02/10/2023
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation proposal defense by John Seymour on “The Extension and Enhancement of Impedance and Modal Based Coupling Approaches."

Candidate Name: John Seymour
Degree: Doctoral
Defense Date: Friday, Feb. 24, 2023
Time: 10 - 11 a.m.
Location: Perry Hall, Room 315

Join Zoom Meeting
Meeting ID: 961 8060 9543
Passcode: 781265

Committee

  • Advisor Peter Avitabile, Ph.D., Professor Emeritus, Mechanical Engineering, University of Massachusetts Lowell
  • Co-Advisor Alessandro Sabato, Ph.D., Assistant Professor, Mechanical Engineering, University of Massachusetts Lowell
  • Jesus Reyes Blanco, Ph.D., Assistant Teaching Professor, Mechanical Engineering, University of Massachusetts Lowell
  • Christopher Niezrecki, Ph.D., Distinguished University Professor, Mechanical Engineering, University of Massachusetts Lowell
  • Javad Baqersad, Ph.D., Assistant Professor, Mechanical Engineering, Kettering University

Brief Abstract:

The term “system modeling” encompasses various techniques and methodologies which involve the coupling or uncoupling of models comprised of at least two components. Originally developed as a method of breaking up large models into smaller components for computational efficiencies, current system modeling approaches are implemented to characterize a coupled system’s dynamics when only information pertaining to the dynamics of each individual component is available. Thus far, system modeling approaches couple physical, modal, and impedance models as well as physical to modal models. Current system modeling techniques lack the capability of directly coupling an impedance model to a modal model. This poses potential problems as a highly tuned FEA model of a component may not exist, or a component’s attachment locations may be inaccessible for a modal test. For example, one component’s dynamic characteristics may be well defined in terms of its modal characteristics (such as a launch vehicle) whereas the other component’s characteristics may only be identified in terms of attachment impedances (such as a payload).

In this work, the Impedance to Modal Substructuring (IMS) method was developed allowing for the direct coupling of an impedance model to a modal model, giving more flexibility to the types of models that may be directly coupled. This work identifies how noisy measurements cause difficulties in the impedance modeling assembly and produces amplified errors in the resulting system model’s FRFs. This work proposes two FRF smoothing techniques which condition noisy measurements to be suitable for substructuring applications. The first method includes the development of an additional form of residual compensation, the Residual Compensation Pole (RCP), calculated during the modal parameter estimation (MPE) process to account for the truncated effects of unmeasured modes in FRF synthesis. The second method of FRF smoothing eliminates the requirement of MPE by directly smoothing noisy measurements using a new FRF enhancement algorithm. Difficulties in experimentally testing for rotational DOFs is also discussed in this work, including current methods of obtaining rotational measurements by means other than experimental testing. This work explores the heightened sensitivity of rotational DOFs to modal truncation errors. A method of residual term expansion from translational to rotational measurements was developed to mitigate modal truncation errors when expanding to rotational DOFs. The proposed methods of FRF denoising via direct smoothing and RCP residual compensation, and the new method of residual term expansion were developed to facilitate the eventual implementation of the IMS system modeling approach in an experimental environment.