Modeling Techniques and Simulation | Behavior Modeling l Alison
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Module 1: Modeling Techniques and Simulation

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Behavior Modeling

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Today we will discuss about the behavior modeling. Behavior modeling one of themodeling method we need to do. Because we have a data modeling, process modeling,and the third one is behavior modeling.(Refer Slide Time: 01:07)
In behavior modeling, we use the method of behavior modeling for modeling thedynamics of the system. So, we want to see how the engineering system works or what isthe dynamics of the engineering system, how the control actions are taking place, how
the particular incidences are triggered, or how the a particular incident stops or particularfunction stops and the next one function starts.So, all these kinds of dynamics of the system can be a modelled using behavior modelingtechniques. Here the control, activation and termination of system functions are basicallymodelled using the behavior model. So, not only the data and the process we want tomodel the control, the activation, and termination of system functions. And for thispurpose, we have various methods. And one method is known as a function flow blockdiagram; that is FFBD, and we have other things like a behavior diagrams and petrinets.So, we will see some of these methods, and then try to understand how this methods canbe used for modeling the behavior of systems, or how the dynamics of the system can bemodelled using behavior diagrams. So, we will take the FFBD first. That is the functionflow block diagram. And then see how to use this function flow block diagram, and thenmodel the behavior.(Refer Slide Time: 02:30)
So, the FFBD’s they provide a hierarchical decomposition of the system function, andshow a control structure that detects the order in which the function can be executed ateach level of the decomposition.So, that is the importance of FFBD. We can actually show the control structure, that theyactually dictate the order in which the functions are executed. And the various level of
decomposition. So, there are different ways of executing the function. They are basicallyclassified into 4 categories. One is the series execution. The other one is the concurrentexecution. And then the selection, and multiple exit. So, these are the ways in which thefunctions can be executed in a system.So, we will see how do you actually model the this kind of behaviors that is a seriesbehavior or concurrent behavior or exit and the selection and exit procedure. So, how doyou actually model this using FFBD, we will take a few examples and then show themethod by which we can do this. So, in series structure, what will having is as the namesuggest the functions will actually execute in a serial way.(Refer Slide Time: 03:38)
So, as we can see here there maybe different functions. So, we will start with thereference function; which may be an external function or a function of a sub system. So,from the that reference we will have the one function executed, and then it will go to thenext function, that is executed and then it will go to the external system or the othersubsystem. So, this is the a serial execution as the name suggests the functions will beexecuted in a serial way.For example, you can see that if you take the system design activities. Then it is aperform system design activity. So, once we complete such system design activities, thenonly we go for the integration activity. So, perform integration. Again, it appears to bevery simple case, because we are telling something which is very obvious, but this is the
way how we actually show the series execution of functions in the functional flow blockdiagram.So, we will complete this function, and then go to the next function; that is the serialexecution of the functions. And in the concurrents or sometimes it is known as parallelalso, in concurrent execution will be having the same reference function, and then wewill be having 2 functions executing the same time 2 or more function executing and it isshown by a block and block. And in this and block we will be connecting all the otherfunctions, and here will be having the concurrent functions listed. And again, once it iscompleted, the next function can start only after the completion of all these functions.All these processes or the functions. And then it will go to the reference function or theexternal function. This is the concurrent or parallel execution. So, here again you canhave examples like a system level design, suppose if you take the same systemengineering, energy system level design. Then you have the subsystem level design,subsystem level and then component level. So, we know that if you want to execute allthis functions we need to have a this all need to be done concurrently or parallelly.So, after that end of this design process only we can go for the testing or integration ofthe components. So, we need to do all this in a concurrent way or in a parallel way, andonce we complete all this design then only go to the next function. That is the concurrentbehavior of the functions. So, this need to be done parallelly or concurrently, and once allthese are completed then only it will go out. So, this a and shows that all these 3 inputsshould be there to for this to go to the next function. That is here the and represents allthese needs should be there this and represents all these will go happen at the same time.So, when this input is coming are the 3 output will go concurrently, and here all these 3input should be there for the next function to execute. There is the concurrent behavior ofthe system. The next one is the selection structure and multiple exit.
