火灾环境下车用CNG钢瓶热力响应及失效机理研究

发布时间：2018-12-07 13:44

【摘要】：在汽车保有量高速增长、世界能源格局变化和环保要求日益提高的背景下,具有良好经济和环保效益的天然气(CNG)汽车得到大力推广和普及,CNG气瓶使用量随之增加,其中CNG钢瓶占据CNG气瓶比例的90%以上。CNG钢瓶使用过程中出现的燃烧、爆炸事故往往引发灾难性后果。由于火灾试验耗资大、危险性高、结果重复性差等原因,数值模拟研究受到越来越广泛的重视。本文对火灾环境下车用CNG钢瓶的热及力学响应进行了数值模拟研究、失效机理分析、失效时间预测和提出安全消防策略,具有一定的理论价值和现实意义。本文主要内容如下： (1)火灾环境下车用CNG钢瓶的热响应数值模拟研究。基于分区求解、边界耦合数值解法和流固耦合传热理论,按真实的火灾试验模型和合理的假设,分别建立火灾环境和CNG钢瓶的物理数学模型；然后利用大型流体动力学分析软件FLUENT对无风和有风火灾环境进行三维数值模拟,计算得到火焰的流场、温度场和钢瓶外壁的热流密度分布,证明无风环境下能提供相对均匀和充足的热量。无风火灾环境下得到的钢瓶外壁的热流密度分布作为钢瓶模型的热边界；同样运用FLUENT软件对钢瓶进行三维瞬态热响应过程进行数值模拟,计算得到在420秒内瓶内介质温度、压力及气瓶壁温度随时间的变化规律。 (2)火灾环境下车用CNG钢瓶的力学响应数值模拟研究。根据顺序热-结构耦合思想和弹塑性力学理论,运用ANSYS workbench13.0集成流体力学分析模块FLUENT和热-结构静力模块ANSYS Mechanical,首先验证了有限元模型具有良好的计算精度,然后对处在不同温度场和压力场共同作用下的气瓶壁进行有限元应力分析,并进行强度校核,证明了钢瓶在420秒前满足强度要求。 (3)火灾环境下车用CNG钢瓶的失效机理初步研究、失效预测和预防。通过失效机理分析,提出了意外火灾环境下钢瓶爆破失效时间点与爆破失效压力的理论预测方法。首先对钢瓶进行失效机理分析,提出失效准则,根据极限载荷有限元分析法得到不同温度和性能条件下气瓶爆破压力的三次多项式拟合曲线,继而根据FLUENT计算气瓶内压变化的热响应曲线,通过二曲线交汇点准确预测意外火灾环境下气瓶爆破失效时间点与爆破失效压力,CNG钢瓶气瓶的失效时间在火烧420秒左右；根据失效机理分析,提出了气瓶安全消防对策。
[Abstract]:Under the background of the rapid growth of automobile ownership, the change of world energy pattern and the increasing requirement of environmental protection, natural gas (CNG) vehicles with good economic and environmental benefits have been vigorously promoted and popularized, and the use of CNG cylinders has increased. CNG cylinders account for more than 90% of CNG cylinders. The combustion of CNG cylinders often leads to catastrophic consequences. Because of the high cost, high risk and poor repeatability of fire test, numerical simulation has been paid more and more attention. In this paper, the thermal and mechanical responses of CNG cylinders in fire environment are numerically simulated, the failure mechanism is analyzed, the failure time is predicted and the fire safety strategy is put forward, which has certain theoretical value and practical significance. The main contents of this paper are as follows: (1) numerical simulation of thermal response of CNG cylinder in fire environment. Based on the partition solution, boundary coupling numerical solution and fluid-solid coupled heat transfer theory, according to the real fire test model and reasonable assumptions, the physical mathematical models of fire environment and CNG cylinder are established respectively. Then using the large-scale fluid dynamics analysis software FLUENT to carry on the three-dimensional numerical simulation to the no-wind and the wind-free fire environment, calculates the flame flow field, the temperature field and the cylinder outer wall heat flux distribution. It is proved that relatively uniform and sufficient heat can be provided in windless environment. The heat flux distribution of the outer wall of the cylinder is used as the thermal boundary of the cylinder model. The three-dimensional transient thermal response process of the cylinder was also simulated by using FLUENT software. The variation of medium temperature, pressure and cylinder wall temperature with time in 420 seconds was calculated. (2) numerical simulation of mechanical response of CNG cylinder in fire environment. According to the theory of sequential thermal-structural coupling and elastoplastic mechanics, the ANSYS workbench13.0 integrated hydrodynamic analysis module FLUENT and the thermal-structural static module ANSYS Mechanical, are used to verify that the finite element model has good calculation accuracy. Then the finite element stress analysis of the cylinder wall under the action of different temperature field and pressure field is carried out and the strength check is carried out. It is proved that the cylinder meets the strength requirement 420 seconds ago. (3) the failure mechanism, failure prediction and prevention of CNG cylinder used in fire environment. Based on the analysis of failure mechanism, the theoretical prediction method of cylinder blasting failure time point and blasting failure pressure under accidental fire environment is put forward. Firstly, the failure mechanism of cylinder is analyzed, and the failure criterion is put forward. According to the finite element analysis of limit load, the cubic polynomial fitting curve of cylinder blasting pressure under different temperature and performance is obtained. Then the thermal response curve of cylinder internal pressure change is calculated according to FLUENT. The blasting failure time point and blasting failure pressure of gas cylinder under accidental fire environment are accurately predicted by the intersection point of two curves. The failure time of CNG cylinder is about 420 seconds after burning. According to the failure mechanism analysis, put forward the gas cylinder safety fire protection countermeasure.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：TH49

【参考文献】