... Check results carefully. Refer to Troubleshooting in the Help System for more details.
This message will appear if the program determines that the initial time increment used in the thermal transient analysis may be too large based on the "Fourier modulus" (Fo). This dimensionless quantity can be used as a guideline to define a conservative time step based on thermal material properties and element sizes. It is defined as:
Fo = k (Δt) / ρ c (lengthe2)
where:
| lengthe = Average element length |
| Δt = Time step |
| k = Thermal Conductivity |
| c = Specific Heat |
| ρ = Density |
Specifically this warning will be issued if the program finds that the Fourier modulus is greater than 100, that is, Fo > 100. Stated in terms of the initial time step (ITS), this warning appears when the ITS is 100 times greater than the time step suggested by the Fourier modulus in the form expressed below:
Δt = lengthe2 / (k / (c ρ))
This check is done on a per body basis and the results are echoed in the Mechanical APDL output listing. For example:
********* Initial Time Increment Check And Fourier Modulus ********* Specified Initial Time Increment: .75 Estimated Increment Needed, le*le/alpha, Body 1: 0.255118 Estimated Increment Needed, le*le/alpha, Body 2: 1.30416 Estimated Increment Needed, le*le/alpha, Body 3: 0.158196 Estimated Increment Needed, le*le/alpha, Body 4: 0.364406
If this warning is issued make sure that the specified time step sizes are sufficiently fine to accurately capture the transient phenomenon. The proper use of this guideline depends on the type of problem being solved and on accuracy expectations.