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Science Technology

Cement Canoe With A Contrarian Approach 103

Posted by timothy from the ignore-that-sinking-feeling dept.
Markgor writes: "There is an article in Wired News today about a group of students at the University of Alabama (Huntsville) who entered into the 2001 ASCE/MBT National Concrete Canoe Competition with a canoe that was built to achieve forward propulsion through matching natural resonance."

"Normally, if two objects share an exact natural resonance, the excited vibrations would usually lead the weaker object to fall apart, much like the Tacoma Narrows Bridge did when the equal frequencies of the wind and the structure of the bridge matched. However, since the canoe was designed with a special mix of concrete, it was flexible enough to withstand the vibrations and harnessed it into forward propulsion. They're now talking about its possible use in space, such as interplanetary probes using natural resonance to propel itself."
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Cement Canoe With A Contrarian Approach More

Cement Canoe With A Contrarian Approach

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  • Slashdot readers have passed the stage of "gee, if it's made of stuff denser than air/water, of course it can't fly/float" long ago. Feel free to teach this at your local kindergarden though.

  • Re:If they can bend concrete... (Score:1)

    by Anonymous Coward
    it's not spelled "ashphalt" because it's not pronouced "ashphalt" [dictionary.com] either.
  • SGA is Student Government Association, AKA Student Council.
    UAH is the university this article is about, the Unversity of Alabama in Huntsville.
  • Step 1. Fill outer space with water.
    Step 2. Propel through water using resonance.
  • Concrete boats aren't news - I held stock in a company specializing in them years ago (did well as I recall.)

    Boats can be made out of anything that that doesn't dissolve quickly and has the strength to displace the requisite volume of water. Iron, steel, concrete, waterproofed paper-laminate, whatever - they need not float on their own; it's displacing a volume of water of greater mass then their own mass that is key.

    Concrete boats are popular in a number of parts of the world. In Africa they're popular as small calm-water ferries for their low cost, durability, and ease of contruction. Often they're a simple mini-barge with a line crossing the river. To power them one either pulls the line directly or employs a simple mechanism, dragging oneself across the water.

    As to the concrete being used in this application - it's made with exotic materials as it has exotic requirements. Light-weight, flexible, etc. aren't usually the priorities for a concrete; durable, high compression strength, low cost usually are. None of this is breakthrough as the materials used in the boat wouldn't likely stand up under a season or two of highway or other civil engineering use.

  • you mean save money on taxes? No, I doubt that this will ever make it to the national highway system.

    Plus, the distance that the road would need to avoid moving would probably make the cost of the matierals far more than the 70 pound canoe.
  • Funny - this was just discussed in the rerun of a Quantum Leap episode yesterday. They did, in fact, have many concrete boats and barges, as PopeAlien mentioned. They were all manned by Merchant Seamen. You can read about the concrete liberty ships here [madforscuba.com].


    Quidquid latine dictum sit, altum viditur.

  • Rules and Regs (Score:3)

    by Kozz ( 7764 ) on Wednesday July 04, 2001 @10:21AM (#108407)
    are posted here [masterbuilders.com]. They're both PDF files. The rules are quite complex, explaining the ratios of different types of cement and so forth. Interesting read.


    Quidquid latine dictum sit, altum viditur.

  • In space? (Score:3)

    by PD ( 9577 ) <slashdotlinux@pdrap.org> on Wednesday July 04, 2001 @09:49AM (#108408) Homepage Journal
    If they aren't expelling mass, they will need to push against something. Perhaps he is suggesting a largish RC circuit that pushes against the earth's magnetic field. This could be interesting, because the power requirements to keep an oscillator going are rather small. But I don't quite understand how resonance would help in that case, since a magnetic field doesn't work the same way as a fluid such as water.

  • ...go back at least 14 years?

    Try more like at least 25 years. The guys in the CE department were making concrete canoes and competing with other schools' CE students back in the early-mid '70s. Us EE students thought they were daft but, then, we were amusing ourselves trying to do useful things with weird things called ``microprocessors''. (One guy was doing speech recognition on the department's Altair. Hand assembly anyone?). The CEs thought we were nuts.


