# How do I simulate a mass flux into a closed subdomain in time-dependent mode?

4 messages
Open this post in threaded view
|

## How do I simulate a mass flux into a closed subdomain in time-dependent mode?

 I would like to simulate an injector pumping gas at a certain ρ into a box and watch the resulting pressure rise over time. I was unable to find any examples (with time-dependency) in the documentation and keep getting the following error: "High-order time stepping schemes not supported with integral constraints." Any help you could lend would be greatly appreciated. Thanks
Open this post in threaded view
|

## Re: How do I simulate a mass flux into a closed subdomain in time-dependent mode?

 Administrator jerrodbouchard wrote I was unable to find any examples (with time-dependency) in the documentation Although probably not directly related to your application, there are several tutorials involving time-dependency, for example:   Quickstart > Wave Equation on a Circle  Heat Transfer > Transient Heat Diffusion in a Rod  Heat Transfer > Shrink Fitting of an Assembly  Fluid Dynamics > Vortex Flow  Multiphysics > Heat Induced Stress in a Brake Disc  Multiphysics > Thermo-Mechanical Bending of a Beam  Multiphysics > Fluid-Structure Interaction - Elastic Beam  Multiphysics > Electro-Osmotic Flow  Classic PDE > Shallow Water Equations jerrodbouchard wrote  and keep getting the following error: "High-order time stepping schemes not supported with integral constraints." Any help you could lend would be greatly appreciated. Without really knowing any details about your model it is hard to say, but I suspect you have set up a model with the Navier-Stokes equations without an outflow. In this case a integral pressure constraint (the integral of the pressure over the domain is zero) is added implicitly in order to mathematically ensure a well posed problem (define a unique pressure). As the error message indicates, such an integral constraint does not work with higher order time-discretization/stepping schemes, and a solution would be to select a low order/1st order time stepping scheme (such as Backward-Euler) in the solver settings. Alternatively, you can avoid having to use a pressure integral constraint by fixing the pressure with a point constraint at at least one point. That said, if you are using the Navier-Stokes they are only valid for incompressible fluids, and as such would probably not apply to the problem you're investigating. But then again, I'm not sure what you have modeled exactly.