Concrete submarine

[dccd]

Would enjoy collaboration with you on some of these new submersiable and semi-sub designs and promotion. I have often thought back to my early semi-sub idea since about 90% of the population gets sea-sick. These designs open up a huge new market. AND if it could be made of that new super concrete.... see: http://www.wired.com/dangerroom/2009...ds/#more-18358

Also: "Seasoned boaters at Sailing Issues report that 90 percent of the population undergoes symptoms at some time and can't always prepare for the causes of seasickness.

Livestrong.com"

Originally Posted by dccd

Would enjoy collaboration with you on some of these new submersiable and semi-sub designs and promotion. I have often thought back to my early semi-sub idea since about 90% of the population gets sea-sick. These designs open up a huge new market. AND if it could be made of that new super concrete.... see:

Also: "Seasoned boaters at Sailing Issues report that 90 percent of the population undergoes symptoms at some time and can't always prepare for the causes of seasickness.

You´re right, there are advanced concrete mixtures and casting procedures on the market. And we would be very pleased if Mr Ellmer would let us know which of them are used in his boats. But by so far we did not get one proper reply. Let alone all the related technical stuff like air conditioning (in its straight sense).


The figure of seasickness is by far too high. At seastates were recreational boating commonly happens, the figure is below 10%. At stormy weather that raises to about 15 to 20%, and goes up to about 30 to 50% at force 12 and above. Of course those figures are very rough, due to the fact that there always are just very few people aboard a yacht, one can watch.
And sure, skilled crew is below that percentage, guests are sometimes above.

Regards
Richard

[Knut Sand]

Seem to me that the max you'd expect is in the area 60 MPa of concrete for compression loads... Some are in the area of 96-105 MPa, but that's very specialized processes behind that production.

http://www.tfhrc.gov/safety/pubs/05063/chapt2.htm

So to me 20 - 30 MPa seem to be a sensible, as a rugged surface will be where fault lines (or vindows) can start.... and if.... they'll go in the hull's length and in 45° The inverse version of a burst hotdog.

On that fault line again. The reinforcement steel will not be worth too much in a case like that, as the concrete may just crush its way past these reinforcements....

About using FEM analysis for concrete (or how to make the record for the biggest man-made earthquake in the known history):

http://www.civ.utoronto.ca/vector/jo...tions/jp33.pdf

http://www.ima.umn.edu/~arnold/disasters/sleipner.html

Took me a while to "get" why the assumed stress was wrong by some 40%, think I've got it now... I talked with some of the guys on the surface rig afterwards (The company I worked for had delivered valves and actuators and hydraulic / pneumatic control systems for the ballast system.... Got a new "fastorder" just afterwards....).

They said, they were running all pumps but it still moved down (control centre was inside one of the legs...). They got on the radio; "Get the f** out!! NOW!!!" They ran the stairs.... up, out, stopped looked; "**** it's going.... down??!" started cutting lines, some were using axes. when the substructure went down, it all went strangely quiet, then all the remaining ropes/ wires tensioned, broke.... not a good situation on the deck there, and then quiet again...

Then, the structure hit the bottom, broke, made us Norwegians the world record holders of a manmade earthquake 3.0. The air trapped inside started on its way to the surface, as a giant bubble... When at the surface it was a mix of water/ air with close to zero bouyancy, the barracks were almost going down , "was like looking into hell"

As I recall not a single person was injured. God was working overtime that day...

Now, make a sub the wrong way.... some may probably get injured/ dead.

That's why I ask for what kind of concrete, what documented compression strength is available? What procedures to control the building process? (A GRP boat can be documented in these ways; Bach no of Woven glass, polyester resin batch, temperature, humidity, clock/ date start/ stop for first layer, all this for all the next layers, if there were grinded after a layer (over the weekend?) Resulting thickness....).

A "similar" documentation is normally used for concrete (cement batch no, sand quality (size) water, weight, volume, test slabs, test reports, average strength).

[bntii]

Knut,

Could you comment on the following statement in regards to you analysis?:

"It was found that both longitudinal and circumferential prestress must be used in the construction of the pressure hull."

[Knut Sand]

Bntii; I didn't type that??

