System Simulation:User Specific Representation of Simulation Results

User Specific Representation of Simulation Results

The above-mentioned simulators provided by EDA industry have extensive possibilities for the graphic representation of simulation results. The most important representation forms in electronics and control theory are:

• timing functions of analog and digital signals (transient simulation);

• attenuation and phase characteristics of linear circuits (AC analysis);

• frequency spectra (obtained, e.g., from the conversion between time and frequency domain by means of Fourier transforms);

• root locus and pole-zero representations (e.g., for stability analysis of control systems).

The display tools of such simulators offer a variety of possibilities for trace handling: zooming; measuring of curve characteristics by markers and rulers; as well as ‘calculator functions’ for adding, multiplying, calculating the logarithm, . . . of traces.

All of these possibilities are needed for system simulation, but they are not sufficient. Eye diagrams and scatter diagrams, e.g., are important in the design of telecommunication systems (fig. 13.13). Eye diagrams supply – similarly to scatter diagrams – information about how well disturbed signals can be detected. The result of a transient simulation for 0-1-sequences of the input signal will be periodically written in the same diagram, one above the other. The transients in the system, distortions, and random disturbances lead to char- acteristics of the output signal, as is represented in fig. 13.29. A separation of the 0 and the 1 level by a decider circuit will be possible if the ‘eye’ inside the diagram, i.e., the central white area between the curves, is large enough. With some simulators an eye diagram can be generated by clever use of the waveform tools for the transient simulation. Similarly, special display tools for scatter diagrams have to be used or developed.

For simulation in the microsystems technology domain (MEMS) it is important to have two- and three-dimensional representations of mechanical deformations, pressures, temperatures, distribution of electrical currents, electric potential fields, and others. These visualization capabilities are part of the standard scope of FEM simulators.

But for other complex systems very specialized or problem-dependent display tools have to be programmed. There is a good software support for writing one’s own visualization tools [13.18]:

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• public domain software: gnuplot [13.30];

• Java libraries [13.37];

• for larger visualization tasks: commercially

available libraries such as IMSL [13.35] and IDL (Interactive Data Language) [13.34];

• the use of manifold visualization routines of Matlab/Simulink and MatrixX, which has open interfaces to the user and other simulators.

Just for system simulation the desired visualization of simulation results transcends one- or two- dimensional curve representations considerably. E.g., it can be very helpful for a designer of a complex control system for automobiles or air- crafts to see simulation results not only as number series or traces, but also to visualize the results as pictures like a speedometer, an altimeter, or a compass. An input of a signal value can also be achieved by copying the position of a real knob or a pedal or by a moveable glider on the display. After the simulation of motion sequences (e.g., of robots or vehicles) a ‘cine-like’ visualization is useful, which is often called animation. Figure shows a representation of a robot arm whose position will change as a result of the simulation (for the simulation of mechatronic systems the simulator DYMOLA [13.22] has been used).

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Because its independence of a software platform and its wide use in the Internet, Java will become widespread. Java includes class libraries of 2D and

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3D graphics, so the user can program his own very complex visualization tools easily.

VRML is a standardized file format for 3D scenarios and the description of projection areas, that corresponds to the movement of an observer going through the space. Only by the use of such standards it is possible to couple general-purpose system simulators with additional visualization and animation tools.

Many simulation systems have tools for the animation of simulation results already built in. STATEMATE, e.g., has a so-called ‘panel generator’ [13.7]. It offers prefabricated symbols for speedometers, thermometer, level indicators, setting devices, ..., which can be combined together into a graphic representation of complex systems (e.g., an airplane cockpit or a measurement arrangement). A calculated speed will then be shown as a speedometer deflection. VAPS [13.71], a visualization and animation software of the company Virtual Prototyping, can be used for such problem-specific tasks.

Matlab/Simulink offers similar animation possibilities. In fig. 13.31 a control system for the control of an ‘inverse pendulum’ is shown.

A simply supported rod, mounted on a wagon, is held in balance by moving the wagon in such a way that a falling rod would be set back standing up. Therefore the wagon has to be moved to the falling direction of the rod and the inertial forces will set the rod upright. The design and dimensioning of the control system are challenging tasks and it is important to check the design by simulation. In fig.

a system description for Matlab/Simulink is shown. The movement of the wagon and the position of the rod is visualized by the block ‘animation’. Figure 13.32 shows a snapshot of the falling rod.

More detailed and quantitative information about the simulated processes in the system can surely better be shown by traces and value tables of simulation results. But a first glance animation of complex sequences can also be an essential addendum, e.g., in the use of simulation for educational purposes. In this respect flight simulators and state-of-the-art play stations show a top performance, but the EDA tools also achieve respectable capabilities. But the effort for the elaboration of an informative and also aesthetic visualization and animation environment is quite high: days and weeks for the concept and for programming have to be scheduled.

Of course, in this short chapter only some aspects of system simulation and of problem-specific visualization of simulation results could be demonstrated. But the reader will probably be faced with this problem more often in future. Besides the use of EDA tools for the design of new circuits and systems, lifelong learning activities will play a big role in the future. Computer aided education will extensively use the Internet, will include interactive simulation, and its efficiency will be essentially determined by graphical communication.

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