考虑钻具接头影响的环空压耗计算

控压钻井是针对"窄安全压力窗口"现象所引起的勘探开发过程中的钻井难题所提出的,井筒压力分布的准确预测是保证控压钻井顺利实施的前提,为提高井筒压力的预测精度需准确计算环空摩阻压耗,应用量纲分析理论,综合考虑钻具接头、钻具旋转的影响,修正了环空摩阻压耗计算模型,提高了井筒压力的预测精度.模型研究表明:随着钻井液排量的增加,钻井液从层流变为紊流,局部摩阻压耗明显增加;且井越深,接头的累计压耗越大,接头对总摩阻压耗的贡献增加.随着钻具旋转速度的增加,环空压耗的增加或减少取决于惯性力与剪切稀释的共同作用.     

环形断面管道水击波速公式推导及其摩阻损失分析

为研究石油开采、轴流泵等工程中环形断面管道液流的运动规律和现象,探讨目前鲜见研究的环形断面管道水击问题．文章针对环形断面管道的结构特点和流体运动特性,推导了环形断面管道水击波速的计算公式,讨论了公式中液流摩阻项的计算方法和对公式的影响．得出的环形断面管道水击波速公式,可为其液流流动规律和特性的进一步研究提供参考.     

精确计算Bingham流体圆管层流压降及速度分布规律的新方法

Bingham(宾汉)模型情况下,多采用通用公式进行圆管层流压降的解析计算,即将Bingham模型本构方程代入粘性流体圆管层流流动通用公式进行计算,仅能得到压降的解析解.新方法结合Bingham流体本构方程与运动方程,建立有关力学平衡方程,并运用代数方程的根式解理论对圆管层流流动时的非线性方程进行求解,可直接求得Bingham流体圆管层流压降及速度流核区半径的解析解,进一步可求得圆管层流速度解析解;Bingham流体圆管层流速度的直接影响因素为流量、塑性粘度和屈服值,研究发现速度流核宽度与屈服值成正比,与流量及塑性粘度成反比,且流核的宽度越大,流核区的速度越小.     

关于浅海中简正波衰减与群速的讨论

详细地讨论了浅海简正波衰减与群速的计算问题,并提出了一种新的计算简正波衰减与群速的修正加权权分公式.在 Pekeris浅海情况下,比较了该公式与循环距离公式、加权积分公式的计算精度和适用范围,并研究了上述3种公式对浅海声传播计算的影响.理论分析与数值结果表明,修正加权积分公式比国际上流行的加权积分公式有更高的精度,可广泛应用于浅海声场的计算.     

光滑壁面明渠均匀紊流水力特性

水流进入光滑壁面明渠后,沿水流方向历经层流边界层,转捩区,紊流边界层,充分发展紊流边界层及明渠均勻紊流等流动区域。明渠均匀紊流中流动的时均及紊动特性均不再沿程变化。光滑壁面明渠均勻紊流中,沿水深方向流动具有明显的分区结构。本文给出了分区界限及各分区中时均流速分布公式及脉动流速的特征。本文提出当明渠的宽深比W/H大于10时方可将中心区流动视为二维流动,并给出了断面平均流速及阻力系数的计算公式。     

黏性分层流中椭球体俯仰振荡研究

以黏性密度分层流下椭球体自由俯仰振荡衰减过程为研究内容,建立了密度连续分层流数值计算模型.通过对经典小球黏性绕流场的数值模拟和增阻系数的计算验证了数值模型的正确性.以初始45°攻角下的椭球体俯仰振荡过程为研究对象,采用基于Aitken亚松弛适应算法的双向流固耦合方法,数值模拟了不同内Froude(弗汝德)数Fri下椭球体俯仰衰减振荡的动态绕流场.数值研究结果表明,俯仰振荡将上下搅动周围流体,在椭球体上下两侧对称形成四个密度涡环,密度的垂向分层限制了涡环的垂向传播,也加速了涡环的消失,这种限制助长了水平运动的发展,远场尾涡流场将以水平波动的形式传播.在较高的内Froude数Fri和Reynolds(雷诺)数Re下,双向耦合抑制了数值震荡.研究还发现,随着来流速度的增加,阻力系数不增反降,这说明,对于自由俯仰振荡的椭球体,负阻尼现象仍然会出现.     

