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The dynamic characteristics of an aluminum honeycomb sandwich panel are experimentally determined under free boundary conditions and the computational model is updated according to the experimental results. The study confirms that the adhesives used to bond the core and face sheets affect the dynamic response of the sandwich panel through the adhesive fillets formed between the face sheets and the core during the bonding process. The viscous damping of the structure is also determined by experimental modal analysis. It is observed that the results of the experimental and computational results agree well when the effects of adhesive fillets and viscous damping are considered. Furthermore, a dynamic response analysis under random vibration is conducted to reveal the differences between the results of the initial and the updated models. [ABSTRACT FROM AUTHOR]

The dynamic response of a thermoplastic composite sandwich structure is optimized under random vibration. First, the experimental modal analysis data of a set of test samples are processed by a sequential set of statistical analysis such as descriptive statistics, factor analysis, and paired sample t-test. Then, the sample with the highest ability to represent the group is taken as the reference data. Three different computational models, which are defined according to whether the solid to be meshed is considered an area or a volume, are constructed. Modal analysis results of the computational models are compared to the reference experimental data to evaluate the performance of the models. To predict the dynamic response of the sandwich beam, it is excited through a random signal in the transverse direction. The nodal acceleration responses are computed in 17 evenly spaced points located on the upper finishing layer of the sandwich beam. Finally, a geometry optimization study is conducted to predict the optimum thicknesses of the 7 layers bonded together to form the sandwich beam. The optimum layer thicknesses that minimize the nodal accelerations at 17 evenly spaced points on the sandwich beam are computed. The current study shows that the shell model has the closest values to the experimental data compared to other models. As far as the dynamic response of a TPC sandwich structure is concerned, it is concluded that the shell model better represents the structure during the modeling phase and leads to concurrently reduced weight and nodal acceleration, when optimized. [ABSTRACT FROM AUTHOR]

It is important to analyse the multipurpose music classrooms (MMCs), where active teaching and music practice are held in the same space, with an eligible acoustical parameter set. In the current study, three different operational conditions (OCs) are introduced to determine such a parameter set, which includes T30, EDT, D50, C80, and STI. The aim of the study is to outline the acoustical performance of the MMCs according to the OCs. The acoustical performance of three MMCs located in three different schools is investigated. For the experimental component of the study, impulse response tests are conducted in the MMCs. The computational analysis incorporates the construction of 3D models of the MMCs. To cope with the epistemic uncertainties, a model update study is performed by synthesizing the experimental and computational outcomes. The results of the updated models are then compared to the regulations and the relevant studies available in the literature. [ABSTRACT FROM AUTHOR]

Under the excitation of an engine, an exhaust system vibrates, and the vibrational energy is transmitted to the vehicle body through the exhaust mounts. The transmitted energy makes contribution to the vibration of the body, which in turn increases the overall vehicle noise level. Noise contributed by the exhaust can be eliminated up to a certain level by reducing the force transmitted through the exhaust mounts. In this study, an objective function, which represents the force transmitted through the exhaust mounts, is defined. The aim is to minimise the transmitted force to achieve better vibration isolation. First, structural dynamic analysis of the vehicle exhaust system is evaluated using computational and experimental procedures. The finite element model of the exhaust system is complemented and validated by following an experimental modal analysis procedure. In the correlation procedure, it is observed that boundary conditions of the exhaust system have significant effects on the results. Hence, the definitions and the assumptions of boundary conditions are studied in detail to achieve a better correlation between the computational and the experimental models. Then, the validated computational model is used for optimisation studies. Moreover, a mass is attached to the exhaust system to reduce the forces transmitted to the vehicle body. For the optimisation problem, the stiffness and the location of exhaust mounts and the weight and the location of hanging mass are defined as design variables. Significant improvements are achieved compared to the initial design. [ABSTRACT FROM AUTHOR]

Low frequency booming problem, which is frequently observed in automobiles, negatively affects the acoustic performance and reduces the total comfort. In the current study, vibration and acoustic characteristics of a sedan are examined. In this work, where it is aimed to improve the acoustic comfort of a vehicle, an approach that uses both experimental and computational methods together is adopted. The study is confined to the 33-193 Hz bandwidth, where low frequency booming problems are observed. A finite element model of the vehicle is constructed and structural and acoustical modes are computed. The structural modes of the vehicle are calculated experimentally, as well, and the computational model is updated using experimental results. The effective forces that act on the structure are identified experimentally using transfer path analysis. The low frequency booming problems, which could not have been predicted at the design stage, are diagnosed by assessing both the results of experimental data and computational analysis. In accordance with the outcomes, modification studies are performed on the experimentally verified finite element model using tuned mass dampers. [ABSTRACT FROM AUTHOR]

Computational models that are constructed to identify the noise transmission in engineering structures are examined using the experimental data. Since damping data are often unavailable, undamped models are used in computational studies, which are performed to model and to suppress noise. To achieve high correlation coefficients, experimental models should be undamped, as well. The current study offers an analytical solution to separate damping from the noise transfer functions. The proposed solution is exemplified through a case study. Noise transfer functions of an automobile are measured experimentally. For the experimental study, the source-path-receiver approach is employed. The damping information embedded in the experimental data is separated using the proposed analytical solution. The computational model is updated using the undamped transfer functions. Final model is obtained by imposing the identified damping information to the updated model. [ABSTRACT FROM AUTHOR]

The coupled vibro-acoustic response of a sedan is analysed, and the effect of the folding rear-seat aperture is studied. First, a simplified model of an acoustic cavity that consists of two adjacent boxes connected by an aperture is modelled. An analytical solution is proposed to calculate the acoustic eigenfrequencies of the simplified model. Then, the uncoupled acoustic eigenfrequencies of the actual cavity (where the trunk cavity and the cabin cavity are connected through an aperture) are computed. It is shown that the planar acoustic eigenfrequencies of the sedan can be calculated approximately using the analytical solution proposed. To clarify the effect of the folding rear-seat aperture further, the coupled vibro-acoustic response of the sedan is analysed using different case studies. It is observed that the booming noise is highly correlated with the calculated uncoupled planar acoustic eigenfrequencies. [ABSTRACT FROM AUTHOR]