Study On Anti-vibration Performance Of Vehicle Cryogenic Insulated Cylinder

Liquefied Natural Gas Vehicle (LNGV) is widely promoted for the advantages of clean, environmental protection and long-endurance mileage. Vehicle Cryogenic Insulated Cylinder, which is used to contain LNG, is a key component of LNGV. The structure of high vacuum multi-layer insulation is adopted by it. The inner is fixed on the outer shell in form of one end fixed, the other end sliding. The cylinder is not only bears internal pressure load, but also vibrates with car bumps, acceleration or deceleration. Thus, failure caused by vibration is one of the most important failure modes. While, at present, there are still lack of effective anti-vibration design methods of the cylinders, and the anti-vibration performance can only be verified by vibration test. Therefore, it is important to improve the safety of the vehicle cryogenic insulated cylinders by studying the inherent mechanism of the impact of the key structures on anti-vibration performance, and presenting reasonable design methods at the same time. The paper was subsidized by CSEI of the project "The Study of Anti-vibration Design Method of vehicle liquefied natural gas cylinders". In this paper, the finite element model of vehicle cryogenic insulated cylinder was established by using ANSYS software, anti-vibration performance was analyzed, and the structural optimization was carried out for the key parts. The contents and results are as follows:(1) Considering inertial load and medium impact load caused by vibration, the equivalent static analysis model of vehicle cryogenic insulated cylinder was established, and stress distribution of key parts was analyzed. The results showed that:the stress in the root of support neck and the front head joint was greatly influenced by inertial load, so that vibration must be taken into consideration when structure optimization. While the stress in circumferential weld between vacuum chamber and the head, circumferential weld of opening of front head and transition corner of the liner head was mainly influenced by internal pressure load, the inertial load induced by vibration did minimal impact on it. The research results can provide a basis for structure optimization of anti-vibration performance of cylinder.(2) Judging by heat transfer loss and structural strength, optimization of support neck structure, neck length and front head joint structure was conducted. The results showed that: the support neck combined with extension tube which was local thinned, were better supporting structures. With a benchmark of 160mm,increasing the length of neck by step of 10%, the heat leak through neck decreased by 5%-7%, while the stress of the neck root increased by 9%-20%. Comprehensively considered heat transfer loss and strength, the neck length was allowed to rise to 1.2 times of original length. Then, heat leak decreased by 13% and strength allowance still remained 10%. After comparing the stress distribution of two structures of front head joint, using transition arc connection can transfer the maximal stress from weld to head, lowering the possibility of fatigue damage caused by weld defect.(3) Modal analysis model of vehicle cryogenic insulated cylinder was established, at the same time, the effects of liquid filling ratio and the length of cylinder shell on the resonance frequency of gas cylinders were investigated. The results showed that:with the increasing of filling ratio, resonance frequency decreased, the smallest resonance frequency is 77.4Hz, which was still more than the maximum excitation frequency 40Hz applied by vibration test. Sympathetic vibration of the cylinder would not be triggered. However, with the increasing of shell length, the resonant frequency of cylinder would approach to maximum excitation frequency applied by vibration test, and then sympathetic vibration of the cylinder would be triggered easily.(4) The random vibration analysis model of vehicle cryogenic insulated cylinder was established. The excitation power spectrum density under different levels of road surface was calculated. The stress distribution and displacement amplitude, the displacement response, velocity response and acceleration response of maximum stress point were analyzed. Under excitation of concrete pavement and macadam pavement, the dynamic response mutation of vehicle cryogenic insulated cylinder was not occur. And the position, which most prone to fatigue damage, was located in the root of supporting neck. But all supporting structures, which had good anti-vibration performance, had enough fatigue strength. Due to the lower fatigue strength margin of the macadam road, the driving time should be reduced in poor quality pavement for the safety of the vehicle cryogenic insulated cylinder.