Evaluation of Initial Design Ideas

EVALUATION OF INITIAL DESIGN IDEAS

DESIGN IDEA #

1~ Features & Functional Description:

The design features a central floatation jacket, which acts as the core foundation for the attachment of the stabilising pontoons. It also helps to add to the initial buoyancy of the tower, by providing a large increase in the volume of waterdisplacement for a relatively small gain in weight.

This is then surrounded by four individual floatation pods, which can move freely up and down with the movement of the waves, but can also rotate through a slight angle back and forth about their longitudinal axes. The further out these pods sit from the centre, the stronger the effect they have of stabilising the tower.

An upper ring is also connected by pistons, the purpose of which is to stabilise tilting and rocking motions by way of restricting the movement of the top-half of the tower. Again, the higher up this sits, the greater its stabilising effect.

A Gas-Transfer System also features as a potential option, in which the compression of one piston forces gas out of it, and into the piston on the opposite side, hence causing it to simultaneously expand by the same length, and at the same time. The result is that as the piston on one side raises, the piston on the other side lowers by the same distance. This serves to keep the tower upright: it stops the raising of one pontoon pushing the tower over, by way of extending a support to the other side and hence holding it up. The four floatation pods are independent of each other, and so can move freely and randomly, accommodating the sporadic chaos of wave actionon the North Sea.

The inner floatation ring of this design allows the tower to be held high out of the water, and hence alleviates previous concerns over the tower sinking if the lower base became submerged. This also reduces the risk of the tower striking the sea floor.

However, holding the tower and its Centre of Mass so high out of the water in this way may in fact have its implications. For one, it may make the tower quite unstable, with so much mass at the top being free to move. It also increases the size of the gap between the base of the tower and the sea floor. With further to fall, the tower will eventually hit the floor at a greater velocity, and hence experience larger, potentially damaging impact forces.

Four floatation pods provide universal, Omni-directional stability, as mandated by the Specification. The weight of these pistons is going to be huge, impeding on the probable buoyancy of the whole system.

They will also be exhaustive and costly in manufacture, both in time and in raw materials. With this implication already existing on such a phenomenal scale due solely to the size of the tower itself, we should really be looking to minimise these extra costs.

The articulated joints will also be complex, and will need to be substantial so as to stand up to the intense stresses of the moving pistons.

As the outer floatation ring is effectively split into 4 separate sections, it may be slightly flimsy, so to speak, and if these pods shift by different amounts at different times, which they inevitably will, then the tower may be forced into precarious positions on the water.

The Gas-Transfer System assumes that opposing floatation pods will shift alternately and uniformly, which clearly may not be the case. It is also intrinsically complex, and is likely to be another point of potential failure.

2~ Features & Functional Description:

This design provides stabilisation in a much more omniscient manner, in the sense that supporting forces can be exerted from all directions, all at once or at any one time, indeed in any way necessary depending on the action of the waves at a given point in time. This is provided by the Uniform, Omni-directional stability is again provided by the circular ring.

The inner ring and damping pistons allow the tower to move about freely inside, but help to absorb the shocks and dramatic movements of the With the tower hanging so low in the water, there is the obvious collision-risk in shallow waters.

More pistons are used here, which, needless to say, is detrimental in weight and complexity, though it is not

STRENGTHS (+) WEAKNESSES (-)

all-surrounding floatation ring, whose 8 pistons can absorb shocks from the tower’s motion in any direction. Furthermore, the pivotal pin-joints at either end of each piston, coupled with their extensibility, allow the tower to reciprocate up and down as needed as well as back and forth, and soon. Water-inlet valves are placed beneath the floatation jacket so as to make best use of the water pressure above in order to fill the tower effectively.

3~ Features & Functional Description:

This design is essentially a collaboration of the previous two, in which the outer floatation ring has been coupled with an upper fixing ring, such that a compromise may be met between firmness of the base (through being a wide, solid unit) and catering for the tower being so high out of the water (through the upper fixing ring). The inherent instability derived from moving the Centre of Mass so high is compensated for by the height of the upper fixing, which helps the restrict the movement of the top part of the tower.

As before, the articulated pistons connecting the inner and outer rings allow the tower to move freely in any of the x (Side → Side), y (Front → Back) and z (Up → Down) axes, in variable magnitudes and at any time, be them simultaneous or individual.

As in the previous design, the Gas-Transfer System suggested by the first design has been dispelled on account of is complexity, inappropriateness and lack of necessity. This design still provides excellent all-round stability through the circular outer floatation ring.

