Dynamics of swaying of Picea sitchensis.
Dynamics of swaying of Picea sitchensis.
复制标题
DOI：
10.1093/treephys/9.3.383
复制
发表时间：
1991-10
期刊：
影响因子：
4
通讯作者：
R. Milne
中科院分区：
文献类型：
--
作者：
R. Milne
苏格兰种植园中生长的六棵 26 年树龄的西加云杉 (Picea satchensis (Bong.) Carr.) 树被手动摇晃，以确定它们的机械动力学。完整树木（1.3 m 处平均高度 14.2 m，平均茎直径 14.5 cm）的自然摇摆频率平均为 0.35 Hz。人们发现工程力学理论可以很好地描述该频率随树木大小的变化。特别是，可以为完整的和无枝的树木定义形状参数，连同茎的大小、密度和弹性，可以使用简单的公式预测自然摇摆频率。研究发现，摇摆阻尼由三个部分组成：(1) 树枝与相邻树枝的干扰，(2) 叶子上的空气动力阻力，(3) 茎中的阻尼。对于跨越实验地点直径范围的六棵树样本，对于中等大小的树来说，这三个分量对整体阻尼的重要性为 5/4/1。邻居之间的干扰取决于与邻居的距离，以及所选树及其邻居的大小。对于较大的树木，空气动力阻尼较大，并且该力损失的能量与使用已发表的风洞和其他研究的阻力系数计算出的能量损失的大小相似。阀杆的阻尼量与阀杆直径线性相关。
Six 26-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) trees growing in a Scottish plantation were swayed manually to determine their mechanical dynamics. The natural frequency of sway of the intact trees (mean height 14.2 m and mean stem diameter 14.5 cm at 1.3 m) was on average 0.35 Hz. The variation of this frequency with tree size was found to be well described by engineering mechanics theory. In particular, shape parameters could be defined for both intact and branchless trees, which, along with stem size, density and elasticity, could predict the natural sway frequency using a simple formula. The damping of sway was found to consist of three components, (1) interference of branches with those of neighbors, (2) aerodynamic drag on foliage, and (3) damping in the stem. For the sample of six trees, which spanned the diameter range at the experimental site, the importance of these three components to overall damping was in the ratio 5/4/1 for the median sized tree. Interference between neighbors depended on the distance to neighbors, as well as on the sizes of the chosen tree and its neighbors. Aerodynamic damping was larger for larger trees and the energy lost to this force was similar in magnitude to that calculated to be lost using drag coefficients from published wind tunnel and other studies. The amount of damping from the stem was linearly related to stem diameter.