About Liviu Lebrescu

Many people have posted on the heroism of Emeritus Professor Liviu Lebrescu, who held the door to his classroom shut to allow his students more time to escape. The man was 76 years old, but was still teaching, still doing research and publishing papers, and still devoted enough to his students to give up his life for them. It made me want to know more, so I went to the VA Tech web site and looked at his work.

Oh my God.

For starts, the man’s CV spans 61 pages. 61. Pages. In similar formatting, mine would be about 5.

Then you look at his fields of expertise, which covered some of the toughest problems in mechanics and fluids (which are normally separate disciplines, by the way). Here’s a list of some of what he worked on, together with my notes on why it’s impressive:

• Aeroelastic stability of flight vehicle structures: when you say “aeroelastic,” you’re talking about how flexible structures behave in flight. The tough part is that the flexing changes the air flow around, and the geometry of, the flight vehicle, so you get this nasty interdependent problem.
• Nonlinear aeroelasticity of structures in supersonic and hypersonic flow fields: same as above, but with the added complications of shock waves (supersonic flows) and temperatures high enough to make O2 and maybe N2 molecules break apart (hypersonic flows). Any time you see the word “nonlinear,” you know that some analyst somewhere is suffering, but Librescu thrived on these problems.
• Unsteady aerodynamics and magnetoaerodynamics of supersonic flows with applications: Hokay. Aerodynamics relies on this nasty equation called the Navier-Stokes equation, and finding solutions to that equation usually involves simplifying it to make it easier (or even possible) to solve. The first simplification we like to make is that the flow is steady (i.e., doesn’t change with time). That gets rid of an entire variable (time). So tackling unsteady problems is kind of like leaning into a punch. Then you add supersonic flow, which has shock waves. Shock waves are basically sharp boundaries between areas of high density air and low density air. That’s fine, except that most computational methods hate sharp boundaries like that. On top of all that, he was adding equations for electromagnetism (I don’t know why) to the already intractable flow problem. Glutton for punishment.
• Response and behavior of structures to underwater and in-air explosions: Explosions are obviously very fast, involving supersonic flows and often perturbed or contaminated media (where media = water or air). Trying to evaluate structural responses to explosions is yet another nasty combination of fluid mechanics and structural mechanics

Basically Prof. Librescu was a math stud who tackled the toughest analytic problems in fluids and structures. Unlike most mathematical types, however, he was apparently also outstanding at applying his mathematical insight to real-world problems.

That’s a rare combination.

He truly was an exceptional man, long before fate required him to be a hero as well. Some people never give, but fortunately they are balanced out by those who never stop. Liviu Librescu was a giant among the givers.

UPDATE: Here is a Pajama Medias report from the funeral.