    --

  • Once they've managed to build the concrete canoe, maybe they can start at looking at the paper canoe? At least it will give a use to all the waste produced by today's offices ;)
  • "You can cause something to move with very little energy input"

    Try portaging it across land and get back to me. :)
  • If you're interested in more details, swing by the UAH concrete canoe team homepage [uah.edu]. It even talks a little about their recent launch of the world's first concrete-reinforced rocket [uah.edu]!
  • Why would you machine or drill it?

    You make this by making a mould from with the formwork and your reinforcing bars then pour in the concrete. Shape it when it's wet and let it set.

    We never had concrete canoes when I was a civil eng student, but we did have bridges made out of spaghetti. Lets see a spaghetti canoe contest!

    dave
  • Up here we know what to do with concrete. It's a great use of concrete engineering too. More info on the UW concrete toboggan team here [dyndns.org]
  • There's absolutely NOTHING to push against in space (last I check, there's no air to push up against there).

    actually the sun sends alot of hydrogen ions into space. these are more commonly known as solar wind [dictionary.com]. these travel very fast, and i would suspect that it would be possible to use the natural resonance of the solar wind to power the ship.

    use LaTeX? want an online reference manager that
  • i think they were referring the durability with respect to space materials. i dont believe they were suggesting you use the vibrational aspects of the concrete. i suppose it is possible to match the resonance with the solar winds.

    i wonder if they have tested the materials under the extreme conditions one would encounter in space? it gets really cold at night and really hot during the day up there. i really doubt the latex component will withstand really extreme conditions.

    use LaTeX? want an online reference manager that
  • The concrete doesn't ever need to be lighter than water.

    just the mass of the canoe and riders must be less than the mass of the water displaced if the water were at the lip of the canoe.

    use LaTeX? want an online reference manager that
  • IANAPNWAEB (I am not, and probably never was an engineer, but...)

    While some of this guy's interview reminds me
    of psuedo science from things like the time cube,
    I think their underlying principle is similar to that of a Tesla coil.

    Tesla coils (for those who don't know) are able to generate huge
    amounts of electricity from a small amount (yes, there are tradeoffs...
    loss of amperage for one, but anyways) by the same principle
    of oscillation: imagine you're pushing a friend in a swingset...
    while it's a lot of effort for _them_ to push themselves so that
    they swing up really high, all _you_ have to do is push a little with
    your pinky, each time they hit the highest point in their swing
    (ie, the resonance frequency).

    Tesla coils use this idea to
    generate immense arcs of electricity from a small amount, using
    the small drive voltage to "push" the larger current which
    is being generated in the circuit.
    Sort of.

    The end effect of this principle, whether
    in coil or canoe, is that you still doing
    all the work, it's just that it's amortized,
    your work cumulatively builds upon the last...
    it's not exactly breaking themodynamics,
    it's just raising your mechanical efficientcy
    somewhat nicely.

    Still... this looks like an interesting idea,
    though I really hope the man realizes there's
    no water in outerspace... hopefully,
    the Wired guys just took him out of context.

    There was something else I was going to say...
    oh yeah... I strongly encourage everyone
    to go on the web to check for technical
    accuracy of what I just said... I have a
    generalist's idea of what I'm talking about.

    -Slackergod
  • Did you actually read the whole article? The interesting part is not that it's made of concrete, it's the "forward propulsion through matching natural resonance".
  • They suggest that we build a space ships/vehicles which 'operate at [their] natural frequency and use the energy this produces for propulsion.'.

    TANSTAAFL. Sure, in a river I can conceive of harnessing the power of the waves/water by getting the boat to resonate with some frequency and then use that somehow to push the boat. (Having read the article, I'm still a little unclear on the concept.) But how do you use this in a (near) vacuum?

    To get something 'operating' at its resonant frequency, someone has to be putting power into the system. I just don't understand what's supposed to be vibrating the space ship that's giving you the power.

    Anyone understand this? Is it harnessing external sources, or just an attempt to make use of every last scrap of effort put into moving the boat?

  • I live about 4 miles from there (near I-90 and I-405). Where can you see the remnants of the old bridge?
  • Slashdot editors haven't, though.

  • They were building conrete canoes in a civil engineering competition at the University of Toronto in 1979. Not even hard -- concrete is half the density of steel, and steel ships are everywhere.


    More insteresting is the resonant part of it, but I would think that steel is better because it's elastic limit is higher and the modulus is lower to give more elastic deformation.

