Numerical model of the three-dimensional isothermal flow patterns and mass fluxes in a pitched-roof greenhouse

The three-dimensional isothermal flow patterns and mass fluxes in a full-scale, pitched-roof, single-span greenhouse were numerically resolved, and data from tests on a full scale were used to validate the code, the inlet boundary conditions and the greenhouse design grid method. For numerical solution of turbulent flow, a high-Reynolds-number k-ε model is suitable. Computational domain sizes were selected so as to fulfil the requirements of free-stream conditions whilst ensuring that grid geometrical characteristics satisfy the physical limitations of the standard k-ε model. A special feature of a case of a wind blowing parallel to a ridge (0°) is that the flow in the leeward half of the greenhouse comprises two vortexes with opposite senses of rotation, which bring in air mass through the vents and deliver it to the windward half. A spiral type of flow was found for winds blowing at 15-75° to the ridge direction: part of the air enters via the windward wall vent near the leeward gable-wall and emerges through the leeward roof vent near the windward gable-wall.Mass fluxes and flow patterns on wind direction, and on the opening angles of the windward and leeward vents. Thus, the ventilation rate induced by a wind directed perpendicularly to the greenhouse ridge is 4-4.9 times as great as that induced by a wind parallel to the ridge. A ventilation rate of a simulated greenhouse type was found to be significantly less responsive to a change in wind direction from 45° to 90° than to one from 0° to 45°. Present numerical results are in good agreement with those of other experiments and observations.     

Model development and experimental validation of a floriculture greenhouse under natural ventilation

Greenhouse technology is an effective method of cultivation of flowers, crops, etc. under controlled environment. For any greenhouse, ventilation performance is a major factor in production, influencing the yield and quality of the products. Natural ventilation can be effectively used to maintain greenhouse microclimate, conducive to plant growth, when the ambient conditions are not extreme. The present paper discusses the modeling aspects of a floriculture greenhouse suitable for operation in typical Indian climate under natural ventilation. Combined ridge and sidewall ventilation is considered in the model. The model is validated against the test results of an experimental greenhouse. Parametric analysis is also done to understand the effects of variations in parameters such as wind speed, solar radiation intensity, effective greenhouse height etc. The study reveals that the performance of a greenhouse under natural ventilation is influenced considerably by parameters such as intensity of solar radiation, effective distance between the side and the roof vents, free wind speed etc.     

上海地区热压通风间层通风性能的实测研究

与建筑良好结合的太阳能热压通风构造可以达到夏季防热、冬季供暖的效果,是一种十分节能的被动式技术。通风量是评价该系统运行效果的重要参数之一。目前,采用的通风量预测方法多基于理论分析与实验室研究的结果,缺乏自然条件下该系统实际通风效果的分析。通过在上海嘉定某试验房中建设热压通风间层,调整试验房的旋转机构与可调通风口,分析了当地太阳辐射、通风口尺寸、风速风向对该通风层通风性能的影响。结果表明典型工况下的实测通风量始终大于预测通风量,且偏差较大。其原因主要来自室外风场、集热墙温度的不均匀性等方面。     

平屋盖围护构件设计风荷载研究

GB 50009-2012《建筑结构荷载规范》中未给出复杂体型且重要建筑物的风荷载局部体型系数,此类建筑物的风荷载需通过风洞试验确定。基于此,提出了基于风洞试验的围护构件设计风荷载计算方法,将规范中阵风系数与局部体型系数的乘积修改为局部体型系数与脉动风压系数极值之和的形式,称为风压系数极值。提出的围护构件设计风荷载计算方法不仅适用于迎风面围护构件设计风荷载的计算,也适用于气流分离区围护构件设计风荷载的计算。在脉动风压系数极值的计算中,考虑了气流分离区非正态风压时程的特性,采用非正态峰值因子的简化计算式,可简便确定非正态风压时程的峰值因子。以平屋盖围护构件设计风荷载的确定过程为例,对比了我国规范方法与文中方法的异同,提出了平屋盖围护构件风压系数极值的设计建议值。结果表明,采用文中提出的围护构件设计风荷载计算方法,基于风洞试验数据可确定气流分离区围护构件的设计风荷载,采用日本风荷载规范的屋盖风荷载分区方法是合理的;采用风洞试验得到的局部体型系数,套用GB 50009-2012规范方法确定气流分离区围护构件的设计风荷载,可能严重低估风荷载取值。     

