The new moderation guidelines suggest to me that this thread has passed its "sell-by" date. However, I am prepared to discuss this topic openly with anyone, and I am also curious about the outcome of the moderating experiment. In that spirit, I will honor your request,
MirageMemories.
Let's see, I write a very long reply post to the several you made to me. I honestly address your points without distorted quotes or personal attacks on your credibility and what do you do?
...
Is it too much to ask that you stay on point? That you address my responses to the many points of yours that I honestly replied to without the use of smear tactics?
I am assuming you are referring to
this post of yours. Very well, I will do as you ask, and respond to
every single point in that post, without the merest scent of smear tactics.
Regarding my supposed misquotes from your replies, that was not intentional. In the interest of brevity, I only quoted what I thought was the essence of your message. I'm sorry it's so tedious.
Apology accepted. I find that when in doubt, quoting a larger block in context and eschewing any alteration of the quote text is an effective means to prevent misinterpretation.
Your statement was confusing and lacked clarity so I applied it as best I could. To me, "does not agree very well" and "but it's not bad" don't co-exist well and frankly contradict each other.
As I stated
a page before your reply, if you substitute
"perfectly" for
"very well" my intent should become clear.
Is a large mass supposed to equate to a unified mass or just a large accumulation of aircraft particles? By saying that with a few tweaks, within the margin of observational error, that the mass could be the landing gear, do you mean it could have the equivalent mass or actually could be physically characteristic of the actual landing gear? It's a very important distinction.
Because the model is homogeneous, actually there is no distinction. Nevertheless, the simulation suggests that moving the point of impact a few feet horizontally or vertically, which is well within the margin of observational error, would make it possible for the "actual landing gear" to break loose. This is what NIST is saying on page 343 of
NIST NCSTAR1-2B (page 149 of the PDF). Also, consider the different engine trajectories experienced with only slight vertical changes presented in Figure 5-19, page 107 (page 203 of the
first half PDF). This demonstrates quite clearly how minute changes of input conditions give rise to significant differences in the evolution of individual components.
Again I apparently misquoted you about massive chunks of aircraft. You are very easy to misquote unfortunately..or slippery.
Anyway, in the more severe case "chunks" of something, apparently from the aircraft, was comparable in size to the landing gear or a wheel and that for you, this was in excellent agreement.
That's correct. Because the aircraft model is homogeneous, the source location of an individual piece of debris is far less relevant than the total amount of debris that passes through the building. As you have argued yourself, the principal issue is one of energy transfer. Since the total amount of debris pass-through in the baseline and more severe cases plausibly matches the actual event, whereas the less severe case shows virtually nothing making it across the core, let alone the whole structure, NIST (and I) conclude that the less severe case is the worst fit out of the three cases.
In the case of the WTC 2 simulation, in the more severe case, a chunk of simulated landing gear exited at a velocity higher than, but not impossible compared to, the estimates of the real event (230 MPH simulated vs. 102 MPH estimated real-world, pp. 350-351 or 155-156 of the part 2 PDF). There was no exit of landing gear in the baseline or less severe cases, though there was substantial exit of other debris in the baseline case.
Therefore, if we were to follow your line of reasoning, you
must conclude that, in the case of WTC 2, only the more severe case fits. WTC 1 is still blurry by your standard.
Well I've looked at the their graphics and see the progression of the aircrafts through the towers. It's not particularly clear to me how they can be sure that what appears to be a small amount of debris exit is actually from the aircraft, or pieces from inside the building when it was impacted by pieces of the aircraft?
NIST can be quite sure of this because elements in their model are labeled. They have more than just those graphics to go on. When NIST says, as they do on page 284 (page 90 of the PDF):
"The less severe impact produced little content damage on the far side of the core and did not extend fully through the tower. Little or no debris penetration of the south wall of the tower was expected for the less severe impact condition." -- you may be sure they have adequate tools to make that determination.
It's important because particles or groups of particles would not be as significant as a large object known to definitely come from the aircraft. As we know, the only aircraft components capable of remaining relatively intact were the heavy steel components like the titanium engine and landing gear. The rest of the aircraft and it's contents, due to lack of material strength would have become part of the debris cloud.
