EBUS504 Operations Modelling and Simulation

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).

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 gainedimmense 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.

- 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.

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.

3. Practical questions: Multi-Criteria Decision-Making

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 Implementation Feasibility.

• 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 identified:

• 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.