# Change of coefficient of thermal expansion does not change evaluated stresses

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,,5.48e-7 !Bulk modulus,coefficient of thermal expansion,density1.86e-3

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,,5.48e-7 !Bulk modulus,coefficient of thermal expansion,density3.0e-3

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.

## Comments

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