Hi, when I solve a PDE, it takes a lot of time. I closed the programme with task manager of windows. When I reopen the file, the programme is "reinitializing GUI" . I wait for almost an hour and nothing changed. At this time I cann't do anything else in the software. How can I solve this problem?
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"Reinitializing GUI" for a long time
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Solve PDE on 1D domain?
Hy guys, I have a problem with solving a PDE based model defined by me, it is not a default template in COMSOL.
My problem is that the equation is solved for the time domain, but not for the geometry specified. ( Interval )
Does the solver automatically solve with respect to 'x axis' ( it represents the height of a reactor x=[0,20] m )?
The PDE I'm trying to solve is the following:
dT/dt=-VL*dT/dx-constant
where VL and constant are known.
Could you help me with this,
Thank you.
My problem is that the equation is solved for the time domain, but not for the geometry specified. ( Interval )
Does the solver automatically solve with respect to 'x axis' ( it represents the height of a reactor x=[0,20] m )?
The PDE I'm trying to solve is the following:
dT/dt=-VL*dT/dx-constant
where VL and constant are known.
Could you help me with this,
Thank you.
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Time dependent simulation
Hello Ivar,
I need a big favor from you.
Its a request since my model is giving weird results. I have worked on it but I need to get the physics right.
So I decided to try the time dependent study which should give the instantaneous current values which are then used in the stationary study, that is my thinking.
So I created current variables in the parameters section, ix and iy. These currents are dependent on time, t. So I thought the parameters will be able to access the variable t, but ????
I defined the current in a coil as -ix on one coil-side and +ix on the other coil-side, is this right in the multi-turn coil domain under MF.
The other difficulty I faced is defining relative permeability which will change depending on the H and B values for non-linear material, since mu_r = 1/mu_0 * B/H, where B and H are from the BH curve.
So how do you go about this issue. I was not able to define relative permeability as defined above.
I also Imported with both the 1st and 3rd quadrant, you can check a plot to see how it looks like and I hope its OK.
From the plots of the magnetic vector component, it can be seen that the flux is not penetrating the silicon steel sections ????
Regards and thanks in advance
NB: I attached an m-file by mistake but the model is as attached.
I also submitted the same to the technical support.
Wanjiku
I need a big favor from you.
Its a request since my model is giving weird results. I have worked on it but I need to get the physics right.
So I decided to try the time dependent study which should give the instantaneous current values which are then used in the stationary study, that is my thinking.
So I created current variables in the parameters section, ix and iy. These currents are dependent on time, t. So I thought the parameters will be able to access the variable t, but ????
I defined the current in a coil as -ix on one coil-side and +ix on the other coil-side, is this right in the multi-turn coil domain under MF.
The other difficulty I faced is defining relative permeability which will change depending on the H and B values for non-linear material, since mu_r = 1/mu_0 * B/H, where B and H are from the BH curve.
So how do you go about this issue. I was not able to define relative permeability as defined above.
I also Imported with both the 1st and 3rd quadrant, you can check a plot to see how it looks like and I hope its OK.
From the plots of the magnetic vector component, it can be seen that the flux is not penetrating the silicon steel sections ????
Regards and thanks in advance
NB: I attached an m-file by mistake but the model is as attached.
I also submitted the same to the technical support.
Wanjiku
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How to combine the Frequency Domain and Coil Current Calculation
Hello everyone,
i´m trying to simulate an numerical coil with alternating current. The coil is built with the "Multi-Turn Coil Domain". My coil type is numeric wich requires an additional "Coil Current Calculation" step before my "Frequency Domain" step in my study. I solved it for 50,500,5000 Hz and looked at the coil paramters. My coil excitation is set to 0.15A wich should be the coil current for all frequencies. The "Coil voltage" and "Coil resistance" should be different for each frequency which is not, if i do a global evaluation for those two parameters.
Anyone got an idea how i can solve my problem? I´m attaching my modelfile, if someone is willing to take a look at it.
