基于有限元的树木移植机铲刀挖掘力分析

铲刀是树木移植机的关键部件,其结构直接影响到树木移植机的工作性能.根据树木移植机工作特点,对铲刀受力情况进行理论分析,建立相关的力学模型;基于ANSYS/LS-DYNA建立菱形铲刀与土壤相互作用的虚拟仿真模型,分析切削过程中土壤的应力变化情况及铲刀受力变化情况;分析不同切削角度下铲刀受土壤反作用力的变化情况,为铲刀进一步设计提供理论依据.     

模型铲预测树木移植机下铲阻力的研究

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。     

树木长高长粗的秘密

一颗细小的树木种子,如何从入土发芽逐渐成长为高大的树木的呢?植物生理学家早就揭开了这个自然之谜,无论是整个树木,还是树木的个别器官,它们的生长,都是通过细胞的增多和加大来实现的。树木细胞的生长和所有植物细胞的生长过程一样,都要经过细胞分裂、细胞伸长扩大和细胞成熟分化三个时期。细胞的分裂期又称为胚胎期。这个时期细胞较小,细胞壁     

基于地面激光雷达点云数据的单木三维建模综述

对利用野外树木激光扫描获取的海量点云数据来提取树木几何与拓扑特征并以此来构建树木三维模型的方法进行综述.在总结基于激光点云的树木建模基本原理和步骤的基础上,围绕单树点云数据的分割、树枝骨架的提取与优化、单木模型的表面重建等主要过程,对各种具体实现技术或方法进行分类、分析和评价,最后对生成的树木模型的精度和未来的技术发展趋势进行简要分析.     

新栽树木的养护

正树木栽种后必须进行及时合理的养护管理才能成活。通常情况下,树木成活率低的原因,主要是栽后养护管理不及时或管理不当造成的,所谓"三分种,七分养",养护是树木能否成活的关键因素之一。笔者现将苗木成活期养护管理经验总结如下。扶正。如果树木刚栽不久出现歪斜,应立即扶正。首先应检查根入土的深度,如果栽植较深,应在     

新栽树木的养护

<正>树木栽种后必须进行及时合理的养护管理才能成活。近期我们对一些新栽树木进行了调查,分析树木成活率低的原因,主要是栽后养护管理不及时或管理不当造成的,所谓"三分种,七分养",养护是树木能否成活的关键因素之一,现将苗木成活期养护管理经验总结如下:一、扶正如果树木刚栽不久歪斜,应立即扶正。首先应检查根颈入土的深度,如果栽植较深,应在树木倒向的一侧,根盘以外挖沟至根颈下方,用锹或木板伸到根团以下向上     

基于影像分割的树木特征点提取方法研究

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.     

园林树木移栽成活的关键因素及措施

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。     

新裁树木的养护

树木栽种后必须进行及时合理的养护管理才能成活.近期我们对一些新栽树木进行了调查,分析树木成活率低的原因,主要是栽后养护管理不及时或管理不当造成的,所谓“三分种,七分养”,养护是树木能否成活的关键因素之一,现将苗木成活期养护管理经验总结如下: 一、扶正 如果树木刚栽不久歪斜,应立即扶正.首先应检查根颈入土的深度,如果栽植较深,应在树木倒向的一侧,根盘以外挖沟至根颈下方,用锹或木板伸到根团以下向上撬起,向根底塞土压实,扶正即可.大树扶正培土以后还应设立支架.     

基于HALCON的树木检测方法应用研究

本文基于机器视觉的方法,对树木基本测树因子的检测进行初步尝试,叙述利用HALCON软件进行目标树的树高和直径等的检测过程;同时对检测精度进行了分析。验证使用机器视觉技术测量树木的可行性;同时也说明了利用机器视觉技术可以提高树木测量的准确性和效率,为数字林业的建设提供了基本的研究方法。     

深松插干植树机牵引阻力的试验研究

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。     

Finite element study of growth stress formation in wood and related distortion of sawn timber

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.     

Reduction of electric field strength by two species of trees under power transmission lines

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.     

联合整地机牵引机架的有限元分析

针对联合整地机牵引机架工作过程中出现的振动大、强度不足、影响整地质量等问题，分析其极限状态下的受力情况，并利用三维设计软件CATIA中的Product模块和Analysis＆ Simulation／Generative Structural模块，进行有限元模型的建立、单元类型的设置、网格划分、施加约束和载荷、求解和观察分析，结果表明：联合整地机牵引机架最大应力远远小于材料的许用应力，满足强度和刚度要求，结构还有较大的优化潜力。因此为进一步的设计与研究提供必要的理论依据。     

塑料排水板加固软土地基的数值分析

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。     

果树缺铁性黄化的原因及防治技术

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     

Integrating belowground carbon dynamics into Yield-SAFE,a parameter sparse agroforestry model

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.     

Role of <Emphasis Type="Italic">tao</Emphasis> (<Emphasis Type="Italic">Belotia mexicana</Emphasis>) in the traditional Lacandon Maya shifting cultivation ecosystem

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.     

秸秆覆盖对林地土壤肥力及树体生长的影响

秸秆覆盖降低了土壤温度,缓和了暴风雨对土壤的直接侵蚀,减少了水、土、肥的流失;促进了土壤有机质和营养物质的积累、分解和转化,从而复壮了树势,提高了树体的生长量及养分含量。本文通过综述秸秆覆盖的发展及其所产生的土壤效应、环境效应和对树体营养生长的影响,为探索秸秆覆盖对其它经济林的影响提供参考和依据。     

厦门大学校园内石栗生长不良原因初步研究

通过对石栗 (Aleuritesmolucana)个体生长状况、生理指标、土壤养分和盐分含量及叶片元素含量的分析 ,初步认定厦门大学校园内的石栗生长不良的主要原因是盐害 ,而不是由于土壤养分缺乏。石栗是一种比较耐盐的园林绿化树种 ,在盐度不高于 3 5mg·g-1的土壤上能正常生长