Comparison of Wind Speed-Up over Escarpments Derived from Numerical Modeling and Wind-Loading Codes

Wind flow and sediment flux profiles for vegetated surfaces in a wind tunnel and field-scale windbreak

Estimation of the aerodynamic load on trees is essential for urban tree management to mitigate the risk of tree failure. To assess that in a cost-effective way, scaled down tree models and numerical simulations were utilized. Scaled down tree models reduce the cost of experimental studies and allow the studies to be conducted in a controlled environment, namely in a wind or water tunnel, but the major challenge is to construct a tree model that resembles the real tree. We constructed 3D-printed scaled down fractal tree models of major urban tree species in Singapore using procedural modelling, based on species-specific growth processes and field statistical data gathered through laser scanning of real trees. The tree crowns were modelled to match the optical porosity of real trees. We developed a methodology to model the tree crowns using porous volumes filled with randomized tetrahedral elements. The wind loads acting on the tree models were then measured in the wind tunnel and the velocity profiles from selected models were captured using particle image velocimetry (PIV). The data was then used for the validation of Large Eddy Simulations (LES), in which the trees were modelled via a discretized momentum sink with 10–20 elements in width, height, and depth, respectively. It is observed that the velocity profiles and drag of the simulations and the wind tunnel tests are in reasonable agreement. We hence established a clear relationship between the measured bulk drag on the tree models in the wind tunnel, and the local drag coefficients of the discretized elements in the simulations. Analysis on the bulk drag coefficient also shows that the effect of complex crown shape could be more dominant compared to the frontal optical porosity.

Three-center cylindrical latticed shell closed cargo shed is a typical wind-sensitive structure, and wind load is one of the control loads in structural design. Based on the background of three three-center cylindrical latticed shell closed cargo sheds in a comprehensive wharf project, wind tunnel tests and numerical analysis on various factors affecting wind load of closed sheds were carried out. The influence of the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions on the wind load of the closed cargo shed was studied, the calculation results of closed cargo sheds designed by the wind load in wind tunnel test results, load codes and related literature are compared. Through the research, it is found that the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions had great influence on the wind tunnel test results, there were potential safety hazards in the structural design of closed sheds by the wind load in load codes and related literatures, the wind tunnel test of this kind of long-span closed sheds should be conducted before the detailed design, and the various actual working conditions of the sheds should be taken into account and correctly reflected during the wind tunnel test.

Anumerical model was developed to investigate flow around and through a two-dimensional peaked-roof building dimensionally similar to a typical poultry building. Differential equations for vorticity and stream function were solved using finite differences. Converged solutions were obtained with solid building walls and a laminar upstream velocity profile at Reynolds numbers (Re)* of 10, 50, and 75, and with equal 25, 50, and 75% wall openings on windward and leeward walls at Re = 10 and 50. An algebraic model was developed to predict ventilation rates for laminar and turbulent flow to compensate for the low Re limitation of the numerical model. Algebraic and numerical model predictions were compared to flow in a wind tunnel study using a physical model of the same shape and Re of 20,000 (Bottcher et al., 1986), and to wind ventilation rates calculated according to ASHRAE (1981). Dimensionless ventilation rates from the numerical model were lower than those measured in the wind tunnel study. Ventilation rates calculated using the algebraic model for laminar flow were comparable to numerical model results. Ventilation rates calculated using the algebraic model for turbulent flow with the wind tunnel and power-law velocity profiles were comparable to wind tunnel measurements and to recommendations from ASHRAE (1981), respectively.

Dam break is an important phenomenon which significantly affects the environment as well as the inhabitants of the downstream areas of the dam. In the present study, the hydraulic break of Malpasset dam as a result of sudden flooding was simulated numerically using the FLOW-3D software. The two-equation k-ε turbulence models and RNG k-ε turbulence model were used to simulate the flow field turbulence. Also, the free-surface variations of the flow were simulated using the VOF (Volume of Fluid) scheme. The results obtained from the numerical model were in good agreement with those predicted by the EDF model. Based on the simulation results, the maximum pressure occurred at the lower layers of the flow and reduced as the free surface of the flow was approached. The maximum pressure increased at each point in time. The maximum longitudinal velocity occurred at the front of the advancing wave resulting from break of the dam, and subsequently decreased due to the increasing depth at the downstream of the dam. Additionally, the effects of obstacles with different shapes on the flow pattern arising from dam break (due to sudden flooding) were also investigated. Examination of these effects revealed that the cubic obstacle placed obliquely in the flow direction produced the maximum separation region at its downstream. Conversely, this separation region was eliminated completely when a cylindrical obstacle was used. The maximum and minimum Froude numbers were obtained for the flow encountering the perpendicular cubic obstacle and the flow impacting the cylindrical obstacle, respectively.

In general, the study of a high-rise building’s behaviour when subjected to a horizontal load (wind or earthquake) is carried out through numerical modelling with finite elements method. This paper proposes a new, original approach based on the use of a multi-beams model. By redistributing bending and axial stiffness of horizontal elements (beams and slabs) along vertical elements, it becomes possible to produce a system of differential equations able to represent the structural behaviour of the whole building. In this paper this approach is applied to the study of bending behaviour in a 37-storey building (Torre Pontina, Latina, Italy) with a regular reinforced concrete structure. The load considered is the wind, estimated in accordance with Italian national technical rules and regulations. To simplify the explanation of the approach, the wind load was considered uniform on the height of building with a value equal to the average value of the wind load distribution. The system of differential equations’ is assessed numerically, using Matlab, and compared with the obtainable solution from a finite elements model along with the obtainable solutions via classical Euler-Bernoulli beam theory. The comparison carried out demonstrates, in the case study examined, an excellent approximation of structural behaviour.