A multi-objective structural optimization method for serviceability design of tall buildings

Structural optimization design aims to identify optimal design variables corresponding to a minimum objective function with constraints on performance requirements. To this end, many optimization frameworks have been proposed to determine optimal structural systems that are subjected to seismic and wind hazards in isolation. However, some modern tall buildings are sensitive to seismic and wind excitation owing to their complex structural systems and geographic regions. Therefore, a proper structural optimization method for such buildings is required to ensure that the expected performance is achieved in a multi-hazard scenario. This study proposes a multi-objective serviceability design optimization methodology for buildings in multi-hazard seismic and wind environments by combining optimality criteria and the nondominated sorting genetic algorithm II (NSGA-II). Seismic and wind effects can be instantaneously updated due to changes in the structural dynamic properties during the optimal design process. A neural-network-based surrogate model with self-updating is proposed to predict the structural natural frequency so that the overall computation time of the optimization process can be reduced. The proposed method was used to optimize a 50-story frame-tube building and was compared against the general genetic algorithm and general NSGA-II to verify the feasibility and effectiveness.     

Interaction of Sprinklers with Smoke and Heat Vents

There has been an ongoing controversy about the use of sprinklers and smoke/heat vents together, and dozens of position papers have been published over the decades. This paper reviews 13 experimental studies that have some relevance to the claims posed for and against the combined use of sprinklers and smoke/heat vents. These studies are used to evaluate the positive and negative claims that have been made with regard to the combined use of sprinklers and smoke/heat vents. Three of the studies investigate the use of smoke/heat vents alone. Four investigations include sprinklers, but do not include roof vents. Three of these are test series in which perimeter vents were used in the test facility, and the fourth included sprinklers, a partial draft curtain, and no smoke/heat vents. Four test series included sprinklers, smoke/heat vents, and draft curtains, but utilized spray or pool fires which were not subject to extinguishment by the sprinklers. Four test series included sprinklers, smoke/heat vents, draft curtains, and used Class A fuels which were subject to extinguishment.The studies of smoke and heat venting used in conjunction with sprinklers show clearly that venting does not have a negative effect on sprinkler performance. Experimental studies have shown that venting does limit the spread of products of combustion by releasing them from the building within the curtained compartment of fire origin. This improves visibility for building occupants and firefighters who need to find the seat of the fire to complete fire extinguishment. Limiting the spread of smoke and heat also reduces smoke and heat damage to the building. In the event that sprinklers do not operate, venting remains a valuable aid to manual control of the fire.The experimental studies have shown that early vent activation has no detrimental effects on sprinkler performance and have also shown that current design practices are likely to limit the number of vents operated to one and vents may in fact not operate at all in very successful sprinkler operations. Design practices should move to methods that assure early operation of vents, and vent operation should be ganged so that the benefit of roof vents is fully realized. Sprinkler design with vents and draft curtains needs to take full account of draft curtains as obstructions. Curtains should be placed in aisles rather than over storage.     

Prediction of Fire Hazards Associated with Chemical warehouses

This paper describes the application of computational fluid dynamics (CFD) to the task of predicting fire product emissions from warehouses containing hazardous materials. A growing pool fire is modelled inside a warehouse with automatic, heat-detector-operated roof vents and various prescribed external wind flows. The first 5 min of the fire are simulated, by which time the heat release rate of the fire has reached 26 MW and all vents have opened. It is found that the strong thermal and entrainment processes associated with the fire are such that moderate external winds have only a second-order influence on the mass, momentum and buoyancy fluxes of the emissions. The response time of the roof vents is found to have a significant effect on the transient behaviour of the emissions. The potential and limitations for using CFD models as part of a broader environmental hazard analysis are reviewed.     

