UNBALNC

Bulk Data Entry Defines the unbalanced rotating load during a rotor dynamic analysis in Modal Frequency Response, Linear Direct Transient or Small Displacement Nonlinear Direct Transient solution sequences. The unbalanced load is specified in a cylindrical system where the rotor rotation axis is the Z-axis.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
UNBALNC SID MASS GRID X1 X2 X3
ROFFSET THETA ZOFFSET T/FON T/FOFF

Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
UNBALNC 200 1.2 3103 1.0 0.0 0.0
0.3 45.0 0.1 2 110

Definitions

Field Contents SI Unit Example
SID
setid
Set identification number.

No default < Integer > 0>

MASS Defines the magnitude of unbalanced mass. 4

No default <Integer > 0/Real>

GRID Grid Point identification number of node at which the unbalanced load is applied.

No default <Integer>

X1, X2, X3 Components of a vector that are used to define a cylindrical coordinate system centered at "GRID". The vector components are defined from "GRID" in the displacement coordinate system of the grid point at "GRID". 6

No default <Real>

ROFFSET
<Integer > 0>
If an integer value (must be greater than 0) is input, it references the identification number of a TABLEDi entry that specifies the offset values as a function of frequency. 4
<Real>
This field defines the distance by which the unbalanced mass is offset in the X-Y plane perpendicular to the Z direction (spin axis, Figure 1).

If a real number is input, the offset value is considered constant.

Default = 1.0 <Integer > 0/Real>

THETA Angular position (in degrees) of the unbalanced mass in the cylindrical coordinate system defined by X1, X2, and X3.

Default = 0.0 <Real>

ZOFFSET
<Integer > 0>
If an integer value (must be greater than 0) is input, it references the identification number of a TABLEDi entry that specifies the offset values as a function of time/frequency. 4
<Real>
This field defines the distance by which the unbalanced mass is offset in the Z direction (spin axis, Figure 1).

If a real number is input, the offset value is considered constant.

Default = 0.0 <Integer > 0/Real>

T/FON Defines the starting time/frequency at which the unbalanced load is applied. 5

Default = 0.0 <Real ≥ 0>

T/FOFF Defines the stopping (final) time/frequency at which the unbalanced load is applied. 5

Default = 999999.0 <Real ≥ 0>

1. Currently, models containing multiple UNBALNC Bulk Data Entries with the same set identification number (SID) are not supported. Each UNBALNC Bulk Data Entry must have a unique SID.
2. For frequency response analysis, the UNBALNC Bulk Data Entry is referenced by a DLOAD Subcase Information Entry. For transient analysis, the UNBALNC Bulk Data Entry can either be referenced by a DLOAD or RGYRO Subcase Information Entry.
3. An unbalanced load on the rotating system is generated as a consequence of these three factors:
• Unbalanced mass of the system (rotor) about its axis of rotation (MASS field on the UNBALNC entry).
• The magnitude of separation between the rotating axis and the unbalanced mass (ZOFFSET and ROFFSET fields on the UNBALNC entry).
• The angular spin speed of the rotor (specific fields on the RGYRO and RSPINR Bulk Data Entries).
4. ROFFSET field:
• Each entry in the TABLEDi entry specifies the distance by which the unbalanced mass is offset in the X-Y plane (perpendicular to the axis of rotation of the rotor).
ZOFFSET field:
• Each entry in the TABLEDi entry specifies the distance by which the unbalanced mass is offset in the Z direction (axis of rotation of the rotor).
5. The rotation of the unbalanced load occurs in the positive Z direction which is defined by GRIDA and GRIDB on the RSPINR Bulk Data Entry.
6. The initial position of the unbalanced mass and the direction of its subsequent rotation are defined with respect to a cylindrical coordinate system. Its angular position is measured from the plane defined by both the Z-axis and the vector (X1, X2, and X3) with THETA=0.0 being the direction of the vector (X1, X2, and X3) itself. The rotation of the unbalanced load occurs in the positive Z direction.
7. For frequency response, the UNBALNC load can only be used for a synchronous analysis. This is because in asynchronous whirl, the loading frequency is different from the rotor speed, and the latter is the frequency of the unbalance load vector.