tdynreference manual


Problem Data

Problem data refers to all the information required for performing the analysis and it does not concern any particular geometrical entity. This differs from the previous definitions of conditions and materials properties, which are assigned to different entities. Some examples of general problem data are the type of solution algorithm used by the solver, the value of the time step, convergence conditions and so on.

Problem data is separated in three different groups:

·        Problem

·        Solver

·        Units

Problem

This group of data refers to all the information required to define the problem to be analysed and it does not concern any particular geometrical entity. Some examples of general problem data are:  problems or variables to be solved, the value of the time step, turbulence model to be used, etc.

Options available in Problem tag

 

Solve Fluid: Select Yes to solve any fluid problem. If you select No, fluid domains in the solution of the problem will be ignored.

Remarks:

Option only available in RANSOL module. It is necessary to select Yes in this option to solve the Navier Stokes problem.

Solve Temperature in Fluid: Select Yes to solve a temperature problem in fluid. . If you select No, the temperature problem in fluid domains will be ignored in the solution process.

Remarks:

Option only available in HEATRANS module.

Solve Compressibility in Fluid: Select Yes to take into account compressibility effects in fluid. If you select No, the compressibility effects in fluid domains will be ignored in the solution process.

Remarks:

Only slightly compressible fluids can be simulated with Tdyn. See Compressibility field in Fluid Material section for further information.

Solve Species Advection in Fluid: Select Yes to solve a species advection problem in fluid. .. If you select No, the species advection problem in fluid domains will be ignored in the solution.

Remarks:

Option only available in ADVECT module.

Solve Transpiration in Fluid: Select Yes to solve a transpiration free surface problem in fluid. If you select No, the transpiration free surface problem in fluid domains will be ignored in the solution.

Remarks:

Option only available in NAVAL module of Tdyn 3D.

Solve Solid: Select Yes to solve a solid problem. If you select No, solid domains in the solution of the problem will be ignored. 

Solve Temperature in Solid: Select Yes to solve a temperature problem in solid. If you select No, the temperature problem in solid domains will be ignored in the solution.

Remarks:

Option only available in HEATRANS module.

Law of the Wall: Select New to use the improved implementation of the Law of the Wall (version 4.0 or higher). If Old is selected the standard implementation will be used.

Options available in General tag

Number of Steps: Number of steps of the simulation. Total physical time to be simulated will be Number of Steps x Time increment. Recommended value to achieve steady state is:

where NOS is the Number of Steps, dt is the time increment and V, LD, characteristics velocity and length.

Time Increment: Time step of the simulation. Total physical time to be simulated will be Number of Steps x Time increment. The recommended value is:

where dt is the Time Increment,V, LD, characteristics velocity and length and 0.1 < C < 0.01.

For transient solutions a value of dt calculated as 1/10 to 1/100 of the period or characteristic time of the problem is usually more appropriate.

Time increment Units: Units of the time step of the simulation.

Max Iterations: Maximum number of iterations of the non-linear algorithm for solution of the problem. Recommended values come from 3 to 10, depending on the value of the convergence norms (see below Solver data).

Remarks:

In some cases the algorithm may not converge in the initial time-steps, due to the start up process, resulting in the appearing of a warning message More than…number…iterations may be necessary. If only the steady state is of interest, this message may be simply ignored, otherwise Max Iterations value should be increased.

Output Step: Each Output Step time steps the results will be written to disk.

Remarks:

This value will control the size of the results file.

Output Start: The results will be written each Output Step time steps after Output Start steps.

Remarks:

This value will control the size of the results file.

Initial Steps: During first Initial Steps some controls are carried out in the algorithm in order to stabilise the problem during the start up process. It is strongly recommended to define Initial Steps » 10% Number of Steps in problems with free surface.

Start Up Control: if activated, during first Initial Steps the start up process is smoothed. This can be done by creating a adequate acceleration in the flow (Speed), by smoothly increasing the time increment (Time) or Both.

Restart: if On, the restart file is used to define the initial data. The Restart file taken will be "ProblemName.flavia.rst". This file is automatically written by Tdyn with the rest of the results.

Options available in Turbulence tag

 

Turbulence Model: Select the turbulence model to be used in the solution of the fluid flow problem.

Laminar: Navier Stokes equations are solved (i.e. Reynolds stress tensor is neglected and therefore only direct simulation of turbulence is done).

