[jferrari]

I'm trying to run pimpleDyMFoam with a pointDisplacement file (like the wingMotion tutorial). The code below runs, but I'm not really sure about what exactly it's doing.

value - not sure why this is needed, but it is
axis (0 0 1) - no problem here, rotating about the z-axis
origin (0 0 0) - no problem here, rotating about the z-axis through point (0 0 0)

I expect that the last three are related as

angle = angle0 + amplitude * sin(2*pi*omega*t)

Is this relationship correct?
Are angle0 and amplitude expressed in degrees?
Is omega expressed in Hz?
Is there a 2pi factor in the sine function?

    airfoil
    {
        type            angularOscillatingDisplacement;
	value		uniform (0 0 0);
	axis		(0 0 1);
	origin		(0 0 0);
	angle0		0;
	amplitude	10;
	omega		0.174;
    }

[jferrari]

Working to the following code:

    airfoil
    {
        type            angularOscillatingDisplacement;
	axis		(0 0 1);
	origin		(-1 0 0);
	angle0		0;
	amplitude	5;
	omega		0.3183098862;
        value           uniform (0 0 0);
    }

After this runs 0.215 seconds, there is a lot of displacement going on (seen below).


This means that angularOscillatingDisplacement isn't doing anything close to what I think it's doing.

Searching...........................

A bit from oscillatingRotatingMotion.C:

Foam::septernion
Foam::solidBodyMotionFunctions::oscillatingRotatingMotion::
transformation() const
{
    scalar t = time_.value();

    vector eulerAngles = amplitude_*sin(omega_*t);

    // Convert the rotational motion from deg to rad
    eulerAngles *= pi/180.0;

    quaternion R(eulerAngles.x(), eulerAngles.y(), eulerAngles.z());
    septernion TR(septernion(CofG_)*R*septernion(-CofG_));

    Info<< "solidBodyMotionFunctions::oscillatingRotatingMotion::"
        << "transformation(): "
        << "Time = " << t << " transformation: " << TR << endl;

    return TR;
}

Based on this code it's converting from degrees to radians... so amplitude should be in degrees..... and it also looks like omega is in rad/s, also what I thought it was......

Okay so I'm a bit lost now. Can anyone explain how angularOscillatingDispalcment works?

[kmooney]

Howdy,

A good place to start might be reverse engineering the source code. The file of interest is located here in 1.6-ext:

~/OpenFOAM/OpenFOAM-1.6-ext/src/dynamicMesh/meshMotion/fvMotionSolver/pointPatchFields/derived/angularOscillatingDisplacement/angularOscillatingDisplacementPointPatchVectorField.C

Good luck!

[jferrari]

Originally Posted by kmooney

Howdy,

A good place to start might be reverse engineering the source code. The file of interest is located here in 1.6-ext:

~/OpenFOAM/OpenFOAM-1.6-ext/src/dynamicMesh/meshMotion/fvMotionSolver/pointPatchFields/derived/angularOscillatingDisplacement/angularOscillatingDisplacementPointPatchVectorField.C

Good luck!

Ah, apparently I was looking at the wrong source code. Thanks for pointing me in the right direction!

[kmooney]

It can be easy to get pretty lost down in the depths of the boundary condition directory structures.

[jferrari]

This looks like the subroutine that does the actual rotating:

void angularOscillatingDisplacementPointPatchVectorField::updateCoeffs()
{
    if (this->updated())
    {
        return;
    }

    const polyMesh& mesh = this->dimensionedInternalField().mesh()();
    const Time& t = mesh.time();

    scalar angle = angle0_ + amplitude_*sin(omega_*t.value());
    vector axisHat = axis_/mag(axis_);
    vectorField p0Rel(p0_ - origin_);

    vectorField::operator=
    (
        p0Rel*(cos(angle) - 1)
      + (axisHat ^ p0Rel*sin(angle))
      + (axisHat & p0Rel)*(1 - cos(angle))*axisHat
    );

    fixedValuePointPatchField<vector>::updateCoeffs();
}

There's still the relationship I suspected earlier - starting angle plus a sine-varying angle, though I don't see any conversion to radians. angle0 and amplitude may be expressed in radians and not degrees - I have a case running with angle0 = 0 radians and amplitude = 0.0872664626 radians = 5 degrees now to test whether or not this is the case. I still think omega is rad/s. In the case I'm currently running I wanted a period of 0.1 s, so f = 10 and omega = 62.831853 rad/s. I'll update this thread when it finishes - though it'll be a while.... it kept crashing until I brought the max courant number down to 0.1.....

[jferrari]

Yep, everything is in radians or radians/second.

