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MapleSim Hydraulics Library from Modelon

Multi Port Oil Volume  Lumped volume with pressure-dependent bulk modulus, with vectorized connector

The Multi Port Oil Volume component describes a lumped volume with pressure-dependent bulk modulus. The pressure in the volume is calculated by:

tp=βqvolumeρ

The bulk modulus is given by:

β=βp

Variables used in the above equations

p

pressure in the volume Pa

β

bulk modulus, pressure-dependent Pa

volume

geometric volume of oil under pressure (parameter) m3

q

port_A.q kgs

The calculated pressure is not limited to the vapor pressure but can reach unlimited negative values. A limitation is done in TwoPortComp where all pressures used to compute the differential pressure between the ports are limited to the vapor pressure.

Model Oil Volume is the default model for all lumped volumes in the library. The equations are also used in the cylinder models.

Use the modifier

port_A(p(start=2e6,fixed=true))

to set the initial condition for the pressure of the lumped volume in Pa.

The compressibility is an important property of the oil and influences the dynamic behavior of the circuit. Besides the bulk modulus of "pure" (that is, air-free) oil, the amount of undissolved air, the pressure, and the compliance of the component determine the "effective bulk modulus". The default model in the Hydraulics library includes all these effects and describes a typical circuit. However, there are situations when it makes sense to use other models (for example, for a sensitivity analysis to check that the overall dynamic response of the circuit doesn't heavily depend on the oil model).

Figure Bulk modulus of different models as a function of pressure.

Connections

Name

Description

Modelica ID

ports

 

ports

oil

 

oil

Parameters

General Parameters

Name

Default

Units

Description

Modelica ID

nports

0

 

Number of ports

nPorts

ΔTsystem

0

K

Temperature offset from system temperature

dT_system

steady-state init

false

 

Steady state initialization

steadyStateInit

volume

10-6

m3

volume

volume

See Also

Oil Volume, Volumes, MapleSim Hydraulics Library from Modelon Overview


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