External flow effects on the discharge coefficients of two types of ventilation opening

Envelope flow models are commonly used in the design of naturally ventilated buildings. Such models rely on specification of the discharge coefficient, C_z, of ventilation openings, such as air vents and chimneys (stacks). Current practice is to make use of values obtained from laboratory tests under still-air conditions. These values may not be appropriate when the ventilation is due to wind, due to the external flow around the opening which is characterized by unsteadiness of both the velocity and pressure fields. Experimental tests have been carried out in a wind tunnel on two types of openings, namely a sharp-edged orifice (flush to the wall) and a long opening (chimney). Using an analytic result for the still-air case and simple dimensional analysis it is argued that the local crossflow velocity ratio, V/u, is an important parameter for the orifice and the experimental results support this (as do some simple CFD calculations). The experimental results for the sharp-edged opening are similar to earlier work on generally larger openings. For the long opening the effects of external flow are smaller. In particular, the effects are negligible when the outlet of the opening lies in the external flow. Estimates are made of the consequential uncertainties arising in envelope flow calculations for natural ventilation design.     

高层建筑设置常开和常闭风口比较

本文对高层建筑中设置常开风口和常闭风口的特点和两种风口设置所需的风量进行了总结及计算比较，探讨了不同场所设置风口的不同形式。     

Integrated aerodynamic load determination and stiffness design optimization of tall buildings

Modern tall steel buildings are wind sensitive and are prone to dynamic serviceability problems. Although wind tunnel techniques have emerged as valuable tools in providing reliable prediction of the wind‐induced loads and effects on tall buildings, current design practice normally considers the wind tunnel‐derived loads as constant static design loads. Such practice does not take into account the change in wind‐induced structural loads while the dynamic properties of a building are modified during the design synthesis process. This paper presents a computer‐based technique that couples together an aerodynamic wind tunnel load analysis routine and an element stiffness optimization method to minimize the cost of tall steel buildings subject to the lateral drift design criteria, while allowing for instantaneous prediction and updating of wind loads during the design synthesis process. Results of a full‐scale steel building framework with the same geometric shape of the Commonwealth Advisory Aeronautical Research Council (CAARC) standard building indicate that not only is the proposed technique able to produce the cost‐effective element stiffness distribution of the structure satisfying the serviceability wind drift design criteria, but a potential benefit of reducing the design wind loads can also be achieved by the stiffness optimization method. Copyright © 2007 John Wiley & Sons, Ltd.     

Sensitivity of air change rates in a naturally ventilated atrium space subject to variations in external wind speed and direction

Design guidelines for natural ventilation (NV) in buildings focus on the potential hourly air change (ACH) rates based on the building space parameters. Critically, external airflow data is often assumed on the basis of a single mean wind speed and an associated prevailing wind direction. This can result in significant variation in ventilation rates and comfort conditions when non-design external wind conditions prevail. This paper describes a CFD study aimed at examining the influence of variations in external wind speed and direction on the air change rate for the atrium space of a two-storey naturally ventilated building. The building atrium is ventilated by a series of entry vents on one wall of the building in conjunction with roof vents. External wind speeds from 25 to 250% of the mean site wind speed (5.7 m/s) were examined and found to result in an almost linear increase in the ACH rate. For a single wind speed, the relationship between wind direction and the ACH rate was also found to be approximately linear for wind directions between 0° and 90° (orthogonal and parallel) to the wall vent openings, but non-linear for other wind directions (90–135°). More generally, the significant variation in the atrium ACH rate with changes in external wind conditions, evident in this particular building model, illustrates the importance of considering non-design wind conditions when designing NV buildings.     

