Effect of Finite Rotation on the Propagation of Elastic Waves in Constrained Mechanical Systems

1992 ◽  
Vol 114 (3) ◽  
pp. 384-393 ◽  
Author(s):  
Wei-Hsin Gau ◽  
A. A. Shabana
Keyword(s):  
Phase Velocity ◽  
Material Properties ◽  
Elastic Waves ◽  
Wave Motion ◽  
Coefficient Of Restitution ◽  
Wave Number ◽  
Harmonic Waves ◽  
Finite Rotation ◽  
Phase Velocities ◽  
The Impact

In structural systems, impact-induced longitudinal elastic waves travel with finite speeds that depend on the material properties. Using Fourier method of analysis, the exact wave motion can be described as the sum of infinite number of harmonic waves which have the same phase velocity. In this case the medium is said to be nondispersive, since the phase velocities of the harmonic waves are equal and equal to the group velocity of the resulting wave motion. In mechanism systems with intermittent motion, on the other hand, elastic members undergo finite rotations. In this investigation, the effect of the finite rotation, coefficient of restitution, and impact conditions on the propagation of the impact-induced waves in costrained elastic systems is examined. The system equations of motion are developed using the principle of virtual work in dynamics. The jump discontinuities in the system variables as the result of impact are predicted using the generalized impulse momentum equations that involve the coefficient of restitution. It is shown that the phase velocities of different harmonic waves are no longer equal, that is, dispersion occurs in perfectly elastic mechanism members as the result of the finite rotation. The analysis presented in this paper shows that the finite rotation has more significant effect on the phase velocity of the low frequency harmonics as compared to the high frequency harmonics. A rotation-wave number that depends on the material properties and the wave length is defined for each harmonic wave. It is shown that if the angular velocity of the elastic member becomes large such that the rotation-wave number of a mode exceeds one, the associated modal displacement is no longer oscillatory.

SIMULATION OF DYNAMIC EVENT OF IMPACT USING EXPLICIT 3D FEM MODEL AND VALIDATION BY EXPERIMENT AND CONTACT MODELS

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Akshay Mallikarjuna ◽  
Dan Marghitu ◽  
P.K. Raju
Keyword(s):  
Material Properties ◽  
Permanent Deformation ◽  
Oblique Impact ◽  
Coefficient Of Restitution ◽  
Impact Behavior ◽  
3D Fem ◽  
Dynamic Event ◽  
Contact Models ◽  
Explicit Dynamic ◽  
The Impact

— In this study, an optimized method to simulate the dynamic 3D event of the impact of a rod with a flat surface has been presented. Unlike the 2D FEM based contact models, in this study both the bodies undergoing the impact are considered elastic(deformable) and simulation is the dynamic event of the impact, instead of predefined 2D symmetric contact analysis. Prominent contact models and plasticity models to define material properties in ANSYS are reviewed. Experimentation results of normal and oblique impact of the rod for different rods provided the coefficient of restitution. Experimental results of permanent deformation on the base for different impact velocity is derived out of a prominent impact study. The simulation results are in co-relation with experiment and both indentation and flattening models on the coefficient of restitution (COR) and permanent deformation of the base and rod after the impact. Thus, the presented 3D Explicit Dynamic simulation of impact is validated to analyze the impact behavior of the 2 bodies without any predefined assumptions with respect to boundary conditions or material properties.

Phase velocity effects in tertiary wave interactions

1962 ◽  
Vol 12 (3) ◽  
pp. 333-336 ◽  
Author(s):  
M. S. Longuet-Higgins ◽  
O. M. Phillips
Keyword(s):  
Phase Velocity ◽  
Continuous Spectrum ◽  
Deep Water ◽  
Wave Train ◽  
The Other ◽  
Wave Number ◽  
Wave Interactions ◽  
Single Wave ◽  
Phase Velocities ◽  
Wave Trains

It is shown that, when two trains of waves in deep water interact, the phase velocity of each is modified by the presence of the other. The change in phase velocity is of second order and is distinct from the increase predicted by Stokes for a single wave train. When the wave trains are moving in the same direction, the increase in velocity Δc2 of the wave with amplitude a2, wave-number k2 and frequency α2 resulting from the interaction with the wave (a1, k1, σ1) is given by Δc2 = a21k1σ1, provided k1 < k2. If k1 > k2, then Δc2 is given by the same expression multiplied by k2/k1. If the directions of propagation are opposed, the phase velocities are decreased by the same amount. These expressions are extended to give the increase (or decrease) in velocity due to a continuous spectrum of waves all travelling in the same (or opposite) direction.

