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Experiments on the rectangular prisms with side ratios of 2. 0, 2.5, 3.0, 3.5 and 4. 0 are reported. Wind pressure measurements were carried out on five rectangular prisms for the testing Reynolds number Re ranging from l. 1 x 105 to 6. 8 x 105. The Reynolds number effects on the wind pressure distributions and the base pressure coefficients were studied, then the mechanisms of Reynolds number effects on rectangular prisms were described by analyzing the variation of the flow around the model. The results are summarized as follows; wind pressure distributions of five rectangular prisms are all sensitive to Re, and the Reynolds number affects the wind pressure distributions not only in the reattachment region, but also in the separation bubble. The sensitivity to the Reynolds number effects is changed with the side ratio of the rectangular prism, and the B/D = 4 .0 rectangular prism appears to be the most sensitive to the Re. Its separated shear layer is easier to reattach to the body at high Re, and the flow reattachment point moves towards the leading edge suddenly at the critical Re = 6. 8 x 105. In addition, with the increasing of Re, the absolute value of base pressure coefficient for the B/D =4. 0 prism increases firstly, and then decreases rapidly. [ABSTRACT FROM AUTHOR]

Using several formulas of across-wind aerodynamic forces and aerodynamic damping of rectangular super-high-rise buildings with side ratios smaller than 2 proposed previously by the authors, across-wind equivalent static loads and responses of super-high-rise buildings are evaluated through a proper combination of resonant and background components. The resonant component is computed according to the power spectral density of the base moment and the aerodynamic damping. The background component, whose vertical distribution is derived from background moment responses at different heights and then expressed as a cubic equation of the relative height, is computed using the base moment coefficients. Furthermore, comparisons are made for the equivalent static wind loads and responses of a hypothetical typical building between the present method and the AIJ (1996) method, which indicate the applicability of the present method. Finally, the effects of background component and aerodynamic damping on the equivalent wind loads and responses are also discussed. [ABSTRACT FROM AUTHOR]

Based on the pressure measurements of wind tunnel test on a rigid structural model, the equivalent objective responses induced by fluctuating wind were firstly calculated. Then, according to a linear combination method of inertial loads, the equivalent static wind loads (ESWL) of fluctuating wind loads on a largespan roof were obtained, the computational results indicate that the errors are rather large when the numbers of structural modes are inadequate. Hereby, based on the response difference between the equivalent objective responses and computational responses, a new compensated method for computing ESWL of fluctuating wind loads was proposed to overcome the biggish errors produced by only taking inadequate numbers of structural modes into consideration. At last, the new method was applied to a real large-span roof structure. The results show that the method has the merits of explicit physical meaning, simple computational principles and high computational accuracy, which can satisfy the requirements of engineering designs. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents numerical and experimental investigations of wind-induced interference effects on the pressure distributions on a building adjacent to another one in staggered arrangement. The wind tunnel tests were carried out in a low-speed boundary layer wind tunnel. Mean and fluctuating pressure and moment measurements on the principal building with interference from surroundings at different wind directions are obtained. The numerical predictions for pressure distribution on the principal building are performed by solving the Reynolds-averaged Navier–Stokes (RANS) equations using the renormalization group (RNG) k–ε turbulence model and then compared with the measurements. The computational method is based on a pressure correction algorithm of the SIMPLEC-type. The simulated pressure, base force and base moment coefficients in different wind directions are generally in good agreement with the corresponding wind tunnel data. [Copyright &y& Elsevier]

