I’m currently doing a modal analysis of a 63m tower. I used the program Modes v.2.2 to calculate the modes. Below the input for Modes.
[code]False Blade Switch: True = Blade, False = Tower
0.0 Steady state angular velocity of rotor (rpm) [Ignored for towers]
0.0 Pitch angle for blades (degrees) [Ignored for towers]
63.0 Total beam length (m)
0.0 Rigid beam length (m)
28850.0 End mass (kg)
5 Number of modes shapes or coefficients
2 Order of first coefficient
10 Number of input stations for distributed parameters
1.0 Factor to adjust mass
1.0 Factor to adjust tower stiffness
1.0 Factor to adjust in-plane stiffness [Ignored for towers]
0.00E+00 1.8797984E+03 6.4919605E+10
1.11E-01 1.7732607E+03 5.4495781E+10
2.22E-01 1.3267888E+03 3.2870718E+10
3.33E-01 1.1738875E+03 2.2766165E+10
4.44E-01 1.0259185E+03 1.5197022E+10
5.56E-01 8.8288178E+02 9.6859372E+09
6.67E-01 8.5328798E+02 8.7442928E+09
7.78E-01 7.0137313E+02 5.9951282E+09
8.89E-01 5.0270006E+02 2.7937987E+09
1.00E+00 6.4997856E+02 3.1947576E+09
For the lines of distributed parameters, the first column is the fractional
distance along the flexible portion of the tower. It must go from 0 to 1.
The second column is the mass/length in kg/m, and the third column is the
stiffness in N m^2.[/code]
Output of Modes:
[code] Shape 1 Shape 2 Shape 3 Shape 4 Shape 5
------- ------- ------- ------- -------
Freq (hz) 0.4459 2.8752 8.0611 19.6116 26.3147
x^2 0.5963 -15.8018 48.2225 -621.2538 631.6574 x^3 -0.1676 8.9338 327.6914 3204.8274 -4760.0376 x^4 1.7325 -32.1423 -1542.1295 -5478.7134 12354.1416 x^5 -1.4457 82.9072 1838.8284 3606.8958 -13313.1475 x^6 0.2845 -42.8969 -671.6127 -710.7558 5088.3857[/code]
I’m trying now to compare now the shapes 1&2 with a simple MATLAB script that I wrote. The first and second frequencies look very plausibel and the discrepancy between both models are very low.
My problem occurs when I want to plott them. I’m plotting with Matlab the shapes with the polynomial functions:
And I get the following functions:
For comparison I scaled the x-axis with my model but still the shapes don’t look right.
I already looked up to BModes but I didn’t find something that could help me to plot them right. Am I missing some correction factor or something similar?
Thank you in advance!!