Discussion Forum

COMSOL offers numerous ways to provide time-varying boundary conditions depending on how your conditions are defined.

Functions are most common. If your condition is an analytical equation, then an Analytic Function is easiest, allowing use of the time variable t as a parameter. If your condition is described by a set of points over time, then an Interpolation Function would be ideal. If it is a common time-varying waveform, COMSOL has numerous functions for that already built in, e.g. sine wave. Then use the function for the boundary condition, e.g. fun1(t).

You can combine different function types using Piecewise Functions. Repeating functions can be implemented by specifying only a single cycle and using the mod function on the time (make sure start and end values are same to avoid discontinuities).

You can also use functions from Matlab if complex. Another option is to use an ODE or PDE to create your boundary condition if applicable. I have used the Poisson equation on a non-planar boundary to generate a parabolic flow profile, scaled it with an interpolation function based on time, and used it on a boundary.

If you provide more specifics on your boundary, boundary condition and how it varies over time, I may be able to give more specific advice.

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Steven Conrad, MD PhD
LSU Health

Thanks a lot steven sir for replying,
Actually i am working on blood flow simulation and want to check the interaction of blood with the artery (a FSI study) and i am using COMSOL as a tool and trying to learning it
Initially i am trying it with a straight pipe so i can understand how software works. then i will move on to constrained pipe.
I am just trying to input WOMERSLEY No, as a input . i also want to input the variable pressure rate in the CCA (common carotid artery) , just like input pressure coming from heart then want to analyse the results.

Please help me to propagate my problem to solution. if you have any file or tutorial regarding to my learning the software in interaction of blood with artery then please share.

With regards
Abhishek

The following model from the application library may help you set up your FSI model:

www.comsol.com/model/fluid-structure-interaction-in-a-network-of-blood-vessels-660

You may elect to leave out the cardiac muscle domain for your initial studies.

The easiest way to simulate the inlet pressure waveform is to digitize one from an image, put the values of time and pressure into an Interpolation Function in COMSOL, and use that function as your inlet pressure, e.g. inlet_fun(t). Alternatively, I've seen a number of publications that describe ways to generate a simulated arterial pressure waveform, but don't have any of them available at the moment.

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Steven Conrad, MD PhD
LSU Health

Thank you sir for your valuable guidance,
I am now able to understand some basics of software.
Again i need your help, I am now going for some experimental part, Actually i needed a synthetic model aorta valve whose mechanical properties are similar to aorta valve that could be feasible for experimentation purpose.
Before going to real one i wanna go for synthetic part. please suggest me the synthetic aorta value that could also available me easily.

I don't know where to get a synthetic model valve. Abiomed once marketed a ventricular assist device with synthetic valves, but it is no longer available. Your best option will be to get an animal valve, if that is possible at your institution.

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Steven Conrad, MD PhD
LSU Health

Although I do not know much about the subject you mentioned. But it sounds like a really amazing one. Wish you can make it! Looking forward!