3-D simulations of freak waves based on high-order spectral method

Three-dimensional ( 3-D) directional wave focusing is one of the mechanisms that contribute to the generation of freak waves. To simulate and analyze this phenomenon,a 3-D wave focusing model is proposed based on the enhanced high-order spectral method,which solves the fully nonlinear potential flow equations with a free surface within periodic unbounded 3-D domains. The numerical model is validated against a fifth-order Stokes solution for regular waves. Laboratory-scale freak waves are observed with wave components having equal amplitudes. Investigations of the appearance and propagation of freak-wave events in a 3-D open wavefield defined by a directional wave spectrum are then realized.     

理想结合两层无限大弹性板中波的传播

针对理想结合的两层无限大弹性板，研究了Lamb波的传播特性.从基本特征方程式出发，理论上导出了两组非耦合的求解截止频率的方程式；利用泰勒展开技术，给出了长波区域弯曲振动模式和伸缩振动模式的弥散曲线渐近表达式；利用行列式运算规则，得到了弥散曲线在短波区域的渐近行为.数值计算表明，两层无限大弹性板频谱曲线图上存在且只有两个分支通过原点；在相速度谱曲线上，长波区域存在且只有一个极限相速度，在短波区域有两条分支分别趋近于两种板的Rayleigh波波速.     

电磁波在非均匀等离子体波导中的传播

利用麦克斯韦方程和线性理论推导了电磁波在径向非均匀未磁化等离子体波导中传播的色散方程,对其传播特性进行了讨论,对等离子体在径向具有线性和二次抛物线分布的色散曲线进行了数值计算;发现了电磁波相对于均匀等离子体分布的一些变化规律:HE模式的电磁波截止频率降低,EH模式的电磁波截止频率升高。     

非线性波在动脉内传播的理论

提出了一个新的非线性脉搏波在动脉内传播的理论模型,推导了一个新的血管壁一外周组织系统的非线性运动方程组。这组运动方程与代表血液流动的粘性不可压缩运动的方程、连续方程以及流体和血管壁本构方程相结合,可用数值方法求解非线性脉搏波在动脉内的传播。其数值解包含压力脉搏波、血流速度波和血流量波以及血管壁的波动和变形等。     

非均匀介质中弹性波的传播

对弹性波在非均匀介质传播时的波幅进行了研究,用解析方法探讨了非均匀区域性质变化时对弹性波波幅的影响,将非均匀区域离散成薄层,建立了波动方程和波幅传递矩阵,通过数值计算结果与解析解的比较,为弹性波在工程中的应用提供了计算分析的依据.     

非线性波在动脉内传播的数值研究

伍时桂和李兆治所建设的非线性波传播方程组是做了某些数学简化和变换。无条件稳定的三时间层加权隐式差分方法和SIMPLE方法,分别用来求解动脉壁的运动方程和血液流动方程,得到了包括血液的压力、速度和流量以及动脉壁的位移和速度等非线性脉搏波传播的完全数值解。     

规则波浪中舰船操纵运动计算

当船舶在波浪中处于尾斜浪或顺浪航行时,可能出现稳性丧失和横甩等现象,所以船舶在波浪中的操纵性问题已引起人们的关注.目前,关于该问题的大多数研究往往局限在有限的浪向角范围内.本文在船舶静水操纵性基础上,直接迭加高频的波浪力,建立一个波浪中高频运动响应的操纵性预报方法.用二维Frank源汇分布法计算船舶随摇荡频率变化的附加质量———波浪的辐射力,以及规则波浪的扰动力———Froud Krylov力,在六自由度运动方程上直接迭加所计算的波浪力,并引用静水操纵中船、桨、舵水动力的计算模型,建立了规则波浪中船舶操纵运动预报模型,并数值计算了一条高速方尾船舶在不同规则波浪的波长、波高和浪向角下的操纵舵回转运动和Z形操纵舵运动,附加质量和波浪扰动力根据运动中的遭遇频率和浪向角确定.数值计算的回转角速度、横倾角和纵倾角的变化规律与文献中单桨单舵船模试验有着相似结果.     