Vibration control study on a supertall building

Vibration control of a 288‐m supertall building with connective structure is studied in this work. Fluctuating wind time series of the structure in forward and reverse Y‐direction in a 10‐year frequency are simulated by modified auto‐regressive method (AR method) to perform wind vibration analysis, and six minor and major earthquake waves are provided by building designer to perform earthquake analysis. Three vibration control schemes with nonlinear viscous dampers are proposed to control structural dynamic responses under wind and earthquake excitations. The dynamic responses of the structure with the proposed control schemes in wind and earthquake excitations are investigated and their vibration control effects are analysed comparatively. The study results show that the modified AR method is reliable and effective for simulating the fluctuating wind exerted on the building. The excessive dynamic responses induced by wind and earthquake excitations can be controlled effectively by the proposed schemes. The peak acceleration of top storey can be reduced by almost 40% for the proposed control schemes in wind excitation. The elastic working state of the connective body between the high tower part and the low tower part in major earthquakes can also be ensured totally. So, the validity and feasibility of the proposed schemes in reducing structural vibration responses can be fully approved. Some suggestions about structural analysis and design under wind and earthquake excitations are proposed. Copyright © 2010 John Wiley & Sons, Ltd.     

大跨屋盖结构风致抖振响应研究

建立基于非定常风荷载的大跨屋盖结构风致动力响应的试验和分析方法。该方法采用多通道测压系统扩大同步测压点的数目,更全面地获得屋盖表面风压的时空特性,为准确计算结构风致响应奠定了基础。在动力分析方法上应用CQC法计算屋盖结构的风振响应,考虑多模态及模态间的耦合影响,编制了结构风致动力效应计算程序SWDP。最后对上海铁路南站工程屋盖结构的抖振响应结果进行了计算和分析。结果表明,采用多通道测压系统可以有效地扩大同步测压点的数目;基于非定常风荷载的CQC方法是计算复杂大跨屋盖结构风振响应的有效方法;背景响应对于总响应的贡献通常是不可忽略的。     

武汉某剧院空调气流组织分析

结合现场所测的数据对观众厅部分现有空调喷口送风的气流组织做简要的计算和分析,并简要计算了设计工况下速度分布和温度分布,得出该送风形式下的池座和楼座的气流组织存在诸多问题,进而针对池座提出用旋流风口代替球形喷口垂直下送,楼座则建议改为座椅下送风。     

Wind effects on buildings with varying leakage characteristics—wind-tunnel investigation

A wind-tunnel investigation has been conducted on a simple cubical model to see the effect of outside wall leakage on internal and external pressures. Three wind directions have been studied. The results have been extended to smoke-control problems. A method has been developed to modify the roof-vent design calculations to take wind effects into account. It is also shown that failure of vent systems may be more common than would be expected from current design methods.     

Aerodynamic and water penetration investigations upon pitched roof vents

Pitched roof vents (PRVs) can be used both to extract air into the atmosphere (‘blowing’) and to draw in fresh air (‘sucking’). In both of these situations, the PRV facilitates the exchange of air between the inside and outside of a building. Photographs of typical generic PRV designs are presented. As shown in these photographs, PRVs are mounted within a pitched roof, and may or may not protrude slightly above the roof surface. Hence their performance is likely to be influenced strongly by wind flowing above and around the roof. The internal and external design of PRVs is complex, and PRVs are designed to strike a balance between aerodynamic efficiency, weather-tightness performance, and cost of manufacture.Experiments have been undertaken at Building Research Establishment (BRE) to test the weather-tightness and aerodynamic performance of PRVs. This paper describes the test rig and the methods used to obtain experimental results. A particular feature of this test rig is that it is able to discriminate between leakage through the PRV, the roof covering, and the interface between the roof covering and the PRV.A wide range of UK domestic and industrial marketplace PRV products were tested. For the aerodynamic performance tests, typical results are presented for different wind speeds and different roof pitch angles. An empirical equation is presented that was found to describe well the aerodynamic performance of every PRV tested. For the weather-tightness tests, a new visual criteria is suggested which, although subjective in nature, provides very useful information about water penetration that cannot be obtained in any other way. A typical weather-tightness plot is presented that uses the new visual criteria, together with the more traditional method of weighing the water ingress. For both the aerodynamic and weather-tightness tests, the findings and conclusions of the overall test programme are presented.     

