John O'Callahan - Mentor, Advisor, Associate, Friend

May 19, 2021

Let me expound and shed some additional light on the small giant with the big technical stick.
John was truly brilliant and gifted.
Solid Mechanics, FEA, computer science, modal analysis, computers, composites, … you name it.
I first met John in 1977 when I was doing some FEA work where he was a consultant where I worked.
We were making FEA models – there were no commercial codes available in those days.
But John had his own FEA codes that he had written. If the code didn’t do what we wanted to do then we just revised the code.
And there were no graphics back in those days. So John just wrote code to be able to see the FEA mesh we developed. And it was funny because sometimes when we checked older models when the graphics were developed, we would find models where there were parts of the model where there were elements missing.
John gave the analyst an F for those models!
While these models are small compared to today’s standards, these models would run for hours.
I remember in one month in 1980, I had a computer bill that was close to $20,000 – typically our computer bills were only $1000 or so in a busy month.
So John and I had a very close working relationship from the 70s. At the end of the 70s, I was working on my MS thesis on test-analysis correlation and structural dynamic modification – very popular topics in those early days. And in 1985, I came up to the University of Lowell and joined John and Dudley Shepard in what was then the Modal Analysis and Controls Laboratory. At that time, we had a great collection of hardware and software for analytical and experimental modal analysis. This was the beginning of what is now the Structural Dynamics and Acoustic Systems Laboratory today.
And back in those days, I would run across all different people in New England who would know John and would have a story to tell about how John would come in and solve a perplexing problem that helped them out. Or how he would write some specialized software to help them efficiently solve a complicated problem. John was always there helping solve complicated problems. I was always amazed when he would talk to well-known experts in the field and explain complicated engineering problems. I remember one late night at the Control Data Corporation facility in Waltham (where computer facilities were housed for access to computational needs) when John bumped into the renown Klaus Jurgen Bathe and had some intricate discussions about some FEA issue. I was amazed how many people knew who John was – the small giant with a big technical stick.
And when I did join the university, I remember looking at some of John’s textbooks on FEA, computation, modal analysis and such.
And many times, I would see John’s handwritten notes that were written in the edge space of the text commenting on theory that was missing a critical piece or an equation not quite correct. And in the famous FEA text by Bathe, you could see John’s scribblings where he would note how the FORTRAN code was inefficiently written and how he could modify the code and improve the computation significantly or where a step in the code was totally unnecessary. That level of detail and insight just completely blew me away – but for John that was just a simple obvious fact.
And I remember how many students would comment how great John’s classes were. Now I didn’t say they were easy classes but they were chucked full of a massive amount of information. As I started at the university, I would remember seeing John at his desk and developing theoretical notes. He would have pages and pages of derivations … done one way … then done another way … and yet even another way. His stacks of notes were massive. And then he would parade down the hall to class with several folders of these notes under his arms. He would arrive in class and put the stack of notes on the corner of the desk. And it was then that you noticed a calm and quiet across the class as all the students got their notebooks out to start writing what would be an extensive set of notes for that lecture.
I write pretty small and I would fill up 9 to 10 pages of detailed derivations in each class. The amazing fact was that he never, ever referred to any of the extensive notes he brought with him. That complete 3 hour lecture would be done with precision and flow that you would never know it was a live presentation.
And this was his ritual for every class he ever taught, all semester long … arrive at class with a huge stack of notes that were placed on the corner of the desk, never refer to them, complete a 3 hour lecture, pick up the notes and leave class. And one student attested to this just now saying “But when he began teaching, he never really opened the folder. He had such incredible knowledge that he spoke without any break during the entire 3 hours of that lecture.”
And the other amazing fact was that when asked a question that was off topic from the class lecture, he would just go into a roll on that material as if he had been preparing that off topic material that day too.
And this wasn’t just a casual discussion of the topic. John would go into a full blown theoretical development (if it was necessary) with an ease and elegance that was totally unbelievable.
And it wasn’t until today (as I write these notes) that I think I finally realize that those notes that he was writing all day long were not for the class lecture – it was probably some other development he was working on and he just wanted those notes close to him – almost like a security blanket. He knew the class lecture notes cold. He didn’t need to practice those at all.
John was a truly unique individual. When we would be at the IMAC Conference, people would seek him out to discuss their problems and pick his brain to help solve their problem. And John was always very open in discussing anyone’s problems.
And I remember the long days and nights when we were developing and writing technical papers for IMAC. We would always pull all-nighters getting everything assembled and shipped off to SEM by the deadline. And there were many, many long night ordeals over the years. That was the way we worked together all the time.
Those years from when I started at the university until when John retired, were the most important and influential years in my life. John and I worked together to build the lab up. There were papers and courses and even week-long seminars for industry that were developed. And, of course, the famous MAT-SAP program that John developed that is still in use today in graduate courses.
Back in 2004 when John retired, I remember trying to identify the right person to roast John. Someone who knew him for a long time over the years of his contributions. The realization was that I was probably the closest to John and was the obvious choice for the roast. I asked for some testimonials that I am including here (but leaving the names as anonymous in most cases).


In 1987, you firmly put U Lowell on the map in the modal analysis community with contributions in correlation and updating. Quite some innovations! LMS utilized those techniques. You were the gifted numerical analysis person to bridge the gap to test in exceptional ways. A great vision on the value from test and analysis complementing each other – confirmed even today.”

- Jan Leuridan Executive Vice-President & CTO LMS International

Thank you for all your hard work and dedication in teaching the best modal analysis courses available anywhere. My favorite parts of each class were the projects, which drove home the important aspects. It was great to be part of the MACL as a research assistant, preparing for and attending IMAC conferences to see first-hand how well respected you and the program you put together at the University of Lowell are internationally.”

‘The endless oral exams were intimidating… now an engineering executive meeting is considered mild. College became more than just "school". In the MACL lab, working with you, Pete, and others, it became more of a community – it was a great place to spend time and learn. The MACL days felt like my real University time, where we worked on larger, more open-ended projects that were a transition to the type of work I do now. This is ultimately my most memorable and special time at ULowell.’

Congratulations … for an outstanding teaching and research career that has so positively influenced many aspiring students at UMASS Lowell. You made enormous contributions on building the credibility of the university in modal analysis that I frequently hear your name synonymous with the UMass Lowell modal analysis program being one of the best, if not the best program in the country.”

“I only had one course with Professor O’Callahan, but it was a semester that helped me define both my academic and career path. His abilities as a teacher and his passions for the subject hooked me. For a man with such a mastery of a complex subject to be able to possess such patience and understanding with students very much his junior was amazing to me. A professor of his caliber will leave a hole at the university and impossible to fill."

I am most indebted to Dr. John O'Callahan for his help, guidance and support throughout all of this research. In addition to this work, Dr. O'Callahan has been a very important influence during the many years of association prior to this work. Words cannot describe my appreciation for having the rare opportunity to be associated with him and learning from him for over 20 years. His dedication to his work and his students is rarely seen. The sacrifices that his family has given has allowed many students, including myself, to become who we are today.”

In closing …
John’s contributions to the structural dynamics community were significant and long lasting. He will be remembered by many people, in many different ways, depending on their interaction with him in their various dealings. But rest assured John will not be forgotten. He has touched many in different ways. I am the beneficiary of having known John, worked with John, and learned from John for many decades.


Peter Avitabile
President 2016, Society for Experimental Mechanics
Professor Emeritus, Mechanical Engineering
Structural Dynamics and Acoustics Systems Laboratory
University of Massachusetts Lowell
One University Avenue
Lowell, Massachusetts 01854
Phone: 978-934-3176