Activity Index and I, C, R, S and RS elements

In the bond graph formalism, energy is conserved, power flow paths can be identified, and power flow associated with elements and their connections can be readily determined.

Generalized inertias (I) and capacitances (C) store energy as a function of the system state variables, which are generalized momenta and displacements. The time derivatives of generalized momentum p and displacement q are generalized effort e and flow f, the product of which is power.

Generalized resistors (R) remove energy from the system and have a constitutive law relating generalized effort to generalized flow. Sources of effort and flow (Se and Sf) represent ports through which the system interacts with its environment.

I, C, and R elements are the most common in Simcenter Amesim. However, S sources have been implemented in components where energy is supplied in an implicit manner (i.e. without flowing explicitly through any of its physical ports). Combined RS elements are also used where a resistive effect coexists with an implicit source, matching the bond graph formalism with thermal effects.

Activity Index physical types and domains

The Activity Index facility is a powerful analysis tool based on energy transfer in the submodels of a system. Energy is split into physical types:

• R: dissipation
• C: capacitance
• I: inertia
• S: source
• RS: resistive source

and into the following physical domains:

• Hydraulic
• Mechanical
• Electrical
• Thermal
• Magnetic
• Thermodynamic

Taking the mechanical domain as an example, it mainly has components of I, C, and R physical types, found in submodels such as:

• MAS001: mechanical inertia
• SPR000A: mechanical capacitance
• DAM000: mechanical dissipation

For a given domain, one submodel can have more than one physical type, e.g. SD0000A: mechanical capacitance and mechanical dissipation.

The documentation includes a figure ("Figure 4: Examples of some I, C, R elements in Simcenter Amesim") illustrating further examples of I, C, R elements across domains.

The Activity Index can identify the most energy-active components of a system and the most energy-active physical phenomena, so that a reduced/simplified model can be built that nonetheless remains accurate enough to simulate the phenomena being studied.