# Auto Solution Strategy

The goal of the Auto Solution Strategy branch is to completely automate the specification of all the solution strategy commands based on the minimum possible parameters defined in this section.

- Analysis Type
- This parameter specifies the type of analysis to be used. There are two types of analysis Steady and Transient.
- Max Time Steps
- This parameter specifies the maximum number of time steps allowed for the run. The run may terminate earlier due to other criteria such as convergence. If this parameter is zero, this option is ignored.
- Final Time
- This parameter is active only with Transient analysis type and specifies the final time of the run. The run will terminate when the analysis time reaches the final time. The run may terminate due to other criteria. If this parameter is zero, this option is ignored.
- Initial Time Increment
- This parameter specifies the initial value of the time increment for auto time increment or the constant value of the time increment for a fixed time increment. The solution of the simulation advances at this time increment. If zero, this parameter is set according to a CFL = 1 condition.
- Auto Time Increment
- This parameter is used only with Transient and specifies whether or not to automatically control the time increment. If on, AcuSolve determines the time increment depending on the rate of convergence.
- Min Time Increment
- This parameter specifies minimum time increment when using the auto time increment option. If zero, it is reset at the beginning of each time step so that the maximum CFL number is one.
- Max Time Increment
- This parameter specifies the maximum time increment when using the auto time increment option. If zero, this option is ignored.
- Convergence Tolerance
- This parameter specifies the tolerance value for residuals and the solution is assumed to be converged once all of the residuals of all parameters, such as velocity, pressure, eddy viscosity and temperature, measured is less than this convergence tolerance. The smaller the convergence tolerance the more accurate the solution is, but there is larger simulation time.
- Min. Stagger Iterations
- This parameter is active only with Transient analysis and specifies the minimum number of stagger iterations, that is, the minimum number of times an equation, like flow, turbulence equation, has to be iterated before advancing to the next time step. If zero, AcuSolve sets this parameter to two when Auto time increment is off and a value of four when Auto time increment is on.
- Max. Stagger Iterations
- This parameter is active only with Transient analysis and specifies the maximum number of stagger iterations to be performed before advancing to the next time step. If zero, AcuSolve sets this parameter to two when Auto time increment is off and a value of four when Auto time increment is on.
- Num. Krylov Vectors
- AcuSolve uses GMRES (Generalised Minimal Residuals), BiCGStab (BiConjugate Gradient Stabilized) and CG (Conjugate Gradient) algorithms as linear equation solvers. Both GMRES and BiCGStab algorithms require a set Krylov vectors, whose sizes are defined by this parameter Num. Krylov vectors. Larger vectors typically increase the robustness and the rate of convergence of the algorithm, but require more memory. For simple problems the Krylov vectors of 10 is sufficient. For harder problems a larger number of Krylov vectors should be used.
- Relaxation Factor
- This parameter is used to smooth the solution convergence for hard problems. Increasing the relaxation factor smoothens the solution convergence. If zero, this parameter is ignored.
- Flow
- This parameter specifies whether or not to solve the flow equations. This parameter is set to on if the flow equations are to be solved in the simulation and set to off if the solution from flow equations is not desired.
- Temperature
- This parameter specifies whether or not to solve the temperature equations. This parameter is set to on if the temperature equations are to be solved in the simulation and set to off if the solution from temperature equations is not desired.
- Temperature Flow
- This parameter is active only when both Flow and Temperature are on and specifies whether or not to solve thermal-flow problems fully coupled. To solve a thermal-flow problems with a fully-coupled strategy Temperature flow is set to on, otherwise these problems are solved with a staggered strategy. The choice generally depends on degree of coupling (that is buoyancy) between the momentum and thermal equations. A forced convection problem can be solved staggered, while a free convection problem usually benefits form the more expensive coupled approach.
- Enclosure Radiation
- This parameter specifies whether or not to solve the radiation equations. This parameter is set to on if the radiation equations are to be solved in the simulation and set to off if the solution from radiation equations is not desired.
- Species 1
- This parameter specifies whether or not to solve the corresponding species equation. Depending on the number of species specified under the Num. species parameter in Problem Description all of the species can be individually provided whether or not to solve the species equation.
- Turbulence
- This parameter specifies whether or not to solve the turbulence equations. This parameter is set to on if the turbulence equations are to be solved in the simulation and set to off if the solution from turbulence equations is not desired.
- Mesh
- This parameter specifies whether or not to solve the mesh equations. This parameter is set to on if the mesh equations are to be solved in the simulation and set to off if the solution is not affected by mesh displacement.
- Viscoelastic
- This parameter specifies whether or not to solve the viscoelastic stress equations. This parameter is set to on if the viscoelastic stresses are to be solved in the simulation and set to off if the solution is not affected by viscoelastic stresses.
- External Code
- This parameter specifies whether or not to solve solid/structural equations with external code.
- Particle Trace
- This parameter specifies whether or not to solve the particle equations in a coupled particle-flow interaction using AcuTrace.