Single-Acting Actuator (MA)

R2026b

Single-acting linear actuator in a moist air network

Since R2024a

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Single-Acting Actuator (MA) block

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Libraries:
Simscape / Fluids / Moist Air / Actuators

Description

The Single-Acting Actuator (MA) block models a linear actuator with a piston controlled by a single moist air chamber. The actuator generates force in the extension and retraction strokes, but the actuation force depends on the gauge pressure in the chamber.

The figure shows the key components of an actuator. Port A represents the moist air chamber inlet, port R represents the translating actuator piston, and port C represents the actuator case. Port H represents the thermal interface between the moist air chamber and the environment.

Displacement

The block measures the piston displacement as the position at port R relative to port C. The Mechanical orientation parameter identifies the direction of piston displacement. The piston displacement is neutral, or 0, when the chamber volume is equal to the value of the Dead volume parameter. When the Piston displacement parameter is Provide input signal from Multibody joint, you input the piston displacement using port p. You can ensure that the derivative of the position signal is equal to the piston velocity by using a Translational Multibody Interface block to provide the piston displacement.

The direction of the piston motion depends on the Mechanical orientation parameter. If the mechanical orientation is positive, then the piston translation is positive in relation to the actuator case when the gauge pressure at port A is positive. The direction of motion reverses when the mechanical orientation is negative.

Hard Stop

A set of hard stops limit the piston range of motion. The block uses an implementation of the Translational Hard Stop block, which treats hard stops like spring-damper systems. The spring stiffness coefficient controls the restorative component of the hard-stop contact force and the damping coefficient the dissipative component.

The hard stops are located at the distal ends of the piston stroke. If the mechanical orientation is positive, then the lower hard stop is at x = 0, and the upper hard stop is at x = +stroke. If the mechanical orientation is negative, then the lower hard stop is at x = -stroke, and the upper hard stop is at x = 0.

Block Composite

This block is a composite component based on these Simscape™ Foundation blocks:

• Translational Mechanical Converter (MA)

• Translational Hard Stop

• Ideal Translational Motion Sensor

Ports

Input

p — Multibody piston position input, m

physical signal

Physical signal input associated with the piston position, in m. Connect this port to a Simscape Multibody™ network using a Translational Multibody Interface block.

Dependencies

To enable this port, set Piston displacement to Provide input signal from Multibody joint.

Programmatic Use

Port: p_in

Output

p — Piston position, m

physical signal

Physical signal output associated with the piston position, in m.

Dependencies

To enable this port, set Piston displacement to Calculate from velocity of port R relative to port C.

Programmatic Use

Port: p_out

Conserving

A — Liquid port

moist air

Moist air conserving port associated with chamber A.

Programmatic Use

Port: A

C — Actuator casing

translational mechanical

Translational mechanical conserving port associated with the actuator casing.

Programmatic Use

Port: C

R — Actuator piston

translational mechanical

Translational mechanical conserving port associated with the actuator piston.

Programmatic Use

Port: R

H — Heat transfer

thermal

Thermal conserving port associated with the thermal mass of the moist air volume.

Programmatic Use

Port: H

Parameters

Actuator

Mechanical orientation — Piston displacement direction

Pressure at A causes positive displacement of R relative to C (default) | Pressure at A causes negative displacement of R relative to C

Piston displacement direction. When you set this parameter to:

• Pressure at A causes positive displacement of R relative to C, the piston displacement is positive when the volume of moist air at port A is expanding. This motion corresponds to rod extension.

• Pressure at A causes negative displacement of R relative to C, the piston displacement is negative when the volume of moist air at port A is expanding. This motion corresponds to rod contraction.

Programmatic Use

Parameter:	mech_orientation
Values:	"foundation.enum.MechOrientationTranslational.Positive" | "foundation.enum.MechOrientationTranslational.Negative"

Piston cross-sectional area — Cross-sectional area of piston rod

0.01 m^2 (default) | positive scalar

Cross-sectional area of the piston rod.

Programmatic Use

Parameter: piston_area

Piston stroke — Maximum piston travel distance

0.1 m (default) | positive scalar

Maximum piston travel distance.

Programmatic Use

Parameter: stroke

Dead volume — Fluid volume at full piston retraction

1e-5 m^3 (default) | positive scalar

Volume of moist air when the piston displacement is 0. This parameter is the moist air volume when the piston is against the actuator end cap.

Programmatic Use

Parameter: dead_volume

Cross-sectional area at port A — Area at port A

0.01 m^2 (default) | positive scalar

Cross-sectional area of port A.

