Change of coefficient of thermal expansion does not change evaluated stresses

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  • Last Post 13 March 2020
fischr posted this 13 March 2020

Hello,

I am trying to simulate a simplified diaphragm seal system. I used a command block to insert HSFLD242 Elements to model a fluid that is fully enclosed by solids (containing vessels) in a static structural simulation at 400°C. for some reason the coefficient of thermal expansion for the fluid is not taken into account during the simulation .

This is the command snippet i used to model the fluid:

fini
/prep7
*get,typemax,ETYP,,NUM,MAX    ! max defined element type
*get,realmax,RCON,,NUM,MAX    ! max defined real constant
*get,mat_max,MAT,,NUM,MAX     ! max defined material
*get,nodemax,NODE,,NUM,MAX    ! highest numbered node in model
                   ! Create a new higher number for element type, real, and material
newnode=nodemax+1000          ! number for pressure node for HSFLD242
newnumber=typemax+1
*if,realmax,ge,newnumber,then
   newnumber=realmax+1
*endif
*if,mat_max,ge,newnumber,then
   newnumber=mat_max+1
*endif
et,newnumber,HSFLD242         ! 3-D Hydrostatic Fluid Element
keyopt,newnumber,1,0          ! UX, UY, UZ, plus HDSP at pressure node
keyopt,newnumber,5,1          ! Fluid mass calculated based on the volume of the fluid element
keyopt,newnumber,6,1          ! incompressible

tb,fluid,newnumber,2,,,liquid ! Liquid Properties
tbtemp,20.0
tbdata,1,1800,9.71e-4,9.36e-7 !Bulk modulus,coefficient of thermal expansion,density
tbtemp,400.0
tbdata,1,2000,1.86e-3,5.48e-7 !Bulk modulus,coefficient of thermal expansion,density                             
r,newnumber                 
type,newnumber
mat,newnumber
real,newnumber

cmsel,s,bro                   ! Select nodes on interior
esln                          ! Select elements that touch these nodes
n,newnode,0,0,7.2          ! newnode as pressure node for ESURF of HSFLD242
ESURF,newnode                 ! ESURF HSFLD242 elements over solid element faces
                     
allsel
fini
/solu

I am simulating at an environment temperature of 400°C so that the thermal expansion of the liquid and the solid has to be considered. But if i simulate with different coefficients of thermal expansion for the fluid, i get exactly the same results for the stresses in the component, although they should differ due to different thermal expansions.

I changed the material properties for the fluid from this:

tb,fluid,newnumber,2,,,liquid  ! Liquid Properties
tbtemp,20.0
tbdata,1,1800,9.71e-4,9.36e-7 !Bulk modulus,coefficient of thermal expansion,density
tbtemp,400.0
tbdata,1,2000,1.86e-3,5.48e-7 !Bulk modulus,coefficient of thermal expansion,density

to this:

tb,fluid,newnumber,2,,,liquid  ! Liquid Properties
tbtemp,20.0
tbdata,1,1800,9.71e-4,9.36e-7  !Bulk modulus,coefficient of thermal expansion,density
tbtemp,400.0
tbdata,1,2000,3.0e-3,5.48e-7 !Bulk modulus,coefficient of thermal expansion,density

however, the results for stresses are exactly the same. Do i need to set up a zero thermal strain reference temperature for the fluid material data ? why is thermal expansion not taken into account for the fluid ?

Thanks for your help.

fischr posted this 13 March 2020

here is a picture of the component. the HSFLD242 elements are unfortunately not displayed in workbench:

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