International Shipbuilding Progress - Volume 9, issue 97

Authors: Kotik, Jack | Mangulis, Visvaldis

Article Type: Research Article

Abstract: It is shown, for the case of forced simple harmonic heave, that if the damping parameter is known for all frequencies then the virtual mass parameter (minus its value at infinite frequency) is readily determined for all frequencies, and vice versa, by an integral transform (equations (3) and (4) ). These relations are called the Kramers-Kronig relations. It follows that any approximate method for computing damping gives rise to an approximate method for computing added mass, and vice versa. Also, the response (for all time) to an impulse in acceleration can be calculated if either the damping or added-mass parameters …are known for all frequencies (equation (A-5)). Some approximate added-mass parameters obtained in this way are presented and compared with exact results. Some asymptotic consequences of the Kramers-Kronig relations are also presented. It is expected that these relations can be derived for any motion, with forward speed, and can therefore play a very useful role in ship motion theory. Show more

DOI: 10.3233/ISP-1962-99701

Citation: International Shipbuilding Progress, vol. 9, no. 97, pp. 361-368, 1962

Authors: Janssen, J.H.

Article Type: Research Article

Abstract: The aim of this report on the acoustical properties of ships is to present data for the assessment of the relative importance of noise sources, noise paths and noise reduction measures in ships as far as human comfort is concerned. It is therefore a more practical parallel to a preceding report “Acoustal principles in ship design”. The instruments used for the measurements by the Technisch Physische Dienst are described briefly. Also some information on recent trends in noise criteria is given. Noise spectra, as measured in cabins of different ships, are compared, stressing the importance of the distance between …noise source (e.g. engine room or propellers) and cabin. Results of measurements on structure-borne sound (vibrations) and on air-borne sound due to propellers or engines are compared with results obtained during excitation of parts of a ship’s structure by means of a tapping machine. With the aid of theoretical and experimental models the various possible noise paths are identified and investigated as to their respective contributions to noise in a cabin. The conclusions about the origins of a cabin noise may be of some value for an “engineering estimate”, as is illustrated in the last chapter. A list of references is given. For practical reasons the report is published in two parts; part I (chapters 1, 2, 3, 9 and 10) containing introduction, information on instruments, criteria and a summary and illustration of results; part II (chapters 4, 5, 6, 7 and 8) containing the results of measurements and some theoretical considerations. Show more

DOI: 10.3233/ISP-1962-99702

Citation: International Shipbuilding Progress, vol. 9, no. 97, pp. 369-390, 1962

Authors: Pemberton, H.N.

Article Type: Research Article

Abstract: Knowledge of service experience, especially in regard to machinery defects, is of considerable value to both marine engine builders and shipowners, particularly if this knowledge can be utilized in improving design or materials or in preventing mal-operation of machinery. Lloyd’s Register of Shipping, with its world wide network of surveyors surveying some 11,000 ocean going merchant ships, is in a unique position to know what happens to ships’ machinery in service and how the more important casualties are dealt with. It is right that some of this information should be fed back into industry, and one of the ways in …which this can be done is for the Society’s Chief Engineer Surveyor to present a paper from time to time describing some of the serious cases that have come to his notice. The present paper, which is by no means comprehensive, deals mainly with cases which impinge on design, construction and materials. Some of the failures mentioned in the paper were due to causes which may not have arisen previously; others are of a type reasonably well known but which nevertheless continue to recur, either because their importance is not appreciated or the lessons that they teach have not been sufficiently studied. Show more

DOI: 10.3233/ISP-1962-99703

Citation: International Shipbuilding Progress, vol. 9, no. 97, pp. 391-406, 1962