Numerical analysis of free vibrations of damped rotating structures
Gupta, K. K.
1977-01-01
This paper is concerned with the efficient numerical solution of damped and undamped free vibration problems of rotating structures. While structural discretization is achieved by the finite element method, the associated eigenproblem solution is effected by a combined Sturm sequence and inverse iteration technique that enables the computation of a few required roots only without having to compute any other. For structures of complex configurations, a modal synthesis technique is also presented, which is based on appropriate combinations of eigenproblem solution of various structural components. Such numerical procedures are general in nature, which fully exploit matrix sparsity inherent in finite element discretizations, and prove to be most efficient for the vibration analysis of any damped rotating structure, such as rotating machineries, helicopter and turbine blades, spinning space stations, among others.
Takács, Gergely
2012-01-01
Real-time model predictive controller (MPC) implementation in active vibration control (AVC) is often rendered difficult by fast sampling speeds and extensive actuator-deformation asymmetry. If the control of lightly damped mechanical structures is assumed, the region of attraction containing the set of allowable initial conditions requires a large prediction horizon, making the already computationally demanding on-line process even more complex. Model Predictive Vibration Control provides insight into the predictive control of lightly damped vibrating structures by exploring computationally efficient algorithms which are capable of low frequency vibration control with guaranteed stability and constraint feasibility. In addition to a theoretical primer on active vibration damping and model predictive control, Model Predictive Vibration Control provides a guide through the necessary steps in understanding the founding ideas of predictive control applied in AVC such as: · the implementation of ...
Complex modes and frequencies in damped structural vibrations
DEFF Research Database (Denmark)
Krenk, Steen
2004-01-01
It is demonstrated that the state space formulation of the equation of motion of damped structural elements like cables and beams leads to a symmetric eigenvalue problem if the stiffness and damping operators are self-adjoint, and that this is typically the case in the absence of gyroscopic force...
Vibrational Damping of Composite Materials
Biggerstaff, Janet M.
2006-01-01
The purpose of this research was to develop new methods of vibrational damping in polymeric composite materials along with expanding the knowledge of currently used vibrational damping methods. A new barrier layer technique that dramatically increased damping in viscoelastic damping materials that interacted with the composite resin was created. A method for testing the shear strength of damping materials cocured in composites was developed. Directional damping materials, where the loss facto...
Design of three-element dynamic vibration absorber for damped linear structures
Anh, N. D.; Nguyen, N. X.; Hoa, L. T.
2013-09-01
The standard type of dynamic vibration absorber (DVA) called the Voigt DVA is a classical model and has long been investigated. In the paper, we will consider an optimization problem of another model of DVA that is called three-element type DVA for damped primary structures. Unlike the standard absorber configuration, the three-element DVA contains two spring elements in which one is connected to a dashpot in series and the other is placed in parallel. There have been some studies on the design of the three-element DVA for undamped primary structures. Those studies have shown that the three-element DVA produces better performance than the Voigt DVA does. When damping is present at the primary system, to the best knowledge of the authors, there has been no study on the three-element dynamic vibration absorber. This work presents a simple approach to determine the approximate analytical solutions for the H∞ optimization of the three-element DVA attached to the damped primary structure. The main idea of the study is based on the criteria of the equivalent linearization method in order to replace approximately the original damped structure by an equivalent undamped one. Then the approximate analytical solution of the DVA's parameters is given by using known results for the undamped structure obtained. The comparisons have been done to verify the effectiveness of the obtained results.
Directory of Open Access Journals (Sweden)
Minh-Nghi Ta
2006-01-01
Full Text Available Damping is a mechanism that dissipates vibration energy in dynamic systems and plays a key role in dynamic response prediction, vibration control as well as in structural health monitoring during service. In this paper a time domain and a time-scale domain approaches are used for damping estimation of engineering structures, using ambient response data only. The use of tests under ambient vibration is increasingly popular today because they allow to measure the structural response in service. In this paper we consider two engineering structures excited by ambient forces. The first structure is the 310 m tall TV tower recently constructed in the city of Nanjing in China. The second example concerns the Jinma cable-stayed bridge that connects Guangzhou and Zhaoqing in China. It is a single tower, double row cable-stayed bridge supported by 112 stay cables. Ambient vibration of each cable is carried out using accelerometers. From output data only, the modal parameter are extracted using a subspace method and the wavelet transform method.
Vibrational damping of composite materials
Biggerstaff, Janet M.
The purpose of this research was to develop new methods of vibrational damping in polymeric composite materials along with expanding the knowledge of currently used vibrational damping methods. A new barrier layer technique that dramatically increased damping in viscoelastic damping materials that interacted with the composite resin was created. A method for testing the shear strength of damping materials cocured in composites was developed. Directional damping materials, where the loss factor and modulus could be tailored by changing the angle, were produced and investigated. The addition of particles between composite prepreg layers to increase damping was studied. Electroviscoelastic materials that drastically changed properties such as loss factor and modulus with an applied voltage were manufactured and tested.
Composite Struts Would Damp Vibrations
Dolgin, Benjamin P.
1991-01-01
New design of composite-material (fiber/matrix laminate) struts increases damping of longitudinal vibrations without decreasing longitudinal stiffness or increasing weight significantly. Plies with opposing chevron patterns of fibers convert longitudinal vibrational stresses into shear stresses in intermediate viscoelastic layer, which dissipate vibrational energy. Composite strut stronger than aluminum strut of same weight and stiffness.
Natural vibration frequency and damping of slender structures founded on monopiles
DEFF Research Database (Denmark)
Zania, Varvara
2014-01-01
the damping. The modified SSI eigenfrequency and damping was mostly affected by the soil–pile properties, when the structural eigenfrequency was set between the first and second eigenfrequency of the soil layer. Caution is suggested when selecting one of the popular design approaches for OWTs, since...
Vibration Damping Circuit Card Assembly
Hunt, Ronald Allen (Inventor)
2016-01-01
A vibration damping circuit card assembly includes a populated circuit card having a mass M. A closed metal container is coupled to a surface of the populated circuit card at approximately a geometric center of the populated circuit card. Tungsten balls fill approximately 90% of the metal container with a collective mass of the tungsten balls being approximately (0.07) M.
Structural dynamic modification using additive damping
Indian Academy of Sciences (India)
Some current trends for vibration control are also discussed. Keywords. Structural modifications; viscoelastic damping; perturbation; sensitivity analysis; optimization; vibration control. 1. Introduction. Vibrations in machines and structures, if not properly controlled, may cause component fatigue and human discomfort.
NOISE AND VIBRATION DAMPING FOR YACHT INTERIOR
Directory of Open Access Journals (Sweden)
Murat Aydın
2016-12-01
Full Text Available Vibration damping and sound insulation are essential for all vehicles. Because moving parts and external factors such as wind, tracks, etc. can cause vibration and noise. Wave which is a dynamic force, drive system and HVAC systems are the main vibration and noise generators in a vessel. These all can affect comfort level on board yachts. Different types of isolators and absorbers such as sylomer®, cork panels, etc. are used to reduce these effects. Comfort level on board yachts can be increased using these types of materials. Otherwise, discomfort of passenger and crew may increase. These materials not only reduce structure-borne and air-borne noise and vibrations from waves, air, engines, pumps, generators and HVAC systems but also protect vibration sensitive interior or fittings. Noise and vibration evaluation is an important issue for this reason. And, measurement tools must be used not only to minimize this problem but also fulfill the regulations such as “comfort class”. Besides, providing quiet and low vibration increases the costs too. From this point of view, this study aims to explain clearly how noise and vibration damping can be done in a yacht.
Directory of Open Access Journals (Sweden)
Zhengchao Xie
2009-01-01
Full Text Available Due to the large number of design variables that can be present in complex systems incorporating visco-elastic damping, this work examines the application of genetic algorithms in optimizing the response of these structures. To demonstrate the applicability of genetic algorithms (GAs, the approach is applied to a simple viscoelastically damped constrained-layer beam. To that end, a finite element model (FEM derived by Zapfe, which was based on Rao's formulation, was used for a beam with constrained-layer damping. Then, a genetic algorithm is applied to simultaneously determine the thicknesses of the viscoelastic damping layer and the constraining layer that provide the best response. While the targeted response is ultimately at the discretion of the designer, a few different choices for the fitness function are shown along with their corresponding impact on the vibratory response. By integrating the FEM code within the GA routine, it is easier to include the frequency-dependence of both the shear modulus and the loss factors for the viscoelastic layer. Examples are provided to demonstrate the capabilities of the method. It is shown that while a multi-mode optimization target provides significant reductions, the response for that configuration is inferior to the response when only single-mode reduction is considered. The results also reveal that the optimum configuration has a lower response level than when a thick layer of damping material is used. By demonstrating the applicability of GA for a simple beam structure, the approach can be extended to more complex damped structures.
Vibration Analysis and Control of Flexible Beam by Using Smart Damping Structures
Chen, Q.; Levy, C.
1999-01-01
The temperature effects on frequency, loss factor and control of a flexible beam with a constrained viscoelastic layer and shape memory alloy layer (SMA) are discussed. It is shown that the temperature in the SMA (actuation) layer is very important in the determination of frequency and loss factor of such a structure. The effects of damping layer shear modulus and damping layer height as affected by the temperature are also discussed. As temperature plays such an important role, it is, therefore, imperative to evaluate temperature effects on the control of the system as well. Results with and without active control are discussed.
Accurate calibration of RL shunts for piezoelectric vibration damping of flexible structures
DEFF Research Database (Denmark)
Høgsberg, Jan Becker; Krenk, Steen
2016-01-01
Piezoelectric RL (resistive-inductive) shunts are passive resonant devices used for damping of dominantvibration modes of a flexible structure and their efficiency relies on precise calibration of the shuntcomponents. In the present paper improved calibration accuracy is attained by an extension...
Modified Composite Struts Would Damp Vibrations
Chen, Gun-Shing; Dolgin, Benjamin P.
1993-01-01
Composite-material (fiber/matrix laminate) struts damping longitudinal vibrations fabricated more easily in proposed new design. Prior design described in "Composite Struts Would Damp Vibrations" (NPO-17914). New design similar except pattern of fibers includes rounded bends (instead of sharp bends) in fibers.
Passively damped vibration welding system and method
Tan, Chin-An; Kang, Bongsu; Cai, Wayne W.; Wu, Tao
2013-04-02
A vibration welding system includes a controller, welding horn, an anvil, and a passive damping mechanism (PDM). The controller generates an input signal having a calibrated frequency. The horn vibrates in a desirable first direction at the calibrated frequency in response to the input signal to form a weld in a work piece. The PDM is positioned with respect to the system, and substantially damps or attenuates vibration in an undesirable second direction. A method includes connecting the PDM having calibrated properties and a natural frequency to an anvil of an ultrasonic welding system. Then, an input signal is generated using a weld controller. The method includes vibrating a welding horn in a desirable direction in response to the input signal, and passively damping vibration in an undesirable direction using the PDM.
Resonant Electromagnetic Shunt Damping of Flexible Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Becker
2016-01-01
Electromagnetic transducers convert mechanical energy to electrical energy and vice versa. Effective passive vibration damping of flexible structures can therefore be introduced by shunting with an accurately calibrated resonant electrical network thatcontains a capacitor to create the desired...... resonance and a resistor to dissipate the correct amount of vibration energy. The modal interaction with residual vibration forms not targeted by the resonant shunt is represented by supplemental flexibility and inertia terms. This leads to modified calibration formulae that maintain the desired damping...
Damping of wind turbine tower vibrations
DEFF Research Database (Denmark)
Brodersen, Mark Laier; Pedersen, Mikkel Melters
Damping of wind turbine vibrations by supplemental dampers is a key ingredient for the continuous use of monopiles as support for offshore wind turbines. The present thesis consists of an extended summary with four parts and appended papers [P1-P4] concerning novel strategies for damping of tower...... in a stroke amplifying brace, which amplifies the displacement across the damper and thus reduces the desired level of damper force. For optimal damping of the two lowest tower modes, a novel toggle-brace concept for amplifying the bending deformation of the tower is presented. Numerical examples illustrate...... that a minimum of three braces in a symmetric circumferential configuration are needed to introduce homogeneous damping in the two lowest vibration modes, independent of the rotor direction. A novel hybrid viscous damper concept is described in the second part. The hybriddamper consists of a viscous dash...
Experimental identification of viscous damping in linear vibration
Srikantha Phani, A.; Woodhouse, J.
2009-01-01
This paper is concerned with the experimental evaluation of the performance of viscous damping identification methods in linear vibration theory. Both existing and some new methods proposed by the present authors [A.S. Phani, J. Woodhouse, Viscous damping identification in linear vibration, Journal of Sound and Vibration 303 (3-5) (2007) 475-500] are applied to experimental data measured on two test structures: a coupled three cantilever beam with moderate modal overlap and a free-free beam with low modal overlap. The performance of each method is quantified and compared based on three norms and the best methods are identified. The role of complex modes in damping identification from vibration measurements is critically assessed.
Damping Estimation Using Free Decays and Ambient Vibration Tests
DEFF Research Database (Denmark)
Magalhães, Filipe; Brincker, Rune; Cunha, Álvaro
2007-01-01
The accurate identification of modal damping ratios of Civil Engineering structures is a subject of major importance, as the amplitude of structural vibrations in resonance is inversely proportional to these coefficients. Their experimental identification can be performed either from ambient...... vibration or from free vibration tests. In the last case, the structural response after application of an impulse or after the application of harmonic loads can be used. Ambient vibration tests have the strong advantage of being more practical and economical. However, recent applications of both approaches...
Resonant Electromagnetic Shunt Damping of Flexible Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Becker
2016-01-01
Electromagnetic transducers convert mechanical energy to electrical energy and vice versa. Effective passive vibration damping of flexible structures can therefore be introduced by shunting with an accurately calibrated resonant electrical network thatcontains a capacitor to create the desired...
Modelling of Dampers and Damping in Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Riess
2006-01-01
The present thesis consists of an extended summary and four papers concerning damping of structures and algorithmic damping in numerical analysis. The first part of the thesis deals with the efficiency and the tuning of external collocated dampers acting on flexible structures. The dynamics......, 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...
1981-05-01
gLAsTic SUPPORTS 114CLUDING DAMPING ’I FINITE ELEMENT ANALYSIS.........................................83 A. M. Sharan, T. S. Sankar and S. Stalks ...nuances of a at the Naval Weapons Center in China Lake, California. So, physical world of shock and vibration. So I asked myself while I am not a...l Fig. 4: Schematic diagram for the experimental set-up. Fig. 5a: Pictorial view of the Instrumentation for frequency analysis. = rot = :&C lo Fig. Sb
Miller, D. W.
1981-01-01
A prototype of a linear inertial reaction actuation (damper) device employing a flexure-pivoted reaction (proof) mass is discussed. The mass is driven by an electromechanic motor using a dc electromagnetic field and an ac electromagnetic drive. During the damping process, the actuator dissipates structural kinetic energy as heat through electromagnetic damping. A model of the inertial, stiffness and damping properties is presented along with the characteristic differential equations describing the coupled response of the actuator and structure. The equations, employing the dynamic coefficients, are oriented in the form of a feedback control network in which distributed sensors are used to dictate actuator response leading to a specified amount of structural excitation or damping.
Linear control strategies for damping of flexible structures
DEFF Research Database (Denmark)
Høgsberg, Jan Riess; Krenk, Steen
2006-01-01
Starting from the two-component representation technique for damping of structures the possible increase in damping efficiency obtained by introducing collocated active damping is illustrated. The two-component representation of the damped vibration mode is constructed as a linear combination of ...
Fluid Surface Damping: A Technique for Vibration Suppression of Beams
Directory of Open Access Journals (Sweden)
Hany Ghoneim
1997-01-01
Full Text Available A fluid surface damping (FSD technique for vibration suppression of beamlikestructures is proposed. The technique is a modification of the surface layer damping method. Two viscoelastic surface layers containing fluid-filled cavities are attached symmetrically to the opposite surfaces of the beam. The cavities on one side are attached to the corresponding cavities on the other side via connection passages. As the beam vibrates, the fluid is pumped back and forth through the connecting passages. Therefore, in addition to the viscoelastic damping provided by the surface layers, the technique offers viscous damping due to the fluid flow through the passage. A mathematical model for the proposed technique is developed, normalized, and solved in the frequency domain to investigate the effect of various parameters on the vibration suppression of a cantilever beam. The steady-state frequency response for a base white-noise excitation is calculated at the beam's free tip and over a frequency range containing the first five resonant frequencies. The parameters investigated are the flow-through passage viscous resistance, the length and location of the layers, the hydraulic capacitance of the fluid-filled cavities, and inertia of the moving fluid (hydraulic inertance. Results indicate that the proposed technique has promising potential in the field of vibration suppression of beamlike structures. With two FSD elements, all peak vibration amplitudes can be well suppressed over the entire frequency spectrum studied.
Shunted Piezoelectric Vibration Damping Analysis Including Centrifugal Loading Effects
Min, James B.; Duffy, Kirsten P.; Provenza, Andrew J.
2011-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue problems which require damping treatments to mitigate vibration levels. One method is the use of piezoelectric materials as passive or active dampers. Based on the technical challenges and requirements learned from previous turbomachinery rotor blades research, an effort has been made to investigate the effectiveness of a shunted piezoelectric for the turbomachinery rotor blades vibration control, specifically for a condition with centrifugal rotation. While ample research has been performed on the use of a piezoelectric material with electric circuits to attempt to control the structural vibration damping, very little study has been done regarding rotational effects. The present study attempts to fill this void. Specifically, the objectives of this study are: (a) to create and analyze finite element models for harmonic forced response vibration analysis coupled with shunted piezoelectric circuits for engine blade operational conditions, (b) to validate the experimental test approaches with numerical results and vice versa, and (c) to establish a numerical modeling capability for vibration control using shunted piezoelectric circuits under rotation. Study has focused on a resonant damping control using shunted piezoelectric patches on plate specimens. Tests and analyses were performed for both non-spinning and spinning conditions. The finite element (FE) shunted piezoelectric circuit damping simulations were performed using the ANSYS Multiphysics code for the resistive and inductive circuit piezoelectric simulations of both conditions. The FE results showed a good correlation with experimental test results. Tests and analyses of shunted piezoelectric damping control, demonstrating with plate specimens, show a great potential to reduce blade vibrations under centrifugal loading.
Structural Damping with Friction Beams
Directory of Open Access Journals (Sweden)
L. Gaul
2008-01-01
Full Text Available In the last several years, there has been increasing interest in the use of friction joints for enhancing damping in structures. The joints themselves are responsible for the major part of the energy dissipation in assembled structures. The dissipated work in a joint depends on both the applied normal force and the excitation force. For the case of a constant amplitude excitation force, there is an optimal normal force which maximizes the damping. A ‘passive’ approach would be employed in this instance. In most cases however, the excitation force, as well as the interface parameters such as the friction coefficient, normal pressure distribution, etc., are not constant. In these cases, a ‘semi-active’ approach, which implements an active varying normal force, is necessary. For the ‘passive’ and ‘semi-active’ approaches, the normal force has to be measured. Interestingly, since the normal force in a friction joint influences the local stiffness, the natural frequencies of the assembled structure can be tuned by adjusting the normal force. Experiments and simulations are performed for a simple laboratory structure consisting of two superposed beams with friction in the interface. Numerical simulation of the friction interface requires non-linear models. The response of the double beam system is simulated using a numerical algorithm programmed in MATLAB which models point-to-point friction with the Masing friction model. Numerical predictions and measurements of the double beam free vibration response are compared. A practical application is then described, in which a friction beam is used to damp the vibrations of the work piece table on a milling machine. The increased damping of the table reduces vibration amplitudes, which in turn results in enhanced surface quality of the machined parts, reduction in machine tool wear, and potentially higher feed rates. Optimal positioning of the friction beams is based on knowledge of the mode
Directory of Open Access Journals (Sweden)
Tai-Hong Cheng
2015-01-01
Full Text Available Composite materials are increasingly used in wind blade because of their superior mechanical properties such as high strength-to-weight and stiffness-to-weight ratio. This paper presents vibration and damping analysis of fiberreinforced composite wind turbine blade with viscoelastic damping treatment. The finite element method based on full layerwise displacement theory was employed to analyze the damping, natural frequency, and modal loss factor of composite shell structure. The lamination angle was considered in mathematical modeling. The curved geometry, transverse shear, and normal strains were exactly considered in present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The frequency response functions of curved composite shell structure and wind blade were calculated. The results show that the damping ratio of viscoelastic layer is found to be very sensitive to determination of magnitude of composite structures. The frequency response functions with variety of thickness of damping layer were investigated. Moreover, the natural frequency, modal loss factor, and mode shapes of composite fiber reinforced wind blade with viscoelastic damping control were calculated.
Vibration damping using a spiral acoustic black hole.
Lee, Jae Yeon; Jeon, Wonju
2017-03-01
This study starts with a simple question: can the vibration of plates or beams be efficiently reduced using a lightweight structure that occupies a small space? As an efficient technique to damp vibration, the concept of an acoustic black hole (ABH) is adopted with a simple modification of the geometry. The original shape of an ABH is a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral. In numerical simulations, the damping performance increases as the arc length of the Archimedean spiral increases, regardless of the curvature of the spiral in the mid- and high-frequency ranges. Adding damping material to an ABH can also strongly enhance the damping performance while not significantly increasing the weight. In addition, the radiated sound power of a spiral ABH is similar to that of a standard ABH.
Damping heat coefficient - Theoretical and experimental research on a vibrating beam
Mihalec, Marko; Javh, Jaka; Cianetti, Filippo; Moretti, Michele; Rossi, Gianluca; Slavič, Janko; Boltežar, Miha
2017-07-01
Vibrating systems dissipate their vibrational energy through different mechanisms, commonly referred to as damping. Damping converts the vibrational energy into other forms, such as heat and sound radiation. Heating of the material is often assumed to be one of the biggest drains of energy; however, the measurable temperature increase is at the level of milli Kelvin and hard to measure. This research introduces a damping heat coefficient, the coefficient of total dissipated energy that is converted into heat. Using this coefficient, the expected temperature change of a beam is theoretically related to its damping ratio. In addition, the damping heat coefficient is determined experimentally by measuring the temperature increase of a vibrating beam. Based on modal damping, it is shown that different amounts of energy are dissipated at different parts of the structure. The numerical heat model was experimentally confirmed.
Razzaq, Zia; Mykins, David W.
1987-01-01
Potential passive damping concepts for use in space structures are identified. The effectiveness of copper brush, wool swab, and silly putty in chamber dampers is investigated through natural vibration tests on a tubular aluminum member. The member ends have zero translation and possess partial rotational restraints. The silly putty in chamber dampers provide the maximum passive damping efficiency. Forced vibration tests are then conducted with one, two, and three damper chambers containing silly putty. Owing to the limitation of the vibrator used, the performance of these dampers could not be evaluated experimentally until the forcing function was disengaged. Nevertheless, their performance is evaluated through a forced dynamic finite element analysis conducted as a part of this investigation. The theoretical results based on experimentally obtained damping ratios indicate that the passive dampers are considerably more effective under member natural vibration than during forced vibration. Also, the maximum damping under forced vibration occurs at or near resonance.
Damping of Torsional Beam Vibrations by Control of Warping Displacement
DEFF Research Database (Denmark)
Høgsberg, Jan Becker; Hoffmeyer, David; Ejlersen, Christian
2016-01-01
Supplemental damping of torsional beam vibrations is considered by viscous bimoments acting on the axial warping displacement at the beam supports. The concept is illustrated by solving the governing eigenvalue problem for various support configurations with the applied bimoments represented...
Damping and energy dissipation in soft tissue vibrations during running.
Khassetarash, Arash; Hassannejad, Reza; Enders, Hendrik; Ettefagh, Mir Mohammad
2015-01-21
It has been well accepted that the vibrations of soft tissue cannot be simulated by a single sinusoidal function. In fact, these vibrations are a combination of several vibration modes. In this study, these modes are extracted applying a recently developed method namely, partly ensemble empirical mode decomposition (PEEMD). Then, a methodology for estimating the damping properties and energy dissipation caused by damping for each mode is used. Applying this methodology on simulated signals demonstrates high accuracy. This methodology is applied to the acceleration signals of the gastrocnemius muscle during sprinting and the differences between the damping properties of different vibration modes were identified. The results were 1) the damping property of high-frequency mode was higher than that for low-frequency modes. 2) All identified modes were in under damped condition, therefore, the vibrations had an oscillatory nature. 3) The damping ratios of lower modes are about 100% increased compared to higher modes. 4) The energy dissipation occurred in lower modes were much more than that for higher mode; According to the power spectrum of the ground reaction force (GRF), which is the input force into the body, the recent finding supports the muscle tuning paradigm. It is suggested that the damping properties and energy dissipation can be used to distinguish between different running conditions (surface, fatigue, etc.). Copyright © 2014 Elsevier Ltd. All rights reserved.
Choudhary, Nitin; Kaur, Davinder
2015-03-01
The present review explores an overall view of the vibration damping materials ranging from traditionally used viscoelastic materials for macroscale damping to hybrid thin film heterostructures for micro-electro-mechanical systems (MEMS). Vibration damping materials like rubbers, polymers, metals, metal-matrix composites and smart materials are reviewed in terms of damping capacity, stiffness, mechanical strength and figure of merit. Nanoscale shape memory alloys, piezoelectric materials, carbon nanotubes, their composites and thin films are promising materials for future nanoscale damping devices. The main focus of this article is on our development of new vibration damping approach for MEMS structures comprising of ferroelastic/ferroelastic thin film heterostructures. For the first time, nanoindentation has been explored as an alternative tool to evaluate the damping capability of actual components (e.g., thin films for MEMS) where production of dynamic mechanical analyzer (DMA) test samples is not feasible. A comprehensive insight on the existing vibration damping materials and our new approach would definitely trigger some important applications in nano- and micro-electro-mechanical systems.
Damping element for reducing the vibration of an airfoil
Campbell, Christian X; Marra, John J
2013-11-12
An airfoil (10) is provided with a tip (12) having an opening (14) to a center channel (24). A damping element (16) is inserted within the opening of the center channel, to reduce an induced vibration of the airfoil. The mass of the damping element, a spring constant of the damping element within the center channel, and/or a mounting location (58) of the damping element within the center channel may be adjustably varied, to shift a resonance frequency of the airfoil outside a natural operating frequency of the airfoil.
Uniform stability of damped nonlinear vibrations of an elastic string
Indian Academy of Sciences (India)
Here we are concerned about uniform stability of damped nonlinear transverse vibrations of an elastic string fixed at its two ends. The vibrations governed by nonlinear integro-differential equation of Kirchoff type, is shown to possess energy uniformly bounded by exponentially decaying function of time. The result is ...
Uniform stability of damped nonlinear vibrations of an elastic string
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
Abstract. Here we are concerned about uniform stability of damped nonlinear trans- verse vibrations of an elastic string fixed at its two ends. The vibrations governed by nonlinear integro-differential equation of Kirchoff type, is shown to possess energy uni- formly bounded by exponentially decaying function of time.
Research overview on vibration damping of mistuned bladed disk assemblies
Directory of Open Access Journals (Sweden)
Liang ZHANG
2016-04-01
Full Text Available Bladed disk assemblies are very important parts in auto engine and gas turbine, and is widely used in practical engineering. The mistuning existing commonly in the bladed disk assemblies can destroy the vibration characteristics of the bladed disk assemblies, which is one of the reasons for the high cycle fatigue failure of bladed disk assemblies, so it is necessary to research how to reduce the vibration of the bladed disk assemblies. On the basis of the review of relevant research at home and abroad, the mistuning vibration mechanism of the bladed disk assemblies is introduced, and the main technical methods of the vibration damping of bladed disk assemblies are reviewed, such as artificially active mistuning, collision damping, friction damping and optimization of the blade position. Some future research directions are presented.
Fractal Theory and Contact Dynamics Modeling Vibration Characteristics of Damping Blade
Directory of Open Access Journals (Sweden)
Ruishan Yuan
2014-01-01
Full Text Available The contact surface structure of dry friction damper is complicate, irregular, and self-similar. In this paper, contact surface structure is described with the fractal theory and damping blade is simplified as 2-DOF cantilever beam model with lumped masses. By changing the position of the damper, lacing and shroud structure are separately simulated to study vibration absorption effect of damping blade. The results show that both shroud structure and lacing could not only dissipate energy but also change stiffness of blade. Under the same condition of normal pressure and contact surface, the damping effect of lacing is stronger than that of shroud structure. Meanwhile, the effect on changing blade stiffness of shroud structure is stronger than that of lacing. This paper proposed that there is at least one position of the blade, at which the damper dissipates the most vibration energy during a vibration cycle.
Vibration Analysis of Cylindrical Sandwich Aluminum Shell with Viscoelastic Damping Treatment
Directory of Open Access Journals (Sweden)
Tai-Hong Cheng
2013-01-01
Full Text Available This paper has applied the constrained viscoelastic layer damping treatments to a cylindrical aluminum shell using layerwise displacement theory. The transverse shear, the normal strains, and the curved geometry are exactly taken into account in the present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The damped natural frequencies, modal loss factors, and frequency response functions of cylindrical viscoelastic aluminum shells are compared with those of the base thick aluminum panel without a viscoelastic layer. The thickness and damping ratio of the viscoelastic damping layer, the curvature of proposed cylindrical aluminum structure, and placement of damping layer of the aluminum panel were investigated using frequency response function. The presented results show that the sandwiched viscoelastic damping layer can effectively suppress vibration of cylindrical aluminum structure.
1986-08-01
jBfr 5? JOR JS T SIONAL/lBRATIONjerF^EAR-RANCHED PROPULSION.gVSTEMS j... 117 / H.F. Tavares, Cepstrum Engenharia Ltda., Rio de Janeiro, Brazil and V...MODELLING IN FINITE ELEMENT ANALYSES OF TORSIONAL VIBRATION OF GEAR-BRANCHED PROPULSION SYSTEMS H. F. Tavares Cepstrum Engenharia Ltda. S8o Paulo
System Reduction and Damping of Flexible Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Riess; Krenk, Steen
2007-01-01
An increasing number of flexible structures such as cable-stayed bridges, pedestrian bridges and high-rise buildings are fitted with local dampers to mitigate vibration problems. In principle the effect of local dampers can be analyzed by use of complex modes, e.g. in conjunction with an averaging...... technique for local linearization of the damper characteristics. However, the complex mode shapes and frequencies depend on the magnitude of the damper and therefore are less suitable for design of the damper system. An efficient alternative consists in the use of a two-component representation...... of the damped modes of the structure. The idea is to represent the damped mode as a linear combination of the modes that occur in two distinctly different situations representing extreme conditions: the mode shape of the structure without the damper(s), and the mode shape of the structure, when the damper...
New Damped-Jerk trajectory for vibration reduction
BEAREE, Richard
2014-01-01
This paper derives a jerk-shaped profile to address the vibration reduction of underdamped flexible dynamics of motion system. The jerk-limited profile is a widespread smooth command pattern used by modern motion systems. The ability of the jerk-limited profile to cancel the residual vibration of an undamped flexible mode is clearly explained using an equivalent continuous filter representation and the input shaping formalism. This motivates the design of a new jerk-shaped profile, named Damp...
DEFF Research Database (Denmark)
Bajrić, Anela; Høgsberg, Jan Becker; Rüdinger, Finn
2018-01-01
Reliable predictions of the lifetime of offshore wind turbine structures are influenced by the limited knowledge concerning the inherent level of damping during downtime. Error measures and an automated procedure for covariance driven Operational Modal Analysis (OMA) techniques has been proposed...... techniques are discussed and illustrated with respect to signal noise, measurement time, vibration amplitudes and stationarity of the ambient response. The best bias-variance error trade-off of damping estimates is obtained by the COV-SSI. The proposed automated procedure is validated by real vibration...
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....
Identification of Light Damping in Structures
DEFF Research Database (Denmark)
Jensen, J. L.; Brincker, Rune; Rytter, A.
1990-01-01
Different methods to identification of linear and nonlinear damping in lightly damped structures are discussed in this paper. The discussion is based on experiments with a 4 meter high monopile. Two alternative methods have been used for experimental cases of linear and nonlinear damping. Method 1...... case was a naturally damped monopile which was considered to be linear viscous damped. The second case was nonlinear viscous damping of the monopile due to a mounted damper on the monopile. The two cases illustrates identification of lightly damping in the linear and nonlinear case....
Identification of Light Damping in Structures
DEFF Research Database (Denmark)
Jensen, Jacob Laigaard; Brincker, Rune; Rytter, Anders
Different methods to identification of linear and nonlinear damping in lightly damped structures are discussed in this paper. The discussion is based on experiments with a 4 meter high monopile. Two alternative methods have been used for experimental cases of linear and nonlinear damping. Method 1...... case was a naturally damped monopile which was considered to be linear viscous damped. The second case was nonlinear viscous damping of the monopile due to a mounted damper on the monopile. The two cases illustrate identification of lightly damping in the linear and the nonlinear case....
High Frequency Longitudinal Damped Vibrations of a Cylindrical Ultrasonic Transducer
Directory of Open Access Journals (Sweden)
Mihai Valentin Predoi
2014-01-01
Full Text Available Ultrasonic piezoelectric transducers used in classical nondestructive testing are producing in general longitudinal vibrations in the MHz range. A simple mechanical model of these transducers would be very useful for wave propagation numerical simulations, avoiding the existing complicated models in which the real components of the transducer are modeled by finite elements. The classical model for longitudinal vibrations is not adequate because the generated longitudinal wave is not dispersive, the velocity being the same at any frequency. We have adopted the Rayleigh-Bishop model, which avoids these limitations, even if it is not converging to the first but to the second exact longitudinal mode in an elastic rod, as obtained from the complicated Pochhammer-Chree equations. Since real transducers have significant vibrations damping, we have introduced a damping term in the Rayleigh-Bishop model, increasing the imaginary part and keeping almost identical real part of the wavenumber. Common transducers produce amplitude modulated signals, completely attenuated after several periods. This can be modeled by two close frequencies, producing a “beat” phenomenon, superposed on the high damping. For this reason, we introduce a two-rod Rayleigh-Bishop model with damping. Agreement with measured normal velocity on the transducer free surface is encouraging for continuation of the research.
Passive damping concepts for free and forced member and grillage vibration
Razzaq, Zia; Najjar, Bassam
1988-01-01
The performance of potential passive damping concepts is investigted for a long tubular aluminum alloy member, and a two-bar grillage structure. The members are restrained partially at the ends and are of the type being considered by NASA for possible use in the construction of a future space station. Four different passive damping concepts are studied and include nylon brush, wool swab, copper brush, and silly putty in chamber dampers. Both free and forced vibration tests are conducted. It is found that the silly putty in chamber damper concept provides considerably greater passive damping as compared to that of the other three concepts. For the grillage natural vibration, a five wool swab damper configuration provides greater damping than the five silly putty dampers in chamber configuration. Due to the constrained motion imposed by the vibrator used in the tests, the effectiveness of the passive dampers could not be adequately evaluated for the individual member. However, it is found that for the grillage under forced vibration, the five silly putty dampers in chamber damper configuration provides very effective passive damping although only at and around the resonant frequency. At resonance, these dampers provide a 51 percent reduction in the dynamic magnification factor for this case.
Active vibration damping using smart material
Baras, John S.; Yan, Zhuang
1994-01-01
We consider the modeling and active damping of an elastic beam using distributed actuators and sensors. The piezoelectric ceramic material (PZT) is used to build the actuator. The sensor is made of the piezoelectric polymer polyvinylidene fluoride (PVDF). These materials are glued on both sides of the beam. For the simple clamped beam, the closed loop controller has been shown to be able to extract energy from the beam. The shape of the actuator and its influence on the closed loop system performance are discussed. It is shown that it is possible to suppress the selected mode by choosing the appropriate actuator layout. It is also shown that by properly installing the sensor and determining the sensor shape we can further extract and manipulate the sensor signal for our control need.
Piezoelectric Vibration Damping Study for Rotating Composite Fan Blades
Min, James B.; Duffy, Kirsten P.; Choi, Benjamin B.; Provenza, Andrew J.; Kray, Nicholas
2012-01-01
Resonant vibrations of aircraft engine blades cause blade fatigue problems in engines, which can lead to thicker and aerodynamically lower performing blade designs, increasing engine weight, fuel burn, and maintenance costs. In order to mitigate undesirable blade vibration levels, active piezoelectric vibration control has been investigated, potentially enabling thinner blade designs for higher performing blades and minimizing blade fatigue problems. While the piezoelectric damping idea has been investigated by other researchers over the years, very little study has been done including rotational effects. The present study attempts to fill this void. The particular objectives of this study were: (a) to develop and analyze a multiphysics piezoelectric finite element composite blade model for harmonic forced vibration response analysis coupled with a tuned RLC circuit for rotating engine blade conditions, (b) to validate a numerical model with experimental test data, and (c) to achieve a cost-effective numerical modeling capability which enables simulation of rotating blades within the NASA Glenn Research Center (GRC) Dynamic Spin Rig Facility. A numerical and experimental study for rotating piezoelectric composite subscale fan blades was performed. It was also proved that the proposed numerical method is feasible and effective when applied to the rotating blade base excitation model. The experimental test and multiphysics finite element modeling technique described in this paper show that piezoelectric vibration damping can significantly reduce vibrations of aircraft engine composite fan blades.
Energy Technology Data Exchange (ETDEWEB)
Lay, A.
2000-07-01
This thesis deals with the direct velocity feedback (DVF) and the positive position feedback (PPF) two so-called local control strategies (LAC) for active vibration damping of structures. The influence of the dynamics of the components needed for technical realization on the control performance is investigated. Piezoelectric ceramics are used as actuators and sensors. An integral procedure is chosen so the aspects structural mechanics, control theory, measuring technique, the electrical engineering and digital signalprocessing are taken into account, since only the consideration of all components, their characteristics and the their reciprocal interaction leads to an optimal system. For both control strategies the influence of the dynamics of the actuator and sensor amplifiers, the analog lowpass filter and the digitization is investigated. The investigations show that it is absolutely necessary to consider the dynamics of the components. Otherwise DVF can only be used restrictively. Using PPF, these additional dynamics limit the parameters during the control design. The investigations further show, that knowing the poles and the zeros of the structure is of crucial importance. The results of the investigations are collected in guidelines choosing the components and the control design, respectively. The experiments corroborate the investigations and show the potential of the local control strategies. PPF is to be preferred to DVF because of its better robustness against additional dynamics. (orig.) [German] Die vorliegende Arbeit befasst sich mit der Untersuchung des Einflusses der Dynamik der zur technischen Realisierung erforderlichen Komponenten bei der direkten Geschwindigkeitsrueckfuehrung (DVF) und der positiven Postitionsrueckfuehrung (PPF), zwei lokalen Regelungsverfahren zur aktiven Schwingungsdaempfung von Strukturen. Als Aktoren und Sensoren werden piezoelektrische Materialien verwendet. Gewaehlt wird ein integrales Vorgehen, um die Aspekte der
Vibration Control in Periodic Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Becker
2017-01-01
Within the framework of periodic structures, the calibration of RL shunted piezoelectric inclusions is investigated with respect to maximum damping of a particular wave form. A finite element setting is assumed, with local shunted inclusions inside the unit cell. The effect of the shunts is repre....... The presentation contains dispersion diagrams and vibration amplitude curves for the optimally calibrated RL shunt system in a 1-D periodic structure with local piezoelectric inclusions....
Use of electro-magnetic damping for vibration control
DEFF Research Database (Denmark)
Stein, George Juraj; Darula, Radoslav; Sorokin, Sergey
2012-01-01
Vibration of machines is an unwanted phenomenon, and it is usually of interest to eliminate it. There are various means to be used in order to reach the goal, where the utilization of the electromagnet augmented by an external shunt circuit is analyzed in the paper. The magnetic force is used...... to introduce additional electromagnetic damping into vibrating mechanical system. The hysteretic losses and eddy currents are included in the model, to take into account more realistic dynamic behaviour of the system. The mathematical model of the controller is derived using lumped parameter approach...
On Coulomb and Viscosity damped single-degree-of-freedom vibrating systems
DEFF Research Database (Denmark)
Jakobsen, J.; Sivebæk, Ion Marius
2016-01-01
Attention on friction damping mechanisms could be of interest for vibration reduction, and appears therefore to be desirable. Presentations of textbook analyses on mechanical vibration of a viscosity damped single degree system [mass, spring and eventually damping] are numerous. Often they begin...
Suboptimal Rayleigh damping coefficients in seismic analysis of viscously-damped structures
Pan, Danguang; Chen, Genda; Wang, Zuocai
2014-12-01
An optimization method for the consistent evaluation of two Rayleigh damping coefficients is proposed. By minimizing an objective function such as an error term of the peak displacement of a structure, the two coefficients can be determined with response spectral analysis. The optimization method degenerates into the conventional method used in current practices when only two modes of vibration are included in the objective function. Therefore, the proposed method with all significant modes included for simplicity in practical applications results in suboptimal damping coefficients. The effects of both spatial distribution and frequency content of excitations as well as structural dynamic characteristics on the evaluation of Rayleigh damping coefficients were investigated with a five-story building structure. Two application examples with a 62-story high-rise building and a 840 m long cable-stayed bridge under ten earthquake excitations demonstrated the accuracy and effectiveness of the proposed method to account for all of the above effects.
Numerical Investigation of Damping of Torsional Beam Vibrations by Viscous Bimoments
DEFF Research Database (Denmark)
Hoffmeyer, David; Høgsberg, Jan Becker
2017-01-01
Damping of torsional beam vibrations of slender beam–structures with thin–walled cross–sections is investigated. Analytical results from solving the differential equation governing torsion with viscous bimoments imposed at the boundary, are compared with a numerical approach with three......–dimensional, is oparametric elements. The viscous bimoments act on the axial warping displacements associated with in homogeneous torsion, and are in a numerical format realized by suitable configurations of concentrated, axial forces describing discrete dampers.It is illustrated by an example that significant damping ratios...
Free-Vibration Analysis of Structures
Gupta, K. K.
1985-01-01
Improved numerical procedure more than twice as fast as previous methods. Unified numerical algorithm efficiently solves free-vibration problems of stationary or spinning structures with or without viscous or structural damping. Algorithm used to solve static problems involving multiple loads and to solve quadratic matrix eigenvalue problems associated with finite-dynamic-element structural discretization.
Vibration damping and heat transfer using material phase changes
Kloucek, Petr [Houston, TX; Reynolds, Daniel R [Oakland, CA
2009-03-24
A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.
Vibration damping and heat transfer using material phase changes
Kloucek, Petr (Inventor); Reynolds, Daniel R. (Inventor)
2009-01-01
A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.
Importance of Added Mass and Damping in Flow-Induced Vibration Analysis of Tubes Bundle: An Overview
Directory of Open Access Journals (Sweden)
Faisal Karim Shami
2012-01-01
Full Text Available Flow-induced vibration is of prime concern to the designers of heat exchangers subjected to high flows of gases or liquids. Excessive vibration may cause tube failure due to fatigue or fretting-wear. Tube failure results in, expensive plant upholding and suffers loss of production. Therefore, tube failure due to unwarranted vibration must be avoided in process heat exchangers and nuclear steam generators, preferably at design stage. Such vibration problems may be avoided through a comprehensive flowinduced vibration analysis before fabrication of heat exchangers. However, it requires an understanding of vibration mechanism and parameters related to flow-induced vibration. For an accurate vibration analysis, it is of prime importance to have good estimates of structural and flow related dynamic parameters. Thus dynamic parameters such as added mass and damping are of significant concern in a flow regime. The purpose of this paper is to provide an overview of our state of knowledge and role of dynamic parameters in flow-induced vibration on tube bundles due to current trend of larger heat exchangers. The present paper provides published data, analysis, evaluation, formulation, and experimental studies related to hydrodynamic mass and damping by a large number of researchers. Guidelines for experimental research and heat exchangers design related to added mass and damping mechanisms subjected to both single and two-phase flow are outlined in this paper.
Biffi, Carlo Alberto; Bassani, P.; Tuissi, A.; Carnevale, M.; Lecis, N.; LoConte, A.; Previtali, B.
2012-12-01
Shape memory alloys (SMAs) are very interesting smart materials not only for their shape memory and superelastic effects but also because of their significant intrinsic damping capacity. The latter is exhibited upon martensitic transformations and especially in martensitic state. The combination of these SMA properties with the mechanical and the lightweight of fiberglass-reinforced polymer (FGRP) is a promising solution for manufacturing of innovative composites for vibration suppression in structural applications. CuZnAl sheets, after laser patterning, were embedded in a laminated composite between a thick FGRP core and two thin outer layers with the aim of maximizing the damping capacity of the beam for passive vibration suppression. The selected SMA Cu66Zn24Al10 at.% was prepared by vacuum induction melting; the ingot was subsequently hot-and-cold rolled down to 0.2 mm thickness tape. The choice of a copper alloy is related to some advantages in comparison with NiTiCu SMA alloys, which was tested for the similar presented application in a previous study: lower cost, higher storage modulus and consequently higher damping properties in martensitic state. The patterning of the SMA sheets was performed by means of a pulsed fiber laser. After the laser processing, the SMA sheets were heat treated to obtain the desired martensitic state at room temperature. The transformation temperatures were measured by differential scanning calorimetry (DSC). The damping properties were determined, at room temperature, on full-scale sheet, using a universal testing machine (MTS), with cyclic tensile tests at different deformation amplitudes. Damping properties were also determined as a function of the temperature on miniature samples with a dynamical mechanical analyzer (DMA). Numerical modeling of the laminated composite, done with finite element method analysis and modal strain energy approaches, was performed to estimate the corresponding total damping capacity and then
Piezoelectric RL shunt damping of flexible structures
DEFF Research Database (Denmark)
Høgsberg, Jan Becker; Krenk, Steen
2015-01-01
Resonant RL shunt circuits represent a robust and effective approach to piezoelectric damping, provided that the individual shunt circuit components are calibrated accurately with respect to the dynamic properties of the corresponding flexible structure. The balanced calibration procedure applied...
Nonlinear Vibration Characteristics of a Flexible Blade with Friction Damping due to Tip-Rub
Directory of Open Access Journals (Sweden)
Dengqing Cao
2011-01-01
Full Text Available An approximate approach is proposed in this paper for analyzing the two-dimensional friction contact problem so as to compute the dynamic response of a structure constrained by friction interfaces due to tip-rub. The dynamical equation of motion for a rotational cantilever blade in a centrifugal force field is established. Flow-induced distributed periodic forces and the internal material damping in the blade are accounted for in the governing equation of motion. The Galerkin method is employed to obtain a three-degree-of-freedom oscillator with friction damping due to tip-rub. The combined motion of impact and friction due to tip-rub produced a piecewise linear vibration which is actually nonlinear. Thus, a complete vibration cycle is divided into successive intervals. The system possesses linear vibration characteristic during each of these intervals, which can be determined using analytical solution forms. Numerical simulation shows that the parameters such as gap of the tip and the rotational speed of the blades have significant effects on the dynamical responses of the system. Finally, the nonlinear vibration characteristics of the blade are investigated in terms of the Poincare graph, and the frequency spectrum of the responses and the amplitude-frequency curves.
DEFF Research Database (Denmark)
Thomsen, Bo; Hansen, Mikkel Bo; Seidler, Peter
2012-01-01
We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. T...
Damping Effects in Aerospace Structures
1979-10-01
dapeadeat «a the applied damping values. Incorrect daoping values m^ lead to an inpropcr desigo. CoUeetioB and evaluation of available wmavanA...23) (24) Ref. [36] n b^ rr a Z , r rk (a Z ^ s rk arV < E rk u b r rr (25) where: y is the oodal daoping factor t> /2üI and e is a
Active Damping of Vibrations in High-Precision Motion Systems
Babakhani, B.
2012-01-01
Technology advancements feed the need for ever faster and more accurate industrial machines. Vibration is a significant source of inaccuracy of such machines. A light-weight design in favor of the speed, and avoiding the use of energy-dissipating materials from the structure to omit any source of
CLIC Waveguide Damped Accelerating Structure Studies
Dehler, M; Wuensch, Walter
1996-01-01
Studies of waveguide damped 30 GHz accelerating structures for multibunching in CLIC are described. Frequency discriminated damping using waveguides with a lowest cutoff frequency above the fundamental but below the higher order modes was considered. The wakefield behavior was investigated using time domain MAFIA computations over up to 20 cells and for frequencies up to 150 GHz. A configuration consisting of four T-cross-sectioned waveguides per cell reduces the transverse wake below 1% at typical CLIC bunch spacings.
