Study On Dynamics Characteristics Of Hovercraft Shafting Based On Virtual Prototyping

Because of structure characteristics of hovercraft, coupling problems of ship hull-shafting were more and more obvious under action of complex sea excitement. Traditional research methods of ship shafting were based on rigid ship hull or static deforming of hull because coupling characters was very complex between ship shafting and ship hull. These simplified methods sever connection between shafting and hull. At present, effective study method still is absent to coupling characters study between shafting and ship hull acted by complex environment. So, how to solve the dynamics problems of hovercraft's propulsion shafting is significative to development of hovercraft.In the dissertation, present study state of vibration of shafting and ship hull, excitation of complex ocean wave and virtual prototyping were systematically discussed. On the base, dynamics problems of hovercraft were studied particularly applied modern virtual prototyping. The main contents of the dissertation are as follows.1. According to structures characteristics of hovercraft's propulsion shaftig, basic theories of virtual prototyping were studied particularly including FEM, modal synthetic method, multi-body dynamics and optimization theory. In addition, numerical calculation method to analyze multi-body system comprised rigid bodies and flexible bodies were studied.2. According to structure characteristics of hovercraft's propulsion shaftig, a research method that study dynamics characteristics of ship hull-shafting was put forwarded based on virtual prototyping combining muli-body dynamics, solid modeling of computer and multi-field simulation.3. Virtual prototyping of hovercraft's propulsion shaftig comprised flexible ship hull, shaft, bearing systems, elastic couplers and gearbox was studied particularly. Discrete modeling method of ship hull applied Timoshenko elastic beam was compared with modeling method of ship hull applied FEM. Elastic bearing's modeling method and elastic coupler's modeling method were determined in virtual prototype. Parameterize modeling of gear and virtual assembly of gearbox were studied, and contact stiffness of straight gear pair and helical gear pair was studied too. 4. Virtual prototypes model of single shaft-elastic bearing system and model of multi-shaft system were established. These model's frequency response characteristics were analyzed through sine sweep-frequency method, and shafting dynamic responses were studied when foundation of shafting-elastic bearing system was excited by displacements excitation of variant frequency, variant phase and variant displacement amount. And corresponding conclusions were obtained. According to above problems, differences were compared between rigid shaft-elastic bearing system and elastic shafting-elastic shafting system.5. Through creating state variables of real-time deforming of ship hull, dynamic model of coupling system of ship hull-shafting was established in virtual prototype environment. Through simplified dynamic model of ship hull-multi shafts-elastic bearing, factors to influence bearing force were studied.6. Applied the modeling and studied method of ship hull-shafting system that been put forward in the dissertation, simulation model of experimential facility of hovercraft's propulsion shafting was established through structure topology analysis. Some part's dynamics characteristics were obtained including gearbox and middle shaft through simulation research. These research conclusions could have directive effects to research of actual ship.7. Excitement effect of sea wave acted on propeller and hull were introduced,Applied frequency domain analysis method to movement response of ship hull, solution method of frequency-response function of movement of ship hull was determined. Time domain model of random wave and time domain model of wave surface angle were synthesized through linear wave superposition method. These time domain model could be farther excitement import to movement analysis of actual ship.8. Hovercraft's propulsion shafting was as specific study object, how to select objective functions, design variables and restraint functions on optimization design of hovercraft's propulsion shafting were analyzed. Applying parameterize modeling method of virtual prototype, combining the studying results of sea excitement, and using generalized reduced gradient optimization algorithm, structure optimization research of hovercraft's propulsion shafting under whipping condition was done.9. A design idea that a kind of experimental equipment of flexible base-shafting propulsion which could simulate complex sea condition and bese excitement could be controlled was put forward first. A kind of simulation experimential facility having flexible base and propulsion shaft ing was designed and built. The experimential facility could supply effective experimental-research means to study dynamic characteristics of hovercraft's propulsion shafting. Using the experimental facility, experimental research was performed about characteristics of hovercraft's propulsion shafting. Experimental research showed that the studied method that been presented in the dissertation about hovercraft's propulsion shafting was effective and correct.Finally, main originalities of the dissertation were summarized, and some future directions of research were presented by author.