LEE- Makina Dinamiği, Titreşim ve Akustik-Yüksek Lisans
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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.
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ÖgeParametric investigation of a piezoelectric tuned dynamic vibration absorber(Graduate School, 2024-02-02)Dynamic vibration absorbers, which are attached as secondary subsystems on primary systems, are passive devices that are used to suppress the vibrations of primary systems. The idea is well-known and proven by many researchers, and it was first introduced by Ormondroyd and Den Hartog in 1928. Nowadays, the different versions of dynamic vibration absorbers are developed. In this study, piezoelectric tuned dynamic vibration absorbers which are one of these versions of dynamic vibration absorbers are investigated. The classical dynamic vibration absorber model is extended with an attachment of a piezoelectric transducer. Hence an electromechanical system model is developed. Furthermore, the chief objective of this study is to investigate the effects of system parameters on the vibration absorption performance of the proposed piezoelectric tuned dynamic vibration absorber. Especially, effects of resistance and inductance on system are determined. The model developed in this study consists of a primary structure attached to common ground via a linear elastic and dissipative path. The secondary system is directly attached on the primary structure through the piezoelectric transducer with the external shunt circuit. Though, the mechanical stiffness and damping characteristics of the piezoelectric transducer are also considered. Hence, when the effect of piezoelectric transducer is off, the system behaves like a classical dynamic vibration absorber. First, the governing multi-physics equations are obtained and numerically solved for both classical and shunted systems. The results are investigated in both time and frequency domains, and the differences between the dynamic responses of both systems are observed. The investigation is conveyed mainly on the vibratory motion of the primary structure. Second, the coefficients of the electrical resistance and inductance on the shunt circuit are altered at given interval, and the effect of these element on vibration absorption performance of the tuned dynamic vibration absorber is investigated. In conclusion, the system parameters that leads to a maximum vibration attenuation on the primary system are obtained.