المؤلفون: Soares Frazao, Sandra, Franzini, Fabian, Linkens, Jérémy, Snaps, Jean-Charles, River Flow 2018

المساهمون: UCL - SST/IMMC/GCE - Civil and environmental engineering

مصطلحات موضوعية: Porosity models, experiments, wave propagation speed, energy dissipation

الوصف: Porosity-based model rely on the assumption that an urban area can be compared to a porous medium, where the porosity is defined as the ratio between the actual area available to the flow, i.e. not occupied by buildings, and the total area of the considered urban environment. In classical single-porosity models, the resulting value of the porosity parameter is considered as constant and accounts essentially for the reduced water storage capacity and reduced space available for the flow. As a consequence, the source term involving the porosity parameter only accounts for a local head loss at the entrance and at the exit of the urban area. Therefore, the head losses occurring inside the urban area are accounted for using drag-type source terms. In the present work, we tested different definitions of the porosity parameter, showing the benefits of accounting for areas with distributed porosity based on the actual layout of buildings and streets. This formulation is still compatible with the basic idea of porosity-based model, i.e allowing for the use of coarse computational meshes instead of refined meshing of the urban area.

العلاقة: boreal:203035; http://hdl.handle.net/2078.1/203035Test; urn:EISSN:2267-1242

الإتاحة: https://doi.org/10.1051/e3sconf/20184006040Test
http://hdl.handle.net/2078.1/203035Test

المؤلفون: Renaudin, Olivier

المساهمون: UCL - SST/ICTM/ELEN - Pôle en ingénierie électrique, UCL - Ecole Polytechnique de Louvain, Oestges, Claude, Vandendorpe, Luc, Vanhoenacker, Danielle, Louveaux, Jérôme, De Doncker, Philippe, Mecklenbräucker, Christoph, Haneda, Katsuyuki

مصطلحات موضوعية: Vehicle-to-vehicle, Radio wave propagation, MIMO channel measurements, MIMO channel modeling, Non-stationarity, Channel characterization, GSCM

الوصف: In vehicular environments, the scattering environment can change very rapidly, owing to the mobility of the Tx and Rx vehicles, the relatively low height of the antennas and the potentially large number of scatterers in the surrounding environment. Vehicular radio propagation channels thus differ significantly from those of other wireless cellular networks, so that dedicated measurement campaigns and realistic radio propagation channel models are required to fully exploit their potentialities. The main contributions of this thesis are summarized as follows: - Two measurement campaigns of MIMO vehicular radio propagation channels were conducted at 5.3 GHz, - The validity of the WSS and US assumptions is assessed using the CMD, which characterizes the amount of change in the spatial structure of MIMO radio propagation channels. Stationarity distances and frequency bandwidth are 10 to 40 m long and 40 to 50 MHz wide, respectively, depending on the variability and richness of the scattering environment, - The non-stationary fading statistics are characterized stochastically, in terms of Ricean K-factor and RMS delay spread. Their time- and space-variations are strongly related to changes in the richness of the scattering environment and on the presence (or not) of a strong LoS component. They are modeled by multi-modal Gaussian distributions, - A vehicular GSCM is proposed, in which each scatterer is defined and characterized separately: the radio wave propagation with simplified ray-tracing tools and the scattering aspects with a classical fading model. The diffuse scattering is modeled in a purely stochastic manner. The GSCM is then completely parameterized and validated for SISO systems. ; (FSA - Sciences de l'ingénieur) -- UCL, 2013

العلاقة: boreal:133572; http://hdl.handle.net/2078.1/133572Test

الإتاحة: http://hdl.handle.net/2078.1/133572Test

المؤلفون: De Wilde, Juray, Constales, Denis, Heynderickx, Geraldine J., Marin, Guy B.

المساهمون: UCL - FSA/MAPR - Département des sciences des matériaux et des procédés

المصدر: International Journal of Multiphase Flow, Vol. 33, no. 6, p. 616-637 (2007)

مصطلحات موضوعية: linear wave propagation speed, mixture speed of sound, filtering, gas-solid flow, modeling, eigenvalue analysis

الوصف: The propagation speeds of linear waves in gas-solid suspensions depend strongly on the solids volume fraction and the wave frequency. The latter is due to gas-solid momentum transfer and allows a simple test on filtered gas-solid momentum transfer models. Such models may predict linear wave propagation speeds different from those obtained with the nonfiltered model at wave frequencies higher than the filter frequency, but not at wave frequencies lower than the filter frequency. For the filtered drag, an effective drag coefficient approach is shown to alter the linear wave propagation speeds in the entire wave frequency range, independent of the applied effective drag coefficient. Furthermore, as the effective drag coefficient decreases, the high frequency linear wave propagation speeds are gradually introduced at lower wave frequencies. For the filtered momentum transfer due to the correlation between the solids volume fraction and the gas phase pressure gradient, the behavior of an apparent added mass closure model and an apparent history force closure model are investigated. An apparent added mass introduces the filter frequency linear wave propagation speeds to frequencies higher than the filter frequency. The linear wave propagation speeds for wave frequencies lower than the filter frequency are, however, not altered. Furthermore, an apparent added mass introduces no intrinsic wave frequency dependence in the linear wave propagation speeds, in agreement with its source term in the non-filtered model. Hence, the frequency dependence of the linear wave propagation speeds at frequencies lower than the filter frequency is still to be provided by a drag type term. As such, the behavior introduced by an apparent added mass is acceptable for filtered models. Also, to a certain extent, an apparent added mass can restore the linear wave propagation speed behavior at wave frequencies lower than the filter frequency altered by an effective drag coefficient approach. The reformulation of the apparent added mass in terms ...

