Concept Of Damping Research Articles

Design of semi-active steering damper control strategies for sport motorcycles

This work presents the design of a novel control approach for a semi-active steering damper of motorcycles. The goal is to improve two-wheeled vehicles steering stability by damping the weave and wobble modes. The proposed control strategies stem from a parallelism between steering and vertical dynamics of a motorcycle. According to this parallelism, the Sky-Hook and Ground-Hook damping concepts are adapted to the control of steering dynamics. A detailed analysis of the two approaches is presented and the semi-active control strategies are shown to yield better attenuation of both modes than a passive steering damper. Further, both a multi-body simulator and experimental data are employed to validate the proposed control approach.

Rapid step response with limited ringing and light damping.

The time domain step response of an underdamped simple harmonic oscillator can be characterized as having two parts. The first is a transition from the initial position where the structure is accelerated toward a target position by a step force that introduces energy to the system. The second is a ringdown process, involving decaying oscillations about the target position as energy is removed from the structure. This study reports how an array of substantially smaller subordinate oscillators attached to the primary structure can dramatically reduce the time constant of the ringdown (the settling time) without slowing the first phase (rise time) in the way added classical damping does. In addition to having a more rapid initial response, a lightly damped oscillator with such an array of attachments requires less energy to change states than a more heavily damped structure. The approach is based on the concept of apparent damping, where vibration energy is transferred into and trapped by the set of attachments. Numerical results show that the distribution of the individual masses, isolated natural frequencies, and quality factors Q of the attachments, referred to as a subordinate oscillator array, can be tailored to achieve the rapid step response.

Semiactive Coulomb Friction Lead-Lag Dampers

Lead–lag dampers are present in most rotor systems to provide the desired level of damping for all flight conditions. These dampers are critical components of the rotor system and also represent a weight and drag penalty together with a major source of maintenance costs. The performance of semiactive Coulomb friction based lead–lag dampers is examined in this study. First, conceptual designs of semiactive friction dampers for rotorcraft applications are briefly presented. Next, the concept of adaptive damping is discussed: by adjusting the normal contact force at the frictional interface, the energy dissipation characteristics of the device can be tailored, providing “damping on demand.” The behavior of friction dampers in both ground resonance and forward flight is simulated for the UH-60 aircraft and compared with that of present hydraulic dampers. The approach used for modeling the frictional process is presented in detail. The final part of this paper explores the concept of selective damping, in which the energy dissipation capacity of semiactive devices is targeted to a specific mode. Practical implementation of this concept is shown to face many challenges.

Piezoceramic shunted damping concept: testing, modelling and correlation

New laboratory tests are presented for the experimental evaluation and assessment of the piezoceramic shunted damping (PSD) concept for cantilever Aluminium thin (long) beams bonded symmetrically on their upper/lower surfaces with single pairs of small piezoceramic patches. Following these tests outcome, the PSD efficiency measure is proposed to be the so-called modal effective electromechanical coupling coefficient, which is post-processed from free-vibrations analyses under short-circuit and open-circuit electrodes of the patches. For this purpose, the tests are numerically modelled, analysed, and correlated using ABAQUS® commercial finite element (FE) code. Good tests/models correlations were reached after FE models electromechanical updating. This is attributed to the refined FE models in the sense that they have considered realistic and desirable features such as, electrodes equipotentiality, piezoceramic patches poling orientations (same/opposite), and the corresponding (parallel/series) electric wiring (connections).

An adaptronic approach to active vibration control of machine tools with parallel kinematics

In recent years, more and more lightweight components are used in machine tools in order to provide advantages in highly dynamic applications because of their reduced mass. One major drawback of these lightweight systems is their sensitivity to structural vibrations which are induced by high jerks during fast positioning and the machining process itself. Moreover, in case of parallel kinematic structures, the dynamic response depends nonlinearly on the actual pose of the mechanism in the workspace. In this paper, a concept for active vibration control for a machine tool with planar parallel kinematics is presented. For this purpose, an adaptronic rod has been developed and integrated into the existing machine tool. The unit consists of a high-power lead–zirconate–titanate piezo stack actuator, which is able to induce forces in longitudinal direction of the rod, and various sensors so that different control concepts from the field of active vibration control can be implemented and tested. Based on a flexible multibody system model of the machine tool, a hierarchical controller consisting of an integrated force feedback as low authority Control combined with a frequency-shaped linear quadratic regulator has been designed. The experimental results presented here demonstrate the ability of the chosen approach to clearly suppress the first dominating resonance without loss of performance in the low frequency range, which is often a serious problem of active damping concepts.

