Bridge feedback for active damping augmentation
Chen, G.-S.; Lurie, B. J.
1990-01-01
A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.
Active member bridge feedback control for damping augmentation
Chen, Gun-Shing; Lurie, Boris J.
1992-01-01
An active damping augmentation approach using active members in a structural system is described. The problem of maximizing the vibration damping in a lightly damped structural system is considered using the analogy of impedance matching between the load and source impedances in an electrical network. The proposed active damping augmentation approach therefore consists of finding the desired active member impedances that maximize the vibration damping, and designing a feedback control in order to achieve desired active member impedances. This study uses a bridge feedback concept that feeds back a combination of signals from sensors of the axial force and relative velocity across the active member to realize the desired active member impedance. The proposed active damping augmentation approach and bridge feedback concept were demonstrated on a three-longeron softly suspended truss structure.
Adaptive noncolocated velocity feedback for vibration damping
Bayard, David S.; Spanos, John T.
1990-01-01
A method is proposed for adaptive noncolocated velocity feedback control of flexible structure vibrations. The approach, denoted as auto-tuning, is to drive the system into a sequence of controlled oscillations to provide accurate knowledge of the plant characteristics in the vicinity of the phase cross-over frequencies. An allpass phase notch filter cascade is used as the control architecture to phase stabilize each destabilizing mode in the plant transfer function. The allpass phase notch filter cascade is tuned precisely by the information extracted from the controlled oscillations.
Swing Damping for Helicopter Slung Load Systems using Delayed Feedback
DEFF Research Database (Denmark)
Bisgaard, Morten; la Cour-Harbo, Anders; Bendtsen, Jan Dimon
2009-01-01
of swing. The design of the delayed feedback controller is presented as an optimization problem which gives the possibility of an automated design process. Simulations and flight test verifications of the control system on two different autonomous helicopters are presented and it is shown how a significant......This paper presents the design and verification of a swing reducing controller for helicopter slung load systems using intentional delayed feedback. It is intended for augmenting a trajectory tracking helicopter controller and thereby improving the slung load handing capabilities for autonomous...... helicopters. The delayed feedback controller is added to actively reduce oscillations of the slung load by improving the damping of the slung load pendulum modes. Furthermore, it is intended for integration with a feedforward control scheme based on input shaping for concurrent avoidance and dampening...
SOGI-based capacitor voltage feedback active damping in LCL-filtered grid converters
DEFF Research Database (Denmark)
Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang
2015-01-01
The capacitor voltage feedback active damping control is an attractive way to suppress LCL-filter resonance especially for the systems where the capacitor voltage is used for grid synchronization, since no extra sensors are added. The derivative is the core of the capacitor voltage feedback active...... derivative is more suited for capacitor voltage feedback active damping control. Experimental results validate the effectiveness of the proposed method....
Enhanced Stability of Capacitor-Current Feedback Active Damping for LCL-Filtered Grid Converters
DEFF Research Database (Denmark)
Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang;
2015-01-01
The proportional capacitor-current feedback active damping method has been widely used to suppress the LCL-filter resonance. However, the time delay in the damping control loop may lead to non-minimum phase or even unstable responses when the resonance frequency varies in a wide range. To improve...... the robustness of damping, this paper proposes an improved damping controller with the capacitor current feedback loop, which is based on the second-order generalized integrator, instead of a proportional gain, which can effectively mitigate the detrimental effect of the time delay. Robustness of the proposed...
Digital Realization of Capacitor-Voltage Feedback Active Damping for LCL-Filtered Grid Converters
DEFF Research Database (Denmark)
Xin, Zhen; Wang, Xiongfei; Loh, Poh Chiang
2015-01-01
The capacitor voltage of an LCL-filter can also be used for active damping, if it is fed back for synchronization. By this way, an extra current sensor can be avoided. Compared with the existing active damping techniques designed with capacitor current feedback, the capacitor voltage feedback....... To overcome their drawbacks, a new derivative method is then proposed, based on the non-ideal generalized integrator. The performance of the proposed derivative has been found to match the ideal “s” function closely. Active damping based on capacitor voltage feedback can therefore be realized accurately...
Feedback Damping of a Coherent Instability at Small-Laser Equipped Storage Ring, S-LSR
Fujimoto, Shinji; Shirai, Toshiyuki; Noda, Akira; Ikegami, Masahiro; Tongu, Hiromu; Noda, Koji
2006-12-01
A beam test for the feedback damping of a coherent instability at small-laser equipped storage ring (S-LSR) was carried out. The instability caused beam loss, which limited the stored beam current to be about 600 μA during beam stacking with electron cooling. A vertical feedback damping system (VFS) using an electro-static beam position monitor (ESBPM) and a vertical kicker was applied to suppress this beam instability. The VFS realized not only suppressing the vertical coherent instability, but also revealing the characteristics of the feedback damping.
High-performance feedback-type active damping of LCL-filtered voltage source converters
DEFF Research Database (Denmark)
Wang, Xiongfei; Blaabjerg, Frede; Loh, Poh Chiang
2015-01-01
Active damping of LCL-filter resonance based on single-state feedback control is widely used with voltage source converters. Its robustness against grid impedance variation has always been a major concern with its controller design. To deal with this issue, this paper begins by developing......, but ensures also a robust stabilization against the grid parameters variations. For illustration, the approach is applied to design three single-state feedback-damping schemes, and their damping robustness are compared under both inductive and resonant grid impedances. Experimental results validate...
Theoretical Limits of Damping Attainable by Smart Beams with Rate Feedback
Balakrishnan, A. V.
1997-01-01
Using a generally accepted model we present a comprehensive analysis (within the page limitation) of an Euler- Bernoulli beam with PZT sensor-actuator and pure rate feedback. The emphasis is on the root locus - the dependence of the attainable damping on the feedback gain. There is a critical value of the gain beyond which the damping decreases to zero. We construct the time-domain response using semigroup theory, and show that the eigenfunctions form a Riesz basis, leading to a 'modal' expansion.
Pressure Feedback in Fluid Power Systems--Active Damping Explained and Exemplified
DEFF Research Database (Denmark)
Pedersen, Henrik Clemmensen; Andersen, Torben O.
2017-01-01
a given system, and how to adjust the parameters of the pressure feedback to obtain the best results. This is done for both a traditional symmetric cylinder servo system and a system with a differential cylinder using both pressure and nonpressure compensated proportional valves. Based on the presented...... are applied, that they do not benefit from the possibilities for improving the damping by applying (internal) pressure feedback in the systems. In both cases, the result will be degraded performance compared with what may be obtained. Pressure feedback, also referred to as active damping, is not a new method....... However, it is an often overlooked method, and when it is applied, it is not adjusted optimally to also account for model uncertainties, unmodeled system dynamics, and parameter variations. The focus of this paper is to explain various types of pressure feedback that may be applied; how these affect...
Active damping of LLCL-filter resonance based on LC-trap voltage and capacitor current feedback
DEFF Research Database (Denmark)
Huang, Min; Wang, Xiongfei; Loh, Poh Chiang
2015-01-01
. In this paper, different feedback coefficients like the proportional, derivative, integral, high pass and low pass feedback coefficients of the filter capacitor current and the LC-trap circuit voltage are investigated for damping the filter resonance. Active damping methods are analyzed by using the concept...
Dynamic Output Feedback Power-Level Control for the MHTGR Based On Iterative Damping Assignment
Directory of Open Access Journals (Sweden)
Zhe Dong
2012-06-01
Full Text Available Because of its strong inherent safety features and high outlet temperature, the modular high temperature gas-cooled nuclear reactor (MHTGR is already seen as the central part of the next generation of nuclear plants. Such power plants are being considered for industrial applications with a wide range of power levels, and thus power-level control is an important technique for their efficient and stable operation. Stimulated by the high regulation performance provided by nonlinear controllers, a novel dynamic output-feedback nonlinear power-level regulator is developed in this paper based on the technique of iterative damping assignment (IDA. This control strategy can provide the L_{2} disturbance attenuation performance under modeling uncertainty or exterior disturbance, and can also guarantee the globally asymptotic closed-loop stability without uncertainty and disturbance. This newly built control strategy is then applied to the power-level regulation of the HTR-PM plant, and numerical simulation results show both the feasibility and high performance of this newly-built control strategy. Furthermore, the relationship between the values of the parameters and the performance of this controller is not only illustrated numerically but also analyzed theoretically.
Design of output feedback UPFC controller for damping of electromechanical oscillations using PSO
Energy Technology Data Exchange (ETDEWEB)
Shayeghi, H. [Technical Engineering Dept., Univ. of Mohaghegh Ardabili, Ardabil (Iran); Shayanfar, H.A. [Center of Excellence for Power Automation and Operation, Electrical Engineering Dept., Iran Univ. of Science and Technology, Tehran (Iran); Jalilzadeh, S.; Safari, A. [Technical Engineering Dept., Zanjan Univ., Zanjan (Iran)
2009-10-15
In this paper, a novel method for the design of output feedback controller for unified power flow controller (UPFC) is developed. The selection of the output feedback gains for the UPFC controllers is converted to an optimization problem with the time domain-based objective function which is solved by a particle swarm optimization technique (PSO) that has a strong ability to find the most optimistic results. Only local and available state variables are adopted as the input signals of each controller for the decentralized design. Thus, structure of the designed UPFC controller is simple and easy to implement. To ensure the robustness of the proposed stabilizers, the design process takes into account a wide range of operating conditions and system configurations. The effectiveness of the proposed controller for damping low frequency oscillations is tested and demonstrated through nonlinear time-domain simulation and some performance indices studies. The results analysis reveals that the designed PSO-based output feedback UPFC damping controller has an excellent capability in damping power system low frequency oscillations and enhance greatly the dynamic stability of the power systems. Moreover, the system performance analysis under different operating conditions show that the {delta}{sub E} based controller is superior to both the m{sub B} based controller and conventional power system stablizer. (author)
DEFF Research Database (Denmark)
Huang, Min; Wang, Xiongfei; Loh, Poh Chiang
2014-01-01
-phase grid-connected voltage source inverter (VSI). The design method is described through the analysis in the s-domain and the z-domain. Then the robustness and harmonic rejection of the grid voltage with the active damping method is analyzed considering the processing delay. Finally, the performance...... damping method with an extra feedback provides a high rejection of the resonance so that the dynamic is improved. In this paper, taking a Proportional-Resonant (PR) together with a harmonic compensator (HC), resonant-inductor-voltage-feedback active damping is applied on an LLCL-filter based three...
Active Damping of LLCL-Filter Resonance Based on LC-Trap Voltage or Current Feedback
DEFF Research Database (Denmark)
Huang, Min; Wang, Xiongfei; Loh, Poh Chiang;
2016-01-01
. Active damping is presently more efficient, and can easily be realized by feeding back a state variable. For the LCL-filter, the variable is usually its middle capacitor current. However, with computational delays considered, a simple proportional damper cannot be used with the capacitor current. Instead...
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.
Damped Lyman-alpha absorbers as a probe of stellar feedback
Bird, Simeon; Haehnelt, Martin; Sijacki, Debora; Genel, Shy; Torrey, Paul; Springel, Volker; Hernquist, Lars
2014-01-01
We examine the abundance, clustering and metallicity of Damped Lyman-$\\alpha$ Absorbers (DLAs) in hydrodynamic cosmological simulations using the moving mesh code AREPO. We incorporate models of supernova and AGN feedback, and molecular hydrogen formation. We compare our simulations to the column density distribution function at $z=3$, the total DLA abundance at $z=2-4$, the measured DLA bias at $z=2$ and DLA metallicities at $z=2-4$. Our preferred models produce populations of DLAs in good agreement with most of these observations, except the DLA abundance at $z < 3$, which we show requires stronger feedback in $10^{11-12} h^{-1} M_\\odot$ mass halos. While the DLA population probes a range of halo masses, we find the cross-section is dominated by halos of mass $10^{10.5} h^{-1} M_\\odot$ at $z=3$ and $10^{11} h^{-1} M_\\odot$ at $z=2$. Simulations without feedback are in strong tension with all these observables, indicating a need for strong stellar feedback at $z=2-4$ independently of the star formation th...
Grid-Current-Feedback Active Damping for LCL Resonance in Grid-Connected Voltage-Source Converters
Wang, Xiongfei; Blaabjerg, Frede; Loh, Poh Chiang
2016-01-01
This paper investigates active damping of LCL-filter resonance in a grid-connected voltage-source converter with only grid-current feedback control. Basic analysis in the s-domain shows that the proposed damping technique with a negative high-pass filter along its damping path is equivalent to adding a virtual impedance across the grid-side inductance. This added impedance is more precisely represented by a series RL branch in parallel with a negative inductance. The negative inductance helps...
Stellar feedback efficiencies: supernovae versus stellar winds
Fierlinger, Katharina M; Ntormousi, Evangelia; Fierlinger, Peter; Schartmann, Marc; Ballone, Alessandro; Krause, Martin G H; Diehl, Roland
2015-01-01
Stellar winds and supernova (SN) explosions of massive stars ("stellar feedback") create bubbles in the interstellar medium (ISM) and insert newly produced heavy elements and kinetic energy into their surroundings, possibly driving turbulence. Most of this energy is thermalized and immediately removed from the ISM by radiative cooling. The rest is available for driving ISM dynamics. In this work we estimate the amount of feedback energy retained as kinetic energy when the bubble walls have decelerated to the sound speed of the ambient medium. We show that the feedback of the most massive star outweighs the feedback from less massive stars. For a giant molecular cloud (GMC) mass of 1e5 solar masses (as e.g. found in the Orion GMCs) and a star formation efficiency of 8% the initial mass function predicts a most massive star of approximately 60 solar masses. For this stellar evolution model we test the dependence of the retained kinetic energy of the cold GMC gas on the inclusion of stellar winds. In our model w...
Beck, Benjamin; Schiller, Noah
2013-01-01
This paper outlines a direct, experimental comparison between two established active vibration control techniques. Active vibration control methods, many of which rely upon piezoelectric patches as actuators and/or sensors, have been widely studied, showing many advantages over passive techniques. However, few direct comparisons between different active vibration control methods have been made to determine the performance benefit of one method over another. For the comparison here, the first control method, velocity feedback, is implemented using four accelerometers that act as sensors along with an analog control circuit which drives a piezoelectric actuator. The second method, negative capacitance shunt damping, consists of a basic analog circuit which utilizes a single piezoelectric patch as both a sensor and actuator. Both of these control methods are implemented individually using the same piezoelectric actuator attached to a clamped Plexiglas window. To assess the performance of each control method, the spatially averaged velocity of the window is compared to an uncontrolled response.
Relay feedback tuning of robust PID controllers with iso-damping property.
Chen, YangQuan; Moore, Kevin L
2005-02-01
A new tuning method for proportional-integral-derivative (PID) controller design is proposed for a class of unknown, stable, and minimum phase plants. We are able to design a PID controller to ensure that the phase Bode plot is flat, i.e., the phase derivative w.r.t. the frequency is zero, at a given frequency called the "tangent frequency" so that the closed-loop system is robust to gain variations and the step responses exhibit an iso-damping property. At the "tangent frequency," the Nyquist curve tangentially touches the sensitivity circle. Several relay feedback tests are used to identify the plant gain and phase at the tangent frequency in an iterative way. The identified plant gain and phase at the desired tangent frequency are used to estimate the derivatives of amplitude and phase of the plant with respect to frequency at the same frequency point by Bode's integral relationship. Then, these derivatives are used to design a PID controller for slope adjustment of the Nyquist plot to achieve the robustness of the system to gain variations. No plant model is assumed during the PID controller design. Only several relay tests are needed. Simulation examples illustrate the effectiveness and the simplicity of the proposed method for robust PID controller design with an iso-damping property.
Secondo, R; Venturini, M; Fox, J D; Rivetta, C H; Höfle, W
2011-01-01
Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.
An efficient delivery of DAMPs on the cell surface by the unconventional secretion pathway
Energy Technology Data Exchange (ETDEWEB)
Zhu, Haiyan; Wang, Lan; Ruan, Yuanyuan; Zhou, Lei; Zhang, Dongmei [Department of Biochemistry and Molecular Biology, Shanghai Medical Collage, Fudan University, Shanghai 200032 (China); Min, Zhihui [Biomedical Research Center, Zhongshan Hospital, Fudan University, Shanghai 200032 (China); Xie, Jianhui [Department of Biochemistry and Molecular Biology, Shanghai Medical Collage, Fudan University, Shanghai 200032 (China); Yu, Min, E-mail: minyu@shmu.edu.cn [Department of Biochemistry and Molecular Biology, Shanghai Medical Collage, Fudan University, Shanghai 200032 (China); Gu, Jianxin [Department of Biochemistry and Molecular Biology, Shanghai Medical Collage, Fudan University, Shanghai 200032 (China)
2011-01-21
Research highlights: {yields} Hsp60 transported to cell surface through the classical secretory pathway was modified with N-glycosylation. {yields} HSAPB-N18 could efficiently deliver Hsp60 to the cell surface via the unconventional secretory pathway. {yields} Cell surface Hsp60 delivered by HASPB-N18 has a proper conformation. {yields} HASPB-N18 is an efficient delivery signal for other DAMP molecules such as Hsp70 and HMGB1. -- Abstract: Damage-associated molecular patterns (DAMPs) are signals released from dying cells evoking the immune system response in several inflammatory disorders. In normal situations, many of DAMPs are nuclear or cytosolic proteins with defined intracellular function, but they could be found on the cell surface following tissue injury. The biological function of the translocated DAMPs is still not well known and an efficient delivery of these molecules on the cell surface is required to clarify their biological effects. In this study, we demonstrated that an unclassical secretory signal peptide, N-terminal 18 amino acids of HASPB (HASPB-N18), could efficiently deliver Hsp60, Hsp70, and HMGB1 on the cell surface. Furthermore, the delivery of these molecules on the cell surface by HASPB-N18 is not limited to a special cell line because several cell lines could use this delivery signal to deliver these molecules on the cell surface. Moreover, we demonstrated that Hsp60 on the cell surface delivered by HASPB-N18 could be recognized by a soluble form of LOX-1, which implies that DAMPs on the cell surface delivered by HASPB-N18 have a proper conformation during transport. Therefore, delivery of DAMPs by HASPB-N18 is a reliable model to further understand the biological significance of DAMPs on the cell surface.
Energy Technology Data Exchange (ETDEWEB)
Schwarz, H.D.; Judkins, J.G.
1987-03-01
The synchronous phase of a bunch of positrons or electrons being damped in a SLAC Linear Collider (SLC) damping ring is dependent on beam intensity. Injection for alternate bunches into the SLC linac from the damping rings should occur at a constant phase. A phase detector was developed allowing the measurement of phase of a single-stored bunch in the presence of a second bunch in reference to the phase of the linac. The single-bunch phase is derived from beam position monitor signals using a switching scheme to separate the two bunches circulating in each damping ring. The hardware is described including feedback loops to stabilize the extraction phase.
Directory of Open Access Journals (Sweden)
masoud aliakbar golkar
2011-11-01
Full Text Available Nowadays since the speed of reaching to response is getting more important, the random searching algorithms are mostly used instead of the overall search of the problem space. This paper presents the application and the performance comparison of HBMO and PSO optimization techniques for designing an output feedback damping controller for STATCOM in order to enhance the damping of power system. The problem of the damping controller design is considered as an optimization problem with a multi-purpose criterion function and it is solved by HBMO and PSO algorithms. This controller is designed in order to transmit unstable electromechanical modes to the specific area of the complex plane. The proposed controller performance is confirmed by the analysis of the eigenvalue and nonlinear time-domain simulation under various disturbances with both control parameters of STATCOM (capacitor voltage control and terminal voltage control. Simulation results illustrate that the designed controller by HBMO performs better than PSO in finding the solution. Moreover, the design of the controller based on the capacitor voltage control in comparison with terminal voltage control has better low frequency oscillation damping and it increases the dynamical stability of the power system.
The effect of passive damping on feedback control performance of flexible manipulators
Energy Technology Data Exchange (ETDEWEB)
Lew, J.Y.; Evans, M.S.
1994-06-01
This paper discusses the effect of passive damping on long-reach manipulators. Specifically, this paper explains how the addition of structural damping affects the closed-loop system response of the manipulators. A single-link flexible manipulator is used to illustrate the effects of passive damping on the location of the system`s pole s and zeros. The corresponding performance of the system with modified pole/zero locations is discussed. The analysis is performed including colocated and noncolocated flexible-link manipulators.
Ombud's corner: Sincere feedback favours efficiency
Vincent Vuillemin
2012-01-01
In this series, the Bulletin aims to explain the role of the Ombuds at CERN by presenting practical examples of misunderstandings that could have been resolved by the Ombuds if he had been contacted earlier. Please note that, in all the situations we present, the names are fictitious and used only to improve clarity. Everyone can certainly agree that good communication is very important. Leaders should try to give feedback to their supervisees on their work and career so they can benefit from this information. Giving feedback provides personnel with an opportunity to understand what can they can improve or correct should there be some weaknesses in their technical or behavioural skills. It is also a chance to be congratulated for their efforts and dedication. Feedback should be given in a sincere and honest way, so that the person can accept the comments. The keys to giving feedback are: • Speak the truth – even if it is difficult, have the courage to do it; &a...
DEFF Research Database (Denmark)
Wang, Xiongfei; Blaabjerg, Frede; Loh, Poh Chiang
2014-01-01
the grid-side inductor, and the use of a high-pass filter with a negative sign shapes the virtual impedance by an RL damper paralleled by a negative inductance. It is further found that such a negative virtual inductance plays a critical role in mitigating the phase lag caused by the time delay...... in a digital control system. The instability induced by the negative virtual resistance, which is commonly experienced in the feedback-type active damping, can thus be avoided. A systematic design method of the highpass filter is also proposed by the help of root locus analysis in the discrete z-domain. Lastly...
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 ...
Fleet Feedback and Fleet Efficiency Metrics
Energy Technology Data Exchange (ETDEWEB)
Singer, Mark R [National Renewable Energy Laboratory (NREL), Golden, CO (United States)
2017-09-05
The Marine Corps have 10 years of experience implementing a telematics program and several lessons to share with partner agencies. This presentation details results of a Marine Corps survey as well as methods of using telematics to promote fleet efficiency and optimize the vehicle acquisition process.
Mahéo, Laurent; Grolleau, Vincent; Rio, Gérard
2009-11-01
To deal with dynamic and wave propagation problems, dissipative methods are often used to reduce the effects of the spurious oscillations induced by the spatial and time discretization procedures. Among the many dissipative methods available, the Tchamwa-Wielgosz (TW) explicit scheme is particularly useful because it damps out the spurious oscillations occurring in the highest frequency domain. The theoretical study performed here shows that the TW scheme is decentered to the right, and that the damping can be attributed to a nodal displacement perturbation. The FEM study carried out using instantaneous 1-D and 3-D compression loads shows that it is useful to display the damping versus the number of time steps in order to obtain a constant damping efficiency whatever the size of element used for the regular meshing. A study on the responses obtained with irregular meshes shows that the TW scheme is only slightly sensitive to the spatial discretization procedure used. To cite this article: L. Mahéo et al., C. R. Mecanique 337 (2009).
Efficiency at maximum power of a discrete feedback ratchet
Jarillo, Javier; Tangarife, Tomás; Cao, Francisco J.
2016-01-01
Efficiency at maximum power is found to be of the same order for a feedback ratchet and for its open-loop counterpart. However, feedback increases the output power up to a factor of five. This increase in output power is due to the increase in energy input and the effective entropy reduction obtained as a consequence of feedback. Optimal efficiency at maximum power is reached for time intervals between feedback actions two orders of magnitude smaller than the characteristic time of diffusion over a ratchet period length. The efficiency is computed consistently taking into account the correlation between the control actions. We consider a feedback control protocol for a discrete feedback flashing ratchet, which works against an external load. We maximize the power output optimizing the parameters of the ratchet, the controller, and the external load. The maximum power output is found to be upper bounded, so the attainable extracted power is limited. After, we compute an upper bound for the efficiency of this isothermal feedback ratchet at maximum power output. We make this computation applying recent developments of the thermodynamics of feedback-controlled systems, which give an equation to compute the entropy reduction due to information. However, this equation requires the computation of the probability of each of the possible sequences of the controller's actions. This computation becomes involved when the sequence of the controller's actions is non-Markovian, as is the case in most feedback ratchets. We here introduce an alternative procedure to set strong bounds to the entropy reduction in order to compute its value. In this procedure the bounds are evaluated in a quasi-Markovian limit, which emerge when there are big differences between the stationary probabilities of the system states. These big differences are an effect of the potential strength, which minimizes the departures from the Markovianicity of the sequence of control actions, allowing also to
Kuiper, Rolf; Yorke, Harold W
2016-01-01
We perform two-dimensional axially symmetric radiation-hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, the ratio of ejection to accretion rates, and the strength of the wide angle disk wind component. The star formation efficiency, i.e. the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects: First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow are larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very we...
Energy Technology Data Exchange (ETDEWEB)
Roth, Andre
2012-12-15
At the Electron Stretcher Facility ELSA an upgrade of the internal beam current up to 200 mA would be desirable in order to increase the intensity of the extracted electron beam for the future experimental hadron physics program. However, such an upgrade is mainly limited by the excitation of coherent beam instabilities in the stretcher ring. As active counteraction, broadband bunch-by-bunch feedback-systems for the longitudinal, as well as for both transverse planes were installed. After detection of the motion of each of the 27 4 stored bunches via beam position monitors, the systems determine independent correction signals for each bunch using digital signal processors. The amplified correction signals are applied to the beam by means of broadband longitudinal and transverse kicker structures. The detailed setup, the commissioning procedure and measurement results of the damping performance of the systems are presented. In addition, the operation of the longitudinal system during the fast energy ramp of 4 GeV/s from 1.2 GeV to 3.2 GeV is investigated.
On the Feedback Efficiency of Active Galactic Nuclei
Kurosawa, Ryuichi; Proga, Daniel; Nagamine, Kentaro
2009-12-01
We measure and analyze the energy, momentum, and mass feedback efficiencies due to radiation from active galactic nuclei (AGNs) in relatively large-scale outflows (from ~0.01 to ~10 pc). Our measurements are based on the two-dimensional (axisymmetric) and time-dependent radiation-hydrodynamical simulations recently presented in Kurosawa & Proga. In that paper, we studied outflows from a slowly rotating (sub-Keplerian) infalling gas driven by the energy and pressure of the radiation emitted by the AGNs. These simulations follow the dynamics of gas under the influence of the gravity of the central 108 M sun black hole (BH) on scales from ~0.01 to ~10 pc. They self-consistently couple the accretion luminosity with the mass inflow rate at the smallest radius (our proxy for the mass-accretion rate, \\dot{M}_{a}). Over 30 simulations have been performed to investigate how the results depend on the gas density at the outer radius, ρo. A key feature of these simulations is that the radiation field and consequently the gas dynamics are axisymmetric, but not spherically symmetric. Therefore, the gas inflow and outflow can occur at the same time. We compare our \\dot{M}_{a}-ρo relation with that predicted by the Bondi accretion model. For high luminosities comparable to the Eddington limit, the power-law fit (\\dot{M}_{a} ∝ ρ _{o}^{q}) to our models yields q ≈ 0.5 instead of q = 1.0, which is predicted by the Bondi model. This difference is caused by the outflows which are important for the overall mass budget at high luminosities. The maximum momentum and mass feedback efficiencies found in our models are ~10-2 and ~10-1, respectively. However, the outflows are much less important energetically: the thermal and kinetic powers in units of the radiative luminosity are ~10-5 and ~10-4, respectively. In addition, the efficiencies do not increase monotonically with the accretion luminosity but rather peak around the Eddington limit beyond which a steady-state disk
Wolahan, Stephanie M; Li, Zhao; Hsu, Chao-Hsiung; Huang, Shing-Jong; Clubb, Robert; Hwang, Lian-Pin; Lin, Yung-Ya
2014-11-01
Accurate temperature measurement is a requisite for obtaining reliable thermodynamic and kinetic information in all NMR experiments. A widely used method to calibrate sample temperature depends on a secondary standard with temperature-dependent chemical shifts to report the true sample temperature, such as the hydroxyl proton in neat methanol or neat ethylene glycol. The temperature-dependent chemical shift of the hydroxyl protons arises from the sensitivity of the hydrogen-bond network to small changes in temperature. The frequency separation between the alkyl and the hydroxyl protons are then converted to sample temperature. Temperature measurements by this method, however, have been reported to be inconsistent and incorrect in modern NMR, particularly for spectrometers equipped with cryogenically-cooled probes. Such errors make it difficult or even impossible to study chemical exchange and molecular dynamics or to compare data acquired on different instruments, as is frequently done in biomolecular NMR. In this work, we identify the physical origins for such errors to be unequal amount of dynamical frequency shifts on the alkyl and the hydroxyl protons induced by strong radiation damping (RD) feedback fields. Common methods used to circumvent RD may not suppress such errors. A simple, easy-to-implement solution was demonstrated that neutralizes the RD effect on the frequency separation by a "selective crushing recovery" pulse sequence to equalize the transverse magnetization of both spin species. Experiments using cryoprobes at 500 MHz and 800 MHz demonstrated that this approach can effectively reduce the errors in temperature measurements from about ±4.0 K to within ±0.4 K in general.
Babakhani, Bayan; Vries, de Theo J.A.; Amerongen, van Job
2012-01-01
Adding active damping in a collocated fashion to a badly damped mechanical plant guarantees the stability of the closed-loop system. However, collocation is lost beyond a certain frequency due to restrictions imposed by practical implementation. In this paper, the effect of the first noncollocated m
Directory of Open Access Journals (Sweden)
Iman Lorzadeh
2016-08-01
Full Text Available Inductive-capacitive-inductive (LCL-type line filters are widely used in grid-connected voltage source inverters (VSIs, since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion of third order LCL network complicates the current control design regarding the system stability issues because of an inherent resonance peak which appears in the open-loop transfer function of the inverter control system near the control stability boundary. To avoid passive (resistive resonance damping solutions, due to their additional power losses, active damping (AD techniques are often applied with proper control algorithms in order to damp the LCL filter resonance and stabilize the system. Among these techniques, the capacitor current feedback (CCF AD has attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking into account the effect of computation and pulse width modulation (PWM delays along with a detailed analysis on proper design and implementation.
DEFF Research Database (Denmark)
Meng, Lexuan; Dragicevic, Tomislav; Quintero, Juan Carlos Vasquez
2015-01-01
and applied for maintaining system stability. Hardware-in-the-loop simulations are conducted to validate the effectiveness of this method. The results show that the system efficiency is improved by using tertiary optimization control and the desired transient response is ensured with system damping secondary...
Gondek, Dawid; Edbrooke-Childs, Julian; Fink, Elian; Deighton, Jessica; Wolpert, Miranda
2016-05-01
Due to recent increases in the use of feedback from outcome measures in mental health settings, we systematically reviewed evidence regarding the impact of feedback from outcome measures on treatment effectiveness, treatment efficiency, and collaborative practice. In over half of 32 studies reviewed, the feedback condition had significantly higher levels of treatment effectiveness on at least one treatment outcome variable. Feedback was particularly effective for not-on-track patients or when it was provided to both clinicians and patients. The findings for treatment efficiency and collaborative practice were less consistent. Given the heterogeneity of studies, more research is needed to determine when and for whom feedback is most effective.
Efficiency at maximum power for an Otto engine with ideal feedback
Wang, Honghui; He, Jizhou; Wang, Jianhui; Wu, Zhaoqi
2016-10-01
We propose an Otto heat engine that undergoes processes involving a special class of feedback and analyze theoretically its response. We use stochastic thermodynamics to determine the performance characteristics of the heat engine and indicate the possibility that its maximum efficiency can surpass the Carnot value. The analytical expression for efficiency at maximum power, including the effects resulting from feedback, reduces to that previously derived based on an engine without feedback.
Analytical research of damping efficiency and heat generation of magnetorheological damper
Mitrouchev, P.; Klevinskis, A.; Bucinskas, V.; Dragasius, E.; Udris, D.; Morkvenaite-Vilkonciene, I.
2017-06-01
Magnetorheological (MR) dampers are currently used in various areas, such as: human prosthetics, seismic protection, active suspensions, safety systems, amongst other. This paper deals with the proper design of a MR damper in the innovative field for vibration control. A methodology for calculation some principal characteristics of the damper such as: electromagnet’s magnetic field value, emitted heat and damping force is presented. The methodology is based on analytic calculations of the characteristics and finite element method analysis. The obtained theoretical results were confirmed by performed experimental tests, thanks to a specially designed and realised MR damper. Two main geometrical characteristics of the damper, namely: piston thickness and electromagnet width were optimally chosen, thus allowing to reach maximum damping force.
Anand, V; Narendran, R
2016-09-01
In this paper, a technique for estimation of state variables and control of a class of electromechanical system is proposed. Initially, an attempt is made on rudimentary pole placement technique for the control of rotor position and angular velocity profiles of Permanent Magnet Stepper Motor. Later, an alternative approach is analyzed using feedback linearization method to reduce the error in tracking performances. A damping control scheme was additionally incorporated into the feedback linearization system in order to nullify the persistent oscillations present in the system. Furthermore, a robust backstepping controller with high efficacy is put forth to enhance the overall performance and to carry out disturbance rejection. The predominant advantage of this control technique is that it does not require the DQ Transformation of the motor dynamics. A Lyapunov candidate was employed to ensure global asymptotical stability criterion. Also, a nonlinear observer is presented to estimate the unknown states namely load torque and rotor angular velocity, even under load uncertainty conditions. Finally, the performances of all the aforementioned control schemes and estimation techniques are compared and analyzed extensively through simulation.
Kuiper, Rolf; Turner, Neal J.; Yorke, Harold W.
2016-11-01
We perform two-dimensional axially symmetric radiation hydrodynamic simulations to assess the impact of outflows and radiative force feedback from massive protostars by varying when the protostellar outflow starts, and to determine the ratio of ejection to accretion rates and the strength of the wide-angle disk wind component. The star-formation efficiency, i.e., the ratio of final stellar mass to initial core mass, is dominated by radiative forces and the ratio of outflow to accretion rates. Increasing this ratio has three effects. First, the protostar grows slower with a lower luminosity at any given time, lowering radiative feedback. Second, bipolar cavities cleared by the outflow become larger, further diminishing radiative feedback on disk and core scales. Third, the higher momentum outflow sweeps up more material from the collapsing envelope, decreasing the protostar's potential mass reservoir via entrainment. The star-formation efficiency varies with the ratio of ejection to accretion rates from 50% in the case of very weak outflows to as low as 20% for very strong outflows. At latitudes between the low-density bipolar cavity and the high-density accretion disk, wide-angle disk winds remove some of the gas, which otherwise would be part of the accretion flow onto the disk; varying the strength of these wide-angle disk winds, however, alters the final star-formation efficiency by only ±6%. For all cases, the opening angle of the bipolar outflow cavity remains below 20° during early protostellar accretion phases, increasing rapidly up to 65° at the onset of radiation pressure feedback.
Achieving Energy Efficiency Through Real-Time Feedback
Energy Technology Data Exchange (ETDEWEB)
Nesse, Ronald J.
2011-09-01
Through the careful implementation of simple behavior change measures, opportunities exist to achieve strategic gains, including greater operational efficiencies, energy cost savings, greater tenant health and ensuing productivity and an improved brand value through sustainability messaging and achievement.
Richardson, Barbara K
2004-12-01
The emergency department provides a rich environment for diverse patient encounters, rapid clinical decision making, and opportunities to hone procedural skills. Well-prepared faculty can utilize this environment to teach residents and medical students and gain institutional recognition for their incomparable role and teamwork. Giving effective feedback is an essential skill for all teaching faculty. Feedback is ongoing appraisal of performance based on direct observation aimed at changing or sustaining a behavior. Tips from the literature and the author's experience are reviewed to provide formats for feedback, review of objectives, and elements of professionalism and how to deal with poorly performing students. Although the following examples pertain to medical student education, these techniques are applicable to the education of all adult learners, including residents and colleagues. Specific examples of redirection and reflection are offered, and pitfalls are reviewed. Suggestions for streamlining verbal and written feedback and obtaining feedback from others in a fast-paced environment are given. Ideas for further individual and group faculty development are presented.
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-01-01
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids. PMID:27633351
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-09-01
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids.
Lisi, A D; Illuminati, F; Vitali, D; Lisi, Antonio Di; Siena, Silvio De; Illuminati, Fabrizio; Vitali, David
2004-01-01
We introduce an efficient and robust scheme to generate maximally entangled states of two atomic ensembles. The scheme is based on quantum non-demolition measurements of total atomic populations and on quantum feedback conditioned by the measurements outputs. The high efficiency of the scheme is tested and confirmed numerically for photo-detection with ideal efficiency as well as in the presence of losses.
Nguyen, Minh-Hai; Pai, Chi-Feng; Ralph, Daniel C.; Buhrman, Robert A.
2015-03-01
The spin Hall effect (SHE) in ferromagnet/heavy metal bilayer structures has been demonstrated to be a powerful means for producing pure spin currents and for exerting spin-orbit damping-like and field-like torques on the ferromagnetic layer. Large spin Hall (SH) angles have been reported for Pt, beta-Ta and beta-W films and have been utilized to achieve magnetic switching of in-plane and out-of-plane magnetized nanomagnets, spin torque auto-oscillators, and the control of high velocity domain wall motion. For many of the proposed applications of the SHE it is also important to achieve an effective Gilbert damping parameter that is as low as possible. In general the spin orbit torques and the effective damping are predicted to depend directly on the spin-mixing conductance of the SH metal/ferromagnet interface. This opens up the possibility of tuning these properties with the insertion of a very thin layer of another metal between the SH metal and the ferromagnet. Here we will report on experiments with such trilayer structures in which we have observed both a large enhancement of the spin Hall torque efficiency and a significant reduction in the effective Gilbert damping. Our results indicate that there is considerable opportunity to optimize the effectiveness and energy efficiency of the damping-like torque through engineering of such trilayer structures. Supported in part by NSF and Samsung Electronics Corporation.
Ma, Shao-Qiang; Zhu, Han-Jie; Zhang, Guo-Feng
2017-04-01
The effects of different quantum feedback types on the estimation precision of the detection efficiency are studied. It is found that the precision can be more effective enhanced by a certain feedback type through comparing these feedbacks and the precision has a positive relation with detection efficiency for the optimal feedback when the system reach the state of dynamic balance. In addition, the bigger the proportion of |1> is the higher the precision is and we will not obtain any information about the parameter to be estimated if |0> is chosen as initial state for the feedback type λσz.
Loi, Shyeh Tjing; Papaloizou, John C. B.
2017-05-01
Stars are self-gravitating fluids in which pressure, buoyancy, rotation and magnetic fields provide the restoring forces for global modes of oscillation. Pressure and buoyancy energetically dominate, while rotation and magnetism are generally assumed to be weak perturbations and often ignored. However, observations of anomalously weak dipole mode amplitudes in red giant stars suggest that a substantial fraction of these are subject to an additional source of damping localized to their core region, with indirect evidence pointing to the role of a deeply buried magnetic field. It is also known that in many instances, the gravity-mode character of affected modes is preserved, but so far, no effective damping mechanism has been proposed that accommodates this aspect. Here we present such a mechanism, which damps the oscillations of stars harbouring magnetised cores via resonant interactions with standing Alfvén modes of high harmonic index. The damping rates produced by this mechanism are quantitatively on par with those associated with turbulent convection, and in the range required to explain observations, for realistic stellar models and magnetic field strengths. Our results suggest that magnetic fields can provide an efficient means of damping stellar oscillations without needing to disrupt the internal structure of the modes, and lay the groundwork for an extension of the theory of global stellar oscillations that incorporates these effects.
Power-Bandwidth Efficiency and Capacity of Wireless Feedback Communication Systems
Platonov, Anatoliy
2011-01-01
The paper is devoted to the analysis of problems appearing in optimisation and improvement of the power-bandwidth efficiency of digital communication feedback systems (FCS). There is shown that unlike digital systems, adaptive FCS with the analogue forward transmission allow full optimisation and derivation of optimal transmission-reception algorithm approaching their efficiency to the Shannon boundary. Differences between the forward channel capacity and capacity of adaptive FCS as communication unit, as well as their influence of the power-bandwidth efficiency of transmission are considered.
Lucas, William E.; Bonnell, Ian A.; Forgan, Duncan H.
2017-01-01
We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud's envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to ≈0.25 according to α, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.
Optimal Tuning of Amplitude Proportional Coulomb Friction Damper for Maximum Cable Damping
DEFF Research Database (Denmark)
Weber, Felix; Høgsberg, Jan Becker; Krenk, Steen
2010-01-01
This paper investigates numerically the optimal tuning of Coulomb friction dampers on cables, where the optimality criterion is maximum additional damping in the first vibration mode. The expression for the optimal friction force level of Coulomb friction dampers follows from the linear viscous...... damper via harmonic averaging. It turns out that the friction force level has to be adjusted in proportion to cable amplitude at damper position which is realized by amplitude feedback in real time. The performance of this adaptive damper is assessed by simulated free decay curves from which the damping...... is estimated. It is found that the damping efficiency agrees well with the expected value at the theoretical optimum. However, maximum damping is larger and achieved at a force to amplitude ratio of 1.4 times the analytical value. Investigations show that the increased damping results from energy spillover...
Strijbos, Jan-Willem; Narciss, Susanne; Duennebier, Katrin
2010-01-01
Peer-feedback content is a core component of peer assessment, but the impact of various contents of feedback is hardly studied. Participants in the study were 89 graduate students who were assigned to four experimental and a control group. Experimental groups received a scenario with concise general
Angelo, T; Barbalho, G N; Gelfuso, G M; Gratieri, T
2016-09-01
There is yet no consensus among prescribers whether minoxidil (MXD) formulations should be applied on wet/damp or dry scalp and no clear FDA guidelines on the matter. We hypothesized that the use of MXD on damp scalp may lead to higher drug penetration. First, because the drug diffusion and consequent deposition into the hair follicle may be favored when follicle cast is humid. Second, because humidity may also prevent drug crystallization and, therefore, maintain a higher thermodynamic activity for longer periods, which leads to increased penetration. Following in vitro experiments on rat and porcine skin we confirmed the hypothesis, which could markedly improve treatment effectiveness. © 2016 Wiley Periodicals, Inc.
DEFF Research Database (Denmark)
Lorzadeh, Iman; Askarian Abyaneh, Hossein; Savaghebi, Mehdi
2016-01-01
attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking...
Directory of Open Access Journals (Sweden)
Friedrich-W. Wellmer
2015-11-01
Full Text Available Sustainable development with regard to non-renewable resources can best be defined in terms of the inter-generational challenge of the Brundtland commission and the intra-generational challenge worked out in Agenda 21 of the 1992 Rio de Janeiro conference of United Nations Conference on Environment and Development (UNCED. In meeting these challenges, the trilemma of security of supply under conditions of economic viability and environmental sustainability also needs to be addressed in order to achieve sustainable development. To fulfil the natural resources needs of future generations we have three resources at our disposal: (1 the geosphere or primary resources; (2 the technosphere or secondary resources and (3 human ingenuity and creativity driving innovation. Man does not need natural resources as such, only the intrinsic property of a material that enables the fulfilment of a function is required. Any material that can perform the same function more efficiently or cheaply can replace any other material. In our constant drive to secure the supply of efficient raw materials, the feedback control cycle plays an indispensable role by virtue of it reacting to price signals on both the supply and demand sides. The feedback cycle of course goes hand in hand with a continuous learning process. On the supply side, the learning effects are in technology development around primary resources and the increased use of secondary resources; on the demand side with thriftier use of raw materials.
DEFF Research Database (Denmark)
Della Valle, G.; Bozhevolnyi, S. I.
2012-01-01
Recent results on radiation damping suppression in individual plasmonic resonators using conformal bending of the structure, which suppresses the electric-dipole response in favor of magnetic dipole one, are overviewed. It is demonstrated that bending of linear plasmonic nano-antennas increases...... significantly their Q factors above the electrostatic limit while preserving the nature of resonance along with its exceptional features, such as linear size-dependent tunability and robust field enhancement. The approach, which makes use of strong lateral confinement exhibited by the slow plasmonic modes (slow...
Hybrid feedback feedforward: An efficient design of adaptive neural network control.
Pan, Yongping; Liu, Yiqi; Xu, Bin; Yu, Haoyong
2016-04-01
This paper presents an efficient hybrid feedback feedforward (HFF) adaptive approximation-based control (AAC) strategy for a class of uncertain Euler-Lagrange systems. The control structure includes a proportional-derivative (PD) control term in the feedback loop and a radial-basis-function (RBF) neural network (NN) in the feedforward loop, which mimics the human motor learning control mechanism. At the presence of discontinuous friction, a sigmoid-jump-function NN is incorporated to improve control performance. The major difference of the proposed HFF-AAC design from the traditional feedback AAC (FB-AAC) design is that only desired outputs, rather than both tracking errors and desired outputs, are applied as RBF-NN inputs. Yet, such a slight modification leads to several attractive properties of HFF-AAC, including the convenient choice of an approximation domain, the decrease of the number of RBF-NN inputs, and semiglobal practical asymptotic stability dominated by control gains. Compared with previous HFF-AAC approaches, the proposed approach possesses the following two distinctive features: (i) all above attractive properties are achieved by a much simpler control scheme; (ii) the bounds of plant uncertainties are not required to be known. Consequently, the proposed approach guarantees a minimum configuration of the control structure and a minimum requirement of plant knowledge for the AAC design, which leads to a sharp decrease of implementation cost in terms of hardware selection, algorithm realization and system debugging. Simulation results have demonstrated that the proposed HFF-AAC can perform as good as or even better than the traditional FB-AAC under much simpler control synthesis and much lower computational cost.
Damping Undulators vs Damping Wigglers
Muchnoi, Nickolai
2016-01-01
Use of damping wigglers is a common technique for beam emittance reduction in the electron storage rings. The general approach to estimate damping effect is based on evaluation of several radiation integrals for a storage ring itself as well as for insertion devices. In this letter we show that a wiggler radiation integrals should be tweaked to account for the impact of lower harmonics of undulator radiation, which is an equivalent of Thomson scattering. Under certain conditions, these amendments play a decisive role in a formation of equilibrium emittance.
