Research On Forecasting Method Of Green Water Impact Load

The offshore floating structure is very likely to occur green water phenomenon during severe sea conditions,serious green water phenomenon even damages decks and structures above the deck,threatening the safety of floating structures at sea.The severity of the green water problems provide higher requirements for the structural strength against the impact design and impact loads on deck and the structures above the deck,while the key and foundations for these work are accurate prediction of the impact loads to the deck and the structures above.The strong nonlinear factors such as water sputter,impact and vortex generated by the green water phenomenon have significant influence on the green water impact load,which presents a great challenge for theoretical research.At the same time,the existing numerical methods and experimental methods for studying the phenomenon have some disadvantages.In addition,the standard method to solve the green water impact load and structural strength problem caused by it needs to be improved.There is an urgent need for a new and effective method to predict green water impact load on deck.Based on the above situation,this paper mainly studies the following aspects:(1)Numerical prediction method of green water impact load of the ship was studied.In order to guarantee the reliability of the calculation results,the spatial wave making and wave elimination verification of the numerical wave pool and the example verification of the green water impact load on the simple convex structure were carried out,good results have been achieved.Taking the 21KTEU container ship as the research object,the CFD numerical simulation method was used to study the green water problem of the ships,to analyze the flow mechanism of green water on the deck,and to calculate and analyze the impact load on the deck and at the wave baffle.(2)The experimental prediction method of floating green water impact load based on the dam break model was studied.Based on the dam break model,a method of flowing impulse test with water tank as the main body was found.The water height on the bow obtained by the potential flow method was used as the input parameter.Through experiments,the flow of water on deck and the evolution process of current after impact on the model surface in a floating green water impacting phenomenon were studied.The pressure distribution on the deck and the surface of the test model and the impact load at different wave height and impact velocity were studied.(3)Numerical prediction method of green water impact load based on the dam break model was studied.Firstly,the flow process of dam break was simulated,and the load results obtained were compared with the published results to verify the reliability of the method and the calculated results.A three-dimensional method was used to simulate the floating green water impact evolution process under the condition of blocking by the model.The pressure on the deck and the model surface was forecasted and compared with the test results to verify the reliability of the simulation method.(4)The strength of bow structure under the impact load of wave was analyzed.Take 21KTEU container ship as the research object,using the static equivalent method and the transient dynamic analysis method to check the structural strength of the deck and the wave plate,the correlation and differences of the results of the two methods was analyzed.