bluuebunny/crossref_metadata_2025 huggingface dataset:
The Requirement for Hydrostatic Initialisation in LS‐DYNA/USA Finite Element Models
Authors: Hammond Lloyd , Grzebieta Raphael
Published: January 2014

The LS‐DYNA/USA (Underwater Shock Analysis) coupled finite element codes are being investigated as a tool for predicting the local response of compliant plate structures subjected to far‐field underwater explosion.

It had previously been observed in LS‐DYNA/USA models that extraneous pressure build‐ups emanating from the DAA (doubly asymptotic approximation) boundaries may occur in the surrounding fluid region of the model, which inevitably lead to erroneous modelling of fluid‐structure interaction and inaccurate structural responses. These instabilities typically result in divergence of the solution and eventually premature termination of the simulation. After a comprehensive investigation, it was found that the instabilities did not arise if the finite element model was hydrostatically initialised before conducting the LS‐DYNA/USA simulation.

The purpose of this study is to investigate the need for achieving hydrostatic equilibrium prior to the modelling of the shock wave propagation through the fluid‐structure media. The method for achieving static equilibrium with the current version of the LS‐DYNA/USA software is presented. The example simulations presented show that the hydrostatic initialisation procedure is effective in removing instabilities occurring at the DAA‐fluid boundary, associated with the USA ambient hydrostatic pressure condition.
Structural Response of Submerged Air‐Backed Plates by Experimental and Numerical Analyses
Authors: Hammond Lloyd , Grzebieta Raphael
Published: January 2014

This paper presents the results of a series of small‐scale underwater shock experiments that measured the structural responses of submerged, fully clamped, air‐backed, steel plates to a range of high explosive charge sizes. The experimental results were subsequently used to validate a series of simulations using the coupled LS‐DYNA/USA finite element/boundary element codes. The modelling exercise was complicated by a significant amount of local cavitation occurring in the fluid adjacent to the plate and difficulties in modelling the boundary conditions of the test plates. The finite element model results satisfactorily predicted the displacement‐time history of the plate over a range of shock loadings although a less satisfactory correlation was achieved for the peak velocities. It is expected that the predictive capability of the finite element model will be significantly improved once hydrostatic initialisation can be fully utilised with the LS‐DYNA/USA software.
Water Mitigation Effects on the Detonations in Confined Chamber and Tunnel System
Authors: Zhao H.Z. , Lam K.Y. , Chong O.Y.
Published: January 2014

The water mitigation effects on the detonations of explosive in a confined cube chamber are studied by use of a numerical code. Significant mitigation effects on shock pressure at various loading densities, various water/explosive mass ratios and various air gaps are obtained. Reduction of final static pressure is also obtained because water absorbs the energy released from the detonations through being compressed and vaporized. On the basis of this study, the detonations in a tunnel system with vent are further simulated. The numerical results are compared with the experimental data, and the water mitigation effects on shock pressure are verified.
Sliced Wigner Fourth Order Moment Spectra Smoothed by γ‐Method and Its Application to Detection of Valve System Faults in an Engine
Authors: Lee Sang-Kwon
Published: January 2014

The research proposes a method for detecting valve system faults in an engine. The methodology is based on the detection of impulsive sound embedded in the high level of background noise by using the sliced Wigner fourth order moment spectra (SWFOMS) which is inherently more robust in the presence of random (Gaussian) noise. However, in previous work, the SWFOMS for multiple signals had problems with its application which were due to the existence of non‐oscillating cross‐terms not smoothed by conventional methods. In this paper, the γ‐method is developed to smooth non‐oscillation cross‐terms. Finally, the techniques developed are applied to the diagnosis of valve system faults in an engine.
Pressure Measurements on a Deforming Surface in Response to an Underwater Explosion in a Water‐Filled Aluminum Tube
Authors: Chambers G. , Sandusky H. , Zerilli F. , Rye K. , Tussing R. , Forbes Jerry
Published: January 2014

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.
Measurements of Gun Tube Motion and Muzzle Pointing Error of Main Battle Tanks
Authors: McCall Peter L.
Published: January 2014

