Statistical characteristics of the diffusion of a chemically active additive in a turbulent mixing zone

In the article a numerical solution of the connected system of the equations of turbulent transfer for the fields of the velocity and concentration of a chemically active additive is used to calculate a number of the second moments of the concentration field in a flat mixing zone. The system of transfer equations is derived from the equations for a common function of the distribution of the fields of the pulsations of the velocity and the concentration [1] and is simplified in the approximation of the boundary layer. A closed form of the transfer equations is obtained on the level of three moments, using the hypothesis of four moments [2] and its generalized form for mixed moments of the field of the velocity and the field of a passive scalar. The differential operator of the closed system of the equations of turbulent transfer for the fields of the velocity and the concentration is found by a method of closure not of the parabolic type but of a weakly hyperbolic type [3]. An implicit difference scheme proposed in [4] is used for the numerical solution. The results of the numerical solution are compared with the experimental data of [5].     

分数导数粘弹性模型描述的土中管桩竖向振动的频域解

在分数导数粘弹性本构模型的基础上综合考虑桩周土和桩芯土的平衡方程和几何方程建立了桩周土和桩芯土的竖向运动的控制方程．在频率域内利用分离变量法和分数导数的性质求解了桩周土和桩芯土竖向振动控制方程．考虑管桩与桩周土、管桩与桩芯土的边界连续性条件以及三角函数的正交性得到了分数导数粘弹性模型描述的土中管桩的竖向振动,通过数值分析研究了管桩和土体模型参数和几何参数对管桩的桩顶复刚度的影响规律．结果显示：桩芯土本构模型的分数导数的阶数对管桩竖向振动的影响较桩周土本构模型的阶数要小,且与频率有一定关系;桩芯土与桩周土的模型参数比τ1 和τ2 对等效阻尼的影响较对刚度因子的影响要大;管桩桩周和桩芯的直径比d 越小,管桩复刚度的实部和虚部就越大;土体力学性能对管桩竖向振动的影响要比管桩桩身力学性能的影响小．     

放射状椭圆截面均压槽对狭缝节流气浮支承的影响研究

为提高狭缝节流气浮支承静态特性，在有腔狭缝节流气浮支承的基础上增加了表面节流均压槽，均压槽呈放射状，周向截面为扇形，径向截面为椭圆，并对其进行了仿真分析. 结果表明:增加放射状椭圆截面的均压槽作为表面节流方式能够优化其承载力以及刚度，但会增加耗气量. 增加均压槽高度、放射角度、数量和半径均能增加气浮支承的承载力. 刚度峰值对应的气膜厚度会随均压槽高度增加但峰值基本保持不变；刚度峰值对应的气膜厚度会随均压槽辐射角度增加且峰值也会略微增加；当均压槽数量大于4时，随着均压槽数量的增加，刚度峰值均出现在气膜厚度h₂为13 μm附近，但刚度峰值会随均压槽数量的增加而产生较大增幅；刚度峰值对应的气膜厚度会随均压槽半径的增加而减小，但峰值会随均压槽半径的增加而增加.      

薄片炸药与固体靶冲量耦合的计算模型

薄片炸药可用于模拟强脉冲X射线辐照下空间结构的响应,其与固体靶的冲量耦合作用是进行模拟载荷设计的基础。本文中基于有限元模拟技术,研究不同直径薄片炸药的边界稀疏作用和安装支座的反射作用对薄片炸药与固体靶冲量耦合的影响,结果表明:边界稀疏作用对薄片炸药的比冲量起到减弱的作用,由边界稀疏作用引起的薄片炸药比冲量的变化量和薄片炸药直径的倒数近似成线性关系;薄片炸药安装支座的反射作用对薄片炸药的比冲量起到增强的作用,由支座反射作用引起的薄片炸药比冲量的变化量和薄片炸药直径的平方近似成反比;随着薄片炸药直径的增加,薄片炸药比冲量趋于定值,边界稀疏作用和支座反射作用可以忽略;存在一个临界直径,当薄片炸药的直径为临界直径时,薄片炸药的边界稀疏作用和支座反射作用达到平衡,其比冲量大小和薄片炸药的直径为无穷大时的比冲量值相等。     

可变节流高度气浮支承结构设计及动态性能分析

为了使气浮支承的承载力动态可调,设计了一种可变节流高度气浮支承. 通过建立气浮支承计算流体动力学(Computational Fluid Dynamics,CFD)模型,利用CFD动网格技术来模拟小孔节流器的运动,研究小孔节流器的结构参数、运动参数及气浮支承的工作参数对可变节流高度气浮支承动态性能的影响. 结果表明:通过调节小孔节流器的节流高度可以明显改变气浮支承的承载力;在只考虑单一变量的前提下,气浮支承承载力的波动量随着小孔节流器的运动幅值、运动频率、节流高度、直径和气浮支承供气压强的增加而增加,但随着气膜厚度的增大而减小;当小孔节流器直径较小时,随着小孔节流器运动频率的增加,气浮支承动刚度的增幅很小,但当小孔节流器直径增大时,随着小孔节流器运动频率的增加,气浮支承动刚度的增幅会明显变大.      

