Research Areas
Al Ferri


Al Ferri works in the general area of nonlinear dynamics, vibrations, signals and controls. As a member of the Acoustics and Dynamics Research Area Group, his research has been at the intersection of various engineering disciplines.


Dither Cancellation of Friction Induced Oscillations
Friction induced vibration can be an annoying source of chatter and noise in a number of important engineering systems. A good example is in brake systems, where friction plays a key role in the phenomenon of brake squeal. This research, funded by NSF, investigates how high frequency vibration, or dither, can be used to eliminate vibration in such systems. Models of an automobile disc-brake system have been developed and studied numerically and analytically to understand the mechanisms by which dither “smoothes” the frictional nonlinearity, thus preventing the occurrence of stick-slip oscillations. The research also examines which types of dither signals are most effective in different applications.

Publications

  1. Michaux, M.A., Ferri, A.A., and Cunefare, K.A., “Effect Of Tangential Dither Signal On Friction Induced Oscillations In a SDOF Model,” 2005 ASME International Design Engineering Technical Conferences & Computers and Information In Engineering Conference, Long Beach, California, September 24-28, 2005. (Also, ASME. Journal of Computational and Nonlinear Dynamics, Vol 2, No 3, July 2007, p 201-210)

  2. Michaux, M.A., Ferri, A.A., and Cunefare, K.A., “Effect of Waveform on the Effectiveness of Tangential Dither Forces to Cancel Friction-Induced Oscillations,” Proceedings of the 2005 ASME IMECE Conference, Orlando, FL, Nov. 5-11. (Also, accepted for publication, Journal of Sound and Vibration)

  3. Michaux, M.A., Ferri, A.A., and Cunefare, K.A., “Modification of Friction-Induced Instability in a Disk System Through Dither Excitation Forces," Accepted for 2007 ASME International Design Engineering Technical Conferences & Computers and Information In Engineering Conference, Las Vegas, NV, September 4-7, 2007

Diagnostics and Prognostics of Mechanisms
The wide variety and availability of small, accurate sensors presents many opportunities for automated health monitoring of critical components. However, considerable work is needed to develop reliable ways of extracting fault information from sensory outputs. One application studied in this research is a cracked carrier plate in a planetary gear system. Based on a physical understanding of how the crack influences the vibratory signature, a variety of “features” were extracted from the vibratory signals. The research aims not only to diagnose the fault, but also to predict the growth of the crack over time. Such “prognostic” information is very important to determine the remaining use of a part before replacement or maintenance must be scheduled.

Example: Carrier Plate for UH-60 Blackhawk Helicopter

During a routine inspection of a helicopter planetary gear transmission, a large crack was found in the carrier plate. Shown at the right is a photo of the long crack located at the base of one of the post for one of the planet gears. The objective of this research is to determine if evidence of this crack is observable in vibratory sensory output. The two plots below show two accelerometer signals; the signal on the left was obtained from a healthy (unfaulted) transmission, and the signal at the right is from a faulty transmission. Obviously, the difference between the two signals is subtle, and depends on many factors including engine torque. The research aims to develop numerical metrics that can be used to detect the size of the defect, and to predict the evolution of the crack.

Cracked carrier plate

Cracked carrier plate
Cracked carrier plate


Publications

  1. Patrick, R., Orchard, M.E., Zhang, B., Ferri, A.A., Vachtsevanos, G.J., Kacprzynski, G., and Koelemay, M. "An Integrated Approach to Helicopter Planetary Gear Fault Diagnosis and Failure Prognosis," Accepted for IEEE AUTOTESTCON 2007, Baltimore’s Inner Harbor, Baltimore Maryland, Sept 17-20, 2007
  2. Patrick, R., Ferri, A.A., Vachtsevanos, G.J., "Detection of Carrier-Plate Cracks using Sidebands of Vibration Spectra," Accepted for 2007 ASME International Design Engineering Technical Conferences & Computers and Information In Engineering Conference, Las Vegas, NV, September 4-7, 2007.

Vibration of Turbomachinery Blades and Disks
As aircraft engine designers attempt to achieve higher thrust-to-weight ratios, engine structural components have become more vulnerable to vibration problems. High-cycle fatigue of turbine blades, for example, can lead to blade failure, with potentially severe consequences. To reduce vibration levels, designers have relied on dry, Coulombic friction to provide passive damping. In particular, friction at the blade/disk interfaces as well as inter-blade rubbing at the shroud locations are important sources of energy dissipation. This research studies ways to increase the passive damping of turbine and compressor blades through novel design of the frictional interfaces.

