论一类四阶Boussinesq方程的变浅性能

Boussinesq 类水波模型在港口、海岸以及海洋工程领域应用广泛,但以前对这类模型的变浅性能的研究不够充分. 针对Madsen 和Schäffer 提出的一组四阶Boussinesq 方程,从理论和数值两个方面对这一问题进行了探讨. 理论分析了其变浅性能,指出该文献中参数α₂ 和β₂ 的取值是不合理的,并重新确定其取值. 在交错网格下建立了基于混合4 阶Adams-Bashforth-Moulton 格式的预报-校正数值模型. 数值模拟了两个典型算例： 一是缓变平坡地形上波浪的传播变形,二是波浪在淹没梯形潜堤上的波浪演化过程. 计算结果分别与解析结果、物理模型实验结果进行了比较,发现变浅系数的取值对数值结果影响很大,新参数比原文参数模拟结果的吻合程度更高,这佐证了理论分析.     

Complex turbulent compressible flow computation using a two-layer approach

A two-layer approach is proposed to compute complex flows including separations. For high- and low-Reynolds-number regions we use a two-equation k-? model and a one-equation k-L model respectively. A robust algorithm is proposed for the treatment of the convective part of the turbulence equations. Several complex configurations including separations are computed.     

A solution for the vertical variation of stress,rather than velocity,in a three-dimensional circulation model

A simple technique is presented that allows a numerical solution to be sought for the vertical variation of shear stress as a substitute for the vertical variation of velocity in a three-dimensional hydrodynamic model. In its most general form the direct stress solution (DSS) method depends only upon the validity of an eddy viscosity relation between the shear stress and the vertical gradient of velocity. The rationale for preferring a numerical solution for shear stress to one for velocity is that shear stress tends to vary more slowly over the vertical than velocity, particularly near boundaries. Consequently, a numerical solution can be obtained much more efficiently for shear stress than for velocity. When needed, the velocity profile can be recovered from the stress profile by solving a one-dimensional integral equation over the vertical. For most practical problems this equation can be solved in closed form. Comparisons are presented between the DSS technique, the standard velocity solution technique and analytical solutions for wind-driven circulation in an unstratified, closed, rectangular channel governed by the linear equations of motion. In no case was the computational effort required by the velocity solution competitive with the DSS when a physically realistic boundary layer was included. The DSS technique should be particularly beneficial in numerical models of relatively shallow water bodies in which the bottom and surface boundary layers occupy a significant portion of the water column.     

Numerical simulation and experimental verification of silicone oil flow over magnetic fluid under applied magnetic field

Two-layer flow of magnetic fluid and non-magnetic silicone oil was simulated numerically. The continuity equation, momentum equations, kinematic equation, and magnetic potential equation were solved in two-dimensional Cartesian coordinate. PLIC （piecewise linear integration calculation） VOF （volume of fluid） scheme was employed to track the free interface. Surface tension was treated via a continuous surface force （CSF） model that ensures robustness and accuracy. The influences of applied magnetic field, inlet velocity profile, initial surface disturbance of interface and surface tension were analyzed. The computed interface shapes at different conditions were compared with experimental observation.     

Prediction of turbulent wall shear flows directly from wall

The fully elliptic Reynolds-averaged Navier–Stokes equations have been used together with Lam and Bremhorst's low-Reynolds-number model, Chen and Patel's two-layer model and a two-point wall function method incorporated into the standard k-? model to predict channel flows and a backward-facig step flow. These flows enable the evaluation of the performance of different near-wall treatments in flows involving streamwise and normal pressure gradients, flows with separation and flows with non-equilibrium turbulence characteristics. Direct numerical simulation (DNS) of a channel flow with Re =3200 further provides the detailed budgets of each modelling term of the k and ?-transport equations. Comparison of model results with DNS data to evaluate the performance of each modelling term is also made in the present study. It is concluded that the low-Reynolds-number model has wider applicability and performs better than the two-layer model and wall function approaches. Comparison with DNS data further shows that large discrepancies exist between the DNS budgets and the modelled production and destruction terms of the ? equation. However, for simple channel flow the discrepancies are similar in magnitude but opposite in sign, so they are cancelled by each other. This may explain why, even when employing such an inaccurately modelled ?-equation, one can still predict satisfactorily some simple turbulent flows.     

