The solid flame model is an important method in the fire dynamic study, while most of them focus on cylindrical model. However, the cylindrical model is only suitable for the square or circular pool fire. Until now, there is no effective prediction method can estimate the flame radiation of pool fire with different aspect ratios accurately. In this study, the evolution of the view factor and flame emissivity of pool fire with different aspect ratios and mass flow rates of propane has been investigated. The flame radiation of pool fire increases with the increase in the aspect ratio, since its view factor increases with the flame surface at their front side. Based on the cylindrical model, new perspective view factor and flame emissivity model has been improved and established, including the square flame model, hydraulic diameter model, and proportional model. Due to these developed models, the prediction error of thermal radiation for the pool fire with different aspect ratios has been decreased from 75 % to 10 %.

To address the thermal regulation challenges in inverse diffusion combustion, this study quantifies the interdependent evolution of temperature fields and thermal radiation through a novel dual-nozzle burner system with different propane velocities (0.4-2.9 m/s) and central air velocities (0-31.8 m/s). The influence of the central airflow on axial temperature distribution and thermal radiation pattern of the inverse diffusion flame has been investigated. The maximum temperature of inverse diffusion flame is directly proportional to the central air flow, while the thermal radiation is inversely proportional to the air flow. Air entrainment rate is an important reason for the increase in flame temperature. The air entrainment rate increases with the increase in the air flow speed when the air Reynolds number is larger than 2300. A dimensionless correlation of flame temperature distribution in the plume region was established based on the air entrainment coefficient. The thermal radiation evolution of the inverse diffusion flame was analyzed based on the soot generation theory, and a mathematical model between thermal radiation, air flow, and heat release rate of inverse diffusion flame has been developed. These findings provide critical theoretical support for optimizing high-intensity industrial inverse diffusion flame burner, particularly advancing clean combustion technology in energy-intensive applications.

An experimental investigation was performed to study the effect of the central air flow on the turbulent inverse diffusion flame height. The study conducted a series of experiments using two coaxial burners with different nozzle sizes in the atmospheric environment. The experimental results show that the central air flow influences the mixing process between the air/fuel jets and the flame morphology. The inverse diffusion flame height decreased with the increase in air flow rate under the same heat release rate due to the strengthening of air/fuel mixing. The flame height decreases sharply when the air flow is turbulence flow. The air–fuel momentum ratio was found to estimate the inverse diffusion flame height. The momentum flux and buoyancy flux of inverse diffusion flame have been analyzed. Considering the combinational effect of momentum flux and buoyancy flux on the inverse diffusion flame, a new correlation between the inverse diffusion flame height, air flow rate, and heat release rate has been established which provides a valuable resource for designing the inverse diffusion flame burners.

To solve the environmental concerns and cleaner combustion, ammonia has been considered as a new fuel to blend into the traditional hydrocarbon fuels, which acts as a carbon-free hydrogen carrier. The evolution of flame emissivity, view factor and radiative heat flux have been investigated under different flow rates of ammonia and methane or propane, respectively. The experimental results indicate that the flame emissivity, view factor, and radiative heat flux decrease with increasing ammonia concentration. Some correlations have been developed for the flame emissivity, view factor, and radiative heat flux, which play as a function of flame height and flame width. It demonstrates a well predictive capability for the thermal radiation with different ammonia concentrations. These experimental results not only contribute to the fundamental understanding of thermal radiation model of ammonia-hydrocarbon mixed gas, but also useful for fire safety and the burner design for reducing the pollutant emissions.

This study investigated the flame height and liftoff height of turbulent diffusion jet flames of the Propane-Hydrogen mixed gas. A series of experiments have been conducted to examine their flame height and liftoff height with different concentrations of propane and hydrogen. The experimental results show that the flame height decreases with the increase in hydrogen concentration. The accuracy of the Froude number for the prediction of flame height has been verified. The liftoff height is proportional to the propane flow rate, while it was inversely proportional to the hydrogen concentration due to the increased laminar flame speed. A theoretical model incorporating laminar flame speed, heat release rate, and fuel exit velocity has been obtained. These investigations are crucial for enhancing safety in hydrogen-enriched pipeline systems, which is helpful for the use of hydrogen in energy systems and global sustainability efforts.

Inert gases, such as carbon dioxide (COQ), are often presented in fuel gases and influence their combustion characteristics significantly. This paper investigates the horizontal length of buoyant turbulent jet flame under different boundary conditions, including different nozzle diameters, heat release rates, and COQ volume fractions. According to the experiments, it is found that the horizontal length of jet flame increases with the heat release rate under the same nozzle diameter. Additionally, the flame length initially increases with COQ concentration but then decreases. Based on an analysis of the buoyancy and momentum flux of the turbulent jet flame, a new correlation has been developed, which relates the horizontal flame length to the heat release rate and COQ volume fraction. This correlation can be served as a valuable reference for fire prevention and control in gas leakage fire scenarios.

