深切峡谷相邻桥址区风速相关性研究

文章以西南深切峡谷山区大渡河上两座相邻的千米特大桥为工程背景,采用FLUENT对桥址区风场特性进行数值模拟,根据桥位附近历史风向记录,设置了24个来流风向工况,明确了上下游两座大桥的特征位置的风速相关性。研究结果表明:同一桥梁的跨中和桥塔在所有工况下横桥向风速均具有良好的线性相关性;对于上下游桥梁,在排除个别特殊工况后,两桥的跨中依然保持良好的风速相关性;最后,研究发现桥塔风速变化规律与跨中基本一致,但相较跨中,桥塔处风速相关性较弱。     

地形模型的尺度对山区桥址区风特性的影响

数值模拟是研究复杂山区风特性的重要方法之一。为了研究地形模型的尺度对山区桥址区风特性的影响,以西部山区某大跨度悬索桥桥址区为工程背景,建立了以桥位为中心的50 km×50 km的大尺度模型和10 km×10 km的小尺度模型,采用CFD数值模拟的方法,研究了地形模型的尺度对桥址区平均风速和风向角的影响。结果表明：地形模型的尺度对桥址区平均风速的影响十分显著。当来流由小尺度地形模型边界输入时,地势平坦,气流沿河道吹来,桥位上游的风向与入口风向基本平行,桥位风速较高。而当来流由大尺度地形模型边界输入时,由于山体的阻挡,桥位上游的来流风向近似平行于峡谷走向,桥位处风速明显减小,跨中减小幅度约为25%。2种模型在桥位处的气流流向相似,地形模型的尺度对桥位处的风向角的影响相对较小。     

桥位风场特性研究方法探讨

在桥梁设计过程中,特别是初步设计阶段,准确获得大跨径桥梁桥位风场特性参数非常重要。本文以临猗黄河特大桥桥位处风场特性研究为背景,采用数值模拟和风场实测方法对风场特性进行研究。结果发现,风场实测位置处10m、30m、50m、80m高度的平均风速分别为2.7m/s、3.4m/s、3.9m/s、4.4m/s,数值模型对应位置处相同高度的风速计算值分别为2.90m/s、3.24m/s、3.55m/s、3.94m/s,误差分别为7.4%、-4.7%、-9.0%、-10.5%,计算结果满足工程需求。对处于复杂地形特别是峡谷谷口的大跨径桥梁,在初步设计阶段通过数值模拟方法获得桥位处风速数据的方法具有可行性。     

基于外海环境预报的近岸岛礁桥址区波高ANN推算模型

中国跨海桥梁多建于近岸岛礁海域,桥址区的波浪要素随时空演变复杂。桥址区波高的准确推算对于桥梁结构设计和施工组织具有十分重要的意义。提出一种基于外海环境预报数据的近岸岛礁桥址区波高人工神经网络（ANN）推算模型,并以平潭海峡公铁两用大桥桥址海域为研究对象,运用ANN算法中常用的BP神经网络对外海海洋预报台提供的波高、风速数据以及在桥址区实测波高数据进行训练,建立二者之间的映射关系及ANN推算模型。为验证推算模型的可行性和有效性,运用上述模型对桥址区连续80 d的海浪波高进行推算,通过对比前人模型和实测数据发现,推算波高和实测波高的变化趋势基本吻合,均方根误差满足预测要求,获得了理想的预测效果。研究表明,提出的波高ANN推算模型可以利用外海预报信息进行近岸岛礁桥址区的波高推算,且建模过程较为简单。     

三维山体风场特性的风洞试验研究

通过风洞试验对5种坡度的山体模型进行风速测试,对典型陡坡山体的风场特性进行了三维的、细致的研究,并将5种坡度山体山顶和后山脚位置的加速比进行了比较,还将典型陡坡山体山顶位置的加速比与国内外规范进行了比较。最后基于典型陡坡山体风场分布特性,对山地建筑的选址提出了建议。     

