BGMod — Gas accumulator

ACCGas accumulatorGasAccumulator · Газовый аккумулятор

H hydraulic · state x = liquid volume

Liquid inflow compresses gas according to a fixed polytropic law. The accumulator starts partially charged.

V_g = V0 − x · dx/dt = Q_H
p_abs = p0_abs (V0/V_g)ⁿ
p_H = p_abs − reference_pressure_abs
x0 = V0 [1 − (p0_abs/p_init_abs)^1/n]

Parameter	Meaning / unit	Default
V0	Gas volume at precharge [m³]	0.001
p0_abs	Absolute precharge pressure [Pa]	12 × 10⁶
n	Polytropic exponent [1]	1.4
Vg_min	Minimum gas volume [m³]	0.0001
p_init_abs	Absolute initial gas pressure [Pa]	13 × 10⁶

Limits: V0, p0_abs, n > 0; 0 < Vg_min < V0. Initialization requires 0 < x0 < V0 − Vg_min. Simulation stops at empty liquid volume or minimum gas volume.
Outputs: Liquid/gas volumes, gauge pressure, inflow, port power and energy potential W = ∫p_gauge dx.
Scope: Ideal separator and fixed exponent. W is the port’s energy potential, not total thermodynamic energy. No continuation through an empty state with a closed port.

Classic bond graph

Constitutive equivalent: a nonlinear one-port C, with liquid volume x as its state and dx/dt = Q_H. This is implemented directly, not expanded into a constant C macro. The pressure offset uses the document reference pressure; a single constant C cannot reproduce the full gas law. The limits listed above remain part of the model. Half-arrows set positive power references; dashed pink arrows carry signals only. Causal strokes are omitted because they depend on the connected model.