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Load Cases

The Load Cases tab is always visible within the Fatigue Analysis Edition window. The content of the Load cases tab is presented below. The content of this tab however depends on the Calculation method option selected from the General tab: there are 2 different presentations depending on whether the Spectral method or the Rain-flow calculation method is selected.

Load Cases for Spectral damage calculation method

The following Figure presents the contents of the tab when the spectral method is selected:

In case where the spectral method is selected, the Load Cases tab includes 2 parts. The upper part includes 4 action buttons whereas the lower part includes a variable number of tab-sheets. The default state of the Load cases tab, i.e. when creating a new Fatigue Analysis, is with no tab displayed in the lower parts.

The four action buttons are the followings:

  • Create new: this button is used to create a new load case. When the user clicks the button, a new tab must appear in the lower part.

  • Export: This button serves to export the contents of all load cases (i.e. all tabs placed in the lower part) to an external text file.

  • Import: This button serves to import the contents of all load cases (i.e. all tabs placed in the lower part) from an external text file.

  • Delete: this button serves to delete the contents of the current tab (the tab which is currently selected) and remove the associated tab.

The lower part consists in a variable number of tabs which are created or removed by the user through the action buttons placed in the upper part of the Load Cases tab.

Each tab includes:

  • An Edit box: used to specify the name of the load case

  • Several frames: used to select how RAOs are computed when the Spectral method option is selected from the Calculation method frame displayed in the General tab, or to specify the dynamic analyses on which the spectral method must be applied.

  • One grid and radio-buttons: This grid can be used to define the environments on which the spectral method must be run.

The frame titled Wave type includes a drop-down list with several items to let the user choose how the damage must be combined between the different load cases:

When Multi-directional is selected in one of the Bins (the first one or any other), then all other Bins are automatically switched to multi-directional. A warning message is displayed: Combination of Multi-directional sea-states with other types of sea-states is not allowed. All the Load cases will be automatically switched to Multi-directional. Do you wish to proceed?

The bottom part of the Tab includes 2 radio-buttons and one grid. The grid is either visible or invisible depending on the selection of the radio-buttons. The radio-buttons are exclusive from each other and allow to select:

To read the list of sea-states from the Grid

To read the list of sea states from an external *.SCT file.

Load Cases for Rain-flow counting damage calculation method

The following Figure presents the contents of the tab when the rain-flow method is selected.

  • Analysis: The name of the analyses to be used for the fatigue study;
  • Probabilities (%): The probabilities associated to the analysis (sea state probability);
  • Use period: If checked, for regular waves, the fatigue analysis will be performed on the N (NumberOfPeriods) last periods. For irregular waves, the duration is NumberOfPeriods*\(Tp\);
  • Number of periods: The number of periods on which the fatigue analysis will be performed.For irregular waves, the duration is NumberOfPeriods*\(Tp\);
  • From: If 'Use period' is unchecked, start time for the begenning of the fatigue analysis;
  • To: If 'Use period' is unchecked, finished time for the end of the fatigue analysis.