Joint stiffness

A revolute joint will produce a resisting moment about its axis of revolution only if *CONSTRAINED_JOINT_STIFFNESS_ (GENERALIZED, FLEXION-TORSION) is defined in the input deck. Otherwise, the joint will rotate freely, without resistance. Assuming you've included  this joint stiffness via *CONSTRAINED_JOINT_STIFFNESS_GENERALIZED, the JNTFORC file will report the resisting moment as "psi-moment". To plot this psi-moment with LS-Prepost, you must click the JStifR button after loading the JNTFORC file.

JID is the value listed after "joint ID" in jntforc and corresponds to *CONSTRAINED_JOINT_<PLANAR>. If you had used the command *CONSTRAINED_JOINT_PLANAR_ID, you could specify the joint ID on the subsequent line. Without the ID option on the command, the joint ID is assigned automatically (in this case to "1" because it's the first joint). The data immediately below corresponds to the constrained DOF associated with *CONSTRAINED_JOINT_PLANAR and  has nothing to do with *CONSTRAINED_JOINT_STIFFNESS_ (GENERALIZED, FLEXION-TORSION).

joint ID..................................         1
 x-force................................  3.40893E+02
 y-force................................  2.82037E+00
 z-force.................................  0.00000E+00
 x-moment..........................  0.00000E+00
 y-moment..........................  0.00000E+00
 z-moment..........................  9.62622E+02
 resultant force...................  2.82037E+00
 resultant moment............   9.62622E+02

JSID is the value listed after "joint stiffness id number" in JNTFORC and is assigned in the first field of Card 1 of *CONSTRAINED_JOINT_STIFFNESS_ (GENERALIZED, FLEXION-TORSION). The data immediately below corresponds to *CONSTRAINED_JOINT_STIFFNESS_ (GENERALIZED, FLEXION-TORSION) and is wholly separate from *CONSTRAINED_JOINT_<PLANAR>.

joint stiffness id number....         1
 x-displacement..................  8.95355E+05
 d(dispx)/dt...........................  5.37666E+02
 y-displacement..................  0.00000E+00
 d(dispy)/dt...........................  0.00000E+00
 z-displacement..................  1.74889E+00
 d(dispz)/dt...........................  4.99717E+01
 force-x-stiffness.................  6.21757E+02
 force-x-damping................  0.00000E+00
 force-x-total........................  6.21757E+02
 force-y-stiffness.................  0.00000E+00
 force-y-damping................  0.00000E+00
 force-y-total........................  0.00000E+00
 force-z-stiffness.................  1.92379E+03
 force-z-damping................  0.00000E+00
 force-z-total........................  1.92379E+03
 joint energy.........................  1.68268E+03

JID in the 6th field of *CONSTRAINED_JOINT_STIFFNESS_ (GENERALIZED, FLEXION-TORSION) is used only if a table ID, rather than a curve ID, is input (as a negative number) for certain parameters in *CONSTRAINED_JOINT_STIFFNESS_FLEXION-TORSION or _GENERALIZED. In this case, the table (*DEFINE_TABLE) lists n values of reaction force and then n curves are defined (*DEFINE_CURVE) immediately after the table. Each of these curves defines a moment limiting value vs. rotation for a specifc value of 'reaction force' developed by joint JID. JID doesn't apply in the case of *CONSTRAINED_JOINT_STIFFNESS_TRANSLATIONAL.