Structural dynamic modification using additive damping
Indian Academy of Sciences (India)
In order to control dynamic response in structures and machines, modofications using additive viscoelastic damping materials are highlighted. The techniques described for analysis include analytical methods for structural elements, FEM and perturbation methods for reanalysis or structural dynamic modifications for ...
Chen, Shao-Tuan; Du, Sijun; Arroyo, Emmanuelle; Jia, Yu; Seshia, Ashwin
2017-10-01
This paper presents a novel application of utilising nonlinear air damping as a soft mechanical stopper to increase the shock reliability for microelectromechanical systems (MEMS) vibration energy harvesters. The theoretical framework for nonlinear air damping is constructed for MEMS vibration energy harvesters operating in different air pressure levels, and characterisation experiments are conducted to establish the relationship between air pressure and nonlinear air damping coefficient for rectangular cantilever MEMS micro cantilevers with different proof masses. Design guidelines on choosing the optimal air pressure level for different MEMS vibration energy harvesters based on the trade-off between harvestable energy and the device robustness are presented, and random excitation experiments are performed to verify the robustness of MEMS vibration energy harvesters with nonlinear air damping as soft stoppers to limit the maximum deflection distance and increase the shock reliability of the device.
Passive damping concepts for slender columns in space structures
Razzaq, Z.; Ekhelikar, R. K.
1985-01-01
An experimental and theoretical study of three different passive damping concepts is conducted for a slender member with partial rotational end restraints. Over a hundred full-scale natural vibration experiments were conducted to evaluate the effectiveness of mass-string, polyethylene tubing, and chain damping concepts. The damping properties obtained from the experiments were used in the approximate analyses based on the partial differential equation of motion for the problem. The comparison of the experimental and the theoretical deflection-time relations shows that the velocity-dependent damping model used in the theory is adequate. From the experimental results, the effect of end connection friction and induced axial forces on damping is identified. The definition of an efficiency index is proposed based on the damping ratio and the mass of a given passive damping device. Using this definition, the efficiencies of the three damping devices are compared. The polyethylene tubing concept resulted into a low damping efficiency.
Directory of Open Access Journals (Sweden)
Susilo Adi Widyanto
2013-06-01
Full Text Available Stiffness and vibration damping capability are important criteria in design of machine tool structure. In other sides, the weight of machine tool structure must be reduced to increase the handling capability. This paper presents an analysis of the effect of geometric structure on stiffness and vibration damping of wood structure. The stiffness was analysed using numerical method, so called finite element method (FEM, while the vibration damping capability was experimentally tested. Vibration testing was also performed to wood structures with sand powder filled into its rectangular hole to observe the its effect on damping factor. Simulation results show that the cross ribs structure yielded minimum mass reduction ratio compared to the three square holes as well as the single rectangular hole structures. While the vibration test results explained that the damping factor of Shorea laevis wood was higher than that Hevea braziiensis wood. The use of sand powder as vibrating mass in closed-box structure effectively increased the damping capability, for single rectangular hole structure the damping factor was increased from 0.048 to 0.079doi: http://dx.doi.org/10.12777/ijse.4.2.2013.57-60[How to cite the article: Widyanto, S. A., Widodo, A., Nugroho, S., & Siahaan, D. (2013. The effect of geometric structure on stiffness and damping factor of wood applicable to machine tool structure. INTERNATIONAL JOURNAL OF SCIENCE AND ENGINEERING, 4(2, 57-60. doi: http://dx.doi.org/10.12777/ijse.4.2.2013.57-60
Damping mechanisms and models in structural dynamics
DEFF Research Database (Denmark)
Krenk, Steen
2002-01-01
Several aspects of damping models for dynamic analysis of structures are investigated. First the causality condition for structural response is used to identify rules for the use of complex-valued frequency dependent material models, illustrated by the shortcomings of the elastic hysteretic model...
Semi-active on-off damping control of a dynamic vibration absorber using Coriolis force
La, Viet Duc
2012-07-01
A passive dynamic vibration absorber (DVA) moving along a pendulum can cause the nonlinear Coriolis damping to reduce the pendulum swing. This paper proposes a simple semi-active on-off damping controller to improve the passive Coriolis DVA. The aim of the on-off damping control is to amplify the DVA resonance motion to increase the energy dissipated. Moreover, the paper finds the analytical solution of the harmonic vibration of semi-active controlled system. The accuracy of the analytical formulas and the superior performance of the semi-active DVA are verified by numerical simulations.
Dynamic damping of vibrations of technical object with two degrees of freedom
Khomenko, A. P.; Eliseev, S. V.; Artyunin, A. I.
2017-10-01
Approach to the solution of problems of dynamic damping for the technical object with two degrees of freedom on the elastic supports is developed. Such tasks are typical for the dynamics of technological vibrating machines, machining machine tools and vehicles. The purpose of the study is to justify the possibility of obtaining regimes of simultaneous dynamic damping of oscillations in two coordinates. The achievement of the goal is based on the use of special devices for the transformation of motion, introduced parallel to the elastic element. The dynamic effect is provided by the possibility of changing the relationships between the reduced masses of devices for transforming motion. The method of structural mathematical modeling is used, in which the mechanical oscillatory system is compared, taking into account the principle of dynamic analogies, the dynamically equivalent structural diagram of the automatic control system. The concept of transfer functions of systems interpartial relations and generalized ideas about the partial frequencies and frequencies dynamic damping is applied. The concept of a frequency diagram that determines the mutual distribution of graphs of frequency characteristics in the interaction of the elements of the system is introduced.
Vibration absorption in systems with a nonlinear energy sink: Nonlinear damping
Starosvetsky, Y.; Gendelman, O. V.
2009-07-01
In this work, response regimes are investigated in a system comprising of a linear oscillator (subject to harmonic excitation) and a nonlinear energy sink (NES) with nonlinear damping characteristics. An analytical technique for the treatment of certain class of nonlinear damping functions is developed. Special attention is paid to the case of piecewise-quadratic damping, motivated by possible applications. It is demonstrated that the NES with a properly tuned piecewise-quadratic damping element allows complete elimination of undesirable periodic regimes. In this way, an efficient system of vibration absorption is obtained, and its performance can overcome that of a tuned mass damper (TMD). Numerical results agree satisfactorily with the analytical predictions.
Removing damped sinusoidal vibrations in adaptive optics systems using a DFT-based estimation method
Kania, Dariusz
2017-06-01
The problem of a vibrations rejection in adaptive optics systems is still present in publications. These undesirable signals emerge because of shaking the system structure, the tracking process, etc., and they usually are damped sinusoidal signals. There are some mechanical solutions to reduce the signals but they are not very effective. One of software solutions are very popular adaptive methods. An AVC (Adaptive Vibration Cancellation) method has been presented and developed in recent years. The method is based on the estimation of three vibrations parameters and values of frequency, amplitude and phase are essential to produce and adjust a proper signal to reduce or eliminate vibrations signals. This paper presents a fast (below 10 ms) and accurate estimation method of frequency, amplitude and phase of a multifrequency signal that can be used in the AVC method to increase the AO system performance. The method accuracy depends on several parameters: CiR - number of signal periods in a measurement window, N - number of samples in the FFT procedure, H - time window order, SNR, THD, b - number of A/D converter bits in a real time system, γ - the damping ratio of the tested signal, φ - the phase of the tested signal. Systematic errors increase when N, CiR, H decrease and when γ increases. The value of systematic error for γ = 0.1%, CiR = 1.1 and N = 32 is approximately 10^-4 Hz/Hz. This paper focuses on systematic errors of and effect of the signal phase and values of γ on the results.
Perlík, Václav; Šanda, František
2017-08-01
We present a computational model for the spectra of molecular aggregates with signatures of vibronic progression. Vibronic dynamics is implemented by coupling the dynamics of Frenkel excitons with underdamped vibrations. Vibrational dynamics includes linear damping resulting in the exponential decay and quadratic damping inducing subexponential or power law relaxation and increasing vibrational decoherence as demonstrated on lineshapes of the absorption spectrum. Simulations of the third-order coherent response account for bath reorganization during excitonic transport, which allows us to study the line-shape evolution of cross peaks of 2D spectra.
Unimodal optimal passive electromechanical damping of elastic structures
Ben Mekki, O.; Bourquin, F.; Maceri, F.; Merliot, E.
2013-08-01
In this paper, a new electromechanical damper is presented and used, made of a pendulum oscillating around an alternator axis and connected by a gear to the vibrating structure. In this way, the mechanical energy of the oscillating mass can be transformed into electrical energy to be dissipated when the alternator is branched on a resistor. This damping device is intrinsically non-linear, and the problem of the optimal parameters and of the best placement of this damper on the structure is studied. The optimality criterion chosen here is the maximum exponential time decay rate (ETDR) of the structural response. This criterion leads to new design formulas. The case of a bridge under construction is considered and the analytical results are compared with experimental ones, obtained on a mock-up made of a vertical tower connected to a free-end horizontal beam, to simulate the behavior of a cable-stayed bridge during the erection phase. Up to three electromechanical dampers are placed in order to study the multi-modal damping. The satisfactory agreement between the theoretical model and the experiments suggests that a multi-modal passive damping of electromagnetic type could be effective on lightweight flexible structures, when dampers are suitably placed.
Directory of Open Access Journals (Sweden)
Caiyou Zhao
2015-01-01
Full Text Available A promising means of reducing railway noise is to increase the damping of the rail, which decreases the vibration of the rail to reduce noise. To achieve this goal, a slotted stand-off layer damping treatment has been developed, and a compound track model with this treatment is developed for investigating the effectiveness of this treatment in terms of the vibration reduction. Through the dynamic analysis of the track undergoing the slotted stand-off layer damping treatment, some guidelines are proposed on the selection of materials and structure parameters for this treatment. In addition, the prototype of the optimal slotted stand-off layer damping treatment has been built and tested in the laboratory. It is found that the slotted stand-off damping treatment shows significant effects in decreasing the amplitude of the accelerance of the rail and a significant reduction of sound emission reflected as the radiation sound pressure level decreases by 8.2 and 9.4 dB at vertical excitation and lateral excitation, respectively, in the frequency range of 0–4000 Hz.
Miller, G.; Heimann, Paula J.; Scheiman, Daniel A.; Duffy, Kirsten P.; Johnston, J. Chris; Roberts, Gary D.
2013-01-01
Vibration mitigation in composite structures has been demonstrated through widely varying methods which include both active and passive damping. Recently, nanomaterials have been investigated as a viable approach to composite vibration damping due to the large surface available to generate energy dissipation through friction. This work evaluates the influence of dispersed nanoparticles on the damping ratio of an epoxy matrix. Limited benefit was observed through dispersion methods, however nanoparticle application as a coating resulting in up to a three-fold increase in damping.
Two methods for damping torsional vibrations in DFIG-based wind generators using power converters
Zhao, Zuyi; Lu, Yupu; Xie, Da; Yu, Songtao; Wu, Wangping
2017-01-01
This paper proposes novel damping control algorithms by using static synchronous compensator (STATCOM) and energy storage system (ESS) to damp torsional vibrations in doubly fed induction generator (DFIG) based wind turbine systems. It first analyses the operating characteristics of STATCOM and ESS for regulating power variations to increase grid voltage stability. Then, new control strategies for STATCOM and ESS are introduced to damp the vibrations. It is followed by illustration of their effectiveness to damp the drive train torsional vibrations of wind turbines, which can be caused by grid disturbances, such as voltage sags and frequency fluctuations. Results suggest that STATCOM is a promising technology to mitigate the torsional vibrations caused by grid voltage sags. By contrast, the ESS connected to the point of common coupling (PCC) of wind turbine systems shows even obvious advantages because of its capability of absorbing/releasing both active and reactive power. It can thus be concluded that STATCOM is useful for stabilizing power system voltage fluctuations, and ESS is more effective both in regulating PCC voltage fluctuations and damping torsional vibrations caused by grid voltage frequency fluctuations.
A tapered damped accelerating structure for CLIC
Dehler, M; Wuensch, Walter
1998-01-01
A new 30 GHz multibunch accelerating structure incorporating both damping and detuning has been designed for the Compact LInear Collider (CLIC). Each cell of the 150-cell structure is damped by its ow n set of four radial waveguides resulting in a Q of 16 for the lowest dipole mode. A simple linear taper of the beam-pipe dimension provides a detuning frequency spread of 2 GHz (5.4%). Predictions of the transverse wakefield levels in this structure have been made using both uncoupled, and two-band coupled equivalent circuit models with non-perfect loads. The short-range wakefield has been calcula ted to be about 1000 V/(pC.mm.m) decreasing to less than 1% at the second bunch (0.67 ns) and with a long time level below 0.1%.
Fabrication Process of Rounded Damped Detuned Structure
Hitomi, N; Higashi, Y; Higo, T; Koike, S; Suzuki, T; Takata, K; Takatomi, T; Toge, T; Watanabe, Y
2000-01-01
Following the successful design and fabrication of Damped Detuned Structures (DDS), the JLC/NLC linear collider project advanced to Rounded Damped Detuned Structures (RDDS) with curved cross section of the cavity shape for increased shunt impedance. Various advanced techniques for fabricating RDDS1 disks comparing to those for DDS were established to satisfy the dimension accuracy of +-1 micron over the entire surface made by ultra-precision turning. These disks were assembled with almost the same stacking and bonding jigs and processes as those of DDS3 assembly. In consequence, the assembly showed little disk-to-disk misalignment within 1 micron before and after the process. Though, it had 200 micron smooth bowing, which was subsequently corrected as DDS3, and flares at both ends.
Vibration Control of Double-Beam System with Multiple Smart Damping Members
Dominik Pisarski; Tomasz Szmidt; Czesław I. Bajer; Bartłomiej Dyniewicz; Jacek M. Bajkowski
2016-01-01
A control method to stabilize vibration of a double cantilever system with a set of smart damping blocks is designed and numerically evaluated. The externally controlled magnetorheological sheared elastomer damping block is considered, but other smart materials can be used as well. The robust bang-bang control law for stabilization the bilinear system is elaborated. The key feature of the closed loop controller is the efficiency for different types of initial excitement. By employing the fini...
GOES-R Active Vibration Damping Controller Design, Implementation, and On-Orbit Performance
Clapp, Brian R.; Weigl, Harald J.; Goodzeit, Neil E.; Carter, Delano R.; Rood, Timothy J.
2017-01-01
GOES-R series spacecraft feature a number of flexible appendages with modal frequencies below 3.0 Hz which, if excited by spacecraft disturbances, can be sources of undesirable jitter perturbing spacecraft pointing. In order to meet GOES-R pointing stability requirements, the spacecraft flight software implements an Active Vibration Damping (AVD) rate control law which acts in parallel with the nadir point attitude control law. The AVD controller commands spacecraft reaction wheel actuators based upon Inertial Measurement Unit (IMU) inputs to provide additional damping for spacecraft structural modes below 3.0 Hz which vary with solar wing angle. A GOES-R spacecraft dynamics and attitude control system identified model is constructed from pseudo-random reaction wheel torque commands and IMU angular rate response measurements occurring over a single orbit during spacecraft post-deployment activities. The identified Fourier model is computed on the ground, uplinked to the spacecraft flight computer, and the AVD controller filter coefficients are periodically computed on-board from the Fourier model. Consequently, the AVD controller formulation is based not upon pre-launch simulation model estimates but upon on-orbit nadir point attitude control and time-varying spacecraft dynamics. GOES-R high-fidelity time domain simulation results herein demonstrate the accuracy of the AVD identified Fourier model relative to the pre-launch spacecraft dynamics and control truth model. The AVD controller on-board the GOES-16 spacecraft achieves more than a ten-fold increase in structural mode damping of the fundamental solar wing mode while maintaining controller stability margins and ensuring that the nadir point attitude control bandwidth does not fall below 0.02 Hz. On-orbit GOES-16 spacecraft appendage modal frequencies and damping ratios are quantified based upon the AVD system identification, and the increase in modal damping provided by the AVD controller for each structural
Vortex-Induced Vibrations of a Square Cylinder with Damped Free-End Conditions
Directory of Open Access Journals (Sweden)
S. Manzoor
2013-01-01
Full Text Available The authors report the results of vortex-induced vibrations of a square cylinder in a wind tunnel. This constitutes a high mass ratio environment. The square cylinder is mounted in the wind tunnel in such a fashion that it only performs rigid body oscillations perpendicular to the flow direction with damped free-end conditions. This physical situation allows a direct evaluation for analytical models relying on simplified 2D assumptions. The results are also compared with two-dimensional fluid-structure (CFD-CSD numerical simulations. The comparison shows that despite having one-dimensional motion, the analytical model does not predict the VIV region with correctness. Results show that the numerical simulations and experimental results differ from the analytical model for the prediction of reduced velocity corresponding to peak amplitude. Also the analytical reduced velocity envelope is underpredicted compared to both numerical simulations and experimental data despite the structure being lightly damped. The findings are significant as the experimental results for freely oscillating high mass ratio body show differences from the low mass ratio especially in the transition between VIV and galloping regions. However the numerical simulations show comparatively close agreement.
Vibrations of stretched damped beams under non-ideal boundary ...
Indian Academy of Sciences (India)
Stretched beam vibrations; non-ideal boundary conditions; method of multiple time scales. 1. Introduction. Beams are frequently used as design models for vibration analysis. In such analysis, types of support conditions are important and have direct effect on the solutions and natural fre- quencies. Different types of supports ...
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 tuning procedure of the passive tuned mass damper combined with a simple procedure for minimizing the control force is employed for determination of optimum damper parameters and feedback gain values. By time domain simulations conducted in an aeroelastic code, it is demonstrated that the ATMD can...... be used to further reduce the structural response of the wind turbine compared with the passive tuned mass damper and this without an increase in damper mass. A limiting factor of the design of the ATMD is the displacement of the damper mass, which for the ATMD, increases to compensate for the reduction...
Vibration modeling of structural fuzzy with continuous boundary
DEFF Research Database (Denmark)
Friis, Lars; Ohlrich, Mogens
2008-01-01
From experiments it is well known that the vibration response of a main structure with many attached substructures often shows more damping than structural losses in the components can account for. In practice, these substructures, which are not attached in an entirely rigid manner, behave like...... effect of the fuzzy with spatial memory is demonstrated by numerical simulations of a main beam structure with fuzzy attachments. It is shown that the introduction of spatial memory reduces the damping effect of the fuzzy and in certain cases the damping effect may even be eliminated completely....
Vibrations of stretched damped beams under non-ideal boundary ...
Indian Academy of Sciences (India)
A simply supported damped Euler–Bernoulli beam with immovable end conditions are considered. The concept of non-ideal boundary conditions is applied to the beam problem. In accordance, the boundaries are assumed to allow small deﬂections and moments. Approximate analytical solution of the problem is found ...
Comparison of vibration damping of standard and PDCPD housing of the electric power steering system
Płaczek, M.; Wróbel, A.; Baier, A.
2017-08-01
A comparison of two different types of electric power steering system housing is presented. The first considered type of the housing was a standard one that is made of an aluminium alloy. The second one is made of polydicyclopentadiene polymer (PDCPD) and was produced using the RIM technology. Considered elements were analysed in order to verify their properties of vibrations damping. This property is very important taking into account noise generated by elements of a car’s power steering system. During the carried out tests vibrations of analysed power steering housings were measured using Marco Fiber Composite (MFC) piezoelectric transducers. Results obtained for both considered power steering housings in case of the same parameters of vibrations excitations were measured and juxtaposed. Obtained results were analysed in order to verify if the housing made of PDCPD polymer has better properties of vibration damping than the standard one.
Materials for Damping Ambient Acoustic and Vibration Signals Project
National Aeronautics and Space Administration — Long-term exposure to even relatively low levels of acoustic and vibration signals has been shown to be potentially harmful to humans. A new class of piezoelectric...
Optimization of constrained layer damping for strain energy minimization of vibrating pads
Directory of Open Access Journals (Sweden)
Supachai Lakkam1
2012-04-01
Full Text Available An optimization study for brake squeals aims to minimize the strain energy of vibrating pads with constrained layerdamping. To achieve this, using finite element method and experiments were operated and assumed-coupling mode methodwas used to solve it. The integrated global strain energy of the pad over a frequency range of interesting mode was calculated.Parametric studies were then performed to identify those dominant parameters on the vibration response of the damped pad.Moreover, the proposed methodology was employed to search for the optimum of the position/geometry of the constrainedlayer damping patch. Optimal solutions are given and discussed for different cases where the strain energy of the pad over afrequency range is covering the first bending mode and with the inclusion of the restriction of minimum damping materialutilization. As a result, the integrated strain energy is then performed to identify and optimize the position and geometry of thedamping shim. The optimization of the constrained layer damping for strain energy minimization of vibrating pads depend onthe position of the shape of the damping patch. These data can guide to specify the position of the constrained layer dampingpatch under pressure conditions.
Vibration Effects of Nonclassically Damped Building-Piping Systems Subjected to Extreme Loads
Directory of Open Access Journals (Sweden)
YongHee Ryu
2016-01-01
Full Text Available Piping leakage can occur at T-joint, elbows, valves, or nozzles in nuclear power plants and nonnuclear power plants such as petrochemical plants when subjected to extreme loads and such leakage of piping systems can also lead to fire or explosion. For example, leakage of sodium, toxic gases, or nitrogen in hospitals can cause man-made hazards. The primary objective of this research is to understand the vibration effects due to classical/nonclassical damping with building-piping systems under extreme loads. The current evaluation employed finite-element analysis to calculate the effects of the responses of classically and nonclassically damped building-piping systems. Classical and nonclassical damping matrices for a coupled primary-secondary system were developed based on the Rayleigh equation. A total of 10 selected ground motions were applied to single degree of freedom (SDOF primary-SDOF secondary (2-DOF coupled systems in which the ratios of the natural frequencies between the primary and secondary systems ranged between 0.9 and 1.1. It revealed that the vibration effect of nonclassical damping was significant where the natural frequencies of the two systems were nearly tuned. For piping-material nonlinearity, the effects of nonclassical damping on the result forces of piping systems were not significantly different from those of classical damping.
Graphite/Polyurethane Flexible Composites - Mechanical and Vibration Damping Properties
1993-07-01
with an accelerometer. The damping loss factor is determined using either the half power point method or the reverberation time method. Details of the... time and half power point m -.hods. It should be noted that both techniques show similar results with the reverberation time method results less than 10...lower than the half power point method. The reverberation time method results are probably more accurate due to the errors associated in the half
Elfrink, R.; Renaud, M.; Kamel, T.M.; Nooijer, C. de; Jambunathan, M.; Goedbloed, M.; Hohlfeld, D.; Matova, S.; Pop, V.; Caballero, L.; Schaijk, R. van
2010-01-01
This paper describes the characterization of thin-film MEMS vibration energy harvesters based on aluminum nitride as piezoelectric material. A record output power of 85 μW is measured. The parasitic-damping and the energy-harvesting performances of unpackaged and packaged devices are investigated.
Suspended chains damp wind-induced oscillations of tall flexible structures
Reed, W. H., III
1968-01-01
Hanging-chain system, which is a form of impact damper, suppresses wind-induced bending oscillations of tall cylindrical antenna masts. A cluster of chains enclosed in a neoprene shroud is suspended inside the tip of the antenna mast, forming a simple method of damping structural vibrations.
Energy Technology Data Exchange (ETDEWEB)
Thomsen, K.; Thirstrup Petersen, J. [Forskningscenter Risoe (Denmark); Nim, E. [Bonus Energy A/S (Denmark); Oeye, S. [Danmarks Tekniske Univ. (Denmark); Pedersen, B. [LM Glasfiber A/S (Denmark)
2000-01-01
The main result of the investigation is a newly developed method to identify the effective damping for the edgewise blade mode shape for wind turbines. The method consists of an exciter mechanism which makes it possible to excite the edgewise blade mode shapes from the wind turbine nacelle and furthermore of an analysis method, which enables a straightforward determination of the damping. The analysis method is based on a local blade whirl description of the edgewise blade vibrations. The method is verified on a Bonus wind turbine and for this specific turbine the effective damping for edgewise blade vibrations has been determined. The results have been compared with aeroelastic simulations. The potential of the method is that the results can support the further development of aeroelastic models and fine tuning of parameters of importance of the edgewise blade vibration problem and thus improve the certainty in the predicted risk of vibrations. Furthermore, the method can be used for experimental investigation of the risk of edgewise blade vibrations for a specific turbine. (au)
Complex modes of vibration due to small-scale damping in a guitar topplate
Directory of Open Access Journals (Sweden)
J. A. Torres
2010-04-01
Full Text Available Modal analysis is one of the preeminent methods used by scientists and engineers to study vibrating structures. The frequency responsefunctions obtained through this method, are, in general, complex-valued. There is, however, no agreed-upon interpretation given to thereal and imaginary parts of these functions, even though it is acknowledged that their relative magnitude for different frequencies is relatedto the behaviour of the corresponding modes. A simple model is deduced to describe the shape of the spectrum associated with afinite-length time-signal. There is very good agreement between results obtained using this model and numerical results obtained for,in this case, the vibration of a guitar top-plate using finite element methods. One interpretation of the relative magnitudes of the real and imaginary parts of the frequency response functions is advanced. It is found that stationary-wave behaviour is associated with the dominance of the real or imaginary part; traveling-wave behaviour, on the other hand, occurs when the real and imaginary parts are of the same order of magnitude, as long as the scale of damping is large enough and resonance peaks in the spectrum are close enough.
Universal damping mechanism of quantum vibrations in deep sub-barrier fusion reactions
Ichikawa, Takatoshi
2017-11-01
I demonstrate that the coordinate dependence of the coupling strengths of colliding nuclei is important for describing the deep sub-barrier fusion hindrance. To this end, I firstly show the performance of an extended coupled-channel model by phenomenologically introducing a damping factor in the coupling potential. The damping factor stimulates the damping of quantum vibrations occurring near the touching point of colliding nuclei and introduce a coordinate dependence in the coupling strengths. Next, I directly show the coordinate dependence of the transition strengths of colliding nuclei by microscopically calculating excited states using the random phase approximation method. The obtained transition strengths of colliding nuclei as a function of the center-of-mass distance strongly correlate with the damping factor that reproduces very well the fusion hindrance. This is a direct justification for the concept of the coordinate-dependent coupling strengths. Finally, I conclude that the damping of quantum vibrations near the touching point is the universal mechanism for the deep sub-barrier fusion hindrance.
High-damping-performance magnetorheological material for passive or active vibration control
Liu, Taixiang; Yang, Ke; Yan, Hongwei; Yuan, Xiaodong; Xu, Yangguang
2016-10-01
Optical assembly and alignment system plays a crucial role for the construction of high-power or high-energy laser facility, which attempts to ignite fusion reaction and go further to make fusion energy usable. In the optical assembly and alignment system, the vibration control is a key problem needs to be well handled and a material with higher damping performance is much desirable. Recently, a new kind of smart magneto-sensitive polymeric composite material, named magnetorheological plastomer (MRP), was synthesized and reported as a high-performance magnetorheological material and this material has a magneto-enhanced high-damping performance. The MRP behaves usually in an intermediate state between fluid-like magnetorheological fluid and solid-like magnetorheological elastomer. The state of MRP, as well as the damping performance of MRP, can be tuned by adjusting the ratio of hard segments and soft segments, which are ingredients to synthesize the polymeric matrix. In this work, a series of MRP are prepared by dispersing micron-sized, magneto-sensitive carbonyl iron powders with related additives into polyurethane-based, magnetically insensitive matrix. It is found that the damping performance of MRP depends much on magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. Especially, the damping capacity of MRP can be tuned in a large range by adjusting external magnetic field. It is promising that the MRP will have much application in passive and active vibration control, such as vibration reduction in optical assembly and alignment system, vibration isolation or absorption in vehicle suspension system, etc.
Steps for Vibration Reduction of 50kg-Class Micro-Satellite Structure
Nakamura, Masato; Furukawa, Takuya; Chiba, Masakatsu; Okubo, Hiroshi; Akita, Takeshi; Sugiyama, Yoshihiko; Nakamura, Yosuke; Imamura, Hiroaki; Umehara, Nobuhito
The paper reports several steps taken to reduce vibration responses of a 50kg-class micro-satellite structure, which is subjected to severe mechanical/vibratory environment during launching. In order to satisfy the required mechanical interface conditions, anti-vibration design of satellite structure was modified to enhance damping capacity of the structure by applying adherent aisogrid-panel, honeycomb panel, polyimid-tape-inserted connections, and damping pads. Considerable reduction of vibration responses was confirmed by vibration test of structural-thermal model.
Directory of Open Access Journals (Sweden)
Volnei Tita
2001-10-01
Full Text Available This work proposes a procedure to estimate the dynamic damped behavior of fiber reinforced composite beams in flexural vibrations. A set of experimental dynamic tests were carried out in order to investigate the natural frequencies and modal shapes. These results are used to evaluate the damping factors by the program FREQ. These damping factors are then used as input to a damped dynamic analysis by the Finite Element Method, using Rayleigh Model. A good agreement between theoretical and experimental results was obtained. Thus, it became possible to validate the proposed procedure to evaluate dynamic damped behavior of composite beams.
Seeley, Charles; Coutu, André; Monette, Christine; Nennemann, Bernd; Marmont, Hugues
2012-03-01
Hydroelectric power generation is an important non-fossil fuel power source to help meet the world’s energy needs. Fluid-structure interaction (FSI), in the form of mass loading and damping, governs the dynamic response of water turbines, such as Francis turbines. Although the effects of fluid mass loading are well documented, fluid damping is also a critical quantity that may limit vibration amplitudes during service, and therefore help to avoid premature failure of the turbines. However, fluid damping has received less attention in the literature. This paper presents an experimental investigation of damping due to FSI. Three hydrofoils were designed and built to investigate damping due to FSI. Piezoelectric actuation using macrofiber composites (MFCs) provided excitation to the hydrofoil test structure, independent of the flow conditions, to overcome the noisy environment. Natural frequency and damping estimates were experimentally obtained from sine sweep frequency response functions measured with a laser vibrometer through a window in the test section. The results indicate that, although the natural frequencies were not substantially affected by the flow, the damping ratios were observed to increase in a linear manner with respect to flow velocity.
Structure-borne sound structural vibrations and sound radiation at audio frequencies
Cremer, L; Petersson, Björn AT
2005-01-01
Structure-Borne Sound"" is a thorough introduction to structural vibrations with emphasis on audio frequencies and the associated radiation of sound. The book presents in-depth discussions of fundamental principles and basic problems, in order to enable the reader to understand and solve his own problems. It includes chapters dealing with measurement and generation of vibrations and sound, various types of structural wave motion, structural damping and its effects, impedances and vibration responses of the important types of structures, as well as with attenuation of vibrations, and sound radi
Vibration Control of Double-Beam System with Multiple Smart Damping Members
Directory of Open Access Journals (Sweden)
Dominik Pisarski
2016-01-01
Full Text Available A control method to stabilize vibration of a double cantilever system with a set of smart damping blocks is designed and numerically evaluated. The externally controlled magnetorheological sheared elastomer damping block is considered, but other smart materials can be used as well. The robust bang-bang control law for stabilization the bilinear system is elaborated. The key feature of the closed loop controller is the efficiency for different types of initial excitement. By employing the finite element model, the performance of the controller is validated for strong wind blow load and concentrated impact excitement of the particular point of one of the beams. For each of the excitations, the closed loop control outperforms the optimal passive damping case by over 27% for the considered energy metric.
Assessment of FGPM shunt damping for vibration reduction of laminated composite beams
Lezgy-Nazargah, M.; Divandar, S. M.; Vidal, P.; Polit, O.
2017-02-01
This work addresses theoretical and finite element investigations of functionally graded piezoelectric materials (FGPMs) for shunted passive vibration damping of laminated composite beams. The properties of piezoelectric patches are assumed to vary through the thickness direction following the exponent or power law distribution in terms of the volume fractions of the constituent materials. By employing Hamilton's principle, the governing differential equations of motion are derived. The resulting system of equations of vibration is solved by employing an efficient three-nodded beam element which is based on a refined sinus piezoelectric model. The effects of effective electromechanical coupling coefficients (EEMCCs), different electric shunt circuits and different material compositions on the shunted damping performance are investigated. The optimal values of the electric components belonging to each shunt circuit are numerically determined.
MODELING INFLUENCE OF ROLLING BEARING BUSH AND VIBRATION DAMPING IN CATCHING OF TOOTHED WHEELS
Directory of Open Access Journals (Sweden)
P. V. Diachenko
2010-11-01
Full Text Available On the base of dynamic scheme of toothing, a mathematical model for study of the influence of constructive parameters of radial bearings such as a factor of friction, reduced masses and stiffnesses on damping the vibrations in gearing is developed. The solution for the model is obtained using a simulation modeling in the Simulink environment with checking the validity of results in the system MathCad. The oscillograms of the vibrations under investigation and the conclusions on the base of their analysis are presented.
Directory of Open Access Journals (Sweden)
G. N. Reysina
2014-01-01
Full Text Available The paper presents results of the investigations on elastic and damping characteristics of a vibration isolation system. Adequate mathematical models of relative root-mean-square values for acceleration of antivibration mass have been obtained depending on elastic and viscous constituents. The paper reveals that the proposed method of multiple correlation is the most rational one for the analysis of power fluids used in the electro-rheological dampers.
National Research Council Canada - National Science Library
Wang, Kon-Well
2006-01-01
The objective of this research is to advance the state of the art of vibration control of mistuned periodic structures utilizing the electromechanical coupling and damping characteristics of piezoelectric networking...
Tire stiffness and damping determined from static and free-vibration tests. [aircraft tires
Sleeper, R. K.; Dreher, R. C.
1980-01-01
Stiffness and damping of a nonrolling tire were determined experimentally from both static force-displacement relations and the free-vibration behavior of a cable-suspended platen pressed against the tire periphery. Lateral and force-and-aft spring constants and damping factors of a 49 x 17 size aircraft tire for different tire pressure and vertical loads were measured assuming a rate-independent damping form. In addition, a technique was applied for estimating the magnitude of the tire mass which participates in the vibratory motion of the dynamic tests. Results show that both the lateral and force-and-aft spring constants generally increase with tire pressure but only the latter increased significantly with vertical tire loading. The fore-and-aft spring constants were greater than those in the lateral direction. The static-spring-constant variations were similar to the dynamic variations but exhibited lower magnitudes. Damping was small and insensitive to tire loading. Furthermore, static damping accounted for a significant portion of that found dynamically. Effective tire masses were also small.
Structural Vibration Monitoring Using Cumulative Spectral Analysis
Directory of Open Access Journals (Sweden)
Satoru Goto
2013-01-01
Full Text Available This paper describes a resonance decay estimation for structural health monitoring in the presence of nonstationary vibrations. In structural health monitoring, the structure's frequency response and resonant decay characteristics are very important for understanding how the structure changes. Cumulative spectral analysis (CSA estimates the frequency decay by using the impulse response. However, measuring the impulse response of buildings is impractical due to the need to shake the building itself. In a previous study, we reported on system damping monitoring using cumulative harmonic analysis (CHA, which is based on CSA. The current study describes scale model experiments on estimating the hidden resonance decay under non-stationary noise conditions by using CSA for structural condition monitoring.
The peak response distributions of structure-DVA systems with nonlinear damping
Love, J. S.; Tait, M. J.
2015-07-01
Dynamic vibration absorbers (DVAs) with nonlinear damping are often modelled using a power-law equivalent viscous damping relationship. There is currently not a method available to predict the peak response of this type of nonlinear DVA without resorting to computationally expensive nonlinear simulations. Since the peak response of the DVA is required during the design process, it is advantageous to have a simplified method to estimate the peak response. In this study, statistical linearization is employed to represent the nonlinear damping as amplitude-dependent viscous damping and predict the rms response of the structure-DVA system. Subsequently, statistical nonlinearization is used to describe the probability density function of the DVA response amplitude. A probability density function is developed, which enables the peak response expected during an interval of time (e.g. 1-h) to be estimated from the rms response of the structure-DVA system. Higher power-law damping exponents are shown to result in smaller peak factors. Results of nonlinear simulations reveal that the model can estimate the peak structural and DVA responses with acceptable accuracy. A plot is developed to show the peak factors for nonlinear DVAs as a function of the number of system cycles for several power-law damping exponents. This plot can be used to estimate the peak response of a nonlinear DVA as a function of its rms response.
Dynamic soil-pile-interaction effects on eigenfrequency and damping of slender structures
DEFF Research Database (Denmark)
Zania, Varvara
2014-01-01
of the dynamic soil-pile-interaction on the natural vibration characteristics of the flexibly supported structure. For this purpose a two-step iterative procedure has been developed based on two analytical solutions. The frequency dependent dynamic stiffness and damping coefficients are taken into consideration......-conservative overestimation of the eigenfrequency and underestimation of damping especially for small slenderness ratios and high flexibility factor of the soil – pile system (short, rigid piles). The observed trends become even more prominent as the height of the slender structure increases. The effect of the monopile...... foundation properties on the natural vibration characteristics was also examined. The influence of the frequency dependent impedances was proven significant, since the modified SSI eigenfrequency decreased substantially, when the structural eigenfrequency was set between the first and the second...
Dynamic response analysis of a 24-story damped steel structure
Feng, Demin; Miyama, Takafumi
2017-10-01
In Japanese and Chinese building codes, a two-stage design philosophy, damage limitation (small earthquake, Level 1) and life safety (extreme large earthquake, Level 2), is adopted. It is very interesting to compare the design method of a damped structure based on the two building codes. In the Chinese code, in order to be consistent with the conventional seismic design method, the damped structure is also designed at the small earthquake level. The effect of damper systems is considered by the additional damping ratio concept. The design force will be obtained from the damped design spectrum considering the reduction due to the additional damping ratio. The additional damping ratio by the damper system is usually calculated by a time history analysis method at the small earthquake level. The velocity dependent type dampers such as viscous dampers can function well even in the small earthquake level. But, if steel damper is used, which usually remains elastic in the small earthquake, there will be no additional damping ratio achieved. On the other hand, a time history analysis is used in Japan both for small earthquake and extreme large earthquake level. The characteristics of damper system and ductility of the structure can be modelled well. An existing 24-story steel frame is modified to demonstrate the design process of the damped structure based on the two building codes. Viscous wall type damper and low yield steel panel dampers are studied as the damper system.
Structural Stability and Vibration
DEFF Research Database (Denmark)
Wiggers, Sine Leergaard; Pedersen, Pauli
This book offers an integrated introduction to the topic of stability and vibration. Strikingly, it describes stability as a function of boundary conditions and eigenfrequency as a function of both boundary conditions and column force. Based on a post graduate course held by the author at the Uni......This book offers an integrated introduction to the topic of stability and vibration. Strikingly, it describes stability as a function of boundary conditions and eigenfrequency as a function of both boundary conditions and column force. Based on a post graduate course held by the author...... and their derivation, thus stimulating them to write interactive and dynamic programs to analyze instability and vibrational modes....
Study on Forced Torsional Vibration of CFRP Drive-Line System with Internal Damping
Yang, Mo; Hu, Yefa; Zhang, Jinguang; Ding, Guoping; Song, Chunsheng
2017-12-01
The use of CFRP transmission shaft has positive effect on the weight and flexural vibration reduction of drive-line system. However, the application of CFRP transmission shaft will greatly reduce the torsional stiffness of the drive-line, and may cause strong transient torsional vibration. Which will seriously affect the performance of CFRP drive-line. In this study, the forced torsional vibration of the CFRP drive-line system is carried out using the lumped parameter model. In addition, the effect of rotary inertia, internal damping, coupling due to the composite laminate, and excitation torque are incorporated in the modified transfer matrix model (TMM). Then, the modified TMM is used to predict the torsional frequency and forced torsional vibration of a CFRP drive-line with three-segment drive shafts. The results of modified TMM shown that the rotational speed difference of the CFRP transmission shaft segment is much larger than metal transmission shaft segment under excitation torque. And compared the results from finite element simulation, modified TMM and torsional vibration experiment respectively, and it has shown that the modified TMM can accurately predict forced torsional vibration behaviors of the CFRP drive-line system.
Passively Damped Laminated Piezoelectric Shell Structures with Integrated Electric Networks
Saravanos, Dimitris A.
1999-01-01
Multi-field mechanics are presented for curvilinear piezoelectric laminates interfaced with distributed passive electric components. The equations of motion for laminated piezoelectric shell structures with embedded passive electric networks are directly formulated and solved using a finite element methodology. The modal damping and frequencies of the piezoelectric shell are calculated from the poles of the system. Experimental and numerical results are presented for the modal damping and frequency of composite beams with a resistively shunted piezoceramic patch. The modal damping and frequency of plates, cylindrical shells and cylindrical composite blades with piezoelectric-resistor layers are predicted. Both analytical and experimental studies illustrate a unique dependence of modal damping and frequencies on the shunting resistance and show the effect of structural shape and curvature on piezoelectric damping.
System and method for damping vibration in a drill string using a magnetorheological damper
Wassell, Mark Ellsworth [Houston, TX; Burgess, Daniel E [Portland, CT; Barbely, Jason R [East Islip, NY
2012-01-03
A system for damping vibration in a drill string can include a magnetorheological fluid valve assembly having a supply of a magnetorheological fluid, a first member, and a second member capable of moving in relation to first member in response to vibration of the drill bit. The first and second members define a first and a second chamber for holding the fluid. Fluid can flow between the first and second chambers in response to the movement of the second member in relation to the first member. The valve assembly can also include a coil for inducing a magnetic field that alters the resistance of the magnetorheological fluid to flow between the first and second chambers, thereby increasing the damping provided by the valve. A remnant magnetic field is induced in one or more components of the magnetorheological fluid valve during operation that can be used to provide the magnetic field for operating the valve so as to eliminate the need to energize the coils during operation except temporarily when changing the amount of damping required, thereby eliminating the need for a turbine alternator power the magnetorheological fluid valve. A demagnetization cycle can be used to reduce the remnant magnetic field when necessary.
An Improved Model for Air Damping of Perforated Structures
Lu, Cunhao; Li, Pu
2017-07-01
the prediction of air damping of micromachined mechanical resonant structures is significant in the design of high quality factor devices. In rarefied air, based on Bao’s molecule model, Li gives an analytical model for air damping of perforated structures. By studying the action of molecules going through holes and reflected by the fixed plate, this paper gives a probability of molecules through holes going into the gap between the moving plate and the fixed one. Comparison with Li’s model, the new model can play a better performance of air damping for perforated structures, at a wide range of size of holes.
Chen, D
The $\\textbf{DA}$rk $\\textbf{M}$atter $\\textbf{P}$article $\\textbf{E}$xplorer (DAMPE) experiment is a high-energy astroparticle physics satellite mission to search for Dark Matter signatures in space, study the cosmic ray spectrum and composition up to 100 TeV, and perform high-energy gamma astronomy. The launch is planned for end 2015, initially for 3 years, to compliment existing space missions FERMI, AMS and CALET.
Dynamics of vibration isolation system with rubber-cord-pneumatic spring with damping throttle
Burian, Yu A.; Silkov, M. V.
2017-06-01
The study refers to the important area of applied mechanics; it is the theory of vibration isolation of vibroactive facilities. The design and the issues of mathematical modeling of pneumatic spring perspective design made on the basis of rubber-cord shell with additional volume connected with its primary volume by means of throttle passageway are considered in the text. Damping at the overflow of air through the hole limits the amplitude of oscillation at resonance. But in contrast to conventional systems with viscous damping it does not increase transmission ratio at high frequencies. The mathematical model of suspension allowing selecting options to reduce the power transmission ratio on the foundation, especially in the high frequency range is obtained
A frequency domain analysis for damped space structures
Hagood, Nesbitt W.; Crawley, Edward F.
1989-01-01
A method is presented for the analysis of damped structural systems in which the structural components are represented by impedance models and analyzed in the frequency domain. Methods are presented to assemble and condense system impedance matrices, and then to identify approximate mass, stiffness, and damping matrices for systems whose impedances are complicated functions of frequency. Formulas are derived for determination of approximate values for system natural frequencies and damping using frequency domain quantities. The sensitivities of these approximate values to system parameter changes are analyzed. The implementation of these analysis tools is discussed and applied to a simple mechanical system.
Equal modal damping design for a family of resonant vibration control formats
DEFF Research Database (Denmark)
Krenk, Steen; Høgsberg, Jan Becker
2013-01-01
The principle of equal modal damping is used to give a unified presentation and calibration of resonant control of structures for different control formats, based on velocity, acceleration–position or position feedback. When introducing a resonant controller the original resonant mode splits......-velocity formats, while the position and extended position feedback format give a simple stability condition in terms of the gain factors and the structure flexibility matrix. The paper concludes with a simple design procedure based on the desired effective damping of a flexible structure with equal modal control...... of the resulting modal damping ratio. While velocity feedback, and the associated acceleration–position formats, lead to near-equal resonant peak heights of the velocity in a frequency response diagram, position feedback leads to balanced acceleration peaks. It is demonstrated, how a simple additional time...
Weber, F.; Distl, H.
2015-11-01
This paper derives an approximate collocated control solution for the mitigation of multi-mode cable vibration by semi-active damping with negative stiffness based on the control force characteristics of clipped linear quadratic regulator (LQR). The control parameters are derived from optimal modal viscous damping and corrected in order to guarantee that both the equivalent viscous damping coefficient and the equivalent stiffness coefficient of the semi-active cable damper force are equal to their desired counterparts. The collocated control solution with corrected control parameters is numerically validated by free decay tests of the first four cable modes and combinations of these modes. The results of the single-harmonic tests demonstrate that the novel approach yields 1.86 times more cable damping than optimal modal viscous damping and 1.87 to 2.33 times more damping compared to a passive oil damper whose viscous damper coefficient is optimally tuned to the targeted mode range of the first four modes. The improvement in case of the multi-harmonic vibration tests, i.e. when modes 1 and 3 and modes 2 and 4 are vibrating at the same time, is between 1.55 and 3.81. The results also show that these improvements are obtained almost independent of the cable anti-node amplitude. Thus, the proposed approximate real-time applicable collocated semi-active control solution which can be realized by magnetorheological dampers represents a promising tool for the efficient mitigation of stay cable vibrations.
Double-beam cantilever structure with embedded intelligent damping block: Dynamics and control
Szmidt, Tomasz; Pisarski, Dominik; Bajer, Czesław; Dyniewicz, Bartłomiej
2017-08-01
In this paper a semi-active method to control the vibrations of twin beams connected at their tips by a smart damping element is investigated. The damping element can be made of a magnetorheological elastomer or a smart material of another type, for instance vacuum packed particles. What is crucial is the ability to modify the storage and loss moduli of the damping block by means of devices attached directly to the vibrating structure. First, a simple dynamical model of the system is proposed. The continuous model is discretized using the Galerkin procedure. Then, a practical state-feedback control law is developed. The control strategy aims at achieving the best instantaneous energy dissipation of the system. Numerical simulations confirm its effectiveness in reducing free vibrations. The proposed control strategy appears to be robust in the sense that its application does not require any knowledge of the initial conditions imposed on the structure, and its performance is better than passive solutions, especially for the system induced in the first mode.
Active and passive damping based on piezoelectric elements -controllability issues-
Holterman, J.; de Vries, Theodorus J.A.; van Amerongen, J.; Jonker, Jan B.; Jonker, J.B.
2001-01-01
Piezoelectric elements are widely used for damping micro-vibrations in mechanical structures. Active damping can be realised robustly by means of collocated actuator-sensor-pairs, controlled so as to extract vibration energy. Excellent damping performance is possible as long as sufficient
Design, Fabrication, and Properties of High Damping Metal Matrix Composites?A Review
Qianfeng Fang; Zhijun Cheng; Tao Zhang; Xianping Wang; Hui Lu
2009-01-01
Nowadays it is commonly considered that high damping materials which have both the good mechanical properties as structural materials and the high damping capacity for vibration damping are the most direct vibration damping solution. In metals and alloys however, exhibiting simultaneously high damping capacity and good mechanical properties has been noted to be normally incompatible because the microscopic mechanisms responsible for internal friction (namely damping capacity) are dependent up...
Passive and Active Vibration Control of Renewable Energy Structures
DEFF Research Database (Denmark)
Zhang, Zili
The present thesis deals with fundamental researches on passive and active vibration control of renewable energy structures, and provides useful models for practical applications. Effective and robust vibration control methods have been explored for mitigating the lightly damped edgewise blade...... solutions for wave energy point absorbers, in order to maximize the mean absorbed power and to deliver more smooth power to the grid. A novel suboptimal causal control law has been established for controlling the motion of the point absorber, and a new type of point absorber has also been proposed...
