[Mrsimple]

Hello there thank you for looking at this thread, I am trying out certain operations in StarCCM+ and I had faced problems while doing so. I would like to reach out to the community for opinions thus any type of inputs are most welcome!

My purpose is to model a subsea pipeline where natural convection taking place. Thus I have drawn a simple tube which is hollow and could find the pressure and temperature profile of the pipe. Ambient environment is the seawater around it which is around 2deg Celsius.

SolidWorks:
In this domain I had created a pipe and assigned a material with 7850kg/m3 density, exported it as parasolid and exported over to StarCCM+

Pipe:


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StarCCM+:

I had prepared the surface mesh as follows



And also: Physics model



When I expanded out the Eularian multiphase and enter the phases I had chosen PHASE 1 to be Methane Gas: CH4 and the conditions are as follows



I proceeded to input Phase 2 information with 3 multicomponent liquids namely. H2O (Water) , C5H12, C6H14.



I wanted to try to enter the surface tension into the analysis according to 24dyne/cm hence it came out is 0.024 N/m



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After assigning the Mesh Models, I proceeded to assign it to regions. Firstly I split the model into "Split by Patch" into 3 main regions, Wall, inlet and outlet



Inlet was assigned to Velocity Input
Outlet: Pressure Outlet
Wall: Wall
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Problem:

I am not too sure whether to do it by mesh operations and fill holes to extract volume as a single component

The simulation was unable to run and I faced a problem of sum of mass fraction is zero on [ Region 1 ]. Thus I had adjusted the species mass fraction however unable to solve it.



Sorry for the long post, please advice!!

[kguntur]

Hi,

Could you be a little more specific about your problem?
As I understand, you have a pipe (of certain material and thickness) surrounded by seawater. There is hot gas (flowing?) inside the pipe. And you want to see the temperature change in the pipe/gas. Am I correct?
If not, please give a simple problem statement telling what your boundary conditions are and the physics that is actually occurring.

[Mrsimple]

Thank you for replying kgunur, despite it being a lengthy post. I am very new to this and also unsure if the procedure of the flow modelling is appropriate due to my limited expertise in Solidworks. I simply created a model and exported into StarCCM+

I wish to deal with multiphase flow within the pipeline and the fluids inside are supposed to be around 55 degrees celsius together with the pressure drop along the pipeline. However I am unable to complete the simulation and I am facing the error of

A floating point exception has occured: Floating point exception [ invalid operation]. The specific cause cannot be identified. Please refer to troubleshotting section of the User's Guide. Context: star.segregatedflow.segregatedflowsolver

Also, I had trying to extract a volume from a single piece of drawing, the example I had shown was 500m and I wish to extend it to 30kilometers.

Physics Continua:




And the sum of mass fraction is 0, I have tried a few ways to go about it by adjusting the "Species Mass Fraction", "Initial Conditions --> Volume fraction" , "Species Mass Fractions in the region tree" But its not helping it past the error.


Thanks alot! All inputs are welcome!

[kguntur]

for a floating point error, try "Remove invalid cells". That will separate out any bad cells in your mesh.

To extract the volume, you could use surface repair tool in starccm+ and extend it. or you could use your cad program to create a new geometry. Since your geometry is relatively simple, either way is equally easy.

The sum of mass fraction should be 1 in the initial conditions and any boundary conditions other than wall. So look at those areas and make sure the sum is 1.

Another thing, Why are you using Casting model in the physics? Is this a casting problem?

[Mrsimple]

Thank you for you replies! I'm just wondering if extract volume be done by Importing a surface mesh ???? In this scenario will "Surface Remesher" allow me to have volume running inside the empty space of the pipeline ??

Best Regards!

[kguntur]

You can extract volume on imported CAD.

Regarding the rest of the problem, I do not understand what you are trying to achieve. If I can understand that, I may be able to help you better. Can you give a clear problem statement. Not the problem you are facing but what you want to achieve in simple words.
May be a simple schematic would help.

[Mrsimple]

Thank you Kris for being patient, I really appreciate it!

I am investigating the problem of hydrate formation which is a function of pressure and temperature. Thereby at the end of the project I would like to obtain a graph with Pressure Vs Temperature relationship.

The pressure losses were mathematically exhausting for Multiphase Flows if solved by hand hence I decided to use CFD software to carry out my investigation. So probably I need some sort of pressure decrease along the pipeline, probably through pipe losses.

Also the temperature I'm expecting to get is the natural convection problem between the ambient temperature with the fluid in it. I was perturbed by the input of values which explains the need for a wall to be present. And a long pipeline which extends out tens kilometers is kind of difficult to present.

With all these challenges I have, I decided to come here and share and hopefully to achieve some solutions.

I hope this helps in explaining a little! Once again thank you for your time!!

For the schematic , it is just a simple horizontal pipeline

Best Wishes

[kguntur]

Ok. That explains it a little better and here is what I think you could do.

1. You need three regions.
the fluid inside the pipe
the solid wall of the pipe
the ambient conditions (sea water)
2. Create an interface between 1&2 and 2&3. this will transfer information (in this case the heat transfer) between the regions.
3. As you mentioned, modelling 10s of kilometer is not practical. You could model a sample length of the pipe and then extrapolate your results.
4. your physics would include the Eularian multiphase, with all the phases. This will be for the fluid inside your pipe
5. There will be a simple physics with solid as the material for the pipe wall
6. And one more physics for the sea water. (single phase would do).
7. Since you are modeling natural convection, make sure you use anything other than constant density and turn on gravity.

That being said, another thought: think if you really need all the phases in the inside fluid. Can't you use a single phase fluid with some appropriate properties, predict your pressure and temperature, and use them to calculate what ever that you need to calculate.

Hope this helps !!

[Nabeel.E]

hi
I am doing the same things I think

my research is about vibration during flow for straight sub-sea pipeline. the pipe is made of steel coated by cement. If you guys have any suggestion or idea about this please let me know bcz I am still facing many problems regarding of the effects of seawater.