Simulation

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.

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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.

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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.

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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.

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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.

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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.

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Software Simulation in CSMP
CSMP provides for following macros.
Y INTGRL(IC,x), Y(0) IC Y LIMIT(P1,P2,x) YSTEP(P) Y EXP(x) Y ABS(x) Y ALOG(x) Y SIN(x) Y COS(x) Y SQRT(x) Y AMAX1(x1, x2, , xn) Y AMIN1(x1, x2, , xn)
INCON Initial Conditions CONST Constant PARAM Parameter TIMER Time Interval PRINT Printing Variables PRTPLT Plotting Data TITLE Output Heading LABEL Intermediate Headings END End of Program ENDJOB Task Completion
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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)(KF KX
DXDOT) XDOT INTGRL(0.0,X2DOT) X
INTGRL(0.0,XDOT) CONST M 2.0, F 1.0, K
400.0 TIMER DELT0.005, FINTIM1.5,
PRDEL0.05, OUTDEL0.05 PRINT X, XDOT,
X2DOT PRTPLT X LABEL DISPLACE. VS. TIME END STOP
M
X
K
D
F
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Software Simulation in SIMULINK
SIMULINK provides following functional groups.
Discrete Unit Delay, Integrator, 0 Order Hold, 1st Order Hold, DTF, DSS, Dfilter, Dzero-Pole Sources Constant, Signal Generator, Step, Sine, Chirp, Clock, File, Random No.
Linear Gain, Sum, Integrator, TFunction, State-Space, Zero-Pole, Derivative, Dot Product Tool Boxes Communication, DSP, Control, Fuzzy, System ID, NNET, StateFlow, NCD
Connections In, Out, Mux, Demux, From, Goto, Data Store/Read, Memory, Enable, Trigger, Ground, Terminator, IC, Subsystem, Selector, Width Nonlinear Abs, Math, Trig., Floor, MinMax, Product, Logic, Relation, Sign, Rate Limit, Saturation, Function, . Etc.
Sinks Scope, X-Y Graph, Display, File, Stop
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Example of SIMULINK Model

• Suspension System - (Step Response)

M
X
K
D
F
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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.

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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 .

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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.