11/01/2022
By Murat Inalpolat

You are all invited to attend a doctoral dissertation defense in Mechanical Engineering entitled "The Impact of Design and Manufacturing Imperfections on the Dynamic Response Characteristics of Centrifugal Pendulum Vibration Absorbers.”

Ph.D. Candidate: Bahadir Sarikaya
Date: Tuesday, Nov. 15, 2022
Time: 10 a.m. to noon (US EDT)
Location: This will be a virtual defense via Zoom. Those interested in attending should contact Bahadir_Sarikaya@student.uml.edu and 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 imposed 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 vehicles. These current technologies have helped reduce fuel consumption and thus emissions. However, they have also ended up leading to an increase in the engine-generated excitations, resulting in excessive noise and vibrations at lower operational speeds. This problem presents itself within a more heavily used part of the duty cycle for most vehicles, and thus can lead to durability, performance and comfort-related issues. It is also a disturbance to the passengers as well as the environment. Therefore, centrifugal pendulum vibration absorbers (CPVA) have been integrated into vehicles in recent decades to assist in isolating engine-generated noise and vibration from the rest of the driveline. Ideally, these passive absorbers are tuned to target frequencies/orders resolved to suppress the torsional and translational vibrations of the overall system. However, dimensional and weight deviations from the ideal designs are unavoidable in practice owing to imperfections caused by manufacturing errors and operational wear. The existing dynamic modeling and tuning efforts for CPVA generally ignore these imperfections, which can lead to localization, amplification, and instability in the system’s dynamic response and thus exacerbate the NVH (Noise-Vibration-Harshness) issues related to the vehicle.
This dissertation includes a comprehensive investigation on the dynamic response characterization of CPVA systems in the presence of critical design variations and manufacturing imperfections.

These imperfections include, but not limited to absorber spacing, absorber mass, rotor mass, end-stop clearance and absorber path imperfections. The impact of imperfections on the vibration response of CPVA system is investigated to obtain improved tuning conditions, identification tools for response alteration and vibration performance metrics that can help monitor these systems in operation. Initially, the impact of each modeling feature (end-stop, roller, gravity and translational dynamics) on the system’s dynamic response is demonstrated on their own, and later including their dynamic interactions, through numerical and statistical sensitivity analyses. A strategy is proposed to analyze extensive design combinations and obtain a feasible CPVA design based on the system's needs by reducing the computational cost. Secondly, the sensitivity of free and forced vibration response of CPVA are analytically derived for the asymmetric absorber mass, absorber spacing and rotor mass deviations from their nominal values using a first-order eigenperturbation analysis in conjunction with the modal superposition technique. Distortions in the baseline modal structure and deviations from the baseline forced response characteristics are demonstrated with a linearized CPVA model in terms of tuning and excitation order variations. Thirdly, the influence of geometric deviations and imperfections in the absorber end-stop clearances is investigated through numerical integration with the use of a comprehensive nonlinear model developed, including torsional dynamics of the rotor, gravitational effects and the rocking motion of absorbers. The proposed tuning strategies supported by the two newly developed performance metrics offer an enhancement of vibration reduction and impact energy. Finally, the categorized path errors are investigated analytically and numerically with the linear and nonlinear CPVA models to properly tune absorbers within their prescribed tolerance ranges and identify the impact of path imperfections on the response.

This dissertation provides the first comprehensive simulation framework for the modeling, evaluation and interpretation of CPVA dynamic response alterations in the presence of critical design and manufacturing imperfections. The dissertation provides enhanced tuning strategies as well as improved design and diagnostic approaches for CPVA systems with imperfections. Case studies are used to demonstrate that the approaches and indices developed can be used to significantly improve the vibration reduction capability of CPVA systems and increase the likelihood of achieving more durable and silent designs.