Example 4: Distribution of compressed air (1)

• Basic system:
  • simple pneumatic system with pressure source, tee branch, pipe and consumers
    • 
• Model in Modelica:
  • uses PneuBib library
  • PneuBib itself based on MSL Fluid library
  • MSL Fluid library basically describes quasistatic processes
  • run in Dymola →
    • Failed to solve nonlinear system using Newton solver...
      At time T = 5.130275e-04 ...
        the corrector could not converge ...
      Integration will be terminated.
• Mathematical problem:
  • model consists of 170 equations, many are coupled and highly non-linear
  • proper initial values are unknown and guessed by solver
    • → Newton solver does not converge
  • well-known problem of MSL Fluid library
• Reality check:
  • system starts with ambient pressure and zero mass flow everywhere
  • switching on pumps etc.
    • → global pressure difference increases
    • → mass flows increase slowly due to mass inertia
    • → local pressure differences build up