Evaluation of Elastic-Plastic Rebound Properties of Coal Fly Ash Particles for Use in a Universal Turbine Deposition Model

2015 ◽  
Author(s):  
Steven M. Whitaker ◽  
Jeffrey P. Bons
Keyword(s):  
Experimental Data ◽  
Yield Stress ◽  
Material Properties ◽  
Coal Fly Ash ◽  
Impact Angle ◽  
Coefficient Of Restitution ◽  
Deposition Model ◽  
Mechanics Model ◽  
The Impact ◽  
Impact Models

Three particle impact models have been evaluated to determine their ability to predict particle material properties and restitution coefficients using experimental data for the coefficient of restitution of particles impacting a 410 stainless steel plate. The particles consisted of PMMA and three coal fly ashes: JBPS, Bituminous, and Lignite. Particle speeds ranged from approximately 20 to 120 meters per second, and the nominal impact angle was approximately 85 degrees. Flow temperatures for the ash particulate experiments were set at 295 K and 395 K. The impact models were applied to the experimental data via curve fitting to evaluate the yield stress of the particulate, which was known for the PMMA. For the ash particulate, a linear law of mixtures was used to approximate the modulus of elasticity and Poisson’s ratio for use in the yield stress determination. A Hertzian mechanics model was shown to over-predict the yield stress of the PMMA particulate, indicating that, for known material properties, they would under-predict the coefficient of restitution. A Plastic-JKR model and a finite element based model by Wu et al. showed good agreement between the calculated yield stress and known range of yield stress values for the PMMA particulate, indicating that the model would accurately predict restitution coefficients for particulate with known material properties (or could be used to accurately determine the material properties from experimental coefficient of restitution data). However, some questions remain as to the ability of these models to be used for non-spherical, conglomerate type particulate. A thorough overview of the impact process is provided, and the application of the results of the study to the development of a physics-based universal impact and deposition model is presented.

Probing the impact of material properties of core-shell SiO2@TiO2 spheres on the plasma-catalytic CO2 dissociation using a packed bed DBD plasma reactor

2021 ◽  
Vol 46 ◽  
pp. 101468
Author(s):  
Periyasamy Kaliyappan ◽  
Andreas Paulus ◽  
Jan D’Haen ◽  
Pieter Samyn ◽  
Yannick Uytdenhouwen ◽  
...  
Keyword(s):  
Material Properties ◽  
Plasma Reactor ◽  
Packed Bed ◽  
Core Shell ◽  
Dbd Plasma ◽  
The Impact

scholarly journals A FEM-Based 2D Model for Simulation and Qualitative Assessment of Shot-Peening Processes

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2784
Author(s):  
Georgios Maliaris ◽  
Christos Gakias ◽  
Michail Malikoutsakis ◽  
Georgios Savaidis
Keyword(s):  
Process Parameters ◽  
Material Properties ◽  
Shot Peening ◽  
Qualitative Assessment ◽  
Experimental Investigations ◽  
Elastoplastic Material ◽  
Size Distributions ◽  
User Friendly ◽  
The Impact ◽  
2D Model

Shot peening is one of the most favored surface treatment processes mostly applied on large-scale engineering components to enhance their fatigue performance. Due to the stochastic nature and the mutual interactions of process parameters and the partially contradictory effects caused on the component’s surface (increase in residual stress, work-hardening, and increase in roughness), there is demand for capable and user-friendly simulation models to support the responsible engineers in developing optimal shot-peening processes. The present paper contains a user-friendly Finite Element Method-based 2D model covering all major process parameters. Its novelty and scientific breakthrough lie in its capability to consider various size distributions and elastoplastic material properties of the shots. Therewith, the model is capable to provide insight into the influence of every individual process parameter and their interactions. Despite certain restrictions arising from its 2D nature, the model can be accurately applied for qualitative or comparative studies and processes’ assessments to select the most promising one(s) for the further experimental investigations. The model is applied to a high-strength steel grade used for automotive leaf springs considering real shot size distributions. The results reveal that the increase in shot velocity and the impact angle increase the extent of the residual stresses but also the surface roughness. The usage of elastoplastic material properties for the shots has been proved crucial to obtain physically reasonable results regarding the component’s behavior.

