were processed on an unstable platform with Magneto rheological dampers and recorded in a monitor. The electromyography (EMG) signals of the eight muscles in lower extremities were recorded and analyzed in certain time and frequency domain. Muscles researched in this paper were rectus femoris (RF), biceps femoris (BF), tensor fasciae latae (TFL), vastuslateralis (VL), vastusmedialis (VM), gastrocnemius (Ga), tibialis anterior (TA), and soleus (So). Differences of muscular activities during four moving exercises were studied in our experimental results. The rate of the increment of the muscular activities was affected by the condition of the unstable platform with MR dampers, which suggested the difference of moving exercises could selectively train each muscle with varying intensities. Furthermore, these findings also proposed that this training system can improve the ability of postural balance.
Classifying Returns as Extreme
DEFF Research Database (Denmark)
Christiansen, Charlotte
2014-01-01
I consider extreme returns for the stock and bond markets of 14 EU countries using two classification schemes: One, the univariate classification scheme from the previous literature that classifies extreme returns for each market separately, and two, a novel multivariate classification scheme tha...
Optimized damper control of pressure and airflow in ventilation systems
DEFF Research Database (Denmark)
Koulani, Chrysanthi Sofia; Hviid, Christian Anker; Terkildsen, Søren
2014-01-01
Conventional control strategies in variable air volume (VAV) ventilation systems do not take fully into advantage the potential energy savings since the system operation is based on maintaining a constant static pressure (CSP) set point in the main duct irrespective of the actual pressure demand...... by using the Simulink programming tool which is addon software to MATLAB mathematical programming language. A model of a VAV ventilation system was created in Simulink based on the International Building Physics Toolbox (IBPT); the IBPT thermal zone was remodelled in order to calculate dynamically...... the airflow demand according to the zone air temperature. The performance of the Simulink model was evaluated based on the experimental setup of the ventilation system. The SPR control method established stable system operation and was proven efficient to maintain comfortable space conditions while reducing...
Bifurcations in the response of a flexible rotor in squeeze-film dampers with retainer springs
International Nuclear Information System (INIS)
Inayat-Hussain, Jawaid I.
2009-01-01
Squeeze-film dampers are commonly used in conjunction with rolling-element or hydrodynamic bearings in rotating machinery. Although these dampers serve to provide additional damping to the rotor-bearing system, there have however been some cases of rotors mounted in these dampers exhibiting non-linear behaviour. In this paper a numerical study is undertaken to determine the effects of design parameters, i.e., gravity parameter, W, mass ratio, α, and stiffness ratio, K, on the bifurcations in the response of a flexible rotor mounted in squeeze-film dampers with retainer springs. The numerical simulations were undertaken for a range of speed parameter, Ω, between 0.1 and 5.0. Numerical results showed that increasing K causes the onset speed of bifurcation to increase, whilst an increase of α reduces the onset speed of bifurcation. For a specific combination of K and α values, the onset speed of bifurcation appeared to be independent of W. The instability of the rotor response at this onset speed was due to a saddle-node bifurcation for all the parameter values investigated in this work with the exception of the combination of α = 0.1 and K = 0.5, where a secondary Hopf bifurcation was observed. The speed range of non-synchronous response was seen to decrease with the increase of α; in fact non-synchronous rotor response was totally absent for α=0.4. With the exception of the case α = 0.1, the speed range of non-synchronous response was also seen to decrease with the increase of K. Multiple responses of the rotor were observed at certain values of Ω for various combinations of parameters W, α and K, where, depending on the values of the initial conditions the rotor response could be either synchronous or quasi-periodic. The numerical results presented in this work were obtained for an unbalance parameter, U, value of 0.1, which is considered as the upper end of the normal unbalance range of most practical rotor systems. These results provide some insights
Kansas Data Access and Support Center — LIDAR-derived binary (.las) files containing classified points of all returns. We have 3 classifications Unclassified, Ground, Low points. The average Ground Sample...
Directory of Open Access Journals (Sweden)
Yu-Jeong Shin
2014-07-01
Full Text Available Ride quality became a very important factor in the performance of railway vehicles according to the expansion of high-speed railways and speedup of velocity of railway vehicles. In this study, the results of applying the MR (magnetorheological lateral damper on the secondary suspension to reduce the vibration of the car body, directly relating to the ride quality of railway vehicles, were mentioned. In order to verify the control performance of MR dampers, a 1/5 scaled railway vehicle model was constructed, and numerical simulation and experimental tests were conducted. The MR damper for the experimental tests was produced and was attached between the car body and bogie of a full scaled vehicle, and a vibration controlling test was performed to improve ride quality on a roller rig. The skyhook control algorithm was used as the controlling technique, and regarding the test results, the RMS (root mean square value was found by compensating the frequency of the lateral vibration based on the UIC 513 R Standard about the ride quality of railway vehicles. As a result of the test, it could be confirmed that vibration was reduced by approximately 24% when attaching the MR damper between the bogie and the car body compared to when applying a passive damper.
Directory of Open Access Journals (Sweden)
Andrew Jaya Nazar
2017-01-01
Full Text Available Instalasi saluran udara tidak hanya berupa pipa lurus, tetapi juga terdapat fitting/aksesoris perpipaan misalnya elbow 90o dan damper. Aksesoris perpipaan ini berfungsi agar saluran udara dapat terpasang sesuai dengan kebutuhan. Namun, penggunaan aksesoris perpipaan ini menyebabkan bertambahnya pressure drop akibat adanya friction loss dan separation loss. Pemasangan guide vane pada elbow 90o diharapkan dapat mengurangi pressure drop karena dapat mengurangi terjadinya secondary flow, namun hal ini dapat menambah kerugian akibat gaya gesek. Saat ini penghematan energi menjadi sorotan terutama dalam dunia industri. Penurunan pressure drop pada belokan perpipaan sangat diharapkan, agar dapat menghemat energi lebih. Untuk itu perlu dilakukan usaha agar dapat menurunkan pressure drop yang terjadi. Penelitian ini dilakukan secara eksperimen dengan benda uji saluran udara yang terdiri dari: upstream duct (straight duct, square elbow 90o dengan r/Dh=1,5 dan dilengkapi double guide vane, damper, downstream duct (straight duct, dan induced fan. Pengukuran parameter yang dibutuhkan dilakukan dengan menggunakan: pitot tube, inclined manometer, pressure tranducer. Dari eksperimen ini diperoleh bahwa profil kecepatan pada masing-masing variasi sudut bukaan damper sudah mendekati keadaan recovery aliran pada akhir section baik dari bidang vertikal maupun horizontal. Pressure drop yang terjadi semakin naik seiring dengan bertambahnya nilai bilangan Reynolds dan sudut bukaan damper. Nilai konstanta damper semakin naik dari bukaan sudut 0o hingga 30o.
International Nuclear Information System (INIS)
Somaki, Takahiro; Miyamoto, Akinori; Nakatogawa, Tetsundo
2003-01-01
In order to realize the concept of a vertical isolation system (common deck system), research and development on the vertical isolation structure is now underway. In its first step, structure plans of each of the isolation element and the damper element will be drawn up, and in the next step, tests on these elements will be planed, executed, analyzed, and evaluated, to be reflected to the structure plan. In this report, the structure plan and test plan of damper element is reported. At first, it was concluded in the previous work that the steel-materials damper which can be evaluated by Ramberg-Osgood type is applicable to the vertical isolation system required performance. Then, based on this results, the form range of a damper which satisfies was surveyed from both cross section thickness and distribution of strain by analysis. Next, in order to check the performance (limit a damping capability, load carrying capacity, fatigue strength, and deformability) of an actual damper element based on this analysis result, the test plan for actual scale model was drawn up. (author)
Directory of Open Access Journals (Sweden)
Haoxiang He
2016-01-01
Full Text Available In view of the disadvantages such as higher yield stress and inadequate adjustability, a combined low yield point steel plate damper involving low yield point steel plates and common steel plates is proposed. Three types of combined plate dampers with new hollow shapes are proposed, and the specific forms include interior hollow, boundary hollow, and ellipse hollow. The “maximum stiffness” and “full stress state” are used as the optimization objectives, and the topology optimization of different hollow forms by alternating optimization method is to obtain the optimal shape. Various combined steel plate dampers are calculated by finite element simulation, the results indicate that the initial stiffness of the boundary optimized damper and interior optimized damper is lager, the hysteresis curves are full, and there is no stress concentration. These two types of optimization models made in different materials rations are studied by numerical simulation, and the adjustability of yield stress of these combined dampers is verified. The nonlinear dynamic responses, seismic capacity, and damping effect of steel frame structures with different combined dampers are analyzed. The results show that the boundary optimized damper has better energy-dissipation capacity and is suitable for engineering application.
The rheology of shear thickening fluid (STF) and the dynamic performance of an STF-filled damper
International Nuclear Information System (INIS)
Zhang, X Z; Li, W H; Gong, X L
2008-01-01
This paper presents a study of the rheological properties of shear thickening fluid (STF) and its application as a damper. The STF samples, with different weight fractions, were prepared by dispersing nanosized silica particles in a solvent. By using a parallel-plate rheometer, both steady-state and dynamic experiments were carried out to investigate the rheological properties of STFs. Experimental results indicated that these suspensions show an abrupt increase in complex viscosity beyond a critical dynamic shear rate, as well as this increase being reversible. Working with the fabricated STF materials, a prototype damper was fabricated and its dynamic performances were experimentally evaluated. An equivalent linear model through effective elastic stiffness and viscous damping was developed to address both the damping and the stiffness capabilities of the damper. Also, a mathematical model was developed to investigate working mechanisms of STF-based devices
International Nuclear Information System (INIS)
Ito, Tomohiro; Michiue, Masashi; Fujita, Katsuhisa
2009-01-01
In this study, the optimal seismic design methodology that can consider the structural integrity of not only the piping systems but also elasto-plastic supporting devices is developed. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location, capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Four types of evaluation functions are considered. It is found that the proposed optimal seismic design methodology is very effective and can be applied to the actual seismic design for piping systems supported by elasto-plastic dampers. The effectiveness of the evaluation functions is also clarified. (author)
International Nuclear Information System (INIS)
Nicklaus, Dennis; Foster, G.William; Kashikhin, Vladimir
2005-01-01
An end-to-end performance calculation and comparison with beam tests was performed for the bunch-by-bunch digital transverse damper in the Fermilab Main Injector. Time dependent magnetic wakefields responsible for ''Resistive Wall'' transverse instabilities in the Main Injector were calculated with OPERA-2D using the actual beam pipe and dipole magnet lamination geometry. The leading order dipole component was parameterized and used as input to a bunch-by-bunch simulation which included the filling pattern and injection errors experienced in high-intensity operation of the Main Injector. The instability growth times, and the spreading of the disturbance due to newly misinjected batches was compared between simulations and beam data collected by the damper system. Further simulation models the effects of the damper system on the beam
Energy Technology Data Exchange (ETDEWEB)
Silva Navarro, Gerardo; Cabrera Amado, Alvaro [Cinvestav, IPN, Mexico, D.F. (Mexico)
2007-11-15
This paper deals with the problem of semiactive balancing control of a rotor-bearing system, where one journal bearings is supported on two radial Magneto-Rheological (MR) dampers. The mathematical model of the rotor-bearing system results from an orthotropic Jeffcott-like model and the dynamics associated to the MR dampers, whose rheological properties depend on the current inputs. For control purposes we use the Choi-Lee-Park polynomial for the MR dampers, which is quite consistent with the tpical nonlinear and complex hysteresis behavior and also simplifies the physical implementation on an experimental setup. The semiactive control scheme for the unbalance reponse of the rotor-bearing system is synthesized using sliding-mode control techniques. Some numerical and experimental results are included to illustrate the dynamic performance and robustness of the overall system. [Spanish] En este trabajo se abora el problema de control semiactivo del desbalance en un sistema rotor-chumacera, donde una de las chumaceras convencionales se monta sobre una suspension con dos amortiguadores Magneto-Reologicos (MR) radiales. El modelo matematico del sistema rotorchumacera se obtiene de un modelo tipo Jefcott ortotropico y la dinamica de los amortiguadores MR, cuyas propiedades reologicas dependen de las corrientes electricas de alimentacion. Para propositos de control se emplea el modelo polinomial de Choi-Lee-Park para los dos amortiguadores MR, el cual es consistente con el tipico comportamiento no-lineal y de histeresis, permitiendo simplificar su implementacion fisica en una plataforma experimental. El esquema de control semiactivo de la respuesta al desbalance, en el sistema rotor-chumacera, se basa en las tecnicas de control por modos deslizantes. Se presentan algunos resultados de simulacion numerica y experimentos que utilizan el funcionamiento y robustez del sistema completo.
Directory of Open Access Journals (Sweden)
Bintang Mahardhika
2017-03-01
Full Text Available Jembatan Pemali merupakan jembatan yang terletak di Kota Brebes. Jembatan ini menjadi akses penting yang menghubungkan antara Kota Semarang dan Kota Jakarta. Jembatan Pemali sering mengalami perbaikan dalam segi struktural setiap bulannya, hal ini diakibatkan oleh semakin padat volume kendaraan terutama truk dengan muatan berat. Permasalahan ini yang melatarbelakangi pembangunan Jembatan Pemali yang baru agar menunjang dalam sarana transportasi. Penelitian ini memodifikasi Jembatan Pemali menjadi sistem busur rangka baja. Jembatan didesain dengan tinggi 18 meter, bentang 100 meter dan lebar 9 meter. Penelitian ini menggunakan kombinasi pembebanan sesuai SNI T-02-2005 dan SNI 1725-2016. Dengan menggunakan progam bantu SAP2000, kombinasi KUAT 1 (SNI-1725-2016 menghasilkan output gaya yang lebih besar daripada kombinasi lainnya sehingga kombinasi tersebut digunakan untuk menentukan profil rangka atas jembatan. Analisis pengaruh damper dengan tipe Lock-Up Device menggunakan progam bantu SAP2000 dengan kombinasi beban yang menentukan dalam perencanaan damper sebagai longitudinal stopper adalah kombinasi EKSTREM I (SNI-1725-2016. Hasil dari analisis dengan progam bantu SAP2000 profil utama yang terbesar pada jembatan busur menggunakan BOX 500x500x25 serta dengan adanya damper struktur utama jembatan mampu mengurangi deformasi sebesar 16%. Dalam merencanakan bangunan bawah jembatan, dilakukan kontrol guling dan geser pada abutment jembatan serta untuk tiang pancang jembatan dilakukan kontrol berdasarkan daya dukung tanah dan tipe material yang digunakan. Dari perencanaan tersebut, didapatkan dimensi abutment 11x11x10 meter serta kebutuhan tiang pancang jembatan 36 buah. Hasil seluruh perhitungan Penelitian ini dituangkan dalam gambar teknik standar.
Fundamental damper power calculation of the 56 MHz SRF cavity for RHIC
International Nuclear Information System (INIS)
Wu, Q.; Bellavia, S.; Ben-Zvi, I.; Grau, M.; Miglionico, G.; Pai, C.
2011-01-01
At each injection period during RHIC's operation, the beam's frequency sweeps across a wide range, and some of its harmonics will cross the frequency of the 56MHz SRF cavity. To avoid excitation of the cavity at these times, we designed a fundamental damper for the quarter-wave resonator to damp the cavity heavily. The power extracted by the fundamental damper should correspond to the power handling ability of the system at all stages. In this paper, we discuss the power output from the fundamental damper when it is fully extracted, inserted, and any intermediate point. A Fundamental Damper (FD) will greatly reduce the cavity's Q factor to ∼300 during the acceleration phase of the beam. However, when the beam is at store and the FD is removed, the cavity is excited by both the yellow and the blue beams at 2 x 0.3A to attain the required 2MV voltage across its gap. The cavity then is operated to increase the luminosity of the RHIC experiments. Table 1 lists the parameters of the FD. Figure 1 shows the configuration of the FD fully inserted into the 56MHz SRF cavity; this complete insertion is defined as the start location (0cm) of FD simulation, an assumption we make throughout this paper. The power consumed by the cavity while maintaining the beam's energy and its orbit is compensated by the 28MHz accelerating cavities in the storage ring. The power dissipation of the external load is dynamic with respect to the position of the FD during its extraction. As a function of the external Q and the EM field in the cavity, the power should peak with the FD at a certain vertical location. Our calculation of the power extracted is detailed in the following sections. Figure 2 plots the frequency change in the cavity, and the external Q against the changes in position of the FD. The location of the FD is selected carefully such that the frequency will approach the designed working point from the lower side only. The loaded Q of the cavity is 223 when the FD is fully
Modeling and control of an off-road truck using electrorheological dampers
International Nuclear Information System (INIS)
Holzmann, K; Kemmetmueller, W; Kugi, A; Stork, M; Rosenfeldt, H; Schneider, S
2009-01-01
This work deals with the mathematical modeling and control of the semi-active suspension of an MAN off-road truck with a payload of 5 tons which comprises electrorheological dampers. Thereby, a cascaded control structure with four controllers for the control of a quarter-car in the inner control loop and a superimposed control strategy for the overall vehicle is used. The main goal of the control strategy is to reduce the motion of the chassis (especially roll, pitch and vertical movement) while increasing driving stability. The capability of the overall control strategy is demonstrated by means of simulation studies and measurement results.
Application of the optimal homotopy asymptotic method to nonlinear Bingham fluid dampers
Directory of Open Access Journals (Sweden)
Marinca Vasile
2017-10-01
Full Text Available Dynamic response time is an important feature for determining the performance of magnetorheological (MR dampers in practical civil engineering applications. The objective of this paper is to show how to use the Optimal Homotopy Asymptotic Method (OHAM to give approximate analytical solutions of the nonlinear differential equation of a modified Bingham model with non-viscous exponential damping. Our procedure does not depend upon small parameters and provides us with a convenient way to optimally control the convergence of the approximate solutions. OHAM is very efficient in practice for ensuring very rapid convergence of the solution after only one iteration and with a small number of steps.
Application of the optimal homotopy asymptotic method to nonlinear Bingham fluid dampers
Marinca, Vasile; Ene, Remus-Daniel; Bereteu, Liviu
2017-10-01
Dynamic response time is an important feature for determining the performance of magnetorheological (MR) dampers in practical civil engineering applications. The objective of this paper is to show how to use the Optimal Homotopy Asymptotic Method (OHAM) to give approximate analytical solutions of the nonlinear differential equation of a modified Bingham model with non-viscous exponential damping. Our procedure does not depend upon small parameters and provides us with a convenient way to optimally control the convergence of the approximate solutions. OHAM is very efficient in practice for ensuring very rapid convergence of the solution after only one iteration and with a small number of steps.
Application of mathematical model for high viscous damper to dynamic analysis of NPP pipings
International Nuclear Information System (INIS)
Kostarev, V.V.; Bercovsky, A.M.; Kireev, O.B.; Vasiliev, P.S.
1993-01-01
The problems of dynamic analysis of Nuclear Power Plants (NPP) piping systems are considered in the paper. The special calculation program for PC has been developed that enables to estimate the seismic margin for any piping system with different antiseismic devices having nonlinear characteristics. The calculated comparison has been done for two antiseismic supports that are widely used now, namely: a High Viscous Damper (HVD) and a Seismic Stop Support (SSS) with the application, as an example, to the well known pipeline BM3 (USNRC). (author)
Application of mathematical model for high viscous damper to dynamic analysis of NPP pipings
Energy Technology Data Exchange (ETDEWEB)
Kostarev, V V; Bercovsky, A M; Kireev, O B; Vasiliev, P S [CKTI VIBROSEISM (CVS), St. Petersburg (Russian Federation)
1993-07-01
The problems of dynamic analysis of Nuclear Power Plants (NPP) piping systems are considered in the paper. The special calculation program for PC has been developed that enables to estimate the seismic margin for any piping system with different antiseismic devices having nonlinear characteristics. The calculated comparison has been done for two antiseismic supports that are widely used now, namely: a High Viscous Damper (HVD) and a Seismic Stop Support (SSS) with the application, as an example, to the well known pipeline BM3 (USNRC). (author)
Tuned Liquid Dampers for the New European Court of Justice, Luxembourg
DEFF Research Database (Denmark)
Georgakis, Christos; Koss, Hans Holger
2005-01-01
As a consequence of their unique positioning and 3,5:1 plan ratio, the proposed twin 103m buildings of the latest expansion of the European Court of Justice (Luxembourg) led to the commissioning of a comprehensive set of wind-tunnel tests. Experimental testing and numerical analyses showed...... the buildings to be susceptible to unacceptably large wind-induced accelerations at the top levels. To mitigate these vibrations, a Tuned Liquid Damper (TLD) array is proposed and designed for both buildings. With an optimal design of the TLD array, total maximum reductions in top-level accelerations are found...
Directory of Open Access Journals (Sweden)
Filip-Vacarescu Norin
2016-03-01
Full Text Available This paper discusses the concept of a hybrid damper made from a combination of two dissipative devices. A passive hysteretic device like steel Buckling Restrained Brace (BRB can be combined with a magneto-rheological (MR Fluid Damper in order to obtain a hybrid dissipative system. This system can work either as a semi-active system, if the control unit is available, or as a passive system, tuned for working according to performance based seismic engineering (PBSE scale of reference parameters (i.e. interstory drift.
