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Session 3.7: Functional Fault Tree Analysis (FTA)

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Session 3.7: Functional Fault Tree Analysis (FTA)

SESSION 3.7 OUTLINE

3.7.1: Fault Tree Builder 3.7.2: Fault Tree Analysis (Model-Based) 3.7.3: User-defined Fault Tree 3.7.4: User-defined Fault Tree Analysis 3.7.5: Custom Events 3.7.6: Transfer Gates

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER

The Fault Tree Builder identifies all Faults that lead to an End Effect Three different fault tree options are presented:

   User Defined allows to rapidly create a fault tree from scratch using a flexible, interactive workflow
   Model-Based Analysis automatically generates the Functional Fault Tree according to the model
   Hardware Fault Tree generates the Fault Tree based on the Reliability Block Diagram

Reliability Metrics Source

   Baseline uses the original reliability data defined in the model either manually entered from reliability data
     sources or derived using reliability allocation methods

   Revised uses updated reliability values that account for maintenance strategies reflecting Reliability Centered
     Maintenance (RCM) actions or user-defined maintenance actions

Note: Hardware Fault Tree will be covered in Session 4.6.

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER

Model-Based fault trees can be conducted using the different options

   Propagation type:

          FCM � uses the FCM model propagations to construct the Fault Tree
          Bond � uses the Bond model propagations to construct the Fault Tree

   Depth of Analysis:

          Fault, Mechanism, Cause � reports the fault trees to the selected concept

   Level of Analysis:

          System � propagates through the levels of indenture and displays all model items
          Subsystem / Component � propagates only to the selected subsystem / component

   Preferred Gate Logic:

          OR � each gate uses an OR logic
          AND � each gate uses an AND logic according to the model
          K of N � each gate uses an K of N (default K = 1) logic according to the model

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER (CONTINUED)

The Functional Fault Tree Builder allows customization of the Fault Tree

Various gates can be implemented to represent a Various Event types can be assigned to the root specific configuration/use case cause

   OR                                                Basic Event
   AND                                               House Event
   K of N                                            Undeveloped Event
   INHIBIT                                           Conditional Event
   NOR
   NAND
   XOR
   Transfer in

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER (CONTINUED)

Event Types and Probability of Failure can be specified using the Properties viewer Types of Gates:

     OR gates represent the output flow occurring if any one of the input flows occur

     AND gates represent the output flow occurring if all inputs occur

     K of N gates represent the output flow occurring only if `K' of the input flows occur

     INHIBIT gates represent the output flow occurring when the input flow occurs only if a specified condition is also
     satisfied

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER (CONTINUED)

Types of Gates (Continued):

     NOR gates represent the output flow occurring only when none of the input flows occur

     NAND gates represent the output flow occurring when not all input flows occur

     XOR gates represent the output flow occurring when exactly one of the input flows occurs

     Transfer in gates breaks up the fault tree into separate diagrams whilst maintaining connectivity. This is particularly
     useful when the fault tree gets large in size and become hard to follow. It will assist in presenting the fault tree in a
     readable manner, allowing sections of the fault trees to be separated. There is no mathematical calculations
     involved with the Transfer gate

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7 FAULT TREE BUILDER (CONTINUED)

Types of Events:

     Basic Event is an event which does not develop any further
     House Event is an event which is normally expected to occur
     Undeveloped Event is an event which is not further developed either because it is of insufficient consequence or
     because information is unavailable
     Conditional Event is an event which represents a specific condition or state that must exist for a logic gate (such as
     an Inhibit gate) to allow the input event to produce the output

Event Properties:

 Event ID: Pre-assigned ID for the Fault Tree branch
 Event Code: Custom event code to display on the Fault Tree, this field can be used to capture repeat events
 Narrative: Text field to add additional details of the event

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.1 FAULT TREE BUILDER (MODEL-BASED)

To create a Model-Based Functional Fault Tree:

Right-click the `Power Generation' in the Project Explorer Select Fault Tree Fault Tree Builder

   This will be the landing page for the Fault Tree Builder where all Fault Tree analyses will be listed

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.1 FAULT TREE BUILDER (MODEL-BASED) (CONTINUED)

Click to create a new FTA

Enter the following details:

   Name: Demonstration Fault Tree Analysis
   Description: Fault tree with Low Angular velocity as the top event
   Set Fault Tree Type to Model-Based Analysis
   Set Propagation Type to FCM
   Set Depth of Analysis to Fault
   Set the Level of Analysis to System
   Set the Preferred Gate Type to OR
   Select Baseline as Reliability Metrics

Set the first Convert Mechanical � rotational Angular velocity Low (Vehicle System) as the Top Event

Select to generate the fault tree

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.1 FAULT TREE BUILDER (MODEL-BASED) (CONTINUED)

Fault tree is generated from the model

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.2 FAULT TREE ANALYSIS (MODEL-BASED)

The Fault Tree analysis page displays the Fault tree as well as Analysis controls in the window below Edit Mode allow change to be MADE to the Fault Tree Event Table Controls:

