 |
|
|
|
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>>I guess I'm the sort of low-intelligence person who is easier fascinated
>>by simple visual tricks like this. I also enjoy watching fire, and I
>>used to sit and watch the washing machine. Sometimes I sit and watch
>>rain, or river turbulence... I guess I'm just stupid.
>
> When I worked offshore a lot of us indulged in wave counting.
If you're designing some offshore structure then you need to be able to
estimate the loadings from the sea. How do you do this? Well you watch the
waves for a long time and come up with a statistical model.
We did something like this in our "non-linear dynamics" course at
university. Basically you take the statistical model of sea motion, and use
it to design the structure based on some criteria (eg 1% chance of breaking
within 10 years).
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
scott wrote:
> If you're designing some offshore structure then you need to be able to
> estimate the loadings from the sea. How do you do this? Well you watch
> the waves for a long time and come up with a statistical model.
>
> We did something like this in our "non-linear dynamics" course at
> university. Basically you take the statistical model of sea motion, and
> use it to design the structure based on some criteria (eg 1% chance of
> breaking within 10 years).
And I saw a program about "freak waves". Apparently these occur with a
frequency vastly higher than predicted by the standard model. (Standard
model assumes a normal distribution, which means a wave of this size
should happen once every few millennia.) Apparently some solution to the
Schrowonakiarlumlum wave equation predicts this, but nobody noticed
before. And now the redesign implications are quite staggering. Or
something...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> And I saw a program about "freak waves". Apparently these occur with a
> frequency vastly higher than predicted by the standard model. (Standard
> model assumes a normal distribution, which means a wave of this size
> should happen once every few millennia.) Apparently some solution to the
> Schrowonakiarlumlum wave equation predicts this, but nobody noticed
> before. And now the redesign implications are quite staggering. Or
> something...
Yeh wouldn't surprise me. Although I'm sure, as with most structural
engineering, once you have calculated how strong to make something you just
multiply it by 2 to be on the safe side :-)
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
scott wrote:
>> And I saw a program about "freak waves". Apparently these occur with a
>> frequency vastly higher than predicted by the standard model.
>> (Standard model assumes a normal distribution, which means a wave of
>> this size should happen once every few millennia.) Apparently some
>> solution to the Schrowonakiarlumlum wave equation predicts this, but
>> nobody noticed before. And now the redesign implications are quite
>> staggering. Or something...
>
> Yeh wouldn't surprise me. Although I'm sure, as with most structural
> engineering, once you have calculated how strong to make something you
> just multiply it by 2 to be on the safe side :-)
True.
OTOH, if you've expecting a maximum wave hight of X, you design to
withstand 2X, and then suddenly a 12X have hits... hmm, Not Good(tm).
Oh, actually...
http://en.wikipedia.org/wiki/Freak_wave
right! ;-)
PS. Don't you ever hit a point where it's not possible to design for 2x
the maximum? Or do you just decide not to build the thing at all at this
point?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
On Mon, 14 Jan 2008 15:35:40 +0100, "scott" <sco### [at] laptop com> wrote:
>
>If you're designing some offshore structure then you need to be able to
>estimate the loadings from the sea. How do you do this? Well you watch the
>waves for a long time and come up with a statistical model.
Actually "wave counting" was our term for idly leaning on the hand rail looking
at the pretty patterns in the sea:)
>, and use
>it to design the structure based on some criteria (eg 1% chance of breaking
>within 10 years).
>
OMG! I wouldn't want to be on one of your designs :)
Regards
Stephen
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
Invisible wrote:
> PS. Don't you ever hit a point where it's not possible to design for 2x
> the maximum? Or do you just decide not to build the thing at all at this
> point?
It depends what you're building. Fighter jet? No. Passenger airplane?
Yes. Skyscraper? Don't build it. Space station? Go for it.
--
Darren New / San Diego, CA, USA (PST)
It's not feature creep if you put it
at the end and adjust the release date.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> It depends what you're building.
I see...
> Fighter jet? No. Passenger airplane? Yes.
Hmm. That's deep.
> Skyscraper? Don't build it. Space station? Go for it.
LOL!
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> True.
>
> OTOH, if you've expecting a maximum wave hight of X, you design to
> withstand 2X, and then suddenly a 12X have hits... hmm, Not Good(tm).
It's impossible to design anything to be 100% sure of lasting a set time
when it's being attacked by an essentially random force. That's why you
have models and can choose a chance of it being broken in its lifetime, eg
0.1% over 10 years. Of course that means there's a 0.1% chance of a >2X
wave coming along in 10 years, but what else can you do?
> PS. Don't you ever hit a point where it's not possible to design for 2x
> the maximum?
It's never impossible, just sometimes too costly or not practical. Then you
might do some more detailed simulations to bring the 2X figure down to 1.5X
or something with a suitable level of confidence. Or just think up a
different way to solve the problem. Usually it comes down to cost though.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
>> OTOH, if you've expecting a maximum wave hight of X, you design to
>> withstand 2X, and then suddenly a 12X have hits... hmm, Not Good(tm).
>
> It's impossible to design anything to be 100% sure of lasting a set time
> when it's being attacked by an essentially random force. That's why you
> have models and can choose a chance of it being broken in its lifetime,
> eg 0.1% over 10 years. Of course that means there's a 0.1% chance of a
> >2X wave coming along in 10 years, but what else can you do?
My point being "what happens if the model says force X is the largest
that's ever likely to occur, but it turns out the model is wrong and
actually force 12X is fairly common"... Presumably that's a pretty bad
thing?
>> PS. Don't you ever hit a point where it's not possible to design for
>> 2x the maximum?
>
> It's never impossible, just sometimes too costly or not practical. Then
> you might do some more detailed simulations to bring the 2X figure down
> to 1.5X or something with a suitable level of confidence. Or just think
> up a different way to solve the problem. Usually it comes down to cost
> though.
OK. Cool.
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
| |
|
|
> My point being "what happens if the model says force X is the largest
> that's ever likely to occur, but it turns out the model is wrong and
> actually force 12X is fairly common"...
For most things there are "standard models" that are used, and have been
tried and tested for decades. You *must* use these, by law. Of course for
weird things that aren't covered in law, you are free to make your own
design decisions. If you design something to withstand X, and 12X is
"fairly common" you're going to be in *big* trouble when people are injured.
> Presumably that's a pretty bad thing?
Yes. You could end up responsible for lots of people dying and face the
consequences.
It's why we have such things as "Chartered Engineers", who have demonstrated
competence in industry and not just graduated from any old university with a
degree in structural Engineering. Most structural Engineering firms will
not employ any non-chartered Engineers to do anything important.
Post a reply to this message
|
|
| |
| |
|
|
|
|
| |
