Testing

TESTING

All our work and time spent on the project so far was in aim of testing this scale model in similar conditions that the construction would face in the North Sea. However, before we could begin this level of experiment, we had to first test our completed and sealed model on a smaller scale to see whether it would float unaided. There was much dispute among the team’s hypothesis as to the result of this experiment, and after all the bets were taken, we set to work in testing the buoyancy of the model in our very ‘elegantly sourced’ rubbish bin. The aim of this test was to simply find the level at which the base would float and so allow us to know where and how we would have to construct the flotation device which would improve the stability of the base, and would be needed irrespective of the buoyancy.

Therefore, this fairly simple test was a major part of the rest of our testing,and fortunately for us, the next parts of our project were made simpler when we discovered that the model, and thus the scaled up construction, would float at a reasonable level. Quite conveniently we found that the model alone floats so that the water level is 16cm above the base, which is 8m on the real construction, and lies right on a seal, meaning that positioning the floatation device was relatively easier than previously thought. However, the model was unstable and would always topple over unless held upright. This proved the need for a stabilising device as we had already anticipated.

This meant our plans for a floatation device could then be implemented and suited to our model to enable stability in the water. The process of construction of this floatation device meant that we would have to create and estimate the size of the floats before we could work out their effectiveness. A decision was made and the size and material of these floats (Styrofoam) were decided and therefore remained through to the end of the project. This meant we proceeded into the testing phase with a limited number of variables.

• The height of the floatation device • The mass (of water) that the model held so to influence the position that it sat in the water.

The location of the experiments we had chosen to undertake had been decided on the basis of ease of access and to some extent, similarity to the conditions that the real construction would undergo. This meant that a handily located private swimming pool became our experimental ground and site of all further testing on our completed model. Having attached a suitable length of rope to act as our tug, completed a few preliminary runs to adjust the force needed to pull the model and then set up our recording equipment in the form of both camera and video we were ready to proceed.

Aiming for a valid setof results, we implemented our knowledge of the sciences to conduct a reasoned experiment where only one variable changed at a time. This meant that throughout the experiments we tested different masses of water at one height, before changing the height and then repeating said experiment. This order was very much chosen due to the accessibility of the floatation device. Changing the height of such a major component took ill-afforded time,

and would be a greater cause of human error than the regular change in mass. Each variable and interval was tested three times to makesure our findings were reliable. However, we cannot quantify our results for we were not testing against a known scale for stability, thus these results are only our perception of what occurred in the experiment. Although, the outcome is reliable and our preferred choice of variables we remain the same, the perception of the experiment will change for all who participate in it. So, we can qualify our results, and judge them to have met a certain criteria, in this case, stability throughout the experiment, but we cannot quantify our results and set a pattern to them, for as you will see, there are some surprising outcomes. Moreover, this means that the results you see are very limited in their response as there is little more you can perceive about the experiment than whether the model was stable or the rate at which it falls and so once again qualified data is a limiting factor to further analysis.

It must be mentioned though that through this experimental period our ideas of the model developed and we further improved our methods in positioning our ’tug’ to gain the maximum stability from constant variables. These and such other small adjustments can only be made once the model had been completed and used in experimentation for we lacked the experience with such projects to pick up on these details from the start.

There are a few assumptions we have made within our results, since we measured the amount of water added at each intervalin millilitres, we then converted this number into grams. Here, we assumed the water we were using was pure and did not hold any minerals or such materials so that the conversion would mean 1litre = 1kilogram. However, within a realistic situation, salt water would be used, as it is the major source for the construction, so the conversion rate would differ considerably such that 1litre could weight as much as 1.027kilograms11, meaning a reduction in the amount of water needed to create a stable base.

We also started our experimentation where the floatation device was level with the models’ buoyancy level, assuming that moving the floats beneath this would reduce stability and so would be impractical and ill use of time to test. Therefore the results that follow begin where the floatation device is clamped around the central tubing at a height of 50cm from the base (25m on the real model) so that the floats would sit at 16cm (8m) above the base, which is the level at which the model floats.

Waves were simulated both by the movement of the model and by the use of a rugby ball in one corner of the pool so as to keep the wave height small in relation to the model considering

our previous research of such conditions, this allowed us to monitor how well the model moved through these factors and thus assess the stability of motion.

The intervals for our variables were chosen with the precision of our instruments in mind. For example, our measuring jug could only record at a minimum level of 250g so the interval was set by this. Moreover, due to our time constraints we decided to increase the height of the floats by 5cm every time, and by changing this as little as possible we reduced the error in our results. It’s also important to note for our first two tests we had out tugs first attached above the floats then below, and both achieved the same results. This arrangement later changed as mentioned further on.

AT A HEIGHT OF 16CM ABOVE THE BASE

Mass of Water Added (grams) Stability 0 Unstable but moves easily through waves.

250

500

750

1000

More stable however the floats are low inthewaterso the waves affect the motion of the model. Unstable as the floats are too low in the water and the model begins to topple. Unstable and the model falls on entry into the water. Unstable and the model falls on entry into the water.

AT A HEIGHT OF 21CM ABOVE THE BASE

Mass of Water Added (grams) Stability 0 Unstable and falls immediately upon entry into the water.

250

500

1000

1500

2000

Not tested as interval was changed after seeing the previous result(s). Unstable and falls immediately upon entry into the water. Unstable and falls immediately upon entry into the water. Unstable and begins to fall after a force is applied. Unstable and begins to fall after more force is applied.

2500

2750

Stable and floats well under minimal surface conditions. Any sudden movements cause unbalancing and possible sinking. Stable but falls under small force but deals well with surface conditions.

3000

Unstable and falls under small force.

Changes to the Positioning of the Tug

At this point we began to see the affect that the position of the tug was having on the model, so the ropes were adjusted so that two line were attached to each float, one above and one below, so that the force was distributed evenly and provided a more stable tug.

AT A HEIGHT OF 21CM ABOVE THE BASE

Mass of Water Added (grams) Stability 500 Not tested as previous results showed ideal mass.

1000

2000

2500 2750

3000

4000

Unstable and falls immediately upon entry into the water. Unstable and begins to fall after more force is applied. Unstable and falls after movement. Stable and floats well at both a constant velocity and whilst still under rougher surface conditions. Unstable and falls under small force. Sinks immediately

Disaster!

At this point the seal on our construction broke and the model would not hold any water, thus the experiment could not continue for the model had to completely dry before being resealed. However, we believe that we have found from threeseparated experiments that the model is most stable with an added mass of 2750g with the floats positioned 21cm above the base. However, it would be ridiculous for us to say that this is the only solution. For we have not tested all possibilities and entertained all strands of thought about this model but for the variables we have tested, I think we can conclusively say that the model can float with a stable position.