Behind Purdue's computing simulation on the 2001 World Trade Center attack

Behind Purdue's computing simulation on the 2001 World Trade Center attack

Summary: Researchers at Purdue University have completed a computing simulation to detail what likely happened to the World Trade Center when an airline struck the North Tower in the Sept. 11, 2001 terrorist attack.

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TOPICS: Security, Hardware
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Researchers at Purdue University have completed a computing simulation to detail what likely happened to the World Trade Center whwtc1.jpgen an airline struck the North Tower in the Sept. 11, 2001 terrorist attack.

Here's how Purdue describes the simulation results (see video):

The simulation depicts how a plane tore through several stories of the World Trade Center north tower within a half-second and found that the weight of the fuel acted like a flash flood of flaming liquid, knocking out essential structural columns within the building and removing fireproofing insulation from other support structures. The simulation used lines and dots to show the aircraft and building during the event.

To animate those lines and dots to make them more realistic, Voicu Popescu, an assistant professor of computer science, developed an application that creates a link between computer simulations and computer visualization systems. This translator program automatically translates simulation data into a 3-D animation scene. The goal is to make a simulation that's clear to non-expert users yet scientifically accurate.

As for the hardware, Purdue carried out the mathematical models to represent the building and airplane on the Regatta computer, an IBM system roughly equivalent to the combined power of 128 personal computers. The computer is operated by Information Technology at Purdue as part of the Network for Computational Nanotechnology, based at Purdue's Discovery Park and supported by the National Science Foundation. Other computations were delivered via the Northwest Indiana Computational Grid, a consortium of universities and government research labs.

Popescu's custom-built application made the simulation more realistic, but refrained from being too detailed so it wouldn't exploit the event. The overarching goal of the translator was to turn data into visual events.

Popescu's biggest beef was that typical simulations--like those seen on television news programs--are scientifically incorrect.

As for Popescu's application, Purdue provided a lengthy description that frankly I'll only screw up trying to excerpt. Here's the raw description in full:

Simulation codes and computing hardware are now sufficiently powerful to track with high fidelity complex interactions in large-scale digital models, shedding detailed insight into past or hypothetical real-world events. Visualization is an essential tool for collecting the information revealed by the simulation. Most simulation codes are enhanced with visualization modules which allow examining the simulation results visually. Such visualization modules excel at highlighting the quantities of highest relevance to the domain experts that designed the simulation, but they are typically quite limited when it comes to depicting the simulation results in a visual language accessible to the non-expert user. The post-processors called upon to visually render the simulation results are one or several steps behind the state-of-the-art in general purpose visualization.

This limitation is particularly severe when there is strong interest in the simulation beyond the narrow circle of experts that devised it. Such was the case for a high-fidelity simulation of the September 11 Attack on the World Trade Center developed by a Purdue University team of civil engineering and computer science researchers. Using detailed finite element analysis (FEA) models of the top twenty floors of the North Tower and of the airframe, the simulation tracks in great detail the impact over one second of real time. In order to overcome the post-processor’s general-purpose visualization limitations, the Purdue team developed a translator that automatically converts the simulation output data into a 3D scene amenable for high-quality visualization using a state-of-the-art animation system.

Driven by immensely popular entertainment applications such as 3D games and movies, animation systems define the state-of-the-art in computer graphics and general-purpose visualization. Although such animation systems do have simulation capabilities, precisely abiding by the laws of physics is of secondary importance compared to effective story-telling. Consequently, the approach of bridging the worlds of computer simulation and computer animation through a data translator allows combining the advantages of both worlds. A high-quality visualization is computed within the animation system while preserving the highest possible level of physical accuracy conferred by a rigorous state-of-the-art simulation code.

The translator implements two main tasks. First, simulation data with little visualization relevance is discarded. Examples include removing internal faces of structures modeled with opaque solid elements, discarding values of physical quantities not intended to be visualized, simplifying planar surfaces that are not affected by the simulation and are therefore excessively tessellated by finite elements, and removing intermediate positions for nodes with rectilinear and uniform motion.

The second task is to enhance or add detail that has high visual relevance but was only crudely approximated or even ignored due to its little simulation relevance. For example, once an element erodes, the simulation code simply eliminates it from subsequent computations. Assuming that the element breaks into many small fragments, eliminating the element is an acceptable approximation from the simulation standpoint, since the expense of tracking each fragment individually is not justified by the fragments’ impact on the simulation. Another example is adding the geometry needed to model the actual profile of a beam element. The simulation uses only two nodes and a normal per beam elements regardless of the beam profile (the shape is accounted for by physics equation in the FEA) but drawing all beam elements as segments is unacceptable. A third example is the addition of fire visualization. The simulation did not take into account the effects of the explosion and of the ensuing fire. The smoothed particle hydrodynamics (SPH) elements modeling the jet fuel are used by the translator to automatically control the fire visualization matching the dispersing fuel.

