Physics Of 9/11 Events - Part 3, continued from: 9/11 Events- New thread

[continued from 9/11 Events - New thread ]

Previous two threads :
Basic Physics, Correct Analysis of WTC Towers Collapse
911 WTC - Evidence of an Nuclear explosion?

This thread is solely for sci-tech discussion of 9-11. If you want to discuss politics or other things, please find another board.

A. N. Kounadis
Nonlinear Dynamic Buckling and Stability of Autonomous Dissipative Discrete Structural; Systems : Potential Systems
in
NONLINEAR STABILITY OF STRUCTURES: THEORY AND COMPUTATIONAL TECHNIQUES
A.N. Kounadis & W.B. Kratzig (eds.)
Springer, 1995, pp 73--142

has a fine example of a two degree-of-freedom model of a bent, imperfect column. This approximates the condition of the intact core columns in WTC 1 just before collapse initiation. Kounadis then subjects the column model to a suddenly applied load of infinite duration, which again approximates the state of WTC 1 immediately following the wedge-in.

Amazingly, for certain values of the parameters, the column undergoes nonlinear oscillations 'of very small amplitude ... for a period of 45 times the fundamental period of the unloaded undamped system, and thereafter an escaped motion leading to a dynamic buckling is initiated.'

This post has been edited by David B. Benson on Feb 1 2007, 11:12 PM

You'll notice that in Southwark implosion that the demolition squibs precede the implosion, not follow it as in the case of the WTC collapses.

The speed of the air compressed in the WTC collapse is higher than the speed of the descending debris front, allowing for the appearance of "squibs" ahead of the collapse front.

Another explanation for the appearance of "squibs" ahead of the collapse front might be that massive structural elements, due of their greater momentum, were either able to outpace the main collapse front, or simply got a head start on it.

Is it possible that some massive elements such as elevator motors could have achieved enough momentum on their own to overcome the strength of a given area of truss/slab floor?

Another reason for the Squibs could be, fuel air explosions inside the twin towers core. Since the dense black smoke is essentially carbon dust.
The inside of the buildings is coated with carbon dust that plus small particles of Iron dust from fracturing beams could lead to explosions.

Seems most unlikely. The so-called squibs from WTC 2 appear to be coming out the ventilators at stories 75--76. So these appear to be just compressed air escaping down the air shafts.

I previously worked out just how easy it was to overpressurize the towers once the collapse was well started. At just 7% overpressure the windows will begin breaking. Furthermore, NEU-FONZE states that the so-called squibs are moving laterally at about the same speed as the descending mass. This strongly suggests that these are just compressed air.

This post has been edited by David B. Benson on Feb 2 2007, 12:30 AM

Over a year of debate on the technical aspects, begs the question why there was no similar forensic analysis of the incident on behalf of the US government.

I feel this thread has served its purpose.

Wow!

This thread morphs yet again!

But I guess it's the thread that won't die...

The last thread began with this bold proclamation from the moderators:

"This thread will be excessively moderated:
all off-topic, offensive posts and spam will be removed and violators will be banned! This thread is ONLY for discussion of physics behind the fall of the WTC. No politics! No useless links! No irrelevant images! "

Well, so much for that promise (until recently)!

Anyway, lateral and even backwards ejection of debris is to be expected when a brittle target (concrete), undergoes hard impact. The ejecta velocities are in a statistical range that spans values that are less than or equal to the impact velocity. Some impact energy may even be converted to rotational energy of the ejected material but experimental data show this contribution to be relatively small.

NF

This post has been edited by NEU-FONZE on Feb 2 2007, 02:35 AM

For those who want to tinker with a continuum model, there's free software on the web called ODE Toolkit that uses Java. It can be used to predict the position and velocity of the collapse front. See the plots below of front position x vs. t and front velocity v vs. t.

http://odetoolkit.hmc.edu/download.html

For definitions enter:

v' = 9.81 - v^2/x
x' = v

and hit 'enter ODE'. These are the ODEs for stage 1 crush-down for conditions of no resistive force (E1=0), stretch=0 (100% compaction), no mass shedding, and constant mass density.

