# PBUSH

Bulk Data Entry Defines the nominal property values for a generalized spring-damper-mass structural element.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PBUSH PID K K1 K2 K3 K4 K5 K6
KMAG KMAG1 KMAG3 KMAG4 KMAG5 KMAG6
B B1 B2 B3 B4 B5 B6
GE GE1 GE2 GE3 GE4 GE5 GE6
ANGLE ANGLE1 ANGLE2 ANGLE3 ANGLE4 ANGLE5 ANGLE6
M M1 M2 M3 M4 M5 M6

## Example 1

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PBUSH 35 K 4.35 2.4 RIGID     3.1
GE 0.02

## Example 2

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PBUSH 35 B 4.35
M 1.2   7.1

## Example 3

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
PBUSH 35 KMAG 3944.0
ANGLE 15.0

## Definitions

Field Contents SI Unit Example
PID Unique property identification.
Integer
Specifies an identification number for this property.
<String>
Specifies a user-defined string label for this property. 2

No default (Integer > 0 or <String>)

K Flag indicating that the next 1 to 6 fields are stiffness values.

No default (Character)

Ki Nominal stiffness values in directions 1 through 6. 4 6 8

If RIGID is defined, a very high relative stiffness is selected for that degree-of-freedom simulating a rigid connection. The rigid element formulation can be controlled using SYSSETTING(PBUSHFOR).

Default = 0.0 (Real or RIGID)

KMAG Flag indicating that the next 1 to 6 fields are stiffness magnitude (K*) values. 4

No default (Character)

KMAGi Nominal stiffness magnitude (K*) values in directions 1 through 6. 4 6 8 9

Default = 0.0 (Real)

B Flag indicating that the next 1 to 6 fields are force-per-velocity damping.

No default (Character)

Bi Nominal damping coefficients in directions 1 through 6 in units of force per unit velocity.

Default = 0.0 (Real)

GE Flag indicating that the next 1 to 6 fields are the structural damping constants.

No default (Character)

GEi Nominal structural damping constants in directions 1 through 6.

GEi is ignored in transient analysis, if PARAM, W4 is not specified. 4 6

Default = 0.0 (Real)

M Flag indicating that the next 1 to 6 fields are directional masses.
Mi Nominal mass values in directions 1 through 6.
In case of implicit analysis: 10
M1
For translational mass calculation.
Default = 0.0 (Real)
M2, M3
If defined, they must be same as M1.
Default = blank (Real)
M4, M5, M6
For inertia calculation.
In this case, Inertia = max. (M4, M5, M6).
Default = blank (Real)
In case of explicit analysis:
M1
Required for translational mass calculation.
No default (Real)
M2, M3
If defined, they must be same as M1.
Default = blank (Real)
M4
For inertia calculation.
For zero length CBUSH elements:
M4
Required. No default (Real)
For non-zero length CBUSH elements:
M4
Optional. Default = blank (Real)
M5, M6
These are currently ignored.
Default = blank (Real)

ANGLE Flag indicating that the next 1 to 6 fields are Loss angles defined in degrees. 9

No default (Character)

ANGLEi Nominal angle values in directions 1 through 6 in degrees. 4 6 8 9

1. All generalized spring-damper-mass property entries must have unique ID numbers.
2. String based labels allow for easier visual identification of properties, including when being referenced by other cards. (For example, the PID field of elements). For more details, refer to String Label Based Input File in the Bulk Data Input File.
3. The K, B, GE, and M lines may be specified in any order.
4. Ki, KMAGiBi, GEi, ANGLEi or Mi may be made frequency dependent for both direct and modal frequency response by use of the PBUSHT entry.

The nominal values are used for all analysis types except frequency response. For modal frequency response, the normal modes are computed using the nominal stiffness and mass values. The frequency-dependent values are used at every excitation frequency.

5. To obtain the damping coefficient GE, multiply the critical damping ratio $C/{C}_{0}$ by 2.0.
6. For backward compatibility with Nastran, if ONLY GE1 is specified on a PBUSH entry and GEi, i = 2 to 6 are blank on that PBUSH entry, then a single structural damping is assumed and applied to all Ki of that PBUSH. If a PBUSH entry has a GEi, i = 2 to 6 specified (even as 0.0), then the GEi fields are considered variable for that PBUSH entry.
7. The nominal property values specified on the PBUSH entry are used on the corresponding fields (that are blank) of the PBUSHT entry.
8. Rotational stiffness values are input based on rotations defined in Radians.
9. If PBUSH has KMAG and ANGLE, the calculation for stiffness (K) and damping (GE) are: (1)
$K=kmag\cdot \mathrm{cos}\left(angle\right)$
(2)
$GE=\mathrm{tan}·\left(angle\right)$
Where,
$km$
Magnitude of the stiffness
$angle$
Loss angle

KMAG and ANGLE types are alternative types to K and GE. Specifying KMAG and ANGLE along with K and/or GE will generate an OptiStruct error.

10. The contribution of Mi fields to gravity and/or centrifugal loading are not included in case of implicit analysis.
11. This card is represented as a property in HyperMesh.