• Title/Summary/Keyword: offshore structures

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Hydroelastic analysis of a truss pontoon Mobile Offshore Base

  • Somansundar, S.;Selvam, R. Panneer;Karmakar, D.
    • Ocean Systems Engineering
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    • v.9 no.4
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    • pp.423-448
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    • 2019
  • Very Large Floating Structures (VLFS) are one among the solution to pursue an environmentally friendly and sustainable technology in birthing land from the sea. VLFS are extra-large in size and mostly extra-long in span. VLFS may be classified into two broad categories, namely the pontoon type and semi-submersible type. The pontoon-type VLFS is a flat box structure floating on the sea surface and suitable in regions with lower sea state. The semi-submersible VLFS has a deck raised above the sea level and supported by columns which are connected to submerged pontoons and are subjected to less wave forces. These structures are very flexible compared to other kinds of offshore structures, and its elastic deformations are more important than their rigid body motions. This paper presents hydroelastic analysis carried out on an innovative VLFS called truss pontoon Mobile Offshore Base (MOB) platform concept proposed by Srinivasan and Sundaravadivelu (2013). The truss pontoon MOB is modelled and hydroelastic analysis is carried out using HYDRAN-XR* for regular 0° waves heading angle. Results are presented for variation of added mass and damping coefficients, diffraction and wave excitation forces, RAOs for translational, rotation and deformational modes and vertical displacement at salient sections with respect to wave periods.

Shoreline Changes due to the Construction of Offshore Structure and its Numerical Calculation (이안 구조물 건설에 따른 해안선의 변화와 수치계산)

  • 신승호
    • Journal of Korean Port Research
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    • v.15 no.1
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    • pp.47-56
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    • 2001
  • A numerical model for practical use based on the 1-line theory is presented to simulate shoreline changes due to construction of offshore structures. The shoreline change model calculates the longshore sediment transport rate using breaking waves. Before the shoreline change model execution, a wave model, adopting the modified Boussinesq equation including the breaking parameters and bottom friction term, was used to provide the longshore distribution of the breaking waves. The contents of present model are outlined first. Then to examine the characteristics of this model, the effects of the parameters contained in this model are clarified through the calculations of shoreline changes for simple cases. Finally, as the guides for practical application of this model, several comments are made on the parameters used in the model, such as transport parameter, average beach slope, breaking height variation alongshore, depth of closure, etc. with the presentation of typical examples of 3-dimensional movable bed experimental results for application of this model. Here, beach change behind the offshore structures is represented by the movement of the shoreline position. Analysis gives that the transport parameters should be taken as site specific parameters in terms of time scale for the shoreline change and adjusted to achieve the best agreement between the calculated and the observed near the structures.

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Structural impact response characteristics of an explosion-resistant profiled blast walls in arctic conditions

  • Sohn, Jung Min;Kim, Sang Jin;Seong, Dong Jin;Kim, Bong Ju;Ha, Yeon Chul;Seo, Jung Kwan;Paik, Jeom Kee
    • Structural Engineering and Mechanics
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    • v.51 no.5
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    • pp.755-771
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    • 2014
  • Environmental changes, especially global climate change, are creating new challenges to the development of the Arctic regions, which have substantial energy resources. And attention to offshore structures has increased with oil and gas development. The structural impact response of an explosion-resistant profiled blast walls normally changes when it operates in low temperatures. The main objectives of this study are to investigate the structural response of blast walls in low temperature and suggest useful guidelines for understanding the characteristics of the structural impact response of blast walls subjected to hydrocarbon explosions in Arctic conditions. The target temperatures were based on the average summer temperature ($-20^{\circ}C$), the average winter temperature ($-40^{\circ}C$) and the coldest temperature recorded (approximately $-68^{\circ}C$) in the Arctic. The nonlinear finite element analysis was performed to design an explosion-resistant profiled blast wall for use in Arctic conditions based on the behaviour of material properties at low temperatures established by performing a tensile test. The conclusions and implications of the findings are discussed.