大尺度高低跨柱面屋盖的风压系数分区研究

针对大尺度高低跨柱面屋盖体系风压分布变化梯度较大、跨间相互干扰以及此类屋盖风压分区无相关规范可查阅等问题,在得到各种风向下最不利极值风压的基础上,采用K-means聚类的风压系数快速分区方法将高低跨柱面屋盖表面划分为多个区域,并计算了各区域的分区风压系数。同时,在高低跨柱面屋盖风压系数分区研究过程中,对K-means方法的k值取值范围和最佳k值确定方法进行针对性改进。结果表明,高低跨柱面屋盖的边缘属于风敏感部位,而中间部分风压变化较小,因而在进行大尺度平屋盖抗风设计时,采用聚类方法进行风压分区更为合理。     

山地风场特性及其对输电线路风偏响应的影响

山地风场的复杂性和显著的三维特性是困扰山区输电线路抗风设计的关键问题。该研究采用CFD数值模拟与风洞试验相结合的方法研究典型单山脉地形和双山脉峡谷型地形的三维平均风场和脉动风场特征。由于风洞试验测点数及试验风速的限制，输电线路沿线各点的三维平均风场基于CFD数值模拟得到。由风洞试验获取山脉地形的湍流度、湍流积分尺度、沿线路方向的衰减系数等脉动风场参数，在此基础上采用POD法重构生成输电线路沿线各点的三维脉动风速时程，并分析比较跨越峡谷、山脊的输电线路沿线风场特征。建立连续三跨输电线路有限元模型，采用时域法研究山地风场特性对输电线路风偏响应的影响。研究结果表明：山顶、峡谷处风速显著增大，且气流爬坡将导致局部位置产生上升气流；由于近地风场加速效应的影响，沿山脊布置的输电线路全档风偏响应增幅较大，跨峡谷输电线路其爬坡段风偏响应增幅较大；上升气流主要使导线竖向风偏位移增大；山地地貌下考虑脉动风速的影响，绝缘子串风偏角风振系数宜取1.2~1.3。该研究为完善山区输电线路的抗风偏设计提供借鉴。     

Prediction of typhoon design wind speed with cholesky decomposition method

Typhoon simulation method that integrates typhoon wind field model, probability distributions of typhoon key parameters, and Monte Carlo simulation method has long been used to predict typhoon design wind speeds of structures. In the research, the empirical typhoon wind field model with a novel parameter B model of Holland's radial pressure profile is first introduced and validated with typhoon Hagupit's simulation. The results show that relatively good typhoons can be simulated with this empirical typhoon wind field model. Then, the cholesky decomposition method used in typhoon simulation method is proposed that allows achieving all correlated typhoon key parameters simultaneously. Finally, the cholesky decomposition method is used to generating typhoon key parameters in Hong Kong, and typhoon design wind speeds for different return periods are predicted with typhoon simulation method. In addition, typhoon design wind speeds derived from historical typhoon key parameters and typhoon key parameters generated without considering cholesky decomposition method are also predicted, respectively. The predicted typhoon design wind speeds are compared and the results demonstrate that the cholesky decomposition method should be incorporated into typhoon simulation method.     

大跨度煤棚主体结构设计风荷载的神经网络建模研究及应用

风荷载是大跨度煤棚结构设计中的主要控制荷载。随着结构抗风研究尤其是风洞试验数据的积累,结合数据挖掘进行结构智能化抗风设计是一种趋势。基于701组工况4581个柱面及球面屋盖风洞试验样本进行数据挖掘和统计分析,建立了脉动风荷载参数的广义回归神经网络预测模型;通过对12480个工况的单、双层柱面及球面网壳结构进行参数化风振响应分析,总结了等效静风荷载的经验表达式;建立了基于人工神经网络预测气动风荷载的主体结构等效静风荷载的抗风设计基本框架,并通过国内某超大跨度干煤棚张弦结构进行了有效性验证。结果表明：采用本文提出的风荷载数据库预测与等效静风荷载方法效率较高,且能够在一定程度包络风振响应分析结果,可用于结构初步设计阶段对主体结构设计风荷载快速预估。