According to cosmological inflation, all the structures in the universe arise from microscopic fluctuations that were stretched to cosmological scales during a primordial epoch of accelerated expansion. The aim of the internship is to use the tool of numerical simulations of inflation recently developed in the group to shed light on the properties of gravitational-waves forged in the dark ages of inflation. The student will use InflationEasy to study two representative classes of inflationary models, with so-called resonant and sharp features. Depending on taste and progress, two key-questions will be addressed. 1. What is the impact of primordial non-Gaussianity on gravitational-wave backgrounds? 2. To which extent realistic inflationary models can lead to distinctive oscillatory patterns in the gravitational-wave spectrum? Through this internship, the student will discover a large spectrum of the field of theoretical cosmology, from quantum field theory in curved spacetimes to gravitational-wave physics and inflationary cosmology, using both analytical and numerical approaches.