Parameter : Sub-sectors in roughness map analysis

[YOCUI]

Hi wasp experts ,

would you help to explain what is the wasp parameter "Sub-sectors in roughness map analysis" mean ?

how will it effect the roughness rose ?

[Ole Rathmann]

In the WAsP IBZ-flow-model (up to WAsP10 the ONLY flow model) hte surface roughness distribution as seen from a certain point (e.g. a met-mast or a turbine) is represented by a roughness rose with typically 12 or 16 sectors (as selected by the user). For each sector the roughness rose contains the effective rougness value for the consequtive distance-ranges from the point and outwards (e.g. 0-500m, 500-2300m, 2300-7000m). When evaluating these ranges and the corresponding effective roughnesses each sector is divided in subsectors (default 9) and the roughness variations in each sub-sector outwards are then aggregated (averaged) into sequence of ranges in the sector.
If you lower the number of subsectors (to increase calculational speed) the roughness rose evaluation will loose details and thus get more uncertain.

[YOCUI]

Hi rathmann,

thanks for your reply .

as my understand the distance ranges you mentioned (e.g. 0-500m, 500-2300m, 2300-7000m ) should be the roughness length change line right ?

and there is another parameter called : "Max. number of roughness changes/sector"
the default value is 10 , and i think this parameter defines the same rule as you explaination for"Sub-sectors in roughness map analysis" ,then i am confused what is the difference between the two parameters here ?

thank you.

[Duncan]

Hi Youci,

These are different. The rose is formed from directional sectors and sub-sectors. So the sector could be 30 degrees for a 12 sector rose. Then there are sub-sectors within these for higher-resolution analysis.

Within each sector, there are roughness areas separated by changes. That's the number of changes per sector. The maximum is 10, so no matter how many actual roughness change lines intersect with the sector, the roughness view along that sectors direction will only contain 10 'zones'.

To see all this, look in the reference site window, where we let you calculate and display the roughness rose.

HTH, Duncan.

[Guilherme]

Hello,

I was looking for information related to the limitation of roughness changes and found this topic. If it is not suitable, please advise me if I should open a new one, ok?

I was wondering how WASP manages a "high resolution" roughness map with several roughness changes (more than 10 changes in a short distance).

Does WASP do some rounding, resampling or down sampling in order to establish a maximum of 10 changes inside length/area of coverage it needs to consider for its calculation? Or it simply stops to consider the roughness when it "counts" the 10th change?

Or, it does exactly what Rathmann was explaining above: it calculates "effective roughness values" which will be representative of some ranges in terms of distance. Then we would have maximum of 10 ranges (and 10 effective roughness values)?

Thank you in advance,

Guilherme.