Experiments and Numerical Simulations on Scouring around Marine Structures

Abstract

In this paper a series of marine structure scour and scour protection hydraulic model tests were carried out at the Wind-Wave-Current Basin (27m*19m*1m) of the Tainan Hydraulics Laboratory National Cheng Kung University For the scour tests of four different types of marine structures (i e monopile jacket-type gravity pile group) the maximum scour depth and scour range around the marine structure are discussed and the structure protection is evaluated by the scour test results The type of structural scour protection is evaluated by the results of the scour tests then the effects of the protection and the influence of different protection types on the scour around the structures are further explored During the scour test the scour process of the monopile structure was simulated using the scour numerical model and the results of the monopile scour test were verified The scour experiment numerical calculation and scour protection test results are an integrated research and discussion The scour problem encountered in the project is expected to provide the status and solution of its occurrence Marine structures and offshore wind turbine platforms are negatively affected by wave and current actions In Taiwan the water depth of most of the planned wind turbine foundations or marine structures are more than 15m At this water depth scour around marine structure foundations is mainly subject to the ocean current and wave-current interaction which causes damages or collapse of foundations Therefore this study is focused on the influences of ocean current and wave-current interaction on the marine structure foundations Hydraulic model experiments were conducted to investigate the maximum scour depth and scour range around pillars in these foundations Under the effects of current the relationships between the dimensionless maximum scour depth corresponding to the Froude number (Fr) and Reynolds number (Re) were calculated and compared with the experimental results Then a regression curve between the Reynolds number (Re) and the relative scour water depth (ds max/h) was provided empirically which could be used to estimate the maximum scour depth around the monopile jacket-type and gravity foundations under different conditions of current velocity (U) water depth (h) and pile diameter (D) The findings are valuable as a design guideline for offshore wind turbine foundations In addition to the physical model tests the scour depth and scour range around the monopile structure was simulated with numerical model calculations The scour results of physical model tests were preliminary used to verify the accuracy of the numerical model It would reduce the amounts and the times of hydraulic model tests In this paper the FLOW-3D model was used to simulate the topographical variation of the bed around a monopile foundation The scour test results are used to verify and adjust the parameters with higher sensitivity in the sediment scour model Clearly the scour may be a threat to the stability of offshore structures The maximum scour depth and the potential impact scour range around the marine structures were then predicted in the moveable bed experiment Finally based on the experiment results various types of scour protection around the marine structures are explored During the test the scope and thickness of the protection were adjusted as well The appropriate scour protection work around the foundation was proposed and tested to be effective in preventing local scour The study of design solutions with and without scour protection will be investigated by the comparison with respect to technical feasibility risks and costs in the near future

Date of Award	2020
Original language	English
Supervisor	Shih-Chun Hsiao (Supervisor)