(Refer Slide Time: 07:36)
In selection structure and multiple exit, it actually will be having series functions, it maybe having concurrent functions. And it may be having some selection, that you canactually select one of the functions, and you can have multiple exit or a iterations also.So, here again we will take a case of system design.So, if I take perform system design has a function, now I will be having many iterationsof the system design or the system because there may be some kind of repetitions orrepresent this iterations by a block IT, and then there may be some loops through whichit will be going and that is represented by the loop LP, I will explained how these areactually coming into the behavior, and once we complete this system design we need tohave the testing.So, that is a testing function. So, inspection and testing. And after the inspection testing,there are options like some of the components may pass the inspection, some of thecomponents may fail the inspection. So, we need to select this 2 options, and one of theoptions need to be chosen from the multiple options available. So, what we do we havethis 2 options here. So, one will go for the selected one that is passed one and the otherone will go to the which are actually rejected or which is not passing the inspection. So,the cleared system will just go directly to the same main loop and again it will start fromhere to the next function.
So, will see what actually happened to this one. This is the accepted. So, we are selectingaccepted one, and rejected or with some deviation from the required specifications. Andhere we can actually do a fixing of the problem. So, you fix the problem, and again sendit for here. So, once you fix it, there are 2 options one is that it is acceptable. One is itcannot be accepted. So, the small fixing can be done here rejected components can befixed here itself. And once it is fixed we can actually has a take it accepted or rejected.Accept or reject one. And if it is rejected we need to actually have a redesign. So, this isredesign. So, the rejected one was to go redesign, and then it will come here. So now, weknow that there may be this rejected component may go through this or through thisroutes. And many of this routes is acceptable. So, this is an or block. So, we can actuallyanyone of this component comes here, it has to go to the next level. So, it need not bethough there are parallel activities. So, need not wait for the both to happen. So, any oneof this happens it can go to the next level. And then so, this is also will come here.So now we have components coming from both from the inspection the accepted willcome directly and the rejected one may go for redesign or may get accepted and it willcome here, and it will go to the next level. So, here it is an or loop. So, any one of thiswill come here. So, we can see from the inspection there are 2 options. So, one of thisoption go directly. Another option will go through different processes and finally, comehere to the this block. And then here will be having a looping, if there is a deficiencyfixed, they it has to go to this loop again for the inspection. So, some of the componentswill come through this. So, there was a deficiency it was fixed, and it is coming overhere. So, we need to make sure that if it is coming through this loop, then it has to goback again and then do that inspection and testing and see whether it is actually passingthis test or not.If it is passing this test again it will come through this, and once this is completed it willgo to the next level where integration to next subsystem. This is integration thisintegration to next subsystem, and then it will be having that is one subsystem, then itwill be having a iteration this is for the next subsystem design. So, this for nextsubsystem and then it will go out from here to the next function. So, this is a selectionand multiple exit structure. So, this is the loop for if deficiency is fixed. So, if thedeficiency is fixed, then a looping will be there. And this is for each subsystem thisprocess will do
So, for each subsystem we need to complete the same procedure. That is why there is aniteration loop is an iteration and this is a looping because if something is fixed over here.There was a deficiency in one of the components or subsystems, and that will go througha another process where the fixing will be done, and then again it has to go for thetesting. So, that is why it is come back. And then do inspection and testing and if it isaccepted it will go out. And then come to the integration. And then again, we will bedoing the same process for the other subsystems also.So, we will be having many subsystem and the when system design is complete will behaving many subsystems. So, for each subsystem will do the inspection and testing, andif it is accepted it will go out to this block it is not accepted it will go through this loop tofix the deficiency and if it is accepted it will go if it is not accepted it will go forredesign. And whenever there is coming from these loop these output is coming fromthese loop, then this will go for the inspection again and pass and once everything ispassed through this it will go to for the integration. And once the integration of thatsubsystem is completed then this loop will again repeat because the next subsystem willbe taken for inspection, and so on it will continue.So, we can see here we are actually using many blocks here, an iteration, looping andthen of course, the or and or also can be used. And in some cases, we may have to useand also. So, in this case there is no and block, but here we have a or block. So, one ofthese output will be coming out. If both the outputs are need a some situations, then wehave to use the and block as shown here in this block. So, we are used or block there, butsome cases we may have to use and block also.So, this is the selection structure and multiple exit. So, in FFBDs that is in the functionalflow block diagrams.
