Measures to control vehicle movement at exposed sites during windy periods

Measures at present in use in the U.K. to control vehicle movement at exposed sites during windy periods are rather arbitrary and ill defined. This note presents rational methods for such traffic control based on an analytical model developed by the author. A “two level” system of control is proposed with high sided vehicle speed being restricted to 10 m s⁻¹ at a wind gust speed of 17.5 m s⁻¹ and vehicle movement being stopped completely at a windgust speed of 22.5 m s⁻¹. The analytical model suggests that no account should be taken of wind direction, and also shows that the inter-relation between accident wind speed and vehicle speed and wind direction is far from being straightforward.     

Experimental investigation of the aerodynamic stability of the “Endless Column”, Romania

Wind tunnel tests have been performed on several models of the “Endless Column”, a 30 m tall sculpture, created by C. Brancusi in 1938. In spite of its slenderness, the Column, located in Targul Jiu, Romania, has shown a great stability against wind. In order to clarify if the symmetric, original shape has influence upon its stability, we have carried out tests on section models of “Endless Column” shape (EC models) and square shape (SQ models), of various Sc numbers. Across-wind response was determined in smooth flow for wind speeds in wind tunnel of 1–10 m/s (Re=4000–46,000) for angles of attack 0°, 10° and 45°. Furthermore, an aerolastic full model was created and tests under smooth and turbulent flow conditions were performed for angles of attack between 0° and 45°. For low wind speeds, in the area of vortex-induced vibrations, the EC models had similar response with the SQ models; however, for higher wind speeds the EC models proved to be more stable. Based on measurements of aerodynamic drag and lift coefficients and by a verification of Glauert den Hartog criterion, it could be concluded that is a very low possibility for EC model to encounter galloping; for extremely high wind speeds though, this might not be impossible.     

Fatigue model for elastic bars in turbulent wind

Accumulated fatigue damage of an elastic structural bar vibrating in natural turbulent wind may be a primary cause of structural failure. Clumps of strong lateral oscillations may occur randomly with time. These oscillations are due to resonance between the vortex shedding frequency and the natural frequency of the bar. The so-called “lock in” phenomenon apparently extends resonance from a point of coincidence to an interval. An idealized stochastic model is set up on the basis of the empirically observed existence of a critical interval of undisturbed wind velocities upwind of the bar. The upwind velocities are modeled as realizations of a specific stochastic process. A clump of strong lateral, damped harmonic oscillations occurs during any uninterrupted “visit” of the velocity to the critical interval. For velocities outside the critical interval only insignificant lateral oscillations occur. The fatigue damage is assumed to be linearly accumulated according to the Palmgren—Miner rule within each clump and from clump to clump. The goal is to evaluate the structural reliability for any specified period of time. It is expressed in terms of a reliability index.     

基于风洞可视化的环境性能建筑生形方法研究

响应环境的性能化建筑正构建起可持续的建筑未来。城市空间密度的激增带来了愈发严重的室外风热环境的不断恶化,应对这些问题需要建筑师从根本上去认识风这一复杂而又不可见的自然现象。文章介绍了基于定制化物理风洞的建筑生形研究方面的最新成果——在已搭建的适用于设计初期方案优化的小型物理风洞和实验室级大风洞基础上,进行了风环境可视化的定性和定量实验,以此作为建筑形体环境性能评价的依据;同时引入可动模型装置,利用Arduino平台和程序语言进行信号传输控制,选取“扭曲”的建筑形式进行风环境性能找形实验,得出一套系统化的、适用于建筑设计初期、以风环境性能为导向的建筑生形方法。     

Structural response of large stadium roofs due to dynamic wind actions

The paper presents the experimental tests carried out in the Boundary‐Layer Wind Tunnel (BLWT) for the design of large roofs of the new Olympic stadium (Karaiskaki) in Pyraeus (Greece), Manfredonia (Italy) and “Delle Alpi” of Turin (Italy). In addition, a report about some results of the time domain (T. D.) dynamic response analyses performed on the Karaiskaki structure and on the Olympic stadium in Rome will be given. The peculiar shape of these large structures and their particular location (two of them are in the immediate sea vicinity) let arise the question about the actual distribution of the wind loads, i.e. on the pattern of pressure coefficients (c_p) over the entire roof. For every wind direction investigated, the following quantities have been evaluated: mean values of the aerodynamic coefficients c_p, standard deviation of c_p, maximum and minimum values of c_p. Finally, the recorded data have been used for the numerical simulation of the dynamic response of the structure in Time Domain, whose aim is the definition of the design loads of the steel lattice structures. A numerical model of the “Delle Alpi” stadium is also in preparation, allowing results of dynamic response analyses, which are still in progress.     

