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*FLEXJOINT

Data format:

An arbitrary number of lines with 7 values each, as follows:

NEL JO JE IPRO IMAT LENGTH IPROT
...

Purpose :

To define flexible joint elements.

Restriction :

The nodes JO and JE must have been previously defined.

Details :

Parameter Description
NEL Identification number of the flexible joint element
JO Origin node of the flexible joint element
JE End node of the flexible joint element
IPRO Index in the table of elementary mechanical and geometrical properties (previously defined by keyword *SPRINGPRO)
IMAT Index in the table of material mechanical properties previously defined by keyword *FLEXPROADD
LENGTH Reference initial length (not used)
IPROT Torsional property index in the table of elementary mechanical and geometrical properties (previously defined by keyword *SPRINGPRO)

Note

To define a classical flexjoint:

*FLEXJOINT NEL JO JE IPRO IMAT 0

In that case, the stiffness is applied on the total moment (bending + torsion) on the flexjoint. The law is multi-linear (linear if only two couples in *SPRINGPRO)

To define a flexjoint with separate bending and torsion stiffness :

*FLEXJOINT NEL JO JE IPRO IMAT 0 IPROT

The stiffness on the bending is applied thru *SPRINGPRO properties IPRO and the stiffness on torsion is applied thru stiffness on IPROT.

FOR all other options, it is considered that bending and torsion are decoupled :

  1. *FLEXPROADD must be used
  2. IPROT (7th parameter of *FLEXJOINT) must be non zero
  3. Ktorsion , the second parameter of FLEXPROADD is not used anymore. The torsion stiffness must be entered thru a SPRINGPRO property.

Therefore for all other options, IMAT is non zero and IPROT is non zero in FLEXJOINT. The FLEXPROADD properties is used to

  1. Define a non linear law in bending only
  2. Define a damping coefficient in torsion
  3. Define a bending coefficient in bending

All these options are independent.

Example 1 : Simple multi-linear law

*SPRINGPRO
C --- Bending stiffness
3 2 0 0 0.0174533 1e+009
*FLEXJOINT
3 1 3 3 0 0.

The element 3 is a flex-joint connecting node 1 to node 3 with mechanical properties given by the index 3 of *SPRINGPRO.

This element refers to no material index, consequently the torsion mode is not distinguished from the bending mode and the behaviour law is defined by the curve defined in SPRINGPRO.

Example 2 : Multi-linear law in Quasi-static associated with a non-linear law in dynamic

*SPRINGPRO
C --- Bending stiffness
    3 3 0 0 0.00872665 25000 0.0174533 35000
*FLEXPROADD
c IMAT Ktor IFLAG Kdyn_ini Kdyn_Lim Angle_lim Teta CP
c       Nm/rad       Nm/rad       Nm/rad       rad       Nm/rad
2 5.72958e8 1 4.0107e6 1.718873e6 1.74533e-3 0 3.008e6
*FLEXJOINT
3 1 3 3 2 0.

The element 3 is a flex-joint connecting node 1 to node 3 with mechanical properties given by the index 3 of *SPRINGPRO. This element also refers to the material index 2.

Consequently : The torsion mode is distinguished from the bending mode and torsion stifness is 5.72958e8 Nm/rad

In quasi-static, the flexjoint follows a multi-linear law defined in SPRINGPRO by 3 couples (angle,Moment);

In dynamic, the flexjoint follows a non-linear law defined in *FLEXPROADD : - Initial stiffness of 4.0107e6 Nm/rad (i.e. 70 kN :deg) - Asymptotic stiffness of 1.718873e6 Nm/rad (i.e. 30kN/deg), - The critical agnle variation is 1.73533e-3 rad (i.e. 0.1 deg), - The elasto-plasticiy law is bi-linear.

Example 3 : Non-linear law both in quasi-static and dynamic

*FLEXPROADD
c IMAT Ktor IFLAG Kdyn_ini Kdyn_Lim Angle_lim Teta CP
c Nm/rad Nm/rad Nm/rad rad Nm/rad
2 5.72958e8 1 4.0107e6 1.718873e6 1.74533e-3 0 3.008e6
*FLEXJOINT
3 1 3 0 2 0.

The element 3 is a flex-joint connecting node 1 to node 3 with no mechanical properties and a material index by in *FLEXPROADD.

Consequently : The torsion mode is distinguished from the bending mode and torsion stiffness is 5.72958e8 Nm/rad

In quasi-static and dynamic , the flexjoint stiffness follows a non-linear law as such : - Initial stiffness of 4.0107e6 Nm/rad (i.e. 70 kN :deg) - Asymptotic stiffness of 1.718873e6 Nm/rad (i.e. 30kN/deg), - The critical angle variation is 1.73533e-3 rad (i.e. 0.1 deg), - The elasto-plasticiy law is bi-linear.