DEFF Research Database (Denmark)
Nicolaisen, Jeppe; Faber Frandsen, Tove
2008-01-01
The paper introduces a new journal impact measure called The Reference Return Ratio (3R). Unlike the traditional Journal Impact Factor (JIF), which is based on calculations of publications and citations, the new measure is based on calculations of bibliographic investments (references) and returns...... (citations). A comparative study of the two measures shows a strong relationship between the 3R and the JIF. Yet, the 3R appears to correct for citation habits, citation dynamics, and composition of document types - problems that typically are raised against the JIF. In addition, contrary to traditional...
The Returns to Entrepreneurship
DEFF Research Database (Denmark)
Van Praag, Mirjam; Raknerud, Arvid
Empirical studies show low pecuniary returns of switching from wage employment to entrepreneurship. We reconsider the pecuniary gains of this switching by employing a two-stage procedure, where the randomness in the timing of inheritance transfers is used as an exclusion restriction to identify...... causal effects. The model is estimated on data covering the whole Norwegian population of individuals matched to the entire population of firms established in the period 2002-2011. The results indicate that the average returns to entrepreneurship are significantly negative for individuals entering...... entrepreneurship through self-employment and modest, but significantly positive, for incorporated startups....
International Nuclear Information System (INIS)
Shumway, R.W.
1985-01-01
This paper presents a collection of TMIN (temperature of return to nucleate boiling) correlations, evaluates them under several conditions, and compares them with a wide range of data. Purpose is to obtain the best one for use in a water reactor safety computer simulator known as TRAC-B. Return to nucleate boiling can occur in a reactor accident at either high or low pressure and flow rates. Most of the correlations yield unrealistic results under some conditions. A new correlation is proposed which overcomes many of the deficiencies
Sustainable Mars Sample Return
Alston, Christie; Hancock, Sean; Laub, Joshua; Perry, Christopher; Ash, Robert
2011-01-01
The proposed Mars sample return mission will be completed using natural Martian resources for the majority of its operations. The system uses the following technologies: In-Situ Propellant Production (ISPP), a methane-oxygen propelled Mars Ascent Vehicle (MAV), a carbon dioxide powered hopper, and a hydrogen fueled balloon system (large balloons and small weather balloons). The ISPP system will produce the hydrogen, methane, and oxygen using a Sabatier reactor. a water electrolysis cell, water extracted from the Martian surface, and carbon dioxide extracted from the Martian atmosphere. Indigenous hydrogen will fuel the balloon systems and locally-derived methane and oxygen will fuel the MAV for the return of a 50 kg sample to Earth. The ISPP system will have a production cycle of 800 days and the estimated overall mission length is 1355 days from Earth departure to return to low Earth orbit. Combining these advanced technologies will enable the proposed sample return mission to be executed with reduced initial launch mass and thus be more cost efficient. The successful completion of this mission will serve as the next step in the advancement of Mars exploration technology.
Lindsay T McMahon
2007-01-01
With the signing of the Comprehensive Peace Agreement in January 2005, the new Government of South Sudan began to call for the return of the millions of South Sudanese IDP s and refugees. The International Organization for Migration (IOM) has developed a programme to help them do so.
Directory of Open Access Journals (Sweden)
Lindsay T McMahon
2007-07-01
Full Text Available With the signing of the Comprehensive Peace Agreement in January 2005, the new Government of South Sudan began to call for the return of the millions of South Sudanese IDP s and refugees. The International Organization for Migration (IOM has developed a programme to help them do so.
Higher Education Endowments Return
Bahlmann, David; Walda, John D.; Sedlacek, Verne O.
2012-01-01
A new study of endowments by the National Association of College and University Business Officers (NACUBO) and the Commonfund Institute has brought good news to college and universities: While endowment returns dropped precipitously in fiscal year 2009 as a result of the financial crisis and accompanying slide in equity markets, they climbed to an…
Mangan, Marianne
2013-01-01
Call it physical activity, call it games, or call it play. Whatever its name, it's a place we all need to return to. In the physical education, recreation, and dance professions, we need to redesign programs to address the need for and want of play that is inherent in all of us.
Bai, Wen; Dai, Junwu; Zhou, Huimeng; Yang, Yongqiang; Ning, Xiaoqing
2017-10-01
Porcelain electrical equipment (PEE), such as current transformers, is critical to power supply systems, but its seismic performance during past earthquakes has not been satisfactory. This paper studies the seismic performance of two typical types of PEE and proposes a damping method for PEE based on multiple tuned mass dampers (MTMD). An MTMD damping device involving three mass units, named a triple tuned mass damper (TTMD), is designed and manufactured. Through shake table tests and finite element analysis, the dynamic characteristics of the PEE are studied and the effectiveness of the MTMD damping method is verified. The adverse influence of MTMD redundant mass to damping efficiency is studied and relevant equations are derived. MTMD robustness is verified through adjusting TTMD control frequencies. The damping effectiveness of TTMD, when the peak ground acceleration far exceeds the design value, is studied. Both shake table tests and finite element analysis indicate that MTMD is effective and robust in attenuating PEE seismic responses. TTMD remains effective when the PGA far exceeds the design value and when control deviations are considered.
An experimental study on pseudoelasticity of a NiTi-based damper for civil applications
Nespoli, Adelaide; Bassani, Enrico; Della Torre, Davide; Donnini, Riccardo; Villa, Elena; Passaretti, Francesca
2017-10-01
In this work, a pseudoelastic damper composed by NiTi wires is tested at 0.5, 1 and 2 Hz for 1000 mechanical cycles. The damping performances were evaluated by three key parameters: the damping capacity, the dissipated energy per cycle and the maximum force. During testing, the temperature of the pseudoelastic elements was registered as well. Results show that the damper assures a bi-directional motion throughout the 1000 cycles together with the maintenance of the recentering. It was observed a stabilization process in the first 50 mechanical cycles, where the key parameters reach stable values; in particular it was found that the damping capacity and the dissipated energy both decrease with frequency. Besides, the mean temperature of the pseudoleastic elements reaches a stable value during tests and confirms the different response of the pseudoelastic wires accordingly with the specific length and stain. Finally, interesting thermal effects were observed at 1 and 2 Hz: at these frequencies and at high strains, the maximum force increases but the temperature of the NiTi wire decreases being in contraddiction with the Clausius-Clapeyron law.
A Study on the Modeling of the Oil Damper in an Auto-Door Hinge
Energy Technology Data Exchange (ETDEWEB)
Ha, Kwang Soon; Kim, Jong Tae; Kim, Hwan Yeol
2009-11-15
An auto-door hinge, which is one of the automatic door-closing apparatuses, has been widely used to prevent fire propagations in living or commercial buildings. The auto-door hinge consists of a spring to accumulate power for closing a door and an oil damper to control door-closing velocity. To predict and optimize the temporal door behavior during the door-closing period, the auto-door closing system was modeled as a second order-damping system. And a damping coefficient of the oil damper was also theoretically modeled by analyzing Newtonian, incompressible, viscous flow through an oil passage between a oil control rod and a oil piston body. The temporal door behaviors during the door-closing period were predicted with respect to the gap distance of the oil passage, oil viscosity, and pre-compressing of the spring. Temporal door behavior measurement method using an encoder system was also developed to validate the modelling on the oil damping system. As using the developed test apparatus, the temporal door position, velocity, and rotational torque were measured, and the modelling method was evaluated.
Energy Technology Data Exchange (ETDEWEB)
Yang, Wenming, E-mail: wenming_y@126.com [School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Wang, Pengkai [School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Hao, Ruican [School of Mechanical Engineering, Beijing Polytechnic, Beijing 100176 (China); Ma, Buchuan [Beijing Institute of Aerospace Control Devices, Beijing 100854 (China)
2017-03-15
Analytical and numerical calculation methods of the radial magnetic levitation force on the cylindrical magnets in cylindrical vessels filled with ferrofluid was reviewed. An experimental apparatus to measure this force was designed and tailored, which could measure the forces in a range of 0–2.0 N with an accuracy of 0.001 N. After calibrated, this apparatus was used to study the radial magnetic levitation force experimentally. The results showed that the numerical method overestimates this force, while the analytical ones underestimate it. The maximum deviation between the numerical results and the experimental ones was 18.5%, while that between the experimental results with the analytical ones attained 68.5%. The latter deviation narrowed with the lengthening of the magnets. With the aids of the experimental verification of the radial magnetic levitation force, the effect of eccentric distance of magnets on the viscous energy dissipation in ferrofluid dampers could be assessed. It was shown that ignorance of the eccentricity of magnets during the estimation could overestimate the viscous dissipation in ferrofluid dampers. - Highlights: • Experimental method measuring magnetic levitation force of ferrofluid was studied. • A simple but rather witty apparatus was designed and tailored. • The apparatus can measure forces in a range of 0–2.0 N with an accuracy of 0.001 N. • Existing methods calculating magnetic levitation force were verified experimentally.
A Study on the Modeling of the Oil Damper in an Auto-Door Hinge
International Nuclear Information System (INIS)
Ha, Kwang Soon; Kim, Jong Tae; Kim, Hwan Yeol
2009-11-01
An auto-door hinge, which is one of the automatic door-closing apparatuses, has been widely used to prevent fire propagations in living or commercial buildings. The auto-door hinge consists of a spring to accumulate power for closing a door and an oil damper to control door-closing velocity. To predict and optimize the temporal door behavior during the door-closing period, the auto-door closing system was modeled as a second order-damping system. And a damping coefficient of the oil damper was also theoretically modeled by analyzing Newtonian, incompressible, viscous flow through an oil passage between a oil control rod and a oil piston body. The temporal door behaviors during the door-closing period were predicted with respect to the gap distance of the oil passage, oil viscosity, and pre-compressing of the spring. Temporal door behavior measurement method using an encoder system was also developed to validate the modelling on the oil damping system. As using the developed test apparatus, the temporal door position, velocity, and rotational torque were measured, and the modelling method was evaluated
International Nuclear Information System (INIS)
Yang, Wenming; Wang, Pengkai; Hao, Ruican; Ma, Buchuan
2017-01-01
Analytical and numerical calculation methods of the radial magnetic levitation force on the cylindrical magnets in cylindrical vessels filled with ferrofluid was reviewed. An experimental apparatus to measure this force was designed and tailored, which could measure the forces in a range of 0–2.0 N with an accuracy of 0.001 N. After calibrated, this apparatus was used to study the radial magnetic levitation force experimentally. The results showed that the numerical method overestimates this force, while the analytical ones underestimate it. The maximum deviation between the numerical results and the experimental ones was 18.5%, while that between the experimental results with the analytical ones attained 68.5%. The latter deviation narrowed with the lengthening of the magnets. With the aids of the experimental verification of the radial magnetic levitation force, the effect of eccentric distance of magnets on the viscous energy dissipation in ferrofluid dampers could be assessed. It was shown that ignorance of the eccentricity of magnets during the estimation could overestimate the viscous dissipation in ferrofluid dampers. - Highlights: • Experimental method measuring magnetic levitation force of ferrofluid was studied. • A simple but rather witty apparatus was designed and tailored. • The apparatus can measure forces in a range of 0–2.0 N with an accuracy of 0.001 N. • Existing methods calculating magnetic levitation force were verified experimentally.
Using block pulse functions for seismic vibration semi-active control of structures with MR dampers
Rahimi Gendeshmin, Saeed; Davarnia, Daniel
2018-03-01
This article applied the idea of block pulse functions in the semi-active control of structures. The BP functions give effective tools to approximate complex problems. The applied control algorithm has a major effect on the performance of the controlled system and the requirements of the control devices. In control problems, it is important to devise an accurate analytical technique with less computational cost. It is proved that the BP functions are fundamental tools in approximation problems which have been applied in disparate areas in last decades. This study focuses on the employment of BP functions in control algorithm concerning reduction the computational cost. Magneto-rheological (MR) dampers are one of the well-known semi-active tools that can be used to control the response of civil Structures during earthquake. For validation purposes, numerical simulations of a 5-story shear building frame with MR dampers are presented. The results of suggested method were compared with results obtained by controlling the frame by the optimal control method based on linear quadratic regulator theory. It can be seen from simulation results that the suggested method can be helpful in reducing seismic structural responses. Besides, this method has acceptable accuracy and is in agreement with optimal control method with less computational costs.
Design and modeling of semi-active squeeze film dampers using magneto-rheological fluids
International Nuclear Information System (INIS)
Kim, Keun-Joo; Lee, Chong-Won; Koo, Jeong-Hoi
2008-01-01
Conventional squeeze film dampers (SFDs) have shown their effectiveness in suppressing unbalanced vibrations in rotor systems, particularly supported by rolling element bearings. Recently, there is an increasing demand for 'controllable' SFDs to meet the need of modern rotating machinery, characterized by high operating speed and high load capacity. Thus, this paper presents a controllable semi-active SFD using magneto-rheological (MR) fluids, focusing on its design and modeling. It offers a comprehensive design method and an innovative experimental identification and modeling technique for MR-SFDs. The primary goal of the MR-SFD design is set to maximize its dynamic control bandwidth, and the design method includes the material selection, magnetic circuit analysis and sealing element design. After constructing a prototype MR-SFD based on the final design, this work investigated how some of the critical design parameters affect the performance of the MR-SFD (i.e. its dynamic control bandwidth change). Furthermore, it characterized the damper's dynamic behavior experimentally using a novel excitation method that adopts active magnetic bearing (AMB) units. Unlike conventional methods, the AMB system was able to precisely control the amplitude and frequency of the input excitation, enabling us to obtain the nonlinear dynamic stiffness properties of the MR-SFD with varying input current. In modeling the dynamic behavior of the MR-SFD, this study employed the describing function method. The describing function analysis effectively captured the nonlinear dynamic behavior of the MR-SFD
Effect of magneto rheological damper on tool vibration during hard turning
Paul, P. Sam; Varadarajan, A. S.
2012-12-01
Recently, the concept of hard turning has gained considerable attention in metal cutting as it can apparently replace the traditional process cycle of turning, heat treating, and finish grinding for assembly of hard wear resistant steel parts. The present investigation aims at developing a magneto rheological (MR) fluid damper for suppressing tool vibration and promoting better cutting performance during hard turning. The magneto rheological Fluid acts as a viscoelastic spring with non-linear vibration characteristics that are controlled by the composition of the magneto rheological fluid, the shape of the plunger and the electric parameters of the magnetizing field. Cutting experiments were conducted to arrive at a set of electrical, compositional and shape parameters that can suppress tool vibration and promote better cutting performance during turning of AISI 4340 steel of 46 HRC with minimal fluid application using hard metal insert with sculptured rake face. It was observed that the use of MR fluid damper reduces tool vibration and improves the cutting performance effectively. Also commercialization of this idea holds promise to the metal cutting industry.
Improved reliability of wind turbine towers with active tuned mass dampers (ATMDs)
Fitzgerald, Breiffni; Sarkar, Saptarshi; Staino, Andrea
2018-04-01
Modern multi-megawatt wind turbines are composed of slender, flexible, and lightly damped blades and towers. These components exhibit high susceptibility to wind-induced vibrations. As the size, flexibility and cost of the towers have increased in recent years, the need to protect these structures against damage induced by turbulent aerodynamic loading has become apparent. This paper combines structural dynamic models and probabilistic assessment tools to demonstrate improvements in structural reliability when modern wind turbine towers are equipped with active tuned mass dampers (ATMDs). This study proposes a multi-modal wind turbine model for wind turbine control design and analysis. This study incorporates an ATMD into the tower of this model. The model is subjected to stochastically generated wind loads of varying speeds to develop wind-induced probabilistic demand models for towers of modern multi-megawatt wind turbines under structural uncertainty. Numerical simulations have been carried out to ascertain the effectiveness of the active control system to improve the structural performance of the wind turbine and its reliability. The study constructs fragility curves, which illustrate reductions in the vulnerability of towers to wind loading owing to the inclusion of the damper. Results show that the active controller is successful in increasing the reliability of the tower responses. According to the analysis carried out in this paper, a strong reduction of the probability of exceeding a given displacement at the rated wind speed has been observed.
An enhanced nonlinear damping approach accounting for system constraints in active mass dampers
Venanzi, Ilaria; Ierimonti, Laura; Ubertini, Filippo
2015-11-01
Active mass dampers are a viable solution for mitigating wind-induced vibrations in high-rise buildings and improve occupants' comfort. Such devices suffer particularly when they reach force saturation of the actuators and maximum extension of their stroke, which may occur in case of severe loading conditions (e.g. wind gust and earthquake). Exceeding actuators' physical limits can impair the control performance of the system or even lead to devices damage, with consequent need for repair or substitution of part of the control system. Controllers for active mass dampers should account for their technological limits. Prior work of the authors was devoted to stroke issues and led to the definition of a nonlinear damping approach, very easy to implement in practice. It consisted of a modified skyhook algorithm complemented with a nonlinear braking force to reverse the direction of the mass before reaching the stroke limit. This paper presents an enhanced version of this approach, also accounting for force saturation of the actuator and keeping the simplicity of implementation. This is achieved by modulating the control force by a nonlinear smooth function depending on the ratio between actuator's force and saturation limit. Results of a numerical investigation show that the proposed approach provides similar results to the method of the State Dependent Riccati Equation, a well-established technique for designing optimal controllers for constrained systems, yet very difficult to apply in practice.
Directory of Open Access Journals (Sweden)
Jiajia Zheng
2014-02-01
Full Text Available A novel magnetorheological (MR damper with a multistage piston and independent input currents is designed and analyzed. The equivalent magnetic circuit model is investigated along with the relation between magnetic induction density in the working gap and input currents of the electromagnetic coils. Finite element method (FEM is used to analyze the distribution of magnetic field through the MR fluid region. Considering the real situation, coupling equations are presented to analyze the electromagnetic-thermal-flow coupling problems. Software COMSOL is used to analyze the multiphysics, that is, electromagnetic, thermal dynamic, and fluid mechanic. A measurement index involving total damping force, dynamic range, and induction time needed for magnetic coil is put forward to evaluate the performance of the novel multistage MR damper. The simulation results show that it is promising for applications under high velocity and works better when more electromagnetic coils are applied with input currents separately. Besides, in order to reduce energy consumption, it is recommended to apply more electromagnetic coils with relative low currents based on the analysis of pressure drop along the annular gap.
SSME Seal Test Program: Test results for sawtooth pattern damper seal
Childs, D. W.
1986-01-01
Direct and transverse force coefficients for 11, sawtooth-pattern, and damper-seal configurations were examined. The designation damper seal uses a deliberately roughened stator and smooth rotor to increase the net damping force developed by a seal. The designation sawtooth-pattern refers to a stator roughness pattern. The sawtooth pattern yields axial grooves in the stator which are interrupted by spacer elements which act as flow constrictions or dams. All seals use the same smooth rotor and have the same, constant, minimum clearance. The stators examined the consequences of changes in the following design parameters: (1) axial-groove depth; (2) number of teeth: (3) number of sawtooth sections; (4) number of spacer elements; (5) dam width; (6) axially aligned sawtooth sections versus axially-staggered sawtooth sections; and (7) groove geometry. It is found that none of the sawtooth-pattern seal performs as well as the best round-hole-pattern seal. Maximum damping configurations for the sawtooth and round-hole-pattern stators have comparable stiffness performance. Several of the sawtooth pattern stators outperformed the best round-hole pattern seal.
Magnetically tuned mass dampers for optimal vibration damping of large structures
International Nuclear Information System (INIS)
Bourquin, Frederic; Siegert, Dominique; Caruso, Giovanni; Peigney, Michael
2014-01-01
This paper deals with the theoretical and experimental analysis of magnetically tuned mass dampers, applied to the vibration damping of large structures of civil engineering interest. Two devices are analysed, for which both the frequency tuning ratio and the damping coefficient can be easily and finely calibrated. They are applied for the damping of the vibrations along two natural modes of a mock-up of a bridge under construction. An original analysis, based on the Maxwell receding image method, is developed for estimating the drag force arising inside the damping devices. It also takes into account self-inductance effects, yielding a complex nonlinear dependence of the drag force on the velocity. The analysis highlights the range of velocities for which the drag force can be assumed of viscous type, and shows its dependence on the involved geometrical parameters of the dampers. The model outcomes are then compared to the corresponding experimental calibration curves. A dynamic model of the controlled structure equipped with the two damping devices is presented, and used for the development of original optimization expressions and for determining the corresponding maximum achievable damping. Finally, several experimental results are presented, concerning both the free and harmonically forced vibration damping of the bridge mock-up, and compared to the corresponding theoretical predictions. The experimental results reveal that the maximum theoretical damping performance can be achieved, when both the tuning frequencies and damping coefficients of each device are finely calibrated according to the optimization expressions. (paper)
Directory of Open Access Journals (Sweden)
Jong Wan Hu
2014-02-01
Full Text Available In this paper, the superelastic shape memory alloy (SMA slit damper system as an alternative design approach for steel structures is intended to be evaluated with respect to inelastic behavior simulated by refined finite element (FE analyses. Although the steel slit dampers conventionally used for aseismic design are able to dissipate a considerable amount of energy generated by the plastic yielding of the base materials, large permanent deformation may occur in the entire structure. After strong seismic events, extra damage repair costs are required to restore the original configuration and to replace defective devices with new ones. Innovative slit dampers fabricated by superelastic SMAs that automatically recover their initial conditions only by the removal of stresses without heat treatment are introduced with a view toward mitigating the problem of permanent deformation. The cyclically tested FE models are calibrated to experimental results for the purpose of predicting accurate behavior. This study also focuses on the material constitutive model that is able to reproduce the inherent behavior of superelastic SMA materials by taking phase transformation between austenite and martensite into consideration. The responses of SMA slit dampers are compared to those of steel slit dampers. Axial stress and strain components are also investigated on the FE models under cyclic loading in an effort to validate the adequacy of FE modeling and then to compare between two slit damper systems. It can be shown that SMA slit dampers exhibit many structural advantages in terms of ultimate strength, moderate energy dissipation and recentering capability.
