The Experts below are selected from a list of 33 Experts worldwide ranked by ideXlab platform
N. Fonseca - One of the best experts on this subject based on the ideXlab platform.
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Experimental Investigation of the Nonlinear Effects on the Vertical Motions and Loads of a Containership in Regular Waves
Journal of Ship Research, 2004Co-Authors: N. Fonseca, C. Guedes SoaresAbstract:The nonlinear vertical responses of a containership advancing in regular waves are investigated experimentally. The paper presents the results of an experimental program carried out in a seakeeping tank with a model of the ITTC S-175 containership in head regular waves. All the wave frequency ranges of interest were tested, and for each wave frequency several wave amplitudes were used ranging from small to large amplitude. In this way the influence of the wave amplitude on the nonlinear characteristics of the responses was assessed. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the Forward Perpendicular. Strong nonlinear effects were detected, especially on the loads, which can be identified by the variation of the transfer function with the wave amplitude, the asymmetry of the time histories, and the presence of higher harmonics.
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Experimental Investigation of the Nonlinear Effects on the Statistics of Vertical Motions and Loads of a Containership in Irregular Waves
Journal of Ship Research, 2004Co-Authors: N. Fonseca, C. Guedes SoaresAbstract:The paper presents the results of an experimental investigation of the nonlinear effects on the vertical motions and loads on a containership model advancing in irregular waves. The experimental data are compared with numerical results from a nonlinear time domain strip method. The tests were carried out in a seakeeping tank using three sea states with significant wave heights of 4.2 m, 6.1 m, and 9.9 m, thus including very severe conditions. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the Forward Perpendicular. The statistics of the experimental records demonstrate partly the nonlinear behavior of the responses, especially of the structural loads. The probability distributions of the positive and negative peaks show that the heave and pitch motions are only slightly asymmetric and their distributions compare well with the Rayleigh distribution. The vertical loads present distributions of peaks that are highly asymmetric and deviate from the Rayleigh distribution. Comparisons between simulated results and experimental data show that the numerical model is able to represent the nonlinear characteristics of the responses.
O. M. Faltinsen - One of the best experts on this subject based on the ideXlab platform.
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An Experimental Investigation on Bow Water Shipping
Journal of Ship Research, 2003Co-Authors: Marco Barcellona, Maurizio Simos, Marilena Greco, O. M. FaltinsenAbstract:The water on deck caused on a restrained ship model without Forward speed in head waves is studied experimentally by using a transient test technique. A single water-shipping event is induced by the wave packet, and the severity of the interaction is controlled by the wave-packet steepness. Three different bow geometries are considered. Two of them are analytical hull forms, and the last is the ESSO-Osaka tanker. The models are equipped with a transparent-material deck to study the flow-field evolution by image analysis. A vertical wall is placed at a certain distance from the Forward Perpendicular to mimic the presence of deck structures. Velocity of the shipped water along the deck, pressure field on the deck, and horizontal impact force on the wall are measured. The main fluid-dynamic aspects of the green-water phenomenon are highlighted. For the tested cases, water shipping starts always with the free surface exceeding the freeboard, plunging onto the deck, and forming complex cavities entrapping air inside. The geometry of the air cavity depends on the hull form and the wave steepness. Then the water propagates along the deck. In general, the water front is strongly three dimensional because of the water entering along the deck contour. The interaction of the shipped water with the vertical structure consists of impact, run up-run down cycle, and backward plunging of the water onto the deck, still wetted. The evolution of the pressure field follows that of the water front. Pressure peaks are associated with the impact against the vertical wall, and by the backward plunging of the water on the deck, at the end of the run up-run down cycle of the water. It is shown that both these stages can be of importance from the structural point of view. I am sad to report that Maurizio Landrini was killed in a motorcycle accident on June 26, 2003. Maurizio was an outstanding marine hydrodynamist who had been selected as the 2003 Georg Weinblum Lecturer. He was born on March 2, 1963, and earned his Ph.D. degree in Theoretical and Applied Mechanics at the University of Rome. Except for short periods as a visiting researcher at the Ocean Engineering Laboratory, University of California, Santa Barbara, and the Department of Marine Technology, Norwegian University of Science and Technology, he worked his entire career at INSEAN, the Italian Ship Model Basin. He has authored or coauthored over 80 papers. He was a personal friend and innovative researcher with whom I have spent many hours discussing hydrodynamics. He will be greatly missed in the marine hydrodynamics community. Robert F. Beck
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Water Entry of a Wedge with Finite Deadrise Angle
Journal of Ship Research, 2001Co-Authors: O. M. FaltinsenAbstract:The paper presents the results of an experimental investigation of the nonlinear effects on the vertical motions and loads on a containership model advancing in irregular waves. The experimental data are compared with numerical results from a nonlinear time domain strip method. The tests were carried out in a seakeeping tank using three sea states with significant wave heights of 4.2 m, 6.1 m, and 9.9 m, thus including very severe conditions. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the Forward Perpendicular. The statistics of the experimental records demonstrate partly the nonlinear behavior of the responses, especially of the structural loads. The probability distributions of the positive and negative peaks show that the heave and pitch motions are only slightly asymmetric and their distributions compare well with the Rayleigh distribution. The vertical loads present distributions of peaks that are highly asymmetric and deviate from the Rayleigh distribution. Comparisons between simulated results and experimental data show that the numerical model is able to represent the nonlinear characteristics of the responses.
