default wind speed modifiers

[Mathadon]

@kldjonge I just dug into some results where the wind pressure had much less effect than expected. E.g. 3m/s of wind really did not affects the zone tire flow that much. It turns out that these equations:

  pWin = Cs*0.5*CpAct*rho*vWin*vWin;
  Cs = (A0*A0)*((Habs/sim.Hwind)^(2*a))

  parameter Real A0=0.6 "Local terrain constant. 0.6 for Suburban,0.35 for Urban and 1 for Unshielded (Ashrae 1993) "
    annotation(Dialog(group="Wind"));
  parameter Real a=0.28 "Velocity profile exponent. 0.28 for Suburban, 0.4 for Urban and 0.15 for Unshielded (Ashrae 1993) "
    annotation(Dialog(group="Wind"));

are to blame. Cs has a value of 0.11, which seems really low. Furthermore, I'm wondering why we do not have Cs=1 for Habs=sim.Hwind. Wouldn't that be logical.

I propose to revise this implementation or default parameters such that the defaults are more logical for the average user. Perhaps we should create an enumaration where the type of terrain can be selected. We could then use Unshielded as default.

[kldjonge]

Agree!

Unshielded as default is fine for me. I think we decided on this because it was the 'middle' value for A0. No further reason I believe.

[Mathadon]

Okay, let's handle the open issues first before proceeding with this.

[jelgerjansen]

@kldjonge @Mathadon I was looking into this, and noticed that this implementation uses data from the ASHRAE fundamentals book from 1993. Since 2005, ASHRAE reports slightly different values for parameter a and a layer thickness δ instead of local terrain constant A₀

The CONTAM user guide indicates that the local terrain constant can be calculated using the layer thickness δ:
A₀=(δ_met/H_met)^a_met · (H_met/δ)^a
where the subscript met refers to the values for the meteorological station.

Do we implement the latest data from ASHRAE, or do we stick with the older data. If we change, we might also consider changing the default wind measurement height (1 meter seems quite low).

[kldjonge]

@jelgerjansen, fine with an update! I just followed the CONTAM input as that was the reference at that point (assuming, as in CONTAM, that for the 2005 input the equation you metion could be pre-calculated outside of the model.

We allready distinguish between the reference height for the windspeed meassurements (default at 10m) and pressure (default at 1m).

  parameter Modelica.Units.SI.Length Hwind=10 "Height above ground of meteorological wind speed measurement" annotation (Dialog(group="Wind"));
  parameter Modelica.Units.SI.Length  HPres=1 "Height above ground of meteorological atmospheric pressure measurement" annotation (Dialog(group="Wind"));
  parameter Real Cs_coeff = (A0*A0)*((1/Hwind)^(2*a)) "Multiplication factor for Habs" annotation(Dialog(group="Wind"));
  parameter Real Cs= Cs_coeff*(H^(2*a)) "Wind speed modifier"              annotation(Dialog(group="Wind"));

[Mathadon]

Okay for an update :)

[jelgerjansen]

@kldjonge @Mathadon I just pushed (#1448) an updated implementation and added some documentation in the SimInfoManager model to explain the equations and assumptions. Please let me know if you have any remarks.

[kldjonge]

I checked it out, no remarks. It looks good.

[Mathadon]

Looks like a clean implementation and documentation, thanks!