Loads Cascading in the Frequency Domain 2018-01-0138

A previous SAE paper (ref. 1) did a comparative study of automotive system fatigue models processed in the time and frequency domain. A subsequent paper (ref. 2) looked at relative random analysis under base shake loading conditions. This paper proposes to merge these two analysis procedures to implement a new “Loads Cascading” procedure.

The objective of this paper will be to show how loads (accelerations, displacements, forces) can be cascaded (transferred) from input load position such as road load data (RLD) body loads to some internal location, for example a battery pack location. Also note that the response from one “module” could form the input to another, therefore, once the loadings are in the frequency domain, the possibility exists to “cascade” the loads through a system. For example, from the chassis, to the subframe to attached components.

The term “cascading” is used to represent a process (in the frequency domain) where an input is related to an output via a set of system properties (transfer functions). In a conventional analysis, the input might be road load data (forces) applied near the wheels to the body of, for example, a trailer. And, in a conventional analysis, the output might be the stress distribution that will be used for a fatigue life calculation. But with loads cascading the additional requested output could be the same as the input (e.g. force) or another variable used as a loading function to a secondary system, like displacement or acceleration. And the additional advantage is that this kind of loads cascading can be done in parallel with a conventional stress analysis with no additional computational expense. In this way, the loads can be cascaded to multiple required internal locations.

Examples of internal locations could be subframes, battery packs, spare wheel locations, etc. The same truck frame model (or similar) as used in the previous 2016 SAE paper (ref. 1) will be used for the loads cascading analysis.