Research On Optimization Of Hull Line And Motion Performance Of SWATH

SWATH is a kind of high performance ship with high technique and high additional value,and the excellent seakeeping performance of SWATH has gained broad consensus.However,beause of the small water plane area,submergence depth of submerged body and the effect of Munk moment during the sailing,it is easy for SWATH to lose the stability of longitudinal motion at medium and high speed,and the phenomenon of bow trim will happen.Therefore,how to impove the stability of longitudinal motion is critical technical problem of SWATH development and design.The distance between two demi hulls of SWATH is far,so the phenomenon of the coupling of pitch and roll is easy to happen when SWATH is sailing in the condition of oblique seas.Therefore,to deeply understand the characteristic of SWATH seakeeping performance at full wave directions and the relationship between seakeeping performance and speed has practical significance for guiding the ship design and improving the seakeeping performance of ship at full wave directions.This study is based on viscous flow theory,and effective theoretical prediction method for resistance,trim and sinkage of SWATH is discussed.On the goal of improving the longitudinal motion stability of ship,ship form optimization is studied,and optimized ship form is given.Based on viscous flow theory,the flow field and hydrodynamic interaction of bow fin and tail fin is studied,and the effect of bow fin and tail fin on resistance and hull gesture of SWATH is analyzed.Based on the viscous flow correction of potential flow theory,the effective theoretical prediction method of SWATH seakeeping performance at full wave directions is discussed.Take basic SWATH as example,ship resistance and hull gesture are predicted by discussed theoretical method,and the computed result is compared with experimental result to validate the effectiveness of the method.On the basis of basic SWATH,the ship form is optimized,and the effect of shape change of submerged body on longitudinal motion gesture is analyzed,and optimized ship form is given.The resistance and hull gesture of SWATH with fins are predicted.SWATH seakeeping performance of full wave directions at multiple speed points is predicted,and the variation curves of sinkage,trim,roll,bow accelaration,middleaccelaration and stern accelaration with the ratio of wave length to ship length is obtained,and correlation properties are analyzed.The seakeeping performance of ship with different gravity center heights at full wave directions is predicted,and the effect of gravity center heights on seakeeping performance of SWATH at full wave direction and its rule are analyzed.The result shows that the longitudianl motion stability could be improved by appropriate upwarping of the forward part of submerged body.The liftig force of the bow and tail fins decrease because of the flow field and hydrodynamic interaction between the hull and the bow and tail fins.Ship resistance is increased by the effect of bow and tail fins,which could overcome the bow trim phenomenon of SWATH and improve the hull gesture.In the condition of head seas and head oblique seas,with the speed increasing,the first peak of motion response curve will move towards the direction at which the ratio of wave length to ship length is less,and the peak value will decrease.