Theses supervised by Prof. Dr. Hasan Öztürk
10 theses · Dokuz Eylül University, Middle East Technical University
Bir yapının aktif kütle sistemleri ile titreşim kontrolü
Strong earthquake-induced vibrations that endanger human life and the structural integrity of structures as well as wind-induced vibrations of skyscrapers are examples of vibrations in buildings whose amplitudes aimed to be decreased. In order to reduce these types of structural vibrations, active mass damper systems are often used in literature and full-scale applications. In this thesis, the focus is on controller design for ATMD systems in order to reduce the vibration of multi-story buildings, especially earthquake-induced vibrations. Stability of the structure and control mass is guaranteed by Lyapunov-based stability analysis. Robust adaptive backstepping controller, which is a full state feedback control method, is enriched with a new linear regression based design. In this way, the designed controller achieves its control purpose by using fewer sensors feedback. In Lyapunov-based controller designs within the scope of this thesis, the structural parameters are not used and the unknown structural parameters are compensated using adaptive compensation terms. Afterward, a Lyapunov-based controller is designed for a nonlinear structure model that is exposed to nonlinear disturbances and the stability of the structure is ensured while achieving the control purpose. Finally, a controller design based on the natural frequency of the structure has been strengthened with a control structure that limits the range of motion of the controller. As a result, this thesis theoretically proved that vibrations occurring in engineering structures can be controlled by compensating for unknown structural parameters with active mass systems. Stability of the structure for all positive control gains while achieving the control objective is guaranteed by Lyapunov-based stability analysis.
Asılı kütle-yay sisteminin çerçeve yapıların düzlem içi doğal frekansları üzerindeki etkileri
In this study, effects of the suspended mass-spring system on the in-plane natural frequencies, mode shapes and dynamic stability of multi-bay frame structures were investigated. The frame structures were modeled by the finite element method based on the Euler-Bernoulli beam theory. Suspended mass-spring systems are assumed to move only in the vertical direction. The finite element model of the system was created and code was created in the MATLAB program for its solution. The results are compared with the results obtained from ANSYS program. The results obtained in the analyses are given in graphs and tables. Effects of the number, position and spring stiffness of the mass-spring system on the frequency values, mode shapes and dynamic stability of frame structures were determined. In addition, when the natural frequency of the suspended mass-spring system is greater or smaller than the first natural frequency of the frame structures, it is reacted that it affects the natural frequency of the frame structures differently.
Hareketli yüklere maruz kalan kompleks yapıların titreşim analizi
In this doctoral thesis, dynamic responses of the complex structure subjected to vehicles moving at a constant speed V have been studied. The complex structure, that is, multi- bay and multi- storey frames, is thought to be as a model of a viaduct. The dynamic response of the viaduct under passage of the high-speed train is important issue for design of the structures, passenger comfort, derailment of the train, etc. Various vehicle as a model of a train are used: (1) the moving load model, (2) moving oscillator model, (3) the moving 2-axle vehicle with 4 degrees-of-freedom (DOF), (4) the moving 10 DOF multi-body system consisting of 2-bogies and 4-axle. The dynamic analysis of the vehicle-structure interaction (or moving load-structure) system is performed by using the finite element method. The beams and columns forming the frame structure are modelled by the Bernoulli-Euler beam theory. The presence of cracks in the structure is also examined. This is significant because the structure is subjected to high amplitude vibrations for a long time, the fatigue-induced crack formation can occur. The presence of a crack changes the stiffness of the structure. The stiffness is decreased and this implies a reduction of the natural frequency of the structure. Depending on the location of the crack, the reduction effect in stiffness or natural frequency varies. In order to obtain the stiffness matrix of the cracked element, the total elasticity matrix is first calculated. The stiffness matrix of the cracked element in the free-free state is then determined from the condition of equilibrium. The equations of motion are determined by the generalized Lagrange's equation. The equations of motion corresponding to the vehicle-structure system is a coupled second-order differential equations with variable coefficient. The Newmark method and Wilson-theta method of direct integration are used to integrate those equations. In this thesis, the effects of the crack location, the velocity of moving vehicle/load, number of bays/storeys, force span length and mode shapes on the dynamic response of complex structures have been investigated. In order to validate the finite element model, code developed with MATLAB software has been compared with a study in the literature or ANSYS software. Three-dimensional(3D) graphics have been used to evaluate the results.
