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Mechanical Simulation VehicleSim Products

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Paths and Road Surfaces

Reference Paths ...................................................................................................... 2

Coordinate Transformations ............................................................................ 4

Road Surface Physical Properties ......................................................................... 24

Using Road Surfaces ...................................................................................... 25

Road Elevation Screens ................................................................................. 33

Road Friction Screens .................................................................................... 39

Connecting Road Surfaces ................................................................................... 46

Roughness Profiles ............................................................................................... 61

References ............................................................................................................ 66

BikeSim, CarSim, and TruckSim include 3D multibody models that simulate vehicle dynamics

under driver/rider control on a 3D ground surface. The equations of motion for the physics math

models are formulated using global X-Y-Z coordinates; all positions, velocities, and accelerations

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a 2D VS Reference Path — a continuous line that exists in a horizontal plane with continuity in

position and gradient.

surfaces can be connected to efficiently describe the geometric and friction interface to the vehicle

tires wherever the vehicle is likely to go.

Besides representing roads in the vehicle math model, BikeSim, CarSim, and TruckSim generate

3D shapes to help visualize the road surfaces. Two screens used to determine how a road appears

with multiple road surfaces; you can just use the existing road datasets or

make copies and adjust the properties.

The other level of user is the Model Builder. A Model Builder is a more

advanced user who can assemble paths, roads, and other simulation

components to build new scenarios with greater complexity. The road and

path concepts in VehicleSim products support the creation and simulation

of complicated situations.

Reference paths are used to define coordinate systems for roads, as targets

for the driver model for steering and speed control, and to define motions

of objects such as traffic vehicles. Managing some of these options

and gradient. That is, there are no sharp corners.

path of interest. The path coordinates are station S (distance along the path) and lateral coordinate

is perpendicular to the path at the point of intersection (Figure 1). In this coordinate system, the S

coordinate is based on an axis (the path) that is fixed, but not necessarily straight, while the L

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coordinate is based on an axis whose location is variable (it starts from the S location on the path),

and whose direction is variable (perpendicular to the path at S).

while the L coordinate typically covers a more limited range such as the width of a road.

path using S and L.

3. Lanes are defined using constant values of L for a Reference Path, or possibly, with the

Configurable Function LTARG that defines L as a function of S.

4. Road surface elevation and friction are defined as functions of S and L for a road reference

path.

A VS Reference Path is a sequence of contiguous segments. For example, the path shown in Figure

1 might be defined with three segments: a straight line going from point 1 to point 2, a circular arc

going from point 2 to point 3, and a straight line starting at point 3.

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associated with parts that are added by users as needed, such as payloads, sensors, moving objects,

etc. Index numbers are automatically set to start with 1 for the first instance and incremented for

each instance as new datasets of the same type are scanned. For example, SPATH_START(2) is

a parameter for the second path that was defined in a simulation.

about previous results obtained with the function. This is done automatically in the VS Solver for

tires. Each time a path or road function is queried by a tire, any searching begins with the most

previous location. The same is true for moving objects. Some of the functions available for use in

types of coordinate transformations:

1. calculate X and Y for a point given S and L, and

2. calculate S and L for a point given X and Y.

required) for all segment types used in VS Reference Paths. Transformations of this sort are

primarily used to locate and orient moving objects and sometimes to locate and orient the vehicle

for initial conditions.

located and use internal information to quickly locate the correct segment. As noted in the previous

section, each query into a path has an associated query ID, such that when query is repeated at the

next time step, the software will start searching at the previous location associated with the internal

query ID.

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A significant complication arises when there are multiple pairs of S-L coordinates that would be

valid for a single point of interest. For example, Figure 2 shows an aerial view of a racetrack

reference path (blue) and a red point of interest. Any of the points labeled A through I on the

reference path are related to the point of interest with a line perpendicular to the reference path and

therefore yield different, but valid, S-L coordinates for that point, where S is the position on the

path and L is the signed length of the perpendicular line. In this case, point A is probably the desired

location on the path.