The resulting importer is a powerful, scalable, and general tool suitable for visualizing FEA simulations. Although the translator was developed in the context of the commercial simulation system LS-DYNA and the commercial animation system 3ds Max, the translator can be extended to support other pairs of simulation/animation systems. The visualizations produced achieve the dual goal of physical and visual fidelity, surpassing what can be produced with typical postprocessors, yet tracking the physical entities with the rigor if state-of-the-art simulation code.

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  • NIST also did a simulation without the graphics

    The NIST did a simulation of the damage and compared against debris. They took into account a huge amount of information. Turns out that the physical damage just from the impact was enough to cut the structural strength in half. Floors were modeled to collapse at much lower temperatures than what was experienced in side the building. Floor collapse was substantial part of causing the building collapse not the failure of the main support columns. Of course without the lateral support of the floor supports the main columns would eventually buckle. Also it was predicted that temperatures were not so much fuel related as due to secondary files (office furniture and other flammables) The fuel was modeled to burn off in a matter of minutes.

    These are some of the things I remember from reading the report (300 + pages). That was almost a year ago. So there is a lot forgotten.

    It is likely that the insulation was stripped from the main support columns and that the heat would have further weakened them (already bearing 2x Normal load due to collision damage). But if I remember correctly it was the weight of the floors beginning to sheer away from the columns and pancaking the lower floors (weakened as well) until the momentum of the total mass overcame non-weakened flooring and essentially pulling down the building with it. Note the floors besides all the steel were covered in concrete so there was a huge amount of mass there.

    Also the engines were also mentioned as having sufficient mass to sheer support columns not just the outer structural columns. The number of support columns sheered in the simulation was significant.
    DevGuy_z
    • "fires" not files

      Also I think 3 floors were damaged due to the collision. The plane was tilted when it hit.

      NIST also had recommendations for how to design a building so that a similar level of damage would not cause building collapse.

      The cost of the NIST investigation was I think nearly 30 million dollars. The model took relatively small items on the plane into account.
      DevGuy_z
  • Did They Recreate Bush

    Sitting like an idiot in front of all those kids after the attack?

    Must have taken a lot of lines of code to emulate complete idiocy.
    itanalyst
    • Re: Did They Recreate Bush

      Nope, it would just take a few lines of code:


      while [ 1 ];

      do

      echo "Duh... what did I just say"

      sleep 5

      echo "Uh yeah, *droooool*"

      sleep 10

      /usr/local/bin/bank_balance add 1000000

      /usr/local/bin/dump_stock UAUA

      done
      kraterz
      • Dude, THAT Was Funny!!!

        Thanks for the late-night laugh!!
        itanalyst
    • re: Did They Recreate Bush

      Nah, they didn't need to. You're available to fill in for him any time. ;)
      M.R. Kennedy
      • Actually that is why

        we have Windows users! ]:)
        Linux User 147560
      • Dude -- YOU are funny!

        Thanks for a real laugh!
        Mr_Wizard
      • Sorry, No Thanks

        I'm smart enough not to invade another country based on false evidence and admit I am wrong and bring the troops home.

        Bush isn't.
        itanalyst
        • Obviously not

          [i]I'm smart enough...[/i]
          Bzzzzzzt, oh sorry, the only thing that you've shown is that you know how to show your a$$, that's all.
          Mike Hunt
  • Too bad.

    Many will still not believe that Bush & friends didn't blow up the buildings.

    So, in a way, the research was a huge waste of time and money. If you got it to begin with.......
    Mike Hunt
  • Computer simulation silliness

    It is interesting how pretty pictures of airplanes in motion capture children's attention.
    Hydrocarbon fires (those involving jet fuel, gasoline, wood, paper, etc.) can produce maximum temperatures of around 1800 deg F or 900 deg C only under conditions where oxygen is plentiful. On the other hand, the temperatures inside the WTC buildings following the initial explosions (mostly involving fires outside the buildings) were estimated to range between 200 and 500 deg C. Since the structural steel in the WTC buildings was resistant (i.e., would not start to bend) at temperatures below 2000 deg C, it was impossible for fires to have been related to building collapse. A cursory viewing of the videos of the destruction of the WTC towers on 9/11/01 reveals that the tower buildings actually exploted, while WTC 7 was subjected to controlled demolition.
    The computer simulation, presumably involving 'state of the art tools' based on nonsensical assumptions about fundamental properties of metals/materials (not to mention essential principals of construction and engineering), represent a both a waste of time, effort, and taxpayer funding.
    wilwon32@...
    • 200 to 500 degrees? back that up!

