Evaluation

EVALUATION

The success of the project may be assessed from two perspectives: the design itself, and the actual process of getting there.

Technical Evaluation of the Design:

Strengths:

Largely, the strengths of the design have been made clear from the outset: they were discussed in depth in the table of initial ideas, and were therefore the very attributes that led us to the selection of this design in the first place. However, the physical testing process of our representative model has of course confirmed some of these strengths, whilst negating others. To summarise, the revised appraisal is as follows:

• The structure is effective in holding the tower in the upright position • It provides a degree of spring-back stability (self-righting) when the tower is tilted to the left or to the right, but is not quite as effective when tilting the tower forwards or backwards • The hydro-dynamically-streamlined pontoons make towing and manoeuvring the tower a relatively easy task • The framework can be both attached to and removed from the tower very quickly and easily • The design makes provision for adjusting the height of the framework relative to the tower, as per requirement, depending on the conditions of the North Sea at the time of launch • The structure is simplistic, and therefore quick and easy to construct, making it ideal for the production and deployment of large numbers of towers to various locations on the North

Sea • The testing process incidentally gave us the opportunity to devise an effective tow-point strategy, which had of course not been determined prior to this. It works such that the stability of the tower during the towing process may be maximised. The tug is attached to the tower by four individual tow-lines: one to each side of the very top part of the pontoon structure, and one to the bottom of each of the pontoons. With this arrangement, tension in the tow-lines therefore acts both above and below the pivot point on the surface of the water, hence culminating in both clockwise and anti-clockwise moments. These effectively cancel each other out, meaning the tower has the inclination to neither lean backwards, nor forwards.

DIAGRAM DEPICTING TOWING

Source: Primary Creation

Created: April 7th 2012

Weaknesses:

• Instability of the Tower:

As much as the floatation device is successful in keeping the tower upright, it is an extremely delicate system, and the slightest bit of turbulence has the potential to knock the whole thing over. This instability was most profound when acting forwards and backwards, as the tower was most prone to toppling this way (though the system was, in fairness, actually quite stable when moved from side to side, as aforementioned). In leaning back or forth like this, one end of the pontoon would be submerged, while the other would lift out of the water, and once tilted, even by a small angle, the tower would topple completely. Contrary to this, we were really hoping more for it to be able right itself automatically if tilted by a wave, rather than simply keep falling until it hit the surface. This brings our attention to the fact that the floatation device may not be as successful as it may have at first seemed: if this were the real thing, it would stand next to no chance at all of being able to handle the brutal action of the North Sea’s waves and 30 mph winds.

One improvement that was put forward to this end, with the view to alleviating this shortcoming, was to lengthen the pontoons by at least 25% at each end (though this would of course require essential testing before this figure can be quoted for certain).

This suggestion was made, because we knew it would help not only to increase the magnitude of the Buoyant Forces produced by the pontoons (simply because they would displace more water), but also mean forces these being exerted further away from the central pivot, hence amplifying the Turning Moment created in a double sense, and in turn maximising the effect they have of pushing the tower back into its upright position.

True enough, this would be an effective solution, at least to some extent, but what would be equally as effective, albeit for different reasons, would be to provide the tower with an all-round stability, such as that provided by the circular pontoon structures featured in the first three designs. Although hydro-dynamic streamlining was a key requirement for this project, equally so is the provision of stability in all directions, but what we wish to achieve is both. Therefore, in order to evade such implications as drag, bow waves and difficulty of steering, which are intrinsic to circular pontoon designs, it may be worth developing the parallel pontoons from before to such a point where they can provide this omni-directional stability themselves. To this end, a number of pontoon shapes could be tested:

POTENTIAL PONTOON SHAPES

Source: Primary Sketch

Created: March 29th 2012

• Rigidity of the Unified Structure:

The tower and floatation device, collectively as a single unit, together form a very rigid structure. Therefore, the slightest movement in one part of the system will manifest in a similar movement in every other part of the structure as well. This will surely pose a significant problem, in so much as there is no provision whatsoever for keeping the tower upright in the event of the pontoon being tilted by a large wave. If we take a moment to consider a point accentuated previously, in relation to the Turning Moments produced by the tilting of the tower, this attribute will prove to be extremely problematic.

