Shock Isolation Research Articles

Shock Isolation Systems Using Magnetorheological Dampers

This study addresses the feasibility and applicability of a semiactive magnetorheological (MR) shock isolation system to replace a conventional passive shock isolation system for commercial-off-the-shelf (COTS) equipment. To this end, an analysis of a shock isolation system with an MR damper was theoretically developed. To improve shock mitigation performance, semiactive control strategies such as skyhook and sliding mode control were incorporated into our analysis. Controlled responses of the semiactive MR shock isolation system were simulated and compared with those of a conventional passive shock isolation system for two different representative shock loads for COTS equipment.

Damping requirement of a suspension seat subject to low frequency vehicle vibration and shock

Vibration attenuation performance characteristics of a suspension seat are investigated under excitations arising from different road and off-road vehicles. A Two-Degrees-of-Freedom (2-DOF) model of the suspension seat is formulated upon integration of component models, and consideration of the end-stop impacts and potential body-hop motions. Validated analytical model is applied to identify the desirable damping parameters, to achieve improved attenuation of continuous and transient vibration of varying intensities. The results, suggest that a suspension design with relatively higher compression and rebound mode damping would be desirable for realising improved shock and vibration isolation performance for vehicles with predominantly low frequency ride vibration.

Synthesis of a semi-active suspension seat for attenuation of Whole-Body Vibration and shock

In this study, two semi-active control algorithms are synthesised on the basis of the measured nonlinear force-velocity properties of a Magneto-Rheological (MR) damper, including the current-dependent hysteresis and post yield saturation. The control algorithms employ the well-known sky-hook control condition function, suspension travel limits and a modulation function to compensate for the switching discontinuities. The results show that the proposed semi-active control synthesis could help achieve improved shock isolation while retaining adequate control of continuous WBV. A Hardware-In-the-Loop (HIL) test and simulation platform are developed for tuning of the proposed semi-active controllers and validation of the analytical formulations.

Dispersive elastodynamics of 1D banded materials and structures: Design

Within periodic materials and structures, wave scattering and dispersion occur across constituent material interfaces leading to a banded frequency response. In an earlier paper, the elastodynamics of one-dimensional periodic materials and finite structures comprising these materials were examined with an emphasis on their frequency-dependent characteristics. In this work, a novel design paradigm is presented whereby periodic unit cells are designed for desired frequency band properties, and with appropriate scaling, these cells are used as building blocks for forming fully periodic or partially periodic structures with related dynamical characteristics. Through this multiscale dispersive design methodology, which is hierarchical and integrated, structures can be devised for effective vibration or shock isolation without needing to employ dissipative damping mechanisms. The speed of energy propagation in a designed structure can also be dictated through synthesis of the unit cells. Case studies are presented to demonstrate the effectiveness of the methodology for several applications. Results are given from sensitivity analyses that indicate a high level of robustness to geometric variation.

Modeling and analysis of preloaded liquid spring/damper shock absorbers

Preloaded liquid spring/damper based shock isolation systems are suitable for heavy load military applications. In this paper, mathematical models are developed for passive liquid spring shock absorbers. The preloading is achieved by mounting the load between two liquid spring/dampers. Dynamics of such shock absorbers involve coupled hydrodynamic and thermodynamic phenomena. The energy dissipated through orifice due to hydrodynamic losses heats up the working fluid and consequently the heat is dissipated to environment. Such multi-energy domain interaction is well represented in this paper by using bond graph models. Moreover, the developed model accounts for the strain-rate dependent damping offered by the compressible working fluid in the liquid spring. The results show that proper choice of preloading and geometric parameters (spring dimensions and orifice sizes) can, respectively, reduce the thermodynamic and strain-rate dependent damping phenomena.

