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ÖgeDesign optimization and experimental validation of the additively manufactured passive vibration isolator of an inertial measurement unit in aerospace applications(Graduate School, 2023)Vibration is an environmental factor that can affect structures for various reasons and create unwanted consequences on engineering systems. Designers should consider the effects of vibration phenomena and take necessary precautions within the design processes. Especially in aerospace systems, pressure fluctuations, and irregular flow can cause vibrations on structures. Although structural strength is achieved against these vibrations, there may be situations where sensitive avionics systems within aerospace systems cannot operate as desired in this vibration environment affecting them. Inertial measurement units, which are commonly used in aerospace engineering systems such as guided missiles, measure linear acceleration and angular velocity in six degrees of freedom. These measurements are fed to the missile's controller, which controls the missile's control surfaces. Random vibrations that affect the missile over a wide frequency band due to pressure fluctuations and irregular flow can disrupt the measurements made by the inertial measurement unit. While the low-frequency measurements made by the inertial measurement unit are used by the controller, high-frequency measurements need to be eliminated. This way, only low-frequency movements that truly represent the missile's motion are measured and used by the controller. High-frequency filtering can be done digitally or mechanically using passive vibration isolators. Passive vibration isolation is achieved by placing materials such as elastomers with much lower stiffness compared to the structures to be isolated between the isolated structure and the structure that causes excitation. In this way, the elastomer exhibits dynamic behavior under incoming vibrations by resonating, showing the damping of high-frequency excitations to transmit to the structure to be isolated. In this study, a similar approach was taken to isolate an inertial measurement unit (IMU) within a guided missile from vibrations that occur within a broad frequency band induced by fluid flow. Because the IMU measures motion with six degrees of freedom, the mechanical design of the IMU isolation system differs from other passive vibration isolation applications. The decoupled mode shapes of the isolation system enable the IMU to respond minimally to vibrations in other axes when an excitation acts on a particular axis. In other words, since the isolation system does not respond to vibrations in the other axes due to the axis where the excitation originates, the IMU does not make a faulty measurement due to the dynamics of the isolation system in axes where the excitation is absent. The decoupling of the system's mode shapes occurs when the mass center and elastic center of the isolation system coincide. When the mass and elastic centers cannot coincide and the modes are coupled, the system may make a combined movement in various axes at the resonance frequency. For example, if an excitation acts on the IMU as linear acceleration when the mode shapes of the system are not decoupled, it may cause the IMU to make an angular velocity measurement as if it were making an angular movement that the system is not actually making. In this case, the controller will try to control the system as if it were making a movement that it is not happening. Avoiding this situation is critical in systems such as guided missiles. Since the primary goal in aviation systems is generally low mass and surface area, small-volume subsystems are used. In systems where the available space is limited, it may not be easy to coincide the mass and elastic centers. The design of the ring-shaped passive vibration isolator provides an advantage in terms of adding a small volume elastomer layer and coinciding with the mass/elastic centers. Viscoelastic materials used in passive vibration isolation exhibit nonlinear mechanical behavior under factors such as temperature, frequency, and excitation amplitude. When these materials are used in systems that work in extreme environments, such as aerospace, these nonlinear effects must be strictly taken into account. Therefore, a silicone material that can maintain its viscoelastic properties over a wide temperature range is used as a passive vibration isolation element in aerospace applications. However, producing silicone-like materials in complex shapes can create disadvantages in terms of cost and practicality. On the other hand, with the developing additive manufacturing method and innovative materials, complex shapes can be produced in a practical way. For optimum passive vibration isolation, a passive vibration isolator with a complex shape can be produced using viscoelastic material and additive manufacturing methods. In this study, a design of a passive vibration isolator made from an elastomer-like material using the additive manufacturing method, which cannot be produced by conventional methods, was created, and its usability was investigated