Level Of Vibration Reduction Research Articles

Field Testing on active isolation of vibrating foundations in Middle-frequency range

Open or in-filled trenches are usually used for suppressing disturbing ground vibrations induced by various man-made sources such as construction activities, transportation systems and power plants. However, using a trench to suppress low-frequency excitations, may be either impractical or inefficient. This study evaluates different mitigation strategies to suppress middle-frequency ground vibrations (i.e. between 25 and 40 Hz), generated by a rotating mass vibrator mounted on a shallow foundation in the field. The mitigation strategies encompassed placing isolating materials including sand-rubber mixture (SRM) in bags and block-type EPS geofoam, in sidewalls and bottom of a cubic pit excavated underneath the vibrating foundation and then backfilling the pit. Using EPS geofoam resulted in up to 30% and 20% reduction in ground vibration amplitudes of vertical and horizontal components, respectively. However, SRM-filled bags provided better efficiency which increased with rubber content. For instance, up to 40% and 50% reduction were observed, respectively in vertical and horizontal ground vibrations, when a SRM mixture with 25% rubber content was used. The excavation depth in current study was comparably lower than that of an open trench, for the same vibration reduction level, and thus considerably reduced the earthwork volume.

Novel adaptive tuned viscous inertance damper (ATVID) with adjustable inertance and damping for structural vibration control

In this study, we present an approach to alter the inertance of inerter-based devices, depending on the variation of the frequency of the external excitation. In this regard, we propose a newly developed variable inerter which is able to change the inertance using a versatile type of continuously variable transmission (CVT) mounted on a ball-screw inerter, it is called adaptive tuned viscous inertance damper (ATVID). The proposed device is capable of generating a variable inertance and viscous damping simultaneously contributed to provide seamless variability in its frequency. To evaluate the device performance, damping properties of the ATVID-controlled is compared with passive controlled and uncontrolled single-degree-of-freedom structures exposed to the harmonic ground excitation with variable frequency. Results show an excellent level of vibration reduction in structure using ATVID in a large width of the frequency band of the excitation.

Influence of handle shape and size to reduce the hand-arm vibration discomfort.

Non-automated tool handles transmit a large magnitude of vibration to operators' hands, causing discomfort and pain. Therefore, the need for a better handle design is a matter of prime concern to overcome musculoskeletal disorders such as hand-arm vibration syndrome. This study aimed to examine the influence of handle shapes in reducing the transmission of hand-arm vibration. Seven different handles were designed and fabricated using 3D printing technology at the SSN College of Engineering, with consideration for the anatomical shape of the hand. The frequency-weighted Root Mean Square (RMS) values of the vibration levels transmitted were recorded at the wrist of twelve subjects, unaffected by musculoskeletal disorders. Subjective ratings of vibration and comfort perception were measured using the Borg Scale of Perceived Exertion. The total vibration value (ahv) of each of the six novel prototype handles (B-G) was compared to that of the reference handle denoted handle-A. The vibration reductions for handles B to G respectively were 0.542 m/s2 (14.59%), 0.481 m/s2 (12.95%), 0.351 m/s2 (9.45%), 0.270 m/s2 (7.27%), 0.407 m/s2 (10.96%) and 0.192 m/s2 (5.17%). A significant level of vibration reduction was achieved by the prototype handles. Qualitative feedback from the study subjects suggests that they were not aware of the levels of vibration being transmitted to the hand with each handle.

An enhanced base isolation system equipped with optimal tuned mass damper inerter (TMDI)

