Slow Fault Tree Analyser (SFTA)
Project description
Slow Fault Tree Analyser (SFTA)
A slow (also shitty) fault tree analyser inspired by the idea presented in:
- Wheeler et al. (1977). Fault Tree Analysis Using Bit Manipulation. IEEE Transactions on Reliability, Volume R-26, Issue 2. <https://doi.org/10.1109/TR.1977.5220060>
Text-driven
SFTA reads a textual representation of a fault tree. For example:
- time_unit: yr
Gate: FB
- label: Conway causeth floor to be buttered
- type: OR
- inputs: BF, TFBSD
Event: BF
- label: Conway knocketh butter onto floor
- rate: 0.1
Gate: TFBSD
- label: Conway knocketh toast onto floor butter side down
- type: AND
- inputs: TF, TB, BSD
Event: TF
- label: Conway knocketh toast onto floor
- rate: 0.2
Event: TB
- label: Falling toast is buttered
- probability: 0.75
Event: BSD
- label: Buttered toast landeth butter side down
- probability: 0.9
This allows for sensible diffing between two versions of a fault tree.
Output
Output consists of:
- an events summary,
- a gates summary,
- cut set listings, and
- SVGs for all top gates and paged gates.
For the example above, we get the following SVG for the top gate FB
:
Limitations
-
Only supports coherent fault trees, which have only AND gates and OR gates.
-
The probability or rate for a gate is approximated by simply summing the contributions from each minimal cut set (rare event approximation). The higher-order terms (subtraction of pairwise intersections, addition of triplet-wise intersections, etc.) have been neglected. This is conservative, as the first-order sum is an upper bound for the actual probability or rate.
Installation
$ pip3 install sfta
- If simply using as a command line tool, do
pipx
instead ofpip3
to avoid having to set up a virtual environment. - If using Windows, do
pip
instead ofpip3
.
Usage (command line)
$ sfta [-h] [-v] ft.txt
Perform a slow fault tree analysis.
positional arguments:
ft.txt name of fault tree text file; output is written unto the
directory `{ft.txt}.out/`
optional arguments:
-h, --help show this help message and exit
-v, --version show program's version number and exit
Usage (scripting example)
from sfta.core import FaultTree, Gate
fault_tree = FaultTree('''
Event: A
- rate: 0.9
Event: B
- probability: 0.7
Event: C
- rate: 1e-4
Gate: AB
- label: This be an AND gate.
- type: AND
- inputs: A, B
Gate: AB_C
- label: This be an OR gate.
- type: OR
- inputs: AB, C
''')
fault_tree.gate_from_id['AB'].quantity_value
# 0.63
fault_tree.gate_from_id['AB_C'].quantity_value
# 0.6301
fault_tree.gate_from_id['AB_C'].input_ids
# ['AB', 'C']
fault_tree.gate_from_id['AB_C'].type_ == Gate.TYPE_OR
# True
License
Copyright 2022–2024 Conway
Licensed under the GNU General Public License v3.0 (GPL-3.0-only).
This is free software with NO WARRANTY etc. etc., see LICENSE.
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