There are several errors of reasoning here. First, there are other structures in the aircraft that are both massive and with high material strength, such as the main spar, the RAT, and primary oxygen supply.
Second, being massive and high strength did not guarantee that those components would exit intact -- between the two aircraft, we have a total of four engines and six sets of landing gear, out of which only fragments of two engines and one landing gear passed through clealy, with another main gear fragment getting wedged into the exterior columns before falling free.
Third, the strength of components is not the dominant factor in damage estimation, as we will revisit below. As a brief example that I explained to you
before, liberated fuel did plenty of damage, despite having virtually zero material strength. Momentum is the key, momentum that cannot escape the impact zone simply because the event is so large and so fast.
I think NIST definitely erred in using a homogeneous model. It unfairly describes the aircraft, and when combined with the model failing to confirm the only major observable criteria, the exiting engine and landing gear, it raises justifiable concerns when only their extreme case scenario succeeded in a collapse initiation.
Several problems with reasoning here as well, all of them brought up by me as early as
the first page of this thread.
NIST had no choice but to use a homogeneous model. We accept and declare this as a limiting assumption. I note that your early complaints did not include this, but rather you are echoing my acknowledgement of it.
Regardless, whether or not that assumption is a
flaw depends on a sensitivity analysis of the results. This is precisely why NIST ran three cases, and varied the ductility of the aircraft considerably (+/- 25% in the case of WTC 1) to see the effects. What they found was that ductility had only a minor effect on the overall results. The damage in all three cases is driven by the pitch angle of the aircraft, and other factors such as speed, weight, and material strength have only a slight effect. This is evidence that, contrary to your assertion, the homogeneous assumption is valid. It does not introduce a significant amount of uncertainty when compared to the other, irreducible uncertainties in the model. I was surprised to find this, but I accept NIST's conclusion in this respect.
Another major reasoning error is that you refer to engine and landing gear exit above as
"the only major observable criteria," which they are not. I explained to you at length in
this post the wide range of selection criteria, and among them NIST considers the final disposition of engine and gear fragments to be a relatively (but not completely) unimportant observable.
And, as explained back on Page 1, recall that the non-exit of such components means they were stopped by the core, and that means the core suffered
less damage than it did in reality. Therefore, any simulation that does not end with those fragments exiting stage right is an
underestimate. This, again, biases us towards the more severe simulations. Yet somehow, you conclude the exact opposite.
I disagree that the jet fuel, even at 570 mph, as in the extreme case scenario, had enough concentratible momentum to cut the towers steel perimeter columns.
I'm not familiar with the word
"concentratible" when speaking of momentum.
I disagree with your disagreement. The work of
Purdue University confirms that, in aircraft impacts, the blow dealt by the aircraft structure is secondary compared to the effect of the fuel inside.
Furthermore, the NIST
NCSTAR1-2B also discusses the fuel impact, in its simplified core analysis in Chapter 10. Please turn to the P-I chart, figure 10-5, on page 374 (180 of the PDF). The impulse provided by the fuel is seen to be enough to fail
core columns, not just the weaker perimeter columns.
Unless you can support your disagreement, these analyses stand.
That argument may have merit when debating the downward forces acting on the towers at the point of collapse initiation but I feel it is less compelling when dealing with these lateral "slicing" forces.
As above, you have not supported why you find it "less compelling." NIST has described in detail why material strength of impacting materials is not the deciding factor. As shown above, the fuel itself, having virtually zero material strength, is capable of inflicting enormous structural damage.
Yes trajectory of course factors into what lines up with what, and therefore will determine where the relatively clear paths to the exit perimeter wall lay. The major stopper for large, heavy, materially strong objects prior to a clean exit, is of course the heavy steel core columns. Certainly they had the capacity to stop engines and landing gear, while obviously sustaining significant damage to themselves in the process. The fact that a jet engine and landing gear did in fact break through the opposite steel perimeter walls and exit the towers at over 100+ mph indicates a lot of core damaging aircraft components failed to do what the NIST simulation indicates they must have done.
