Opportunities and limitations on vibro-acoustic design of vehicle structures by means of energy flow-based numerical simulation

For future vehicle development, it is necessary to understand the dynamic behavior of body structures based on their virtual design in the early development stages. A promising approach is the numerical finite element simulation of energetic quantities in the frequency domain, which allows for a holistic view of structure-borne and air-borne sound distribution. The objective of this paper is to identify opportunities and limitations of energy flow-based numerical simulation on the vibro-acoustic design of vehicle structures. The energy flow of a structure vibrating in steady state can be visualized by the quantity of active structural intensity (STI), which describes the active energy transport within the structure. The energy flow within the fluid coupled to the vibrating structure is represented by the active sound intensity (SI). Analogous to the STI, the active SI describes the energy transport of air-borne sound radiated from structure to fluid. In this work the entire system, consisting of a structure and a fluid, is modeled in order to improve the system's vibro-acoustic dynamic behavior, such as the sound pressure at a defined position or the averaged structure's velocity. A scientific description of the dynamic system's behavior can be derived from the formerly mentioned energetic quantities. An important advantage of energetic quantities over classical quantities, such as structure velocity or fluid sound pressure, is their consistency as a specific power. Therefore, energetic quantities can be applied to both structure and fluid. Furthermore, the energy transport of all wave types, including the structure's longitudinal waves, can be visualized. In order to purposefully influence the active energy flow in the vibroacoustic system, modifications are applied to the structure as the opportunities for modifying the vehicles' fluid are strongly limited. The effect of these structural modifications can be analyzed by comparing the dynamic behavior of a reference system with the modified systems. Additionally, the energetic characteristics of the systems are compared to quantities of classical engineering approaches, such as transfer path analysis or operational modal analysis. This allows a look at dynamic systems from several points of view and the statements are derived from those different approaches. Finally, limitations for numerical simulations of energetic quantities in a vibro-acoustic vehicle design are discussed and interpreted. These limitations are referred to application scenarios of energetic quantities for the vibro-acoustic development of vehicle structures.