Best wishes,
Andreas Schneider
i´m trying to simulate an numerical coil with alternating current. The coil is built with the "Multi-Turn Coil Domain". My coil type is numeric wich requires an additional "Coil Current Calculation" step before my "Frequency Domain" step in my study. I solved it for 50,500,5000 Hz and looked at the coil paramters. My coil excitation is set to 0.15A wich should be the coil current for all frequencies. The "Coil voltage" and "Coil resistance" should be different for each frequency which is not, if i do a global evaluation for those two parameters.
Anyone got an idea how i can solve my problem? I´m attaching my modelfile, if someone is willing to take a look at it.
Best wishes,
Andreas Schneider
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why are my solutions the same as initial values?
Hi. I build a 1D time-dependent model (transport of diluted species).
using conservative form.
convection transport mechanism
D=0;
u=-k/x^m; (k is a constant)
R=0;
no flux
iniitlal distribution: 1/(x^4*sqrt(2*pi)*log(sigma))*exp(-0.5*((log(x)-log(r_m))/(log(sigma)))^2)
k=4.92*10^(-14)/3600
m=3
sigma=1.2
r_m=0.034
But when I solve it, the solutions at all time are the same as initial values.
I also solve this problem with matlab, the solutions should be in the same shape but different values.
I don't know what had happened. The mph file is too big to be uploaded.
Would you please help me? Thanks very much.
using conservative form.
convection transport mechanism
D=0;
u=-k/x^m; (k is a constant)
R=0;
no flux
iniitlal distribution: 1/(x^4*sqrt(2*pi)*log(sigma))*exp(-0.5*((log(x)-log(r_m))/(log(sigma)))^2)
k=4.92*10^(-14)/3600
m=3
sigma=1.2
r_m=0.034
But when I solve it, the solutions at all time are the same as initial values.
I also solve this problem with matlab, the solutions should be in the same shape but different values.
I don't know what had happened. The mph file is too big to be uploaded.
Would you please help me? Thanks very much.
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how to define Heat source?
Hi,
I use COMSOL to simulate a microheater to heat the polymer waveguide on Silicon substrate.
The model is 2D. Silicon substrate serve as the heat sink at 25 degrees. When I set the microheater to 300 degrees, I can get a right a temperature distribution.
But now I want to set the microheater as the Heat source,and use the general source as 1000 W/m3. I set Bottom boundary at 25 degrees, and other boundaries as the Thermal Insulation. I can't get a right temperature distribution.
Can any experts on COMSOL tell me the reasons? Very urgent! Than you!
The version is Comsol 4.2.
I use COMSOL to simulate a microheater to heat the polymer waveguide on Silicon substrate.
The model is 2D. Silicon substrate serve as the heat sink at 25 degrees. When I set the microheater to 300 degrees, I can get a right a temperature distribution.
But now I want to set the microheater as the Heat source,and use the general source as 1000 W/m3. I set Bottom boundary at 25 degrees, and other boundaries as the Thermal Insulation. I can't get a right temperature distribution.
Can any experts on COMSOL tell me the reasons? Very urgent! Than you!
The version is Comsol 4.2.
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Difficulties with #985 Peristaltic Pump Model
Hi All
(bear with me; I'm new)
Working my way through the peristaltic pump tutorial and all has been a-okay thus far but once I get to the plot of the total volume (bottom of pg. 14) when I try to evaluate the surface integration for the volume it says no solution exists. I am sure that all the boundary conditions are properly defined. Hoping someone has had a similar issue..
Any ideas?
Thanks,
Alexis
(bear with me; I'm new)
Working my way through the peristaltic pump tutorial and all has been a-okay thus far but once I get to the plot of the total volume (bottom of pg. 14) when I try to evaluate the surface integration for the volume it says no solution exists. I am sure that all the boundary conditions are properly defined. Hoping someone has had a similar issue..
Any ideas?
Thanks,
Alexis
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Backward Problem
Dear Comsol Users,
I like to scale a given heatflux distribution to reach a maximum temperature in a domain.
If I know the location where I expect this max. temperature, I can do this via a global equation: f(T-Tmax) to obtain a scaling variable qscale for the heat flux distribution and an integration operator: Tmax=intop(T) specified at the point where I want to reach the temperature Tmax.
But what if I don't know the location of Tmax in the domain?
If I exchange the integration operator intop with a maximum operator maxop on the domain I get:
*******
Failed to find a solution.
