Hydraulic orifice definition

@HYDRAULIC_ORIFICE_DEFINITION {
@HYDRAULIC_ORIFICE_NAME {HydOrfcName} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydModl}
@HYDRAULIC_CHAMBER_NAME {HydChmb0Name, HydChmb1Name}
@FUNCTION_1D_NAME {Fun1DName}
@ORIFICE_AREA {Aorf}
@ORIFICE_DISCHARGE_COEFFICIENT {Cd}
@ORIFICE_ENTRANCE_PRESSURE {pEnt}
@ORIFICE_CIRCUIT_PRESSURE {pCir}
}
}

Introduction

Figure 1. Configuration of the hydraulic orifice.

The hydraulic orifice, shown in fig. 1, allows the flow of hydraulic fluid through an orifice of sectional area Aorf and is associated with hydraulic device model, HydModl. The orifice is connected to two hydraulic chambers, HydChmb0Name and HydChmb1Name, respectively, with pressures p0 and p1, respectively. A pressure differential, Δp = p0 - p1, will drive a flow rate Qorf across the orifice; the positive direction of this flow, indicated on the figure, is from HydChmb0Name to HydChmb1Name.

Pressures p0 and p1 are, in general, the pressures in chambers HydChmb0Name and HydChmb1Name, respectively. For the linear hydraulic actuator, the orifice connects a chamber to an oil supply that can be at the entrance pressure pEnt or at the circuit pressure pCir.. In such case, HydChmb0Name = NULL.

The description and formulation of the hydraulic orifice and elements describes the relationships among these variables.

Computation of the orifice flow

The flow through the orifice, Qorf, is related to the pressure drop, Δp, across the orifice and can be computed in two alternative manners.

1. If the orifice area, Aorf, and the orifice dischage coefficient, Cd, are defined an empirical formula is used: Qorf = Aorf Cd√(2|Δp|/ρ)  sign(Δp), where Aorf is the orifice throttling area and ρ the mass density of the hydraulic fluid. For turbulent flow conditions, the theoretical value of the discharge coefficient is Cd = 0.611. The term sign(Δp) enforces the sign convention.
2. If 1D function, Fun1DName, is defined, the flow through the orifice is computed as Qorf = F(|Δp|)   sign(Δp), where a 1D function, F = F(|Δp|), defines the relationship between the flow and the pressure drop across the orifice through a Chebyshev expansion. 1D function, Fun1DName, must be defined of the type HYDRAULIC_ORIFICE. Typically, the flow-pressure drop relationship is determined experimentally and a Chebyshev approximation is used to fit the data. The empirical formula above corresponds to F(|Δp|) = Aorf Cd√(2|Δp|/ρ).

NOTES

1. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

Sensors

Sensors can be defined to extract information about hydraulic orifices. The following SensorType specifications are allowed for hydraulic orifices: ORIFICE_DATA. (Default value: ORIFICE_DATA).

No u value and v value are accepted for the hydraulic device.