TAILIEUCHUNG - Intro to Naval Architecture 3 2010 Part 11

Tham khảo tài liệu 'intro to naval architecture 3 2010 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 290 VIBRATION NOISE AND SHOCK Table L B 5 6 7 8 9 10 11 12 13 14 15 .700 .752 .787 .818 .840 .858 .872 .887 .900 .910 .919 Js .621 .675 .720 .758 .787 .811 .830 .845 .860 .872 .883 Note 7s and s are for two- and three-node vibrations respectively. kinetic energies of water in three-dimensions relative to two-dimensions. Values of J for two- and three-node vibration 2 and 3 respectively of ellipsoids of varying length to beam ratio were calculated8 to be as in Table . These values are applied to the total virtual added mass calculated on the basis of two-dimensional flow. They are necessarily an approximation and other researchers have proposed different values. Taylor10 proposed lower values as follows L B k k .674 .564 .724 .633 .764 .682 .797 .723 .825 .760 Research using models has been done to find added mass values. One such investigation11 found the Lewis results for two-dimensional flow agreed well with experiment for two-node vibration but higher modes agreed less well. It was found that for ship shapes k B where n number of nodes value for n nodes. These values associated with the Lewis results for two-dimensional flow should give a good estimate of virtual added mass for ship forms in various vibration modes. Rotary inertia The simple formulae given above for a beam with a concenưated mass assumed that the masses executed linear oscillations only. In the relatively deep ship hull the rotation of the mass about a transverse axis VIBRATION NOISE AND SHOCK 291 is also important. A correction is applied based on the ratio of the rotational energy to translational energy rr. The correction to the frequency of vibration calculated ignoring rotation is 1 1 rr 0 5. Direct calculation of vibration Empirical formulae enable a first shot to be made at the frequency of vibration. The accuracy will depend upon the amount of data available from ships on which to base the coefficients. It is desirable to be able to calculate values .

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