|
Post by JayUtah on Feb 22, 2012 19:25:11 GMT -4
I've heard from other people ka9q's complaint about the relative obscurity of the slug unit, but to me, who cares? Indeed, how many non-scientist Europeans know what a newton is or how to use it? ...who were technically required to use SI but habitually received a waiver on the grounds that the contractors' knowledge base and designs were in EES. Clavius uses both: EES in main text, SI in parentheses. But this is sporadic because I grow bored doing comprehensive checks of the site for such consistencies. Indeed, the larger question for non-scientist users is familiarity in the face of arbitrary definitions. At a certain point a temperature is just an arbitrary setting on the oven knob, and it largely doesn't matter to me what the actual number is as long as the recipe and the knob agree. But when cooking from the hip I can guess better in Fahrenheit, but only because I've been using those units all along. I would expect my counterpart in Italy to be more familiar with Celsius oven settings and what you cook at what temperature.
|
|
|
Post by JayUtah on Feb 22, 2012 16:42:06 GMT -4
A lot of engineering still occurs on Earth rather than in space or on other planets, and so a lot of practical engineering still involves dealing with the force of Earth gravity on some sort of mass. This is what continues to motivate a "simple" system of units that requires few arbitrary conversions.
The metric-speaking world still weighs things in kilograms. The imperial-speaking world still weighs things in pounds. This is because our knee-jerk reaction is always still to determine mass by measuring the force of Earth gravity on it. The casual users of both systems just happened to have fallen on different sides of the fence about which unit to use as the practical measure for non-engineering purposes.
But each tradition has created a consistent subset of units that serves formal engineering. One engineers in SI, not metric. One also engineers in EES, not imperial. The flaw in both approaches comes from reusing familiar quantities and concepts from the looser parent systems. Someone who weighs himself in the bathroom at 51 kg that morning and goes to work as an engineer dealing with forces in newtons is going to have just as much mental anguish as the person who weighs himself at 112 lbs and then has to go to his own engineering office and reckon the mass of a beam in slugs.
Once you realize that all the units involved are arbitrary, regardless of the system, and that the problems we face come not from the beauty or clunkiness of the system but from the inherent inconsistency in the problems we want to solve, the advocacy of one system over another becomes distractive. Yes, standardization is a good goal. But as long as our intuitive notion of mass is so inexorably connected to our planet's gravity, we'll have this problem.
|
|
|
Post by JayUtah on Feb 22, 2012 14:49:40 GMT -4
Then does it sound like a place where you really wanna spend time typing responses that are almost sure to get ignored or removed?
|
|
|
Post by JayUtah on Feb 22, 2012 14:45:45 GMT -4
A 179 pound ball on earth takes 6 times more energy to move then a 179 pound (29.8 adjusted for gravity) ball on the moon. No. If you want to lift the ball, then yes it takes more force to do so. Why? Because lifting incorporates more than just moving the ball; it requires opposing and overcoming another force that's trying to move the ball toward the center of the planet. Moving the ball sideways isn't overcoming the force of gravity. It's only overcoming the inertia of the ball, and inertia is a product solely of mass. The problem of moving soil laterally across the surface -- i.e., entraining it in an exhaust flow -- is an inertia problem, not a force-of-gravity problem.
|
|
|
Post by JayUtah on Feb 22, 2012 12:17:52 GMT -4
Is there a way to account for spherical distortion caused by the lens and determine how much it is? Somewhere I have the formal lens model for the Zeiss Biogon, but I've recently moved offices and I have no clue where half my stuff is.
|
|
|
Post by JayUtah on Feb 21, 2012 20:47:56 GMT -4
But the EES unit of mass is the slug, not the pound. Saying "pounds-mass" is as wrong in rigorous engineering as it is to say "kilograms-force." In each system, in the appropriate computations, we use the constant g0 to refer to the conversion between mass and Earth gravity force units, where appropriate. This is the constant that allows us to use the same units for specific impulse whether we're working in EES or SI.
