Engee documentation

Principles of modelling physical systems

Physical Modeling in Engee is a way of modelling systems of blocks corresponding to real physical objects, which can be connected not only by mathematical directional links, but also by physical two-way links. This approach to creating physical (acausal) models greatly simplifies work with systems of physical objects, because it eliminates the need to describe the model itself and the interaction between individual blocks by a system of equations.

Library blocks Physical Modeling differ from the others in that they represent not separate mathematical operations, but functional elements of a physical system: a spring, a capacitor, a pneumatic resistance, etc. These elements interact with each other by exchanging energy through ports. The lines connecting the blocks represent the physical connections that exist between components in a real system, i.e. wires, pipes, mechanical linkages, etc.

The library Physical Modeling consists of several sections that correspond to different subject areas (liquids and gases, electricity, mechanics, heat, etc.). To improve the readability of flowcharts, each subject area in Engee uses a different colour for connecting lines and block icons.

The types of physical elements that are contained in the library Physical Modeling can be divided into two categories:

  • Active elements - deliver energy to the system. They should be orientated strictly according to the direction of action or function they are to fulfil in the system, e.g. force and velocity sources, flow and pressure sources, etc.

  • Passive elements - dissipate or store energy. Can be orientated in any direction, e.g. shock absorbers, resistors, springs, pipework, etc.

Ports and variables

Port types

  • Directional ports of blocks represent physical connections between blocks. These ports are denoted by squares and connected by lines as they would be connected in a real physical system. In the model, the physical connection is expressed as an exchange of energy through non-directional block ports.

    principles physmod modeling 1

    The number of non-directional ports for each block is determined by the number of energy flows it exchanges with other elements in the system. For example, unlike a conventional resistor, a Thermal Resistor has an additional temperature port whose resistance varies with temperature.

    principles physmod modeling 2

    If all ports of a block belong to the same subject area, the entire block icon has the colour of that area. If a block has several types of ports, for example Rotational Mechanical Converter (IL), then the corresponding parts of the block icon acquire styles and line colours that depend on the subject area.

    rotation mechanical converter (il)

    Blocks of different subject areas can be used in the same model, but they can be connected only if the ports belong to the same subject area (have the same colour).

    line colors 01

  • Directional ports transfer the mathematical value of quantities as a scalar, vector or matrix between blocks. These ports are labelled with an arrow and have a direction, source and receiver. They are used in circuits as input ports to give a source reading or output ports to take a sensor reading. Basic library blocks can be associated with them.

    principles physmod modeling 3

Variable types

  • Flow - measured at a single point (sensor connected in series with the element).

  • Difference - expressed as differences and measured at two spatially different points (sensor connected in parallel to the element).

Physical domain Library Longitudinal variables Transverse variables

Pneumatics

Gas

Mass and energy flow

Absolute pressure and temperature

Rotational motion

Mechanical/rotational

Torque

Angular velocity

Progressive motion

Mechanical / translational

Force

Linear velocity

Thermodynamics

Thermal

Heat flow

Temperature

Electricity

Electricity

Current

Voltage

Each variable is characterised by its magnitude and sign. The same variable can be positive or negative, depending on the polarity of the sensor.