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Baltimore's Key Bridge struck by cargo ship, collapses

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Re: Baltimore's Key Bridge struck by cargo ship, collapses

#901

Post by MBCook »

verandaguy wrote: post #609
animex wrote: post #592

Earlier quoted context omitted.

You can train for it, then how many years into your career you actually experience such a scenario are you likely to act instinctually and recover. The best solution would be to improve autopilot assist as it will never forget how to correct (if possible).

If it’s anything like airline pilot training, there’s periodic retraining and evaluation to make sure pilots have the right reactions in case of an emergency.

I wonder if they’re required to keep up training to the degree pilots are. It wouldn’t surprise me if they’re not.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#902

Post by berniedurfee »

acdha wrote: post #856
berniedurfee wrote: post #854

Is it feasible to run large ships on autopilot? Large airliners land mostly on autopilot now, right? Seems like a somewhat solvable problem to combine a bunch of sensor inputs to keep the ship inside of a safe corridor, such that even a loss of power would be accounted for to ensure it would drift safely. Is it a much harder problem than my intuition assumes? Cost issue?

The early reports suggest that the ship was having trouble actively maintaining position - some have theorized a stuck rudder or wind pressure – in which case the only thing an autopilot could do is make the situation worse. I’d wait for the full investigation to come out before speculating about fixes.

Not a fix per se, but a safer system going forward.

Given all the variables, is it feasible to build a system that continuously runs through multiple failure modes, predicts where the ship would end up and then guide the ship on a course where even a loss of power would have the ship drift between the supports.

Was there a configuration of the ship that would have prevented it from hitting the bridge even after the power loss.

This seems like something that could be continuously calculated in realtime to keep a ship in a safe corridor, such that it wouldn’t strike the bridge even if the engines failed, based on winds, currents, size, load, etc.

I’m speculating about fixes, because it seems prudent to think about how to prevent the next strike before it happens. I feel like technology could reduce that risk to some degree.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#903

Post by varrock »

naasking wrote: post #839
anigbrowl wrote: post #527

Earlier quoted context omitted.

It's not the impact, it's the fact that it just keeps pushing. Movies commonly use slow motion and time extension via editing for destruction scenes because (as we've just seen) real time doesn't always look impressive to the untrained eye. Also, there's a lot of mass concentrated in that ship. It's the equivalent of hitting a window with a sledgehammer. Small recreational vessels could probably crash into those pylo…

Indeed, the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material, which means the whole bridge bent until the deflection exceeded the tensile strength of the material. A missile impact with the same total energy would exceed impact strength and would probably have destroyed only part of the bridge.

Thank you for breaking it down like this. As someone without an engineering background, your explanation (along with some Googling for terms and definitions) really helped me grasp what happened.

You got me wondering:

> the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material

When I first read this, it initially threw me off. The cargo ship's impact not exceeding the strength of the bridge sounds like a positive thing, but upon closer reading of your comment, it sounds as if it was the catalyst to the entire bridge collapsing.

So, how do engineers balance these properties of impact strength and tensile strength, especially considering large ships channel through these bridges near their pylons frequently? How much engineering goes into the possibility of large structures hitting their pylons?

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#904

Post by MBCook »

FredFS456 wrote: post #768
dboreham wrote: post #763

Earlier quoted context omitted.

This seems like a system architecture error. Boats do weird shit sometimes and so bridges need to be deigned to not fall down when a boat crashes into them. Requiring a huge boat to be steered to meter resolution when clearly that's not always going to happen is top shelf stupidity. Up there with backup generators in the basement below the water table.

My civ engineer friend says that bridges are supposed to have barriers in front of their pylons for this particular reason - in the event of a collision, the barrier would be destroyed but not the pylon.

They do. I would think that that bridge certainly did as well, it’s part of a busy port. It’s not exactly hard to imagine it happening.

My guess, and it is a total guess, is that the protection on the bridge was nowhere near sufficient for a ship of that tonnage.

I’m assuming it was built to whatever the correct standard was when constructed in the 70s. I’m also assuming the ship weighed far more, or perhaps traveled noticeably faster, than the cargo ships going into the port back then.

Basically I’m guessing it needed an upgrade in its protective barriers but it wasn’t recognized or hadn’t happed if it was.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#905

Post by donw »

MBCook wrote: post #898
araes wrote: post #541

Earlier quoted context omitted.

