Nonsense maybe, but lets think this out.


Diving with the ballast tanks bown dry:

MAYBE, if you had bowplanes (they would be under the surface and thus effective).. and were going flat out on the surface, you MIGHT be able to push the bow down enough to get the water flowing over the hull, thus turning the upper hull into a massive plane surface. The old nuke boats of before the Albacore hulls (pre 637 hulls) had this problem at high speeds. They had to be careful at high speed putting angles on the hull less they lose depth control. I do believe that the rounded hull surface all but eliminated the issue.

They also have a LOT of reserve bouyancy designed into the hull. I do not think you could do this if you tried.

Surfacing the boat with the ballast tanks full:

Yes, easily. You just drive the ship up using the planes and the engines. Once on the surface you have the surface tension of the water to help support you (this is the same thing that allows a needle to 'float' on the suface of the water.

One term for surfacing without blowing the tanks is called 'broaching'. We hate doing it as when you have fairwater planes, you can make a rather LOUD noise and REALLY shake the boat when the planes come down back into the water.

Hm ! Then water tension !? I've seen something concerning waterline length in the book subguru sent me. Could be this. Must check it out.

As for the buoancy reserve, 688 at wikipedia shows 87% of hull volume submerged with standard surfacing procedures. That is 13% of weight which holds the sub 'up'. Really not much, if you consider what forces have effect on the sub at high speeds.

Well I guess I'll post the demo (this weekend quite probably) and I will let you judge if it feels right or not.

An idea ! I guess you all have seen those videos of 688 making emergency surface. If I knew the speed, I have everything ! Pitch can be seen in the video. From the speed, and amount of exposed hull, time it take to submerge again I can compute side lift & drag coefficients, and even forward-backward stabilization forces.
So the questions is .. what is the speed estimate of the sub in this video ?
http://www.youtube.com/watch?v=lxyMzR9K1Dk
If it is realtime, I could even capture the speed from the video. But is it realtime ?

I just made a rough estimate from that footage based on looking at a point on the ocean where it breaks the water and then timing how long it takes half the length of the boat to pass that point, which is about all you can do since the wave and spray obscures stuff soon after. Not very scientific, but it works out to around 21.5 knots by my estimation. Of course that is if the footage is not slowed down at all, which to be honest, it looks like it is a little.

:D Chock

There are many factors that determine ships speed at the surface interface.
Primary factors are:

1) Initial ships speed

2) Initial Depth

3) Rate of bouyancy change

4) Angle on the boat

Lets break them down starting with an ideal system where we are only worried about going up with no casualities:

The inital speed of the boat during an emergency surface is going to effect the final speed. It is more than a simle additive function. The faster you are going the faster you are going to effect a depth change due to the effectiveness of the planes. It will effect the vector change in ships direction and thus have a quantifable change on the other vectors to be listed.

The deeper you are the more speed you have to gain. Why? This is due to having a longer change in bouyancy and a longer speed vector (dependant on initial speed). As the bouyancy increases (see next factor for why this happens) you are going to be gaining speed and thus the longer you have for this to happen the bigger increase you are going to have.

Rate of change of bouyancy is a REAL mind twister. Lets start with some basics.
The deeper you are, the less bouyancy you have. This is due to the compression of the hull due to increasing sea pressure. This is due to a decrease in surface area. Thus as you go shallow, you will gain positive bouyancy and vice versa.
Air in the high pressure flasks has to push against sea pressure to make it into the main ballast tanks. This means that the deeper you are, the LESS air is put into the tanks initially. Also, the air will lose volumn as the depth increases, thus a pound of air at 1000 feet is much less VOLUMN (hence bouyancy) than at say 150 feet. This it due to the surrounding sea pressure. As you go up, the RATE of air going into the main ballast tanks will increase due to decreasing sea pressure. The air will also EXPAND in the main ballast tank as you go shallow thus increasing the rate at which water is expelled from the main ballast tanks thus increasing the amount of positive bouyancy as you approach the surface.