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 – 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.
A Method for Analyzing the Dynamic Response of a Structural System with Variable Mass, Damping and Stiffness
Authors: Zhang Mike D.R. , Sun Huanchun , Song Yaxin
Published: January 2014

In this paper, a method for analyzing the dynamic response of a structural system with variable mass, damping and stiffness is first presented. The dynamic equations of the structural system with variable mass and stiffness are derived according to the whole working process of a bridge bucket unloader. At the end of the paper, an engineering numerical example is given.
Dynamic Characterization of the Joints in a Beam Structure by Using Spectral Element Method
Authors: Lee Usik
Published: January 2014

A frequency‐domain approach is introduced to identify the dynamic characteristics of the mechanical joints within a one‐dimensional structure. In this paper, a cantilevered beam structure with a bolt‐joint is considered as an illustrative problem. The beam structure consists of two Timoshenko‐beams connected to each other by a bolted joint. The bolt‐joint is represented by the equivalent joint model with four parameters, and the four parameters are determined from the experimentally measured frequency response functions (FRF). To improve the accuracy of the identified bolt‐joint parameters, the spectral element models are used for two Timoshenko‐beams. Experiments are conducted for the cantilevered beam structure and the four bolt‐joint parameters determined from the measured FRF. The spectral analysis is conducted to predict the dynamic responses of the beam structure by using the spectral bolt‐joint element that is determined from the identified bolt‐joint parameters. It is found that the analytical predictions are in general quite in good agreement with the experimentally measured dynamic responses.
Asymptotic Method and Numerical Analysis for Self‐Excited Vibration in Rolling Mill with Clearance
Authors: Li Hongguang , Wen Bangchun , Zhang Jianwu
Published: January 2014

In this paper, a dynamic model is proposed for analysis of nonlinear vibrations of rolling mills with fixed and time‐varying clearances. Self‐excited vibrations of the system that is basically involved with piece‐wise nonlinearity and discontinuities are investigated via asymptotic method. It is shown by numerical results obtained for the nonlinear system with a time‐varying clearance that different forms of nonlinear vibrations appear to be periodic, quasi‐periodic and chaotic. Influence of the system parameters on the nonlinear vibration behaviors is examined by applying the Poincare sections, the bifurcation diagram and the largest Lyapunov exponent. New phenomena are observed in nonlinear motions of the rolling mill mechanism and are of significant importance for design of this type of mechanical systems.
Sabot Front Borerider Stiffness vs. Dispersion: Finding the Knee in the Curve
Authors: Hathaway Alan F. , Burnett John R.
Published: January 2014

In the design of armor piercing, fin‐stabilized, discarding sabot projectiles, the radial stiffness of the sabot front borerider has a significant impact on the projectile′s dispersion and is, therefore, an important design consideration. Whether designing a new projectile or trying to improve an existing design, projectile designers can achieve front borerider stiffness without understanding its affect on dispersion characteristics. There is a knee in the stiffness vs. dispersion curve at which a change in the sabot front borerider stiffness will have a significant impact on dispersion or no impact at all depending on whether the stiffness is increased or decreased. The subject of this paper is an analytical approach to quantitatively determine the knee in the curve. Results from using this approach on the M865 APFSDS projectile are also presented.
Comparison of Balance and Out of Balance Main Battle Tank Armaments
Authors: Purdy David J.
Published: January 2014

It has been commonly thought that stabilising an out of balance gun on a moving platform (tank or ship) is very difficult or impossible to achieve. Using models of a balanced and out of balance gun on a main battle tank this is shown not to be the case. The models of the guns used, include the effect of non‐linear friction and out of balance. To improve the stabilisation of the out of balance gun, trunnion vertical acceleration feedforward is used.
Dynamic Response and Fracture of Composite Gun Tubes
Authors: Tzeng Jerome T.
Published: January 2014

The fracture behavior due to dynamic response in a composite gun tube subjected to a moving pressure has been investigated. The resonance of stress waves result in very high amplitude and frequency strains in the tube at the instant and location of pressure front passage as the velocity of the projectile approaches a critical value. The cyclic stresses can accelerate crack propagation in the gun tube with an existing imperfection and significantly shorten the fatigue life of gun tubes. The fracture mechanism induced by dynamic amplification effects is particularly critical for composite overwrap barrels because of a multi‐material construction, anisotropic material properties, and the potential of thermal degradation.
System Non‐Linearities Induced by Skyhook Dampers
Authors: Ahmadian Mehdi , Reichert Brian , Song Xubin
Published: January 2014

