Numerical Research On Thermal-structure Characteristics For Ship Stern-shaft Mechanical Seals

Ship stern-shaft mechanical seals instrument is an important part in the ship propelling system. Usually, under the various coupled load, local higher temperature and stress easily exist on the end faces of the ship stern-shaft mechanical seals instrument. It further induces serious abrasion and end faces leakage, which directly decreases the overall performance of the mechanical seals instrument in a large scale. Therefore, it is important theoretical and practical significance to investigate into the thermal-structure characteristics of the ship stern-shaft mechanical seals instrument.In this thesis, the ship stern-shaft mechanical seals instrument was chosen as the objective to conduct the theoretical and experimental research. The related theoretical research, which includes the load and deformation, temperature field characteristics, steady coupled thermal-structure characteristics, transient coupled field characteristics under the changing working conditions and optimization analysis, is intensively investigated. On the other hand, the experiments on the independently designed test platform were conducted to verify the research results.1. The research on the distribution of fluid film pressure and the load and deformation of the seals end faces was conducted. Based on the predigested Reynolds equation, the distribution of fluid film pressure derived from three kinds of clearance of the seals end faces was inferred, then, it was accurately loaded on the nodes of the seals end faces finite element model by using the user programmed subroutine. Based on the established model, the iterative restraining analysis of the load and deformation of the ship stern-shaft mechanical seals end faces was carried out by the smallest fluid film thickness and the fluid film pressure relative difference. The analyzed results show that the taper-deformation is originated on the seals end faces under the function of pressure and moment, which forms the contact zone and taper opening gap. What's more, pressure and stress are centralized in the contact area.2. The mathematical computation model of the ship stern-shaft mechanical seals instrument for the coupled thermal-structure analysis was established, and numerical calculation of temperature field was carried out. The computation formula about friction heat, friction coefficient and heat convection coefficient were formed. Numerical iteration calculations for the heat distribution coefficient of seals end faces were accomplished by means of the global approach and the isolated approach. Based on above analysis, following conclusions were gained: the temperature on the inner side of rotating ring face is lower than that of the stationary ring. The overall friction heat distribution coefficient of the seals end faces is affected by the properties of sealing rings' material and working condition parameters, and overall friction heat emitted from the rotating ring is higher than that of stationary ring.On the other hand, the heat distribution of the seals end faces in radial direction has close relation with the radius position and material heat conduction coefficient.3. Some characteristics of the seals end faces under the assumption of the steady coupled thermal-structure model were investigated. Two methods for coupling field analysis, which were called coupling node temperature degree of freedom and contact heat conduction coefficient, were proposed and their equivalence was also explained through one typical demonstration. Four computation convergence criterions were proposed, and some characteristics in the steady coupled thermal-structure field analysis were gained by means of the convergence criterions and boundary condition. Above research results show that under the thermal energy function, some characteristics, such as fluid film pressure distribution, contact pressure and temperature increment and so on, interplay and mutually promote to form strongly coupling connection. What's more, higher temperature, contact pressure and stress are all exhibited in the contact zone.4. Some characteristics of the seals end faces under transient coupled thermal-structure effect were investigated. The transient coupling field method was applied to analyze the thermal-structure characteristics of the ship stern-shaft mechanical seals instrument under the typical changing working conditions and alternate load effect. The results indicate that as a result of the integrating effect, the transient characteristics are different from those of the steady analysis .Under the working conditions that speed reduces and outside sea water pressure decreases, there exits temperature changing hysteresis phenomena on the seals end faces, which makes the temperature of seals end faces sometimes not fall with the reduction of the working condition parameters such as speed and load. Under the alternate load function, the seals end faces characteristics such as temperature and pressure and so on are alternate and transient, too.5. The optimization principle of coupled thermal field for the mechanical seals instrument was put forward and its mathematical computation model was established. In addition, the corresponding coupled field optimized analysis was completed by means of BP neural network, genetic optimization algorithm (GA) and the improvement inside heat dissipation effect. It can effectively bate seals end faces temperature increment and ameliorate seals end faces characteristics by using the optimized parameters, i.e. protruding length and width of seals face, and flushing cooling apparatus installed inside the clapboard. Furthermore, the maximum temperature of local seals end faces under the small taper and converging gap can be effectively decreased.6. Some parameters such as temperature, friction torque and rotational speed were tested on the independently designed test platform for the ship stern-shaft mechanical seals instrument. The tested datum is in good agreement with the theoretical calculating results. Therefore, the theoretical conclusions drawn are confirmed based on the experimental results.