Tdyn reference manual


Conditions

Conditions are all properties of a problem (except Materials and Boundaries, see below) that can be assigned to an entity, in order to define the basic boundary conditions of a problem. Conditions should be used to define inflow and outflow boundary conditions, and symmetry or far field conditions.

In Tdyn conditions are available through the menu option Data>Conditions.

Remarks:

The complex boundary conditions, like body wall type (i.e. law of the wall) or free surface, can be easily imposed by using the Boundaries options.

If a mesh has already been generated, any change in the condition assignments, requires meshing again to transfer these new conditions to the mesh. If the conditions were changed and a new mesh was not generated, the user will be warned, when the data for the analysis is being written.


Conditions available in module RANSOL

The following boundary conditions, are available in the RANSOL module of Tdyn.

Fix Pressure

L

 

L

This condition is assigned to geometrical/mesh entities or layers and is used to fix the pressure at the given value.

Fields:

Value: Value (real) of the pressure.

Remarks:

For most of the problems it is strongly recommended to fix the pressure in at least one point of the domain.

When the pressure is not specified in the analysis either directly or indirectly, no reference for the pressure exists, and the resulting distribution can only be used with relative values.

The pressure can be specified at a far field boundary (i.e. at the outflow boundary of the domain, when the boundary is far enough from the region of interest).

The pressure can also be specified at the inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

Units of the pressure boundaries may be defined in Data>Units Data> General.

Pressure Field

L

 

L

This condition is assigned to geometrical/mesh entities and is used to fix the pressure at the value given by the Initial Pressure field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Remarks:

In most of the problems, it is recommended to fix the pressure in at least one point of the domain. When the pressure is not specified in the analysis either directly or indirectly, no reference for the pressure exists, and the resulting distribution can only be used with relative values.

When Pressure Field condition is assigned Initial Pressure entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Initial Pressure entry is common for every Pressure Field condition and can only be modified in the Tdyn Initial and Conditional Data.

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

Units of the pressure boundaries may be defined in Data>Units Data> General.

 

Fields:

Fix Initial: The pressure will be fixed to the initial value (evaluated in t=0) of the function inserted in the Initial Pressure field of the Tdyn Initial and Conditional Data window. Initial Pressure field is evaluated at the initial step (t=0) and pressure is fixed to the resulting value for the rest of the execution.

Fix Field: The pressure will be fixed to the value (for every time step) of the function inserted in the Initial Pressure field of the Tdyn Initial and Conditional Data window. Initial Pressure field is evaluated every step and pressure is fixed to the resulting value.

Remarks:

In most of the problems, it is recommended to fix the pressure in at least one point of the domain. When the pressure is not specified in the analysis either directly or indirectly, no reference for the pressure exists, and the resulting distribution can only be used with relative values.

When Pressure Field condition is assigned Initial Pressure entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Initial Pressure entry is common for every Pressure Field condition and can only be modified in the Tdyn Initial and Conditional Data window.

Sometimes the pressure is specified at a far field boundary (i.e. at the outflow boundary of the domain, when the boundary is far enough from the region of interest).

Sometimes the pressure is specified also at the inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

This condition allows a definition of transient boundary conditions for the pressure. The analytical functions defining transient boundary conditions will be specified in the corresponding function inserted in the Initial Pressure field of the Tdyn Initial and Conditional Data window.

If the boundary conditions for the pressure are steady, this condition can be substituted by the Fix Pressure Point condition. The only difference between these two options in this case is, that when using the Pressure Field Point, the value of the fixed pressure can be changed automatically in every entity by updating the corresponding function inserted in the Initial Pressure field of the Tdyn Initial and Conditional Data window.

Conditional Pressure

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the pressure at the value given by the Initial Pressure field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15 only if the PressureFuncCond data field is greater than 0.

If the evaluation of the PressureFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.

Remarks:

When ConditionalPressure condition is assigned Initial Pressure entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

PressureFuncCond and Initial Pressure entries are common for every Conditional Pressure condition and can only be modified in the Tdyn Initial and Conditional Data.

