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Povzetek: A spatio-temporal video enhancement of a small-scale pool fire is performed to address the typically low spatial resolution and frame rate of inexpensive infrared (IR) cameras. Improving image quality can increase the applicability of low-cost thermal cameras for certain research tasks and analyses. The spatial resolution and frame rate are doubled, from 310 × 250 pixels (px) to 620 × 500 px, and from 25 frames per second (fps) to 50 fps, as well as from 50 fps to 100 fps. Spatial resolution enhancement is achieved using super-resolution methods based on deep learning, employing several pre-trained models: Fast Super-Resolution CNN (FSRCNN), Efficient Sub-Pixel Convolutional Network (ESPCN), Enhanced Deep Super-Resolution (EDSR), Laplacian Pyramid Super-Resolution Network (LapSRN), and Real-ESRGAN. The footage consists of an n-heptane pool fire recorded using a mid-wave infrared (MWIR) FLIR X6981 HS InSb camera. EDSR provides the best performance for both purely resized images and images subjected to complex degradation. For temporal enhancement, a pre-trained frame interpolation model, FLAVR (FlowAgnostic Video Representation), is used. The resulting interpolated frames appear realistic and preserve the overall flow direction and shape of the flame. The interpolated frames are compared with ground-truth data to validate the accuracy of the temporal enhancement.
Ključne besede: image processing, thermal camera, machine learning, pool fire
Objavljeno v DiRROS: 15.06.2026; Ogledov: 100; Prenosov: 70
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Povzetek: With the rise of performance-based structural fire design, understanding the behaviour of materials during both the heating and cooling phases of a fire has become essential. Traditionally, research has focused on the heating phase, resulting in limited data on material properties during cooling, in particular for the free thermal strain of concrete. This gap is critical, as free thermal strain significantly influences load redistribution in reinforced concrete structures. Two experimental campaigns were conducted to expand the available data: one using the UGent HIFREP (‘High Intensity Fast-Response Electric Radiant Panel’) and the other employing an electric furnace. The first test campaign provided an extensive dataset on the residual thermal strain, whereas the time- consuming furnace tests provided data for the entire fire event (heating and cooling). These datasets were used to update an existing model through Bayesian inference, coherently integrating the new information. The outcome is a comprehensive probabilistic model that accurately captures the free thermal strain behaviour of concrete throughout both heating and cooling, allowing for a full reliability-based evaluation of concrete structures in fire.
Ključne besede: concrete, cooling, free thermal strain, fire safety, structural fire engineering, experiments, bayesian inference
Objavljeno v DiRROS: 10.03.2026; Ogledov: 329; Prenosov: 70
Celotno besedilo (1,45 MB)
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Povzetek: Fire resistance tests rely on the use of standardized furnaces to apply specific thermal boundary conditions to assess the performance of construction materials and systems in fire conditions. However, these tests are very expensive and encounter challenges related to repeatability and uncertainties in establishing thermal boundary conditions. Moreover, their incapacitance to tailor experiments hinders advancements in understanding structural behaviour during fire exposure. In this work, a novel type of radiant panel, that operates on electricity, is introduced: the High-Intensity Fast-Response Electric radiant Panel (HIFREP). This innovation offers enhanced sustainability performance while ensuring more precise control over thermal boundary conditions. By eliminating the need for gas combustion, the panel can be used in a traditional structural testing lab to investigate non-combustible materials (e.g. concrete), without requiring extraction hoods and other provisions. The presented electric radiant panel system represents a significant step forward from fire resistance furnace testing.
Ključne besede: radiant panel, fire testing, heat transfer, radiation, heat flux, fire safety, thermal boundary conditions
Objavljeno v DiRROS: 19.12.2024; Ogledov: 1186; Prenosov: 597
Celotno besedilo (1,01 MB)
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Povzetek: Data from thermocouple (TC) measurements play a pivotal role in fire safety science and engineering studies. It is well-known that there are deviations from the actual local gas temperature and many studies have led to the development of correction factors. The present study focuses on these deviations inside compartments through a systematic series of CFD simulations, performed with Fire Dynamics Simulator (FDS), version 6.8.0. A canonical cubic box is used as geometry. This allows for the demonstration of the impact of the presence of smoke, with variable optical thickness, on the TC data as retrieved from FDS. Significant differences are observed between TC measurements and local gas temperatures. Corrections as developed for TC measurements in open atmospheres cannot be readily applied in compartment configurations, where smoke properties change both spatially and temporally.
Ključne besede: thermocouple measurements, CFD simulations, heat transfer, compartment fires, cooling, fire dynamics, FDS
Objavljeno v DiRROS: 28.10.2024; Ogledov: 1158; Prenosov: 451
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Povzetek: The main characteristics of the cooling phase of post-flashover compartment fires are studied using a simplified first-principles heat transfer approach to establish key limitations of more traditional methodologies (e.g., Eurocode). To this purpose, the boundary conditions during cooling are analysed. To illustrate the importance of a first-principles approach, a detailed review of the literature is presented followed by the presentation of a simplified numerical model. The model is constructed to calculate first-order thermal conditions during the cooling phase. The model is not intended to provide a precise calculation method but rather baseline estimates that incorporate all key thermal inputs and outputs. First, the thermal boundary conditions in the heating phase are approximated with a single (gas) temperature and the Eurocode parametric fire curves, to provide a consistent initial condition for the cooling phase and to be able to compare the traditional approach to the first- principles approach. After fuel burnout, the compartment gases become optically thin and temperatures decay to ambient values, while the compartment solid elements slowly cool down. For simplicity, convective cooling of the compartment linings is estimated using a constant convective heat transfer coefficient and all linings surfaces are assumed to have the same temperature (no net radiative heat exchange). All structural elements are assumed to be thermally thick. While these simplifications introduce quantitative errors, they enable an analytical solution for transient heat conduction in a semi-infinite solid that captures all key heat transfer processes. Comparisons between the results obtained using both approaches highlight how, even when considering the same fire energy input, the thermal boundary conditions according to the Eurocode parametric fire curves lead to an increase energy accumulated in the solid after fuel burnout and a delay in the onset of cooling. This is not physically correct, and it may lead to misrepresentation of the impact of post-flashover fires on structural behaviour.
Ključne besede: cooling phase, fire decay, fire dynamics, compartment fires, structural fire engineering, fire safety
Objavljeno v DiRROS: 15.04.2024; Ogledov: 1891; Prenosov: 898
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