Mixing_Length: Basic turbulence model based in the Prandtl [[6]] hypothesis, where the turbulence length scale (L) is given in the ELen Field field.

Smagorinsky: Basic large eddy simulation (LES) turbulence model based on the description done in [[7]]. The implementation includes an eddy viscosity damping in the boundary layer area. See Turbulence modelling section for further information.

Kinetic_Energy: One equation k model for turbulent flows with integration to the wall, where the turbulence length scale (L) is given in the ELen Field field.

K_Energy_Two_Layers: One equation k model for turbulent flows with integration to the wall, where the turbulence length scale (L) is given in the ELen Field field. The implementation of this model includes an eddy viscosity damping in the boundary layer area.

K_E_High_Reynolds: Two-equation k-ε model for turbulent flows. The model implemented is based on the standard formulation with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

K_E_Two_Layers: Two-equation k-ε model for turbulent flows with integration to the wall. This implementation uses the high-Re k-ε model only away from the wall in the fully turbulent region, and the near-wall viscosity affected layer is resolved with a one-equation model involving a length-scale prescription. See Turbulence modelling section for further information.

K_E_Lam_Bremhorst: Two-equation k-ε model for turbulent flows with integration to the wall. The model implemented is based on the description done in [[8]] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

K_E_Launder_Sharma: Two-equation k-ε model for turbulent flows with integration to the wall.  The model implemented is based on the description done by Launder and Sharma [[9]] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

K_Omega: Two equation k-ω model for turbulent flows with integration to the wall.  The model implemented is based on the description done by Wilcox [[10]] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

K_Omega_SST: Two-equation model for turbulent flows with integration to the wall, expressed in terms of a k-ω model formulation.  The k-ω SST shear-stress-transport model combines several desirable elements of standard k-ε and k-ω models. The implementation is based on the description done in [11] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

K_KT: Two-equation k-kτ model for turbulent flows with integration to the wall.  The model implemented is based on the description done by Wilcox [10] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

Spalart_Allmaras: One equation model for turbulent flows with integration to the wall. The implementation is based on the description of the model done in [[11]] with some modifications to be used with different wall boundary conditions. See Turbulence modelling section for further information.

Tvisco Min Ratio: Eddy viscosity ratio with the minimum of initial values of the eddy viscosity, used to calculate the minimum admissible value.

Tvisco Max Ratio: Eddy viscosity ratio with the maximum of initial values of the eddy viscosity, used to calculate the maximum admissible value (> 1.0)..

Kenergy Min Ratio: Eddy kinetic energy (k) ratio with maximum of the initial values of k, used to calculate the minimum admissible value.

Kenergy Max Ratio: Eddy kinetic energy (k) ratio with maximum of the initial values of k, used to calculate the maximum admissible value.

Epsilon Min Ratio: Epsilon (ε) ratio with the maximum of initial values of ε, used to calculate the minimum admissible value.

Epsilon Max Ratio: Epsilon (ε) ratio with the maximum of initial values of ε, used to calculate the maximum admissible value.

Omega Min Ratio: Omega (ω) ratio with the maximum of initial values of ω, used to calculate the minimum admissible value.

Omega Max Ratio: Omega (ω) ratio with the maximum of initial values of ω, used to calculate the maximum admissible value (> 1.0).

K Tau Min Ratio: K Tau () ratio with the maximum of initial values of , used to calculate the minimum admissible value.

K Tau Max Ratio: K Tau () ratio with the maximum of initial values of , used to calculate the maximum admissible value.

Turbulence_Control_Level: Level of turbulence stabilisation control (0 means Off). If unstabilities are found in the eddy viscosity field, refine the mesh when possible, reduce Time_Increment or increase this value. Note that too high values may cause over-diffusive eddy viscosity results. Recommended value is 2.

EddyKEnergy_Production_Limit: Maximum ratio between the Eddy kinetic energy production and reaction term. This limiter may prevent the unrealistic buildup of eddy viscosity in the stagnation region of the bodies. Recommended value is 20.0.

Epsilon_Production_Limit: Maximum ratio between the Epsilon production and reaction term.

Epsilon_Reaction_Limit: Maximum ratio between the Epsilon reaction and production  term.

Omega_Production_Limit: Maximum ratio between the Omega production and reaction term.

Omega_Reaction_Limit: Maximum ratio between the Omega reaction and production  term.