To study the combustion characteristics of turbulent jet flames under different gravity environments, the centerline temperature distribution curve and air entrainment rate of turbulent jet flame from microgravity to hyper gravity was carried out by CFD simulation. Five different gravity values have been considered. The simulation results show that the flame temperature decreases with the increase of gravity in the intermittent flame region and plume region. The maximum temperature decreases with the increase of gravity, while their position decreases accordingly. The evolution of air entrainment has been analyzed under different gravity environments. Based on the hydroxyl concentration distribution, a correlation of flame height has been obtained through dimensionless analysis. The evolution of air entrainment has been described under different heat release rate and gravity environments.

The flame length of turbulent jet inverse diffusion flame in the atmospheric environment was investigated. In order to investigate the combustion characteristics of the inverse diffusion flame length, a series of experiments have been conducted for a coaxial burner using two nozzles with different sizes. The results showed that the inverse diffusion flame length decreased with the increase in the air flow rate under the same heat release rate. The flame length decreases sharply when the air flow is turbulence flow. The momentum flux and buoyancy flux of the inverse diffusion flame were analyzed. Considering the combinational effect of momentum flux and buoyancy flux on the inverse diffusion flame, a new correlation equation between the inverse diffusion flame height, air flow rate, and heat release rate has been established which provides a valuable resource for designing the inverse diffusion flame burners.

钢管混凝土拱桥是一种广泛运用的桥梁结构形式,为研究其在地震作用下的易损性,文章针对下承式钢管混凝土拱桥,以其支座、拱肋和系梁3种构件为研究对象,定义了四级损伤状态.基于增量动力分析(incremental dynamic analysis,IDA)方法对符合工程地质条件的20条地震波进行调幅,对桥梁模型进行地震分析,统计落入每一级损伤状态的频数,计算对应频率.采用对数正态分布的分布函数对频率点进行拟合得到3种构件的易损性曲线,同时考虑各个构件的重要性,引入权重得到桥梁系统的易损性曲线.结果表明,对数正态分布的分布函数对各级损伤状态的损伤概率拟合较好,且桥梁系统的易损性高于主要构件的易损性,考虑权重计算桥梁系统的易损性具有合理性.

SummaryIn order to reduce the undesirable effect of boundary layer separation and plug‐holing in a naturally ventilated tunnel with shaft for smoke extraction, a new design of baffle has been proposed in this paper. Large eddy simulation (LES) was performed with fire dynamics simulator (FDS), the influence of the angle formed by the boards () and the distance between the baffle top and the shaft bottom () has been investigated. The simulation results show that the smoke extraction efficiency is not simply a monotonic function of the distance or the angle , the influence of and has been discussed, and the mechanism has been investigated. With proper configuration of the inverted V‐shaped baffle, the negative effect of plug‐holing can be eliminated, and the boundary layer separation can also be alleviated; the maximal smoke extraction efficiency is 2.04 times of that in the traditional shaft.

文章采用试验与理论相结合的方法,研究了不同喷嘴直径、多火源喷嘴距离及热释放速率下的火焰高度和温度的演化规律;通过无量纲分析,在单火源火焰高度公式的基础上发展了多火源气体射流火的无量纲火焰高度和无量纲热释放速率之间的关系式;通过分析建立了空气卷吸系数、火焰高度和热释放速率之间的关系模型.研究结果表明:在喷嘴距离较小的情况下,火焰发生耦合,火焰高度明显增大;随着喷嘴距离增大,火焰的耦合行为逐渐减弱直至消失;在火焰底部,火焰温度较低,随着高度上升,火焰温度增大,当达到羽流区时,火焰温度随着高度增加而减小.

This study presents a quantitative analysis and interpretation about the effects of natural air flow, opening size and fire location on flame length in the underground vertical channel like car elevator or staircase. The gas burner of 0.1 & times; 0.1 m with five heat release rates (HRR) is used and eight locations are considered in 1/7 scale model. The air flow structure inside the vertical channel is investigated by CFD simulation. Hydraulic diameter and a characteristic length is proposed to calculate the flame length. A specific correlation between the flame length and dimensionless HRR is established to estimate the degree of fire disasters in the vertical channel with different opening size and locations.