Active Vibration Damping and Model‐Based Control for an Adaptronic Actuator

AbstractThe static and dynamic flexibility of a machine tool is often the major limiting factor for the machining quality, especially if high processing speeds as well as high accuracies are desired. Particularly parallel kinematic machines, which have been developed for high processing speeds and accuracy and which often use lightweight structures, can suffer from severe problems with vibrations of system components and the loss of accuracy due to deformations of machine parts. Introducing so–called adaptronic or smart components into the machine tool structure opens up new and interesting possibilities to actively control the deformations and vibrations of flexible machine parts. They allow to specifically target such undesired properties and to significantly reduce or even eliminate their influence on the system performance. Concepts of active vibration damping and model–based control are presented here for such an adaptronic actuator implemented in a machine tool with parallel kinematics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vibration control by recursive time-delayed acceleration feedback

This paper presents a theoretical basis of time-delayed acceleration feedback control of linear and nonlinear vibrations of mechanical oscillators. The control signal is synthesized by an infinite, weighted sum of the acceleration of the vibrating system measured at equal time intervals in the past. The proposed method is shown to have controlled linear resonant vibrations, low-frequency non-resonant vibrations, primary and 1/3 subharmonic resonances of a forced Duffing oscillator. The concept of an equivalent damping and natural frequency of the system is also introduced. It is shown that a large amount of damping can be produced by appropriately selecting the control parameters. For some combinations of the control parameters, the effective damping factor of the system is shown to be inversely related to the time-delay in the small delay limit. Selection of the optimum control parameters for controlling the forced and free vibrations is discussed. It is shown that forced vibration is best controlled by unity recursive gain and smaller values of the time-delay parameter. However, the transient response can be optimally controlled by suitably selecting the time delay depending upon the gain. The delay values for the optimal forced response may be different from that required for the optimum transient response. When both are important, a suboptimal choice of the delay parameters with unity recursive gain is recommended.

와전류 충격완충장치의 실험적 동특성 연구

연구에서는 코일 스프링 및 작동유체가 없는 새로운 감쇠기의 개념을 소개한다. 이 감쇠기는 영구자석과 전도체 실린더로 구성된다. 극성이 반대인 자석은 반발력을 발생시키고, 이는 코일 스프링과 같은 역할을 한다. 영구자석과 전도체 실린더 사이의 상대운동은 기전력을 발생시키는 와전류를 생성하고, 이로 인해 감쇠 유체를 대신할 수 있는 감쇠력을 만든다. 이러한 감쇠를 와전류 감쇠기라고 한다. 본 연구에서 제안된 와전류 감쇠기의 중요한 장점은 감쇠 유체 및 어떠한 외부의 전력도 필요로 하지 않고, 비접촉식이며, 온도에도 민감하지 않다. 본 연구에서는 제안된 와전류 감쇠기를 제작하고 실험을 통하여 감쇠기의 동적 특성을 조사하였다. 본 연구의 결과는 제안된 와전류 감쇠기가 우수한 감쇠 성능을 가짐을 보였다. This paper is concerned with a new concept for the damper without neither a coil spring nor fluid. The new damper concept consists of the permanent magnets and the cylinder of the conducting material. The opposite pole magnets produces the repulsive forces and this is substituted for the coil spring. The relative motion between the magnets and conducting cylinder produces eddy currents thus resulting in the electromagnetic force, which turns out to be the damping force and is substituted for a damping fluid. This damper is called the eddy current damper(ECD). The important advantage of the proposed ECD is that it does not require any damping fluid and any external power and is non-contacting and relatively insensitive to temperature. In the present study, the proposed ECD was constructed and the experiments were performed to investigate its dynamic characteristics. The experiments shows that the proposed ECD has the excellent damping ability.

English

A novel control scheme for the active suspension in a 4-DOFs half-car model is presented.A force cancellation control scheme is used to isolate the sprung and the unsprung masses.Skyhook damper and virtual damper concepts are employed to stabilise the sprung and unsprungmasses respectively. Road-following springs are applied for the sprung mass to follow the trendof the road surface condition and to maintain the suspension stroke within a reasonable range.For efficiency, genetic algorithm is employed to search for the parameters like damping ratio andspring constant to achieve an optimum trade off among ride comfort, handling quality, andsuspension stroke simultaneously for random input. Computer simulations are performed usingMATLAB software to verify the proposed control scheme and effectiveness of the appliedgenetic algorithm.

