Steady State & Transient solution techniques
You can use steady-state thermal analysis to determine temperatures in an object that are caused by thermal loads that do not vary over time. This is general the case of electronics that are "turned-on" and left operating long enough for temperatures to stabilize and no longer change.
A transient thermal analysis follows basically the same procedures as a steady-state thermal analysis except that thermal capacitance and initial temperatures are important. You can simulate cool-downs and warm-ups.