Transient thermal analysis determines temperatures and other thermal quantities that vary over time. Engineers commonly use temperatures that a transient thermal analysis calculates as input to structural analyses for thermal stress evaluations. Many heat transfer applications - heat treatment problems, nozzles, engine blocks, piping systems, pressure vessels, etc. - involve transient thermal analyses.

A transient thermal analysis follows basically the same procedures as a steady-state thermal analysis. The main difference is that most applied loads in a transient analysis are functions of time. To specify time-dependent loads, you can either use the Function Tool to define an equation or function describing the curve and then apply the function as a boundary condition, or you can divide the load-versus-time curve into load steps.

If you use the Function Tool, see Using the Function Tool in the Basic Analysis Guide for detailed instructions.

If you use individual load steps, each "corner" on the load-time curve can be one load step, as shown in the following sketches.

Figure 3.1: Examples of Load vs. Time Curves

For each load step, you need to specify both load values and time values, along with other load step options such as stepped or ramped loadsautomatic time stepping, etc. You then write each load step to a file and solve all load steps together. To get a better understanding of how load and time stepping work, see the example casting analysis scenario in this chapter.