求解应力强度因子的样条虚边界元交替法

为求解平面裂纹问题的应力强度因子,提出基于Muskhelishvili基本解和样条虚边界元法的样条虚边界元交替法.该方法将平面内带裂纹有限域问题分解成带裂纹无限域问题与不带裂纹有限域问题的叠加.带裂纹无限域问题利用Muskhelishvili基本解法直接得出,不带裂纹有限域问题采用样条虚边界元法求解.利用该方法对复合型中心裂纹方板和I型偏心裂纹矩形板进行分析.数值结果表明该方法精度高且适用性强.     

稠油区块年产量预测的新方法

基于稠油区块不同井距下的吞吐开采周期数据,采用前向人工神经网络(BP网络),对稠油区块各井距周期产量进行预测,达到预测稠油区块年产量的目的。经过实际应用结果表明,本文所采用的预测方法是一种预测中短期蒸汽吞吐稠油区块年产量的有效方法,可供油藏工程的有关技术人员参考。     

固体入水的边界压力处理及表面粒子位置的修正

基于传统光滑粒子流体动力学(SPH)方法的边界力法、虚粒子法或耦合力法处理固体入水时,流 体与固体交互界面的粒子密度不连续、压力不稳定、固体边界处会发生部分流体粒子穿透或分离等现象,而流 体表面因为受到力的作用,表面破碎后,液面较粗糙。针对上述问题,结合边界力和虚粒子的优点,对耦合力 法进行改进,处理运动固体边界,阻止流体粒子穿透固体边界;改进交互界面的压力计算方法,提高计算精度, 稳定交互界面压力场;对流体表面的粒子位置进行校正,提升流体表面自由流动液面边界的模拟效果。通过经 典的二维固体入水实验,对该方法进行了验证,实验结果表明,本文方法在流体粒子与固体粒子交互后,交互 界面压力稳定,界面分离清晰无穿透,表面流体粒子分布均匀,流场的运动真实自然。     

极近距离煤层同采工作面错距优化研究

针对现有极近距离煤层联合开采研究方法获取开采错距存在较大误差的问题,以某煤矿9号和10号煤层为工程背景,分析了极近距离同采工作面在30,36,44m开采错距下的矿压规律,研究了3种开采错距下工作面支架工作阻力变化与支承压力的演化特征。结果表明:100402综采工作面支架工作阻力随开采错距增大呈现先减小后增大的特点,36m开采错距下100402综采工作面倾斜方向支架工作阻力利用率变化幅度最为平稳;090402普采工作面超前支承压力峰值随开采错距增大呈现先减小后增大的演化特征,其与支架工作阻力变化规律一致;开采错距为36m时上下工作面两巷受超前支承压力影响,前顶板锚杆压力变化平稳,顶板离层较小,离层量基本稳定在0.6mm以内,说明36m开采错距合理,工作面两巷超前段锚杆压力与顶板离层略有增大,需加强巷道支护。     

边界追踪算法在地质储量计算中的应用

单井控制面积计算是油田开发中原始和剩余地质储量研究的基础。针对注采井网形成的平面变密度离散点集的边界搜索问题,本文提出以角度为判别标准,基于变搜索步长的滚边新算法进行井网边界的追踪。首先通过合理的搜索步长确定当前边界点的邻域,然后对邻域内的离散点按角度进行排序并确定下个合理边界点,最后在井网边界追踪的基础上,进一步给出储量边界外扩和单井控制面积计算方法。该算法简单、高效,可有效识别变密度平面点集的凸边界和凹边界特征,并在大庆油田的原始地质储量复算和剩余潜力评价中得到应用,提高工效5倍以上,表内地质储量复算精度2.7%,取得了很好的应用效果。     

电磁悬浮转子微陀螺悬浮稳定性分析

电磁悬浮转子微陀螺(MGELR)是一种新型的角速率传感器,它和传统机械陀螺具有相同的工作机理.MGELR有望成为具有高精度的微陀螺.对于MGELR来说,转子的稳定悬浮是极为重要的.文中对微转子的稳定悬浮进行了全面的研究.详细分析并给出线圈、转子直径、电流幅值、悬浮高度等因素对微转子悬浮稳定性的影响.文中提出边界效应理论来解释微转子偏心所带来的侧向力.试验结果进一步论证了分析的正确性.文章最后得出稳定悬浮所应满足的条件.文章的研究内容为MGELR的结构设计提供理论基础.     