   Event List displays all the elements within the fault tree with the respective analysis data
   MCSQ displays the minimum cut-set sequences of the fault tree
   RI % Ranking displays the relative importance

Calculations on the fault tree are derived from Minimum Cut-set Sequence methodology which considers repeat events

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.2 FAULT TREE ANALYSIS (MODEL-BASED) (CONTINUED)

Repeat events can be modelled in the fault tree and are denoted by the same Event code The notation for repeat event codes in MADE is Event Code : Number of repeats Once a repeat event is selected, the repeat events are also highlighted

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.2 FAULT TREE ANALYSIS (MODEL-BASED) (CONTINUED)

Probability of Failure Relative Importance type:

  Birnbaum: A value assigned to each basic event indicating its relative increase to risk of failure
  Fussell-Vesely: A value assigned to each basic event indicating its contribution to the top-level event failure

Refresh and Calculate the P(f) values by selecting Select to export the table to a .csv

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.2 FAULT TREE ANALYSIS (MODEL-BASED)

To modify the Event Type and P(f) of a fault, ensure Edit Mode is enabled:

Select the Transmit Mechanical � rotational Torque Low (Half Shaft Rear) Undeveloped event Navigate to the Properties viewer and input the following

   General Tab:

          Event Code: LOW1
          Narrative: Narrative for training

   Event Tab:

          Event Type: Basic Event
          Probability of Failure: Direct Entry, Event P(f): 0.005

Note: Intermediate Events cannot be changed Note: Although we have specified Model-Based for the analysis, there is the

        option to manually adjust P(f) as required.

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.2 FAULT TREE ANALYSIS (MODEL-BASED) (CONTINUED)

Calculate the P(f) of the Fault tree by selecting

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.3 USER-DEFINED FAULT TREE

User-defined fault trees can be rapidly created to represent specific failure scenarios and evaluate the probability of failure

The user-defined fault tree builder allows users to start with a blank Top Event and progressively construct the tree by adding gates and events directly within the analysis workspace

Events can be quickly created and structured under logic gates, with inline editing of attributes such as name, item, and event code. Probability of failure values can be entered manually or inherited from associated model elements

Events can be linked to existing model elements such as functional failures or failure modes, enabling the fault tree to evolve from an initial conceptual structure into a model linked analysis

Custom events can be created and added to the Fault Tree � these can be either Fault, Failure Condition, Failure Mode, Mechanism, Cause or Custom type

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE

To create a User-defined Fault Tree Analysis:

On the Fault Tree Builder landing page, select

In the dialogue, enter the following:

   Name: Control Unit FTA
   Description: The ABS Electronic Control Unit (ECU) fails to

      perform brake control functions such as anti-lock braking,
      stability control, or traction control.
   Select Baseline as Reliability Metrics

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

The Fault Tree Builder will place the blank Top Event on the Fault Tree Builder canvas

   By default, it is set to the `Modeling mode'. This can be toggled selecting
   Fault Tree � Event list can be viewed or hidden by selecting

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Select under the events to quickly build the fault tree in sequential order

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Update Top Event details by double-clicking on the respective field

   Event Name: Brake Control Unit (ABS ECU) Failure
   Event Item: Control Unit

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Update the Intermediate Event 1 (left side branch) details by double-clicking on the respective field

   Event Name: ABS ECU Power Supply Failure
   Event Item: Power Supply System

Double-click each Basic Event under this Intermediate Event to update the following details

   Basic Event 1:
          Event Name: Vehicle Battery Voltage Drop
          Event Item: Vehicle Battery

   Basic Event 2:
          Event Name: Voltage Regulator Failure
          Event Item: Power Regulation Circuit

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Update the Intermediate Event 2 (right side branch) details by double-clicking on the respective field

   Event Name: Loss of Wheel Speed Sensor Input
   Event Item: Wheel Speed Sensor System

Double-click each Basic Event under this Intermediate Event to update the following details

   Basic Event 1:
          Event Name: Front Left Wheel Speed Sensor Failure
          Event Item: Wheel Speed Sensor - Front Left

   Basic Event 2:
          Event Name: Wheel Speed Sensor Wiring Harness Open Circuit
          Event Item: Wiring Harness

   Basic Event 3:
          Event Name: Wheel Speed Sensor Connector Corrosion
          Event Item: Wiring Harness

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Input the Probability of Failure data for Basic Events

   Select the Event
   In the Properties viewer, select Event tab

                      Basic Event                      Input Method                                   Value

Vehicle Battery Voltage Drop Direct Entry Event P(f): 1.50E-03 Voltage Regulator Failure Direct Entry Event P(f): 8.00E-04 Front Left Wheel Speed Sensor Failure Calculated (Lambda) Failure Rate: 25 fpmh, Exposure Time: 1000 hours Wheel Speed Sensor Wiring Harness Open Circuit Calculated (Lambda) Failure Rate: 12 fpmh, Exposure Time: 1000 hours Wheel Speed Sensor Connector Corrosion Calculated (Lambda) Failure Rate: 08 fpmh, Exposure Time: 1000 hours

