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Date: Fri, 14 Sep 2001 22:45:20
From: Vent 7
Subject: Movie night

Hello all
We the members of vent 7 cordially invite you guys to a movie night on Sunday 16 August at 9 pm. The venue is still to be decided. We are going to watch some films about undersea exploration and more significantly undersea robots and manned vehicles. I will mail you later about the exact location.
Vent 7


Date: Sun, 16 Sep 2001 13:27:54
From: Vent 7
Subject: Tonight!!!

Sorry guys, the movies are tonight September 16, not August. I had a long night. Don't ask. Anyway, we're meeting at 8:55 in 10-250. See ya.
Tawanda


Date: Wed, 19 Sep 2001 20:27:32
From: Vent 4
Subject Hab Considerations

Manned Remote Operations and Robotic Remote Operations,

In considering basic design structure, we need to know how you are designing docks and storage space requirements. Please email us all your current details and decisions regarding this issue, and keep us updated.

We will do our best to accommodate all your responses and requests. So, please include all information you think will influence the design of the habitat and state your reasoning behind your requests. Please include "what you want for an A" so that we can get a general idea of "where this is going" and how to incorporate it into the hab design.
Vent 4


Date: Fri, 21 Sep 2001
From: Vent 8
Subject: Safety Regulations Draft

So that you may start designing your structures ASAP, we have decided to send out a premilinary list of guidelines. These WILL change and be added to, but it is at least something to get you started.

1. There must be a doctor on board at all times (yes, a MD)
2. All crew members must be trained in basic medical procedures such as putting in an IV.
3. There must be a place on the station to do surgery.
4. There must be at least two escape pods, each with enough seats for the entire crew.
5. The internal pressure of all vehicles must maintain very close to 1 atm.
6. The main structure must be built such that if there is an earthquake (you are along a fault line), it will not be damaged.
7. In case of a mud slide, the structure must not be buried.
8. The structure should be capable of detaching from the ocean floor in case of a disaster.
9. Fire extinguishers, naturally.
10. No weapons.
11. Any vehicles must be capable of reaching the surface with their supply of oxygen and fuel in case the structure is detached from the ocean floor. 12. Their must be a type II quarantine on any foreign lifeformes brought into the ship.
13. There must be a way to safely transport injured crew members to the surface which will maintain a constant axis, i.e. the ground at the bottom must STAY on the bottom of the vehicle, and it must be designed to reduce jarring.

These are subject to change as we receive more information. Please contact us if you feel these need to change.

-Vent 8
vent8@mit.edu


Date: Fri, 21 Sep 2001 12:44:55
From: Mentor: Todd B. Harland-White
Subject Introduction

Ahoy.

When I sent a request to mentor to Prof Hodges, I was a bit terse, so the webpage describing mentors says very little about me. I should let you know a bit about myself to help the team know what to ask and expect from me. The attached resume is more or less up to date.

I should say, since you are freshmen, that I am an Educational Counselor for MIT, and always interested in info to tell my student applicants about MIT and the decision process that leads people there. Any stories will be appreciated! Is it what you expected so far?

I will also note that I was 100% sure I was a Chemistry major as I started at MIT. It was a survey course on naval architecture my freshman year that changed my mind and got me into the career I have enjoyed for the last 25 years. I then entered into the engineering intership program (XIII-C, co-op) my sophomore year so I had the equivalent of a year real work in the field - and really knew what I was in for - by the time I graduated with a simultaneous BS and MS in 1977. (I just happen to still be at the company I co-op'd with - I think that is unusual.)

I live near the Naval Academy in Annapolis, Maryland and saw the MIT AUV (Autonomous Underwater Vehicle) team win the AUVSI competiton this summer with ORCA. That group might be a fun follow-on to this project (assuming you stay interested).

My family is from Boston, and I hope to come and visit at some point this fall. I will try to line that up with something interesting in the course and drop by.

Thanks, Todd Harland-White

work e-mail: todd_b_harland-white@mail.northgrum.com
home e-mail: todd@alum.mit.edu

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Date: Fri, 28 Sep 2001 06:56:58
From: Mentor: Todd B. Harland-White
Subject: Response query

Greetings. I sent some info to introduce myself to the team at this address earlier this week. Did it get through?