A practical multiscale approach for optimization of structural damping
DEFF Research Database (Denmark)
Andreassen, Erik; Jensen, Jakob Søndergaard
2016-01-01
A simple and practical multiscale approach suitable for topology optimization of structural damping in a component ready for additive manufacturing is presented.The approach consists of two steps: First, the homogenized loss factor of a two-phase material is maximized. This is done in order...... to obtain a range of isotropic microstructures that have a connected stiff material phase. Second,the structural damping of the component is maximized using material interpolations based on the homogenized properties of the microstructures. In order to achieve convergence towards a discrete set of material...
1987-01-01
fatigae equivalent test time of 45-mimates. 1. BACKGROUND subjected to both vibration and loose cargo testing as well an the type and amount of...Environmental Test the track laying environment. Nethods, 10 March 1975. 8. FUTURE EFFORTS 11. Soci, Darrell F., Fatigae Life Estimation Techniques, Technical
Optimized Non-Obstructive Particle Damping (NOPD) Treatment for Composite Honeycomb Structures
Panossian, H.
2008-01-01
Non-Obstructive Particle Damping (NOPD) technology is a passive vibration damping approach whereby metallic or non-metallic particles in spherical or irregular shapes, of heavy or light consistency, and even liquid particles are placed inside cavities or attached to structures by an appropriate means at strategic locations, to absorb vibration energy. The objective of the work described herein is the development of a design optimization procedure and discussion of test results for such a NOPD treatment on honeycomb (HC) composite structures, based on finite element modeling (FEM) analyses, optimization and tests. Modeling and predictions were performed and tests were carried out to correlate the test data with the FEM. The optimization procedure consisted of defining a global objective function, using finite difference methods, to determine the optimal values of the design variables through quadratic linear programming. The optimization process was carried out by targeting the highest dynamic displacements of several vibration modes of the structure and finding an optimal treatment configuration that will minimize them. An optimal design was thus derived and laboratory tests were conducted to evaluate its performance under different vibration environments. Three honeycomb composite beams, with Nomex core and aluminum face sheets, empty (untreated), uniformly treated with NOPD, and optimally treated with NOPD, according to the analytically predicted optimal design configuration, were tested in the laboratory. It is shown that the beam with optimal treatment has the lowest response amplitude. Described below are results of modal vibration tests and FEM analyses from predictions of the modal characteristics of honeycomb beams under zero, 50% uniform treatment and an optimal NOPD treatment design configuration and verification with test data.
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.
Flow-Induced Vibration of Circular Cylindrical Structures
Energy Technology Data Exchange (ETDEWEB)
Chen, Shoei-Sheng [Argonne National Lab. (ANL), Argonne, IL (United States). Components Technology Division
1985-06-01
Flow-induced vibration is a term to denote those phenomena associated with the response of structures placed in or conveying fluid flow. More specifically, the terra covers those cases in which an interaction develops between fluid-dynamic forces and the inertia, damping or elastic forces in the structures. The study of these phenomena draws on three disciplines: (1) structural mechanics, (2) mechanical vibration, and (3) fluid dynamics. The vibration of circular cylinders subject to flow has been known to man since ancient times; the vibration of a wire at its natural frequency in response to vortex shedding was known in ancient Greece as aeolian tones. But systematic studies of the problem were not made until a century ago when Strouhal established the relationship between vortex shedding frequency and flow velocity for a given cylinder diameter. The early research in this area has beer summarized by Zdravkovich (1985) and Goldstein (1965). Flow-induced structural vibration has been experienced in numerous fields, including the aerospace industry, power generation/transmission (turbine blades, heat exchanger tubes, nuclear reactor components), civil engineering (bridges, building, smoke stacks), and undersea technology. The problems have usually been encountered or created accidentally through improper design. In most cases, a structural or mechanical component, designed to meet specific objectives, develops problems when the undesired effects of flow field have not been accounted for in the design. When a flow-induced vibration problem is noted in the design stage, the engineer has different options to eliminate the detrimental vibration. Unfortunately, in many situations, the problems occur after the components are already in operation; the "fix" usually is very costly. Flow-induced vibration comprises complex and diverse phenomena; subcritical vibration of nuclear fuel assemblies, galloping of transmission lines, flutter of pipes conveying fluid, and whirling
Vibration control of active structures an introduction
Preumont, Andre
2002-01-01
This text is an introduction to the dynamics of active structures and to the feedback control of lightly damped flexible structures. The emphasis is placed on basic issues and simple control strategies that work.
Damped critical speeds and stability of a flexible rotor-SFDB-support structure system
He, Xingsuo
1992-07-01
A new iterative method for solving the damped critical speeds and stability of a flexible rotor-SFDB (squeeze-film damper bearing) system is proposed. The parameters of the support structure, including the stiffness, damping, and effective mass of the shell, are taken into account. The proper ranges of parameters for a rotor system to be used in order to reduce vibration are a bearing parameter range of 0.11-0.15 and a clearance ratio range of 0.23-0.365 percent. The proper ranges of the parameters obtained are argued to be more precise than those determined by Feng (1988) and Zhu (1989). Compared with previous methods, the computational time is reduced by about 30 percent.
Attenuation and damping of structure-borne sound
DEFF Research Database (Denmark)
Jacobsen, Finn
1999-01-01
The bias errors in measurements of transfer functions of vibrating structures with FFT analysers are examined, and various experiments that demonstrate the importance of a proper choice of measurement parameters are described....
Meeting Tight Frequency Requirement of Rounded Damped Detuned Structure
Higo, T; Higashi, Y; Hitomi, N; Suzuki, T; Takata, K; Takatomi, T; Toge, N; Watanabe, Y; Li, Z; Miller, R H; Wang, J W
2000-01-01
Following successful design and fabrication of damped detuned structures, the R&D for the accelerating structures of the NLC/JLC linear collider project proceeded to studies of Rounded Damped Detuned Structure with curved cross section of the cavity shape for increased shunt impedance. The important features of the structure are the accurately tuned accelerating mode frequency and the distribution of the first dipole modes smooth and close to the design distribution. These requirements were met based on the high-accuracy diamond turning with its capability to realize the periphery tolerance of two microns. The lowest dipole mode frequencies scattered by 0.6 MHz RMS. The error in the accelerating mode frequency averaged over a structure was 0.1 MHz by applying a feed-forward method.
Directory of Open Access Journals (Sweden)
Hashem S. Alkhaldi
2013-01-01
Full Text Available This paper presents the dynamic response of Bernoulli-Euler homogeneous isotropic fractionally-damped simply-supported beam. The beam is attached to multi single-degree-of-freedom (SDOF fractionally-damped systems, and it is subjected to a vehicle moving with a constant velocity. The damping characteristics of the beam and SDOF systems are described in terms of fractional derivatives. Three coupled second-order fractional differential equations are produced and then they are solved by combining the Laplace transform with the decomposition method. The obtained numerical results show that the dynamic response decreases as (a the number of absorbers attached to the beam increases and (b the damping-ratios of used absorbers and beam increase. However, there are some critical values of fractional derivatives which are different from unity at which the beam has less dynamic response than that obtained for the full-order derivatives model. Furthermore, the obtained results show very good agreements with special case studies that were published in the literature.
On boundary damping for elastic structures
Akkaya, T.
2018-01-01
Many mathematical models, which describe oscillations in elastic structures such as suspension bridges, conveyor belts and elevator cables, can be formulated as initial-boundary value problems for string (wave) equations, or for beam equations. In order to build more durable, elegant and lighter
Monothiodibenzoylmethane: Structural and vibrational assignments
DEFF Research Database (Denmark)
Hansen, Bjarke Knud Vilster; Gorski, Alexander; Posokhov, Yevgen
2007-01-01
The vibrational structure of the title compound (1,3-diphenyl-3-thioxopropane-1-one, TDBM) was studied by a variety of experimental and theoretical methods. The stable ground state configuration of TDBM was investigated by IR absorption measurements in different media, by LD polarization spectros...... to an “open”, non-chelated enethiol form (t-TCC), thereby supporting the previous conclusions by Posokhov et al. No obvious indications of the contribution of other forms to the observed spectra could be found....
Directory of Open Access Journals (Sweden)
Rossikhin Yury A.
2018-01-01
Full Text Available Non-linear damped vibrations of a cylindrical shell embedded into a fractional derivative medium are investigated for the case of the combinational internal resonance, resulting in modal interaction, using two different numerical methods with further comparison of the results obtained. The damping properties of the surrounding medium are described by the fractional derivative Kelvin-Voigt model utilizing the Riemann-Liouville fractional derivatives. Within the first method, the generalized displacements of a coupled set of nonlinear ordinary differential equations of the second order are estimated using numerical solution of nonlinear multi-term fractional differential equations by the procedure based on the reduction of the problem to a system of fractional differential equations. According to the second method, the amplitudes and phases of nonlinear vibrations are estimated from the governing nonlinear differential equations describing amplitude-and-phase modulations for the case of the combinational internal resonance. A good agreement in results is declared.
Basok, B. I.; Gotsulenko, V. V.; Gotsulenko, V. N.
2012-11-01
The reason for the decrease in the amplitude of longitudinal vibration combustion self-oscillations in the combustion chamber of a liquid-propellant rocket engine by means of antipulse partitions has been justified. A mathematical model of the development of combustion instability in such a chamber on attachment of a Helmholtz resonator to it has been obtained. The character of the damping of vibration combustion self-oscillations excited by the action of the Crocco mechanisms and negative thermal resistance, when varying the acoustic parameters of the resonator and of the pressure head characteristics of combustion chamber is established.
Identifying the damping contribution of building components based on measured top vibration
Berg, R.L.J. van den; Steenbergen, R.D.J.M.
2013-01-01
In this paper, a damping model for a high-rise building is introduced. This model is used to investigate the possibilities to identify the relative damping contribution of the internal material damping in building elements, energy loss at element interfaces and energy outflow at the interface with
Power system damping - Structural aspects of controlling active power
Energy Technology Data Exchange (ETDEWEB)
Samuelsson, O.
1997-04-01
Environmental and economical aspects make it difficult to build new power lines and to reinforce existing ones. The continued growth in demand for electric power must therefore to a great extent be met by increased loading of available lines. A consequence is that power system damping is reduced, leading to a risk of poorly damped power oscillations between the generators. This thesis proposes the use of controlled active loads to increase damping of such electro-mechanical oscillations. The focus is on structural aspects of controller interaction and of sensor and actuator placement. On-off control based on machine frequency in a single machine infinite bus system is analysed using energy function analysis and phase plane plots. An on-off controller with estimated machine frequency as input has been implemented. At a field test it damped oscillations of a 0.9 MW hydro power generator by controlling a 20kW load. The linear analysis uses two power system models with three and twenty-three machines respectively. Each damper has active power as output and local bus frequency or machine frequency as input. The power system simulator EUROSTAG is used both for generation of the linearized models and for time simulations. Measures of active power mode controllability and phase angle mode observability are obtained from the eigenvectors of the differential-algebraic models. The geographical variation in the network of these quantities is illustrated using the resemblance to bending modes of flexible mechanical structures. Eigenvalue sensitivities are used to determine suitable damper locations. A spring-mass equivalent to an inter-area mode provides analytical expressions, that together with the concept of impedance matching explain the structural behaviour of the power systems. For large gains this is investigated using root locus plots. 64 refs, 99 figs, 20 tabs
Vibrational Stability of NLC Linac Accelerating Structure
Le Pimpec, F; Bowden, G B; Doyle, E; McKee, B; Seryi, Andrei; Redaelli, S; Adiga, S
2002-01-01
The vibration of components of the NLC linac, such as accelerating structures and girders, is being studied both experimentally and analytically. Various effects are being considered including structural resonances and vibration caused by cooling water in the accelerating structure. This paper reports the status of ongoing work.
Paimushin, V. N.; Firsov, V. A.; Shishkin, V. M.
2017-09-01
The frequency dependence for the dynamic elastic modulus of a Porcher 3692 CFRP at frequencies to 112.5 Hz is obtained from an experimental study on damped flexural vibrations of vertical cantilevered test specimens. A finite-element technique is developed for modeling the dynamic response of a long cantilevered carbon-fiber-plastic plate at resonant flexural vibrations according to the first vibration mode with account of internal damping, aerodynamic drag forces, and the frequency-dependent dynamic elastic modulus of the material. The damping properties of the plate are determined by the logarithmic decrement, which depends on the vibration amplitude of its free edge. Numerical experiments were carried out, which confirmed the accuracy of the technique. It is shown that the logarithmic decrement of the plate in the range of medium and high vibration amplitudes depends mainly on the aerodynamic drag forces.
Advances in structural vibration control application of magneto-rheological visco-elastomer
Directory of Open Access Journals (Sweden)
Zuguang Ying
2017-03-01
Full Text Available Magneto-rheological visco-elastomer (MRVE as a new smart material developed in recent years has several significant advantages over magneto-rheological liquid. The adjustability of structural dynamics to random environmental excitations is required in vibration control. MRVE can supply considerably adjustable damping and stiffness for structures, and the adjustment of dynamic properties is achieved only by applied magnetic fields with changeless structure design. Increasing researches on MRVE dynamic properties, modeling, and vibration control application are presented. Recent advances in MRVE dynamic properties and structural vibration control application including composite structural vibration mitigation under uniform magnetic fields, vibration response characteristics improvement through harmonic parameter distribution, and optimal bounded parametric control design based on the dynamical programming principle are reviewed. Relevant main methods and results introduced are beneficial to understanding and researches on MRVE application and development.
Martel, Carlos; Sánchez-Álvarez, J. J.
2017-06-01
Mistuning can dangerously increase the vibration amplitude of the forced response of a turbomachinery rotor. In the case of damping coming from aerodynamic effects the situation is more complicated because the magnitude of the damping changes for the different travelling wave modes of the system. This damping variability modifies the effect of mistuning, and it can even result in a reduction of the mistuned forced response amplitude below that of the tuned case (this is not possible in the usual case of constant material damping). In this paper the Asymptotic Mistuning Model (AMM) methodology is used to analyze this situation. The AMM is a reduced order model that is systematically derived from the mistuned bladed disk full model using a perturbative procedure based on the small size of the mistuning and the damping. The AMM allows to derive a very simple expression for an upper bound of the maximum amplification factor of the vibration amplitude that the system can experience (an extension of the well known Whitehead 1966 result to include the effect of non-uniform aerodamping). This new upper bound gives information on the mechanisms involved in the amplification/reduction of the mistuned response: (i) the number of modes participating in the response, and (ii) the ratio between the aerodamping of the directly forced mode and that of the of the rest of the modes. A FEM of a mistuned bladed disk is also used to verify the AMM predictions for several different forcing configurations, and both results show a very good quantitative agreement.
An Introduction to the Problem of Dynamic Structural Damping,
1978-01-01
INTRODUCTION TO THE P ROBLEM OF DYNAMIC STRUCTURAL DAMPING by PSa n t ini , A.Castellan i and A.Nappi (stituto di Tecnologia Aerospaziale deIl’Unive rsità di...obtain information s on typical values of ~ to be used in each of the analyses described under Art . 2. It is generally agreed, in fac t , that the...clearly indicate that experimental validation of the results is of vital importance. No safe prediction of the phenomena listed under Art . 2 can be
Development of a unified numerical procedure for free vibration analysis of structures
Gupta, K. K.
1981-01-01
This paper presents the details of a unified numerical algorithm and the associated computer program developed for the efficient determination of natural frequencies and modes of free vibration of structures. Both spinning and nonspinning structures with or without viscous and/or structural damping may be solved by the current procedure; in addition, the program is capable of solving static problems with multiple load cases as well as the quadratic matrix eigenproblem associated with a finite dynamic element structural discretization.
RESEARCH OF BRIDGE STRUCTURE VIBRATION CHARACTERISTICS
Directory of Open Access Journals (Sweden)
V.P. Babak
2005-02-01
Full Text Available Bridge structure test results with using different types of dynamic force have been considered. It has been shown, that the developed technique of registering and processing vibration signals allows obtaining thin spectrum structure. The analysis of its change that is defined by the type of structure loading applied has been carried out. Key parameters of the vibration signals registered have been defined.
DeValve, Caleb Joshua
Fiber-reinforced composites (FRCs) offer a stronger and lighter weight alternative to traditional materials used in engineering components such as wind turbine blades and rotorcraft structures. Composites for these applications are often fabricated using liquid molding techniques, such as injection molding or resin transfer molding. One significant issue during these processing methods is void formation due to incomplete wet-out of the resin within the fiber preform, resulting in discontinuous material properties and localized failure zones in the material. A fundamental understanding of the resin evolution during processing is essential to designing processing conditions for void-free filling, which is the first objective of the dissertation. Secondly, FRCs used in rotorcraft experience severe vibrational loads during service, and improved damping characteristics of the composite structure are desirable. To this end, a second goal is to explore the use of matrix-embedded nanoscale reinforcements to augment the inherent damping capabilities in FRCs. The first objective is addressed through a computational modeling and simulation of the infiltrating dual-scale resin flow through the micro-architectures of woven fibrous preforms, accounting for the capillary effects within the fiber bundles. An analytical model is developed for the longitudinal permeability of flow through fibrous bundles and applied to simulations which provide detailed predictions of local air entrapment locations as the resin permeates the preform. Generalized design plots are presented for predicting the void content and processing time in terms of the Capillary and Reynolds Numbers governing the molding process. The second portion of the research investigates the damping enhancement provided to FRCs in static and rotational configurations by different types and weight fractions of matrix-embedded carbon nanotubes (CNTs) in high fiber volume fraction composites. The damping is measured using
Salt Damage and Rising Damp Treatment in Building Structures
Directory of Open Access Journals (Sweden)
J. M. P. Q. Delgado
2016-01-01
Full Text Available Salt damage can affect the service life of numerous building structures, both historical and contemporary, in a significant way. In this review, various damage mechanisms to porous building materials induced by salt action are analyzed. The importance of pretreatment investigations is discussed as well; in combination with the knowledge of salt and moisture transport mechanisms they can give useful indications regarding treatment options. The methods of salt damage treatment are assessed then, including both passive techniques based on environmental control, reduction of water transport, or conversion to less soluble salts and active procedures resulting in the removal of salts from deterioration zones. It is concluded that cellulose can still be considered as the favorite material presently used in desalination poultices but hydrophilic mineral wool can serve as its prospective alternative in future applications. Another important cause of building pathologies is the rising damp and, in this phenomenon, it is particularly severe considering the presence of salts in water. The treatment of rising damp in historic building walls is a very complex procedure and at Laboratory of Building Physics (LFC-FEUP a wall base hygroregulated ventilation system was developed and patented.
Identification for Active Vibration Control of Flexible Structure Based on Prony Algorithm
Directory of Open Access Journals (Sweden)
Xianjun Sheng
2016-01-01
Full Text Available Flexible structures have been widely used in many fields due to the advantages of light quality, small damping, and strong flexibility. However, flexible structures exhibit the vibration in the process of manipulation, which reduces the pointing precision of the system and causes fatigue of the machine. So, this paper focuses on the identification method for active vibration control of flexible structure. The modal parameters and transfer function of the system are identified from the step response signal based on Prony algorithm, while the vibration is attenuated by using the input shaping technique designed according to the parameters identified from the Prony algorithm. Eventually, the proposed approach is applied to the most common flexible structure, a piezoelectric cantilever beam actuated by Macro Fiber Composite (MFC. The experimental results demonstrate that the Prony algorithm is very effective and accurate on the dynamic modeling of flexible structure and input shaper could significantly reduce the vibration and improve the response speed of system.
Dillman, Kevin L; Shelly, Katherine R; Beck, Warren F
2009-04-30
Ground-state coherent wavepacket motions arising from intermolecular modes with clustered, first-shell solvent molecules were observed using the femtosecond dynamic absorption technique in polar solutions of Zn(II) meso-tetrakis(N-methylpyridyl)porphyrin (ZnTMPyP) with excitation in the Soret absorption band. As was observed previously in bacteriochlorophyll a solution, the pump-probe transients in ZnTMPyP solutions are weakly modulated by slowly damped (effective damping time gamma > 1 ps) features that are assigned to intramolecular modes, the skeletal normal modes of vibration of the porphyrin. The 40 cm(-1) and 215 cm(-1) modes from the metal-doming and metal-solvent-ligand modes, respectively, are members of this set of modulation components. A slowly damped 2-4 cm(-1) component is assigned to the internal rotation of the N-methylpyridyl rings with respect to the porphyrin macrocycle; this mode obtains strong resonance Raman intensity enhancement from an extensive delocalization of pi-electron density from the porphyrin in the ground state onto the rings in the pi* excited states. The dominant features observed in the pump-probe transients are a pair of rapidly damped (gamma modes with solvent molecules. This structural assignment is supported by an isotope-dependent shift of the average mode frequencies in methanol and perdeuterated methanol. The solvent dependence of the mean intermolecular mode frequency is consistent with a van der Waals intermolecular potential that has significant contributions only from the London dispersion and induction interactions; ion-dipole or ion-induced-dipole terms do not make large contributions because the pi-electron density is not extensively delocalized onto the N-methylpyridyl rings. The modulation depth associated with the intermolecular modes exhibits a marked dependence on the electronic structure of the solvent that is probably related to the degree of covalency; the strongest modulations are observed in acetonitrile
Damping Transversal Vibrations of the Offset Cylinder of the Offset Press
Directory of Open Access Journals (Sweden)
Eglė Šalvienė
2012-01-01
Full Text Available Investigation into the influence of a dynamic vibration damper on the intensity of the absolute forced transversal vibrations of the blanket cylinder of the web printing offset press was performed. The analytical and numerical examination of the dynamic model of the cylinder was done. The obtained results have disclosed that the application of the damper decreases the intensity of printing cylinder vibrations.Article in Lithuanian
Theory of Arched Structures Strength, Stability, Vibration
Karnovsky, Igor A
2012-01-01
Theory of Arched Structures: Strength, Stability, Vibration presents detailed procedures for analytical analysis of the strength, stability, and vibration of arched structures of different types, using exact analytical methods of classical structural analysis. The material discussed is divided into four parts. Part I covers stress and strain with a particular emphasis on analysis; Part II discusses stability and gives an in-depth analysis of elastic stability of arches and the role that matrix methods play in the stability of the arches; Part III presents a comprehensive tutorial on dynamics and free vibration of arches, and forced vibration of arches; and Part IV offers a section on special topics which contains a unique discussion of plastic analysis of arches and the optimal design of arches.
Balanced calibration of resonant shunt circuits for piezoelectric vibration control
DEFF Research Database (Denmark)
Høgsberg, Jan; Krenk, Steen
2012-01-01
Shunting of piezoelectric transducers and suitable electric circuits constitutes an effective passive approach to resonant vibration damping of structures. Most common design concepts for resonant resistor-inductor (RL) shunt circuits rely on either maximization of the attainable modal damping...
Damping of Offshore Wind Turbine Tower Vibrations by a Stroke Amplifying Brace
DEFF Research Database (Denmark)
Brodersen, Mark Laier; Høgsberg, Jan Becker
2014-01-01
The potential of installing dampers inside the tower of an offshore wind turbine is investigated through simulations. Dampers are installed at the bottom to act on the curvature of the tower, and it is shown that dampers installed in suitable braces have the potential to increase the critical...... damping ratio of the two lowest tower modes by 1 percent. By using a toggle-brace system, damper stroke is increased, while the damper force is reduced. Finally, by installing the dampers in a symmetric configuration, tuning for maximum damping is approximately independent of the orientation of the rotor......, thereby making this installation of dampers feasible....
Design of a choke-mode damped accelerating structure for CLIC Main LINAC
Shi, J; Grudiev, A; Wuensch, W; Tang, C; Chen, H; Huang, W
2011-01-01
Choke-mode damped accelerating structures are being studied as an alternative to the baseline structure of the compact linear collider (CLIC) by a CERN-Tsinghua collaboration. Choke-mode structures hold the potential for much lower levels of pulsed surface heating and, since milling is not needed, reduced cost. Structures with radial choke attached are simulated in GdfidL to investigate the damping of the transverse wake. The first pass-band of the dipole modes is well damped, while the higher order dipole modes are possibly reflected by the choke. Therefore, the geometry of the choke is tuned to minimize the reflection of these higher order dipole modes. Based on this damping scheme, an accelerating structure with the same iris dimensions as the nominal CLIC design but with choke-mode damping has been designed. A prototype structure will be manufactured and high power tested in the near future.
Optimization of Fuzzy Control for Magnetorheological Damping Structures
Directory of Open Access Journals (Sweden)
Jianguo Ding
2017-01-01
Full Text Available Due to the influence of nonlinearity and time-variation, it is difficult to establish an accurate model of a magnetorheological damping structure that adopts semiactive control. Fuzzy control is a relatively appropriate control method, but fuzzy control design is susceptible to human subjective experience, which will decrease the control effect. This paper proposes new fuzzy control rules based on a genetic algorithm (GA and particle swarm optimization (PSO and performs a numerical simulation for a three-layer reinforced concrete frame structure under conditions of an uncontrolled structure, fuzzy control, fuzzy control optimized by GA, fuzzy control optimized by PSO, and GA-optimized FLC control (GA-FLC proposed by Ali and Ramaswamy (2008. The results show that (1 the fitness values of the convergence of the two types of optimized fuzzy control are close. The speed of the convergence of the fuzzy control optimized by PSO is faster than that of the fuzzy control optimized by GA, but its running speed is slower. (2 Comparing the acceleration and displacement of the structure under the conditions of three different seismic waves, the effect of the optimized fuzzy control is better than that of the human experience fuzzy control and GA-FLC.
Vibration control in forge hammers. [by shock wave damping in foundation platform
Moise, F.; Lazarescu, C.
1974-01-01
Special measures are discussed for calculating, designing and executing a forge hammer foundation, so that the vibrations that occur during its working will not be transmitted to neighboring machinery, workrooms and offices. These vibrations are harmful to the workers near the forge hammer.
Estimation of hysteretic damping of structures by stochastic subspace identification
DEFF Research Database (Denmark)
Bajric, Anela; Høgsberg, Jan Becker
2018-01-01
identification method suitable for random response of dynamic systems with hysteretic damping. The method applies the concept of Stochastic Subspace Identification (SSI) to estimate the model parameters of a dynamic system with hysteretic damping. The restoring force is represented by the Bouc-Wen model...
Free-Vibration Analysis of Structures
Gupta, K. K.
1984-01-01
Unified numerical procedure for free-vibration analysis of structures developed and incorporated into EIGSOL computer program. Dynamic response analysis of primary importance in design of wide range of practical structures such as space-craft, buildings, and rotating machineries. Procedure determines natural frequencies and associated modes in structural design.
Vibration Damping Workshop Proceedings Held at Long Beach, California on 27-29 February 1984.
1984-11-11
variety of damping devices have been suggested [10,111. Other devices for energy dissipation were used such as draping chains over tubes [12] or permitting... devopment /operating cost by 340M UU -2 p 0 i -L . ..’ - . , ,.. . ,, _,_ ... . .-; .. :: -- _. . , .:... : . -.. .*. - - -.- 2 -,-i-. . i
Atomistic theory for the damping of vibrational modes in monoatomic gold chains
DEFF Research Database (Denmark)
Engelund, Mads; Brandbyge, Mads; Jauho, Antti-Pekka
2009-01-01
for the experimentally realized case of gold chains in two different crystallographic directions. The range of the computed damping rates confirms the estimates obtained by fits to experimental data [T. Frederiksen et al., Phys. Rev. B 75, 205413 (2007)]. Our method indicates that an order-of-magnitude variation...
Damping of vibrational excitations in glasses at terahertz frequency: The case of 3-methylpentane
Baldi, Giacomo
2017-10-24
We report a compared analysis of inelastic X ray scattering (IXS) and of low frequency Raman data of glassy 3-methylpentane. The IXS spectra have been analysed allowing for the existence of two distinct excitations at each scattering wavevector obtaining a consistent interpretation of the spectra. In particular, this procedure allows us to interpret the linewidth of the modes in terms of a simple model which relates them to the width of the first sharp diffraction peak in the static structure factor. In this model, the width of the modes arises from the blurring of the dispersion curves which increases approaching the boundary of the first pseudo-Brillouin zone. The position of the boson peak contribution to the density of vibrational states derived from the Raman scattering measurements is in agreement with the interpretation of the two excitations in terms of a longitudinal mode and a transverse mode, the latter being a result of the mixed character of the transverse modes away from the center of the pseudo-Brillouin zone.
Ding, Zhe; Li, Li; Hu, Yujin
2018-01-01
Sophisticated engineering systems are usually assembled by subcomponents with significantly different levels of energy dissipation. Therefore, these damping systems often contain multiple damping models and lead to great difficulties in analyzing. This paper aims at developing a time integration method for structural systems with multiple damping models. The dynamical system is first represented by a generally damped model. Based on this, a new extended state-space method for the damped system is derived. A modified precise integration method with Gauss-Legendre quadrature is then proposed. The numerical stability and accuracy of the proposed integration method are discussed in detail. It is verified that the method is conditionally stable and has inherent algorithmic damping, period error and amplitude decay. Numerical examples are provided to assess the performance of the proposed method compared with other methods. It is demonstrated that the method is more accurate than other methods with rather good efficiency and the stable condition is easy to be satisfied in practice.
DEFF Research Database (Denmark)
Koukoura, Christina; Natarajan, Anand; Vesth, Allan
2015-01-01
maxima of an impulse response caused by a boat impact. The result is used in the verification of the non aerodynamic damping in normal operation for low wind speeds. The auto-correlation function technique for damping estimation of a structure under ambient excitation was validated against the identified...... damping from the decaying time series. The Enhanced Frequency Domain Decomposition (EFDD) method was applied to the wind turbine response under ambient excitation, for estimation of the damping in normal operation. The aero-servo-hydro-elastic tool HAWC2 is validated with offshore foundation load...
Choke-Mode Damped Structure Design for the CLIC Main Linac
Zha, Hao; Chen, Huaibi; Tang, Chuanxiang; Huang, Wenhui; Shi, Jiaru; Grudiev, Alexej; Wuensch, Walter
2012-01-01
Choke-mode damped structures are being studied as an alternative design for the accelerating structures of main linacs of the compact linear collider (CLIC). Choke-mode structures have the potential for much lower pulsed temperature rise, and lower cost of manufacture and fabrication. A new kind of choke-mode structure was proposed and simulated by Gdﬁdl. This structures has comparable wakeﬁeld damping effect as the baseline design of CLIC main linacs.
Vibration modes and frequencies of structures
Durling, R. J.; Kvaternik, R. G.
1980-01-01
SUDAN, Substructuring in Direct Analysis, analyzes natural modes and frequencies of vibration of structural systems. Based on direct method of analysis that employs substructures methodology, program is used with structures that may be represented as equivalent system of beam, springs, and rigid bodies.
Structural, intramolecular hydrogen bonding and vibrational studies ...
Indian Academy of Sciences (India)
An extensive theoretical study on the molecular structure and vibrational analysis of 3-amino-4- methoxy benzamide (3A4MBA) was undertaken using density functional theoretical (DFT) method. The possibility of formation of intramolecular hydrogen bonding was identified from structural parameter analysis and confirmed ...
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
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...... 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...... 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...
Rendl, J.; Rohler, R.; Sieger, C.
1983-12-01
To get quantitative information about principal aspects of the near-field propagation of sound in bone conduction, model experiments were performed with transparent silicon rubber as a vibrating material. Using the transparent silicon rubber instead of the bone itself made it possible to measure amplitudes and phases on interior planes of a solid medium of finite extent. To this end several holographic techniques were employed, among them speckle interferometry for analysing in-plane vibrations. A theory was developed which describes the basic features of wave propagation and shows the influence of the viscosity of the material on propagation behaviour. The application of the results on pracitcal audiometry will be discussed.
Directory of Open Access Journals (Sweden)
Zapoměl J.
2013-12-01
Full Text Available Unbalance is the principal source of increase of time varying forces transmitted between the rotor and its stationary part. Their magnitudes can be considerably reduced if the rotor is flexibly suspended and if the damping devices are added to the support elements. Their damping effect must be high for low rotor velocities and small for velocities approximately higher than the critical one to minimize the transmitted forces and the vibrations amplitude. This implies to achieve maximum efficiency of the damping elements, their damping effect has to be adaptable to the current operating conditions. Such technological solution is offered by application of a squeeze film magnetorheological damper. Its hybrid variant consisting of two damping units (one controllable in a serial arrangement is investigated in this paper. The damping takes place in two concentric lubricating films formed by normal and magnetorheological oils. The damper is equipped with an electric coil generating magnetic flux passing through the layer of the magnetorheological fluid. As resistance against its flow depends on magnetic induction, changing magnitude of the applied current enables to control the damping force. In the computational model, the rotor is considered to be absolutely rigid, unbalanced and the damping elements are represented by force couplings. The goal of the analysis is to study influence of the investigated magnetorheological damper on behaviour of a rigid rotor during different transient regimes. A special attention is focused on passing the rotor through the critical speed and on planning the dependence of the applied current on speed of the rotor rotation to achieve the optimum compromise between minimizing the transmitted forces and maximum attenuation of the rotor vibrations.
ICAN/DAMP-integrated composite analyzer with damping analysis capabilities: User's manual
Saravanos, Dimitrious A.; Sanfeliz, Jose G.
1992-01-01
This manual describes the use of the computer code ICAN/DAMP (Integrated Composite Analyzer with Damping Analysis Capabilities) for the prediction of damping in polymer-matrix composites. The code is written in FORTRAN 77 and is a version of the ICAN (Integrated Composite ANalyzer) computer program. The code incorporates a new module for synthesizing the material damping from micromechanics to laminate level. Explicit micromechanics equations based on hysteretic damping are programmed relating the on-axis damping capacities to the fiber and matrix properties and fiber volume ratio. The damping capacities of unidirectional composites subjected to off-axis loading are synthesized from on-axis damping values. The hygrothermal effect on the damping performance of unidirectional composites caused by temperature and moisture variation is modeled along with the damping contributions from interfacial friction between broken fibers and matrix. The temperature rise is continuously vibrating composite plies and composite laminates is also estimated. The ICAN/DAMP user's manual provides descriptions of the damping analysis module's functions, structure, input requirements, output interpretation, and execution requirements. It only addresses the changes required to conduct the damping analysis and is used in conjunction with the 'Second Generation Integrated Composite Analyzer (ICAN) Computer Code' user's manual (NASA TP-3290).
The Effect of a Vibration Absorber on the Damping Properties of Alpine Skis
Directory of Open Access Journals (Sweden)
Stefan Schwanitz
2018-02-01
Full Text Available Coupled bending-torsion vibrations at the shovel are a severe problem when running an alpine ski at high velocities on hard or icy slopes. Thus, a major goal for ski manufacturers is to dampen vibrations through a proper multi-material design and/or additional absorbers. The aim of this study was to examine the effectiveness of a particular vibration absorber on a commercial slalom ski through a series of laboratory tests as well as a subjective field evaluation. Therefore, two identical pairs of ski were used and the absorber was deactivated on one pair. Laboratory tests revealed reductions of 5% to 49% of bending vibrations on skis with activated absorber. Subjective evaluation by 6 subjects suggested minor differences in the mean of the evaluated criteria turnablity, edge grip, steering behavior and stability towards a better performance of the skis with activated absorber. Subjects were able to identify the absorber mode with a success rate of 61.1%.
Improved Object Detection Using a Robotic Sensing Antenna with Vibration Damping Control.
Feliu-Batlle, Vicente; Feliu-Talegon, Daniel; Castillo-Berrio, Claudia Fernanda
2017-04-13
Some insects or mammals use antennae or whiskers to detect by the sense of touch obstacles or recognize objects in environments in which other senses like vision cannot work. Artificial flexible antennae can be used in robotics to mimic this sense of touch in these recognition tasks. We have designed and built a two-degree of freedom (2DOF) flexible antenna sensor device to perform robot navigation tasks. This device is composed of a flexible beam, two servomotors that drive the beam and a load cell sensor that detects the contact of the beam with an object. It is found that the efficiency of such a device strongly depends on the speed and accuracy achieved by the antenna positioning system. These issues are severely impaired by the vibrations that appear in the antenna during its movement. However, these antennae are usually moved without taking care of these undesired vibrations. This article proposes a new closed-loop control schema that cancels vibrations and improves the free movements of the antenna. Moreover, algorithms to estimate the 3D beam position and the instant and point of contact with an object are proposed. Experiments are reported that illustrate the efficiency of these proposed algorithms and the improvements achieved in object detection tasks using a control system that cancels beam vibrations.
Directory of Open Access Journals (Sweden)
Panagis G. Papadopoulos
2012-01-01
Full Text Available A short computer program, fully documented, is presented, for the step-by-step dynamic analysis of isolated cables or couples of parallel cables of a cable-stayed bridge, connected to each other and possibly with the deck of the bridge, by very thin pretensioned wires (cross-ties and subjected to variation of their axial forces due to traffic or to successive pulses of a wind drag force. A simplified SDOF model, approximating the fundamental vibration mode, is adopted for every individual cable. The geometric nonlinearity of the cables is taken into account by their geometric stiffness, whereas the material nonlinearities of the cross-ties include compressive loosening, tensile yielding, and hysteresis stress-strain loops. Seven numerical experiments are performed. Based on them, it is observed that if two interconnected parallel cables have different dynamic characteristics, for example different lengths, thus different masses, weights, and geometric stiffnesses, too, or if one of them has a small additional mass, then a single pretensioned very thin wire, connecting them to each other and possibly with the deck of the bridge, proves effective in suppressing, by its hysteresis damping, the vibrations of the cables.
DEFF Research Database (Denmark)
Jalkanen, Karl J.
2003-01-01
Here we present several low energy conformers of Leu-enkephalin (LeuE) calculated with the density functional theory using the Becke 3LYP hybrid functional and the 6-31G* basis set. The structures, conformational energies, vibrational frequencies, vibrational absorption (VA) intensities......, vibrational circular dichroism (VCD) intensities and Raman scattering intensities are reported for the conformers of LeuE which are expected to be populated at room temperature. The species of LeuE-present in non-polar solvents is the neutral non-ionic species with the NH2 and CO2H groups, in contrast...... to the zwitterionic neutral species with the NH3+ and CO2- groups which predominates in aqueous solution and in the crystal. All of our attempts to find the zwitterionic species in the isolated state failed, with the result that a hydrogen atom from the positively charged N-terminus ammonium group transferred either...
Anisotropic damping of Timoshenko beam elements
DEFF Research Database (Denmark)
Hansen, M.H.
2001-01-01
This report contains a description of a structural damping model for Timoshenko beam elements used in the aeroelastic code HawC developed at Risø for modeling wind turbines. The model has been developed to enable modeling of turbine blades which oftenhave different damping characteristics...... for ¤flapwise¤, ¤edgewise¤ and ¤torsional¤ vibrations. The structural damping forces acting on the beam element are modeled by viscous damping described by an element damping matrix. The composition of this matrix is basedon the element mass and stiffness matrices. It is shown how the coefficients for the mass...... and stiffness contributions can be calibrated to give the desired modal damping in the complete model of a blade....
Molecular structure, vibrational spectroscopic studies and natural ...
Indian Academy of Sciences (India)
pp. 845–860. Molecular structure, vibrational spectroscopic studies and natural bond orbital analysis of 7-amino-4-trifluoromethyl coumarin ..... [15] A Frisch, A B Nielsen and A J Holder, GAUSSIANVIEW Users Manual, Gaussian. Inc., Pittsburgh, PA (2000). [16] S Selladurai and K Subramanian, Acta Crystallogr. C48, 281 ...
Dynamic stiffness and damping of foundations for jacket structures
DEFF Research Database (Denmark)
Latini, Chiara; Zania, Varvara; Johannesson, Björn
2015-01-01
resistance as defined by Nogami & Novak (1977) is determined, considering 3D wave propagation within linear soil layer with hysteretic damping. Thereafter, the dynamic response of the pile is estimated assuming soil pressure equal to the soil resistance and imposing displacement compatibility. A parametric...... study clarifies the role of the parameters involved i.e. the depth of the soil layer, the pile diameter and the soil layer shear wave velocity. Results are presented in terms of dimensionless graphs which highlight the frequency dependency of the dynamic stiffness and damping....
Taylor, Larry; Leary, Terry; Stewart, Eric
1987-01-01
The damping for structural dynamic models of flexible spacecraft is usually ignored and then added after modal frequencies and mode shapes are calculated. It is common practice to assume the same damping ratio for all modes, although it is known that damping due to bending and that due to torsion are sometimes ignored. Two methods of including damping in the modeling process from its onset are examined. First, the partial derivative equations of motion are analyzed for a pinned-pinned beam with damping. The end conditions are altered to handle bodies with mass and inertia for the Spacecraft Control Laboratory Experiment (SCOLE) configuration. Second, a massless beam approximation is used for the modes with low frequencies, and a clamped-clamped system is used to approximate the modes for arbitrarily high frequency. The model is then modified to include gravity effects and is compared with experimental results.
Smart paint sensor for monitoring structural vibrations
Al-Saffar, Y.; Aldraihem, O.; Baz, A.
2012-04-01
A class of smart paint sensors is proposed for monitoring the structural vibration of beams. The sensor is manufactured from an epoxy resin which is mixed with carbon black nano-particles to make it electrically conducting and sensitive to mechanical vibrations. A comprehensive theoretical and experimental investigation is presented to understand the underlying phenomena governing the operation of this class of paint sensors and evaluate its performance characteristics. A theoretical model is presented to model the electromechanical behavior of the sensor system using molecular theory. The model is integrated with an amplifier circuit in order to predict the current and voltage developed by the paint sensor when subjected to loading. Furthermore, the sensor/amplifier circuit models are coupled with a finite element model of a base beam to which the sensor is bonded. The resulting multi-field model is utilized to predict the behavior of both the sensor and the beam when subjected to a wide variety of vibration excitations. The predictions of the multi-field finite element model are validated experimentally and the behavior of the sensor is evaluated both in the time and the frequency domains. The performance of the sensor is compared with the performance of conventional strain gages to emphasize its potential and merits. The presented techniques are currently being extended to sensors that can monitor the vibration and structural power flow of two-dimensional structures.
Yang, Zhijian; Liu, Zhiming
2017-03-01
The paper investigates the well-posedness and the longtime dynamics of the quasilinear wave equations with structural damping and supercritical nonlinearities: {{u}tt}- Δ u+{{≤ft(- Δ \\right)}α}{{u}t}-\
Reduction of Structural Vibrations by Passive and Semiactively Controlled Friction Dampers
Directory of Open Access Journals (Sweden)
L. Gaul
2014-01-01
Full Text Available Reduction of structural vibrations is of major interest in mechanical engineering for lowering sound emission of vibrating structures, improving accuracy of machines, and increasing structure durability. Besides optimization of the mechanical design or various types of passive damping treatments, active structural vibration control concepts are efficient means to reduce unwanted vibrations. In this contribution, two different semiactive control concepts for vibration reduction are proposed that adapt to the normal force of attached friction dampers. Thereby, semiactive control concepts generally possess the advantage over active control in that the closed loop is intrinsically stable and that less energy is required for the actuation than in active control. In the chosen experimental implementation, a piezoelectric stack actuator is used to apply adjustable normal forces between a structure and an attached friction damper. Simulation and experimental results of a benchmark structure with passive and semiactively controlled friction dampers are compared for stationary narrowband excitation. For simulations of the control performance, transient simulations must be employed to predict the achieved vibration damping. It is well known that transient simulation of systems with friction and normal contact requires excessive computational power due to the nonlinear constitutive laws and the high contact stiffnesses involved. However, commercial finite-element codes do not allow simulating feedback control in a general way. As a remedy, a special simulation framework is developed which allows efficiently modeling interfaces with friction and normal contact by appropriate constitutive laws which are implemented by contact elements in a finite-element model. Furthermore, special model reduction techniques using a substructuring approach are employed for faster simulation.
Analysis of long-range wakefields in CLIC main Linac Accelerating Structures with Damping Loads
De Michele, G
2012-01-01
The baseline design of the CLIC accelerating structure foresees a moderate detuning and heavy damping of high order modes (HOMs), which are the source of long-range transverse wakefields. Such unwanted fields produce bunch-to-bunch instabilities so the HOMs must be suppressed. In order to damp these modes, the CLIC RF structure is equipped with lossy material inserted into four rectangular waveguides coupled to each accelerating cell. The lossy material absorbs EM (electromagnetic) wave energy with little reflection back to the accelerating cells. In the past, computations of the long-range wake of CLIC accelerating modes have been done using perfectly absorbing boundaries to terminate the damping waveguides. In this paper, 3D EM simulations of CLIC baseline accelerating structure with HOMs damping loads will be presented. A comparison between different EM codes (GdfidL, CST PARTICLE STUDIO®) will be discussed as well as the analysis of different types of absorbing materials with respect to the wakefields da...
Active isolation of vibrations with adaptive structures
Guigou, C.; Fuller, C. R.; Wagstaff, P. R.
1991-01-01
Vibration transmission in structures is controlled by means of a technique which employs distributed arrays of piezoelectric transducers bonded to the supporting structure. Distributed PVDF piezoelectric strips are employed as error sensors, and a two-channel feedforward adaptive LMS algorithm is used for minimizing error signals and thereby controlling the structure. A harmonic force input excites a thick plate, and a receiving plate is configured with three pairs of piezoelectric actuators. Modal analyses are performed to determine the resonant frequencies of the system, and a scanning laser vibrometer is used to study the shape of the response of the receiving plate during excitation with and without the control algorithm. Efficient active isolation of the vibrations is achieved with modal suppression, and good control is noted in the on-resonance cases in which increased numbers of PVDF sensors and piezoelectric actuators are employed.
Acoustically Driven Vibrations in Cylindrical Structures
Energy Technology Data Exchange (ETDEWEB)
Chambers, David H. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2013-10-11
The purpose of this investigation is to explore the interaction of acoustics and vibration in fluid-filled cylindrical structures. Our emphasis is on describing longitudinal (axial) propagation within the structure for acoustic signals that enter externally. This paper reviews the historical and theoretical treatments of the relevant phenomenon important to the propagation of these signals along pipe structures. Our specific contribution is a detailed analysis of how external acoustic signals are coupled to a free standing pipe. There have been numerous phenomena for which these analyses are applicable. They have ranged from physical property measurements, to indoor environmental noise abatement, and onto quite significant explorations of active and passive submerged structures.
Active vibration control of civil structures
Energy Technology Data Exchange (ETDEWEB)
Farrar, C.; Baker, W.; Fales, J.; Shevitz, D.
1996-11-01
This is a final report of a one year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Active vibration control (AVC) of structural and mechanical systems is one of the rapidly advancing areas of engineering research. The multifaceted nature of AVC covers many disciplines, such as sensors and instrumentation, numerical modeling, experimental mechanics, and advanced power systems. This work encompassed a review of the literature on active control of structures focusing both on active control hardware and on control algorithms, a design of an isolation systems using magneto-rheological fluid-filled (MRF) dampers and numerical simulations to study the enhanced vibration mitigation effects of this technology.
Energy Technology Data Exchange (ETDEWEB)
Kabbara, Alan; McCarthy, John; Burnett, Timm; Forster, Ian [National Oilwell Varco Downhole Ltd. (NOV), Houston, TX (United States)
2012-07-01
This paper describes the work, on test rigs and full-scale drilling rigs, carried out with respect to placement of an Asymmetric Vibration Damping Tool (AVDT) within drilling while under reaming operations. An AVDT, by virtue of the forward synchronous motion imposed on the drill string, offers benefits in minimizing down hole vibration-related tool failures and therefore maximizing rate of penetration (ROP). Of interest in using the AVDT is the tendency to minimize stick slip by means of the parasitic torque it generates. This is of particular importance during under reaming operations. While under reaming, stick slip can result in low (ROP) and potentially an increased incidence of down hole tool failures. The use of an AVDT in these operations has been shown to significantly reduce stick slip. However, due to the forward synchronous motion caused by the AVDT, there is the potential to cause eccentric wear to the Bottom Hole Assembly (BHA) components in the vicinity of the AVDT. If allowed to progress, this eccentric wear can cause a reduction in down hole tool life and drilling performance. Eliminating eccentric wear would be beneficial in reducing repair costs, extending component life and further improving drilling performance. To minimize eccentric wear and maximize drilling performance, the placement of the AVDT within the BHA is critical. This paper describes how the placement of intermediate stabilizers between the AVDT and the under reamer can minimize eccentric wear to the under reamer and the adjacent drill string due to the forward synchronous whirl induced by the AVDT. This approach allows the full benefits of the AVDT to be recognized while reducing the potentially damaging effects of eccentric wear to other BHA components. The work has drawn upon small-scale rig testing, full-scale testing at the Ullrigg test facility in Norway and from real-world drilling and under reaming operations in the USA. (author)
Optimal Damping of Stays in Cable-Stayed Bridges for In-Plane Vibrations
DEFF Research Database (Denmark)
Jensen, C.N.; Nielsen, S.R.K.; Sørensen, John Dalsgaard
2002-01-01
cable-stayed bridges are often designed as twin cables with a spacing of, say 1m. In such cases, it is suggested in the paper to suppress the mentioned in-plane types of vibrations by means of a tuned mass–damper (TMD) placed between the twin cables at their midpoints. The TMD divides the stay into four...... of the mentioned frequencies. The spring and the damper constants of the TMD are optimized so that the variances of the displacement of the adjacent four half-cables, the support point of the TMD and the secondary mass are minimized. At optimal design, it is shown that the variances reduce below 14% of those...