Efficiency of Blue Organic Light-emitting Diodes Enhanced by Employing an Exciton Feedback Layer
Institute of Scientific and Technical Information of China (English)
Qian-Qian Yu; Xu Zhang; Jing-Xuan Bi; Guan-Ting Liu; Qi-Wen Zhang; Xiao-Ming Wu; Yu-Lin Hua
2016-01-01
We report that a novel exciton feedback effect is observed by introducing the bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (BAlq) inserted between the emitting layer (EML) and the electron transporting layer in blue organic light emitting diodes.As an exciton feedback layer (EFL),the BAlq does not act as a traditional hole blocking effect.The design of this kind of device structure can greatly reduce excitons' quenching due to accumulated space charge at the exciton formation interface.Meanwhile,the non-radiative energy transfer from EFL to the EML can also be utilized to enhance the excitons' formation,which is confirmed by the test of photolumimescent transient lifetime decay and electroluminescence enhancement of these devices.Accordingly,the optimal device presents the improved performances with the maximum current e~ciency of 4.2 cd/A and the luminance of 24600cd/m2,which are about 1.45 times and 1.75 times higher than those of device A (control device) without the EFL,respectively.Simultaneously,the device shows an excellent color stability with a tiny offset of the CIE coordinates (Ax =±0.003,Ay =±0.004) and a relatively lower efficiency roll-off of 26.2％ under the driving voltage varying from 3 V to 10 V.
A bandwidth efficient two-user cooperative diversity system with limited feedback
Institute of Scientific and Technical Information of China (English)
LI Jing; GE JianHua; WANG Yong; TANG YunShuai; XIONG Xiong
2009-01-01
A two-user cooperative diversity system based on Alamouti signaling was proposed, which utilizes the orthogonal structure of Alamouti signaling to make cooperative users relay on the shared channel resources so that the spectral efficiency of the traditional cooperative system can be improved. When M-ary phase shift keying (M-PSK) modulation and an improved selection decode-and-forward (SDF) relaying protocol with limited feedback are used at the users and m(m ≥1) receive antennas are configured at the base station, the average bit-error-rata (BER) system performance for statistically similar uplink channels was derived and it was verified by simulations. Under various channel scenarios of interest, numerical and simulation results show that the diversity gain achieved and the BER performance of the proposed system increase with the interuser channel quality, and the full transmit diversity order of two can be obtained for sufficiently high interuser signal-to-noise ratios (SNRs).
Arfin, Scott K; Sarpeshkar, Rahul
2012-02-01
In this paper, we present a novel energy-efficient electrode stimulator. Our stimulator uses inductive storage and recycling of energy in a dynamic power supply. This supply drives an electrode in an adiabatic fashion such that energy consumption is minimized. It also utilizes a shunt current-sensor to monitor and regulate the current through the electrode via feedback, thus enabling flexible and safe stimulation. Since there are no explicit current sources or current limiters, wasteful energy dissipation across such elements is naturally avoided. The dynamic power supply allows efficient transfer of energy both to and from the electrode and is based on a DC-DC converter topology that we use in a bidirectional fashion in forward-buck or reverse-boost modes. In an exemplary electrode implementation intended for neural stimulation, we show how the stimulator combines the efficiency of voltage control and the safety and accuracy of current control in a single low-power integrated-circuit built in a standard .35 μm CMOS process. This stimulator achieves a 2x-3x reduction in energy consumption as compared to a conventional current-source-based stimulator operating from a fixed power supply. We perform a theoretical analysis of the energy efficiency that is in accord with experimental measurements. This theoretical analysis reveals that further improvements in energy efficiency may be achievable with better implementations in the future. Our electrode stimulator could be widely useful for neural, cardiac, retinal, cochlear, muscular and other biomedical implants where low power operation is important.
An Efficient Expert System Generator for Qualitative Feed-Back Loop Analysis
Directory of Open Access Journals (Sweden)
Manoj Kumar Jain
2012-04-01
Full Text Available Quite often the variables used in system analysis are qualitative in nature. They cannot be defined precisely, whereas software development for system analysis needs a mathematical framework with precise computations. It is not trivial to capture the uncertainty in the system.
Fuzzy sets provide us the facility to capture the uncertainty in the system. In normal crisp set where the membership of an element is always certain in a sense that it would be member or not of the given set. In contrast to this a membership functions or possibility (ranging from 0 to 1, including both values is assigned with each member. System analysis is done through system dynamics which is not very efficient. We present an efficient technique to generate expert system using fuzzy set. In our proposed approach five linguistic qualifiers are used for each variable, namely, Very Low (VL, Low (L, Medium (M, High (H, and Very High
(VH. We capture the influence or feedback in the system with the help of if then else rules and matrices are generated for them which are used for analysis. Complete methodology and its applicability are presented here.
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 ...
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...
Efficiency of Dynamical Friction in Presence of Black Hole Radiative Feedback
Buser, Alexander; Bogdanovic, Tamara; Park, KwangHo
2017-01-01
Dynamical friction is a physical mechanism thought to be responsible for pairing of supermassive black holes (SMBHs) in the aftermath of galactic mergers. It arises when a massive perturber traveling through a background medium creates in it a density wake. The wake, which trails the perturber on its trajectory, causes it to slow down by gravitational interaction. In the case of gas rich galactic mergers, dynamical friction allows the SMBHs immersed in gas to shed orbital energy and angular momentum and to sink to the center of the newly formed galaxy where they can form gravitationally bound pairs. The SMBHs which are subject to gaseous dynamical friction inevitably accrete some of the surrounding gas, giving rise to the emission of ionizing radiation that emerges from the innermost parts of their accretion flows. This radiation can dramatically modify the thermodynamic properties of the surrounding gas including the density wake. We investigate the effect of this form of radiative feedback on the physical properties of the wake, efficiency of dynamical friction and pairing of SMBHs in galactic mergers.
Apker, Gregory A; Dyson, Keith; Frantz, Garrett; Buneo, Christopher A
2015-01-01
Recent studies have shown that patterns of endpoint variability following double-step reach sequences reflect the influence of both planning and execution-related processes, but are strongly dominated by noise associated with the online updating of movement plans based on visual feedback. However, it is currently unclear whether these results reflect the dominant arm/hemisphere's postulated specialization for visual feedback processing, or whether these effects reflect a more general "arm/hemisphere independent" preference for visual feedback in the control of reaching. To explore this, twelve subjects performed double-step reach sequences with their dominant and non-dominant arms to targets in 3D space with and without visual feedback of the arm. Variability was quantified using the volumes, aspect ratios, and orientations of 95% confidence ellipsoids fit to the distributions of reach endpoints. In consonance with previous findings, the availability of visual feedback resulted in ellipsoids that were significantly smaller, had greater aspect ratios, and were more aligned with the depth axis than those performed without visual feedback. Moreover, the effects of vision on aspect ratio and orientation were similar in magnitude for the dominant and non-dominant arms, suggesting that noise associated with planning and execution-related processes is managed in a similar way by the sensorimotor systems of each arm. However, the degree to which vision decreased ellipsoid volume was found to be significantly greater for the dominant arm. This suggests that the feedback control system of the dominant arm uses visual information more efficiently to control reaches to visual targets.
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 the maximum attainable damping are found by maximizing the expression for the damping ratio. The theory is formulated for linear damper models, but may also be applied for non-linear dampers in terms of equivalent linear parameters for stiffness and damping, respectively. The format of the expressions...... only realizable by means of active control. The present thesis demonstrates how stiffness affects both the performance and the tuning of the damper. The final part of the thesis considers algorithmic damping in connection with Newmark time integration. The damping characteristics of the Newmark method...
Directory of Open Access Journals (Sweden)
Saeed Mehrpour
2017-03-01
Full Text Available Believing that providing EFL teachers with effective supervisory feedback during the post-observation conference is essential, researchers in the current study report on the views of Iranian EFL teachers and supervisors as to what constitutes effective supervisory feedback. Having conducted a qualitative content analysis of the data obtained from interviews with teachers and supervisors, researchers came up with a framework of the constituent elements of effective supervisory feedback, which includes 1 adopting a more creative approach 2 using above-the-utterance mitigation 3 gauging the teachers’ ZPD 4 being socioculturally sensitive 5 assessing the teachers’ beliefs and attitudes and 6 developing public relations. The results showed the teachers’ overall dissatisfaction with the present supervisory feedback. The paper concludes by suggestions to include supervisory training courses in the existing teacher development programs to better empower supervisors in their dealing with EFL supervisees throughout the country.
Energy Technology Data Exchange (ETDEWEB)
Ezura, Eizi; Yoshimoto, Shin-ichi; Akai, Kazunori [National Lab. for High Energy Physics, Tsukuba, Ibaraki (Japan)
1996-08-01
This paper describes the present status of the RF feedback development for the KEK B-Factory (KEKB). A preliminary experiment concerning the RF feedback using a parallel comb-filter was performed through a choke-mode cavity and a klystron. The RF feedback has been tested using the beam of the TRISTAN Main Ring, and has proved to be effective in damping the beam instability. (author)
Institute of Scientific and Technical Information of China (English)
金鸿章; 高妍南; 周生彬
2012-01-01
As marine robot navigating with low speed near surface, it has wiling motion caused by the disturbance of wave, which seriously influence its security and performance. Therefore, the zero-speed fin stabilizer system is applied to control the rolling motion. Based on the marine robot's dynamic properties and the features of the lift model of the zero speed fin stabilizer, a roll damping law is developed by using the approach of dynamic feedback linearization. The original system is extended to a new system with apseudostate variable and the system linearization is realized. The problem of the system's nonlinear input caused by the lift model of fin stabilizer is resolved. The theoretical proof and the simulation result show that the controller is stable and effective.%海洋机器人在近水面低速航行时,在海浪干扰下将产生横摇运动,严重影响机器人安全性能,因此利用零航速减摇鳍系统对横摇运动加以有效控制.针对机器人非线性运动模型及零航速减摇鳍升力模型的特点,利用动态反馈线性化方法设计横摇减摇控制规律.该方法通过将原系统扩展为含有伪状态变量的新系统,实现系统线性化,解决由减摇鳍升力模型引起的系统非线性形式控制输入的问题.理论证明及仿真结果表明该横摇控制规律是稳定有效的.
Leger, Lawrence A.; Glass, Karligash; Katsiampa, Paraskevi; Liu, Shibo; Sirichand, Kavita
2017-01-01
We evaluate feedback methods for oral presentations used in training non-quantitative research skills (literature review and various associated tasks). Training is provided through a credit-bearing module taught to MSc students of banking, economics and finance in the UK. Monitoring oral presentations and providing "best practice"…
Leger, Lawrence A.; Glass, Karligash; Katsiampa, Paraskevi; Liu, Shibo; Sirichand, Kavita
2017-01-01
We evaluate feedback methods for oral presentations used in training non-quantitative research skills (literature review and various associated tasks). Training is provided through a credit-bearing module taught to MSc students of banking, economics and finance in the UK. Monitoring oral presentations and providing "best practice"…
Lintz, M.; Phung, D. H.; Coulon, J.-P.; Faure, B.; Lévèque, T.
2017-02-01
We have achieved distributed feedback laser diode line narrowing by simultaneously acting on the diode current via a feed-back loop and on an external electrooptic phase modulator in feed-forward actuator. This configuration turns out to be very efficient in reaching large bandwidth in the phase correction: up to 15 MHz with commercial laser control units. About 98% of the laser power undergoes narrowing. The full width at half maximum of the narrowed optical spectrum is of less than 4 kHz. This configuration appears to be very convenient as the delay in the feed-forward control electronics is easily compensated for by a 20 m optical fiber roll.
Magnetic damping of ski vibrations
Energy Technology Data Exchange (ETDEWEB)
Yonnet, J.-P. [CNRS, St. Martin d' Heres (France). Lab. d' Electrotech. de Grenoble; Patton, A.C.; Philippe; Arnould; Bressan, C. [CNRS, St. Martin d' Heres (France). Lab. d' Electrotech. de Grenoble]|[Skis Dynastar S.A., Sallanches (France)
1998-07-01
An original damping device has been developed to reduce ski vibrations. Ski movement is transmitted to a conductive sheet situated in a multipole magnetic field created by permanent magnets. The conductive sheet is simultaneously submitted to eddy current and friction forces, giving the damping effect. The eddy current damper is more efficient for high frequency than for low frequency vibrations and consequently is very well adapted to ski vibrations. Bench and snow tests show the positive effects of the damper, which will be commercially available before the end of this year. (orig.)
Efficiency of feedbacks for suppression of transverse instabilities of bunched beams
Burov, Alexey
2016-08-01
Which gain and phase have to be set for a bunch-by-bunch transverse damper, and at which chromaticity is it better to stay? These questions are considered for three models: the two-particle model with possible quadrupole wake, the author's nested head-tail (NHT) model with the broadband impedance, and the NHT with the LHC impedance model. Details of 2D areas of stability in the chromaticity-intensity and chromaticity-gain planes and possibilities to use them are discussed. It is shown that resistive feedbacks may generate asymmetry of the tune shift distribution, which requires positively-shifted stability diagrams.
Enhanced damping for bridge cables using a self-sensing MR damper
Chen, Z. H.; Lam, K. H.; Ni, Y. Q.
2016-08-01
This paper investigates enhanced damping for protecting bridge stay cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.
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...
Directory of Open Access Journals (Sweden)
Jianqiu Chen
Full Text Available Many previous studies focused on the removal capability for contaminants when the algae grown in an unexposed, unpolluted environment and ignored whether the feedback of algae to the toxic stress influenced the removal capability in a subsequent treatment batch. The present research investigated and compared algal feedback and removal efficiency in a sequencing batch reactor algae process (SBAR to remove cefradine. Three varied pollution load conditions (10, 30 and 60 mg/L were considered. Compared with the algal characteristics in the first treatment batch at 10 and 30 mg/L, higher algal growth inhibition rates were observed in the second treatment batch (11.23% to 20.81%. In contrast, algae produced more photosynthetic pigments in response to cefradine in the second treatment batch. A better removal efficiency (76.02% was obtained during 96 h when the alga treated the antibiotic at 60 mg/L in the first treatment batch and at 30 mg/L in the second treatment batch. Additionally, the removal rate per unit algal density was also improved when the alga treated the antibiotic at 30 or 60 mg/L in the first treatment batch, respectively and at 30 mg/L in the second treatment batch. Our result indicated that the green algae were also able to adapt to varied pollution loads in different treatment batches.
Sakurai, Y.; Vorobyov, E. I.; Hosokawa, T.; Yoshida, N.; Omukai, K.; Yorke, H. W.
2016-06-01
The formation of supermassive stars (SMSs) is a potential pathway to seed supermassive black holes in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper, we study the evolution of an accreting SMS and its UV emissivity with realistic variable accretion from a circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the protostellar accretion until the stellar mass exceeds 104 M⊙. The disc fragments by gravitational instability, creating many clumps that migrate inward to fall on to the star. The resulting accretion history is highly time-dependent: short episodic accretion bursts are followed by longer quiescent phases. We show that the disc for the direct collapse model is more unstable and generates greater variability than normal Pop III cases. Next, we conduct a stellar evolution calculation using the obtained accretion history. Our results show that, regardless of the variable accretion, the stellar radius monotonically increases with almost constant effective temperature at Teff ≃ 5000 K as the stellar mass increases. The resulting UV feedback is too weak to hinder accretion due to the low flux of stellar UV photons. The insensitivity of stellar evolution to variable accretion is attributed to the fact that time-scales of variability, ≲103 yr, are too short to affect the stellar structure. We argue that this evolution will continue until the SMS collapses to produce a black hole by the general relativistic instability after the mass reaches ≳105 M⊙.
Introduction to Landau Damping
Herr, W
2014-01-01
The mechanism of Landau damping is observed in various systems from plasma oscillations to accelerators. Despite its widespread use, some confusion has been created, partly because of the different mechanisms producing the damping but also due to the mathematical subtleties treating the effects. In this article the origin of Landau damping is demonstrated for the damping of plasma oscillations. In the second part it is applied to the damping of coherent oscillations in particle accelerators. The physical origin, the mathematical treatment leading to the concept of stability diagrams and the applications are discussed.
Marhauser, Frank
2017-06-01
Research and development for superconducting radio-frequency cavities has made enormous progress over the last decades from the understanding of theoretical limitations to the industrial mass fabrication of cavities for large-scale particle accelerators. Key technologies remain hot topics due to continuously growing demands on cavity performance, particularly when in pursuit of high quality beams at higher beam currents or higher luminosities than currently achievable. This relates to higher order mode (HOM) damping requirements. Meeting the desired beam properties implies avoiding coupled multi-bunch or beam break-up instabilities depending on the machine and beam parameters that will set the acceptable cavity impedance thresholds. The use of cavity HOM-dampers is crucial to absorb the wakefields, comprised by all beam-induced cavity Eigenmodes, to beam-dynamically safe levels and to reduce the heat load at cryogenic temperature. Cavity damping concepts may vary, but are principally based on coaxial and waveguide couplers as well as beam line absorbers or any combination. Next generation energy recovery linacs and circular colliders call for cavities with strong HOM-damping that can exceed the state-of-the-art, while the operating mode efficiency shall not be significantly compromised concurrently. This imposes major challenges given the rather limited damping concepts. A detailed survey of established cavities is provided scrutinizing the achieved damping performance, shortcomings, and potential improvements. The scaling of the highest passband mode impedances is numerically evaluated in dependence on the number of cells for a single-cell up to a nine-cell cavity, which reveals the increased probability of trapped modes. This is followed by simulations for single-cell and five-cell cavities, which incorporate multiple damping schemes to assess the most efficient concepts. The usage and viability of on-cell dampers is elucidated for the single-cell cavity since it
Query Efficient PTAS for Minimum Feedback Arc-Set in Tournaments
Ailon, Nir
2010-01-01
We study the problem of Minimum Feedback Arc-Set in Tournaments (MFAST) in a setting where each edge from the input graph is given for a cost, and computations are done for free. We show that a recent PTAS by Kenyon and Schudy from 2007 in a standard computation model (input for free, computation costs) can be converted into a algorithm that requires observing only a sample of the input, with a similar approximation guarantee. Viewed as a machine learning problem, MFAST can be viewed as a supervised learning problem with a finite input distribution consisting of $O(n^2)$ pairs of elements, endowed with an inconsistent (agnostic) preference function. The learner samples preferences and outputs a concept (a permutation), while trying to minimize the loss, defined as the number of mistakes of the output permutation summed over the entire preference space. The algorithm we present constitutes an active learning algorithm, because the preferences used are chosen adaptively by the learner. Viewed as a noisy sorting...
Directory of Open Access Journals (Sweden)
V. Sharma
2011-08-01
Full Text Available This study demonstrates the use of a high-performance feedback neural network optimizer based on a new idea of successive approximation for finding the hourly optimal release schedules of interconnected multi-reservoir power system in such a way to minimize the overall cost of thermal generations spanned over the planning period. The main advantages of the proposed neural network optimizer over the existing neural network optimization models are that no dual variables, penalty parameters or lagrange multipliers are required. This network uses a simple structure with the least number of state variables and has better asymptotic stability. For an arbitrarily chosen initial point, the trajectory of the network converges to an optimal solution of the convex nonlinear programming problem. The proposed optimizer has been tested on a nonlinear practical system consisting of a multi-chain cascade of four linked reservoir type hydro-plants and a number of thermal units represented by a single equivalent thermal power plant and so obtained results have been validated using conventional conjugate gradient method and genetic algorithm based approach.
Sakurai, Yuya; Hosokawa, Takashi; Yoshida, Naoki; Omukai, Kazuyuki; Yorke, Harold W
2015-01-01
The formation of SMSs is a potential pathway to seed SMBHs in the early universe. A critical issue for forming SMSs is stellar UV feedback, which may limit the stellar mass growth via accretion. In this paper we study the evolution of an accreting SMS and its UV emissivity under conditions of realistic variable accretion from a self-gravitating circumstellar disc. First we conduct a 2D hydrodynamical simulation to follow the long-term protostellar accretion until the stellar mass exceeds $10^4~M_\\odot$. The disc fragments due to gravitational instability, creating a number of small clumps that rapidly migrate inward to fall onto the star. The resulting accretion history is thus highly time-dependent: short episodic accretion bursts are followed by longer, relative quiescent phases. We show that the circumstellar disc for the so-called direct collapse model is more unstable and generates greater variability over shorter timescales than normal Pop III cases. We conduct a post-process stellar evolution calculati...
Digital notch filter based active damping for LCL filters
DEFF Research Database (Denmark)
Yao, Wenli; Yang, Yongheng; Zhang, Xiaobin
2015-01-01
. In contrast, the active damping does not require any dissipation elements, and thus has become of increasing interest. As a result, a vast of active damping solutions have been reported, among which multi-loop control systems and additional sensors are necessary, leading to increased cost and complexity....... In this paper, a notch filter based active damping without the requirement of additional sensors is proposed, where the inverter current is employed as the feedback variable. Firstly, a design method of the notch filter for active damping is presented. The entire system stability has then been investigated...... in the z-domain. Simulations and experiments are carried out to verify the proposed active damping method. Both results have confirmed that the notch filter based active damping can ensure the entire system stability in the case of resonances with a good system performance....
Passive damping technology demonstration
Holman, Robert E.; Spencer, Susan M.; Austin, Eric M.; Johnson, Conor D.
1995-05-01
A Hughes Space Company study was undertaken to (1) acquire the analytical capability to design effective passive damping treatments and to predict the damped dynamic performance with reasonable accuracy; (2) demonstrate reasonable test and analysis agreement for both baseline and damped baseline hardware; and (3) achieve a 75% reduction in peak transmissibility and 50% reduction in rms random vibration response. Hughes Space Company teamed with CSA Engineering to learn how to apply passive damping technology to their products successfully in a cost-effective manner. Existing hardware was selected for the demonstration because (1) previous designs were lightly damped and had difficulty in vibration test; (2) multiple damping concepts could be investigated; (3) the finite element model, hardware, and test fixture would be available; and (4) damping devices could be easily implemented. Bracket, strut, and sandwich panel damping treatments that met the performance goals were developed by analysis. The baseline, baseline with damped bracket, and baseline with damped strut designs were built and tested. The test results were in reasonable agreement with the analytical predictions and demonstrated that the desired reduction in dynamic response could be achieved. Having successfully demonstrated this approach, it can now be used with confidence for future designs as a means for reducing weight and enhancing reliability.
Raskutti, Sudhir; Ostriker, Eve C.; Skinner, M. Aaron
2016-10-01
Radiation feedback from stellar clusters is expected to play a key role in setting the rate and efficiency of star formation in giant molecular clouds. To investigate how radiation forces influence realistic turbulent systems, we have conducted a series of numerical simulations employing the Hyperion radiation hydrodynamics solver, considering the regime that is optically thick to ultraviolet and optically thin to infrared radiation. Our model clouds cover initial surface densities between Σ cl,0∼ 10--300 M⊙ pc-2, with varying initial turbulence. We follow them through turbulent, self-gravitating collapse, star cluster formation, and cloud dispersal by stellar radiation. All our models display a log-normal distribution of gas surface density Σ for an initial virial parameter αvir,0=2, the log-normal standard deviation is σln Σ =1-1.5 and the star formation rate coefficient ɛff,ρ=0.3-0.5, both of which are sensitive to turbulence but not radiation feedback. The net star formation efficiency (SFE) ɛfinal increases with Σcl,0 and decreases with α vir,0. We interpret these results via a simple conceptual framework, whereby steady star formation increases the radiation force, such that local gas patches at successively higher Σ become unbound. Based on this formalism (with fixed σln Σ), we provide an analytic upper bound on ɛfinal, which is in good agreement with our numerical results. The final SFE depends on the distribution of Eddington ratios in the cloud and is strongly increased by the turbulent compression of gas.
Critically damped quantum search.
Mizel, Ari
2009-04-17
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we find that there is a critical damping value that divides between the quantum O(sqrt[N]) and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-point quantum search algorithm in which ignorance of the number of targets increases the number of oracle queries only by a factor of 1.5.
Critically damped quantum search
Mizel, Ari
2008-01-01
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we have found that there is a critical damping value that divides between the quantum $O(\\sqrt{N})$ and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-poin...
Optimal constrained layer damping with partial coverage
Marcelin, J.-L.; Trompette, Ph.; Smati, A.
1992-12-01
This paper deals with the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered. An efficient finite element model for dynamic analysis of such beams is used. The design variables are the dimensions and prescribed locations of the viscoelastic layers and the objective is the maximum viscoelastic damping factor. The method for nonlinear programming in structural optimization is the so-called method of moving asymptotes.
Orhan, A Emin; Ma, Wei Ji
2017-07-26
Animals perform near-optimal probabilistic inference in a wide range of psychophysical tasks. Probabilistic inference requires trial-to-trial representation of the uncertainties associated with task variables and subsequent use of this representation. Previous work has implemented such computations using neural networks with hand-crafted and task-dependent operations. We show that generic neural networks trained with a simple error-based learning rule perform near-optimal probabilistic inference in nine common psychophysical tasks. In a probabilistic categorization task, error-based learning in a generic network simultaneously explains a monkey's learning curve and the evolution of qualitative aspects of its choice behavior. In all tasks, the number of neurons required for a given level of performance grows sublinearly with the input population size, a substantial improvement on previous implementations of probabilistic inference. The trained networks develop a novel sparsity-based probabilistic population code. Our results suggest that probabilistic inference emerges naturally in generic neural networks trained with error-based learning rules.Behavioural tasks often require probability distributions to be inferred about task specific variables. Here, the authors demonstrate that generic neural networks can be trained using a simple error-based learning rule to perform such probabilistic computations efficiently without any need for task specific operations.
Energy Technology Data Exchange (ETDEWEB)
Palmer, R.B.
1988-07-01
Structures with slots to strongly damp higher order longitudinal and transverse modes should allow the use, in linear colliders, of multiple bunches, and thus attain luminosities of over 10/sup 34/cm/sup /minus/2/sec/sup /minus/1/. Preliminary measurements on model structures suggest that such damping can be achieved. 10 refs., 9 figs.
Active Compliance And Damping In Telemanipulator Control
Kim, Won S.; Bejczy, Antal K.; Hannaford, Blake
1991-01-01
Experimental telemanipulator system of force-reflecting-hand-controller type provides for active compliance and damping in remote, robotic manipulator hand. Distributed-computing and -control system for research in various combinations of force-reflecting and active-compliance control regimes. Shared compliance control implemented by low-pass-filtered force/torque feedback. Variable simulated springs and shock absorbers soften collisions and increase dexterity.
Damping by branching: a bioinspiration from trees
Theckes, Benoit; Boutillon, Xavier
2011-01-01
Man-made slender structures are known to be sensitive to high levels of vibration, due to their flexibility, which often cause irreversible damage. In nature, trees repeatedly endure large amplitudes of motion, mostly caused by strong climatic events, yet with minor or no damage in most cases. A new damping mechanism inspired by the architecture of trees is here identified and characterized in the simplest tree-like structure, a Y-shape branched structure. Through analytical and numerical analyses of a simple two-degree-of-freedom model, branching is shown to be the key ingredient in this protective mechanism that we call damping-by-branching. It originates in the geometrical nonlinearities so that it is specifically efficient to damp out large amplitudes of motion. A more realistic model, using flexible beam approximation, shows that the mechanism is robust. Finally, two bioinspired architectures are analyzed, showing significant levels of damping achieved via branching with typically 30% of the energy being...
Self-tuning Integral Force Feedback
Holterman, J.; de Vries, Theodorus J.A.; Samali, Bijan
2000-01-01
A self-tuning procedure is proposed for an active structural element with collocated sensing and actuation (a so-called ‘Smart Disc’). The procedure aims at optimal active damping by means of Integral Force Feedback control. In case the behavior of the structure to be damped may be described by a
Vibration damping characteristics of laminated steel sheet
Chen, Y. S.; Hsu, T. J.; Chen, S. I.
1991-03-01
The use of laminated steel sheets as vibration damping materials was studied. The laminate consisted of a viscoelastic layer which was sandwiched between two steel sheets. The study sought to identify parameters affecting the damping efficiency of the laminate. Two viscoelastic materials, a copolymer based on ethylene and acrylic acid (PEAA) and polyvinyl butyral (PVB), were used. A frequency analyzer was used to measure the loss factor of the laminates. A theoretical analysis of damping efficiency based on a model described by Ungar[2] was also carried out. The results showed that the loss factor of the PEAA-based laminates increased monotonically with increasing thickness of the viscoelastic layer and leveled off at 25.9 pct of total thickness. Ungar’s theory predicted a higher loss factor than the experimental data. This might have resulted from interfacial adhesive bonding, a nonuniform viscoelastic layer thickness, and the extrapolation of the rheological data from low to high frequencies. The loss factor of the laminate increased with increasing temperature, reached a maximum value, and then decreased. An optimum temperature for maximum damping was found for each laminate configuration. The PEAA-based laminates possessed higher damping efficiency than the PVB-based laminates at room temperature. The symmetric laminate (with the same steel sheet thickness) possessed a better damping efficiency than asymmetric laminates. The maximum damping peak of the laminates using a polymer blend, when compared to the laminates using unblended resin, exhibited a lower loss factor value, became broader, and occurred at a temperature between the T g’s of the individual components of the polymer blend.
Raskutti, Sudhir; Skinner, M Aaron
2016-01-01
Radiation feedback from stellar clusters is expected to play a key role in setting the rate and efficiency of star formation in giant molecular clouds (GMCs). To investigate how radiation forces influence realistic turbulent systems, we have conducted a series of numerical simulations employing the {\\it Hyperion} radiation hydrodynamics solver, considering the regime that is optically thick to ultraviolet (UV) and optically thin to infrared (IR) radiation. Our model clouds cover initial surface densities between $\\Sigma_{\\rm cl,0} \\sim 10-300~M_{\\odot}~{\\rm pc^{-2}}$, with varying initial turbulence. We follow them through turbulent, self-gravitating collapse, formation of star clusters, and cloud dispersal by stellar radiation. All our models display a lognormal distribution of gas surface density $\\Sigma$; for an initial virial parameter $\\alpha_{\\rm vir,0} = 2$, the lognormal standard deviation is $\\sigma_{\\rm ln \\Sigma} = 1-1.5$ and the star formation rate coefficient $\\varepsilon_{\\rm ff,\\bar\\rho} = 0.3-...
Energy Technology Data Exchange (ETDEWEB)
Rees, John; Chao, Alexander; /SLAC
2008-12-01
Landau damping, as the term is used in accelerator science, is a physical process in which an ensemble of harmonic oscillators--an accelerator beam, for example--that would otherwise be unstable is stabilized by a spread in the natural frequencies of the oscillators. This is a study of the most basic aspects of that process. It has two main goals: to gain a deeper insight into the mechanism of Landau damping and to find the coherent motion of the ensemble and thus the dependence of the total damping rate on the frequency spread.
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The optimal control problem was studied for linear time-varying systems, which was affected by external persistent disturbances with known dynamic characteristics but unknown initial conditions. To damp the effect of disturbances in an optimal fashion, we obtained a new feedforward and feedback optimal control law and gave the control algorithm by solving a Riccati differential equation and a matrix differential equation. Simulation results showed that the achieved optimal control law was realizable, efficient and robust to reject the external disturbances.
Control System Damps Vibrations
Kopf, E. H., Jr.; Brown, T. K.; Marsh, E. L.
1983-01-01
New control system damps vibrations in rotating equipment with help of phase-locked-loop techniques. Vibrational modes are controlled by applying suitable currents to drive motor. Control signals are derived from sensors mounted on equipment.
DAMPs, ageing, and cancer: The 'DAMP Hypothesis'.
Huang, Jin; Xie, Yangchun; Sun, Xiaofang; Zeh, Herbert J; Kang, Rui; Lotze, Michael T; Tang, Daolin
2015-11-01
Ageing is a complex and multifactorial process characterized by the accumulation of many forms of damage at the molecular, cellular, and tissue level with advancing age. Ageing increases the risk of the onset of chronic inflammation-associated diseases such as cancer, diabetes, stroke, and neurodegenerative disease. In particular, ageing and cancer share some common origins and hallmarks such as genomic instability, epigenetic alteration, aberrant telomeres, inflammation and immune injury, reprogrammed metabolism, and degradation system impairment (including within the ubiquitin-proteasome system and the autophagic machinery). Recent advances indicate that damage-associated molecular pattern molecules (DAMPs) such as high mobility group box 1, histones, S100, and heat shock proteins play location-dependent roles inside and outside the cell. These provide interaction platforms at molecular levels linked to common hallmarks of ageing and cancer. They can act as inducers, sensors, and mediators of stress through individual plasma membrane receptors, intracellular recognition receptors (e.g., advanced glycosylation end product-specific receptors, AIM2-like receptors, RIG-I-like receptors, and NOD1-like receptors, and toll-like receptors), or following endocytic uptake. Thus, the DAMP Hypothesis is novel and complements other theories that explain the features of ageing. DAMPs represent ideal biomarkers of ageing and provide an attractive target for interventions in ageing and age-associated diseases. Copyright © 2014 Elsevier B.V. All rights reserved.
Anisotropic Internal Friction Damping
Peters, R D
2003-01-01
The mechanical damping properties of sheet polaroid material have been studied with a physical pendulum. The polaroid samples were placed under the knife-edges of the pendulum, which was operated in free-decay at a period in the vicinity of 10 s. With the edges oriented parallel to the direction of the long molecular chains in the polaroid, it was found that the damping was more than 10% smaller than when oriented perpendicular to the chains.
Institute of Scientific and Technical Information of China (English)
洪峰
2002-01-01
In this paper, existing damping theories are briefly reviewed. On the basis of the existing damping theories, a new kind of damping theory, i.e., the time-delay damping theory, is developed. In the time-delay damping theory, the damping force is considered to be directly proportional to the increment of displacement. The response analysis of an SDOF time-delay damping system is carried out, and the methods for obtaining the solution for a time-delay damping system in the time domain as well as the frequency domain are given. The comparison between results from different damping theories shows that the time-delay damping theory is both reasonable and convenient.
Energy Technology Data Exchange (ETDEWEB)
Svensson, Lars
2000-07-01
This master-thesis report deals with the problem of power oscillations in power networks. The purpose of the work has been to study electro-mechanical oscillations in power systems and in a methodical way analyze the system to identify interesting properties. To increase the damping of especially the inter-area modes, the use of Power System Stabilizers has been investigated. In the control with PSS, local signals such as active power and angular velocity of the generator have first been used as measuring signals. The benefits of using global measuring signals have then been examined. The global signals examined are the derivative of the bus voltage phase angle and also the generators active power. An approach to study the zeros in a control loop is presented and gives, with the use of global measuring signals, a way of choosing a measuring signal to the PSS that affects the control in a beneficial way. A model of the Brazilian south/southeast power system has been used as a test system in the report. To analyze the system, modal analysis has been used and simulations have been performed in EUROSTAG for evaluation of control designs. In use of global signals, communication of signals is needed and therefore the effects of disturbances in this communication need to be considered. The effect of delays in the different signals has been studied and also the scenario of total loss of communication.
Damping modeling in Timoshenko beams
Banks, H. T.; Wang, Y.
1992-01-01
Theoretical and numerical results of damping model studies for composite material beams using the Timoshenko theory is presented. Based on the damping models developed for Euler-Bernoulli beams, the authors develop damping methods for both bending and shear in investigation of Timoshenko beams. A computational method for the estimation of the damping parameters is given. Experimental data with high-frequency excitation were used to test Timoshenko beam equations with different types of damping models for bending and shear in various combinations.
Reliable Damping of Free Surface Waves in Numerical Simulations
Peric, Robinson
2015-01-01
This paper generalizes existing approaches for free-surface wave damping via momentum sinks for flow simulations based on the Navier-Stokes equations. It is shown in 2D flow simulations that, to obtain reliable wave damping, the coefficients in the damping functions must be adjusted to the wave parameters. A scaling law for selecting these damping coefficients is presented, which enables similarity of the damping in model- and full-scale. The influence of the thickness of the damping layer, the wave steepness, the mesh fineness and the choice of the damping coefficients are examined. An efficient approach for estimating the optimal damping setup is presented. Results of 3D ship resistance computations show that the scaling laws apply to such simulations as well, so the damping coefficients should be adjusted for every simulation to ensure convergence of the solution in both model and full scale. Finally, practical recommendations for the setup of reliable damping in flow simulations with regular and irregular...
Stability Analysis and Active Damping for LLCL-filter-Based Grid-Connected Inverters
DEFF Research Database (Denmark)
Huang, Min; Wang, Xiongfei; Loh, Poh Chiang
2015-01-01
to use either passive or active damping methods. This paper analyzes the stability of the LLCL-filter based grid-connected inverter and identifies a critical resonant frequency for the LLCL-filter when sampling and transport delays are considered. In a high resonant frequency region the active damping...... is not required but in a low resonant frequency region the active damping is necessary. The basic LLCL resonance damping properties of different feedback states based on a notch filter concept are also studied. Then an active damping method which is using the capacitor current feedback for LLCL......-filter is introduced. Based on this active damping method, a design procedure for the controller is given. Last, both simulation and experimental results are provided to validate the theoretical analysis of this paper....
Audio Feedback -- Better Feedback?
Voelkel, Susanne; Mello, Luciane V.
2014-01-01
National Student Survey (NSS) results show that many students are dissatisfied with the amount and quality of feedback they get for their work. This study reports on two case studies in which we tried to address these issues by introducing audio feedback to one undergraduate (UG) and one postgraduate (PG) class, respectively. In case study one…
Kanter, D.; Zhang, X.; Shevliakova, E.; Malyshev, S.; Mauzerall, D. L.
2014-12-01
Nitrous oxide (N2O) presents a triple threat to the global environment: it is the third most important anthropogenic greenhouse gas, the largest remaining anthropogenic contributor to stratospheric ozone depletion, and an important component of the nitrogen (N) cascade - where one atom of N can interconvert between a number of forms, each with a unique set of environmental impacts. Here we use a dynamic vegetation model (Princeton-Geophysical Fluid Dynamics Lab (GFDL) LM3 - the interactive land component of the GFDL Earth System Model) to assess how changes in future climate, land-use, and global fertilizer and manure application are projected to affect global N2O emissions from agriculture by 2050. Agricultural land is defined in this study as the sum of cropland and pasture. In a baseline scenario assuming little improvement in global N use efficiency (NUE) by 2050, the model projects a 24-31% increase in global agricultural N2O emissions (with the uncertainty range stemming from differences in climate forcing, land-use and fertilizer and manure consumption between RCP2.6 and RCP8.5, the two climate scenarios used in this study) - rising from 2.9 Tg N2O-N yr-1 in 1990-2000 to 3.6-3.8 Tg N2O-N yr-1 in 2040-2050. This emission increase is considerably less than the projected increases in global fertilizer and manure consumption (42-44%) and previously published projections of global agricultural N2O emission increases (38-75% - again, the uncertainty range reflecting the differences between the climate scenarios used). This disparity appears to be a result of ecological feedbacks captured by the model, where a considerable portion of the increase in fertilizer and manure use is absorbed by agricultural plant biomass rather than lost to the environment. In addition to this dynamic, the model projects that improvements in global NUE of 20-50% could reduce global N2O emissions significantly, delivering important climate and stratospheric ozone benefits over the period
Feedback cooling of a single trapped ion
Bushev, P; Wilson, A; Dubin, F; Becher, C; Eschner, J; Blatt, R; Steixner, V; Rabl, P; Zoller, P; Bushev, Pavel; Rotter, Daniel; Wilson, Alex; Dubin, Francois; Becher, Christoph; Eschner, Juergen; Blatt, Rainer; Steixner, Viktor; Rabl, Peter; Peter Zoller
2005-01-01
Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electro-mechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical Master Equation.
Spatial damping identification in the frequency domain-A theoretical and experimental comparison
Brumat, Matija; Slavič, Janko; Boltežar, Miha
2016-08-01
This paper deals with spatial damping identification methods. In contrast to the commonly used damping methods (modal, proportional) the spatial damping information improves structural models with a known location of the damping sources. The Lee-Kim, Chen-Ju-Tsuei, Fritzen IV and local equation of motion methods were theoretically and experimentally compared. Experimentally, the spatial damping identification was tested against: modal and spatial incompleteness, differences in viscous and hysteretic damping models, the performance of identification methods and the effect of damping treatments. It was found that for a structure with a known equation of motion (beam, plate) the local equation of motion method is more efficient and gives a more precise location of the damping. Full frequency response function (FRF) matrix methods can also identify the spatial damping, but are more demanding because the numerical and measurement effort increases with n2, where n is the number of measurement points and, consequently, the size of the FRF matrix.
Quantitative Analysis and Design of a Rudder Roll Damping Controller
DEFF Research Database (Denmark)
Hearns, G.; Blanke, M.
1998-01-01
A rudder roll damping controller is designed using Quantitative feedback theory to be robust for changes in the ships metacentric height. The analytical constraint due to the non-minimum phase behaviour of the rudder to roll is analysed using the Poisson Integral Formula and it is shown how...
An Active Damping at Blade Resonances Using Piezoelectric Transducers
Choi, Benjamin; Morrison, Carlos; Duffy, Kirsten
2008-01-01
The NASA Glenn Research Center (GRC) is developing an active damping at blade resonances using piezoelectric structure to reduce excessive vibratory stresses that lead to high cycle fatigue (HCF) failures in aircraft engine turbomachinery. Conventional passive damping work was shown first on a nonrotating beam made by Ti-6A1-4V with a pair of identical piezoelectric patches, and then active feedback control law was derived in terms of inductor, resister, and capacitor to control resonant frequency only. Passive electronic circuit components and adaptive feature could be easily programmable into control algorithm. Experimental active damping was demonstrated on two test specimens achieving significant damping on tip displacement and patch location. Also a multimode control technique was shown to control several modes.
Radiation damping on cryoprobes.
Shishmarev, Dmitry; Otting, Gottfried
2011-12-01
Radiation damping on 600 and 800 MHz cryoprobes was investigated. The phase angle β between a vector 90° phase shifted to the precessing magnetization and the rf field induced in the coil was found to depend markedly on whether an FID was being acquired or not. The magnitude of the radiation damping field was sufficiently strong to restore 95% of the equilibrium water magnetization of a 90% H2O sample in a 5 mm sample tube within about 5 ms following a 165° pulse. This can be exploited in water flip-back versions of NOESY and TOCSY experiments of proteins, but care must be taken to limit the effect of the radiation damping field from the water on the Ha protons. Long water-selective pulses can be applied only following corrections. We developed a program for correcting pulse shapes if β is non-zero. The WATERGATE scheme is shown to be insensitive to imperfections introduced by radiation damping.
Burns, J. A.; Sharma, I.
2000-10-01
Motivated by the recent detection of complex rotational states for several asteroids and comets, as well as by the ongoing and planned spacecraft missions to such bodies, which should allow their rotational states to be accurately determined, we revisit the problem of the nutational damping of small solar system bodies. The nutational damping of asteroids has been approximately analyzed by Prendergast (1958), Burns and Safronov (1973), and Efroimsky and Lazarian (2000). Many other similar dynamical studies concern planetary wobble decay (e.g., Peale 1973; Yoder and Ward 1979), interstellar dust grain alignment (e.g., Purcell 1979; Lazarian and Efroimsky 1999) and damping of Earth's Chandler wobble (Lambeck 1980). Recall that rotational energy loss for an isolated body aligns the body's angular momentum vector with its axis of maximum inertia. Assuming anelastic dissipation, simple dimensional analysis determines a functional form of the damping timescale, on which all the above authors agree. However, the numerical coefficients of published results are claimed to differ by orders of magnitude. Differences have been ascribed to absent physics, to solutions that fail to satisfy boundary conditions perfectly, and to unphysical choices for the Q parameter. The true reasons for the discrepancy are unclear since, despite contrary claims, the full 3D problem (nutational damping of an anelastic ellipsoid) is analytically intractable so far. To move the debate forward, we compare the solution of a related 2D problem to the expressions found previously, and we present results from a finite element model. On this basis, we feel that previous rates for the decay of asteroidal tumbling (Harris 1994), derived from Burns and Safronov (1973), are likely to be accurate, at least to a factor of a few. Funded by NASA.
Highly Accurate Derivatives for LCL-Filtered Grid Converter with Capacitor Voltage Active Damping
DEFF Research Database (Denmark)
Xin, Zhen; Loh, Poh Chiang; Wang, Xiongfei
2016-01-01
The middle capacitor voltage of an LCL-filter, if fed back for synchronization, can be used for active damping. An extra sensor for measuring the capacitor current is then avoided. Relating the capacitor voltage to existing popular damping techniques designed with capacitor current feedback would...... are then proposed, based on either second-order or non-ideal generalized integrator. Performances of these derivatives have been found to match the ideal “s” function closely. Active damping based on capacitor voltage feedback can therefore be realized accurately. Experimental results presented have verified...
Main, Robert; Nulsen, Paul; Russell, Helen; Vantyghem, Adrian
2015-01-01
We derive X-ray mass, luminosity, and temperature profiles for 45 galaxy clusters to explore relationships between halo mass, AGN feedback, and central cooling time. We find that radio--mechanical feedback power (referred to here as "AGN power") in central cluster galaxies correlates with halo mass, but only in halos with central atmospheric cooling times shorter than 1 Gyr. This timescale corresponds approximately to the cooling time (entropy) threshold for the onset of cooling instabilities and star formation in central galaxies (Rafferty et al. 2008). No correlation is found in systems with central cooling times greater than 1 Gyr. The trend with halo mass is consistent with self-similar scaling relations assuming cooling is regulated by feedback. The trend is also consistent with galaxy and central black hole co-evolution along the $M_{BH} - \\sigma $ relation. AGN power further correlates with X-ray gas mass and the host galaxy's K-band luminosity. AGN power in clusters with central atmospheric cooling ti...
Directory of Open Access Journals (Sweden)
Rui Yang Chen
2016-09-01
Full Text Available Customer feedback is used to understand customer requirements. Early design phases require the consideration of items including manufacturing, the environment, and sustainability management. Therefore, it is crucial that eco-efficiency is taken into account in the early design phases. Traditionally, eco-efficiency is considered only in terms of eco-design issues, not customer requirements based on business values such as Recency, Frequency, and Monetary (RFM value. In the meantime, integrating innovation from eco-design is one important aspect. Here, I propose that customer feedback-based eco-efficiency and TRIZ-based innovation can be considered in early eco-design based on the RFM value for sustainability management. The analytic hierarchy process (AHP and fuzzy-based AHP were integrated to explore the relative weights of RFM variables for business value evaluation. The innovative method of the paper is using a TRIZ contradiction matrix associated with engineering parameters for eco-design. The experimental study has been carried out, and it meets the forecasting business value for green product usage. The business value was used as the decision-making factor in order to evaluate both environmental and marketing performance.
