Consider that I have built an electrical circuit or any other system at Simulink and to do simulations, Simulink should work in the sense that it builds a state space model of the system, right? If that is the case, is it possible to set an initial condition of this model? And more, is it possible to know what are the state variables of the model built by Simulink?
The Simulink.BlockDiagram.getinitialState method can be used to interrogate the model, and return an appropriate structure giving the current initial value of the states.
The values in the structure can then be changed and the (new) values used with the model configuration parameters to start at a different initial state. See the doc for a usage example.
Related
I am using Dymola 2020x to develop a thermal model and export the FMU to Simulink to simulate controllers.
For implementing advanced controllers, I require an iteratively run framework, which helps to initialize the states after every iteration to the values at end of every previous simulation. This can be done within Dymola through “import initial” and “Continue” commands in the Simulation tab of Dymola.
However, since I am designing the controller in MATLAB, I require a similar feature for that platform. The only way I know right now is to manually change the initial conditions in the FMU block, but since I have a lot of states, it would not be feasible to do it manually. Any scripting ideas are welcome as well.
All in all, I require a framework/method to be able to initialize states of my model through MATLAB/Simulink to the values I get after running a single iteration.
Some help would be appreciated.
Expose the initial conditions of the variables as parameters, and set them from MATLA Scripts with e.g.
FMIKit.setStartValue(gcb, 'step', 'true')
see https://github.com/CATIA-Systems/FMIKit-Simulink/blob/master/docs/fmu_import.md
Initialization could be very cumbersome and easily lead to divergence. A simple strategy is to run the simulation when building a part of the whole system and use the simulation results to modify guess values.
Here is what I got in the PPT from Francesco Casella and the book from Daniel Bouskela.
I found that I could use an option in Dymola as follows, but instead of using the initialization result, I wanna use the result when reaching a steady state. So I'd like to use a python script to extract the result from the .mat result file, then modify the iteration variables automatically. But the key problem is that I don't know when I add more components in my model, the iteration variable set of existing components would change, I don't know what kind of effect would this causes.
Anyone got opinion on this issue, welcome to answer this question.
So my question is where should I find the python
You can use the end values (= steady state) of the simulation result in order to create a new initialization (Dymola Manual 1, section 2.5.12) . If the component names are the same in the sub system model and the total model, you can run the script created in the subsystem model on the larger system model as well. But you have to check if your models have initial equations that hinder an initialization from the outside (see section 4.2 in https://2012.international.conference.modelica.org/proceedings/html/pdf/ecp12076927_KruegerMehlhaseSchmitz.pdf)
It should also be possible to initialize it steady state. Instead of providing initial values for a state x and fixing it, you can provide initial equations for the derivatives such as der(x) = 0;
With that setup activate Save Initial Results and you should be good to go.
I am building model in Dymola. I have defined the mass of this model as a parameter, because it would be transfered into other moduls and called in them. But the mass should be changing during the simulation in different time intervals. For example, during the first 100 seconds the mass should remain 500kg, and during 100 to 200 sec, a passenger is going to get in, so that a new mass should be calculated including the mass of the passenger. But it has been showed, that "The problem is structurally singular", because to the parameter values have been twice assigned. Could someone give some tips to solve this problem? Thanks a lot.
If you define the mass of your component as an input rather than a parameter then you can change it during simulation by assigning e.g. the output from a TimeTable to it. For example
model Component
input Modelica.SIunits.Mass mass "Passenger dependent mass";
equation
...
end Component;
model systemModel
TimeTable timeTable;
Component component(mass=timeTable.y);
OtherComponent otherComponent(mass=component.mass);
equation
...
end systemModel;
Note that the other components using the mass must also have their internal mass 'parameters' defined as input to allow higher variability than parameters.
Best regards
Rene Just Nielsen
Modelica parameters are defined by the fact, that they don't change over time. Therefore you would need to stop the simulation, change the parameter and restart the simulation (see another question). Given you description I would rather not use this possibility, as it seems your variable is designed to change over time.
A better alternative seems to be defining the mass as a variable. If this is done, you can:
Transfer this variable from one model to the others using interfaces. This could be a bit tedious depending on the amount of classes using the variable.
Use inner/outer (basically global variables) is a feasible concept for this use-case. This concept is used in the MultiBody libraries world model.
With both solutions you will have to modify the original mass model, as m would then have to be a variable instead of a mass.
I'am trying to speedup my simulink project and want to use the Accelerator-Simulation mode.
The aim of my project is to control a cyclic process and is structured as followes:
matlab-script, where all parameters and a feedforward control with
parameter estimation is implemented. Also it starts simulating the
simulink model for each iteration.
simulink model, where the dynamic system and the feedforward control (basically a lookup-table) together with a feedback control
is implemented. Parameters of all blocks are set by workspace variables/structs generated by the script.
The feedforward control variable is calculated and parameter are estimated from the simulated data after every simulation pass. Then the model is simulated again. The model is not changing during the iterations, but still it is compiling at every cycle. From the first: Is this solution appropriate for using the Accelerator mode?
I tried to follow theses proposed steps to determine, why it is built at every iteration: mathworks
If i run it with the Accelerator-Mode (referring to the documentation of this function, it now compiles for simulation), I still cannot reproduce why it is compiled at every iteration.
csdet1.ContentsChecksum.Value ~= csdet2.ContentsChecksum.Value
is true, but the proposed code does not find any details.
csdet1.InterfaceChecksum.Value ~= csdet2.InterfaceChecksum.Value
is also true, the proposed code outputs that
UserDefinedTypesChecksum
is different. What does that mean and how can I resolve this?
Sidefact: When I run Simulink.BlockDiagram.getChecksum() with the Model opened in Simulink and Normal-Mode chosen, I get this error:
Continuous update specified for this chart chartname This is not
supported for RTW."
But this chart is a Matlab-Function block, not a stateflow chart?!
I'm new to Dymola and I have to implement a chemical reactor in Dymola.
I modeled the behaviour of the reactor in 3 different models, because the reactor behaves different depending on a variable x. So that model a is valid for x<=0.1, model 2 is valid for 0.75>x<0.1 and model 3 is valid for x>0.75. Is there any way to run only one of the three models in each simulation step? I have looked into the "if" statement to put all 3 model equations in one model, but that didn't work. Is there anyone out there who can help me? Any hint would be great! Thank you!
Modelica does not handle variable structure problems. What this means is that the set of variables cannot change during the simulation.
Most people who are trying to solve such systems typically find a way to keep all variables present but somehow "deactivate" different sets by switching equations (which can, to some extent, change during the simulation).
If you give a bit more information about the types of models you need to switch between, I could try to give you some hints about how to "deactivate" them from one phase to another.