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2003 Course Reliability Eng. (Elective I)

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Total No. of Questions : 11] P976 [Total No. of Pages : 4 [3664] - 157 B.E. (Production Sandwich) RELIABILITY ENGINEERING (411122) (Elective - I) (Revised 2003) Time : 3 Hours] [Max. Marks : 100 Instructions to the candidates: 1) Answers to the two sections should be written in separate books. 2) Neat diagrams must be drawn wherever necessary. 3) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 4) Assume suitable data, if necessary. 5) All questions are compulsory. SECTION - I Q1) a) b) Q2) a) b) Explain the following : [8] i) Reliability. ii) Hazard rate. iii) Mean time to failure (MTTF). iv) Probability density functions of failure. Following table shows the results of life tests carried out on 100 components simultaneously. Operating 0 10 20 30 40 50 60 70 80 90 100 Time (hours) Number of 100 90 81 73 66 60 55 50 45 41 37 surviving Components Evaluate hazard rate, failure density function and reliability and plot these functions to scale against time. [8] OR Following table shows the results of life tests carried out on 100 components simultaneously. Operating Time 0 1 2 3 4 5 6 7 8 9 10 (hours) Number of 50 30 80 70 90 80 30 50 15 05 failures Evaluate hazard rate, failure density function and reliability and plot these functions to scale against time. [8] [8] Prove that MTTF = 1 N f dk ( k t ) . P.T.O. Q3) a) A logic gate diagram for FMEA study has been shown in figure. The basic failure modes of A, B and C have failure 0.001, 0.003 and 0.002 per hour respectively. Find out the system failure rate of T0. Assume mission time of 100 hours. [8] b) Explain the methodology of constructing Fault tree diagram. What are the various gates commonly used in a logic diagram leading to FMEA? [8] OR Q4) a) b) What is meant by FMEA and FMECA? What are the specific advantages that could be derived from an FMEA diagram in minimizing potential failures? [8] How Boolean Algebraic principles can helping simplifying the FMEA diagram, so that the estimation of overall failure probability becomes easier? [8] Q5) a) What is meant by Tie sets & Cut sets ? State their application in determining the reliability of a system shown in the figure below. [10] b) Explain with example : Matrix Method of estimating system reliability. [8] OR [3664] - 157 -2- Q6) a) b) Evaluate reliability using conditional Method for the given system shown in the figure. [12] Explain : i) Active ii) Passive & iii) Partially active redundancy. [6] SECTION - II Q7) a) b) What is meant by Reliability Effort function ? Explain its significance in Life Cycle Costing. [8] A system consists of 6 sub-systems connected in series. The system reliability goal is 0.998 for a period of 20 hours operation. The necessary information for the sub-system is given below : Sub-system Number of Importance Operating time Modules (Ni) factor (Wi) t hours 1 30 1.00 20 2 75 0.98 18 3 40 1.00 20 4 50 0.95 16 5 60 0.93 14 6 70 1.00 20 Compute the reliability goal for each sub-system using AGREE method of allocation. State any assumptions made. [8] OR Q8) a) b) Explain Bath-Tub Curve with reference to failure modes. The following data refers to a certain test of equipment [3664] - 157 -3- [8] Failure No. 1 2 3 4 5 6 7 Operating time 18 12 8 22 26 35 30 to failure (Hrs) Find out the reliability by i) Mean Method and ii) Median Method and compare the two by plotting. 8 40 [8] Q9) a) b) c) Define : availability and maintainability. How Operational availability is different from inherent availability ? [6] If the inherent availability of a system is 0.92 when the MTBF is 220 hours, what if the maximum value of MTTR? Assuming logistic time for administrative support is 30% of the total down time, find out the operational availability. [6] Explain the significance of safety margin in engineering design reliability. [4] OR Q10)a) b) What is meant by Reliability Centered Maintenance? Explain the part played by CBM (condition based monitoring) is assuming specific level of reliability. [8] Distinguish between Breakdown Maintenance and Preventive Maintenance. State any quantitative method of decision making in regarding suitability of Breakdown Maintenance and Preventive Maintenance. [8] Q11)Write short notes on (any three) : a) Risk Priority Number. b) MTTR & MTBF. c) Total Productive Maintenance. d) Accelerated Life Testing. e) DTMC & CTMS models. [3664] - 157 -4- [18]

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