[desert_1250]

Hello all
i wanna use linear motion vs time to calculate aerodynamic coeffs for angle of attack=0 to 25 degrees of an airfoil. for this, i added "t.value()" to the oscillation function as following :
angle = angle0_ + amplitude_*sin(omega_*t.value())+ t.value();

by substituting angle0=0 and amplitude=0 in it. now:

1- would you tell me the steps of how to compile the new modified code?!
2- did you have another suggestion for solving this problem?

tnx alot
____________
Rasoul

[desert_1250]

Hello again
i compiled the new code successfully using wmake libso command and it is up to date. but when i used it in the 0 > poitDisplacement file, the following error apear :

unknown patchField type myAngularOscillatingDisplacement for patch type wall...

the boundary type that i used is :

wing
{
type myAngularOscillatingDisplacement;
axis (0 0 1);
origin (0 0 0);
amplitude 0;
omega 6.283;
value uniform (0 0 0);
}

Can anyone tell me how to solve this problem?

tnx
_____
Rasoul

[CHAYANIT]

Originally Posted by jferrari

I'm trying to run pimpleDyMFoam with a pointDisplacement file (like the wingMotion tutorial). The code below runs, but I'm not really sure about what exactly it's doing.

value - not sure why this is needed, but it is
axis (0 0 1) - no problem here, rotating about the z-axis
origin (0 0 0) - no problem here, rotating about the z-axis through point (0 0 0)

I expect that the last three are related as

angle = angle0 + amplitude * sin(2*pi*omega*t)

Is this relationship correct?
Are angle0 and amplitude expressed in degrees?
Is omega expressed in Hz?
Is there a 2pi factor in the sine function?

    airfoil
    {
        type            angularOscillatingDisplacement;
    value        uniform (0 0 0);
    axis        (0 0 1);
    origin        (0 0 0);
    angle0        0;
    amplitude    10;
    omega        0.174;
    }

I am facing problem running this case.The following problem is occuring .


GAMG: Solving for cellDisplacementx, Initial residual = 1, Final residual = 9.00145e-06, No Iterations 3
GAMG: Solving for cellDisplacementy, Initial residual = 1, Final residual = 7.73384e-06, No Iterations 3
GAMG: Solving for pcorr, Initial residual = 1, Final residual = 0.0147208, No Iterations 16
time step continuity errors : sum local = 1.33772e-05, global = 5.47826e-20, cumulative = 5.47826e-20
PIMPLE: iteration 1
smoothSolver: Solving for Ux, Initial residual = 1, Final residual = 0.0342088, No Iterations 1
smoothSolver: Solving for Uy, Initial residual = 1, Final residual = 0.028379, No Iterations 1
#0 Foam::error:rintStack(Foam::Ostream&) at ??:?
#1 Foam::sigFpe::sigHandler(int) at ??:?
#2 ? in "/lib/x86_64-linux-gnu/libc.so.6"
#3 Foam::GAMGSolver::scale(Foam::Field<double>&, Foam::Field<double>&, Foam::lduMatrix const&, Foam::FieldField<Foam::Field, double> const&, Foam::UPtrList<Foam::lduInterfaceField const> const&, Foam::Field<double> const&, unsigned char) const at ??:?
#4 Foam::GAMGSolver::Vcycle(Foam::PtrList<Foam::lduMa trix::smoother> const&, Foam::Field<double>&, Foam::Field<double> const&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::Field<double>&, Foam::PtrList<Foam::Field<double> >&, Foam::PtrList<Foam::Field<double> >&, unsigned char) const at ??:?
#5 Foam::GAMGSolver::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#6 Foam::fvMatrix<double>::solveSegregated(Foam::dict ionary const&) at ??:?
#7 Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
#8 ? at ??:?
#9 __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#10 ? at ??:?
Floating point exception (core dumped)





Kindly help

[Jim_Hao]

Hi Chayanit,

I have the same issue as you faced, have you figured out this issue?

In my case, when this issue happens, the forces on the airfoil became extremely large.

Do you also have this issue?

Thanks,
Jim

[quarkz]

Hi,

I tried and realised that amplitude should be in rad, not degrees. I checked the latest 1912 source code and there seems to be a conversion, so not sure if we're looking at the correct file.

wing
    {
    type        angularOscillatingDisplacement;
    value           uniform (0 0 0);
	axis		(0 0 1);
	origin (0.25 0.007 0.125);
	angle0		 0;
	amplitude       0.358;  //units of rad ~ 20deg
	omega           6.28;       //units of rad/s ~ 1 period /s

Btw, try using:

moveDynamicMesh -noFunctionObjects

to test and preview the mesh motion in Paraview before actually computing the solution. Can also be done in parallel.