Stability analysis and active damping for LLCL-filter based grid-connected inverters
DEFF Research Database (Denmark)
Huang, Min; Blaabjerg, Frede; Loh, Poh Chiang
2014-01-01
A higher order passive power filter (LLCL-filter) for the grid-tied inverter is becoming attractive for the industrial applications due to the possibility to reduce the cost of the copper and the magnetic material. To avoid the well-known stability problems of the LLCL-filter it is requested to use...... either passive or active damping methods. This paper analyzes the stability when damping is required and when damping is not necessary considering sampling and transport delay. Basic LLCL resonance damping properties of different feedback states are also studied. Then an active damping method which...... is using the capacitor current feedback for LLCL-filter is introduced. Based on this method, a design procedure for the control method is given. Last, both simulation and experimental results are provided to validate the theoretical analysis of this paper....
Mouhot, Clément
2011-09-01
Going beyond the linearized study has been a longstanding problem in the theory of Landau damping. In this paper we establish exponential Landau damping in analytic regularity. The damping phenomenon is reinterpreted in terms of transfer of regularity between kinetic and spatial variables, rather than exchanges of energy; phase mixing is the driving mechanism. The analysis involves new families of analytic norms, measuring regularity by comparison with solutions of the free transport equation; new functional inequalities; a control of non-linear echoes; sharp "deflection" estimates; and a Newton approximation scheme. Our results hold for any potential no more singular than Coulomb or Newton interaction; the limit cases are included with specific technical effort. As a side result, the stability of homogeneous equilibria of the non-linear Vlasov equation is established under sharp assumptions. We point out the strong analogy with the KAM theory, and discuss physical implications. Finally, we extend these results to some Gevrey (non-analytic) distribution functions. © 2011 Institut Mittag-Leffler.
Huang, Susie Y; Witzel, Thomas; Wald, Lawrence L
2008-11-01
Control of the longitudinal magnetization in fast gradient-echo (GRE) sequences is an important factor in enabling the high efficiency of balanced steady-state free precession (bSSFP) sequences. We introduce a new method for accelerating the return of the longitudinal magnetization to the +z-axis that is independent of externally applied RF pulses and shows improved off-resonance performance. The accelerated radiation damping for increased spin equilibrium (ARISE) method uses an external feedback circuit to strengthen the radiation damping (RD) field. The enhanced RD field rotates the magnetization back to the +z-axis at a rate faster than T(1) relaxation. The method is characterized in GRE phantom imaging at 3T as a function of feedback gain, phase, and duration, and compared with results from numerical simulations of the Bloch equations incorporating RD. A short period of feedback (10 ms) during a refocused interval of a crushed GRE sequence allowed greater than 99% recovery of the longitudinal magnetization when very little T(2) relaxation had time to occur. An appropriate application might be to improve navigated sequences. Unlike conventional flip-back schemes, the ARISE "flip-back" is generated by the spins themselves, thereby offering a potentially useful building block for enhancing GRE sequences.
Feedback systems for linear colliders
Hendrickson, L; Himel, Thomas M; Minty, Michiko G; Phinney, N; Raimondi, Pantaleo; Raubenheimer, T O; Shoaee, H; Tenenbaum, P G
1999-01-01
Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 1997-98 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an intregal part of the design. Feedback requiremetns for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, rf and interaction point will operate at hi...
Energy Technology Data Exchange (ETDEWEB)
Nesvadba, N H; Lehnert, M D; Eisenhauer, F; Gilbert, A M; Tecza, M; Abuter, R
2007-06-26
To explain the properties of the most massive low-redshift galaxies and the shape of their mass function, recent models of galaxy evolution include strong AGN feedback to complement starburst-driven feedback in massive galaxies. Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we searched for direct evidence for such a feedback in the optical emission line gas around the z = 2.16 powerful radio galaxy MRC1138-262, likely a massive galaxy in formation. The kpc-scale kinematics, with FWHMs and relative velocities {approx}< 2400 km s{sup -1} and nearly spherical spatial distribution, do not resemble large-scale gravitational motion or starburst-driven winds. Order-of-magnitude timescale and energy arguments favor the AGN as the only plausible candidate to accelerate the gas, with a total energy injection of {approx} few x 10{sup 60} ergs or more, necessary to power the outflow, and relatively efficient coupling between radio jet and ISM. Observed outflow properties are in gross agreement with the models, and suggest that AGN winds might have a similar, or perhaps larger, cosmological significance than starburst-driven winds, if MRC1138-262 is indeed archetypal. Moreover, the outflow has the potential to remove significant gas fractions ({approx}< 50%) from a > L* galaxy within a few 10 to 100 Myrs, fast enough to preserve the observed [{alpha}/Fe] overabundance in massive galaxies at low redshift. Using simple arguments, it appears that feedback like that observed in MRC1138-262 may have sufficient energy to inhibit material from infalling into the dark matter halo and thus regulate galaxy growth as required in some recent models of hierarchical structure formation.
Quantifying acoustic damping using flame chemiluminescence
Boujo, E.; Denisov, A.; Schuermans, B.; Noiray, N.
2016-12-01
Thermoacoustic instabilities in gas turbines and aeroengine combustors falls within the category of complex systems. They can be described phenomenologically using nonlinear stochastic differential equations, which constitute the grounds for output-only model-based system identification. It has been shown recently that one can extract the governing parameters of the instabilities, namely the linear growth rate and the nonlinear component of the thermoacoustic feedback, using dynamic pressure time series only. This is highly relevant for practical systems, which cannot be actively controlled due to a lack of cost-effective actuators. The thermoacoustic stability is given by the linear growth rate, which results from the combination of the acoustic damping and the coherent feedback from the flame. In this paper, it is shown that it is possible to quantify the acoustic damping of the system, and thus to separate its contribution to the linear growth rate from the one of the flame. This is achieved by post-processing in a simple way simultaneously acquired chemiluminescence and acoustic pressure data. It provides an additional approach to further unravel from observed time series the key mechanisms governing the system dynamics. This straightforward method is illustrated here using experimental data from a combustion chamber operated at several linearly stable and unstable operating conditions.
A Five-Freedom Active Damping and Alignment Device Used in the Joule Balance
Xu, Jinxin; Zhang, Zhonghua; Li, Zhengkun; Li, Shisong
2016-01-01
Damping devices are necessary for suppressing the undesired coil motions in the watt/joule balance. In this paper, an active electromagnetic damping device, located outside the main magnet, is introduced in the joule balance project. The presented damping device can be used in both dynamic and static measurement modes. With the feedback from a detection system, five degrees of freedom of the coil, i.e. the horizontal displacement $x$, $y$ and the rotation angles $\\theta_x$, $\\theta_y$, $\\theta_z$, can be controlled by the active damping device. Hence, two functions, i.e. suppressing the undesired coil motions and reducing the misalignment error, can be realized with this active damping device. The principle, construction and performance of the proposed active damping device are presented.
HEADTAIL Feedback Module Implementation and Results
Thompson, J R; Höfle, Wolfgang; Rumolo, G
2008-01-01
A feedback module has been implemented in the HEADTAIL simulation code in order to investigate the feasibility of a transverse feedback system to damp the electron cloud instability. This instability provokes vertical oscillations within a bunch in the SPS when operated at and above nominal LHC beam current and 25 ns bunch spacing. In the present report the feedback module is described and applied to the case of the SPS at 55 GeV/c, previously identified as worst case energy for the LHC type beams in the SPS in terms of electron cloud instability. The numerical simulations show that a feedback system operating up to 500 MHz with a normalized gain of 0.16 can damp the instability. In contrast, a feedback system only acting on the rigid dipole bunch oscillation cannot cure the high frequency content of the motion.
Kannan, Govind; Milani, Ali A; Panahi, Issa M S; Briggs, Richard W
2011-12-01
Functional magnetic resonance imaging (fMRI) acoustic noise exhibits an almost periodic nature (quasi-periodicity) due to the repetitive nature of currents in the gradient coils. Small changes occur in the waveform in consecutive periods due to the background noise and slow drifts in the electroacoustic transfer functions that map the gradient coil waveforms to the measured acoustic waveforms. The period depends on the number of slices per second, when echo planar imaging (EPI) sequencing is used. Linear predictability of fMRI acoustic noise has a direct effect on the performance of active noise control (ANC) systems targeted to cancel the acoustic noise. It is shown that by incorporating some samples from the previous period, very high linear prediction accuracy can be reached with a very low order predictor. This has direct implications on feedback ANC systems since their performance is governed by the predictability of the acoustic noise to be cancelled. The low complexity linear prediction of fMRI acoustic noise developed in this paper is used to derive an effective and low-cost feedback ANC system.
Energy Technology Data Exchange (ETDEWEB)
Di, Sheng; Berrocal, Eduardo; Cappello, Franck
2015-01-01
The silent data corruption (SDC) problem is attracting more and more attentions because it is expected to have a great impact on exascale HPC applications. SDC faults are hazardous in that they pass unnoticed by hardware and can lead to wrong computation results. In this work, we formulate SDC detection as a runtime one-step-ahead prediction method, leveraging multiple linear prediction methods in order to improve the detection results. The contributions are twofold: (1) we propose an error feedback control model that can reduce the prediction errors for different linear prediction methods, and (2) we propose a spatial-data-based even-sampling method to minimize the detection overheads (including memory and computation cost). We implement our algorithms in the fault tolerance interface, a fault tolerance library with multiple checkpoint levels, such that users can conveniently protect their HPC applications against both SDC errors and fail-stop errors. We evaluate our approach by using large-scale traces from well-known, large-scale HPC applications, as well as by running those HPC applications on a real cluster environment. Experiments show that our error feedback control model can improve detection sensitivity by 34-189% for bit-flip memory errors injected with the bit positions in the range [20,30], without any degradation on detection accuracy. Furthermore, memory size can be reduced by 33% with our spatial-data even-sampling method, with only a slight and graceful degradation in the detection sensitivity.
System Reduction and Damping of Flexible Structures
DEFF Research Database (Denmark)
Høgsberg, Jan Riess; Krenk, Steen
2007-01-01
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...... good estimate for use in design calculations. The efficiency of the damper configuration depends on damper placement as well as damper properties. Thus a stiffness component in the damper characteristic leads to a decrease in damping efficiency. The method is illustrated by some simple examples, also...
Magnetically Damped Furnace (MDF)
1998-01-01
The Magnetically Damped Furnace (MDF) breadboard is being developed in response to NASA's mission and goals to advance the scientific knowledge of microgravity research, materials science, and related technologies. The objective of the MDF is to dampen the fluid flows due to density gradients and surface tension gradients in conductive melts by introducing a magnetic field during the sample processing. The MDF breadboard will serve as a proof of concept that the MDF performance requirements can be attained within the International Space Station resource constraints.
D'Alonzo, Marco; Dosen, Strahinja; Cipriani, Christian; Farina, Dario
2014-01-01
An important reason for the abandonment of commercial actuated hand prostheses by the users is the lack of sensory feedback. Wearable afferent interfaces capable of providing electro- or vibro-tactile stimulation have high potential to restore the missing tactile and/or proprioceptive information to the user. By definition, these devices can elicit single modality (i.e., either vibrotactile or electrotactile) substitute sensations. In a recent research we have presented a novel approach comprising hybrid vibro-electrotactile (HyVE) combined stimulation, in order to provide multimodal sensory feedback. An important advantage of this approach is in the size of the design: the HyVE interface is much more compact than two separated single-modality interfaces, since electro- and vibro-tactile stimulators are placed one on top of the other. The HyVE approach has been previously tested in healthy subjects and has shown to provide a range of hybrid stimuli that could be properly discriminated. However, this approach has never been assessed as a method to provide multi-channel stimuli, i.e., stimuli from a variety of stimulators, mapping information from a multitude of sensors on a prosthesis. In this study, the ability of ten healthy subjects to discriminate stimuli and patterns of stimuli from four different five-channel interfaces applied on their forearms was evaluated. We showed that multiple HyVE units could be used to provide multi-channel sensory information with equivalent performance (∼95 percent for single stimuli and ∼80 percent for pattern) to single modality interfaces (vibro- or electro-tactile) larger in size and with better performance than vibrotactile interfaces (i.e., 73 percent for single stimuli and 69 percent for pattern) with the same size. These results are promising in relation to the current availability of multi-functional prostheses with multiple sensors.
Hayman, Marilyn J.
1981-01-01
Investigated the effectiveness of supervisor feedback in contributing to learning counseling skills. Counselor trainees (N=64) were assigned to supervisor feedback, no supervisor feedback, or control groups for three training sessions. Results indicated counseling skills were learned best by students with no supervisor feedback but self and peer…
The Duffing oscillator with damping
DEFF Research Database (Denmark)
Johannessen, Kim
2015-01-01
An analytical solution to the differential equation describing the Duffing oscillator with damping is presented. The damping term of the differential equation and the initial conditions satisfy an algebraic equation, and thus the solution is specific for this type of damping. The nonlinear term....... It is established that the period of oscillation is shorter compared to that of a linearized model but increasing with time and asymptotically approaching the period of oscillation of the linear damped model. An explicit expression for the period of oscillation has been derived, and it is found to be very accurate....
Derivatives of repeated eigenvalues and corresponding eigenvectors of damped systems
Institute of Scientific and Technical Information of China (English)
XIE Hui-qing; DAI Hua
2007-01-01
A procedure is presented for computing the derivatives of repeated eigenvalues and the corresponding eigenvectors of damped systems. The derivatives are calculated in terms of the eigenvalues and eigenvectors of the second-order system, and the use of rather undesirable state space representation is avoided. Hence the cost of computation is greatly reduced. The efficiency of the proposed procedure is illustrated by considering a 5-DOF non-proportionally damped system.
Energy Technology Data Exchange (ETDEWEB)
Wouda, P.
2004-10-27
Following the success of the first Worldwide Energy Efficiency Benchmark (WEEB) in the brewing Industry in 2000 using the data from 1999, a second WEEB was set up in 2004 using the data from 2003. The results of the energy benchmark 2003 are presented in this report. The Dutch and Belgium brewers commissioned the study and a consortium of KWA Business Consultants (Amersfoort, The Netherlands) and Brewing Research International (Surrey, UK) performed a world-wide benchmarking study on energy efficiency in the brewing industry. 158 breweries from all over the world, representing 26% of the world's beer production, took part in this project (all with an output of at least 0.5 million hectolitres beer per year). This report consists out of two parts: a description of the methodology, used for benchmarking the energy efficiency in the brewing industry; and the results of the benchmark in world wide figures.
Husemann, B; Bennert, V N; Manieri, V; Woo, J -H; Kakkad, D
2015-01-01
Enormous observational effort has been made to constrain the energetics of AGN feedback by mapping the kinematics of the ionized gas on kpc scale with integral-field spectroscopy. Here, we investigate how the observed kinematics and inferred energetics are affected by beam smearing of a bright unresolved NLR due to seeing effects. We analysed optical IFU spectroscopy of a sample of twelve luminous unobscured QSOs (0.4
Damping of Ni-Mn-Ga epoxy resin composites
Institute of Scientific and Technical Information of China (English)
Wei Liang; He Yu; Liu Yufeng; Yang Naibin
2013-01-01
By combining the advantages of efficient damping and high mechanical properties, Ni-Mn-Ga particle composites have a very good prospect for applications in damping structure design. In this paper, a ferromagnetic shape memory alloy Ni-Mn-Ga composite is prepared. Ni-Mn-Ga particle/bisphenol-A epoxy composite cantilever beam vibration tests under a magnetic field and without the magnetic field are conducted to analyze the structural damping ratios n. Meanwhile, the damping characteristics of the Ni-Mn-Ga composite are studied through the axial loading-unloading method and the acoustic emission signals method. The damping coefficient of the composite for different Ni-Mn-Ga volume fractions is obtained. The interface properties of the composite are discussed by micro examination and axial loading. The relationships between the damping of the composite and that of the component materials are discussed. The specific damping capacity (SDC) and acoustic emission counts diagram of different specimens with different Ni-Mn-Ga volume fractions are analyzed.
Bullock, Jack C.; Kelly, Benjamin E.
1980-01-01
A valve having a mechanism for damping out flow surges in a vacuum system which utilizes a slotted spring-loaded disk positioned adjacent the valve's vacuum port. Under flow surge conditions, the differential pressure forces the disk into sealing engagement with the vacuum port, thereby restricting the flow path to the slots in the disk damping out the flow surge.
Gilbert Damping in Noncollinear Ferromagnets
Yuan, Zhe; Hals, Kjetil M.D.; Liu, Yi; Starikov, Anton A.; Brataas, Arne; Kelly, Paul J.
2014-01-01
The precession and damping of a collinear magnetization displaced from its equilibrium are well described by the Landau-Lifshitz-Gilbert equation. The theoretical and experimental complexity of noncollinear magnetizations is such that it is not known how the damping is modified by the noncollinearit
Park, Young-Min; Kim, Kwang-Joon
2011-05-01
Piezoelectric exciters have been receiving greater attention recently as a vibration source for tactile feedback in devices with touch screens, such as a mobile phones, in place of DC motors due to lower energy consumption and smaller volume. Their insufficient excitation level, however, still remains a problem. In this paper, dynamic modeling and design improvement of a piezoelectric exciter are presented. The excitation performance is defined as the acceleration response at the center of a touch screen per electric power and to be maximized around 250 Hz where the index finger is most sensitive. The piezoelectric exciter consists of a z-shaped metal beam, a piezoelectric layer on the long horizontal segment and an adhesive layer between the short horizontal segment and the touch screen. Assuming that the piezoelectric exciter is attached onto a rigid ground due to its low mechanical impedance compared with that of the touch screen, the piezoelectric exciter is dynamically modeled by applying Hamilton's principle, where the adhesive layer is treated as a distributed stiffness. The touch screen is modeled approximately as a simply supported beam such that it may have the same fundamental natural frequency and bending stiffness as the screen based on measurements. The performance improvement is focused on the change of five geometric parameters of the piezoelectric exciter: length of the long horizontal segment, thickness of the piezoelectric layer, thickness of the elastic metal layer, width of the beams and tip mass. The procedure to improve the performance of the piezoelectric exciter via dynamic modeling is presented together with experimental results on a prototype. Effectiveness of the design modification and limitations in practice are further discussed as well.
Oscillations with three damping effects
Energy Technology Data Exchange (ETDEWEB)
Wang Xiaojun [Department of Physics, Georgia Southern University, Statesboro, GA (United States)]. E-mail: xwang@gasou.edu; Schmitt, Chris; Payne, Marvin [Department of Physics, Georgia Southern University, Statesboro, GA (United States)
2002-03-01
Experiments on oscillatory motion are described with three different damping effects. The first experiment is a physical pendulum whose damping mechanism is due to sliding friction; the second is magnetic resistance due to eddy currents; and the third experiment involves a pendulum setup where air resistance is the dominant factor. These three damping mechanisms yield constant ({nu}-bar/ vertical bar {nu}-bar vertical bar), linear, and quadratic resistances in velocity respectively. Approximation methods are described for treating the three damping effects and a general solution is derived for the damping with a very general velocity dependence. A sonic rangefinder is used to record the oscillatory motions of the pendulums. The experimental measurements and theoretical calculations are in a good agreement. (author)
Damping Bearings In High-Speed Turbomachines
Von Pragenau, George L.
1994-01-01
Paper presents comparison of damping bearings with traditional ball, roller, and hydrostatic bearings in high-speed cryogenic turbopumps. Concept of damping bearings described in "Damping Seals and Bearings for a Turbomachine" (MFS-28345).
Energy Technology Data Exchange (ETDEWEB)
Gallo, A.; Boni, R.; Ghigo, A.; Marcellini, F.; Serio, M.; Zobov, M. [Instituto Nazionale de Fisica Nucleare, Frascati (Italy). Lab. Nazionale di Frascati
1996-08-01
The multibunch operation of DA{Phi}NE calls for a very efficient feedback system to damp the coupled-bunch longitudinal instabilities. A collaboration program among SLAC, LBL and LNF laboratories on this subject led to the development of a time domain, digital system based on digital signal processors that has been already successfully tested at ALS. The feedback chain ends with the longitudinal kicker, an electromagnetic structure capable of transferring the proper energy correction to each bunch. A cavity kicker for the DA{Phi}NE bunch-by-bunch longitudinal feedback system based on a pill-box loaded by six waveguides has been designed and a full-scale aluminium prototype has been fabricated at LNF. Both simulations and measurements have shown a peak shunt impedance of about 750 ohm and a bandwidth of about 220 MHz. The large shunt impedance allows to economize on the costly feedback power. Moreover, the damping waveguides drastically reduce the device HOM longitudinal and transverse impedances. One cavity pre ring will be sufficient to operate the machine up to 30 bunches while a second device per ring together with a feedback power improvement will be necessary to reach the ultimate current. (G.T.)
Impedance and instabilities in the NLC damping rings
Energy Technology Data Exchange (ETDEWEB)
Corlett,J.; Li, D.; Pivi, M.; Rimmer, R.; DeSantis, S.; Wolski, A.; Novokhatski,A.; Ng, C.
2001-06-12
We report on impedance calculations and single-bunch and multi-bunch instabilities in the NLC damping rings. Preliminary designs of vacuum chambers and major components have addressed beam impedance issues, with the desire to increase instability current thresholds and reducing growth rates. MAFIA calculations of short-range and long-range wakefields have allowed computations of growth rates and thresholds, which are presented here. Resistive wall instability dominates long-range effects, and requires a broadband feedback system to control coupled-bunch motion. Growth rates are within the range addressable by current feedback system technologies. Single-bunch instability thresholds are safely above nominal operating current.
Design of passive piezoelectric damping for space structures. Final Report Ph.D. Thesis
Hagood, Nesbitt W., IV; Aldrich, Jack B.; Vonflotow, Andreas H.
1994-01-01
Passive damping of structural dynamics using piezoceramic electromechanical energy conversion and passive electrical networks is a relatively recent concept with little implementation experience base. This report describes an implementation case study, starting from conceptual design and technique selection, through detailed component design and testing to simulation on the structure to be damped. About 0.5kg. of piezoelectric material was employed to damp the ASTREX testbed, a 500kg structure. Emphasis was placed upon designing the damping to enable high bandwidth robust feedback control. Resistive piezoelectric shunting provided the necessary broadband damping. The piezoelectric element was incorporated into a mechanically-tuned vibration absorber in order to concentrate damping into the 30 to 40 Hz frequency modes at the rolloff region of the proposed compensator. A prototype of a steel flex-tensional motion amplification device was built and tested. The effective stiffness and damping of the flex-tensional device was experimentally verified. When six of these effective springs are placed in an orthogonal configuration, strain energy is absorbed from all six degrees of freedom of a 90kg. mass. A NASTRAN finite element model of the testbed was modified to include the six-spring damping system. An analytical model was developed for the spring in order to see how the flex-tensional device and piezoelectric dimensions effect the critical stress and strain energy distribution throughout the component. Simulation of the testbed demonstrated the damping levels achievable in the completed system.
Radiative feedback and the low efficiency of galaxy formation in low-mass halos at high redshift
Ceverino, Daniel; Klimek, Elizabeth; Trujillo-Gomez, Sebastian; Churchill, Christopher W; Primack, Joel
2013-01-01
Any successful model of galaxy formation needs to explain the low rate of star formation in the small progenitors of today's normal galaxies. The low efficiency of star formation is necessary for reproducing the low stellar-to-halo mass fractions, as suggested by current abundance matching models. We found that the main driver of this low efficiency is the radiation pressure exerted by ionizing photons from massive and young stars. We model the effect of radiation pressure in cosmological, zoom-in galaxy formation simulations, as a non-thermal pressure that acts locally around dense and optically thick star-forming regions. We also include the effect of photoionization and photoheating on the gas cooling and heating rates. In some conditions, the full photoionization of HI reduces the HI peak of the cooling curve, effectively preventing cooling in the 10^4-10^4.5 K regime. We also consider a simple model for the boosting of radiation pressure due to the trapping of infrared radiation. The main effect of the l...
Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring
Energy Technology Data Exchange (ETDEWEB)
Macek, R.J.; /Los Alamos; Assadi, S.; /Oak Ridge; Byrd, J.M.; /LBL, Berkeley; Deibele, C.E.; Henderson, S.D.; /Oak Ridge; Lee, S.Y.; /Indiana U.; McCrady, R.C.; /Los Alamos; Pivi, M.F.T.; /SLAC; Plum, M.A.; /Oak Ridge; Walbridge, S.B.; /Indiana U.; Zaugg, T.J.; /Los Alamos
2008-03-17
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback.
Insights from a refined decomposition of cloud feedbacks
Zelinka, Mark D.; Zhou, Chen; Klein, Stephen A.
2016-09-01
Decomposing cloud feedback into components due to changes in several gross cloud properties provides valuable insights into its physical causes. Here we present a refined decomposition that separately considers changes in free tropospheric and low cloud properties, better connecting feedbacks to individual governing processes and avoiding ambiguities present in a commonly used decomposition. It reveals that three net cloud feedback components are robustly nonzero: positive feedbacks from increasing free tropospheric cloud altitude and decreasing low cloud cover and a negative feedback from increasing low cloud optical depth. Low cloud amount feedback is the dominant contributor to spread in net cloud feedback but its anticorrelation with other components damps overall spread. The ensemble mean free tropospheric cloud altitude feedback is roughly 60% as large as the standard cloud altitude feedback because it avoids aliasing in low cloud reductions. Implications for the "null hypothesis" climate sensitivity from well-understood and robustly simulated feedbacks are discussed.
Active Vibration Control of Beam Using Electro-magnetic Constrained Layer Damping
Institute of Scientific and Technical Information of China (English)
Niu Hongpan; Zhang Yahong; Zhang Xinong; Xie Shilin
2008-01-01
This paper investigates vibration control of beam through electro-magnetic constrained layer damping (EMCLD) which consists of electromagnet layer, permanent magnet layer and viscoelastic damping layer. When the coil of the electromagnet is electrified with proper control strategy, the electromagnet can exert magnetic force opposite to the direction of structural deformation so that the struc- tural vibration is attenuated. A mathematical model is developed based on the equivalent current method to calculate the electromagnetic control force produced by EMCLD. The governing equations of the system are obtained using Hamilton's Principle and then reduced with the assumed-mode method. A simulation on vibration control of a cantilever beam is conducted under the velocity proportional feedback to demonstrate the energy dissipation capability of EMCLD, and the beam system with the same parameter is experimented. The results of experiment and simulation are compared and the results show that the EMCLD is an effective means for suppressing modal vibration. The results also indicate that the beam system has better control performance for larger control current. The EMCLD method presented in this paper provides an applicable and efficient tool for the vibration control of structures.
Landau damping in space plasmas
Thorne, Richard M.; Summers, Danny
1991-01-01
The Landau damping of electrostatic Langmuir waves and ion-acoustic waves in a hot, isotropic, nonmagnetized, generalized Lorentzian plasma is analyzed using the modified plasma dispersion function. Numerical solutions for the real and imaginary parts of the wave frequency omega sub 0 - (i)(gamma) have been obtained as a function of the normalized wave number (k)(lambda sub D), where lambda sub D is the electron Debye length. For both particle distributions the electrostatic modes are found to be strongly damped at short wavelengths. At long wavelengths, this damping becomes less severe, but the attenuation of Langmuir waves is much stronger for a generalized Lorentzian plasma than for a Maxwellian plasma. It is concluded that Landau damping of ion-acoustic waves is only slightly affected by the presence of a high energy tail, but is strongly dependent on the ion temperature.
Feedback control of coupled-bunch instabilities
Energy Technology Data Exchange (ETDEWEB)
Fox, J.D.; Eisen, N.; Hindi, H.; Linscott, I.; Oxoby, G.; Sapozhnikov, L. [Stanford Linear Accelerator Center, Menlo Park, CA (United States); Serio, M. [Istituto Nazionale di Fisica Nucleare, Frascati (Italy). Lab. Nazionale di Frascati
1993-05-01
The next generation of synchrotron light sources and particle accelerators will require active feedback systems to control multi-bunch instabilities. Stabilizing hundreds or thousands of potentially unstable modes in these accelerator designs presents many technical challenges. Feedback systems to stabilize coupled-bunch instabilities may be understood in the frequency domain (mode-based feedback) or in the time domain (bunch-by-bunch feedback). In both approaches an external amplifier system is used to create damping fields that prevent coupled-bunch oscillations from growing without bound. The system requirements for transverse (betatron) and longitudinal (synchrotron) feedback are presented, and possible implementation options developed. Feedback system designs based on digital signal-processing techniques are described. Experimental results are shown from a synchrotron oscillation damper in the SSRL/SLAC storage ring SPEAR that uses digital signal-processing techniques.
Simple suppression of radiation damping.
Khitrin, A K; Jerschow, Alexej
2012-12-01
Radiation damping is known to cause line-broadening and frequency shifts of strong resonances in NMR spectra. While several techniques exist for the suppression of these effects, many require specialized hardware, or are only compatible with the presence of few strong resonances. We describe a simple pulse sequence for radiation damping suppression in spectra with many strong resonances. The sequence can be used as-is to generate simple spectra or as a signal excitation part in more advanced experiments.
Spin amplification in solution magnetic resonance using radiation damping.
Walls, Jamie D; Huang, Susie Y; Lin, Yung-Ya
2007-08-07
The sensitive detection of dilute solute spins is critical to biomolecular NMR. In this work, a spin amplifier for detecting dilute solute magnetization is developed using the radiation damping interaction in solution magnetic resonance. The evolution of the solvent magnetization, initially placed along the unstable -z direction, is triggered by the radiation damping field generated by the dilute solute magnetization. As long as the radiation damping field generated by the solute is larger than the corresponding thermal noise field generated by the sample coil, the solute magnetization can effectively trigger the evolution of the water magnetization under radiation damping. The coupling between the solute and solvent magnetizations via the radiation damping field can be further improved through a novel bipolar gradient scheme, which allows solute spins with chemical shift differences much greater than the effective radiation damping field strength to affect the solvent magnetizations more efficiently. Experiments performed on an aqueous acetone solution indicate that solute concentrations on the order of 10(-5) that of the solvent concentration can be readily detected using this spin amplifier.
Eddy damping effect of additional conductors in superconducting levitation systems
Energy Technology Data Exchange (ETDEWEB)
Jiang, Zhao-Fei; Gou, Xiao-Fan, E-mail: xfgou@hhu.edu.cn
2015-12-15
Highlights: • In this article, for the eddy current damper attached to the HTSC, we • quantitatively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. • presented four different arrangements of the copper damper, and comparatively studied their damping effects and Joule heating, and finally proposed the most advisable arrangement. - Abstract: Passive superconducting levitation systems consisting of a high temperature superconductor (HTSC) and a permanent magnet (PM) have demonstrated several fascinating applications such as the maglev system, flywheel energy storage. Generally, for the HTSC–PM levitation system, the HTSC with higher critical current density J{sub c} can obtain larger magnetic force to make the PM levitate over the HTSC (or suspended below the HTSC), however, the process of the vibration of the levitated PM, provides very limited inherent damping (essentially hysteresis). To improve the dynamic stability of the levitated PM, eddy damping of additional conductors can be considered as the most simple and effective approach. In this article, for the HTSC–PM levitation system with an additional copper damper attached to the HTSC, we numerically and comprehensively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. Furthermore, we comparatively studied four different arrangements of the copper damper, on the comprehensive analyzed the damping effect, efficiency (defined by c/V{sub Cu}, in which V{sub Cu} is the volume of the damper) and Joule heating, and finally presented the most advisable arrangement.
PENDULUM WITH LINEAR DAMPING AND VARIABLE LENGTH
Institute of Scientific and Technical Information of China (English)
蔡建平; 杨翠红; 李怡平
2004-01-01
The methods of multiple scales and approximate potential are used to study pendulums with linear damping and variable length. According to the order of the coefficient of friction compared with that of the slowly varying parameter of length, three different cases are discussed in details. Asymptotic analytical expressions of amplitude, frequency and solution are obtained. The method of approximate potential makes the results effective for large oscillations. A modified multiple scales method is used to get more accurate leading order approximations when the coefficient friction is not small. Comparisons are also made with numerical results to show the efficiency of the present method.
Tower Based Load Measurements for Individual Pitch Control and Tower Damping of Wind Turbines
Kumar, A. A.; Hugues-Salas, O.; Savini, B.; Keogh, W.
2016-09-01
The cost of IPC has hindered adoption outside of Europe despite significant loading advantages for large wind turbines. In this work we presented a method for applying individual pitch control (including for higher-harmonics) using tower-top strain gauge feedback instead of blade-root strain gauge feedback. Tower-top strain gauges offer hardware savings of approximately 50% in addition to the possibility of easier access for maintenance and installation and requiring a less specialised skill-set than that required for applying strain gauges to composite blade roots. A further advantage is the possibility of using the same tower-top sensor array for tower damping control. This method is made possible by including a second order IPC loop in addition to the tower damping loop to reduce the typically dominating 3P content in tower-top load measurements. High-fidelity Bladed simulations show that the resulting turbine spectral characteristics from tower-top feedback IPC and from the combination of tower-top IPC and damping loops largely match those of blade-root feedback IPC and nacelle- velocity feedback damping. Lifetime weighted fatigue analysis shows that the methods allows load reductions within 2.5% of traditional methods.
Tracking controller for robot manipulators via composite nonlinear feedback law
Institute of Scientific and Technical Information of China (English)
Peng Wendong; Su Jianbo
2009-01-01
A composite nonlinear feedback tracking controller for motion control of robot manipulators is de-scribed. The structure of the controller is composed of a composite nonlinear feedback law plus full robot nonlinear dynamics compensation. The stability is carried out in the presence of friction. The controller takes advantage of varying damping ratios induced by the composite nonlinear feedback control, so the transient performance of the closed-loop is remarkably improved. Simulation results demonstrate the feasibility of the proposed method.
Theoretical prediction of the damping of a railway wheel with sandwich-type dampers
Merideno, Inaki; Nieto, Javier; Gil-Negrete, Nere; Giménez Ortiz, José Germán; Landaberea, Aitor; Iartza, Jon
2014-09-01
This paper presents a procedure for predicting the damping added to a railway wheel when sandwich-type dampers are installed. Although there are different ways to reduce the noise generated by a railway wheel, most devices are based on the mechanism of increasing wheel damping. This is why modal damping ratios are a clear indicator of the efficiency of the damping device and essential when a vibro-acoustic study of a railway wheel is carried out. Based on a number of output variables extracted from the wheel and damper models, the strategy explained herein provides the final damping ratios of the damped wheel. Several different configurations are designed and experimentally tested. Theoretical and experimental results agree adequately, and it is demonstrated that this procedure is a good tool for qualitative comparison between different solutions in the design stages.
Institute of Scientific and Technical Information of China (English)
吕永灿; 林桦; 杨化承; 罗咏
2013-01-01
To track the given sinusoidal current under stationary frame and suppress the effect of the low harmonics in the grid, a multi-resonant proportional resonant (PR) controller was adopted for pulse width modulation (PWM) converter with LCL filter based on capacitor current feedback active damping. Because the system is of high order, many parameters and complicated, the effects of the control parameters on the current-loop performance were investigated with frequency theory, i.e. the stability, steady-state error and phase margin. Based on this, a decoupling-simplified analytic design method was proposed. According to the requests of the stability, steady-state error and phase margin, the capacitor-current-feedback coefficient, the relative resonant gain factor and the proportional factor could be designed separately. The proposed method uses the analytic method and simplifies the couple of the parameters without trial-and-error procedure. Finally, a battery storage power conversion system (PCS) was built. Experiment results verify the effectiveness of the proposed design method.%基于电容电流反馈有源阻尼的LCL型脉宽调制(pulse width modulation，PWM)变换器并网电流控制中，通常采用多谐振比例谐振(proportional resonant，PR)控制器来实现静止αβ坐标系下正弦电流给定的无静差跟踪和抑制电网电压特定次谐波影响。针对电流环控制器复杂、参数多、设计难的问题，采用频率域理论分析电容电流反馈系数和准PR控制器各参数对电流环性能的影响。在此基础上，提出一种电流环控制器参数解耦简化解析设计方法，根据稳定性、稳态误差和相位裕度要求，分别设计电容电流反馈系数及PR控制器相对谐振增益系数和比例系数。该设计方法简化了控制器参数之间的耦合关系，且多采用解析计算，不需要反复试凑。实验结果验证了所提出的参数解耦解析设计方法是可行和有效的。
DEFF Research Database (Denmark)
Hyldahl, Kirsten Kofod
Denne bog undersøger, hvordan lærere kan anvende feedback til at forbedre undervisningen i klasselokalet. I denne sammenhæng har John Hattie, professor ved Melbourne Universitet, udviklet en model for feedback, hvilken er baseret på synteser af meta-analyser. I 2009 udgav han bogen "Visible...
Damping mechanisms of a pendulum
Dolfo, Gilles; Castex, Daniel; Vigué, Jacques
2016-11-01
In this paper, we study the damping mechanisms of a pendulum. The originality of our setup is the use of a metal strip suspension and the development of extremely sensitive electric measurements of the pendulum velocity and position. Their sensitivity is absolutely necessary for a reliable measurement of the pendulum damping time constant because this measurement is possible only for very low oscillation amplitudes, when air friction forces quadratic in velocity have a negligible contribution to the observed damping. We have thus carefully studied damping by air friction forces, which is the dominant mechanism for large values of the Reynolds number Re but which is negligible in the Stokes regime, {Re} ∼ 1. In this last case, we have found that the dominant damping is due to internal friction in the metal strip, a universal effect called anelasticity, and, for certain frequencies, to resonant coupling to the support of the pendulum. All our measurements are well explained by theory. We believe this paper would be of interest to students in an undergraduate classical mechanics course.
Dampness in buildings and health
DEFF Research Database (Denmark)
Bornehag, Carl-Gustaf; Blomquist, G.; Gyntelberg, F.
2001-01-01
Several epidemiological investigations concerning indoor environments have indicated that "dampness" in buildings is associated to health effects such as respiratory symptoms, asthma and allergy The aim of the present interdisciplinary review is to evaluate this association as shown in the epidem......Several epidemiological investigations concerning indoor environments have indicated that "dampness" in buildings is associated to health effects such as respiratory symptoms, asthma and allergy The aim of the present interdisciplinary review is to evaluate this association as shown...... in the epidemiological literature. A literature search identified 590 peer-reviewed articles of which 61 have been the foundation for this review. The review shows that "dampness" in buildings appears to increase the risk for health effects in the airways, such as cough, wheeze and asthma. Relative risks...... definitions of dampness have been used in the studies, but all seems to be associated with health problems. Sensitisation to mites may be one but obviously not the only mechanism. Even if the mechanisms are unknown, there is sufficient evidence to take preventive measures against dampness in buildings....
High Damping Alloys and Their Application
Institute of Scientific and Technical Information of China (English)
Fuxing Yin
2000-01-01
Damping alloys show prospective applications in the elimination of unwanted vibrations and acoustic noise. The basic definitions and characterization methods of damping capacity are reviewed in this paper. Several physical mechanisms controlled by the alloy microstructure are responsible for the damping behavior in the damping alloys. Composite, dislocation, ferromagnetic and planar defect types are commonly classified for the alloys, which show the different damping behavior against temperature, frequency of vibration,amplitude of vibration and damping modes. Development of practically applicable damping alloys requires the higher mechanical properties and adequate workability, besides the high damping capacity. A new Mn-Cu damping alloy, named as M2052 alloy, is recently developed with possible industrial applications.
Landau damping of auroral hiss
Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.
1994-01-01
Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.
IMPACT GRINDING OF DAMP MATERIALS
Directory of Open Access Journals (Sweden)
Ladaev Nikolay Mikhaylovich
2012-10-01
Centrifugal grinders were used to analyze the grinding process. The experimental data have proven that the probability of destruction of damp samples is a lot higher than the one of dry samples, given the same initial dimensions of particles and the loading intensity. The rise in the probability of destruction is stipulated by the fact that that the grinder speed at which crushing is triggered is lower in case of damp samples than in case of dry ones. Expressions for speed that describes destruction initiation and the probability of destruction depending on the type of materials, the moisture content and the loading intensity have been derived.
Tropp, James; Van Criekinge, Mark
2010-09-01
The basic equation describing radiation damping in nuclear magnetic resonance (NMR) is rewritten by means of the reciprocity principle, to remove the dependence of the damping constant upon filling factor - a parameter which is neither uniquely defined for easily measured. The new equation uses instead the transceive efficiency, i.e. the peak amplitude of the radiofrequency B field in laboratory coordinates, divided by the square root of the resistance of the detection coil, for which a simple and direct means of measurement exists. We use the efficiency to define the intrinsic damping constant, i.e. that which obtains when both probe and preamplifier are perfectly matched to the system impedance. For imperfect matching of the preamp, it is shown that the damping constant varies with electrical distance to the probe, and equations are given and simulations performed, to predict the distance dependence, which (for lossless lines) is periodic modulo a half wavelength. Experimental measurements of the radiation-damped free induction NMR signal of protons in neat water are performed at a static B field strength of 14.1T; and an intrinsic damping constant measured using the variable line method. For a sample of 5mm diameter, in an inverse detection probe we measure an intrinsic damping constant of 204 s(-1), corresponding to a damping linewidth of 65 Hz for small tip angles. The predicted intrinsic linewidth, based upon three separate measurements of the efficiency, is 52.3 Hz, or 80% of the measured value.
Zheng, Ling; Zhang, Dongdong; Wang, Yi
2011-02-01
In this paper, the application of active constrained layer damping (ACLD) treatments is extended to the vibration control of cylindrical shells. The governing equation of motion of cylindrical shells partially treated with ACLD treatments is derived on the basis of the constitutive equations of elastic, piezoelectric and visco-elastic materials and an energy approach. The damping of a visco-elastic layer is modeled by the complex modulus formula. A finite element model is developed to describe and predict the vibration characteristics of cylindrical shells partially treated with ACLD treatments. A closed-loop control system based on proportional and derivative feedback of the sensor voltage generated by the piezo-sensor of the ACLD patches is established. The dynamic behaviors of cylindrical shells with ACLD treatments such as natural frequencies, loss factors and responses in the frequency domain are further investigated. The effects of several key parameters such as control gains, location and coverage of ACLD treatments on vibration suppression of cylindrical shells are also discussed. The numerical results indicate the validity of the finite element model and the control strategy approach. The potential of ACLD treatments in controlling vibration and sound radiation of cylindrical shells used as major critical structures such as cabins of aircraft, hulls of submarines and bodies of rockets and missiles is thus demonstrated.
Natural frequencies and damping estimation based on continuous wavelet transform
Institute of Scientific and Technical Information of China (English)
DAI Yu; SUN He-yi; LI Hui-peng; TANG Wen-yan
2008-01-01
The continuous wavelet transform (CWT) based method was improved for estimating the natural fre-quencies and damping ratios of a structural system in this paper. The appropriate scale of CWT was selected by means of the least squares method to identify the systems with closely spaced modes. The important issues relat-ed to estimation accuracy such as mode separation and end effect, were also investigated. These issues were as-sociated with the parameter selection of wavelet function based on the fitting error of least squares. The efficien-cy of the method was confirmed by applying it to a simulated 3dof damped system with two close modes.
Negative Resistance Circuit for Damping an Array of Coupled FitzHugh-Nagumo Oscillators
DEFF Research Database (Denmark)
Tamaševičius, Arūnas; Adomaitienė, Elena; Bumelienė, Skaidra;
2015-01-01
An analog circuit, based on a negative impedance converter and a capacitor, for damping oscillations in an array of mean-field coupled neuronal FitzHugh–Nagumo (FHN) type oscillators is described. The circuit is essentially a two-terminal feedback controller. When coupled to an array of the FHN...
LCL-Filter Design for Robust Active Damping in Grid-Connected Converters
DEFF Research Database (Denmark)
Pena-Alzola, Rafael; Liserre, Marco; Blaabjerg, Frede;
2014-01-01
Grid-connected converters employ LCL-filters, instead of simple inductors, because they allow lower inductances while reducing cost and size. Active damping, without dissipative elements, is preferred to passive damping for solving the associated stability problems. However, large variations...... in the grid inductance may compromise system stability, and this problem is more severe for parallel converters. This situation, typical of rural areas with solar and wind resources, calls for robust LCL-filter design. This paper proposes a design procedure with remarkable results under severe grid inductance...... variation. The procedure considers active damping using lead-lag network and capacitor current feedback. Passive damping is also discussed. The design flow, with little iteration and no complex algorithms, selects the proper ratios between the switching and resonance frequency, the grid and converter...
Experimental investigation of a self-sensing active constrained layer damping treatment
Yellin, Jessica M.; Shen, I. Y.
1996-05-01
A variational formulation of active constrained layer (ACL) damping treatments has indicated that the power dissipated through the active damping is the product of the electric field and the axial velocity of the piezoelectric constraining layer at the boundaries. This feature, unique to this formulation, suggests that a self-sensing and actuating piezoelectric constraining layer using rate of strain feedback may be an appropriate method of dissipating vibration energy with less instability, since the sensor and actuator are truly collocated. A partial ACL damping treatment design for an Euler-Bernoulli beam using a self-sensing actuator (SSA) as the active layer has been developed. The open loop transfer functions of the treated beam given by the SSA rate of strain circuit show great similarity to transfer functions taken from a reference sensor laminated directly to the beam. It has been shown experimentally that this beam treatment significantly increased the damping coefficient of the first mode in closed loop.
WAMS Based Damping Control of Inter-area Oscillations Employing Energy Storage System
Directory of Open Access Journals (Sweden)
MA, J.
2012-05-01
Full Text Available This paper presents a systematic design procedure for a wide-area damping controller (WADC employing Energy Storage Systems (ESSs. The WADC is aimed at enhancing the damping of multiple inter-area modes in a large scale power system. Firstly, geometric measures of controllability and obsevability are used to select the control locations for ESSs and most effective stabilizing signals, respectively. Then, the WADC coordinates these signals to achieve multiple-input-multiple-output (MIMO controllers with the least Frobenius norm feedback gain matrix. The simulation results of frequency and time domains verify the effectiveness of the wide-area damping controller for various operating conditions. Furthermore, the robustness of the wide-area damping controller is also tested with respect to time delay and uncertainty of models.
Detection of directional energy damping in vibrating systems
Indian Academy of Sciences (India)
B R Amruth; Souri Banerjee
2009-04-01
The transmission efficiency, frequency and amplitude alteration have been measured by a simple technique of coupled oscillators with a frequency gradient and in a system of non-Newtonian fluid in the form of corn-flour slime. The system of coupled oscillators was found to exhibit preferential energy transfer towards the low frequency end with the reverse propagation severely damped. Energy transfer in all directions was damped in the non-Newtonian fluid in comparison with water. Also the damping in non-Newtonian fluids works only after a lower limit for input amplitude. While most of the previous studies focussed on dissipation of energy within shock-absorbing systems, we demonstrate the contribution of re-distribution of energy reaching the output end to achieve shock absorbing.