through simulations and tests.Additionally, a passive vibration isolator design methodology has been proposed for an inertial measurement unit to be used within a specified missile geometry throughout this study. Firstly, the limited dimensions of a ring-shaped vibration isolator were obtained by adhering to the usable area limits where the elastomer material design could be integrated, which were dictated by the unmodifiable missile and inertial measurement unit geometries. In passive vibration isolation, the natural frequency of the system determines the frequency band of the isolation. The ring-shaped passive vibration isolator was parameterized, and the natural frequency of the system was made changeable through systematic extrusion from the isolator geometry. The systematic extrusion were made in such a way that the coincidence of mass and elastic center was continuously ensured. In order to model with the finite element method, the mechanical properties of the thermoplastic polyurethane material used in the additive manufacturing process were obtained through dynamic mechanical analysis (DMA). The temperature and frequency-dependent non-linear mechanical properties of the material was obtained such as the storage and loss modulus. Hence, the temperature and frequency-dependent viscosity change of the thermoplastic polyurethane material were modeled using the Williams-Landel-Ferry (WLF) function by using time-temperature superposition. The parametrized geometry of the passive vibration isolator was optimized through a simplified finite element model to ensure that the natural frequencies determining the vibration isolation were within a certain frequency range. During optimization, the modal shapes of different geometries were controlled by including the modal assurance criterion (MAC) parameter in the optimization. As a result, the optimum geometry of the passive vibration isolator was obtained and analyzed in depth with a detailed nonlinear finite element model to investigate the isolation performance of the system. The isolation performance of the system, and the effect of excitation frequency and temperature on the natural frequency, were obtained with this detailed model. Nonlinearly simulated optimum vibration isolator geometry was produced using the additive manufacturing method. The produced passive vibration isolator was tested and vibration transmissibility measured experimentally to investigate its vibration isolation performance. In the experimental studies, sine sweep and random vibration tests were performed on the system in two different translational axes. By changing the amplitudes and frequency sweep rates used in sine sweep tests, the vibration isolation performance and behavior of the thermoplastic polyurethane (TPU85A) were investigated. In addition, the random vibration that the missile was exposed to under operational conditions in a wide frequency range was experimentally examined by applying random vibration tests to the test setup. Finally, the test results were compared with the simulation. In conclusion, this study presents a methodology for designing passive vibration isolation for an inertial measurement unit. The issues to be considered in the design of an inertia measurement unit passive vibration isolator, which requires special attention in terms of vibration isolation, are discussed in detail. The vibration isolation performance of the optimized geometry from a non-linear material was obtained in the simulation environment by using the finite element method. Afterward, the passive vibration isolator was manufactured and tested by additive manufacturing. Finally, the simulation and test results, in a good agreement with each other, showed that the desired vibration isolation performance was achieved in the temperature regime where TPU85A showed rubber properties, which were determined by the results of dynamic mechanical analysis.
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ÖgeRoller bearing fault detection using rotary encoder(Graduate School, 2024-01-26)For many industrial complex machines, there are various challenging issues which include reducing machine downtime, managing repairs and maximising operating times. Any problem or fault in machines can cause failures and downtimes which in turn can lead to significant economic losses. Therefore, industrial companies need to plan organized maintenance strategies for optimum productivity. Condition based monitoring stands out as a highly effective and dependable method widely utilized in the field of maintenance. For rotating systems, rolling bearings are one of the commonly used essential machine elements that are prone to unexpected failures. Traditional monitoring methods predominantly rely on conventional vibration measurements. In recent years, a novel approach to monitoring the condition of bearings using torsional vibration signals via encoder has attracted great attention by scholars. Encoder signals offer notable benefits over standard vibration signals. For instance, encoders have higher signal to noise ratio than accelerometers because they are located close to the rotary components while accelerometers