Dynamic Simulations |
 
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Dynamic Simulations |
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Once the static equilibrium configuration of the entire system has been achieved following the Model Building process, the ambient environmental loads due to wind and waves may be defined, and dynamic simulations may be performed. The following guidelines are helpful in this regard. Typically a single dynamic analysis is examined initially, to ensure that the dynamic response to a sample environmental simulation is consistent with expectations.
•Set up a new Time Domain Analysis input file, restarting from the preceding static solution, and select appropriate Time Variables. In standard offshore applications, appropriate time variables are typically dependent on the ambient seastate. For wind turbine modelling, NREL recommend that the solution time step for aerodynamic calculations be set such that there are at least 200 time steps per rotor revolution.
•Create a link between the structural (Flexcom) and aerodynamic (AeroDyn) models, via the *AERODYN DRIVER inputs. This identifies key locations in the model, such as the hub node and tower elements, which act as central points for information exchange between the two solvers. Load case specific inputs such as wind Loading and blade rotational speed are also defined at this stage.
•Define the wind loading. Steady wind is the simplest option, and is invoked in Flexcom by specifying a constant Wind Speed and Shear Exponent via the *AERODYN DRIVER keyword (or the Wind Component if you are using the Flexcom Wind module). For any of the more advanced wind field definitions, you specify the name of the InflowWind file (via the *INFLOWWIND keyword or the Wind Component), which you will need to have created in advance. Refer to InflowWind Overview for further details. You will also need to generate a turbulent wind field using TurbSim - refer to TurbSim Overview for further information.
•Define the wind turbine control system via the *SERVODYN keyword. You can vary generator torque to control rotor speed and/or vary blade pitch via a Bladed-style dynamic link library (dll). Refer to ServoDyn Overview for further details.
•Choose from the range of options for applying Wave Loading.
After a successful dynamic simulation, the next logical step is to proceed to examining a matrix of simulations.
•Set up some Parameters to represent key inputs. For example, you may wish to create seastate parameters such as wave period and wave direction, or wind parameters such as wind speed or shear exponent.
•Use Keyword Based Variations (ideal for parameters which vary in fixed increments) or Spreadsheet Based Variations (for arbitrary variations) to examine the effect of varying key parameters. One master template input file automatically generates all the required input files to simulate each unique combination of different parameters.
If you would like to see an example of how these inputs are used in practice, refer to J03 - Summary Postprocessing Collation.