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JefW
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re: Engineering disasters
JefW   7/18/2012 11:39:25 AM
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I am a(n old) sparky. First you check with your meter that it is live, then you kill the breaker then you check it is dead.

Tim R Johnson
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Rookie
re: Engineering disasters
Tim R Johnson   7/18/2012 8:55:55 AM
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About Apollo 13. I did some reading up on what went wrong after it happened. There were 2 fundamental problems, being penny-wise but dollar foolish, and poor documentation. The tank that exploded was originally installed on an earlier Apollo flight. There was trouble pressurizing it during the launch sequence, so it was removed and replaced by a spare. Instead of tossing it, it was refurbished and approved for use on a later flight. When it was used on Apollo 13, again they had problems pressurizing it. But this time, instead of replacing it they used an alternate approved procedure. It was approved, but it had never been used before. Remember the Apollo 1 fire? The command module was extensively redesigned as a result of the fire to improve safety. As part of that redesign, the in-capsule DC bus voltage was lowered. The gantry bus voltage retained the original higher bus voltage. The alternate procedure included powering the tank from the gantry bus rather than the in-capsule bus, because it had been written for the earlier design when the bus voltages were the same and was inadvertently not updated when the capsule was redesigned. The higher voltage was thought to have damaged the insulation on the wiring for the stirring motor inside the tank. It was when one of the astronauts turned on this stirring motor that the tank exploded.

Mineyes
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Rookie
re: Engineering disasters
Mineyes   7/16/2012 8:40:39 PM
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For those of you who are electronic engineers, in the USA NFPA70E is about electrical safety. 3 Phase power if shorted phase to phase can develop an arc flash that is fatal. Power engineers are trained to be aware. http://www.youtube.com/watch?v=AFlBLQjOAJI The video shows arc flash events with mannikins. NFPA 70E has many requirements, such as eliminating live work. After lock out tag out, phase conductors must be tested with approved meter using live-dead-live testing. NFPA 70E is very serious material. No laughing matter.

Bert22306
User Rank
CEO
re: Engineering disasters
Bert22306   7/16/2012 7:53:15 PM
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*These* are what I consider to be "EE disasters." Not burning your finger tip on a soldering iron, which really has nothing to do with DESIGN or EE. Anyway, it's always best to have the control system deconflict the info provided by many different sensors, so as to not have to rely so much on pilot expertise.

Brakeshoe
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Rookie
re: Engineering disasters
Brakeshoe   7/16/2012 7:52:37 PM
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At Georgia Tech in the early 1980's, the head of system protection for the Southern Company (Georgia Power, Alabama Power and one of the Florida power companies), Clayton Griffin, PE taught the undergrad & graduate system protection, coordination and relaying courses. We just completed the graduate section on the sizing of distribution ground fault protection, including discussing why (at the time) monitoring for high impedance ground faults was difficult when, in south Georgia, three kids were killed by a downed line in their yard over a weekend. That Monday in class, Griffin showed up, but he was as white as a ghost, visibly shaken~

Brakeshoe
User Rank
Rookie
re: Engineering disasters
Brakeshoe   7/16/2012 7:40:34 PM
NO RATINGS
"Not every Airbus that lands in the water is piloted by Captain Sullenberger" ~Dan Schwartz, 2009 It was an Air France Airbust 340 over the Atlantic; and although when the plane splashed the engines were running full throttle, the plane was in a stall and the pilots flew it right into the drink. According to the black box, one pilot was pulling back on the yoke and the other was (correctly) pushing it forward, to bring the nose down and restore lift.

Brakeshoe
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Rookie
re: Engineering disasters
Brakeshoe   7/16/2012 7:36:44 PM
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And that is what also delayed the AirBust 380, as the Dassault & some other CAD software at a second plant couldn't deal with one being metric & the other English!

Brakeshoe
User Rank
Rookie
re: Engineering disasters
Brakeshoe   7/16/2012 7:34:26 PM
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Corrected for proportional typeface: No shear (original): ....l... ....l... ....l... ------- ....l... ....l... ....l... ---*--- Some shear: ....l... ....l... ....l... ---*-------*--- .............l... .............l... .............l... -----------*... Infinite shear: ...l... ...l... ...l... ---**--- .....l... .....l... .....l... ----*---

Brakeshoe
User Rank
Rookie
re: Engineering disasters
Brakeshoe   7/16/2012 7:31:28 PM
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@j_brooks: Yes, you did miss something, and it'll take a Georgia Tech engineer to explain it. Although @rpcy below quoted the wikipedia article, in fact we covered this in our Statics class back in 1982. What happened is that, as @rpcy corrctly stated, the original suspension called for single rods, which meant the tensile load was supported entirely on the steel rods, with no additional shear forces on the 4th floor walkway. However, because of the offset on the 4th floor walkway, a shear force was generated between the rod coming from the roof truss, and the rod connecting to the the 2nd floor walkway. Now, let's look at this new, additional shear force on the 4th floor walkway concrete: The closer the rods, the higher the shear force; and in fact as the rods move closer, this shear force goes to infinity. No shear (original): ...l... ...l... ...l... ------- ...l... ...l... ...l... ---*--- Some shear: ...l... ...l... ...l... ---*-------*--- ...........l... ...........l... ...........l... -----------*... Infinite shear: ...l... ...l... ...l... ---**--- ....l... ....l... ....l... ----*--- Dan Schwartz~

Streetrodder
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Rookie
re: Engineering disasters
Streetrodder   7/16/2012 6:46:41 PM
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John - I apprecuate how you view that. I wish more medical equipment companies did. I took my EE and went into 'clinical engineering', dealing with how all this works in the hospital. i was on the end user side of that recall.

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