Yazar "Gokdag, Hakan" seçeneğine göre listele
Listeleniyor 1 - 7 / 7
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Artificial neural network-based parameter identification of a beam-3D tip attachment system(Taylor & Francis Inc, 2025) Gokdag, Hakan; Kati, Hilal DoganayIn this study, an artificial neural network (ANN)-based approach is proposed for estimating the tip mass attachment and structural damping parameters in a beam-3D mass system undergoing combined bending and torsional vibrations. The study begins with a detailed explanation of the calculation of the frequency response functions (FRFs) for this specific system. Subsequently, a difference vector is defined, based on the discrepancy between experimental and numerical FRF curves. This vector is dependent on ten parameters: the mass of the tip attachment, its mass moments of inertia, and the coordinates of the mass center, and the structural damping ratios of the beam. An orthogonal design method is then employed to create a design space for these parameters, and the elements of the difference vector are calculated for each point within this space. The points in the design space and the computed difference vectors are utilized as input and output data for training the ANN. The optimization process conducted with the obtained ANN model allows for realistic estimation of the tip mass parameters and damping values. The analysis reveals that as the design space widens, the parameter estimation process becomes increasingly challenging. This, in turn, necessitates a larger number of points in the design space and more neurons in the hidden layers of the trained network. In cases where the design space is small to medium in size, the parameter estimation errors are observed to be <5%. However, for wider design spaces, the estimation errors tend to increase.Öğe CEVAP YÜZEYİ YAKLAŞIMI İLE TAŞIT KOLTUĞU SONLU ELEMAN MODELİNİN GÜNCELLENMESİ(Bursa Uludağ Üniversitesi, 2019) Gokdag, Hakan; Arısoy, Yılmaz; Kopmaz, OsmanAna sanayi firmaları üretimini talep ettikleri taşıt koltuklarının belirli şartnamelere uygun olmasını isterler. İmalatçı firma bu durumda koltuğun prototipini üretip birtakım değiştirme ve iyileştirmelerle teknik şartları sağlamaya çalışabilir. Fakat bu yol pahalı ve zaman alıcıdır. Bu durumda alternatif yöntem koltuğun sonlu eleman modelini geliştirmek ve üzerinde parametrik çalıştırmalar gerçekleştirmektir. Bu çalışmada öncelikle bir ticari araç koltuğunun iskelet aksamına eklenen sünger, kılıf, sırt tahtası gibi katmanların koltuğun ileri-geri ve yanal doğrultudaki modal parametrelere etkisi deneysel olarak incelenmiştir. Buradan elde edilen sonuçlara göre koltuk iskeleti sonlu eleman modeline katmanlar çeşitli kütle ve katılık parametreleriyle eklenmiştir. Daha sonra sonlu eleman modelinin gerçek koltuk modeliyle uyumlu olması için bu parametrelerin uygun değerleri cevap yüzeyi yaklaşımı ile belirlenmiştir. Ayrıca bu yöntemle, ilgili katmanların hangilerinin daha etkili olduğu da görülmüştür. Sonuç olarak, sonlu eleman modeli ile elde edilen temel frekansların her iki doğrultu için deneysel frekanslarla uyumlu olduğu, özellikle ileri-geri harekette frekans cevabı fonksiyonu genliklerinin de birbirine oldukça yakın olduğu görülmüştür.Öğe Effect of Printing Parameters on the Dynamic Characteristics of Additively Manufactured ABS Beams: An Experimental Modal Analysis and Response Surface Methodology(Mdpi, 2025) Doganay Kati, Hilal; He, Feiyang; Khan, Muhammad; Gokdag, Hakan; Alshammari, Yousef Lafi A.This study investigates the dynamic characteristics of three-dimensional (3D) printed acrylonitrile butadiene styrene (ABS) cantilever beams using Experimental Modal Analysis (EMA). The effects of Fused Deposition Modelling (FDM) process parameters-specifically infill pattern, infill density, nozzle size, and raster angle-on the natural frequency, mode shapes, and damping ratio were examined. Although numerous studies have addressed the static mechanical behaviour of FDM parts, there remains a significant gap in understanding how internal structural features and porosity influence their vibrational response. To address this, a total of seventy-two specimens were fabricated with varying parameter combinations, and their dynamic responses were evaluated through frequency response functions (FRFs) obtained via the impact hammer test. Damping characteristics were extracted using the peak-picking (half power) method. Additionally, the influence of internal porosity on damping behaviour was assessed by comparing the actual and theoretical masses of the specimens. The findings indicate that both natural frequencies and damping ratios are strongly influenced by the internal structure of the printed components. In particular, gyroid and cubic infill patterns increased structural stiffness and resulted in higher resonant frequencies, while low infill densities and triangle patterns contributed to enhanced damping capacity. Response Surface Methodology (RSM) was employed to develop mathematical models describing the parameter effects, providing predictive tools for applications sensitive to vibration. The high R2 values obtained in the RSM models based on the input variables show that these variables explain the effects of these variables on both natural frequency and damping ratio with high accuracy. The models developed (with R2 values up to 0.98) enable the prediction of modal behaviour, providing a valuable design tool for engineers optimizing vibration-sensitive components in fields such as aerospace, automotive, and electronics.