General Variable Mass
Mass element with variable inertial properties
Libraries:
Simscape /
Multibody /
Body Elements /
Variable Mass
Description
The General Variable Mass block adds to the attached frame a mass element with constant or time-varying inertial properties. The mass element can be a point mass without rotational inertia or a custom mass with rotational inertia. The inertial properties include mass, center of mass, moments of inertia, and products of inertia. Each inertial property can be independently configured as constant or time-varying.
The geometry of the mass element is unspecified. A marker or equivalent inertia ellipsoid identifies the mass element in the visualization pane of Mechanics Explorer. An inertia ellipsoid provides a graphical representation of the principal moments of inertia of the mass element. The block includes an option to hide the variable mass element in the Mechanics Explorer visualization window.
Limitations
The General Variable Mass block does not conserve the angular momentum when simulated without an external moment. Instead of the angular momentum, the angular velocity remains unchanged.
Ports
Input
m — Mass
physical signal specified as a scalar with units of mass
Input port for the time-varying mass.
Dependencies
This port is enabled when the Inertia > Mass parameter is set to
Time-Varying
.
com — Center of mass
physical signal specified as a 3-by-1 or 1-by-3 vector with units of
length
Input port for the time-varying center-of-mass coordinates. Specify
the coordinates in the order [x y z]
relative to the
block reference frame.
Dependencies
This port is enabled when the Inertia > Center of Mass parameter is set to
Time-Varying
.
I — Inertia
physical signal specified as a 3-by-3 matrix with units of mass
× length^2
Input port for the time-varying inertia tensor. Specify the tensor
elements in the order [Ixx Ixy I xz; Iyx Iyy Iyz; Izx Izy
Izz]
. The elements are defined relative to a frame with
origin at the center of mass and axes aligned with the reference frame.
See the Inertia tensor parameter description for
the definitions of the moments and products of inertia.
Dependencies
This port is enabled when the Inertia > Type parameter is set to
Custom
.
Frame
R — Reference frame
frame
Local reference frame of the variable mass element. Connect the port to a frame line or another frame port to define the relative position and orientation of the variable mass.
Parameters
Inertia
Type — Choice of point or distributed mass
Custom
(default) | Point Mass
Choice of point or distributed mass. Select Point
Mass
to model a concentrated mass with no rotational
inertia. Select Custom
to model a distributed
mass with the specified inertia tensor and center of mass.
Mass — Mass parameterization
Time-Varying
(default) | Constant
Choice of fixed or variable mass. Select
Time-Varying
to specify the mass as a
variable using physical signal input port m. Select
Constant
to specify the mass as a
constant parameter.
Mass: Value — Aggregate mass of the mass element
1 kg
(default) | scalar with units of mass
Aggregate mass of the mass element. The mass can be a positive or negative value. Specify a negative mass to model the aggregate effect of voids and cavities in a compound body. The mass is constant when this parameter is active.
Dependencies
This parameter is enabled when the Mass
parameter is set to Constant
.
Center of Mass — Center-of-mass parameterization
Time-Varying
(default) | Constant
Choice of fixed or variable center of mass. Select
Time-Varying
to specify the center of
mass as a variable using physical signal input port
com. Select Constant
to specify the center of mass as a constant parameter.
Center of Mass: Value — 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 origin of the reference frame. The center of mass coincides with the center of gravity in uniform gravitational fields only. The center of mass is constant when this parameter is active.
Dependencies
This parameter is enabled when the Center of
Mass parameter is set to
Constant
.
Inertia Matrix — Inertia-matrix parameterization
Time-Varying
(default) | Constant
Choice of a variable or fixed inertia matrix. Select
Time-Varying
to specify the inertia
matrix as a variable using physical signal input port
I. Select Constant
to specify the moments and products of inertia separately as constant
block parameters.
