Hey, i am having some problems creating the steamlines for my Helmholtz coil. I followed the steps for the one of the model on comsol website for Helmholtz coil except other than revolve to create the coils i did extrusion instead. Now i am getting something really weird for my streamline and I compared with the Helmholtz coil file i downloaded from the website and i looks like I did the exact same thing with the example. I couldn't figure out what might possibly go wrong. I have attached a picture of the streamline I have now. Can you tell me what I did wrong and help me fix it? Thank you.
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streamline problem
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Poisson-continuity coupled equation
Hello,
I try to model the corona discharge in wire-cylinder geometry governed by the equations:
nabla (V) =- rho/epsilon0 (Poisson equation) and
grad (rho) * grad (V) = rho ^ 2/epsilon0 (equation of current continuity)
with boundary conditions:
V_w = V0 (on the wire)
V_cyl = 0 (on the cylinder)
As rho is unknown, I should compile until the electric field on the wire is equal to a given value Es.
knowing that I can give an initial estimate for rho on the wire --> rho_w.
My problem is I dont know how to solve these two coupled equations.
I try to model the corona discharge in wire-cylinder geometry governed by the equations:
nabla (V) =- rho/epsilon0 (Poisson equation) and
grad (rho) * grad (V) = rho ^ 2/epsilon0 (equation of current continuity)
with boundary conditions:
V_w = V0 (on the wire)
V_cyl = 0 (on the cylinder)
As rho is unknown, I should compile until the electric field on the wire is equal to a given value Es.
knowing that I can give an initial estimate for rho on the wire --> rho_w.
My problem is I dont know how to solve these two coupled equations.
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saw sensor for pressure measurement
hello,
i am designing a saw sensor for pressure measurement.can somebody suggest me which formula i need to use in comsol in order to measure pressure. it should be related to change in frequency of saw sensor by application of pressure.
i am designing a saw sensor for pressure measurement.can somebody suggest me which formula i need to use in comsol in order to measure pressure. it should be related to change in frequency of saw sensor by application of pressure.
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numerical oscillation in modelling corona discharge with coefficient form PDEs and Electrostatic
Hi,everyone
I,m working on modelling corona discharge in air with coefficient form PDEs and Electrostatics interface. I'm encountering the problem of numerical oscillation in the simulation area (unexpected negative values show up), but the solver does not give error massage about convergence. Did anybody encounter the same problem? The possible reason for it is that the mesh is not fine enough. I have tried to make the mesh finer, but the problems remain. I want to know whether there are more reasons for the problems. Any advice will be greatly appreciated.
Thanks in advance.
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fucheng
I,m working on modelling corona discharge in air with coefficient form PDEs and Electrostatics interface. I'm encountering the problem of numerical oscillation in the simulation area (unexpected negative values show up), but the solver does not give error massage about convergence. Did anybody encounter the same problem? The possible reason for it is that the mesh is not fine enough. I have tried to make the mesh finer, but the problems remain. I want to know whether there are more reasons for the problems. Any advice will be greatly appreciated.
Thanks in advance.
--
fucheng
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Thermal Stress Static analysis
Dear Concerned,
I have comsol 4.2 version package. In this regard i am facing a problem to define spatially varying force on a boundary in 2D space. For instance, if i have a line extending along x-axis with length of 100mm. I only want to apply normal force to this line on a small region like 10 mm from the right edge. Is this possible without creating extra point on the line at a distance of 10 mm from right extremity and rather define the variation of force using a function defined over x-coordinate.
Please help me in this regard, looking forward to any guidance.
I have comsol 4.2 version package. In this regard i am facing a problem to define spatially varying force on a boundary in 2D space. For instance, if i have a line extending along x-axis with length of 100mm. I only want to apply normal force to this line on a small region like 10 mm from the right edge. Is this possible without creating extra point on the line at a distance of 10 mm from right extremity and rather define the variation of force using a function defined over x-coordinate.
Please help me in this regard, looking forward to any guidance.
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Structural analysis 2-D stress plot overlapping
Dear Concerned,
How can i overlap von mises plot of 2D asymmetric formulation with a 2D plane stress formulation for the Same Geometry.