suffer from long and complicated transfer paths. Moreover, encoders are usually built-in type sensors which make them part of the available systems, and this brings additional economic advantages for condition monitoring. However, captured encoder signals are impacted by adverse factors like speed uncertainties due to random load fluctuations and variations in electric supply. These factors predominantly affect low-level signals, where diagnostic information is frequently masked by noise. In order to overcome this challenging problem, researchers continuously strive to create sophisticated signal processing strategies for the effective extraction of crucial diagnostic insights from signals with significant noise interference. In this thesis, conventional and relatively well-established signal processing methods typically employed in vibration-based fault detection are examined and their implementations in encoder-based fault diagnosis are investigated. Particular attention is paid to signal de-noising and enhancement of the measured signals to improve fault detection performance of proposed method. In the first chapter, the problem addressed in this thesis is introduced in detail and the existing literature is thoroughly reviewed. In the second chapter, encoder specific details and employed signal processing methods are described. Briefly, working principle of encoders and Instantaneous Angular Speed (IAS) measurement concept are examined. Theoretical background of the the signal processing methods used in this thesis are also presented in this chapter. The subsequent chapter details the experimental setup and outlines the specifics of the measurement campaign. For the experimental part of the study, an existing Bosch test bench, designed for endurance validation of high-pressure pumps, is employed. For the experimental validation of the fault detection methods used in this thesis, artificial faults are created on the inner rings of cylindrical roller bearings. Due to the complicated design of the setup and the adverse effects encountered during the signal acquisition, measured data inherently contained significant amount of background noise. Chapter four focuses on the signal processing of the measured raw data, aiming to extract hidden information which is critical for detecting bearing faults. An open-source software, Python, along with its signal processing libraries, are employed to process the measured signal and apply various signal processing methods for extracting diagnosic information from measured data. This software choice is based on the diverse range of available techniques and exponential growth observed in this area. In this chapter, three different methodologies for fault detection are introduced. The first employs envelope analysis and spectral kurtosis for detection of faults on the bearing's inner ring. In this context, different fault sizes are examined, and the effectiveness of a hybrid approach is investigated. The results clearly indicate that successful identification of the fault frequency of the bearing's inner ring can be captured via the envelope spectra. In the second method, signal de-noising is the main focus of the investigation. Empirical mode decomposition and singular value decomposition-based bearing fault detection methodology is proposed and proposed method is compared with direct empirical mode decomposition applied signal without prior signal de-noising. The findings reveal that the proposed methodology effectively identifies the bearing inner ring fault frequency in the presence of considerable amount of background noise. In contrast, approaches relying solely on spectrum analysis and the direct application of empirical mode decomposition demonstrate limited effectiveness under similar conditions. When analyzing instantaneous angular speed variations captured by an encoder, directly detecting fault-indicative frequency components is challenging since the bearing fault carries low energy in the signal. Therefore, the third method focuses on removing the most deterministic components from the signal. After filtering, fault frequencies and harmonics were distinguishable in the signal spectra at various speeds, yielding consistent results. Modulation-related sidebands were also observed in the signal. Upon examining the effect of speed, it was found that in our case, detecting bearing frequencies at relatively lower rpms was easier due to the increase in noise content with rising speed. As a result, findings in this thesis leads to the conclusion that encoder signal-based fault detection methods offer an important alternative in bearing condition monitoring. Besides, bearing fault detection capability of the existing methods can be significantly improved by the use of signal de-noising.
