Autori: Dinu Taraza, Nicolae Buzbuchi

Editorial: SAE Technical Paper Series 941697, Milwaukee, Wisconsin, 1994.

Rezumat:

Una dintre cele mai importante cauze ale producerii fenomenelor vibratorii la bordul navelor o constituie elicea navala. In cazul unei nave cu o singura linie de arbori actionati direct de un motor Diesel este foarte important, inainte de a lua o decizie in ceea ce priveste caracteristicile elicei, sa cunoastem frecventele proprii ale liniei de arbori actionte de motorul naval. Devine deci necesara evitarea posibilitatii de aparitie a unui raspuns rezonant al liniei de arbori si, in aceasta optica, calajul optim al elicei in raport cu arborele cotit; prin aceasta modalitate, vibratiile torsionale ale arborelui cotit pot fi diminuate considerabil, situtie in care acestea pot fi in opozitie de faza cu excitatiile provenind de la elice, ceea ce constituie obiectul prezentului studiu. Metodologia prezentata este aplicata pe linia de arbori a unui motor naval lent cu sase cilindri in linie, dezvoltand puterea de 17,400 CP la turatia nominala de 122 rot/min, instalat pe nave tip bulk-carrier de 55,000 tdw din dotarea flotelor romanesti. In marine propulsion system with direct-coupled two-stroke large diesel engines, the angular position of the propeller with respect to the crankshaft remains unchanged during the whole operation of the engine.

The interference between major harmonic orders of the engine torque is avoided by choosing a number of blades, different from any divisor of the cylinder number. However, interferences between other harmonic orders of the engine torque and the major harmonic order of the propeller torque – which is equal to the number of blades – may increase the amplitude of torsional vibrations.

The paper shows that there is an optimum phasing between crankshaft and propeller for which a decrease, up to 20% of the dynamic shear stress of the shafting – in comparison with the worst possible phasing – may be achieved. This results points out the importance of being able to calculate, in design stage, the best phasing of engine and propeller.

Cuvinte cheie: Motor naval, propulsor, vibratii torsionale ale liniei de arbori // Marine engines, propeller, shafting system torsional vibration