Efficient active feedback scheme of image multi-class classification%结合主动反馈的图像多分类框架
Institute of Scientific and Technical Information of China (English)
刘君; 王银辉; 李黎; 张宇
2011-01-01
为了解决图像语义分类中的训练数据不对称、小样本训练和噪声数据这3个难题,提出结合主动反馈的图像多分类框架.该框架将主动选择的策略应用到图像的多分类中,通过主动的选择出不确定的图片给用户手动标记,扩大训练图片集,提高分类的精度.为了验证该框架的有效性,提出一种有效的结合主动选择的图像多分类算法,即结合投票的DDAG SVM(decision directed acyclic graph support vector machine)算法.该算法提出了新的主动选择策略,即结合投票和旁移机制的主动选择策略.实验结果表明,该算法能有效应用到图像多分类中,比DDAGSVM和采用普通主动选择策略的DDAGSVM具有更高的分类的精度.%In order to solve three difficulties of image classification, including asymmetry of training data, small sample issue and noise sample problem, efficient active feedback scheme of image multi-class classification which introduce active selecting technique into image multi-class classification is proposed. By actively selecting doubtful images for users to label, more training samples can be gotten and more accurate classification can be done. In order to validate the scheme, an image multi-class classification algorithm combining with active selecting is fulfilled, which is named as DDAG SVM (decision directed acyclic graph support vector machine) with voting.Experiments show that the algorithm has more accuracy than DDAG SVM and DDAG SVM with normal selecting strategy, so it is efficient and the proposed scheme is also good for image multi-class classification.
An Improved Force Feedback Control Algorithm for Active Tendons
Directory of Open Access Journals (Sweden)
Ligang Cai
2012-08-01
Full Text Available An active tendon, consisting of a displacement actuator and a co-located force sensor, has been adopted by many studies to suppress the vibration of large space flexible structures. The damping, provided by the force feedback control algorithm in these studies, is small and can increase, especially for tendons with low axial stiffness. This study introduces an improved force feedback algorithm, which is based on the idea of velocity feedback. The algorithm provides a large damping ratio for space flexible structures and does not require a structure model. The effectiveness of the algorithm is demonstrated on a structure similar to JPL-MPI. The results show that large damping can be achieved for the vibration control of large space structures.
Physically Damped Noise Canceling Hydrophone
2016-06-24
300075 1 of 10 PHYSICALLY DAMPED NOISE CANCELING HYDROPHONE STATEMENT OF GOVERNMENT INTEREST [0001] The invention described herein may be...transducer with an electromechanical driver comprising a plurality of single crystal piezoelectric elements joined to an inner surface and arranged to form...an electromechanical stack assembly. Each single crystal piezoelectric element has a surface, an opposite surface, and a Attorney Docket No
Waves, damped wave and observation
Phung, Kim Dang
2009-01-01
We consider the wave equation in a bounded domain (eventually convex). Two kinds of inequality are described when occurs trapped ray. Applications to control theory are given. First, we link such kind of estimate with the damped wave equation and its decay rate. Next, we describe the design of an approximate control function by an iterative time reversal method.
Red cell DAMPs and inflammation.
Mendonça, Rafaela; Silveira, Angélica A A; Conran, Nicola
2016-09-01
Intravascular hemolysis, or the destruction of red blood cells in the circulation, can occur in numerous diseases, including the acquired hemolytic anemias, sickle cell disease and β-thalassemia, as well as during some transfusion reactions, preeclampsia and infections, such as those caused by malaria or Clostridium perfringens. Hemolysis results in the release of large quantities of red cell damage-associated molecular patterns (DAMPs) into the circulation, which, if not neutralized by innate protective mechanisms, have the potential to activate multiple inflammatory pathways. One of the major red cell DAMPs, heme, is able to activate converging inflammatory pathways, such as toll-like receptor signaling, neutrophil extracellular trap formation and inflammasome formation, suggesting that this DAMP both activates and amplifies inflammation. Other potent DAMPs that may be released by the erythrocytes upon their rupture include heat shock proteins (Hsp), such as Hsp70, interleukin-33 and Adenosine 5' triphosphate. As such, hemolysis represents a major inflammatory mechanism that potentially contributes to the clinical manifestations that have been associated with the hemolytic diseases, such as pulmonary hypertension and leg ulcers, and likely plays a role in specific complications of sickle cell disease such as endothelial activation, vaso-occlusive processes and tissue injury.
Satellite Dynamic Damping via Active Force Control Augmentation
Varatharajoo, Renuganth
2012-07-01
An approach that incorporates the Active Force Control (AFC) technique into a conventional Proportional-Derivative (PD) controller is proposed for a satellite active dynamic damping towards a full attitude control. The AFC method has been established to facilitate a robust motion control of dynamical systems in the presence of disturbances, parametric uncertainties and changes that are commonly prevalent in the real-world environment. The usefulness of the method can be extended by introducing intelligent mechanisms to approximate the mass or inertia matrix of the dynamic system to trigger the compensation effect of the controller. AFC is a technique that relies on the appropriate estimation of the inertial or mass parameters of the dynamic system and the measurements of the acceleration and force signals induced by the system if practical implementation is ever considered. In AFC, it is shown that the system subjected to a number of disturbances remains stable and robust via the compensating action of the control strategy. We demonstrate that it is possible to design a spacecraft attitude feedback controller that will ensure the system dynamics set point remains unchanged even in the presence of the disturbances provided that the actual disturbances can be modeled effectively. In order to further facilitate this analysis, a combined energy and attitude control system (CEACS) is proposed as a model satellite attitude control actuator. All the governing equations are established and the proposed satellite attitude control architecture is made amenable to numerical treatments. The results show that the PD-AFC attitude damping performances are superiorly better than that of the solely PD type. It is also shown that the tunings of the AFC system gains are crucial to ensure a better attitude damping performance and this process is mandatory for AFC systems. Finally, the results demonstrate an important satellite dynamic damping enhancement capability using the AFC
Damped Oscillator with Delta-Kicked Frequency
Manko, O. V.
1996-01-01
Exact solutions of the Schrodinger equation for quantum damped oscillator subject to frequency delta-kick describing squeezed states are obtained. The cases of strong, intermediate, and weak damping are investigated.
I.P. van Staveren (Irene)
2009-01-01
textabstractThe dominant economic theory, neoclassical economics, employs a single economic evaluative criterion: efficiency. Moreover, it assigns this criterion a very specific meaning. Other – heterodox – schools of thought in economics tend to use more open concepts of efficiency, related to comm
Feedback strategies for wireless communication
Ozbek, Berna
2014-01-01
This book explores the different strategies regarding the feedback information for wireless communication systems. The text analyzes the impact of quantization and correlation of channel state information (CSI) on the system performance. The authors show the effect of the reduced and limited feedback information and gives an overview about the feedback strategies in the standards. This volume presents theoretical analysis as well as practical algorithms for the required feedback information at the base stations to perform adaptive resource allocation efficiently and mitigate interference coming from other cells.
Modal approximations to damped linear systems
Veseli/'c, K
2009-01-01
We consider a finite dimensional damped second order system and obtain spectral inclusion theorems for the related quadratic eigenvalue problem. The inclusion sets are the 'quasi Cassini ovals' which may greatly outperform standard Gershgorin circles. As the unperturbed system we take a modally damped part of the system; this includes the known proportionally damped models, but may give much sharper estimates. These inclusions are then applied to derive some easily calculable sufficient conditions for the overdampedness of a given damped system.
On porous-elastic system with localized damping
Santos, M. L.; Almeida Júnior, D. S.
2016-06-01
In this article, we are considering the one-dimensional equations of an homogeneous and isotropic porous elastic solid, where the localized damping involves the sum of displacement velocity of a solid elastic material and the volume fraction velocity. First we show, using a result due to Benchimol (SIAM J Control Optim 16:373-379, 1978), that the semigroup associated with the system is strongly stable if and only if the boundary of the support of feedback control intersects that of the interval under consideration. Then we use the frequency domain method combined with careful inequalities obtained using multiplicative techniques to prove that the semigroup under consideration is exponentially stable.
Semi-Active Friction Damping of Large Space Truss Structures
Directory of Open Access Journals (Sweden)
L. Gaul
2004-01-01
Full Text Available The present approach for vibration suppression of flexible structures is based on friction damping in semi-active joints. At optimal locations conventional rigid connections of a large truss structure are replaced by semi-active friction joints. Two different concepts for the control of the normal forces in the friction interfaces are implemented. In the first approach each semi-active joint has its own local feedback controller, whereas the second concept uses a global, clipped-optimal controller. Simulation results of a 10-bay truss structure show the potential of the proposed semi-active concept.
Decoherence and damping in ideal gases
Polonyi, Janos
2010-01-01
The particle and current densities are shown to display damping and undergo decoherence in ideal quantum gases. The damping is read off from the equations of motion reminiscent of the Navier-Stokes equations and shows some formal similarity with Landau damping. The decoherence leads to consistent density and current histories with characteristic length and time scales given by the ideal gas.
Review: Modeling Damping in Mechanical Engineering Structures
Directory of Open Access Journals (Sweden)
Michel Lalanne
2000-01-01
Full Text Available This paper is concerned with the introduction of damping effects in the analysis of mechanical engineering structures. Damping can be considered as being generated by concentrated elements, by distributed elements, or by several effects existing simultaneously. Modeling damping for different engineering situations is described and some applications are presented briefly.
2008-01-01
A dynamic extension for position feedback of port-Hamiltonian mechanical systems is studied. First we look at the consequences for the matching equations when applying Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC). Then we look at the possibilities of asymptotically stabilizing a class of port-Hamiltonian mechanical systems without having to know the velocities, as once presented for Euler-Lagrange (EL) systems. Here it is shown how the idea of damping injection by ...
DEFF Research Database (Denmark)
Eriksson, Tor Viking; Poulsen, Anders; Villeval, Marie Claire
2009-01-01
This paper experimentally investigates the impact of different pay schemes and relative performance feedback policies on employee effort. We explore three feedback rules: no feedback on relative performance, feedback given halfway through the production period, and continuously updated feedback. ...
DEFF Research Database (Denmark)
Adamczyk, Andrzej Grzegorz; Teodorescu, Remus; Rodriguez, Pedro
2011-01-01
to Full-Scale Converter based type. Moreover resemblance of such Wind Power Plant to modern FACTS devices is recognized and exploited. Paper discusses many aspect of damping controller design, including feedback signal selection and control effectiveness with respect to wind farm location. Analysis......Damping of low frequency power oscillations is one of essential aspects of maintaining power system stability. In literature can be found publications on damping capability of Doubly Fed Induction Generator based wind turbines. This paper extends discussion on Wind Power Plant damping capability...... and design is based on modal analysis, therefore matching modeling approach for wind power plant is proposed. Finally, performance of Wind Power Plant damping control is compared to a regular power system stabilizer installed on a synchronous generator....
Sensitivity of quantum-dot semiconductor lasers to optical feedback.
O'Brien, D; Hegarty, S P; Huyet, G; Uskov, A V
2004-05-15
The sensitivity of quantum-dot semiconductor lasers to optical feedback is analyzed with a Lang-Kobayashi approach applied to a standard quantum-dot laser model. The carriers are injected into a quantum well and are captured by, or escape from, the quantum dots through either carrier-carrier or phonon-carrier interaction. Because of Pauli blocking, the capture rate into the dots depends on the carrier occupancy level in the dots. Here we show that different carrier capture dynamics lead to a strong modification of the damping of the relaxation oscillations. Regions of increased damping display reduced sensitivity to optical feedback even for a relatively large alpha factor.
DAMPs, Ageing, and Cancer: The ‘DAMP Hypothesis’
Huang, Jin; Xie, Yangchun; Sun, Xiaofang; Zeh, Herbert J.; Kang, Rui; Lotze, Michael T.; Tang, Daolin
2014-01-01
Ageing is a complex and multifactorial process characterized by the accumulation of many forms of damage at the molecular, cellular, and tissue level with advancing age. Ageing increases the risk of the onset of chronic inflammation-associated diseases such as cancer, diabetes, stroke, and neurodegenerative disease. In particular, ageing and cancer share some common origins and hallmarks such as genomic instability, epigenetic alteration, aberrant telomeres, inflammation and immune injury, reprogrammed metabolism, and degradation system impairment (including within the ubiquitin-proteasome system and the autophagic machinery). Recent advances indicate that damage-associated molecular pattern molecules (DAMPs) such as high mobility group box 1, histones, S100, and heat shock proteins play location-dependent roles inside and outside the cell. These provide interaction platforms at molecular levels linked to common hallmarks of ageing and cancer. They can act as inducers, sensors, and mediators of stress through individual plasma membrane receptors, intracellular recognition receptors (e.g., advanced glycosylation end product-specific receptors, AIM2-like receptors, RIG-I-like receptors, and NOD1-like receptors, and toll-like receptors), or following endocytic uptake. Thus, the DAMP Hypothesis is novel and complements other theories that explain the features of ageing. DAMPs represent ideal biomarkers of ageing and provide an attractive target for interventions in ageing and age-associated diseases. PMID:25446804
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.
The Damped String Problem Revisited
Gesztesy, Fritz
2010-01-01
We revisit the damped string equation on a compact interval with a variety of boundary conditions and derive an infinite sequence of trace formulas associated with it, employing methods familiar from supersymmetric quantum mechanics. We also derive completeness and Riesz basis results (with parentheses) for the associated root functions under less smoothness assumptions on the coefficients than usual, using operator theoretic methods (rather than detailed eigenvalue and root function asymptotics) only.
Active damping of unidimensional structures
Tartakovskiy, B. D.
1973-01-01
The vibration characteristics of an unidimensional structure are discussed. The cases considered are: (1) a rigid pipe in which a wave propagates, (2) an infinite string along which a transverse wave propagates, (3) a rod along which longitudinal or torsional columns propagate, and (4) generally a unidimensional propagation of some one mode of vibrations which is nondegenerating with distance. Mathematical models are developed to show the performance of the mechanical devices under various damping conditions.
Radiation damping in real time.
Mendes, A C; Takakura, F I
2001-11-01
We study the nonequilibrium dynamics of a charge interacting with its own radiation, which originates the radiation damping. The real-time equation of motion for the charge and the associated Langevin equation is found in classical limit. The equation of motion for the charge allows one to obtain the frequency-dependent coefficient of friction. In the lowest order we find that although the coefficient of static friction vanishes, there is dynamical dissipation represented by a non-Markovian dissipative kernel.
The DAMPE silicon tungsten tracker
Gallo, Valentina; Asfandiyarov, R; Azzarello, P; Bernardini, P; Bertucci, B; Bolognini, A; Cadoux, F; Caprai, M; Domenjoz, M; Dong, Y; Duranti, M; Fan, R; Franco, M; Fusco, P; Gargano, F; Gong, K; Guo, D; Husi, C; Ionica, M; Lacalamita, N; Loparco, F; Marsella, G; Mazziotta, M N; Mongelli, M; Nardinocchi, A; Nicola, L; Pelleriti, G; Peng, W; Pohl, M; Postolache, V; Qiao, R; Surdo, A; Tykhonov, A; Vitillo, S; Wang, H; Weber, M; Wu, D; Wu, X; Zhang, F; De Mitri, I; La Marra, D
2017-01-01
The DArk Matter Particle Explorer (DAMPE) satellite has been successfully launched on the 17th December 2015. It is a powerful space detector designed for the identification of possible Dark Matter signatures thanks to its capability to detect electrons and photons with an unprecedented energy resolution in an energy range going from few GeV up to 10 TeV. Moreover, the DAMPE satellite will contribute to a better understanding of the propagation mechanisms of high energy cosmic rays measuring the nuclei flux up to 100 TeV. DAMPE is composed of four sub-detectors: a plastic strip scintillator, a silicon-tungsten tracker-converter (STK), a BGO imaging calorimeter and a neutron detector. The STK is made of twelve layers of single-sided AC-coupled silicon micro-strip detectors for a total silicon area of about 7 $m^2$ . To promote the conversion of incident photons into electron-positron pairs, tungsten foils are inserted into the supporting structure. In this document, a detailed description of the STK constructi...
Sub-synchronous resonance damping using high penetration PV plant
Khayyatzadeh, M.; Kazemzadeh, R.
2017-02-01
The growing need to the clean and renewable energy has led to the fast development of transmission voltage-level photovoltaic (PV) plants all over the world. These large scale PV plants are going to be connected to power systems and one of the important subjects that should be investigated is the impact of these plants on the power system stability. Can large scale PV plants help to damp sub-synchronous resonance (SSR) and how? In this paper, this capability of a large scale PV plant is investigated. The IEEE Second Benchmark Model aggregated with a PV plant is utilized as the case study. A Wide Area Measurement System (WAMS) based conventional damping controller is designed and added to the main control loop of PV plant in order to damp the SSR and also investigation of the destructive effect of time delay in remote feedback signal. A new optimization algorithm called teaching-learning-based-optimization (TLBO) algorithm has been used for managing the optimization problems. Fast Furrier Transformer (FFT) analysis and also transient simulations of detailed nonlinear system are considered to investigate the performance of the controller. Robustness of the proposed system has been analyzed by facing the system with disturbances leading to significant changes in generator and power system operating point, fault duration time and PV plant generated power. All the simulations are carried out in MATLAB/SIMULINK environment.
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...... into two, and if these are required to have the same modal damping ratio, the characteristic equation conforms to a two-parameter format. By selecting a suitable relative separation of the modal frequencies, the design problem defines a one-parameter family – determined, for example, in terms...
Nonlinear damping identification from transient data
Smith, Clifford B.; Wereley, Norman M.
1999-06-01
To study new damping augmentation methods for helicopter rotor systems, accurate and reliable nonlinear damping identification techniques are needed. For example, current studies on applications of magnetorheological (MR) dampers for rotor stability augmentation suggest that a strong Coulomb damping characteristic will be manifested as the field applied to the MR fluid is maximized. Therefore, in this work, a single degree of freedom (SDOF) system having either nonlinear Coulomb or quadratic damping is considered. This paper evaluates three analyses for identifying damping from transient test data; an FFT-based moving block analysis, an analysis based on a periodic Fourier series decomposition, and a Hilbert transform based technique. Analytical studies are used to determine the effects of block length, noise, and error in identified modal frequency on the accuracy of the identified damping level. The FFT-based moving block has unacceptable performance for systems with nonlinear damping. These problems were remedied in the Fourier series based analysis and acceptable performance is obtained for nonlinear damping identification from both this technique and the Hilbert transform based method. To more closely simulate a helicopter rotor system test, these techniques were then applied to a signal composed of two closely spaced modes. This data was developed to simulate a response containing the first lag and 1/rev modes. The primary mode of interest (simulated lag mode) had either Coulomb or quadratic damping, and the close mode (1/rev) was either undamped or had a specified viscous damping level. A comprehensive evaluation of the effects of close mode amplitude, frequency, and damping level was performed. A classifier was also developed to identify the dominant damping mechanism in a signal of 'unknown' composition. This classifier is based on the LMS error of a fit of the analytical envelope expression to the experimentally identified envelope signal. In most
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).
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).
Exploring Damped Lyα System Host Galaxies Using Gamma-Ray Bursts
Toy, Vicki L.; Cucchiara, Antonino; Veilleux, Sylvain; Fumagalli, Michele; Rafelski, Marc; Rahmati, Alireza; Cenko, S. Bradley; Capone, John I.; Pasham, Dheeraj R.
2016-12-01
We present a sample of 45 Damped Lyα system (DLA; {N}{{H}{{I}}} ≥slant 2× {10}20 {{cm}}-2) counterparts (33 detections, 12 upper limits) which host gamma-ray bursts (GRB-DLAs) in order to investigate star formation and metallicity within galaxies hosting DLAs. Our sample spans z˜ 2{--}6 and is nearly three times larger than any previously detected DLA counterparts survey based on quasar line-of-sight searches (QSO-DLAs). We report star formation rates (SFRs) from rest-frame UV photometry and spectral energy distribution modeling. We find that DLA counterpart SFRs are not correlated with either redshift or H i column density. Thanks to the combination of Hubble Space Telescope and ground-based observations, we also investigate DLA host star formation efficiency. Our GRB-DLA counterpart sample spans both higher efficiency and low efficiency star formation regions compared to the local Kennicutt-Schmidt relation, local star formation laws, and z˜ 3 cosmological simulations. We also compare the depletion times of our DLA hosts sample to other objects in the local universe; our sample appears to deviate from the star formation efficiencies measured in local spiral and dwarf galaxies. Furthermore, we find similar efficiencies as local inner disks, SMC, and Lyman-break galaxy outskirts. Finally, our enrichment time measurements show a spread of systems with under- and over-abundance of metals, which may suggest that these systems had episodic star formation and a metal enrichment/depletion as a result of strong stellar feedback and/or metal inflow/outflow.
Cracks Detection Using Active Modal Damping and Piezoelectric Components
Directory of Open Access Journals (Sweden)
B. Chomette
2013-01-01
Full Text Available The dynamics of a system and its safety can be considerably affected by the presence of cracks. Health monitoring strategies attract so a great deal of interest from industry. Cracks detection methods based on modal parameters variation are particularly efficient in the case of large cracks but are difficult to implement in the case of small cracks due to measurement difficulties in the case of small parameters variation. Therefore the present study proposes a new method to detect small cracks based on active modal damping and piezoelectric components. This method uses the active damping variation identificated with the Rational Fraction Polynomial algorithm as an indicator of cracks detection. The efficiency of the proposed method is demonstrated through numerical simulations corresponding to different crack depth and locations in the case of a finite element model of a clamped-clamped beam including four piezoelectric transducers.
Quantum secure direct communication over the collective amplitude damping channel
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
An efficient quantum secure direct communication protocol is presented over the amplitude damping channel.The protocol encodes logical bits in two-qubit noiseless states,and so it can function over a quantum channel subjected to collective amplitude damping.The feature of this protocol is that the sender encodes the secret directly on the quantum states,the receiver decodes the secret by performing determinate measurements,and there is no basis mismatch.The transmission’s safety is ensured by the nonorthogonality of the noiseless states traveling forward and backward on the quantum channel.Moreover,we construct the efficient quantum circuits to implement channel encoding and information encoding by means of primitive operations in quantum computation.
Quantum secure direct communication over the collective amplitude damping channel
Institute of Scientific and Technical Information of China (English)
QIN Suduan; WEN QiaoYan; MENG LuoMing; ZHU FuChen
2009-01-01
An efficient quantum secure direct communication protocol is presented over the amplitude damping channel. The protocol encodes logical bits in two-qubit noiseless states, and so it can function over a quantum channel subjected to collective amplitude damping. The feature of this protocol is that the sender encodes the secret directly on the quantum states, the receiver decodes the secret by per-forming determinate measurements, and there is no basis mismatch. The transmission's safely is en-sured by the nonorthogonality of the noiseless states traveling forward and backward on the quantum channel. Moreover, we construct the efficient quantum circuits to implement channel encoding and information enooding by means of primitive operations in quantum computation.
On the experimental prediction of the stability threshold speed caused by rotating damping
Vervisch, B.; Derammelaere, S.; Stockman, K.; De Baets, P.; Loccufier, M.
2016-08-01
An ever increasing demand for lighter rotating machinery and higher operating speeds results in a raised probability of instabilities. Rotating damping is one of the reasons, instability occurs. Rotating damping, or rotor internal damping, is the damping related to all rotating parts while non-rotating damping appearing in the non-rotating parts. The present study describes a rotating setup, designed to investigate rotating damping experimentally. An efficient experimental procedure is presented to predict the stability threshold of a rotating machine. The setup consists of a long thin shaft with a disk in the middle and clamped boundary conditions. The goal is to extract the system poles as a function of the rotating speed. The real parts of these poles are used to construct the decay rate plot, which is an indication for the stability. The efficiency of the experimental procedure relies on the model chosen for the rotating shaft. It is shown that the shaft behavior can be approximated by a single degree of freedom model that incorporates a speed dependent damping. As such low measurement effort and only one randomly chosen measurement location are needed to construct the decay rate plot. As an excitation, an automated impact hammer is used and the response is measured by eddy current probes. The proposed method yields a reliable prediction of the stability threshold speed which is validated through measurements.
Cancer immunogenicity, danger signals, and DAMPs: what, when, and how?
Garg, Abhishek D; Dudek, Aleksandra M; Agostinis, Patrizia
2013-01-01
Cancer immunosurvelliance usually leads to formation of cancer cells that have been "immunoedited" to resist anti-tumor immunity. One of the consequences of immunoediting that is, reduced immunogenicity, is an important roadblock in revival of stable and long-lasting anti-tumor immune responses. Research done during the last decade has shown that emission by the dying cancer cells of immunomodulatory factors or damage-associated molecular patterns (DAMPs), which can act as danger signals, is a critical event in accentuating the immunogenicity of cancer cells, in response to a subset of anticancer treatments. Recent evidence has defined that an apoptotic cell death subroutine and its underlying biochemistry, which has been termed as "immunogenic cell death (ICD)" or "immunogenic apoptosis," is required for the efficient emission of DAMPs and inciting anti-tumor immunity. Here, we review the basic concepts of ICD, like cancer immunogenicity, danger signals, and DAMPs. Moreover, we discuss the emerging molecular links between endoplasmic reticulum (ER) stress, induction of a viral response-like gene expression, danger signals, and anti-tumor immunity. We envisage that along with ER stress-based trafficking of DAMPs (which is a "short-range communicator" of danger), the accompanying induction of a viral response-like gene expression and the secretion of anti-tumorigenic cytokines may become a crucial signature of ICD induction by anticancer therapy.
Spatial damping of propagating sausage waves in coronal cylinders
Guo, Ming-Zhe; Chen, Shao-Xia; Li, Bo; Xia, Li-Dong; Yu, Hui
2015-09-01
Context. Sausage modes are important in coronal seismology. Spatially damped propagating sausage waves were recently observed in the solar atmosphere. Aims: We examine how wave leakage influences the spatial damping of sausage waves propagating along coronal structures modeled by a cylindrical density enhancement embedded in a uniform magnetic field. Methods: Working in the framework of cold magnetohydrodynamics, we solve the dispersion relation (DR) governing sausage waves for complex-valued, longitudinal wavenumber k at given real angular frequencies ω. For validation purposes, we also provide analytical approximations to the DR in the low-frequency limit and in the vicinity of ωc, the critical angular frequency separating trapped from leaky waves. Results: In contrast to the standing case, propagating sausage waves are allowed for ω much lower than ωc. However, while able to direct their energy upward, these low-frequency waves are subject to substantial spatial attenuation. The spatial damping length shows little dependence on the density contrast between the cylinder and its surroundings, and depends only weakly on frequency. This spatial damping length is of the order of the cylinder radius for ω ≲ 1.5vAi/a, where a and vAi are the cylinder radius and the Alfvén speed in the cylinder, respectively. Conclusions: If a coronal cylinder is perturbed by symmetric boundary drivers (e.g., granular motions) with a broadband spectrum, wave leakage efficiently filters out the low-frequency components.
Introduction to DAMPE event reconstruction (On behalf of DAMPE collaboration)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. To measure basic attributes of cosmic ray particles, DAMPE is equipped with four sub-detectors, BGO calorimeter (BGO), plastic scintillator detector (PSD), silicon tungsten tracker (STK) and neutron detector (NUD). On orbit, the high energy particle data are acquired and recorded by well-designed Data Acquisition system. After that, a series of elaborate event reconstruction algorithms are implemented to determine the energy, direction and particle ID of each event. The energy reconstruction algorithm firstly treats the sum of the BGO crystal energy as the overall energy estimator and various corrections are performed to calculate energy leakage from side and back of the calorimeter. The track reconstruction starts with cluster finding in STK, then shower axis of BGO and barycentre of clusters are used to extract seed of tracks. These seeds will be projected on the next layer by Kalman Filter method which will finally give location and direction of particle tracks. Based on shower development in BGO and tracks reconstructed by STK, we also combine data from PSD and NUD and developed a series of algorithms to evaluate particle's charge and identification. In this talk, we will describe technical strategies of event reconstruction and provide their basic performance.
Air Damping Analysis in Comb Microaccelerometer
Directory of Open Access Journals (Sweden)
Wu Zhou
2014-04-01
Full Text Available Air damping significantly influences the dynamical characteristics of MEMS accelerometers. Its effects at micro-scale level sharply depend on the structure layouts and size of MEMS devices. The damping phenomenon of comb microaccelerometers is investigated. The air between fixed plate electrodes and movable plate electrodes cannot flow freely and is compressed. The air damping, therefore, exhibits both viscous effects and stiffness effects. The former generates a drag force like that in macromechanical systems, and the damping force is proportional to the velocity of movable electrodes. The latter stiffens the rigidity of structure, and the stiffening level is related to the gap value of capacitors, internal pressure, and temperature. This paper focuses on the dependence of the squeeze film air damping on capacitor gaps. The simulation and experiments indicate that the squeeze film effect is sharply affected by the gap value when the structural dimensions decrease. And the influence of fabrication errors is considered in damping design in comb microaccelerometers.
Damped transverse oscillations of interacting coronal loops
Soler, Roberto
2015-01-01
Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations compared to those of an isolated loop. Here we theoretically investigate resonantly damped transverse oscillations of interacting non-uniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. ...
Optimal Design of High-Order Passive-Damped Filters for Grid-Connected Applications
DEFF Research Database (Denmark)
Beres, Remus Narcis; Wang, Xiongfei; Blaabjerg, Frede
2016-01-01
design procedures, the proposed method simplifies the iterative design of the overall filter while ensuring the minimum resonance peak with a lower damping capacitor and a lower rated resistor. It is shown that there is only one optimal value of the damping resistor or quality factor to achieve a minimum......Harmonic stability problems caused by the resonance of high-order filters in power electronic systems are ever increasing. The use of passive damping does provide a robust solution to address these issues, but at the price of reduced efficiency due to the presence of additional passive components...
Quantizing the damped harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Latimer, D C [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)
2005-03-04
We consider the Fermi quantization of the classical damped harmonic oscillator (dho). In past work on the subject, authors double the phase space of the dho in order to close the system at each moment in time. For an infinite-dimensional phase space, this method requires one to construct a representation of the CAR algebra for each time. We show that the unitary dilation of the contraction semigroup governing the dynamics of the system is a logical extension of the doubling procedure, and it allows one to avoid the mathematical difficulties encountered with the previous method.
Vitreous Enamel Damping Material Development.
1982-11-01
PROCEDURES 3 2.1. EXPERIMENTAL 3 2.1.1. GLASS PREPARATION 3 2.1.2. METHOD OF COATING APPLICATION 3 2.1.3. VIBRATION DAMPING MEASUREMENTS 3 2.2. CALCULATION OF...discussion in this report. fL 2 SECTION II TECHNICAL PROCEDURES 2.1 EXPERIMENTAL 2.1.1 Glass Preparation All of the compositions, except the standard...After heat treatments of composition "B", a- cristobalite and devitrite (Na20.3CaO-6SiO 2) appear as crystalline phases; a- cristobalite being the major
Radiation damping in metal nanoparticle pairs.
Dahmen, Christian; Schmidt, Benjamin; von Plessen, Gero
2007-02-01
The radiation damping rate of plasmon resonances in pairs of spherical gold nanoparticles is calculated. The radiative line width of the plasmon resonance indicates significant far-field coupling between the nanoparticles over distances many times the particle diameter. The radiation damping of the coupled particle-plasmon mode alternates between superradiant and subradiant behavior when the particle spacing is varied. At small particle spacings where near-field coupling occurs, the radiation damping rate lies far below that of an isolated particle.
Parametric Landau damping of space charge modes
Macridin, Alexandru; Stern, Eric; Amundson, James; Spentzouris, Panagiotis
2016-01-01
Landau damping is the mechanism of plasma and beam stabilization; it is caused by energy transfer from collective modes to incoherent motion of resonant particles. Normally this resonance requires the wave frequency in the particle frame to match the resonant particles frequency. Using the Synergia modeling package to study transverse coherent modes of bunched beams with space charge, we have identified a new kind of damping mechanism, parametric Landau damping, driven by the modulation of the wave-particle interaction.
Nonlinear theory of magnetic Landau damping
Energy Technology Data Exchange (ETDEWEB)
Kirpichnikov, A.P.; Yusupov, I.U.
1978-05-01
The nonlinear Cerenkov damping of helical electromagnetic waves in a magnetized plasma is analyzed. The nonlinear mechanism which leads to oscillations in the wave amplitude and limits the damping is the trapping of resonant particles in the potential well of the wave, as in the O'Neil problem. The factors of the type exp (-..cap alpha..t/sup 2/) in the expression for the nonlinear damping rate for a Maxwellian particle distribution lead to a damping of the amplitude oscillations of the helical wave which is much more rapid than for a plasma wave.
Phenomenology of chiral damping in noncentrosymmetric magnets
Akosa, Collins Ashu
2016-06-21
A phenomenology of magnetic chiral damping is proposed in the context of magnetic materials lacking inversion symmetry. We show that the magnetic damping tensor acquires a component linear in magnetization gradient in the form of Lifshitz invariants. We propose different microscopic mechanisms that can produce such a damping in ferromagnetic metals, among which local spin pumping in the presence of an anomalous Hall effect and an effective “s-d” Dzyaloshinskii-Moriya antisymmetric exchange. The implication of this chiral damping in terms of domain-wall motion is investigated in the flow and creep regimes.
The next linear collider damping ring lattices
Energy Technology Data Exchange (ETDEWEB)
Wolski, Andrzej; Corlett, John N.
2001-06-20
We report on the lattice design of the Next Linear Collider (NLC) damping rings. The damping rings are required to provide low emittance electron and positron bunch trains to the NLC linacs, at a rate of 120 Hz. We present an optical design, based on a theoretical minimum emittance (TME) lattice, to produce the required normalized extracted beam emittances gex = 3 mm-mrad and gey = 0.02 mm mrad. An assessment of dynamic aperture and non-linear effects is given. The positron pre-damping ring, required to reduce the emittance of the positron beam such that it may be accepted by a main damping ring, is also described.
Hysteretic damping in rotordynamics: An equivalent formulation
Genta, Giancarlo; Amati, Nicola
2010-10-01
The hysteretic damping model cannot be applied to time domain dynamic simulations: this is a well-known feature that has been discussed in the literature since the time when analog computers were widespread. The constant equivalent damping often introduced to overcome this problem is also discussed, and its limitations are stated, in particular those linked with its application in rotordynamics to simulate rotating damping. An alternative model based on the nonviscous damping (NVD) model, but with a limited number of additional degrees of freedom, is proposed, and the relevant equations are derived. Some examples show applications to the rotordynamics field.
Asymptotically optimal feedback control for a system of linear oscillators
Ovseevich, Alexander; Fedorov, Aleksey
2013-12-01
We consider problem of damping of an arbitrary number of linear oscillators under common bounded control. We are looking for a feedback control steering the system to the equilibrium. The obtained control is asymptotically optimal: the ratio of motion time to zero with this control to the minimum one is close to 1, if the initial energy of the system is large.
一个面向可变形模型实时有效的接触反馈框架%Real Time and Efficient Haptic Feedback Framework for Deformable Objects
Institute of Scientific and Technical Information of China (English)
薛喜梅; 杨光; 王田苗
2002-01-01
由于力反馈需要很高的计算速度及变形反馈需要详细的图形信息,本文提供一个实时有效的接触反馈框架, 通过在粗糙三角形网格上进行局部细分来实现.当检测到接触后,将发生碰撞的表面细分以产生一个粒子系统.利用此粒子系统,用近似速度锥理论对形变进行模拟.同时,采用弹簧-阻尼模型计算形变力.最后,对此框架进行了测试并实际应用于一个医疗规化仿真系统.%On account of the high computational speed required for force feedback and the detailed graphic required for deformation feedback, this paper presents a real time and efficient haptic feedback framework by subdividing the area of interest on a relatively coarse triangular mesh. When a contact is detected, a portion of the colliding surface is subdivided and a particle system produced, which is used for deformation based on the approximate velocity cone theory. Simultaneously, a spring-damper model is used for computing the contact force. Finally, these techniques are tested and implemented in a surgery planning simulation system.
Petitjean, P.; Ledoux, C.
Recently, Prochaska & Wolfe (1997) have used Keck spectra of 17 DLA absorbers to investigate the kinematics of the neutral gas using unsaturated low excitation transitions such as Si iiλ 1808. They show that the absorption profiles are inconsistent with models of galactic haloes with random motions, spherically infalling gas and slowly rotating hot disks. The CDM model (Kauffmann 1996) is rejected as it produces disks with rotation velocities too small to account for the large observed velocity broadening of the absorption lines. Models of thick disks (h ~0.3 R, where h is the vertical scale and R the radius) with large rotational velocity (v 225kms-1) can reproduce the data. By combining new data on five damped systems with information gathered in the literature, we study the kinematics of the low and high-ionization phases in a sample of 26 damped Lyman-α systems in the redshift range 1.17 - 4.38. We show that the broader the line the more asymmetric, as expected in case rotation dominates the line broadening. However this correlation does not hold for velocities larger than 150 km/s indicating that evidence for rotational motions if any is restricted to velocity broadenings Δ V 200kms-1 are peculiar with kinematics consistent with random motions. They show sub-systems as those expected if the objects are in the process of merging.
Damped and detuned accelerator structures
Energy Technology Data Exchange (ETDEWEB)
Deruyter, H.; Farkas, Z.D; Hoag, H.A.; Ko, K.; Kroll, N.; Loew, G.A.; Miller, R.; Palmer, R.B.; Paterson, J.M.; Thompson, K.A.; Wang, J.W.; Wilson, P.B.
1990-09-01
This paper reports continuing work on accelerator structures for future TeV linear colliders. These structures, in addition to having to operate at high gradients, must minimize the effects of wakefield modes which are induced by e{sup {plus minus}} bunch trains. Two types of modified disk-loaded waveguides are under investigation: damped structures in which the wakefield power is coupled out to lossy regions through radial slots in the disks and/or azimuthal rectangular waveguides, whereby the external Q of the undesirable HEM{sub 11} mode is lowered to values below 20, and detuned structures in which the frequencies of these modes are modified from one end to the other of each section by {approximately}10%, thereby scrambling their effects on the beam. Beam dynamics calculations indicate that these two approaches are roughly equivalent. MAFIA, ARGUS and URMEL codes have been used extensively in conjunction with low-power tests on S- and X-band models to identify mode patterns, dispersion curves and Q values, and to demonstrate damping or detuning of the HEM modes. Results of calculations and measurements on the various structures are presented and evaluated.
Acoustic transducer with damping means
Smith, Richard W.; Adamson, Gerald E.
1976-11-02
An ultrasonic transducer specifically suited to high temperature sodium applications is described. A piezoelectric active element is joined to the transducer faceplate by coating the faceplate and juxtaposed active element face with wetting agents specifically compatible with the bonding procedure employed to achieve the joint. The opposite face of the active element is fitted with a backing member designed to assure continued electrical continuity during adverse operating conditions which can result in the fracturing of the active element. The fit is achieved employing a spring-loaded electrode operably arranged to electrically couple the internal transducer components, enclosed in a hermetically sealed housing, to accessory components normally employed in transducer applications. Two alternative backing members are taught for assuring electrical continuity. The first employs a resilient, discrete multipoint contact electrode in electrical communication with the active element face. The second employs a resilient, elastomeric, electrically conductive, damped member in electrical communication with the active element face in a manner to effect ring-down of the transducer. Each embodiment provides continued electrical continuity within the transducer in the event the active element fractures, while the second provides the added benefit of damping.
Active damping of the camera support mast of a Cherenkov Gamma-ray telescope
Energy Technology Data Exchange (ETDEWEB)
Smrz, M. [Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague (Czech Republic); Bastaits, R., E-mail: rbastait@ulb.ac.b [Active Structures Laboratory, Universite Libre de Bruxelles, CP. 165-42, 50 Av. F.D. Roosevelt, B-1050 Brussels (Belgium); Preumont, A., E-mail: andre.preumont@ulb.ac.b [Active Structures Laboratory, Universite Libre de Bruxelles, CP. 165-42, 50 Av. F.D. Roosevelt, B-1050 Brussels (Belgium)
2011-04-11
This paper explores the possibility of damping actively the camera support mast of Gamma-ray telescopes with a configuration similar to the MAGIC telescope, where the camera is supported by a curved mast and an array of cables. This is achieved by replacing a set of passive cables by a set of active ones, controlled by active tendons. Each active tendon consists of a displacement actuator collocated to a force sensor with independent force feedback control loops. The paper outlines the theory of decentralized active damping of cable-structures, points out the main design parameters, and evaluates the amount of damping that the control system can provide. The effect of the control on the wind response and on the transient response of the telescope is estimated.
Robust Design of LCL-Filters for Active Damping in Grid Converters
DEFF Research Database (Denmark)
Alzola, Rafael Pena; Liserre, Marco; Blaabjerg, Frede
2013-01-01
elements. However, large variations in the grid inductance and resonances arising from parallel converters may still compromise the system stability. This calls for a robust design of LCL-filters with active damping. This paper proposes a design flow with little iteration for two well-known methods, namely......Grid converters require a simple inductor or an LCL-filter to limit the current ripples. The LCL-filter is nowadays the preferred solution as it allows lower inductance values. In order to solve the stability concerns, active damping is preferred to passive damping since it does not use dissipative...... lead-lag network and current capacitor feedback. The proposed formulas for the resonance frequency, grid and converter inductance ratio, and capacitance of the LCL-filter allow calculating all the LCL-filter parameters. An estimation for the achieved Total Harmonic Distortion (THD) of the grid current...
Quasienergy formulation of damped response theory.
Kristensen, Kasper; Kauczor, Joanna; Kjaergaard, Thomas; Jørgensen, Poul
2009-07-28
We present a quasienergy-based formulation of damped response theory where a common effective lifetime parameter has been introduced for all excited states in terms of complex excitation energies. The introduction of finite excited state lifetimes leads to a set of (complex) damped response equations, which have the same form to all orders in the perturbation. An algorithm is presented for solving the damped response equations in Hartree-Fock theory and Kohn-Sham density functional theory. The use of the quasienergy formulation allows us to obtain directly the computationally simplest expressions for damped response functions by applying a set of response parameter elimination rules, which minimize the total number of damped response equations to be solved. In standard response theory broadened absorption spectra are obtained by ad hoc superimposing lineshape functions onto the absorption stick spectra, whereas an empirical lineshape function common to all excitations is an integrated part of damped response theory. By superimposing the lineshape functions inherent in damped response theory onto the stick spectra of standard response theory, we show that the absorption spectra obtained in standard and damped response theory calculations are identical. We demonstrate that damped response theory may be applied to obtain absorption spectra in all frequency ranges, also those that are not readily addressed using standard response theory. This makes damped response theory an effective tool, e.g., for determining absorption spectra for large molecules, where the density of the excited states may be very high, and where standard response theory therefore is not applicable in practice. A thorough comparison is given between our formulation of damped response theory and the formulation by Norman et al. [J. Chem. Phys. 123, 194103 (2005)].
Anomalous feedback and negative domain wall resistance
Cheng, Ran; Zhu, Jian-Gang; Xiao, Di
2016-11-01
Magnetic induction can be regarded as a negative feedback effect, where the motive-force opposes the change of magnetic flux that generates the motive-force. In artificial electromagnetics emerging from spintronics, however, this is not necessarily the case. By studying the current-induced domain wall dynamics in a cylindrical nanowire, we show that the spin motive-force exerting on electrons can either oppose or support the applied current that drives the domain wall. The switching into the anomalous feedback regime occurs when the strength of the dissipative torque β is about twice the value of the Gilbert damping constant α. The anomalous feedback manifests as a negative domain wall resistance, which has an analogy with the water turbine.
Passivation of Underactuated Systems with Physical Damping
Gómez-Estern, F.; Schaft, A.J. van der; Acosta, J.A.
2004-01-01
In recent works, Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) has been succesfully applied to mechanical control problems with no physical damping present. In some cases, the friction terms can be obviated without compromising stability in closed loop. However in method
Magnetic dipole oscillations and radiation damping
Stump, Daniel R.; Pollack, Gerald L.
1997-01-01
We consider the problem of radiation damping for a magnetic dipole oscillating in a magnetic field. An equation for the radiation reaction torque is derived, and the damping of the oscillations is described. Also discussed are runaway solutions for a rotating magnetic dipole moving under the influence of the reaction torque, with no external torque.
Gyroscopic Stabilization of Indefinite Damped Systems
DEFF Research Database (Denmark)
Kliem, Wolfhard; Müller, Peter C.
1997-01-01
Modelling of mechanical systems with sliding bearings, or with dry friction, can lead to linear systems with an indefinite damping matrix. We ask under what conditions such a system is unstable (the indefiniteness of the damping matrix is not enough) and under what conditions we can stabilize...
Understanding the Damped SHM without ODEs
Ng, Chiu-king
2016-01-01
Instead of solving ordinary differential equations (ODEs), the damped simple harmonic motion (SHM) is surveyed qualitatively from basic mechanics and quantitatively by the instrumentality of a graph of velocity against displacement. In this way, the condition b ? [square root]4mk for the occurrence of the non-oscillating critical damping and…
Damping Characteristics of Metal Matrix Composites
1989-05-25
Sin . ........... Inches x 106 (Microinches) IR&D ......................... n e t Research and Development.K ...................... Kelvin LPSS...Proper Sitan Ampliutde Dependence for a Dislocation Damping Mechanism 5.4 SUMMARY Damping measurements of pitch 55 graphite fiber reinforcement in high
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...
On Collisionless Damping of Ion Acoustic Waves
DEFF Research Database (Denmark)
Jensen, Vagn Orla; Petersen, P.I.
1973-01-01
Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero.......Exact theoretical treatments show that the damping of ion acoustic waves in collisionless plasmas does not vanish when the derivative of the undisturbed distribution function at the phase velocity equals zero....
DEFF Research Database (Denmark)
Li, Zipeng; Jiang, Aiting; Shen, Pan;
2016-01-01
, this paper presents a systematic design method for the LCL-LC filtered grid-connected photovoltaic (PV) system. With this method, controller parameters and the active damping feedback coefficient are easily obtained by specifying the system stability and dynamic performance indices, and it is more convenient...
Magnetic damping of rotation. [in satellites
Opik, E. J.
