A kind of extended Korteweg-de Vries equation and solitary wave solutions for interfacial waves in a two-fluid system

This paper considers interfacial waves propagating along the interface between a two-dimensional two-fluid with a flat bottom and a rigid upper boundary. There is a light fluid layer overlying a heavier one in the system, and a small density difference exists between the two layers. It just focuses on the weakly non-linear small amplitude waves by introducing two small independent parameters： the nonlinearity ratio ε, represented by the ratio of amplitude to depth, and the dispersion ratio μ, represented by the square of the ratio of depth to wave length, which quantify the relative importance of nonlinearity and dispersion. It derives an extended KdV equation of the interfacial waves using the method adopted by Dullin et al in the study of the surface waves when considering the order up to O（μ^2）. As expected, the equation derived from the present work includes, as special cases, those obtained by Dullin et al for surface waves when the surface tension is neglected. The equation derived using an alternative method here is the same as the equation presented by Choi and Camassa. Also it solves the equation by borrowing the method presented by Marchant used for surface waves, and obtains its asymptotic solitary wave solutions when the weakly nonlinear and weakly dispersive terms are balanced in the extended KdV equation.

High-order targeted essentially non-oscillatory scheme for two-fluid plasma model

The weakly ionized plasma flows in aerospace are commonly simulated by the single-fluid model,which cannot describe certain nonequilibrium phenomena by finite collisions of particles,decreasing the fidelity of the solution.Based on an alternative formulation of the targeted essentially non-oscillatory(TENO)scheme,a novel high-order numerical scheme is proposed to simulate the two-fluid plasmas problems.The numerical flux is constructed by the TENO interpolation of the solution and its derivatives,instead of being reconstructed from the physical flux.The present scheme is used to solve the two sets of Euler equations coupled with Maxwell's equations.The numerical methods are verified by several classical plasma problems.The results show that compared with the original TENO scheme,the present scheme can suppress the non-physical oscillations and reduce the numerical dissipation.

Screening effect of plasma flow on the resonant magnetic perturbation penetration in tokamaks based on two-fluid model

Numerical simulation on the resonant magnetic perturbation penetration is carried out by the newly-updated initial value code MDC(MHD@Dalian Code).Based on a set of two-fluid fourfield equations,the bootstrap current,parallel,and perpendicular transport effects are included appropriately.Taking into account the bootstrap current,a mode penetration-like phenomenon is found,which is essentially different from the classical tearing mode model.To reveal the influence of the plasma flow on the mode penetration process,E×B drift flow and diamagnetic drift flow are separately applied to compare their effects.Numerical results show that a sufficiently large diamagnetic drift flow can drive a strong stabilizing effect on the neoclassical tearing mode.Furthermore,an oscillation phenomenon of island width is discovered.By analyzing it in depth,it is found that this oscillation phenomenon is due to the negative feedback regulation of pressure on the magnetic island.This physical mechanism is verified again by key parameter scanning.

激光光热效应对双层流体热毛细对流主动调控机理研究

热毛细对流不稳定性的主动调控是微重力流体力学和传热传质学领域的前沿问题,为了实现双层流体热毛细对流不稳定性的有效控制,提出利用激光光热效应对其不稳定性进行主动调控,并模型化研究了激光光热效应参数(激光束位置、激光功率和光斑尺寸)对双层热毛细对流不稳定性的调控作用机理.计算结果显示,激光功率和光斑尺寸的调整能够显著改变双层流体热毛细对流的对流涡结构,并减小温度波的振动幅度.在一定工况下,热源附近温度波动范围由0.7 K变为0.1 K,变化显著;随光斑尺寸增大,温度振荡幅度先减小后增大.激光位置的调整能够影响液层局部对流涡的位置,进而改变激光位置两侧对流强度,实现局部区域的振荡不稳定流动的控制,通过光热效应参数的合理选择,可以实现对双层流体热毛细对流的有效控制.

