Numerical Simulation Of Flow-payload Interaction Using OpenFOAM

With the accelerated development of marine powerful nation policy,the exploration and development of offshore oil,gas and mineral resources require the use of marine engineering equipment.The offshore crane which used for the installation of underwater production equipment is the key equipment in the deep water offshore engineering.When lowered into the water,the payload of the offshore crane may be subject to ocean flow,causing undesired payload motion.The undesired motion could cause damages or cable breaks and further cause accidents and impair the safety of life and property.In order to lower payload safely and effectively while working in the ocean flow,the ability to model the interaction between ocean flow and payloads is of vital importance.To investigate how to lower the payload of the offshore crane with ocean flow disturbance,position velocity,and force exerted by flow of the payload are investigated,the main works and contributions of the dissertation are as followed:Firstly,in order to study the interaction between payload and ocean flow,a two-dimensional numerical model is established based on the open source computational fluid dynamics software OpenFOAM.In order to verify the accuracy of the flow model,the force together with lift coefficient,drag coefficient and pressure coefficient on a horizontal cylinder which is placed in uniform flow is calculated.The experimental results are compared with the published literatures to verify the accuracy of the numerical model.Further,contours of the velocity and pressure fields around the cylinder in different Reynolds numbers are obtained.It is found that the variation properties of lift and drag coefficients are consistent with those of vortex shedding in the contours.Secondly,in order to study the three-dimensional characteristics of the flow around cylinder,the two-dimensional numerical model established above is extended to three-dimensional.In the three-dimensional numerical model,the pressure coefficients of a fixed vertical cylinder and a fixed inclined cylinder in constant flow are calculated respectively.Through the analysis of the pressure coefficients,the mechanical characteristics of the three dimensional cylinder with finite length along the axis of the cylinder are summarized.By modifying the grid,the vertical cylinder is changed into an inclined cylinder,and the hydrodynamic changes in the upstream and downstream flow field of the inclined cylinder model are studied.These data can be used to predict the motion of the inclined cylinder in the ocean flow.Finally,on the basis of the above numerical model,a numerical model for the interaction between the moving cylinder and the ocean flow is proposed to solve the safety problem in the process of the deep-sea crane lowering.The effects of gravity,the ocean flow and the cable constraint are considered in the model.To begin with,the motion response of the cylinder subjected to gravity is simulated without considering the velocity of the fluid,and the data are compared with published literature.Then,the flow is taken into consideration,and the motion response data of the cylinder under the combined action of flow and gravity are calculated.It is found that the water velocity is the main factor affecting the horizontal motion of the cylinder.At last,the simulation calculations are carried out considering the effects of gravity,flow and cables at the same time,and the influences of the cylinder density,flow speed and cable length on the movement of the cylinder in different directions are obtained.It is found that under the restraint of cable,flow can make the cylinder to be displaced in the vertical direction,and the cylinder would be stationary or moving up and down due to the influence of ocean flow speed and cylinder density.Based on OpenFOAM,a numerical model solving the interaction between payload and ocean flow is proposed in this paper.The numerical results provide data guidance for the safe work of lifting and discharging payload of cranes in ocean flow,and also provide reference for further application of OpenFOAM in hydrodynamic performance analysis of crane payload.