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Custom Hydraulic Fluid

Working fluid properties, set by specifying parameter values

Library

Hydraulic Utilities

Description

The Custom Hydraulic Fluid block lets you specify the type of hydraulic fluid used in a loop of hydraulic blocks. It provides the hydraulic fluid properties, such as kinematic viscosity, density, and bulk modulus, for all the hydraulic blocks in the loop. These fluid properties are assumed to be constant during simulation time.

The Custom Hydraulic Fluid block lets you specify the fluid properties, such as kinematic viscosity, density, bulk modulus, and relative amount of entrapped air, as block parameters.

The Custom Hydraulic Fluid block has one port. You can connect it to a hydraulic diagram by branching a connection line off the main line and connecting it to the port. When you connect the Custom Hydraulic Fluid block to a hydraulic line, the software automatically identifies the hydraulic blocks connected to the particular loop and propagates the hydraulic fluid properties to all the hydraulic blocks in the loop.

Each topologically distinct hydraulic loop in a diagram requires the properties of the working fluid to be specified. You can specify these properties by using either a Custom Hydraulic Fluid block or a Hydraulic Fluid block, which is available with Simscape™ Fluids™ libraries. If no Hydraulic Fluid block or Custom Hydraulic Fluid block is attached to a loop, the hydraulic blocks in this loop use the default fluid, which is equivalent to fluid defined by a Custom Hydraulic Fluid block with the default parameter values.

Parameters

Fluid density

Density of the working fluid. The default value is 850 kg/m^3.

Kinematic viscosity

Kinematic viscosity of the working fluid. The default value is 1.8e-5 m^2/s.

Bulk modulus at atm. pressure and no gas

Bulk modulus of the working fluid, at atmospheric pressure and with no entrapped air. The default value is 8e8 Pa.

Relative amount of trapped air

Amount of entrained, nondissolved gas in the fluid. The amount is specified as the ratio of gas volume at normal conditions to the fluid volume in the chamber. In practice, the relative amount of trapped air is always greater than 0. If set to 0, ideal fluid is assumed, but you will get a warning upon simulation. The default value is 0.005.

Absolute pressure below absolute zero in blocks with fluid compressibility

During simulation, the software checks that the absolute pressure does not fall below absolute zero. This check is performed only for those blocks in the hydraulic circuit where fluid compressibility is important. The value of this parameter determines how the block handles the out-of-range assertion during simulation:

  • Error — If the pressure falls below absolute zero, the simulation stops and you get an error message. This is the default.

  • Warning — If the pressure falls below absolute zero, you get a warning but the simulation continues. Use this option when modeling systems where cavitation can occur in extreme cases.

Ports

The block has one hydraulic conserving port.

Introduced in R2007a

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