Solution Space and Optimality Concerns for the Shafting System Alignment of a Typical Bulk Carrier

Abstract

A study of the shafting system of an 82.000DWT bulk carrier is conducted, comparing the initial alignment of the vessel against the performance corresponding to different bearing offset combinations. The shaft is modelled as a beam and the bearings as single support points. Radial shaft loads, thermal expansion of the engine and propeller thrust eccentricity are taken into account. Simulations are performed for 4 propeller immersion conditions and for various new offset combinations, deviating up to 10mm from the initial offsets. The results are evaluated according to rule requirements and classified as; (i) acceptable, (ii) marginal and (iii) not acceptable.

A π-Theorem-Based Advanced Scaling Methodology for Similarity Assessment of Marine Shafting Systems

“…Shaft alignment simulations are performed to validate the bearing reaction forces and calculate influence factors, utilizing the "Shaft Alignment Tool" an in-house software that had been developed in the department of Marine Engineering of School of Naval Architecture and Marine Engineering of National Technical University of Athens (NTUA). The "Shaft Alignment Tool" is a beam element solver that enables modeling of the shafting system as a series of Euler beam elements [10,11] and was used to assess both the Real and the Scaled Models, with shaft deflection (UY) estimated both in the Real Model and reverse engineered using the Scale Model data and the Equivalent Scale Model. Discrepancies are observed between the predictions from the simple Scale Model, especially in the aft shaft area, due to the complexity of the system and conflicts in terms of similarity for different beam types (simply supported and cantilever beams).…”

“…More particularly several concerns have been addressed especially regarding the design of the stern-tube area and the need for a single or double-sloped aft stern-tube bearing (ASTB) [10]. Furthermore, the assessment of existing designs has been analyzed in [11], raising some concerns regarding the underlying design optimization functions. In that particular case study of the shafting system of an 82,000 DWT bulk carrier, the initial alignment of the vessel was compared against the performance corresponding to different bearing offset combinations.…”