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.3 USER-DEFINED FAULT TREE (CONTINUED)

Calculate the P(f) of the Fault tree by selecting

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.4 USER-DEFINED FAULT TREE ANALYSIS

The default gate type in the Fault Tree is an OR gate. To change gate type:

Right-click on the gate and use the drop-down menu to select the Gate Alternatively, select the gate, in the Properties viewer, use the drop-down

menu to select the Gate Alternatively, select the gate, use the icon toolbar and select the

appropriate Gate

To change an event type:

Select the event, in the Property window, use the drop-down menu to select the Event Type

Alternatively, select the event, use the icon toolbar and select the appropriate event type

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.4 USER-DEFINED FAULT TREE ANALYSIS (CONTINUED)

In the Fault Tree � Event List view there are three different tables which can be viewed:

 Event List
 MCSQ
 RI% Ranking

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.4 USER-DEFINED FAULT TREE ANALYSIS (CONTINUED)

Event List

 The event list shows the fault tree content in a list form
 The Relative Importance column is calculated using one of two methods:

       Birnbaum
       Fussell-Vesely

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.4 USER-DEFINED FAULT TREE ANALYSIS (CONTINUED)

MCSQ (Minimum Cut-set Sequence)

 Displays the minimum cut set with the relevant information.

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.4 USER-DEFINED FAULT TREE ANALYSIS (CONTINUED)

RI% Ranking

 Displays the list of root causes and the calculated relative importance

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.5 CUSTOM EVENTS

Custom events can be created to capture events which are not modelled. These can be in the form of a fault, failure condition, failure mode, mechanism, cause, or custom. If a failure mode custom event is created, the flow type is also required to be specified.

The Custom events created will have a user-defined P(f)

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.5 CREATING A CUSTOM EVENT

To create a Custom Event:

On the Fault Tree Builder landing page, click on Custom Event Library (top-right corner)

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.5 CREATING A CUSTOM EVENT (CONTINUED)

Within the Custom Event dialog, select New Custom Event > to add Custom Event details Input the following details:

   Item Name: Engine #2
   Failure Name: Green Smoke
   Failure Type: Failure Condition

Click Create

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.5 CREATING A CUSTOM EVENT (CONTINUED)

Add two more Custom Events with the following details:

   Item Name: Engine
   Failure Name: Burning
   Failure Type: Fault

   Item Name: Coupling
   Failure Name: High Torque
   Failure Type: Failure Mode
   Flow Type: Energy

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 ADDING A CUSTOM EVENT TO THE FAULT TREE

To add the custom events to the fault tree:

Select under the Loss of Wheel Speed Sensor Input (Wheel Speed Sensor System) event

This adds a blank Basic Event under it

Right-click on the blank Basic Event: Replace > Custom Event

Select High Torque event

Select to add the event to the Fault Tree

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 ADDING A CUSTOM EVENT TO THE FAULT TREE (CONTINUED)

Add User-defined P(f) value for the custom event Select v to re-calculate the P(f)

Event P(f) High Torque (Coupling) 5.20 E-06

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 ADDING A CUSTOM EVENT TO THE FAULT TREE (CONTINUED)

Session 3.7: Functional Fault Tree Analysis (FTA)

DISCUSSION 3.7.6 TRANSFER GATE

Transfer gates are used to segment larger fault trees for easier viewing Each Transfer tree can be used for independent analysis Transfer gates can be used to attach existing Fault Trees to other Fault Tree Analyses

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 CREATING A TRANSFER GATE

To Transfer a branch to its own Fault Tree Analysis:

Right click on the Loss of Wheel Speed Sensor Input event and select Transfer In A dialog will appear to confirm the transfer fault tree details. Select OK to continue

   This will move all events below the event to its own Fault Tree for analysis

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 CREATING A TRANSFER GATE (CONTINUED)

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 CREATING A TRANSFER EVENT

To connect an existing Fault Tree Analysis to the fault tree:

Create a new User-defined Fault Tree with the following details:

   Name: Engine Fault Tree Analysis
   Description: User-defined fault tree for the Engine component
   Fault Tree Type: User-defined
   Reliability Metrics: Baseline

Session 3.7: Functional Fault Tree Analysis (FTA)

EXERCISE 3.7.6 CREATING A TRANSFER EVENT (CONTINUED)

Right click on the Top Event and select Add Transfer Event A dialog will appear to select an existing FTA to link Select Transfer to Wheel Speed Sensor System Select OK to add the Transfer Event

   This will automatically populate the event on the Fault Tree with an
      automatic Transfer Gate to the Transfer Fault Tree Analysis

Select to calculate the P(f)

Note: Reliability Metrics type (Baseline or Revised) shall match when adding a Transfer Event.

Session 3.7: Functional Fault Tree Analysis (FTA)

SESSION 3.7 SUMMARY

3.7.1: Fault Tree Builder 3.7.2: Fault Tree Analysis (Model-Based) 3.7.3: User-defined Fault Tree 3.7.4: User-defined Tree Analysis 3.7.5: Custom Events 3.7.6: Transfer Gates

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