For evaluating system architectures using Reliability Block Diagrams
(Reliability / Safety Analysis)
BFiab is used to model systems as a Reliability Block Diagram (RBD) based on Boolean logic, which produces simple models suited to all domains (aeronautics, automobile, rail, oil & gas, etc.). The BFiab module uses ALBIZIA, the BDD (Binary Decision Diagram) computation engine developed by Total. ALBIZIA offers the advantage of running accurate analytical computations and providing extensive information on the system under study.
Modeling and computations
Users can easily create RBD via an intuitive graphical interface, and enter connectors (in series, in parallel, K out of N) and blocks according to the logic of the system studied and many probability laws (Exponential, Weibull, Gamma-Lambda-Mu, Periodic-Test…).
When the RBD is built, it is easy to distinguish the groups of components subject to common cause failures.
ALBIZIA provides many results:
- Unavailability: Q(t), U(t) or PFD(t), Availability : A(t), Reliability: R(t), Unreliability: F(t);
- Frequency: W(t), UFI(t) or PFH(t);
- Equivalent failure rate: λeq(t), λv(t) or CFI(t);
- Many importance factors (Birnbaum MIF, Critical CIF, Vesely, DIF…);
- Minimal cut-sets;
Specificities and strengths
Computing the time spent in the SIL zones:
In addition to the computations mentioned above, ALBIZIA is the only engine able to compute how long the PFD(t), PFH(t) or EqLambda(t) of a system spends in an interval during its mission period.
The figure opposite shows a mean availability of 8.44E-3, which corresponds to a SIL2. However, it also indicates the percentage of time the system spent in each SIL over its 30-year mission. In this case, 39.77% of its time was spent in SIL1.
Factoring in uncertainties:
To be as close as possible to real conditions, parameter-related uncertainties can be factored in. It is possible, for example, to indicate that a failure rate follows a Uniform, Normal or Log-normal law. A Monte-Carlo simulation is performed in addition to the BDD computation in order to obtain mean values. Finally, a quintile computation is run to provide a dispersion interval on each result.
With the automatic layout function, users can neatly organize their RBD just by pressing on F7. You can quickly duplicate blocks using copy/paste. Each block can have a specific image in order to improve diagram readability. Moreover, you can and comments and curves to build your report directly from the PDF printing.
GRIF evolves each year, taking remarks from users into consideration to make the program more user-friendly and computerize repetitive tasks.
Data exploitation and results
- Synthesis of input data in the form of tables that makes it easier to control the quality of an entry.
- Possibility of automating calculations (batch run).
- Results stored in the same document and exportable in different formats (csv, XML, Excel, etc.).
- Visualization of results as curves, pie charts or histograms.
- Vector printing of graphic elements and curves in PDF format which maintains optimum quality, even in A3 or A2 format.
- Interaction with the operating system: option to copy/paste curves, systems or results to word processing software, spreadsheets or presentation tools.
- RBD can be exported into Fault-Tree
Groups and sub-systems
In addition to the pages that enable you to organize your diagram and make it easier to print, this module enables you to create systems which in turn comprise sub-systems. This notion of hierarchy means that the model can be divided up according to the actual deconstruction of the system. You can add or remove as many inputs/outputs as you want. A preview of the sub-system always appears on the block so that its composition can be seen at all times.
The BFiab module is part of the GRIF-Workshop Boolean package. All the RBDs made with this module can be used in Bool module which gathers all functionalities of Boolean modules. It is possible, in the same document, to make calculations using Event Trees (Etree), Fault Trees (Tree), Reliability Block Diagrams (BFiab) and Safety Instrumented Systems (SIL) together.