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.
Related
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
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 :)
I have written a matlab program for a simulink model and taking control through it programmatically, but I am facing one problem while using set_param('testmodel11', 'SimulationCommand', 'start');.
It gives all the values at once, that is gives the entire scope and workplace values all at the same time, but I don't want this. I would like to run the program and execute at that point, seeing only rest of the values should be zero. How can I stop the simulation at that point and fetch plots and values from that point only, the rest should be zero. And ideally have this same behavior for the next break points too?
There is a way to pause the simulation at certain breakpoints (simulation points), plot the output or do whatever is desired of it, and then continue the simulation until the next breakpoint.
However, at any breakpoint, you will get output data from all the time samples till the breakpoint is reached. To isolate data from a certain timestamp, you can calculate its index based on the sample time and extract it from the workspace (output data is stored as an array)
Here is the link to my answer which will be helpful, pls go through it:
https://stackoverflow.com/a/38348315/6580313
Now, in the m-file which you will run when the simulation is paused, you can change the value of the constant block which specifies the next simulation time at which simulation needs to be paused. In the m-file, you can also write a code snippet to access the output data.
Once the simulation continues, it will be paused at the new simulation time specified in the constant block.
Let me know in case you have any queries.
It sounds like you want to use the Simulink Debugger. Check out the documentation for more details on how to use it. The main command-line interface to it is sldebug.
Is it possible to use the previous value of the time varying variable
for eg:
Suppose I have pipe whose inlet temperature is 298K with a specified uniform mass flow(m_flow), now suppose i am heating the pipe using a heater of 100 watts.
The outlet temperature will be attain a higher temperature of suppose 302K, now if i have to use this outlet temperature as my inlet temperature (in the sense i am recircuilating the water), how would i be doing it?
is it possible to update the value of the inlet temperature based on the outlet temperature at the previous timestep? so that for the next iteration the inlet temperature will be the same as the oulet temperature in the previous iteration (in other words the fluid would be recirculating).
Thanks
You cannot access the value in the previous time step. The closest you can get in Modelica is using delay(exp,T) to get the value T units of time ago.
The timestep does not enter into it at all. A model that uses information about timestep is just wrong. Nature doesn't know or care about integration time steps, the model should reflect that.
It seems to me what you want to capture is transport delay. Transport delay is the delay introduced by the time it takes for molecules, electrons, etc. through the system. So presumably what you wish to model is the time it takes the inlet fluid to reach the exit. Again, this has nothing to do with the integration timestep but rather the velocity of the fluid and the distance it must travel. Once you know how long that takes (by either a priori knowledge of the system of by looking at the simulation results themselves), you can follow Marco's suggestion of using the delay operator.
In order to setup a proper model for the system you described I suggest you to look at the example :
Modelica.Thermal.FluidHeatFlow.Examples.IndirectCooling
of the modelica standard library ver. 3.2. Instead of one pipe you can put an ambient or control volume component to better suit you needs. Moreover using continous and differentiable equations (the delay function is not) you will benefit from some of the advantages of the Modelica code, e.g. you will be able to reuse your models in a much wider range of cases, solve inverse problems, solve initial value problems, ...
I hope this helps,
Marco
I am trying to control a simulink from a M-file.
What I want to do in the M-file is give the simulink model some input, run the simulink model, change one input value at 0.6 seconds, continue running the simulink model with the new input.
I already know that by using set_param, I can start, pause and continue the simulink, but the problem is I don't know how to pause the simulink model at a certain time(0.6s), is it possible to get the current time from simulink model and read it in the M-file?
Another way I already know is using sim to run simulink model from 0 to 0.6s, and use SimState to save the information at 0.6s, then load these information to resume the simulation. I am trying to change the input before the simulation resumed, but it seems that the model will load the input values from the information it saved, it won't take the new input value.
I stuck in this problem for a very long time, could someone help me with this please?
Thank you very much.
You can get the current time of a running simulation with:
get_param('simulink_model_name', 'SimulationTime');
So for instance by checking this value from your M-file during simulation by using
timer(...)
you can detect when the simulation is at 0.6 seconds.
I used a combination of simulink and m-script to achieve a similar goal.
In your model, add one 'assert' block. Double click it, and uncheck 'Stop Simulation when assertion fails'. In the 'Simulation Callback when assertion fails' field, add three commands:
set_param(bdroot,'SimulationCommand','pause');
run('myscript.m'); %insert the script name
set_param(bdroot,'SimulationCommand','continue');
Now connect the inport of this block to a 'not equal to' relational operator. Connect the first inport of the relational operator to a clock (pls set the decimation for analog clock or the sample time [usually -1 for inherited] for the digital clock).
The second inport is connected to constant block with a value of 0.6
On simulating the model, the simulation will pause at 0.6 sec, execute the m-file to change the input parameter (considering that it's tunable) and then continue with the simulation.
The assertion block is called when its input signal becomes 0. At 0.6 sec, the output of the relational operator will be 0.
Let me know if it worked.
This is not currently possible from an M-file. If you want to dynamically change the input at a given time externally, it will require an S-Function. Even this solution is difficult and wrought with flakey-ness since the Mathworks does not want to support this functionality in that it defeats one of the features of another toolbox they sell. In time, I believe they will grant this privledge, but it does not exist today. Also, why not use a dynamic input block to change the input value, like a map, signal builder, etc. ?