  • If they can bend concrete... (Score:4)

    by homebru ( 57152 ) on Wednesday July 04, 2001 @09:55AM (#108424)
    If they can bend concrete, they may have just saved the national highway system. One of the biggest problems is roads that self-destruct when the soil under them shifts. With enough wet/dry, expand/contract, up/down cycles, our highways are in constant need of repair. If even a small portion of this rework can be avoided with the "flexible concrete", the potential savings are enormous.

  • The real news here is that they're positioning this cement blend for use in space structures.

    They should wait till this guy [bbc.co.uk] launches his cement mixer.
  • There's absolutely NOTHING to push against in space (last I check, there's no air to push up against there).

    This is not an application of Newton's 3rd law (used in rocketry). In a rocket, the mass of the propellant reaction products excaping the nozzle generates the reaction needed to push the rocket forward, here, there's no mass ejected, only a structure "wriggling".

    Conceivability, you could laminate a sheet of piezoelectric element, and generate power from that, and feed the power to an ion engine. But ion engines still require fuel (a tank of xenon or a gas with a hefty mass, see above for reason why), so it still wouldn't be an unlimited source of power, as far as propulsion is concerned...

    -=- SiKnight

  • The shedding frequency of the flow from the bridge approached the natural frequency of the bridge. As this occurred the bridge began to oscillate. Once the bridge begins to move the frequencies will lock, and increasing the or decreasing the flow velocity passing over the bridge will alter the magnitude of the forcing, but the forcing will always be positive. About two years ago I helped an undergraduate ME student set-up an experiment to look at the potential for extracting energy from a low-speed flow using a simple sring mounted cylinder.. He saw that once the cylinder began to move he could up the flow velocity and watch the amplitude of the oscillations increase to a maximum.. Similarly, he could reduce the velocity to a point below where it would begin oscillating..

  • It's easy.. Embed something like a piezo actuator into the structure. As the piezo element is strained it will generate a voltage.. Now make the structure a couple hundred yards long and let it orbit the earth.. Each time it orbits the earth it undergoes a thermal cycle associated with passing through the earths shadow. If the structure is designed like a big bimetallic strip the thermal cycle will induce and oscillation.. Pow! Electricity via structural vibrations..

  • Note: I'm just guessing here
    You do have something to push against when using propellant.
    I am thinking maybe thruster nozzles that resonate as the propellant is pushed past them. That might be used to maximize the thrust produced by the engines.
  • I see something silverish, wibbling back and forth against a black sky full of sharp white stars. It is not ejecting mass. It has no surfaces to catch the solar wind. It has nothing to move against. Its crew is getting violently ill from side to side motion.

    Exactly how is this thing supposed to do anything besides wiggle?

    I recall Hughes Satellite salvaging a communications satellite using minor engine burns and a slingshot around the moon to move a failed launch into a useful geosyncrhonous orbit [cnn.com]. Is this what the article's author(s) are talking about?
  • But there is something to push against... The earth, the sun and some other bodies. And you can push against them at a distance by utilizing a magnetic field...
  • Sadly, there is also an embedded sound file. Perhaps this web faux pas offended the Wired team so greatly they were forced to exclude the link.

    Well, that's where I'm putting MY quarter.....

  • Re:Concrete? (Score:5)

    by Chairboy ( 88841 ) on Wednesday July 04, 2001 @10:18AM (#108433) Homepage
    Don't confused concrete and cement. Concrete is a simple name for composite construction. A concrete highway is often made up of a composite of steel rebar, cement, gravel, etc.

    Cement, on the other hand, is a specific name for a substance, often alumina, silica, lime, iron oxide, and magnesium oxide. Cement is often used in the construction of concrete as part of the composite.

    Composite structures != carbon fiber/kevlar/etc exclusively. Composites have been used for hundreds of years to make lightweight, strong things. This is merely the latest example of exactly that.

  • tacoma narrows (Score:3)

    by stang ( 90261 ) on Wednesday July 04, 2001 @10:26AM (#108434)

    like the Tacoma Narrows Bridge did when the equal frequencies of the wind and the structure of the bridge matched

    Just to do a little karma whoring...

    Google [google.com] has some nice links [google.com] to video of the Tacoma Narrows bridge moving. This one [airspacemag.com] from the Smithsonian is pretty good.


