Autori: Nicholas Buzbuchi, Dinu Taraza, Dimitrios. V. Lyridis

Editorial: Bulletin of the Marine Engineering Society in Japan (MESJ), the Fifth International Symposium on Marine Engineering ISME, Yokohama, 1995.

Rezumat:

Datorita formei complicate a arborelui cotit aferent motoarelor navale de propulsie, deformatiile sale vor avea si ele o forma complexa, generand fenomene de cuplaj ale diverselor tipuri individuale de vibratie: torsionale, de incovoiere si axiale. Pana in momentul de fata, vibratiile liniilor de arbori antrenati de motoarele diesel navale s-au calculat doar prin luarea in consideratie fenomenul de cuplaj torsional-axial, fie au luat in consideratie un model simplificat al arborelui cotit. Prezentul studiu propune un model mai flexbil si mai apropiat de realitate, bazat pe metoda elementelor finite pentru calculul vibratiilor cuplate ale liniilor de arbori navali. Modelul este realizat prin considerarea unei structuri spatiale de bare cu mase distibuite uniform sau concentrate in nodurile specifice. S-a luat in consideratie intregul set de excitatii ale liniei de arbori, provenind atat din partea motorului, cat si din partea propulsorului. Modelul a fost verificat experimental, concluzia cea mai importanta fiind aceea ca vibratiile torsionale sunt determinante in excitarea celor axiale, in detrimentul fluctuatiilor fortei de impingere ale elicei. Modelul si metoda propuse evidentiaza tipul de vibratii axiale, mai putin studiat, care poate atinge nivele prohibitive uneori in functionare, ceea ce atrage necesitatea instalarii unor amortizoare de vibratii axiale. Due to the complicated shape of the marine Diesel engine crankshaft, its deformations also have a complex nature causing coupling phenomena among its individual vibration types: torsional, bending and axial. Up to now, the vibrations of shafting systems driven by marine Diesel engines were in general calculated by considering only the torsion and axial coupling, or by much simplifying the real formula of the crank. The present study proposes a more flexible and realistic model based on the finite element method (FEM) for the calculation of the excitations on coupled vibrations of marine Diesel engines. The model assumes a spatial beam structure with a uniformly distributed mass and concentrated masses in specific nodes. The entire set of exciting forces (including engine and propeller excitations) has been taken into account. This model has been verified through experimental investigations. It has been concluded that the torsion vibrations are dominant relatively to the propeller thrust fluctuations in exciting axial vibrations. The method reveals that the axial vibrations reach annoying levels and occasionally indicates the necessity of axial dampers mounting.

Cuvinte cheie: Motor naval lent, linia de arbori, vibratii cuplate // Two-stroke marine Diesel, Diesel engine shafting system, coupled vibrations