PistonAccumulator

Description

Model of a gas-loaded accumulator with a piston separating the media. Fluid inertia is not considered. The gas is modelled as an ideal gas.

The parameters Biasing pressure, Nominal volume, Dead volume, and Additional gas volume describe the accumulator in the unconnected state.

At a piston stroke of 0 m only the Dead volume remains in the accumulator. Due to the typically small dead volume, a high mathematical stiffness of the accumulator can result. This behavior might require choosing a correspondingly small timestep.

The parameter Polytropic exponent characterizes how pressure changes affect the volume and stiffness of the gas volume. If Polytropic exponent is set to unity, the change of state within the gas is isothermal. This implies perfect heat transfer between the gas in the bladder and the environment such that no change of temperature occurs in the gas. This situation is encountered in hydraulic accumulators if the load cycles of the liquid are lengthy.

If the Polytropic exponent is set to the isentropic exponent (1.4 for air), the gas undergoes an adiabatic change of state which means that no heat exchange with the environment can occur. This is typically the case for very short load cycles.

The Biasing pressure (rel.) is converted according to the ratio of Biasing Temperature and fluid temperature and the Polytropic exponent at the beginning of the simulation.

The parameters Breakaway friction force, Constant friction/Coulomb force, Velocity dependent friction and Velocity parameter for Stribeck friction (velocity where the friction force begins to grow linearly) characterize the velocity dependence of the friction force between piston and cylinder.