If you use a periodicity lenght Lx different from the periodicity lenght Lz, you are assuming the different integral lenghts, an assumption on the physics.

That happens in many other test on turbulence, for example in channel flows. You retain the homogeneity along the directions.

The second question is not clear, are you computing 1D or 3D spectra?

Thanks Dr. Denaro

I have used Saad et al. (2017) "Scalable Tools for Generating Synthetic Isotropic Turbulence with Arbitrary Spectra" to generate HIT inside a rectangular shape in 3D.

In my case mesh size are qual and cubic. Also, Nx=Nz but Ny is different, now how should I calculate power spectrum in 3D for my case?

Thanks,

Farzad

Farzad Farajidizaji

1- It is possible to generate a harmonic impact test (HIT) inside a rectangle, but the specific terminology for this type of test may vary. HIT is a type of test used to study the response of a structure to dynamic loading. A HIT inside a rectangle would involve applying a dynamic load to a structure in the shape of a rectangle. The specific terminology used to describe this test may vary depending on the field or industry.

2- If Nx = Nz but Ny is different, you can still calculate the power spectrum by analyzing the frequency components of the signals along the three different axes (Nx, Ny, Nz). The frequency components can be obtained using a Fast Fourier Transform (FFT) or similar technique. The power spectrum can be calculated by squaring the magnitude of the FFT and normalizing the result by the number of data points. To account for the difference in Ny, you may need to apply some modifications to the normalization or analysis process.