Therefore, such that this implication may be resolved, one possible solution may be to fix the pontoon’s support structure with more of a loose fitting, in which the tower is held in place, but is free to swing, on a single pin joint, in any direction within the structure’s enclosure. If supported in this manner, the tower will be free to adopt an upright vertical position, even if the pontoon support structure is forced to contort into a different angle. This will help the tower to maintain its stability by keeping the Centre of Mass within as close a proximity to the central pivot point as possible, and hence reducing the magnitude of Turning Moments produced by the tower’s weight during a tilt.

Having said that, this would inevitably lead to some fairly prominent complications, particularly from a structural point of view. Needless to say, there would certainly be significant difficulties transpiring in the design of a pin joint that can not only handle gargantuan sheer stresses, in excess of 37 MN, but also stand up to enormous torsional stresses at the same time, and still maintain freedom in the joint’s movement. The pin would also need to resist intense wear from high-magnitude frictional forces.

• General Solution Through Suggested Design Change:

Instead, therefore, it would certainly be an appropriate solution to build a more robust, effective articulation system into the existing parallel pontoon design we already have in place. This would be useful, because it would remain in keeping with the design features we already have in place, whilst building upon its as yet decidedly limited effectiveness, by affording it the degree of flexibility just mentioned. Moreover, by virtue of adhering to the use of parallel, hydro-dynamically-streamlined pontoons, this solution would also maintain the previous design’s directionality, minimal drag and ease of steering. One way in which this could be achieved would in fact be quite similar to the first design idea put forward, as shown.

ALTERNATIVE PONTOON DESIGN

Source: Primary Sketch

Created: March 28th 2012

As can be seen from the diagram, the use of two parallel pontoons is continued, but connected at the ends (to the central tower) by four very strong, robust pneumatic pistons, with two of them to each pontoon. The system of articulation that this provides is therefore much more reliable than the minimal number of tenuous pin joints mentioned before. In addition, the compressibility of these pistons, apart from enabling the tower to uphold its vertical standing position as required, also helps to absorb the shocks and impacts of persistent wind and wave attack whilst out on the North Sea.

Alternatively, design idea 2 could well be used to much the same effect. However, the major drawback with this design is the use of the circular pontoon. Whilst this does certainly offer excellent all-round stability, perhaps in such a way that cannot really be beaten, the width of the design poses tremendous difficulties to the towing process, due to high levels of drag, considerable wake (bow waves) and difficulties in steering the thing!

• Provision for Pistons Over-Heating:

Had we included the compressible pistons that were initially put in the design work to begin with, these would have enabled the model to absorb any shocks exerted by ripples during the testing, (hence reducing the likelihood of the structure toppling over when buffeted in this way), just as they are intended to in the context of the real tower. However, the very design of these pistons was incidentally another particular point of weakness in this project. As disclosed at a previous stage, pressurisation of the gas inside these pistons will, after repeated compressions, make them extremely hot. With no designed system with which to keep them cool, this will inevitably lead to physical and structural failure of the metals used in their construction.

That said, the wind and sea water would certainly contribute to the cooling effect anyway, but to aid it, the simple solution would be to conceive a basic coolant system that would help to draw excessive heat away from the piston and hence optimise their function. For example, radiating fins could be made to shroud the outside of the outer piston-sleeves. The large surface area that these would provide would help to dissipate heat quickly, but could also be complemented by coating these in a smooth, shiny and therefore highly radiant surface. In addition, if these fins were made hollow, the cavity inside could be filled with Ammonia gas, whose high Specific Heat Capacity and Thermal Conductivity would enable it to conduct excess

DESIGN #2, FEATURING CIRCULAR PONTOON

Source: Primary Sketch

Created: November 29th 2011

thermal energy down the Temperature Gradient (from the surface of the hot piston to the cold adjacent air) very quickly and efficiently. This would be a suitable alternative to lubricants, hence evading the risk of them being washed away by the sea-water. That said, it may well be that, because of intense levels of friction in the pistons, a lubricant is not something that can be avoided anyway, and so, the Ammonia-storing fins may well have to simply accompany a lubricant, rather than replace it.

Evaluation of the Team & Design Procedure:

Strengths:

One thing we felt was done particularly well throughout the project was the delegation and sharing of tasks. This had two main benefits. Firstly, it enabled us to manage time very successfully. Tasks could be done simultaneously, and so, with more than one thing getting done at once, tasks were completed much more quickly than they would have been had each one had to wait until the completion of the previous. This was in fact complemented by the individual, personal organisation of members of the team. By filling in the GANTT Chart regularly, and taking down minutes of each meeting in a permanent record, we were able to keep a constant eye on the project’s progress, as well as foresee that which had to be completed next. One example of where this was of particular benefit to us was in the few weeks leading up to the Residential Visit in December. Forward planning of what we were aiming to get done by the end of the trip meant that we were able to get straight on with it once we arrived, and also that no time was wasted at the start in thinking about what we were going to try and achieve.