In most of the problems, it is recommended to fix the pressure in at least one point of the domain. When the pressure is not specified in the analysis either directly or indirectly, no reference for the pressure exists, and the resulting distribution can only be used with relative values.

Sometimes the pressure is specified at a far field boundary (i.e. at the outflow boundary of the domain, when the boundary is far enough from the region of interest).

Sometimes the pressure is specified also at the inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

Units of the pressure boundaries may be defined in Data>Units Data> General.


Fix Velocity

L

 

L

This condition is assigned to geometrical/mesh entities or layers and is used to fix the velocity at the given value.

Fields:

X Component: Value (real) of the OX component of the velocity.

Fix X: Only if marked the OX component of the velocity will be fixed.

Y Component: Value (real) of the OY component of the velocity.

Fix Y: Only if marked the OY component of the velocity will be fixed.

Z Component: Value (real) of the OZ component of the velocity.

Fix Z: Only if marked the OZ component of the velocity will be fixed.

 

Remarks:

The velocity has to be prescribed at the inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

Units of the velocity boundaries may be defined in Data>Units Data> General.

Fix Velocity Component

 

 

This condition is assigned to geometrical/mesh and is used to specify the value of a component of the velocity vector.

Fields:

Local Axes: Orientation of the Cartesian axes used to define the direction of the component of the velocity vector. These can be local axes of the geometry (-Automatic- option) or any user defined system.

Type: Axis of the Local Axes definition. The component of the velocity vector, parallel to this axis, will be fixed to the given value. The normal velocity component to a line or a surface can be fixed by selecting Y_Axis or Z_Axis. To see the defined Local Axes, press the button Draw.

Value: Value of the component of the velocity in the direction given by Type axis.

Remarks:

This option is used to prescribe slipping boundary conditions on a velocity field. Since the normal vector is sometimes undefined in some complex areas (i.e. dihedral angles) of the geometry, in some cases it is better to use the Body Boundary options instead.

Units of the velocity boundaries may be defined in Data>Units Data> General.

Fix Velocity Direction

 

 

This condition is assigned to geometrical/mesh entities and may be used to define the direction of the velocity, according to the orientation of the skew system.

Fields:

Local Axes: Orientation of the Cartesian axes used to define the direction of the component of the velocity vector. These can be local axes of the geometry (-Automatic- option) or any user defined system.

Type: Axis of the Local Axes definition. The component of the velocity vector, parallel to this axis, will be fixed to the given value. The normal velocity component to a line or a surface can be fixed by selecting Y_Axis or Z_Axis. To see the defined Local Axes, press the button Draw.

Remarks:

Usually, the direction of the velocity has to be prescribed in someedges or areas with strong geometrical changes of the geometry.

The direction of the velocity can be automatically imposed by using the Body Boundary options (see Fix Angle option, Figure 13).

Remove Velocity Conditions

 

 

This condition is assigned to geometrical/mesh entities and layers and makes the program to ignore any specification on the velocity field.

Fields:

Free Velocity: The velocity will be removed only if this  field is marked.

Remarks:

This option allows the solver to accomplish the Kutta-Jukowsky condition. In these cases the Remove Velocity Point condition will be assigned to the extreme point of the tail of a profile. It is also possible to automatically correct velocity prescriptions in these areas by using the Body Boundary options (see Sharp Angle option, Figure 12).

Velocity Field

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the velocity at the value given by the corresponding functions of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Remarks:

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

 

Fields:

Fix Initial X: The OX component of the velocity will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Tdyn Initial and Conditional Data window (Initial Velocity X field) only if the field is marked. Initial Velocity X field is evaluated at the initial step (t=0) and velocity component is fixed to the resulting value for the rest of the execution.

Fix Initial Y: The OY component of the velocity will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Tdyn Initial and Conditional Data window (Initial Velocity Y field) only if the field is marked. Initial Velocity Y field is evaluated at the initial step (t=0) and velocity component is fixed to the resulting value for the rest of the execution.

Fix Initial Z: The OZ component of the velocity will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Tdyn Initial and Conditional Data window (Initial Velocity Z field) only if the field is marked. Initial Velocity Z field is evaluated at the initial step (t=0) and velocity component is fixed to the resulting value for the rest of the execution.

