Data Category 15 is used in all programs in the Aqwa suite, except Aqwa-Line, to input the 'starting conditions' for the analysis. Although data categories for each type of analysis are similar, they are documented separately as each requires information appropriate to the type of analysis. This description of Data Category 15 is appropriate to Aqwa-Naut only.

Aqwa-Naut solves the second order differential equations of motion by integrating them to form a time-history. The program therefore requires the initial conditions in order to begin the integration. These initial conditions are referred to as starting conditions.

Starting Conditions - Defaults

As the differential equation is second order, the solution requires two initial conditions which may be input by the user. These are the position and velocity at the start of the time-history in all 6 degrees of freedom. However, default starting conditions will be assumed by Aqwa-Naut if the user omits any, or all (the latter by entering NONE for the Data Category Keyword) of the data records in this data category.

The default starting position is the position of the structure as originally defined by the user in Data Categories 1 to 4. The default starting velocity is zero in all 6 degrees of freedom.

Starting Conditions with the RDEP option

If the RDEP option (Administration and Calculation Options for the Aqwa Suite) is used with a filename given on the RESTART data record (e.g FILE01), then the positions in the file FILE01.EQP will override the default positions. However, if starting positions are defined in Data Category 15 these will in turn override the data in the .EQP file.

The starting velocity will be zero.

Starting Conditions specified in Data Category 15

If the POS* or VEL* data records are used in Data Category 15 the values on these data records will override the defaults or the values in the .EQP file. Note that blank fields on these data records are treated as zero values.

Slow velocity and position are not used in Aqwa-Naut. If the SLP* or SLV* data records are used they will be ignored.

Initial Reactions

It is not possible to specify the initial articulation reactions in Aqwa-Naut. If the positions are correct the articulation reactions will reach equilibrium in the 1st time step.