Gap
(UNITS: mm.)

This is a multiple use field defined as follows:

TYPE = X Y Z GUI LIM RX RY RZ

GAP (UNITS: mm.)

GAP - Distance along the restraint line of action the restrained node may travel before resistance to movement begins. The gap value must be positive. For rotational restraints the gap is given in degrees. If the translational restraint is not preceded by a sign, then the restraint is double acting and the gap will be taken to exist for both positive and the negative displacements along the line of action (i.e. if a 0.25 in. gap is specified at a +Y restraint, then the restrained node may move freely 0.25 in. in the minus Y direction before restraint occurs. The gap specification does not affect the amount of free displacement that can occur along the positive Y direction in this example).

When defining windows of allowed movement it is not uncommon to place two restraints having the same line of action, but with different signs at the same node. This configuration is perfectly legal. The user is cautioned to remember to form the window with signs on restraints rather than with signs on gaps. In CAESAR II a gap is a measure of length and is always positive.

Examples:

TYPE GUI GAP 1/4 ... One quarter mm. gap on either side of the "guided" restraint.

TYPE +Y GAP 3.0 ... Three mm. gap BELOW the support that must be closed before the +Y support begins acting.

TYPE RX GAP 5.0 ... Five degree gap about the X axis about which the pipe may rotate freely before rotational restraint occurs.

TYPE = XROD YROD ZROD

Len (UNITS: mm.)

Len - Swinging length of the rod or hanger. Distance along the restraint line of action from the restrained node to the pivot point. The restraint swings about the pivot point. If a CNODE is defined then the restraint swings about the CNODE. "Len" is a required entry.

TYPE = X2 Y2 Z2 RX2 RY2 RZ2


K2 (UNITS: N./mm. <or> N.m./deg )

K2 - Post yield stiffness of a bilinear restraint. When the load on the restraint exceeds Fy then the stiffness on the restraint changes from K1 to K2. The value of K2 may be negative, modeling shallow trench or groove-type pipeline supports. K2 VALUES OF ZERO WILL BE TREATED AS RIGID. For very small stiffnesses enter a value of 1.0.

TYPE = XSPR YSPR ZSPR


"x" (UNITS: mm.)

"x" - Travel along the spring axis before "bottom-out" occurs. In the case of a typical YSPR, this is the movement in the negative "Y" direction before the spring bottoms out.

TYPE = XSNB YSNB ZSNB

dmp - Future use intended for snubber damping value.

I don't believe you can correctly model a damper in CAESAR II at the present time. A damper and a snubber are totally different animals. Dampers are like sticks, attached to the pipe, that sit in a tub of goo -- so the pipe squishes around while it vibrates.

Our understanding is:

1. The damper should have no effect on the static model.
2. The damper should have no impact on the mode shapes or frequencies.
3. The damper's impact on modal analysis cannot be determined.
4. As far as we can figure, dampers can only be simulated by multiplying the nodal velocity times the damping value (which, by the way is frequency dependent, so the damper has a different value for every mode) to get a time-varying force which then should be added to the force profile.

So how would somebody model this? They would have to estimate its impact as a time dependent force, and include that force profile in the Time History (not an easy matter).

This is a subject we are studying for possible inclusion in the software.

Ok thanks - I'll remove that from the "help".

If and when we get around to damping, it will likely be defined in the dynamic input.

I remember (from my first physics class) that a mode (natural frequency) is the "free, undamped" vibration of the system.

[M]{a} + [K]{x} = 0

There is no " [C]{v} " component in this equation.