Parametric study on buffeting performance of a long-span triple-tower suspension bridge

The triple-tower suspension bridge is a brand new type of structural form that is equipped with a dominant mid-tower. The dynamic characteristics of this multiple main-span suspension bridge present a significant difference with that of the conventional single main-span suspension bridge. Hence, taking the Taizhou Yangtze River Bridge as an example, the buffeting performance of a long-span triple-tower suspension bridge under strong winds is comprehensively investigated via finite element method. Specifically, the sensitivity of structural buffeting performance to some major structural parameters, aerodynamic parameters as well as parameters of turbulence inputs is analysed in time domain. It was found that the structural buffeting performance heavily depends on the dead load of the main girder, sag-to-span ratio of the main cable, longitudinal stiffness and structural type of the mid-tower. Also, appropriate selection of aerodynamic admittance function, power spectrum model of fluctuating wind and the spatial coherence coefficient is important in the buffeting analysis. Besides, the self-excited forces have small impact on the calculation of buffeting responses of such a bridge. The analytical results can provide references for the buffeting analyses and wind-resistant design of similar long-span triple-tower suspension bridges.     

预焙阳极生产过程收尘粉回收利用技术的开发与应用

针对预焙阳极生产过程中产生的收尘粉,以循环经济3R原则为指导思想,对各点收尘粉的性能进行比较筛选,确定适宜炭生产使用的收尘粉;根据空气动力学和固体颗粒稀相输送原理,成功开发出预焙阳极生产过程收尘回收利用技术,并创新收尘粉进入球磨机给料方式,消除因外来收尘粉对球磨粉的粒度影响,使球磨粉-0.074 mm的纯度稳定控制在68%～75%,实现球磨粉纯度的稳定控制。     

Concentration and flow distributions in urban street canyons: wind tunnel and computational data

The goal of this paper is to present bluff body flow and transport from steady point sources of pollutants, or chemical and biological agents in an idealized urban environment This paper includes ventilation behavior in different street canyon configurations. To evaluate dispersion in a model urban street canyon, a series of tests with various street canyon aspect ratios (B/H) are presented. Both open-country roughness and urban roughness cases are considered. The flow and dispersion of gases emitted by a point source located between two buildings inside an urban street canyon were determined by the prognostic model FLUENT using four different RANS turbulent closure approximations and in the model fire dynamics simulator using a large eddy simulation methodology. Calculations are compared against fluid modeling in the Industrial Meteorological Wind Tunnel at Colorado State University. A basic building shape, the Wind Engineering Research Field Laboratory building (WERFL) at Texas Tech University, was used for this study. The urban street canyon was represented by a 1:50 scale WERFL model surrounded by models of similar dimensions. These buildings were arranged in various symmetric configurations with different separation distances and different numbers of up- or downwind buildings. Measurements and calculations reveal the dispersion of gases within the urban environment are essentially unsteady, and they are not always well predicted by the use of steady-state prediction methodologies.     

Optimisation and performance analysis of vertical axis wind turbine with blade pitching at best position angle for different tip speed ratios

ABSTRACT

Best pitch position of each blade in the rotation of turbine at different azimuth angle has been calculated at different Tip Speed Ratios (TSRs) by using the aerodynamic analysis. This paper analyses and optimises the various design parameters and its influence on the starting turbine by itself, power coefficient and overall performance of the Vertical Axis Wind Turbine (VAWT). The results indicate that the best pitch position blade method improves the self-starting capacity and power coefficient. The best position blade pitching curve-1 gives maximum power coefficient at 45° pitch angles for TSRs of 0.5 and the best position blade pitching curve-5 with 15° pitch angle gives maximum coefficient of power about 0.49 for TSRs at 2.5. The results indicate that the variation of pitch angle from 45° to 10° with six best position blade pitching curves give the maximum power coefficient for TSRs from 0.5 to 3.     

