The 9/11 Forum

OneWhiteEye wrote:Opinion and speculation follows.

Ablation is secondary to the whack, a consequence of the whack, and a bit of a stretch of the term. Most of the simple models work with accretion, mass gets swept up in the descent. Mass shedding, in this scenario, acts to slow descent. With ablation, mass gets left behind. It doesn't cause anything to speed up, rather it can allow certain parts to continue to descend at very nearly the rate prior to collision because other parts were left dead stopped and detachment occurs with much less energy than accretion and crushing.

Ah, like a diffusion limited aggregate

War Wheel wrote:Ah, like a diffusion limited aggregate

searching... learning...

I should say that the analogy to DLA is (strictly) with the accretion part of the story. Ablation rate would be determined by the natural size chuncks these types of structures like to pull apart into. Obviously that will be a function particle "stiffness"

Ahh, OK. That's a pretty picture, and a fascinating subject.

I was thinking in terms of the arrow of time reversed. Or negative sticking coefficient? Diffusion enhanced erosion?

A accretion model sweeps everything up on the way down. An ablative model loses mass at the weakest points subjected to stress from collision. Obviously it's energetically favorable under certain circumstances to break pieces off and leave them behind.

Just to get this through my skull, are we talking about mass loss from the objects being pulverized at the crush front, or mass working its way loose from the accretion blob? The blob is going to have a structure like the pretty picture. It's basically a giant dust bunny (only heavier).

War Wheel wrote:are we talking about

Watch the video until you go blind, then say what you see...is a good rule of thumb


http://www.youtube.com/watch?v=Ya95idZayPw

femr2 wrote:

War Wheel wrote:are we talking about

Watch the video until you go blind, then say what you see...is a good rule of thumb


http://www.youtube.com/watch?v=Ya95idZayPw

I am officially blind.

If the "ablation" rate ends up being a function of velocity (intuitively seems so), the hammer driving the nail will tend to converge on a distinct size and maintain.

There has not been much study of the visual behaviour of the south side.

What would productive is discussion of the various features.

One question would be...

What causes the south side *dust jet* to emerge significantly before the west face plume ? They are at the same vertical position, roughly. The internal structures which may have been suggested as explanation, such as the internal corridors, don't support an over-pressure effect in a reasonable way.

Another would be...

The SW corner. How can the corner behave so similarly to the NE corner of WTC 2 ? The impact damage was entirely different, and the SE corner damage to WTC 2 was supposedly caused by the engine of the impacting aircraft. That behaviour cannot apply to WTC 1, so what could cause such a similar focus on position ?

Etc...

War Wheel wrote:Just to get this through my skull, are we talking about mass loss from the objects being pulverized at the crush front, or mass working its way loose from the accretion blob?

The former; mass loss from the 'upper block' as it descends, not entraining material but rather paring down erosively or even catastrophically.

The blob is going to have a structure like the pretty picture. It's basically a giant dust bunny (only heavier).

If instead the upper block is considered the dust bunny (with some dense and strong components, not necessarily both), and if DLA were extended with a negative range of sticking coefficients which allowed for breaking pieces off the aggregate as well as sticking, then I think that describes the situation I'm imagining. The simple 1D accretion models would have a sticking coefficient of 1 in this scheme, and it's pretty obvious that didn't really happen. What I see is a reaction proceeding in both directions but dominated early on by loss, a scenario which, if interpreted within the framework of accretion (a mistake) would lead to a slower collapse front progression. If interpreted correctly, it provides a means of achieving the natural terminal velocity more rapidly via less resistance at the lower velocities and a steeper rise of resistance as the mode switches over to accretion. That would happen (excluding a deflection-dominated phase in between - cleaver mode - but that's another subject) because:

If the "ablation" rate ends up being a function of velocity (intuitively seems so), the hammer driving the nail will tend to converge on a distinct size and maintain.

Most astute! Yes, and I think that final form will preferentially be a hard dense nugget as the 'dust' of the dust bunny gets blown away, with a shape and orientation suitable for the cleaver stage, otherwise it wouldn't happen. But, if it can happen, it should. I think it could be a wedge composed of some part of core, perimeter and hat truss, with interstitial flooring, slipped inside the south perimeter.

Or the race-ahead in the SW could be the shock of the whack (harmless elastic waves), rapid eccentric loading ripping the structure apart, or a series of charges.

Now, I should stop derailing the topic. There are many curious things visible in the video, these should be discussed.

OneWhiteEye wrote:Now, I should stop derailing the topic. There are many curious things visibe in the video, these should be discussed.

Nah. Carry on. My head went a little numb there, but am sure if I read it a few times.
Is it worth a specific thread you think ?

femr2 wrote:

OneWhiteEye wrote:Now, I should stop derailing the topic. There are many curious things visibe in the video, these should be discussed.

Nah. Carry on. My head went a little numb there, but am sure if I read it a few times.
Is it worth a specific thread you think ?

It would be, but I just shot my wad up there. Someday, there may be more to say. I just think it came a step closer to being possible, either in the rigid wedge or rubblized context. I see a bucket being tapped out - hard.

Someday, there may be more to say. I just think it came a step closer to being possible, either in the rigid wedge or rubblized context. I see a bucket being tapped out - hard

Basically this is a more realistic way to cause what we have called OOSRD. Nobody has been able to describe how rubble vs OOS flooring really works that matches observables.

Your comments are consistent with what I see in the rubble. You would think that after 90 floors of OOSRD we would see evidence of it in the rubble at the base of the OOS regions within the footprint.

I don't see sh*t. There is no noticable pile-up of rubble at the base of OOS regions.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Back on subject, the collision seems to stand out the most. This is the first blunt, structure vs structure collision we see in WTC1, 2, 7.

First question: Why collision? Two major firm discontinuities are making contact in the dust and smoke after about a 10 floor fall. WHat are they? For a natural collapse we expect a somewhat continuous runaway process as top and bottom destroy one another. How can a major discontinuity in the process be explained from the point of view of natural collapse?


(I can from a demo point of view as floor 104 meets fl 92. Manipulation along all 47 CC bolted connections located on fls 92, 95, 98, 101, 104 naturally lead to the expectation of a major discontinuity as 92 meets 104).

The 104, 105 fl fire on the west face, south side flairs up during the fall. We can see the fire fall downwards and then it stops (presumably when the 104, 105 floors were crushed).

Using the fire we can see how far fl 104 was able to fall without being destroyed. It looks like the fire stops moving downwards at about floor 98? That makes the collision after about a 6 floor fall?


A clip from the north shows the antenna jerk to the east, from einsteen

http://www.youtube.com/user/einsteen?blend=2&ob=1#p/u/8/e64yr9SZb-Q

Slightly different version, richer colour information, but a bit more fuzzy...have focussed on the fire in the GIF, but the video is full frame...

http://www.youtube.com/watch?v=jhqKoRLP7BA

Any comment on the traversal of fire from the east half ?

I will do a compound difference time lapse of this and post it here.

War Wheel wrote:I will do a compound difference time lapse of this and post it here.

It'll need stabilising first. SynthEyes does a great job.