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Good luck p 0.5[ms] Pulse width https://www.comsol.com/blogs/which-study-type-should-i-use-for-my-electrothermal-analysis/ Good luck There are not only the heaviside functions, you can also make piecewise sinus steps which are also deriveable a few times can you please guide I . Walter, Hello Clare, Piecewise function: t(s)time I0(A)current t 0-0.002 I0sin(2pift) 0.002-0.1 0 The periodic function has a period of 0.1 seconds, and I want to calculate 15 seconds.The software I use is Comsol Multiphysics5.4. Apologies for asking the same problem over and over. [QUOTE] Best. Was it enough? The pulse will be a repeating rectangle function -- the voltage will be turned on and off repeatedly to create fatigue stress in the trace. As you can see the lattice temperature is not cooling down to room temperature. I am trying to use similar kind of pulse wave with on time as 0.5 ms and off time as 0.495 ( frequency is 20Hz) total period is : 0.05 Regards, If you have some of them, temperature should not get stuck, but drop slowly. How can I implement a staircase-like load that has continuous 2nd derivatives and is smoothed as you recommend? The settings for the applied heat flux boundary condition use the Discrete States variable. . Next, we can use two Explicit Events that can change the ONOFF variable. f 40[Hz] Repitition rate My time range is: Now that weve introduced the concepts, we will take a look at implementing these Explicit Events. You can find the example model here: I wanted to simulate pulse train and added analytic function, two explicit events and multiply initial temperature in focal spot on analytic fucntion. Ce*(d/dt)*Te= d/dz(k*(d/dz)*Te)- G(Te-Tl)+S(z,t) You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version Many thanks for your blog, its very usefull for me. or I have already posted in other thread. My specific question is how can I use the Events Interface to switch on or off the electromagnetic heating in Multiphysics coupling? Regards, With respect to alpha: It appears that there are some misunderstanding here, and it is not particularly germane to this discussion about the usage of Events. I was wondering did you figure out how to cool the lattice in between pulses? Note that while COMSOL employees may participate in the discussion forum, . I would appreciate if kindly help me. Best Regards, How should I implement my function together with the mod-function? Modeling Mechanical Stress in the Silicon Fabrication Process using Comsol-Multiphysics. The initial phase forms the final part of the argument in the following function. Smoothing a pulse made with Analytic function Posted 20 janv. . Although there are many different approaches in which this could be solved, the most appropriate way of modeling this situation is described in this article: http://www.comsol.com/blogs/modeling-a-periodic-heat-load -- The Explicit Event settings. Can I apply the step function as a Heaviside function shown in the figure? The tutorial forms part of a video series . Thanks for your previous help IVAR. Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. step1(t[1/s]) Above all the function working good after selecting "Strick" time stepping. Surely he mistook the node "Thermal Insulation 2" and he intended to cool the piece with, for instance, a typical "Convective Heat Flux" with some positive value for h. Obviously his piece had no opportunity to cool, simply the heat couldn't get out! A comparison of unpulsed (left) and pulsed (right) heat loads. 36 Replies, Please login with a confirmed email address before reporting spam. I found where am I wrong, I didn't select "strick" time stepping in time dependent solver. For example, suppose I have some high-frequency function within my model. You may want to double-check your implementation, as this method does work for any pulse duration. could you please tell me what is wrong in it The starting frequency of the sweep is and the frequency at time is . I am currently trying to model the two temperature model on multiple femtosecond pulses. Is it possible to use a supergaussian with similar parameters for the laser pulse? I hope this helps. I like all your posts so far and they are extremely helpful. If I input the Young's modulus of the channel to about 1 [GPa], the. I enjoy reading your blog. Such "flat initial" conditions can mislead the solver laser pulsing can be simulated in comsol using wave functions such as triangular, rectangular etc. i have to apply pulse train voltage with( 13kv and 1khz) on cable termination to get its effect on temp. One of the more common questions we are asked is about the modeling of periodic, or pulsed, heat loads. I'm not sure why, but I cannot make an analytoical function an1, calling rect1(), because you have (at least in v4.1) also the "make periodic" for an analytical function If one does not also carefully consider these variables, there is a good chance that the errors you describe in the beginning are driven mostly by a poor mesh density. mod((flc1hs(t[1/s]-1e-9,1e-9)-flc1hs(t[1/s]-9e-9,1e-9)),0.01)*f[1/Hz]) Note that while COMSOL employees may participate in the discussion forum, COMSOL software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team. You can fix this by pressing 'F12' on your keyboard, Selecting 'Document Mode' and choosing 'standards' (or the latest version In the second way, I specify it using a piecewise function func Start End Function 0 50 