Basis selection for nonintrusive reduced order models of nonlinear geometric response: experience with a stiffened, strongly asymmetric structure

The focus of this investigation is on furthering the development of reduced order models (ROMs) of structures undergoing dynamic response in the nonlinear geometric regime and more specifically on improving the basis selection process which is one of their key components. To this end, their application to a hat section, as an example of stiffened structures, is studied in detail. This structure includes several features never considered before in the context of nonlinear nonintrusive reduced order models, e.g., a very strong asymmetry, a significant low frequency-high frequency coupling with potential internal resonance, and large modal forces of high frequency modes. It is found that, even when outside of the excitation band, these high frequency modes can have significant effects on the response and thus must be carefully introduced in the basis. Three related bases are considered the first two of which lead to reasonable predictions of the response in the excitation band but a poor matching of full finite element results above it. The sources of this poor matching are then identified leading to a third basis that provides an accurate matching of the finite element response within and above the excitation band. These findings allow a sharpening of the guidelines for the basis selection, progressing one step further toward its automatic selection which is desirable for routine engineering analyses and design. It is noted that the reduced order models developed here are nonintrusive, i.e., they are obtained from finite element models constructed in commercial software, Nastran in the present case, to enable their use by the broad structural dynamics community.