Fluid-Structure-Thermal Couple

- August 3, 2023 at 2:42 am
  
  HB Z
  Subscriber
  
  I have got the error message " The calculated specific heat at constant strain (Cv) is negative. (See section "Thermoelasticity" of the Theory Reference for the definition of Cv.) Please verify the input of thermal material quantities for consistency", I used custom materials in the mechanical. In additiona, the solution information shows this error "property EX of materical 1 is defined over a temperature range from 20 to 700 thich does not include the uniform temperature(15)"
- August 3, 2023 at 2:27 pm
  
  Dave Looman
  Ansys Employee
  
  In the past this has been due to Cp being incorrect as described below. The other message can be ignored.
  Knowledge Base Solution 845568:
  Why am I getting the error message below with PLANE223? The calculated specific heat at constant strain is negative. Please verify the input of thermal material quantities for consistency.
  Product Family: Structural Mechanics
  Product: ANSYS Mechanical APDL
  Version: 11.0
  Area: General
  SubArea: N/A
  Last Updated: April 17 2020
  Answer:
  PLANE223 is different because it has two way thermal-structural coupling. You may be getting the negative Cv message because your value of Cp is too small. From the numerical values in your input, it appears as though you are using the length unit off mm. The table below from the Coupled Field Guide gives units of length^2 for specific heat, so the MKS value of 460 for specific heat should be multiplied by 1e6 to produce a value of 460e6. This will make the value of Cv very positive.
  
  Refs:
  
  Theory Manual Equation 11-31
  Coupled Field Guide Section 2.6.2 points a through d.

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