Ingeniería Mecanica Y Minera

Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame.

This paper provides with a set of full-scale experimental data of atrium fires. These data could be used as benchmarks for future numerical validation studies. In particular, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. Experimentally, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDS). Experimentally, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume into more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. Numerically, the simulations agree well with the experiments for the cases with make-up air velocities lower than 1 m/s. Poor agreement has been found for the case with inlet velocities higher than 1 m/s.

The use of computational fluid dynamics (CFD) as a tool for the design of smoke control systems and fire protection in large spaces has become more frequent as accuracy and computational speeds increase. In the present work Fire Dynamic Simulator (FDSv5) has been used to study two full-scale experiments conducted in Murcia (Spain) of 1.36 MW and 2.34 MW pool fires burning inside a 20 m cubic atrium under natural ventilation conditions. Different cartesian-grid approximations to the real geometry of the pyramidal roof have been investigated in order to assess the effect of stair stepping on the smoke layer and the temperature field. In general terms, good agreement between experiments and numerical simulations is found for all model roof geometries, especially far away from the fire source and the centreline. For example, at a height of 15 m, the temperature differences between all geometry approximations are lower than 10%. This shows that the cartesian-grid simplifications proposed here are a good choice and allow for saving some computational resources. In order to extend the results to different designs, the model has then been applied to study a range of 16 different atrium geometries, varying the area-to-height-squared ratio from 0.4 to 3.8. In addition, a comparison with simulation with a previous version of the code, FDSv4, shows that it predicts higher temperatures and slower ascends of the smoke layer than FDSv5, the difference being lower than 12% and 100 s respectively.

The present paper is focused on the fluid dynamics of the make-up air at the vents in case of an atrium fire, its influence on the fire-induced conditions and the necessity of properly model it to obtain an accurate numerical prediction. For this aim, experimental data from two full-scale atrium fire tests conducted in a 20 m cubic facility, with venting conditions involving mechanical smoke exhaust and make-up air velocities larger than 1 m/s, and with different fire powers, are presented. Subsequent numerical simulations of these tests have been performed with the code Fire Dynamics Simulator v5.5.3. Two different approaches have been followed to simulate the make-up air inlet fluid dynamics, involving one domain which only considers the inside of the building and another which includes part of the outside. In the former simulations, anomalous phenomena around the fire appear, while the inclusion of the exterior domain provides with a completely different fluid dynamics inside the facility which agrees better with the experimental data. A detailed analysis of the fluid mechanics at the air inlet vents is conducted to explain these discrepancies. Finally, further simulations are performed varying the make-up area to assess the appearance of the aforementioned phenomenon.

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The dynamics of a plane air sheet surrounded by a coflowing water sheet, discharging into stagnant air, has been investigated by means of experiments and numerical simulations with the aim at proposing new geometrical configurations for air bubble generation. In this case, the problem is governed by the Weber number, W e = ρ w u 2 w h a /σ, and the water-to-air velocity ratio, Λ = u w /u a , being u w and u a the mean velocities of the water and air sheets respectively, ρ w the water density and h a the half-thickness of the air sheet at the exit. For a fixed liquid-togas thickness ratio, a = h w /h a = 5.52, and a constant Weber number, two different flow regimes have been observed, i.e. a jetting and a bubbling regime. High-speed video images have been used to determine experimentally the transition curve from a jetting regime to a bubbling regime in the W e − Λ parameter space, as well as to measure several relevant parameters in the bubbling regime, such as the bubbling frequency and the size of the bubbles formed. In addition, direct numerical simulations have been performed by means of the Volume of Fluid technique (VoF), and the results compared with the experimental measurements.

We present an experimental and numerical study of the periodic breakup of an air sheet surrounded by two co-flowing water streams. For a fixed liquid-togas thickness ratio, h = h w /h a ' 5.27, we explore the dependence of the bubbling regime on the two main governing parameters, namely the Weber number, We ¼ q w u 2 w h a =r, and the velocity ratio, K = u w /u a , where u w and u a are the mean water and air velocities at the exit slit, respectively, and h a and h w are the half-thicknesses of the air and water sheets at the outlet. The bubble formation frequencies obtained experimentally are in good quantitative agreement with the results of numerical computations performed with the volume-of-fluid technique. The analysis of the results obtained allows a detailed characterization of the dynamics of the bubble formation process in planar co-flows. In particular, using the pressure fluctuations in the gas stream and the time evolution of the bubble interface, both obtained from the numerical simulations, the bubbling process is described through a two-stage mechanism governed by distinct physical phenomena: the first stage is characterized by the formation of a neck that moves downstream at the liquid velocity, and it collapses towards the symmetry plane during the second stage. A simple scaling law is proposed for the bubbling frequency, that shows a good agreement with our experimental and numerical results.

