Hydraulic device model definition

@HYDRAULIC_DEVICE_MODEL_DEFINITION {
@HYDRAULIC_DEVICE_MODEL_NAME {HydModlName} {
@HYDRAULIC_DEVICE_TYPE {HydType}
@OIL_PROPERTY_NAME {OilPropName}
@HYDRAULIC_CHAMBER_NAME {ChamberName0}
@HYDRAULIC_CHAMBER_NAME {ChamberName1}
@HYDRAULIC_ORIFICE_NAME {OrificeName0}
@HYDRAULIC_ORIFICE_NAME {OrificeName1}
@PRESSURE_RELIEVE_VALVE_NAME {PrvlName0}
@PRESSURE_RELIEVE_VALVE_NAME {PrvlName1}
@FUNCTION_1D_NAME {Fun1DName}
@NUMBER_OF_SUB_TIME_STEPS {n}
@COMMENTS {CommentText}
}
}

Introduction

The hydraulic device model definition describes the parameters associated with various types of hydraulic devices. Such devices consist of a combination of hydraulic chambers, hydraulic orifices, and pressure relief valves. Hydraulic devices are connected to flexible multibody systems via force element interface elements. The physical properties of the oil used in the hydraulic devices are defined by the oil properties, OilPropName.

Three types of hydraulic devices can be defined.

  1. If HydType = HYDRAULIC_ACTUATOR, the hydraulic device is a linear hydraulic actuator.
  2. If HydType = SIMPLE_HYDRAULIC_DAMPER, the hydraulic device is a simple hydraulic damper.
  3. If HydType = HYDRAULIC_DAMPER_WITH_RELIEF_VALVES, the hydraulic device is a hydraulic damper with pressure relief valves.

NOTES

  1. To guarantee the accuracy of the simulations, n sub-time steps are used to integrate governing equations of the device. For more details, see the formulation of force element interfaces.
  2. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.

Linear hydraulic actuator

Figure 1. Configuration of the linear hydraulic actuator.

Linear hydraulic actuators combine two hydraulic chambers, ChamberName0 and ChamberName1, and two hydraulic orifices, OrificeName0 and OrificeName1, to form the configuration depicted in fig. 1. Hydraulic orifice OrificeName0 flows from NULL to chamber ChamberName0; hydraulic orifice OrificeName1 flows from NULL to chamber ChamberName1. A time function, Fun1DName controls the entrance pressures of the hydraulic orifices.

Hydraulic chambers ChamberName0 and ChamberName1 are under pressures p0 and p1, respectively; note that the λ factors are +1 and -1 for the two chambers, respectively. The hydraulic OrificeName0 and OrificeName1 generate flows Q0 and Q1 into ChamberName0 and ChamberName1, respectively. The two orifices are opening to entrance pressures pEnt 0 and pEnt 1, respectively. To increase the length of the actuator, valves controlled by time function, Fun1DName, will set the entrance pressure of OrificeName0 to a high value, ph, such that pEnt 0 = ph, while the entrance pressure of OrificeName1 remains at a low value pCir (the hydraulic circuit background pressure), such that pEnt 1 = pCir. To decrease the length of the actuator, the control valves reverse the pressure level at the entrance to the two orifices.

The description and formulation of linear hydraulic actuators provides the relationships among these variables in more details.

Simple hydraulic damper

Figure 2. Configuration of the simple hydraulic damper.

Simple hydraulic dampers combine two hydraulic chambers, ChamberName0 and ChamberName1, and one hydraulic orifice, OrificeName0, connecting the two chambers to form the configuration depicted in fig. 2. Hydraulic orifice OrificeName0 flows from chamber ChamberName0 to chamber ChamberName1.

Hydraulic chambers ChamberName0 and ChamberName1 are under pressures p0 and p1, respectively; note that the λ factors are +1 and -1 for the two chambers, respectively. The hydraulic orifice generates a flow Q from ChamberName0 into ChamberName1. If the length of the damper increases, pressure p1 increases whereas pressure p0 decreases. This generates a pressure differential across the orifice and hence, a flow Q into ChamberName0 that tends to equilibrate the pressures in the chambers. The force generated by the damper always opposes the motion and is therefore a damping force.

The description and formulation of simple hydraulic dampers provides the relationships among these variables in more details.

Hydraulic damper with pressure relief valves

Figure 3. Configuration of the hydraulic damper with pressure relief valves.

Rotorcraft hydraulic lead-lag dampers present a configuration similar to that of the simple damper described in the previous section. However, this simple design suffers an important drawback: under a high stroking rate, the pressure differential in the chambers can be rather high, and hence, high damping forces are generated. These high forces must be reacted at the hub and at the root of the blade, creating high stresses and decreasing fatigue life. To limit the forces in the hydraulic damper, two pressure relief valves are added to the configuration, as shown in figure 3. Hydraulic orifice OrificeName0 flows from chamber ChamberName0 to chamber ChamberName1. To prevent low pressures to occur in the chambers, two additional hydraulic orifices, OrificeName1 and OrificeName2 connect chambers ChamberName0 and ChamberName1, respectively, to oil supply reservoirs. Hydraulic orifice OrificeName1 flows from NULL to chamber ChamberName1; hydraulic orifice OrificeName2 flows from NULL to chamber ChamberName1.

