Numerical Investigation On Hydrodynamic Performance Of A WEC With An Air Filled Flexible Bag

Wave energy is a kind of clean and renewable resources,distributed in vast ocean which covers 71% of the earth's surface area,with a large energy density per unit area,and it is relatively stable along the time.But because of the complex nature of the Marine environment,the use of wave energy can be very low.In order to achieve the goal of effective utilization of wave energy,people have designed and experimented for all kinds of wave energy conversion device(WEC)since the last century.The typical form of WEC are with oscillating water column(OWC),point absorption WEC,pendulum WEC,overtopping WEC,etc.,and all this kinds of WEC has its own characteristics,advantages and disadvantages.In this paper,a type of wave energy conversion device is studied,this WEC absorbs wave through the compressive elongation of the air bag and the air flowing through the PTO.Because of the existence of airbag,the device has the advantages of low metal parts,simple structure,more convenient installation,better durability,suitable for harsh environment,relatively low cost and so on.The device is made up of the float,the sinker submerged under the water,an air bag and the PTO part.According to isentropic process,I analyzed the relationship between the deformation and internal force of the air movement;Based on the linear potential flow theory,the equations of motion of the float and the sinker are established respectively.Because the air bag and the sinker are submerged in the water,the wave forces acting on the air bag and the sinker are neglected.Then I analyzed how the bag volume and the float drift will change when change different parameters of the device in static balance status;at last,we use the potential flow theory,build the equation of motion of the device in the frequency method to solve the response of the float and the sinker,give the energy capture width,airbag pressure change amplitude.By means of using different parameters of the device,analysis the impact on the hydrodynamic characteristics of the device.The analysis of hydrodynamic characteristics is mainly from the following aspects:1)Change the flowing damping coefficient BPTO to find the best or better BPTO value range,and analyze the change of the motion response and the power.2)Changing the volume of the air bag,the volume of the inner cavity of the float,the initial pressure of the air bag and the radius of the air bag,then analyzing the variation of the motion response,the extraction power and the pressure amplitude under the better damping,give the appropriate selection of the above parameters.