1977-01-01
Based on Wilson's (1977) article on the magnetic effects on space vehicles and other celestial bodies, the magnetic damping of rotation is considered. The inadequacy of the interstellar magnetic field in overcoming solar wind shielding and thus influencing the rotation of bodies is described. The ionospheric shielding of the interstellar field is discussed along with the permeability and magnetic damping by the solar or stellar wind. Star formation and angular momentum is discussed and attention is given to the magnetic damping of unshielded small bodies. Calculations of the rate for damping through random particle impact are made. Theories concerning the rotation of asteroids and the origin of meteorites are reviewed. The shielding process of ionospheric plasmas is outlined and the damping effect of the geomagnetic field on the rotation of artificial satellites is evaluated.
Quantum dynamics of the damped harmonic oscillator
Philbin, T G
2012-01-01
The quantum theory of the damped harmonic oscillator has been a subject of continual investigation since the 1930s. The obstacle to quantization created by the dissipation of energy is usually dealt with by including a discrete set of additional harmonic oscillators as a reservoir. But a discrete reservoir cannot directly yield dynamics such as Ohmic damping (proportional to velocity) of the oscillator of interest. By using a continuum of oscillators as a reservoir, we canonically quantize the harmonic oscillator with Ohmic damping and also with general damping behaviour. The dynamics of a damped oscillator is determined by an arbitrary effective susceptibility that obeys Kramers-Kronig relations. This approach offers an alternative description of nano-mechanical oscillators and opto-mechanical systems.
Damping characteristics of damaged fiber composite components
Eberle, K.
1986-01-01
Defects in fiber composite components produce changes with respect to the vibrational characteristics of the material. These changes can be recognized in the form of a frequency shift or an alteration of the damping process. The present investigation is concerned with questions regarding the possibility of a utilization of the changes in suitable defect-detecting inspection procedures. A description is given of a method for measuring the damping characteristics of a specimen. This method provides a spectrum of the damping coefficients of the sample as a basis for a comprehensive evaluation of the damping behavior. The correlation between defects and change in the damping characteristics is demonstrated with the aid of results obtained in measurements involving specimens of carbon-fiber composites and a component consisting of glass-fiber-reinforced plastics.
Practical Damping Identification of FAST Cable Suspension
Directory of Open Access Journals (Sweden)
Jinghai Sun
2014-03-01
Full Text Available FAST focus cabin is suspended and driven by 6 parallel large span cables. Low stiffness of cables makes the cabin sensitive to disturbance and difficult to control. Structural damping then becomes a key factor that can improve control ability. Therefore, a reasonable damping estimation is important for system design. In this paper, a practical damping identification method is developed based on Ibrahim-time-domain algorithm. The method shows satisfied performance on accuracy and reliability in simulation test and is utilized in vibration experiments to identify damping ratios of both single cable model and FAST 3 m scale cable suspension model. Finally, a preliminary analysis of the damping properties is given out based on the results of identification.
Dampness in Buildings and Health
DEFF Research Database (Denmark)
Clausen, Geo; Rode, Carsten; Bornehag, Carl-Gustaf
1999-01-01
will maintain close contact with international, not the least Nordic, research groups by facilitating possibilities for exchange visits and guest positions. The centre will be very active in educating new Ph.D.'s.Next to presenting the setting, the paper gives an overview of the research tasks within the centre...... academic positions. It is anticipated that the research council's support for the centre will be prolonged for another five years, during which period it will be gradually reduced and the centre will be indulged as a permanent activity at DTU.The ambition of the research is to extend the knowledge....... The main themes are:· Continued research in human perception of indoor air quality, especially by identification of the factors that may cause annoyance to the occupants. Such annoyances may be emissions from materials or biological activity, and is often linked to the dampness of buildings.· Studies...
A New Fine Damping Method for Solid ESG Rotor
Institute of Scientific and Technical Information of China (English)
LIU Chun-ning; TIAN Wei-feng; JIN Zhi-hua
2006-01-01
For the electrostatically suspended gyro(ESG) with solid rotor, because the equatorial photoelectric sensor won't sense the equatorial marking line and output the correct damping control information when the nutation angle is small, the active damping with equatorial marking line will bring considerable error. The passive damping method by applying strong DC magnetic field requires too much time. So an active damping method by longitude marking lines is proposed to fulfill the fine damping for solid ESG rotor. The shape of rotor marking lines and the principle of fine damping are introduced. The simulation results prove that this fine damping method can effectively solve the problem of damping error introduced by active damping with equatorial marking line. The estimating results for damping time indicate that the fine damping time is less than 10 percent of passive damping time.
Energy Technology Data Exchange (ETDEWEB)
Chortis, D I; Chrysochoidis, N A; Saravanos, D A [Department of Mechanical Engineering and Aeronautics, University of Patras, Patras 26500 (Greece)
2007-07-15
The paper presents a brief description of composite damping mechanics for blade sections of arbitrary lamination and geometry. A damped 3-D shear beam element is presented enabling the assembly of damped structural dynamic models of blades with hollow multi-cell tubular laminated sections. Emphasis is placed to the inclusion of composite material coupling effects, first in the blade section stiffness and damping matrices and finally into the stiffness and damping matrices of the finite element. Evaluations of the beam element are presented, to quantify the material coupling effect on composite beams of simple box sections. Correlations between predicted and measured modal frequencies and damping values in small model Glass/Epoxy are also shown. Finally, the damped modal characteristics of a 35m realistic wind-turbine blade model design, are predicted.
Calibration of BGO Calorimeter of the DAMPE in Space
Wang, Chi
2016-07-01
The Dark Matter Particle Explore (DAMPE) is a satellite based experiment which launched on December 2015 and aims at indirect searching for dark matter by measuring the spectra of high energy e±, γ from 5GeV up to 10TeV originating from deep space. The 3D imaging BGO calorimeter of DAMPE was designed to precisely measurement the primary energy of the electromagnetic particle and provides a highly efficient rejection of the hadronic background by reconstruct the longitudinal and lateral profiles of showers. To achieve the expected accuracy on the energy measurement, each signal channel has to be calibrated. The energy equalization is performed using the signal that Minimum Ionizing Particles (MIP) leave in each BGO bar, the MIPs measurement method with orbit data and, data quality, time stability using MIPs data will be presented, too.
Optical variability of quasars: a damped random walk
Ivezic, Zeljko
2013-01-01
A damped random walk is a stochastic process, defined by an exponential covariance matrix that behaves as a random walk for short time scales and asymptotically achieves a finite variability amplitude at long time scales. Over the last few years, it has been demonstrated, mostly but not exclusively using SDSS data, that a damped random walk model provides a satisfactory statistical description of observed quasar variability in the optical wavelength range, for rest-frame timescales from 5 days to 2000 days. The best-fit characteristic timescale and asymptotic variability amplitude scale with the luminosity, black hole mass, and rest wavelength, and appear independent of redshift. In addition to providing insights into the physics of quasar variability, the best-fit model parameters can be used to efficiently separate quasars from stars in imaging surveys with adequate long-term multi-epoch data, such as expected from LSST.
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...
Feedback Control of a Class of Nonholonomic Hamiltonian Systems
DEFF Research Database (Denmark)
Sørensen, Mathias Jesper
Feedback control of nonholonomic systems has always been problematic due to the nonholonomic constraints that limit the space of possible system velocities. This property is very basic, and Brockett proved that a nonholonomic system cannot be asymptotically stabilized by a time-invariant smooth...... turns out to be useful when stabilizing the nonholonomic system. If the system is properly actuated it is possible to asymptotically stabilize the primary part of the configuration coordinates via a passive energy shaping and damping injecting feedback. The feedback is smooth and time...... of the closed loop system some extensions are provided: integral action for asymptotic stabilization under the influence of disturbances, and an adaptive damping scheme ensuring that the robot travels at a predefined speed when tracking a path. Both of these extensions are defined in the framework...
Fan, Rongping; Meng, Guang; Yang, Jun; He, Caichun
2009-01-01
Interior noise and vibration reduction has become one important concern of railway operating environments due to the influence of increased speeds and reduced vehicle weights for energy efficiency. Three types of viscoelastic damping materials, bitumen-based damping material, water-based damping coating and butyl rubber damping material, were developed to reduce the vibration and noise within railway vehicles. Two sleeper carriages were furnished with the new materials in different patterns of constrained-layer and free-layer damping treatment. The measurements of vibration and noise were carried out in three running carriages. It is found that the reduction effect of damping treatments depends on the running speed. The unweighted root-mean-square acceleration is reduced by 0.08-0.79 and 0.06-0.49 m/s 2 for the carriage treated by bitumen-based as well as water-based damping materials and water-based damping material, respectively. The first two materials reduce vibration in a wider frequency range of 63-1000 Hz than the last. It turns out that the damping treatments of the first two reduce the interior noise level by 5-8 dBA within the carriage, and the last damping material by 1-6 dBA. However, the specific loudness analysis of noises shows that the noise components between 125 and 250 Hz are dominant for the overall loudness, although the low-frequency noise is noticeably decreased by the damping materials. The measure of loudness is shown to be more accurate to assess reduction effect of the damping material on the acoustic comfort.
Zhabitsky, V. M.
2010-12-01
The stability of an ion beam in synchrotrons with digital filters in the feedback loop of a transverse damper is treated. A transverse feedback system (TFS) is required in synchrotrons to stabilize the high intensity ion beams against transverse instabilities and to damp the beam injection errors. The TFS damper kicker (DK) corrects the transverse momentum of a bunch in proportion to its displacement from the closed orbit at the location of the beam position monitor (BPM). The digital signal processing unit in the feedback loop between BPM and DK ensures a condition to achieve optimal damping. Damping rates of the feedback systems with digital filters are analysed in comparison with those in an ideal feedback system.
Effect of chemical exchange on radiation damping in aqueous solutions of the osmolyte glycine.
Rodríguez, Juan Carlos; Jennings, Patricia A; Melacini, Giuseppe
2002-06-05
Radiation damping is of central relevance in NMR spectroscopy especially with the advent of ultrahigh-field magnets and of supersensitive probes. Furthermore, the recent realization that the combined effect of the distant dipole field and of radiation damping causes the resurrection of undesired crushed water magnetization emphasizes the need for a thorough understanding of all the factors affecting radiation damping. While the effects of pulsed-field gradients and of active feedback have been extensively investigated, the consequences on radiation damping of chemical exchange between water and co-solutes is not as well understood. Here it is demonstrated that the rate of water radiation damping is significantly affected by free glycine (Gly), a representative of an important class of biocompatible osmolytes often used at molar concentrations as protein stabilizers. The pH and temperature dependencies of this effect were investigated and rationalized in terms of radiation damping attenuation caused by incoherent dephasing occurring in the intermediate exchange regime. For instance, at pH 6.0 and at a temperature of 313 K the Gly NH3+/water exchange has the same dramatic effect on radiation damping as a series of repeated weak PFGs, increasing the water inversion-recovery zero-crossing delay from approximately 30 ms to approximately 2.3 s. In addition, under these conditions, the Gly NH3+/water exchange suppresses the resurrection of unwanted crushed water magnetization. When used in combination with PFGs and water flip-back schemes, glycine is therefore expected to tame chaotic dynamics and improve the reproducibility of the NMR experiments affected by it.
Calculation of continuum damping of Alfv\\'en eigenmodes in 2D and 3D cases
Bowden, G W; Könies, A
2015-01-01
In ideal MHD, shear Alfv\\'{e}n eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfv\\'{e}n continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfv\\'{e}n eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD code CKA . ...
Damping Of Low Frequency Oscillations In Power System Using Device Upfc With Fuzzy Logic
Directory of Open Access Journals (Sweden)
B.Divya Lakshmi
2014-04-01
Full Text Available Power stability is an important issue that is becoming increasingly important to an power systems at all levels. We are unable to achieve the stability of the system due to some factors. Low frequency oscillation’s is one of the major factors that affect the transmission line capacity. Traditionally power system stabilizers(PSS are being used to damp these inevitable oscillations. In advanced technology FACTS devices such as unified power flow controllers (UPFC are used to control the power flow in transmission lines. They can also replace the PSS to damp the low frequency oscillations effectively through direct control of voltage and power. In our model, single machine infinite bus power system with UPFC is considered. The designed FUZZY based UPFC controllers adjusts four UPFC inputs by appropriately processing of input error signal and provides an efficient damping. The results of the simulation show that the UPFC with FUZZY LOGIC controller is effectively damping the LOW FREQUENCY OSCILLATIONS.
Directory of Open Access Journals (Sweden)
Irene Y. H. Gu
2007-01-01
Full Text Available This paper describes an efficient yet accurate methodology for estimating system damping. The proposed technique is based on linear dynamic system theory and the Hilbert damping analysis. The proposed technique requires capacitor switching waveforms only. The detected envelope of the intrinsic transient portion of the voltage waveform after capacitor bank energizing and its decay rate along with the damped resonant frequency are used to quantify effective X/R ratio of a system. Thus, the proposed method provides complete knowledge of system impedance characteristics. The estimated system damping can also be used to evaluate the system vulnerability to various PQ disturbances, particularly resonance phenomena, so that a utility may take preventive measures and improve PQ of the system.
Identification and testing of an efficient hopfield neural network magnetostriction model
Energy Technology Data Exchange (ETDEWEB)
Adly, A.A. E-mail: amradlya@intouch.com; Abd-El-Hafiz, S.K. E-mail: salwahafiz@link.net
2003-07-01
Magnetostriction models are indispensable to different crucial computational activities such as those dealing with active vibration damping devices and optimum clamping stresses for transformer sheets. This paper presents an efficient magnetostriction Preisach-type model based on the effective field approach. According to this approach, the total applied field may be regarded as a super position of the actual magnetic field and a stress-dependent feedback term. Construction and identification of the model is carried out by providing experimental training data to a modular discrete Hopfield neural network-linear neural network combination. Experimental testing suggests that this model can lead to good qualitative and quantitative simulation results.
DEFF Research Database (Denmark)
Li, Hui; Liu, Shengquan; Ji, Haiting
2014-01-01
This study investigates the inter-area low-frequency damping control strategies of a doubly fed induction generator (DFIG)-based wind farm through oscillation transient energy function (OTEF) analysis. Based on the OTEF descent expressions, the feasibility of damping the inter-area low...... oscillation of the wind turbine shaft. The proposed additional fuzzy control strategy with the active/reactive power loop has better damping performance than the presented PSS control, especially for damping the inter-area low-frequency oscillation.......-frequency oscillation is theoretically analyzed through the active/reactive power control of grid-connected wind farms. Additional damping control strategies with the active/reactive power loop of the DFIG-based wind farm are presented using the feedback signal of the transmission line active power flow based...
Reproducing the Kinematics of Damped Lyman-alpha Systems
Bird, Simeon; Neeleman, Marcel; Genel, Shy; Vogelsberger, Mark; Hernquist, Lars
2014-01-01
We examine the kinematic structure of Damped Lyman-alpha Systems (DLAs) in a series of cosmological hydrodynamic simulations using the AREPO code. We are able to match the distribution of velocity widths of associated low ionisation metal absorbers substantially better than earlier work. Our simulations produce a population of DLAs dominated by halos with virial velocities around 70 km/s, consistent with a picture of relatively small, faint objects. In addition, we reproduce the observed correlation between velocity width and metallicity and the equivalent width distribution of SiII. Some discrepancies of moderate statistical significance remain; too many of our spectra show absorption concentrated at the edge of the profile and there are slight differences in the exact shape of the velocity width distribution. We show that the improvement over previous work is mostly due to our strong feedback from star formation and our detailed modelling of the metal ionisation state.
Landau Damping of Beam Instabilities by Electron Lenses
Energy Technology Data Exchange (ETDEWEB)
Shiltsev, V. [Fermilab; Alexahin, Yuri; Burov, A. [Fermilab; Valishev, A. [Fermilab
2017-06-26
Modern and future particle accelerators employ increasingly higher intensity and brighter beams of charged particles and become operationally limited by coherent beam instabilities. Usual methods to control the instabilities, such as octupole magnets, beam feedback dampers and use of chromatic effects, become less effective and insufficient. We show that, in contrast, Lorentz forces of a low-energy, a magnetically stabilized electron beam, or "electron lens", easily introduces transverse nonlinear focusing sufficient for Landau damping of transverse beam instabilities in accelerators. It is also important that, unlike other nonlinear elements, the electron lens provides the frequency spread mainly at the beam core, thus allowing much higher frequency spread without lifetime degradation. For the parameters of the Future Circular Collider, a single conventional electron lens a few meters long would provide stabilization superior to tens of thousands of superconducting octupole magnets.
Identification of integrating and critically damped systems with time delay
Institute of Scientific and Technical Information of China (English)
BAJARANGBALI; Somanath MAJHI
2015-01-01
This paper presents identification of second order plus dead time (SOPDT) integrating and critically damped systems based on relay feedback testing. Relay with hysteresis is applied to the unknown system to get the sustained oscillations also called as limit cycle. The limit cycle parameters are utilized in mathematical expressions which are derived using state space technique so that exact process model parameters are estimated. As the relay with hysteresis helps in generating sustained oscillations and also reduces effect of measurement noise which is an important issue in system identification. Different types of processes in the form of transfer function models are considered to show the efficacy of the proposed method and results are compared with available methods in the literature with and without noise effect.
Local structural modeling for implementation of optimal active damping
Blaurock, Carl A.; Miller, David W.
1993-09-01
Local controllers are good candidates for active control of flexible structures. Local control generally consists of low order, frequency benign compensators using collocated hardware. Positive real compensators and plant transfer functions ensure that stability margins and performance robustness are high. The typical design consists of an experimentally chosen gain on a fixed form controller such as rate feedback. The resulting compensator performs some combination of damping (dissipating energy) and structural modification (changing the energy flow paths). Recent research into structural impedance matching has shown how to optimize dissipation based on the local behavior of the structure. This paper investigates the possibility of improving performance by influencing global energy flow, using local controllers designed using a global performance metric.
The time scales of the climate-economy feedback and the climatic cost of growth
Energy Technology Data Exchange (ETDEWEB)
Hallegatte, Stephane [CIRED - CNRM, Nogent-sur-Marne (France)
2005-04-01
This paper is based on the perception that the inertia of climate and socio-economic systems are key parameters in the climate change issue. In a first part, it develops and implements a new approach based on a simple integrated model with a particular focus on an innovative transient impact and adaptation modelling. In a second part, a climate-economy feedback is defined and characterized. It is found that: (i) it has a 70-year characteristic time, which is long when compared to the system's other time-scales, and it cannot act as a natural damping process of climate change; (ii) mitigation has to be anticipated since the feedback of an emission reduction on the economy is significant only after a 20-year delay and really efficient after a one-century delay; (iii) the IPCC methodology, that neglects the feedback from impacts to emissions, is acceptable up to 2100, whatever is the level of impacts. This analysis allows also to define a climatic cost of growth as the additional climate change damages due to the additional emissions linked to economic growth. Usefully, this metric for climate change damages is particularly independent of the baseline scenario. (orig.)
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%.
Structural dynamic modification using additive damping
Indian Academy of Sciences (India)
B C Nakra
2000-06-01
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 complex structures. Optimisation techniques are used for damping effectiveness include multi-parameter optimisatoin techniques and a technique using dynamic sensitivity analysis and structural dynamic modification. These have been applied for optimum dynamic design of structures incorporating viscoelastic damping. Some current trends for vibraton control are also discussed.
Radiation damping of a polarizable particle
Novotny, Lukas
2017-09-01
A polarizable body moving in an external electromagnetic field will slow down. This effect is referred to as radiation damping and is analogous to Doppler cooling in atomic physics. Using the principles of special relativity we derive an expression for the radiation damping force and find that it solely depends on the scattered power. The cooling of the particle's center-of-mass motion is balanced by heating due to radiation pressure shot noise, giving rise to an equilibrium that depends on the ratio of the field's frequency and the particle's mass. While damping is of relativistic nature, heating has its roots in quantum mechanics.
Damping Properties of Flexible Epoxy Resin
Institute of Scientific and Technical Information of China (English)
WANG Xiang; LIU Hanxing; OUYANG Shixi
2008-01-01
Amino-terminated polyethers and amino-terminated polyurethane were used as curing agent to cure the epoxy resin together and get a series of cured products. The damping properties of the composites were studied by DMA test at different measurement frequencies. Damping mechanical tests show that the flexible epoxy resin has higher loss factor than common epoxy. The highest loss factor reaches 1.57. Also the height and position of loss factor peak of the flexible epoxy resin varies by changing the content of amino-terminated polyethers. Results shows that the flexible epoxy resin can be used as damping polymer materials at room temperature or in common frequency range.
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...... is identification by ARMA models assuming a white noise input. Method 2 is identification by simulation of a free decay response. Experimental data on the free decay response has been obtained directly by measurement as well as by the random decrement technique. Two experimental cases has been considered. The first...
Nonlinear Landau damping of Alfven waves.
Hollweg, J. V.
1971-01-01
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
LHC Transverse Feedback System and its Hardware Commissioning
Baudrenghien, P; Höfle, Wolfgang; Killing, F; Kojevnikov, I; Kotzian, G; Lebedev, N I; Louwerse, R; Makarov, A A; Montesinos, E; Rabtsun, S V; Rossi, V; Schokker, M; Thepenier, E; Valuch, D; Zhabitsky, V
2008-01-01
A powerful transverse feedback system ("Damper") has been installed in LHC. It will stabilise coupled bunch instabilities in a frequency range from 3 kHz to 20 MHz and at the same time damp injection oscillations originating from steering errors and injection kicker ripple. The transverse damper can also be used as an exciter for purposes of abort gap cleaning or tune measurement. The power and lowlevel systems layouts are described along with results from the hardware commissioning. The achieved performance is compared with earlier predictions and requirements for injection damping and instability control.
Damping capacity and compressive characteristic in some aluminum foams
Institute of Scientific and Technical Information of China (English)
程和法; 黄笑梅; 魏建宁; 韩福生
2003-01-01
The compressive behavior, energy absorption and damping capacity of Al-28% Zn alloy foam, Al-10% Mg alloy foam and commercial pure aluminum foam with open cell were investigated. The Al-28 % Zn alloy foam exhibits the typical deformation behavior of brittle foam in static compression, and a much higher energy absorption capacity than the Al-10%Mg alloy foam and pure aluminum foam to the densification strain. Over a large plastic strain range, the energy absorption efficiency of the Al-28 % Zn alloy foam keeps nearly constant and above 80%. The experiments on the internal friction of the three foams are also conducted on a multifunction internal friction apparatus (MFIFA). The Al-28%Zn alloy foam exhibits a high damping capacity which is three to four times larger than those of the pure aluminum foam and Al-28%Mg alloy foam around room temperature. The mechanism for the high damping capacity of the foamed Al-28%Zn alloy may be associated with the viscous sliding at the interface between the soft phase α and the brittle rich Zn phase η in its base metal during vibration.
Finite element model calibration using frequency responses with damping equalization
Abrahamsson, T. J. S.; Kammer, D. C.
2015-10-01
Model calibration is a cornerstone of the finite element verification and validation procedure, in which the credibility of the model is substantiated by positive comparison with test data. The calibration problem, in which the minimum deviation between finite element model data and experimental data is searched for, is normally characterized as being a large scale optimization problem with many model parameters to solve for and with deviation metrics that are nonlinear in these parameters. The calibrated parameters need to be found by iterative procedures, starting from initial estimates. Sometimes these procedures get trapped in local deviation function minima and do not converge to the globally optimal calibration solution that is searched for. The reason for such traps is often the multi-modality of the problem which causes eigenmode crossover problems in the iterative variation of parameter settings. This work presents a calibration formulation which gives a smooth deviation metric with a large radius of convergence to the global minimum. A damping equalization method is suggested to avoid the mode correlation and mode pairing problems that need to be solved in many other model updating procedures. By this method, the modal damping of a test data model and the finite element model is set to be the same fraction of critical modal damping. Mode pairing for mapping of experimentally found damping to the finite element model is thus not needed. The method is combined with model reduction for efficiency and employs the Levenberg-Marquardt minimizer with randomized starts to achieve the calibration solution. The performance of the calibration procedure, including a study of parameter bias and variance under noisy data conditions, is demonstrated by two numerical examples.
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...
DAMPING PERFORMANCE OF EUCOMMIA ULMOIDES GUM
Institute of Scientific and Technical Information of China (English)
Ji-chuan Zhang; Zhao-hong Xue; Rui-fang Yan
2011-01-01
Eucommia ulmoides gum (EU gum), known as gutta percha in Southeast Asia, is a natural polymer with double characteristics of rubber and plastic. In present paper, tanδ-T curve and hysteresis loss (HL) were chosen to characterize its damping property. The results indicated that its tanδvalue would increase with rising of temperature when T＞ 0°C and form another damping peak at 40-80°C besides Tg peak. This phenomenon resulted fiom meltage of crystals of EU gum could increase its damping property at ambient-high temperature. Its tanδ value even exceeded those of conventional damping rubbers, such as nitrile-butadiene rubber (NBR) and chlorinated isobutene-isoprene rubber (CIIR).
Simplified Model of Nonlinear Landau Damping
Energy Technology Data Exchange (ETDEWEB)
N. A. Yampolsky and N. J. Fisch
2009-07-16
The nonlinear interaction of a plasma wave with resonant electrons results in a plateau in the electron distribution function close to the phase velocity of the plasma wave. As a result, Landau damping of the plasma wave vanishes and the resonant frequency of the plasma wave downshifts. However, this simple picture is invalid when the external driving force changes the plasma wave fast enough so that the plateau cannot be fully developed. A new model to describe amplification of the plasma wave including the saturation of Landau damping and the nonlinear frequency shift is proposed. The proposed model takes into account the change of the plasma wave amplitude and describes saturation of the Landau damping rate in terms of a single fluid equation, which simplifies the description of the inherently kinetic nature of Landau damping. A proposed fluid model, incorporating these simplifications, is verified numerically using a kinetic Vlasov code.
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...
Modification of spastic gait through mechanical damping.
Maki, B E; Rosen, M J; Simon, S R
1985-01-01
The effect of dissipative mechanical loads on spastic gait has been studied, to evaluate the feasibility of using mechanically damped orthoses to effect functional improvements in the gait of spastic patients. This concept is based on a hypothesis citing uninhibited, velocity-dependent stretch reflexes as a possible causal factor in spastic gait abnormalities, such as equinus and back-kneeing. In order to screen potential experimental subjects and to quantify velocity-dependent reflex behaviour, ankle rotation experiments and filmed gait analysis were performed. The results supported the existence of a velocity threshold. Orthosis simulation experiments were performed with one spastic subject, using a wearable, computer-controlled, electromechanical, below-knee orthosis simulator to apply a variety of damping loads to the ankle as the subject walked. Results indicated that appropriate damping can improve local joint kinematics. The damping causes a reduction in muscle stretch velocity which apparently results in reduced spastic reflex activity.
Dynamic damping property of magnetorheological elastomer
Institute of Scientific and Technical Information of China (English)
李剑锋; 龚兴龙
2008-01-01
Magnetorheological elastomer(MRE) is a new kind of smart materials,its dynamic mechanic performances can be controlled by an applied magnetic field.MRE is usually used as a stiffness-changeable spring in the semi-active vibration absorber.In order to get perfect vibration control effect,low dynamic damping of MRE is need.But the dynamic damping of MRE was not studied deeply in the past.The dynamic damping of MRE was studied and analyzed.The influences of different test conditions including test strain amplitude,test frequency and test magnetic field were deeply studied.MRE sample and pure silicone rubber sample were prepared and tested under different conditions.The test results show that the main source of dynamic damping is the friction between iron particles and rubber matrix.And the friction is mainly influenced by the strain amplitude and test magnetic field.
Techniques for Thermal Damping in Tube Bundles
Directory of Open Access Journals (Sweden)
QAMAR IQBAL
2010-10-01
Full Text Available Flow-induced vibration in heat exchangers has been a source of concern in the process, power generation and nuclear industry for several decades. Damping has a major influence on the flow induced vibrations and is dependant on a variety of factors such as mechanical properties of the tube material, geometry of intermediate supports, the physical properties of shell-side fluid, type of tube motion, number of supports, tube frequency, shell-side temperature etc. Various damping mechanisms have been identified and quantified. Generally the effects of the higher operating temperatures on the various damping mechanisms are neglected in the general design procedure. This paper focuses on the thermal aspects of damping mechanisms subjected to single phase cross-flow in shell and tube heat exchanger and a comparison is carried out safer design based on experimental and empirical formulations.
Damping Wiggler Study at KEK-ATF
Naito, Takashi; Honda, Yosuke; Korostelev, Maxim S; Kubo, Kiyoshi; Kuriki, Masao; Kuroda, Shigeru; Muto, Toshiya; Nakamura, Norio; Ross, Marc; Sakai, Hiroshi; Terunuma, Nobuhiro; Urakawa, Junji; Zimmermann, Frank
2005-01-01
The effects by damping wiggler magnets have been studied at KEK-ATF. The damping ring of the KEK-ATF is a 1.3 GeV storage ring capable of producing ultra-low emittance electron beams. It is significant issue to realize fast damping in the damping ring. The tuning method with 4 sets of wiggler was investigated for the ultra-low emittance beam. The performance on the beam quality, which is related to the transverse (x and y) and the longitudinal (z and dp/p), has been measured by the SR monitor, the laser wire, the streak camera and the energy spread monitor at the extraction line. We report on the operation condition and the measurement results.
ON DAMPING COEFFICIENT DUE TO PHASE TRANSFORMATION
Institute of Scientific and Technical Information of China (English)
Din-YuHSIEH
2003-01-01
The damping coefficient of capillary waves due to the evaporation-condensation process at the interface of the two phases of a fluid is evaluated. To highlight the mechanism of the effect of heat and mass transfer across the interface between regions of liquid and vapor, potential flow of incompressible fluids are assumed. Thus other mechanisms of damping are neglected. To fascilitate the analysis, the method of multiple-scale is employed in the analysis, even though the problem is linear.
Diffusion-damped domain wall dynamics
Energy Technology Data Exchange (ETDEWEB)
Varga, R; Infante, G [Inst. Phys., Fac. Sci., UPJS, Park Angelinum 9, 04154 Kosice (Slovakia); Badini-Confalonieri, G A; Vazquez, M, E-mail: rvarga@upjs.s [Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049, Madrid (Spain)
2010-01-01
In the given work, the influence of diffusional damping on the domain wall dynamics of heat treated FeSiBP microwires is presented. Two regions of the domain wall dynamics have been found. At low applied fields diffusion damping prevails, keeping the domain wall velocity and mobility low. At higher fields, the diffusional effects are overcomed and domain wall velocity increases steeply and so does the domain wall mobility.
Turbine blade with tuned damping structure
Energy Technology Data Exchange (ETDEWEB)
Campbell, Christian X.; Messmann, Stephen J.
2015-09-01
A turbine blade is provided comprising: a root; an airfoil comprising an external wall extending radially from the root and having a radially outermost portion; and a damping structure. The external wall may comprise first and second side walls joined together to define an inner cavity of the airfoil. The damping structure may be positioned within the airfoil inner cavity and coupled to the airfoil so as to define a tuned mass damper.
On a Nonlocal Damping Model in Ferromagnetism
Directory of Open Access Journals (Sweden)
M. Moumni
2015-01-01
Full Text Available We consider a mathematical model describing nonlocal damping in magnetization dynamics. The model consists of a modified form of the Landau-Lifshitz-Gilbert (LLG equation for the evolution of the magnetization vector in a rigid ferromagnet. We give a global existence result and characterize the long time behaviour of the obtained solutions. The sensitivity of the model with respect to large and small nonlocal damping parameters is also discussed.
Analysis of nonlinear damping properties of carbon
Kazakova, Olga I.; Smolin, Igor Yu.; Bezmozgiy, Iosif M.
2016-11-01
This paper describes research results of nonlinear damping properties of carbon fiber reinforced plastics. The experimental and computational research is performed on flat composite specimens with the gradual structure complication (from 1 to 12 layers). Specimens are subjected to three types of testing which are modal, harmonic and transient analyses. Relationships between the amplitude response and damping ratio are obtained by means of the analysis of variance as the result of this research.
Numerical studies of shear damped composite beams using a constrained damping layer
DEFF Research Database (Denmark)
Kristensen, R.F.; Nielsen, Kim Lau; Mikkelsen, Lars Pilgaard
2008-01-01
Composite beams containing one or more damping layers are studied numerically. The work is based on a semi-analytical model using a Timoshenko beam theory and a full 2D finite element model. The material system analysed, is inspired by a train wagon suspension system used in a EUREKA project Sigma......!1841. For the material system, the study shows that the effect of the damping layer is strongly influenced by the presence of a stiff constraining layer, that enforces large shear strain amplitudes. The thickness of the damping rubber layer itself has only a minor influence on the overall damping...
Smith, Clifford B.; Wereley, Norman M.
1996-10-01
The first objective of this paper is to evaluate the performance of damping identification algorithms. The second objective is to determine the feasibility of damping augmentation in rotating composite beams via passive constrained layer damping (PCLD). Damping identification schemes were applied to four rectangular cross-section laminated composite beams with cocured integral damping layers over the span of the beam. The cocured beam consisted of a twenty-ply balanced and symmetric cross-ply Gr/Ep composite host structure, a top and bottom damping layer of viscoelastic material (VEM), and a 2-ply Gr/Ep constraining layer sandwiching the viscoelastic material to the host structure. Four VEM thicknesses were considered: 0, 5, 10, and 15 mils. The cantilevered beams were tested at rotational speeds ranging from 0 to 900 RPM in a vacuum chamber. Excitation in bending was provided using piezo actuators, and the bending response was measured using full strain gauge bridges. Transient data were analysed using logarithmic decrement, a Hilbert transform technique, and an FFT- based moving block analysis. When compared to the beam with no VEM, a 19.2% volume fraction (15 mil layer) of viscoelastic in the beam produced a 400% increase in damping ratio in the non-rotating case, while at 900 RPM, the damping ratio increased only 360%. Overall structural damping was reduced as a function of RPM, due to centrifugal stiffening.
EXPERIMENTAL MODAL ANALYSIS OF VISCO-ELASTICALLY DAMPED STRUCTURES
Institute of Scientific and Technical Information of China (English)
1998-01-01
The form of the modal analysis of viscoelastically damped structures is simplified and this simplified form is similar to the form of the modal analysis of linear viscously damped structures. As a result of this simplified form, the experimental modal analysis methods of linear viscously damped structures are applied to the experimental modal analysis of viscoelastically damped structures.
Thermal damping and retardation in karst conduits
Directory of Open Access Journals (Sweden)
A. J. Luhmann
2014-08-01
Full Text Available Water temperature is a non-conservative tracer in the environment. Variations in recharge temperature are damped and retarded as water moves through an aquifer due to heat exchange between water and rock. However, within karst aquifers, seasonal and short-term fluctuations in recharge temperature are often transmitted over long distances before they are fully damped. Using analytical solutions and numerical simulations, we develop relationships that describe the effect of flow path properties, flow-through time, recharge characteristics, and water and rock physical properties on the damping and retardation of thermal peaks/troughs in karst conduits. Using these relationships, one can estimate the thermal retardation and damping that would occur under given conditions with a given conduit geometry. Ultimately, these relationships can be used with thermal damping and retardation field data to estimate parameters such as conduit diameter. We also examine sets of numerical experiments where we relax some of the assumptions used to develop these relationships, testing the effects of variable diameter, variable velocity, open channels, and recharge shape on thermal damping and retardation to provide some constraints on uncertainty. Finally, we discuss a tracer experiment that provides field confirmation of our relationships. High temporal resolution water temperature data are required to obtain sufficient constraints on the magnitude and timing of thermal peaks and troughs in order to take full advantage of water temperature as a tracer.
Damp heat stable doped zinc oxide films
Energy Technology Data Exchange (ETDEWEB)
Hüpkes, J., E-mail: j.huepkes@fz-juelich.de [IEK5–Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich (Germany); Owen, J.I. [IEK5–Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich (Germany); Wimmer, M.; Ruske, F. [Institute of Silicon Photovoltaics, Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstraße 5, 12489 Berlin (Germany); Greiner, D.; Klenk, R. [Institute for Heterogeneous Materials Systems, Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Zastrow, U. [IEK5–Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich (Germany); Hotovy, J. [IEK5–Photovoltaik, Forschungszentrum Jülich GmbH, 52425 Jülich (Germany); Faculty of Electrical Engineering and Information Technology, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava (Slovakia)
2014-03-31
Zinc oxide is widely used as transparent contact in thin film solar cells. We investigate the damp heat stability of aluminum doped ZnO (ZnO:Al) films sputter deposited at different conditions. Increase in resistivity upon damp heat exposure was observed for as-deposited ZnO:Al films and the water penetration was directly linked to this degradation. Deuterium was used as isotopic marker to identify the amount of water taken up by the films. Finally, we applied a special annealing step to prepare highly stable ZnO:Al films with charge carrier mobility of 70 cm{sup 2}/Vs after 1000 h of damp heat treatment. A grain boundary reconstruction model is proposed to explain the high stability of ZnO:Al films after annealing. - Highlights: • Study of damp heat degradation on electrical properties of ZnO:Al • Demonstration of fast water penetration and replacement mechanism • Damp heat stable ZnO:Al films with high mobility after damp heat treatment.
The next linear collider damping ring complex
Energy Technology Data Exchange (ETDEWEB)
Corlett,J.; Atkinson,D.; De Santis,S.; Hartman, N.; Kennedy, K.; Li, D.; Marks, S.; Minamihara, Y.; Nishimura, H.; Pivi, M.; Reavill, D.; Rimmer, R.; Schlueter, R.; Wolski, A.; Anderson,S.; McKee,B.; Raubenheimer, T.; Ross, M.; Sheppard, J.C.
2001-06-12
We report progress on the design of the Next Linear Collider (NLC) Damping Rings complexes. The purpose of the damping rings is to provide low emittance electron and positron bunch trains to the NLC linacs, at a rate of 120 Hz. As an option to operate at the higher rate of 180 Hz, two 1.98 GeV main damping rings per beam are proposed, and one positron pre-damping ring. The main damping rings store up to 0.8 amp in 3 trains of 190 bunches each and have normalized extracted beam emittances {gamma}{var_epsilon}x = 3 mm-mrad and {gamma}{var_epsilon}y = 0.02 mm-mrad. The optical designs, based on a theoretical minimum emittance lattice (TME), are described, with an analysis of dynamic aperture and non-linear effects. Key subsystems and components are described, including the wiggler, the vacuum systems and photon stop design, and the higher-order-mode damped RF cavities. Impedance and instabilities are discussed.
Energy Technology Data Exchange (ETDEWEB)
Jain, Atul K. [Univ. of Illinois, Urbana-Champaign, IL (United States)
2016-09-14
The overall objectives of this DOE funded project is to combine scientific and computational challenges in climate modeling by expanding our understanding of the biogeophysical-biogeochemical processes and their interactions in the northern high latitudes (NHLs) using an earth system modeling (ESM) approach, and by adopting an adaptive parallel runtime system in an ESM to achieve efficient and scalable climate simulations through improved load balancing algorithms.
Sun, Xiaoqiang; Yuan, Chaochun; Cai, Yingfeng; Wang, Shaohua; Chen, Long
2017-09-01
This paper presents the hybrid modeling and the model predictive control of an air suspension system with damping multi-mode switching damper. Unlike traditional damper with continuously adjustable damping, in this study, a new damper with four discrete damping modes is applied to vehicle semi-active air suspension. The new damper can achieve different damping modes by just controlling the on-off statuses of two solenoid valves, which makes its damping adjustment more efficient and more reliable. However, since the damping mode switching induces different modes of operation, the air suspension system with the new damper poses challenging hybrid control problem. To model both the continuous/discrete dynamics and the switching between different damping modes, the framework of mixed logical dynamical (MLD) systems is used to establish the system hybrid model. Based on the resulting hybrid dynamical model, the system control problem is recast as a model predictive control (MPC) problem, which allows us to optimize the switching sequences of the damping modes by taking into account the suspension performance requirements. Numerical simulations results demonstrate the efficacy of the proposed control method finally.
A new analysis methodology for estimating the eigenfrequencies of systems with high modal damping
Ozbek, Muammer; Rixen, Daniel J.
2016-01-01
Contemporary system identification algorithms are well proven to provide accurate eigenfrequency estimates in analyzing the systems with low modal damping. Since most engineering structures usually have low damping ratios the corresponding response characteristics can easily be obtained by conventional methods. Indeed, these modes can be extracted by using relatively short measurement durations (150-200 cycles of the lowest frequency included in the data block). However, some specific applications such as analyzing the in-operation vibration behavior of MW scale large wind turbines also require an accurate estimation of the modes with high damping. For a rotating wind turbine, some important turbine modes (e.g. flapwise rotor modes) have very high aeroelastic damping, which make them very difficult (if not impossible) to be detected. Extracting these high damping modes is a challenging task for almost all system identification techniques that are currently in use. In this work, a new method, which is based on Natural Excitation Technique (NExT), is proposed as an alternative approach for extracting the eigenfrequencies of high damping modes in an efficient way. NExT is a well established experimental dynamic analysis tool which was specifically developed to extract the dynamic characteristics of wind turbines in the early 90s. However, during the analyses it was observed that conventional NExT algorithm requires analyzing very long measurement durations (4500-5000 cycles) to be able to estimate the high damping modes accurately. A new method proposed in this work enables the eigenfrequencies of high damping modes to be estimated by using data series which are approximately 30 times shorter (around 150 cycles) than those required for a standard NExT algorithm.
SELF TUNING CONTROLLERS FOR DAMPING LOW FREQUENCY OSCILLATIONS
Directory of Open Access Journals (Sweden)
SANGU RAVINDRA
2012-09-01
Full Text Available This paper presents a new control methods based on adaptive Neuro-Fuzzy damping controller and adaptive Artificial Neural Networks damping controller techniques to control a Unified Power Flow controller (UPFC installed in a single machine infinite bus Power System. The objective of Neuro-Fuzzy and ANN based UPFC controller is to damp power system oscillations.Phillips-Herffron model of a single machine power system equipped with a UPFC is used to model the system. In order to damp power system oscillations, adaptive neuro-fuzzy damping controller and adaptive ANN damping controller for UPFC are designed and simulated. Simulation is performed for various types of loads and for different disturbances. Simulation results demonstrate that the developed adaptive ANN damping controller has an excellent capability in damping electromechanical oscillations which exhibits a superior damping performance in comparison to the neuro-fuzzy damping controller as well as conventional lead-lag controller.
VIBRATION CONTROL OF FLUID- FILLED PRISMATIC SHELL WITH ACTIVE CONSTRAINED LAYER DAMPING TREATMENTS
Institute of Scientific and Technical Information of China (English)
LIU Lijun; ZHANG Zhiyi; HUA Hongxing; ZHANG Yi
2008-01-01
Active constrained layer damping (ACLD) combines the simplicity and reliability of passive damping with the light weight and high efficiency of active actuators to obtain high damping over a wide frequency band. A fluid-filled prismatic shell is set up to investigate the validity and efficiency of ACLD treatments in the case of fluid-structure interaction. By using state subspace identification method, modal parameters of the ACLD system are identified and a state space model is established subsequently for the design of active control laws. Experiments are conducted to the fluid-filled prismatic shell subjected to random and impulse excitation, respectively. For comparison, the shell model without fluid interaction is experimented as well. Experimental results have shown that the ACLD treatments can suppress vibration of the fluid-free and fluid-filled prismatic shell effectively. Under the same control gain, vibration attenuation is almost the same in both cases.
Galaxy-scale AGN Feedback - Theory
Wagner, A Y; Umemura, M; Sutherland, R S; Silk, J
2015-01-01
Powerful relativistic jets in radio galaxies are capable of driving strong outflows but also inducing star-formation by pressure-triggering collapse of dense clouds. We review theoretical work on negative and positive active galactic nuclei feedback, discussing insights gained from recent hydrodynamical simulations of jet-driven feedback on galaxy scales that are applicable to compact radio sources. The simulations show that the efficiency of feedback and the relative importance of negative and positive feedback depends strongly on interstellar medium properties, especially the column depth and spatial distribution of clouds. Negative feedback is most effective if clouds are distributed spherically and individual clouds have small column depths, while positive feedback is most effective if clouds are predominantly in a disc-like configuration.
Information Feedback and Learning in Construction Bidding
Directory of Open Access Journals (Sweden)
Bee Lan Oo
2011-09-01
Full Text Available Information feedback condition in recurrent construction bidding is an important design variable about optimal procurement design. Contractors tend to optimize their bids in recurrent bidding with positive review of historic bids. Our experiment examines the effects of partial and no information feedback conditions on student (inexperienced bidders’ bidding trends, and the extent to which their bidding trends agree with the behavioural patterns proposed by learning direction theory. The results show that the variations in bids over time for both information feedback conditions are statistically significant. Although the bidders with partial bidding feedback information are more likely to vary their bids as indicated by learning direction theory, their bids are less competitive than those with no bidding feedback information. Construction clients would need to consider the information feedback conditions in their procurement of construction services with the goal to achieve efficiency in construction bidding.
Electric Generator in the System for Damping Oscillations of Vehicles
Serebryakov, A.; Kamolins, E.; Levin, N.
2017-04-01
The control systems for the objects of industry, power generation, transport, etc. are extremely complicated; functional efficiency of these systems determines to a great extent the safe and non-polluting operation as well as convenience of service and repair of such objects. The authors consider the possibility to improve the efficiency of systems for damping oscillations in transport using a combination of electrical (generators of rotational and linear types) and hydraulic means. Better efficiency of functioning is achieved through automatic control over the operational conditions of such a system in order to make it adaptive to variations in the road profile and ambient temperature; besides, it is possible to produce additional electric energy.
Institute of Scientific and Technical Information of China (English)
Ming Li; Zeng He; Huiming Zheng; Ning Zhang
2008-01-01
A cantilever beam with Damping Material Applying Rubber Magnetic Powder (DRM)has been investigated.Two methods are selected to hold DRM to a vibrating steel beam,one is to attach DRM by the magnetic attractive force (called DRM beam) and the other by adhesive bonding (called AB-DRM beam).Different from the damping property of AB-DRM beam caused by shear deformation of damping material,the damping property of DRM beam is characterized by the sliding frictional loss together with the internal loss of damping material.The authors established a formulation to predict the damping characteristics of DRM beam,which was validated experimentally.It is found that rubber material loss factor/β has a decisive influence on damping improvement of DRM beam versus AB-DRM beam.If/β is smaller than the critical value around 0.8255,a valid range of vibratory amplitude always exists in which DRM beam can achieve better damping than AB-DRM beam;conversely,if/β is bigger than the critical value,the valid range does not exist when slide occurs.Such results are used to determine the merits and limitations of DRM and develop design guidelines.