隧道洞口段非均质及各向异性土质裂缝仰坡稳定性上限解

针对忽略岩土体非均质和各向异性将导致边坡稳定性评价产生误差的问题，应用极限分析上限理论及抗剪强度系数折减法，推导土体强度非均质和各向异性影响下隧道洞口含裂缝仰坡稳定性解析式，探究土体强度非均质和各向异性对仰坡稳定性系数、坡顶裂缝位置、隧道拱顶失稳范围及仰坡安全系数的影响。结果表明，裂缝深度及坡角越大，仰坡稳定性系数越小；非均质系数越大和各向异性系数越小，维持仰坡稳定的临界坡高越大；非均质系数及各向异性系数越大，裂缝距坡顶边缘越远，隧道拱顶失稳范围越大；非均质系数增大有利于仰坡稳定，而各向异性系数越大仰坡越易失稳。     

Plane explosion wave in soils

It is shown in the article that simple analytical expressions can be used to determine the velocity of the front of a plane shock wave and the parameters of the soil behind the front in the region from the boundary of the charge of explosive up to the moment of the emission of sound. The calculated data are compared with the results of field tests. The calculations are based on the use of a diagram of the compression of the soil constructed taking account of the results of the experiment.     

The regions of flutter and divergence instability of a column subjected to Beck's generalized load, taking into account the torsional flexibility of the loaded end of the column

Investigations into a slender system subjected to Beck's generalized load taking into account two rotational springs situated at each end of the system are presented in the paper. One spring models the finite rigidity of the mounting, while the second restricts the rotation of the loaded end of the system. The regions of divergence and flutter instability of the considered system were determined using the kinetic criterion of the stability. The boundary value of the rigidity of the spring situated at the loaded end of the column was also determined. The boundary value of the rigidity separates the regions of divergence and flutter instability. In respect of the problem of vibrations, the characteristic curves in the plane: load - natural frequency were presented. All computations were carried out using the parameters of the considered system, including the rigidity of the springs and the follower coefficient of the load.     

隔水管弯曲对钻柱振动影响的计算与分析

海洋油气资源钻探中隔水管的弯曲对钻柱振动以及钻进特性有特别的影响。为得到隔水管弯曲对钻柱振动的影响规律,对南海已钻深水井使用非线性有限元软件建立全井钻井数值计算模型,研究获得了不同垂深时隔水管弯曲对钻柱振动特性的影响规律。研究表明:隔水管弯曲会加剧钻柱的振动,钻柱振动加剧会导致钻井能耗上升、钻头切削能力下降并且会加快钻柱疲劳;当隔水管的弯曲达到某临界值,钻柱与隔水管间的接触力会陡增;井口的钩载越大,隔水管弯曲带来的井口钩载波动量越大;井越深,隔水管弯曲对全井钻柱最大弯矩和钻头切削能力的影响越小。     

Boundary layer on the moving surface of a cylinder

A study is made of the problem of the boundary layer on a cylinder with a moving surface when the cylinder moves with constant velocity in an incompressible fluid. Expressions are obtained for the distributions of the frictional stress on the surface of the cylinder and the coordinate of the singular point in the solution of the boundary layer equations that indicates the appearance of a region of reverse flow for different values of the relative velocity of the motion of the surface of the cylinder. Numerical calculations have been made of the work of the force of friction associated with displacement of the cylinder, the work expended on the motion of its surface, and, in the case of flow separation, the work of the pressure forces (it being assumed here that the pressure and friction on the wall behind the singular point are constant and equal to the pressure and friction at the singular point).     

Investigation of the dynamics of the development of cracks by the method of photoelasticity

An experimental investigation was made of the process of the development of cracks in two materials: polymethyl methacrylate and a polymerized epoxy resin. For these materials, determinations were made of their optical and mechanical characteristics, such as density, the speed of sound, the critical value of the coefficient of singularity of the stress field at the tip of cracks. As the dynamic characteristic of the process of the development of cracks, an investigation is made of the dependences connecting the coefficient of the singularity of the stress field at the tip of a moving crack and the rate of development of the crack. The question of the interaction between two cracks moving in a previously elongated sample is discussed.     

