## General Mechanical

#### Leakage or not

• Lovisa Svanborg
Subscriber

Hi!

Have do you define if it leakage in seals with fluid pressure? Does this leak or not?

Contact pressure

Fluid pressure

Regards Lovisa

• John Doyle
Ansys Employee

Try post processing contact status.

• peteroznewman
Subscriber

Hello Lovisa,

You sent me this link to an excellent tutorial on O-rings and fluid pressure.

https://courses.ansys.com/index.php/courses/structural-nonlinearity/lessons/homework-quizzes-simulation-examples-nonlinearity-lesson-4/

You are using the APDL commands to add fluid penetration pressure as described in that tutorial.

In Workbench, using the Contact Tool, I plot Fluid Pressure as you have done.

The tutorial shows which edge to apply the pressure to and where to define the start_pt.

Best regards,  Peter

• Lovisa Svanborg
Subscriber

• Lovisa Svanborg
Subscriber

Thank you both.

Thank you Peter for the explanation.

The starting point

and pressure

• peteroznewman
Subscriber

That may mean you have to slice the O-ring into 4 pieces and have 3/4 of the edge assigned to the Named Selection called pressure.

• peteroznewman
Subscriber

I would like to know if these post-processing commands:

plot the same data as the Fluid Pressure result in the Contact tool in Mechanical.

• Lovisa Svanborg
Subscriber

The different plots show some differnce.

The last one shows maximum fluid pressure for the total area.

Regards Lovisa

• peteroznewman
Subscriber

Yes, the plots look different.  The Workbench plot looks wrong. How can the pressure suddenly change from red to green when there is no contact?  It should be red all the way around the curve since that is where the pressure should be applied. Is there a mistake in the model that causes this plot to look wrong?

The Tutorial model plot looks correct. Red is continuous along the edge until the O-ring makes contact and only then does it begin to turn green and then blue.

• Lovisa Svanborg
Subscriber

I see! I will try to change presure to around the whole seal and start point down corner instead. I not sure about the problem.

• peteroznewman
Subscriber

Please read the ANSYS Help description of the algorithm used in Fluid Pressure.

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v222/en/ans_ctec/ctecfluidpress.html

Fluid pressure along normal and tangential directions can penetrate into the contact interface from one or multiple locations. The fluid pressure-penetration load has a path-dependent nature. The penetrating path can propagate and vary, and it is determined iteratively. At the beginning of each iteration, the program first detects starting points which are exposed to the fluid pressure. Among the starting points, the program then finds fluid penetrating points where the contact status is open or lost, or where the contact pressure is smaller than the user-defined pressure-penetration criterion. When a contact detection point has a contact condition of “penetrating,” it is subjected to the fluid pressure, and its nearest neighboring nodes are considered to be the starting points which are exposed to the fluid pressure as well.

The fluid pressure is not applied to an area having a contact status of open unless the edges/ends of the area belong to the starting points.

After reading the above, it seems that choosing a point on the bottom of the O-ring is a better choice.