关于门式刚架设计中的风荷载体型系数

分别采用《门式刚架轻型房屋钢结构技术规程》(CECS102∶2002)和《建筑结构荷载规范》(GB50009-2001)的风荷载体型系数,对不同跨高比、荷载等级、基本风压的荷载效应组合进行分析,其结果可供设计人员参考。     

Flutter and buffeting performances of Third Nanjing Bridge over Yangtze River under yaw wind via aeroelastic model test

Third Nanjing Bridge over Yangtze River in China is a long-span steel cable-stayed bridge with a main span of 648 m and a closed streamline cross-section of single box. The flutter and buffeting performances of the bridge under yaw winds were investigated via a wind tunnel test of full bridge aeroelastic model at a geometric scale of 1:120. The service state and three key construction states including the longest single-cantilever state, the longest double-cantilever state with a temporary pier, and the longest double-cantilever state without any temporary pier, were considered in the test. The test was conducted in both smooth and simulated boundary layer wind fields with various combinations of wind yaw angle and inclination angle. The model was elaborately designed and manufactured, and the modal properties of the service-state model were checked before the test. The natural frequencies and mode shapes were identified automatically using a self-developed special software from the acceleration signals recorded in an ambient vibration test, where an “artificial” turbulent wind with lower mean speed of 1 m/s was used as a major ambient excitation addition to the “natural” one from the slight ground trembling. The modal damping ratios were checked using free-decay vibration approach. The testing results show that the bridge has enough aerodynamic stability for all structural states and wind directions concerned, and the most unfavorable buffeting responses often occur in yaw wind case with a yaw angle between 5° and 30°.     

Mumford's Metaphors: Sticks and Stones versus Ships and the Sea

In Sticks and Stones (1924), a critical account of the sources and prospects of American architecture, Lewis Mumford argues that when “the economic basis of provincial life shifted from the farm to the sea … [it] broke up the internal unity of the village.” His argument is augmented by metaphors: the instabilities of wind, sea, and ship are opposed to the virtues of “good building” and “rooted dignity.” The stable earth and the village architecture it supports are portrayed as organically superior to the chaotic fluidity of the sea. Mumford's metaphors and rhetorical skill bolster a historical narrative that continues to influence prevalent notions of “tradition” in American architecture. Nevertheless, the sea metaphors he deprecates are vital to exemplify American architecture, art, and literature.     

Energy savings due to changes in design of ventilation and air flow systems

Procedures for the design of ventilation and air flow systems are shown to be energy wasteful. The cause lies both in the methodologies and their technical bases, and in the influence of other factors that enter into a final systems choice for a building (particularly economics).The issue of general outside air requirements is discussed. It is found that any system in which outside air supply is sufficient to control body odor necessarily meets oxygen requirements many times over, and that the ventilation rate can be reduced by about 45% to 60% if higher humidities are used. The long-standing belief that required ventilation flow rate for odor control must increase as air space per occupant decreases has previously been proven untrue, yet a survey of the ASHRAE recommendations and various building codes shows that present standards are based on this inaccurate and energy-wasteful principle. New standards, including a rate of 7.5 cmf/person of outdoor air (not conditioned) during the heating season, are proposed based on the result that the ventilation rate is independent of air space per person.Air distribution systems and sub-systems are analyzed in terms of minimum energy requirements. Energy saving by velocity reduction is discussed. Fan power requirements for a high velocity air distribution system are increased by 2500% over that for a low velocity system in commercial buildings.A comparison of the “old” ASHRAE definition of Effective Temperature, which serves as a thermal comfort criterion in AC systems design, is made with the “new” definition, and the consequent energy savings that should result when the “new” definition is accepted in practice is demonstrated.     

Interference excitation of twin tall buildings

The enhanced dynamic response of a tall square building under interference excitation from neighbouring tall buildings has been studied in a series of wind-tunnel model tests. In a low-turbulence wind environment and under normal strong wind conditions, the dynamic loads on the upstream of an identical pair of tall buildings may increase by a factor of up to 4.4. The dynamic loads on the downstream building of the pair may increase by a factor of up to 3.2 due to “resonant buffeting”. Measurements of along-wind and cross-wind force spectra and a number of wake spectra provide an explanation for the observed behaviour. Possible excitation mechanisms are discussed and critical building arrangements presented. The large interference loads found in this study indicate that interference excitation should be carefully considered in the design of tall buildings.     

