The 9/11 Forum

femr2 · by **femr2** on Wed Nov 04, 2009 11:37 pm

Initial data for linear ejecta traversal from West face of WTC 1:

http://femr2.ucoz.com/photo/linear_2/6-0-217
http://femr2.ucoz.com/photo/6-0-217-3 (1280x720px/74.6Kb)

Source video in H264 format (1280x720x25fps):
http://femr2.ucoz.com/ffdemhd_264.avi

Crop of West Face Ejecta:

http://www.youtube.com/watch?v=BMeTGfCZWMI
http://www.youtube.com/watch?v=2F5Tw2ITMF8

http://femr2.ucoz.com/photo/6-0-219-3 (1234x731px/67.0Kb)

http://femr2.ucoz.com/photo/6-0-220-3 (1224x730px/87.3Kb)

Code: Select all: Tracker1 0 721.476 375.888 1 721.696 375.767 2 721.786 375.408 3 721.557 376.272 4 721.589 375.405 5 721.523 375.117 6 721.536 374.440 7 721.702 374.986 8 721.823 374.718 9 721.890 373.537 10 721.904 373.412 11 722.034 373.501 12 722.239 373.204 13 722.288 373.265 14 722.315 372.381 15 722.423 372.789 16 722.255 372.125 17 722.535 372.497 18 722.852 372.621 19 722.631 371.841 20 722.793 371.743 21 722.827 371.847 22 722.981 371.589 23 723.136 371.182 24 723.382 370.738 25 723.224 370.404 26 723.224 370.024 27 723.677 369.614 28 724.114 369.077 29 723.977 368.649 30 723.831 368.179 31 723.895 367.813 32 723.816 366.855 33 724.307 366.007 34 724.275 365.239 35 724.010 364.010 36 722.378 365.754 37 722.322 364.987 38 722.356 364.142 39 722.513 363.098 40 722.643 361.575 41 723.096 360.693 42 723.314 360.003 43 723.005 358.306 44 722.755 356.862 45 722.338 353.314 46 721.611 349.568 47 721.799 348.582 48 721.889 347.614 49 721.201 345.762 50 720.922 344.640 51 720.986 344.161 52 721.178 343.460 53 721.100 342.730 54 721.049 341.913 55 720.598 340.999 56 720.528 339.843 57 720.435 339.126 58 720.551 337.950 59 720.641 336.576 60 720.600 333.557 61 720.632 332.382 62 720.666 331.251 63 720.977 328.214 64 721.196 324.659 65 721.027 324.176 66 720.872 323.056 67 720.715 319.442 68 721.311 316.582 69 721.420 314.769 70 721.152 311.920 71 721.441 309.419 72 722.035 306.544 73 722.081 304.624 74 721.956 300.797 75 721.828 298.748 76 721.627 299.510 77 721.540 298.074 78 721.502 297.110 79 721.428 296.212 80 721.376 294.837 81 721.423 292.971 82 721.756 291.283 83 721.655 289.267 84 721.697 287.807 85 721.738 285.502 86 721.548 283.144 87 721.064 279.980 88 720.074 280.793 89 719.950 280.047 90 719.805 279.261 91 719.800 279.212 92 719.511 279.090 93 716.514 267.100 94 716.386 266.929 95 716.764 266.540 96 716.956 266.266 97 717.002 265.814 98 717.003 265.281 99 717.080 264.576 100 717.133 263.321 101 717.282 263.370 102 717.346 262.469 103 717.545 260.871 104 717.946 257.634 105 717.865 251.882 106 718.090 250.194 107 718.073 248.865 108 718.098 245.680 109 718.037 239.270 110 718.085 237.249 111 718.387 236.537 112 718.721 235.793 113 718.519 233.065 114 718.472 228.316 115 718.422 227.104 116 718.653 225.120 117 718.545 222.672 118 719.019 221.439 119 722.126 213.375 120 722.246 211.262 121 722.001 209.885 122 721.852 207.668 123 721.908 206.588 124 722.097 204.839 125 721.176 201.106 126 722.181 200.257 127 722.095 197.693 128 721.876 195.204 129 721.547 191.086 130 720.900 188.512 131 722.005 190.771 132 721.005 189.940 133 720.947 189.156 134 722.433 186.081 135 721.467 186.299 136 721.357 185.068 137 721.178 184.047 138 722.741 180.704 139 721.809 179.750 140 721.815 177.667 141 722.808 176.460 142 721.805 174.569 143 721.649 172.482 144 721.519 169.953 145 721.750 167.671 146 721.297 164.847 147 721.582 163.334 148 722.217 161.045 149 721.223 158.648 150 721.321 154.494 151 720.598 147.592 152 720.305 143.547 153 720.073 141.692 154 720.971 140.331 155 721.675 140.290 156 720.780 139.178 157 721.064 137.044 158 721.232 134.618 159 721.280 132.761 160 721.083 129.975 161 721.170 127.780 162 721.291 125.300 163 721.254 123.477 164 721.098 120.468 165 721.266 119.545 166 721.144 118.425 167 721.476 116.745 168 721.339 115.437 169 721.787 114.309 170 721.950 113.038 171 722.083 113.299 172 722.955 106.587 173 723.276 106.367 174 723.597 106.324 175 723.774 99.059

