BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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28 GheorgheNegru In Eqs. (5)-(7), f is the number of the specific failure event, F is the total number of evaluated failures and t fi is the time between the failures in issue δ f 1 = . (8) MTBF 5. Calculate the total costs per failures per year TCP f , costs generated by the different failure events, with the following expression TCP F = ∑ δ C . (9) f f f f The equivalent total annual cost represents the value of the money that will be needed, every year, to pay for the problems caused by failure events during the expected years of useful life. 6. Calculate the total costs per failure in net present value NPV(TCP f ). Given a yearly value TCP f this is the amount of money that needs to be saved (today) to be able to pay this annuity for the expected number of years of useful life T, and for a discount rate i. The expression used to estimate the NPV(TCP f ) is T ( 1+ i) −1 NPV ( TCPf ) = TCPf . (10) T i ( 1+ i ) Finally, as in previous models, the rest of the costs evaluated (investment, planned maintenance, operations, etc.) are added to the cost calculated for nonreliability and the total cost is obtained in annual equivalent value. The result is then compared for the different options. 3. Case Study 3.1. Input Data In the present study case will be applied the above presented method in order to analyze the costs generated by the low reliability of a specialized wheeled vehicle system (Fig. 1). The main components of the system are presented in Table 2. S2 S4 S5 S1 S3 Fig. 1 – A schematic view of the specialized wheeled vehicle system The time between failures t f for 27 failures during 10 year time period for a specialized wheeled vehicle system is defined based on the recorded statistics data (Table 3).
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 3, 2012 29 Table 2 Main components of the specialized wheeled vehicle system System Destination S1 Vehicle platform S2 Communication and information system S3 Electrono-optic system S4 Software interface system S5 Vehicle platform control engineering Table 3 Failures synthesis t f Failed system Failure 1 5 S1 Failure 2 7 S2 Failure 3 3 S3 Failure 4 6 S1 Failure 5 2 S4 Failure 6 5 S5 Failure 7 3 S2 Failure 8 3 S3 Failure 9 7 S1 Failure 10 7 S2 Failure 11 2 S4 Failure 12 4 S5 Failure 13 5 S2 Failure 14 4 S3 Failure 15 2 S1 Failure 16 4 S2 Failure 17 3 S4 Failure 18 7 S5 Failure 19 6 S2 Failure 20 4 S2 Failure 21 4 S3 Failure 22 7 S1 Failure 23 4 S4 Failure 24 3 S5 Failure 25 5 S2 Failure 26 3 S3 Failure 27 4 S1 3.2. Output Data According to those presented in Sec. 2: i) identify, for each alternative to evaluate, the main failure modes (f) where f=1…F, for F failure modes. We assume F=1 failure mode; ii) determine the time between failures t f , see Table 3;
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BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

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