1.1 Functions

Multilevel Flow Modelling is an ontology for modelling system functionality. Models are made up of functions and relations connecting the functions. A function is a node which is connected with adjacent nodes through relations.

Six different types of functions exist in MFM: Source, transport, storage, balance, barrier and sink.

1.1.1 Boundaries

The source acts as an input to a system. Everywhere somethings is being input to the system, this is modelled with a source. When modelling a system, the boundaries of the system needs to be defined. The boundaries represent the interaction between the model, and everything which is not included in the model. Thus everything happening before a source is not considered in the model.

A sink acts as an output of a system. Similarly, everything happening after a sink is not included in the model.

In the figure below, water is being recirculated in a closed system by a pump. There is no interaction between the system and the outside world.

boundaries2

In this instance, there is no need for any source nor sink. A simple example of how this can be modelled is shown below.

no_boundaries_egolf

 

An alternative system shown in the figure below, contains a pump, a tank and two valves controlling the input and output of water. In this case we have chosen to only consider a certain part of a larger process system.

boundaries1

The resulting model is shown in the figure below. Here a source is used as an input to the system, and a sink is used as an output from the system. The input and output that represents the boundaries of the system, are thus modeled with a source and a sink.

boundaries_EGolF2

 

  • A system input is modelled with a source function.
  • A system output is modelled with a sink function.
  • Sources and sinks can be used to define system boundaries to only model parts of a system.

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