International Shipbuilding Progress - Volume 6, issue 54

Authors: Weinblum, G. | Brooks, S. | Golovato, P.

Article Type: Research Article

Abstract: Investigation is made at the David Taylor Model Basin of the damping and added mass coefficients of a 7 to 1 prolate spheroid subjected to small free-heaving oscillations near the surface. Tests were performed at various depths from surfaced to deep submergence, over a range of Froude numbers, and for a limited frequency range. Similar tests were performed for a model of a surfaced aircraft carrier of 0.6 prismatic at several displacements. A detailed evaluation is made of previous work in the field of near-surface oscillations. Although of limited frequency range, the results of the present tests show reasonable …agreement with available theoretical results. Tests for surface ship models using forced-oscillation techniques have been performed recently by the third author [20]. Show more

DOI: 10.3233/ISP-1959-65401

Citation: International Shipbuilding Progress, vol. 6, no. 54, pp. 45-62, 1959

Authors: Radosavljević, Lj.B.

Article Type: Research Article

Abstract: The motion of a ship in a seaway may be expressed by two simultaneous linear unhomogeneous second-order differential equations with constant coefficients. The terms in those equations which cause them to be coupled arc usually neglected in engineering practice, and the frequencies of free oscillations are determined from the uncoupled equations of motion. The problem dealt with by the author of the present paper is as follows: to find out the connection of the frequencies of free oscillations of a ship when determined from the uncoupled viz. coupled equations of motion, i.e., in other words, to estimate the influence …of the neglected “coupling” upon the frequencies of free oscillations. By introducing the principal coordinates, the author has proposed an analysis of the problem as a function of three parameters, i.e.: a. χ 1 = N c / i of the ratio of the abscissa of the center of gravity of the flotation surface and of the radius of gyration of the flotation surface for transverse axis. b. χ 2 = i 1 / i of the ratio of the radius of gyration of the mass of the ship for transverse axis and the radius of gyration of the flotation surface for transverse axis. c. K of the coefficient of added masses. The author has shown that in certain cases the frequencies of the free oscillations cannot be determined from uncoupled equations of motion. However, such a treatment, connected with various assumptions is usual in engineering practice, and even widely recommended in technical literature. The author has introduced the coefficients μ 1 and μ 2 , in order to be able to estimate this influence. The analytical expressions, derived by the author, were used for calculations of numerical values of those coefficients, the variations of parameters χ 1 , χ 2 and K being within the limits encountered in practice. The values of the coefficients μ 1 and μ 2 are given in tables, whereas the plotted diagrams may be useful for practice. Show more

DOI: 10.3233/ISP-1959-65402

Citation: International Shipbuilding Progress, vol. 6, no. 54, pp. 63-71, 1959

Authors: Kafali, K.

Article Type: Research Article

DOI: 10.3233/ISP-1959-65403

Citation: International Shipbuilding Progress, vol. 6, no. 54, pp. 72-75, 1959

Authors: Aertssen, G.

Article Type: Research Article

Abstract: It is now generally recognized that an adequate instrumentation on board is very useful for the analysis of both measured-mile and service performance trials. The author was fortunate enough to attend these trials on two ships of the same service speed, about 16 knots, but with very different block-coefficients. One was a passenger-cargo liner with a block-coefficient of 0.672, the other a large tanker with a block-coefficients of 0.770. The ships were equipped with torsionmeter and pitometer log. The results of the analysis of measured-mile trials are given and compared with the predicted power derived from tank tests. The …effect of fouling and deterioration of the hull as well as the effect of weather on power and speed are established from an analysis of service data. Most of the data were obtained in the nearly fully-loaded condition, although a less important number of observations enabled the effect of weather in the medium-loaded condition to be fairly well estimated. Information is also given on the power that can be developed in a heavy sea without damage to the ship. In the case of the large tanker, details are given of the velocity distribution within the boundary layer measured by means of the pitometer log. Show more

DOI: 10.3233/ISP-1959-65404

Citation: International Shipbuilding Progress, vol. 6, no. 54, pp. 76-91, 1959