离散元模拟中颗粒材料剪切波速的剪切振动确定方法
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摘要
砂土等颗粒材料的剪切波速是反映其工程性质的重要参数,离散元模拟中实现剪切波速实时测试对研究砂土材料力学性质变化的细观机理具有重要意义。本文基于软件PFC3D,在试样模型中设置激发源和接收源,通过对激发源施加产生剪切振动的速度脉冲、在接收源监测扰动信号,实现了剪切波在颗粒材料中的传播模拟和信号监测,提出了利用激发和接收信号的互相关系数确定剪切波传播时间和评价剪切波传播质量的方法。系统分析了激发频率、激发幅值、激发源和接收源尺寸、阻尼等因素对剪切波速测定的影响,给出了合理的参数取值范围。研究结果得到了均匀颗粒试样理论解的验证。
Shear wave velocity is an important parameter to reflect the engineering properties of granular materials like sand.The measurement of shear wave velocity throughout the discrete element simulation is of great significance to understand the microscopic mechanism of variation of the mechanical properties.Numerical simulation of shear wave propagation using DEM is implemented by applying a velocity pulse to the transmitter in a certain direction and monitoring the corresponding average velocity of the receiver.The cross-correlation analysis is adopted due to its superiority of both determining the travel time and identifying similarities between two signals.The shear wave velocity is calculated using the wave travel time and the distance of the travel path,in exactly the same way as in laboratory tests.The influencing factors including excitation frequency,excitation amplitude,size of transmitter and receiver as well as damp are carefully analyzed,and reasonable values of the parameters for shear wave modeling are proposed.It is found that the appropriate excitation amplitude should be chosen on the basis of avoiding the generation of frictional work.It is also indicated that fruitful results will be obtained if both the radius of transmitter and receiver are chosen as one half of that of DEM specimen's.The research results are verified through the outcomes of even-particle assemblies.
Shear wave velocity is an important parameter to reflect the engineering properties of granular materials like sand.The measurement of shear wave velocity throughout the discrete element simulation is of great significance to understand the microscopic mechanism of variation of the mechanical properties.Numerical simulation of shear wave propagation using DEM is implemented by applying a velocity pulse to the transmitter in a certain direction and monitoring the corresponding average velocity of the receiver.The cross-correlation analysis is adopted due to its superiority of both determining the travel time and identifying similarities between two signals.The shear wave velocity is calculated using the wave travel time and the distance of the travel path,in exactly the same way as in laboratory tests.The influencing factors including excitation frequency,excitation amplitude,size of transmitter and receiver as well as damp are carefully analyzed,and reasonable values of the parameters for shear wave modeling are proposed.It is found that the appropriate excitation amplitude should be chosen on the basis of avoiding the generation of frictional work.It is also indicated that fruitful results will be obtained if both the radius of transmitter and receiver are chosen as one half of that of DEM specimen's.The research results are verified through the outcomes of even-particle assemblies.
引文
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[3]TRENT B C,MARGOLIN L G.A numerical laboratory for granular solids[J].Engineering Computations,1992,9:191–197.
[4]LI L,HOLT R M.Particle scale reservoir mechanics[J].Oil&Gas Science and Technology,2002,57(5):525–538.
[5]郭易圆,李世海.有限长岩柱中纵波传播规律的离散元数值分析[J].岩石力学与工程学报,2002,21(8):1124–1129.(GUO Yi-yuan,LI Shi-hai.Distinct element analysis on propagation characteristics of P-wave in rock pillar with finite length[J].Chinese Journal of Rock Mechanics and Engineering,2002,21(8):1124–1129.(in Chinese))
[6]TOOMEY A,BEAN C J.Numerical simulation of seismic waves using a discrete particle scheme[J].Geophysical Journal International,2000,141:595–604.
[7]HAZZARD J F,YOUNG R P.Simulating acoustic emissions in bonded-particle models of rock[J].International Journal of Rock Mechanics and Mining Sciences,2000,37:867–872.
[8]THOMAS C N,BESKOU S P,MYLONAKIS G.Wave dispersion in dry granular materials by distinct element method[J].Soil Dynamics and Earthquake Engineering,2009,29:888–897.
[9]SADD M H,TAI Q M,SHUKLA A.Contact law effects on wave propagation in particulate materials using distinct element modeling[J].International Journal of Non-linear Mechanics,1993,28(2):251–265.
[10]SADD M H,GAO J,SHUKLA A.Numerical analysis of wave propagation through assemblies of elliptical particles[J].Computers and Geotechnics,1997,20(3/4):323–343.
[11]SADD M H,ADHIKARI G,CARDOSO F.DEM simulation of wave propagation in granular materials[J].Powder Technology,2000,109:222–233.
[12]HOLT R M,KJOLAAS J,LARSEN I,et al.Comparison between controlled laboratory experiments and discrete particle simulations of the mechanical behavior of rock[J].International Journal of Rock Mechanics and Mining Sciences,2005,42:985–995.
[13]Itasca Consulting Group Inc.Manual of particle flow code in 3-dimension[M].Version 4.0,Minnesota,2008.
[14]PENNINGTON D S,NASH D F T,LINGS M L.Horizontally mounted bender elements for measuring anisotropic shear moduli in triaxial clay specimens[J].ASTM Geotechnical Testing Journal,2001,24(2):133–144.
[15]AHN J,BISCONTIN G,ROESSET J M.Wave propagation in nonlinear one-dimensional soil model[J].International Journal for Numerical and Analytical Methods in Geomechanics,2009,33:487–509.
[16]SANTAMARINA J C,FRATTA D.Introduction to discrete signals and inverse problems in civil engineering[M].Virginia:ASCE Press,1998.
[17]SANTAMARINA J C,KLEIN K A,FAM M A.Soils and waves[M].NewYork:John Wiley&Sons,LTD,2001.
[18]WALTON K.The effective elastic moduli of a random packing of spheres[J].Journal of the Mechanics and Physics of Solids,1987,35(2):213–226.
[19]ODA M,KAZAMA H.Microstructure of shear bands and its relation to the mechanisms of dilatancy and failure of dense granular soils[J].Géotechnique,1998,48(4):465–481.
[20]孙其诚,王光谦.颗粒物质力学导论[M].北京:科学出版社,2009.(SUN Qi-cheng,WANG Guang-qian.Introduction to the mechanism of granular materials[M].Beijing:Science Press,2009.(in Chinese))
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