| As an important tool of railway transportation,diesel locomotive has the unique advantages of less investment,flexibility,reliability and strong mobility.It still has a long-term demand in the domestic and foreign markets.In order to adapt to the development trend of high-speed railway passenger transport and heavy freight,it is necessary to continuously optimize its own structure and improve the technical performance of diesel locomotives.A diesel locomotive adopts an integral load-bearing fuel tank,which is a part of the underframe and is rigidly connected with the diesel generator set directly above it.The fuel tank should not only bear the shaking and impact of the internal oil,but also bear the vibration load from the diesel generator set.It is in a multi axis random vibration environment under the action of liquid-solid coupling.Taking the integral fuel tank as the research object,through the comparison of test and simulation,the impact strength of its structure under liquid-solid coupling effect and the fatigue life prediction under multi axis random vibration environment are carried out.Firstly,the frequency sweep test of the empty tank and the two media of water and diesel at the liquid filling ratio of 25%,50% and 75% is carried out on the vibration test-bed.It is found that with the increase of the liquid filling ratio in the tank,the liquid-solid coupling effect becomes more obvious,and the liquid-solid coupling effect caused by the liquid with higher density and higher mass proportion will become more obvious,resulting in the reduction of the modal frequency of the box structure and the increase of the damping coefficient,which changes the natural characteristics of the box.The finite element model is modified according to the empty box parameters and solved by three liquid-solid coupling methods.Compared with the test results,it is considered that the virtual mass method is the most accurate,and the modal frequency error of the box obtained from the test is within10%.Secondly,the impact test of the liquid storage test box is carried out.In order to determine the simulation method of impact condition,the vertical impact test of cantilever structure is carried out.Compared with the three simulation methods of inertia release method,overall acceleration method and transient finite element method,it is considered that the result of transient finite element method is the most accurate and is used for the impact simulation solution of liquid storage tank.Then,with the help of multi axis vibration test-bed,the longitudinal,transverse and vertical single axis and three-axis synchronous sinusoidal and random vibration tests of the box are carried out.It is found that the root mean square value of the stress response of the liquid storage tank model under the accumulation of uniaxial vibration is always less than the root mean square value of triaxial synchronous vibration,and the difference between the two is quite different when different excitation is applied.Triaxial synchronous vibration has obvious multiaxial effect.Whether under sinusoidal vibration excitation or random vibration excitation,the root mean square value of stress response at each measuring point will increase with the increase of liquid filling ratio,and the liquid-solid coupling effect has a great influence on the vibration characteristics of liquid storage tank.The simulation results are in good agreement with the finite element test results.Finally,using the transient method and virtual mass method verified by the liquid storage test box in the previous chapters,the longitudinal impact strength of the locomotive fuel tank under empty tank and different liquid filling ratio and the fatigue life prediction under multi axis random vibration environment are evaluated.The liquid-solid coupling effect has a great influence on the impact strength and fatigue life of the structure,but even under the condition of 75% liquid filling ratio,the maximum impact stress of 118.170 MPa is far less than its yield strength of 345 MPa;The vibration fatigue life is 51.815 years,and the fuel tank structure meets the requirements of impact strength and 30-year service life. |
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