General Mechanical

General Mechanical

BF and IC in the same APDL command: Only one works

    • Janne
      Subscriber

      Hello,


      I am using HSFLD242 element in Mechanical. The element works as it should.


      I want to add temperature and pressure to the node "Q" of the HSFLD242 element.


      I use this APDL command just prior the Ansys Solve command:


      !Gas properties


      TB,FLUID,newnumber,1,,GAS    !Fluid is gas


      TBDATA,1,1.7e-9          !Density of the gas kg/mm3


      TOFFST,273.15              !Specifies the temperature offset from absolute zero to zero.


      TREF,20                 !Defines the reference temperature for thermal strain calculations.


      BF,newnode,TEMP,20          !Assign a temperature to pressure node


      IC,newnode,HDSP,0.000


      Now when the BF=20 and HDSP=0, nothing happens, naturally. When I change BF=30 (body load 10) and keep HDSP=0 the model works correctly. I have an analytical method to validate it. Similarly, if change HDSP=0.001 and keep BF=20 (body load 0) the model works correctly.


      But, If I change both of them, the results are not correct. If IC command is before BF command, then BF is neglected. But if they are as they are presented above, the results are compelety bizarre.


      My questions:


      1) Can I use IC & BF to define hydrostatic pressure and temperature, respectively, at the same time?


      2) Both commands do not work unless "Large deflections" are activated in Static Structural. Why is this?


      (My model is so that I can replace HDSP load by inserting 2 conventional pressures at surfaces (one positive, one negative) but it is not as conventient. In this way the results are correct, even with superimposed temperature loads)

    • Wenlong
      Ansys Employee

      Hi, 


      1) In the MAPDL command documentation(https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/ans_cmd/Hlp_C_IC.html?q=initial%20condition%20IC), it quotes



      "For thermal analyses, any TUNIF specification should be applied before the IC command; otherwise, the TUNIF specification is ignored. If the IC command is input before any TUNIF specification, use the ICDELE command and then reissue any TUNIF specification and then follow with the IC command."



      Here TUNIF applies a uniform temperature to the body, so it works as the same as BF. So BF should go before IC command. 


      2) When you say "do not work", do you mean it does not run or the result is not correct? I don't see restrictions of HSFLD element and IC, BF to nonlinear analysis only. So it should be able to run in both cases. As for the result accuracy, turning "large deflection" on will definitely give you a more accurate result. 


      Regards,


      Wenlong


       

    • Janne
      Subscriber

      Hi Wenlong and thank you for taking the time to answer.


      1) I tried this but results are utterly wrong. Not even in the same region as the should be. But I shall not waste anyones time with this and I will just use pressure loads on surfaces to simulate initial pressure condition.


      2) I mean that the analysis runs but the results are zero in terms of everything. HSFLD runs with linear analysis fine when there is a pressure load applied. But the APDL command temperature or pressure (BF and IC) seems to only active with nonlinear analysis. 


      Br,


      Jaboust

    • Janne
      Subscriber

      Hello again,


      I would like try my luck here again with question number 2. Again, I have HSFLD element that works completely fine. The element has pressure node Q. Using BF APDL command, I insert body temperature load to that node Q. The simulation runs.


      Now, if I had "large deflections" activated in static structural, the structure deforms due to the temperature load (pressure increases).


      If I have linear analysis, nothing happens. The body load however appears normally in the solution output but does not result in any deformation in structure. 


      I have tried everything but nothing seems to help. Furthermore, I cannot apply the BODY LOAD via GUI because I cannot make a named selection of the pressure node Q because it is created in the PREP7.


       

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