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首页> 外文期刊>International Journal for Numerical Methods in Fluids >Semi-coupled air/water immersed boundary approach for curvilinear dynamic overset grids with application to ship hydrodynamics
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Semi-coupled air/water immersed boundary approach for curvilinear dynamic overset grids with application to ship hydrodynamics

机译：曲线动态交叠网格的半耦合气/水浸入边界法及其在船舶流体力学中的应用

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For many problems in ship hydrodynamics, the effects of air flow on the water flow are negligible (the frequently called free surface conditions), but the air flow around the ship is still of interest. A method is presented where the water flow is decoupled from the air solution, but the air flow uses the unsteady water flow as a boundary condition. The authors call this a semi-coupled air/water flow approach. The method can be divided into two steps. At each time step the free surface water flow is computed first with a single-phase method assuming constant pressure and zero stress on the interface. The second step is to compute the air flow assuming the free surface as a moving immersed boundary (IB). The IB method developed for Cartesian grids (Annu. Rev. Fluid Mech. 2005; 37:239-261) is extended to curvilinear grids, where no-slip and continuity conditions are used to enforce velocity and pressure boundary conditions for the air flow. The forcing points close to the IB can be computed and corrected under a sharp interface condition, which makes the computation very stable. The overset implementation is similar to that of the single-phase solver (Comput. Fluids 2007; 36:1415-1433), with the difference that points in water are set as IB points even if they are fringe points. Pressure-velocity coupling through pressure implicit with splitting of operators or projection methods is used for water computations, and a projection method is used for the air. The method on each fluid is a single-phase method, thus avoiding ill-conditioned numerical systems caused by large differences of fluid properties between air and water. The computation is only slightly slower than the single-phase version, with complete absence of spurious velocity oscillations near the free surface, frequently present in fully coupled approaches. Validations are performed for laminar Couette flow over a wavy boundary by comparing with the analytical solution, and for the surface combatant model David Taylor Model Basin (DTMB) 5512 by comparing with Experimental Fluid Dynamics (EFD) and the results of two-phase level set computations. Complex flow computations are demonstrated for the ONR Tumblehome DTMB 5613 with superstructure subject to waves and wind, including 6-DOF motions and broaching in SS7 irregular waves and wind.
机译：对于船舶流体动力学中的许多问题，气流对水流的影响可以忽略不计（通常称为自由水面条件），但仍然围绕着船舶周围的气流。提出了一种方法，其中水流与空气溶液解耦，但是空气流使用不稳定水流作为边界条件。作者称这是一种半耦合的空气/水流方法。该方法可以分为两个步骤。在每个时间步长，首先使用单相方法计算自由表面水流量，假设界面上的压力恒定且应​​力为零。第二步是以自由表面为移动浸入边界（IB）的方式计算气流。为笛卡尔网格开发的IB方法（Annu。Rev. Fluid Mech。2005; 37：239-261）扩展到曲线网格，其中使用无滑移和连续性条件来强制气流的速度和压力边界条件。可以在尖锐的界面条件下计算和校正接近IB的强制点，这使计算非常稳定。重叠实现与单相求解器的实现类似（Comput。Fluids 2007; 36：1415-1433），不同之处在于，即使水中的点是边缘点，也将其设置为IB点。通过算力分裂或投影方法隐含的压力的压力-速度耦合用于水计算，而投影方法用于空气。每种流体的方法都是单相方法，因此可以避免由于空气和水之间的流体特性差异大而导致的数值系统条件不佳。计算仅比单相版本慢一点，在自由表面附近完全没有杂散速度振荡，这在完全耦合方法中经常出现。通过与分析解决方案进行比较，对波浪形边界上的层状库埃特流进行验证，并通过与实验流体动力学（EFD）和两相水准集的结果进行比较，对表面战斗机模型David Taylor模型盆地（DTMB）5512进行验证计算。演示了ONR Tumblehome DTMB 5613的复杂流动计算，其上部结构易受波浪和风的影响，包括6自由度运动和SS7不规则波浪和风的拉削。

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