Publicações

Long motorway tunnels equipped with two independent unidirectional galleries are usually provided with longitudinal ventilation. This ventilation scheme, when applied to smoke control, can generate significant pressure differences between both roadway galleries, which may have an impact on the use of transverse galleries (escape routes). This paper present two-case studies where the results of measure- ments of these pressure differences taken in Mara ?o and Gardunha tunnels allowed the assessment of relevant flow parameters, as the pressure loss coefficient of the entrance portal, the friction factor in the tunnel and the coefficient of installation of the jet fans. The assessed parameters were used in the steady-flow energy equation for a streamtube to predict the impact of pressure differences on the protection of trans- verse galleries (emergency exits) in the case of fire. The results show that the pre- dicted pressure in the fire road gallery increases upstream the location of the fire and decreases downstream that location, when taking the pressure profile of the flow without fire as a reference. The models show that predicted pressure differences between the two road galleries in case of fire may be within the interval [200 Pa; - 100 Pa] in Mara ?o tunnel and [12 Pa; - 48 Pa] in Gardunha Tunnel, while the mea- surements in the no fire case show that they lay within the interval [29 Pa; - 50 Pa] in Mara ?o tunnel and [- 13 Pa; - 35 Pa] in Gardunha Tunnel

A tunnel fire is a dangerous accident, which may lead to serious injuries and deaths. This work studies the flow of combustion products during naturally ventilated tunnel fires, i.e., without a mechanical ventilation system. In such an event, two stratified layers with opposing velocity directions are formed. The safety of tunnel users is compromised if the smoke, initially flowing in the upper layer, contaminates the lower one, which has been found to happen abruptly at a distance xc from the fire. This is caused by the cooling of the jet leading to a large enough decrease in momentum for the smoke to be entrained by the lower layer. Natural ventilation may be an effective and inexpensive smoke control strategy if the fire-to-portal distance is shorter than xc. However, there is a lack of research to predict under which conditions this occurs and how xc is influenced by factors such as natural wind. An open-source Computational Fluid Dynamics (CFD) code, fireFoam, was used to conduct Large Eddy Simulations (LES) of naturally ventilated tunnel fires. The numerical model was validated by performing a simulation of a large-scale tunnel fire test. Additionally, 7 fire scenarios with varying wind velocities were simulated. The contamination distance xc was found to decrease for higher wind velocities. Furthermore, a simple semi-analytical model was employed to obtain quick estimates of xc, by calculating ceiling jet properties using balance equations and empirical correlations. Model coefficients were calculated using the CFD results.

Abstract: Vertical air curtains are often used to separate two different zones to reduce contaminant transfer or even to provide aerodynamic sealing from one zone to the other. In this isothermal full-size experimental research work, the contaminant transfer between zones is reduced using an air extraction from the “contaminated” compartment and an air curtain. This work correlates the minimum exhaust air flow rate required to reach the aerodynamic sealing at the opening connecting two different zones with the jet nozzle velocity for small nozzle thicknesses (5 mm, 10 mm and 16 mm), particularly for Reynolds numbers below 3800. Following the experimental study, a general physical law that relates the jet parameters (angle, nozzle thickness and jet velocity at the nozzle) with the average velocity through the opening (for the condition of acceptable contaminant tightness) was obtained. The results showed that the average velocity of the flow across a door protected by an air curtain required to keep the aerodynamic sealing varies linearly with Re. The slope, however, is different below and above Re = 3820.

The Indoor Environment Quality study takes on a very significant challenge when analyzed, mainly, in buildings that encompass a more sensitive and susceptible type of population, as is the case of children. To comply with a set of requirements, namely the concentration of pollutants and the conditions of hygrothermal comfort, is a necessary condition to keep an interior environment suitable for the permanence of the occupants. A research project, that studied Indoor Environment Quality in four buildings which hold nurseries and kindergartens, was carried out in two cities in central Portugal, Viseu and Covilhã. The following main conclusions may be drawn: most compartments are not comfortable in terms of ambient temperature, but the relative humidity has reasonable values. Air change rates generally have low values and the measured pollutants have worrying values. Based on the observed problems and reached conclusions, some recommendations are proposed.

