川渝裂缝性地层自动压井环空多相压力波速特性研究北大核心CSCD

考虑虚拟质量力、环空沿程压力、气液相间阻力、气体滑脱、环空空隙率等因素,基于小扰动理论,提出了裂缝性地层自动压井环空多相压力波速数学模型,结合半显式差分方法,以彭州PZ-5-3D井(垂深5827 m)为实例,对模型编程求解.结果表明:裂缝性地层出气具有段塞流特点,随空隙率增大,压力波速呈现先减小后增大趋势;空隙率在0%至16%区间,压力波速以液弹为主,压力波速呈急剧下降趋势;空隙率在16%至40%区间,压力波速趋于平缓恒定值;空隙率在42%至100%区间,压力波速呈现增大趋势,压力波速以气弹为主;随环空井深减小,环空空隙率减小,压力波速整体呈现减小趋势;随压井循环排气井口回压增大,压力波速整体呈现增大趋势;环空空隙率在0%至13%区间内,气体滑脱速度对压力波速影响不大;环空空隙率在13%至85%区间内,随气体滑脱速度增大,压力波速呈现减小趋势;节流阀调阀时间间隔与井底压力响应时间具有跟随性,随井底压力响应时间增大,调阀时间间隔增大.     

Ⅰ型动态扩展裂纹尖端的弹粘-理想塑性场

由于材料在扩展裂纹尖端的粘性效应的存在,考虑粘性效应并假设粘性系数与塑性等效应变率的幂次成反比,对理想塑性材料中平面应变扩展裂纹尖端场进行了弹粘塑性渐近分析,得到了不含间断的连续解,并讨论了Ⅰ型裂纹数值解的性质随各参数的变化规律．分析表明,应力和应变均具有幂奇异性,通过分析使尖端场的弹、粘、塑性可以合理匹配．对于Ⅰ型裂纹,裂尖场不含弹性卸载区．趋于极限情况时,裂纹尖端处于一种超粘性状态,并积聚了大量的能量,在各个受压应力状态下裂纹扩展．     

基于内变量理论的电流变液本构关系

研究了电流变液的微结构本构关系.其理论框架是基于内变量理论和机理的分析.电流变液是由高介电常数的颗粒悬浮在某种液体中组成的.在电场作用下,极化的颗粒将沿着电场方向聚集在一起形成链状结构.颗粒聚集体的大小和方向将随外加电场和应变率的变化进行调整,因而可以通过建立起能量守恒方程和力平衡方程来确定颗粒聚集体的大小和方向的变化.那么,一个三维的、清晰的本构关系可以由相互作用能和系统的耗散能导出.具体考虑和讨论了在简单剪切载荷作用下的系统响应,发现电流变液的切变剪薄粘滞系数同系统Mason数之间近似于幂指数∝(Mn)-082的关系.     

多孔介质平板通道传热模型的两种求解方法

基于Brinkman Darcy扩展模型和非局部热平衡模型,考虑液相和固相含有内热源的情况,建立了多孔介质平板通道传热的一般模型.分别采用直接法和间接法将液相与固相能量方程解耦,进而求得充分发展传热条件下的多孔介质温度场.与直接解耦法相比,间接解耦法可在原始边界条件下求解二阶微分方程,更加简单易行.通过对无量纲温度表达式系数以及温度分布的比较,验证了两种求解方法的等价性.在两种极限情形下,间接法所得温度分布解析解与现有文献结果相当吻合,这也在一定程度上证明了所建模型更具一般性.参数分析表明,液固两相温差随着Biot数或有效导热系数比的增大而减小,Nusselt数随着内热源比的增大而减小.     

FPSO船与低充水率下LNG液舱晃荡耦合运动的数值模拟

应用数值模拟方法对FPSO船舶运动与LNG液舱晃荡耦合问题进行了研究.这种全耦合问题的研究基于开源平台OpenFOAM开发的船舶与海洋工程水动力CFD求解器——naoe-FOAM-SJ-TU进行计算.液舱内部流场与外部流场同时求解.采用带有两个LNG液舱的FPSO船作为对象进行数值模拟,船舶放开3个自由度运动,并在90°浪向的规则波中进行模拟.液舱充水率为20％～20％,低于船外自由水面高度.这种低充水率的液舱会大大减少船舶的横摇运动,并且舱内的流体情况较为复杂.考虑了4种不同的入射波频率下船舶的运动,与实验结果进行了对比.数值模拟结果与实验结果对比吻合良好,验证了数值求解方法的可靠性.还对大波高情况下带有低充水率LNG液舱的船舶运动进行了数值模拟分析.在船舶运动与液舱晃荡全耦合情况下,观察到了液舱内流体的剧烈晃荡和舱壁的脉冲压力.     

