Study On Stability Behavior Of Canned Components In Large-scale Canned Motor Main Pump

As one of the key components in the canned motor main pump,the canned components are the unique structures.The canned components are composed of the stator can,the rotor can and ring-ribs outside the stator can.Under the condition of high temperature and high pressure,the canned components are subjected to initial stress,fluid forces caused by the helical flow,the thermal loads caused by temperature variation besides the system pressure.Under multi-loads,the canned components are prone to buckling instabilities which mean a lot to the normal operation the primary loop of the plant.Furthermore,the safety operation of the canned motor is influenced by losing stability.Therefore,the stability of such structures has always been a focus point by numerous scholars.There are few research achievements on the canned components,due to their special application fields.This paper presents the stability study on the canned components subjected to initial pressur(preload),fluid load,thermal load in order to provide theoretical basis and technical means for performance prediction and safety assessment of such system.The canned components are assumed to be coaxial cylindrical shells consisted of rigid inner shell-type body and elastic outer shell due to their particular geometric structures in present study.The influences of single and combined action of initial pressur(preload),fluid load,thermal load on dynamics and stability of such structures are studied.The main contents are given as follows:1)Due to the water pressure,there is initial stress in the canned components.Based on Donnell shell theory,the nonlinear equilibrium equations of ring stiffened shell under the system pressure taking account into initial stress have been represented.Effects of geometric parameters,ring-stiffeners on stability behaviors are analyzed.The variation law of the critical pressure of losing stability with the initial stress is given.2)Based on Donnell shell theory and the potential flow theory,the equations for analyzing the dynamic stability of coaxial cylindrical shells subjected to ideal helical annular flow are obtained.The Numerical analyses are conducted by the zero-level contour method.Effects of geometric parameters,ring-stiffeners on stability behaviors are analyzed.The new instability criteria of the structures are established.This study reveals the mechanism of losing stability of such structures subjected to helical annular flow.3)Based on the potential flow theory and fully developed turbulent theory,the fluid-dynamic forces and the steady viscous forces are obtained.Considering preloads induced by the steady viscous forces,the equations for analyzing the dynamic stability of coaxial cylindrical shells subjected to viscous helical annular flow are established.With the aid of the weighted residual technology,the zero-level contour method is used to determined numerical results.Effects of geometric parameters,ring-stiffeners on stability behaviors are analyzed.It can be conclude that the decreation of flow velocities of losing stability can be ascribed to the fluid viscosity effect.4)The thermal loads are determined by the thermo-elastic theory.On the basis of previous studies,the equations for analyzing the dynamic stability of coaxial cylindrical shells under the combined action of preload,fluid load,thermal load are established.The zero-level contour method is used to determined numerical results.Effects of the thermal loads on the flow velocities of losing stability are analyzed.This study reveals the mechanism of losing stability of such structures subjected to muliti-loads.Based on the above theoretical analysis,the design basis of ring-stiffeners outside the stator can into large-scale canned motor main pump is elastabished.The safety of such system is assessed in extreme condition.The safety assessment method based on the axial flow velocity of cooling water is proposed.