Öğe Free vibration of a Timoshenko beam carrying three dimensional tip mass: Analytical solution and experimental modal testing(Carl Hanser Verlag, 2017) Katı Doğanay, Hilal; Gokdag, HakanIn this work, free vibration of a Timoshenko beam carrying three dimensional tip mass whose center of gravity is not coincident with beam end is dealt with. The beam performs bending in two orthogonal planes plus torsional deformation about the beam axis. Since the tip mass center of gravity is not coincident with beam end point, these deformations are coupled through the boundary conditions. First, an analytical model is developed for the considered system and solved. Later, the analytical results are compared with the experimental and finite element results. Experimental values are obtained by the impact testing, and peak picking approach is employed to extract modal data. Furthermore, finite element results are obtained by ANSYS, a famous finite element software. According to the relevant literature, this is the first study including experimental data for the considered system. It is observed that analytical results, in general, agree with the numerical and experimental results. Thus, the analytical model developed in this work may safely be used for later studies where lower modal data of the structure is required.Öğe Identification of the tip mass parameters in a beam-tip mass system using response surface methodology(Walter De Gruyter Gmbh, 2024) Gokdag, Hakan; Kati, Hilal DoganayIn this study, a response surface based approach is introduced to determine the physical parameters of the tip mass of a beam - tip mass system, such as mass, mass moment of inertia and coordinates of the centre of gravity with respect to the beam end point. To this end, first, a difference function was formulated based on the differences between the peak frequencies and peak amplitudes of the experimental and analytical frequency response functions. Later, observation points were established in the design space using orthogonal arrays, and a response surface was developed using the difference function values at these points. Next, the tip mass parameters were determined by minimizing the response surface with genetic algorithm and particle swarm optimization as well as fmincon, a gradient-based solver of the Matlab program. For comparison purposes, those parameters were obtained by also direct minimization of the difference function with the same algorithms. It was concluded that the tip mass parameters were successfully determined within reasonable error limits by the response surface method with less computational burden. Finally, the effect of design space width on the response surface quality is demonstrated numerically.Öğe Real-Time Tracking and Position Control of an Elastic Cable-Driven Winch System(Mdpi, 2025) Sen, Deniz Kavala; Arisoy, Aydemir; Gokdag, HakanThis study explores the sliding mode control (SMC) strategy to address challenges such as nonlinear dynamics, steady-state errors, and torque fluctuations in elastic cable-driven winch systems. While traditional Proportional-Derivative (PD) control is sufficient for linear systems, it struggles with instability and accuracy issues in flexible systems. SMC provides robustness against uncertainties but can cause mechanical wear and performance degradation due to its chattering effect. To mitigate this, a continuous control signal-based SMC approach was adopted, reducing chattering and improving system stability. This study focuses on tracking and position control, as well as managing motor torque fluctuations during position control, emphasizing controller parameter optimization. Experimental results demonstrate that SMC outperforms PD control in tracking, position control, and torque management.Öğe Vibration analysis of a Timoshenko beam carrying 3D tip mass by using differential transform method(Techno-Press, 2018) Katı Doğanay, Hilal; Gokdag, HakanDynamic behaviour of beam carrying masses has attracted attention of many researchers and engineers. Many studies on the analytical solution of beam with concentric tip mass have been published. However, there are limited works on vibration analysis of beam with an eccentric three dimensional object. In this case, bending and torsional deformations of beam are coupled due to the boundary conditions. Analytical solution of equations of motion of the system is complicated and lengthy. Therefore, in this study, Differential Transform Method (DTM) is applied to solve the relevant equations. First, the Timoshenko beam with 3D tip attachment whose centre of gravity is not coincident with beam end point is considered. The beam is assumed to undergo bending in two orthogonal planes and torsional deformation about beam axis. Using Hamilton's principle the equations of motion of the system along with the possible boundary conditions are derived. Later DTM is applied to obtain natural frequencies and mode shapes of the system. According to the relevant literature DTM has not been applied to such a system so far. Moreover, the problem is modelled by Ansys, the well-known finite element method, and impact test is applied to extract experimental modal data. Comparing DTM results with finite element and experimental results it is concluded that the proposed approach produces accurate results.
