波流共同作用下近海大尺度孤立建筑物基础冲刷研究

Large offshore engineering structure (D/L≥0.2), especially the large isolated structure mounted in shallow and very shallow water, such as the platforms which sit on the seabed, the circularly closed artificial island and the sand-rock piled artificial island. Under the action of coexisting wave and current, there is serious local scour around the foundation of the isolated large structure mounted on erodible seabed. It threatens the safety and stability of the structure. This project investigate the scour pattern and the largest scour depth around the foundation of the large structure in wave-current coexisting field through physical model test, numerical simulation and the analysis of collected field data. The content of this research include: first, establish the mathematic model of scour pattern around large isolated structure, which comprise of the numerical models of wave-current, the bed shear stress and the scour and deposition model; second, give out the formula of predicting the largest local scour depth..Based on the physical model test of the flow field around the foundation of large structure in coexisting wave-current condition and the analysis of scour mechanism, a mathematical model of local scour around the foundation of large structure is established. This model is comprised of four sub-models: the wave model, the current model, the bed shear stress model and the scour and deposition model. Software of plotting the scour pattern around the foundation of large structure is developed. The scour pattern plotted by the software shows the calculated scour patterns coincide reasonable well with the laboratory data of model test..The project analyzes the main factors that influence the scour pattern around the foundation of large structure in coexisting wave-current condition. It shows hat the main factors of the largest scour depth are the relative water depth（h/L）, the relative diameter（D/L）and the Froude .number characterized by current velocity . Using the linear recurrence method, a formula of the largest scour depth around the foundation of larger vertical cylinder yields: The discrepancy of the largest scour depth around the foundation of large structure in coexisting wave-current condition predicted by above formula to the measured data (including field data) is within 30%.In present the investigation of scour pattern and the largest scour depth around the foundation of large isolated structure in coexisting wave-current condition is seldom both in China and in Foreign country. The mathematical model of scour pattern and the experiential formula of the largest scour depth given by this project could be used to predict the local scour around isolated structure located offshore and seashore quantitatively, and provide basis to the design of offshore structure..

采用水池模型试验和数值模拟方法，研究座落在海床上的近海大尺度孤立建筑物，在波浪与水流共同作用下，其周围冲淤形态，局部最大冲刷位置、深度、范围及圆柱周边最大冲刷深度的定量评价方法，并提出最大冲刷深度表达式。该研究可对座落在近海可冲刷海床上的大尺度孤立建筑物（重力式平台、人工岛、坐底式钻井平台等）的稳定和安全提供设计依据。