Calculation and design of tunnel ventilation systems using a two-scale modelling approach

This paper develops a novel modelling approach for ventilation flow in tunnels at ambient conditions (i.e. cold flow). The complexity of full CFD models of flow in tunnels or the inaccuracies of simplistic assumptions are avoided by efficiently combining a simple, mono-dimensional approach to model tunnel regions where the flow is fully developed, with detailed CFD solutions where flow conditions require 3D resolution. This multi-scale method has not previously been applied to tunnel flows. The low computational cost of this method is of great value when hundreds of possible ventilation scenarios need to be studied. The multi-scale approach is able to provide detailed local flow conditions, where required, with a significant reduction in the overall computational time. The coupling procedures and the numerical error induced by this new approach are studied and discussed. The paper describes a comparison between numerical results and experimental data recorded within a real tunnel underlining how the developed methodology can be used as a valid design tool for any tunnel ventilation system.This work sets the foundations for the coupling of fire-induced flows and ventilation systems where further complexities are introduced by the hot gas plume and smoke stratification.     

Simulating longitudinal ventilation flows in long tunnels: Comparison of full CFD and multi-scale modelling approaches in FDS6

The accurate computational modelling of airflows in transport tunnels is needed for regulations compliance, pollution and fire safety studies but remains a challenge for long domains because the computational time increases dramatically. We simulate air flows using the open-source code FDS 6.1.1 developed by NIST, USA. This work contains two parts. First we validate FDS6’s capability for predicting the flow conditions in the tunnel by comparing the predictions against on-site measurements in the Dartford Tunnel, London, UK, which is 1200 m long and 8.5 m in diameter. The comparison includes the average velocity and the profile downstream of an active jet fan up to 120 m. Secondly, we study the performance of the multi-scale modelling approach by splitting the tunnel into CFD domain and a one-dimensional domain using the FDS HVAC (Heating, Ventilation and Air Conditioning) feature. The work shows the average velocity predicted by FDS6 using both the full CFD and multi-scale approaches is within the experimental uncertainty of the measurements. Although the results showed the prediction of the downstream velocity profile near the jet fan falls outside the on-site measurements, the predictions at 80 m and beyond are accurate. Our results also show multi-scale modelling in FDS6 is as accurate as full CFD but up to 2.2 times faster and that computational savings increase with the length of the tunnel. This work sets the foundation for the next step in complexity with fire dynamics introduced to the tunnel.     

Analysis of structural interaction in tunnels using the covergence–confinement approach

The rock-support interaction in tunnels is studied through the use of the convergence–confinement method. The equations that characterize the behaviour of the most important support types are given together with a set of conceptual interaction schemes. As far as the behaviour of the support is concerned, reference is made to the ultimate limit state concept, which is widely used in civil engineering. This approach is linked to the classical convergence–confinement method. The interaction between the temporary support system and the final lining is dealt with, and the noteworthy case of presupport ahead of the face, followed by a further internal support (usually steel sets and shotcrete) is also included. Finally, the ‘ground reaction curve of the reinforced tunnel’, which allows one to analyse the interaction between the reinforcement around the tunnel and supports, is introduced.     

Concurrent multi-scale modelling and updating of long-span bridges using a multi-objective optimisation technique

This paper aims at developing an innovative technique of concurrent multi-objective optimisation for updating the multi-scale model of long-span bridges. A multi-scale model is established for the purpose of concurrently analysing the global response of the structure and nonlinear local damages in order to assess structural state and local damage evolution or deteriorating, respectively. A multi-objective optimisation technique is proposed in this work for concurrent multi-scale model updating, in which several key issues including the determination of the objective functions and constraint conditions, the multi-objective optimisation algorithm and how to find the optimal solution from many non-inferior solutions are studied. The proposed concurrent multi-objective optimisation technique is applied to update the initial multi-scale model of Runyang Suspension Bridge (RYSB) near Shanghai, and the updated model is validated by the data from the field tests conducted for obtaining the response in global (dynamic properties) and local levels.     

