移动喷雾施药对杂草防治效果的风洞试验

设计并构建了一套移动喷雾施药对杂草防治效果的风洞试验平台,该试验平台能精确控制移动喷雾施药时的外部环境风速与喷雾移动速度。为了研究风速与喷雾移动速度对雾滴沉积量密度的影响,进行了2因素(风速、喷雾移动速度) 3水平的全面试验,分析了雾滴沉积量密度随风速、喷雾移动速度变化趋势及其原因。以杂草马齿苋为例,在不同风速与喷雾移动速度条件下,研究烟嘧磺隆对不同生长时期马齿苋的防治效果。采用配比为0.013 3%质量分数烟嘧磺隆药液对二叶、四叶和六叶一心生长时期马的齿苋喷雾施药,分析了风速、喷雾移动速度与烟嘧磺隆沉积量密度对不同生长时期马齿苋的防治效果。试验结果表明:从风速、喷雾移动速度对雾滴沉积量密度显著性分析结果可知,风速、喷雾移动速度均对雾滴沉积量密度有显著性影响,且风速对雾滴沉积量密度显著性影响程度高于喷雾移动速度。烟嘧磺隆沉积量密度分别至少达到1.52,3.22和6.09μL/cm2时,二叶、四叶和六叶一心生长时期的马齿苋鲜质量防治效果可达到80%以上,在相同烟嘧磺隆沉积量密度条件下,二叶、四叶和六叶一心生长时期的马齿苋鲜质量防效明显高于株防效。喷施烟嘧磺隆防治马齿苋的最佳时期是马齿苋生长的二叶至四叶时期。试验结果为移动喷雾施药防治杂草的应用中选择合适的喷雾参数、合理利用环境条件提供了参考依据。     

斜齿轮接触与热效应分析模拟

斜齿轮相较于直齿轮，承载能力更强，传动更为平稳，是大功率高精度传动系统不可缺少的传动部件之一，常用于高速重载的应用场景。更高的转速与更大的载荷导致了斜齿轮更高的本体温度，而温度是齿轮胶合失效的重要表征参数。以一对斜齿轮为研究对象，通过MATLAB商业软件建立了斜齿轮接触模型，基于赫兹接触理论、传热学理论，计算并研究了斜齿轮啮合时齿面接触应力、摩擦热流密度与不同位置的对流换热条件，提出了斜齿轮稳态温度场的计算方法，同时分析了不同转矩与转速条件下斜齿轮摩擦热流密度，最后将计算结果代入ANSYS Workbench商业软件中进行仿真分析，研究了不同转矩条件下斜齿轮稳态温度场分布。研究结果可为斜齿轮胶合失效提供一定参考。     

槽式太阳能聚热器风载荷数值模拟研究

采用计算流体力学(CFD)理论建立了计算模型,对槽式太阳能聚热器不同角度、不同风速、聚热器板之间不同缝隙对风载荷的影响进行了分析。结果表明:聚热器随风速和角度变化对载荷影响较大,聚热器之间缝隙对风载荷影响几乎不变。     

地铁站火灾烟气运动及控制方法研究

地铁建设是缓解城市交通压力、节约城市土地资源的有效手段，但同时也给消防工作带来了一定的挑战。地铁站属于人员密集场所，可燃物种类多、随机因素复杂，一旦发生火灾，人员疏散难度大，故开展地铁站火灾研究非常重要。通过数值模拟软件，选取典型火灾场景下的工况进行计算，分析屏蔽门及扶梯开口处的风速对火灾烟气的影响，为地铁防火工作提供参考。     

文峪河上游河岸林的群落结构与多样性特征

文峪河上游垂直河岸40 m的区域存在泛滥平原和山坡两种地貌.在实地踏查和河岸林群落划分的基础上,对河岸带两种地貌的森林群落结构与多样性进行了差异比较,以期为该区河岸带宽度确定提供植被依据.结果表明,56个样地分别属于13种群落,泛滥平原的林分密度、物种丰富度与植物多样性都显著大于毗邻山坡,而林木断面积与均匀度在两种地貌...     

铝合金搅拌摩擦焊接热力耦合分析

采用库伦摩擦和粘着摩擦生热作为生热驱动力,模型中被焊材料与夹具之间建立接触关系,在温度场分析中热流密度和生热载荷采用一种自适应载荷,在力学分析中采用简化的搅拌头机械载荷。对铝合金薄板搅拌摩擦焊接过程进行热力学方面的模拟得到其温度场和残余应变场。     