    --
  • The real news here is that they're positioning this cement blend for use in space structures. They claim it's lighter than and as strong as carbon fiber composites, but able to bend without breaking, and less subject to harm from high energy particles in space. Cement has also been explored for building cheap submarines for third world countries -- I think they tend to look a lot like the sea floor acoustically, so it's really easy for them to hide on the ocean floor and pop up to launch a torpedo.
    When I saw this article yesterday I found it really interesting because I'd just been thinking about the submarine thing, and that cement/concrete might be a really cheap and easy material for amateur/private exploration of space, instead of having to have all the nasty chemicals and expensive machines necessary to work with composites.
    Anyone contacted this group and found out what the exact proportions of the ingredients are? It might be interesting to mix up a batch and do some testing.
  • Yeah, they don't usually mold carbon composite frames for the space station in outer space either. Unless you were going to capture the water evaporating as it cured, it'd be wasted expense launching it, too.
  • I'm sorry, I don't speak acronymish... what are SGA and UAH?

    ----
  • I suppose they could match the natural resonance of the hydrogen ions that the sun shoots out (solar wind). I read a few months ago about a group that was designing a system to use hydrogen ions in space propultion by creating an elecromagnetic "sail". Methinks that that would be easier.

    ----
  • "because the suspension cable were placed at equal distances"

    If that were true, every suspension bridge with parabolic suspenders would collapse.

    ----
  • There was a strong wind that blew down a weak bridge. Yes, it happened to hit it just right, but it wasn't just the hum of air molecules in tune with the wood and steel.
  • lets hear it for the tripod!
  • Lets see a spaghetti canoe contest!

    Yeah, and make the contestants paddle through I giant course filled with bolognaise : )

    Mmmmm, giant course filled with bolognaise......

  • I suspect this may not be flexible like a giant rubber sheet, but more flexible like one of those pieces of steel they bang on to make thunder noises.
  • There was also an idea to make gigantic ships out of ice... Well, actually a frozen slurry of wood fiber called "Pycrete" after it's invntor, Jeoffery Pyke. The plan was to build a gigantic (for the time anyway) aircraft carrier out of the stuff. Here's a Google search if anybody's intereste in reading up on it further.

    Poses the question... If they could do it then, why hasn't it been resurrected now that we've got better technology?


    --Fesh

  • Doh! I thought I had the link specified right... Anyway:

    The link. [google.com]


    --Fesh

  • Yeah, but does it weigh the same as a duck?


    --Fesh

  • strangely, Wired didn't include the homepage for the UAH Concrete Canoe Team:

    http://www.uah.edu/student_life/organizations/ASCE / [uah.edu]

    There's a pretty good shot of the canoe on the first page.

    _f
  • The Mulberry harbours used during the D-Day landings were concrete as well, I believe.

    For a while, concrete boats were popular amongst the build-your-own-yacht community. Quite a few are still going, although few are made these days since GRP is so easy, cheap and convenient. The advent of GRP pretty much stopped concrete dead.

    The advantages (when done properly) are durability and ease of repair - the hull is very strong, and if you do hole it then you can make a permanent repair using materials available anywhere they build houses or roads. By contrast, GRP and metal require specialist materials and/or equipment to make permanent repairs. The thicker hull is also better at insulating than other materials.

    The downsides are that they're heavier than other boats (particularly GRP ones), they don't have the nice smooth finish of GRP and steel hulls, and the extra hull thickness reduces the living area somewhat. It shares with GRP the problem that minor dents can cause holes, where steel just dents. But the main problem is just that since it was so popular amongst build-your-own ppl, there's loads of poorly-made, badly-designed and generally horrible boats were produced in concrete, and that's damaged its reputation.

    Grab.

  • Yeah, I missed something there too! I wonder if they're envisioning a kind of nozzle that would use reasonance to expel some kind of propellant. I dunno.

  • Here's something to give people new to Seattle the willies! You know those bridges that connect Bellvue to Seattle and some of the other islands and pennisulas? Well, they're floating bridges and they're made of concrete! This freaked me the first time I heard that, then I worked out the whole buyoncy thing and said "Cool!" If I understand the design, the engineers basically made a bunch of concrete hulls, floated them and connected them together with cables and ran the road over the top. Several years ago, one of the bridges did indeed sink, but that was because an inspector at some point in the past had left an access hatch open, then one year there was some really rough water and the structure began taking on water. A couple of days later the whole thing sank. They put a new one in, but when I was last tehre you could still see the remnants of the old bridge right next to the new one.

