Analysis And Experimental Study On Fluid Solid Interaction Vibration Of Ship Stern Structure

Fluid-solid interaction(FSI)problem exists in all aspects of all walks of life.As for ship,when sailing on the sea,the side and bottom of ship structure will contact with water.If the internal tank exists,both side of the structure will interact with water.FSI will be critical and should be well considered when design the ship structure.Lewis method and virtual mass method are adopted to simplify such problem in engineering application which means the outer sea water is considered as added mass.The internal fluid is considered as equivalent mass points The aforementioned methods ignore interactions of fluid and structures,thus will introduce some uncertainties.Stern is one of the critical area where the FSI cannot be ignored,but most of the analysis is based on numerical method rather than directexperimental study due to the complicated form and large volume of ship structures.In this thesis,the author will perform coupled analysis of structures with both internal and external fluid with numerical method,verify the numerical method with experimental results and study the effects of various parameters.The main research work of this thesis can be summarized as follow:(1)External fluid domain FSI vibration analysis: the common plate on ship structures is selected as the research object,and fluid element method in ANSYS and NASTRAN and virtual mass method are adopted respectively to study the property of the plate vibration.Effect of water depth on vibration property of the plate with single side and double side of the structure in water are investigated,and the effect of boundary conditions is also studied.Then,vibration analysis of one catamaran is performed,and the differences with the ordinary monohull is analyzed.On this basis,by establishing the finite element model of two regular cylindrical shell,the influence of distance between catamaran and the applicability of virtual mass method can be analyzed.(2)Internal fluid domain FSI vibration analysis: a tank is selected as the research object,and fluid element method in ANSYS and NASTRAN and virtual mass method are adopted respectively to study the property of the cabin vibration under the condition of half-full and full filled.Meanwhile,the effect of inner liquid level on vibration mode is analyzed,and the influence on vibration can also be found caused by liquid distribution in adjacent tank.(3)Based on a ship scale model,the modal parameter identification method by vibration model test and the phase resonance method are introduced.The fluid element method in ANSYS and virtual mass method in NASTRAN are performed to compute vibration property with the stern model of dry and wet condition considering with or without inner water.Compared the calculation results with experimental results,then applicability by two different methods can be found,and the effect of inner and outboard water on vibration property can be analyzed.