|
user_name: |
Heli Peltola |
| user_organisation: |
University of Joensuu
Faculty of Forestry
Joensuu
Finland |
| date: |
1October 1997 |
| model_name: |
HWIND |
| description: |
The mechanistic model for wind and snow damage of single trees attempts to fully describe the mechanistic behaviour of trees under wind and snow loading. The model takes site and stand information and predicts the canopy top mean windspeeds at which the trees will uproot and break due to wind and/or snow loading both at the stand edge and for various distances from the stand edge (also for various gap sizes). To provide a measure of total turning moment on tree, model calculates first the mean wind loading and gravity based force (caused by stem, crown and snow weight) at each height in the canopy using a predicted wind profile at the stand edge and the vertical distribution of stem, crown and snow weights. HWIND calculates then gust factor, which relates then mean wind loading of one hour and extreme wind loading of 3 second gusts, to distance from stand edge, stand density and tree height based on wind tunnel studies (Gardiner and Stacey 1996, see Gardiner and Peltola 1997, Peltola et al. 1997). Furthermore, the effect of gap size on wind loading at the margins of stand edges can also be taken into account based on wind tunnel studies by Gardiner and Stacey (1996) (see also Gardiner and Peltola 1997, Peltola et al. 1997).
To calculate the resistance to uprooting model uses a prediction of root-soil plate mass to derive a resistive moment. The prediction of stem breakage relies on values of Modulus of Rupture determined for different timbers. To date the model covers especially Scots pine, Norway spruce and Birch sp growing on podzolic soils in Finnish conditions. However, also other tree species and soil types for various geographical locations can be used by changing the controlling parameters (and equations if needed) to cover new species and soils. |
| software: |
C++ (and visual basic for graphics in Windows) |
| operating_system: |
PC in DOS and Windows, also UNIX |
| isumm: |
Tree species and soil type
a. Tree species
b. Soil type
Tree and stand characteristics
a. One tree simulation
- Tree height
- Tree diameter at 1.3m above base (dbh)
- Stand density
b. Rotation simulation
- If many years are simulated simultaneously, tree characteristics should be available in existing file named *.inp (including age, height, dbh, stand density) or the new file should be created.
Wind
a. Simulation windspeed (mean)
b. Gust factor
Snow load
a. Snow load kg/tree
b. Snow load kg/m2 of crown area
Simulation conditions (stand edge/within the stand with gap size)
a. Distance from stand edge in tree heights
b. Gap size in meters
Other inputs
a. Crown streamlining
b. Simulation without leaves
|
| ispecfile |
Tree species and soil selected from menus.
Tree height, diameter, stand density and other possible inputs from keyboard (to the input window).
See below:
Select Tree species
Scots pine (Spine1.par)
Norway spruce (Nspruce1.par)
Birch sp (pbirch1.par)
Select Soil type
Podzol (podzol.spr)
Tree and stand characteristics
One year simulation
- Set Tree height to <20> metres
- Set Tree diameter at 1.3m above base to <20> cm
- Set Stand density to <690> trees/ha
Rotation simulation
- Same tree characteristics as for one year simulation should be available in existing file named *.inp (simulation year, height, dbh, stand density) or the new file should be created.
Wind
Set simulation windspeed (default is that the program seeks damaging windspeed)
Set gust factor (default is to let the program calculate i
Snow load (default is no snow load)
Set Snow load kg/tree
Set snow load kg/m2 of crown area
Simulation conditions (stand edge/within the stand)
Set Distance from stand edge in tree heights (default: stand edge)
Set Gap size in meters (default: if not given then gap size is 10 tree heights)
Other inputs
Set Crown streamlining (default: model calculates it as a function of windspeed)
Set simulation without leaves (default is with leaves)
|
| iexpspecfile |
This model is an interactive version of a model designed to read input files and output critical windspeeds (mean of one hour) and mean turning moments to cause uprooting and stem breakage of single trees. |
| ivar1 |
Tree species |
| idescr1 |
Descriptor selected from menu
Select Tree species
Scots pine
Norway spruce
Birch sp |
| isensitiv1 |
Sensitive |
| isensdescr1 |
Comparisons are available for Scots pine, Norway spruce and Birch sp for a variety of tree heights and stem diameters on podzolic soil (see Peltola et al. 1997). Especially Birch sp without leaves differs a lot from Scots pine and Norway spruce. |
|
ivar2 |
Soil type |
|
idescr2 |
Descriptor selected from menu |
|
isensitiv2 |
|
isensdescr2 |
None available at the moment. |
|
ivar3 |
Tree height |
|
idescr3 |
metres |
|
isensitiv3 |
Not very sensitive |
|
isensdescr3 |
Comparisons are available for Scots pine, Norway spruce and birch sp. for a variety of tree heights on podzolic soil (see Peltola et al. 1997). Comparisons cover critical windspeeds. |
|
ivar4 |
Tree diameter |
|
idescr4 |
centimetres |
|
isensitiv4 |
Sensitive |
|
isensdescr4 |
Comparisons are available for Scots pine, Norway spruce and birch sp. for a variety of stem diameters on podzolic soil (see Peltola et al. 1997). |
