Physical Component Modeling

Signal Versus Physical Component Diagrams

The process of modeling dynamic systems includes assembling blocks that exchange data through a network of input and output ports. Though possible to model physical systems with the basic Twin Activate blocks, the process requires translating into explicit form the implicit equations that represent the behavior of the physical components. In addition, the resulting diagrams have an unconventional appearance compared to component-based diagrams as you can see in the following figure.

Figure 1. Component-Based Diagram (left) and Twin Activate Diagram (right)

The fundamental reason why regular blocks are not well-suited for modeling physical components is that component ports are connectors which, unlike block ports, need not be specified as inputs or outputs. A component places general constraints on its port signals. For example an electrical resistor specifies relations between the currents and voltages on its ports, in particular that the sum of currents flowing in is zero and the difference of voltages is proportional to the current, but the component does not require any current or voltage to be an input or output.

Benefits of Modeling with Implicit Blocks

A better way to model physical components is to use implicit blocks in which the behavior of the blocks is specified through symbolic equations. Unlike regular blocks that can be regarded as black boxes, implicit blocks expose the implicit equations of a corresponding component. The software can through symbolic manipulation implement these equations to produce efficient code for models obtained from the interconnection of implicit blocks. The symbolic specification of the behavior of implicit blocks is accomplished with Modelica language. The resulting model is more efficient and closely resembles a conventional physical component as you can see in the following figure:

Figure 2. Conventional Diagram (left) and Twin Activate Diagram with Implicit Blocks (right)

Combining Component and Block Models

A component model and block model can be interconnected using special interface blocks as you see in the following diagram:

The interface blocks, FromModelica and ToModelica, can be added manually from the Interfaces palette, but in most cases the blocks are included automatically when a link is created to join the blocks.

Additional information on modeling physical components is available in the Extended Definitions for Advanced Users.