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VDMS Program Architecture


VDMS is programmed in Simulink but run through the MATLAB Command Window. Knowledge of Simulink is not required (unless the user wishes to modify the model itself). A basic knowledge of MATLAB is required.

Below is the top level Simulink block diagram. This shows the general layout of the VDMS simulation. Each box (block) is a subsystem containing another set of blocks--possibly more subsystems. VDMS contains over 100 subsystems. Blocks, subsystems and signals are labeled and units are often provided.

VDMS Top Level Simulink Block Diagram
Top Level Block Diagram.  Click to Enlarge.

All blocks and signals are accessible to the user with the following exceptions. First, the Core Equations of Motion block contains several compiled S-Functions. These are compiled versions of the source code shared with MMM, LTS and VDS (and developed over the last 30+ years). MRA's Nondimensional Tire Model is also compiled as an S-Function and the source code is not accessible by the user.

This type of architecture offers distinct advantages:

  • Compiled code runs faster than regular Simulink blocks
  • Compiled code avoids unintentional modification of key equations
  • Compiled code is mostly physics and mathematics that describe the way our world works--there should be no reason for the user to need to alter it.
  • The rest of the code is OPEN TO THE USER
  • Users can add-in proprietary blocks representing vehicle systems, active systems, control algorithms, etc.
  • Subsystems are easily substituted when a new model of a particular item is desired
  • Program flow and execution are easy to determine and understand

VDMS uses multirate, fixed-stepsize integration. The wheel spin degrees of freedom are integrated at a faster rate than the other degrees of freedom to improve simulation accuracy. The integration rates are user-defined.

Solution time for a simulation is roughly 1 second of computer time for every second of simulation time. Past versions of VDMS have been compiled for real-time and hardware-in-the-loop applications.


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