Complementary mild-slope equations in a two-layer fluid

Mild-slope (MS) type equations are depth-integrated models, which predict under appropriate conditions refraction and diffraction of linear time-harmonic water waves. By using a streamfunction formulation instead of a velocity potential one, the complementary mild-slope equation (CMSE) was shown to give better agreement with exact linear theory compared to other MS-type equations. The main goal of this work is to extend the CMSE model for solving two-layer flow with a free-surface. In order to allow for an exact reference, an analytical solution for a two-layer fluid over a sloping plane beach is derived. This analytical solution is used for validating the results of the approximated MS-type models. It is found that the two-layer CMSE model performs better than the potential based one. In addition, the new model is used for investigating the scattering of linear surface water waves and interfacial ones over variable bathymetry.     

液—液旋流分离管中强旋湍流的K—ε …

采用标准ｋ－ε湍流模型,对一种典型液－液旋流分离管中的强旋湍流进行了数值模拟研究。结果表明：该模型对切向速度的数值预报夸大了Ｒａｎｋｉｎｅ涡中的似固核范围。抹煞了似固核外的位涡区;对轴向速度的数值预报未给出心回流区;对其它流场参数的预报结果也都存在有明显的不合理之处。由此证明这种基于Ｂｏｕｓｓｉｎｅｓｑ假设的各向同性湍流模型,虽然在管道流、平面射流和无旋流等简单流动问题中经受住了大量计算实践的检验     

破碎带波浪的数值模拟

基于一组色散关系得到改进的完全非线性Boussinesq方程建立了一个波浪模型可以模拟近岸水域的波浪变浅、破碎以及在海滩上的爬高等多种变形.波浪破碎引起的能量衰减是在动量方程中引入一个在空间和时间上都只作用于波前的涡粘项来模拟.动海岸线边界用窄缝法处理.波浪爬高用非线性浅水方程推导的非破碎波浪在斜坡上爬高的解析解来验证.本模型还模拟了波浪在斜坡上不同类型的破碎变形过程,并将其波高和平均水位的沿程变化和物理模型实验的结果比较,两者符合良好.     

圆柱形有壳装药侧向飞散速度分布的预估

对圆柱形有壳装药侧向飞散速度的分布,本文提出了一种改进的预估方法,与实验结果有较好相符。这一方法是从装药侧面冲量分布出发,加以适当变换(经验修正),既比用HEMP程序计算来得省钱,也可象用HEMP程序计算那样适合多种起爆方式。为实用目的,文中还给出了侧向飞散最大速度值的估算方法。     

Love wave dispersion in pre-stressed homogeneous medium over a porous half-space with irregular boundary surfaces

The paper investigates the existence of Love wave propagation in an initially stressed homogeneous layer over a porous half-space with irregular boundary surfaces. The method of separation of variables has been adopted to get an analytical solution for the dispersion equation and thus dispersion equations have been obtained in several particular cases. Propagation of Love wave is influenced by initial stress parameters, corrugation parameter and porosity of half-space. Velocity of Love waves have been plotted in several figures to study the effect of various parameters and found that the velocity of wave decreases with increases of non-dimensional wave number. It has been observed that the phase velocity decreases with increase of initial stress parameters and porosity of half-space.     

港口非线性波浪耦合计算模型研究

建立了外域用差分法求解高阶Boussinesq方程、内域用边界元法求解Laplace方程的二维船非线性波浪力时域计算的耦合模型. 研究了该类耦合模型的匹配条件、耦合求解过程和内域、外域公共区域长度的确定. 该耦合模型计算结果与只用边界元求解Laplace方程模型的计算结果和实验结果对比表明,该耦合模型不仅计算精度高,而且计算效率快,适用于研究较大区域内波浪对物体的非线性作用.