Using Fault Trees

BlockSim's fault trees can be configured as analytical diagrams (which use the exact mathematical solution for the system model but impose limitations on what can be modeled and what results can be obtained) or simulation diagrams (which provide more modeling options and results but must be analyzed with discrete event simulation).

Fault trees and reliability block diagrams (RBDs) can be used together in the same analysis (e.g., a subdiagram block in a fault tree can point to an RBD and vice versa).

The basic steps for using an analytical fault tree are:

  1. ClosedAdd fault tree diagram

    2. Right-click the Fault Trees folder in the current project explorer and choose Add Analytical Fault Tree.

  2. ClosedAdd gates

    3. Right-click inside the diagram and choose the type of gate to add. (See Fault Tree Block Types.)

  3. ClosedAdd events

    4. Right-click a gate and choose Fault Tree > Add Event > [Type of Event]. When a gate is selected, the event will be added below the gate, already connected.

  4. ClosedConnect blocks (if applicable)

    5. If you need to create a new connection, hold down the ALT key, click the source block and drag a line to the destination block.

  5. ClosedSet block properties

    6. To edit a block's properties, right-click it and choose Block Properties. For gate blocks, you can change the name and identifiers. For event blocks, specify any operational and cost properties and use universal reliability definitions (URDs) to specify the reliability properties. (See Creating and Selecting Resources.)

    • To select an existing URD, click inside the URD field.
    • To create a new URD, click inside the Model - Reliability field and follow the wizard. You can create a new model (left) or select an existing model (right). Existing models may have been manually created, or may have been published from other analyses in BlockSim, Weibull++ or Lambda Predict.

  6. ClosedAnalyze the diagram

    7. Click the Analyze icon on the control panel.

    To view the calculated reliability or unreliability at a specific time for each block, select Show Results on the control panel and specify the time. To view the algebraic equations for the system reliability, pdf and failure rate, click the Results valid as of field on the control panel. (See Equation Viewer.) Note that starting in Version 2022, you have a choice of analysis methods for analytical fault trees; algebraic equations are available only for the Equation analysis type, not for the new Binary Decision Diagram analysis types. (See Fault Tree Analysis Types.)

  7. ClosedCalculate metrics

    8. Click the QCP icon on the control panel to open the Quick Calculation Pad. (See Analytical QCP for available calculations.)

  8. ClosedView plots

    9. Click the Plot icon on the control panel to open the plot sheet. (See Analytical Plots for available plot types.)

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