Research On Basic Theories Of The Radiation Sound Quality From Plate Strucutres

Due to the structural noise is one of the main noise sources, designers and manufacturers are often faced with negative reactions to the sound or noise radiated from the product. A typical response to such reactions is confusion due to the"structural sound quality"of the problem. For the product, sound represents a more complex set of attributes, both aesthetic and functional, the structural sound quality becomes a key problem in product design. Sound quality includes a series of parameters, such as loudness, fluctuation strength and roughness, etc. These parameters influence the human hearing sensation by different ways. On the other hand, sound quality has other useful applications in engineering. For example, one can judge the status of the automobile power transfer system by the help of the fluctuation strength radiated form it. Therefore, for low noise and high performance product design, the study on structural sound quality is crucial on theory. This study also has wide application future on other engineering problems.Analytical method is the main method used in this dissertation. Integrated with numerical method, this dissertation does a deep study systemically for the radiated sound and sound quality from the plate or plate-like structures with different forms. At first, the structural sound radiation model is established for the un-baffled finite plates. Because the different boundary conditions have different effects on the radiated sound, the analytical model is prompted for the calculation of the sound radiated from the plates. Based on the Zwicker loudness model and the corrected PEAQ (Perceptual Evaluation of Audio Quality) method, a model of sound loudness, which is radiated from the plates, is established for forecasting. For calculating the sound radiated from plates with mixed boundary conditions, the GDQ (Generalized Differential Quadrature) method is developed and corrtected in this dissertation. Based on the GDQ method, the model of sound radiation and sound fluctuation strength from the plates with mixed boundary conditions are established. The parameters, which affect the radiated sound fluctuation strength, are also discussed. Using the main domain discretization method prompted in this dissertation, the model of the sound radiation and sound roughness from the plates with arbitrary geometry forms or arbitrary boundary conditions is established. For revealing the effects of the stiffeners and its combined forms on the sound loudness radiated from the stiffened plates, the model of sound radiation and sound loudness from the stiffened plates is established. A new research field, active control of structural sound quality, is prompted in this dissertation. Based on the theory of sound radiation mode, this dissertation develops an active control strategy to control the sound loudness radiated from the plates. Some valuable study results are obtained through the theoretical analysis and numerical calculation in this dissertation. These results provide the theoretical foundation stone for the design of the structural sound quality and the virtual product radiated sound design.Comparing with the current research results, the features obtained in this dissertation are mainly as follows:The model of the sound radiation characteristic from the un-baffled rectangular plates is established. An analytical method is prompted to calculate the sound radiated from the plate with elastic support boundary conditions. The sound power level radiated from the un-baffled plates is numerically calculated by using a double layer integral representation of the sound radiation pressure and the modal coupling coefficients. The sound power level radiated from the baffled rectangular plates with the same boundary conditions are calculated in numerical experiments for comparison. From the viewpoint of energy, average velocity square of the un-baffled and the baffled rectangular plates with different boundary conditions is calculated, respectively. The relationship of sound radiation efficiency between the un-baffled and the baffled rectangular plates is deduced.The effects of boundary conditions on sound radiation characteristics from the rectangular plates are studied. Using analytical method, five different boundary conditions are analyzed and calculated in numerical experiments as examples. The results reveal the effects of simple support, free support and clamped support on the sound radiated from the rectangular plates. Rectangular plates with different point force location and different plate thickness are calculated for verifying the effects of boundary conditions. On the other hand, because of the frequency selectivity of human hearing, the effects of boundary conditions on sound quality are different from the one on physical sound. Based on the Zwicker's loudness model and the corrected PEAQ method, the sound loudness radiated from the vibrating plates and the effects of simple support, clamped support and free support on sound loudness are separately studied. The effects of boundary conditions on sound intensity level, sound intensity density and critical-band level are also studied under the condition of taking the frequency selectivity of human hearing system into account. The transformation progress of sound intensity level to sound loudness radiated from the rectangular plates, which is caused by the human hearing frequency selectivity characteristic, is illustrated in this dissretation. The research results provide analytical method for the forecasting and design of the sound loudness radiated from the plates or plate-like strucutres.For the structural sound, two separate psycho-acoustical parameters, sound fluctuation strength and sound roughness, appears when the radiated sound is modulated by other sounds. The generalized differential quadrature method is developed for calculating the sound radiated from the forced vibrating rectangular plates with mixed boundary conditions. The fluctuation strength of the radiated sound, which is modulated by another sound near the plates, is studied. The effects of the modulation frequency and the modulation degree on the sound fluctuation strength are revealed. The effects of the radiated sound frequency and the structural modal density are also studied and compared, respectively. The numerical results are presented to show the characteristics of the fluctuation strength of the modulated sound radiated from the rectangular plates with mixed boundary conditions. For further generalizing, this dissertation reveals the effects of the modulation-sound pressure level and the modulation-sound frequency on the modulated sound roughness radiated from the rectangular plates with non-uniform boundary conditions. A generalized method is developed to calculate the radiated sound from such plates. Using this method, the sound roughness is calculated and compared with different modulation-sound frequency and modulation-sound pressure level, including the radiated sound frequency. Moreover, the effect of the plate mode density on the sound roughness is also illustrated.This dissertation reveals the effects of the stiffeners on the radiated sound loudness from the stiffened rectangular plates. Based on the hierarchical trigonometric functions and the corrected PEAQ method, the sound loudness radiated from different stiffened plates and the effects of the stiffeners'form are studied, respectively. The effects of the stiffener on the radiated sound intensity level and the critical-band level are also studied. Due to the frequency selectivity of human hearing, the difference of the physical sound and the human hearing sensation are illustrated. Moreover, the effect of the mode density on the radiated sound loudness is also illustrated. The results provide theoretical model and a forecasting method for the controlling of the structural sound loudness by stiffeners.A new research filed, active control of structural sound quality, is prompted. The active loudness control of the sound radiated from the rectangular plates is studied. Basing on the radiation modes, the sound loudness model is developed for the active loudness control. According to the radiation modes and the developed sound loudness model, an active loudness control strategy is prompted. By comparing the different boundary conditions on the edge of the plate, the effects of the boundary conditions on the active sound loudness control are also illustrated. The calculation results show that the radiated sound loudness is effectively controlled by the strategy. The results also reveal that, for the reason of the frequency selectivity of the human hearing, the active control of structural radiated sound loudness is quite different from the active control of structural vibration and the tradiational active control of noise.