刚性平压头作用下双重孔隙介质半平面接触问题

针对刚性平压头与双重孔隙介质半平面接触时的静力响应展开研究。基于Biot型双重孔隙介质弹性理论及接触边界条件建立基本求解方程;考虑Fourier积分变换域内特征值的特性,再通过求解柯西积分方程,得到了问题频域内的解析解,包括应力场、位移场。利用Fourier逆变换进行数值求解,分析了基质孔隙与裂隙孔隙之间交互作用对接触表面附近力学响应的影响规律。结果表明:随着两种孔隙率的增大,竖向位移和孔隙压力随之增大,而竖向正应力则减小,且基质孔隙率的影响较为显著。     

地下爆炸气体输运的一种双孔隙度数学模型

考虑气体在压力驱动下的渗透、气体和岩体的热传导以及气体的扩散,建立了用于模拟地下爆炸气体输运的二维轴对称双孔隙度双渗透率数学模型,并编制了数值模拟程序;研究了参数在取值范围内变化对计算结果的影响。结果显示：泄漏到地表的气体随着裂隙区域圆心角的增大而先增大后减小,随裂隙渗透率的增大而增大,随介质孔隙度和孔隙渗透率的增大而减小。用该模型对一次砂砾岩中地下爆炸实验气体的泄漏行为进行了数值模拟。将数值模拟结果与气体泄漏实测结果进行对比,反推出当地介质的裂隙渗透率在4×10^-11 m2～5×10^-11 m2之间。利用反推得到的介质参数,可以对同类介质中地下爆炸气体泄漏行为进行预测。     

液氮作用下煤样结构损伤规律研究

为研究液氮浸泡对低渗煤体结构损伤增透的影响,对不同尺寸煤样进行周期性液氮浸泡实验。通过CT扫描观测煤样浸泡前后内部孔隙、裂隙变化情况,采用高倍照相机观测煤样表面形貌,利用超声测速仪测定煤样波速变化,分析液氮浸泡周期对不同尺寸煤样内部结构损伤规律的影响,提出了液氮作用下煤样损伤模型,解释了液氮作用下煤样损伤机理。结果表明:同尺寸煤样,其内部孔隙率、表面裂隙尺寸及波速衰减率随液氮作用周期数的增加而增大,煤样损伤加剧;同周期浸泡条件下,随着煤样尺寸的增大,液氮作用后的煤样孔隙率逐渐降低;液氮作用周期为1T时,煤样孔隙率增加相对显著,损伤效果明显,1T后煤样孔隙率增加幅度逐渐减小;液氮的超低温作用使煤岩基质收缩,煤岩内部产生新微孔隙,多次作用后,微孔隙发育、扩展和贯通使煤岩出现宏观裂纹并发生破坏。     

基于孔与裂隙网络模型的平行微裂隙对驱油的影响规律研究

认识双重多孔介质中油水两相微观渗流机制是回答形成什么类型的裂隙网络可提高油藏采收率的关键. 微裂隙的分布可以提高多孔介质的绝对渗透率,但对于基质孔隙中的流体介质,微裂隙的存在会引起多孔介质中局部流体压力和流场的变化,导致局部流动以微裂隙流动为主,甚至出现窜流现象,降低驱油效率. 本文基于孔与裂隙双重网络模型,在网络进口设定两条平行等长且具有一定间隔的微裂隙,分析微裂隙的相对间隔(微裂隙之间距离/喉道长度)和微裂隙相对长度(微裂隙长度/喉道长度)对于微观渗流特征的影响. 结果表明:随微裂隙相对长度的增加,出现驱油效率逐渐降低,相对渗透率曲线中的油水共渗区水饱和度和等渗点增加,油水两相的共渗范围减小等现象;随着微裂隙之间相对间隔增大,周围越来越多的基质孔穴间的压力差减小,在毛管压力的限制下,驱替相绕过这些区域,而导致水窜现象.      

基于孔与裂隙网络模型的平行微裂隙对驱油的影响规律研究

认识双重多孔介质中油水两相微观渗流机制是回答形成什么类型的裂隙网络可提高油藏采收率的关键.微裂隙的分布可以提高多孔介质的绝对渗透率,但对于基质孔隙中的流体介质,微裂隙的存在会引起多孔介质中局部流体压力和流场的变化,导致局部流动以微裂隙流动为主,甚至出现窜流现象,降低驱油效率.本文基于孔与裂隙双重网络模型,在网络进口设定两条平行等长且具有一定间隔的微裂隙,分析微裂隙的相对间隔(微裂隙之间距离/喉道长度)和微裂隙相对长度(微裂隙长度/喉道长度)对于微观渗流特征的影响.结果表明:随微裂隙相对长度的增加,出现驱油效率逐渐降低,相对渗透率曲线中的油水共渗区水饱和度和等渗点增加,油水两相的共渗范围减小等现象;随着微裂隙之间相对间隔增大,周围越来越多的基质孔穴间的压力差减小,在毛管压力的限制下,驱替相绕过这些区域,而导致水窜现象.     