Singular matrix.
There are 1 void equations (empty rows in matrix) for the variable mod1.qscale
at coordinates: (0,0), ...
Returned solution is not converged.
******
Can this issue be solved without the optimization module ?
Thank you very much for any help.
--
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Flanell
I like to scale a given heatflux distribution to reach a maximum temperature in a domain.
If I know the location where I expect this max. temperature, I can do this via a global equation: f(T-Tmax) to obtain a scaling variable qscale for the heat flux distribution and an integration operator: Tmax=intop(T) specified at the point where I want to reach the temperature Tmax.
But what if I don't know the location of Tmax in the domain?
If I exchange the integration operator intop with a maximum operator maxop on the domain I get:
*******
Failed to find a solution.
Singular matrix.
There are 1 void equations (empty rows in matrix) for the variable mod1.qscale
at coordinates: (0,0), ...
Returned solution is not converged.
******
Can this issue be solved without the optimization module ?
Thank you very much for any help.
--
______
Flanell
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Optical coupling between laser wave-guides and optical fiber
Hello Everyone,
First of all, I am a beginner to use this software and getting to know this from the tutorials posted. I am trying to model 'Optical coupling between laser wave-guides and optical fiber'. I am curious to know whether there are any pre-defined templates for optical fiber and laser wave-guides. If no, can any one help me how to build those ones in the COMSOL software. It would be of great help if anyone give a thumbs-up.
Thanks in advance.
Regards,
Saivivek Bheemanathini
First of all, I am a beginner to use this software and getting to know this from the tutorials posted. I am trying to model 'Optical coupling between laser wave-guides and optical fiber'. I am curious to know whether there are any pre-defined templates for optical fiber and laser wave-guides. If no, can any one help me how to build those ones in the COMSOL software. It would be of great help if anyone give a thumbs-up.
Thanks in advance.
Regards,
Saivivek Bheemanathini
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minimum time value under condition
Hi
I have a problem on my simulation
I have a time dependent simulation and I want to get the minimum time value when a phenomena occur ( The voltage V raise a value above a certain threshlod)
I want to get the time when the phenomena occur and I want it to be settle because I will use it in the simulation
I use a max and min function like this
max((V>threshlod)*min(t))
the minimum give the value when the phenomena occur and the max avoid that the final is equal to 0
But the max and min are function definied in domain and NOT GLOBALLY that means that max and min are looked in the model regarding the value computed before in the simulation
At the end I juste want the variable give me 0 before V<threshold and the minimal time value after V>threshold and this value has to stay constant
Thanks a lot
Guillaume
I have a problem on my simulation
I have a time dependent simulation and I want to get the minimum time value when a phenomena occur ( The voltage V raise a value above a certain threshlod)
I want to get the time when the phenomena occur and I want it to be settle because I will use it in the simulation
I use a max and min function like this
max((V>threshlod)*min(t))
the minimum give the value when the phenomena occur and the max avoid that the final is equal to 0
But the max and min are function definied in domain and NOT GLOBALLY that means that max and min are looked in the model regarding the value computed before in the simulation
At the end I juste want the variable give me 0 before V<threshold and the minimal time value after V>threshold and this value has to stay constant
Thanks a lot
Guillaume
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magnetic field gradient in 3D return zero!
Hi everybody
If anybody knows that why the gradient of magnetic field in 3D models is always zero? I checked the different methods. for example I wrote d(Bx,x) or different component of B and H. Even d(d(Ax,x),x) is always zero! I am using the quadratic discretization. It is OK when I simulating in 2D or 2D axisymmetric, However the similar geometry in 3D give the zero for gradient of magnetic field.
could somebody help me?
If anybody knows that why the gradient of magnetic field in 3D models is always zero? I checked the different methods. for example I wrote d(Bx,x) or different component of B and H. Even d(d(Ax,x),x) is always zero! I am using the quadratic discretization. It is OK when I simulating in 2D or 2D axisymmetric, However the similar geometry in 3D give the zero for gradient of magnetic field.
could somebody help me?
