Is it defying the law of Archimedes?

Thanks for the clarifications. Would everyone excuse my poor skills in English ? Indeed, in France, where I live, it is very common to call the inhabitant of India the Hindu, although an Hindu is a term that refers to religious people. The fault may come from Cristoforo Colombo who was looking for a route to India, but meets the Natives in America. in France, we also call them "Indian"....

The idea of looking down the roots of any concept, like Gravity, is to find early meanings, that could have been lost in science history. These early meanings, in a common vision, shall be those, which are the closest to the original observations. To find improvements on actual technologies, some people think that it may be of a help to reconsider the generally admitted conclusions, and make new ones.

For instance, and, staying in line with the initial subject, I am not so enthusiastic by the intensive use of lifting foils on sailing boats. Our "weapons" to defy Gravity are very primitive, also costfull... 600 000 euros for an Imoca Foil seems, in my opinion, too much of a price regarding the difficulty to sail with this dynamic momentum constantly pushing on the tiller.

Neither can I forget the comment I read in the Sailing Anarchy before the launch of the last version of the ACC, where the boat was compared to that :

(Cannot stop laughing for weeks.....)

Indeed, I start learning how to sail on multihulls. Indeed, as a consequence, it could be said that my mastering of dog fights and racing is very limited. I admit I have fun just speeding on water and making trips no monohull can make. A fun that increased with the discover of the planning mode...Planning with a catamaran or a windsurf truly make you feel that you escape the gravity. It's an incredible feeling that is totally absent when foiling.

How would you describe the planning phenomenon, to your experience ?

 

Total Nonsense. If you investigate the Etymology of the word Gravity
"(in gravity (sense 2)): from Old French, or from Latin gravitas ‘weight, seriousness’, from gravis ‘heavy’. gravity (sense 1) dates from the 17th century."
Its like saying every word that non - English that starts with G is the predecessor of Gravitas or Gravity.

Even the OP said "I suspect that Newton knew it, but never spoke a word on it."
He didn't!

 

This is absolutely true that there is no declaration by Isaac Newton saying that he used any philosophical Indian background to conceive its theory, aside from the falling apple image. Nevertheless, I wouldn't be so sure that we can qualify of "non-sense" my allegations, which are based on already published papers and analysis. As a consequence, one could say that the concept of Gravity and its etymological roots are still subject to debate, as we can see.

However, it is very interesting that, RWatson, you cite the latin root of the word Gravity, trying to invalidate the Indian origin of the word. Have you ever heard of the indo-european origin of language ? Did you see the allele dissemination of the rhesus factor in the whole Eurasian continent ? It happens that my Latin professor was also a specialist in Indo-European languages, and explained to me, in details, 30 years ago, the prolific advantages that we could have to re-consider the migrations of people and knowledge of more that 10 000 years ago.

It seems to me that this theory is very well established, today, from a linguistic point of view, and, from a genetic point of view also. Having trouble to clearly establish these links from a cultural point of view is very understandable, RWatson, because, by nature, what defines a culture are his specificities, settled by mutual recognition among groups of people, wars and politics. That is why Historians are so important. Because one culture following another is prompt to crush and replace older knowledge, we are bound to re-discover our history eternally.

Regarding the use of the linguistic, in our case, I will add, dear RWatson, that there is also some solid evidences and a vivid debate that the English language could have NO indo-european origins. It then may be absolutely possible that the word Gravity, in English, comes from the Latin word, and that the Latin word comes from the Sanskrit word.

 

gravityhist2 https://einstein.stanford.edu/STEP/information/data/gravityhist2.html

Manchester Univ. Confirms: This is How Isaac Newton Stole Concept of Gravity from a Hindu Gurukul By ankit sharma https://www.google.com/amp/s/panindiahindu.wordpress.com/2017/11/22/manchester-univ-confirms-this-is-how-isaac-newton-stole-concept-of-gravity-from-a-hindu-gurukul-by-ankit-sharma/amp/

The title is a little click-bait-ish, but the article is interesting and mostly true with some speculation sprinkled in.