As you can see, the amount of positive bouyancy addition starts small, but increases rapidly as you go up.

Angle on the boat is difficult to explain. The higher the angle, the faster you approach the surface, too steep and you can actually "tailslide' right back down after you pierce the surface interface as the ship can not 'tip over' fast enough to stay on the surface. This means you have to be aggressive to get up, but not TOO aggressive or you might go right back down. One of the limiting factors is that if you are TOO steep, you let the air out of the bottom of the ballast tanks and that is NOT want you want to do it you WANT to stay on the surface.

One thing you might not know, AFTER you surface you do not stay there. You sink back down then come back up again. The amount of depth that you go down is dependant on the intial depth of the boat (think INTERIA). It is not like the old WWII diesel boats that popped up, tipped over and then stayed on the surface. Oh no... You BLAST up and out.. make a HUGE wave.. then disappear horizontaly down. Then you pop back up and well.. 'bob' on the surface for a few seconds until you are stable on the surface.

----------------------------------------------------------------------------------------------------------------

Time to discuss other operational factors.

You can do an EMBT blow from a slow speed while shallow and just let the boat go up. You can being doing a standard bell, order an Emergence surface and do things by the book. This means answering a preset bell, order a sudden rise to a preset angle, and thus make the whole evolution go MUCH faster. These are things that you can not tell from the video. You do not know the inital factors and HOW the EMBT was ordered. This will greatly effect the final ships speed and how it looks on the surface.

At the start, I said lets do this in a ideal system. Now, lets add some factors so you can see how each of the factors interact with each other and WHY they are so important to know.

Flooding:

Water is heavy. Water in the people tank is BAD. When you are flooding you are DECREASING the bouyancy of the boat. The deeper you are the FASTER the water comes in. Think of your water hose and your lawn. The more pressure (the more you open the valve) the MORE water you get. Sea pressure is your valve.

In flooding you want to get shallow. This means pointing the boat in the proper direction. The slower you are going initially, the longer it is going to take the boat to respond to the Helmsman yanking back on the yoke in ships control to try and attain a specific preset up-angle.

To counter this, the throttlman is going to increase the ships bell automatically. This increases the speed of the boat and makes the Helmsman job easier by making his planes more effective. You also now have the HUGE propellor PUSHING you up.

This is the inital response to ANY flooding call.

This is CRITICAL desision time. The OOD has to wonder: Is the water coming in faster than the pumps have get rid of it? Is the IN-RATE of seawater flow slowing down fast enough to so that I can still get up to handle this. Remember, the DEEPER you are, the FASTER this is all happening. You may only have a few seconds to think this thru. You also have to have in mind WHERE the flooding is coming from. Is it from the Engine room? If so, this is going to possibly effect his ability to increase speed. This could effect his helmsmans ability to control the ship. This could GREATLY hamper the ability of the boat to recover from flooding. Is it in the torpedo room? This is going to add LOTS of mass in the front of the boat which is going to make it difficult to point the nose UP.

He makes a decision.. Emergency Surface.

The air starts to blow, the ships going up, but is it fast enough? Is the decrease of depth fast enough to give the air time to get into the ballast tanks? Are we losing too much bouyance due to the water we are taking on?

Only now is the REST of the crew starting to respond. The Helmsman and the throttlemans response are about the ONLY things that can be done quickly. The COW can hit the EMBT switches fast as well but it takes TIME for the bouyancy to change once he hits them. The REST of the recovery effort takes TIME. Time that you might not have depending on the severity of the situation.

My experience??:

You want to talk adrenalin?? NO drug could make you go into hyperspeed this fast. I have stood throttleman when the CO decided to have an unannounced flooding drill in engine room lower level in the middle of the backwatch (00:00 - 06:00). We were deep and we did things like they were for real. It was SCARY. Your heart THUMPS and you do your job. You KNOW that you one of THREE people who is now holding the lives of ALL your shipmates in your hands. Just before we surfaced I saw the ships speed indicator and I could not believe how fast we were going. It was the best carnival ride in the world. Once we were informed that it was a drill, the laughter started, and then we went about our business as usual.


