실선 계측을 통한 축발전기 일체형 추진축계의 동적 하중 재분배 메커니즘 및 횡진동 특성 규명

다국어 초록 (Multilingual Abstract)

In recent years, the application of shaft generators has been increasingly adopted in large commercial vessels as an effective measure to comply with the stringent environmental regulations imposed by the International Maritime Organization （IMO）. In particular, shaft generator systems driven by the main propulsion engine have been widely employed in large container ships because of their advantages in reducing fuel consumption and improving energy efficiency. Owing to machinery space limitations, shaft generators are frequently integrated directly into the propulsion - xiv shafting system. However, the large rotor of a shaft generator introduces additional mass and mass moment of inertia into the shafting system, which may affect shaft alignment characteristics, bearing load distribution, and lateral vibration behavior. Furthermore, because a shaft generator requires a constant air gap between the rotor and stator, a higher level of structural integrity and vibration performance is required than that of conventional propulsion shafting systems. Previous studies on shaft generators have primarily focused on PTO/PTI systems, power conversion technologies, energy efficiency improvement, and torsional vibration characteristics. In contrast, relatively limited attention has been paid to the alignment and lateral vibration characteristics of propulsion shafting systems equipped with shaft generators. In particular, experimental investigations on dynamic load variation and lateral vibration responses under actual operating conditions remain scarce. Conventional shafting design and verification procedures are mainly based on static alignment analysis and jack-up test results, whereas the dynamic behavior induced by
fluctuating propeller loads, hull deformation, and environmental loading conditions during vessel operation has not been sufficiently considered. In this study, a large container vessel equipped with a shaft generator integrated propulsion shafting system was investigated through shaft alignment analysis, lateral vibration analysis, and full-scale onboard measurements to evaluate the dynamic behavior of the shafting system under actual operating conditions. First, shaft alignment analysis based on the matrix structural analysis method was performed to evaluate bearing reactions, shaft deflections, and bending stresses. In addition, finite element based free and forced lateral vibration analyses were conducted to examine natural frequencies, vibration modes, and dynamic response characteristics.
The operational stability of the shaft generator was also assessed through evaluation of the air-gap condition between the rotor and stator. For full-scale measurements, strain gauges were installed on the propulsion shaft to measure shaft bending moments, while non-contact displacement sensors were installed near the shaft generator rotor to measure lateral vibration responses. The measured shaft bending moments were used to estimate the reaction forces and bearing pressures of the stern tube bearings. These results were compared with the static alignment analysis results to investigate the dynamic load redistribution characteristics occurring during vessel operation. Furthermore, orbit analysis and order tracking analysis were performed to evaluate the actual lateral vibration
behavior of the propulsion shafting system. The results revealed significant differences between the bearing load distributions predicted by static alignment analysis and those obtained under actual operating conditions. In particular, the loads acting on the stern tube bearings were found to be redistributed owing to dynamic propeller loading, indicating that static alignment analysis alone is insufficient to accurately represent the actual load conditions of the propulsion shafting system during operation. In addition, the measured lateral vibration responses were dominated by specific blade-order excitation components generated by the
propeller. Comparisons between numerical predictions and measurement results confirmed the actual vibration response characteristics of the propulsion shafting system under service conditions. Furthermore, comparisons of vibration responses under shaft generator operating and non-operating conditions indicated that the electromagnetic field generated during shaft generator operation influenced the dynamic characteristics of the propulsion shafting system. In particular, reductions in the amplitudes of specific order components and changes in shaft center orbit behavior were observed, demonstrating that shaft generator operation can affect the lateral vibration response characteristics of the propulsion shafting system. This study identified the dynamic load redistribution phenomenon and lateral vibration response characteristics of a shaft generator integrated propulsion shafting system through a combination of full-scale measurements and numerical analyses. The findings demonstrate the limitations of conventional static-based shafting design and verification procedures and highlight the necessity of considering actual operating conditions in shafting system assessment. The results of this study provide valuable engineering data and practical design guidelines for the design, reliability assessment, and operational criteria development of propulsion shafting systems equipped with shaft generators.