AAIR Project: Sub Task 4.1 Wind loading on trees depending on stand position
Participant : The Forestry Authority,
Northern Research Station,
Roslin, Midlothian,
Scotland, EH25 9SY
Contact: C P Quine, B A Gardiner, P D Bell.
Description:
To obtain relationships for how wind-loading depends upon position within the stand. These mathematical relationships to represent distance from stand edge, width of upwind gaps, tree spacing and tree height.
Inputs:
Distance from edge, upwind gap width, tree height, tree spacing.
Outputs:
Multipliers to adjust standard gust factor used in Task 3.1 by Forestry Authority for position in stand.
Method:
A number of 2-D airflow models will be used - including Li et al (1990), S Green (1990) and M Baker (unpublished). Results of a number of simulations (using different canopy densities and heights, and different openings in the canopy) will be compared with wind tunnel and field results and the generalised relationships developed.
Uses:
To modify relationships developed in sub tasks 3.1 by Forestry Authority, 3.2 by Umea, and 3.3 by Joensuu, for position in stand.
References:
Gardiner, B.A., Stacey, G. R., Belcher, R. E. and Wood C. J. 1995. Field and wind tunnel assessment of the implications of respacing and thinning on tree stability. In preparation.
Green, S. J. 1990. Airflow through and above a forest of widely spaced trees. PhD thesis, University of Edinburgh
Irvine, M. R. 1994. Turbulence and turbulent transport above and within coniferous forests. PhD thesis, University of Liverpool.
Li, Z. J., Lin, J. D. and Miller, D. R. 1990. Airflow over and through a forest edge: A steady state numerical simulation. Boundary Layer Meterorology, 51, 179-197.
Peltola, H. 1995. Studies on the mechanism of wind-induced damage of Scots pine. PhD, Faculty of Forestry, University Of Joensuu, Finland.
Sub Task: 4.1
Participant: The Forestry Authority
MODELS USED FOR DATA ANALYSIS
I. Model Name: UCFWF.FOR
II. Source of Model: D.Miller, University of Connecticut; S. Green, DSIR, New Zealand; M. Baker, Forestry Authority (in development)
III. Computer language: Microsoft Fortran, PHOENIX CFD Package.
IV. Hardware needed: 386/486/586 PC
V. Data Inputs needed: Tree height, profile of canopy leaf area and drag coefficient.
VI. Model Outputs
VII. Accuracy/Sources of Uncertainty/Method of Handling:
There are still theoretical problems in developing models which accurately predict airflow across forest edges. These are mainly related to the development of the correct turbulence closure schemes and correct parameterisation of the canopy aerodynamic drag. A new turbulence closure scheme is currently being developed at the Forestry Authority by Martin Baker. The drag coefficient parameterisation will have to rely on tests of the model against Forestry Authority data of flow across a forest edge in the field (Irvine, 1994) and in the wind tunnel (Stacey et al., 1994). The wind tunnel experiments represent an excellent data source for testing not only the flow predictions of the model but the variation of applied bending moment with distance from the forest edge or size of gap in the forest.
VIII. Existing linkages between data and software:
Data exist from field experiments at Harwood Forest, Northumberland of the change in turbulent characteristics across the transition from open moorland to 7 metre tall Sitka spruce forest. Data also exist from experiments carried out at the edge of a Scots pine forest by Peltola (1995) at Joensuu. Wind tunnel data exist of the turbulent development across a model forest edge and across different size clearings. There is also wind tunnel data of the change in bending moment back from the edge of forests of different spacings (Gardiner et al., 1995) and at the downwind edge of different sized gaps in the forest. Such data is central to the testing of the airflow models and the subsequent development of multipliers.
IX. GIS Software used:
X. Modelling Software used:
XI. Database Software used:
XII. Any other comments:
Prepared by C P Quine/B A Gardiner/ P D Bell
May 1995