Post-Processing Load Case Results
A number of post-processing calculations allow a whole list of variables to be processed across a whole list of load cases. If appropriate, the results are accumulated over the turbine lifetime (or any other desired period) assuming a particular wind speed distribution, and a frequency of occurrence for transient events. Otherwise the results are stored as additional outputs for each load case.
In the window for the required post-processing calculation, click
Multiple Channels to bring up the Multiple Processing window.
Use the Add Load Case and Add Variable buttons to build up the
required lists of load cases and variables. Add Many Load Cases
allows all the calculations in a selected directory (including
subdirectories if desired) to be added in one go. In most cases,
multiple variables can be selected in one go by dragging over a number
of variables, or holding down the Ctrl key and clicking on the
required variables.
It is important to ensure that the output specifications for all the load cases are the same. In other words the same outputs and the same blade and tower stations have been requested.
Load cases tab: If accumulating results over the lifetime, the
Load Cases window is loaded with all the relevant load cases, and a
weighting is applied to each load case to reflect its contribution to
the lifetime. For transient (T) load cases such as stops and starts,
enter the occurrences per year of this load case. For stationary (S)
cases, such as load cases representing an ongoing situation or state of the
turbine, there is a choice of three weighting methods:
“One run per bin”: Specify the wind speed bin represented by this load case, by giving the bottom and top of the bin. Eventually the whole wind speed range, starting from 0 m/s, should be represented. The wind distribution also needs to be defined so that the appropriate weightings can be calculated.
“Hours per year”: In this case, the number of hours per year for which each load case is representative is specified.
“Pre-defined bins”: In this case, the bins are defined independently, as is the wind distribution, and the details of each load case are automatically interrogated to allocate it to one of the bins. If a bin contains more than one run, the time in the bin is split equally between each simulation in the bin.
At the bottom, enter the turbine lifetime. Note that it is possible to treat a stationary load case as transient, or vice versa, by clicking on the S or T indicator. At the bottom, enter the turbine lifetime, and ensure a wind speed distribution wind distribution is defined (not required if all the load cases are transient). The length of transient simulations will not be included in the turbine lifetime.
Variables tab: If available, for each variable, enter the number an0d range of the bins to be used. If the Minimum and Maximum are both left as zero, a bin range will be calculated which is suitable across all the load cases. For rainflow cycle and fatigue analysis, it is possible to specify a minimum range below which cycles are not counted.
Last updated 30-08-2024