Error in a vehicle model

Errors in the input data file can be of different kind, below is a list of different type of errors:

Syntax errors
Syntax errors occurs when program CALC don't understand what is written in the input data file, or if any limits in the input data file has been exceeded. In this case program CALC writes an error message and stops the execution.
Values greater then 1.e30
If the simulation stops with the error message:
```
 ***ERROR*** In Store_v:
             Value of variable "XXXX" is greater then 1.e29.
             the value cannot be written to MPdat-file.
```
- Set the output time step tout to a small value.
- Write output to a .gp animation-file with command s_var gpdat_r1
- Animate the vehicle slowly step by step in program GPLOT.
Unexpected vibrations
If a mass is vibrating and you don't know what is exciting the mass. Please command s_var force_on and enter the name of the mass and the direction of the vibrations.
Initial errors
Errors in the initial conditions can occur due to one of the following examples:
- Wrong lengths has been given for couplings with a working direction equal to x, y, z, f, k, p or m.
- The prestress forces given for the vertical springs does not correlate to the actual masses in the model.
- Two cars are connected to each other with longitudinal couplings, but the two cars are located at the same place on the track.
- Zero gauge
If the error is relatively small, program TSIM can manage to finish the simulation, but vibrations can occur in the beginning of the simulation. In this case the user can look at the quasistatic values in the end of the simulation, and from plots showing all degree of freedom of all Masses the user can figure out what is wrong in the model.
If the error is big, large initial value and high spring stiffnesses. In this case it looks like the model is exploding, and TSIM may not manage to finalize the simulation. In order to look at the initial conditions the user must start a calculation with the input data parameter idebug set equal to 1. When idebug is equal to 1 the file calc.out will be printed, and in that file the user has the possibility to check all initial conditions. Search in calc.out for the following variables:
- Look for all accelerations for all masses: axl_111.ax, axl_111.ay,,, bog_11.ax, bog_11.ay,,, etc.
- Look for all couplings connected to the mass above having a very high acceleration.
- Check the coupling which gives a high force and a big acceleration of the mass.
When the mass with high acceleration and coupling with high force has been found, correct the error and make a new test.
In program TSIM, vibrations with an increasing amplitude
The calculations starts normally but after a while vibrations with an increasing amplitude starts. Possible error:
- A mode of vibration has negative damping
- Numerical instability in the integrator
Possible solutions:
- Make a modal analysis in program MODAL and look for any eigenvalues having a positive real part. A positive real part in the complex eigenvalue leads to a negative damping of the system.
- Look for the biggest absolute value of all eigenvalues. The biggest absolute value indicates max time-step for which a explicit integrator is stable.
  For integrator Runge_Kutta tstep < 2. / (max_abs_value)
  For integrator Heun tstep < 1. / (max_abs_value)
  For integrator Euler tstep < .5 / (max_abs_value)
- If not a modal analysis above solves the problem try to locate the mass and degree where the vibrations starts. This can be done by setting print-commands in the input data file. The print-commands print_all or print06_all can be used for printing the value of a variable. By printing the value of the speed of each degree of freedom the user can see where the vibrations starts. In most cases the error is very close this degree of freedom.
In program TSIM, the whole model drifts away
Possible error:
- No flanges on the wheels
- No vertical stiffness in the track
Solution: make a shorter simulation before the model has moved too far away. Look in the plots and try to find out why the track, primary suspension or secondary suspension not will produce proper reaction forces in order to keep the vehicle on the track.