梯度磁电弹材料界面的Stoneley波波速研究

研究均匀弹性半空间(y ≤ 0)和功能梯度磁电弹半空间(y≥0)界面的Stoneley波的波速.基于弹性介质和磁电弹介质的本构方程、运动方程和界面连续条件,得到了弹性半空间(y≤0)和磁电弹半空间(y≥0)界面处的Stoneley界面波波速方程,并讨论了梯度系数对波速的影响.研究结果对于界面波器件的研制提供理论依据.     

再装股票期权的Esscher变换定价

近年来,公司为了吸引和激励股票的执行者而引入了一系列的非传统期权.本文将讨论其中的一种:再装期权,运用Esscher变换给出了再装期权(只装一次)的闭式解,并提供了数值计算的例子,为实践者提供了理论上的参考价格.     

基于L-S广义热弹性理论YSZ在超短脉冲下的热力响应北大核心CSCD

基于L-S广义热弹性理论,考虑材料比热容随温度变化,建立了含有内热源的热弹耦合系统控制方程.利用有限元方法研究了氧化钇四方氧化锆(YSZ)在超短脉冲激光作用下的热力响应,获得了材料比热容随温度变化、激光的脉冲宽度等对热力响应的影响,以及机械波在材料中的反射.研究发现,多次脉冲作用下,材料的应力、位移曲线均出现波动,力学响应对加热更加敏感,比热容随温度变化会导致热力响应降低,该研究对提高超短脉冲激光加工质量具有重要的指导作用.     

刘徽数学思想的新认识——纪念刘徽“割圆术”1753周年

刘徽《割圆术》(公元263年)千古之谜被破解,发现使用了外推法,由此引发新的认识.将综述刘徽的极限和外推思想,并比较了国外的工作.最后指出如何用外推预报提出求解偏微分方程的高效算法.     

大挠度圆柱壳在温度场中的热弹耦合振动分析

对温度场与与应力场耦合时的圆柱壳的非线性热弹耦合的振动问题,推导得到了基本的振动方程,热传导方程和协调方程,对短圆柱壳运用伽辽金(Galerkin)法求解,得出振幅随时间变化的数值解,得到一些有价值的结论．即随着温度幅值和耦合系数的增大,振动衰减的速度变缓,热弹耦合效应减弱．随着长径比、长厚比的增大,振幅衰减的速度变快,同时热振动频率也随之增大,即热弹耦合效应增强．耦合系数越大,轴向应力、轴向力以及轴向弯矩越小．     

粉末注射成形填充过程的数值模拟

本文将粉末注射成形喂料在薄壁模腔中的流动视为二维流动，以流变学的基本方程为基础，建立了从动量方程、连续方程和热传递方程得到的描述PIM喂料充模二维流动的数学模型。在无滑移边界的条件下，推导了喂料熔体流导率的计算公式和压力场的控制方程，得到的压力场控制方程是一非线性椭圆偏微分方程．从而可用Galerkin方法进行数值求解，使模型的数值求解成为可能，为进一步对粉末注射成形进行计算机模拟和数值分析奠定了数学基础。     

A direct method for determining the mass of gases in ICF shell

In the present paper, the defects of dew point method for measuring the mass of gas filled in ICF shells are analyzed. An accurate state equation for gas D2 is deduced from Benedict-Webb-Rubin (BWR) equation and experimental data in planar phase. A direct method to determine gas mass in ICF shells via measuring the temperature and pressure outside the shells and solving the equation of state by numerical method is proposed. It overcomes the theoretical defects of dew point method and the complexities of equipment. In the present method, the state equation can be improved by more accurately measuring P-V-T values of gas D2, so the measuring precision of the mass of gas in the shells can also be improved. The present method is effective for treating mix gases filled in the shells as well. The errors between the computational results and experimental data are very small. Some cases in the filling process are predicted, and the proper temperature and pressure for filling gases effectively are also suggested.     

Unification of Filled Function and Tunnelling Function in Global Optimization

In this paper,two auxiliary functions for global optimization are proposed.These two auxiliaryfunctions possess all characters of tunnelling functions and filled functions under certain general assumptions.Thus,they can be considered as the unification of filled function and tunnelling function.Moreover,the processof tunneling or filling for global optimization can be unified as the minimization of such auxiliary functions.Result of numerical experiments shows that such two auxiliary functions are effective.     

