Study On Stability Of Waves On A New Type Of Offshore Fishing-boat

The stability of the ship on the waves is more and more concerned by the designers and researchers.The severe swinging motion on the waves poses a great threat to the safety of the ships.At present,the research on the stability of the ship is gradually increasing.Especially for the five new stability failure modes proposed by the International Maritime Organization(IMO),the surf riding and broaching are one of the five stability failure modes with dynamic characteristics,the current research is relatively few.The new type of offshore fishing-boat to be considered in this paper is characterized by its slender ship shape and high speed.It is a typical type of ship that is easy to surf-ride and broach in following seas.In addition,the main navigation waters of the target ship have larger wave height.According to a large number of sailing accidents,theoretical analysis and experiments,it is proved that the ship parameters and wave conditions are within the threshold of surf-riding and broaching.In order to ensure the stability of the target fishing boat sailing on the waves,this paper uses numerical simulation Method to forecast the occurrence of surf-riding on the waves.In this paper,a unified model of ship seakeeping and maneuvering surge based on unified theory is adopted.The maneuvering motion model is based on the MMG model and the hydrodynamic derivatives are calculated by the empirical formula.The seakeeping motion model is based on the impulse response function method.The radiation and the diffraction force in the frequency domain are calculated according to the STF slice theory.Finally,according to the unified theory,the two motion models are superimposed on the same spatial coordinate system at the same time scale to form a unified motion model.When the ship sails in following seas,the most influential factors for the occurrence of surf-riding and broaching are speed and wave steepness,the greater speed and wave steepness may threaten the stability of the ship,while the initial stability height is related to rolling restoring force,which determines the occurrence of rolling and capsizing to the ship in the event of transverse disturbance.Therefore,in this paper,we calculate the time domain response of the ship with different initial stability height,speed and wave steepness in following seas,observe the changes of its movement stability,analysis the reason and condition of surf-riding and broaching,and discover the four motion modes of the fishing boat sailing in following seas and the boundary between each mode.This can provide guidance and reference for the stability of the fishing boat and help it to avoid instability and the phenomenon of surf-riding and broaching.