1,854 research outputs found

    Characteristics of wind pressures on large cantilevered roofs: Effect of roof inclination

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    Wind pressure distributions on both surfaces of a cantilevered roof are measured on a wind tunnel model. The investigation covers a down-sloping roof configuration at -5° roof angle and two up-sloping roof configurations of roof angles 5° and 10°. The results supplement an earlier study made on a horizontal roof. The wind pressure pattern on the upper surface of an up-sloping roof suggests that there exists a preferred mode of flow separation on that surface. The pattern shows two localized regions of high suction, which are separately located towards the two ends of the roof span. On the up-sloping roofs, this pressure pattern is observed in the time-averaged mean distribution as well as during the occurrence instant of a peak total uplifting force on the roof. On the horizontal roof, this particular pattern of flow separation is not obviously observed in the time-averaged mean wind pressure pattern but is revealed by the conditional sampling technique which captures the wind pressure distribution during the generation of a peak uplifting force on the roof. The wind pressure signals are analysed to study the characteristics of the total wind force on the roof and also the wind forces on individual roof surfaces. © 2002 Elsevier Science Ltd. All rights reserved.postprin

    Two-phase velocity measurement in a particle-laden jet

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    Centerline velocity decay of a circular jet in a counterflowing stream

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    We use an advection hypothesis to analyze the decay of centerline velocity of a circular jet issuing into a counterflowing stream. Working in the Lagrangian frame, we follow the locations and velocity gradients of jet fluid particles along the jet central axis while the particles are being advected backwards by the counterflow. The spatial velocity gradient along the jet centerline is thus obtained and subsequently integrated to describe the spatial decay of axial velocities. Laser-doppler velocity measurements are performed in the laboratory and the data are well predicted by our analytical expression of centerline velocity decay. Looking from another view, our treatment supports that the effect of an external axial flow stream on the jet flow field can be represented by a certain degree of stretching or contracting of the jet in the axial direction. © 1998 American Institute of Physics.published_or_final_versio

    Asymmetric vortex shedding flow past an inclined flat plate at high incidence

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    This paper reports an experimental investigation of the vortex shedding wake behind a long flat plate inclined at a small angle of attack to a main flow stream. Detailed velocity fields are obtained with particle-image velocimetry (PIV) at successive phases in a vortex shedding cycle at three angles of attack, α=20°, 25° and 30°, at a Reynolds number Re≈5,300. Coherent patterns and dynamics of the vortices in the wake are revealed by the phase-averaged PIV vectors and derived turbulent properties. A vortex street pattern comprising a train of leading edge vortices alternating with a train of trailing edge vortices is found in the wake. The trailing edge vortex is shed directly from the sharp trailing edge while there are evidences that the formation and shedding of the leading edge vortex involve a more complicated mechanism. The leading edge vortex seems to be shed into the wake from an axial location near the trailing edge. After shedding, the vortices are convected downstream in the wake with a convection speed roughly equal to 0.8 the free-stream velocity. On reaching the same axial location, the trailing edge vortex, as compared to the leading edge vortex, is found to possess a higher peak vorticity level at its centre and induce more intense fluid circulation and Reynolds stresses production around it. It is found that the results at the three angles of attack can be collapsed into similar trends by using the projected plate width as the characteristic length of the flow. © 2004 Elsevier SAS. All rights reserved.postprin

    Wind-induced loading and dynamic responses of a row of tall buildings under strong interference

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    This paper studies wind-induced interference effects on a row of five square-plan tall buildings arranged in close proximity. Mean and fluctuating wind loads are measured on each building member and wind-induced dynamic responses of the building are estimated with the high-frequency force-balance technique. The modifications of building responses from interference over a practical range of reduced velocities are represented by an envelope interference factor. Wind tunnel experiments and response analysis are carried out under all possible angles of wind incidence, at four different building separation distances, and for two arrangement patterns of buildings in the row, that is the parallel and diamond patterns. It is found that building interference leads to amplified dynamic responses in many cases but reduction in responses also occurs at some wind incidence. For a building row of the parallel pattern, five distinct wind incidence sectors of different levels and mechanisms of interference effect can be identified. The largest values of envelope interference factors can reach 2.4 for the torsional responses. When the row of tall buildings is arranged in the diamond pattern, increase in wind excitation occurs at many wind angles due to a "wind catchment" effect. The interference factors have larger peak values, reaching 2.1 in the sway directions and above 4 in torsion. However, all large amplifications of building responses do not occur in the situations of peak resonant dynamic responses of the single isolated building. Thus, the design values of peak dynamic responses of a tall building are not significantly magnified when placed in a row. © 2011 Elsevier Ltd.postprin

    Shape-appearance-correlated active appearance model

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    © 2016 Elsevier Ltd Among the challenges faced by current active shape or appearance models, facial-feature localization in the wild, with occlusion in a novel face image, i.e. in a generic environment, is regarded as one of the most difficult computer-vision tasks. In this paper, we propose an Active Appearance Model (AAM) to tackle the problem of generic environment. Firstly, a fast face-model initialization scheme is proposed, based on the idea that the local appearance of feature points can be accurately approximated with locality constraints. Nearest neighbors, which have similar poses and textures to a test face, are retrieved from a training set for constructing the initial face model. To further improve the fitting of the initial model to the test face, an orthogonal CCA (oCCA) is employed to increase the correlation between shape features and appearance features represented by Principal Component Analysis (PCA). With these two contributions, we propose a novel AAM, namely the shape-appearance-correlated AAM (SAC-AAM), and the optimization is solved by using the recently proposed fast simultaneous inverse compositional (Fast-SIC) algorithm. Experiment results demonstrate a 5–10% improvement on controlled and semi-controlled datasets, and with around 10% improvement on wild face datasets in terms of fitting accuracy compared to other state-of-the-art AAM models