Analysis Of Loads And Response On Marine Riser Under The Combined Action Of Wave And Current

With the continuous development of the deep sea resources, the research of the motion response of the ocean structures such as marine riser became the hot spot. Based on the comprehensively review and analysis of the domestic and foreign research methods and latest research status about numerical tank and the loads and response on the marine riser, the time domain method and viscous flow theory as the theoretical basis, the continuity equation and Navier-Stokes equations of the incompressible fluid and structural dynamic equation as the basic equations, viscous numerical tanks are established by commercial software Ansys Workbench 14.5 platform. Paper main specific job and research about the loads and response on the marine riser are as follows:(1) 2D and 3D numerical wave/wave-current tanks with high effective wave-making and wave-absorbing function are established by using velocity boundary and damping wave as well as VOF method technique on the platform of FLUENT 14.5 in combination with UDF programs. The change rule of the wave parameters under combined effects of different wave and current velocity are analyzed. The conclusion shows that the wavelength grow longer and the amplitude reduce when the wave and current has the same direction and the results are opposite to the above when wave and current has the opposite direction.(2) A rigid riser model is build and the stress on it under the combined effects of wave and current is simulated based on the establishment of the numerical tank. The analysis of the surface pressure and horizontal force illustrates that stress and Cd increases when the wave and current are in the same direction and the stress and Cd decreases when the direction of wave and current are opposite.(3) By using the two-way coupling separation thought, transferring the date of the fluid domain and structure domain in the module System Coupling, the motion response of a flexible riser with the aspect ratio of 8 in the numerical tank is simulated. The conclusion is that the balance position of the vibration biases in the direction of the current and the vibration amplitude increases in direction of wave/current while no obvious change in vertical direction compared to the wave tank when the tank consists of wave and current. The analysis of Cd verifies the feasibility of the FSI method at the same time.(4) The motion response of a flexible riser with the aspect ratio of 103 in the numerical tank is simulated. The result means that the wave and current plays a more obvious effect when the riser has a larger aspect ratio. The balance position of the vibration in direction of wave/current apparently biases in the current direction and the vibration in vertical direction can not be ignored under the action of the current when there is flow. Besides, when the wave and current is in the same direction, the vibration amplitude increases and the whole stress moves down. Similarly, the results will be the reversed if the direction of the wave and the current is opposite.