Publications

  1. Anderson, J.R., and Ferri, A.A., "Behavior of a Single-Degree-of-Freedom System with a Generalized Friction Law," J. Sound and Vibration, Vol. 140(2), 1990, pp. 287-304.
  2. Ferri, A.A., "Friction Damping and Isolation Systems," J. Vibration and Acoustics, Vol. 117(B), June 1995, pp. 196-206.
  3. Whiteman, W.E., and Ferri, A.A., "Displacement-Dependent Dry Friction Damping of a Beam-Like Structure," J. Sound and Vibration, Vol. 198, no. 3, 1996, pp. 313-329
  4. Ferri, A.A., and Heck, B.S., "Vibration Analysis of Dry Friction Damped Turbine Blades Using Singular Perturbation Theory," ASME J. Vibration and Acoustics, Vol. 120, No. 2, 1998, pp. 588-595.
  5. Whiteman, W.E., and Ferri, A.A., "Multi-Mode Analysis of Beam-Like Structures Subjected to Displacement-Dependent Dry Friction Damping," J. Sound and Vibration, Vol. 201, No. 3, 1997, pp. 403-418.
  6. Whiteman, W.E., and Ferri, A.A., "Multi-Mode Analysis of Beam-Like Structures Subjected to Displacement-Dependent Dry Friction Damping," J. Sound and Vibration, Vol. 201, No. 3, 1997, pp. 403-418.
  7. Whiteman,W.W., and Ferri, A.A., “Suppression of Bending-Torsion Flutter Through Disp-lacement-Dependent Dry Friction Damping,” AIAA Journal, Vol. 37, No. 1, 1999, pp. 79-83.
  8. Ferri, A.A., "Damping Through Use of Passive and Semi-Active Dry Friction Forces," in Dynamics with Friction: Modeling, Analysis, and Experiment, Part II, Vol. 7, Series on Stability, Vibration, and Control of Structures, World Scientific Publishing, 2001, pp. 253-308.
  9. Ferri, A.A., and Whiteman, W.E., “Stability Analysis of A Vibrational System Subject To Negative Viscous Damping And Displacement-Dependent Dry Friction Damping,” Proceedings of the ASME 2003 Design Engineering Technical Conferences, Chicago, Illinois USA, September 2-6, 2003.
  10. Ferri, A.A., and Whiteman, W.E., “Free Response of a System with Negative Viscous Damping and Displacement-Dependent Dry Friction Damping.” Journal of Sound and Vibration, Vol. 306(3-5), 9 October 2007, pp 400-418.

Modeling of Multibody Systems

This project addresses the accurate and efficient modeling of multibody flexible structures such as those encountered in deployable space structures. Such systems are characterized by having large-order linear components interconnected with various types of joints and fasteners. In the case of revolute joints, friction plays a very important role in facilitating (or impeding) deployment, and in increasing the passive damping capacity of the system. Accurate models are needed to predict the operation of these systems before they are built and launched. This research, fucded by AFOSR, is focused on incorporating advanced friction models into multibody computer codes. The goal is to develop a modeling capability that is accurate, but numerically efficient.

Publications

  1. Ferri, A.A., "Modeling and Analysis of Nonlinear Sleeve Joints of Large Space Structures," AIAA J. Spacecraft and Rockets, Vol. 25, No. 5, Sept.-Oct. 1988, pp. 354-360.
  2. Ferri, A.A., and Heck, B.S., "Analytical Investigation of Damping Enhancement Using Active and Passive Structural Joints," AIAA J. Guidance, Control, and Dynamics, Vol. 15, No. 5, September-October, 1992, pp. 1258-1264.
  3. Ferri, A.A., and Bindemann, A.C., "Vibration of Flexible Beams with Various Types of Frictional Support Conditions," ASME J. Vibration and Acoustics, Vol. 114, No. 3, July 1992, pp. 289-296.
  4. Bindemann, A.C., and Ferri, A.A., "Large Amplitude Vibration of a Beam Restrained by a Non-Linear Sleeve Joint," J. Sound and Vibration, Vol 184, No.1, 1995, pp. 19-34.
  5. Ferri, A.A., "Damping Through Use of Passive and Semi-Active Dry Friction Forces," in Dynamics with Friction: Modeling, Analysis, and Experiment, Part II, Vol. 7, Series on Stability, Vibration, and Control of Structures, World Scientific Publishing, 2001, pp. 253-308.
  6. Do, N., Ferri, A.A., and Bauchau, O.A., “Efficient Simulation of a Dynamic System with LuGre Friction,” 2005 ASME International Design Engineering Technical Conferences & Computers and Information In Engineering Conference, Long Beach, California, September 24-28, 2005.
  7. Do, N., and Ferri, A.A., “Energy Transfer and Dissipation in a Three-Degree-of-Freedom System with Stribeck Friction,” Proceedings of the 2005 ASME IMECE Conference, Orlando, FL, Nov. 5-11.