Small Waterplane Area Twin Hull Slamming Load Prediction And Structural Strength Analysis

The small waterplane area twin hull(SWATH)is a type of high performance vessel that has received widespread attention from both the civil and military sectors for its excellent wave resistance,manoeuvrability and wide deck.With the application of small waterplane area twin hull in deep and distant seas,the trend is inevitably towards larger scale tonnage.At the same time,ocean voyages will also encounter more adverse sea conditions,with slamming and upwelling being among the problems frequently encountered.Severe slamming and upwelling can have a significant impact on the local structural strength and overall strength of the hull,posing a threat to the structural safety of the vessel.This paper takes a large scale small waterplane area twin hull as the research object,establishes the numerical prediction method of thumping load on the cross-deck structure of a small waterplane area twin hull in waves based on potential flow theory and viscous flow theory,analyses the effect of slamming on the structural load of the cross-deck and the total strength of the hull,and then develops the method of determining the design value of the hull beam and local structural slamming load under the action of slamming.The main research elements include:(1)Potential flow method for predicting the full-service motion of a small waterplane area twin hull: The hydrodynamic and motion analysis of a small waterplane area twin hull is carried out based on the potential flow method,combining the slamming load characteristics and kinematic occurrence conditions of the cross-deck of this vessel type,calculating and analysing the typical speed,bending moment and shear load/overall motion of the vessel for different wave down profiles,and comparing the results with the normative calculations.Afterwards several hazardous conditions are selected by the design wave method for later CFD simulation analysis.(2)The numerical simulation method of the slamming load of the cross-deck structure of a catamaran with a small waterline surface is studied: firstly,the numerical simulation method of the upper wave slamming is verified,and the numerical simulation results are compared with the model tests to verify the reliability of the numerical simulation method.Afterwards,CFD method is used to simulate the slamming load of the bridge structure of a catamaran with a small waterline surface for the dangerous working conditions selected by the potential flow method.(3)Total hull strength analysis based on hull beam theory: Based on the above research,the overall strength analysis of hull beams under slamming loads is carried out based on beam theory,the design values of slamming loads are discussed and the total longitudinal and transverse strength of hull beams under the combined action of slamming loads and wave loads of the cross-deck structure is investigated.It was found that the numerical simulation can well observe the physical phenomenon of the cross-deck slamming,where the main factors affecting the wet deck slamming load of the connecting bridge are wavelength and speed,and the main factor affecting the wave slamming on the deck is the wave amplitude.Meanwhile,the slamming load has a greater effect on the longitudinal strength of the hull and a smaller effect on the transverse strength.