# Advances in Vibroacoustics and Aeroacustics of Marine, Aerospace and Automotive Systems
## 2 The Present Issue  
We are deeply honored to be the guest editors of this thematic issue, which includes original articles and reviews of interest for the scientific community working on these subjects, as well as for industrial R&D departments. We are particularly grateful to the several leaders in these areas who decided to honor us with their valuable contributions. We want to thank them and their collaborators for the effort they have accomplished for publishing their works in this issue of _Applied Sciences_. We are equally thankful to many colleagues who have helped us evaluating and reviewing these manuscripts with substantial improvements. This Special Issue highlighted the latest studies on vibroacoustics and aeroacustics problems and aimed at analyzing specific industrial problems. Many similar contributions can already be found in the literature, underlining the relevant efforts provided by scientists and researchers in tackling these critical designing aspects (see [3, 4]). In the work of [5], the dynamic stiffness method (DSM) was formulated to study the out-of-plane natural vibration of thin orthotropic plates using the classical plate theory (CPT). [PERSON]'s principle was implemented to derive the governing differential equation of motion for free vibration, whereas the Wittrick-Williams (W-W) algorithm was used as a solution technique to compute the natural frequencies. The complete procedure was implemented in a computer program using a combination of MATLAB and ANSYS. This enabled the calculation of any natural frequency and a validation against finite element method results was provided finally. The newly dataset of natural frequencies obtained by the DSM for different geometries and materials represented a benchmark for future comparison purposes. In the work of [6], the structural vibration response of a re-entry vehicle during a ballistic flight was simulated numerically. Once the pressure fluctuations on the outersurface were modelled, the vibroacoustic response was derived for the re-entry vehicle metallic aeroshell. Similarly to the work of [7], the low-frequency response was simulated through a FEM-BEM model, whereas the Statistical Energy Analysis was used to compute the high-frequency behavior. A validation of these models was provided through a comparison with ground experimental data under a diffuse-field acoustic loading provided by loudspeakers in a dedicated reverberation chamber. In the full-frequency range provided by both deterministic and statistical modelling procedures, the models were proven to be complementary in simulating the whole full-frequency vibroacoustic response. The work proposed in [8] reported a further simulation investigation based on BEM to perform passive noise control (PNC) assessments for passenger aircraft headsets. In particular, two PNC improvements of headsets were designed to reduce the sound pressure level (SPL) at the passengers' ears in an aircraft cabin during flight; the first was based on the optimization of the headrest shape, whereas the second consisted of partially or fully covering the headrest surface with a new highly sound-absorbing nanofibrous textile. An experimental validation campaign was conducted in a semi-anechoic chamber to provide a comparison. An acceptable correlation between experimental and numerical results was obtained and, based on these findings, general guidelines were proposed for the acoustical design of advanced headsets. Document [9] presented a comparison among FEM simulation procedures for the modelling of the numerous bolt connections of a four-stroke, four-cylinder petrol engine. A full 3D modelling of the bolts was preliminarily validated through a comparison with experimental test data available for the whole engine. Two further modelling approaches, a 1D approach and a contact-based (0D) approach, were benchmarked considering their influence on the accuracy for the dynamic analysis of an engine.