Thanks, Todd Harland-White todd@alum.mit.edu


Date: Mon, 01 Oct 2001 18:06:20
From: Vent 4
Subject: Docking Design from Vent 4

Hey, We were reviewing a number of old emails and came across one from vent 6 on docking.
To be perfectly honest the design of the docks is our lowest concern at the moment. Moreover, we did not include it in our "Requirements for an A" statement. We planned on leaving the docking to teams 5,6,7. Although we are willing to work with another group on docking, the key is working together as groups. In other words, habitat design team (vent 4) is not soley responsible for docking. It seemed from the email that you might have a few ideas; if you could elaborate on them slightly, we'll research their implications on the habitat design and which are feasible. We can progress together as a team from there.

-JoHanna
vent 4, Habitat


Date: Tue, 2 Oct 2001 07:25:08
From: Mentor: Todd B. Harland-White
Subject: Pressure

I'll point to some useful material.

1. Best source of info on this is a mechanical engineer's book by "Roark" which gives all the stress formulas for different types of construction. Anybody in Course 2 should have it. It covers situations that no one has even thought of yet.

2. However, because of your deep depth, your case is rather simple. You will almost certainly have a uniform wall thickness, and you will find the equations for this in in the early parts of most nearly any Strength of Materials book. I used "Timoshenko & McCullough", there is also "Timoshenko & Young" or other materials course book; or even most Engineering Handbooks such as "Marks."

(You will have a uniform wall thickness - a monocoque structure - instead of the thin wall with widely spaced stiffening ribs that we use for shallower depths in subs. The reason: the issue with external pressure is not just strength, but also "buckling" or collapse - think of a coke can that gets crushed. We can make a lighter structure for shallow depth by using a thin wall and ribs that prevent the buckling. However, by the time you get real deep, you will need to make the ribs so close together that you go to a uniform wall.)

3. Use a lot of allowance for safety factor. We design for at least 50% greater depth than operations most of the time, and 100% extra if using composite materials.

4. Even if you use a cylinder, you are still likely to use (hemi-)spherical ends.

5. Compare your results with Alvin. There are other hull examples in Allmendinger's book as well.

6. At these depths, your hull will not likely float on its own. That is why most deep diving boats have big blocks of "syntactic" foam. That is glass microspheres in an epoxy matrix - each cubic foot of foam can support about 32 pounds of weight (ie, it weighs 32 pounds per cubic foot but displaces 64 pound per cubic foot water).

That should help.

Todd Harland-White Northrop Grumman Corporation
(410) 260-5180


Date: Thu, 04 Oct 2001 11:23:31
From: Vent 4
Subject: Energy

We are aware that you will require a large amount of power and have taken it into consideration. We are still research the best power sources or a combination thereof. The list includes nuclear, sterling engines modified for deep sea applications, and batteries (generally for backup systems). Since at moment we do not have any numbers (output, efficiency, cost, size, etc), we cannot tell you which we will use. If you could give an estimate on the amount of power your vehicle will require and how often you might recharge it, that would help us in selecting the power source.

Thanks,
JoHanna


Date: Tue, 09 Oct 2001 11:16:45
From: Mentor: David Midell
Subject: Reply to our Introduction

OK-- but I'll need a little more info on what you are trying to do before I can help you out. Have you contacted the people at Woods Hole who design and operate the ALVIN?
dm


Date: Wed, 10 Oct 2001 07:32:28
From: Mentor: Todd B. Harland-White
Subject: Shaft and Other Questions

Dear Kabir and team

Question 1 - Range

The question here is really how to scale drag and power requirements versus volume and weight for battery. This is a fun exercise with units and proportionality, and it is NOT linear with vehicle dimensions. Drag is often based on surface area (square feet) - friction. Compare that with volume (cubic feet) and see which grows faster as you increase vehicle size - and then see which shrinks quicker as you make a small vehicle... This way use can compare the likely potential ranges of two different vehicles. (This was done in the first seminar series I took - and explains why "Gulliver's Travels" is fiction.)