The purpose of this post??

I will lay odds that the sub in question started no deeper than 300 feet from a low bell and a standard EMBT blow angle. I base this on the sinkout and recovery from the EMBT blow.

Really nice info. I think I understand all said. Amount of these effects will be judged on life simulation. I worked on this maneuver today and I think I have all important effect simulated except air expanding inside the tanks and hull expansion.

If you 'were there' .. could you pop few numbers ? Speeds especially ? What speed can sub make during EMTB ? What is the target buoyancy ? Is the 13% (which is told standard for surface cruise) or more ? Do I put some air into the tanks and let it expand later or do I put everything I have ? If so, what is the maximum buoyancy

What are the max elevations are used for planes and rudder ?
What angular speed can planes or rudder make ? Subjective judgement will help me too. For example: boat is submerged level at 10kts. How long does it take to pitch it to 5 degrees ? What planes elevation is used for that ? What are emergency possibilities ? If he pulled as much as possible what is the maximum pitch he can achieve ? If the boat makes maximum turn at cruise speed, how much can it be felt inside ? Is it slow that you hardly can feel it or is it fast as in car, or even jet ?

Little goodie .. going to sleep .. more tomorrow.

http://roger.questions.cz/other/688.jpg

My friend, if you are going to do an EMBT blow you are going to blow it ALL. There is FAR more air in the air flasks (by volumn) than there is water in the main ballast tanks. The design criteria is to be able to FILL the main ballast tanks with air all the way down to crush and beyond. You are not going to do half measures when you butt is on the line. If you blow all the water out of the ballast tanks you may be in a situation that due to the amount of water taken into the pressure hull you are STILL in a negative bouyancy situation. That is why there is in up-angle and a serious bell made when flooding situation happens.

With that being said, if you are gonna do it for real, you are gonna hold the switches till you are on the surface or until you implode.

What happens to the excess air when you get to surface? It expands and goes out the ballast tank lower vents (where the water enters normally) and makes lots of pretty bubbles.

Pretty much the same as you see in game.

A lot of this is priveledged info, but I can say that that the speed of which the pitch changes is directly influenced by ships speed. The faster you go, the more responsive it becomes.

Can you feel it inside?? During torpedo evasions it is a BLAST. The boat can accelerate fast enough that you can feel it move from under your feet. It is like stepping onto a moving escalator for a few seconds. You bank and turn like an airplane. I have experienced 30 down-angles with 30-40 degree rolls. When they want to, they can move the boat as gently as they want. By using the trim system, they can change depth with only minor changes in ships pitch and/or roll.

Wow 30-40 degree rolls?!?!?!? That's amazing.

Damn thats a fine model you have there. http://www.hwupgrade.it/forum/images_hwu/smilies/38.gif http://www.hwupgrade.it/forum/images_hwu/smilies/12.gif http://www.hwupgrade.it/forum/images_hwu/smilies/12.gif

Credit goes to Xabbarus. Textures now are 5 minutes in mspaint, but it looks quite OK even now. :|\\

The model even without textures is really nice, good job Xabbarus.
I know that you're working on the physics engine for the time being, but what about the graphics engine ? :hmm:
Are you going with opengl ?

Bubblehead Nuke,

Although it is rather late this year, you should contact Neal for the 2009 Subsim Almanac. Those stories you tell about radical maneuvers on a sub are a good read and also your writing style is good too. You would definitely do well with a chapter in one of Neal's annual publications. I think he pretty much solicits in Q2 and wrap up is around the end of Q3. He had asked me this year about doing something on getting old subsims running on newer machines, but being in poor health these days I tend to avoid making committments to projects. But it sounds like you have some great stories to tell!

