[HN Gopher] Naval Architecture
___________________________________________________________________
Naval Architecture
Author : todsacerdoti
Score : 653 points
Date : 2021-07-27 15:03 UTC (1 days ago)
(HTM) web link (ciechanow.ski)
(TXT) w3m dump (ciechanow.ski)
| nraynaud wrote:
| https://www.youtube.com/c/DatawaveMarineSolutions for people
| interested, there is a youtube channel on the topic. There is
| real content, even if it's with marketing intent.
| tfang17 wrote:
| How many of us read this as Naval (Ravikant) Architecture?
| dirtyid wrote:
| Very intuitive. I wish there was a list of exemplar
| visualizations for different subject matters. It's 2021, there's
| still a lot of bad textbooks out there, emphasis on books.
| garaetjjte wrote:
| Maybe https://explorabl.es/?
| uberdru wrote:
| Reminds of something my father, a sailor in the British Merchant
| Marine, told me. He was recounting a ridiculous North Sea gale,
| basically hurricane force winds. The ship plunged into the trough
| and then topped the waves, the screws coming well out of the
| water every time. "It gave me a new respect for naval
| architects", he said.
| nwsm wrote:
| This blog never ceases to amaze me.
| mncharity wrote:
| I'm reminded of https://www.youtube.com/watch?v=ckaJs_u2U_A , an
| aluminum foil boat floating on dense SF6 _gas_ , which I think
| fun.
| supernova87a wrote:
| That demo is always fun, but I cringe at the use of SF6. That
| stuff is 23,000x the potency of CO2 in terms of greenhouse gas
| potency.
| NickNameNick wrote:
| Is that really a problem? Isn't it so dense it will pretty
| much stay put?
| _Microft wrote:
| _Some hull shapes are inherently unstable. The slightest
| deviation from pristine vertical balance will make the ship flip.
| However, even hull shapes that are initially stable at some angle
| reach their limits. All of these examples assume the deck is
| perfectly sealed and that water doesn't get into the hull._
|
| Loosely related: here is a video of the German Maritime Search
| and Rescue Service (DGzRS) trying to 'sink' one of their (then
| new) smaller rescue lifeboats which has self-righting
| capabilities:
|
| https://www.youtube.com/watch?v=dz_N6MG5tt0
|
| (Ofcourse it was a test if it does have these capabilities, not
| an attempt at actually sinking it.)
| dtgriscom wrote:
| Interesting. The designers can probably analyze the rate at
| which the boat righted to quantify its stability.
| lambdasquirrel wrote:
| One cool thing to think about is the effect of tumblehome hull
| forms. Kind of makes you check in, that you really know what
| the center of buoyancy is.
|
| https://www.dco.uscg.mil/Portals/9/DCO%20Documents/5p/CG-5PC...
| jasonwatkinspdx wrote:
| Yeah, this is a fantastic blog post but is a little inaccurate
| in some edge cases.
|
| In solo around the world races like Vendee Globe, the boats are
| required to be fully buoyant and self righting no matter how
| they end up. The most common approach to achieving this is to
| rig a canting keel with a device that when the boat capsizes,
| lets the keel swing to one side, creating a weight imbalance
| that rights the boat. They're quite serious about it too: you
| don't get to race the boat unless you demonstrate it works that
| way at the pier.
| JshWright wrote:
| It's not inaccurate though... The hull shape does reach a
| point of instability, at which point the hull shape changes.
| jasonwatkinspdx wrote:
| There are hull forms (without the canting keels I
| mentioned) that have positive righting moment through 180
| degrees. Life rafts are universally designed this way. For
| boats it's just not that necessary ultimately, as capsize
| is pretty dang rare on keel boats as a baseline. Vendee
| Globe et all are hardasses about it because they know if
| the worst happens, there's no rescue possible on a short
| timeline.
| ljhsiung wrote:
| Does anyone know how he creates these animations? I like the
| representation and would like to create them as well.
| jimhefferon wrote:
| Expanding on that question, does anyone know of a place where
| work like this gets discussed? I was unaware of his stuff,
| which is indeed wonderful, and if there is a way to meet with
| others who are interested in this kind of thing, and in doing
| it for ourselves, I'd sure like to be there.
