Response of a sailing boat to heave and pitch motion under waves

A sailing boat is mainly divided into two different parts, the topside and the bottom. Thefirst one is in contact with the air and the second with the water.When the boat is in equilib-rium, the forces on the topside,created by air, which are mainly forces on the sails, are equalto the forces on the bottom which are generated by the water. Those forces are created bythe interaction between the fluid and the solid body.Aerodynamic forces are related to theair-body interactions while hydrodynamic forces to water-body interactions.In this thesis thehydrodynamic forces acting on the hull of the boat will be analyzed .The main objective isto determine the response of the vessel to heave and pitch motions in regular waves head seaat low forward speed.In order to obtain those motions some simplification are done. Heaveand pitch motions are decoupled from all the other motions (surge,sway,roll,yaw) and a lin-ear theory approach is used(which is valid for small oscillations).A boat moving in waves,when considering only the two previous motions, can be compared to a 2 degree of freedommass-spring-damper system and under certain conditions those motions can be decoupledand two SDOF systems can be considered. An analytical method to predict heave and pitchmotions is carried out and the results are compared with the ones obtained by means ofSTARCCM®.The analytical method is carried out using MATLAB®and uses linear the-ory and Strip theory to predict the steady state response of pitch and heave motions.Thegeometry of the vessel is divided in many 2D cross sections and the 2D forces acting onthis cross sections are calculated.A summation of all those forces gives the total 3D forcesacting on the vessel.The forces are divided in hydrodynamic forces (added masses and damp-ing coefficients), hydrostatic forces (restoring forces) and wave-exciting forces.The MatLabcode®solve the 2DOF differential equations after discretizing the geometry of the vesselin many cross sections.Finally the results obtained by analytical computation are comparedwith the numerical results.Valid results are obtained for small oscillations and low forwardsiii speed where the non-linear effect are negligible and the hydrostatic forces are more relevant than the lifting forces.