Fix Field X: The OX component of the velocity will be fixed to the value (for every time step) of the corresponding function of Tdyn Initial and Conditional Data window(Initial Velocity X field) only if the field is marked. Initial Velocity X field is evaluated every step and the corresponding velocity component is fixed to the resulting value.

Fix Field Y: The OY component of the velocity will be fixed to the value (for every time step) of the corresponding function of the Tdyn Initial and Conditional Data window(Initial Velocity Y field)only if the field is marked. Initial Velocity Y field is evaluated every step and the corresponding velocity component is fixed to the resulting value.

Fix Field Z: The OZ component of the velocity will be fixed to the value (for every time step) of the corresponding function of the Tdyn Initial and Conditional Data window(Initial Velocity Z field) only if the field is marked. Initial Velocity Z field is evaluated every step and the corresponding velocity component is fixed to the resulting value.

Remarks:

The velocity has to be prescribed at every inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

When Velocity Field condition is assigned Initial Velocity entries are used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

This condition allows definitions of transient boundary conditions for the velocity. The analytical functions defining transient boundary conditions will be specified in the corresponding Tdyn Initial and Conditional Data window.

If the boundary conditions for the velocity are steady, this condition can be substituted by the Fix Velocity condition. The only difference between these two options in this case is, that when using the Velocity Field, the value of the fixed velocity can be changed automatically in every entity by updating the corresponding Tdyn Initial and Conditional Data window.

Units of the velocity boundaries may be defined in Data>Units Data> General.

Conditional Velocity

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the velocity at the value given by the corresponding functions of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15 only if the given conditional data field is greater than 0 (see VelocityFuncCond fields in Figure 15).

If the evaluation of the corresponding VelocityFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.

Remarks:

When Conditional Velocitycondition is assigned Initial Velocity entries are used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

VelocityFuncCond entries are common for every Conditional Velocity condition and can only be modified in the Tdyn Initial and Conditional Data.

The velocity has to be prescribed at every inlet boundary. If the conditions at inlet are not well known, it is effective to move the boundary as far from the region of interest as possible.

Units of the velocity boundaries may be defined in Data>Units Data> General.

Fix Turbulence

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to fix all the turbulence variables (those solved in the turbulence problem) at the initial (evaluated for t=0) value given by the corresponding functions (Initial EddyKEner and Initial EddyLength) of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Fields:

Fix: The turbulence will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15only if this field is marked. Initial EddyKEner and Initial EddyLength give the value of the eddy energy and turbulence length scale or mixing length (see Turbulence modelling section), respectively.

 

Remarks:

The turbulence variables have to be prescribed at every inlet boundary. In those entities where all components of the velocity have been prescribed, Tdyn automatically fixes all turbulence variables at the initial (evaluated for t=0) value given in the Initial EddyKEner and Initial EddyLength fields of theTdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15. Therefore, assignment of this condition should not be necessary in most of the cases.

Fix Null Gradient

 

 

This condition is assigned to geometrical/mesh entities and is used to impose a null gradient of the problem variables, in the given direction.

Fields:

Local Axes: Orientation of the Cartesian axes used to define the direction of the gradient of the corresponding variable. These can be local axes of the geometry (-Automatic- option) or any user defined system.

Type: Axis of the Local Axes definition. The gradient of the, parallel to this axis, will be fixed to zero. The normal velocity component to a line or a surface can be fixed by selecting Y_Axis or Z_Axis. To see the defined Local Axes, press the button Draw.

Value: Value of the normal component of the velocity.

Remarks:

This option can be used to define outflow boundaries.

Warning:

This option is not fully operative.


Conditions available in module HEATRANS

The following boundary conditions are available in the HEATRANS module of Tdyn.

Fix Temperature

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to fix the temperature in a point at the given value.

Fields:

Value: Value of the temperature.

Temperature Field

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to fix the temperature at the value given by the function inserted in the Initial Temperature field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Fields:

Fix Initial: The temperature will be fixed to the initial value (evaluated in t=0) of the function inserted in the Initial Temperature field of the Tdyn Initial and Conditional Data window only if the field is marked. Initial Temperaturefield is evaluated initial step (t=0) and temperature is fixed to the resulting value for the rest of the execution.