6000 50 75 4000 and then use func(t]1/d]) in the mass flux text field. rect1(mod(t[1/s],20E-3)) For that I created a rectangle function under Global. I will be very grateful to you if you can please kindly help me and provide me some guidance regarding this problem. Modeling Tools & Definitions, Parameters, Variables, & Functions We can avoid having to tighten the tolerances by using Explicit Events, which are a way of letting the solver know that it should evaluate the solution at a specified point in time. mod((flc2hs(t-1e-9,1e-9)-flc2hs(t-9e-9,1e-9)),0.01) Is it possible to set the time inbetween to zero to get a real square pulse train? Thanks for your reply. I'm trying to implement this condition by appling following equation. when I used the sin (t) as I(t) i got some results. My problem is : Even if I get the pulse train of frequecy 20Hz and pulse width 0.5 ms, which I can plot on analytic function, but my output remains ON only for the first pulse and rest is OFF. With a periodic heat load, the temperature rise is more gradual and the temperature variations at any point in time are smaller. are you in 3.5 or 4 ?, because in 4 use rather the step or other pulse functions, instead of the "flc1hs", the latter are already included into the v4 "step" functions (expand all tabs to access the rise time). Nice meeting you! See this Wikipedia link for a good explanation: Sigma is the standard deviation which is a measure of the dispersion or spread of the curve. Nagi Elabbasi But the different value of the two parameters presents various photogram, just illustrated as follow: The structure is a free-clamped cantilever, where the impulse force is applied at the free end. How do I feed COMSOL with the correct information in order to avoid a kind of aliasing, i. e. COMSOL sees the function correctly? See this Wikipedia link for a good explanation: http://en.wikipedia.org/wiki/Standard_deviation, Hi then you need to search a bit more in the help, the definition of the gaussian is in there but not on the first page about gaussian that appear, not sure why. https://www.comsol.com/model/laser-heating-of-a-silicon-wafer-13835. after 3 hours. Note: when I write t[1/ms], this means that the resulting value pushed to the function is 1000*t with T in seconds, therefore the modulo 20 as this is now modulo 20 msec However if I run the solver using the initial values = Solver 1, after running the simulation once, the pulse looks correct! In the case of frequency domain models, you simply need to have a mesh fine enough to resolve the shortest wavelength in each material domain. Veryst Engineering, Hello, I tried to use the suggestion given on January 12, 2011 (reply) and also tried to implement different suggestion on the Comsol Forum , but I havenot achieved desired result. To start a new discussion with a link back to this one, click here. Currently, I am trying to manually couple the electromagnetic losses to bioheat heat module using Heat Source domain. The first of these events will trigger initially at two seconds and set the ONOFF state variable to zero (turning off the heat load). You should NOT use fully rectangular pulses, because the steps does not allow to define any gradients or derivatives at the step, and the solver needs the first derivative to find its way in an efficient way. www.comsol.com/community/forums/general/thread/31879, www.comsol.com/model/laser-heag-a-self-guided-tutorial-12317, www.comsol.com/paper/download/63243/poulain_paper.pdf, www.comsol.com/blogs/modeling-laser-material-interactions-in-comsol-multiphysics, www.comsol.com/blogs/modeling-laser-material-interactions-with-the-beer-lambert-law, www.comsol.com/blogs/tracking-material-damage-with-the-previous-solution-operator, www.comsol.com/blogs/modeling-a-periodic-heat-load, www.comsol.com/blogs/implementing-simple-temperature-controller-component-coupling, Design an App to Efficiently Model the Flash Method Procedure, RF Signal Transformation Between the Time and Frequency Domains, Sampling from Phase Space Distributions in 3D Charged Particle Beams, Reverse proxy setup for Model Manager server. I'm defining rectangle function in comsol-v4.2, Hello Walter, Hitesh, Hi Comments? The name of this variable is ONOFF, and it takes on an initial value of 1, as shown in the screenshot below. then you should note that the rect() function start with this smooth step such that we are midway at t=0. Hello Melvin, However when I solve the boundary stays at the same temperature. I'm using "Electrodeposition" module right now. Ivar, Hi, bu I have some confusion that is the time dependet solver setting, the range you set range(0,0.001,0.01 ) ,range (0.01,0.01,20) ,how do setting in comsol ,can you give me any suggestions? but the problem when i plot the output electric potential on the electrode vs time, I found the output one pulse only not a train of pulses. My study is Time dependent. But even then, I am unsure if you would be able to have high enough sampling to capture that jump discontinuity. rect1() with Lower limit = 0.05*1E-3, Upper limit =0.55*1E-3, size of transition =0.1*1E-3, and then call it with a Jesus. How i can chose the system configuration (processor, ram). I am new to comsol and I want to generate a single pulse of 0.7 v of 20us . Thanks again, Hence my off- time is (to)= 0.05-0.0005s=0.0495 s I wrote the expression as : flc2hs(mod(t,0.5)-1E-3,1E-3)-flc2hs(mod(t,0.5)-20E-3,1E-3) The information provided may be out of date. Ivar, Hi, Thanks