波在双孔隙与单孔隙介质界面上的反射与透射

基于Biot理论和双重孔隙介质理论研究了弹性波在双重孔隙介质与流体饱和单一孔隙介质 界面的反射和透射问题，在界面上假定裂缝孔隙流体相对于固体骨架的位移为零，推导了反 射系数和透射系数的计算公式，数值讨论了反射系数和透射系数随入射角和频率的变化关 系. 同时，讨论了双重孔隙介质中3种压缩波(P-1, P-2和P-3波)和一种剪切波(S波) 的频散和衰减特性.     

基于逾渗理论的机械密封界面静态泄漏预测方法

针对现有机械密封泄漏机理研究存在的不足,利用Hertz理论研究机械密封界面接触力学问题,揭示了孔隙率随端面形貌、端面载荷等参数的变化规律;基于逾渗理论,探讨了不同网格层数下密封界面的逾渗阈值与孔隙率的关系,建立了密封界面泄漏通道模型,以及泄漏率与端面形貌参数关系表达式;研制了机械密封静态泄漏测试装置,测试了6组不同端面形貌试件在一定介质压力下的泄漏率.结果表明:密封界面的初始孔隙率?0随着分形维数D的增大而增大;端面比压pc增大,孔隙率?减小,并随着D的增大和尺度系数G的减小,?快速减小,直至填实.在端面比压作用下,密封界面的孔隙率均大于0.593,密封界面泄漏通道可以简化为单层网格逾渗模型.密封环的表面越粗糙,其密封界面的孔隙率越大,而由孔隙连通形成的泄漏微通道孔喉尺寸就越大,致使密封界面的泄漏率越大;泄漏率理论预测值与试验结果具有良好的吻合度,验证了本文泄漏预测方法的合理性.     

斜拉桥塔-索-桥面连续耦合参数振动特性分析

针对端部激励作用下斜拉索与桥塔、桥面协同振动问题,考虑拉索几何非线性、倾角、阻尼以及拉索重力弦向分力的影响,引入拉索高精度抛物线形,建立了桥塔-索-桥面连续非线性精细化振动模型,推导了拉索与桥塔和桥面共同在激励作用下的耦合振动方程组,研究了桥塔-索-桥面结构系统参数的振动特性,并用数值仿真方法分析桥面与拉索频率比、桥面激励幅值、索力及拉索阻尼对结构耦合振动特性的影响规律。结果表明:桥面与拉索的频率比分别为1∶2和2∶1时,拉索会发生不同模式的大幅振动;相比于超谐波共振模式,亚谐波共振模式的拉索振幅更大,但达到共振所需时间较长;拉索振幅随桥面激励幅值的增大呈非线性增大,桥面激励幅值越大,拉索积蓄共振能量所需的时间越短;拉索振幅随索力增大而减小;拉索自身阻尼对其振动的影响较小,增大拉索阻尼时,拉索振幅虽有减小趋势,但是减小幅度有限。     

小长高比腔体内的摆动行波

通过流体力学基本方程组的数值模拟,探讨了具有Soret效应(分离比ψ=?0.47)和小长高比(Γ=8)腔体中混合流体摆动行波对流的动力学特性。研究表明:在相对瑞利数r3.467时系统出现了行波状态;在r=3.647～6.227的范围内,发现了摆动行波对流;且对流振幅随着时间的变化存在两种不同特性,其摆动周期随瑞利数r增大而减小,对流振幅和努塞尔数随瑞利数r增大而增加;当r增大到r=6.228时,摆动行波过渡到定常对流状态。因此,在行波对流向定常对流过渡的过程中存在摆动行波对流.     

流体饱和弹性半空间裂隙对平面P_I波的衍射

采用间接边界元法,求解了饱和半空间裂隙对平面PI波的二维衍射问题。基于单层位势理论,将边界离散并直接在边界单元上施加虚拟荷载(水平作用力、竖向作用力和流量源的叠加)以构造散射波场,并由边界条件确定虚拟荷载密度,总波场由自由波场和散射波场共同组成。通过参数分析研究了入射波频率、入射倾角、埋深、孔隙率、边界渗透条件等因素对饱和半空间中裂隙对平面PI波衍射的影响规律。结果表明:裂隙随埋深增大,地表位移谱振荡加剧,峰值有所降低;随着入射频率增加,孔隙率影响逐渐增大;垂直入射时,水平位移的放大区域主要分布在裂隙两端,斜入射时,主要集中在裂隙正上方地表附近;透水和不透水两种情况下的地表位移幅值和相位差别较小,但干土情况与饱和情况下的位移幅值相差较大。     

Force Action of a Body with a Permeable Boundary on a Wall in a Fluid

The ideal fluid flow due to fluid penetration through the boundary of an infinitely long solid cylinder in contact with a solid wall is determined. A formula is derived according to which the force exerted by a finite-length part of the cylinder on the wall is directed into the wall and can thus have an arbitrarily large absolute value. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 82–84, January–February, 2006.     

