Research Of The Porpoising Limits Of Prismatic Planing Vessels Based On Semi-analytical Water Impact Theory

This paper mainly focus on semi-analytic models of two dimensional water impact load and the predictions of the hydrodynamic lift acting on planing vessels and longitudinal instability.First of all, we comprehensively described the meanings of prediction of the porpoising behavior of planing vessels, reviewed the experimental study and theoretical studies on hydrodynamic performance of planing vessels which are done by researchers from all over the world in recent eighty years and we also reviewed the researches on the prediction of hydrodynamic impact load.In chapter 2 of this paper, we apply mathematical theories, such as complex variables functions and matched asymptotic expansion method, to rederived Wagner, OLM, MLM and GWM theoretical analytical models of water impact, and builds a theoretical analytic model, which can calculate the total water impact load of a finite wedge body with knuckles based on the analytical water impact model. Then we also introduce a fully nonlinear numerical method which can calculate hydrodynamic impact load.In chapter 3,we compare the different results of impact loads through different impact theory for infinite and finite wedge with different deadrise angles. There are some problems on the choice of the assistant angle in the theoretical water impact model which concluded flow separation in chapter 2, therefore, the writer gives some suggestions about how to choose the assistant angle base on the results by calculating different assistant angle.In chapter 4, the governing equation and boundary conditions which can be used to calculate the velocity potential around the planing vessels is derived by using matched asymptotic expansion method, thus we discover that they can be the same as the definite condition of 2D Wagner theoretical models, under slender ship and shallow draft&flat bottom ship assumptions. Then we can apply the 2D+t idea and finite wedge body water impact analytical model to calculate the resistance of a planing vessel which is straight navigating in calm water, and determine the added mass and damping coefficient when the planing vessel is under longitudinal harmonic forced motion. At last, we predict the porpoising and dynamic behavior of planning vessels in calm water.