(Refer Slide Time: 15:38)
We have series execution, you have concurrent execution, and we have selectionstructure and multiplex. It also any of these methods or a combination of this can be usedfor representing the actual design of a system or actual behavior of a system. So, somesubsystem we may have to model the behavior of the subsystem using this method. So,we can actually use the series concurrent or selection and multiple exit or a combinationof these to represent the dynamics of the system.Let me take an example, and then show how it is actually done. I will take an example ofthe auto link system, what we discussed in the previous class. So, in the auto link system,we will see how the functions can be represented, or how the dynamics can berepresented using the FFBD.
(Refer Slide Time: 16:40)
So, will take a reference function or an external system or a previous subsystem, andthen see what are the concurrent activities to be carried out. So, there are manyconcurrent activities to be carried out in the auto link system. So, we will see that thereare parallel functions to be executed. So, this is the navigation activities, this is theitinery of the page passenger or the person who is using the system. And this is thevehicle condition function basically looking at the status of the vehicle customer support.So, these are the 4 functions need to be executed parallelly in order to provide a precedeservice to the passenger or the person who is using auto link system. If we need toprovide the required service like knowing the location or in an emergency providing thesupport, all this parallel function should be executed. So, what are these functions wewill write down those functions here. Basically, we will be looking at the latitude andlongitude calculation. Latitude longitudes, and then integrating the current position withthe map. So, integrate current position because we get the latitude and longitude once weget this can actually integrate the current position with the map. That will help thepassenger for the navigation or the driver for navigation. And that is the required fornavigation purpose, and then here we have to calculate the display route. Because basedon the input given by the user, he will be giving the itinery where he wants to go, andonce that information is obtained, the route has to be calculate using a database. And thenthat present latitude and longitude will be calculated and based on that map will begenerated to show where he is at present.
And then vehicle condition need to be assessed, because if the vehicle is in goodcondition or not these to be assessed to help the user. So, vehicle condition or vehiclestatus or vehicle health status. So, vehicle health status need to be assessed, and then thecustomer support for. So, need to identify the client, who is actually using it whether heis authorized to use the system or not. So, identify the client assess that sensor databasically whether all the sensors are working properly and whether GPS data is correct.So, this kind of information to be collected. So, as a sensor data, and then if neededcontact emergency. Contact emergency services, that is contact emergency and this allthese need to be executed concurrently in order to provide the service. So, that is theoutputs.So, here you can see in this case the auto link system a customer or a driver wants to getthe some assistant from the auto link system for his navigation purpose. Or hisemergency response whatever the situation is. So, in this case the auto link system shouldexecute all this function in a concurrent way, then only he will be able to the system willbe able to provide the necessary output. So, the functions need to be provided are thenavigation assistance the itinery especially to calculate the route, the condition of thevehicle whether vehicle is in good condition, and then the customer support in variousways like the client is an authorized person. And whether the all the data systems arefunctioning properly and whether the emergency service can be provided.This need to be in a serial way. So, all this functions are executed in a serial way, as youcan see here. Here also this has to be done in a serial way. So, a generate the latitude andlongitude data, and then integrate that with the current position with the map. So, thatwill help the user to navigate himself. And then this is to calculate the routes if the usergives the his itinery the route can be calculated, and this can actually be once the route iscalculated and this position is not that can actually given to the passenger or the user.So, that actually we need these 2 for the output. Similarly, we need to know the vehiclecondition and the other customer support services. So, all these are provided and once wehave all this information then the an output can be given to the customer to use thefacility. So, that is the way how we actually represents the behavior of the system usingFFBD. So, we are using the FFBD that is a functional flow block diagram to representsthe so, dynamic behavior that is an example for the auto link system. And how do we usethe function flow block diagram to represent the dynamics of auto link system.
