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CONTENTS
Volume 2, Number 3, September 2012
 

Abstract
In this study we investigate the reliability of a bar subjected to a random tensile load in presence of corrosion. We consider linear, quadratic and exponential models that connect the stress in the bar with the corrosion rate. Two probability densities are considered for the load, with attendant derivation of the time-dependant reliability. The design time of operation is determined utilizing the requirement that the reliability must not be less than the required value.

Key Words
reliability; corrosion; bar; time to failure

Address
Isaac Elishakoff : Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton,
FL33431-0991, USA
Clement Soret : Departement Structures et Mecanique des Materiaux, Institut Francais de Mecanique Avancee,
Aubiere, 63170, France

Abstract
New experiments focusing on the evolution characteristics of nonlinear wave trains were conducted in a large wave flume. A series of wave trains with added sidebands, varying initial steepness, perturbed amplitudes and frequencies, were physically generated in a long wave flume. The experimental results show that the increasing wave steepness, increases the speed of sidebands growth. To study the frequency and phase modulation, the Morlet wavelet transform is adopted to extract the instantaneous frequency of wave trains and the phase functions of each wave component. From the instantaneous frequency, there are local frequency downshifts, even an effective frequency downshift was not observed. The frequency modulation increases with an increase in amplitude modulation, and abrupt changes of instantaneous frequencies occur at the peak modulation. The wrapped phase functions show that in the early stage of the modulation, the phase of the upper sideband first diverges from that of the carrier waves. However, at the later stage, the discrepancy phase from the carrier wave transformed to the lower sideband. The phase deviations appear in the front of the envelope\'s peaks. Furthermore, the evolution of the instantaneous frequency exhibits an approximate recurrence-type for the experiment with large imposed sidebands, even when the corresponding recurrence is not observed in the Fourier spectrum.

Key Words
nonlinear waves; evolution; modulation instability; instantaneous frequency; spectra; wavelet transform

Address
G.H. Dong, Y.X. Ma, W. Zhang and X.Z. Ma : State Key Laboratory Of Coastal And Offshore Engineering, Dalian University Of Technology, Dalian 116023, China
X.Z. Ma : State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University,
Nanjing 210098, P. R. China

Abstract
Recently, interest of offshore structure construction in South Korea is growing as the land space becomes limited for further development and the renewable energy grows to be more attractive for the replacement of the fossil energy. In order for the optimal construction of optimum offshore floating structures, development of safe and economical offshore foundation technologies is a priority. In this study, the large-deformation behavior of a suction pile, which markets are rapidly growing nowadays, is analyzed for three different loading locations (top, middle, and bottom of the suction pile) with three different displacement inclinations (displacement controlled with displacement inclinations of 0, 10, and 20 degrees from the horizontal). The behavior analysis includes quantifications of maximum resistances, translations, and rotation angles of the suction pile. The suction pile with its diameter of 10 m and height of 25 m is assumed to be embedded in clay, sand, and multi layers of subsea foundation. The soil properties of the clay, sand, and multi layers were determined based on the results of the site investigations performed in the West sea of South Korea. As analyses results, the maximum resistance was observed at the middle of the suction pile with the displacement inclination of 20 degrees, while the translations and rotations resulting from the horizontal and inclined pullouts were not significant until the horizontal components of movements at the loading points reach 1.0 m.

Key Words
suction pile; numerical analysis; resistance; polar decomposition; translation; rotation

Address
Dongwook Kim and Juhyung Lee : Goetechnical Engineering Research Division, Korea Institute of Construction Technology, Goyang 411-712, Korea
Ernest Nsabimana and Young-Hoon Jung : Department of Civil Engineering, Kyung Hee University, Yongin 446-701, Korea

Abstract
As the size of container ships continues to increase, not many existing harbors can host the super-container ship due to its increased draft and the corresponding dredging requires huge budget. In addition, the minimization of waiting and loading/offloading time is the most important factor in harbor competitiveness. In this regard, mobile-harbor concept has been developed in Korea to achieve much improved harbor capacity and efficiency. In developing the concept, one of the most important elements is the operability of crane between two or more floating bodies in side-by-side arrangement. The container ship is to be stationed through a hawser connection to an outside-harbor fixed-pile station with the depth allowing its large draft. The mobile harbors with smart cranes are berthed to the sides of its hull for loading/offloading containers and transportation. For successful operation, the relative motions between the two or more floating bodies with hawser/fender connections have to be within allowable range. Therefore, the reliable prediction of the relative motions of the multiple floating bodies with realistic mooring system is essential to find the best hull particulars, hawser/mooring/fender arrangement, and crane/docking-station design. Time-domain multi-hull-mooring coupled dynamic analysis program is used to assess the hydrodynamic interactions among the multiple floating bodies and the global performance of the system. Both collinear and non-collinear wind-wave-current environments are applied to the system. It is found that the non-collinear case can equally be functional in dynamics view compared to the collinear case but undesirable phenomena associated with vessel responses and hawser tensions can also happen at certain conditions, so more care needs to be taken.

Key Words
mobile harbor; fixed-pile station; side-by-side arrangement; hawser/fender; mooring lines; multiple floating bodies; relative motions; hull-mooring coupled dynamics; non-collinear wind; wave; current

Address
H.Y. Kang and M.H. Kim : Ocean Engineering Program, Department of Civil Engineering, Texas A&M University College Station, Texas, USA

Abstract
We discuss the bi - stability that is possibly exhibited by a liquid free surface in a parametrically - driven two-dimensional (2D) rectangular tank with finite liquid depth. Following the method of adaptive mode ordering, assuming two dominant modes and retaining polynomial nonlinearities up to third-order, a nonlinear finite-dimensional nonlinear modal system approximation is obtained. A \"continuation method\" of nonlinear dynamics is then used in order to elicit efficiently the instability boundary in parameters\' space and to predict how steady surface elevation changes as the frequency and/ or the amplitude of excitation are varied. Results are compared against those of the linear version of the system (that is a Mathieu-type model) and furthermore, against an intermediate model also derived with formal mode ordering, that is based on a second - order ordinary differential equation having nonlinearities due to products of elevation with elevation velocity or acceleration. The investigation verifies that, in parameters space, there must be a region, inside the quiescent region, where liquid surface instability is exhibited. There, behaviour depends on initial conditions and a wave form would be realised only if the free surface was substantially disturbed initially.

Key Words
parametric sloshing; modal method; adaptive ordering; continuation analysis

Address
Christos C. Spandonidis and Kostas J. Spyrou : School of Naval Architecture and Marine Engineering, National Technical University of Athens, Athens, Greece


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