Numerical Simulation of Ocean Environmental Change Due to Very Large Offshore Structures in a Bay

本项目对巨型近海结构物引起的海洋环境变化进行了基础性研究。以有莱克湾的一个近海机场为例，对该海湾有无近海机场进行了潮汐模拟。对河流中COD的扩散进行了模拟，并与COD浓度分布的结果进行了比较。在潮汐模拟中，采用准静态近似来考虑水对潮汐沼泽的运动影响。1993年，对填海机场和简化浮式机场的三个位置进行了评估函数的比较，这些评估函数以机场建设对潮位和流速的影响范围来确定。机场的位置对海湾的潮流和化学需氧量的扩散是非常重要的。1994年，针对浮筒式漂浮机场编制了新的数值程序。浮式机场试验结果表明，浮式机场对海洋EN…的影响较小环境变化比填海机场更多。研究了一种平坦浮式平台的动力定位系统。系泊用于保持浮动平台的位置不受海流和风引起的准恒定外力的影响，推进器控制缓慢漂移振荡。采用线性二次型积分(LQI)控制系统来抑制这种振荡。对不规则波、流和风中的运动进行了仿真，给出了LQI控制系统的性能。对由多个驳船型模块组成的超大型浮式结构物上的波浪漂移力进行了理论和实验研究。对两种模数连接件--转动铰链连接件和转动刚性连接件--对多点浮体结构的波浪力进行了估算。给出了连接体条件和体数对波浪漂移力的影响，提出了一种计算任意几何形状港口浮体水动力的新方法。该方法由求解港口响应的有限元方法和求解浮体响应的边界元方法组成。给出了矩形港内驳船的一些数值结果。较少

Fundamental studies on ocean environmental changes due to a huge offshore structure are carried out in this project. An offshore airport in Ariake Bay is taken as an example and tidal simulations are conducted in the bay with/without the offshore airport. The deffusion simulations of COD from rivers are also conducted and the results of COD density patterns are compared. In tidal simulations, the moving effects of water on the tidal marsh are taken into account by the quasi-stastic approximation. In 1993, three location of a reclaimed airport and a simplified floating airport are compared in assessment functions which are defined by the area affected in tidal level and current velocity by the construction of the airport. The location of the airport is found to be very important in the tidal currents and deffusion of COD in the bay. In 1994, a new numerical program is developed for a pontoon type floating airport. Results of a floating airport show that it gives less effects on ocean en … More vironmental changes than reclaimed airports.A dynamic positioning system of a mooed floating platform is studied. Mooring is used to maintain the position of a floating platform against quasi-constant external forces induced by current and wind, and thrusters control slow drift oscillation. The LQI (Linear Quadratic with Integral) control system was adopted to prevent this oscillation.Simulations of motions in irregulay waves, currents and wind were carried out and the performance of LQI control system was presented.The wave drifting forces acting on a very large floating structure consisting of multiple barge type modules is studied theoretically and experimentally. The wave drifting forces on the multiple floating structure are estimated for two module connectors, a rotationally-hinge connector and a rotationlly-rigid connector. The effects of connector conditions and the number of bodies on wave drifting forces are presented graphically.A new method for computation of the hydrodynamic forces acting on a floating body in a harbor of arbitrary geometry is developed. The method is composed of the finite element method (FEM) for solving the harbor response and the boundary element method (BEM) for the floating body response. Some numerical results are presented for a barge in a rectangular harbor. Less