Build intuition. Test your understanding.
ModelSim Lab connects mathematical models to the physical behavior they describe.
A place to experiment
Designed for university courses in system dynamics, modeling, controls, vibrations and mechatronics. Change one condition, make a prediction, then compare a new run with a baseline. Equations and explanations stay close to the experiment.
The application works without an account or an external AI service. Theme, scenarios and comparison baselines are saved in this browser when storage is available.
What is being simulated?
- Mass–Spring–Damper — 2 physical states, mechanical.
- Inverted Pendulum — 4 physical states, control.
- Quarter-Car Suspension — 4 physical states, mechanical.
- DC Motor — 3 physical states, electrical.
- Rotational Spring–Damper — 2 physical states, mechanical.
- Series RLC Circuit — 2 physical states, electrical.
- Thermal First-Order System — 1 physical state, thermal.
- Liquid Tank Level — 1 physical state, fluid.
Numerical method
ModelSim uses classical fourth-order Runge–Kutta (RK4). Requested output spacing is separate from integration step size. The solver limits internal steps according to the fastest model rate and input waveform, splits steps at input discontinuities, and checks for nonfinite values.
For fast dynamics, output spacing is automatically refined to preserve response peaks and oscillation counts. At most 30,000 output samples and an estimated 500,000 internal steps are allowed. Difficult combinations are rejected with an explanation instead of silently lowering accuracy. Longer or stiffer simulations may need a different numerical solver.
Expensive runs execute in a Web Worker. Charts reduce rendering density when necessary; CSV exports keep every retained output sample.
Reading the results honestly
The value at the end of a run is a measured sample. Equilibrium is a model prediction. Settling time is an observed last entry into a 2% transition band, with a trailing observation period; a longer simulation can reveal later behavior.
Step overshoot is reported only for suitable nonzero constant or step inputs from zero initial state. Periodic and transient forcing do not receive a fabricated constant steady-state metric. Comparison text reports observed changes and identifies changes to multiple conditions.
Assumptions and limits
Each Model tab documents coordinate conventions and approximations. Components are idealized: linear springs and dampers, a point-mass pendulum, maintained tire contact, a lumped thermal body, and a gravity-drained tank with no overflow limit. PID is a local regulator, not a swing-up controller.
Physical instability means a modeled disturbance grows. Numerical instability means the solver cannot represent the requested trajectory reliably. The application distinguishes these conditions.
ModelSim Lab is educational software. It does not replace certified engineering analysis, hardware validation or specialist judgment for safety-critical design.