| capableweb wrote:
| https://news.ycombinator.com is pretty great for that
| specific area :)
|
| And:
|
| https://hn.algolia.com/?query=Naval%20Architecture&type=stor.
| ..
|
| https://news.ycombinator.com/from?site=ciechanow.ski
| [deleted]
| thamer wrote:
| It looks like raw HTML5 canvas with some WebGL (2D):
| https://ciechanow.ski/js/navarch.js with some helper functions
| in https://ciechanow.ski/js/base.js
| mihaifm wrote:
| Also interested. Looks like a lot of it is JS code written by
| hand. This is certainly readable code:
| https://ciechanow.ski/js/navarch.js
| mLuby wrote:
| First time I've ever seen JS blocks statements in the wild; I
| wonder if the author is coming from a language where that's
| common.
| bruce343434 wrote:
| >JS blocks statements
|
| What are those?
| fuzzylightbulb wrote:
| I had the same question. (Putting this here so that I can come
| back later.)
| blueyes wrote:
| There is an excellent book by Elting Morison that includes a
| chapter on naval architecture, and the ways it was held back at
| the behest of naval commanders who wanted to preserve the culture
| of sailors that would be destroyed by the introduction of more
| powerful engines and faster hulls.
|
| https://mitpress.mit.edu/books/men-machines-and-modern-times...
| vishnugupta wrote:
| Bartosz is back :-)
| WalterBright wrote:
| > at the scales we're interested in we can assume its value
| doesn't change.
|
| The reason submarines can be neutrally buoyant at specific depths
| is because water is compressible, and water's density changes
| with depth. Adjust the submarine's density to match the water's
| density at a certain depth, and the sub will be neutrally buoyant
| at that depth.
| IshKebab wrote:
| No it isn't. Submarines can be neutrally buoyant at any depth
| _because_ they have the ability to control their density. The
| fact that water is slightly compressible has no effect on
| submarines ' operation.
| WalterBright wrote:
| Think about what you wrote a bit more :-)
| IshKebab wrote:
| I did and I have no idea what you're talking about.
|
| Edit: Ah I think you just worded it badly and we're
| agreeing.
| nradov wrote:
| Submarines seldom operate at neutral buoyancy. Usually they
| rely on the planes and propulsion for depth keeping.
| WalterBright wrote:
| To go silent while being depth-charged, they'll want to sit
| at neutral buoyancy with the propulsion off. They don't want
| to sink to crush depth or surface.
| andreofthecape wrote:
| Very well done!
| el_benhameen wrote:
| These are so well done. I gave my 4 year old the internal
| combustion engine page to play around with, thinking that he'd
| just find the animations fun to play around with. He ended up
| with a pretty good (4 year old level) understanding of how
| different parts of an engine work.
| niels_olson wrote:
| My first job out of college was as a junior engineering officer
| on a ship. I had taken naval architecture and the daily draft
| report was part of my job. The fuel king had a spreadsheet where
| the engineering watch input all the tank levels overnight. I
| added a sheet that took that data and solved all the tank
| problems, bouncy, incline, etc, and printed the report. So
| instead of two hours of number crunching, or one of my enlisted
| guys doing what he did (which was basically copy forward and
| subtract an inch a day), the report was completely automated,
| with fore, aft, and center draft. With zero human effort.
|
| Apparently the guy who took my job when I left had a nervous
| breakdown. I feel a little bad about that, but not really. He
| should have paid attention in class.
| WalterBright wrote:
| The Wright brothers, in trying to figure out how to design an
| airscrew (propeller), assumed it would work like a ship's screw,
| and went looking for the theory behind it.
|
| There was no theory, ship's screws were designed by trial and
| error.
|
| So the Wrights invented the first propeller mathematical theory.
| It produced propellers that were 90% efficient, about double the
| efficiency of other experimenters' ad hoc propellers.
|
| Double the efficiency meant the Wrights needed half the
| horsepower to get into the air.
| Stevvo wrote:
| Interestingly, whilst computers play an ever more dominant
| role, there is still a large amount of trial and error that
| goes into hull design.
|
| All famous hull designers draw their curves by hand.
