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Ship Maneuvering Including The Effects Of Transient Motions

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Ship Maneuvering Including The Effects Of Transient Motions

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Author : Carl Alden Scragg
language : en
Publisher:
Release Date : 1976

Ship Maneuvering Including The Effects Of Transient Motions written by Carl Alden Scragg and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1976 with Ships categories.

In the traditional approach to the problems of ship maneuvering, on uses a set of linearized equations of motion that excludes the possibility that the hydrodynamic forces and moments might be affected by the history of the motion. Using ideas introduced by Cummins, one can obtain another linearized set of the equations of motion which contains a 'memory function' as well as the added mass and damping coefficients. These stability coefficients have been evaluated by an impulse-response techniques, a method that is new to ship maneuvering problems and that appears to represent a substantial improvement over the traditional regular-oscillatory-motion tests. Results from both experimental methods are presented for comparison. To examine the effect of the memory function upon predictions of standard ship maneuvers, predictions of a few standard maneuvers have been calculated using both sets of the linearized equations of motion. The differences between the predicted motions were found to be small for all the cases we examined. (Author).

Manoeuvring Behaviour Of Ships In Extreme Astern Seas

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Author : Zafer Ayaz
language : en
Publisher:
Release Date : 2003

Manoeuvring Behaviour Of Ships In Extreme Astern Seas written by Zafer Ayaz and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2003 with categories.

In an attempt to contribute the efforts for the robust and effective numerical tools concerning ship motions in astern seas, this thesis presents the development of a coupled non-linear 6-DOF model with frequency dependent coefficients, incorporating memory effects in random waves with a new axis system that allows straightforward combination between seakeeping and manoeuvring model whilst accounting for extreme motions. A combination of seakeeping and manoeuvring is achieved through the adoption of relatively new "horizontal body axis system" which accounts for large vertical motions as well. Furthermore, the frequency dependent terms are incorporated in order to improve the accuracy of the numerical model for non-zero encounter frequencies which are experienced especially when the ship has large heading angle. The effect of encounter frequency and so called "memory effects" are calculated in terms of radiation forces using convolution integrals. Equations of motions and external forces are described in terms of a new axis system. The wave forces are calculated through incident and diffraction wave forces. The incident wave forces are calculated using the instantaneous wave surface while low encounter frequency model is adopted for the calculation of diffraction forces. Finally, the whole numerical model is expressed in random sea environment including the convolution terms to carry out the simulations in more realistic sea environments. The validation of the numerical model with the results of benchmark tests commissioned by ITTC Specialist Group on Stability, showed reasonably satisfactory agreement while the inclusion of frequency dependent terms affected the accuracy of the numerical model. Parametrical studies were carried out to investigate the effect of different environmental and operational parameters to ship motions in extreme astern seas along with the effects of degrees of freedom and encounter frequency. In order to enhance the accuracy of the numerical model and to obtain further information about the coupling of the motions and the adequacy of the numerical model to carry out further simulations regarding dangerous situations during ship motions in random following and quartering seas, extensive captive and free running model tests were carried out. The numerical model provided good agreement with the experiments. The terms resulting from the coupling of vertical motions and large heeling angle to wave forces are obtained. It is believed that the numerical model has a good potential for providing a more rational basis for predicting the dangerous conditions which a ship could face in extreme astern seas, and for offering insights about the link of behaviour with the design parameters of a ship in the light of the validation with the experiment results and parametrical studies.

Transient Motions In Ship Canal Systems

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Author : S J. Murray
language : en
Publisher:
Release Date : 1983

Transient Motions In Ship Canal Systems written by S J. Murray and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1983 with categories.

Ship Motions And Drag Reduction

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Author : Johannes Krzywinski Lunde
language : en
Publisher:
Release Date : 1966

Ship Motions And Drag Reduction written by Johannes Krzywinski Lunde and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1966 with Frictional resistance (Hydrodynamics) categories.

Maneuvering Performance Of High Speed Ships With Effect Of Roll Motion

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Author : Haruzo Eda
language : en
Publisher:
Release Date : 1978

Maneuvering Performance Of High Speed Ships With Effect Of Roll Motion written by Haruzo Eda and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1978 with categories.

On The Unstable Rolling Motions Of Ships Resulting From Nonlinear Coupling With Pitch Including The Effect Of Damping In Roll

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Author : W. D. Kinney
language : en
Publisher:
Release Date : 1961

On The Unstable Rolling Motions Of Ships Resulting From Nonlinear Coupling With Pitch Including The Effect Of Damping In Roll written by W. D. Kinney and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 1961 with Ships categories.

The equations of motion for a ship pitching and rolling in a calm sea were found to be coupled by means of a second order term in the rolling equation of motion. When the pitching motion is simple harmonic the equation of motion in roll is of the Mathieu type, the two independent parameters being pitching amplitude and frequency. The stability diagram of the Mathieu equation including the effect of linear damping is determined theoretically and verified by solving the Mathieu equation on an analogue computer. In experiments with one ship model form, it was found that the transition from stable to unstable motion occurred for the value of the parameters predicted by the theory, and that the rolling motions obtained experimentally closely resembled the computer solutions. It was concluded that (1) unstable rolling motions are possible for very small pitching amplitudes, (2) when the natural frequency of pitch is twice that of roll the amplitude required to produce unstable motion is a minimum, and (3) for any pitching frequency, the greater the amount of damping, the greater the amplitude of pitching must become to produce unstable rolling motions. (Author).