Introduction to the scientific application system of DAMPE (On behalf of DAMPE collaboration)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. The science data processing and payload operation maintenance for DAMPE will be provided by the DAMPE Scientific Application System (SAS) at the Purple Mountain Observatory (PMO) of Chinese Academy of Sciences. SAS is consisted of three subsystems - scientific operation subsystem, science data and user management subsystem and science data processing subsystem. In cooperation with the Ground Support System (Beijing), the scientific operation subsystem is responsible for proposing observation plans, monitoring the health of satellite, generating payload control commands and participating in all activities related to payload operation. Several databases developed by the science data and user management subsystem of DAMPE methodically manage all collected and reconstructed science data, down linked housekeeping data, payload configuration and calibration data. Under the leadership of DAMPE Scientific Committee, this subsystem is also responsible for publication of high level science data and supporting all science activities of the DAMPE collaboration. The science data processing subsystem of DAMPE has already developed a series of physics analysis software to reconstruct basic information about detected cosmic ray particle. This subsystem also maintains the high performance computing system of SAS to processing all down linked science data and automatically monitors the qualities of all produced data. In this talk, we will describe all functionalities of whole DAMPE SAS system and show you main performances of data processing ability.
Proximal Blade Twist Feedback Control for Heliogyro Solar Sails
Smith, Sarah Mitchell
mode is on the order of 0.005%, meaning there is almost no inherent damping in the blade. Next, the proximal blade twist feedback control design was successful in overcoming friction in the root actuator and added damping to the blade. The damping ratio for the lowest frequency torsional mode was increased from 0.001% to 0.09%, which is a significant amount for a heliogyro spacecraft. Finally, the camera sensor used for the proximal differential twist measurement proved to be feasible and quantization from these measurements only decreased the damping ratio to 0.075%. This research provides the first indication that a physically realizable blade root controller can deal with friction in an effective way, thus taking a step towards advancing the technology readiness level of the heliogyro spacecraft.
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.
Notes on the nonlinear beam dynamics with strong damping in the CLIC Damping Ring
Levichev, Eugene; Shatilov, Dmitry
2010-01-01
The beam is injected into the CLIC damping ring with the relatively large emittance and energy spread and then is damped to the extremely low phase volume. During the damping process the betatron frequency of each particle changes due to the space charge tune shift and nonlinear dependence of the betatron tune on the amplitude. This nonlinearity is produced by the strong chromatic sextupoles, wiggler nonlinear field components and, again, by the space charge force. During the damping, the particle cross resonances, which can trap some fraction of the beam, cause the loss of intensity, the beam blow up and degrade the beam quality. In this paper we study the evolution of the beam distribution in time during the damping for the original lattice of the CLIC DR (May 2005). Geneva, Switzerland June 2010 CLIC – Note – 850
DEFF Research Database (Denmark)
Hagerhed, L.; Bornehag, Carl-Gustaf; Sundell, Jan
2002-01-01
Questionnaire data on 8681 dwellings included in the Swedish study "Dampness in Buildings and Health" have been analysed for associations between dampness indicators, perceptions of indoor air quality and building characteristics such as time of construction, type of ventilation and type of found...... of "Dry air" in 17.3 and 33.7% respectively. Older buildings and the use of natural ventilation were associated with increased frequency of dampness indicators as well as to increased frequencies of complaints on bad indoor air quality.......Questionnaire data on 8681 dwellings included in the Swedish study "Dampness in Buildings and Health" have been analysed for associations between dampness indicators, perceptions of indoor air quality and building characteristics such as time of construction, type of ventilation and type...
Unwrapped phase inversion with an exponential damping
Choi, Yun Seok
2015-07-28
Full-waveform inversion (FWI) suffers from the phase wrapping (cycle skipping) problem when the frequency of data is not low enough. Unless we obtain a good initial velocity model, the phase wrapping problem in FWI causes a result corresponding to a local minimum, usually far away from the true solution, especially at depth. Thus, we have developed an inversion algorithm based on a space-domain unwrapped phase, and we also used exponential damping to mitigate the nonlinearity associated with the reflections. We construct the 2D phase residual map, which usually contains the wrapping discontinuities, especially if the model is complex and the frequency is high. We then unwrap the phase map and remove these cycle-based jumps. However, if the phase map has several residues, the unwrapping process becomes very complicated. We apply a strong exponential damping to the wavefield to eliminate much of the residues in the phase map, thus making the unwrapping process simple. We finally invert the unwrapped phases using the back-propagation algorithm to calculate the gradient. We progressively reduce the damping factor to obtain a high-resolution image. Numerical examples determined that the unwrapped phase inversion with a strong exponential damping generated convergent long-wavelength updates without low-frequency information. This model can be used as a good starting model for a subsequent inversion with a reduced damping, eventually leading to conventional waveform inversion.
Radiation damping in microcoil NMR probes.
Krishnan, V V
2006-04-01
Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-microL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.
Anti-damping effect of radiation reaction
Wang, G.; Li, H.; Shen, Y. F.; Yuan, X. Z.; Zi, J.
2010-01-01
The anti-damping effect of radiation reaction, which means the radiation reaction does non-negative work on a radiating charge, is investigated at length by using the Lorentz-Dirac equation (LDE) for the motion of a point charge respectively acted on by (a) a pure electric field, (b) a pure magnetic field and (c) the fields of an electromagnetic wave. We found that the curvature of the charge's trajectory plays an important role in the radiation reaction force, and the anti-damping effect cannot take place for the real macroscopic motions of a point charge. The condition for this anti-damping effect to take place is that the gradient of the external force field must exceed a certain value over the region of magnitude of the classical radius of massive charges (~10-15 m). Our results are potentially helpful to lessen the controversy on LDE and justify it as the correct classical equation describing the radiating charge's motion. If this anti-damping effect of LDE were a real existing physical process, it could serve as a mechanism within the context of classical electrodynamics for the stability of hydrogen atoms. Using the picture of an electron in quantum electrodynamics, namely the negative bare charge surrounded by the polarized positive charges of vacuum, we can obtain a reasonable explanation for the energy transferred to the electron during the occurrence of the anti-damping effect, on which the venerable work of Wheeler and Feynman has thrown some light.
Fluid damping of cylindrical liquid storage tanks.
Habenberger, Joerg
2015-01-01
A method is proposed in order to calculate the damping effects of viscous fluids in liquid storage tanks subjected to earthquakes. The potential equation of an ideal fluid can satisfy only the boundary conditions normal to the surface of the liquid. To satisfy also the tangential interaction conditions between liquid and tank wall and tank bottom, the potential flow is superimposed by a one-dimensional shear flow. The shear flow in this boundary layer yields to a decrease of the mechanical energy of the shell-liquid-system. A damping factor is derived from the mean value of the energy dissipation in time. Depending on shell geometry and fluid viscosity, modal damping ratios are calculated for the convective component.
Biomimetic Gradient Polymers with Enhanced Damping Capacities.
Wang, Dong; Zhang, Huan; Guo, Jing; Cheng, Beichen; Cao, Yuan; Lu, Shengjun; Zhao, Ning; Xu, Jian
2016-04-01
Designing gradient structures, mimicking biological materials, such as pummelo peels and tendon, is a promising strategy for developing advanced materials with superior energy damping capacities. Here a facile and effective approach for fabricating polymers with composition gradients at millimeter length scale is presented. The gradient thiol-ene polymers (TEPs) are created by the use of density difference of ternary thiol-ene-ene precursors and the subsequent photo-crosslinking via thiol-ene reaction. The compositional gradients are analyzed via differential scanning calorimeter (DSC), compressive modulus testing, atomic force microscopy (AFM) indentation, and swelling measurements. In contrast to homogeneous TEPs networks, the resultant gradient polymer shows a broader effective damping temperature range combining with good mechanical properties. The present result provides an effective route toward high damping materials by the fabrication of gradient structures.
Resolving photons from cosmic ray in DAMPE
Xu, Zunlei; Chang, Jin; Li, Xiang; Dong, TieKuang; Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer(DAMPE), which took to the skies on 17 December, is designed for high energy cosmic ray ion detection. The proportion of photons in the cosmic ray is very small, so it's difficult to distinguish between photons and 'background', but necessary for any DAMPE gamma-ray science goals.The paper present a algorithm to identify photons from 'background' mainly by the tracker/converter, which promote pair conversion and measure the directions of incident particles, and an anticoincidence detector,featuring an array of plastic scintillator to detect the charged particles.The method has been studied by simulating using the GEANT4 Monte Carlo simulation code and adjusted by the BeamTest at CERN in December,2014.In addition,DAMPE photon detection capabilities can be checked using the flight data.
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...... dominated vibrations.The first part of the thesis presents the theoretical framework for implementation of supplemental dampers in wind turbines. It is demonstrated that the feasibility of installing dampers at the bottom of the tower is significantly increased when placing passive or semiactive dampers...... 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...
The parallel computation of the smallest eigenpair of an acoustic problem with damping
Gijzen, M.B. van; Raeven, F.A.
1995-01-01
Acoustic problems with damping may give rise to large quadratic eigenproblems. Efficient and parallelizable algorithms are required for solving these problems. The recently proposed Jacobi-Davidson method is well suited for parallel computing: no matrix decomposition and no back or forward
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 ...
Dynamic Feedback in Ferromagnet-Spin Hall Metal Heterostructures
Cheng, Ran; Zhu, Jian-Gang; Xiao, Di
2016-08-01
In ferromagnet-normal-metal heterostructures, spin pumping and spin-transfer torques are two reciprocal processes that occur concomitantly. Their interplay introduces a dynamic feedback effect interconnecting energy dissipation channels of both magnetization and current. By solving the spin diffusion process in the presence of the spin Hall effect in the normal metal, we show that the dynamic feedback gives rise to (i) a nonlinear magnetic damping that is crucial to sustain uniform steady-state oscillations of a spin Hall oscillator at large angles and (ii) a frequency-dependent spin Hall magnetoimpedance that reduces to the spin Hall magnetoresistance in the dc limit.
Radiation Damping in a Focusing Channel
Ruth, Ronald D.
1996-05-01
In electron storage rings synchrotron radiation leads to the damping of the three degrees of freedom of the particle trajectory towards a stable closed orbit transversely and a fixed stable phase longitudinally. At the same time, the emission of discrete quanta leads to diffusion in all three degrees of freedom. These two competing effects result in an equilibrium beam emittance that depends upon the parameters of the storage ring. In the case above, the radiation in the bending fields dominates, and the radiation due to the focusing fields is either neglected or taken into account perturbatively. In this talk we study the opposite case, a continuous focusing channel in which the radiation and its reaction are dominated by the strong focusing field. If there is a bending field, it is much weaker than the focusing field. In such focusing systems, we find that the radiation is synchrotron-like for larger betatron oscillation amplitudes and undulator-like for smaller amplitudes. However, quantum excitation is absent for any oscillation amplitude, and the damping exhibits asymmetry in favor of the transverse degree of freedom as the amplitude becomes smaller. In the undulator regime, the damping turns into exponential in the transverse direction, much faster than the total energy damping in this system. In principle, the particle could damp to the transverse ground state of the harmonic oscillator, reaching a minimum normalized emittance, γ ɛ_min = hbar/2mc, limited only by the uncertainty principle. In the case of a bent focusing system, we find that the lack of quantum excitation and asymmetric damping still hold provided that the bending field is sufficiently weak.
Damping Functions correct over-dissipation of the Smagorinsky Model
Pakzad, Ali
2016-01-01
This paper studies the time-averaged energy dissipation rate $\\langle \\varepsilon_{SMD} (u)\\rangle$ for the combination of the Smagorinsky model and damping function. The Smagorinsky model is well known to over-damp. One common correction is to include damping functions that reduce the effects of model viscosity near walls. Mathematical analysis is given here that allows evaluation of $\\langle \\varepsilon_{SMD} (u)\\rangle $ for any damping function. Moreover, the analysis motivates a modified van Driest damping. It is proven that the combination of the Smagorinsky with this modified damping function does not over dissipate and is also consistent with Kolmogorov phenomenology.
Fault Tolerant Feedback Control
DEFF Research Database (Denmark)
Stoustrup, Jakob; Niemann, H.
2001-01-01
An architecture for fault tolerant feedback controllers based on the Youla parameterization is suggested. It is shown that the Youla parameterization will give a residual vector directly in connection with the fault diagnosis part of the fault tolerant feedback controller. It turns out...... that there is a separation be-tween the feedback controller and the fault tolerant part. The closed loop feedback properties are handled by the nominal feedback controller and the fault tolerant part is handled by the design of the Youla parameter. The design of the fault tolerant part will not affect the design...... of the nominal feedback con-troller....
Hybrid damper with stroke amplification for damping of offshore wind turbines
DEFF Research Database (Denmark)
Brodersen, Mark L.; Høgsberg, Jan
2016-01-01
tower. The proposed hybrid damper consists of a passive viscous dashpot placed in series with a load cell and an active actuator. By integrated force feedback control of the actuator motion, the associated displacement amplitude over the viscous damper can be increased compared with the passive viscous......The magnitude of tower vibrations of offshore wind turbines is a key design driver for the feasibility of the monopilesupport structure. A novel control concept for the damping of these tower vibrations is proposed, where viscous-type hybrid dampers are installed at the bottom of the wind turbine...... control leads to performance similar to that of passive viscous damping and substantial amplification of the damper deformation without actuator drift. Copyright © 2016 John Wiley & Sons, Ltd....
Variable stiffness and damping magnetorheological isolator
Institute of Scientific and Technical Information of China (English)
Yang ZHOU; Xingyu WANG; Xianzhou ZHANG; Weihua LI
2009-01-01
This paper presents the development and characterization of a magnetorheological (MR) fluid-based variable stiffness and damping isolator. The prototype of the MR fluid isolator is fabricated, and its dynamic behavior is measured under various applied magnetic fields. The parameters of the model under various magnetic fields are identified, and the dynamic perfor-mance of the isolator is evaluated in simulation. Experi-mental results indicate that both the stiffness and damping capability of the developed MR isolator can be controlled by an external magnetic field.
Classical Statistical Mechanics and Landau Damping
1997-01-01
We study the retarded response function in scalar $\\phi^4$-theory at finite temperature. We find that in the high-temperature limit the imaginary part of the self-energy is given by the classical theory to leading order in the coupling. In particular the plasmon damping rate is a purely classical effect to leading order, as shown by Aarts and Smit. The dominant contribution to Landau damping is given by the propagation of classical fields in a heat bath of non-interacting fields.
Wind turbine blade with viscoelastic damping
Energy Technology Data Exchange (ETDEWEB)
Sievers, Ryan A.; Mullings, Justin L.
2017-01-10
A wind turbine blade (60) damped by viscoelastic material (54, 54A-F) sandwiched between stiffer load-bearing sublayers (52A, 52B, 56A, 56B) in portions of the blade effective to damp oscillations (38) of the blade. The viscoelastic material may be located in one or more of: a forward portion (54A) of the shell, an aft portion (54D) of the shell, pressure and suction side end caps (54B) of an internal spar, internal webbing walls (54C, 54E), and a trailing edge core (54F).
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...... frequency - containing the resulting modal damping via the imaginary part - is given by an explicit formula. For very flexible structures, e.g. cables, only moderate damping is involved, and the explicit approximation is very accurate. However, even for stiffer structures the explicit form gives a quite...
Shock Performance of Different Semiactive Damping Strategies
Directory of Open Access Journals (Sweden)
N. Ferguson
2010-08-01
Full Text Available The problem of shock generated vibration is presented and analyzed. The fundamental background is explainedbased on the analysis of a single degree-of-freedom model with passive stiffness and damping. The advantages andlimitations of such a shock mount are discussed. Afterwards, different semi-active strategies involving variabledamping are presented. These strategies have been used for harmonic excitation but it is not clear how they willperform during a shock. This paper analyzes the different variable damping schemes already used for harmonicvibration in order to find any potential advantages or issues for theoretical shock pulses.
Feedback strategies for visual search in airframe structural inspection.
Gramopadhye, A K; Drury, C G; Sharit, J
1997-05-01
Feedback of information has consistently shown positive results in human inspection, provided it is given in a timely and appropriate manner. Feedback serves as the basis of most training schemes; traditionally this has been performance feedback. Other forms of feedback which provide strategy information rather than performance information may have a role in improving inspection. This study compared performance feedback and cognitive feedback in a realistic simulation of an aircraft structural inspection task. Performance (time, errors) feedback showed the greatest improvements in performance measures. Cognitive feedback enhanced efficiency measures of search strategy. When cognitive feedback consisted of visual representations of the path and the coverage of the search sequence, subjects also were able to use this task information to improve their search performance.
COA based robust output feedback UPFC controller design
Energy Technology Data Exchange (ETDEWEB)
Shayeghi, H., E-mail: hshayeghi@gmail.co [Technical Engineering Department, University of Mohaghegh Ardabili, Ardabil (Iran, Islamic Republic of); Shayanfar, H.A. [Center of Excellence for Power System Automation and Operation, Electrical Engineering Department, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Jalilzadeh, S.; Safari, A. [Technical Engineering Department, Zanjan University, Zanjan (Iran, Islamic Republic of)
2010-12-15
In this paper, a novel method for the design of output feedback controller for unified power flow controller (UPFC) using chaotic optimization algorithm (COA) is developed. Chaotic optimization algorithms, which have the features of easy implementation, short execution time and robust mechanisms of escaping from the local optimum, is a promising tool for the engineering applications. The selection of the output feedback gains for the UPFC controllers is converted to an optimization problem with the time domain-based objective function which is solved by a COA based on Lozi map. Since chaotic mapping enjoys certainty, ergodicity and the stochastic property, the proposed chaotic optimization problem introduces chaos mapping using Lozi map chaotic sequences which increases its convergence rate and resulting precision. To ensure the robustness of the proposed stabilizers, the design process takes into account a wide range of operating conditions and system configurations. The effectiveness of the proposed controller for damping low frequency oscillations is tested and demonstrated through non-linear time-domain simulation and some performance indices studies. The results analysis reveals that the designed COA based output feedback UPFC damping controller has an excellent capability in damping power system low frequency oscillations and enhance greatly the dynamic stability of the power systems.
Parameterized design of nonlinear feedback controllers for servo positioning systems
Institute of Scientific and Technical Information of China (English)
Cheng Guoyang; Jin Wenguang
2006-01-01
To achieve fast, smooth and accurate set point tracking in servo positioning systems, a parameterized design of nonlinear feedback controllers is presented, based on a so-called composite nonlinear feedback (CNF) control technique. The controller designed here consists of a linear feedback part and a nonlinear part. The linear part is responsible for stability and fast response of the closed-loop system. The nonlinear part serves to increase the damping ratio of closed-loop poles as the controlled output approaches the target reference. The CNF control brings together the good points of both the small and the large damping ratio cases, by continuously scheduling the damping ratio of the dominant closed-loop poles and thus has the capability for superior transient performance, i.e. a fast output response with low overshoot. In the presence of constant disturbances, an integral action is included so as to remove the static bias. An explicitly parameterized controller is derived for servo positioning systems characterized by second-order model. Practical application in a micro hard disk drive servo system is then presented, together with some discussion of the rationale and characteristics of such design. Simulation and experimental results demonstrate the effectiveness of this control design methodology.
Directory of Open Access Journals (Sweden)
Jilian Wu
2013-01-01
Full Text Available We discuss several stabilized finite element methods, which are penalty, regular, multiscale enrichment, and local Gauss integration method, for the steady incompressible flow problem with damping based on the lowest equal-order finite element space pair. Then we give the numerical comparisons between them in three numerical examples which show that the local Gauss integration method has good stability, efficiency, and accuracy properties and it is better than the others for the steady incompressible flow problem with damping on the whole. However, to our surprise, the regular method spends less CPU-time and has better accuracy properties by using Crout solver.
On precise time integration method for non-classically damped MDOF systems
Institute of Scientific and Technical Information of China (English)
Wang Mengfu; Zhou Xiyuan
2006-01-01
In the complex mode superposition method, the equations of motion for non-classically damped multipledegree-of-freedom (MDOF) discrete systems can be transferred into a combination of some generalized SDOF complex oscillators. Based on the state space theory, a precise recurrence relationship for these complex oscillators is set up; then a delicate general solution of non-classically damped MDOF systems, completely in real value form, is presented in this paper.In the proposed method, no calculation of the matrix exponential function is needed and the algorithm is unconditionally stable. A numerical example is given to demonstrate the validity and efficiency of the proposed method.
Parameter Estimation of Gaussian-Damped Sinusoids from a Geometric Perspective
Pelaia, Thomas
2016-01-01
The five parameter gaussian damped sinusoid equation is a reasonable model for betatron motion with chromatic decoherence of the proton bunch centroid signal in the ring at the Spallation Neutron Source. A geometric method for efficiently fitting this equation to the turn by turn signals to extract the betatron tune and damping constant will be presented. This method separates the parameters into global and local parameters and allows the use of vector arithmetic to eliminate the local parameters from the parameter search space. Furthermore, this method is easily generalized to reduce the parameter search space for a larger class of problems.
Calculation of continuum damping of Alfvén eigenmodes in tokamak and stellarator equilibria
Energy Technology Data Exchange (ETDEWEB)
Bowden, G. W.; Hole, M. J. [Plasma Theory and Modelling, Research School of Physics and Engineering, Australian National University, Acton 2601, Australian Capital Territory (Australia); Könies, A. [Max-Planck-Institut für Plasmaphysik, EURATOM-Association, D-17491 Greifswald (Germany)
2015-09-15
In an ideal magnetohydrodynamic (MHD) plasma, shear Alfvén eigenmodes may experience dissipationless damping due to resonant interaction with the shear Alfvén continuum. This continuum damping can make a significant contribution to the overall growth/decay rate of shear Alfvén eigenmodes, with consequent implications for fast ion transport. One method for calculating continuum damping is to solve the MHD eigenvalue problem over a suitable contour in the complex plane, thereby satisfying the causality condition. Such an approach can be implemented in three-dimensional ideal MHD codes which use the Galerkin method. Analytic functions can be fitted to numerical data for equilibrium quantities in order to determine the value of these quantities along the complex contour. This approach requires less resolution than the established technique of calculating damping as resistivity vanishes and is thus more computationally efficient. The complex contour method has been applied to the three-dimensional finite element ideal MHD Code for Kinetic Alfvén waves. In this paper, we discuss the application of the complex contour technique to calculate the continuum damping of global modes in tokamak as well as torsatron, W7-X and H-1NF stellarator cases. To the authors' knowledge, these stellarator calculations represent the first calculation of continuum damping for eigenmodes in fully three-dimensional equilibria. The continuum damping of global modes in W7-X and H-1NF stellarator configurations investigated is found to depend sensitively on coupling to numerous poloidal and toroidal harmonics.
Altay, Gabriel; Schaye, Joop; Booth, C M; Vecchia, Claudio Dalla
2013-01-01
We compute the z = 3 neutral hydrogen column density distribution function f(NHI) for 19 simulations drawn from the OWLS project using a post-processing correction for self-shielding calculated with full radiative transfer of the ionising background radiation. We investigate how different physical processes and parameters affect the abundance of Lyman-limit systems (LLSs) and damped Lyman-alpha absorbers (DLAs) including: i) metal-line cooling; ii) the efficiency of feedback from SNe and AGN; iii) the effective equation of state for the ISM; iv) cosmological parameters; v) the assumed star formation law and; vi) the timing of hydrogen reionization . We find that the normalisation and slope, D = d log10 f /d log10 NHI, of f(NHI) in the LLS regime are robust to changes in these physical processes. Among physically plausible models, f(NHI) varies by less than 0.2 dex and D varies by less than 0.18 for LLSs. This is primarily due to the fact that these uncertain physical processes mostly affect star-forming gas w...
Damping of the wrist joint during voluntary movement.
Milner, T E; Cloutier, C
1998-10-01
Damping characteristics of the musculoskeletal system were investigated during rapid voluntary wrist flexion movements. Oscillations about the final position were induced by introducing a load with the characteristics of negative damping, which artificially reduced the damping of the wrist. Subjects responded to increases in the negatively damped load by stronger cocontraction of wrist flexor and extensor muscles during the stabilization phase of the movement. However, their ability to counteract the effects of the negatively damped load diminished as the negative damping increased. Consequently, the number and frequency of oscillations increased. The oscillations were accompanied by phase-locked muscle activity superimposed on underlying tonic muscle activation. The wrist stiffness and damping coefficient increased with the increased cocontraction that accompanied more negatively damped loads, although changes in the damping coefficient were less systematic than the stiffness. Analysis of successive half-cycles of the oscillation revealed that the wrist stiffness and damping coefficient increased, despite decreasing muscle activation, as oscillation amplitude and velocity declined. This indicates that the inverse dependence of the damping coefficient on oscillation velocity contributes significantly to damping of joint motion. It is suggested that this property helps to offset a negative contribution to damping from the stretch reflex.
Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers
Directory of Open Access Journals (Sweden)
H. K. Lee
2016-05-01
Full Text Available We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO and Pt capped LSMO thin films on SrTiO3 (001 substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1 × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.
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.
Institute of Scientific and Technical Information of China (English)
Mai Tong; Thomas Liebner
2007-01-01
In a viscous damping device under cyclic loading, after the piston reaches a peak stroke, the reserve movement that follows may sometimes experience a short period of delayed or significantly reduced device force output. A similar delay or reduced device force output may also occur at the damper's initial stroke as it moves away from its neutral position.This phenomenon is referred to as the effect of "deadzone". The deadzone can cause a loss of energy dissipation capacity and less efficient vibration control. It is prominent in small amplitude vibrations. Although there are many potential causes of deadzone such as environmental factors, construction, material aging, and manufacture quality, in this paper, its general effect in linear and nonlinear viscous damping devices is analyzed. Based on classical dynamics and damping theory, a simple model is developed to capture the effect of deadzone in terms of the loss of energy dissipation capacity. The model provides several methods to estimate the loss of energy dissipation within the deadzone in linear and sublinear viscous fluid dampers.An empirical equation of loss of energy dissipation capacity versus deadzone size is formulated, and the equivalent reduction of effective damping in SDOF systems has been obtained. A laboratory experimental evaluation is carried out to verify the effect of deadzone and its numerical approximation. Based on the analysis, a modification is suggested to the corresponding formulas in FEMA 356 for calculation of equivalent damping ifa deadzone is to be considered.
Chemical treatment of papaya seeds aiming at long-term storage and control of damping off
Directory of Open Access Journals (Sweden)
Silvia de Carvalho Campos Botelho
2014-06-01
Full Text Available Damping off is a nursery disease of great economic importance in papaya and seed treatment may be an effective measure to control. The aim of this work was to evaluate the quality of papaya seeds treated with fungicides and stored under two environmental and packaging conditions. Additionally, the efficiency of fungicide treatments in the control of damping-off caused by Rhizoctonia solani was evaluated. Papaya seeds were treated with the fungicides Captan, Tolylfluanid and the mixture Tolylfluanid + Captan (all commercial wettable powder formulations. Seeds of the control group were not treated. The seeds were stored for nine months in two conditions: packed in aluminum coated paper and kept at 7 ± 1ºC and in permeable kraft paper and kept in non-controlled environment. At the beginning of the storage and every three months the seed quality (germination and vigor tests, emergence rate index, height, dry mass and damping of plants in pre and post-emergence (in contaminated substrate and mycelia-free substrate were analyzed. Both storage conditions as well as the fungicide treatments preserved the germination and seed vigor. In the infested substrate, seedling emergence was favored by fungicides, but in post-emergence, fungicides alone did not control the damping off caused by R. solani. Symptoms of damping off were not observed in the clean substrate. The results showed that the fungicide treatments may be used to pretreat papaya seed for long-term storage and commercialization.
DEFF Research Database (Denmark)
Sørensen, Jesper Hemming; Koike-Akino, Toshiaki; Orlik, Philip
2012-01-01
This paper proposes a concept called rateless feedback coding. We redesign the existing LT and Raptor codes, by introducing new degree distributions for the case when a few feedback opportunities are available. We show that incorporating feedback to LT codes can significantly decrease both...... the coding overhead and the encoding/decoding complexity. Moreover, we show that, at the price of a slight increase in the coding overhead, linear complexity is achieved with Raptor feedback coding....
Active Damping Using Distributed Anisotropic Actuators
Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.
2010-01-01
A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.
Damping of Crank–Nicolson error oscillations
DEFF Research Database (Denmark)
Britz, Dieter; Østerby, Ole; Strutwolf, J.
2003-01-01
The Crank–Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one...
The DAMPE silicon–tungsten tracker
Energy Technology Data Exchange (ETDEWEB)
Azzarello, P., E-mail: philipp.azzarello@unige.ch [Département de Physique Nucléaire et Corpusculaire, University of Geneva, Geneva (Switzerland); Ambrosi, G. [Istituto Nazionale di Fisica Nucleare Sezione di Perugia, Perugia (Italy); Asfandiyarov, R. [Département de Physique Nucléaire et Corpusculaire, University of Geneva, Geneva (Switzerland); Bernardini, P. [Dipartimento di Matematica e Fisica “E. De Giorgi”, Università del Salento, Lecce (Italy); Istituto Nazionale di Fisica Nucleare Sezione di Lecce, Lecce (Italy); Bertucci, B.; Bolognini, A. [Istituto Nazionale di Fisica Nucleare Sezione di Perugia, Perugia (Italy); Dipartimento di Fisica e Geologia, Università di Perugia, Perugia (Italy); Cadoux, F. [Département de Physique Nucléaire et Corpusculaire, University of Geneva, Geneva (Switzerland); Caprai, M. [Istituto Nazionale di Fisica Nucleare Sezione di Perugia, Perugia (Italy); De Mitri, I. [Dipartimento di Matematica e Fisica “E. De Giorgi”, Università del Salento, Lecce (Italy); Istituto Nazionale di Fisica Nucleare Sezione di Lecce, Lecce (Italy); Domenjoz, M. [Département de Physique Nucléaire et Corpusculaire, University of Geneva, Geneva (Switzerland); Dong, Y. [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing (China); Duranti, M. [Istituto Nazionale di Fisica Nucleare Sezione di Perugia, Perugia (Italy); Dipartimento di Fisica e Geologia, Università di Perugia, Perugia (Italy); Fan, R. [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing (China); and others
2016-09-21
The DArk Matter Particle Explorer (DAMPE) is a spaceborne astroparticle physics experiment, launched on 17 December 2015. DAMPE will identify possible dark matter signatures by detecting electrons and photons in the 5 GeV–10 TeV energy range. It will also measure the flux of nuclei up to 100 TeV, for the study of the high energy cosmic ray origin and propagation mechanisms. DAMPE is composed of four sub-detectors: a plastic strip scintillator, a silicon–tungsten tracker–converter (STK), a BGO imaging calorimeter and a neutron detector. The STK is composed of six tracking planes of 2 orthogonal layers of single-sided micro-strip detectors, for a total detector surface of ca. 7 m{sup 2}. The STK has been extensively tested for space qualification. Also, numerous beam tests at CERN have been done to study particle detection at silicon module level, and at full detector level. After description of the DAMPE payload and its scientific mission, we will describe the STK characteristics and assembly. We will then focus on some results of single ladder performance tests done with particle beams at CERN.
Radiation Damping at a Bubble Wall
Lee, J; Lee, C H; Jang, J; Lee, Jae-weon; Kim, Kyungsub; Lee, Chul H.; Jang, Ji-ho
1999-01-01
The first order phase transition proceeds via nucleation and growth of true vacuum bubbles. When charged particles collide with the bubble they could radiate electromagnetic wave. We show that, due to an energy loss of the particles by the radiation, the damping pressure acting on the bubble wall depends on the velocity of the wall even in a thermal equilibrium state.
The Nonlinear Spatial Damping Rate in QGP
Jiarong, L
1998-01-01
The derivative expansion method has been used to solve the semiclassical kinetic equations of quark-gluon plasma (QGP). The nonlinear spatial damping rate, the imaginary part of the wave vector, for the longitudinal secondary color waves in the long wavelength limit has been calculated numerically.
First stars in Damped Lyman Alpha systems
Salvadori, Stefania; Ferrara, Andrea
2011-01-01
In order to characterize Damped Lyman Alpha systems (DLAs) potentially host- ing first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The merger tree method previo
Passivation of underactuated systems with physical damping
Gomez-Estern, F.; Schaft, van der A.J.; Acosta, J.A.; Allgöwer, Frank; Zeitz, Michael
2005-01-01
In recent works, IDA-PBC has been succesfully applied to mechanical control problems with no physical damping present. In some cases, the friction terms can be obviated without compromising stability in closed loop. However in methods that modify the kinetic energy, a controller designed for stabili
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...
Active damping in precision equipment using piezo
Babakhani, B.; de Vries, Theodorus J.A.
2010-01-01
In this paper, the rotational vibration in the linearly actuated precision machines with low damping is discussed. This so called Rocking mode is e.g. caused by the compliance in the guiding system of a linear actuator and leads to a long settling time of the end-effector. Another problem occurs
DETERMINISTIC HOMOGENIZATION OF QUASILINEAR DAMPED HYPERBOLIC EQUATIONS
Institute of Scientific and Technical Information of China (English)
Gabriel Nguetseng; Hubert Nnang; Nils Svanstedt
2011-01-01
Deterministic homogenization is studied for quasilinear monotone hyperbolic problems with a linear damping term.It is shown by the sigma-convergence method that the sequence of solutions to a class of multi-scale highly oscillatory hyperbolic problems converges to the solution to a homogenized quasilinear hyperbolic problem.
Chiral damping of magnetic domain walls
Jué, Emilie
2015-12-21
Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics1, current-induced spin–orbit torques2, 3, 4, 5, 6, 7 and some topological magnetic structures8, 9, 10, 11, 12. In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The DW dynamics associated with the chiral damping and those with Dzyaloshinskii–Moriya interaction (DMI) exhibit identical spatial symmetry13, 14, 15, 16, 17, 18, 19. However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture. When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism. The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref. 20).
Active damping based on decoupled collocated control
Holterman, J.; de Vries, Theodorus J.A.; Auer, Frank; Gardonio, P.; Rafaely, B.
2002-01-01
High-precision machines typically suffer from small but persistent vibrations. As it is difficult to damp these vibrations by passive means, research at the Drebbel Institute at the University of Twente is aimed at the development of an active structural element that can be used for vibration
First stars in Damped Lyman Alpha systems
Salvadori, Stefania; Ferrara, Andrea
In order to characterize Damped Lyman Alpha systems (DLAs) potentially host- ing first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The merger tree method
First Stars in Damped Lyman Alpha systems
Salvadori, Stefania; Ferrara, Andrea
In order to characterize Damped Lyα Absorption systems (DLAs) potentially hosting first stars, we present a novel approach to investigate DLAs in the context of Milky Way (MW) formation, along with their connection with the most metal-poor stars and local dwarf galaxies. The model explains the
Nonlinear Landau damping and Alfven wave dissipation
Vinas, Adolfo F.; Miller, James A.
1995-01-01
Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.
An Equivalent Circuit for Landau Damping
DEFF Research Database (Denmark)
Pécseli, Hans
1976-01-01
An equivalent circuit simulating the effect of Landau damping in a stable plasma‐loaded parallel‐plate capacitor is presented. The circuit contains a double infinity of LC components. The transition from stable to unstable plasmas is simulated by the introduction of active elements into the circuit....
Chiral damping of magnetic domain walls
Jué, Emilie; Safeer, C. K.; Drouard, Marc; Lopez, Alexandre; Balint, Paul; Buda-Prejbeanu, Liliana; Boulle, Olivier; Auffret, Stephane; Schuhl, Alain; Manchon, Aurelien; Miron, Ioan Mihai; Gaudin, Gilles
2016-03-01
Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics, current-induced spin-orbit torques and some topological magnetic structures. In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The DW dynamics associated with the chiral damping and those with Dzyaloshinskii-Moriya interaction (DMI) exhibit identical spatial symmetry. However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture. When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism. The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref. ).
Brookhart, Susan M.
2012-01-01
Feedback is certainly about saying or writing helpful, learning-focused comments. But that is only part of it. What happens beforehand? What happens afterward? Feedback that is helpful and learning-focused fits into a context. Before a teacher gives feedback, students need to know the learning target so they have a purpose for using the feedback…
Developing Sustainable Feedback Practices
Carless, David; Salter, Diane; Yang, Min; Lam, Joy
2011-01-01
Feedback is central to the development of student learning, but within the constraints of modularized learning in higher education it is increasingly difficult to handle effectively. This article makes a case for sustainable feedback as a contribution to the reconceptualization of feedback processes. The data derive from the Student Assessment and…
Cooperative Feedback for MIMO Interference Channels
Huang, Kaibin
2010-01-01
Multi-antenna precoding effectively mitigates the interference in wireless networks. However, the precoding efficiency can be significantly degraded by the overhead due to the required feedback of channel state information (CSI). This paper addresses such an issue by proposing a systematic method of designing precoders for the two-user multiple-input-multiple-output (MIMO) interference channels based on finite-rate CSI feedback from receivers to their interferers, called cooperative feedback. Specifically, each precoder is decomposed into inner and outer precoders for nulling interference and improving the data link array gain, respectively. The inner precoders are further designed to suppress residual interference resulting from finite-rate cooperative feedback. To regulate residual interference due to precoder quantization, additional scalar cooperative feedback signals are designed to control transmitters' power using different criteria including applying interference margins, maximizing sum throughput, an...
The structural damping of composite beams with tapered boundaries
Coni, M.; Benchekchou, B.; White, R. G.
1994-11-01
Most metallic and composite structures of conventional construction are lightly damped. It is obviously advantageous, in terms of response to in-service dynamic loading, if damping can be increased with minimal weight addition. This report describes finite element analyses and complementary experiments carried out on composite, carbon fiber reinforced plastic, beams with tapered boundaries composed of layers of highly damped composite material. It is shown that modal damping of the structure may be significantly increased by this method.
Anti-damping effect of radiation reaction
Energy Technology Data Exchange (ETDEWEB)
Wang, G; Yuan, X Z [School of Physics and Electric Information, Wenzhou University, Wenzhou 325035 (China); Li, H [Department of Physics, Yantai University, Yantai 264005 (China); Shen, Y F [Department of Physics, China University of Mining and Technology, Xuzhou 221008 (China); Zi, J [National Laboratory of Surface Physics, Fudan University, Shanghai 200433 (China)], E-mail: gz_wang131@yahoo.cn
2010-01-15
The anti-damping effect of radiation reaction, which means the radiation reaction does non-negative work on a radiating charge, is investigated at length by using the Lorentz-Dirac equation (LDE) for the motion of a point charge respectively acted on by (a) a pure electric field, (b) a pure magnetic field and (c) the fields of an electromagnetic wave. We found that the curvature of the charge's trajectory plays an important role in the radiation reaction force, and the anti-damping effect cannot take place for the real macroscopic motions of a point charge. The condition for this anti-damping effect to take place is that the gradient of the external force field must exceed a certain value over the region of magnitude of the classical radius of massive charges ({approx}10{sup -15} m). Our results are potentially helpful to lessen the controversy on LDE and justify it as the correct classical equation describing the radiating charge's motion. If this anti-damping effect of LDE were a real existing physical process, it could serve as a mechanism within the context of classical electrodynamics for the stability of hydrogen atoms. Using the picture of an electron in quantum electrodynamics, namely the negative bare charge surrounded by the polarized positive charges of vacuum, we can obtain a reasonable explanation for the energy transferred to the electron during the occurrence of the anti-damping effect, on which the venerable work of Wheeler and Feynman has thrown some light.
Bachmann, F.; de Oliveira, R.; Sigg, A.; Schnyder, V.; Delpero, T.; Jaehne, R.; Bergamini, A.; Michaud, V.; Ermanni, P.
2012-07-01
Emission reduction from civil aviation has been intensively addressed in the scientific community in recent years. The combined use of novel aircraft engine architectures such as open rotor engines and lightweight materials offer the potential for fuel savings, which could contribute significantly in reaching gas emissions targets, but suffer from vibration and noise issues. We investigated the potential improvement of mechanical damping of open rotor composite fan blades by comparing two integrated passive damping systems: shape memory alloy wires and piezoelectric shunt circuits. Passive damping concepts were first validated on carbon fibre reinforced epoxy composite plates and then implemented in a 1:5 model of an open rotor blade manufactured by resin transfer moulding (RTM). A two-step process was proposed for the structural integration of the damping devices into a full composite fan blade. Forced vibration measurements of the plates and blade prototypes quantified the efficiency of both approaches, and their related weight penalty.
Negative Resistance Circuit for Damping an Array of Coupled FitzHugh-Nagumo Oscillators
DEFF Research Database (Denmark)
Tamaševičius, Arūnas; Adomaitienė, Elena; Bumelienė, Skaidra;
2015-01-01
An analog circuit, based on a negative impedance converter and a capacitor, for damping oscillations in an array of mean-field coupled neuronal FitzHugh–Nagumo (FHN) type oscillators is described. The circuit is essentially a two-terminal feedback controller. When coupled to an array of the FHN o...... oscillators, it stabilizes their unstable steady states. Both, numerical simulations and hardware experiments with the analog electronic circuits have been performed. The results for an array, composed of three mean-field coupled FHN oscillators, are presented....
Design and control of LCL-filter with active damping for Active Power Filter
DEFF Research Database (Denmark)
Zeng, Guohong; Rasmussen, Tonny Wederberg; Ma, L
2010-01-01
In the application of shunt Active Power Filter (APF) to compensate nonlinear load's harmonic, reactive and negative sequence current, it is more effective to use a LCL-filter than an L-filter as an interface between the Voltage Source Converter (VSC) and grid. In this paper, a designing procedure...... of LCL-filter for APF is introduced, which is aimed for simplified the implementation. To suppress the resonance that may be excited in the system, which brings in stability problems, an active damping control strategy using the current feed-back of the filter capacitor is adopted. By selecting two equal...
Negative Resistance Circuit for Damping an Array of Coupled FitzHugh-Nagumo Oscillators
DEFF Research Database (Denmark)
Tamaševičius, Arūnas; Adomaitienė, Elena; Bumelienė, Skaidra
2015-01-01
An analog circuit, based on a negative impedance converter and a capacitor, for damping oscillations in an array of mean-field coupled neuronal FitzHugh–Nagumo (FHN) type oscillators is described. The circuit is essentially a two-terminal feedback controller. When coupled to an array of the FHN...... oscillators, it stabilizes their unstable steady states. Both, numerical simulations and hardware experiments with the analog electronic circuits have been performed. The results for an array, composed of three mean-field coupled FHN oscillators, are presented....
Allergy and respiratory health effects of dampness and dampness-related agents in schools and homes
DEFF Research Database (Denmark)
Holst, G; Høst, Arne; Doekes, G;
2016-01-01
Little is known about the health effects of school-related indoor dampness and microbial exposures. In this study we investigated dampness and dampness-related agents in both homes and schools and their association with allergy and respiratory health effects in 330 Danish pupils. Classroom dampness...... ), forced vital capacity (zFVC) and the ratio zFEV1 /zFVC using GLI-2012-prediction-equations. The parents reported children's allergies, airway symptoms and doctor-diagnosed asthma. High classroom dampness, but not bedroom dampness, was negatively associated with zFEV1 (β-coef. -0.71; 95%CI -1.17 - -0.......23), zFVC (β-coef. -0.52; 95%CI -0.98 - -0.06) and positively with wheezing (OR 8.09; 95%CI 1.49-43.97). No consistent findings were found between any individual microbial components or combination of microbial components and health outcomes. Among other indoor risk factors, environmental tobacco smoke...
Recovering the damping rates of cyclotron damped plasma waves from simulation data
Schreiner, Cedric; Spanier, Felix
2016-01-01
Plasma waves with frequencies close to the particular gyrofrequencies of the charged particles in the plasma lose energy due to cyclotron damping. We briefly discuss the gyro-resonance of low frequency plasma waves and ions particularly with regard to particle-in-cell (PiC) simulations. A setup is outlined which uses artificially excited waves in the damped regime of the wave mode's dispersion relation to track the damping of the wave's electromagnetic fields. Extracting the damping rate directly from the field data in real or Fourier space is an intricate and non-trivial task. We therefore present a simple method of obtaining the damping rate {\\Gamma} from the simulation data. This method is described in detail, focusing on a step-by-step explanation of the course of actions. In a first application to a test simulation we find that the damping rates obtained from this simulation generally are in good agreement with theoretical predictions. We then compare the results of one-, two- and three-dimensional simul...
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.
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.
Seismic isolation effect of lined circular tunnels with damping treatments
Institute of Scientific and Technical Information of China (English)
Seyyed M. Hasheminejad; Amir K. Miri
2008-01-01
The Havriliak-Negami model for dynamic viscoelastic material behavior and Biot's theory of poroelasticity are employed to develop an exact solution for three-dimensional scattering effect of harmonic plane P-SV waves from a circular cavity lined with a multilayered fluid-filled shell of infinite length containing viscoelastic damping materials and embedded within a fluid-saturated permeable surrounding soil medium. The analytical results are illustrated with numerical examples where the effects of liner/coating structural arrangement, viscoelastic material properties, liner-soil interface bonding condition, seismic excitation frequency, and angle of incidence on the induced dynamic stress concentrations are evaluated and discnssed to obtain representative values of the parameters that characterize the system. It is demonstrated that incorporating viscoelastic damping materials with a low shear modulus in the constrained layer configuration is an efficient means of enhancing the overall seismic isolation performance, especially for near-normally incident seismic shear waves where the amplitudes of induced dynamic stresses may be reduced by up to one-third of those without isolation in a relatively wide frequency range. Some additional cases are considered and good agreements with solutions available in the literature are obtained.
Bowen, G
2002-01-01
In classical information theory the capacity of a noisy communication channel cannot be increased by the use of feedback. In quantum information theory the no-cloning theorem means that noiseless copying and feedback of quantum information cannot be achieved. In this paper, quantum feedback is defined as the unlimited use of a noiseless quantum channel from receiver to sender. Given such quantum feedback, it is shown to provide no increase in the entanglement-assisted capacities of a noisy quantum channel, in direct analogy to the classical case. It is also shown that in various cases of non-assisted capacities, feedback can increase the capacity of many quantum channels.
