Shock Isolation Research Articles

Pre‐Acting Control for Shock and Impact Isolation Systems

Pre‐acting control in shock/impact isolation systems is studied. With pre‐acting control, the isolation system begins to respond to an impact before this impact has been applied to the base. The limiting performance of the isolator with pre‐acting control is investigated for a single‐degree‐of‐freedom system subject to an instantaneous impact. The isolation performance index is defined as the maximum of the absolute value of the displacement of the object to be isolated relative to the base, provided that the magnitude of the control force transmitted to the object does not exceed a prescribed value. It is shown that there is a substantial advantage in the use of pre‐acting isolators over isolators without pre‐action. Particular attention is given to a pre‐acting isolator based on a passive elastic element (a spring) separating the object to be protected from the base. An example illustrates the calculation of the design parameters of such an isolator.

Irreversible Passive Energy Transfer in Coupled Oscillators with Essential Nonlinearity

We study numerically and analytically the dynamics of passive energy transfer from a damped linear oscillator to an essentially nonlinear end attachment. This transfer is caused by either fundamental or subharmonic resonance capture, and in some cases is initiated by nonlinear beat phenomena. It is shown that, due to the essential nonlinearity, the end attachment is capable of passively absorbing broadband energy at both high and low frequencies, acting, in essence, as a passive broadband boundary controller. Complicated transitions in the damped dynamics can be interpreted based on the topological structure and bifurcations of the periodic solutions of the underlying undamped system. Moreover, complex resonance capture cascades are numerically encountered when we increase the number of degrees of freedom of the system. The ungrounded essentially nonlinear end attachment discussed in this work can find application in numerous practical settings, including vibration and shock isolation of structures, seism...

Impact Isolation Limiting Performance Analysis for Three-Component Models

For the crashworthiness analysis of transport vehicles a three-component system that consists of a base, a container, and an object to be protected, connected by shock isolators, can be utilized as a model. An approach for a limiting performance analysis of shock isolation for such a model is proposed. This approach involves the reduction of the optimal control problem for the three-component system to an auxiliary optimal control problem for a two-component system. A detailed description of the technique for the determination of the absolute minimum of the performance index and construction of the optimal control is presented. A proposition that provides a mathematical substantiation for this technique is stated and proven. Example problems included in the paper demonstrate the effectiveness of the proposed technique.

Isolated Resonance Captures and Resonance Capture Cascades Leading to Single- or Multi-Mode Passive Energy Pumping in Damped Coupled Oscillators

We examine passive energy pumping in a system of damped coupled oscillators. This is a one-way, passive and irreversible energy flow from a linear main system to a nonlinear attachment that acts, in essence, as a nonlinear energy sink (NES). Energy pumping is caused by 1:1 resonance captures on resonant manifolds of the damped systems. We show that the NES is capable of absorbing significant portions of the energies generated by transient, broadband external excitations. By performing a series of numerical simulations we confirm that the energy dependence of the nonlinear normal modes (NNMs) of the underlying undamped, unforced system determines, in essence, the resonance capture and energy pumping dynamics in the corresponding damped system. We present numerical simulations of single- and multi-mode energy pumping, that involve isolated resonance captures or resonance capture cascades, respectively. In addition, we discuss methodologies for enhancing the nonlinear energy pumping phenomenon by properly selecting the system parameters. The described technique of passively localizing and locally eliminating externally induced energy provides a new paradigm for vibration and shock isolation of mechanical oscillators.

Dynamics and Control of Machines

Dynamics and Control of Machines

Seismic Applications of Energy Dampers

Damping devices based on the operating principle of high velocity fluid flow through orifices have found numerous applications in the shock and vibration isolation of aerospace and defence systems. The study aims to investigate the feasibility of using energy dissipating fluid viscous dampers in structures to protect against seismic loads and to prove analytically and experimentally that fluid viscous dampers can improve the seismic capacity of a structure by reducing damage and displacement without increasing stresses. Both steel and concrete structures were considered. Extensive analytical and experimental investigations have led to the hazad mitigation applications on buildings bridges. A series of experiments were performed to demonstrate the benefits of fluid viscous damping devices in steel moment frame and reinforced concrete building models and a steel bridge model were tested, and all exhibited improved resistance to a variety of seismic loads. Furthermore, fluid dampers would be used as elements of seismic isolation systems forenhancing their energy dissipation capability.

