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Re: Sloshing Damping

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On Nov 22, 2006, at 2:20 PM, refugio rochin wrote:

why not throw aside the equations, and run a discreet FE model trying to match actual activity in a tank.
One reason is that the problem isn't trivial. Anyone who thinks a good 3D element makes him king of the world should pay heed to the following--

FABLE
FEA is like a sharp stick. The newbie may pick up such a stick and heft it a little and try out the sharp point on his finger. 'My, what a nice stick,' he thinks. He waves it around and people step aside; he uses it to spear ants, then beetles and even tiny lizards. He finds the stick useful as a lever for moving large objects with comparative ease. Picking up a book he sees duellists overcoming their enemies, obtaining free drinks and sexual favors with things that resemble sharp sticks. So the newbie says to himself, 'This stick makes me powerful and superior to others who have no stick. The stick allows me to overcome nature and force people to do my bidding. I shall become a duellist and win free drinks and sexual favors because I am a cool stick-master.'

Now engineering is like a tiger. Both are powerful and elegant but when mishandled they can be very dangerous. An engineering project, like a tiger, requires judgement and a respectful approach because small errors can have catastrophic results. Like the large energetic objects encountered in engineering practice, the tiger is also large and energetic and behaves according to its nature, not always as we think proper. A wise person makes allowances for such behavior and acts cautiously and thinks over each move carefully.

As for the newbie, as he strolled along the forest path waving his stick and spearing beetles, he encountered a dead tiger. 'Ha!,' says he. 'I shall illustrate my power over nature by poking this dead creature with my stick and thus gain many free drinks and sexual favors.' Fortunately for the tiger, but unfortunately for the newbie, the tiger was merely napping, and at the first poke it swatted the newbie and killed him with a single blow. And after lunch, the tiger amused itself by batting around the stick and the remains of the newbie before urinating on both and raking leaves and dirt over the mess.

The lesson, O beloveds, is this: The wise newbie does not mistake marginal skill with a useful tool for knowledge, and takes a stepwise approach to large energetic objects with due regard for the consequences of poor judgement.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw/


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