Modelling of inflow-conditions for vortex particle methods to simulate atmospheric turbulence and its induced aerodynamic admittance on line-like bluff bodies

ABSTRACT

This paper presents a novel method for the simulation of aerodynamic admittance of turbulent wind on bluff line-like structures using a pseudo 3D model of Vortex Particle Method (VPM). The method is a computationally efficient extension of the 2D VPM, where a coupled set of simulation slices accounts for the 3D nature of the oncoming wind flow. Pre-computed vortex particles are seeded in each of the parallel 2D simulation slices in order to model the turbulent velocity perturbations. Here, the modelling of the inflow seeding particles is enhanced, reducing the computational cost and allowing extendibility into quasi 3D domain. This a priori computation of the seeding vortex particles is based on modelling the atmospheric turbulence characteristics. The method is applied to simulate turbulent flow around an infinitesimally thin flat-plate, to asses its validity at the viscous-rotational boundary layer, which is important for accurate fluid-structure Interaction simulations. Furthermore, sensitivity analysis to different attributes is assessed     

环境模拟实验室中近地层风速廓线的形成研究

在环境模拟实验室中利用阻尼网对实验区形成的近地层风速廓线进行了数值模拟和实验研究.阻尼网的布置方案以变孔隙率阻尼网作为指导,选用30目和16目定孔隙率阻尼网4种不同高度的混合式布置方式.数值模拟采用Fluent软件,将结构复杂的阻尼网简化为具有一定厚度的多孔介质模型,湍流模型为标准k-\varepsilon模型.结果表明可将阻尼网作为多孔介质处理,定孔隙率阻尼网的组合可在短实验段内形成所需近地层的风速廓线,模拟值与实验值吻合良好.     

基于风洞的设备健康管理与数据有效性判定平台研究

低速增压风洞是满足我国航空工业科技发展而建设的一座气动力重大基础试验设施。为了保障该设施的高效率和可靠地运行,以各机电设备、电气测控设备、机械装置为对象,根据其故障模式和故障特点选取合适的监测点,获取实时工作状态数据,再以数据为基础,进行状态监测、故障诊断、故障预测,实现预先性决策和针对性快速维修。基于OSA-CBM 体系构建的风洞健康管理系统,根据设备的运行状态,实现对试验数据的有效性进行实时判定,并实现了风洞装备由事后维修向视情维修转变;实现了装备从使用、维护、管理模式由分散式管理向集约式管理的转变;实现了装备系统故障诊、预测及判读从人工智能向机器智能的转变。     

Closed-form expressions for the macroscopic flexural rigidity coefficients of periodic brickwork

Approximate expressions for the macroscopic out-of-plane elastic coefficients of brick masonry with a regular pattern are derived in closed form using a homogenization approach for periodic media. Following an approach similar to the Method of Cells for fiber reinforced composites, a (piecewise-)differentiable expression depending on very a limited number of degrees of freedom and fulfilling suitable periodicity conditions is proposed for the microscopic transverse displacement field over any Representative Volume Element (RVE). Some of the equilibrium conditions at the interfaces between bricks and mortar joints are also fulfilled. By averaging the moment and curvature fields over the RVE, the macroscopic bending stiffness coefficients can be explicitly obtained. Using the FE solution of a masonry panel subjected to elementary load conditions as a benchmark, the proposed approach is found to accurately match the numerically obtained stiffness coefficients, for masonry elements of different geometry and different mechanical properties. In several instances, the proposed expressions agree with the numerical predictions better than other analytical expressions available in the literature.     

Progress in wind tunnel experimental techniques for wind turbine

Based on the unsteady aerodynamics experiment (UAE) phase VI and the model experiment in controlled conditions (MEXICO) projects and the related research carried out in China Aerodynamic Research and Development Center (CARDC), the recent progress in the wind tunnel experimental techniques for the wind turbine is summarized. Measurement techniques commonly used for different types of wind tunnel experiments for wind turbine are reviewed. Important research achievements are discussed, such as the wind tunnel disturbance, the equivalence of the airfoil inflow condition, the three-dimensional (3D) effect, the dynamic inflow influence, the flow field structure, and the vortex induction. The corresponding research at CARDC and some ideas on the large wind turbine are also introduced.     

