Numerical study of air curtain systems for blocking smoke in tunnel fires

A tunnel fire is very dangerous to drivers because of generated poisonous gases. For dealing with this hazardous situation, ventilation systems for smoke control are installed so that drivers can be safely evacuated from the site of the fire. An air curtain system is one of these ventilation systems, and such a system in a tunnel generates an air wall to block the passage of poisonous gases. In this study, airflow discharge patterns of air curtain systems were analyzed using Computational fluid dynamics (CFD), with two design parameters—to predict the ability of the air curtain to block the contaminated adverse air-flow in the tunnel. The considered two design parameters were the installed angle of the slit nozzle (N_A) and the discharged air velocity at the slit nozzle outlet (N_V). The tunnel geometry for the CFD analysis was a two-lane type with a tunnel length of 100 m and an elliptical cross section. The height of the tunnel was approximately 7.3 m and the height of the installed air curtain was about 4.9 m from the road surface. In this study, the heat release rates of the fire, the distance from the fire site, and the temperature of the working fluid were respectively assumed to about 20 MW, 50 m and 473 K, on the basis of the NFPA 502. The CFD analysis demonstrated that an N_A of 0 deg could not block the adverse air flow due to a realistic tunnel inlet-outlet static pressure difference (ΔP_S). An N_A of 20 deg was required to effectively block the adverse flow. The blocking failure first formed at the sidewall of the tunnel, and it proceeded toward the center of the tunnel cross section when the adverse wind was strong. That aspect of the blocking failure was judged to be due to the fact that the tunnel cross section is elliptical. Anyway, when the tunnel ΔP_S was increased, that showed the need for a high N_V.     

Reducing the risk of fires in large reciprocating air compressor systems

A review of the background to selecting and testing reciprocating air compressor lubricants as regards their carbon forming tendencies is given in this paper. The results of field trials of a synthetic hydrocarbon type oil and the role played by the volatility of this lubricant in reducing carbon deposits are discussed.     

An analysis of force distribution in shear spinning of cone

An analytic model for calculation of shear spinning force incorporate factor of over-roll (press down) of the blank is derived. The effects of blank thickness, roller nose radius, mandrel revolution and roller feed on the spinning force are discussed. Results obtained from calculation were compared with the experiment and other theoretical predictions. It is found that the present findings yield optimum results.     

超音速风洞大口径蝶阀流场分析及改进

介绍了超音速风洞大口径蝶阀的配置形式。运用COSMOSFloWorks软件分析了不同结构蝶板及蝶阀不同开度情况下的流场情况。通过在蝶板上增加蒙皮以及在蒙皮上开孔的方式改善了蝶阀的流场,蝶阀配置旁路阀的方式改善了蝶阀的使用工况,从而降低了蝶阀的故障率,延长了蝶阀的使用寿命。     

An experimental study of acoustically driven medium-scale pool fires

A set of experiments has been conducted on a medium-scale propane fueled pool fire acoustically forced in order to facilitate repeatable measurements defining the flame’s transient behavior. The fuel flow was slightly perturbed at the pool fire’s natural frequency by a sine waveform driven with a loudspeaker which was installed under the burner. As a result of the perturbation, the puffing behavior of the pool fire and the fire shape were modified. As the magnitude of the sine wave was increased larger perturbations were clearly observed, based on the measurement of the radiative heat flux and image analysis. Temperature and soot volume fractions were measured along the center line and throughout a slice of the flame. The soot volume fractions in the flame region are in good agreement with the data of other researchers. The reproducibility of these measurements was established through several experiments. The acoustically driven flame provides the possibility of more repeatable measurements of the transient behavior of these pool fires.     

巷道内通风系统模拟分析

应用FLUENT软件对局部通风的内部流动状态进行了模拟，给出了模拟结果并对其进行了分析。     

Passive reduction of large pressure variation for a high-speed express train in a narrow tunnel using an extra dummy tunnel duct

When a train travels through tunnel at a high speed, large pressure variations are produced on the train surface by pressure waves. In particular, when an express train travels through a narrow tunnel at a speed higher than that of a conventional train, more severe pressure variations can occur and cause passengers ear discomfort. This paper presents a very simple and effective reduction method of the large pressure variation for a narrow conventional tunnel. When a compression wave and an expansion wave are superposed, the pressure variation can be greatly reduced. Using this phenomenon, this study proposes the construction of a dummy tunnel duct which superposes the pressure waves and reduces the large pressure variation. Using the proposed method, the construction cost is much lower compared to other methods because the dummy tunnel duct can be constructed at the entrance or at the exit of an existing tunnel with a simple tunnel shape. To investigate the change in the maximum pressure difference and pressure variation ratio with the application of a dummy tunnel duct, full-scale tests and numerical analyses were conducted. The results showed that the maximum pressure changes and pressure variation ratio are significantly reduced by a short dummy tunnel duct. From these results, the dummy tunnel duct is expected to be a very economical and practical solution to passenger ear discomfort problems for express trains traveling through conventional narrow tunnels.     