Çatlaklı kompozit plakaların dinamik kararlılığı
In recent decades, composite plates are widely used in a wide variety of engineering applications such as the automotive industry, aerospace, marine, rail vehicles and civil engineering structures. Composite plates are subjected to static and dynamic loads. In this study, the dynamic stability of cracked composite plates has been investigated numerically by using the finite element method. Isotropic thin plate based on the Kirchhoff's thin plate theory is modelled by using the principles of the finite element method. In addition to, a composite plate based on classical lamination theory is modelled by using the finite element method. It is assumed that the boundary condition of the thin plate is fixed on one side and the other sides are free. The thin plate is divided into square plate elements. These square plates have four nodes and each node have one translational and two rotational degrees of freedom, so these square plates have twelve degrees of freedom. Mathieu-Hill type motion equation which is used to calculate the dynamic stability of the plate, is created by using energy expressions obtained from the Lagrange equation. The developed MATLAB finite element code is used to examine the effect of crack on natural frequency, critical buckling load and dynamic stability for isotropic and composite plates. Furthermore, MATLAB results are compared with the results of ANSYS model and very good agreement between these results is observed.
Ön gerilmeli çatlaklı kompozit ve izotropik eğri plakaların statik ve dinamik analizi
Plates, which are frequently used in engineering structures, are generally used in curved form because of their higher stiffness values. Some of the plates in the assembly stage are produced in a curved form, and some of them are bent during assembly due to their usage places and used in the pre-stressed state. However, creating a realistic mathematical model covering different situations before production and knowing the critical free vibration values are important for the structure's durability and cost. Within the scope of the thesis, it is aimed to examine the free vibration of pre-stressed composite and isotropic curved plates with cracks. An external distributed vertical load is applied at the free end of a cantilever plate, and then the free edge where the load is applied is fixed to obtain a pre-stressed curved thin plate. The non - linear deflection curve of the large deflected flexible plate is obtained from the large deflection equation. The finite element model used in the thesis comprises the combination of classical plate theory and four-node quadrilateral element. In addition, the effect of curvature on free vibration and mode shapes is examined. The present theory and the ANSYS results are compared for the same load parameters to verify the present model's accuracy and validity. The different mode shapes for the curve model depending on the changing of load parameter and the different effects of crack depending on the changing of mode shapes are presented.
Alüminyum-mineral kompozit kirişlerin ve plakaların mekanik ve dinamik analizi
Frame structures are widely used in aerospace, maritime industries, construction, etc. These structures are subjected to static and dynamic loads, which may cause buckling, dynamic instability, or resonance. Hence, it is essential to determine the right material and understand the mechanic and dynamic properties of such structures. This thesis investigates the free vibration, buckling, and dynamic stability of isotropic and orthotropic curved beam and plate frame structures using the finite element method and beam or plate theory. The effects of the radius of curvature and stacking order of the single-bay and two-bay curved frame structures on the natural frequency, critical buckling load, and unstable regions are investigated. Similarly, the effects of the aspect ratio on the dynamic and buckling characteristics of the curved frame structures are examined. Besides, the effects of the thickness on the natural frequency and critical buckling load of the isotropic curved beam frame structure are investigated. Euler – Bernoulli Beam Theory and Classical Plate Theory is employed with the Finite Element Method to obtain isotropic and orthotropic beam frame structures. Curved plate frame structures are modeled considering Kirchhoff – Love Plate Theory for isotropic frames, whereas the Classical Plate Theory and First-Order Shear Deformation Theory for orthotropic frames. Results are validated with those of ANSYS and SolidWorks. Aluminum – potassium feldspar metal matrix composite materials are fabricated via the stir casting method. The mechanical properties of such materials are obtained by tensile testing. Free vibration, buckling, and dynamic stability analyses are performed considering a plate of such material.
İnsan vücudu için masaj mekanizması tasarımı, analizi ve kontrolü
Ofiste çalışan kişilerin en büyük rahatsızlıklarından biri, ergonomik olmayan ortamlarda çalışmalarından dolayı, kalıcı rahatsızlıklara yakalanmalarıdır. Ortaya çıkan rahatsızlıklar ile ilgili olarak çalışmalar yapılıp, firmaların rahatsızlanan çalışanlarından ötürü senelik zararları üzerine raporlar hazırlanmıştır. Uluslararası bir sorun olan ergonomik olmayan çalışma koşulları hakkında yoğun çalışmalar gerçekleştirilmektedir. Tez içeriğinde Dokuz Eylül Üniversitesi Tekstil Mühendisliği ile yapılan ortak çalışmalar BAP Koordinasyon Birimi ve Bilim, Sanayi ve Teknoloji Bakanlığı, San-Tez programı tarafından desteklenmiştir. Tasarlanacak mekanizmalar ile ilgili ölçü, çalışma sıklığı, çalışma frekansı gibi değerlerin belirlenmesi amacıyla 2013.KB.FEN.036 numaralı BAP projesinde çalışmalar yürütülmüştür. Bu çalışmalar kapsamında akademik ve idari personele anket uygulaması yapılmış ve uygun ölçülerde mekanizmaların üretilebilmesi için antropometrik ölçüler alınmıştır. Elde edilen bilgiler ışığında 0185.STZ.2013-1 numaralı San-Tez projesi dahilinde 2 adet masaj mekanizmasının tasarımı gerçekleştirilmiştir. Üretimden önce mekanizmaların statik, yorulma ve doğal frekans analizleri yapılmış ve oluşabilecek sorunlar üretime geçilmeden tespit edilmiştir. Daha sonra imal edilen mekanizmalar, Bürosit firması tarafından projeye özel olarak üretilen ofis koltuklarına monte edilmişlerdir. Ayrıca bu çalışmada tasarlanmış olan masaj mekanizması entegre edilmiş konstrüksiyon ile, Türk Standartları Enstitüsü' ne patent başvurusunda bulunulmuştur (Patent Başvuru Numarası: 2016/12074).
