Shock Absorber

Spring and damper system that absorbs translational shocks

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Libraries:
Simscape / Driveline / Couplings & Drives

Description

The Shock Absorber block represents a spring-damper system that absorbs vibrations. An internal force acts between ports R and C. This force is the sum of spring stiffness, damping, Coulomb friction, and hard-stop contributions. All force contributions are optional.

The block is a composite of these blocks:

Block	Function	Library
Loaded-Contact Translational Friction	Coulomb friction	Simscape / Driveline / Brakes & Detents / Translational
Translational Damper	Damping	Simscape / Foundation Library / Mechanical / Translational Elements
Translational Spring	Spring
Translational Hard Stop	Hard stop

Assumptions and Limitations

• Setting Hard stop to Compliant hard stop or setting Coulomb friction force to a nonzero value enhances model fidelity, but reduces simulation speed. For more information, see Driveline Simulation Performance.

Ports

Conserving

C — Case

mechanical translational

Mechanical translational conserving port associated with one end of the shock absorber. Positive force acts from port R to port C.

R — Rod

mechanical translational

Mechanical translational conserving port associated with one end of the shock absorber. Positive force acts from port R to port C.

Parameters

Spring-Damper

Spring stiffness — Stiffness of spring

1e4 N/m (default) | nonnegative scalar

Value of the spring stiffness constant, k.

Viscous friction coefficient — Viscous friction coefficient

1e2 N*s/m (default) | nonnegative scalar

Value of the viscous damping constant, b.

Coulomb friction force — Coulomb friction force

0 N (default) | nonnegative scalar

Value of the Coulomb friction force. Setting the value to 0 eliminates the Coulomb friction force contribution, which enhances simulation speed and makes the model more suitable for HIL testing.

Ratio of static to kinetic friction — Static-to-kinetic friction ratio

1.1 (default) | scalar greater than or equal to 1

Value of the ratio of static friction to kinetic friction, F_s/F_k.

Velocity tolerance — Slip velocity threshold

0.001 m/s (default) | positive scalar

Value of the relative velocity below which ports R and C lock and translate together. When the relative velocity is greater than this value, the ports slide relative to one another.

Hard Stops

Hard stop — Hard stop option

No hard stops - Suitable for HIL simulation (default) | Compliant hard stops

Whether to model translational hard stops. Select from these options:

• No hard stops — Suitable for HIL simulation — Enhance simulation speed by excluding the hard-stop force contribution.

• Compliant hard stops — Enhance model fidelity by including the hard-stop force contribution.

Upper bound — Gap between slider and upper bound

0.1 m (default) | scalar

Upper hard-stop position, UB. Positive displacement beyond the upper bound activates the hard-stop contact force. The value must be greater than the Lower bound parameter.

Dependencies

To enable this parameter, set Hard Stop to Compliant hard stops.

Lower bound — Gap between slider and lower bound

-0.1 m (default) | scalar

Lower hard-stop position, LB. Negative displacement beyond the lower bound activates the hard-stop contact force. The value must be smaller than the Upper bound parameter.

Dependencies

To enable this parameter, set Hard Stop to Compliant hard stops.

Contact stiffness — Contact stiffness constant

1e6 N/m (default) | nonnegative scalar

Value of the hard-stop stiffness constant, k_HS.

Dependencies

To enable this parameter, set Hard Stop to Compliant hard stops.

Contact damping — Contact damping constant

1e4 N*s/m (default) | positive scalar

Value of the hard stop damping constant, b_HS. This parameter specifies a dissipating property of colliding bodies. The greater the value of the parameter, the more energy the hard stop dissipates during an interaction.

Dependencies

To enable this parameter, set Hard Stop to Compliant hard stops.

Hard stop model — Hard stop transition behavior

Stiffness and damping applied smoothly through transition region, damped rebound (default) | ...

Stiffness and rebound options for the hard stop model. The block uses a composite implementation of the Translational Hard Stop block. You can choose from the following options:

• 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

• Based on coefficient of restitution

Transition region — Hard-stop transition distance

0.1 mm (default) | positive scalar

Region where the force ramps up from zero to the full value. At the end of the transition region, the block applies full stiffness and damping.

Dependencies

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

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 to Compliant hard stops and Hard stop model to Based on coefficient of restitution.

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 the stop before collision. When the slider hits the case with speed less than the value of this 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 to Compliant hard stops and Hard stop model to Based on coefficient of restitution.

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

0.001 N (default)

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

Dependencies

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

Extended Capabilities

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

Version History

Introduced in R2013a

R2023a: Composite Hard Stop Updates

Due to updates in the Translational Hard Stop block, the Hard stop model parameter now features the Coefficient of restitution option.