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 – although always present – 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.
Aerodynamic Jump: A Short Range View for Long Rod Projectiles
Authors: Bundy Mark
Published: January 2014

It is shown that aerodynamic jump for a nonspinning kinetic energy penetrator is not – as conventional definitions may infer – a discontinuous change in the direction of motion at the origin of free flight, nor is it the converse, a cumulative redirection over a domain of infinite extent. Rather, with the aid of an alternative kinematical definition, it is shown that aerodynamic jump for such a projectile is a localized redirection of the center‐of‐gravity motion, caused by the force of lift due to yaw over the relatively short region from entry into free flight until the yaw reaches its first maximum. A rigorous proof of this statement is provided, but the primary objective of this paper is to provide answers to the questions: what is aerodynamic jump, what does it mean, and what aspects of the flight trajectory does it refer to, or account for.
Dynamic Analysis of a 155 mm Cannon Breech
Authors: O’Hara G. Peter
Published: January 2014

This report describes a finite element analysis of the breech closure for the 155 mm Cannon M199, which is normally mounted on the Towed Howitzer M198. In this configuration it has has an excellent record for reliability in the field and is easy to service. However when the breech is used in an ammunition test environment, some maintenance problems exist. The analysis is for a 9 body problem with 13 contact surfaces and was solved for both static and dynamic load cases. The two dynamic loads were of similar shape with different loading times. The 9 bodies in the model include, a facility mount, four major structural components, the obturator seal and 3 minor components. The results show that the major components are normally subjected to quasi‐static loading but under fast `pressure spike′ loadings, the dynamic effect can be important. This is particularly true for the contact between minor components which can show extreme behavior with the fast loading rates.
Energy Dissipation from Vibrating Floor Slabs due to Human‐Structure Interaction
Authors: Brownjohn James M.W.
Published: January 2014

Lightweight pre‐cast flooring systems using post‐tensioning to increase strength but not stiffness are increasingly popular, and vibration serviceability problems tend to govern design of such floors where human occupants are increasingly concerned with vibrations. At the same time as inducing response, stationary human observers can also participate in the response as mitigating influence and it is clear that a human behaves as a highly effective damper, even when seated.

Experiments were done to study energy flow and storage in a 1.2 tonne vibrating concrete plank with a human occupant. Results showed that damping could increase to as much as 10% frequency shifts (usually decreases) in the slab apparent resonant frequency, depending on occupant posture. Simple lumped mass mathematical models were also used to study the vibrating human‐structure system through dynamic simulations, corroborating the findings.

Further corroboration was provided from measurements on a prototype full‐scale floor slab occupied by several hundred people who were either jumping or sitting. Modal analysis of vibration response signals showed that normal floor resonance associated with jumping at a sub‐harmonic of the floor natural frequency was almost completely damped out by the passive (seated) people.
Combining Response Surface Optimization and Stochastic Analysis for Crashworthiness Design – an Introductory Study
Authors: Fredriksson Lars A. , Schramm Uwe
Published: January 2014

Objective of the design process are cost effective designs that meet certain expectations with respect to functionality and appearance. Designs are created in an iterative process where analyses of the structural behavior lead to changes in the design. The use of optimization technology makes design changes to be driven directly by analysis results. The application of optimization allows an efficient search for the right combination of design variables for a certain design. Additional use of stochastic methods in order to analyze the design from a statistical standpoint adds robustness to the design and prevents unpleasant surprises in later physical testing.

This paper discusses methodology to optimize structures that undergo impact loading. Objective and constraints are transient dynamic responses. The optimization problem is solved using a sequential response surface method. An explicit finite element code is used to solve the transient dynamic problem. The optimization is not performed on results from single simulations but on statistical results from a stochastic analysis. The stochastic analysis is driven using a Monte Carlo method. Commercial software is used for the implementation of the methodology.