Proctor, Margaret P.; Gunter, Edgar J.
2007-01-01
A case study of a high-speed seal test rotor shows how rotor dynamic analysis can be used to diagnose the source of high vibrations and evaluate a proposed remedy. Experimental results are compared with the synchronous and non-synchronous whirl response analysis of a double overhung, high-speed seal test rotor with ball bearings supported in 5.84- and 12.7-mm-long, un-centered squeeze-film oil dampers. Test performance with the original damper of length 5.84 mm was marginal. Non-synchronous whirling occurred at the overhung seal test disk and there was a high amplitude synchronous response near the drive spline above 32,000 rpm. Nonlinear synchronous unbalance and time transient whirl studies were conducted on the seal test rotor with the original and extended damper lengths. With the original damper design, the nonlinear synchronous response showed that unbalance could cause damper lockup at 33,000 rpm. Alford cross-coupling forces were also included at the overhung seal test disk for the whirl analysis. Sub-synchronous whirling at the seal test disk was observed in the nonlinear time transient analysis. With the extended damper length of 12.7 mm, the sub-synchronous motion was eliminated and the rotor unbalance response was acceptable to 45,000 rpm with moderate rotor unbalance. Seal test rotor orbits and vibration levels with the extended squeeze film dampers showed smooth operation to 40,444 rpm.
Higher-order-mode damper as beam-position monitors; Higher-Order-Mode Daempfer als Stahllagemonitore
Energy Technology Data Exchange (ETDEWEB)
Peschke, C.
2006-03-15
In the framework of this thesis a beam-position monitor was developed, which can only because of the signals from the HOM dampers of a linear-accelerator structure determine the beam position with high accuracy. For the unique determination of the beam position in the plane a procedure was developed, which uses the amplitudes and the start-phase difference between a dipole mode and a higher monopole mode. In order tocheck the suitability of the present SBLC-HOM damper as beam position monitor three-dimensional numerical field calculations in the frequency and time range and measurements on the damper cell were performed. For the measurements without beam a beam simulator was constructed, which allows computer-driven measurements with variable depositions of the simulated beam with a resolution of 1.23 {mu}m. Because the complete 6 m long, 180-cell accelerator structure was not available for measurements and could also with the available computers not be three-dimensionally simulated simulated, a one-dimensional equivalent-circuit based model of the multi-cell was studied. The equivalent circuits with 879 concentrated components regards the detuning from cell to cell, the cell losses, the damper losses, and the beam excitation in dependence on the deposition. the measurements and simulations let a resolution of the ready beam-position monitor on the 180-cell in the order of magnitude of 1-10 {mu}m and a relative accuracy smaller 6.2% be expected.
Czech Academy of Sciences Publication Activity Database
Ferfecki, P.; Zapoměl, Jaroslav; Kozánek, Jan
2017-01-01
Roč. 104, February (2017), s. 1-11 ISSN 0965-9978 R&D Projects: GA ČR GA15-06621S Institutional support: RVO:61388998 Keywords : magnetorheological squeeze film dampers * magnetorheological oils * closed form formulas * multiphysical problem Subject RIV: JR - Other Machinery OBOR OECD: Mechanical engineering Impact factor: 3.000, year: 2016
Dittrich, M.G.; Graafland, F.; Eisses, A.R.; Nijhof, M.J.J.
2015-01-01
Rail dampers and sound absorbing plates have been tested on a high speed railway slab track in a walled cutting at a noise sensitive location. Their noise reduction has been determined from pass-by measurements during service and predicted using BEM calculations. The cutting depth, noise barrier
Energy Technology Data Exchange (ETDEWEB)
Xiao, Ping; Gao, Hong [Anhui Polytechnic University, Wuhu (China); Niu, Limin [Anhui University of Technology, Maanshan (China)
2017-07-15
Due to the fail safe problem, it was difficult for the existing Magnetorheological damper (MD) to be widely applied in automotive suspensions. Therefore, permanent magnets and magnetic valves were introduced to existing MDs so that fail safe problem could be solved by the magnets and damping force could be adjusted easily by the magnetic valve. Thus, a new Magnetorheological damper with permanent magnet and magnetic valve (MDPMMV) was developed and MDPMMV suspension was studied. First of all, mechanical structure of existing magnetorheological damper applied in automobile suspensions was redesigned, comprising a permanent magnet and a magnetic valve. In addition, prediction model of damping force was built based on electromagnetics theory and Bingham model. Experimental research was onducted on the newly designed damper and goodness of fit between experiment results and simulated ones by models was high. On this basis, a quarter suspension model was built. Then, fruit Fly optimization algorithm (FOA)-optimal control algorithm suitable for automobile suspension was designed based on developing normal FOA. Finally, simulation experiments and bench tests with input surface of pulse road and B road were carried out and the results indicated that working erformance of MDPMMV suspension based on FOA-optimal control algorithm was good.
Energy Technology Data Exchange (ETDEWEB)
Takano, H.; Ogasawara, M.; Shimosato, T. [Metropolitan Public Corp., Tokyo (Japan); Yamada, H. [Yokohama National Univ. (Japan)] Murakami, T. [NKK Corp., Tokyo (Japan). Applied Technology Research Center
1998-03-20
In a long cable-stayed bridge, countermeasure against wind induced vibration should be often taken at the same time together with the measure against angular bent phenomena (phenomena in which secondary bending stress is generated on the front of fixing socket by live load). The conventional countermeasure is a combined use of buffer rubber and dampers. This study points out problems in the conventional countermeasure on the application to the cables of the Tsurumi Tsubasa Bridge and combination of dampers and angular bending buffer device is examined. The result shows that a combined use of high-damping rubber and oil dampers enables installation of the dampers in a lower position while maintaining the performance and is excellent in the easiness in installation and maintenance and in aesthetic view. This system was applied to the Tsurumi Tsubasa Bridge and the effectiveness on damping and angular bending relaxation was confirmed through the model tests, and vibration tests and field observation on the cables. 9 refs., 20 figs., 7 tabs.
DEFF Research Database (Denmark)
Shaharudin, Mohd Rizaimy; Govindan, Kannan; Zailani, Suhaiza
2017-01-01
The aim of this study is to examine the extent to which product returns motivate manufacturing firms to adopt closed-loop supply chain activities that influence the effectiveness of reverse supply chains. The hypotheses have been tested using data from a sample of 150 environmental management...... system ISO 14001 certified manufacturing firms in Malaysia through the census sampling approach. The results of the empirical test using LISREL Version 8.70 for the structural equation modeling support the fundamental explanation of the influence of the institutional forces towards the adoption of closed...... eventually impacts the firm's effectiveness in the reverse supply chain. The findings also help managers to understand the factors that can improve the outcome of the adoption of closed-loop supply chain activities by intensifying the extent of involvement in product returns, which provides a valuable...
Duct corrosion in the ventilating air conditioning system for Main Control Room
International Nuclear Information System (INIS)
Yamada, Kohei; Kobayashi, Takashi; Minami, Akiko; Fukuba, Kazushi
2014-01-01
Higashidori Nuclear Power Station, start-of-operation in December 2005, is a relatively new plant. We decided to get original data of air duct condition to determine maintenance policy of air duct, because planned maintenance of air duct has never been done and the corrosion of air duct has occurred in other plant. In January 2014, we found a corrosion-hole at the downstream of the inlet damper in the ventilating air conditioning system for Main Control Room (MCR). We supposed that the cause of rapid corrosion is related to the characteristic environment of this site. (author)
Nonlinear Dynamics Analysis of the Semiactive Suspension System with Magneto-Rheological Damper
Directory of Open Access Journals (Sweden)
Hailong Zhang
2015-01-01
Full Text Available This paper examines dynamical behavior of a nonlinear oscillator which models a quarter-car forced by the road profile. The magneto-rheological (MR suspension system has been established, by employing the modified Bouc-Wen force-velocity (F-v model of magneto-rheological damper (MRD. The possibility of chaotic motions in MR suspension is discovered by employing the method of nonlinear stability analysis. With the bifurcation diagrams and corresponding Lyapunov exponent (LE spectrum diagrams detected through numerical calculation, we can observe the complex dynamical behaviors and oscillating mechanism of alternating periodic oscillations, quasiperiodic oscillations, and chaotic oscillations with different profiles of road excitation, as well as the dynamical evolutions to chaos through period-doubling bifurcations, saddle-node bifurcations, and reverse period-doubling bifurcations.
Active Tuned Mass Dampers for Control of In-Plane Vibrations of Wind Turbine Blades
DEFF Research Database (Denmark)
Fitzgerald, B.; Basu, Biswajit; Nielsen, Søren R.K.
2013-01-01
matrices. The aim of this paper is to determine whether ATMDs could be used to reduce in-plane blade vibrations in wind turbines with better performance than compared with their passive counterparts. A Euler–Lagrangian wind turbine mathematical model based on energy formulation was developed......, centrifugal, and turbulent aerodynamic loadings. Investigations show promising results for the use of ATMDs in the vibration control of wind turbine blades.......This paper investigates the use of active tuned mass dampers (ATMDs) for the mitigation of in-plane vibrations in rotating wind turbine blades. The rotating wind turbine blades with tower interaction represent time-varying dynamical systems with periodically varying mass, stiffness, and damping...
Coupled-Mode Flutter of Wind Turbines and its Suppression Using Torsional Viscous Damper
DEFF Research Database (Denmark)
Zhang, Zili; Chen, Bei; Nielsen, Søren R. K.
2017-01-01
The trend towards lighter and more flexible blades may lead to aeroelastic instability of wind turbines under certain circumstances, resulting in rapid destructive failure or limit-cycle oscillations of the structural components. For pitch-regulated wind turbines, classical flutter is believed...... between blade vibrations with tower and drivetrain motions are also considered, making this model capable for coupled-mode flutter analysis of a complete wind turbine system. The parameters of the model have been calibrated to the DTU 10MW wind turbine, and the critical flutter speed of the rotor is shown...... to be about 1.6 times its nominal rotational speed. A novel torsional viscous damper is then proposed to suppress torsional blade vibration and to enhance flutter stability of wind turbines....
International Nuclear Information System (INIS)
Kostarev, V.V.; Petrenko, A.V.; Vasilyev, P.S.; Reinsch, K.-H.
2005-01-01
This paper concerns a further development of High Viscous Damper (HVD) approach for essential decreasing of structure's floor response spectra. Usually restraining of components and pipelines by HVD is used for significant decreasing of operational vibration and seismic loads. A new approach consists of dampers installation for essential upgrading of a whole system's damping that is much more efficient in both technical and economical points of view than restraining of each component of the system. In that way using of HVD means high energy dissipation for whole dynamic system 'Building-Components' subjected to the base seismic or other extreme load excitation. The specific feature of each NPP site is an existing of a few closely spaced buildings: reactor building, turbine hall and so on. As the rule such buildings play sufficiently different roles in NPP operation and therefore have sufficiently different design, natural frequencies (periods) and distortion of floors and different rocking modes on a soil. The main idea explained in the paper is an interconnection of buildings by HVD. Then differences in their mechanical properties provide their out-of-phase relative motions during an earthquake and therefore effective dissipative work provided by HVD devices. At the same time implementation of HVD approach allows to eliminate possible interactions and collisions in the gaps between building structures that wears potential threat of building failure. The detailed 3D finite element models of reactor building, turbine hall and special building were developed for NPP with VVER-1000 MWt reactor type. Performed analysis has shown high efficiency of suggested approach for protection of buildings, structures, systems and components against seismic and other impacts. (authors)
Pisal, Alka Y.; Jangid, R. S.
2016-06-01
The effectiveness of tuned mass friction damper (TMFD) in reducing undesirable resonant response of the bridge subjected to multi-axle vehicular load is investigated. A Taiwan high-speed railway (THSR) bridge subjected to Japanese SKS (Salkesa) train load is considered. The bridge is idealized as a simply supported Euler-Bernoulli beam with uniform properties throughout the length of the bridge, and the train's vehicular load is modeled as a series of moving forces. Simplified model of vehicle, bridge and TMFD system has been considered to derive coupled differential equations of motion which is solved numerically using the Newmark's linear acceleration method. The critical train velocities at which the bridge undergoes resonant vibration are investigated. Response of the bridge is studied for three different arrangements of TMFD systems, namely, TMFD attached at mid-span of the bridge, multiple tuned mass friction dampers (MTMFD) system concentrated at mid-span of the bridge and MTMFD system with distributed TMFD units along the length of the bridge. The optimum parameters of each TMFD system are found out. It has been demonstrated that an optimized MTMFD system concentrated at mid-span of the bridge is more effective than an optimized TMFD at the same place with the same total mass and an optimized MTMFD system having TMFD units distributed along the length of the bridge. However, the distributed MTMFD system is more effective than an optimized TMFD system, provided that TMFD units of MTMFD system are distributed within certain limiting interval and the frequency of TMFD units is appropriately distributed.
Acoustic response of Helmholtz dampers in the presence of hot grazing flow
Ćosić, B.; Wassmer, D.; Terhaar, S.; Paschereit, C. O.
2015-01-01
Thermoacoustic instabilities are high amplitude instabilities of premixed gas turbine combustors. Cooled passive dampers are used to attenuate or suppress these instabilities in the combustion chamber. For the first time, the influence of temperature differences between the grazing flow in the combustor and the cross-flow emanating from the Helmholtz damper is comprehensively investigated in the linear and nonlinear amplitude regime. The flow field inside the resonator and in the vicinity of the neck is measured with high-speed particle image velocimetry for various amplitudes and at different momentum-flux ratios of grazing and purging flow. Seeding is used as a tracer to qualitatively assess the mixing of the grazing and purging flow as well as the ingestion into the neck of the resonator. Experimentally, the acoustic response for various temperature differences between grazing and purging flow is investigated. The multi-microphone method, in combination with two microphones flush-mounted in the resonator volume and two microphones in the plane of the resonator entrance, is used to determine the impedance of the Helmholtz resonator in the linear and nonlinear amplitude regime for various temperatures and different momentum-flux ratios. Additionally, a thermocouple was used to measure the temperature in the neck. The acoustic response and the temperature measurements are used to obtain the virtual neck length and the effective area jump from a detailed impedance model. This model is extended to include the observed acoustic energy dissipation caused by the density gradients at the neck vicinity. A clear correlation between temperature differences and changes of the mass end-correction is confirmed. The capabilities of the impedance model are demonstrated.
Directory of Open Access Journals (Sweden)
Hamed Rahman Shokrgozar
2017-02-01
Full Text Available Tuned mass and tuned liquid dampers are most common passive control systems that used for decrease of seismic responses of buildings. In this study, the performance of high-rise buildings with TM and TL dampers are evaluated under seven near-fault and seven far-fault earthquakes. For this purpose, a twenty-four stories steel moment frame building has been considered and the time history dynamic analyses are performed for both of controlled and uncontrolled states. Moreover, this building has been also modelled with five various mass, stiffness and damping ratios.The results have been shown that decreasing the structural responses at tall buildings against near-fault earthquakes are more than far-fault earthquakes due to the effect of higher modes. Furthermore, the tuned mass damper has better performance at decreasing of the responses in comparison of tuned liquid dampers.
Mars Sample Return Architecture Overview
Edwards, C. D.; Vijendran, S.
2018-04-01
NASA and ESA are exploring potential concepts for a Sample Retrieval Lander and Earth Return Orbiter that could return samples planned to be collected and cached by the Mars 2020 rover mission. We provide an overview of the Mars Sample Return architecture.
DEFF Research Database (Denmark)
Dalgaard, Carl-Johan Lars; Hansen, Henrik
2017-01-01
We estimate the average rate of return on investments financed by aid and by domestic resource mobilisation, using aggregate data. Both returns are expected to vary across countries and time. Consequently we develop a correlated random coefficients model to estimate the average returns. Across...... different estimators and two different data sources for GDP and investment our findings are remarkably robust; the average gross return on ‘aid investments’ is about 20 per cent. This is in accord with micro estimates of the economic rate of return on aid projects and with aggregate estimates of the rate...
DEFF Research Database (Denmark)
Olwig, Karen Fog
2012-01-01
Research on female migrant caregivers has tended to focus upon the emotional and social problems they encounter working abroad, given women’s traditional role as caregivers for their own families. This article analyses how Caribbean women who have returned after a period abroad as domestic workers...... inscribe their migration experiences within the gendered narrative of the good relative who migrates to help the family left behind and therefore deserves social recognition in the community of origin. It argues that this narrative allows the women to both affirm and reinterpret local family and gender...... roles within the context of migration. This analysis points to the close connection between narrative structures, accounts of migration experiences, and self-presentations and suggests that narratives about family and gender roles not only reflect people’s lives, but are also a malleable resource...
Takeya, Kouichi; Sasaki, Eiichi; Kobayashi, Yusuke
2016-01-01
A bridge vibration energy harvester has been proposed in this paper using a tuned dual-mass damper system, named hereafter Tuned Mass Generator (TMG). A linear electromagnetic transducer has been applied to harvest and make use of the unused reserve of energy the aforementioned damper system absorbs. The benefits of using dual-mass systems over single-mass systems for power generation have been clarified according to the theory of vibrations. TMG parameters have been determined considering multi-domain parameters, and TMG has been tuned using a newly proposed parameter design method. Theoretical analysis results have shown that for effective energy harvesting, it is essential that TMG has robustness against uncertainties in bridge vibrations and tuning errors, and the proposed parameter design method for TMG has demonstrated this feature.
Directory of Open Access Journals (Sweden)
Xiufang Lin
2016-08-01
Full Text Available Magnetorheological dampers have become prominent semi-active control devices for vibration mitigation of structures which are subjected to severe loads. However, the damping force cannot be controlled directly due to the inherent nonlinear characteristics of the magnetorheological dampers. Therefore, for fully exploiting the capabilities of the magnetorheological dampers, one of the challenging aspects is to develop an accurate inverse model which can appropriately predict the input voltage to control the damping force. In this article, a hybrid modeling strategy combining shuffled frog-leaping algorithm and adaptive-network-based fuzzy inference system is proposed to model the inverse dynamic characteristics of the magnetorheological dampers for improving the modeling accuracy. The shuffled frog-leaping algorithm is employed to optimize the premise parameters of the adaptive-network-based fuzzy inference system while the consequent parameters are tuned by a least square estimation method, here known as shuffled frog-leaping algorithm-based adaptive-network-based fuzzy inference system approach. To evaluate the effectiveness of the proposed approach, the inverse modeling results based on the shuffled frog-leaping algorithm-based adaptive-network-based fuzzy inference system approach are compared with those based on the adaptive-network-based fuzzy inference system and genetic algorithm–based adaptive-network-based fuzzy inference system approaches. Analysis of variance test is carried out to statistically compare the performance of the proposed methods and the results demonstrate that the shuffled frog-leaping algorithm-based adaptive-network-based fuzzy inference system strategy outperforms the other two methods in terms of modeling (training accuracy and checking accuracy.
Kruep, Stephanie Jean
2007-01-01
This thesis presents the details of a study regarding both the use of linear viscous fluid dampers in controlling the interstory drift in steel moment frames, and the use of incremental dynamic analysis as a method of visualizing the behavior of these moment frames when subjected to seismic load effects. Models of three story and nine story steel moment frames were designed to meet typical strength requirements for office buildings in Seattle, Washington. These models were intentionally des...
International Nuclear Information System (INIS)
Zhabitskij, V.M.; Korenev, I.L.; Yudin, L.A.
1991-01-01
The resistive instability damper system for the coasting beam in the accelerator is discussed. The system for each of two directions of beam transverse coherent oscillations includes two pairs of pick-up electrodes and damping kickers connected by delayed negative feedback. It has been shown that damping regime can be achieved for one and the same pick-up and kicker location independently on imQ. 8 refs.; 4 figs
Computing return times or return periods with rare event algorithms
Lestang, Thibault; Ragone, Francesco; Bréhier, Charles-Edouard; Herbert, Corentin; Bouchet, Freddy
2018-04-01
The average time between two occurrences of the same event, referred to as its return time (or return period), is a useful statistical concept for practical applications. For instance insurances or public agencies may be interested by the return time of a 10 m flood of the Seine river in Paris. However, due to their scarcity, reliably estimating return times for rare events is very difficult using either observational data or direct numerical simulations. For rare events, an estimator for return times can be built from the extrema of the observable on trajectory blocks. Here, we show that this estimator can be improved to remain accurate for return times of the order of the block size. More importantly, we show that this approach can be generalised to estimate return times from numerical algorithms specifically designed to sample rare events. So far those algorithms often compute probabilities, rather than return times. The approach we propose provides a computationally extremely efficient way to estimate numerically the return times of rare events for a dynamical system, gaining several orders of magnitude of computational costs. We illustrate the method on two kinds of observables, instantaneous and time-averaged, using two different rare event algorithms, for a simple stochastic process, the Ornstein–Uhlenbeck process. As an example of realistic applications to complex systems, we finally discuss extreme values of the drag on an object in a turbulent flow.
