应力波在落叶松活立木中的传播规律

【目的】探究应力波在落叶松活立木中的传播形式和传播规律,为人工林材质预测评估提供理论基础。【方法】依据固体介质中的应力波传播理论和弹性力学理论,基于活立木的正交各向异性假定,利用COMSOL Multiphysics多物理场仿真软件对应力波在活立木中传播的波阵面进行了模拟计算,并通过试验验证数值模拟方法的合理性。【结果】应力波传播波阵面在开始阶段为倾斜曲线(二维)或倾斜曲面(三维),且曲线和曲面都弯向脉冲力输入点,随着距离的增大,波阵面倾斜度逐渐减小,直至最后与活立木的长度方向近似垂直,即应力波在活立木中由三维膨胀波传播形式逐渐转向准平面波传播形式;波阵面倾斜度的减小速度随着活立木直径的减小而加快;传播距离对波速没有影响,波速总体上随着直径的增大而增加。最后,通过试验验证,证明了这种数值模拟研究应力波在活立木中传播规律的方法是可行的。【结论】通过数值模拟手段研究应力波在活立木中的传播规律以及直径和传播距离对波速的影响是合理可行的,直径和传播距离都会对应力波在活立木中的传播形式及规律造成影响,但二者对波速的影响不同。

Stress wave propagation patterns in larch standing trees

Objective] The primary purpose of this study was to explore the propagation patterns of stress waves traveling in larch standing trees,and pave a theoretical foundation for further study on the prediction and evaluation of the mechanical properties of these plantation trees.Method] In this study,the wave fronts of stress waves propagating in standing trees were simulated,and the forms of two-dimensional and three-dimensional propagation patterns of the stress waves propagating in standing trees were studied by using COMSOL Multiphysics finite element analysis software,based on the stress wave propagation theory in a solid medium and the orthotropic assumption for standing trees.Finally,a field experiment for the measurement of stress-wave timing was conducted to verify the validity of the numerical simulation method.Result] It was found that the wavefront at the starting stage was a sloping curve or surface,bending to input point of force pulse and with the increase in distance,the inclination of the wavefront decreased gradually until it was approximately vertical to the length direction,i.e.,the wavefront gradually changed from a 3D wave to a quasi-plane wave.The rate of decrease of the wavefront inclination increased with decreasing tree diameter.The travel distance had no effect on the wave velocity,but the wave velocity generally increased with increasing diameter.Finally,the feasibility of the simulation method used for investigating the stress-wave propagation pattems in standing trees was verified.Conclusion] The numerical simulation method is practicable for the study of the propagation patterns of stress waves in standing trees and the effects of the diameter and propagation distance on the wave velocity.The diameter as well as the propagation distance could influence the propagation patterns of stress waves in standing trees,but their effects on stress-wave velocity were different.