Research On Mechanical Mechanism And Modeling Method Of Double-layer Flexible Joint Of Aircraft Fuel Pipe

Double-layer flexible joint is a pipe joint used for connecting aircraft fuel pipes,which can compensate for the displacement and rotation angle between the connected pipes,and has complex mechanical characteristics.Currently,the design of fuel pipes mainly relies on foreign standards,and designers do not yet understand the mechanical mechanism of double-layer flexible joint.At the same time,the joint contains relatively complex contact characteristics,making system level static strength analysis difficult.Therefore,the research on mechanical mechanism analysis and modeling methods of double-layer flexible joints in this paper has important theoretical significance and engineering value for aircraft fuel pipe system design.The main work and content of the paper are as follows:(1)This paper introduces the structure and working principle of the double-layer flexible joint,analyzes the stress state of the double-layer flexible joint during operation,and establishes a dynamic model of the double-layer flexible joint based on the transfer matrix method.At the same time,a solid finite element model of the casing unit containing a double-layer flexible joint is established,and a simplified model method of the double-layer flexible joint based on the CONNECTOR function in ABAQUS is proposed.(2)Pressure load analysis,forced displacement load analysis,modal analysis,and harmonic response analysis were performed on typical casing unit to obtain the static and dynamic characteristics of the casing unit.The difference in pipe stress between casing units with and without double-layer flexible joint was compared,and the mechanical mechanism of double-layer flexible joint was understood.The influence of the contact friction coefficient on the static and dynamic characteristics of the casing unit was investigated,providing guidance for accurate modeling of the double-layer flexible joint.(3)The equivalent connection parameters of the double-layer flexible joint are obtained by force-state mapping method,and a simplified model of the double-layer flexible joint in the aircraft APU fuel supply system is established.Based on the equivalent model,static and dynamic analysis of the casing unit is carried out.The applicability of the simplified model to the static analysis of casing units is demonstrated by comparing the analysis results of the equivalent model and the solid model.In addition,the identified equivalent connection parameters can also be used to solve the dynamic model of double-layer flexible joint.(4)Build a dynamic test rig for aircraft fuel double-layer flexible joint,design the test scheme,and conduct modal tests for the double-layer flexible joint assembly.The correctness of the dynamic model of the double-layer flexible joint is verified by comparing the results of free mode tests and numerical calculations;By comparing the constrained modal test and simulation results,the accuracy of the finite element solid model of the casing element was verified,further demonstrating the correctness of the equivalent model of the double-layer flexible joint.