Li, Zhengqi; Kuang, Min; Zhang, Jia; Han, Yunfeng; Zhu, Qunyi; Yang, Lianjie; Kong, Weiguang
2010-02-01
Cold airflow experiments were conducted to investigate the aerodynamic field in a small-scale furnace of a down-fired pulverized-coal 300 MW(e) utility boiler arranged with direct flow split burners enriched by cyclones. By increasing the staged-air ratio, a deflected flow field appeared in the lower furnace; larger staged-air ratios produced larger deflections. Industrial-sized experiments on a full-scale boiler were also performed at different staged-air damper openings with measurements taken of gas temperatures in the burner region and near the right-side wall, wall heat fluxes, and gas components (O(2), CO, and NO(x)) in the near-wall region. Combustion was unstable at staged-air damper openings below 30%. For openings of 30% and 40%, late ignition of the pulverized coal developed and large differences arose in gas temperatures and heat fluxes between the regions near the front and rear walls. In conjunction, carbon content in the fly ash was high and boiler efficiency was low with high NO(x) emission above 1200 mg/m(3) (at 6% O(2) dry). For fully open dampers, differences in gas temperatures and heat fluxes, carbon in fly ash and NO(x) emission decreased yielding an increase in boiler efficiency. The optimal setting is fully open staged-air dampers.
Dobre, A.; Andreescu, C. N.; Stan, C.
2016-08-01
Due to their simplicity and controllability, adaptive dampers became very popular in automotive engineering industry, especially in the passenger cars industry, in spite of technological obstacles inherent and the high cost of the magnetic fluid. “MagneRide” is the first technology which uses smart fluids in the shock absorbers of the vehicles adaptive suspensions. Since the discovery of the magneto-rheological effect there is a consistent progress regarding the control algorithms and hardware part itself. These magneto-rheological devices have a major potential which can be explored in various fields of applications. At present many companies make researches for the improvement of the response time and for obtaining a better response at low frequency and amplitude of the body car oscillations. The main objective of this paper is to determine the damping characteristic of a magnetorheological shock absorber of a passenger car. The authors aim to observe how to modify the damping characteristic by changing the intensity of the electric current. The experimental researches have being carried out on a complex and modern test bench especially built for testing shock absorbers, in order to compare the damping characteristic of the classical damper with the magneto-rheological damper.
Directory of Open Access Journals (Sweden)
H. P. Jagadish
2013-01-01
Full Text Available Squeeze film dampers are novel rotor dynamic devices used to alleviate small amplitude, large force vibrations and are used in conjunction with antifriction bearings in aircraft jet engine bearings to provide external damping as these possess very little inherent damping. Electrorheological (ER fluids are controllable fluids in which the rheological properties of the fluid, particularly viscosity, can be controlled in accordance with the requirements of the rotor dynamic system by controlling the intensity of the applied electric field and this property can be utilized in squeeze film dampers, to provide variable stiffness and damping at a particular excitation frequency. The paper investigates the effect of temperature and electric field on the apparent viscosity and dynamic (stiffness and damping characteristics of ER fluid (suspension of diatomite in transformer oil using the available literature. These characteristics increase with the field as the viscosity increases with the field. However, these characteristics decrease with increase in temperature and shear strain rate as the viscosity of the fluid decreases with temperature and shear strain rate. The temperature is an important parameter as the aircraft jet engine rotors are located in a zone of high temperature gradients and the damper fluid is susceptible to large variations in temperature.
ZHU, C. S.; ROBB, D. A.; EWINS, D. J.
2002-05-01
The multiple-solution response of rotors supported on squeeze film dampers is a typical non-linear phenomenon. The behaviour of the multiple-solution response in a flexible rotor supported on two identical squeeze film dampers with centralizing springs is studied by three methods: synchronous circular centred-orbit motion solution, numerical integration method and slow acceleration method using the assumption of a short bearing and cavitated oil film; the differences of computational results obtained by the three different methods are compared in this paper. It is shown that there are three basic forms for the multiple-solution response in the flexible rotor system supported on the squeeze film dampers, which are the resonant, isolated bifurcation and swallowtail bifurcation multiple solutions. In the multiple-solution speed regions, the rotor motion may be subsynchronous, super-subsynchronous, almost-periodic and even chaotic, besides synchronous circular centred, even if the gravity effect is not considered. The assumption of synchronous circular centred-orbit motion for the journal and rotor around the static deflection line can be used only in some special cases; the steady state numerical integration method is very useful, but time consuming. Using the slow acceleration method, not only can the multiple-solution speed regions be detected, but also the non-synchronous response regions.
International Nuclear Information System (INIS)
Praveen Kumar; Jangid, R.S.; Reddy, G.R.
2013-01-01
Highlights: ► Piping system with semi-active variable stiffness damper is investigated under different seismic excitations. ► Switching control law and modified switching control law are adopted. ► There exist an optimum parameters of the SAVSD. ► Substantial reduction of the seismic response of piping system with SAVSD is observed. ► Good amount of energy dissipation is observed. -- Abstract: Seismic loads on piping system due to earthquakes can cause excessive vibrations, which can lead to serious instability resulting in damage or complete failure. In this paper, semi-active variable stiffness dampers (SAVSDs) have been studied to mitigate seismic response and vibration control of piping system used in the process industries, fossil and fissile fuel power plant. The SAVSD changes its stiffness depending upon the piping response and accordingly adds the control forces in the piping system. A study is conducted on the performance of SAVSD due to variation in device stiffness ratios in the switching control law and modified switching control law, which plays an important role in the present control algorithm of the damper. The effectiveness of the SAVSD in terms of reduction in the responses, namely, displacements, accelerations and base shear of the piping system is investigated by comparing uncontrolled responses under four different artificial earthquake motions with increasing amplitudes. The analytical results demonstrate that the SAVSDs under particular optimum parameters are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping systems
Energy Technology Data Exchange (ETDEWEB)
Praveen Kumar, E-mail: praveen@barc.gov.in [Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Jangid, R.S. [Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076 (India); Reddy, G.R. [Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)
2013-05-15
Highlights: ► Piping system with semi-active variable stiffness damper is investigated under different seismic excitations. ► Switching control law and modified switching control law are adopted. ► There exist an optimum parameters of the SAVSD. ► Substantial reduction of the seismic response of piping system with SAVSD is observed. ► Good amount of energy dissipation is observed. -- Abstract: Seismic loads on piping system due to earthquakes can cause excessive vibrations, which can lead to serious instability resulting in damage or complete failure. In this paper, semi-active variable stiffness dampers (SAVSDs) have been studied to mitigate seismic response and vibration control of piping system used in the process industries, fossil and fissile fuel power plant. The SAVSD changes its stiffness depending upon the piping response and accordingly adds the control forces in the piping system. A study is conducted on the performance of SAVSD due to variation in device stiffness ratios in the switching control law and modified switching control law, which plays an important role in the present control algorithm of the damper. The effectiveness of the SAVSD in terms of reduction in the responses, namely, displacements, accelerations and base shear of the piping system is investigated by comparing uncontrolled responses under four different artificial earthquake motions with increasing amplitudes. The analytical results demonstrate that the SAVSDs under particular optimum parameters are very effective and practically implementable for the seismic response mitigation, vibration control and seismic requalification of piping systems.
International Nuclear Information System (INIS)
Ammerich, M.
2009-01-01
This article goes back over the incidents occurring during the summer 2008, that is to say the uranium release from the Socatri facility in the South of France. From this point, the purpose studies the radiological situation of the Camargue seashore; the levels of radioactivity are from 3 to thirty times higher than these ones expected in this area, but the natural radioactivity with thorium and uranium coming from the granitic massifs erosion brings an important part. It is difficult to make the part between human and natural contribution to ambient radioactivity. However, it appears that to limit the water consumption until the time of dilution played its part was absolutely necessary. Then, because it is question of water, the drinking water is tackled. Some mineral waters go over the recommended limits of doses. A last return to the past with the radioactive watches, but this time with actual watches that activate detection. Two watches contained promethium 147, 147 Pm is a beta emitter but also gamma emitter. To end, in Ireland and Great Britain, some fire detectors contain americium 241. In fact, this article constitutes a summary of different abnormalities around radioactivity. (N.C.)
Directory of Open Access Journals (Sweden)
S. Griffioen
2011-06-01
Full Text Available Religion is back in Philosophy as a respectable subject. Part 1 first charts what MacIntyre, Taylor and Derrida have meant in this regard. Subsequently, it turns to the Enlightenment to determine what constituted the breakthrough. It is found that even where the Enlightenment gave maximum room to religion i.e. as a civic religion and as “religion of the heart” it still excluded a constitutive relation to a transcendent revelation. Part 2 centres on the religion-faith distinction in reformational philosophy. Similar to the Enlightenment, religion is understood as part of human nature. However, human nature itself is conceived as intrinsically religious and depending for its light on revelation. Secondly, “religion” in this context also encompasses idols and religious substitutes. Thus, it directs attention to shopping malls, football stadiums, health policy, et cetera, as possible contexts of a return of religion. Examples show that this has become a popular approach. However, most of the publications surveyed fail to distinguish between an “analogical” and a “pistically qualified” use of religion, and are open to exaggerations (the shopping mall and football stadiums as temples, etc.. At this junction, the relevance is shown of the religion-faith distinction as well as of Elaine Botha’s theory of metaphors. The epilogue offers an integration of parts one and two.
International Nuclear Information System (INIS)
Anon.
1990-01-01
In the first of what it says will be annual cost-of-capital proceedings to set returns on equity and rates of return on rate base for electric utilities, the California Public Utilities Commission (PUC) lowered from 1989 levels the 1990 returns on common equity (ROE) and rates of return (ROR) for the state's four major investor-owned electric utilities. Under this fast-track procedure, by May 8 of every year, utilities will have to file an application for rate adjustments that reflect their projected costs of capital for the following year
DEFF Research Database (Denmark)
Dalgaard, Carl-Johan Lars; Hansen, Henrik
We investigate the marginal productivity of investment across countries. The aim is to estimate the return on investments financed by foreign aid and by domestic resource mobilization, using aggregate data. Both returns are expected to vary across countries and time. Consequently we develop...... a correlated random coefficients model, to estimate the average aggregate return on ‘aid investments’ and ‘domestic investments’. Across different estimators and two different sources for GDP and investment data our findings are remarkably robust; the average gross return on ‘aid investments’ is about 20 per...
Analysis of Two-Phase Flow in Damper Seals for Cryogenic Turbopumps
Arauz, Grigory L.; SanAndres, Luis
1996-01-01
Cryogenic damper seals operating close to the liquid-vapor region (near the critical point or slightly su-cooled) are likely to present two-phase flow conditions. Under single phase flow conditions the mechanical energy conveyed to the fluid increases its temperature and causes a phase change when the fluid temperature reaches the saturation value. A bulk-flow analysis for the prediction of the dynamic force response of damper seals operating under two-phase conditions is presented as: all-liquid, liquid-vapor, and all-vapor, i.e. a 'continuous vaporization' model. The two phase region is considered as a homogeneous saturated mixture in thermodynamic equilibrium. Th flow in each region is described by continuity, momentum and energy transport equations. The interdependency of fluid temperatures and pressure in the two-phase region (saturated mixture) does not allow the use of an energy equation in terms of fluid temperature. Instead, the energy transport is expressed in terms of fluid enthalpy. Temperature in the single phase regions, or mixture composition in the two phase region are determined based on the fluid enthalpy. The flow is also regarded as adiabatic since the large axial velocities typical of the seal application determine small levels of heat conduction to the walls as compared to the heat carried by fluid advection. Static and dynamic force characteristics for the seal are obtained from a perturbation analysis of the governing equations. The solution expressed in terms of zeroth and first order fields provide the static (leakage, torque, velocity, pressure, temperature, and mixture composition fields) and dynamic (rotordynamic force coefficients) seal parameters. Theoretical predictions show good agreement with experimental leakage pressure profiles, available from a Nitrogen at cryogenic temperatures. Force coefficient predictions for two phase flow conditions show significant fluid compressibility effects, particularly for mixtures with low mass
International Nuclear Information System (INIS)
Sarrafan, Atabak; Zareh, Seiyed Hamid; Khayyat, Amir Ali Akbar; Zabihollah, Abolghassem
2012-01-01
Magnetorheological (MR) damper is a prominent semi-active control device to vibrate mitigation of structures. Due to the inherent non-linear nature of MR damper, an intelligent non-linear neuro-fuzzy control strategy is designed to control wave-induced vibration of an offshore steel jacket platform equipped with MR dampers. In the proposed control system, a dynamic-feedback neural network is adapted to model non-linear dynamic system, and the fuzzy logic controller is used to determine the control forces of MR dampers. By use of two feed forward neural networks required voltages and actual MR damper forces are obtained, in which the first neural network and the second one acts as the inverse dynamics model, and the forward dynamics model of the MR dampers, respectively. The most important characteristic of the proposed intelligent control strategy is its inherent robustness and its ability to handle the non-linear behavior of the system. Besides, no mathematical model needed to calculate forces produced by MR dampers. According to linearized Morison equation, wave-induced forces are determined. The performance of the proposed neuro-fuzzy control system is compared with that of a traditional semi-active control strategy, i.e., clipped optimal control system with LQG-target controller, through computer simulations, while the uncontrolled system response is used as the baseline. It is demonstrated that the design of proposed control system framework is more effective than that of the clipped optimal control scheme with LQG-target controller to reduce the vibration of offshore structure. Furthermore, the control strategy is very important for semi-active control
Corporate Governance and Equity Returns
Uchida, Shigeru
2012-01-01
This paper analyses the relationship between corporate governance and equity returns from the small investors view point. A primary survey has been conducted to gather the data required to examine the link. Preliminary result of the study shows that the four elements of governance: board structure, transparency, fairness and responsibility are positively related with equity returns.
Energy Technology Data Exchange (ETDEWEB)
Wang, Dongqiang; Wu, Chengjun [Xi' an Jiaotong University, Xi' an (China)
2016-03-15
Particle damping technology is widely used in mechanical and structural systems or civil engineering to reduce vibration and suppress noise as a result of its high efficiency, simplicity and easy implementation, low cost, and energy-saving characteristic without the need for any auxiliary power equipment. Research on particle damping theory has focused on the vibration response of the particle damping structure, but the acoustic radiation of the particle damping structure is rarely investigated. Therefore, a feasible modeling method to predict the vibration response and acoustic radiation of the particle damping structure is desirable to satisfy the actual requirements in industrial practice. In this paper, a novel simulation method based on multiphase flow theory of gas particle by COMSOL multiphysics is developed to study the vibration and acoustic radiation characteristics of a cantilever rectangular plate with Particle dampers (PDs). The frequency response functions and scattered far-field sound pressure level of the plate without and with PDs under forced vibration are predicted, and the predictions agree well with the experimental results. Results demonstrate that the added PDs have a significant effect on vibration damping and noise reduction for the primary structure. The presented work in this paper shows that the theoretical work is valid, which can provide important theoretical guidance for low-noise optimization design of particle damping structure. This model also has an important reference value for the noise control of this kind of structure.
Altunişik, Ahmet Can; Yetişken, Ali; Kahya, Volkan
2018-03-01
This paper gives experimental tests' results for the control performance of Tuned Liquid Column Dampers (TLCDs) installed on a prototype structure exposed to ground motions with different directions. The prototype structure designed in the laboratory consists of top and bottom plates with four columns. Finite element analyses and ambient vibration tests are first performed to extract the natural frequencies and mode shapes of the structure. Then, the damping ratio of the structure as well as the resonant frequency, head-loss coefficient, damping ratio, and water height-frequency diagram of the designed TLCD are obtained experimentally by the shaking table tests. To investigate the effect of TLCDs on the structural response, the prototype structure-TLCD coupled system is considered later, and its natural frequencies and related mode shapes are obtained numerically. The acceleration and displacement time-histories are obtained by the shaking table tests to evaluate its damping ratio. To consider different excitation directions, the measurements are repeated for the directions between 0° and 90° with 15° increment. It can be concluded from the study that TLCD causes to decrease the resonant frequency of the structure with increasing of the total mass. Damping ratio considerably increases with installing TLCD on the structure. This is more pronounced for the angles of 0°, 15°, 30° and 45°.
Experimental Research on an Active Sting Damper in a Low Speed Acoustic Wind Tunnel
Directory of Open Access Journals (Sweden)
Jinjin Chen
2014-01-01
Full Text Available Wind tunnels usually use long cantilever stings to support aerodynamic models in order to reduce support system flow interference on experimental data. However, such support systems are a potential source of vibration problems which limit the test envelope and affect data quality due to the inherently low structural damping of the systems. When exposed to tunnel flow, turbulence and model flow separation excite resonant Eigenmodes of a sting structure causing large vibrations due to low damping. This paper details the development and experimental evaluation of an active damping system using piezoelectric devices with balance signal feedback both in a lab and a low speed acoustic wind tunnel and presents the control algorithm verification tests with a simple cantilever beam. It is shown that the active damper, controlled separately by both PID and BP neural network, has effectively attenuated the vibration. For sting mode only, 95% reduction of displacement response under exciter stimulation and 98% energy elimination of sting mode frequency have been achieved.
Modeling mechanical properties of a shear thickening fluid damper based on phase transition theory
Wei, Minghai; Lin, Kun; Guo, Qian
2018-03-01
Shear thickening fluids (STFs) are highly concentrated colloidal suspensions consisting of monodisperse nano-particles suspended in a carrying fluid, and have the capacity to display both flowable and rigid behaviors, when subjected to sudden stimuli. In that process, the external energy that acts on an STF can be dissipated quickly. The aim of this study is to present a dynamic model of a damper filled with STF that can be directly used in control engineering fields. To this end, shear stress during phase transition of the STF material is chosen as an internal variable. A non-convex function with bifurcation behavior is used to describe the phase transitioning of STF by determining the relationship between the behavioral characteristics of the microscopic phase and macroscopic damping force. This model is able to predict force-velocity and force-displacement relationships as functions of the loading frequency. Efficacy of the model is demonstrated via comparison with experimental results from previous studies. In addition, the results confirm the hypothesis regarding the occurrence of STF phase transitioning when subject to shear stress.
Comparison between two rheocasting processes of damper cooling tube method and low superheat casting
Directory of Open Access Journals (Sweden)
Zhang Xiaoli
2014-09-01
Full Text Available To produce a high quality semisolid slurry that consists of fine primary particles uniformly suspended in the liquid matrix for rheoforming, chemical refining and electromagnetic or mechanical stirring are the two methods commonly used. But these two methods either contaminate the melt or incur high cost. In this study, the damper cooling tube (DCT method was designed to prepare semisolid slurry of A356 aluminum alloy, and was compared with the low superheat casting (LSC method - a conventional process used to produce casting slab with equiaxed dendrite microstructure for thixoforming route. A series of comparative experiments were performed at the pouring temperatures of 650 °C, 638 °C and 622 °C. Metallographic observations of the casting samples were carried out using an optical electron microscope with image analysis software. Results show that the microstructure of semisolid slurry produced by the DCT process consists of spherical primary α-Al grains, while equiaxed grains microstructure is found in the LSC process. The lower the pouring temperature, the smaller the grain size and the rounder the grain morphology in both methods. The copious nucleation, which could be generated in the DCT, owing to the cooling and stirring effect, is the key to producing high quality semisolid slurry. DCT method could produce rounder and smaller α-Al grains, which are suitable for semisolid processing; and the equivalent grain size is no more than 60 μm when the pouring temperature is 622 °C.
Improved seismic response of rc frame structures by using fluid viscous dampers
International Nuclear Information System (INIS)
Khan, Q.S.; Qazi, A.U.; Ilyas, M.
2013-01-01
In modern era passive control devices are used to improve the seismic response of structures during large magnitude earthquakes. In this research an analytical study is carried out on commercial FEM program SAP 2000 by modeling five, seven and nine storey RC frame structures. Response to four earthquake ground motions on modeled frame structures is studied and is effectively controlled by varying the characteristic properties of Fluid viscous dampers (FVD). Response in terms of frequency, displacement, velocity, acceleration, storey drift, base shear and energy dissipation is studied. Quantitatively in the modeled frames damage in terms of percentage change in global stiffness and natural frequency is determined. Qualitatively damage in terms of performance levels as per ATC-40 and FEMA-440 is considered. With an increase in Additional Stiffness Ratio of FVD corresponding increase in natural frequency and reduction in dynamic response is observed. FVDs significantly improve structural performance level of frames from Completely Damage to Immediate Occupancy/Operational Level during large magnitude earthquakes. (author)
International Nuclear Information System (INIS)
Dubey, P.N.; Reddy, G.R.; Vaze, K.K.; Ghosh, A.K.
