Sir,

how can i extract the local span blade loads and moments from fast v7 ? Is this the case that I can get blade local loads for just blade 1? I wish to examine blade loads on the all the 3 blades of the 5mw turbine.

I read that bldgagnd is the specified location of the nodes that I can access. But how can I access the time series at each node? Do the blade nodes get placed at equally spaced distances as per “BldNodes” ?

Thanks

Subham

Dear @Kashyap.Subham,

In FAST v7, the structural blade analysis nodes are aligned with the aerodynamic blade analysis nodes, as defined within the AeroDyn input file. `BldGagNd`

is a list of up to `NBlGages`

nodes (limit 9) that you can select for output. The specific outputs whose time series will be generated are listed in the `OutList`

, e.g., output `Spn2MLxb3`

is the local edgewise bending moment at the 2nd node in the `BldGagNd`

list for blade 3.

Best regards,

Sir,

Do I use Spn2FLxb3 (Is this a valid output in FAST v7?) for the local span edgewise force? Also, how can I estimate the angle of attack at the analysis node?

Thanks

Subham

Dear @Kashyap.Subham,

Yes, the local sectional reaction forces, such as `Spn2FLxb3`

, are available outputs from FAST v7.

The angle of attack at each aerodynamic analysis node can be output from FAST v7 by setting `PrnElm`

= PRINT at the corresponding node in AeroDyn.

Best regards,

Dear Sir,

Thank You for attending to my queries. How do I know the exact location of the strain gages on the blade? Suppose I want to know the distance of gage #12 from the tip of the blade or the root of the blade. Does it correspond to RNode in the aerodyn.ipt file?

Thanks

Subham

Dear @Kashyap.Subham,

In FAST v7, the number of blade gages for output is limited to 9 (12 is too high). Regardless, I agree that AeroDyn input `RNodes`

defines the location of the aerodynamic and structural analysis nodes in FAST v7. So, e.g., if the 5th `BldGagNd`

entry is 17, then the 5th gage is located in the 17th row of the `RNodes`

table.

Best regards,

Dear Sir,

Will, there be a difference if I measure the tower acceleration at a local node (in the tower base coordinate system) and tower top acceleration (in the tower top coordinate system)? The confusion is related the coordinate system. I wish to measure both in the same coordinate system.

Thanks

Subham

Dear @Kashyap.Subham,

I’m not sure I understand your question. The tower accelerations output from FAST v7 are all absolute, but expressed in different coordinate systems, depending on which output is selected.

Best regards,

YawBrTAxp (TowerTop reference coordinate system) TwHt1ALxt (Tower Base coordinate system).

How do I compare them in an absolute reference frame or the same reference frame?

Thanks

Subham

Dear @Kashyap.Subham,

I’m still not sure what you want to do. Presumably you’ve placed tower gage node 1 near the tower-top. If so, I would expect the vector magnitude of `YawBrTAxp`

to be very similar to that of `TwHt1ALxt`

because they are both absolute accelerations. But these outputs are expressed in different coordinate systems, so, the values will not be exactly the same.

Best regards,

Dear Sir,

I wish to compare the tower top acceleration and the platform base acceleration values. I want to check for any phase/time lag between the acceleration time series. I am using FAST v7 Seismic module. Hence, I have the confusion of how to measure the acceleration at tower top and platform base (or tower base) in the same coordinate axes.

Thanks

Subham

Dear @Kashyap.Subham,

OK. Then you’ll have to convert the acceleration outputs into a different coordinate system. It is probably easiest of you go in the source code and change these outputs to the global inertial-frame coordinate system. Alternatively, you could calculate the rotation matrix (or direction cosine matrix) based on the rotations output and convert the existing acceleration outputs to a different coordinate system based on multiplication of the acceleration vector with this matrix.

Best regards,