I am doing my project with Abaqus ​​​​​​​and I need to use fluid cavity capability of this software. This option considers a steady pressure of fluid inside a container and calculate pressure and volume changes during the simulation. Just like the simulation of a Tennis racket and ball. 

I have searched a lot about this option. All the examples in the software documentations and internet are in dynamic situation. However, my simulation is static. Abaqus said this option could be used in both static and dynamic simulations and the settings seem do not depend on the type of simulation.  My problem is that:

I am using fluid cavity capability for simulation of a water-filled container with Abaqus-Static-Standard. According to the realistic condition of the model, the container surface should be meshed with Membrane element.  

The container has an initial pressure and Part of its wall is been surrounded by another solid layer (C3D8H element) with UMAT Material property. Its lid is free to move while the bottom and other parts of wall is fixed.

I need to simulate the reaction of outer layer according to the inside pressure of the container. However, inside pressure of the container fall to zero at the first increments and simulation continue with zero pressure! I am sure that defined fluid cavity is completely closed, as there is no “Not enclosed” warning in *.dat file.

If someone can help, I'll be very grateful.