The effect of inlet velocity profile on the bifurcation COPD airway flow

Downbursts are acknowledged for being a major loading hazard for horizontally-extending structures like transmission line systems. With these structures being inherently flexible, it is important to characterize the turbulence associated with the wind flow of downburst events being essential to quantify dynamic excitations on structures. Accordingly, the current study numerically characterizes the downburst wind field of open terrain simulated at the Wind Engineering, Energy and Environment (WindEEE) dome testing facility at The University of Western Ontario in Canada through a high-resolution large eddy simulation (LES). The study validates the numerical simulation considering both the mean and the turbulent components of the flow. It then provides a detailed visual description of the flow at WindEEE through the capabilities enabled by LES to identify the key factors affecting the flow. The study also presents the spatial distribution of turbulence intensities and length scales computed from the numerical model and compares them with previous values reported in the literature. The comparison shows the ability of the downburst simulated at WindEEE to reproduce turbulence characteristics similar to those reported from field measurements. The study also indicates that downburst turbulence is well-correlated circumferentially which imposes high correlated loads on horizontally-distributed structures such as transmission lines.

Wind tunnel testing is very expensive, especially due to the handmade models and the cost of building and operation of wind tunnels. Therefore, numerical modelling such as computational fluid dynamics can be a more cost efficient solution and is seen to take the leading position in the future. The following research contains the validation of the Computational Fluid Dynamics tool VXFlow by comparing the numerical results with values in literature, the Eurocode and wind tunnel measurements. The study includes the analysis of static wind loads for different wind barrier geometries for the example of the Suderelbebrucke in Hamburg. VXFlow is found to give good results in a short computational time but tends to overpredict the drag coefficient. The application is aligned for investigations in the preliminary design of bridge decks and can be also used for wind tunnel validation. Keywords: Bridge deck, CFD tools, VXFlow, static wind loads, wind barrier

Gust response envelope approach to the equivalent static wind load for large-span grandstand roofs

Downwind sound propagation over a noise screen is investigated by numerical computations and scale model experiments in a wind tunnel. For the computations, the parabolic equation method is used, with a range-dependent sound-speed profile based on wind-speed profiles measured in the wind tunnel and wind-speed profiles computed with computational fluid dynamics (CFD). It is found that large screen-induced wind-speed gradients in the region behind the screen are responsible for a considerable reduction of the performance of the screen, for receivers near the boundary of the shadow region behind the screen. The screen-induced wind-speed gradients cause a considerable reduction of the size of the shadow region. If the screen-induced wind-speed gradients are taken into account, computed sound-pressure levels near the shadow boundary are in reasonable agreement with levels measured in the wind tunnel. In contrast, computed levels are considerably lower, up to 10 dB, if the screen-induced wind-speed gradients are ignored. This implies that the performance of a screen can be considerably improved if the screen-induced wind-speed gradients can be suppressed, e.g., by the use of “vented” screens.

Physical scale modeling (PSM) is an experimental technology that has been used to evaluate and design shipboard impressed current cathodic protection (ICCP) systems by various researchers and designers. PSM is also a preferred tool for validating ICCP numerical modeling results, owing to the well-controlled conditions in PSM experiments. However, one issue in using PSM for the validation of numerical modeling results is the lack of information on the actual polarization behavior of the cathodes on a model hull during PSM experiments. Consequently, the polarization curve data used as boundary conditions in numerical modeling trials is usually different from the polarization behavior of the cathodes in PSM experiments. This difference can result in a discrepancy between the numerical modeling and the PSM results, which is difficult to separate from other numerical errors. A discrete area current control (DACC) technique was developed in a previous ICCP PSM study to simulate the polarization behavior of a propeller material under various conditions. The present study extended the DACC technique to simulate the polarization curve behavior of four discrete cathodes representing one nickel aluminum bronze (NAB) propeller and three discrete steel patches. This study also demonstrated that use of the DACC technique can ensure that both PSM and numerical modeling studies use identical polarization curve relationships as boundary conditions. The technique facilitates the use of the PSM results for comparison with numerical modeling results. The comparison study showed good agreement between the PSM results and numerical modeling results, in both simulated static and dynamic flow conditions.

Wind tunnel scale model testing of suspended cables and numerical comparison

All the countries have their own wind loading codes, and all the standard wind codes give some principle and procedure for the calculation of wind load and wind effect on high-rise buildings. In this paper, a study on the comparison of response on building due to two different wind codes AS/NZS 1170 (Part 2)-2011 and Indian (IS 875 (2015)-part 3) is presented. The study is carried out on a 150 m tall structure to see the wind effects due to different codes. The results are found from the different codes and compared them for terrain category 3 for both the cases. Different parameters like design wind pressure, wind load, lateral deflection, storey drift, storey shear and storey moment are also compared.KeywordsWind loadBuildingWind pressurePressure coefficientWind speed

Single-grain Silicon Technology for Large Area X-ray Imaging