In this paper, we present the double Beta spline curved surface which is controlled by double parameters including the algorithm principles, the treatment of boundary conditions, the alternation of projection, the alg...In this paper, we present the double Beta spline curved surface which is controlled by double parameters including the algorithm principles, the treatment of boundary conditions, the alternation of projection, the algorithms of elimination hiddle line, the process to display and the primiples to produce the shaded curved surface. Based on all the above, a freedom surface modeling system (FSMS) is designed and some examples developed on FSMS are verified and analyzed.展开更多
In modern terrain-following guidance it is an important index for flight vehicle to cruise about safely and normally. On the basis of a constructing method of digital surface model (DSM), the definition, classificatio...In modern terrain-following guidance it is an important index for flight vehicle to cruise about safely and normally. On the basis of a constructing method of digital surface model (DSM), the definition, classification and scale analysis of an isolated obstacle threatening flight safety of terrain-following guidance are made. When the interval of vertical-and cross-sections on DSM is 12. 5 m, the proportion of isolated obstacles to the data amount of DSM model to be loaded is optimal. The main factors influencing the lowest flying height in terrain-following guidance are analyzed, and a primary safe criterion of the lowest flying height over DSM model is proposed. According to their test errors, the lowest flying height over 1:10 000 DSM model can reach 40. 5 m^45. 0 m in terrain-following guidance. It is shown from the simulation results of a typical urban district that the proposed models and methods are reasonable and feasible.展开更多
The N-GAS model for predicting smoke toxicity has been proposed for many years by NIST.However,almost all the existing CFD software cannot accurately predict the toxicity of smoke using the model because of the absenc...The N-GAS model for predicting smoke toxicity has been proposed for many years by NIST.However,almost all the existing CFD software cannot accurately predict the toxicity of smoke using the model because of the absence of the toxic gas concentration of HCN,NO x,HCl and HBr.In this work,an approach for predicting fire smoke toxicity was developed and demonstrated.A detailed mechanism including these fire effluents was constructed firstly,and the subsequent generation of state relationship among fire effluents,mixture fraction and strain rate was conducted by using opposed-flow flame technique.A mixture fraction-based combustion model used in FDS code was modified,and meanwhile the scalar dissipation rate transport equation was numerically solved.Thus the concentration of fire effluents as the function of mixture fraction and scalar dissipation rate can be calculated through a look-up table,and the toxic potency based on the 7-gas model can be obtained.The method was applied into an underground commercial street in Chongqing.It showed that the results between the 7-gas model and 3-gas model(CO,CO 2,and O 2) were obviously different.It indicated that there needs some modifications in conclusions and results from 3-gas model for fire-risk assessments.展开更多
文摘In this paper, we present the double Beta spline curved surface which is controlled by double parameters including the algorithm principles, the treatment of boundary conditions, the alternation of projection, the algorithms of elimination hiddle line, the process to display and the primiples to produce the shaded curved surface. Based on all the above, a freedom surface modeling system (FSMS) is designed and some examples developed on FSMS are verified and analyzed.
基金This project was supported by the National Natural Science Foundation of China (60072009).
文摘In modern terrain-following guidance it is an important index for flight vehicle to cruise about safely and normally. On the basis of a constructing method of digital surface model (DSM), the definition, classification and scale analysis of an isolated obstacle threatening flight safety of terrain-following guidance are made. When the interval of vertical-and cross-sections on DSM is 12. 5 m, the proportion of isolated obstacles to the data amount of DSM model to be loaded is optimal. The main factors influencing the lowest flying height in terrain-following guidance are analyzed, and a primary safe criterion of the lowest flying height over DSM model is proposed. According to their test errors, the lowest flying height over 1:10 000 DSM model can reach 40. 5 m^45. 0 m in terrain-following guidance. It is shown from the simulation results of a typical urban district that the proposed models and methods are reasonable and feasible.
基金sponsored by National Natural Science Foundation of China(No.50676091,No.50876097)Program for New Century Excellent Talents in University of China(NCET-06-0546)
文摘The N-GAS model for predicting smoke toxicity has been proposed for many years by NIST.However,almost all the existing CFD software cannot accurately predict the toxicity of smoke using the model because of the absence of the toxic gas concentration of HCN,NO x,HCl and HBr.In this work,an approach for predicting fire smoke toxicity was developed and demonstrated.A detailed mechanism including these fire effluents was constructed firstly,and the subsequent generation of state relationship among fire effluents,mixture fraction and strain rate was conducted by using opposed-flow flame technique.A mixture fraction-based combustion model used in FDS code was modified,and meanwhile the scalar dissipation rate transport equation was numerically solved.Thus the concentration of fire effluents as the function of mixture fraction and scalar dissipation rate can be calculated through a look-up table,and the toxic potency based on the 7-gas model can be obtained.The method was applied into an underground commercial street in Chongqing.It showed that the results between the 7-gas model and 3-gas model(CO,CO 2,and O 2) were obviously different.It indicated that there needs some modifications in conclusions and results from 3-gas model for fire-risk assessments.
