Mission Profile Analysis

Transcription

1 Chapter 12 Mission Profile Analysis 321 Chapter 12 Mission Profile Analysis RAM Commander provides a mission profile analysis module that simulates the product tree under varying conditions. Define a mission phase by specifying its operating mode, duration, temperature, alpha and number of cycles. A mission profile analysis report describes the product s reliability throughout the mission defined. Defining a Mission Profile The first step in performing a mission profile analysis is to define the mission profile and its phases. You must be in operating or non-operating mode to access the Mission profile module. For a review of project operating modes, see Chapter 5. A mission profile is a progression of phases. Each phase is characterized by the following: Operating or Non-operating mode Environment Temperature Time Test coverage (alpha) Number of on/off cycles per 1,000 hours (non-operating mode only) Complex mission profiles using many phases can be built. For example, you can design an airplane s mission profile starting at hangar storage, takeoff, various altitude climbs, and return to base.

2 322 RAM Commander User s Guide Each of these phases can be broken down into smaller phases, until you fine tune your mission so that it closely resembles the airplane s actual operational conditions. To add a mission profile 1 Activate the Product tree view. 2 From the Modules menu, choose Mission Profile; the Mission Profile dialog box opens. 3 Choose Add MP; the Add Mission Profile dialog box opens. 4 In the Add Mission Profile dialog box, enter a mission profile name 5 Choose OK. RAM Commander redisplays the Mission Profile dialog box. You can now access the new mission profile by choosing it from the MP Name list box.

3 Chapter 12 Mission Profile Analysis 323 To add a mission profile phase 1 In the Mission Profile dialog box, select the mission profile to which you want to add a phase from the MP Name list box. 2 Choose Add Phase; the Add Mission Phase dialog box opens. 3 Enter values for the following fields: Phase Description Mode Environment Temperature Time Test Coverage Nc 4 Choose OK. Name of the mission phase Operating or non-operating One of the reliability environments Temperature during the phase Phase duration When 0, no test is performed; when 1, full test coverage is assumed Number of on/off cycles per 1,000 hours (non-operating mode only) RAM Commander redisplays the Mission Profile dialog box with the new phase.

4 324 RAM Commander User s Guide To edit a mission profile phase To edit a mission profile phase, select it with the mouse and choose Edit Phase. Follow steps 3 4 in the previous procedure. RAM Commander redisplays the Mission profile dialog box with the phase s new characterization. To delete a mission profile phase Caution Use care when deleting mission profile phases. There is no undo facility to easily return the mission profile to its original state. 1 In the Mission Profile dialog box, select the phase by clicking on its number under the # column. 2 Choose Delete Phase. 3 Enter your confirmation in the dialog box. RAM Commander displays the updated Mission Profile dialog box. To delete a mission profile Caution Use care when deleting mission profiles. There is no undo facility to easily restore the mission profile. 1. In the Mission Profile dialog box, Choose Delete MP. 2. Enter your confirmation in the dialog box. RAM Commander displays the updated Mission Profile dialog box. To copy a mission profile 1. In the Mission Profile dialog box, Choose Save As 2. Enter new Mission Profile name and press ok. Copy of your Mission Profile will be created under new name.

5 Chapter 12 Mission Profile Analysis 325 Mission Profile Reports After defining a mission profile, you can obtain reliability estimates for the product. Note Recalculate the product tree before computing a mission profile. See Chapter 10 for reliability calculation techniques. To compute mission profile reliability 1 Activate the Product tree view. 2 From the Modules menu, choose Mission Profile; the Mission Profile dialog box opens. 3 Select the mission profile from the MP Name list box. 4 Choose Report. RAM Commander displays the mission profile report in a report window. The report includes the following information: Description of all mission phases Failure rate during each phase MTBF during each phase Failure rate phase duration Reliability for each phase Unreliability for each phase Total mission reliability You can manage the mission profile report using the techniques described in Chapter 11.

6 326 RAM Commander User s Guide Total Failure Rate Formula The total failure rate for a mission containing n + 1 phases is calculated as follows: where λ Σ = ( 1 α λ λ n n n t n )( 1 1 Σ ) n λ Σn+1 - total mission failure rate over n + 1 phases λ = ( α ) λ t - total mission failure rate for the first phase Σ α 1 - test coverage during transition from first phase to second phase; a fraction in the range [0; 1] where 0 means no testing, and 1 means complete fault isolation between phases. λ 1 - total failure rate of the system for the first phase t 1 - duration in hours of the first phase Summary In this chapter, you learned about RAM Commander s mission profile analysis module. Using this module, you can build detailed models of a project s environmental conditions, compute the reliability values, and perform analysis. An important result of the mission profile module is the probability that the project will complete the mission.