Beginning in 1990, the US Army Aberdeen Test Center (ATC) began testing a prototype cannon mounted in a non-armored turret fitted to an M1A1 Abrams tank chassis. The cannon design incorporated a longer gun tube as a means to increase projectile velocity. A significant increase in projectile impact dispersion was measured early in the test program. Through investigative efforts, the cause of the error was linked to the increased dynamic bending or flexure of the longer tube observed while the vehicle was moving. Research and investigative work was conducted through a collaborative effort with the US Army Research Laboratory, Benet Laboratory, Project Manager &#x2013; Tank Main Armament Systems, US Army Research and Engineering Center, and Cadillac Gage Textron Inc. New test methods, instrumentation, data analysis procedures, and stabilization control design resulted through this series of investigations into the dynamic tube flexure error source. Through this joint research, improvements in tank fire control design have been developed to improve delivery accuracy. This paper discusses the instrumentation implemented, methods applied, and analysis procedures used to characterize the tube flexure during dynamic tests of a main battle tank and the relationship between gun pointing error and muzzle pointing error.

Peter L. McCall

Measurements of Gun Tube Motion and Muzzle Pointing Error of Main Battle Tanks

The application of magneto rheological dampers for controlling recoil dynamics is examined, using a recoil demonstrator that includes a single-shot 50 caliber BMG rifle action and a MR damper. The demonstrator is selected such that it can adequately represent the velocities that commonly occur in weapons with a recoil system, and can be used for collecting data for analyzing the effects of MR dampers on recoil dynamics. The MR damper is designed so that it can work effectively at the large velocities commonly occurring in gun recoil, and also be easily adjusted to reasonably optimize the damper performance for the recoil demonstrator. The test results show that it is indeed possible to design and use MR dampers for recoil applications, which subject the damper to relative velocities far larger than the applications that such dampers have commonly been used for (i.e., vehicle applications). Further, the results indicate that the recoil force increases and the recoil stroke decreases nonlinearly with an increase in the damping force. Also of significance is the fact that the adjustability of MR dampers can be used in a closed-loop system such that the large recoil forces that commonly occur upon firing the gun are avoided and, simultaneously, the recoil stroke is reduced. This study points to the need for several areas of research including establishing the performance capabilities for MR dampers for gun recoil applications in an exact manner, and the potential use of such dampers for a fire out of battery recoil system.

Mehdi Ahmadian

James C. Poynor

An Evaluation of Magneto Rheological Dampers for Controlling Gun Recoil Dynamics

The recoil from an electromagnetic (EM) railgun is discussed and compared with that from conventional, propellant gas driven cannon. It is shown that, under similar launch conditions, the recoil of the EM gun is less than that of the powder gun; however, use of a muzzle brake on a powder gun can alter this relative behavior.

Edward M. Schmidt

Comparison of the Recoil of Conventional and Electromagnetic Cannon

This paper will summarize the successful application of muzzle-end vibration absorbers to reduce cannon vibration. This technology constitutes a weapons stabilization approach that focuses on passive mechanical structural modification of the cannon, rather than relying upon an external control law to actively cancel vibrations. Challenges encountered during field testing, non-ideal behavior, and performance evaluation using digital signal processing will be highlighted.

Eric Kathe

Lessons Learned on the Application of Vibration Absorbers for Enhanced Cannon Stabilization

We study the damping effects of a cantilever beam system consisting of a gun tube wrapped with a constrained viscoelastic polymer on terrain induced vibrations. A time domain solution to the forced motion of this system is developed using the GHM (Golla-Hughes-McTavish) method to incorporate the viscoelastic properties of the polymer. An impulse load is applied at the free end and the tip deflection of the cantilevered beam system is determined. The resulting GHM equations are then solved in MATLAB by transformation to the state-space domain.

Margaret Z. Kiehl

C.P.T. Wayne Jerzak

Modeling of Passive Constrained Layer Damping as Applied to a Gun Tube

Fluid cavitation constitutes an expensive computational nuisance in underwater-shock response calculations for structures at or just below the free surface. In order to avoid the use of a large array of cavitating acoustic finite elements (CAFE), various wet-surface approximations have been proposed. This paper examines the performance of two such approximations by comparing results produced by them for 1-D canonical problems with corresponding results produced by more rigorous CAFE computations. It is found that the fundamental limitation of wet-surface approximations is their inability to capture fluid-accretion effects. As an alternative, truncated CAFE fluid meshes with plane-wave radiation boundaries are shown to give good results. In fact, a single layer of CAFE is found to be comparable in accuracy to the better of the wet-surface approximations. The paper concludes with an examination of variations in CAFE modeling.

Michael A. Sprague

Thomas L. Geers

Computational Treatments of Cavitation Effects in Near-Free-Surface Underwater Shock Analysis

The nonlinearities induced by skyhook dampers are studied experimentally and analytically using a single degree of freedom base-excited system that is representative of the systems that such dampers are often used in. The experimental results are used to show that the nonlinearities introduced by skyhook dampers manifest themselves as high frequency peaks in the frequency spectrum of the system response. More precisely, using a pure tone input with a known frequency, it is shown that these peaks occur at odd multiples of the system input (or driving) frequency. Using a Fourier series analysis, it is proven that the nonlinearities are caused by the switching policy of skyhook dampers, in which the damper force is changed according to the relative sign of the sprung mass absolute velocity and the relative velocity across the damper. The analysis shows that the skyhook damper force always contains a frequency component that is equal to the frequency of the system input (as is expected for a linear system), in addition to other frequencies that are odd multiples of the input frequency. The damping force peak that occurs at the input frequency is necessary for controlling the forced response of the system. The peaks at higher frequencies, however, are not desirable &#x2013; although always present &#x2013; because they introduce corresponding peaks in the system response that can cause ancillary vibration problems. For most systems, the high frequency peaks can significantly diminish any isolation benefits that are gained by the skyhook damper. When using skyhook dampers, such effects must be considered and their impact on the system dynamics studied carefully.

Brian Reichert

Xubin Song

System Non-Linearities Induced by Skyhook Dampers

Experiments have been conducted to benchmark DYSMAS computer code calculations for the dynamic interaction of water with cylindrical structures. Small explosive charges were suspended using hypodermic needle tubing inside Al tubes filled with distilled water. Pressures were measured during shock loading by tourmaline crystal, carbon resistor and ytterbium foil gages bonded to the tube using a variety of adhesives. Comparable calculated and measured pressures were obtained for the explosive charges used, with some gages surviving long enough to record results after cavitation with the tube wall.

G. Chambers

H. Sandusky

F. Zerilli

K. Rye

R. Tussing

Jerry Forbes

Pressure Measurements on a Deforming Surface in Response to an Underwater Explosion in a Water-Filled Aluminum Tube

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 - Table of contents 2001

title

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. 

Shock and Vibration