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WEC-Sim / WDRT

WEC Design Response Toolbox (WDRT)
http://wec-sim.github.io/WDRT/
Apache License 2.0
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Doubt on example_fatigue.py #53

Open mmartini1987 opened 3 years ago

mmartini1987 commented 3 years ago

Good morning all, while I appreciate that WDRT is no longer being developed, I would still try to share a doubt I have related to the fatigue calculation example in example_fatigue.py.

My doubt is related to how the 1-year DEL is calculated - starting from the 1-hour DELs.

In line 40 of the code, you sum up the contributions to the 1-year DEL as: 

    Feq_1y = Feq_1y + (Feq_1h[i][j]**m) * N1h * P[i][j]

where N1h is the average number of cycles in 1 hour. I wonder why you don't multiply this by 24 * 365, which is the number of hours in one year, to get the 1-year damage contribution of Feq_1h[i][j].

I came across this doubt when looking at the DEL of 1.04 MN you calculate in the example, which looks a bit low - in 8 out of 9 cells of the scatter diagram (75% of occurrences), the 1-hour DEL is higher than the calculated DEL, which makes me think that the 1-year DEL should be somehow larger than 1.04 MN.

Thanks in advance for your patience and kindness.

Best regards Michele Martini

j-vanrij commented 3 years ago

Yes, I believe you are correct, this example contains an error. Line 40 should be:

Feq_1y = Feq_1y + (Feq_1h[i][j]*m) N1y * P[i][j]

(Which is the same as multiplying it by 24*365, as you’ve noted.)

This would then give ~4.74 MN for the equivalent 1-year load.

Sorry for the error/confusion.

Thanks, Jennifer van Rij