两层流中波浪与二维结构相互作用的频域模拟

发布时间：2018-08-09 10:08

【摘要】：海洋内波分布范围广、形式多样,其研究具有重要的工程价值和学术价值。在开发海洋资源的同时,海洋分层效应已越来越成为不可忽略的重要因素。本文基于两层流体的简化模型,对层化海洋环境下二维结构物的水动力特性进行了数值模拟研究。为了可以推广到研究复杂海洋结构,采用外域级数展开和内域边界元数值方法相结合的手段建立了频域数学模型,在外域和内域交界的辐射面上利用连续性条件建立联立方程组。边界元方法可以将问题降维处理,只需要在域表面划分网格,减少了计算量。同时内域计算采用Rankine源作为格林函数,既避免了求解复杂的格林函数,又可直接获得自由水面及内界面上的速度势。外域采用级数展开的解析式表达,将辐射面上速度势的求解转化为求解解析式中的待定系数。经过与级数展开的解析方法对比,以及两层流中波能流守恒的验证,证明了本文建立的这一联合数值模型的正确性。为了研究两层流中存在结构物时表面波模态和内波模态波浪的转化情况,定义了两层流中各模态波浪的反射和透射系数,利用这一数值模型通过计算反射系数和透射系数的变化情况,分析了两层流中结构物的反射和透射特性。研究了上下层密度比、水深比等层化参数对反、透射系数的影响。发现两层流体密度差小时,内界面很容易受到扰动产生大幅振动。计算并分析了两层流中结构物的附加质量和辐射阻尼,给出了结构物作强迫振荡时,自由水面和内界面的波面升高情况。最后,分析研究了结构物分别在表面波模态和内波模态波浪入射时的运动响应问题。研究发现,两层流中内波模态波浪入射时,结构物运动响应受层化参数变化的影响较明显。
[Abstract]:The research of ocean internal wave has important engineering value and academic value because of its wide range of distribution and various forms. At the same time, ocean stratification effect has become an important factor that can not be ignored. Based on the simplified two-layer fluid model, the hydrodynamic characteristics of two-dimensional structures in stratified marine environment are numerically simulated in this paper. In order to extend to the study of complex ocean structures, a frequency-domain mathematical model is established by combining the outer domain series expansion with the internal domain boundary element numerical method. The simultaneous equations are established by using the continuity condition on the radiation surface at the boundary between the outer and inner domains. The boundary element method can reduce the dimension of the problem, only need to mesh the surface of the domain, and reduce the computational complexity. At the same time, the Rankine source is used as the Green's function in the inner domain calculation, which avoids solving the complex Green's function and directly obtains the velocity potential on the free water surface and the inner interface. The solution of velocity potential on the radiation surface is transformed into the undetermined coefficient in the solution of the analytic formula by using the analytic expression of the series expansion in the outer domain. The validity of the proposed joint numerical model is proved by comparing the analytical method with the series expansion and verifying the conservation of the wave energy flow in the two-layer flow. In order to study the transformation of surface wave mode and internal wave mode wave in the presence of structure in two-layer flow, the reflection and transmission coefficients of each mode wave in two-layer flow are defined. By using this numerical model, the reflection and transmission characteristics of structures in two-layer flow are analyzed by calculating the variation of reflection and transmission coefficients. The effects of stratification parameters such as the upper and lower layer density ratio and the water depth ratio on the inversion and transmission coefficient are studied. It is found that when the density of the two layers of fluid is small, the inner interface is easily disturbed to produce large vibration. The additional mass and radiation damping of the structure in two laminar flow are calculated and analyzed. The rise of the wave surface of the free water surface and the inner interface is given when the structure is forced to oscillate. Finally, the motion response of the structure under the surface wave mode and the internal wave mode is analyzed. It is found that the dynamic response of the structure is obviously affected by the variation of the stratification parameters when the internal wave mode is incident into the two-layer flow.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P75;P731.2

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