I wrote a C S function which has a variable number of states depending on one parameter, which is passed to it (I'm using computational fluid dynamics and the parameter is the number of cells). I want to output a bus object from my S function that contains a temperature profile. Problem is I don't know the length of the output when I create the bus object in Simulink (in Bus Editor). Is there a way to dynamically set the size of the bus object from the C S function?
I think you can set the DimensionsMode property to "variable" instead of "fixed" (the default). See Simulink.BusElement and Variable-Size Signal Basics in the documentation for more details. Not sure how to code this in the S-function though.
Related
I am attempting to define the parameter of a model (block) as a variable. For example:
Real WallThickness = 0.5;
Real WallConductance = 10*WallThickness;
Modelica.Thermal.HeatTransfer.Components.ThermalConductor TopPanelConductor(G=WallConductance);
I would like to define "G" so that it remains constant throughout the simulation but the coefficient is updated prior to the simulation based on the other variable "WallThickness". When defining the ThermalConductor parameter "G" as a variable in the model, which is being calculated elsewhere, I get the error message:
The variability of the definition equation:
TopPanelConductor.G = WallConductance;
is higher than the declared variability of the variables.
I would like to define the parameters of a model as a variable. This allows me to create parametric definitions as the geometry of the all changes. Is there a way I can make this definition work?
You mean the geometry changes during simulation? If so, you'll have to rewrite the ThermalConductor model to work with a variable G, because a variable cannot be assigned to a parameter. A variable may vary during the course of simulation. A parameter is fixed at the start of simulation, but can be changed from run to run without recompiling the model, which allows for quicker iteration/design work.
Note that you can also calculate a parameter from other parameters that you define, e.g. to calculate a heat transfer coefficient from a given wall thickness (which you vary from simulation run to simulation run).
An alternative to re-writing the component models is to make the parameter study/variation outside the simulation model. There are at least three approaches:
Export your system model as an FMU (Co-simulation). Import it in Python w. PyFmi and write for loops that vary the parameter value for each iteration. See for example http://www.jmodelica.org/assimulo_home/pyfmi_1.0/pyfmi.examples.html. This is not as complicated as it might sound.
Make the parameter variation loop in a Modelica Script (mos file). I don't have much experience with this though.
If you are varying geometrical parameters in order to find an optimum of some kind you can use the Optimization Library which is shipped with Dymola (as of version 2017 FD01).
Using one of the above suggestions you can reuse all the components from MSL out of the box.
Best regards,
Rene Just Nielsen
There is a heirachery for varaibales/parameters that restrict their use. As you are now aware, parameters are not permitted to vary with within the simulations. Thus, you get the error stating that you are trying to define a parameter with a variable value or input variable.
If you need that functionality I would recommend duplicating the ThermalConductor and change the variable type:
parameter Modelica.SIunits.ThermalConductance G
"Constant thermal conductance of material";
to
input Modelica.SIunits.ThermalConductance G
"Constant thermal conductance of material" annotation (Dialog(group=”Input Variables”));
That all there is to it. Note the additional annotation on the input variable. By default inputs do not show up in the parameter GUI. The annotation will permit them to be seen just like parameters (be careful to clearly label it an input variable versus a parameter though!)
There is work underway that has completely redone the Thermal library but is not yet released and the most-straightforward approach would probably try what I have discussed.
I am loading my Simulink Model to a microprocessor. After that I want to change a value of a Block parameter.
In the picture below the data comes to Matlab Function block is coming from Serial Port. Now, appearently th incoming data is assigned to input u of Matlab Function block. In that Matlab Function block I want to write a code that changes , for example, coefficient of s in the Transfer Fcn block. Or it can change any other parameter you can give in code hypothetically.
If anybody can give me any solution that would be ver much appreaciated!. Thank you in advance.