Question 2 - Shaft Seals

The easy way to solve the problem is to avoid it (often the best strategy): put the motor outside and doon't take a shaft from atmospheric spaces out into the high pressure sea. One way to make this work is to put the motor and electrics into a box of oil at the same pressure as the sea so all you need is a low pressure seal. At your depths, this may be the only answer. Work has also gone on encapsulating the motor in ceramic so it can operate in direct contact with the sea.

You might also see if you can get some information on thrusters used on deep water robotic vehicles (ROVs). Woods Hole folks know about these.

There are a whole collection of ways to solve this problem at lower pressures.

(And when you really want some fun and have some money to spend, try also making the motor silent....)

Question 3 - Docking

The taper flange design you have drawn for you docking is similar to the "flare" that you will find on many hoses and other mechanical piping connections. It works fine at lower pressures. However, with the high pressures you will have at depth, it is unnecessary, and there a flat "face" seal is used. This prevents distorion of the sealing surfaces under pressure, and ends up being more reliable at depth. You will find examples of this on higher pressure piping fittings.

I have attached a picture of the Australian Manta submarine rescue vehicle mated to a submarine. (Search the web - you can find details on vehicles from several countries: Manta, DSRV, LR-5.) It is a tethered vehicle, rather than a free swimmer like the current American DSRV, and the skirt has a fancy mechanism that lets it swivel before mating, but the general docking is similar - and very much like the process you describe except that the mating surfaces are flat. (All submarines put a special flat surface around their hatches so that any country's rescue system will be able to mate.)

One thing to note - and it isn't easy - is that the submarine hatch - in your case the habitat hatch - opens into the space inside the dock. This is just like you described, and the process is like you described too: make contact, vent a little pressure to secure the seal, and then dump all the pressure to lock everything together. To leave, let the pressure equalize and away you go. (Rescue vehicles have to do this without help from the sub in case the folks in the sub are incapacitated.)

Thanks, Todd

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Date: Thu, 11 Oct 2001 07:29:54
From: Mentor: Todd B. Harland-White
Subject: Cooling

Dear Kabir,

#1: You might need cooling for other operating conditions than being near the vent - say during testing and training and when on or near the surface. Or, you might want your design to be useful for other expeditions to help pay for the initial design cost. (Remember to get ALL the requirements - some are not obvious. For example, our vehicles spend more hours running while up on deck or in air in the factory than in the water, and overheating IS a big concern.) You might want to look at heat pumps - they can do both heating and cooling.

#2: I'd take a look at the expansion of materials due to temperature - there are tables of "coefficients of thermal expnasion" for most materials. Look also at the conductivity of the metal - I have a feeling that heat applied in one spot will spread out quicker than it will raise a localized blister. This worry would not be high on my list. (Note: in 25 years around subs of various sizes, I have NEVER gone down in one and NEVER WILL.)

#3: Nuclear subs distill water: they have 60 megawatts to play with. If you calculate the power to distill it - and purify it (remember that you are visiting the vents to find strange new life - no reason to believe it is harmless), I think carrying a few bottles of water will be a great solution. Distillation might make more sense back at the habitat. (If you can charter the expedition under the British flag, then grog and rum will be on board anyway.)

Thanks, Todd


Date: Mon, 15 Oct 2001 07:31:33
From: Mentor: Todd B. Harland-White
Subject: Docking

Dear Waseem,

I think that the life support team will have real trouble with almost every aspect of or material used for submarine repair if performed within the habitat's closed atmosphere. Welding, use of epoxies, cleaning solutions, soldering flux, lubricants, battery electrolyte.... These are hazardous operations in a factory!

And what about vent life sticking to the outside of the sub?

And, if you are going to do repairs in the habitat, you need all your backup systems designed to get you back to the habitat - propulsion, guidance, etc - versus up to the surface. And once there, do you have the right equipment to test the sub after any repair?

My vote would be taking the boat up to the surface, then maybe into port to fix if it can't be fixed on the surface ship. (I can't picture people on the bottom of the ocean without a ship overhead ready to offer aid anyhow.)

