Simple?
To quote you; "I personally have some issues with some of their choices.The best guess they constructed does not agree very well with the landing gear observation."
This is growing tedious, even compared to other Troothers.
You modified my quote again, MirageMemories. You left off the second half of the sentence, which explains what I really meant:
The best guess they constructed does not agree very well with the landing gear observation, but it's not bad -- while they don't predict landing gear break-through, they do predict a large mass of aircraft breaking through in similar fashion, and with only minor tweaks that are inside the margin of observational error, that mass can be the landing gear.
Perhaps I should have substituted the word
"perfectly" for
"very well", but if you're going to continue quote-mining to that degree, I doubt that fool-proof expressions exist.
You say that in the more severe case the wheel didn't exist? but other massive chunks of aircraft did? yet none of these 'chunks' in reality, left the tower?
I said nothing of the kind.
I said, for at least the fourth time, that in the more severe case chunks of comparable size to the wheel did exit the structure. If you substitute one of these chunks for the wheel, which is completely reasonable given how they constructed their model, you get excellent agreement.
You'll have to excuse my inability to follow that, considering the landing gear did exist, and the landing gear which is in effect, a big chunk, did exit the tower in reality.
Take all the time you need. The argument is quite simple, and it's put forth in the NIST report for your perusal.
I can understand that orientation of the aircraft at the point of entry into the tower would effect what aircraft pieces did what and of course effect which aircraft 'pieces' had a clear enough path to exit the tower.
By George, I think you've got it! That's precisely the point. Very small changes to the aircraft parameters have a large effect on exactly what pieces make it through the core. Because the model assumes a homogeneous aircraft, it doesn't matter what pieces they are, so we don't care.
Except in the case of the less severe trials, in which hardly anything makes it through the core, so there's nothing to substitute. That's the whole point.
I don't see the reasoning behind your statement that "the total amount is roughly the same", unless 'roughly' is used very loosely? A titanium jet engine or landing gear represents a more significant 'chunk' than a piece of luggage for instance.
No. Not in the NIST model. Out of necessity they modeled the aircraft as homogeneous.
In real life, there will be some differences, but they are not as great as you seem to think. Regarding your firefight with
beachnut, you should keep in mind that even jet fuel, which has virtually zero tensile strength, is more than capable of cutting perimeter columns at those speeds...
Using this assumption for the base and extreme case scenarios to cover the absence of a landing gear exit is an unsupported claim in my opinion. Concentrated titanium debris, the landing gear or engine, does not equate to a similar accumulation of the same mass in the form of luggage, glass and aluminum fragments. At least as far as it's potential impact damage potential is concerned.
You need to need look at reality and not let the Model become reality.
No, not really. Exiting the far side of the Tower depends on two things -- trajectory, and whether or not core and perimeter columns were cleared out by something in front. The total energy captured by the tower, and the energy dissipated by the core columns, are the most important features, and energy is a function of
m v2 rather than the inherent strength of the components. A stronger component may actually deliver
less damage in some situations, because more energy can be dissipated by deforming the component!
To clarify my issues with the NIST model: The key differences between the modeled impact and reality are the disposition of engine fragments and landing gear. These differences are pretty minor, but worth discussion. The components have three things in common -- they are relatively solid, they are likely to detach as a unit, and they are round.
If I was conducting this investigation from scratch, I would be leery of using a homogeneous material assumption, but to do otherwise might be too complex to actually compute. What I would be tempted to do is consider the aircraft as a series of assemblies, joined by connectors as in the actual aircraft. I would then model those assemblies dimensionally according to blueprints, thickening them to match weight variances, but I would size the connectors to match the breaking strength of the real connectors rather than any blueprint. If done right, this would result in a model in which the aircraft engines and landing gear broke off of the airframe relatively intact.
Another approach would be to two-stage the model, treating the engine cores and landing gear as separate objects, but only initiating them when damage on the initial model reached a certain threshold.
Both engines and wheels would be more damage resistant than the rest of the aircraft structure, the first by virtue of its high-strength alloys, the second due to its shape and rubber coating. In the model this could be included as a ballistic "fudge factor," or if treated as independent objects, they could be granted a higher component strength.
The landing gear, as I have noted yet again above, is really not that big a problem. The engine fragments, on the other hand, are tricky. As NIST notes in their report,
all three cases could plausibly eject engine fragments, because -- not captured in their model -- the engine starts with considerable rotational momentum. They treated it as static. They didn't know how to deal with this, and I don't either. The best I can think of is to flag engine core components and add a centripetal velocity once any piece gets detached.
In the end, though, neither of these concerns is such a big deal, except to malcontents looking for any trace of uncertainty upon which to build a tirade. The global results of the NIST simulation are surprisingly accurate, and even more surprisingly, not overly sensitive to changes in input conditions. I am impressed with the quality of their answers, even though I had some doubts based on their approach.
It bears repeating that the simulations NIST conducted are (were) at the cutting edge of research in computational dynamics, not just in impact but in fluid and fire dynamics as well. Ten years ago, such an approach would have been unthinkable. Naturally it's not going to be perfect, but it's still well done.
MirageMemories, before quoting me again, please read for content.
And let me refresh my latest question, since you seem to have ignored the previous formulation:
In your opinion, which of the three cases is
the best fit to all the observed evidence? The less severe, baseline, or more severe case? Choose only one.
