Numerical Examination Of Wave Forces On Horizontal Circular Cylinders Based On Viscous Fluid Theory

With the development of ocean exploration towards the deep sea,the characteristics of deep-sea structures have been the research focus.A submerged horizontal circular cylinder near the free surface is widely applied in ocean engineering.It is an important issue to accurately predict the wave forces on the cylinder structures for safety research.Under the large-amplitude wave action or undergoing forced oscillation,the hydrodynamic forces on horizontal circular cylinder components are influenced by viscous effect,and the slamming action of waves should be considered in predicting the wave forces on the cylinders.In addition,this issue also involves complex free-surface problem.Owing to the inherent limitations,the potential flow methods cannot produce accurate predictions in the above mentioned issues.Thus,the study on the wave forces on horizontal circular cylinders based on the viscous fluid theory is of great importance.Under such research background,a viscous fluid numerical wave tank model(NWT)is established in this study.Then,the numerical examinations on the wave forces on a completely submerged horizontal circular cylinder,the wave forces on an incompletely submerged horizontal circular cylinder near free surface and the hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation are conducted,respectively.The mechanism of the viscous effects on the wave force are revealed and a prediction method for the wave force and slamming force are proposed.First,the viscous fluid NWT is established in this study based on the OpenFOAM package,while the flow motion is solved based on the Navier-Stokes equation.The numerical model is equipped with a Finite Volume Method(FVM)for numerical discretization,a Renormalization-group(RNG)model for turbulent closure,a Volume of Fluid(VOF)technique for interface capture,a no-reflection wave generator and a necessary wave-damping function for a long numerical simulation.Regarding the limitation of the numerical method,a numerical correction zone is added into the interface area to improve the capabilities of the numerical model.Second,the accuracy of the NWT model in predicting large-amplitude nonlinear wave propagation and hydrodynamic forces on structures is validated against available analytical solutions,experimental data and numerical results in the published research.Third,the viscous fluid NWT is adopted to study the issue of wave forces on a submerged horizontal circular cylinder.The accuracy of the numerical model in predicting the wave forces under viscous effect is validated against available experimental data.Comparisons of the flow fields predicted by the viscous fluid model and the potential flow model explain the over-prediction of the wave forces by the potential model.In addition,the influence of vortex shedding from the cylinder on the wave forces is also addressed.Considering the limitations of previous studies,the wave forces at various wave frequencies and the wave forces under different scales are studied in this work.These studies is remarkable for the engineering calculation and analysis.Fourth,the NWT model is used to study the issue of wave forces on an incompletely submerged horizontal circular cylinder near free surface.The influence of the wave amplitude,the wave frequency and the location of the cylinder in the vertical direction on the wave forces are mainly concerned.Since the slamming force cannot be neglected when the fluid velocity reaches to a certain extent,studying on the slamming force is necessary.A modified Morison's equation for calculating the wave forces is derived which not only considers the inertia force,the drag force and the buoyancy force,but also considers the slamming force.The coefficients of inertia,drag and slamming are fitted and analyzed.Afterwards,the wave forces predicted by the modified Morison's equation are compared with the numerical results for engineering applications.Finally,based on the above work,numerical simulations are conducted to investigate the hydrodynamic forces on a submerged horizontal circular cylinder undergoing forced oscillation.The comparisons of the hydrodynamic forces on the circular cylinder by viscous fluid model and the potential flow model are performed to show the viscous effects on the hydrodynamic forces.By studying the flow fields,the mechanism of the viscous effects is revealed.The influence of the body-fitted vortices on the pressure forces on the circular cylinder by analyzing the force components.And then the basic reason for the difference between the results based on the two theories is explained.