On the numerical damping of time integrators for coupled mechatronic systems

The generalized-α time integrator is considered for the simulation of mechatronic systems. In this context, the fundamental concept of numerical damping is analysed for coupled sets of first and second-order differential–algebraic equations. First, it appears that the algebraic variables do not influence the spectral properties of the dynamic variables. Second, we demonstrate that the coupling between the dynamic variables does not influence the high-frequency spectral response, so that the numerical damping can be determined as usual from elementary characteristic polynomials. Those results are exploited to assess the stability properties of the scheme and to select an algorithm with optimal damping properties.

Finite element prediction of damping of composite GFRP and CFRP laminates – a hybrid formulation – vibration damping experiments and Rayleigh damping

The work reported in this paper describes the development of a hybrid methodology for the prediction of damping properties of vibrating composite laminates; this method could also be applied to homogeneous materials. This hybrid methodology consists of experimental identification of damping, using vibration damping testing methods, and utilization of FEA. The experimentally identified damping property is that of specific damping capacity (SDC), a measure of damping during the first mode of resonant vibration of beams. The finite element (FE) approach utilizes the concept of Rayleigh damping, and in particular mass proportional damping for the modeling of the damped response of vibrating systems. It is shown that by using such a methodology, damping data can be extracted for cases, where application of continuum mechanics analytical solutions cannot provide reliable information. Furthermore, the development of the finite element models is described. The association of damping properties with material reinforcement is highlighted. A series of continuous and woven, cross ply and quasi isotropic GFRP and CFRP coupons were vibrated. The FE damped response prediction was in very good agreement with laboratory observations.

Vibration Control of a Cantilever Beam with Time Delay State Feedback

The primary and subharmonic resonance of order one-third of a cantilever beam under state feedback control with a time delay are investigated. Using the method of multiple scales, we obtain two slow flow equations for the amplitude and phase. The first-order approximate solution is derived and the effect of time delay on the resonance is investigated. The concept of an equivalent damping, related to the delay feedback, is proposed and an appropriate choice of the feedback gains and the time delay is discussed from the viewpoint of vibration control. The fixed points corresponding to the periodic motion of the starting system are determined, and the frequency-response and external excitation-response curves are shown. Bifurcation analysis is conducted in order to examine the stability of the system.

Near-irreversibility in a conservative linear structure with singularity points in its modal density

Through two complementary approaches, using modal response and wave propagation, the analyses presented here show the conditions under which a decaying impulse response, or a nearly irreversible energy trapping, takes place in a linear conservative continuous system. The results show that the basic foundation of near-irreversibility or apparent damping rests upon the presence of singularity points in the modal density of dynamic systems or, analogously, in the wave-stopping properties associated with these singularities. To illustrate the concept of apparent damping in detail, a simple undamped beam is modified to introduce a singularity point in its modal density distribution. Simulations show that a suitable application of a compressive axial force to an undamped beam placed on an elastic foundation attenuates its impulse response with time and develops the characteristics of a nearly irreversible energy trap.

Finite element prediction of damping of composite GFRP and CFRP laminates – a hybrid formulation – vibration damping experiments and Rayleigh damping

The work reported in this paper describes the development of a hybrid methodology for the prediction of damping properties of vibrating composite laminates; this method could also be applied to homogeneous materials. This hybrid methodology consists of experimental identification of damping, using vibration damping testing methods, and utilization of FEA. The experimentally identified damping property is that of specific damping capacity (SDC), a measure of damping during the 1st mode of resonant vibration of beams. The finite element approach utilizes the concept of Rayleigh damping, and in particular mass proportional damping for the modeling of the damped response of vibrating systems. It is shown that by using such a methodology, damping data can be extracted for cases where application of continuum mechanics analytical solutions cannot provide reliable information. Furthermore, the development of the finite element models is described. The association of damping properties with material reinforcement is highlighted. A series of continuous and woven, cross ply and quasi isotropic GFRP and CFRP coupons were vibrated. The FE damped response prediction was in very good agreement with laboratory observations.

Passive Vibration Control via Electromagnetic Shunt Damping

This work will present a new type of passive vibration control technique based on the concept of electromagnetic shunt damping. The proposed technique is similar to piezoelectric shunt damping, as an appropriately designed impedance is shunted across the terminals of the transducer. Theoretical and experimental results are presented for a simple electromagnetic mass spring damper system.