Modelling of blast-induced damage in tunnels using a hybrid finite-discrete numerical approach

This paper presents the application of a hybrid finite-discrete element method to study blast-induceddamage in circular tunnels. An extensive database of field tests of underground explosions above tunnelsis used for calibrating and validating the proposed numerical method; the numerical results areshown to be in good agreement with published data for large-scale physical experiments. The method isthen used to investigate the influence of rock strength properties on tunnel durability to withstand blastloads. The presented analysis considers blast damage in tunnels excavated through relatively weak（sandstone） and strong （granite） rock materials. It was found that higher rock strength will increase thetunnel resistance to the load on one hand, but decrease attenuation on the other hand. Thus, undercertain conditions, results for weak and strong rock masses are similar.
2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.     

Solar thermal modelling of a building with a roof pond and ventilation control systems

The paper proposes and presents thermal modelling of a ventilation-controlled, non-air-conditioned building with evaporative cooling (e.g. open water pond) over the roof for passive solar air conditioning. The ventilation rate, expressed in terms of number of air changes per hour, is assumed to be time-dependent, as should be the case in normal practice. A self-consistent periodic heat transfer analysis for a non-air-conditioned building with roof cooling and ventilation control systems, furnishing (assumed isothermal mass), windows, door and basement ground heat storage effects has been developed to assess the feasibility of the proposed passive space air-conditioning. It is shown that for no-ventilation summer nights the inside air temperature remains higher than the ambient air temperature even with an effective roof cooling system, and hence the windows should be opened to lose the internal heat and to introduce cool and fresh outside air. It is found that for a ventilation-controlled building with a roof pond the passive solar air conditioning can be achieved more effectively.     

Numerical modelling of masonry joints degradation in built tunnels

Old tunnels are generally supported by masonry structure. Nowadays, these constructions present many instability problems (cracks, collapses, convergence, etc.) due to aging phenomena on both blocks and mortars. After the analysis of blocks mechanical behaviour over time [Idris, J., Verdel, T., Al-Heib, M., 2008a. Numerical modelling and mechanical behaviour analysis of ancient tunnel masonry structures. Tunnelling and Underground Space Technology 23, 251–263.], we try in this paper to simulate the evolution of masonry joints mechanical behaviour in built tunnels and to quantify the influence of their mechanical proprieties on the tunnel behaviour by the help of the experimental design method and distinct elements numerical modelling.     

The influence of decreasing vehicle exhaust emissions on the standards for ventilation systems for urban road tunnels

The strengthening of vehicle emission standards in the Federal Republic of Germany has also served to reduce exhaust emissions in road tunnels. The effect of the stricter standards was investigated by STUVA [Research Association for Underground Transportation Facilities] (Cologne, Germany) and Schindler Haerter AG (Zurich, Switzerland) with regard to the influence of exhaust emissions on construction costs and the costs of operating ventilation systems. The study covered topics such as ventilation systems, vehicle exhaust emissions, fresh air requirements, dispersion of pollutants outside the tunnel, and fire safety standards. The research was sponsored by the Federal Ministry of Transport, Bonn, Germany. In the future, the fresh air requirement will be governed by the traffic states “congestion” and “at a standstill”, in addition to the exhaust components smoke and carbon monoxide. It is essential to introduce particle filters for diesel-engine, heavy-duty vehicles in order to reduce demands on the ventilation systems of tunnels (e.g., for number of fans and space for air ducts) at the planning stage, as well as to reduce power consumption and/or running times of existing ventilation systems. If particle filters are made obligatory by 1995, the fresh air requirement will decrease by about 30% to 45% by the year 2000. Vehicle emission factors are calculated for vehicle speeds of up to 100 km/h for the future design of ventilation systems, up to the year 2000. In the event of fire in tunnels lacking rescue/ escape facilities, the ventilation system must be capable of delivering 80 m³ (s·km) to 200 m³/(s·km) of fresh air, depending on the ventilation system. In such cases, recirculation of air must be strictly avoided.     

