UNBALNC

Bulk Data Entry

UNBALNC – Unbalanced Load (Rotor Dynamics)

Description

This entry defines the unbalanced rotating load during a rotor dynamic analysis in Frequency Response 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	FON	FOFF

(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

Argument	Options					Description
SID	<Integer > 0> No default			setid		Set identification number.

MASS	<Integer > 0/Real> No default			Defines the magnitude of unbalanced mass (see comment 4).

GRID	<Integer> No default			Grid Point identification number of node at which the unbalanced load is applied.

X1, X2, X3	<Real> No default			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” (see comment 6).

ROFFSET	<Integer > 0/Real> Default = 1.0	<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 (see comment 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.

THETA	<Real> Default = 0.0	Angular position (in degrees) of the unbalanced mass in the cylindrical coordinate system defined by X1, X2, and X3.

ZOFFSET	<Integer > 0/Real> Default = 0.0	<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 (see comment 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.

FON	<Real > 0> Default = 0.0	This field defines the starting frequency at which the unbalanced load is applied (see comment 5).

FOFF	<Real > 0> Default = 999999.0		This field defines the stopping (final) frequency at which the unbalanced load is applied (see comment 5).

Comments

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.

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).

unbalnc

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.

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.