Person: KOPMAZ, OSMAN
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Publication Free vibration analysis of a monosymmetric open section euler-bernoulli beam by means of two different methods(Pamukkale Univ, 2008-01-01) KOPMAZ, OSMAN; Gökdağ, Hakan; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; 0000-0003-3070-6365In this paper, coupled flexural-torsional free vibration of a monosymmetric open section Euler-Bernoulli beam is studied by using two different methods, i.e. the dynamic transfer matrix method (DTMM) and the finite element method (FEM). The natural frequencies obtained from the FEM are observed to be closer to the exact values compared to the DTMM, since the beam deformation functions selected in the FEM have the same form as the real deflection curve of beam has. When the two methods are compared in terms of cpu time, the DTMM requires less computation time to yield reasonably accurate natural frequencies. This advantage of the DTMM is mainly due to the size of the transfer matrix, which remains unchanged independent of the number of elements while the size of coefficient matrix leading to the characteristic equation in the FEM increases with increasing element number. In addition, the mode shapes obtained from the DTMM are found to be satisfactorily accurate. Moreover, the DTMM requires less algebra to derive the transfer matrix. It is concluded that the DTMM, due to its advantages mentioned above, would be superior to the FEM especially in handling lattice type structures.Publication Two practical methods for the forward kinematics of 3-3 type spatial and 3-RRR planar parallel manipulators(MDPI, 2022-12-01) Düzgün, Ercan; Kopmaz, Osman; DÜZGÜN, ERCAN; KOPMAZ, OSMAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü; 0000-0002-9429-9300; 0000-0002-6455-9730; HJS-9844-2023; DAF-9103-2022The forward kinematics in parallel manipulators is a mathematically challenging issue, unlike serial manipulators. Kinematic constraint equations are non-linear transcendental equations that can be reduced to algebraic equations with appropriate transformations. For this reason, sophisticated and time-consuming methods such as the Bezout method, the Groebner bases method, and the like, are used. In this paper, we demonstrate that these equations can be solved by non-complicated mathematical methods for some special types of manipulators such as the 3-3 and 6-3 types of Stewart platforms, and the 3-RRR planar parallel manipulator. Our first method is an analytical approach that exploits the special structure of kinematic constraint equations and yields polynomials of 32nd and 16th order, as mentioned in the previous works. In the second method, an error function is defined. This error function is employed to find the most appropriate initial values for the non-linear equation solver which is used for solving kinematic constraint equations. Determining the initial values in this manner saves computation time and guarantees fast convergence to real solutions.Publication Optimal design of a five-bar planar manipulator and its controller by using different algorithms for minimum shaking forces and moments for the largest trajectory in a usable workspace(Mdpi, 2022-11-01) Kavala Şen, Deniz; Yıldız, Ahmet; Kopmaz, Osman; Kavala Şen, Deniz; YILDIZ, AHMET; KOPMAZ, OSMAN; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makina Mühendisliği Bölümü.; 0000-0001-5434-4368; 0000-0002-2429-8927; T-8076-2018; FVJ-8195-2022; DAF-9103-2022In this paper, a structural design and controller optimization process for a five-bar planar manipulator are studied using three different population-based optimization techniques: particle swarm optimization, genetic algorithm, and differential evolution. First, the desired kinematic properties of the manipulator, such as the position, velocity, and acceleration of the endpoint, are determined using inverse kinematics. Then, an optimization problem is created to minimize the shaking force and moments, and the desired kinematic quantities are implemented as constraints. All the link properties of the manipulator are defined as design variables, and the optimization results are obtained. The results show that it is possible to significantly reduce the shaking force and moment significantly thanks to the optimal design parameters. Finally, the controller is optimized to find the best PID gains considering the forward kinematics of the manipulator. It is observed that the shaking force and shaking moment can be reduced by 99% and 54%, respectively, which has a very positive effect on the accuracy of the trajectory tracking. Moreover, the performances of the optimization methods are compared by using the same number of iterations in the calculations, and thus, it can be seen that the GA method achieves the best results compared to the others. Therefore, the results of this study are of utmost importance for a manufacturer, who wants to design a five-bar planar