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__author__ = "Vishnu Pradeep"
__maintainer__ = "Johannes Mueller"
import numpy as np
from pylife.rainflow_ext import fourpoint_loop
from .general import AbstractDetector
[docs]
class FourPointDetector(AbstractDetector):
r"""Implements four point rainflow counting algorithm.
.. jupyter-execute::
from pylife.stress.timesignal import TimeSignalGenerator
import pylife.stress.rainflow as RF
ts = TimeSignalGenerator(10, {
'number': 50,
'amplitude_median': 1.0, 'amplitude_std_dev': 0.5,
'frequency_median': 4, 'frequency_std_dev': 3,
'offset_median': 0, 'offset_std_dev': 0.4}, None, None).query(10000)
rfc = RF.FourPointDetector(recorder=RF.LoopValueRecorder())
rfc.process(ts)
rfc.recorder.collective
Alternatively you can ask the recorder for a histogram matrix:
.. jupyter-execute::
rfc.recorder.histogram(bins=16)
We take four turning points into account to detect closed hysteresis loops.
Consider four consecutive peak/valley points say, A, B, C, and D If B and C are
contained within A and B, then a cycle is counted from B to C; otherwise no cycle is
counted.
i.e, If ``X ≥ Y AND Z ≥ Y`` then a cycle exist ``FROM = B`` and ``TO = C``
where, ranges ``X = |D–C|``, ``Y = |C–B|``, and ``Z = |B–A|``
::
Load -----------------------------
| x B F x
--------/-\-----------------/-----
| / \ x D /
------/-----\-/-\---------/-------
| / C x \ /
--\-/-------------\-----/---------
| x A \ /
--------------------\-/-----------
| x E
----------------------------------
| Time
So, if a cycle exsist from B to C then delete these peaks from the turns array
and perform next iteration by joining A&D else if no cylce exsists, then B would
be the next strarting point.
"""
[docs]
def __init__(self, recorder):
"""Instantiate a FourPointDetector.
Parameters
----------
recorder : subclass of :class:`.AbstractRecorder`
The recorder that the detector will report to.
"""
super().__init__(recorder)
[docs]
def process(self, samples, flush=False):
"""Process a sample chunk.
Parameters
----------
samples : array_like, shape (N, )
The samples to be processed
flush : bool
Whether to flush the cached values at the end.
If ``flush=False``, the last value of a load sequence is
cached for a subsequent call to ``process``, because it may or may
not be a turning point of the sequence, which is only decided
when the next data point arrives.
Setting ``flush=True`` forces processing of the last value.
When ``process`` is called again afterwards with new data,
two increasing or decreasing values in a row might have been
processed, as opposed to only turning points of the sequence.
Examples
--------
>>> from pylife.stress.rainflow.recorders import FullRecorder
>>> detector = FourPointDetector(recorder=FullRecorder())
>>> (
... detector
... .process([1, 2], flush=False) # flush=False → 2 not a turning point
... .process([3, 1])
... .recorder.collective
... )
Empty DataFrame
Columns: [from, to, index_from, index_to]
Index: []
>>> detector = FourPointDetector(recorder=FullRecorder())
>>> (
... detector
... .process([1, 2], flush=True) # flush=True → 2 is considered a turning point
... .process([3, 1])
... .recorder.collective
... )
from to index_from index_to
0 2.0 3.0 1 2
Returns
-------
self : FourPointDetector
The ``self`` object so that processing can be chained
"""
samples = np.asarray(samples)
residuals = samples[:1] if self._residuals.size == 0 else self._residuals[:-1]
turns_index, turns_values = self._new_turns(samples, flush)
turns_np = np.concatenate((residuals, turns_values, samples[-1:]))
turns_index = np.concatenate((self._residual_index, turns_index.astype(np.uintp)))
(
from_vals,
to_vals,
from_index,
to_index,
residual_index
) = fourpoint_loop(turns_np, turns_index)
self._recorder.record_values(from_vals, to_vals)
self._recorder.record_index(from_index, to_index)
self._residuals = turns_np[residual_index]
self._residual_index = turns_index[residual_index[:-1]]
self._recorder.report_chunk(len(samples))
return self