Note: The first section of data is very difficult to determine (the curved section) and further work is required to separate the initial descent ejecta from the latter linear ejecta.

Correlation with other videos will be required to improve data quality, specifically this close-up BBC footage:
http://www.youtube.com/watch?v=zb1PfiBT7A0

I also need to determine the scale in order to convert the raw data into velocity...

Footage is 25fps. Data is per-frame.

---

OneWhiteEye wrote:First, it's not precisely linear, though that is a reasonable approximation after about 2 seconds. Taking the running averages and the fit, the speed increases to a plateau then begins to decrease. This is most interesting. If the peak is less than or equal to terminal velocity as calculated by David B. Benson for the standard model, then it is somewhat less interesting but still would leave much to explain.

OneWhiteEye wrote:Roughly, I get about 25 m/s at about 5 seconds in. However, most of that speed is achieved by the 3 second mark, so if it ends up being more nearly constant, the time interval to reach peak ~ terminal speed is maybe closer to 3 than 5 seconds.

It may be more appropriate to think of the rest of the internal progression being slow, rather than this part being fast. Roofline fast, inside slow, except for the part with the most mass on it and where the upper may have slipped inside. Hmmm.....

Double-checking encouraged.

I'll check for aspect ratio, and scale to vertical features rather than the horizontal scaling I've used, but 25m/s seems a reasonable mark (I get 27 with very dodgy measurements

)

David B. Benson wrote:
femr2 wrote:What was DBB's terminal velocity figure ?
About 28.8 m/s for the advance of the crushing front (material speed is necessarily less) but already at 3.76+ seconds the crushing front is advancing at 28.5 m/s. At 3.0 seconds the crushing front was advancing at 26.35 m/s by the calculation I'm currently looking at (and reporting).

David B. Benson · by **David B. Benson** on Wed Nov 04, 2009 11:58 pm

OneWhiteEye --- From the B&L thread: Interesting to note that the model is quite close, even more interesting since the propagation is not uniform laterally and this is the very fastest part we're talking about, of what can be seen.
Laterally? Do you mean horizontally?
What is the nonuniformity?

OneWhiteEye · by **OneWhiteEye** on Thu Nov 05, 2009 12:04 am

Yes, I do mean in the horizontal dimension. The non-uniformity is that the measurement is for the lowest, fastest indicator of destruction, most of the rest of the visible exterior shows no signs of anything. This part is way ahead.* So, non-uniform location of crush front as one moves around in either horizontal coordinate.

* or the rest is way behind, a not so subtle difference.

David B. Benson · by **David B. Benson** on Thu Nov 05, 2009 12:13 am

OneWhiteEye wrote:The non-uniformity is that the measurement is for the lowest, fastest indicator of destruction, most of the rest of the visible exterior shows no signs of anything.

Surely dirty air is being expelled?

This part is way ahead.

Way ahead of what? How far ahead, vertically?

So, non-uniform location of crush front as one moves around in either horizontal coordinate.

Sorry, but this sentence communicated nothing to me. Does this mean this phenomenon (whatever it is) is different on the three observable faces? Help, I'm lost.

femr2 · by **femr2** on Thu Nov 05, 2009 12:30 am

David B. Benson wrote:
OneWhiteEye wrote:The non-uniformity is that the measurement is for the lowest, fastest indicator of destruction, most of the rest of the visible exterior shows no signs of anything.
Surely dirty air is being expelled?

No. Here's a closer view. The focus is upon the ejecta directly from the West face:

This part is way ahead.
Way ahead of what? How far ahead, vertically?

Quite a bit.

So, non-uniform location of crush front as one moves around in either horizontal coordinate.
Sorry, but this sentence communicated nothing to me. Does this mean this phenomenon (whatever it is) is different on the three observable faces? Help, I'm lost.