SummaryIn seismic base isolation, most of the earthquake‐induced displacement demand is concentrated at the isolation level, thereby the base‐isolation system undergoes large displacements. In an attempt to reduce such displacement demand, this paper proposes an enhanced base‐isolation system incorporating the inerter, a 2‐terminal flywheel device whose generated force is proportional to the relative acceleration between its terminals. The inerter acts as an additional, apparent mass that can be even 200 times higher than its physical mass. When the inerter is installed in series with spring and damper elements, a lower‐mass and more effective alternative to the traditional tuned mass damper (TMD) is obtained, ie, the TMD inerter (TMDI), wherein the device inertance plays the role of the TMD mass. By attaching a TMDI to the isolation floor, it is demonstrated that the displacement demand of base‐isolated structures can be significantly reduced. Due to the stochastic nature of earthquake ground motions, optimal parameters of the TMDI are found based on a probabilistic framework. Different optimization procedures are scrutinized. The effectiveness of the optimal TMDI parameters is assessed via time history analyses of base‐isolated multistory buildings under several earthquake excitations; a sensitivity analysis is also performed. The enhanced base‐isolation system equipped with optimal TMDI attains an excellent level of vibration reduction as compared to the conventional base‐isolation scheme, in terms not only of displacement demand of the base‐isolation system but also of response of the isolated superstructure (eg, base shear and interstory drifts); moreover, the proposed vibration control strategy does not imply excessive stroke of the TMDI.

A numerical investigation of damping in fuzzy oscillators with poroelastic coating attached to a host structure

This paper analyzes efficacy of fuzzy oscillators combined with poroelastic coatings to reduce low frequency vibrations. The authors had previously shown that the poroelastic interactions across contact interfaces are tunable for broadband rate-independent damping. As a follow-up to that work, dynamic analyses are conducted on a host structure interacting with multiple fuzzy oscillators through contact interfaces across poro/viscoelastic coatings. Contact interactions are modeled by Fractional Zener Models. As viscoelastic coating material, hevea rubber is chosen because of its exceptionally high damping characteristics (i.e., highest loss tangent). For the poroelastic coating, relaxed and unrelaxed compliances as well as maximum damping capacity are assumed as identical to the viscoelastic rubber coating. In the first step, the dominant vibration mode of a host structure is modeled as a single degree-of-freedom system. The modal frequency of the host structure is first assumed to match peak relaxation frequency of the viscoelastic coating (220 kHz). Then, the modal frequency is reduced to lower frequencies (20,100 and 200 Hz). In the next step of the analysis, the investigation is extended to a host structure modeled as a two degree of freedom system. Results show that, if relaxation frequencies of the viscoelastic and poroelastic materials are close to the modal frequency of the host structure, the vibration suppression performances of both coatings are similar. However, poroelastic coating outperforms the viscoelastic coating at lower modal frequencies due to its tunable dynamic relaxation properties. Viscoelastic coating, in contrast, responds as a spring, and loses its damping capacity away from its peak relaxation frequency. To explore the best possible performance of the poroelastic coatings for low frequency damping, an optimization routine is adopted, and optimal number of fuzzy oscillators with optimally distributed mass and frequency properties is found. Results promise up to ∼35 dB vibration reduction around the structural modes for the single degree of freedom systems. For two degree of freedom system, vibration reduction level is predicted up to ∼27 dB reduction for the first mode and ∼15 dB for the second mode.

Novel type of tuned mass damper with inerter which enables changes of inertance

In this paper we propose the novel type of tuned mass damper and investigate its properties. Characteristic feature of the device is that it contains a special type of inerter equipped with a continuously variable transmission and gear-ratio control system which enables stepless and accurate changes of inertance. We examine the damping properties of the proposed tuned mass damper with respect to one-degree-of-freedom harmonically forced oscillator. To prove the potential of introduced device we test its four different embodiments characterized by four different sets of parameters. We generalize our investigation and show that proposed device has broad spectrum of applications, we consider three different stiffness characteristics of damped structure i.e. linear, softening and hardening. We use the frequency response curves to present how considered devices influence the dynamics of analyzed systems and demonstrate their capabilities. Moreover, we check how small perturbations introduced to the system by parametric and additive noise influence system׳s dynamics. Numerical results show excellent level of vibration reduction in an extremely wide range of forcing frequencies.

