#hydrodynamics

The field of active matter looks at the collective motion of particles and organisms--how birds flock and fish school. (Image and research credit: T. Zhou and J. Brady; via APS)

I don't particularly post anymore, mostly because I've felt less motivated to as of late. I've always had friction with the posting process; the formatting, the polishing, the tagging. Writing has mostly been a thing I've done consistently privately, so this is just a return to form, mostly.

But I have the Limitless paper, at least. And I am proud of it. So I've returned to put it out on my blog.

Happy reading.

Daniel Bernoulli – Scientist of the Day

Daniel Bernoulli, a Swiss mathematician, died Mar. 17, 1782, at the age of 82.

One thing I am particularly interested in is this idea of hydrodynamic stability. That is as a cetacean swims, is the center of pressure, the point through which all hydrodynamic forces can be said to act, behind our center of mass. This would make us inherently stable. It is likely that this is the case as without it anytime we were not actively steering we would become upset, turn sideways, and effectively stop. This would be very inefficient especially migrating, but it would allow for significantly increased maneuverability. Delphinidae in particular tend to have large dorsal fins which are further up on the body compared to minke, fin, and brydes whales, the only mysticetes with proper dorsal fins. This would make sense as rorquals, which the three above belong to, tend to lunge feed and so do not require the speed or accuracy of the dolphins and porpoises.

I was curious about the ability to model this simply. There are a number of programs which can calculate the center of pressure, among them open rocket. However when simulated the center of pressure is always forward of the center of mass, making the system unstable.

There are a couple parts to this though. This program does not well allow differentiation between center of pressure points on the horizontal axis versus the vertical. If the number of fins on the aft is increased to four, thus allowing equal stability in both horizontal and vertical direction, the center of pressure is comfortably aft of the center of gravity.

There are of course limitations to this program, the most basic of which is whales do not have a circular cross section, this is especially true in the peduncle of the whale. Our bodies are instead taller than they are thin which cannot really effectively be simulated here.

However, just looking at the shape of the flukes then, how do minke whales help balance this? One thing to note is when actively traveling, the flippers are normally held at 45 degrees or even lower. This helps provide additional control on that horizontal axis.

(Both are dwarf minke whales but it remains the same either way)

Taking a short break from trying to figure out my dynamic energy budget models and switching focus to hydrodynamic & particle tracking models!

Hopefully I'll use this to simulate mussel larvae moving around the Scottish West coast :)