07/01/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a Doctoral Dissertation Proposal defense by John Matthews on "Methodologies to Enable Field Response Recreation."

Candidate Name: John Matthews
Degree: Doctoral
Defense Date: Thursday, July 10, 2025
Time: 10 a.m. - noon
Location: PER-115

Committee:

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

Abstract:
Currently, field to laboratory boundary condition compensation techniques are being deployed to allow for accurate and reliable environments testing. Fixture Neutralization (FINE) is one such technique being deployed, but there is little guidance as to what critical items are needed to effectively perform the steps required. A multitude of tools were developed to help aid the FINE field to laboratory response recreation process; specifically, the INSPECT, PLF, SAFE and STRAC are important tools developed for this analysis.

The FINE process requires a number of forces equal to the number of effective connections that exist in the configuration being tested. The number of effective connections does not necessarily equal the number of physical connections. Thus, a metric to determine the effective connections in the system was developed. This metric is called the Iterative Nullification of Singular-Value Process for Effective Connections Technique (INSPECT). The Singular Value Decomposition (SVD) is utilized in an iterative process to determine the effective connection set in a configuration. By iteratively removing chosen input locations from a total input location set and observing the resulting error on the singular values, an effective connection set can be found. This reduced effective connection set can be utilized as shaker locations, reducing the total number of shakers utilized and relaxing the need for an excessive number of input force locations.

Force reconstruction is a research field that aims to recreate forces that produced a set of measured responses. A variety of tools, such as the Primary Locator Function (PLF), have been developed to aid the force reconstruction process. These tools are utilized to better condition the matrix inversion step that occurs and allow for more accurate input location determination. These force reconstruction techniques were morphed to utilize a field and laboratory configuration. This allows for the adaptation of these tools, such as the PLF, for FINE testing. Utilization of a fixture gives a formulation similar to traditional FINE techniques. Further extension of force reconstruction techniques were made to directly locate and calculate connection forces on a test article to allow for fixtureless laboratory testing.

Both force reconstruction and FINE techniques are susceptible to modal truncation errors during the calculations. The Scaled Accumulation of FRF Error (SAFE) metric was developed to determine modal truncation effects in a system from a given mode set. SAFE uses target responses to scale FRF residual error to graphically represent FRF truncation error for given mode sets. The SAFE metric is useful to allow for better conditioning of inversion steps performed in the previous techniques developed.

Finally, the Scale Time Response Assurance Criteria (STRAC) was developed to determine scale factors between two time responses being compared. This allows for more robust correlation metrics to be found in conjunction with the traditional TRAC metric.