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Roll response of ship fitted with passive stabilizing tank

Balcer L.

Polish Maritime Research

2004

nr 3

12-20

Physical and mathematical models of roll motions of a ship equipped with a roll stabiliŹzing tank of working liquid free surface, is presented. Elaboration of the physical model was based on the idea of two mutually coupled mathematical pendulae. On the basis of the physical model, motion equations of the ship with the tank were determined and solŹved. A way of using the achieved solutions is shown, as well as calculation formulae for coefficients of the motion equations, directly related to the main parameters of the ship and tank, are presented. Such form of the coefficients enhances possibility of application of the equations and their solutions in ship design practice. Some examples of the use of the solutions for analysis of stabilizing effectiveness of a designed tank for a given ship, are also attached. Moreover, guideŹlines for correct design of the stabilizing tanks having free surface of liquid, based on the proposed physical model of the ship-tank system, are offered. It is also indicated that on the basis of the presented results it would be possible to search for ways to make operation of the stabilizing tanks in question more effective.

Location of ship rolling axis

Balcer L.

Polish Maritime Research

2004

nr 1

3-7

In the paper is presented a definition of ship rolling axis and a method for determination of location of the axis. Location of rolling axis depends not only on ship mass distribution but also on the so-called "added masses" which are equivalents of the hydrodynamic forces acting on ship hull during its motion. It has been assumed that the rolling axis is fixed with respect to ship's hull, and its location is determined with accounting for the added masses accompanying ship rolling, whereas the influence of damping forces is neglected. For a representative group of ships appropriate coefficients of hydrodynamic forces were calculated on the basis of the experimental test results available in the subject-matter literatuŹre. It has been assumed that the rolling axis passes through a common centre of ship's mass and relevant added masses. As a result proposed are simple approximate formulas which make it possible to calculate location of ship rolling axis on the basis of the typical ship data available at the preliminary design stage.