Documentation

Shock Absorber

Mechanism for damping translational vibrations

Library

Simscape / Driveline / Couplings & Drives

Description

The Shock Absorber block represents a spring-damper system commonly used to dampen vibration in mechanical systems. 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 Shock Absorber block uses the models of these blocks:

BlockContributionLibrary
Loaded-Contact Translational FrictionCoulomb frictionSimscape / Driveline / Brakes & Detents / Translational
Rotational DamperDampingSimscape / Foundation Library / Mechanical / Translational Elements
Rotational SpringSpring
Rotational Hard StopHard stop

Assumptions and Limitations

Ports

Conserving

C

Mechanical translational port associated with the slider that travels between stops installed on the case.

R

Mechanical translational port associated with the rod.

Parameters

Spring-Damper

Restoring spring stiffness

Enter the value of the viscous spring stiffness constant, k. The default value is 1e4 N/m. The value must be greater than or equal to zero.

Viscous friction coefficient

Enter the value of the viscous damping constant, b. The default value is 1e2 m/s. The value must be greater than or equal to zero.

Coulomb friction force

Enter the value of the Coulomb friction force. Setting the value to 0 eliminates the Coulomb friction force contribution. This enhances simulation speed, making the model more suitable for HIL testing. The default value is 0 N. The value must be greater than or equal to zero.

Ratio of static to kinetic friction

Enter the value of the static/kinetic friction ratio, that is Fs/Fk. The value must be greater than one. The default value is 1.1. The value must be greater than or equal to one.

Velocity tolerance

Enter the value of the relative velocity below which ports R and C lock and translate together. The default value is 0.001 m/s. The value must be greater than zero.

Hard Stops

Hard stop

Include or exclude hard-stop force by selecting one of these options:

  • No hard stops — Suitable for HIL simulation — To enhance simulation speed by excluding the hard-stop force contribution, select this default option.

  • Compliant hard stops — To enhance model fidelity by including the hard-stop force contribution, select this option. Selecting this option enables other parameters.

Upper bound

Upper hard-stop position, UB. Positive displacement beyond the upper bound activates the hard-stop contact force. The default value is 0.1 m. The value must be greater than the lower bound.

Selecting Compliant hard stops for the Hard stop parameter enables this parameter.

Lower bound

Lower hard-stop position, LB. Negative displacement beyond the lower bound activates the hard-stop contact force. The default value is -0.1 m. The value must be smaller than the upper bound.

Selecting Compliant hard stops for the Hard stop parameter enables this parameter.

Contact stiffness

Enter the value of the hard-stop stiffness constant, kHS. The default value is 1e6 N/m. The value must be greater than or equal to zero.

Selecting Compliant hard stops for the Hard stop parameter enables this parameter.

Contact damping

Enter the value of the hard-stop damping constant, bHS. This parameter specifies dissipating property of colliding bodies. The greater the value of the parameter, the more energy dissipates during an interaction. The default value is 1e4 N/(m/s). The value must be greater than zero.

Selecting Compliant hard stops for the Hard stop parameter enables this parameter.

Hard stop model

Select the hard-stop model:

  • Stiffness and damping applied smoothly through transition region, damped rebound — Specify a transition region, in which the force is scaled from zero. At the end of the transition region, the full stiffness and damping are applied. This model has damping applied on the rebound, but it is limited to the value of the stiffness force. In this sense, damping can reduce or eliminate the force provided by the stiffness, but never exceed it. All equations are smooth and produce no zero crossings.

    Selecting this option enables the Transition region parameter.

  • Full stiffness and damping applied at bounds, undamped rebound — This model has full stiffness and damping applied with impact at upper and lower bounds, with no damping on the rebound. Equations produce no zero crossings when velocity changes sign, but there is a position-based zero crossing at the bounds. Having no damping on rebound helps to push the slider past this position quickly. This model has nonlinear equations.

  • Full stiffness and damping applied at bounds, damped rebound — This model has full stiffness and damping applied with impact at upper and lower bounds, with damping applied on the rebound as well. Equations are switched linear, but produce position-based zero crossings. Use this hard-stop model if simscape.findNonlinearBlocks indicates that this is the block that prevents the whole network from being switched linear.

Selecting Compliant hard stops for the Hard stop parameter enables this parameter.

Transition region

Region where the force is ramped up from zero to the full value. At the end of the transition region, the full stiffness and damping are applied. The default value is 0.1 mm.

Selecting Stiffness and damping applied smoothly through transition region, damped rebound for the Hard stop model enables this parameter.

Initial Conditions

Initial deformation

Enter the initial value of the spring deformation. The default value is 0 m.

Extended Capabilities

Real-Time and Hardware-in-the-Loop Simulation

For optimal simulation performance, use the Hard Stops > Hard stop parameter default setting, No hard stops - Suitable for HIL simulation.

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