-Will

 

Perfect for my meridional pause. Thanks, Will.

These two articles present two different approaches of the subject. Always good to have many point of views, keeping the general picture, even if this general picture, in the case of the Gravity, is not very clear. What is sure, is that my wording "to come from" to describe the ascendance of a concept is indeed a very poor language that only brings confusion.
Gravity is a hard case. Let's see a clear case, just to be sure that, if the Gravity word has no Indian root, there are indeed scientific concepts based on Indian philosophie.

In that case, my best example would be some very famous mathematical series, brought to our knowledge by Fibonacci, which is one of the few to have mentioned his source.

In Europe, Fibonacci’s Liber Abaci in 1202 describe these numbers; the book was meant to introduce the Indian number system and its mathematics which he had learnt in North Africa from Arab teachers while a young man growing up there. Fibonacci speaks of his education in North Africa thus: “My father, who had been appointed by his country as public notary in the customs at Bugia acting for the Pisan merchants going there, summoned me to him while I was still a child, and having an eye to usefulness and future convenience, desired me to stay there and receive instruction in the school of accounting.
There, when I had been introduced to the art of the Indians' nine symbols through
remarkable teaching, knowledge of the art very soon pleased me above all else and I
came to understand it.”

 

@sun, I hope you have not become too frustrated with the direction your thread has turned.

I find that one of the problems we have in visualizing the effects of things like buoyancy and flying and hydrofoil vs gravity is our familiarity with living in a world where air seems to offer little resistance to our pedestrian movement through it, while the ground holds us firmly up against gravity. We take these things as so natural that we hardly give them a thought.

In fact, fluids offer a resistance to movement and forces that encourage movement. Even if that resistance is in a medium through which a keel allows for directional movement. This works in any direction, port, starboard, up, down. Gravity is resisted, but not escaped. You dive off a diving board and fall through the air, accelerating until air resistance increases with your speed through it, and you may, if the height is high enough, reach a terminal velocity. Resistant force equals the gravitational force.

If you are still going a reasonable speed when you hit the water in the pool, the resistance from the denser, more viscous fluid takes over and gravity is further defied, slowing your speed until the buoyant force can take over.

All this resists the constant force of gravity. Even before you bring in bernoulli's equation.

-Will

 

Of course, you don't need Bernoulli's equation (or any equation, for that matter), if you are only speaking qualitatively.

Trying to be more precise and quantifying things is a different matter however.

 

I think humans discovered that things fall, and are heavy, a long time before written history.

 

A first attempt in being quantitative, using the Bernouilli's equations applied to lifting profiles could be the conformal transformation of Joukowsky ; which has shown that is it possible to calculate a lift in an ideal fluid. For the drag calculations, it is another story.

Joukowsky transform - Wikipedia https://en.m.wikipedia.org/wiki/Joukowsky_transform

 

Yeah, yeah. You have NO evidence.
The Latin spoken by Romans had no derivations from the Sanskrit language.
"We do not know what language the founders of Rome spoke before Latin developed, but it bore a close resemblance to Oscan and Umbrian dialects."

In fact, rather than Sanskrit being an origin for European languages, Sanskrit itself was most likely introduced TO India FROM Europe.
"newer scholarship has shown that even though Sanskrit did indeed share a common ancestral homeland with European and Iranian languages"
Sanskrit being introduced to India from the Baltic states. about 1800 bce. (about the same time as Latin developed in Italy.)
"the Pontic steppe continues to be the most widely accepted region from where the source of Sanskrit and European languages emerged."

"Fibonacci’s Liber Abaci in 1202 "
A flailing apologetic half thought out theory. The roots of Latin were 2000 years earlier.

"(even if) the Gravity word has no Indian root, there are indeed scientific concepts based on Indian philosophie."
So? THAT has NO bearing on your language origin assertations.
But as far as Gravity goes, there is ZERO evidence that either Newton or Leibnitz had any contact with the concept from Sanskrit scholars.

