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  • 251.
    Willstrand, Ola
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Karlsson, Peter
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Brandt, Jonas
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    New certification rules for fire detection in vehicles2017Inngår i: 16th International Conference on Automatic Fire Detection & Suppression, Detection and Signaling Research and Applications Conference: Proceedings, 2017, Vol. 2, s. 105-112Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Detection of fires in vehicle engine compartments is challenging. High airflows, large temperature variations, dirty environment and complicated geometries make it difficult to determine the optimal type of detection technology and adequate location of sensors. A new test method has been developed for evaluation of fire detection systems meant for engine compartments of heavy vehicles. The test method considers all typical challenges normally encountered in an engine compartment, evaluating both detection system performance and durability. Certification rules connected to the new test method will ensure high quality and high performance of certified fire detection systems, increasing fire safety of vehicles.

    This paper gives an outline of the new certification rules, test method and corresponding research.

  • 252.
    Willstrand, Ola
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Karlsson, Peter
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Rosengren, Max
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Brandt, Jonas
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    New certification system for enhanced fire safety of vehicles2018Inngår i: Proceedings of 7th Transport Research Arena TRA 2018, 2018Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    RISE has initiated and developed a certification scheme for the vehicle industry that will enable manufacturers, operators and service centres (workshops) to certify their fire risk mitigation process. The fire risk management required in the certification is a key safety element, used to identify and evaluate fire hazards. For best results, it is important that manufacturers, operators and service centres are equally dedicated to solve the fire problem. Vehicle fire investigations reveal that design, production, operation and maintenance can all be responsible, however, most important is to ensure that information and experiences from fire incidents and identified fire hazards are linked to relevant personnel, practices, manuals, and quality procedures. The certification cannot guarantee the elimination of vehicle fires, but can ensure that manufacturers, operators and service centres will operate at the front line of vehicle fire safety engineering.

    Fulltekst (pdf)
    fulltext
  • 253.
    Xu, Dai
    et al.
    University of Edinburgh, UK.
    Welch, Stephen
    University of Edinburgh, UK.
    Rush, David
    University of Edinburgh, UK.
    Charlier, Marion
    ArcelorMittal, Sweden.
    Anderson, Johan
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    CHARACTERISING NATURAL FIRES IN LARGE COMPARTMENTS – REVISITING AN EARLY TRAVELLING FIRE TEST (BST/FRS 1993) WITH CFD2019Inngår i: Interflam 2019, proceedings / [ed] Stephen Grayson, Interscience Communications, 2019, Vol. 15, s. 2111-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This paper presents a careful assessment of fire conditions in a long enclosure, open only at one end, which contained a regularly spaced timber crib fire load and is dominated by under-ventilated combustion. Though the geometrical arrangement, with fully enclosed side walls, differs from many more recent “travelling fire” tests, the essential fire behaviour shows a very clear progression of the main burning zone, driven by a combination of fire spread, ventilation and fuel burn out. By contrast many other travelling fire tests have been designed to be fuel-controlled, in much more open structures. Moreover, due to the enclosed nature of the test, it was observed to result in very high temperatures in the protected and unprotected steel beam members, especially during the phase when the fire travelled back from the opening to the ignition location at the rear of the compartment. The investigated test in this paper is Test number 2, which is one of nine tests carried out at the BRE Cardington laboratory in the UK, led by British Steel Technical (BST) and hosted by the Fire Research Station (FRS).CFD modelling, with NIST’s Fire Dynamics Simulator (FDS), is invoked to assist in exploration and interpretation of the test results, and to evaluate model capabilities for this complex fire scenario. For simplicity, instead of modelling the complex pyrolysis and combustion of timber on a stick-by-stick basis, the entire wood cribs are represented in the FDS model as single objects. Thus ignition and burning are represented in a simplified manner at the scale of the individual crib faces, with idealised mass loss curves derived from measurements in selected rows. Though tied to empirical mass loss, the model is stretched in representing heavily under-ventilated conditions occurring in certain domains. Despite these simplifications and challenges the model does prove capable of representing the qualitative behaviours to a satisfactory level. In particular, with appropriate parameter choice for reaction-to-fire properties, the FDS models are able to represent the fire spread rates for the two distinct stages of the fire: the fire travelling from rear to the front of the compartment in search of oxygen; and the fire travelling back from the opening to the rear as fuel is consumed. The results suggest the potential value of such simplified representations of cribs in FDS for travelling fire scenarios.In the calibrated model, the magnitude of the thermocouple (TC) temperatures at three locations (ignition location, centre location, and opening location) shows generally good agreement between the FDS model and the test at the stage when the fire travels to the opening. However, significantly higher discrepancy appears at the stage when the fire travels back. In addition to the highly simplified representation of crib burning, another likely reason for the latter may be the malfunction of the mass loss measurement in several wood cribs at this stage, which led to significant uncertainties in prescribed burning rates. Another large source of uncertainty relates to residual heat in compartment boundaries and fuel embers, the latter not being easy to represent in CFD models. These results suggest avenues to explore in future model development.