Flutter derivatives show great importance on analysis of bridge wind-induced vibration. They can be extracted through wind tunnel tests and CFD simulation. In this paper, a novel approach based on the CFD discrete time aerodynamic model is presented to identify flutter derivatives. This method employs the 3211 multi-step as input of velocity to excite CFD model, which can provide aerodynamic forces acting on the body through CFD simulation. An aerodynamic model in discrete time domain, defined on frequency range of interesting, can be developed based on the input-output relationship. Then the obtained aerodynamic model can be used to simulate aerodynamic response for any harmonic input with suitable frequency. Finally, flutter derivatives can be identified based on input and output time histories. The present method can extract flutter derivatives under arbitrary reduced wind speed, requiring respectively only once round of CFD Simulation for heaving or pitching motion. Identification of flutter derivatives of a thin plate is carried Out by using the present method, reasonable agreements between the identified flutter derivatives and those from wind tunnel tests validate the efficiency of the present approach. [ABSTRACT FROM AUTHOR]

Abstract: Rain–wind-induced vibration of cables in cable-stayed bridges is presently a worldwide problem of great concern. Because it is sensitively influenced by many parameters, this peculiar phenomenon is difficult to be replicated in laboratory conditions; its mechanism has not been well explained yet. In this paper, the phenomenon of rain–wind-induced vibration of a cable model is successfully reproduced under actual rain conditions in a wind tunnel. The effects of several main factors, including the inclination angle, frequency and damping of the cable as well as the wind yaw angle, etc. on the characteristics of rain–wind-induced vibration are investigated in detail in the test. The countermeasures of double-spiral wires and dampers for the mitigation of the vibration are also experimentally studied. The results show that the size and twine direction and the pitch of the spiral wires twined on the surface of cables have great effects on the mitigation efficiency of rain–wind-induced vibration of cables. [Copyright &y& Elsevier]

A numerical model based on Lagrangian description is developed in this study to predict wind-induced snow drifting on flat roofs, which fully considers the key physical processes of snow particle saltation. A scaled experiment of snow redistributions on the model roof was carried out in the wind tunnel for the verification and evaluation of different numerical methods selected from related literature. The optimal model is determined by comparing the predicted transport rate on the roof with estimations from empirical formulas and by comparing simulated snow distributions with experimental data. Characteristics of the saltation layer above the flat roof surface are then presented in detail based on the developed model. The rebound particles account for approximately 60% of the total transported particles above the roof, indicating the dominant role of rebound in the lift-off process for saltating snow particles. The developing snow transport along the roof span leads to the increase of surface erosion flux caused by the splash entrainment with downwind distance. The splash entrainment could thus contribute considerably to unsaturated snow transport on the flat roof, which is also found to be influenced by the approaching wind velocity and threshold friction velocity to varying degrees. • A numerical model is developed using the Lagrangian approach to investigate the mechanisms of snow drifting on flat roofs. • A scaled experiment of snow redistributions on flat roof is conducted in the wind tunnel to evaluate the simulated results. • Characteristics of the saltation layer above the flat roof are presented based on the developed model. • The role of splash entrainment and its contribution to unsaturated snow transport on flat roofs are preliminarily explored. [ABSTRACT FROM AUTHOR]

This paper studied the loads on the configuration details of low-rise building roofs by the rigid model pressure measurement tests, which were often destroyed in wind disasters. The pressure coefficients and drag coefficients of the ridge, protruding gable wall and eaves gutter were examined, which were of varied heights and with or without the other 2 types of configuration details. The results show that the negative pressure of interior surface ( the leeward surface for the ridge) of the configuration details end varies severely and the amplitude occurs when the wind obliquely blows to the exterior surface (the windward surface for the ridge) , which leads to the very large worst peak net pressure coefficient towards the roof. The worst peak net pressure coefficients of the protruding gable wall, ridge and eaves gutter are about 18.0, 10.5 and 7.0, respectively. However the peak pressure away from the roof ( towards the windward surface for the ridge) is relatively stable. The worst peak net negative pressure of the lower tap is 5 larger than that of the higher tap on the same vertical plan of the protruding gable wall, while that of the lower tap is only O. 8 larger than that of the higher tap for the eaves gutter. When the roof is equipped with the other 2 types of configuration details, the worst peak net negative pressure coefficients of the ridge and protruding gable wall decrease much to 7.5 and 6.0 from 10.5 and 18.0, respectively, while that of the eaves gutter decreases to 6 from 7. The worst peak drag coefficients of the ridge and eaves gutter are not affected by whether the roof is attached with the other 2 types of configuration details or not, while that of the protruding gable wall is smaller when the roof is attached with ridge and eaves gutter. The worst peak drag coefficients of the protruding gable wall and eaves gutter are larger with the increase of each height. [ABSTRACT FROM AUTHOR]

