[OOTB]

Hi all...


I'm looking to set a boundary condition on an inlet patch as to specify alpha.water = 1 below a certain z position (interFoam). Using the expression version of Function 1 as per the OpenFoam documentation I tried the following:


alpha.water

inlet
{
type uniformFixedValue;
uniformValue
{
type expression;
expression #{ (pos().z < 38.2) ? 1 : 0 #};
}
}

It however gives a syntax error just after pos().z


Does anyone perhaps know the correct syntax for using pos()?

[Tobi]

In which OpenFOAM version can one apply this syntax? Is it implemented in the ESI version? In any case, I guess you cannot use the pos() function out of the box, because you need a reference to an object. You even did not specify the error message so it is a bit hard to give valuable feedback.

Nevertheless, as you showed the condition you set (please use code tags - update your post), it seems to be somehow similar to the codedMixed boundary condition. If I am right, you need an object first. An example:

inlet
{
    type uniformFixedValue;
    uniformValue
    {
        type         expression;
        expression 
        #{
                // Actual time   --> t is an object of type scalar
                const scalar t = *this->db().time().runTime();
        #};
}

However, while checking your code, I found that you had a missing simicolon at the end of your if-else condition:

inlet
{
    type uniformFixedValue;
    uniformValue
    {
        type         expression;
        expression 
        #{
                   (pos().z < 38.2) ? 1 : 0      // << ; missing
        #};
}

However, as I don´t know this kind of implementation, I am not sure if my hints are fine or totally wrong. But on the other hand, you did not provide enough information.

[OOTB]

Hi Tobi, thanks for the reply.
I'm using OpenFoam v2006. They have an example here (attached a clip) https://www.openfoam.com/releases/openfoam-v2006/pre-processing.php

The error code is generated when running setFields and is as follows:

--> FOAM FATAL IO ERROR:

Syntax error in expression at position:9
<<<<
pos().z < 38.2 ? 1 : 0;

.............^^^^ near here
>>>>

[olesen]

Originally Posted by OOTB

Hi all...


I'm looking to set a boundary condition on an inlet patch as to specify alpha.water = 1 below a certain z position (interFoam). Using the expression version of Function 1 as per the OpenFoam documentation I tried the following:


alpha.water

It however gives a syntax error just after pos().z


Does anyone perhaps know the correct syntax for using pos()?

The documentation : https://www.openfoam.com/documentati...on-syntax.html

In swak4foam I think you could have '.z', but for the OpenFOAM expressions you need '.z()' for the component. This makes it looks more like C++ code, and also makes the parser more deterministic.
For a similar reason we have 'pi()', which looks like a function call, but actually maps to a constant value. For things like 'degToRad()' you can have both versions, as a constant or a function. Eg,

    45 * degToRad()



    degToRad(45)

[olesen]

Originally Posted by Tobi

In which OpenFOAM version can one apply this syntax? Is it implemented in the ESI version? In any case, I guess you cannot use the pos() function out of the box, because you need a reference to an object.

The 'pos()' will be defined if you are using an expressionPatchFunction1, since it already knows that it associated with a patch. In this context it will mean the face centres.

Originally Posted by Tobi

...
However, while checking your code, I found that you had a missing simicolon at the end of your if-else condition:

inlet
{
    type uniformFixedValue;
    uniformValue
    {
        type         expression;
        expression 
        #{
                   (pos().z < 38.2) ? 1 : 0      // << ; missing
        #};
}

However, as I don´t know this kind of implementation, I am not sure if my hints are fine or totally wrong. But on the other hand, you did not provide enough information.

The expressions are self-contained, so they do not have a semi-colon.

[OOTB]

Thank you Mark.. it worked! Its much appreciated.

[JNSN]

Hi,


just for sake of completeness: You could achive same much simpler by just using fixedValue BC and initialize with setFields (as done e.g in the DTCHull tutorial). Or initialization with setWaves tool would even allow to set alpha values indipendent of the cell coordinates, giving you "correct" vof values between 0 and 1 for partially filled cells.


Best,
Jan

[OOTB]

Thank you Jan,

I want to set different fixed levels on the inlet and outlet patches.. I'm not sure how to do it with setFields.

regards

[JNSN]

you can define separate boxes, including only inlet or outlet. Values for the patches are set within the boxToFace block. However, no idea how to ensure consistent initialization within the domain. But I think you have same problem when using the uniformFixedValue BC in combination with expression.


Best,
Jan