## Fluids

#### Oscillatory Shear Index Calculation

• carlos11194
Subscriber

Hello everyone I am trying to obtain an contour with the variable of the Oscillatory Shear Index Calculation is shown below, as it is presented in some articles of aneurysm growth, now I am working with real geometries obtained by angiographies, someone can guide me, in the way to enter the equations in a transient simulation in cfd or fluent. here T denotes the period of the cardiac cycle.

• Karthik R

Hello,

You can code these variables in a UDF and store them in what is called User Defined Memory (UDM). Fluent will calculate these variables using the equations and store the values in the User Defined Memory locations. For more help, please refer to the Fluent Users, Theory, and Customization manuals.

Thank you.

Best Regards,

Karthik

• carlos11194
Subscriber

Thank you very much, I'm trying to learn a little fluent, I'm currently trying to solve it is cfx by entering this formula that they mention is equivalent to entering the OSI: AA = ((Wall Shear X) ^ 2 + (Wall Shear Y) ^ 2 + (Wall Shear Z) ^ 2) ^ 0.5 OSI = 0.5 * (1 - ((((Wall Shear X.Trnavg) ^ 2 + (Wall Shear Y.Trnavg) ^ 2 + (Wall Shear Z.Trnavg) ^ 2) ^ 0.5) / (AA.Trnavg)) ). I have problems wanting to get AA.Trnavg, it marks me the following unrecognized name was referenced: RR. Trnavvg. Where could you advise me on how to perform this operation? thank you

Ansys Employee

Hi,

Request CFX experts to pitch in here.

Regards,

Keyur

• anmehta
Ansys Employee

Hello ,

In CFX pre , we need to define transient statistic of wall shear variable so that Wall shear.Trnavg (all three directions) will be available in CFD post . Then in CFD post we can write expression as given by you but in single expression .

OSI = 0.5 * (1-((abs((Wall Shear X.Trnavg)+(Wall Shear Y.Trnavg)+(Wall Shear Z.Trnavg)))/((abs(Wall Shear X.Trnavg))+(abs(Wall Shear Y.Trnavg))+(abs(Wall Shear Z.Trnavg)))))

We can create variable from above expression and use for plotting .

In your case , you have used another expression to define AA as denominator part . But CFD post doesnt have variable as AA.Trnavg as that quantity is not part of transient statistic.

I hope this will solve your problem .

Regards,

Anup Mehta

• Noushin
Subscriber
@anmehta

Dear experts, can I use this formula for OSI calculation in CFD?

Thank you.

Sincerely

Noushin Anan

• rupalipandey
Subscriber

I have implemented your method in my calculating OSI. But the problem I am facing that CFD Post is calculating the values of OSI only for the start and end of the cycle while its showing values undefined in the mid of the cycle. Same problem I am facing during plotting. Although I have saved my simulation after every 5 time steps. Please help me to solve this problem and let me know where I am doing a mistake. Hoping to hear from you soon.

• Mai_Elzayat
Subscriber
i am trying to do the same code nif there is any possibility to send me any examples of the code , pls help men