轻型木结构剪力墙保温性能测试与分析

以国内首栋六层梁柱框架-轻型木结构剪力墙——山东鼎驰木业有限公司研发大楼为研究对象，对其一楼质检部墙体A与二楼仓库墙体B的传热系数进行测定分析。热流计分别呈横向与纵向布置，分别采取空调加热和电暖器加热，测试不同部位墙体的保温隔热性能；参照标准GB 50176—2016计算墙体理论传热系数；采用Abaqus软件对墙体传热系数进行模拟并对墙体内部温度与热流密度分布展开分析。研究结果表明：墙体A(横向)与墙体A(纵向)的平均传热系数分别为0.463、0.465 W/(m²·K)，墙体B的平均传热系数为0.374 W/(m²·K)，均达到了寒冷地区甲类公共建筑外墙标准；各测点传热系数实测值有一定差异，墙体保温性能不均匀，受施工条件与结构形式影响较大；墙体传热系数的理论结果与数值模拟结果分别为0.238 W/(m²·K)和0.233 W/(m²·K)；保温层墙骨柱区域热流密度相比于保温棉区域显著提高，墙骨柱处易形成热桥，导致热流量和传热系数大幅上升，保温隔热性能下降。     

基于热流耦合的木材干燥窑风速温度分布解算

为构建木材干燥窑内部循环风速和温度合理分布,采用二维数值模拟方法,利用Fluent软件对试验型小型干燥窑进行仿真模拟,对比安装导流板前后干燥窑内温度和分布情况。木材干燥窑的设计,风速、温度分布是关键问题。首先利用ICEM CFD软件对结构简化的试验型小型干燥窑进行参数化建模,将简化的模型进行网格划分,利用Fluent软件对木材干燥窑内的流动与传热耦合环境进行数值模拟,得出风速分布云图和温度分布云图,研究干燥窑内热流耦合系统,得出其内部速度和温度的具体状态,通过导流板安装前后数值对比,找到导流板合理性的参数。采用二维数值的模拟方法,不能代表实际干燥窑工作状况,具有一定的局限性。     

雷州半岛尾巨桉人工林树干液流对台风天气的响应

[目的]为正确认识台风对桉树人工林蒸腾耗水的影响。[方法]采用热扩散茎流计对尾巨桉树干液流在台风前后进行连续监测,分析其对台风天气的响应,并同步测定林分气象条件,分析台风过程中树干液流与气象因子之间的相关性。[结果]表明:台风当天,树干液流密度与台风登陆前后(单峰)不同,呈不规律多峰型曲线,树干日均液流密度(2.89 mL·h~(-1)·cm~(-2))较台风前减少53%,夜间液流波动较大;日间最大峰值(7.76 mL·h~(-1)·cm~(-2))出现在下午,峰值较台风前降低55%,树干液流日通量极显著小于台风登陆前后;台风登陆前树干液流密度峰值(17.4 mL·h~(-1)·cm~(-2))及平均液流密度(6.15 mL·h~(-1)·cm~(-2))分别是台风登陆过后的1.24倍和1.14倍,台风后树干液流日通量较台风前均有所下降;台风当天,影响液流的主要气象因子为风速、大气温度、空气湿度、水汽压亏缺和降雨量,液流与风速的相关系数较台风前增大52%,与降雨量的相关系数是台风前的2.6倍,与其他因子的相关系数较台风前均下降了50%左右,而台风登陆前后之间的主要影响因子差异不大。[结论]台风当天的日均液流密度、白天的平均液流密度和日通量均极显著小于台风前后,而夜间液流显著大于台风前后;台风前后的日均液流密度差异不显著,夜间液流台风前显著大于台风后;台风过程中风速成为影响液流的关键因子,与太阳辐射相关性不显著,其他影响因子与台风前后相同,但相关系数除风速和降雨量外均显著下降。     

樟树人工林经营效果分析

对福建省永安国有林场和福建农林大学莘口教学林场樟树人工林进行了调查分析,结果表明：立地条件、造林方式对樟树人工林生长效果影响明显。培育樟树丰产用材林应选择I级立地、并以山坡下部为宜。樟树混交林比纯林具有明显的生长优势,适宜与樟树混交的树种有杉木、福建柏、闽楠等。福建柏、闽楠是樟树理想的混交伴生树种和林冠下套种混交树种;杉木与樟树混交,种间竞争比较激烈,需确定目的树种并及时调整林分密度。     

森林火灾中烟气与林木间的传热分析

对烟气与大乔木、小乔木、灌木主干及大乔木叶间的对流、辐射换热进行了计算,分别比较了它们的总传热量和单位面积上的传热量.讨论了烟气流速、温度、林木尺寸、回流区等因素对换热的影响.在此基础上,对不同林木的火险特性进行了预测.     