Ice Load Generation in Time Domain Based on Ice Load Spectrum for Arctic Offshore Structures (극지해양구조물 성능평가를 위한 스펙트럼 기반 시간역 빙하중 생성에 관한 연구)

  • Kim, Young-Shik;Kim, Jin-Ha;Kang, Kuk-Jin;Han, Solyoung;Kim, Jinwhan
    • Journal of Ocean Engineering and Technology
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    • v.32 no.6
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    • pp.411-418
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    • 2018
  • This paper introduces a new method of ice load generation in the time domain for the station-keeping performance evaluation of Arctic offshore structures. This method is based on the ice load spectrum and mean ice load. Recently, there has been increasing interest in Arctic offshore technology for the exploration and exploitation of the Arctic region because of the better accessibility to the Arctic ocean provided by the global warming effect. It is essential to consider the ice load during the development of an Arctic offshore structure. In particular, when designing a station-keeping system for an Arctic offshore structure, a consideration of the ice load acting on the vessel in the time domain is essential to ensure its safety and security. Several methods have been developed to consider the ice load in the time domain. However, most of the developed methods are computationally heavy because they consider every ice floe in the sea ice field to calculate the ice load acting on the vessel. In this study, a new approach to generate the ice load in the time domain with computational efficiency was suggested, and its feasibility was examined. The ice load spectrum and mean ice load were acquired from a numerical analysis with GPU-event mechanics (GEM) software, and the ice load with the varying heading of a vessel was reconstructed to show the feasibility of the proposed method.

Design Verification Method of Offshore Separation Systems Based on System Dynamics (시스템 다이내믹스 기반 해양구조물 분리시스템의 설계검증 방법에 관한 연구)

  • Hwang, John-Kyu;Ko, Jae-Yong;Lee, Dong-Kun;Park, Bon-Yeong
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.26 no.6
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    • pp.715-722
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    • 2020
  • This paper proposes a design verification method based on system dynamics for offshore separation systems. Oil and gas separation systems are key components of offshore oil platforms; these systems determine the competitiveness of engineering, procurement, and construction (EPC) projects, especially in terms of added value. However, previous research on design verification has been limited to the process and deliverables of design. To address this, the study aims to develop a comprehensive design verification method and the associated functions from the perspective of project management, for the entire project life-cycle of offshore structures. The proposed methodology for design verification is expected to contribute toward effective and detailed designs as well as improve the competitiveness of EPC companies in constructing of shore structures during the early design stages. We first analyzed the separation system of the FPSO using the design verification method adopted by advanced countries and compared it with the system dynamics process formalized as ISO 15288. Subsequently, a tailored process for the design verification of the offshore structure was derived. It is shown that the proposed design verification method can be applied to the front-end engineering design process of of shore structures. Moreover, it can contribute toward the successful performance of offshore projects in the future and also minimize design changes and critical risks during the construction of these offshore structures.

Nonlinear response of fixed jacket offshore platform under structural and wave loads

  • Abdel Raheem, Shehata E.
    • Coupled systems mechanics
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    • v.2 no.1
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    • pp.111-126
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    • 2013
  • The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under structural and wave loading is presented, the structure is discretized using the finite element method, wave plus current kinematics (velocity and acceleration fields) are generated using 5th order Stokes wave theory, the wave force acting on the member is calculated using Morison's equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-yr return period wave and must be able to survive the 100-yr return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

A numerical and experimental approach for optimal structural section design of offshore aluminium helidecks