Nasser, Fatima; Li, Zhongyang; Gueguen, Philippe; Martin, Nadine
2016-06-01
This paper deals with the application of the Automatic Model-Based Approach (AMBA) over actual buildings subjected to real-world ambient vibrations. In a previous paper, AMBA was developed with the aim of automating the estimation process of the modal parameters and minimizing the estimation error, especially that of the damping ratio. It is applicable over a single-channel record, has no parameters to be set, and no manual initialization phase. The results presented in this paper should be regarded as further documentation of the approach over real-world ambient vibration signals.
Characterization of Slosh Damping for Ortho-Grid and Iso-Grid Internal Tank Structures
Westra, Douglas G.; Sansone, Marco D.; Eberhart, Chad J.; West, Jeffrey S.
2016-01-01
Grid stiffened tank structures such as Ortho-Grid and Iso-Grid are widely used in cryogenic tanks for providing stiffening to the tank while reducing mass, compared to tank walls of constant cross-section. If the structure is internal to the tank, it will positively affect the fluid dynamic behavior of the liquid propellant, in regard to fluid slosh damping. As NASA and commercial companies endeavor to explore the solar system, vehicles will by necessity become more mass efficient, and design margin will be reduced where possible. Therefore, if the damping characteristics of the Ortho-Grid and Iso-Grid structure is understood, their positive damping effect can be taken into account in the systems design process. Historically, damping by internal structures has been characterized by rules of thumb and for Ortho-Grid, empirical design tools intended for slosh baffles of much larger cross-section have been used. There is little or no information available to characterize the slosh behavior of Iso-Grid internal structure. Therefore, to take advantage of these structures for their positive damping effects, there is much need for obtaining additional data and tools to characterize them. Recently, the NASA Marshall Space Flight Center conducted both sub-scale testing and computational fluid dynamics (CFD) simulations of slosh damping for Ortho-Grid and Iso-Grid tanks for cylindrical tanks containing water. Enhanced grid meshing techniques were applied to the geometrically detailed and complex Ortho-Grid and Iso-Grid structures. The Loci-STREAM CFD program with the Volume of Fluid Method module for tracking and locating the water-air fluid interface was used to conduct the simulations. The CFD simulations were validated with the test data and new empirical models for predicting damping and frequency of Ortho-Grid and Iso-Grid structures were generated.
Directory of Open Access Journals (Sweden)
Dang Xuan Truong
2014-12-01
Full Text Available The report presents a methodology to determine the directions of the stiffness principal axis (in this case subject to the linear displacement and forced rotation angle of a solid object interact with the surrounding environment by resilient bearing supports. The results also show that determining the coordinates of the stiffness center in the vibrating system with damping factors is necessary in our research.
Weiss, Johannes; Maier, Martin; Herrmann, Hans-Georg; Steibler, Philipp
2004-07-01
In the automotive industry, the need for affordable lightweight structures rises as new fuel consumption regulations tighten and customers demand for performance increases. One way of achieving a cost-effective and weight-optimal design is by means of structural optimization. In 1991, A. Baumgartner, S. Burkhardt and C. Mattheck published their first paper on topology optimization based on bionic principles. Nature is inevitably dependent on the most efficient use of the body's mass. Using a fully-stressed-method, the original SKO-method is able to optimize engineering components with regard to maximum strength and stiffness. For several years now, the SKO-method has been successfully applied and enhanced for complex structural optimization at the Research & Technology Division of DaimlerChrysler AG. The subject presented in this paper was investigated in cooperation with the Institut fur Verbundwerkstoffe GmbH at the Technical University of Kaiserslautern. The aim is to present the new developments concerning the SKO-method. Starting with a short introduction to the original SKO-method, the newly implemented FreedOpt (Frequency and Damping Optimization) module is explained afterwards. FreedOpt can tune natural frequencies to a desired level. In cases were the tuning of frequencies is not sufficient, damping is needed. The new module is able to optimize the utilization of damping material with a new approach based on maximizing the dissipated vibration energy. The main focus of the paper is on the verification of the simulation results with physical tests. Finally, the new tool is applied to automotive parts. Concluding, the authors give an outlook for future work.
Occupant traffic estimation through structural vibration sensing
Pan, Shijia; Mirshekari, Mostafa; Zhang, Pei; Noh, Hae Young
2016-04-01
The number of people passing through different indoor areas is useful in various smart structure applications, including occupancy-based building energy/space management, marketing research, security, etc. Existing approaches to estimate occupant traffic include vision-, sound-, and radio-based (mobile) sensing methods, which have placement limitations (e.g., requirement of line-of-sight, quiet environment, carrying a device all the time). Such limitations make these direct sensing approaches difficult to deploy and maintain. An indirect approach using geophones to measure floor vibration induced by footsteps can be utilized. However, the main challenge lies in distinguishing multiple simultaneous walkers by developing features that can effectively represent the number of mixed signals and characterize the selected features under different traffic conditions. This paper presents a method to monitor multiple persons. Once the vibration signals are obtained, features are extracted to describe the overlapping vibration signals induced by multiple footsteps, which are used for occupancy traffic estimation. In particular, we focus on analysis of the efficiency and limitations of the four selected key features when used for estimating various traffic conditions. We characterize these features with signals collected from controlled impulse load tests as well as from multiple people walking through a real-world sensing area. In our experiments, the system achieves the mean estimation error of +/-0.2 people for different occupant traffic conditions (from one to four) using k-nearest neighbor classifier.
Nonlinear frequency response analysis of structural vibrations
Weeger, Oliver; Wever, Utz; Simeon, Bernd
2014-12-01
In this paper we present a method for nonlinear frequency response analysis of mechanical vibrations of 3-dimensional solid structures. For computing nonlinear frequency response to periodic excitations, we employ the well-established harmonic balance method. A fundamental aspect for allowing a large-scale application of the method is model order reduction of the discretized equation of motion. Therefore we propose the utilization of a modal projection method enhanced with modal derivatives, providing second-order information. For an efficient spatial discretization of continuum mechanics nonlinear partial differential equations, including large deformations and hyperelastic material laws, we employ the concept of isogeometric analysis. Isogeometric finite element methods have already been shown to possess advantages over classical finite element discretizations in terms of higher accuracy of numerical approximations in the fields of linear vibration and static large deformation analysis. With several computational examples, we demonstrate the applicability and accuracy of the modal derivative reduction method for nonlinear static computations and vibration analysis. Thus, the presented method opens a promising perspective on application of nonlinear frequency analysis to large-scale industrial problems.
Vibrational Based Inspection of Civil Engineering Structures
DEFF Research Database (Denmark)
Rytter, Anders
and Structural Engineering at the University of Aalborg since the beginning of 1992. Both projects have been supported by the Danish Technical Research Council. Further, the first mentioned project was supported by the Danish Energy Agency. Their financial support is gratefully acknowledged.......The thesis has been written in relation to two different research projects. Firstly, an offshore test programme, Integrated Experimental/Numerical Analysis of the Dynamic behavior of offshore structures, which was performed at the department of Building Technology and Structural Engineering...... at the University of Aalborg from 1988 to 1991. Secondly, a research project, In-Field Vibration Based Inspection of Civil Engineering Structures, which has been performed as a pilot project by the Consulting Engineers Rambøll, Hannemann and Højlund in cooperation with the department of Building Technology...
Vibration health monitoring for tensegrity structures
Ashwear, Nasseradeen; Eriksson, Anders
2017-02-01
Tensegrities are assembly structures, getting their equilibrium from the interaction between tension in cables and compression in bars. During their service life, slacking in their cables and nearness to buckling in their bars need to be monitored to avoid a sudden collapse. This paper discusses how to design the tensegrities to make them feasible for vibrational health monitoring methods. Four topics are discussed; suitable finite elements formulation, pre-measurements analysis to find the locations of excitation and sensors for the interesting modes, the effects from some environmental conditions, and the pre-understanding of the effects from different slacking scenarios.
Agnes, Gregory Stephen
Linear vibration absorbers are a valuable tool used to suppress vibrations due to harmonic excitation in structural systems. Limited evaluation of the performance of nonlinear vibration absorbers for nonlinear structures exists in the current literature. The state of the art is extended in this work to vibration absorbers in their three major physical implementations: the mechanical vibration absorber, the inductive-resistive shunted piezoelectric vibration absorber, and the electronic vibration absorber (also denoted a positive position feedback controller). A single, consistent, physically similar model capable of examining the response of all three devices is developed. The performance of vibration absorbers attached to single-degree-of-freedom structures is next examined for performance, robustness, and stability. Perturbation techniques and numerical analysis combine to yield insight into the tuning of nonlinear vibration absorbers for both linear and nonlinear structures. The results both clarify and validate the existing literature on mechanical vibration absorbers. Several new results, including an analytical expression for the suppression region's location and bandwidth and requirements for its robust performance, are derived. Nonlinear multiple-degree-of-freedom structures are next evaluated. The theory of Non-linear Normal Modes is extended to include consideration of modal damping, excitation, and small linear coupling, allowing estimation of vibration absorber performance. The dynamics of the N+1-degree-of-freedom system reduce to those of a two-degree-of-freedom system on a four-dimensional nonlinear modal manifold, thereby simplifying the analysis. Quantitative agreement is shown to require a higher order model which is recommended for future investigation. Finally, experimental investigation on both single and multi-degree-of-freedom systems is performed since few experiments on this topic are reported in the literature. The experimental results
Vibration Analysis and Design of a Structure Subjected to Human Walking Excitations
Directory of Open Access Journals (Sweden)
M. Setareh
2010-01-01
Full Text Available Annoying building floor vibrations have become a serious serviceability issue. This is mainly due to decrease in the system mass resulting from the use of higher strength materials; use of computer-assisted design and the Load and Resistance Factor Design Method to optimize the structure based on the strength requirements; fewer partitions and more innovative designs by architects achieving long, column free spans resulting in a reduction in the natural frequency and damping. This paper provides details of the vibration analysis and design of a novel office building. Three-dimensional computer models of the structure were created and various modifications were made to the original structure, designed based on static loads, to reduce the possible excessive floor vibrations when subjected to walking excitations. Tuned mass dampers were also designed as a back-up vibration control system. A series of dynamic tests were conducted on the building floor to identify the dynamic properties of the structure and these were then used to update the original computer model. Finally, various forcing functions representing human walks and the updated computer model of the structure were used to evaluate the accuracy of the walking excitation force models to predict the structural response. Conclusions are made on the validity of each forcing function studied here.
Study of modal coupling procedures for the shuttle: A matrix method for damping synthesis
Hasselman, T. K.
1972-01-01
The damping method was applied successfully to real structures as well as analytical models. It depends on the ability to determine an appropriate modal damping matrix for each substructure. In the past, modal damping matrices were assumed diagonal for lack of being able to determine the coupling terms which are significant in the general case of nonproportional damping. This problem was overcome by formulating the damped equations of motion as a linear perturbation of the undamped equations for light structural damping. Damped modes are defined as complex vectors derived from the complex frequency response vectors of each substructure and are obtained directly from sinusoidal vibration tests. The damped modes are used to compute first order approximations to the modal damping matrices. The perturbation approach avoids ever having to solve a complex eigenvalue problem.
A New Control Structure for Multi-Terminal dc Grids to Damp Inter-Area Oscillations
DEFF Research Database (Denmark)
Eriksson, Robert
2014-01-01
This article analyzes the control structure of the multi-terminal dc (MTDC) system to damp ac system interarea oscillations through active power modulation. A new control structure is presented that maximizes the relative controllability without the need for communication among the dc terminals....... In point-to-point high voltage dc (HVDC) transmission, the active power modulation of the two terminals occurs in opposite directions. In this case the control direction is given and only needs to be phase compensated to align for maximal damping. In the case of MTDC systems the control direction...
Acceleration response spectrum for prediction of structural vibration due to individual bouncing
Chen, Jun; Wang, Lei; Racic, Vitomir; Lou, Jiayue
2016-08-01
This study is designed to develop an acceleration response spectrum that can be used in vibration serviceability assessment of civil engineering structures, such as floors and grandstands those are dynamically excited by individual bouncing. The spectrum is derived from numerical simulations and statistical analysis of acceleration responses of a single degree of freedom system with variable natural frequency and damping under a large number of experimentally measured individual bouncing loads. Its mathematical representation is fit for fast yet reliable application in design practice and is comprised of three equations that describe three distinct frequency regions observed in the actual data: the first resonant plateau (2-3.5 Hz), the second resonant plateau (4-7 Hz) and a descension region (7-15 Hz). Finally, this paper verifies the proposed response spectrum approach to predict structural vibration by direct comparison against numerical simulations and experimental results.
Study on Structure Property of Cantilever Piezoelectric Vibration Generator
National Research Council Canada - National Science Library
Yan Zhen; He Qing; Liu Junfeng
2014-01-01
For increasing generating capacity of cantilever piezoelectric vibration generator with limited volume, influence rule of structure parameter to generating capacity of unimorph, bimorph in series...
Directory of Open Access Journals (Sweden)
Yakai Xu
2017-01-01
Full Text Available Dynamic stiffness and damping of the headstock, which is a critical component of precision horizontal machining center, are two main factors that influence machining accuracy and surface finish quality. Constrained Layer Damping (CLD structure is proved to be effective in raising damping capacity for the thin plate and shell structures. In this paper, one kind of high damping material is utilized on the headstock to improve damping capacity. The dynamic characteristic of the hybrid headstock is investigated analytically and experimentally. The results demonstrate that the resonant response amplitudes of the headstock with damping material can decrease significantly compared to original cast structure. To obtain the optimal configuration of damping material, a topology optimization method based on the Evolutionary Structural Optimization (ESO is implemented. Modal Strain Energy (MSE method is employed to analyze the damping and to derive the sensitivity of the modal loss factor. The optimization results indicate that the added weight of damping material decreases by 50%; meanwhile the first two orders of modal loss factor decrease by less than 23.5% compared to the original structure.
MECHANISM OF ORIGIN OF STRUCTURAL VIBRATIONS IN CONICAL ROLLER BEARINGS
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V.І. Marchuk
2014-09-01
Full Text Available This paper investigates the mechanism of origin of structural, structural and technological defects of rollers. The technique for integrated indicator of vibration working surfaces of the rings to determine the level of life of the finished part to the operation as part of the bearing and predict the vibroacoustic characteristics of rolling bearings. It was established that technological defects cause low-frequency and high-frequency vibrations. The question about the extent to which it is necessary to strengthen the tolerances on the parameters of bearings on which vibration level is determined not errors bearing parts and their structural properties. Calculated values of the amplitudes vibroacceleration due to the rigidity of the bearing vibrations are so small that in some cases adopted precision calculations turned enough to detect such vibrations. Thus, when tested on the vibro-acoustic installations structural vibration does not play an important role.
DEFF Research Database (Denmark)
Kook, Junghwan; Jensen, Jakob Søndergaard
2014-01-01
relation expressing how an increased damping due to the acoustic medium surrounding the microbeam affect the MDR of the macrobeam. We further analyze the effect of including dissipation of the acoustic medium by using finite element (FE) analysis with acoustic-structure interaction (ASI) using a simple...
Distribution of large-earthquake input energy in viscous damped outrigger structures
Morales Beltran, M.G.; Turan, Gursoy; Yildirim, Umut
2017-01-01
This article provides an analytical framework to assess the distribution of seismic energy in outrigger structures equipped with viscous dampers. The principle of damped outriggers for seismic control applications lies on the assumption that the total earthquake energy will be absorbed by the
Directory of Open Access Journals (Sweden)
Douglas Domingues Bueno
2008-01-01
Full Text Available This paper deals with the study of algorithms for robust active vibration control in flexible structures considering uncertainties in system parameters. It became an area of enormous interest, mainly due to the countless demands of optimal performance in mechanical systems as aircraft, aerospace, and automotive structures. An important and difficult problem for designing active vibration control is to get a representative dynamic model. Generally, this model can be obtained using finite element method (FEM or an identification method using experimental data. Actuators and sensors may affect the dynamics properties of the structure, for instance, electromechanical coupling of piezoelectric material must be considered in FEM formulation for flexible and lightly damping structure. The nonlinearities and uncertainties involved in these structures make it a difficult task, mainly for complex structures as spatial truss structures. On the other hand, by using an identification method, it is possible to obtain the dynamic model represented through a state space realization considering this coupling. This paper proposes an experimental methodology for vibration control in a 3D truss structure using PZT wafer stacks and a robust control algorithm solved by linear matrix inequalities.
Chortis, Dimitris I
2013-01-01
This book concerns the development of novel finite elements for the structural analysis of composite beams and blades. The introduction of material damping is also an important aspect of composite structures and it is presented here in terms of their static and dynamic behavior. The book thoroughly presents a new shear beam finite element, which entails new blade section mechanics, capable of predicting structural blade coupling due to composite coupling and/or internal section geometry. Theoretical background is further expanded towards the inclusion of nonlinear structural blade models and damping mechanics for composite structures. The models effectively include geometrically nonlinear terms due to large displacements and rotations, improve the modeling accuracy of very large flexible blades, and enable the modeling of rotational stiffening and buckling, as well as, nonlinear structural coupling. Validation simulations on specimen level study the geometric nonlinearities effect on the modal frequencies and...
Stiffness and damping in mechanical design
National Research Council Canada - National Science Library
Rivin, Eugene I
1999-01-01
... important conceptual issues are stiffness of mechanical structures and their components and damping in mechanical systems sensitive to and/or generating vibrations. Stiffness and strength are the most important criteria for many mechanical designs. However, although there are hundreds of books on various aspects of strength, and strength issues ar...
Magnetic sensor for building structural vibrations.
García, Alfonso; Morón, Carlos; Tremps, Enrique
2014-02-05
This paper shows a new displacement-to-frequency transducer based on the variation of a coil inductance when a magnetic core is partially or completely inserted inside. This transducer is based on a Colpitts oscillator due its low manufacturing price, behavior and immunity to noise. A tank circuit with a configuration in parallel was used because it can be employed at lower frequencies and it enables it to make a direct analysis. The sensor has a dynamic range equal to the length of the coil. The cores can exchange sensors (coils with its ferromagnetic core) using the same electronic measuring system. In this way, with only an electronic circuit, the core sensor determines the measurement range. The obtained resolution is higher than 1/100,000, and the sensor also allows the measurement and knowing in real time the effect of vibration, thermal expansion, referred overload movements, etc.., that can occur in the structural elements of a building.
Dolgin, Benjamin P. (Inventor)
1994-01-01
A superconductive load bearing support without a mechanical contact and vibration damping for cryogenic instruments in space is presented. The levitation support and vibration damping is accomplished by the use of superconducting magnets and the 'Meissner' effect. The assembly allows for transfer of vibration energy away from the cryogenic instrument which then can be damped by the use of either an electronic circuit or conventional vibration damping mean.
Review of vibration effect during piling installation to adjacent structure
Rahman, Nurul Aishah Abd; Musir, Adhilla Ainun; Dahalan, Nurol Huda; Ghani, Abdul Naser Abdul; Khalil, Muhamad Kasimi Abd
2017-12-01
Basically, many major structures across the world such as towers, high rise building, houses and bridges utilize pile as a support material. The use of pile is important to strengthen the structures. However, this has led to another problem to the nearest surrounding structures resulted from pile driving. As part of a construction work, unavoidable pile driving activity generates a vibration towards the surrounding structures if uncontrolled may cause damage to the adjacent structure. As the current construction works are frequently located in urban areas where the distance between the nearest building structures is not far, vibration may cause damage to nearby structures. Knowing which part of the building that is mostly affected by various vibration patterns from the impact of pile driving is crucial. Thus, it is very important to predict the impact of vibration during piling installation work. This paper reviews the vibrations generated by piling activity toward surrounding structures in terms sources of vibration, impact of piling installation, pile-soil interaction, and factors affecting the vibration impact of building as well as to study the parameters involved in vibration generation during piling works.
Time-History Analysis of Frictionally Damped Structures
Ştefancu, Andrei-Ionuţ; Budescu, Mihai; Păluleţ-Crăiniceanu, Fideliu
2011-01-01
During major seismic actions, a significant amount of energy is induced to structures. The means by which this energy is dissipated, determines the level of structural degradation. Special emphasis is placed on avoiding loss of human lives due to the earthquake action. In order to achieve this, the structures are designed ductile so that energy is dissipated by the system’s elements by bending, twisting or degradation. This dissipative mechanism involves significant degradation of the structu...
Preliminary Study on the Damping Effect of a Lateral Damping Buffer under a Debris Flow Load
Directory of Open Access Journals (Sweden)
Zheng Lu
2017-02-01
Full Text Available Simulating the impact of debris flows on structures and exploring the feasibility of applying energy dissipation devices or shock isolators to reduce the damage caused by debris flows can make great contribution to the design of disaster prevention structures. In this paper, we propose a new type of device, a lateral damping buffer, to reduce the vulnerability of building structures to debris flows. This lateral damping buffer has two mechanisms of damage mitigation: when debris flows impact on a building, it acts as a buffer, and when the structure vibrates due to the impact, it acts as a shock absorber, which can reduce the maximum acceleration response and subsequent vibration respectively. To study the effectiveness of such a lateral damping buffer, an impact test is conducted, which mainly involves a lateral damping buffer attached to a two-degree-of-freedom structure under a simulated debris flow load. To enable the numerical study, the equation of motion of the structure along with the lateral damping buffer is derived. A subsequent parametric study is performed to optimize the lateral damping buffer. Finally, a practical design procedure is also provided.
Nonlinear vibration with control for flexible and adaptive structures
Wagg, David
2015-01-01
This book provides a comprehensive discussion of nonlinear multi-modal structural vibration problems, and shows how vibration suppression can be applied to such systems by considering a sample set of relevant control techniques. It covers the basic principles of nonlinear vibrations that occur in flexible and/or adaptive structures, with an emphasis on engineering analysis and relevant control techniques. Understanding nonlinear vibrations is becoming increasingly important in a range of engineering applications, particularly in the design of flexible structures such as aircraft, satellites, bridges, and sports stadia. There is an increasing trend towards lighter structures, with increased slenderness, often made of new composite materials and requiring some form of deployment and/or active vibration control. There are also applications in the areas of robotics, mechatronics, micro electrical mechanical systems, non-destructive testing and related disciplines such as structural health monitoring. Two broader ...
Stiffness and Damping related to steady state soil-structure Interaction of monopiles
DEFF Research Database (Denmark)
Bayat, Mehdi
The present thesis concerns soil–structure interaction affecting the dynamic structural response of offshore wind turbines with focus on soil stiffness and seepage damping due to pore water flow generated by cyclic motion of a monopile. The thesis aims to improve modelling of the dynamic...... and dashpots. An appropriate model based on considering the effect of dynamic behaviour of soil–structure interaction has been explored. In this regard, the coupled equations for porous media have been employed in order to account for soil deformation as well as pore pressure. The effects of drained versus...... undrained behaviour of the soil and the impact of this behaviour on the stiffness and damping related to soil–structure interaction at different load frequencies have been illustrated. Based on the poroelastic and Kelvin models, more realistic dynamic properties have been presented by considering the effect...
Gibson, Frederick W
1956-01-01
Results of an experimental investigation of the structural damping of six full-scale helicopter rotor blades, made to determine the variation of structural damping with materials and methods of construction, are presented. The damping of the blades was determined for the first three flapwise bending modes, first chordwise bending mode, and first torsion mode. The contribution of structural damping to the total damping of the blades is discussed for several aerodynamic conditions in order to point out situations where structural damping is significant.
Damping Proceedings Held in Las Vegas, Nevada on 5-7 March 1986. Volume 1
1986-05-01
Vibrations by Means of Viscoelastic Laminate," Section III of Structural Damping, ASME, pp. 49-88, 1959. 14. H. Oberst and K. Frankenfeld, " Uber die Dampfung...Vibrations by Means of Viscoelastic Laminate," Section III of Structural Damping, ASME, pp. 49-88, 1959. 14. H. Oberst and K. Frankenfeld, " Uber die...extreme care and payment of full attention to specimen dimensions. For example, the resonance techniques2 (3) are shown to be useful from 100 to 1000
Finite Element Vibration and Dynamic Response Analysis of Engineering Structures
Directory of Open Access Journals (Sweden)
Jaroslav Mackerle
2000-01-01
Full Text Available This bibliography lists references to papers, conference proceedings, and theses/dissertations dealing with finite element vibration and dynamic response analysis of engineering structures that were published from 1994 to 1998. It contains 539 citations. The following types of structures are included: basic structural systems; ground structures; ocean and coastal structures; mobile structures; and containment structures.
Design of high gradient, high repetition rate damped C -band rf structures
Alesini, David; Bellaveglia, Marco; Bini, Simone; Gallo, Alessandro; Lollo, Valerio; Pellegrino, Luigi; Piersanti, Luca; Cardelli, Fabio; Migliorati, Mauro; Mostacci, Andrea; Palumbo, Luigi; Tocci, Simone; Ficcadenti, Luca; Pettinacci, Valerio
2017-03-01
The gamma beam system of the European Extreme Light Infrastructure-Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C -band structures, 1.8 m long with a field phase advance per cell of 2 π /3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM) damping system to avoid beam breakup (BBU). They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC) rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping.
Design of high gradient, high repetition rate damped C-band rf structures
Directory of Open Access Journals (Sweden)
David Alesini
2017-03-01
Full Text Available The gamma beam system of the European Extreme Light Infrastructure–Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C-band structures, 1.8 m long with a field phase advance per cell of 2π/3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM damping system to avoid beam breakup (BBU. They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping.
Innovation in Active Vibration Control Strategy of Intelligent Structures
Directory of Open Access Journals (Sweden)
A. Moutsopoulou
2014-01-01
Full Text Available Large amplitudes and attenuating vibration periods result in fatigue, instability, and poor structural performance. In light of past approaches in this field, this paper intends to discuss some innovative approaches in vibration control of intelligent structures, particularly in the case of structures with embedded piezoelectric materials. Control strategies are presented, such as the linear quadratic control theory, as well as more advanced theories, such as robust control theory. The paper presents sufficiently a recognizable advance in knowledge of active vibration control in intelligent structures.
Yaw control for active damping of structural dynamics
Energy Technology Data Exchange (ETDEWEB)
Ekelund, T. [Chalmers Univ. of Technology, Goeteborg (Sweden). Control Engineering Lab.
1996-12-01
Yaw torque control for reduction of structural dynamic loads in a two-bladed wind turbine is investigated. The models are obtained using rigid-body mechanics. Linear quadratic control theory is utilized for design and analysis. The analysis of two simple examples, where the teeter angle and the tower lateral bending motion are regarded, shows that a time-varying controller has some advantages compared with a time-invariant controller. 6 refs, 9 figs
Nondestructive determination of fatigue crack damage in composites using vibration tests.
Dibenedetto, A. T.; Gauchel, J. V.; Thomas, R. L.; Barlow, J. W.
1972-01-01
The vibration response of glass reinforced epoxy and polyester laminates was investigated. The complex modulus and the damping capacity were measured as fatigue crack damage accumulated. Changes in the Young's modulus as well as the damping capacity correlated with the amount of crack damage. The damping was especially sensitive to debonding of the reinforcement from the resin matrix. Measurement of these vibration response changes shows promise as a means to nondestructively test the structural integrity of filament-reinforced composite structural members.
Vibration of hydraulic machinery
Wu, Yulin; Liu, Shuhong; Dou, Hua-Shu; Qian, Zhongdong
2013-01-01
Vibration of Hydraulic Machinery deals with the vibration problem which has significant influence on the safety and reliable operation of hydraulic machinery. It provides new achievements and the latest developments in these areas, even in the basic areas of this subject. The present book covers the fundamentals of mechanical vibration and rotordynamics as well as their main numerical models and analysis methods for the vibration prediction. The mechanical and hydraulic excitations to the vibration are analyzed, and the pressure fluctuations induced by the unsteady turbulent flow is predicted in order to obtain the unsteady loads. This book also discusses the loads, constraint conditions and the elastic and damping characters of the mechanical system, the structure dynamic analysis, the rotor dynamic analysis and the system instability of hydraulic machines, including the illustration of monitoring system for the instability and the vibration in hydraulic units. All the problems are necessary for vibration pr...
Ultra-low damping in lift-off structured yttrium iron garnet thin films
Krysztofik, A.; Coy, L. E.; Kuświk, P.; Załeski, K.; Głowiński, H.; Dubowik, J.
2017-11-01
We show that using maskless photolithography and the lift-off technique, patterned yttrium iron garnet thin films possessing ultra-low Gilbert damping can be accomplished. The films of 70 nm thickness were grown on (001)-oriented gadolinium gallium garnet by means of pulsed laser deposition, and they exhibit high crystalline quality, low surface roughness, and the effective magnetization of 127 emu/cm3. The Gilbert damping parameter is as low as 5 ×10-4. The obtained structures have well-defined sharp edges which along with good structural and magnetic film properties pave a path in the fabrication of high-quality magnonic circuits and oxide-based spintronic devices.
Vibrations in lightweight structures - Efficiency and reduction of numerical models
Flodén, Ola
2014-01-01
Multi-storey wood buildings have been increasing in popularity since a century-old ban on the construction of such buildings was lifted in 1994. Compared to conventional concrete structures, it is more difficult to build lightweight structures in such a way that noise and disturbing vibrations is avoided. To design buildings of high performance regarding sound and vibrations, it is desirable to have tools for predicting the effects of structural modifications prior to construction. The long-t...
Design, Fabrication, and Properties of High Damping Metal Matrix Composites—A Review
Directory of Open Access Journals (Sweden)
Qianfeng Fang
2009-08-01
Full Text Available Nowadays it is commonly considered that high damping materials which have both the good mechanical properties as structural materials and the high damping capacity for vibration damping are the most direct vibration damping solution. In metals and alloys however, exhibiting simultaneously high damping capacity and good mechanical properties has been noted to be normally incompatible because the microscopic mechanisms responsible for internal friction (namely damping capacity are dependent upon the parameters that control mechanical strength. To achieve a compromise, one of the most important methods is to develop two-phase composites, in which each phase plays a specific role: damping or mechanical strength. In this review, we have summarized the development of the design concept of high damping composite materials and the investigation of their fabrication and properties, including mechanical and damping properties, and suggested a new design concept of high damping composite materials where the hard ceramic additives exhibit high damping capacity at room temperature owing to the stress-induced reorientation of high density point defects in the ceramic phases and the high damping capacity of the composite comes mainly from the ceramic phases.
Attractor of Beam Equation with Structural Damping under Nonlinear Boundary Conditions
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Danxia Wang
2015-01-01
Full Text Available Simultaneously, considering the viscous effect of material, damping of medium, and rotational inertia, we study a kind of more general Kirchhoff-type extensible beam equation utt-uxxtt+uxxxx-σ(∫0l(ux2dxuxx-ϕ(∫0l(ux2dxuxxt=q(x, in [0,L]×R+ with the structural damping and the rotational inertia term. Little attention is paid to the longtime behavior of the beam equation under nonlinear boundary conditions. In this paper, under nonlinear boundary conditions, we prove not only the existence and uniqueness of global solutions by prior estimates combined with some inequality skills, but also the existence of a global attractor by the existence of an absorbing set and asymptotic compactness of corresponding solution semigroup. In addition, the same results also can be proved under the other nonlinear boundary conditions.
Vibration Antiresonance Design for a Spacecraft Multifunctional Structure
Directory of Open Access Journals (Sweden)
Dong-Xu Li
2017-01-01
Full Text Available Spacecraft must withstand rigorous mechanical environment experiences such as acceleration, noise, vibration, and shock during the process of launching, satellite-vehicle separation, and so on. In this paper, a new spacecraft multifunctional structure concept designed by us is introduced. The multifunctional structure has the functions of not only load bearing, but also vibration reduction, energy source, thermal control, and so on, and we adopt a series of viscoelastic parts as connections between substructures. Especially in this paper, a vibration antiresonance design method is proposed to realize the vibration reduction. The complex zero-point equations of the vibration system are firstly established, and then the vibration antiresonance design for the system is achieved. For solving the difficulties due to viscoelastic characteristics of the connecting parts, we present the determining formulas to obtain the structural parameters, so that the complex zero-point equations can be satisfied. Numerical simulation and ground experiment demonstrate the correctness and effectiveness of the proposed method. This method can solve the structural vibration control problem under the function constraints of load bearing and energy supplying and will expand the performance of spacecraft functional modules.
A high phase advance damped and detuned structure for the main linacs of CLIC
Khan, V.F.; Grudiev, A.; Jones, R.M.; Wuensch, W.
2010-01-01
The main accelerating structures for the CLIC are designed to operate at an average accelerating gradient of 100 MV/m. The accelerating frequency has been optimised to 11.994 GHz with a phase advance of 2π/3 [1] of the main accelerating mode. The moderately damped and detuned structure (DDS) design [2-3] is being studied as an alternative to the strongly damped WDS design [1]. Both these designs are based on the nominal accelerating phase advance. Here we explore high phase advance (HPA) structures in which the group velocity of the rf fields is reduced compared to that of standard (2π/3) structures. The electrical breakdown strongly depends on the fundamental mode group velocity. Hence it is expected that electrical breakdown is less likely to occur in the HPA structures. We report on a study of both the fundamental and dipole modes in a CLIC_DDS_ HPA structure, designed to operate at 5π/6 phase advance per cell. Higher order dipole modes in both the standard and HPA structures are also studied.
Vibration Response Characteristics of the Cross Tunnel Structure
Directory of Open Access Journals (Sweden)
Jinxing Lai
2016-01-01
Full Text Available It is well known that the tunnel structure will lose its function under the long-term repeated function of the vibration effect. A prime example is the Xi’an cross tunnel structure (CTS of Metro Line 2 and the Yongningmen tunnel, where the vibration response of the tunnel vehicle load and metro train load to the structure of shield tunnel was analyzed by applying the three-dimensional (3D dynamic finite element model. The effect of the train running was simulated by applying the time-history curves of vibration force of the track induced by wheel axles, using the fitted formulas for vehicle and train vibration load. The characteristics and the spreading rules of vibration response of metro tunnel structure were researched from the perspectives of acceleration, velocity, displacement, and stress. It was found that vehicle load only affects the metro tunnel within 14 m from the centre, and the influence decreases gradually from vault to spandrel, haunch, and springing. The high-speed driving effect of the train can be divided into the close period, the rising period, the stable period, the declining period, and the leaving period. The stress at haunch should be carefully considered. The research results presented for this case study provide theoretical support for the safety of vibration response of Metro Line 2 structure.
Ferré, Michel A.; Clerc, Marcel G.; Coulibally, Saliya; Rojas, René G.; Tlidi, Mustapha
2017-06-01
Driven damped coupled oscillators exhibit complex spatiotemporal dynamics. An archetype model is the driven damped sine-Gordon equation, which can describe several physical systems such as coupled pendula, extended Josephson junction, optical systems and driven magnetic wires. Close to resonance an enveloped model in the form Lugiato-Lefever equation can be derived from the driven damped sine-Gordon equation. We compare the dynamics obtained from both models. Unexpectedly, qualitatively similar dynamical behaviors are obtained for both models including homogeneous steady states, localized structures, and pattern waves. For large forcing, both systems share similar spatiotemporal chaos.
Truncated acoustic black hole structure with the optimized tapering shape and damping coating
DEFF Research Database (Denmark)
Ih, Jeong-Guon; Kim, Miseong; Lee, Ik Jin
2016-01-01
The acoustic black hole (ABH) structure can be an option as a vibration damper by providing a tapered wedge at the end of a beam or plate. However, not much work has been done on design to yield an effective ABH design for such a plate. We attempt to optimize the shape of the ABH to effectively...
Natural Frequency and Damping Estimation of an Offshore Wind Turbine Structure
DEFF Research Database (Denmark)
Damgaard, Mads; Andersen, Jacob K. F.; Ibsen, Lars Bo
2012-01-01
of an offshore wind turbine located in the North Sea. Simple Fourier Transformation and least square fitting to the vibration decay of ten “rotor stop” tests make it possible to evaluate the dynamic properties of the wind turbine structure. Based on the traditionally p-y curve method (Winkler type approach...
Equilibrium structure and atomic vibrations of Nin clusters
Borisova, Svetlana D.; Rusina, Galina G.
2017-12-01
The equilibrium bond lengths and binding energy, second differences in energy and vibrational frequencies of free clusters Nin (2 ≤ n ≤ 20) were calculated with the use of the interaction potential obtained in the tight-binding approximation (TBA). The results show that the minimum vibration frequency plays a significant role in the evaluation of the dynamic stability of the clusters. A nonmonotonic dependence of the minimum vibration frequency of clusters on their size and the extreme values for the number of atoms in a cluster n = 4, 6, 13, and 19 are demonstrated. This result agrees with the theoretical and experimental data on stable structures of small metallic clusters.
The Shock and Vibration Digest. Volume 12, Number 10,
1980-10-01
bearings [243]. A pressurized gas damping, and the vibrations of damped structures. squeeze film has also been used as a journal damper ...2251 Key Words: Bearings , Gas bearings , Journal bearings , Whirl- Torsional Oscillations of the Rotor Disc for Horizon- ing, Squeeze - film dampers tal... Squeeze Film Highly Damped Structures," Shock Vib. Dig., Journal Damper ," Rep. No. NASA-CR-155533 9 (7), pp 3-11 (July 1977). (Dec 1977). 235. Rusnak,
Vibration Analysis of Structures with Rotation and Reflection Symmetry
Directory of Open Access Journals (Sweden)
Baojian Li
1996-01-01
Full Text Available The article applies group representation theory to the vibration analysis of structures with Cnv symmetry, and presents a new structural vibration analysis method. The eigenvalue problem of the whole structure is divided into much smaller subproblems by forming the mass and stiffness matrices of one substructure and than modifying them to form mass and stiffness matrices in each irreducible subspace, resulting in the saving of computer time and memory. The modal characteristics of structures with Cnv symmetry are derived from theoretical analysis. Computation and modal testing are used to verify the validity of the theoretical deductions.
Parametric and Non-Parametric Vibration-Based Structural Identification Under Earthquake Excitation
Pentaris, Fragkiskos P.; Fouskitakis, George N.
2014-05-01
The problem of modal identification in civil structures is of crucial importance, and thus has been receiving increasing attention in recent years. Vibration-based methods are quite promising as they are capable of identifying the structure's global characteristics, they are relatively easy to implement and they tend to be time effective and less expensive than most alternatives [1]. This paper focuses on the off-line structural/modal identification of civil (concrete) structures subjected to low-level earthquake excitations, under which, they remain within their linear operating regime. Earthquakes and their details are recorded and provided by the seismological network of Crete [2], which 'monitors' the broad region of south Hellenic arc, an active seismic region which functions as a natural laboratory for earthquake engineering of this kind. A sufficient number of seismic events are analyzed in order to reveal the modal characteristics of the structures under study, that consist of the two concrete buildings of the School of Applied Sciences, Technological Education Institute of Crete, located in Chania, Crete, Hellas. Both buildings are equipped with high-sensitivity and accuracy seismographs - providing acceleration measurements - established at the basement (structure's foundation) presently considered as the ground's acceleration (excitation) and at all levels (ground floor, 1st floor, 2nd floor and terrace). Further details regarding the instrumentation setup and data acquisition may be found in [3]. The present study invokes stochastic, both non-parametric (frequency-based) and parametric methods for structural/modal identification (natural frequencies and/or damping ratios). Non-parametric methods include Welch-based spectrum and Frequency response Function (FrF) estimation, while parametric methods, include AutoRegressive (AR), AutoRegressive with eXogeneous input (ARX) and Autoregressive Moving-Average with eXogeneous input (ARMAX) models[4, 5
Comparing Sources of Damping of Cross-Wind Motion
DEFF Research Database (Denmark)
Tarp-Johansen, Niels Jacob; Mørch, Christian; Andersen, Lars
2009-01-01
Cross-wind vibrations due to wave loading misaligned with the wind causes fatigue known to be design driving for support structures of large turbines offshore increasing fatigue loads notably compared to the along-wind fatigue. The small amount of damping assumed for cross-wind motion in current...... practise plays a key role in this. The questions are: does more damping exist and is one of the sources of damping the main contributor allowing for site-independent guidelines. The aim of this paper is to address these issues. It is demonstrated that tower dampers are important in order to tackle...
The effect of dispersion damping functions on the structure of water clusters
Hernández-Rojas, J.; Wales, David J.
2014-11-01
We investigate the structural predictions obtained using new force fields for rigid water models proposed recently (Nicolini et al., 2013) for (H2O)n clusters. These new force fields are characterized by dispersion damping functions. The putative global minima of these new models up to n < 21 are obtained using basin-hopping global optimization technique and compared with previous results for the TIP4P potential and with ab initio calculations. The new models often give different morphologies, and generally exhibit fewer hydrogen bonds, and will require reparameterization if they are to be used for clusters.
Active control of noise radiation from vibrating structures
DEFF Research Database (Denmark)
Mørkholt, Jakob
The thesis is concerned with the active control of randomly vibrating structures by means of feedback control, with particular emphasis on reducing the sound radiation from such structures. A time domain model of the structural and radiation dynamics of an actively controlled plate has been...... optimal and robust discrete-time feedback controllers for active vibration control of multimodal structures have been compared. They have been showed to yield controllers with identical frequency response characteristics, even though they employ completely different methods of numerical solutions...... developed, based on the theory of radiation filters for estimating the sound radiation from multimodal vibrations. This model has then been used in simulations of optimal feedback control, with special emphasis of the stability margins of the optimal control scheme. Two different methods of designing...
Effect of structural design on traffic-induced building vibrations
DEFF Research Database (Denmark)
Persson, Peter; Andersen, Lars Vabbersgaard; Persson, Kent
2017-01-01
are related to the type of construction material (if it would be a light or heavy structure), and to the slab thickness. The finite element method is employed for discretizing the building structure that is coupled to a semi-analytical model considering a layered ground. © 2017 The Authors. Published......Population growth and urbanization results in densified cities, where new buildings are being built closer to existing vibration sources such as road-, tram- and rail traffic. In addition, new transportation systems are constructed closer to existing buildings. Potential disturbing vibrations...... properties, and type and size of the building are governing factors. In the paper, a study is presented aiming at investigating the influence of various parameters of the building's structural design on vibration levels in the structure caused by ground surface loads, e.g. traffic. Parameters studied...
Efficiency of Nearly Periodic Structures for Mitigation of Ground Vibration
DEFF Research Database (Denmark)
Andersen, Lars Vabbersgaard; Peplow, Andrew; Bucinskas, Paulius
2017-01-01
be introduced by periodic inclusions or changes to the ground surface geometry. However, for vibration mitigation in the context of real civil-engineering problems related to ground-borne noise from railways, for example, the excitation is not strictly harmonic and a steady state of the response is usually......Periodic structures are known to produce passbands and stopbands for propagation of vibration energy within the frequency domain. Sources vibrating harmonically at a frequency within a passband can lead to propagation of energy through propagating modes over long distances. However, sources...... vibrating at a frequency within a stopband excite only nearfields in the form of attenuating and evanescent modes, and the energy decays with distance. The decay phenomena are due to destructive interference of waves reflected and scattered by interfaces or obstacles placed periodically within or between...
Evaluation of blast-induced vibration effects on structures 1
Energy Technology Data Exchange (ETDEWEB)
Lee, Jong Rim; Jeon, Gyu Shick; Lee, Dae Soo; Joo, Kwang Ho; Lee, Woong Keon [Korea Electrotechnology Research Inst., Changwon (Korea, Republic of); Ryu, Chang Ha; Chung, So Keul; Lee, Kyung Won; Shin, Hee Soon; Chun, Sun Woo; Park, Yeon Jun; Synn, Joong Ho; Choi, Byung Hee [Korea Inst. of Geology Mining and Materials, Taejon (Korea, Republic of)
1995-12-31
Due to the difficulties of obtaining construction site for new plants, following ones are inevitably being built in the site adjacent to existing power plants. Therefore considerable thought has been recently given to the dynamic loading generated by blasting works near the plants to maintain the safety of structures and facilities in power plants. Our own standard for safety level of blast vibration is not prepared yet, and foreign standards have been generally employed without theoretical and experimental verification. Safety-related structures of power plants and facilities have to be protected against the effects of possible hazards due to blast vibration. Earthquakes have been considered a major dynamic design loading as a requirement of plant design, but the effects of blast-induced vibration are not. In order to ensure the safety, rational safe criterion should be established and blast design should be satisfy it, which requires the development of a model for prediction of vibration level through more systematic measurement and analysis. The main objectives of the study are : to provide background data for establishing the rational safe vibration limits, to develop models for prediction of blast vibration level, to establish safe blast design criterion, and to accumulate techniques for field measurements, data acquisition and analysis (author). 80 refs., 347 figs.
A Novel Strain Gauge with Damping Capability
Directory of Open Access Journals (Sweden)
Xiaohua LI
2009-10-01
Full Text Available The goal of this work is to investigate the properties of a new type of multifunctional composite which is based on multi-walled carbon nanotubes (MWCNT. The composite was prepared from a paper like MWCNT film which was sandwiched between two adhesive layers. Two point probe and four point probe methods were used to test its mechanical strain sensing properties. Nanoindentation and direct shear tests were used to acquire the Young’s modulus and shear modulus of MWCNT film composite. Its structural damping properties were investigated via a free vibration test. This new type of carbon nanotube based composite may potentially serve simultaneously as both a strain gauge and a damping treatment for use in structural vibration control.
Damage to surface structures due to blast vibration
Energy Technology Data Exchange (ETDEWEB)
P.K. Singh; M.P. Roya [Central Institute of Mining and Fuel Research, Dhanbad (India). Blasting Research Group
2010-09-15
This paper describes effect of blast produced ground vibration on damage potential to residential structures to determine safe levels of ground vibration for the residential structures and other buildings in mining areas. Impacts of 341 blasts detonated at two mines were monitored at the test structures and 1871 blast vibrations signatures were recorded on or near the test structures. Cosmetic cracks in a native brick-mud-cement house were detected at peak particle velocities (PPV) between 51.6 and 56.3 mm/s. The reinforced concrete and cement mortar (RCC) structure experienced cosmetic cracks at PPVs of 68.6-71.3 mm/s at the first floor, whereas at second floor it was detected at PPV levels of 71.2-72.2 mm/s. Minor damage in brick-mud-cement house was recorded at PPV levels of 81.0-89.7 mm/s. The RCC structure at first and second floors experienced minor damage at PPV levels of 104 and 98.3-118 mm/s, respectively. The brick-mud-cement house experienced major damage at PPV level of 99.6-113.0 mm/s, while major damage was recorded in RCC structure on first floor at PPV of 122 mm/s, the second floor at PPV levels of 128.9-161 mm/s. Recommended threshold limits of vibrations for the different type of structures is based on these measurements and observations.
Structural health monitoring with a wireless vibration sensor network
Basten, T.G.H.; Schiphorst, F.B.A.
2012-01-01
Advanced maintenance strategies for infrastructure assets such as bridges or off shore wind turbines require actual and reliable information of the maintenance status. Structural health monitoring based on vibration sensing can help in supplying the input needed for structural health monitoring
DESIGN OF VIBRATION AND NOISE CONTROL SYSTEM FOR FLEXIBLE STRUCTURES
Directory of Open Access Journals (Sweden)
В. Макаренко
2012-04-01
Full Text Available In the article the control system is created, which is able to reduce steady-state vibration response of thinwalled flexible structure in the wide band of low frequencies. It is supposed, that the flexible structure is subject to external harmonic force with variable frequencies, and parameters of that force are available for the usage by the control system. The control system is based on pattern search algorithm and suggestion about the dependence of signal, which is formed by the control system, from the steady-state vibration response of the flexible structure. Developed software allows to use pattern search algorithm as the control system for plate vibration in real-time. The influence on control system operation of signal delay of executive device of compensating path and transition process after the change of control signal parameters is done by the usage of the additional idle time. During idle time the control signal is supported. It has parameters that have taken place before the beginning of idle mode. Step reset option for resuming of search after the long-term steady-state vibration of flexible structure do not derange control system operation, because step change take place only after polling cycle termination. The efficiency of proposed system is illustrated experimentally on the example of clamped plate. Experimental results analysis showed the necessity of multiple compensating devices application for vibration reduction in wide frequency range.
