Modelagem numérica de sistemas de áudio em habitáculo veicular

• Ano de defesa: 2018
• Autor(a) principal: Rafael Morais Cunha
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Sistemas de som automotivo; Método numérico dos elementos finitos; Impedância acústica; Alto-falantes; Método dos elementos finitos; Automóveis Equipamento de som; Engenharia mecânica
• Link de acesso: http://hdl.handle.net/1843/BUOS-B8WFCY

Due to the growing need to obtain high performance automotive sound systems in a short development cycle, predictive methods for the characterization of the acoustic response in vehicle passenger compartments have been increasingly used by vehicle engineering, with the main purpose of estimating the sound field at points of interest of the cavity. A possible solution to this is through the computational modeling of a discrete and pre-processed geometric model of the internal air volume of the passenger compartment. With the proper mathematical representation of the passive boundary conditions (interior materials) and the active boundary conditions (sound radiation sources), it is possible to use the numerical method of finite elements to simulate sound reflections and radiations in the cabin in order to estimate the acoustic response of sound systems up to the frequency limit of the method, which is linked to the hardware used in the simulations. Based on this, the present work aimed to numerically model an automotive sound system consisting of mid-range loudspeakers mounted on the front door panels of a medium hatch category standard vehicle in order to estimate the acoustics response of these systems at the listening points of the driver, up to the maximum frequency of 1.000 Hz. In order to do that, a passenger compartment finite element model of the analyzed car was created, taking into account the geometry and exact positions of the speakers mid-range, in addition to a discretized geometric representation of the driver's torso and head, necessary to include the phenomenon of diffraction of sound waves in the region near the ears of the occupant. After that, the acoustically absorbent materials in cabin were tested to estimate the specific acoustic impedance parameter, which was done by a B&K impedance tube. Then the electromechanical response of the speakers was measured by means of a Doppler laser vibrometer, which resulted in a frequency response function between the acceleration in the center of these transducers and the input voltage in the coils, evaluated while the cone of the loudspeaker was in its first vibrating mode. With the boundary conditions properly represented, they were applied in the discretized model of the passenger compartment cavity, and the model was executed and configured in the software LMS Virtual.Lab 13.7, which in fact resulted in the acoustic response of the sound system analyzed in the listening points. These results were confronted with experimental curves of the same nature and a good frequency correlation was found. However, the modal damping factor was underestimated due to the negligence of the acoustic vibro-couplings that contribute, especially below 200 Hz, in the dynamics of sound reflections in the boundaries of the passenger compartment. In addition, the electromechanical response of the speakers validated the mathematical model of piston in a infinity baffle. Such a finding shows that up to the first resonance frequency of the membranes, the sources of automotive sound systems can be simulated by the finite element model without the need to characterize its electromechanical response