Numerical Analysis On Overhead Pipe Under High Temperature Combined Blast Loads

The issues of long distance transport of dangerous materials for pipeline structures which is used as the mode of transport in today's society as essential are solved. However, due to issues of design, construction and quality of defects, the pipeline may cause fire or explosion accidents in its service. Once it encounters both fire and explosion, huge losses of life and property will be caused, and the leakage of the medium in the pipe may also cause environmental pollution. In most cases, the explosion occurs with the fire accident simultaneously. Many previous research results of damage mechanism under blast loads and fire are published, but research of that under the explosion and fire is less reported. Therefore, it has a wide prospect on pipeline structures under explosion and fire, and the problems need to be solved urgently.The numerical simulation method is not only regarded as the auxiliary means of theoretical and experimental studies, it has also become a kind of basic scientific research methods independent of theory and experiment. Because of the high risk and complicated operability of explosion and fire experiment, the numerical simulation can be instead of the traditional experiment which is very good at calculating complex problems and mechanics research. Therefore, the technique of numerical simulation has become one of the important means in the analysis of such issues.In this dissertation, both ANSYS and LS-DYNA are used for pipeline dynamic response analysis of under explosion with fire loads by using finite element method. The fundamental principles of explosion analysis and thermal analysis are firstly summarized. Then, through analysis of the principle and comparative relevant parameters as well as literature review, a finite element model under blast load is established to numerically develop the pipeline structure with internal pressurized fluid dynamic response under blast and temperature field and thermal stress under fire loads. Finally, dynamic responses and failure modes under explosion combined with high temperature loads are analyzed by using restart method.The fluid-solid coupled model with the pipeline, internal liquid, air and TNT are established and solved in the dissertation by LS-DYNA, and the explosion is simulated by applying the TNT material model in the program, and the numerical results show that the internal liquid and pressure filled in pipe have a positive effect to blast resistant. Then, the temperature field and thermal stress under high temperature of the liquid filled in pipe in different environmental conditions are analyzed. A method called the restart method is applied in this dissertation to numerically analyze pie structures under blast and temperature, so as to simulate the effect of both loads on the pipeline structure. The results show that when the pipeline suffered fire after blast loading, the temperature is higher, the pipeline has lower anti-impact capability, and the influence of fire temperature on pipeline anti explosion ability is remarkable; when the pipeline structure is subjected to impact loading after the first fire load, the influence for the blast on the pipeline structure follow-up fire resistant ability is not obvious. If the explosion happens during the fire and pipeline structure cannot lose the bearing capacity during the blast, the ultimate temperature for the pipeline structure is almost the same as that without an explosion.