In cold and snowy regions, roof slopes can affect the snow distribution on the gable roof. The finite area element (FAE) method is modified by considering the effect of the snow transport rate, the developmental law of snow transport and the saturated transport distance on the calculation of drifting snow load in this paper. Saltation and suspension of snow transport are also considered respectively in the process of modification. Then, based on the modified FAE method and computational fluid dynamics (CFD), the influence of roof slopes (10°, 20°, 30° and 40°) on the gable roof snow distribution is studied. Meanwhile, for compare the simulation results of the modified FAE method with different combinations of the snow transport rate, the developmental law of snow transport and the saturated transport distance, the test of wind-blown snow redistribution is completed in the wind tunnel using the substitute particles (silica sand) on the scaled gable roofs. The results show that when the saturated transport distance of snow is 210 m, the modified FAE method can reproduce the snowdrift phenomenon on the gable roof more reasonably if adopting the snow transport rate proposed by Owen (1964) and the developmental law of snow transport suggested by O'Rourke et al. (2005) at the same time. Through CFD simulation, it's discovered that the distribution of flow field around the gable roof and friction velocity on snow surface change noticeably with roof slopes, resulting in the increase of the upwind erosion flux and the leeward deposition flux with the incoming wind speed and the roof slope. In addition, when the incoming wind speed remains unchanged, simulation results using the modified FAE method show that the larger slope of the gable roof, the more likely it is to cause the uneven distribution of snow load on the windward and leeward roofs. Moreover, fresh snow is more likely to cause the uneven distribution of snow load on gable roofs than aged snow through analysis sensitivity of the threshold friction velocity. • The FAE method is modified based on the development process of snow transport and CFD simulation. • The modified FAE method is validated through wind tunnel tests. • The snow distribution on gable roofs is simulated using the modified FAE method. • The influence of slope on the snowdrift load coefficient is analyzed though the characteristics of snow distribution. [ABSTRACT FROM AUTHOR]

This paper presents a wind tunnel investigation of the autorotation of plates. The effects of geometry, the Reynolds number, and rotation direction on the aerodynamics of the plate, including the rotation rate, lift and drag coefficient, are analyzed. The autorotation rate of plate with smaller aspect ratio is more sensitive to the thickness ratio, whereas when the aspect ratio is larger than 1.5, its effect on the sensitivity of the autorotation rate to the thickness ratio can be ignored. The lift coefficient of plate with larger aspect ratio and smaller thickness ratio is larger when aspect ratio is smaller than 2. Otherwise, the lift coefficient increases first and then decreases with an increase in the thickness ratio. Meanwhile, the lift coefficient of plate decreases as Reynolds number increases, and the relationship between the lift coefficient and the Reynolds number is close to a straight line in logarithmic coordinate. Moreover, the clockwise rotation direction leading to upward lift was found to have a higher absolute value of the lift coefficient than the counterclockwise direction leading to downward lift, especially at low rotation rates. However, the drag coefficient, which fluctuates around a constant of 1.3, is independent of such factors. • The geometry effect on the aerodynamics of rotating plate was investigated. • Previous interpretation of Reynolds number effect on lift and drag coefficient is inaccurate. • The lift coefficient is found to be a function of geometry, Reynolds numbers and rotation direction. • The drag coefficient, which fluctuates around a constant of 1.3, is independent of such factors. [ABSTRACT FROM AUTHOR]