  • Seo, Jung Kwan;Park, Dae Kyeom;Jo, Sung Woo;Park, Joo Shin;Koo, Jeong Bon;Ha, Yeong Su;Jang, Ki Bok
    • Structural Engineering and Mechanics
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    • v.59 no.6
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    • pp.993-1017
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    • 2016
  • Helicopters are essential for supporting offshore oil and gas activities around the world. To ensure accessibility for helicopters, helideck structures must satisfy the safety requirements associated with various environmental and accidental loads. Recently, offshore helideck structures have used aluminium because of its light weight, low maintenance requirements, cost effectiveness and easy installation. However, section designs of aluminum pancakes tend to modify and/or change from the steel pancakes. Therefore, it is necessary to optimize section design and evaluate the safety requirements for aluminium helideck. In this study, a design procedure was developed based on section optimization techniques with experimental studies, industrial regulations and nonlinear finite element analyses. To validate and verify the procedure, a new aluminium section was developed and compared strength capacity with the existing helideck section profiles.

Risk Assessment of Offshore Wind Turbine Support Structures Considering Scouring (세굴을 고려한 해상풍력터빈 지지구조물 위험도 평가)

  • Kim, Young Jin;Lee, Dae Yong;Kim, Dong Hyawn
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.32 no.6
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    • pp.524-530
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    • 2020
  • The risk of offshore wind turbine support structures by scour has been proposed. The proposed utilize probabilities of scour depths and fragilities according to scour depth and a modification of a seismic risk analysis method. The probability distribution of scour depth was calculated using a equation which is suitable to consider marine environmental conditions such as significant wave height, significant period, and current velocity, and dynamic analysis was performed on an offshore wind turbine equipped with an suction bucket to find fragility. Then, the risk of offshore wind turbine support structure considering scour can be found by integrating the scour probability and the fragility.

Experimental Study of Heave Responses of Subsea Equipment during Installation Operation Using Offshore Crane (해상크레인을 이용한 다양한 해저 장비의 설치 작업 시 상하운동응답특성에 관한 모형 시험 연구)

  • Choi, Young-Myung;Nam, Bo Woo;Kim, Nam Woo;Park, In Bo;Hong, Sa Young;Kim, Jong Wook
    • Journal of Ocean Engineering and Technology
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    • v.30 no.2
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    • pp.75-83
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    • 2016
  • An experimental study on a subsea installation using an offshore crane was conducted. Concrete blocks, suction piles, and manifolds were considered in this study. Free decay tests were conducted to investigate the fluid characteristics of the subsea structures. The added masses of the structures were estimated. The motion response amplitudes of the subsea structures were compared for different structures and water depths. In addition, the dynamic tension transfer function of the crane wire was investigated. The root mean square values of the heave motion and the dynamic amplification factor of the wire tension were investigated in irregular waves.

Natural frequency of bottom-fixed offshore wind turbines considering pile-soil-interaction with material uncertainties and scouring depth

  • Yi, Jin-Hak;Kim, Sun-Bin;Yoon, Gil-Lim;Andersen, Lars Vabbersgaard
    • Wind and Structures
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    • v.21 no.6
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    • pp.625-639
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    • 2015
  • Monopiles have been most widely used for supporting offshore wind turbines (OWTs) in shallow water areas. However, multi-member lattice-type structures such as jackets and tripods are also considered good alternatives to monopile foundations for relatively deep water areas with depth ranging from 25-50 m owing to their technical and economic feasibility. Moreover, jacket structures have been popular in the oil and gas industry for a long time. However, several unsolved technical issues still persist in the utilization of multi-member lattice-type supporting structures for OWTs; these problems include pile-soil-interaction (PSI) effects, realization of dynamically stable designs to avoid resonances, and quick and safe installation in remote areas. In this study, the effects of PSI on the dynamic properties of bottom-fixed OWTs, including monopile-, tripod- and jacket-supported OWTs, were investigated intensively. The tower and substructure were modeled using conventional beam elements with added mass, and pile foundations were modeled with beam and nonlinear spring elements. The effects of PSI on the dynamic properties of the structure were evaluated using Monte Carlo simulation considering the load amplitude, scouring depth, and the uncertainties in soil properties.