Concept of a platform-based impact isolation system for protection of wheelchair occupants from injuries in vehicle crashes

To improve the protection of a wheelchair-seated person with disabilities traveling in a vehicle from injuries in a crash, it is proposed to attach the wheelchair to a movable platform separated from the vehicle body by means of a shock isolator. The control of the platform is designed to reduce the occupant's injury risk, as compared with the case of the attachment of the wheelchair directly to the vehicle. The isolator design is based on the minimization of the force transmitted to the wheelchair occupant, provided that the space allowed for the platform to move relative to the vehicle is constrained. The possibility of pre-acting control, when the isolator is engaged for a time prior to the crash, is discussed. Passive tiedown and restraint systems are studied, although it is recognized that active systems could provide even lower injury risks. A multibody model of the platform-based occupied wheelchair is utilized for full-scale simulation of the response of the system to a crash pulse. The simulation shows a noticeable reduction in the injury risk due to the platform and an even greater reduction of injury with pre-acting control.

“Your Job No Longer Exists!”: From Experiences of Alienation to Expectations of Resilience—A Phenomenological Study

We have entered the age of the contingent or temporary worker, the consultant and the subcontractor. Workers are expected to be pliable and tractable; to “fit in.” Being made redundant is also an area where modern workers are expected to be flexible and resilient. However, when these so-called “flexible” workers are told their job no longer exists, the accompanying sense of rejection and alienation can be excruciating. Stories of being made redundant were collected during an exploratory, qualitative study, using Heideggerian phenomenology as the methodological vehicle to capture the lived experiences of those affected. Focused, in-depth interviews were conducted with the ten respondents; nine men and one woman. The stories shared suggest that being made redundant is an alienating experience with respondents sharing feelings of powerlessness, shock, betrayal, shame and social isolation. Unfortunately, those having experienced redundancy were also not as resilient as is routinely assumed. They did not “bounce back” unchanged, but reported significant negative outcomes including fear for the future, underemployment, family disruptions and an erosion of trust. Recommendations are made orienting organisations towards a more human process of redundancy.

Self-powering shock, vibration and acoustic isolation system

A shock and vibration isolation system for mounting equipment to a base wall uses a semi-active damper in parallel with a spring arrangement to provide optimum isolation with respect to both shock and vibration. The system comprises a load plate configured for attachment of the equipment thereto and a base plate configured for attachment to the base wall. The base plate is substantially parallel to the load plate. The system further comprises a spring arrangement disposed intermediate the load plate and the base plate. The spring arrangement engages the load plate and the base plate to bias the load plate and the base plate in a separated relationship. A semi-active damper is also disposed intermediate the load plate and the base plate. The a semi-active damper is adapted for providing a selectively variable reaction force to the load plate and the base plate responsive to a relative displacement of the load plate with respect to the base plate. A damper controller is operatively connected to the semi-active damper for controlling the reaction force applied to the load plate and the base plate. The damper controller includes a rechargeable power supply. The isolation system also comprises a recharging arrangement in electrical communication with the rechargeable power supply. The recharging arrangement is mounted to one of the base plate and the load plate and is adapted for converting vibratory motion to electrical energy for storage in the rechargeable power supply.

Semi-active isolator

A shock and vibration isolator that includes a double acting mechanical spring assembly that is mounted to act in parallel with a fluid or liquid spring assembly. The mechanical spring is arranged to provide a first spring rate over a first displacement range and a second spring rate over a further second displacement range. The liquid spring is connected to an accumulator by control circuitry that is under the control of a microprocessor to release stored energy which combines with that of the mechanical spring to rapidly dissipate the input G forces to a level sufficient to protect a substructure.

Combination Optimization Design Method of Vibration Isolation and Shock Resistance System

The optimization design problem of vibration isolation and shock resistance system is studied in consideration of acoustical concealment performance and life-force of ships. The weakness of design method based on continuity is pointed out and combination optimal design method is brought forward. Then the limiting performance of shock isolation system is analyzed and two realization methods are discussed. One method is to adopt linear stiffness component with large damping. The other method is to use multiple linear stiffness components without damping. Simulation results showed that the optimal loss factor is still 0.4 when the stiffness of shock bumper is much larger than that of vibration isolator, just the same with that suffering from only shock loads. Simulation results also showed that limiting performance can be achieved by configuration optimal design using multiple linear components. The two discussed methods can be used to direct engineering application.