障碍物强化爆震起爆和传播的数值模拟与验证

采用非稳态二维轴对称数值模拟的方法研究了圆环形障碍物对爆震起爆和传播的影响,并通过实验进行了验证。研究表明:爆震形成之前,激波的反射与聚交能够产生高温高压点,并大大提高该区域的反应速率,促成局部能量的快速释放,产生局部爆炸;火焰传播速度与相对于障碍物的位置有关,具有极高的脉动特性;DDT(deflagration to detonation transition)过程中迅速增压是在火焰传播到一定区域后开始,在该区域形成向2个方向传播的压缩波,向未燃区传播的压缩波不断加强形成爆震,向已燃区传播的压缩波称为回传爆震,不断衰减;障碍物导致爆震管中压力温度分布极不均匀,与没有障碍物的爆震管完全不同。     

基于保色散关系的迎风WENO格式的研究

W ENO(W eighted E ssentially N on-O scillatory)格式能够高分辨率地捕捉诸如激波等间断,而保色散关系(D issipation-R elation-P reserv ing,DRP)格式适宜于处理高频波传播问题。计算气动声学(Com putational-A eroacoustics,CAA)领域有大量的既有高频波传播又带有激波的问题,结合W ENO格式和DRP格式的优点基于保色散关系构造出优化的迎风W ENO格式。数值实验中比较该格式捕捉波数的能力和精度,显示处理CAA基本问题具有高精度、高分辨率的特点。     

近似到O(μ2)阶完全非线性的Boussinesq水波方程

为了获得具有更优性能的波浪传播数学模型,对一组近似到O(μ2)阶完全非线性的Boussinesq方程进行了改进,加强过程保留高阶非线性项,改进后的方程色散性能和非线性性能均有提高.该方程可以简化为多个以水深平均速度表达的二阶Boussinesq类水波方程.理论分析了加强对方程二阶非线性和三阶非线性的影响,并将其同传统加强方式进行了比较,结果表明,含高阶非线性项的加强方式得到的方程性能更好.基于该方程,在非交错网格下建立了基于有限差分方法的高精度数值模型.利用数值模型模拟波浪在潜堤上的传播变形,探讨了2种不同加强方式以及非线性对数值结果的影响,结果表明,加强过程保留高阶非线性的方程模拟结果更佳.     

流体饱和多孔隙固体中波动方程的数值模拟

利用Ｇａｌｅｒｋｉｎ法推导出了流体饱和多孔隙介质中波动方程的有限元方程。数值模拟的结果验证了Ｂｉｏｔ关于流体饱和多孔隙介质中存在两类纵波的预言。     

二维数值水槽波浪生成过程及波浪形态分析

为了弥补物理模型试验投资大、模型相似性差等缺点，利用数学模型进行流体力学研究越来越普遍。基于物理水槽造波原理，在FLUENT流体软件中通过设定造波板边界的运动来模拟实际造波板的运动过程，实现了二维规则波的数值模拟，并给出了波高随造波板运动周期、振幅及坐标的变化规律。对波浪形态的分析表明，利用本文研究的数值模拟方法所生成的波浪符合实际造波形态。通过改变边界条件，用该方法也可以实现二维不规则波和随机波的数值模拟。     

Prediction of the dynamic effective properties of particle-reinforced composite materials

The prediction behaviors of some coherent plane wave equations for the effective velocities and attenuations of the coherent plane waves propagating through a composite material and for the effective elastic moduli of the composites are studied. The numerical results obtained by Waterman & Truell's, Twersky's and Gubernatis's equations for Glass-Epoxy composites with various volume fractions are compared. It is found that the predictions by both Twersky's and Gubernatis's equations underestimate the effective velocities and the effective elastic moduli when compare with the predictions by Waterman & Truell's equation. Furthermore, the deviations are more evident for the shear wave than that for the longitudinal wave. But these deviations decrease gradually with the increase of the frequency and increase gradually with the increase of the volume fraction.     

Mechanism of Pendulum-type wave phenomenon in deep block rock mass

Pendulum-type (μ wave) wave is a new type of elastic wave propagated with low frequency and low velocity in deep block rock masses. The μ wave is sharply different from the traditional longitudinal and transverse waves propagated in continuum media and is also a phenomenon of the sign-variable reaction of deep block rock masses to dynamic actions, besides the Anomalous Low Friction (ALF) phenomenon. In order to confirm the existence of the μ wave and study the rule of variation of this μ wave experimentally and theoretically, we first carried out one-dimensional low-speed impact experiments on granite and cement mortar blocks and continuum block models with different characteristic dimensions, based on the multipurpose testing system developed by us independently, The effects of model material and dimensions of models on the propagation properties of 1D stress wave in blocks medium are discussed. Based on a comparison and analysis of the propagation properties (acceleration amplitudes and Fou-rier spectra) of stress wave in these models, we conclude that the fractures in rock mass have considerable effect on the attenuation of the stress wave and retardarce of high frequency waves. We compared our model test data with the data of in-situ measurements from deep mines in Russia and their conclusions. The low-frequency waves occurring in blocks models were validated as Pendu-lum-type wave. The frequencies corresponding to local maxima of spectral density curves of three-directional acceleration satisfied several canonical sequences with the multiple of (√2),most of those frequencies satisfied the quantitative expression(√2)iVP/2△.     

