利用网格划分软件和缓坡方程计算港内波浪场

提出了一套可方便应用于波浪场计算的方法。该方法包含了准确的边界输入输出技术,简便的地形输入技术,高质量的计算网格生成以及加速查寻、排序的数据结构。应用双曲型缓坡方程计算了港湾内的波浪场,数值计算时提出了处理建筑物表面部分反射边界条件的方法。将计算结果与边界元方法的结果和实验值进行了比较,证明该方法应用于波浪场可得到较理想的结果。对大连港区内的波浪折射绕射进行了计算,表明本方法可以应用于实际港口的波浪场计算中。     

加卸载作用下加筋垫层变形特征试验研究

加筋垫层由于具有诸多优点而被广泛应用于反复加卸载作用下公路、铁路路基等工程构筑物中。为研究加卸载作用下加筋垫层结构的变形特征,针对加筋与未加筋垫层2组模型,开展了单次加卸载静力试验。测试并获得了不同荷载作用下垫层竖向变形、筋材应变变化规律,对比分析了加筋与未加筋垫层的变形特征,并从能量角度对加筋垫层工作机制进行了探讨。结果表明：与未加筋情况相比,荷载作用下加筋垫层（加载板处）的沉降变形和残余变形更小。加筋后垫层表面（加载板范围外）的竖向变形及其受影响范围均增大,且在卸载过程中垫层表面竖向变形的水平分布曲线特征由“凹”型变为“凸”型,其加卸载曲线呈“∞”型。格宾网筋材应变沿横向呈现非均匀分布特点,其最大应变小于0.06%,筋材始终处于弹性变形状态。加筋垫层中筋材具有储存、释放及横向传递应变能效应,这使得加筋后垫层具有更好的承载能力与弹性性能,进而可降低循环加卸载作用下垫层的塑性变形或累计变形。     

A mesh deformation algorithm for free surface problems

Employing the simple iterative technique of adjusting the element positions using computed potentials to locate the free surface can lead to finite elements with large aspect ratios as the free surface drops towards the base of the mesh. In particular, free surface modelling of earth dams with base drains suffer from this problem. The paper suggests a number of steps which can be taken to alleviate mesh distortion problems and improve the numerical stability of the iterative finite element analysis. This leads to a mesh deformation algorithm which adjusts element widths in a simple fashion depending on the free surface height as the iterations proceed. The algorithm is specialized to the sloped earth dam problem, but may find application to other geometries. © 1997 by John Wiley & Sons, Ltd.     

三维正交非结构网格数值模型中物理流场的定义方法与改进

使用Casulli等(2000)的数值方法建立了基于正交非结构网格的U型渠道的三维近岸正压水动力数值模型,检验了模型使用ELM(Eulerian-Lagrangian Method)方法处理平流项时,物理流场的定义对模拟结果的作用。数值试验和结果分析说明,使用ELM方法计算平流项所需的物理流场对计算结果影响明显,而目前常用的两种物理流场定义方法都存在一定不足——水位计算值对流速变化的反映不灵敏或者会产生小扰动等。针对常用物理流场定义方法的不足之处,作者在Casulli方法的基础上利用对多边形切向流速分量进行平均的方法改进了物理流场定义,抑制了小扰动。     

Transmittance investigation on capacitive mesh on thick dielectric substrates as output windows for optically pumped terahertz lasers

This paper reports that an output window for optically pumped terahertz (THz) laser has been fabricated by depositing a capacitive nickel-mesh on a thick high-resistivity silicon substrate (approximating to 5 mm thick). Unlike the conventional process of depositing a gold film approximating to 100 nm on negative photoresist using electron-beam evaporation, a nickel film approximating to 1.5 μm thick is directly deposited on the clean surface of dielectric substrate using magnetron sputtering and then a positive photoresist is spun onto the nickel metal surface at 6000 r for 60 s. A transmittance spectrum of the output window in a certain frequency range (say, from zero to 1 THz) has been obtained by using THz time domain spectroscopy. Moreover a transmittance spectrum simulated numerically has also been estimated with respect to the output window using the transmission-line model (TLM) containing attenuation component from dielectric substrate. The simulation results show that the TLM can explain well the experimental curve in a certain frequency range from zero to 1 THz. Thus it is demonstrated that the improved optical component can be efficiently used as both output coupler and output window for optically pumped THz lasers.     