EddyViscoT_Production_Limit: Maximum ratio between the Spallart-Almarax model production and reaction term.

EddyViscoT_Reaction_Limit: Maximum ratio between the Spallart-Almarax model reaction and production  term.

Options available in Write Results Tag

Initial Data: Mark to write in the results file some general data of the preliminary operations.

Velocity: Mark to write velocity field in the results file.

Pressure: Mark to write pressure field in the results file.

Temperature: Mark to write temperature field in the results file.

Temperature Gradient: Mark to write temperature gradient field in the results file.

Species Concentration: Mark to write species concentration field in the results file.

Wave Elevation: Mark to write wave elevation field in the results file.

Wave Elevation Vector: Mark to write wave elevation vector field in the results file.

Density: Mark to write density field field in the results file.

Viscosity: Mark to write viscosity field in the results file.

Compressibility factor: Mark to write compressibility factor field in the results file.

Wall Law Traction: Mark to write wall stress given by the Law of the Wall (if exits) in the results file.

Tau Parameter: Mark to write tau parameter (local Courant number) field in the results file.

Distance: Mark to write distance to bodies field) in the results file. This field is only available for some turbulence models.

Eddy Viscosity: Mark to write eddy viscosity field in the results file.

EddyKin Energy: Mark to write eddy kinetic energy field in the results file.

Epsilon: Mark to write epsilon (turbulence variable) field in the results file.

Omega: Mark to write omega (turbulence variable) field in the results file.

Tau Eddy: Mark to write Tau variable (of K_Tau turbulence model) field in the results file.

UserDefinedF1: Mark to write FluidFunction1 (user defined function field 1 for fluid) in the results file. Results data are calculated and written in IS units in the analysis group USERDEF.

FluidFunction1: Insert the fluid function to be evaluated and written. Results data are written in IS units in the analysis group USERDEF. See Function Syntax section for further information.

UserDefinedF2: Mark to write FluidFunction2 (user defined function field 2 for fluid) in the results file. Results data are calculated and written in IS units in the analysis group USERDEF.

FluidFunction2: Insert the fluid function to be evaluated and written. Results data are written in IS units in the analysis group USERDEF. See Function Syntax section for further information.

UserDefinedS1: Mark to write SolidFunction1 (user defined function field 1 for solid) in the results file. Results data are calculated and written in IS units in the analysis group USERDEF.

SolidFunction1: Insert the solid function to be evaluated and written. Results data are written in IS units in the analysis group USERDEF. See Function Syntax section for further information.

UserDefinedS2: Mark to write SolidFunction2 (user defined function field 2 for solid) in the results file. Results data are calculated and written in IS units in the analysis group USERDEF.

SolidFunction2: Insert the solid function to be evaluated and written. Results data are written in IS units in the analysis group USERDEF. See Function Syntax section for further information.

Options available in Other Tag

Give Gravity: Select Yes if you want to define the gravity vector.

GravityOX: Gravity Vector OX component.

GravityOY: Gravity Vector OY component.

GravityOZ: Gravity Vector OZ component.

Gravity Units: Gravity vector units.

Use Total Pressure: Mark if you want to use total pressure (including fluid-static term) as internal variable in the solution of the fluid flow problem.

Remarks:

In most of the cases the solution of the fluid problem without fluid-static term is the most accurate one.

If this option is selected, please check the correctness of the pressure boundary conditions. These should take into account the fluid-static pressure term.

Give Pressure Origin: Mark if you want to define the origin of the fluid-static pressure term.

Pressure Origin OX: OX component of the total pressure origin.

Pressure Origin OY: OY component of the total pressure origin.

Pressure Origin OZ: OZ component of the total pressure origin.

Pressure Origin Units: Pressure origin units.

Xplane Symmetry in Fluid: Mark if you want to define symmetry planes in the fluid problem, perpendicular to OX axis.

Xplane Symmetry Position: Position of the symmetry planes in the fluid problem, perpendicular to OX axis, given in the units of the geometry.

Yplane Symmetry in Fluid: Mark if you want to define symmetry planes in the fluid problem, perpendicular to OY axis.

Yplane Symmetry Position: Position of the symmetry planes in the fluid problem, perpendicular to OY axis, given in the units of the geometry.

Zplane Symmetry in Fluid: Mark if you want to define symmetry planes in the fluid problem, perpendicular to OZ axis.

Zplane Symmetry Position: Position of the symmetry planes in the fluid problem, perpendicular to OZ axis, given in the units of the geometry.

