Equivalent Design Pressure Of Moving Slamming Loads And Local Response Of Ship Structures

In the current rules for ship slamming,the slamming pressure is usually regarded as static pressure for pressure prediction and hull plate design.In fact,the slamming pressure is a pulse pressure that moves along the hull surface.It will be more reasonable and accurate to predict the slamming pressure,predict the structural response and design the hull structure by fully considering the propagation characteristics and pulse dynamic characteristics of the slamming pressure.In this paper,an automated slamming experiment facility is developed.A series of slamming experiments were designed and carried out.The propagation characteristics of the slamming pressure are studied experimentally.The propagation characteristics refer to the changing characteristics of pulse shape,pressure coefficient,duration and propagating speed during the propagation of slamming pressure.Then a new simplified model of propagating slamming pressure and equivalent methods to transform the propagating slamming pressure to an equivalent static load are proposed.The theoretical and numerical methods for dynamic response of hull plates under propagating slamming pressure are developed.Thus,a slamming pressure assessment system based on the propagation characteristics of the slamming pressure is established and applied to the prediction of the bow flare equivalent static pressure of a container ship.The main contents are as follows:(1)Developing an automated slamming experiment facility that can accurately control the deadrise angle and the drop height and is easy to operate.The influence and requrements of the acquisition frequency on the slamming pressure are studied.A series of slamming experiments on rigid and elastic wedges with deadrise angles ranging from 0° to 45° were designed and carried out.Particularly,the variation of slamming pressure at small deadrise angles ranging from 0° to 3°,is studied by a large number of tests with small increments such as 0.1° and 0.2°.A series of slamming experiments with different closed boundary models were designed and carried out.(2)The propagating characteristics of the slamming pressure and the influence of drop height,deadrise angle and structural elasticity on the propagating feature are investigated.The simplified model of propagating slamming pressure and uniformly distributed slamming pressure are established.The influence of structural elasticity on the parameters of the simplified model is studied.The effects and mitigation of the double-sided and four-sided closed plates on the slamming pressure are studied.(3)The dynamic response of hull plate under a moving pulse load is derived,and the effects of moving pulse shape,moving speed,pulse duration,hull plate boundary conditions,length-width ratio and elastoplastic deformation on dynamic response are studied.(4)The numerical method of dynamic elastoplastic response of hull plates and stiffened plates under a moving pulse load is developed.The effects of deadrise angle,immersion speed and moving load parameters on the elastoplastic dynamic response of hull plates and stiffened plates are studied.(5)A new equivalent design method is proposed to transform the propagating slamming pressure to an equivalent static pressure that produces the same magnitude of deflection of ship plates as the propagating pressure.The effects of pulse shape,slamming velocity,deadrise angle and boundary conditions on the equivalent parameters are studied.The equivalent static design coefficient of slamming pressure and its calculation formula are put forward.The equivalent design method and the equivalent static design coefficient method are applied to predict the bow flare equivalent static pressure of a container ship.