- How to select discretization scheme in comsol 5.3 how to#
- How to select discretization scheme in comsol 5.3 full#
The convergence of energy equation slows down significantly.
![how to select discretization scheme in comsol 5.3 how to select discretization scheme in comsol 5.3](https://cdn.comsol.com/release/53/studies-and-solvers/bem-oil-rig.jpg)
Have the interfaces of porous and fluid domains been changed to internal? Has a monitor for heat transfer through all walls been created? Do not include inlets and outlets. In FLUENT, have contour plots been created? This helps avoid repeating the process while setting up different cases with same geometry. Has the monitor points been created for global mass imbalance? Has the discretization schemes set to first order for initial 500 ~ 1000 iterations? Gradually move to second order. Has the convergence criteria been set to low value such as 1e-05 or lesser? Run may stop early if set to higher number such as 1e-3. Has the relaxation factors for k, ε and turbulent viscosity been reduced to value lower than 1.0 say 0.25 or 0.50?
How to select discretization scheme in comsol 5.3 full#
Has the auto-save frequency and file name correctly defined? For runs on clusters, specify only file name without full path.įor transient simulations, have the specific heat capacity and density of solids been correctly assigned? Has the density, viscosity and thermal conductivity of fluid been correctly assigned as per operating temperature and pressure? Has the basic checks been made: scale of mesh, quality, default interfaces settings (CFX may create unwanted interfaces)? Compressible flows are characterized by Mach number of the flow whereas compressible behaviour of fluid refers to equation of state such as ideal gas law, essential change in density due to change in pressure and temperature.Ĭhecklist of Solver Settings including Boundary Conditions No. Note that the "compressible flows" and "compressible gas" are not the same concepts. The density at each cell is calculated from equation of state (ideal gas law or real gas laws like Redlich-Kwong and IAPWS equation of state for steam). Note the the field variables solved during CFD simulation are velocity vector, pressure, temperature (enthalpy). Here stability refers to the property when errors caused by small perturbations in numerical method remains bound. The purpose of all these settings is to get a numerical scheme which is consistent, stable and convergent.
How to select discretization scheme in comsol 5.3 how to#
This section deals with solution controls for solvers including topics like CFL Number, Time-step for Transient Simulations, Psuedo-time Marching, Parallel Computing, Nodes and Cluster, HPC - High Performance Computing, Threading, Partitioning, MPI - Message Passing Interface and Scalability.Īny program does only one thing: "Solves exactly what one tells it to solve and how to solve, nothing else!" Solver settingThis activity of a CFD simulatin process involves selection of solver type (pressure-based or density-based, stead-state or transient), selection of, gravity ON/OFF, creation of monitor points and monitor planes. If you want to be able to predict these effects, you have to know your scheme.Solver Setting Type of Solvers and Solution Control Parameters As far as I know, only the Crank-Nicolson scheme and Gauss-collocation methods preserve the essential dynamics, but even for those, certain features of your solution may be amplified or suppressed in an unphysical way, if your timestep is too large. The terms used to categorize the dynamics of timestepping schemes are A-, L-, and B-stability. I know of simulations where a single backward Euler step every 100 Crank-Nicolson steps made an oscillatory solution stationary. And the opposite holds: if you use a method that is too stable, turbulent, instationary flow might be turned into honey. And this goes both ways: a perfectly stable solution can be converted to an explosion if you use the wrong method with a large timestep. This question goes beyond explicit or implicit. Unfortunately, most timestepping schemes also change the dynamics of your system, which is usually subsumed under the term stability.
![how to select discretization scheme in comsol 5.3 how to select discretization scheme in comsol 5.3](https://www.mdpi.com/minerals/minerals-11-00452/article_deploy/html/images/minerals-11-00452-g004.png)
That would be a good balance for accuracy. You want to choose your time step such that this error is balanced with a comparable error of the space discretization. There are two factors that are influenced by time step size and the choice of scheme: accuracy and stability.Īccuracy is typically measured by the "local error" or "consistency error" of the scheme.