Research On The Ship-ice-wave Coupling Numerical Model Based On The SPH Method

Under the influence of global climate change,the sea ice in the Arctic Ocean is disappearing,and a new Arctic channel will be opened up soon.With the rise of Polar Engineering,the developing of an accurate and effective numerical model to predict the navigation performance and ice load of ships in the polar area has become an urgent problem to be solved,which can provide necessary guidance for the design and operation of icebreaker.The interaction between waves and sea ice is the main feature in the marginal ice zone.With the gradual expansion of the marginal ice zone,the wave-ice interaction will gradually threaten the operation safety of ships and marine structures in the ice area.At present,the research work on ships and other structures in ice area mainly focuses on the ship-ice interaction in level ice or broken ice,most of which do not consider the real flow field.And the numerical study of ship-ice interaction under wave action can not be realized in these studies.Therefore,it is necessary and significant to establish a numerical model of ship-ice-wave interaction.The interaction process of ship(structure)-ice-wave is very complex,which not only includes the complex failure process of ice,but also involves multiple coupling problems such as ship-ice coupling,wave-ice coupling and ship-ice-wave interaction.Considering the applicability of smooth particle hydrodynamics(SPH)in the simulation of hydrodynamics,large deformation and fracture of solid materials and fluid-solid coupling problems,a numerical model of ship-ice-wave interaction based on the SPH method is established to investigate the ice failure,movement of ice floes and ice load on ship hull during the process of ship-ice-wave interaction in this paper.In this paper,the basic idea,control equation,particle approximation and boundary treatment of SPH are introduced firstly.A simplified finite difference method is used to improve the accuracy of traditional SPH method.Then the elastoplastic constitutive model of ice is given,and the failure model based on the elastic-plastic constitutive equation and D-P yield criterion and cohesion softening rule is established.The improved SPH method combined with the above failure model is used to establish a numerical model to simulate the failure process of ice.The validation of effectiveness and accuracy of the numerical model in simulating ice failure is implemented by simulating two typical failure behaviors:bending and compression failure of ice.Then,an adaptive ice-fluid coupling SPH model is established for the numerical simulation of wave-ice interaction.In this coupling method,the ice particles are regarded as the virtual boundary particles for fluid particles in the interaction region.And the coupling between ice and fluid particles can be realized by satisfying the boundary conditions of kinematics and dynamics.Some problems existing in the ice-fluid coupling method are corrected and improved.For example,the density ratio of ice to fluid is introduced to make the pressure evaluation of ice particles as boundary particles more accurate and reasonable;the imbalance of interaction force between the ice and fluid particles caused by the inconsistent time step is improved.In addition,the unreasonable interaction between the ice particles at both ends of the crack is eliminated by numerical treatment.With these improvements,the ice-fluid coupling algorithm can get better accuracy and applicability in the model of ice-fluid interaction problem.This ice-fluid interaction algorithm does not need the geometric information of particles at the coupling boundary,so it is easy to realize even with complex boundary shape.The validity and accuracy of the above ice-fluid coupling model are verified by the simulation of wave-ice interaction problems,such as the kinematic response,bending deformation and fracture failure of ice floe under the wave actions.Then,in order to realize the numerical research of ship(structure)-ice-wave interaction,the ship(structure)-ice-fluid coupled SPH model is developed firstly on the basis of the above validated ice-fluid coupled model.The ship hull is included in the ice-fluid interaction model by taking the icebreaker(structure)as the boundary of ice phase and fluid phase and using the virtual particle boundary treatment method.Thus the ship(structure)-ice-fluid coupling SPH calculation model is established.And the numerical treatment is adopted to eliminate the unreasonable interaction between the particle pair of ship-ice separated by the fluid and the ship-sluid particle pair separated by the ice,which can make the simulation of the interaction between the ship-ice-fluid particles be more reasonable and accurate.The ship-ice-fluid interaction process under the continuous ice breaking mode by icebreaker in level ice is simulated firstly.The ice breaking progress and the movement of broken ice are investigated and the influence of fluid on the ice breaking process is also compared and analyzed.Then the ice load of ship hull during the ice-breaking progress is predicted.The influences of ship speed,ice thickness and ice properties on ice load are summarized.By comparing with the experimental results,it is verified that the ship(structure)-ice-fluid coupled SPH model can simulate the process of ship(structure)-ice-fluid interaction and predict the ice resistance effectively.Finally,by adding numerical wave model into the above ship-ice-fluid coupling model,the ship-ice-wave coupling model is established.And the numerical simulation of ship-ice-wave interaction in broken ice area is carried out.The effects of ship speed,the concentration and average size of ice floes on ice load without wave action are analyzed.The validity and accuracy of the numerical model are verified by comparing the numerical results with the experimental data.Then,the numerical simulation of ship-ice-wave interaction process under wave is carried out.The influence of wave on the navigation process of ship in broken ice is studied and analyzed.The characteristics of ice load under the wave action with different wave height,wavelength and concentration of ice floes are summarized.The research results show that the ship-ice-wave(water)coupling numerical model can simulate the failure progress of ice layer during the process of icebreaking and the ship-ice floe interaction under the wave action,and can effectively predict and analyze the ice load.