Learning Forum

[wa167]

Hello,

I was wondering about the concepts of compliance and strain energy density when it came to Structural Optimization (SO), and how it is applied on Ansys. In the Static Structural modules prior the SO simulation (with a compliance minimization objective), if I plot the strain energy, the total strain energy is equal to the initial "objective value" in the SO simulation (when I go into the Optimization Output file):

As the SO objective is to minimise compliance, and based on a few papers / posts I read, I understand that the compliance and the total strain energy are supposed to represent the same thing so I should not be surprised to find the same value. However, where I am confused is regarding the unit to be used for compliance. Shouldn't the compliance represent also the inverse of stiffness, so 1/MPa? Why would it be "equal" to mJ then? And why, in the Optimization Output file, the unit is listed as "MPA"?

Sorry if this is a very beginner-level question, but I just want to make sure I fully undertsand the concept of compliance and the correct unit.

Thanks!

[Matthew Middleton]

The line "units = MPA" is not for one specific quantity. This specifies the system of units used:

 MPA UNITS SPECIFIED FOR INTERNAL    
  LENGTH      = MILLIMETERS (mm)
  MASS        = TONNE (Mg)
  TIME        = SECONDS (sec)
  TEMPERATURE = CELSIUS (C)
  TOFFSET     = 273.0
  FORCE       = NEWTON (N)
  HEAT        = MILLIJOULES (mJ)