Parameters Parameters

The &PARAMETER command is used to define parameters used in various computations. One of these commands is included in the file moses.cus so that one can alter these settings to suit their particular purposes. This file should be consulted to ascertain what settings are being used. This command functions in a manner similar to the &DEFAULT command in that any option specified on some other command with the same name as that here will override the default. The form of this command is:


     &PARAMETER, -OPTIONS

Again as with &DEFAULT, there are two basic options:


     -SAVE

     -REMEMBER

which allow for temporarily altering the parameters and returning to the previous ones. In particular, the -SAVE option instructs the program to save the current dimensions so that when -REMEMBER is used, the ones previously saved will then be used.

The options:


     -DRGTUB, RE(1), DC(1), RE(2), DC(2), ........

     -F_CD_TUBE, CDTFREQ

     -FM_ROD, ROD_FACTOR

     -DRGPLA, DCP

     -AMCTUB, AMT

define the hydrodynamic properties of generalized plates and tubular members. The added mass coefficients of tubular members and generalized plates are taken to be constant. The drag coefficient for tubular members is a function of the Reynold's Number in the time domain and constant in the frequency domain, and are defined with the options -DRGTUB and -F_CD_TUBE. The -FM_ROD option performs for rod elements the same task as -F_CD_TUBE does for tubes. The drag coefficient for generalized plates is defined with the -DRGPLA option. The added mass for generalized plates and panels, is computed as described in the section on Forces and for tubes it is defined with the -AMCTUB option.

The options:


     -WCSTUBE, CSHAPE

     -REL_WIND, YES/NO

control computation for wind forces. The wind shape coefficient for tubular members is defined by the option -WCSTUBE and here CSHAPE is the new value for the coefficient. The -REL_WIND option defined whether or not the wind force will be computed based on the relative wind velocity or the wind velocity itself.

Normally MOSES computes slam loads on plates and tubes by computing the derivative of the added mass. This can be a numerically sensitive computation and the two options:



     -SL_TUBE, SCT


     -SL_PLATE, SCP

can be used to define a slamming coefficient that is independent of time. A slam force will only be computed when the element has a waterplane intersection. To return to the normal way, one should specify AUTOMATIC for SCT or SCP. Theoretically, there should be slamming for both the element entering the water and when it is exiting. The option



     -SLAM_BOTH, YES/NO

controls this. If YES/NO is YES then slams occur for both cases. If it is NO then slams only occur when the element is entering the water.

The option



     -T_AVERAGE, TYPE

defines the way that the "average period" is computed when doing fatigue or cycle counting in the frequency domain. If TYPE is DNV then the average period is the associated with the "average zero up crossing frequency" defined in DNV RP-C206 (Section 6.9.4). Otherwise, it will be computed with the traditional formulae:

     Tav = 2 pi  sqrt { M2 / [ M0 ( 1 - eps ) ] }
     eps = sqrt { [ M0 * M4 - M2**2 ] / ( M0 M4 ) }

The options:



     -API_TDRAG, YES/NO


     -AF_ENVIRONMENT, YES/NO

are used in computing velocity square forces. The first one controls the relative velocity for tubes. If YES/NO is YES then the relative velocity is the component normal to the tube as in API RP2A. If YES/NO is NO then it is the true relative velocity. The second one controls the way wind and drag are computed on areas. If YES/NO is YES then the drag force is in the direction of the environment. If YES/NO is NO then it is perpendicular to the area. One should use YES to have the force depend on the projected area.

In many cases, MOSES will perform a numerical integration over either an area or a length. The precision of this integration can be controlled via the options:



     -MAXLEN, LENGTH


     -MAXAREA, AREA


     -MAXREFINE, REFINE_NUMBER

Here, MOSES will divide an element into pieces such that each length or area of each piece will be less than LENGTH (feet or meters) or AREA (ft**2 or m**2). The maximum number of pieces any one element will be broken into is REFINE_NUMBER.

The option:



     -M_DISTANCE, DISTANCE

is used to define the amount of refinement which will be performed on a diffraction mesh when hydrodynamic properties are computed. Here, DISTANCE (feet or meters) defines a maximum distance which the side of a panel or the length of a strip can have. Use of this option allows one to define a quite crude mesh and have MOSES automatically refine it to achieve any desired degree of precision.

The options:



     -STRETCH_SEA, YES/NO


     -NONL_SEA, YES/NO

control how the wave kinematics are computed. If YES/NO is YES for the first option, then the sea will be "stretched" above the mean water level. If not, then the linear kinematics equation will be used directly above the mean water level. If YES/NO is YES for the second option, then the wave profile will be computed using an estimate of the nonlinear pressure term. This results in the wave crest being higher than a trough is low. If it is NO, then a linear wave profile will be generated.

The option:



     -IN_SCF, TYPE

is used to define the method used to compute the "inline" stress concentration factors between two tubular sections. The section on SCF Binding discusses this in greater detail.