Latest Discussions - COMSOL Forums

Nonlinear solver did not converge.

Mon, 25 Mar 2019 21:29:11 +0000

Hello,

I made a fully coupled model of two physics (Darcy's law and Heat transfer in porous media) for 2D horizontal geothermal heat exchanger (i.e., coupled heat and moisture transfer in soil under thermal gradient). Once I ran the model, error messages came up regarding convergence issues with time dependent solver (i.e. nonlinear solver did not converge). I studied many resources in COMSOL website and followed the tips that posted (e.g. change method to ease tolerance factor). I've also learned that coarse mesh may cause the convergence issue. I thus set extremely fine mesh, especially near the boundaries between domains. Even the model was running for overnight, I still got same error messeage. Does anyone know the solution to fix this issue? I am looking for a way that I can stay with my normal mesh and run the model without error.

Setting last time step as initial conditions of next thermal model run

Mon, 25 Mar 2019 19:32:55 +0000

Hello,

I've been trying to create long time scale thermal models (2000yr+) by running them in 100 year segments and using the final time step to start the next 100 year run, saving each 100 year run in its own file. For some reason using the final time step of a 100 year run (with 1 day steps) produces the following error:

There are 53046 void equations (empty rows in matrix) for the variable comp1.ht.dt2Inv_T. at coordinates: (64.0549,-0.0610404), (62.5617,-1.55478), (62.5627,-4.54318), (64.056,-59.9383), (62.5614,-58.4453), ... and similarly for the degrees of freedom (empty columns in matrix). Last time step is not converged.

If I run the model for only 60 days it has no problem using the final time step for the next set of 60 days and I can repeat the process for as many times as I would like.

Currently I have it structured to delete all but the final time step from the previous solution by using "combine solution" to save memory and speed it up, this is not an issue for the 60 day model.

Does anybody have an idea as to how I can fix this? I've been having this issue for weeks.

Thanks!

RFID_TAG

Mon, 25 Mar 2019 06:34:19 +0000

hello sir,I wanted to design a RFID Antenna tag in Comsol software. I need the proper guideline for this field so that i can design it

Current Source Question

Sun, 24 Mar 2019 11:47:21 +0000

Hello all, I'm trying to apply a current through 3 electrodes to my geometry, it works fine with ac sources, however when I try to change the current source to Pulse it crashes and gives the following error: Undefined variable. - Variable: t - Global scope Failed to evaluate operator. - Operator: if - Global scope Failed to evaluate expression. - Expression: if(t<comp1.cir.I1.td,0,comp1.cir.pulse((t-comp1.cir.I1.td)/comp1.cir.I1.Tper,comp1.cir.I1.tr/comp1.cir.I1.Tper,comp1.cir.I1.tf/comp1.cir.I1.Tper,comp1.cir.I1.pw/comp1.cir.I1.Tper)) Failed to evaluate variable. - Variable: comp1.cir.I1_isrc - Defined as: (if(t<comp1.cir.I1.td,0,comp1.cir.pulse((t-comp1.cir.I1.td)/comp1.cir.I1.Tper,comp1.cir.I1.tr/comp1.cir.I1.Tper,comp1.cir.I1.tf/comp1.cir.I1.Tper,comp1.cir.I1.pw/comp1.cir.I1.Tper))comp1.cir.I1.value)+comp1.cir.I1.offset Failed to evaluate variable. - Variable: comp1.cir.I1_i - Defined as: comp1.cir.I1_isrc Failed to evaluate variable. - Variable: comp1.cir.gnd1_p_i - Defined as: comp1.cir.I1_i Failed to evaluate variable. - Variable: comp1.cir.I1_p_i - Defined as: comp1.cir.gnd1_p_i Failed to evaluate variable. - Variable: comp1.cir.termI1_i - Defined as: -comp1.cir.I1_p_i Failed to evaluate variable. - Variable: comp1.ec.I0_1 - Defined as: comp1.cir.termI1_i Failed to evaluate expression. - Expression: d(comp1.ec.I0_1test(comp1.ec.term1.V0_ode),{test@1}) Failed to evaluate Jacobian of expression. - Expression: comp1.ec.I0_1*test(comp1.ec.term1.V0_ode)

Fluid damper simulation

Sat, 23 Mar 2019 22:00:21 +0000

I go through the fluid damper simulation .

I need piaton motion for different time .

But in simulation it cannot show me piston motion . It only shows the velocity change.

