Mehmet Çalışkan

Integrated FEM/BEM approach to the dynamic and acoustic analysis of plate structures

An integrated finite element/boundary element method approach to the prediction of the interior acoustic radiation of open ended box structures is presented. Dynamic response of the structure is predicted in terms of the nodal displacements under sinusoidal point force excitation using the finite element method. Theoretical results obtained in terms of frequency response functions are verified using the results from tests performed on a box structure. The interior acoustic field is then examined by the boundary element method using the boundary conditions obtained from the finite element analysis. Sound pressure levels produced inside the structure are calculated and the results are compared with the experimental measurements.

Analysis of near field sound radiation from a resonant unbaffled plate using simplified analytical models

Near field radiation behavior of an unbaffled square plate with free edges, which is excited by a harmonic force at its midpoint, is analytically, computationally and experimentally studied. Emphasis is on the applicability of simplified analytical models to predict the near field sound pressures and spatially-averaged surface and acoustic intensities. First, the plate is computationally discretized into equal segments that are replaced by simple, phase-correlated discrete acoustic sources. Piston radiator models (with and without mutual radiation impedance terms) as well as pulsating sphere models are employed to exhibit the contribution of mutual impedance terms. The near field pressure and spatially-averaged intensity radiated from phase-correlated discrete sources are calculated based on the premise that their individual phases are obtained from the plate (surface) vibration measurements. The importance of mutual impedance terms on the near field radiation is highlighted. Second, the two-microphone acoustic intensity and the surface intensity techniques are employed to determine the spatially-averaged intensity spectra, like analytical models. Results are examined on both narrow and 1/3 octave band bases up to 1600 Hz covering radiation from several plate vibration modes. Finally, an indirect boundary element model is used to predict spatially-averaged intensity spectra, as well as to simulate the two-microphone method given surface vibration data. All predictions are compared with analogous measurements. Discrepancies between theory and experiments (and even between two intensity measurements) are discussed along with possible sources of error.

Acoustical Design and Noise Control in Metro Stations: Case Studies of the Ankara Metro System

The aim of this research is to demonstrate the importance of initial strategies in acoustical design of underground metro stations. The paper searches for practical design solutions by evaluating different materials for providing optimum acoustical conditions in such spaces. Acoustical designs of three metro stations on a new expansion line in Ankara including Sogutozu, Bilkent and ODTU metro stations are presented through computer simulation. Predictions of room acoustical parameters are presented for both platform and ticket office floors in terms of parameters like reverberation time (RT), speech transmission index (STI) and A-weighted sound level (SPL) distribution within spaces. Simulated reverberation times are evaluated in view of legislative requirements. The study confirms the importance of using sound absorbing materials on the ceiling and sidewalls together. The nonwoven material, used behind perforated metal suspended ceilings, has proved effective in reverberation control.

Investigations on sound energy decays and flows in a monumental mosque

This work investigates the sound energy decays and flows in the Süleymaniye Mosque in İstanbul. This is a single-space superstructure having multiple domes. The study searches for the non-exponential sound energy decay characteristics. The effect of different material surfaces and volumetric contributions are investigated using acoustic simulations and in situ acoustical measurements. Sound energy decay rates are estimated by Bayesian decay analysis. The measured data reveal double- or triple-slope energy decay profiles within the superstructure. To shed light on the mechanism of energy exchanges resulting in multi-slope decay, spatial sound energy distributions and energy flow vectors are studied by diffusion equation model (DEM) simulations. The resulting sound energy flow vector maps highlight the contribution of a sound-reflective central dome contrasted with an absorptive carpeted floor in providing delayed energy feedback. In contrast, no multi-slope energy decay pattern is observed in DEM simulations with a bare marble floor, which generates a much more diffuse sound field than in the real situation with a carpeted floor. The results demonstrate that energy fragmentation, in support of the non-exponential energy decay profile, is due to both the sound absorption characteristics of materials and to their distributions, as well as to relations between the subvolumes of the mosques interior.