Effects of diamagnetic drift on nonlinear interaction between multi-helicity neoclassical tearing modes

A numerical study of the diamagnetic drift effect on the nonlinear interaction between multi-helicity neoclassical tearing modes(NTMs) is carried out using a set of four-field equations including two-fluid effects.The results show that,in contrast to the single-fluid case,5/3 NTM cannot be completely suppressed by 3/2 NTM with diamagnetic drift flow.Both modes exhibit oscillation and coexist in the saturated phase.To better understand the effect of the diamagnetic drift flow on multiple-helicity NTMs,the influence of typical relevant parameters is investigated.It is found that the average saturated magnetic island width increases with increasing bootstrap current fraction f_(b) but decreases with the ion skin depth δ.In addition,as the ratio of parallel to perpendicular transport coefficients χ_(‖)/χ_(⊥) increases,the average saturated magnetic island widths of the 3/2 and 5/3 NTMs increase.The underlying mechanisms behind these observations are discussed in detail.

Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model

Optical superconducting transition-edge sensor(TES)has been widely used in quantum information,biological imaging,and fluorescence microscopy owing to its high quantum efficiency,low dark count,and photon number resolving capability.The temperature sensitivity(α_(I))and current sensitivity(β_(I))are important parameters for optical TESs,which are generally extracted from the complex impedance.Here we present a method to extractα_(I)andβ_(I)based on a two-fluid model and compare the calculated current-voltage curves,pulse response,and theoretical energy resolution with the measured ones.This method shows qualitative agreement that is suitable for further optimization of optical TESs.

Two-fluid oscillatory flow in a channel

The validity of Navier’s partial slip condition is investigated by studying the oscillatory flow in a coated channel.The two-fluid model is used to solve the unsteady viscous equations exactly.Partial slip is experienced by the core fluid.It is found that Naviers condition does not hold for an unsteady core fluid.

Anisotropic Plane Symmetric Two-Fluid Cosmological Model with Time-Varying G and A

We investigate a two-fluid anisotropic plane symmetric cosmological model with variable gravitational constant G（t） and cosmological term A（t）. In the two-fluid model, one fluid is chosen to be that of the radiation field modeling the cosmic microwave background and the other one a perfect fluid modeling the material content of the universe. Exact solutions of the field equations are obtained by using a special form for the average scale factor which corresponds to a specific time-varying deceleration parameter. The model obtained presents a cosmological scenario which describes an early acceleration and late-time deceleration. The gravitation constant increases with the cosmic time whereas the cosmological term decreases and asymptotically tends to zero. The physical and kinematical behaviors of the associated fluid parameters are discussed.

两层及三层流体间内波理论研究进展

内波作为一种发生在层化海洋内部的波动,在世界海洋范围内普遍存在。深入研究内波生成、演化等特性,对我国的海洋开发有着重要意义。针对两层及三层流体间内波理论,选取目前国内外广泛应用的KdV (Korteweg-de Vries)内波理论、MCC (Miyata-Choi-Camassa)内波理论、层析内波理论以及DJL (Dubreil-Jacotin-Long)内波理论综述其研究进展。从数学模型、理论研究以及数值模拟等方面,讨论了不同内波理论的优势以及局限性。从数学推导的角度,证明了MCC内波理论与第一级别层析内波理论是一致的。

悬浮物清除系统的射流器两相紊流数值模拟研究

通过水系统悬浮物清除系统所需射流器建立的三维紊动射流数学模型,对特殊结构形式的射流器进行流场结构和射流紊流动力学性能的研究,通过数学模型计算射流器的紊流流场分布,掌握流场的流体动力学机理,从而获得最接近射流器紊流流场实际状态的描述方法。