But as I understand it; in order to make sure the hull is always subjected to compression forces, the steel reinforcement should be prestressed during hardening of the concrete (like in bridges), that way you'll make sure the concrete is subjected to compression stress, not tension stress, also when landing the hull at a dock, or seabed, especially if accidentely grounding the lower front part of the hull in 3 knot speed forwaer, hitting the bottom... If prestressed properly, the hull should even under an impact situation remain stressed by internal compression forces, NOT BY tension stress (as an unreinforced hull would be). Tension stress in the inside of the hull in a situation like this, would without doubt (inside my head at least) result in an implosion, as only the outer area of that hull in that situation would have compression, the other half of the hull cross section in that area would experience tensile stress...

So, the hull thickness must be able to hold the prestress from the reinforcment, PLUS the external depth pressure, PLUS safety margins...

The main reason to avoid tension stress contrary to the compression stress (at almost any cost), is that the ratio between tension / compression strength in concrete is in the area of 1:10. Concrete and tension stress is a bloody bad combination if you don't design for it...

Just me and my silly 5 pence opinions here....

But then again, I'm not a concrete guy.... I'm waiting for Wellmer to supply further info.

[wardd]

wouldn't steel be a cheaper hull?

and easier to control stress loading?

it could be rings and cast end caps

[bntii]

Knut,

Wellmer provides the following research for proof of concept:

"FEASIBILITY STUDY FOR CONCRETE SUBMARINE

Accession No 00127041
Authors SMITH, D A
Corp. Authors
/ Publisher Society of Naval Architects and Marine Engineers information
Publication Date 19750300
Description 39 p.; References(19)

A feasibility study was conducted by utilizing classical analysis techniques and state of the art construction methods. Concrete was found to be a viable material for shallow to medium depth submersibles. It was also found that concrete offers both performance and economic advantages over steel. The performance advantages include: freedom from maintenance, durability, readily-available materials, superior performance under impact and accident conditions, non temperature-sensitive, easily formed into compound curvature, and concrete has good insulating properties. Economic analysis has indicated that the concrete pressure hull would cost between 50% and 60% of the equivalent steel hull.
http://imulead.com/tolimared/concretesubmarine/


Oddly- he has modified the text when citing this research on his site. He removed three statements and the condition that the concrete must be prestressed.
Here is the original text of the quoted abstract:

FEASIBILITY STUDY FOR CONCRETE SUBMARINE
Accession No 00127041
Authors SMITH, D A
Corp. Authors
/ Publisher Society of Naval Architects and Marine Engineers information
Publication Date 19750300
Description 39 p.; References(19)
A feasibility study was conducted by utilizing classical analysis techniques and state of the art construction methods. Prestressed concrete was found to be a viable material for shallow to medium depth submersibles. A replica of an existing steel-hulled submarine was used in the calculations to enable both economic and performance characteristics to be analyzed and compared. It was found that both longitudinal and circumferential prestress must be used in the construction of the pressure hull. To facilitate this, a modular-segmental construction was employed. It was also found that concrete offers both performance and economic advantages over steel. The performance advantages include: freedom from maintenance, durability, readily-available materials, superior performance under impact and accident conditions, non temperature-sensitive, easily formed into compound curvature, and concrete has good insulating properties. Economic analysis has indicated that the concrete pressure hull would cost between 50% and 60% of the equivalent steel hull."
Source:
http://ntlsearch.bts.gov/tris/record/tris/00127041.html

The text in bold was removed.
I understand the importance of prestressed concrete structures.
I was wondering if you could put numbers on the two conditions- with prestressed and without...?

[wardd]

how would you prestress around such a short curve?

and i question how that tensile stress would be maintained

[rwatson]

Originally Posted by apex1

Do´nt worry Tom, he did´nt give me the prize either, though my answer was right!

Oh yes - you ARE right!

I had just got the bit about beating people with hammers and thought that lost you the point.

You are a bitter old b^%&$%d, arnt you

Let me skimp on a comment here rw..............when you took that for serious....not worth.

[Knut Sand]

Originally Posted by wardd

how would you prestress around such a short curve?

and i question how that tensile stress would be maintained

Thanx to Bntii;

It was found that both longitudinal and circumferential prestress must be used in the construction of the pressure hull. To facilitate this, a modular-segmental construction was employed

First I'd suspect that a inner hull were cast, with grooves for wires (circimferal)/ tensioner (longitudinal/ lengthwise) rods, all these should then be tightened to specified stress in the hardened concrete /inner hull. Then the outer hull should be cast, outside this again, according to specified thickness, wait till the concrete is fully cured, take off the tension. Molds should/ ior must be used almost about everywhere.

