VUFLUIDEXCHEFFAREA

User subroutine to define the effective area for fluid exchange.

can be used to define an effective area for fluid exchange that depends on the material state in the underlying elements on the fluid exchange surface;
will be called for blocks of material calculation points on the fluid exchange surface;
can be used only if the specified surface over which the fluid exchange occurs is a surface defined over membrane elements; and
can be used with any fluid exchange property type.

The following topics are discussed:

Defining effective area
User subroutine interface
Variables to be defined
Variables passed in for information

Defining effective area

The contribution of each material point can be defined as a function of:

the original area associated with the material point;
the current material state in the underlying elements; and
the temperature and pressure in the primary fluid cavity and the secondary fluid cavity or environment.

The effective area for fabric materials can depend on the nominal strain in the yarn directions and the change in angle between the two yarn directions, as well as the current angle between the two yarn directions. For nonfabric materials the effective area can depend on the material point strain.

User subroutine interface

      subroutine vufluidexcheffarea(
C Read only (unmodifiable) variables -
     1     nblock, nprop, props,
     2     stepTime, totalTime, fluExchName,
     3     cMatName, lFabric, braidAngle,
     4     strain, origArea, 
     5     pcav, ctemp,
C Write only (modifiable) variables 
     6     effArea)
c
      include 'vaba_param.inc'
c
      parameter (ndir = 3, nshr=1)
c
c     pointers for retrieving fabric constitutive strains
      parameter( iFiberStrain1    = 1,
     *           iFiberStrain2    = 2,
     *           iFiberChangeAng  = 4)
c     
      dimension props(nprop), 
     1     braidAngle(nblock),
     2     strain(nblock, ndir+nshr), 
     3     origArea(nblock),
     4     pcav(2),ctemp(2),
     5     effArea(nblock)

      character*80 fluExchName, cMatName

c      do k = 1, nblock
c	      User coding to update effArea(k) = area associated with 
c	      material point contributing to area for fluid exchange
c	      (leakage).
c      end do
      
      return
      end

Variables to be defined

effArea(nblock): Area associated with the material point contributing to the total effective area for fluid exchange. The subroutine is called with effArea set to the current area associated with the material point and should be updated to reflect the area that contributes to fluid exchange.

Variables passed in for information

nBlock: Number of material points to be processed in this call to VUFLUIDEXCHEFFAREA.
nprop: User-specified number of user-defined fluid exchange properties required to define the effective area.
props(nprop): User-defined fluid exchange properties.
stepTime: Value of time since the step began.
totalTime: Value of total time. The time at the beginning of the step is given by totalTime−stepTime.
fluExchName: User-specified fluid exchange name.
cMatName: User-specified material name associated with material points processed in this call.
lFabric: Flag indicating whether the subroutine is called for material points on the fluid exchange surface with a fabric material (lFabric=1 if fabric material, lFabric=0 otherwise).
braidAngle(nblock): Angle in radians between the two yarn directions for fabric materials.
strain(nblock, ndir+nshr): Fabric constitutive strains (nominal strain in the yarn directions and change in angle between the two yarn directions) or strains for nonfabric materials at current location.
origArea(nblock): Original area associated with current material point.
pcav(2): Absolute pressure in primary and secondary (or ambient) fluid cavities at the start of the increment.
ctemp(2): Temperature in primary and secondary (or ambient) fluid cavities at the start of the increment.