基于大数据的试井解释参数分析

试井解释是通过检查、分析试井资料的特征获取有关油藏信息和描述油藏物理本性参数的过程。现有试井解释方法都是基于图版拟合的方式,仍需依靠经验指导和人工参与进行单井分析。针对试井解释无法实现精简化与专家经验重用的问题,提出基于大数据的试井解释参数分析方法。通过数据驱动的方式结合大数据分析技术,分析试井解释中长期积累的海量数据。通过描述性分析,研究压力导数双对数曲线所反映的同类型试井的共性特征以及曲线特征的描述方法。采用相关分析揭示数据间隐藏的模式并识别相关性,确定与试井解释参数相关的独立变量。最后通过神经网络构建试井解释参数预测模型。研究表明,该分析方法可以避免由于图版拟合的固有误差、拟合主观性以及拟合结果不唯一等问题引起的误导性结果。     

受轴向激励弹性支承梁的稳定性分析

对于广泛存在的弹性支撑梁,首次呈现支承弹簧刚度对轴向激励下梁横向振动稳定性的影响.应用Hamilton原理,建立了两端由线性弹簧支撑的受轴向激励梁的动力学控制方程.通过解析方法计算了受轴向压力梁的固有频率,得到了支撑弹簧刚度与系统固有频率和临界轴力的关系.Galerkin截断后,通过多尺度法和Runge-Kutta法,计算得到了梁参激振动稳态响应的半解析与数值解.讨论了激励幅值、支撑弹簧刚度、平均轴力对系统非线性响应幅值及软硬特性的影响.利用Routh-Hurwitz稳定性判据,求得系统的参激稳定边界,着重讨论了支撑弹簧刚度、阻尼系数的影响.研究发现,边界支撑弹簧的刚度可以显著改变受轴向激励梁的参激稳定边界.因此,研究结果将为广泛存在受到轴向激励结构的设计提供指导.     

用能量法分析体外预压力对简支梁动力性能的二阶效应

精细地考虑了体外筋变形中的二阶项,用能量法推导了体外预应力梁的自振频率,阐明了体外预压力对梁自振频率的效应.计算结果表明:体外预压力压缩软化效应的影响系数,主要取决于转向座的数量.无转向座时,体外筋偏心距损失为最大,影响系数为1,体外预压力的效应与外轴力的效应相同.随着转向座数量的增加,偏心距损失减小,体外筋接近于无粘结筋,影响系数降低至接近于0,即接近于无粘结筋预压力的零效应.当梁转向座的数量≥2时,由于影响系数显著地小于1,可以忽略体外预压力的压缩软化效应.随着体外筋面积和偏心距的增加,梁的第1自振频率增大.不过,体外筋对其他阶自振频率的影响很小,可以忽略.     

基于机器视觉的编码器光栅装配偏心调整技术

编码器光栅装配的过程中, 光栅实际回转中心与编码器主体轴的回转中心很难重合, 这样会影响编码器的输出信号的精度。为了解决编码器光栅与主轴的偏心问题, 提出一种基于机器视觉的光栅偏心自动调整系统。对光栅表面图像进行分析处理, 对边界跟踪提取及基于Hough变换圆弧检测等算法进行研究。根据光栅装配要求搭建了偏心计算系统的硬件系统。对光栅图像进行预处理及形态学操作, 在分析提取光栅基圆部分圆弧边界的基础上, 通过Hough变换的圆弧检测原理还原出光栅基圆并标定其圆心。介绍了系统通过多幅光栅基圆圆心拟合回转圆, 确定光栅偏心位置。实验结果表明, 基于机器视觉的编码器光栅偏心计算方法成功计算出光栅与主轴的偏心位置, 为光栅偏心调节奠定了基础。采用光栅偏心计算系统在编码器光栅的装配作业中具有很好的可行性。     

Analysis of unsteady compressible boundary layer flow via finite elements

This paper is concerned with the discrete formulation and numerical solution of unsteady compressible boundary layer flows using the Galerkin-finite element method. Linear interpolation functions for the velocity, density, temperature and pressure are used in the momentum equation and equations of continuity, energy and state. The coupled nonlinear finite element equations are approximated by a third order Taylor series expansion as temporal operator to integrate in time with Newton-Raphson type iterations performed until convergence within each time step. As an example, a boundary layer problem of a perfect gas behind a normal shock wave is solved. A comparison of the results with those by other method indicates a favorable agreement.     

Manifold method coupled velocity and pressure for Navier-Stokes equations and direct numerical solution of unsteady incompressible viscous flow

Numerical manifold method (NMM) application to direct numerical solution for unsteady incompressible viscous flow Navier-Stokes (N-S) equations was discussed in this paper, and numerical manifold schemes for N-S equations were derived based on Galerkin weighted residuals method as well. Mixed covers with linear polynomial function for velocity and constant function for pressure was employed in finite element cover system. The patch test demonstrated that mixed covers manifold elements meet the stability conditions and can be applied to solve N-S equations coupled velocity and pressure variables directly. The numerical schemes with mixed covers have also been proved to be unconditionally stable. As applications, mixed cover 4-node rectangular manifold element has been used to simulate the unsteady incompressible viscous flow in typical driven cavity and flow around a square cylinder in a horizontal channel. High accurate results obtained from much less calculational variables and very large time steps are in very good agreement with the compact finite difference solutions from very fine element meshes and very less time steps in references. Numerical tests illustrate that NMM is an effective and high order accurate numerical method for unsteady incompressible viscous flow N-S equations.     

