Assume that you have a Simulink simulation where a certain signal is first positive and after some time t in a given interval, it becomes negative. Your goal is to find the zero-crossing.
A first approach would be to plot the signal over the given interval, save it and calculate the zero-crossing.
When repeating this simulation numerous times for varying parameters, it would be beneficial to be able to stop the simulation after the signal has become negative. Then there is already enough information for the calculation of the zero-crossing in Matlab. How could you do that?
Yes, use the Stop Simulation block with the appropriate logical input to the block:
You can use an if / else block to control the flow in the Simulink model. In the if / else block, you can choose the condition if u > 0, continue as normal if it's true, and use the else-option to bypass the rest of the flow you would otherwise run. For instance jump directly to the scope.
Another ways:
You can use Hit Crossing Block in Simulink to find time at the moment of hitting zero.
Another way - use any Trigger or Resettable system. It detects the zero crossing too. For example: this question at SO.
Of course you can also use User Defined function to detect zero crossing by your hand and do whatever you want with the signal at the same time.
About making a lot of simulations and then stops:
you can use Check Upper Static Bound for automatically stops simulation at the moment when zero will be crossed in nth time. For example:
I set upper bound = 10 for this block and this stops at 10th crossing.
There are a lot of ways to save function values in this points or just array of times but this is an another question :)
Related
I have two Matlab function blocks that one is producing zero signal for the other. I want to store the exact time that signal changes to one in another parameter in order to use it elsewhere.
How can I do it?
This type of functinality is achieved using a Triggered Subsystem, as per the image below,
The output of the trigger block will take on value of the input (which in this case is the simulation time) every time the trigger signal rises. Look at the parameters of the Trigger block inside the subsystem for other options such as falling edge, or both edge, triggering.
I'm making a dynamical system model in Simulink. It is a drop test on 2 springs. I want that after first drop the object will stop, so that in the accelaration graph there will be only 1 maximum. Am asking for a detailed answer. Thanks in advance.
The system to model
Current acceleration Graph
Simulink model
I know the time of the first cycSimulink modelle, but I calculate it only in the end of the run. I understand that I can use Matlab function in Simulink, and maybe a Subsystem.
when_shock=(acc.Time(two_times(2))+acc.Time(two_times(1)))/2;
I need the accelatarion graph to have only one peak. Meaning only one drop accures, after which the object stops. The force where the arrow shoud be zero after force drop.
I make a structure using Comsol then I want to make this structure subjected to a temperature variation ( T(begain)=25C then a temperature ramp (100 C/min) till T=250C and it lasts for 30 min then another temperature ramp (-100 C/min) till T=25C ).How could I make these temperature sweep?
You can define a function (e.g foo) that follows exactly your desired temperature with time profile. Then in the place where you specify your temperature (whether it is a boundary condition or domain condition) you insert foo(t), t being COMSOL's exclusive variable name for time.
You can do that for other variables too, space for instance. The easiest way to define foo is through the 1D interpolation option. Unfortunately, I do not currently have a COMSOL license to check it but I think you can simply enter the time and temperature values in the 1D interpolation table, choose a name and the interpolant style and just use it in the later part of the program.
I'am simulating magnetic fields in time domain with moving coils. Time dependent solver is needed for the movement and for temperature ramps as well. I think that you can use something like this, T=T_start+rate_of_change*t. The t variable is available with the time dependent solver and you can simply write the equation I mentioned. However, I think that you need to use time dependent solver three times, one for ramp up second for the constant temperature and third for the ramp down. Set the times for time dependent solvers so that you can made the desired temperatures.
First t=0s->(225/100*60)135s
second t=135s->(135+30*60)1935s
and last one t=1935s->(1935+135)2070s
You might also need to use compile solutions steps as well to add these three solutions together. I can try to do this tomorrow and check it.
Hope that this helped a bit
I have a system with some embedded Matlab blocks where I'd like to perform some actions after a certain amount of time, in this case turn on lights and switches in an interface to which I send signals from Simulink.
The problem is that I thought I'd use "tic"-"toc" and "while" in a Matlab function block to perform these actions, say one parameter becoming 1 after 5 seconds, the following parameter becoming 1 after 12 seconds and so on, but I noticed that tic-toc apparently doesn't work in Simulink for embedded functions.
Is there any similar functions that could be used in Simulink for embedded functions or is there any other way to do this?
Edit: I've tried to get the clock's time as well, but it's a growing value. Is there any way to "lock" the time as a parameter when the block's function is executed?
You shouldn't be using absolute time in an embedded system, which is at least one of the reasons why tic-toc and clock from MATLAB don't work with Simulink Coder.
You should create your own counter, which you start and stop when you need to.
This is pretty easy to do using a Unit Delay and Summation block.
If you need to be able to enable and/or reset the counter then use the appropriate block from the Additional Discrete library.
I have a matlab function block (which is not relevant) whose input is his previous output (loop). For example, if in a sample period the output is X, his input in the next sample period will be X, and so on.
This image shows a simplification of my simulation. I initialize the input of my function for the first loop.
The problem is that matlab functions recieves an event based signal from de initialization block in the first sample period (zero-duration), which I must convert to a timed based signal (so I can apply the unit delay that avoids an inifite loop, and allows to generate the next input as explained before). So, when I do so, I lose the information contained in the event-based signal (due to the zero-duration values) and the loop does not work.
If there was a way to intialize the loop in the time-based domain (green part of the image) so, in the first sample time, it is not a zero-duration signal, it would avoid the problem.
Is there any way to do so? Or, a different approach for this problem?
Two approaches come to mind
The initial condition can be set in the Unit Delay block, so it's not clear from your simplified example why you need the specific Initialization block.
You could just use a persistent variable inside the MATLAB Function block to maintain the state from one execution of the block to the next (noting that since it is event driven the block may not get called at every time step, only at each event triggger).