Secondly, this principle of task delegation also made extremely effective and suitable use of different people’s skills, so as to ensure that each task was completed to the best quality it possibly could. For example, editorial and presentational tasks were given to Oliver, on account of his excellent graphical skills, while the practical skills offered by Adam and Owen meant that they both had a considerable part to play in the manufacture of the test model, the outcome of which was in consequence notably successful. If, on the other hand, we had attempted to get every single person directly involved in each and every single task, the whole project would have descended into anarchy. Many tasks only require one person to do them for example, and can in fact be hindered by the intervention of others. Completing the technical drawings is a good example of this.

That said, there are, on the other hand, numerous examples of tasks that cannot be completed by one person alone, and full team participation is therefore required. Whenever this came to be the case, we displayed good team-working skills, such that the task could be completed effectively. For example, when we went about testing the tower in a swimming pool, all four of us got stuck in from the word go, and maintained thorough participation throughout, until we had finished. Whilst I was in the pool handling the model, Adam and Owen set about towing it across the surface and providing external control via the tow-lines, and Oliver went about recording the results and taking photographs.

So, in summary, the team performed well throughout the course of the project, collaborating well with a common goal, to accomplish which we all shared the same strive, which undoubtedly lead us to a successful outcome.

Weaknesses:

To start off with, there were a number of things that we actually overlooked in the course of the project, and could certainly have paid more attention to if we were looking to improve the outcome of our project:

• Rate of fill and rate of sinking • Bedding the tower down on the sea floor • Clamping the pontoon structure to the tower • Design of the valves

That said, we felt as a team that, by overlooking these areas in this way, we did not necessarily have a detrimental impact on that outcome. We had a direction in our project, in which we chose to focus specifically on the stability of the tower during the towing process. Rather than briefly addressing everything, we opted instead to focus more specifically on one particular aspect, and assess the design’s capabilities within this area to a greater level of detail than would otherwise be feasible.

Nonetheless, if we had tested all aspects of the brief, we could certainly have obtained a broader and therefore (arguably) more insightful understanding of the capabilities of our design. For example, it is all well and good perfecting the tower’s capability of being towed, but if it hits the sea bed with such impact that it breaks, there is little use in this. As such, it is clear that one of the team’s most rudimentary shortcomings was the quantity of crucial information that we overlooked, which potentially hindered us in the quality of our proposal and write-up.

However, if we had gone down this route, and tried to assess everything we possibly could, we inevitably would have sacrificed the level of detail with which we could address each one. Working in the way we did enabled us to ensure a very thorough scrutiny of the aspect we chose to study, and hence ensure that it was designed to work in the best way it possibly could be. Surely, this is more beneficial than having lots of features that only partially work, because it reduces the need for returning to certain areas at a later stage to iron out the flaws. We therefore believe, as a team, that this was not to detriment us very much at all in the grand scheme of things, and in fact seemed to have more positive effects than it did negative ones.

On the other hand, one prominent blow we did take to the ultimate quality of our outcome was related to the accuracy with which the physical aspects of the project (that is, construction and testing of the model) were actually realised. Whilst on the Residential Workshop, a decidedly limited availability of material resources had the unfortunate consequence that not every part of the model could be kept to the correct, required scale. For example, in being made on a 1:100 scale, the top part of the tower ought to have had a diameter of 80 mm, but in reality turned out to be over 100 mm, simply because we couldn’t find any 80 mm PVC pipe! The obvious effect of this was to have a detrimental impact on the accuracy with which the model emulated the weight distribution of the real thing. This we endeavoured to overcome, through use of the weight ratio seen previously, which mandated that the bottom half of the tower was to be 8.74 times the weight of the top half. In knowing that the linear scale factor of the model was ideally 1:100, we were able to determine that the volume scale factor was 1:1000000 (the

cube of the linear scale factor). As the mass, and in turn the weight, are both directly proportional to the volume, it was also possible to ascertain that the mass and weight scale factors were also 1:1000000, meaning that the model ought to be 1000000 times lighter than the model. This of course also applies individually to the two separate halves, and so by using the weight ratio and the weight scale factor in tandem, we used mass loadings of steel and aluminium to ensure that the accuracy of the weight distribution was restored. That said, a limited availability of resources once again made it extremely difficult to ensure that that was done accurately as well; after all, imagine trying to machine a block of steel to exactly 274.379…… g!

