A series of reduced-scale tunnel fire tests were carried out to investigate ceiling smoke temperature attenuation in a naturally ventilated tunnel under double fire sources of various sizes and distances. Experimental results showed that the interactions between the two flames affect excess gas temperature attenuation. Under a given fire size, the ceiling smoke temperature gradually decays more slowly when the spacing between the two fire sources is longer and then goes through a steady stage. Moreover, for different smoke spread regions (i.e., the radial ceiling jet region, the shooting flow region and the one-dimensional tranquil flow region), the ceiling smoke temperature attenuation trends are different. Models of non-dimensional excess ceiling smoke temperature attenuation in the radial ceiling jet and shooting flow regions were proposed using the plume radius at the ceiling level as the characteristic length scale. In the one-dimensional tranquil flow region, an exponential model was developed by theoretical analysis to predict non-dimensional ceiling smoke temperature. The lumped attenuation coefficient k was observed to decrease first and then approach a relatively stable value with an increasing fire spacing. This study is of great significance to the design and protection of tunnel structures under multiple fire sources.
The Australian prefabricated construction market has been developing rapidly in recent years. New prefabrication-related technologies, materials, systems and services are also emerging in the current Australian market. Although some studies have been undertaken to explore the benefits and challenges of implementing prefabrication in Australia over the past 15 years, they do not reflect the recent changes in the industry. Therefore, this study aims to fill this gap and identify the major changes in the current Australian prefabricated construction industry from industrial perceptions. Through literature reviews and industry interviews, factors reflecting major changes in the current Australian prefabricated construction, including prefabrication industry development, emerging benefits and challenges, were identified and discussed in this study. The challenges identified from interviews were classified into eight aspects related to feasibility, design, manufacturing, transportation, on-site construction, standardisation, skills and knowledge, finance and market. Furthermore, 21 recommendations and related key responsible parties were identified to tackle these challenges. The findings will provide useful references for various stakeholders to have a better understanding of the current prefabrication industry development in the Australian context and re-think how to adapt to future changes for the uptake of prefabricated construction in Australia.
No abstract is provided for this article.
A Collins formula method with a scaling factor between the target-and source-plane has been proposed for the laser propagation in the optical system design, which can be used to evaluate the laser optical system performance and the tolerance analysis. The laser propagation in the optical systems can be calculated by the Collins integral formula, and an angular spectrum method has been derived by coordinate substitution. A scaling factor m is introduced to make the choice of the observation-plane more flexibility and the calculation more accurate. The laser optical system has been designed, and its tolerance analysis is conducted by the Angular-Spectrum method. The evaluating criterion is the laser spot radius in the far field, which is defined by 86.5% power in bucket (PIB). The radius of the laser spot in 90m between 0.8mm and 1.4mm with the expectation of 0.92mm is calculated by the tolerance analysis, and the experimental result is 1.01mm. In the distance of 47m, the radius is between 0.42mm and 0.73mm with the expectation of 0.48mm calculated by the tolerance analysis, the experimental result is 0.46mm. The experiment agrees the result of the tolerance analysis well. The focal shift for laser propagation in the optical systems is validated. The experiment results confirm the calculation and it proved the use of the method in laser focus optical system design.
Graph Neural Networks (GNNs) have exhibited remarkable efficacy in learning from multi-view graph data. In the framework of multi-view graph neural networks, a critical challenge lies in effectively combining diverse views, where each view has distinct graph structure features (GSFs). Existing approaches to this challenge primarily focus on two aspects: 1) prioritizing the most important GSFs, 2) utilizing GNNs for feature aggregation. However, prioritizing the most important GSFs can lead to limited feature diversity, and existing GNN-based aggregation strategies equally treat each view without considering view quality. To address these issues, we propose a novel Multi-View Graph Neural Network with Reliable Structural Enhancement and Aggregation (RSEA-MVGNN). Firstly, we estimate view-specific uncertainty employing subjective logic. Based on this uncertainty, we design reliable structural enhancement by feature de-correlation algorithm. This approach enables each enhancement to focus on different GSFs, thereby achieving diverse feature representation in the enhanced structure. Secondly, the model learns view-specific beliefs and uncertainty as opinions, which are utilized to evaluate view quality. Based on these opinions, the model enables high-quality views to dominate GNN aggregation, thereby facilitating representation learning. Experimental results conducted on five real-world datasets demonstrate that RSEA-MVGNN outperforms several state-of-the-art GNN-based methods.
No abstract is provided for this article.
