Talk:Wave loading

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It has been requested that users cite the sources for this article, but I removed the template because it is going to be deleted. -Frazzydee|✍ 19:12, 16 Feb 2005 (UTC)

Contents

[edit] From PNA/Physics

  • Wave loading This article was apparently created to support another on liquefaction and seems to be rather limited and makes some dubious claims with no references. I don't know enough about the physics involved to either verify or expand it. Vsmith 04:53, 8 Jan 2005 (UTC)

[edit] Accuracy dispute

  1. Most of the "examples" superficially fit the term 'wave loading', as they are loads caused by waves, but don't really fit the given definition.
    1. In the current version of the article, the second, third, and fourth list items deal with surface waves. In my somewhat ignorant assessment, the most hazardous feature of the loadings here is not their pulsed, repetitive character but their individual strength; i.e. an oil platform should care more about the strength of each individual wave pulse than about their number.
    2. The first list item deals with waves of surf, which, though they are cyclical processes, are not waves in the physics definition. Additionally, everything I said in point 1.1 holds true for this item as well.
  2. Some of the examples don't hold up to simple physics scrutiny. Admittedly, I haven't studied any of these topics specifically, so my assessments may miss some important points.
    1. Patently false. What we see here is a case of (1) turbulence caused by your foot and (2) erosion of the sand into the turbulent flow.
    2. Also patently false. This is another case of turbulence and erosion. A column of water 10 m high exerts a pressure of roughly 1 atm, so the change in hydrostatic pressure due to passing waves is on the order of a tenth of an atmosphere for ordinary beach waves, and maybe two atmospheres for truly colossal waves. Any motion of water caused by expansion due to these pressure changes should be negligible compared to turbulence and erosion.
    3. Possibly valid. This case is too complex for me to comment on.
    4. It hardly makes any claims - how can it be false?
    5. Yes, things will break if you run avalanches over them.
    6. IMHO no accuracy whatsoever. I won't even get into everything that's wrong with this picture.

--Smack (talk) 07:12, 28 Mar 2005 (UTC)