The front and end could be made of normal steel. (spherical in shape).

The remaining tension will remain in the concrete, prestressing the concrete, so that for instance, when docked, the hull will in all areas still have compression stress.... No areas with bending.... and the dangerous tension in the inside material of the hull is avoided...

One can avoid this, but without prestressing, it's a wild guess that the hull will need to have a doubled thickness....

I'd like to point out that the link Bntii pulled out, and copyed from, actually used the word "must"...

[Knut Sand]

I need some good arguments soon or I'll go completely for the steel solution also in "affordable" lowcost submersibles...

Wassnt there one fellow inhere somwhere who had some large propane tanks laying around?

hmm.....

Won't be that big, but with some luck you'd still be able to walk away from a dented hull....

[Knut Sand]

Knew I'd mess up a good explanation....

Ok the steel remains inside the hull/ beam, stressed all the time during curing, the stress/ results in an elongation of the steel. After curing, (of the concrete) the tension is taken off, but due to anchors etc, the tension in the steel does not go back, the elongation remains. Causing a compression stress in the cross section of the concrete.

A symmetric steel beam would have "zero pressure line" in the middle compression at the top, tension at the bottom.

A symmetric concrete beam without prestress reinforcement woild not have zero pressure in the middle, as stated earlier the ability to withstand compression pressure is approx 10 times that of tension stress. So 1/10 of the top cross section would manage to hold the bending force and the lower 9/10 would probably break.... so the "zero pressure line" is 1/10 from the top

With prestressing you move the "zero pressure line" down, making more of the cross section work for you. the stressed steel reinforcment shall remain in the structure, leaving the concrete in a compressed state even when not in what we would consider a stressed situation

Like prestressing bolts, thats just a smaller scale, in a way... sort of....
(you must consider the surrounding material though).

[Knut Sand]

Come to think of something, a complete digression...

When the Two Towers were attacked in NY. There were some theories of additional explosives in the buildings, as they found structures that looked like they had been exposed for explosions. What probably happened was prestessed wires/ reinforcments, getting warm from the fires, warmer steel can't be stressed as much at steel at room temperatures (design temperatures), and when loosing the ability to hold the tension; steelrods/ wires go "snap" and they don't go silently....

So the prestressed concrete structures had these wires inside them that suddenly snapped, leaving the mark of something that looked very similar to what an internal explosion would do, in addition to metal (in some areas molten).

[wellmer]

We have heard quite a bit of "theories" about how a concrete hull will fail, we had buckling, notch effects, waterjet effects, fault line effects, unroundness, roghness, etc, etc, all painting "dominating factors" for surprising failure at not expected depths.

On contrary the reality of thick walled concrete pressure hulls (as the studies presented indicate, and our own research shows, the failure depth is a very LINEAR function of hull thickness - free of surprises.

Which means for my understanding that no "spooky effect" whatsoever is playing a important role at failure - all test findings are well explained by basic compression arches - no rocket science - well understood by roman craftsman, 2000 years ago.

All roughness and unroundness, concret quality etc... etc... factors of our hulls are in the zone where they do not become "dominating factors" in the failure mode at all. The only surprise in failure of thick walled tubular concrete structures at hydrostatic load is, that the failure occures "surprisingly predictible" as a linear function of wall thickness - as the study mention.

One of the great things of thick walled concrete pressure hulls is, that the "complicated" factor is ruled out when buckling is ruled out as expected failure mode.

What concerns prestressing i agree completly that it is a MUST when the design objective is a concrete hull with SUPERIOR impact resistance (by mines and weapons) compared to the steel hulls in use today. As mentioned in the study.

It is also a strong plus when the hull has the typical military sub shape, and is built where military segmented sub building is state of the art.

For civil use where mine impacts play a minor role and shape is somewhat different, operation envelope is very different, military MUSTS are frequently relative benefits and should be checked for usefulness...

What concerns the obvious fact that some participants of this forum seem to "hate our concept scientififically" but continue to fail to bring up valid points continues to be self explaining... as said before i am always open to answer to people who bring up a point in a scientific correct and well educated way.