[HN Gopher] Naval Architecture
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Naval Architecture
Author : todsacerdoti
Score : 296 points
Date : 2021-07-27 15:03 UTC (7 hours ago)
(HTM) web link (ciechanow.ski)
(TXT) w3m dump (ciechanow.ski)
| 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.
| _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.
| 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]
| 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
| fuzzylightbulb wrote:
| I had the same question. (Putting this here so that I can come
| back later.)
| andreofthecape wrote:
| Very well done!
| 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.
| 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.
| 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.
| 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.
| 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!
| 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).
| bopbeepboop wrote:
| I think the point was intuition differs:
|
| That the weight of a volume is linear in its footprint
| seems obvious to me -- but other people will imagine the
| situation differently, so they won't come to the same
| opinion on what's "obvious".
| 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.
| 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.
| 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.
| 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.
| 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.
| 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!
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(page generated 2021-07-27 23:00 UTC)