A decision support tool approach based on the Electre TRI-B method for the valorisation of tropical timbers from the Congo Basin: an application for glulam products

An alternative approach to the formal management strategy of tropical timber species from the Congo Basin was investigated. It focused on the development of glulam, with an aim to specify a decision support model for the valorisation of tropical timber species considered for use in these products. There were 76 forest species analysed regarding ecological, engineering and social criteria according to their major uses. The Electre TRI-B multicriteria sorting method was used. The main result was a new and robust classification tool of timber species from the Congo Basin, corresponding to their multicriteria consensus degree. The potentials of the new grouping system were analysed. Species that meet a great majority of criteria were identified. They were highly suitable for sustaining the market position of glulam products. Implementing this strategy may significantly improve the management and increase the value of the timber species from the Congo Basin, while preserving endangered species.     

阔叶树小径材热压干燥工艺的研究

通过对荷木和米槠两种华南地区常用阔叶树小径材薄板材热压干燥工艺的研究，探讨热压干燥工艺参数对小径材板材干燥质量（包括密度，厚度压缩率，尺寸稳定性及部分力学性能）的影响，试验结果表明，热压干燥工艺可以大大改善小径材的物理力学性能。     

Structural mechanics of wood composite materials I: Ultrasonic evaluation of internal bond strength during an accelerated aging test

This research attempts to observe indirectly the variation of internal bond characteristics for wood composite materials during accelerated aging test treatment using ultrasonic pulse-transmission techniques. Particleboard (PB) and oriented strandboard (OSB) were the representative specimens. The transit time of the ultrasonic wave propagating through the samples along the nominal length and thickness directions was recorded using an apparatus called PUNDIT (C.N.S. Electronic, London). The transit times were measured in the samples under an oven-dried condition after treating them with boiling water at different treating time stages, and the velocity was then calculated based on the transit time. Examination of the internal bond strength conducted on the same samples was done according to JIS A 5908. A study of the relations among springback, internal bond strength, and velocity indicated that a high correlation existed between ultrasonic velocity measured in the length or thickness direction and the internal bond strength for the PB specimen, but no significant correlation was observed between the velocity measured in the length direction and the internal bond strength for the OSB specimen. The results of this research suggested that ultrasound techniques can be applied to predict or evaluate the internal bond state of some wood-composite materials made of relatively small particles, such as PB especially, during accelerated aging test treatment processes.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997     

意杨薄板材干燥工艺研究

应用高温干燥与常温干燥有机结合的工艺技术(简称蒸汽综合干燥法),对意杨25mm厚板材进行处理,在预热阶段进行充分的汽蒸处理,而后进入常压过热蒸汽干燥工艺阶段,当含水率降到25%时,转入常温干燥工艺阶段,直到干燥阶段结束。这样既缩短了干燥周期又提高了干燥质量,同时也提高了干燥窑的生产效率。     

Study on drying rate in contact drying with flexible screen

IntroductionA new type contact dryer with non-metal flexibleplaten was patented in 1998 in China, which specialstructure and material solved the problem of low productivity in platen drying. The machine was similar tohot press. Direct contact betWeen wood and heatedplaten allows rapid heat transfer by conduction (Sandoe 1983). Though the flexible screen conducts heatslower than metal platen does, it transfers massmuch fast6r. So water removing rate decides veneerdrying rate in the new machin…     

Modelling and simulation of deformation behaviour during drying using a concept of linear difference method

This study deals with the development of a two-dimensional model to simulate the deformations in wood samples during the wood drying process for the evaluation of the drying quality. The samples cut from sapwood of beech were used to analyse the moisture content distribution of the samples at two different drying conditions. A new concept based on a linear difference method was developed to use the moisture content distribution of the samples for the simulation process to predict deformation due to casehardening. The real deformations of the prongs were compared with the simulated ones for further improvements. The results show that the model can be used to simulate the deformations independently from different drying times and drying conditions. A good comparison between real and simulated changes in deformation was found for the drying process at constant climate conditions. The results provide a useful basis for further investigations on the modelling and simulation of the deformation of the samples due to different drying processes.     

