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.

D.V. Balandin

N.N. Bolotnik

W.D. Pilkey

Pre-Acting Control for Shock and Impact Isolation Systems

The history of the development of Cap constitutive models is reviewed. The Cap family of models provides a powerful, yet adaptable way of representing many aspects of the dynamic stress-strain behavior of geological materials. These models have been extensively used for more than three decades to characterize the highly nonlinear behavior of soils, rocks and concrete, and are particularly well suited to the dynamic analysis arising in ground shock and seismic applications. The modern series of Cap Models is based on the adaptation of several earlier models, and was introduced in the early 1970&#x2019;s as a result of university and corporate R&#x26;D technology development sponsored by the United States government. Dr. Eugene Sevin played a role in these activities during his tenure at the Defense Nuclear Agency. In this paper, the basic behavior of the early models is briefly discussed and compared, and the reasons for the introduction of Cap Models are outlined. Many adaptations of the Cap Model have been developed since the first model was introduced, and the salient features of some of these model extensions are also reviewed.

Ivan S. Sandler

Review of the Development of Cap Models for Geomaterials

A spherical model for the bubble created by an underwater explosion is enhanced to account, in approximate fashion, for the effect of bubble distortion on translation and dilation. The enhancement consists of introducing artificial drag in the form <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>C</mml:mi><mml:msup><mml:mrow><mml:mrow><mml:mo>|</mml:mo><mml:mi>v</mml:mi><mml:mo>|</mml:mo></mml:mrow></mml:mrow><mml:mi>P</mml:mi></mml:msup></mml:mrow></mml:math>
, where &#x3bd; is translation velocity, and C, P produce an optimum fit to empirical formulas for the second dilation maximum and first two translation jumps. The recommended values are C &#x3D; 0.4 and P &#x3D; 1 for charge weights between 100 lb&#x2013;1000 lb and and depths exceeding 200 ft.

Thomas L. Geers

Chung-Kyu Park

Optimization of the G&#x26;H Bubble Model

The numerical solution of underwater shock fluid &#x2013; structure interaction problems using boundary element/finite element techniques became tractable through the development of the family of Doubly Asymptotic Approximations (DAA). Practical implementation of the method has relied on the so-called augmentation of the DAA equations. The fluid and structural systems are respectively coupled by the structural acceleration vector in the surface normal direction on the right hand side of the DAA equations, and the total pressure applied to the structural equations on its right hand side. By formally solving for the acceleration vector from the structural system and substituting it into its place in the DAA equations, the augmentation introduces a term involving the inverse of the structural mass matrix. However there exist at least two important classes of problems in which the structural mass matrix is singular. This paper develops a method to carry out the augmentation for such problems using a generalized inverse technique.

John A. DeRuntz Jr.

Augmentation of DAA Staggered &#x2013; Solution Equations in Underwater Shock Problems for Singular Structural Mass Matrices

A method for modelling arbitrary growth of dynamic cracks without remeshing is presented. The method is based on a local partition of unity. It is combined with level sets, so that the discontinuities can be represented entirely in terms of nodal data. This leads to a simple method with clean data structures that can easily be incorporated in general purpose software. Results for a mixed-mode dynamic fracture problem are given to demonstrate the method.

Goangseup Zi

Hao Chen

Jingxiao Xu

Ted Belytschko

The Extended Finite Element Method for Dynamic Fractures

Walter Pilkey

Nicholas Perrone

Thomas Geers

Kent Goering

Dedicated to Eugene Sevin

As vibration control requirements become increasingly stringent, designers and users of vibration control equipment turn to devices and systems combining various physical mechanisms. Subsystems based on different physical effects can be combined to achieve the optimal performance for the application. Building an optimal product line that would cover a wide field of applications by combining several products, as opposed to creating one optimal device for a particular application, presents an optimum vibration control problem. This paper reviews optimum vibration control problems based on the idea of limiting performance, and discusses recent development of vibration control devices.

V.M. Ryaboy

Vibration Control Systems for Sensitive Equipment: Limiting Performance and Optimal Design

About this journal

Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience. 

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Shock and Vibration | Hindawi

Shock and Vibration

This Issue is now open for submissions.
Papers are published upon acceptance, regardless of the Special Issue publication date.

Shock and Vibration

Dedicated to Eugene Sevin

Dedicated to Eugene Sevin

Articles

Pre-Acting Control for Shock and Impact Isolation Systems

Review of the Development of Cap Models for Geomaterials

Optimization of the G&H Bubble Model

Augmentation of DAA Staggered – Solution Equations in Underwater Shock Problems for Singular Structural Mass Matrices

The Extended Finite Element Method for Dynamic Fractures

Dedicated to Eugene Sevin

Vibration Control Systems for Sensitive Equipment: Limiting Performance and Optimal Design