Air flow behavior and gas dispersion in the recirculation ventilation system of a twin-tunnel construction

Forced ventilation and recirculation systems are usually used in the construction of long twin tunnels as they offer large amounts of fresh air economically. However, because of the confluence near the cross-aisle, the fluid behavior and gas concentration are very different than in traditional forced ventilation for a single tunnel. A three-dimensional numerical model was built to study the air flow behavior and hazardous gas dispersion near the cross-aisle of a twin-tunnel construction. Field measurements were also carried out to validate the numerical model. The results show that there is a “dead zone” ahead of the cross-aisle which has a much lower air velocity than in other parts of the twin tunnels and where hazardous gases are more concentrated and uniformly distributed. In the cross-aisle and confluence zone of the air flow-out tunnel, methane tends to gather at the top and hydrogen sulfide tends to gather at the bottom. Increasing the recirculation velocity does not eliminate the “dead zone” near the cross-aisle although it consumes a huge amount of energy. Increasing the air velocity of the duct is an effective method to improve the air quality, but it is also expensive, especially when the air duct is long. When a jet fan was placed ahead of the cross-aisle in this study, the “dead zone” was eliminated completely. With respect to the recirculation ventilation system of twin tunnels, local jet fans offer an effective and economical way to eliminate the “dead zone”.     

Spatial pattern of population mobility among cities in China: Case study of the National Day plus Mid-Autumn Festival based on Tencent migration data

Population migration, social check-in, vehicle navigation, and other spatial behavior big data have become vital carriers characterizing users' spatial behavior. “Tencent Migration” big data can real-timely, dynamically, completely and systematically record population flow routs using LBS device. Through gathering residents daily mobility among 299 cities in China during the period of “National Day–Mid-Autumn Festival” (NDMAF) vacation (from September 30 to October 8) in 2017 in “Tencent Migration” and defining three periods with “travel period, journey period, return period”, this paper is designed to analyze and explore the characteristics and spatial patterns of daily flow mobility cities from the perspective of population daily mobility distribution levels, flow distribution layers network aggregation, spatial patterns and characteristics of the complex structure of the flow network. Results show that “Tencent migration” big data clearly discovers the temporal-spatial pattern of population mobility in China during the period of NDMAF. The net inflow of population showed a diamond shaped with cross frame support in each period, the four nodes of the diamond contain Beijing, Shanghai, Guangzhou and Xi'an. Main mobility assembling centers are distributed in the urban agglomerations of Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta and Chengdu-Chongqing, and those centers have strong coherence with those urban hierarchies. Most cities are in a state of “relative equilibrium” in the population flow, and clear hierarchical structure and level distinction can be identified. Spatial patterns of population mobility present obvious core-periphery structures. The Dali-Hegang line exhibits a significant network of spatial differences in terms of boundary divisions. In this context, the spatial distribution of urban network could be summarized as “dense in the East and sparse in the West”, and the core linkages of urban network could be characterized as “parallel in the East and series in the West”. The whole network exhibits a typical “small world” network characteristic, which shows that China's urban population flow network has high connectivity and accessibility during the period of NDMAF. The network has a distinct “community” structure in the local area, including 2 national communities, 2 regional communities and 3 local-level communities.     

Pollution of the Dutch coast by oil from the “Eline V” — July 1978

In July 1978 the Dutch coast was polluted by oil over a distance of more than 100 km. Gas chromatographic studies of samples of oil from the beaches showed that this oil was very similar to that released from the oil Tanker “Eline V”, which collided with the “Rosaline” off the coast of East Anglia, England on 6 May 1978. An examination of wind strength, wind direction and sea currents, which determine oil movements on the sea, suggests that the oil pollution on the Dutch beaches originated from the bow section of the ship, which was blown up on 30 May 1978.     

Turbulent winds and pressure effects around a rough cylinder at high Reynolds number

Time histories of the fluctuating wind pressure differential across the shell of a full-scale cooling tower were measured in 1974 by Princeton University personnel. Data were recorded around a single level, at the throat, at a height of ～100 m. A set of simultaneous three-minute records from these data is examined statistically in the present paper. The methods employed include spectral and correlation analyses, plus parametric time-series characterization of the data.Aside from its direct engineering interest as an aid in defining dynamic wind-loading conditions, the fluctuating flow activity around the tower throat may be interpreted as a fair example of turbulent flow about a rough circular cylinder at a Reynolds number approaching 10⁸. This aspect is emphasized in the present paper. In this situation the relation of the spectrum of the incident wind to pressure spectra about the cylindrical section may be of interest in connection with theories of the deformation of turbulence by bluff bodies. Further, the spatial distribution of the “parsimonious” parameters obtained from an autoregressive time-series analysis of the data reveals strong correlations with clearly identifiable flow phenomena around the perimeter, such as key points of the pressure distribution, flow separation, etc.The study, although limited to a single wind record, sixteen peripherally spaced pressure records, and only three minutes of selected time-history data, develops a coherent picture of a turbulent flow phenomenon at high Reynolds number.     

