Autori: Dinu Taraza, Nicolae Buzbuchi, Jean Sever Popovici

Editorial: SAE Technical Paper Series 941698, 1994.

Rezumat:

Problema analizei corecte a tuturor surselor de excitatie a vibratiilor complexe ale liniilor de arbori a devenit tot mai acuta, in ultimii ani, odata cu introducerea pe piata a noilor generatii de motoare navale, motoare care dezvolta puteri mari la turatii reduse, avand un raport cursa/alezaj si presiuni de ardere ridicate, in conditiile unui consum redus de combustibil. Liniile de arbori ale unor astfel de motoare sunt caracterizate prin momente de inertie mecanica si rigiditati tot mai mari, de unde si oportunitatea unor astfel de studii.
Prin prezenta lucrare se realizeaza, intr-o prima faza, analiza surselor clasice de vibratii ale liniilor de arbori ale motoarelor cu ardere interna, si anume componentele tangentiale si radiale ale fortelor de presiune a gazelor si a fortelor de inertie ale maselor in miscare de translatie.
Ca o particularitate a motoarelor navale lente de propulsie, s-a tratat in mod special analiza vibratiilor induse de elicea navala in liniile de arbori cuplate direct de motoarele navale. Acesta problema s-a rezolvat prin utilizarea modelului turbionar al elicei, paralel cu care s-a prezentat si o metoda bazata pe teoria liniei portante, rezultatele aplicatiei numerice efectuate pe un motor naval cu sase cilindri in linie, cu puterea de 17,400 CP la turatia nominala de 122 rot/min, montat pe nave tip bulk-carrier din dotarea flotelor romanesti, fiind comparate si validate, in final, cu masuratorile experimentale ale excitatiilor induse de propulsorul naval in linia de arbori, efectuate pe model in tunelul de cavitatie al Institutului de Cercetari si Proiectari Navale ICEPRONAV Galati.

Among the excitation sources of vibration for the marine propeller shafting, the propeller itself plays a significant role. It is one of the excitation sources for the axial vibrations and a major contributor among the excitation sources for torsional vibrations. Thus, the possibility to predict the harmonic structure of the torque and thrust, in the design stage of the propeller system, has a great importance for the designer. In this direction, the paper presents two computation methods of calculation of the propeller torque and thrust, the first being a semi-analytic one, based upon the wake field diagrams experimentally determined, and the second based on the propeller series diagrams and general empirical formula for the wake and suction coefficients. This second analytical method was presented more detailed, being a possible primary tool for the designer. A vortex model of the marine propeller, based on Prandtl lifting-line theory, has been developed. Considering the system of bounded and free vortices representing the propeller blade and its interaction with the incipient wake generated by hull motion, the velocity field around the blade profile is determined. Based upon a non-dimensional expression of the circulation, as a function of blade radius and angle of rotation, torque and thrust are computed and expressed as Fourier series.
Parallel to the theoretic study, experimental investigation have been carried-out, both in cavitation tunnel and towing tank, showing an acceptable agreement between calculated and measured fluctuations of torque and thrust

Cuvinte cheie: propulsor naval, structuta armonica a momentului si impingerii // Propeller, harmonic structure of the torque and thrust