DEM在林火行为模拟中的应用

林火行为具有时间和空间特征,利用DEM(Digital Elevation Model)对林火行为进行3维模拟是一个很有前景的研究方向。本研究利用ArcView实现DEM数据源的提取、模型转换,通过林相图和地形图的配准,将影响林火蔓延的可燃物因子与DEM结合,进行效果图显示,为林火行为的3维模拟进行了有益的实践。     

Deformation analysis of timber-framed panel dome structure I: simulation of a dome model connected by elastic springs

This study develops an analytical method that enables the simulation of the deformation of timber-framed plywood panel dome structures, of which strength is largely governed by the rigidity of joints. A hybrid truss structure model was employed to analyze this structure. In this model, we aimed to incorporate the mechanical properties of bolted and nailed joints, which were employed to build the structures, although the present investigation focused on the deformation characteristics of a dome in which the panel elements were connected mutually by elastic springs. The results of the theoretical analysis are compared with those obtained by experiments. The simulated results were found to be in good agreement with the results of the experiments under similar loading conditions.     

Economic evaluation of forest drainage and fertilization in northern Ontario peatlands with an investment decision model

Drainage and fertilization of an existing peatland black spruce (Picea mariana (Mill.) B.S.P.) stand and 24 possible methods of planting a clear-cut area near Cochrane, Ontario were evaluated by means of a recently developed forestry investment decision model, FIDME.Results indicate that, on the basis of the cost estimates used and assumptions made, drainage of the existing stand is the most economical treatment if it can reduce the rotation age by 30 years or more. Drainage combined with fertilization is the second best alternative if this treatment can reduce the rotation age by 40 years or more. Fertilization of the undrained site ranks a distant third, and then only if it reduces the rotation age by 10 years; otherwise, it will be uneconomical to apply.In the case of the clear-cut area, planting bare-root stock on a mechanically prepared but undrained site without weed control ranked first among the 24 alternatives considered; the same treatment, but with weed control included, ranked second. Planting containerized seedlings on a mechanically prepared but undrained site with weed control ranked third, followed by planting bare-root stock on a mechanically prepared and drained site with weed control. In contrast, planting containerized seedlings on an unprepared site and with no weed control ranked as the least cost-effective method considered.     

基于表面建模技术的数控车床动态加工仿真模型研究

在充分考虑数控车床加工表面特征的基础上,对以往仿真模型的不足进行了分析,提出了基于螺旋曲面的加工表面模型。该模型充分考虑了数控程序中主轴转速和进给速率两个重要参数,并提出了数控车床动态加工过程仿真的时间驱动机制。     

三江平原蒙古栎次生林效应带生态功能模拟

以三江平原试验区为背景,采用植物生态场技术开展次生林效应带生态功能模拟,研究结果表明:蒙古栎林6m效应带产生斑块效应,8m效应带出现边缘效应;4m,6m和8m带的光能利用与风流动模式与效应带的分布方位关系密切,根据光能利用效率总结出蒙古栎林效应带依照8 m带→6m带→4m带逐步演化。     

基于Pro/E与ADAMS蜗轮蜗杆传动仿真研究

论述了基于Pro/E与ADAMS的蜗轮蜗杆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,对仿真结果和理论计算结果进行了对比.     

A framework for a modular modelling approach for agroforestry

There are a number of problems with conventional methods for implementing models of agroforestry systems, including the difficulties of building, modifying and understanding them. One way of addressing these problems is to adopt a modular modelling approach, in which a model is constructed by linking a number of submodels, which in turn may consist of smaller computational units.This paper presents a basic framework for the design of a modular modelling approach suitable for agroforestry modelling. This approach is based on a close correspondence between the notion of module in modelling and of subroutine in a programming implementation of a model, so that selecting and linking modules is analogous to choosing and issuing calls to subroutines. This approach has the potential for enabling the complex modelling structures that are required for agroforestry modelling, such as spatial aspects and the representation of individual trees, to be handled in a consistent and uniform manner.The approach requires that subroutines should be held as symbolically-represented structures, rather than just source code in a programming language, so that they can be referenced as discrete units, and internally modified by symbol-processing operations. It is shown that the logic-programming language Prolog is well-suited to the task of representing subroutines in template form, ready to be fleshed out and combined into a single program in response to the selections made by a user. Prolog's suitability for the development of a user-friendly model design interface is also discussed, enabling models to be constructed simply by selecting options from a menu of design choices.     

Numerical experiments of watershed-scale soil water movement and bedrock infiltration using a physical three-dimensional simulation model

Numerical experiments of soil water movement and bedrock infiltration based on a simplified simulation method were conducted to analyze watershed-scale rainfall-runoff processes. To verify the model accuracy, it was applied to a Minamitani watershed (0.45 ha). The simulation was performed with 2.5-m space grids horizontally and five cells vertically. Results of long-term calculation of this model proved that this simulation model is robust and demonstrated good computational water mass conservation. Calculation results showed the best agreement with observed hydrographs and the number of groundwater levels simultaneously when laboratory-tested soil hydraulic characteristics for topsoil were used and infiltration into bedrock was included in numerical calculations. Numerical experiments show that bedrock infiltration generated a stable base flow and suppressed the secondary discharge peak. The reproducibility achieved by observed soil hydraulic characteristics with the assumption of bedrock flow demonstrates the effectiveness of the simulation model used in this article for analyses of watershed-scale soil water movements.     

Characteristics and decomposition rates of pruning residues from a shaded coffee system in Southeastern Brazil

In the Zona da Mata Mineira of Southeastern Brazil the development of sustainable land requires the integration of crops with trees. The objectives of this study then were to (i) characterize prunings from the main tree species in an agroforestry system; (ii) determine the effects of the physical and chemical characteristics of the prunings on their decomposition patterns in the laboratory; (iii) assess the effect of mixing leaves of different species on decomposition rates; and (iv) propose a decomposition index for the residues studied. The study was carried out with pruning residues from Cajanus cajan, Solanum variable, Cassia ferruginea, Piptadenia gonoacantha, Croton urucurana, and Melinis multiflora. The materials were characterized for total C, N, P, Ca, Mg and K contents; lignin, cellulose, hemicellulose and soluble polyphenols contents. The pruning residues had high polyphenols and lignin contents, high C:N and C:P ratios, and low contents of Ca, Mg, and K. The low decomposition rates of the prunings were related to the P, K, hemicellulose and polyphenol contents. The rates of N mineralization from most of the residues indicate that there is a potential to supply the needs of a crop of maize. The residues of some species, if decomposed alone, would not supply sufficient nutrients, and need to be mixed with leaves of other species.This revised version was published online in November 2005 with corrections to the Cover Date.