Calculation Of Shafting Vibration And Alignment And Re-development Of Software

In the actual work of the vessel, shafting vibration characteristicshave a great impact on its design, installation and overall vibration. Thecalculation of shaft alignment can guarantee the safe operation of the mainengine and shafting, as well as reducing the hull vibration, which manifeststhe importance of the vibration and alignment’s calculation. In this paper, afinite element model was established according to the actual structuralcharacteristics of the shafting on the hovercraft for analyzing its lateralvibration, longitudinal vibration and torsional vibration, and then thecalculation in straight shaft alignment and in optimum alignment has beenconducted. Finally re-development of software was done based onANSYS.On the base of considering the hull stiffness, the region of resonancespeed and blade resonance speed of the shafting was calculated underdifferent bearing stiffness and compared with the condition of taking noconsideration of the hull stiffness. Although overall stiffness would bereduced considering the hull stiffness, it still can be concluded that thelateral vibration of the shafting is in safety in accordance with workingspeed. The gyroscopic effect on the lateral vibration of the shafting wastested through calculation. The natural frequencies and the correspondingmode shapes of the longitudinal vibration and torsional vibration weredetermined. Bearing Stiffness effect on shafting vibration frequency wasalso discussed. Furthermore, by analyzing the sources of the excitationforce and moment in forced vibration and presenting the shaft response to excitation, the influence of damping on shafting vibration response wasanalyzed. Calculation in alignment can be divided into two parts. Instraight shaft alignment, it showed that bearing reactions decreased, whileshear force and moment had no change taking consideration of bearingstiffness. Influence coefficient of load and moment were calculated in twodifferent conditions and the reason of the differences was also given. Inoptimum alignment, specific optimization scheme showed that theoptimization results in OPT of ANSYS and the bearing loads wereimproved. The allowable bearing offsets in warm condition caused bytemperature rise were obtained, which provided technical references forsafe operation of the shafting.Finally, based on Visual C++and APDL，this paper developed aspecial software for calculation the shafting vibration and alignment whichis convenient for the engineers to achieve parametric modeling andcalculation who are not familiar with the finite element software.