The results from the study indicate that a combination of optimization and stochastic analysis can add safety margins to a design with respect to robustness against physical errors in the design itself and against changes in load levels and load cases. However, this initial study must be followed up by more in‐depth investigations to fully understand the benefits of combined optimization‐stochastic analysis.
Vibration Protection of Sensitive Components of Infrared Equipment in Harsh Environments
Authors: Veprik A.M. , Babitsky V.I. , Pundak N. , Riabzev S.V.
Published: January 2014

This article addresses the principles of optimal vibration protection of the internal sensitive components of infrared equipment from harsh environmental vibration. The authors have developed an approach to the design of external vibration isolators with properties to minimise the vibration‐induced line‐of‐sight jitter which is caused by the relative deflection of the infrared sensor and the optic system, subject to strict constraints on the allowable sway space of the entire electro‐optic package. In this approach, the package itself is used as the first‐level vibration isolation stage relative to the internal highly responsive components.

It was predicted analytically, and confirmed experimentally, that the proposed vibration isolation system would be capable of a sixfold reduction of the dynamic response of the infrared sensor as compared to the case of rigid mounting of the entire package.
Dynamic Analysis of a Rigid Body Mounting System with Flexible Foundation Subject to Fluid Loading
Authors: Tao J.S. , Liu G.R. , Lam K.Y.
Published: January 2014

This paper presents an investigation of the force transmission from a rigid body mounting system to a flexible foundation with light and heavy fluid loading under the force and moment excitation. The analytical expression has been derived in which the flexible foundation effects are incorporated into a revised system stiffness matrix that is derived from the receptance matrix at mounting points. A typical case with a thin infinite plate as the foundation has been studied with the point and transfer receptances theoretically and numerically analysed in the case of light and heavy fluid loading. The results show that, compared with the rigid foundation, the force transmission is reduced and system natural frequencies are shifted. The detailed analysis demonstrates that the force reduction and frequency shifting are more obvious at low frequencies where the receptance value is significant. The study is also carried out to compare the transfer receptances from different waves in plate as it couples with water with the objective to simplify the calculation of receptance. It is found that, in the low frequency and after a short distance from driving point, the transfer receptance calculation for the heavy fluid loading can be simplified by only accounting the contribution from free wave which may easily be evaluated from the point receptance in air. It implies the plate response under heavy fluid loading could be directly derived from that with light fluid loading.
Application of Non‐Linear System Model Updating Using Feature Extraction and Parameter Effects Analysis
Authors: Schultze John F. , Hemez François M. , Doebling Scott W. , Sohn Hoon
Published: January 2014

This research presents a new method to improve analytical model fidelity for non‐linear systems. The approach investigates several mechanisms to assist the analyst in updating an analytical model based on experimental data and statistical analysis of parameter effects. The first is a new approach at data reduction called feature extraction. This approach is an expansion of the `classic′ update metrics to include specific phenomena or character of the response that is critical to model application. This is an extension of the familiar linear updating paradigm of utilizing the eigen‐parameters or frequency response functions (FRFs) to include such devices as peak acceleration, time of arrival or standard deviation of model error. The next expansion of the updating process is the inclusion of statistical based parameter analysis to quantify the effects of uncertain or significant effect parameters in the construction of a meta‐model. This provides indicators of the statistical variation associated with parameters as well as confidence intervals on the coefficients of the resulting meta‐model. Also included in this method is the investigation of linear parameter effect screening using a partial factorial variable array for simulation. This is intended to aid the analyst in eliminating from the investigation the parameters that do not have a significant variation effect on the feature metric. Finally, an investigation of the model to replicate the measured response variation is examined.
Dispersion Analysis of the XM881APFSDS Projectile
Authors: Erline Thomas F. , Patton Brendan J. , Hathaway Alan F.
Published: January 2014

This study compares the results of a dispersion test with mathematical modeling. A 10‐round group of modified 25‐mm XM881 Armor Piercing Fin Stabilized Discarding Sabot projectiles was fired from the M242 chain gun into a designated target. The mathematical modeling results come from BALANS, a product of Arrow Tech Associates. BALANS is a finite‐element lumped parameter code that has the capability to model a flexible projectile being fired from a flexible gun. It also has the unique feature of an automated statistical evaluation of dispersion. This study represents an effort to evaluate a simulation approach with experiment.
Comparison of the Recoil of Conventional and Electromagnetic Cannon
Authors: Schmidt Edward M.
Published: January 2014

