Dynamics Analysis Of Fully Balanced Reciprocating Compressor Crankshaft System

With the continuous development of marine oil and gas resources in China,higher requirements have been put forward for marine natural gas gathering and transmission reciprocating compressors.To solve the problems of large noise and severe vibration in marine high-power compressors,fully balanced reciprocating compressors are used in marine natural gas gathering and transmission.As the core component of reciprocating compressor,the crankshaft affects the size and quality of compressor,and even affects the reliability and life of compressor.The crankshaft structure of the fully balanced reciprocating compressor is symmetrical,which is different from the traditional opposed structure and V-shaped structure.The cylinder and piston are arranged on both sides of the cylinder,and the adjacent cylinders are on the same axis,which has the balance advantage in the structure and mechanism.In this paper,the crankshaft system of marine high-power fully balanced reciprocating compressor is studied,and its motion mechanism,balance characteristics,modal characteristics and dynamic response are systematically studied,providing the basis and technical guidance for further design and research of crankshaft system.Firstly,according to the working requirements and design parameters of the marine high power compressor,the balance scheme of the fully balanced compressor is designed.The characteristics of the fully balanced compressor are introduced.The motion analysis of the fully balanced crankshaft system is carried out.The characteristics of the fully balanced symmetric crankshaft are demonstrated from the static balance,the dynamic balance and the mechanism balance,and the contrastive analysis is made with the opposed and V-shaped crankshaft structures.The analysis results show that the fully balanced symmetrical crankshaft can balance inertia force and torque through its own structure,therefore,the fully balanced compressor has more balanced advantages and is more suitable for marine natural gas gathering and transportation.Secondly,based on the theory of finite element in ANSYS workbench,establish the finite element model of the crankshaft.The free modal and constrained modal analysis of the fully balanced crankshaft are carried out respectively,and the free and constrained modal frequencies and modes of crankshaft are obtained.The difference between the two modal frequencies and shapes have large differences.And under the constraint mode,the critical speed of different oil film bearings under the forward stiffness is calculated,and the curve of the critical speed with the forward stiffness is obtained.The critical speed of the crankshaft is calculated,and found that the crankshaft does not resonate at the rated speed.Then,the transient response of the fully balanced symmetric crankshaft is analyzed in the finite element analysis software ANSYS.Through the transient response analysis,the stress and deformation of the crankshaft in one cycle are obtained,and the static strength and fatigue of the maximum stress region are obtained,and the crankshaft design is qualified and meets the requirements for use.Finally,establish the three-dimensional model of the crankshaft and connecting rod mechanism,the rigid crankshaft is flexibly processed in ANSYS,and the dynamics simulation software ADAMS is used to establish the rigid-flexible coupling dynamic model of the crankshaft mechanism,and the dynamic simulation analysis is performed to obtain the load changes of main shaft neck and crank pin in a period,and provide the basis for further intensity analysis.Through the above research,it can provide a certain theoretical basis and reference for the further optimization design of the compressor crankshaft structure.