Solution of the direct problem of the flow of a two-phase mixture of a gas and foreign solid or liquid particles in a laval nozzle

Within the framework of a two-liquid (two-velocity and two-temperature) model of a continuous medium, the article considers the flow of a mixture of a gas and foreign particles in the subsonic, transonic, and supersonic parts of a Laval nozzle. In the case of a thin layer of pure gas near the wall, the problem is solved in two stages. First, the method of establishment is used to calculate the core of the flow, where the gas with the particles is flowing; under these circumstances, the parameters in the layer of pure gas are determined approximately; then simplified equations (of the type of the equations of the boundary layer) are used to find the distribution of the parameters in the zone of pure gas, and the flow in the core of the stream is refined. Examples of the calculation are given. Use of the method developed permitted establishing some of the special characteristics of the flow of a mixture of gas with particles in a Laval nozzle in the case of Stokes flow around the foreign particles.     

变截面爆炸成型弹丸垂直侵彻装甲钢板靶后破片质量模型

考虑爆炸成型弹丸(explosively-formed projectile，EFP)变截面的特性，基于流体力学Bernoulli方程和绝热剪切理论，改进了EFP垂直侵彻装甲钢板靶后破片质量模型，结合已有的试验数据和数值仿真方法检验了改进后模型的准确性。在此基础上，分析了靶板厚度和EFP着靶速度对靶板和EFP产生的靶后破片质量的影响规律。结果表明:相比于改进前的模型，改进后的模型能够更准确地解释靶板和EFP产生的靶后破片质量随靶板厚度和EFP着靶速度的变化规律；当EFP着靶速度为1 650 m/s时，随着靶板厚度从30 mm增大到70 mm，EFP变截面的特性对靶板和EFP产生靶后破片质量的影响不断增强；当靶板厚度为40 mm时，随着EFP着靶速度从1 650 m/s升高到1 860 m/s，EFP变截面的特性对靶板和EFP产生靶后破片质量的影响不断减弱。     

Investigation of Mechanisms of Excitation and Growth of Unstable Perturbations in Pulsating Flows

General laws of the processes of generation and amplification of secondary perturbations in oscillating viscous fluid flows are studied theoretically. The stability and receptivity are analyzed with reference to perturbations generated by fluctuations of the flow rate of Poiseuille flow induced by small two-dimensional roughnesses of the channel walls. It is shown that the presence of roughness leads to excitation in the flow of perturbations at all multiples of the main flow oscillation frequency. Using the Fourier transform along the streamwise coordinate, the problem of calculating the frequency harmonics is reduced to a system of equations of the Orr-Sommerfeld type interrelated via the oscillatory component of the main flow. On the basis of an investigation of the analytic properties of the Fourier-image it is shown that upstream and downstream of the roughness the perturbation can be represented in the form of a superposition of modes of the time-dependent Poiseuille flow. The modes are classified and their spectrum is calculated. The structure of the mean-square fluctuations generated by free perturbations is investigated. Examples of calculating the evolution of forced perturbations are given for cases in which the scattering of the oscillations of the main flow on the roughness leads to the generation of one or two modes growing downstream.     

Combustion of a gas suspension of metal particles

The combustion of a gas suspension of particles reacting in accordance with a heterogeneous mechanism was considered in [1–4]. It was assumed that the reaction rate at the surface of the individual particles does not depend on the thickness of the oxide film, or that a film does not form, i.e., the reaction products are gaseous. With the oxidation of many metals the oxide film formed inhibits the reaction, i.e., with its growth, the rate of the reaction decreases. The special characteristics of the process of the combustion of individual particles of metals arising as a result of the effect of the oxide film were considered in [5], in which it was shown that the dependence of the reaction rate on the thickness of the film has a considerable effect on the laws governing the combustion of individual particles. In the present work, a study was made of the process of the combustion of a gas suspension of particles of metals oxidizing in accordance with the so-called parabolic law (the reaction rate is inversely proportional to the thickness of the oxide film). The results are compared with the laws governing the combusion of a gas suspension of particles reacting in accordance with a purely heterogeneous mechanism in the absence of an oxide film.     