This study presents a quantitative analysis and interpretation of the variation in oil tank fire flame lengths for different oil tank sizes, top cover widths, and horizontal air flow velocities. The experimental results show that, at first, the flame length rises slowly with an increase in air flow speed. Then, once over a critical speed (0.6 m/s), the flame length decreases significantly with a further increase in air flow speed. Based on the characteristic length, a new dimensionless heat release rate is obtained, allowing the correlation between flame length, air flow speed, and dimensionless heat release rate to be calculated, which can be used to predict the flame length of an oil tank fire under different air flow speeds, lip heights, and cover widths.

针对不同的隔震形式对高位转换体系抗震性能的影响,文章利用Ansys软件,建立高位转换结构的基础隔震与转换层隔震有限元分析模型,并对其进行弹塑性地震时程分析.研究发现,设置隔震支座后高位转换结构的层间剪力和层间位移角明显减小;当采用转换层隔震时,可能会加剧转换层位置传力途径的突变,对结构安全造成不利影响.

Traffic accident may bring vehicle fire in the street canyons. With its high temperature and numerous hazardous materials, the smoke produced by the vehicle fire may cause serious damage to the human body and the properties nearby, such as the glass curtain walls of buildings. The influence of the ambient air flow speed and street aspect ratio on the dispersion of fire smoke in street canyon has been analyzed by FDS software and theoretical analysis in this study. The impact of different windward building heights and different ambient air flow speeds u0 on the fire smoke were investigated. The results show that the fire smoke tilts towards the opposing direction of the ambient air flow within the street canyon, while the ambient air flow is perpendicular to the windward building. The results indicate that the critical re-entrainment velocity decreases at first, and then increases until it attains a constant with the building height ratio H1/H2. Finally, a predictive model of the critical re-entrainment velocity was developed under different building height ratios H1/H2.

This paper presents an investigation on the flame height of rectangular pool fires bounded by a sidewall. A series of experiments were conducted to investigate the flame height of pool fire bounded by a sidewall with different distances and aspect ratios. Four pools with identical area but different aspect ratios of 1:1, 1:2, 1:4, and 1:8 are studied. Experimental results show that flame height is strongly related to the distance between the fire source and the sidewall and the aspect ratio. The flame height increases with the decreases in the distance and the aspect ratio. A hydraulic diameter has been conducted to develop a correlation for calculating the total flame height. One more hydraulic diameter has been assumed to develop the correlation for the height of flame attached to the sidewall.

In this study, a series of experiments were performed to investigate the flame height of double rectangular pool fires with different aspect ratios and distances in open space. Two identical rectangular gas burners with the same heat release rate were used as the fire sources. Four gas burners with the same surface area but with different aspect ratios were used. Different distances between two gas burners were considered. The experimental results indicated that the flame height decreased sharply with the increase of distance and subsequently exhibited a slight change with further increase of distance. The buoyancy force in the region between these two pools is the main factor to influence the flame height. A characteristic length D, which depends on the gas burner geometrical shape and distance, were proposed, and the experimental data indicate that the value of coefficient C decreases with the increase of D. A correlation has been achieved which can estimate the flame height of the rectangular pool fires with different aspect ratios in open space.

吊杆断裂是中承式提篮拱桥典型的损伤形式.为了研究其在吊杆断裂情况下的易损性问题,以一座中承式提篮拱桥为对象,通过建立有限元模型,得出吊杆断裂情况下的动态响应,进而计算出静力放大系数,再采用静力放大系数法考虑吊杆断裂的冲击作用,以此对其易损性进行评估.结果表明:不同位置的单吊杆断裂时,其相邻吊杆易损性指数变化较大,其中在长吊杆位置处的易损性指数较大,已超过设计弯曲应力容许值,对结构安全不利.

This paper presents computer simulation investigations on the fire smoke movement above street canyons under a velocity condition. Two buildings with different aspect ratios, when the range of windward building height is 5 ~ 17 m and the leeward building height is remain at 18 m, have been considered. Besides, the width of the street canyon has been taken as an important factor to influence the critical velocity here. It is shown that the critical velocity of the fire smoke, which moves from windward building to the leeward building, decreases with the height of windward building firstly, but increases with its further increase. According to the theoretical analysis, it is found that the critical velocity is a function of dimensionless width of street canyon. And a developed model has been developed to predict the critical velocity above the street canyon.

Finite element model updating technique has been widely used in monitoring and evaluating the performance and damage identification of bridge structures in service life.It is a common practice to carry out finite element model correction based on bridge load test data.However,due to the impact of objective conditions such as test level, the reliable test data can not be completely guaranteed.In the previous model revision,the objective function based on the weighted least squares method could not reflect its robustness to the test data.The paper presented an objective function based on weight function, which had good robustness to the test data.A three-span continuous beam model was used to verify the function.Finally,the model was updated to verify the feasibility of the function based on the experimental data of Yinghe Bridge in Donghuan Road,Fuyang city.