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Post by jeff on Nov 24, 2016 4:09:11 GMT
For years scientists have been looking for ways to make invisibility cloaks a reality, by shielding objects from light and other electromagnetic waves. But what if we could make floating objects, such as an oil platform or storage tanker, invisible to physical, water waves? Professor Mohammad-Reza Alam may have found the answer. Alam, a fluid mechanician, and his team of researchers at the University of California, Berkeley, have come up with a technique to make these structures immune to the up-and-down motion of rough seas. www.offshore-technology.com/features/featurecloak-invisibility-shielding-oil-rigs-rocky-waves/
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Post by Deleted on Nov 24, 2016 5:10:40 GMT
Quoting the article: "(note that the idea is efficient in relatively shallow water, not the deep ocean)"
I think he is basically engaging the various frequencies of the pressure waves that make surface waves, and attempting to cancel them with some gentle phase shifting. But the article is really vague.
And putting things (except for an anchor) on the bottom is usually a serious no-no in the usa.
The actual url, minus this site's tracking bits: http:www.offshore-technology.com/features/featurecloak-invisibility-shielding-oil-rigs-rocky-waves/
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Post by jeff on Nov 24, 2016 6:26:00 GMT
web.mit.edu/alam/www/Files/Alam%20-%202012%20-%20Broadband%20Cloaking%20in%20Stratified%20Seas(2).pdfBroadband Cloaking in Stratified Seas Mohammad-Reza Alam1 1 Department of Mechanical Engineering, University of California, Berkeley, California 94720, USA (Received 13 September 2011; published 23 February 2012) Here we show that floating objects in stratified fluids can be cloaked against broadband incident waves by properly architecting the bottom corrugations. The presented invisibility cloaking of gravity waves is achieved utilizing a nonlinear resonance concept that occurs between surface and internal waves mediated by the bottom topography. Our cloak bends wave rays from the surface into the body of the fluid. Wave rays then pass underneath the floating object and may be recovered back to the free surface at the downstream bearing no trace of diffraction or scattering. The cloak is the proper architecture of bottom corrugations only, and hence is surface noninvasive. The presented scheme is a nonlinear alternative to the transformation-based cloaking, but in the context of dispersive waves.
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Post by jeff on Nov 24, 2016 7:22:14 GMT
Possible correlation... www.nature.com/articles/srep02106Role of Huge Geometric Circular Structures in the Reproduction of a Marine Pufferfish Methods The study pufferfish is thought to be a new species of the genus Torquigener (Tetraodontidae, Tetraodontiformes) because distribution of small spinules and the body colour pattern do not match that of any other fish of the genus Torquigener (K. Matsuura, personal communication). Thus far, the fish has only been found in the coastal waters off southern Amami-Oshima Island, the subtropical region of Japan. Despite our extensive underwater SCUBA search at less than 30 m water depth off the Island, the fish has been found, in small numbers, in very restricted areas off Seisui (28°07′N, 129°19′E) and Katetsu (28°08′N, 129°20′E). Regular observations (1–3 times/week) were made from April to September in 2011 and 2012 to check for the presence/absence of the circular structures and the pufferfishes at Seisui and Katetsu. An observation area of approximately 50 m × 30 m was set up on the sandy bottom of Seisui (23–28 m water depth) and Katetsu (18–23 m water depth) for intensive surveys conducted from 11 June to 13 July 2012. Underwater observations (1–3 times/day, approximately 30–40 min/dive, at various times between 5:00–21:00) were performed every day, except during stormy weather, at one or both sites. Most observations were made in front of the circular structures, and male and female behaviour was recorded on portable digital still cameras and video cameras for analysis of behavioural patterns. Monitoring video cameras were also set up in front of the structures to record behaviour over a longer period of time at the same angle. The video footage recorded at Katetsu (18 m water depth) from 7 to 13 July 2012 was used to clarify the construction process, and 10–50 min of video were analysed each day. The water temperature was 24°C–27°C, and the current reached approximately 0.8 m/s in the observation area during the period of intensive survey. The hydrodynamic experiment was performed at Chiba Experiment Station, Institute of Industrial Science, the University of Tokyo, on 20 July 2012. A 1/2-scale model of the circular structure (diameter, 1 m) with strings for determining the direction of water flow was set in a circulating water channel with a wind blower and wave maker (length, 25 m; width, 1.8 m; depth, 2 m; maximum speed of water current, 1 m/s), and the direction of water flow in the circular structure was observed. Current speed inside and outside the circular structure was measured with an electromagnetic current meter. www.nature.com/articles/srep02106/figures/7(a) Model of the circular structure with red strings for determining the direction of water flow. (b) Schematic diagram of the circular structure and directions of water flow. See text for the meaning of arrows.
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Post by bobdohse on Nov 30, 2016 0:51:17 GMT
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Post by jeff on Nov 30, 2016 6:04:11 GMT
Mechanical linkage wear, for all the forces, is going to be an issue, as well as orientation. First, water, especially seawater, is highly corrosive, second impacts are not going to be evenly distributed, nor always from the same direction. The seesaw action doesn't altogether eliminate lateral forces.
His cylindrical concept will also require a substantial mooring, to work independently of the vessel surrounded.
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Post by bobdohse on Dec 1, 2016 11:24:11 GMT
I agree, Jeff.
I suspect that the most practical way for a seastead to deal with surface waves would be to create a hortizontal layer of <i>something</i> surrounding the seastead ...
... that would dissipate wave energy by lifting submerged objects at the very exterior of the barrier and then simply scattering the remaining surface waves randomly within the interior portion of the protective ring.
If you can imagine how rings connect on <i>chain mail</i> armor ...
... that type of 'connected circles' construction provides flexibility without creating stress points found with hard connections.
In theory, certain types of mangroves and kelp could be grown on that type of scaffolding.
Does my description of that type of structure help create a mental picture of the design, or was that "as clear as mud"?
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Post by jeff on Dec 1, 2016 22:37:05 GMT
The problem with floating extra structures is extra costs, and both mooring/maintaining them, and maintaining a working distance within the space they protect.
Whether using natural, or man-made bottom structures, merely mooring inside the protected waters would be sufficient.
Making structures for bottom placement can be as simple as shaped wire-mesh and solar panels, to make hollow seacrete structures, then place and fill with material from the seafloor, to give them the mass to remain in place as gravity structures.
At the same time, such areas using bottom-structure protection can be freely entered and exited, rather than needing some opening in the case of a surface floating circle.
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Post by Deleted on Dec 2, 2016 4:19:59 GMT
If you can imagine how rings connect on <i>chain mail</i> armor ... ... that type of 'connected circles' construction provides flexibility without creating stress points found with hard connections. In theory, certain types of mangroves and kelp could be grown on that type of scaffolding. I have made a lot of chainmaille. While it looks like a sloppy loose construction, it is only until the slack is removed during tension, at which point, in my experience, something breaks. I don't think kelp will have enough strength, stiffness, or mass to be useful. And tree roots will go only so deep into the water column. If the kelp or the tree roots is going to dissipate the energy of the wave simply by being there, then you are asking the plants to convert the wave energy to heat within their bodies. Whether you deal with the water's energy as a moving height on the surface, or a pressure wave below the surface, your material hasto absorb or relocate or redirect the energy (or the water itself). If you can extract useable energy of some form, so much the better. A cliff face absorbs and reflects the energy by brute force. A sloping beach drags the bottom of the pressure wave slowing it, while making it possible for the water to physically grow higher, and it trips and breaks on forwards into a trough. I think our solution will be found in accelerating that process in a short inexpensive distance, or maybe reversing the process (tripping the wave backwards from the top?). If you can keep enough floating stiff plant to interact with the moving water enough to slow the top of the water 180 degrees out of phase from moving the way the pressure waves wants it to, you'll have a wave shelter, but it won't be on the bottom and it will be huge.
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Post by jeff on Dec 2, 2016 15:47:13 GMT
One thing different is that a kelp farm can be a top-down system, instead of bottom-up. The influence on waves would be opposite the natural. Instead of laying down, like natural kelp does, it starts with a floating suspension, a line, and a weight to hold the lines relatively vertical. The bottom can be free to move, so the deflection would be the lower end. The mooring would have to be sufficient to maintain position, with respect to expected forces against the entire project, but, like any floating design, could use quick-disconnects and potentially be towed out of harms way, for hurricanes, the return and reattach. www.ecowatch.com/underwater-vertical-seaweed-farm-restores-our-oceans-while-providing-f-1882118488.html
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Post by jeff on Dec 2, 2016 15:50:27 GMT
Biorock/Seacrete uses the electrolysis of seawater to cause accretion of Calcium Carbonate onto electrodes. Water current and duration of the supplied electricity affect the rate of deposition, as well as the total amount. It is possible to create structures as strong as bone, that are also active environments for natural sea life, such as corals. Essentially, make an artificial reef, of almost any shape. One project is attempting to make a boat hull, another proposes to make a floating concert hall. My suggestion is to use the same process to make hollow Tetrapods, or Crablocks of appropriate size, to create the seafloor wave-break, position them, and fill with sand/mud from the local sea-floor. www.naturalbuildingblog.com/seacreteseamentbiorock/en.wikipedia.org/wiki/Biorocksst2015-s207iss-a.blogspot.sg/p/annex-group-engineering-proposal.htmllh4.googleusercontent.com/s2FrXVEhUzwkQY_Imyx4lN16M01NJHgK7UGZP9d80clZYK44xvT_jiCxugskmWv0uZWSjX8GUfTkWA1g_JzdX_2kA59EmpJ2XBFhpGCakLXn5MktvdPhdvz-jDKochuT78O4SmE
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Post by bobdohse on Dec 2, 2016 19:11:21 GMT
A surface wave can only propagate through a liquid medium, which is why we end up with swells in the ocean ... because the surface wave cannot propagate through the air, so the effect of the wave is to raise water up into a swell (and, conversely, create the trough).
The distance from swell to trough is double the amplitude.
And, given the wave form, the wave periodically goes down and comes back up ... which, as one cycle, is the wavelength.
So far, I think we are in agreement (assuming I remembered the science correctly).
My point on the "kelp bed or mangrove forest" idea is that the surface wave can intercept a horizontal surface just as easily as a vertical surface.
With all of the "verticle" designs, the surface wave is refracted in some way.
With a "horizontal" design (e.g., a mangrove forest), the wave form (visible as a swell) pushes water up ... and dissipates energy by lifting up what is simultaneously being pulled down by gravity.
We know this to be true by tossing a rock into a pond ... the ripples dissipate as the wave propagates outward, because energy in the wave is fighting gravity as it moves away from the center.
Therefore ...
... a horizontal SWORD with sufficient horizontal depth could "bleed off" the surface wave energy in the same way that the gravitational pull on water does when the rock is tossed into the pond.
The design would require a partially submerged scaffold, but it's a practical alternative.
I'm not trying to say it SHOULD be done ... but it COULD be done.
And, given the typical seastead designs that are rather devoid of "nature" ... I would think that a vegetative habitat around a seastead would be a welcomed "park" environment. Great for fishing, too. 😀
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