Issues with Pipe Flow and Surface Radiation interaction

April 21, 2016, 5:52 am

≫ Next: List of function in Comsol 5.2

≪ Previous: A Vortex Pair Impinging on a Solid Boundary

$

0

0

Hello Comsolers!

I am very new to the program, and I am having some issues regarding Non Isothermal Pipe Flow, Heat Transfer in Solids, and Heat Transfer with Surface to Surface Radiation.

I have a 1D pipe circuit, where the the inlet and outlet (plus 1 meter pipe for each of them) sections are resting on top of a block of soil, and the rest is buried underground. There is a flow of water in the pipe.

The main idea is to simulate the pipes being heated by the Sun's radiation, observe an increase in temperature in the pipe, and observe how the ground is being heated by the thermal transfer between the fluid-pipe-ground.

For some reason, I am not observing a Radiation - Thermal transfer interaction, and I do not know what am I doing wrong.

Here's the boundaries that I have:

For Surface to Surface Radiation: Defined an external radiation source by solar position, a diffuse surface and heat flux (both of these only on the side of the block that is illuminated by the Sun), defined a constant temperature at the base of the block of soil (which is not illuminated).

For Non Isothermal Pipe Flow: Defined an Inlet with a volumetric flow rate, a Heat Outflow at the outlet, and a wall heat transfer with internal film resistance.

For the Heat Transfer in Solid, I have defined a Heat Flux in all applicable domains.

Any help is greatly appreciated! I can provide more details if needed.

Thank you all,

Aaron

---

List of function in Comsol 5.2

April 21, 2016, 10:45 am

≫ Next: Variable boundary conditions

≪ Previous: Issues with Pipe Flow and Surface Radiation interaction

$

0

0

Dear All,

Can anybody help me with finding the list of inbuilt functions of comsol 5.2. I want to equate my equation in the expression box of 1D plot group.

I am using heat transfer module for conjugate analysis. Have already been through all the reference manual available with the program document.

Regards

Variable boundary conditions

April 21, 2016, 7:26 pm

≫ Next: Heat Source in Turbulent High mach number flow !

≪ Previous: List of function in Comsol 5.2

$

0

0

Hi all, I'm using the API to run my COMSOL model multiple times in a loop in MATLAB with different initial and boundary conditions.

I was just wondering if it would be possible to set the initial conditions from the last time step of the previous solution, and the boundary conditions as the time varying value of one of the independent variables at the last node point in my mesh.

The problem is one dimensional, and writing the conditions in as a polynomial function using polyval isn't ideal as this seems to produce ill conditioned polynomials with the data I have.

Basically, can you specify the initial and boundary conditions as arrays of values corresponding to either time steps or locations?

Heat Source in Turbulent High mach number flow !

April 22, 2016, 3:57 am

≫ Next: Moving Mesh issue at the inlet/outlet

≪ Previous: Variable boundary conditions

$

0

0

Dear COMSOLERS ;

I am trying to simulate an electric arc in a flowing gas through a nozzle. as you can see in the attached model, the arc heat is been added as a heat source in the hmnf interface. also i created a ramp parameter to sweep the heat source value in the auxiliary sweep.

Now , as the ramp value goes higher , the solver gives the following error :

Failed to find a solution for all parameters,
even when using the minimum parameter step.
In Segregated Step 2:
Segregated iteration leads to undefined function value.
There was an error message from the linear solver.
The relative residual (1.2e+003) is greater than the relative tolerance.
Returned solution is not converged.

I tried different type of meshes , ramping the materiel properties and it didn't work out.
it would be great if any could help me solve this problem.

Best Regards ;

Moving Mesh issue at the inlet/outlet

April 22, 2016, 4:43 pm

≫ Next: Plasma plume expansion induced during laser ablation

≪ Previous: Heat Source in Turbulent High mach number flow !

$

0

0

Hello,

I am working on a 2D model on a channel with some obstacles.
The study is time-dependent and I have used the Moving Mesh (ALE).
The lower boundary of my model is moving down. The inlet and the outlet are moving too in order to increase the height of the channel.
I have some issue because the geometry is moving but all the results (especially the velocity) are given as if the geometry doesn't change. So I can see that the geometry is moving in the player but the results keep the first geometry.
I tried to change a lot of options to fix that but I can't find out the problem.

Please, anyone can help me? I attached pictures of the inlet options, the moving boundary options and the results.

Thank you for your time.