Night natural ventilation systems have been receiving increased attention in recent years because of their energy saving potential and environmental protection when used in passive instead of active cooling. A novel system recently proposed for cooling the building concrete slab is studied numerically in the present work. The system relies only on night ventilation as a means for cooling down the structure of the building. It consists of a new type of suspended ceiling with a peripheral gap between it and the walls combined with the positioning of the air supply and extraction grilles between the ceiling slab and the suspended ceiling. This study focuses on the use of Computational Fluid Dynamics (CFD) to predict the airflow and thermal performance of this strategy for an office room. Ansys-Fluent is used to perform the calculations both for a reduced and a full-scale room. Transient simulations were performed for a period of 24 h and the predictions for the reduced-scale model were validated by experiments under different operating conditions. The results show that the mathematical and numerical models provide satisfactory predictions of the temperature evolution in the reduced-scale model, allowing the analysis to be extended for full scale. The predictions for the office room at full scale confirm the effectiveness of the proposed cooling technique, revealing that the air peak temperature during the day is lower, as well as the temperature of the slab and the temperature of the air in the plenum during the night.

Abstract. Night natural ventilation systems have been receiving increased attention in recent years because of their energy saving potential and environmental protection when used in passive instead of active cooling. A recently proposed novel system for cooling the building concrete slab is studied numerically in the present work. It consists of a new type of a Suspended Ceiling (SC) with a peripheral gap between it and the walls, combined with the positioning of the air supply and extraction grilles between the ceiling slab and the SC. The system relies only on night ventilation as a means for cooling down the structure of the building. This study focuses on the use of Computational Fluid Dynamics (CFD) to predict the airflow and thermal performance of this strategy and it is applied to a full scale office room. The calculations show that a SC with a gap can reduce the difference between the average temperatures at the end of the heating and the end of the cooling periods by 25% compared with the case of a full covered slab room scenario (tight SC). CFD proved to be a useful and accurate tool to predict indoor conditions in buildings.

An air curtain is used to ensure an adequate separation between two compartments that is aimed torestrict, a clean one and a contaminated one. The air curtain performance is improved with the use of anair extraction from the “contaminated” compartment. The aerodynamic sealing of an optimized aircurtain is assessed regarding particulate matter. The evaluation using visual assessment of the aerody-namic sealing using a cold smoke source is validated against PM 10 detection.It is shown that the air curtain presents a good aerodynamic sealing for the particulate of PM10 and PM2.5classes and that the visual assessment method can lead to similar results. An equation was obtained with aview to be used to predict the level of aerodynamic sealing of the air curtain when the exhaust ratebecomes too low. Another equation was obtained for predicting the average velocity through the doorprotected by the air curtain required to obtain an aerodynamic sealing, as a function of the jet parameters(nozzle average velocity and thickness). These test results prove that the air curtain, complemented withan air exhaust from the “contaminated compartment”, is suitable to provide an acceptable aerodynamicsealing for the particulate matter.

Abstract: Controlling air quality is of the utmost importance within today's buildings. Vertical air curtains are often used to separate two different climatic zones in order to reduce heat transfer. This research work proposes an air curtain aimed to ensure a proper separation between two zones, a clean one and a contaminated one, which is to be used together with an air extraction from the ?contaminated? compartment. A CFD parametric study was carried out in order to assess the optimal parameters for achieving the aerodynamic sealing of the air curtain. The software OpenFOAM was used to carry out the simulations. This paper presents the numerical validation of the computational fluid dynamics model for contaminant control applications and the final simulation results. Furthermore, it refers to the test results obtained in the framework of previous research, which were obtained in both small scale and full size testing, and demonstrates that the simulation results are coherent with the experiments. This research work shows that, when properly implemented, the air curtains provide the adequate aerodynamic sealing to maintain the air contaminants within the ?contaminated? compartment. The appropriate performance can be obtained for nozzle speeds as low as 1 m/s and for a nozzle thickness of 10 mm. The best performance is obtained when the extraction flowrate of the ?contaminated? compartment corresponds to the total flowrate entrained by the air curtain from the ?non-contaminated? side.

This paper analyses the possibility of using air curtains to prevent smoke flow from fire compartments. Full size experiments have been carried out and several relevant conditions to assess smoke-tightness have been tested. The smoke temperature during the tests was ranging from 182ºC to 351ºC, the angle measured between the curtain axis and the vertical plane was ranging from 18º and 26º, the nozzle thickness was ranging from 0.017 m to 0.045 m and the velocity at the nozzle was ranging from 8.3 m/s to 19.9 m/s. During the tests, the air curtain’s nozzle was positioned horizontally at the top of a permanent opening (door). With this configuration, we obtained an approximately vertical downward jet through the used opening. This paper includes the final results of the tests and develops an analytical tool for predicting the performance of air curtains. It was concluded that it is possible to achieve smoke-tightness, provided that the adequate plane jet parameters and the compartment’s smoke exhaust are correctly adjusted. According to this analysis, the smoke-tightness limit corresponds to equation B=??P?_a???P?_s =-0.30 u_a?u_(a_min) +1.25 (with 1.30? u_a?u_(a_min) ?1.67).

