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Moving Spring

The MovingSpring element simulates a moving spring (a combination of spring and damper) rolling on a line or surface defined by beam elements.

Fig. 4.12-1 MovingSpring Element on a Line Composed of Beams

Fig. 4.12-1. MovingSpring Element on a Line Composed of Beams

Fig. 4.12-2 MovingSpring Element on a 3D Surface

Fig. 4.12-2. MovingSpring Element on a 3D Surface

Fig. 4.12-3 MovingSpring Element on a 2D Surface

Fig. 4.12-3. MovingSpring Element on a 2D Surface

▪ Notes

  • When performing dynamic analysis, a preliminary static analysis considering self-weight must be conducted first.
  • To activate the MovingSpring element, the speed must be defined using *Field, Type=MovingSpringSpeed.
  • If damping is considered, the overall stiffness matrix will become an asymmetric matrix.
Example
*ELSET, Name=rail
 Beam

*SECTION, TYPE=PointMass, Name=PM
 5750

*SECTION, TYPE=MovingSpring, Name=MS
 Ky=1595E3 Cy=1000E3 # R=1.,2.,3.
 Line=rail  

*Element, TYPE=PointMass, ELSET=PM
 1000 1000, S=PM 

*Element, TYPE=MovingSpring, ELSET=MS
 1001 1000, S=MS

*Distribution, TYPE=MovingSpringInitialPosition
 1001, 0.0

*Load, TYPE=Gravity, Name=SelfWeight
 1000,0,-9.81, 0.

*STEP, TYPE=Static Name=S
*Activate, TYPE=Element
 Beam, PM, MS
*Activate, TYPE=Constraint
 BC
*Activate, TYPE=Load
 SelfWeight

*STEP, TYPE=Dynamic Name=Dyn, Prev=S
 EquiTime=0.02,2.
*Field, Type=MovingSpringSpeed
 MS, 27.78

*Element, Type=MovingSpring

*Element, Type=MovingSpring, ELSet=elset
 id, n1{, S=section, P=x,y}
 ...
First dataline and subsequent datalines
  • P=x,y: Initial position relative to the reference point. Defined in the ECS. When targeting beam elements, the y value is ignored.
Specifications
  • No. of nodes: 1
  • No. of integration points: 1
  • Fields: SF=[...], SE=[...], DF=[...], DE=[...] at the element center.
  • Compatible section: MovingSpring
  • Active DOFs: Can include Y and Z depending on the definition.

Refer to *Element, TYPE=Spring for explanations of SF, SE, DF, and DE.

*Section, Type=MovingSpring

Defines the properties for a MovingSpring.

*Section, Type=MovingSpring, Name=name 
  surface, refx, refy, refz, g1x, g1y, g1z, xRigid, yRigid, zRigid
  oneDof, k,kmat, c, cmat    # oneDof = Y, Z
  ...

*Section, Type=MovingSpring, Name=name
  line, xRigid, yRigid, zRigid
  oneDof, k,kmat, c, cmat    # oneDof = Y, Z
  ...
First dataline for Line
  • line: Target beam elset ... The beams should be connected.
  • xRigid, yRigid, zRigid: Position vector from the reference node (rigid arm vector). x1 is required, others are optional.
First dataline for Surface
  • surface: Target surface (required).
  • refx, refy, refz: Reference point (optional, default is 0, 0, 0).
  • g1x, g1y, g1z: Direction of travel (1, 0, 0).
  • xRigid, yRigid, zRigid: Position vector from the reference node (rigid arm vector) (optional, default is 0, 0, 0).
Second dataline
  • oneDof: Degree of freedom to which the spring/damper is applied, either Y or Z.
  • k, km: Spring coefficient and model for the specified degree of freedom; km is optional.
  • c, cm: Damping coefficient and model for the specified degree of freedom; cm is optional.
Third dataline if necessary
  • oneDof: Degree of freedom to which the spring/damper is applied, either Y or Z.
  • k, km: Spring coefficient and model for the specified degree of freedom; km is optional.
  • c, cm: Damping coefficient and model for the specified degree of freedom; cm is optional.