Filtering in WE_Mode=0 in ROSCO 2.10

[ghuwart]

Hi all,

I noticed changes between ROSCO 2.9.7 and ROSCO 2.10.0 for the wind speed estimation in mode 0, i.e., filtering of hub height wind speed.

Here is the line in question:

ROSCO/rosco/controller/src/ControllerBlocks.f90

Line 377 in 974290e

LocalVar%HorWindV_F = cos(LocalVar%NacVaneF*D2R) * LPFilter(LocalVar%HorWindV, LocalVar%DT, CntrPar%F_WECornerFreq/10, LocalVar%FP, LocalVar%RestartWSE, LocalVar%restart, objInst%instLPF, LocalVar%WE_Vw)

There are two changes, one is related to the projection with the vane orientation (the cos part) and the other is the frequency for the filtering of the signal (the F_WECornerFreq part). I reproduced the 2.9.7 results by reverting this line back.

Regarding the change on the filtering frequency, there is now a division by 10 to the frequency. The values in the corresponding DISCON.IN files did not change so it really alters the filtering. The wind speed estimation signal is very flattened due to this excessive filtering.

Is there a particular reason for this change from CntrPar%F_WECornerFreq to CntrPar%F_WECornerFreq/10?

Thank you.

[dzalkind]

In v2.10, we are using HorWindV_F to substitute for the wind speed estimate (WSE) when the inputs to the WSE leave the bounds of normal operation and WE_Mode = 2. The division by 10 is to ensure a smooth transition. I'll admit that it's a bit of an arbitrary choice and if both signals (the WSE and point measurement of the wind) have the same filter, they should (in theory) have the same frequency content.

You raise an interesting point, but I consider using WE_Mode of 0 primarily for debugging or backup, so I'm not sure how we should address this. It seems like you understand the filtering well enough to work around it.

[ghuwart]

Thank you for the quick reply.

I understand your points especially if WE_Mode = 0 should only be seen as fallback.

This F_WECornerFreq is used only for the wind speed estimator in mode 0. The default value is 0.209440 rad/s and can be found here:

ROSCO/rosco/toolbox/inputs/toolbox_schema.yaml

Lines 493 to 498 in 974290e

	f_we_cornerfreq:
	type: number
	description: Corner frequency (-3dB point) in the first order low pass filter for the wind speed estimate [rad/s]
	minimum: 0
	unit: rad/s
	default: 0.209440

A workaround for me if I want to keep the original ROSCO code is to define a bigger value for f_we_cornerfreq in the ROSCO Toolbox yaml input or to change the F_WECornerFreq in the .IN file directly. What I find peculiar in that case is that the filter is actually not filtering at the F_WECornerFreq.

Maybe a nicer fix would be to change the default value in the toolbox_schema.yaml file and remove the /10 in the ROSCO code?

I understand this is very niche and maybe not worth the trouble.

[dzalkind]

It's worth another look, or at least clearer input definitions, at some point. Thanks for bringing it up. I'll transfer this to an issue and re-visit it when preparing the next release.

[ghuwart]

Thank you.