An exact analysis of a hydrostatic journal bearing with a large circumferential sill

An exact theoretical analysis of a four-recess hydrostatic journal bearing, which may be applied to bearings with a large or a small circumferential sill is presented. The pressure distribution and bearing performance were obtained by solving the governing Reynolds equation. Load capacity and flow requirement of the bearing were determined in conjunction with capillary compensation. Comparison of bearing performance with a commonly used approximate solution shows that the approximate analysis predicts a correct solution at small values of circumferential sill, but the present analysis is necessary at higher values of circumferential sill.     

大型平台的刚度分析

大型承载平台在工程中应用日益广泛,例如海洋钻井平台、简易的过街天桥等.在平台的设计中,一般都要保证平台具有足够的刚度,以完成其基本用途.因此对平台进行刚度校核是极其必要的.利用有限元进行计算是最有效、全面、正确的方法之一,但是由于条件的限制,许多地方还无法利用有限元进行计算,在此介绍一种利用材料力学的基本方法对其进行刚度校核的方法.     

一例大直径螺栓失效原因分析和改进设计

本文对质量检验合格的螺栓在施工中失效的一真实案例进行了失效原因分析,提出了改进设计方案.同时对检验条件与工程实践间的差距及解决方法做了有益的探讨.     

直流式低速风洞壳体有限元分析

根据试验要求所设计的直流式低速风洞为薄壁结构,风洞的风扇位于动力段内。运行过程中,动力电机不可避免地会将振动传到壳体上,诱导其振动,并影响风洞试验段的流场品质。针对此种现象,利用有限元分析方法,对壳体模型进行网格划分,分析风洞全流场和壳体模态,得到了风洞试验段湍流度和风洞壳体模态分析结果。结果表明,直流式低速风洞的壳体结构设计合理,模态频率分布适当,在保证低速风洞试验段流场品质满足实验要求的前提下,壳体发生共振的可能性很小。     

大型甲醇和一氧化碳生产装置在线分析系统的设计和应用

介绍了大型甲醇和一氧化碳生产装置在线分析系统的设计和应用。对仪器选定的评估标准、取样系统设计和制作、在线分析系统安装和投运等问题作了讨论。此在线分析系统已成功投入运行。     

大型铸造起重机减速器故障分析

重点介绍了马鞍山钢铁股份有限公司第一钢轧总厂加料跨190／63t铸造起重机大减速器的故障、原因分析、处理方法，提出解决了解决减速器故障的处理方案。供相关设计单位和用户参考。     

雷达大型转台静力分析

概述了某雷达大型转台的静力分析情况,为方案形成和工程设计提供理论依据。     

大间隙磁力驱动系统空间磁场分布规律研究

为提高大间隙、高转速条件下磁力传动系统的可靠性,以双T型电磁体为例,分析了大间隙磁力传动系统空间磁场耦合机理,利用ANSYS软件,仿真了电磁体在NS、SS、SN和NN等四种状态时空间磁场的分布规律,并通过实验验证了空间磁场仿真模型的正确性,找到了双T型电磁体作为主动磁极时与永磁转子在空间的最佳安装位置,为轴流式血泵等永磁转子获得较大的驱动力矩提供了依据.     

小波分析在大轴承故障诊断中的应用

从Fourier分析和卷积滤波入手,从工程角度来讨论小波分析的基本原理,并利用小波带滤波方法对大轴承的振动信号进行时频分析,确定了大轴承故障的部位、类型和程度,经现场拆卸验证,结论是正确的。     

大吨位隧道混凝土管片真空吸吊翻转机的设计与研制

阐述了隧道施工用混凝土管片的结构特点及对管片吸吊翻转的要求,根据真空吸吊工作原理讨论了真空吸吊翻转机相关设计参数的确定.最后介绍了研制成功的真空吸吊翻转机的结构组成、功能及其应用情况.     

An investigation of velocity distribution in rotating magnetohydrodynamic bearings

An analysis based on the Navier-Stokes equations is made for the flow of a liquid in magnetohydrodynamic circular bearings under rotating conditions. The analysis presents expressions for both radial and tangential velocities with and without inertia effects. The results show that the application of a magnetic field reduces both radial and tangential velocities. The rotational inertia effect has a greater effect on the radial velocity at small film thicknesses.     

PSV and marker detection techniques for investigating the wake of an oscillating cylinder in a large wind tunnel

Although Particle Image Velocimetry techniques are widely used in the experimental investigation of the flow structure around obstacles, the application of these techniques in wind tunnels is frequently limited by the dimension of the areas involved, which make the image acquisition set-up expensive.This paper examines the use of Particle Streak Velocimetry (PSV) and marker detection techniques to measure the flow field around bodies with relatively large dimensions. In spite of its minimal requirements in terms of acquisition set-up, the method permits the investigation of complex phenomena.The tests described in the paper were carried out in air using a rigid cylinder, free to oscillate in a wind tunnel. Coupling PSV and marker detection techniques with the phase average of the measured velocity fields, the evolution of vortex shedding behind a cylinder with a diameter of 200 mm was measured with an acquisition area of about 1000×1200 mm.