Yes. Not visible on North Face. Some similar behaviour on East face, but would need to illustrate the difference. South face is an unknown as far as I'm aware.

Will probably have to include additional footage to prove to you that the ejecta is not from the South face, but no problem to do so. The video's linked by MT and myself earlier in the original thread illustrate quite clearly. My estimate is at least 1/3 towards North Face.

OneWhiteEye · by **OneWhiteEye** on Thu Nov 05, 2009 12:30 am

David B. Benson wrote:
OneWhiteEye wrote:The non-uniformity is that the measurement is for the lowest, fastest indicator of destruction, most of the rest of the visible exterior shows no signs of anything.
Surely dirty air is being expelled?

Yeah, you'd think, and it is elsewhere. Nevertheless, I have a very hard time reconciling that with what I see. I know you haven't been convinced by arguments concerning overpressurization in a plenum (open floor plan), but try thinking of it as an overpressure that occurs on a given floor that manages to blow chunks out violently across a localized region but somehow doesn't seem to affect the rest of the floor.

Way ahead of what? How far ahead, vertically?

Way ahead of anything else visible. How far, I'll need to look. Long ways.

So, non-uniform location of crush front as one moves around in either horizontal coordinate.
Sorry, but this sentence communicated nothing to me. Does this mean this phenomenon (whatever it is) is different on the three observable faces? Help, I'm lost.

Yes, that's pretty much what it means. The phenomena is only visible on the south side of the west wall, of the two faces that are visible. The third face is slightly out of view, but if it were spewing like this it might be visible anyway.

This is like setting off a bomb (sorry, it's the only analogy I could come up with) inside a car and having only one window blow out, with seats, dashboard and steering wheel all exiting out the one hole.

I'd much sooner believe it's a localized wedge of the remnant upper block moving down inside according to your mechanics, than I would any advanced overpressure. As I say, there are those, too, but they are something else. Like friggin rocket motors firing out a window. This is a wave traveling down a localized portion of the exterior. It is coherent in perimeter location from story to story, though its vertical displacement is in fits and starts.

David B. Benson · by **David B. Benson** on Thu Nov 05, 2009 12:40 am

femr2 wrote:The focus is upon the ejecta directly from the West face:

Thank you, I follow that! I take that as the location of the crushing front, although maybe 1--2 stories below.

Quite a bit.

I'll have to take your word for it, don't see it myself.

OneWhiteEye --- Either overpressure well ahead of the actual crushing front or just possibly (parts of) the core collapse faster than the main portion; stuff can fall down elevator shafts, for example.

Trippy · by **Trippy** on Thu Nov 05, 2009 2:45 am

This part is way ahead.
Way ahead of what? How far ahead, vertically?

Quite a bit.[/quote}
That's something that has always intrigued me.

Why does the debris cloud (the falling debris) look like it has a lean on it.
I've noticed it in shots similar to this, and it almost always seems to be there (read always, as far as I can recall), but I don't think it's something i've ever seen adressed or discussed.

To me, the debris to the left of the image look like they're falling towards the tower, and the debris to the right look like they're falling away from it.

OneWhiteEye · by **OneWhiteEye** on Thu Nov 05, 2009 3:17 am

I kinda see it as something ripping through the medium in much the same way as... something does on the north side! Only much sooner than the north side.

Sure, there could be overpressure expulsion at the leading edge of this, can't deny that. I'd bet if a floor diaphragm were punched at 25+ m/s by a large part of another floor and its contents (and so on), debris would blow out from the story below well ahead of the bulk of descending mass impacting the floor. No doubt it would contribute to pressurizing the open space and core passages, which then might produce limited expulsions on floors farther ahead or vent above.

Qualitatatively, there is no way I've found to distinguish the characteristics of this front from the other one coming down later on the north side. On the north half, expulsions appearing very similar proceed in fits and starts at the front, increase in intensity (volume and ejection speed) and are followed by empty space appearing above, where formerly there was structure. Now, the difference with what's happening on the southern half of the west wall is that you can't immediately and directly see the state of the structure after this wave passes. Too much debris cloud.

Huge amounts of stuff is blown out, keeps blowing out as long as you can see it. I've watched it again and again while typing this. Nice; thanks femr2.

It really looks like there are at least two separate collapses going on. More than two, just two easily identifiable. I've loosely cut it into north and south halves, but it's an inaccurate simplification.

