Function object "energySpectrum"

Hello

I have installed OpenFOAM v1812 into Ubuntu 16.04 LTS. OpenFOAM itself seemed to be working well (there was no problem with testing a "cavity" problem using icoFoam). I also tested a "Decay of homogeneous isotropic turbulence" tutorial as itself without any modification, but function object "energySpectrum" did not work. In fact, OpeFOAM did not generate a file "energySpectrum.dat" in each time directory even though other results seemed to be O.K. I have already tried to do many things to fix it, but it did not work yet. Your prompt assistance will be appreciated.

Thank you.