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Manned Operations | |
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Introducing EVE Hull Design Exostructure Power Propulsion Docking Ballast Sensors & Sampling Manipulators Life Support Navigation Communication Viewing Systems Control Systems ROV |
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The Ballast System
As with any sea vehicle, submersibles have to worry about buoyancy. Unlike surface ships, submersibles want to stay about neutral almost all the time. That way the submersible neither sinks nor floats when it doesn’t need to. Since most of EVE’s operations will be on the seafloor, it will be going horizontally almost always. So the first problem to confront is to make EVE neutrally buoyant. This is not easy because it has a lot of heavy metal to help it withstand the pressure. Thus, it is negatively buoyant and tends to sink. In most cases a little Styrofoam would solve this problem, but at the pressure that we are at, Styrofoam would quickly be crushed. Instead, we shall use special foam that can withstand the pressure. It is called syntactic foam, and it is made of tiny hollow glass balls that are held in foam to keep the balls together. The size of the balls, and thus the density of the foam, is determined by the pressure that it has to withstand. For example, the higher the pressure, the smaller the balls have to be and the denser the foam is. To determine how much foam EVE needs we figure out the wet weight of the submersible. This is how heavy EVE would feel when it is in water. It is simply the difference between the dry weight and the weight of the water that it displaces. Here is a table with all the components with significant weight and the total wet weight of the submersible.
Displacement | (kg) | water displaced (kg) | (kg) | |
| Hull | 21.87 | 23891 | 21870 | 2111 |
| Exostructure | 1.51 | 1809 | 1510 | 299 |
| Batteries | 0.672 | 1740 | 672 | 1068 |
| Motors | 0.25 | 500 | 250 | 250 |
| Manipulators | 0.05 | 200 | 50 | 150 |
| Fixed Ballast | 0 | 200 | 0 | 200 |
| Hatch | 0.195 | 374 | 195 | 179 |
| Computer/Controls | 0 | 50 | 0 | 50 |
| Life Support | 0 | 100 | 0 | 100 |
| Pilots | 0 | 240 | 0 | 240 |
| Miscellaneous | 0 | 100 | 0 | 100 |
| Total | 24.55 | 29294 | 24547 | 4747 |
The following are the parameters of the foam used:
Density: 0.40 g/cubic cm
Foam Buoyancy: 0.60 g/cubic cm
Foam Volume: 7.91 cubic m
The equations we used for this table are:
Water displaced = Displacement * 1000kg/cubic meters (where 1000 is the density of water.)
Wet weight = Dry weight – Weight of water displaced.
Foam buoyancy = 1 Foam density.
Foam volume = Total wet weight / (Foam buoyancy / 1000)
The 1000 in the equation above is used to convert the units to cubic meters.
7.91 cubic meters seems like a lot of foam, but EVE is large and the foam could be put between the exostucture and the pressure hull. There will be enough if it is 15cm thick all the way round the pressure hull. The foam must be spread out evenly or else the sub will tilt.
Now that EVE is neutrally buoyant, we need two was to make it deviate from neutral. The first is a variable ballast system. This system consists of two pressure tanks. One is in front of the pressure hull and the other is near the batteries the back (both inside the exostructure.) They will be variable by 200kg. That is 0.2 cubic meters, so each tank is about 0.1 cubic meters (100 liters). There are two high pressure pumps that can pump the water in and out of the tanks. The pumps will be able to fill or empty the tanks in 30 seconds and are rated to 6000psi. When the water is pumped out, EVE is 200 kg lighter and it will float. If the tanks are completely full, EVE is heavier and will sink. The water ballast will also be used as the trim system. If one tank is filled more than the other, the submersible pitches up or down.
The other ballast we shall use is a fixed ballast and will be used only during emergencies. It consists of two lead cylinders on either side of the outside of the shell. They each weigh 100kg. That way, no matter what is the situation is with the variable ballast, if they are dropped, EVE will float to the surface. They can be dropped with a solenoid that is controlled from the inside of the sub. The switch has its own power source. So if the power goes out the people in EVE can still get to the surface.