Dynamics Characteristic Study On Lifting And Under-water Towing Operation Of A Subsea Module

In the lifting operations of a subsea module,structural damage can be caused by the severe slamming,and the large wave load will affect the safety of the operation.And in the underwater transportation process,the hydrodynamic forces on the module and its motion states affect the selection of the towing equipment.In this thesis,based on the Reynolds-averaged Navier–Stokes equations and the finite volume method,numerical verification and simulation of the forced water–entry and lifting operation in wave of a protection cover of deep-water equipment are performed by computational fluid dynamics software Star-CCM+.The model experiment and numerical study of the cable tension and the motion state of the structure in underwater towing are carried out eventually.The main contents of this paper are as follows:(1)This paper introduces the basic principles of finite volume method and governing equations.The free surface conditions and boundary conditions applied are described,and the application of overset mesh and adaptive mesh refinement technology in this study are discussed.(2)The numerical model of forced water–entry process is established.The veracity of the numerical model is verified by comparing the numerical results of vertical force with the experimental ones.The maximum vertical force coefficient,slamming time,impact duration and impulse are used to quantify the effect of vertical velocity on hydrodynamic force.The influence of the porous plates and cavity shells in the structure are analyzed by the pressure and flow field.A simplified estimation of vertical force is carried out to determine the maximum lifting speed.(3)The numerical models of lifting operation in regular and irregular waves are established.The veracity of the numerical models are verified according to the results of the previous lifting model tests.The effects of regular wave period and wave height on the cable tension and on the motion state of the structure are mainly studied.That effect on cable tension is quantitatively studied by estimating the floating dynamic effect.According to the numerical results of the model in regular waves,the limit sea states of lifting operation is identified.The characteristic parameters and minimum number of simulations of lifting operation under a common sea state are determined by a series of lifting simulations in irregular waves.(4)The model experiment of underwater towing is carried out.The numerical model is established and verified by the experimental results.We implement the underwater towing experiments and simulations under five different speeds and two directions to analyze the influence of velocity and heading on cable tension,offset angle and motion.Based on the numerical model,the effects of towing velocity,direction and cavity shells on the vorticity and flow field around the structure are studied.Finally,the components of resistance on the structure are analyzed to determine the best towing method.