6,818 research outputs found
Experiments of thermographic landmine detection with reduced size and compressed time
No full textInfrared thermography is a promising technique for the detection of buried landmines. Its effectiveness is not yet satisfactory, but it can presumably be improved by means of proper data-processing tools. The development of these tools, however, necessitates large amounts of reference data. On-field experiments are required to generate reference data, but they can be very demanding, since it is arduous to control the thermal problem outdoors and all over a whole day. In view of that, a method was developed to reproduce in the laboratory, with reduced size and duration, experiments of thermographic mine detection. The method was devised by the dimensional analysis of the governing equations, for which a generalized formulation is presented, and it was implement by a purposely built apparatus, which allows taking into account the directional properties of the solar radiation. A few test cases with reduced scale are reported here, to show the potential of the proposed experimental approach
Land-mine detection by infrared Thermography: reduction of the size and duration of the experiments
No full textThe effectiveness of infrared thermography applied to the detection of abandoned land mines is not yet acceptable. It can probably be improved, however, by computerized processing of the thermal images. This requires reference data, which must be provided mainly by experiments. A method is presented here, by which the heating and cooling cycles of a soil with a buried land mine can be replicated with reduced size and duration. The reference data acquired in the laboratory can be associated to realistic on-field tests by simply stretching the space and time scales. This will permit to reproduce indoors, quickly and effortlessly, the outdoor conditions of any place where the detection of buried land mines must be performed. In this paper, the general thermal problem is described, and the proposed method is comprehensively explained. The results of computer simulations and some laboratory tests are finally reported for validation
Mine detection by infrared thermography: reduction of size of the experiments
No full textA very promising technique for the detection buried land-mines is infrared thermography. In particular, the presence of a mine can be associated to a specific pattern in the temperature of the soil surface measured by a videothermographic camera. The pattern is induced by the interaction of the daily heating and cooling cycles with the thermal anomaly introduced in the ground by the mine.The specific effectiveness of the thermographic mine detection can be increased by exploiting computerized data-processing tools such as neural-networks, genetic algorithms, or the fusion of dual-band data, to enhance and identify the thermal signature of the mine. The development and ‘training’ of these tools, however, as well as the optimization of the detection equipment and procedure, require a large amount of reference data.Simulations are powerful tools to generate reference data, as they allow fast and inexpensive parametrical analyses. Unfortunately, computer models cannot take care of all the variables influencing a real-world problem and, furthermore, they need a proper calibration. On the other hand, performing parametrical analyses by on-field experiments can be long and challenging, since in an outdoor test environment and along the 24-hour long day period it is arduous to control selectively the phenomena that influence the thermal problem, especially the weather conditions.In view of this, the main objective of the present work is to develop a method by which the cycles of heating and cooling of the soil can be replicated in the laboratory with a reduced scale, either in time or in space, but obtaining measures that can be directly correlated to realistic on-field tests. The result is sought through the dimensional analysis of the equations governing the thermal problem, and it is verified by computer simulations and experiments
Scale reduction in modeling landmine detection by IR Termography
No full textA method has been proposed to reproduce in the laboratory experiments of infrared landmine detection with reduced length- and time-scale. In this work, the method is verified experimentally. Models of landmines are purposely built by a rapid prototyping technique. The surface response of the soil-landmine system is then monitored by an infrared camera. Preliminarily, the response measured above full-scale models is cross-checked against that measured above actual landmines. Full-scale and reduced-scale models are subsequently tested outdoors and in the laboratory, respectively. The measured distribution and time-evolution patterns of surface temperature are eventually compared, in order to assess the reliability of the scale reduction method
Analisi CFD dei campi di moto e di temperatura dell'aria in una cattedrale
No full textNel presente lavoro viene proposta un’indagine teorica e numerica sul campo di moto e sulla distribuzione della temperatura dell’aria all’interno della National Shrine of the Immaculate Conception, una cattedrale di imponenti proporzioni situata nel campus della Catholic University of America a Washington, D.C., U.S.A.Lo studio è finalizzato a valutare differenti modalità di riscaldamento dell’ambiente interno della cattedrale, e trae motivazione dal gran numero di edifici per il culto che presentano dimensioni e caratteristiche simili e dall’esigenza diffusa di ottimizzarne gli impianti di climatizzazione, in termini di benessere delle persone e di risparmio energetico.Dal punto di vista teorico, si propone un’analisi adimensionale del problema, basata sul numero di Rayleigh. Le simulazioni numeriche sono effettuate mediante il codice CFD industriale Fluent, prodotto da Fluent Inc., Lebanon, N.H., U.S.A