| pomian wrote:
| Have you ever tried to model a sailboat hull in AutoCAD,
| SketchUp? I remember trying out all the"new" cad software in
| the 80/90's, it was impossible. I still think it extremely
| difficult. What you can do by hand is easy, conceptually and
| practically. Software is there now, but still extremely
| complicated. Not a single bit of straight line, anywhere, in
| any direction!
| WJW wrote:
| That is mostly because you only get to be famous as a hull
| designer if you make "beautiful" hulls (ie for yaghts and
| stuff), and beauty is very difficult to express
| mathematically. The people designing containers ships don't
| draw their lines by hand but rely on large amounts of
| computing power to compute hull stresses and squeeze every
| last bit of storage space out of their designs.
|
| As an interesting anecdote, when I was still working for the
| (Dutch) navy they had a project going on to use constraint
| solvers to generate new submarine designs. The design team
| would generate 10 designs every week, take them to the sub
| guys who would spot new problems ("there is no bathroom close
| to the command deck" for example) and then go back and
| translate all the problems into new constraints for the
| solver. Later iterations even had VR models so they could
| "walk" through the virtual ship.
| WalterBright wrote:
| Reminds me of designing a house. Want a bigger bathroom?
| The closet shrinks.
| Ichthypresbyter wrote:
| >There was no theory, ship's screws were designed by trial and
| error.
|
| The early marine propeller designs consisted of an Archimedes-
| type screw with multiple full turns. During tests of one such
| design on a small boat in the Paddington Canal in London, half
| of the propeller broke off. The broken propeller (with only one
| turn) turned out to be able to propel the boat twice as fast.
| [0]
|
| The inventor, Francis Smith, amended the patent to describe
| either a single-turn screw propeller or one with two screw
| threads each describing half a turn (essentially a two-bladed
| propeller).
|
| [0]https://www.bluebird-electric.net/boats_images/propellers-
| fr...
| WalterBright wrote:
| The propeller efficiency aspect is why I don't believe all the
| other "first powered flight" claims. The Wright Flyer had
| barely enough power to get airborne, and that's with the
| double-efficiency propeller.
|
| Attempts to build flying replicas of the other claimants'
| machines don't impress me because they don't address the power
| needed to get those contraptions into the air with the engines
| available at the time. (The Wrights couldn't find an engine
| with the power/weight needed, and had to design/build their own
| powerplant.)
| LargoLasskhyfv wrote:
| That was interesting, and FUN! 'Explorable Explanations', Yay!
|
| Excellent. Bookmarked.
| robotnikman wrote:
| Playing the game From the Depths (if you like games like kerbal
| space program I highly recommend it) taught me a lot about naval
| architecture and hull design.
|
| I already knew some about it since I already liked playing Naval
| games, but it took at least 12 hours or learning and
| experimenting before I could design a hull design which didnt
| sink or roll over, or other odd behavior. This is all despite the
| game not modeling some of the other aspects like water pressure,
| and being simpler compared to real life.
|
| Basically, there is a lot more to designing ships that meets the
| eye.
| tobmlt wrote:
| Nice visualizations! Next how about response amplitude operators
| and statistical response in a random wavy sea? Spectra of Motion,
| force, etc are really compact tools for design analysis. The
| linear theory is quite beautiful in my opinion. Not Maxwell's
| equations beautiful, but up there.
|
| Speaking (indirectly) of the equations of motion, I didn't see
| added-mass as I scanned through. Could be fun to talk about as
| well as diffraction radiation.
|
| Somehow the above are more fun sounding to me than Navier Stokes.
| I dunno. My burnout shifts with time.
| panic wrote:
| The way the slider matches the position of the block as it floats
| is very satisfying.
| dtgriscom wrote:
| My personal money-shot: "the center of buoyancy is just the
| center of gravity of the displaced water." Very clear, very cool.
| tastyfreeze wrote:
| Fantastic material! Material like this blows the pants off of a
| textbook and is an example of what educational material online
| should be.
| jonshariat wrote:
| "It's worth stressing that in these static cases the pressure at
| a given level depends purely on the height of the body of water."
|
| How did I not know this? It's so counter intuitive that a thin
| column of water can cause the same pressure as a wide one.
|
| The video they link shows this in action:
| https://www.youtube.com/watch?v=EJHrr21UvY8
|
| One mind bending fact she shares in the video is that a thin
| layer of water, touching the damn wall, is the same pressure as
| an entire lake.
