In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and ...In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i. e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.展开更多
Renormalization group theory applied to turbulence will be reviewed in this article.Techniques associated are used for analyzing thermally-induced turbulence.Transport properties such as effective viscosity and therma...Renormalization group theory applied to turbulence will be reviewed in this article.Techniques associated are used for analyzing thermally-induced turbulence.Transport properties such as effective viscosity and thermal diffusivity are derived.展开更多
We investigate the depinning of two-dimensional fluids interacting with quenched disorder, based on Langevin simulations. For weak disorder the fluids depin elastically and flow in an ordered state. A power-law scalin...We investigate the depinning of two-dimensional fluids interacting with quenched disorder, based on Langevin simulations. For weak disorder the fluids depin elastically and flow in an ordered state. A power-law scaling lit between velocity and driving force can be obtained for the onset of motion in the elastic regime. This is in good agreement with that of colloid, charge density wave, and superconducting vortex systems. With an increasing strength of the disorder, we find a sharp crossover to plastic de. Pinning, accompanied by a substantial increase in the depinning force. The scaling fit obtained in the elastic regime becomes invalid when plastic flow occurs. In the plastic regime, the fluids flow in channels and the hexatic order decays exponentially with drives.展开更多
Adequate provision of natural ventilation in tropical areas is regarded as one of the design cntena for assessing ‘green'' or ’‘sustainable'' building. Driving forces for natural ventilation in thos...Adequate provision of natural ventilation in tropical areas is regarded as one of the design cntena for assessing ‘green'' or ’‘sustainable'' building. Driving forces for natural ventilation in those areas are basically wind-induced action, not stack effect nor buoyancy of warm air columns. Wind-induced air movement is a transient phenomenon depends not only on the wind speeds measured in some designated sites, but strongly affected by the surrounding environment. This is particularly obvious in a dense urban area where buildings are closely built together. For a building located adjacent to a taller building, turbulent effects due to incident wind fields would be important. Note that windows or even refuge floors might be opened at some levels, giving flow paths to change the entire patterns of air flow and pressure distnbution. In this paper, the wind-induced indoor airflow in a building adjacent to a vertical wall is studied by Computational Fluid Dynamics. A CFD software based on large-eddy simulations is selected. Different scenanos on building height, openings and distances away from the vertical wall will be simulated. Incident airflows of a parabolic boundary layer and a top-hat flow pattern are considered. The separate flow at the sharp comer would be different for these two incident airflow profiles. Results are useful not only for providing better ventilation design, but also for working out fire safety management in case of accidents. Note that smoke, or even flame, will spread by following the wind-induced air motion.展开更多
基金Supported by " Experimental Scale Studies in Smoke Control Strategy in Large Linear Atria in HKSAR" (B Q372)
文摘In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i. e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.
文摘Renormalization group theory applied to turbulence will be reviewed in this article.Techniques associated are used for analyzing thermally-induced turbulence.Transport properties such as effective viscosity and thermal diffusivity are derived.
文摘We investigate the depinning of two-dimensional fluids interacting with quenched disorder, based on Langevin simulations. For weak disorder the fluids depin elastically and flow in an ordered state. A power-law scaling lit between velocity and driving force can be obtained for the onset of motion in the elastic regime. This is in good agreement with that of colloid, charge density wave, and superconducting vortex systems. With an increasing strength of the disorder, we find a sharp crossover to plastic de. Pinning, accompanied by a substantial increase in the depinning force. The scaling fit obtained in the elastic regime becomes invalid when plastic flow occurs. In the plastic regime, the fluids flow in channels and the hexatic order decays exponentially with drives.
文摘Adequate provision of natural ventilation in tropical areas is regarded as one of the design cntena for assessing ‘green'' or ’‘sustainable'' building. Driving forces for natural ventilation in those areas are basically wind-induced action, not stack effect nor buoyancy of warm air columns. Wind-induced air movement is a transient phenomenon depends not only on the wind speeds measured in some designated sites, but strongly affected by the surrounding environment. This is particularly obvious in a dense urban area where buildings are closely built together. For a building located adjacent to a taller building, turbulent effects due to incident wind fields would be important. Note that windows or even refuge floors might be opened at some levels, giving flow paths to change the entire patterns of air flow and pressure distnbution. In this paper, the wind-induced indoor airflow in a building adjacent to a vertical wall is studied by Computational Fluid Dynamics. A CFD software based on large-eddy simulations is selected. Different scenanos on building height, openings and distances away from the vertical wall will be simulated. Incident airflows of a parabolic boundary layer and a top-hat flow pattern are considered. The separate flow at the sharp comer would be different for these two incident airflow profiles. Results are useful not only for providing better ventilation design, but also for working out fire safety management in case of accidents. Note that smoke, or even flame, will spread by following the wind-induced air motion.