2010-05-01
Three layouts have been considered for AHWR downcomer for codal qualification in order to ensure its structural integrity under normal and occasional loads. In addition to codal qualification a good piping layout should have less number of bends and weld joints in order to reduce the in-service inspection cost. Less number of bends will reduce the pressure drop in natural circulation and lesser number of weld joints will reduce the total time of in-service inspection that finally reduces the radiation dose to the workers. Conventional seismic design approach of piping with snubbers leads to high cost, maintenance and possible locking causing undue higher thermal stress during normal operation. New seismic supports in the form of Elasto-Plastic Damper (EPD) are the best suited for nuclear piping because of their simple design, low cost, passive nature and ease in installation. In this report the characteristics of EPD obtained from theory, finite element analysis and tests have been presented and comparison has also been made among the three. Analysis method and code qualification of AHWR downcomer piping considering the loadings due to normal operating and occasional loads such as earthquake have been discussed in detail. This report also explains the concept of single support and multi-support response spectrum analysis methods. The results obtained by using both types of supports i.e. conventional and EPD supports have been compared and use of EPD supports in AHWR downcomer pipe is recommended. (author)
Optimum Parameters for Tuned Mass Damper Using Shuffled Complex Evolution (SCE Algorithm
Directory of Open Access Journals (Sweden)
Hessamoddin Meshkat Razavi
2015-06-01
Full Text Available This study is investigated the optimum parameters for a tuned mass damper (TMD under the seismic excitation. Shuffled complex evolution (SCE is a meta-heuristic optimization method which is used to find the optimum damping and tuning frequency ratio for a TMD. The efficiency of the TMD is evaluated by decreasing the structural displacement dynamic magnification factor (DDMF and acceleration dynamic magnification factor (ADMF for a specific vibration mode of the structure. The optimum TMD parameters and the corresponding optimized DDMF and ADMF are achieved for two control levels (displacement control and acceleration control, different structural damping ratio and mass ratio of the TMD system. The optimum TMD parameters are checked for a 10-storey building under earthquake excitations. The maximum storey displacement and acceleration obtained by SCE method are compared with the results of other existing approaches. The results show that the peak building response decreased with decreases of about 20% for displacement and 30% for acceleration of the top floor. To show the efficiency of the adopted algorithm (SCE, a comparison is also made between SCE and other meta-heuristic optimization methods such as genetic algorithm (GA, particle swarm optimization (PSO method and harmony search (HS algorithm in terms of success rate and computational processing time. The results show that the proposed algorithm outperforms other meta-heuristic optimization methods.
Zhao, Xuefei; Wang, Shuguang; Du, Dongsheng; Liu, Weiqing
2017-01-01
In this study, simplified numerical models are developed to analyze the soil-structure interaction (SSI) effect on frame structures equipped with viscoelastic dampers (VEDs) based on pile group foundation. First, a single degree-of-freedom (SDOF) oscillator is successfully utilized to replace the SDOF energy dissipated structure considering the SSI effect. The equivalent period and damping ratio of the system are obtained through analogical analysis using the frequency transfer function with adoption of the modal strain energy (MSE) technique. A parametric analysis is carried out to study the SSI effect on the performance of VEDs. Then the equilibrium equations of the multi degree-of-freedom (MDOF) structure with VEDs considering SSI effect are established in the frequency domain. Based on the assumption that the superstructure of the coupled system possesses the classical normal mode, the MDOF superstructure is decoupled to a set of individual SDOF systems resting on a rigid foundation with adoption of the MSE technique through formula derivation. Numerical results demonstrate that the proposed methods have the advantage of reducing computational cost, however, retaining the satisfactory accuracy. The numerical method proposed herein can provide a fast evaluation of the efficiency of VEDs considering the SSI effect.
Vibration Reduction of Wind Turbines Using Tuned Liquid Column Damper Using Stochastic Analysis
International Nuclear Information System (INIS)
Alkmim, M H; De Morais, M V G; Fabro, A T
2016-01-01
Passive energy dissipation systems encompass a range of materials and devices for enhancing damping. They can be used both for natural hazard mitigation and for rehabilitation of aging or deficient structures. Among the current passive energy dissipation systems, tuned liquid column damper (TLCD), a class of passive control that utilizes liquid in a “U” shape reservoir to control structural vibration of the primary system, has been widely researched in a variety of applications. This paper focus in TLCD application for wind turbines presenting the mathematical model as well as the methods used to overcome the nonlinearity embedded in the system. Optimization methods are used to determine optimum parameters of the system. Additionally, a comparative analysis is done considering the equivalent linearized system and the nonlinear system under random excitation with the goal of compare the nonlinear model with the linear equivalent and investigated the effectiveness of the TLCD. The results are shown using two types of random excitation, a white noise and a first order filters spectrum, the latter presents more satisfactory results since the excitation spectrum is physically more realistic than white noise spectrum model. The results indicate that TLCDs at optimal tuning can significantly dissipate energy of the primary structure between 3 to 11%. (paper)
An improved design method of a tuned mass damper for an in-service footbridge
Shi, Weixing; Wang, Liangkun; Lu, Zheng
2018-03-01
Tuned mass damper (TMD) has a wide range of applications in the vibration control of footbridges. However, the traditional engineering design method may lead to a mistuned TMD. In this paper, an improved TMD design method based on the model updating is proposed. Firstly, the original finite element model (FEM) is studied and the natural characteristics of the in-service or newly built footbridge is identified by field test, and then the original FEM is updated. TMD is designed according to the new updated FEM, and it is optimized according to the simulation on vibration control effects. Finally, the installation and field measurement of TMD are carried out. The improved design method can be applied to both in-service and newly built footbridges. This paper illustrates the improved design method with an engineering example. The frequency identification results of field test and original FEM show that there is a relatively large difference between them. The TMD designed according to the updated FEM has better vibration control effect than the TMD designed according to the original FEM. The site test results show that TMD has good effect on controlling human-induced vibrations.
Compliant liquid column damper modified by shape memory alloy device for seismic vibration control
International Nuclear Information System (INIS)
Gur, Sourav; Mishra, Sudib Kumar; Bhowmick, Sutanu; Chakraborty, Subrata
2014-01-01
Liquid column dampers (LCDs) have long been used for the seismic vibration control of flexible structures. In contrast, tuning LCDs to short-period structures poses difficulty. Various modifications have been proposed on the original LCD configuration for improving its performance in relatively stiff structures. One such system, referred to as a compliant-LCD has been proposed recently by connecting the LCD to the structure with a spring. In this study, an improvement is attempted in compliant LCDs by replacing the linear spring with a spring made of shape memory alloy (SMA). Considering the dissipative, super-elastic, force-deformation hysteresis of SMA triggered by stress-induced micro-structural phase transition, the performance is expected to improve further. The optimum parameters for the SMA-compliant LCD are obtained through design optimization, which is based on a nonlinear random vibration response analysis via stochastic linearization of the force-deformation hysteresis of SMA and dissipation by liquid motion through an orifice. Substantially enhanced performance of the SMA–LCD over a conventional compliant LCD is demonstrated, the consistency of which is further verified under recorded ground motions. The robustness of the improved performance is also validated by parametric study concerning the anticipated variations in system parameters as well as variability in seismic loading. (paper)
An improved tuned mass damper (SMA-TMD) assisted by a shape memory alloy spring
International Nuclear Information System (INIS)
Mishra, Sudib K; Gur, Sourav; Chakraborty, Subrata
2013-01-01
The tuned mass damper (TMD) is a well acclaimed passive control device for vibration control of structures. However, the requirement of a higher mass ratio restricts its applicability for seismic vibration control of civil engineering structures. Improving the performance of TMDs has been attempted by supplementing them with nonlinear restoring devices. In this regard, the ability of shape memory alloy (SMA) in dissipating energy through a hysteretic phase transformation of its microstructure triggered by cyclic loading is notable. An improved version of TMD assisted by a nonlinear shape memory alloy (SMA) spring, referred as SMA-TMD, is studied here for seismic vibration mitigation. Extensive numerical simulations are conducted based on nonlinear random vibration analysis via stochastic linearization of the nonlinear force–deformation hysteresis of the SMA. A design optimization based on minimizing the root mean square displacement of the main structure is also carried out to postulate the optimal design parameters for the proposed system. The viability of the optimal design is verified with respect to its performance under recorded earthquake motions. Significant improvements of the control efficiency and a reduction of the TMD displacement at a much reduced mass ratio are shown to be achieved in the proposed SMA-TMD over those in the linear TMD. (paper)
Feasibility study of tuned liquid column damper for ocean wave energy extraction
Wong, Yihong; King, Yeong-Jin; Lai, An-Chow; Chong, Kok-Keong; Lim, Boon-Han
2017-04-01
Intermittent nature and low efficiency are the major issues in renewable energy supply. To overcome these issues, one of the possible methods is through a hybrid system where multiple sources of renewable energy are combined to compensate each other's weaknesses. The hybrid of solar energy and wave energy becomes possible through the introduction of a stable floating platform which enables solar energy generation above it and wave energy harvesting underneath it. This paper is intended to study the feasibility of harnessing ocean wave energy using a tuned liquid column damper (TLCD), a type of passive damping device that is designed to suppress externally induced vibration force at a specific frequency range. The proposed TLCD is to be implemented within a floating offshore structure to serve as a vibration mitigating mechanism by reducing the dynamic response of the structure and simultaneously utilize the flowing motion of liquid within the TLCD for generating electricity. The constructed TLCD prototype is tuned according to theoretical study and tested using a shaking table with a predetermined frequency range. The oscillating motion of water within the TLCD and the potential of installation of hydro turbine generator in term of recoverable amount of energy are studied.
Seismic energy dissipation study of linear fluid viscous dampers in steel structure design
Directory of Open Access Journals (Sweden)
A. Ras
2016-09-01
Full Text Available Energy dissipation systems in civil engineering structures are sought when it comes to removing unwanted energy such as earthquake and wind. Among these systems, there is combination of structural steel frames with passive energy dissipation provided by Fluid Viscous Dampers (FVD. This device is increasingly used to provide better seismic protection for existing as well as new buildings and bridges. A 3D numerical investigation is done considering the seismic response of a twelve-storey steel building moment frame with diagonal FVD that have linear force versus velocity behaviour. Nonlinear time history, which is being calculated by Fast nonlinear analysis (FNA, of Boumerdes earthquake (Algeria, May 2003 is considered for the analysis and carried out using the SAP2000 software and comparisons between unbraced, braced and damped structure are shown in a tabulated and graphical format. The results of the various systems are studied to compare the structural response with and without this device of the energy dissipation thus obtained. The conclusions showed the formidable potential of the FVD to improve the dissipative capacities of the structure without increasing its rigidity. It is contributing significantly to reduce the quantity of steel necessary for its general stability.
Testing and performance of a new friction damper for seismic vibration control
Martínez, Carlos A.; Curadelli, Oscar
2017-07-01
In the last two decades, great efforts were carried out to reduce the seismic demand on structures through the concept of energy dissipation instead of increasing the stiffness and strength. Several devices based on different energy dissipation principles have been developed and implemented worldwide, however, most of the dissipation devices are usually installed using diagonal braces, which entail certain drawbacks on apertures for circulation, lighting or ventilation and architectural or functional requirements often preclude this type of installations. In this work, a conceptual development of a novel energy dissipation device, called Multiple Friction Damper (MFD), is proposed and examined. To verify its characteristics and performance, the MFD was implemented on a single storey steel frame experimental model and tested under different conditions of normal force and real time acceleration records. Experimental results demonstrated that the new MFD constitutes an effective and reliable alternative to control the structural response in terms of displacement and acceleration. A mathematical formulation based on the Wen's model reflecting the nonlinear behaviour of the device is also presented.
Seismic Retrofitting of an Existing Steel Railway Bridge by Fluid Viscous Dampers
Gangopadhyay, Avijit; Ghosh, Aparna Dey
2016-09-01
There are over a lakh of bridges in the Indian Railways, many of which have become seismically deficient, either through aging or due to inadequate seismic design considerations. The extensive damage of bridges all over the world in recent earthquakes has propelled significant advancement in earthquake protection and retrofitting of bridges. Amongst various passive control systems that are reliable as well as cost-effective, Fluid Viscous Dampers (FVDs) are proving to be successful in bridge vibration control. Orificed FVDs, commercially available as Taylor Devices, have already been successfully installed in several bridges worldwide. However, there has been no such application or study related to Indian railway bridges. In this paper, an existing thirty years' old railway bridge in Jharkhand, India, has been analyzed in SAP2000v14 considering reduced stiffness and found deficient when subjected to spectrum-compatible accelerograms. Subsequent retrofitting of the bridge superstructure with FVDs has been carried out and the results indicate substantial reductions in the responses of the bridge deck.
Superelastic SMA U-shaped dampers with self-centering functions
Wang, Bin; Zhu, Songye
2018-05-01
As high-performance metallic materials, shape memory alloys (SMAs) have been investigated increasingly by the earthquake engineering community in recent years, because of their remarkable self-centering (SC) and energy-dissipating capabilities. This paper systematically presents an experimental study on a novel superelastic SMA U-shaped damper (SMA-UD) with SC function under cyclic loading. The mechanical properties, including strength, SC ability, and energy-dissipating capability with varying loading amplitudes and strain rates are evaluated. Test results show that excellent and stable flag-shaped hysteresis loops are exhibited in multiple loading cycles. Strain rate has a negligible effect on the cyclic behavior of the SMA-UD within the dynamic frequency range of typical interest in earthquake engineering. Furthermore, a numerical investigation is performed to understand the mechanical behavior of the SMA-UD. The numerical model is calibrated against the experimental results with reasonable accuracy. Then, the stress–strain states with different phase transformations are also discussed.
Probabilistic analysis of wind-induced vibration mitigation of structures by fluid viscous dampers
Chen, Jianbing; Zeng, Xiaoshu; Peng, Yongbo
2017-11-01
The high-rise buildings usually suffer from excessively large wind-induced vibrations, and thus vibration control systems might be necessary. Fluid viscous dampers (FVDs) with nonlinear power law against velocity are widely employed. With the transition of design method from traditional frequency domain approaches to more refined direct time domain approaches, the difficulty of time integration of these systems occurs sometimes. In the present paper, firstly the underlying reason of the difficulty is revealed by identifying that the equations of motion of high-rise buildings installed with FVDs are sometimes stiff differential equations. Thus, an approach effective for stiff differential systems, i.e., the backward difference formula (BDF), is then introduced, and verified to be effective for the equation of motion of wind-induced vibration controlled systems. Comparative studies are performed among some methods, including the Newmark method, KR-alpha method, energy-based linearization method and the statistical linearization method. Based on the above results, a 20-story steel frame structure is taken as a practical example. Particularly, the randomness of structural parameters and of wind loading input is emphasized. The extreme values of the responses are examined, showing the effectiveness of the proposed approach, and also necessitating the refined probabilistic analysis in the design of wind-induced vibration mitigation systems.
Ankle Joint Intrinsic Dynamics is More Complex than a Mass-Spring-Damper Model.
Sobhani Tehrani, Ehsan; Jalaleddini, Kian; Kearney, Robert E
2017-09-01
This paper describes a new small signal parametric model of ankle joint intrinsic mechanics in normal subjects. We found that intrinsic ankle mechanics is a third-order system and the second-order mass-spring-damper model, referred to as IBK, used by many researchers in the literature cannot adequately represent ankle dynamics at all frequencies in a number of important tasks. This was demonstrated using experimental data from five healthy subjects with no voluntary muscle contraction and at seven ankle positions covering the range of motion. We showed that the difference between the new third-order model and the conventional IBK model increased from dorsi to plantarflexed position. The new model was obtained using a multi-step identification procedure applied to experimental input/output data of the ankle joint. The procedure first identifies a non-parametric model of intrinsic joint stiffness where ankle position is the input and torque is the output. Then, in several steps, the model is converted into a continuous-time transfer function of ankle compliance, which is the inverse of stiffness. Finally, we showed that the third-order model is indeed structurally consistent with agonist-antagonist musculoskeletal structure of human ankle, which is not the case for the IBK model.
A passive eddy current damper for vibration suppression of a force sensor
International Nuclear Information System (INIS)
Chen Weihai; Jiang Jun; Liu Jingmeng; Bai Shaoping; Chen Wenjie
2013-01-01
High performance force sensors often encounter the problem of vibrations during the process of calibration and measurement. To address this problem, this paper presents a novel passive eddy current damper (ECD) for vibration suppression. The conceived ECD utilizes eight tubular permanent magnets, arranged in Halbach array, and a conductive copper rod to generate damping. The ECD does not require an external power supply or any other electronic devices. In this paper, an accurate, analytical model for calculating the magnetic field distribution and damping coefficient is developed. The dynamics of the system is obtained by applying an energy method and an equivalent pseudo-rigid-body model. Moreover, finite element simulations are conducted to optimize the design. Experiments are carried out to validate the effectiveness of the design. The results indicate that the proposed ECD has a damping coefficient of 4.3 N s m −1 , which can provide a sufficient damping force to quickly suppress the sensor's vibration within 0.1 s. (paper)
Hussan, Mosaruf; Sharmin, Faria; Kim, Dookie
2017-08-01
The dynamics of jacket supported offshore wind turbine (OWT) in earthquake environment is one of the progressing focuses in the renewable energy field. Soil-structure interaction (SSI) is a fundamental principle to analyze stability and safety of the structure. This study focuses on the performance of the multiple tuned mass damper (MTMD) in minimizing the dynamic responses of the structures objected to seismic loads combined with static wind and wave loads. Response surface methodology (RSM) has been applied to design the MTMD parameters. The analyses have been performed under two different boundary conditions: fixed base (without SSI) and flexible base (with SSI). Two vibration modes of the structure have been suppressed by multi-mode vibration control principle in both cases. The effectiveness of the MTMD in reducing the dynamic response of the structure is presented. The dynamic SSI plays an important role in the seismic behavior of the jacket supported OWT, especially resting on the soft soil deposit. Finally, it shows that excluding the SSI effect could be the reason of overestimating the MTMD performance.
Research on Fluid Viscous Damper Parameters of Cable-Stayed Bridge in Northwest China
Directory of Open Access Journals (Sweden)
Xiongjun He
2017-01-01
Full Text Available To optimize the aseismic performance of nonlinear fluid viscous dampers (FVD of cable-stayed bridge in the highly seismic zone, Xigu Yellow River Bridge in northwest China is taken as an example. Nonlinear time-history analysis method is used to research on the relation among the internal forces, displacements, and damping parameters of the 650 tonnage FVD. The method of getting the minimum of binary functions is used to obtain the optimal parameters of FVD. Also, the 1 : 1 full-scale FVD model is made and used in the constitutive relation test. Then the test result of the damping parameters can be got by normal equation method. The optimized method to obtain the damping parameters is further verified. The results indicate that seismic response in key positions of the cable-stayed bridge can be reduced by installing longitudinal nonlinear FVD between the towers and girders if choosing reasonable damping parameters C and ξ. The optimal damping parameters can be calculated accurately by the proposed method of optimizing damping parameters of nonlinear FVD, and the constitutive relation test verifies the correctness of the optimization analysis method. Conclusions concerned can be applied to the design of nonlinear FVD for cable-stayed bridges.
Design of a power amplifier for the LAMPF proton storage ring transverse damper system
International Nuclear Information System (INIS)
Lunsford, J.S.