Evaluation of the Effect of a Step Change in Piezo Actuator Structure on Vibration Reduction Level in Plates

Abstract This paper presents numerical analyses and a physical experiment on efficiency of different shapes and material composition of piezo actuators on vibration reduction. For this purpose numerical models of a plate clamped on all sides with piezo actuators attached were developed. The elements used were either standard homogeneous elements or the proposed two-part elements with different material composition for inner and outer part of piezo ceramic. Numerical analyses were performed using ANSYS software

Proportional-Integral Sliding Mode Control for Trajectory Tracking and Vibration Control of a Flexible Single Link Manipulator

This paper presents investigations into the development of a Proportional-Integral Sliding Mode Control (PI-SMC) for trajectory tracking and vibration control of a flexible single link manipulator. The motor at the single rotating joint is the control actuator. Two SMC control laws are reviewed. The classical discontinuous control based on the signum function and a modified control law where the servomotor output voltage depends on the instantaneous values of the states. The selection of the discontinuity gain is reviewed for exact model (certain case) as well as when the parameter variations are present (uncertain case). To prove the reaching condition, we use the Lyapunov stability criteria. It is proven that this design is equivalent to a full state feedback with its steady state motion constrained to the sliding hyper-surfaces. Simulation results of the response of the flexible manipulator with both controllers are presented. The performances of the control schemes are examined for input tracking capability, level of vibration reduction and time response specifications. A comparative assessment of both control techniques shows the effectiveness of the second control law and its invariance to so-called matched uncertainty.

Using an inerter‐based device for structural vibration suppression

SUMMARYThis paper proposes the use of a novel type of passive vibration control system to reduce vibrations in civil engineering structures subject to base excitation. The new system is based on the inerter, a device that was initially developed for high‐performance suspensions in Formula 1 racing cars. The principal advantage of the inerter is that a high level of vibration isolation can be achieved with low amounts of added mass. This feature makes it an attractive potential alternative to traditional tuned mass dampers (TMDs). In this paper, the inerter system is modelled inside a multi‐storey building and is located on braces between adjacent storeys. Numerical results show that an excellent level of vibration reduction is achieved, potentially offering improvement over TMDs. The inerter‐based system is compared to a TMD system by using a range of base excitation inputs, including an earthquake signal, to demonstrate how the performance could potentially be improved by using an inerter instead of a TMD. Copyright © 2013 John Wiley & Sons, Ltd.

Composite Fuzzy Logic Control Approach to a Flexible Joint Manipulator

The raised complicatedness of the dynamics of a robot manipulator considering joint elasticity makes conventional model-based control strategies complex and hard to synthesize. This paper presents investigations into the development of hybrid intelligent control schemes for the trajectory tracking and vibration control of a flexible joint manipulator. To study the effectiveness of the controllers, a collocated proportional-derivative (PD)-type Fuzzy Logic Controller (FLC) is first developed for the tip angular position control of a flexible joint manipulator. This is then extended to incorporate a non-collocated Fuzzy Logic Controller, a non-collocated proportional-integral-derivative (PID) and an input-shaping scheme for the vibration reduction of the flexible joint system. The positive zero-vibration-derivative-derivative (ZVDD) shaper is designed based on the properties of the system. The implementation results of the response of the flexible joint manipulator with the controllers are presented in time and frequency domains. The performances of the hybrid control schemes are examined in terms of input tracking capability, level of vibration reduction and time response specifications. Finally, a comparative assessment of the control techniques is presented and discussed.

Optimum geometrical properties of active isolation

Vibratory waves generated by dynamic loads exerted on a foundation can be propagated to a noticeable distance through the soil, having detrimental effects on sensitive structures in the path of the wave train. The present work examines, for different cases, the efficiency of annular open trenches in screening vibration energy induced by a shallow foundation. The results obtained are verified by reference to published field test data and numerical research, and suggest that the depth of the trench is the most crucial factor in its effectiveness. The trench performance improves as its depth increases, but this effect is coupled in a complex manner with the effects of other parameters, such as trench width and location. A trench excavated in loose materials is observed to have more efficiency, and as the soil density decreases, an increase in trench efficiency is apparent. Placing a trench adjacent to the source causes larger displacement; at greater distances from the source, the vibration reduction level (trench efficiency) increases. To provide a quantitative evaluation of active isolation performance in two zones concurrently, in front of and behind the trench, a new criterion, the trench efficiency index, is introduced, and the optimum geometric trench parameters are discussed in the paper.

