查看更多>>摘要：A short-term wind speed prediction framework is proposed for bridge traffic control under strong winds. The framework mainly focuses on improving the prediction accuracy for the timeframe of traffic control during a typhoon. Two concepts are newly proposed to achieve the goal: 1) hybrid modeling of wind speed at the bridge; and, 2) the adoption of a time-shifted data correction (TSDC) method. First, the hybrid modeling considers two available data types, one from a structural health monitoring system of the bridge and the other from the regional specialized meteorological center (RSMC). The training features of a long short-term memory (LSTM) approach are chosen based on the maximum sustained winds of a typhoon. Second, the TSDC method accounts for a time delay phenomenon between the maximum wind speed at the bridge deck and the maxima or minima of the selected features. The Mean Absolute Error (MAE)-based grid search method determines the preferable combinations of two parameters: input data length and the time-shifted length of the training data. As a numerical example, typhoons from 2020 are used as test data to demonstrate the improvement in prediction performance via the use of hybrid modeling and the TSDC method.
查看更多>>摘要：Multiple toxic gases, such as carbon monoxide (CO), are generated after blasting of plateau tunnel. To study the influence of high-altitude environment on the diffusion and concentration distribution of hazardous gases after tunnel blasting, a ventilation model for construction tunnel was established based on a tunnel of the Sichuan Tibet Railway, and the dynamic diffusion of CO at different altitudes was numerically simulated. The obtained results demonstrate that: In the area near the working face with forced ventilation, a vortex area was formed under the combined action of jet and backflow, the distribution of CO in the tunnel was closely related to the flow field. The CO migrated to the outside of the tunnel due to ventilation, and was gradually diluted and diffused in the process. The equivalent mass concentration of CO in the tunnel increased exponentially with the increase of altitude, the altitude correction coefficient of CO mass concentration was e(0.1H) at an altitude of H (km), the concentration value increased by 88% when the altitude rose from 0m to 6000m. To directly obtain the CO concentration value in the construction tunnel under different conditions by calculation, the functional relationship between the CO concentration after blasting and the time (t), distance (x) and other parameters was determined according to the simulation results, and the calculation function was verified by considering field data. The fitting function has wide applicability and can be used to judge whether the environment in the tunnel has reached a safe state, thus providing guidance for the safety of plateau tunnel construction.
查看更多>>摘要：The wake characteristics of a utility-scale wind turbine under realistic atmospheric boundary layer conditions are affected by the continuously changing wind direction arriving at the wind turbine. In the present study, the effects of continuous changes in the incoming wind direction were studied for a wind turbine on flat terrain, with the objective of understanding the wake characteristics of the wind turbine. Thus, understanding the effects of continuously changing incoming wind direction on the wake characteristics of wind turbines over flat terrain is important in the design of wind farm layouts, including in the design of offshore wind power plants. For this purpose, a computational fluid dynamics (CFD) approach using large-eddy simulations (LES) was adopted in the present study. An in-house LES-solver based on the actuator line (AL) aerodynamics technique was constructed in order to successfully capture the wake structure behind the wind turbine. First, experimental investigations on both a blade-only wind turbine scale model and a full 3D wind turbine scale model (isolated wind turbine) were conducted for a fixed inlet wind condition, the latter including the nacelle and the tower. Through a detailed comparison of the wind tunnel experimental and numerical results, the prediction accuracy of the in-house LESsolver was verified and validated for fixed inlet wind conditions. On the basis of the validation results obtained, and using the full 3D wind turbine scale model, the effects of the continuously changing inlet wind conditions on the wake characteristics in the near-and far-wake regions were numerically investigated. In addition, the effects of the wind turbine nacelle and tower on the wake characteristics were also investigated. The numerical results show that the most significant impact of the effects of the continuously changing wind direction was the rapid recovery of the mean velocity deficits in the wind turbine wake region. Further, at the x = 10D position (D is the rotor diameter) downstream of the wind turbine, the non-dimensional streamwise mean velocity was 0.93, which nearly matches the approaching flow speed, under an optimal tip speed ratio of 4.0, compared to the fixed wind direction scenario.
