/PROP/TYPE33 (KJOINT)

Block Format Keyword Describes the joint type spring.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/PROP/TYPE33/prop_ID/unit_ID or /PROP/KJOINT/prop_ID/unit_ID
prop_title
Type Skflag                
skew_ID1 skew_ID2 Xk Cr        
Spherical Joint (Type 1)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Krx Kry Krz    
fct_IDXR fct_IDYR fct_IDZR              
Crx Cry Crz        
fct_IDXRC fct_IDYRC fct_IDZRC              
Revolute Joint (Type 2)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Krx fct_IDXR          
Crx fct_IDXRC              
Cylindrical Joint (Type 3)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Ktx Krx fct_IDXT fct_IDXR    
Ctx Crx fct_IDXTC fct_IDXRC        
Planar Joint (Type 4)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Kty Ktz fct_IDYT fct_IDZT    
Krx fct_IDXR              
Cty Ctz Crx        
fct_IDYTC fct_IDZTC fct_IDXRC              
Universal Joint (Type 5)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Kry Krz fct_IDYR fct_IDZR    
Cry Crz fct_IDYRC fct_IDZRC        
Translational Joint (Type 6)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Ktx fct_IDXT          
Ctx fct_IDXTC              
Oldham Joint (Type 7)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn Kty Ktz fct_IDYT fct_IDZT    
Cty Ctz fct_IDYTC fct_IDZTC        
Rigid Joint (Type 8)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Kn                
Free Joint (Type 9)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Ktx Kty Ktz        
Krx Kry Krz        
fct_IDXT fct_IDYT fct_IDZT              
fct_IDXR fct_IDYR fct_IDZR              
Ctx Cty Ctz        
Crx Cry Crz        
fct_IDXTC fct_IDYTC fct_IDZTC              
fct_IDXRC fct_IDYRC fct_IDZRC              

Definitions

Field Contents SI Unit Example
prop_ID Property identifier

(Integer, maximum 10 digits)

 
unit_ID Unit Identifier

(Integer, maximum 10 digits)

 
prop_title Property title

(Character, maximum 100 characters)

 
Type Joint type.
= 1
Spherical joint
= 2
Revolute joint
= 3
Cylindrical joint
= 4
Planar joint
= 5
Universal joint
= 6
Translational joint
= 7
Oldham joint (planar without rotation DOF)
= 8
Fixed (rigid) joint
= 9
Free joint

(Integer)

 
Skflag Skew frame selection. 10
= 0 (Default)
Joint is defined in a mean skew frame.
= 1
Joint is defined in the first body skew frame.

(Integer)

 
skew_ID1 First skew system identifier.

(Integer)

 
skew_ID2 Second skew system identifier.

(Integer)

 
Xk Stiffness for interface.

(Real)

[ N m ]
Cr Critical damping factor.

Default = 0.0 (Real)

 
Kn Stiffness for blocked DOF.

(Real)

[ N m ]
Krx X rotational stiffness coefficient. 12

Default = 1.0 (Real)

[ Nm rad ]
Kry Y rotational stiffness coefficient. 12

Default = 1.0 (Real)

[ Nm rad ]
Krz Z rotational stiffness coefficient . 12

Default = 1.0 (Real)

[ Nm rad ]
fct_IDXR X rotational stiffness function

(Integer)

 
fct_IDYR Y rotational stiffness function.

(Integer)

 
fct_IDZR Z rotational stiffness function.

(Integer)

 
Crx X rotational viscosity coefficient. 13

Default = 1.0 (Real)

[ Nms rad ]
Cry Y rotational viscosity coefficient. 13

Default = 1.0 (Real)

[ Nms rad ]
Crz Z rotational viscosity coefficient. 13

Default = 1.0 (Real)

[ Nms rad ]
fct_IDXRC X rotational viscosity function.

(Integer)

 
fct_IDYRC Y rotational viscosity function.

(Integer)

 
fct_IDZRC Z rotational viscosity function.

(Integer)

 
fct_IDXT X translational stiffness function.

(Integer)

 
fct_IDYT Y translational stiffness function.

(Integer)

 
fct_IDZT Z translational stiffness function.

(Integer)

 
Ktx X translational stiffness coefficient. 12

Default = 1.0 (Real)

[ N m ]
Kty Y translational stiffness coefficient. 12

Default = 1.0 (Real)

[ N m ]
Ktz Z translational stiffness coefficient. 12

Default = 1.0 (Real)

[ N m ]
Ctx X translational viscosity coefficient. 13

Default = 1.0 (Real)

[ Ns m ]
Cty Y translational viscosity coefficient. 13

Default = 1.0 (Real)

[ Ns m ]
Ctz Z translational viscosity coefficient. 13

Default = 1.0 (Real)

[ Ns m ]
fct_IDXTC X translational viscosity function

(Integer)

 
fct_IDYTC Y translational viscosity function

(Integer)

 
fct_IDZTC Z translational viscosity function

(Integer)

 

