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    Determination of the acoustical performance of multipurpose music classrooms
    (Taylor & Francis Ltd, 2024) Aslan, Ahmet; Oktav, Akin; Metin, Buket
    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.
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    Determination of the effect of adhesive fillets and viscous damping on the dynamic response of aluminum honeycomb sandwich panels
    (Taylor & Francis Inc, 2024) Oktav, Akin
    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.
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    Dynamic response optimization of a thermoplastic composite sandwich beam under random vibration
    (Taylor & Francis Inc, 2024) Oktav, Akin; Basaran, Murat Alper; Daricik, Fatih
    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.
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    Evaluation of Dynamic Response Variability in Aluminum Honeycomb Sandwich Panels Using PCE and Kriging-Based Metamodel
    (Gazi Univ, 2025) Oktav, Akin; Basaran, Murat Alper
    The aim of this study is to model the dynamic response variability in commercial aluminum honeycomb sandwich panels. An experimental modal analysis is performed on 35 identical commercial AHSPs. Based on 10,000 samples, a computational model is constructed according to the estimated weight of the panel. The modal frequencies of the 35 samples for the first 10 flexible modes are compared with the computational results and deviations are referred to as errors. The thickness of the facing sheets and thickness of the cell wall of the core are considered as sources of uncertainty. A data-driven meta-model called PCE-Kriging is created.
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    The Impact of HVAC Systems on Speech Intelligibility in University Classrooms
    (Polska Akad Nauk, Polish Acad Sciences, Inst Fundamental Tech Res Pas, 2025) Oktav, Akin; Ener, Arda; Ozenc, Faruk; Sari, Sila
    Good speech intelligibility in university classrooms is crucial to the learning process, ensuring that students can clearly hear all conversations taking place in the classroom. While it is well known that speech intelligibility depends on the geometrical characteristics of a space and the properties of its surfaces, other factors need also to be considered. Among the most important are: the heating, ventilation, and air conditioning (HVAC) systems used in classrooms. Fan noise from HVAC systems increases the background noise level (BNL), negatively affecting speech intelligibility. In addition, the movement of air caused by these systems alters room acoustic variables. Although this dynamic situation is often overlooked in the early design stages, HVAC systems are often active during lectures and influence acoustics variables, especially the speech transmission index (STI). In this study, the impact of HVAC systems on the STI was measured in five different unoccupied classrooms in the Rafet Kay & imath;,s Faculty of Engineering at Alanya Alaaddin Keykubat University. The results were evaluated according to relevant standards. The results of these evaluations offer insights for researchers, architects, and engineers working in the field of acoustics.
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    The Variation in the Acoustic Response of the Karadeniz Kemenche Depending on the Thickness of the Soundboard
    (Springer Singapore Pte Ltd, 2025) Oktav, Akin
    The variation in the acoustic response of the Karadeniz kemenche, a bowed string musical instrument, depending on the thickness of the soundboard is investigated. The most important challenge in obtaining an updated model for the musical instruments is the uncertainties arising from the orthotropic wood materials used. A model update procedure is implemented to resolve uncertainties in the mechanical properties of materials. The model is updated and complemented through an experimental modal analysis study. An analytical solution for the calculation of acoustic mode frequencies is implemented. A vibroacoustic analysis is performed to model the fluid-structure interaction. An acoustic response analysis is conducted by applying the experimentally measured nonlinear triaxial acceleration signal to the bridge of the musical instrument to simulate the slip-stick behaviour of the bow. Finally, the effect of soundboard thickness on the amplitude of acoustic pressure is examined. It is revealed that the amplitude of acoustic pressure substantially increases at the resonances that appeared at 340 Hz and 900 Hz, when the thickness of soundboard is 2.1 mm, and the amplitudes of pitch frequencies are observed to be higher in a broadband range. When the thickness of the soundboard of the instrument is 1.7 mm, it is seen that the amplitude of the pitch frequency of 1040 Hz increases significantly, and thus, it can produce a higher-pitched sound. When the soundboard thickness of the instrument is 2.9 mm, a strong pitch frequency of around 700 Hz can be obtained, according to the results of the studied model.
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    Variation of the acoustic response of Karadeniz kemenche due to the size and geometry of the sound holes
    (Elsevier Sci Ltd, 2024) Alkin, Ali; Oktav, Akin
    This study deals with the changes in acoustic response caused by variations in the geometry and size of the sound holes in the Karadeniz kemenche, a bowed string musical instrument. Starting from a 3D scan of the instrument, a finite element model is built. The structural model is verified with the results of an experimental modal analysis study, followed by a model update procedure implemented by frequency optimization. The acoustic cavity is simplified to a rectangular geometry to analytically verify the acoustic cavity modes. Before analysing the variation of the sound holes, a verification of the structure-borne noise of the musical instrument is performed. The variation of acoustic response depending on the size and geometry of the sound holes are studied using the verified vibroacoustic model. The various geometries are inspired by shapes chosen for both ancestral and contemporary bowed string instruments. The normalized loudness levels attributed to each variation are computed and examined to see if a relationship could be found to evaluate the variations.