The new design combines two hydraulic chambers, ChamberName0 and ChamberName1, one orifice connecting the two chambers, two pressure relief valves, PrvlName0 and PrvlName1, and two orifices to an oil reservoir, OrificeName1 and OrificeName2. Hydraulic ChamberName0 and ChamberName1 are under pressures p0 and p1, respectively; note that the λ factors are +1 and -1 for the two chambers, respectively. Hydraulic orifice OrificeName0 generates a flow Q from ChamberName0 into ChamberName1. When open, the pressure relief valves regulate the pressures in ChamberName0 and ChamberName1 and generate flows Q0 and Q1, respectively. Finally, OrificeName1 and OrificeName2 are associated with flows Q2 and Q3, respectively.

If the length of the damper increases, pressure p1 increases whereas pressure p0 decreases. This generates a pressure differential across the orifice and hence, a flow Q into ChamberName0 that tends to equilibrate the pressures in the chambers. If the stroking rate is high, the pressure differential in the chambers will become high enough to open pressure relief PrvlName1, resulting in an additional flow Q1 from ChamberName1 into ChamberName0. Given the sign of the pressure differential, PrvlName0 will remain closed. The opening of the valve and the ensuing flow controls the magnitude of the pressure differential. The force generated by the damper always opposes the motion and is therefore a damping force.

Examples

Example 1

The following input defines a hydraulic actuator.

@HYDRAULIC_DEVICE_MODEL_DEFINITION {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator} {
@HYDRAULIC_DEVICE_TYPE {HYDRAULIC_ACTUATOR}
@OIL_PROPERTY_NAME {OilProp}
@HYDRAULIC_CHAMBER_NAME {HydChamber0}
@HYDRAULIC_CHAMBER_NAME {HydChamber1}
@HYDRAULIC_ORIFICE_NAME {HydOrifice0}
@HYDRAULIC_ORIFICE_NAME {HydOrifice1}
@FUNCTION_1D_NAME {ScheduleActuator}
@NUMBER_OF_SUB_TIME_STEPS {25}
}
}
@HYDRAULIC_CHAMBER_DEFINITION {
@HYDRAULIC_CHAMBER_NAME {HydChamber0} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@CHAMBER_SECTIONAL_AREA {5.61e-04}
@CHAMBER_INITIAL_VOLUME {-7.228e-05}
@CHAMBER_INITIAL_PRESSURE {1.0e+06}
}
}
@HYDRAULIC_CHAMBER_DEFINITION {
@HYDRAULIC_CHAMBER_NAME {HydChamber1} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@CHAMBER_SECTIONAL_AREA {2.78e-04}
@CHAMBER_INITIAL_VOLUME {1.07e-04}
@CHAMBER_INITIAL_PRESSURE {1.0e+06}
}
}
@HYDRAULIC_ORIFICE_DEFINITION {
@HYDRAULIC_ORIFICE_NAME {HydOrifice0} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@ORIFICE_THROTTLING_AREA {1.0e-05}
@ORIFICE_DISCHARGE_COEFFICIENT {0.611}
@HYDRAULIC_CHAMBER_NAME {NULL, HydChamber0}
@ORIFICE_ENTRANCE_PRESSURE {2.06e+07}
@ORIFICE_CIRCUIT_PRESSURE {1.0e+06}
}
}
@HYDRAULIC_ORIFICE_DEFINITION {
@HYDRAULIC_ORIFICE_NAME {HydOrifice1} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@ORIFICE_THROTTLING_AREA {9.8e-07}
@ORIFICE_DISCHARGE_COEFFICIENT {0.611}
@HYDRAULIC_CHAMBER_NAME {NULL, HydChamber1}
@ORIFICE_ENTRANCE_PRESSURE {2.06e+07}
@ORIFICE_CIRCUIT_PRESSURE {1.0e+06}
}
}

Example 2

The following input defines a simple hydraulic damper.

@HYDRAULIC_DEVICE_MODEL_DEFINITION {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator} {
@HYDRAULIC_DEVICE_TYPE {SIMPLE_HYDRAULIC_DAMPER}
@OIL_PROPERTY_NAME {OilProp}
@HYDRAULIC_CHAMBER_NAME {HydChamber0}
@HYDRAULIC_CHAMBER_NAME {HydChamber1}
@HYDRAULIC_ORIFICE_NAME {HydOrifice}
@NUMBER_OF_SUB_TIME_STEPS {25}
}
}
@HYDRAULIC_CHAMBER_DEFINITION {
@HYDRAULIC_CHAMBER_NAME {HydChamber0} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@CHAMBER_SECTIONAL_AREA {5.61e-04}
@CHAMBER_INITIAL_VOLUME {7.228e-04}
@CHAMBER_INITIAL_PRESSURE {1.0e+06}
}
}
@HYDRAULIC_CHAMBER_DEFINITION {
@HYDRAULIC_CHAMBER_NAME {HydChamber1} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@CHAMBER_SECTIONAL_AREA {5.61e-04}
@CHAMBER_INITIAL_VOLUME {7.228e-04}
@CHAMBER_INITIAL_PRESSURE {1.0e+06}
}
}
@HYDRAULIC_ORIFICE_DEFINITION {
@HYDRAULIC_ORIFICE_NAME {HydOrifice} {
@HYDRAULIC_DEVICE_MODEL_NAME {HydActuator}
@ORIFICE_THROTTLING_AREA {1.0e-05}
@ORIFICE_DISCHARGE_COEFFICIENT {0.611}
@HYDRAULIC_CHAMBER_NAME {HydChamber0, HydChamber1}
}
}

Sensors

Sensors can be defined to extract information about hydraulic devices. The following SensorType specifications are allowed for hydraulic devices: DEVICE_DATA, ORIFICE_DATA, ORIFICE_DATA_0, ORIFICE_DATA_1, RELIEF_VALVE_DATA_0, RELIEF_VALVE_DATA_1. (Default value: DEVICE_DATA).

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