Probably too conservative, Todd


Date: Wed, 17 Oct 2001 15:00:05
From: Vent 2
Subject: Remote or Manned Core Sampling

Hello. My name is Stephen Fantone. I am from vent 2, geology. we are going to need a manned or unmanned vehicle that is capable of taking core samples up to 10 meters in depth through sediment. The core samples can be relativly small, perhaps less than an inch in diameter. Also, the robot must, if at all possible, be able to somehow plug the hole left by the core sample. These cre samples would give us a record of the history of the vent, including change in outputs, age, and variations of chemical precipitation.

Thank you
Steve (vent2)


Date: Thu, 18 Oct 2001 01:08:56
From: Vent 7
Subject: Core Sampling

ROVs as in those constantly used in oil drilling would probably be more effective than your manned vehicle. But if you want to design that into your system, cool. How are you communicating back to the base? Are you cabled? I sent a description of our current ideas to the board, your group might be interested in talking about what our group is doing. Give us your suggestions and decision about the drilling mechinism. It could always be an ROV controlled by your vehicle, assuming you guys carry LOTS of power to drive the machinery.

-Heather
vent7


Date: Fri, 19 Oct 2001 08:01:41
From: Mentor: Todd B. Harland-White
Subject: Hull Design

I can't give a long or complete answer right now, but let me quickly note that the inner hull - sphere or cylinder - takes ALL the pressure loads. The exostructure is not continuous, and allows water pressure to pass through: it simply provides a place to hang stuff and serves as a fairing to reduce drag.

I'll try to send a more complete answer later today.

Todd


Date: Sat, 20 Oct 2001 11:16:22
From: Mentor: Todd B. Harland-White
Subject: Hull Design

Dear Waseem,

So, you have gone from democracy to a (hopefully benevolant) dictatorship. There comes a time in every project where that is tempting, and it isn't always a bad thing. Having a firm schedule of the decisions that HAVE to be made and WHEN can keep things from slipping too late. Learning everything between Thanksgiving and Christmas makes for a tough term...

Questions and answers:

1- From what I've read and from the diagrams I've seen, I can imagine a simplified picture of the exostructure as a shell that encloses the inner shell where our scientists will reside. Is this picture right? (I'm not using shell to mean empty sphere, I just mean any hollow structure.) If it is, then why is the exostructure usually made from thin sheets of metal, while the pressure hull is much thicker? Doesn't the outer shell take much of the water pressure? If for example you have a strong metal sphere with another glass sphere inside it, and you put the spheres under very high pressure, won't the glass sphere be protected as long as the metal sphere does not collapse? If so, why should the pressure hull be stronger than the outer hull?

The exostructure does not resist pressure. Obviously the material is exposed to it, but it allows the pressure to be the same both inside and outside the exostructure. Only the internal pressure hull resists the pressure and forms a one atmosphere dry space. The exostructure is just used as a fairing and a way of holding all the equipment together. (You can't attach stuff directly to the pressure hull because 1) it will change dimensions slightly under pressure and 2) the stresses from the external equipment could cause local distorions of the hull that would lead to its collapse. Think of the pressure hull as a egg and the exostructure as a framework that protects it.)

On a "real" submarine which goes to much shallower depths than you have to, they make much of the pressure hull cylindrical and use it for both pressure hull and fairing shape - saving money and weight. But the nose and tail shapes you see are really exostructures extending past the ends of the pressure hull - and that's where they can put sonars and anchors and ballast tanks, etc.

2- I've seen pressure hulls built usually to be spherical or some other strong shape. On the other hand, outer hulls are built in all kinds of fancy shapes to make them more streamlined. Doesn't this make them lose their strength? And does a streamlined outer hull eliminate the need for a streamlined pressure hull?

Inner pressure hull, being buried within the outer hull, doesn't have to be streamlined and can instead be made in the best shape to handle pressure. Spheres are very good, and as you are considering, intersecting spheres are also good while not adding a lot of "useless" volume. Fairing can be any good streamlined shape.

By separating the hull into two portions - the pressure hull and the exostructure - long term maintenance and upgrades of the submersible are facilitated. For example, in the case of a couple of the Navy's deep diving boats (Turtle and Seacliffe, sisters of Alvin), the spherical pressure hulls were removed and replaced with thicker hulls to increase the depth capability, but they were still considered to be the "same" boat as before the upgrades.

