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2003 Course Reliability Eng.

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Total No. of Questions : 11] [Total No. of Pages : 7 [3764]-175 P1468 B.E. (Production / Production S/W) RELIABILITY ENGINEERING (411085) Time : 3 Hours] [Max. Marks : 100 Instructions to candidates : 1) Answer any 3 questions from each section. 2) Question No. 11 is compulsory. Out of the remaining attempt 3 questions from section I and 2 questions from Section II. 3) Answers to the two sections should be written in separate books. 4) Neat diagrams must be drawn wherever necessary. 5) You are advised to attempt not more than 3 questions. 6) Use of logarithmic tables, slide rule, Mollier charts, electronic pocket calculator and steam tables is allowed. 7) Assume suitable data, if necessary. SECTION - I Q1) a) A series of tests conducted under certain stipulated conditions on 800 electronic components. The total duration of tests is 15 hrs. The number of components that fail during each hourly interval is noted. The results obtained are tabulated as shown in table. Time (t) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 No. of failures 00 120 85 71 62 53 45 41 37 35 29 50 45 63 35 29 Based on the failure data or survival test results shown in table. Define & calculate failure density (fd) : failure rate (Z) and Reliability (R). [12] b) Explain with neat sketch different failure modes of Bath tub curve.[4] OR Q2) a) In order to test the strength of a new glue, ten similar structures constructed using the glue were subjected to a continuous vibratory load, and the duration of survival of each structure was noted, the values obtained the following: Specimen Number 01 02 03 04 05 06 07 08 09 10 Hours of Survival 60 62 58 50 61 55 59 62 54 55 Calculate the mean time to failures (MTTF) from this data. [6] P.T.O. b) In a test involving continuous satisfactory performance of 110 electronic instruments under excessive vibration conditions, the following failure frequencies were observed, the total test period being 8 hrs. Time interval Number of failures 0-1 1-2 2-3 3 16 22 3-4 4-5 5-6 6-7 7-8 42 11 09 04 03 Calculate the mean time to failures (MTTF) from this data. c) Q3) a) [6] Define MTBF & MTTR. [4] The power required for the total operation is provided either from the mains or if the mains fail, from an auxiliary genset (or from an uninterrupted power supply unit). The cooling system consist of a compressor unit, a heat exchanger and an expander with coolant pipes. The compressor unit receives its power either from the mains or from the genset. The heat exchanger receives its water supply from one of the three alternative sources namely metro, overhead tank or sump and pump system. The pump is supplied power either from the mains or from the genset. The computer is not allowed to function if there is no supply of cold air. Construct a fault tree from Fig. 1. [8] A) Genset. B) Mains. C) Compressor. D) Heat exchanger. E) Expander. F) Blower. G) Sump Pump. H) Overhead. I) J) Metro. K) Uninterrupted Power Supply. [3764]-175 2 Computer. b) For an emergency operation theatre in a hospital, the power is obtained from the main city supply through a transformer connected in series. To ensure an uninterrupted supply, an auxiliary generator is also connected with a suitable switch over. The probability of failure of the city supply is 0.01 and the transformer reliability is 0.996. The auxiliary power generator has a reliability factor of 0.99. Draw schematic diagram and block diagram for the system. Construct the fault tree and based on this calculate the reliability of the system. [8] OR Q4) a) Explain the concept of Techno-Physico Constraints with a conceptual system. [4] b) Construct fault tree and find system reliability of Fig. 2. [6] c) Construct fault tree and find system reliability of Fig. 3. [6] [3764]-175 3 Q5) a) What do you mean by the term redundancy? Explain active and passive redundancy. [6] b) For the system represented by Fig. 4. Calculate the reliability using tieset and cut-set methods. [6] c) Find the system reliability of the following series parallel configurations. Component reliabilities are given in Fig. 5. [6] [3764]-175 4 OR Q6) a) Explain with sketch: i) Series configuration. ii) [6] Mixed configuration. b) Find the system reliability of the given configurations. Component reliabilities are given in Fig. 6. [6] c) For the block diagram shown in the Fig. 7, write down the minimal tiesets and minimal cut-set. Using these, calculate the reliability of the system, assuming the elements to be independent and identical. [6] [3764]-175 5 SECTION - II Q7) a) Differentiate between : Design FMEA and Process FMEA. Explain methodology of system analysis. [8] b) A company is planning to acquire a truck. Two makes of trucks are available in the market. The cost of garaging and the driver s wages are same for both. The other data on cost are provided in the table. Parameters Truck A Truck B Capital cost Rs. 2 Lakhs Rs. 3 Lakhs Annual Road Tax & Insurance Rs. 7,000 Rs. 8,000 a) fuel consumption 20 km/lit. 24 km/lit. b) oil consumption 2 lit/1000 km 2 lit/1500 km c) fuel cost Rs. 4/lit. Rs.4/lit. d) oil cost 20/lit. 20/lit. Operating Cost Maintenance Cost a) service interval Every 5,000 km. Every 6,000 km. b) cost of service Rs. 4,000 c) random breakdown Every 8,000 km. Every 30,000 km. d) cost of breakdown Rs. 6,000 Rs. 10,000 Expected life 10 yrs. 10 yrs. Rs. 2,000 Calculate annual maintenance cost for a period of 30,000 km & find out which truck is advantageous? [8] OR Q8) a) b) Explain mean, median and mode ranking method. [8] The following data refer to Mean time to failure of a equipment used in electric power house installation. No. of failure MTTF/MTBF (Hrs) 1 2 3 4 5 6 7 8 9 31.3 45.9 78.3 22.1 2.3 4.8 8.1 11.3 17.3 Plot the reliability against time using the method median statistics. How will values changes with mean statistics? [8] [3764]-175 6 Q9) a) Explain: [6] i) Inherent availability. ii) Achieved availability. iii) Operational availability. b) If two components having failure rates 1, 2 respectively are connected in parallel show that the Reliability of this parallel configuration at time t is given as. Rp(t) = e 1t + e 2t e ( 1 + 2)t [10] OR Q10)a) b) Explain the term availability and maintainability of system. [6] The following data have been collected at the plant: Mean time before failure = 60 hrs. Mean time to repair = 30 hrs. Administrative logistic time is 30% of Mean Down Time (MDT). Calculate the operational availability and inherent availability of the plant. [5] c) Explain different types of maintenance system. Q11)Write short note on (Any 3): [18] a) Tie-set & cut-set . b) Reliability - Quality & cost. c) Grouped, ungrouped and censored data. d) Logic gates. e) (RPN) Risk priority number in FMEA. f) Quality & safety. Y [3764]-175 [5] 7

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