Open-source Höhenwindkraftwerk (Drachen) in Freecad - FreeCAD Forum (open-source airborne wind energy project in freecad)

[Windy_Skies]

@thomas_neemann

my observations in nature are the treetops that swing back and forth in the wind.

That doesn’t need to be because of wind gusts. Apparently trees are like springs or cantilevered beams or pendulums.

Questions I would have are: what natural frequency does my system have, and how much damping (energy extraction) can I do?

Here are some results I get from searching for “trees swaying in the wind”:

The Secret Messages of Swaying Trees - WSJ.

An architectural understanding of natural sway frequencies in trees.pdf (970.4 KB)

The relationship between form and function in trees is the subject of a longstanding debate in forest ecology and provides the basis for theories concerning forest ecosystem structure and metabolism. Trees interact with the wind in a dynamic manner and exhibit natural sway frequencies and damping processes that are important in understanding wind damage. Treewind dynamics are related to tree architecture, but this relationship is not well understood. We present a comprehensive view of natural sway frequencies in trees by compiling a dataset of field measurement spanning conifers and broadleaves, tropical and temperate forests. The field data show that a cantilever beam approximation adequately predicts the fundamental frequency of conifers, but not that of broadleaf trees. We also use structurally detailed tree dynamics simulations to test fundamental assumptions underpinning models of natural frequencies in trees. We model the dynamic properties of greater than 1000 trees using a finite-element approach based on accurate threedimensional model trees derived from terrestrial laser scanning data. We show that (1) residual variation, the variation not explained by the cantilever beam approximation, in fundamental frequencies of broadleaf trees is driven by their architecture; (2) slender trees behave like a simple pendulum, with a single natural frequency dominating their motion, which makes them vulnerable to wind damage and (3) the presence of leaves decreases both the fundamental frequency and the damping ratio. These findings demonstrate the value of new three-dimensional measurements for understanding wind impacts on trees and suggest new directions for improving our understanding of tree dynamics from conifer plantations to natural forests.

https://www.frontiersin.org/articles/10.3389/ffgc.2020.00089/full

Age Dynamics of Wind Risk and Tree Sway Characteristics in a Softwood Plantation

Damien Sellier1* and Satoru Suzuki2

• 1Forest Systems, New Zealand Forest Research Institute (Scion), Rotorua, New Zealand
• 2Center for Forest Damage and Risk Management, Forestry and Forest Products Research Institute, Tsukuba, Japan

Quantifying wind risk in planted forests is critical to ensure the provision of wood-based biomaterials and forest ecosystem services in the future. Tree sway dynamics play a major role in determining their vulnerability to wind storms. While structural engineering theory can greatly assist in predicting tree and branch motion accurately, the effects of forest aging and silvicultural treatments on motion and the likelihood of mechanical failure are still poorly understood. In this study, we simulate the growth of an individual model tree and its architecture for a managed, even-aged pure Cryptomeria japonica D. Don. stand. The dynamic behavior of the tree is predicted for a rotation period at a 5-year interval using finite element analysis. Results show that tree natural sway frequency is subject to a 5-fold decrease over the tree’s lifetime. The tree is thus more susceptible to absorb turbulent kinetic energy from the wind as it grows older. The damping ratio, which measures how rapidly the tree can return to its rest position after being deflected, is predicted to increase by a factor of four. By simulating the mechanical response to a wind gust, the model predicts a quick transition from a low risk of failure in the juvenile phase to a high-risk situation in the mature phase. The transition occurs between ages 15 and 30 when canopy closure takes place, when juvenile wood formation stops in the lower stem region and when the first thinning is carried out. Wind risk plateaus after the transition period. The age-risk relationship shown by the model is consistent with post-typhoon damage patterns documented by inventories in Japanese planted forests, albeit with a sharper transition.