08/04/2021
By Sokny Long

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a doctoral proposal defense by Bahadir Sarikaya on "The Impact of Design and Manufacturing Imperfections on the Response Characteristics of Centrifugal Pendulum Vibration Absorbers.”

Ph.D. Candidate: Bahadir Sarikaya
Date: Friday, Aug. 13, 2021
Time: 10 to noon EST
Location: This will be a virtual defense via Zoom. Those interested in attending should contact candidate Bahadir_Sarikaya@student.uml.edu or advisor Murat_Inalpolat@uml.edu at least 24 hours prior to the defense to request access to the meeting.

Committee Chair: Murat Inalpolat, Ph.D., Associate Professor, Mechanical Engineering, UMass Lowell (Advisor)

Dissertation Committee Members:

  • Christopher Niezrecki, Ph.D., Professor, Mechanical Engineering, UMass Lowell
  • Peter Avitabile, Ph.D., Professor, Mechanical Engineering, UMass Lowell
  • David Talbot, Ph.D., Assistant Professor, Mechanical Engineering, The Ohio State University

Abstract:
The global restrictions on emission requirements have prompted the use of advanced technologies such as cylinder deactivation and engine start-stop systems with downsized engines to create more fuel-efficient and environment-friendly passenger cars and transportation vehicles. These current technologies have helped reduce fuel consumption and thus emissions, though they mostly ended up shifting the engine-generated dominant vibrational frequencies down and resulting in excessive vibration and noise problems to occur at lower operational speeds. These relatively low frequency noise and vibration signals are generated at speeds from within a more heavily used part of the duty cycle for most vehicles, can lead to durability, performance and comfort related issues, and is a disturbance to the passengers as well as to the environment. Centrifugal pendulum vibration absorbers (CPVA) have been recently integrated into passenger cars to further minimize vibrations and noise by isolating engine generated oscillations from the rest of the driveline. The CPVA needs to be tuned to a particular order of frequencies associated with the dominant excitation source to eliminate vibrations in a rotating dynamic system. However, dimensional and weight deviations among absorbers are inevitable due to various manufacturing tolerances and errors as well as operational wear and tear induced imperfections. The existing modeling and tuning efforts generally ignore the CPVA design and manufacturing imperfections, which can lead to deviations and instability in the system’s dynamic response and exacerbate the overall NVH (Noise-Vibration-Harshness) problems of the vehicle.

The proposed work includes a comprehensive investigation on the response characterization of CPVA systems in the presence of critical design and manufacturing imperfections such as absorber spacing, absorber mass, rotor mass, end-stop clearance and absorber path imperfections. The impact of CPVA imperfections on the vibration response will be analyzed both at the component level (only the CPVA itself) and the system level (not only the CPVA but also other parts of the drivetrain).

Initially, sensitivity of free and forced response of a generalized CPVA system has been analytically derived for the asymmetric absorber mass, spacing and rotor mass errors using the eigensensitivity and the modal superposition techniques. Distortions in the baseline modal structure and deviations from the baseline forced response characteristics were demonstrated with a linearized CPVA model in the context of the tuning and excitation order variations. Secondly, the effect of end-stop clearance errors will be investigated through numerical integration with the developed, comprehensive nonlinear model including both torsional and translational motions, as well as gravitational effects and roller dynamics. Thirdly, the offset, waviness, pit and random type path errors will be investigated analytically and numerically with the developed nonlinear model to tune absorbers properly according to the tolerance ranges and identify the path imperfections. Lastly, the effect of CPVA imperfections in the system-level driveline model will be shown experimentally and numerically through variations of mass errors among absorbers considering the interactions between CPVA and gearbox dynamic response.

The research proposed will provide the first comprehensive framework for the modeling, evaluation and interpretation of CPVA response alterations in the presence of critical design and manufacturing imperfections such as absorber spacing, mass, rotor mass, end-stop clearance and path. The proposed dissertation will enhance the existing CPVA tuning strategies and provide guidelines for the design and diagnostics of CPVA systems with imperfections to significantly improve the vibration reduction capability and increase the likelihood of more durable designs.

All interested students and faculty members are invited to attend the online defense via remote access.