A new approach to regenerating heat and moisture in ventilation systems

For countries with a cold climate the large difference (30–60 °C) in winter between indoor and outdoor temperatures leads to (a) large heat losses in ventilation systems; (b) moisture freezing at the systems exit; (c) great reduction in the indoor humidity. Here we present a new approach for regenerating heat and moisture in ventilation systems in cold climates which allows resolution of these problems. The method has been tested under climatic conditions of West Siberia (winter 2005–2006). The prototype system requires very little maintenance, has a low capital cost, is compact and energy efficient. Technical, economic and social aspects of this method are discussed.     

Practical aspects of the ventilation of high-speed developing tunnels in hot working environments

The excavation of ramps and tunnels often requires high-speed development with [or without] the use of high-energy mining equipment such as loaders, dump trucks, TBMs and roadheaders. This highspeed development creates a challenge in terms of providing a safe and productive working environment. For example, heat from continuously exposed surrounding rock, heat from broken rock, heat generated by mining equipment, potential inflows of hot ground water, pollution from associated diesel equipment, and the distance of the advancing face from fresh through-ventilation all have to be taken into account when designing ventilation systems for high-speed ramp and tunnel developments. This paper discusses methods of achieving acceptable environments at the face and along the length of the tunnel. The methodology has been successfully implemented in the development of long [up to 20 km] TBM drives in the Lesotho Highlands Project and in mining projects in hot rock using drill-and-blast methods as well as in mechanised methods using continuous miners and roadheaders. The determination of heat loads includes calculation of the heat flow within the surrounding rock, evaluation of the operating cycle of the equipment and the contribution to the overall heat load of the broken rock as it travels out of the tunnel. The determination of heat loads from surrounding rock in new tunnels required a modification of the algorithms generally used for established excavations. The paper also examines the use of, for example, mobile duct and fan systems to ensure that fresh air is delivered to the specific areas where workers are located.     

地铁隧道内有害渗漏气体的通风排除

分析了有害气体的组成,给出了有害气体渗气量的计算方法,研究了列车活塞风对有害气体分布的影响以及如何应用通风系统排除渗入隧道内的有害气体,确保地铁安全运营。     

Forecasting fire growth using an inverse zone modelling approach

A new methodology to effectively forecast fire dynamics based on assimilation of sensor observations is presented and demonstrated. An inverse modelling approach with a two-zone model is used to forecast the growth of a compartment fire. Sensor observations are assimilated into the model in order to estimate invariant parameters and thus speed up simulations and recover information lost by modelling approximations. A series of cases of a compartment fire radially spreading at different growth rates (slow, medium and fast) are used to test the methodology. Spread rate, entrainment coefficient and smoke transport time are the invariant parameters estimated via a gradient-based optimization method with tangent linear differentiation. The parameters were estimated accurately within minutes after ignition and the heat release rate reproduced satisfactorily in all cases. Moreover, the temperature and the height of the hot layer are forecasted with a positive lead time between 50 and 80 s, depending on the fire growth rate. The results show that the simple mass and energy conservation equations and plume correlation of the zone model are suitable to forecast the main features of a growing fire. Positive lead times are reported here for the first time in fire dynamics. The results also suggest the existence of an optimal width for the assimilation window. The proposed methodology is subject to ongoing research and the results are an important step towards the forecast of fire dynamics to lead the emergency response.     