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ÖgeInvestigation of the damping effectiveness of particle damper integrated structures design produced by laser powder bed fusion under different boundary conditions(Graduate School, 2023)Particle damper (PD) technology has been increasingly adopted as a passive damping mechanism in structures to minimize vibrations and improve their performance. This technology is particularly advantageous due to its design simplicity, low cost, and applicability in harsh conditions, making it an attractive alternative to traditional damping techniques. The production of structures with integrated PDs using additive manufacturing, particularly the Laser Powder Bed Fusion (LPBF) process, has become increasingly studied in recent times. This approach eliminates the need for external dampers to be implemented into the structure, simplifying the design process and reducing costs. However, in order to fully utilize the potential of PDs, a deeper understanding of their dynamic behavior is required. To this end, a study is conducted to investigate the impacts of integrated PDs on the dynamic behavior of additively manufactured structures. The study examined 16 different cases of integrated PDs with different sizes, numbers, and positions on the structure. For example, PDs with different total volumes were designed and located at various positions in the structure to understand the size and position impact on the dynamic behavior at the first and second modes of the structure. Hammer impact tests were performed on the additively manufactured samples to calculate the frequency response functions (FRFs). The modal parameters such as the natural frequency and damping ratio were obtained using the rational fraction polynomial (RFP) method. According to the findings, the damping performance of the parts was improved up to 10 times by using body-integrated PDs compared to the fully fused specimen. It was also observed that the effectiveness of body-integrated PDs depend significantly on the volume and spatial location. For instance, damping was generally increased when the volume fraction was increased. This increase in volume fraction also reduced the total weight of the specimens by up to 60 g. Moreover, the damping performance significantly increased for a specific mode if the PDs were located around the maximum displacement regions. Another design group was created to investigate the boundary conditions. The samples in this group were tested with both free-free and fixed-free boundary conditions. According to the results, although higher results were obtained for the fixed-free boundary conditions for the first mode, it was revealed that there are many parameters to be investigated such as mode shapes and system dampings. The findings of this study are of great significance to the manufacturing industry as they provide insights into the potential benefits of using integrated PDs in structures. With the ability to reduce vibrations and improve performance, structures incorporating PDs can be designed to fulfill the particular requirements of various industries such as aerospace, automotive, and civil engineering. Additionally, the study highlights the potential of additive manufacturing to produce structures with integrated PDs. With the flexibility of the powder bed fusion process, designers can easily incorporate PDs into their designs, without the need for external dampers. This approach not only simplifies the design process but also reduces costs, making it an attractive alternative to traditional damping techniques. It is worth noting that while the results of this study are promising, additional researches are required to fully understand the dynamic behavior of structures with integrated PDs. Future studies should focus on optimizing the size, shape, and location of PDs to achieve maximum damping performance. Moreover, research is required to investigate the effectiveness of integrated PDs on other modes of the structure, as well as on structures subjected to different loads and operating conditions. In conclusion, the use of particle damper technology in structures has the potential to improve their performance and reduce vibrations. By incorporating PDs into structures using additive manufacturing, designers can achieve greater design flexibility and reduce costs. However, further research is needed to fully realize the potential of this technology and optimize the design of structures with integrated PDs.
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ÖgeNiCoCrAlY+YSZ ile kaplanmış kanatçıklı diskin dinamik sonluelemanlar analizi ve toplu parametreli sistem ile modellenmesi(Lisansüstü Eğitim Enstitüsü, 2023)Günümüzde havacılık sektörü her geçen gün hızla gelişmekte ve ortaya çıkan yeni üretim yöntemleriyle kullanılan teknolojinin sürekli olarak ilerlemesi üzerine çalışmalar devam etmektedir. Bu tez çalışmasında, havacılık endüstrisinin üzerine çalıştığı araştırma ve geliştirme faaliyetlerinin bir hedefi olan hafif, dayanıklı, etkili uçak yapılarının tasarımı ve analizine yönelik bir çalışma ele alınmıştır. Bu bağlamda, türbin motorlarında kullanılan yüksek hızlı dönen yüzeylere sahip entegre kanat ve disk yapıları olan kanatçıklı diskler, hava taşıtlarının performansını doğrudan etkileyen önemli bileşenler arasında yer almaktadır. Ancak, kanatçıklı diskler gibi bileşenlerde meydana gelen düzensizlikler, yapısal kusurları etkileyebilmekte ve hatta titreşim davranışlarını değiştirebilmektedir. Bu yapısal düzensizlikle; malzemeden kaynaklı