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How to make sure AC/DC and Structural models are coupled? SIMULATION ATTACHED
I'm doing my thesis on the magneto-mechanical coupled analysis. The attached file is only a simple example showing what I want to do about magneto-mechanical coupling. I chose to use the AC/DC model, ALE, Structural mechanics model. In the model, there are a permanent magnet and a steel rod. One end of the rod is fixed, while the other is free. The magnet will draw the rod and cause deflection of the steel rod. Once the steel rod deflects, it goes nearly to the magnet, which cause a increment of magnetic force. The magnetic force will then make the rod's deflection greater.
My concern are as follows:
1. I use 'segregated' in the stationary solver. When I run the simulation, an 'error vs. iteration' plot always come out, which includes three lines. What's the meaning of those lines? Are they converging lines?
2. Though I've arranged the ALE, AC/DC, structural mechanics as the 1st, 2nd and 3rd segregated group to be solved. I'm not sure if they have been coupled. Does COMSOL do automatically coupling?
3. If my model in the attached file is a successful coupled model, how can I make sure the results have converged? How can I show the magnetic force is increasing vs. iterations? Do I need to store the results?
THANKS VERY MUCH.:)
My concern are as follows:
1. I use 'segregated' in the stationary solver. When I run the simulation, an 'error vs. iteration' plot always come out, which includes three lines. What's the meaning of those lines? Are they converging lines?
2. Though I've arranged the ALE, AC/DC, structural mechanics as the 1st, 2nd and 3rd segregated group to be solved. I'm not sure if they have been coupled. Does COMSOL do automatically coupling?
3. If my model in the attached file is a successful coupled model, how can I make sure the results have converged? How can I show the magnetic force is increasing vs. iterations? Do I need to store the results?
THANKS VERY MUCH.:)
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Use eigenfrequency found in study 1 as a parameter in study 2
Hello all,
My simulation is divided into 2 studies:
Study 1: Eigenfrequency (model: solid1)
Study 2: Frequency domain (model: solid2)
Have you an idea how to use one of the eigenfrequencies found in Study 1 (say, the 2nd eigenfrequency in the list), and use it as a parameter in Study 2?
Best regards,
DTN
My simulation is divided into 2 studies:
Study 1: Eigenfrequency (model: solid1)
Study 2: Frequency domain (model: solid2)
Have you an idea how to use one of the eigenfrequencies found in Study 1 (say, the 2nd eigenfrequency in the list), and use it as a parameter in Study 2?
Best regards,
DTN
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Initial Concentration in Reacting Flow in Porous Media
Hello,
I need to know if I can add a starting concentration for a variable in the Reacting Flow in Porous Media, that will then change via the Reactions Node. The Initial Values Node does not seem to do that.. does anyone know if there is another way to give a domain an initial value?
I am trying to simulate 2 reactions occurring in a packed bed- the consumption of a chemical (ac), and the growth of the biomass that is consuming the chemical (ac).
There are 2 reactions:
R_ac = -k_rate*X*(ac/(ac+K_ac))
R_X = Y*-rfds.R_ac-(m*X)
where k_rate, K_ac, Y, and m are constants. The consumption of the chemical, ac, is dependent on the concentration of biomass, and the growth of the biomass depends on the rate of ac consumption. Is there a way to implement this successfully?
Also in case of negative concentration I introduced a variable B = max(eps^2,X) , which I used in my reactions in place of X.
The R_ac, R_X, and X go to essentially zero (e-38). I added an initial concentration for the X but it did not seem to matter. I would like to somehow add a starting concentration of biomass to the domain of the model, but cannot see a way to do that since the initial conditions node does not seem to do that.
One thing that does give me reasonable numbers is to set one of the boundaries with a constant concentration using the concentration node within reacting flow in porous media, but then that boundary will not change with the rest of the model. I would prefer NOT to take this route.
Do you have any other suggestions of advice on how to do this?
Thank you,
Kelley Rabjohns
I need to know if I can add a starting concentration for a variable in the Reacting Flow in Porous Media, that will then change via the Reactions Node. The Initial Values Node does not seem to do that.. does anyone know if there is another way to give a domain an initial value?
I am trying to simulate 2 reactions occurring in a packed bed- the consumption of a chemical (ac), and the growth of the biomass that is consuming the chemical (ac).
