Finite Element Analysis Two wind loading cases were considered for the analysis of the stand. The loading of the wind turbine assumed that the entirety of the wind was deflected out and around the wind turbine, which overestimates the total force on the blades of the turbine. The wind speed of 25 m/s corresponds to the highest average sustained wind speed per year based on Rochester, NY conditions at a height above the ground of 3 m. The second case assumed a wind speed of 70 m/s, which is the survival wind speed of the turbine. The SolidWorks stand model was imported into ANSYS workbench. The material properties were gathered from the materials library in SolidWorks. Galvanized steel pipe was used for the upright pole while ductile iron pipe was used for the base legs. Properties can be seen below. Galvanized Steel Ductile Iron Property Val ue Units Property Val ue Units Elastic Modulus 200 GPa Elastic Modulus 120 GPa Poisson's Ratio 0.2 9 Poisson's Ratio 0.3 1 Density 787 0 kg/ m^3 Density 710 0 kg/ m^3 Tensile Strength 356 MPa Tensile Strength 861 MPa Yield Strength 203 .9 MPa Yield Strength 551 MPa The loading of the stand is shown below. The loading from the wind was calculated as follows: F = ρ * V 2 * A The blade area was found from the following equation: A = Blade Length * Blade Width * cos (45) * 3
Transcript
Finite Element Analysis
Two wind loading cases were considered for the analysis of the stand. The loading of the wind turbine assumed that the entirety of the wind was deflected out and around the wind turbine, which overestimates the total force on the blades of the turbine. The wind speed of 25 m/s corresponds to the highest average sustained wind speed per year based on Rochester, NY conditions at a height above the ground of 3 m. The second case assumed a wind speed of 70 m/s, which is the survival wind speed of the turbine.
The SolidWorks stand model was imported into ANSYS workbench. The material properties were gathered from the materials library in SolidWorks. Galvanized steel pipe was used for the upright pole while ductile iron pipe was used for the base legs. Properties can be seen below.
Galvanized Steel Ductile Iron
PropertyValue Units Property
Value Units
Elastic Modulus 200 GPa Elastic Modulus 120 GPaPoisson's Ratio 0.29 Poisson's Ratio 0.31Density 7870 kg/m^3 Density 7100 kg/m^3Tensile Strength 356 MPa Tensile Strength 861 MPa
Yield Strength203.
9 MPa Yield Strength 551 MPa
The loading of the stand is shown below. The loading from the wind was calculated as follows:
F = ρ * V2 * A
The blade area was found from the following equation:
A = Blade Length * Blade Width * cos (45) * 3
A blade length of 65 cm and an average blade width of 5 cm were assumed based on specifications.
For the first case, a moderately heavy wind speed of 25 m/s was assumed.
A = .65 m * .05 m * cos(45) * 3
A = .069 m2
F = (1.22 kg/m3) * (25 m/s)2 * (.069 m2)
F = 52.97 N
The same loading model was applied for this 70 m/s wind speed below.
F = (1.22 kg/m3) * (70 m/s)2 * (.069 m2)
F = 412.48 N
The wind loads were placed horizontally at the top of the tower. The weight of the turbine was assumed at 100 N and also placed at the top of the stand pole. Two loading conditions were analyzed with respect to orientation of the wind relative to the legs of the stand. The first orientation condition considered the wind profile parallel to one leg of the stand, where the second orientation condition analyzed the wind profile at 45 degrees to the legs of the stand. The results will follow later in the analysis report, but the orientation did not make a substantial difference in forces or displacements of the stand.
The model was set up using extension springs as the cables. The model attaches the cables at the union between the two sections of vertical pole to each of the eye hooks welded to the legs. Note that only two cables were modeled rather than all four. The cables do not contribute any compressive strength to the model, and the two cables modeled are the ones that would act in tension during the wind and force orientations used.
In the model, the legs of the stand were assumed as fixed to the ground. This allows the viewing of the stress concentration at the point where the vertical shaft of the stand attaches to the flange at the base.
For the case of the wind speed of 25 m/s, the maximum stress over the two orientation scenarios was 21.79 MPa, compared to the yield strength of 203 MPa. This maximum value occurred at the location on the vertical pole at the point where the cables attach in the 45 degree orientation case. The model then indicates that for a moderately heavy wind, the stand should not see stresses close to yield. The stress corresponded to a maximum displacement of .00799 m at the top of the stand. Plots for loading conditions, von Mises stresses, maximum von Mises stress location and total displacement can be seen in the figures below.
For the case of the wind speed of 70 m/s, the maximum stress over the two orientation cases was 171.39 MPa, seen at the mounting point of the supporting cables, slightly lower than the yield strength of the material of 203.9 MPa. This was seen in the 45 degree orientation case. This indicates that our model suggests the stand would survive the survival wind speed of the turbine. The model also over exaggerates the force on the turbine blades. This stress correlates to a maximum displacement of .062 m, seen at the top of the stand. Plots for loading conditions, von Mises stresses, maximum von Mises stress location and total displacement can be seen in the figures below.