| zwkrt wrote:
| A fun thought experiment is to realize that if the earths
| atmosphere were totally removed except for a cylinder that
| encircled your house and went into space, you would feel
| physically the same. Just like in the water, in some sense the
| only thing air pressure cares about is how much air is directly
| on top of your head.
| abraae wrote:
| I'm building a system for measuring levels in water tanks using
| submersible pressure sensors (triggered by living in a dry area
| and being totally dependant on our tanks).
|
| Quality sensors cost a lot - too much for domestic purposes.
| Much cheaper ones can be bought from China, so I've been
| looking for some way to test them, without actually altering
| the level in a gigantic water tank.
|
| It occurred to me I should be able to just use a thin vertical
| pipe. But as you say, this seems counter intuitive, especially
| if the pipe is barely wider than the sensor itself. Just
| doesn't... Feel right.
| zsmi wrote:
| I can totally relate.
|
| I've been using ohm/square for decades. I know the math. I've
| measured it. It works. I know it's true. But my mind refuses
| to accept that ohms/square can possibly be a unit. Every
| single time my mind is like, "ohms per square what?"
|
| http://www.esdjournal.com/techpapr/ohmmtr/ohm.htm
| tbrownaw wrote:
| My understanding of that is that it's using "square" as in
| aspect ratio like how screens are 16:9 or whatever, while
| "square" in units is more commonly used as in `exp(n, 2)`.
| And that terminology mismatch is why it often doesn't seem
| to make sense.
| RantyDave wrote:
| If you stick the sensor at one end of a hose pipe (with water
| in it) then you can just change the height of the other end
| to change the pressure.
| abraae wrote:
| Nice idea, thank you.
| RantyDave wrote:
| Hey, also, why not just find the height of the water level by
| attaching something ultrasonic to the inspection hatch (or
| whatever). https://www.adafruit.com/product/4664
| abraae wrote:
| Not accurate enough. I want to be able to quantify e.g how
| much water was used to water the garden. In a 25K litre
| tank, that's a very small change in level.
| groby_b wrote:
| You'll have the same issue with pressure sensors, though?
|
| Maybe a flow meter is a better choice for that. (Bonus,
| you can use that to cross-calibrate with the
| pressure/level sensor)
| snovv_crash wrote:
| Yep, if you use flow plus pressure, you can run an EKF to
| get much more accurate results.
| vosper wrote:
| Not only is this a really cool idea, that sensor is
| awesome! I love that you can get something like that for
| $30.
| lazide wrote:
| It's called head - and it's a key calculation in if a dam is
| worthwhile. The pipe feeding the turbine can be quite small
| for a lot of power if the head is large.
|
| You could also use a small pressure vessel/sealed tank, and
| pump in water with a hand pump. You could simulate nearly any
| sized tank that way too.
| morpheos137 wrote:
| why is it counter intuitive for you? It is not to me at all.
| Gravity pulls down. There is essentially no lateral component
| to gravity. Height is measured in the verticle dimension, the
| same as gravity. Now imagine water column as a stack of
| pennies. The more pennies are added to the stack the more
| pressure is on the lower pennies. It does not matter how many
| stacks are in front of or behind or to side of the stack you
| are looking at.
| Iv wrote:
| > There is essentially no lateral component to gravity
|
| Yet you can distribute the weight of a structure on larger
| bases. If you put two columns on pennies on a steel plate,
| the pressure under the plate will be higher than if you put
| only one column.
|
| It is easy to imagine the bottom vessel as similar to such a
| plate.
|
| I think the key to make this intuitive is to realize a few
| things:
|
| - pressure in liquids are transmitted differently - water is
| actually very slightly compressible - atmospheric pressure is
| also an important part of the system
| abdullahkhalids wrote:
| > Yet you can distribute the weight of a structure on
| larger bases.
|
| In the case of solid objects, indeed. This is because in
| solids atoms are bonded together and so the weight can
| distribute. An easy and extreme case of this last statement
| is to imagine standing on a bridge. Your weight is
| supported not just by the part of the bridge underneath
| you, but, via transmission, by the two end points attached
| to land.