 

That we have for sure ! It is very interessant theory that you have. It is also sure.
If the absence of evidence is an evidence of absence.

Genetic testing reveals that Europe is a melting pot, made of immigrants https://www.nationalgeographic.com/culture/article/first-europeans-immigrants-genetic-testing-feature

If we stay on the main subject, the notion of induced force is of some importance. We couldn't help but imagine that the induced effects will provide us a way to escape the primary force itself.

This suject reminds me a study that we've made for a racing catamaran 120' Q6. This study has been conducted in the Engineering laboratories of CENTRAL NANTES, which were in charge, with the same code, of the simulation of our french warships. NextFlow, developing next-generation CFD software - Centrale Nantes https://www.ec-nantes.fr/who-we-are/partners-and-networks/nextflow-developing-next-generation-cfd-software



Induced forces of lift were to be balanced for our new hull (Y-momentum stands for Pitch momentum). The basic idea was that, playing with the slope counter (back) angle of the hulls, around the average awaited speed, will allow us to generate a lifting force in way of transom.



We compared Q6 with the preceeding hull forms, which have already broken the record we were to push out of his limit again...) First results were encouraging, but not satisfying at greater speed than 30kts.


We analysed in details the results. The drag curves around the hulls showed that we should have to make our focus downstream !


As an aeronautical engineer, I checked the skin friction coefficient value (Skin-Friction Coefficient - an overview | ScienceDirect Topics https://www.sciencedirect.com/topics/engineering/skin-friction-coefficient) without approximations, but truly in exploiting the local values of the U field to calculate ∂τ/∂y. NO APPROXIMATIONS OTHER THAN THOSE INTRODUCED BY OUR FINITE ELEMENT ITSELF.


The diagnostic was direct. We could identify the regions of the hull responsible for the generations of the effects, or forces, that we wanted to get rid of. From this study, we made the definitive hull forms, making the geometrics changes that were required.


We spoke over the force, over the media (too much of a little, because it doesn't seems to put anyone in distress in this conversation the fact that, being stuck to Bernouilli shouldn't allow to speak of real fluids at all...but...anyway.....). We should also speak about the shape, because there is no induced force without a proper shape to create it.

 

@rwatson

I note that you have there an interessant driveline.

Besides my small years of lazy and evasive research on the dynamic of populations, world wide, it happens that I found, some years ago, an excellent article about the human colonization of Sahul, showing also link between Tasmany and India...
It's encouraging ! The concept may also emanate from southern countries.

Peopling of Sahul: mtDNA Variation in Aboriginal Australian and Papua New Guinean Populations - ScienceDirect https://www.sciencedirect.com/science/article/pii/S0002929707623349[/QUOTE]

 

Ludwig Prandtl had the insight to overcome your objection.

In thin boundary-layer theory, the pressure is assumed constant in the direction normal to a surface, so the pressure distribution on a wing can be determined from the flow in the inviscid region outside its boundary layer.

Bernoulli's equation is thus still useful in flows that can be modeled with viscous/inviscid interaction techniques, but it's not a big part of the calculations. Finding the flow velocities may require hundreds or thousands of lines of code, whereas deriving the pressures from the velocities might only take a half dozen more.

 

Indeed, at the ONERA and in the DLR, we used mixed formulations, to overcome and minimize the work of computation. Even when working with supercomputers.

Ideal fluid outside the boundary layer, boundary layers equations inside. An asymptotic developmental between... Classic. If you look at my previous example, if you follow this link Skin-Friction Coefficient - an overview | ScienceDirect Topics https://www.sciencedirect.com/topics/engineering/skin-friction-coefficient, you will find all the theorical background that i used to exploite the boundary layer theory even if the code we used for the study was no formal boundary layer code.