The reduction in the number of pistons is effective in reducing weight, complexity, consumption of raw materials and hence cost.

The tower sits higher in the water, and hence eliminates the implications met by design 2 in shallow waters.

With the outer ring being taller, it will have more control over the top of the tower, as the upper pistons will be connected between the two at less of an angle and will hence be able to exert a greater force component onto, and in the direction of, the tower, hence confining its sway-motion more effectively.

The inner ring provides support to the base of the tower, and overcomes previous concerns over the tower sinking if the lower base became submerged. It also adds to its initial buoyancy, by significantly As there are far fewer pistons involved, each one will effectively have to take a greater level of stress, and in turn, the articulated joints will also be stressed more severely as well.

With the tower sitting higher in the ring, the centre of mass will be moved further from the point of fixing, and consequently, greater Turning Moments will be produced in the sway of the tower, though this is to an extent mitigated by the height of the outer ring, which will be effective in controlling the position of the top part of the tower.

In being a circular base, its hydro-dynamic stream-lining is somewhat limited, and as such will make towing a tricky process. The large cross-sectional area exposed to the flow of water will increase both the Drag CoEfficient, and indeed the thickness of the wake trailing behind it, hence increasing the overall Drag Force. This is a crucial point from the specification that this design

outer ring (due to wave attack), and thus reducing the degree of movement transferred into the tower itself. As the tower sits lower in the ring, it will have less distance to drop when sunk, and this will hence reduce the impact on the tower when it hits the sea floor.

The pivot point of the tower (where it is fixed at the inner ring) is very close to the Centre of Mass of the tower, and consequently, Turning Moments exerted onto it as the Centre of Mass is displaced from the central point of pivot will be reduced, hence mitigating the effect of sway. essential to have quite that many.

Both the fixing points of the inner ring and the holes for filling the tower with water are submerged, which will make the process of sinking the tower extremely difficult.

increasing the volume of water displacement, without increasing the weight by any major amount.

4~ Features & Functional Description:

This design works in much the same way as the previous one, except that the pistons have been replaced with high tension steel cables.

These function in a very similar manner, and that is to slow the motion of the towertop during a sway, gradually, and hence prevent it from toppling whilst reducing sudden impact stress during such movements. A drastic reduction in weight is obviously achieved through the use of cables in this manner, but sadly, that is about all that can be said for this design! The predominant issue here is the risk of the steel cables snapping, which would be extremely dangerous.

The cables would go slack when the ring moves closer to the tower, rendering them useless, and when the ring moves the other way; they are pulled taut and hence become very dangerous.

Potential corrosion in the cable would exacerbate this danger.

To reduce this slacking, the cables could be pre-stressed, but this would be extremely difficult, as the cables in this context would have to be highly substantial.

Complications would also arise in deploying the rings, and sinking the tower. For example, when the upper ring is detached, the cables will go slack, and the ring will hence plummet, leading to inevitable damage below.

fails to meet.

With the outer ring being so much taller, it will of course be heavier and therefore more exhaustive and costly to manufacture, though this is of course compromised by the reduction in the number of pistons.

SPRING DAMPING FOR TENSILE CABLES

This helps to offer the tensile cables a little give when tensile stresses are applied to them, such that they do not snap or having the unwanted effect of stopping the tower too abruptly.

The spring allows tensile give, hence absorbing the shock of the movement in the outer ring. This would also alleviate the issue of the cable going slack as the tower approaches the ring, at least to an extent.

The oil provides very effective critical damping, and would hence slow these motions down very well.

The oil also allows dissipation of heat from the stressed spring.

This is quite a complex system, and just adds more and more weight to the overall system.

It is also something else to look after, and another aspect to break or go wrong.

Significant implications would arise in the event of an oil leak.

The spring would, however, filter the oil, but in doing so, would get clogged up with debris. This would hinder it

5~ Features & Functional Description:

As a completely radical divergence form the previously circular design ideas seen so far, this design features a double Catamaran pontoon layout, so as to afford the tower good hydro-dynamic proficiency, directional control and ease of glide whilst in tow.

The two pontoons run parallel to each other, either side of the tower, and are independently articulated on damping pistons such that they can absorb the chaotic motion of the waves and hence keep the tower from toppling.

