# RFORCE

Bulk Data Entry Defines a static loading condition due to a centrifugal force field. It can also be used to define the EXCITEID field (Amplitude "A") of dynamic loads in RLOAD1, RLOAD2 , TLOAD1 and TLOAD2 Bulk Data Entries.

## Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
RFORCE SID G CID A R1 R2 R3
RACC MB IDRF

## Example

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
RFORCE 2 5   0.0 0.0 1.0 2.2
1.0

## Definitions

Field Contents SI Unit Example

No default (Integer > 0)

G Grid point identification number through which the rotation vector acts.
= 0 or blank
Origin of the basic coordinate system.

Default = 0 (Integer ≥ 0)

CID Coordinate system defining the components of the rotation vector.
= 0 or blank
The rotation vector acts at the origin of the basic coordinate system.
Integer
Specifies an identification number for this coordnate system.
<String>
Specifies a user-defined string label for this coordinate system. 6

Default = 0 (Integer ≥ 0 or <String>)

A Scale factor of the rotational velocity in revolutions per unit time.

Default = 0.0 (Real)

R1,R2,R3 Rectangular components of rotation direction vector. The vector defined will pass through point G.

No default (Real; R12 + R22 + R32 > 0.0)

RACC Scale factor of the rotational acceleration in revolutions per unit time squared. The continuation line containing RACC is optional.

(Real)

MB Specifies the Bulk Data section in which CID is defined.
This entry is applicable only for partitioned superelements. 7
-1
The coordinate system is defined in the main Bulk Data section.
0 (Default)
The coordinate system is defined in the Bulk Data section of the partitioned superelement.

(Integer ≥ -1)

IDRF Set identification number of an element set (SET Bulk Data Entry) to which this RFORCE entry applies. This field can be used to define different rotational forces to different parts of the model.

1. The rotational forces that are created with an RFORCE entry for a constant angular velocity ($\stackrel{\to }{\omega }$ ), act in the positive radial direction. They represent the initial forces on the structure due to a constant angular velocity. The rotational forces defined for a constant angular acceleration (RACC), act in the same direction as the angular acceleration. They would be opposite to the inertia forces on the structure due to a constant angular acceleration. The following plot shows that the RFORCE vector at node Gi is given by:(1)
${\left\{\stackrel{\to }{F}\right\}}_{i}={\left[m\right]}_{i}\left[\stackrel{\to }{\omega }×\left(\stackrel{\to }{\omega }×\left(\stackrel{\to }{{r}_{i}}-\stackrel{\to }{{r}_{a}}\right)\right)+\stackrel{\to }{\alpha }×\left(\stackrel{\to }{{r}_{i}}-\stackrel{\to }{{r}_{a}}\right)\right]$
Where,
angular velocity
= $\stackrel{\to }{\omega }\left(\text{radians}/\text{unit} \text{time}\right)=2\pi A\cdot \stackrel{\to }{R}$
angular acceleration
= $\stackrel{\to }{\alpha }\left(\text{radians}/\text{unit} \text{time} \text{squared}\right)=2\pi \mathit{RACC}\cdot \stackrel{\to }{R}$
2. The RFORCE load is selected for use in a subcase by the Subcase Information Entry LOAD.
3. The load vector generated by this entry can be printed using the I/O Option OLOAD.
4. For CONM1 and CONM2 entries, OptiStruct calculates the torque, due to rotation, as:(2)
$T=I\alpha -\omega ×\left(I\omega \right)$

Where, $I$ is the moment of inertia.

5. For mass penalization information when RFORCE is used in a Topology optimization, see Design Variables for Topology Optimization in the User Guide.
6. String based labels allow for easier visual identification, including when being referenced by other entries. For more details, refer to String Label Based Input File.
7. In the context of partitioned superelements, the coordinate systems in the main Bulk Data section are defined with respect to the assembly basic coordinate system, which is fixed. This feature is useful when loading needs to be defined in a fixed coordinate system, irrespective of the orientation of the superelement, defined by a partitioned Bulk Data section.
8. This card is represented as a load collector in HyperMesh.