Fix Field: The temperature will be fixed to the value (for every time step) of the function inserted in the Initial Temperature field of the Tdyn Initial and Conditional Data window. Initial Temperature field is evaluated every step and temperature is fixed to the resulting value.

Remarks:

This condition allows definitions of transient boundary conditions for temperature. The analytical functions defining transient boundary conditions will be specified in the Initial Temperature field of the Tdyn Initial and Conditional Data window.

If the boundary conditions for the temperature are steady, this condition can be substituted by the Fix Temperature condition. The only difference between these two options in this case is, that when using the Temperature Field, the value of the fixed temperature can be changed automatically in every entity by updating the Initial Temperature field of the Tdyn Initial and Conditional Data window.

When Temperature Field condition is assigned Initial Temperature entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the temperature boundaries may be defined in Data>Units Data> General.

Conditional Temperature

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the temperature at the value given by the Initial Temperature field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15 only if the TemperatureFuncCond data field is greater than 0.

If the evaluation of the TemperatureFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.

Remarks:

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

TemperatureFuncCond and Initial Temperature entries are common for every Conditional Temperature condition and can only be modified in the Tdyn Initial and Conditional Data.

When Conditional Temperature condition is assigned Initial Temperature entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the temperature boundaries may be defined in Data>Units Data> General.


Conditions available in module ADVECT

Fix Concentration

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to fix the value of the concentration of species at the given value.

Fields:

Species Name: Name of the species (see material Fluid/Solid description in sectionMaterials) which concentration is to be fixed.

Value: Value of the concentration of the species.

Remarks:

The value of the concentration of every species should be prescribed at every inlet boundary.

Units of the concentration boundaries may be defined in Data>Modules Data> ADVECT>Reference Units.

Concentration Field

L

 

L

This condition is assigned to geometrical/mesh entities and is used to fix the concentration of species at the value given by the Initial Concentration field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Fields:

Species Name: Name of the species (see material Fluid/Solid description in sectionMaterials) which concentration is to be fixed.

Fields:

Fix Initial: The concentration of the species will be fixed to the initial value (evaluated in t=0) of the function inserted in the Initial Concentration field of the Tdyn Initial and Conditional Data window. Initial Concentrationfield is evaluated at the initial step (t=0) and concentration is fixed to the resulting value for the rest of the execution.

Fix Field: The concentration will be fixed to the value (for every time step) of the function inserted in the Initial Concentration field of the Tdyn Initial and Conditional Data window. Initial Concentration field is evaluated every step and concentration is fixed to the resulting value.

Remarks:

The value of the concentration of every species should be prescribed at every inlet boundary.

This condition allows definitions of transient boundary conditions for concentration. The analytical functions defining transient boundary conditions will be specified in the Initial Concentration field of the Tdyn Initial and Conditional Data window.

If the boundary conditions for the concentration are steady, this condition can be substituted by the Fix Concentration condition. The only difference between these two options in this case is, that when using theConcentrationField, the value of the fixed concentration can be changed automatically in every entity by updating the Initial Concentration field of the Tdyn Initial and Conditional Data window.

When ConcentrationField condition is assigned Initial Concentration entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the concentration boundaries may be defined in Data>Modules Data> ADVECT>Reference Units.

Conditional Concentration

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the concentration of species at the value given by the Initial Concentration field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15 only if the SpeciesFuncCond data field is greater than 0.

If the evaluation of the SpeciesFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.

Remarks:

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

SpeciesFuncCond and Initial Concentration entries are common for every Conditional Concentration condition and can only be modified in the Tdyn Initial and Conditional Data.

When Conditional Concentration condition is assigned Initial Concentration entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the concentration boundaries may be defined in Data>Modules Data> ADVECT>Reference Units.


Conditions available in module URSOLVER

Fix Variable

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to fix the value of the variable at the given value.

Fields:

Phis Name: Name of the variable (see material Fluid/Solid description in sectionMaterials) which value is to be fixed.

Value: Value of the variable.

