This study applied the numerical simulator tool FDS （fire dynamics simulator）, Version 5.53, and focused on the simulation of the natural smoke flow ventilation design system, an innovative ventilation design using ...This study applied the numerical simulator tool FDS （fire dynamics simulator）, Version 5.53, and focused on the simulation of the natural smoke flow ventilation design system, an innovative ventilation design using the parallel processing technology MPI （message passing interface）. The design was then compared with the exhaust efficiency of a typical natural smoke vent. The natural smoke flow ventilation design system was located at the top of the factory, where smoke streams effectively converged. Therefore, the source of fire was designed to be 2 MW, which has a better exhaust efficiency than typical natural smoke vent with same area. The simulation discovered that the exhaust efficiency of the natural smoke ventilation design systems is higher than that of typical natural smoke vent with 2 times the opening area and that was not affected by external wind speed, Instead, external wind speed can help to enhance the exhaust efficiency. Smoke exhaust of typical natural smoke vents was affected by external wind speed, even leading them to become air inlets which would disturb the flow of air indoors, leading to smoke accumulation within the factory.展开更多
The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine t...The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.展开更多
This study performed a three-dimensional numerical prediction for the induced airflow patterns and mean age of air(MAGE)around and inside a naturally ventilated school building,while accounting for the wind profile ef...This study performed a three-dimensional numerical prediction for the induced airflow patterns and mean age of air(MAGE)around and inside a naturally ventilated school building,while accounting for the wind profile effect.Various fenestrations,hallways,and shading devices on the windward side of building were analyzed to determine how they affected wind velocity,the incident angle of airflow,and MAGE distribution inside classrooms.The numerical scheme is based on a commercial computational fluid dynamics(CFD)code,PHOENICS.The incline of incoming wind was observed on higher floors that decreased the air exchange rate in the simulated room.The inclined airflow could be effectively deflected downward through the breathing zone by hallways,1.2-m shades as overhangs,and 0.6-m louvers.Based on this research,an appropriate combination of external attachments on the windward side of building façade can be utilized to enhance ventilation in school buildings.(See Appendix 1 for nomenclature.)展开更多
Finding ways to cool buildings by natural,passive techniques is crucial in the context of global warming.For centuries,wind towers(traditi onal win dcatchers)have been used in the Middle East for cooling purposes.In t...Finding ways to cool buildings by natural,passive techniques is crucial in the context of global warming.For centuries,wind towers(traditi onal win dcatchers)have been used in the Middle East for cooling purposes.In this study,the use of funnels at the openings of wind towers for wind ingress and egress is proposed primarily to increase the mass flow captured by the wind tower.The use of funnels in the wind in gress openings in creases the inlet area,improving the capture of wind.In parallel,the use of funnels in the egress openings modifies the wake of the tower,which aims to ease the exit of the flow from inside the building.Several design configurations are presented,where the length and width of the funnels are changed and tested separately by computational fluid dynamics(CFD).Results of over 120 CFD simulations are presented and compared.The volumetric flow entering the wind towers in creases by 10.7% in several cases.These results in dicate that adding funnels to wind towers could positively in fluence their performance.Changing the dimensions of the funnels affects their efficacy and can increase or decrease the airflow entering the tower.展开更多
文摘This study applied the numerical simulator tool FDS （fire dynamics simulator）, Version 5.53, and focused on the simulation of the natural smoke flow ventilation design system, an innovative ventilation design using the parallel processing technology MPI （message passing interface）. The design was then compared with the exhaust efficiency of a typical natural smoke vent. The natural smoke flow ventilation design system was located at the top of the factory, where smoke streams effectively converged. Therefore, the source of fire was designed to be 2 MW, which has a better exhaust efficiency than typical natural smoke vent with same area. The simulation discovered that the exhaust efficiency of the natural smoke ventilation design systems is higher than that of typical natural smoke vent with 2 times the opening area and that was not affected by external wind speed, Instead, external wind speed can help to enhance the exhaust efficiency. Smoke exhaust of typical natural smoke vents was affected by external wind speed, even leading them to become air inlets which would disturb the flow of air indoors, leading to smoke accumulation within the factory.
基金Supported by the National Natural Science Foundation of China under Grant No.50708015the foundation of State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology
文摘The topic of offshore wind energy is attracting more and more attention as the energy crisis heightens.The blades are the key components of offshore wind turbines,and their dynamic characteristics directly determine the effectiveness of offshore wind turbines.With different rotating speeds and blade length,the rotating blades generate various centrifugal stiffening effects.To directly analyze the centrifugal stiffening effect of blades,the Rayleigh energy method (REM) was used to derive the natural frequency equation of the blade,including the centrifugal stiffening effect and the axial force calculation formula.The axial force planes and the first to third order natural frequency planes which vary with the rotating speed and length were calculated in three-dimensional coordinates.The centrifugal stiffening coefficient was introduced to quantitatively study the relationship between the centrifugal stiffening degree and the rotating speed,and then the fundamental frequency correction formula was built based on the rotating speed and the blade length.The analysis results show that the calculation results of the fundamental frequency correction formula agree with the theoretical calculation results.The error of calculation results between them is less than 0.5%.
文摘This study performed a three-dimensional numerical prediction for the induced airflow patterns and mean age of air(MAGE)around and inside a naturally ventilated school building,while accounting for the wind profile effect.Various fenestrations,hallways,and shading devices on the windward side of building were analyzed to determine how they affected wind velocity,the incident angle of airflow,and MAGE distribution inside classrooms.The numerical scheme is based on a commercial computational fluid dynamics(CFD)code,PHOENICS.The incline of incoming wind was observed on higher floors that decreased the air exchange rate in the simulated room.The inclined airflow could be effectively deflected downward through the breathing zone by hallways,1.2-m shades as overhangs,and 0.6-m louvers.Based on this research,an appropriate combination of external attachments on the windward side of building façade can be utilized to enhance ventilation in school buildings.(See Appendix 1 for nomenclature.)
文摘Finding ways to cool buildings by natural,passive techniques is crucial in the context of global warming.For centuries,wind towers(traditi onal win dcatchers)have been used in the Middle East for cooling purposes.In this study,the use of funnels at the openings of wind towers for wind ingress and egress is proposed primarily to increase the mass flow captured by the wind tower.The use of funnels in the wind in gress openings in creases the inlet area,improving the capture of wind.In parallel,the use of funnels in the egress openings modifies the wake of the tower,which aims to ease the exit of the flow from inside the building.Several design configurations are presented,where the length and width of the funnels are changed and tested separately by computational fluid dynamics(CFD).Results of over 120 CFD simulations are presented and compared.The volumetric flow entering the wind towers in creases by 10.7% in several cases.These results in dicate that adding funnels to wind towers could positively in fluence their performance.Changing the dimensions of the funnels affects their efficacy and can increase or decrease the airflow entering the tower.
