Smoke is the main cause of fire death. In order to minimize the potential danger of smoke hazard, a rational VR based fire training simulator should fully consider all aspects of smoke hazard. In the simulator, the vi...Smoke is the main cause of fire death. In order to minimize the potential danger of smoke hazard, a rational VR based fire training simulator should fully consider all aspects of smoke hazard. In the simulator, the visualization of data based on FDS (Fire Dynamics Simulator) and FED fire dynamic data and volume rendering is further optimized, which can be effectively and quickly applied to virtual fire protection. In addition, a comprehensive smoke hazard assessment model based on FED and FED is established to assess the IHD value of different paths, which represents the safety of different paths, and can be used for evacuation or rescue in virtual training. Taking the case of campus fire drill as an experiment, the research shows the accuracy and effectiveness of smoke assessment based on FDS and FED model. The road force with the highest safety can be selected through the comprehensive model. So the assessment model is proved to be valuable.展开更多
Flight feathers of birds interact with the air flow during flight.How the observed low drag and high lift values at wind speeds from 9.0 to 19.8 m/s can be achieved due to the feather aerodynamics remains unknown.In t...Flight feathers of birds interact with the air flow during flight.How the observed low drag and high lift values at wind speeds from 9.0 to 19.8 m/s can be achieved due to the feather aerodynamics remains unknown.In the present paper,we tested and compared morphological changes,drag reduction and flow visualization results of intact,damaged,and artificial feathers at different wind speeds in a wind tunnel.Through the analysis of the drag force and resultant force angle,we proved that the integrity of feathers,whose barbs are usually closely interconnected,played an important role in the drag,which potentially triggers excellent drag reduction performance.The wind tunnel tests indicated that intact secondary feathers had a surprisingly high maximum drag reduction property at v?=?9 m/s compared with the feathers,where the integrity of barbs was damaged.The hook cascades facilitated elasticity under pressure and suitable permeability in an intact feather,when the hooks were interlocked.It was indicated that the suitable permeability of intact feathers would prevent flow separation and reduce drag force at low wind speed;at high wind speed,elasticity under pressure and suitable permeability in an intact feather would facilitate strong squeezing effect,helping feathers withstand larger aerodynamic forces to which they might be subjected during flight.It was revealed that the intact secondary feather is a compromise between strong lift generation and drag reduction,which has a great significance for the bird’s flight.展开更多
Experiments were conducted to study the temperature field,flow field,3-D characteristics and self-sustained oscillation of the natural air convection in a 3-D shallow cavity which was heated from underneath. The exper...Experiments were conducted to study the temperature field,flow field,3-D characteristics and self-sustained oscillation of the natural air convection in a 3-D shallow cavity which was heated from underneath. The experiments were conducted by the methods of laser holographic interferometry photography and smoke visualization. To ensure the temperature of both plates to be constant and the accuracy of laser interferometer,the instrument was calibrated and error has was analyzed. The results showed that the flow field was stable at lower Rayleigh numbers. When the Rayleigh number increased,the flow field became instable and the isotherms distorted. The rolls merged at Ra=12500 and formed along both axes when Ra was over 18500. The air rose from the middle and descended in the circumference while the flow field and heat transfer converted to 3-D characteristic from 2-D characteristic. When the Rayleigh number increased,the flow field became more instable. The rolls became irregular and time dependent when Ra≥Rac(=30500) ,which is nonlinear. When lateral walls were heated or cooled,the rolls merged along the long axis and two rolls formed along the short axis. Three rolls formed occasionally in the process.展开更多
文摘Smoke is the main cause of fire death. In order to minimize the potential danger of smoke hazard, a rational VR based fire training simulator should fully consider all aspects of smoke hazard. In the simulator, the visualization of data based on FDS (Fire Dynamics Simulator) and FED fire dynamic data and volume rendering is further optimized, which can be effectively and quickly applied to virtual fire protection. In addition, a comprehensive smoke hazard assessment model based on FED and FED is established to assess the IHD value of different paths, which represents the safety of different paths, and can be used for evacuation or rescue in virtual training. Taking the case of campus fire drill as an experiment, the research shows the accuracy and effectiveness of smoke assessment based on FDS and FED model. The road force with the highest safety can be selected through the comprehensive model. So the assessment model is proved to be valuable.
基金This work was supported by the Chinesisch-Deutsches Zentrumfur Wissenschaftsforderung to SNG and ZDD(Grant No.GZl154)the National Natural Science Foundation of China(Grant Nos.51875281,51861135306)。
文摘Flight feathers of birds interact with the air flow during flight.How the observed low drag and high lift values at wind speeds from 9.0 to 19.8 m/s can be achieved due to the feather aerodynamics remains unknown.In the present paper,we tested and compared morphological changes,drag reduction and flow visualization results of intact,damaged,and artificial feathers at different wind speeds in a wind tunnel.Through the analysis of the drag force and resultant force angle,we proved that the integrity of feathers,whose barbs are usually closely interconnected,played an important role in the drag,which potentially triggers excellent drag reduction performance.The wind tunnel tests indicated that intact secondary feathers had a surprisingly high maximum drag reduction property at v?=?9 m/s compared with the feathers,where the integrity of barbs was damaged.The hook cascades facilitated elasticity under pressure and suitable permeability in an intact feather,when the hooks were interlocked.It was indicated that the suitable permeability of intact feathers would prevent flow separation and reduce drag force at low wind speed;at high wind speed,elasticity under pressure and suitable permeability in an intact feather would facilitate strong squeezing effect,helping feathers withstand larger aerodynamic forces to which they might be subjected during flight.It was revealed that the intact secondary feather is a compromise between strong lift generation and drag reduction,which has a great significance for the bird’s flight.
基金supported by the National Natural Science Foundation of China (Grant No. 50978120)the Shanghai Leading Academic Discipline Project (Grant No. 05EZ18)the Doctoral Fund Project of Jilin Institute of Architectural and Civil Engineering (Grant No. 861055)
文摘Experiments were conducted to study the temperature field,flow field,3-D characteristics and self-sustained oscillation of the natural air convection in a 3-D shallow cavity which was heated from underneath. The experiments were conducted by the methods of laser holographic interferometry photography and smoke visualization. To ensure the temperature of both plates to be constant and the accuracy of laser interferometer,the instrument was calibrated and error has was analyzed. The results showed that the flow field was stable at lower Rayleigh numbers. When the Rayleigh number increased,the flow field became instable and the isotherms distorted. The rolls merged at Ra=12500 and formed along both axes when Ra was over 18500. The air rose from the middle and descended in the circumference while the flow field and heat transfer converted to 3-D characteristic from 2-D characteristic. When the Rayleigh number increased,the flow field became more instable. The rolls became irregular and time dependent when Ra≥Rac(=30500) ,which is nonlinear. When lateral walls were heated or cooled,the rolls merged along the long axis and two rolls formed along the short axis. Three rolls formed occasionally in the process.