Optimal Performance of Variable Stiffness Devices for Structural Control

This paper addresses control of structural vibrations using semi-active actuators that are capable of manipulating stiffness and∕or producing variable stiffness. Usually vibration suppression is achieved using damping devices rather than stiffness ones. However, stiffness devices can produce large forces and have significant advantages for shock isolation purposes. In this work we use a passivity approach to establish the requirements for the control law for a structure equipped with semi-active stiffness devices. We also solve an optimal control problem that demonstrates that our passive, resetting feedback control law approximates the optimal control. Simulation and experimental results are presented in support of the proposed approach.

Passive low pass filtering effect of mechanical vibrations by a granular bed composed of microglass beads

Passive low pass filtering characteristics of a granular bed composed of microglass beads (MGBs) are investigated for military applications to a shock isolator. The granular bed attenuates the transmission of vibrations over a given frequency range sensitive to electronic devices through kinetic energy absorption like low pass filters in electric system. The experimental studies on five kinds of MGB with different diameters demonstrate that the cutoff frequency and the steepness of rolloff of the granular bed are inversely proportional to the diameter of MGB, and the vibration absorptivity is proportional to the diameter of MGB. The granular bed composed of 68μm diameter MGB absorbs incident mechanical vibrations with the cutoff frequency of 16.0±1.5kHz, the vibration absorptivity of 0.22, and the stopband transmittance of 1%–10%.

Fe–Mn martensitic alloys for control of noise and vibration in engineering applications

Conventional methods for reducing vibration in engineering designs may be undesirable or inadequate in conditions where size or weight must be minimized or where complex vibration spectra exist. Alloys which combine high-damping capacity with good mechanical properties can provide attractive technical and economic solutions to problems involving seismic, shock and vibration isolation. To meet these trends, we have developed a new high-damping Fe–17% Mn alloys. Also, the alloy has advantages of good mechanical properties and more economical than any other known damping alloys (one-quater of the cost of non-ferrous damping alloy). Thus, the high-damping Fe–17% Mn alloy can be widely applied to household appliances, automobiles, industrial facilities and power plant components with its excellent damping capacity (SDC, 30%) and mechanical property (UTS 700 MPa). It is the purpose of this paper to introduce the characterization of the high-damping Fe–17% Mn alloy and the results of retrofit several such applications.

Optimal Control: Basis for Performance Comparison of Passive and Semiactive Isolation Systems

Passive damping in shock and vibration isolation systems reduces the deformation of the isolation system but can increase the acceleration sustained by the isolated object. Semiactive (i.e., controllable) damping systems offer a solution to the problem of increased vibration transmissibility at high frequencies. Semiactive damping is especially relevant to protecting acceleration-sensitive components to the effects of large impulsive earthquakes. In this paper, we compare three semiactive control policies, i.e., pseudonegative-stiffness control, continuous pseudoskyhook-damping control, and bang-bang pseudoskyhook-damping control, in terms of their effectiveness in addressing the deficiencies of passive isolation damping. In order to establish a performance goal for these suboptimal semiactive control rules, we present a method for true optimization of the response of dynamically excited, semiactively controlled structures subjected to constraints imposed by the dynamics of a particular semiactive device....

Design optimization of low impact transmission foundation for forging hammers

Purpose – The objective of this work is to introduce a new method to carry out design optimization of a mechanical system for vibration and shock isolation, in particular, the viscous spring isolator mounting system for a forging hammer.Design/methodology/approach – The system dynamics model for an isolated foundation and solution technique for obtaining system response under impact loads is introduced. A design optimization problem is formulated to minimize the maximum impact force transmissibility under design constraints, using stiffness and damping coefficients of the isolator, mass of the foundation block and support area of soil as design variables. A dedicated simulated annealing (SA) algorithm is applied to solve the optimization problem.Findings – Viscous spring isolator mounting system, if properly designed, can considerably reduce shock and vibration transmission and the size of the foundation. The optimization leads to a mounting system with superior impact and vibration isolation capability o...