But our troubles of inaccuracy did not stop there. In being so much more voluminous than it should have been, the tower also had the problem of displacing too much water for a given submersion, when trying to represent that of the real thing. As such, it could be argued that the buoyancy of the model was too great, but again, the inaccurate weight distribution from before would make it hard to say for sure. As before, therefore, a simple matter of paying even more attention to details during the construction process would be effective in resolving this issue.

Moreover, the actual process of testing could itself have been more accurate. For one, although we took repeats of the tests, time constraints limited this to less than we would have liked. This undoubtedly impinged on the range and reliability of the results attained, because the consequently limited sample range would have hindered our ability to spot continued trends, variations within these trends, or even identify anomalous results.

To add to this, our selection of numerical, quantifiable, or even comparable data, with which we could have drawn graphs or charts, was limited. Rather, we made visual observations of the tower’s behaviour in the water and passed qualified comments in response, exposing us to such issues as subjectivity and ambiguity in the data. The obvious effect that this would have inflicted is to impede us from having been able to make clear comparisons between different floatation and towing methods, as to which was the most effective. This also made it even more difficult for us to spot anomalies, or even take averages of repeated tests. As such, it is hard for us to be certain as to whether or not the decision we have made is truly the best: in essence, our results are incomplete, and potentially less accurate than wouldhave been preferred.

This was, of course, only exacerbated by the lack of precision in the equipment we used. For example, we had no way of determining: the angle to which the tower could be tilted before it toppled, the speed at which the tower could befeasibly towed in order for it to remain stable, or the time taken for the tower to fall from upright to horizontal. Furthermore, the precision of the ruler we used to measure the height of the floats and the submersion depth of the tower, and the jug used to determine the volume of water present inside the tower, also had a limited degree of precision.

It is also plausible to say that the validity of our experiments was hindered too, simply because we often changed more than one variable (including float-height, position of the tow-point and mass of the water inside the tower) at a time, based on what we had observed in previous tests, rather than testing the tower in all possible combinations these three variables. The consequence of this is that there are potentially very effective arrangements or solutions that we overlooked. For example, it could well be that, by positioning the floats right at the very top of the tower, with the tower itself filled with a much larger mass of water than previously tested

so as to submerge it very deeply, the system could have operated much more effectively. But then again, who knows?

From this, it is therefore clear that essential improvements could, and in fact should, be made to the physical construction and testing aspects of the project by any or all of the following:

• Fabricating a more accurate model, by sourcing materials that are more appropriate and suitable to our specific design requirements. This would help make both the tower’s buoyancy and its weight distribution more accurate, and also easier to keep it that way. • Carry out a broader sample range of tests, with more repeats of each test so as to improve reliability and accuracy • Plan the tests so as to obtain numerical, quantifiable data with which to enable clear comparisons, identification of anomalies, drawing of graphs and calculating of averages • Enforce better control of appropriate variables in order to improve validity • Employ a broader range of more sensitive equipment, hence improving precision, but also enabling testing of a greater range of trends and correlations.

Lastly, we did actually suffer quite a significant drawback when it came to completing all the tests we wanted, the effect of which was to hinder us from sinking the tower in a controlled manner. As such, we were unable to test the rate of fill or the rate of sinking for the tower. The actual problem was that the silicone acetate seal that lined the base of the model broke! This, we suspect, resulted from a combination of the weight of the water stored inside the tower at the time, and the stresses exerted whilst attempting to remove the framework from it, and consequently led to an uncontrollable leak of water from inside. In view of the time constraints, and the presence of other,more pressing priorities, such as completing the write-up, we decided as a team not to try and mend it so that we might have continued testing. By this point we felt we had just enough data from which to be drawing reasoned conclusions, so getting any more was not entirely necessary, although desirable.

Summary:

To conclude, we feel as a team that we have been predominantly successful in our approach to the project as a whole, and certainly displayed a good level of teamwork when it came to getting things done. Although we did not conceive a design solution that was 100% successful at performing its intended role, we believe that our scientific methods, and approach to designing, predicting and testing outcomes was appropriate, and certainly helped bring our attention to the reality of that which we were intending to design (that is, the fact that it didn’t work!).

The four of us have certainly enjoyed partaking in the Engineering Education Scheme, and the principles it has taught us with regards to the world of engineering will certainly remain with us for years to come.

The success of the project may be assessed from two perspectives: the design itself, and the actual process of getting there.