High-order time splitting for the Stokes equations

A pseudo-spectral (or collocation) approximation of the unsteady Stokes equations is presented. Using the Uzawa algorithm the spectral system is decoupled into Helmholtz equations for the velocity components and an equation with the Pseudo-Laplacian for the pressure. In order to avoid spurious modes the pressure is approximated with lower order (two degrees lower) polynomials than the velocity. Only one grid (no staggered grids) with the standard Chebyshev Gauss-Lobatto nodes is used. Here we further compare our treatment with a Neumann boundary value problem for the pressure. The highly improved accuracy of our method becomes obvious. In the time discretization a high order backward differentiation scheme for the intermediate velocity is combined with a high order extrapolant for the pressure. It is numerically shown that a stable third order method in time can be achieved.     

三维非定常扩散方程的虚边界元法

根据位势问题虚边界元法的基本思想,结合扩散方程与时间有关的基本解,提出了针对单层热势的三维非定常扩散方程虚边界元-配点法的一个具体实施方案.该方法既保留了边界元法的优点,也避免了传统边界元法中时间和空间上的奇异积分计算,采用较少的边界单元即可达到较高的精度.算例表明此方法的有效性和可行性,不过虚实边界比例选取范围比虚边界元方法应用于椭圆型问题时狭窄很多,对此本文进行了探讨,但还应继续从理论上加以论证.     

MHD flow in a rectangular duct with a perturbed boundary

The unsteady magnetohydrodynamic (MHD) flow of a viscous, incompressible and electrically conducting fluid in a rectangular duct with a perturbed boundary, is investigated. A small boundary perturbation $\epsilon$ is applied on the upper wall of the duct which is encountered in the visualization of the blood flow in constricted arteries. The MHD equations which are coupled in the velocity and the induced magnetic field are solved with no-slip velocity conditions and by taking the side walls as insulated and the Hartmann walls as perfectly conducting. Both the domain boundary element method (DBEM) and the dual reciprocity boundary element method (DRBEM) are used in spatial discretization with a backward finite difference scheme for the time integration. These MHD equations are decoupled first into two transient convection–diffusion equations, and then into two modified Helmholtz equations by using suitable transformations. Then, the DBEM or DRBEM is used to transform these equations into equivalent integral equations by employing the fundamental solution of either steady-state convection–diffusion or modified Helmholtz equations. The DBEM and DRBEM results are presented and compared by equi-velocity and current lines at steady-state for several values of Hartmann number and the boundary perturbation parameter.     

Finite element solutions of nonsteady incompressible viscous flow between two rotating concentric spheres

The problem of unsteady, incompressible viscous flow between two rotating concentric spheres has been investigated here. The full Navier-Stokes equations in terms of the velocity components u, v w and the pressure p, using spherical coordinates for axially symmetric flow, were solved by means of the finite element method in the spatial dimension and the alternating-direction method in the time dimension using Glowinski's algorithm. The element used is an annular-sector-type element with a bilinear approximation for the velocity components and with constant pressure within the element. Reynolds numbers in the range from 1 to 1000, gap size 0.5 and different combinations of the angular velocity of the inner and outer spheres were studied. In some of these cases a steady-state solution was possible, while in others only a transient solution was possible. This method proved to be successful and powerful in predicting the behavior of the flow for these nonlinear-type problems.     

An approach to modelling high pressure waterjet oil barriers

A numerical model is employed to study flow characteristics of high pressure waterjet barriers. The high pressure waterjet barrier has been developed as a means of containing and deflecting oil spills that float on water. An array of waterjets directed above the contaminated surface will generate an air flow that moves the oil. A two-dimensional model of the turbulent entrained air flow is done using the spectral element method. The moving boundaries of the air flow are modeled analytically and implemented in the computer code. The upper boundary, represented by the high pressure waterjet, is assumed to be moving with the centerline velocity of the jet. The lower boundary is the interface of the air-driven wavy liquid surface for which interfacial shear and pressure drop are directly related to waviness characteristics and mobility of the interface. This boundary is modeled as a solid-like wavy surface. The interfacial speed is neglected at this stage since it is much smaller than the air speed. An algebraic turbulence closure model is used for estimating shear stress at the lower boundary. A case study is presented where the numerical model has been applied to a base case for which experimental data are available. The predicted air flow velocities of the model compare relatively well with experimental values. Results of the model have also shown that the air flow maintains significant momentum over a long distance beyond the range when the waterjet itself has ceased.     

Computation of natural frequencies and mode shapes of arch dams as an inverse problem

In this paper, a procedure is developed which can be used to identify the natural frequencies and natural modes of an Arch-Dam in a vacuum, from forced vibration testing data of partially filled reservoir, throughout removing the effect of hydrodynamic, by using an effective algorithm. The resonance frequency and the resonance mode of the dam–reservoir system have been computed from the in situ tested data. The solution strategy is verified by studying the dynamic response of simple structures, like beam with the fluid interaction effect taken into account, as the analytical results of its modal properties were available for comparison. The hydrodynamic pressure of the reservoir is calculated using the boundary element method. In the inverse problem procedure, the calculated resonance replaces the measured resonance, which has been obtained practically throughout the in situ testing. In this paper the strategies are extended to analyse the dynamic beam–fluid interaction problem with compressible water. The results derived by solving an inverse problem are compared with the exact analytical responses of the beam.