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CONTENTS
Volume 2, Number 1, March 2012
 

Abstract
Offshore wind turbines are complex structural and mechanical systems located in a highly demanding environment. This paper proposes a multi-level system approach for studying the structural behavior of the support structure of an offshore wind turbine. In accordance with this approach, a proper numerical modeling requires the adoption of a suitable technique in order to organize the qualitative and quantitative assessment in various sub-problems, which can be solved by means of sub-models at different levels of detail, both for the structural behavior and for the simulation of loads. Consequently, in a first place, the effects on the structural response induced by the uncertainty of the parameters used to describe the environmental actions and the finite element model of the structure are inquired. After that, a mesolevel FEM model of the blade is adopted in order to obtain the detailed load stress on the blade/hub connection.

Key Words
probabilistic analysis; performance-based design; uncertainty propagation; rotating blades

Address
Francesco Petrini and Konstantinos Gkoumas : School of Engineering, Sapienza Universita di Roma, Via Eudossiana 18, Rome, Italy
Wensong Zhou and Hui Li : School of Civil Engineering, Harbin Institute of Technology, 202 Haihe Road, Nan\'gang District, Harbin 150090, China

Abstract
This study investigated the behavior of a non-isothermal CO2 bubble formed through a leak process from a high-pressure source in a deep sea. Isenthalpic interpretation was employed to predict the state of the bubble just after the leak. Three modes of mass loss from the rising bubble were demonstrated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. A graphical interpretation of the last mode was provided in the pressure-enthalpy diagram. A threshold pressure (17.12 bar) was identified below which the last mode was no longer present. The second mode was as effective as the first for a bubble formed in deep water, leading to faster mass loss. To the contrary, only the first mode was active for a bubble formed in a shallow region. The third mode was insignificant for all cases.

Key Words
CO2; bubble; depletion; dissolution; condensation; isenthalpic expansion

Address
Daejun Chang and Sang Heon Han : Division of Ocean Systems Engineering, Korea Advanced Institute of Science and Technology, Daejeon,Republic of Korea
Kyung-won Yang : Det Norske Veritas Korea, Busan, Republic of Korea

Abstract
This study revealed the behavior of droplets formed through leak process in deep water. There was a threshold depth named the universal attraction depth (UAD). Droplets rose upward in the zone below the UAD called the rising zone, and settled down in the zone above the UAD called the settling zone. Three mass loss modes were identified and formulated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. The first two were active for the settling zone, and all the three were effective for the rising zone. In consequence, the life time of the droplets in the rising zone was far shorter than that of the droplets in the settling zone.

Key Words
CO2; droplet; depletion; universal attraction depth (UAD); dissolution; condensation; isenthalpic expansion

Address
Daejun Chang and Sang Heon Han : Division of Ocean Systems Engineering, Korea Advanced Institute of Science and Technology, Daejeon,Republic of Korea
Kyung-won Yang : Det Norske Veritas Korea, Busan, Republic of Korea

Abstract
In this paper, an offshore process front end engineering design (FEED) method is systematically introduced and reviewed to enable efficient offshore oil and gas production plant engineering. An integrated process engineering environment is also presented for the topside systems of a liquefied natural gas floating production, storage, and offloading (LNG FPSO) unit, based on the concepts and procedures for the process FEED of general offshore production plants. Various activities of the general process FEED scheme are first summarized, and then the offshore process FEED method, which is applicable to all types of offshore oil and gas production plants, is presented. The integrated process engineering environment is presented according to the aforementioned FEED method. Finally, the offshore process FEED method is applied to the topside systems of an LNG FPSO in order to verify the validity and applicability of the FEED method.

Key Words
offshore process FEED; integrated process engineering environment; topside systems; offshore oil and gas production plants; LNG FPSO; offshore projects

Address
Ji-Hyun Hwang : Department of Naval Architecture and Ocean Engineering, Seoul National University, Shinlim-Dong,
Seoul, 151-742, Korea
Myung-Il Roh : School of Naval Architecture and Ocean Engineering, University of Ulsan, Mugeo-Dong, Nam-gu, Ulsan,
680-749, Korea
Kyu-Yeul Lee: Department of Naval Architecture and Ocean Engineering, Research Institute of Marine Systems Engineering, Seoul National University, Shinlim-Dong, Seoul, 151-742, Korea,

Abstract
Presented herein is a study on reducing the hydroelastic response of very large floating structures (VLFS) by altering their plan shapes. Two different categories of VLFS geometries are considered. The first category comprises longish VLFSs with different fore/aft end shapes but keeping their aspect ratios constant. The second category comprises various polygonal VLFS plan shapes that are confined within a square boundary or a circle. For the hydroelastic analysis, the water is modeled as an ideal fluid and its motion is assumed to be irrotational so that a velocity potential exists. The VLFS is modeled as a plate by adopting the Mindlin plate theory. The VLFS is assumed to be placed in a channel or river so that only the head sea condition is considered. The results show that the hydroleastic response of the VLFS could be significantly reduced by altering its plan shape.

Key Words
very large floating structure (VLFS); geometries; arbitrary shapes; mitigation methods; hydroelastic response

Address
Z.Y. Tay and C.M. Wang : Department of Civil and Environmental Engineering, National University of Singapore,
Kent Ridge, Singapore, 119260


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