  • 254.
    Xu, Hui
    et al.
    Imperial College London, UK.
    Cantwell, Chris D.
    Imperial College London, UK.
    Monteserin, Carlos
    DTU Technical University of Denmark, Denmark.
    Eskilsson, Claes
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Aalborg University, Denmark.
    Engsig-Karup, Allan P.
    DTU Technical University of Denmark, Denmark.
    Sherwin, Spencer J.
    Imperial College London, UK.
    Spectral/hp element methods: Recent developments, applications, and perspectives2018Inngår i: Journal of Hydrodynamics, ISSN 1001-6058, E-ISSN 1000-4874, Vol. 30, nr 1, s. 1-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spectral/hp element method combines the geometric flexibility of the classical h-type finite element technique with the desirable numerical properties of spectral methods, employing high-degree piecewise polynomial basis functions on coarse finite element-type meshes. The spatial approximation is based upon orthogonal polynomials, such as Legendre or Chebychev polynomials, modified to accommodate a C0 - continuous expansion. Computationally and theoretically, by increasing the polynomial order p , high-precision solutions and fast convergence can be obtained and, in particular, under certain regularity assumptions an exponential reduction in approximation error between numerical and exact solutions can be achieved. This method has now been applied in many simulation studies of both fundamental and practical engineering flows. This paper briefly describes the formulation of the spectral/hp element method and provides an overview of its application to computational fluid dynamics. In particular, it focuses on the use of the spectral/hp element method in transitional flows and ocean engineering. Finally, some of the major challenges to be overcome in order´to use the spectral/hp element method in more complex science and engineering applications are discussed

  • 255.
    Yang, S-H.
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Analysis ofinteraction effects between WECs in four types of wave farms2018Inngår i: Advances in Renewable Energies Offshore - Proceedings of The 3rdInternational Conference on Renewable Energies Offshore (RENEW 2018),, 2018, s. 647-658Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The development of Wave Energy Converters (WECs) is often carried out based on detailed analysis of a single unit. However, successful prototypes that will become commercial will be installed inwave farms where additional effects due to interactions between the WECs will occur. The current study presents results from time-domain coupled simulations, which are used to calculate, among others, the Levelised Cost of Energy (LCoE) and fatigue lives of moorings of the WEC system. Four types of wave farms were compared using the same point-absorbing WEC but with different mooring designs and array patterns. The fatigue damage of the moorings was found to increase for the arrays with strong hydrodynamic interactions and mechanical couplings. The results show that the LCoE value for a WEC array farm is sensitive to the hydrodynamic interaction between WECs and the mechanical couplings in the mooring design.

  • 256.
    Yang, Shun-Han
    et al.
    Chalmers Universtiy of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers Universtiy of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chalmers University of Technology, Sweden.
    Parametric study of the mechanical characteristics of power cables under dynamic motions2015Inngår i: Proceedings of the 11th European Wave and Tidal Energy Conference (EWTEC 2015), 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To maximise the harvesting of wave energy, solutions have been proposed that utilize wave energy converters (WECs) installed in arrays. This investigation presents a case study in which several WECs are located around a central hub, with each WEC connected to the hub by a power cable. To be incorporated in a WEC array system, the free-span of the cable is limited. Moreover, the cable is subject to the motion and load of the WEC, waves and currents. In this paper, the characteristics of the power cables are assessed with a numerical model applied through a parametric analysis, which varies important design parameters, such as the cable length, mass, and bending stiffness. The results of the numerical simulations are compared and discussed in terms of the forces that act on the power cables, including dynamic motion, curvature, cross sectional forces, and accumulated fatigue damage.

