Research On Dynamic Responses Of ACV's Flexible Skirt Considering Nonlinear Factors

The Air Cushion Vehicle(ACV),equipped peripheral skirts at it bottom,can travel at high speeds over water and ground.For its excellent speed and amphibiousness,ACVs are widely used in the military and civilian transportation.However,due to the working mechanism of fully supported ACVs,they possess many features and characteristics that conventional ships do not have,for instance,the flexible skirt system,lifting system,as well as the coupled dynamic response.The dynamic response of skirt system has a significant influence on the stability,seaworthiness and seakeeping of the craft.To simulate the dynamics of skirts,rigorous mathematic model of dynamics and accurate numerical procedures are required.At present,the amount of studies reported in the literature is very limited,and none of them has taken into the diversity of the stern-skirt structures,not even mention the dynamic characteristics of them.Thus,the author,staring from the theoretic derivation,investigated the dynamic response of flexible skirt structures.The work that has been completed includes:1.Derivation of the aerodynamic model of lifting system.By analyzing the characteristics of fan and airway,the flow-pressure characteristic curve of the flow from the fan to the skirts was studied.Based on the Bernoulli equation and ideal gas state equation,the aerodynamic model of the lifting system is established.2.The dynamic model of the ACV.Based on the theory of Lagrangian mechanics,the skirts were simplified into a dynamic system of two-degrees-of-freedom(DOF),and the dynamic model of the bag and finger skirts was established.Through the coupling of the aerodynamic model and the skirts dynamics model,the dynamic model of the hovercraft was established.3.Numerical study of the dynamic response of the skirt structure.Based on the analysis of the dynamic model,a suitable numerical method was determined for solving the nonlinear differential equations.Finally,the dynamic response of the flexible skirt and the movement of the ACV are obtained.4.Study on the dynamic response of the three-bag stern skirt.Based on the theory of Lagrangian mechanics,the dynamic model of the three-bag 4DOF stern skirt was derived,and by combining with the model of gas dynamics,the dynamic response of the stern skirt was obtained by deriving the mechanical model of the ACV and choosing a reasonable numerical method.By comparing with the relevant design codes and their own,it is found that the numerical results accord with the motion rule of skirt,and lay the foundation for predicting the environmental load of ACV in the future.In this thesis,through the derivation of the dynamic model of the ACV and the determination of suitable numerical procedures,the dynamic response of the ACV skirt is obtained.Comparison of the results with the relevant rules as well as the available data shows that the numerical results are consistent with the pattern of skirt motions.The findings of this study can be used as reference and also paves the foundation for more accurate calculation of the motion as well as the wave load on the ACV.