Laval nozzle flow calculation

The inverse problem of the theory of the Laval nozzle is considered, which leads to the Cauchy problem for the gasdynamic equations; the streamlines and the flow parameters are found from the known velocity distribution on the axis of symmetry.The inverse problem of Laval nozzle theory was considered in 1908 by Meyer [1], who expanded the velocity potential into a series in powers of the Cartesian coordinates and constructed the subsonic and supersonic solutions in the vicinity of the center of the nozzle. Taylor [2] used a similar method to construct a flowfield which is subsonic but has local supersonic zones in the vicinity of the minimal section. Frankl [3] and Fal'kovich [4] studied the flow in the vicinity of the nozzle center in the hodograph plane. Their solution, just as the Meyer solution, made it possible to obtain an idea of the structure of the transonic flow in the vicinity of the center of the nozzle.A large number of studies on transonic flow in the vicinity of the center of the nozzle have been made using the method of small perturbations. The approximate equation for the transonic velocity potential in the physical plane, obtained in [3–6], has been studied in detail for the plane and axisymmetric cases. In [7] Ryzhov used this equation to study the question of the formation of shock waves in the vicinity of the center of the nozzle, and conditions were formulated for the plane and axisymmetric cases under which the flow will not contain shock waves. However, none of the solutions listed above for the inverse problem of Laval nozzle theory makes it possible to calculate the flow in the subsonic and transonic parts of the nozzles with large gradients of the gasdynamic parameters along the normal to the axis of symmetry.Among the studies devoted to the numerical calculation of the flow in the subsonic portion of the Laval nozzle we should note the study of Alikhashkin et al., and the work of Favorskii [9], in which the method of integral relations was used to solve the direct problem for the plane and axisymmetric cases.The present paper provides a numerical solution of the inverse problem of Laval nozzle theory. A stable difference scheme is presented which permits analysis with a high degree of accuracy of the subsonic, transonic, and supersonic flow regions. The result of the calculations is a series of nozzles with rectilinear and curvilinear transition surfaces in which the flow is significantly different from the one-dimensional flow. The flowfield in the subsonic and transonic portions of the nozzles is studied. Several asymptotic solutions are obtained and a comparison is made of these solutions with the numerical solution.The author wishes to thank G. D. Vladimirov for compiling the large number of programs and carrying out the calculations on the M-20 computer.     

DYNAMIC RESPONSE OF THE CATENARY RISER IN DEEP-SEA MINING SYSTEMS 1)

基于有限元模型,模拟、分析深海采矿系统悬链线立管在海流和水面船运动约束下的动力响应。结果表明：悬链线立管的最大等效应力和最大位移随时间呈周期性变化,且存在半个周期的相位差;当水面船运动到最高点时,悬链线立管位移达到最大值。悬链线立管最大 等效应力和最大位移随水面船运动位移幅值的增加而增加,随运动周期的增加而减小。进一步对比发现,水面船运动位移和周期对立管等效应力的影响大于对其位移的影响。     

Plastic extension of a shear crack at a circular inclusion

The plastic relaxation of a shear crack situated normal to the interface of a second phase particle of circular cross-section is quantitatively analyzed. The ratio of applied stress to yield stress and the relative displacement of the crack faces at the tips of the crack in the matrix and the interface in the second phase are related to the crack parameters namely the length of the crack, the width of the plastic zone in the matrix and the second phase. The effect of the shear modulus and size of the second phase particle on the behaviour of the plastic zones is determined. A critical value of the relative displacement of the crack faces at the tip of the crack is used as the criterion to determine the tendency to brittle crack extension into the matrix and the second phase.     

半圆柱壳挠曲问题解析解精确性的研究

壳体力学已于上世纪由多位专家发展成熟,其中简支柱壳挠曲问题采用改进莱维解法的三角级数法解出,但是其解法复杂,手算难以完成．为讨论其结果的精确性,通过编写运行基于MATLAB的运算程序导出实例化解析解,与基于力学基本理论的推想假设对比,再引入有限元计算结果进行比较研究．最终发现,理论解析解应力和位移具有分布形式大致准确性,但仍存在不容忽视的细节与局部性问题．研究表明,理论解法工程意义有限,结果尚需改进．     

垂向冲击下穿戴装备对乘员损伤影响研究

军事人员在战斗中需要穿戴装备,穿戴装备后对车内乘员承受车辆底部爆炸垂向冲击时的损伤有影响。通过垂向冲击试验与仿真模拟的方法,研究了穿戴装备在身上的分布对于乘员损伤的影响。根据AEP55乘员伤害准则,以盆骨z向加速度和腰椎轴向力为乘员损伤的参考目标,首先通过垂向冲击试验的进行,研究了不同穿戴装备质量对于乘员损伤的影响;接着通过有限元模型对试验进行验证和优化,进而研究穿戴装备位置与松紧度对于垂向冲击下乘员损伤的影响。结果表明随着穿戴装备质量的增加,乘员腰椎损伤加重,脊柱损伤概率减小;装备分布在躯干位置越靠近上部,与身体接触松紧度越紧,乘员腰椎与脊柱的负荷越小,越不易受伤。