Heiwa · by **Heiwa** on Thu Nov 05, 2009 5:24 am

According DBB (and BLGB?) ejecta shall be 20% of "crushed" materials/elements. Remaining 80% shall form a compressed, high density (5X the original density of the structure) rubble layer, B, inside the foot print of the structure that is supposed to form a 4000m² large 'crush front'.
Are there any methods to verify this when checking the ejecta velocity?

femr2 · by **femr2** on Thu Nov 05, 2009 5:37 am

OneWhiteEye wrote:I'd much sooner believe it's a localized wedge of the remnant upper block moving down inside according to your mechanics, than I would any advanced overpressure. As I say, there are those, too, but they are something else. Like friggin rocket motors firing out a window. {chop}
Sure, there could be overpressure expulsion at the leading edge of this, can't deny that. I'd bet if a floor diaphragm were punched at 25+ m/s by a large part of another floor and its contents (and so on), debris would blow out from the story below well ahead of the bulk of descending mass impacting the floor. No doubt it would contribute to pressurizing the open space and core passages, which then might produce limited expulsions on floors farther ahead or vent above.

Do you think it is possible to have the *dust jet* ejections (I like the rocket motor analogy :wink:

) and any other forms of overpressure occurring in the same region, at the same time ? Would mutually exclusive be reasonable ?

(Duty bound to add I think the ol' dust jets still require discussion, specifically position, orientation to core, sequence, scale, ...)

femr2 · by **femr2** on Thu Nov 05, 2009 5:44 am

Trippy wrote:Why does the debris cloud (the falling debris) look like it has a lean on it.

Worth actually checking out (I haven't for your specific question) but I'd imagine the result *could* be that it's an effect of the wind...prevailing wind direction was ESE/SE. The smoke column does shift as a whole...

http://www.youtube.com/watch?v=0f6oJHj-_GA
http://www.youtube.com/watch?v=xtNf8GXQ6wg

Very strange smoke column behaviour when watched on loop

Not saying it *is* wind, but it's possible (and the simplest and least scary possibility).

Trippy · by **Trippy** on Thu Nov 05, 2009 7:18 am

femr2 wrote:Do you think it is possible to have the *dust jet* ejections (I like the rocket motor analogy ) and any other forms of overpressure occurring in the same region, at the same time ? Would mutually exclusive be reasonable ?

Consider the point that an over-pressure isn't actually required to generate these dust jets - remember the calculations I did elsewhere - I'll go into a little more detail.

WTC 1&2 were 63.4m on each side, and the floors are 3.66m apart (both figures rounded to 3sf) this gives us a total volume of air between the floors of 63.4*63.4*3.66 m^3 or 14,700 m^3 (again, rounded to 3sf).

The first thing to realize is that this volume includes the space occupied by the core columns, which introduces an error in the form of a volume of air that will be included in the calculations, but can not be expelled by the collapse.

Now, if we assume we are dealing with the first collapsing floor, and, for the sake of simplicity, assume that it falls as one intact piece onto the floor below it, then we can calulate (using s=(gt^2)/2 that it takes 864ms (3sf) for an object to free fall 3.66m, this tells us that we have 864ms for all 14,700 m^3 of air to be expelled from between the floors.

Calculating a flow rate is simple, it's simple the volume moved/time taken, so in this case 14,700/0.864 which is 17,000 m^3/s (3sf).

Now, when we're dealing with a pipe, the flow velocity of the material in the pipe is equal to the flow rate/cross sectional area of the pipe. In the case of WTC 1&2 the pipe isn't a pipe per se, however there are a number of apetures that the air can move through, represented by the voids in the core, and the windows. Now, I'll be honest, and say that i've forgotten precisely how I derived the figure of 1067 m^2 that I mentioned - I was at work at the time, but, I do recall it was based off the total number of windows multiplied by their width multiplied by the distance between floors added to 40% of the volume occupied by the core divided by the space between the floors.

And so, 17,000 m^3/s / 1067 m^2 gives us a flow velocity of 16.0 m/s (3sf) - with the differences from the previous figure (15.2 m/s) due to rounding errors (not as bad as it seems, it's 15.96 m/s to 4sf).

So even without taking into consideration the over pressure of 0.5PSI that David B mentioned was possible, we find ourself with flow velocities analgous to a moderate gale (Force 7 on the Beaufort scale).

Now consider that over pressure would elevate this further, as would the fact that if we conside the second floor collapsing onto the third floor, then the conservation of momentum suggests that because of the momentum of the first floor, then v_0 for the second floor will not be zero, which, because it reduces the amount of time available for the air to be expelled in, increases the velocity with which the air is expelled. Also note that these are average velocities that fall out, not peak velocities (as the floor continues to fall, the size of the apeture reduces, as does the amount of air remaining to be expelled).