  • 257.
    Yang, Shun-Han
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chalmers University of Technology, Sweden.
    Hu, Zhiquang
    Newcastle University, UK.
    Biofouling on mooring lines and power cables used in wave energy converter systems - analysis of fatigue life and energy performance2017Inngår i: Applied Ocean Research, ISSN 0141-1187, E-ISSN 1879-1549, Vol. 65, s. 166-177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents an analysis of a wave energy converter (WEC) system consisting of a buoy, a mooring system, and a power cable connected to a hub. The investigated WEC system is currently under full-scale testing near Runde in Norway. The purpose of the study was to investigate the characteristics of the entire system, primarily with regard to energy performance and the fatigue life of the mooring lines and power cable, considering the effects of marine biofouling and its growth on the system’s components. By means of parametric study, the energy performance and fatigue life of the mooring lines and power cable were investigated considering two mooring configurations, three biofouling conditions, four sea states in a scatter diagram, and three wave and current directions. Hydrodynamic and structural response simulations were conducted in a coupled response analysis using the DNV-GL software SESAM. Energy performance analyses and stress-based rainflow counting fatigue calculations were performed separately using an in-house code. The results show that, for a WEC system which has been deployed for 25 years, biofouling can reduce the total power absorption by up to 10% and decrease the fatigue life of the mooring lines by approximately 20%

  • 258.
    Yang, Shun-Han
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas W.
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chalmers University of Technology, Sweden.
    Parametric study of the dynamic motions and mechanical characteristics of power cables for wave energy converters2017Inngår i: Journal of marine science and technology, Vol. 23, nr 1, s. 10-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A case study of a point-absorber wave energy converter (WEC) system is presented. The WEC system forms an array, with several WECs located around a central hub to which they are each connected by a short, free-hanging power cable. The objective of the study is to analyse the dynamic characteristics and estimate the fatigue life of the power cable which is not yet in use or available on the commercial market. Hence, a novel approach is adopted in the study considering that the power cable’s length is restricted by several factors (e.g., the clearances between the service vessel and seabed and the cable), and the cable is subject to motion and loading from the WEC and to environmental loads from waves and currents (i.e., dynamic cable). The power cable’s characteristics are assessed using a numerical model subjected to a parametric analysis, in which the environmental parameters and the cable’s design parameters are varied. The results of the numerical simulations are compared and discussed regarding the responses of the power cables, including dynamic motion, curvature, cross-sectional forces, and accumulated fatigue damage. The effects of environmental conditions on the long-term mechanical life spans of the power cables are also investigated. Important cable design parameters that result in a long power cable (fatigue) service life are identified, and the cable service life is predicted. This study contributes a methodology for the first-principle design of WEC cables that enables the prediction of cable fatigue life by considering environmental conditions and variations in cable design parameters.

  • 259.
    Yang, Shun-Han
    et al.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas W
    Chalmers University of Technology, Sweden.
    Johnson, Erland
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chalmers University of Technology, Sweden.
    Hu, Zhiqiang
    Newcastle University, UK.
    Bergdahl, Lars
    Chalmers University of Technology, Sweden.
    Duan, Fei
    Shanghai Jiao Tong University, China.
    Experimental and numerical investigation of a taut-moored wave energy converter: A validation of simulated buoy motions2018Inngår i: Journal of Engineering for the Maritime Environment (Part M), ISSN 1475-0902, E-ISSN 2041-3084, Vol. 232, nr 1, s. 97-115Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents an experimental and numerical investigation of a taut-moored wave energy converter system with a point-absorber type of wave energy converter. The wave energy converter system consists of a buoy, a unique three-leg two-segment mooring system with submerged floaters, and a power take-off system designed for the current experiment as a heave plate. The main objective of the study is to validate a numerical simulation model against experiments carried out in an ocean basin laboratory. Two physical models in model scales 1:20 and 1:36 were built and tested. The detailed experimental testing programme encompasses tests of mooring system stiffness, decay tests, and different sea state conditions for ocean current, regular, and irregular waves. A numerical model in the model scale 1:20 was developed to simulate coupled hydrodynamic and structural response analyses of the wave energy converter system, primarily using potential flow theory, boundary element method, finite element method, and the Morison equation. Several numerical simulations are presented for each part of the experimental testing programme. Results for the wave energy converter buoy motions under operational conditions from the experiments and the numerical simulations were compared. This study shows that the simulation model can satisfactorily predict the dynamic motion responses of the wave energy converter system at non-resonant conditions, while at resonant conditions additional calibration is needed to capture the damping present during the experiment. A discussion on simulation model calibration with regard to linear and non-linear damping highlights the challenge to estimate these damping values if measurement data are not available.