Wind tunnel simulation is a very important approach to studying snow drifting and predicting drift snow loads on roofs. A complete simulation of the full process of wind-induced snow accumulation on a roof should include snow drifting both during snowfall and after snowfall. However, in most of the previous studies, snow drifting phenomenon was only simulated without concurrence of snowfall. We herein describe simulations of snow drifting on a flat roof during snowfall, which were carried out in a cryogenic wind tunnel using artificial snow particles. Based on the results, we demonstrate the differences and similarities between snow drifting during snowfall and that without concurrent snowfall. The developments of snow transport before saturated state apparently follow the same rule, no matter whether there is concurrent snowfall or not. However, it seems that the required fetch distance for a saturated saltation state can be reduced by snowfall. A formula is proposed to more reasonably describe the development of snow transport rate. Based on test results and deductions, some discussions on similarity requirements for modelling snow drifting on roofs during snowfall will be presented. Finally, a prediction of the prototype fetch distances under different wind and snowfall conditions will also be presented, which can provide a guide for further research and engineering application. • Wind tunnel tests of snow drifting during snowfall are described. • Drifting development during snowfall follows the same rule as that without snowfall. • Snowfall may reduce the required fetch distance for a saturated state of drifting. • Similarity requirements for simulating snowfall are discussed and proposed. [ABSTRACT FROM AUTHOR]

Roof slopes would have a great impact on snow drifting on roofs. The existing Eulerian-Lagrangian model is not suitable for simulations of snow drifting on gable roofs. This study improves the Eulerian-Lagrangian snow drifting model by modifying the threshold friction velocity and the splash functions to fully consider the impact of the roof slope. To evaluate the rationality of the improved model, scaled tests of snow redistributions on gable roofs were conducted in a wind tunnel. The improved model is demonstrated to perform better on the prediction of snow redistributions on gable roofs. Characteristics of snow drifting on gable roofs with different slopes are investigated in terms of flow pattern, particle motion and snow transport. For roofs with different slopes, features of particle motion near the snow bed show significant differences, which are reflected in the spatial distribution, the saltation height and the impact velocity of snow particles. Snow erosion occurs on the windward roof at each slope, and it also occurs on the leeward side at the slope of 5° or 10°. However, on the entire leeward surface at the slope of 15° and near the ridge at the slope of 20°, snow deposition would occur. • An Eulerian-Lagrangian snow drifting model for gable roofs considering the effect of roof slope is established. • Scaled wind tunnel tests of snow redistributions on gable roofs were conducted to evaluate the rationality of the model. • Features of particle motion close to the roof surface are revealed through the analyses of the simulated results. • Characteristics of snow erosion/deposition flux and snow transport rate on gable roofs are discussed. [ABSTRACT FROM AUTHOR]

The insight into the influences of roof slope on the characteristics of snow drifting on monoslope roofs during snowfall is still inadequate so far. Scaled tests of snow drifting on monoslope roofs with varying slopes (0° to 25°) were thus carried out in a wind tunnel equipped with a snowfall simulator, employing silica sand particles to model the snow precipitation environment. Typical snowdrift patterns on monoslope roofs were summarized, and elaborations were provided on the variation for the characteristics of snow drifting with roof slope. Similar features in terms of particle distributions, transport rate, and degree of erosion are observed for lower-sloped roofs (0°, 5°, and 10°), which all differ from those on higher-sloped roofs (15°, 20°, and 25°). The difference caused by the variation of approaching wind velocity on particle erosion is found to be more pronounced compared with that of snowfall intensity, and the increase in the degree of erosion with snowfall intensity can be reasonably represented by the linear relationship. The flow pattern around the roof and surface friction velocity before (without snow) and after snowfall (with snow cover) were then explored via numerical simulation for different roof slopes. Based on the simulated flow characteristics, the mechanisms of snow drifting on the sloped roofs under snowfall were further discussed. • Scaled tests of snow drifting on monoslope roofs with the concurrence of snowfall are conducted in a wind tunnel. • Effects of the approaching wind velocity and snowfall intensity on the characteristics of snow drifting are discussed. • Flow pattern around the roof and surface friction velocity before and after snowfall are explored via numerical simulation. • Typical snow distribution patterns on monoslope roofs with different slopes are presented. [ABSTRACT FROM AUTHOR]

