# Problem 1: Show that the mean time to failure of a parallel system of n identical components, each with an exponential time to failure with mean 1/?, is

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MANU 2117, Semester 2, 2020
Answer all the questions.
Submission Time: 9:30 pm on Canvas portal only. Make sure to upload before time. No email submissions will be accepted or marked. Your submission must pass through Turn-it-in software on Canvas. Do not send question or cover sheet.
Problem 1: Show that the mean time to failure of a parallel system of n identical components, each with an exponential time to failure with mean 1/?, is
1/?(1+1/2+1/3+?+1/n).
(8 points)
Problem 2). A pump/filter system supplies clean fluid to a production process. The system consists of two subsystems in parallel (S1 and S2), to increase reliability. Each subsystem consists of one pump and a filtering element in series. S1 has one filter as the filtering element. The filtering element of S2 has two filters in parallel. Failure rate of each pump is 1.5 per year (failure time exponentially distributed), and of each filter, 2.5 per year (exponentially distributed), when they operate.
a). Draw the reliability block diagram of the pump/filter system.
b). Calculate the reliability of the system for 9 months of operation.
c) Find Mean Time To Failure (MTTF) of the system.
(6 points)
Problem 3).
a). What are the operational risks in a supply chain network? How do they differ from disruption risks? Explain with appropriate examples.
b). How well are supply chain risks recognised across a network? What can Companies do to enhance supply chain risk management capabilities?
c). A large medical device manufacturer has experienced a number of disruptions to operations and customer service within their supply chain. As a result of this, the supply management team at the company is tasked with creating a framework to better understand the drivers that create supply disruptions and mitigate the risk. How will the team develop a framework for reducing the impact of disruptions to the supply chain?
d). How can the implementation of Supply Chain Risk Management processes be organised within and across companies?
e). How would you reduce risk in the auto parts supply chain which has been threatened?
(Note: No credit will be given if you copy and paste from class lecture notes or other sources. You need to write the answers in your own words).
(8 points)
Problem 4). The current reliability of Complex GA Aircraft Systems is unknown. The ability to gain insight into this unknown will provide the aviation community with a valuable benchmark that will assist in the development of reliability and safety requirements for future aircraft. This benchmark must be established in order to ensure that technology development, design guidelines, and work on certification standards progresses towards the effective goal of affordable technologies for small engine airplanes.
In order to provide relevant information regarding GA aircraft reliability that is conducive to the engineering goal of ensuring development of an affordable, advanced single pilot transportation aircraft, it is necessary to include airplanes that share many of the characteristics of future aircraft design. The proposed future aircraft design will consist of an aircraft with a cruise speed of 160 knots and a range of 700 nm. This aircraft is considered to be a single pilot, four-place, light-single engine piston aircraft with near all weather capability.
Complex GA Aircraft have retractable landing gear, flaps, and a constant-speed propeller. The systems of the future aircraft will be very similar to current Complex GA Aircraft Systems and therefore, represent the population of GA aircraft used in this study. Where the futuristic airplane model did not provide guidance into design complexity or definition, typical Complex GA Aircraft architecture was assumed.
The approach used in performing the reliability study is to define the Complex GA Aircraft Systems and Subsystems for complex aircraft, collect failure data from a random sample of complex aircraft, and then analyze the data in order to determine reliability estimates. To accomplish this, Complex GA Aircraft were divided into the following two systems indicating primary function:
Airframe – any component or structure that is essential to the structural integrity of the aircraft.
Control – any component that controls the aircraft’s attitude, heading, and altitude or changes the aerodynamic characteristics of the aircraft in the air or on the ground (excluding powerplant).
After researching many data sources and collection methods, it is determined that failure data obtained from operational aircraft would provide a good benchmark of current system reliability and that logbooks of complex aircraft could provide the source of this failure data.
The method selected for estimating the reliability of the GA Aircraft Systems is to first determine the proper distribution that models the collected failure data for each sub-system. This is accomplished by placing the failure data collected from the total number of aircraft sampled into a database and separating them according to the defined subsystems. By constructing probability plots for each subsystem, distributions that describe the failure process can then be obtained. This information can then be used to determine the probability distribution parameters.
Airframe has many components connected in series and if any of the components fails, airframe system fails. Here is the data for airframe failure times.
Given the following 15 failure times in hours:
141 325 640
180 400 700
233 450 735
270 490 770
305 550 830
b. Assume failure times are distributed according to the two-parameter Weibull distribution.