3-What is the buoyancy factor? The book refers to it as the weight of the hull over the weight of the water it displaces. This means that for a low buoyancy factor, the hull should be light and the weight of the water it displaces (which is proportional to its volume, right?) should be large. Then, in the next paragraph, it says that submarines operating in deep water should have a low buoyancy factor. I simply don't get that. Why should a submarine working in a deep environment be light? Shouldn't it be heavy so that it sinks down to deep water?

First, I haven't heard of "buoyancy factor" by that name - that just isn't a term I've run across. However, the concept of comparing weight to buoyancy is common. I might say that I require 300 pounds of hull weight to get 1000 pounds of buoyancy: (30% weight/buoyancy ratio, about what I see in UUVs) - so I would be able to float and carry a lot (700 pounds in this example) of equipment. In your case, you will end up with a lot of weight to get a little buoyancy - maybe that is what the author meant by low buoyancy factor - and in fact your pressure hull will not float by itself. You will have to add something inside the exostructure to be able to float the overall sub. This flotation material can very commonly be syntactic foam - glass spheres in an epoxy matrix - or even a lightweight liquid like gasoline for maximum depths (Trieste).

I would also appreciate it if you can also go the incomplete page I've written and tell me if the simplistic approach I'm using would work in practice(I personally think it won't.) The page is at: web.mit.edu/12.000/www/m2005/a2/6/hull.shtml

The pressure hull you show is not wrong. You should just expect to put an exostructure around it.

Todd

Date: Wed, 31 Oct 2001 12:31:49
From: Vent 4
Subject: Batteries

Hi guys, We were wondering what you are using for batteries. Could you send us any information about the batteries too?

Thanks,
JoHanna
Vent 4 (habitat)


Date: Wed, 31 Oct 2001 19:01:04
From: Mentor: Todd B. Harland-White
Subject: Power and Propulsion

Dear Waseem,
Ah, the harsh light of reality. Submersibles move slow because of the energy concerns and inability to carry or afford big batteries. It is a real nuisance and there hasn't been much of an answer available yet. Even diesel submarines that run on batteries when submerged don't usually go more than 5-6 knots.

Deep Flight does not exist yet. It intends to be able to go fast by being very small - think of a sled with a canopy more than a working vehicle. By greatly reducing both surface area and exposed equipment, it is supposed to be able to get reduced drag. To show how this might work for a real in-the-field example, some of our torpedo-shaped minehunting vehicles (21" diameter x 20' long) are able to get about 6 knots on 500 watts of power - and 6 knots is a pretty good match to sensors that can see mines. (Those sensors consume about 1000 watts - the ratio of propulsion power to sensors power of 1 to 2 can be derived mathematically as the optimum.)

You will have to use thrusters to maneuver at low speeds - maybe below 3 knots - with fins only becoming effective above that. The configuration you mention sounds good for normal running, but you might need more to provide vertical control to be able to safely dock with the habitat - the variable ballast will not respond quickly enough.

I'm not that familiar with aluminum-seawater batteries, but I know about aluminum-oxygen fuel cells which can be used for 3000 watt, and about magnesium-seawater batteries that can provide more than 100,000 watts for torpedo applications. However, all of these will be hard to recharge, requiring that you phyically replace the metal plates between uses.

I have seen higher power thrusters than 10 Hp, but only hydraulically operated on big work ROVs where they can provide a lot of power down the tow cable to run a big power plant to serve not only the thrusters but also work and digging tools.

I have a manned sub with over 1 megawatt-hour of battery. The only real limit is how much you can afford to float - and afford to buy! Do note that it will take a long time to recharge a big battery - you have to worry about overheating it (particulary the center where heat isn't reduced by being close to the seawater), and so a good rule of thumb is to put energy in no faster than you take it out.

Good luck, Todd


Date: Thu, 1 Nov 2001 08:01:03
From: Mentor: Todd B. Harland-White
Subject: Speed Design

Waseem,

Re: your questions last night about submarine speed and power. I, and a number of the other mentors, are probably going to get caught up in a new program seeking to create a manned sub that can go 60 (yes, sixty) knots. See http://www.DARPA.mil/ato/programs/loki.htm

Always new challenges, Todd