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Re: nope

Posted by David Aiken (A) on October 7, 2005 at 20:50:32

In Reply to: nope posted by CD on October 7, 2005 at 14:59:27:

Re: "(a) "very little of a horizontal force will"

if you are using a roller or something horizontally compliant, sure, but a sharp spike sticking into a shelf will normally *not* allow horizontal movement of shelf relative to spike."

First it's worth while noting that the tips of many cones are not "sharp spikes", they are much more rounded, and they don't "stick into the shelf". The relatively flat original Tiptoes had a hemispherical section tip, as do the Black Diamond Racing cones I have used and many other cone designs. Such 'blunt pointed" designs do allow for some degree of motion between the cone tip and the shelf.

And second, as I said, energy is transferred to the cone as a vector force and the vertical vector component of a horizontal force is significantly less than the horizontal vector component.

Re: "(b) "The wave wraps around the pier support which absorbs very little energy..."

A patently inapt analogy to a spike supporting a shelf or resting on one. With wave-pier it's obvious where the extra energy is going -- into to shore. Spike-shelf, on the other hand, is no different from any rigid structure which incorporates slender pillars."

Well, I would have thought that it was obvious where the extra energy was going if my analogy was correct - it's remaining in the shelf and being conducted from the shelf via the shelf supports, whatever they are. Small contact areas aren't going to work equally well for energy transfer at all frequencies and, as I said, it's a vector transfer so not all of it can be transferred anyway.

And I think there is are significant differences between a cone point resting on a shelf and slender pillars supported by a rigid structure. A shelf is often not a particularly rigid structure in a lot of ways - much less rigid than a solid floor, for instance. More importantly, support pillars don't simply rest on their supporting structure - they're actually physically connected to that structure in a much more substantial manner and to a much greater depth than any penetration by a cone, especially a cone with a rounded rather than a pointed tip, plus there's a much greater contact area as a result. The mechanics of energy tranfer to a pillar are going to be different to those of a cone resting on a shelf. I'm not so sure that the analogy is all that inept.

Also, don't forget that *ALL* of the vibrational energy present in the shelf is not flowing into the cone. I never suggested that there was any energy disappearing into thin air - vibrational energy is dissipated by conversion to heat or other forms of energy or it flows via physical conduction into other objects where it is dissipated by conversion into other forms of energy. Cones supporting a component are only one pathway that the vibration has for conduction elsewhere from the shelf - there are also the shelf supports to be considered - and some energy is most definitely converted into heat and movement within the shelf. Energy seeks the most efficient method of dissipation and transmission through cones may well not be the most efficient pathway in a given situation. What isn't transmitted through the cones is simply dissipated more effectively elsewhere.

All I have said in my previous posts is that there are reasons why a cone is not a perfect conductor and why it may have some frequency dependent behaviour. I don't think you'd want to argue that they are perfect conductors which operate equally well at all frequencies. I most definitely wasn't suggesting that cones were isolators. In fact, in my first post I said "There are no perfect isolators or couplers, but to regard one kind of device as the other simply because it doesn't work perfectly and, at frequencies outside of its operational bandwidth, it passes some vibration we would prefer it didn't, or blocks some that we would prefer it did, is missing the point."

Further,in my second post I said "Put the 2" -ie the vector force and the impact of contact area on transmission - "together and you have a combination of vector and wavelength factors affecting how much vibration will enter the cone to be transferred to the other side." I think that remains a fair and accurate statement and I see nothing in your comments that could be used to suggest otherwise unless you want to suggest that all vibrational energy in a shelf will be dissipated via conduction through cones if cones are present, and I would argue most strongly against that.

"It's not like this is a matter of seculation either -- this is well-understood at the theoretical and practical level, and vibration it measurable."

"Seculation" - do you mean "speculation"? And yes, vibration is measurable but I've yet to see a reliable study on what effect cones have on vibration transfer in a real life situation and in the absence of some actual measured results, about all we can do is speculate to some degree. If you know of such an account, I'd be most happy to see a reference. I am prepared to bet however, even without reading it if you know of such a study, that cones don't transfer equally well at all frequencies, that they don't transfer all of the energy from whatever the tip is in contact with to whatever the flat side is in contact with and vice versa, and that how effectively they do transfer vibrational energy depends on the axis of vibration relative to the cone's vertical alignment. That's what I've claimed is happening and you've said nothing to indicate that any of those claims is wrong.

David Aiken

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