Feedback-induced Bistability of an Optically Levitated Nanoparticle: A Fokker-Planck Treatment
Ge, Wenchao; Bhattacharya, M
2016-01-01
Optically levitated nanoparticles have recently emerged as versatile platforms for investigating macroscopic quantum mechanics and enabling ultrasensitive metrology. In this article we theoretically consider two damping regimes of an optically levitated nanoparticle cooled by cavityless parametric feedback. Our treatment is based on a generalized Fokker-Planck equation derived from the quantum master equation presented recently and shown to agree very well with experiment [1]. For low damping, we find that the resulting Wigner function yields the single-peaked oscillator position distribution and recovers the appropriate energy distribution derived earlier using a classical theory and verified experimentally [2]. For high damping, in contrast, we predict a double-peaked position distribution, which we trace to an underlying bistability induced by feedback. Unlike in cavity-based optomechanics, stochastic processes play a major role in determining the bistable behavior. To support our conclusions, we present a...
Feedback in an Age of Efficiency
Nichols, T. Philip
2012-01-01
Joseph Weizenbaum, a professor at MIT, designed ELIZA in 1964 as an experiment in artificial intelligence. ELIZA was constructed with a library of ready-made questions that could be summoned at a moment's notice in response to human input. When users' statements fell outside the program's scripting, ELIZA could adapt by rephrasing the words into a…
CHAOTIC DUFFING TYPE OSCILLATOR WITH INERTIAL DAMPING
DEFF Research Database (Denmark)
Tamaševicius, Arunas; Mykolaitis, Gytis; Kirvaitis, Raimundas
2009-01-01
A novel Duffing-Holmes type autonomous chaotic oscillator is described. In comparison with the well-known non-autonomous Duffing-Holmes circuit it lacks the external periodic drive, but includes two extra linear feedback sub-circuits, namely a direct positive feedback loop, and an inertial negative...
Active vibration isolation feedback control for Coriolis Mass-Flow Meters
Ridder, van de L.; Beijen, M.A.; Hakvoort, W.B.J.; Dijk, van J.; Lötters, J.C.; Boer, de A.
2014-01-01
Active Vibration Isolation Control (AVIC) can be used to reduce the transmissibility of external vibrations to internal vibrations. In this paper a proposal is made for integrating AVIC in a Coriolis Mass-Flow Meter (CMFM). Acceleration feedback, virtual mass and virtual skyhook damping are added to
DEFF Research Database (Denmark)
Lukassen, Niels Bech; Wahl, Christian; Sorensen, Elsebeth Korsgaard
2016-01-01
This study addresses the conceptual challenge of providing students with good quality feedback to enhance student learning in an online community of practice (COP). The aim of the study is to identify feedback mechanisms in a virtual learning environment (VLE) and to create a full formative...... feedback episode (FFE) through an online dialogue. The paper argues that dialogue is crucial for student learning and that feedback is not only something the teacher gives to the student. Viewing good quality feedback as social, situated, formative, emphasis is put on the establishment of dialogue. We...... refer to this type of feedback as, Situated Formative Feedback (SFF). As a basis for exploring, identifying and discussing relevant aspects of SFF the paper analyses qualitative data from a Moodle dialogue. Data are embedded in the qualitative analytic program Nvivo and are analysed with a system...
DEFF Research Database (Denmark)
Eriksson, Tor Viking; Poulsen, Anders; Villeval, Marie Claire
2009-01-01
This paper experimentally investigates the impact of different pay schemes and relative performance feedback policies on employee effort. We explore three feedback rules: no feedback on relative performance, feedback given halfway through the production period, and continuously updated feedback. We...... use two pay schemes, a piece rate and a tournament. We find that overall feedback does not improve performance. In contrast to the piece-rate pay scheme there is some evidence of positive peer effects in tournaments since the underdogs almost never quit the competition even when lagging significantly...... behind, and front runners do not slack off. But in both pay schemes relative performance feedback reduces the quality of the low performers' work; we refer to this as a "negative quality peer effect"....
TWO FEEDBACK PROBLEMS FOR GRAPHS WITH BOUNDED TREE-WIDTH
Institute of Scientific and Technical Information of China (English)
ZhangShaoqiang; LiGuojun; SohnMoo-Young
2004-01-01
Many difficult (often NP-complete) optimization problems can be solved efficiently on graphs of small tree-width with a given tree decomposition. In this paper,it is discussed how to solve the minimum feedback vertex set problem and the minimum vertex feedback edge set problem efficiently by using dynamic programming on a tree-decomposition.
Energy Technology Data Exchange (ETDEWEB)
Fox, J.D.; Claus, R.; Hindi, H.; Linscott, I.; Prabhakar, S.; Ross, W.; Teytelman, D. [Stanford Linear Accelerator Center, P.O. Box 4349, Stanford, California 94309 (United States); Drago, A.; Serio, M. [INFN-Laboratori Nazionali di Frascati, P.O. Box 13, I-00044 Frascati (Roma) (Italy); Byrd, J.; Corlett, J.; Stover, G. [Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, California 94563 (United States)
1997-01-01
The operation of a longitudinal multibunch damping system using digital signal processing (DSP) techniques is shown via measurements from the Lawrence Berkeley Laboratory (LBL) Advanced Light Source (ALS). The feedback system (developed for use by PEP-II, ALS, and DA{Phi}NE) uses a parallel array of signal processors to implement a bunch-by-bunch feedback system for sampling rates up to 500 MHz. The programmable DSP system allows feedback control as well as accelerator diagnostics. A diagnostic technique is illustrated which uses the DSP system to excite and then damp the beam. The resulting 12-ms time domain transient is Fourier analyzed to provide the simultaneous measurement of growth rates and damping rates of all unstable coupled-bunch beam modes. {copyright} {ital 1997 American Institute of Physics.}
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.
Topology Optimization in Damping Structure Based on ESO
Institute of Scientific and Technical Information of China (English)
GUO Zhong-ze; CHEN Yu-ze; HOU Qiang
2008-01-01
The damping material optimal placement for the structure with damping layer is studied based on evolutionary structural optimization (ESO) to maximize modal loss factors. A mathematical model is constructed with the objective function defined as the maximum of modal loss factors of the structure and design constraints function defined as volume fraction ofdamping material. The optimal placement is found. Several examples are presented for verification. The results demonstratethat the method based on ESO is effective in solving the topology optimization of the structure with uncon-strained damping layer and constrained damping layer. This optimization method suits for free and constrained damping structures.
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.
Directory of Open Access Journals (Sweden)
Shitao Tian
2016-01-01
Full Text Available Constrained layer damping treatments promise to be an effective method to control vibration in flexible structures. Cutting both the constraining layer and the viscoelastic layer, which leads to segmentation, increases the damping efficiency. However, this approach is not always effective. A parametric study was carried out using modal strain energy method to explore interaction between segmentation and design parameters, including geometry parameters and material properties. A finite element model capable of handling treatments with extremely thin viscoelastic layer was developed based on interlaminar continuous shear stress theories. Using the developed method, influence of placing cuts and change in design parameters on the shear strain field inside the viscoelastic layer was analyzed, since most design parameters act on the damping efficiency through their influence on the shear strain field. Furthermore, optimal cut arrangements were obtained by adopting a genetic algorithm. Subject to a weight limitation, symmetric and asymmetric configurations were compared. It was shown that symmetric configurations always presented higher damping. Segmentation was found to be suitable for treatments with relatively thin viscoelastic layer. Provided that optimal viscoelastic layer thickness was selected, placing cuts would only be applicable to treatments with low shear strain level inside the viscoelastic layer.
Active damping of capillary oscillations on liquid columns
Thiessen, David B.; Wei, Wei; Marston, Philip L.
2002-05-01
Active control of acoustic radiation pressure and of electrostatic stresses on liquid columns has been demonstrated to overcome the Rayleigh-Plateau instability that normally causes long liquid columns to break [M. J. Marr-Lyon et al., J. Fluid Mech. 351, 345 (1997); Phys. Fluids 12, 986-995 (2000)]. Though originally demonstrated for liquid-liquid systems in plateau tanks, the electrostatic method also works on columns in air in reduced gravity [D. B. Thiessen, M. J. Marr-Lyon, and P. L. Marston, ``Active electrostatic stabilization of liquid bridges in low gravity,'' J. Fluid Mech. (in press)]. In new research, the electrostatic stresses are applied in proportion to the velocity of the surface of the column so as to actively dampen capillary oscillations of the surface. The mode amplitude is optically sensed and the rate-of-change is electronically determined. Plateau tank measurements and theory both show that the change in damping rate is proportional to the feedback gain. The results suggest that either active control of electrostatic stresses or of acoustic radiation stresses can be used to suppress the response of interfaces to vibration. [Work supported by NASA.
Charge Fluctuation of Dust Grain and Its Impact on Dusty-Acoustic Wave Damping
Atamaniuk, B
2007-01-01
We consider the influence of dust charge fluctuations on damping of the dust-ion-acoustic waves. It is assumed that all grains have equal masses but charges are not constant in time - they may fluctuate in time. The dust charges are not really independent of the variations in the plasma potentials. All modes will influence the charging mechanism, and feedback will lead to several new interesting and unexpected phenomena. The charging of the grains depends on local plasma characteristics. If the waves disturb these characteristic, then charging of the grains is affected and the grain charge is modified, with a resulting feedback on the wave mode. In the case considered here, when the temperature of electrons is much greater than the temperature of the ions and the temperature of electrons is not great enough for further ionization of the ions, we show that attenuation of the acoustic wave depends only on one phenomenological coefficient
Supplementary Controller Design for SSR Damping in a Series-Compensated DFIG-Based Wind Farm
Directory of Open Access Journals (Sweden)
Minqiang Hu
2012-11-01
Full Text Available The increasing presence of wind power in power systems will likely drive the integration of large wind farms with electrical networks that are series-compensated to sustain large power flows. This may potentially lead to subsynchronous resonance (SSR issues. In this paper, a supplementary controller on the grid-side converter (GSC control loop is designed to mitigate SSR for wind power systems based on doubly fed induction generators (DFIGs with back-to-back converters. Different supplementary controller feedback signals and modulated-voltage injecting points are proposed and compared based on modal analysis and verified through root locus analysis to identify the optimal feedback signal and the most effective control location for SSR damping. The validity and effectiveness of the proposed supplemental control are demonstrated on the IEEE first benchmark model for computer simulations of SSR by means of time domain simulation analysis using Matlab/Simulink.
A soft damping function for dispersion corrections with less overfitting
Ucak, Umit V.; Ji, Hyunjun; Singh, Yashpal; Jung, Yousung
2016-11-01
The use of damping functions in empirical dispersion correction schemes is common and widespread. These damping functions contain scaling and damping parameters, and they are usually optimized for the best performance in practical systems. In this study, it is shown that the overfitting problem can be present in current damping functions, which can sometimes yield erroneous results for real applications beyond the nature of training sets. To this end, we present a damping function called linear soft damping (lsd) that suffers less from this overfitting. This linear damping function damps the asymptotic curve more softly than existing damping functions, attempting to minimize the usual overcorrection. The performance of the proposed damping function was tested with benchmark sets for thermochemistry, reaction energies, and intramolecular interactions, as well as intermolecular interactions including nonequilibrium geometries. For noncovalent interactions, all three damping schemes considered in this study (lsd, lg, and BJ) roughly perform comparably (approximately within 1 kcal/mol), but for atomization energies, lsd clearly exhibits a better performance (up to 2-6 kcal/mol) compared to other schemes due to an overfitting in lg and BJ. The number of unphysical parameters resulting from global optimization also supports the overfitting symptoms shown in the latter numerical tests.
Barotropic FRW cosmologies with Chiellini damping
Energy Technology Data Exchange (ETDEWEB)
Rosu, Haret C., E-mail: hcr@ipicyt.edu.mx [IPICyT, Instituto Potosino de Investigacion Cientifica y Tecnologica, Camino a la presa San José 2055, Col. Lomas 4a Sección, 78216 San Luis Potosí, SLP (Mexico); Mancas, Stefan C., E-mail: stefan.mancas@erau.edu [Department of Mathematics, Embry–Riddle Aeronautical University, Daytona Beach, FL 32114-3900 (United States); Chen, Pisin, E-mail: pisinchen@phys.ntu.edu.tw [Leung Center for Cosmology and Particle Astrophysics (LeCosPA) and Department of Physics, National Taiwan University, Taipei 10617, Taiwan (China)
2015-05-08
It is known that barotropic FRW equations written in the conformal time variable can be reduced to simple linear equations for an exponential function involving the conformal Hubble rate. Here, we show that an interesting class of barotropic universes can be obtained in the linear limit of a special type of nonlinear dissipative Ermakov–Pinney equations with the nonlinear dissipation built from Chiellini's integrability condition. These cosmologies, which evolutionary are similar to the standard ones, correspond to barotropic fluids with adiabatic indices rescaled by a particular factor and have amplitudes of the scale factors inverse proportional to the adiabatic index. - Highlights: • Chiellini-damped Ermakov–Pinney equations are used in barotropic FRW cosmological context. • Chiellini-damped scale factors of the barotropic FRW universes are introduced. • These scale factors are similar to the undamped ones.
DAMPING OF SUBSYNCHRONOUS MODES OF OSCILLATIONS
Directory of Open Access Journals (Sweden)
JAGADEESH PASUPULETI
2006-06-01
Full Text Available The IEEE bench mark model 2 series compensated system is considered for analysis. It consists of single machine supplying power to infinite bus through two parallel lines one of which is series compensated. The mechanical system considered consists of six mass, viz, high pressure turbine, intermediate pressure turbine, two low pressure turbines, generator and an exciter. The excitation system considered is IEEE type 1 with saturation. The auxiliary controls considered to damp the unstable subsynchronous modes of oscillations are Power System Stabilizer (PSS and Static var Compensator (SVC. The different cases of power system stabilizer and reactive power controls are adapted to study the effectiveness of damping these unstable subsynchronous modes of oscillations.
Study on damping properties of magnetorheological damper
Institute of Scientific and Technical Information of China (English)
ZHOU Yu-feng; CHEN Hua-ling
2006-01-01
To research the properties of a new kind of smart controllable MR (magnetorheological) fluid,in this paper,the rheological models are discussed.On the basis of analyzing the structural forms of MR dampers,an improved structure of the MR damper is introduced;the properties of the novel MR damper are then tested.The experimental resuits reveal that the Herschel-Bulkley model predicts the force-velocity well;the damping properties of the ameliorated structure of the MR damper have improved;when the excitation is a trigonal signal,the MR damper reveals a thinning effect at high velocity;and when the excitation is a sinusoidal signal,the MR damper reveals a nonlinear hysteretic property between the damping force and relative velocity.Finally,the main unsolved problems have been put forward.
Wakefield Damping for the CLIC Crab Cavity
Energy Technology Data Exchange (ETDEWEB)
Ambattu, P.K.; Burt, G.; Dexter, A.C.; Carter, R.G.; /Cockcroft Inst. Accel. Sci. Tech. /Lancaster U.; Khan, V.; Jones, R.M.; /Cockcroft Inst. Accel. Sci. Tech. /Manchester U.; Dolgashev, V.; /SLAC
2011-12-01
A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely proportional to the operating frequency. The short bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to dipole kicks demand very high damping of the inter-bunch wakes, the major contributor to the luminosity loss of colliding bunches. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using various damping schemes to suppress them effectively.
Nonlinear Dynamics of A Damped Magnetic Oscillator
Kim, S Y
1999-01-01
We consider a damped magnetic oscillator, consisting of a permanent magnet in a periodically oscillating magnetic field. A detailed investigation of the dynamics of this dissipative magnetic system is made by varying the field amplitude $A$. As $A$ is increased, the damped magnetic oscillator, albeit simple looking, exhibits rich dynamical behaviors such as symmetry-breaking pitchfork bifurcations, period-doubling transitions to chaos, symmetry-restoring attractor-merging crises, and saddle-node bifurcations giving rise to new periodic attractors. Besides these familiar behaviors, a cascade of ``resurrections'' (i.e., an infinite sequence of alternating restabilizations and destabilizations) of the stationary points also occurs. It is found that the stationary points restabilize (destabilize) through alternating subcritical (supercritical) period-doubling and pitchfork bifurcations. We also discuss the critical behaviors in the period-doubling cascades.
Damping effects in Penning trap mass spectrometry
George, S; Kowalska, M; Dworschak, M; Neidherr, D; Blaum, K; Schweikhard, L; Ramirez, E M; Breitenfeldt, M; Kretzschmar, M; Herfurth, F; Schwarz, S; Herlert, A
2011-01-01
Collisions of ions with residual gas atoms in a Penning trap can have a strong influence on the trajectories of the ions, depending on the atom species and the gas pressure. We report on investigations of damping effects in time-of-flight ion-cyclotron resonance mass spectrometry with the Penning trap mass spectrometers ISOLTRAP at ISOLDE/CERN (Geneva, Switzerland) and SHIPTRAP at GSI (Darmstadt, Germany). The work focuses on the interconversion of the magnetron and cyclotron motional modes, in particular the modification of the resonance profiles for quadrupolar excitation due to the damping effect of the residual gas. Extensive experiments have been performed with standard and Ramsey excitation schemes. The results are in good agreement with predictions obtained by analytical continuation of the formulae for the undamped case.
Accelerator physics measurements at the damping ring
Rivkin, L.; Delahaye, J. P.; Wille, K.; Allen, M. A.; Bane, K.; Fieguth, T.; Hofmann, A.; Button, A.; Lee, M.; Linebarger, W.
1985-05-01
Besides the optics measurements described elsewhere, machine experiments were done at the Stanford Linear Collider (SLC) damping ring to determine some of its parameters. The synchrotron radiation energy loss which gives the damping rates was measured by observing the RF-voltage dependence of the synchronous phase angle. The emittance was obtained from the synchrotron light monitor, scraper measurements and by extracting the beam through a doublet and measuring its size for different quadrupole settings. Current dependent effects such as parasitic mode losses, head tail instabilities, synchrotron and betatron frequency shifts were measured to estimate the impedance. RF-cavity beam loading and its compensation were also studied and ion collection was investigated. All results agree reasonably well with expectations and indicate no limitations to the design performance.
Linear Inviscid Damping for Monotone Shear Flows
Zillinger, Christian
2014-01-01
In this article we prove linear stability, inviscid damping and scattering of the 2D Euler equations around regular, strictly monotone shear flows $(U(y),0)$ in a periodic channel under Sobolev perturbations. We treat the settings of an infinite channel, $\\mathbb{T} \\times \\mathbb{R}$, as well as a finite channel, $\\mathbb{T} \\times [0,1]$, with impermeable boundary. We first prove inviscid damping with optimal algebraic rates for strictly monotone shear flows under the assumption of controlling the regularity of the scattered vorticity. Subsequently, we establish linear stability of the scattering equation in Sobolev spaces under perturbations which are of not too large wave-length with respect to $x$, depending on $U''$.
Power Oscillations Damping in DC Microgrids
DEFF Research Database (Denmark)
Hamzeh, Mohsen; Ghafouri, Mohsen; Karimi, Houshang
2016-01-01
This paper proposes a new control strategy for damping of power oscillations in a multi-source dc microgrid. A parallel combination of a fuel cell (FC), a photovoltaic (PV) system and a supercapacitor (SC) are used as a hybrid power conversion system (HPCS). The SC compensates for the slow...... transient response of the FC stack. The HPCS controller comprises a multi-loop voltage controller and a virtual impedance loop for power management. The virtual impedance loop uses a dynamic droop gain to actively damp the low-frequency oscillations of the power sharing control unit. The gain of virtual...... impedance loop is determined using small signal analysis and pole placement method. The Mesh analysis is employed to further study the stability of low-frequency modes of the overall dc microgrid. Moreover, based on the guardian map theorem, a robust stability analysis is carried out to determine...
Relativity Damps OPEP in Nuclear Matter
Banerjee, Manoj K.
1998-09-01
Using a relativistic Dirac--Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. We find that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. We show that the damping of derivative-coupled OPEP is actually due to the decrease of M*/M with increasing density. We point out that if derivative-coupled OPEP is the preferred form of nuclear effective Lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of M* it cannot replicate the damping. We suggest an examination of the feasibility of using pseudoscalar coupled πN interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Relativity Damps OPEP in Nuclear Matter
Banerjee, M K
1998-01-01
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. We find that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. We show that the damping of derivative-coupled OPEP is actually due to the decrease of $M^*/M$ with increasing density. We point out that if derivative-coupled OPEP is the preferred form of nuclear effective lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of $M^*$ it cannot replicate the damping. We suggest an examination of the feasibility of using pseudoscalar coupled $\\pi$N interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Radiation Damping in Einstein-Aether Theory
Foster, B Z
2006-01-01
This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory-an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian-order are waveforms for the metric and vector fields far from a nearly-Newtonian system and the rate of energy radiated by the system. The expressions depend on the quadrupole moment of the source, as in standard general relativity, but also contain monopolar and dipolar terms. There exists a one-parameter family of Einstein-aether theories for which only the quadrupolar contribution is present, and for which the expression for the damping rate is identical to that of general relativity to lowest order. Because observations from binary pulsar systems already test the damping rate beyond this order, this family cannot yet be declared observationally viable.
Damping behavior of synthetic graphite beams
Directory of Open Access Journals (Sweden)
Luiz Cláudio Pardini
2006-06-01
Full Text Available The main objective of this work was to obtain the damping factor (xi as well as the elasticity modulus (E of two kinds of synthetic graphite (HLM and ATJ, using the modal analysis technique. Prismatic beams of square section (~ 11 x 11 mm and length over thickness ratio (L/t of about 22.7 were tested in the free - free boundary condition. The first four modes of vibration were taken into account in the non-destructive evaluation of the materials. In addition, numerical simulations were also carried out in this investigation. The agreement between the theoretical and the experimental results was quite good. The average values of E and xi for the HLM graphite were 20% and 90% higher, respectively, than those presented by the ATJ graphite, indicating that the HLM graphite has, proportionally, more damping mechanisms than the ATJ graphite.
Experimental investigation of damping force of twin tube shock absorber
Directory of Open Access Journals (Sweden)
Sandip K. Kadu
2014-09-01
Full Text Available A shock absorber is a mechanical device to damp shock impulse and convert kinetic energy into thermal energy. The damping effect of shock absorber depends on damping force and damping force is affected by various process parameters. In this analysis three process parameters damping diameter(A, number of holes(B and suspension velocity(C were considered and their effect on damping force of shock absorber was studied and accordingly suitable orthogonal array was selected by taguchi method. Experiment conducted on servo hydraulic testing machine and after conducting experiments damping force was measured and with the help of S/N ratio, ANOVA, Regression analysis optimum parameter values can be obtained and confirmation experiments was carried out. Twin tube shock absorber was used to carry out experimentation.
Beam halo study on ATF damping ring
Wang, Dou; Yokoya, Kaoru; Naito, Takashi; Gao, Jie
2016-01-01
Halo distribution is a key topic for background study. This paper has developed an analytical method to give an estimation of ATF beam halo distribution. The equilibrium particle distribution of the beam tail in the ATF damping ring is calculated analytically with different emittance and different vacuum degree. The analytical results agree the measurements very well. This is a general method which can be applied to any electron rings.
Cubic Lienard Equations with Quadratic Damping (Ⅱ)
Institute of Scientific and Technical Information of China (English)
Yu-quan Wang; Zhu-jun Jing
2002-01-01
Applying Hopf bifurcation theory and qualitative theory, we show that the general cubic Lienard equations with quadratic damping have at most three limit cycles. This implies that the guess in which the system has at most two limit cycles is false. We give the sufficient conditions for the system has at most three limit cycles or two limit cycles. We present two examples with three limit cycles or two limit cycles by using numerical simulation.
On circular flows: linear stability and damping
Zillinger, Christian
2016-01-01
In this article we establish linear inviscid damping with optimal decay rates around 2D Taylor-Couette flow and similar monotone flows in an annular domain $B_{r_{2}}(0) \\setminus B_{r_{1}}(0) \\subset \\mathbb{R}^{2}$. Following recent results by Wei, Zhang and Zhao, we establish stability in weighted norms, which allow for a singularity formation at the boundary, and additional provide a description of the blow-up behavior.
Proceedings of Damping Volume 2 of 3
1993-06-01
Inc., 1979. [101 N. Balabanian and T. Bickert. Electrical Network Theory. Jonh Wiley and Sons, Inc., 1969. [111 D. Wang and M. Vidyasagar. Passive...1987). Dynamics of Polymeric Liquids, J. Wiley , New York, NY. Dargush, G.E and Banerjee, P.K. (1991a). "A Time-dependent Incompressible Viscous BEM for...414. 11. Nashif, A. D., Jones, D. I. G. and Henderson, J. P. (1985). Vibration Damping, Wiley -Interscience Publication, New York. 12. Bland, D. R. and
Damping of roll vibrations of vehicle suspension
Le, K. C.; Pieper, A.
2014-04-01
Small forced vibrations of an axle model of independent suspensions having four degrees of freedom are studied. The exact analytical solution of the generalised Lagrange equation enables one to produce 3D plots of the normalised amplitudes of forced vibrations versus frequency and excitation ratio or phase difference of the road inputs. The analysis of these plots exhibits some deficiency in damping of roll vibrations of conventional vehicle suspensions. The possibilities of improvement are discussed.
Coulomb collision effects on linear Landau damping
Energy Technology Data Exchange (ETDEWEB)
Callen, J. D., E-mail: callen@engr.wisc.edu [University of Wisconsin, Madison, Wisconsin 53706-1609 (United States)
2014-05-15
Coulomb collisions at rate ν produce slightly probabilistic rather than fully deterministic charged particle trajectories in weakly collisional plasmas. Their diffusive velocity scattering effects on the response to a wave yield an effective collision rate ν{sub eff} ≫ ν and a narrow dissipative boundary layer for particles with velocities near the wave phase velocity. These dissipative effects produce temporal irreversibility for times t ≳ 1/ν{sub eff} during Landau damping of a small amplitude Langmuir wave.
Accurate integration of forced and damped oscillators
García Alonso, Fernando Luis; Cortés Molina, Mónica; Villacampa, Yolanda; Reyes Perales, José Antonio
2016-01-01
The new methods accurately integrate forced and damped oscillators. A family of analytical functions is introduced known as T-functions which are dependent on three parameters. The solution is expressed as a series of T-functions calculating their coefficients by means of recurrences which involve the perturbation function. In the T-functions series method the perturbation parameter is the factor in the local truncation error. Furthermore, this method is zero-stable and convergent. An applica...
Residential Feedback Devices and Programs: Opportunities for Natural Gas
Energy Technology Data Exchange (ETDEWEB)
Kerr, R.; Tondro, M.
2012-12-01
Behavior-based approaches have been a growing interest in the energy efficiency field over recent years and the use of residential energy feedback has garnered particular interest. By providing an increased level of detail, feedback can greatly increase a consumer's understanding of how energy is used in their home. This project reviewed the existing body of research on electricity feedback to identify parallel lessons for gas, discussed the benefits and challenges of different types of feedback, and identifying three feedback options that show strong potential for natural gas savings.
Residential Feedback Devices and Programs. Opportunities for Natural Gas
Energy Technology Data Exchange (ETDEWEB)
Kerr, R. [Building America Partnership for Improved Residential Construction (BA-PIRC), Cocoa, FL (United States); Tondro, M. [Building America Partnership for Improved Residential Construction (BA-PIRC), Cocoa, FL (United States)
2012-12-01
Behavior-based approaches have been a growing interest in the energy efficiency field over recent years and the use of residential energy feedback has garnered particular interest. By providing an increased level of detail, feedback can greatly increase a consumer’s understanding of how energy is used in their home. This project reviewed the existing body of research on electricity feedback to identify parallel lessons for gas, discussed the benefits and challenges of different types of feedback, and identifying three feedback options that show strong potential for natural gas savings.
Damping of liquid sloshing by foams
Sauret, Alban; Cappello, Jean; Dressaire, Emilie; Stone, Howard A
2014-01-01
When a container is set in motion, the free surface of the liquid starts to oscillate or slosh. Such effects can be observed when a glass of wa ter is handled carelessly and the fluid sloshes or even spills over the rims of the container. However, beer does not slosh as readily as water, wh ich suggests that foam could be used to damp sloshing. In this work, we study experimentally the effect on sloshing of a liquid foam placed on top of a liquid bath. We generate a monodisperse two-dimensional liquid foam in a rectangular container and track the motion of the foam. The influence of the foam on the sloshing dynamics is experimentally characterized: only a few layers of bubbles are sufficient to significantly damp the oscill ations. We rationalize our experimental findings with a model that describes the foam contribution to the damping coefficient through viscous dissi pation on the walls of the container. Then we extend our study to confined three-dimensional liquid foam and observe that the behavior of 2D a...
Synchrosqueezed wavelet transform for damping identification
Mihalec, Marko; Slavič, Janko; Boltežar, Miha
2016-12-01
Synchrosqueezing is a procedure for improving the frequency localization of a continuous wavelet transform. This research focuses on using a synchrosqueezed wavelet transform (SWT) to determine the damping ratios of a vibrating system using a free-response signal. While synchrosqueezing is advantageous due to its localisation in the frequency, damping identification with the original SWT is not sufficiently accurate. Here, the synchrosqueezing was researched in detail, and it was found that an error in the frequency occurs as a result of the numerical calculation of the preliminary frequencies. If this error were to be compensated, a better damping identification would be expected. To minimize the frequency-shift error, three different strategies are investigated: the scale-dependent coefficient method, the shifted-coefficient method and the autocorrelated-frequency method. Furthermore, to improve the SWT, two synchrosqueezing criteria are introduced: the average SWT and the proportional SWT. Finally, the proposed modifications are tested against close modes and the noise in the signals. It was numerically and experimentally confirmed that the SWT with the proportional criterion offers better frequency localization and performs better than the continuous wavelet transform when tested against noisy signals.
Radiative damping in plasma-based accelerators
Kostyukov, I. Yu.; Nerush, E. N.; Litvak, A. G.
2012-11-01
The electrons accelerated in a plasma-based accelerator undergo betatron oscillations and emit synchrotron radiation. The energy loss to synchrotron radiation may seriously affect electron acceleration. The electron dynamics under combined influence of the constant accelerating force and the classical radiation reaction force is studied. It is shown that electron acceleration cannot be limited by radiation reaction. If initially the accelerating force was stronger than the radiation reaction force, then the electron acceleration is unlimited. Otherwise the electron is decelerated by radiative damping up to a certain instant of time and then accelerated without limits. It is shown that regardless of the initial conditions the infinite-time asymptotic behavior of an electron is governed by a self-similar solution providing that the radiative damping becomes exactly equal to 2/3 of the accelerating force. The relative energy spread induced by the radiative damping decreases with time in the infinite-time limit. The multistage schemes operating in the asymptotic acceleration regime when electron dynamics is determined by the radiation reaction are discussed.
Radiation damping in pulsed Gaussian beams
Harvey, Chris; Marklund, Mattias
2012-01-01
We consider the effects of radiation damping on the electron dynamics in a Gaussian-beam model of a laser field. For high intensities, i.e., with dimensionless intensity a0≫1, it is found that the dynamics divides into three regimes. For low-energy electrons (low initial γ factor, γ0) the radiation damping effects are negligible. At higher energies, but still at 2γ0a0 one is in a regime of radiation-reaction-induced electron capture. This capture is found to be stable with respect to the spatial properties of the electron beam and results in a significant energy loss of the electrons. In this regime the plane-wave model of the laser field provides a good description of the dynamics, whereas for lower energies the Gaussian-beam and plane-wave models differ significantly. Finally the dynamics is considered for the case of an x-ray free-electron laser field. It is found that the significantly lower intensities of such fields inhibit the damping effects.
DAMPs and influenza virus infection in ageing.
Samy, Ramar Perumal; Lim, Lina H K
2015-11-01
Influenza A virus (IAV) is a serious global health problem worldwide due to frequent and severe outbreaks. IAV causes significant morbidity and mortality in the elderly population, due to the ineffectiveness of the vaccine and the alteration of T cell immunity with ageing. The cellular and molecular link between ageing and virus infection is unclear and it is possible that damage associated molecular patterns (DAMPs) may play a role in the raised severity and susceptibility of virus infections in the elderly. DAMPs which are released from damaged cells following activation, injury or cell death can activate the immune response through the stimulation of the inflammasome through several types of receptors found on the plasma membrane, inside endosomes after endocytosis as well as in the cytosol. In this review, the detriment in the immune system during ageing and the links between influenza virus infection and ageing will be discussed. In addition, the role of DAMPs such as HMGB1 and S100/Annexin in ageing, and the enhanced morbidity and mortality to severe influenza infection in ageing will be highlighted. Copyright © 2015 Elsevier B.V. All rights reserved.
Collisional damping rates for plasma waves
Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.
2016-06-01
The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.
Damping of acoustic vibrations in gold nanoparticles
Pelton, Matthew; Sader, John E.; Burgin, Julien; Liu, Mingzhao; Guyot-Sionnest, Philippe; Gosztola, David
2009-08-01
Studies of acoustic vibrations in nanometre-scale particles can provide fundamental insights into the mechanical properties of materials because it is possible to precisely characterize and control the crystallinity and geometry of such nanostructures. Metal nanoparticles are of particular interest because they allow the use of ultrafast laser pulses to generate and probe high-frequency acoustic vibrations, which have the potential to be used in a variety of sensing applications. So far, the decay of these vibrations has been dominated by dephasing due to variations in nanoparticle size. Such inhomogeneities can be eliminated by performing measurements on single nanoparticles deposited on a substrate, but unknown interactions between the nanoparticles and the substrate make it difficult to interpret the results of such experiments. Here, we show that the effects of inhomogeneous damping can be reduced by using bipyramidal gold nanoparticles with highly uniform sizes. The inferred homogeneous damping is due to the combination of damping intrinsic to the nanoparticles and the surrounding solvent; the latter is quantitatively described by a parameter-free model.
Metallic materials for mechanical damping capacity applications
Crăciun, R. C.; Stanciu, S.; Cimpoeșu, R.; (Dragoș Ursanu, A. I.; Manole, V.; Paraschiv, P.; Chicet, D. L.
2016-08-01
Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.
First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO
Blair, Carl; Abbott, Richard; Aston, Stuart; Betzwieser, Joseph; Blair, David; DeRosa, Ryan; Evans, Matthew; Frolov, Valera; Fritschel, Peter; Grote, Hartmut; Hardwick, Terra; Liu, Jian; Lormand, Marc; Miller, John; Mullavey, Adam; O'Reilly, Brian; Zhao, Chunnong; Authors, LSC Instrument
2016-01-01
Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15,538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electro-static actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nNrms was required to maintain the acoustic mode at its minimum amplitude...
Active vibration control of multibody system with quick startup and brake based on active damping
Institute of Scientific and Technical Information of China (English)
TANG Hua-ping; TANG Yun-jun; TAO Gong-an
2006-01-01
A kind of active vibration control method was presented based on active damping and optimization design for driving load of multibody system with quick startup and brake. Dynamical equation of multibody system with quick startup and brake and piezoelectric actuators intelligent structure was built. The optimum driving load was calculated by applying the presented method. The self-sensing and self-tuning closed-loop active vibration control in quick startup and brake process was realized. The control algorithm, using local velocity negative feedback, i.e. the output of a sensor only affects the output of the actuator collocated, can induce damping effectively to actively suppress the system vibration. Based on the optimization design for driving load of multibody system with quick startup and bake, the active damping of piezoelectric actuators intelligent structure was used to farther suppress the vibration of system. Theoretical analysis and calculation of numerical show that the proposed method makes the vibration of system decrease more than the optimal design method for driving load of multibody system.
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.
Decoupling negative damping signals in a power system through dynamic gain reduction measures
Energy Technology Data Exchange (ETDEWEB)
Coowar, F.; Magdy, M.A. (Univ. of Wollongong, Wollongong, N.S.W. (AU)); Grainger, W. (Electricity Commission of New South Wales, Sydney, N.S.W. (AU))
1992-08-01
Low frequency oscillations occurring in a power system can be accentuated in generators through a feedback loop which connects the output of the system to the summing junction of the Automatic Voltage Regulator (AVR) where the Power System Stabilizer (PSS) is also connected. A method of decoupling these oscillations without compromising the benevolent effects of other control loops in that system is presented. A notch filter, located in the forward path of the negative damping signal, provides the necessary Dynamic Gain Reduction (DGR) for switching off the detrimental signals. This paper provides relevant frequency domain analysis of the closed loop transfer function of a typical power system which reflects the effect of tie-line disturbances on power angle oscillations. This leads to a restructuring of the transfer blocks in the system and the design of a DGR block that allows the decoupling of the negative damping signals. Additional insight into the effect of negative damping signals and their subsequent decoupling is provided through the examination of loop and transfer block signals.
Progress In Transverse Feedbacks and Related Diagnostics for Hadron Machines
Hofle, W
2013-01-01
Today Hadron Accelerators with high intensity and high brightness beams increasingly rely on transverse feedback systems for the control of instabilities and the preservation of the transverse emittance. With particular emphasis, but not limited to, the CERN Hadron Accelerator Chain, the progress made in recent years, and the performances achieved are reviewed. Hadron colliders such as the LHC represent a particular challenge as they ask for low noise electronic systems in these feedbacks for acceptable emittance growth. Achievements of the LHC transverse feedback system used for damping injection oscillations and to provide stability throughout the cycle are summarized. This includes its use for abort gap and injection cleaning as well as transverse blow-up for diagnostics purposes. Beyond systems already in operation, advances in technology and modern digital signal processing with increasingly higher digitization rates have made systems conceivable to cure intra-bunch motion. With its capabilities to both ...
A new damping factor algorithm based on line search of the local minimum point for inverse approach
Zhang, Yaqi; Liu, Weijie; Lu, Fang; Zhang, Xiangkui; Hu, Ping
2013-05-01
The influence of damping factor on the convergence and computational efficiency of the inverse approach was studied through a series of practical examples. A new selection algorithm of the damping (relaxation) factor which takes into account of both robustness and calculation efficiency is proposed, then the computer program is implemented and tested on Siemens PLM NX | One-Step. The result is compared with the traditional Armijo rule through six examples such as U-beam, square box and cylindrical cup et al, confirming the effectiveness of proposed algorithm.
Damped and zero-damped quasinormal modes of charged, nearly-extremal black holes
Zimmerman, Aaron
2015-01-01
Despite recent progress, the complete understanding of the perturbations of charged, rotating black holes as described by the Kerr-Newman metric remains an open and fundamental problem in relativity. In this study, we explore the existence of families of quasinormal modes of Kerr-Newman black holes whose decay rates limit to zero at extremality, called zero-damped modes in past studies. We review the nearly-extremal and WKB approximation methods for spin-weighted scalar fields (governed by the Dudley-Finley equation) and give an accounting of the regimes where scalar zero-damped and damped modes exist. Using Leaver's continued fraction method, we verify that these approximations give accurate predictions for the frequencies in their regimes of validity. In the non-rotating limit, we argue that gravito-electromagnetic perturbations of nearly-extremal Reissner-Nordstr\\"{o}m black holes have zero-damped modes in addition to the well-known spectrum of damped modes. We provide an analytic formula for the frequenci...
Nembach, Hans T; Shaw, Justin M; Boone, Carl T; Silva, T J
2013-03-15
We demonstrate a strong dependence of the effective damping on the nanomagnet size and the particular spin-wave mode that can be explained by the theory of intralayer transverse-spin pumping. The effective Landau-Lifshitz damping is measured optically in individual, isolated nanomagnets as small as 100 nm. The measurements are accomplished by use of a novel heterodyne magneto-optical microwave microscope with unprecedented sensitivity. Experimental data reveal multiple standing spin-wave modes that we identify by use of micromagnetic modeling as having either localized or delocalized character, described generically as end and center modes. The damping parameter of the two modes depends on both the size of the nanomagnet as well as the particular spin-wave mode that is excited, with values that are enhanced by as much as 40% relative to that measured for an extended film. Contrary to expectations based on the ad hoc consideration of lithography-induced edge damage, the damping for the end mode decreases as the size of the nanomagnet decreases. The data agree with the theory for damping caused by the flow of intralayer transverse spin currents driven by the magnetization curvature. These results have serious implications for the performance of nanoscale spintronic devices such as spin-torque-transfer magnetic random access memory.
Neural cryptography with feedback
Ruttor, Andreas; Kinzel, Wolfgang; Shacham, Lanir; Kanter, Ido
2004-04-01
Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message.
Neural cryptography with feedback.
Ruttor, Andreas; Kinzel, Wolfgang; Shacham, Lanir; Kanter, Ido
2004-04-01
Neural cryptography is based on a competition between attractive and repulsive stochastic forces. A feedback mechanism is added to neural cryptography which increases the repulsive forces. Using numerical simulations and an analytic approach, the probability of a successful attack is calculated for different model parameters. Scaling laws are derived which show that feedback improves the security of the system. In addition, a network with feedback generates a pseudorandom bit sequence which can be used to encrypt and decrypt a secret message.
Social Security Administration — The Policy Feedback System (PFS) is a web application developed by the Office of Disability Policy Management Information (ODPMI) team that gathers empirical data...
Feedback Loop Gains and Feedback Behavior (1996)
DEFF Research Database (Denmark)
Kampmann, Christian Erik
2012-01-01
Linking feedback loops and system behavior is part of the foundation of system dynamics, yet the lack of formal tools has so far prevented a systematic application of the concept, except for very simple systems. Having such tools at their disposal would be a great help to analysts in understanding...... large, complicated simulation models. The paper applies tools from graph theory formally linking individual feedback loop strengths to the system eigenvalues. The significance of a link or a loop gain and an eigenvalue can be expressed in the eigenvalue elasticity, i.e., the relative change...... of an eigenvalue resulting from a relative change in the gain. The elasticities of individual links and loops may be found through simple matrix operations on the linearized system. Even though the number of feedback loops can grow rapidly with system size, reaching astronomical proportions even for modest systems...
Damping of Inter-Area Low Frequency Oscillation Using an Adaptive Wide-Area Damping Controller
DEFF Research Database (Denmark)
Yao, Wei; Jiang, L.; Fang, Jiakun
2013-01-01
This paper presents an adaptive wide-area damping controller (WADC) based on generalized predictive control (GPC) and model identification for damping the inter-area low frequency oscillations in large-scale inter-connected power system. A recursive least-squares algorithm (RLSA) with a varying...... forgetting factor is applied to identify online the reduced-order linearlized model which contains dominant inter-area low frequency oscillations. Based on this linearlized model, the generalized predictive control scheme considering control output constraints is employed to obtain the optimal control signal...... in each sampling interval. Case studies are undertaken on a two-area fourmachine power system and the New England 10-machine 39-bus power system, respectively. Simulation results show that the proposed adaptive WADC not only can damp the inter-area oscillations effectively under a wide range of operation...
Kim, Seok-Kyoon; Song, Hwachang; Yoon, Tae-Woong
2015-04-01
On the basis of the non-linear third-order generator model, this article proposes a dual control scheme for a single synchronous machine equipped with an energy storage device to regulate the terminal voltage while enhancing the damping. Based on the input-output feedback linearisation method, the exciter controller is designed such that the terminal voltage robustly converges to its predetermined reference in the presence of a model uncertainty. In addition, the control input of the energy storage device feedbacks only the relative speed. It is shown that this controller can effectively increase the damping of the synchronous machine and that there is a set of initial conditions such that all trajectories started from this set go to the equilibrium point, satisfying input constraints. Moreover, it is also verified that all generator variables are bounded except for the power angle. The simulation results show that the closed-loop performance is satisfactory despite a transmission line fault and a model uncertainty in which the non-linear fourth-order generator model (two-axis) is used.
Improving e-learning by Emotive Feedback
DEFF Research Database (Denmark)
Sharp, Robin; Gjedde, Lisa
2011-01-01
This paper considers the use of feedback with emotive elements in order to improve the efficiency of e-learning for teaching complex technical subjects to the general public by stimulation of implicit learning. An example is presented, based on an effort to investigate the current level of IT sec......This paper considers the use of feedback with emotive elements in order to improve the efficiency of e-learning for teaching complex technical subjects to the general public by stimulation of implicit learning. An example is presented, based on an effort to investigate the current level...
An adaptive phase alignment algorithm for cartesian feedback loops
Gimeno-Martin, A.; Pardo-Martin, J.; Ortega-Gonzalez, F.
2010-01-01
An adaptive algorithm to correct phase misalignments in Cartesian feedback linearization loops for power amplifiers has been presented. It yields an error smaller than 0.035 rad between forward and feedback loop signals once convergence is reached. Because this algorithm enables a feedback system to process forward and feedback samples belonging to almost the same algorithm iteration, it is suitable to improve the performance not only of power amplifiers but also any other digital feedback system for communications systems and circuits such as all digital phase locked loops. Synchronizing forward and feedback paths of Cartesian feedback loops takes a small period of time after the system starts up. The phase alignment algorithm needs to converge before the feedback Cartesian loop can start its ideal behavior. However, once the steady state is reached, both paths can be considered synchronized, and the Cartesian feedback loop will only depend on the loop parameters (open-loop gain, loop bandwidth, etc.). It means that the linearization process will also depend only on these parameters since the misalignment effect disappears. Therefore, this algorithm relieves the power amplifier linearizer circuit design of any task required for solving phase misalignment effects inherent to Cartesian feedback systems. Furthermore, when a feedback Cartesian loop has to be designed, the designer can consider that forward and feedback paths are synchronized, since the phase alignment algorithm will do this task. This will reduce the simulation complexity. Then, all efforts are applied to determining the suitable loop parameters that will make the linearization process more efficient.
Feedback og interpersonel kommunikation
DEFF Research Database (Denmark)
Dindler, Camilla
2016-01-01
Som interpersonel kommunikationsform handler feedback om at observere, mærke og italesætte det, som handler om relationen mellem samtaleparterne mere end om samtaleemnet. Her er fokus på, hvad der siges og hvordan der kommunikeres sammen. Feedback er her ikke en korrigerende tilbagemelding til...
"Feedback" For Instructioal Television.
