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An improved constant volume cycle (CVC) model is developed to analyze the nozzle effects on the thrust and specific impulse of pulse detonation rocket engine (PDRE). Theoretically, this model shows that the thrust coefficient/specific impulse of PDRE is a function of the nozzle contraction/expansion ratio and the operating frequency. The relationship between the nozzle contraction ratio and the operation frequency is obtained by introducing the duty ratio, by which the key problem in the theoretical design can be solved. Therefore, the performance of PDRE can be accessed to guide the preliminary shape design of nozzle conveniently and quickly. The higher the operating frequency of PDRE is, the smaller the nozzle contraction ratio should be. Besides, the lower the ambient pressure is, the larger the expansion ratio of the nozzle should be. When the ambient pressure is 1.013 × 105 Pa, the optimal expansion ratio will be less than 2.26. When the ambient pressure is reduced to vacuum, the extremum of the optimal thrust coefficient is 2.236 9, and the extremum of the specific impulse is 321.01 s. The results of the improved model are verified by numerical simulation.

Numerical prediction can analyze the cause and process of the accident comprehensively with the application of mathematical models. The computed results are more reliable and intuitive compared with the qualitative analysis results. Therefore, based on the Computational Fluid Dynamics (CFD) and the related theory of safety system science, leak and diffusion processes of high pressure liquid oxygen in spherical tank area, and the subsequent potential oxygen poisoning was analyzed by accident consequence assessment method. The given poisoning area and damage situation provide a reference for the safety analysis of oxygen storage and transportation.

Oil-gas migration is an important process of the reservoir formation. Based on this discussion, a numerical simulation was conducted to study on oil-gas migration and aggregation. With considering the flow behavior of gas-liquid two-phase flow, based on Navier-Stocks equations and the Darcy’s law, the movement characteristics of natural gas within the typical fault passage are predicted by using the finite volume method and pressure-velocity coupled algorithm. The velocity distribution of natural gas is discussed under the primary migration condition, as well as the diffusion concentration at different locations. Moreover, the position of spill points affecting natural gas aggregation is analyzed, which provides a theoretical basis for predicting reservoir formation and transport processes.

Using alternative fuels is an effective way to reduce air pollution and transform energy structure. The characteristics of four kinds vehicle alternative fuels (LPG, DME, CNG and hydrogen), and the advantages and disadvantages in practical application are studied in this paper. By using the methods which combines safety system engineering and Computational Fluid Dynamics (CFD), the diffusion process of fuels leakage, and the damage area were analyzed quantitatively. Moreover, potential fire accidents for alternative fuels during storage and transportation were evaluated by consequence assessment method. The study results show damage area of the fireball's radiation, which provides reference for fuel safety analysis.

Concrete mechanical properties under dynamic load such as blast and impact are very complex. Shock wave propagation law and damage effect in the concrete were studied numerically in the paper by using TNT explosive ignition and growth model, concrete dynamic damage model, and SPH method. And shock wave properties of different mass explosives in the concrete were analyzed with the similarity theory. The result shows that TNT shock wave propagation law meets the internal-blast similarity law. Peak pressure, positive pressure impulse, maximum velocity and maximum acceleration in the concrete decrease with the increase of scaled distance. And time needed for reaching peak pressure increases linearly with the increase of scaled distance. A theoretical basis of structure and protection design for constructions is achieved in the paper.

Underwater explosion is very important for underwater weapons-design technology and research on the damage effect of target structure. In this paper, the flow-out boundary and variable step-size multi-material Euler algorithm were utilized to analyze numerically the whole process of shock wave generation and propagation, as well as bubble formation and impulse of underwater explosion. The computed results reveal the energy output characteristics of underwater explosion by TNT charge, which provide an important scientific basis for formulation design of charge and improvement of damage effects for underwater target.

Blast can cause serious loss of people live and property，and heavy damage on building structures. So, a numerical study on internal-blast-field characteristics and dynamic response of concrete by aluminized explosive was conducted. Moreover, three energy release models of aluminized explosive with combustion effects were compared and analyzed. The numerical study shows that the ignition and growth model is one three-form equation of reaction rate, which can describe unsteady detonation process of non-ideal explosives well. So, in this paper, the energy release model of aluminized explosive based on the Lee-Tarver rate equation was utilized, and an internal-blast dynamic model of concrete was established. The smoothed particle hydrodynamics (SPH) method was adopted to research the explosion field and damage effects of concrete, and provides an important way to evaluate the damage effect of internal-blast of the concrete.

Fire accident in the ultra-long tunnel could bring significant losses to human lives and economic.In this paper, by using computational fluid dynamics method and the theory of ventilation, physical and mathematical models were established, and a numerical study had been conducted to analyze characteristics of smoke flow near the shield tunneling machine in case of fire. Furthermore, temperature distribution of tunnel field in the middle cross-section of construction was discussed, then corresponding ventilation plans to control the heat around the shield and smoke spread were also extensively proposed, which provide a theoretical foundation to ensure security, and economy of construction in long-distance tunnel.

Transformers are set underground and embedded in pit for a long time, so heat problem is very prominent. In this paper, the DGSR11-H-315/10 transformer was directly buried in pit, heat transfer models of embedding system (including embedding transformer, pit flow and soil medium) were established, and the numerical simulation was conducted for temperature and flow-field distribution. Comparison of computed and test results indicates the feasibility of the model and numerical method. Based on above, the pit structure of corrugated-type transformer with the capacity of 80KVA is designed, and the study on heat transfer process of embedding system is conducted, which provide theory basis for developing technology of medium-voltage-transmission as well as application of embedding transformers in Shanghai.

Solving inverse problems requires multiple forward calculations of measured signals. We present a fast method combining graphic processing unit-accelerated Monte Carlo simulations of individual photons and a new perturbation scheme for a 300-fold speedup in comparison to conventional CPU-based approaches. The method allows rapid calculations of the diffuse reflectance and transmittance signals from a turbid sample of absorption coefficient μ(a), scattering coefficient μ(s), and anisotropy factor g based on the principle of correlated sampling. To demonstrate its strong utility, we have applied the method for determining the optical parameters of diluted intralipid samples with satisfactory results.