含排水孔裂隙岩体渗流与法向应力耦合的复合单元算法

提出了含排水孔裂隙岩体的渗流与法向应力耦合的复合单元算法。基于“空气单元”和“充填模型”,提出的复合单元耦合模型视排水孔和裂隙为虚拟的具有高空隙率的“充填介质”,采用复合单元前处理程序,排水孔和裂隙依据其具体位置和方位可自动离散模拟在复合单元内部,计算网格生成时无需考虑排水孔和裂隙的存在,网格划分不受限制。基于复合单元法,采用两场交叉迭代算法,建立了含排水孔裂隙岩体的渗流与法向应力耦合算法。此耦合算法不仅考虑了排水孔和裂隙中的渗流,而且考虑了排水孔和裂隙与相邻岩块之间的流量交换。通过复合单元和传统有限元两种数值模型进行简单算例分析,可知两种算法结果基本一致,进一步验证了提出的含排水孔裂隙岩体的渗流与法向应力耦合算法的有效性,同时可看出复合单元耦合模型的前处理简便快捷。     

高层建筑标准模型脉动风压特性大涡模拟适用方法研究

为提高钝体建筑结构绕流模拟结果的精度,基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法,分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法,进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照,在对大气边界层湍流风场进行模拟验证的基础上,详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异,并着重从脉动风压非高斯特性角度进行探讨,检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面,采用两种方法模拟的脉动风压基本都符合高斯特性;而在受分离流和尾流作用的侧风面和背风面,采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明,为了满足99.38%的保证率,CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5,侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

Study on suitable method to simulate fluctuating wind pressurecharacteristics of standard high-rise building model based on LES

为提高钝体建筑结构绕流模拟结果的精度，基于两种大涡模拟(large eddy simulation, LES)入口湍流生成方法，分别为NSRFG（narrow band synthesis random flow generation）方法和CDRFG（consistent discretizing random flow generation）方法，进行CAARC(commonwealth advisory aeronautical research concil)高层建筑标准模型绕流的数值模拟比较研究。以风洞试验结果为参照，在对大气边界层湍流风场进行模拟验证的基础上，详细对比分析采用上述两种方法模拟得到的建筑表面平均和脉动风压系数、绕流场湍流结构、风压系数概率密度分布特性等的差异，并着重从脉动风压非高斯特性角度进行探讨，检验采用上述两种方法模拟钝体建筑结构绕流的适用性和准确性。结果显示：在受来流直接作用的建筑迎风面，采用两种方法模拟的脉动风压基本都符合高斯特性；而在受分离流和尾流作用的侧风面和背风面，采用NSRFG方法能更好地反映建筑表面脉动风压的非高斯特性。极值风压分析表明，为了满足99.38%的保证率，CAARC标准模型迎风面极大与极小峰值因子需分别取为3.0和2.5，侧风面和背风面极大和极小峰值因子需分别取为2.5和4.0。     

Numerical simulation of wind flow near a forest edge

This paper presents a computational fluid dynamics (CFD) model to simulate wind flow near a forest edge for the purpose of wind energy applications. The model uses a porous media analogy combined with a modified k–ε turbulence model to simulate momentum losses and turbulence generation within the forest. The momentum losses are represented by a drag coefficient and a leaf area density. Two directions were investigated: wind flow entering and wind flow leaving the forest. A fully developed solution with original boundary conditions was used as the inlet boundary condition in the two-dimensional CFD model for wind flow leaving the forest. Original boundary conditions were also proposed for the ground boundary within the forest. The model was solved using FLUENT 6.2 and validated against field measurements from three different authors. A sensitivity analysis was performed on two key parameters: drag coefficient and leaf area density. The results obtained using the proposed method show good agreement with the wind velocity and turbulence intensity measured experimentally.     

Wind response of large roofs of stadions and arena

The paper presents the experimental tests carried out in the boundary layer wind tunnel (BLWT) for the design of large roofs of the new Olympic stadium (Karaiskaki) in Pyraeus (Greece), Manfredonia (Italy) and “Delle Alpi” of Turin (Italy). In addition, a report about some results of the T.D. dynamic response analyses performed on the Karaiskaki structure and on the Olympic stadium in Rome will be given. The peculiar shape of these large structures and their particular location (two of them are in the immediate sea vicinity) let arise the question about the actual distribution of the wind loads, i.e., on the pattern of pressure coefficients (c_p) over the entire roof. For every wind direction investigated, the following quantities have been evaluated: mean values of the aerodynamic coefficients c_p, standard deviation of c_p and maximum and minimum values of c_p. Finally, the recorded data have been used for the numerical simulation of the dynamic response of the structure in Time Domain, whose aim is the definition of the design loads of the steel lattice structures. A numerical model of the “Delle Alpi” stadium is also in preparation, allowing results of dynamic response analyses, which are still in progress.