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.
Active Noise Feedback Control Using a Neural Network
Authors: Qizhi Zhang , Yongle Jia
Published: January 2014

The active noise control (ANC) is discussed. Many digital ANC systems often based on the filter‐x algorithm for finite impulse response (FIR) filter use adaptive filtering techniques. But if the primary noise path is nonlinear, the control system based on adaptive filter technology will be invalid. In this paper, an adaptive active nonlinear noise feedback control approach using a neural network is derived. The feedback control system drives a secondary signal to destructively interfere with the original noise to cut down the noise power. An on‐line learning algorithm based on the error gradient descent method was proposed, and the local stability of closed loop system is proved using the discrete Lyapunov function. A nonlinear simulation example shows that the adaptive active noise feedback control method based on a neural network is very effective to the nonlinear noise control.
Extended Range of a Gun Launched Smart Projectile Using Controllable Canards
Authors: Costello Mark
Published: January 2014

This effort investigates the extent to which moveable canards can extend the range of indirect fire munitions using both projectile body and canard lift. Implications on terminal velocity and time of flight using this mechanism to extend range are examined for various canard configurations. Performance predictions are conducted using a six‐degree‐of‐freedom simulation model that has previously been validated against range data. The projectile dynamic equations are formed in the body frame and aerodynamic loads from the body and canards are Mach number and angle of attack dependent. The projectile body aerodynamic moments include unsteady aerodynamic damping. The focus of the study is directed toward low cost competent munitions that extend range and as such a simple flight control system is considered which utilizes only timer, roll rate, and roll attitude inputs.
Phase Plane Method for the Parameter Identification of Strongly Nonlinear Systems
Authors: Jiashi Tang
Published: January 2014

A phase plane method is presented for the parameter identification of strongly nonlinear systems. The phase trajectory equation is taken as the mathematical model and the system parameters are identified by using the optimum technique. The method can be applied to conservative and non‐conservative systems. The value ranges of the parameters are not limited. All examples simulated by computer show that the efficiency and accuracy of this approach are very good.
An Evaluation of Magneto Rheological Dampers for Controlling Gun Recoil Dynamics
Authors: Ahmadian Mehdi , Poynor James C.
Published: January 2014

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.
The Introduction of Spin to an Existing Flexible Shot Model within a Gun Dynamics Simulation
Authors: Bulman David N.
Published: January 2014

The paper describes the enhancement of an existing gun dynamics simulation package, to introduce spin to the flexible shot model. The original one or two piece flexible shot model was based on finite element beam theory, and therefore spin needed to take into account the moments of inertia at each node. Each node is therefore treated as an independently spinning body, each with its own spinning axes which can be related to the next node so that stiffness forces between them can be calculated. The stiffness coefficients are recalculated as deformation takes place, which is particularly important with long rod penetrators because of the high accelerations involved which induce buckling moments in the rod as it bends. The relationship between the nodes and the stiffness coefficients is maintained by updating the direction cosines for each node, plus a set for the overall beam.

The final model has been validated against known rigid model cases, by increasing stiffness until flexing is reduced. Comparisons have then been made with standard whirling cases.
Active Vibration Isolation Using an Induced Strain Actuator with Application to Automotive Seat Suspensions
Authors: Malowicki Mark , Leo Donald J.
Published: January 2014

Active vibration isolation of automotive seats requires actuators that achieve millimeter‐range displacements and forces on the order of 300 N. Recent developments in piezoceramic actuator technology provide a means for achieving these force and displacement levels in a compact device. This work demonstrates that prestressed, curved piezoceramic actuators achieve the force and displacement levels required for active isolation of automotive seats. An estimate of the force and displacement requirements are obtained from numerical simulations on a four‐degree‐of‐freedom car and seat model that utilize representive road accelerations as inputs. An actuator that meets these specifications is designed using piezoceramic materials. Free displacement of 4.4 mm and blocked force greater than 300 N are measured. The actuator is integrated within a dead mass setup that simulates the isolation characteristics of an automotive seat. Control experiments demonstrate that active vibration is achievable with realistic road disturbances. Feedback control is able to eliminate any amplification due to mechanical resonance and reduce the isolation frequency from 9.5 Hz to 2 Hz.
A Methodology for Characterizing Gun Barrel Flexure due to Vehicle Motion
Authors: Bundy Mark , Newill James , Marcopoli Vince , Ng Michael , Wells Charles
Published: January 2014

