Related Topics:

Failure Modes and Reliability Analysis (FMRA)

Quantitative Criticality Analysis

Performing Calculations with the FMRA

The FMRA can perform a variety of analytical and simulation-based calculations. These calculations are based on the configuration of the FMRA hierarchy and the properties that you define for the records in the hierarchy.

This topic contains information on:

Setting up the FMRA

To perform any of the FMRA's calculations, you must first set up the FMRA hierarchy and define the relevant properties for each record:

Tip: To perform more complex calculations that do not assume a series configuration, you can use ReliaSoft's BlockSim 8 software to synchronize the FMRA with reliability block diagrams. The blocks can then be arranged in any configuration that is supported by BlockSim.

Note: The fields that are enabled in the interface will depend on the interface style settings that have been defined for the current project. You can choose Project > Management > Configurable Settings > Interface Style to open the Edit Interface Style (This Project) window and change the settings for the current project.

Continuous operation at the rated load is considered to be a duty cycle of 1. Any other level of usage is expressed as a percentage of the rated load value or operating time. For example, consider the DVD drive mentioned above; its duty cycle value would be 18 min / 60 min = 0.3. A duty cycle value higher than 1 indicates a load in excess of the rated value.

Reliability Calculations

To calculate the reliabilities of the records after you set up the FMRA hierarchy, choose FMRA > RAM Analysis > Calculate (Reliability). The reliability for each record at the specified operating time will appear in the Reliability (Analytical) column of the FMRA, if the column is selected to be displayed.

The reliability for each item will also be displayed in the Current Reliability field of the Properties tab when the item is selected. This value will be highlighted in red if it is below the specified target reliability.

You can also show the calculated probability of failure (1 – R) by displaying the Probability of Failure (Analytical) columns, as shown next. If you display the Analytical Results Status column (also shown next), it will show green indicator lights when the results are based on the current inputs, and red lights when the results are not current.

Tip: If you are using the FMRA to estimate the system's baseline reliability, you may wish to thoroughly review and vet the first draft of the FMRA in order to improve the results. The ReliaWiki resource portal has more information on estimating reliability with the FMRA at: http://www.ReliaWiki.org/index.php/Using_FMRA_to_Estimate_Baseline_Reliability.

Criticality Calculations

If you wish to perform a quantitative criticality analysis, the software can calculate the probabilities of failure and use that information to calculate the criticality. Before you can calculate the criticality, you must make sure the applicable criticality analysis fields have been enabled for the project. To see the calculated values, make sure the four columns shown next are selected in the Customize Columns window, which you can access by right-clicking any of the column headers in the FMRA.

For more information on performing quantitative criticality analysis, see Quantitative Criticality Analysis.

System Availability and Cost Calculations

The FMRA can also be used to perform simulation-based calculations to predict the system's availability, the cost of operation and other values based on the reliability and the maintenance characteristics of the FMRA records.

In simulation, random failure times are generated from each component's failure distribution. These failure times are then considered in accordance with the way the components are reliability-wise arranged within the system. The overall results are analyzed in order to determine the behavior of the entire system. Simulation can be used for complex scenarios involving a multitude of probabilistic events, such as corrective maintenance, preventive maintenance, inspections, imperfect repairs, crew response times, spare part availability, etc.

To perform system availability and cost calculations, set up the FMRA and then choose FMRA > RAM Analysis > Simulate (Availability). A window will open where you can change the simulation settings. Click OK to perform the simulation. The following values are obtained from the simulation and may be shown on the FMRA tab of the System panel. To change which results columns are visible, right-click the column headers of the FMRA, then click Customize Columns.

Note: It is not possible to simulate failure times for components whose reliability is defined by a constant value. Failure times can be simulated only in contexts where reliability is time-dependent. Thus, the calculated operating costs for any component with a constant reliability will be zero. In these situations, it may be advisable to change the model from a constant value to a time-dependent distribution. See Changing Constant Probability Models to Distributions.

 

© 1992-2013. ReliaSoft Corporation. ALL RIGHTS RESERVED.