Performance Analysis of Suspension Seats under High Magnitude Vibration Excitations: Part 1: Model Development and Validation

Performance analyses of suspension seats subject to high magnitude excitations require particular modeling considerations associated with impacts against the motion limiting elastic buffers, possible loss of contact between the seat and the occupant, and component characterization over a wide range of inputs. In this study, three different suspension seats are considered to formulate a generalized model that would be applicable under low to high magnitude excitations. The static and dynamic characteristics are evaluated in the laboratory under a wide range of excitations and seat preloads. General model structures are proposed to characterize the components of the selected suspension seats as functions of the preload and nature of excitation. A general model for the suspension seats is formulated upon integration of the component models and consideration of the potential body-hop motions. The validity of the proposed model is examined under a number of excitations representing continuous random vibration environment of different vehicles, such as urban buses and class-1 construction machinery (EM1), and transient sprung mass oscillations in the vicinity of the suspension seat natural frequency. The validity of the model is further examined for all three seats subject to amplified excitations of the urban buses and the construction machinery. The results of the study suggest that the proposed model can be effectively applied to assess the suspension performance under high magnitude excitations that induce repetitive impacts with motion limiting buffers. The influences of various design parameters on the shock and vibration isolation performance of the selected suspension seats are presented in the second part of this work.

Shock Isolation Through the Use of Nonlinear Energy Sinks

We consider shock isolation designs based on the use of nonlinear energy sinks (NESs). These are a priori determined points of a system where unwanted disturbances are transmitted (“pumped”) and then eliminated by passive or active means. The underlying dynamic phenomenon that causes nonlinear energy to pump into a sink is resonance capture on a 1:1 resonance manifold of the dynamics. In this work, essentially nonlinear stiffness elements are used to couple the NES with the primary system in order to achieve robust energy pumping, in a sufficiently fast timescale. “Fast” energy pumping at the early stage of the motion is important in order to achieve the shock isolation objectives. The proposed shock isolation design is practical and realizable. Its modular form enables the alteration of the global dynamics of a system by attaching a number of local NESs. The proposed design has the additional interesting feature of dual mode shock isolation, e.g., the capacity to significantly reduce the level of unwanted disturbances initiated at different points of the system.

A New Simulation Method Providing Shock Mount Selection Assurance

This paper presents the development and assessment of a practical and efficient process for assessing and/or designing shock isolation systems. This process combines practical methods for determining relative displacements and accelerations (e.g. shock response spectrum analysis) with a new, efficient, easy to use, 6 degree of freedom (6DOF) simulation method known as Shock Isolation Mount Predictions & Loading Estimates (SIMPLE). SIMPLE is also a tool that can easily account for uncertainties in isolated systems and their environments. The implementation of 6DOF rigid body theory in SIMPLE is validated by comparing simulation results with other analytical methods. This paper also summarizes assessments and designs for 60 different mounting systems using SIMPLE. In addition, experimental results from shock tests are compared with pre-test SIMPLE sensitivity simulations and with results of post-test model calibrations. These comparisons show the validity of: 1) using 6DOF analysis; 2) using statically derived load-deflection data for simulations; and 3) assessing and designing isolated systems using uncertainties in model parameters.

Multi-axis shock and vibration isolation system

A shock and vibration isolator system that includes a frame in which a shock and vibration sensitive mass is suspended by double acting shock absorbers with vibration isolation capabilities. Wire rope isolators are also mounted between walls of the mass and adjacent walls of the frame so that shock and vibrations moving along the vertical, horizontal and longitudinal axes of the system are effectively attenuated.

