Inertia

Mass element with fixed inertial properties

Libraries:
Simscape / Multibody / Body Elements

Description

The Inertia block adds to the attached frame a point or distributed mass with fixed inertial properties. The type of mass (point or distributed) depends on the parameterization selected for the block. A selection of Point Mass assumes the mass to be concentrated at a point and therefore devoid of rotational inertia. A selection of Custom assumes the mass to be distributed in space, allowing it to possess nonzero moments of inertia, products of inertia, and center-of-mass coordinates (the latter against the reference frame of the block).

A choice of marker provides a means to identify the inertia in the model visualization. The visualization opens (by default) in Mechanics Explorer at the start of simulation or upon diagram update. Use the marker to track the motion of the inertia against the remainder of the model. Various marker shapes are available—an inertia icon, a sphere, a cube, a frame—each with configurable dimensions. To eliminate the inertia from the model visualization (while retaining its effects on the model dynamics), the block provides an option of None.

Examples

Full Vehicle on Four Post Testrig

Models a passenger vehicle on a four-post testrig. The posts move up and down to replicate the vertical movement of the wheels as it travels along a road. The simulation results and animation show the response of the vehicle body and suspension as it is subjected to the motions from the testrig. The roll and pitch of the vehicle body can be observed, and by varying the inputs wheel hop frequencies can be determined. The vehicle model can be configured to use different suspension types for the front suspension with different linkage combinations.

Open Model

Ports

Frame

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R — Reference frame
frame

Local reference frame of the inertia element. Connect to a frame line or frame port to define the relative position and orientation of the inertia.

Parameters

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Inertia

Type — Inertia parameterization to use
`Point Mass` (default) | `Custom`

Inertia parameterization to use. Select Point Mass to represent a mass with no rotational inertia. Select Custom to represent a distributed mass with rotational inertia.

Mass — Total mass of the solid element
`1 kg` (default) | scalar with units of mass

Total mass to attribute to the solid element. This parameter can be positive or negative. Use a negative value to capture the effect of a void or cavity in a compound body (one comprising multiple solids and inertias), being careful to ensure that the mass of the body is on the whole positive.

Custom: Center of Mass — Center-of-mass coordinates
`[0 0 0] m` (default) | three-element vector with units of length

[x y z] coordinates of the center of mass relative to the block reference frame. The center of mass coincides with the center of gravity in uniform gravitational fields only.

Custom: Moments of Inertia — Diagonal elements of inertia tensor
`[1 1 1] kgm^2` (default) | three-element vector with units of masslength^2

Three-element vector with the [I_xx I_yy I_zz] moments of inertia specified relative to a frame with origin at the center of mass and axes parallel to the block reference frame. The moments of inertia are the diagonal elements of the inertia tensor

$(\begin{matrix} I_{x x} \\ I_{y y} \\ I_{z z} \end{matrix}),$

where:

$I_{x x} = \int_{m} (y^{2} + z^{2}) d m$
$I_{y y} = \int_{m} (x^{2} + z^{2}) d m$
$I_{z z} = \int_{m} (x^{2} + y^{2}) d m$

Custom: Products of Inertia — Off-diagonal elements of inertia tensor
`[0 0 0] kgm^2` (default) | three-element vector with units of masslength^2

Three-element vector with the [I_yz I_zx I_xy] products of inertia specified relative to a frame with origin at the center of mass and axes parallel to the block reference frame. The products of inertia are the off-diagonal elements of the inertia tensor

$(\begin{matrix} I_{x y} & I_{z x} \\ I_{x y} & I_{y z} \\ I_{z x} & I_{y z} \end{matrix}),$

where:

$I_{y z} = - \int_{m} y z d m$
$I_{z x} = - \int_{m} z x d m$
$I_{x y} = - \int_{m} x y d m$

Graphic

Type — Graphic to use in the visualization of the inertia
`Marker` (default) | `None`

Type of graphic to use in the visualization of the inertia, specified as Marker or None. Set this parameter to Marker to represent the inertia as a marker, and set this parameter to None to hide the inertia from the model visualization.

Shape — Shape of marker to represent to the inertia
`Inertia Icon` (default) | `Sphere` | `Cube` | `Frame`

Shape of the marker, specified as Inertia Icon, Sphere, Cube, or Frame. The motion of the marker reflects the motion of the inertia itself.

Dependencies

To enable this parameter, set Type to Marker.

Size — Width of the marker in pixels
20 `pixels` (default) | scalar

Width of the marker in pixels, specified as a scalar. This width does not scale with zoom level. Note that the apparent size of the marker depends partly on screen resolution, with higher resolutions packing more pixels per unit length, and therefore producing smaller icons.

Dependencies

To enable this parameter, set Type to Marker.

Visual Properties — Parameterizations for color and opacity
`Simple` (default) | `Advanced`

Parameterizations for specifying visual properties. Select Simple to specify Diffuse Color and Opacity. Select Advanced to specify more visual properties, such as Specular Color, Ambient Color, Emissive Color, and Shininess.

Dependencies

To enable this parameter, set Type to Marker.

Diffuse Color — Color of light due to diffuse reflection
[0.5 0.5 0.5] (default) | 3-by-1 or 1-by-3 vector with values in the range of 0 to 1 | 4-by-1 or 1-by-4 vector with values in the range of 0 to 1

Color of the light due to diffuse reflection, specified as an [R,G,B] or [R,G,B,A] vector with values in the range of 0 to 1. The vector can be a row or column vector. The optional fourth element specifies the color opacity. Omitting the opacity element is equivalent to specifying a value of 1.

Dependencies

To enable this parameter, set Type to Marker.

Opacity — Graphic opacity
1.0 (default) | scalar in the range of 0 to 1

Graphic opacity, specified as a scalar in the range of 0 to 1. A scalar of 0 corresponds to completely transparent, and a scalar of 1 corresponds to completely opaque.