This paper aims to study the influence of different make-up air configurations on the inner conditions induced by low-power fires within an atrium. For this objective, three full scale fire tests in a 19.5 m x 19.5 m x 19.5 m facility have been conducted. In these tests, symmetric and non-symmetric make-up air configurations, as well as different air inlet areas have been assessed. Later FDSv4 simulations of the tests have been performed and comparisons between measurement and predictions are reported. Experimentally, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. Numerically, the simulations agree well with the experiments for the cases with make-up air velocities lower than 1 m/s. Poor agreement has been found for the case with inlet velocities higher than 1 m/s.

A. M. Ortega et al.: Real-time measurements of SOA formation and aging ical ages is dominated by heterogeneous oxidation followed by fragmentation/evaporation. A comparison of urban SOA formation in this study with a similar study of vehicle SOA in a tunnel suggests the importance of vehicle emissions for urban SOA. Pre-2007 SOA models underpredict SOA formation by an order of magnitude, while a more recent model performs better but overpredicts at higher ages. These results demonstrate the value of the reactor as a tool for in situ evaluation of the SOA formation potential and OA evolution from ambient air.

Ambient pine forest air was oxidized by OH, O 3 , or NO 3 radicals using an oxidation flow reactor (OFR) during the BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H 2 O, Organics and Nitrogen-Rocky Mountain Biogenic Aerosol Study) campaign to study biogenic secondary organic aerosol (SOA) formation and organic aerosol (OA) aging. A wide range of equivalent atmospheric photochemical ages was sampled, from hours up to days (for O 3 and NO 3) or weeks (for OH). Ambient air processed by the OFR was typically sampled every 20-30 min, in order to determine how the availability of SOA precursor gases in ambient air changed with diurnal and synoptic conditions, for each of the three oxidants. More SOA was formed during nighttime than daytime for all three oxidants, indicating that SOA precursor concentrations were higher at night. At all times of day, OH oxidation led to approximately 4 times more SOA formation than either O 3 Published by Copernicus Publications on behalf of the European Geosciences Union. B. B. Palm et al.: Ambient forest air in an oxidation flow reactor oxidation produced SOA with elemental O : C and H : C similar to the least-oxidized OA observed in local ambient air, and neither oxidant led to net mass loss at the highest exposures, in contrast to OH oxidation. An OH exposure in the OFR equivalent to several hours of atmospheric aging also produced SOA with O : C and H : C values similar to ambient OA, while higher aging (days-weeks) led to formation of SOA with progressively higher O : C and lower H : C (and net mass loss at the highest exposures). NO 3 oxidation led to the production of particulate organic nitrates (pRONO 2), while OH and O 3 oxidation (under low NO) did not, as expected. These measurements of SOA formation provide the first direct comparison of SOA formation potential and chemical evolution from OH, O 3 , and NO 3 oxidation in the real atmosphere and help to clarify the oxidation processes that lead to SOA formation from biogenic hydrocarbons.

In case of fire, atria constructive features favor the spread of smoke, becoming its management a challenge. Thus, the effect of different venting conditions on the dynamics of atrium fires is studied herein. Five full-scale fire experiments have been numerically analyzed to explore the influence of the make-up air. Due to the lack of experiments that exists in atria extensive modeling to extract more knowledge is required. Subsequently, 84 simulations with FDS v6 have been carried out, considering different vent areas (air velocity from 0.4 m/s to 5.3 m/s) and configurations, two Heat Release Rate values (2.5 and 5 M W), and two pan locations. It is demonstrated that make-up air velocities lower than the prescribed limit of 1 m/s may induce adverse conditions, being recommended to assess the complete fire scenario with even lower values, depending on the inlets distribution, in terms of smoke production. The results also show that asymmetric configurations are prone to induce circulation around the flame which can generate fire whirls. Thus, this numerical study links two fire types allowing the connection of pool fires to fire whirls, which completely differ in behaviour, for the sake of design of fire safety.

We investigate experimentally and numerically the transient development of the wake induced by a constant acceleration of a D-shaped bluff body, starting from rest and reaching a permanent regime of Reynolds number Re = 2000, under different values of acceleration and implementing three distinct rear geometrical configurations. Thus, alongside the classical blunt base, two control passive devices, namely, a straight cavity and an optimized, curved cavity, recently designed using adjoint optimization techniques, have also been used to assess their performance in transient flow conditions. Particle image velocimetry measurements were performed in a towing tank to characterize the near wake development in the early transient stages. It has been observed that the flow first develops symmetric shear layers with primary eddies attracted toward the base of the body due to the flow suction generated by the accelerated motion. Eventually, the interaction between the upper and lower shear lay...

