Dynamic Modeling And Optimal Design Of Metal Braided Hoses With Laminated Damping

Metal braided hoses are an important connection component in modern industrial pipe systems,consisting of external metallic braiding,corrugated bellows and joints,which play an important role in vibration and noise reduction as well as compensation of system displacements.The analysis and optimization of the dynamic performance of metal hoses,the investigation of relationships between internal pressure conditions,geometric and material parameters of the laminated damping and the structural loss factor,can provide guidance for the design and manufacture of metal hoses and their engineering applications.In this paper,a non-linear equivalent model of the external metallic braiding is proposed,and the dynamics of the metal hose is analyzed according to the viscoelastic damping energy dissipation theory,mechanical vibration theory and the modal strain energy method.The effects of damped/undamped conditions,internal pressure conditions,damping layer thickness and damping material parameters on the dynamic performance of the metal hose are discussed.Finally,the design of the metal hose is optimized to improve the damping performance of the structure.The main research elements and conclusions of the thesis are as follows.(1)A theoretical study of viscoelastic damping structures,metallic braiding,finite element analysis methods and optimized design is conducted,followed with the calculation of equations of motion and loss factors for viscoelastic structures,a discussion of equivalent modelling methods for metallic braiding,and a brief introduction to non-linear finite element and modal analysis theory.(2)A non-linear equivalent stiffness method based on tensile testsIn this paper,an equivalent modelling method for metallic braiding is proposed.The material parameters of the hyper-elastic function are fitted to the load-displacement response derived from the tensile test of a metal hose,so as to obtain an equivalent homogeneous model that can describe the non-linear force-deformation relationship of the braiding more accurately,and the mainstream hyper-elastic function models are compared horizontally using this method,concluding that the Ogden model fits the metallic braiding’s non-linear characteristics most effectively.(3)Finite element modelling of metal hosesUsing the structural parameters of the metal hose as a reference,the finite element method is applied to model,simplify,mesh and carry out modal analysis of the metal hose.The modal parameters of the first five orders,including the natural frequency and modes,are obtained by means of experiments,in which the relative errors of the natural frequencies of the second,third,fourth and fifth orders are as low as 0.54% and as high as 8.55%,verifying the accuracy of the model.(4)Dynamics analysis of metal hoses under different conditions and variablesIn this paper,the loss factor of the damping material is first measured by resonant beam test,and vibration analysis is carried out for undamped laminated metal hose and damped laminated metal hose with and without internal pressure load.The effect of internal pressure on the loss factor of the metal hose is compared.The dynamic response and root-mean-square(RMS)vibration level difference are compared under different conditions,concluding that in addition to suppressing the resonance peak response of the metal hose,the damping layer can also extend the frequency domain with damping effect.Finally,the modulus and density of the damping material as well as the thickness of the damping layer are selected as variables for vibration analysis,and the relationship between the above variables,the vibration level difference and loss factor is investigated.It was found that the density had no effect on the loss factor,but was positively correlated with the vibration level drop in the low frequency range,and the thickness and modulus were positively correlated with the structural loss factor.(5)Optimization of the bellow and damping layer of the metal hoseA three-layer parametric corrugated bellows model is established for the metal hose structure of one third of its length,and the ratio of damping strain energy to structural strain energy is selected as the objective function to take the maximum value for the optimization design using genetic algorithm.The optimized model has a maximum improvement of 64.3% in damping energy dissipation.