This was an example for the function flow block diagram. And the next method is wehave the method called petri net. So, petri net is also a method used for modelling thedynamics of the system. That is, how the input output can be controlled, how theconcurrent activation as well as the status of different functions and how do we actuallystart a particular process, or what are the condition under which a process can be started.All this can be represented using petri nets.(Refer Slide Time: 23:26)
So, as we can see here the petri net was introduced by carl adam petri in 1962 which is adiagrammatic tool to model concurrency and synchronization in distributed system. So,we will show the concurrency of systems, but then in some cases we need concurrencyas well as synchronization. For example, if you take the traffic light on the roads, weneed to have some kind of a synchronization between the other lights; when you have ajunction will be having multiple traffic light. So, we need to have some kind of asynchronization between this traffic light. So, how do we actually represent that kind ofsynchronization and concurrency, or that can actually be done using petri nets. And thenused as a visual communication aid to model the system behaviour.So, as we know this a graphical tool. So, it actually helps us a visual aid to show thesynchronization. And of course, there are strong mathematical foundation for thesemethods. And it actually captures the precedence relations, and structural interactions ofpotentially concurrent and asynchronous events. So, that actually captures the
precedence relations. So, what is the precedence which function should precede orsucceed the a particular process. So, that actually if this petri net captures thatprecedence relationship. And structural interactions of potentially concurrent andasynchronous events.So, there maybe asynchronous events. So, we will actually able to capture the structuralinteraction between these events using petri nets. We will see a how to develop the petrinets. So, petri net has got a few basic specifications.(Refer Slide Time: 25:02)
So, it actually consists of 3 types of components. Places transition and arcs. So, these arethe 3 components which actually forms the a petri net. So, in petri net we use the places.
(Refer Slide Time: 25:18)
So, the places are represented by circles, and then you have the transitions. Thetransitions are represented by rectangles. This is a place, transition, and then we have thearcs which actually represents the movement of the or the dynamics of the system.So, we can actually have the arcs which actually connecting the places and transitions.So, this actually is a place. So, it actually shows one stage, and this transition representsthe change of state. So, if there is a change in the state of a system, that actually can beactivated by the transition block. So, the translation block when you activate the placevalue will change, and that is actually shows that this has changed from this state to thisstate. Or this it has changed it is place value from once to the other one. So, thistransition actually represents the transition from 1 place to another place that is the placetransition, and the arc which actually represent these are the basic building blocks for thepetri net. And then they mentioned the places represent possible states of the system.So, this are the possible states. So, we can represent this as p 1 p 2 etcetera.
(Refer Slide Time: 26:41)
The possible states. So, they will be having we can have multiple transitions, andmultiple places. So, p 1 p 2 p 3. So, this will be T 1 transition 1 transition 2 like that. So,we can have many number of places and transition in a petri net. Then the transitions areevents or actions which cause the change of stage. So, as I told you. So, it is actuallychanging from this state to this state. So, the transitions are the which actually makes theplace value to change or the status to change from one to the other one.So, every arc connects a place with a transition or a transition with a place. So, that is thearc. So, we have the state transition and arc, place transition and arc, and place actuallyrepresent the states p 1 p 2 p 3, and transition represents the change from one state toother state. And the state of petri net is defined by the marking. In again this marking; so,the state of a petri net or a state of a particular position is represented by a the marking isa black circle a filled circle will be represented to show the status whether it is in activemode or not will be shown by this black circle or filled circle. And this is known astokens.So, the tokens represent the basically the status. So, the state will be represented by thistokens.
(Refer Slide Time: 28:09)
And the change of state that is a the state of a particular place is shown by the token. Andchange of state by is denoted by the transfer of tokens. So, when this state is changed tothis one is actually show the transfer of this token. So, we have a token here. So, when Iactivate this T 1.(Refer Slide Time: 28:27)
And this is activated this token will be shifted to this one. So now, this is in there activemodes. So, that is the change of position or the change of transfer of token.