Substitute a custom-made subsystem for the transfer function whose parameters have to change, and create the subsystem from basic blocks so that coefficients can be read from signal sources. You might be interested in this
http://blogs.mathworks.com/seth/2011/03/08/how-do-i-change-a-block-parameter-based-on-the-output-of-another-block/
Even if you don't want to change parameters at every time step, the restriction
"[...] calls to set_param also preclude the model from ever being compiled
into a real-time application."
seems relevant to your case.
Anyway, as far as I know the post linked above still applies in 2014.
Hope that helps.
I substituted my originial question, the problem is still the same, but the conditions are now different. To review the original question, have a look at the revisions.
I'm looking for a way to interactively select the signals I want to get displayed in my scope Block. The Bus Selector Block with the property Output as Bus does exactly that. I can select all desired signals conveniently without changing any block or signal dimensions.
But the scope block can obviously not handle properly signal names of buses. Therefore my scope legends are wrong:
If I don't set the Output as Bus property and Mux the signal together into the scope block it displays the right signal names. But this is no option as I'd need to adjust the Mux-dimension according to the signals selected.
Are there any workarounds?
(A Floating Scope is no option either)
The problem:
In my simulink model, I have a bus creator that will send all the signals to a block. The block purpose is to make a selector and a switch dynamically based on an index. Example : I have 3 objects, each with a position and a velocity signal, and I want to get the position of the 3 objects, so 3 signals (this means the bus selector will have 3 output and the multi switch will have 4 (one for the index)). The block is working correctly, with a recursive function script called in the callback, it checks the bus for all possible signals and count the number of objects, and modifies the bus selector and the switch accordingly. The problem is that this block is linked to a library, so I have to disable the link in order for the callback script to work.
The questions:
What should i change in order to avoid disabling the link?
Is there another way of making dynamic wiring and don't use a callback script?
I suggest a using vector concatenation block instead of bus creator plus a matlab function block to choose. Here is the model
and here is the code in matlab function:
In this way the block in the library does not need to change each time. Also if you have to keep your buses you can use a bus to vector block to convert them to vector.
The idea of using a MATLAB Function block to do the selecting is a good one, but I would try and stay with a Bus input to preserve the advantages of working with busses, rather than convert to vector and back. So instead of having your code as a callback to the bus selector block, my suggestion would be to implement it in a MATLAB Function block with a bus input and the signal input used to do the selection in the bus, and define the output still as a bus object.
Using this Simulink model file as a reference, I'm trying to figure out the two following errors:
alt text http://imagebin.ca/img/dSV8YO.png
alt text http://imagebin.ca/img/OXDf0v.png
I have no idea what has gone wrong with the data type consistency/conversion problems. Do you know what the error messages mean exactly in the context of a model? It would be great to get an interpretation of the problem to solve it. Thanks in advance.
Is the block 'Inner Loop/e^(-s)' driving the block 'Inner Loop/Sum'? It looks like the 'e^(-s)' block is trying to set the Sum block to be double, but the Sum block is already set to some other data type. I'm not sure why that's happening, but here's a snippet from the help for the Sum block documentation,
Inherit: Inherit via internal rule
Simulink chooses a combination of output scaling and data type that requires the smallest amount of memory consistent with accommodating the calculated output range and maintaining the output precision of the block and with the word size of the targeted hardware implementation specified for the model. If the Device type parameter on the Hardware Implementation configuration parameters pane is set to ASIC/FPGA, Simulink software chooses the output data type without regard to hardware constraints. Otherwise, Simulink software chooses the smallest available hardware data type capable of meeting the range and precision constraints. For example, if the block multiplies an input of type int8 by a gain of int16 and ASIC/FPGA is specified as the targeted hardware type, the output data type is sfix24. If Unspecified (assume 32-bit Generic), i.e., a generic 32-bit microprocessor, is specified as the target hardware, the output data type is int32. If none of the word lengths provided by the target microprocessor can accommodate the output range, Simulink software displays an error message in the Simulation Diagnostics Viewer.
You can try forcing the output data type to be double, if that's what you really want, or you can try putting a Data Type Conversion block in front of the Sum block. One other thing that can help is to try turning on Port Data Types from the Format menu. It should show you all the propagated data types when the error happens.