pyyeti.rainflow package¶

Module contents¶

Provides C and straight Python modules for rainflow cycle counting.

A higher level interface (which uses the fast C version if available) is provided in module pyyeti.cyclecount.

Submodules¶

pyyeti.rainflow.c_rain module¶

This module provides an interface for rainflow counting in C.

pyyeti.rainflow.c_rain.rainflow()¶

Rainflow cycle counting, compiled C version.

Usage:

rf = rainflow(peaks, getoffsets=False)

Parameters:

peaks (1d array_like) – Vector of alternating peaks (as returned by pyyeti.cyclecount.findap(), for example)
getoffsets (bool; optional) – If True, the tuple (rf, os) is returned; otherwise, only rf is returned.

Returns:

rf (2d ndarray) – n x 3 matrix with the rainflow cycle count information [amp, mean, count]:
- amp is the cycle amplitude (half the peak-to-peak range)
- mean is mean of the cycle
- count is either 0.5 or 1.0 depending on whether it’s half or full cycle
os (2d ndarray; optional) – n x 2 matrix of cycle offsets [start, stop]. Only returned if getoffsets is True. The start and stop values are:
- start is the offset into peaks for start of cycle
- stop is the offset into peaks for end of cycle

Notes

This algorithm is derived from reference [1] and is very fast. The plain Python version uses the same logic.

References

Examples

Run the example from the ASTM paper:

>>> from pyyeti.rainflow.c_rain import rainflow
>>> rainflow([-2, 1, -3, 5, -1, 3, -4, 4, -2])
array([[ 1.5, -0.5,  0.5],
       [ 2. , -1. ,  0.5],
       [ 2. ,  1. ,  1. ],
       [ 4. ,  1. ,  0.5],
       [ 4.5,  0.5,  0.5],
       [ 4. ,  0. ,  0.5],
       [ 3. ,  1. ,  0.5]])

With offsets:

>>> rf, os = rainflow([-2, 1, -3, 5, -1, 3, -4, 4, -2],
...                   getoffsets=True)
>>> rf
array([[ 1.5, -0.5,  0.5],
       [ 2. , -1. ,  0.5],
       [ 2. ,  1. ,  1. ],
       [ 4. ,  1. ,  0.5],
       [ 4.5,  0.5,  0.5],
       [ 4. ,  0. ,  0.5],
       [ 3. ,  1. ,  0.5]])
>>> os
array([[0, 1],
       [1, 2],
       [4, 5],
       [2, 3],
       [3, 6],
       [6, 7],
       [7, 8]]...)

pyyeti.rainflow.py_rain module¶

Plain Python version of the rainflow algorithm. Numba (numba.jit(nopython=True)) is used if available to achieve speeds comparable to the compiled-c version.

pyyeti.rainflow.py_rain.rainflow(peaks, getoffsets=False)[source]¶

Rainflow cycle counting in plain Python (slow).