Barrel centerline curvature is known to influence the location of projectile shot impacts. Superimposed on the unique manufactured barrel centerline is the flexed barrel shape that can occur prior to firing while the vehicle is on the move. In order to understand and quantify the effects of barrel flexure on gun accuracy, it is necessary to determine what combination of fundamental mode shapes is most likely to occur. A method to accomplish this task is described in this paper. The method is demonstrated by enumerating the 10 most likely flexed barrel shapes that were found to occur in a tank‐mounted gun barrel while it traversed a bump course.
Experimental and Numerical Investigations on Deformation of Cylindrical Shell Panels to Underwater Explosion
Authors: Ramajeyathilagam K. , Vendhan C.P. , Rao V. Bhujanga
Published: January 2014

Experimental and numerical investigations on cylindrical shell panels subjected to underwater explosion loading are presented. Experiments were conducted on panels of size 0.8 × 0.6 × 0.00314 m and shell rise‐to‐span ratios h/l = 0.0, 0.05, 0.1 , using a box model set‐up under air backed conditions in a shock tank. Small charges of PEK I explosive were employed. The plastic deformation of the panels was measured for three loading conditions. Finite element analysis was carried out using the CSA/GENSA [DYNA3D] software to predict the plastic deformation for various loading conditions. The analysis included material and geometric non‐linearities, with strain rate effects incorporated based on the Cowper‐Symonds relation. The numerical results for plastic deformation are compared with those from experiments.
Modeling of Passive Constrained Layer Damping as Applied to a Gun Tube
Authors: Kiehl Margaret Z. , Jerzak C.P.T. Wayne
Published: January 2014

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.
A Study of Axial Impact of Composite Rods Using SPH Approach
Authors: Lam K.Y. , Shen Y.G. , Gong S.W.
Published: January 2014

A computational simulation of axial impact between composite rods is presented in this paper. The smoothed particle hydrodynamic (SPH) method is coded and implemented for this study, in which the property and strength for different materials are included. The SPH formulation for impact between rods as well as its computatinal procedure is also expounded. The present approach is used to study impact between composites rods parametrically. The effects of material properties and configurations of composite rod on impact response are then examined in detail. In addition, the present SPH results are compared with those from theoretical analysis.
Computational Treatments of Cavitation Effects in Near‐Free‐Surface Underwater Shock Analysis
Authors: Sprague Michael A. , Geers Thomas L.
Published: January 2014

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.
Modeling of Shock Propagation and Attenuation in Viscoelastic Components
Authors: Rusovici R. , Lesieutre G.A. , Inman D.J.
Published: January 2014

Protection from the potentially damaging effects of shock loading is a common design requirement for diverse mechanical structures ranging from shock accelerometers to spacecraft. High damping viscoelastic materials are employed in the design of geometrically complex, impact‐absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material behavior over a wide frequency range. The Anelastic Displacement Fields (ADF) method is employed herein to model frequency‐dependence within a time‐domain finite element framework. Axisymmetric, ADF finite elements are developed and then used to model shock propagation and absorption through viscoelastic structures. The model predictions are verified against longitudinal wave propagation experimental data and theory.
Free Vibration Characteristics of Cylindrical Shells Using a Wave Propagation Method
Authors: Ghoshal A. , Parthan S. , Hughes D. , Schulz M.J.
Published: January 2014