  • 260.
    Yao, Yongzheng
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Fire Behaviors and smoke transportation law of tunnel fires under confined portal boundaries2019Rapport (Annet vitenskapelig)
    Abstract [en]

    An increasing number of tunnels have been built around the world. They play an important role to relieve traffic congestions and facilitate goods transportation. However, in the event of a fire in tunnels, the consequences can be serious due to its narrow-long structure. The previous studies about tunnel fire dynamics and mitigation measures are mostly based on good ventilation conditions in tunnels, such as longitudinal ventilation and natural ventilation with the premise that a tunnel has two open portals. However, the studies about the characteristics of tunnel fires under confined portal boundaries with complete or incomplete sealing at both portals are rare. Typical fire scenarios can appear in a subway train, a building corridor, an underground utility tunnel, a mining tunnel, a tunnel during construction and the application of sealing tunnel portals for fighting large tunnel fires and so on. The knowledge of tunnel fire dynamics for tunnels under good ventilation conditions is probably not applicable to the scenarios of tunnel fires under confined portal boundaries. Conducting the studies of tunnel fires under confined portal boundaries is of great significance for better understanding the characteristics of this type of tunnel fires and developing tunnel fire mitigation measures. Therefore, by combining model-scale tunnel experiments and theoretical analyses, this thesis studies the fire behaviors and smoke transportation law of tunnel fires under confined portal boundaries. The main research contents include:

    1.Scaling effects of mass loss rate per unit area (MLRPUA) for well-ventilated pool fires are studied by summarizing large amounts of experimental data from the literature together with theoretical analyses. As a further extension of tunnel fire similarity theory, it provides the basis and reference for later model/medium-scale tunnel experiments. Results show that when a small-scale pool fire (D<1 m) occurs in the open, increasing wind velocity tends to increase the MLRPUA, especially for pools with D<0.2 m. This is because the ventilation significantly increases the conductive and convective heat feedbacks (leading role). But when small-scale pool fires occurs in tunnels with a short distance between the pool surface and ceiling (Hef/D<3), the radiative heat feedback from the tunnel ceiling is probably dominating, leading to a much higher MLRPUA than that in the free burn. When subjected to longitudinal flows, the MLRPUA decreases due to the reduced radiation effect from the ceiling. With the increase of pool diameter, the influence of wind on the MLRPUA decreases gradually, no matter whether the pool occurs in the open or in a tunnel. Finally, when the pool diameter exceeds 1 m, the radiation from flame itself is probably predominant. The MLRPUA is not significantly affected by increasing wind velocity and most likely fluctuates within 30% for a wide range of wind velocities based on the test data collected.

    2.The flame behaviors and the maximum gas temperature rise beneath the ceiling in an enclosed tunnel are studied using a model-scale tunnel. Results show that when a fire (small fire) is not located at the tunnel center, the flame inclines towards the closer tunnel end due to the asymmetric flow field on both sides of the flame. The flame inclination angle keeps increasing when the fire is moving away from the tunnel center. Furthermore, when a fire is in Region I (0< ≤0.64), the maximum gas temperature rise decreases with the increasing dimensionless fire distance due to the increasing flame inclination angle. When a fire is in Region II (0.64< <1), the maximum gas temperature rise increases with the increasing dimensionless fire distance due to the heat feedback of returned hot smoke bounced from the end wall. By introducing a concept of equivalent ventilation velocity based on the flame inclination mechanism, a prediction model of maximum gas temperature rise beneath the ceiling in Region I is developed. Beyond that, an extra correction factor is proposed to the improved model in Region II with a consideration of heat feedback of returned hot smoke bounced from the end wall. Besides, further dimensional analysis indicates that the normalized maximum gas temperature rise follows an exponential attenuation law with the dimensionless fire distance.