How can i overlap von mises plot of 2D asymmetric formulation with a 2D plane stress formulation for the Same Geometry.
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coupling model, extrusion 2D-axy towards 3D
Hello,
Is it possible to re-use temperature boundary results of a 2D-axy simulation towards a boundary destination of a 3D model (4.3a version)?
Which operator could I use if it's possible?
Thank you
Julien
Is it possible to re-use temperature boundary results of a 2D-axy simulation towards a boundary destination of a 3D model (4.3a version)?
Which operator could I use if it's possible?
Thank you
Julien
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how to enter a Channel thickness
Hi everybody,
how to enter the Channel thickness?
I use the (laminar flow -> mass flow -> mass flow rate -> normal mass flow rate), but get an error!
I read a comsol documentation and I think I must enter a Channel thickness (maybe!!), but don't find where I can to enter a Channel thickness!
please help me, 1- how to enter a Channel thickness? 2- why get an error when I choose "normal mass flow rate" ?
thanks a lot
how to enter the Channel thickness?
I use the (laminar flow -> mass flow -> mass flow rate -> normal mass flow rate), but get an error!
I read a comsol documentation and I think I must enter a Channel thickness (maybe!!), but don't find where I can to enter a Channel thickness!
please help me, 1- how to enter a Channel thickness? 2- why get an error when I choose "normal mass flow rate" ?
thanks a lot
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safe to manually delete?
hey there
I uninstalled all the old version of COMSOL over control panel but I still found lotsa old directories
C:\Users\xxx\.comsol\v(n)
is it safe to delete all of the old ones manually?
Appreciate your advise. Thanks in advance!
regards
Liwah
I uninstalled all the old version of COMSOL over control panel but I still found lotsa old directories
C:\Users\xxx\.comsol\v(n)
is it safe to delete all of the old ones manually?
Appreciate your advise. Thanks in advance!
regards
Liwah
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COMSOL external MATLAB function
Hello forum.
I want to use an external matlab function to define a local heat transfer coefficient distribution.
If I use a very simple external function, everything works fine:
for example:
function value=alpha(z)
value = ones(size(z))*65000;
end
My function will load an object with the current data from a *mat - file and will read the data and give it back to COMSOL
something like that:
function out=AlphaZ1(z)
global pipe1;
path('V:\30_Numerik\COMSOL\Thermosyphon_2.0alpha\20130218001\classes',path)
strStoredVariableDataFileName = 'V:\30_Numerik\COMSOL\Thermosyphon_2.0alpha\20130218001\pipe1.mat';
load(strStoredVariableDataFileName)
value=pipe1.CondenserSection.GetAlphaZ(z');
out=round(value');
end
Unfortunately I always get an error message:
Attempted to access value(:,1); index out of bounds because size(value)=[0,0].
with no further details
If I save the z - vector to an mat-file and later try to call the function with this z-vector, it works properly and I get the correct heat transfer distribution.
Is there a way to analyse the error message and to find where it occurs? I already tried to catch all errors with a try-catch statement in MATLAB, but that does not help
Matthias
I want to use an external matlab function to define a local heat transfer coefficient distribution.
If I use a very simple external function, everything works fine:
for example:
function value=alpha(z)
value = ones(size(z))*65000;
end
My function will load an object with the current data from a *mat - file and will read the data and give it back to COMSOL
something like that:
function out=AlphaZ1(z)
global pipe1;
path('V:\30_Numerik\COMSOL\Thermosyphon_2.0alpha\20130218001\classes',path)
strStoredVariableDataFileName = 'V:\30_Numerik\COMSOL\Thermosyphon_2.0alpha\20130218001\pipe1.mat';
load(strStoredVariableDataFileName)
value=pipe1.CondenserSection.GetAlphaZ(z');
out=round(value');
end
Unfortunately I always get an error message:
Attempted to access value(:,1); index out of bounds because size(value)=[0,0].
with no further details
If I save the z - vector to an mat-file and later try to call the function with this z-vector, it works properly and I get the correct heat transfer distribution.
Is there a way to analyse the error message and to find where it occurs? I already tried to catch all errors with a try-catch statement in MATLAB, but that does not help
Matthias
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magnetic shielding with mumetal(nonlinear - saturation)
Hi
I need some help with my model....
