Dear Jason

```
I am trying to model a floating offshore wind turbine in FAST.v8. My tower and turbine are the same as OC4 DeepC semi-submersible wind turbine. The top of my platform is 15m above the still water level. So, I have to move the tower and turbine 5m along the +z axis. I changed the TowerHt and TowerBsHt in ElastoDyn input file (with 92.6 and 15 respectively) and the TweElev in AeroDyn (v15) input file (add 5 to all the TwrElev values). The ServoDyn input file is also the same as OC4.
1) When I run FAST v8 with stiil air (CompElast=1, CompInflow=0,CompAero=0,CompServo=1), the FAST can be run normally. When I run FAST v8 with still air (CompElast=2, CompInflow=0,CompAero=0,CompServo=1), the Fast is aborted with the following error information:
```

FAST_Solution:FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after

the maximum number of iterations

FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum

number of iterations

FAST_AdvanceStates:BD_GA2:BD_DynamicSolutionGA2:Solution does not converge after the maximum

number of iterations

```
2) When I run FAST v8 with steady wind (CompElast=1, CompInflow=1,CompAero=2,CompServo=1), the FAST can be run normally. When I run FAST v8 with steady wind (CompElast=2, CompInflow=1,CompAero=2,CompServo=1), the FAST is aborted with the following error information:
```

[b]FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UpdateStates(node 5, blade

1):BEMT_UnCoupledSolve:DeterminePhiBounds:There is no valid value of phi for these operating

conditions! Vx = 1.3574, Vy = -20.182, rlocal = 11.739, theta = 0.21597

FAST encountered an error at simulation time 7.50000E-02 of 300 seconds.

Simulation error level: FATAL ERROR[/b]

```
3)When I run FAST v8 with turbulence wind (CompElast=1, CompInflow=1,CompAero=2,CompServo=1), the FAST is aborted with the following error information:(the wind file is produced by TurbSim, the HubHt=95,and the GridHeight*GridWidth=170*170)
```

[b]Timestep: 66 of 300 seconds. Estimated final completion at 22:10:09.

FAST_Solution:FAST_AdvanceStates:AD_UpdateStates:BEMT_UpdateStates(node 6, blade

2):BEMT_UnCoupledSolve:DeterminePhiBounds:There is no valid value of phi for these operating

conditions! Vx = -0.62872, Vy = 17.29, rlocal = 15.844, theta = 0.20038

FAST encountered an error at simulation time 66.263 of 300 seconds.

Simulation error level: FATAL ERROR[/b]

What’s wrong with my model? Should I change something else? Please give me some suggestions!

`Sincerely`