      "Steel loses about 50 percent of its strength at 1100?F," notes senior engineer Farid Alfawak-hiri of the American Institute of Steel Construction. "And at 1800? it is probably at less than 10 percent." NIST also believes that a great deal of the spray-on fireproofing insulation was likely knocked off the steel beams that were in the path of the crashing jets, leaving the metal more vulnerable to the heat."
      Tigertank
      • Yeah, but what good are facts compared to "prisonplanet"?

        One's mind would have to be so "open" that the brain falls out, in order to believe what he posted. Yet he does believe........oh, I have to go, I just spotted Elvis........!
        Mike Hunt
    • You didn't even read the results?

      And if you did, your comprehension skills need polishing.

      It may be futile, but lets start with your nonsense about the temp not being hot enough to "bend" the steel. The whole Purdue study (along with rare-sense and numerous other expert findings) showed how the already weakened structure collapsed with a little more help from the fires.

      Talk about [i]nonsensical [b]ass[/b]umptions[/i].....
      Mike Hunt
    • Pancake

      When two solid planes with gas between them are forced together, the gas is displaced. When dust and smoke is suspended within the gas and it's in the act of being displaced, the process of displacement can easily be observed with organic human optics. Unthinking individuals might even describe the sight of this rapid displacement of hazy gas as looking like an explosion.

      It's also possible to melt raised freeways to the ground with gasoline.
      People
  • film won't persuade true believers

    The techical details will be believable to those trained scientifically, but true believers will just find something else to "refute" it. For example, on youtube, one commenter said steel buildings don't fall down if he FEELS something is true, of course, it is true, never mind technical details.

    Hopefully the commentator won't be the one who fixes my car, flies my airplane, or does my appendectomy.
    tioedong@...
  • RE: Behind Purdue's computing simulation on the 2001 World Trade Center attack

    Purdue, I wonder is this the same Purdue you all are about to read about, if it is boy oh boy, this is goning to smarten you all up a bit.
    This day of 9/11 will all ways be in my mind and my heart, that day caused a system failure of our Government System and this came in to my life and now I am within this Matrix of a Internet where I will write words of truth that will become a anomaly that will be as sur-real as that day of 9/11. I will never stop writing and I will never forgive, even at the cost of my soul.
    As it would seem, the Social Grace of the Rich is above the Law as long as the dollar support is at the back door.
    Do you wish to end this War and this Drug Epidemic , then stage a protest march that will awaken the American People, then take this War / drug issue against Purdue Pharmaceutical Company.... I am tired of seeing our Men and Women of the United States Military die as the American Dollar supports our enemy.
    Join Us...in the
    International Boycott Of The Arabic Drug Empire Phase 2
    Welcome to FASC Concepts , The Day The World Stood Still , We are at War with a Drug Empire
    For nine years we have been at war and I still ask the big why ? Why is there a hands off policy that prevent the destruction of these poppy plants ? Did you know that American Dollars supported the Terrorist Attack on 9/11/2001, and thousands of lives have been lost. Who are the investors of the Pharmaceutical Company Purdue that makes Oxycontin and how are they above the Law ? Oxycontin is Heroin made from the opium / poppy plants. It is Illegal by Law to buy and resale Heroin. Purdue is responsible for the deaths on 9/11 and the on going addiction here in America. If it was Purdue who wished to be known as the largest heroin dealer in the USA, well congratulations and for showing the people who you do business with. Purdue, you guys just dont get it, you all look like a bunch of idiots in the face of our enemy, and the American People look stupid. You all at Purdue are now in my way.
    This drug from the poppy plant and the fight against its use goes back around 4000 to 6000 years and man seeks to control that which has shown that the poppy plant is as nature selected, uncontrollable. This is like a old saying as the Scorpion stung the Frog as he swim across the water and the Frog said why did you do this , now both of us will die ? And the Scorpion said it is my nature....
    This is my Little War against the Arabic Drug Empire. Please allow me to share a concept with the People Of America, that will build for tomorrow. The Great Wall Of China in America. A 10 year project, and within the respect of why China built that wall and even as of today China makes money from that wall. This project will build towns and cities on both sides of the border and will bring peace and security. Another concepts is,
    To find a way into the hearts of children, first you must allow a truth to be shared and then let this share build within their hearts and you will see children open their minds to things not known.
    I read these things and I see where the Arabic Drug Empire is involved with the Mexican Drug Lords. What lost of understanding is that according to the faith of Bin Laden it is forbidden by God to walk among the infidels. That all infidels are to be vanquished from this world in order that the chosen ones will repopulate the world. It is a well known fact that the Arabic Drug Empire seek biological war tactics and it has been heard that a chemical balance is sought of how to implement Biological with Drugs, in order for it to be undetectable. The betraying of the Mexican Drug Lords by The Arabic Drug Empire will bring death to Mexico and the United States. Why should the Mexican Drug Empire take faith in my words, first If you and I stood before God I say to you that this is true it is the words of the streets that hold credit, and nothing is offered to them, The Mexican Drug Lords, dealing drugs is illegal.
    I know that some of the issues I write about is a bit over the top, but hey, if this post, by me makes you mad, welcome to a mad, mad drug world. I wonder how much in tax dollars this is going to cost the American People.....
    So join Us International Boycott Of The Arabic Drug Empire Phase 2
    Henry Massingale / FASC Concepts in and for Pay It Forward covers the web post on google Drop by and see why we built a anti crime / war form in a Health Care Reform Concept. To strategically Rebuild America www.fascmovement.mysite.com on google look for page 1 american dream official site
    Henry Massingale
  • RE: Behind Purdue's computing simulation on the 2001 World Trade Center attack