|
| In liquids, the atoms are not bonded, so the same
| distribution cannot happen.
| morpheos137 wrote:
| pressure is measured in force per surface area. It is
| disheartening to see HN so quantitatively illiterate.
| simonh wrote:
| Nobody is saying this fact about liquids isn't true. We
| all know it's true, so proving it doesn't change
| anything.
|
| It is counter intuitive though precisely because the
| pennies analogy doesn't work.
|
| If I put a 1m stack of quarters on a pressure gauge, then
| I put one quarter on the gauge and a stack of pennies on
| top of it up to 1m high, I get two different readings.
| Conversely if I measure the pressure at the bottom of two
| bottles the same shape as the stacks of coins, I get the
| same readings.
| morpheos137 wrote:
| If you measure the pressure at the bottom of two bottles
| containing different density liquids the same shape as
| the two stacks of different coins you get two different
| pressure readings.
|
| In case it was not clear in my analogy a "penny" (it can
| be anything solid and incompressible) is representative
| of a water molecule. If you want to compare the pressures
| of stacks of pennies and quarters because for some reason
| you are fixated in these specific physical coins rather
| than what they represent then I will make it explicit.
| Imagine pennies represent water and quarters represent
| mercury. Two different liquids, two different coins, two
| different pressures. I don't get what you guys don't get.
|
| Can you explain to me why you think it is intuitive that
| the downward pressure of a liquid at the bottom of a
| container should vary for equal depths but different
| volumes? E.g. you seem to intuitively think that if you
| have a big pan filled with 1 inch of water the water
| pressure at the bottom of the pan is greater than the
| pressure at the bottom of a 50 ml flask also filled with
| one inch of water. This is false but I am interested as
| to why you and the others think it is "intuitive?" Where
| does the additional force come from to increase the
| pressure in the bigger pan? Gravity pulls straight down.
| Iv wrote:
| In my case, the difference in intuitiveness is that I am
| used to things crushing because of weight/force but not
| because of pressure.
|
| If you have a bottle of 1 kg of water and put it on a
| plank between two stools, what matters to know if the
| plank will break is the total weight (and torque) of the
| bottle and the surface of contact. The shape of the
| bottle is irrelevant.
|
| When you have that image in mind and someone suddenly
| tells you that actually no, 1 kg of water on a 50 meters
| high column can actually break things 1kg of water in a
| bucket can't, it is very counterintuitive.
|
| And the stack of pennies is really unhelpful I feel. Make
| an inverse pyramid with 1000 pennies, all of them resting
| on one at the bottom tip, or make a column of these, the
| force exerted on the bottom one will be the same. The
| force per area as well. Not so with water.
|
| The difference is that the water molecules move until
| they find an equilibrium in which there is a gradient of
| pressure and where molecules push back in every direction
| equally. Pennies do not, they are content exerting
| "pressure" in a single direction
| morpheos137 wrote:
| Water exerts pressure in a single direction too: down.
| There is no PSI gradient in the lateral direction. This
| is intuitive because there is no force acting in that
| direction. I do not believe water molecules ever find a
| topological equilibrium in a liquid phase. Because then
| they would be a solid or a crystal. Water as a liquid can
| flow but it still only exerts pressure in the downward
| direction. To my analogy, pennies can slide or move from
| one stack to another (e.g. waves). The only thing
| affecting the pressure on the bottom penny of a given
| stack at a given instant is the number of pennies in that
| same stack resting on top of it. What is going on in the
| adjacent stacks does not matter, because gravity only
| pulls down.
| bilog wrote:
| The intuition with the columns of pennies over a plate
| doesn't translate because in the plate case the surface is
| fixed (the surface of the plate) so the pressure depends on
| how much weight you put on it. In the case of multiple
| columns of water, the pressure you're looking at is the
| pressure on the combined surface of both columns, which
| remains constant because both the weight AND the surface
| are increasing proportionally, keeping the ratio (that
| gives you the pressure) constant.
| jvanderbot wrote:
| This is a great explanation, actually.
| JKCalhoun wrote:
| Hmmm ... reinforces my counter-intuition. The stack of
| pennies might explain why the bottom of the jar would
| explode, but not the sides, area not below the stack of
| pennies.