Programmatic Use

Parameter: area_A

Environment pressure specification — Reference environment pressure

Atmospheric pressure (default) | Specified pressure

Environment reference pressure. When you select Atmospheric pressure, the block assumes a pressure of 0.101325 MPa.

Programmatic Use

Parameter:	environment_spec
Values:	"foundation.enum.pressure_spec.atmospheric" | "foundation.enum.pressure_spec.specified"

Environment pressure — User-defined environmental pressure

0.101325 MPa (default) | positive scalar

User-defined environmental pressure.

Dependencies

To enable this parameter, set Environment pressure specification to Specified pressure.

Programmatic Use

Parameter: environment_pressure

Hard Stop

Hard stop model — Hard stop model

Stiffness and damping applied smoothly through transition region, damped rebound (default) | Full stiffness and damping applied at bounds, undamped rebound | Full stiffness and damping applied at bounds, damped rebound | Based on coefficient of restitution

Hard stop model to use when the piston is at full extension or full extraction. See the Translational Hard Stop block for more information.

Programmatic Use

Parameter:	hardstop_model
Values:	"simscape.enum.hardstop.smooth" | "simscape.enum.hardstop.fullundamped" | "simscape.enum.hardstop.fulldamped" | "simscape.enum.hardstop.modechart"

Hard-stop stiffness coefficient — Stiffness coefficient

1e10 N/m (default) | positive scalar

Piston stiffness coefficient.

Dependencies

To enable this parameter, set Hard stop model to one of these settings:

• Stiffness and damping applied smoothly through transition region, damped rebound

• Full stiffness and damping applied at bounds, undamped rebound

• Full stiffness and damping applied at bounds, damped rebound

Programmatic Use

Parameter: stiff_coeff

Hard-stop damping coefficient — Damping coefficient

150 N*s/m (default) | positive scalar

Piston damping coefficient.

Dependencies

To enable this parameter, set Hard stop model to one of these settings:

• Stiffness and damping applied smoothly through transition region, damped rebound

• Full stiffness and damping applied at bounds, undamped rebound

• Full stiffness and damping applied at bounds, damped rebound

Programmatic Use

Parameter: damping_coeff

Transition region — Application range of hard stop force model

0.1 mm (default) | positive scalar

Application range of the hard stop force model. The block does not apply the hard stop model when the maximum extension or retraction of the piston is outside of this range. In this situation, there is no additional force on the piston.

Dependencies

To enable this parameter, set Hard stop model to Stiffness and damping applied smoothly through transition region, damped rebound.

Programmatic Use

Parameter: transition

Coefficient of restitution — Ratio of final-to-initial relative speed between slider and stop after collision

0.7 (default) | unitless value between 0 and 1

Ratio of the final to the initial relative speed between the slider and the stop after the slider bounces.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Programmatic Use

Parameter: coeff_rest

Static contact speed threshold — Threshold relative speed between slider and stop before collision

0.001 m/s (default) | nonnegative scalar

Threshold relative speed between the slider and stop before collision. When the slider hits the case with a speed less than the value of the Static contact speed threshold parameter, they stay in contact. Otherwise, the slider bounces. To avoid modeling static contact between the slider and the case, set this parameter to 0.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Programmatic Use

Parameter: v_tol

Static contact release force threshold — Force needed to transition from contact mode to free mode

0.001 N (default) | positive scalar

Minimum force needed to release the slider from a static contact mode.

Dependencies

To enable this parameter, set Hard stop model to Based on coefficient of restitution.

Programmatic Use

Parameter: f_tol

Initial Conditions

Piston displacement — Method for determining piston position

Calculate from velocity of port R relative to port C (default) | Provide input signal from Multibody joint

Method for determining the piston position. The block can receive the position from a Multibody block when set to Provide input signal from Multibody joint, or can calculate the position internally and report the position at port p. The position is between 0 and the value of the Piston stroke parameter when the mechanical orientation is positive and between 0 and the negative value of the Piston stroke parameter when the mechanical orientation is negative.

Programmatic Use

Parameter:	displacement_spec
Values:	"foundation.enum.DisplacementSpec.Calculate" | "foundation.enum.DisplacementSpec.InputSignal"

Initial piston displacement — Piston position at start of simulation

0 m (default) | scalar

Piston position at the start of the simulation.

Dependencies

To enable this parameter, set Piston displacement to Calculate from velocity of port R relative to port C.

Programmatic Use

Parameter: x0

Initial pressure — Moist air pressure at start of simulation

0.101325 MPa (default) | positive scalar

Moist air pressure at the start of the simulation.

Programmatic Use

Parameter: p_init

Initial temperature — Moist air temperature at start of simulation

293.15 K (default) | scalar

Moist air temperature at the start of simulation.