c. By the graphic method, find the Weibull parameters. The Weibull shape and scale
parameters must be estimated using the Weibull probability plot paper.
Determine the reliability of the Airframe at 250 hours.
Aircraft Control system (ACS) also has numerous parts connected in series and if any of the parts fails the aircraft control system fails. Assuming Weibull distribution, the failure times in hours data are given:
22 29 37 45
69 86 95 103
139 174 203 221.
d. Find the Weibull parameters using the Weibull probability paper. Determine the reliability of Aircraft Control system at 250 hours.
(8 points)
Problem 5). A). Suppose we would like to own and operate a Motor Boat dealership in the coastal region of Melbourne city. We would sell a range of new motor boats and repair existing boats.
Define our objectives and develop a business case,
Decide where it will be – potential location sites,
Decide on type of business – ownership or franchise, and the feasibility of expanding the business to other coastal cities in Australia,
Plan for day to day operations from an ILS perspective, including the ten elements discussed in class.
Develop an ILS plan to conduct a Logistics Support Analysis.
(6 points)
b). Explain how design for supportability relates to the following:
(i) design for reliability
(ii) design for maintainability
iii). design for human factors (3 points)
c). What is Reliability-centred-maintenance (RCM)? Its benefits? How do the results of the RCM relate to the system safety? How can the RCM be used to improve the design? (3 points)
d). What is LORA? Its purpose? When can it be applied in the system life-cycle? Describe how the results of the LORA and the MTA can impact each other? (3 points)
(Note: No credit will be given if you copy and paste from class lecture notes or other sources. You need to write the answers in your own words).
Problem 6).
In the Westralia Fire Safety Case Study (available on course web-site) and attached here): (5 Points)
(a). Discuss the role of governance, planning, documentation and operation of maintenance in the Westralia case and the deficiencies related to the mis-handling of these aspects of maintenance.
(b). Elaborate the maintenance and logistics system that you will put in place if you have the opportunity to re-design the support solution for this case.
The ship’s maintenance contractor has four maintenance engineers and two support technicians and a clerical staff for data recording and book keeping.
Tasks are to be performed by ADI on either a ‘continual’ basis for the period of the contract, or on a ‘fee for service’ for occasional tasks.
In order to carry out maintenance under the RPLSS contract, ADI set up the RPLSS office at Rockingham. It was initially staffed with a team of four (4) staff who would perform the core RPLSS functions including a project manager/ship’s agent, two technical specialists (hull and electrical), an information document officer (a clerical assistant/librarian). The RPLSS contract further provided that six (6) subcontract staff would be engaged by ADI to form the AMP management team
The RPLSS office was principally staffed with former senior sailors with tradesman qualifications or equivalent. The senior staff member was the project manager/ship’s agent WESTRALIA. He left the RAN as a Chief Petty Officer Electrical Technical – Communications. A mechanical supervisor or mechanical technical specialist was employed in February 1998 as a result of problems encountered during WESTRALIA’s AMP11 in August 1997. The mechanical supervisor had served in the RAN from 1972 to 1983 and was a Petty Officer Marine Technical – Propulsion Diesel when he left. Before joining ADI he worked, from 1993 to 1997, with Dawsons Engineering, the company that the RAN had contracted with to perform HMAS WESTRALIA’s logistic support.
(Note: No credit will be given if you copy and paste from Case Study handout. You need to write the answers in your own words).

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