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.     

The influence of longitudinal ventilation systems on fires in tunnels

Many tunnels are equipped with longitudinal ventilation systems to control smoke in the event of a fire. However, the influence of such ventilation on fire development and fire spread has rarely been considered. This paper presents the results of a study investigating the influence of forced longitudinal ventilation on car fires, pool fires and heavy goods vehicle fires in tunnels. A Bayesian probabilistic approach is used to refine estimates, made by a panel of experts, with data from experimental fire tests in tunnels. Results are presented and the implications are discussed. The influence of longitudinal ventilation on heavy goods vehicle fires is predicted to be much larger than the experts’ estimates, causing a fire to grow ten times larger than if natural ventilation was used. The effect of ventilation on a pool fire in a tunnel depends on the size of the pool; the heat release rate of small pool fires may be reduced by forced ventilation, whereas it may be enlarged for large pool fires. The size of a car fire is not expected to be greatly affected by forced ventilation at low ventilation velocities.     

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.     

Study of the critical velocity in tunnels with longitudinal ventilation and spray systems

Based on the Froude similarity law, a small-scale tunnel model (1/14) was built based in this study to investigate critical velocities of tunnels. Critical velocity is the minimum air velocity required to resist the spread of smoke from a fire upstream in a tunnel. A set of experiments was conducted to investigate the critical velocities under different experimental conditions by varying the heat release rate of the fire, ambient temperature, operating pressure and arrangement of the nozzles. The results of the tests with no spray indicated that the ambient temperature has little impact on the critical velocity. Moreover, based on the dimensionless analysis method, a new correlation was established to predict the critical velocities in the tunnel without Water spray-based Fixed Fire Fighting Systems (WFFFS). The accuracy of the correlation was illustrated by the results of the present tests and a number of tests on different scales published by other scholars. Furthermore, 60 tests with WFFFS activation were carried out. The results show that the critical velocity is significantly reduced after the water spray discharged from the nozzles. The maximum reduction of the critical velocity is approximately 31%. The reduction of the critical velocity strongly depends on the number, positions and operating pressures of the nozzles. The mechanisms of the reduction of the critical velocity caused by spraying were discussed. The cooling effect of the water droplets on hot gas is not the only mechanism for decreasing the critical velocity caused by spraying. Spraying increases the inertial force of the longitudinal airflow and is the other mechanism for the reduction.     

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.     

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.     

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.     

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.     

Modelling the heat consumption in district heating systems using a grey-box approach

The heat consumption in a large geographical area is considered together with climate measurements on a single location in the area. The purpose is to identify a model linking the heat consumption to climate and calendar information.The process of building a model is split into a theoretical based identification of an overall model structure followed by data-based modelling, whereby the details of the model are identified. This approach is sometimes called grey-box modelling, but the specific approach used here does not require states to be specified. Overall, the paper demonstrates the power of the grey-box approach.     

管道燃气厨房事故通风问题辨析

讨论使用管道燃气的公共厨房实际运行中燃气泄漏的可能性,分析现行国家相关标准规范的有关规定,指出其中的不明确、不协调之处,认为通风良好的管道燃气厨房无需设置事故通风。通过统计分析近年来国内重大燃气爆炸事故案例,参考借鉴美国相关标准,对相关标准的制修订以及以确保防火安全为目的的燃气厨房通风系统设计提出一些意见和建议。     

Model-based airflow controller design for fire ventilation in road tunnels

This paper describes a new approach to design the proportional-integral-derivative (PID) controller of the longitudinal airflow velocity in road tunnels for fire situations. Our work shows clearly that the use of a proper model provides valid data for model-based tuning of tunnel controllers, which is demonstrated by real tunnel tests. The design uses the simplified mathematical model of airflow dynamics based on Bernoulli and continuity equations, which describe the airflow dynamics in one dimension. Optimizing controller parameters on site is very time consuming and this problem increases in the case of complex tunnels with several entrance and exit ramps, which typically have occurrences of traffic congestion. Our approach is based on the design of the controller through simulations, which use the mathematical model of airflow velocity in the tunnel. This approach spares a lot of work and time with the controller tuning within tunnel tests. Moreover, it can discover potential problems, which can occur during real instances of fire in the tunnel. The additional advantage of this approach is a possibility to simulate a scenario of errors and failures of some devices, which are important for reliable control of longitudinal airflow velocity. Although this approach is focused primarily on complex road tunnels, due to their complexity and significant time savings with the controller tuning, it can be also used for simpler tunnels with no ramps (usually highway tunnels) where the design of the airflow controller is not as complex compared to the case of road tunnels. This paper also includes a case study of the airflow controller design for the Blanka tunnel complex in Prague, Czech Republic, which is the largest city tunnel in Central Europe.     

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.     

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。     

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.     

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.