This data category is used to input the frequencies and directions at which the values of the hydrodynamic parameters in the equations of motion of large floating structures are to be computed, or to access existing information from a previous analysis. Values of added mass, and radiation damping are associated with each frequency. Values of diffraction forces, Froude Krylov forces and Response Amplitude Operators (RAO) are associated with each frequency and with each direction.

Rules Governing Input of Frequencies/Periods

The frequencies and values of the radiation/diffraction analysis parameters are naturally of fundamental importance to all analyses of the motions of a large floating structures. Unfortunately maximum flexibility in specifying these parameters usually results in errors which can go undetected right through the analysis procedure. The format of input of these parameters is designed to avoid the errors whilst retaining this flexibility which is considered essential to the accurate modeling of a structure in such a complex environment.

The following rules and manner in which the frequencies/periods are input at first may appear complicated just to specify a single series of ascending/descending values. However, the user will rapidly become aware of value of the rules with both simple analysis procedures and use of the more advanced facilities of the program.

(a) Frequency/period numbers must be unique.

(b) There must be no 'gaps' in frequency/period numbers when all data records in this data category have been input, e.g. if a total of five frequencies/periods are input then these must be numbered 1 through 5.

(c) Frequencies/periods must be distinct and unique.

(d) When all data records in this data category have been input, ascending numbers must correspond to ascending frequency values, or, if periods are input, to descending period values.