A computational study of the aerodynamic forces acting on a tractor-trailer vehicle on a bridge in cross-wind

This paper examines the effect of truck speed on the aerodynamic forces acting on a standard sized, North American transport truck travelling across a bridge under conditions of cross-wind. The objective is to establish a relationship between wind speed, truck speed and propensity for truck rollover that may be used to devise strategies for accident avoidance. Conditions of a moving truck travelling in both windward and leeward lanes were considered with a cross-wind speed of 120 km/h and truck speeds of 0-120 km/h. Using the calculated pressure distributions on the surface of the truck; the aerodynamic lift, drag and moment coefficients were determined for relative wind directions. The results show that the aerodynamic moment tending to overturn a truck in the windward lane of the bridge rises from approximately 120 kN m at low speeds (0-40 km/h) to 217 kN m at a truck speed of 120 km/h. For a truck in the leeward lane, the corresponding moments are substantially less, at 82 and 154 kN m, respectively. The 1.1 m barrier wall along the side of the bridge is a contributing factor to the aerodynamic difference between windward and leeward lanes.     

Wind turbine aerodynamic response under atmospheric icing conditions

This article deals with the atmospheric ice accumulation on wind turbine blades and its effect on the aerodynamic performance and structural response. The role of eight atmospheric and system parameters on the ice accretion profiles was estimated using the 2D ice accumulation software lewice Twenty‐four hours of icing, with time varying wind speed and atmospheric icing conditions, was simulated on a rotor. Computational fluid dynamics code, FLUENT, was used to estimate the aerodynamic coefficients of the blade after icing. The results were also validated against wind tunnel measurements performed at LM Wind Power using a NACA64618 airfoil. The effects of changes in geometry and surface roughness are considered in the simulation. A blade element momentum code WT‐Perf is then used to quantify the degradation in performance curves. The dynamic responses of the wind turbine under normal and iced conditions were simulated with the wind turbine aeroelastic code HAWC2. The results show different behaviors below and above rated wind speeds. In below rated wind speed, for a 5 MW virtual NREL wind turbine, power loss up to 35% is observed, and the rated power is shifted from wind speed of 11 to 19 m s^?1. However, the thrust of the iced rotor in below rated wind speed is smaller than the clean rotor up to 14%, but after rated wind speed, it is up to 40% bigger than the clean rotor. Finally, it is briefly indicated how the results of this paper can be used for condition monitoring and ice detection. Copyright © 2012 John Wiley & Sons, Ltd.     

高速列车单车通过隧道压力波的研究

采用计算流体力学的数值计算方法对基于三维、瞬态、可压缩Navier-Stokes方程和κ-ε两方程紊流模型进行求解,模拟高速列车单车通过隧道时列车外流场的特性,分析高速列车单车通过隧道的压力波特性及阻力变化规律。结果表明列车单车通过隧道的压力波最小负压值与速度为二次函数的关系,列车阻力主要由压差阻力构成。研究结果可为解决隧道空气动力学问题提供参考依据。     

A numerical analysis of transient flow past road vehicles subjected to pitching oscillation

Conventionally, the pitching instability of road vehicles has been controlled mechanically through the application of suspension systems. The present study demonstrates how unsteady aerodynamics can be exploited for such control by properly configuring vehicle body shapes. To discern the effect of unsteady aerodynamics on road vehicle stability, large eddy simulation has been conducted to simulate the flow past simplified vehicle models. Forced-sinusoidal-pitching oscillation was imposed on the models during the simulation to probe their dynamic responses. Numerical results were compared with wind tunnel measurements for validation, and good agreement is attained. Unsteady flow structures above the rear section of the vehicles were found to significantly affect their pitching stability. Depending on the vehicle body shape configurations, the induced aerodynamic force tended to either enhance or restrain the vehicles' pitching instability.     

直升机模拟器的现状和发展趋势研究

简要阐述了直升机模拟器的基本组成和各部分的功能、现状和关键技术,重点介绍了计算机系统中直升机飞行动力学的相关理论和技术发展趋势。