Emphasis added for clarity. That's exactly correct, but it supports
my conclusion, not yours. The NIST less severe and baseline cases indicated the core columns etc. stopped those large fragments. Therefore, those cases either underestimated the severity of impact, or overestimated the strength of those elements. In either case, it means we must prefer the more severe simulations over the less severe ones. That's precisely what I've been saying this whole time.
You are arguing energy totals as the key ingredient and I disagree. Certainly the total energy is something to be considered and given a large enough energy budget, the landing gear and the engines could be ruled out as inconsequential in the greater scheme of things.
I'm not saying the landing gear and engines are inconsequential. I'm saying they are
indistinguishable in the model. Whether it's those specific fragments or other fragments, so long as the energy total is the same, we expect the model results to be valid.
The fact that the less severe and base scenarios failed to create a collapse initiation indicates there wasn't an overwhelming energy budget available.
No, it does not. The eventual collapse involved additional steps, simulating the fires and their effects on the structure. At this stage of calculation, NIST evaluated the less severe and baseline scenarios against other observable evidence, and found they were not the best fit --
independent of the ultimate finding of the investigation.
Additionally, as remarked above, the biggest factor in the simulation is the pitch angle of the aircraft. The energy budget isn't really the issue, it's where that budget goes. If the aircraft is pitched down, as in the less severe case, it expends too much energy on floor slabs, which reduces damage on core columns and doesn't match the clear pictures we have of sagging floors, damaged but still attached and contributing to the collapse. Also, as
Dr. Greening calculated, the aircraft had sufficent energy to
completely destroy (pg. 10-11) an entire floor's worth of core columns, had it hit with the right geometry and avoided the other energy sinks present.
The columns were vulnerable to focused energy and less vulnerable to dispersed energy of the same amount. Think of a karate chop. The same amount of energy delivered with the flat of the hand (large surface area) vs. the side of the hand (small surface area), when striking a board is going to produce two different results. I won't insult your intelligence by explaining that further.
If you were to concentrate the entire impacting energy of the aircraft into a single point, it would be certain to slice clean through the building, but that doesn't mean distributed forces can be neglected. It's not true. Distributed forces were responsible for nearly all of the damage to the core columns. Again, read Chapter 10 of NIST NCSTAR1-2B.
Because the aircraft was severely damaged on impact, there are few solid masses left to deliver these "concentrated" blows. Because few solid masses flew out the other side, and those that did were decelerated considerably, we conclude those masses delivered nearly all of their energy.
"Aircraft debris external to the towers (landing gear for WTC 1 and landing gear and engine for WTC 2) as documented by photographic evidence."
xc NIST NCSTAR 1-2B, WTC Investigation
NOT engine fragments but the whole heavy titanium steel engine!
Which only serves to support my contention that NIST over compromised their Model!
Again, backwards. If NIST had overcompromised their model, their model would predict
more debris exiting the structure, not less.
A complete heavy titanium steel engine in the case of WTC2, not just fragments which only lessens the apparent significance!
Ditto.
Not a big deal? Malcontents? Excuse me for not rolling over and accepting every word of the NIST conclusions. The global results of the NIST simulations are surprisingly accurate? I guess accuracy is based on the fact that sure enough, NIST tweaked the extreme case scenario and sure enough the towers fell. just like in reality..case closed.
Again, the global results of the NIST impact simulations were compared to numerous observations, none of which was whether or not the towers fell. That conclusion depends on other, later scenarios.
I am impressed by NIST's beautifully presented final report. It looks sweet doesn't it? 10,000 marvelous pages of professional excellence! Who could not love text that looks so good? Well I hate to tear the wrapping paper but the bottomline is the content.
As stated above, your misgivings about the content appear to be rooted in personal incredulity, which is not tempered by professional experience, training, or calculations. I freely admit it is not perfect, indeed I outlined in detail my concerns, but even if we follow your arguments we should agree with their conclusion -- that the more severe trial is the best fit out of the three, for both WTC 1 and WTC 2.
I'm sorry, it doesn't matter if 9,999 pages of the report are true, if one page of critical flaws remain.
That depends, but thus far you have not demonstrated a single flaw.
Which makes their results and conclusions all the more subject to question!
I hope I haven't distorted your quotes this time.
