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Hi, Ivar Kjelberg please help

Posted 10 déc. 2011, 07:36 UTC−5 Version 5.1 6 Replies

Navin Verma
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Hi,

I am trying to design a model, in which I am supposed to see a animation showing effect on water flow due to rotation of a propeller.
Propeller is on the surface of flowing water. when it will rotate, then flow of water will also get affected.
I have working on the model for 2 months. I couldn't still know that what model should I use. I am very confused among moving mesh, fluid structure interaction and structure mechanics etc.

Basic problem is how to rotate any body about a point or axis in COMSOL 3.5a?
What model should I use to see the effect on fluid?


If you can solve in COMSOL 3.5a, please attach file.
Would you please answer me, treating as a beginner?
Please reply,
Millions of Thanks..

Regards,
Navin Verma
IIT Bombay,
India
6 Replies Last Post 16 sept. 2015, 10:22 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 10 déc. 2011, 12:43 UTC−5
Hi

Sorry but I cannot solve that like that for you, first of all it's not a trivial task, It would also take me a week or more, then I do not have 3.5a working any longer, it's really getting too old for me.
However, there are the propeller example of a rotating air blower. If I remember right it uses an assembly mode of two overlapping circles to define the rotating region

--
Good luck
Ivar
Hi Sorry but I cannot solve that like that for you, first of all it's not a trivial task, It would also take me a week or more, then I do not have 3.5a working any longer, it's really getting too old for me. However, there are the propeller example of a rotating air blower. If I remember right it uses an assembly mode of two overlapping circles to define the rotating region -- Good luck Ivar
Navin Verma
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Posted: 1 decade ago 10 déc. 2011, 13:00 UTC−5
Thanking you for reply,

Would you just tell with what model should I proceed just for rotating a body?

Regards,
Thanking you for reply, Would you just tell with what model should I proceed just for rotating a body? Regards,
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 11 déc. 2011, 05:19 UTC−5
Hi
I remember there was a model (perhaps its also on the forum, a couple of years ago) in the model library of a rotating fan, I believe it belonged to the chemistry module, as most CFD was then included in that library, but as I do not have 3.5 running I cannot search it out any longer.

--
Good luck
Ivar
Hi I remember there was a model (perhaps its also on the forum, a couple of years ago) in the model library of a rotating fan, I believe it belonged to the chemistry module, as most CFD was then included in that library, but as I do not have 3.5 running I cannot search it out any longer. -- Good luck Ivar
Navin Verma
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Posted: 1 decade ago 18 déc. 2011, 23:29 UTC−5
Hi Ivar,

Extremely thanks for help. I got all things. But I am getting errors.

-Failed to find consistent initial values.
-Last time step is not converged.

How to get rid of these?

Thanking you.
Hi Ivar, Extremely thanks for help. I got all things. But I am getting errors. -Failed to find consistent initial values. -Last time step is not converged. How to get rid of these? Thanking you.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 19 déc. 2011, 01:40 UTC−5
Hi

well as already stated, there can be many errors linked, if you are sure about your BC's (enough, independent, ...) then remains the initial conditions (default = 0, often a "worst case" choice) and for CFD the mesh density w.r.t. local effects. (turbulence is the worst, and neither not "my pot of tea", ther you need other to better help).

One way that might work is to ramp a velocity or pressure gently, but this consumes many time steps and might neither not work.
Another way is to set up a steady state case to get a first flow, then release the time dependent study.
Often when such things happen for me in 3D i go back to 2D because it solves so much quicker, and try to debug therein (i.e. use a 2D projected velocity field into the 3D domain as initial conditions.
If you have diffusion effects, the solution is often along an erfc() function, then setting up a preliminary initial condition with this function could help. Astonishly, there are several of these "standard PDE solution" operators missing from the default list of COMSOL predefined operators, the ERFC() is quickly defined in a analytical function, but then the derivative is often needed, this is also known, so I bleieve COMSOL could use it better internally, so as it's not there one have to define this by hand, and sometimes it's better to knpow what one is doing, no ?



--
Good luck
Ivar
Hi well as already stated, there can be many errors linked, if you are sure about your BC's (enough, independent, ...) then remains the initial conditions (default = 0, often a "worst case" choice) and for CFD the mesh density w.r.t. local effects. (turbulence is the worst, and neither not "my pot of tea", ther you need other to better help). One way that might work is to ramp a velocity or pressure gently, but this consumes many time steps and might neither not work. Another way is to set up a steady state case to get a first flow, then release the time dependent study. Often when such things happen for me in 3D i go back to 2D because it solves so much quicker, and try to debug therein (i.e. use a 2D projected velocity field into the 3D domain as initial conditions. If you have diffusion effects, the solution is often along an erfc() function, then setting up a preliminary initial condition with this function could help. Astonishly, there are several of these "standard PDE solution" operators missing from the default list of COMSOL predefined operators, the ERFC() is quickly defined in a analytical function, but then the derivative is often needed, this is also known, so I bleieve COMSOL could use it better internally, so as it's not there one have to define this by hand, and sometimes it's better to knpow what one is doing, no ? -- Good luck Ivar
Bilal Javed Butt
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Posted: 9 years ago 16 sept. 2015, 10:22 UTC−4
Hi Ivar,
I am compressing rubber gasket (to find Creep) which has very small sensor inside. Top plates are placed between the gasket, bottom plate is stationary, but I am getting error "Failed to find consistent initial values, Last time step is not converged". With one study either stationary or time dependent simulation is working fine but when I am running it with 2 studies and defining value of dependent variable as stationary study in time dependent, in this case I am getting this error.
I have checked mesh as it seems fine but don't know why getting this error. Could you please help me out in this? Simulation is attached.

Would be really thankful to you

Many Greetings,
Bilal Javed
Hi Ivar, I am compressing rubber gasket (to find Creep) which has very small sensor inside. Top plates are placed between the gasket, bottom plate is stationary, but I am getting error "Failed to find consistent initial values, Last time step is not converged". With one study either stationary or time dependent simulation is working fine but when I am running it with 2 studies and defining value of dependent variable as stationary study in time dependent, in this case I am getting this error. I have checked mesh as it seems fine but don't know why getting this error. Could you please help me out in this? Simulation is attached. Would be really thankful to you Many Greetings, Bilal Javed

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