Berenice

Plasma plume expansion induced during laser ablation

April 24, 2016, 9:21 am

≫ Next: Rotary woofer simulation

≪ Previous: Moving Mesh issue at the inlet/outlet

$

0

0

Hello,

We are trying are to set up a model to study plasma plume expansion induced during pulsed laser deposition. Model is based on compressible Navier stokes equations consisting of mass, momentum and energy conservation. We are using equation based module of COMSOL (PDEs interface). We have implemented these equations of plasma plume into COMSOL and due to some reason it is not converging.
Can anyone assistance in this regards. Thank you.

Saba

Rotary woofer simulation

April 26, 2016, 7:59 pm

≫ Next: how to use two boundary conditions at same boundary

≪ Previous: Plasma plume expansion induced during laser ablation

$

0

0

Hello.

I am trying to simulate this recently developed rotary woofer:
www.rotarywoofer.com/
www.jpark.us/pubs/JASA_125(4)_RotaryWoofer_2009.pdf

My main goals are to find out air flux and energy flux rates going through it, as a function of rotation velocity and signal frequency.

Is that possible?
I reckon simulating an axial fan is probably the first step to take, but I get a bit lost in comsol even for that.
Any tips or directions?

Thanks

how to use two boundary conditions at same boundary

September 22, 2015, 5:20 am

≫ Next: Energy balance with variable density

≪ Previous: Rotary woofer simulation

$

0

0

I have been solving darcy's module in which i am supposed to add BCS of inlet pressure as well as mass flux which is at same boundary. But when i add 1 boundary condition it gets overridden by another one. Since i want to use both data in my model iss there any method to add both bcs at same place?

---

Energy balance with variable density

January 22, 2016, 6:04 am

≫ Next: Modify continuity on internal bounderies

≪ Previous: how to use two boundary conditions at same boundary

$

0

0

Hello everyone,

I am interested in finding the temperature in a system that changes the density in time and I would like to formulate the energy balance using this variable density.

What I have in mind is to use

Cp * d( rho T)/dt = Q

but I find it pretty tricky to implement it in COMSOL, because of the derivative. Does anyone have any experience with this?

Nomenclature: Cp is the specific heat, rho is the density (rho = f(t)), T is the temperature and Q is the heat source in W/m3, which can be any number (just for reference)]

Modify continuity on internal bounderies

April 27, 2016, 6:34 am

≫ Next: About check the fluid setting

≪ Previous: Energy balance with variable density

$

0

0

Hi everyone,

I have some doubts about how to modify continuity condition on internal boundaries
and I would ask for some help.
I want to solve hydrodynamics on a unit cell of the Taylor flow (known also as
slug flow or bubble-train flow) in a circular millichannel. This unit cell is composed by a
bubble and two liquid half-slugs. I consider that bubble have a fixed shape and
remains immobile.
So, what I want is to solve Navier-Stokes equations into the two subdomains (bubble and liquid)
considering the gas-liquid interface as an internal boundary but establishing a "No
penetration" condition as done by the "slip boundary condition".

Thanks in advance,
Freddy

About check the fluid setting

April 27, 2016, 10:24 pm

≫ Next: Boundary condition

≪ Previous: Modify continuity on internal bounderies

$

0

0

Hello when i calculate the fluid model where and How could i know the Reynolds number and Stokes number?

Boundary condition

April 28, 2016, 3:20 am

≫ Next: Defining a variable limited only for the boundary

≪ Previous: About check the fluid setting

$

0

0

How to impose perfect contact (equal displcaement) between internal boundaries of different surface (resin-mold interface).

Defining a variable limited only for the boundary

April 28, 2016, 7:46 am

≫ Next: cone-jet mode in electrostatic field

≪ Previous: Boundary condition

$

0

0

Can we define a dependent variable for a physics which is only valid for particular boundary and not for the whole domain?

cone-jet mode in electrostatic field

August 30, 2012, 11:13 pm

≫ Next: Form assembly or Form union

≪ Previous: Defining a variable limited only for the boundary

$

0

0

Hi,

Here is my problem.
I want to simulate a electrohydrodynamic (EHD) phenomenone , a nozzle with full water (or electrolyte) in a electrostatic field, the the water is polarized and deformed the Taylor cone,then comes the cone-jet mode. My models include the level set -laminar flow and electrostatic,but still cann't get the cone-jet result.Is there anybody also working on a similar model like mine?Did you get the cone-jet results?

Thank you.

Form assembly or Form union

April 29, 2016, 7:34 pm

≫ Next: Warning: SOR line did not find any lines.

≪ Previous: cone-jet mode in electrostatic field

$

0

0

Dear All,

I encountered a problem when I models fluid flow through conduit surrounded by solids at two sides. The models involves laminar flow module and structure module. According to the description of reference manual, When the contact features are included in structure mechanics, the "form assembly" in geometry is recommended. So I choose the "form assembly" box. However, when I imposed no-slip BC at the interface between solid and liquid domains, and run it, the error occurs.
Undefined variable.
- Variable: comp1.spf.U
- Geometry: geom1
- Domain: 2

Form the attached image, we can see that domain 2 is solid zone, no fluid, whereas the error didn't detect fluid velocity in the soild zone. It seems weird. I try many times to resolve it but failed.

