Grid Surface

Grid surface for contact modeling

Since R2021b

Libraries:
Simscape / Multibody / Curves and Surfaces

Description

The Grid Surface block creates a Cartesian grid surface that you can use to model contact problems. You can model contacts between the grid surface and various types of geometries. For the supported geometries, see Supported Geometries. In addition, the Grid Surface block supports the Custom Tire Force and Torque and Magic Formula Tire Force and Torque blocks.

You must use the positive normal side of the grid surface for contact, which the positive z-axis of the reference frame points to. Otherwise, the block ejects the contacting part through the surface to the positive side.

Illustration of the positive normal side of a grid surface

The grid surface has a similar format to the grid generated by the ndgrid function in MATLAB^®. To model a grid surface, use the X Grid Vector and Y Grid Vector parameters to specify the coordinates in the x and y directions of the grid surface, then use the Z Heights parameter to specify the elevations of the grid points in the z direction. You can use the block to create a surface that represents a square, rectangular, or non-uniform grid.

Grid types

The image shows an illustration of a grid surface whose Z Heights parameter is [0 0 0.5 0.5; 0 0 0.5 0.5; 0 0 0 0; 0 0 0 0]. The columns of the matrix are along the x-axis, and the rows of the matrix are along the y-axis.

Grid parameters

To create a grid surface using LiDAR data, you must convert the scattered data to gridded data before using it in the Grid Surface block. To convert the data, you can use a scatteredInterpolant object to create an interpolant function by using the x, y, and z values of the LiDAR data, create x and y grid vectors that represent the domain of the grid, and then use the grid vectors as the query points of the interpolant function to produce z values for the grid surface. The produced z values form a matrix in the ndgrid format that you can use to specify the Z Heights parameter. You can also use the griddata function to produce z values for a grid surface, but you need to transpose the output matrix to the ndgrid format.

Note

For the best simulation performance, make the spacing in the x and y grid vectors as large as possible while also being small enough to represent the surface with sufficient accuracy. To change the spacing of the grid vectors and compute the corresponding z values , use the griddedInterpolant object or interp2 function.

Generally, you need to clean the LiDAR data before converting it to gridded data, such as removing outliers or NaN values. To clean the data, use the isnan and isoutlier functions.

Examples

Contact Modeling - Ball on Grid Surface

A ball and dumbbell rolling down on an L-shaped surface. Grid Surface block is used to generate the L-shaped membrane. Point Cloud blocks are used to model the contact between the ball/dumbbell and the surface. The number of point blocks can be controlled by varying the point cloud density. This example demonstrates the capabilities of Grid Surface and Point Cloud blocks to model contacts between complex shaped bodies.

Open Model

Ports

Frame

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R — Local reference frame
frame

Grid surface reference frame. Connect this frame to another block to specify the location and orientation of the grid surface.

Geometry

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G — Geometry
geometry

Geometry that represents the grid surface defined by this block. Connect this port to a Spatial Contact Force block to model contacts with supported geometries.

Parameters

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X Grid Vector — Coordinates in x-direction
[0 1 2 3] `m` (default) | 1-by-m vector

Coordinates in the x-direction of the grid surface, specified as a real 1-by-m vector. m must be greater than 2, and the vector elements must be strictly monotonic and increasing. This vector corresponds to the rows of the matrix specified in the Z Heights parameter.

Illustration of the relationship between x grid vector and z height matrix

Y Grid Vector — Coordinates in y-direction
[0 1 2 3] `m` (default) | 1-by-n vector

Coordinates in the y-direction of the grid surface, specified as a real 1-by-n vector. n must be greater than 2, and the vector elements must be strictly monotonic and increasing. This vector corresponds to the columns of the matrix specified in the Z Heights parameter.

Illustration of the relationship between y grid vector and z height matrix

Z Heights — Elevations of grid points
[0 0 .5 .5; 0 0 .5 .5; 0 0 0 0; 0 0 0 0] `m` (default) | m-by-n matrix

Elevations of the grid points in the grid surface, specified as a real m-by-n matrix. m and n are the lengths of the vectors for the X Grid Vector and Y Grid Vector parameters.

Graphic

Type — Visual representation of grid surface
`From Geometry` (default) | `None`

Visual representation of the grid surface. Set this parameter to From Geometry to show the visual representation of the grid surface. Set this parameter to None to hide the grid surface in the model visualization.

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 From Geometry.

Diffuse Color — Graphic color
[0.5 0.5 0.5] (default) | three-element vector | four-element vector

Color of the graphic 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 (A) specifies the color opacity on a scale of 0–1. Omitting the opacity element is equivalent to specifying a value of 1.

Dependencies

To enable this parameter, set Type to From Geometry.

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.