Associating SN Curves with Points Associating SN Curves with Points

An SN curve must be associated with each fatigue point. The details differ based on the type of fatigue being computed, but in all cases it is accomplished with an -SN option. For mooring line and tubular joint fatigue, the "current" SN name will be used; i.e. the last name specified on either a &REP_SELECT command or its equivalent.

For elements (other than mooring lines) there are three ways to define them: on a &DEFAULT command, on the ~CLASS command, or on the element definition command. In any case failure to include a definition results in the last definition being used; i.e.

For the &DEFAULT command, the default SN curves at various points on an element are defined with the option

     -SN, TYPE(1), SN1_A, SN1_B, SN1_R, \
     TYPE(2), SN2_A, SN2_B, SN2_R, ......

Here, TYPE(i) defines a section type and must be either: TUBE, CONE, BOX, WBOX, PRI, IBEAM, G_IBEAM, TEE, CHANNEL, ANGLE, D_ANGLE, LLEG, or PLATE. SN1_A is the SN curve name for the A end of the element, SN1_B is for the B end, and SN1_R is for all remaining segments. This sequence can be repeated for as many section types as desired. Also, if only one SN curve name is provided, the same SN name is used for all locations along the element. If two SN names are specified, the first name applies to the "A" end of the element, and the second SN names applies to the "B" end and all segments in between. Of course, the SN curve specified here must be defined to MOSES using the appropriate commands, such as &REP_SELECT.

For the element and class definition commands, the situation is a bit different. Here, we know how many fatigue points we have so we can directly define an SN curve for each one of them. Thus, for classes, we have the option for each segment of


Here, CURVEA is the SN curve which will be used at the beginning of the segment and CURVEB is the curve used at the end of the segment. If one uses two names for each segment, the one in the middle will be defined twice. If this is done, the second definition will actually be used; i.e. the first curve specified will, in fact, be used for the beginning of the segment. Also, CURVEB needs to be specified only on the last segment.

For elements, we have

     -SN, i, CURVE

which defines the SN curve for the "ith" fatigue point of the element to be "CURVE". Here, -SNA defines curve at the A end, -SNB defines curve at the B end, -SN1 defines curve at the end of the first segment, etc.