Comments

  1. Joints are defined by a spring and two local coordinate axes, which belong to connected bodies. Assume that the connected bodies are rigid to ensure the orthogonality of their local axes. Yet, deformable bodies may be connected with a joint, but a warning will be displayed by Radioss in this case; moreover if the axis becomes non-orthogonal during deformation, the stability of the joint cannot be insured.
  2. Joint properties are defined in a local frame computed with respect to two connected coordinate systems. They do not need to be initially coincident. If the initial position of the local coordinate axis coincides at any time, the joint local frames are defined at a mean position. If the local axes' are not initially coincident, they are first transformed into a mean position between the initial state. Then the joint local frame will be computed with respect to these rotated axes.
  3. Total number of joint DOF's computed in the local skew frame is six:
    δ X , δ Y , δ Z , θ X , θ Y , θ Z

    clip0095
    Figure 1.
  4. Blocked and free DOFs are distinguished for each joint type.
  5. The blocked DOFs are characterized by a constant stiffness.
  6. Selecting a high value with respect to the free DOF stiffness is recommended. The free DOF have user-defined characteristics, which can be linear or nonlinear elastic, combined with a sub-critical viscous damping.
  7. The translational and rotational DOF are defined as:
    (1)
    δ = d x 2 d x 1
    Where d x 1 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGKbGaamiEamaaBaaaleaacaaIXaaabeaaaaa@3BA4@ and d x 2 MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWGKbGaamiEamaaBaaaleaacaaIXaaabeaaaaa@3BA4@ are total displacements of two joint nodes in the local coordinate system.(2)
    θ = θ 2 θ 1

    Where θ 1 and θ 2 are total relative rotations of two connected body axes, with respect to the local joint coordinate frame.

  8. Forces and moments calculation:
    • The force in direction δ is computed as:
      Linear spring:(3)
      F = K t δ + C t δ ˙

      Κ t MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWHAoWaaSbaaSqaaiaadshaaeqaaaaa@3B22@ : translational stiffness ( K t x , K t y , K t z )

      C t MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWHdbWaaSbaaSqaaiaadshaaeqaaaaa@3AC8@ : translational viscosity ( C t x , C t y , C t z )

      Nonlinear spring:(4)
      F = K t f ( δ ) + C t g ( δ ˙ )
    • The moment in θ direction is computed as:
      Linear spring:(5)
      M = K r θ + C r θ ˙

      Κ r MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWHAoWaaSbaaSqaaiaadshaaeqaaaaa@3B22@ : rotational stiffness (Krx, Kry, and Krz)

      C r MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKf MBHbqefqvATv2CG4uz3bIuV1wyUbqedmvETj2BSbqefm0B1jxALjhi ov2DaebbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8 qqaqFr0xc9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9 q8qqQ8frFve9Fve9Ff0dmeaacaGacmGadaWaaiqacaabaiaafaaake aacaWHdbWaaSbaaSqaaiaadshaaeqaaaaa@3AC8@ : rotational viscosity (Crx, Cry, and Crz)

      Nonlinear spring:(6)
      M = K r f ( θ ) + C r g ( θ ˙ )
    • The joint length may be, but is not necessarily equal to 0. It is recommended; however, to use a 0 length spring to define a spherical joint or an universal joint.
    • To satisfy the global balance of moments in a general case, correction terms in the rotational DOF are calculated as:(7)
      M θ x = M θ x + L y × F z L z × F y
      (8)
      M θ y = M θ y + L z × F x L x × F z
      (9)
      M θ z = M θ z + L x × F y L y × F x
  9. Available joint types:
    Table 1. Available Joints
    Type No. Joint Type dx dy dz θ X θ Y θ Z
    1 Spherical x x x 0 0 0
    2 Revolute x x x 0 x x
    3 Cylindrical 0 x x 0 x x
    4 Planar x 0 0 0 x x
    5 Universal (development source only) x x x x 0 0
    6 Translational 0 x x x x x
    7 Oldham x 0 0 x x x
    8 Rigid x x x x x x
    9 Free 0 0 0 0 0 0

    Where:

    x: denotes a blocked DOF

    0: denotes a free (user-defined) DOF:
    • Joints do not have user-defined mass or inertia, so the nodal time step is always used.
    • There are two ways to introduce viscous damping:
    1. Defining a critical damping (for blocked DOF only):

      Viscous damping is defined in terms of the critical damping factor. The critical damping coefficient is calculated using the blocking stiffness value of the element. The mass and inertia are equal to half of the values of each rigid body connected to the joint. The approximation is then satisfactory, if only one joint is connected to each rigid body. Otherwise, the critical damping is over-estimated, in which case the damping factor in the Radioss input should be decreased. The same damping is applied to all blocked DOF.

    2. User-defined constant or nonlinear damping:

      It is possible to define independent damping parameters for each free DOF.

  10. If Skflag = 1, the joint local frame is chosen as the local coordinate system of the first connected body. In this case, a mean skew position is not calculated. However, the second local coordinate system must still be defined.
  11. For a universal joint, this option is not active, and both skew axes are always used to calculate the local joint frame.
  12. Coefficients Krx, Kry, Krz, Ktx, Kty, and Ktz are used for linear joint if there are no user-defined functions. If a function number in any DOF is not 0, the corresponding stiffness coefficient becomes a scale factor for the function. This rule is applied to any DOF of all joint types.
  13. Coefficients Crx, Cry, Crz, Ctx, Cty, and Ctz are used as linear viscosity coefficients if there are no user-defined functions. If a function number in any DOF is not 0, the corresponding coefficient becomes a scale factor for the function.
  14. The universal joint length must be equal to 0, in the initial state. The universal joint local skew system is defined as:

    Y local axis = X-axis of the first body local skew system

    Z local axis = X-axis of the second body local skew system

    X local axis = YΛ Z

  15. This local frame must be initially orthogonal. The X-axis of two defining body skew axes must; therefore, be orthogonal in the initial position. The joint local frame can further become non-orthogonal due to deformation. The forces and moments are then computed in this non-orthogonal frame.
  16. Each /PROP/KJOINT uses a unique definition of local coordinate system; therefore, one property can refer to only one spring element.