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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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

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Hi everyone

I´m trying to create another equation of state model based on Bussinesq, but when i write "wmake" the next set of errors and warnings are printed in the terminal of OF4Win 20.09:

Can you please give me some help with this problem? Thanks in advance

I am using OpenFoam 20.9 for Windows 10.When i run the motorBike tutorial - no problem .If i use my own stl file which i have used many times on all OpenFoam platforms i get the error u will see in attached file. Once decomposePar has run going to snappyHexMesh those errors show. Also when simulation run the stl file lOpenFOAM for Windows 20.09 (v2)

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Hi everyone !

It's my first post here and I have a few questions on post-processing's manipulations and on variables' meaning :

1) How can I get the surface areas of the components' interfaces on TCAE (Paraview interface) or in the calculation case's folders ?

2) The TCAE user manual indicate that here are 2circumferential angles : the axial and the radial circumferential angles. To analyse my data, I need to extract the radial circumferential angle. However, withe the option 'calculateAngles on' in .../stationary/system/interfaces.fun, I only get one circumferential angle : circAng. How can I know which one is it (radial or axial) ? Or a mix of both ?

3) How is the mass flow rate calculated on the interfaces, with the absolute speed or with the flow speed (the radial speed for the mass flow at the outlet of a centrifugal impeller for example) ?

I hope someone will be able to help me on these topics... Thanks in advance !

Test topic 2 - will be removed soon.

In CFD we generally have a problem when we encounter something that is supposed to move on its "free will". One of these problems is an unknown rotation speed of a turbomachinery rotor. Common practice is that the user prescribes flow boundary conditions for one specific case or does a full spectrum of operational conditions including rotation speed. But what if he knows an input aerodynamic or shaft torque and wants to obtain a stable rotation speed (with no acceleration)?

One way is to use the TOPT algorithm where you look for a minimum of optimization function prescribed as (target_torque - calculated_torque)^2. 

First I calculated a torque for 187 RPM. Then I set this torque to our optimization function and ran TOPT with RPMs as a parameter.

Test topic - will be removed

Testing New Topic For Mail

Axial Turbine Stage - test topic. Axial Turbine Stage CFD. It is hard not to be emotional when seeing an axial turbine stage CFD. The axial turbine stage was our first big CFD project made here at CFDSUPPORT. In a way, it had preset our destiny - turbomachinery simulations. Here is a little example of how now, ten years later, TCAE runs the whole complex process in one command (or click). By TCFD: https://www.cfdsupport.com/axial-turbine-cfd-simulation.html