分裂导线自阻尼振动特性研究

为了掌握线路的振动状态,确定线路抗振能力,保证线路安全,需要明确架空输电导线的风致振动响应．本文针对江苏境内某特高压工程LGJ-630/45型导线,建立其振动控制能量平衡方程,编制了Fortran程序以高效准确地求解该超越方程,计算分析了单导线及四种分裂导线微风振动状态下的振动及耗能特性．结果表明,单导线在风振平衡点处的双振幅最大值在最低频率上,约为导线直径的两倍;四种分裂导线风振平衡点处的幅值在15Hz附近达到最大值;导线单位长度功耗在60Hz附近达到最高,功耗能力在较低频域(10Hz~20Hz)上较弱,在较高频域(30Hz~80Hz)较强;导线分裂数越大,分裂导线的振幅越小,八分裂导线的防振消振效果相对最好;四种分裂导线在在10Hz~20Hz频域振动幅值大而单位功耗水平低,因此10Hz~20Hz频段是分裂导线的危险频段,防振措施应该针对这一频段设置．研究方法与成果为LGJ-630/45导线的抗振设计提供了科学依据．     

风机塔筒结构横向振动特性的快速计算方法

本文提出了一种风机塔筒结构横向振动特性的快速计算方法．将机舱和叶片整体、连接法兰盘分别简化为集中质量,塔筒简化为非均匀悬臂梁,建立风机塔筒结构横向振动方程．给出了用假设模态法计算塔筒结构固有频率和模态函数的过程．通过与文献及有限元数值结果比较验证了方法的有效性．本文方法仅需给出结构的基本参数,如截面半径变化规律、法兰盘位置和质量、机舱及叶片质量,便可快速求解其频率和模态,无需建立其复杂的力学模型．     

Three-phase coupled modelling research on rain–wind induced vibration of stay cable based on lubrication theory

Cables of cable-stayed bridges may vibrate with large amplitude under wind and rain, which is known as rain–wind induced vibration (RWIV). According to the pervious researches, the formations and oscillations of rivulets on stay cable surface play important roles in RWIV. In this paper, four different 2D models are presented based on lubrication theory, and the best way of simulating RWIV through lubrication theory is confirmed by the comparisons of rivulet motions and cable vibration responses between these four models and pervious researches. On this basis, the relations among rivulet motions, cable aerodynamic forces and vibration responses are investigated to reveal the mechanism of RWIV. Numerical simulation results show that when RWIV occurs, the periodic oscillations of rivulets around cable lead to the periodic fluctuations of cable lift and drag, whose frequencies are almost equal and close to cable natural frequency. Under the periodically fluctuant lift and drag, cable vibrates with large amplitude in across-wind and along-wind directions, which may further enhance the circumferential oscillations of rivulets conversely. These confirm the conclusion that the resonance between rivulets and cable oscillation may be one of the main reasons for RWIV.     

Numerical modeling of current loads on a net cage considering fluid–structure interaction

In this paper we propose and discuss a numerical method to model the current loads on a net cage. In our numerical model, the fluid–structure interaction is taken into consideration. The net cage is modeled on the mass-spring model; the flow field is modeled by the finite volume method (FVM). A novel hybrid volume approach is used to add the resistance force of the net cage into the flow field for coupling the fluid and net. The net resistance to the flow is calculated directly by the net’s current load using Newton’s Third Law. The resistance force is discretized in the hybrid volume and represented in the source term of the Navier–Stokes equation. By using the hybrid volume method, the mesh grid is separated from the net shape, and sparse grid (0.1 m) can be used to calculate the flow field for computational efficiency. Based on the detailed flow field, we can predict the net’s current load more accurately. The final results are derived by the segregated iterative calculation of net shape and flow field. Current forces acting on both rigid and flexible net cages are simulated at water velocity from 0 to 1 m/s; the simulation results of proposed numerical method are compared with the existing experiments, good agreements are shown in both flow field and current force, the mean normalized absolute error of the current force between simulations and measurements is about 5%.     

屋面光伏板风荷载特性数值分析

风荷载在屋面光伏阵列结构体系设计中起控制作用。采用计算风工程的方法分析讨论了屋面光伏板的风荷载特性。数值算法采用分离涡模拟方法。数值计算结果与现有风洞实验数据的比较,验证了本文方法的正确性。考虑影响光伏板风荷载的因素主要有光伏板在屋面上的安装位置、安装倾角、光伏阵列之间的距离和风向等。计算结果表明,屋面处脱落的涡对安装在不同位置的光伏阵列风荷载的影响较明显。当倾角由15°增加到45°时,电池板受到的风荷载随着倾角的增加而增大。在一定阵列间距范围内,光伏板风荷载主要表现为前排对下游光伏板的遮挡影响。本文方法与结果能为屋面光伏建筑结构设计提供重要参考。