浅谈交通换气力对公路隧道通风换气的影响

本文利用日本有关的研究和实验结果，用计算方法求得我国大型车和小型车的正面投影面积Ａｃ，可据以计算两者的阻力系数及相应的交通换气力。交通换气力对隧道通风的影响是不容忽视的。在采用纵流换气方式的单向交通隧道中，可将交通换气力全部利用；而在纵流换气的双向交通隧道中，交通换气力只能视为较大的阻力。     

Accurate water demand spatial allocation for water networks modelling using a new approach

The paper presents an alternative approach regarding the spatial allocation of the actual water demand (at node level) when developing a pipe network's hydraulic simulation model. The process takes into account the respective demand patterns of the various types of water users, considering the water being lost through leaks/breaks occurring, as a competitive use. This new method accurately approximates the demand allocation of a network when there is no GIS data, thus having a significant impact on its cost effectiveness. Kos Town (Greece) water pipe network is used as the case study to demonstrate the entire process and the problems encountered. Finally, to prove its effectiveness the results of the new method were compared to MW-Voronoi diagram method's results and to field measurements.     

Improved modelling of downburst outflows for wind engineering applications using a cooling source approach

Large eddy simulations (LES), with a range of different practical ground roughness lengths (z₀=0.001-0.1 m), are used to compare near surface outflow features of a physically realistic cooling source downburst model, previously validated by meteorological observations, with those of the more commonly used transient impinging impulsive jet. A scaling procedure is proposed, based on length, velocity, and vorticity scales from within the outflow, allowing for direct comparison between outflows from the two models. Five scaling parameters are presented, capturing the horizontal and vertical position of maximum velocity, the ring vortex aspect ratio, the height of the ring vortex above the surface, and a non-dimensional vorticity term representative of the relative contribution of the ring vortex to the near surface wind field. It is shown that the impinging jet model is not capable of capturing the outflow features predicted by the cooling source model, due to its unrealistic forcing parameters, and is, therefore, unable to capture the physics of an actual downburst event. This difference dominates the non-dimensional vorticity term, showing that impinging jet results deviate by at least 56% from the cooling source results, at times when all other scaling parameter differences are minimized.     

高原隧道爆破施工技术探讨

从爆破与爆破施工的角度分析了影响高原隧道爆破效果的主要因素，提出了适用于高原隧道爆破施工的建议参数，同时介绍了青藏铁路羊八井1#隧道的施工方法。     

A study of the effectiveness of mechanical ventilation systems of a hawker center in Singapore using CFD simulations

A two interlinked approach was utilized to investigate the effectiveness of mechanical ventilation systems of a hawker center in Singapore. Field measurements and thermal comfort survey were conducted to evaluate the thermal comfort perceptions of the users of the hawker center, and the areas with poor thermal comfort conditions were identified. The CFD simulations were conducted to study the impact on thermal comfort of three kinds of fans (wall fans, ceiling fans and extract fans) and to determine the type of the fan which could improve the thermal conditions more effectively in the hawker center.     

竖井型公路隧道自然通风过程的实验研究

采用量纲分析法得到竖井型公路隧道自然通风相似性准则.采用近似模拟的方法,在1:10缩尺模型隧道内进行了车辆单向运动实验,测试表明,进入自模区所要求的最小风速为0.33 m/s,达到最小风速要求的3种有效车况为f0.8v.1.6,f0.8v,2和f1.3vt2.通过量纲一化的测试数据与理论计算结果的比较,验证了准则的正确性.     

公路隧道自然通风模型实验相似性研究

针对某个实际的顶部开孔的城市公路隧道自然通风模型实验,分析了隧道内交通车流和隧道气流的相互关系,指出在模型实验时应同时保证这两种流动的相似,确定了需要满足的相似特征数以及模型与原型之间的换算关系.     

Experimental study of water mist fire suppression in tunnels under longitudinal ventilation

This paper studies water mist fire suppression under different longitudinal ventilation velocities in tunnels by small-scale experiments. After a scaling study, two mist nozzles are used for suppressing crib fires under 5 ventilation speeds. The result comes out that fire suppression process can be divided into three stages including flame unitary restraining stage, surface flame extinguishing stage and inside flame suppression stage. Several factors influencing efficiency are investigated. When the interval between mist nozzle and fire source enlarges, the relationship curve between fire suppression time and ventilation velocity shows a ‘V’ figure. The best ventilation speed exists. Following the rules summarized, a coupling system of water mist and ventilation may increase fire suppression efficiency remarkably.