I have no issue with questioning the NIST results. I encourage it. What I am endeavoring to counteract are misunderstandings of what those results are, and the illogical conclusions drawn from this misapprehension.
NONE!
I place more importance on the only proven observable than you do!
As I have asked you repeatedly, and you still have not answered, one of the three cases is the best fit to what we observed. We need to select one before we can proceed. NIST selected the most severe cases and justified their choices. I agree with them. You have not disagreed, instead you reject selecting
any of the three.
And as explained above, the final distribution of landing gear is
not the only proven observable, nor is it even the most significant.
Regarding NIST and pdf page numbers, I know the difference and I always reference to the NIST page numbers which are clearly marked. If I was in error in saying you didn't do this, I apologize.
Yes I made a typo on elastic/inelastic.
Apology accepted and correction acknowledged.
I am well aware that there was a "cloud" of objects moving at high velocity inside the towers once the aircraft disintegrated after punching through the perimeter wall.
Just because I isolated the effect of one object, does not negate my point about deformation damage as invalid.
Some of the objects were trapped inside the WTC and some of the objects punched the perimeter walls, making high velocity exits, carrying their remaining destructive potential with them.
Diffused energy due to a high velocity spread of small, relatively soft particles is not going to have the potential for deformation damage that large relatively intact titanium steel jet engines and landing gear will.
Again, you state this from personal incredulity. It is not true. The majority of impact damage in the core
was due to "diffused energy," essentially a pressure load on the columns themselves. This is because the aircraft almost completely shattered as it smashed through the perimeter columns.
Focused energy is more damaging to the core than distributed energy.
It isn't in this case because the focused energy was a very small fraction of the total. Had the aircraft been unloaded, empty of fuel, etc., the significance of the landing gear and engines would have been greater.
I won't argue that liquid moving at high speed carries significant mass and thus significant force, momentum and transferable energy. Since the bulk of fuel is carried inside the wings, it's impact force will be significantly spread out while being further lessened by contact with office components and interior walls. I really question how much impact damage the jet fuel had on critical building structural members.
The NIST report answers this question.
I have no wish to go off on a tangent by including the Pentagon in this discussion.
A pity, because besides the Pentagon, I am unaware of even a single other example where a fueled aircraft hit an office building at cruising speed. These are very rare situations we're talking about, and the Pentagon is perhaps the best parallel that exists.
However, if you decide to read the
Pentagon BPR, you will discover that, just like the WTC cases, the structure shows almost no signs of column damage due to blunt impact. The majority of columns that failed in the Pentagon interior failed because of so-called "distributed loads." This is yet more evidence that your assertions above, that the massive fragment trajectories dictate damage in the WTC cores, is totally incorrect.
No doubt in the volume of posts I have omitted replys to some of your questions. If my answers are important to you, I suggest you re-ask or move on.
I have asked my questions several times. I am also quite aware that you have seen them, because you replied to both of them without giving me an answer. However, I sympathize with the sheer weight of this discussion, although you did ask for clarity and thoroughness, which I have now delivered. Let me then restate the question, carefully and thoroughly:
The NIST impact model, captured in NIST NCSTAR1-2, is principally concerned with the state of the
core columns immediately following aircraft impact. This is because the perimeter columns were photographed, allowing a direct assessment of their status, whereas the core was impossible to inspect. To this end, NIST created a simulation of each impact. Each impact had multiple uncertainties with respect to the state of the aircraft and the relative strength of both aircraft and structure.
NIST therefore created three cases for each simulation. The baseline contained the best guess for all of the uncertain parameters above. The less severe case contained a reasonable lower bound (think of this as "one sigma") for all uncertain parameters. The more severe case contained a reasonable upper bound (except for WTC 2, it was forced closer to the baseline). The results from all three trials were compared against each other to ascertain sensitivity, and to the catalogue of observations to determine which was closest to reality.
Before proceeding, NIST had to decide which one was the best fit. In both cases, NIST decided the more severe case was the best fit, and furthermore concluded it was in acceptable agreement with observations.
Here's the question: Which one do you think is the best fit? And why? Like NIST, you must choose one, and only one answer.
Thank you for your careful attention.