Inertia Matrix: Moments of Inertia — Diagonal elements of the inertia matrix
[1 1 1] kg * m^2
(default) | three-element vector with units of mass*length^2
Moments of inertia of the variable mass element specified in the order [Ixx Iyy Izz]. The moments of inertia are defined relative to a frame with origin at the center of mass and with axes parallel to the reference frame axes. The moments of inertia are the diagonal elements of the inertia tensor,
where:
Dependencies
This parameter is enabled when the Inertia
Matrix parameter is set to
Constant
.
Inertia Matrix: Products of Inertia — Off-diagonal elements of the inertia matrix
[0 0 0] kg * m^2
(default) | 3-element array with units of mass * length^2
Products of inertia of the variable mass element specified in the order [Iyz Izx Ixy]. The products of inertia are defined relative to a frame with origin at the center of mass and with axes parallel to the reference frame axes. The products of inertia are the off-diagonal elements of the inertia matrix,
where:
Dependencies
This parameter is enabled when the Inertia
Matrix parameter is set to
Constant
.
Graphic
Type — Geometry type to use in model visualizations
Equivalent Inertia
Ellipsoid
(default) | Marker
| None
Visualization setting for this variable mass, specified as
Equivalent Inertia Ellipsoid
,
Marker
, or
None
. Set the parameter to
Equivalent Inertia Ellipsoid
to represent
the variable mass as an ellipsoid. Set the parameter to
Marker
to represent the variable mass as
a marker. Set the parameter to None
to hide
the variable mass in the model visualization.
Shape — Shape of marker to represent to variable mass
Sphere
(default) | Cube
| Frame
Shape of the marker by means of which to visualize the variable mass,
specified as Sphere
,
Cube
, or
Frame
. The motion of the marker reflects the
motion of the variable mass itself.
Dependencies
To enable this parameter, set Type to
Marker
.
Size — Width of the marker in pixels
10 pixels
(default) | scalar
Width of the marker in pixels. 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
Equivalent Inertia Ellipsoid
or
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.
The diffuse color reflects the main color of the graphic and provides shading that gives the graphic a three-dimensional appearance.
Dependencies
To enable this parameter, set Type to
From Geometry
or
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.
Dependencies
To enable this parameter, set:
Type to
Equivalent Inertia Ellipsoid
orMarker
Visual Properties to
Simple
Specular Color — Color of light due to specular reflection
[0.5 0.5 0.5 1.0] (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 specular 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. This parameter changes the color of the specular highlight, which is the bright spot on the graphic due to the reflection of the light from the light source.
Dependencies
To enable this parameter, set:
Type to
Equivalent Inertia Ellipsoid
orMarker
Visual Properties to
Advanced
Ambient Color — Color of ambient light
[0.15 0.15 0.15 1.0] (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 ambient light, 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.
Ambient light refers to a general level of illumination that does not come directly from a light source. The Ambient light consists of light that has been reflected and re-reflected so many times that it is no longer coming from any particular direction. You can adjust this parameter to change the shadow color of the graphic.
Dependencies
To enable this parameter, set:
Type to
Equivalent Inertia Ellipsoid
orMarker
Visual Properties to
Advanced
Emissive Color — Self-illumination color
[0.0 0.0 0.0 1.0] (default) | 3-by-1 or 1-by-3 vector with values in the range of 0 to 1
Color due to self illumination, specified as an [R,G,B] or [R,G,B,A] vector 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.
The emission color is color that does not come from any external source, and therefore seems to be emitted by the graphic itself. When a graphic has an emissive color, the graphic can be seen even if there is no external light source.
Dependencies
To enable this parameter, set:
Type to
Equivalent Inertia Ellipsoid
orMarker
Visual Properties to
Advanced
Shininess — Highlight sharpness
75 (default) | scalar with value constrained to 0–128
Sharpness of specular light reflections, specified as a scalar number on a 0–128 scale. Increase the shininess value for smaller but sharper highlights. Decrease the value for larger but smoother highlights.
Dependencies
To enable this parameter, set:
Type to
Equivalent Inertia Ellipsoid
orMarker
Visual Properties to
Advanced
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
Version History
Introduced in R2016b
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