For initial conditions enter:

t: 0
v: 0
x: 52.92 (the height of the 14-story upper block in m)

Hit 'solve forward'. The graph will show the v vs. t or x vs. t plot. The graphs sometimes get skewed a little when switching back and forth between graphs. Hit the 'clear all' and then 'solve forward' button to refresh if needed.

x equals 416 m when the front reaches the ground (x is measured from the top of the tower). The x vs. t graph shows that t equals about 11.7 s at 416 m. This is the duration for stage 1 and is close to Greening's discrete model value of 11.6 s (see first pic).

At x=416 m the v vs. t graph shows that front speed v is about 52 m/s. That value also agrees with Greening's value of 51.2 m/s (second pic).

t = 11.7 s (stage 1 duration)
v = 52 m/s (front velocity at ground)

Different values of x can be tried to see what happens to the duration for different upper block sizes.

For WTC2, x=109.6 m (size of upper block)

t: 0
v: 0
x: 109.6

The ODE solver at x=416m gives:

t = 9.8 s
v = 52 m/s

Those values agree with Greening's 9.7 s and 50.7 m/s.



http://i134.photobucket.com/albums/q91/sha...E/wtc1ode1x.jpg

http://i134.photobucket.com/albums/q91/sha...DE/wtc1odev.jpg

This post has been edited by shagster on Feb 2 2007, 07:09 AM

The ODEs had to be written as follows for the software to recognize them.

v' = 9.81 - v^2/x
x' = v

The original diffeq that was derived in a previous post for stage 1 was:

x'x' + xx'' = xg

The software wants primes to be on only the left side of the equation. Solving for x'' gives:

x'' = g - x'x'/x

The software also can't deal with double primes, so an extra equation is needed:

x' = v

That gives:

v' = g - v^2/x
x' = v

v' = 9.81 - v^2/x
x' = v

The two graphs below are plots of x vs. t and v vs. t for three cases: WTC1, WTC2, and a hypothetical case where the upper block is of infinitesimal height. For the third case, I selected x=0.001. The solver hiccups if x is zero.

Notice that for the case of x=0.001, the velocity is linear with time which means the acceleration is constant. The slope of v vs. t is about 52.5/16 = 3.28 m/s^2 which is g/3. At x=416m, t is about 16 seconds. This is the boundary condition for the case that Cherenapov was referring to. It doesn't represent the towers since the size of the upper blocks were 52.92 m for WTC1 and 109.6 m for WTC2. Those sizes give stage 1 collapse durations of 11.7 and 9.8 seconds, which are much shorter than 16 seconds.

When the upper block is of finite height, the front acceleration varies with elapsed time.





http://i134.photobucket.com/albums/q91/sha...ODE/wtcode4.jpg

http://i134.photobucket.com/albums/q91/sha...DE/wtc3ode5.jpg

This post has been edited by shagster on Feb 2 2007, 07:13 AM

" -v^2 + a. v^2 / 2a = - g. v^2 / 2a,

in which case a = g !!!!!!.
Perhaps this explains why the WTC 7's collapse, which was entirely crush up, was so fast.....

NF"

For the case of E1=0, stretch=0, and constant mass density, a bottom-up will occur at an acceleration of g. Even with a moderate value of E1, the duration will be close to that of free fall since the collapse starts with the entire mass of the buildng falling.

See the last set of figures in BV. For the towers collapsing bottom-up, the duration would be 10 seconds or less for values of E1 of 2 GJ per story or less. For E1=0.5 GJ, the duration is nearly the same as that for free-fall.

This post has been edited by shagster on Feb 2 2007, 07:37 AM

I remember reading comments by a FDNY fire chief who detailed how unburned combustible gases could collect in the floors above the fires in the WTC towers, and then upon mixing with sufficient oxygen, could ignite and explode.

