Curves Curves

The &DATA command is used to define "curves" which used in various computations. Here, one associates a name with a function (set of data) and then uses that name to refer to the function. The form of this command is:


     &DATA CURVES, TYPE, NAME, DATA -OPTIONS

Here, TYPE is the type of data which is being defined, NAME is the name you wish to give to the curve, and DATA is the numbers used to define the curve. DATA is an n-tuple where normally n is two; i.e. normally you define a curve with an independent variable and a single dependent variable. TYPE must be either C_PROFILE, P_SPECTRUM, F_SPECTRUM, M_GROWTH, W_HISTORY. LT_MULTIPLIER, CT_LENGTH, EFFICIENCY, CS_VELOCITY, or, AM_PRESSURE. The behavior of any of these can be obtained with

     &STATUS CURVES  NAME -PLOT

Where NAME is the name of the curve about which you want information.

The first five of these define curves which are used in defining the environment.

LT_MULTIPLIER is used to define load multipliers which vary with time. Here DATA is T(1), V(1), .... T(n), V(n) where T(i) is the time and V(i) is the multiplier at that time. The TYPE of curve accepts the option:



     -PERIODIC

If this option is specified, then the defined values will be repeated with a period of the last time in the list. If the option is not used, the last value in the list will be used for times larger than the last.

The next two curve TYPEs are used with connectors. CT_LENGTH is used to define the rate of change of the length of a connector. Here DATA is T(1), V(1), .... T(n), V(n) where T(i) is the time and V(i) is the rate of change of length (ft/sec or m/sec) at T(i). EFFICIENCY is used to define the propeller efficiency as a function of water particle velocity. Here DATA is V(1), E(1), ..... V(n), E(n) where V is the water particle velocity (ft/sec or m/sec) and E is the efficiency.

The type CS_VELOCITY is used to define a drag coefficient which varies with the relative speed. Here the DATA is pairs of velocities and drag coefficients.

The last curve TYPE, AM_PRESSURE, is used to define added mass pressures as a function of submergence. Here DATA is a set of four "n" numbers S(1), AP_SURGE(1), AP_SWAY(1), AP_HEAVE(1), ....., S(n), AP_SURGE(n), AP_SWAY(n), AP_HEAVE(n). Here S(i) is the submergence (feet or meters) and AP_SURGE, AP_SWAY, and AP_HEAVE are the surge, sway, and heave added mass pressures (feet or meters) of water.