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Simulation Study Using Simul8

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Simulation Study

Pilkington Library Main Issuing Desk

Abstract: This paper investigates the activity of the main issuing desk at the 3rd floor of Pilkington Library during weekdays between 5 and 6pm. The aim is to find ways of minimizing queuing times and respond to flexibility in demand. Two sets of data have been analysed and transposed into a simulation study using the Simul8 software package. The results of the simulation are presented in support of our optimization proposals.


With more than 370,000 books issued last year, serving almost 15,000 users which made up to 600,000 enquires, the Pilkington Library is definitely one of the busiest place on campus especially when it gets near the examination period.

One of the library objective is:

"To support and facilitate the research, learning, teaching and administrative activities of the University, by organising, maintaining and providing access to appropriate literature and information resources in such a way as to provide optimum benefit for Library users." (Loughborough Library)

Of course, the library is a complex facility providing a range of services which far exceeds our simulation capabilities requiring the support of over 80 staff and use of specialised computer packages to track all items, users, requests and staff resources ensuring the functionality of the whole system.

The scope of our research therefore will be limited to the long-loan counter at the 3rd floor of the library which is the main contact point between the users and the library circulation system. Our aim is consistent with the library's own objective of optimizing the service for the benefit of its users. One way of doing this is by finding ways to minimize queuing times and respond to flexibility in demand.

Data Collection

In order to gain a better understanding of how the issuing desk operate we ran 2 sessions of data collection (1 hour each). We decided to collect the data on Monday and Tuesday between 5pm and 6pm. During these sessions we looked at how the system operates starting with a sketch of our conceptual model and analysing whether the scope of our project should include any other information. For example beside the main counter there is a drop-in box for returns only and there are another 2 self-service issuing machines. We decided to include these into our research since they can be often used to supplement or substitute the main counter duties. Regarding short-loan items we decided not to include them since they are organised as a self-contained system.

Since users (especially students) DO NOT come to the library in a orderly deterministic fashion there is a high level of uncertainty and the system presents a stochastic behaviour. To accommodate this problem we decided to use a diary of significant events in which we recorded the following information:

* Initial length of each queue

* Time when somebody joins a queue (main, self-service, drop-in box)

* Time when somebody joins counter (which counter)

* Time when somebody leaves counter (which counter)

We used the following tables:

N Joins queue

(main) Joins counter 1 Joins counter 2 Joins counter 3 Leaves counter

N Joins queue

(self service) Joins counter 1 Joins counter 2 Leaves counter

N Joins queue

(drop-in box) Starts unloading Leaves

* tables are provided in appendix A

The Conceptual Model

Once our data collection was over we had to develop our computer model in order to simulate the real system. According to Oakshott, 1997 "a conceptual model of a system should be developed before specifying the computer model. The conceptual model will specify the interactions between the different components of a system". Oakshott recommends the use of activity cycle diagrams in which all components of the system are assumed to have a life cycle, and the purpose of the diagram is "to show how the different life cycles combine to create the system."

Before composing the simulation model, we made some assumptions about the library system. These were as follows:

* If a person had an enquiry, they would use a counter if it was available and staffed.

* Once a person had finished their enquiry or action, they would move away from the counter, drop-in box or machine so it was free again.

* Enquiries would be able to be solved by the member of staff behind the counter.

* Both self-issue machines were in working order

* Drop-in box is not full

* People will queue in an orderly fashion

We believe our conceptual model gives a good representation of the library system that we observed. It takes into account the assumptions we made and therefore we took this forward as a basis for the Simul8 model.

Below is a screenshot of the model which was created. Starting from the left hand side, the first 3 icons are work entry points. They represent the entrance to the queuing systems for the counters, self-issue systems and drop-in boxes respectively. These work entry points are then joined to storage areas which represent the queues for each of the different points of service. From the



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