|
|
|
Post by JayUtah on Feb 21, 2012 17:39:47 GMT -4
Of course much of this is just hairsplitting. The method we're using is intended to do no more than provide a ballpark figure to see if it's reasonable to expect the formation of a large crater. Yeah I've been sort of sitting on my hands here because it's fun watching Bob run numbers. The method here makes several important but perfectly valid simplifications, such as assuming uniform regolith density, uniform plume density, and ideal energy transfer. What we hope for here is a good order-of-magnitude estimation. We're looking at centimeters at most, so regardless of how you populate the estimates with reasonable values, your not going to get a deep hole. Professionally I would report these results as "0-5 cm expected erosion." The method Bob has chosen supports no greater precision. What you really want is a scour model. Scouring occurs when you have (a) a moving fluid, (b) erosible elements, and (c) non-erosible elements. The patterns of fluid flow around non-erosible elements (rocks, the landing legs, the denser portion of the regolith etc.) effects a pattern of erosion and displacement in the erosible elements (loose regolith). Scour, for example, describes the movement of river water around bridge piers and over the river bed, and of air around tall buildings situated in natural erosible environments. Typically rough material called rip-rap is used to break up the fluid flow and render it turbulent otherwise vortices and eddies form on the downstream side of the piers and scour away the supporting riverbed. A scour model incorporates an erosibles model, in this case a distribution of particle sizes, shapes, and masses. Particle shape dictates mechanical cementation, which in turn dictates how fluid impingement produces a dynamic response. Rip-rap is commonly rough-hewn rock, but increasingly cast concrete shapes are being used. Particle mass and size (which are listed as distributions rather than considered uniform) determine particle entrainment response aside from cementation. Different distributions of particle size and shape have different aggregate results, and susceptibility to displacement through entrainment does not vary linearly with either. We borrow particle models from settling and piling-shear models. A scour model incorporates a fluid dynamics model, in this case a compressible gas model of the exhaust plume. Exhaust plume models are problematic. The Navier-Stokes models either of compressible or non-compressible flow do not describe plume dynamics well inside the thrust chamber. However, for purposes of fluid impingement on a suitably distant surface, they do. In other words, combustion products inside a thrust chamber are not always fully Newtonian, but they become Newtonian a sufficient distance from the engine throat. For impingement on an erosible or irregular surface, turbulence must be modeled -- and the typical models do not account for this except through time-averaged values. Thus only large-scale fluid movement can be modeled, and this will necessarily fail to model centimeter-sized local turbulence effects. The fluid-dynamics model easily handles non-erosible obstacles as well as the compression of the fluid as it approaches the surface. Having handwaved the basics of the problem, I can now tentatively say that this is a three-week modeling effort at a professional footing. I would bid this at right around $12,000 labor costs and $20,000 computer time, for $32,000. And I would expect to see a conical crater (deeper in the center, negligible at the edges) with a maximum depth of 3 cm. The cheapness of Bob's solution is its reward. I highly doubt anyone wants to pay $32,000 for my refinement using best methods. Bob gave you a defensible answer for free.
|
|
|
Post by JayUtah on Feb 21, 2012 12:25:00 GMT -4
No, it is not correct. Mass is mass, irrespective of gravity.
|
|
|
Post by JayUtah on Feb 21, 2012 12:19:01 GMT -4
This value had not been adjusted to lunar gravity, bulking value of regolith should be 0.22 gms/cm3 Why are you adjusting a mass density for gravity?
|
|
|
Post by JayUtah on Feb 16, 2012 17:28:55 GMT -4
The original cm3 of exhaust gas will now have accumulated 138 cm3 of exhaust gas compressed into a 1 cm3 area. You can't possibly believe how wrong this is.
|
|
|
Post by JayUtah on Feb 15, 2012 13:59:18 GMT -4
Indeed, writing the evasive walls of text is time-consuming, but then he has to go to all the different sock-puppet sites and write all the congratulatory posts praising the wall of text.
|
|
|
Post by JayUtah on Feb 15, 2012 11:12:27 GMT -4
Actually, I had intended this as damnation with faint praise... A gilded bullet?
|
|
|
Post by JayUtah on Feb 14, 2012 17:29:39 GMT -4
I when I did a quick calculation for myself... Present your calculations. Error analysis, please? Oh, that's right -- you don't know how to do any of those. "Lost" is your word, whether posting as Fattydash or as whatever you're calling yourself now. "Found" is another. You use these as black-and-white concepts, which you define conveniently and variously to fall on the wrong side of whatever question you need to come out wrong from time to time. It's nothing more than a word game. No, just one equivocation. You refuse to see this problem the way the people did who operated this system. They're thinking in continuous terms of precisions, error analysis, and tolerances for various different applications, while you're trying to make everything fit two simultaneously indistinct and rigid categories. Where did you learn to fake Moon landing missions? Is there a school for that somewhere? If not, why should your expectations be the gold standard? How cute of you to pretend there was any sort of rigor associated with your wild handwaving claims. "Me and my girlfriends know all about science, even though we aren't actual scientists." Really, Patrick? Have we stooped to blatant equivocation now?
|
|
|
Post by JayUtah on Feb 14, 2012 14:38:00 GMT -4
My view is that an examination of the data on outer space radiation and the science of radiation health and disease would not be a fruitful road for prohoax types to travel down. It seems to me that the yield in terms of proving a hoax based on this approach would be exceedingly low. Indeed, it's much more profitable for hoax enthusiasts to go look at pictures and say, "Well, that doesn't look like the Moon to me." Much more rigorous. That's the problem with hoax arguments -- they never want closure. They want to run around in endless circles of second-guessing and question-begging, so that they can write the same things over and over again and call it "ongoing research." The radiation argument -- while treated ignorantly by some hoax theorists -- actually has sound scientific principles and well-documented engineering solutions. Since we know that you have no actual scientific skills, as evidenced by your long-standing failure to provide any sort of rigor and your colossal and comical blunders when trying to deal with scientific topics, this would be a dangerous road to pursue. Sooner or later you'd be expected to show some actual rigor, and you know you cannot.
|
|
|
Post by JayUtah on Feb 14, 2012 2:30:25 GMT -4
Pretty hard to read it any other way I think. Patrick, knock it off. Begging the question is your particular argumentation idiom.
|
|