A wave model for rigid-frame porous materials using lumped parameter concepts

The work presented in this paper concerns the behaviour of porous media when exposed to a normal incidence sound field. A propagating wave model based on lumped parameter concepts of acoustic mass, stiffness and damping is used to investigate the absorption phenomena due to the wave propagation in the layer(s) and interference effects due to the wave reflection–transmission at the interfaces of the layer(s). Results from the theoretical model have been validated by measurements on samples of consolidated rubber granulate material. Two typical installations where a layer of porous material is placed next to a rigid wall, and where it is placed at a distance from a rigid wall are used as reference cases. The geometrical and physical properties of porous materials can be described by such parameters as the non-dimensional shape factor and the porosity. The propagating model introduced is used to investigate the effect of these two parameters on acoustic absorption and thus relate the physical properties to the acoustic behaviour.

Capacity evaluation of statnamic tested long piles

A procedure that uses the structural damping (SD) concept for estimating the capacity of a pile based on the Statnamic (STN) pile load test results, formerly used by the authors for short piles, is extended in this paper for the STN tested long piles. Similar to segmental unloading point method procedures for long piles, the shaft length is divided into several segments and each segment is assumed to behave as a mass of a single degree of freedom. The SD concept is then applied to each segment to consider the displacement related soil damping instead of the velocity dependent damping. Instrumented strain gauge data at different levels of the shaft are required for the interpretation method. Three case studies are presented in this paper to study the validity and applicability of the present method. The predicted results are also compared to the available test or analytical data.

Simulation and Characterization of Particle Damping in Transient Vibrations

Particle damping is a technique of providing damping with granular particles embedded within small holes in a vibrating structure. The particles absorb kinetic energy through particle-to-wall and particle-to-particle frictional collisions. While the concept of particle damping seems to be simple and it has been used successfully in many fields for vibration reduction, it is difficult to predict the damping characteristics due to complex collisions in the dense particle flow. In this paper, we utilize the 3D discrete element method (DEM) for computer simulation and characterization of particle damping. With the DEM modeling tool validated with experimental results, it is shown that the particle damping can achieve a very high value of specific damping capacity. Furthermore, simulations provide information of particle motions within the container hole during three different regions and help explain their associated damping characteristics. The particle damping is a combination of the impact and the friction damping. The damping is found to be highly nonlinear as the rate of energy dissipation depends on amplitude. Particularly, the damping effect results in a linear decay in amplitude over a finite period of time. These characteristics are examined with respect to a simple single-mass impact damper and a dry-friction damper. It is concluded that the particle damping is a mix of these two damping mechanisms. It is further shown that the relative significance of these damping mechanisms depends on a particular arrangement of the damper. This study represents an effort towards a deeper understanding of particle damping to provide a comprehensive methodology for its analysis and design.

Modelling and experiment of railway ballast vibrations

The vibration of railway ballast is a key factor to cause track geometry change and increase of track maintenance costs. So far the methods for analyzing and testing the vibration of the granular ballast have not been well formed. In this paper, a five-parameter model for analysis of the ballast vibration is established based upon the hypothesis that the load-transmission from a sleeper to the ballast approximately coincides with the cone distribution. The concepts of shear stiffness and shear damping of the ballast are introduced in the model in order to consider the continuity of the interlocking ballast granules. A full-scale field experiment is carried out to measure the ballast acceleration excited by moving trains. Theoretical simulation results agree well with the measured results. Hence the proposed ballast vibration model has been validated.

Proof of the equivalence of residues and induced torque coefficients for use in the calculation of eigenvalue shifts

Several recent papers have introduced the concept of induced torque coefficients (ITCs). The concept of induced torque coefficients is essentially a generalization of the concept of damping and synchronizing torques to a multimachine, multimodal power system. This generalization allows the interactions between each stabilizing device and each machine in the system to be quantified for the purposes of a more systematic coordination of stabilizers (both PSSs and FACTS damping controllers) on a system-wide basis. In this process, a key feature is the ability to estimate, from the ITCs, the shift in system eigenvalues due to a perturbation in the gain of a stabilizer. Independently, others have developed techniques for the coordination of stabilizers based on the calculation of eigenvalue shifts from the residues. In this paper, it is shown that the eigenvalue shifts estimated by both these techniques are mathematically equivalent; the ITC approach, however, provides additional information.