Defining Points Defining Points

To define a point, one issues the command:


     *, NAM, X, Y, Z, -OPTIONS

and the available options are:



     -REFERENCE, *RPA, *RPB, ..

     -RECT

     -CYLINDER

     -SPHERICAL

     -LOCATION, XO, YO, ZO, RX, RY, RZ
     -LOCATION, XO, YO, ZO, *PT(1), *PT(2), *PT(3), *PT(4)

     -DEL, DOF(1), .... DOF(i)

     -JNTCLASS, PRCK, PRCT, PRCX

     -BBC_MUL, MULT

     -EFF_CHD_LEN, ECHD_LEN


     -CO_SCF, SCF_TYPE


     -LEN_FACTOR, FRACHOL


     -MAX_CHD_LEN, MAXCHOL


     -CHD_FIXITY, CHD_FIX


     -MIN_SCF, MIN_SCF

where *NAM is the name of the point defined, and X, Y, Z are the coordinates (feet or meters) in the "current point system" defined by the &DEFAULT command. If the option -REFERENCE is employed, then the coordinates are relative to the specified points; otherwise, they are with respect to the part origin.

If one reference point is specified, then X, Y, and Z define a vector from this reference point to point *NNAM. If two points are specified, then X specifies the distance from the point *RPA to point *NNAM, along a line from *RPA to *RPB, and Y and Z are ignored. If three points are specified, then they will define a local coordinate system with the origin being at the first point, the x axis being from point 1 to point 2, the z axis being perpendicular to the plane formed by the three points, and the y axis given by the right hand rule. Again, X, Y, and Z are local coordinates in this system. If four points are specified, then a point is first located at the intersection of the two lines which connect *RPA and *RPB, and *RPC and *RPD. The X, Y, and Z coordinates then define the vector from this point to point *NNAM. Remember that if one changes the coordinates of a point being referenced, then the coordinates of the defined point will also change. Some examples of using reference points are shown below:

     *PT3  10 -REFERENCE *PT1 *PT2

This will create a point 10 feet (or meters) from *PT1 along a line formed by *PT1 and *PT2. This example is handy for defining points along a battered jacket leg.

     *PT5 -REFERENCE *PT1 *PT2 *PT3 *PT4

This will create a point at the intersection of the lines formed by points *PT1 and *PT2, and *PT3 and PT4, which is useful for defining points at the middle of X braces.

If one wished to temporarily override the current system, he may do so by specifying any of the options -RECT, -CYLINDER, -SPHERICAL, or -LOCATION which were discussed with the &DEFAULT command.

The option -DEL is used to delete the degrees of freedom of a point which specified by DOF(i) which must be either X, Y, Z, RX, RY, or RZ. If no DOFs are specified, then all degrees of freedom will be fixed. Notice that this option only has meaning if the point is also a node.

All of the remaining options define the "joint" behavior of points. MOSES automatically classes joints based on the load path. In some rare cases, one may wish to override the automatic joint classification. This can be accomplished with the -JNTCLASS option. Here, PRCK, PRCT, and PRCX are the percentages of K, T, and X joint types used to classify a joint. When this option is used, the specified classification for all load cases.

In Joint Crushing MOSES treats the joint as a two dimensional ring. Two basic assumptions here are that the braces do not alter the stresses in the ring and that an effective length of the chord is used to distribute the load. The -BBC_MUL option allows a factor of the bending stress under a brace to be used. In other words, if one believes that the brace will prevent any bending stress in the chord under its footprint, then he should specify a value for 0 with the -BBC_MUL option. The opposite, conservative, view is that the brace has no effect in the bending of the chord where one specifies a value of 1 for MULT. Of course, one can specify any value between these two. The -EFF_CHD_LEN option is used to change the effective chord length for Joint Crushing from the default behavior computed according to API RP2A for both joints with and without rings.

The remainder of the options control the computation of SCFs for tubular joints. These options were discussed in the section Associating SCFs with Tubular Joints.