共查询到20条相似文献,搜索用时 46 毫秒
1.
2.
3.
我国大径材原料供需形势严峻,培育华北落叶松人工林大径材可以缓解用材紧张现状。笔者在借鉴他人对桉树、杉木大径材培育研究的基础上,从优质种源、立地条件和栽培技术3方面综述了华北落叶松人工林大径材培育技术,以期为华北落叶松人工林大径材培育提供理论参考。 相似文献
4.
5.
日本落叶松大径材培育技术的研究 总被引:1,自引:1,他引:0
《防护林科技》2015,(10)
通过对26年生日本落叶松大径材的培育试验研究,结果表明:以保留密度600株·hm-2和750株·hm-2的效果最佳,伐后5年大径木可增加50%左右,是对照区的3倍,小径木下降70%左右。主伐时产量预测为:600株·hm-2的林分材积416.94 m3·hm-2,产值91.96万元·hm-2;750株·hm-2的林分材积453.28 m3·hm-2,产值93.62万元·hm-2。 相似文献
6.
7.
通过在辽宁省新宾县陡岭林场进行的长白落叶松不同密度生长对比试验,结果表明,保留密度为525 ̄600株/hm^2的林分,胸径和材积生长量最大,建议在土壤肥沃、长白吕松纯林面积大、采伐周期集中的国有林场进行长白落叶松大径材培育,这对于提高单位面积木材产量、调整林龄结构、满足市场对大径材的需要是非常有效的技术措施。 相似文献
9.
10.
11.
Summary In part 1 of this series, a three-dimensional, structural analysis, finite element program has been developed to predict the stress distribution in wood poles with and without spiral grain and variable material properties. This program serves as a basis for a model to predict the strength and failure location in full-size wood poles. Fundamental to this model is the ability to quantify the effects of key material and geometric properties of the pole. This paper deals with the enhancement of the program to quantify the effect of knots and their associated cross grain on the stress distribution of wood poles. The technique is based on the theoretical behavior of laminar fluid flow around an elliptical obstruction. The flow-grain analogy was employed to develop empirical relationships between knot diameter and pertinent variables (grain deviation angle near the knot and area of influence of the knot). Prior to the development of the empirical relationships, a study was conducted to determine the size and distribution of knots in Douglas-fir and western redcedar poles.The validity of the technique to describe knot behavior is reflected in the ability of the finite element model to predict the strength and failure location of wood poles. The results suggested that the flow-grain analogy is a rational mechanism to quantify the fiber orientation near a knot. Furthermore, this technique could have meaningful implication in improving visual grading methods for wood poles.The authors would like to recognize the contributions of Engineering Data Management, Inc. of Ft. Collins, Colorado for their contribution of test materials and facilities for this study. 相似文献
12.
Summary This is the first of two papers designed to describe the most recent efforts in using contemporary technology to predict strength and failure location in wood poles. In this report, a three-dimensional finite element model is presented which was developed to provide a rational stress analysis tool for wood poles. Due to practical considerations, only critical pole segments were subjected to stress analyses. Twelve-inch (30.5 cm) segments were selected for analysis which contained knots or knot clusters deemed consequential.The linear elastic model assumes small-deflection theory, and exploits linear strain, 15-node wedge and 20-node parallelepiped, isoparametric finite elements. Element geometry was selected to reflect knot size distribution found in full-size wood poles used in North America. Boundary conditions represented both applied loading and support considerations.Model verification studies were conducted on poles with isotropic (steel) and anisotropic (wood) material properties with and without spiral grain and variable longitudinal elastic properties along the pole radius. The results showed excellent agreement between theoretical and numerically-predicted pole stresses. The effect of boundary conditions on predicted stress distribution was defined, and the element geometry was appropriately modified. The developed model proved to be a rational basis for a more enhanced version to predict the mechanical behavior of wood poles with several inherent growth characteristics. 相似文献
13.
Summary This paper studies the title problem on the basis of the consideration of the generalized plane deformation of a cylindrically aeolotropic body.