Design and Evaluation of Hydro-Pneumatic Friction Damper Suspension System

Perceived comfort level and ride stability are the two most important factors in the evaluation of suspension system in a mobile vehicle. It is extremely difficult to simultaneously maintain a high standard of vehicle ride, handling and body control in the vehicle by using conventional passive suspension system. However, the use of active suspensions would result in better comforts than the passive ones. This paper presents the design and analysis of a pneumatic friction damper and hydro-pneumatic friction damper. A non-linear quarter car model is developed, which includes pneumatic actuation by pressure regulation. The performance of the proposed model was assessed in terms of level of vibration reduction. Simulations on a prototype model show that the proposed system has good performance and robustness.

A model to study the reduction of turbine blade vibration using the snubbing mechanism

Blade vibration reduction is an important task in high performance turbo machinery for power generation, in order to avoid the risk of blade failure due to the overcoming of fatigue limit. A possible way to obtain this result is a contact related phenomenon, i.e. by physically limiting the vibration amplitude on the blade tip leaving a small gap between the shrouds of adjacent blades. When the relative displacement between adjacent blades exceeds the gap, in a certain vibration mode of the blade row, a contact occurs between the shrouds, the relative motion is restricted and energy is dissipated by friction and impact during the contact. This is called the snubbing mechanism.In this paper, an original simplified model of bladed disks, in which the snubbing mechanism can occur, is presented and numerical integration in time domain furnishes the time histories of the vibrations of the blades. The level of vibration reduction is then evaluated in some different modes that could be excited for instance by the fluid flow. It is also shown that unlucky combinations of system and excitation parameters can effect also a certain magnification instead of a reduction of the vibration amplitudes.Experimental results on single blade and blade groups of a steam turbine are used to tune the parameters of the system.

Analysis of vibration reduction level in an 8/6 switched reluctance machine by active vibration cancellation

This paper proposes an analytical model for predicting the maximum vibration reduction level in a four-phase 8/6 switched reluctance machine (SRM) by employing active vibration cancellation (AVC), one of the most effective and convenient methods for reducing the vibration and acoustic noise produced by SRMs. Based on the proposed method, the factors that influence the vibration reduction level are analyzed in detail. The relationships between vibration and noise reduction levels at resonance frequency and rotor speed are presented. Moreover, it is shown that a large damping factor will lead to smaller vibration reduction level with AVC while, in contrast, a large resonance frequency will increase the vibration reduction level. Both finite element analyses and experiments were carried out on a prototype 8/6 SRM to validate the proposed method.

Robust Backstepping Sliding Mode Attitude Tracking and Vibration Damping of Flexible Spacecraft with Actuator Dynamics

This paper presents a dual-stage control system design method for the attitude tracking control and vibration stabilization of a spacecraft with flexible appendages embedded with piezoceramics as sensor and actuator. In this design approach, attitude control system and vibration suppression were designed separately using a lower order model. Based on the sliding mode control (SMC) and backstepping technique, a new attitude controller in the form of the input voltage of the reaction wheel is derived to control the attitude motion of a spacecraft, in which the reaction wheel dynamics is also considered from the real applications point of view. Here the sliding mode technique is used to achieve an asymptotic convergence of the attitude and angular velocity tracking errors in the presence of parameter variation and disturbance by providing a virtual torque input at the rigid body while the backstepping technique is used to regulate the input voltage of the actuator to provide the required torque. The asymptotic stability is shown using a Lyapunov analysis. Furthermore, an adaptive version of the proposed attitude control law is also designed for adapting the unknown upper bounds of the lumped disturbance so that the limitation of knowing the bound of the disturbance in advance is released. For actively suppressing the induced vibration, strain rate feedback control methods are presented by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. The performances of the hybrid control schemes are assessed in terms of attitude tracking and level of vibration reduction in comparison to the proportional-derivative and conventional SMC. Both analytical and numerical results are presented to show the theoretical and practical merit of this hybrid approach.