Watzky, A.
1992-02-01
In the numerous works trying to describe the free vibration of stretched elastic strings, phenomena due to non-linear geometrical modifications in a three-dimensional large amplitude motion are separated from those due to the string's stiffness, in which case torsional vibrations cannot be taken into account. In order to fill this gap with a more complete model and to specify its field of validity the problem set up again, starting from three-dimensional elasticity for finite displacements with small strains of a slender homogeneous elastic cylindrical rod under initial stress. The original geometrical construction which gives the cross-section's orientation during the motion is detailed. With the symmetry of the problem preserved, it provides a description of simple physical meaning and in particular the torsion is used as a parameter. The goal of this study being the determination of the deformed shape of the central line, the three spatial variables are reduced to one through expressions for the resultant forces and moments on the cross-sections, leading to macroscopic equations of motion which are simplified in the case of uncoupled transverse and longitudinal modes. For the first time, the equations of motion introduce a coupling torsion term and include existing string and beam models, which can thus be considered as particular cases. The assumptions and generalizations are discussed and the influences of the different terms are described. While this work is based on the limits imposed by material linearity, it provides a useful basic tool for the study of the transverse vibrations of slender elastic beams, including the commonly avoided torsional phenomena.
Maciejewski, I.; Meyer, L.; Krzyzynski, T.
2010-09-01
The paper describes the simulated dynamic response of an active vibro-isolating pneumatic suspension seat. Active control of the air-spring force is used to improve its vibro-isolation properties. For the active vibration isolating system described, a triple feedback loop control system was developed and analysed. The system robustness for different load masses was investigated using the verified active seat suspension model. The Seat Effective Amplitude Transmissibility factor (SEAT) and the maximum suspension deflection were used as the seat performance indices.
Neugebauer, Reimund; Pagel, K.; Bucht, A; Wittstock, V.; Pappe, A.
2010-01-01
Additional piezo-based components in drive trains can significantly improve the dynamic behaviour of machine tools. In this article we present a piezo-based actuator-sensor-unit that is able to reduce uniaxial vibrations in ball screw driven feed axis of machine tools. A complex model of a feed axis including ASU was developed to design a controller. The control concept is based on the direct velocity feedback. A modular test bench was designed, assembled and investigated to verify the ASU's ...
A Resonant Damping Study Using Piezoelectric Materials
Min, J. B.; Duffy, K. P.; Choi, B. B.; Morrison, C. R.; Jansen, R. H.; Provenza, A. J.
2008-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue (HCF) problems requiring damping treatments to mitigate vibration levels. Based on the technical challenges and requirements learned from previous turbomachinery blade research, a feasibility study of resonant damping control using shunted piezoelectric patches with passive and active control techniques has been conducted on cantilever beam specimens. Test results for the passive damping circuit show that the optimum resistive shunt circuit reduces the third bending resonant vibration by almost 50%, and the optimum inductive circuit reduces the vibration by 90%. In a separate test, active control reduced vibration by approximately 98%.
Optimal Vibration Control of Civil Engineering Structures
DEFF Research Database (Denmark)
Thesbjerg, Leo
In designing large civil engineering structures, an important consideration is prospective dynamic loadings which may include earthquake ground motion, wind gusts, severe sea states and moving vehicles, rotating and reciprocating machinery and others. successful design of such structures requires...
Atomistic Mechanisms for Viscoelastic Damping in Inorganic Solids
Ranganathan, Raghavan
the microstructural length-scale of the composite. The second class of materials consist of structurally heterogeneous binary alloys that are either ordered, random or glassy. Vastly different mechanisms for viscoelastic damping arise for the three structures - random alloy and glass are observed to exhibit significant damping owing to large anharmonicity in the coupling between vibrational modes, which is a direct consequence of the chemical heterogeneity. Additionally, at low shear frequencies, glass exhibits significant long-time scale structural relaxation that results in persistent damping over a large range of frequencies. Finally, a critical analysis of various factors that affect damping in inorganic glasses is made. We show that damping in glasses exhibits a striking commonality - at high frequencies, vibrational anharmonicity leads to a peak in damping for all glasses commensurate with the range of vibrational frequencies of the glass; at intermediate and low frequencies, structural relaxation leads to persistent, nearly-constant damping. The frequency-dependent damping mechanisms and structure-property relations observed with respect to damping are expected to enable the design of novel structures with favorable damping characteristics.
Damped accelerator structures for future linear e/sup/plus minus// colliders
Energy Technology Data Exchange (ETDEWEB)
Deruyter, H.; Hoag, H.A.; Lisin, A.V.; Loew, G.A.; Palmer, R.B.; Paterson, J.M.; Rago, C.E.; Wang, J.W.
1989-03-01
This paper describes preliminary work on accelerator structures for future TeV linear colliders which use trains of e/sup +-/ bunches to reach the required luminosity. These bunch trains, if not perfectly aligned with respect to the accelerator axis, induce transverse wake field modes into the structure. Unless they are sufficiently damped, these modes cause cummulative beam deflections and emittance growth. The envisaged structures, originally proposed by R. B. Palmer, are disk-loaded waveguides in which the disks are slotted radially into quadrants. Wake field energy is coupled via the slots and double-ridged waveguides into a lossy region which is external to the accelerator structure. The requirement is that the Q of the HEM/sub 11/ mode be reduced to a value of less than 30. The work done so far includes MAFIA code computations and low power rf measurements to study the fields. A four-cavity 2..pi../3 mode standing-wave structure has been built to find whether the slots lower the electric breakdown thresholds below those reached with conventional disk-loaded structures. We set out to assess the microwave properties of the structure and the problems which might be encountered in fabricating it. 4 refs., 7 figs.
Measurements of High Order Modes in High Phase Advance Damped Detuned Accelerating Structure for NLC
Khabiboulline, N; Carter, H
2004-01-01
The RF Technology Development group at Fermilab is working together with the NLC and JLC groups at SLAC and KEK on developing technology for room temperature X-band accelerating structures for a future linear collider. We have built several series of structures for high gradient tests. We have also built 150° phase advance per cell, 60 cm long, damped and detuned structures (HDDS or FXC series). Some of these structures will be used for the 8-pack test at SLAC by the end of 2004, as part of the JLC/NLC effort to demonstrate the readiness of room temperature RF technology for a linear collider. HDSS structures are very close to the final design for the linear collider, and it was very interesting to study the properties of high order modes in the structures produced by semi-industrial methods. In this study advanced RF technique and methods developed at Fermilab for structure low power testing and tuning have been used. The results of these measurements are presented in this paper.
Vibration transmission through periodic structures using a mobility power flow approach
Cuschieri, J. M.
1990-01-01
The transmission of vibrational power (time averaged) through multiple coupled (periodic) structures is examined. The analysis is performed in the frequency domain and the coupling between the sub-elements of the periodic structure is expressed in terms of structural mobility functions for the junction points and between the junction points of the sub-elements. Equal length spans between stiffeners or supports of the periodic structure are considered. Through the use of the mobility power flow approach, the influence of sub-element and junction parameters, including damping at the joints, can be investigated. The results from the analysis can be in the form of either structural intensity or alternatively structural power content for each of the sub-elements. The examples discussed are for a thin, perfectly periodic beam with a finite number of spans with different types of stiffeners and/or supports between the spans. The excitation of the structure is by a point load located midway along the first span.
Modelling flow-induced vibrations of gates in hydraulic structures
Erdbrink, C.D.
2014-01-01
The dynamic behaviour of gates in hydraulic structures caused by passing flow poses a potential threat to flood protection. Complex interactions between the turbulent flow and the suspended gate body may induce undesired vibrations. This thesis contributes to a better understanding and prevention of
Formula for Forced Vibration Analysis of Structures Using Static ...
African Journals Online (AJOL)
This Paper proposed and examined a formula for forced vibration analysis of structures using static factored response as equivalent dynamic response. Some methods of dynamic analysis are based on using static factored response as equivalent dynamic response thereby excluding the formulation of the equations of ...
Prediction of Vibration Transmission within Periodic Bar Structures
DEFF Research Database (Denmark)
Domadiya, Parthkumar Gandalal; Andersen, Lars Vabbersgaard; Sorokin, Sergey
2012-01-01
The present analysis focuses on vibration transmission within semi-infinite bar structure. The bar is consisting of two different materials in a periodic manner. A periodic bar model is generated using two various methods: The Finite Element method (FEM) and a Floquet theory approach. A parameter...
Effect of curvature on structures and vibrations of zigzag carbon ...
Indian Academy of Sciences (India)
First-principles pseudopotential-based density functional theory calculations of atomic and electronic structures, full phonon dispersions and thermal properties of zigzag single wall carbon nanotubes (SWCNTs) are presented. By determining the correlation between vibrational modes of a graphene sheet and of the ...
Uncertainty Quantification for Monitoring of Civil Structures from Vibration Measurements
Döhler, Michael; Mevel, Laurent
2014-05-01
Health Monitoring of civil structures can be performed by detecting changes in the modal parameters of a structure, or more directly in the measured vibration signals. For a continuous monitoring the excitation of a structure is usually ambient, thus unknown and assumed to be noise. Hence, all estimates from the vibration measurements are realizations of random variables with inherent uncertainty due to (unknown) process and measurement noise and finite data length. In this talk, a strategy for quantifying the uncertainties of modal parameter estimates from a subspace-based system identification approach is presented and the importance of uncertainty quantification in monitoring approaches is shown. Furthermore, a damage detection method is presented, which is based on the direct comparison of the measured vibration signals without estimating modal parameters, while taking the statistical uncertainty in the signals correctly into account. The usefulness of both strategies is illustrated on data from a progressive damage action on a prestressed concrete bridge. References E. Carden and P. Fanning. Vibration based condition monitoring: a review. Structural Health Monitoring, 3(4):355-377, 2004. M. Döhler and L. Mevel. Efficient multi-order uncertainty computation for stochastic subspace identification. Mechanical Systems and Signal Processing, 38(2):346-366, 2013. M. Döhler, L. Mevel, and F. Hille. Subspace-based damage detection under changes in the ambient excitation statistics. Mechanical Systems and Signal Processing, 45(1):207-224, 2014.
Vibrational spectra and normal coordinate analysis on structure of ...
Indian Academy of Sciences (India)
journal of. December 2008 physics pp. 1291–1300. Vibrational spectra and normal coordinate analysis on structure of chlorambucil and thioguanine. S GUNASEKARAN1, S KUMARESAN2,∗, ... methoprexate are most effective in the treatment of leukemia [5–10] in children. Thioguanine interferes with the conversion of ...
The ABRAVIBE toolbox for teaching vibration analysis and structural dynamics
DEFF Research Database (Denmark)
Brandt, A.
2013-01-01
Vibration analysis is a subject where students often find it hard to comprehend the fundamental theory. The fact that we have, in general, almost no intuition for dynamic phenomena, means that students need to explore various dynamic phenomena in order to grasp the subject. For this reason......, a MATLAB toolbox (the ABRAVIBE toolbox) has been developed as an accompanying toolbox for the recent book "Noise and Vibration Analysis" by the author. This free, open software, published under GNU Public License, can be used with GNU Octave, if an entirely free software platform is wanted, with a few......). In this paper, an overview of the functionality is given and recommended use in teaching is discussed. It is also shown how the toolbox can be used for general vibration analysis using data from multichannel measurements. Finally, some laboratory exercises for structural dynamics teaching are discussed...
Vibration Analysis and Models of Adjacent Structures Controlled by Magnetorheological Dampers
Directory of Open Access Journals (Sweden)
Michela Basili
2017-01-01
Full Text Available This paper deals with the vibration analysis of adjacent structures controlled by a magnetorheological (MR damper and with the discussion of a numerical procedure for identification and definition of a reliable finite element model. The paper describes an extensive experimental campaign investigating the dynamic response, through shaking table tests, of a tridimensional four-story structure and a two-story structure connected by an MR device. Several base excitations and intensity levels are considered. The structures were tested in nonconnected and connected configuration, with the MR damper operating in passive or semiactive mode. Moreover, the paper illustrates a procedure for the structural identification and the definition of a reliable numerical model valid for adjacent structures connected by MR dampers. The procedure is applied in the original nonconnected configuration, which represents a linear system, and then in the connected configuration, which represents a nonlinear system due to the MR damper. In the end, the updated finite element model is reliable and suitable for all the considered configurations and the mass, damping, and stiffness matrices are derived. The experimental and numerical responses are compared and the results confirm the effectiveness of the identification procedure and the validation of the finite element model.
Particle Damping with Granular Materials for Multi Degree of Freedom System
Directory of Open Access Journals (Sweden)
Masanobu Inoue
2011-01-01
Full Text Available A particle damper consists of a bed of granular materials moving in cavities within a multi degree-of-freedom (MDOF structure. This paper deals with the damping effects on forced vibrations of a MDOF structure provided with the vertical particle dampers. In the analysis, the particle bed is assumed to be a single mass, and the collisions between the granules and the cavities are completely inelastic, i.e., all energy dissipation mechanisms are wrapped into zero coefficient of restitution. To predict the particle damping effect, equations of motion are developed in terms of equivalent single degree-of-freedom (SDOF system and damper mass with use made of modal approach. In this report, the periodic vibration model comprising sustained contact on or separation of the damper mass from vibrating structure is developed. A digital model is also formulated to simulate the damped motion of the physical system, taking account of all vibration modes. Numerical and experimental studies are made of the damping performance of plural dampers located at selected positions throughout a 3MDOF system. The experimental results confirm numerical prediction that collision between granules and structures is completely inelastic as the contributing mechanism of damping in the vertical vibration. It is found that particle dampers with properly selected mass ratios and clearances effectively suppress the resonance peaks over a wide frequency range.
A data driven control method for structure vibration suppression
Xie, Yangmin; Wang, Chao; Shi, Hang; Shi, Junwei
2018-02-01
High radio-frequency space applications have motivated continuous research on vibration suppression of large space structures both in academia and industry. This paper introduces a novel data driven control method to suppress vibrations of flexible structures and experimentally validates the suppression performance. Unlike model-based control approaches, the data driven control method designs a controller directly from the input-output test data of the structure, without requiring parametric dynamics and hence free of system modeling. It utilizes the discrete frequency response via spectral analysis technique and formulates a non-convex optimization problem to obtain optimized controller parameters with a predefined controller structure. Such approach is then experimentally applied on an end-driving flexible beam-mass structure. The experiment results show that the presented method can achieve competitive disturbance rejections compared to a model-based mixed sensitivity controller under the same design criterion but with much less orders and design efforts, demonstrating the proposed data driven control is an effective approach for vibration suppression of flexible structures.
Rotorcraft airframe structural optimization for combined vibration and fatigue constraints
Sareen, Ashish K.; Schrage, Daniel P.; Murthy, T. S.
1991-01-01
This paper addresses the application of a formal optimization technique in rotorcraft airframe structural design studies to reduce the structural weight, to lower airframe vibrations, and to enhance fatigue life of the structure. Vibration and fatigue considerations in airframe design are described. An optimization methodology based on the use of a nonlinear programming technique to size airframe structural members subjected to constraints on weight, vibration response and fatigue stresses under dynamic loads, are described. The paper focuses on the development of necessary computational tools for airframe structural optimization and describes the sensitivity analysis procedure for these types of design constraints. Further, the paper describes the optimization procedure as implemented in a computer code called DYNOPT which is a unique operational combination of several newly developed Fortran codes as well as modification of existing codes consisting of the direct matrix abstraction modules of the MSC/NASTRAN Program and CONMIN optimizer. The application of the optimization procedure is demonstrated using an elastic-line model of the Bell AH-1G helicopter airframe structure and computational results are discussed.
DEFF Research Database (Denmark)
Han, Yang; Shen, Pan; Zhao, Xin
2017-01-01
In this paper, the modeling, controller design, and stability analysis of the islanded microgrid (MG) using enhanced hierarchical control structure with multiple current loop damping schemes is proposed. The islanded MG is consisted of the parallel-connected voltage source inverters using LCL...... of the state matrix. The moving average filter-based sequence decomposition method is proposed to extract the fundamental positive and negative sequences, and harmonic components. The multiple inner current loop damping scheme is presented, including the virtual positive, virtual negative and variable harmonic...... frequency, and virtual variable harmonic impedance loop at harmonic frequencies, and the inner voltage and current loop controllers. A small-signal model for the primary and secondary controls with additional phase-shift loop is presented, which shows an over-damped feature from eigenvalue analysis...
Hybrid carbon fiber/carbon nanotube composites for structural damping applications.
Tehrani, M; Safdari, M; Boroujeni, A Y; Razavi, Z; Case, S W; Dahmen, K; Garmestani, H; Al-Haik, M S
2013-04-19
Carbon nanotubes (CNTs) were grown on the surface of carbon fibers utilizing a relatively low temperature synthesis technique; graphitic structures by design (GSD). To probe the effects of the synthesis protocols on the mechanical properties, other samples with surface grown CNTs were prepared using catalytic chemical vapor deposition (CCVD). The woven graphite fabrics were thermally shielded with a thin film of SiO2 and CNTs were grown on top of this film. Raman spectroscopy and electron microscopy revealed the grown species to be multi-walled carbon nanotubes (MWCNTs). The damping performance of the hybrid CNT-carbon fiber-reinforced epoxy composite was examined using dynamic mechanical analysis (DMA). Mechanical testing confirmed that the degradations in the strength and stiffness as a result of the GSD process are far less than those encountered through using the CCVD technique and yet are negligible compared to the reference samples. The DMA results indicated that, despite the minimal degradation in the storage modulus, the loss tangent (damping) for the hybrid composites utilizing GSD-grown MWCNTs improved by 56% compared to the reference samples (based on raw carbon fibers with no surface treatment or surface grown carbon nanotubes) over the frequency range 1-60 Hz. These results indicated that the energy dissipation in the GSD-grown MWCNTs composite can be primarily attributed to the frictional sliding at the nanotube/epoxy interface and to a lesser extent to the stiff thermal shielding SiO2 film on the fiber/matrix interface.
Investigation of structure and vibrational properties of cyclobutane pirimidine dimer
Directory of Open Access Journals (Sweden)
Petković Milena M.
2013-01-01
Full Text Available We performed a theoretical analysis of the structure and vibrational properties of cyclobutane pyrimidine dimer, which is the main product in a photochemical reaction involving two molecules of 1-methylthymine. Thymine is a pyrimidine base that has the highest yield of the dimerization photoproducts. Methylation in position one was chosen because in this position thymine is linked to sugar in DNA. The calculations were performed at the B3LYP/cc-pVTZ level with a Gaussian program package. All molecular geometries were optimized without symmetry constraints in vacuum and D2O. Vibrational frequencies were calculated in the harmonic approximation. It was shown that there are two stable isomers, CPD(cis-syn and CPD(trans-syn. CPD(trans-syn is more stable both in vacuum and in D2O. By dissolving these molecules in D2O, both structures become more stable, although the stabilization of the less stable isomer is more pronounced due to its larger dipole moment. Thus, the difference in stability of the two isomers in D2O is almost two times lower than in vacuum. Because of the similarity of the two isomers’ structures, the difference in their vibrational spectra is not pronounced. Within the harmonic approximation, there is only a slight difference in the C=O and C-H stretching region. The difference in the N-H stretching region is more pronounced; in the CPD(cis-syn molecule the two bonds vibrate separately, whereas in the CPD(trans-syn the two modes couple, and this coupling results in symmetric and asymmetric N-H stretching. The observation shows that a slight difference in geometry can be reflected in the shape of the infrared spectra. A more detailed analysis of the vibrational properties would involve computation of anharmonic coupling terms, which would enable a more precise determination of the peak positions.
Energy Technology Data Exchange (ETDEWEB)
Martins, N.; Pinto, H.J.C.P.; Bianco, A. [Centro de Pesquisas de Energia Eletrica (CEPEL), Rio de Janeiro, RJ (Brazil); Macedo, N.J.P. [FURNAS, Rio de Janeiro, RJ (Brazil)
1994-12-31
This paper describes control structures and computer methods to enhance the practical use of thyristor controlled series compensation (TCSC) in power systems. The location and controller design of the TCS devices, to damp system oscillations, are based on modal analysis and frequency response techniques, respectively. Results are given for a large practical power system. (author) 15 refs., 18 figs., 5 tabs.
Assements of Level of Comfort on a Vibrating Structure
DEFF Research Database (Denmark)
Pedersen, Lars
2008-01-01
The serviceability limit state of structures is subject to increasing attention. Flooring-systems may encounter vertical vibrations that may be perceived as annoying by stationary persons sitting or standing on the structure. This can happen on office floors, on grand stands etc. where humans...... in motion (for instance people walking or jumping) can bring the structure into vibration. The paper looks into human perception of decaying oscillations of floors by doing experiments with a test floor with stationary humans atop. An impulsive load is directed to the floor, and after the decay, the persons...... on the floor are asked to rate the level of discomfort on a scale from 1 to 10, and to assess the size of floor displacement (the initial amplitude of the decay). Tests are carried out with different numbers of people present on the test floor, and with different initial amplitudes of the decay. The paper...
Molecular structure, vibrational spectroscopic studies and natural ...
Indian Academy of Sciences (India)
Home; Journals; Pramana – Journal of Physics; Volume 74; Issue 5. Molecular structure ... The entropy of the title compound was also performed at HF using the hybrid functional BLYP and B3LYP with 6-31 G(d,p) as basis set levels of theory. Natural bond orbital (NBO) analysis of the title molecule is also carried out.
14th International Conference on Acoustics and Vibration of Mechanical Structures
Marinca, Vasile
2018-01-01
This book is a collection of papers presented at Acoustics and Vibration of Mechanical Structures 2017 – AVMS 2017 – highlighting the current trends and state-of-the-art developments in the field. It covers a broad range of topics, such as noise and vibration control, noise and vibration generation and propagation, the effects of noise and vibration, condition monitoring and vibration testing, modeling, prediction and simulation of noise and vibration, environmental and occupational noise and vibration, noise and vibration attenuators, as well as biomechanics and bioacoustics. The book also presents analytical, numerical and experimental techniques for evaluating linear and non-linear noise and vibration problems (including strong nonlinearity). It is primarily intended for academics, researchers and professionals, as well as PhD students in various fields of the acoustics and vibration of mechanical structures.
Free vibration analysis of spinning flexible space structures
Gupta, K. K.
1976-01-01
Efficient computation of natural frequencies and associated free vibration modes of spinning flexible structures is required to accurately determine the nature of interaction between the flexible structure and the attitude control system, which is vital in relating control torques to attitude angles. While structural discretization is effected by the finite element method, the resulting eigenvalue problem is solved by a combined Sturm sequence and inverse iteration procedure that yields a few specified roots and associated vectors. An eigenvalue procedure, based on a simultaneous iteration technique, provides efficient computation of the first few roots and vectors; a modal synthesis procedure proves to be useful for eigenproblem solutions of unusual structures such as spacecraft.
Fay, Temple H.
2012-01-01
Quadratic friction involves a discontinuous damping term in equations of motion in order that the frictional force always opposes the direction of the motion. Perhaps for this reason this topic is usually omitted from beginning texts in differential equations and physics. However, quadratic damping is more realistic than viscous damping in many…
Elementary damping properties in braided composite materials
Dion, Bernard L.; Sadler, Robert; Silverberg, Larry
1994-05-01
This paper investigates the damping level trends of three-dimensionally braided composites as a function of matrix material, fiber-matrix interface, fiber braid angle, fiber volume, and axial fiber tow size. With knowledge of such trends, designers may increase the structural damping in a 3-D braided composite component, thereby reducing component vibration, shock response, and fatigue. The logarithmic decrements of the fundamental mode response of cantilevered, 3-D braided composite beam specimens were calculated for comparison. Although the logarithmic decrements of two specimens, differing only in their matrix materials (Tactix 123 and Epon 828), were essentially identical, both were considerably larger than that for steel. The value for the decrement of these two composite specimens' response was taken as a reference. Altering the nature of the fiber-matrix interface by lubricating the fibers before specimen consolidation greatly increased the damping relative to the baseline. Trends of increasing damping were measured with both increasing fiber braid angle and fiber volume. Finally, increasing levels of damping are reported for decreases in axial fiber tow size. Explanations for these trends, based on the possible microscopic and macroscopic nature of the braided composites, are offered.
DEFF Research Database (Denmark)
Stein, George Juraj; Darula, Radoslav; Sorokin, Sergey
2012-01-01
A theoretical analysis of an electromagnetic vibration controller is presented. The analyzed device consists of a pot-type iron core with a coil and a permanent magnet as a source of constant magnetic flux. The magnetic circuit is closed by a yoke, excited by an external harmonic mechanical force....... The so generated magnetic flux variation induces alternating voltage in the electric circuit, which is dissipated in a shunt resistor. The induced current driven through the coil generates magnetic force, which damps the excitation force and changes the damped natural frequency of the oscillatory system...
Free vibration analysis of spinning structural systems.
Gupta, K. K.
1973-01-01
This article presents an efficient digital computer procedure, along with the complete listing of the associated computer program, which may be conveniently utilized for the accurate solution of a wide range of practical eigenvalue problems. Important applications of the present work are envisaged in the natural frequency analysis of spinning structures discretized by the finite element technique, and in the determination of transfer functions associated with the dynamic blocks of control systems of spacecraft utilizing gas jets or reaction wheels for attitude control, as well as of spin-stabilized and dual-spin-stabilized satellites. The validity of the Sturm sequence property is first established for the related matrix formulation involving Hermitian and real symmetric, positive-definite matrices, both being usually of highly banded configuration. A numerically stable algorithm based on the Sturm sequence method is then developed which fully exploits the banded form of the associated matrices.
Vibrations of structurally orthotropic laminated shells under thermal power loading
Kogan, E. A.; Lopanitsyn, E. A.
2017-05-01
On the basis of the linearized version of equations obtained in a geometrically nonlinear statement and describing the nonaxisymmetric strain of nonshallow sandwich structure orthotropic shells under thermal power loading, the Rayleigh-Ritz method with polynomial approximation of displacements and shear strains is used to solve the problem of small free vibrations of axisymmetrically thermally preloaded freely supported three-layer conical shell. The causes of dynamical fracture of the shell under study are revealed.
Optimization of the impact multi-mass vibration absorbers
Directory of Open Access Journals (Sweden)
Ivan Kernytskyy
2017-09-01
Full Text Available The problem of attaching dynamic vibration absorber (DVA to a discrete multi-degree-of-freedom or continuous structure has been outlined in many papers and monographs. An impact damping system can overcome some limitations by impact as the damping medium and impact mass interaction as the damping mechanism. The paper contemplates the provision of DVA with the several of the impact masses. Such originally designed absorbers reduce vibration selectively in maximum vibration mode without introducing vibration in other modes. An impact damper is a passive control device which takes the form of a freely moving mass, constrained by stops attached to the structure under control, i.e. the primary structure. The damping results from the exchange of momentum during impacts between the mass and the stops as the structure vibrates. The paper contemplates the provision of the impact multi-mass DVA’s with masses collisions for additional damping. For some cases of DVA optimization such a design seems more effective than conventional multi-mass DVA with independent mass moving. A technique is developed to give the optimal DVA’s for the elimination of excessive vibration in harmonic stochastic and impact loaded systems.
Vibrational spectroscopic and structural investigations on fullerene: A DFT approach
Energy Technology Data Exchange (ETDEWEB)
Christy, P. Anto; Premkumar, S.; Asath, R. Mohamed; Mathavan, T.; Benial, A. Milton Franklin, E-mail: miltonfranklin@yahoo.com [Department of Physics, N.M.S.S.V.N. College, Madurai-625 019, Tamil Nadu (India)
2016-05-06
The molecular structure of fullerene (C{sub 60}) molecule was optimized by the DFT/B3LYP method with 6-31G and 6-31G(d,p) basis sets using Gaussian 09 program. The vibrational frequencies were calculated for the optimized molecular structure of the molecule. The calculated vibrational frequencies confirm that the molecular structure of the molecule was located at the minimum energy potential energy surface. The calculated vibrational frequencies were assigned on the basis of functional group analysis and also confirmed using the GaussView 05 software. The frontier molecular orbitals analysis was carried out. The FMOs related molecular properties were predicted. The higher ionization potential, higher electron affinity, higher softness, lower band gap energy and lower hardness values were obtained, which confirm that the fullerene molecule has a higher molecular reactivity. The Mulliken atomic charge distribution of the molecule was also calculated. Hence, these results play an important role due to its potential applications as drug delivery devices.
Vibration of imperfect rotating disk
Directory of Open Access Journals (Sweden)
Půst L.
2011-12-01
Full Text Available This study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.
Inoue, Katsumi; Krantz, Timothy L.
1995-01-01
While the vibration analysis of gear systems has been developed, a systematic approach to the reduction of gearbox vibration has been lacking. The technique of reducing vibration by shifting natural frequencies is proposed here for gearboxes and other thin-plate structures using the theories of finite elements, modal analysis, and optimization. A triangular shell element with 18 degrees of freedom is developed for structural and dynamic analysis. To optimize, the overall vibration energy is adopted as the objective function to be minimized at the excitation frequency by varying the design variable (element thickness) under the constraint of overall constant weight. Modal analysis is used to determine the sensitivity of the vibration energy as a function of the eigenvalues and eigenvectors. The optimum design is found by the gradient projection method and a unidimensional search procedure. By applying the computer code to design problems for beams and plates, it was verified that the proposed method is effective in reducing vibration energy. The computer code is also applied to redesign the NASA Lewis gear noise rig test gearbox housing. As one example, only the shape of the top plate is varied, and the vibration energy levels of all the surfaces are reduced, yielding an overall reduction of 1/5 compared to the initial design. As a second example, the shapes of the top and two side plates are varied to yield an overall reduction in vibration energy of 1/30.
CFD evaluation of added damping due to fluid flow over a hydroelectric turbine blade
Gauthier, J. P.; Giroux, A. M.; Etienne, S.; Gosselin, F. P.
2016-11-01
To estimate structural fatigue, vibrational response to realistic spectrum of excitations and associated equivalent damping are of paramount importance. In this paper, an approach to quantify flow-induced damping of a relatively heavy fluid on a vibrating hydraulic turbine blade using numerical simulations is presented. First, mode shapes and frequencies of the immersed structure are obtained by modal analysis using the finite element method. Then, forced oscillatory modal motion is prescribed on the structural boundary of unsteady Reynolds-averaged Navier-Stokes flow simulations. Damping is finally computed as the normalized work done by the resulting fluid load on the structure. Validation is achieved by comparing the numerical results with available experimental data for a steel hydrofoil oscillating in flowing water. For this case, the linear increase in the damping ratio with the flow velocity is reproduced within 10% of the experimental values. Application of the method to an actual hydroelectric propeller turbine blade yields a fluid damping value of around 15% of critical damping for its first vibration mode.
Directory of Open Access Journals (Sweden)
Wangqiang XIAO
2014-04-01
Full Text Available We established a friction energy dissipation model for particle damping based on powder mechanics. We investigated the influence of geometric features of the damper on damping characteristics; and the geometric feature studied was the depth and length of the rectangular particle container. The work done by the frictional force between the particle layer and the effect of particle filling rate on the vibration damping characteristics was also explored. We analyzed the friction energy dissipation model, and the relationship between the particle filling rate and the vibration damping. The experimental results show good agreement with the friction energy dissipation model, which verifies the proposed simulation prediction. The results have shown that the particle damping technology can greatly consume the structure kinetic energy, and the vibration reduction effect of particle damping depends mainly on the interaction of the particles near the top. A proper filling rate of particle systems can result in an optimal effect on vibration reduction, which will provide the engineering applications with the theoretical guidance and design criteria.
NASTRAN nonlinear vibration analysis of beam and frame structures
Mei, C.; Rogers, J. L., Jr.
1975-01-01
A capability for the nonlinear vibration analysis of beam and frame structures suitable for use with NASTRAN level 15.5 is described. The nonlinearity considered is due to the presence of axial loads induced by longitudinal end restraints and lateral displacements that are large compared to the beam height. A brief discussion is included of the mathematical analysis and the geometrical stiffness matrix for a prismatic beam (BAR) element. Also included are a brief discussion of the equivalent linearization iterative process used to determine the nonlinear frequency, the required modifications to subroutines DBAR and XMPLBD of the NASTRAN code, and the appropriate vibration capability, four example problems are presented. Comparisons with existing experimental and analytical results show that excellent accuracy is achieved with NASTRAN in all cases.
Numerical Analysis of Vibrations of Structures under Moving Inertial Load
Bajer, Czeslaw I
2012-01-01
Moving inertial loads are applied to structures in civil engineering, robotics, and mechanical engineering. Some fundamental books exist, as well as thousands of research papers. Well known is the book by L. Frýba, Vibrations of Solids and Structures Under Moving Loads, which describes almost all problems concerning non-inertial loads. This book presents broad description of numerical tools successfully applied to structural dynamic analysis. Physically we deal with non-conservative systems. The discrete approach formulated with the use of the classical finite element method results in elemental matrices, which can be directly added to global structure matrices. A more general approach is carried out with the space-time finite element method. In such a case, a trajectory of the moving concentrated parameter in space and time can be simply defined. We consider structures described by pure hyperbolic differential equations such as strings and structures described by hyperbolic-parabolic differential equations ...
Stabilizing Optical Path Length On A Vibrating Structure
Spanos, John T.; Rahman, Zahidul H.
1995-01-01
Prototype apparatus constructed to test feasibility of feedback control concept for stabilization of length of optical path between two points on vibrating flexible structure. In original intended application, structure is truss having dimensions of order of meters and supports optical components of stellar interferometer. Interferometry and feedback control reduce path-length disturbances. Some aspects of present feedback control concept and prototype apparatus described in "Controllable Optical Delay Line for Stellar Interferometry" (NPO-18686), and "Test Bed for Control of Optical-Path Lengths" (NPO-18487).
Feasibility of structural monitoring with vibration powered sensors
Elvin, Niell G.; Lajnef, Nizar; Elvin, Alex A.
2006-08-01
Wireless sensors and sensor networks are beginning to be used to monitor structures. In general, the longevity, and hence the efficacy, of these sensors are severely limited by their stored power. The ability to convert abundant ambient energy into electric power would eliminate the problem of drained electrical supply, and would allow indefinite monitoring. This paper focuses on vibration in civil engineering structures as a source of ambient energy; the key question is can sufficient energy be produced from vibrations? Earthquake, wind and traffic loads are used as realistic sources of vibration. The theoretical maximum energy levels that can be extracted from these dynamic loads are computed. The same dynamic loads are applied to a piezoelectric generator; the energy is measured experimentally and computed using a mathematical model. The collected energy levels are compared to the energy requirements of various electronic subsystems in a wireless sensor. For a 5 cm3 sensor node (the volume of a typical concrete stone), it is found that only extreme events such as earthquakes can provide sufficient energy to power wireless sensors consisting of modern electronic chips. The results show that the optimal generated electrical power increases approximately linearly with increasing sensor mass. With current technology, it would be possible to self-power a sensor node with a mass between 100 and 1000 g for a bridge under traffic load. Lowering the energy consumption of electronic components is an ongoing research effort. It is likely that, as electronics becomes more efficient in the future, it will be possible to power a wireless sensor node by harvesting vibrations from a volume generator smaller than 5 cm3.
The Vibration Ring. Phase 1; [Seedling Fund
Asnani, Vivake M.; Krantz, Timothy L.; Delap, Damon C.; Stringer, David B.
2014-01-01
The vibration ring was conceived as a driveline damping device to prevent structure-borne noise in machines. It has the appearance of a metal ring, and can be installed between any two driveline components like an ordinary mechanical spacer. Damping is achieved using a ring-shaped piezoelectric stack that is poled in the axial direction and connected to an electrical shunt circuit. Surrounding the stack is a metal structure, called the compression cage, which squeezes the stack along its poled axis when excited by radial driveline forces. The stack in turn generates electrical energy, which is either dissipated or harvested using the shunt circuit. Removing energy from the system creates a net damping effect. The vibration ring is much stiffer than traditional damping devices, which allows it to be used in a driveline without disrupting normal operation. In phase 1 of this NASA Seedling Fund project, a combination of design and analysis was used to examine the feasibility of this concept. Several designs were evaluated using solid modeling, finite element analysis, and by creating prototype hardware. Then an analytical model representing the coupled electromechanical response was formulated in closed form. The model was exercised parametrically to examine the stiffness and loss factor spectra of the vibration ring, as well as simulate its damping effect in the context of a simplified driveline model. The results of this work showed that this is a viable mechanism for driveline damping, and provided several lessons for continued development.
Passive vibration control: a structure-immittance approach
Zhang, Sara Ying; Jiang, Jason Zheng; Neild, Simon A.
2017-05-01
Linear passive vibration absorbers, such as tuned mass dampers, often contain springs, dampers and masses, although recently there has been a growing trend to employ or supplement the mass elements with inerters. When considering possible configurations with these elements broadly, two approaches are normally used: one structure-based and one immittance-based. Both approaches have their advantages and disadvantages. In this paper, a new approach is proposed: the structure-immittance approach. Using this approach, a full set of possible series-parallel networks with predetermined numbers of each element type can be represented by structural immittances, obtained via a proposed general formulation process. Using the structural immittances, both the ability to investigate a class of absorber possibilities together (advantage of the immittance-based approach), and the ability to control the complexity, topology and element values in resulting absorber configurations (advantages of the structure-based approach) are provided at the same time. The advantages of the proposed approach are demonstrated through two case studies on building vibration suppression and automotive suspension design, respectively.
Thermoelastic damping in torsion microresonators with coupling effect between torsion and bending
Tai, Yongpeng; Li, Pu; Fang, Yuming
2014-02-01
Predicting thermoelastic damping (TED) is crucial in the design of high Q MEMS resonators. In the past, there have been few works on analytical modeling of thermoelastic damping in torsion microresonators. This could be related to the assumption of pure torsional mode for the supporting beams in the torsion devices. The pure torsional modes of rectangular supporting beams involve no local volume change, and therefore, they do not suffer any thermoelastic loss. However, the coupled motion of torsion and bending usually exists in the torsion microresonator when it is not excited by pure torque. The bending component of the coupled motion causes flexural vibrations of supporting beams which may result in significant thermoelastic damping for the microresonator. This paper presents an analytical model for thermoelastic damping in torsion microresonators with the coupling effect between torsion and bending. The theory derives a dynamic model for torsion microresonators considering the coupling effect, and approximates the thermoelastic damping by assuming the energy loss to occur only in supporting beams of flexural vibrations. The thermoelastic damping obtained by the present model is compared to the measured internal friction of single paddle oscillators. It is found that thermoelastic damping contributes significantly to internal friction for the case of the higher modes at room temperature. The present model is validated by comparing its results with the finite-element method (FEM) solutions. The effects of structural dimensions and other parameters on thermoelastic damping are investigated for the representative case of torsion microresonators.
Energy harvesting from structural vibrations of magnetic shape memory alloys
Farsangi, Mohammad Amin Askari; Cottone, Francesco; Sayyaadi, Hassan; Zakerzadeh, Mohammad Reza; Orfei, Francesco; Gammaitoni, Luca
2017-03-01
This letter presents the idea of scavenging energy from vibrating structures through magnetic shape memory alloy (MSMA). To this end, a MSMA specimen made of Ni50Mn28Ga22 is coupled to a cantilever beam through a step. Two permanent magnets installed at the top and bottom of the beam create a bias field perpendicular to the magnetization axis of the specimen. When vibrating the device, a longitudinal axial load applies on the MSMA, which in turn changes the magnetization, due to the martensitic variant reorientation mechanism. A pick-up coil wounded around the MSMA converts this variation into voltage according to the Faraday's law. Experimental test confirms the possibility of generating voltage in a vibrating MSMA. In particular, 15 μW power is harvested for acceleration of 0.3 g RMS at a frequency of 19.1 Hz, which is comparable with piezoelectric energy harvesters. It is also found that the optimum bias magnetic field for maximum voltage is lower than the starting field of pseudo elastic behavior.
Vibration Based Methods For Damage Detection In Structures
Directory of Open Access Journals (Sweden)
Manoach E.
2016-01-01
Full Text Available Vibration based damage detection methods are among the most popular and promising approaches for health monitoring of structures. In this work a critical review of different methods for damage detection methods of structures is presented. The theoretical bases of the most popular methods based on the changes in the modal properties of the structures are deduced. The review includes the modal displacements, the mode shape slopes, the modal curvatures and the strain energy methods. The efficiency of all these methods is compared by using a finite element analysis of intact and damaged beams. The methods are tested experimentally by using a scanning laser vibrometer to measure the modal properties of specially prepared composite beams with defects. All this methods are compared with the damage detection method based on the analysis of the Poincaré maps of the motion of the structures. Conclusions concerning the advantages and the applicability of the considered methods are deduced.
Acoustically Induced Vibration of Structures: Reverberant Vs. Direct Acoustic Testing
Kolaini, Ali R.; O'Connell, Michael R.; Tsoi, Wan B.
2009-01-01
Large reverberant chambers have been used for several decades in the aerospace industry to test larger structures such as solar arrays and reflectors to qualify and to detect faults in the design and fabrication of spacecraft and satellites. In the past decade some companies have begun using direct near field acoustic testing, employing speakers, for qualifying larger structures. A limited test data set obtained from recent acoustic tests of the same hardware exposed to both direct and reverberant acoustic field testing has indicated some differences in the resulting structural responses. In reverberant acoustic testing, higher vibration responses were observed at lower frequencies when compared with the direct acoustic testing. In the case of direct near field acoustic testing higher vibration responses appeared to occur at higher frequencies as well. In reverberant chamber testing and direct acoustic testing, standing acoustic modes of the reverberant chamber or the speakers and spacecraft parallel surfaces can strongly couple with the fundamental structural modes of the test hardware. In this paper data from recent acoustic testing of flight hardware, that yielded evidence of acoustic standing wave coupling with structural responses, are discussed in some detail. Convincing evidence of the acoustic standing wave/structural coupling phenomenon will be discussed, citing observations from acoustic testing of a simple aluminum plate. The implications of such acoustic coupling to testing of sensitive flight hardware will be discussed. The results discussed in this paper reveal issues with over or under testing of flight hardware that could pose unanticipated structural and flight qualification issues. Therefore, it is of paramount importance to understand the structural modal coupling with standing acoustic waves that has been observed in both methods of acoustic testing. This study will assist the community to choose an appropriate testing method and test setup in
Active Vibration Control of a Monopile Offshore Structure
DEFF Research Database (Denmark)
Nielsen, Søren R. K.; Kirkegaard, Poul Henning; Thesbjerg, L.
1999-01-01
of the fluid velocity relative to the platform, and only this quantity need to be measured, which is easily performed by a flow meter fixed to the platform. The efficiency of the described closed loop control system has been verified by model tests in a wave flume in both regular and irregular wave conditions......In the Danish part of the North Sea monopile platforms with a cylindrical shaft have been used at the exploitation of marginal fields. In the paper a new principle for active vibration control of such structures is suggested. The principle is based on a control of the boundary layer flow around...
Semi-decentralized Strategies in Structural Vibration Control
Directory of Open Access Journals (Sweden)
F. Palacios-Quiñonero
2011-04-01
Full Text Available In this work, the main ideas involved in the design of overlapping and multi-overlapping controllers via the Inclusion Principle are discussed and illustrated in the context of the Structural Vibration Control of tall buildings under seismic excitation. A detailed theoretical background on the Inclusion Principle and the design of overlapping controllers is provided. Overlapping and multi-overlapping LQR controllers are designed for a simplified five-story building model. Numerical simulations are conducted to asses the performance of the proposed semi-decentralized controllers with positive results.
Fay, Temple H.
2012-01-01
Viscous damping is commonly discussed in beginning differential equations and physics texts but dry friction or Coulomb friction is not despite dry friction being encountered in many physical applications. One reason for avoiding this topic is that the equations involve a jump discontinuity in the damping term. In this article, we adopt an energy…
Harvesting Energy from Vibrations of the Underlying Structure
DEFF Research Database (Denmark)
Han, Bo; Vssilaras, S; Papadias, C.B.
2013-01-01
The use of wireless sensors for structural health monitoring offers several advantages such as small size, easy installation and minimal intervention on existing structures. However the most significant concern about such wireless sensors is the lifetime of the system, which depends heavily on th...... an improved Maximum Power Point Tracking technique on the conversion circuit, the proposed method is shown to maximize the conversion coefficient from kinetic energy to applicable electrical energy....... emerges as a technique that can harvest energy from the surrounding environment. Among all possible energy harvesting solutions, kinetic energy harvesting seems to be the most convenient, especially for sensors placed on structures that experience regular vibrations. Such micro-vibrations can be harmful...... on the type of power supply. No matter how energy efficient the operation of a battery operated sensor is, the energy of the battery will be exhausted at some point. In order to achieve a virtually unlimited lifetime, the sensor node should be able to recharge its battery in an easy way. Energy harvesting...
Analytical and Experimental Studies of Beam Waveguide Absorbers for Structural Damping.
1988-03-01
8217% ibration control mecans such as isolaIon1, detuineIL. cearc damping anid dxnatnic absorption. All of- these approaches have Kecn stuameu rm!icr tlioOU~hI...the energy loss Factor of’ the constrained layer beam. The impedance of r1he high damping constrained laver beam shows the smooth and shilcd...frequency range (�z) the impedances of the test , plate were higher than those of’ waveguide absorbers and at high frequency range >lJ .)lz) impedances
Vibration control of a flexible structure with electromagnetic actuators
DEFF Research Database (Denmark)
Gruzman, Maurício; Santos, Ilmar
2016-01-01
This work presents the model of a shear-frame-type structure composed of six flexible beams and three rigid masses. Fixed on the ground, outside the structure, two voltage-controlled electromagnetic actuators are used for vibration control. To model the flexible beams, unidimensional finite...... elements were used. Nonlinear equations for the actuator electromagnetic force, noise in the position sensor, time delays for the control signal update and voltage saturation were also considered in the model. For controlling purposes, a discrete linear quadratic regulator combined with a predictive full......-order discrete linear observer was employed. Results of numerical simulations, where the structure is submitted to an impulsive disturbance force and to a harmonic force, show that the oscillations can be significantly reduced with the use of the electromagnetic actuators....
Control of noise and structural vibration a MATLAB-based approach
Mao, Qibo
2013-01-01
Control of Noise and Structural Vibration presents a MATLAB®-based approach to solving the problems of undesirable noise generation and transmission by structures and of undesirable vibration within structures in response to environmental or operational forces. The fundamentals of acoustics, vibration and coupling between vibrating structures and the sound fields they generate are introduced including a discussion of the finite element method for vibration analysis. Following this, the treatment of sound and vibration control begins, illustrated by example systems such as beams, plates and double plate structures. Sensor and actuator placement is explained as is the idea of modal sensor–actuators. The design of appropriate feedback systems includes consideration of basic stability criteria and robust active structural acoustic control. Single and multi-mode positive position feedback (PPF) control systems are also described in the context of loudspeaker–duct model with non-collocated loudspeaker–microp...
Modeling of interfacial friction damping of carbon nanotube-based nanocomposites
Lin, R. M.; Lu, C.
