The `rainflow` module¶

Rainflow counting¶

A module performing rainflow counting

class pylife.stress.rainflow.AbstractRainflowCounter¶

The common base class for rainflow counters

Subclasses implementing a specific rainflow counting algorithm are supposed to implement a method process() that takes the signal samples as a parameter, append all the hysteresis loop limits to self._loops_from and self.loops_to and return self. The process() method is supposed to be implemented in a way, that the result is independent of the sample chunksize, so rfc.process(signal) should be equivalent to rfc.process(signal[:n]).process(signal[n:]) for any 0 < n < signal length.

Todo

write a 4 point rainflow counter
accept the histogram binning upfront so that loop information has not to be stored explicitly. This is important to ensure that the memory consumption remains O(1) rather than O(n).

get_rainflow_matrix¶

Calculates a histogram of the recorded loops

Parameters:	bins (int or array_like or [int, int] or [array, array], optional) – The bin specification (see numpy.histogram2d)
Returns:	H (ndarray, shape(nx, ny)) – The bi-dimensional histogram of samples (see numpy.histogram2d) xedges (ndarray, shape(nx+1,)) – The bin edges along the first dimension. yedges (ndarray, shape(ny+1,)) – The bin edges along the second dimension.

get_rainflow_matrix_frame¶

Calculates a histogram of the recorded loops into a pandas.DataFrame.

An interval index is used to index the bins.

Parameters:	bins (int or array_like or [int, int] or [array, array], optional) – The bin specification: see numpy.histogram2d
Returns:	A pandas.DataFrame using a multi interval index in order to index data point for a given from/to value pair.
Return type:	pandas.DataFrame

residuals¶

Returns the residual turning points of the time signal so far

The residuals are the loops not (yet) closed.

class pylife.stress.rainflow.RainflowCounterFKM¶

Implements a rainflow counter as described in FKM non linear

See the here in the demo for an example.

The algorithm has been published by Clormann & Seeger 1985 and has been cited havily since.

process¶

Processes a sample chunk

Parameters:	samples (array_like, shape (N, )) – The samples to be processed
Returns:	self – The `self` object so that processing can be chained
Return type:	RainflowCounterFKM

Example

>>> rfc = RainflowCounterFKM().process(samples)
>>> rfc.get_rainflow_matrix_frame(128)

class pylife.stress.rainflow.RainflowCounterThreePoint¶

Implements 3 point rainflow counting algorithm

See the here in the demo for an example.

We take three turning points into account to detect closed hysteresis loops.

start: the point where the loop is starting from
front: the turning point after the start
back: the turning point after the front

A loop is considered closed if following conditions are met:

the load difference between front and back is bigger than or equal the one between start and front. In other words: if the back goes beyond the starting point. For example (A-B-C) and (B-C-D) not closed, whereas (C-D-E) is.
the loop init has not been a loop front in a prior closed loop. For example F would close the loops (D-E-F) but D is already front of the closed loop (C-D-E).
the load level of the front has already been covered by a prior turning point. Otherwise it is considered part of the front residuum.

When a loop is closed it is possible that the loop back also closes unclosed loops of the past by acting as loop back for an unclosed start/front pair. For example E closes the loop (C-D-E) and then also (A-B-E).

Load -----------------------------
|        x B               F x
--------/-\-----------------/-----
|      /   \   x D         /
------/-----\-/-\---------/-------
|    /     C x   \       /
--\-/-------------\-----/---------
|  x A             \   /
--------------------\-/-----------
|                    x E
----------------------------------
|              Time

process¶

Processes a sample chunk

Parameters:	samples (array_like, shape (N, )) – The samples to be processed
Returns:	self – The `self` object so that processing can be chained
Return type:	RainflowCounterThreePoint

Example

>>> rfc = RainflowCounterThreePoint().process(samples)
>>> rfc.get_rainflow_matrix_frame(128)

pylife.stress.rainflow.get_turns¶

Finds the turning points in a sample chunk

Parameters:	samples (1D numpy.ndarray) – the sample chunk
Returns:	positions (1D numpy.ndarray) – the indeces where sample has a turning point turns (1D numpy.ndarray) – the values of the turning points

The rainflow module¶

Rainflow counting¶

The `rainflow` module¶