Static Process Questions


Q: Why there is a difference in centers of buoyancy and gravity between the &status command and the STATIC PROCESS STABILITY output for the same event number?
REV 6.02

A: Results for &STATUS are in the body system while for the STATIC PROCESS STABILITY report they are in the global system. Also, the results for &STATUS are the true values while the static process report added the flooding into the center of gravity and includes the hookload as a buoyancy in the center of buoyancy.


Q: How can I simulate a vent valve closed during upending using the static process?
REV 6.01

A: You need to use &compart -int_pre :cname 1e-5 100, see the MOSES Reference Manual for more details.


Q: Why do the roll and pitch angles seem to be swapped in the STATIC PROCESS menu?
REV 6.01

A: The default setting of &DEFAULT -SP_ORIENT 0 1 0 1 0 0 found in moses.cus does not apply for the coordinate system used to define your particular jacket model. Change the vector values to suite your model. If roll and pitch are truly swapped, then use "&DEFAULT -SP_ORIENT 1 0 0 0 1 0.


Q: What is the difference between these three commands: "EQUI, &EQUI and BEGIN"?
REV 5.08

A: The EQUI command in the HSTATIC menu is a three degree of freedom equilibrium solver. It is actually the short form of EQUI_H. It works on roll, pitch and heave, and applies to only single bodies without connectors. The BEGIN command is the same type of solver. You probably have a different starting position for these two commands, which will yield different results. A good starting position helps in finding good equilibrium positions.

The &EQUI command uses all six degrees of freedom, includes connectors, and works on all bodies in the model.


Q: What is the "Error V. Force" column in MOSES upending standard results?
REV 5.08

A: The "Error V. Force" is the weight - displacement + hook load, and it gives an indication of how good your equilibrium position is. Normally, our default tolerance settings do a better job than your 78 Mtons indicates. This usually means your jacket model could use a better buoyancy distribution. If you have large point loads of buoyancy, this can cause problems with equilibrium. You could try to tighten the tolerances using the -CLOSURE options on the commands in STATIC_PROCESS, but too much will cause the error "equilibrium not found".