1. Practical questions: Operations modelling (40 Marks)
In a wax manufacturing, WAXs arrives every 1hr in lot sizes of 4 to a buffer. Each wax is sent to
assembly machine named OVEN where it is combined with Mould into one part. The oven needs 5
mins for set up which requires an operator. Then the oven runs another 15mins to combine the wax
to the mould. Once the combined part is done, it is sent to a cooling for at least 40 mins. Eventually,
the combined part needs to be split from the mould in a split machine for 5 mins after the cooling.
Once the wax is split, it is a finished product and is ready-to-ship.
a) Regarding above description, map out the overall WAX manufacturing processes with a process
mapping tool of your choice. (10 marks).
b) Considering a configuration of two ovens, one operator, 3 moulds, one cooling and one split
machine, use a Gantt Chart to identify the bottleneck of the total outputs of above operation. You
may need some explanations and calculations to back up your arguments. (10 marks).
c) Use witness to simulate the described process and to quantify one key operations performance
from the process. Propose a solution to double its performance based on the settings of
Question(b). Details of your analysis need to be explained. (20 Marks).
2. Practical questions: System Dynamics (30 Marks)
The COVID-19 pandemic has a massive negative impact on human wellbeing and the global economy
since its outbreak at the end of 2019. Early studies have shown that using Personal Protective
Equipment (PPE) helps for protection against the spread of the disease. Therefore, retailers have put
an enormous effort on the stable, reliable, and rapid management of PPE supply chain. During the
pandemic, the procurement and inventory management for PPE has gained immense attention.
Retailers believe that system dynamics might help them plan procurement, inventory and sales
planning for PPE. It is very well known that if there is no PPE inventory, there can be no sales. In other
words, PPEs are sold from inventory. It is also known that if there is no PPE procurement, there is no
PPE inventory. Each PPE item first goes into inventory once they arrive. If the PPE sales increase,
retailers purchase more PPE.
To be on the relatively safe side, retailers have a target inventory which is equal to coverage level (c
months) times PPE sales (i.e. target inventory is c months of sales). There is a time to replenish PPE
inventory and it is called lead time.
a) Draw the Causal-loop diagram, put the sign (positive or negative) for the whole model, discuss the
model and write equations for variables. (10 Marks).
b) A retailer has a coverage level of 4 months and the lead time of PPE is 2 months. Assume that the
retailer has an initial inventory level of 100000 PPE and the demand of PPE has a step-wise function.
Demand is 20000 units between 0-25 months, demand is 45000 between 25-75 months, and finally
demand is 60000 units between 75-100 months. (15 Marks).
– Establish complete model on Vensim and report model as screenshot in the report. Run this model
on Vensim for 100 months with time step of 0.25.
– Discuss results for inventory level, procurement level and show graphs of results.
– Make recommendations to the retailer.
Questions to: Dr. Jorge Hernandez – jorgehh@Liverpool.ac.uk
c) Apart from retailers, governments also have a similar problem of PPE procurement and inventory
management as their frontline workers need PPE for free of charge. If you are asked to solve this
problem for a government organisation, what would change in your model and in your parameters?
Critically discuss this new setting. (5 Marks).
3. Practical questions: Multi-Criteria Decision-Making (30 Marks)
In one organisation there are several types of projects to be implemented, but the organisation
needs help to prioritise them, so that they know how to plan their tasks for the next year under
potential pandemic scenarios.
For the selection of each project, and based on several focus groups within the organisation, the
following main criteria has been identified: Stakeholders Commitment, Financial, Strategic,
Implementation feasibility. After this identification, and based on several join analysis within the
organisation, the following relationships were also identified:
• Stakeholders Commitment is four times less important than Financial, six times more
important than Strategic and five times less important than Implementation Feasibility.
• Financial is three times less important than Strategic and six times less important than
• Strategic is six times more important than Implementation Feasibility.
In the same way, for each criteria, the following sub-criteria and their relationships have been
• Stakeholders commitment: Organisation commitments, Team Commitment and Project
Manager commitment. Where relationships amongst them are as follows:
o Organisation commitments is seven times more important than Team Commitment
and two times more important than Project Manager commitment.
o Team Commitment is two times less important than Project Manager commitment.
• Financial: profit, return on investment and net present value. Where relationships amongst
them are as follows:
o Profit is three times more important than Return on investment and equally
important to Net present value.
o Return on investment is two times less important than Net present value.
• Strategic: Access to international market, continuous improvement and reputation. Where
relationships amongst them are as follows:
o Access to international market is four times less important than continuous
improvement and seven times less important than Reputation.
o Continuous improvement is three times less important than Reputation.
• Implementation feasibility: Risk Organisation, Urgencies management and Internal
knowledge. Where relationships amongst them are as follows:
o Risk Organisation is five times more important than Urgencies management and
seven times more important than Internal knowledge.
o Urgencies management is five times more important than Internal knowledge.
Questions to: Dr. Jorge Hernandez – jorgehh@Liverpool.ac.uk
In this context, the Random index table is as follows:
Regarding to this information please elaborate an MCDM excel matrix to support your answers to the
a) Elaborate the hierarchical tree and identify each Weights for each criteria and sub-criteria.
Provide the global and local weights. Based on the results, what are the most desirable aspects
a project should consider? (10 Marks).
b) Calculate the consistency ratio. Analyse the result. (5 Marks).
c) The organisation has received five project proposals and they are looking now to know which
one will be the most convenient. Each proposal was interviewed to obtain the information
about which criteria they prioritize. Considering the collected information about each project
prioritiesshown below, please provide the benefit from each proposal and analyse the results.
Which project should be selected?: (15 Marks).
o Project 1: Team commitment, net present value, Access to international markets,
o Project 2: Project Manager commitment, net present value, reputation, internal
o Project 3: Organisation commitment, profit, reputation, Risk Organisation.
o Project 4: Team commitment, profit, continuous improvement, Risk Organisation.
o Project 5: Project Manager commitment, return on investment, reputation, Urgencies