John O'Callahan has written many papers over the years covering analytical model reduction techniques, structural dynamic modification, estimation of rotational dof, correlation of analytical/experimental modal models, and analytical model improvement.

• In Search of the IRS, J.C.O'Callahan, Twenty-Third International Modal Analysis Conference, Orlando, Florida, Feb 2005
• Reallocation of System Mass and Stiffness for Achieving Target Specifications using a Superelemt/Substructuring Methodology, P.Avitabile, J.C.O'Callahan, H.Tsuji, J.P.DeClerck, Twenty-Second International Modal Analysis Conference, Dearborn, Michigan, Jan 2004
• Complex Vector Scaling and Expansion using CPOC and CSEREP, J.C.O'Callahan, Twenty-First International Modal Analysis Conference, Kissimmee, Florida, Feb 2003
• System Matrix Optimization using a Complex Analytical Modal Improvement (CAMI), J.C.O'Callahan, Twenty-First International Modal Analysis Conference, Kissimmee, Florida, Feb 2003
• Reallocation of System Mass and Stiffness for Achieving Target Specifications, P.Avitabile, H.Tsuji, J.C.O'Callahan, J.P.DeClerck, Twenty-First International Modal Analysis Conference, Kissimmee, Florida, Feb 2003
• Development of Standard Beam Element with Modified End Effects, J.C.O'Callahan, Twentieth International Modal Analysis Conference, Los Angeles, California, Feb 2002
• Mass and Stiffness Skyline Optimization using Element Localization, J.C.O'Callahan, Nineteenth International Modal Analysis Conference, Kissimmee, Florida, Feb 2001
• Dynamic Expansion of Frequency Response Functions for the Full FRF Matrix, P.Avitabile, J.C.O'Callahan, Nineteenth International Modal Analysis Confernce, Kissimmee, Florida, Feb 2001
• Reduced Model Concepts, J.C.O'Callahan, Eighteenth International Modal Analysis Conference, San Antonio, Texas, Feb 2000
• Dynamic Expansion of Frequency Response Functions, F.Piergentili, P.Avitabile, J.C.O'Callahan, Seventeenth International Modal Analysis Conference, Kissimmee, Florida, Feb 1999
• Correlation Considerations - Part 4 (Modal Vector Correlation Techniques), J.C.O'Callahan, Sixteenth International Modal Analysis Conference, Santa Barbara, California Feb 1998
• SEREP Expansion , J.C.O'Callahan, P.Li, Fourteenth International Modal Analysis Conference, Detroit, Michigan, Feb 1996
• Input Force Estimation using Operational Data , J.C.O'Callahan, F.Piergentili, Fourteenth International Modal Analysis Conference, Detroit, Michigan, Feb 1996
• The Effect of Modal Vector Expansion on Model Updating, J.C.O'Callahan, P.Li, Thirteenth International Modal Analysis Conference, Nashville, Tennessee, Feb 1995
• Development of a General Pseudo Orthogonality Procedure, J.C.O'Callahan, Thirteenth International Modal Analysis Conference, Nashville, Tennessee, Feb 1995
• Mass and Stiffness Orthogonality Checks without a Mass or Stiffness Matrix, P.Avitabile, J.O'Callahan, Thirteenth International Modal Analysis Conference, Nashville, Tennessee, Feb 1995
• Automatic Selection of Reduced Degrees of Freedom, J.O'Callahan, P.Li, Twelfth International Modal Analysis Conference, Honolulu, Hawaii, Feb 1994
• A Non-Smoothing SEREP Process for Modal Expansion, J.O'Callahan, P.Li, Twelfth International Modal Analysis Conference, Honolulu, Hawaii, Feb 1994
• Comparison of Reduction vs. Expansion for Orthogonality Checks, P.Avitabile, T.Foster, J.O'Callahan, Twelfth International Modal Analysis Conference, Honolulu, Hawaii, Feb 1994
• Effects on System Optimization using Higher Order Finite Elements, J.O'Callahan, P.Li, Eleventh International Modal Analysis Conference, Orlando, Florida, Feb 1993
• Techniques for Forced Response Involving Discrete Nonlinearities, Part I - Theory, P.Avitabile, J.O'Callahan, Tenth International Modal Analysis Conference, San Diego, California, Feb 1992
• Techniques for Forced Response Involving Discrete Nonlinearities, Part II - Applications, P.Avitabile, J.O'Callahan, Tenth International Modal Analysis Conference, San Diego, California, Feb 1992
• Understanding Structural Dynamic Modification and the Effects of Truncation, P.Avitabile, J.O'Callahan, International Journal of Analytical and Experimental Modal Analysis, invited contribution, Oct 91,Vol 6, No 4
• An Efficient Method for Forced Nonlinear Response using a Structural Dynamic Modification Technique, P.Avitabile, J.O'Callahan, International Journal of Analytical and Experimental Modal Analysis, invited contribution, Jul 91, Vol6, No 3
• Determination of Analytical Model Differences using System Optimization Techniques with Modal Models, J.O'Callahan, 15th International Conference on Structural Dynamics, Leuven, Belgium, September 1990 (invited paper)
• Efficient Techniques for Forced Response Involving Discrete Nonlinearities, P.Avitabile, J.O'Callahan, 15th International Conference on Structural Dynamics, Leuven, Belgium, September 1990 (invited paper)
• Determination of Analytical Model Differences using Modal Updating, J.O'Callahan, Eighth International Modal Analysis Conference, Orlando, Florida, January 1990
• Comparison of Reduced Model Concepts, J.O'Callahan, Eighth International Modal Analysis Conference, Orlando, Florida, January 1990
• Understanding Structural Dynamic Modification Truncation, P.Avitabile, J.O'Callahan, F.Pechinsky, Eighth International Modal Analysis Conference, Orlando, Florida, January 1990
• An Efficient Method for Forced Nonlinear Response using a Structural Dynamic Modification Technique, P.Avitabile, J.O'Callahan, Eighth International Modal Analysis Conference, Orlando, Florida, January 1990
• An Application of New Techniques for Integrating Analytical and Experimental Structural Dynamic Models, J.O'Callahan, P.Avitabile, R.Riemer, 1989 NASTRAN User's Conference, Los Angeles, CA, March, 1989.
