da Costa, Bernardo MoraisWang, JungaoJakobsen, Jasna BogunovicOiseth, Ole Andre...
14页
查看更多>>摘要：An improved bridge buffeting theory is established with an emphasis on skew wind directions, for both turbu lence-and motion-dependent forces. It provides simplifications and generalizations of previously established methods. The formulation starts with a preferred 3D approach, which is suitable when aerodynamic coefficients for different yaw and inclination angles are readily available. The 3D approach includes a new convenient choice of coordinate systems and an intuitive derivation of transformation matrices, supporting clear and compact wind load expressions as well as a more accurate formulation of the quasi-steady motion-dependent forces. When the aerodynamic coefficients have only been obtained for wind normal to the bridge girder, an alternative 2D approach is provided. The 2D approach, where only the normal projection of the wind is considered, is further expanded to include mean wind directions that are both yawed and inclined, axial forces in the longitudinal direction (1D) in an optional 2D + 1D format, and forces due to all in-plane and out-of-plane motions. All expressions are first presented in a compact non-linear format and then linearized through numerous multivariate Taylor series approximations. A general, more straightforward and more accurate framework is thus established for both time-and frequency-domain analyses of the buffeting response.
Whiteman, Michael L.Fernandez-Caban, Pedro L.Phillips, Brian M.Masters, Forrest J....
15页
查看更多>>摘要：This study explores the use of a cyber-physical systems (CPS) framework for the design and optimization of the aerodynamics of a tall building through aeroelastic boundary layer wind tunnel (BLWT) testing. The framework is a fully-automated combination of traditional experimental wind tunnel testing with numerical optimization strategies to evaluate a wide range of candidate designs both accurately and quickly. In this study, candidate designs are achieved through the physical adjustment of the aerodynamic shape of a multi-degree-of-freedom (MDOF) aeroelastic tall building model. BLWT testing is carried out at the University of Florida Natural Haz-ard Engineering Research Infrastructure (NHERI) Experimental Facility (EF). The specimen is equipped with an actuation system consisting of a series of individually-controllable slotted fins comprising an active fin system (AFS), which enable precise modifications of the aerodynamic shape of the envelope. The wind-induced building response of the specimen is directly captured using a series of accelerometers and laser displacement sensors. A stochastic optimization algorithm is then employed in the aerodynamic CPS framework to evaluate the fitness of each candidate design based on specified performance criterion related to either occupant comfort or building drift. Optimization results indicate that the CPS framework can reliably achieve the optimal solution which minimizes the response (i.e., horizontal accelerations and lateral displacements) of the aeroelastic specimen.
查看更多>>摘要：The improved delayed detached-eddy simulation (IDDES) method is used to investigate the aerodynamic performance of a high-speed train with cowcatchers having different ground clearances. The numerical results were verified by wind tunnel tests, and validation on the Reynolds number and geometry generality were also conducted. It was proved that the ground clearance under the cowcatcher has a significant effect on the train's timeaveraged and transient aerodynamic forces. A smaller ground clearance reduces the aerodynamic drag of the front part of the train body, strength the negative lift while increases the drag of the middle and rear parts as well as the positive lift. Smaller ground clearance also significantly reduces the aerodynamic of its neighboring downstream components. A lower ground clearance makes its power spectral (PS) value stronger and increases the dominant frequency of the neighboring downstream components. The flow pattern on the train body and its surroundings will also be locally affected by the ground clearance, such as slipstream and vorticity distribution.
查看更多>>摘要：An S-transform (ST) based data-driven simulation methodology is proposed of multivariate nonstationary wind velocity with explicit introduction of the time-varying coherence functions. This framework differs from that based on the evolutionary spectral theory that uniform or non-uniform modulation functions needs to be assigned. In defining the time-frequency power spectral density (TFPSD) in accordance with the ST coefficients, the Parseval's theorem is considered to ensure energy preservation. The proposed method is firstly applied to simulated nonstationary wind velocity. For comparisons, the results of the discrete orthonormal S transform (DOST) are also included. The research demonstrates that the ST based results agree well with the original, but a bias exists between the results simulated by DOST and the original, indicating that the feasibility of the proposed method. Employing four measured downburst records to simulate multivariate nonstationary wind velocity by the proposed method further validates its feasibility. In order to enhance the simulation fidelity, the inverse S transform (IST) based regulation and control method (IST-RCM) of high precision is developed, where the balancing parameter is defined and formulated to express quantitatively the relationship between accuracy and efficiency. It is found that the results with IST-RCM get more close to the actual wind velocity records.
Tadeu, Antonioda Silva, F. MarquesRamezani, BaharehRomero, Antonio...
13页
查看更多>>摘要：The present work analyses the wind load effects on the 516 Arouca bridge, the world's longest pedestrian suspension bridge in 2020. Computational fluid dynamics (CFD) was used to model a range of wind angles of attack between - 8 degrees and +8 degrees. The simulations were performed by solving the steady-state Reynolds averaged NavierStokes (RANS) equations with the k-omega shear stress transport (SST) model. The fluid domain size was analysed by comparing the fluid flow behaviour for three different downstream sizes. It was shown that the downstream flow is not greatly affected by the bridge body due to the high opening surfaces of the bridge. Therefore, the most appropriate domain size considering the computation time was selected. The simulations were carried out for different bridge configurations to determine the influence of the upper guard of the tray deck and the suspended cables on the generated loads. The numerical results were validated by performing different wind tunnel tests using a reduced scale prototype. The predicted aerodynamic characteristics showed good agreement with the experimental results.
Alam, Md MahbubRastan, M. R.Wang, LongjunZhou, Yu...