    3.The coupling control effects of sealing ratio and initial sealing time on the fire development (large fire) are studied using a model-scale tunnel. Results show that sealing tunnel portals can decrease the mass loss rate of fuel and gas temperature inside the tunnel, no matter whether the sealing is complete or incomplete. The earlier the initial sealing time is, the better the fire can be controlled. For the incomplete sealing, when the sealing is implemented during the violent burning stage, the sealing not only does not limit the fire growth but also exacerbates the tunnel fire, producing an extremely high CO concentration at tunnel portals and a longer ceiling flame jet. This will result in a huge threat to the rescue service at tunnel portals. Besides, if the tunnel portals are sealed incompletely, it will leave a small area for the exchange of smoke and air. The smoke will not continue to spread horizontally after leaving the tunnel portals under the action of inertial forces. In order to maintain the combustion of fuel, the fresh air from external environment flows into the tunnel vigorously and quickly from the gap and then uplifts the smoke out of the tunnel portals, which is also an important phenomenon for firefighters and needs to draw their attentions.

    4.The critical conditions for the occurrence of under-ventilated tunnel fires and the combustion mechanisms under confined portal boundaries are studied by using both model-scale and medium-scale tunnels. Results show that the critical equivalence ratio for the occurrence of under-ventilated tunnel fires is within 0.53 - 0.6, which is less than the theoretical value of 1. This is related to the occurrence of vitiation, consequently reducing the level of oxygen around the flame by diluting the O2 concentration. The low ventilation rate and vitiation result in a low O2 volume fraction around the flame, and then the MLRPUA starts to decrease and at the same time the air mass flow into the tunnel becomes almost constant. Also, an oscillating MLRPUA and lifted flame are observed in the model-scale tests. Consequently, the ventilation rate approaches and even reaches the amount required for complete combustion of vaporized fuel. This means that the insufficient combustion in early under-ventilated tunnel fires has converted to sufficient combustion (from the perspective of the change of equivalence ratio, the fire has converted from under-ventilated to well-ventilated). As a result, no significant increase in CO production in under-ventilated fires is observed in both test series.

    5.The critical conditions for the occurrence of self-extinguishment and influencing factors in under-ventilated tunnel fires are studied in a model-scale tunnel during construction. The tunnel consists of an inclined access tunnel and a horizontal main tunnel. Results show that when a fire is in the horizontal main tunnel, the critical equivalence ratio for self-extinguishment is within 0.28 - 1.38 for the propane gas burner and 1.11 - 3.6 for the fibre board soaked with heptane. The difference is related to the burning behavior of the different fuels used. Moreover, the critical O2 volume fraction is about within 12 - 15% when the fires self-extinguish. When a fire is at the closed end of the horizontal main tunnel, the stratification of smoke is destroyed after hitting the closed end, and then the smoke seems to spread over the entire cross section of the tunnel. The smoke spread velocity is proportional to the ventilation rate. However, when a fire occurs at the closed end of the inclined access tunnel, the fire does not self-extinguish, even when the ventilation rate is 0 m3/s. The corresponding smoke spread velocity is higher than that in the horizontal main tunnel. This is probably related to the increasing component of buoyancy in the longitudinal direction in the inclined access tunnel. Besides, no insignificant vitiation behind the fire is found. These two characteristics in the inclined access tunnel increase the temperature of smoke flowing out of the tunnel portal and in turn promote the natural ventilation and increase the O2 volume fraction.

    Fulltekst (pdf)
    fulltext
  • 261.
    Yao, Yongzheng
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. University of Science and Technology of China, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Cheng, Xudong
    University of Science and Technology of China, China.
    Scale effect of mass loss rates for pool fires in an open environment and in tunnels with wind2019Inngår i: Fire safety journal, ISSN 0379-7112, E-ISSN 1873-7226, Vol. 105, s. 41-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the influence of wind on mass loss rate per unit area (MLRPUA) of fuel-controlled pool fires both in an open environment and inside tunnels and the scale effect of pool fires is also investigated. Large pool fires with a diameter D greater than 1 m (D > 1 m) are of key concern but small pool fires (D < 1 m) are also considered for comparison. This is done by analyzing large amounts of experimental data from the literature. Results show that for small pool fires (D < 1 m) in an open environment, increasing wind speed tends to increase the MLRPUA, especially for pools with D < 0.2 m, where the MLRPUA could increase significantly with the increase of wind speed. But when small pool fires occur in tunnels, the results are more complex. When the ratio of effective tunnel height to pool diameter is less than 3, increasing wind speed tends to decrease the MLRPUA. When this ratio is greater than 3, the influence of wind on MLRPUA of pool fires in tunnels is similar to that in an open environment. The influence of wind on the MLRPUA decreases for larger pool diameters, no matter whether the pool fire occurs in an open environment or in a tunnel. For large pools with D > 1 m, the MLRPUA is not affected significantly by increasing wind speed and most likely varies within 30% for a wide range of wind speeds based on the test data collected. This influence is far less than the values concluded by previous studies based on small pool fire experiments. The outcome of this study contributes to improving the understanding of burning characteristics of pool fires under windy conditions, especially large pool fires, which are much more meaningful than small pool fires from the perspectives of fire protection engineering and fire hazard assessment.