1981-01-01
A power amplifier has been designed to drive the 50-Ω stripline deflection structures in the transverse active damper of the Los Alamos 800-MeV Proton Storage Ring (PSR). The unit will provide 600-V peak-to-peak with a dc-to-100-MHz bandwidth. Other important characteristics include < 40-ns delay time, 50-dB voltage gain, and 4-ns risetime with < 5% overshoot and ringing. Because of the current-drive properties of the amplifier, two amplifiers could be combined to provide over 1000-V peak-to-peak into 50 Ω, with very little bandwidth degradation. Components in the power amplifier that represent new designs are a 20-tube distributed-amplifier output stage; a driver stage, using VMOS FET and bipolar transistors; a high-voltage probe, with good dc stability and 150-MHz bandwidth; a transient suppressor circuit, using PIN diodes to protect the transistorized drivers from tube arcing; a nonlinear amplifier to compensate for the nonlinear characteristics of the distributed amplifier; and a first-fail indicator circuit to aid in locating the prime causes of equipment failures
International Nuclear Information System (INIS)
Jiang, Z; Christenson, R
2011-01-01
Control devices can be used to dissipate the energy of a civil structure subjected to dynamic loading, such as earthquake, wave and wind excitation, thus reducing structural damage and preventing failure. The magneto-rheological (MR) fluid damper is a promising device for use in civil structures due to its mechanical simplicity, inherent stability, high dynamic range, large temperature operating range, robust performance, and low power requirements. The MR damper is intrinsically nonlinear and rate dependent. Thus a challenging aspect of applying this technology is the development of accurate models to describe the behavior of such dampers for control design and evaluation purposes. In particular, a new type of experimental testing called real-time hybrid simulation (RTHS) combines numerical simulation with laboratory testing of physical components. As with any laboratory testing, safety is of critical importance. For RTHS in particular the feedback and dynamic interaction of physical and numerical components can result in potentially unstable behavior. For safety purposes, it is desired to conduct pretest simulations where the physical specimen is replaced with an appropriate numerical model yet the numerical RTHS component is left unchanged. These pretest simulations require a MR damper model that can exhibit stability and convergence at larger fixed integration time steps, and provide computational efficiency, speed of calculation, and accuracy during pretest verification of the experimental setup. Several models for MR dampers have been proposed, including the hyperbolic tangent, Bouc–Wen, viscous plus Dahl and algebraic models. This paper examines the relative performance of four MR damper models of large-scale 200 kN MR dampers as needed for pretest simulations of RTHS. Experimental tests are conducted on two large-scale MR dampers located at two RTHS test facilities at the Smart Structures Technology Laboratory at the University of Illinois at Urbana
Yang, Derek; Davies, April; Burge, Bailey; Watkins, Phillip; Dissanaike, Sharmila
2018-01-01
The standard treatment of necrotizing soft tissue infection (NSTI) includes extensive surgical debridement. Care of these debridements is challenging because of the size of the wound and associated pain. A potential solution is to leave the wounds open-to-air in the period after the initial debridement, allowing for regular inspection at bedside while reducing pain associated with frequent dressing changes. We evaluated the feasibility of this approach from a pain control standpoint. An audit of wound care modalities used on adult patients with NSTI admitted to a regional burn center between January 2009 and May 2014 was performed. Patients with at least one operation were included. Those opting for palliative care were excluded. Wound care was divided into four categories: open-to-air (OTA), negative-pressure wound therapy (NPWT), packing, and ointment. Wound care, pain score, pain medication use, and number of operations were collected for the first seven days after initial debridement. Pain management was assessed by pain scores. Analgesic use was measured and compared using conversion to morphine milligram equivalents (MME). Ninety-six patients were included; 67% were men with average age of 50 years, resulting in a total of 672 days of wound care evaluated: 69 days of OTA, 127 days of NPWT, 200 days of packing, and 126 days of ointment (150 days were undocumented). Average daily pain score from all wound care modalities was 2.00. Negative pressure wound therapy had the highest reported daily pain score (2.18, p = 0.034), whereas OTA had the lowest pain score (1.63, p < 0.05). Mortality was lower in the OTA cohort but was not statistically significant; there were no other differences in long-term outcome. Leaving wounds OTA is a safe and viable option in the immediate post-debridement period of NSTI to reduce pain, while permitting frequent re-evaluation for quick recognition of disease progression and repeat operative debridement if necessary.
Lu, Zheng; Lu, Xilin; Lu, Wensheng; Masri, Sami F.
2012-04-01
This paper presents a systematic experimental investigation of the effects of buffered particle dampers attached to a multi-degree-of-freedom (mdof) system under different dynamic loads (free vibration, random excitation as well as real onsite earthquake excitations), and analytical/computational study of such a system. A series of shaking table tests of a three-storey steel frame with the buffered particle damper system are carried out to evaluate the performance and to verify the analysis method. It is shown that buffered particle dampers have good performance in reducing the response of structures under dynamic loads, especially under random excitation case. It can effectively control the fundamental mode of the mdof primary system; however, the control effect for higher modes is variable. It is also shown that, for a specific container geometry, a certain mass ratio leads to more efficient momentum transfer from the primary system to the particles with a better vibration attenuation effect, and that buffered particle dampers have better control effect than the conventional rigid ones. An analytical solution based on the discrete element method is also presented. Comparison between the experimental and computational results shows that reasonably accurate estimates of the response of a primary system can be obtained. Properly designed buffered particle dampers can effectively reduce the response of lightly damped mdof primary system with a small weight penalty, under different dynamic loads.
Energy Technology Data Exchange (ETDEWEB)
Nosovsky, Anatolij
1995-09-01
Despite the catastrophic accident at the Chernobylsk 4 reactor in 1986, the Ukraine is currently expanding its nuclear industry. The government is committed to increasing the share of nuclear output to 40% of the country`s electric power and the Chernobyl plant is included in this plan. All the Chernobyl reactors were closed down at the time of the accident, but units 1, 2 and 3 had all been restarted after safety modifications by December 1987. A fire in the turbine hall of unit 2 in 1991 resulted in the closure of that reactor and precipitated a political decision to close the entire plant by 1993. The economic consequences of such action and the safe operation of the remaining two reactors led, however, to the reversal of that decision. Work is now far advanced on unit 2 for a restart in 1996 and the management wants to upgrade all three reactors according to IAEA guidelines. Nevertheless, the question of closure of the Chernobyl plant remains in the air. A conditional acceptance of closure by 2000 has been made by the Ukraine provided the shortfall in power is taken up by a new gas-fired station. International finance is being sought for decommissioning, for urgent action on the decaying sarcophagus of unit 4, and for the gas-fired plant. Closure of the plant, given the social upheaval of the accident and recent political events, could contribute to the health of the Ukrainian national psyche. (UK).
International Nuclear Information System (INIS)
Nosovsky, Anatolij.
1995-01-01
Despite the catastrophic accident at the Chernobylsk 4 reactor in 1986, the Ukraine is currently expanding its nuclear industry. The government is committed to increasing the share of nuclear output to 40% of the country's electric power and the Chernobyl plant is included in this plan. All the Chernobyl reactors were closed down at the time of the accident, but units 1, 2 and 3 had all been restarted after safety modifications by December 1987. A fire in the turbine hall of unit 2 in 1991 resulted in the closure of that reactor and precipitated a political decision to close the entire plant by 1993. The economic consequences of such action and the safe operation of the remaining two reactors led, however, to the reversal of that decision. Work is now far advanced on unit 2 for a restart in 1996 and the management wants to upgrade all three reactors according to IAEA guidelines. Nevertheless, the question of closure of the Chernobyl plant remains in the air. A conditional acceptance of closure by 2000 has been made by the Ukraine provided the shortfall in power is taken up by a new gas-fired station. International finance is being sought for decommissioning, for urgent action on the decaying sarcophagus of unit 4, and for the gas-fired plant. Closure of the plant, given the social upheaval of the accident and recent political events, could contribute to the health of the Ukrainian national psyche. (UK)
Bereaved Employee: Returning to Work
... Work Working Through Grief About Us The Bereaved Employee: Returning to Work By Helen Fitzgerald, CT After ... One employer called a grief therapist to help employees after a co-worker reported the death of ...
Total anomalous pulmonary venous return
... pulmonary venous return, x-ray References Fraser CD, Kane LC. Congenital heart disease. In: Townsend CM Jr, ... 62. Review Date 10/17/2017 Updated by: Michael A. Chen, MD, PhD, Associate Professor of Medicine, ...
Lu, Zheng; Huang, Biao; Zhang, Qi; Lu, Xilin
2018-05-01
Eddy-current tuned mass dampers (EC-TMDs) are non-contacting passive control devices and are developed on the basis of conventional tuned mass dampers. They comprise a solid mass, a stiffness element, and a damping element, wherein the damping mechanism originates from eddy currents. By relative motion between a non-magnetic conductive metal and a permanent magnet in a dynamic system, a time-varying magnetic field is induced in the conductor, thereby generating eddy currents. The eddy currents induce a magnetic field with opposite polarity, causing repulsive forces, i.e., damping forces. This technology can overcome the drawbacks of conventional tuned mass dampers, such as limited service life, deterioration of mechanical properties, and undesired additional stiffness. The experimental and analytical study of this system installed on a multi-degree-of-freedom structure is presented in this paper. A series of shaking table tests were conducted on a five-story steel-frame model with/without an EC-TMD to evaluate the effectiveness and performance of the EC-TMD in suppressing the vibration of the model under seismic excitations. The experimental results show that the EC-TMD can effectively reduce the displacement response, acceleration response, interstory drift ratio, and maximum strain of the columns under different earthquake excitations. Moreover, an analytical method was proposed on the basis of electromagnetic and structural dynamic theories. A comparison between the test and simulation results shows that the simulation method can be used to estimate the response of structures with an EC-TMD under earthquake excitations with acceptable accuracy.
Piao, YongJun; Choi, YounJung; Kim, JungJa; Kwan, TaeKyu; Kim, Nam-Gyun
2009-03-01
Adequate postural balance depends on the spatial and temporal integration of vestibular, visual, and somatosensory information. Especially, the musculoskeletal function (range of joint, flexibility of spine, muscular strength) is essential in maintaining the postural balance. Muscular strength training methods include the use of commercialized devices and repeatable resistance training tools (rubber band, ball, etc). These training systems cost high price and can't control of intensity. Thus we suggest a new training system which can adjust training intensity and indicate the center of pressure of a subject while the training was passively controlled by applying controlled electric current to the Magneto- Rheological damper. And we performed experimental studies on the muscular activities in the lower extremities during maintaining, moving and pushing exercises on an unstable platform with Magneto rheological dampers. A subject executed the maintaining, moving and pushing exercises which were displayed in a monitor. The electromyographic signals of the eight muscles in lower extremities were recorded and analyzed in the time and frequency domain: the muscles of interest were rectus femoris, biceps femoris, tensor fasciae latae, vastus lateralis, vastus medialis, gastrocnemius, tibialis anterior, and soleus. The experimental results showed the difference of muscular activities at the four moving exercises and the nine maintaining exercises. The rate of the increase in the muscular activities was affected by the condition of the unstable platform with MR dampers for the maintaining and moving exercises. The experimental results suggested the choice of different maintaining and moving exercises could selectively train different muscles with varying intensity. Furthermore, the findings also suggested the training using this system can improve the ability of postural balance.
Return Migration and Working Choices
TANI, Massimiliano; MAHUTEAU, Stéphane
2008-01-01
Collective Action to Support the Reintegration of Return Migrants in their Country of Origin (MIREM) This paper uses the recent survey carried out in the framework of the MIREM project on returnees to Algeria, Morocco and Tunisia and studies the duration of emigration and the labour force status upon returning. The results suggest that age and the year of emigration play a central role in the migration decision, but they do not support the hypothesis that the duration of migration is deter...
Capital Structure and Stock Returns
Ivo Welch
2002-01-01
U.S. corporations do not issue and repurchase debt and equity to counteract the mechanistic effects of stock returns on their debt-equity ratios. Thus over one- to five-year horizons, stock returns can explain about 40 percent of debt ratio dynamics. Although corporate net issuing activity is lively and although it can explain 60 percent of debt ratio dynamics (long-term debt issuing activity being most capital structurerelevant), corporate issuing motives remain largely a mystery. When stock...
[Organising a successful return home].
Mézière, Anthony
Discharge from hospital is a major component of the quality and efficiency of the healthcare system. The failures of the return home of elderly people testify to the difficulties of applying guidelines in the area of hospital discharge. The action plan decided in the hospital for a successful return home can be jeopardised for personal, relational, functional and structural reasons originating from the different players involved in the hospital discharge. Copyright © 2018 Elsevier Masson SAS. All rights reserved.
Active structural control of a floating wind turbine with a stroke-limited hybrid mass damper
Hu, Yaqi; He, Erming
2017-12-01
Floating wind turbines are subjected to more severe structural loads than fixed-bottom wind turbines due to additional degrees of freedom (DOFs) of their floating foundations. It's a promising way of using active structural control method to improve the structural responses of floating wind turbines. This paper investigates an active vibration control strategy for a barge-type floating wind turbine by setting a stroke-limited hybrid mass damper (HMD) in the turbine's nacelle. Firstly, a contact nonlinear modeling method for the floating wind turbine with clearance between the HMD and the stroke limiters is presented based on Euler-Lagrange's equations and an active control model of the whole system is established. The structural parameters are validated for the active control model and an equivalent load coefficient method is presented for identifying the wind and wave disturbances. Then, a state-feedback linear quadratic regulator (LQR) controller is designed to reduce vibration and loads of the wind turbine, and two optimization methods are combined to optimize the weighting coefficients when considering the stroke of the HMD and the active control power consumption as constraints. Finally, the designed controllers are implemented in high fidelity simulations under five typical wind and wave conditions. The results show that active HMD control strategy is shown to be achievable and the designed controllers could further reduce more vibration and loads of the wind turbine under the constraints of stroke limitation and power consumption. "V"-shaped distribution of the TMD suppression effect is inconsistent with the Weibull distribution in practical offshore floating wind farms, and the active HMD control could overcome this shortcoming of the passive TMD.
Compressed Air Production Using Vehicle Suspension
Ninad Arun Malpure; Sanket Nandlal Bhansali
2015-01-01
Abstract Generally compressed air is produced using different types of air compressors which consumes lot of electric energy and is noisy. In this paper an innovative idea is put forth for production of compressed air using movement of vehicle suspension which normal is wasted. The conversion of the force energy into the compressed air is carried out by the mechanism which consists of the vehicle suspension system hydraulic cylinder Non-return valve air compressor and air receiver. We are co...
DEFF Research Database (Denmark)
Wu, Weimin; Lin, Zhe; Sun, Yunjie
2013-01-01
Grid-tied inverters have been widely used to inject the renewable energies into the distributed power generation systems. However, a large variation of the grid impedance challenges the stability of the high-order power filter based grid-tied inverter. Many passive and active damping methods have...... been proposed to overcome this issue. Recently, a composite passive damping method for a high-order power filter based grid-tied inverter with an RC parallel damper and an RL series damper was presented to eliminate this problem, but at the cost of more material and power losses. In this paper...
Sealed Planetary Return Canister (SPRC), Phase II
National Aeronautics and Space Administration — Sample return missions have primary importance in future planetary missions. A basic requirement is that samples be returned in pristine, uncontaminated condition,...
Wright, C.; O'Sullivan, K.; Murphy, J.; Pakrashi, V.
2015-07-01
The offshore wind industry is rapidly maturing and is now expanding to more extreme environments in deeper water and farther from shore. To date fixed foundation types (i.e. monopoles, jackets) have been primarily used but become uneconomical in water depths greater than 50m. Floating foundations have more complex dynamics but at the moment no design has reached commercialization, although a number of devices are being tested at prototype stage. The development of concepts is carried out through physical model testing of scaled devices such that to better understand the dynamics of the system and validate numerical models. This paper investigates the testing of a scale model of a tension moored wind turbine at two different scales and in the presence and absence of a spring damper controlling its dynamic response. The models were tested under combined wave and wind thrust loading conditions. The analysis compares the motions of the platform at different scales and structural conditions through RAO, testing a mooring spring damper for load reductions.
John, Shaju; Wereley, Norman M.
2003-07-01
Dampers based on electrorheological (ER) and magnetorheolgical (MR) fluids can be analyzed under assumptions of quasi-steady, fully developed flow behavior. Models that have been used to characterize ER and MR dampers include the Bingham-plastic, the Herschel-Bulkley and biviscous models. In the Bingham-plastic and the Herschel-Bulkley models, the fluid exhibits rigid behavior in the preyield flow region. The difference between these two models lie in the modeling of the postyield behavior. In the case of the Bingham-plastic model, the postyield behavior is such that the shear stress is proportional to the shear rate. In contrast, the Herschel-Bulkley model assumes that the shear stress is proportional to a power law of the shearrate. In the biciscous model, the relationship between the shear stres and shear rate is linear in both the preyield and postyield regions with constant values of viscosities for the two regions. However, the preyield flow behavior exhibits a much high viscosity than that in the postyield. In the propose model, the assumption of preyield rigid behavior within the Herschel-Bulkley model has been relaxed while the postyield relationship based on the power law has been retained. Here the fluid undergoes Newtonian preyield viscous flow and has a non-Newtonian postyield behavior. Based on this model, we have analyzed the performance of a rectangular duct ER or MR valve. Typical results include shear stress and velocity profiles across the valve gap, equivalent damping and damping coefficients.
Directory of Open Access Journals (Sweden)
Said Elias
Full Text Available Abstract The effect of soil-structure interaction (SSI on the dynamic responses of seismically isolated three-span continuous reinforced concrete (RC bridge is investigated. Also, tuned mass damper(s (TMD/s is/are installed to control undesirable bearing displacement, even under the SSI effect. The TMDs are placed at the mid-span of the bridge and each tuned with a modal frequency, while controlling up to first few modes as desirable. The soil surrounding the foundation of pier is modeled by frequency independent coefficients. Dynamic analysis is carried out in time domain using direct integration method. In order to specify the effects of the SSI, the responses of the non-isolated, isolated, and controlled isolated bridge are compared. It is observed that the soil surrounding the pier has significant effects on the bearing displacement of the isolated RC bridges. In addition, it is observed that the seismic responses of isolated RC bridge reduced significantly with installation of the TMDs.
Directory of Open Access Journals (Sweden)
Weiqing Fu
2017-03-01
Full Text Available The conventional isolation structure with rubber bearings exhibits large deformation characteristics when subjected to infrequent earthquakes, which may lead to failure of the isolation layer. Although passive dampers can be used to reduce the layer displacement, the layer deformation and superstructure acceleration responses will increase in cases of fortification earthquakes or frequently occurring earthquakes. In addition to secondary damages and loss of life, such excessive displacement results in damages to the facilities in the structure. In order to overcome these shortcomings, this paper presents a structural vibration control system where the base isolation system is composed of rubber bearings with magnetorheological (MR damper and are regulated using the innovative control strategy. The high-order single-step algorithm with continuity and switch control strategies are applied to the control system. Shaking table test results under various earthquake conditions indicate that the proposed isolation method, compared with passive isolation technique, can effectively suppress earthquake responses for acceleration of superstructure and deformation within the isolation layer. As a result, this structural control method exhibits excellent performance, such as fast computation, generic real-time control, acceleration reduction and high seismic energy dissipation etc. The relative merits of the continuity and switch control strategies are also compared and discussed.
International Nuclear Information System (INIS)
Phu, Do Xuan; Shah, Kruti; Choi, Seung-Bok
2014-01-01
This paper presents a new adaptive fuzzy controller and its implementation for the damping force control of a magnetorheological (MR) fluid damper in order to validate the effectiveness of the control performance. An interval type 2 fuzzy model is built, and then combined with modified adaptive control to achieve the desired damping force. In the formulation of the new adaptive controller, an enhanced iterative algorithm is integrated with the fuzzy model to decrease the time of calculation (D Wu 2013 IEEE Trans. Fuzzy Syst. 21 80–99) and the control algorithm is synthesized based on the H ∞ tracking technique. In addition, for the verification of good control performance of the proposed controller, a cylindrical MR damper which can be applied to the vibration control of a washing machine is designed and manufactured. For the operating fluid, a recently developed plate-like particle-based MR fluid is used instead of a conventional MR fluid featuring spherical particles. To highlight the control performance of the proposed controller, two existing adaptive fuzzy control algorithms proposed by other researchers are adopted and altered for a comparative study. It is demonstrated from both simulation and experiment that the proposed new adaptive controller shows better performance of damping force control in terms of response time and tracking accuracy than the existing approaches. (papers)
Abnormal Returns and Contrarian Strategies
Directory of Open Access Journals (Sweden)
Ivana Dall'Agnol
2003-12-01
Full Text Available We test the hypothesis that strategies which are long on portfolios of looser stocks and short on portfolios of winner stocks generate abnormal returns in Brazil. This type of evidence for the US stock market was interpreted by The Bondt and Thaler (1985 as reflecting systematic evaluation mistakes caused by investors overreaction to news related to the firm performance. We found evidence of contrarian strategies profitability for horizons from 3 months to 3 years in a sample of stock returns from BOVESPA and SOMA from 1986 to 2000. The strategies are more profitable for shorter horizons. Therefore, there was no trace of the momentum effect found by Jagadeesh and Titman (1993 for the same horizons with US data. There are remaing unexplained positive returns for contrarian strategies after accounting for risk, size, and liquidity. We also found that the strategy profitability is reduced after the Real Plan, which suggests that the Brazilian stock market became more efficient after inflation stabilization.
Dynamic returns of beta arbitrage
Nascimento, Mafalda
2017-01-01
This thesis studies the patterns of the abnormal returns of the beta strategy. The topic can be helpful for professional investors, who intend to achieve a better performance in their portfolios. Following the methodology of Lou, Polk, & Huang (2016), the COBAR measure is computed in order to determine the levels of beta arbitrage in the market in each point in time. It is argued that beta arbitrage activity can have impact on the returns of the beta strategy. In fact, it is demonstrated that...
Sovereign Risk and Currently Returns
DEFF Research Database (Denmark)
Della Corte, Pasquale; Sarno, Lucio; Schmeling, Maik
We empirically investigate the relation between sovereign risk and exchange rates for a broad set of currencies. An increase in the credit default swap (CDS) spread of a country is accompanied by a significant depreciation of the exchange rate. More generally, CDS spread changes have substantial...... explanatory power for currency returns which is largely driven by shocks to global credit risk. Consistent with the notion that sovereign risk is priced, we find that a country's exposure to global credit risk forecasts excess returns to trading exchange rates as well as to trading on the volatility, skewness...