for the prompt reply!!!! thanks a lot for another great post. thanks Your Discussion has gone 30 days without a reply. In order to run simulation in time of 100fs, do i need the work station. Good luck Sigma is the standard deviation which is a measure of the dispersion or spread of the curve. Your guidance is highly appeciated. See, for example, the modeling and meshing notes in this article: https://www.comsol.com/blogs/modeling-of-materials-in-wave-electromagnetics-problems/, Thanks a lot for good helping post. In the Heat Source domain, I am multiplying the electromagnetic losses with an Analytic pulse to switch them on or off. Could you please guide me where am I going wrong? Thank you for your quick answer-making ! If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help. Discussion Closed This discussion was created more than 6 months ago and has been closed. Hitesh, Dear ivar: Ivar, Hi Ivar Thank you Walter! I used analytic function to define a train of pulses Good luck Best regards. 4 Replies, Please login with a confirmed email address before reporting spam. One thing though: I do not read anything hereabove about the the relation between mesh density, that links to the material heat diffusivity alpha equal to k/rho/Cp and the time steps used. Should it be at the start of middle or end of the voltage step? function x=mychirp (t,f0,t1,f1,phase . Posted Apr 26, 2013, 4:47 a.m. EDT That is, a heat load that turns on and off repeatedly at known times. The examples just for average current and variable electrolyte concentration. I am also working on laser processing. Modeling such a situation accurately and efficiently in COMSOL Multiphysics is quite easy to do with the Events interface. Hello Walter, thank you very much. Would you have any ideas why this is occurring? Ivar, Hi, Normalized Pulse [a.u.] First, you will need to open the Settings window for Time-Dependent Solver. I followed the tutorials and learned how to create a pulse, but i can't figure out a way to make pulse train. You need to dig into the COMSOL help and search for Gaussian pulse to find the full formula with the normalisation used, then define your Gaussian function and include it into an analytical one such that you get the desired amplitude or integral value to fit your desired height or area / energy / power -- Good luck Ivar Samy Abdallah (avg_pd)*(mod(t-p,0.05)*f)*(flc2hs(t-0.0005,0)-flc2hs(t-0.0005,0.0005) 13 Replies, Please login with a confirmed email address before reporting spam. Thanks a lot for your help, -- With respect to how you do the mesh refinement: You can perform either manual refinement or automatic adaptive mesh refinement. The reason i want to do this, is because i want to observe the behavior of the pulse under various evolving . We do recommend that you start a new discussion thread for this question. We can also observe that the spacing of the points shows the varying time steps used by the solver. In this case, I have disabled the Multiphysics coupling feature (electromagnetic heating) in COMSOL. the accepted variable is : If you want a train of pulses, you can use sin function with sign function, like Hi Heat Transfer & Phase Change I have no idea how to do this. I find your study is very excellent. Posted Sep 4, 2013, 5:42 a.m. EDT The function is then: listed if standards is not an option). Hi everyone, I would like to simulate a simple structure under the action of an impulsive force. You can define a function of your own under 'Global Definitions'. please suggest system requirement to solve my problem. you are trying to pass to the function called Volt the argument "sec", but "sec" is not defined. For the general topic of laser heating as you're describing here, please also see: For the general topic of laser heating as you're describing here, please also see: We have looked at using the Events interface for modeling a periodic heat load over time and introduced why it provides a good combination of accuracy and low computational requirements. https://www.comsol.com/support/knowledgebase/1245/. Thank you kindly for your time, We can of course mitigate this by using tighter tolerances, but a better option exists. http://www.comsol.com/blogs/modeling-a-periodic-heat-load/ rect1(mod(t[1/s],0.1)*0.1) However, I would like to switch off and on the frequency domain electromagnetic losses in transient thermal simulations to get results for pulsed heating. mod(a,b) https://www.comsol.com/model/setting-up-periodic-heat-loads-for-simulation-46791 How can i coupled these two equations in PDE ? -- or Screenshot of the Discrete States within the Events interface. Good luck In the interests of keeping these conversations more focused, we will close this particular discussion thread. If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base. looks like this ;) this will act as a voltage to a structure and the structure will get heated up. Thank you very much for this helpful post. Online support center: https://www.comsol.com/support Hitesh, My variables are: Can i solve coupled PDEs of Two Temperature Model equation for ultrashort pulse laser heating ? [/QUOTE] hence if you wanf to use myFunc (myVar) as a force input in Newtons, you should write: 1 [N]*myfunc (myVar [1/myVar_Units]) or just. Note: This discussion is about an older version of the COMSOLMultiphysics software. But the problem is that the modulo operator fills in the time between the pulses with a linearly growing line from 0 to 1 and not