Steady State Passive Nonlinear Energy Pumping in Coupled Oscillators: Theoretical and Experimental Results

We study theoretically and experimentally the effect that anonlinear energy sink (NES) has on the steady state dynamics of a weaklycoupled system. The NES possesses essentially nonlinear(nonlinearizable) stiffness nonlinearity of the third degree. We findthat, in contrast to the classical linear vibration absorber, the NES iscapable of absorbing steady state vibration energy from the linearoscillator over a relatively broad frequency range. This results inlocalization of the steady state vibration in the NES, away from thedirectly forced subsystem. For a forward frequency sweep the localizedbranch of steady state motions is suddenly eliminated by a jump to alinearized low-amplitude motion, whereas, for a backward frequency sweepa reverse jump occurs. The difference in the frequencies of the twojumps introduces a nonlinear hysteresis loop. This work extends to thesteady state case of earlier transient passive energy pumping results.The notion of passively transferring vibration energy to an a prioridetermined NES, weakly attached to a main structure, is novel. The useof nonlinear energy sinks for passively absorbing energy from a linearmain structure can form the basis of relatively simple and modularvibration and shock isolation designs of mechanical systems.

Shock isolation using ‘smart’ damping

AbstractApplications of shock isolation range from vehicle suspension systems to packaging which protects para‐dropped equipment in the military expeditionary logistics environment. Both passive and active shock isolation systems have been investigated. However, passive systems are limited in that they cannot adapt to different load conditions; active systems are not practical in many applications, as they may require large power supplies. Another solution to the problem is to implement a ‘smart’ damping system, which typically requires little power, is controllable in real time, and achieves nearly the same performance as an active system. This paper focuses on shock isolation using these ‘smart’ damping devices. Following the basic problem formulation, the optimal active shock isolator synthesis is given. These results are then extended to the ‘smart’ (semi‐active) shock isolation case. Theoretical analysis shows that if the linear spring stiffness is properly chosen and the control force is appropriately regulated, the shock isolator using ‘smart’ damping can achieve optimal performance and has better robustness than the passive shock isolators. Copyright © 2002 John Wiley & Sons, Ltd.

Vibration exposure in a forestry machine fitted with a saddle type suspension seat

The shock and vibration isolation performance of two suspension seats with identical suspension mechanisms were tested in a forestry machine. The first seat was a standard suspension seat commonly used on forwarders; the second seat was a prototype suspension seat shaped like a saddle. The vibration exposure of two drivers using the machine on two test tracks was compared using acceleration and absorption of energy methods. On the test track designed to simulate off-road driving, there was little difference between the vibration exposures measured using the two different seats. The absorption of energy at the seat was consistently lower for the saddle seat, but absorption at the feet was higher for the saddle seat. Measurements of vibration exposure on the test track designed to generate end-stop impacts showed that there was less probability of an impact occurring for the saddle type seat than for the standard seat. It is concluded that a reduction in vibration exposure might be possible if a saddle type suspension seat is used in preference to a standard suspension seat.

Optimal Protection from Impact, Shock, and Vibration

Optimal Protection from Impact, Shock, and Vibration

Optimal Protection From Impact and Shock: Theory and Methods

This review article gives a historical perspective of the achievements in the theory and methods of optimization of isolation systems and outlines the most important results, including some practical applications. The effectiveness of shock isolation is reviewed and the fact that in some cases the utilization of isolators does not lead to a reduction in the force transmitted to the body to be protected is discussed. Mathematical formulations of basic problems of optimization of shock isolation systems are surveyed, including those for the case where the external disturbance is not precisely prescribed. Particular attention is given to the limiting performance analysis aimed at the establishment of an absolute optimum of the response of the system, irrespective of its design and engineering implementation. A significant portion of this paper is devoted to the basic achievements in the theory of shock isolation of systems with one degree of freedom. Analytical solutions for such systems are reviewed in detail. Various computational techniques are outlined and compared. Promising potential directions of further developments are discussed. An extensive bibliography of relevant publications is provided. Included in this review are numerous publications from the former Soviet Union which heretofore have not received much exposure elsewhere. This review article contains 234 references.