  • 262.
    Yao, Yongzheng
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. University of Science and Technology of China, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Cheng, Xudong
    University of Science and Technology of China, China.
    The characteristics of under-ventilated pool fires in both model and medium-scale tunnels2019Inngår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 87, s. 27-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the characteristics of under-ventilated fires in tunnels. This was done by using both model and medium-scale tunnels. The fuels used were heptane and xylene. The mass loss rates per unit area, ventilation rates from tunnel inlet, flame characteristics, O 2 , CO and CO 2 concentrations, optical densities and heat release rates were measured and recorded. Results show that the fire behaviors in under-ventilated tunnel fires are different from that in well-ventilated fires. In under-ventilated fires, the mass loss rate per unit area is found to decrease during identical periods due to the low oxygen concentration resulting from the low ventilation rate and vitiation, meanwhile the flame size dramatically reduces with a lifted and fluttering flame. This was clearly observed in model-scale tests, but due to limited optical view there was no possibility to observe this in the medium-scale tests. As a result, the ventilation rate approaches the amount required for complete combustion of vaporized fuel. This indicates that the combustion has converted from ventilation-controlled to fuel-controlled. No significant increase in CO production is observed in under-ventilated fires. Besides, the equivalence ratio and combustion efficiency were analyzed in order to judge whether the combustion is fuel-controlled or ventilation-controlled. This study provides new experimental information that contributes to improving the understanding of characteristics of under-ventilated fires in tunnel and can help firefighters to make right judgements and take related protective measures during the rescue processes.

  • 263.
    Yao, Yongzheng
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. University of Science and Technology of China, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Lönnermark, Anders
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Cheng, Xudong
    University of Science and Technology of China, China.
    Study of tunnel fires during construction using a model scale tunnel2019Inngår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 89, s. 50-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper presents a study on the characteristics of tunnel fires during construction. A model-scale tunnel was built and fire tests were conducted. The tunnel consists of an inclined access tunnel and a horizontal main tunnel. The main tunnel has two dead ends (excavation faces) and the only opening is from one side of the access tunnel. Propane gas burner and the fibre board soaked with the heptane were used as fuels. The flame characteristics, O 2 and CO volume fraction and gas temperature were measured and recorded. Two typical characteristics of self-extinguishment and smoke spread were found in the tunnel fires during construction. Results indicate that when a fire occurs in the horizontal main tunnel, the critical equivalence ratio for the occurrence of self-extinguishment is within 0.28–1.38 for the propane gas burner and 1.11–3.6 for the fibre board soaked with heptane. The difference is related to the burning behavior of the different fuels used. The fire location in the horizontal tunnel also has a significant influence on the fire development. A well-ventilated fire at the center of the horizontal tunnel becomes under-ventilated due to vitiation when it is located at the closed end of the horizontal tunnel. Besides, when a fire occurs at the closed end of the horizontal main tunnel, the stratification of smoke is destroyed after hitting the closed end, and then the smoke seems to spread over the entire cross section of the tunnel. The smoke spread velocity is found to be proportional to the ventilation rate. However, when a fire occurs at the closed end of the inclined access tunnel (lower end), the fire does not self-extinguish, even when the ventilation rate is 0 m 3 /s. The corresponding smoke spread velocity is higher than that in the horizontal main tunnel. The outcomes of this study provide new experimental information that contributes to improve the understanding of characteristics of tunnel fires during construction and can help firefighters to make better decisions during the rescue processes.

