Hey everyone,

I’m working on a harmonic analysis simulation and have a question about splitting the frequency range.

Let’s say the frequency range I’m analyzing is from 10 Hz to 100 Hz. Instead of running the harmonic simulation for the entire range in one go, is it feasible to split the range into smaller intervals, for example:

• One simulation for 10-50 Hz, and

• Another for 50-100 Hz?

I’m trying to understand if this approach would still provide accurate results or if there are any drawbacks, particularly at the boundaries where the ranges are split. Has anyone used this method in their analysis, and if so, were there any issues with accuracy or continuity?

From my understanding, harmonic analysis calculates the steady-state response at a specific frequency. For example, consider the system at 10 Hz, assuming no damping. We know the equation is:

M(x′′)+k(x)=Fsin⁡(ωt)M(x'') + k(x) = F \sin(\omega t)M(x′′)+k(x)=Fsin(ωt)

Since 10 Hz is the starting frequency, the initial displacement at all nodes would be zero, x(t)=0x(t) = 0x(t)=0. By solving this, we get the response for this frequency.

Now, when the solver moves to 11 Hz, will it assume the initial displacement is zero again, or will it consider the solution from the previous frequency?

I’d appreciate any insights or suggestions regarding the feasibility of splitting the frequency range and how solvers handle initial conditions between different frequencies.

This is more like an open question than a fully formed topic with both question and answer.

I am running an incompressible laminar flow simulation with the pimpleFoam solver. It has two openings on one side (n1 and n2) and one on the other (n3). I have set up the pressure boundary conditions so that the flow is driven primarily by the pressure applied at n3. The flow should be changing direction halfway. Realistically, the total volume passing through an opening should be the same for the two flow direction. Yet, when I sum over the patch flow rates (postProcessing function) of the two flow directions and compare them, they are different. What could be the potential reason(s) for this phenomenon?

Following is the pressure boundary condition I set up:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  10
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/

FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    n1
	{
		type            totalPressure;
		p0              uniform 0;  // Reference total pressure (e.g., atmospheric pressure in Pascals)
		U               U;               // Velocity field name
		phi             phi;             // Flux field name
		rho             none;            // Density, use 'none' for incompressible flow
		psi             none;            // Compressibility, use 'none' for incompressible flow
		gamma           1;               // For incompressible flow, use 1
	}

	n2
	{
		type            totalPressure;
		p0              uniform 0;  // Reference total pressure
		U               U;
		phi             phi;
		rho             none;
		psi             none;
		gamma           1;
	}


    n3
    {
		type		uniformTotalPressure;
	p0
	{
		type		sine;
		frequency	0.3333333333333333;
		amplitude	-50.0;
		level		0;
	}


    }
    walls
    {
        type            zeroGradient;
    }

    defaultFaces
    {
        type            empty;
    }

}

// ************************************************************************* //



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Hello, I am very new to CFD and simulations, I am trying to simulate the power output of a kaplan hydro turbine. I have made the geometry, but when I try to mesh it, after 15 minutes it fails. Is there any function in TCAE that I can use to check the mesh, I think it might not be water tight, but I don't know where. Also, the setup check passes without errors.

If you need any more information, please let me know.

Thank you in advance.

Hello,

I tried to run the benchmark cases NACA0012 and now I am at TCAE module. I have noticed that the running time of TCAE is long and I want to accelerate it but I haven't found places to set the number of processors. Is  that means the module cannot be computed in parallel? By the way, no my CPU utilization is low but memory is full. 

Thanks for help.

Hello, I tried to run the benchmarks case DJI9450 that I downloaded from CFD SUPPORT. But the  CFD calculation failed after 100 hours running and it showns that "Application redDyMsolver failed" . And there was nothing in the error log. I haven't change anything except the number of processor. Would it be OK if I run it again?

Thanks for your help.

Hi there

I don't know if tihs would help but I was wondering if anyone can help me to apply a "opening" condition in OpenFoam, in the picture you can see almost a square, and what I have in my problem is that from a little part of the left side I have an inlet and a part of the top part I have an outlet. Also I know that my outlet takes twice the flow that goes in from the inlet, and in the right side its like a room, we have more space, so what I wanted to do is to stablish an opening boundary to make my system have air outside of that, I'm currently using a pressure of 0 and the velocity I don't know what to set, I have set "zeroGradient' "opening" "fixedGradient" "calculatedValue" and nothing work, my simulation always diverges.

I hope someone could help me, 

thanks in advance

Hello everyone,


I have questions about the calculation of circumferential angles circA by TCAE.


