Difference between revisions of "OpenModelica/C2/Control-flow-and-Event-handling/English-timed"

|| Welcome to the spoken tutorial on '''Control flow and Event handling'''.

|| In this tutorial, we are going to learn:How to use '''if-else''' statement , How to handle '''time''' and '''state''' events,  How to use '''when''' statement.

|| To record this tutorial, I am using : '''OpenModelica 1.9.2''' and '''Ubuntu Operating''' system version 14.04.

||branching in any programming language , '''class''' definition in '''Modelica'''

||Now, let us add a '''constraint''' to it.  

||Ball is at rest until '''t = 0.5''' seconds.  Free fall under '''gravity''' starts at time '''t = 0.5''' seconds.

||Please download and save all the files in '''Code Files''' link.  

|| Type '''OMEdit''' in the '''Search bar''' and click on '''OMEdit''' icon. Let me go back.

|| '''Comments''' such as this, may be written on the first line of a '''model''' or '''class'''.

|| Now, let us see how to insert the '''constraint''' explained in slides.

|| Note that there is an '''if-else block''' in '''equation''' section as shown.

||Let us try to understand each statement of this '''if-else block'''.  

|| '''if statement''' places a '''constraint''' on '''time''' variable.

|| '''else branch''' contains '''equations''' which are executed when time is less than '''0.5''' seconds.

||To delete the result, right click on '''timeEventExample''' in Variables browser and select '''Delete Result'''.

|| Now, let me delete the second '''equation''' in '''else branch'''.  

||Go to the '''Messages browser''' and scroll up to see the error message.

||Therefore, the number of '''equations''' in '''if''' and '''else branches''' should each be equal to the number of variables.

|| Note that '''der(h) = v''' is an '''equation''' which is common to both '''if''' and '''else branches'''.  

||Hence, the '''if-else block''' can be replaced by two '''statements'''.

||Delete the '''if-else block''' first.

|| Copy the two equations.

||Do a right-click and select '''Paste'''

|| This is an '''if-else statement''' which indicates that if '''time >= 0.5''' '''dv/dt = g''' otherwise '''dv/dt = 0'''.

|| Now let me go back to the slides.

||Please note that the number of '''equations''' in '''if branch''' should be equal to the  number of equations in '''else branch'''.  

||And both of them should be equal to the number of variables in the '''class''' or '''model'''.

||'''Events''' may be categorized into time events and state events.

||'''state event''' occurs when a system variable cross a certain value.

||A ball under free fall, faces a '''state event''' on touching the ground.

|| '''e''' is coefficient of restitution for inelastic collision of ball with Earth.

||It is a parameter and its value remains constant at 0.8 throughout the simulation run.

|| '''radius''' represents the radius of ball in '''m'''.

|| '''when statement''' is used to signal an event.  

|| To simulate this model Click on '''Simulation Setup''' button in the toolbar.

||Under '''General''' tab, change '''Stop Time''' field to 30 units and  Click on '''Simulate'''.

||Note that '''h''' drops below zero, which is unacceptable.

|| '''when statement''' is used to signal an event.

|| Watch the video available at following link.'''http://spoken-tutorial.org/ http://spoken-tutorial.org] /What\_is\_a\_Spoken\_Tutorial'''

||It summarises the '''Spoken Tutorial''' project

|| We conduct workshops using spoken tutorials Give certificates Please contact us.

||We give honorarium and certificates to those who do this. For more details please visit the following website.

|| Under '''Lab Migration Project''' we help migrate commercial simulator labs to OpenModelica.