Abaqus FEA
Using Abaqus, I completed a finite element analysis to optimize the curve radius of the two front foils and ensure my fiberglassing plan will yield a foil strong enough to withstand the applied loads. Using Abaqus to perform this testing will save me time and money in developing the foils.
Assumptions Made:
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The foils can be modeled as a shell; in reality they will be foam with fiberglass laid around them. The inner foam will not provide any substantial strength so can be ignored in the study.
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The number of layers of fiberglass can be approximated by increasing the shell thickness. I estimated the thickness of one layer to be .001016 m and concluded that 4 layers of fiberglass will be a reasonable amount, leading to a total shell thickness of .004064 m.
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The connection to the boat can be approximated as a fixed support
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Each foil will be expected to withstand a lift force of 600 N distributed evenly across the submerged portion of the foils
Technical Details
Material Properties used for 12 oz Biaxial Fiberglass in a 45-45 degree configuration:​
E1 = 1.00E+10 Pa
E2 = 1.00E+10 Pa
E3 = 4.00E+10 Pa
E1 = 1.00E+10 Pa
E2 = 1.00E+10 Pa
E3 = 4.00E+10 Pa
G12 = 1.00E+10 Pa
G13 = 1.00E+10 Pa
G23 = 4.00E+10 Pa
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Each foil length was adjusted so the total surface area underwater is the same, regardless of the curve (same lift fore)
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Utilized a quad shaped mesh with a global size of .01 m, each foil has 5195 elements. (One improvement of the study would be to increase the mesh size in the curve area)​
Results
R = .086 m:
R = .386 m (left) vs R =.686 m (right):
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Stress becomes more evenly distributed at higher radii, but the highest stress overall is larger
Max deflection and mises stress plotted against radius
The ultimate stress of my fiberglass is listed at 355.6 Mpa, and a typical yield stress of fiberglass is ~ 150 MPa. All the design choices would be fine for the material properties, however the .086 radius foil would be close to the yield stress. Ultimately, the .286 design is the optimal choice because it is on the lower end of the max stress plot, and has reasonably low deflection. The smaller radius will also be easier to manufacture.
One final conclusion is that strengthening the curved portion, either with a metal support or 3D printed part, would be a good decision. The highest stress is concentrated on the front of the curve in every foil design. Additionally, most of the deflection at the tip of the foil is caused by bending in the curved portion. A strengthened curve will help mitigate both of these issues, without adding unnecessary weight to other parts of the foil