In the present paper, concept of a periodic structure is used to study the characteristics of the natural frequencies of a complete unstiffened cylindrical shell. A segment of the shell between two consecutive nodal points is chosen to be a periodic structural element. The present effort is to modify Mead and Bardell′s approach to study the free vibration characteristics of unstiffened cylindrical shell. The Love‐Timoshenko formulation for the strain energy is used in conjunction with Hamilton′s principle to compute the natural propagation constants for two shell geometries and different circumferential nodal patterns employing Floquet′s principle. The natural frequencies were obtained using Sengupta′s method and were compared with those obtained from classical Arnold‐Warburton′s method. The results from the wave propagation method were found to compare identically with the classical methods, since both the methods lead to the exact solution of the same problem. Thus consideration of the shell segment between two consecutive nodal points as a periodic structure is validated. The variations of the phase constants at the lower bounding frequency for the first propagation band for different nodal patterns have been computed. The method is highly computationally efficient.
Lessons Learned on the Application of Vibration Absorbers for Enhanced Cannon Stabilization
Authors: Kathe Eric
Published: January 2014

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.
Fatigue Failure Results for Multi‐Axial versus Uniaxial Stress Screen Vibration Testing
Authors: Whiteman Wayne E. , Berman Morris S.
Published: January 2014

To date, the failure potential and prediction between simultaneous multi‐axial versus sequentially applied uniaxial vibration stress screen testing has been the subject of great debate. In most applications, current vibration tests are done by sequentially applying uniaxial excitation to the test specimen along three orthogonal axes. The most common standards for testing military equipment are published in MIL‐STD‐810F and NAVMAT P‐9492. Previous research had shown that uniaxial testing may be unrealistic and inadequate. This current research effort is a continuing effort to systematically investigate the differences between fatigue damage mechanisms and the effects of uniaxial versus tri‐axial testing. This includes assessing the ability of the tri‐axial method in predicting the formation of damage mechanisms, specifically looking at the effects of stress or fatigue failure. Multi‐axial testing achieves the synergistic effect of exciting all modes simultaneously and induces a more realistic vibration stress loading condition. As such, it better approximates real‐world operating conditions. This paper provides the latest results on the differences between multi‐axial and uniaxial testing of a simple notched cantilever beam.
Obtaining Mode Shapes through the Karhunen‐Loève Expansion for Distributed‐Parameter Linear Systems
Authors: Wolter Claudio , Trindade Marcelo A. , Sampaio Rubens
Published: January 2014

The Karhunen‐Loève expansion is a powerful spectral technique for the analysis and synthesis of dynamical systems. It consists in decomposing a spatial correlation matrix, which can be obtained through numerical or physical experiments. The decomposition produces orthogonal eigenfunctions or proper orthogonal modes, and eigenvalues that provide a measurement of how much energy is contained in each mode. The relation between KL modes and mode shapes of linear vibrating systems has already been derived and demonstrated for two and three dofs mass‐spring‐damper systems. The purpose of this paper is to extend this investigation to more complex distributed‐parameter linear systems. A plane truss and a simply supported plate subjected to impulsive forces, commonly used in modal analysis are studied. The resulting KL modes are compared to the analytical mode shapes. Damping and random noise effects in the procedure performance are evaluated. Two methods for indirectly obtaining natural frequencies are also presented.
An Introduction to the Composite Element Method Applied to the Vibration Analysis of Trusses
Authors: Arndt Marcos , Machado Roberto Dalledone , Hecke Mildred Ballin
Published: January 2014

This paper introduces a new type of Finite Element Method (FEM), called Composite Element Method (CEM). The CEM was developed by combining the versatility of the FEM and the high accuracy of closed form solutions from the classical analytical theory. Analytical solutions, which fulfil some special boundary conditions, are added to FEM shape functions forming a new group of shape functions. CEM results can be improved using two types of approach: h‐version and c‐version. The h‐version, as in FEM, is the refinement of the element mesh. On the other hand, in the c‐version there is an increase of degrees of freedom related to the classical theory (c‐dof). The application of CEM in vibration analysis is thus investigated and a rod element is developed. Some samples which present frequencies and vibration mode shapes obtained by CEM are compared to those obtained by FEM and by the classical theory. The numerical results show that CEM is more accurate than FEM for the same number of total degrees of freedom employed. It is observed in the examples that the c‐version of CEM leads to a super convergent solution.
Vibration Pattern Related to Transverse Cracks in Rotors
Authors: Bachschmid Nicolò , Tanzi Ezio
Published: January 2014

