The Optimization And Fatigue Failure Analysis Of VATT Blade Structure

The main purpose of this paper is to study the fatigue failure problem of the vertical axis tidal turbine(VATT)blade.The analysis was mainly based on the numerical method which was employed to deal with the modal analysis problem and the fluid-solid iteration(FSI)problem.The analysis of the fatigue life of the structure was based on linear cumulative damage theory(Miner).The numerical calculation was carried out using ANSYS commercial software.Modal analysis was performed using ANSYS Mechanical based on the finite element method.The finite element and finite volume coupling solver CFX and ANSYS Mechanical were used in the FSI analysis.The major reason for the fatigue failure of the VATT blade is the fatigue crack inside the blade.The causes of the fatigue crack are mainly due to the structural resonance caused by the external load and the shortcomings of long-term cyclic loading.The structural resonance failure problem can be dealt with the modal analysis method while designing the blade.By optimizing the internal structure,we are able to avoid the structural natural frequency from target environmental load frequency.In this paper,the Modal module in ANSYS software is used to obtain the dry mode analysis of blade and turbine,the influence of structure change and turbine rotation on its vibration characteristics were considered.The wet-mode analysis of blade was obtained using fluid-solid coupling method,the effects of water environment on the vibration characteristics of the blade were studied.In order to study the fatigue failure of the blade under long-term cyclic loading,the stress response of the key parts of the blade under the impact of water flow is determined.Based on CFX and ANSYS Mechanical,the one-way and two-way FSI was obtained,the transient stress response of the blade was achieved.In order to verify the accuracy of the FSI calculation,a two-way FSI analysis was carried out,the calculation of the lift coefficient and the drag coefficient of a stationary blade were included.The results of the FSI analysis were found in good agreement with the experimental results,and the correctness of the coupling method was shown.In this paper,a coupling contact analysis method of shell element and solid element is used.Shell element was used to discretize the blade skin to help convergence and simplify the model.Solid element was used to discretize the internal structure of the blade to ensure the accuracy of the calculation.As the stress response of the blade was obtained,the stress cycling amplitude and the stress cycle number of the key parts of the blade were calculated using rain flow counting method.The fatigue life of the blade was estimated based on the S-N curve of the material.