Hydraulic crane co-simulation

This demo generates two Chrono FMUs and uses them in a co-simulation.

The first FMU, demo_FMI_craneFMU, encapsulates a simple multibody system consisting of an inverted pendulum (connected through a revolute joint to the ground) representing the main mast of the crane and a second pendulum representing the payload. The crane body accepts an externally-provided actuation force applied at a point on the body (as its primary continuous input FMI variable) and provides the actuator length and length rate of change as main FMI continuous outputs.

The second FMU, demo_FMI_actuatorFMU, encapsulates a hydraulic actuator consisting of a hydraulic piston, a directional valve, hoses, a pump, and an oil tank. As main FMI variables, this FMU accepts as continuous input the actuator length and length rate of change and provides as continuous output the actuator force.

demo_FMI_hydraulic_crane_cosim illustrates the use of these two FMUs in an explicit force-displacement co-simulation loop.
Chrono::Vehicle FMUs

If both the Chrono::FMI and the Chrono::Vehicle modules are enabled, several FMUs encapsulating vehicle systems are generated:
- FMU_WheeledVehicle is a co-simulation FMU encapsulating a wheeled vehicle system with 4 wheels. The vehicle includes a powertrain and transmission, but no tires.
  
  The wrapped Chrono::Vehicle model is defined through JSON specification files for the vehicle, engine, and transmission. This vehicle FMU must be co-simulated with a driver system which provides vehicle commands and 4 tire systems which provide tire loads for each of the 4 wheels (of type TerrainForce).
  
  This vehicle FMU defines continuous output variables for:
  - vehicle reference frame (of type ChFrameMoving)
  - wheel states (of type WheelState)
- FMU_ForceElementTire is a co-simulation FMU encapsulating a "force element" (handling) tire system.
  
  The wrapped Chrono::Vehicle tire model is defined through a JSON specification file which is assumed to define a tire of ChForceElementTire type.
  
  This tire FMU must be co-simulated with a vehicle system which provides the current wheel state (of type WheelState) and a terrain system which provides local terrain information (height, normal, and coefficient of friction) at a single query point.
  
  This tire FMU defines continuous output variables for:
  - wheel tire/terrain load (of type TerrainForce)
  - location of the terrain query point (of type ChVector3)
- FMU_PathFollowerDriver is a co-simulation FMU encapsulating a vehicle path-follower driver system. The driver model includes a lateral path-following PID controller and a longitudinal PID cruise controller.
  
  The wrapped Chrono::Vehicle driver model is defined through a data file specifying the path for the lateral controller.
  
  This driver FMU must be co-simulated with a vehicle system which provides the current vehicle reference frame (of type ChFrameMoving).
  
  This driver FMU defines continuous output variables for:
  - sterring command (in [-1,1])
  - throttle command (in [0,1]
  - braking command (in [0,1])

To see how these FMUs can be used together in a co-simulation loop, we provide two demo programs:

demo_VEH_FMI_WheeledVehicle_a

This program uses the WheeledVehicle and PathFollowerDriver, together with a set of 4 Chrono::Vehicle tires and a Chrono::Vehicle terrain system to co-simulate a vehicle following a prescribed path at constant speed.
demo_VEH_FMI_WheeledVehicle_b

This program uses the WheeledVehicle, 4 instances of the ForceElementTire, and the PathFollowerDriver, in conjunction with a Chrono::Vehicle terrain system to co-simulate a vehicle following a prescribed path at constant speed.