A method for calculating the breathing behavior of transverse cracks of different types in rotating shafts is described. Thermal effects are included. Some results in terms of vibration excitation related to different shapes of cracks are presented.
Vent Control as a Means of Enhancing Airbag Performance
Authors: Zimmermann Richard E.
Published: January 2014

Typical automotive airbag systems have a fixed area vent for exiting gasses. The US Army Cockpit Airbag System (CABS) is unvented to prolong the period during which the system can provide occupant protection during extended helicopter crash scenarios. In each application, system performance may be enhanced by providing a controlled vent area. This paper describes work conducted under a Phase I SBIR program sponsored by the NASA Langley Research Center. The work was focused on eventual inflatable restraint system applications in general aviation aircraft, and showed that appropriate vent control offers many enhancements. Two series of tests conducted during Phase I showed that inflatable restraint system size and weight can be reduced without degrading performance, injury potential in an out of position situation (OOPS) deployment can be reduced, and peak bag pressures can be reduced (at any temperature) during normal operation.
Prehension and Perception of Size in Left Visual Neglect
Authors: McIntosh R. D. , Pritchard C. L. , Dijkerman H. C. , Milner A. D. , Roberts R. C.
Published: January 2014

Right hemisphere damaged patients with and without left visual neglect, and age‐matched controls had objects of various sizes presented within left or right body hemispace. Subjects were asked to estimate the objects’ sizes or to reach out and grasp them, in order to assess visual size processing in perceptual‐experiential and action‐based contexts respectively. No impairments of size processing were detected in the prehension performance of the neglect patients but a generalised slowing of movement was observed, associated with an extended deceleration phase. Additionally both patient groups reached maximum grip aperture relatively later in the movement than did controls. For the estimation task it was predicted that the left visual neglect group would systematically underestimate the sizes of objects presented within left hemispace but no such abnormalities were observed. Possible reasons for this unexpected null finding are discussed.
Impaired Initiation But Not Execution of Contralesional Saccades in Hemispatial Neglect
Authors: Behrmann Marlene , Ghiselli-Crippa Thea , Dimatteo Ilaria
Published: January 2014

Patients with unilateral neglect are impaired at making saccades to contralesional targets. Whether this problem arises from a deficit in perception, in planning the saccade or in executing the eye movement or some combination thereof remains unclear. We measured several variables related to the initiation and execution of saccades in an experiment which crossed two factors: target side (left, right) and direction of saccade (leftwards, rightwards). Relative to control subjects, patients with left‐sided neglect were impaired in planning but not executing the contralesional saccade; while the latency to move their eyes following the onset of the target was increased, the duration and velocity to reach the target were normal. In addition, there were also no directional differences for saccades that were hypometric or inaccurate in the patients, further ruling out an execution impairment. Interestingly, this directional initiation deficit was exaggerated for leftward saccades to left targets, compared with all other conditions. We suggest that the disadvantage for contralesional saccades in neglect patients is attributable to a deficit not only in perceiving contralateral targets but also in planning leftward saccades. Once the saccade is initiated, however, execution apparently proceeds unimpaired.
Vibration Measurements by Tracking Laser Doppler Vibrometer on Automotive Components
Authors: Castellini P.
Published: January 2014

This paper describes the application of a Tracking Laser Doppler Vibrometer (TLDV) to the measurement of vibration of some typical automotive component.

After a presentation and discussion of the measurement technique, the attention is focused on the development of specific version optimised for each application.

The first component analysed is the sidewall of a tire during its rotation in a typical drum test‐bench. An optimised version of the TLDV was developed for the specific application adding a trajectory assessment tool based on image analysis, in order to fulfil the accuracy specifications imposed by tire manufacturer.

The second automotive component is a timing belt.

This application presents problems related to the high‐speed linear motion and to data processing for noise rejection. The third application is on windscreen wipers. In this case the tracking approach fully demonstrate his capabilities, representing the only technique able to give information in the time domain on the dynamic behaviour of the rubber blade in operative conditions.

All the application shows as the TLDV allows to obtain realistic results on the dynamic characteristics under simulated operative conditions.

A Lagrangian approach was adopted: data were acquired with the target in continuously changing conditions and that impose a not traditional approach on LDV data such as a joint time‐frequency analysis.