  • Just be careful that the mechinism dosn't break making the canoe just go faster and faster.

    KFG
  • Mmmmm.... amoebas.....

    Just remember to drink from the center of the deep lakes. That's usually pretty good (although I prefer hard water for drinking).
  • What the poster doesn't realize, and another poster tried to explain above is that roads require durability. As you may have read in the article, concrete canoes are far from durable. The one that is being described here as "extremely fragile". Back when I helped make and design a concrete canoe for one of these contests, we made one that was durable. A couple of other contestants agreed to have a collision contest when it was all over. It was fun to watch them fall apart as we rammed our steel grating reinforced hull through their wimpy creations. MUHAHAH! Seriously though, the concrete explained here would fall apart so quickly under road conditions that it would have legislators looking for heads to whallop off their pitiful little owner's necks.
  • I must say, this sounds really cool. The Wired article is a little light on photos though.

    They've actually made flexible concrete by mixing a few other ingredients with it and applying it in a thin layer, and they're USING the natural resonance of the material to their advantage instead of trying to find ways of avoiding it like in traditional construction.

    of course when you first hear of it the first thought it "a concrete boat?" What's next? Concrete Nikes?

  • good point... I was thinking the same thing while going through the article. The whole time they're talking about resonance in water making the boat go faster, and then they say "imagine it's uses in space!"

    I imagine flexible concrete will start showing up in loads of places in the future, might as well mess around with it in zero-G too. =)

  • You're right - I was curious about the composite ratio in the rules.. I've now found out - The official rules [masterbuilders.com] state that the mix must contain 75% portland cement, and the UAH pdf [uah.edu] list their mix as containing 80% portland cement. In fact they are using the same mix as the team from the previous year. I must admit I am suprised that a composite with 80% Portland cement could be that flexible. br>

  • Re:Concrete rowboats (Score:3)

    by PopeAlien ( 164869 ) on Wednesday July 04, 2001 @09:59AM (#108457) Homepage Journal
    Oddly enough concrete boats [ferroboats.com] are not as rare as they may sound - There are many many large boats made of concrete, and from what I've seen they get real ugly, but last and last. A concrete boat sounds kind of silly at first, but when you consider that a lot of boats are made out of Iron and other heavy metals, its not that strange..

  • Rubber Roads (Score:3)

    by PopeAlien ( 164869 ) on Wednesday July 04, 2001 @10:17AM (#108458) Homepage Journal
    ..Yeah, and if we could engineer the roads to the right resonant frequency we could save on gas! boing ..boing ..boing .. Probably have to beef up the suspension on the cars that travel them tho' ---this ain't the Dukes of Hazzard..

  • Concrete? (Score:4)

    by PopeAlien ( 164869 ) on Wednesday July 04, 2001 @09:53AM (#108459) Homepage Journal
    The concrete is made up of a mix of Portland cement, glass micro-beads (microscopic hollow spheres), latex, acrylic fortifier and water.
    Mix these in the right proportions, allow the mixture to dry for 12 hours and presto -- you have concrete so flexible that it will bend and snap right back with nary a crack.

    Hmm.. Yeah its got Portland Cement in it, but it sounds like it is primarily rubber and plastic.. Are there no limitation in the rules about the composition of your 'concrete'?

  • Near as I can remember, during WW 2 the US made what they called "Liberty" ships for transport duty. The hulls were made out of cement because metal was in short supply.

    They could produce an entire "Liberty" ship in 25 days and, in 1942, built and launched a 10,500-ton freighter in four days, 15 hours and 26 minutes.
    ----

  • I thought that the Tacoma Narrows bridge collapsed because the suspension cable were placed at equal distances which allowed for the formation of a standing wave pattern when the wind swayed the bring and had to do with the strength of the wind and not the frequency in which it blew.

  • Yes, concrete ships were made way back during WWI. There were three ships built in Oakland in 1917, but they were never used. One of them is sunk at Seacliff State Beach in Santa Cruz, Ca. You can read a little more about it here [ca.gov].

  • About ten years ago I saw a TV program with a concrete spring. They'd used something of this sort to make the spring. I remember it was much lighter than what we normally think of as concrete.

    They were suggesting that it would be excellent for mounting Hi-Fi Speakers on.