Nonlinear evolution equation for describing waves in a viscoelastic tube

Propagation of the nonlinear waves in a viscoelastic tube filled with a liquid is studied. The bending of the tube wall is taken into account. By using the reductive perturbation method the fifth order nonlinear evolution equation is derived. Exact solutions for this equation is obtained by means of the simplest equation method. Properties of nonlinear waves in a viscoelastic tube filled with a liquid are discussed.     

多层感知器信用评模型及预警研究

本文利用多层感知器 ( MLP)原理建立神经网络信用评价模型 ,用来对我国 2 0 0 0年 1 0 6家上市公司进行信用评级 ,并进一步对我国 2 0 0 1年公布的 1 3家预亏公司进行预警研究 .按照各上市公司的经营状况分为“好”、“差”两类 ,每一类由 5 3家上市公司构成数据样本 .对于每一家上市公司 ,主要考虑其经营状况的四个财务指标 :每股收益 ,每股净资产 ,净资产收益率和每股现金流量 .仿真结果表明 ,本文所建立的神经网络信用评价模型有很高的分类准确率 ,达到 98.1 1 % .又由于该信用评价模型有很强的适应能力 ,故可以进一步用来对企业的财务危机进行预警研究 .预警实证分析表明 ,该信用评价模型对我国 2 0 0 1年公布的 1 3家预亏公司进行预警分析 ,预警准确率达到 1 0 0 % .此外 ,文中还给出 MLP网络模型的学习算法和步骤     

Weak oscillations of a gas bubble in a spherical volume of compressible liquid

The following spherically symmetric problem is considered: a single gas bubble at the centre of a spherical flask filled with a compressible liquid is oscillating in response to forced radial excitation of the flask walls. In the long-wave approximation at low Mach numbers, one obtains a system of differential-difference equations generalizing the Rayleigh-Lamb-Plesseth equation. This system takes into account the compressibility of the liquid and is suitable for describing both free and forced oscillations of the bubble. It includes an ordinary differential equation analogous to the Herring-Flinn-Gilmore equation describing the evolution of the bubble radius, and a delay equation relating the pressure at the flask walls to the variation of the bubble radius. The solutions of this system of differential-difference equations are analysed in the linear approximation and numerical analysis is used to study various modes of weak but non-linear oscillations of the bubble, for different laws governing the variation of the pressure or velocity of the liquid at the flask wall. These solutions are compared with numerical solutions of the complete system of partial differential equations for the radial motion of the compressible liquid around the bubble.     

Joined dissimilar thin elastic tubes containing steady perfect flow

Two tubes of circular cross-section and of the same radius initially, but composed of different elastic materials, are joined together to form a single straight tube with discontinuous properties. Stretching in the axial direction causes radial displacement that varies along the length of the tube. In a perfect inviscid incompressible flow through the tube of variable cross-section the internal pressure varies as described by Bernoulli's equation, and the variable pressure also causes variation of the radial displacement. The equations of coupled finite deformation and fluid pressure problem can be integrated explicitly (using membrane theory for the tube) for arbitrary material properties, but determination of the integration constants is not trivial. The results are interpreted numerically for Mooney materials. Also considered in this context is the similar problem where two semi-infinite cylindrical membranes of the same material are separated by a cuff of different material. Numerical illustrations are obtained for various upstream velocities. The results obtained here thus solve the problem of steady internal pressure loading of this type in extended dissimilar thin isotropic tubes. The tube will become unstable if the fluid velocity is too large. Applications to engineering structures are possible.     

贫铀合金材料自锻弹丸的数值模拟

利用SPH(Smooth Particle Hydrodynamic)算法对贫铀合金材料自锻弹丸过程进行了数值模拟。其中使用了人造爆轰压力,即给定了爆轰压力的时间分布与空间分布。为了描述材料在高压作用下的变形性能,材料模型采用了Johnson-Cook关系。通过数值计算,给出了自锻弹丸的飞行速度、弹丸几何尺寸及炸高等参数。     

一类广义Bent型S-Box的构造

S-box是密码理论与实践中十分重要的一种装置 ,它的密码性能由其分量函数所决定 .于是 ,选择适当的分量函数来构造 S-box就成了一个重要的研究课题 .在一定意义上 ,Bent函数是最优良的密码函数 .本文通过函数序列半群和置换群来构造其任何非零线性组合为 Bent函数与线性函数之和的函数组 ,从而可由 Bent函数构造出具有高度非线性度和其他良好性状的 S-box