计算流体力学在食品加工贮藏中的应用

介绍了计算流体力学（CFD）广泛应用的几种软件。结合具体实例,概括了近年来CFD在食品加工贮藏领域中的应用,探讨并展望CFD在食品加工贮藏工业领域中所占的优势及发展前景。     

三边形桅杆风荷载谱模型试验研究

对三边形格构式桅杆进行了均匀流和两种紊流下的高频测力天平风洞试验,得到了顺风向、横风向和扭转向的气动力系数以及脉动风荷载谱。采用基于风速谱的数学模型对顺风向脉动风荷载谱进行拟合,验证了该经验公式在不同流场下的适用性。根据试验所得横风向和扭转向脉动风荷载功率谱曲线的特点,建立由紊流激励和旋涡脱落激励两部分组成的谱函数数学模型,最小二乘法拟合结果与风洞试验结果吻合良好。横风向脉动风荷载谱以紊流激励为主,紊流强度15%时旋涡脱落激励贡献仅占10%,扭转向脉动风荷载谱中旋涡脱落激励贡献明显增大,达到40%。     

燃烧加热污染空气对超燃冲压发动机性能影响研究

针对燃烧加热地面试验设备存在的工质污染问题,采用数值模拟方法研究了燃烧加热污染空气对氢燃料超燃冲压发动机性能的影响。以飞行马赫数Ma=6.5,当量油气比ER=0.6为计算基准状态,分别对纯净空气和污染空气来流下氢燃料超燃冲压发动机的整机流场和性能进行了对比计算分析。燃烧化学反应模拟采用了改进的H₂/O₂七组分八方程模型,湍流模型为标准的 k-ε模型,并采用直连式燃烧室试验数据进行了数值方法的验证。研究结果表明:(1)相对于纯净空气来流,污染空气来流下的超燃冲压发动机推力和比冲均有所下降。(2)采用酒精燃烧加热器的前提下,来流参数匹配静温、静压、马赫数时,发动机性能与纯净空气来流下的结果最为接近,而匹配总温、总压、马赫数时相差最大。(3)来流参数匹配总焓、静压、马赫数的前提下,采用氢燃烧加热器时发动机性能与纯净空气来流下的结果最为接近,而采用甲烷燃烧加热器时相差最大。      

北京沟域产业融合发展机制与路径研究

沟域经济是北京提出以山区沟域为单元,在生态保护前提下,通过产业融合促进农村产业结构优化和升级,实现区域经济发展的一种模式。驱动产业融合是沟域经济发展的动态特性。本文运用自组织的竞争和协同理论,阐述了沟域产业融合机制、产业融合模式和演变趋势,在总结实践经验基础上,提出各类产业融合模式和实现路径。研究显示,北京沟域经济已经迈入产业融合发展阶段,主导产业发展、产业间的关联和外部环境变化是产业融合的内在主要动力。因此,实现沟域发展就是要加强三次产业高度关联度和深入挖掘农业多功能性,促使产业结构朝纵深“两维”方向发展,可采取服务型融合和生态型融合两种路径。     

基于隔离布防护的水稻冠层上方风速分布特征

为了确定隔离布防护转基因水稻基因漂流效果,设计了隔离布防护措施的田间试验,研究防护区内、外水稻冠层上方的风速分布特征。结果表明,背风面不同风向角的1 m高度风速变化规律基本相同,1~2.5 H（H为隔离布高度,2 m）区域内风速降低幅度最大;其次是2.5~5 H区域内,而在5~10 H区域内风速降低幅度相对较小;随着风向角的增大,风速降低幅度有所减小。迎风面不同风向角的1 m高度风速在2.5 H处风速降低幅度最大,为60%~70%。隔离区内1 m高度风速整体减小,越靠近隔离布,风速减小越明显。因此,隔离布防护风障降低隔离区内外风速明显,可有效缩短转基因水稻花粉扩散距离。     

用流苏大砧三部位插皮嫁接日香桂

所谓三部位嫁接,即在一棵砧木上采用插皮嫁接技术一次性嫁接好三个部位的方法。此法具有接后成活率高、生长迅速等多种优点。在春季树皮刚能脱骨时,选取大粗度的流苏树(若是地栽,可现挖上盆,当即嫁接)在适宜高度横切断,沿横断面外周把骨皮层处削光滑,并沿外周确定三个点为插接部位。然后先取其中一点,将刀尖朝     

北京沟域经济发展模式的典型调研与思考

沟域经济发展模式对北京山区经济发展和实现城乡统筹发展目标具有重要意义。研究典型沟域经济发展的成功经验、面临问题和有关政策需求等,将为山区经济建设工作提供可借鉴经验和参考。本文采用走访、问卷和座谈等方式,对北京市2011年率先启动的7条重点沟域进行了调研。调研显示,重点沟域经济建设,在选择主导产业、改善生态环境、建设新村民居和促进山区经济建设等方面取得了显著成绩,但在理论探索、模式创新、生态保护、缩小城乡差距等方面仍有不足,需要不断加强理论研究、培育主导产业、促进农业体质增效和完善土地管理政策。     