Wall Law Type: Law of the wall implementation to be used. DepTau implementation corrects the stress to be imposed as boundary condition on the wall, depending of the data given by the user and the law of the wall stress. If FixTau is selected, Tdyn will impose the law of the wall stress as boundary condition (as done in Tdyn 3.5 and below).

Remarks:

DepTau scheme is normally more accurate for small or large y+ values, while FixTau scheme should be used for intermediate values.

Wall_Law_Vfor: If On, when possible law of the wall data will be used to calculate viscous forces. If Off, viscous forces will be evaluated using velocity field.

Solver

This group of data refers to all the information required to define the integration scheme and solver data of the problem to be analysed. Examples of these data are the type of solvers and convergence norms to be used and so on.

Options available in Fluid Solver tag

 

FTime Integration: Time integration scheme used in the solution process of the fluid problem:

Backward Euler: Implicit 1st order scheme.

Crank Nicolson : Implicit 2nd order scheme.

NS_Advect Stabilisation: Order of the FIC advection stabilisation term in the Navier Stokes equations. Three available options are Auto, 4th_Order and 2nd_Order.

Remarks:

The 4th order term increases the accuracy of the solution and is recommended in most of the cases. However in some problems it may cause instabilities.

Auto mode will automatically switch between 4th and 2nd order scheme, depending on the smoothness of the solution.

TB_Advect Stabilisation: Order of the FIC advection stabilisation term in the turbulence equations. Three available options are Auto, 4th_Order and 2nd_Order.

Remarks:

The 4th order term increases the accuracy of the solution and is recommended in most of the cases. However in some problems it may cause instabilities.

Auto mode will automatically switch between 4th and 2nd order scheme, depending on the smoothness of the solution.

TM_Advect Stabilisation: Order of the FIC advection stabilisation term in the temperature equation. Three available options are Auto, 4th_Order and 2nd_Order.

Remarks:

The 4th order term increases the accuracy of the solution and is recommended in most of the cases. However in some problems it may cause instabilities.

Auto mode will automatically switch between 4th and 2nd order scheme, depending on the smoothness of the solution.

AS_Advect Stabilisation: Order of the FIC advection stabilisation term in the transport of species equations. Three available options are Auto, 4th_Order and 2nd_Order.

Remarks:

The 4th order term increases the accuracy of the solution and is recommended in most of the cases. However in some problems it may cause instabilities.

Auto mode will automatically switch between 4th and 2nd order scheme, depending on the smoothness of the solution.

StabTauV MinRatio: Minimum admissible ratio (τ/dt, being dt the time increment) for the stabilisation parameter τ of the velocity solver. It will be also used for temperature and advection of species problems.

Remarks:

Advection stabilisation term is proportional to the parameter τ. In most of the cases, the minimum value of this parameter should not be fixed (i.e. τ/dt = 0.0), otherwise oscillations may appear.

StabTauP MinRatio: Minimum admissible ratio (τ/dt, being dt the time increment) for the stabilisation parameter τ of the pressure solver.

Remarks:

Advection stabilisation term is proportional to the parameter τ. In some cases with very small elements close to the wall, a value greater than 0.0 is required, in order to stabilise the pressure solution.

Fsolver NonSymmetric: Solver type used in the solution of the non-symmetric linear systems of equations.

BiConjugateGradient: Biconjugate gradient solver.

StabBiConjugateGradient:  Stabilised biconjugate gradient solver.

GMRes: Generalised minimum residual solver.

SquaredConjugateGradient: Squared conjugate gradient solver.

Explicit: Jacobi type solver.

NS1 Tolerance: Tolerance used in the solution of the non-symmetric linear systems of equations (see Fsolver NonSymmetric). A value smaller than 1.0·10-6 is recommended.

NS1 MaxIter: Maximum number of iterations of the non-symmetric linear systems of equations (see Fsolver NonSymmetric).

NS1 Preconditioner: Preconditioner used in the solution of the non-symmetric linear systems of equations (Fsolver NonSymmetric).

Remarks:

In some cases using elements with high aspect ratio the diagonal preconditioner may work better than others.

NS1 Kdim: Dimension of internal direct solver used in GMRes solver (see Fsolver NonSymmetric). A value greater than 20 is recommended.

Fsolver Symmetric: Solver type used in the solution of the symmetric linear systems of equations.

