This was a group project with Chantelle Hamilton and Maryam Aghajani. The point was to design a structure with 7m or more clear span, based on a natural structure. We chose lilypads, specifically the Victoria Amazonica, which is strong enough to hold up small children. We called our structure Lilivoltaiq because it is a solar collector in addition to being a floating pavilion that can be used for picnics or enjoying views over the water.
The model was made with plastic transparencies, two gauges of wire, a flexible plumbing connector, and glue. The materials were chosen as much as possible to scale with the real-life materials that would have been used: molded 1/8″ polycarbonate, 1″ and 2″ stainless steel pipe, thin-film solar cells, glue, electrical wire, and likely a battery pack.
Lilivoltaiq would have had an electrical core of some kind to take the power coming in from the solar cells, and send it down the cable anchoring it to shore and the electrical grid. The ribbed underside imitates the structure of the actual lilies, and provides structural strength. The peaks are inspired by the crinkliness of the unfurling leaves, and increase the solar collection surface and the possible angles it can catch sun at.
To promote the project, we created this poster that diagrams the physical forces that support the structure, and explains its purpose. Chantelle and Maryam built the model while I drew the diagrams and designed the poster. Given how fiddly the model was to build, I think they had the lion’s share of the work on the deliverables.
Fun with Physics
Of course, none of this would be any good if Lilivoltaiq couldn’t float, so before building our model, we researched materials and calculated weight, buoyancy, and load. Since 1/8″ polycarbonate has a tensile yield strength of 8990 psi (versus a load of perhaps 9 psi), we could have eliminated the steel ribbing entirely. We kept it because our professor and we were enchanted with making such heavy material float, and it related Lilivoltaiq to the lilypad. The steel pipe likewise is much stronger than required. 1
Now that we knew it wouldn’t crack under the load, the question was whether it would float. Buoyancy is the tendency of water and other fluids to press upwards against objects (partially) immersed in them. In our case, if Lilivoltaiq displaces at least as many kilograms of water as it itself weighs, then it will float.
Lilivoltaiq weighs 553 kg. Happily for us, water is heavy. With only its ribbing submerged, Lilivoltaiq displaces 745 kg of water, and will float like, well, a lilypad. And thanks to its 30cm rim (also borrowed from the original), it can safely support an extra 9773 kg on top of its own weight, and still have 5cm of clearance to avoid swamping.
- This paper found that a steel pipe with 7.9 mm (0.311″) walls and 609.6 mm (~24″) outside diameter could take 100-200 kN of load before bending so much as 2.5 mm (0.1″). That pipe likely had a bursting pressure around 2000 psi. Our 1″ and 2″ pipe had burst strength of 7414 psi and 4105 psi respectively, so it should be fine with a mere 4 or 5 kN of load on it. ↩