There are 2 reactions:
R_ac = -k_rate*X*(ac/(ac+K_ac))
R_X = Y*-rfds.R_ac-(m*X)
where k_rate, K_ac, Y, and m are constants. The consumption of the chemical, ac, is dependent on the concentration of biomass, and the growth of the biomass depends on the rate of ac consumption. Is there a way to implement this successfully?
Also in case of negative concentration I introduced a variable B = max(eps^2,X) , which I used in my reactions in place of X.
The R_ac, R_X, and X go to essentially zero (e-38). I added an initial concentration for the X but it did not seem to matter. I would like to somehow add a starting concentration of biomass to the domain of the model, but cannot see a way to do that since the initial conditions node does not seem to do that.
One thing that does give me reasonable numbers is to set one of the boundaries with a constant concentration using the concentration node within reacting flow in porous media, but then that boundary will not change with the rest of the model. I would prefer NOT to take this route.
Do you have any other suggestions of advice on how to do this?
Thank you,
Kelley Rabjohns
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COMSOL in parallel mode: a speedup of 20% using 4 cores?
Hello everyone,
I have performed the following experiment. Using the command -np #cores, I have forced COMSOL Multiphysics to use 1, 2, 4 or 8 of the available cores on my computer. I also used the default configuration of COMSOL Multiphysics, i.e, without the command -np. I performed the experiment using two models comprising two drift-diffusion equations coupled with the Poisson equation - one is quasi-linear, the other is highly non-linear. The solver used was Pardiso. The results are in the attached file.
I have obtained a speed-up of about 20% when I activated 4 cores, as compared with the duration of calculations using only 1 core. Do you believe that this improvement of 20% is the typical speedup that can be obtained? Does anyone have some more data or experience on this issue?
Thank you for your help.
Kind regards,
Pedro
I have performed the following experiment. Using the command -np #cores, I have forced COMSOL Multiphysics to use 1, 2, 4 or 8 of the available cores on my computer. I also used the default configuration of COMSOL Multiphysics, i.e, without the command -np. I performed the experiment using two models comprising two drift-diffusion equations coupled with the Poisson equation - one is quasi-linear, the other is highly non-linear. The solver used was Pardiso. The results are in the attached file.
I have obtained a speed-up of about 20% when I activated 4 cores, as compared with the duration of calculations using only 1 core. Do you believe that this improvement of 20% is the typical speedup that can be obtained? Does anyone have some more data or experience on this issue?
Thank you for your help.
Kind regards,
Pedro
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negative concentrations with high reaction terms in biokinetic models
Hi,
I am using a biokinetic model based on the ASM (activated sludge models) to simulate water contaminant removal in a gravel filter. This kind of models consider the degradation of the influent solute components by several species of microorganisms. As a result of the degradation, this microorganisms also grow.
For the flow simulation I am using Darcy's Law. The contaminant removal is modeled using the solute transport module with a reaction term, in which monod-like expressions are deffined. These reaction expressions are also multiplied by the concentration of the different species of microorganisms that consume each solute component (the higher the concentration of microorganisms the more they consume).
The growth of bacteria is modeled using PDE general form expressions.
This works just fine for short periods of time (e.g. 1 day), but when bacteria start to grow considerably, the reaction terms become very big and negative (consumption), and thus the concentrations of the solutes become also negative. I've tackled this by deffinig variables s=max(eps^2,S), were S is the concentration of the solute. So when S becomes negative, in the next time step it is seen as a 0 instead of a negative value. If I don't do this, a part from getting negative solute concentrations, the growth of bacteria also gets corrupted (as it depends on S), and therefore this error impacts the whole model. I also tried to add expressions such as *(S>0) in the reaction term of S, but I have not been successful either.
I have checked the solutions suggested in this link, www.comsol.com/support/knowledgebase/952/ but it did not help much.
Could anyone tell me how to make the reaction rate 0 when the concentration of the substrate becomes zero? I do not understand where exactly should I introduce the term max(eps^2,Q).
Hope I made myself clear.