Discrete element modelling of an underground explosion in a jointed rock mass

The purpose of this paper is to investigate the application of the discrete element program UDEC for modelling underground explosions in a jointed rock mass. A field underground explosion test has been conducted and UDEC and AUTODYN were utilised in a coupled manner to predict the rock mass response due to the underground explosion. The dynamic equation for the state of the rock material obtained from impact tests was incorporated into the calibration modelling. The comparison of modelling results with test results and empirical formulas shows that UDEC is capable of modelling explosion wave propagation in jointed rock mass with high reliability.     

河北省变网格数值预报系统设计和试验

设计了一种将原ＭＭ４模式的均匀网格变换成非均匀网格的方案,构造了一套适合河北省特点的变网格预报模式,同时建立了一套可投入业务使用的变网格数值预报系统,最后通过一次暴雨过程的模拟分析,证明变网格数值预报优于均匀网格数值预报     

无压渗流分析的复合单元法

针对无压渗流问题,在传导矩阵调整法的基础上,对穿越自由面的单元用复合单元来处理,每个复合单元具有两套结点水头,一套用于饱和区的水头插值;另一套则用于无水区。通过变分原理,推出了控制方程并在程序中实现。应用复合单元法可以较好地解决自由面的插值问题,消除了穿过自由面单元的水上部分对自由面附近结点水头的贡献,同时对逸出面边界条件的处理也更加方便和准确。算例表明了该方法的有效性。     

An unstructured-grid, finite-volume, nonhydrostatic, parallel coastal ocean simulator

A finite-volume formulation is presented that solves the three-dimensional, nonhydrostatic Navier–Stokes equations with the Boussinesq approximation on an unstructured, staggered, z-level grid, with the goal of simulating nonhydrostatic processes in the coastal ocean with grid resolutions of tens of meters. In particular, the code has been developed to simulate the nonlinear, nonhydrostatic internal wave field in the littoral ocean. The method is based on the formulation developed by Casulli, in that the free-surface and vertical diffusion are semi-implicit, thereby removing stability limitations associated with the surface gravity wave and vertical diffusion terms. The remaining terms in the momentum equations are discretized explicitly with the second-order Adams–Bashforth method, while the pressure-correction method is employed for the nonhydrostatic pressure in order to achieve overall second-order temporal accuracy. Advection of momentum is accomplished with an Eulerian discretization which conserves momentum in cells that do not contain the free surface, and scalar advection is discretized in a way that ensures consistency with continuity, thereby ensuring local and global mass conservation using a velocity field that conserves volume on a local and global basis. The nonhydrostatic pressure field is solved efficiently using a block-Jacobi preconditioner, and while stability is limited by the internal gravity wave speed and vertical advection of momentum, applications requiring relatively small time steps due to accuracy or stability constraints are run efficiently on parallel computers, since the present formulation is written entirely with the message-passing interface (MPI). The ParMETIS libraries are employed in order to achieve a load-balanced parallel partitioning that minimizes interprocessor communication, and the grid is reordered to optimize per-processor performance by limiting cache misses while accessing arrays in memory. Test cases demonstrate the ability of the code to efficiently and accurately compute the nonhydrostatic lock exchange and internal waves in idealized as well as real domains, and we evaluate the parallel efficiency of the code using up to 32 processors.     

Numerical modeling of local scour due to submerged wall jets using a strict vertex-based,terrain conformal,moving-mesh technique in OpenFOAM

This study presents the implementation and validation of a new sediment-scour model with a strict vertex-based,terrain conformal,moving-mesh technique within the framework of OpenFOAM.OpenFOAM lacks the ability to simulate large-amplitude motion needed for analysis of sediment-scour problems,and,thus,its application normally is restricted to small-amplitude cases to prevent computational divergence due to mesh deterioration.The proposed simple,moving-mesh technique in OpenFOAM is implemented to overcome the shortcomings of the conventional automatic mesh-motion techniques in handling large-amplitude moving geometries.The model is used to simulate a simple case of prescribed boundary motion,a previous experiment in the literature,and a new laboratory experiment for local scour due to submerged wall jets.The results are compared with both the experimental and other numerical results.The comparisons demonstrate that the proposed model has the novel advantage of allowing for more severe topographic variations,and can provide more reliable predictions for the key characteristics and evolution of the bed profiles in wall jet scour problems.Furthermore,to improve the practice of modeling wall jet scour,various turbulence modeling approaches and bedload equations also are evaluated and compared.