Stability Analysis

The Stability Analysis event can be used to simulate two-wheeler models on various road surfaces to evaluate the weave and wobble modes of the vehicle. A user-defined road property file determines the road input.

The Stability Analysis event is supported by the Two-Wheeler vehicle libraries.

Figure 1. Motorcycle Stability Modes

Parameters

Parameter Name Description
Units Describes the Length, Velocity, and Acceleration units.
  • Length (Model, m, ft)
  • Velocity (Model, m/s, km/h, mph).
  • Acceleration (Model, m/s2, g’s).
Velocity Constant demand velocity input.
Steer release time Used in the Pulse force and General force analysis mode. Time at which steer control is released. Note: For the Linear analysis mode, the steer control is released at the end time and a Linear analysis is run.
Disturbance start time Used in the Pulse force analysis mode. Start time for the pulse force disturbance defined in the Force inputs tab.
End time End time for the simulation.
Path profile Defines the path the vehicle follows. Three options are available:
  • Straight Line: the vehicle follows a straight line path.
  • Road centerline: The vehicle follows the road centerline (Road centerline is generated in a DDF file before the start of the simulation).
  • Curve: Option to attach a MotionView x-y curve as the path input.
    • Units: Units of curve inputs [model units, m, ft].
    • Curve: MotionView curve attachment.
    • Interpolation: Selection for interpolation scheme [AKIMA,CUBIC, LINEAR, QUINTIC].
Analysis mode Defines the type of analysis in the event. Three options are available:
  • Linear: Option for running linear analysis at the end of the simulation after steer control is deactivated.
  • Pulse Force: Option for running transient analysis after deactivating the steer control at Steer release time to End time with disturbance applied at Disturbance start time. Body, point, and reference frame for the disturbance force can be defined in the Force Settings Connectivity tab. Type of force can be chosen from Force along Y or Torque about Z. These are typical cases where disturbance is caused by applying lateral force on the frame or steering torque is applied about steering revolute joint. Amplitude, Length of pulse, and Function type can be defined describing the pulse force like the Pulse steer event.
  • General force: Option for running transient analysis after deactivating the steer control at Steer release time to End time. Body, point, and reference frame for the disturbance force can be defined in the Force Settings Connectivity tab. Disturbance can be defined using MotionSolve expressions in six directions using the Translational Properties and Rototation properties tabs.

Controller Settings

LONGITUDINAL – TRACTION CONTROLLER SETTINGS
  • Use additional control: Enables the additional feedback control for the traction control. The gains for the controller can be edited by toggling this check box.
    Kp Proportional gain for the feedback PID controller
    Ki Integral gain for the feedback PID controller
    Kd Derivative gain for the feedback PID controller
LATERAL – STEERING CONTROLLER SETTINGS
  • The Lean PID and Lateral Error PID controllers only apply to leaning vehicles (for example, motorcycles and scooters).
    Steer control: Control mode for steering can be switched between ‘MOTION’ and ‘TORQUE’
    Lean control
    The Lean PID takes as input a demand lean angle and outputs front fork (steering) angle. For open loop events the lean angle demand is a function of time. For closed loop path following events the demand lean angle is computed based on the vehicle speed and the path curvature with a correction for lateral path error.
    Kp Proportional gain for the lean controller
    Ki Integral gain for the lean controller
    Kd Derivative gain for the lean controller
    Lateral error control
    The Lateral Error PID takes as input the predicted lateral path error and outputs an increment to the demanded lean angle. The lateral error is computed by predicting the vehicle’s lateral position relative to the path by the look ahead time in the future. The Lateral Error PID acts to lean the vehicle toward the path.
    Look ahead time Look ahead time for the feedforward model to evaluate future states of the vehicle
    Kp Proportional gain for the lateral error controller
    Ki Integral gain for the lateral error controller
    Kd Derivative gain for the lateral error controller

    For more information see the Leaning Two and Three Wheeler Vehicles and Gain Tuning for Leaning Two and Three Wheeler Vehicles topics.

Signal Settings

Use the signal settings to set minimum, maximum, smooth frequency and initial values for Steering, Throttle, Brake, Gear, and Clutch signals output by the driver.

The smoothing frequency is used to control how fast the Driver changes signals. Only closed loop control signals from the Driver are smoothed. Open loop signals are not smoothed.

Road Settings

Three options are available to specify the road in the event, Flat Event, Road File, and Tires.
Flat Road
Uses a flat smooth road for the event with no required road file.
When the Flat Road is selected, the Graphics Setting option is available with the following parameters:
  • View path centerline: Enables the visualization of the event path.
    • This check box is disabled for open loop events without a path.
  • View grid graphics: Enables the visualization of the road grid graphics.
    • When view grid graphics check box is toggled, road grid parameters can be edited in the Grid Settings tab.
    Grid length Defines the length of the road. Enter a positive value in the model units.
    Grid Width Defines the width of the road. Enter a positive value in the model units.
    Grid X offset Gives a distance offset to the road graphics in the longitudinal direction. Enter a positive value in the model units.
    Grid Y offset Gives a distance offset to the road graphics in the lateral direction. Enter a positive value in the model units.
Road File
The road file option enables the selection of a road file to be used in the event. Using this option, all tires in the model consider the event specified road file instead of the file included in the tire entities.
Tires
Using Tire as road selection option, the road file specified in the tire entity is used in the events simulation.

Automated Output Report

The list of outputs present in a Double lane change event report are as follows:
Report Name Report Signals
Analysis Mode = Linear
  • Animation of the Event
  • Eigenvalues reported by MotionSolve for the model (.eig file)
Analysis Mode = Apply Pulse/Apply Disturbance
  • Animation of the Event
  • Applied Pulse or Disturbance
    • Force Magnitude
    • Torque Magnitude
  • Steering Wheel Angle
    • Steer Angle vs Time
    • FFT Magnitude of Steer Angle
  • Vehicle Displacements
    • Roll Angle vs Time
    • FFT Magnitude of Roll Angle
    • Yaw Angle vs Time
    • FFT Magnitude of Yaw Angle