|
| My intuition (wrong here) is that the extra surface _not_
| beneath the stack of pennies (your analogy) would in fact
| _distribute_ the pressure and therefore represent a lower
| PSI on all sides of the jar.
| jvanderbot wrote:
| I guess I translated "pennies" into "little bags of
| water". The little bag of water at the bottom only gets
| pressurized from the little bags of water above it.
|
| And so the bottom bag's "pushing" outward from
| compression would be affected only by those above it.
| RealityVoid wrote:
| Actually, yours is not such a great explanation, since a
| stack of quarters would manifest greater pressure than a
| stack of pennies. Whereas, a fluid column would manifest the
| same pressure no matter the diameter.
| Ma8ee wrote:
| No, a stack of pennies would manifest a greater force, but
| the pressure would be the same. Pressure is force per area,
| which means that the increased weight from a wider column
| is exactly cancelled by the increased area that the force
| is distributed over.
| Denvercoder9 wrote:
| Technically a stack of quarters would exert a greater
| pressure, but only because they're made of a denser
| material than pennies.
| RealityVoid wrote:
| Ok, yes, this holds true if the support surface increases
| the same. But the parallels still do not hold too well.
| Imagine sort of a funnel holding water, no matter the
| thickness of the base or top, the fluid pressure at the
| base is the same. Whereas with coins it does not work the
| same.
| morpheos137 wrote:
| penny is symbolic. diameter is irrelavent if scale is
| undefined.
| Nathanael_M wrote:
| Super conter-intuitive for me as well. I appreciate your
| explanation!
| zarzavat wrote:
| Perhaps you are conflating pressure and force?
|
| Pressure is force per area, the area doesn't matter by
| definition. Similarly to how we measure rainfall in
| millimetres: volume / area = length.
|
| Whereas if you were to place a bucket of water on your head,
| the area of the bucket would surely make a big difference to
| the force you feel, all else being equal.
| pkaye wrote:
| Its basically the Bernoulli's equation. Its because pressure is
| force over area and the mass of the body of water above it is
| area times height time density so the area cancels out. You can
| add velocity into the equation and its a conservation of energy
| equation. Similarly there is a continuity equation which is a
| conservation of mass. These two are the backbone of a beginning
| fluid mechanics course in engineering.
| jvanderbot wrote:
| Intuition fails! Quick, point out the math! Your comment is
| exactly what is derived / demonstrated in the article.
|
| Parent was simply commenting how that math was not intuitive
| (and so repeating that it was just math doesn't do much).
| [deleted]
| tobmlt wrote:
| Fluid has so much to bend the mind. Soliton waves, shocks,
| expansions, critical transition phenomena (besides phase
| transition) Look at froude number and planning hulls, the
| purpose of chines, steps, etc. in a high speed hull to manage
| skin friction vs wave drag. Wave Dispersion, wave
| superposition, etc. the free surface itself means if you are
| solving for flow, flow then determines the free surface which
| then determines the flow.. add infinitum. It's nonlinear like a
| baby general relativity in that way. The shallow water
| equations are hyperbolic so you get shocks etc. deep water,
| long wavelength waves act in linear fashion so you get
| superposition effects. On and on. Fun times.
| awestroke wrote:
| Can you recommend any books on this?
| mr_overalls wrote:
| Fluid mechanics is a standard course in many undergraduate
| engineering curriculum. A quick Google search reveals lots
| of open-source and downloadable pdfs of printed texts.
|
| https://open.umn.edu/opentextbooks/textbooks/85
|
| http://civilcafe.weebly.com/uploads/2/8/9/8/28985467/fluid_
| m...
| throwawaysea wrote:
| There must be a few general equations that capture all these
| behaviors in fluids right? That is, aren't all these just
| "emergent" aspects of some fundamental physics?
| bilog wrote:
| The equations are conceptually simple: Navier-Stokes
| equations (conservation of momentum) and conservation of
| mass. The behavior is emergent.
| tragomaskhalos wrote:
| Fluid dynamics was an entire optional module in my maths
| degree, there is so much complex content there. (I didn't
| take it, it looked too hard!)
| vishnugupta wrote:
| For me the aha/eureka moment about the force of water pressure
| was when I read that water jet is used sometimes to precision
| cut diamonds.