Predicting structural responses under joint action of wind and snow loads is important in ensuring the safety of lightweight roof structures in snowy regions. In this paper, a series of similarity parameters that should be satisfied in the wind tunnel test to simulate structural responses under joint action of wind and snow loads are proposed from the perspective of similarity of wind field, particle movement, flow around the building, and structural dynamics. Then, with a double-pitched roof structure as research object, an aeroelastic model test with substituted snow particles is designed and structural responses are obtained through the wind tunnel test. The other two types of tests, namely, aeroelastic model test with additional weights and pressure measurement test, are also conducted; their results are compared with those of the aeroelastic model test with substituted snow particles. The mean and RMS response of the other two types of tests are both significantly lower than those of the aeroelastic model test with substituted snow particles. The preliminary conclusion is that wind-induced structural vibration is influenced by snowdrift and possible asynchronous vibration of the particle layer and roof structure, which could lead to a considerable increase in structural dynamic responses. [ABSTRACT FROM AUTHOR]

Owing to the controllability and reliability, wind tunnel experiment is considered as a powerful and effective approach for the investigation of snow drifting. Most of the previous experimental studies were mainly concerned with snow drifting on roofs without snowfall, in which a layer of particles was uniformly paved on the roof surface to model the initial snow cover. Hence, a cryogenic wind tunnel experiment using artificial snow particles was conducted to investigate snow drifting on flat roofs during snowfall. The similarity requirement related to snowfall intensity is derived according to the similarities of snow distribution pattern and the development of snow transport. Based on the results of snow distributions and transport rates for different roof spans and snowfall intensities, the features of snow drifting under snowfall conditions are analyzed in detail. The concurrence of snowfall is further revealed to greatly affect the development of snow drifting on flat roofs and thereby result in a reduction in the required fetch for reaching the saturated state. And the typical distribution patterns for snow drifting on flat roofs with and without snowfall are also summarized. Besides, the snow transport rate is found to increase along the roof surface before the achievement of the saturated state, whereas a slight decrease in the degree of snow erosion with roof span is observed. But the location of the crest formed near the windward edge is nearly unaffected by roof span as well as snowfall intensity. The results also indicate obvious linear characteristics in the relationship between the degree of erosion on the roof surface and snowfall intensity. And the normalized development process of snow transport before reaching the saturated state is nearly independent of snowfall intensity, although both the saturated transport rate and the required fetch for saturated drifting are strongly affected in the meantime. • A cryogenic experiment of snow drifting on flat roofs under different roof spans and snowfall intensities is presented. • The location of the crest formed near the windward edge is nearly unaffected by roof span and snowfall intensity. • Transport rate increases along the roof before reaching the saturated state whileerosion slightly decreases with roof span. • The relationship between the degree of erosion and snowfall intensity presents obvious linear characteristics. • Normalized development process of snow transport before the saturated state is nearly independent of snowfall intensity. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the influences of two important problems in computational wind engineering (CWE), which are the modeling of equilibrium atmosphere boundary layer (ABL) and the specification of turbulence model parameters, on the numerical simulations of wind pressure distributions on a typical low-rise building are investigated sequentially through detailed comparisons between the numerical results and the wind tunnel test data. The capability of the proposed inflow turbulence boundary conditions in constructing equilibrium ABL is verified, and the effect of the turbulence parameters on the numerical results is illustrated. The combination of the carefully considered inflow boundary conditions, and the turbulence parameters can improve the numerical simulation accuracy of the wind pressures of the low-rise building. The present work seems to be helpful to further realize the importance of these two problems as well as to provide a referential study to the accuracy improvement of CWE. [Copyright &y& Elsevier]