甜菜夜蛾性诱剂田间应用技术研究

为进一步提高甜菜夜蛾性诱剂的田间诱捕效率,完善其田间应用技术,开展了不同甜菜夜蛾诱芯、诱捕器悬挂高度以及风向对甜菜夜蛾诱集效果影响的研究。研究结果表明：诱芯以美国MSTR Technologies Inc. 生产的硅橡胶塞型诱芯（两种组份、二枚合用）为最佳,诱捕器的悬挂高度以离地50cm为宜;设置在上风口位置的诱捕器诱集量最大,其拟合程度可达81.08%。     

LAPS地面资料在低纬山区的分析效果检验

为了检验LAPS系统在低纬山区的分析应用效果,对2016 年贵州LAPS分析值与气象监测要素进行对比。结果表明：气温、相对湿度、风速的相关系数逐渐降低,但均方根误差由小到大分别为风速、气温、相对湿度。分析值与监测实况间的差异与贵州的地形分布有关：气温准确率呈东高西低;风力低于1.8 m/s 时分析值偏小,高于1.8 m/s 时分析值偏大,u、v 风的准确率较低;相对湿度准确率西高东低;能见度等级准确率为77.82%,且随海拔高度增高准确率偏低。可见,在低纬山区LAPS分析的气温、风速和能见度等级偏差小,实用性较高;能见度数值和相对湿度相关性通过信度检验,可参考使用;风向在低纬山区的可用性较差。     

北京沟域经济背景下山区生态旅游市场开发研究

近年来,山区沟域经济已经成为北京农村发展的新模式,实现了经济发展和生态保护双赢。北京山区县依托山区自然风光、人文遗迹、民俗文化和生态农业等资源,形成了以生态旅游业为龙头产业的经济形态。作为都市型现代农业发展的一种新形式,沟域经济在北京山区具有广阔的发展前景。本文在分析北京沟域经济内涵和发展现状的基础上,从需求类型、需求动机、市场潜力等方面对北京山区生态旅游的市场需求进行了深入探讨,并从开发旅游产品、加大宣传力度、打开知名度等方面提出发展山区生态旅游的市场策略。     

Load Analysis of Butteting Bridges by CFD

An improved computational method for buffeting forces of long span bridges, which substitutes the traditional wind tunnel test with the bridge segment model for CFD method, is proposed. In the case study of Tsing Ma Bridge, the pressure distribution induced by the wind field of the bridge decks was simulated. The nodal buffeting forces were computed and the local stress responses were obtained according to the CFD simulation and the refined finite element model. Preparation for buffeting induced fatigue analysis of bridges and structural health monitoring are provided.     

沿海防护林网防风效应数值模拟研究

为研究沿海防护林网的防风效能,采用计算流体力学软件FLUENT对上海浦东新区的水杉林网周围的气流场分布进行了数值模拟。结果表明：水杉林网对气流有着明显的削弱作用,风速在林带前5 H左右处逐渐下降,在林带后出现回流现象,随后林带对气流的作用逐渐减弱,风速逐渐恢复。各林带的有效防护距离在10 H左右,因此,林网中林带间距设置在15 H左右比较合适。     

Energy consumption analysis and reconstruction of subway platform screen doors in northern cities for energy saving

To analyze the influence of the platform screen doors (PSD) on energy consumption of subway environmental control systems in northern cities and to make good use of piston wind, EnergyPlus, an energy analysis and thermal load simulation program, is used to evaluate such systems in northern cities. A computational fluid dynamics (CFD) simulation is made to model the velocity and temperature field of a subway station and to predict the effect on PSD reconstruction using Airpak. Compared to a system with automatic platform gates, a PSD system has 2% lower energy consumption. Thus, PSDs are inefficient for saving energy in northern cities. Because electricity consumption by ventilation equipment increases notably when PSDs are used, particularly by under platform exhaust fans, little difference exists in the overall energy consumption with or without PSD. More thoroughly using piston wind in transition seasons and the winter is the key to solving the high energy consumption problem. The energy analysis and CFD simulation results show that the adjustable vents in PSD can use the piston process to introduce outside air, thereby reducing ventilation energy consumption notably. Because the vents can be closed, PSDs also can save energy in the summer. Using these recommendations can reduced annual energy consumption 30%.     

机械通风降温效果的数值评估

地槽通风是机械通风的常用形式,是保证粮食安全储存和保持粮食品质的重要措施.常规的试验研究测量方法难以全面和准确评估设计的有效性和合理性.本研究利用计算机流动模拟的方法(CFD)对常用的U形地槽通风方案进行了数值研究,获得了风道中流速和压力分布的关键性数据,发现了与实际现象相符合的通风死角区域,同时又发现了常规测量手段中难以探测到的风道之间存在的通风薄弱区域,在理论上分析了存在通风死角和风道压力损失的原因.计算流体力学研究方法的运用可成为机械通风优化设计研究的有效工具,为今后机械通风应用技术的发展提供针对性和实用性的依据.     

