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BGModBond graph laboratory
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Build and simulate a bond graph

Dimensionless Signal provides Constant, Boolean Schedule, Piecewise Constant and Piecewise Linear blocks. Connect out to a component’s u input; outputs can feed several inputs. Signal wires carry no power. MR has one hydraulic power port, like R. Connect OpenTank directly to MR for a simple drainage test. Commands must stay within the input range; pump commands are exactly 0 or 1.

  1. Add elements from the library. Drag them across the canvas.
  2. Click “Bond” or press B, then select the first and second elements. You can start a bond from a circular port.
  3. R/C/I/Se/Sf have one port; 0/1 junctions have a separate port for each bond. Select named ports on library components: M is translational, R is rotational, E is electrical, and hydraulic components use H or named fluid ports.
  4. Set parameters and initial states in the panel on the right. All quantities use SI units.
  5. “Analyze” shows causality, equations and errors. “Simulate” plots time series.

At a 1-junction, +/− labels fix the port signs when a bond is created. “Reverse reference” changes the signs of flow and power along the arrow while preserving the port signs and physical model. To change a port connection, delete the bond and recreate it in the opposite order.

TF is available in all four physical domains with same-domain P/S ports and a positive ratio n. It conserves power: eP = n·eS and fS_local = −n·fP_local. For hydraulics this converts pressure and flow. For translation it models a constant-ratio lever or polyspast; four supporting rope strands use n = 0.25. Choose the pressure-transformer or polyspast example to explore the ratios.

For rotational models, effort is torque (N·m) and flow is angular velocity (rad/s). I represents inertia J and stores angular momentum; C stores spring twist in rad. Enter stiffness K in N·m/rad; compliance C = 1/K is saved internally. The ideal gear TF uses n = N₁/N₂: T₁ = n·T₂ and ω₂ = n·ω₁, with a positive axis chosen for each shaft.

For electrical models, effort is voltage (V), flow is current (A), C stores charge (C), and I represents inductance (H) and stores flux linkage (Wb). The common return conductor is the zero-voltage reference.

For hydraulics, C stores generalized volume q and I stores pressure momentum Γ. The pump uses an approximate 7A curve; the cylinder uses ideal transformers and the accumulator uses a polytropic gas law. Simulation stops at stroke, gas-volume or pressure limits. Cavitation, end-stop contact and regulator dynamics are not modeled.

Save drafts as JSON. Analysis checks connection errors. Choose educational examples from the top selector. The 7A bench starts with a partially charged accumulator. Internal component graphs are available after analysis.