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CONTENTS
Volume 3, Number 1, March 2013
 

Abstract
This brief study aims at providing a model to predict the time of service of a cracked bar in corrosive environment, in view of both the fracture mechanics and elastic failure criteria. Dolinskii\'s assumption on the relationship between stress and the corrosion rate is adopted. It is superimposed with fracture mechanics consideration. A comparison between the time of service of a cracked bar and that of a uniform bar is provided.

Key Words
crack; corrosion; Dolinsky\'s relationship

Address
Yohann Miglis, Isaac Elishakoff and Francisco Presuel-Moreno : Department of Ocean and Mechanical Engineering, Florida Atlantic University, Boca Raton, FL33431-0991,
USA

Abstract
Submarine pipelines encounter significant wave forces in shallow coastal waters due to the action of waves. In order to reduce such forces (also to protect the pipe against anchors and dropped objects) they are buried below the seabed. The wave force variation due to burial depends on the engineering characteristics of the sub soil like hydraulic conductivity and porosity, apart from the design environmental conditions. For a given wave condition, in certain type of soil, the wave force can reduce drastically with increased burial and in certain other type of soil, it may not. It is hence essential to understand how the wave forces vary in soils of different hydraulic conductivity. Based on physical model study, the wave forces on the buried pipeline model is assessed for a wide range of wave conditions, for different burial depths and for four types of cohesion-less soils, covering hydraulic conductivity in the range of 0.286 to 1.84 mm/s. It is found that for all the four soil types, the horizontal wave force reduces with increase in depth of burial, whereas the vertical force is high for half buried condition. Among the soils, well graded one is better for half buried case, since the least vertical force is experienced for this situation. It is found that uniformly graded and low hydraulic conductivity soil attracts the maximum vertical force for half buried case. A case study analysis is carried out and is reported. The results of this study are useful for submarine buried pipeline design.

Key Words
submarine pipeline; wave forces; safe burial depth; hydraulic conductivity; cohesionless soil; crude oil pipe

Address
S. Neelamani and K. Al-Banaa : Coastal Management Program, Environmental and Urban Development Division,
Kuwait Institute for Scientific Research, P.O. Box: 24885, 13109 SAFAT, KUWAIT

Abstract
In this study, a hybrid floating structure with cylinder was introduced to reduce the hydrodynamic motions of the pontoon type. The hybrid floating structure is composed of cylinders and semi-opened side sections to penetrate the wave impact energy. In order to exactly investigate the hydrodynamic motions and structural behavior of the hybrid floating structure under the wave loadings, integrated analysis of hydrodynamic and structural behavior were carried out on the hybrid floating structure. Firstly, the hydrodynamic analyses were performed on the hybrid and pontoon models. Then, the wave-induced hydrodynamic pressures resulting from hydrodynamic analysis were directly mapped to the structural analysis model. And, finally, the structural analyses were carried out on the hybrid and pontoon models. As a result of this study, it was learned that the hybrid model of this study was showed to have more favorable hydrodynamic motions than the pontoon model. The surge motion was indicated even smaller motion at all over wave periods from 4.0 to 10.0 sec, and the heave and pitch motions indicated smaller motions beyond its wave period of 6.5 sec. However, the hybrid model was shown more unfavorable structural behavior than the pontoon model. High concentrated stress occurred at the bottom slab of the bow and stern part where the cylinder wall was connected to the bottom slab. Also, the hybrid model behaved with the elastic body motion due to weak stiffness of floating body and caused a large stress variation at the pure slab section between the cylinder walls. Hence, in order to overcome these problems, some alternatives which could be easily obtained from the simple modification of structural details were proposed.

Key Words
hybrid; floating structure; integrated analysis; motions; structural behavior; concrete; alternatives

Address
Youn-Ju Jeong, Du-Ho Lee, Min-Su Park and Young-Jun You : Infra-Structure Research Department, Korea Institute of Construction Technology ilsan, Goyang, Gyeonggi 411-712, Korea

Abstract
A composite breakwater with an upper horizontal porous plate and a lower rubble mound is proposed and studied in this work. By means of matched eigenfunction expansions, a semi-analytical solution is developed for analyzing the hydrodynamic performance of the breakwater. The semi-analytical solution is verified by known solutions for special cases and an independently developed multi-domain boundary element method solution. Numerical examples are given to examine the reflection, transmission and energy loss coefficients of the breakwater and the wave force acting on the horizontal porous plate. Some useful results are presented for engineering applications.

Key Words
composite breakwater; horizontal porous plate; rubble mound; semi-analytical solution

Address
Yong Liu and Hua-jun Li : Shandong Provincial Key Laboratory of Ocean Engineering, Ocean University of China,
Qingdao 266100, China

Abstract
The effective tracking area of ultra short baseline (USBL) systems strongly relates to the safety of autonomous underwater vehicles (AUVs). This problem has not been studied previously. A method for determining the effective tracking area using acoustic theory is proposed. Ray acoustic equations are used to draw rays which ascertain the effective space. The sonar equation is established in order to discover the available range of the USBL system and the background noise level using sonar characteristics. The available range defines a hemisphere like enclosure. The overlap of the effective space with the hemisphere is the effective area for USBL systems tracking AUVs. Lake and sea trials show the proposed method\'method\'s validity.

Key Words
ultra short baseline system; track; AUV; ray equations; sonar equations

Address
Daxiong Ji, Jian Liu and Rong Zheng : State Key Laboratory of Robotics, Shenyang Institute of Automation, Chinese Academy of Sciences, Shenyang 110016, China


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