Until reading the chimney fire article, it hadn't occurred to me that those same exhaust elements could also condense out onto structural members, and in time build up and ignite.

It was a way to transport combustibles from the fuel rich office areas to the fuel deficient areas of the cores.

While the areas of combustion constantly moved, the pathways for exhaust seemed to remain constant. This would allow for the deposition of reactive exhaust products to concentrate in specific pathways.

If the ignition of these combustible layers in turn led to ignition of structural members themselves, it could have been a contributing cause of the collapses.

Chainsaw, you've probably been making this argument for some time, but in my case it didn't sink in until now.

MMC,

Yes the thread has proved a purpose. As my favorite sport casters like to say "Let's go to the tape!"

Most scientific polls are pointing to better than 85% of the American population feel they are not being told the truth about 911.

The information stage is getting into the end game. It will soon be time to clarify and promote patriotic and legal action.

NIST has had 6 years and despite changing their story more than once, they still can't tell us why the buildings fell. Six years later and they are just getting around to showing their ignorance about Building 7.

Alright, so let's clarify the issues.

1. Molten steel is heading the list. NIST's discovery of sulferization of the steel is confirming evidence to Dr. Jones' theory of thermite/thermate. Occam's Razor is favoring this as being the most probable cause for the "molten steel" pools that burned for a 100 days. (OT: Perhaps Robert Hawkins is right and we should find out "who" those "cable up" guys were just before 911. Still not physics or science related to 911 unless you include criminology as an acceptable venue for these boards. I don't think the moderators will buy it)

2. "Cancer Cluster" in the 911 on site people and the following medical examinations should rule out, or for, a nuclear event being the cause for the molten steel.

3. Dust studies are in the works and probably will be studied for a century to come.

4. Seismic evidence will be hotly debated.

5. Action: NIST/FEMA must release all the data. The data must at a bare minimum be public information for the scientific community.

Please feel free to add to the list of scientific study yet to come. There are so many!

I think this thread did a lot to wake up a few people. Where it goes is another thing. We all saw Building 7 going into almost perfect free fall, and "lucky" Larry confessing to "pull it," but to date, nothing changed.

Help me identify the French Philosopher that discovered "the only constant in life is change." Or did he say "the more things change, the more they stay the same."

This post has been edited by beijingyank on Feb 2 2007, 01:27 PM

I was under the impression that the wings of the planes pretty much shredded upon entering the towers, until I read this statement by Stanley Praimnath, who was on the 81st floor of WTC 2 when the plane struck.

His office was in the southwest corner of the 81st floor, which would put his office door and the plane wing on the interior of the floor, possibly close to the core.

I assumed most of the wreckage ended up in the northeast corner.

A wing in the vicinity of the core would make a potent source of heat if ignited.

beijingyank

About the same percentage think the Creation story in Genisis is a factual acount. Never underestimate the ability of the general public to be misinformed. Science is NEVER a popularity contest.

NIST did an excellent investigation and explanation of the towers collapse. Just because you have not read/understood it does not change the FACT that it stands unchallenged.

You have yet to show a single instance where molten STEEL was found anywhere in the WTC complex. Molten steel is still just a disinformation mantra from the know-nothing crowd. All such reports turned out to be bogus.

The cancer and other ailments are caused by the inhalation of dust, according to the medical community. Any speculation about nuclear devices is illogical and foolish. A nuclear event would have been obvious and would have immediately destroyed everything for blocks around the complex. The smallest nuclear explosion possible would have left a glass lined smoking crater and the electro-magnetic pulse would have wiped the memories of every video camera within line of site. There was no nuclear event on 9/11, this is just the speculations of an ignorant mind and a red herring.

Not by the experts(expert=someone who knows what he is talking about), they have already ruled out any explosives(which leave distinctive traces absent in all the data).

Already done(which you would know if you bothered to look).

Grumpy