العلاقة: boreal:37528; http://hdl.handle.net/2078.1/37528Test; urn:ISSN:0301-9322; urn:EISSN:1879-3533

الإتاحة: https://doi.org/10.1016/j.ijmultiphaseflow.2006.12.003Test
http://hdl.handle.net/2078.1/37528Test

المؤلفون: Stouffs, Pascal, Giot, Michel

المساهمون: UCL - SST/IMMC/TFL - Thermodynamics and fluid mechanics

المصدر: European Journal of Mechanical and Environmental Engineering, Vol. 45, no.1, p. 11 - 18 (2000)

مصطلحات موضوعية: wave propagation, viscoelactic line, propagation modes, unsteady turbulent flow

الوصف: Small amplitude axisymmetric sinusoidal waves in an orthotropic, viscoelastic, rough pipe carrying a compressible liquid in turbulent flow are considered. The wall behaviour is described after Kuiken (1984) and the turbulent flow is described by means of an eddy viscosity profile model. We use a four-region model presented by Ohmi & Usui (1976), slightly modified in order to take into account the wall roughness. A one-dimensional dispersion equation is derived, which can predict the two lowest modes of propagation for waves of low frequency. The effects of Reynolds number, pipe roughness or wall viscoelasticity on phase velocity and attenuation factor are presented.

العلاقة: boreal:196545; http://hdl.handle.net/2078.1/196545Test; urn:ISSN:1371-6980

الإتاحة: http://hdl.handle.net/2078.1/196545Test

المؤلفون: Van Hauwaert, A, Thimus, Jean-François, Delannay, Francis

المساهمون: UCL - FSA/MAPR - Département des sciences des matériaux et des procédés

المصدر: Ultrasonics, Vol. 36, no. 1-5, p. 209-217 (1998)

مصطلحات موضوعية: Concrete, Steel Fibre-reinforced Concrete, Ultrasonic Wave Propagation, Non-destructive Testing

الوصف: Cubes made of steel fiber reinforced concrete (SFRC) were progressively sawed, while recording the ultrasonic parameters between the saw-cuts. The waves were analyzed in terms of ultrasonic wave velocity, peak amplitude and wave energy. Different relative positions between transducers and notch were considered. It was found that a relation between the ultrasonic parameters and the notch length could be drawn according to the layout of the transducers: the energy and amplitude drop once the portion of material between both transducers is diminished by sawing, whilst the velocity only changes once this whole portion of material has been cut out. The findings were then used to follow the crack growth of a SFRC beam during a bending test. The propagation of ultrasonic compression waves through the samples was recorded at regular time intervals during the tests. The interpretation of the signals was in this case complicated due to the facts that micro-cracking occurred, that the macro-crack was much thinner than a saw-cut and that it was moreover bridged by fibres. It appeared that in this case both peak amplitude and energy dropped before the onset of a visible macro-crack, because of extensive micro-cracking, while the velocity only changed after considerable crack growth. (C) 1998 Elsevier Science B.V.

العلاقة: boreal:62505; http://hdl.handle.net/2078.1/62505Test; urn:ISSN:0041-624X; urn:EISSN:1874-9968

الإتاحة: https://doi.org/10.1016/S0041-624XTest(97)00129-7
http://hdl.handle.net/2078.1/62505Test

المؤلفون: vandeKamp, MMJL, Tervonen, JK, Salonen, ET, Vanhoenacker-Janvier, Danielle, Vasseur, H., Ortgies, G

المساهمون: UCL

المصدر: Electronics Letters, Vol. 32, no. 18, p. 1650-1652 (1996)

مصطلحات موضوعية: satellite links, tropospheric electromagnetic wave propagation, radiowave propagation

الوصف: Otung and Evans presented some results of slant path scintillation measurements from Sparsholt (UK) which indicate that tropospheric scintillation is dependent on polarisation angle. However, results from Kirkkonummi (Finland), Lessive (Belgium) and Darmstadt (Germany), which are presented, do not show any significant polarisation dependence. The theoretical basis given by Otung and Evans is studied further, showing that tropospheric scintilation is not expected to be significantly influenced by polarisation angle.

العلاقة: boreal:46944; http://hdl.handle.net/2078.1/46944Test; urn:ISSN:0013-5194; urn:EISSN:1350-911X

الإتاحة: https://doi.org/10.1049/el:19961115Test
http://hdl.handle.net/2078.1/46944Test

المؤلفون: Vasseur, H., Vanhoenacker-Janvier, Danielle

المساهمون: UCL

المصدر: Electronics Letters, Vol. 32, no. 12, p. 1075-1077 (1996)

مصطلحات موضوعية: atmospheric electromagnetic wave propagation, satellite links

الوصف: Experimental results of long term attenuation and depolarisation statistic at 20 and 30 GHz using ESA's Olympus satellite are discussed and compared with current prediction methods. While copolar attenuation (CPA) is accurately estimated, crosspolar attenuation (XPD) is poorly predicted, mainly owing to an inadequate account of the ice depolarisation effect.

العلاقة: boreal:47111; http://hdl.handle.net/2078.1/47111Test; urn:ISSN:0013-5194; urn:EISSN:1350-911X

الإتاحة: https://doi.org/10.1049/el:19960720Test
http://hdl.handle.net/2078.1/47111Test