Programmatic Use

Parameter: T_init

Initial humidity specification — Quantity to use to describe initial humidity level

Relative humidity (default) | Specific humidity | Mole fraction | Humidity ratio | Wet-bulb temperature

Whether to describe the initial moist air humidity level using the relative humidity, specific humidity, water vapor mole fraction, or humidity ratio.

Programmatic Use

Parameter:	humidity_spec
Values:	"foundation.enum.HumiditySpec.RelativeHumidity" | "foundation.enum.HumiditySpec.SpecificHumidity" | "foundation.enum.HumiditySpec.MoleFraction" | "foundation.enum.HumiditySpec.HumidityRatio" | "foundation.enum.HumiditySpec.WetBulbTemperature"

Initial relative humidity — Relative humidity at start of simulation

0.5 (default) | scalar in the range [0,1]

Moist air relative humidity at the start of simulation.

Dependencies

To enable this parameter, set Initial humidity specification to Relative humidity.

Programmatic Use

Parameter: RH_init

Initial specific humidity — Specific humidity at start of simulation

0.01 (default) | scalar in the range [0,1]

Moist air specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the start of simulation.

Dependencies

To enable this parameter, set Initial humidity specification to Specific humidity.

Programmatic Use

Parameter: x_w_init

Initial water vapor mole fraction — Mole fraction of water vapor at start of simulation

0.01 (default) | scalar in the range [0,1]

Mole fraction of the water vapor in a moist air mixture at the start of simulation.

Dependencies

To enable this parameter, set Initial humidity specification to Mole fraction.

Programmatic Use

Parameter: y_w_init

Initial humidity ratio — Humidity ratio at start of simulation

0.01 (default) | scalar in the range [0,1]

Moist air humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the start of simulation.

Dependencies

To enable this parameter, set Initial humidity specification to Humidity ratio.

Programmatic Use

Parameter: HR_init

Initial wet-bulb temperature — Wet-bulb temperature at start of simulation

287 K (default) | positive scalar

Wet-bulb temperature of the moist air mixture at the start of simulation.

Dependencies

To enable this parameter, set Initial humidity specification to Wet-bulb temperature.

Programmatic Use

Parameter: Tw_init

Initial trace gas specification — Quantity to use to describe initial trace gas level

Mass fraction (default) | Mole fraction

Whether to use the mass fraction or mole fraction to describe the trace gas level at the start of simulation.

Programmatic Use

Parameter:	trace_gas_spec
Values:	"foundation.enum.trace_gas_spec.mass_fraction" | "foundation.enum.trace_gas_spec.mole_fraction"

Initial trace gas mass fraction — Mass fraction of trace gas at start of simulation

0.001 (default) | scalar in the range [0,1]

Mass fraction of the trace gas in a moist air mixture at the start of simulation.

Dependencies

To enable this parameter, set Initial trace gas specification to Mass fraction.

Programmatic Use

Parameter: x_g_init

Initial trace gas mole fraction — Mole fraction of trace gas at start of simulation

0.001 (default) | scalar in the range [0,1]

Mole fraction of the trace gas in a moist air mixture at the start of simulation.

Dependencies

To enable this parameter, set Initial trace gas specification to Mole fraction.

Programmatic Use

Parameter: y_g_init

Initial mass ratio of water droplets to moist air — Ratio of water droplets to moist air

0 (default) | positive scalar

Initial mass ratio of water droplets to moist air.

Programmatic Use

Parameter: r_d_init

Relative humidity at saturation — Relative humidity above which condensation occurs

1 (default) | positive scalar

Relative humidity above which condensation occurs in the chamber.

Programmatic Use

Parameter: RH_ws

Water vapor condensation time constant — Time scale for condensation

1e-3 s (default) | positive scalar

Characteristic time scale at which an oversaturated moist air volume returns to saturation by condensing out excess humidity.

Programmatic Use

Parameter: time_constant_cond

Water droplets evaporation time constant — Time scale for evaporation

1e-3 s (default) | positive scalar

Characteristic time scale at which water droplets evaporate to vapor.

Programmatic Use

Parameter: time_constant_evap

Fraction of condensate entrained as water droplets — Fraction of condensate in water droplets

1 (default) | scalar in the range [0,1]

Fraction of the condensate in the moist air that is entrained as water droplets.

Programmatic Use

Parameter: fraction_entrained

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2024a

R2024b: Model water droplets suspended in moist air flow

Blocks in the moist air domain can now model water droplets suspended in a moist air flow. To model water droplets, select Enable entrained water droplets in the Moist Air Properties (MA) block connected to your moist air network.