So kindly provide me the detail how to apllied piston dispalcement for different time

DEP effect on GUVs

Sat, 23 Mar 2019 14:33:27 +0000

i have generated the Gaint unilamellar vesicles from DPhPc lipid rehydrated with sucrose of PH-7. i need to check the DEP force on GUVs of different diameters. is it possible to do it ? and how to find the DEP parameters too for simulating this ?

Segregated group 2 Failed to evaluate variable. - Variable: material.mur13

Fri, 22 Mar 2019 15:56:29 +0000

I'm simulating magnetic field in a current carrying conductor. I have a 3D model and the following are the sub-modules included: Ampere's law Magnetic Insulation initial Values and External Current Density -> this is inmported from the Jouls Heating module.

Just the jouls heating works fine. but i have issue when I include heating. I get the following error I get: Segregated group 2 Failed to evaluate variable. - Variable: material.mur13 - Geometry: 1 - Domain: 1 Failed to evaluate variable. - Variable: mod1.mf.murxz - Defined as: material.mur13 Failed to evaluate variable. - Variable: mod1.mf.murinvyz - Defined as: (((mod1.mf.murxzmod1.mf.muryx)-(mod1.mf.muryzmod1.mf.murxx))/(((((mod1.mf.murzy(mod1.mf.murxzmod1.mf.muryx))+((mod1.mf.murzz(mod1.mf.muryymod1.mf.murxx))+(mod1.mf.murzx(mod1.mf.muryzmod1.mf.murxy))))-(mod1.mf.murzy(mod1.mf.muryzmod1.mf.murxx)))-(mod1.mf.murzz(mod1.mf.murxymod1.mf.muryx)))-(mod1.mf.murzx(mod1.mf.muryymod1.mf.murxz))))

Failed to evaluate variable. - Variable: mod1.mf.Hy - Defined as: (((mod1.mf.Bzmod1.mf.murinvyz)+((mod1.mf.murinvyxmod1.mf.Bx)+(mod1.mf.murinvyymod1.mf.By)))/mu0_const) Failed to evaluate expression. - Expression: d((mod1.mf.d(-mod1.mf.Hxtest(mod1.curlAx)-mod1.mf.Hytest(mod1.curlAy)-mod1.mf.Hztest(mod1.curlAz)))(dvol),{test@1})

any light on this will be much appericiated.

Thank you!

Multiturn Coil Voltage Excitation: Problem with Coil Current Results

Fri, 22 Mar 2019 11:21:47 +0000

Hello everyone

I'm trying to simulate a multiturn coil with an iron core, with a certain BH curve. Simulations run well, but for the same applied voltage, but different coil resistances, it always gives me the same current.

I've tried to use the electrical circuit physics as in the E-Core Transformer example, but the results are the same.

Can anyone help? How is the coil current calculated?

Thanks in advance

Frequency Response for a clamped beam with many vibration absorbers.

Thu, 21 Mar 2019 17:03:39 +0000

Hello all,

I have a thin plate modeled as 3D in solid mechanics module. On the top of this plate, I have places a mass-spring resonator (vibration absorber) (please see the attached figure) where I have modeled it in COMSOL using the lumped mechanical system. The helix spring is just for schematic where the actual 3D plate is shown in second figure. I coupled the two systems using the “External Source” from the lumped mechanical system and I exert the reactions from this external source to the solid 3D plate. The eigenfrequencies obtained from the eigenfrequency study matched perfectly with the in-house FE code. However, now I am trying to study frequency response to a harmonic force of an amplitude 1 while changing its frequency. Since I am applying the reaction forces from the external source of the lumped mechanical system to the 3D solid plate, how can I apply the harmonic force?

I tried to add something like this:

“-lms.E136_f2 + linper(1)”

where “-lms.E136_f2” is the reaction force from the external source and “linper(1)” is my harmonic force but still I could not succeed. I will be really appreciated if I can find an answer.

Thank you

Abdullah

View Factor Computation (?!)

Thu, 21 Mar 2019 15:08:03 +0000

Has anyone succesfully computed view factors in a 2D geometry yet? I have tried to follow this blog: https://www.comsol.com/blogs/computing-view-factors-with-the-heat-transfer-module/, but when trying this within a square cavity, I get either errors or zeros with the used function from the blog.

Sharing your succesful model or steps for implementation would be appreciated a lot!

Kind regards,

Marvin

Regarding Rosette configuration

Thu, 21 Mar 2019 14:21:17 +0000

Hello all,

    How to make strain mesurement using Rosette Configuration in Comsol, If known please let me know the procedure.

Create inner surface by heat transfer

Thu, 21 Mar 2019 11:16:34 +0000

Dear Users,

I need your help with a hopefully simple thing. I have two geometric bodies. The problem is that the surface between them dont exist so I can´t create a thin layer to simulate the heat transfer from them. Do you have an answer as to how it is possible to create an inner surface or just divide one surface into two parts?

