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Dolosse – a South African invention used over the world

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Re: Dolosse – a South African invention used over the world

#11

Post by s03nk3 »

gilleain wrote: post #6
walski wrote: post #5

Earlier quoted context omitted.

Ok I stand corrected these are NOT tetrapods. Sorry for the confusion

Well, confusingly, the last picture on the blogpost look (to my untrained eye) to be tetrapods. Those are 'tetrahedral' (ish) shapes. In contrast, the https://en.wikipedia.org/wiki/Dolos (plural 'Dolosse') are two tapering cylinders at right angles to each other. They have the same symmetry, but a different structure. Does that make any difference to how effective they are? No idea! edit: When I said the "same symmet…

Maybe the form variations were just for patent circumvention.

Re: Dolosse – a South African invention used over the world

#12

Post by petesergeant »

mk_stjames wrote: post #7

Interestingly the author shows a photo of a spot in Cape Town where there are two distinct structures in use - close up, in the photo, are actually Tetrapods - as pointed out in other comments, these are an earlier invention from France and also used quite extensively throughout many parts of the world (including... right here where the Dolosse were invented). Further down that jetty are structures with the actual Do…

The Wikipedia article:

> A dolos ... is a type of tetrapod

but also, the Wikipedia article for tetrapod:

> One of the earliest designs is the Tetrapod, invented in 1950. Other proprietary designs include the Modified Cube (United States, 1959), the Stabit (United Kingdom, 1961), the Akmon[W] (The Netherlands, 1962), the Dolos (South Africa, 1963), the Stabilopod [ro] (Romania, 1969),[7] the Seabee (Australia, 1978), the Accropode[W] (France, 1981), the Hollow Cube (Germany, 1991), the A-jack[W] (United States, 1998), the Xbloc[W] (The Netherlands, 2001) and KOLOS[W] (India, 2010) among others.

I have put Ws next to ones with their own Wikipedia page.

Re: Dolosse – a South African invention used over the world

#13

Post by arcza »

liotier wrote: post #8

Save yourself the blogspam, go directly to https://en.wikipedia.org/wiki/Wave-dissipating_concrete_bloc... and enjoy the whole collection !

Bizarre hate towards someone's little blog. And it's not even LLM spam, just someone running their own WP site. By your logic I should save myself the Wikipedia verbosity and just ingest LLM output for any query I have forever.

Re: Dolosse – a South African invention used over the world

#14

Post by close04 »

Someone wrote: post #10
mk_stjames wrote: post #7

Interestingly the author shows a photo of a spot in Cape Town where there are two distinct structures in use - close up, in the photo, are actually Tetrapods - as pointed out in other comments, these are an earlier invention from France and also used quite extensively throughout many parts of the world (including... right here where the Dolosse were invented). Further down that jetty are structures with the actual Do…

Mathematically, I think they both may be tetrahedons. The Tetrapod models it by 4 lines connecting each of its vertices to its center, the Dolosse by two opposite edges connected by a line through the middle. I’m saying “may be” because it is possible that the center “arm” of the Dolosse is too large to make a true tetrahedon. That’s a degree of freedom in the design. > It would be interesting to know if, specificall…

That connecting "spine" is there to improve the interlocking of the tetrapods. They can "hook" better to each other. That's the theory at least, I don't know the if it's better in practice.

Re: Dolosse – a South African invention used over the world

#15

Post by nusq »

Finnally something I have knowledge of. Dolosse were invent in South Africa many years ago, but they are only one type of concrete block for wave dissipation and protection. Many others exist and some of them are patented and require the payment of royalties to be used. Anyway, in Portugal we do not use dolosse ever. We used it once in Sines deepwater breakwater, which suffered a catastrophic collapse in 1979. The promise of dolosse is that the blocks work together because of their shape and thus the individual block can be lighter and cheaper. This does not work in practice, at least in high energy seas. The ocean is unforgiven. What happens is that if only a few blocks break the whole structure will quickly collapse during a storm. And things can break due to a series of problems and risks. Concrete is only good at resist compression stresses and reinforcement with rebar is almost always a bad idea in ocean conditions, so complex shapes are hard to make and to move without introducing unwanted stresses that reduce the design strength conditions. Other types of blocks rely mostly on their design weight and density, and the shape is just used for increasing energy dissipation and overtopping. For example, tetrapods can be moved with only compression forces on the block.

Re: Dolosse – a South African invention used over the world

#16

Post by cookiengineer »

Not sure why Dolosse are so special?

There's lots of different forms and shapes of wave breakers, like the Tetrapods [1] that you can find over here across pretty much every coast in Europe.

Maybe I'm just not getting it why the Dolosse shape is superior?

[1] https://en.wikipedia.org/wiki/Tetrapod_(structure)

Re: Dolosse – a South African invention used over the world

#17

Post by markdown »

nusq wrote: post #15

Finnally something I have knowledge of. Dolosse were invent in South Africa many years ago, but they are only one type of concrete block for wave dissipation and protection. Many others exist and some of them are patented and require the payment of royalties to be used. Anyway, in Portugal we do not use dolosse ever. We used it once in Sines deepwater breakwater, which suffered a catastrophic collapse in 1979. The pr…

> reinforcement with rebar is almost always a bad idea in ocean conditions

While a little more costly, 316 stainless steel should work just fine.

Re: Dolosse – a South African invention used over the world

#19

Post by Havoc »

walski wrote: post #4

In Germany (on the island Sylt) they recently removed all of these structures again after decades of them being a staple on Sylt's beaches. They were found to have no positive effect on protecting their shores. I'm having a hard time to find a good source to quote but look for: "sylt tetrapoden" if you want to dive deeper.

I find it hard to believe they have not protective effect. You can throw pretty much anything hard with an irregular shape down and it’ll help scatter energy

Re: Dolosse – a South African invention used over the world

#20

Post by tclancy »

duggan wrote: post #3

Interesting. Been to South Africa a bunch but never clocked that they were different from the more common antecedent, the tetrapod[1]. 1: https://en.wikipedia.org/wiki/Tetrapod_(structure)

“Hast thou considered the tetrapod?” can finally be answered positively on HackerNews. Hail Satan.
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