So, every transition basically causes the change of the token or a transfer of the token.So, this change of state is denoted by moment of token from place to place and is causedby the firing of a transition. So, the firing of the transition, causes the token to movefrom this place to this place. So, that actually represents the change of state of a thatparticular function or the process. In the firing represents an occurrence of the event oran action taken. The firing is subject to the input conditions denoted by token. So, that isanother important point the firing is subjected to the initial conditions.Now, if this is connected this transition suppose you have a transition like this T 1. So,we can actually have multiple places connected to this. So, if it is given like this. So, thefiring of this token is subjected to the status of this position. So, if there is a token in boththese places, then only this transition can take place. So, the firing is subjected to thiscondition. If this firing has to happen then both this should be having the token.If there is only one token, then this transition cannot take place; that means, these 2condition need to be satisfied for this transition to take place. So, in this case when I dothe firing of this transition, both the tokens will be going to here and this will show astatus over here.(Refer Slide Time: 30:05)
So, this will be removed, and this will be there will be a token over here for when this is
fired.
If there is only one token then this cannot be fired there will not be any transition therewill not be any change in the status of the that particular place. This is one situation, andanother one is if you have like this, and if you have this kind of a situation. So, you haveonly one token here. So, these are simply petri net. So, we do not have any place valuesas such at present.(Refer Slide Time: 30:40)
So, you have a place connected to p 1 connected to this T 1 and p 2 and p 3 and if there isa token here available.So, if this is the situation, when we can fire this transition. Because now it is allcondition satisfied that there is a token over here. So, we can actually fire this transition,and when you fire this transition both will be activated. So, both the places will beactivated. So, this the numbers does not really matter how many places are connected.The transition simply shows that from this status it has moved to this status any numberof places can be connected to this transition or this will be concurrently activated. So,that is the condition for transition, and then after transition what is happening.
(Refer Slide Time: 31:32)
So, basically the petri net if they has got this place transition and arcs and using placetransition an arc we can actually show many dynamic situations. So, as shown here. So,if this the condition for transition is basically having set has to satisfy the inputconditions. So, if there is a token then only it can be fired otherwise it cannot be fired;that means, if this condition is not satisfied there is no possibility for changing this statusto another status. So, that is the condition for transfer of tokens.(Refer Slide Time: 32:03)
So, this is what I already explain. A transition is firable or enabled when there aresufficient tokens in it is input places. So, there should be sufficient tokens in it is inputplaces to make a firing. And after firing token will be transferred from the input places tothe output places denoting the new state. So, once you do the firing the tokens will betransferred from the input to the output it is actually represents the change of state.(Refer Slide Time: 32:30)
We will be take a an example, and show you how to actually represent a scenario usingthe petri nets.So, here we take again a simple example in electronic fund transfer point of sale. So, weknow that we normally go to an ATM machine or an electronic point of sale we have toinsert the card and give the password, and then only it will accept the card and thentransaction will take place. So, how do we actually show this using a petri net. It is a verysimple example for use of petri net petri net can be used for very more complexsituations, but you know to understand the use of petri net, we will take this example.So, look at this diagram. So, this is the initial status. So, we have this initial tokenavailable, and the card is inserted the next is basically you need to give the password tothe system. So, here actually you can see there are 4 digit. So, you can have 4 digitsinserted. This is the digit 1, then digit 2 this is a second digit the third digit and forthdigit. And once all the 4 digits then you can have a an transition, and then approve thetransaction and then get the approved transaction out.
So, here you can see 4 digits need to be inserted and (Refer Time: 33:44) you can see thatis a transaction. So, one digit is considered as a transition. So, you can actually give firstdigit, once there is an input this initial token is available you can provide the first digit asa transition. And once you do this then this status will come that is there is a token overhere, then you can insert the next digit. And once you have the next digit, then you haveyour next transition. This is a third digit. Then the place will come here, and then keep ongoing to this loop, but in between suppose you give one digit then there is somethingcalled OK button.So, this OK button can actually be activated, once you have a token over here. So, thisOK can be activated if you have a token at d 1, but then it will get rejected because youhave just entered only one digit. So, it will do not work similarly you can see the other

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