Drag and Inertia Coefficients Form

Access the Drag and Inertia Coefficients form as follows:

Ensure that the Offshore license has been enabled.
Display the Define Loads form using either of the following methods:

Click the Define menu > Load Cases command.
Ensure that the Bridge Modeler license is enabled; display the Bridge Wizard; and then select the Analysis Cases item and click the Define/Show Loads button.

Specify a Wave Load Type and an Auto Lateral Load other than None and click the Add New Load button.
Highlight the name of the newly define load and click the Modify Lateral Load button to display the Wave Load form.
Click the Drag and Inertia Coefficients Add button or select a previously defined coefficient definition from the drop-down list and click the Modify/Show button to display the Drag and Inertia Coefficients form.

Use the Drag and Inertia Coefficients form to define drag and inertia coefficients for a specified number of vertical elevations. The data can then be used to calculate the wave forces acting on a structure.

Drag and Inertia Coefficient Name edit box. Use the default or enter a new name in this edit box.
Number of Elevations edit box. Input the number of vertical elevations at which the drag and inertia coefficient data are specified.
Drag and Inertia Coefficient Data spreadsheet. After a value has been entered in the Number of Elevations edit box and the Enter key on your keyboard has been pressed or another text box on the form has been clicked, the number of rows in the Drag and Inertia Coefficient Data spreadsheet will change to match the value specified in the Number of Elevations edit box.

Input the vertical elevation (measured from the datum) and drag and inertia coefficients at each data point in descending vertical elevation order. Clicking the Order Rows button will reorder the data. Note, however, that the program will automatically reorder the data in descending vertical elevation order when you click the OK button to close the form.

The drag and inertia coefficient values used at a particular vertical elevation are linearly interpolated from the specified data.

The drag and inertia coefficients are used in Morison’s equation when calculating the wave forces acting on the structure. By default, a wave load is specified to have API Default drag and inertia coefficients. The values for the API Default drag and inertia coefficients depend on whether the location considered is above or below the specified high tide elevation, as shown in the following table.

Location	Drag Coefficient	Inertia Coefficient
Above High Tide Elevation (Smooth)	0.65	1.6
Below or At High Tide Elevation (Smooth)	1.05	1.2