Linear vs. Nonlinear Analysis
A nonlinear thermal problem, as opposed to a linear one, typically involves:- Temperature-dependent material properties
- Temperature-dependent boundary conditions
Thermal vs. Thermal Stress Analysis
A Thermal Analysis solves a thermal problem with only thermal quantities as results like temperatures and heat fluxes. A Thermal Stress Analysis (also called thermo-elastic analysis) solves for the mechanical behavior of a model in terms of stress, strain, deformation, etc. induced due to thermal loads, in addition to calculating the response due to other mechanical loads and boundary conditions. → Therefore, a thermal stress analysis is essentially a static structural analysis. An additional thermal property, the coefficient of thermal expansion of the material, must be defined. The coefficient of thermal expansion (SI units: 1/K) describes how the size of an object changes with a change in temperature.Note: The thermal stress analysis capability in nTop is uncoupled, i.e., only mechanical effects driven by thermal loads are calculated and not vice versa.
Steady-State vs. Transient Thermal Analysis
A steady-state thermal analysis calculates the thermal response at thermal equilibrium, with all thermal loads and boundary conditions in steady-state, with all effects of time essentially neglected. This type of analysis is analogous to solving a static structural FEA problem. A transient thermal analysis calculates a model’s thermal response over a period of time. Thermal inertia effects due to density and specific heat of the material, therefore, become relevant. Solving a transient thermal analysis is analogous to solving a dynamic structural FEA problem.Tip: A steady-state thermal analysis applies when time behavior is irrelevant and only the results at equilibrium conditions are needed. A transient thermal analysis applies when thermal inertial effects are important or if there are extreme non-linearities in the model.