调整松林密度控制清源山松突圆蚧危害的试验

通过对发生区内松林进行间伐、修枝等营林措施将郁闭度调整至0 5左右,松林中松突圆蚧的虫口密度从调整松林密度前的每束2 61头下降至0 63头,虫口密度下降75 86%,表明调整松林密度能有效地控制松突圆蚧对松林的危害;同时发现,阳坡上松林的虫口密度较阴坡上松林的虫口密度大,从阳坡向阴坡逐步过渡,松突圆蚧的虫口密度也随之下降,表明松突圆蚧的虫口密度与坡向有关,在景区绿化规划设计上应针对不同的坡向营造不同的树种,以防止松突圆蚧的发生和危害。     

SOME EFFECTS OF SHELTERBELTS UPON LOCAL AND MICRO CLIMATE

Attention is drawn to recent work on wind and shelter and acomprehensive list of references is given. Diagrams illustratethe main effects of barriers on the flow of air and these effectsare discussed. The author then considers shortly the influenceof wide tree belts on wind and their other effects such as shade,temperature, and humidity, as they present practical problemsto the hill farmer. A diagram gives the isopleths of annualmean wind speed for the British Isles together with correspondingdata for individual hill sites. This diagram provides a roughestimate of those regions where shelter would seem a necessity.     

林火蔓延过程中辐射换热和点燃特性分析

【目的】基于辐射换热原理和火行为模型,从理论角度研究林火蔓延过程中火源辐射换热规律以及辐射点燃的特点。【方法】林火蔓延过程中的燃烧区为辐射源,其向火蔓延前方的热辐射等效为矩形辐射面。矩形热辐射面的长度为火焰长度,宽度对应火线宽度;环境风速的变化导致热辐射面出现不同程度的倾斜。选取枯立木和枯倒木这2类林火环境中典型可燃物作为辐射接受体,并分别设定接受体微元距地面1.5 m高和贴于地面。将林火蔓延以及至林缘后熄灭过程中对目标物的辐射换热分2个阶段计算,由此推导出接受体的瞬态辐射换热通量和累积的辐射换热量的计算式,并相应构筑辐射点燃的判据。与此同时,结合以往对林火行为规律的认识建立起林火蔓延以及至林缘衰弱熄灭过程中火行为参数间的关系式以辅助模型计算。基于火灾安全计算的有效性原则,设定火灾场景为最糟糕情形,即火焰温度赋值为1 200 K、发射率为1.0,并且一般情形下热辐射在大气中透过率为1.0。计算过程中,取火焰火宽度50 m,火焰长度变化范围为5 m～40 m,而风速变化范围则为0 m·s^-1～10 m·s^-1。【结果】针对特定野外试验工况试算结果确认,辐射换热通量计算结果与野外测量数据高度一致,由此验证了辐射换热模型的可靠性。针对若干火灾场景开展系列计算表明,无论是接受到的辐射换热通量还是累积辐射换热量,枯立木相对于枯倒木都占有优势,但这种优势随环境风速增大有所削弱。火焰蔓延至林缘后对接受体的辐射换热为其能量积累做出主要贡献,是造成辐射点燃的主要能量来源。【结论】随着接受体与林缘间距离的增大,目标物的能量积累水平迅速降低;火焰长度和环境风速则通过改变热辐射辐射换热效率和持续时间以影响辐射点燃的条件。以林缘附近枯立木作为接受体开展热辐射点燃条件的计算证实,当树冠火焰长度增至40 m,30 m以上间隔都能有效避免辐射点燃现象。如果替换成生物防火林带,该间隔则可以大大缩短。本项工作凸显生物防火林带在阻隔林火中的重要性,同时为林火阻隔系统的设计以及林区设施的保护提供特定理论指导。     

不同坡位对天然水竹生长的影响

水竹是我国优良的笋用竹和材用竹,是经济效益和生态效益兼具的竹种.在一定海拔范围内,坡位是影响林木生长的关键因子,它代表着水分、养分等环境因素的生态梯度变化,直接影响着水肥的再分配.本研究对海子坪省级自然保护区天然水竹林在不同坡位的生长情况进行调查,结果表明:坡位对水竹无性系种群密度、产量、胸径和高度有显著影响,即随着坡位的上升水竹无性系种群密度逐渐变小,而随着坡位的下降水竹无性系分株呈现纤细化和低矮化的趋势.     

孟加拉国丘陵地带桔园和灌木林地土壤物理性质的比较评价

The physical properties of soil on two hill slopes of 35% and 55% in orange orchard cultivated by the Mro tribe of Chittagong Hill Tracts （CHTs） were evaluated and compared with those of bushy hill forests. Soil samples were collected from three different depths （0-5 cm, 5-15 cm and 15-30 cm）, digging three profiles in each land use for determining moisture content, organic matter content and particle density. Maximum water holding capacity, field capacity, dry and moist bulk density and porosity were determined only for the surface soils. Moisture content at all the soil depths was significantly higher （p≤ 0.05） in orange orchard than in forest on both the slopes. Orange orchard contained lower mean soil organic matter than forest on 55% slope, while it contained higher values on 35% slope compared to forest. The highest value of the above two properties was found at surface soil in both the land uses on both the slopes, decreasing with the increase of soil depth. On both the slopes maximum water holding capacity and porosity of surface soil and particle density at all soil depths were lower in orange orchard compared to those in forest. Field capacity values of surface soil did not show consistency in trend for the differences between the two land uses on both the slopes. Bulk density value of moist and dry surface soil was higher in orange orchard than in forest on both the hill slopes.     