Kiln drying behavior of lumber from ten fast-growth plantation species in Costa Rica

Abstract

Plantation wood from tropical climate has been introduced rapidly in the national market; however, there is lack of knowledge about the process. The main objective of this study was to investigate the kiln drying behavior of 10 plantation-grown wood species from natural forest in Costa Rica using the recommended drying schedule. Initial moisture content (MCi), final moisture content (MCf), drying rate, drying time, and drying defects were evaluated. The drying schedule applied produced the following results: (1) high MCi (over 110%) in four species and lower values in two species. (2) The largest drying time was found in species with high MCi, and the shortest drying time in species with lower MCi. (3) Significant variations of target MCf were found in some species, despite equalization and conditioning. (4) Exponential relationship MC=a*?^?t*b was used to establish a moisture content (MC) decrease model, which is not a good indicator of drying time for fives species. (5) High incidence of drying defects was found in Alnus acuminata and Vochysia guatemalensis. According to the above results, it is necessary to test other drying schedule oriented to improve lumber quality and to decrease variability of MC in wood from plantation trees.     

基于SVM的木材干燥过程含水率软测量研究

介绍木材干燥过程含水率主要测量方法,以及支持向量机回归原理。针对干燥过程木材含水率测量存在的问题,提出采用基于支持向量机的软测量方法测量干燥过程的木材含水率。通过对柞木试材干燥数据的仿真实验,结果表明支持向量机软测量模型具有良好的泛化性,能够准确预测干燥过程的木材含水率。     

A microwave applicator for on line wood drying: Temperature and moisture distribution in wood

Summary An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy, meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the position of each applicator in a larger scale microwave pilot plant. Received 25 February 1997     

A global rheological model of wood cantilever as applied to wood drying

In the process of wood drying inevitable stresses are induced. This often leads to checking and undesired deformations that may greatly affect the quality of the dried product. The purpose of this study was to propose a new rheological model representation capable to predict the evolution of stresses and deformations in wood cantilever as applied to wood drying. The rheological model considers wood shrinkage, instantaneous stress–strain relationships, time induced creep, and mechano-sorptive creep. The constitutive law is based on an elasto–viscoplastic model that takes into account the moisture content gradient in wood, the effect of external load, and a threshold viscoplastic (permanent) strain which is dependent on stress level and time. The model was implemented into a numerical program that computes stresses and strains of wood cantilever under constant load for various moisture content conditions. The results indicate that linear and nonlinear creep behavior of wood cantilever under various load levels can be simulated using only one Kelvin element model in combination with a threshold-type viscoplastic element. The proposed rheological model was first developed for the identification of model parameters from cantilever creep tests, but it can be easily used to simulate drying stresses of a piece of wood subjected to no external load. It can therefore predict the stress reversal phenomenon, residual stresses and maximum stress through thickness during a typical drying process.     

木材干燥应力连续监测方法的研究

本文在卡普法的基础上，提出了木材干燥应力连续监测方法，并设计了所需的配套装置。该方法采用涡流传感器对干燥过程中卡普片的矢高进行连续测试，同时通过计算机自动采集、存储数据。结果表明：矢高与干燥时间存在精密的相关性，它们之间的相关系数大部分达到0．99以上，从而实现了木材干燥应力的自动与连续监测。     

微波处理中木材内温度分布的数学模拟

从热传导的物理规律出发,建立微波加热过程中木材内部热传导模型,并通过理论模拟揭示不同微波加热方式对预处理中木材内部温度分布的影响规律。结果表明:微波处理过程中,木材内部的温度分布规律及均匀性与微波加热方式直接相关;当采用单向微波辐射的方式进行加热时,沿着微波入射方向,木材温度逐渐降低,木材内部温差较大,且温度分布均匀性较差;当使用双向微波辐射的方式进行加热时,木材内能形成内高外低的温度梯度,且温度分布均匀性较好。     

