This data category is used to input the regular wave drift forces acting on each structure at the frequencies and directions previously defined in Data Category 6.

The drift forces are applicable to the following programs:

Aqwa-Fer: used to calculate the drift frequency motions in the frequency domain.

Aqwa-Drift: used to calculate the drift frequency motions in the time domain.

Aqwa-Line: used only to change the values of the drift forces in the backing file.

Aqwa-Librium: used to calculate the steady drift forces contributing to the equilibrium position and the dynamic stability of drift frequency motions.

Aqwa-Naut: not applicable.

This data category is used when:

(a) the user wishes to input a database of hydrodynamic coefficients obtained from a source other than Aqwa-Line.

or

(b) the user wishes to change some of the values calculated by a previous Aqwa-Line run, for the current analysis (Aqwa-Fer/ Drift/Librium), or within the backing file (Aqwa-Line only).

The normal mode of operation of the programs using the drift forces is to read these values from the backing file of a previous Aqwa-Line run. Therefore, unless (a) or (b) above apply, the user should omit these data categories by entering 'NONE' for the data category keyword (see Compulsory Data Category Keyword and Omission of Data Categories).

WARNING when running Aqwa-Line

Aqwa-Line handles the hydrodynamic coefficients in sets with each set relating to one frequency. It has two ways to obtain these sets of coefficients.

(a) It can import them from a previously calculated database or from the .DAT file or (for the QTFs) a separate ASCII file

or

(b) it can carry out a radiation/diffraction calculation to calculate them.

These two methods cannot be mixed. If the program imports any data for a particular frequency it assumes all the data is to be imported and does NOT do a calculation for that frequency. This means that if you want to change some of the coefficients for a particular frequency (e.g. the surge drift coefficients) you must:

(1) carry out a "standard" Aqwa-Line radiation/diffraction analysis to populate the whole database

and then

(2) carry out a 2nd Aqwa-Line run, reading in the previously calculated database (.HYD file) and using DRFX data records to change the relevant drift coefficients.