Fire in large-volume buildings poses separate and distinct challenges from compartmented spaces. In particular, the risk it poses on life safety is mostly due to the smoke it produces, its effects on the evacuation process, and how it can affect the firefighters when they approach the building to fight the fire and rescue the occupants. This is why smoke control in large-volume enclosures is of utter importance for life safety, property protection and business continuity. This research presents an experimental and numerical study of the smoke dynamics from four fire sources (combined heat release rate of 5.2 MW) with different ignition times and under transient ventilation conditions, inside a 20 m high cubic atrium. Temperature measurements in the plume and close to the walls have been recorded using 59 thermocouples. The data was used in the determination of the smoke layer interface height, with the least-square and the N-Percent methods. Results show that significantly worse conditions are induced by multiple sources than those in a single fire of equal power. The results have been obtained using the computational fluid dynamics code FDS (Fire Dynamics Simulator, v6.7.1). The comparison shows that in the far field the temperature predictions are accurate inside the smoke layer (10 m and 15 m) with discrepancies lower than 10%, whereas higher significant discrepancies were observed at the smoke layer interface, i.e. 5 m high, with discrepancies up to 20%. Furthermore, a grid analysis has been performed showing that grid resolutions, D*/?, based on the global HRR of the fire might be sufficient to predict the fire induced conditions far from the fire. The analysis confirmed the applicability of FDS to the assessment of the smoke dynamics under complex fire conditions away from flames. Ultimately, the present work shows the importance of considering fires with multiple sources due to the faster smoke production compared with single fires.

The authors want to acknowledge the Centro Tecnologico del Metal of Murcia for the use of their test rig, the Professor J. L. Torero, T. Steinhaus, C.Abecassis-Empis, P. Reszka, W. Jahn, from the University of Edinburgh, for their technical suggestions and supervision. Simulations have been carried out at the computational facilities of the Technological Research Services of the Technical University of Cartagena (SAIT) and the University of Jaen. This work has been supported by Ministerio de Educacion y Ciencia of Spain (Projects CT/G30572473, and FIT-020700-2004-25 and grant TRA2006-15015) and by the Junta de Andalucia of Spain (Project number P07-TEP-02693).

The calculation of the smoke layer interface height in case a fire breaks out in an atrium is determinant to make an appropriate fire safety system design. Most of the expressions used to calculate it assume no mass flow through the smoke layer interface. With this object a numerical model that simulate fire-induced thermal and fluid fields in an atrium using the finite volumes procedure code FLUENT has been developed. The model has been validated from new full-scale fire experimental tests performed at the 'Fire Atrium' of the Technological Metal Centre, Murcia, Spain. At the present work the experimental data from one fire experiment are shown. In this experiment an heptane pool fire placed at the centre of the floor was used, releasing an average heat of 1.8 MW. A comparison between one empirical expression commonly used and an experimental temperature criterion, both for computing the smoke layer interface height, with the one predicted by the model is performed. The model agrees better with the second one and shows a mass of air across the smoke layer interface should be taken into account.

The city of Lorca (Spain) was hit on May 11th, 2011, by two consecutive earthquakes of magnitudes 4.6 and 5.2 M w , causing casualties and important damage in buildings. Many of the damaged structures were reinforced concrete frames with wide beams. This study quantifies the expected level of damage on this structural type in the case of the Lorca earthquake by means of a seismic index /" that compares the energy input by the earthquake with the energy absorption/dissipation capacity of the structure. The prototype frames investigated represent structures designed in two time periods (1994-2002 and 2003-2008), in which the applicable codes were different. The influence of the masonry infill walls and the proneness of the frames to concentrate damage in a given story were further investigated through nonlinear dynamic response analyses. It is found that (1) the seismic index method predicts levels of damage that range from moderate/severe to complete collapse; this prediction is consistent with the observed damage; (2) the presence of masonry infill walls makes the structure very prone to damage concentration and reduces the overall seismic capacity of the building; and (3) a proper hierarchy of strength between beams and columns that guarantees the formation of a strong column-weak beam mechanism (as prescribed by seismic codes), as well as the adoption of countermeasures to avoid the negative interaction between non-structural infill walls and the main frame, would have reduced the level of damage from I v = l (collapse) to about /" = 0.5 (moderate/severe damage).

Forjado reticular Ensayo de laboratorio Fisuración distribuida del hormigón Leyes constitutivas en tensiones-deformaciones medias Elementos tipo fibra Elementos tipo capa r e s u m e n En este artículo se analizan distintas alternativas para modelar conexiones interiores forjado reticularpilar de hormigón armado y se propone una solución que con un coste computacional razonable proporcione resultados muy próximos a los experimentales. El modelo propuesto se valida numéricamente con los resultados obtenidos previamente de un ensayo de laboratorio realizado sobre un espécimen a escala 3/5 de la misma tipología estructural, sometido a ensayo cuasi-estático hasta el colapso. Para tal fin, se aplica la teoría avanzada de mecánica no lineal de hormigón armado sobre un modelo tridimensional de elementos finitos en análisis no-lineal: elementos tipo fibra para componentes unidimensionales y tipo capa para los bidimensionales. Los resultados principales de la simulación fueron: a) la obtención de la curva de capacidad mediante un análisis de empuje incremental (push-over) con control de desplazamientos; b) las curvas histeréticas en la losa, y c) los patrones de fisuras, logrando una concordancia revelada con los resultados experimentales.