tdynreference 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 wall-body or free surface , should be 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 entities or layers and is used to fix the pressure at the given value.

Fields:

Value: Value of the pressure.

Remarks:

For 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.

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.

Fix Velocity

L

 

L

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

Fields:

X Component: Value of the OX component of the velocity.

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

Y Component: Value of the OY component of the velocity.

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

Z Component: Value 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.

Fix Velocity Component

 

 

This condition is assigned to points, lines and surfaces 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 normal component of the velocity.

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.


Fix Velocity Direction

 

 

This condition is assigned to lines 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 6).


Remove Velocity Conditions

 

 

This condition is assigned to geometrical 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 5).

Pressure Field

L

 

L

This condition is assigned to geometrical entities and is used to fix the pressure in a point at a value given by a corresponding function of a Fluid material (see Fluid material, field Pres Field).

Fields:

Fix Initial: The pressure will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Fluid material (see Fluid material, field Pres Field) only if this field is marked.

Fix Field: The pressure will be fixed to the value (for every time step) of the corresponding function of the Fluid material (see Fluid material, field Pres Field) only if this field is marked.

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.

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 Fluid material options (see Fluid material, field Pres Field).

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 Fluid material options (see Fluid material, field Pres Field).

Velocity Field

L

 

L

This condition is assigned to geometrical entities and layers and is used to specify the velocity at the value given by the corresponding function of the Fluid material (see Fluid material, fields VelX Field, VelY Field and VelX Field).

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 Fluid material (see Fluid material, field VelX Field) only if the field is marked.

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 Fluid material (see Fluid material, field VelY Field) only if the field is marked.

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 Fluid material (see Fluid material, field VelZ Field) only if the field is marked.

Fix Field X: The OX component of the velocity will be fixed to the value (for every time step) of the corresponding function of the Fluid material (see Fluid material, field VelX Field) only if the field is marked.

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 Fluid material (see Fluid material, field VelY Field) only if the field is marked.

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 Fluid material (see Fluid material, field VelZ Field) only if the field is marked.

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.

This condition allows definitions of transient boundary conditions for the velocity. The analytical functions defining transient boundary conditions will be specified in the corresponding Fluid material options (see Fluid material, fields VelX Field, VelY Field and VelX Field).

If the boundary conditions for the velocity are steady, this condition can be substituted by the Fix Velocity Line condition. The only difference between these two options in this case is, that when using the Velocity Field Line, the value of the fixed pressure can be changed automatically in every entity by updating the corresponding Fluid material options (see Fluid material, fields VelX Field, VelY Field and VelX Field).

Fix Turbulence

L

 

L

This condition is assigned to geometrical 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 in the corresponding function of the Fluid material (see Fluid material, fields Kenr Field, Epsl Field, Omeg Field and Ktau Field).

Fields:

Fix: The turbulence will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Fluid material (see Fluid material, fields Kenr Field, Epsl Field, Omeg Field and Ktau Field) only if the field is marked.

 

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 corresponding function of the Fluid material (see Fluid material, fields Kenr Field, Epsl Field, Omeg Field and Ktau Field). Therefore, assignment of this condition should not be necessary in most of the cases.

Fix Null Gradient

 

 

This condition is assigned to points, lines and surfaces 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.

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 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 entities and layers and is used to fix the temperature in a line at the value given by the corresponding function introduced in the Fluid material window (see Fluid material, field Temp Field).

Fields:

Fix Initial: The temperature will be fixed to the initial value (evaluated in t=0) of the corresponding function of the Fluid material window (see Fluid material, field Temp Field) only if the field is marked.

Fix Field: The temperature will be fixed to the value (for every time step) of the corresponding function of the Fluid material window (see Fluid material, field Temp Field) only if the field is marked.

Remarks:

This condition allows definitions of transient boundary conditions for a temperature. The analytical functions defining transient boundary conditions will be specified in the corresponding Fluid material options (see Fluid material, field Temp Field).

If the boundary conditions for the temperature are steady, this condition can be substituted by the Fix Temperature Line condition. The only difference between these two options in this case is, that when using the Temperature Field Line, the value of the fixed pressure can be changed automatically in every entity by updating the corresponding Fluid material options (see Fluid material, field Temp Field).

Conditions available in module ADVECT

Fix Concentration

L

 

L

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

Fields:

Species: Identifier (index) of the species (see material Fluid). This identifier corresponds to the index of the row of the matrix of data defined in the Fluid material window (see Concentration Properties of the Advect tag).

Value: Value of the concentration of the species. This value must be in the interval [0, 1].

Remarks:

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

Concentration Initial

L

 

L

This condition is assigned to geometrical entities and layers. It is used to fix the value of the concentration of species at the value given by the corresponding Fluid material field (see material Fluid \ Concentration Properties \ Initial I).

Fields:

Species: Identifier (index) of the species (see material Fluid). This identifier corresponds to the index of the row of the matrix of data defined in the Fluid material window (see Concentration Properties of the Advect tag).

Fix Initial: The concentration will be fixed to the value given in the field  Fluid \ Concentration Properties \ Initial I only if the field is marked.

Remarks:

The value of the concentration of species must be in the interval [0, 1].

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

Conditions available in module NAVAL

Fix Beta

L

 

L

This condition is assigned to geometrical 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 General Data \ 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).