查看更多>>摘要：The wind veering phenomenon caused by the Coriolis force is frequently observed in the atmospheric boundary layer (ABL) and may affect the wind and turbulence characteristics of the ABL, thus influencing the wind effects on structures, especially high-rise structures. To investigate the Coriolis effect, this study firstly reproduces a realistic thousand-meter height ABL with a wind veering phenomenon by large eddy simulation. The simulated vertical profiles of mean wind speed and twist angle are validated against field observations. Three typical terrain types are considered in the simulation and the corresponding vertical profiles of wind and turbulence characteristics are presented and discussed. Furthermore, an additional group of reference cases not considering the Coriolis force is also considered for comparison to quantify the Coriolis effects on the wind and turbulence characteristics. The results show that both the Coriolis force and terrain type significantly affect the vertical profiles of mean wind speed and turbulence intensity in three orthogonal directions. The Coriolis effect on the turbulence integral length scale is more appreciable in the streamwise direction than in the other two orthogonal directions. The vertical profiles of wind speed and turbulence properties in the ABL simulated with consideration of the Coriolis force may serve as a crucial reference for the more reliable wind-resistant design of high-rise structures.
查看更多>>摘要：ABSTR A C T Wind barriers are an important wind protection facility that has been commonly used in high-speed railways to ensure the ride comfort and driving safety of high-speed trains in wind-prone areas. This paper presents an experimental study on the protective effect of wind barriers on the moving head and tail train vehicles under crosswinds for the first time. This study utilized a novel wind tunnel test device of a moving train model. The effects of the wind speed and the height and porosity of the wind barriers on the protective effect for moving trains were investigated considering the aerodynamic characteristics of the moving train. The protective effects of the wind barrier on the head and tail vehicles were compared, and the relationship between the vehicle aerodynamic characteristics with and without employing the porous wind barrier was discussed to simplify the test conditions and improve the evaluation efficiency of the protective effect of the wind barrier. The results indicated that the protective effect of the wind barriers on the moving train varied with different yaw angles. In addition, the height and porosity of the wind barriers significantly affected the protective effect of the wind barriers. Furthermore, the relationship between the vehicle overturning moment coefficient, an important in-dicator for vehicle safety evaluation, with and without employing the porous wind barrier, is quantified via a wind speed reduction coefficient. The wind speed reduction coefficient enables fast prediction of the vehicle overturning moment coefficient after the installation of porous wind barrier at any given yaw angle beta, without conducting additional wind tunnel tests.
Daus, ReginaKoch, HerbertLopes, Antonio M. G.Vicente, Antonio H. S. N....
16页
查看更多>>摘要：Wind turbine wakes have a strong impact on wind farms as they affect the power output and the turbulence level. These factors have a determinant impact on turbines lifetime. Thus, wake modelling is of critical importance to the wind energy industry, playing a central role in the optimization of wind farm layouts. This work aims at assessing some of the available analytical wake models that modify the computed wind field by CFD as a postprocessing correction tool. Such validation was done with recourse to experimental SCADA data obtained in an onshore wind farm with eight wind turbines distributed by two rows. Conclusions were drawn for the Jensen, Jensen2D, Larsen, Gaussian BPA and Gaussian Ishihara models, by analyzing the computed velocity ratio relative to the upstream leading turbine, both in a single wake and in multiple wake situations.