Thank you in advance
I am using a biokinetic model based on the ASM (activated sludge models) to simulate water contaminant removal in a gravel filter. This kind of models consider the degradation of the influent solute components by several species of microorganisms. As a result of the degradation, this microorganisms also grow.
For the flow simulation I am using Darcy's Law. The contaminant removal is modeled using the solute transport module with a reaction term, in which monod-like expressions are deffined. These reaction expressions are also multiplied by the concentration of the different species of microorganisms that consume each solute component (the higher the concentration of microorganisms the more they consume).
The growth of bacteria is modeled using PDE general form expressions.
This works just fine for short periods of time (e.g. 1 day), but when bacteria start to grow considerably, the reaction terms become very big and negative (consumption), and thus the concentrations of the solutes become also negative. I've tackled this by deffinig variables s=max(eps^2,S), were S is the concentration of the solute. So when S becomes negative, in the next time step it is seen as a 0 instead of a negative value. If I don't do this, a part from getting negative solute concentrations, the growth of bacteria also gets corrupted (as it depends on S), and therefore this error impacts the whole model. I also tried to add expressions such as *(S>0) in the reaction term of S, but I have not been successful either.
I have checked the solutions suggested in this link, www.comsol.com/support/knowledgebase/952/ but it did not help much.
Could anyone tell me how to make the reaction rate 0 when the concentration of the substrate becomes zero? I do not understand where exactly should I introduce the term max(eps^2,Q).
Hope I made myself clear.
Thank you in advance
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what is wrong with the ALE
(all are in the .doc attachment. Thanks)
Hi,everyone,
I ‘m building a simple model based on the “heat transfer” module and the “ALE” module. The geometry is a simple rectangle. In the heat transfer node, the upper boundary is a heat flux BC, and other three are thermal insulation. In the ALE node, a prescribed normal mesh velocity is implemented on the upper boundary, other three are fixed.
Recently, I have encountered some problems relative to the ALE. Due to this reason, I deactivate the ALE module and solve the model where there is only a “heat transfer” module with some local variable to see where the error and mistake is (to ensure whether there is any wrong variable definition). In the ALE node, a “prescribed normal mesh velocity” is implemented on the upper boundary, where the ”normal mesh velocity Vn” is setting “to roeB_r+rolB_r” (m/s), After solving the model without the ALE, the theoretical normal mesh velocity (I defined a local variable with the expression of “roeB_r+rolB_r” to visualize the variable) is illustrated in the Fig. 1. In the Fig.1, we can see there should be a moving of the boundary.
(see the Fig. 1 in the attachment)
But when I activate the ALE node, the following error occurs (also as the Fig.2 shown).
Attempt to evaluate non-integral power of negative number. - Function: ^ Failed to evaluate temporary symbolic derivative variable. - Variable: mod1.rolB_r@VDN${mod1.genext1@13} - Defined as: ((1/(mod1.dB*((unit_m_cf^2)*unit_s_cf)))*((((((((log((mod1.TB/T_m))*(unit_s_cf*(mod1.DB*2)))/(r_0*unit_m_cf))^(-0.5))*0.5)*((1/(r_0*unit_m_cf))*((((((1/(mod1.dB*mod1.hcB))*(((1/(unit_K_cf*unit_m_cf))*unit_W_cf))))*2)*unit_s_cf)*log((mod1.TB/T_m)))))*unit_kg_cf)*((mod1.Pr_sB/unit_Pa_cf)^0.25))*((((unit_m_cf^3)*mod1.dB)/unit_kg_cf)^0.75))) Failed to evaluate temporary symbolic derivative variable. - Variable: mod1.ale.vn@VDN${mod1.genext1@13} - Defined as: (((1/(mod1.dB*((unit_m_cf^2)*unit_s_cf)))*((((((((log((mod1.TB/T_m))*(unit_s_cf*(mod1.DB*2)))/(r_0*unit_m_cf))^(-0.5))*0.5)*((1/(r_0*unit_m_cf))*((((((1/(mod1.dB*mod1.hcB))*(((1/(unit_K_cf*unit_m_cf))*unit_W_cf))))*2)*unit_s_cf)*log((mod1.TB/T_m)))))*unit_kg_cf)*((mod1.Pr_sB/unit_Pa_cf)^0.25))*((((unit_m_cf^3)*mod1.dB)/unit_kg_cf)^0.75)))) Failed to evaluate expression. - Expression: d(d(((mod1.ale.xt_free*mod1.ale.nx+mod1.ale.yt_free*mod1.ale.ny-mod1.ale.vn)*test(-x_lm))*(dvol),{test@0}),{mod1.genext1@13})
I’m quite puzzled about that, I can solve the model and evaluate all the relative variables without the ALE. This means there is no any wrong with the parts except the ALE section. While the above-mentioned error “fail to evaluate the relative variable” puzzles me a lot.