OpenGL, right. Sound will be OpenAL (nothing now). I'm keeping the possible ports to Linux or Mac in mind.
The graphics are very simple now, only 'feature' is that under the water there is more fog then above the water. I'm making least possible steps in each area now. GUI was first, then some basic graphics, now some basic mechanics (well it's more then basic now but still just a pilot), now will come the stations, then sonar.

Ok .. so here comes the first live simulation.

http://roger.questions.cz/other/sim.zip

Just unzip, read the readme.txt for controls, go to bin, run the exe. It runs in window, it can be resized as you wish, just note that the picture will try to keep aspect from 3:4 to 16:10.

You can control: speed, planes, rudder, tanks and there is also course autopilot.

What is simulated now:
Engine thrust, speed and angle dependent drag. Drag caused by turbulences while surfaced is not simulated.
Dynamic lift - you can try to dive the boat with empty tanks or surface boat with full tanks.
Dynamic stabilization - boat tries to point to where it goes, just try surfacing from deep with zero speed.
Hydrostatic lift, hydrostatic stabilization in pitch axis - visible especially on the surface, ship tries to 'lie on the water'.
Bank axis is fixed for now. If you try to pitch your boat to 90 degrees it will collide with rudder effect and boat will twist in very very weird fashion. Don't do that or your submariners will get sick ! :-D Will be solved later.
Change of weight (flooding tanks) - buoyancy change is constant, does not depend on depth at the moment.
Most effect depends on how much the boat is submerged (drag for example) so even jumping out of the water should be more or less correct (like the boat will eventually fall down).

Only animated part of the boat is the screw now. There is some limit of how fast it rotates because some ugly interferences shows up at the high speeds. We will need some blurred screw model for these high speeds, similar to what flight sims use.

There is no depth limit, no fuel or HP air limit. There is no ground. Water is flat now, no waves or spherical shape.

So take this as a basis, do some tests .. and tell me what do you think about it, especially about the physics.

BTW: I know I was talking about the particles .. there are none at the moment, sorry for that.

Planes are very very powerful, and seem to react instantly. I just did an outward loop. Going to surface upside down now :D

Well this is possible only at high speeds and high planes deflection. My judgement is that they must react well at low speeds too, I based their effectiveness on that. It would be hard to turn real sub on it's back. It would turn sail up because of different centers of gravity and buoyancy, but as I said, I do not simulate bank axis now at all. I guess crew would not like it too :-D

The sub upside down looks like a airship .. or dead fish .. lol. New Navy model .. 889.

Btw. the depth is from center of gravity and in meters, not feet. Speed is in kts anyway.

Just curious how you are modeling your physics?

I recall from flight sim design there are two standard approaches:

(1) Equation driven.

(2) Table driven.

#1 has the advantage a greater accuracy and avoiding discontinuities across the range of behavior. The disandvantage being more complex the get correct and computationally expensive.

#2 has the advantage of easy to implement; does not require lots of theory and delivers good performance. Also, easy to tweak and unlike equations does not necessarily produce a ripple effect throughout the entire model.

Thanks.

I'm aware of 'oversimulation' .. I will use as many tables as possible and convenient. Especially for the tweaking. I can for example compute hydrostatics completely from the 3d model and most probably even realtime, but that would be really hard to tune to what you want. Good for ship design .. not good for game.

For now there are no tables, just basic approximations with sin and cos. For example submerged volume is interpolated with single sinus function now. I have little program to draw graphs and I made a curve of what would it really would look like for 688 .. and the sin fits it with few percent difference and much less space for mistakes. Later I will swap it for table. I still didn't decided interpolation curves for the tables. Anyway for example Orbiter seems to do just right with linear approximation only (for lift & drag curves for example).

One time, while trying to clear a radio broadcast in a high sea state while at PD, we were experiencing high AND low level alarms concurrently on the primary and secondary systems.

Those of you who have been as sea know how far we were rock and rolling. You could ALMOST walk on the walls. We could for sure walk down passageways with one foot on the deck and the other on the wall, hopping from side to side as the boat rolled.