Schramm, Wilbur
A number of different methods have been used by instructional television (ITV) projects to obtain audience feedback, and some of these are now being used in the ITV system in El Salvador. We know that pretesting programs on a representative sample can bring considerable gains in learning. Another feedback source can be a classroom of pupils in the…
ENSO feedbacks and their relationships with the mean state in a flux adjusted ensemble
Ferrett, Samantha; Collins, Matthew
2016-11-01
The El Niño Southern Oscillation (ENSO) is governed by a combination of amplifying and damping ocean-atmosphere feedbacks in the equatorial Pacific. Here we quantify these feedbacks in a flux adjusted HadCM3 perturbed physics ensemble under present day conditions and a future emissions scenario using the Bjerknes Stability Index (BJ index). Relationships between feedbacks and both the present day biases and responses under climate change of the mean equatorial Pacific climate are investigated. Despite minimised mean sea surface temperature biases through flux adjustment, the important dominant ENSO feedbacks still show biases with respect to observed feedbacks and inter-ensemble diversity. The dominant positive thermocline and zonal advective feedbacks are found to be weaker in ensemble members with stronger mean zonal advection. This is due to a weaker sensitivity of the thermocline slope and zonal surface ocean currents in the east Pacific to surface wind stress anomalies. A drier west Pacific is also found to be linked to weakened shortwave and latent heat flux damping, suggesting a link between ENSO characteristics and the hydrological cycle. In contrast to previous studies using the BJ index that find positive relationships between the index and ENSO amplitude, here they are weakly or negatively correlated, both for present day conditions and for projected differences. This is caused by strong thermodynamic damping which dominates over positive feedbacks, which alone approximate ENSO amplitude well. While the BJ index proves useful for individual linear feedback analysis, we urge caution in using the total linear BJ index alone to assess the reasons for ENSO amplitude biases and its future change in models.
Energy Technology Data Exchange (ETDEWEB)
Hoener, Markus
2015-07-01
At the 1.5-GeV synchrotron radiation source DELTA, operated by the TU Dortmund University, intensive synchrotron radiation in the spectral range from hard X-rays to THz radiation is generated by the circular deflection of highly relativistic electron bunches. Interacting with the vacuum chamber wall, the electron bunches create electric fields, which can act back on subsequent bunches. With increasing beam current, the excitation is enhanced so that the electron beam is unstable, which means that the electron bunches oscillate longitudinally or transversely relative to their reference position. The oscillations reduce the quality of the synchrotron radiation and limit the maximum storable beam current. Within the scope of this thesis, the beam instabilities at the storage ring were systematically investigated. A digital bunch-by-bunch feedback system was installed and commissioned, which allows to detect and digitize the position of each electron bunch at each turn. Based on the input signal, a correction signal is calculated in order to suppress transverse and longitudinal oscillation of the bunches. In addition, it is possible to excite dedicated bunches. The systematic excitation of all coupled-bunch modes allowed for the first time to determine the damping rates of all 192 eigenmodes of the electron beam. The current dependence of the damping rates was investigated and an instability threshold was found. Besides the investigation of multibunch instabilities, single-bunch instabilities are discussed. In addition, the acquisition unit of the digital feedback system can be triggered on external events. This was used to investigate the injection process and beam losses. It was shown that the transverse feedback system increases the injection efficiency. Another aspect of this thesis is the improvement of the signal quality of ultrashort coherent synchrotron radiation pulses, which are generated by the short-pulse facility at DELTA. The short-pulse facility is based
On the origin of nonlocal damping in plasmonic monomers and dimers
DEFF Research Database (Denmark)
Tserkezis, Christos; Yan, Wei; Hsieh, Wenting
2017-01-01
The origin and importance of nonlocal damping is discussed through simulations with the generalized nonlocal optical response (GNOR) theory, in conjunction with time-dependent density functional theory (TDDFT) calculations and equivalent circuit modeling, for some of the most typical plasmonic ar...... the interface. Diffusive nonlocal theories provide therefore an efficient means to tackle plasmon damping when electron tunneling can be safely disregarded, without the need to resort to more accurate, but time-consuming fully quantum-mechanical studies.......The origin and importance of nonlocal damping is discussed through simulations with the generalized nonlocal optical response (GNOR) theory, in conjunction with time-dependent density functional theory (TDDFT) calculations and equivalent circuit modeling, for some of the most typical plasmonic...... calculations in few-nm particles or few-to-sub-nm gaps. Through the evaluation of a local effective dielectric function, it is shown that absorptive losses appear dominantly close to the metal surface, in agreement with TDDFT and the mechanism of Landau damping due to generation of electronâ€“hole pairs near...
Foucault pendulum with eddy-current damping of the elliptical motion
Mastner, G.; Vokurka, V.; Maschek, M.; Vogt, E.; Kaufmann, H. P.
1984-10-01
A newly designed Foucault pendulum is described in which the mechanical Charron ring, used throughout in previous designs for damping of the elliptical motion of the pendulum, is replaced by an electromagnetic eddy-current brake, consisting of a permanent magnet attached to the bottom of the bob and a metallic ring. This damping device is very efficient, as it is self-aligning, symmetrical in the damping effect, and never wears out. The permanent magnet is also used, together with a coil assembly and an electronic circuitry, for the dipole-torque drive of the pendulum as well as for accurate stabilization of the amplitude of the swing. A latched time display, controlled by Hall probes activated by the magnet, is used to visualize the Foucault rotation. The pendulum system and its associated electronic circuitry are described in detail. The optimizing of the drive mode is discussed. Measurements of deviations from theoretical value of the Foucault rotation velocity made automatically in a continuous run show a reproducible accuracy of ±1% or better in individual 360° rotations during the summer months. The quality factor of the pendulum as mechanical resonator was measured as a function of the amplitude in the presence of the eddy-current damping ring.
DEFF Research Database (Denmark)
Sortkær, Bent
2017-01-01
Feedback bliver i litteraturen igen og igen fremhævet som et af de mest effektive midler til at fremme elevers præstationer i skolen (Hartberg, Dobson, & Gran, 2012; Hattie & Timperley, 2007; Wiliam, 2015). Dette på trods af, at flere forskere påpeger, at feedback ikke altid er læringsfremmende...... (Hattie & Gan, 2011), og nogle endda viser, at feedback kan have en negativ virkning i forhold til præstationer (Kluger & DeNisi, 1996). Artiklen vil undersøge disse tilsyneladende modstridende resultater ved at stille spørgsmålet: Under hvilke forudsætninger virker feedback i matematik læringsfremmende......? Dette gøres ved at dykke ned i forskningslitteraturen omhandlende feedback ud fra en række temaer for på den måde at besvare ovenstående spørgsmål....
DEFF Research Database (Denmark)
Eriksson, Tor Viking; Poulsen, Anders; Villeval, Marie-Claire
This paper experimentally investigates the impact of different pay and relative performance information policies on employee effort. We explore three information policies: No feedback about relative performance, feedback given halfway through the production period, and continuously updated feedback....... The pay schemes are a piece rate payment scheme and a winner-takes-all tournament. We find that, regardless of the pay scheme used, feedback does not improve performance. There are no significant peer effects in the piece-rate pay scheme. In contrast, in the tournament scheme we find some evidence...... of positive peer effects since the underdogs almost never quit the competition even when lagging significantly behind, and frontrunners do not slack off. Moreover, in both pay schemes information feedback reduces the quality of the low performers' work....
DEFF Research Database (Denmark)
Lukassen, Niels Bech; Wahl, Christian; Sorensen, Elsebeth Korsgaard
2016-01-01
feedback episode (FFE) through an online dialogue. The paper argues that dialogue is crucial for student learning and that feedback is not only something the teacher gives to the student. Viewing good quality feedback as social, situated, formative, emphasis is put on the establishment of dialogue. We...... refer to this type of feedback as, Situated Formative Feedback (SFF). As a basis for exploring, identifying and discussing relevant aspects of SFF the paper analyses qualitative data from a Moodle dialogue. Data are embedded in the qualitative analytic program Nvivo and are analysed with a system...... theoretical textual analysis method. Asynchronous written dialogue from an online master’s course at Aalborg University forms the empirical basis of the study. The findings suggests in general that students play an essential role in SFF and that students and educators are equal in the COP, but holds different...
Image Restoration Using the Damped Richardson-Lucy Iteration
White, R. L.
describe a new image restoration iteration that dramatically reduces noise amplification while retaining the good characteristics and efficiency of the RL method. The method is based on a modified form of the Poisson likelihood function that is flatter in the vicinity of a good fit. The resulting iteration is very similar to the RL iteration, but with a new spatially adaptive damping factor that prevents noise amplification in regions of the image where a smooth model provides an adequate fit to the data; thus, I call this the damped RL iteration . The damped iteration converges as fast or faster than the RL method. Results will be shown for both simulated data and Hubble Space Telescope images.
Damping in high-temperature superconducting levitation systems
Energy Technology Data Exchange (ETDEWEB)
Hull, John R.
2009-12-15
Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magnetic field and a magnet (e.g. a rotor) supported by the magnetic field are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magnetic field on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.
Whistler damping at oblique propagation - Laminar shock precursors
Gary, S. P.; Mellott, M. M.
1985-01-01
This paper addresses the collisionless damping of whistlers observed as precursors standing upstream of oblique, low-Mach number terrestrial bow shocks. The linear theory of electromagnetic waves in a homogeneous Vlasov plasma with Maxwellian distribution functions and a magnetic field is considered. Numerical solutions of the full dispersion equation are presented for whistlers propagating at an arbitrary angle with respect to the magnetic field. It is demonstrated that electron Landau damping attenuates oblique whistlers and that the parameter which determines this damping is beta-e. In a well-defined range of parameters, this theory provides damping lengths which are the same order of magnitude as those observed. Thus electron Landau damping is a plausible process in the dissipation of upstream whistlers. Nonlinear plasma processes which may contribute to precursor damping are also discussed, and criteria for distinguishing among these are described.
Damping in high-temperature superconducting levitation systems
Hull, John R.
2009-12-15
Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magnetic field and a magnet (e.g. a rotor) supported by the magnetic field are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magnetic field on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.
Damping behaviors of metal matrix composites with interface layer
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A novel technique of designing the interface layer in metal matrix composites of high damping capacity was developed via different CVD coatings on carbon fibers in Cf/Al composites. It was shown that the interface layer improved the tensile strength, elastic modulus and damping capacity of the Cf/Al composites. A carbon layer showed the highest improvement and a silicon layer the lowest, while a mixed carbon and silicon layer exhibited an intermediate effect. Moreover, the thickness of interface layer also influences the damping capacity. A thicker carbon layer produced a better damping capacity because the dependence of damping capacity on strain amplitude was increased. It is suggested that a micro-sliding action occurring in the interface layer is the main mechanism responsible for the high damping capacity of the composites.
The damping performance of aluminum-based composites
Energy Technology Data Exchange (ETDEWEB)
Updike, C.A.; Bhagat, R.B.; Pechersky, M.J.; Amateau, M.F. (Harris Corp., Government Aerospace Systems Div., Melbourne, FL (USA) Pennsylvania State Univ., University Park (USA))
1990-03-01
Metal-matrix-composites may offer better damping properties than unreinforced alloys. Because damping properties (and metal-matrix composites) are becoming important in airframe design, the damping capabilities of a number of aluminum-matrix composites were measured over a wide range of frequencies at low strain amplitudes, using a new laser vibrometer technique. Silicon carbide and alumina reinforcements resulted in a material with damping properties similar to that of unreinforced aluminum 6061-T6, but unidirectional and planar-random graphite continuous-fiber reinforcements increased the damping by 5 and 14 times, respectively. The increased damping of the continuous fiber composites is attributed to the absence of interfacial reaction resulting from the high-pressure infiltration method used for their manufacture. 25 refs.
Design of damping valve for vehicle hydro pneumatic suspension
Institute of Scientific and Technical Information of China (English)
Mingming DONG; Hua HUANG; Lian GU
2008-01-01
According to the design features of a hydro pneumatic spring, the necessity of a separate damping valve is proposed. Based on a 1/4 vehicle linear suspension model, the optimum damping coefficient is worked out and the parameters of the damping valve are determined with the equivalent linearization method. A practical structure of the damping valve is proposed having a small size, high flowrate when the valve opens, and the ability of enduring high back pressure. Based on bench tests, the damping valve has been found to properly work and be suitable. The design method and damping valve structure are useful guides for hydro pneumatic suspension, especially for the design of heavy-duty vehicles.
Dynamic analyses of viscoelastic dielectric elastomers incorporating viscous damping effect
Zhang, Junshi; Zhao, Jianwen; Chen, Hualing; Li, Dichen
2017-01-01
In this paper, based on the standard linear solid rheological model, a dynamics model of viscoelastic dielectric elastomers (DEs) is developed with incorporation of viscous damping effect. Numerical calculations are employed to predict the damping effect on the dynamic performance of DEs. With increase of damping force, the DEs show weak nonlinearity and vibration strength. Phase diagrams and Poincaré maps are utilized to detect the dynamic stability of DEs, and the results indicate that a transition from aperiodic vibration to quasi-periodic vibration occurs with enlargement of damping force. The resonance properties of DEs including damping effect are subsequently analyzed, demonstrating a reduction of resonant frequency and resonance peak with increase of damping force.
Researches on Track Reconstruction for DAMPE
Lu, T. S.; Lei, S. J.; Zang, J. J.; Chang, J.; Wu, J.
2016-05-01
The Dark Matter Particle Explorer (DAMPE) is aimed to study the existence and distribution of dark matter via observation of high energy particles in space with unprecedented large energy bandwidth, high energy resolution, and high space resolution. The track reconstruction is to restore the positions and angles of the incident particles using the multiple observations of different channels at different positions, and its accuracy determines the angular resolution of the detector. The track reconstruction is mainly based on the observations of two sub-detectors, namely, the Silicon Tracker (STK) detector and the BGO (Bi_4Ge_3O12) calorimeter. In accordance with the design and structure of the two sub-detectors and using the data collected during the beam tests and ground tests, we provide a detailed introduction of the track reconstruction of DAMPE data, including three basic steps, the selection of track hits, the fitting of track hits, and the judgement of the best track among (most probably) many of them. Since a high energy particle most probably leaves more than one hit in each level of the STK and BGO, we first provide a method to constrain the STK clusters for the track reconstruction using the rough result of the BGO reconstruction. We apply two different algorithms, the Kalman filter and the least square linear fitting, to fit the track hits. The consistency of the results obtained independently via the two algorithms confirms the validity of our track reconstruction results, and we discuss the advantages/disadvantages of each method. Several criteria combining the BGO and STK detection are discussed for picking out the most possible track among all the tracks found in the track reconstruction. Using the track reconstruction methods mentioned in this article and the beam test data, we confirm that the angular resolution of DAMPE satisfies the requirement in design.
System for damping vibrations in a turbine
Energy Technology Data Exchange (ETDEWEB)
Roberts, III, Herbert Chidsey; Johnson, Curtis Alan; Taxacher, Glenn Curtis
2015-11-24
A system for damping vibrations in a turbine includes a first rotating blade having a first ceramic airfoil, a first ceramic platform connected to the first ceramic airfoil, and a first root connected to the first ceramic platform. A second rotating blade adjacent to the first rotating blade includes a second ceramic airfoil, a second ceramic platform connected to the second ceramic airfoil, and a second root connected to the second ceramic platform. A non-metallic platform damper has a first position in simultaneous contact with the first and second ceramic platforms.
Problem of the gyroscopic stabilizer damping
Directory of Open Access Journals (Sweden)
Šklíba J.
2009-06-01
Full Text Available The gyroscopic stabilization of the vibro-isolation system of an ambulance couch is analyzed. This paper follows several previous papers, which concern the derivation of the complete system of appropriate differential equations and some analyses were provided there, as well. It was supposed that mass matrix, stiffness matrix and gyroscope impulse-moment remain constant and the stability of equilibrium state was solved according to different alternatives of the damping and of the radial correction. Little known theorems of the stability were used there. With respect to these theorems, vibro-isolation systems can be classified according to odd or even number of generalized coordinates.
Mode damping in a commensurate monolayer solid
DEFF Research Database (Denmark)
Bruch, Ludwig Walter; Hansen, Flemming Yssing
1997-01-01
with an elastic-continuum theory of the response of modes of either parallel or perpendicular polarization for a spherical adsorbate on a hexagonal substrate. The results are applied to the discussion of computer simulations and inelastic atomic-scattering experiments for adsorbates on graphite. The extreme...... 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...
Gyroscopic Stabilization of Indefinite Damped Systems
DEFF Research Database (Denmark)
Kliem, Wolfhard; Müller, Peter C.
1996-01-01
The paper deals with linear systems of differential equationswith symmetric system matrices M,D, and K.The mass matrix M and the stiffness matrix K are both assumed to bepositive definite. The damping matrix D is indefinite. Three questionsare of interest: 1) When is the system unstable? Apparently...... not always,if the matrix D is indefinite. 2) What can we say about conditions whichensure that an unstable system can be stabilized by adding a gyroscopicterm Gdx/dt? 3) What is, in this case, a suitable or optimal matrixG? The questions are answered in the frame of a first order perturbationapproach....
Glued trees algorithm under phase damping
Energy Technology Data Exchange (ETDEWEB)
Lockhart, J. [School of Electronics, Electrical Engineering and Computer Science, Queen' s University, Belfast, BT7 1NN (United Kingdom); Di Franco, C., E-mail: c.difranco@qub.ac.uk [Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen' s University, Belfast, BT7 1NN (United Kingdom); Paternostro, M. [Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen' s University, Belfast, BT7 1NN (United Kingdom)
2014-01-17
We study the behaviour of the glued trees algorithm described by Childs et al. in [1] under decoherence. We consider a discrete time reformulation of the continuous time quantum walk protocol and apply a phase damping channel to the coin state, investigating the effect of such a mechanism on the probability of the walker appearing on the target vertex of the graph. We pay particular attention to any potential advantage coming from the use of weak decoherence for the spreading of the walk across the glued trees graph.
Radiation damping in closed expanding universes
Bernui, Armando
The dynamics of a coupled model (harmonic oscillator-relativistic scalar field) in Conformal Robertson-Walker (k = +1) spacetimes is investigated. The exact radiation-reaction equation of the source-including the retarded radiation terms due to the closed space geometry - is obtained and analyzed. A suitable family of Lyapunov functions is constructed to show that, if the spacetime expands monotonely, then the source's energy damps. A numerical simulation of this equation for expanding Universes, with and without Future Event Horizon, is performed.
Relativity Damps OPEP in Nuclear Matter
Banerjee, Manoj K.
1998-01-01
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. We find that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. We show that the damping of derivative-coupled OPEP is actually due to the decrease of $M^*/M$ with increasing density. We point out that if derivative-coupled OPEP...
Feedback valence affects auditory perceptual learning independently of feedback probability
Amitay, S.; Moore, D. R.; Molloy, K.; Halliday, L. F.
2015-01-01
Previous studies have suggested that negative feedback is more effective in driving learning than positive feedback. We investigated the effect on learning of providing varying amounts of negative and positive feedback while listeners attempted to discriminate between three identical tones; an impossible task that nevertheless produces robust learning. Four feedback conditions were compared during training: 90% positive feedback or 10% negative feedback informed the participants that they wer...
Optimal Constrained Layer Damping of Beams: Experimental and Numerical Studies
Directory of Open Access Journals (Sweden)
J.-L. Marcelin
1995-01-01
Full Text Available This article deals with the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered. The design variables are the dimensions and locations of the viscoelastic layers and the objective function is the maximum damping factor. The discrete design variable optimization problem is solved using a genetic algorithm. Numerical results for minimum and maximum damping are compared to experimental results. This is done for a various number of materials and beams.
Test particle study of Landau damping of steepening magnetosonic waves
Matsumoto, H.; Barnes, A.
1982-01-01
A test particle study of Landau damping of steepening large-amplitude magnetosonic waves is made. Motions of test particles in a model of a steepening large-amplitude magnetosonic wave are traced. The kinetic energy change of the ensemble of test particles is computed to estimate the effective Landau damping rate of the magnetosonic wave. The numerical results are compared with the linear kinetic theory of Landau damping and interpreted in terms of a simple physical picture for particle trapping.
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...... as viscous boundary conditions. It is demonstrated that properly calibrated viscous bimoments introduce a significant level of supplemental damping to the targeted vibration mode and that the attainable damping can be accurately estimated from the two undamped problems associated with vanishing and infinite...
Feedback som tredjeordensiagttagelse
Directory of Open Access Journals (Sweden)
Ane Qvortrup
2013-09-01
Full Text Available Feedback tilskrives stor betydning for læring, men trods intensiv forskning på området synes det svært at fange, hvori feedbacks særlige potentiale består. I forsøgene på at gøre dette knyttes an til en række faktorer eller parametre, der fremhæves som centrale. En af disse faktorer er tid, hvor der kredses om forskellen mellem umiddelbar og forsinket feedback samt om fordele og ulemper ved hver af de to. I denne artikel knyttes der an til en forståelse af feedback som tredjeordensiagttagelse, og der sættes herfra fokus på, hvordan man i en praktisk undervisningssituation kan imødekomme tidsfaktoren knyttet til feedback. Med udgangspunkt i et undervisningsforløb på bachelorniveau, hvor der er arbejdet systematisk med feedback understøttet af Wikis, belyses det, hvordan et sådant arbejde synes at have potentiale for understøttelse af såvel læring som undervisning. En sådan teoretisk reflekteret belysning kan udgøre et refleksionsprogram for fremtidig planlægning af og løbende refleksion over undervisning. The article investigates the effect of feedback on learning. Feedback has been shown to be one of the most powerful influences on achievement in education. But, in spite of much research on the matter, there is no agreement on how the special potential of feedback can be described, and consequently no agreement on what is good and bad feedback. This article sets out to rectify this omission by seeking a new theoretical framework that is sensitive to the complexity of the impact of feedback. The author propose a system theoretical frame and through its use identifies significant didactical issues. Although feedback is described as an internal, system-relative construction, when seen through a system theoretical lens different teaching environments create diverse conditions for feedback constructions. The final section of the paper explores this idea in relation to wikis.
Feedback som tredjeordensiagttagelse
Directory of Open Access Journals (Sweden)
Ane Qvortrup
2013-09-01
Full Text Available Feedback tilskrives stor betydning for læring, men trods intensiv forskning på området synes det svært at fange, hvori feedbacks særlige potentiale består. I forsøgene på at gøre dette knyttes an til en række faktorer eller parametre, der fremhæves som centrale. En af disse faktorer er tid, hvor der kredses om forskellen mellem umiddelbar og forsinket feedback samt om fordele og ulemper ved hver af de to. I denne artikel knyttes der an til en forståelse af feedback som tredjeordensiagttagelse, og der sættes herfra fokus på, hvordan man i en praktisk undervisningssituation kan imødekomme tidsfaktoren knyttet til feedback. Med udgangspunkt i et undervisningsforløb på bachelorniveau, hvor der er arbejdet systematisk med feedback understøttet af Wikis, belyses det, hvordan et sådant arbejde synes at have potentiale for understøttelse af såvel læring som undervisning. En sådan teoretisk reflekteret belysning kan udgøre et refleksionsprogram for fremtidig planlægning af og løbende refleksion over undervisning. The article investigates the effect of feedback on learning. Feedback has been shown to be one of the most powerful influences on achievement in education. But, in spite of much research on the matter, there is no agreement on how the special potential of feedback can be described, and consequently no agreement on what is good and bad feedback. This article sets out to rectify this omission by seeking a new theoretical framework that is sensitive to the complexity of the impact of feedback. The author propose a system theoretical frame and through its use identifies significant didactical issues. Although feedback is described as an internal, system-relative construction, when seen through a system theoretical lens different teaching environments create diverse conditions for feedback constructions. The final section of the paper explores this idea in relation to wikis.
Toward broadband electroacoustic resonators through optimized feedback control strategies
Boulandet, R.; Lissek, H.
2014-09-01
This paper presents a methodology for the design of broadband electroacoustic resonators for low-frequency room equalization. An electroacoustic resonator denotes a loudspeaker used as a membrane resonator, the acoustic impedance of which can be modified through proportional feedback control, to match a target impedance. However, such impedance matching only occurs over a limited bandwidth around resonance, which can limit its use for the low-frequency equalization of rooms, requiring an effective control at least up to the Schroeder frequency. Previous experiments have shown that impedance matching can be achieved over a range of a few octaves using a simple proportional control law. But there is still a limit to the feedback gain, beyond which the feedback-controlled loudspeaker becomes non-dissipative. This paper evaluates the benefits of using PID control and phase compensation techniques to improve the overall performance of the electroacoustic resonator. More specifically, it is shown that some adverse effects due to high-order dynamics in the moving-coil transducer can be mitigated. The corresponding control settings are also identified with equivalent electroacoustic resonator parameters, allowing a straightforward design of the controller. Experimental results using PID control and phase compensation are finally compared in terms of sound absorption performances. As a conclusion the overall performances of electroacoustic resonators for damping the modal resonances inside a duct are presented, along with general discussions on practical implementation and the extension to actual room modes damping.
Structural dynamic analysis with generalized damping models analysis
Adhikari , Sondipon
2013-01-01
Since Lord Rayleigh introduced the idea of viscous damping in his classic work ""The Theory of Sound"" in 1877, it has become standard practice to use this approach in dynamics, covering a wide range of applications from aerospace to civil engineering. However, in the majority of practical cases this approach is adopted more for mathematical convenience than for modeling the physics of vibration damping. Over the past decade, extensive research has been undertaken on more general ""non-viscous"" damping models and vibration of non-viscously damped systems. This book, along with a related book
Excitation of magnetization using a modulated radiation damping field.
Walls, Jamie D; Huang, Susie Y; Lin, Yung-Ya
2006-10-12
In this work, pulsed-field gradients are used to modulate the radiation damping field generated by the detection coil in an NMR experiment in order that spins with significantly different chemical shifts can affect one another via the radiation damping field. Experiments performed on solutions of acetone/water and acetone/DMSO/water demonstrate that spins with chemical shift differences much greater than the effective radiation damping field strength can still be coupled by modulating the radiation damping field. Implications for applications in high-field NMR and for developing sensitive magnetization detectors are discussed.
Design Rules for High Damping in Mobile Hydraulic Systems
Axin, Mikael; Krus, Petter
2013-01-01
This paper analyses the damping in pressure compensated closed centre mobile working hydraulic systems. Both rotational and linear loads are covered and the analysis applies to any type of pump controller. Only the outlet orifice in the directional valve will provide damping to a pressure compensated system. Design rules are proposed for how the system should be dimensioned in order to obtain a high damping. The volumes on each side of the load have a high impact on the damping. In case of a ...
Damping factor estimation using spin wave attenuation in permalloy film
Energy Technology Data Exchange (ETDEWEB)
Manago, Takashi, E-mail: manago@fukuoka-u.ac.jp [Department of Applied Physics, Fukuoka University, 8-19-1 Nanakuma, Jonan, Fukuoka 814-0180 (Japan); Yamanoi, Kazuto [Department of Physics, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581 (Japan); Kasai, Shinya; Mitani, Seiji [National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047 (Japan)
2015-05-07
Damping factor of a Permalloy (Py) thin film is estimated by using the magnetostatic spin wave propagation. The attenuation lengths are obtained by the dependence of the transmission intensity on the antenna distance, and decrease with increasing magnetic fields. The relationship between the attenuation length, damping factor, and external magnetic field is derived theoretically, and the damping factor was determined to be 0.0063 by fitting the magnetic field dependence of the attenuation length, using the derived equation. The obtained value is in good agreement with the general value of Py. Thus, this estimation method of the damping factor using spin waves attenuation can be useful tool for ferromagnetic thin films.
Strategies for effective feedback.
Kritek, Patricia A
2015-04-01
Provision of regular feedback to trainees on clinical performance by supervising providers is increasingly recognized as an essential component of undergraduate and graduate health sciences education; however, many individuals have not been formally trained in this pedagogical skill. At the bedside or in the clinic, effective performance feedback can be accomplished by following four key steps. Begin by setting expectations that incorporate the trainee's personal goals and external objectives. Delineate how and when you will provide feedback to the learner. Next, directly observe the trainee's performance. This can be challenging while engaged on a busy clinical service, but a focus on discrete activities or interactions (e.g., family meeting, intravascular volume assessment using bedside ultrasound, or obtaining informed consent) is helpful. The third step is to plan and prioritize the feedback session. Feedback is most effective when given in a timely fashion and delivered in a safe environment. Limit the issues addressed because learners often disengage if confronted with too many deficiencies. Finally, when delivering feedback, begin by listening to the trainee's self-evaluation and then take a balanced approach. Describe in detail what the trainee does well and discuss opportunities for improvement with emphasis on specific, modifiable behaviors. The feedback loop is completed with a plan for follow-up reassessment. Through the use of these relatively simple practices, both the trainee and teacher can have a more productive learning experience.
Characterization of damping in microfibrous material
Soobramaney, Pregassen; Flowers, George T.; Dean, Robert N.
2012-04-01
MEMS gyroscopes are used in many applications including harsh environments such as high-power, high-frequency acoustic noise. If the latter is at the natural frequency of the gyroscope, the proof mass will be overexcited giving rise to a corrupted gyroscope output. To mitigate the effect of the high-power, high-frequency acoustic noise, it is proposed to use nickel microfibrous sheets as an acoustic damper. For this purpose, the characterization of vibration damping in Nickel microfibrous sheets was examined in the present research effort. The sheets were made from nickel fibers with cellulose as a binding agent using a wet-lay papermaking technique. Sintering was done at 1000 °C to remove all the cellulose giving rise to a porous material. Square sheets of 20 cm were made from three diameters of nickel fibers namely 4, 8, and 12 microns. The sheets were cut into smaller pieces to fit the requirements of a fixture specially designed for this study. The fixture was attached to a LDS V408 shaker with a mass resting on a stack of the microfibrous sheets to simulate transmitted vibration by base motion with the sheet stack acting as a damper. A series of experiments was conducted using these 3 fiber diameters, different number of layers of microfibrous sheets and varying the vibration amplitude. From the collected vibration data, the stiffness and damping ratio of the microfibrous material was characterized.
Gyroscopic stabilization and indefimite damped systems
DEFF Research Database (Denmark)
Pommer, Christian
a class of feasibel skew-Hermitian matrices A depending on the choise of M. The theory can be applied to dynamical systems of the form x''(t) + ( dD + g G) x'(t) + K x(t) = 0 where G is a skew symmetric gyrocopic matrix, D is a symmetric indefinite damping matrix and K > 0 is a positive definite stiffness......An important issue is how to modify a given unstable matrix in such a way that the resulting matrix is stable. We investigate in general under which condition a matrix M+A is stable,where M is an arbitrary matrix and A is skew-Hermitian. We show that if trace(M) > 0 it is always possible to find...... matrix. d and g are scaling factors used to control the stability of the system. It is quite astonnishing that when the damping matrix D is indefinite the system can under certain conditions be stable even if there are no gyroscopic forces G present The Lyapunov matrix equation is used to predict...
DEFF Research Database (Denmark)
Bjerresgaard, Helle
2016-01-01
Feedback til elever, som enten er gået midlertidigt i stå eller i værste tilfælde oplever sig selv magtesløse, skal hjælpe dem til at etablere en tro på, at de kan øve indflydelse på og være betydningsfulde for deres omgivelser. Feedback sættes ofte i forbindelse med ’læring’. I denne artikel...... påvirket af en målrettet, individuel feedback – eller manglen på samme....
The Effect of Information Feedback in Construction Bidding
Directory of Open Access Journals (Sweden)
Alexander Soo
2010-07-01
Full Text Available With the goal to achieve efficiency in bidding competitions, many codes of bidding procedure recommend clients provide contractors with bidding feedback information. Contractors strive to bid competitively via learning based on their experiences in past bidding attempts. The level of bidding feedback information, however, varies across clients. In many cases, clients do not provide feedback or provide insufficient feedback to contractors. Focussing on two information feedback conditions (full and partial, we examine: (i the changes in bidding trend over time, and (ii the effects of bidding feedback information on bidders’ competitiveness in bidding. Data were gathered using a bidding experiment that involved student (inexperienced bidders with a construction project management background. The results show that the variations in bids over time for full information feedback condition are statistically significant, but not for bids from bidders with partial bidding feedback information. Bidders with full bidding feedback information are more competitive than those with partial bidding feedback information. The findings add to both our theoretical and empirical understanding of construction bidding: an understanding of the process of changes in the price of building work, and how the process can be manipulated through the release of bidding feedback information.
Give Better Feedback on Engineering Drawings
Cobb, Robert, Jr.; Graham, Tony; Kapur, Arjun; Rhodes, Craig; Blackwell, Ellinor
2005-01-01
Most, if not all, systems have a mechanism that collects information to facilitate monitoring performance. This information is primarily used to modify the system to make it more efficient in performing desired tasks and, thus, attaining desired results. Similar to electrical, mechanical, or hydraulic systems, the feedback mechanism in an…
Timely Diagnostic Feedback for Database Concept Learning
Lin, Jian-Wei; Lai, Yuan-Cheng; Chuang, Yuh-Shy
2013-01-01
To efficiently learn database concepts, this work adopts association rules to provide diagnostic feedback for drawing an Entity-Relationship Diagram (ERD). Using association rules and Asynchronous JavaScript and XML (AJAX) techniques, this work implements a novel Web-based Timely Diagnosis System (WTDS), which provides timely diagnostic feedback…
Timely Diagnostic Feedback for Database Concept Learning
Lin, Jian-Wei; Lai, Yuan-Cheng; Chuang, Yuh-Shy
2013-01-01
To efficiently learn database concepts, this work adopts association rules to provide diagnostic feedback for drawing an Entity-Relationship Diagram (ERD). Using association rules and Asynchronous JavaScript and XML (AJAX) techniques, this work implements a novel Web-based Timely Diagnosis System (WTDS), which provides timely diagnostic feedback…
Chaos control using notch filter feedback.
Ahlborn, Alexander; Parlitz, Ulrich
2006-01-27
A method for stabilizing periodic orbits and steady states of chaotic systems is presented using specifically filtered feedback signals. The efficiency of this control technique is illustrated with simulations (Rössler system, laser model) and a successful experimental application for stabilizing intensity fluctuations of an intracavity frequency-doubled Nd:YAG laser.
Using Technology to Enhance Feedback to Student Teachers
Gibson, Lenwood; Musti-Rao, Shobana
2016-01-01
The importance of effective and efficient feedback is paramount during the student teaching experience. This experience is a vital component of many teacher preparation programs. During these limited experiences, supervisors deliver performance feedback that is designed to improve the way student teachers implement evidence-based practices and/or…
Internet-Mediated Corrective Feedback for Digital Natives
Saadat, Mahboobeh; Mehrpour, Saeed; Khajavi, Yaser
2016-01-01
In this article, the authors examine different ways of using the Internet to receive feedback, and discuss advantages of language learners' use of the Internet to improve their own writing. In effect, the article elaborates on how Internet-mediated corrective feedback (IMCF) can be used as an efficient tool by language learners to become competent…
Analysis of active damping of LCL filter used in single-phase PV system in discrete domain
Zhang, Ningyun; Tang, Houjun; Yao, Chen
2015-06-01
Sampling and computational delay are necessary in digital control, though they may alter the characteristics of the actual controlled plant when considered in the discrete domain. Accordingly, this article establishes a mathematical model of a single-phase grid-connected inverter with an LCL filter in the discrete domain. Three active damping control delay times: 0, ?, ? are analysed, considering the influences introduced by digital control of the plant. Further, the range of the capacitor current feedback coefficient used in active damping control is derived to guarantee that the controlled plant does not have poles outside the unit circle. Using Nyquist diagrams, the proper proportional-resonant (PR) controller parameters can be intuitively determined. The theoretical analysis is verified using MATLAB and a 3 kW laboratory prototype based on a digital signal processor (TMS320F2808).
Reduced Order Models for Dynamic Behavior of Elastomer Damping Devices
Morin, B.; Legay, A.; Deü, J.-F.
2016-09-01
In the context of passive damping, various mechanical systems from the space industry use elastomer components (shock absorbers, silent blocks, flexible joints...). The material of these devices has frequency, temperature and amplitude dependent characteristics. The associated numerical models, using viscoelastic and hyperelastic constitutive behaviour, may become computationally too expensive during a design process. The aim of this work is to propose efficient reduced viscoelastic models of rubber devices. The first step is to choose an accurate material model that represent the viscoelasticity. The second step is to reduce the rubber device finite element model to a super-element that keeps the frequency dependence. This reduced model is first built by taking into account the fact that the device's interfaces are much more rigid than the rubber core. To make use of this difference, kinematical constraints enforce the rigid body motion of these interfaces reducing the rubber device model to twelve dofs only on the interfaces (three rotations and three translations per face). Then, the superelement is built by using a component mode synthesis method. As an application, the dynamic behavior of a structure supported by four hourglass shaped rubber devices under harmonic loads is analysed to show the efficiency of the proposed approach.
Farm Service Agency, Department of Agriculture — The NAIP 2015 Imagery Feedback web application allows users to make comments and observations about the quality of the 2015 National Agriculture Imagery Program...
Farm Service Agency, Department of Agriculture — The NAIP 2014 Imagery Feedback map allows users to make comments and observations about the quality of the 2014 National Agriculture Imagery Program (NAIP)...
Ochoa, Agustin
2016-01-01
This book describes a consistent and direct methodology to the analysis and design of analog circuits with particular application to circuits containing feedback. The analysis and design of circuits containing feedback is generally presented by either following a series of examples where each circuit is simplified through the use of insight or experience (someone else’s), or a complete nodal-matrix analysis generating lots of algebra. Neither of these approaches leads to gaining insight into the design process easily. The author develops a systematic approach to circuit analysis, the Driving Point Impedance and Signal Flow Graphs (DPI/SFG) method that does not require a-priori insight to the circuit being considered and results in factored analysis supporting the design function. This approach enables designers to account fully for loading and the bi-directional nature of elements both in the feedback path and in the amplifier itself, properties many times assumed negligible and ignored. Feedback circuits a...
Radiation feedback in dusty clouds
Ishiki, Shohei; Okamoto, Takashi
2017-03-01
We have investigated the impact of photoionization and radiation pressure on a dusty star-forming cloud using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. We find that, in a cloud of mass 105 M⊙ and radius 17 pc, the effect of radiation pressure is negligible when star formation efficiency is 2 per cent. The importance of radiation pressure increases with increasing star formation efficiency or an increasing dust-to-gas mass ratio. The net effect of radiation feedback, however, becomes smaller with the increasing dust-to-gas mass ratio, since the absorption of ultraviolet photons by dust grains suppresses photoionization and hence photoheating.
Transverse beam feedback system for PLS storage ring
Huang, J Y; Kim, D T; Kang, H S; Hwang, W H; Nam, S H
2001-01-01
As the stored beam current increases over 240 mA, transverse coupled-beam instability limits higher beam current in Pohang Light Source. A bunch by bunch transverse feedback system has been developed to cure these beam instabilities. It consists of beam oscillation detectors, betatron phase adjuster, power amplifiers and a stripline kicker. Design of each circuit and its functions are described with simple trigonometric equations. The result of the beam test has shown more than 30 dB damping of the beam oscillation in the full bandwidth of the system.
Radiation-damping effects in a birdcage resonator with hyperpolarised 3He gas NMR at 1.5 T.
Teh, Kevin; de Zanche, Nicola; Wild, Jim M
2007-03-01
The presence and diagnosis of radiation damping could have major implications in NMR experiments with hyperpolarised gases, where accurate knowledge of the flip angle is imperative. In this work radiation damping was observed and investigated in a low-pass birdcage resonator (Q=250) with samples of hyperpolarised 3He at 1.5 T. With an initially highly polarised (P=38%) sample of 3He in a spherical cell, the observed FID had a distorted line shape with a spectral line width that was three times that of the same sample in a virtually depolarised state (1 Hz line width for Pradiation damping. With highly polarised samples, significant radiation damping was observed and the effect was a lower than expected rate of depletion of M0 in RF flip angle calibration experiments, which led to significant underestimate of the RF flip angle. To our knowledge this is the first report of radiation damping in a birdcage resonator with samples hyperpolarised or otherwise. Experimental observation of radiation damping could be used as means of measuring coil efficiency as an alternative to the geometrical filling factor (eta) the definition of which is open to question for a birdcage resonator. Estimates of the birdcage filling factor from the measured damping time constants (eta(RD)=0.4%) are compared to those derived from electromagnetic energy ratios (eta(E)=1.6%) and metallic sphere frequency shift methods (eta(fs)=1.4%). These figures are much lower than the simple volume geometrical upper limit of eta(v)=3.7% derived from the ratio of cell volume to total coil volume (shield included). The physical explanation for this shortfall is that the bulk of the magnetic energy stored in the birdcage is spatially distributed predominantly between the rungs and the shield, and not in the coil centre where the sample is placed and where the B1+ field has its highest spatial homogeneity.
Random distributed feedback fibre lasers
Turitsyn, Sergei K.; Babin, Sergey A.; Churkin, Dmitry V.; Vatnik, Ilya D.; Nikulin, Maxim; Podivilov, Evgenii V.
2014-09-01
of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres). This review presents the current status of research in the field of random fibre lasers and shows their potential and perspectives. We start with an introductory overview of conventional distributed feedback lasers and traditional random lasers to set the stage for discussion of random fibre lasers. We then present a theoretical analysis and experimental studies of various random fibre laser configurations, including widely tunable, multi-wavelength, narrow-band generation, and random fibre lasers operating in different spectral bands in the 1-1.6 μm range. Then we discuss existing and future applications of random fibre lasers, including telecommunication and distributed long reach sensor systems. A theoretical description of random lasers is very challenging and is strongly linked with the theory of disordered systems and kinetic theory. We outline two key models governing the generation of random fibre lasers: the average power balance model and the nonlinear Schrödinger equation based model. Recently invented random distributed feedback fibre lasers represent a new and exciting field of research that brings together such diverse areas of science as laser physics, the theory of disordered systems, fibre optics and nonlinear science. Stable random generation in optical fibre opens up new possibilities for research on wave transport and localization in disordered media. We hope that this review will provide
Random distributed feedback fibre lasers
Energy Technology Data Exchange (ETDEWEB)
Turitsyn, Sergei K., E-mail: s.k.turitsyn@aston.ac.uk [Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET (United Kingdom); Novosibirsk State University, 2 Pirogova str., 630090, Novosibirsk (Russian Federation); Babin, Sergey A. [Novosibirsk State University, 2 Pirogova str., 630090, Novosibirsk (Russian Federation); Institute of Automation and Electrometry SB RAS, 1 Ac. Koptug. ave., 630090, Novosibirsk (Russian Federation); Churkin, Dmitry V. [Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET (United Kingdom); Novosibirsk State University, 2 Pirogova str., 630090, Novosibirsk (Russian Federation); Institute of Automation and Electrometry SB RAS, 1 Ac. Koptug. ave., 630090, Novosibirsk (Russian Federation); Vatnik, Ilya D.; Nikulin, Maxim [Institute of Automation and Electrometry SB RAS, 1 Ac. Koptug. ave., 630090, Novosibirsk (Russian Federation); Podivilov, Evgenii V. [Novosibirsk State University, 2 Pirogova str., 630090, Novosibirsk (Russian Federation); Institute of Automation and Electrometry SB RAS, 1 Ac. Koptug. ave., 630090, Novosibirsk (Russian Federation)
2014-09-10
generation of a stationary near-Gaussian beam with a narrow spectrum. A random distributed feedback fibre laser has efficiency and performance that are comparable to and even exceed those of similar conventional fibre lasers. The key features of the generated radiation of random distributed feedback fibre lasers include: a stationary narrow-band continuous modeless spectrum that is free of mode competition, nonlinear power broadening, and an output beam with a Gaussian profile in the fundamental transverse mode (generated both in single mode and multi-mode fibres). This review presents the current status of research in the field of random fibre lasers and shows their potential and perspectives. We start with an introductory overview of conventional distributed feedback lasers and traditional random lasers to set the stage for discussion of random fibre lasers. We then present a theoretical analysis and experimental studies of various random fibre laser configurations, including widely tunable, multi-wavelength, narrow-band generation, and random fibre lasers operating in different spectral bands in the 1–1.6 μm range. Then we discuss existing and future applications of random fibre lasers, including telecommunication and distributed long reach sensor systems. A theoretical description of random lasers is very challenging and is strongly linked with the theory of disordered systems and kinetic theory. We outline two key models governing the generation of random fibre lasers: the average power balance model and the nonlinear Schrödinger equation based model. Recently invented random distributed feedback fibre lasers represent a new and exciting field of research that brings together such diverse areas of science as laser physics, the theory of disordered systems, fibre optics and nonlinear science. Stable random generation in optical fibre opens up new possibilities for research on wave transport and localization in disordered media. We hope that this review will provide
Feedback and rewards, part II: formal and informal feedback reviews.
Harolds, Jay
2013-02-01
There are 2 major classes of feedback. One class of feedback consists of the informal, numerous conversations between various people in the organization regarding the performance, behavior, and goals of an individual. Another class of feedback consists of formal reviews held once or twice a year between a supervisor and an individual. This article discusses both types of feedback.
Asymptotic stability of solutions to elastic systems with structural damping
Directory of Open Access Journals (Sweden)
Hongxia Fan
2014-11-01
Full Text Available In this article, we study the asymptotic stability of solutions for the initial value problems of second order evolution equations in Banach spaces, which can model elastic systems with structural damping. The discussion is based on exponentially stable semigroups theory. Applications to the vibration equation of elastic beams with structural damping are also considered.
Global well-posedness of damped multidimensional generalized Boussinesq equations
Directory of Open Access Journals (Sweden)
Yi Niu
2015-04-01
Full Text Available We study the Cauchy problem for a sixth-order Boussinesq equations with the generalized source term and damping term. By using Galerkin approximations and potential well methods, we prove the existence of a global weak solution. Furthermore, we study the conditions for the damped coefficient to obtain the finite time blow up of the solution.
Nonlinear Landau damping in quark-gluon plasma
Xiaofei, Zhang; Jiarong, Li
1995-08-01
The semiclassical kinetic equations for the quark-gluon plasma (QGP) are discussed by the multiple time-scale method. The mechanism of nonlinear Landau damping owing to non-Abelian and nonlinear wave-particle interactions in QGP is investigated, and the nonlinear Landau damping rate for the longitudinal color eigenwaves in the long-wavelength limit is calculated.
Damping characteristics of a footbridge: Mysteries and truths
DEFF Research Database (Denmark)
Cantieni, Reto; Bajric, Anela; Brincker, Rune
2016-01-01
As a consequence of a paper presented by Michael Mistler at the VDI-Baudynamik-Tagung in Kassel, Germany, in April 2015, the authors checked the damping coefficients having been estimated for a footbridge in autumn 2014. Mistler stated that the critical damping ratio estimated from a halfpower ba...
Simple model with damping of the mode-coupling instability
Energy Technology Data Exchange (ETDEWEB)
Pestrikov, D.V. [AN SSSR, Novosibirsk (Russian Federation). Inst. Yadernoj Fiziki
1996-08-01
In this paper we use a simple model to study the suppression of the transverse mode-coupling instability. Two possibilities are considered. One is due to the damping of particular synchrobetatron modes, and another - due to Landau damping, caused by the nonlinearity of betatron oscillations. (author)