A Tribute to Allan Acosta: My Advisor, Mentor, and Friend!

How many people can say they’ve known someone for over half a century? That’s how long I’ve known Allan—and what fond memories I have!

I came to Caltech in 1967 and chose Allan as my advisor, for which I feel extremely fortunate and forever grateful.  I vividly remember my first “encounter” with him, which formed my lasting impression about him: a tall lanky fellow with a handsome tanned look who was very kind to the fledgling intellectual toddler that I was.  I was minimally prepared academically – a confused twenty-something lad from Korea, which at the time was better known as a poverty-stricken third world country still reeling and barely recovering from the total destruction of the war.  I needed to assimilate to an entirely new world. I had a lot to catch up with the Caltech way of learning – like drinking from the fire hose, figuratively speaking. Allan was generous enough to take me under his wing.  He was patient and understanding while I wrestled to adjust to the new academic environment. 

I quickly discovered one of Allan’s great talents – he seemed to know how to get to the heart of complicated matters without beating the bushes.  I once tried to write a FORTRAN program to solve a problem on a mainframe computer and discussed it with him.  He did not seem amused at my approach although he did not disapprove it.  A couple of days later, he showed me how he did it on a pocket calculator (the pocket calculator had just come out in the mid-1960s) using an iteration.  I was duly impressed by his simple way. Allan was often able to simplify seeming complexities to a manageable level.  I eventually settled down working on my thesis, which was about the unsteady cavity in internal flows.  It was an analytical study of a two-dimensional supercavitating flow past a flat plate at a small angle of attack with heaving and pitching motion of small amplitudes in a choked tunnel and another study on a finite cavity flow over a wedge in the middle of a tunnel with a mass oscillation.  After graduation, Allan introduced me to cavitation problems in turbomachinery.  He explained how the positive feedback of an unsteady cavity flow into the inducer pump of a liquid propellant rocket engine could lead to a thrust oscillation resulting in the so-called POGO instability.  He also explained how a fluctuating cavity flow could cause a surge in a closed hydraulic loop.  What little knowledge I learned in BC (before Caltech) was mostly through classroom lectures based on standard textbooks, so all these things were a fascinating revelation to me.  Allan guided me to extend my earlier studies to this new problem, first to a tunnel flow and then to cavitating turbopumps.

Allan was gentle and sensitive and showed personal interests in our conversations, technical or nontechnical, always giving his full attention to our talks.  Once I told him I was planning to visit Yosemite and his eyes lighted up. He suggested many things I could see and do there – I remember him describing the loveliness of the Tuolumne Meadow —   Another time, he said he knew too many things about airplanes that could go wrong so he would drink and quickly fall asleep whenever he flew!  He had commuted from Seal Beach to Pasadena until his retirement, and he said he would stay in a safe lane on the freeway and not change it unless absolutely necessary — a good safety lesson for me.

We once had an interesting discourse about my courses.  Allan suggested that I take an economics course, so I asked him in mild protest, “Why economics for an engineer?” He said, “Because you asked the question, that’s why!”  His response settled the issue, and I am so glad that I took his advice as it broadened my horizon, although it has not made me a billionaire (yet!).  I was also advised to take a full academic year of a graduate course in quantum mechanics in the Physics Department.  As an ME student taking a QM course, I struggled a bit but am proud that I added the two diametrically dissimilar disciplines to my repertoire, one known as dismal and the other abysmal.  The odd combination has occasionally given me an edge via an interesting perspective that my colleagues did not seem to fathom. 

After I left Caltech, I still maintained contact with Allan, albeit sparsely, as I transitioned from the cavitation area a few years afterward into nuclear energy.  I was aware of his activities in cavitation-induced turbo pump structural instabilities. When I organized the Korea-USA Fluids Engineering Seminar sponsored by the US NSF, I jumped at the opportunity to invite Allan to Korea. He presented a nice opening talk “Impeller-Induced Rotor-Dynamic Forces”, which he fondly called ABC paper (co-authored by Acosta, Brennen, Caughey). This appeared as the lead article in the proceedings.   We also met at a couple of ISROMAC conferences in Honolulu. In particular, he was honored to receive an ISROMAC Award at ISROMAC-4 conference in 1992.  He seemed happy and wistful to be back in Hawaii, which he had visited such a long time before in his Navy days. I remember him reminiscing about Waikiki, tall thin palm trees, and the historic Moana Hotel building still standing on the Waikiki Beach. My youngest daughter Janice accompanied my wife Jungsuh and me on a couple of these Hawaii trips, and although she was just a young teenager at the time, she remembers Allan to this day—his presence was large and his personality memorable to her.

Allan was a trailblazer. He used to say it was important to look for new areas and problems and, true to his form, he would open up new areas and move on.  As a young man who was intent on solving problems rather than finding new ones, I did not understand at that time his fixation on seeking new problems but later fully appreciated it, especially as a project manager at EPRI (Electric Power Research Institute in Palo Alto) and later as an academic person myself.

Jungsuh and I visited him many years after we left Caltech and finally enjoyed the privilege of seeing his famous boathouse.  He told us how he sailed in it to Baja, and I thought it must have been dangerous!  We were so pleased to see him again in the summer of 2018 but the boathouse was no longer.  He even put his old house up for sale, preparing to move to Encinitas.  He seemed reflective and pensive about leaving the place he had lived for nearly 50 years and having to clean up all the memorabilia. He was emotional about having to dispose all the research related materials including the dissertations of his former students and the publications he wrote with them that he had kept all those years.

There is a saying in Korea: “If strangers’ sleeves so much as touch each other, it makes a relationship.” My humble interpretation is that we are all interrelated and even such a chance encounter is a blessing although we may not realize it in the initial moment.  I have had so much more than merely touching Allan’s sleeves – I feel I am a most blessed man as I learned directly from him for over half a century and find myself still learning from him every day.

It has been said that one’s character, more than anything else, defines a person.  For all my admiration for Allan’s brilliance and numerous achievements, I personally value his character the most: his charm, kindness, sensibility, integrity, and love of wine!  Allan does not use big words nor does he have an oversize ego.  I never heard him boast or exaggerate – that is not his style.  Rather he has a keen sense and tender heart that eases and encourages those around him. This is the art of his fine character, and I am still trying to learn it.

Over half a century is a long time. I have accumulated my share of wonderful memories about Allan and wish to continue making more.  I owe him so much but don’t know how to repay all the care and kindness I received from him, so I will sum it up in these simple words: Allan, I wish you good health and many blessings.

With deep gratitude and best wishes, 

Jong H. Kim

Sent from Korea in October 2019