On a Paradox in the Motion of a Rigid Particle along a Wall in a Fluid

The results of an experimental investigation of spherical particles with different surface roughnesses rolling under their own weight down an inclined pipe wall in a Newtonian fluid at low Reynolds numbers, both with (friction should be taken into account) and without contact with the wall, are presented. It is shown that a fixed particle moves differently in different fluids with similar viscosities and densities. This fact, as well as the possibility of particle motion without contact with the wall, cannot be explained within the framework of the usual hydrodynamic theories. An example is the dependence of the particle motion on the static pressure.     

Simulation by a source of a thin jet from a body

An exact analytic solution is found to the following plane hydrodynamic problem. An unbounded flow of an ideal incompressible fluid flows around a plate BB' placed at right angles to the velocity vector of the flow at infinity. The pressure on the free boundary P is equal to the pressure in the flow. From an opening in the center of the plate, a jet with flow rate Q from a cavity with pressure P₀ encounters the flow head-on. As a result of the solution, it is found that for fixed width of the opening the values of Q allowed by the scheme are limited. In the limiting case Q = 0 Chaplygin's flow is obtained with stagnation region at the front [1], and in the limiting case Q = Q_max a jet out of a cavity with pressure P₀ into a cavity with pressure P. As Q varies in this interval, the total drag, regarded as the drag of the plate and the chamber from which the jet emerges, takes a minimal value at a certain point. If the width of the opening tends to the length of the slab, the problem of the collision of two jets is obtained; if the width of the opening tends to zero (Q o), the problem of jet flow past a slab with a source is obtained. It is shown that the replacement of the jet by the source gives a good approximation in both the sense of the force characteristics and in the sense of the behavior of the free streamlines.Translated from Izvestiya Akademii Nauk SSSR, Hekhanika Shidkosti i Gaza, No. 5, pp. 47–54, September–October, 1979.We thank L. I. Sedov for his interest in the work and G. Yu. Stepanov for proposing the method of solution and for a helpful discussion.     

Unsteady-state filtration of a liquid in a fractured-porous stratum to a well with a hemispherical end-face

A study is made of the motion of a liquid toward a well with a hemispherical end-face with unsteady-state spherical-radial filtration in a fractured-porous stratum consisting of hemispherical regions with different values of the permeability of the system of cracks, superposed one on another. A Laplace transform is used to find exact solutions to the problem of the lowering of the stratum pressure as a function of time and distance as well as of the output of a well working with a constant end-face pressure. The article discusses partial cases corresponding to the exploitation of closed and bounded open fractured-porous strata by a central well with a hemispherical end-face. On the basis of numerical calculations, the effect of the parameters of fractured-porous strata on the change in the indices of the process of their exploitation is established. It is established that, with the exploitation of fractured-porous strata, the process of the lowering of the end-face pressure of the well and its output become stabilized with sufficiently large values of the time.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 115–123, November–December, 1973.     

Torsion problems for a cylinder with a rectangular hole and a rectangular cylinder with a crack

Using the method of singular integral equation and the crack-cutting technique, the rigorous solutions are obtained for a cylinder with a rectangular hole and a rectangular cylinder with a crack, which exactly satisfy the boundary conditions and the conditions at the corner points. After that the torsional rigidities and the stress intensity factors at the crack tip are determined. Next, for the doubly connected circular cylinder with a rectangular hole the expressions for the singular stresses around the concave corner points are derived and the generalized stress intensity factors are then defined. Since the crack-cutting technique is used in this paper, the solution of the matching rectangular cylinder is also obtained and its numerical results coincide with those in references. Thus the method proposed here is verified. The project supported by National Natural Science Foundation of China     

Interaction of a cylinder with a free surface and a jet

The problem of the asymmetric flow around a cylinder of a nonviscous jet is considered and, in particular, of flow with one free boundary. The problem of the choice of circulation is posed, based on a generalization of the Zhukovskii-Chaplygin postulate. Several possibilities are considered and the principle of the minimum of the maximum velocity on a contour is proposed, which qualitatively and quantitatively truly reflects certain aspects of the interaction of the cylinder with the flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 50–58, September–October, 1977.     

On the interaction between a dislocation and a crack in a material with a nonlinear stress-strain law

The problem of the interaction of a crack and a dislocation in a medium with a nonlinear stress-strain law is considered for the case of a semi-infinite crack in a displacement loaded strip under longitudinal shear deformation. A power law stress-strain relation is considered and the dislocation is assumed positioned so that the net effect of its interaction with the crack is to produce a zero stress intensity factor when combined with the effect of the applied displacements. Thus the Atkinson-Kay superdislocation model of a relaxed crack tip is extended to the situation where the material satisfies a power-law stress-strain relationship.