环境低温和液流速率协同影响活立木声波传播速度变化规律和突变机理

Wood quality testing and assessment of plantation standing trees based on acoustic wave technology is becoming one of hot research topics in the field of nondestructive testing of wood, but the "uncertainty" of wood quality grade of standing tree caused by“saltation”of acoustic wave velocity measured around freezing point of water has not been well solved, which reduces the accuracy of wood quality evaluation using acoustic wave technology. In order to solve this problem, this study tries to investigate the relationship between sap flow velocity, moisture content and ice formation amount around the freezing point of water（-4～4℃） ,characterize the frozen extent of the tree stem using sap flow velocity, and model the relationship between sap flow velocity and acoustic wave velocity to qualitatively and quantitatively analyze the changing law and changing mechanism of acoustic velocity around the freezing point, and finally to solve the "uncertainty" problem of wood quality grade prediction. For the temperature below freezing temperature (below -4℃), the statistical relationship between temperature, moisture content, ice amount and acoustic velocity will be established. The mechanism of effect of temperature on acoustic wave velocity will be revealed by the combination with image characteristics of ice stock and distribution in the conductive tissue of sap wood below freezing point. This study aims to establish accurate wood quality evaluation method for plantation standing trees and improve the level of effective management of plantations. This study also aims to provide theoretical support to realize the fast prediction for frozen extent of standing tree using the methods of acoustic wave technology and thermal expansion technology.

应用声波传导技术对人工林活立木进行质量检测与评估，是当前木材无损检测领域的研究热点之一。而由冰点附近声波传播速度“突变”所引起的活立木质量等级“测不准”的问题，至今尚未解决，制约了活立木质量评价的精度。针对这一问题，本项目拟研究冰点温度附近（-4～4℃）树干液流速率、含水率与结冰量的关系，通过液流速率表征冰点附近活立木结冰程度，建立液流速率与活立木中声波传播速度的关系模型，定性和定量解析冰点附近活立木声波传播速度的突变规律和突变原理，解决冰点附近活立木质量等级“测不准”问题；针对冰点以下温度（低于-4℃），建立温度、含水率、结冰量与声波速度统计关系，并结合输导组织结冰存量及分布的图像特征，揭示冰点以下温度对活立木声波传播速度影响规律产生的机理。该研究旨在建立准确的人工林活立木质量评价方法，提高人工林合理经营水平，同时为利用声波传导技术和热扩撒技术法实现活立木冻结程度的快速预测提供理论支撑

声波传导技术是目前活立木质量检测与评估中最常用的方法，而由环境低温而引起的声波传播速度的变化尤其是冰点附近的“突变”，进而引起的活立木质量等级“测不准”的问题，是目前木材无损检测领域所面对的一个技术难点，制约了活立木质量评价的精度。针对这一问题，本项目研究了环境温度、声波传播速度、液流速率、活立木密度和木材冻结程度之间的关系。通过研究环境温度对活立木液流速率的影响以及有无液流通过时活立木的结冰程度情况，建立了温度、含水率和液流速率之间的关系，确定了温度和结冰对液流速率的影响；通过建立环境温度、树干温度和含水率、声波传播速度等指标的关系模型，确定了结冰程度对声波速度的影响；并初步建立了木材冻结程度的预测的模型以及声波在冻结木材中传播的理论模型。该研究结果为解决低温尤其是冰点附近活立木质量等级“测不准”的问题奠定了理论基础，为建立准确的人工林活立木质量评价方法、提高全气候条件下人工林活立木质量检测精度、人工林合理经营水平，以及利用声波传导技术和热扩撒技术实现冰点附近活立木冻结程度的快速预测的可能性提供了理论参考。