  • 264.
    Yao, Yongzhenh
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. University of Science and Technology of China, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Cheng, X.
    University of Science and Technology of China, China.
    Numerical study on overall smoke control using naturally ventilated shafts during fires in a road tunnel2019Inngår i: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 140, s. 491-504Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper studies the overall smoke control of natural ventilation systems with vertical shafts during fires in a common road tunnel by numerical modelling. The variables studied include the heat release rate, longitudinal fire location along the tunnel, length of shafts and the interval between two shafts. Simulation results indicate that the total smoke spread length on both sides of fire source is closely independent of the heat release rate and longitudinal fire locations. For a given dimensionless shaft interval (the ratio of the shaft interval to shaft length), with the increase of shaft length, the smoke spread length firstly increases, reaching a maximum at 12 m, and then decreases significantly until 18 m. For a fire less than 30 MW, the first shaft pair on both sides of fire source prevents the critical-temperature smoke (270 °C) from spreading beyond this shaft. For a 100 MW fire, in the cases with shorter shaft lengths (L shaft ≤9 m), the critical-temperature smoke can't be controlled between the first shaft pair. The gas temperature at human height (1.8 m) is less than 60 °C in all cases with shafts. Downdraught occurs when the smoke front stabilizes at the bottom of a shaft and the buoyancy force could be too low to overcome the kinetic pressure of the air flow flowing into this shaft, consequently destroying the structure of smoke layer. In most scenarios, the total exhaust area of shafts that is required to exhaust all the smoke is about 100 m 2 . The first shaft pair plays a critical role to exhaust the smoke, and its exhaust efficiency is also affected significantly by the shaft length. This study investigates how to control the smoke by using vertical shafts in a road tunnel fire and the conclusions are useful to tunnel fire protection engineering.

  • 265.
    Zhang, Yafan
    et al.
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Hammam, Tag
    RISE - Research Institutes of Sweden, Swerea, Swerea KIMAB AB.
    Belov, Ilja
    Jönköping University, Sweden.
    Sjögren, Torsten
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Bakowski, Mietek
    RISE - Research Institutes of Sweden, ICT, Acreo.
    Nee, Hans Peter
    KTH Royal Institute of Technology, Sweden.
    Thermomechanical Analysis and Characterization of a Press-Pack Structure for SiC Power Module Packaging Applications2017Inngår i: IEEE Transactions on Components, Packaging, and Manufacturing Technology, ISSN 2156-3950, E-ISSN 2156-3985, Vol. 7, nr 7, s. 1089-1100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an experimental methodology for the characterization of thermomechanical displacement and friction properties in a free-floating press-pack structure, and evaluation of the tensile stress on the semiconductor die through simulation of different mechanical and thermal loading conditions. The press-pack structure consists of a single silver-metallized (1 &#x03BC;m) silicon carbide die (400 &#x03BC;m) in contact with rhodium-coated (0.4 &#x03BC;m) molybdenum square plates. The thermomechanical displacements in the press-pack structure have been obtained using the digital image correlation technique, and the mean random error has been $&#x00B1; $0.1 &#x03BC;m, which is approximately 10 ppm of the measured length (10.5 mm). The developed experimental method has led to an analytical estimation of friction coefficients on the interfaces' silicon carbide-molybdenum and molybdenum-copper. The results demonstrate that the thin silver layer behaves as a solid film lubricant. A 2-D finite-element model representing the experimental setup has been implemented. The difference in displacement between measurement and simulation is less than 8&#x0025;. Furthermore, the coinfluence of the design parameters on the thermomechanical performance of the stacked structure has been analyzed through simulations. Finally, design guidelines to reduce the tensile stress on the silicon carbide die have been proposed regarding free-floating press-pack power electronics packaging.

  • 266.
    Zhao, Shengzhong
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chongqing University, China.
    Li, Y. Z.
    Chongqing University, China.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Liu, F.
    Chongqing University, China.
    A theoretical and experimental study on the buoyancy-driven smoke flow in a tunnel with vertical shafts2019Inngår i: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 141, s. 33-46Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, a series of small-scale experiments was carried out in a model scale tunnel with dimensions of 20 m (Length) × 2 m (Width) × 1 m (Height) to investigate the characteristics of buoyancy-driven smoke flow in a tunnel with vertical shafts. Different shaft settings and four different longitudinal ventilation velocities were tested in the experiments. A theoretical model for the mass flow rate of buoyancy-driven smoke flow in the shaft was developed and validated. The gas temperature along the tunnel ceiling and smoke stratification were subsequently analyzed and discussed. The results showed that more shafts, greater shaft heights and greater shaft cross sectional areas can significantly increase the smoke extraction rate, and the total smoke mass flow rate in the shafts increases with the increasing ventilation velocity. The local pressure loss coefficient at the shaft inlet may not be a fixed value. An average value of 1.0 for this coefficient was recommended for engineering estimation and design of rectangular-shaped natural shafts. The presence of vertical shaft is beneficial to the smoke stratification and could increase the height of the smoke layer interface, especially for the downstream of the shaft.

