Vibration analysis of the chassis is an important problem in automotive design. The engine mounted on the chassis acts as the source of vibrations and also as a pathway for vibrations from one part of the chassis to another. Simulating the engine and the chassis together makes the problem size huge, and the time and memory requirement to solve the combined problem becomes impractically high.
A substructure modeling approach enables us to break down the problem into multiple subsystems, analyze the individual subsystems separately and still capture the dependence of subsystems onto each other in the whole assembly.
In this example, a detailed simulation of the engine running at a particular frequency is done to compute the vibrations at the engine mounts. These vibrations are applied on the chassis as external loads. For the vibration analysis of the chassis, the entire engine structure is abstracted into a single (mathematical) element between the mounts with the same mechanical behavior as the engine. This approach makes the entire simulation multiple times faster.