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1. COURSEWORK/PROJECT COVERSHEET This document is the coursework/project coversheet for all NAME classes conducted at University of Strathclyde for academic year 2013-14.…
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  • 1. COURSEWORK/PROJECT COVERSHEET This document is the coursework/project coversheet for all NAME classes conducted at University of Strathclyde for academic year 2013-14. Please do the following when submitting your coursework: • Staple a completed printed copy of this form to every piece of coursework/project work you submit for classes in the Department of Naval Architecture & Marine Engineering. • Avoid the use of document containers such as cardboard or plastic covers, document wallets, ring binders or folders (unless otherwise instructed by the class lecturer). We do not wish to discourage students from discussing their work with fellow students and collaborating in solving problems. However you must ensure that your submitted work distinguishes your own intellectual contribution. The key point is that you must not present the results of another person’s work “as though they were your own”. SUBMISSION DETAILS Please ensure that the details you give are accurate and completed to the best of your knowledge. Registration Number : Name : Class Code : Coursework Title: Lecturer : Declaration I have read and understood the University of Strathclyde guidelines on plagiarism. http://www.strath.ac.uk/media/ps/cs/gmap/academicaffairs/policesandprocedures/student-guide- to-academic-practice-and-plagiarism.pdf I declare that: 1. This is my coursework/project assignment. This is the version that I am submitting for assessment. I understand the penalties of plagiarism. 2. Wherever published, unpublished, printed, electronic or other information sources have been used as a contribution or component of this work, these are explicitly, clearly and individually acknowledged by appropriate use of quotation marks, citations, references and statements in the text. Signature: _____________________________________ Date of Submission: ________________ My Documents/Template Edited Sept. 2013
  • 2. Ship & Offshore Consultancy Department of Naval Architecture, Ocean & Marine Engineering NM983 - Group Project - SOT Arctic Circular-Shaped FLNG with Hydrodynamic Wave & Ice Loading Analysis Team Members: Torsten Wessels (201383387) Alexander Steinert (201388205) Stanimir Yankov (201379385) Chen Zeng (201375033) Yuwei Li (201376225) Date: May 6, 2014
  • 3. i Executive Summary of Overall Project With the increasing demand of natural resources the oil and gas industry turns more and more to the further development of the Arctic area. The region however presents significant challenges for the safe development and production. The present report offers a hull-concept of an Arctic FLNG-floater with improved shape to reduce ice-loads. The analysis done in the report are adjusted to the Shtokman field in the Russian part of the Barents Sea. The SOTCON-floater has conical shape which has significant advantages in contrast to classical ship-shaped constructions. Furthermore it will be compared to a SEVAN Marine Design concept with circular shaped hull. In the current report several tasks have been challenged. First, a parametric analytical solution was conducted for the estimation of the ice loads on the external hull. The purpose was to evaluate an optimal slope with regards to the load coming from a first year ice-ridge formation. Afterwards a numerical solution was conducted with the optimal slope. An analytical mooring analysis was conducted as well. The mooring system con- sists of two symmetrically stationed mooring lines. The lines are composed of three segments – chain, wire rope and another chain. A parametric study was undertaken in order to evaluate a resulting force from a possible displacement of the platform. Also the behaviour of the mooring lines was observed for estimation of the optimal segments lengths and physical properties. The final task conducts a numerical wave analysis which utilises a wide range of different waves and hence includes the sea-spectrum of the Shtokman field. In this part the global response and loads on the structure due to waves of the SOTCON- floater is calculated and compared to the SEVAN Marine Design. Here, the global response includes the response amplitude operator (RAO) for heave, pitch and surge. Due to symmetry roll and sway are not considered. Furthermore the cumulative displacement due to heave and pitch in z-direction is shown. The hydrodynamic wave load analysis considers wave pressure on the hull. The purpose of this project is to evaluate the governing design condition in which the floater would operate in the presented area. The results from the analysis were therefore compared to assess whether the wave or the ice loads represent bigger threat for the structure. Hence the external shape of the platform will be finalized with accordance to the governing loads.
  • 4. ii Acknowledgements The SOTCON-team would like to show their gratitude of a number of scholars who helped them in reaching the final goal. The guidance and assistance of Dr. Narakorn Srinil throughout the preparation of the presented paper were most helpful and are much appreciated. Furthermore the members of the team also show deep gratitude to another member of staff - Dr. Erkan Oterkus - who provided guidance for the numerical simulations. Also without the help and constructive suggestions of a number of Ph.D.-researchers, the progress of this project would have been slower. Therefore, great many thanks to Dennj De Meo, Junfeng Ding, and Minglu Chen. To all of them as a part of the department of Naval Architecture, Ocean and Marine Engineering in the University of Strathclyde this team would like to say thank you.
