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 timedependency) in the documentation and keep getting the following error:
"Highorder time stepping schemes not supported with integral constraints." Any help you could lend would be greatly appreciated. Thanks 
Administrator

Although probably not directly related to your application, there are several tutorials involving timedependency, 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 > ThermoMechanical Bending of a Beam Multiphysics > FluidStructure Interaction  Elastic Beam Multiphysics > ElectroOsmotic Flow Classic PDE > Shallow Water Equations Without really knowing any details about your model it is hard to say, but I suspect you have set up a model with the NavierStokes 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 timediscretization/stepping schemes, and a solution would be to select a low order/1st order time stepping scheme (such as BackwardEuler) 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 NavierStokes 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. 
Thank you very much for the reply.
I started with a “pressure vessel” defined as a 2D unit square (1m x 1m) with boundaries labeled as 1 [bottom], 2 [right], 3 [top], 4 [left]. I assigned the physics mode as NavierStokes and I assigned the domain as initially filled with air at ambient conditions (277 degrees K, 101325 Pa, and Gas Constant 287 J/Kg*K). I’ve entered rho as ideal gas law (p/(R*T)), miu just as fixed 17.34e6 Pa*s, and Fy as gy*(p/(R*T)). I defined R in the model constants and expressions tab with the value noted above as well as defined gy as 9.81 m/s2 to account for gravity. I then added the heat transfer physics mode so I can couple the dependent variable T and also coupled u and v. I used specific heat as 1e3 J/Kg*K and used k = 1.4. I assigned T0 as 277K. I left Q as 0 assuming no added heat flux. My goal is to add a mass source to flow additional air into the pressure vessel through a boundary or somewhere in the domain at some m_dot value for X seconds and be able to observe the tank pressurizing as a function of time. How do I assign a mass source and tie into the continuity, momentum, and energy equations in FEATool. In other tools, there is simply an option to assign a mass source/sink and define subsequent parameters. Thanks again for all of your help! 
Administrator

Thank you for explaining your model. Are you sure this is a valid approach to model compressibility. My understanding of the NavierStokes equations is that it would only be valid for very weakly compressible fluids with modifications such as the Boussinesq equations (for modeling buoyancy effects)? In other cases the fully compressible equations would be more suitable? 
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