Solar chimney has been primarily utilized for natural ventilation, but its application to smoke exhaustion was rarely explored. A 1:3 reduced-scale test platform with a dimension of 1.5m × 1.5m × 0.9m (height) was used to optimize solar chimney under natural ventilation and smoke exhaustion, considering four influencing factors, including height of cavity inlet from the floor (0.2–0.8m), cavity depth (2.5–17.5cm), solar radiation (400–1200W/m2), and fire size (6.8–15.8kW). Both natural ventilation and smoke exhaustion follow the same trend along the air inlet height and cavity depth, which confirms its viability on smoke exhaustion under fire condition without compromising the performance of natural ventilation. Experimental results suggested a chimney configuration of 0.5m high air inlet and 12.5cm cavity depth with optimized functions. External radiation shows obvious benefits in enhancing natural ventilation, while its influence on smoke exhaustion is limited. An empirical model was developed to predict the flow rate under normal and fire conditions. The outcomes of this study provide technical guidance for the design of solar chimney under scenarios of both natural ventilation and smoke exhaustion.
Maximum smoke temperature beneath the tunnel ceiling is always one of determining factors of the safety assessment of a tunnel fire. Although many studies have been undertaken, the double long-narrow space fire, such as in a subway tunnel with a train on fire, has been rarely considered and investigated. To benefit the fire safety assessment, the smoke temperature characteristics beneath the tunnel ceiling under various fire sizes and locations were then investigated in this study both numerically and theoretically. A new parameter called dimensionless offset distance ( d ∗ ) was proposed to address the influences of fire locations on fire behaviors. It was then known, as the d ∗ keeps increasing, the maximum temperature moves from above fire source to above the train end. The change of the maximum temperature along with d ∗ can be divided into two regions, namely Region I ( 0 ≤ d ∗ < 0.46 ) and Region II ( 0.46 ≤ d ∗ < 1 ). A new empirical model was also developed to predict the maximum temperature rise considering fire size and fire location. The smoke temperature rise was found attributing to the increased level of smoke accumulation inside the train, which can be characterized by factor a f . Critical a f for the transition from Region I to II was found between 0.145 and 0.165. This study will provide a reference for the relevant detection, protection and fire rescue in tunnel fires.
No abstract is provided for this article.
No abstract is provided for this article.
The interaction between solar chimney and wind were investigated numerically and theoretically. A higher wind velocity does not represent a better performance, which depends on wind angle (α), which is the angle between wind direction and outward normal of the wall with the window. A windward situation (0°≤α < 90°) is suggested, where the scenario with α = 0 shows the best performance. It is surprising that the leeward scenario with α = 180° presents a slightly positive effect, but scenarios with 90°≤α < 180° show negative effects. Window area (A w ) presents a positive effect on the airflow rate, which shows a linear relationship with A w 0.34 and A w 0.46 when the α is 0° and 45°, respectively. A theoretical model was developed to predict the airflow rate under α < 90°, where for 90°≤α < 180° the related predictions can be based on the scenario without wind. The predictions are fitting quite well with numerical results. Critical wind velocity was also proposed to represent the wind velocity which overrules the performance that solar chimney is no longer dependent on solar radiation but wind. The critical wind velocity keeps increasing under higher solar radiation, where for the analysed model it increases from 0.65 to 1.55 m/s when solar radiation rises from 100 to 1300 W/m2.
The interaction between solar chimney and wind was investigated numerically and theoretically. A higher wind velocity does not represent a better performance, which depends on wind angle (α), which is the angle between wind direction and outward normal of the wall with the window. A windward situation (0 degrees ≤α<90degrees) is suggested, where the scenario with α=0 shows the best performance. It is surprising that the leeward scenario with α=180 degrees presents a slightly positive effect, but scenarios with 90≤α<180 degrees show negative effects. Window area (A w) presents a positive effect on the airflow rate, which shows a linear relationship with A w 0.34 and A w 0.46 when the α is 0 and 45 degrees, respectively. A theoretical model was developed to predict the airflow rate under α<90 degrees, where for 90 degrees ≤α<180 degrees the related predictions can be based on the scenario without wind. The predictions are fitting quite well with numerical results. Critical wind velocity was also proposed to represent the wind velocity which overrules the performance that solar chimney is no longer dependent on solar radiation but wind. The critical wind velocity keeps increasing under higher solar radiation, where for the analyzed model it increases from 0.65 to 1.55m/s when solar radiation rises from 100 to 1300W/m2.