Shock and vibration isolation system

An apparatus is provided for attenuating shock and vibration energy levels within a spacecraft interface isolation system. The apparatus includes one or more spring plate assemblies fitted with mechanical stops and damping devices. The isolation system is typically incorporated into an interface unit, which is connected between the launch vehicle and the payload, in order to reduce the shock and vibration load energy imposed on the payload during the fairing separation processes. The mechanical stops maintain a desired level of stiffness for the payload supporting structure during lift-off and Max q, and the damping devices reduce the spring plate oscillation tendency during fairing separation. The combination of spring plate, stop, and damping device provides a significant reduction in shock and vibration energy levels in the approximate frequency range of 100 to 300 Hz.

Multiobjective evolutionary optimization of periodic layered materials for desired wave dispersion characteristics

An important dispersion-related characteristic of wave propagation through periodic materials is the existence of frequency bands. A medium effectively attenuates all incident waves within stopbands and allows propagation within passbands. The widths and locations of these bands in the frequency domain depend on the layout of contrasting materials and the ratio of their properties. Using a multiobjective genetic algorithm, the topologies of one-dimensional periodic unit cells are designed for target frequency band structures characterizing longitudinal wave motion. The decision variables are the number of layers in the unit cell and the thickness of each layer. Binary and mixed formulations are developed for the treatment of the optimization problems. Designs are generated for the following novel objectives: (1) maximum attenuation of time harmonic waves, (2) maximum isolation of general broadband pulses, and (3) filtering signals at predetermined frequency windows. The saturation of performance with the number of unit-cell layers is shown for the first two cases. In the filtering application, the trade-off between the simultaneous realization of passband and stopband targets is analyzed. It is shown that it is more difficult to design for passbands than it is to design for stopbands. The design approach presented has potential use in the development of vibration and shock isolation structures, sound isolation pads/partitions, and multiple band frequency filters, among other applications.

Biomechanical Efficiency of Wrist Guards as a Shock Isolator

Despite the use of wrist guards during skate- and snowboard activities, fractures still occur at the wrist or at further proximal locations of the forearm. The main objectives of this study were to conduct a human subject testing under simulated falling conditions for measurement of the impact force on the hand, to model wrist guards as a shock isolator, to construct a linear mass-spring-damper model for quantification of the impact force attenuation (Q-ratio) and energy absorption (S-ratio), and to determine whether wrist guards play a role of an efficient shock isolator. While the falling direction (forward and backward) significantly influenced the impact responses, use of wrist guards provided minimal improvements in the Q- and S-ratios. It was suggested based on the results under the submaximal loading conditions that protective functions of the common wrist guard design could be enhanced with substantial increase in the damping ratio so as to maximize the energy absorption. This would bring forth minor deterioration in the impact force attenuation but significant increase in the energy absorption by 19%, which would help better protection against fall-related injuries of the upper extremity.

Dynamics of a linear beam with an attached local nonlinear energy sink

We provide numerical evidence of passive and broadband targeted energy transfer from a linear flexible beam under shock excitation to a local essentially nonlinear lightweight attachment that acts, in essence, as nonlinear energy sink—NES. It is shown that the NES absorbs shock energy in a one-way, irreversible fashion and dissipates this energy locally, without ‘spreading’ it back to the linear beam. Moreover, we show numerically that an appropriately designed and placed NES can passively absorb and locally dissipate a major portion of the shock energy of the beam, up to an optimal value of 87%. The implementation of the NES concept to the shock isolation of practical engineering structures and to other applications is discussed.

SHOCK ISOLATION THROUGH PASSIVE ENERGY PUMPING CAUSED BY NONSMOOTH NONLINEARITIES

We investigate shock isolation designs based on nonlinear energy pumping caused by nonsmooth stiffness elements. In particular, we numerically study the shock isolation properties of a primary linear system of two coupled nonconservative oscillators with weakly coupled attachments possessing clearance nonlinearities. Under shock excitation the nonlinear attachments (termed nonlinear energy sinks — NESs) can be designed to absorb a significant portion of the input energy, thus enhancing the shock isolation performance of the primary system. In contrast to the classical linear vibration absorber whose operation is restricted to narrowband frequency ranges, the NESs are capable of efficiently absorbing energies caused by transient broadband disturbances, a feature that facilitates their implementation in practical applications. Moreover, the nonsmooth nonlinearities considered in this work are easily implementable since they are realized by means of linear stiffness elements.