查看更多>>摘要：The exploitation of offshore wind resources is considered to have considerable potential in providing carbon-free energy. To increase the economic viability of wind farms, improvement in power generation is sought by mitigating the wake losses. While the industrial standards still favour turbine-level power maximization, the concept of collaborative yaw-based plant-level control has gained significant attention in recent years. The present work investigates the potential of such a wind farm control strategy employing different wake deficit models, for a range of atmospheric conditions and plant layouts. The utilized wake velocity deficit models are the top-hat Jensen model, the Gaussian-shaped Bastankhah model and its novel extension, termed Gauss-Curl Hybrid model, which accounts for secondary steering effects. The yaw control optimization is conducted on a row of eight NREL 5-MW turbines using the FLORIS modelling utility and the SLSQP optimization algorithm. Generally speaking, the Jensen model shows a lack of robustness and is not recommended for yaw control studies. In contrast, the two Gaussian-shaped models are well handled by the optimization algorithm and produce consistent results. More specifically, the Bastankhah model prefers yaw offsets of nearly equal magnitude throughout the whole wind farm except for the most downstream machine that remains aligned with the freestream. On the other hand, the GCH model suggests a large offset at the most upstream turbine, which is gradually reduced at consecutive machines. For the reference wind farm considered, the total power improvement was 3.59% and 14.66% for the Bastankhah and GCH models, respectively.
查看更多>>摘要：Accurately simulating the aerodynamic characteristics is important to the safety and stability of high-speed train, especially when it operates under strong crosswinds. In recent, long span highway-railway bridge has been developed rapidly to enable the high-speed rail to cross wide rivers and valleys, where the truss bridges are usually served as the main girder type. This study aims to investigate the unique interference effects on the aerodynamic characteristics of the high-speed train caused by the truss bridge, i.e., the so-called shielding effect and internode effect. The shielding effect of the truss bridge on the mean aerodynamic coefficients is firstly quantified based on a moving train model test in wind tunnel. Combined with a 3-D computational fluid dynamic (CFD) model validated by the wind tunnel test, a series of numerical simulations are conducted to study the mechanism of internode effect, where the airflow field and pressure distributions around the train body and on the bridge surface are interpreted. The results reveal that the truss bridge has an obvious whole and local shielding effects, with the first effect introducing a remarkable decrease on the aerodynamic forces of trains at the entrance and the second effect leading to an intermittent excitation.
查看更多>>摘要：The vortex-induced vibration (VIV) of slender flexible structures is usually estimated based on two-dimensional aerodynamic parameters determined by sectional model wind tunnel tests. Before converting such test results into a prototype flexible structure, many complicated factors, such as the spanwise correlation of aerodynamic force and vibration mode shape, should be considered. In this study, wind tunnel tests of a 5:1 rectangular taut strip model and its sectional model with the same geometry were first conducted to analyze the relationship between the VIV amplitude of the flexible structure and sectional model. The results showed that the taut strip model sustained an approximately 15% higher VIV amplitude than the sectional model, indicating that the VIV amplitude could be underestimated if the sectional model test results were directly used. Next, based on the identified spanwise correlation function of the 5:1 rectangular cylinder, several existing VIV response estimation approaches based on Scanlan's semi-empirical vortex-induced force (VIF) model were examined and compared. Finally, an improved approach was proposed by which the correlation coefficients based on the partial spanwise correlation theory could be approximated with more comprehensive consideration of the spanwise correlation, allowing for a more accurate evaluation of the VIV amplitude for flexible structures.
查看更多>>摘要：The introduction of performance-based wind engineering has opened the door to the potential of designing wind excited structural systems with controlled inelasticity. The possibility of adopting the state of dynamic shakedown as a target system-level limit state is attracting growing interest. However, there is a lack of frameworks that enable the efficient assessment of the reliability of structural systems at dynamic shakedown. To overcome this limitation, a stochastic simulation-based reliability assessment framework is presented in this paper, in which the dynamic shakedown problem is formulated within the setting of distributed stress-resultant plasticity. In addition, the framework allows the estimation of traditional component-level first yield limit states therefore enabling direct comparison between reliabilities associated with system-level inelastic limit states and those aligned with current design practices. A full scale archetype is studied, from which it is seen that the limit state of dynamic shakedown occurs at load levels far beyond those inducing first yield, resulting in significant increases in reliability at dynamic shakedown as compared to component and system first yield. The straightforward estimation of the reliabilities through the proposed framework illustrated the potential of adopting dynamic shakedown as a target system-level limit state for design with controlled inelasticity.
NSTL
Elsevier