Hello FAST team,

I am a new user of FAST and I am trying to develop an understanding of your software. To this end I have been trying to run some simple test cases using the Cert Test cases provided with the software. I have been using test case #25 which I modified in the following way for my simplified tests.

Test25.fst

I removed control and electrical-drive dynamics by setting CompServo = 0.

ElastoDyn:

All DoFs restrained

Initial Conditions:

No rotor speed
No initial platform pitch or surge offset

AeroDyn:

No wake induction model

No tower potential flow influence

No tower aerodynamic loads

HydroDyn:

No wave

I ran three tests:

1.In this test the FWT system was restrained in all degrees of freedom and wind load applied to non-rotating blades.

2.As test 1 except the platform was unconstrained in the surge degree of freedom and a uniform current of 5m/s was applied to push the platform in the wind direction along the longitudinal axis to see the effect of wind loading on non-rotating blades moving through the wind flow.

3.As test 2 except that I removed the current and applied a regular wave of Hs 3m & Tp 10s, 0⁰ heading to push the platform in the direction of the wind flow to see the effect of wind loading on non-rotating blades moving through the wind flow.

Results

Test Case 1

The rotor aerodynamic force in the x direction at the hub is a constant force as expected.

Test Case 2

The platform drifts off in the surge direction as expected with current applied. The rotor aerodynamic force in the x direction at the hub varies as the platform drifts. I was expecting the force to be the same constant as the first case as even though the platform is moving the hub height in the wind should remain constant therefore a constant force?

Case 3

The surge plot in this case is suggesting the platform is moving forward on the wave crest and back in the trough? Essentially, the platform is surging forward and backward in the wind. The plot of rotor aerodynamic force in the x direction at the hub suggests that this movement has an influence on the loading which again I was not expecting.

So my question is; do the rotors translating in the longitudinal X direction with the wind somehow have an additional loading on the blades?