3种不同处理方法对木材渗透性影响的研究

本文通过对长白鱼鳞云杉和臭冷杉生材分别进行普通气干处理和酒精置换处理以及对其气干材进行水浸处理,研究了这３种不同处理方法对木材气渗透性的影响及其影响机理。研究结果表明,长白鱼鳞云杉边材、心材和臭冷杉心村的生材经普通气干处理后,其气体渗透性较低,分别约为０．１１４、０．０４５和０．１１１ｄａｒｃｙ;长白鱼鳞云杉边材、心材和臭冷杉心材的生材经酒精置换处理后,其气体渗透性分别约为１１．７１３、０．０７４和０．１４４ｄａｒｃｙ,比普通气干处理对照组试样的平均渗透性分别增加约１０１．５倍、６２％和３０％,ｔ检验表明,前者差异非常显著,但后两者差异不显著;已气干１８个月的长白鱼鳞云杉边材、心材和臭冷杉心材经水浸处理后,其平均气体浸透性较处理前分别增加约８５％、４９％、６５．５％,ｔ检验表明差异均显著。长白鱼鳞云杉生材边材经     

辐射松与杉木在高温干燥中萜烯类释放浓度研究

以40 mm厚的辐射松(Pinus radiata)和人工林杉木(Cunninghamia lanceolat)锯材为对象,研究高温干燥过程中干燥温度和锯材含水率对萜烯类产物释放浓度的影响,并与辐射松常规干燥中的萜烯类释放浓度作比较。高温和常规干燥过程中采抽气样次数均为5次,抽气速度为1.0 L/min,采样时间为30 min,采用Tenax管收集干燥过程中萜烯类产物,用气相色谱仪分析其成分及浓度。结果表明:高温干燥辐射松萜烯类释放浓度高于常规干燥辐射松与高温干燥人工林杉木,但萜烯类挥发物的组分有所差别。常规干燥辐射松锯材萜烯类释放浓度对环境是安全的,然而在高温干燥过程中,尤其在干燥中后期,当萜烯类挥发物浓度大于1.5 mg/m3时,对辐射松和人工林杉木释放萜烯类挥发物应采取回收措施,以确保对环境的安全。     

湿地草本植物冠层昆虫群落的中性理论验证

生物多样性中性理论（Unified Neutral Theory of Biodiversity）对群落中物种共存机制和多度分布提出不同于传统生态位理论的另一种解释：由处于同一营养级的物种构成的群落中,不同物种的个体间在生态学上是等价的;物种多度的分布主要决定于随机过程,如物种灭绝和物种迁入/新物种分化之间的动态平衡。对于中性理论模型是否可以准确预测物种多度分布一直存在不小的争论。本文对生长在天目山地区的湿地草本植物冠层的昆虫群落进行取样调查,分别采用中性理论模型和对数正态模型预测昆虫多度分布。采用置信区间、拟合优度检验和卡方检验等方法验证中性理论的预测。中性模型拟合的基本多样性指数θ=5.89,迁移率m=0.208 8。实测物种多度数据全部落入中性模型预测的95%置信区间内,说明中性模型预测的多度分布与实测数据基本吻合。Pearson相关性检验、Kolmogorov-Smirnov检验和卡方检验的结果表明,中性最优拟合曲线（200次中性模型模拟的平均值）的拟合优度与对数正态模型很接近,但中性理论模型的预测结果只在4%～14%的情况下（中性模型模拟200次）优于对数正态模型。因此,中性理论模型可以较好地预测天目山湿地草本植物冠层中的昆虫群落的多度分布情况,但其拟合优度并不优于对数正态模型。     

Mathematical modeling to predict drying deformation and stress due to the differential shrinkage within a tree disk

Although many mathematical models for wood drying have been developed to predict the drying behavior of lumber, there were limited results on drying models dealing with tree disks. This study attempted to try to develop mathematical models to predict the drying stresses and crack formation in a tree disk assumed as a cylindrically orthotropic material with radial variations of properties. The results showed that the drying stress changes nonlinearly with decreasing moisture content (MC) due to mechano-sorptive effects. The higher the orthotropic properties of tree disks are, the larger the drying stress occurs. The developed mathematical model showed that the pattern of cracks such as V-crack or heart check significantly depended on the MC distribution along the radial direction. The model also indicated that a dominant factor controlling the drying behavior of tree disk was the differences in MC between heartwood and sapwood within a tree disk of a given species without any chemical or mechanical treatments. Received 8 September 2000 The authors wish to thank Prof. H.S. Jung, Seoul National University, Korea, for his valuable advice. This work was supported by the grant of Post-Doc. Program, Chonbuk National University in Korea (2000).     

