Soon I'll be conducting experiments in a wave facility (flume) for my MSc thesis. And I would like to analyse wave spectra (amplitude and energy density).
The time step (or 'accuracy') of the wave maker, is by default dt = 0.001 s.
The sampling frequency of the measurement instruments (wave gauges) is 100 Hz (previously 25 Hz).
I'll start with bichromatic waves, which can be more or less be treated as being deterministic. I would like to prevent spectral leakage as much as possible.
The fundamental frequency is different for different experiments: short waves with a wave period of around 2.5 s. The wave maker includes bound waves (subharmonics), with the wave period Tbound one over the difference frequency of the short waves in the bichromatic wave train.
So far, previous students have set the FFT length to a power of 2. From what I read this is not necessary with modern implementations of the FFT.
One example of a previous student:
Fs = 25 Hz,
N = D*Fs = 2^13 (power of 2)
This results in a duration of the experiment of D = N/Fs = 327.68 s
with a spectral resolution of df = 1/D = 0.00305175781 Hz.
To avoid spectral leakage, frequencies of all my wave components should be a multiple of this number if I am correct.
Since I've set my wave gauges at a sampling frequency 100 Hz, I'm wondering if it's fine to increase my duration to D = 1000 s, so N = 100*1000 and is not a power of 2.
The resulting spectral resolution is: df = 1/D = 0.001 Hz and I'll round the frequencies of all my wave components to a multiple of this number.