    Is this the same Purdue you all are about to read about ? if so well, all them brains and no know how...
    This day of 9/11 will all ways be in my mind and my heart, that day caused a system failure of our Government System and this came in to my life and now I am within this Matrix of a Internet where I will write words of truth that will become a anomaly that will be as sur-real as that day of 9/11. I will never stop writing and I will never forgive, even at the cost of my soul.
    As it would seem, the Social Grace of the Rich is above the Law as long as the dollar support is at the back door.
    Do you wish to end this War and this Drug Epidemic , then stage a protest march that will awaken the American People, then take this War / drug issue against Purdue Pharmaceutical Company.... I am tired of seeing our Men and Women of the United States Military die as the American Dollar supports our enemy.
    Join Us...in the
    International Boycott Of The Arabic Drug Empire Phase 2
    Welcome to FASC Concepts , The Day The World Stood Still , We are at War with a Drug Empire
    For nine years we have been at war and I still ask the big why ? Why is there a hands off policy that prevent the destruction of these poppy plants ? Did you know that American Dollars supported the Terrorist Attack on 9/11/2001, and thousands of lives have been lost. Who are the investors of the Pharmaceutical Company Purdue that makes Oxycontin and how are they above the Law ? Oxycontin is Heroin made from the opium / poppy plants. It is Illegal by Law to buy and resale Heroin. Purdue is responsible for the deaths on 9/11 and the on going addiction here in America. If it was Purdue who wished to be known as the largest heroin dealer in the USA, well congratulations and for showing the people who you do business with. Purdue, you guys just dont get it, you all look like a bunch of idiots in the face of our enemy, and the American People look stupid. You all at Purdue are now in my way.
    This drug from the poppy plant and the fight against its use goes back around 4000 to 6000 years and man seeks to control that which has shown that the poppy plant is as nature selected, uncontrollable. This is like a old saying as the Scorpion stung the Frog as he swim across the water and the Frog said why did you do this , now both of us will die ? And the Scorpion said it is my nature....
    This is my Little War against the Arabic Drug Empire. Please allow me to share a concept with the People Of America, that will build for tomorrow. The Great Wall Of China in America. A 10 year project, and within the respect of why China built that wall and even as of today China makes money from that wall. This project will build towns and cities on both sides of the border and will bring peace and security. Another concepts is,
    To find a way into the hearts of children, first you must allow a truth to be shared and then let this share build within their hearts and you will see children open their minds to things not known.
    I read these things and I see where the Arabic Drug Empire is involved with the Mexican Drug Lords. What lost of understanding is that according to the faith of Bin Laden it is forbidden by God to walk among the infidels. That all infidels are to be vanquished from this world in order that the chosen ones will repopulate the world. It is a well known fact that the Arabic Drug Empire seek biological war tactics and it has been heard that a chemical balance is sought of how to implement Biological with Drugs, in order for it to be undetectable. The betraying of the Mexican Drug Lords by The Arabic Drug Empire will bring death to Mexico and the United States. Why should the Mexican Drug Empire take faith in my words, first If you and I stood before God I say to you that this is true it is the words of the streets that hold credit, and nothing is offered to them, The Mexican Drug Lords, dealing drugs is illegal.
    I know that some of the issues I write about is a bit over the top, but hey, if this post, by me makes you mad, welcome to a mad, mad drug world. I wonder how much in tax dollars this is going to cost the American People.....
    So join Us International Boycott Of The Arabic Drug Empire Phase 2
    Henry Massingale / FASC Concepts in and for Pay It Forward covers the web post on google Drop by and see why we built a anti crime / war form in a Health Care Reform Concept. To strategically Rebuild America www.fascmovement.mysite.com on google look for page 1 american dream official site
    Henry Massingale
  • Core columns

    Don't skyscrapers sway in the wind. Didn't the core columns move as a result of sheer forces.

    So why don't the core columns move as a result of the impact in the Purdue simulation? There is a video of a WTC survivor saying that the floor moved like a wave. There is a graph of the oscillation of the south tower in the NCSTAR1 report. So how did Purdue put so much work into making their simulation look pretty but get something that simple completely wrong.
    psikeyhackr