LEE- Gemi İnşaatı ve Gemi Makinaları Mühendisliği-Doktora
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Konu "Ship handling" ile LEE- Gemi İnşaatı ve Gemi Makinaları Mühendisliği-Doktora'a göz atma
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ÖgeNumerical modeling and experimental analysis on coupled torsional-longitudinal and lateral vibrations of propulsion shaft system(Lisansüstü Eğitim Enstitüsü, 2021) Halilbeşe, Akile Neşe ; Özsoysal, Osman Azmi ; 691729 ; Gemi İnşaatı ve Gemi MakineleriShips are the most leading option for the development and progress of water transportation. The main engine, which is one of the main components of the propulsion system, is to produce more power than ever with oversizing the ship because of increased tonnage demands. As an inevitable result of this fact, the number of failures increases due to the increased drive power of ships because of the complex running conditions under harmonic and impact loads. The propulsion shaft system is the heart of the ship. When the operating conditions cannot be predicted correctly and the impact loads miscalculated, the reliability of the propulsion systems will be reduced. The main purpose of this thesis is to develop a multi-purpose computer code to investigate the behavior of a conventional propulsion shaft system in where three different coupled vibration case occurs and to observe how the vibration responses vary. Simultane vibration responses are in different directions. Excitation frequency and ultimate amplitudes that may occur with the coupled vibration are generally ignorable and so done. Whenever the vibration forms are considered separately instead of coupled, the numerical results can be quite different from the actual measurements. Ignoring the coupled vibration approach or pure uncoupled vibration calculations is not realistic since the harmonic forces do not excite only the power transmission shaft in the propulsion chain but also the bearings and ship hull, and causes a significant raising at noise level. Similarly, it negatively affects the running performance of the shaft system and leads to loss of durability, breakage, tribological problems, and finally failures. For this reason, it always needs to examine the coupled vibration modes for the cruising reliability of each ship. It is noticed that the unwanted vibration reactions generally occur in the longitudinal, torsional, and lateral modes and their coupled forms. Even if the numerical error margin will increase during the coupled vibration modeling (i.e. torsional, longitudinal, and lateral), the interaction of two axes is inevitably taken into account. Common studied forms about the coupled vibration are coupled torsional-longitudinal vibration, coupled torsional-lateral, and coupled longitudinal-lateral vibration. In this research, taking advantage of the small-scaled model of a propulsion shaft system at the Wuhan University of Technology, the experimental results are compared with the results of numerical simulation codes about the coupled vibration cases such as the torsional-longitudinal, the torsional-lateral, and the longitudinal-lateral. Numerical outcomes were validated by examining the time-based displacement values at different shaft speeds and comparing them with test results. The theoretical approach is based on a mass-spring system for coupled torsional-longitudinal vibrations. The theoretical model for coupled torsional-longitudinal vibration is sufficiently compatible that it can respond quickly to changes in values such as the stiffness coefficient, damping coefficient, and rotational speed. External forces and forced vibration responses, including torque and longitudinal forces with different amplitudes, were taken into account. Besides, since the propeller is not included in the experimental mechanism, the numerical model is created using the coupled vibration coefficient in the literature. A theoretical solution has been obtained to verify the proposed mass-spring model. Depending on the change of rotational speed and loading condition, the change of frequency response and maximum ultimate amplitude.were presented. Coupled vibration effect is also investigated by comparing maximum displacement values for coupled and uncoupled vibration. The effect of the parameters such as the shaft length, shaft diameter, stiffness coefficient, and damping coefficient, etc., for coupled torsional-longitudinal vibrations were also examined. The vibration stress that occurs in the system was further compared with the allowable stress required by DNV. Coupled torsional-lateral vibrations of the propulsion shaft system are caused by the rotation of the propeller, the mass of shaft components, the external and internal forces affecting the bearings, axial displacement caused by the transmission of the force of the gears to each other. As a result of the structural properties of the shaft and the imbalances that occur during the rotation process, axial displacements occur between the center of the mass and the center of the cross-section of the shaft. The movement of the shaft always results in axial displacement horizontally when not intervened externally in real operating conditions. This eccentric effect of the shaft causes the vibration response to be more complex and intense. In addition to vibration control techniques that reduce the wrong alignment of the bearing and shaft, the dissertation has focused mainly on theoretical and practical methods that support the prediction of shaft vibrations. Therefore, minimizing the vibration density of the propeller shaft on the horizontal and vertical axis is of great interest. The majority of the studies about coupled lateral-torsional vibration in literature are belong to aerospace engineering. In those studies, the shaft system is modeled according to the torsional-lateral vibrations with a disk of mass m located at the midpoint of a massless shaft called with the Jefcott Rotor model. Taking advantage of these studies, the Jefcott Rotor model has been revised and applied to the propeller-shaft system in this doctoral research work. Thus, a numeric model was obtained considering sufficiently suitable and responsive to influencing factors such as the eccentricity of the cross-section, the damping coefficient, stiffness coefficient, and the shaft length-diameter ratio. This method is suitable for predicting dynamic performance and numerical solutions with the above impact factors. The experiment was repeated at different shaft speed values to validate the proposed numerical model, and time-dependent displacement values were compared for validation. Based on the proposed model, the effect of the change of impact factors such as the eccentricity of the cross-section, the damping coefficient, the coefficient of stiffness, and the length-diameter ratio of the shaft were discussed. Additionally, a new coupling coefficient value has been proposed, and the importance of accurately defining the coupling coefficient value was shown. At the final step of this doctoral work, the coupled longitudinal-lateral vibrations were investigated due to axial forces that occur in the propeller and cause misalignment of the shaft. The numerical model for the coupled longitudinal-lateral vibrations involves the equation of motion by the Energy Method. In the model, the equations are complex, and it is tough to simplify and bring into matrix form and solve in Matlab. Consequently, the equation of motion is solved with the help of the Ansys APDL program by modeling the system with the mass-spring method. The coupled vibration effect is given in the system with the angular velocity. To verify the proposed mass-spring model, the results were compared with data obtained from the experimental setup. Depending on the change of rotational speed and loading condition, the change of frequency responses and maximum displacements are presented. The frequency response values of the system were obtained with the harmonic solution. The effect of parameters such as the shaft length-diameter and stiffness coefficient, damping coefficient of the bearing in the numerical method for coupled longitudinal-lateral vibrations were also examined. Validated numerical results by the experimental ones show that the code and the thesis offer suitable solutions for the safety performance of any power transmission system about significant problems by the multiple coupled vibrations.