| palijer wrote:
| This is one of those physics phenomenon where I feel like they
| are a software bug. Bell's Theorem and a lot of quantum
| entanglement stuff is like that as well.
|
| https://youtu.be/zcqZHYo7ONs
| jschwartzi wrote:
| It's actually quite intuitive, as the force is distributed
| over a larger area. So although the pressure gradient isn't
| affected by the discontinuity in the container size, if you
| compare forces exerted by the pressure on a plate in either
| section of the chamber you'll observe that the force on the
| wider plate would be reduced to compensate for the increased
| area in the presence of the same pressure.
| garmaine wrote:
| I'm not sure why you're being down-voted. If you double the
| size of a water column, you of course double the total
| weight pressing down. But you've also doubled the cross-
| sectional area, so the weight-per-unit-area (pressure)
| remains the same. This is pretty intuitive if you
| understand what pressure is.
| Ma8ee wrote:
| The force would scale with the area, since pressure is
| force per area. Not the other way around.
| ummonk wrote:
| That's interesting because it seems perfectly intuitive to me.
|
| Both in terms of understanding the physics (weight of water
| above the column divided by the area of that column, and then
| any water around the column just has to have the same pressure
| to contain that column) and just plain practical experience
| from e.g. dipping underwater in the ocean and not getting
| crushed like a bug.
| Iv wrote:
| It is very counterintuitive when you reason in terms of
| weight though. If you imagine a pile of rocks for instance,
| it makes sense that the strain on the base of a pyramid is
| lower than on the base of a column of the same height and
| base area.
|
| You have to visualize the atmospheric air pressure to
| reconcile the result with intuition.
| ummonk wrote:
| I mean it's perfectly intuitive to me that a pyramid of
| rocks isn't going to collapse, so you don't need a
| container to hold it in. The closer analogue would be
| pouring sand in to a tube vs. pouring it in to a bottle
| that widens below the neck - it's intuitive to me that the
| bottle would be under enormous strain to hold the sand in.
| (And, incidentally, the part of the bottle where it widens
| would be applying extra "weight" to the sand below it)
| marcosdumay wrote:
| On those oddly shaped reservoirs, the walls compensate for the
| lack of a water column above the places where it widens. The
| actual force on the water is the same as would be in a
| cylinder.
| josh_today wrote:
| Thought this was a new form of philosophy by @naval
| jefurii wrote:
| These are some very nice visualizations!
| masswerk wrote:
| I've always thought that metacentric height would make the
| perfect try-at-home in your bath tube experiment against Flat
| Earth. If the center of buoyancy and the center of gravity were
| indeed the same, every ship would be rolling like a log and there
| weren't any differences in types of ships and hull shapes at all.
|
| However, I guess, those adhering to said fancy model must not be
| bothered by such complexity of thought...
| gk1 wrote:
| Naval architecture is a fascinating and beautiful discipline.
| This post does it justice.
|
| It's too bad there aren't many naval architecture careers in the
| US. We hardly design or build any ships here anymore. The one
| exception is military ships. So if you have a naval architecture
| degree your main employer options are a) government or b)
| government contractor.
|
| Source: Naval architecture degree.
| [deleted]
| ghoward wrote:
| Hey, you might be able to answer this: if someone who wants to
| learn naval architecture deeply (but not for a career), how
| should they go about it?
|
| I'd love to design ships as a career, but as you said, there
| isn't much work, but why not learn for the sake of learning?
|
| Also, aeronautical engineers, I'd love to learn that too. How
| to go about it?
| 5555624 wrote:
| It depends on what you mean by "deeply" and how you wish to
| go about it.
|
| If you want to try and pick it up on your own, start with the
| book "Introduction to Naval Architecture" by Thomas Gillmer
| and Bruce Johnson, from the US Naval Institute. From there,
| if you're still interested, probably "Applied Naval
| Architecture" by Robert Zubaly or something from SNAME
| (Society for Naval Architects and Marine Engineers).
|
| If you want to go to school and you don't want to get a
| degree in it, you can study something similar; but, related.
| (I majored in Ocean Engineering, which included a number of
| naval architecture courses.)
| ghoward wrote:
| Thank you. :) I am putting those books on my shopping list.