Asılı kütle-yay sistemlerine sahip eğri kirişin dinamik kararlılık analizi
In this study, the dynamic stability of a curved beam with the suspended spring-mass system is investigated for both isotropic material and layered composite. The beam is considered to Euler-Bernoulli beam and uniform cross-section. The effective flexural modulus have been employed for the composite curved beam. The curved beam fixed both ends and subjected to a uniformly distributed periodic axial load. The curved beam modeled by using the finite element model based on energy equations in conjunction with Bolotin's approach. The developed MATLAB finite element code is used to determine the dynamic instability regions. The natural frequencies and critical buckling load parameters of the curved beam are also determined. Those are compared with the results of ANSYS model and other studies existing literature and very good agreement is found. The effect of the stiffness coefficients, position of the spring-mass system, dynamic load parameter, and static load parameter on the dynamic regions are investigated for various subtended angle and radius of the curved beam. The results are presented by tables and graphics.
Püskürtme ince kaplamaların sünme davranışı analizi
Thin Spray-on Liner (TSL) is a relatively thin (2–5 mm) and fast-setting liner material used by spraying onto rock surfaces to support underground excavations. Areal support materials that are sprayed onto the rock, such as shotcrete or liners, are able to generate support resistance at small rock deformations and can prevent underground rockfalls from happening in the first place. However, where large ground convergence occurs, the more flexible TSLs may provide superior support over the full range of rock deformations. In this study, the creep behaviour of two TSLs were determined in the laboratory environment. Under constant stress levels, strain-time behaviours of two TSLs were determined up to 2 months of the testing period. For this purpose, dogbone shape test samples were prepared with different curing times (1-2, 7, and 14 days) and were tested under 23 ± 2 °C laboratory conditions according to the ASTM standards. Four different constant stress levels (80%, 60%, 40%, and 20% of the tensile strength) were applied until rupture of the specimens. The resultant correlations are explained using inter-related equations to make a forecast about the service life of the material (creep rupture envelopes) were derived. The proposed correlations may offer an insight into both the effective permanent support time and the strain amount at the liner failure. Experimental data were used to construct viscoelastic and viscoplastic models. A good agreement was generally observed between the presented models and the experimental results. In addition, the developed constitutive stress-strain-time relations were introduced to finite element software ABAQUS with a new subroutine. After verification of the implemented subroutines, the support performance of the TSLs on the global stability in the underground openings has been investigated. As a result of this study, the creep behaviours of TSLs were investigated for the first time in the literature and it has been found that TSLs are extremely sensitive to creep behaviour. The effective block bearing time of TSL's with different wedge dimension scenarios of underground excavations were determined. As a result of the numerical studies, performed in 4 different representative rock mass squeezing behaviours with different TSL application thicknesses, it was concluded that the effect of TSL on global stability was extremely small.
Batı Raman petrol sahası madenciliğinde kullanılan yeraltı açıklıklarının duraylılık ve yenilme analizi
Batı Raman holds the Turkey's proven largest oil reserve (1.85 billion barrels). The reserve is located at an average depth of 1450 m within a fractured limestone. This heavy oil has a 12° API gravity and a viscosity of 200-2000 cp. A future plan for this reserve is to use a "mining assisted heavy oil production" method. The idea behind this method is to reach the reserve by a decline from the surface and continue opening up galleries beneath the reserve from which fan shape up holes will be drilled in the reserve. Steam will be injected from these up holes to decrease the viscosity of heavy oil and production will be done by gravity drainage. In this thesis, stability of all the openings based on the scenario above is carried out using a numerical modelling code, FLAC. In the first stage, tunnel openings were first investigated based on analytical solutions, then 2D and 3D analyzes were carried out. It has been shown that the 20m wall-to-wall pillar, which is planned to be left between the tunnels, will remain stable. Then, the effects of boreholes to be used in oil production in the reservoir were modelled, and it was determined that the extends of the failure zones occurred along the tunnel and in the regions where the boreholes were opened. It was compared with a physical model test made with the found failure zones, and it was concluded that 2.23% of the heavy oil production determined in the experiment was due to borehole openings. A parametric study was conducted by analyzing a total of 15 models by following the ratio found, and Excavation Induced Damage Production Ratio (EIDPR) was defined. As a result of the parametric study, a regression model was created, and the model's equation was shared. Keywords: Heavy Oil, Deep Tunnels, TBM, Stability, Batı Raman, MAHOP