Study On The Resistance And Wake Field Characteristics Of Ship-Ice-Water Coupling In Ice Floe Areas

In recent years,many countries have stepped up efforts in the construction of ice-going ship to make it survive and development.Navigation in the severe environment of icy waters is a challenging task,and the additional load caused by the attachment of ice should be taken into consideration.The hull-ice-current,ice-propeller-current,and ice-hull-propeller-current interactions are highly complex,and have a direct impact on ship resistance and wake fields in the propeller's working area in the stern.During ice-breaking navigation,level ice is broken up and slides underneath the ship along the keel,enveloping the hull before sliding into the front of the propeller plane.As the ship sails through pack ice channels and ice floe zones,most of the ice blocks floating near the free surface simply slide along the ship towards the stern,whereas pack ice or ice floes impact on the hull and slide underneath the ship,driven by its wash.Ice blocks at a certain depth beneath the free surface may also slide towards the front of the propeller's working region.Any pack ice that attaches to the front of the propeller's working region as it slides along the keel will severely impact the incident flows at the stern,and subsequently affect flow fields in the vicinity of the propeller.This degrades the propeller's wake and impairs its hydrodynamic performance.Firstly the research status of resistance and wake field characteristics of ship-ice-water coupling in ice floe areas is summarized which includes the status of resistance in ice floes,the status of marginal ice zone(MIZ)and the status of flow field characteristics.It is based on discrete element method(DEM)to study the resistance and motion of ice-going ships in ice floes.A combined method of CFD-DEM was used to calculate the resistance and interaction of ship-crushed ice.The ship-fluid interaction is based on Euler framework,and the ship-ice interaction is based on Lagrange framework by using DEM method.Tetrahedron and polyhedron models were selected to conduct unidirectional coupling and bidirectional coupling for the crushed ice channel with tetrahedron shape.The mechanism between ship-ice interactions was analyzed and the calculated results was compared to HSVA model test.It is shown that,the interaction process of ship-crushed ice can be simulated well and the rolling,accumulation,slipping,and sinking of crushed ice can be clearly observed.The contact force and total resistance are gradually increased and then stabilized.The total resistance error for tetrahedron model is 5.03%and for polyhedron model is 7.23%.The research work in this paper can provide a reference for the numerical prediction of ship sailing in crushed ice channel and the correctness of the numerical method is proved.A ship model resistance test is conducted under the combined effects of waves and ice floes based on paraffin wax model ice.The motion of the ship model is more unstable in the MIZ than in ice floes.Furthermore,the degree of the ship-ice interaction increases under the wave-ice interaction.The test results show that the total ship resistance is not equal to the sum of the open-water resistance,wave-added resistance,and ice floe resistance because of the wave-ice floe-ship interaction.The increase in resistance resulting from the combination of these three components must be considered while designing an ice-going ship.The influence of the added coupling resistance is associated with the wave length,wave height,and ice concentration.The wake field in ice floes is measured based on underwater stereo particle image velocimetry(PIV).And another wake field experiment with model ice attached under the ship bottom is taken also in the towing tank.The ice intensity distribution is 60%,70%,80%and 90%with the ship velocity of 0.383m/s,0.669m/s,0.997m/s and 1.150m/s.The results show that:The attached ice block adds a "virtual thickness" to the ship's stern that is equal to the thickness of the ice blocks.The interferes between ice blocks and ship's wake field results in significant expansions of the ship's axial velocity contours compared with the ice-free state,which also leads to the formation of severe velocity blockage zones within the wake field against the incident flows of the propeller.The attachment of model ice to hull and the ice floes all lead to interference in the stern's wake fields,and disrupts the streamlined in the vicinity of the hull.Furthermore,the non-streamlined shape of the model ice generates complex vortices that interfered with the bilge vortices of the bare hull.The level of interference varies according to the size,shape and distribution of the model ice attachments,and the bilge vortices tends to weaken or shift outwards.Then,the test data were corrected based on momentum theory to be more close to the real phenomena.