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Interface between hydraulic and mechanical translational domains
The Translational Hydro-Mechanical Converter block models an ideal transducer that converts hydraulic energy into mechanical energy, in the form of translational motion of the converter output member, and vice versa. The compressibility option makes the converter account for dynamic variations of the fluid density.
Using this block as a basic element, you can build a large variety of hydraulic cylinder models by adding application-specific effects, such as leakage, friction, hard stops, and so on.
The converter is simulated according to the following equations:
$$q=\frac{d\left(\frac{\rho}{{\rho}_{l}^{0}}V\right)}{dt}=\frac{d\left(\frac{\rho}{{\rho}_{l}^{0}}\right)}{dt}V+\frac{\rho}{{\rho}_{l}^{0}}\cdot \epsilon \cdot ({v}_{R}-{v}_{C})\cdot A$$
$$F=\epsilon \cdot p\cdot A$$
$$\rho =\{\begin{array}{ll}\frac{\left(\frac{\alpha}{1-\alpha}\right){\rho}_{g}^{0}+{\rho}_{l}^{0}}{\left(\frac{\alpha}{1-\alpha}\right){\left(\frac{{p}_{0}}{p}\right)}^{\frac{1}{\gamma}}+{e}^{-\frac{p-{p}_{0}}{{\beta}_{l}}}}\hfill & \text{ifcompressibilityison}\hfill \\ {\rho}_{l}^{0}\hfill & \text{ifcompressibilityisoff}\hfill \end{array}$$
where
q | Flow rate to the converter chamber |
A | Effective piston area |
v_{R} | Converter rod velocity |
v_{C} | Converter case velocity |
F | Force developed by the converter |
p | Gauge pressure of fluid in the converter chamber |
V | Piston volume |
α | Relative amount of trapped air |
ρ_{l}^{0} | Fluid density at atmospheric conditions |
ρ_{g}^{0} | Gas density at atmospheric conditions |
p_{0} | Atmospheric pressure |
γ | Specific heat ratio |
β_{l} | Bulk modulus at atmospheric conditions and no gas |
ε | Converter orientation with respect to the globally assigned positive direction. If pressure applied at port A exerts force in positive direction, ε equals 1. If pressure applied at port A exerts force in negative direction, ε equals –1. |
The piston volume is computed according to
$$\begin{array}{l}V={V}_{dead}+A\cdot \left({x}_{0}+x\right)\\ \frac{dx}{dt}=\epsilon \cdot \left({v}_{R}-{v}_{C}\right)\end{array}$$
where
V_{dead} | Chamber dead volume |
x_{0} | Piston initial position |
x | Piston displacement from initial position |
Port A is a hydraulic conserving port associated with the converter inlet. Ports R and C are translational mechanical conserving ports associated with the rod and the case of the converter, respectively.
The block dialog box does not have a Source code link. To view the underlying component source, open the following files in the MATLAB^{®} editor:
For incompressible converter implementation — matlabroot\toolbox\physmod\simscape\library\m\+foundation\+hydraulic\+elements\translational_converter_incompressible.ssc
For compressible converter implementation — matlabroot\toolbox\physmod\simscape\library\m\+foundation\+hydraulic\+elements\translational_converter_compressible.ssc
where matlabroot is your root folder.
The block simulates an ideal converter, with an option to account for fluid compressibility. Other effects, such as hard stops, inertia, or leakage, are modeled outside of the converter.
Effective piston area. The default value is 5e-4 m^2.
Specifies converter orientation with respect to the globally assigned positive direction. The converter can be installed in two different ways, depending upon whether it exerts force in the positive or in the negative direction when pressure is applied at its inlet. If pressure applied at port A exerts force in negative direction, set the parameter to Acts in negative direction. The default value is Acts in positive direction.
Specifies whether fluid density is taken as constant or varying with pressure. The default value is Off, in which case the block models an ideal transducer. If you select On, the block dialog box displays additional parameters that let you model dynamic variations of the fluid density without adding any extra blocks.
Initial offset of the piston from the cylinder cap. The default value is 0.
Volume of fluid in the chamber at zero piston position. The default value is 1e-4 m^3.
Gas-specific heat ratio. The default value is 1.4.
Initial pressure in the chamber. This parameter specifies the initial condition for use in computing the block's initial state at the beginning of a simulation run. The default value is 0.