Diffusion Equation-Based Finite Element Modeling of a Monumental Worship Space

In this work, a diffusion equation model (DEM) is applied to a room acoustics case for in-depth sound field analysis. Background of the theory, the governing and boundary equations specifically applicable to this study are presented. A three-dimensional geometric model of a monumental worship space is composed. The DEM is solved over this model in a finite element framework to obtain sound energy densities. The sound field within the monument is numerically assessed; spatial sound energy distributions and flow vector analysis are conducted through the time-dependent DEM solutions.

Numerical Analysis of One-Dimensional Sound Propagation Through a Duct Containing Water Droplets

In this paper sound propagation through an air-filled circular duct containing water droplets has been studied by solving numerically one-dimensional linearized Euler equations in frequency domain. Interactions between the liquid and gas phases were accounted for by proper source terms. Waves were introduced into the domain via Perfectly Matched Layers (PML) equations applied in finite regions adjacent to the truncated ends of the duct. Absorption and dispersion results due to energy transfer from air to the water droplets were obtained as a function of average droplet diameter and droplet concentration as well as finite mass loading. Results agree well with those available in the literature.

A Correlation Improvement Technique for Model Updating of Structures

This study proposes a new correlation improvement technique for the optimum node removal location to get improved modal assurance criterion (MAC) matrix. The technique is applied to updating of the finite element model (FEM) of a structure. The developed routine is tried on a utility helicopter. It is proven that it is capable of showing better performance than the coordinate MAC (coMAC), commonly used in such analyses. Commercial software is utilized for the finite element analysis of the helicopter fuselage and tail. Experimental modal analyses are also performed for updating the model for tail of the helicopter to demonstrate the effectiveness of the new technique.

Acoustical design of Turkish Religious Affairs Mosque

The new Turkish Religious Affairs Mosque(DIB) with its prayer capacity and outstanding volume is the largest neo-classic mosque project of the past decade built in Ankara, Turkey. The Mosque is also one of unique examples of its scale for which the room acoustic design is applied in its design phase. Acoustical design of DIB Mosque is critical considering speech and music related activity patterns held in such religious spaces. Interior surface forms and materials of walls, floor, flat ceilings and dome are studied simultaneously with the architectural design as early as in the concept phase. Impedance tube is used for testing alternative materials for specifying sound absorption characteristics of reliefs and perforations. Computer simulation is applied as an acoustical design tool and estimations are held by ODEON v.11.23. Objective acoustical parameters including reverberation time, speech transmission index and A-weighted sound levels are assessed with and without sound reinforcement systems for fully...

Prediction of ground-borne vibrations due to elevated railway traffic

This study investigates the impact of ground-borne vibrations on people in dwellings nearby elevated railway traffic. Assessments are conducted over predicted vibrations with respect to national regulations. Main excitation mechanism is taken as the dynamic loading due to rail and wheel irregularities. Frequency response functions at the rail head are obtained from harmonic analyses by finite element modeling of the elevated structure. In the prediction procedure, dynamic model of the vehicle is coupled with these frequency response functions. Dynamic loading on the railhead is determined and dynamic reaction forces on the legs of the elevated structure are calculated in frequency domain. Ground vibrations are then estimated by implementing a Fourier transform based theoretical model for the layered ground. Assessment in the frequency range from 1 Hz to 100 Hz in one-third octave bands are conducted for groundborne vibrations calculated at the foundation level of dwellings.

Prediction of ground-borne vibrations on historical structures due to tram traffic in Antalya, Turkey

This study investigates the ground-borne vibrations on historically landmarked structures in the city of Antalya due to tram traffic. Assessments are conducted over predicted vibrations with respect to international standards. The study serves as a guidance for the tenders in the upcoming tender process for projects of upgrading existing tram lines as well as construction of new lines. In the prediction procedure, an existing Fourier transform based theoretical model for the track and layered ground is implemented coupling vehicle dynamics. Groundborne vibrations calculated at the base level of structures are considered. Vibration assessment criteria taken from ISO 2631 standard are employed in the evaluations of predicted vibrations at the respective locations in three mutually perpendicular directions.