Fish Creek

Fish Creek Idaho

Sometimes it seems like you have to go a long way to get back to some wilderness. But when you do, it sure is a sight to look at. When I get to wilderness my eyes just go Ahhh! when I look at the trees changing color, the brown moss in the river, the silvered decaying tree trunks, and the white light bouncing off the ripples in the water. It is a sight, some places better than others, but when you know you are in a place that has never really been disturbed, you can take a look and try to memorize it. Last place I was at that made me feel this way was in New Mexico, a place where folks said "there are elk back here, if you look, over the top of the scrub, back behind where the farm is, over toward the mountains" And I replied, well I saw an elk once, and it was like nothing else, but for me it is enough to see the red light from the setting sun hitting the tops of the mountain, and lighting up the snow. The folks both looked, and we didnt say anything more.

Well the last time I wrote was pretty upsetting, the Salinas Creek entry was written about four days after the hurricane hit New Orleans. Way back in my life I was a hydrology simulation computer programmer for flooding on the Mississippi. I didn't know much but I learned about what they call rain graphs, hyetographs, and how the government engineers decide which projects are the most important to do for flood prevention. After the government engineer prioritizes, Congress and the President approve the projects, and it usually doesn't have anything to do with what the engineer said, so I eventually gave up on that career.

But I did learn enough to know for sure that New Orleans was likely to flood, and it turns out that the encylopedia that ships on Apple Computers also mentions that it is below sea level. So it seems like pretty common knowledge that it would flood, its in the encyclopedia. Look it up in your Funk and Wagnalls. So the day I was writing in Salinas was the day that Matt Lauer kept saying over and over that no one imagined it would flood, and it was more obvious than usual but Matt didn't know beans about floods. That was the days when the TV was filled with images of people near despair because they had been trapped by flood waters for three days and there was no sign that they were about to be rescued, or given any water, and meanwhile the commentaters on TV were eternally damning them for reports of lawlessness and looting.

Because I knew for damn sure that FEMA was supposed to be there after an emergency, because the local government was gone, it was unable to cope, and where was FEMA? It had to be deliberate that FEMA was not there, there are too many dedicated career professionals for this to be a random fuck up. The whole organization fucked up at once, systematically. And the only reason I could think of for FEMA not to be there is the President didn't know it was going to flood, he thought it was only going to be an average emergency, and he wanted the locals and the Red Cross to handle it, so he could say we don't need FEMA. But how do you prove that? I guess I don't know how.

So I think if you read the Salinas entry you can tell I was upset, just from the grammar, and the continuity, I edited some stuff out badly.

Anyway, I said I wanted to talk about magnetically aligned fluids, which I do, but in thinking about it I realized there is just a heck of a lot of stuff I need to go into first. I need to talk about vortexes, and how there is a speed at which the dimple forms - such as when you stir the coffee with a spoon. I need to talk about Kutta-Joukouski transformations, which are a fancy mathematical way of transforming the shape of a wing into the shape of whats called a "hodograph" - or a graph of Navier Stokes pressures that will be generated by the wing. All this stuff is covered in the Milne-Thompson book on aerodynamics and the neat things are that you can make a hodograph, and if you do a complex transformation on it you get a nice shape that looks like a wing crossection. The vortex is important in wings because you can model the flow over the wing crossection as two vortexes, a large one and a little one, do the hodographs and check the pressures, adjust it, and convert back.

In the old days it was the only way to go, and time consuming to try to optimize your wing. I have seen some recent work and it seems like what they do now is finite point analysis without the hodograph conversion, because digital computers can do the grunt work, but they can't do the complex transformations as easily. I guess it probably used to take a few days to analyze a hodograph and convert it to a wing shape, and then you generate some approximate vortexes and try to minimize the size of the smaller one.

In a wing the wasted energy is in the wake. The equations for wake vortices were worked out by von Karman, and these are the nastiest equations I ever saw, including some equations worked out by Nernst for the solution of electrolysis problems. The von Karman equations are nearly impossible to visualize but if you can minimize the wake turbulence you can optimize your wing. And most of the wake turbulence is in the wingtip vortices.

Now one of the things about vortexes is that there is an angular speed beyond which "flow cannot be contemplated." Milne-Thomson has some nice equations for this, and a diagram, and the coffee cup is the most comfortable example for most people. It also is the subject of a 1914 paper by August Betz about how to create a vortex in an inviscid fluid. The idea here is that without viscosity you can't generate continuously differentiable flow velocities throughout the fluid. You can't make a vortex. Betz uses the coffee cup as an example. The cup, not the saucer.

In hydraulics they talk about cavitation in a fluid, where an object moves so rapidly through the fluid that the fluid cannot move quickly enough to fill in the space behind the object. As Ogata says: "When the velocity of the liquid flow is increased locally and the liquid flows into a region where the pressure is reduced to vapor pressure, it boils, and vapor pockets develop...the vapor bubbles are carried along with the liquid until a region of higher pressure is reached and they suddenly collapse." The collapse causes the noise and vibration.

Now if you are a nice swimmer doing a crawl, and you stroke your hand straight into the water you might push an air bubble or two under your fingernail. But if you do it just right you can see air bubbles continuously forming during the downstoke into the water. Its continuous, its only under the longest finger, and as the bubbles peel off only one or two of them (out of a half dozen) reach the surface. You are cavitating!

This illustrates that these kind of effects are fairly common. Another example that might make you think is streamlining of a car. I have a van, and I just measured that it reaches its maximum height of 6.5 feet at a distance of 5 feet from the front bumper. It is not very streamlined compared to a sportscar that might be no more than four feet high. If I approximate the front end of my van as a 6.5 foot circle, then the center of the circle would be at ground level about 1.5 feet behind my front wheel, just under the door handle.

So now if I look at the air flowing past my car as air moving past a non rotating disk I find something interesting. The angular acceleration is a function of the velocity squared, over the radius. The critical acceleration would be the one that accelerates some molecules up to the speed of sound. For my van this works out to be 58.9 MPH - the same speed at which the air over the van starts to whistle and whine.

Now for the sports car, so low to the ground that it is approximately a 50 meter radius, with the center being 49 meters below ground, the critical acceleration, when all the air whistles, occurs at about 292 MPH. It is quiet, the air almost never whistles like a truck, or a van, or an RV.

Similarly I once worked out that a baseball generated accelerations over 2600 MPH, or Mach 3.5. Talk about heat! And curveballs, at 1800RPM are Mach 5 in acceleration, high enough that some O2 molecules might dissociate.

Finally, if you take a foot long dowel rod you can tell how humid it is by swishing it through the air like Harry Potter. On a dry day you can make it whistle holding it in the middle. On a wet day, when air pressure is lower, you have to hold the rod by the end to make it move fast enough to whistle.

So here we have some examples of cavitation, streamlining, and accelerations that are as fast as sound, not by creating high speed air flows, but by making the fluid change direction through various means. We still don't know how everyone in FEMA screwed up at the same time, and we still don't know why the new FEMA manager came on board and said, as if he were Matt Lauer, that the hurricane caused "unimaginable" damage. Because it was imaginable, and every disaster plan imagined it, and every flooding expert in every water district in the whole country knows it.