Documentation

# Variable Brick Solid

Solid brick with variable mass and size

• Library:
• Simscape / Multibody / Body Elements / Variable Mass ## Description

The Variable Brick Solid block adds to the attached frame a solid brick with variable mass and size. The mass and side lengths (x, y, and z) of the brick can each be a constant or vary with time. A variable quantity can be specified directly as a physical signal or it can be calculated as a function of the remaining quantities. Only one quantity, either mass or one side length, can be calculated during simulation.

A reference frame encodes the position and orientation of the solid in a model. The frame origin is located at the midpoint of the x- and y-dimensions and at the lower end of the z-dimension. These relationships are preserved during simulation. The z-dimension increases asymmetrically relative to the lower z-plane, along the positive direction of the z-axis.

Variable Brick with z-Dimension Calculated from Mass Visualization is dynamic. Solid dimensions update continuously as they occur, in the visualization pane of Mechanics Explorer. The initial dimensions of the solid depend on the parameters and physical signals that you specify. It is possible for a variable dimension to begin with a zero value—for example, if it derives from a physical signal whose initial value is zero also.

Density can itself be constant or variable. This quantity is specified as a constant if at least one solid parameter is calculated during simulation. It is calculated as a variable if all solid parameters are explicitly specified, either as (constant) block parameters or as physical signals. As in the case of the solid blocks, you can specify a negative density, for example, to model voids in compound bodies.

## Ports

### Frame

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Local reference frame of the solid. This frame is fixed with respect to the solid geometry. Its origin is on the xy plane, in the geometrical center of the xy cross section. Connect this port to a frame entity—port, line, or junction—to resolve the frame placement in a model. For more information, see Working with Frames.

### Physical Signal Input

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Input port for the x-dimension of the brick.

Input port for the y-dimension of the brick.

Input port for the z-dimension of the brick.

Input port for the mass of the brick.

### Physical Signal Output

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Output port for the x-dimension of the brick.

Output port for the y-dimension of the brick.

Output port for the z-dimension of the brick.

Output port for the mass of the brick.

Output port for the center of mass of the brick, reported as a three-element vector with Cartesian coordinates resolved in the reference frame of the solid.

Output port for the inertia matrix of the brick, reported as a nine-element matrix and resolved in the reference frame of the block. The diagonal matrix elements are the moments of inertia. The off-diagonal elements are the products of inertia.

## Parameters

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#### Geometry and Inertia

Parameterization of the x dimension of the solid—the length along the x-axis of the local reference frame. Select `Constant` to specify a fixed value as a block parameter. Select `Provided by Input` to specify a variable value as a physical signal input. Use the default setting (`Calculated from Mass`) to obtain this parameter from the specified solid density and remaining dimensions. Selecting `Provided by Input` exposes a new physical signal input port, labeled lx, through which to specify the variable value.

Length of the solid along the x-axis of the local reference frame. The x dimension is constant when this block parameter is active.

#### Parameter Dependencies

This parameter is active when the X Length parameter is set to `Constant`.

Parameterization of the y dimension of the solid—the length along the y-axis of the local reference frame. Select `Constant` to specify a fixed value as a block parameter. Select `Provided by Input` to specify a variable value as a physical signal input. Use the default setting (`Calculated from Mass`) to obtain this parameter from the specified solid density and remaining dimensions. Selecting `Provided by Input` exposes a new physical signal input port, labeled ly, through which to specify the variable value.

Length of the solid along the y-axis of the local reference frame. The y dimension is constant when this block parameter is active.

#### Parameter Dependencies

This parameter is active when the Y Length parameter is set to `Constant`.

Parameterization of the z dimension of the solid—the length along the z-axis of the local reference frame. Select `Constant` to specify a fixed value as a block parameter. Select `Provided by Input` to specify a variable value as a physical signal input. Use the default setting (`Calculated from Mass`) to obtain this parameter from the specified solid density and remaining dimensions. Selecting `Provided by Input` exposes a new physical signal input port, labeled lz, through which to specify the variable value.