2010-11-01
Carbon nanotube-based composite is becoming increasingly popular and offers great potential for highly demanding practical high strength and high damping applications. The excellent damping capacity of CNTs is primarily due to the interfacial friction between carbon nanotubes and polymer resins and the extremely large interfacial surface area over a given specific mass (specific area). In this paper, damping characteristics of carbon nanotube-based composites have been investigated, with an objective of developing an effective and accurate analytical model, which can be used as a design tool for the damping design of such materials. Based on the interfacial slips between the resin and nanotubes and between the nanotubes themselves, a micro stick-slip damping model has been developed. Such a physically derived model is believed to be appropriate and representative of the actual complex damping mechanism of the material system. The model, developed for the first time, is analytical and relates explicitly the material properties of the resin and nanotubes and the processing parameters to the overall material damping loss factor and hence it offers the possibility for material engineers to possibly optimize the damping for required applications. Due to the nonlinear force-displacement relationship derived under the micro stick-slip, a harmonic linearization method, the Describing Function method, has been employed to analyse its vibration characteristics and to derive the required damping loss factors. From the analytical formula, it can be seen that the damping loss factor of the material system depends on the individual material properties of the resin and the nanotubes, structural deformation, nanotube volume fraction and the critical shear stresses at which interfacial slips take place. By taking careful considerations of these design parameters, optimized carbon nanotube-based composites for advanced damping applications can be developed. Extensive numerical
Features of vibrations of structural inhomogeneous solid media
Karimbaev, Telman; Baishagirov, Khairulla; Nurgaliyeva, Saltanat
2017-09-01
Homogeneous or quasi-homogeneous classic models of deformation are generally used at a mathematical de-scription of deformation composite materials (CM). These theories, however, are limited within initial conditions and do not cover the most important properties of CM: heterogeneity of inertia and elasticity of components, their interaction when deforming, etc. Among the models that complement the classical theories, it is possible to allocate the so-called theory of mixture where CM is considered as two (or more) interacting homogeneous continuum. Therefore, the model increase of motion freedom degrees of the particles of such heterogeneous medium allows each component of CM to show their inertial properties. This leads to the identification of such exclusive features as "bifurcation of fre-quencies", i.e., to description of motion on each form of normal modes at two different frequencies. In the research this phenomenon was investigated by the analysis of biquadratic equation obtained at solving the proper value problem of heterogeneous medium, and was verified by testing the normal mode of frequencies of blades made of CM. In the particular case there was received a simple calculation formula for determination of bar technical frequencies from CM on the basis of the characteristic equation of natural vibrations. In this case the numerical results for the lower forms of the vibration normal mode coincide with the experimental data for homogeneous medium. The characteristic equation contains the introduced physical parameters of the two-component theory; therefore, it describes the other forms of vibration. However, in this case the freedom of structural fluctuations of CM each component is limited to their coupling and interaction, providing continuity and shared the compound materials.
Vibration measurement on large structures by microwave remote sensing
Gentile, Carmelo
2012-06-01
Recent advances in radar techniques and systems have led to the development of microwave interferometers, suitable for the non-contact vibration monitoring of large structures. In the first part of the paper, the main techniques adopted in microwave remote sensing are described, so that advantages and potential issues of these techniques are addressed and discussed. Subsequently, the results of past and recent tests of full-scale structures are presented, in order to demonstrate the reliability and accuracy of microwave remote sensing; furthermore, the simplicity of use of the radar technology is exemplified in practical cases, where the access with conventional techniques is uneasy or even hazardous, such as the stay cables of cable-stayed bridges.
Free vibration analysis of coupled fluid-structure systems
Gupta, K. K.
1982-01-01
An efficient numerical technique for the eigenvalue solution in the free vibration analysis of compressible fluid-structure coupled systems is presented. The fluid is assumed to be compressible in nature and the incompressible problem is only a special case of the present generalized algorithm. A natural frequency analysis of the structure in the absence of any fluid is achieved by a combined Sturm sequence and inverse iteration technique that computes only the required eigenvalues and vectors. A special inverse iteration scheme is then developed for the coupled system that uses the computed eigenvalues as starting iteration values for convergence. Numerical results obtained by solving a number of standard test cases indicate the pattern of root convergence corresponding to various simplifying assumptions.
Molecular and vibrational structure of thiosulfonate S-esters
DEFF Research Database (Denmark)
Luu, Thi Xuan Thi; Duus, Fritz; Spanget-Larsen, Jens
2013-01-01
/cc-pVTZ). The vibrational spectra of 2 and 3 are sensitive to the orientation of the alkyl group attached to the sulfonylic sulfur atom. Rotamers corresponding to anti and gauche conformations are thus predicted to have distinctly different vibrational transitions in the 800–400 cm–1 region. The observed vibrational...
Yang, Yongchao; Nagarajaiah, Satish
2016-06-01
Randomly missing data of structural vibration responses time history often occurs in structural dynamics and health monitoring. For example, structural vibration responses are often corrupted by outliers or erroneous measurements due to sensor malfunction; in wireless sensing platforms, data loss during wireless communication is a common issue. Besides, to alleviate the wireless data sampling or communication burden, certain accounts of data are often discarded during sampling or before transmission. In these and other applications, recovery of the randomly missing structural vibration responses from the available, incomplete data, is essential for system identification and structural health monitoring; it is an ill-posed inverse problem, however. This paper explicitly harnesses the data structure itself-of the structural vibration responses-to address this (inverse) problem. What is relevant is an empirical, but often practically true, observation, that is, typically there are only few modes active in the structural vibration responses; hence a sparse representation (in frequency domain) of the single-channel data vector, or, a low-rank structure (by singular value decomposition) of the multi-channel data matrix. Exploiting such prior knowledge of data structure (intra-channel sparse or inter-channel low-rank), the new theories of ℓ1-minimization sparse recovery and nuclear-norm-minimization low-rank matrix completion enable recovery of the randomly missing or corrupted structural vibration response data. The performance of these two alternatives, in terms of recovery accuracy and computational time under different data missing rates, is investigated on a few structural vibration response data sets-the seismic responses of the super high-rise Canton Tower and the structural health monitoring accelerations of a real large-scale cable-stayed bridge. Encouraging results are obtained and the applicability and limitation of the presented methods are discussed.
Directory of Open Access Journals (Sweden)
Xiuting Sun
2016-01-01
Full Text Available The nonlinear effect incurred by time delay in vibration control is investigated in this study via a vibration absorber coupled with a continuous beam structure. The stability of the vibration absorber coupled structure system with time-delay coupling is firstly studied, which provides a general guideline for the potential time delay to be introduced to the system. Then it is shown that there is a specific region for the time delay which can bring bifurcation modes to the dynamic response of the coupling system, and the vibration energy at low frequencies can be transferred or absorbed due to the bifurcation mode and the vibration in the corresponding frequency range is thus suppressed. The nonlinear mechanism of this vibration suppression incurred by the coupling time delay is discussed in detail, which provides a novel and alternative approach to the analysis, design, and control of vibration absorbers in engineering practice.
Air damping effect on the air-based CMUT operation
Cha, Bu-Sang; Kanashima, Takeshi; Lee, Seung-Mok; Okuyama, Masanori
2015-08-01
The vibration amplitude, damping ratio and viscous damping force in capacitive micromachinedultrasonic transducers (CMUTs) with a perforated membrane have been calculated theoretically and compared with the experimental data on its vibration behavior. The electrical bias of the DC and the AC voltages and the operation frequency conditions influence the damping effect because leads to variations in the gap height and the vibration velocity of the membrane. We propose a new estimation method to determine the damping ratio by the decay rate of the vibration amplitudes of the perforated membrane plate are measured using a laser vibrometer at each frequency, and the damping ratios were calculated from those results. The influences of the vibration frequency and the electrostatic force on the damping effect under the various operation conditions have been studied.
Microwave Spectra, Structure, and Ring-Puckering Vibration of Octafluorocyclopentene.
Long, B E; Arsenault, Eric A; Obenchain, Daniel A; Choi, Yoon Jeong; Ocola, Esther J; Laane, Jaan; Pringle, Wallace C; Cooke, S A
2016-11-03
The rotational spectra of octafluorocyclopentene (C5F8) has been measured for the first time using pulsed jet Fourier transform microwave spectroscopy in a frequency range of 6 to 16 GHz. As in the molecule cyclopentene, the carbon ring is nonplanar, and inversion through the plane results in an inversion pair of ground state vibrational energy levels with an inversion splitting of 18.4 MHz. This large amplitude motion leads to the vibration-rotation coupling of energy levels. The symmetric double minimum ring-puckering potential function was calculated, resulting in a barrier of 222 cm-1. The rotational constants A0 = 962.9590(1) MHz, B0 = 885.1643(4) MHz, C0 = 616.9523(4) MHz, A1 = 962.9590(1) MHz, B1 = 885.1643(4) MHz, C1 = 616.9528(4) MHz, and two centrifugal distortion constants for each state were determined for the parent species and all 13C isotopologues. A mixed coordinate molecular structure was determined from a least-squares fit of the ground state rotational constants of the parent and each 13C isotopologue combined with the equilibrium bond lengths and angles from quantum chemical calculations.
Beam dynamics and wakefield suppression in interleaved damped and detuned structures for CLIC
D'Elia, A; Khan, V F; Jones, R M; Latina, A; Nesmiyan, I; Riddone, G
2013-01-01
Acceleration of multiple bunches of charged particles in the main linacs of the Compact Linear Collider (CLIC) with high accelerating fields provides two major challenges: firstly, to ensure the surface electromagnetic fields do not cause electrical breakdown and subsequent surface damage, and secondly, to ensure the beam-excited wakefields are sufficiently suppressed to avoid appreciable emittance dilution. In the baseline design for CLIC, heavy wakefield suppression is used (Q ~ 10) [1] and this ensures the beam quality is well-preserved [2]. Here we discuss an alternative means to suppress the wakefield which relies on strong detuning of the cell dipole frequencies, together with moderate damping, effected by manifolds which are slot-coupled to each accelerating cell. This damped and detuned wakefield suppression scheme is based on the methodology developed for the Japanese Linear Collider/Next Linear Collider (JLC/NLC) [3]. Here we track the multi-bunch beam down the complete collider, u...
Directory of Open Access Journals (Sweden)
Yifan Luo
2017-01-01
Full Text Available This paper proposes a novel inerter-based dynamic vibration absorber, namely, electromagnetic resonant shunt tuned mass-damper-inerter (ERS-TMDI. To obtain the performances of the ERS-TMDI, the combined ERS-TMDI and a single degree of freedom system are introduced. H2 criteria performances of the ERS-TMDI are introduced in comparison with the classical tuned mass-damper (TMD, the electromagnetic resonant shunt series TMDs (ERS-TMDs, and series-type double-mass TMDs with the aim to minimize structure damage and simultaneously harvest energy under random wind excitation. The closed form solutions, including the mechanical tuning ratio, the electrical damping ratio, the electrical tuning ratio, and the electromagnetic mechanical coupling coefficient, are obtained. It is shown that the ERS-TMDI is superior to the classical TMD, ERS-TMDs, and series-type double-mass TMDs systems for protection from structure damage. Meanwhile, in the time domain, a case study of Taipei 101 tower is presented to demonstrate the dual functions of vibration suppression and energy harvesting based on the simulation fluctuating wind series, which is generated by the inverse fast Fourier transform method. The effectiveness and robustness of ERS-TMDI in the frequency and time domain are illustrated.
Intelligent failure-proof control system for structural vibration
Energy Technology Data Exchange (ETDEWEB)
Yoshida, Kazuo [Keio Univ., Yokohama (Japan). Faculty of Science and Technology; Oba, Takahiro [Keio Univ., Tokyo (Japan)
2000-11-01
With progress of technology in recent years, gigantism and complication such as high-rise buildings, nuclear reactors and so on have brought about new problems. Particularly, the safety and the reliability for damages in abnormal situations have become more important. Intelligent control systems which can judge whether the situation is normal or abnormal at real time and cope with these situations suitably are demanded. In this study, Cubic Neural Network (CNN) is adopted, which consists of the controllers possessing cubically some levels of information abstracting. In addition to the usual quantitative control, the qualitative control is used for the abnormal situations. And, by selecting a suitable controller, CNN can cope with the abnormal situation. In order to confirm the effectiveness of this system, the structural vibration control problems with sensory failure and elasto-plastic response are dealt with. As a result of simulations, it was demonstrated that CNN can cope with unexpected abnormal situations which are not considered in learning. (author)
Smart nanocoated structure for energy harvesting at low frequency vibration
Sharma, Sudhanshu
Increasing demands of energy which is cleaner and has an unlimited supply has led development in the field of energy harvesting. Piezoelectric materials can be used as a means of transforming ambient vibrations into electrical energy that can be stored and used to power other devices. With the recent surge of micro scale devices, piezoelectric power generation can provide a convenient alternative to traditional power sources. In this research, a piezoelectric power generator composite prototype was developed to maximize the power output of the system. A lead zirconate titanate (PZT) composite structure was formed and mounted on a cantilever bar and was studied to convert vibration energy of the low range vibrations at 30 Hz--1000 Hz. To improve the performance of the PZT, different coatings were made using different percentage of Ferrofluid (FNP) and Zinc Oxide nanoparticles (ZnO) and binder resin. The optimal coating mixture constituent percentage was based on the performance of the composite structure formed by applying the coating on the PZT. The fabricated PZT power generator composite with an effective volume of 0.062 cm3 produced a maximum of 44.5 μW, or 0.717mW/cm3 at its resonant frequency of 90 Hz. The optimal coating mixture had the composition of 59.9%FNP + 40% ZnO + 1% Resin Binder. The coating utilizes the opto-magneto-electrical properties of ZnO and Magnetic properties of FNP. To further enhance the output, the magneto-electric (ME) effect was increased by subjecting the composite to magnetic field where coating acts as a magnetostrictive material. For the effective volume of 0.0062 cm 3, the composite produced a maximum of 68.5 μW, or 1.11mW/cm 3 at its resonant frequency of 90 Hz at 160 gauss. The optimal coating mixture had the composition of 59.9% FNP + 40% ZnO + 1% Resin Binder. This research also focused on improving the efficiency of solar cells by utilizing the magnetic effect along with gas plasma etching to improve the internal reflection
Yang, Yongchao; Dorn, Charles; Mancini, Tyler; Talken, Zachary; Nagarajaiah, Satish; Kenyon, Garrett; Farrar, Charles; Mascareñas, David
2017-03-01
what is required by the Shannon-Nyquist sampling theorem for output-only modal analysis. In particular, the spatio-temporal uncoupling property of the modal expansion of structural vibration responses enables a direct modal decoupling of the temporally-aliased vibration measurements by existing output-only modal analysis methods, yielding (full-field) mode shapes estimation directly. Then the signal aliasing properties in modal analysis is exploited to estimate the modal frequencies and damping ratios. The proposed method is validated by laboratory experiments where output-only modal identification is conducted on temporally-aliased acceleration responses and particularly the temporally-aliased video measurements of bench-scale structures, including a three-story building structure and a cantilever beam.
Kim, Heung Soo; Sohn, Jung Woo; Jeon, Juncheol; Choi, Seung-Bok
2013-02-06
In this work, active vibration control of an underwater cylindrical shell structure was investigated, to suppress structural vibration and structure-borne noise in water. Finite element modeling of the submerged cylindrical shell structure was developed, and experimentally evaluated. Modal reduction was conducted to obtain the reduced system equation for the active feedback control algorithm. Three Macro Fiber Composites (MFCs) were used as actuators and sensors. One MFC was used as an exciter. The optimum control algorithm was designed based on the reduced system equations. The active control performance was then evaluated using the lab scale underwater cylindrical shell structure. Structural vibration and structure-borne noise of the underwater cylindrical shell structure were reduced significantly by activating the optimal controller associated with the MFC actuators. The results provide that active vibration control of the underwater structure is a useful means to reduce structure-borne noise in water.
Directory of Open Access Journals (Sweden)
Seung-Bok Choi
2013-02-01
Full Text Available In this work, active vibration control of an underwater cylindrical shell structure was investigated, to suppress structural vibration and structure-borne noise in water. Finite element modeling of the submerged cylindrical shell structure was developed, and experimentally evaluated. Modal reduction was conducted to obtain the reduced system equation for the active feedback control algorithm. Three Macro Fiber Composites (MFCs were used as actuators and sensors. One MFC was used as an exciter. The optimum control algorithm was designed based on the reduced system equations. The active control performance was then evaluated using the lab scale underwater cylindrical shell structure. Structural vibration and structure-borne noise of the underwater cylindrical shell structure were reduced significantly by activating the optimal controller associated with the MFC actuators. The results provide that active vibration control of the underwater structure is a useful means to reduce structure-borne noise in water.
Energy Technology Data Exchange (ETDEWEB)
Doebling, S.W.; Farrar, C.R.; Prime, M.B.; Shevitz, D.W.
1996-05-01
This report contains a review of the technical literature concerning the detection, location, and characterization of structural damage via techniques that examine changes in measured structural vibration response. The report first categorizes the methods according to required measured data and analysis technique. The analysis categories include changes in modal frequencies, changes in measured mode shapes (and their derivatives), and changes in measured flexibility coefficients. Methods that use property (stiffness, mass, damping) matrix updating, detection of nonlinear response, and damage detection via neural networks are also summarized. The applications of the various methods to different types of engineering problems are categorized by type of structure and are summarized. The types of structures include beams, trusses, plates, shells, bridges, offshore platforms, other large civil structures, aerospace structures, and composite structures. The report describes the development of the damage-identification methods and applications and summarizes the current state-of-the-art of the technology. The critical issues for future research in the area of damage identification are also discussed.
Active Vibration Control of a Flexible Structure Using Piezoceramic Actuators
Directory of Open Access Journals (Sweden)
J. Fei
2008-03-01
Full Text Available Considerable attention has been devoted recently to active vibration control using intelligent materials as actuators. This paper presents results on active control schemes for vibration suppression of flexible steel cantilever beam with bonded piezoelectric actuators. The PZT patches are surface bonded near the fixed end of flexible steel cantilever beam. The dynamic model of the flexible steel cantilever beam is derived. Active vibration control methods, strain rate feedback control (SRF, positive position feedback control (PPF are investigated and implemented using xPC Target real-time system. Experimental results demonstrate that the SRF control and PPF control achieve effective vibration suppression results of steel cantilever beam.
Mitigating ground vibration by periodic inclusions and surface structures
DEFF Research Database (Denmark)
Andersen, Lars Vabbersgaard; Bucinskas, Paulius; Persson, Peter
2016-01-01
Ground vibration from traffic is a source of nuisance in urbanized areas. Trenches and wave barriers can provide mitigation of vibrations, but single barriers need to have a large depth to be effective-especially in the low-frequency range relevant to traffic-induced vibration. Alternatively......-dimensional finite-element model. The laboratory model employs soaked mattress foam placed within a box to mimic a finite volume of soil. The dynamic properties of the soaked foam ensure wavelengths representative of ground vibration in small scale. Comparison of the results from the two models leads...
Implications of interaction between Humans and Structures
DEFF Research Database (Denmark)
Pedersen, Lars
2015-01-01
as structural damping and therefore also structural vibration levels). The paper addresses this subject and explores implications of having passive humans present on the structure. In experimental tests with a laboratory floor it is examined to which degree the posture of humans passively sitting on the floor...... influences the damping added to the floor. A numerical case study explores how passive humans may influence vibration levels of a floor....
Wind Turbine Rotors with Active Vibration Control
DEFF Research Database (Denmark)
Svendsen, Martin Nymann
This thesis presents a framework for structural modeling, analysis and active vibration damping of rotating wind turbine blades and rotors. A structural rotor model is developed in terms of finite beam elements in a rotating frame of reference. The element comprises a representation of general...... formulation. The element provides an accurate representation of the eigenfrequencies and whirling modes of the gyroscopic system, and identifies lightly damped edge-wise modes. By adoption of a method for active, collocated resonant vibration of multi-degree-of-freedom systems it is demonstrated...... that these are geometrically well separated. For active vibration control in three-bladed wind turbine rotors the present work presents a resonance-based method for groups of one collective and two whirling modes. The controller is based on the existing resonant format and introduces a dual system targeting the collective...
Yang, Yang; Pan, Yayue; Guo, Ping
2017-04-01
Creating orderly periodic micro/nano-structures on metallic surfaces, or structural coloration, for control of surface apparent color and optical reflectivity has been an exciting research topic over the years. The direct applications of structural coloration include color marking, display devices, and invisibility cloak. This paper presents an efficient method to colorize metallic surfaces with periodic micro/nano-gratings using elliptical vibration texturing. When the tool vibration is coupled with a constant cutting velocity, controlled periodic ripples can be generated due to the overlapping tool trajectory. These periodic ripples with a wavelength near visible spectrum can act as micro-gratings to introduce iridescent colors. The proposed technique also provides a flexible method for color marking of metallic surfaces with arbitrary patterns and images by precise control of the spacing distance and orientation of induced micro/nano-ripples. Theoretical analysis and experimental results are given to demonstrate structural coloration of metals by a direct mechanical machining technique.
Numerical methods for analysis of structure and ground vibration from moving loads
DEFF Research Database (Denmark)
Andersen, L.; Nielsen, S.R.K.; Krenk, Steen
2007-01-01
An overview of the main theoretical aspects of finite-element and boundary-element modelling of the response to moving loads is given. The moving loads represent sources of noise and vibration generated by moving vehicles, and the analysis describes the propagation of the disturbances generated...... in soil. A finite-element time-domain analysis in convected coordinates with a simple upwind scheme is presented, including a special set of boundary conditions permitting the passage of outgoing waves in the convected coordinate system. The modification of frequency-dependent damping to convected...
Gómez, S.S.; Metrekine, A.
2017-01-01
The aim of this paper is to identify the local energy dissipation in a lab-scale structure by means of the energy flow analysis. In most of the existing approaches the damping is identified either in terms of the modal damping factors or at the material scale. In this paper, an alternative method to
Structured illumination microscopy for vibrational molecular imaging (Conference Presentation)
Watanabe, Kozue; Palonpon, Almar F.; Smith, Nicholas I.; Chiu, Liang-da; Kasai, Atsushi; Hashimoto, Hitoshi; Kawata, Satoshi; Fujita, Katsumasa
2016-09-01
Raman microscopy is a powerful tool for analytical imaging. The wavelength shift of Raman scattering corresponds to molecular vibrational energy. Therefore, we can access rich chemical information, such as distribution, concentration, and chemical environment of sample molecules. Despite these strengths of Raman microscopy, the spatial resolution has been a limiting factor for many practical applications. In this study, we developed a large-area, high-resolution Raman microscope by utilizing structured illumination microscopy (SIM) to overcome the spatial resolution limit. A structured line-illumination (SLI) Raman microscope was constructed. The structured illumination is introduced along the line direction by the interference of two line-shaped beams. In SIM, the spatial frequency mixing between structured illumination and Raman scattering from the sample allows access to the high spatial frequency information beyond the conventional cut-off. As a result, the FWHM of 40-nm fluorescence particle images showed a clear resolution enhancement in the line direction: 366 nm in LI and 199 nm in SLI microscope. Using the developed microscope, we successfully demonstrated high-resolution Raman imaging of various kinds of specimens, such as few-layer graphene, graphite, mouse brain tissue, and polymer nanoparticles. The high resolution Raman images showed the capability to extract original spectral features from the mixed Raman spectra of a multi-component sample because of the enhanced spatial resolution, which is advantageous in observing complex spectral features. The Raman microscopy technique reported here enables us to see the detailed chemical structures of chemical, biological, and medical samples with a spatial resolution smaller than 200 nm.
Another approach to vibrational analysis of stepped structures
CSIR Research Space (South Africa)
Fedotov, I
2006-01-01
Full Text Available Hz. First resonance is a pendulum mode at which the stepped bar vibrates as “rigid” pendu- lum. All other modes are “longitudinal”. Geometry of the bar was specially chosen so that vibration amplitude of the junction between the cylindrical...
Modelling, structural, thermal, optical and vibrational studies of a ...
Indian Academy of Sciences (India)
sis of all the fundamental vibration modes using the VEDA. 4 program [21]. Scaling factors used in this study were taken from literature [22]. In order to take into account the effect of intermolecular interactions on geometrical parameters and vibrational spectroscopy, we have considered an appropriate cluster model built up ...
Active structural elements within a general vibration control framework
Holterman, J.; de Vries, Theodorus J.A.; Isermann, R.
2000-01-01
High-precision machines typically suffer from small but annoying vibrations. As the most appropriate solution to a particular vibration problem is not always obvious, it may be convenient to cast the problem in a more general framework. This framework may then be used for frequency response
Structural characterization of carbon nanotubes via the vibrational density of states
Pool, Albert J.; Jain, Sandeep K.; Barkema, Gerard T.
2017-01-01
The electrical and chemical properties of carbon nanotubes vary significantly with different chirality and diameter, making the experimental determination of these structural properties important. Here, we show that the vibrational density of states (VDOS) contains information on the structure of
Flow induced vibrations of the CLIC X-Band accelerating structures
Charles, Tessa; Boland, Mark; Riddone, Germana; Samoshkin, Alexandre
2011-01-01
Turbulent cooling water in the Compact Linear Collider (CLIC) accelerating structures will inevitably induce some vibrations. The maximum acceptable amplitude of vibrations is small, as vibrations in the accelerating structure could lead to beam jitter and alignment difficulties. A Finite Element Analysis model is needed to identify the conditions under which turbulent instabilities and significant vibrations are induced. Due to the orders of magnitude difference between the fluid motion and the structure’s motion, small vibrations of the structure will not contribute to the turbulence of the cooling fluid. Therefore the resonant conditions of the cooling channels presented in this paper, directly identify the natural frequencies of the accelerating structures to be avoided under normal operating conditions. In this paper a 2D model of the cooling channel is presented finding spots of turbulence being formed from a shear layer instability. This effect is observed through direct visualization and wavelet ana...
Stochastic Response of Energy Balanced Model for Vortex-Induced Vibration
DEFF Research Database (Denmark)
Nielsen, Søren R.K.; Krenk, S.
of lightly damped structures are found on two branches, with the highest amplification branch on the low-frequency branch. The effect free wind turbulence is to destabilize the vibrations on the high amplification branch, thereby reducing the oscillation amplitude. The effect is most pronounced for very......A double oscillator model for vortex-induced oscillations of structural elements based on exact power exchange between fluid and structure, recently proposed by authors, is extended to include the effect of the turbulent component of the wind. In non-turbulent flow vortex-induced vibrations...... lightly damped structures. The character of the structural vibrations changes with increasing turbulence and damping from nearly regular harmonic oscillation to typical narrow-banded stochastic response, closely resembling observed behaviour in experiments and full-scale structures....
Directory of Open Access Journals (Sweden)
Gergely Takács
2015-01-01
Full Text Available This paper presents a structural health monitoring and parameter estimation system for vibrating active cantilever beams using low-cost embedded computing hardware. The actuator input and the measured position are used in an augmented nonlinear model to observe the dynamic states and parameters of the beam by the continuous-discrete extended Kalman filter (EKF. The presence of undesirable structural change is detected by variations of the first resonance estimate computed from the observed equivalent mass, stiffness, damping, and voltage-force conversion coefficients. A fault signal is generated upon its departure from a predetermined nominal tolerance band. The algorithm is implemented using automatically generated and deployed machine code on an electronics prototyping platform, featuring an economically feasible 8-bit microcontroller unit (MCU. The validation experiments demonstrate the viability of the proposed system to detect sudden or gradual mechanical changes in real-time, while the functionality on low-cost miniaturized hardware suggests a strong potential for mass-production and structural integration. The modest computing power of the microcontroller and automated code generation designates the proposed system only for very flexible structures, with a first dominant resonant frequency under 4 Hz; however, a code-optimized version certainly allows much stiffer structures or more complicated models on the same hardware.
Vibration-based localisation of structural deterioration in frame-like civil engineering structures
DEFF Research Database (Denmark)
Ulriksen, Martin Dalgaard; Damkilde, Lars
2016-01-01
to other structural systems, for instance, wind turbines—can provide reliable damage localisation in frame-like structures. The performance of the method, which is based on statistical interrogation of changes in a surrogate of the transfer matrix, is tested in a Monte Carlo setting with a numerical steel......With the existing trend of minimising material use in typical frame-like civil engineering structures, such as buildings, bridges, and offshore platforms, these structures will typically be subjected to substantial wind induced vibrations. Besides being a source of disturbance for the occupants...... frame model subjected to white noise excitation....
A Stepwise Optimal Design of a Dynamic Vibration Absorber with Tunable Resonant Frequency
Directory of Open Access Journals (Sweden)
Jiejian DI
2014-08-01
Full Text Available A new kind of dynamic vibration absorber (DVA with tunable resonant frequency is presented. The kinematics differential equation about it is built and the stepwise optimization is performed. Firstly, four main system parameters involving the ratios of mass m, natural frequency f, vibration frequency g and damping z are solved by small-step-search method to obtain optimal steady state amplitude. Secondly, the sizing optimization of the dynamic vibration absorber is proceeded to search an optimal damping effect based on the optimal parameters (g, m, z, f. And such the damping effect is simulated in a flat structure, and the results show that the working frequency band and damping effect of the DVA after optimization won 20 % of the effect of ascension compared with that before optimization.
2010-04-01
... the structure to withstand transportation shock and vibration. 3280.903 Section 3280.903 Housing and... structure to withstand transportation shock and vibration. (a) The cumulative effect of highway transportation shock and vibration upon a manufactured home structure may result in incremental degradation of...
Vibration based structural health monitoring of a composite T-beam
Ooijevaar, T.H.; Loendersloot, Richard; Warnet, Laurent; de Boer, Andries; Akkerman, Remko
2010-01-01
A vibration based damage identification method is investigated experimentally for a 2.5-dimensional composite structure. The dynamic response of an intact and a locally delaminated 16-layer unidirectional carbon fibre PEKK reinforced T-beam is considered. A force–vibration set-up, including a laser
Vibration analysis of continuous maglev guideways with a moving distributed load model
Teng, N. G.; Qiao, B. P.
2008-02-01
A model of moving distributed load with a constant speed is established for vertical vibration analysis of a continuous guideway in maglev transportation system. The guideway is considered as a continuous structural system and the action of maglev vehicles on guideways is considered as a moving distributed load. Vibration of the continuous guideways used in Shanghai maglev line is analyzed with this model. The factors that affect the vibration of the guideways, such as speeds, guideway's spans, frequency and damping, are discussed.
Free vibration and dynamic response analysis of spinning structures
1986-01-01
The proposed effort involved development of numerical procedures for efficient solution of free vibration problems of spinning structures. An eigenproblem solution procedure, based on a Lanczos method employing complex arithmetic, was successfully developed. This task involved formulation of the numerical procedure, FORTRAN coding of the algorithm, checking and debugging of software, and implementation of the routine in the STARS program. A graphics package for the E/S PS 300 as well as for the Tektronix terminals was successfully generated and consists of the following special capabilities: (1) a dynamic response plot for the stresses and displacements as functions of time; and (2) a menu driven command module enabling input of data on an interactive basis. Finally, the STARS analysis capability was further improved by implementing the dynamic response analysis package that provides information on nodal deformations and element stresses as a function of time. A number of test cases were run utilizing the currently developed algorithm implemented in the STARS program and such results indicate that the newly generated solution technique is significantly more efficient than other existing similar procedures.
Vibrational spectra and structure of cyclopentane and its isotopomers.
Ocola, Esther J; Bauman, Leslie E; Laane, Jaan
2011-06-23
The infrared and Raman spectra of vapor, liquid, and solid state cyclopentane and its d(1), 1,1-d(2), 1,1,2,2,3,3-d(6), and d(10) isotopomers have been recorded and analyzed. The experimental work was complemented by ab initio and density functional theory (DFT) calculations. The computations confirm that the two conformational forms of cyclopentane are the twist (C(2)) and bent (C(s)) structures and that they differ very little in energy, less than about 10 cm(-1) (0.1 kJ/mol). The bending angle for the C(s) form is 41.5° and the dihedral angle of twisting is 43.2° for the C(2) form. A reliable and complete vibrational assignment for each of the isotopomers has been achieved for the first time, and these agree very well with the DFT (B3LYP/cc-pVTZ) computations. The ab initio CCSD/cc-pVTZ calculations predict a barrier to planarity of 1887 cm(-1), which is in excellent agreement with the experimental value of 1808 cm(-1).
Yigit, Ufuk; Cigeroglu, Ender; Budak, Erhan
2017-09-01
Chatter is a self-excited type of vibration that develops during machining due to process-structure dynamic interactions resulting in modulated chip thickness. Chatter is an important problem as it results in poor surface quality, reduced productivity and tool life. The stability of a cutting process is strongly influenced by the frequency response function (FRF) at the cutting point. In this study, the effect of piezoelectric shunt damping on chatter vibrations in a boring process is studied. In piezoelectric shunt damping method, an electrical impedance is connected to a piezoelectric transducer which is bonded on cutting tool. Electrical impedance of the circuit consisting of piezoceramic transducer and passive shunt is tuned to the desired natural frequency of the cutting tool in order to maximize damping. The optimum damping is achieved in analytical and finite element models (FEM) by using a genetic algorithm focusing on the real part of the tool point FRF rather than the amplitude. Later, a practical boring bar is considered where the optimum circuit parameters are obtained by the FEM. Afterwards, the effect of the optimized piezoelectric shunt damping on the dynamic rigidity and absolute stability limit of the cutting process are investigated experimentally by modal analysis and cutting tests. It is both theoretically and experimentally shown that application of piezoelectric shunt damping results in a significant increase in the absolute stability limit in boring operations.
An investigation on structural, vibrational and nonlinear optical ...
Indian Academy of Sciences (India)
The electron rich regions residing on all the oxygen atoms O1, O1W, O2, O3, and O3W represent the electronegative regions and so, these are the binding sites for electrophilic attack. The values of HOMO, LUMO and Frontier orbital energy gap are given in table 2. 3.4 Vibrational Assignments. 3.4a C-H Vibration: Generally, ...
DEFF Research Database (Denmark)
Friis, Lars; Ohlrich, Mogens
2008-01-01
is considered as one or more fuzzy substructures that are known in some statistical sense only. Experiments have shown that such fuzzy substructures often introduce a damping in the master which is much higher than the structural losses account for. A special method for modeling fuzzy substructures with a one...
Noise Abatement and Internal Vibrational Absorption in Potential Structural Materials
1976-11-01
as advertising nor IS an officirl indorument or rpprovrl of such products or companies by the United Strtos Government. DISPOSITION INSTRUCTIONS...made from the high damping iron-chromium-aluminum alloy were obtained from Toshiba Electric Company. The plates have been delivered and are...distributed _ by Toshiba Electric Co. (17) on a proprietary Fe-Cr-Al alloy and the existence of a miscribility gap in the Fe - Cr system shown in
Theory of vibration protection
Karnovsky, Igor A
2016-01-01
This text is an advancement of the theory of vibration protection of mechanical systems with lumped and distributed parameters. The book offers various concepts and methods of solving vibration protection problems, discusses the advantages and disadvantages of different methods, and the fields of their effective applications. Fundamental approaches of vibration protection, which are considered in this book, are the passive, parametric and optimal active vibration protection. The passive vibration protection is based on vibration isolation, vibration damping and dynamic absorbers. Parametric vibration protection theory is based on the Shchipanov-Luzin invariance principle. Optimal active vibration protection theory is based on the Pontryagin principle and the Krein moment method. The book also contains special topics such as suppression of vibrations at the source of their occurrence and the harmful influence of vibrations on humans. Numerous examples, which illustrate the theoretical ideas of each chapter, ar...
Sweeping shunted electro-magnetic tuneable vibration absorber: Design and implementation
Turco, E.; Gardonio, P.
2017-10-01
This paper presents a study on the design and implementation of a time-varying shunted electro-magnetic Tuneable Vibration Absorber for broad-band vibration control of thin structures. A time-varying RL-shunt is used to harmonically vary the stiffness and damping properties of the Tuneable Vibration Absorber so that its mechanical fundamental natural frequency is continuously swept in a given broad frequency band whereas its mechanical damping is continuously adapted to maximize the vibration absorption from the hosting structure where it is mounted. The paper first recalls the tuning and positioning criteria for the case where a classical Tuneable Vibration Absorber is installed on a thin walled cylindrical structure to reduce the response of a resonating flexural mode. It then discusses the design of the time-varying shunt circuit to produce the desired stiffness and damping variations in the electro-magnetic Tuneable Vibration Absorber. Finally, it presents a numerical study on the flexural vibration and interior sound control effects produced when an array of these shunted electro-magnetic Tuneable Vibration Absorbers are mounted on a thin walled cylinder subject to a rain-on-the-roof stochastic excitation. The study shows that the array of proposed systems effectively controls the cylinder flexural response and interior noise over a broad frequency band without need of tuning and thus system identification of the structure. Therefore, the systems can be successfully used also on structures whose physical properties vary in time because of temperature changes or tensioning effects for example.
Tau Siesakul, Bamrung; Gkoktsi, Kyriaki; Giaralis, Agathoklis
2015-05-01
Motivated by the need to reduce monetary and energy consumption costs of wireless sensor networks in undertaking output-only/operational modal analysis of engineering structures, this paper considers a multi-coset analog-toinformation converter for structural system identification from acceleration response signals of white noise excited linear damped structures sampled at sub-Nyquist rates. The underlying natural frequencies, peak gains in the frequency domain, and critical damping ratios of the vibrating structures are estimated directly from the sub-Nyquist measurements and, therefore, the computationally demanding signal reconstruction step is by-passed. This is accomplished by first employing a power spectrum blind sampling (PSBS) technique for multi-band wide sense stationary stochastic processes in conjunction with deterministic non-uniform multi-coset sampling patterns derived from solving a weighted least square optimization problem. Next, modal properties are derived by the standard frequency domain peak picking algorithm. Special attention is focused on assessing the potential of the adopted PSBS technique, which poses no sparsity requirements to the sensed signals, to derive accurate estimates of modal structural system properties from noisy sub- Nyquist measurements. To this aim, sub-Nyquist sampled acceleration response signals corrupted by various levels of additive white noise pertaining to a benchmark space truss structure with closely spaced natural frequencies are obtained within an efficient Monte Carlo simulation-based framework. Accurate estimates of natural frequencies and reasonable estimates of local peak spectral ordinates and critical damping ratios are derived from measurements sampled at about 70% below the Nyquist rate and for SNR as low as 0db demonstrating that the adopted approach enjoys noise immunity.
Cazzulani, Gabriele; Resta, Ferruccio; Ripamonti, Francesco
2012-04-01
Large mechanical structures are often affected by high level vibrations due to their flexibility. These vibrations can reduce the system performances and lifetime and the use of active vibration control strategies becomes very attractive. In this paper a combination of resonant control and a disturbance estimator is proposed. This solution is able to improve the system performances during the transient motion and also to reject the disturbance forces acting on the system. Both control logics are based on a modal approach, since it allows to describe the structure dynamics considering only few degrees of freedom.
Actuator Control of Edgewise Vibrations in Wind Turbine Blades
DEFF Research Database (Denmark)
Staino, A.; Basu, B.; Nielsen, Søren R.K.
2012-01-01
Edgewise vibrations with low aerodynamic damping are of particular concern in modern multi-megawatt wind turbines, as large amplitude cyclic oscillations may signiﬁcantly shorten the life-time of wind turbine components, and even lead to structural damages or failures. In this paper, a new blade ...
Aeroelastic vibrations and stability of plates and shells
Algazin, Sergey D
2015-01-01
Back-action of wind onto wings causes vibrations, endangering the whole structure. By careful choices of geometry, materials and damping, hazardous effects on wind engines, planes, turbines and cars can be avoided. This book gives an overview of aerodynamics and mechanics behind these problems and describes a range of mechanical effects. Numerical and analytical met
VIBRATION OF FRAME BUILDING STRUCTURES CAUSED BY UNDERGROUND TRAINS
Directory of Open Access Journals (Sweden)
P. V. Аliavdin
2011-01-01
Full Text Available The paper contains investigations on element vibration of a real residential 9-storeyed reinforced-concrete frame building induced by train movement in the shallow subway. A design model for a problem on propagation of bending waves within the limits of the typical fragment of a skeleton is presented in the paper. The steady state vibrations of a column and reinforced-concrete slab induced by an excited force which is equivalent to the impact of the subway trains have been investigated in the paper. The problem has been solved numerically on the basis of the ANSYS FEA program. Numerical results have been compared with an approximate analytical solution and data on full-scale experiment. A prediction technique for vibration propagation in the designed buildings is offered in the paper.
Vibration Control via Stiffness Switching of Magnetostrictive Transducers
Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.
2016-01-01
This paper presents a computational study of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magnetomechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.25; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping.
Vibration analysis of structural elements using differential quadrature method
Directory of Open Access Journals (Sweden)
Mohamed Nassar
2013-01-01
Full Text Available The method of differential quadrature is employed to analyze the free vibration of a cracked cantilever beam resting on elastic foundation. The beam is made of a functionally graded material and rests on a Winkler–Pasternak foundation. The crack action is simulated by a line spring model. Also, the differential quadrature method with a geometric mapping are applied to study the free vibration of irregular plates. The obtained results agreed with the previous studies in the literature. Further, a parametric study is introduced to investigate the effects of geometric and elastic characteristics of the problem on the natural frequencies.
Global structural condition assessment of highway bridges by ambient vibration monitoring
Feng, Maria Q.; Chen, Yangbo; Tan, Chin-An
2005-05-01
Structural condition assessment of highway bridges has long been relying on visual inspection, which, however, involves subjective judgment of the inspector and detects only local flaws. Local flaws might not affect the global performance of the bridge. By instrumenting bridges with accelerometers and other sensors, one is able to monitor ambient or forced vibration of the bridge and assess its global structural condition. Ambient vibration measurement outwits forced vibration measurement in that it requires no special test arrangement, such as traffic control or a heavy shaker. As a result, it can be continuously executed while the bridge is under its normal serving condition. For short-to mid-span highway bridges, ambient vibration is predominantly due to traffic excitation, inducing the bridge to vibrate mainly in vertical direction. Based on its physical nature, traffic excitation is modeled as moving loads from the passing vehicles whose arrivals and speeds are extracted from digital video. Traffic-induced vibration provides valuable information for assessing the health of super-structure, but is less sensitive to possible seismic damage in the sub-structure. During earthquakes, bridges are excited in all directions by short-duration un-stationary ground motion, and are expected to better reveal their sub-structure integrity. Therefore, traffic-induced and ground-motion-induced ambient vibration data are treated separately in this paper for different assessment objectives, because of the different characteristics and measurability of the excitation. By continuously monitoring the ambient vibration of the instrumented bridge, its global structural conditions of both super- and sub-structures can be evaluated with possible damage locations identified, which will aid local non-destructive evaluation or visual inspection to further localize and access the damage.
A fractional-order controller for vibration suppression of uncertain structures.
Aghababa, Mohammad Pourmahmood
2013-11-01
The problem of active control of vibration structures has attracted much attention over the past decades. A general description of the control problem of vibration systems is to design an active controller to suppress the vibrations of the system induced by external disturbances such as an earthquake. In this paper, a novel fractional-order sliding mode control is introduced to attenuate the vibrations of structures with uncertainties and disturbances. After establishing a stable fractional sliding surface, a sliding mode control law is proposed. Then, the global asymptotic stability of the closed-loop system is analytically proved using fractional Lyapunov stability theorem. Finally, the robustness and applicability of the technique are verified using two examples, including a three degree of freedom structure and a two-story shear building. Copyright © 2013 ISA. Published by Elsevier Ltd. All rights reserved.
Influence of Structural Periodicity on Vibration Transmission in a Multi-Storey Wooden Building
DEFF Research Database (Denmark)
Andersen, Lars Vabbersgaard
2013-01-01
Noise is a nuisance to people, and buildings should therefore be designed to prevent propagation of sound and vibration in the audible frequency range as well as the range of frequencies relevant to whole-body vibrations of humans. In heavy structures made of concrete and masonry, a source...... with high energy content is required to mobilise the inertia. However, for lightweight building structures made of wood, less energy is required to produce vibrations since the mass is smaller. This leads to a high risk of sound and vibration propagation in terms of direct as well as flanking transmission...... is known to result in pass bands and stop bands regarding wave propagation. The paper focuses on analysing and quantifying the effects that a change in the structure, especially regarding the periodicity, has on the overall dynamic performance in the low to mid frequency range up to 250 Hz. The analysis...
Structural, vibrational, NMR, quantum chemical, DNA binding and ...
Indian Academy of Sciences (India)
Smith B C 1996 In Infrared Spectral Interpretation. (Boca Raton, FL: CRC Press). 31. Green J H S, Harrison D J and Kynaston W 1971. Spectrochim. Acta A 27 2199. 32. Varsanyi G 1974 In Assignments for Vibrational Spectra of Seven Hundred Benzene Derivatives. Vols. 1 and 2. (Budapest: Adam Hilger). 33. Lutz E T G ...
Effect of curvature on structures and vibrations of zigzag carbon ...
Indian Academy of Sciences (India)
Wintec
By determining the correlation between vibrational modes of a graphene sheet and ... graphene lattice. Thus, each SWCNT is uniquely labeled with a pair of integers (n, m) describing its chirality. (n, n) CNTs are called as 'armchair' nanotubes and (n, 0). CNTs are ... semiconductor transitions can be induced more readily in.
Coupled thermal, structural and vibrational analysis of a hypersonic engine for flight test
Energy Technology Data Exchange (ETDEWEB)
Sook-Ying, Ho [Defence Science and Technology Organisation, SA (Australia); Paull, A. [Queensland Univ., Dept. of Mechanical Engineering (Australia)
2006-07-15
This paper describes a relatively simple and quick method for implementing aerodynamic heating models into a finite element code for non-linear transient thermal-structural and thermal-structural-vibrational analyses of a Mach 10 generic HyShot scram-jet engine. The thermal-structural-vibrational response of the engine was studied for the descent trajectory from 60 to 26 km. Aerodynamic heating fluxes, as a function of spatial position and time for varying trajectory points, were implemented in the transient heat analysis. Additionally, the combined effect of varying dynamic pressure and thermal loads with altitude was considered. This aero-thermal-structural analysis capability was used to assess the temperature distribution, engine geometry distortion and yielding of the structural material due to aerodynamic heating during the descent trajectory, and for optimising the wall thickness, nose radius of leading edge, etc. of the engine intake. A structural vibration analysis was also performed following the aero-thermal-structural analysis to determine the changes in natural frequencies of the structural vibration modes that occur at the various temperatures associated with the descent trajectory. This analysis provides a unique and relatively simple design strategy for predicting and mitigating the thermal-structural-vibrational response of hypersonic engines. (authors)
Center Impedance Method for Damping Measurement
Directory of Open Access Journals (Sweden)
D. Malogi
2009-01-01
Full Text Available Damping materials are used extensively for reduction of vibration and noise. These damping materials have viscoelastic characteristics and are used by automotive and other industries. Testing of these materials is important in order to predict their performance and traditionally the damping properties are measured by the Oberst method. This paper discusses an alternate method called the Center Impedance method where force and response are measured directly and the damping properties are obtained. The Center Impedance method is easy to use requiring only standard vibration equipment for excitation, namely, shaker, and is easy to control the experiment for repeatability. Results of beams tested by both Oberst and Center Impedance methods are presented in order to validate this test method.
Hofmann, A
2006-01-01
Abstract Landau damping is the suppression of an instability by a spread of frequencies in the beam. It is treated here from an experimental point of view. To introduce the concept we consider a set of oscillators having a spread in resonant frequencies !r and calculate the response of their there center-of-mass to an external driving force. A pulse excitation gives each oscillator the same initial velocity but, due to their different frequencies, the center-of-mass motion will decay with time. A harmonic excitation with a frequency ! being inside the distribution in !r results in oscillators responding with different phases and only a few of them having !r ! will grow to large amplitudes and absorb energy. The oscillator response to a pulse excitation, called Green function, and the one to a harmonic excitation, called transfer function, serve as a basis to calculate Landau damping which suppresses an instability at infinitesimal level before any large amplitudes are reached. This is illustrated by a negativ...
Optimization procedure to control the coupling of vibration modes in flexible space structures
Walsh, Joanne L.
1987-01-01
As spacecraft structural concepts increase in size and flexibility, the vibration frequencies become more closely-spaced. The identification and control of such closely-spaced frequencies present a significant challenge. To validate system identification and control methods prior to actual flight, simpler space structures will be flown. To challenge the above technologies, it will be necessary to design these structures with closely-spaced or coupled vibration modes. Thus, there exists a need to develop a systematic method to design a structure which has closely-spaced vibration frequencies. This paper describes an optimization procedure which is used to design a large flexible structure to have closely-spaced vibration frequencies. The procedure uses a general-purpose finite element analysis program for the vibration and sensitivity analyses and a general-purpose optimization program. Results are presented from two studies. The first study uses a detailed model of a large flexible structure to design a structure with one pair of closely-spaced frequencies. The second study uses a simple equivalent beam model of a large flexible structure to obtain a design with two pairs of closely-spaced frequencies.
Wang, Jie; Paszti, Zoltan; Clarke, Matthew L; Chen, Xiaoyun; Chen, Zhan
2007-05-31
We demonstrate both theoretically and experimentally that the combination of vibrational spectroscopic techniques on samples can be used to deduce more detailed structural information of interfacial proteins and peptides. Such an approach can be used to elucidate structures of proteins or peptides at interfaces, such as at the solid/liquid interface or in cell membranes. We also discuss that the controlled perturbations may provide more measured parameters for structural studies on such proteins and peptides. In this paper, we will demonstrate that optical spectroscopic techniques such as polarized Fourier transform infrared spectroscopy (FTIR), sum frequency generation (SFG) vibrational spectroscopy, and higher order nonlinear vibrational spectroscopies can be used to deduce different and complementary structural information of molecules at interfaces (e.g., orientation information of certain functional groups and secondary structures of interfacial proteins). Also, we believe that controlled perturbations on samples, such as variation of sample temperature, application of electrical fields, and alternation of substrate roughness, can provide more detailed information regarding the interfacial structures of proteins and peptides. The development of nonlinear vibrational spectroscopies, such as SFG and four-wave mixing vibrational spectroscopy, to examine interfacial protein and peptide structures, and introduction of external perturbations on samples should be able to substantially advance our knowledge in understanding structures and thus functions of proteins and peptides at interfaces.