    I can't really remember any more details - but it always struck me as cool.
  • Well, yes and no... most highways are ashphalt, not concrete... However, there may be uses in replacing the concrete that surrounds the ashphalt on bridges etc...

  • Near as I can remember, during WW 2 the US made what they called "Liberty" ships for transport duty. The hulls were made out of cement because metal was in short supply.

    There's one such ship, the SS Selma [crystalbeach.com] (made for WW I) sitting in the harbor in Galveston Bay. At the bottom. Not being a big believer in concrete ships, I was always slightly amused by this. Apparently, though, it made it home after cracking when running aground and was deliberately scuttled in the harbor.

  • of course when you first hear of it the first thought it "a concrete boat?" What's next? Concrete Nikes?
    Well, I suppose a lot of people did, but ferrocement (reinforced concrete) has been used for hull construction since at least WWII.

    It's all about enclosing a volume -- it's not like a block of steel floats either, but nobody blinks at a steel ship.

  • ...if you'll ask me. My roommate is the incoming president of UAH's ASCE chapter, and he was highly involved with this year's competition.

  • My thought in regard to using this material in space was that they would somehow use the resonance to create mechanical energy, which they would then convert to electrical energy in order to power the propulsion system. If the material flexed enough, those flexes could push a fixed piston which ran a generator.

    Of course, I could be way off base, but that was the initial impression that I had when I read about its uses in space.

  • I don't know if the concrete they used this year floated, but they have in the past. I was on SGA at UAH when the concrete canoe group was asking for some funding, and they brought a bucket of water with them with a hunk of concrete floating in it. That was a little weird to see.
  • I'm off to register boatse.cx [boatse.cx] right away!

  • Re:Cavitation + Resonance? (Score:3)

    by ipinkus ( 238283 ) on Wednesday July 04, 2001 @11:35AM (#108471) Journal
    Sure going a few hundred mph is fun for a while. What do you do for kicks after you have a whale embedded in the tip of your vessel?

  • Project lead Jed Clampett is eagerly anticipating the first trials of the concrete canoe in the "see-ment pond".


  • You'd need to machine the concrete because you want a smooth exterior surface on the canoe for moving efficiently through the water. The surface of the newly moulded concrete canoe will have small burrs and ridges which need to be removed by sanding. You might also want to attach toe-rests and other fittings to the canoe which could be glued on, or more effectively, screwed onto the concrete after drilling into it.


  • Seriously I hope they wore filtered breathing apparatus if they did any machining or drilling while working on the concrete in their canoe. It was reported by the BBC Newsnight program that concrete used for building block materials has been contaminated by admixture with incinerator fly ash [bbc.co.uk] containing toxic dioxin chemicals. Concrete dusts can be nasty.

  • When on tour at a coal burning power plant, I asked what they did with the ash, and the plant foreman said that it is usually sold to concrete companies as an additive to the cement to make it more flexible. The flexible concrete is used for bridge supports, concrete beams, and (ironically) the huge concrete chimneys at the power plant, which can swing back and forth as much as three feet in hurricane force winds without any damage. Actually, coal ash has many uses, from road beds to sheet rock. See http://minerals.usgs.gov/minerals/pubs/commodity/c oal/874499.pdf (Copy then paste the link onto the address bar and then delete the space between c and o in coal that appeared due to a wraparound bug in /.'s post comment form.)
  • More than 30 years ago, after hiking through the woods for several hours in Algonquin Provincial Park, we came out on a small lake where... there was a concrete rowboat tied up. Unlike the UAH canoe, this one was nowhere near any sort of resonance and probably weighed 600 or 700 pounds, but... there it was, floating.

    Turtle
    ---------------------------------------

  • Like you said, there's nothing to push against in space. There is also nothing there to push on the ship, (no waves, like the ones that cause the vibration of the ship) so there wouldn't be any vibrations, and there would be no power to harness from the vibrations that wouldn't be occuring. This theory would be *completely* useless in space. (Not even ion engines.)
  • Good question. It's a subtle point, but it is mentioned once in the article. When you vibrate something, there are two things going on. First, the driving oscillations introduce energy into the system. The system responds by vibrating at the driving frequency. Everything has a resonant frequency, a preferred frequency of oscillation. If you drive the system at any other frequency, you encounter a great deal of resistance. However, if you drive it at resonance, you encounter a negligable amount of resistance. This means that nearly all the energy put into the system results in the mechanical motion of the system.