C. Guedes Soares - One of the best experts on this subject based on the ideXlab platform.
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Experimental Investigation of the Nonlinear Effects on the Vertical Motions and Loads of a Containership in Regular Waves
Journal of Ship Research, 2004Co-Authors: N. Fonseca, C. Guedes SoaresAbstract:The nonlinear vertical responses of a containership advancing in regular waves are investigated experimentally. The paper presents the results of an experimental program carried out in a seakeeping tank with a model of the ITTC S-175 containership in head regular waves. All the wave frequency ranges of interest were tested, and for each wave frequency several wave amplitudes were used ranging from small to large amplitude. In this way the influence of the wave amplitude on the nonlinear characteristics of the responses was assessed. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the Forward Perpendicular. Strong nonlinear effects were detected, especially on the loads, which can be identified by the variation of the transfer function with the wave amplitude, the asymmetry of the time histories, and the presence of higher harmonics.
C. Guedes Soares - One of the best experts on this subject based on the ideXlab platform.
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Experimental Investigation of the Nonlinear Effects on the Statistics of Vertical Motions and Loads of a Containership in Irregular Waves
Journal of Ship Research, 2004Co-Authors: N. Fonseca, C. Guedes SoaresAbstract:The paper presents the results of an experimental investigation of the nonlinear effects on the vertical motions and loads on a containership model advancing in irregular waves. The experimental data are compared with numerical results from a nonlinear time domain strip method. The tests were carried out in a seakeeping tank using three sea states with significant wave heights of 4.2 m, 6.1 m, and 9.9 m, thus including very severe conditions. The measured responses include the absolute and relative motions, vertical accelerations, and cross-sectional loads at midship and ¼ Lpp from the Forward Perpendicular. The statistics of the experimental records demonstrate partly the nonlinear behavior of the responses, especially of the structural loads. The probability distributions of the positive and negative peaks show that the heave and pitch motions are only slightly asymmetric and their distributions compare well with the Rayleigh distribution. The vertical loads present distributions of peaks that are highly asymmetric and deviate from the Rayleigh distribution. Comparisons between simulated results and experimental data show that the numerical model is able to represent the nonlinear characteristics of the responses.
Jesper Dietz - One of the best experts on this subject based on the ideXlab platform.
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Estimation of sea state parameters by the wave buoy analogy with comparisons to third generation spectral wave models
Ocean Engineering, 2020Co-Authors: Ulrik Dam Nielsen, Jesper DietzAbstract:Abstract This paper presents a study focused on sea state estimation along the route of an in-service container ship. The paper is concerned with the wave buoy analogy in which wave-induced motions of the ship are processed and analysed together with corresponding motion transfer function to give the directional wave spectrum exactly at the point of operation. In this study, a simple and inexpensive instrumentation of the vessel is considered, and wave spectrum estimation is based on measurements from one motion response unit mounted close to the Forward Perpendicular of the ship. The estimates by the wave buoy analogy are compared with two sets of results from third generation spectral wave models, with one set provided by a commercial supplier and with another set obtained from the Copernicus Climate Change Service Information. Motion measurements from a seven-days voyage across the Pacific Ocean are studied, and it is shown that the wave buoy analogy estimates wave conditions, in terms of sea state parameters, in good agreement with the reports by the sets of ocean wave hindcasts. Along with the comparisons, the paper discusses some of the inherent drawbacks of the wave buoy analogy, notably the fact that a ship acts as a low-pass filter.
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Ocean wave spectrum estimation using measured vessel motions from an in-service container ship
Marine Structures, 2020Co-Authors: Ulrik Dam Nielsen, Jesper DietzAbstract:Abstract This article is about the use of measured wave-induced vessel motions for estimation of ocean wave spectra by application of the wave buoy analogy. In the study, data from a larger, in-service container ship is considered. The estimation of wave spectra, equivalently sea state parameters, is based on measurements from, respectively, a gyro and two accelerometers leading to the simultaneous use of the pitching motion together with the horizontal and vertical accelerations in a position close to the Forward Perpendicular. The study of in-service data leads to contemplations about the vessel's advance speed, as the possible existence of sea current means that speed-over-ground (SOG) and speed-through-water (STW) will be different. The article discusses aspects related to advance speed in the context of the wave buoy analogy, and a smaller sensitivity study is conducted. Preceding to the sensitivity study, a comparison is made between sea state estimates by the wave buoy analogy and estimates obtained from a hindcast study. The article shows an acceptable agreement between the two sets of estimates. Following, the main conclusion from the sensitivity study on advance speed is that errors and uncertainties in the speed log have an effect on the estimates of the wave buoy analogy. In fact, the effect can be severe if reliable STW measurements are not available. In the final part, the article includes a few discussions about (non)stationary conditions in the context of the wave buoy analogy, and, although the effect on results is not necessarily detrimental, care must be shown when the wave buoy analogy is applied during in-service conditions.