19页
查看更多>>摘要：The paper presents a systematic experimental study on the dynamics of flow around two nonparallel tandem cylinders at a Reynolds number of 5.6 x 10(4). Three generic configurations of the cylinders are considered: 1 the upstream cylinder yawed and downstream cylinder upright, 2 both cylinders yawed oppositely, and 3 the upstream cylinder upright and the downstream cylinder yawed. Extensive measurements are conducted of the surface flow pattern, fluid forces, shedding frequencies, and velocity fields around the cylinders. The flow is classified into three regimes based on the behaviors of shear layers around the cylinders for all configurations. The wake in each regime is characterized in detail, including its recirculation strength, vortex formation length, wake width, Strouhal numbers, and mean and fluctuating fluid forces on the cylinders. Conceptual flow structure models are proposed for each configuration. It has been found that the flow around two nonparallel cylinders is characterized by spiral vortices, with either upward or downward motion or both. These vortices play a crucial role in fluid dynamics, producing a profound impact on the fluid forces as well as flow three-dimensionality.
查看更多>>摘要：Crosswind stability of rolling stocks running on an embankment has been a key focus for decades, stemmed from the high overturning risks under crosswind. The correct reproduction of the embankment layout in a wind tunnel is therefore of great significance for estimating the train's aerodynamics and running safety. In this study, four different 6-m-high embankment layouts are proposed to replicate realistic wind tunnel configurations with the improved detached eddy simulation (IDDES) method. These helped to estimate the aerodynamics of a leading vehicle when subjected to a block wind profile of 45 m/s at the typical yaw angle of 30 degrees. Furthermore, a static wind tunnel test with a 1:20 scaled train/embankment model enabled the validation of the numerical algorithm. The overall results indicate that all the aerodynamic coefficients of the leading vehicle mounted on the leeward track of the embankment top, decrease rapidly with the extending length of the upstream embankment. Similar aerodynamic performance appears on scenarios such as wall-to-wall (W2W) and partially wall-to-wall (P-W2W), which highlight equivalences between W2W and P-W2W under yaw effects. However, those particular scenarios considerably underestimate the aerodynamic coefficients compared with a more realistic scenario based on open domain (OD) and motion boundaries. Therefore, the conservative assessment of the vehicle aerodynamic characteristics based on the finite-length-embankment in a wind tunnel test could be taken into consideration for determining the running safety.
查看更多>>摘要：Aeolian transport driven by extremely strong winds over Gobi areas with high gravel coverage remains poorly understood. In this study, field observations of aeolian transport over a Gobi surface with 70-94% gravel coverage were performed in the Hundred Miles windy area along the Lanzhou-Xinjiang High-Speed Railway. The results reveal that during a typical transport event, approximately continuous saltation can occur in the most intense transport period under such high gravel coverage, and the average saltation layer height (0.58 +/- 0.12 m) is approximately 6 times larger than that over sand surfaces. The annual sediment transport rate reached 46.31 kg m(-1).a(-1) under an annual sand drift potential of 705.14 vector units (VU), indicating that wind-blown sand activities are still strong over Gobi surfaces with high gravel coverage in extremely strong windy areas. Furthermore, the grain size distribution indicates that the saltation height of sand particles can reach 2 m, and the cumulative frequency of the sediment flux density indicates that 99% of sand is transported within 0-3 m of the surface. Our findings suggest that the height of sand fences should be raised from the present 2 m-3 m, which can trap more transported sand particles.
Nguyen, Cung H.Nguyen, Dinh T.Owen, John S.Hargreaves, David M....
22页
查看更多>>摘要：This paper presents a wind tunnel investigation of the aerodynamic characteristics (force and pressure coefficients) of a static 3:2 rectangular cylinder in smooth flow for angles of attack between -4 degrees and 90 degrees at various values of Reynolds number. In contrast to much of the existing literature, this study shows clear dependence of the mean drag coefficients on Reynolds number. In addition, the variation of aerodynamic parameters with angle of attack is fully mapped for a symmetric section revealing that the peak values of the mean values of drag, lift, moment and Strouhal number do not occur at the same critical angle of attack. The present study also presents the first map for identifying the locations of the reattachment and stagnation points as well as the zones of angle of attack where the flow is separated and attached on a face of the section. The phenomenon of switching flow is observed at the angle of attack 25 degrees, leading to strong non-stationarity and non-Gaussian distributions of the aerodynamic forces and pressure. Another phenomenon, so-called unsteady low-frequency vortex shedding, is also observed at higher angles of attack. These phenomena need to be accounted for when estimating wind loading and aeroelastic instability for these sections.
查看更多>>摘要：Using controlled tests in a wind tunnel, we simulated the pollution of four different street canyons formed by four 3D urban array models. The urban models differed by the geometry of roofs (pitched and flat roofs) and buildings (courtyard and solid buildings). We simulated traffic pollution from a ground-level source positioned in the middle of the street canyons. We show that the courtyard buildings significantly improve (by a factor of 1.3) the ventilation of the street canyons only in the cases with pitched roofs. We explain the differences between the ventilation performances of the street canyons by analysing the dynamics of the coherent structures. The buildings at the roof level shed two main vortex structures into the flow. However, the street canyon with pitched roofs and the courtyard buildings shed more stable structures that collide and penetrate deeper downstream near the wind-facing eaves. Near the pedestrian zone, ventilation is driven by advection, manifested as corner vortices at the street ends and flow convergence from the windward to the leeward side in the middle of the street canyons. The corner vortices are more pronounced in the courtyard buildings regardless of roof shape, resulting in higher concentrations than solid buildings.
NSTL
Elsevier