So I am wondering whether the "form assembly" in my model is the criminal. But considering the contact feature in my model (circled region in red line), I am not sure for it.

Does anyone give me some hints or suggestion on that? I will appreciate your assistance.

---

Warning: SOR line did not find any lines.

April 30, 2016, 5:30 pm

≫ Next: How to add a mass source term to NS equation

≪ Previous: Form assembly or Form union

$

0

0

Hi everyone,
I am running a laminar two-phase flow (level set) simulation with a 3D geometry. I had previously simulated the same geometry in 2D with the same initial values and boundary conditions and have no problem reaching a solution. However, when I try to run the simulation with a 3D geometry, the warning "SOR line did not find any lines" keeps coming up and eventually I get error saying
Nonlinear solver did not converge.
Divergence of the linear iterations.
Time : 0
Last time step is not converged.

Has anyone encountered this warning before and know what to do with it? Thanks a lot in advance!

How to add a mass source term to NS equation

May 2, 2016, 6:08 pm

≫ Next: serval questions of heat transfer in my project

≪ Previous: Warning: SOR line did not find any lines.

$

0

0

Hello everyone

I have a problem in adding a mass source term to the NS equation. I use it to account the mass loss due to vaporization during laser melting process. Currently I use the interface moving speed based on mass flux in the moving mesh module. But I'm not sure if it works properly.

Previously in V3, I can easily add the source term to the NS equation in the equation system.
But in the current V5 or V4 COMSOL, I cannot find the equation system, or any method to add a weak contribution to the continuity equation.

Do you have the solution? Thank you very much for your help.

serval questions of heat transfer in my project

May 2, 2016, 11:52 pm

≫ Next: Gas mixture flow simulation

≪ Previous: How to add a mass source term to NS equation

$

0

0

Hello
As the figure shows, I am using the fllowing models
(Heat Transfer>Conjugate Heat Transfer>Laminar Flow
Stationary situation
Surface-to-Surface Radiation), and try to find the temperature distribution of the air and the spheres.
I simplified the original object into two spheres,since its shape was very complex. The latter sphere has a boundary heat source.
I have some questions to solve:
1.Since the object was simplified, so the real convective area was changed, i need to modify the convective heat transfer coefficient, but I can't find the modify interface in comsol.
2.The Surface-to-Surface Radiation was considered, and the model is periodic, so I need to define the periodic boundaries as perfect mirrors (the default insulated conditions are just fine to the convective heat transfer and conduction heat transfer)， but I can't find the interface in comsol,too.
3. Since the original object was simplified into two spheres, so the heat conduction was incorrect，because the spheres are not contacted.I want to find the ht.gardT between the spheres and use the Fourier's law of heat conduction to define extra heat source on spheres, is it right?
thank you

Gas mixture flow simulation

May 3, 2016, 3:20 am

≫ Next: Matrix has zero on diagonal

≪ Previous: serval questions of heat transfer in my project

$

0

0

Hi everybody,

Gas 1 is flowing in my geometry (a round pipe) and I want to inject gas 2 into the flow.

My idea was to assign both gases to the same geometry (using pipe flow module twice) and then use the transport of concentrated species module to adjust the molar fraction of gases in a way to tell COMSOL that initially there was just gas 1 and then an x molar fraction of gas 2 is injected into the flow.

My question is: Is this a right way to deal with the problem and how to tell COMSOL to assign different materials (gas 1 or gas 2) to the same domain dependent on the physics?

Thanks.

Matrix has zero on diagonal

May 3, 2016, 10:29 am

≫ Next: Non-isothermal pipe flow (nipfl)

≪ Previous: Gas mixture flow simulation

$

0

0

I have to solve a lid driven cavity (laminar flow) + melting problem (heat transfer in fluids and solids with moving mesh). I was able to successfully implement this in 2D.

I have now shifted to a 3D model, still solving the same physics. I get an distinct ( i haven't encountered this previously) error message which I’m unable to understand :
Failed to find a solution for the initial parameter.
Matrix has zero on diagonal for the SSOR update submatrix in the Vanka algorithm.
Returned solution is not converged.

In the Comsol reference manual, explanation for matrix equation for vanka algorithm is attached in the picture

Is the diagonal element (Sj) = 0? This S corresponds to the average values of the velocity vectors?
My initial condition is set to zero.

I have also attached my model file.

Kindly help