Sovereign Risk and Currency Returns
DEFF Research Database (Denmark)
Della Corte, Pasquale; Sarno, Lucio; Schmeling, Maik
We empirically investigate the relation between sovereign risk and exchange rates for a broad set of currencies. An increase in the credit default swap (CDS) spread of a country is accompanied by a significant depreciation of the exchange rate. More generally, CDS spread changes have substantial...... explanatory power for currency returns which is largely driven by shocks to global credit risk. Consistent with the notion that sovereign risk is priced, we find that a country's exposure to global credit risk forecasts excess returns to trading exchange rates as well as to trading on the volatility, skewness...
Czech Academy of Sciences Publication Activity Database
Zapoměl, Jaroslav; Ferfecki, P.; Forte, P.
2017-01-01
Roč. 52, December (2017), s. 558-575 ISSN 0307-904X R&D Projects: GA ČR GA15-06621S Institutional support: RVO:61388998 Keywords : magnetorheological squeeze film damper * bilinear material * stability of computational procedures * Bingham theoretical material Subject RIV: JR - Other Machinery OBOR OECD: Mechanical engineering Impact factor: 2.350, year: 2016
DEFF Research Database (Denmark)
Feng, Ju; Ying, Zu-Guang; Zhu, Wei-Qiu
2012-01-01
A minimax stochastic optimal semi-active control strategy for stochastically excited quasi-integrable Hamiltonian systems with parametric uncertainty by using magneto-rheological (MR) dampers is proposed. Firstly, the control problem is formulated as an n-degree-of-freedom (DOF) controlled, uncer...
DEFF Research Database (Denmark)
Zhang, Zili; Staino, Andrea; Basu, Biswajit
2016-01-01
Highlights •Performance evaluation of full-scale tuned liquid dampers carried out for wind turbines. •Coupled blade-tower model considered in the numerical sub-structure. •Stochastic turbulence due to rotationally sampled spectra considered. •Effect of damping screens experimentally investigated...
Comet coma sample return instrument
Albee, A. L.; Brownlee, Don E.; Burnett, Donald S.; Tsou, Peter; Uesugi, K. T.
1994-01-01
The sample collection technology and instrument concept for the Sample of Comet Coma Earth Return Mission (SOCCER) are described. The scientific goals of this Flyby Sample Return are to return to coma dust and volatile samples from a known comet source, which will permit accurate elemental and isotopic measurements for thousands of individual solid particles and volatiles, detailed analysis of the dust structure, morphology, and mineralogy of the intact samples, and identification of the biogenic elements or compounds in the solid and volatile samples. Having these intact samples, morphologic, petrographic, and phase structural features can be determined. Information on dust particle size, shape, and density can be ascertained by analyzing penetration holes and tracks in the capture medium. Time and spatial data of dust capture will provide understanding of the flux dynamics of the coma and the jets. Additional information will include the identification of cosmic ray tracks in the cometary grains, which can provide a particle's process history and perhaps even the age of the comet. The measurements will be made with the same equipment used for studying micrometeorites for decades past; hence, the results can be directly compared without extrapolation or modification. The data will provide a powerful and direct technique for comparing the cometary samples with all known types of meteorites and interplanetary dust. This sample collection system will provide the first sample return from a specifically identified primitive body and will allow, for the first time, a direct method of matching meteoritic materials captured on Earth with known parent bodies.
Phobos Sample Return: Next Approach
Zelenyi, Lev; Martynov, Maxim; Zakharov, Alexander; Korablev, Oleg; Ivanov, Alexey; Karabadzak, George
The Martian moons still remain a mystery after numerous studies by Mars orbiting spacecraft. Their study cover three major topics related to (1) Solar system in general (formation and evolution, origin of planetary satellites, origin and evolution of life); (2) small bodies (captured asteroid, or remnants of Mars formation, or reaccreted Mars ejecta); (3) Mars (formation and evolution of Mars; Mars ejecta at the satellites). As reviewed by Galimov [2010] most of the above questions require the sample return from the Martian moon, while some (e.g. the characterization of the organic matter) could be also answered by in situ experiments. There is the possibility to obtain the sample of Mars material by sampling Phobos: following to Chappaz et al. [2012] a 200-g sample could contain 10-7 g of Mars surface material launched during the past 1 mln years, or 5*10-5 g of Mars material launched during the past 10 mln years, or 5*1010 individual particles from Mars, quantities suitable for accurate laboratory analyses. The studies of Phobos have been of high priority in the Russian program on planetary research for many years. Phobos-88 mission consisted of two spacecraft (Phobos-1, Phobos-2) and aimed the approach to Phobos at 50 m and remote studies, and also the release of small landers (long-living stations DAS). This mission implemented the program incompletely. It was returned information about the Martian environment and atmosphere. The next profect Phobos Sample Return (Phobos-Grunt) initially planned in early 2000 has been delayed several times owing to budget difficulties; the spacecraft failed to leave NEO in 2011. The recovery of the science goals of this mission and the delivery of the samples of Phobos to Earth remain of highest priority for Russian scientific community. The next Phobos SR mission named Boomerang was postponed following the ExoMars cooperation, but is considered the next in the line of planetary exploration, suitable for launch around 2022. A
Kumar, Gaurav; Kumar, Ashok
2017-11-01
Structural control has gained significant attention in recent times. The standalone issue of power requirement during an earthquake has already been solved up to a large extent by designing semi-active control systems using conventional linear quadratic control theory, and many other intelligent control algorithms such as fuzzy controllers, artificial neural networks, etc. In conventional linear-quadratic regulator (LQR) theory, it is customary to note that the values of the design parameters are decided at the time of designing the controller and cannot be subsequently altered. During an earthquake event, the response of the structure may increase or decrease, depending the quasi-resonance occurring between the structure and the earthquake. In this case, it is essential to modify the value of the design parameters of the conventional LQR controller to obtain optimum control force to mitigate the vibrations due to the earthquake. A few studies have been done to sort out this issue but in all these studies it was necessary to maintain a database of the earthquake. To solve this problem and to find the optimized design parameters of the LQR controller in real time, a fast Fourier transform and particle swarm optimization based modified linear quadratic regulator method is presented here. This method comprises four different algorithms: particle swarm optimization (PSO), the fast Fourier transform (FFT), clipped control algorithm and the LQR. The FFT helps to obtain the dominant frequency for every time window. PSO finds the optimum gain matrix through the real-time update of the weighting matrix R, thereby, dispensing with the experimentation. The clipped control law is employed to match the magnetorheological (MR) damper force with the desired force given by the controller. The modified Bouc-Wen phenomenological model is taken to recognize the nonlinearities in the MR damper. The assessment of the advised method is done by simulation of a three-story structure
Financial Integration and Asset Returns
P Martin; H Rey
2000-01-01
The paper investigates the impact of financial integration on asset return, risk diversification and breadth of financial markets. We analyse a three-country macroeconomic model in which (i) the number of financial assets is endogenous; (ii) assets are imperfect substitutes; (iii) cross-border asset trade entails some transaction costs; (iv) the investment technology is indivisible. In such an environment, lower transaction costs between two financial markets translate to higher demand for as...
Returning to work after disability.
Quinn, P Roger
2002-06-01
After a workplace injury or disability, there is a period of hardship and adjustment for the injured party as well as all stakeholders in the workers' compensation process. Ultimately, however, return to work is considered. The author reviews this often challenging exercise from the Canadian perspective and stresses the need for timely intervention, honest communication, the coordination of information and resources--and the need for flexibility. A case study on low back pain is included.
Onnela, Jukka-Pekka; Töyli, Juuso; Kaski, Kimmo
2009-02-01
Tick size is an important aspect of the micro-structural level organization of financial markets. It is the smallest institutionally allowed price increment, has a direct bearing on the bid-ask spread, influences the strategy of trading order placement in electronic markets, affects the price formation mechanism, and appears to be related to the long-term memory of volatility clustering. In this paper we investigate the impact of tick size on stock returns. We start with a simple simulation to demonstrate how continuous returns become distorted after confining the price to a discrete grid governed by the tick size. We then move on to a novel experimental set-up that combines decimalization pilot programs and cross-listed stocks in New York and Toronto. This allows us to observe a set of stocks traded simultaneously under two different ticks while holding all security-specific characteristics fixed. We then study the normality of the return distributions and carry out fits to the chosen distribution models. Our empirical findings are somewhat mixed and in some cases appear to challenge the simulation results.
Directory of Open Access Journals (Sweden)
Keun Ryu
2018-04-01
Full Text Available The current work introduces a new semi-floating ring bearing (SFRB system developed for improving the rotordynamic and vibration performance of automotive turbochargers (TCs at extreme operation conditions, such as high temperature, severe external force excitation, and large rotor imbalance. The new bearing design replaces outer oil films, i.e., squeeze film dampers (SFDs, in TC SFRBs with wire mesh dampers (WMDs. This SFRB configuration integrating WMDs aims to implement reliable mechanical components, as an inexpensive and simple alternative to SFDs, with consistent and superior damping capability, as well as predictable forced performance. Since WMDs are in series with the inner oil films of SFRBs, experimentally determined force coefficients of WMDs are of great importance in the design process of TC rotor-bearing systems (RBSs. Presently, the measurements of applied static load and ensuing deflection determine the structural stiffnesses of the WMDs. The WMD damping parameters, including dissipated energy, loss factor, and dry friction coefficient, are estimated from the area of the distinctive local hysteresis loop of the load versus WMD displacement data recorded during consecutive loading-unloading cycles as a function of applied preload with a constant amplitude of motion. The changes in WMD loss factor and dry friction coefficient due to increases in preload are more significant for the WMDs with lower density. The present work shows, to date, the most comprehensive measurements of static load characteristics on the WMDs for application into small automotive TCs. More importantly, the extensive test measurements of WMD deflection versus increasing static loads will aid to anchor predictions of future computation model.
Daneshjou, Kamran; Alibakhshi, Reza
2018-01-01
In the current manuscript, the process of spacecraft docking, as one of the main risky operations in an on-orbit servicing mission, is modeled based on unconstrained multibody dynamics. The spring-damper buffering device is utilized here in the docking probe-cone system for micro-satellites. Owing to the impact occurs inevitably during docking process and the motion characteristics of multibody systems are remarkably affected by this phenomenon, a continuous contact force model needs to be considered. Spring-damper buffering device, keeping the spacecraft stable in an orbit when impact occurs, connects a base (cylinder) inserted in the chaser satellite and the end of docking probe. Furthermore, by considering a revolute joint equipped with torsional shock absorber, between base and chaser satellite, the docking probe can experience both translational and rotational motions simultaneously. Although spacecraft docking process accompanied by the buffering mechanisms may be modeled by constrained multibody dynamics, this paper deals with a simple and efficient formulation to eliminate the surplus generalized coordinates and solve the impact docking problem based on unconstrained Lagrangian mechanics. By an example problem, first, model verification is accomplished by comparing the computed results with those recently reported in the literature. Second, according to a new alternative validation approach, which is based on constrained multibody problem, the accuracy of presented model can be also evaluated. This proposed verification approach can be applied to indirectly solve the constrained multibody problems by minimum required effort. The time history of impact force, the influence of system flexibility and physical interaction between shock absorber and penetration depth caused by impact are the issues followed in this paper. Third, the MATLAB/SIMULINK multibody dynamic analysis software will be applied to build impact docking model to validate computed results and
Bi-directional vibration control of offshore wind turbines using a 3D pendulum tuned mass damper
Sun, C.; Jahangiri, V.
2018-05-01
Offshore wind turbines suffer from excessive bi-directional vibrations due to wind-wave misalignment and vortex induced vibrations. However, most of existing research focus on unidirectional vibration attenuation which is inadequate for real applications. The present paper proposes a three dimensional pendulum tuned mass damper (3d-PTMD) to mitigate the tower and nacelle dynamic response in the fore-aft and side-side directions. An analytical model of the wind turbine coupled with the 3d-PTMD is established wherein the interaction between the blades, the tower and the 3d-PTMD is modeled. Aerodynamic loading is computed using the Blade Element Momentum method where the Prandtls tip loss factor and the Glauert correction are considered. JONSWAP spectrum is adopted to generate wave data. Wave loading is computed using Morisons equation in collaboration with the strip theory. Via a numerical search approach, the design formula of the 3d-PTMD is obtained and examined on a National Renewable Energy Lab (NREL) monopile 5 MW baseline wind turbine model under misaligned wind, wave and seismic loading. Dual linear tuned mass dampers (TMDs) deployed in the fore-aft and side-side directions are utilized for comparison. It is found that the 3d-PTMD with a mass ratio of 2 % can improve the mitigation of the root mean square and peak response by around 10 % when compared with the dual linear TMDs in controlling the bi-directional vibration of the offshore wind turbines under misaligned wind, wave and seismic loading.
International Nuclear Information System (INIS)
Andronov, I.N.
1999-01-01
The attempts to development of the rotor-dampers universal model with ability of fast correction of the parameters of mock-up rotor and dampers, their construction were made. The model that takes into account viscous characteristics of the material of the centrifuge rotor and allows research numerically into the rotor behaviour during over-speeding is suggested. The examples of calculations as show good effect of electromagnetic damping on the dynamics of the centrifuge rotor are given [ru
EPA's air research provides the critical science to develop and implement outdoor air regulations under the Clean Air Act and puts new tools and information in the hands of air quality managers and regulators to protect the air we breathe.
Ray, S. E.; Pagano, T. S.; Fetzer, E. J.; Lambrigtsen, B.; Olsen, E. T.; Teixeira, J.; Licata, S. J.; Hall, J. R.; Thompson, C. K.
2015-12-01
The Atmospheric Infrared Sounder (AIRS) on NASA's Aqua spacecraft has been returning daily global observations of Earth's atmospheric constituents and properties since 2002. With a 12-year data record and daily, global observations in near real-time, AIRS data can play a role in applications that fall under many of the NASA Applied Sciences focus areas. For vector-borne disease, research is underway using AIRS near surface retrievals to assess outbreak risk, mosquito incubation periods and epidemic potential for dengue fever, malaria, and West Nile virus. For drought applications, AIRS temperature and humidity data are being used in the development of new drought indicators and improvement in the understanding of drought development. For volcanic hazards, new algorithms using AIRS data are in development to improve the reporting of sulfur dioxide concentration, the burden and height of volcanic ash and dust, all of which pose a safety threat to aircraft. In addition, anomaly maps of many of AIRS standard products are being produced to help highlight "hot spots" and illustrate trends. To distribute it's applications imagery, AIRS is leveraging existing NASA data frameworks and organizations to facilitate archiving, distribution and participation in the BEDI. This poster will communicate the status of the applications effort for the AIRS Project and provide examples of new maps designed to best communicate the AIRS data.
Returning to sports after a back injury
... medlineplus.gov/ency/patientinstructions/000518.htm Returning to sports after a back injury To use the sharing ... Back pain - returning to sports Which Type of Sport is Best? In deciding when and if to ...
Returns to Tenure or Seniority?
DEFF Research Database (Denmark)
Buhai, Ioan Sebastian; Portela, Miguel; Teulings, Coen
This study documents two empirical regularities, using data for Denmark and Portugal. First, workers who are hired last, are the first to leave the firm (Last In, First Out; LIFO). Second, workers' wages rise with seniority (= a Worker's tenure relative to the tenure of her colleagues). We seek...... at the moment of separation). The LIFO rule provides a stronger bargaining position for senior workers, leading to a return to seniority in wages. Efficiency in hiring requires the workers' .bargaining power to be in line with their share in the cost of specific investment. Then, the LIFO rule is a way...
Common Factors in International Bond Returns
Driessen, J.J.A.G.; Melenberg, B.; Nijman, T.E.
2000-01-01
In this paper we estimate and interpret the factors that jointly determine bond returns of different maturities in the US, Germany and Japan.We analyze both currency-hedged and unhedged bond returns.For currency-hedged bond returns, we find that five factors explain 96.5% of the variation of bond
Foreign currency returns and systematic risks
Galsband, V.; Nitschka, T.
2015-01-01
We apply an empirical approximation of the intertemporal capital asset pricing model (ICAPM) to show that cross-sectional dispersion in currency returns can be rationalized by differences in currency excess returns' sensitivities to the market return's cash-flow news component. This finding echoes
International Nuclear Information System (INIS)
Ito, Tomohiro; Michiue, Masashi; Fujita, Katsuhisa
2010-01-01
In this study, the applicability of a previously developed optimal seismic design methodology, which can consider the structural integrity of not only piping systems but also elasto-plastic supporting devices, is studied for seismic waves with various frequency characteristics. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location and the capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model. As a result, it is shown that the proposed optimal seismic design methodology is applicable to the seismic design of piping systems subjected to seismic waves with various frequency characteristics. The mechanism of optimization is also clarified. (author)
Concerning temporary method for return transport of plutonium
International Nuclear Information System (INIS)
1990-01-01
One of the urgent matters under deliberation in the Working Group for Nuclear Fuel Cycle, Atomic Energy Comission of Japan, is to develop a method for smooth and safe transport of plutonium to be returned from Britain and France, where spent fuel sent from Japan is reprocessed by contract. Return transport of plutonium from these nations will start in 1992. Preparatory work has been conducted in Japan for air transport of plutonium, which is to be used by Power Reactor and Nuclear Fuel Development Corporation. For this, efforts have been made since 1984 to develop containers for air transport of plutonium. Though the corporation will continue research, it will take considerable time until practical containers are developed, so the material have to be transported by sea for the time being. The corporation should play the leading role in conducting the return transport operation in cooperation with other organizations concerned including power companies. To achieve this, the corporation should be active in making preparations including the development of transport plans. (N.K.)
Energy Technology Data Exchange (ETDEWEB)
Brune, M.; Poetter, K. [BMW Group, Muenchen (Germany). Fachbereich Betriebsfestigkeit und Werkstoffe
2008-07-01
The use of mechatronical devices in car-design is of growing importance. The purpose of these control systems is to improve driving dynamics and comfort. As an example the roll-stabilisation and the variable damper can be mentioned. Both systems influence the component stress of suspension and chassis parts. Therefore they have to be integrated in numeric- and experimental fatigue analysis. On the basis of examples, this paper describes current methods of resolution and future challenges.
Syrakos, Alexandros; Dimakopoulos, Yannis; Tsamopoulos, John
2018-03-01
The flow inside a fluid damper where a piston reciprocates sinusoidally inside an outer casing containing high-viscosity silicone oil is simulated using a finite volume method, at various excitation frequencies. The oil is modeled by the Carreau-Yasuda (CY) and Phan-Thien and Tanner (PTT) constitutive equations. Both models account for shear-thinning, but only the PTT model accounts for elasticity. The CY and other generalised Newtonian models have been previously used in theoretical studies of fluid dampers, but the present study is the first to perform full two-dimensional (axisymmetric) simulations employing a viscoelastic constitutive equation. It is found that the CY and PTT predictions are similar when the excitation frequency is low, but at medium and higher frequencies, the CY model fails to describe important phenomena that are predicted by the PTT model and observed in experimental studies found in the literature, such as the hysteresis of the force-displacement and force-velocity loops. Elastic effects are quantified by applying a decomposition of the damper force into elastic and viscous components, inspired from large amplitude oscillatory shear theory. The CY model also overestimates the damper force relative to the PTT model because it underpredicts the flow development length inside the piston-cylinder gap. It is thus concluded that (a) fluid elasticity must be accounted for and (b) theoretical approaches that rely on the assumption of one-dimensional flow in the piston-cylinder gap are of limited accuracy, even if they account for fluid viscoelasticity. The consequences of using lower-viscosity silicone oil are also briefly examined.
LDDX: A High Efficiency Air Conditioner for DOD Buildings
2017-02-01
Additional Benefits ........................................................................................................ 3 1.2.6 Deliverables...inadequate latent cooling can lead building managers to restrict ventilation to minimal levels that further compromise both the comfort and health of...bulb temperatures for outdoor air and return air respectively per ANSI/AHRI Standard 210/240 “Performance Rating of Unitary Air-Conditioning and Air
Stock Returns and Risk: Evidence from Quantile
Directory of Open Access Journals (Sweden)
Thomas C. Chiang
2012-12-01
Full Text Available This paper employs weighted least squares to examine the risk-return relation by applying high-frequency data from four major stock indexes in the US market and finds some evidence in favor of a positive relation between the mean of the excess returns and expected risk. However, by using quantile regressions, we find that the risk-return relation moves from negative to positive as the returns’ quantile increases. A positive risk-return relation is valid only in the upper quantiles. The evidence also suggests that intraday skewness plays a dominant role in explaining the variations of excess returns.
2011-04-22
... Specified Tax Return Preparers Required To File Individual Income Tax Returns Using Magnetic Media... Register on Wednesday, March 30, 2011 (76 FR 17521) providing guidance to specified tax return preparers who prepare and file individual income tax returns using magnetic media pursuant to section 6011(e)(3...