Moisture content gradient in a softwood board during drying: simulation from a 2-D model and measurement

Summary A 2-D mathematical model was developed to simulate moisture movement and heat transfer in width and thickness directions within a softwood board during drying. The model is based on wood physiological features and behaviour observed during drying. In sapwood, liquid water movement is assumed to be a consequence of capillary action between liquid and gas phases inside the cell lumens. However, liquid flow does not occur in wood close to the exposed surfaces because at timber surfaces the wood cells are damaged during the sawing process and consequently the liquid column is broken. In heartwood, liquid flow is negligible since the pits are normally aspirated during the formation of heartwood in the growing tree. Water vapour moves under a partial vapour pressure gradient while bound water diffuses within the wood material due to differences in chemical potential. The model was solved numerically to predict moisture-content profiles. Experiments were undertaken to measure the moisturecontent gradient. Samples were removed from a tunnel dryer at intervals throughout drying, frozen overnight and then cut into slices for moisture-content determination. The experimental results were used to verify the model.This work is supported by the New Zealand Foundation of Research, Science and Technology under contract CO4415     

Foliar temperature tolerance of temperate and tropical evergreen rain forest trees of Australia

Australian rain forests extend from tropical climates in the north to temperate climates in the south, providing an opportunity to investigate physiological responses to temperature of both temperate and tropical species within the same forest type. Eight, rain forest canopy tree species were selected to cover the 33 degrees latitudinal range of rain forests in eastern Australia. Temperature tolerance was measured in 6-year-old plants grown in a common environment, by exposing leaves to a series of high temperatures during late summer and a series of freezing temperatures during midwinter. Damage was evaluated based on chlorophyll fluorescence measurements made 2 h after exposure and by visual assessment of leaf damage made a week after exposure. Leaves of the tropical species were more heat tolerant and less frost tolerant than leaves of the temperate species, which is consistent with their climate distributions. In contrast, the temperature tolerance of the photosynthetic apparatus was unrelated to climate in a species' native habitat. However, the tropical species underwent significant photoinhibition during winter. All species maintained the integrity of the photosynthetic apparatus and avoided tissue damage over a similar span of temperatures (about 60 degrees C), reflecting the similar annual temperature ranges in Australia's temperate and tropical rain forests. Chlorophyll fluorescence measurements and visual assessment of leaf damage provided different estimates of the absolute and relative temperature tolerances of the species, thus emphasizing the importance of a direct assessment of tissue damage for determining a species' temperature tolerance.     

马占相思木干燥工艺的研究

马占相思属速生树种,其人工林木材径级小,幼龄材含量高,易干燥,但容易产生皱缩及内裂,宜采用低温软基准,且干燥过程中要增加调湿处理次数,减少表层的干燥应力及塑性变形,采用气干和窑干联合干燥方式时,不仅有效避免皱缩及内裂等干燥缺陷,而且可缩短干燥时间,减少能源消耗,降低干燥成本。     

干燥过程中木材含水率神经网络预测模型

将人工神经网络应用于木材干燥控制研究中,建立可用于木材含水率预测的时延神经网络基准模型,并给出其网络辨识结构。通过3个树种的实际干燥数据对所建立的网络模型进行训练和验证,仿真结果表明预测模型是可行而有效的,具有较好的动态跟踪能力和预报特性,实现了木材干燥基准的数学模型化,对进一步优化木材干燥基准实施与控制具有重要的指导意义和应用价值。