管道冲蚀液-固数值模拟的研究进展

在石油和天然气行业中,管道输送系统的弯管和管汇处极易受到固体颗粒的冲蚀,从而导致管道内承受高压能力削弱,加大了在传输过程的风险。首先对固体颗粒冲蚀机理的发展历程进行了回顾,总结了现阶段固体颗粒冲蚀磨损行为的研究现状,概述了塑性材料和脆性材料冲蚀理论模型。其次,分别从液体流动属性和固体颗粒流动属性两个方面对冲蚀的影响因素进行了阐述,评价了各湍流模型和冲蚀模型的优势和适用范围。随后,综述了中外流体仿真软件在管道冲蚀模拟的研究进展。从弯管到管汇,再到高压泵和旋流分离器等,模拟对象有着复杂的几何形状;网格划分由不变形到可变形,再到无网格划分,大大增加了计算的模拟精度。最后,提出了冲蚀模拟仿真在管道行业的下一步研究和发展方向。为今后的整体管道系统冲蚀预测和位置布局设计提供参考。

致密气藏二开结构水平井钻井液体系及现场应用

为解决苏里格气田致密气藏二开结构水平井钻井施工中地层塌漏矛盾突出、降摩减阻及井眼净化困难等技术难题,基于地质特性和泥岩坍塌机理分析,建立摩阻扭矩计算模型,对比变更井身结构摩阻及扭矩变化规律。通过室内研究筛选采用纳米乳液、软硬结合的封堵剂、多元复配的润滑剂和高效提切剂,研发出新型强封堵超润滑水基钻井液体系。室内研究显示,该钻井液体系具有强抑制性和封堵防塌性,能够有效延长硬脆性泥岩失稳周期,进而深度维持井壁稳定,同时也具备良好的流变性和润滑性,且含砂和固相含量低,降摩减阻效果显著。现场应用表明,应用该钻井液体系后下套管摩阻控制在350 kN以内,钻进下放摩阻降低24.21%,扭矩降低34.31%,平均钻井周期为29.04 d,平均机械钻速为17.64 m/h,较三开结构水平井提速36.5%,井塌划眼损失时间降低89.50%,为苏里格气田致密气藏二开结构水平井推广应用提供了有力保障。

Prediction of pressure gradient and hold-up in horizontal liquid-liquid pipe flow

This paper aims to propose correlations to predict pressure gradient,friction factor and fluid phase hold-up in liquid-liquid horizontal pipe flow.To develop the correlations,experiments are conducted using high viscous oils(202 and 630 mPa⋅s)in a steel pipe of length 11.25 m and length-to-diameter ratio of 708.In addition,the experimental data from the literature comprising wide range of flow and fluid properties is analyzed.For the analysis,the liquid-liquid pipe flow data is categorized into two as:stratified and dispersed.The existing friction factor correlations are modified to incorporate the effects of viscosity of the oil phase,interfacial curvature(contact/wetting angle-in lieu of material of the pipe)and fluid phase fraction.In the two-fluid model of stratified flow,the wall stress and interfacial stress correlations are substituted with superficial velocities of fluids and superficial Reynolds numbers of fluid phases replacing fluid phase velocities and fluid Reynolds numbers.Similarly,for dispersed flow,an effective Reynolds number is described as the sum of superficial Reynolds number of oil and water phases.Substituting the generally employed mean or mixture Reynolds number with the effective Reynolds number into the existing single-phase turbulent flow friction factor correlation,an effective friction factor for oil-water flow is proposed.Employing the proposed correlations,the pressure gradient across the oil-water flow and hold-up volume fraction are predicted with significant reduction in error compared with that of conventionally employed correlations.The average error and standard deviation values of−7.06%,20.72%and 0.31%,18.79%are found for stratified flow and dispersed flow respectively.