Thank you for your help!

Question regarding the calculation of area

Thu, 21 Mar 2019 09:26:19 +0000

Hi all,

I have a 3D geometry and I was trying to get the boundary area of certain portion as an input for the further calculation.

As suggested, there are two ways to get the area value: 1. Use measure under the geometry tag to get the boundary area. 2. Use intergration function for this boundary (such as expression intop(1)) to get the area.

However, I found the values from these two method are a bit different. For example, for a circular plane, from integration method it got 9.7193E-12 [m^2], but from the measure methode it showed 1.0169E-11 [m^2]

Why there is a difference? And which one should I trust?

Thank you

Thermo Hydro Mechanical Modeling of Porous media

Thu, 21 Mar 2019 07:52:27 +0000

Dear Users, I am working on the thermo-hydro-mechanical model of porous media. At the time of solving I am getting the problem under time dependent study. For the time period (i.e., in s) (0, 0.1, 1) is converging promisingly. But that will not be happening during the time period from minutes onwards (i.e., from minutes to hr). I need solve this problem for the 1000 days with 1 day time gap (i.e., from 0, 1, 1000). Please help in this regard. It will be very helpful to me for continuing my research in the COMSOL Multiphysics for the coupling of various physics and their application in the Petroleum industry.

Herewith I am attaching the file that I need to simulate.

Thanking you Regards Dr. Manojkumar Gudala Institute PostDoc Fellow Indian Institute of Technology-Madras.

Modal assurance criterion (MAC) calculation

Thu, 21 Mar 2019 05:08:06 +0000

Does COMSOL calculate MAC of mode shapes obtained by FEA and mode shapes derived from experimental modal analysis (EMA)?

Is there a command for MAC?

Thank you!

Error: Failed to generate mesh for domain, Intersecting face elements

Wed, 20 Mar 2019 17:43:11 +0000

Hello,

I am attempting to simulate the electric field of an imported CAD geometry (attached below) that includes a wire readout plane. My naive approach of generating a physics-defined mesh yields a long list of errors, due to supposed intersecting face elements and faces/edges that are shorter than the specified minimum element size. Most of the issues seem to occur where the small wires are attached to the board.

After going through some of the blogs and tutorials, I have made some attempts to separate the edges (using the Edge operation) and define an "Extremely fine" mesh for the wires, but I still run into the same issues down the road when I mesh the "Remaining" domains.

Could anybody please give a recipe for how to best tackle these issues? Is this better solved at the level of the CAD file or can I work within COMSOL?

Many thanks for any advice you can offer, Michael

ECM (Electro Chemical Machining)

Wed, 20 Mar 2019 16:35:20 +0000

if any one is working ecm process in 3d geomerty. please help me because i am also working on ecm

pipe-flow-and-surface-radiation-interaction

Wed, 20 Mar 2019 14:47:54 +0000

The below post is related to an archived discussion

Hello Aaron Valle

hope you are well. I see your issue now. do you solve your problem?

Peiravi M. M.

magnetic_gear_2d_geometry_sequence.mph.

Wed, 20 Mar 2019 11:54:03 +0000

Hi I'm looking for magnetic_gear_2d_geometry_sequence.mph file I couldn't find it in the application library I'm following this pdf to practice https://www.comsol.fi/model/download/308751/magnetic_gear_2d.pdf

please

Some problems with parameters in module post-processing

Wed, 20 Mar 2019 11:28:37 +0000

Simulations in acoustic modules and solid mechanics modules have been done recently. I would like to ask some questions about the parameters in the post-processing of these two modules. There are some misunderstandings in this regard, I hope help and support.

Firstly, in the acoustic frequency domain, the sound pressure and sound intensity distribution on the whole model can be obtained by applying the sound pressure signal, but in the acoustic time domain interface, there is only the spatiotemporal distribution of sound pressure except sound intensity distribution. Why and how to solve this problem (maybe use the relationship between sound pressure and sound intensity to seek sound strength, is this correct? ie I=actd.p_t^2 /rho/c).

Secondly, in the solid mechanics module, the load direction is applied along the z-axis in the time domain (two-dimensional axisymmetric), and the calculation model is obtained to obtain the distribution of stress and strain. When extracting the velocity distribution at a certain point, there are several Different speeds which are not very misleading. I don't know what the specific meanings are, such as solid_vel and solid_utz. Assuming that solid_disp represents the total displacement, which one represents the slope of the displacement?