But yes, what i'm suggesting is that dust jet ejections like that don't neccessarily require an over pressure to occur.

Trippy · by **Trippy** on Thu Nov 05, 2009 7:20 am

femr2 wrote:
Trippy wrote:Why does the debris cloud (the falling debris) look like it has a lean on it.

Worth actually checking out (I haven't for your specific question) but I'd imagine the result *could* be that it's an effect of the wind...prevailing wind direction was ESE/SE. The smoke column does shift as a whole...

http://www.youtube.com/watch?v=0f6oJHj-_GA
http://www.youtube.com/watch?v=xtNf8GXQ6wg

Very strange smoke column behaviour when watched on loop
Not saying it *is* wind, but it's possible (and the simplest and least scary possibility).

I was under the impression that those were large pieces of debris?

femr2 · by **femr2** on Thu Nov 05, 2009 9:11 am

Trippy wrote:Consider the point that an over-pressure isn't actually required to generate these dust jets

My point is to highlight to OWE and DBB that if the linear ejecta detailed was simply air being expelled, then having a focussed jet and the south side ejecta at the same time would be reasonably described as mutually exclusive. Data and opinion on the dust jets themselves is probably best held within a specific thread.

As you've gone to some effort, I'll respond likewise, but again suggest as much specicivity in threads. (Especially ones I start

)

WTC 1&2 were 63.4m on each side

63.0936m external. Less internally (using window insets).

, and the floors are 3.66m apart (both figures rounded to 3sf)

3.6576m for standard floor, though of course 0.1016m of concrete slab must be subtracted outside the core (for standard floors), and 0.1270m within the core, also taking into account that the external floor region and core region did not descend together as a single piston. (Thinking of piston... http://www.youtube.com/watch?v=acTcwA_YHuA ...motion detection by subtraction.)

this gives us a total volume of air between the floors of 63.4*63.4*3.66 m^3 or 14,700 m^3 (again, rounded to 3sf).

Rather less, but...

The first thing to realize is that this volume includes the space occupied by the core columns, which introduces an error in the form of a volume of air that will be included in the calculations, but can not be expelled by the collapse.

Second thing to realise is that the volume taken up by ALL of the other SDL, CDL and LL masses must also be accounted for, as do all air flow restrictions imposed by structure, partitioning, ...

Now, if we assume we are dealing with the first collapsing floor, and, for the sake of simplicity, assume that it falls as one intact piece onto the floor below it

An over simplification in terms of the subsequent justification IMO.

, then we can calulate (using s=(gt^2)/2 that it takes 864ms (3sf) for an object to free fall 3.66m, this tells us that we have 864ms for all 14,700 m^3 of air to be expelled from between the floors.

That would assume zero air-resistance, and also other resisting factors, further distorting the calculation, and assuming free-fall...hm.

Calculating a flow rate is simple, it's simple the volume moved/time taken, so in this case 14,700/0.864 which is 17,000 m^3/s (3sf).

Now, when we're dealing with a pipe, the flow velocity of the material in the pipe is equal to the flow rate/cross sectional area of the pipe. In the case of WTC 1&2 the pipe isn't a pipe per se, however there are a number of apetures that the air can move through, represented by the voids in the core

There are some core corridors which may have played a part, but that is why I suggest a separate thread, as detailing each jet individually is important to understanding their nature.

, and the windows.

Ah. For your purposes, the windows cannot be treated as an aperture really, as the focus must be produced elsewhere IMO (core corridors for example).

{snip}

But yes, what i'm suggesting is that dust jet ejections like that don't neccessarily require an over pressure to occur.

Being more specific, the dust jet being highlighted (for the purpose highlighted) occurs at the same level as the linear ejecta. Other dust jets occur in front of the linear ejecta. That makes no sense at all. All behaviours must be explainable. The linear ejecta represents the very lowest *crush front* and shows firstly that internal destruction was asymmetrical and did not result from complete storey collapses, but instead the south side descent was in advance of the north. Such behaviours mess with the simplifications significantly.

Thoughts on the linear/terminal velocity ejecta very welcome. Dust jets...new thread :wink:

The 9/11 Forum

WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

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Re: WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

Re: WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

Re: WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

Re: WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

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Re: WTC1 Debris Ejecta Traversal Rate (Linear/Terminal Velocity)

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