• A New Procedure for an Improved Reduced System (IRS), J.O'Callahan, Seventh International Modal Analysis Conference, Las Vegas, Nevada, February 1989
• System Equivalent Reduction Expansion Process (SEREP), J.O'Callahan, P.Avitabile, R.Riemer, Seventh International Modal Analysis Conference, Las Vegas, Nevada, February 1989
• Comparison of System Characteristics Using Various Model Reduction Techniques, P.Avitabile, J.O'Callahan, J.Milani, Seventh International Modal Analysis Conference, Las Vegas, Nevada, February 1989
• System Model Development Using Analytically Enhanced Experimental Data, P.Avitabile, J.O'Callahan, J.Milani, E.Pan, Seventh International Modal Analysis Conference, Las Vegas, Nevada, February 1989
• Effects of Various Model Reduction Techniques on Computed System Response, P.Avitabile, J.O'Callahan, E.Pan, Seventh International Modal Analysis Conference, Las Vegas, Nevada, February 1989
• Localization of Model Changes for Optimized System Matrices using Modal Test Data, J.O'Callahan, C.M.Chou, Sixth International Modal Analysis Conference, Orlando, Florida, February, 1988
• Model Correlation and Orthogonality Criteria, P.Avitabile, J.O'Callahan, Sixth International Modal Analysis Conference, Orlando, Florida, February, 1988
• Errors Associated With Structural Dynamic Modification Using Assumed Proportional Modal Vectors, P.Avitabile, J.O'Callahan, J.Milani, Sixth International Modal Analysis Conference, Orlando, Florida, February, 1988
• Expansion of Rotational Degrees of Freedom for Structural Dynamic Modification, P.Avitabile, J.O'Callahan, C.M.Chou, V.Kalkunte, Fifth International Modal Analysis Conference, London, England, April 1987
• Consistent Scaling of Rigid Body and Experimental Flexural Modes, J.O'Callahan, P.Avitabile, C.M.Chou, C.H.Wu, Fifth International Modal Analysis Conference, London, England, April 1987
• Improved Modal Data Base for Generalized Beam Modifications, C.M.Chou, J.O'Callahan, P.Avitabile, AMD Vol. 76, Symposium of Reanalysis of Structural Dynamic Models, 1986 ASME Winter Annual Meeting, Anaheim, CA, December 1986
• Development of an Improved Modal Data Base for Structural Dynamic Modifications, J.O'Callahan, P.Avitabile, C.M.Chou, Symposium of Signal Processing and Modal Analysis in Engineering Acoustics and Vibration, 1986 American Society for Engineering Education Conference, Cinn., OH, June 1986
• Improved Starting Vectors for Subspace Iteration Eigensolution using Dynamic Condensation, J.O'Callahan, C.M.Chou, R.Koung, Fourth International Modal Analysis Conference, Los Angeles, CA, Feb 1986
• Structural Modification Using Active and Passive Structural Elements, G.D.Shepard, J.O'Callahan, P.Avitabile, Fourth International Modal Analysis Conference, Los Angeles, CA, Feb 1986
• An Efficient Method Of Determining Rotational Degrees Of Freedom From Analytical And Experimental Modal Data, J.O'Callahan, P.Avitabile, R.Madden, I.W.Lieu, Fourth International Modal Analysis Conference, Los Angeles, CA, Feb 1986
• A Study Of Local Eigenvalue Modification Procedure Using A Generalized Beam Element, J.O'Callahan, C.M.Chou, P.Avitabile, 1984 American Controls Conference, San Diego, CA, Jun 1984
• Structural Dynamic Modification Using Generalized Beam Mass And Stiffness Matrices, J.O'Callahan, C.M.Chou, Third International Modal Analysis Conference, Orlando, Florida, January 1985
• Determination Of Rotational Degrees Of Freedom For Moment Transfers In Structural Modifications, J.O'Callahan, C.M.Chou, I.W.Lieu, Third International Modal Analysis Conference, Orlando, Florida,, January 1985
• Optimization Of Mass And Stiffness Matrices Using A Generalized Inverse Technique On The Measured Modes, J.O'Callahan, R.Leung, Third International Modal Analysis Conference, Orlando, Florida, January 1985
• Study Of A Structural Modification Procedure With Three Dimensional Beam Elements Using A Local Eigenvalue Modification Procedure, J.O'Callahan, C.M.Chou, Second International Modal Analysis Conference, Orlando, Florida, February 1984
• Development Of Mass and Stiffness Matrices For An Analytical Model Using Experimental Modal Data, J.O'Callahan, P.Avitabile, R.Leung, Second International Modal Analysis Conference, Orlando, FL, Feb 1984
• Complex Mode Extraction By A Conjugate Subspace Inverse Power Method, J.O'Callahan, C.Finch, First International Modal Analysis Conference, Orlando, Florida, November 1982
• A Structural Modification Procedure Using Complex Modes, J.O'Callahan, P.Avitabile, First International Modal Analysis Conference, Orlando, FL, Nov 1982
• Dynamic Response And Input Identification Of MDOF Structures Subjected To Coupled Random Vector Inputs, J.C.O'Callahan, G.D.Shepard, J.McElman, AIAA Journal 78-520, 1978

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