BiConjugateGradient: Biconjugate gradient solver.

StabBiConjugateGradient:  Stabilised biconjugate gradient solver.

GMRes: Generalised minimum residual solver.

SquaredConjugateGradient: Squared conjugate gradient solver.

Explicit: Jacobi type solver.

NS2 Tolerance: Tolerance used in the solution of the symmetric linear systems of equations (see Fsolver Symmetric). A value smaller than 1.0·10-6 is recommended.

NS2 MaxIter: Maximum number of iterations of the symmetric linear systems of equations (see Fsolver Symmetric).

NS2 Preconditioner: Preconditioner used in the solution of the symmetric linear systems of equations (see Fsolver Symmetric).

Remarks:

In some cases using elements with high aspect ratio the diagonal preconditioner may work better than others.

NS2 Kdim: Dimension of internal direct solver used in GMRes solver (see Fsolver Symmetric). A value greater than 20 is recommended.

Options available in Solid Solver tag

STime Integration: Time integration scheme used in the solution process of the solid problem:

Backward Euler: Implicit 1st order scheme.

Crank Nicolson : Implicit 2nd order scheme.

Ssolver NonSymmetric: Solver type used in the solution of the symmetric linear systems of equations.

BiConjugateGradient: Biconjugate gradient solver.

StabBiConjugateGradient:  Stabilised biconjugate gradient solver.

GMRes: Generalised minimum residual solver.

SquaredConjugateGradient: Squared conjugate gradient solver.

Explicit: Jacobi type solver.

S Tolerance: Tolerance used in the solution of the symmetric linear systems of equations (see Ssolver Symmetric). A value smaller than 1.0·10-6 is recommended.

S MaxIter: Maximum number of iterations of the symmetric linear systems of equations (see Ssolver Symmetric).

S Preconditioner: Preconditioner used in the solution of the symmetric linear systems of equations (see Ssolver Symmetric).

Remarks:

In some cases using elements with high aspect ratio the diagonal preconditioner may work better than others.

S Kdim: Dimension of internal direct solver used in GMRes solver (see Ssolver Symmetric). A value greater than 20 is recommended.

Options available in Convergence Norms tag

Velocity Norm: Velocity Euclidean norm used to check convergence in the non-linear iteration loop.

Pressure Norm: Pressure Euclidean norm used to check convergence in the non-linear iteration loop.

Temperature Norm: Temperature Euclidean norm used to check convergence in the non-linear iteration loop.

Concentration Norm: Concentration Euclidean norm used to check convergence in the non-linear iteration loop.

Advection Norm: Euclidean convergence norm of the velocity, used for recalculating or not advective terms. A value smaller than 1.0·10-5 is recommended.

Steady State Norm: Euclidean norm used to detect the steady state. If each variable increment is smaller than this norm, the problem is stopped and results are written to the disk.

Units

This group of data refers to all the general units required to identify general and boundary conditions data of the problem.

Options available in OutPut Units tag

Output Length Units: Length units used in the output data (written in the results file).

Output Mass Units: Mass units used in the output data (written in the results file).

Output Time Units: Time units used in the output data (written in the results file).

Options available in Geometry Units tag

Geometry Units: Length units used in the geometrical definition of the problem.

Options available in Boundary Units tag

Boundary Length Units: Length units used in the definition of the boundary conditions of the problem.

Boundary Mass Units: Mass units used in the definition of the boundary conditions of the problem.

Boundary Time Units: Time units used in the definition of the boundary conditions of the problem.

Boundary Velocity Units: Velocity units used in the definition of the boundary conditions of the problem.

Boundary Pressure Units: Pressure units used in the definition of the boundary conditions of the problem.

Boundary Kenr Units: Eddy kinetic energy (k) units used in the definition of the boundary conditions of the problem. They are also used for Kenr_Field fields in Fluid Material window.

Boundary Elen Units: Turbulence length scale (L) units used in the definition of the boundary conditions of the problem.

Boundary Acceleration Units: Acceleration units used in the definition of the boundary conditions of the problem (see AccOX Field, AccOY Field and AccOZ Field).

Boundary Temperature Units: Temperature units used in the definition of the boundary conditions of the problem.

Heat Source Units: Heat source units used in the definition of the heat transfer problem (Heat Source fields).

Heat Flux Units: Heat flux units used in the definition of the heat transfer problem (Heat Flux fields).