Very good analysis. I might suggest re: 1.1 that the repetitve action might have importance if the frequency is such that a resonance enhancement is set up in regards to some structure.
Please have a go at correcting the article - I had put in a couple modifications and listed it as needing attention, but didn't feel qualified to do a complete re-write that it needs. The creationists have a vested interest in this topic and will probably resist changes. See also the liquefaction article that this was originally (I think) written to support and that makes some of the same errors that you have pointed out above. Vsmith 13:53, 28 Mar 2005 (UTC)
bizarre conspiracy theories aside, i'm open to corrections. but since neither of you have any background in the issues in question, i can only wonder why you feel qualified to challenge their accuracy. perhaps your critiques would be more meaningful if they were backed with cited sources who provide different explanations for the phenomena in question? Particularly in the case of number 2, perhaps you should read the cited article before questioning its accuracy? Ungtss 13:56, 28 Mar 2005 (UTC)
Yes, but, I don't keep my back issues of Discover - would promote a paper wave loading problem in my library :-). Would be nice to have a ref to the orig. published work. And, that is the only ref in the article, the absence of references opens the issue completely to challenge - even by unqualified questioners like us. Now, I'm a geologist and Smack is studying engineering, seems to be some relation there somewhere to "background in the issues in question". Of course we don't have degrees in "flood geology" or other such religious fantasies, is that what your cute remark was about? I think we are fully qualified to challenge the accuracy of the errors here just as you were qualified to make them. -Vsmith 15:32, 28 Mar 2005 (UTC)
my "cute remark" was in reference to his comment that "Admittedly, I haven't studied any of these topics specifically, so my assessments may miss some important points" and your comment that you "didn't feel qualified to do a complete re-write that it needs." I don't have a problem with improvement. improve away. this article has absolutely nothing to do with flood geology -- i just thought it was pretty cool -- so please, put your religious conspiracies to rest and tell me everything you know about wave-loading. ultimately, i find it rather odd to criticize the article without providing substantive critiques, or claiming sufficient knowledge of the topic to make an educated rewrite. but no more odd than insisting on no reference to consensus science in the intro to scientific consensus ... Ungtss 15:44, 28 Mar 2005 (UTC)
How do those cites make you feel? Ungtss 15:49, 28 Mar 2005 (UTC)
On second examination of 2.2, I realize that I may have simply misunderstood the description of the phenomenon. When you say that "water rises from the sand", do you mean (a) that water sitting beneath wave crests moves laterally into the region beneath the wave trough, pushing water already there upward, or (b) that the aqueous component of the seafloor mud rises? I interpreted your statement as b, and gave my opinion of it. I have no dispute with a, but I stand by my claim that b is of highly dubious merit.
Also, I must apologize for calling your statements "patently false" after making a disclaimer as to my imperfect understanding of the underlying physics. However, I would say that you, for your part, might wish to lay off the ad hominem jibes and provide a scientific defense of your claim. As User:Vsmith points out, we can't be expected to have back issues of magazines from thirteen years ago sitting in our closets. Though parts of the November 1992 issue of Discover are easily accessible, I could find nothing authored by either Inman or Conly. The website seems only to contain major articles, and I suspect that page 14 was devoted to little notices (whatever they may be called).
That said, I'd be glad to talk science with you. If you want to debate any of my assessments, or call me out on my treatment of 2.6 (or lack thereof), place a subheading and let's begin. --Smack (talk) 04:38, 29 Mar 2005 (UTC)
I have no dispute with a, but I stand by my claim that b is of highly dubious merit.
let's go with A then:). Ungtss 04:47, 29 Mar 2005 (UTC)
However, I would say that you, for your part, might wish to lay off the ad hominem jibes and provide a scientific defense of your claim.
I'd love to. and now that mr. smith has moved beyond his misapprehension that everything i do or say is intended to promote creationism, we can really start getting places:). Ungtss 04:47, 29 Mar 2005 (UTC)
I could find nothing authored by either Inman or Conly. The website seems only to contain major articles, and I suspect that page 14 was devoted to little notices (whatever they may be called).
yeah -- you got it -- it's a section on real short notes on recent experiments. the online version doesn't have it, but any university library will:). Ungtss 04:47, 29 Mar 2005 (UTC)
If you want to debate any of my assessments, or call me out on my treatment of 2.6 (or lack thereof), place a subheading and let's begin.
reply moved to new section below

Very good, thanks. The refs are a real improvement. As to all that other stuff - it's an odd world :-) Vsmith 17:30, 28 Mar 2005 (UTC)

Thanks:). Cheers:). Ungtss 17:47, 28 Mar 2005 (UTC)

[edit] Sand washing away from underfoot

Moved from above:

well ... you said that it is "turbulence and erosion" that causes our feet to sink in the sand on the beach. how can this be, since the sand recedes from BENEATH my feet, and in fact recedes MOST where most of my weight is ... the place where there would be the least appreciable turbulance and/or erosion? Why is there not the most erosion around the sides of my feet, as Bernoulli's principle would predict? Ungtss 04:47, 29 Mar 2005 (UTC)