I have attached my .mph model, is anyone kind to check and give me some suggest?
If you wish, we can cooperate together and co-author, plz contact me.
Thanks sincerely in advance for your response.
Best wishes to you and your family.
Yours
FM Huang
Dec.22th.2011
Hi,everyone,
I ‘m building a simple model based on the “heat transfer” module and the “ALE” module. The geometry is a simple rectangle. In the heat transfer node, the upper boundary is a heat flux BC, and other three are thermal insulation. In the ALE node, a prescribed normal mesh velocity is implemented on the upper boundary, other three are fixed.
Recently, I have encountered some problems relative to the ALE. Due to this reason, I deactivate the ALE module and solve the model where there is only a “heat transfer” module with some local variable to see where the error and mistake is (to ensure whether there is any wrong variable definition). In the ALE node, a “prescribed normal mesh velocity” is implemented on the upper boundary, where the ”normal mesh velocity Vn” is setting “to roeB_r+rolB_r” (m/s), After solving the model without the ALE, the theoretical normal mesh velocity (I defined a local variable with the expression of “roeB_r+rolB_r” to visualize the variable) is illustrated in the Fig. 1. In the Fig.1, we can see there should be a moving of the boundary.
(see the Fig. 1 in the attachment)
But when I activate the ALE node, the following error occurs (also as the Fig.2 shown).
Attempt to evaluate non-integral power of negative number. - Function: ^ Failed to evaluate temporary symbolic derivative variable. - Variable: mod1.rolB_r@VDN${mod1.genext1@13} - Defined as: ((1/(mod1.dB*((unit_m_cf^2)*unit_s_cf)))*((((((((log((mod1.TB/T_m))*(unit_s_cf*(mod1.DB*2)))/(r_0*unit_m_cf))^(-0.5))*0.5)*((1/(r_0*unit_m_cf))*((((((1/(mod1.dB*mod1.hcB))*(((1/(unit_K_cf*unit_m_cf))*unit_W_cf))))*2)*unit_s_cf)*log((mod1.TB/T_m)))))*unit_kg_cf)*((mod1.Pr_sB/unit_Pa_cf)^0.25))*((((unit_m_cf^3)*mod1.dB)/unit_kg_cf)^0.75))) Failed to evaluate temporary symbolic derivative variable. - Variable: mod1.ale.vn@VDN${mod1.genext1@13} - Defined as: (((1/(mod1.dB*((unit_m_cf^2)*unit_s_cf)))*((((((((log((mod1.TB/T_m))*(unit_s_cf*(mod1.DB*2)))/(r_0*unit_m_cf))^(-0.5))*0.5)*((1/(r_0*unit_m_cf))*((((((1/(mod1.dB*mod1.hcB))*(((1/(unit_K_cf*unit_m_cf))*unit_W_cf))))*2)*unit_s_cf)*log((mod1.TB/T_m)))))*unit_kg_cf)*((mod1.Pr_sB/unit_Pa_cf)^0.25))*((((unit_m_cf^3)*mod1.dB)/unit_kg_cf)^0.75)))) Failed to evaluate expression. - Expression: d(d(((mod1.ale.xt_free*mod1.ale.nx+mod1.ale.yt_free*mod1.ale.ny-mod1.ale.vn)*test(-x_lm))*(dvol),{test@0}),{mod1.genext1@13})
I’m quite puzzled about that, I can solve the model and evaluate all the relative variables without the ALE. This means there is no any wrong with the parts except the ALE section. While the above-mentioned error “fail to evaluate the relative variable” puzzles me a lot.
