Index

Giesekus model

Ver: 1
 

DESCRIPTION

For the Giesekus model, the extra-stress tensor T can be written as
  T = T1 + T2


where T1 and T2 are tensors which obey the the following constitutive equations :
 

[ I + alpha * trelax / visc1 * T1 ] * T1 + trelax * T1up = 2 * visc1 * D T2 = 2 * visc2 * D


Here, D is the symmetric part of the velocity gradient tensor, trelax is the relaxation time,
visc1 and visc2 are partial shear viscosities, alpha is a material constant, and the subscript "up"
denotes the upper-convected derivative operator.
 

visc1 = (1-ratio)*visc
visc2 = ratio*visc


The parameter ratio of the Newtonian viscosity to the total shear viscosity is defined by:
 

ratio = visc2 / ( visc1 + visc2 )


The default values of trelax and visc are both unity; the default values of alpha and ratio are zero.

Selecting an option allows the user to modify the corresponding material parameter.

  OPTIONS
 
 -1
   Upper level menu
  1
   Modification of visc
  2
   Modification of trelax
  3
   Modification of alpha
  4
   Modification of ratio
NOTES A large relaxation time leads to strong non-linearities. The use of a non-linear strategy is recommended
for increasing this parameter : the current task should, therefore, be of the pseudo-evolution type.

The user should be aware of the system of units, if dimensional values are used.

The units for the marerial parameters, as well as for T and D are :
 
parameter
mass
length
time
temperature
trelax
-
-
 1
 -
visc
1
-1
-1
 -
ratio
-
-
-
 -
alpha
-
-
-
 -
T
1
-1
-2
 -
D
-
-
-1
 -

SEE ALSO