Adaptive Predictive Based on Equal-Dimension and New Information for the Hydraulic Mechanism of Wave Motion Compensating Platform

2010 ◽  
Vol 20-23 ◽  
pp. 236-242 ◽  
Author(s):  
Zhi Gang Zeng ◽  
Guo Hua Chen
Keyword(s):  
Predictive Control ◽  
Wave Motion ◽  
Control Policy ◽  
Least Square ◽  
Problem Solution ◽  
New Information ◽  
Hydraulic Mechanism ◽  
Heave Motion ◽  
Adaptive Predictive Control ◽  
The Impact

A wave motion compensating platform has the function of compensating the ship’s generalized heave motion (a coupling result of roll, pitch and heave). It can decrease the impact of ship motion on some sea works and equipments. The hydraulic mechanism of platform system has the characteristics of nonlinear and big inertia. In order to compensate generalized heave motion effectively, an adaptive predictive control policy is used for controlling the hydraulic mechanism. Based on equal-dimension and new information, an automation regressive model can get adaptive multi-step prediction. The model parameter estimation based on the least square algorithm is easy to blow up and be unstable when the system has random noise. To improve the problem solution, a damped recursive least square algorithm is proposed to estimate the parameters on line. For the short regulation time, strong anti-disturbance ability and great robustness, a nonlinear PID controller whose gain parameters vary with errors is suitable for controlling the hydraulic mechanism. Using the collected experimental data, the simulations suggest that adopting the above adaptive predictive control policy to control hydraulic mechanism is able to decrease the generalized heave amplitude of wave motion compensating platform.

Finite-Difference Modeling and Characteristics Analysis of Love Waves in Anisotropic-Viscoelastic Media

2021 ◽  
Author(s):  
Shichuan Yuan ◽  
Zhenguo Zhang ◽  
Hengxin Ren ◽  
Wei Zhang ◽  
Xianhai Song ◽  
...  
Keyword(s):  
Finite Difference ◽  
Phase Velocity ◽  
Velocity Dispersion ◽  
Love Waves ◽  
Velocity Anisotropy ◽  
Viscoelastic Media ◽  
Phase Velocities ◽  
Phase Velocity Dispersion ◽  
Anisotropic Elastic ◽  
Attenuation Anisotropy

ABSTRACT In this study, the characteristics of Love waves in viscoelastic vertical transversely isotropic layered media are investigated by finite-difference numerical modeling. The accuracy of the modeling scheme is tested against the theoretical seismograms of isotropic-elastic and isotropic-viscoelastic media. The correctness of the modeling results is verified by the theoretical phase-velocity dispersion curves of Love waves in isotropic or anisotropic elastic or viscoelastic media. In two-layer half-space models, the effects of velocity anisotropy, viscoelasticity, and attenuation anisotropy of media on Love waves are studied in detail by comparing the modeling results obtained for anisotropic-elastic, isotropic-viscoelastic, and anisotropic-viscoelastic media with those obtained for isotropic-elastic media. Then, Love waves in three typical four-layer half-space models are simulated to further analyze the characteristics of Love waves in anisotropic-viscoelastic layered media. The results show that Love waves propagating in anisotropic-viscoelastic media are affected by both the anisotropy and viscoelasticity of media. The velocity anisotropy of media causes substantial changes in the values and distribution range of phase velocities of Love waves. The viscoelasticity of media leads to the amplitude attenuation and phase velocity dispersion of Love waves, and these effects increase with decreasing quality factors. The attenuation anisotropy of media indicates that the viscoelasticity degree of media is direction dependent. Comparisons of phase velocity ratios suggest that the change degree of Love-wave phase velocities due to viscoelasticity is much less than that caused by velocity anisotropy.

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