利用CFD模型研究苹果冷藏库内的空气流动

苹果冷藏库内的空气流动可调节库内环境,且气流速度对改善果实品质具有重要的作用,因此有必要研究苹果贮藏库内的空气流动特性。本研究采用CFD（Computational Fluid Dynamics）方法,运用大型计算流体动力学软件Fluent建立模型,以标准湍流模型对苹果冷藏库内的空气流动做三维模拟。模拟时以苹果堆码区作为多孔介质,研究库内堆码苹果时的空气流动状况,并对库内的空气流速进行试验测定和验证。结果表明,通过气流场模拟能较为直观地显示冷库内部的流场特征和流动状态,气流从风扇流出,在风机与货物堆码区形成明显的涡流;气流在货物堆码区分布较为均匀,靠近风机的货物堆码区气流速度均高于远离风机的货物堆码区气流速度。冷库流场的测量值与CFD模拟的结果进行对比,最大误差在10%以内,测量值和模拟值之间的相关系数在0.9以上,说明了CFD模拟的可靠性。该模拟结果可为商用苹果冷藏库的优化和库内环境调节提供一定的理论依据。     

Wind Vibration Analysis on the Large -span Curtain Wall

The large-span structure requires wind vibration analysis when computing the wind load;however,the formula in current code on wind vibration coefficient can hardly be applied in large-span structure,making its computation difficult and troublesome.This paper makes wind vibration analysis on the large-span curtain wall combined with certain engineering background in the methods of both time domain and frequency domain,and then the derived results are compared.The analytical results demonstrate identical distribution and contiguous numerical value of wind vibration coefficient concluded from the two varied methods;furthermore,even if the method in time domain is higher in computational complexity,more data on the response of structure under wind can be obtained,which provides reference for the theoretical analysis and engineering design.     

Wind Loads Distribution on Typical Vaulted Shells

The distribution characteristics of shape factors and fluctuating wind pressure coefficients on two vaulted shells were investigated by simultaneous measurement of external and internal wind pressures on static models in wind tunnel. The effects of orifices on bottom and blocking at ends on wind loads distribution are discussed. It is shown that the wind pressure distribution is significantly affected by changes on orifices at bottom and blocking at ends. Wind pressure on ends decrease effectively and wind pressure on surface is distributed smoothly by blocking ends with highly curved surface shell. Small orifices at bottom not only contribute to degreasing negative pressure because of count acting effects of internal and external pressures, but also to extending the positive pressures region and increasing positive pressures. Wind loads suggestions on these structures are described at end.     

Wind-induced Response Analysis on a Large-span Membrane Roof by Considering Non-gaussian Stochastic Wind Pressure Field

The stochastic fluctuating wind pressure field acting on a large-span membrane roof consists of Gaussian and non-Gaussian regions in the sense of statistics. Simulation of this stochastic field is presented based on the zero memory nonlinearity (ZMNL) transformation method. A case study is then given to show that the stochastic wind pressure field samples generated by the proposed method can well represent the specified statistical characteristics of data from the wind tunnel experiment. After that, the wind-induced response analysis is conducted on a membrane roof structure using the Gaussian/non-Gaussian composed wind pressure field samples generated by the proposed method and the Gaussian samples by the traditional method, respectively. Results indicate that response values of some components of the structure induced by the Gaussian samples are lower than those by the Gaussian/non-Gaussian composed wind pressure samples, which means the non-Gaussian characteristics of the stochastic wind pressure should not be ignored. Meanwhile, the total gust response factors of the components caused by the wind excitation are given to meet with the requirement of the designers.     

Influence Factors on Wind induced Fatigue Life of Steel Circular Antenna with Asymmetric Brace

Wind induced responses of a single steel circular antenna with an asymmetric brace were computed considering wind speed and direction joint distribution function at location of the structure, and then wind induced fatigue life of the structure was estimated in frequency domain and time domain, respectively. Some parameters, including wind direction, surface roughness, vortex induced resonance and mean wind speed, which would have effects on the wind induced fatigue life of the structure,were discussed. It is found that 1) wind direction has great effects on wind induced fatigue damage, that is, significant fatigue can occur in wind direction of high probability; 2) the more roughness the surface of structure is, the shorter the wind induced fatigue life is; 3) the effects of vortex resonance on wind induced fatigue life should not be neglected; 4) the mean velocity has slight impact on the wind induced fatigue life of the structure.     

Automatic head recognition by integrating mean shift with multiple features

To improve the head detection accuracy in video sequences captured with fixed vertical monocular camera, a novel method of head recognition based on mean shift and multiple features is proposed. Firstly, mean shift based image segmentation algorithm with color information and spatial information is suggested to derive the candidate head components in images. Furthermore, by referring to two features that the contour of human head regions are approximate round and the hair color distribution is clustered, the evaluation models based on the contour information and inside color information of candidate head components are presented for head recognition. The experimental results show that the proposed algorithm can effectively reduce the light interfere and eliminate fake target whose color information is similar to hair color distribution. The detection rate for static images can reach about 89.4%.