2000-01-02 – The Floating Island problem- The actual construction idea

Ok, this is where the philosophy ends, and real physics and experimentation starts!

So, there are two ideas in the main, seacrete, and plastic cups.

Seacrete is unlikely to be as useful as we hoped. Recent experiments show that the accretion rate is too slow for anything, and uses the sum of the power from the seven 100MW OTEC plants. That’s a lot of power, and yet it would still take some 27 years. It is a shame we want to put the OTEC’s on the seacrete first!

This leaves plastic cups, big plastic cups, mind! Whilst the LUF list has been rabbiting on about full scale tests and who is going to pay for them, I have been playing in the bath. Using a large number of disposable plastic vending machine cups “recycled” from a bin at work, and a £4 hot-glue gun, the results are as follows:

A single cup falls over after a few seconds with a slight wave.

Two cups fall over almost instantly, without waves.

A triangle of cups is almost totally stable, which was surprising, even with simulated waves that were several inches high, which is comparative to the height of the cups.

A square/diamond was also very, very stable.

Six arranged as a pool-ball rack was ultra-stable.

\"FiveA hexagon shape with a central cup inverted was also ultra-stable even when filled with water to simulate loading.

Notably, every structure was as stable the other way up! I had started the experiment with the cups upside down, to form open bottomed closed cells to the surface. This wasn’t needed, but is recommended for several reasons.

Due to the low loading on the structures, all the stable structures rode over everything. Further tests were due last weekend, but personal circumstances and the UK fuel “wars” have prevented this trip to the seaside, to meet real waves. Further Tests.

The beauty of the design with a varied selection of cups of various sizes and volumes, some of which are inverted, is apparent when you consider crop growth. A tree requires many feet of soil, and so there a container would be “right way up” so the tree would have roots below sea level, supported by the surrounding inverted containers. Inverted containers can also have a number of “top-up” holes. Every so often, the containers will require more air pumped into them, to support more load, or to replace gases absorbed by seawater or used by sea creatures. Another reason is the ease of increasing the load support of the structure, by disconnecting a cell and flooding it, and replacing with a deeper walled one of the same dimensional cross-section. By disconnecting and then passing a hose from the underside to the top-up port, then adding a load, the container will slowly sink, allowing it to be towed away by divers, and the replacement to be brought in. This would be held in the right place and a small amount of air would be vented into it, forcing it up into the hole. Once fully connected, the rest of the air would be pumped in, forcing the water out, and so increasing the buoyancy to the required level.

A note on the air: Air would not, in fact, be used very often for supporting of a cell. It would be foolish to, as, aside from the ease with which it is acquired, it is not the best solution. The use of Nitrogen is the majority of cells would increase the buoyancy somewhat, as N2 is slightly lighter than air. However, the main reason is the majority of sea-life would choose not to live in the buoyancy space, but on the underside, due to the lack of oxygen and carbon dioxide in the voids. This will reduce fouling to a large degree, as well as massively reducing the fire risks. Cells will also need less topping up and no buoyancy will be lost due to the 23% oxygen being used up by photosynthesis ad other processes. Some cells would contain air, and would be a visibly different colour to prevent a man overboard from taking air in the wrong cell.

Some cells would be right way up with a filling of sand, and constructions of concrete or seacrete to act as a firebreak and mass builder for the whole colony. I suggest the use of Hexagonal shaped blocks with straight sides as these are easily stacked in an optimal fashion, have regular ridges for strength and flat sides are easier for fixing and fixings. A greater torque can be exerted on them without the hand slipping, which will help underwater, and they allow for friction fitting from the external bowing caused by the internal pressure of the air due to the weight above, whilst having a small gap at each corner which will allow for ducting and pipes to be routed under the surface.

The integrity of each cell could be cheaply and easily monitored using a fibre-optic system using time-domain reflectometery. A single wire would be passed under and into each of the cells, with the loop of the wire pulled to a fairly tight angle, and attached just above the waterline. The fibre would then continue unbroken to the next cell, and so on, throughout the entire structure. The end would be free whereever the end was. The reflectometer would then pulse a laser source down the cable and examine the reflections. If water entered the cell, the backscatter level would change dramatically, and the damaged cell would be easily identified from the map showing the path of the cable, and the distance/time of flight to the incident. A similar system would use two fibre cables to each cell, monitored independantly. From the decrease in returned light from one cable being cross-referenced with the other cable, the damaged cell could be identified. The advantages of fibre optics is that the cables are very fine, lightweight, rugged, non-contact and non electrical, with no moving parts. Installation time would be very short, and projected lifetimes of over twenty years are common. The cable never needs to be broken, yet will always provide warning. Reflectometry has the disadvantage of higher cost top-level equipment and set-up, yet is still very cheap, but the advantage of the use of a single cable underwater, so massively reducing the underwater set-up time and cost, and the disadvantage of perhaps requiring a complex map. Any other system would require a map system, and in my opinion reflectometry wins due to low maintenance.

What is Time Domain Reflectometry?

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