    For the canoe, the designers were clever and harnessed this motion to propell the craft. In the case of the Tacoma Narrows Bridge (a.k.a. Galloping Gertie), the energy provided by the wind shook the structure to pieces. (It literally shook to pieces. Search for video of the thing, you will be amazed.) Usually, engineers design to avoid disasters like Galloping Gertie. However, this wastes a lot of energy.

    The resonance they are discussing here is a classical phenomenon, so does not involve anything like quarks.

    On a wholly unrelated point, I have a problem with the "Canoe Experts." They poo-pooed the canoe as "primarily an engineering project," stating that they have years of research behind them. Yeah, well, their years of research began with engineering projects. Are those guys really scientists and engineers? They don't sound like it. They sound like marketing bozos--very safe, very pussy. What a couple of twits. I bet they haven't come up with a single original engineering or scientific idea in their lives.

    Of course, that is just the humble opinion of a physics graduate student with an B.S. in engineering.
  • You apply conservation of energy to a fluid (like a body of water) to derive Bernoulli's equation.

    In the case of the canoe, you can model the water as an energy source for the canoe. The key is that the energy has to come from somewhere, and it has to go somewhere. In the case of a non-resonant excitation, most of the energy is lost due to dissipation. In the case of resonance, most of the energy goes into the motion of the system.
  • The rule says 75% by weight. Cement has a pretty high density, and by the look of thinks the rest of the solids ought to have a very low density. So 80% by weight, bit maybe only 20% by volume.

    --
  • Sounds to me like they just crossed the streams
    -----
  • When reading this, remember that water is 1,000 kg/m^3 (1.000 for the Euros); a bit more if it's sea-water:

    http://www.silicafume.net/PDF/C4-20-NORDHORDLAND.p df [silicafume.net]

    I think the pontoons are hollow.

    --Blair

    P.S. 1,615 m is almost exactly one mile and three Smoots, give or take an ear.
  • From the Purpose, Canoe Design and Past Winners [masterbuilders.com] page at the canoe contest website [masterbuilders.com]

    "The trick is to create a concrete mix that is less dense or lighter than water. Regular concrete is 140 pounds per cubic foot, but the students create concrete that is as light as 41 pounds per cubic foot. Water is 62.4 pounds per cubic foot, so the less dense concrete will float. However, students can create heavier canoes that will float, as long as the canoes displace their own weight (and the weight of the paddlers) in water."


    The concrete doesn't ever need to be lighter than water. The boat plus passengers and gear needs to be lighter than water. Which means the maximum displacement of the boat (fully loaded volume including outside hull sectioned at a plane level with the waterline) needs to weigh less than the load plus the boat. The concrete itself can be far more dense than water.

    Having concrete that is lighter than water means you can make a raft out of concrete. It means your boat won't sink if it floods. It also means your boat has less inertia.

    It looks like a minor point, I know, but this is an engineering contest. It's all about minor points and the error bars on them. To put conflicting statements in the brochure is to sandbag the less-experienced contestants.

    The real trick is that normal building concrete is much heavier than water (and somewhat absorbent, which reduces its effective displacement in contact with water). But this contest years ago ceased to be about floating a hunk of sidewalk.

    --Blair

  • Like Homer says (Score:5)

    by thejake316 ( 308289 ) on Wednesday July 04, 2001 @09:48AM (#108484) Homepage Journal
    In this house we obey the laws of thermodynamics!
  • i think they were referring the durability with respect to space materials. i dont believe they were suggesting you use the vibrational aspects of the concrete. i suppose it is possible to match the resonance with the solar winds. From the article:
    "Imagine you have a large structure in space -- like a satellite -- made of this material," said Vaughan. "You could construct it to operate at its natural frequency and use the energy this produces for propulsion." Sounds like he means straight-forward mechanics, but I don't see how. The canoe works because there's water to push against. Maybe I should have taken more physics... Anybody know what's up with this?
  • If it really does act on the principles of resonance, then it's an incredible design, although I, too, fail to see its application as far as space probes go. Would it work off of radio resonance, or is it something else?