|
ivar5 |
Stand density |
|
idescr5 |
trees/ha |
|
isensitiv5 |
Not as sensitive at stand edge as within the stand. |
|
isensdescr5 |
Comparisons are available for Scots pine, Norway spruce and birch sp. for a variety of tree heights and stem diameters for various distances from stand edge on podzolic soil (see Peltola et al. 1997). |
|
ivar6 |
Distance from stand edge |
|
idescr6 |
tree heights |
|
isensitiv6 |
Very sensitive |
|
isensdescr6 |
Comparisons are available for Scots pine, Norway spruce and birch sp. for a variety of tree heights and stem diameters for various distances from stand edge on podzolic soil (see Peltola et al. 1997). |
|
ivar7 |
Crown streamlining |
|
idescr7 |
The crown area is assumed to streamline as a function of windspeed, i.e. the reduction of crown area being 20% for windspeeds of less than 10 m/s and 60% for windspeeds of more than 20 m/s, the value of streamline between these two points being interpolated (Raymer 1962, Walshe and Fraser 1963, see Peltola and Kellom„ki 1993). However, if snow loading exists the streamlining should not be used. |
|
isensitiv7 |
Very sensitive |
|
isensdescr7 |
Computations available at the moment for Scots pine (see Gardiner and Peltola 1997, Peltola et al. 1997). |
|
ivar8 |
Snow load |
|
idescr8 |
The snowload (kg/m2) is assumed to correspond to snowfall (mm) accumulated in the crown based on the projected crown area against ground surface (e.g. Petty and Worrel 1981). |
|
isensitiv8 |
Not very sensitive |
|
isensdescr8 |
Comparisons are available for Scots pine, Norway spruce and birch sp. for a variety of tree heights and stem diameters on podzolic soil (see Peltola et al. 1997). However, because no streamlining of crown should be expected due to snow loading, the overall effect of snow loading on critical windspeeds is much greater than that only due to change in snow loading. |
|
ivar9 |
Simulation without leaves |
|
idescr9 |
If the tree is simulated without leaves, the projected crown area is expected to be only 20% of that with leaves (adapted from Halldin's (1985) work in regard to crown area distribution of Scots pine without needles). Respectively the leafless crown mass ratio is assumed to equal 68% of that with leaves based on M„lkonen (1977). This alternative will be valid especially for Birch sp. (from late autumn up to early spring). |
|
isensitiv9 |
Sensitive |
|
isensdescr9 |
Some comparisons are available for birch sp. |
|
Ivar10 |
Effect of Gap size |
|
idescr10 |
given in meters (see Gardiner and Stacey 1996, Gardiner and Peltola 1997, Peltola et al. 1997) |
|
isensitiv10 |
Very sensitive |
|
csumm |
Various constants are used to calculate mean and extreme wind loading and another loading due to gravity (crown, stem and snow mass), resistance to uprooting and stem breakage. These constants are currently fixed but will be improved if more proper information will be available (see references for constants/parameters presented below in details from Peltola and Kellom„ki (1993), Peltola (1995), Peltola et al. (1997), and Gardiner and Peltola (1997). |
| Constants |
Overall Aerodynamic constants (see Peltola et al. 1997) |
| p (air density) | 1.2226 |
| k (von Karman's constant) | 0.41 |
| d/h (zero plane displacement) | 0.0 |
| Zo/h (roughness lenght parameter) | 0.06 |
| Tree species dependent constants (see Peltola et al. 1997) |
| Cd (drag coefficient) |
| Scots pine | 0.29 |
| Norway spruce | 0.35 |
| Birch sp. | 0.29 (assumed to be S.pine) |
| green density of stem |
| Birch sp. | 900 |
| green density of roots |
| All species | 1000 |
| basic density of roots |
| Scots pine | 473 |
| Norway spruce | 452 |
| Birch sp. | 445 |
| conversion of dbh to stump diameter |
| All species | 1.33 |
| crown ratio |
Scots pine | 0.42 |
Norway spruce | 0.76 |
Birch sp. | 0.50 |
| crown stem mass ratio |
Scots pine | 0.30 |
Norway spruce | 0.50 |
Birch sp. | 0.30 |
| crown center point |
Scots pine | 0.50 |
Norway spruce | 0.70 |
Birch sp. | 0.50 |
| leafless crown area ratio |
Birch sp. | 0.20 |
| leafless crown mass ratio |
Birch sp. | 0.68 |
| Soil type depending constants (see Peltola et al. 1997) |
| Soil density (fresh) |
| Podzol | 1500 |
| Uprooting resistance constants (see Peltola et al. 1997) |
| RSmean |
| All species | 0.21 |
| Arsw |
| Scots pine | 0.30 |
| Norway spruce | 0.20 |
| Birch sp. | 0.30 (uses value for S. pine) |
| Tree Breakage constants (see Peltola et al. 1997) |
| MOR (Modulus of rupture) |
| Scots pine | 39.1 |
| Norway spruce | 30.6 |
| Birch sp. | 53.6 |
| E (Modulus of elasticity) |
| Scots pine | 7000 |
| Norway spruce | 6300 |
| Birch sp. | 9900 |
| cexpspecfile |
Press here for example of input files for Scots pine, Norway spruce and birch sp on podzolic soil
(*1.par includes specific parameters for individual species and *2.par parameters for tree characteristic relationships, respectively *.spr includes soil parameters). |
| Osumm |
Model outputs mean critical windspeed at canopy top and mean turning moment at the stem base for uprooting and stem breakage of tree caused by the wind and/or critical snow loading (see 6.dat). It outputs also mean wind profile at stand edge and turning moment distribution, and contributions of wind and snow load, stem and crown mass for total turning moment of trees for various heights above ground (i.e. it outputs 7 tables and various figures). |