Steinchen, Wolfgang; Gan, Ymin; Kupfer, Gerhard; Maeckel, Peter
2003-05-01
University of Kassel and isi-sys have extended the application of shearography to quantitative vibration analysis and developed a portable automatic controlled shearography system. The Vibrograph is already used for vibration measurements in industry for example of electronic boards typically in combination with laboratory shakers in harmonic excitation modes. Now a small portable piezo shaker permits local excitation of the defects such as delaminations and disbonds. Vibrating in their natural mode shapes the Vibrograph detects the location of the defects within the fiber structure.
Simulation of Heat Generating In a Vibrating Structure Using COMSOL Multiphysics
Directory of Open Access Journals (Sweden)
Ali Kamil Jebur
2016-03-01
Full Text Available This paper dealt with heat generating in a beam structure model subjected to small vibrations to know the viscos elastic behavior under heat and vibration. The model first computed coupled thermal – structural interaction. The results obtained from this analysis of the model treated by the finite element method to calculate amount of heat generation in the material. A transient heat transfer analysis then simulated the slow rising temperature in the beam using these heat source terms. The model has been constructed from two blocks, the first block from Aluminum while the second block made from β –Titanium. The model was constrained from one side, while the other side free, so vibrations that occur along the model. These vibrations led to heat generating, so yields that residual stresses through the model. The result obtained represented in curves which give good agreement with international published researches
Belle, Lucas Van; Claeys, Claus; Deckers, Elke; Desmet, Wim
2017-11-01
Recently, locally resonant metamaterials have come to the fore in noise and vibration control engineering, showing great potential due to their superior noise and vibration attenuation performance in targeted and tunable frequency ranges, referred to as stop bands. Damping has an important influence on the performance of these materials, broadening the frequency range of attenuation at the expense of peak attenuation. As a result, understanding and including the effects of damping is necessary to more accurately predict the attenuation performance of these locally resonant metamaterials. Classically, these often periodic structures are analysed using a unit cell modelling approach to predict wave propagation and thus stop band behaviour, discarding damping. In this work, a unit cell method including damping is used to analyse the complex dispersion curves of a locally resonant metamaterial design. The wave solutions in and around the stop band frequency range are compared to those of the unit cell method discarding damping. The influence on the dispersion curves of damping in resonator and host structure is discussed and the obtained dispersion curves are validated through an experimental dispersion curve measurement based on an Extended Inhomogeneous Wave Correlation method using Scanning Laser Doppler Vibrometry for a metamaterial plate manufactured at a representative scale. Excellent agreement is obtained between the numerically predicted and experimentally retrieved dispersion curves.
Vibration test on KMRR reactor structure and primary cooling system piping
Energy Technology Data Exchange (ETDEWEB)
Chung, Seung Hoh; Kim, Tae Ryong; Park, Jin Hoh; Park, Jin Suk; Ryoo, Jung Soo [Korea Atomic Energy Research Institute, Taejon (Korea, Republic of)
1994-10-01
Most equipments, piping systems and reactor structures in nuclear power plants are subjected to flow induced vibration due to high temperature and high pressure coolant flowing inside or outside of the equipments, systems and structures. Because the flow induced vibration sometimes causes significant damage to reactor structures and piping systems, it is important and necessary to evaluate the vibration effect on them and to prove their structural integrity. Korea Multipurpose Research Reactor (KMRR) being constructed by KAERI is 30 MWt pool type research reactor. Since its main structures and piping systems were designed and manufactured in accordance with the standards and guidelines for commercial nuclear power plant, it was decided to evaluate their vibratory response in accordance with the standards and guidelines for commercial NPP. The objective of this vibration test is the assessment of vibration levels of KMRR reactor structure and primary cooling piping system for their structural integrity under the steady-state or transient operating condition. 38 figs, 14 tabs, 2 refs. (Author).
Loendersloot, Richard; Ooijevaar, T.H.; Warnet, Laurent; Akkerman, Remko; de Boer, Andries; Meguid, S.A.; Gomes, J.F.S.
2009-01-01
The feasibility of a vibration based damage identification method is investigated. The Modal Strain Energy method is applied to a T–beam structure. The dynamic response of an intact structure and a damaged, delaminated structure is analysed employing a commercially available Finite Element package.
Optimal design of damping layers in SMA/GFRP laminated hybrid composites
Haghdoust, P.; Cinquemani, S.; Lo Conte, A.; Lecis, N.
2017-10-01
This work describes the optimization of the shape profiles for shape memory alloys (SMA) sheets in hybrid layered composite structures, i.e. slender beams or thinner plates, designed for the passive attenuation of flexural vibrations. The paper starts with the description of the material and architecture of the investigated hybrid layered composite. An analytical method, for evaluating the energy dissipation inside a vibrating cantilever beam is developed. The analytical solution is then followed by a shape profile optimization of the inserts, using a genetic algorithm to minimize the SMA material layer usage, while maintaining target level of structural damping. Delamination problem at SMA/glass fiber reinforced polymer interface is discussed. At the end, the proposed methodology has been applied to study the hybridization of a wind turbine layered structure blade with SMA material, in order to increase its passive damping.
Vibrations in a Multi-Storey Lightweight Building Structure
DEFF Research Database (Denmark)
Andersen, Lars Vabbersgaard; Kirkegaard, Poul Henning
2013-01-01
This paper provides a quantification of the changes in vibration level that can be expected in a lightweight multi-storey wooden building due to reduced connection stiffness or added nonstructural mass. Firstly, the impact of changes in the floor-to-wall connections is examined. Secondly, a study...... is performed regarding variations of the vibration level due to different placements of nonstructural mass inside the building. The analyses are carried out by means of a modular three-dimensional finite-element model. Each floor and wall panel is modelled in high detail, including door and window openings....... By a substructure approach, the panels are assembled to construct a global building model that allows analysis within a reasonable computation time....
Surface vibrational and structural properties of polymers by HREELS
Pireaux, J. J.; Gregoire, C.; Vermeersch, M.; Thiry, P. A.; Caudano, R.
1987-10-01
The extremely promising applications of electron induced vibrational spectroscopy to study the surfaces of polymers and other organic materials are reviewed. It is demonstrated that this technique, which is known as HREELS: high-resolution electron-energy loss spectroscopy, is selectively surface sensitive: information on both the composition and morphology of the polymer surfaces is obtained. However, a quantitative interpretation of the data is not straightforward, as the exact interaction mechanism(s) between the probing electron and the molecular vibrations are not yet ascertained. One of the many illustrations given is the study of the incipient interface formation between a clean cured polyimide film and deposited aluminum which will demonstrate the specific completeness and capabilities of HREELS.
DEFF Research Database (Denmark)
Pedersen, Lars
Passive humans (sitting or standing) might well be present on flooring-systems, footbridges or other structures that carry humans. An active croud of people might generate structural vibrations, and these might be problematic. The passive crowd of people, however, will interact with the structural...
Sohn, Jung Woo; Jeon, Juncheol; Choi, Seung-Bok
2014-10-01
Vibration control performance of the ring-stiffened cylindrical shell structure is experimentally evaluated in this work. In order to achieve high control performance, advanced flexible piezoelectric actuator whose commercial name is Macro-Fiber Composite (MFC) is adapted to the shell structure. Governing equation is derived by finite element method and dynamic characteristics are investigated from the modal analysis results. Ring-stiffened cylindrical shell structure is then manufactured and modal test is conducted to verify modal analysis results. An optimal controller is designed and experimentally realized to the proposed shell structure system. Vibration control performance is experimentally evaluated in time domain and verified by simulated control results.
Hédoux, Alain; Guinet, Yannick; Carpentier, Laurent; Paccou, Laurent; Derollez, Patrick; Brandán, Silvia Antonia
2017-06-01
In this work, three monomeric forms of arabinitol, usually named arabitol, and their dimeric species have been structural and vibrationally studied by using the micro-Raman spectra in the solid phase accomplished with theoretical calculations based on the theory of the functional of the density (DFT). The hybrid B3LYP method was used for all the calculations together with the 6-31G* and 6-311++g** basis sets. Two different L structures with minima energies were predicted in accordance to the two polymorphic structures revealed by recent X-ray diffraction experiments. The studies by natural bond orbital (NBO) calculations reveals high stabilities of the L form as compared with the D one but the topological properties by using the atoms in molecules (AIM) suggest a higher stability of the D form due to a strong H bond interactions. The scaled mechanical force fields (SQMFF) procedure was used to perform the complete vibrational assignments for the monomeric forms and their dimer. On the other hand, the similarity in the gap values computed for the three forms of arabitol with those observed for sucrose, trehalose, maltose and lactose in gas phase at the same level of theory could partially explain the sweetening property of this alcohol. In addition, the influences of the size of the basis set on some properties were evidenced.
Fuzzy Semiactive Vibration Control of Structures Using Magnetorheological Elastomer
Directory of Open Access Journals (Sweden)
Xuan Bao Nguyen
2017-01-01
Full Text Available In this research, a novel variable stiffness vibration isolator that uses magnetorheological elastomers (MREs accompanied with a fuzzy semiactive vibration control was developed. Firstly, the viscoelastic characteristics of MREs in shear mode were clarified systematically in order to achieve a mathematical basis for the controller development. Secondly, the fuzzy semiactive vibration control with a strategy based on the Lyapunov theory and dynamic characteristic of MREs was proposed for minimizing the movement of the isolator. In the conventional semiactive algorithm, the command applied current of MRE-based isolator is set at either minimum or maximum value which causes high acceleration and jerk peaks periodically, thus leading to the degeneration of the overall system quality. However, the fuzzy semiactive algorithm presented here is able to produce the sufficient applied current and thus viscoelastic force is desirably produced. The effectiveness of the developed isolator was evaluated numerically by MATLAB simulation and experimentally in comparison with the performances of a passive system and a system with on-off type semiactive controller. The results showed that the developed controller was successful in overcoming the disadvantages of conventional on-off semiactive control.
Dry, Carolyn M.
1996-04-01
Preventing buildings and bridges from damage from severe dynamic loading events is a primary goal of civil infrastructure. Present designs attempt to control structural response by making the structures more massive, by increasing lateral stiffness through bracing, and by damping technology such as mass damping and base-isolation. These attempts affect portions of the governing equation: for an idealized building frame or bridge, the free vibrational behavior is described by Mu + cu + ku equals -mug(t) where m equals mass, c equals damping coefficient, k equals lateral stiffness, u equals deflection, and ug(t) equals ground acceleration. The use of adhesive released internally in a material based way of addressing the problem. The time release of low modulus adhesive chemicals would assist the damping characteristics of the structure, use of a stiffer adhesive would allow the damaged structure to regain some lateral stiffness (k) and adjustment of the set times of the adhesives would act to control the deflection. These can be thought of as potential new method of controlling vibration of behavior in case of a dynamic loading event. In past experiments, self-healing concrete matrices were shown to increase post-yield deflection and load carrying capability by the release and setting of adhesives. The results were promising in resisting damage of dynamic loads applied to frames. This indicates that self-healing concrete would be extremely valuable in civil engineering structures that were subjected to failure-inducing loads such as earthquakes.
Zhang, Yulong; Wang, Tianyang; Zhang, Ai; Peng, Zhuoteng; Luo, Dan; Chen, Rui; Wang, Fei
2016-12-01
In this paper, we present design and test of a broadband electrostatic energy harvester with a dual resonant structure, which consists of two cantilever-mass subsystems each with a mass attached at the free edge of a cantilever. Comparing to traditional devices with single resonant frequency, the proposed device with dual resonant structure can resonate at two frequencies. Furthermore, when one of the cantilever-masses is oscillating at resonance, the vibration amplitude is large enough to make it collide with the other mass, which provides strong mechanical coupling between the two subsystems. Therefore, this device can harvest a decent power output from vibration sources at a broad frequency range. During the measurement, continuous power output up to 6.2-9.8 μW can be achieved under external vibration amplitude of 9.3 m/s2 at a frequency range from 36.3 Hz to 48.3 Hz, which means the bandwidth of the device is about 30% of the central frequency. The broad bandwidth of the device provides a promising application for energy harvesting from the scenarios with random vibration sources. The experimental results indicate that with the dual resonant structure, the vibration-to-electricity energy conversion efficiency can be improved by 97% when an external random vibration with a low frequency filter is applied.
National Research Council Canada - National Science Library
M. Podworna; M. Klasztorny
2014-01-01
...) bridge/track structure/high-speed train system (BTT), developed in Part 2, advanced computer algorithms for the BTT numerical modelling and simulation as well as a computer programme to simulate vertical vibrations of BTT systems are developed...
DEFF Research Database (Denmark)
Park, Kidong; Shim, Jeong; Solovyeva, Vita
2012-01-01
We examined the hydrodynamic loading of vertically resonating microfabricated plates immersed in liquids with different viscosities. The planar structures were patterned with focused ion beam, perforating various shapes with identical area but varying perimeters. The hydrodynamic loading of vario...
Seismic damage diagnosis of a masonry building using short-term damping measurements
Kouris, Leonidas Alexandros S.; Penna, Andrea; Magenes, Guido
2017-04-01
It is of considerable importance to perform dynamic identification and detect damage in existing structures. This paper describes a new and practical method for damage diagnosis of masonry buildings requiring minimum computational effort. The method is based on the relative variation of modal damping and validated against experimental data from a full scale two storey shake table test. The experiment involves a building subjected to uniaxial vibrations of progressively increasing intensity at the facilities of EUCENTRE laboratory (Pavia, Italy) up to a near collapse damage state. Five time-histories are applied scaling the Montenegro (1979) accelerogram. These strong motion tests are preceded by random vibration tests (RVT's) which are used to perform modal analysis. Two deterministic methods are applied: the single degree of freedom (SDOF) assumption together with the peak-picking method in the discrete frequency domain and the Eigen realisation algorithm with data correlations (ERA-DC) in the discrete time domain. Regarding the former procedure, some improvements are incorporated to locate rigorously the natural frequencies and estimate the modal damping. The progressive evolution of the modal damping is used as a key indicator to characterise damage on the building. Modal damping is connected to the structural mass and stiffness. A square integrated but only with two components expression for proportional (classical) damping is proposed to fit better with the experimental measurements of modal damping ratios. Using this Rayleigh order formulation the contribution of each of the damping components is evaluated. The stiffness component coefficient is proposed as an effective index to detect damage and quantify its intensity.
DEFF Research Database (Denmark)
Ohlrich, Mogens; Henriksen, Eigil; Laugesen, Søren
1997-01-01
errors can be largely compensated for by an absolute calibration of the transducers and inverse filtering that results in very small residual errors. Experimental results of this study indicate that these uncertainties will be in the order of one percent with respect to amplitude and two tenth......Uncertainties in power measurements performed with piezoelectric accelerometers and force transducers are investigated. It is shown that the inherent structural damping of the transducers is responsible for a bias phase error, which typically is in the order of one degree. Fortunately, such bias...... of a degree for the phase. This implies that input power at a single point can be measured to within one dB in practical structures which possesses some damping. The uncertainty is increased, however, when sums of measured power contributions from more sources are to be minimised, as is the case in active...
Dual resonant structure for energy harvesting from random vibration sources at low frequency
Directory of Open Access Journals (Sweden)
Shanshan Li
2016-01-01
Full Text Available We introduce a design with dual resonant structure which can harvest energy from random vibration sources at low frequency range. The dual resonant structure consists of two spring-mass subsystems with different frequency responses, which exhibit strong coupling and broad bandwidth when the two masses collide with each other. Experiments with piezoelectric elements show that the energy harvesting device with dual resonant structure can generate higher power output than the sum of the two separate devices from random vibration sources.
Component mode synthesis and large deflection vibrations of complex structures. [beams and trusses
Mei, C.
1984-01-01
The accuracy of the NASTRAN modal synthesis analysis was assessed by comparing it with full structure NASTRAN and nine other modal synthesis results using a nine-bay truss. A NASTRAN component mode transient response analysis was also performed on the free-free truss structure. A finite element method was developed for nonlinear vibration of beam structures subjected to harmonic excitation. Longitudinal deformation and inertia are both included in the formula. Tables show the finite element free vibration results with and without considering the effects of longitudinal deformation and inertia as well as the frequency ratios for a simply supported and a clamped beam subjected to a uniform harmonic force.
Optical Measurement of Cable and String Vibration
Directory of Open Access Journals (Sweden)
Y. Achkire
1998-01-01
Full Text Available This paper describes a non contacting measurement technique for the transverse vibration of small cables and strings using an analog position sensing detector. On the one hand, the sensor is used to monitor the cable vibrations of a small scale mock-up of a cable structure in order to validate the nonlinear cable dynamics model. On the other hand, the optical sensor is used to evaluate the performance of an active tendon control algorithm with guaranteed stability properties. It is demonstrated experimentally, that a force feedback control law based on a collocated force sensor measuring the tension in the cable is feasible and provides active damping in the cable.
DEFF Research Database (Denmark)
Pawlowski, F; Jorgensen, P; Olsen, Jeppe
2002-01-01
A detailed study is carried out of the accuracy of molecular equilibrium geometries obtained from least-squares fits involving experimental rotational constants B(0) and sums of ab initio vibration-rotation interaction constants alpha(r)(B). The vibration-rotation interaction constants have been...... calculated for 18 single-configuration dominated molecules containing hydrogen and first-row atoms at various standard levels of ab initio theory. Comparisons with the experimental data and tests for the internal consistency of the calculations show that the equilibrium structures generated using Hartree......-Fock vibration-rotation interaction constants have an accuracy similar to that obtained by a direct minimization of the CCSD(T) energy. The most accurate vibration-rotation interaction constants are those calculated at the CCSD(T)/cc-pVQZ level. The equilibrium bond distances determined from these interaction...
Reducing vibration transfer from power plants by active methods
Kiryukhin, A. V.; Milman, O. O.; Ptakhin, A. V.
2017-12-01
The possibility of applying the methods of active damping of vibration and pressure pulsations for reducing their transfer from power plants into the environment, the seating, and the industrial premises are considered. The results of experimental works implemented by the authors on the active broadband damping of vibration and dynamic forces after shock-absorption up to 15 dB in the frequency band up to 150 Hz, of water pressure pulsations in the pipeline up to 20 dB in the frequency band up to 600 Hz, and of spatial low-frequency air noise indoors of a diesel generator at discrete frequency up to 20 dB are presented. It is shown that a reduction of vibration transfer through a vibration-isolating junction (expansion joints) of pipelines with liquid is the most complicated and has hardly been developed so far. This problem is essential for vibration isolation of power equipment from the seating and the environment through pipelines with water and steam in the power and transport engineering, shipbuilding, and in oil and gas pipelines in pumping stations. For improving efficiency, reducing the energy consumption, and decreasing the overall dimensions of equipment, it is advisable to combine the work of an active system with passive damping means, the use of which is not always sufficient. The executive component of the systems of active damping should be placed behind the vibration isolators (expansion joints). It is shown that the existence of working medium and connection of vibration with pressure pulsations in existing designs of pipeline expansion joints lead to growth of vibration stiffness of the expansion joint with the environment by two and more orders as compared with the static stiffness and makes difficulties for using the active methods. For active damping of vibration transfer through expansion joints of pipelines with a liquid, it is necessary to develop expansion joint structures with minimal connection of vibrations and pulsations and minimal
Directory of Open Access Journals (Sweden)
M. Prakash
1999-01-01
Full Text Available The present work examines the effects arising from the nonlinear Landau damping and the bounced motion of protons (trapped in the mirror geometry of the geomagnetic field in the formation of nonlinear Alfvénic structures. These structures are observed at distances 1-5AU in the solar wind plasma (with ß ~ 1. The dynamics of formation of these structures can be understood using kinetic nonlinear Schrodinger (KNLS model. The structures emerge due to balance of nonlinear steepening (of large amplitude Alfvén waves by the linear Landau damping of ion-acoustic modes in a finite ß solar wind plasma. The ion-acoustic mode is driven nonlinearly by the large amplitude Alfvén waves. At the large amplitudes of Alfvén wave, the effects due to nonlinear Landau damping become important. These nonlinear effects are incorporated into the KNLS model by modifying the heat flux dissipation coefficient parallel to the ambient magnetic field. The effects arising from the bounced motion (of mirroring protons are studied using a one-dimensional Vlasov equation. The bounced motion of the protons can lead to growth of the ion-acoustic mode, propagating in the mirror geometry of the geomagnetic field. The significance of these studies in the formation of dissipative quasistationary structures observed in solar wind plasma is discussed.
Transverse Resonant Vibration of Non-Bearing Structures Caused by Wind
Jendzelovsky, Norbert; Antal, Roland
2017-10-01
Nowadays, there are increasing use of very thin, subtle and light structures in the field of building constructions. We can find such a structures as part of roofs or design facades. By using these lamellas like, non-bearing structures as a part of architectural design of buildings, it is necessary to consider wind effects on these structures. Subtle structures of this type are prone to vibration in the transverse direction of the wind flow. The fact that the vibration occurs depends on wind parameters (wind velocity, direction of an air flow) and it also depends on the properties of lamella (shape, length, mass, natural frequency, support type). The principal idea of this article is to show susceptibility of lamellae-like structures to transverse resonant vibration caused by the phenomenon called Von Karman effect. Comparison of susceptibility to transverse resonance vibration was analysed on the different shapes of lamellas loaded by different wind speed. Analysis was based on usage of empirically derived equations. Von Karman effect arise from wind flow past an object. Turbulence in the form of vortices are formed at the object and shed into the flowing stream intermittently. The potential problem is that this turbulence can induce vibrations into the lamella itself. In terms of this vibration problem, two frequencies are interesting. Von Karman shedding frequency is the frequency at which the vortices are formed and shed at the object. The vortex-shedding frequency increases with the velocity of the wind flow and decreases with the size of the object. Natural frequency of the object depends on the construction of the lamella itself. Parameters of lamella as a shape, mass, length, elasticity modulus of material and support types are directly involved in the calculation of natural frequency. Worst case scenario in the term of transverse resonant vibration occurs when the natural frequency of lamella is equal to the vortex-shedding frequency. In this case
Zhang, Z.; Piatkowski, L.; Bakker, H.J.; Bonn, M.
2011-01-01
Knowledge of the interfacial water structure is essential for a basic understanding of the many environmental, technological, and biophysical systems in which aqueous interfaces appear. Using ultrafast two-dimensional surface-specific vibrational spectroscopy we show that the structure of heavy
Phononic band gaps and vibrations in one- and two-dimensional mass-spring structures
DEFF Research Database (Denmark)
Jensen, Jakob Søndergaard
2003-01-01
The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous dampin...
Brian K. Brashaw; Robert Vatalaro; Xiping Wang; Kevin Sarvela; James P. Wacker
2008-01-01
Approximately 4,000 vehicle bridges in the State of Minnesota contain structural timber members. Recent research at the University of Minnesota Duluth Natural Resources Research Institute (UMD NRRI) has been conducted on vibration testing of timber bridges as a means of developing rapid in-place testing techniques for assessing the structural health of bridges. The...
Structural dynamics in complex liquids studied with multidimensional vibrational spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Tokmakoff, Andrei [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2013-08-31
The development of new sustainable energy sources is linked to our understanding of the molecular properties of water and aqueous solutions. Energy conversion, storage, and transduction processes, particularly those that occur in biology, fuel cells, and batteries, make use of water for the purpose of moving energy in the form of charges and mediating the redox chemistry that allows this energy to be stored as and released from chemical bonds. To build our fundamental knowledge in this area, this project supports work in the Tokmakoff group to investigate the molecular dynamics of water’s hydrogen bond network, and how these dynamics influence its solutes and the mechanism of proton transport in water. To reach the goals of this grant, we developed experiments to observe molecular dynamics in water as directly as possible, using ultrafast multidimensional vibrational spectroscopy. We excite and probe broad vibrational resonances of water, molecular solutes, and protons in water. By correlating how molecules evolve from an initial excitation frequency to a final frequency, we can describe the underlying molecular dynamics. Theoretical modeling of the data with the help of computational spectroscopy coupled with molecular dynamics simulations provided the atomistic insight in these studies.
DFT study of the molecular and crystal structure and vibrational analysis of cisplatin
Georgieva, I.; Trendafilova, N.; Dodoff, N.; Kovacheva, D.
2017-04-01
DFT and periodic-DFT (PAW-PBE method, code VASP) calculations have been performed to study the structural and vibrational characteristics of cis-diamminedichloroplatinum(II) (cisplatin) at molecular and outside molecular level. To estimate the effect of the intermolecular interactions in crystal on the structural and vibrational properties of cisplatin, three theoretical models are considered in the present study: monomer (isolated molecule), hydrogen bonded dimer and periodic solid state structures. The work focused on the role of the theoretical models for correct modeling and prediction of geometrical and vibrational parameters of cisplatin. It has been found that the elaborate three-dimensional intermolecular hydrogen bonding network in the crystalline cisplatin significantly influences the structural and vibrational pattern of cisplatin and therefore the isolated cisplatin molecule is not the correct computational model regardless of the theoretical level used. To account for the whole intermolecular hydrogen bonding network in direction of both a and c axis and for more reliable calculations of structural and vibrational parameters periodic DFT calculations were carried out in the full crystalline periodic environment with the known lattice parameters for each cisplatin polymorph phase. The model calculations performed both at molecular level and for the periodic structures of alpha and beta cisplatin polymorph forms revealed the decisive role of the extended theoretical model for reliable prediction of the structural and vibrational characteristics of cisplatin. The powder diffraction pattern and the calculated IR and Raman spectra predicted beta polymorph form of our cisplatin sample freshly synthesized for the purposes of the present study using the Dhara's method. The various rotamers realized in the polymorph forms of cisplatin were explained by the low population of the large number of rotamers in solution as well as with the high rotamer
DEFF Research Database (Denmark)
Pedersen, Lars
Passive humans (sitting or standing) might well be present on flooring-systems, footbridges or other structures that carry humans. An active croud of people might generate structural vibrations, and these might be problematic. The passive crowd of people, however, will interact with the structura...
A unified solution for vibration analysis of plates with general structural stress distributions
Directory of Open Access Journals (Sweden)
Nian Yang
2016-11-01
Full Text Available Complex stress distributions often exist in ocean engineering structures. This stress influences structural vibrations. Finite Element Methods exhibit some shortcomings for solving non-uniform stress problems, such as an unclear physical interpretation, complicated operation, and large number of computations. Analytical methods research considers mainly uniform stress problems, and often, their methods cannot be applied in practical marine structures with non-uniform stress. In this paper, an analytical method is proposed to solve the vibration of plates with general stress distributions. Non-uniform stress is expressed as a special series, and the stress influence is inserted into a vibration equation that is solved through decoupling to obtain an analytical solution. This method has been verified using numerical examples and can be used in arbitrary stress distribution cases. This method requires fewer computations and it provides a clearer physical interpretation, so it has advantages in some qualitative research.
Human-in-the-loop evaluation of RMS Active Damping Augmentation
Demeo, Martha E.; Gilbert, Michael G.; Scott, Michael A.; Lepanto, Janet A.; Bains, Elizabeth M.; Jensen, Mary C.
1993-01-01
Active Damping Augmentation is the insertion of Controls-Structures Integration Technology to benefit the on-orbit performance of the Space Shuttle Remote Manipulator System. The goal is to reduce the vibration decay time of the Remote Manipulator System following normal payload maneuvers and operations. Simulation of Active Damping Augmentation was conducted in the realtime human-in-the-loop Systems Engineering Simulator at the NASA Johnson Space Center. The objective of this study was to obtain a qualitative measure of operational performance improvement from astronaut operators and to obtain supporting quantitative performance data. Sensing of vibratory motions was simulated using a three-axis accelerometer mounted at the end of the lower boom of the Remote Manipulator System. The sensed motions were used in a feedback control law to generate commands to the joint servo mechanisms which reduced the unwanted oscillations. Active damping of the Remote Manipulator System with an attached 3990 lb. payload was successfully demonstrated. Six astronaut operators examined the performance of an Active Damping Augmentation control law following single-joint and coordinated six-joint translational and rotational maneuvers. Active Damping Augmentation disturbance rejection of Orbiter thruster firings was also evaluated. Significant reductions in the dynamic response of the 3990 lb. payload were observed. Astronaut operators recommended investigation of Active Damping Augmentation benefits to heavier payloads where oscillations are a bigger problem (e.g. Space Station Freedom assembly operators).
Directory of Open Access Journals (Sweden)
Daniel A. Castello
2005-01-01
Full Text Available The present work is aimed at assessing the performance of adaptive Finite Impulse Response (FIR filters on the identification of vibrating structures. Four adaptive algorithms were used: Least Mean Squares (LMS, Normalized Least Mean Squares (NLMS, Transform-Domain Least Mean Squares (TD – LMS and Set-Membership Binormalized Data-Reusing LMS Algorithm (SM – BNDRLMS. The capability of these filters to perform the identification of vibrating structures is shown on real experiments. The first experiment consists of an aluminum cantilever beam containing piezoelectric sensors and actuators and the second one is a steel pinned-pinned beam instrumented with accelerometers and an electromechanical shaker.
Adhikary, Ramkrishna; Zimmermann, Jörg; Romesberg, Floyd E
2017-02-08
Vibrational spectroscopy provides a direct route to the physicochemical characterization of molecules. While both IR and Raman spectroscopy have been used for decades to provide detailed characterizations of small molecules, similar studies with proteins are largely precluded due to spectral congestion. However, the vibrational spectra of proteins do include a "transparent window", between ∼1800 and ∼2500 cm-1, and progress is now being made to develop site-specifically incorporated carbon-deuterium (C-D), cyano (CN), thiocyanate (SCN), and azide (N3) "transparent window vibrational probes" that absorb within this window and report on their environment to facilitate the characterization of proteins with small molecule-like detail. This Review opens with a brief discussion of the advantages and limitations of conventional vibrational spectroscopy and then discusses the strengths and weaknesses of the different transparent window vibrational probes, methods by which they may be site-specifically incorporated into peptides and proteins, and the physicochemical properties they may be used to study, including electrostatics, stability and folding, hydrogen bonding, protonation, solvation, dynamics, and interactions with inhibitors. The use of the probes to vibrationally image proteins and other biomolecules within cells is also discussed. We then present four case studies, focused on ketosteroid isomerase, the SH3 domain, dihydrofolate reductase, and cytochrome c, where the transparent window vibrational probes have already been used to elucidate important aspects of protein structure and function. The Review concludes by highlighting the current challenges and future potential of using transparent window vibrational probes to understand the evolution and function of proteins and other biomolecules.
Active Vibration Control of a Monopile Offshore Structure
DEFF Research Database (Denmark)
Nielsen, Søren R. K.; Kirkegaard, Poul Henning; Thesbjerg, L.
1996-01-01
coefficient should be obtained in order to have a relatively small excitation on the cylinder. The drag coefficient can be controlled if the separation points of the boundary layers can be controlled. It is proposed to control the separation points by blowing compressed air out of the holes in the cylinder....... If the natura1 separation points of the boundary layers are rejected by blowing air out of the holes the drag coefficient will increase while it will decrease if it is possible to attach the boundary layer. The results from the experimental test have shown that it is possible to increase the drag coefficient...... with a factor 1.5-2 by blowing air out of the holes in a cylinder vibrating in a stationary water flow....
Strength and Dislocation Structure Evolution of Small Metals under Vibrations
Ngan, Alfonso
2015-03-01
It is well-known that ultrasonic vibration can soften metals, and this phenomenon has been widely exploited in industrial applications concerning metal forming and bonding. In this work, we explore the effects of a superimposed small oscillatory load on metal plasticity, from the nano- to macro-size range, and from audible to ultrasonic frequency ranges. Macroscopic and nano-indentation were performed on aluminum, copper and molybdenum, and the results show that the simultaneous application of oscillatory stresses can lower the hardness of these samples. More interestingly, EBSD and TEM observations show that subgrain formation and reduction in dislocation density generally occurred when stress oscillations were applied. These findings point to an important knowledge gap in metal plasticity - the existing understanding of ultrasound softening in terms of the vibrations either imposing additional stress waves to augment the quasi-static applied load, or heating up the metal, whereas the metal's intrinsic deformation resistance or dislocation interactive processes are assumed unaltered by the ultrasound, is proven wrong by the present results. Furthermore, in the case of nanoindentation, the Continuous Stiffness Measurement technique for contact stiffness measurement assumes that the imposed signal-carrier oscillations do not intrinsically alter the material properties of the specimen, and again, the present results prove that this can be wrong. To understand the enhanced subgrain formation and dislocation annihilation, Discrete Dislocation Dynamics (DDD) simulations were carried out and these show that when an oscillatory stress is superimposed on a quasi-static applied stress, reversals of motion of dislocations may occur, and these allow the dislocations to revisit repeatedly suitable configurations for annihilation. DDD, however, was unable to predict the observed subgrain formation presumably because the number of dislocations that can be handled is not large
Vibration analysis of hydropower house based on fluid-structure coupling numerical method
Directory of Open Access Journals (Sweden)
Shu-he Wei
2010-03-01
Full Text Available By using the shear stress transport (SST model to predict the effect of random flow motion in a fluid zone, and using the Newmark method to solve the oscillation equations in a solid zone, a coupling model of the powerhouse and its tube water was developed. The effects of fluid-structure interaction are considered through the kinematic and dynamic conditions applied to the fluid-structure interfaces (FSI. Numerical simulation of turbulent flow through the whole flow passage of the powerhouse and concrete structure vibration analysis in the time domain were carried out with the model. Considering the effect of coupling the turbulence and the powerhouse structure, the time history response of both turbulent flows through the whole flow passage and powerhouse structure vibration were generated. Concrete structure vibration analysis shows that the displacement, velocity, and acceleration of the dynamo floor respond dramatically to pressure fluctuations in the flow passage. Furthermore, the spectrum analysis suggests that pressure fluctuation originating from the static and dynamic disturbances of hydraulic turbine blades in the flow passage is one of the most important vibration sources.
The Study of Damped Harmonic Oscillations Using an Electronic Counter
Wadhwa, Ajay
2009-01-01
We study damped harmonic oscillations in mechanical systems like the loaded spring and simple pendulum with the help of an oscillation measuring electronic counter. The experimental data are used in a software program that solves the differential equation for damped vibrations of any system and determines its position, velocity and acceleration as…
Cartmell, Matthew P.
2016-09-01
The Editor wishes to make the reader aware that the paper "A new method for predicting nonlinear structural vibrations induced by ground impact loading" by Jun Liu, Yu Zhang, Bin Yun, Journal of Sound and Vibration, 331 (2012) 2129-2140, did not contain a direct citation of the fundamental and original work in this field by Dr. Mark Svinkin. The Editor regrets that this omission was not noted at the time that the above paper was accepted and published.
The structure of filled skutterudites and the local vibration behavior of the filling atom
Zhou, Xiaojuan; Zong, Peng-an; Chen, Xihong; Tao, Juzhou; Lin, He
2017-02-01
Both of atomic pair distribution function (PDF) and extended x-ray absorption fine structure (EXAFS) experiments have been carried out on unfilled and Yb-filled skutterudites YbxCo4Sb12 (x=0, 0.15, 0.2 and 0.25) samples. The structure refinements on PDF data confirm the large amplitude vibration of Yb atom and the dependence of Yb vibration amplitude on the filling content. Temperature dependent EXAFS experiment on filled skutterudites have been carried out at Yb LⅢ-edge in order to explore the local vibration behavior of filled atom. EXAFS experiments show that the Einstein temperature of the filled atom is very low (70.9 K) which agrees with the rattling behavior.
The structure of filled skutterudites and the local vibration behavior of the filling atom
Energy Technology Data Exchange (ETDEWEB)
Zhou, Xiaojuan [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Dongguan Institute of Neutron Science, Dongguan 523808 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zong, Peng-an [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Chen, Xihong [Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Tao, Juzhou, E-mail: taoj@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Dongguan Institute of Neutron Science, Dongguan 523808 (China); Lin, He, E-mail: linhe@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Science, Shanghai 201204 (China)
2017-02-15
Both of atomic pair distribution function (PDF) and extended x-ray absorption fine structure (EXAFS) experiments have been carried out on unfilled and Yb-filled skutterudites Yb{sub x}Co{sub 4}Sb{sub 12} (x=0, 0.15, 0.2 and 0.25) samples. The structure refinements on PDF data confirm the large amplitude vibration of Yb atom and the dependence of Yb vibration amplitude on the filling content. Temperature dependent EXAFS experiment on filled skutterudites have been carried out at Yb L{sub Ⅲ}-edge in order to explore the local vibration behavior of filled atom. EXAFS experiments show that the Einstein temperature of the filled atom is very low (70.9 K) which agrees with the rattling behavior.
Vibration Control via Stiffness Switching of Magnetostrictive Transducers
Scheidler, Justin J.; Asnani, Vivake M.; Dapino, Marcelo J.
2016-01-01
In this paper, a computational study is presented of structural vibration control that is realized by switching a magnetostrictive transducer between high and low stiffness states. Switching is accomplished by either changing the applied magnetic field with a voltage excitation or changing the shunt impedance on the transducer's coil (i.e., the magnetostrictive material's magnetic boundary condition). Switched-stiffness vibration control is simulated using a lumped mass supported by a damper and the magnetostrictive transducer (mount), which is represented by a nonlinear, electromechanical model. Free vibration of the mass is calculated while varying the mount's stiffness according to a reference switched-stiffness vibration control law. The results reveal that switching the magnetic field produces the desired change in stiffness, but also an undesired actuation force that can significantly degrade the vibration control. Hence, a modified switched-stiffness control law that accounts for the actuation force is proposed and implemented for voltage-controlled stiffness switching. The influence of the magneto-mechanical bias condition is also discussed. Voltage-controlled stiffness switching is found to introduce damping equivalent to a viscous damping factor up to about 0.13; this is shown to primarily result from active vibration reduction caused by the actuation force. The merit of magnetostrictive switched-stiffness vibration control is then quantified by comparing the results of voltage- and shunt-controlled stiffness switching to the performance of optimal magnetostrictive shunt damping. For the cases considered, optimal resistive shunt damping performed considerably better than both voltage- and shunt-controlled stiffness switching.
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.
Sepahvand, K.
2017-07-01
Damping parameters of fiber-reinforced composite possess significant uncertainty due to the structural complexity of such materials. Considering the parameters as random variables, this paper uses the generalized polynomial chaos (gPC) expansion to capture the uncertainty in the damping and frequency response function of composite plate structures. A spectral stochastic finite element formulation for damped vibration analysis of laminate plates is employed. Experimental modal data for samples of plates is used to identify and realize the range and probability distributions of uncertain damping parameters. The constructed gPC expansions for the uncertain parameters are used as inputs to a deterministic finite element model to realize random frequency responses on a few numbers of collocation points generated in random space. The realizations then are employed to estimate the unknown deterministic functions of the gPC expansion approximating the responses. Employing modal superposition method to solve harmonic analysis problem yields an efficient sparse gPC expansion representing the responses. The results show while the responses are influenced by the damping uncertainties at the mid and high frequency ranges, the impact in low frequency modes can be safely ignored. Utilizing a few random collocation points, the method indicates also a very good agreement compared to the sampling-based Monte Carlo simulations with large number of realizations. As the deterministic finite element model serves as black-box solver, the procedure can be efficiently adopted to complex structural systems with uncertain parameters in terms of computational time.
EFFECT OF PARTICLE SIZE AND PACKING RATIO OF PID ON VIBRATION AMPLITUDE OF BEAM
Directory of Open Access Journals (Sweden)
P.S. Kachare
2013-06-01
Full Text Available Everything in the universe that has mass possesses stiffness and intrinsic damping. Owing to the stiffness property, mass will vibrate when excited and its intrinsic damping property will act to stop the vibration. The particle impact damper (PID is a very interesting damper that affects impact and friction effects of particles by means of energy dissipation. PID is a means for achieving high structural damping by using a particle-filled enclosure attached to a structure. The particles absorb the kinetic energy of the structure and convert it into heat through inelastic collisions between the particles themselves and between the particles and the walls of the enclosure. In this work, PID is measured for a cantilever mild steel beam with an enclosure attached to its free end; copper particles are used in this study. The PID is found to be highly nonlinear. The most useful observation is that for a very small weight penalty (about 7% to 8 %, the maximum damped amplitude of vibration at resonance with a PID, is about 9 to 10 times smaller than that without a PID. It is for more than that of with only intrinsic material damping of a majority of structural metals. A satisfactory comparison of damping with and without particles through experimentation is observed. The effect of the size of the particles on the damping performance of the beam and the effective packing ratio can be identified. It is also shown that as the packing ratio changes, the contributions of the phenomena of impact and friction towards damping also change. It is encouraging that despite its deceptive simplicity, the model captures the essential physics of PID.
Guy cable design and damping for vertical axis wind turbines
Carne, T. G.
1981-01-01
Guy cables are frequently used to support vertical axis wind turbines since guying the turbine reduces some of the structural requirements on the tower. The guys must be designed to provide both the required strength and the required stiffness at the top of the turbine. The axial load which the guys apply to the tower, bearings, and foundations is an undesirable consequence of using guys to support the turbine. Limiting the axial load so that it does not significantly affect the cost of the turbine is an important objective of the cable design. The lateral vibrations of the cables is another feature of the cable design which needs to be considered. These aspects of the cable design are discussed, and a technique for damping cable vibrations was mathematically analyzed and demonstrated with experimental data.
Cribbs, Richard Clay
This dissertation describes the development of a coupled rotor/flexible fuselage aeroelastic response model including rotor/fuselage aerodynamic interactions. This model is used to investigate fuselage vibrations and their suppression using active control of structural response (ACSR). The fuselage, modeled by a three dimensional structural dynamic finite element model, is combined with a flexible, four-bladed, hingeless rotor. Each rotor blade is structurally modeled as an isotropic Euler-Bernoulli beam with coupled flap-lag-torsional dynamics assuming moderate deflections. A free wake model is incorporated into the aeroelastic response model and is validated against previous studies. Two and three dimensional sources model the fuselage aerodynamics. Direct aerodynamic influences of the rotor and wake on the fuselage are calculated by integrating pressures over the surface of the fuselage. The fuselage distorts the wake and influences the air velocities at the rotor which alters the aerodynamic loading. This produces fully coupled rotor/fuselage aerodynamic interactions. The influence of the aerodynamic refinements on vibrations is studied in detail. Results indicate that a free wake model and the inclusion of fuselage aerodynamic effects on the rotor and wake are necessary for vibration prediction at all forward speeds. The direct influence of rotor and wake aerodynamics on the fuselage plays a minor role in vibrations. Accelerations with the improved aerodynamic model are significantly greater than uniform inflow results. The influence of vertical separation between the rotor and fuselage on vibrations is also studied. An ACSR control algorithm is developed that preferentially reduces accelerations at selected airframe locations of importance. Vibration reduction studies are carried out using this improved control algorithm and a basic algorithm studied previously at UCLA. Both ACSR methods markedly reduce acceleration amplitudes with no impact on the rotor
DEFF Research Database (Denmark)
Frimand, Kenneth; Bohr, Henrik; Jalkanen, Karl J.
2000-01-01
A detailed comparative study of structures, vibrational absorption (VA) and vibrational circular dichroism (VCD) spectra has been carried out for the zwitterionic structure of the amino acid L-alanine. Theoretically determined structures necessary for deriving VA and VCD spectra were calculated...... at the density functional theory level using the B3LYP functional with the 6-31G* basis set. The Hessians and atomic polar tensors and atomic axial tensors were all calculated at the B3LYP/6-31G* level of theory. An important result is the method of treating solvent effects by both adding explicit water...
Semi-active vibration absorber based on real-time controlled MR damper
Weber, F.
2014-06-01
A semi-active vibration absorber with real-time controlled magnetorheological damper (MR-SVA) for the mitigation of harmonic structural vibrations is presented. The MR damper force targets to realize the frequency and damping adaptations to the actual structural frequency according to the principle of the undamped vibration absorber. The relative motion constraint of the MR-SVA is taken into account by an adaptive nonlinear control of the internal damping of the MR-SVA. The MR-SVA is numerically and experimentally validated for harmonic excitation of the primary structure when the natural frequency of the passive mass spring system of the MR-SVA is correctly tuned to the targeted structural resonance frequency and when de-tuning is present. The results demonstrate that the MR-SVA outperforms the passive TMD at structural resonance frequency by at least 12.4% and up to 60.0%.
Free vibrations of an arbitrary structure in terms of component modes.
Dowell, E. H.
1972-01-01
A method for the analysis of the free vibrations of an arbitrary structure in terms of component modes is presented based upon the use of the normal, free-free modes of the components in a Rayleigh-Ritz analysis with the constraint or continuity conditions
DEFF Research Database (Denmark)
Barron, L.D.; Blanch, E.W.; McColl, I.H.
2003-01-01
On account of its sensitivity to chirality Raman optical activity (ROA), which may be measured as a small difference in vibrational Raman scattering from chiral molecules in right- and left-circularly polarized incident light, is a powerful probe of structure and behaviour of biomolecules in aque...
Structural, vibrational, elastic and topological properties of PaN under pressure
DEFF Research Database (Denmark)
Modak, P.; K. Verma, Ashok; Svane, A.
2013-01-01
Electronic, structural, vibrational and elastic properties of PaN have been studied both at ambient and high pressures, using first principles methods with several commonly used parameterizations of the exchange-correlation energy. The generalized gradient approximation (GGA) reproduces the ground...
Structure and intermolecular vibrations of 7-azaindole-water 2:1 ...
Indian Academy of Sciences (India)
Structure and intermolecular vibrations of 7-azaindole-water 2:1 complex in a supersonic jet expansion: Laser-induced fluorescence spectroscopy and quantum chemistry calculation. #. MONTU K HAZRAa,b, MOITRAYEE MUKHERJEEc, V RAMANATHANa,d and. TAPAS CHAKRABORTYc,∗. aDepartment of Chemistry ...
Structure and intermolecular vibrations of 7-azaindole-water 2: 1 ...
Indian Academy of Sciences (India)
Structure and intermolecular vibrations of 7-azaindole-water 2:1 complex in a supersonic jet expansion: Laser-induced fluorescence spectroscopy and quantum ... Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208 016, India; Department of Chemistry and Biochemistry, University of California, San ...
Khatir, Z.; Pozarlik, Artur Krzysztof; Kok, Jacobus B.W.; Cooper, R.K.; Watterson, J.W.; Oñate, E.; Papadrakakis, M.; Schrefler, B.
2007-01-01
Numerical investigations of fluid structure interaction between unsteady flow and vibrating liner in a combustion chamber are undertaken. The computational study consist of two approaches. Firstly, a partioned procedure consists of coupling the LES code AVBP for combustion modelling with the FEM
Effect of Space Vehicle Structure Vibration on Control Moment Gyroscope Dynamics
Dobrinskaya, Tatiana
2008-01-01
Control Moment Gyroscopes (CMGs) are used for non-propulsive attitude control of satellites and space stations, including the International Space Station (ISS). CMGs could be essential for future long duration space missions due to the fact that they help to save propellant. CMGs were successfully tested on the ground for many years, and have been successfully used on satellites. However, operations have shown that the CMG service life on the ISS is significantly shorter than predicted. Since the dynamic environment of the ISS differs greatly from the nominal environment of satellites, it was important to analyze how operations specific to the station (dockings and undockings, huge solar array motion, crew exercising, robotic operations, etc) can affect the CMG performance. This task became even more important since the first CMG failure onboard the ISS. The CMG failure resulted in the limitation of the attitude control capabilities, more propellant consumption, and additional operational issues. Therefore, the goal of this work was to find out how the vibrations of a space vehicle structure, caused by a variety of onboard operations, can affect the CMG dynamics and performance. The equations of CMG motion were derived and analyzed for the case when the gyro foundation can vibrate in any direction. The analysis was performed for unbalanced CMG gimbals to match the CMG configuration on ISS. The analysis showed that vehicle structure vibrations can amplify and significantly change the CMG motion if the gyro gimbals are unbalanced in flight. The resonance frequencies were found. It was shown that the resonance effect depends on the magnitude of gimbal imbalance, on the direction of a structure vibration, and on gimbal bearing friction. Computer modeling results of CMG dynamics affected by the external vibration are presented. The results can explain some of the CMG vibration telemetry observed on ISS. This work shows that balancing the CMG gimbals decreases the effect
Durlak, Piotr; Berski, Sławomir; Latajka, Zdzisław
2016-01-01
The molecular structure, conformational preferences, topological and vibrational analysis of allicin has been investigated at two different approaches. Calculations have been carried out on static (DFT and MP2) levels with an assortment of Dunning's basis sets and dynamic CPMD simulations. In this both case within the isolated molecule approximation. The results point out that at least twenty different conformers coexist on the PES as confirmed by the flexible character of this molecule. The topological analysis of ELF showed very similar nature of the Ssbnd S and Ssbnd O bonds. The infrared spectrum has been calculated, and a comparative vibrational analysis has been performed.