Experiments on scale reduction in infrared landmine detection
No full textA method has been proposed to reproduce in the laboratory the heating and cooling cycles of a soil with a buried land-mine. The method allows the length-scale and time-scale of the experiments to be drastically decreased. This is achieved by dimensional analysis of the thermal problem. A preliminary confirmation of the used approach was obtained with simplified tests [1-3].In the present work, the method is verified experimentally. Models of different types of land-mine are produced for this purpose. Full-scale and scaled-down models are built by a rapid prototyping technique, using materials with thermal properties similar to those of the actual land-mines.The response of the soil surface is monitored during the thermal cycles by an infrared camera. Preliminarily, the surface response measured above full-scale models is cross-checked against that measured above actual land-mines. Full-scale and scaled-down models are then tested outdoors and in the laboratory, respectively. The measured distribution and time-evolution patterns of surface temperature are eventually compared, in order to assess the reliability of the scale reduction method
Analysis of the impact of surface heat transfer on a new modification of the Angstroem’s method
No full textA new modification of the Angstroem’s method for thermal diffusivity measurement has been developed. This relies on the propagation of harmonic thermal waves with mean value equal to the ambient temperature. The diffusivity is evaluated by relatively simple processing of temperature data, acquired by infrared thermography.The evaluation is based on a mathematical model, in which the heat transfer coefficient at the specimen surface is assumed to be constant. This work is aimed at verifying that assumption. In particular, the effects of natural convection in air are investigated theoretically by numerical simulation. A strategy to improve the test procedure is finally outlined
Solar reflecting tile coverings for traditional South-European Buildings
No full textAn effective solution to summer overheating of buildings is provided by “cool roofs”. These are building coverings with high reflectance to solar radiation and high emittance in the infrared range. They have been investigated extensively in the U.S.A., where certification procedures have already been developed by independent bodies, and certified products are commercially available.Common cool roof products have white or very light colors. As a result, they are difficult to use in most ancient or traditional south-European buildings, which typically have steep-slope roofs covered by red clay tiles. On the other hand, in places like the historical centers of Italian and other Mediterranean cities the rooms immediately below the roof are often inhabited, so that the relatively low solar reflectance of tile coverings makes summer overheating a major problem. This can be effectively addressed by using tiles coated with “cool colors”, that is colors with the same spectral response of clay tiles in the visible, but highly reflecting in the near infrared range, which includes about half of solar radiation. Cool colors can yield the same visible aspect of common building surfaces, but much higher solar reflectance.In the aim of verifying the potential of cool color tile coverings, an investigation was started at the DIMeC. Materials for cool color coating were analyzed in the laboratory, verifying their radiation properties as a function of composition and pigment content. Prototypes of red roof tiles have been built using easily available materials with solar reflectance almost twice that of conventional tiles
Modellazione termica del dispositivo di scarico di motori a.c.
No full textSi presenta un modello matematico volto alla previsione delle temperature dei gas e delle temperature di parete di dispositivi di scarico dei gas combusti prodotti da motori ad accensione comandata. Il modello, pur nell'ambito delle forti semplificazioni in esso implicite, consente la previsione del comportamento termico dei condotti di scarico con sufficiente attendibilità, come comprovato da esperienze al banco, eseguite presso il Centro Ricerche FIAT di Orbassano - TO. La tecnica predittiva proposta può consentire un più rapido sviluppo di prototipi dei nuovi sistemi di scarico, atti a meglio soddisfare i limiti di emissione sempre più stringenti proposti dalle normative internazionali
Theoretical, numerical and experimental investigation of a one-side measurement technique for thermal diffusivity
No full textA modified Angstrom’s method for the measurement of thermal diffusivity in solid materials is presented, aimed at overcoming the limits of ordinary techniques with one-side measurements. The method requires a periodic thermal input to be supplied to the specimen, alternating heating and cooling stages. The thermal diffusivity is estimated by monitoring the temperature oscillations on the free surface of the specimen.The conditions at which a real three-dimensional test-system can be studied by means of a one-dimensional thermal model are investigated. Algorithms to estimate the thermal diffusivity are determined analytically and verified by numerical simulation. The method is finally validated by experimental measurements
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