General Mechanical

General Mechanical

Change of coefficient of thermal expansion does not change evaluated stresses

    • fischr
      Subscriber

      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
      Subscriber

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



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