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Hydraulics Library 4.1 adds new thermodynamic effects

Jim Claesson February 4, 2015

Hydraulics Library leaps forward with new thermodynamic effects

The Modelica Hydraulics Library 4.1 has taken a leap forward with its new thermodynamic effects. Thermodynamic effects are useful in applications such as vehicle cooling and aircraft fuel-feeding systems.

Analyzing temperature impact

Effects in the new ThermoHydraulics models include temperature rise due to compression in hydraulic cylinders, pressure rise due to heating up of volumes, and cooling due to pressure drop over an orifice.  The effects enable users to analyze how big of an impact temperature has on the hydraulic system, since all oil properties are temperature-dependent.

In practice this means that specific enthalpy is included in the hydraulic ports and a dynamic energy balance in the hydraulic volumes. Hydraulics without thermodynamic effects have only pressure as a state variable and a dynamic mass balance in the volumes. ThermoHydraulics comes with a guide that provides valuable tips on how to create user-defined oils.

If the user does not wish to have thermodynamic effects modeled in the hydraulic system, the original fluids may be used. In that case, everything works just like in the previous versions of the Hydraulics Library. It is easy to switch between ThermoHydraulics and regular Hydraulics by just changing the oil model class.


The ThermoHydraulic oil models are coefficient-based. The user can either define an oil model or simply use a pre-defined model. Coefficients can easily be calculated from tables with provided conversion functions. The ThermoHydraulics oil models run faster than many of the regular oil models.

Modeling knowledge required

The addition of thermodynamic effects requires deeper knowledge of modeling, and care has to be taken to properly connect volume and flow models. Connecting several volumes or flow models requires creating large non-linear systems of equations, and the resulting model may lead to numerical difficulties. Modelon has expertise in thermodynamic modeling and can provide cost-effective assistance to those who need it.

Interfacing with other libraries

ThermoHydraulics makes it possible to interface with ThermoFluid components in the Modelon Base Library (MBL), which is included with the Hydraulics Library (see Figure). The MBL contains every thermodynamic component one could possibly need, including five different heat-exchanger models.

All two-port components (e.g. restriction models) include conditional wall dynamics, making it possible to specify material, thickness and area. The wall dynamics can be used with the Modelica Standard Library heat-transfer components or the dynamic energy balance within the hydraulic volumes.

Find out more

More information and release notes are available on our Hydraulics Library product webpage.

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