completley with zero. I am attaching my model for reference. Nagi Elabbasi Discussion Closed This discussion was created more than 6 months ago and has been closed. Apologies for the same since I am a new user of COMSOL. However, I am not sure if it is the right way to do this. Gravity is applied to the nanosheets to check for displacement and stress. Finally, Id like to run the data up to 50000 s, currently Im running 1000 s with a step of 1 s. Increasing the length will increase the size of the results file which is already approaching 9 GB. what I did is defined a rectangle function with lower limit as 20 us and upper limit as 40 us and then i try to use 0.7*rect1(t1) as a input voltage . In comsol model. Hi, Trying to make a pulse train by combining the heaviside function with the modulo function, as described in a previous post. The inconsistent units issue is a warning that can be removed by properly setting the units. Is there any way to do this. I tried it with mod(t,T0) aswell, but by multiplying my function with mod the steps are no longer 0 to 1 in height (less than 1). How would I do this? Will get back to you as soon as I do the things which you mentioned in your reply. After solving this study, I can see that my output is not correct and only gives me single pulse. I'm currently struck with the problem to define a function for laser pulse train , which is not getting solved, may be it just a small silly mistake, but it holding back from my actual results. And as periodic pulse he uses the analytic function "an1" with expression "rect1(mod(t[1/s],0.1))", but he ALSO sets this function as periodic: one of both is enough, or else he sets as periodic or he uses "mod()". rect1(mod(t[1/ms],20)] you should get your pulse train. If you have only some input heat flux (energy over time), you need to define where and how thes heat flux is incident on your boundaries, use HT in conjonction to solid to mix both physics and have COMSOL define the temperature distribution from the heat equations http://www.comsol.com/blogs/tracking-material-damage-with-the-previous-solution-operator Your reply is highly appreciated. Then to avoid "orange" units warning, you should learn that COMSOL assumes unitless values for all functions so you should write: Hello Zain, when I used the sin (t) as I (t) i got some results. From the point of view of computational efficiency and accuracy for transient heat transfer problems when pulsing a thermal load on and off, I would recommend: As Ivar said, I think you can check out the gallery: www.comsol.com/model/laser-heag-a-self-guided-tutorial-12317 Hi That is, if t_s and t_e move very close to each other, the magnitude of the total heat load is too small for the specified tolerance. for my pulse train, Pulse width = 5e-4 sec, frequency = 10Hz, period = 0.1 sec How does this looks like in a frequency-domain study? I multiply this by the source term. Finally, it's rather simple, no ? Ivar Regards, These algorithms choose a time step based upon a user-specified tolerance. But My o/p is completely opposite to the desired (my on time is 0.0005s but in the graph its showing 0.0495sec) and hence I can assume that my inpult pulse is not correct. The techniques we will introduce are applicable to many classes of time-dependent simulations in which you have changes in loads that occur at known times. I am waiting for reply. If I do implement the smoothed staircase, should I continue to use the explicit event? https://www.comsol.com/support/knowledgebase/1245 Comsol is investigating deformation due to gravity. Hitesh, Dear Ivar: Cordially, it says orange error I wish to pulse the laser spot and so I have defined a pulse train expression using the heaviside function: (flc2hs(mod(t,0.01)-1,1)-flc2hs(mod(t,0.01)-3,1) I then multiply this step function by a large heat flux on the appropriate boundary. but i cannot use when Hitesh, Hi You can define a function of your own under 'Global Definitions'. Since I only care about the data just before and just after a step, how can I make the solver solve for those points only? Art. rect1() with Lower limit = 5e-4, Upper limit =5.5e-4, size of transition =0.1e-4, pic attached Nt=I (t)/ (q*Va)+g0* (N-N0)*S/ (1+eps*S)+N/tan well I would say, define an anlyticl function T(t) the temperature profile versus time, test it out (plot it) then define your geoemtry and physics and apply the temperature function to the material. Hi avg_pd_new is only single pulse wave. My question was about At a tighter relative tolerance of 0.01 the solution is reasonably well resolved. In this video, you learn how to model Heat Transfer effects caused by a single laser pulse in COMSOL Multiphysics. Can you please help me to resolve my problem. This wave function should be multiplied by heat input/ heat flux equation. To minimize the temperature variation over the wafer during the heating process, we want to turn the laser off periodically, while the heat source is in the center of the wafer. -- I wonder if someone has encountered this problem before. Heat flux = avg_pd_new2*((t, Hi Hitesh, i used the rect function along with mod function to get an analytic function an1= rect1(mod(t[1/s],1e-9)) but when i plot this for time t = 0 to 1 sec i get zero magnitude , after solving i also found out that heat flux is zero throughout the time . I want to solve the following couple ordinary equation by comsol, which I (t) is pulse current.
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