Attitude manoeuvring and vibration reducing control of flexible spacecraft using smart materials

The question of robust attitude control and vibration reduction of flexible spacecraft during manoeuvre is considered. The design approach presented here treats the problem of spacecraft attitude control separately from the elastic vibration suppression, by designing a dynamic controller, using attitude measures alone for desired attitude rotation and smart materials for active vibration suppression. The proposed attitude controller does not need the knowledge of modal variables and spacecraft angular velocity, which is compensated by appropriate dynamics of the controller. For actively suppressing the vibrations introduced to the flexible appendages, embedded piezoelectric ceramic patches are used as both sensors and actuators, to detect and counter-react the induced vibration during and after the manoeuvre. Here, a modified positive position feedback (PPF) control strategy, targeting at the first three flexible modes of the flexible spacecraft is taken into account. The performances of this approach are assessed in terms of the level of vibration reduction at resonance modes and the speed of response. For comparison, the proportional plus derivative control strategy is adopted and compared with proposed control approach. Simulation results demonstrate the effectiveness of the controller design strategy for attitude control and the modified PPF compensators for active vibration suppression.

Active vibration control of a flexible one-link manipulator using a multivariable predictive controller

This article presents a new application of model-based predictive controller (MPC) for vibration suppression of a flexible one-link manipulator using piezoceramic actuators. Simulation and experimental studies were conducted to investigate the applicability of the MPC strategy to control vibration of the flexible structure having multiple inputs and multiple outputs (MIMO). The performance of the proposed technique was assessed in terms of level of vibration reduction. The results demonstrated that the proposed predictive control strategy is well suited for multivariable control of vibration suppression on flexible structures.

Hybrid Learning Control Schemes with Acceleration Feedback of a Flexible Manipulator System

This paper presents investigations into developing a hybrid iterative learning control scheme with acceleration feedback. An experimental flexible manipulator rig and corresponding simulation environment are used to demonstrate the effectiveness of the proposed control strategy. A collocated proportional-derivative controller utilizing hub-angle and hub-velocity feedback is developed for control of rigid-body motion of the system. This is then extended to incorporate iterative learning control with acceleration feedback and genetic algorithms for optimization of the learning parameters for control of vibration (flexible motion) of the system. The system performance with the controllers is presented and analysed in the time and frequency domains. The performance of the hybrid learning control scheme without and with acceleration feedback is assessed in terms of input tracking and level of vibration reduction at resonance modes and robustness to variation in payload.

Hybrid learning control schemes with input shaping of a flexible manipulator system

The paper describes a practical approach to investigate and develop a hybrid iterative learning control scheme with input shaping. An experimental flexible manipulator rig and corresponding simulation environment are used to demonstrate the effectiveness of the proposed control strategy. A collocated proportional-derivative (PD) controller utilizing hub-angle and hub-velocity feedback is developed for control of rigid-body motion of the system. This is then extended to incorporate iterative learning control with acceleration feedback and genetic algorithms (GAs) for optimization of the learning parameters and a feedforward controller based on input shaping techniques for control of vibration (flexible motion) of the system. The system performance with the controllers is presented and analysed in the time and frequency domains. The performance of the hybrid learning control scheme with input shaping is assessed in terms of input tracking and level of vibration reduction. The effectiveness of the control schemes in handling various payloads is also studied.

Techniques for vibration control of a flexible robot manipulator

This paper presents investigations into the applications and performance of positive and negative input shapers in command shaping techniques for the vibration control of a flexible robot manipulator. A constrained planar single-link flexible manipulator is considered and the dynamic model of the system is derived using the finite element method. An unshaped bang-bang torque input is used to determine the characteristic parameters of the system for design and evaluation of the input shaping control techniques. The positive and specified amplitude negative input shapers are designed based on the properties of the system. Simulation results of the response of the manipulator to the shaped inputs are presented in the time and frequency domains. Performances of the shapers are examined in terms of level of vibration reduction, time response specifications and robustness to parameters uncertainty. The effects of derivative order of the input shaper on the performance of the system are investigated. Finally, a comparative assessment of the impact amplitude polarities of the input shapers on the system performance is presented and discussed.