  • 267.
    Zhao, Shengzhong
    et al.
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. Chongqing University, China.
    Li, Ying Zhen
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Kumm, Mia
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Ingason, Haukur
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Liu, Fang
    Chongqing University, China.
    Re-direction of smoke flow in inclined tunnel fires2019Inngår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 86, s. 113-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The re-direction of smoke flow in inclined tunnel fires refers to the phenomenon that the smoke flow direction suddenly changes due to the changes of thermal buoyancy or outside pressure or the activation of fans. This poses special risk for fire rescue services fighting fires in tunnels. Both small-scale tunnel fire tests (28 scenarios) and numerical simulations of full-scale tunnel fires (31 scenarios) were conducted to study this special phenomenon. A one-dimensional model was used to predict the flow velocity in the inclined tunnels, based on two different methods for calculating the mean smoke temperature (Method I and Method II, respectively). Results show that the smoke flow direction could be well predicted by the model with Method II. When the ventilation velocity is relatively large and the flow tends to be one dimensional, both methods produce similar results. Further, the influences of important factors on the re-direction of smoke flows were systematically analyzed. These factors include heat release rate, tunnel slope, tunnel length, friction factor, tunnel cross sectional area and fire source location.

  • 268.
    Östman, Birgit
    et al.
    Linneaus University, Sweden.
    Schmid, Joakim
    ETH, Switzerland.
    Klippel, Michael
    ETH, Switzerland.
    Just, Alar
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. TUT Tallinn University of Technology, Estonia.
    Werther, Norman
    Technical University of Munich, Germany.
    Brandon, Daniel
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Fire design of CLT in Europe2018Inngår i: Wood and Fiber Science, ISSN 0735-6161, Vol. 50, s. 68-82Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fire safety design of cross-laminated timber (CLT or X-Lam) in Europe is governed by the Construction Products Regulation and its essential requirements, as for all other building products. These requirements are mandatory, to be used in all European countries. They include classification systems for reaction to fire of building products, fire resistance of building elements, and structural Eurocodes. The reaction-to-fire performance of CLT in accordance with the European classification system is specified. Higher classes can be reached by chemical treatments, but the durability of the reaction-to-fire performance needs to be fulfilled according to a new European system. The fire resistance design of CLT building elements is not included in Eurocode 5, the structural Eurocode for timber, but can be either tested according to European standards or calculated by using design methods being developed recently. This article provides information about both reaction to fire and fire resistance of CLT in Europe. Furthermore, the importance of proper detailing in building design and in practice is stressed. Finally, performance-based design is introduced and some further research needs suggested.

  • 269.
    Dederichs, Anne ()
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety. DTU Technical University of Denmark.
    Zawadowska, Aleksandra ()
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    Hemmarö, Linnea ()
    RISE - Research Institutes of Sweden, Säkerhet och transport, Safety.
    NFSD Nordic Fire & Safety Days: Book of abstracts from the NFSD Nordic Fire & Safety Days 20-21 August 2019 in Copenhagen, Denmark2019Rapport (Annet vitenskapelig)
    Abstract [en]

    It is our pleasure to hand over to you this book of abstracts for the Nordic Fire & SafetyDays 2019 organized by RISE Research Institutes of Sweden in collaboration Technical University of Denmark, Norwegian University of Science and Technology, Lund University, Aalto University, Luleå University, University of Stavanger, Western Norway University of Applied Sciences and Iceland University as well as VTT Technical Research Centre of Finland Ltd and Danish Institute of Fire and Security Technology.We are very proud to present the abstracts of 63 Nordic and international contributions in the present book of abstracts. The work demonstrates a significant scientific depth and societal relevance. The conference is a response to the extensive interest in the areas of fire and safety engineering in the Nordic countries in the past decades. As the programme and the abstracts show, the NFSD follow up on challenges with respect to safety dealing with aspects of fire and human behaviour as well as rescue service and risk management.

    Anne S. Dederichs, RISE Research Institutes of SwedenConference chair

    Fulltekst (pdf)
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