I have a 3D sim, A current line that generates my field and a mumetal infinite plane(1m*1m*0.5mm)
The 0.5mm is the thickness of my mumetal. I have 0.5T on the surface of the shield and i want to see the B behind the shield.
a.I use relative permeability constant at 7000.
b. I use a non-linear equation with saturation for relative permeability
μr= 1+[(μrmax-1)^(-1) + (μ0*/Η/ / B_sat)^(1/n)] ^(-1)
where mu_rmax=7000, B_sat=0.7T and n=1
c. I use the B-H and H-B curves filling them with my data curves.
Am I correct in any way of these models or I need some refinements to be more precise;
I can see the saturation and the B-H curve; How we can change the scales from a plot in comsol;
Also I attach some photos of my model.
Thanks in advance.
I need some help with my model....
I have a 3D sim, A current line that generates my field and a mumetal infinite plane(1m*1m*0.5mm)
The 0.5mm is the thickness of my mumetal. I have 0.5T on the surface of the shield and i want to see the B behind the shield.
a.I use relative permeability constant at 7000.
b. I use a non-linear equation with saturation for relative permeability
μr= 1+[(μrmax-1)^(-1) + (μ0*/Η/ / B_sat)^(1/n)] ^(-1)
where mu_rmax=7000, B_sat=0.7T and n=1
c. I use the B-H and H-B curves filling them with my data curves.
Am I correct in any way of these models or I need some refinements to be more precise;
I can see the saturation and the B-H curve; How we can change the scales from a plot in comsol;
Also I attach some photos of my model.
Thanks in advance.
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Manipulating variables from 3d to 2d temporal
Hi: I'm working with a coupled heat transfer - momentum equations, but what I need to do is to use a dependent variable previously solved which depends on x, y and z axis in a 3D system, being transformed in a 2D temporal system. I mean first I've got a solved a 3D model variable u(x,y,z) then I need to use it as u(x,y,t) in a second model.
I need to do this in order to calculate accurate Nusselt numbers in the entrance, and I'm having out of memory issues, and using Weak Constraints on my T=cte boundary conditions, convergence issues when using a iterative solver.
Thank In advance.
I need to do this in order to calculate accurate Nusselt numbers in the entrance, and I'm having out of memory issues, and using Weak Constraints on my T=cte boundary conditions, convergence issues when using a iterative solver.
Thank In advance.
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Generating shear waves induced by a piston hitting to a model
I want to generate sinusoidal shear waves and observe its propagation induced by a piston hitting a 3D model. I think what I would like to do is similar to paper presented by S.Audiere (www.comsol.com/papers/8297/). I am using Solid Mechanics Module but I do not know how to make a piston hit to a 3D model. Should I use boundary load or something else?
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magned no moving
Hey.
I have this problem:
I have two magnets oriented so that the north pole of one facing the North Pole 2 in the common axis X. Magnets are so close to each other should be
repel.
But magnets will not move.
Geometry in 2D.
What should I do to make magnets moved apart?
Thank you.
Goodbye.
I have this problem:
I have two magnets oriented so that the north pole of one facing the North Pole 2 in the common axis X. Magnets are so close to each other should be
repel.
But magnets will not move.
Geometry in 2D.
What should I do to make magnets moved apart?
Thank you.
Goodbye.
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Computing the inductance of a Wire
Hi!
I read "Computing the Resistance of a Wire" post. It is easy for compute resistance of wire, but how i can compute the inductance of this wire?
I read "Computing the Resistance of a Wire" post. It is easy for compute resistance of wire, but how i can compute the inductance of this wire?
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PDE solving or defining force in terms of displacement
Hi,
I hope you are doing well,
I am a new user of Comsol.
At this moment, I am trying to model a cantilever beam with an applied force on its edge as a function of displacement.
So, what I need is either:
define the force on the boundary as a function of displacement. I am trying to do this in equation view but it seems that it does not take expression and it asks me just values in x and y directions.
or:
write a PDE and try to solve it. The equation is derived from the Euler-Bernoulli theory as:
EI uxxxx=F(u)
I tried to find a predefined PDE and change the coefficients but I could not to do it.
Could you please help me on this issue?
I hope you are doing well,
I am a new user of Comsol.
