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Simple Non-Isothermal Pipe Flow Loop - Singular Matrix Error
Posted Sep 16, 2015, 5:15 p.m. EDT Fluid & Heat Version 4.4 1 Reply
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Hello friends,
I am a new COMSOL user, and I have a problem with a simple model. I am modeling a pipe in a steady state, closed loop. It is a 20cm diameter pipe with water flowing at 1 m/s forced by a pump at 31 kg/s. I am using the "Non-Isothermal Pipe Flow" module. I am using this specific module because I will add some transient heating physics later.
I cannot even get the stationary, unheated solution however. I get the familiar "Failed to find a solution. Singular matrix" error. I've read that error can be caused by too coarse a mesh or a poor initial guess. There are plenty of nodes in this simple geometry, and the initial conditions are very close to the analytical solution. There must something obvious I am missing because I am a new user.
Would anyone be willing to look my very simple model (attached) and educate me? Thank you for your time.
-Andrew
I am a new COMSOL user, and I have a problem with a simple model. I am modeling a pipe in a steady state, closed loop. It is a 20cm diameter pipe with water flowing at 1 m/s forced by a pump at 31 kg/s. I am using the "Non-Isothermal Pipe Flow" module. I am using this specific module because I will add some transient heating physics later.
I cannot even get the stationary, unheated solution however. I get the familiar "Failed to find a solution. Singular matrix" error. I've read that error can be caused by too coarse a mesh or a poor initial guess. There are plenty of nodes in this simple geometry, and the initial conditions are very close to the analytical solution. There must something obvious I am missing because I am a new user.
Would anyone be willing to look my very simple model (attached) and educate me? Thank you for your time.
-Andrew
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1 Reply Last Post Sep 25, 2015, 8:59 a.m. EDT
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Posted:
9 years ago
Dear Andrew,
Often singular matrix issues are caused due to your model being underconstrained. In your model, you do not prescribe the pressure nor the temperature anywhere.
When you add a pressure point constraint on 1 of your points, and add "wall heat transfer" on all your pipes, your model converges easily.
Best regards,
Frank
Often singular matrix issues are caused due to your model being underconstrained. In your model, you do not prescribe the pressure nor the temperature anywhere.
When you add a pressure point constraint on 1 of your points, and add "wall heat transfer" on all your pipes, your model converges easily.
Best regards,
Frank
Attachments: