Numerical Investigations Of Gap Resonance Excited By Focused Transient Wave Groups

In the field of marine engineering,the joint operation of two adjacent floating bodies is a common arrangement.Typically,there exists a slender gap between the two adjacent floating structures,which is much smaller than the dimensions of the structures themselves.Engineering practices have shown that incident waves with specific frequencies may induce large-amplitude free-surface oscillations within the narrow gap,leading to significant motion and wave loads on the floating bodies.This phenomenon is commonly referred to as "gap resonance".When gap resonance occurs,the intense fluid oscillations can cause a rapid increase in the wave forces acting on the structures,exacerbating the motion response of the floating bodies and potentially leading to collisions between them,which directly threaten the safety of engineering operations and personnel.Therefore,this thesis will conduct a comprehensive study and analysis of this phenomenon.In this thesis,a two-dimensional numerical wave tank is established based on OpenFOAM.The accuracy and reliability of the numerical model are proved by verifying the grid convergence and the physical experimental data in the relevant literature.The influence of the free heave of the upstream floating body on the slit resonance in the two adjacent floating body systems caused by the incident focused wave group and the influence of the free heave of the downstream floating body on the slit resonance in the two adjacent floating body systems are systematically studied,including the heave motion of the floating body,the amplification of the free water surface elevation in the slit and the wave load on the double floating body.The results of heave and fixed structure systems and two heave structure systems are compared and analyzed.The research work and results of this thesis are as follows:(1)For the narrow gap resonance between the free heaving upstream floating body and the fixed downstream floating body,the dimensionless maximum heaving displacement of the upstream floating body increases first and then decreases with the spectral peak period in the considered spectral peak period range.In the range of the focused wave amplitude considered,the maximum heave displacement decreases with the increase of the incident focused wave amplitude.(2)For the narrow gap resonance between the free heaving upstream floating body and the fixed downstream floating body,the fluid resonance period in the narrow gap of the heave structure system is larger than that of the fixed structure system.Moreover,in terms of wave loads(including vertical wave force,horizontal wave force and moment),as the spectral peak period increases,the shielding effect of the upstream floating body on the downstream floating body becomes weaker and weaker.(3)For the narrow gap resonance between the fixed upstream floating body and the freely heaving downstream floating body,the dimensionless maximum heaving displacement of the downstream floating body increases first and then decreases with the spectral peak period in the considered spectral peak period range.In the range of the focused wave amplitude considered,the dimensionless maximum heave displacement decreases with the increase of the incident focused wave amplitude.In addition,the fluid resonance period of the heave structure system is significantly larger than that of the fixed structure system.(4)For the narrow gap resonance between the fixed upstream floating body and the freely heaving downstream floating body,the upstream floating body always has a good shielding effect on the downstream floating body in terms of vertical wave force in the spectral peak period considered.As far as the horizontal wave force is concerned,the upstream floating body always shields the downstream floating body,but the shielding effect gradually weakens with the increase of the spectral peak period.In terms of moment,the shielding effect of the upstream floating body on the downstream floating body is similar to the horizontal wave force.(5)For the comparison of gap resonance hydrodynamics between the double floating body system with free heave motion of the upstream floating body and the double floating body system with free heave motion of the downstream floating body,the fluid resonance period of the double floating body system with free heave motion of the upstream floating body is smaller than that of the double floating body system with free heave motion of the downstream floating body.In addition,in terms of the maximum wave load,the maximum horizontal force and maximum moment of the double floating body system with free heave motion of the upstream floating body are greater than the corresponding wave force of the double floating body system with free heave motion of the downstream floating body.