UM Pneumatic Systems

UM Pneumatic Systems

Simulation of multibody systems with pneumatic elements


Program package Universal Mechanism includes a specialized module UM Pneumatic Systems, which contains tools for simulation of models with pneumatic elements. The following elements are available in the current version of the module:

  • Air springs
  • Rigid chambers
  • Pneumatic lines
  • Orifices
  • Height control  (leveling ) valves
  • Compressors




Air springs (AS)


The following AS models are available:

  • Tabular model: the description of force element includes tabular experimental data on force and volume
  • Nishimura model
  • Berg model
  • Thermodynamic model
Air spring 1T15-M0
UM tabular model of AS

Manufacturers often supply information about AS properties in the form of a static data charts, which include load/height and volume/height diagrams. An example of such charts for 1T15-M0 is shown in the figure. Such data allow development of rather exact mathematical models of AS.

Pneumatic lines

Stationary pipeline models

Pipe length 3m, diameter 5 mm

Three mass flow rate versus pressure drop models for pneumatic lines are implemented:

  • "Atlas"
  • Fluid mechanics
  • Darcy-Weisbach

Time domain pipeline model

The dynamic model of a pipeline is described by a system of differential equations. The model allows taking into account transient processes and inertial properties of long pipelines.

Verification of dynamic pipeline model

Sketch of experimental equipment for verification of time domain model of pipeline
Frequency response: simulation vs. experiment
Orifice models


Similar to a pipeline, an orifice (nozzle, valve) is a connection between two nodes of pneumatic system. The mathematical model of an orifice includes a dependence of the mass flow rate on the pressure drop. The following orifice models are available in UM:

    • Nozzle
    • ISO 6358
 Height control valve (leveling valve)





Examples of HCV

A height control valve (HCV) or leveling valve is used in automotive and railway industry for supporting a desired value of the suspension height when the load changed.


HCV flow curve

Pneumatic systems


A pneumatic system in UM is considered as a graph, which nodes are connected by edges. Each node of a graph corresponds to one of the pneumatic elements:

  • Rigid chamber
  • Air spring (AS)
  • Simple node

The graph edges are:

  • Pneumatic lines
  • Orifices
AS are connected by two T-junctions
AS are connected by pipelines with auxiliary chambers


     Model of a pneumatic system with HCV

Verification tests

Case 1: Air spring connected by pipeline with auxiliary chamber

Scheme of experiment for study of pipeline influence on dynamic stiffness and damping of air spring with auxiliary chamber
Dynamic stiffness vs. frequency: comparison of simulation and experiment

Case 2: AS connected by orifice with auxiliary chamber

Air spring and auxiliary chamber
a = 1mm a = 2.5mm
a = 5mm a = 7.5mm
Comparison of simulation and experimental results


Simulation example: Heigh speed railway motor car


Vehicle model
Bogie model with two AS
Comparison of simulation results for AS connected with auxiliary chambers and isolated AS with additional dampers in secondary suspension