WF16: Generate Model-based Functional Fault Tree Analysis

Pre-requisites

• SRA Module: access to the Safety and Risk Assessment (SRA) module enables a Functional Fault Tree Analysis (FTA) to be generated.
• FBD Model: defined with functions and functional flows required to map out Fault Tree paths. Inclusion of failure diagrams would improve detail of Fault Trees (see WF06).
• Reliability Data: consists of RBD groupings, failure values based on a distribution type (Exponential, Weibull, Markov) and duration of operation (inherent from Mission Profile).

Detailed Descriptions (numbered steps)

1. Select 'Analyses' of main menu bar, then 'Fault Tree' then 'Functional' or via right-click context menu opened in the Project Explorer / System model viewer.
2. Define Analysis name (required) and description (optional) of the functional Fault Tree Analysis (FTA).
3. Select a Functional Failure Mode (FFM), from the list, as the top event of the fault tree.
4. Select Fault Tree Options from the dialog:
   • Model-based Analyses – this generates model-based FTA
   • FCM or Bond Propagation type
   • Depth of failure concepts
   • Level of Analysis
   • Preferred Gate Type (OR, AND or K/N)
   • Source for P(f) values
5. Click 'OK' to generate a functional FTA.
6. Select 'Calculate Probability of Failure' button:
   • Select 'Event List' in 'Event Table Controls' to review the events of the functional FTA.
   • Select 'MCSQ' in 'Event Table Controls' to review the generated minimum cut set sequences of the functional FTA.
   • Select 'RI% Ranking' in 'Event Table Controls' to review the Relative Impact (RI) of the basic events of the functional FTA.

Outputs

• FTA Screen Capture: functional FTA fault tree exported as a .png file.
• Event List Raw Data: Event list can be exported as a .csv file.
• MCSQ Raw Data: MCSQ list can be exported as a .csv file.
• RI% Ranking Raw Data: Event list with inherent Relative Impact (RI) values can be exported as a .csv file.
• FTA Report: Event list & image of the fault tree can be generated from Report Wizard.
• FTA Cut Set Report: Cut set list & inherent images of the fault tree can be generated from Report Wizard.

Screenshot walkthrough (captions/labels extracted)

Step 1: Create Functional FTA

• 'Analyses' menu: Fault Tree (submenu highlighted) > Fault Tree Builder, Functional (highlighted), Hardware - RBD; Response Paths, Connection Matrix, Common Mode Analysis, Critical Item Analysis, Criticality & Reliability Editor, Diagnostic Analyses, Failure Rate Prediction, Markov Analysis, RBD Analysis, Reliability Allocation Editor, Back-Fit RCM, Classic RCM, Maintenance Cost Estimates.
• Right-click context menu in Project Explorer on System item: New > System Model, Failure Diagram, Bond Graph, Functions, Functional Diagram; Maintenance Actions, Mission Profiles; Cut/Copy/Paste, Delete, End Effect Item; Fault Tree (submenu highlighted) > Fault Tree Builder, Functional (highlighted), Hardware - RBD; Response Paths, Save to Library, Advanced Properties.

Step 2: Define Analysis Details

• "Fault Tree Analysis" dialog: warning "The current selection is not valid, select a Top Event failure from the list below." "Analysis Details": Name "New Fault Tree Analysis", Description "Description for demonstration purposes." "Fault Tree Type": radio User-defined (with checkbox "Show only connected Failure Conditions") / Model-based Analysis (selected) — sub-options Propagation Type (FCM selected / Bond), Depth of Analysis (Fault selected / Mechanism / Cause), Level of Analysis dropdown "System", Preferred Gate Type dropdown "OR"; radio Hardware Fault Tree. "Reliability Metrics": "Select the Source for Probability of Failure (P(f)) Values": Baseline ("Use the original reliability metrics as the source for P(f) values. These values represent the baseline reliability, either manually entered or derived.") / Revised (selected) ("Use the updated reliability metrics that account for maintenance strategy effectiveness. These values reflect the expected reliability after applying Reliability Centered Maintenance (RCM) or user-defined maintenance actions."). Note: "Adjust the default Depth of Analysis at Preferences → Project Preferences →". Right panel "Top Event" (Model-based tab): searchable tree — Vehicle System > Convert Mechanical - rotational Angular velocity Low/High (Vehicle System) x4, Coupling > Function 1/2 of Coupling Mechanical - rotational Angular velocity Low/High (Coupling), Driveline, Power Generation, Vehicle; Symptoms ("No Symptoms were found"). Buttons OK (disabled), Cancel.

Step 3: Select Top Event

• Same dialog with a Top Event selected (highlighted): "Function 1 of Coupling Mechanical - rotational Angular velocity Low (Coupling)". OK button now enabled.

Step 4: Select Fault Tree Options

• Same dialog with "Fault Tree Type" and "Reliability Metrics" sections highlighted, confirming Model-based Analysis / FCM / Fault / System / OR gate / Revised reliability source selections.

Step 5: Generate Function FTA

• "Fault Tree Builder" view for "New Fault Tree Analysis": tree diagram with Top Event "Function 1 of Coupling Mechanical - rotational Angular velocity Low (Coupling)" (item "Coupling", gate ID E1) branching via an OR gate into: "FM1 of Function 2 of Coupling (Coupling)" (item Coupling, gate E4) → "Delaminated (Coupling)"; "FM1 of Function 1 of Coupling (Coupling)" (item Coupling, gate E3) → "Delaminated (Coupling)"; and "Delaminated (Coupling)" (basic event, R1:3). Bottom panel "Fault Tree - Requires Re-calculation": Event Table Controls tabs Event List (selected)/MCSQ/RI% Ranking; "Probability of Failure": RI Type dropdown "Birnbaum", P(f) State "Calculation Required"; Search Events field; Report/Export buttons. Table columns ID/Logic/Event Type/Item/Event Name/RI(F)/P(f): E1 (OR(B2+E3+E4), Top Event, Coupling, "Function 1 of Coupling Mechanical - rotational Angular v...", N/A, 1.00E+00), E3/E4 (Intermediate Event, Coupling, "FM1 of Function 1/2 of Coupling (Coupling)", N/A, 1.00E+00), R1(3) grouped Basic Events (Coupling, "Delaminated (Coupling)", N/A, 1.00E+00 each).

Step 6: Calculate FTA P(f) Values

• Same Fault Tree Builder view after running "Calculate Probability of Failure" (right-click menu shown: Calculate Probability of Failure, Cut/Copy/Paste, Delete, Zoom In/Out). All nodes now show P(f)=1.53E-08. Bottom panel header: "Fault Tree - Top Event P(f) = 1.53E-08". Table: E1 (OR(B2+E3+E4), Top Event, 1.53E-08), E3/E4 (Intermediate Event, 1.53E-08), R1(3) Basic Event group (1.53E-08 each).

Related workflows

• WF06 – Create Failure Diagram
• WF17 – Generate Hardware Fault Tree Analysis