【作者】 杨晨；

【导师】 陶建华；

【作者基本信息】 天津大学 ， 流体力学， 2006， 硕士

【摘要】 波浪是海岸、海洋工程最重要的动力因素之一。海上结构物所承受的波浪荷载通常是结构物设计的控制荷载,它对工程的造价、安全度及寿命起着重要作用。因此,研究海浪对结构物的作用是很重要的。海岸和海洋工程中,把特征尺度D与波浪的特征波长L的比值满足D / L≤0.15的结构物称为小尺度结构物,小尺度桩柱的组合结构在实际工程中应用十分广泛。本文采用时变雷诺方程作为控制方程,并用k ?ε湍流模型来封闭雷诺方程,建立了模拟波浪与结构物相互作用的三维数学模型。采用能模拟波浪破碎的流体体积函数(VOF)方法跟踪波动自由表面;为了避免在网格内采用斜面表示自由表面时的复杂的几何计算,采用“施主-受主”算法计算网格内的流体体积函数值,并在网格内用水平或垂直的平面重构自由表面。采用能消去造波板二次反射的可吸收式数值造波机进行数值造波;在开边界处,采用了适合本模型的海绵层吸收方法。雷诺方程的求解采用两步投影法:第一步,不考虑压强梯度对速度场的贡献,即在动量方程中略去压力梯度项,且时间项采用向前差分,得到中间速度场;第二步将此速度场向无散度的空间投影,得到满足连续性方程的流场。积分压强得到小尺度结构物上的惯性力,利用速度场计算得到小尺度结构物上的粘性力。为了验证模型对流场和自由面的模拟以及小尺度桩柱波浪力计算的准确性,本文用数学模型模拟了(1)孤立波在直立墙前的爬高过程(2)小尺度孤立柱上受到的波浪力,用解析解和实验结果进行了验证,数值结果与解析解和实验结果符合较好。利用本文建立的数学模型,对不同波浪场中的小尺度孤立柱所受的波浪力进行了模拟,并且和Morison公式的计算结果进行了比较,两个结果比较接近。最后,对波浪流过纵向和横向排列的两个柱以及2×2的柱群的过程进行了数值模拟,得到了不同情况下该种结构物的水波动力学特性及每个柱的干扰系数。计算方法和计算结果对小尺度结构物的设计施工有一定的参考价值。更多还原

【Abstract】 Water wave is a key hydrodynamic factor in offshore and coastal engineering, and wave forces acting on the structures are usually the control load for design. It is necessary to study the interaction between water waves and coastal structures. In coastal and ocean engineering, the structure with the ratio of its diameter to the wavelength being less than 0.15 is regarded as small-diameter structure, and the structures of arrays of small-diameter cylinders are widely used in practice. Three dimensional numerical model based on the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations which being closed with k ?εturbulence model has been developed to simulate the interaction between water waves and coastal structures in this study. The VOF (Volume of Fluid) method is used to track the free surface. An active generating-absorbing numerical wave paddle is used to generate waves, and an active sponge layer is introduced at the open boundaries to absorb waves.Two-steps projection method is used to calculate the URANS. Firstly, the effect of pressure on velocity is ignored. Secondely, the temp velocity is projected into a none-divergent space to calculate the real veolocity. The inertia force is obtained by integrating the pressure and the drag force is calculated by using the veolocity field.In order to validate the numerical model, two examples were simulated by using the numerical model, given as follows: (1) solitary wave run-up on a vertical wall (2) wave forces on a solitary small-diameter cylinder. The numerical results of velocity fields, free surface and wave forces agree with the analytical and experimental results very well.Wave forces on solitary small-diameter cylinder in different wave fields were simulated, and the results were compared with the results obtained by using the Morison equation, the two results are similar. Finally, the interaction between water waves and arrays of small diameter cylinders were simulated. The hydrodynamic properties of the structures and the interference coefficients of every cylinder were analysed.更多还原