Simulation with variable speed

In the document analyse_brake.html. the speed of the vehicle changes due to applied traction or brake force. Sometimes the track has a given speed profile which the vehicle ahall follow. This document shows how to create a regulator which applies pitch moment on the axles in order to make the vehicle to follow a given speed profile.

In the beginning of the input data file. Define the variable Vo as a non-constant variable, for example:

                                                
 func  intpl_l Vo= time   0. 130/3.6            
                         20. 130/3.6            
                         30  160/3.6            
                         50  160/3.6            
                         60  130/3.6            
                         80  130/3.6

In the end of the input data file, create a regulator which applies pitch moment on the axles in order to follow the variable speed. The following example shows a simple PI-regulator:

                                                                                
##                                                                              
##  Regulate the pitch moment on the axles                                      
##  --------------------------------------------------------------------------  
 func const FactP=  5e4                                                         
 func const FactI= .2e6                                                         
 func operp MtracP=   FactP * car_1.vx           # P-regulator                  
 func operp MtracI=   FactI * car_1.x            # I-regulator                  
                                                                                
 func operp Mtrac= MtracP + MtracI                                              
                                                                                
 if_then Mtrac .gt.  0.1*9.81*(mc+2*mb+4*ma)/4            # Max traction force  
  no_warning func copy Mtrac=  0.1*9.81*(mc+2*mb+4*ma)/4                        
 endif                                                                          
 if_then Mtrac .lt. -0.1*9.81*(mc+2*mb+4*ma)/4            # Max brake force     
  no_warning func copy Mtrac= -0.1*9.81*(mc+2*mb+4*ma)/4                        
 endif                                                                          
                                                                                
 force rel_lsys1  F_traction_111  axl_111  0 0 -ro   0. 0. 0.  0. Mtrac 0.      
 force rel_lsys1  F_traction_112  axl_112  0 0 -ro   0. 0. 0.  0. Mtrac 0.      
 force rel_lsys1  F_traction_121  axl_121  0 0 -ro   0. 0. 0.  0. Mtrac 0.      
 force rel_lsys1  F_traction_122  axl_122  0 0 -ro   0. 0. 0.  0. Mtrac 0.

In the variables FactP and FactI the user can choose how fast the vehicle shall respond to changes in the speed.