Reduced-order modeling and nonlinear system identification in structural dynamics and material characterization

Dalisay, Jon Dewitt Enriquez

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https://hdl.handle.net/2142/113905 Copy

Description

Title

Reduced-order modeling and nonlinear system identification in structural dynamics and material characterization

Author(s)

Dalisay, Jon Dewitt Enriquez

Issue Date

2021-12-03

Director of Research (if dissertation) or Advisor (if thesis)

• Vakakis, Alexander F
• Bergman, Lawrence A

Doctoral Committee Chair(s)

Vakakis, Alexander F

Committee Member(s)

• Tawfick, Sameh H
• Spencer, Billie F
• Eriten, Melih

Department of Study

Mechanical Sci & Engineering

Discipline

Theoretical & Applied Mechans

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• reduced-order modeling
• nonlinear system identification
• structural dynamics
• material characterization

Abstract

The dynamic analysis of complex structures often involves simplified models to minimize computational complexity and cost. For instance, lightweight local attachments are often exempted from detailed modeling and replaced by discrete linear impedance elements. However, it may be the case that the interfaces between local attachments and their host structure exhibit geometric or clearance nonlinearities that induce unexpected, sometimes undesirable, effects in the global dynamics. Another example of model simplification in structural dynamics is in the analysis of jointed structures where joint friction and clearance nonlinearities are often neglected. In this work, reduced-order modeling (ROM) and nonlinear system identification (NSI) were used to study various structural dynamical systems. First, the transient and steady-state dynamic behavior of a large linear host structure with small local nonlinear attachments was studied. Two types of nonlinear attachments were considered: geometrically nonlinear stores and vibro-impacting vibration absorbers. It was demonstrated that through nonlinear modal interactions, small local nonlinear attachments affect the global transient and steady-state dynamics of the large linear structure to which they are attached. Next, the transient dynamic behavior of a structure with several vibro-impacting joints was investigated. The joints were prismatic-revolute, and finite axial clearances allowed vibro-impacts between structural components. It was shown that for large joint clearances, fast energy dissipation is achieved even when the joint friction coefficient is minimal. Given that ROM and NSI are effective for studying structural dynamical systems with local nonlinearities, their application on the characterization of nonlinear materials was also explored in this work. Soft materials find ever-growing use in load-bearing applications, and hence, there is an imminent need for accurate modeling and characterization of their mechanical properties. Nonlinearities and rate-dependence are inherent in their mechanical response due to their multiphasic constituents. Rapid changes in their constituents due to environmental factors add further challenge to their mechanical characterization. In this regard, transient response testing promises a suitable testing modality for soft materials that undergo rapid compositional changes and degradation. A framework for characterizing the transient hyper-viscoelastic behavior of soft materials was designed and validated in this work. The framework was shown to be reliable and quick, making it suitable for fragile and time-sensitive samples such as biological tissues.

Graduation Semester

2021-12

Type of Resource

Thesis

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http://hdl.handle.net/2142/113905

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Copyright 2021 Jon Dewitt Dalisay

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