Most office buildings are designed to be ventilated and cooled using mechanical systems. However, in a temperate climate, passive ventilation and cooling techniques can reduce energy consumption when the outdoor temperatures are favourable, e.g., at night. Nevertheless, decorative components like the suspended ceiling (SC) contribute to insulation, preventing the desired thermal exchange with the slab. This work investigates an innovative solution to the optimization of the night cooling phenomenon by using a SC with a peripheral gap and taking advantage of the plenum formed by the space between the slab and the SC for cooling purposes. The experiments were carried out on a reduced scale model. It was found that a SC with a gap allows part of the heat dissipated in the room during the occupation period to be used to heat the slab, thus reducing the air temperature during the day, in comparison with a conventional SC with no gap. Moreover, a SC with a gap, and with supply and extraction slots placed above it, improves the air cooling during the night, and reduces the temperatures in the occupation zone during the following day, in comparison with a conventional SC with no gap, and with the ventilation slots located below it.

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Os túneis rodoviários longos dotados de duas galerias unidirecionais independentes são normalmente dotados de ventilação longitudinal. Este esquema de ventilação, quando aplicado ao controlo do fumo, pode gerar diferenças de pressão significativas entre ambas as galerias rodoviárias, o que pode ter impacto na utilização das galerias transversais do túnel. Nesta comunicação são apresentados resultados de medições dessas diferenças de pressão em túneis que serviram de referência experimental para validar um modelo analítico de previsão do escoamento em túneis. É realizada uma análise de sensibilidade desse modelo que permite evidenciar o impacte que essas diferenças de pressão podem ter na utilização das galerias transversais.

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SUMMARY Alqueva multipurpose project, located in the Alentejo region (southern Portugal), is an important project, which main objectives are: the creation of a strategic water reserve in a region with a trend to desertification; the water supply to the population and to irrigation; and the production of electricity. For the project development two main structures were erected: Alqueva and Pedrógão dams. Beyond of its benefits these two dams are also a potential risk for the downstream valley: the probability of failures occurrence in their water retaining capabilities is very low but still possible. In contemporary society potential dam failures as well as the public pressure for a safer environment make mandatory the development of risk mitigation instruments as emergency plans and early warning systems. The paper presents the main characteristics of Alqueva and Pedrógão dams and a risk analysis for the dam-break flood prone area downstream. Finally, it focuses on the technical details of the early warning solution developed to improve the people safety in the nearest zones of the downstream valley.

A presente publicação foi elaborada a fim de constituir apoio didáctico ao curso de “Elementos de Sistemas e de Análise e Processamento de Sinais” leccionado no Laboratório Nacional de Engenharia Civil (LNEC), curso primordialmente dirigido a licenciados em ramos de engenharia que, por qualquer razão, não tenham anteriormente recebido formação específica sobre esta área do conhecimento. Como o nome sugere, o curso tem como objectivo tratar dos “elementos” da teoria dos sistemas e da análise e processamento de sinais. Uma formação detalhada sobre estas matérias implicaria uma ocupação excessiva, logo desmotivadora, face ao tempo que profissionais de outros domínios normalmente dispõem para uma formação de pós-graduação. Por outro lado, uma formação do tipo de sensibilização para um dado assunto, com destaque apenas para aspectos do género de “o que é” e “para que serve”, estaria, neste caso, para aquém das intenções delineadas. Optou-se assim por algo de intermédio visando rasgar horizontes que conduzam a um posterior aprofundamento. São abordadas as noções fundamentais, os conceitos de base e os aspectos essenciais relacionados com a teoria dos sistemas e com a análise e processamento de sinais; procurou-se assegurar que o formalismo matemático, obviamente necessário, seja utilizado de modo a não se sobrepor e a não interferir com a apreensão das noções e interpretações físicas. Dada a sua actual importância, é posta ênfase na análise digital. No entanto, por razões didácticas, começa-se por abordar os conceitos numa perspectiva contínua (analógica), transpondo-os, em seguida, para a perspectiva discreta (digital).

O presente relatório apresenta um procedimento para a calibração de higrómetros de espelho elaborado no LCAM/LNEC.

O presente relatório apresenta um procedimento para a calibração de termohigrógrafos de tambor elaborado no LCAMILNEC.

O presente relatório apresenta um procedimento para a calibração de termohigrógrafos, termohigrómetros e cadeias de medição com sensores de humidade relativa, elaborado no LCAMILNEC.

O presente relatório apresenta um procedimento para a calibração de termopares elaborado no LCAMILNEC.