düzensizlikler, üretim prosedürleri ve kullanım sırasında meydana gelen hasarlar gibi çeşitli faktörlerden kaynaklanabilmektedir. Bu nedenle, kanatçıklı diskler (blisk)'lerin doğal frekanslarını belirlemek ve bozulmaların bu frekansları nasıl etkilediğini anlamak son derece önemlidir. Bu çalışmada, kaplanmış kanatlı bir diskin dinamik davranışını analiz etmek ve modellemek için toplu parametreli sistem kullanılmıştır. Parametreli sistemde, öncelikle sektörel bağlamda ilgili model kurulup devamında toplu parametre modeli ile sistem geneli incelenmiştir. İlerleyen aşamalarda çözüm yöntemine dair geliştirmede bulunulup mevcuttaki toplu parametreli sistemin serbestlik dereceleri arttırılmış ve çıkan sonuçlar sonlu elemanlar çözümü ile karşılaştırılarak sistemin optimizasyonu ve daha detaylı bir çözümleme tekniği ele alınmıştır. Ayrıca, bu çalışma blisklerde meydana gelen düzensiz titreşimlerin sert kaplamalar aracılığıyla düşürülmesi ve literatürdeki analitik çözüm yöntemlerine alternatif bir çözüm sunma amacını taşımaktadır. Sistemin doğal frekans değerlerinin incelenmesi ve analitiksonlu elemanlar çözümleri arasındaki hata paylarının yeni parametreli sistem ile azaltılması hedeflenmektedir. Çalışmanın ilk aşamasında, ilgili literatürde yapılan çalışmalar detaylı bir şekilde incelenmiş ve elde edilen bulgular, tezin yönünü belirlemede önemli bir rehberlik sağlamıştır. Ardından, kanatçıklı diskin çözümlemesinin temelini oluşturan sayısal analiz ve sonlu elemanlar model aşamaları için kullanılan yazılımların yöntem ve teknikleri detaylı bir şekilde açıklanmıştır. Teorik bilgilerin edinilmesinden sonra, sonlu elemanlar simülasyon çalışmaları için sıklıkla tercih edilen bir dinamik analiz yazılımında kanatçıklı diske ait katı cisim geometrisine paralel ilgili parçanın önceden belirlenmiş sınır koşulları altında dinamik frekans analizi kurulumu gerçekleştirilmiştir. Aynı zamanda, analitik sistem modeli kurulmuş ve çözüm için gerekli parametrelerin elde edilmesine yönelik çalışmalar yapılmıştır ve ilgili sonuçlar elde edilmiştir. Elde edilen veriler, yeni oluşturulan toplu kütle modeliyle sonlu elemanlar modelinden gelen sonuçların uyumlu olduğunu göstermiştir. Sayısal ve dinamik sistem çözümlemelerine ait sonuçlar ayrı bir bölümde detaylı bir şekilde paylaşılmıştır. Çalışmanın son bölümünde, genel bir değerlendirme yapılmış ve gelecekte yapılacak çalışmalar için öneriler sunulmuştur. Yapılan çalışma, kanatçıklı disklerde meydana gelen düzensiz titreşimlerin analizine ve sistem karakteristiklerinin incelenmesine yönelik bir katkı sunulması hedeflemektedir. Ayrıca, geliştirilmiş toplu parametreli sistem analitik ve sonlu elemanlar çözümleri arasındaki hata paylarını azaltma potansiyelini göstermektedir.
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ÖgeModal balancing of flexible rotors with gyroscopic effects using kalman filter(Graduate School, 2023)At present day, rotating machinery is being used at numerous different fields. Looking to its development so far, demand from the rotating components is evolving towards becoming lighter and spinning faster by still keeping the same or higher amount of life cycles. The mentioned trend makes rotating components less stiff and increases their operating speed range. This can possibly introduce vibration driven problems such as noise, excessive wear or shortened fatigue life. One topic related with vibrations is the balancing of the rotating hardware. Balancing approach of rotating components differ depending on the classification of a rotor being "rigid" or "flexible". The difference between the two is, a rigid rotor operates significantly less than its first critical bending speed and a flexible rotor operates close to or above its first critical bending speed. Balancing of rigid rotors are very well-known theoretically and practically. On the other hand, flexible rotor balancing is not standardized and there are various approaches for the process. This study will try to develop a robust and precise flexible balancing procedure considering the gyroscopic effect which is usually neglected at many flexible balancing techniques. The developed approach will be suitable for both test rig and in-site balancing. The approach hosts a FE model to be used and does not require any trial mass. It is necessary to collect displacement data from the rotating hardware at close to critical speeds. FE model and sensor data are adequate to generate the unbalance values and positions using a series of calculations. These calculations require a force reconstruction method to be used and it is decided to use Augmented Kalman Filter. A regular Augmented Kalman Filter is not suitable for capturing the desired phenomena's, thus, some additional tweaks are made so that it fits better for the nature of rotordynamics. When the forces are generated, it is an easy effort to obtain unbalance masses and positions. The balancing can be done at close to critical speeds, mode by mode using modal approach and without upsetting the previously balanced modes. An important point on setting the balancing criteria is using the complex eigenvalue analysis to obtain modal properties due to existence of gyroscopic effect.