High damping Fe–Mn martensitic alloys for engineering applications

Conventional methods for reducing vibration in engineering designs (i.e. by stiffening or detuning) 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 alloy. Also, the alloy has advantages of good mechanical properties and is more economical than any other known damping alloys (a quarter 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 (T.S. 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 of several such applications.

Limiting Performance Analysis of Underwater Shock Isolation of a System with Biodynamic Response Using Genetic Algorithm

Biodynamic response of shipboard crew to underwater shock is of a major concern to navies. An underwater shock can produce very high accelerations, resulting in severe human injuries aboard a battleship. Protection of human bodies from underwater shock is implemented by installing onboard isolators. In this paper, the optimal underwater shock isolation to protect human bodies is studied. A simple shock-structure-isolator-human interaction model is first constructed. The model incorporates the effect of fluid-structure interaction, biodynamic response of human body, isolator influence. Based on this model, the optimum shock isolation is then formulated. The performance index and restriction are defined. Thirdly, GA (genetic algorithm) is employed to solve the formulated optimization problem. GA is a powerful evolutionary optimization scheme suitable for large-scale and multi-variable optimization problems that are otherwise hard to be solved by conventional methods. A brief introduction to GA is given in the paper. Finally, the method is applied to an example problem and the limiting performance characteristic is obtained.

PERFORMANCE OF NON-LINEAR ISOLATORS AND ABSORBERS TO SHOCK EXCITATIONS

To improve the performance of a non-linear shock isolator, four different alternatives are being considered and compared. These are (i) an isolator with a Coulomb damper, (ii) a three-element isolator, (iii) an isolator along with vibration absorber and (iv) a two-stage isolator. Three different types of shock inputs are considered as the base motion to be isolated. Three different indices are used to judge the overall performance characteristics of the isolator. Overall, it is seen that the three-element and two-stage isolators are preferable in the presence of a non-linear cubic damping.

A New Approach to Shock Isolation and Vibration Suppression Using a Resetable Actuator1

A novel low power control technique along with a new class of actuators is developed for shock isolation and control of structural vibrations. In contrast to other techniques, including conventional viscous or rate damping, the force produced by the actuator has no velocity dependence. Several experimental, analytical, and simulation results are presented in support of this new, semi-active technique for structural control. The basic approach is to manipulate the system stiffness through the use of resetable actuators. With the proposed control approach, the actuator behaves like a linear spring. However, at appropriate times, the effective unstretched length of the actuator is changed—or reset—to extract energy from the vibrating structure. Experimental validation of the actuator model, analytical results on stability and actuator-placement, and simulation results for earthquake applications are presented. [S0022-0434(00)01603-8]

Nonlinear analysis of automotive hydraulic mounts for isolation of vibration and shock

A detailed nonlinear analysis of hydraulic mounts with flexible chambers, employed in various automotive applications, is performed to investigate their shock and vibration isolation characteristics. The analytical model of a mount with long orifice is initially developed incorporating the reported measured compliance properties of the chambers and oscillation flows within a long orifice. The influence of "oscillation flow effects" associated with commonly used long orifice on the shock and vibration isolation performance is investigated. In view of the performance limitations under shocks and high amplitude vibration, a concept of hydraulic mount with short and long orifice is proposed. The results of the study are discussed to demonstrate the influence of oscillation flow effects and flows through the short orifice under shocks of varying severity and high amplitude vibration excitations. The results show that inclusion of oscillation flow effects yields lower dynamic stiffness and loss angle. It is also concluded that addition of a short orifice within the mount offers considerable potential to enhance the shock and vibration isolation performance.