Development of a finite dynamic element for free vibration analysis of two-dimensional structures
Gupta, K. K.
1978-01-01
The paper develops an efficient free-vibration analysis procedure of two-dimensional structures. This is achieved by employing a discretization technique based on a recently developed concept of finite dynamic elements, involving higher order dynamic correction terms in the associated stiffness and inertia matrices. A plane rectangular dynamic element is developed in detail. Numerical solution results of free-vibration analysis presented herein clearly indicate that these dynamic elements combined with a suitable quadratic matrix eigenproblem solution technique effect a most economical and efficient solution for such an analysis when compared with the usual finite element method.
Energy Technology Data Exchange (ETDEWEB)
Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)
2017-04-11
The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.
Synthesis, structure and Hirshfeld surface analysis, vibrational and ...
Indian Academy of Sciences (India)
-dimensional architecture. Hirshfeld surface analysis for visually analysing intermolecular interactions in crystal structures employing molecular surfacecontours and 2D fingerprint plots has been used to scrutinize molecular shapes.
Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine
Srivastava, Santosh K.; Singh, Vipin B.
2013-11-01
Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.
Ligand effects on the structure and vibrational properties of the thiolated Au18 cluster
Directory of Open Access Journals (Sweden)
Alfredo Tlahuice-Flores
2016-10-01
Full Text Available Most of the studies devoted to thiolated gold clusters suppose that their core and Au-S framework do not suffer from distortion independently of the protecting ligands (-SR and it is assumed as correct to simplify the ligand as SCH3. In this work is delivered a systematic study of the structure and vibrational properties (IR and Raman of the Au18(SR14 cluster. The pursued goal is to understand the dependency of the displayed vibrational properties of the thiolated Au18 cluster with the ligands type. A set of six ligands was considered during calculations of the vibrational properties based on density functional theory (DFT and in its dispersion-corrected approach (DFT-D.
Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane.
Ocola, Esther J; Medders, Cross; Cooke, Joel M; Laane, Jaan
2014-09-15
Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent. Copyright © 2014 Elsevier B.V. All rights reserved.
Vibrational spectra, theoretical calculations, and structure of 4-silaspiro(3,3)heptane
Ocola, Esther J.; Medders, Cross; Cooke, Joel M.; Laane, Jaan
2014-09-01
Theoretical computations have been carried out for 4-silaspiro(3,3)heptane (SSH) in order to calculate its structure and vibrational spectra. SSH was found to have two puckered four-membered rings with dihedral angles of 34.2° and a tilt angle of 9.4° between the two rings. The puckering and tilting reduce the D2d symmetry to C2. Nonetheless, the vibrational assignments can be done quite well on the basis of D2d symmetry. This is confirmed by the fact that all but the lowest E vibrations show insignificant splitting into A and B modes of C2 symmetry. However, the observed splittings of the lowest frequency modes do confirm the lower conformational symmetry. The calculated infrared and Raman spectra were compared to the experimental spectra collected for the vapor, liquid, and solid states, and the agreement is excellent.
Effect of T6 heat treatment on damping characteristics of Al/RHA ...
Indian Academy of Sciences (India)
torsional vibration condition. Since then much investiga- tion have been made and various damping mechanisms were discovered in metallic materials. Rohatgi et al (1994) investigated the damping capacity of graphite and silicon carbide particulate reinforced Al alloy composites. The damping capacity of graphite/Al alloy ...
Uncertainty and Variation of Vibration in Lightweight Structures
DEFF Research Database (Denmark)
Dickow, Kristoffer Ahrens
2012-01-01
Multi-family dwellings and ofﬁces build from lightweight materials are becoming a cost efﬁcient and environmentally friendly alternative to traditional heavy structures.......Multi-family dwellings and ofﬁces build from lightweight materials are becoming a cost efﬁcient and environmentally friendly alternative to traditional heavy structures....
Extension of vibrational power flow techniques to two-dimensional structures
Cuschieri, Joseph M.
1988-01-01
In the analysis of the vibration response and structure-borne vibration transmission between elements of a complex structure, statistical energy analysis (SEA) or finite element analysis (FEA) are generally used. However, an alternative method is using vibrational power flow techniques which can be especially useful in the mid frequencies between the optimum frequency regimes for SEA and FEA. Power flow analysis has in general been used on 1-D beam-like structures or between structures with point joints. In this paper, the power flow technique is extended to 2-D plate-like structures joined along a common edge without frequency or spatial averaging the results, such that the resonant response of the structure is determined. The power flow results are compared to results obtained using FEA results at low frequencies and SEA at high frequencies. The agreement with FEA results is good but the power flow technique has an improved computational efficiency. Compared to the SEA results the power flow results show a closer representation of the actual response of the structure.
Analytical and Experimental Random Vibration of Nonlinear Aeroelastic Structures.
1987-01-28
dinamics . Sijthoff- Hilton, H H. and Feigen. M. Minimum weight analysis based on structural Noordhoff Co, Netherlands. reliability. J Aerospace Sc, 27...AEROELASTIC STRUCTURES January 28, 1987 ELECT Tpp. AIM" 0OV 7PTCE OF 9r(’TF1CP RESCH JAMi) NOTI-CE OF wIM 1 T AL TO D .TAC’ ..hirte;h-tz’ l rer)t ’(V...freedom aeroelastic structural model in the neighborhood of combination internal resonance condition. The Fokker:Planck equation approach is used to
Structural, thermal behaviour and vibrational study of a new mixed ...
Indian Academy of Sciences (India)
These anions show a 4° rotation around the fourfold axis against the cubic arrangement of the K2PtCI6 type structure. The monovalent cations (Cs+/NH 4 + ) are located between the octahedra ensuring the stability of the structure by ionic and hydrogen bonding contacts: Cs…Cl/Br and N-H … … Cl/Br. A DTA/TGA ...
Dynamic testing of cable structures
Directory of Open Access Journals (Sweden)
Caetano Elsa
2015-01-01
Full Text Available The paper discusses the role of dynamic testing in the study of cable structures. In this context, the identification of cable force based on vibration measurements is discussed. Vibration and damping assessment are then introduced as the focus of dynamic monitoring systems, and particular aspects of the structural behaviour under environmental loads are analysed. Diverse application results are presented to support the discussion centred on cable-stayed bridges, roof structures, a guyed mast and a transmission line.
Out-of-plane free vibration analysis of a cable-arch structure
Kang, H. J.; Zhao, Y. Y.; Zhu, H. P.
2013-02-01
Cable-arch structure has been widely used in many long-span structures such as cable roofs and cable-stayed arch bridges, but its dynamics is still not well understood. In this paper, the out-of-plane dynamic behavior of a cable-arch structure is investigated. The equations governing the out-of-plane free vibration of the structure are derived using d'Alembert's principle. A transfer matrix method is used to solve the governing equations and determine the frequencies of the out-of-plane vibration. The theories are then used to study two specific cases: free vibration of a model cable-arch and simulation of an arch erection process. The effects of some key parameters of cable and arch, such as tension of cable and radius, open-angle and shape of arch, are examined. The results indicate that in-plane and spatial cables can largely improve the out-of-plane dynamic behavior of arch structures, which are further verified by analyzing the out-of-plane buckling of cable-arch structures. The present work should be valuable and significant not only for the fundamental research but also engineering design of roofs and bridges.
Recentering Shape Memory Alloy Passive Damper for Structural Vibration Control
Directory of Open Access Journals (Sweden)
Hui Qian
2013-01-01
Full Text Available This paper presents a preliminary study on the evaluation of an innovative energy dissipation system with shape memory alloys (SMAs for structural seismic protection. A recentering shape memory alloy damper (RSMAD, in which superelastic nitinol wires are utilized as energy dissipation components, is proposed. Improved constitutive equations based on Graesser and Cozzarelli model are proposed for superelastic nitinol wires used in the damper. Cyclic tensile-compressive tests on the damper with various prestrain under different loading frequencies and displacement amplitudes were conducted. The results show that the hysteretic behaviors of the damper can be modified to best fit the needs for passive structural control applications by adjusting the pretension of the nitinol wires, and the damper performance is not sensitive to frequencies greater than 0.5 Hz. To assess the effectiveness of the dampers for structural seismic protection, nonlinear time history analysis on a ten-story steel frame with and without the dampers subjected to representative earthquake ground motions was performed. The simulation results indicate that superelastic SMA dampers are effective in mitigating the structural response of building structures subjected to strong earthquakes.
Fluid-structure finite-element vibrational analysis
Feng, G. C.; Kiefling, L.
1974-01-01
A fluid finite element has been developed for a quasi-compressible fluid. Both kinetic and potential energy are expressed as functions of nodal displacements. Thus, the formulation is similar to that used for structural elements, with the only differences being that the fluid can possess gravitational potential, and the constitutive equations for fluid contain no shear coefficients. Using this approach, structural and fluid elements can be used interchangeably in existing efficient sparse-matrix structural computer programs such as SPAR. The theoretical development of the element formulations and the relationships of the local and global coordinates are shown. Solutions of fluid slosh, liquid compressibility, and coupled fluid-shell oscillation problems which were completed using a temporary digital computer program are shown. The frequency correlation of the solutions with classical theory is excellent.
Structural and Vibrational Study on Monomer and Dimer Forms and Water Clusters of Acetazolamide
Directory of Open Access Journals (Sweden)
Aysen E. Ozel
2013-01-01
Full Text Available Experimental IR and Raman spectra of solid acetazolamide have been analysed by computing the molecular structures and vibrational spectra of monomer and dimer forms and water clusters of acetazolamide. The possible stable conformers of free acetazolamide molecule in the ground state were obtained by scanning the potential energy surface through the dihedral angles, D1 (1S-2C-6S-9N, D2 (4N-5C-12N-14C, and D3 (5C-12N-14C-16C. The final geometry parameters for the obtained stable conformers were determined by means of geometry optimization, carried out at DFT/B3LYP/6-31G++(d,p theory level. Afterwards the possible dimer forms of the molecule and acetazolamide-H2O clusters were formed and their energetically preferred conformations were investigated using the same method and the same level of theory. The effect of BSSE on the structure and energy of acetazolamide dimer has been investigated. The assignment of the vibrational modes was performed based on the potential energy distribution of the vibrational modes, calculated by using GAR2PED program. The experimental vibrational wavenumbers of solid acetazolamide are found to be in better agreement with the calculated wavenumbers of dimer form of acetazolamide than those of its monomeric form. NBO analysis has been performed on both monomer and dimer geometries.
Active damping of the 1D rocking mode
Babakhani, B.; de Vries, Theodorus J.A.
Active damping of a rotational vibration mode in the linear guidance of a precision machine in a one dimensional (1D) setting is considered in this paper. This so-called rocking mode presents itself in machines having linear actuation. The limitation this vibration mode imposes on the machine
Influence of bearing support structures on shaft vibration of large hydraulic pump/turbines
Energy Technology Data Exchange (ETDEWEB)
Pistner, C.A.; Greenplate, B.S. [Voith, Hydro, Inc., Pennsylvania, PA (United States); Waddell, A.M. [Tennessee Valley Authority, Chattanooga, TN (United States)
1995-12-31
Start-up transient loads from pump/turbine impellers can cause excessive vibration problems in the shaft system. If the radial guide bearing supports are structurally soft or loose, or if the bearings are worn, the resulting radial shaft movement causes abnormal wear. The wear normally occurs at the impeller sealing surfaces, main shaft seals, motor/generator components, piping, brackets, foundation connections, etc. This paper explores the critical factors causing shaft system vibration problems at the Tennessee Valley Authority`s Raccoon Mountain Pumped Storage Plant, as well as the unique modifications which were implemented to strengthen and improve the units. The solution involved extensive three-dimensional finite element structural and thermal transient analyses of the original and re-designed turbine shoe bearing, bearing housings, and support structures. The conclusion compares the calculated and measured shaft system response to transient loads of the original and modified system.
Directory of Open Access Journals (Sweden)
Adrien Oth
2012-01-01
Full Text Available Major threats to bridges primarily consist of the aging of the structural elements, earthquake-induced shaking and standing waves generated by windstorms. The necessity of information on the state of health of structures in real-time, allowing for timely warnings in the case of damaging events, requires structural health monitoring (SHM systems that allow the risks of these threats to be mitigated. Here we present the results of a short-duration experiment carried out with low-cost wireless instruments for monitoring the vibration characteristics and dynamic properties of a strategic civil infrastructure, the Adolphe Bridge in Luxembourg City. The Adolphe Bridge is a masonry arch construction dating from 1903 and will undergo major renovation works in the upcoming years. Our experiment shows that a network of these wireless sensing units is well suited to monitor the vibration characteristics of such a historical arch bridge and hence represents a low-cost and efficient solution for SHM.
Brandán, Silvia A
2014-01-01
A Structural and Vibrational Study of the Chromyl Chlorosulfate, Fluorosulfate and Nitrate Compounds presents important studies related to the structural and vibrational properties on the chromyl compounds based on Ab-initio calculations. The synthesis and the study of such properties are of chemical importance because the stereo-chemistries and reactivities of these compounds are strongly dependent on the coordination modes that adopt the different ligands linked to the chromyl group. In this book, the geometries of all stable structures in gas phase for chromyl chlorosulfate, fluorosulfate, and nitrate are optimized by using Density functional Theory (DFT). Then, the complete assignments of all observed bands in the infrared and Raman spectra are performed combining DFT calculations with Pulay´s Scaled Quantum Mechanics Force Field (SQMFF) methodology and taking into account the type of coordination adopted by the chlorosulfate, fluorosulfate and nitrate ligands as monodentate and bidentate. Moreover, the ...
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.
Zilletti, Michele; Elliott, Stephen J.; Rustighi, Emiliano
2012-01-01
The tuning of a dynamic vibration absorber is considered such that either the kinetic energy of the host structure is minimised or the power dissipation within the absorber is maximised. If the host structure is approximated as a damped single degree of freedom, the optimal values for the ratio of the absorber's natural frequency to the host structure and the optimal damping ratio of the absorber are shown to be the same whether the kinetic energy of the host structure is minimised or the pow...
Molecular and vibrational structure of 2,2'-dihydroxybenzophenone
DEFF Research Database (Denmark)
Birklund Andersen, Kristine; Langgård, M.; Spanget-Larsen, Jens
1999-01-01
2,2'-dihydroxybenzophenone (DHBP) contains similar bifold intramolecular H-bonding as the psoriatic drug anthralin, but because of steric interference the phenolic rings are twisted in a propeller-like manner, resulting in a molecular structure of C2 symmetry. In contrast to the case of C2v...
An active vibration control method of bridge structures by the ...
African Journals Online (AJOL)
With the on-growing construction of transport and communication structures in rural and urban zones due to economic requirements, and with occurrence of seismic events in past years in particular in Cameroon, one of the purposes of the present work is to display the feasibility and advantages of applying active tendon ...
Synthesis, structure and Hirshfeld surface analysis, vibrational and ...
Indian Academy of Sciences (India)
The water molecule is placed between the layers formed by organic cations along the b axis. Net- work hydrogen-bonding and π–π interactions lead to the formation of a three-dimensional architecture. Hirshfeld surface analysis for visually analysing intermolecular interactions in crystal structures employing molecular sur-.
Energy Technology Data Exchange (ETDEWEB)
Jurado, J. F.; Londono C, A.; Jurado L, F. F.; Romero S, J. D., E-mail: jfjurado@unal.edu.co [Universidad Nacional de Colombia, Laboratorio de Propiedades Termicas Dielectricas de Compositos, A. A. 127, Manizales (Colombia)
2014-07-01
The synthesis of Zn O by reaction in solid state from two precursor salts (zinc acetate and zinc sulfate), presented significant differences concerning morphology, structure, vibrational order and optical gap. As well as covering in the size of the compounds, a homogeneous distribution of nanoparticles of 21±3 nm and micro stars of 1.03±0.19 μm respectively. The Zn O showed a structural phase with a vibrational state of the hexagonal type (wurtzite). The variation in the morphology due to the precursor is attributed to the disorder within of lattice, which contributes to vibrational changes and is correlated to the degrees of freedom of molecules. Measurements of UV-Vis of nanoparticles displayed a band gap (E{sub g}) lower than the one reported for the bulk material. The structural characterization of the compounds was carried out by using a X-ray Bruker D8 Advance diffractometer. The vibrational order was assessed throughout micro-Raman with a monochromatic radiation source of 473 nm). (Author)
Power oscillation damping controller
DEFF Research Database (Denmark)
2012-01-01
A power oscillation damping controller is provided for a power generation device such as a wind turbine device. The power oscillation damping controller receives an oscillation indicating signal indicative of a power oscillation in an electricity network and provides an oscillation damping control...... signal in response to the oscillation indicating signal, by processing the oscillation damping control signal in a signal processing chain. The signal processing chain includes a filter configured for passing only signals within a predetermined frequency range....
Laminated Thin Shell Structures Subjected to Free Vibration in a Hygrothermal Environment
Gotsis, Pascal K.; Guptill, James D.
1994-01-01
Parametric studies were performed to assess the effects of various parameters on the free-vibration behavior (natural frequencies) of (+/- theta)(sub 2) angle-ply, fiber composite, thin shell structures in a hygrothermal environment. Knowledge of the natural frequencies of structures is important in considering their response to various kinds of excitation, especially when structures and force systems are complex and when excitations are not periodic. The three dimensional, finite element structural analysis computer code CSTEM was used in the Cray YMP computer environment. The fiber composite shell was assumed to be cylindrical and made from T300 graphite fibers embedded in an intermediate-modulus, high-strength matrix. The following parameters were investigated: the length and the laminate thickness of the shell, the fiber orientation, the fiber volume fraction, the temperature profile through the thickness of the laminate, and laminates with different ply thicknesses. The results indicate that the fiber orientation and the length of the laminated shell had significant effects on the natural frequencies. The fiber volume fraction, the laminate thickness, and the temperature profile through the shell thickness had weak effects on the natural frequencies. Finally, the laminates with different ply thicknesses had an insignificant influence on the behavior of the vibrated laminated shell. Also, a single through-the-thickness, eight-node, three dimensional composite finite element analysis appears to be sufficient for investigating the free-vibration behavior of thin, composite, angle-ply shell structures.
DEFF Research Database (Denmark)
Liang, Shanshan; Crovetto, Andrea; Peng, Zhuoteng
2016-01-01
and experiments with piezoelectric elements show that the energy harvesting device with the bi-resonant structure can generate higher power output than that of the sum of the two separate devices from random vibration sources at low frequency, and hence significantly improves the vibration-to- electricity...
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...... frame structure. As demonstrated in the literature effective damping of flexible structures is obtained by a suitable combination of pure friction and negative damper stiffness. This damper model is rate-independent and fully described by the desired shape of the hysteresis loops or force...... mode of the structure. The neural network control is then developed to reproduce the desired force based on damper displacement and velocity as network input, and it is therefore referred to as an amplitude dependent model reference control method. An inverse model of the MR damper is needed...
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...... frame structure. As demonstrated in the literature effective damping of flexible structures is obtained by a suitable combination of pure friction and negative damper stiffness. This damper model is rate-independent and fully described by the desired shape of the hysteresis loops or force...... mode of the structure. The neural network control is then developed to reproduce the desired force based on damper displacement and velocity as network input, and it is therefore referred to as an amplitude dependent model reference control method. An inverse model of the MR damper is needed...
Earthquake Vibration Control of Structures using Tuned Liquid Dampers: Experimental Studies
Directory of Open Access Journals (Sweden)
Pradipta Banerji
2010-12-01
Full Text Available Earlier studies have shown conclusively that a Tuned Liquid Damper (TLD is effective for controlling vibrations in structures subjected to narrow-banded wind excitations. A recent numerical study has shown that if the design parameters of a TLD are properly set, this device could also be very effective for controlling structural vibration to broad-banded earthquake excitations. Here the results of a reasonably comprehensive set of experiments are presented to investigate the overall effectiveness of TLDs and the specific effect of TLD parameters (depth and mass ratios for earthquake vibration control of structures. Effects of various earthquake ground motions parameters such as amplitude, frequency content, duration of excitation etc. are also evaluated. It is shown that there is good agreement between the numerical simulation and experimental results. This experimental study conclusively shows that a properly designed TLD reduces structural response to broad-band earthquake excitations. It is also observed that effectiveness of TLD increases with increase in mass ratio, depth ratio and amplitude of ground motion.
Afzali, R.; Vakili, M.; Boluri, E.; Tayyari, S. F.; Nekoei, A.-R.; Hakimi-Tabar, M.; Darugar, V.
2018-02-01
An interpretation of the experimental IR and Raman spectra of Aluminum (III) trifluoroacetylacetonate (Al(TFAA)3) complex, which were synthesized by us, is first reported here. The charge distribution, isomerism, strength of metal‑oxygen binding and vibrational spectral properties for this complex structure were theoretically investigated through population analysis, geometry optimization and harmonic frequency calculations, performed at B3LYP/6-311G* level of theory. In the population analysis, two different approaches reffered to as ;Atoms in molecules (AIM);, and ;Natural Bond Orbital (NBO); were used. According to the calculation resuls, the energy difference between the cis and trans isomers of Al(TFAA)3 is very small and indicates that both isomers coexist in the sample in comparable proportions. Comparison of the calculated frequency and intensity data with the observed IR and Raman spectra of the complex has supported this conclusion. On the other hand, comparison of the structural and vibrational spectral data of Al(TFAA)3, which were experimentally measured and calculated at B3LYP/6-311G* level, with the corresponding data of Aluminum acetylacetonate (Al(AA)3) has revealed the effects of CF3 substitution on the structural and vibrational spectral data associated with the CH3 groups in the complex structure.
Cao, Bochao
Slender structures representing civil, mechanical and aerospace systems such as long-span bridges, high-rise buildings, stay cables, power-line cables, high light mast poles, crane-booms and aircraft wings could experience vortex-induced and buffeting excitations below their design wind speeds and divergent self-excited oscillations (flutter) beyond a critical wind speed because these are flexible. Traditional linear aerodynamic theories that are routinely applied for their response prediction are not valid in the galloping, or near-flutter regime, where large-amplitude vibrations could occur and during non-stationary and transient wind excitations that occur, for example, during hurricanes, thunderstorms and gust fronts. The linear aerodynamic load formulation for lift, drag and moment are expressed in terms of aerodynamic functions in frequency domain that are valid for straight-line winds which are stationary or weakly-stationary. Application of the frequency domain formulation is restricted from use in the nonlinear and transient domain because these are valid for linear models and stationary wind. The time-domain aerodynamic force formulations are suitable for finite element modeling, feedback-dependent structural control mechanism, fatigue-life prediction, and above all modeling of transient structural behavior during non-stationary wind phenomena. This has motivated the developing of time-domain models of aerodynamic loads that are in parallel to the existing frequency-dependent models. Parameters defining these time-domain models can be now extracted from wind tunnel tests, for example, the Rational Function Coefficients defining the self-excited wind loads can be extracted using section model tests using the free vibration technique. However, the free vibration method has some limitations because it is difficult to apply at high wind speeds, in turbulent wind environment, or on unstable cross sections with negative aerodynamic damping. In the current
Ramoji, Anuradha; Yenagi, Jayashree; Tonannavar, J
2008-03-01
Vibrational spectral measurements, namely, infrared (4000-400 cm(-1)) and Raman (3500-50 cm(-1)) spectra have been made for 2-Bromohydroquinone. Optimized geometrical structures, harmonic vibrational frequencies and intensities have been computed by the ab initio (RHF), B-based (BLYP, BP86) and B3-based (B3P86, B3LYP, B3PW91) density functional methods using 6-31G(d) basis set. A complete assignment of the observed spectra has been proposed. Coupling of vibrations has been determined by calculating potential energy distributions (PEDs) at BP86/6-31G(d) level of theory. In the computed equilibrium geometries by all the levels, the bond lengths and bond angles show changes in the neighborhood of Bromine. Similarly, the vibrational spectra exhibit some marked spectral features unlike in hydroquinone and phenol. On the other hand, the infrared spectrum shows a clear evidence of O-H...O bonding near 3200 cm(-1) as in hydroquinone. Evaluation of the theoretical methods demonstrates that all the levels but the RHF have reproduced frequencies fairly accurately in the 2000-500 cm(-1); below 500 cm(-1) the RHF has performed reasonably well.
Moorthi, P. P.; Gunasekaran, S.; Swaminathan, S.; Ramkumaar, G. R.
2015-02-01
A collective experimental and theoretical study was conducted on the molecular structure and vibrational spectra of mannitol. The FT-IR and FT-Raman spectra of mannitol were recorded in the solid phase. The molecular geometry, vibrational frequencies, thermodynamic functions and atomic charges of mannitol in the ground state have been calculated by using the ab initio HF (Hartree-Fock) and density functional methods (B3LYP) invoking cc-pVDZ basis set. The complete vibrational assignments were performed on the basis of Total Energy Distribution (TED) of the vibrational modes. The UV absorption spectra of the title compound dissolved in water. Natural bond orbital analysis has been carried out to explain the charge transfer or delocalization of charge due to the intra-molecular interactions. The 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of the molecule were calculated by GIAO methods. The first order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of mannitol are calculated using B3LYP/cc-pVDZ and HF/cc-pVDZ methods on the finite-field approach. By using TD-DFT calculation, electronic absorption spectra of the title compound have been predicted and a good agreement with experimental one is established. In addition, the molecular electrostatic potential (MEP) have been investigated using theoretical calculations, the calculated HOMO and LUMO energies shows that the charge transfer within the molecule.
Mode damping in a commensurate monolayer solid
DEFF Research Database (Denmark)
Bruch, Ludwig Walter; Hansen, Flemming Yssing
1997-01-01
The normal modes of a commensurate monolayer solid may be damped by mixing with elastic waves of the substrate. This was shown by Hall, Mills, and Black [Phys. Rev. B 32, 4932 (1985)], for perpendicular adsorbate vibrations in the presence of an isotropic elastic medium. That work is generalized...... anisotropy of the elastic behavior of the graphite leads to quite different wave-vector dependence of the damping for modes polarized perpendicular and parallel to the substrate. A phenomenological extension of the elasticity theory of the graphite to include bond-bending energies improves the description...
Mei, Chuh; Shen, Mo-How
1987-01-01
Multiple-mode nonlinear forced vibration of a beam was analyzed by the finite element method. Inplane (longitudinal) displacement and inertia (IDI) are considered in the formulation. By combining the finite element method and nonlinear theory, more realistic models of structural response are obtained more easily and faster.
Ultrafast vibrational and structural dynamics of the proton in liquid water.
Woutersen, Sander; Bakker, Huib J
2006-04-07
The dynamical behavior of excess protons in liquid water is investigated using femtosecond vibrational pump-probe spectroscopy. By resonantly exciting the O-H+-stretching mode of the H9O4(+) (Eigen) hydration structure of the proton and probing the subsequent absorption change over a broad frequency range, the dynamics of the proton is observed in real time. The lifetime of the protonic stretching mode is found to be approximately 120 fs, shorter than for any other vibration in liquid water. We also observe the interconversion between the H9O4(+) (Eigen) and H5O2(+) (Zundel) hydration structures of the proton. This interconversion, which constitutes an essential step of proton transport in water, is found to occur on an extremely fast (< 100 fs) time scale.
Vibration-based structural health monitoring of the aircraft large component
Pavelko, V.; Kuznetsov, S.; Nevsky, A.; Marinbah, M.
2017-10-01
In the presented paper there are investigated the basic problems of the local system of SHM of large scale aircraft component. Vibration-based damage detection is accepted as a basic condition, and main attention focused to a low-cost solution that would be attractive for practice. The conditions of small damage detection in the full scale structural component at low-frequency excitation were defined in analytical study and modal FEA. In experimental study the dynamic test of the helicopter Mi-8 tail beam was performed at harmonic excitation with frequency close to first natural frequency of the beam. The index of correlation coefficient deviation (CCD) was used for extraction of the features due to embedded pseudo-damage. It is shown that the problem of vibration-based detection of a small damage in the large scale structure at low-frequency excitation can be solved successfully.
Vibration and Sound Damping in Polymers
Indian Academy of Sciences (India)
IAS Admin
characterization and applications of nano- multiferroics, nano- semiconductors, nano- composites, nanophosphors and nanosensors. 4Sabu Thomas is at the. Mahatma ... elastic solid obeys Hooke's Law, i.e., within the elastic limit, stress is directly .... Hence, sound travels fast in solids, but it is slow in liquids and gases.
Vibration Damping Response of Composite Materials
1991-04-01
unidirectional composite panels were made having thicknesses as specified in the ASTM D3039 -76 test procedure. After fabrication, these panels were...established procedures which are typically utilized. Specifically, the ASTM test methodologies were utilized. To determine El, E2, V, and V21...glass/3501-6, the ASTM D2584-68 Ignition Loss of Cured Reinfoiced Resins test procedure was used. In all cases, the fiber volume fraction was
Vibration and Sound Damping in Polymers
Indian Academy of Sciences (India)
V G Geethamma1 R Asaletha2 Nandakumar Kalarikkal1 Sabu Thomas3. Mahatma Gandhi University, Kerala. Cochin University of Science and Technology. Director International and Inter-University Centre for Nanoscience and Nanotechnology & School of Chemical Sciences Mahatma Gandhi University Kottayam 686 ...
Mei, Chuh
1987-01-01
A finite element method is presented for the large amplitude vibrations of complex structures that can be modelled with beam and rectangular plate elements subjected to harmonic excitation. Both inplane deformation and inertia are considered in the formulation. Derivation of the harmonic force and nonlinear stiffness matrices for a beam and a rectangular plate element are presented. Solution procedures and convergence characteristics of the finite element method are described. Nonlinear response to uniform and concentrated harmonic loadings and improved nonlinear free vibration results are presented for beams and rectangular plates of various boundary conditions.
Improved orthogonality check for measured modes. [from ground vibration testing of structures
Berman, A.
1980-01-01
A method is proposed for performing an orthogonality check for normal modes derived from ground vibration testing. The method utilizes partitioned mass and stiffness matrices for a linear undamped representation of a structure. The normalization of the modes by the proposed method inherently includes the effects of significant displacements which were not measured; and the method may allow the use of fewer measurement points than would be necessary with the conventional method.
Ab-initio study of structural, vibrational and optical properties of solid oxidizers
Energy Technology Data Exchange (ETDEWEB)
Yedukondalu, N.; Vaitheeswaran, G., E-mail: gvsp@uohyd.ernet.in
2016-09-15
We report the structural, elastic and vibrational properties of five ionic-molecular solid oxidizers MNO{sub 3} (M = Li, Na, K) and MClO{sub 3} (M = Na, K). By treating long range electron-correlation effects, dispersion corrected method leads to more accurate predictions of structural properties and phase stability of KNO{sub 3} polymorphs. The obtained elastic moduli show soft nature of these materials and are consistent with Ultrasonic Pulse Echo measurements. We made a complete assignment of vibrational modes which are in good accord with available experimental results. From calculated IR and Raman spectra, it is found that the vibrational frequencies show a red-shift from Li → Na → K (Na → K) and N → Cl for nitrates (chlorates) due to increase in mass of metal and non-metal atoms, respectively. The calculated electronic structure using recently developed Tran-Blaha modified Becke-Johnson potential show that the materials are wide band gap insulators with predominant ionic bonding between M{sup +} (metal) and NO{sub 3}{sup −}/ClO{sub 3}{sup −} ions and covalent bonding (N−O and Cl−O) within nitrate and chlorate anionic group. From the calculated optical spectra, we observe that electric-dipole transitions are due to nitrate/chlorate group below 20 eV and cationic transitions occur above 20 eV. The calculated reflectivity spectra are consistent with the available experimental measurements. - Highlights: • Ground state properties with inclusion of dispersion correction method. • Elastic constants and mechanical properties. • Vibrational spectra and their complete assignment. • Raman and IR spectra. • Electronic structure and optical properties using TB-mBJ potential.
Review on structural damage assessment via transmissibility with vibration based measurements
Zhou, Yun-Lai; Hongyou, Cao; Zhen, Ni; Abdel Wahab, Magd
2017-05-01
In this study, transmissibility based damage assessment techniques with vibration measurement are reviewed with highlighting the recent advancements since damage might induce severe changes and cause huge economic losses in both civil and mechanical engineering structures. In recent years, transmissibility underwent booming and divergent application for damage assessment both in experimental model and engineering application, and this review provides a fundamental understanding for transmissibility based damage assessment by summarizing those research outputs, which can serve as useful reference for further investigations.
The Shock Vibration Bulletin. Part 4. Structural Dynamics and Modal Test and Analysis
1987-01-01
Feb. 1971. 17 16. B. Bresler, and A. C. Scordelis , ’Shear Strength of Reinforced Concrete Beams-,Series 100, Issue 13, Structure and Material Research...their adequacy. Dynamic analyses, choice of failure thresholds of failure are even harder to theories , and an accurate dynamic model are estimate...without experimental evidence. shown to be crucial in fulfilling the 29 71 L requirements. Vibration testing data are theories of failure have to be
Energy Technology Data Exchange (ETDEWEB)
Trendafilova, I, E-mail: Irina.Trendafilova@strath.ac.uk [Department of Mechanical Engineering, University of Strathclyde, 75 Montrose street, Glasgow, G1 1XJ (United Kingdom)
2011-07-19
Vibration-based structural interrogation and health monitoring is a field which is concerned with the estimation of the current state of a structure or a component from its vibration response with regards to its ability to perform its intended function appropriately. One way to approach this problem is through damage features extracted from the measured structural vibration response. This paper suggests to use a new concept for the purposes of vibration-based health monitoring. The correlation between two signals, an input and an output, measured on the structure is used to develop a damage indicator. The paper investigates the applicability of the signal cross-correlation and a nonlinear alternative, the average mutual information between the two signals, for the purposes of structural health monitoring and damage assessment. The suggested methodology is applied and demonstrated for delamination detection in a composite beam.
Structural, electronic, vibrational and optical properties of Bin clusters
Liang, Dan; Shen, Wanting; Zhang, Chunfang; Lu, Pengfei; Wang, Shumin
2017-10-01
The neutral, anionic and cationic bismuth clusters with the size n up to 14 are investigated by using B3LYP functional within the regime of density functional theory and the LAN2DZ basis set. By analysis of the geometries of the Bin (n = 2-14) clusters, where cationic and anionic bismuth clusters are largely similar to those of neutral ones, a periodic effect by adding units with one to four atoms into smaller cluster to form larger cluster is drawn for the stable structures of bismuth clusters. An even-odd alteration is shown for the properties of the clusters, such as the calculated binding energies and dissociation energies, as well as frontier orbital energies, electron affinities, ionization energies. All the properties indicate that the Bi4 cluster is the most possible existence in bismuth-containing materials, which supports the most recent experiment. The orbital compositions, infrared and Raman activities and the ultraviolet absorption of the most possible tetramer bismuth cluster are given in detail to reveal the periodic tendency of adding bismuth atoms and the stability of tetramer bismuth cluster.
Structure, Vibrational Spectra and Ring Puckering Barrier of Cyclobutane
Energy Technology Data Exchange (ETDEWEB)
Xantheas, Sotiris S.; Blake, Thomas A.
2006-09-02
We present the results of high level ab initio calculations on the structure and puckering barrier of cyclobutane in an effort to establish the minimum theoretical requirements needed for their accurate description. Our best computed value for the puckering angle is 29.68o. Furthermore we found that accurate estimates for the barrier between the minimum (D2d) and transition state (D4h) configurations require both higher levels of electron correlation [MP4, CCSD(T)] and basis sets of quadruple-z quality or larger. By performing CCSD(T) calculations with basis sets as large as cc-pV5Z we obtained a complete basis set (CBS) estimate of 498 cm-1 for the puckering barrier. Our estimate for the barrier is within 10 cm-1 to the value proposed originally, but it lies ~50 cm-1 higher than the one obtained more recently, therefore revisiting the analysis of the experimental data might be warranted. The results of the current study can serve as a guide for calculations on the substituted four member ring compounds. To this end we present a method for estimating the barrier height at higher levels of electron correlation [MP4, CCSD(T)] from the MP2 results.
Coupled vibrations of a structure and fluid excited by pressure shocks. [BWR
Energy Technology Data Exchange (ETDEWEB)
Arros, J.
1979-12-01
The dynamic behavior of an axisymmetric boiling water reactor suppression pool structure and the embedded water under the excitation of the pressure waves from collapsing steam bubbles was studied with a finite element model. The structure was analyzed with thin shell elements. The fluid volume is divided into isoparametric quadrilateral toroidal elements with pressure as the nodal parameter. A water source element was utilized to model the pressure shock excitation. Nonaxisymmetric pressure loads and vibration modes were expressed as a Fourier series in the circumferential coordinate. The system of equations for the structure and fluid was integrated in time using the central difference scheme.
Solution of quadratic matrix equations for free vibration analysis of structures.
Gupta, K. K.
1973-01-01
An efficient digital computer procedure and the related numerical algorithm are presented herein for the solution of quadratic matrix equations associated with free vibration analysis of structures. Such a procedure enables accurate and economical analysis of natural frequencies and associated modes of discretized structures. The numerically stable algorithm is based on the Sturm sequence method, which fully exploits the banded form of associated stiffness and mass matrices. The related computer program written in FORTRAN V for the JPL UNIVAC 1108 computer proves to be substantially more accurate and economical than other existing procedures of such analysis. Numerical examples are presented for two structures - a cantilever beam and a semicircular arch.
Tsuchiya, J.; Tsuchiya, T.
2013-12-01
Serpentine is formed by reaction between peridotite and water which is released from hydrous mineral in subducting slab under pressure. Partially serpentinized peridotite may be a significant reservoir for water in the subducted cold slab and is considered to play an important role in subduction zone processes such as generation of arc magmatism. Precise determination of structure, vibrational and elastic properties of serpentine become the basis for understanding the transporting processes of water into deep Earth interior. Here we investigate by first principles calculation, the detailed structures, vibrational and elastic properties of lizardite, chlorite, and antigorite which are major hydrous minerals in the serpentinized peridotite. We found a very sudden softening of the elastic constants at high pressure condition. This anomaly is associated with a slight change in the compressibility of the c axis which corresponds to the layer normal direction. The calculated OH stretching frequencies also increase suddenly associated with the anomaly and these vibrational behaviors are consistent with the previous Raman measurements. Since other hydrous phyllosilicates such as clay minerals, and mica have similar crystal structures to these hydrous minerals, these anomalous softening is also expected in these minerals under pressure. Research supported in part by special coordination funds for promoting science and technology (Supporting Young Researchers with Fixed-term Appointments) and Grants-In-Aid for Scientific Research from the Japan Society for the Promotion of Science (Nos. 21740380, 20103005, and 24740357).
Directory of Open Access Journals (Sweden)
Vasilescu Ionuţ
2015-12-01
Full Text Available The present paper presents the structural and seismic retrofit solution for the structure of the Catalytic Cracking Reactor, from Petrobrazi Refinery, Ploiești, Romania. The spatial truss type steel structure was designed and built during 1965-1968, following United States codes of that time. The capacity of the reactor is intended to be increased, thus its weight increases by approx. 43%. The retrofit solution had to take into consideration many criteria, not only technical, but also technological. After analyzing several possibilities, it was decided that the only feasible solution in order to fulfill all these requirements was to significantly increase the viscous damping of the structure – by introducing viscous dampers in its diagonals, accompanied by the strengthening of steel structure and changing the structural system into a moment resisting frame.
Directory of Open Access Journals (Sweden)
Shijia Pan
2017-05-01
Full Text Available This paper presents a collaboratively adaptive vibration monitoring system that captures high-fidelity structural vibration signals induced by pedestrians. These signals can be used for various human activities’ monitoring by inferring information about the impact sources, such as pedestrian footsteps, door opening and closing, and dragging objects. Such applications often require high-fidelity (high resolution and low distortion signals. Traditionally, expensive high resolution and high dynamic range sensors are adopted to ensure sufficient resolution. However, for sensing systems that use low-cost sensing devices, the resolution and dynamic range are often limited; hence this type of sensing methods is not well explored ubiquitously. We propose a low-cost sensing system that utilizes (1 a heuristic model of the investigating excitations and (2 shared information through networked devices to adapt hardware configurations and obtain high-fidelity structural vibration signals. To further explain the system, we use indoor pedestrian footstep sensing through ambient structural vibration as an example to demonstrate the system performance. We evaluate the application with three metrics that measure the signal quality from different aspects: the sufficient resolution rate to present signal resolution improvement without clipping, the clipping rate to measure the distortion of the footstep signal, and the signal magnitude to quantify the detailed resolution of the detected footstep signal. In experiments conducted in a school building, our system demonstrated up to 2× increase on the sufficient resolution rate and 2× less error rate when used to locate the pedestrians as they walk along the hallway, compared to a fixed sensing setting.
VIBRATION ISOLATION SYSTEM PROBABILITY ANALYSIS
Directory of Open Access Journals (Sweden)
Smirnov Vladimir Alexandrovich
2012-10-01
Full Text Available The article deals with the probability analysis for a vibration isolation system of high-precision equipment, which is extremely sensitive to low-frequency oscillations even of submicron amplitude. The external sources of low-frequency vibrations may include the natural city background or internal low-frequency sources inside buildings (pedestrian activity, HVAC. Taking Gauss distribution into account, the author estimates the probability of the relative displacement of the isolated mass being still lower than the vibration criteria. This problem is being solved in the three dimensional space, evolved by the system parameters, including damping and natural frequency. According to this probability distribution, the chance of exceeding the vibration criteria for a vibration isolation system is evaluated. Optimal system parameters - damping and natural frequency - are being developed, thus the possibility of exceeding vibration criteria VC-E and VC-D is assumed to be less than 0.04.
CoFeB/MgO/CoFeB structures with orthogonal easy axes: perpendicular anisotropy and damping
Głowiński, H.; Żywczak, A.; Wrona, J.; Krysztofik, A.; Gościańska, I.; Stobiecki, T.; Dubowik, J.
2017-12-01
We report on the Gilbert damping parameter α, the effective magnetization 4π M_eff , and the asymmetry of the g-factor in bottom-CoFeB(0.93 nm)/MgO(0.90–1.25 nm)/CoFeB(1.31 nm)-top as-deposited systems. Magnetization of CoFeB layers exhibits a specific noncollinear configuration with orthogonal easy axes and with 4π M_eff values of +2.2 kG and -2.3 kG for the bottom and top layers, respectively. We show that 4π M_eff depends on the asymmetry g_\\perp - g_\\Vert of the g-factor measured in the perpendicular and the in-plane directions revealing a highly nonlinear relationship. In contrast, the Gilbert damping is practically the same for both layers. Annealing of the films results in collinear easy axes perpendicular to the plane for both layers. However, the linewidth is strongly increased due to enhanced inhomogeneous broadening.
Effects of Landau-Lifshitz-Gilbert damping on domain growth
Kudo, Kazue
2016-12-01
Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG equation, it merely describes the precession of magnetization with a ferromagnetic interaction. However, even without the damping, domains that look similar to those of scalar fields are formed, and they grow with time. It is demonstrated that the damping has no significant effects on domain growth laws and large-scale domain structure. In contrast, small-scale domain structure is affected by the damping. The difference in small-scale structure arises from energy dissipation due to the damping.
Edighoffer, H. H.
1979-01-01
A component mode desynthesis procedure is developed for determining the unknown vibration characteristics of a structural component (i.e., a launch vehicle) given the vibration characteristics of a structural system composed of that component combined with a known one (i.e., a payload). At least one component static test has to be performed. These data are used in conjunction with the system measured frequencies and mode shapes to obtain the vibration characteristics of each component. The flight dynamics of an empty launch vehicle can be determined from measurements made on a vehicle/payload combination in conjunction with a static test on the payload.
Ivanco, Thomas G. (Inventor)
2014-01-01
A vibration damper includes a rigid base with a mass coupled thereto for linear movement thereon. Springs coupled to the mass compress in response to the linear movement along either of two opposing directions. A converter coupled to the mass converts the linear movement to a corresponding rotational movement. A rotary damper coupled to the converter damps the rotational movement.
Dzung Nguyen, Sy; Kim, Wanho; Park, Jhinha; Choi, Seung-Bok
2017-04-01
Vibration control systems using smart dampers (SmDs) such as magnetorheological and electrorheological dampers (MRD and ERD), which are classified as the integrated structure-SmD control systems (ISSmDCSs), have been actively researched and widely used. This work proposes a new controller for a class of ISSmDCSs in which high accuracy of SmD models as well as increment of control ability to deal with uncertainty and time delay are to be expected. In order to achieve this goal, two formualtion steps are required; a non-parametric SmD model based on an adaptive neuro-fuzzy inference system (ANFIS) and a novel fuzzy sliding mode controller (FSMC) which can weaken the model error of the ISSmDCSs and hence provide enhanced vibration control performances. As for the formulation of the proposed controller, first, an ANFIS controller is desgned to identify SmDs using the improved control algorithm named improved establishing neuro-fuzzy system (establishing neuro-fuzzy system). Second, a new control law for the FSMC is designed via Lyapunov stability analysis. An application to a semi-active MRD vehicle suspension system is then undertaken to illustrate and evaluate the effectiveness of the proposed control method. It is demonstrated through an experimental realization that the FSMC proposed in this work shows superior vibration control performance of the vehicle suspension compared to other surveyed controller which have similar structures to the FSMC, such as fuzzy logic and sliding mode control.
Ab initio structural and vibrational properties of GaAs diamondoids and nanocrystals
Directory of Open Access Journals (Sweden)
Mudar Ahmed Abdulsattar
2014-12-01
Full Text Available Gallium arsenide diamondoids structural and vibrational properties are investigated using density functional theory at the PBE/6-31(d level and basis including polarization functions. Variation of energy gap as these diamondoids increase in size is seen to follow confinement theory for diamondoids having nearly equiaxed dimensions. Density of energy states transforms from nearly single levels to band structure as we reach larger diamondoids. Bonds of surface hydrogen with As atoms are relatively localized and shorter than that bonded to Ga atoms. Ga-As bonds have a distribution range of values due to surface reconstruction and effect of bonding to hydrogen atoms. Experimental bulk Ga-As bond length (2.45 Å is within this distribution range. Tetrahedral and dihedral angles approach values of bulk as we go to higher diamondoids. Optical-phonon energy of larger diamondoids stabilizes at 0.037 eV (297 cm-1 compared to experimental 0.035 eV (285.2 cm-1. Ga-As force constant reaches 1.7 mDyne/Å which is comparable to Ga-Ge force constant (1.74 mDyne/Å. Hydrogen related vibrations are nearly constant and serve as a fingerprint of GaAs diamondoids while Ga-As vibrations vary with size of diamondoids.
Two methods for estimating aeroelastic damping of operational wind turbine modes from experiments
DEFF Research Database (Denmark)
Hansen, Morten Hartvig; Thomsen, Kenneth; Fuglsang, Peter
2006-01-01
show that turbine vibrations related to the first two tower bending modes can be excited by blade pitch and generator torque variations. However, the excited turbine vibrations are not pure modal vibrations and the estimated damping is therefore not the actual modal damping. The second method is based......The theory and results of two experimental methods for estimating the modal damping of a wind turbine during operation are presented. Estimations of the aeroelastic damping of the operational turbine modes (including the effects of the aerodynamic forces) give a quantitative view of the stability...... characteristics of the turbine. In the first method the estimation of modal damping is based on the assumption that a turbine mode can be excited by a harmonic force at its natural frequency, whereby the decaying response after the end of excitation gives an estimate of the damping. Simulations and experiments...
Shundalau, M. B.; Chybirai, P. S.; Komyak, A. I.; Zazhogin, A. P.; Ksenofontov, M. A.; Umreiko, D. S.
2011-07-01
We present results of ab initio and DFT calculations of the structure and IR vibrational spectra of the monomer and dimers of N,N-dimethylformamide (DMF). The calculations were carried out in the B3LYP/cc-pVDZ approximation with subsequent force-field scaling. The calculated characteristics of the vibrational spectra of DMF show satisfactory agreement with experimental values, allowing them to be used in spectral and structural analysis.