PistonAccumulator

    PistonAccumulator

Library

HydraulicsByFluidon/Components/Volumes

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.

Parameters

PistonAccumulator_0

NameLabelDescriptionData TypeValid Values

mo_pistonDiameter

pistonDiameter

Diameter of piston

Scalar

mo_nominalVolume

nominalVolume

Nominal volume

Scalar

mo_gasDeadVolume

gasDeadVolume

Additional gas volume

Scalar

mo_deadVolume

deadVolume

Fluid dead volume

Scalar

mo_angle

angle

Inclination angle

Scalar

mo_massPiston

massPiston

Piston mass

Scalar

mo_relBiasingPressure

relBiasingPressure

Biasing pressure (rel.)

Scalar

mo_biasingTemperature

biasingTemperature

Biasing Temperature

Scalar

mo_polytropicExponent

polytropicExponent

Polytropic exponent

Scalar

mo_enableStrokeOutput

enableStrokeOutput

Enable stroke output

Number

0
1

mo_enableVelocityOutput

enableVelocityOutput

Enable velocity output

Number

0
1

mo_enableVolumeOutput

enableVolumeOutput

Enable fluid volume output

Number

0
1

mo_cylinderLength

cylinderLength

Cylinder length

Scalar

PistonAccumulator_1

NameLabelDescriptionData TypeValid Values

mo_fProp

fProp

Velocity dependent friction

Scalar

mo_fCoulomb

fCoulomb

Constant friction/Coulomb force

Scalar

mo_fBreakaway

fBreakaway

Breakaway friction force

Scalar

mo_vM

vM

Velocity parameter for Stribeck friction

Scalar

PistonAccumulator_2

NameLabelDescriptionData TypeValid Values

mo_stroke

stroke

stroke

Structure

mo_stroke/fixed

fixed

Cell of scalars

true
false

mo_stroke/start

start

Cell of scalars

mo_velocity

velocity

velocity

Structure

mo_velocity/fixed

fixed

Cell of scalars

true
false

mo_velocity/start

start

Cell of scalars

mo_pA

pA

pA

Structure

mo_pA/fixed

fixed

Cell of scalars

true
false

mo_pA/start

start

Cell of scalars

mo_strokeOut

strokeOut

strokeOut

Structure

mo_strokeOut/fixed

fixed

Cell of scalars

true
false

mo_strokeOut/start

start

Cell of scalars

mo_velocityOut

velocityOut

velocityOut

Structure

mo_velocityOut/fixed

fixed

Cell of scalars

true
false

mo_velocityOut/start

start

Cell of scalars

mo_volumeOut

volumeOut

volumeOut

Structure

mo_volumeOut/fixed

fixed

Cell of scalars

true
false

mo_volumeOut/start

start

Cell of scalars

Ports

NameTypeDescriptionIO TypeNumber

fluidPort

implicit

Hydraulic port

input

1

Port 2

implicit

Stroke of piston

output

mo_enableStrokeOutput

Port 3

implicit

Velocity of piston

output

mo_enableVelocityOutput

Port 4

implicit

Fluid volume

output

mo_enableVolumeOutput