# Vibroacoustic Assessment of an Innovative Composite Material for the Roof of a Coupe Car
## 1 Introduction  
The vibroacoustic analysis of structural components, used in aircraft [1], spacecraft [2], land vehicles [3], and ships [4, 5], plays a vital role in the design of these systems with regard to human health and living comfort. The numerical tools of the Finite Element Method [6, 7] and Boundary Element Method [8] have been applied extensively for modeling acoustic problems. Such numerical techniques are adopted stand-alone or in conjunction (hybrid methods) [9]. New materials as alternatives to petroleum-based composite materials are needed due to the adverse effects of the latter on nature. On the other hand, there is a need to characterize and evaluate such new alternative materials to be effectively used in practical applications. Nowadays, in the automotive field, it is usual to see isotropic materials for vibrating plates replaced by composite materials, also due to their superior damping characteristics [10], even if their vibroacoustic characteristics have not yet been extensively examined. In particular, the main challenge in implementing a new composite roof for a car bodyis related not only to its structural assessment but also to guarantee its compliance with vibroacoustic requirements. In [PERSON] et al. [11], the traditional metallic roof has been compared with the newly proposed solution in terms of structural and vibroacoustic performances. The different stiffness and the different mass of the roof change the vibrational behavior of the entire vehicle and consequently its transmission loss. Lightweight components are typically stiff and thin-walled and thus tend to have significant sound radiation. Due to structure complexity, composites exhibit great variability in mechanical properties and need to be analyzed on the basis of different ply angles, wall thickness, and damping ratio [12]. Namely, using fiber-reinforced materials offers a wide range of possibilities for adjusting their properties, such as stiffness and damping, by manipulating layup, fiber, and matrix material, or fiber volume content [13]. With such numerous degrees of freedom when designing a composite, there is a need for efficient simulation methods for vibroacoustic analyses involving complex multi-physical models, possibly with allowance for fluid-structure interaction. Fiber-reinforced composites exhibit random fiber orientations due to the manufacturing tolerances. The study in [14] concerns with a numerical investigation of the vibrational behavior of the long fiber-reinforced composites under uncertainty in fiber orientations. A numerical case study is used to illustrate the features of the method, where the impact of the uncertainty in fiber orientations on the natural frequencies and mode shapes of a rectangular composite plate with nominal orientation is investigated. The vibroacoustic behavior of bio-composites, including damping and elastic properties, sound absorption, and transmission loss levels, are investigated in [15]. Despite having less detrimental environmental effects and thorough availability, natural fibers are still unsuitable for wide implementation in industrial components. Some shortcomings, such as the presence of moisture contents, thicker diameter, and lower antifungus quality, hold up the progress of natural fiber composites in staying competitive with synthetic composites. The review in [16] aims at investigating the acoustic absorption behavior of natural fiber composites due to the incorporation of granular materials. The possible influential factors of fibers and grains were described for the enhancement of low-frequency acoustic absorption of the composites. The impact of elastic parameter uncertainty on the natural frequency and the radiated acoustic power of laminated composite plates is investigated in [17]. Numerical results show that the natural frequencies and the radiated acoustic powers are strongly affected by uncertainty in input parameters. Coupled vibroacoustic analyses of plates produced from composite materials can be performed by using finite element analysis software.