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根据对开式模锻变形过程的理论分析,论述了几种主要工艺参数对锻模寿命的影响,提出了降低锻模机械负荷提高锻模寿命的主要工艺措施.实践证明,这些工艺措施是行之有效的. 相似文献
53.
Liquefied natural gas (LNG) is widely used to cost-effectively store and transport natural gas. However, a spill of LNG can create a vapor cloud, which can potentially cause fire and explosion. High expansion (HEX) foam is recommended by the NFPA 11 to mitigate the vapor hazard and control LNG pool fire. In this study, the parameters that affect HEX foam performance were examined using lab-scale testing of foam temperature profile and computational fluid dynamics (CFD) modeling of heat transfer in vapor channels. A heat transfer model using ANSYS Fluent® was developed to estimate the minimum HEX foam height that allows the vapors from LNG spillage to disperse rapidly. We also performed a sensitivity analysis on the effect of the vaporization rate, the diameter of the vapor channel, and the heat transfer coefficient on the required minimum height of the HEX foam. It can be observed that at least 1.2 m of HEX foam in height are needed to achieve risk mitigation in a typical situation. The simulation results can be used not only for understanding the heat transfer mechanisms when applying HEX foam but also for suggesting to the LNG facility operator how much HEX foam they need for effective risk mitigation under different conditions. 相似文献
54.
Accidental explosions are a plausible danger to the chemical process industries. In the event of a gas explosion, any obstacles placed within the path of the flame generate turbulence, which accelerates the transient flame and raises explosion overpressure, posing a safety hazard. This paper presents numerical studies using an in-house computational fluid dynamics (CFD) model for lean premixed hydrogen/air flame propagations with an equivalence ratio of 0.7. A laboratory-scale combustion chamber is used with repeated solid obstacles. The transient compressible large eddy simulation (LES) modelling technique combined with a dynamic flame surface density (DFSD) combustion model is used to carry out the numerical simulations in three-dimensional space. The study presented uses eight different baffle configurations with two solid obstructions, which have area blockage ratios of 0.24 and 0.5. The flame speed, maximum rate of pressure-rise as well as peak overpressure magnitude and timing are presented and discussed. Numerical results are validated against available published experimental data. It is concluded that, increasing the solid obstacle area blockage ratio and the number of consecutive baffles results in a raised maximum rate of pressure rise, higher peak explosion overpressure and faster flame propagation. Future model development would require more experimental data, probably in a more congested configuration. 相似文献
55.
Reinhard Furrer Stephan R. Sain Douglas Nychka Gerald A. Meehl 《Environmental and Ecological Statistics》2007,14(3):249-266
Numerical experiments based on atmosphere–ocean general circulation models (AOGCMs) are one of the primary tools in deriving
projections for future climate change. Although each AOGCM has the same underlying partial differential equations modeling
large scale effects, they have different small scale parameterizations and different discretizations to solve the equations,
resulting in different climate projections. This motivates climate projections synthesized from results of several AOGCMs’
output. We combine present day observations, present day and future climate projections in a single highdimensional hierarchical
Bayes model. The challenging aspect is the modeling of the spatial processes on the sphere, the number of parameters and the
amount of data involved. We pursue a Bayesian hierarchical model that separates the spatial response into a large scale climate
change signal and an isotropic process representing small scale variability among AOGCMs. Samples from the posterior distributions
are obtained with computer-intensive MCMC simulations. The novelty of our approach is that we use gridded, high resolution
data covering the entire sphere within a spatial hierarchical framework. The primary data source is provided by the Coupled
Model Intercomparison Project (CMIP) and consists of 9 AOGCMs on a 2.8 by 2.8 degree grid under several different emission
scenarios. In this article we consider mean seasonal surface temperature and precipitation as climate variables. Extensions
to our model are also discussed. 相似文献
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Based on the ability to attenuate thermal radiation of droplets, water curtain plays an important role in fire prevention in the oil and gas terminal, traffic tunnel and other outdoor spaces. Radiation transfer characteristics of large droplets are determined by the Mie theory, and the Two-flux model is used to simplify the radiative transfer equation. Combined with an empirical formula to calculate the droplet diameter, a novel method is given for calculating the transmissivity of water curtain. Based on the method, influences of both the pressure and the width of water curtain on the transmissivity are fit for exponential relationship. Compared with experimental data, an ideal agreement is found between calculation results and experimental data for both single pipe water curtain and double pipe water curtain, only in the case of triplex pipe water curtain the deviation between calculation and experiment is more than 25%. A better calculation result can be obtained under the condition of the optical thin media. The method is effective in the scope of that the transmitted radiation is stronger than the environmental radiation. 相似文献
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海南属于典型的热带季风海洋性气候,每年因气候条件产生的雷电、热带气旋(台风)、阵风(地形风)、太阳暴晒、暴雨、海水侵蚀等自然灾害给露天作业的大型起重机械造成很大的损失。本文通过分析热带季风海洋性气候对露天作业大型起重机械安全的影响,并提出相应的防范措施,给起重机械相关单位提供技术参考。 相似文献
60.