Simulation & Modelling

1. Simulation & Modelling Lecture-2: Simulation Types, Tools and Simulators Systems Engineering Training Programme for DRDO Scientists at IAT, Pune 2nd July 2003

2. Lecture Outline • Software Simulation & Languages • Concept of a Simulator. • Engineering Simulators. • Basic Philosophy of Simulator Building • Examples of Software Simulators. • Examples of Hardware Based Simulators.

3. Why Software Simulation? Software simulation is usually a low cost, quick turn-around time option for most of the design cycles. Ability to solve complex mathematical equations (e.g. CFD) enhances the utility of software simulation to the design & development process. Availability of fast and powerful digital computers have rendered software simulation quite popular. Pure software simulations can come fairly close to real system, as an aid in crucial decision making.

4. What is Software Simulation? Software simulation pertains to solution of a purely mathematical model. Software simulation generates system response to inputs, without actual product realization. In involves writing a program that is executed on a computer, to create the ‘real’ situation. Software simulations can be both “Offline” as well as “real-time” simulation.

5. Software Simulation Tools Software simulation is carried out by programming a digital computer suitably. Programming is usually carried out in a higher level language, either general purpose or special purpose. Extensive graphic support is needed to set up a software simulation. Operating System also plays an important role in setting up a software simulation.

6. Software Simulation Languages General purpose simulation languages are usually not designed for specific needs of simulation. FORTRAN, C, C++ etc. are examples of such general purpose languages which can be used for setting up a software simulation. These are designed for many different applications and programming effort, to create a specific simulation, can be quite large. However, these are highly portable across different computer hardware, Operating System & Compiler, resulting in cost-effective simulations.

7. Software Simulation Languages Special purpose simulation languages are designed keeping in mind, specific needs of simulation. These contain a library of pre-defined macros (or “tools”) which minimize overall programming effort. CSMP is a popular language for continuous system simulation. For discrete system models, GPSS, SIMLIB, ALGOL, SIMSCRIPT II, SIMULA, etc. are used. Non-portability is usually the main drawback for these special purpose language, making them costly.

8. Software Simulation Languages Another class of languages, called symbolic language, also find use in setting up simulations. These provide a library of mathematical functions which can be put together to create a simulation. MATLAB is one such symbolic language that has acquired significant popularity as a simulation language, mainly because of programming simplicity. Provision of a variety of tool boxes in MATLAB has made it applicable to a large set of Engg. problems.

9. Software Simulation in CSMP CSMP provides for following macros.

10. Example of CSMP Code • Suspension System - (Step Response) TITLE SUSPENSION SYSTEM PARAM D = (5.56,16.9,39.5,56.5) X2DOT = (1.0/M)*(K*F – K*X – D*XDOT) XDOT = INTGRL(0.0,X2DOT) X = INTGRL(0.0,XDOT) CONST M = 2.0, F = 1.0, K = 400.0 TIMER DELT=0.005, FINTIM=1.5, PRDEL=0.05, OUTDEL=0.05 PRINT X, XDOT, X2DOT PRTPLT X LABEL DISPLACE. VS. TIME END STOP M X K D F

11. Software Simulation in SIMULINK SIMULINK provides following functional groups.

12. Example of SIMULINK Model • Suspension System - (Step Response) M X K D F

13. Simulation in FORTRAN or C • Suspension System - (Step Response) Main Program Data Structures Data Communication Strategy Integration Subroutine Plotting Subroutine M X K D F

14. Flight Simulation Flight simulation pertains to solution and visualization of controlled aircraft motion. There are many levels at which flight simulation is performed, depending on the need. At the lowest end, we have “Design Simulation”, which is a purely mathematical exercise. It contains highly idealized sub-system models. Next, is the Engineering Simulator, in which more accurate and detailed models of many sub-systems are available. However, no hardware is included.

15. Flight Simulation “Iron Bird” simulation is the next level of flight simulation wherein a majority of sub-system hardware, excepting aircraft, are integrated with software models. “Pilot-in-Loop” simulation caters for man-machine interface development and is usually carried out at number of stages. In-Flight simulation is a technique used to check out new sub-system designs (especially Control Laws) on an existing proven aircraft. Ground based Real Time Simulation, on a motion platform, is closest to “Flight Simulation” .

16. Summary of Software Simulation Software simulation is a design tool that needs to be configured based on specific needs. Computer, Operating System and Languages play an important role in software based simulations. Simulator is the system that is capable of performing simulations as per the need. Next part of lecture deals with simulator related issues.