Numerical Investigations Of Roll Motion Of Floating Bodies Coupling With Fluid Resonance In Narrow Gap

When closely spaced floating bodies are in side-by-side operations,there will be a narrow gap leaving between them.As the incident wave frequency is close to the natural frequency of the fluid confined in the narrow gap,extremely large wave oscillation in gap occurs,that is,the fluid resonance in the narrow gap or briefly the gap resonance problem.In addition to the gap resonance,the roll motion of the floating bodies may have complex nonlinear behaviors.Such that a highly coupled nonlinear dynamic system involving both the gap resonance and roll motion of the floating bodies is formed.This thesis deals with the coupling dynamic interactions between the roll motion of floating bodies and the fluid resonance in narrow gap in waves.A Navier-Stokes solver based two-dimensional viscous numerical wave flume is established in the frame of Arbitrary-Lagrangian-Eulerian(ALE)point of view with moving mesh strategy to treat the fluid and structure interaction.The free surface is captured by using the VOF method.The accuracy of the numerical model is validated against available experimental data.And good agreements are obtained.In this paper,a numerical study is carried out on the coupling of rolling motion of twin parallel floating bodies and fluid resonance in narrow gap.The results show that,compared with the fixed floating bodies,the rolling motion of twin floating bodies will aggravate the resonance wave height of the fluid in the narrow gap and reduce the resonance frequency.There is an obvious nonlinear jump phenomenon in the coupled motion response of the fluid in the narrow gap and the floating bodies,which constitutes a highly coupled dynamic response system.There is a high frequency doubling response of the main control frequency for the steady wave surface motion in the narrow gap between floating bodies.The results show that the corner shape of the floating structure has an important influence on the resonance response of the fluid in the narrow gap.With the increase of the corner radius of the floating bodies,the resonance frequency of fluid in the narrow gap gradually moves to the high frequency direction,and the resonance wave height tends to increase linearly.Through the analysis of the vorticity field characteristics in the narrow gap under the resonance condition,it is found that there is a high-strength shear layer on the wall of the structure.At the bottom corner of the gap entrance,the vortex shedding is obviously weakened under theinfluence of the fillet,which also means that the influence of the wall friction and the flow separation caused by the sharp corner on the mechanical energy loss cannot be ignored.In this paper,the coupling interaction of the rolling motion of the floating body and the large-scale fluid resonance in the gap close to large floating body/straight wall is further studied.Through the above-mentioned numerical simulation of viscous flow,the influence of the geometric parameters of the floating bodies on the resonance characteristics of the fluid in the narrow gap and rolling response characteristics is systematically studied,including the width of the narrow gap,the width of the floating bodies,the draft of the floating bodies,and the corner radius of the rolling floating body.The effects of the parameters on the response characteristics of fluid resonance in the narrow gap and rolling motion,wave reflection coefficient and energy dissipation coefficient are clarified.The results show that the resonant frequency decreases linearly with the increase of the width of the narrow gap,and the relative resonant wave height and the amplitude of the roll response decrease gradually,and the roll motion is basically around the initial equilibrium position.When the width of the floating bodies is changed,the width of the seaward rolling floating body has a more significant influence on the coupled dynamic response.The draft of the rolling floating body has a nonlinear effect on the amplitude of the rolling response,while the position of the rolling balance gradually becomes larger and the amplitude is very obvious.With the increase of the corner radius of the rolling floating body,the amplitude of the rolling response increases gradually,and the offset of the balance position shows an irregular trend.With the increase of incident wave height,the corresponding relative resonance wave height decreases and the trend is gradually gentle,which shows that the mechanical energy loss increases correspondingly in the process of fluid resonance in narrow gap.The rolling motion of the floating body and the fluid oscillation in the narrow gap close to the large floating body/straight wall maintain a highly coupled dynamic system,while the coupling response does not appear sudden jump phenomenon in resonance.