| lazide wrote:
| If you can afford it, go ahead! At least aeronautical
| engineering is a solid (and not easy) full time degree
| program. Embry-Riddle is one well known school, and they may
| be doing online classes/have some coverage.
| ghoward wrote:
| Thank you. Online might be doable.
| mLuby wrote:
| If you're on Twitter, two accounts you might appreciate in
| one tweet:
| https://twitter.com/R_P_one/status/1413506570575515655
| pomian wrote:
| There is a cool program at Memorial University, Newfoundland.
| https://www.mun.ca/undergrad/programs/engineering/ocean--
| nav...
| tofuahdude wrote:
| I'm so traumatized by silicon valley that I immediately assumed
| this was about Naval Ravikant. Sigh.
| sandworm101 wrote:
| >> It turns out it's a proper scientific discipline dedicated to
| the engineering of ships.
|
| No. It is about the engineering of all sorts of things. Ships are
| a subset. I'd say that it covers all things that float, but that
| wouldn't include docks, cranes and other things that integrate
| with ships.
|
| >>As containers are added the ship will sink a little and
| increase its draft - the distance between the bottom of the hull
| and the waterline.
|
| This is the wikipedia answer. In the real world "draft" is the
| lowest part of the ship, which might be something other than the
| hull. Sailboats especially measure draft from the bottom of their
| keel, a thing lower than the hull. The "hull" is the watertight
| body and doesn't include things like keels and rudders which,
| while uncommon on large vessels, normally extend well below the
| hull's depth.
| opium_tea wrote:
| It's amazing what different people take from articles. That
| someone would read through this page and instead of
| appreciating the effort and craft their response would be an
| absolute textbook example of tedious internet pedantry.
| sandworm101 wrote:
| Or someone who has to spend too much time around navy people
| who obsess about these definitions, people for whom small
| errors can lead to poorly loaded holds or vessels hitting
| rocks because they didn't know their draft from their hull
| depth.
| NotEvil wrote:
| But thise people won't come here to find answers to there
| questions. Whould they? They will learn it in there
| professional or academic life.
| VLM wrote:
| I live in a recreation state, and to provide some numbers
| there are well over three times as many registered boats
| in my home state than there are naval O-6 rank ship
| captains. Just in one state.
|
| Admittedly "beaching" a nuclear air craft carrier is more
| important to the USA than a local bubba beaching his fish
| trawler on a sandbar; but to bubba as an individual, its
| more important not to beach his fishing boat as avoidance
| of beaching his fishing boat is actionable for bubba,
| whereas watching TV reports of a naval accident are not.
| pomian wrote:
| Bravo. As usual, Ciechanowski makes extremely easy to understand,
| graphical expressions of complex ideas. Highly recommend this
| site and his other topics.
| cjdell wrote:
| This page is so well done. All physical and mechanical problems
| should be taught this way. I just loved playing with the sliders.
| I felt like I didn't even need to read the text to understand the
| concepts. This could be a great alternative teaching style for
| bored kids.
| defaultname wrote:
| This is the person who did the astonishing internal combustion
| engine and camera entries with the same dedication to detail.
|
| https://ciechanow.ski/internal-combustion-engine/
|
| https://ciechanow.ski/cameras-and-lenses/
|
| They do fantastic work.
| quenix wrote:
| I am just fascinated by the amount of work and effort that
| goes into this. A simple view-source shows tens of
| _thousands_ of lines of code... for a free blog. Incredible
| content_sesh wrote:
| Really nice explanations and visualizations. The discussion about
| ship stability and the moment arm between center of gravity and
| center of buoyancy gave me flashbacks of my undergrad aircraft
| stability and control classes (where the moment arms between CG
| and center of lift on the wings determines static stability).
|
| The discussion about propeller design is also very similar to
| aircraft as well - not just aircraft propellers but also
| compressors in turbofan engines.
|
| The fact that there's a ton of similarity between the disciplines
| isn't too surprising, but the great visuals in this blog post
| made that connection seem particularly satisfying.
| djrogers wrote:
| Wow - this is amazing work. Great explanations, wonderfully
| useful animations, and plenty of detail to keep even the most
| curious interested.
|
| Well done!
___________________________________________________________________
(page generated 2021-07-28 19:02 UTC)