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How to change a dimensioned model to a dimensionless model
Posted Jun 3, 2023, 10:44 a.m. EDT Modeling Workflow Version 5.6 2 Replies
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If l want to change a dimensionless model to dimensionless, what needs to be modified, is it necessary to reduce the value of the model parameters and physical parameters to dimensionless, and then select the unit as none, or simply modify the unit to none?
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Hi Tao Zhou, If you question is to change a "with dimension" towards a dimensionless model : changing the unit is not strictly necessary, although it is recommended as it is best practices. Changing the unit to None is the way to go, you need to do this everywhere it applies. If you do not do it, for instance with incompressible Navier-Stokes, adjust density rho = 1, and viscosity eta = 1/Re (Re = Reynolds number, that you can define in Parameter), you'll get a warning with orange color saying the units are incorrect, but that won't prevent the solution to run smoothly. Of course the geometry and time scales need to be consistent. You want to use 1[m] as you scaling in space, for instance, instead of your real geometry scale. All this is dependent on how you defined your non-dimensional scalings. Hope this helps, Best regards, Eric Favre
-------------------Eric Favre
Renaissance Fusion
Please login with a confirmed email address before reporting spam
Hi Tao Zhou, If you question is to change a "with dimension" towards a dimensionless model : changing the unit is not strictly necessary, although it is recommended as it is best practices. Changing the unit to None is the way to go, you need to do this everywhere it applies. If you do not do it, for instance with incompressible Navier-Stokes, adjust density rho = 1, and viscosity eta = 1/Re (Re = Reynolds number, that you can define in Parameter), you'll get a warning with orange color saying the units are incorrect, but that won't prevent the solution to run smoothly. Of course the geometry and time scales need to be consistent. You want to use 1[m] as you scaling in space, for instance, instead of your real geometry scale. All this is dependent on how you defined your non-dimensional scalings. Hope this helps, Best regards, Eric Favre
Hi Eric Favre. Thank you very much! Your suggestions are useful. How to change a dimensioned model to a dimensionless model? Because the model turns out to be dimensional, the control equation is also dimensional, and I made the control equation dimensionless according to the reference parameters, but how to couple it to the comsol software. How to make the control equations of physics dimensionless. My understanding is that the control equation is dimensionless in order to substitute dimensionless parameters, is that right?