超音速平板边界层转捩中层流突变为湍流的机理研究

采用空间模式,对来流Mach数为4.5的平板边界层转捩过程做了直接数值模拟．对结果进行的分析发现,在层流-湍流转捩的突变(breakdown)过程中,层流剖面得以快速转变为湍流剖面的机理在于平均剖面的修正导致了其稳定性特征的显著变化．虽然在层流下第2模态T-S波更不稳定,但在层流突变为湍流的过程中,第1模态不稳定波也起了重要作用．     

高超音速零攻角尖锥边界层转捩的机理

先计算出高超音速零攻角尖锥边界层的定常层流流场．然后在计算域的入口引入两组有限幅值的T-S波扰动,对空间模式的转捩过程进行了直接数值模拟．分析了转捩过程的机理,发现平均流剖面稳定性的变化是其关键．并进一步讨论了不同模态初始扰动在高超音速尖锥边界层中的演化规律．     

填充烧结铜球的T型管中流体混合的大涡模拟

在FLUENT软件平台上,运用大涡模拟湍流模型及Smagorinsky-Lilly亚格子尺度模型,对填充有烧结铜球多孔介质的T型管道内冷热流体混合过程的流动与传热情况进行了数值计算,与未填充多孔介质时混合区域内的平均温度和温度波动、平均速度和速度波动等数据进行了对比,并对温度波动进行了功率谱密度分析．数值结果表明,多孔介质可有效削弱T型通道流体混合区域内的温度和速度波动,有效降低1 Hz至10 Hz频域中的温度波动的功率谱密度．     

一种适用于非均匀地形的高阶Boussinesq水波模型

推导了适用于变地形情况的高阶Boussinesq波浪模型．该模型采用自由表面边界条件作为时间步进方程,利用势函数满足的Laplace方程的解析解形式建立了自由表面边界速度和底面边界速度之间的关系,使得问题封闭．以0.5倍相对水深处的速度为基本未知量,在对Laplace方程解析解进行级数求逆时保留水深梯度的高阶项,改进了速度场的Taylor展开式．对于线性特性,进行了线性浅化和Booij反射的验证性计算．为了检验有背景流动情况下拓展的Boussinesq模型的性态,对波-流相互作用问题进行了数值模拟．数值计算结果与现有理论解或其他完全势流的数值解吻合良好,表明该模型的应用范围可以扩展到含有非均匀变化地形的问题．     

分析管流水力-热力瞬变的双特征线法

研究了管道内流体流动的水力瞬变及热力瞬变,改进了分析介质顺序输送管流水力瞬变的特征线法;推导了含流速v的 3次方的热力瞬变方程,构造了相应的特征线法;建立了分析介质顺序输送管流耦合的水力-热力瞬变的双特征线法。     

Damping of water hammer oscillations – comparison of 3D CFD and 1D calculations using two selected models for pipe friction

Water hammer calculations are important for power plants, drinking water systems and procedural facilities. In most cases, the piping systems are very big and the probability of a resonance between a part of the piping system and a hydraulic oscillation resulting from water hammer is very high. The limiting factors for the amplitudes of the structural stresses and strains are the structural and hydraulic damping. In general, one-dimensional codes based on the method of characteristics with quasi-steady friction models are used to calculate the hydraulic system. This results in too small damping of the pressure oscillation and thus in an overestimation of the structural loads. Two models from the literature for a more physical reproduction of the fluid damping using one-dimensional codes are presented and compared with a quasi-steady pipe friction model. Additionally, a three-dimensional computational fluid dynamics simulation of a water hammer oscillation in a small pipe section including a 90°-bend was carried out. A comparison of the results of the three-dimensional simulation and the one-dimensional calculations with regard to the pressure and friction velocity distributions was performed, the performance of the models was evaluated and the limits of validity were identified. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of temperature-dependent viscosity and variable thermal conductivity on MHD non-Darcy mixed convective diffusion of species over a stretching sheet

A numerical model is presented to study the effects of temperature-dependent viscosity and variable thermal conductivity on mixed convection problem. Two important types of wall heating conditions namely, prescribed surface temperature and prescribed wall heat flux which arise in polymer industries are considered. The problem is solved numerically by using the fifth-order Runge–Kutta Fehlberg method with shooting technique. It is found that the Prandtl number is to decrease the skin friction coefficient, local Nusselt number and local Sherwood number. The effects of non-uniform heat source/sink and porous parameter are analyzed on velocity, temperature, skin friction co-efficient, Nusselt and Sherwood numbers.     

放/吸热流体在两个充满多孔材料的竖直平行板之间作不稳定的自然对流

在一个由两块无限竖直平行板组成的管道中,充满着多孔的介质材料,使用Darcy模型(Brinkman模型的推广)的动量方程,连同能量方程,计算不可压缩、粘性、放/吸热流体在该管道中的不稳定自然对流,即Couette流动.流动是由于边界平板有不对称的加热,以及作加速运动所引起.选用合理的无量纲参数,对控制方程进行简化,通过Laplace变换进行解析求解,得到闭式的速度和温度分布曲线解,随后导出表面摩擦力和传热率.发现在竖直管道中的不同剖面,流体的流动及温度分布曲线随着时间而增加,且在运动平板附近更高.特别是,流体的速度和温度随着平板间距的增加而增加,但是,表面摩擦力和热传导率随着平板间距的增加而减小.     

Mathematical modelling of hydraulic transients in simple systems

Efficiency and economy in the design and operation of a hydraulic system, as well as its safety, are objectives needing precise calculations of pressures and flowrates within the system. The calculations are typically very time-consuming and, depending on the characteristics of the system, very complicated and difficult to organize. A suitable mathematical modelling of the different ingredients in a hydraulic system is necessary to get useful results, which help fulfill those objectives. In this paper, the mathematical modelling used to develop a computer program to simulate hydraulic transients in a simple system is described. The program (DYAGATS), developed by the authors, is currently being used by organizations and consultancies to simulate and, consequently, analyze hydraulic transients in water systems. It makes use of the so-called elastic model, also known as waterhammer, to model the behavior of the fluid within the pipes. Also, lump models for the different elements that introduce, damp, modify, absorb, etc., perturbations in the systems are presented in a unified treatment. The main objective is to provide users with a powerful tool to devise the potential risks to which an installation may be exposed and to develop suitable protection strategies.     

计及Hall和离子滑移电流的旋转流体在与时间相关初值条件下的MHDCouette流动

考虑Hall和离子滑移电流的影响,在旋转系统中研究导电流体非稳定的MHD Couette流动．在小数值磁场Reynolds数假定下,推导出基本的控制方程,使用著名的Laplace变换技术,数值地求解该基本方程．分两种情况:磁场相对于流体或者移动平板固定时,得到速度和表面摩擦力统一的闭式表达式．用图形讨论了问题的不同参数,对速度和表面摩擦力的影响．所得结果显示,主流速度u和次生速度v随着Hall电流而增大．离子滑移电流的增大,也会导致主流速度u的增大,但会使次生速度v减小．还给出了旋转、Hall和离子滑移参数的综合影响,确定了次生运动对流体流动的贡献．     

Analytical Formulation of the Classical Friction Model for Motion Analysis and Simulation

Starting from a precise definition of friction torque when velocity vanishes that distinguishes the case of instantaneous zero crossing from that where the velocity is zero over a time interval, this paper proposes a compact analytical formulation of the classical discontinuous friction model that is useful for motion analysis. A finite state machine that allows a numerically robust computation of motion equations when velocity vanishes or motion restarts is then defined. Simulation results show that the discontinuous model can be seen as an asymptotic approximation, infinitely fast, of a recently proposed continuous, dynamic friction model.     

壁面马赫数分布规律可控的新型内收缩基准流场设计方法

根据有旋特征线理论,设计出了沿程马赫数下降规律可控的轴对称基准流场,分析了基准流场的几何参数(前缘压缩角及中心体半径)的影响规律,发现选取较小的前缘压缩角和中心体半径有利于得到性能优良的基准流场;然后在设计状态Ma=6时研究了三种典型的马赫数下降规律对这种轴对称流场性能的影响。最后考虑了粘性的影响,并进行了粘性修正探索,结果表明,采用附面层位移厚度修正方法后,基准流场的壁面压力分布和无粘情况吻合良好。      

剪切平行板间密集颗粒流的接触力分布及各向异性分析

研究了剪切平行板间密集颗粒流的接触力分布规律、接触力网络的各向异性、颗粒摩擦因数对宏观流变特性及细观力链分布的影响等．为了研究以上内容,应用计算机建立了离散元数值分析模型．数值分析结果表明,颗粒之间的接触力分布按幂函数规律变化;接触角分布服从指数函数规律,平均法向接触力随平均接触角任意上下振荡变化;波动速度大小为宏观流变顺畅与否的关键性评价指标,而在细观力链方面,当剪切平行板间颗粒流变不畅时会伴随着超强力链数目显著增加．     

Friction and wear of certain thermoplastic materials in physiological solution

The wear resistance of certain thermoplastics has been subjected to comparative investigation together with the velocity dependence of the coefficients of friction at various pressures and after various periods of contact with a model physiological solution.Priorov Central Scientific-Research Institute of Traumatology and Orthopedics. Moscow Technological Institute of the Food Industry. Second Moscow Pirogov State Medical Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1116–1119, November–December, 1971.