manipulator and its controller.Publication Effects of drive side pressure angle on gear fatigue crack propagation life for spur gears with symmetric and asymmetric teeth(Amer Soc Mechanical Engineers, 2020-01-01) KARPAT, FATİH; DOĞAN, OĞUZ; Yılmaz, Tufan; YILMAZ, TUFAN GÜRKAN; Yüce, Celalettin; YÜCE, CELALETTİN; KARPAT, ESİN; KOPMAZ, OSMAN; Kalay, Onur Can; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Mekatronik Mühendisliği Bölümü.Today gears are one of the most crucial machine elements in the industry. They are used in every area of the industry. Due to the high performances of the gears, they are also used in aerospace and wind applications. In these areas due to the high torques, unstable conditions, high impact forces, etc. cracks can be seen on the gear surface. During the service life, these cracks can be propagated and gear damages can be seen due to the initial cracks. The aim of this study is to increase the fatigue crack propagation life of the spur gears by using asymmetric tooth profile.Nowadays asymmetric gears have a very important and huge usage area in the industry. In this study, the effects of drive side pressure angle on the fatigue crack propagation life are studied by using the finite element method. The initial starting points of the cracks are defined by static stress analysis. The starting angles of the cracks are defined constant at 45 degrees. The crack propagation analyses are performed in ANSYS SMART Crack-Growth module by using Paris Law. Four different drive side pressure angles (20 degrees-20 degrees, 20 degrees-25 degrees, 20 degrees-30 degrees and 20 degrees-35 degrees) are investigated in this study. As a result of the study the fatigue crack propagation life of the gears is increased dramatically when the drive side pressure angle increase. This results show that the asymmetric tooth profile not only decrease the bending stress but also increase the fatigue crack propagation life strongly.Publication Fatigue performances of helicopter gears(Walter De Gruyter Gmbh, 2023-01-27) Doğan, Oğuz; Yılmaz, Tufan Gürkan; YÜCE, CELALETTİN; Kalay, Onur Can; Karpat, Esin; Kopmaz, Osman; KOPMAZ, OSMAN; Karpat, Fatih; KARPAT, FATİH; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Makine Mühendisliği Bölümü.; Bursa Uludağ Üniversitesi/Mühendislik Fakültesi/Elektrik ve Elektronik Mühendisliği Bölümü.; 0000-0001-8643-6910; 0000-0003-1387-907X; 0000-0003-4203-8237; 0000-0003-3772-7871; 0000-0001-8474-7328; A-5259-2018; V-6153-2017; R-3733-2017Gears are widely used machine elements to transmit power and motion in the industry. During the power transmission, the gears are subjected to cyclic loads. Thus the fatigue resistance of the gears should be deeply investigated. In particular, this issue is gaining much more importance in the space and aviation fields. In this study, the fatigue life of gears made of 9310-VIM-VAR steel used in the aviation field was determined experimentally, and the crack propagation paths obtained were numerically verified. To this end, the SAE J1619 standard single-tooth bending fatigue test apparatus was redesigned and manufactured in order to adapt it to the helicopter gears. Totally 28 single-tooth bending fatigue tests were carried out for various loading conditions. Accordingly, the S-N curves for the helicopter gears were created. The experimental results were verified by the finite element fatigue crack propagation analysis in terms of the initial crack location, crack initialization angle, and crack propagation paths. Conducted experiments and numerical studies are found as compatible with each other.Publication Structural damage detection in an open cross section beam using continuous wavelet transform(Pamukkale Üniversitesi, 2008-01-01) Gökdağ, Hakan; Kopmaz, Osman; Gökdağ, Hakan; KOPMAZ, OSMAN; Uludağ Üniversitesi/Mühendislik Mimarlık Fakültesi/Makine Mühendisliği Bölümü; 0000-0003-3070-6365; JAL-3855-2023; DAF-9103-2022This paper is concerned with the determination of the damage location and extent of an open cross section beam by continuous wavelet transform on its first mode shape. To extract the mode shape, the finite element method is used, and the damage is modeled by a local decrease in the Young modulus of a beam element. The classic modal analysis techniques based on changes in frequency or mode shape curvature are demonstrated to be insufficient for the damage conditions considered. The technique of wavelet analysis is shown to be more effective than the curvature change method especially in the case of noisy data. Since the beam cross section is not symmetric, the mode shape to be measured is essentially dependent on the location of displacement transducer on the beam width, resulting that the sensitivity of wavelet coefficients to damage will be different. Therefore, in this study, it is also explained where the correct measurement locations must be to obtain the wavelet coefficients more sensitive to damage.