Inquiry on TLCD Liquid Displacement Output ($w$) in OpenFAST v5.0

[ShunxinWeng]

Description:
In previous discussions (e.g., Issue #2187), it was noted that specific outputs for Tuned Liquid Column Dampers (TLCDs), such as the internal liquid displacement $w$, were missing from the source code. Since my research focuses on distributed TLCD control for floating wind turbines, tracking this internal state is critical for validation.I have reviewed the OutListParameters.xlsx for v5.0 and found generic structural control (StC) output channels. I would like to clarify if these channels now correctly capture the TLCD liquid motion.
Questions:
Is the TLCD liquid displacement w now available as a standard output in v5.0?

If yes, which specific parameters should be used in the OutList?

Based on the Excel documentation, are SStC#_ZQ (for platform-based TLCDs) or TStC#_ZQ (for tower-based) the intended channels for liquid displacement?

Does the "Z" direction in these outputs consistently map to the internal U-tube coordinate w, regardless of the physical orientation of the TLCD on the platform?
Environment:OpenFAST Version: v5.0.0Module: ServoDyn / StC (Structural Control)

[jjonkman]

Dear @ShunxinWeng,

I presume you meant to link to the following OpenFAST issue outlining limitations / propose enhancements to the TLCD model available in the Structural Control (StC) submodel of ServoDyn: #2896. Unfortunately, this issue has not been fixed in the recent OpenFAST v5.0 release. I'm going to close this issue, as it appears to be duplication of #2896. Please follow up on that issue if you have further comments to add.

Best regards,

[ShunxinWeng]

Dear Jonkman,
Thank you for the clarification regarding the current status of TLCD output enhancements in v5.0.Following up on that, I noticed that even when the structural control type is set to TLCD, the parameter SStC1_XQ (displacement relative to rest position in StC reference frame) still provides non-zero output during the simulation.Could you please clarify the physical interpretation of SStC1_XQ in the specific context of a TLCD? Since a TLCD doesn't have a solid moving mass like a TMD, can this output be interpreted as the internal liquid displacement (w) along the U-tube, or does it represent something else ?
Understanding what this existing channel currently tracks would be very helpful for my research validation while waiting for the dedicated TLCD outputs. And I see an articel "Vibration mitigation of floating offshore wind turbine using tuned liquid
column damper under typical limit states", in Figure 6 (c), it has a outcome of TLCD w in openfast model as shown below.

https://www.sciencedirect.com/science/article/pii/S0960148125005063?via%3Dihub

Best regards,

[jjonkman]

Dear @ShunxinWeng,

Good point. Looking at the source code, I do see that the liquid displacement in the TLCD model is represented using the same internal states (XQ, etc.) as the TMD displacement, so, the same displacement outputs apply to both TMDs and TLCDs.

Best regards,