Application of Simulators

ProModel from ProModel Corp (Orem, UT) is a discrete-event (i.e. dynamic) simulation software used for evaluating, planning or designing manufacturing, warehousing and logistics. It is a Windows-based system with a graphical interface and object-oriented modelling constructs that can eliminate the need for programming (Benson, 1997).

The user interface is in ‘spreadsheet’ format. While complex features of manufacturing systems can be built from pre-existing model elements within the software, programming using languages such as C may be carried out externally and linked to ProModel and accessed any time during runtime for increased flexibility (www.promodel.com).

Companies who have used the software include Pfizer, Johnson & Johnson and Bristol Myers Squibb. A case study released by ProModel Solutions (formed from 2000 merger of ProModel Corp and QuestOne Decision Sciences) describes the use of ProModel by independent consultants to increase the efficiency of a generic

pharmaceutical firm’s QC laboratory throughput. A series of ‘what if’ scenarios were used as a form of sensitivity analysis of the performance of the lab, answering such questions as

- The impact of changing the mix of sample releases on lab efficiency - Staff shift assignments and team organisation of the operating efficiency - Identification of production bottlenecks

- Effect of planned and unplanned equipment downtime on lab workflow

(www.promodel.com). 

ExtendSim (Imagine That!) is another visual simulation tool which allows model building using pre-built components without the need for programming (Krahl, 2000).

Extend models are built using blocks which describe calculations or process steps.

Groups of blocks with similar characteristics can be found in block libraries incorporated in the software. The internal database also allows for a large amount of parameter storage within the software itself and can be accessed by all library blocks.

There are certain features of the ExtendSim software which include reusability of blocks within each model and the ability to save within the system for other models, ability to process large scale system models, simple graphical representation and interactivity with other applications such as Excel. Extend also has an optimisation block which determines the best model configuration. Further flexibility comes from its programmability feature – its built-in C-based language, ModL, can be used to develop new modelling components (Krahl 2000) thus allowing for greater specificity for the user and the project. This integrated programming feature distinguishes it from simulation tools such as ProModel which allow for external programming of model components which are then linked to the model.

An example of the application of ExtendSim is given by Sharda and Bury (2008) where they used the simulation software to determine the reliability of a chemical plant by understanding the key equipment components that contribute towards maximum production losses. According to the Sharda and Bury, Extend was chosen for this application due to its capabilities in modelling both discrete and continuous process elements simultaneously and also it’s hierarchical structure, allowing for

intuitive model. In order to determine plant reliability they ran a series of scenarios based analysis, using the Extend database to store and export data for analysis. As a result they were able to determine areas of concern with regard to component efficiency.

Lim et al (2004) describe the use of Extend to model and compare perfusion-based and fed-batch based processes in the production of monoclonal antibodies, looking at features such as resource management, mass balance analysis, in-process testing and costing. Lim et al (2004) use the database SDI tool to transfer data via the interface with Excel. This is a complex method of data transfer and it requires an expensive plug-in for Excel. However for the more complex models with a great number of Excel tables which need to be linked it is the better choice as it allows for automatic importation of all similarly structured tables and ease of use when relating the data or attributes to items. With regards to calculations, instead of carrying these out in Excel and then linking the results of those calculations to the Extend model via tables, calculations are carried out in Extend. Lim (2004) comments on the limitations of this approach.For a complex model calculations done in Extend slow the simulation runs down significantly. In fact a run of this particular model took 10 minutes on an average processor rather than a few seconds. Calculations done in Extend also often cause the software to crash which is highly inconvenient.

However, Lim et al (2004) also comment on the advantages of using the Extend simulation tool stating that the graphical representation creates an intuitive simulation environment while the animation during model runs enables the user to view events as they occur and allows for debugging.

Rajapakse et al (2004) use Extend to map the development, manufacture and testing stages of the three clinical trial phases along with the proceeding 20 years in market for 6 drugs. The fundamental aim of the model is to calculate the estimated number of drug successes and NPV based on development times, capital and human resource constraints and taking into account the implications of contract manufacturing. Here, Rajapakse et al (2004) introduce stochastic modelling, adding probability distributions to uncertain input parameters, to perform sensitivity analyses. No limitations of the software tool are stated.

Simul8™ (Simul8 Corporation) is a discrete event simulator which interfaces to common external programs such as Excel or Visio. It is targeted at many industries including manufacturing and capacity planning. A Simul8 simulation involves processing work items. These enter the system via work entry points, pass through work centres, may temporarily reside in storage areas and leave via work exit points (Hauge and Paige, 2001). Hauge and Paige (2001) state that when creating a model using the Simul8 platform, the starting point is to add a few items onto the workspace and connect them, creating the basic logic of the simulation.Further details can then be specified via dialogue boxes, including changing the names of the objects. This functionality is very similar to other discrete event simulators. SIMUL8 can also be used to conduct extensive trial runs. When a trial is complete the software automatically prepares summary reports of the results. Specific areas can then be picked from the summary and further analysed by the various statistical tools and diagrams made available.

The Simul8 simulation tool allows analysis of manufacturing processes without the requirement of programming knowledge. However, importantly, its simplicity creates a utility threshold beyond which more complex workbench tools such as Extend would serve a company better in seeking answers to more in-depth design and manufacturing questions.