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About Reliability Importance


 ReliaWiki: Reliability Allocation

 Reliability Allocation and Optimization using BlockSim

 Allocation Analysis Example

Allocation Analysis

The allocation analysis tool can help you determine the reliability requirements for individual components/assemblies that would be needed to achieve an overall reliability goal. To use the tool, you do the following:

  1. Create the allocation analysis.

  2. Specify a target reliability for the system at a particular time and select which of the individual blocks in the system you would like to consider for improvement.

  3. Choose the allocation type or method that you want to use.

  4. Perform the optimization.

You can also create an allocation analysis from within the FMRA view. These allocation analyses offer some features suited to FMRA use.

What's Changed? In BlockSim 7, this kind of system optimization was performed by selecting certain blocks to be considered in the calculation and specifying their maximum achievable reliability and the feasibility of achieving that reliability via their properties windows; the QCP was then used to perform the calculations. The allocation analysis tool provided in the Synthesis version allows you to select the blocks for consideration, specify the required values and perform the calculations in a single window, thereby making it simpler to set up and modify your calculations.

Create the Allocation Analysis

To add an allocation analysis to the project, choose Insert > Tools > Allocation Analysis.

In the Select Diagram window that appears, select the diagram that you want to perform an allocation analysis for. Allocation analysis can be performed only for analytical diagrams, so all of the diagrams that are available in this window will be analytical diagrams. You can select any diagram that is currently in an analyzed state; diagrams that have not been analyzed will be displayed in the list but cannot be selected. (You can hide these diagrams by selecting the Hide unavailable diagrams check box at the bottom of the window.) When the allocation analysis folio is created, the name of the diagram that it is based on will be displayed at the bottom of the control panel; you can click the diagram name to open it.

In the allocation analysis folio, you will see a table that displays the current reliability and the reliability importance of each of the blocks in the selected diagram. Reliability importance is a measure of the relative importance of each component in a system with respect to the overall reliability of the system. These values are calculated at the mission time specified in the control panel; you can change that value in the control panel and click the Refresh button to update the values in the table accordingly. The current reliability for the entire system is displayed in the Outputs area of the control panel, and is also dependent upon the specified mission time.

Tip: The order of the blocks in the table is controlled by the Set Block Order command in the associated diagram.

The color coding used in the Reliability Importance column provides a quick visual indicator of how important the blocks are to the system reliability. You can adjust the threshold for the colors by clicking the Adjust Color Limits button (...) in the Color Limits field in the control panel. Move the sliders to indicate the values below which you want everything to be displayed in green (i.e., least important) and above which you want everything to be displayed in red (i.e., most important). To automatically determine a min/max for the Color Limits based on the values in the Reliability Importance column of the current tab, click the Calculate Color Limits button.

Specify Included Blocks and Settings

Select the check box in the first column for each block that you want to consider for improvement in the allocation analysis. Any block that has a model assigned to it can be considered in the optimization process; standby and load sharing configurations are considered at the container/gate level, not at the contained block/dependent event level. You can select or clear the check box in the column header to select or clear all of the individual check boxes. The goal of an allocation analysis is to improve the reliability of the system; this purpose is best served if you do not select blocks with very low reliability importance or with very high current reliability values.

In the Inputs area of the control panel, enter the following information:

Choose the Allocation Type

The software provides three allocation types that can be used to logically apportion the system reliability across the selected blocks. Select the desired allocation type in the Allocation Type field in the control panel. Available allocation types include:

Since the evaluation is relative, any feasibility functions that you enter should be correlated with one another. In addition, you should not use your own functions for some components and the predefined feasibility values for others unless you are sure that your functions are correlated to the function used to calculate the predefined values.[1] For this reason, it is preferable to use the predefined values unless you have a compelling reason to do otherwise.

Perform the Analysis

Click the Optimize icon.

Once optimization has been performed, the following information will be displayed for each selected block:

In addition, the System Reliability field in the Outputs area of the control panel will display the reliability of the system if the optimum scenario is implemented (i.e., if all selected blocks are improved to their target reliability values).

Note: Subdiagram blocks are displayed as hyperlinks. You can click the name of the subdiagram block to add another tab to the allocation analysis folio, where you can perform allocation analysis for the subdiagram.

You can click the Transfer to Spreadsheet icon to save the results in a Synthesis Workbook.

The Select Workbook window that appears allows you to select an existing workbook or add a new one to the project. If you select an existing workbook, you can select the Overwrite Existing Sheets check box to overwrite the current contents of the workbook. If you do not select this check box, a new sheet will be added to the workbook. If you select to add a new workbook, you will be prompted for the workbook name.

You can click the Send to Excel icon to save the results as an Excel file.

In either a Synthesis Workbook or an Excel file, the results will look like the ones shown next.

The first row displays the name of the optimized diagram and the allocation type that was used in the optimization. For each selected block, the following information is shown:

The System Results include the following:

FMRA Allocation Analysis

Following the steps above, you can create an allocation analysis based on any analytical FMRA diagram that inherits its reliability from its dependents. You can also create allocation analyses for such diagrams directly within the FMRA view by choosing FMRA > Calculations > Allocation Analysis.

Allocation analyses created in this way offer some different features that are suited to FMRA use.

An allocation analysis created from within the FMRA view will not appear in the current project explorer. However, you can reopen it by choosing the command again.

 

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