基于Pro/E与ADAMS行星轮系仿真研究

论述了基于Pro/E与ADAMS的行星轮系设计及动态仿真的方法和过程,介绍了Parasolid文件接口的使用以及ADAMS齿轮副中啮合点的创建方法,对仿真和理论计算结果进行了对比.     

基于PRO/E和ADAMS的伐区剩余物压缩装置的设计

利用PRO/ENGINEER软件绘制出直观的三维立体模型。将PRO/ENGINEER模型导入到ADAMS中,建立齿轮啮合力仿真模型。利用ADAMS对模型进行动力学仿真,得出速度、转矩和啮合力曲线。通过对仿真结果进行分析,在理论上确保传动机构的可行性和合理性,为压缩装置各项运动参数和结构参数的优化设计提供依据。     

欧式木窗双端复合精铣自动上料定位装置设计与研究北大核心

为解决欧式木窗上料及定位方式加工效率低和定位精度差的问题,设计了一种双端复合精铣自动上料及定位装置,通过SolidWorks软件完成了整机装置的结构构建。双端复合精铣自动上料及定位装置采用搬运天车龙门、MTB60中空旋转平台和机械夹紧手作为主要上料机构,夹紧手运动方式为齿轮齿条传动,采用TN双轴气缸和定位销进行内端定位。运用ANSYS Workbench软件对其内端定位进行静力学仿真分析,并根据分析结果对定位销的数量与位置进行优化,发现采用八销定位木窗受力更均匀。该装置实现了上料及定位一体化,能够提高加工效率及定位精度,可为木窗实际生产装置的研究和改进提供依据。     

基于UG的山地自行升降式采种机运动仿真

虚拟仿真分析是现代机械产品设计中的重要环节,能够在制造物理样机之前模拟机械的实际工作情况,暴露设计中存在的问题并加以完善。首先介绍UG运动仿真模块UG/Motion的功能及其基本流程,在此基础上建立采种机虚拟模型和仿真模型,对其进行运动仿真,模拟采种机实际中的运动情况,得到其运动规律和参数,并通过动画和图表输出仿真结果。实践证明,运用UG/Motion进行运动仿真,是进行机械设计的有效辅助手段,可有效提高工作效率和完善设计。     

复杂齿轮组自动装配防撞齿齿轮研究

齿轮作为重大装备中运动和传递动力的重要基础件，其传动的平稳性以及承载强度的可靠性，是制约重大装备发展的瓶颈。撞齿问题是复杂齿轮组在快速、高效自动装配过程中的主要技术难点。利用Siemens NX三维设计软件来设计、优化齿轮结构，根据防撞齿齿轮的接触应力、传动压力角、齿轮基本齿廓等参数作为理论依据来建立齿轮模型，并以此对齿轮的结构进行了新型圆弧齿轮防撞齿设计。     

一种毛竹根挖掘机的设计和优化

以轻便、高效、可靠为设计目标,提出了一种毛竹根挖掘机的设计和优化方法。首先依据文献和试验选定动力源为汽油机及其型号,确定二级齿轮减速器为传动机构,并求取齿轮减速器在满足约束条件下的最优解;其次选择圆筒旋转磨切机构切割竹鞭,并对双螺旋导泥片的起始角度、旋转半径进行分析计算;最后在Solidworks环境下建立样机三维模型,用simulation模块对圆筒旋转磨切机构模型进行动力学仿真分析,根据数据的拟合曲线推导出满足挖掘所需强度的条件同时质量较小的尺寸,并对该模型进行静态分析以检验其强度是否达到要求。仿真优化结果表明:筒顶镂空偏移角θ和开口槽的半径R对圆筒强度影响较大,但开口槽的距离d对其影响甚微。最终毛竹根挖掘机的总质量为12 kg,其中执行机构最终的质量为1.25 kg。该优化方法在满足机器安全系数的条件下,能有效减少挖掘机尺寸、减轻机器质量,满足毛竹根挖掘生产中对机器质量及性能的要求。     

齿轮倒角机刚柔耦合模型建模及仿真研究

采用混合建模的仿真分析方法,运用机械造型软件Pro-E和多体动力学仿真软件ADAMS建立倒角机的刚柔耦合虚拟样机模型,并对其进行具体的仿真分析。研究结果表明,使用硬质合金刀具,齿轮倒角机在工作时震动小,工作较平稳;仿真分析过程中,选择最少2个旋转分布的铣刀片已能得出仿真数据且保证其精度,增加铣刀数目会带来建模困难和降低仿真速度。该建模方法和仿真分析对齿轮倒角机结构的优化设计提供依据。     

轮系分析系统化的研究

本文提出了一种轮系分析的系统化方法。这种方法以轮系组成机构符号为基础,直接构造出轮系分析的数学模型,利用现有的计算机程序进行处理。它不仅能处理各种不同轮系的分析问题,还能将同一轮系不同分析问题(如运动学问题,动力学问题和功率问题)的求解一体化、程序化,可作为轮系CAD的基础。     

YP2.0-A遥控跑车减速机构动态特性分析与仿真

以YP2.0-A遥控跑车的减速机构为研究对象,应用Solidworks软件对增速箱齿轮系统进行总体参数化建模。通过合理假设,简化复杂机构并对各零部件进行精确装配。合理设置仿真参数,结合动力学软件ADAMS领先的“功能化数字样机”技术,对遥控跑车传动机构的齿轮实体造型、数学建模、动力学及其他动态特性进行仿真分析。采用这样的仿真分析方法可以从根本上解决传统设计模式中的漏洞,避免多次试制物理样机的同时也提高了设计质量。     

基于神经网络的圆弧齿轮模糊可靠性优化设计

以圆弧齿轮传动的小齿轮齿数、法面模数、螺旋角及齿宽的均值为设计变量,考虑影响齿轮传动的各种因素的随机性和模糊性,以两圆弧齿轮的体积和最小为目标函数,应用模糊和可靠性设计理论,建立双圆弧齿轮传动的模糊可靠性优化设计的数学模型,应用Hopfield神经网络算法对其进行计算.     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。