|
ospecfile |
Produces six output files. Click here for example files for one tree simulation |
| Scope and limitations of model |
Empirical relations
Tree stem weight calculation is based on empirical relationships presented by Laasasenaho (1982) as a function of tree species and tree height and breast height diameter, and on green density of stem wood (e.g. Tamminen 1962). The canopy width, which is needed for calculation of the crown projected area against wind as well as snow load accumulation on the crown is also based on empirical relationship calculated by Hakkila (1971) between the longest branch in the crown and breast height diameter of the tree. Root-soil plate depth is obtained as a function of stump diameter (and respectively dbh) based on empirical relationship presented by Hakkila (1972). However, for Norway spruce, the equation for depth of the root-soil plate has been modified using Finnish tree pulling data; and thus having 1.30 as a multiplyer for Hakkila's (1972) relationship, which does not take into account roots having diameter less than 5 cm (this is a problem especially for Norway spruce). Respectively, based on Finnish tree pullings, Hakkila's (1972) equation for Scots pine's rooting depth is used also for Birch sp. (see in details Peltola et al. 1997, Gardiner and Peltola 1997). Root-soil plate width is expexted to be equal with crown width (see Peltola et al. 1997).
HWIND uses also existing empirical relationships derived by Gardiner and Stacey (1996) from wind tunnel studies to calculate the gust factor and gap size factor, which relates mean and extreme wind loading to distance from stand edge, stand density and tree height and gap size as well (see in details Peltola et al. 1997, Gardiner and Peltola 1997).
Mechanistic relations
There are mechanistic relationships used to calculate the mean wind loading and gravity based loading on the tree based on tree height, dbh, stand density, canopy depth and width. This involves calculating the mean wind loading on the tree (e.g. Oliver and Mayhead 1974) and the force due to gravity (caused by stem, crown and snow weight) at each height in the canopy (e.g. Grace 1977, Jones 1983) using a predicted wind profile at stand edge and the vertical distribution of stem, crown and snow weights (Peltola and Kellom„ki 1993, see Peltola et al. 1997, Gardiner and Peltola 1997).
The crown area is also assumed to streamline as a function of windspeed, i.e. the reduction of crown area being 20% for windspeeds of less than 10 m/s and 60% for windspeeds of more than 20 m/s, the value of streamline between these two points being interpolated (Raymer 1962, Walshe and Fraser 1963, see Peltola and Kellom„ki 1993).
To calculate the resistance to uprooting model uses a prediction of root-soil plate mass to derive a resistive moment (Coutts 1986, see Peltola and Kellom„ki 1993).
The prediction of stem breakage is based on engineering principles and relies on values of Modulus of Rupture determined for different timbers (see Lavers 1969, Peltola and Kellom„ki 1993, Peltola et al. 1997).
|
Scope, Assumptions and Limitations of model and parameters |
The empirical relationships used for various tree characteristics are based currently on data of Scots pine, Norway spruce and Birch sp growing on podzolic soil in Finland (especially moraine formation). Trees growing in other countries may have different relationships for various tree characteristics (e.g. due to different weather and soil conditions) and also different relationships between resistance to uprooting (e.g. different rooting characteristics even in same soil type) and different MOR values (depending e.g. on wood density). To date, the sensitivity tests have been conducted for HWIND-model to determine critical parameters involved and the reliability that can be placed on the critical windspeed predictions (see Peltola et al. 1997, Gardiner and Peltola 1997). More information will be added in the future, i.e. another tree species and soil types.
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Copyright information |
None.
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|
Contact person |
Heli Peltola
This model is based on the preliminary mechanistic wind damage model already developed for Scots pines along the stand edge by Peltola and Kellom„ki (1993).
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Other information which is important to the full understanding of the model |
Gardiner, B. A. and Peltola, H. 1997. The development and testing of models for predicting the critical windspeed to damage trees. To be submitted.
Peltola, H. and Kellom„ki, S. 1993. A mechanistic model for calculating windthrow and stem breakage of Scots pines at stand edge. Silva Fennica 27(2):99-111.
Peltola, H., Kellom„ki, S., V„is„nen, H. and Ikonen, V-P. 1997. HWIND: A mechanistic model for wind and snow damage of Scots pine, Norway spruce and birch sp. Manuscript to be submitted.
Peltola, H. Kellom„ki, S. Hassinen, A., and Granander, M. 1997. Mechanical stability of Scots pine, Norway spruce and birch sp: analysis of tree pulling experiments in Finland. To be submitted.
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