Deng, Zhangxian
The Villari effect, through which mechanical energy is transferred to magnetic energy in magnetostrictive materials can be utilized in energy harvester and damper designs. Significant research has been conducted on two magnetostrictive materials, Terfenol-D (TbxDy1-xFe2.0, x ≈ 0.3) and Galfenol (Fe1-xGax, 0.15 ≤ x ≤ 0.3), due to their high magnetomechanical coupling. Both materials have strengths and weaknesses. Terfenol-D exhibits low eddy current loss, but it is brittle and difficult to machine. Terfenol-D also provides higher magnetostriction while requiring a large magnetic field. On the other hand, Galfenol is mechanically robust, and thus can be machined, welded, and formed into complex geometries. However, due to its severe eddy current effect, lamination is necessary in high frequency applications. This work first characterized the Villari effect of Galfenol in terms of the piezo-magnetic constant d33* and hysteresis loss. The stress-flux density loops of oriented, polycrystalline Fe18.4Ga81.6 Galfenol were measured at quasi-static and dynamic regimes (up to 800 Hz). Advanced modeling tools are necessary for magnetostrictive device development. On the material level, this work proposed a dynamic, discrete energy-averaged (DEA) model incorporating time-dependent volume fractions into the static DEA framework. This dynamic DEA model took eddy current loss, mechanical loss, and pinning site loss into account and accurately simulated the measured Villari effect up to 600 Hz. On the system level, this work integrated a hysteresis static DEA model with a 3D finite element (FE) framework, and accurately modeled stress-flux density minor loops in a quasi-static state. Based on the assumption that the magnetostriction and magnetization are uniaxial, this work also proposed an efficient 2D FE framework describing nonlinear magnetostrictive responses via interpolation functions. This enhanced knowledge of the Villari effect facilitates magnetostrictive vibration
Evaluation of trade-offs in costs and environmental impacts for returnable packaging implementation
Jarupan, Lerpong; Kamarthi, Sagar V.; Gupta, Surendra M.
2004-02-01
The main thrust of returnable packaging these days is to provide logistical services through transportation and distribution of products and be environmentally friendly. Returnable packaging and reverse logistics concepts have converged to mitigate the adverse effect of packaging materials entering the solid waste stream. Returnable packaging must be designed by considering the trade-offs between costs and environmental impact to satisfy manufacturers and environmentalists alike. The cost of returnable packaging entails such items as materials, manufacturing, collection, storage and disposal. Environmental impacts are explicitly linked with solid waste, air pollution, and water pollution. This paper presents a multi-criteria evaluation technique to assist decision-makers for evaluating the trade-offs in costs and environmental impact during the returnable packaging design process. The proposed evaluation technique involves a combination of multiple objective integer linear programming and analytic hierarchy process. A numerical example is used to illustrate the methodology.
Air pollution is a mixture of solid particles and gases in the air. Car emissions, chemicals from factories, ... Ozone, a gas, is a major part of air pollution in cities. When ozone forms air pollution, it's ...
Lu, Fei; Wang, Xiao-Ke; Han, Bing; Ouyang, Zhi-Yun; Zheng, Hua
2010-05-01
Straw returning is considered to be one of the most promising carbon sequestration measures in China's cropland. A compound model, namely "Straw Returning and Burning Model-Expansion" (SRBME), was built to estimate the net mitigation potential, economic benefits, and air pollutant reduction of straw returning. Three scenarios, that is, baseline, "full popularization of straw returning (FP)," and "full popularization of straw returning and precision fertilization (FP + P)," were set to reflect popularization of straw returning. The results of the SRBME indicated that (1) compared with the soil carbon sequestration of 13.37 Tg/yr, the net mitigation potentials, which were 6.328 Tg/yr for the FP scenario and 9.179 Tg/yr for the FP + P scenario, had different trends when the full budget of the greenhouse gases was considered; (2) when the feasibility in connection with greenhouse gas (GHG) mitigation, economic benefits, and environmental benefits was taken into consideration, straw returning was feasible in 15 provinces in the FP scenario, with a total net mitigation potential of 7.192 TgCe/yr and the total benefits of CNY 1.473 billion (USD 216.6 million); (3) in the FP + P scenario, with the implementation of precision fertilization, straw returning was feasible in 26 provinces with a total net mitigation potential of 10.39 TgCe/yr and the total benefits of CNY 5.466 billion (USD 803.8 million); (4) any extent of change in the treatment of straw from being burnt to being returned would contribute to air pollution reduction; (5) some countermeasures, such as CH(4) reduction in rice paddies, precision fertilization, financial support, education and propaganda, would promote the feasibility of straw returning as a mitigation measure.
Vibration survey of internal combustion engines for use on unmanned air vehicles
International Nuclear Information System (INIS)
Duanis, B.
1998-01-01
This paper describes the method, the procedure and data results of engine vibration test which is carried out on engines for use on unmanned air vehicles. The paper focuses on the testing of rotating propulsion systems powered by an internal combustion engine which is composed of main rotating components such as the alternator, gearbox, propeller , dampers and couplings. Three measurement methods for measuring torsional and lateral vibrations are presented: a. Gear tooth pulse signal. b. Shaft Strain Gage. c. Laser Displacement Sensors The paper also presents data from tests which were performed using each method and discusses the applications, the advantages and disadvantages of each method
2017-10-26
TO OTHER ZONE DAMPERS N.O. TEMPERATURE SENSOR CHILLED WATER ZONE 1 STAT SUPPLY FAN COLD DECK COIL TO OTHER ZONE DAMPERS ZONE 1 DAMPER ACTUATOR HOT... water pump usage were considered. Figure 25. Condensing Boiler Combustion Efficiencies 3. Chilled water system losses : Similarly, electrical energy...required to meet cooling demands at the chilled water coil BTU meter is dependent on network losses and chiller energy efficiency ratios. Using
Xu, Lang; Lu, Yuhua; Liu, Qian
2018-02-01
We propose a novel method to simulate soft tissue deformation for virtual surgery applications. The method considers the mechanical properties of soft tissue, such as its viscoelasticity, nonlinearity and incompressibility; its speed, stability and accuracy also meet the requirements for a surgery simulator. Modifying the traditional equation for mass spring dampers (MSD) introduces nonlinearity and viscoelasticity into the calculation of elastic force. Then, the elastic force is used in the constraint projection step for naturally reducing constraint potential. The node position is enforced by the combined spring force and constraint conservative force through Newton's second law. We conduct a comparison study of conventional MSD and position-based dynamics for our new integrating method. Our approach enables stable, fast and large step simulation by freely controlling visual effects based on nonlinearity, viscoelasticity and incompressibility. We implement a laparoscopic cholecystectomy simulator to demonstrate the practicality of our method, in which liver and gallbladder deformation can be simulated in real time. Our method is an appropriate choice for the development of real-time virtual surgery applications.
Momtaz, Ali Ajilian; Abdollahian, Mohamadreza Akhavan; Farshidianfar, Anooshiravan
2017-12-01
In recent years, construction of tall buildings has been of great interest. Use of lightweight materials in such structures reduces stiffness and damping, making the building more influenced by wind loads. Moreover, tall buildings of more than 30 to 40 stories, depending on the geographical location, the wind effects are more influential than earthquakes. In addition, the complexity of the effects of wind flow on the structure due to the interaction of the fluid flow and solid body results in serious damages to the structure by eliminating them. Considering the importance of the issue, the present study investigates the phenomenon of wind-induced vibration on high-rise buildings, taking into account the effects of vortices created by the fluid flow and the control of this phenomenon. To this end, the governing equations of the structure, the fluid flow and the tuned mass damper (TMD) are first introduced, and their coefficient values are extracted according to the characteristics of ACT skyscraper in Japan. Then, these three coupled equations are solved using a program coded in MATLAB. After validation of the results, the effects of wind loads are analyzed and considered with regard to the effects of vortices and the use of TMD, and are compared with the results of the state where no vortices are considered. Generally, the results of this study point out the significance of vibrations caused by vortices in construction of engineering structures as well as the appropriate performance of a TMD in reducing oscillations in tall buildings.
International Nuclear Information System (INIS)
Moutinho, Carlos
2015-01-01
This paper is focused on the control problems related to semi-active tuned mass dampers (TMDs) used to reduce harmonic vibrations, specially involving civil structures. A simplified version of the phase control law is derived and its effectiveness is investigated and evaluated. The objective is to improve the functioning of control systems of this type by simplifying the measurement process and reducing the number of variables involved, making the control system more feasible and reliable. Because the control law is of ON/OFF type, combined with appropriate trigger conditions, the activity of the actuation system may be significantly reduced, which may be of few seconds a day in many practical cases, increasing the durability of the device and reducing its maintenance. Moreover, due to the ability of the control system to command the motion of the inertial mass, the semi-active TMD is relatively insensitive to its initial tuning, resulting in the capability of self-tuning and in the possibility of controlling several vibration modes of a structure over a significant broadband frequency. (paper)
Munigety, Caleb Ronald
2018-04-01
The traditional traffic microscopic simulation models consider driver and vehicle as a single unit to represent the movements of drivers in a traffic stream. Due to this very fact, the traditional car-following models have the driver behavior related parameters, but ignore the vehicle related aspects. This approach is appropriate for homogeneous traffic conditions where car is the major vehicle type. However, in heterogeneous traffic conditions where multiple vehicle types are present, it becomes important to incorporate the vehicle related parameters exclusively to account for the varying dynamic and static characteristics. Thus, this paper presents a driver-vehicle integrated model hinged on the principles involved in physics-based spring-mass-damper mechanical system. While the spring constant represents the driver’s aggressiveness, the damping constant and the mass component take care of the stability and size/weight related aspects, respectively. The proposed model when tested, behaved pragmatically in representing the vehicle-type dependent longitudinal movements of vehicles.
Directory of Open Access Journals (Sweden)
Jong Wan Hu
2016-01-01
Full Text Available The bridge bearing is one of the component members which provide resting supports between piers and decks. The bridge bearing is intended to control longitudinal movement caused by traffic flow and thermal expansion, thereby reducing stress concentration. In high seismicity area, the bridge bearing has been utilized as the base isolation system to mitigate acceleration transferred from the ground. Although the existing bridge bearing installed between superstructure and substructure provides extra flexibility to the base of the entire structure, considerable permanent deformation occurs due to lack of recentering capacity after earthquake. It is required to spend extra cost for repairing impaired parts. The bridge bearings integrated with superelastic shape memory alloy (SMA devices used for upgrading the recentering effect into the friction damper are proposed in this study. The refined finite element (FE analyses are introduced to reproduce the response of such new structures under cyclic loading condition. The bridge bearing systems that maintain uniform recentering capability are designed with various friction coefficients so as to examine energy dissipation and residual deformation through FE analyses. After observing FE analysis results, optimal design for the recentering bridge bearing system will be proposed to take advantage of energy dissipation and self-centering capacity.
International Nuclear Information System (INIS)
Wang, Han; Song, Gangbing
2011-01-01
Fault detection and isolation (FDI) in real-time systems can provide early warnings for faulty sensors and actuator signals to prevent events that lead to catastrophic failures. The main objective of this paper is to develop FDI and fault tolerant control techniques for base isolation systems with magneto-rheological (MR) dampers. Thus, this paper presents a fixed-order FDI filter design procedure based on linear matrix inequalities (LMI). The necessary and sufficient conditions for the existence of a solution for detecting and isolating faults using the H ∞ formulation is provided in the proposed filter design. Furthermore, an FDI-filter-based fuzzy fault tolerant controller (FFTC) for a base isolation structure model was designed to preserve the pre-specified performance of the system in the presence of various unknown faults. Simulation and experimental results demonstrated that the designed filter can successfully detect and isolate faults from displacement sensors and accelerometers while maintaining excellent performance of the base isolation technology under faulty conditions
Becnel, Andrew; Hu, Wei; Hiemenz, Gregory J.; Wereley, Norman M.
2010-04-01
A magnetorheological shock absorber (MRSA) prototype is designed, fabricated and tested to integrate semiactive shock and vibration mitigation technology into the existing Expeditionary Fighting Vehicle (EFV) forward seating positions. Utilizing Bingham-Plastic (BP) constitutive fluid relationships and a steady state fluid flow model, the MR valve parameters are determined using magnetic circuit analysis, and subsequently validated via electromagnetic finite element analysis (FEA). Low speed (up to 0.9 m/s) simulations of normal vibration mode operation are conducted on the MRSA prototype using single frequency sinusoidal displacements by a servohydraulic testing machine. The high speed (up to 2.2 m/s) design procedure is verified by using a rail-guided drop test stand to impact a known payload mass onto the damper shaft. A refined hydromechanical model of the MRSA under both cyclic and impact loadings is developed and validated using the measured test data. This ratedependent, mechanisms-based model predicts the time response of the MRSA under both loading conditions. The hydromechanical analysis marks a significant improvement over previous linear models. Key design considerations for the MRSA to accommodate both vibration and shock spectra using a single MR device are presented.
Stock returns and foreign investment in Brazil
Reis, Luciana; Meurer, Roberto; Da Silva, Sergio
2008-01-01
We examine the relationship between stock returns and foreign investment in Brazil, and find that the inflows of foreign investment boosted the returns from 1995 to 2005. There was a strong contemporaneous correlation, although not Granger-causality. Foreign investment along with the exchange rate, the influence of the world stock markets, and country risk can explain 73 percent of the changes that occurred in the stock returns over the period. We also find that positive feedback trading play...
Maximizing ROI (return on information)
Energy Technology Data Exchange (ETDEWEB)
McDonald, B.
2000-05-01
The role and importance of managing information are discussed, underscoring the importance by quoting from the report of the International Data Corporation, according to which Fortune 500 companies lost $ 12 billion in 1999 due to inefficiencies resulting from intellectual re-work, substandard performance , and inability to find knowledge resources. The report predicts that this figure will rise to $ 31.5 billion by 2003. Key impediments to implementing knowledge management systems are identified as : the cost and human resources requirement of deployment; inflexibility of historical systems to adapt to change; and the difficulty of achieving corporate acceptance of inflexible software products that require changes in 'normal' ways of doing business. The author recommends the use of model, document and rule-independent systems with a document centered interface (DCI), employing rapid application development (RAD) and object technologies and visual model development, which eliminate these problems, making it possible for companies to maximize their return on information (ROI), and achieve substantial savings in implementation costs.
Risk-return of Belgian SRI funds
Van Liedekerke, Luc; De Moor, Lieven; Vanwalleghem, Dieter
2007-01-01
We analyse the risk-return profile of Belgian SRI funds versus conventional investment funds. We apply a four-factor conditional Carhart model to establish whether there are significant differences in risk-return profile between an SRI portfolio and a conventional portfolio and test for learning effects in SRI funds. We show that there is no difference in risk-return profile between SRI and conventional funds. If return is not the problem, then what is it that limits the development of an SRI...
Money growth and aggregate stock returns
Böing, Tobias; Stadtmann, Georg
2016-01-01
We empirically evaluate the predictive power of money growth measured by M2 for stock returns of the S&P 500 index. We use monthly US data and predict multiperiod returns over 1, 3, and 5 years with long-horizon regressions. In-sample regressions show that money growth is useful for predicting returns. Higher recent money growth has a significantly negative effect on subsequent returns of the S&P 500. An out-of-sample analysis shows that a simple model with money growth as a single predictor ...
Construction and testing of a blower-door assembly for regulation of air pressure within structures
International Nuclear Information System (INIS)
Steele, W.D.
1987-09-01
The Technical Measurements Center is evaluating several methods to decrease the time required to determine an annual average radon-daughter concentration in structures. One method involves stabilizing the air pressure within the structure at a constant pressure with reference to external atmospheric or soil-gas pressure. This report describes the construction and preliminary testing of a blower-door system to maintain a constant differential air pressure within a structure. The blower-door assembly includes a collapsible frame and a large fan to occlude a doorway, a damper with an actuator to control air flow, a controller to drive the damper actuator, and a pressure transducer to measure the differential pressure. Preliminary testing of the system indicates that pressure within the structure in the range of 1 to 20 Pascals can be held to within approximately +-1 Pa of the set point. Further testing of the blower-door system is planned to provide data on the applicability of this method to short-duration tests for annual average radon-daughter concentration estimates. 13 figs., 1 tab
Maximizing your return on people.
Bassi, Laurie; McMurrer, Daniel
2007-03-01
Though most traditional HR performance metrics don't predict organizational performance, alternatives simply have not existed--until now. During the past ten years, researchers Laurie Bassi and Daniel McMurrer have worked to develop a system that allows executives to assess human capital management (HCM) and to use those metrics both to predict organizational performance and to guide organizations' investments in people. The new framework is based on a core set of HCM drivers that fall into five major categories: leadership practices, employee engagement, knowledge accessibility, workforce optimization, and organizational learning capacity. By employing rigorously designed surveys to score a company on the range of HCM practices across the five categories, it's possible to benchmark organizational HCM capabilities, identify HCM strengths and weaknesses, and link improvements or back-sliding in specific HCM practices with improvements or shortcomings in organizational performance. The process requires determining a "maturity" score for each practice, based on a scale of 1 (low) to 5 (high). Over time, evolving maturity scores from multiple surveys can reveal progress in each of the HCM practices and help a company decide where to focus improvement efforts that will have a direct impact on performance. The authors draw from their work with American Standard, South Carolina's Beaufort County School District, and a bevy of financial firms to show how improving HCM scores led to increased sales, safety, academic test scores, and stock returns. Bassi and McMurrer urge HR departments to move beyond the usual metrics and begin using HCM measurement tools to gauge how well people are managed and developed throughout the organization. In this new role, according to the authors, HR can take on strategic responsibility and ensure that superior human capital management becomes central to the organization's culture.
Return-to-Work Program for Injured Workers: Factors of Successful Return to Employment.
Awang, Halimah; Shahabudin, Sharifah Muhairah; Mansor, Norma
2016-11-01
This study examined the factors of successful return to employment among participants in the return to work program (RTW) following work-related injury. Data were obtained from the Social Security Organization database containing 9850 injured workers who underwent RTW in 2010 to 2013. About 65% had successfully returned to employment. Significant factors of successful return include gender, employer interest, motivation, age, intervention duration, and type of injury. Male and motivated employees were more likely to return to employment compared with female and unmotivated employees, respectively. Participants from interested employers were 23.22 times more likely to return to work than those from uninterested employers, whereas participants whose intervention period exceeded 5 months were 41% less likely to return to work compared with those whose intervention period was within 3 months. Appropriate strategy and enhanced collaboration between the stakeholders would improve the proportion of successful return to employment. © 2016 APJPH.
Heat pipe heat exchanger for heat recovery in air conditioning
Energy Technology Data Exchange (ETDEWEB)
Abd El-Baky, Mostafa A.; Mohamed, Mousa M. [Mechanical Power Engineering Department, Faculty of Engineering, Minufiya University, Shebin El-Kom (Egypt)
2007-03-15
The heat pipe heat exchangers are used in heat recovery applications to cool the incoming fresh air in air conditioning applications. Two streams of fresh and return air have been connected with heat pipe heat exchanger to investigate the thermal performance and effectiveness of heat recovery system. Ratios of mass flow rate between return and fresh air of 1, 1.5 and 2.3 have been adapted to validate the heat transfer and the temperature change of fresh air. Fresh air inlet temperature of 32-40{sup o}C has been controlled, while the inlet return air temperature is kept constant at about 26{sup o}C. The results showed that the temperature changes of fresh and return air are increased with the increase of inlet temperature of fresh air. The effectiveness and heat transfer for both evaporator and condenser sections are also increased to about 48%, when the inlet fresh air temperature is increased to 40{sup o}C. The effect of mass flow rate ratio on effectiveness is positive for evaporator side and negative for condenser side. The enthalpy ratio between the heat recovery and conventional air mixing is increased to about 85% with increasing fresh air inlet temperature. The optimum effectiveness of heat pipe heat exchanger is estimated and compared with the present experimental data. The results showed that the effectiveness is close to the optimum effectiveness at fresh air inlet temperature near the fluid operating temperature of heat pipes. (author)
Return on Investment from Biochar Application
Current literature has yet to fully address the cost of biochar application or the return on investment to the grower. The objectives were to identify possible on-farm spreader equipment, spreader capacity, application expenses, and rate of return needed for growers to apply biochar economically. Bi...
Aggregate Unemployment Decreases Individual Returns to Education
Ammermueller, Andreas; Kuckulenz, Anja; Zwick, Thomas
2009-01-01
Aggregate unemployment may affect individual returns to education through qualification-specific responses in participation and wage bargaining. This paper shows that an increase in regional unemployment by 1% decreases returns to education by 0.005 percentage points. This implies that higher skilled employees are better sheltered from labour…
A Perishable Inventory Model with Return
Setiawan, S. W.; Lesmono, D.; Limansyah, T.
2018-04-01
In this paper, we develop a mathematical model for a perishable inventory with return by assuming deterministic demand and inventory dependent demand. By inventory dependent demand, it means that demand at certain time depends on the available inventory at that time with certain rate. In dealing with perishable items, we should consider deteriorating rate factor that corresponds to the decreasing quality of goods. There are also costs involved in this model such as purchasing, ordering, holding, shortage (backordering) and returning costs. These costs compose the total costs in the model that we want to minimize. In the model we seek for the optimal return time and order quantity. We assume that after some period of time, called return time, perishable items can be returned to the supplier at some returning costs. The supplier will then replace them in the next delivery. Some numerical experiments are given to illustrate our model and sensitivity analysis is performed as well. We found that as the deteriorating rate increases, returning time becomes shorter, the optimal order quantity and total cost increases. When considering the inventory-dependent demand factor, we found that as this factor increases, assuming a certain deteriorating rate, returning time becomes shorter, optimal order quantity becomes larger and the total cost increases.