December 29, 2008

A história da Mecânica dos Fluidos em versos

Sabe-se que a história da mecânica dos fluidos moderna originou-se com a formidável destreza em unir o esforço da pesquisa analítica dos séculos 19 e 20 com o vasto conhecimento empírico e experimental sobre hidráulica que o homem vem armazenando ao longo dos anos. O encontro destas duas vertentes ocorreu de fato em 1904 com Ludwig Prandtl e o desenvolvimento da Teoria da Camada Limite, que foi verificada experimentalmente. A mecânica dos fluidos moderna (1900~1975) vem sendo desenvolvida com técnicas analíticas e experimentais concomitantemente.

Com a evolução do poder de processamento e armazenamento dos computadores, a fluidodinâmica computacional surge para auxiliar no desenvolvimento e evolução da mecânica dos fluidos aliando técnicas numéricas e visualização científica. Muito trabalho ainda deve ser feito para unir essas três vertentes. Contudo, já existem simulações fluidodinâmicas que são confiáveis o bastante para substituir em parte ou totalmente o trabalho experimental (por ex., simulações DNS).

Em uma das minhas "andanças" pela internet encontrei um poema interessante e gostaria de compartilhá-lo com vocês. Este aborda a história da mecânica dos fluidos clássica até a fase moderna. Enjoy!

The Turbulent History of Fluid Mechanics

It all started with Archimedes, way back in BC,
Who was faced with an interesting problem, you see...


The king came to me, and this story he told:
I am not sure if my crown is pure gold.
You are a wise man, or so it is said,
Tell me: is it real, or is it just lead?

I paced and I thought, and I scratched my head,
But the answer eluded me, to my dread.
I sat in my bath, and pondered and tried,
And then ... Eureka! Eureka! I found it! I cried.

As I sat in my tub and the water was splashing,
I knew suddenly that a force had been acting.
On me in the tub, its proportional, see,
To the water that was where now there is me.

Of course, Archimedes caused quite a sensation
But not because of his great revelation;
As he was running through the streets of Syracuse
He didnt notice he was wearing only his shoes.

The great Leonardo oh what a fellow
No, not diCaprio, DaVinci I tell you!
He did more than just paint the lovely Mona,
He also studied fluid transport phenomena.

Then came Pascal, who clarified with agility,
Basic concepts of pressure transmissibility.
Everyone knows how a barometer looks,
But he figured out just how it works.

How can we talk about great scientists,
Without mentioning one of the best:
Sir Isaac Newton, the genius of mathematics,
Also contributed to fluid mechanics.

One thing he found, and its easy as pie,
Is that shear stress, τ equals μ dv/dy.
His other work, though, was not as successful;
His studies on drag were not all that useful.
He thought he knew how fast sound is sent,
But he was way off, by about twenty percent.

And then there was Pitot, with his wonderful tubes,
Which measure how fast an airplane moves.
Poiseuille, d'Alembert, Lagrange and Venturi
Through his throats fluid pass in a hurry.

Here is another hero of fluid mechanics,
In fact, he invented the word hydrodynamics.
It would take a book to tell you about him fully,
But here is the short tale of Daniel Bernoulli:

Everyone thinks is just one Bernoulli
It is not so! There are many of us, truly.
My family is big, many scientists in this house,
With father Johan, nephew Jacob and brother Nicolaus.

But the famous principle is mine, you know,
It tells of the relationship of fluid flow,
To pressure, velocity, and density too.
I also invented the manometer - out of the blue!

Yes, Bernoulli did much for fluids, you bet!
He even proposed the use of a jet.
There were others too, all wonderful folks,
Like Lagrange, Laplace, Navier and Stokes.

Here is another well-known name,
A mathematician and scientist of great fame:
He is Leonard Euler, I'm sure you all know,
His equations are basis for inviscid flow.

He did more than introduce the symbols π, I, e,
He also derived the equation of continuity.
And with much thought and keen derivation,
He published the famous momentum equation.

Those wonderful equations and diagrams you see?
They are all thanks to Moody, Weisbach and Darcy.
Then there was Mach, and the road that he paves,
After studying the shocking field of shock waves.

Rayleigh studied wave motion, and jet instability,
How bubbles collapse, and dynamic similarity.
He was also the first to correctly explain.
Why the sky is blue except when it rains.

Osborne Reynolds, whose number we know,
Found out all about turbulent flow.
He also examined with much persistence,
Cavitation, viscous flow, and pipe resistance.

In the discovery of the boundary layer
Prandtl was the major player.
Its no wonder that all the scientists say,
He's the father of Modern Fluid Mechanics, hooray!

It is because of Prandtl that today we all can
Describe the lift and drag of wings of finite span.
If it werent for him, then the brothers Wright
Would probably never have taken flight.

And so we come to the end of this story,
But its not the end of the tales of glory!
The list goes on, and it will grow too
Maybe the next pioneer will be you?
Escrito por Naomi Tsafnat,
em 17 de maio de 1999.

Ps. 1: Para maiores detalhes sobre os famosos pesquisadores, clique nos links destacados no poema. Em especial, gostei muito da biografia de Newton, d'Alembert e Lagrange. A leitura vale a pena.


Ps. 2: Desejando a todos um ótimo 2009, cheio de felicidades, realizações, novas descobertas e tempo para escrever no blog.

December 21, 2008

Feliz Natal, Feliz Ano Novo E Mil Desculpas

Eu estava devendo um tópico esse ano. Eu poderia dizer que tive dezenas de problema pessoais e que não tive tempo para escrever nesse blog, mas a verdade é que eu tenho outro blog que confirma os problemas que tive, mas deixa claro que teria sido possível escrever mais vezes aqui.

Eu não escrevi mais vezes por pura falta de planejamento. Sim, planejamento. Eu errei quase todas as escolhas que fiz quando pensei no Notas em CFD e isso refletiu nesse meu completo abandono nesse ano. Felizmente, o Luiz manteve um fluxo aceitável de tópicos para o blog.

O maior desafio que eu tenho aqui, é escrever sobre algo que não é trivial de uma forma que seja entendido porque quiser ler. Isso não é algo que eu faça em uma hora ou duas. Faltou planejamento nesse ano de 2008. Mas eu farei de tudo para não faltar planejamento no ano de 2009 e nos que vierem por aí. Já agendei um tópico para o início do ano de 2009 e já listei as idéias que eu quero desenvolver como texto no próximo ano.

Para esse ano resta, além do meu pedido de desculpas, desejar ótimo Natal e Ano Novo para todos. Sinceramente !