Remarks:

The value of the variable should be prescribed at every inlet boundary.

Units of the variable boundaries may be defined in Data>Modules Data> ADVECT>Reference Units.

Variable Field

L

 

L

This condition is assigned to geometrical/mesh entities and is used to fix the value of a variable at the value given by the Initial Variable field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15.

Fields:

Phis Name: Name of the variable (see material Fluid/Solid description in sectionMaterials) which value is to be fixed.

Fields:

Fix Initial: The variable will be fixed to the initial value (evaluated in t=0) of the function inserted in the Initial Variable field of the Tdyn Initial and Conditional Data window. Initial Variablefield is evaluated at the initial step (t=0) and variable is fixed to the resulting value for the rest of the execution.

Fix Field: The variable will be fixed to the value (for every time step) of the function inserted in the Initial Variable field of the Tdyn Initial and Conditional Data window. Initial Variablefield is evaluated every step and Variable is fixed to the resulting value.

Remarks:

The value of the variable should be prescribed at every inlet boundary.

This condition allows definitions of transient boundary conditions for variables. The analytical functions defining transient boundary conditions will be specified in the Initial Variable field of the Tdyn Initial and Conditional Data window.

If the boundary conditions for the variable are steady, this condition can be substituted by the Fix Variable condition. The only difference between these two options in this case is, that when using theVariableField, the value of the fixed variable can be changed automatically in every entity by updating the Initial Variable field of the Tdyn Initial and Conditional Data window.

When VariableField condition is assigned Initial Variable entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the variable boundaries may be defined in Data>Modules Data> URSOLVER>Reference Units.

Conditional Variable

L

 

L

This condition is assigned to geometrical/mesh entities and layers and is used to specify the value of a variable at the value given by the Initial Variable field of the Tdyn Initial and Conditional Data window (Data>Initial Data) shown in Figure 15 only if the VariableFuncCond data field is greater than 0.

If the evaluation of the SpeciesFuncCond field results in a value less than 0, the boundary conditions will not be applied. If the value is 0, the boundary condition will be applied only if it was applied in the previous time step.

Remarks:

Entries of the Tdyn Initial and Conditional Data window may be defined by functions (see Function Syntax section).

SpeciesFuncCond and Initial Variable entries are common for every Conditional Variable condition and can only be modified in the Tdyn Initial and Conditional Data.

When Conditional Variable condition is assigned Initial Variable entry is used both for defining initial values (t = 0) when starting calculation and for evaluating the assigned condition the rest of time steps.

Units of the Variable boundaries may be defined in Data>Modules Data> URSOLVER>Reference Units.


Conditions available in module NAVAL

Fix Beta

L

 

L

This condition is assigned to geometrical/mesh entities and layers. It is used to fix the value of the wave elevation at its initial value. The initial value is the difference between the OZ coordinate of the point and the reference height of the free surface (see Data > Problem Data > OTHER > Give pressure origin).

Fields:

Fix: The wave elevation will be fixed to its initial value only if the field is marked.

 

Remarks:

This option is effective in the stern of some geometries to keep the stability of the free surface. In most of the cases it can be automatically imposed by using the Body Boundary options (see Stern C Angle option and Stern flow modelling in transpiration problem section).


Conditions available in module ALEMESH

Fix Mesh Deformation

L

 

L

This condition is assigned to geometrical/mesh entities and layers. It is used to fix the value of the mesh deformation to cero or to the value given in the Fluid/Solid Deformation Increment field (see Data > Modules Data > ALEMESH).

Fields:

Type: Type of mesh deformation. If Fix Field is selected, imposed mesh deformation will be defined by Fluid/Solid Deformation Increment field (see Data > Modules Data > ALEMESH). If Fix Null is selected, mesh deformation is imposed to be cero. Finally, if No Fix is selected, any other imposition on the mesh deformation field is ignored.

 

Remarks:

Mesh deformation type may be defined in the Tdyn Modules Data window (see Data > Modules Data > ALEMESH > Fluid/Solid Mesh Deformation).


Conditions available in module RAMSOLID

A description of every available option of this module can be found in the RamSeries user and reference manual.