I haven't stood in the surf in a while, but as I recall, the sand begins to wash away around the edges of the foot, digging deeper and deeper until one is standing on just a narrow patch of sand running from the center of the heel to the base of the toes. The foot does not significantly sink into the sand, as it would if sand were being removed from beneath its entire surface. The small degree of sinking that I recall can probably be explained by structural settling of the narrow patch of sand.
Here's my explanation. In the absence of an obstacle, the flow of a receding wave is more or less laminar. It carries with it some sand, but not much. If you put your foot in the way, it becomes turbulent around the edges of the obstacle. The turbulence somehow (I'm not sure how; again, I'm no expert in fluid dynamics) causes sand to be carried away from the point where water meets sand and foot.
What does Bernoulli's principle have to do with anything? --Smack (talk) 00:42, 30 Mar 2005 (UTC)
Perhaps we've been standing on different beaches:). What you're describing has happened to me on beaches with hard sand ... but in soft sand (such as in Cote d'Ivoire, my feet consistently sink. bernoulli's principle is relevent, because the increased speed (and turbulence) of the water traveling around the sides of the foot would cause more erosion than the water going under your feet ... Ungtss 14:09, 30 Mar 2005 (UTC)
What's the distinction between "hard" and "soft" sand? Also, you're not being very clear with this Bernoulli's principle thing. Sure, there's a decrease in pressure. But why is that important? What are the consequences of low pressure? --Smack (talk) 04:13, 31 Mar 2005 (UTC)
soft beaches have a more pliable sand -- more like a dune and less like cement. on the beaches at san diego, oregon, and georgia, i don't sink, while in places like cote d'ivoire, ghana, and saudi arabia, i do. i'm gonna try and dig up some primary sources on this to help both of us out:). as to the bernoulli principle, the water is flowing FASTER and HARDER around the sides of my feet, at a lower pressure, and with greater turblence -- all those factors combined should lead to more erosion around the sides of my feet rather than underneath. Ungtss 14:21, 2 Apr 2005 (UTC)
You're still not being clear. Yes, there's a loss of pressure in the flowing water at the edges of your feet. How exactly does it lead to erosion? --Smack (talk) 04:51, 4 Apr 2005 (UTC)
Hmm. lemme try again. i'm trying to compare this to the wing of an airplane. because the top surface is curved, the air is forced to go faster over that surface to "catch up" with the air going a more direct route under the bottom surface. same with the feet. the water is forced to go faster around the sides of my feet to "catch up" with the water going directly back to the sea, and is undergoing more turbulence. so we would EXPECT more erosion in that area; and we would CERTAINLY expect more erosion there than under my feet, where my feet prevent waterflow entirely. but i find that my feet sink in deeper than the sand around them. that's counterintuitive. you've got more sinking where there's less water flow. why? Ungtss 17:17, 4 Apr 2005 (UTC)
← This has crept far enough to the right. Carriage return.

I don't see why the water colliding with the sides of the feet has to remain abreast of the laminar water. Water in different parts of a flow does not have to travel at the same rate. Consider a straight river with a symmetric cross-section. Water in the river is slowed by viscous interaction with the river bottom. If the middle of the riverbed is the deepest part, this means that the water in the middle of the river and at the surface is the most separated from these viscous effects and travels fastest.

Now consider an island directly in the middle of the river. Assume that it's sufficiently pointy at both ends that laminar flow is perserved. The fast water in the middle of the river now runs into this obstacle and begins to experience viscous effects. Thus, it slows down. However, the moderately fast water halfway between the banks and the centerline is little affected, and continues on its merry way. When the river reaches the end of the island, the halfway water has passed up the middle water.

So much for that claim. You've spoken about my proposed explanation of sinking feet. I hesitate to say whether you've criticized it or not - at times you've just repeated it back to me, and at times ignored it entirely. I'm still waiting for you to offer your own. Do you believe that the low pressure coupled with the pressure of the foot somehow combine to push sand out from underneath the foot? --Smack (talk) 06:13, 6 Apr 2005 (UTC)

Give me a few days. I'm going to try to contact the authors of some of the articles to clarify. Ungtss 13:56, 6 Apr 2005 (UTC)

[edit] Undersea pipes

I just took a look at the article again, and found that the example of undersea pipes bursting is now cited to an article entitled "Large Diameter Underwater Pipeline for Nuclear Power Plant Designed Against Soil Liquefaction." If a discussion results, I'll try to find this journal (which, given the oddities of my university's library system, should be easier to locate than Discover, assuming that we have it). However, even without the journal itself in hand, I'd like to note that the wiki article claims that pipes may "break" or experience "resonance vibrations", and says nothing about liquefaction. --Smack (talk) 06:13, 6 Apr 2005 (UTC)