[HN Gopher] Naval Architecture ___________________________________________________________________ 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! ___________________________________________________________________ (page generated 2021-07-27 23:00 UTC)