    Regardless, this is a major step forward for water propulsion especially in an energy crisis like today's.
  • I think the idea is that a little power, applied at the right frequency, would set up a reaction with BIG results??? I'm not sure, I go to UAH, but that doesn't mean I understand much of what these guys have to say (I hide in 'puter lab) Anyways...at UAH, every peice of engineering is being readied for space travel...that's what the university is there for...founded a couple of years after Wehner Von Braun came to Huntsville
  • Every year, American coal-burning power plants use approximately 800 million tons (source: UAB Magazine [uab.edu]; one of the older issues that isn't online or I'd give a URL) -- that's a lot of ash to dump on an annual basis. Now imagine instead of dumping that ash, you use it as a matrix in your concrete. And for the folks in marketing: imagine you can sell your waste instead of paying someone to haul it off. Example stucture of the day: the Georgia Dome in Atlanta.

    Interesting tidbit about fly ash in concrete: new federal nitrogen oxide emission standards have forced power plants to install different burners -- this gives the ash a higher carbon content that isn't ideal for building materials. One of our researchers and his students are working on methods to use the high-carbon ash -- so if you're into this kind of thing, I highly recommend checking out the numerous journal articles written by Dr. Fouad H. Fouad.

  • Design so horrible that Wired cant stand it? say it isn't so!
  • Theres another one near Rookvalds if you want to see it.
  • Actually, the concrete conoe has a long and proud (?) history. Way bak in the stone age (mid 70's) University Civil Eng. studnets were competing in concrete canoe races. Teams form schools would apply the latest technology to produce lighter, stronger, and better canoes. Of course, teh races could be fun - I've seen canoes break in two, and watched as inexperienced paddlers tried to turn a canoe around unsuccessfully. As with many things, you say something (concrete) and people immediately go to the familar (the stuff their driveways made of), which makes for interesting headlines but often misses the point.
  • Yes, there is a certain percent of cement they need. I don't remember the numbers off the top of my head but if your really interested let me know and I can ask one of my roomates. Both are on the concrete canoe team here at Drexel. Our canoe was cooler, while it didn't do funny things like move forward of it's own accord, it was painted like a lightsaber (we had a star wars theme) and our cheer was "We did it all for the" "Wookie!!!" No one likes UAH... they stayed at a different hotel than all the other teams and don't associate with any other teams. Of course I guess you don't need to when you win every year. -Chris
  • Actually, there presentation wasn't that great but since it's sponsered by asce it's kindof an academic thing so the presentation/paper etc... is worth more. -Chris
  • Thank you
  • They've been putting polystyrene granules in cement for roadbeds for years or talking about it anyway. It also weighs alot less than sand based mixes & has a certain give.Wether it can be tuned to generate a peristaltic rythm along its bottom remains to be seen.I made a screen mount for a rowboat that moved forward as the rowboat bobed up & down... just barely.As the screen plunged down, the vanes flip up driving the water back...as the screen came up the vanes flip down also pushing the water back. Trouble... it had to bob several inches befor the screens biased to drive the water.

    In space it would be wiser to utilize a rotating magetic matrix which due to Lenz' Law would configuire into a magnetic 'ion drill bit. Can't wait to try that. NASA wouldn't let me it would work a whole lot better than the crap they're working on now.

  • I think you are off topic. Strange though, as almost nobody here seems to be actually on topic, aside from the basic pondering of concrete rowboats and wondering if the propulsion mechanism has anything to do wih harnessing the energy of polarized repressed crutons and why talking about physics that one has only a very vague conception on an internet discussion forum shouldn't itself violate any major conservation laws. I personally think the that the theory that the flexible concrete resonance boat works by propelling itself forward against the magnetic field is the best hypothesis so far since it succinctly describes why this conversation tends to spin around in tiny little circles (vortices of magnetic flux) rather than moving forward. For extra credit, I will accept a full page explanation of why the Heisenberg uncertanty principle prevents one from citing an exact reference for anything.
  • Mmm well, the problem with that assumption is that we know many other flexible materials that could replace asphalt to make highways more durable.

    The question is not there, the question is friction between tires and ... something. Believe me friction between rubber and ordinary concrete is poor. We already have some concrete highways around here. They last longer all right, however you might not want to drive to your mom's place in a big snow storm ;)

    So, you might want to ask these guys about the friction coefficient of their material first and then talk about highways.

  • ...explored for building cheap submarines for third world countries...

    I don't know about you, but if I lived in a third world country I'd have better uses for my money than cheap submarines...

  • "What's next? Concrete Nikes?" - I think the mafia already uses concrete nikes...

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