Book citation, in the link. Jean Cousteix DMAE-ONERA

This is why I doubt that you can show me efficient Prandtl formulation that can predict correctly the drag of an old America's cup keel bulb. Induced drag calculations on elliptic wings, were somehow an apogee, with the Spitfire. Sure we love playing with fluid's behaviour to induce lift, still, we have to also manage the drag, induced and not induced, to be able to make a convergent design process that includes all the constraints. This is were, in general, the bottom hurts, because I don't know why, there has been not so much research in sailing science to upgrade the theory, since then. Money money money....​

As a result, cheap codes are used without a proper background by most users of CFD code. Prantl's method are versatile, and can produce some results, in some case, with a simple bureautic computers. This is good. For instance, a mobile phone processor can handle practical lift coefficient calculations on wings with a agreement sufficient in some real world case.


And this is sad also (and not good to the business, because, constantly saying that, with bare dick and knife, calculations can be made, without the help of qualified specialists, does not help in having validated data to compare with. That is the most important if you want to rise up your skills.

In consequence, there has been not much evolution in yacht science the last century regarding aerodynamics and hydrodynamics effects (except rare occasions, like hypersonic torpedos, ground effect boats and ekranoplan, crafts we don't see too often).


Hydrofoiling History - Hydrofoil http://www.hydrofoil.org/history.html

In general we are bound to use those basic foils to lift a boat, doing not much with them than what's was made out of metallic dump on North American motorcrafts since more than 100 hundred years...because, I guess, we keep doing and doing the same calculations, over and over, with the same tools.

Apart from the aeropace industry, the automotive industry (which is a very big consumer of Prantl's codes also for drag estimation) succeed during the petrol's crisis of the xx century, in reducing the consumptions of the car making precise reviews of their outside design. What is probably not clear for those unqualified users of Prantl's code, is that this industry has made prolific their use because of heavily validated datas obtained by windtunnels and high end CFD. Nothing is free in this world.

No pain, no gain

Post scriptum : I left a piece of a code on this forum : a 3d Prandtl's formulation for keel shapes, with or without bulb, or for rudders. Of course, I do only put the master file of the code, but, as you said, Doug, Bernouilli's like code are very light and everybody with a little knowledge will identify the method that I used. There is not much missing. I have quite a few ideas of what could be made with this code (curved foil calculations..., Genetic optimization of shapes, VPP...format conversion) Perhaps have you got also ideas. In that case, I would be really happy to re open this code and share with anyone willing to give me a hand. No pain...



Of course, you will have also to accept, in using Prantl's formulation, not being able to calculate the friction drag. I recall Prantl < Bernouilli < ideal fluid. In a Prandtl's formulation, you've got to add one more approximation if you want the polar curves. In that case, it is common to add an ITTC57 for flate plates, in approximation.

 

If coding panel codes does not feed you, perhaps that you want to play with a truly amazing code and simple navier-stockes code, written seriously and well documented, there is this one : Hydrodynamica.

Some of you may already know it, since it can be found on the internet, a long time ago. Since, I continue to use it in some very practical cases, here, to estimate the height of my chimney to skip the air column collapse during strong winds. To always be safe and warm. Preventing also a monoxide peril !!!!!
I must say also I used it to make rough but not stupid estimates of the energy ratio of a turbosail system in the scope of a research program, here, in La Rochelle. Dick !!!! Knife !!!!



When playing with this very cute and simple example, I wish that we can share the feeling that I have that ; the fluid, the surface and the force are really three component that shouldn't be taken appart in any applications of any theory. Induced forces are created inside a media in presence of material. This is basically all that we know, in short. It is very interessant that Will has re-questionned the role of the compressibility in the explanations of the lift created by a foil. It is an absolute rightfull question that is worse quite a long time of thinking, before giving an answer, to my opinion. Because you must know, that, besides these colorfull CFD images that we like, kind of representing the proudity of our knowledge, some mathematician and scientist are using very primitive formulas to question also the law of conservation itself....

Bernouilli must be turning in his grav(ity) !!!