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本文应用相似理论和模型试验,采用比例缩尺n_L=2的模型铲刀,建立树木移植机下铲阻力与土壤状况、铲刀类型和铲刀下铲阻力距离等因素之间的经验公式。试验表明,该经验公式在试验取值范围内具有较高的预测精度。 相似文献
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树木处于复杂的自然环境中,加之其本身的不规则性,使得影响树木影像检测和识别质量的参数难以确定.采用一种基于集群聚类的方法对树木影像进行影像分割,在聚类中心的定义方式上不是简单地以各类的灰度重心作为聚类中心,而是采用了一种最大—最小距离法进行聚类中心的动态选择.在聚类过程中除了合并过程还加入了类别分裂处理,对每一次迭代过程中标准差最大的类别分裂成新类,并将新类中的像元重新加入到距离判别过程中,成功地将树木从背景影像中分离出来.在此基础上选择合适的特征提取算法,分别对原始影像和分割结果进行特征点的提取,对提取结果进行比较,得到了更好的特征点提取结果,为后续的树木影像匹配等研究工作提供可靠的数据基元. 相似文献
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园林树木作为确保城市景观协调、美化的重要因素,不仅可以对城市环境起到改善作用,同时还可以对城市绿化进程起到推进作用,具有较大的种植意义。目前,园林树木移栽逐渐成为园林绿化的重要手段,并主要以移栽成活大树为主。在此过程中,需要工作人员及时做好移栽成活管理工作与优化工作,以确保园林树木移栽成活率得以有效提升。针对于此,结合对影响园林树木移栽成活率关键因素的分析,探讨了优化园林树木移栽成活的主要措施。 相似文献
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深松插干造林在我国是一种较新的深栽造林作业方式,用于这种造林作业的植树机所能划开的松土沟深度是影响造林成活率的关键。在半干旱的科尔沁沙地腹部,对这种植树机的松土深度与牵引阻力的关系进行了实地测试。取得的数据表明,植树机的牵引阻力随松土深度增大而增大,所做的曲线为一近似直线。进而得出在科尔沁沙地的土壤条件下,使用国产的东方红履带式拖拉机作为植树机的牵引动力,其最大深松作业深度不大于80cm。 相似文献
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Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain. 相似文献
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Electrical pollution is a worldwide concern,because it is potentially harmful to human health.Trees not only play a significant role in moderating the climate,but also can be used as shields against electrical pollution.Shielding effects on the electric field strength under transmission lines by two tree species,Populus alba and Larix gmelinii,were examined in this study.The electrical resistivity at different heights of trees was measured using a PiCUS sonic tomograph,which can image the electrical impedance for trees.The electric field strength around the trees was measured with an elf field strength measurement system,HI-3604,and combined with tree resistivity to develop a model for calculating the electric field intensity around trees using the finite element method.In addition,the feasibility of the finite element method was confirmed by comparing the calculated results and experimental data.The results showed that the trees did reduce the electric field strength.The electric field intensity was reduced by 95.6%,and P.alba was better than L.gmelinii at shielding. 相似文献
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调查表明 ,果树缺铁性生理病害在碱性大的土壤里表现严重 ,导致果树枝梢枯死 ,生长不良 ,果实减产甚至绝收。采取改土、降低土壤 p H值、增加土壤有机质、降低地下水位以及补施铁元素 (含 Fe EDTA,EDDHA-Fe)等可有效克服缺铁性生理病害 ,使果树生长充实 ,结果优良 相似文献
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主要对分层填筑情况下排水板处理的软土地基沉降进行数值模拟,分析荷载与沉降曲线关系,以便于工程应用。采用固结度等效原则,将砂井地基转换成平面应变有限元。对哈尔滨绕城高速公路软基路堤,利用ABAQUS有限元软件,进行二维有限元数值计算,并将模拟结果与监测数据进行对比,其吻合度较好。计算结果表明:排水板具有加快土体沉降,减少固结时间的作用;同时可为路面施工时间的确定提供依据,以保证试验路段的工后沉降满足设计要求。 相似文献
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J. H. N. Palma J. Crous-Duran A. R. Graves S. Garcia de Jalon M. Upson T. S. Oliveira J. A. Paulo N. Ferreiro-Domínguez G. Moreno P. J. Burgess 《Agroforestry Systems》2018,92(4):1047-1057
Agroforestry combines perennial woody elements (e.g. trees) with an agricultural understory (e.g. wheat, pasture) which can also potentially be used by a livestock component. In recent decades, modern agroforestry systems have been proposed at European level as land use alternatives for conventional agricultural systems. The potential range of benefits that modern agroforestry systems can provide includes farm product diversification (food and timber), soil and biodiversity conservation and carbon sequestration, both in woody biomass and the soil. Whilst typically these include benefits such as food and timber provision, potentially, there are benefits in the form of carbon sequestration, both in woody biomass and in the soil. Quantifying the effect of agroforestry systems on soil carbon is important because it is one means by which atmospheric carbon can be sequestered in order to reduce global warming. However, experimental systems that can combine the different alternative features of agroforestry systems are difficult to implement and long-term. For this reason, models are needed to explore these alternatives, in order to determine what benefits different combinations of trees and understory might provide in agroforestry systems. This paper describes the integration of the widely used soil carbon model RothC, a model simulating soil organic carbon turnover, into Yield-SAFE, a parameter sparse model to estimate aboveground biomass in agroforestry systems. The improvement of the Yield-SAFE model focused on the estimation of input plant material into soil (i.e. leaf fall and root mortality) while maintaining the original aspiration for a simple conceptualization of agroforestry modeling, but allowing to feed inputs to a soil carbon module based on RothC. Validation simulations show that the combined model gives predictions consistent with observed data for both SOC dynamics and tree leaf fall. Two case study systems are examined: a cork oak system in South Portugal and a poplar system in the UK, in current and future climate. 相似文献
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For centuries, the Lacandon Maya have farmed the forest while also preserving and regenerating it. The Lacandon manage their
fallow by planting certain tree species, and removing volunteer trees that are not optimal for soil fertility. This study
focused on tao (Belotia mexicana), one of the Lacandon tree fallow species, and its impact on the soil as it matures in the secondary forest. The effect of
tao on soil fertility was evaluated using the following soil fertility parameters: phosphorus, carbon, nitrogen, earthworm density,
pH, and soil moisture. Results were compared using a split-plot analysis. Soil C:N ratios decreased with age of tao, indicating an improvement of litter quality over time. Soil extractable phosphorus decreased with age of tao and increased with distance from tao, which suggests that tao is depleting phosphorus. These results provide an introduction for further analysis into how native trees enhance soil fertility
in the Lacandon system. 相似文献
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