I have understood that, if a surface is oriented in the radial direction, circA on this surface will be the angle between the tangent and the velocity in the radial/tangential plane. According to graphical representation of the manual, circA shoud be positiv when the projection of the velocity in the radial/tangential plane points out (of the cylinder in the picture), and negativ when it points in.


Let's imagine that we are on a surface radially oriented where some back flow occurs and that the absolute velocity has a circA > 90° when there is no back-flow. In most of the cells of the surface, circA points out of the cylinder (90° < circA < 180°), but when back-flow occurs, circA points in the cylinder (-180° < circA < -90°). Thus, there are positiv and negativ values of circA at the same time, isn't it ? Therefore, because the circA are either > 90° or < -90°, in the in the interfaces-final.csv file in simulationRun1/TCFD/stationary/postProcessing/surfaceName/0/ folder, it seems to me that surface averaged value of circA is distorted.

I had this reflection because I find particularly high values of circA on some surfaces of my simulations.

Could someone confirm my interpretation ? Or explain me why it isn't true ?

Besides, does someone know how to visualize circA angles on Paraview after a calculation ?


Thanks in advance !


Zacharie

Hi,

I installed OF4Win-20.09v2-win64.exe on my Windows PC. I am interested in using swak4Foam to set specific boundary conditions in my case. Do I need to compile it or what would be the necessary steps?

Thank you.

Hey, I was wondering if anyone could help me to understand the different solvers OpenFoam has for different purposes, I thing I have understood icoFoam and simpleFoam but if anyone could help me to know when and how to use the potentialFoam and all of them I would appreciate it a lot.

Thanks in advance for the help 

Hi, I'm a newbie to OpenFoam and I was trying to do the tutorials, I've been doing great but then I got to the motorbike one and tried to run in parallel the meshing and simulation but didn't work.

As you can see I set my meshing for parallel and gives me errors no matter if I use mpirun or mpiexec (I used both of them because I saw in other forums one of those should work), however if I delete the "-parallel" part it does everything normal.

My computer has 16 cores and the decomposePar works perfectly, it has for subDomains 6 and when i run it it gives me the processor0-processor5 folder

I would appreciate if anyone could help me

Thanks,

Armando

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I am reconstructing the case of the cyclone separator using the Euler-Euler approach given in this link. Unfortunately, many of the images and tables are corrupted, making the process quite difficult.

I have some specific questions about the Allrun file found here, especially regarding the following fragment:

echo "Modifiing and adding files in/to 0 dir..."

cd 0

rm -rv uniform

cp -v U U.water

mv -v U U.particles

rm -v nut

mv -v epsilon epsilon.water

mv -v k k.water

mv -v p p_rgh

cp -v ../0.euler/nut.particles .

cp -v ../0.euler/nut.water .

cp -v ../0.euler/T.water .

cp -v ../0.euler/T.particles .

cp -v ../0.euler/Theta.particles .

cp -v ../0.euler/alphat.particles .

cp -v ../0.euler/alpha.particles .

cp -v ../0.euler/alphat.water .

cp -v ../0.euler/alpha.water .

cp -v ../0.euler/p .

cd ..

echo "                                     ...done"

1. Why is the p field renamed to p_rgh, considering that p in simpleFoam is in Pressure/density units, and p_rgh is in Pressure units?
2. Why is nut removed and reinitialized when simpleFoam handles it?

Other questions regarding the simulation are:

Which is the drag model more adequated for solid-fluid simulation?

I would also like to know if anyone has the case folder available.

Thank you for your help.

I want to invoke API from OpenFoam for Windows, using c++ in VS under Windows. But I don't know which folder this API is located in the installation directory. Which headers should be included in my program? Additionally, is the API in the site bellow:

https://www.openfoam.com/documentation/guides/latest/api/modules.html

still available? Have their header's names and locations changed?

Greetings,

I am doing a fluent study on the tail types that UAVs have on Fluent. After entering the mesh settings in the attached style, I added pressure-farfield as a boundary condition around the inlet, outlet and enclosure in Fluent. After selecting the turbulence model k-omega, I changed the solution method to density-based. After measuring the Y + coefficient value 134 after the first analysis, I repeated the solution accordingly. At the same time, as the flow type in the solution steering section, I first selected subsonic flow and then incompressible when I did not get a result. 

My question is, while there is a converge state when solving on the inverted-v tail, I cannot get a converge state when doing this on the T-tail. Do you have any solution suggestions about this?