def test_minersum(self):
"""
Test that correct fatigue Miner sum is calculated using bilinear S-N curve.
"""
c_sea = self.sn_c_sea
start, stop = c_sea.fatigue_strength(1e7), c_sea.fatigue_strength(1e5)
srange = np.linspace(start, stop, 20) # stress range histogram
d = 0.5 # target damage
count = np.array([c_sea.n(s) for s in srange]) / srange.size * d
self.assertAlmostEqual(minersum(srange, count, c_sea), d, places=8,
msg="Wrong fatigue life (damage) from minersum()")
def test_minersum_scf(self):
"""
Test that correct fatigue Miner sum is calculated using bilinear S-N curve.
"""
studless = self.sn_studless
start, stop = studless.fatigue_strength(1e7), studless.fatigue_strength(1e5)
srange = np.linspace(start, stop, 20) # stress range histogram
d = 0.5 # target damage (excl. SCF)
scf = 1.15 # stress concentration factor
d_scf = d * scf ** studless.m # damage incl. SCF
count = np.array([studless.n(s) for s in srange]) / srange.size * d
self.assertAlmostEqual(minersum(srange, count, studless, scf=scf), d_scf, places=8,
msg="Wrong fatigue life (damage) from minersum() with SCF specified")
from math import pi
from qats import TsDB
from qats.fatigue.sn import SNCurve, minersum
# load time series
db = TsDB.fromfile(os.path.join("..", "..", "..", "data", "simo_p_out.ts"))
# initiate SN-curve: DNVGL-OS-E301 curve for studless chain
sncurve = SNCurve(name="Studless chain OS-E301", m1=3.0, a1=6e10)
# Calculate fatigue damage for all mooring line tension time series (kN)
for ts in db.getl(names='tension_*_qs'):
# count tension (discarding the 100s transient)
cycles = ts.rfc(twin=(100., 1e12))
# unpack cycle range and count as separate lists (discard cycle means)
ranges, _, counts = zip(*cycles)
# calculate cross section stress cycles (118mm studless chain)
area = 2. * pi * (118. / 2.)**2. # mm^2
ranges = [r * 1e3 / area for r in ranges] # MPa
# calculate fatigue damage from Palmgren-Miner rule (SCF=1, no thickness correction)
damage = minersum(ranges, counts, sncurve)
# print summary
print(f"{ts.name}:")
print(f"\t- Max stress range = {max(ranges):12.5g} MPa")
print(f"\t- Total number of stress ranges = {sum(counts)}")
print(f"\t- Fatigue damage = {damage:12.5g}\n")