Current personal suspicion after watching your linked video (excellent discussion by the wgowshipping author) is: Catastrophic engine failure (1:24) causing wide scale power loss. No rudder control, rudder drift, and ship alignment drift (1:24-1:25:30) Power restored and ship reengages prop with bad ship/ruddder alignment (1:25). However, ship is now pushing itself into a further bad turn. Pilot likely stomps the bra…

Admittedly very naive question: would they have an anchor? Would it be long enough to hit the channel bed? Could dropping it have helped prevent, or at least slow down, the ship? Or even if so was it just too late when it all went down and it wouldn’t have made a meaningful difference?

Given the forces involved, dropping anchor probably would probably massively damage the ship without sufficiently arresting its momentum, and add another uncontrollable variable into its trajectory.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#906

Post by donw »

gonzo wrote: post #900
jethro_tell wrote: post #825

Earlier quoted context omitted.

This is actually common for a 2 stroke type engine and used in things like gas golf carts and snow machines. The direction the engine is started is the direction it runs. So to accomplish this for propulsion, you'd add a reverse polarity switch for your starter and you're good to go.

You can even get a (2-stroke) Detroit Diesel to run in reverse. You don’t want to do it very long, because they don’t make oil pressure in reverse.

> You don’t want to do it very long, because they don’t make oil pressure in reverse.

US energy policy has entered the chat.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#907

Post by MBCook »

Gare wrote: post #664
semi-extrinsic wrote: post #534

Earlier quoted context omitted.

Throwback to the scene in The Day After Tomorrow where the cargo ship comes to an almost instant halt after impacting a bus wreck under water. For some reason it managed to stand out as ridiculous even in that movie.

Speed 2: Cruise Control on the other hand: https://www.youtube.com/watch?v=gBxaGB65TB8

I just saw in a YouTube video yesterday that they actually built a full-size model of the ship (or at least the bow area) and the bit of town it hit. The director didn’t want to use CGI or miniatures.

He spent a full quarter of the movie’s budget on that one scene.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#908

Post by WalterBright »

naasking wrote: post #839
anigbrowl wrote: post #527

Earlier quoted context omitted.

It's not the impact, it's the fact that it just keeps pushing. Movies commonly use slow motion and time extension via editing for destruction scenes because (as we've just seen) real time doesn't always look impressive to the untrained eye. Also, there's a lot of mass concentrated in that ship. It's the equivalent of hitting a window with a sledgehammer. Small recreational vessels could probably crash into those pylo…

Indeed, the whole bridge failed because the impact didn't exceed the impact strength of the bridge's material, which means the whole bridge bent until the deflection exceeded the tensile strength of the material. A missile impact with the same total energy would exceed impact strength and would probably have destroyed only part of the bridge.

There's also the loads are balanced on the pylon. When the collapse took out the bridge on one side of the pylon, the other side failed as well. You can see that in the video as the bridge on the right side of the pylon is no longer counterbalanced by the bridge on the left side, and collapses.

Imagine you're holding up a barbell with heavy weights at each end. If the weights on one end drop off, the bar will tilt strongly in the other direction, dropping the weights off on the other end.

Re: Baltimore's Key Bridge struck by cargo ship, collapses

#909

Post by sho »

moritonal wrote: post #586
bastardoperator wrote: post #494

Earlier quoted context omitted.

The video is surreal, it looks like it barely bumps the bridge and 2 seconds later the entire thing is gone. I don't know what I was expecting, the bridge just looked extremely fragile, makes me wonder what other bridges are at risk of an event like this.

When you play about with game engines long enough, you start to realise that momentum is the key metric to track rather than speed. Especially in water magnitude can be very deceiving but to give some quick math, this vessel had a momentum at impact of about 154,000,000kg⋅m/s. For a car to have equivalent momentum it'd have hit the bridge at 156,580 mph. Humans are just less adept at appreciating mass vs velocity.

Hm. I'm no physicist but I think your math is off. Remember it's velocity squared. Your car going that fast is has more than a kiloton of TNT or approaching 5 terajoules of energy... that can't be right.

For a 2 tonne car, my very rough math puts it at more like 2100 mph.

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