[sinhavivekananda318]

Hello,
I am trying to incorporate a sinusoidal velocity profile at the inlet boundary. recently I came across the "oscillatingFixedValue" bc in a tutorial. but I am unable to find this bc in the derived bc in the finite volume patch fields. I have done my further research and came to know that OF v 4.1 does not have this bc.

Is friends there any way to have this sinusoidal velocity inlet in OF 4.1?

regards
vivek

[Bloerb]

Use a boundary condition with Function1. Example:

{
type uniformFixedValue;
uniformValue constant 0.2;
}

Instead of constant you can use polynomial or sinus, a table file etc...

[sinhavivekananda318]

thanku sir for your kind reply. In my case I hve to use a velocity profile which has the following expression: U=a*f*Cos( 2*Pi*a*f*t).
Here, a=amplitude;f=frequency; and t=time;
In this case how should I specify my amplitude , frequency and time?
please give me some advice..

regards
vivek

[Bloerb]

Function1 is located here:
https://github.com/OpenFOAM/OpenFOAM...ions/Function1

Inside sine.h you'll find:

 Templated sine function with support for an offset level.
        \f[
            a sin(2 \pi f (t - t_0)) s + l
        \f]
    where
    \vartable
        symbol  | Description       | Data type
        a       | Amplitude         | Function1<scalar>
        f       | Frequency [1/s]   | Function1<scalar>
        s       | Type scale factor | Function1<Type>
        l       | Type offset level | Function1<Type>
        t_0     | Start time [s]    | scalar
        t       | Time [s]          | scalar
    \endvartable
    Example for a scalar:
    \verbatim
        <entryName> sine;
        <entryName>Coeffs
        {
            frequency 10;
            amplitude 0.1;
            scale     2e-6;
            level     2e-6;
        }
    \endverbatim
    Example for a vector:
    \verbatim
        <entryName> sine;
        <entryName>Coeffs
        {
            frequency 10;
            amplitude 1;
            scale     (1 0.1 0);
            level     (10 1 0);
        }
    \endverbatim
SourceFiles
    Sine.C

One example can be found here
https://github.com/OpenFOAM/OpenFOAM...hVectorField.H

Simply check which boundary conditions contain function1. It should be loaded at the top of the .h file. Most boundary conditions can be found here:
https://github.com/OpenFOAM/OpenFOAM...Fields/derived

I have not tested this, but this should work with minor tweaking:

inlet
{
type uniformFixedValue;
uniformValue sine;
        uniformValueCoeffs
        {
            frequency 10;
            amplitude 1;
            scale     (1 0 0); 
            level     (0 0 0); // offset
            t0  0; // shift this for a Cosinus
        }
}

This is the exact definition:

        amplitude_->value(t)
       *sin(constant::mathematical::twoPi*frequency_->value(t)*(t - t0_))
       *scale_->value(t)
      + level_->value(t);

[sinhavivekananda318]

thank you sir...yesterday i generated a sinusoidal inlet profile with uniformfixedvalue. Its coming nice. but sir I have some doubts. I have tried to find out what an offset is. It is defined as the vertical distance of the base line. and in the syntaxes, it is written as (10 1 0). What these three value stand for? similar doubt for scale as well. scale is a factor by which the signal is amplified. but what are these three values in the syntax of scale? and sir I also did not understand the "t0 0 ; // shift this for cosinus" line.Please explain

regards
vivek

[Bloerb]

As I have already shown the formula is:

        scale*amplitude*sin(2*Pi*frequency*(t - t0)) + level

Since you have chosen a boundary condition that expects a vector your profile needs to be a vector. Hence scale and level are vectors.
Example:

        (1 0 0)^T*amplitude*sin(2*Pi*frequency*(t - t0)) + (0 1 0)^T

will give you an oscilation in x direction with a constant y velocity.

Now you want U=a*f*Cos( 2*Pi*a*f*t). Hence level is (0 0 0). Since amplitude is also inside your cos set it to 1 and use the amplitude inside scale. If your inlet is in x direction you should format your values in this fashion:

inlet
{
type uniformFixedValue;
uniformValue sine;
        uniformValueCoeffs
        {
            frequency a*f;
            amplitude 1;
            scale     (a*f 0 0); 
            level     (0 0 0); // offset
            t0  0.25/(a*f); // shift this for a Cosinus
        }
}

t0 results from the fact that sin(x+pi/2)=cos(x)

[hiuluom]

I think t0 = -0.25/(a*f) because:

2pi*a*f*(t-t0) = pi/2 + 2pi*a*f*t => t0 = -0.25/(a*f)

based on sin(pi/2 + x) = cos (x)

[FloatingSolar]

hey,

I am trying to create a multiphase model of a floating object which is subjected to a sinusoidal wave input. Would anybody be able to explain to me how I can achieve this? I have tried using a 'uniformFixedValue' inlet with a sine as 'uniformValue', but I can't get it to work properly. (I get very weird waves if any at all.) Any directions on how to set up the boundary conditions would be much appreciated!

Kind regards,
Daan