简易峡谷地形模型风场特性试验研究

为了获得桥址处于峡谷地形时的风场特性分布规律,采用圆锥形山体制作了具有不同谷坡斜率的系列简易峡谷模型,并通过风洞试验测试了其风场特性,最终得出了一些有参考价值的结论。     

台风边缘区风场特性及其作用下高耸桅杆结构风效应实测研究

以深圳356 m气象梯度塔记录的风速时程数据为基础,分析了台风“圆规”边缘区风场平均风速、湍流度及风谱特性,并进一步探讨了台风作用下梯度塔的风致响应特征。结果表明：台风边缘区域大风时段风剖面指数均值为0.243,高度40 m以下湍流强度介于GB 50009—2012《建筑结构荷载规范》中C类与D类场地之间,高度320 m处湍流强度则接近C类场地的;von Karman谱与高度320 m处实测风谱吻合较好,但与低空实测谱存在一定差异;台风激励下梯度塔以横风向振动为主,且风振多模态参与特征明显,纤绳振动不可忽略;结构加速度响应幅值对梯度塔的模态频率和阻尼存在一定影响;结构x向和y向前三阶模态频率整体呈现随加速度响应增大而减小的趋势;阻尼比的识别结果较为离散,y向的前三阶和x向的一阶模态阻尼比随结构加速度响应增大而增大,而x向的二阶和三阶模态阻尼比则随响应增大呈减小的趋势。     

大跨度桥梁结构空间受力特性研究

以大跨度斜拉桥为例,利用空间有限元模型分析方法,对其结构受力特性进行了分析,为大跨度桥梁的斜拉桥梁的施工和维护提供了理论基础。     

跨线箱梁桥切割拆除的数值模拟及施工关键技术研究

以某上跨既有运营线路的箱梁桥拆除工程为例,为保证拆除施工过程的安全性,开展了数值模拟和施工关键技术研究。从对周边环境影响和对既有运营线路行车安全的角度出发,进行拆除施工方案比选,最后选定采取机械无震荡分块切割、汽车吊吊装外运、场外破除的方法;通过Midas软件进行拆除过程数值模拟分析,综合考虑拆除方向、切割分块、切割顺序等因素对结构的内力和位移影响。结果表明,在每个施工工况下,结构的内力和位移均满足相关规范要求,但在A7和A5龙门架拆除时,桥梁在纵桥向发生最大位移,为防止其发生倾覆,建议在龙门架拆除前需增加相应的支撑或约束措施。     

被上游建筑遮挡的下游建筑表面风压CFD模拟的可靠性研究

研究城市通风或建筑风环境的主要目的是探索建筑之间和建筑内外的气流运动及污染物扩散规律,主要手段有风洞实验和计算流体动力学（CFD）模拟,后者相对前者的优点是易操作且成本低,但由于流体运动的高度不确定性,其结果的准确性存疑。在城市中,建筑之间的互相遮挡是主要特征之一,提取其中最基本单元,把两个建筑之间的遮挡问题分为上游建筑有孔（如穿堂风）与无孔两种情况,运用CFD中的雷诺平均模型（RANS）模拟下游建筑表面的风压,并与风洞实验进行严格对比,以讨论CFD方法在这一基本单元问题中的可靠性。网格敏感性分析显示,建筑表面最小网格为建筑高度的2%时,可获得可靠的结果。5种常用RANS模型的结果与风洞实验严格对比表明：RANS模型对模拟上游有孔遮挡的可靠性明显高于模拟无孔遮挡;RANS模型对于建筑上部的风压模拟结果普遍好于建筑下部;其中,SST k-ω模型准确性最高,在上游有孔时,平均误差11%,上游无孔遮挡时,则为16%。     