At this moment, I am trying to model a cantilever beam with an applied force on its edge as a function of displacement.
So, what I need is either:
define the force on the boundary as a function of displacement. I am trying to do this in equation view but it seems that it does not take expression and it asks me just values in x and y directions.
or:
write a PDE and try to solve it. The equation is derived from the Euler-Bernoulli theory as:
EI uxxxx=F(u)
I tried to find a predefined PDE and change the coefficients but I could not to do it.
Could you please help me on this issue?
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PDE - Contact Resistance
Hi Everyone,
I am wondering how to implement electrical or thermal contact resistance when using the PDE physics.
I am using the PDE coefficient form to model thermoelectric effects at a metal-semiconductor interface. I have a working thermoelectric model, but I want to include the effects of contact resistance at the interface.
I am aware the Heat Transfer physics has a "Thin Thermally Resistive Layer" which introduces a resistance to heat flow and a discontinuity in the temperature at a boundary. However, I have been unable to simulate a similar interface resistance using PDE physics.
I am using COMSOL 4 and I appreciate any help anyone can provide.
Thank you,
- Kyle
I am wondering how to implement electrical or thermal contact resistance when using the PDE physics.
I am using the PDE coefficient form to model thermoelectric effects at a metal-semiconductor interface. I have a working thermoelectric model, but I want to include the effects of contact resistance at the interface.
I am aware the Heat Transfer physics has a "Thin Thermally Resistive Layer" which introduces a resistance to heat flow and a discontinuity in the temperature at a boundary. However, I have been unable to simulate a similar interface resistance using PDE physics.
I am using COMSOL 4 and I appreciate any help anyone can provide.
Thank you,
- Kyle
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Nanoparticle heating with Surface Plasmon Resonance (SPR)
Hi Fellas,
I am trying to model heating of metallic nanoparticles when exposed to Laser/Solar light with Heat Transfer module. I am new to comsol and I do not now how to model the incident light and its interaction with NPs in this module.
The NPs are confined in a nanochannel and the surrounding liquid is water.
Can anybody introduce a similar simulation?
Thanks in advance.
I am trying to model heating of metallic nanoparticles when exposed to Laser/Solar light with Heat Transfer module. I am new to comsol and I do not now how to model the incident light and its interaction with NPs in this module.
The NPs are confined in a nanochannel and the surrounding liquid is water.
Can anybody introduce a similar simulation?
Thanks in advance.
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How to implement a biphasic asymmetric waveform?
Hello everyone. I'm trying to figure out how to implement a biphasic asymmetric waveform in Comsol 4.3a. I need to be able to use the following electrical simulator settings in order to stimulate an array of electrodes. Does anyone know how to do such a thing in Comsol? Your help would be greatly appreciated. Thanks.
Here is the information for the 4 channel electrical stimulator settings:
Channels 1+2 output as one biphasic waveform:
Channel 1:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = 10 V
Channel 2:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = -0.32 V
Channels 3+4 output as one biphasic waveform:
Channel 3:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = 0.32 V
Channel 4:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = -10 V
I look forward to hearing from anyone who may be of some help for me on this topic. Thanks again!
Here is the information for the 4 channel electrical stimulator settings:
Channels 1+2 output as one biphasic waveform:
Channel 1:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = 10 V
Channel 2:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = -0.32 V
Channels 3+4 output as one biphasic waveform:
Channel 3:
-- Pulse width = 5 msec
-- Pulse period = 10 msec
-- Amplitude = 0.32 V
Channel 4:
-- Pulse width = 0.160 msec
-- Pulse period = 10 msec
-- Amplitude = -10 V
I look forward to hearing from anyone who may be of some help for me on this topic. Thanks again!
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streamline problem
Hey, i am having some problems creating the steamlines for my Helmholtz coil. I followed the steps for the one of the model on comsol website for Helmholtz coil except other than revolve to create the coils i did extrusion instead. Now i am getting something really weird for my streamline and I compared with the Helmholtz coil file i downloaded from the website and i looks like I did the exact same thing with the example. I couldn't figure out what might possibly go wrong. I have attached a picture of the streamline I have now. Can you tell me what I did wrong and help me fix it? Thank you.
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