The authors wish to express their sincere appreciation to Dr. E. R. Mark, Department of Forestry, University of Kentucky, Lexington, Kentucky. This problem was encountered in some of his research project under the sponsorship of the McIntire-Stennis Cooperative Research Program of the U.S. Department of Agriculture. 相似文献
Zusammenfassung Die vorliegende Studie beschäftigt sich mit der Frage der Isotropie im Zentrum einer geraden zylindrischen Säule aus Holz. Zugrundegelegt ist die Annahme der grundsätzlich ebenen Verformung eines zylindrischen anisotropen Körpers.
The authors wish to express their sincere appreciation to Dr. E. R. Mark, Department of Forestry, University of Kentucky, Lexington, Kentucky. This problem was encountered in some of his research project under the sponsorship of the McIntire-Stennis Cooperative Research Program of the U.S. Department of Agriculture. 相似文献
14.
Increasing woodland area in the United Kingdom is strongly supported in policies, but there is evidence of low rates of new planting, infrequent uptake of farm forestry, and negative attitudes to woodland among farmers. Additionally, there is a wider context of increasing farm diversification, and a need for greater understanding of farmers' attitudes and behaviour related to afforestation. This paper uses a representative survey of Scottish farmers (survey year: 2013, respondents used in analysis: 1735) to compare farmers who intended to expand forestry in future and farmers with alternative combinations of intended and past behaviour in relation to forestry. Overall, we find that certain characteristics: already operating forestry, reporting types of non-farming activities, involvement in environmental schemes, having a high education level, having a relatively high number of employees, and being relatively recent entrants to holdings, were more frequently found among farmers intending to increase forestry in future than farmers described as ‘non-increasers’ who did not intend to increase forestry and also had not expanded it in the past. Farmers with these characteristics could be a useful focus in attempts to expand woodland at larger scales, and encouraging small-scale tree planting could be an effective policy approach. 相似文献
15.
Germar Eisenacher Robert Scheidemann Martin Neumann Bernhard Droste Holger Völzke 《Wood Science and Technology》2013,47(2):369-380
An extensive series of large deformation crushing tests with spruce wood specimens was conducted. Material orientation, lateral constraint and loading rate were varied. Regarding material orientation, a reduction in the softening effect and the general force level was observed with a higher fiber-load angle. A comparison with characteristics gained by application of Hankinson’s formula showed discrepancies in compression strength and the beginning of the hardening effect. Lateral constraint of the specimens caused a multiaxial stress state in the specimens, which was quantified with the applied measuring method. Further, a higher force level compared to specimens without lateral constraint and significant hardening effect at large deformations resulted. Thus, the influence of a multiaxial stress state on the force level could be determined. An increase in the loading rate led to higher force levels at any displacement value and material orientation. 相似文献
17.
利用20年生落叶松全同胞子代树高、胸径的观测数据,以小区平均数为据,采用Griffing配合力分析方法4的程序对生长性状的配合力分析,结果表明:树高、胸径的一般配合力均占优势,分别为79.82%、53.42%,说明日本落叶松生长性状的遗传主要受基因的加性效应所控制。采用配合力效应筛选的优良亲本为:宽10,草41,草13,永10,用其组建1.5世代种子园的改良效果为:树高、胸径、材积分别提高2.95%、9.70%、14.08%,筛选的优良杂交组合为:草13×草6、草82×永11、草82×503、永10×永8、草82×草13、草13×永11,用其建立人工控制授粉的杂交种子园的改良效果为:树高、胸径、材积分别提高8.28%、13.21%、27.60%。 相似文献
18.
19.
以二氢槲皮素的得率为指标,分别采用超声、微波和加热提取法(冷浸、温浸和回流等)从落叶松中提取二氢槲皮素。先后对提取溶剂的体积分数、料液比和提取次数等共性因素及提取时间和能量强度等核心因素进行考察,3类方法中微波提取得率最高,可达0.116%,回流提取的累积得率可达微波法的95.9%,而超声提取的累积得率仅能达到微波法累积得率的55.2%。规模化生产可采用体积分数60%乙醇作为提取溶剂,料液比1∶12,微波700 W提取2次,每次10 min或80℃回流提取3次,每次240 min。扫描电子显微镜观察结果表明:尽管超声对植物细胞组织破壁或变形的机械效应较强,但二氢槲皮素的得率仍较微波和回流提取法低,二氢槲皮素的溶出主要是导致热效应的贡献。 相似文献