Numerical simulation of wind flow over transverse and pyramid dunes

Wind tunnel experiment and computational fluid dynamics (CFD) simulation of the flow past a scaled transverse dune model were performed, after which a validated numerical method was used to evaluate the flow characteristics over a full-scale pyramid dune. The dimensional effect of the CFD simulation was analyzed by comparing the results of two- and three-dimensional (2D and 3D) models with the same mesh method and flow condition. There was excellent agreement between the wind tunnel measurements and the 2D and 3D sectional CFD results, proving that the simplified numerical model could simulate the sectional flow pattern of dunes. However, the lateral inhomogeneity of the flow field is significant although with simple transverse dunes, and 3D simulation is required to capture the lateral inhomogeneity of flow patterns after the dune crest line. Survey data of the topography of a pyramid dune, located at the eastern foot of the Mingsha Megadune, Dunhuang, China, were used to build numerical geometry. The flow fields over this pyramid dune under three inlet flow directions are significantly different from each other, and the lateral variances of flow patterns at different vertical planes are profound. The location, shape, and magnitude of the reverse flow zone change corresponding to the dune topography.     

住宅小区风环境数值模拟

建立了某典型住宅小区风环境的物理和数学模型,并应用计算流体动力学方法求解了三种来流角度下的稳态三维湍流流场,给出了速度、压力、湍流度参数的分布;分析了街区涡流、巷道风及活塞风等效应,研究了风压作用下建筑群的迎风及背压区,讨论了湍流入流边界对合理湍流分布的作用;比较了不同来流角度下五个观测点位置的风环境参数。     

Dynamic overset 2D CFD numerical simulation of a small vertical axis wind turbine

ABSTRACT

The environmental friendly sources of power have been explored due to increased environment degradation. In this regard, wind energy may be a viable option. A renewed involvement in Vertical axis wind turbines (VAWT) was found. A wide variety of factors such as the cut-in, cut-out wind speed will decide the beneficence of VAWT as a function of energy production and reliability. In this research work, 2D computational fluid analysis of an aggregate small type of vertical axis wind turbine is performed using pecuniary codes of GAMBIT 2.3 and FLUENT 6.3. At starting, the simulation model and numerical method of small type of vertical axis wind turbine is presented in detail having classical NACA0018, NACA0021 and NACA0025 three-bladed rotor. The result shows that NACA0025 bladed rotor has the highest moment of 2.9195?Nm and power 43.7924?W at a tip speed ratio?=?6.     

Experimental and numerical study on natural ventilation performance of various multi-opening wind catchers

Wind catcher as a natural ventilation system is increasingly used in modern buildings to minimize the consumption of non-renewable energy and reduce the harmful emissions. Height, cross section of the air passages and also place and the number of openings are the main factors which affect the ventilation performance of a wind catcher structure. In this study, experimental wind tunnel, smoke visualization testing and computational fluid dynamic (CFD) modeling were conducted to investigate ventilation performance of wind catchers with different number of openings to find how the number of opening affects hydrodynamic behavior of wind catchers. To achieve this particular aim, five cylindrical models with same cross section areas and same heights were employed. The cross sections of all these wind catchers were divided internally into various segments to get two-sided, three-sided, four-sided, six-sided and twelve-sided wind catchers. The experimental investigations were conducted in an open circuit subsonic wind tunnel. For all these five shapes, the ventilated air flow rate into the test room was measured at different air incident angles. Numerical solutions were used for all these five configurations to validate the proposed measuring techniques and the corresponding wind tunnel results. The results show that the number of openings is a main factor in performance of wind catcher systems. It also shows that the sensitivity of the performance of different wind catchers related to the wind angle decreases by increasing the number of openings. Moreover, comparing with a circular wind catcher a rectangular system provides a higher efficiency.     