Length of the solid along the z-axis of the local reference frame. The z dimension is constant when this block parameter is active.

#### Parameter Dependencies

This parameter is active when the Z Length parameter is set to `Constant`.

Parameterization of the mass of the solid. Select ```Calculate from Geometry``` to obtain this parameter from the specified solid density and dimensions. Use the default setting (```Provided by Input```) to specify this parameter directly as a time-variable physical signal. This option exposes a new physical signal input port, labeled M, through which to specify the time-variable solid mass.

Mass per unit volume of material. The mass density can take on a positive or negative value. Specify a negative mass density to model the effects of a void or cavity in a solid body. The default value, ```1000 kg/m^3```, is characteristic of polymers such as ABS plastic.

#### Parameter Dependencies

This parameter is active when the Mass parameter is set to `Calculate from Geometry`.

#### Sensing

Sensing selection for the x dimension of the solid. Check to expose a new physical signal output port, labeled lx, through which to output the time-varying value of the x dimension.

Sensing selection for the y dimension of the solid. Check to expose a new physical signal output port, labeled ly, through which to output the time-varying value of the y dimension.

Sensing selection for the z dimension of the solid. Check to expose a new physical signal output port, labeled lz, through which to output the time-varying value of the z dimension.

Sensing selection for the total mass of the solid. Check to expose a new physical signal output port, labeled m, through which to output the time-varying value of the solid mass.

Sensing selection for the coordinates of the center of mass of the solid. Check to expose a new physical signal output port, labeled com, through which to output the time-varying coordinates. The output is a three-element vector with Cartesian coordinates resolved in the reference frame of the solid.

Sensing selection for the inertia matrix of the solid. Check to expose a new physical signal output port, labeled I, through which to output the time-varying inertia matrix. The output is a nine-element matrix with the moments of inertia in the diagonal positions and the products of inertia in the off-diagonal positions. The moments and products of inertia are resolve in the inertia frame of resolution—a frame with axes parallel to those of the reference frame but origin at the center of mass.

#### Graphic

Visualization setting for this solid. Use the default setting, `From Geometry`, to show the solid geometry. Select `Marker` to show a graphic marker such as a sphere or frame. Select `None` to disable visualization for this solid.

Geometrical shape of the graphic marker. Mechanics Explorer shows the marker using the selected shape.

Size of the marker in units of pixels. The size does not change with zoom level.

Parameterization for specifying visual properties. Select `Simple` to specify color and opacity. Select `Advanced` to add specular highlights, ambient shadows, and self-illumination effects.

RGB color vector with red (R), green (G), and blue (B) color amounts specified on a 0–1 scale. A color picker provides an alternative interactive means of specifying a color. If you change the Visual Properties setting to `Advanced`, the color specified in this parameter becomes the Diffuse Color vector.

Graphic opacity specified on a scale of 0–1. An opacity of `0` corresponds to a completely transparent graphic and an opacity of `1` to a completely opaque graphic.

True color under direct white light specified as an [R,G,B] or [R,G,B,A] vector on a 0–1 scale. An optional fourth element specifies the color opacity also on a scale of 0–1. Omitting the opacity element is equivalent to specifying a value of `1`.

Color of specular highlights specified as an [R,G,B] or [R,G,B,A] vector on a 0–1 scale. The optional fourth element specifies the color opacity. Omitting the opacity element is equivalent to specifying a value of `1`.

Color of shadow areas in diffuse ambient light, specified as an [R,G,B] or [R,G,B,A] vector on a 0–1 scale. The optional fourth element specifies the color opacity. Omitting the opacity element is equivalent to specifying a value of `1`.

Surface color due to self illumination, specified as an [R,G,B] or [R,G,B,A] vector on a 0–1 scale. The optional fourth element specifies the color opacity. Omitting the opacity element is equivalent to specifying a value of `1`.

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.