混凝土中的Lamb波传播

将PZT压电陶瓷片直接粘贴在混凝土梁表面来产生和接收超声波，由该系统发射不同频率的超声脉冲，依据接收的时域波形测量幅值最大波包在混凝土内的传播时间，由此得到波速随频率变化的频散关系。通过比较理论的与实测的频散曲线，表明PZT系统能在混凝土内产生某些模态的Lamb波。在50～100kHz的频率范围内，混凝土中的Lamb波模态接近于A3模态。而在110-160kHz的频率范围内，Lamb波模态接近S4模态。     

Characteristics of transmitting channel wave in a coal seam

An embedded underground coal seam carries channel waves of low seismic velocity along a stratigraphic rock-coal-rock sequence. In a homogeneous and isotropic seam, seismic waves propagate as trapped waves within the seam, which leads to propagation of channel waves. We describe how to set up a field test for transmission in order to acquire channel waves in a coal seam. Because channel wave signals are non-stationary in their frequencies and amplitudes, a necessary velocity spectrum and wavelet transformation analysis are applied to interpret the characteristics of channel waves. The advantage of using a wavelet transformation is that different resolutions can be obtained at different times and different frequencies. According to analysis of the seismic signals acquired in the S7 sensor hole, it was clearly shown that the characteristics of channel waves are lower frequencies and attenuation which can guide an effective wave for detecting voids, boundaries and faults in coal seams with strong roofs and floors.     

滑坡涌浪高性能有限元计算软件研发

高速运动的滑坡、泥石流及冰川等入水冲击水库、湖泊、河道及海湾等封闭水域内的水体时会诱发涌浪,并由此产生大规模的灾害。为有效防止涌浪灾害,需要研究涌浪特性与规模等的预测方法。为缩短大规模涌浪分析的计算时间,需要开发基于稀疏线性方程组多核多线程并行求解器的涌浪高性能有限元计算软件。本研究中,利用Intel MKL提供的共享内存机器上实现的稀疏线性方程组求解器PARDISO,开发了涌浪高性能有限元分析程序。垂直水坝溃坝的理论解和数值计算结果,以及室内实验结果与数值计算结果的比较情况表明,研发的涌浪高性能有限元软件可以快速得到可靠的计算结果。     

Elastic Wave Scattering From a Partially Debonded Elastic Cylindrical Inclusion

ＥｌａｓｔｉｃＷａｖｅＳｃａｔｔｅｒｉｎｇＦｒｏｍａＰａｒｔｉａｌｌｙＤｅｂｏｎｄｅｄＥｌａｓｔｉｃＣｙｌｉｎｄｒｉｃａｌＩｎｃｌｕｓｉｏｎＷＡＮＧＹｕｅｓｈｅｎｇＷＡＮＧＤｕｏ（汪越胜，王铎）（Ｄｅｐｔ．ｏｆＡｓｔｒｏｎａｕｔｉｃｓａｎｄＭｅｃｈａ...     

近水面悬停远航程AUV受波浪的影响

远航程自主水下航行器(简称:AUV)在水下航行一定的距离后需要上浮到近水面悬停进行GPS导航定位,而在近水面AUV受波浪的影响不能忽略,因此有必要研究AUV在近水面悬停时受波浪的影响。在建立AUV六自由度运动数学模型的基础上,基于二元规则波的波浪理论建立了AUV所受波浪力的计算模型,并仿真计算了AUV在近水面悬停时受海洋波浪力的影响。结果表明AUV在2级和4级海况下都可以稳定地完成在近水面悬停作业的任务。     

对称正则长波方程的精确行波解

为研究对称正则长波（SRLW）方程,采用 Fan 子方程法并借助 Maple 软件得到了该方程丰富的行波解：三角函数解、双曲函数解、双周期Jacobi椭圆函数解,并给出了解的数值模拟图。结果表明,Fan子方程法对求解非线性方程是一种非常有效的工具。