Computational fluid dynamics and artificial neural network-based analysis and forecasting of wind effects on obliquely parallel multiple building models using categorical variable encoding

This research investigates the influence of wind on four closely spaced parallel building models using computational fluid dynamics (CFD). The buildings are positioned either perpendicular to the wind direction or at various oblique angles. The aerodynamic results obtained for these buildings in an interfering condition are compared to those of an isolated tall building using the interference and obliquity effect (IOE) factor. Graphical comparisons are made among the different models and faces, considering various obliquity angles (OAs). The inner building models exhibit higher pressure and force coefficients at higher OAs. The variation of pressure coefficients along the horizontal peripheral direction is also analyzed, and the trade-offs of higher and lower OAs are discussed for the different building models. Furthermore, an artificial neural network (ANN) is trained using surface pressure coefficients from approximately 6000 data points distributed over different facets of building models. Categorical encoding is employed using one-hot encoding-based dummy variables for different building models, while numerical variables such as OA and X, Y, and Z coordinates are included as input for the ANN. The ANN is trained using a total of 238,340 data points (considering different building models and different OA scenarios), and its parameters are monitored during training to minimize errors and achieve high predictability. Finally, a representative case is used to plot the pressure contour obtained from the trained ANN, which is shown to be highly comparable to the CFD-based contour.     

洞口设置对高层建筑静力风荷载的影响研究

本文对涉及两种开洞率、三种不同开洞位置和全封闭(无洞口)的八个高层建筑刚性模型的表面平均风压分布进行了风洞试验研究,并与计算流体动力学(CFD)大型商业软件Fluent6.0的计算结果进行了对比分析。结果表明,开洞建筑平均风压的减少主要是受荷面积减少引起的,但其减少的比率大于开洞率。此外,借助Fluent6.0对不同开洞率情况下的建筑模型进行了大量算例分析,得到了中部开洞建筑模型的平均风压系数相对值和基底弯矩系数相对值与开洞率之间的相关方程;探讨了底部开洞建筑模型洞内平均风速的增大效应与洞口大小、来流方向之间的关系。分析表明,在最不利来流风向角情况下,洞中最大平均风速可超过建筑模型顶部的远处来流风速,应引起建筑风环境设计者的关注。     

The methodology for aerodynamic study on a small domestic wind turbine with scoop

The aim of this study is to investigate the possibility of improving wind energy capture, under low wind speed conditions, in a built-up area, and the design of a small wind generator for domestic use in such areas. This paper reports the first part of this study: the development of the methodology using physical tests conducted in a boundary layer wind tunnel and computer modelling using commercial computational fluid dynamics (CFD) code. The activities reported in this paper are optimisation of a scoop design and validation of the CFD model. The final design of scoop boosts the airflow speed by a factor of 1.5 times equivalent to an increase in power output of 2.2 times with the same swept area. Wind tunnel tests show that the scoop increases the output power of the wind turbine. The results also indicate that, by using a scoop, energy capture can be improved at lower wind speeds. The experimentally determined power curves of the wind generator located in the scoop are in good agreement with those predicted by the CFD model. This suggests that first the developed computer model was robust and could be used later for design purposes. Second the methodology developed here could be validated in a future study for a new rotor blade system to function well within the scoop. The power generation of such a new wind turbine is expected to be increased, particularly at locations where average wind speed is lower and more turbulent. The further study will be reported elsewhere.     

Large-eddy simulation of wind effects on a super-tall building in urban environment conditions

A combined study of large-eddy simulation (LES), wind tunnel testing and full-scale measurement is conducted for the evaluation of wind effects on a super-tall building in a complex urban area. To validate the numerical simulations, the wind tunnel experiments including synchronous multi-pressure and high-frequency force balance model tests are conducted in a boundary layer wind tunnel laboratory. The numerical predictions are then compared with the experimental results, demonstrating that the LES can provide comparable predictions of the wind effects on the super-tall building. Furthermore, the cross-validation of the predicted displacement responses by the LES against the wind tunnel and full-scale measurements are presented and the agreement among them is reasonably good. The main objective of this study is to explore an effective numerical approach for the accurate estimation of wind effects on tall buildings in urban environment conditions and promote the practical use of the LES in the wind-resistant design of complex structures.