Introducing Modeling and Simulation Tools

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Introducing Modeling and Simulation Tools

• Steven Gordon
• Senior Director of Education and Client Services
• sgordon_at_osc.edu

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Introductory Modeling Tools

• Requirement for tools that meet current level of
  students
• Four major (arbitrary) groups
• Traditional programming languages C, C,
  Fortran, Java
• Higher level programming languages MATLAB,
  Maple, Mathematica
• Graphical modeling packages Vensim, Stella,
  Berkeley Madonna, AgentSheets
• Specialized domain specific packages Fluent,
  Gaussian, Ansys, OpenFoam, Comsol
• Pros and Cons to Each
• Applicability
• Level of expertise required
• Time allocated for the work
• Relationship to overall curriculum
• Relevance to industry

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Covering a Range of Examples

• Presenting at least one of each type in this
  workshop
• Others may be available as we go farther into the
  week
• Overview for the afternoon
• Vensim and Introductory MATLAB
• More advanced MATLAB
• OpenFoam
• COMSOL

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Vensim Basics

• Systems dynamics modeling tool
• Best suited for phenomena that vary over time or
  space
• Visually oriented tool that allows construction
  of causal loops and stock and flow diagrams
• Excellent to help conceptualize and test model
  structures
• Built-in functions allow building of mathematics
  associated with the model with a minimal efforts
• Output of graphs and tables for any part of the
  model automatic

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Examples for Today

• Several documents with introductory materials
• Resources broad array of sites with models
  prepared as parts of other projects or
  contributed by users to software vendor sites
• MATLAB models specific examples of engineering
  models in MATLAB
• Vensim and other models specific examples using
  Vensim, Stella, Java applets, Excel

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Building A Vensim Model

• Start Vensim on your computer
• File New
• Choose a time period of 0 to 12 months
• Build a simple model of a shoe department showing
  available stock with a goal
• Given a discrepancy between the stock and the
  goal, how long a delay in orders should we
  tolerate to keep close to the goal?

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Model In Text Format
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A More Complex Model

• Save your model
• Copy the file BODvensim to your local drive
• Open the file
• Model of dissolved oxygen in a stream
• Impacted by several major variables
• Organic waste from sewage (BOD)
• Stream temperature
• Channel characteristics
• Mixing of effluent with stream volume

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Simulation Goals

• Keep Dissolved Oxygen above 4.0 ppm during the
  critical summer period
• Low flow conditions
• Higher temperature holds less DO
• Manage the volume of and treatment level of the
  waste
• Many simplifications not explained here

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Vensim Features

• Multiple views of the model
• Click to see View2
• Shows how you can customize a view of model
  inputs and outputs to facilitate exploration
• Slider bars to change the values of major
  parameters
• Graphs and tables to show the impacts of changes
  and even compare different scenarios
• Example
• Click on the SET icon along the top toolkit
• Change the value of BOD sewage to 25
• Change the title to BOD25
• Run the model