PLA沙障防风效益研究

为了解新材料PLA沙障对近地表气流的影响,通过测定铺设PLA沙障沙丘距地表不同高度的风速,并以铺设麦草沙障沙丘及裸沙丘为对照,对比研究各种规格、迎风坡、坡顶及背风坡地表粗糙度、风速效能及风速廓线差异。     

Does growing on a slope affect tree xylem structure and water relations?

Variations in slope, exposure, relief and substrate over a short distance and their influences on plant function are poorly understood. We investigated the influences of soil hydrological characteristics on internal stem structure and hydraulic properties of downy oak (Quercus pubescens Willd.) growing along a hill slope. Increment wood cores were extracted from the base and at breast height (BH) of tree stems. Relative wood water content (W(c)) and wood density (D(w)) were measured in the sapwood. Wood compression strength (delta) in the longitudinal direction was measured with a fractometer. Thin sections were cut from the transversal face of each core and vessel lumen area (V(A)) was measured and xylem theoretical hydraulic conductivity (L(th)) estimated over the sapwood. Topsoil volumetric water content (theta(v)) was determined around trees and the hydrological behavior of the slope was studied through field surveys. Data were used as input to a hydrological model to simulate topsoil water distribution along the slope. Results showed that theta(v) tends to decrease with increasing altitude. Groundwater levels were lower upslope than downslope, and results from the hydrological model confirmed these trends. Mean W(c) at the base of each tree decreased significantly with increasing altitude, whereas at BH, no differences were found along the slope. There was a significant positive relationship between W(c) measured at the tree base and theta(v) along the hill slope, but not for W(c) measured at BH. Values of D(w) and delta measured at both stem positions increased significantly with increasing altitude and decreasing theta(v). Significant negative relationships were found between delta and theta(v) measured at the stem base and at BH. At both stem positions, delta was closely related to D(w) and L(th). Vessel lumen areas at BH and the stem base were significantly regressed with altitude, theta(v), D(w) and delta. Xylem theoretical hydraulic conductivity at both stem positions was negatively related to altitude and soil theta(v), but only L(th) measured at the stem base was negatively regressed with D(w). The results are discussed in the context of how tree position along a hill slope influences water uptake and internal xylem structure.     

What the towers don't see at night: nocturnal sap flow in trees and shrubs at two AmeriFlux sites in California

At the leaf scale, it is a long-held assumption that stomata close at night in the absence of light, causing transpiration to decrease to zero. Energy balance models and evapotranspiration equations often rely on net radiation as an upper bound, and some models reduce evapotranspiration to zero at night when there is no solar radiation. Emerging research is showing, however, that transpiration can occur throughout the night in a variety of vegetation types and biomes. At the ecosystem scale, eddy covariance measurements have provided extensive data on latent heat flux for a multitude of ecosystem types globally. Nighttime eddy covariance measurements, however, are generally unreliable because of low turbulence. If significant nighttime water loss occurs, eddy flux towers may be missing key information on latent heat flux. We installed and measured rates of sap flow by the heat ratio method (Burgess et al. 2001) at two AmeriFlux (part of FLUXNET) sites in California. The heat ratio method allows measurement and quantification of low rates of sap flow, including negative rates (i.e., hydraulic lift). We measured sap flow in five Pinus ponderosa Dougl. ex Laws. trees and three Arctostaphylos manzanita Parry and two Ceanothus cordulatus A. Kellog shrubs in the Sierra Nevada Mountains, and in five Quercus douglasii Hook and Arn. trees at an oak savanna in the Central Valley of California. Nocturnal sap flow was observed in all species, and significant nighttime water loss was observed in both species of trees. Vapor pressure deficit and air temperature were both well correlated with nighttime transpiration; the influence of wind speed on nighttime transpiration was insignificant at both sites. We distinguished between storage-tissue refilling and water loss based on data from Year 2005, and calculated the percentage by which nighttime transpiration was underestimated by eddy covariance measurements at both sites.     

淄博市周边破坏山体立地类型划分

以淄博市周边破坏山体为研究对象,根据野外调查结合植被恢复的影响程度,确定了破坏山体外貌形态、边坡高度、坡度、土层厚度和砾石含量5个立地因子,并对之进行了分级量化;利用聚类分析法将破坏山体划分为7个立地类型和16个亚型;不同立地类型特征和植被恢复难易程度不同。