3.3 Power production with transient wind

1. Open the demo_a project (if not open)
In Bladed, File > Open > demo_a.prj (this project is located within the Bladed application folder, e.g. C:\DNV\Bladed 4.18\DemoModels\Demo_a\demo_a.prj).

2. Check the Power production settings
Double-click the Power Production Loading option under Simulations in the Calculations window. Stay on the Simulation Control tab, the parameters we're interested in are the following:

• Output time step defines the frequency it writes the outputs of the simulation.
• Time to start writing output defines the time to initialize simulation.
• Simulation time is the length of the simulation inclusive of the Time to Start writing output.
• Length of output buffer determines how often to write results to file. This is a trade-off between speed of simulation vs. available RAM on the computer.

In the video we are using the default settings.

3. Check the wind definition
Click the Wind option in the main window. Stay on the Time varying wind tab.
By default the simulation is set to 3D turbulent wind simulation (see the radio options on the left-hand side). For this simulation you need to change it to Transients, this means there is no turbulence, and the wind is deterministic allowing you to simulate gusts, changes in direction, horizontal or vertical shear that vary over time.
For this simulation we're going to simulate a gust (an increase in wind speed).

4. Define a gust (an increase in wind speed)
Define the following settings:

• Start value is the starting wind speed. We use 12 m/s
• Amplitude of change is how much the wind speed changes. We use 6 m/s
• Time to start cycle is when the gust takes place. We want this to be 10 seconds, however we need to add the initialization time from earlier, so 10 +7 = 17 seconds.
• Time period of cycle is how long the gust will last for. We use 10 seconds
• Type of cycle (half / full). We use Full.

Did you know? The IEC-2 standards option is often referred to as a 'Mexican Hat' due to the shape of the wave cycle.

5. Save the settings
Do not close the window yet, click Apply near the bottom right of the window to make sure your settings have saved.

6. Check the Wind shear settings
In the same window select the Wind shear tab. Wind shear is the vertical change in wind.
In the video we use the default settings.

7. Check the Tower shadow model
This allows you do model if the turbine is upwind or downwind.
In the video we use the default settings (Potential flow) as we're modelling an upwind turbine.

8. Close the window
Click OK when you have finished checking and editing settings.

9. Run calculation
Click Run Now in the Calculations window.

10. Choose a Run Name and specify the location for the calculation output
In the Output settings window, try renaming the run using the Run Name field. Now select a new sub-folder in the directory (you can either select the results folder, or create a new folder by editing the file path and typing the new folder's name).

11. Start the simulation
Click OK to run simulation.

1. Open Bladed Results Viewer
You can use the Windows search feature to find and launch the software.

2. Add calculations to view
Click the Add calculations button located near the left-hand corner. Find the power production calculation output file that you created earlier and click Open to add it.

3. Plot the hub wind speed magnitude
Use the Output group dropdown to select Summary information. This will then display a list of variables below, select Hub wind speed magnitude from the list. You should see the results plotted on the graph, reflecting your settings in the previous video.

4. Plot further outputs and interpret what's happening
Return to the Variables list on the left-hand side. Now plot the Rotor speed, Electrical power and Pitch angle. See the video (1:10) for an explanation of the results.

5. Plot the nacelle motion to understand how the turbine is moving
First, hide the visibility of all inputs except the wind speed. You can toggle the visibility of the data by clicking the eye icon next to the plots, towards the bottom of Results Viewer.
Then return to the Output group list and select Nacelle motion, followed by selecting Nacelle fore-aft arm displacement from the Variables list. See the video (3:52) for an explanation of the results.

6. Investigate why the turbine is moving
Try plotting some loads to investigate why the turbine is moving this way. Make some hypothesis and see if they are verified by plotting loads. We might assume this is caused by the aerodynamic loads that get reduced. Verify this by plotting loads, Select the Output group list, select Hub loads: fixed frame GL coordinates, followed by selecting Stationary hub Fx (force / thrust in the direction of the shaft) from the Variables list. See the video (5:55) for an explanation of the results.
Try plotting some other loads to investigate the effects of the gust.

Define a loading condition known as the “Mexican hat” (due to the wind speed shape).

The simulation must have the following settings:

• A 12 m/s northerly (0 degrees) wind
• "IEC2" gust cycle with 9 m/s amplitude and 20s period, happens 5 seconds into the simulation (see hint for help).
• A direction changes to 20 degrees angle in 10 seconds starting 5 seconds after the 'Mexican hat' starts.

To properly time the gust, you have to calculate the actual seconds into the simulation by taking into consideration whatever is in Time to start writing output under Calculation Parameters.

Check the settings in the screenshot below, did you get the same?