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Shock Absorber

Mechanism for damping translational vibrations

Library

Couplings & Drives

Description

The 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 net internal force satisfies the expression

$F={F}_{spr}+{F}_{d}+{F}_{c}+{F}_{HS},$

where:

• F — Net internal force

• Fspr — Spring force, ${F}_{k}=-k\cdot x$

• Fd — Damping force, ${F}_{d}=-b\cdot v$

• Fc — Coulomb friction force,

${F}_{c}=\left\{\begin{array}{cc}-{F}_{k}\cdot \mathrm{sign}\left(v\right),& \text{when}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{unlocked}\\ -{F}_{s},& \text{when}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{locked}\end{array},$

• FHS — Hard stop force,

${F}_{HS}=\left\{\begin{array}{cc}-{k}_{HS}\cdot \left(x-UB\right)-{b}_{HS}\cdot v,& x\ge UB\\ 0& UB\ge x\ge LB\\ -{k}_{HS}\cdot \left(x-LB\right)+{b}_{HS}\cdot v,& LB>x\end{array},$

• k — Restoring spring stiffness

• b — Viscous damping coefficient

• x — Relative displacement between ports R and C

• v — Relative velocity between R and C

• Fk — Kinetic friction force

• Fs — Static friction force

• kHS — Hard stop contact stiffness coefficient

• kHS — Hard stop damping coefficient

• UB — Hard stop upper bound

• LB — Hard stop lower bound

The shock absorber block is based on the blocks listed in the table. For more information, see the corresponding block reference pages.

BlockLibrary
Loaded-Contact Translational FrictionSimDriveline Brakes & Detents/Translational
Translational SpringSimscape Foundation Library/Mechanical/Translational
Translational Damper
Translational Hard Stop

Assumptions and Limitations

• The use of hard-stop and Coulomb friction enhances model fidelity, but reduces simulation speed. See Improve Performance in the product documentation.

Dialog Box and Parameters

Spring-Damper

Restoring spring stiffness

Enter the value of the viscous spring stiffness constant, k. The value must be greater than or equal to zero.

The default value is 1e+4. the default unit is N/m.

Viscous friction coefficient

Enter the value of the viscous damping constant, b. The value must be greater than or equal to zero.

The default value is 100. The default unit is m/s.

Coulomb friction force

Enter the value of the Coulomb friction force. The value must be greater than or equal to zero. 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. The default unit is N.

Ratio of static to kinetic friction

Enter the value of the static/kinetic friction ratio (Fs/Fk). The value must be greater than one.

The default value is 1.1.

Velocity tolerance

Enter the value of the relative velocity below which ports R and C lock and translate together. The value must greater than zero.

The default value is 0.001. The default unit is m/s.

Hard Stops

Hard stop model

Select hard stop model. Selecting No hard-stops — Suitable for HIL simulation eliminates the hard stop force contribution. This enhances simulation speed.

The default setting is No hard stops — Suitable for HIL simulation.

Initial Conditions

Initial deformation

Enter the initial value of the spring deformation.

The default value is 0. The default unit is m.

Ports

PortDescription
CTranslational conserving port
RTranslational Conserving port