Investigations Of Reducing Resonant Wave Response In Narrow Gap Between Mutiple Floating Barges

In offshore engineering,there are many floating structures arranged side by side:the combination processes between the liquefied natural gas vessel(LNG)and the floating production storage with unloading unit(FPSO),the very large floating structure(VLFS)composed of many separate modules and a ship berthed in the front of the dock.For the cases above-mentioned,there are narrow gaps between the structures.When the incident wave frequency is close to the natural frequency of the confined fluid bulk in the gaps,the fluid resonance will occur,the large vertical vibration of the water surface in the narrow gap,leading to the sharp increase of responses and hydrodynamic loads on the structures.It seriously endangers the safety of the offshore operation.Therefore,it is of great engineering significance to study the suppression of fluid resonance amplitude in narrow gaps between floating bodies.In this thesis,air curtain and open-hole metal nets are separately selected to suppress the resonance amplitude of fluid in the narrow gaps between floating bodies,and the corresponding performance is studied in a systematic way.In order to adopt effectively the air curtain to suppress the resonance amplitude of the fluid in narrow gaps,the understanding about the characteristics of the interaction between the air curtain and the waves is first conducted by physical experiments.Including the influence about the structure form of the air curtain,the draught depth d,and the amount of air supply Q on the wave elimination.The wave elimination performance of single row and double rows air curtain are also studied.The experimental results show that the air curtain has a better wave-elimination-performance on the relatively short incident waves.Either the larger the air supply Q of the air curtain or the greater the underwater depth d of the air curtain,the better wave-elimination-performance on the incident waves.For the same incident wave condition,when the spacing between two air curtains is half of the incident wavelength,the double rows has a better wave-removal performance than the single-row.Based on the above experimental studies,we further conducted experimental studies on suppressing the resonance amplitude of the fluid in the narrow gap between the double floating bodies by using the air curtain.In the experiment,two square boxes are used to model the double floating structures on the sea.The influence of the placement position of air curtain and air supply Q of air curtain on the performance about the suppression on resonance amplitude of the water in the narrow gap were studied.The results show that when the box is out of the disturbances range of the air curtain but within the influence scope of horizontal flow generated by air bubble,the air curtain has the best effect on the suppression of fluid resonance in the narrow gap Moreover,when the air curtain is placed on the above-mentioned ranges,the greater the gas supply,the better the resonance suppression effect on the fluid in the narrowgap.However,if the square boxes are placed in the disturbances range of air curtain,the air curtain may increase the resonance amplitude of the fluid in the narrow gap between the floating bodies.Finally,the performance of using open-hole metal nets to suppress the resonance amplitude is studied.The two factors,the porosity and width of open-hole metal mesh,were experimentally and numerically studied.The results show that the structure of the open metal mesh can inhibit the fluid resonance amplitude and reduce the horizontal wave force F_x on the floating body.Either the smaller the porosity of the pen-hole metal mesh or the larger width of open-hole metal nets,the better effect of inhibiting the fluid resonance amplitude in the narrow gap.However,the porosity and the width of open-hole metal mesh has a little effect on the vertical wave force F_y on the floating body.