卵石地层泥水盾构环流管道排渣特性研究

为明晰泥水盾构环流系统管道排渣特性,结合实际设备环流管道的设计与现场应用,使用EDEM(engineering discrete element method)与Fluent耦合的固液两相流仿真技术,对水平-倾斜-水平的连续环流管道渣石和泥浆的运动规律及分布状态进行研究。研究结果显示:1)DDPM模型(dense discrete phase model)相对于DPM模型(discrete phase model)计算精确度更高,更加符合实际情况。2)在初始水平段渣石首先进行悬浮运动,在重力作用下,渣石逐渐沉降在管道底部并进行推移运动。3)渣石在斜管中运动时出现明显的堆积和速度分层现象,斜管截面渣石分布数和最大泥浆流速随着斜管角度的增加先增加后减小,两者均在斜管角度为45°时最大,在90°时最小。4)斜管中渣石平均运动速度随着斜管角度的增加先减小后增加,在斜管角度为45°时最小,在90°时最大。说明渣石在斜管角度为45°左右时堆积比较严重,实际设计中应避免45°左右的斜管。

双流体超细雾化抑尘系统在某金矿的应用

在简介了传统除尘技术及其局限性的基础上,详细介绍了新型、高效除尘系统——双流体超细雾化抑尘系统的构成、工作原理、适用范围和优点,并通过介绍该设备在甘肃礼县某大型金矿破碎机入料口、移动卸料皮带两侧落料口、大型物料堆场进料口以及整体密闭的厂房内等位置的应用,揭示了该系统具有实现水汽喷雾一体化效果,可有效治理无组织排放和有组织排放的粉尘,且没有粉尘的二次污染,矽尘浓度符合职业卫生接触限值的要求,有价资源也得到了充分回收。在国家对环境保护高度重视的背景下,推广、应用双流体超细雾化抑尘系统可以大大减轻企业的环保压力,而且节能减排效果突出。

基于RELAP5的海洋条件下反应堆热工水力系统分析程序开发

研究了倾斜、起伏和摇摆等海洋条件的数学模型。通过修改控制方程,开发了国内首个基于先进的、自由节点划分的RELAP5程序,并且适用于海洋条件的反应堆热工水力系统分析程序RELAP5/MC。用RELAP5/MC对海洋条件下简单两环路系统的自然循环特性进行了计算,其结果都能得到合理解释,由此表明程序开发是初步成功的。

多个两流体程序耦合的核电站系统热工水力建模及仿真研究

为了增加核电站工程模拟器的仿真范围和精度,介绍了基于多个两流体程序耦合的热工水力系统建模方法,并利用RCV与主系统的耦合模型对其准确性进行了验证。基于此,建立了比较全面的核电站系统热工水力模型,并将其在工程模拟器上进行了应用。结果表明,基于多个两流体程序耦合的模型扩展,在保证精度的基础上,增加了模拟器的计算范围,而且可以解决单一模型中节点数量有限、模型庞大导致计算速度较慢、调试困难等问题,从而为提高工程模拟器的性能提供了一个方便可行的方法。

关于振荡型的界面孤立波

当计及表面张力时,对于二流体系统中两层流体深度比的一种临界情形,界面孤立波可用推广的KdV方程来描述,这一方程难以解析地求出孤立波解。本文采用作者提出的推广的PLK方法求得了三阶近似孤立波解,并采用Lindstedt-Poincare方法对所得的结果作了验证,从而首次解析地证实了振荡型界面孤立波的存在性。

永川洗煤泥流变特性和泵送参数选择

从选煤厂排出的洗煤泥，水分在２５％～４０％区间，是一种非牛顿流体，常规仪器不易测准它的粘度．采用管道压降法测定永川高浓度洗煤泥的流变特性，并用数值方法按含水率拟合流变特性的参数方程，通过阻力特性计算求得泵送系统设计参数，并经模拟试验和实际系统运行实测数据验证．

水平磁场对双层流体热毛细对流的影响

三维数值研究了零重力时水平温度梯度作用下,B_2O_3封闭液与InP熔液组成的双层流体系统在水平磁场作用下的热毛细对流.结果显示,当磁场强度较小时,上层流体中对流涡的结构变化甚微,而下层流体中的逆对流涡得到了抑制;随着磁场的增强,温度场分布逐渐趋于均匀,涡量强度逐渐减小,表明热毛细对流强度逐步地得到削弱.当磁场增强到Bx=0.4 T时,上层流体中的对流涡较均匀地充满上层流体区,而下层流体中对流涡紧贴着交界面.