The 4 Post event attaches your vehicle model to a 4-Post test rig and provides a variety of options for exercising the vehicle. The vehicle is attached to the 4 jacks/posts using bushings and sforces.

Bushings are used between the wheel centers and the ground for longitudinal and lateral stiffness/damping. Sforces are used between the vertical jack parts for vertical stiffness/damping. Inplane jprims fix the wheel center to the top jack part and this allows the wheels to move laterally and longitudinally. Two jack parts are used at each corner of the vehicle and the stiffness/damping is applied between these two parts. The displacement input is applied to the bottom jack part.

The vertical static tire stiffness for this event is obtained from the front and rear tire property file and the vertical static tire damping is computed as a percentage by the following parameter in the front and rear Wheel/Tires subsystem files:

The lateral and longitudinal static tire stiffnesses are contained within the modeling template and require a personal version of (install_dir)/pre_py/tire/static_tire.py for modification.
 

Input Fields:

 Simulation Time and Output Frequency - Determines the end time and number of steps for the transient simulation.
 
Peak Ram Velocity and Frequency Range (applicable only to Constant Velocity Swept Sine type 4 Post simulation) - Inputs to the jack motion statements.
 

4 Post Types:
Constant velocity swept sine:

This type of 4 Post event uses a constant velocity swept sine forcing function as the input motion to the 4 jacks. The different modes available are:

LF_Phase  RF_Phase  LR_Phase  RR_PhaseHeave         1         1         1         1 Pitch         1         1        -1        -1 Roll          1        -1         1        -1 Warp          1        -1        -1         1 Front Axle    1         1         0         0 Rear Axle     0         0         1         1 Left Side     1         0         1         0 Right Side    0         1         0         1 Left Front    1         0         0         0 Right Front   0         1         0         0 Left Rear     0         0         1         0 Right Rear    0         0         0         1 Where 1 implies in-phase, -1 implies out-of-phase and 0 implies no motion is applied.

MD Adams Solver Expressions: With this feature, the user has the flexibility in creating MD Adams Solver expressions for each of the wheels which will then be used as inputs to define the jack motions.

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The RPC Data option is the 4-Post Adams/Durability event. This attaches your vehicle model to a 4-Post test rig and drives the jack motion via RPC test data. For each jack you specify a RPC file name, channel ID, and scale factor. The scale factor must be such that the resulting displacement used in the model is mm (For example if the RPC file contains data in meters, use a scale factor of .001).

Input Fields:

Simulation Time and Output Frequency - They determine the end time and number of steps for the transient simulation.
Channel Number (for all 4 jacks) - Channel ID (integer) to use in specified RPC file
Scale (for all 4 jacks) - Factor so resulting displacement is mm
RPC File (for all 4 jacks) - RPC file specification (.rsp)