PRINCIPLES OF LAYING DOWN LIMITS OF ELASTIC SYSTEM FREE VIBRATION FREQUENCIES IN MOTORSHIP ENGINE ROOMS

摘要

Results of studies of vibration of main engines, mechanisms and arrangements in the engine-room of the motorships of Far Eastern shipowners (more than 20 ships of different series) have been summed up. In all the cases problems were caused by a high level of vibration, which resulted in fatigue damages in hull constructions and mechanical equipment. The main reason causing those damages is resonances in forced vibrations of elastic systems from the action of unbalanced moments of the main low-speed engines. 1 hat is why when elaborating measures to remove resonance vibrations of elastic systems, formed by mechanisms and arrangements with their fastening constructions the chief principle was used: raising frequencies of free vibrations of those systems at the expense of stiffness increase (by making additional bonds with hull constructions). While doing it in every case a requirement of standardizing frequencies of the free vibrations proceeding from the number of cylinders (from 4 to 9 and more) of the main engines was observed. The lowest frequency should be 30% more (a near-resonance zone) than the frequency of the main order of diesel engine equal the number of its cylinders, i.e. f_1 > 1.3·z·n, (Hz), where z is the number of its cylinders and n is rotation speed of the main engine. This standard should be inserted in the Rules of the Shipping Register (Part 7, Chapter 1.15) and observed when designing and modernizing ships