I have attached my .mph model, is anyone kind to check and give me some suggest?
If you wish, we can cooperate together and co-author, plz contact me.
Thanks sincerely in advance for your response.
Best wishes to you and your family.
Yours
FM Huang
Dec.22th.2011
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Convergence behaviour in a stationary solver
Dear Comsol gurus,
I have been dealing with a CFD/transport of diluted species (TDS) simulation for a while and I was hoping you could bring some light to the subject.
I am simulating a flow in a micro mixer (related to example: www.comsol.com/showroom/gallery/320/) using laminar flow and transport of diluted species. I want to emulate the behaviour of the so called "chaotic mixers" in which a laminar flow with an initial concentration of a specie "c" is "streched and bent" in order to mix "c" in the entire volume. The chaotic mixer is used in small channels (µm and mm) due to the lack of turbulent forces.
I am not having any results so far. I have uploaded the convergence plots for both step 1: laminar flow, step 2: TDS and my model. At the beginning I wanted to define a lateral (zx in this case) boundary as symmetric boundary for then mirror it. The latter was unsuccessful and I defined it as a wall without results. I have used the default iterative solver and direct solver, I have change the mesh from coarser to fine, I also changed the multigrid mesh coarsening factor from 2 to 1.5 and increase the relative tolerance, all of them at the same time or each one separatelly without any success.
My first guess is that the large "turbulence" made by the bending and streching of the flow might increase each time the error in each iteration leading to a never ending iterative process. But the people involved in the original article was successful in their simulation using periodic boundary conditions but I dont know how to use them.
Sorry for the long post but I wanted to give you a better picture of my situation. Your ideas are more than welcome
My best regards
Miguel
I have been dealing with a CFD/transport of diluted species (TDS) simulation for a while and I was hoping you could bring some light to the subject.
I am simulating a flow in a micro mixer (related to example: www.comsol.com/showroom/gallery/320/) using laminar flow and transport of diluted species. I want to emulate the behaviour of the so called "chaotic mixers" in which a laminar flow with an initial concentration of a specie "c" is "streched and bent" in order to mix "c" in the entire volume. The chaotic mixer is used in small channels (µm and mm) due to the lack of turbulent forces.
I am not having any results so far. I have uploaded the convergence plots for both step 1: laminar flow, step 2: TDS and my model. At the beginning I wanted to define a lateral (zx in this case) boundary as symmetric boundary for then mirror it. The latter was unsuccessful and I defined it as a wall without results. I have used the default iterative solver and direct solver, I have change the mesh from coarser to fine, I also changed the multigrid mesh coarsening factor from 2 to 1.5 and increase the relative tolerance, all of them at the same time or each one separatelly without any success.
My first guess is that the large "turbulence" made by the bending and streching of the flow might increase each time the error in each iteration leading to a never ending iterative process. But the people involved in the original article was successful in their simulation using periodic boundary conditions but I dont know how to use them.
Sorry for the long post but I wanted to give you a better picture of my situation. Your ideas are more than welcome
My best regards
Miguel
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"Reinitializing GUI" for a long time
Hi, when I solve a PDE, it takes a lot of time. I closed the programme with task manager of windows. When I reopen the file, the programme is "reinitializing GUI" . I wait for almost an hour and nothing changed. At this time I cann't do anything else in the software. How can I solve this problem?
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Solve PDE on 1D domain?
Hy guys, I have a problem with solving a PDE based model defined by me, it is not a default template in COMSOL.
My problem is that the equation is solved for the time domain, but not for the geometry specified. ( Interval )
Does the solver automatically solve with respect to 'x axis' ( it represents the height of a reactor x=[0,20] m )?
The PDE I'm trying to solve is the following:
dT/dt=-VL*dT/dx-constant
where VL and constant are known.
Could you help me with this,
Thank you.
My problem is that the equation is solved for the time domain, but not for the geometry specified. ( Interval )
Does the solver automatically solve with respect to 'x axis' ( it represents the height of a reactor x=[0,20] m )?
The PDE I'm trying to solve is the following:
dT/dt=-VL*dT/dx-constant
where VL and constant are known.
Could you help me with this,
Thank you.
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