If the tower leans to one side, the upper section of the tower will push down, through its support structure and upper linkage strut, onto the pontoon below. Met by resistance from the pontoon’s Buoyant Force, the pontoon will therefore displace outwards to the side, hence extending the piston beneath. Once the piston reaches its maximum extension, it begins to pull the pontoon down. This submerges it slightly, and the increased Buoyant Force that arises from this acts upwards, and therefore begins to resist the downward force of the leaning tower. This both pulls up on the extended piston and pushes up on the linkage strut above, thereby raising the tower back into its upright position. Unlike the previously circular pontoon designs, this style provides greater directionality to the structure, meaning that it will glide through the water more efficiently, and also that the process of manoeuvring it will be much easier and indeed safer.

The size of the pontoons will provide very large buoyant forces, hence resisting the unwanted motion of the top of the tower (due to sway) very powerfully indeed, proving effective at preventing a complete topple.

The independent movement of each of the pontoons allows for the sporadic irregularity of wave action on the North Sea. The reduction in the number of component parts of this system (pontoons, pistons and articulated joints) is effective in minimising the complexity of the design, and hence reducing consumption of time, money, raw materials and energy in manufacture. Deployment of the tower will be extremely difficult, because the fixings of the lower pistons are in fact submerged.

The tower does actually hang quite low in the water in this design, which will be a major implication in shallow waters, certainly.

Also, with so much of the tower hanging below the fixing point on the upper ring, the tower may be quite susceptible to the lower half swinging like a pendulum. This will of course inflict major sheer stresses on the pin-joint fixings featured both on top of and underneath the floatation pontoon.

The length of the pontoons may make it difficult to implement a change in the tower’s course of direction. With the two pontoons being so far apart, it will be difficult to fix a single tow point from which the tugs can pull the structure through the water.

6~ Features & Functional Description:

This is a much simpler version of design five, and yet serves no fewer functions. Again, in being suspended from the structure above by a pair of pistons, each pontoon is free to oscillate vertically, independently of the other, and of course they both move up and down with the movement of the waves so as to absorb their motion and minimise its translation into movement of the tower.

As the tower leans to one side, the top of the tower will of course push down on the pontoon on that side, hence compressing the pistons supporting it as resistance is met with its Buoyant Force. In response, the gas inside these pistons will pressurise, and this increased pressure will eventually serve to push back up against the structure The straight, streamlined, narrow pontoons will, as before, offer this design far superior directionality and ease of tow in comparison to previous designs.

The pistons act as struts, clearly, holding the pontoons onto the structure, but help to slow the movement of the tower down as they are compressed by the upward motion of the waves below.

The tower is attached to its support structure by a single point of fixing at the very top. This means that the tower can simply be dropped out from this position, straight down In being one single unit, with the tower very much rigidly fixed to its pontoons, there is little or no allowance for maintaining the tower’s upright position in the event of a very large wave tilting the whole structure over to one side. Although this is not likely to tip the whole thing over (due to its great width and indeed weight), it will certainly put immense stresses on whichever pontoon the base happens to be pivoting on, and of course its respective pistons.

Again, the length of this system’s pontoons may make steering tricky.

in carrying out its primary function, as it would not be able to stretch or recoils as efficiently.

above, and in turn against the top part of the tower, finally restoring it into its original position. Any submersion that the pontoon experiences during this process will simply add to this effect, because the increased Buoyant Force will also push back up against the tilted tower and hence move back into its upright position.

The piston on the far side, meanwhile, will extend, as the tower lifts away from the water on that side, and the pontoon drops away under its own weight. That pontoon therefore stays in relatively close contact with the surface of the water, in readiness to hold the tower up when it rights itself again. into the water below by way of unfastening a single set of clamps. This means that attachment and deployment of the floatation device from the tower is in fact incredibly easy.

This design has far fewer articulated pin joints than any of the other designs. This is an extremely important attribute that this design exhibits, because such joints are not only complex, but also points of weakness, so by virtue of minimising them here, the overall strength and structural integrity of this pontoon is optimised. As with design five, the positioning of a fixed towpoint may prove to be difficult on account of the large gap between the two pontoons.

As the entire weight of the tower and support structure combined will inevitably be supported by just the four vertical pistons, these will have to be incredibly strong so as to support such great loads.

They will also require some form of triangulated support structure, like slanted struts, ties or triangular webs. Otherwise, they will simply stand as basic, unsupported columns. Being so tall, yet having such a narrow base, this will make them vulnerable to collapsing, bending or toppling.