  • 5. Contents iii Contents 1. Introduction and Field Information 1 1.1. Field Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.1. Reservoir Capacities . . . . . . . . . . . . . . . . . . . . . . . 1 1.1.2. Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.3. Water Masses and Water Flow . . . . . . . . . . . . . . . . . . 2 1.1.4. Additional Design Issues in the Barents Sea . . . . . . . . . . 3 1.2. Field Development Concepts . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. SOTCON Shtokman Production Concept . . . . . . . . . . . . . . . . 5 1.3.1. SOTCON Arctic FLNG Concept . . . . . . . . . . . . . . . . 6 1.3.2. Required Analysis and Design of Structural Systems for the SOTCON FLNG Concept . . . . . . . . . . . . . . . . . . . . 7 2. Theoretical Models & Analytical Studies 8 2.1. Conical Shaped Hull Form . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. Environmental Ice Loading . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3. Ice loads on vertical wall . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3.1. Parameters of the ridge and platform . . . . . . . . . . . . . . 10 2.3.2. First year ice-ridge load . . . . . . . . . . . . . . . . . . . . . 11 2.4. Parametric study for ice loads on conical shaped platform . . . . . . . 14 2.4.1. Ice and platform parameters . . . . . . . . . . . . . . . . . . . 14 2.4.2. Consolidated layer load on conical platform . . . . . . . . . . 15 2.4.3. Conclusion of analytical ice loading estimation . . . . . . . . . 18 2.5. Mooring system analysis . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.5.1. Wave loading . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.5.2. Wind loading . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.6. Mooring line analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.6.1. Mooring line analysis . . . . . . . . . . . . . . . . . . . . . . . 25 3. Numerical Analysis Methodologies 27 3.1. Wave Analysis of FLNG . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.1.1. Geometrical Set-up (GeniE) . . . . . . . . . . . . . . . . . . . 27 3.1.2. Hydrodynamic Analysis (HydroD) . . . . . . . . . . . . . . . . 29 3.1.3. Hydrodynamic Wave Loading Analysis . . . . . . . . . . . . . 31 3.1.4. Calculation of Wave Loads in Wadam . . . . . . . . . . . . . . 31 3.2. Numerical solution for the ice loading . . . . . . . . . . . . . . . . . . 32 3.2.1. Structure geometry (ANSYS) . . . . . . . . . . . . . . . . . . 32 3.2.2. Ice modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2.3. Disadvantages and inaccuracy . . . . . . . . . . . . . . . . . . 35 4. Numerical Analysis Results 36 4.1. Results of Wave Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 36 4.1.1. Results of Global Response . . . . . . . . . . . . . . . . . . . 36 4.1.2. Results of Displacement . . . . . . . . . . . . . . . . . . . . . 39 4.1.3. Conclusion of Global Response Analysis . . . . . . . . . . . . 42 4.1.4. Results of Hydrodynamic Loading on Cylindrical Hull Shape . 42 4.1.5. Results of Hydrodynamic Loading on Conical Hull Shape . . . 43
  • 6. Contents iv 4.1.6. Comparison and Conclusion of Hydrodynamic Loading . . . . 44 4.1.7. Discussion and Conclusion of Wave Analysis . . . . . . . . . . 45 4.2. Ice analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 4.2.1. Results and discussions of numerical ice analysis . . . . . . . . 46 4.2.2. Ice loads - overall results and discussions . . . . . . . . . . . . 47 4.2.3. Ice - Future work . . . . . . . . . . . . . . . . . . . . . . . . . 49 5. Final Conclusion and Remarks 51 Bibliography 52 A. Geometrical Set-Up (GeniE) 55 B. Hydrodynamic Wave Load Analysis 56
  • 7. List of Figures v List of Figures 1.1. The seabed at the Shtokmans field. The shown area is 35x48 kilometer according to [32]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3. Concept of the offshore processing of the Shtokman Development AG concept [8]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Cross sections for models with sloped and vertical hull shape at the waterline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. First-year ridge model with its main geometrical parameters [12]. . . 10 2.4. Initial interaction between ice and sloping structure.[11] . . . . . . . . 15 2.5. General interaction between ice and sloping structure.[11] . . . . . . . 16 2.6. Comparation of 2D and 3D theory of ice loads.[11] . . . . . . . . . . . 17 2.7. Tendency of the horizontal and vertical ice loads with decreasing hull inclination α. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.8. Geometry for the analytical mooring line analysis. . . . . . . . . . . . 22 2.9. Relationship between horizontal displacement and horizontal force acting on the structure for the whole system consisting of two mooring lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.10. Relationship between horizontal displacement and horizontal force acting on the structure for the system consisting of only one mooring lines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 3.1. GeniE model of vertical walls. It shows the hull plates, applied panel load areas for and applied point loads for mass calculation of the FLNG. 28 3.2. GeniE model of SOTCON FLNG design, showing the hull mesh, panel load areas and applied point loads for mass calculation of the FLNG. 28 3.3. Panel Model with Offbody Points in HydroD. . . . . . . . . . . . . . 30 3.4. Hydrostatic pressure distribution along the two different hull shapes. 31 3.5. Geometry of the model used for the estimation of the ice load on the vertical wall in ANSYS with the boundary conditions of the structure. 34 3.6. Geometry of the model used for the estimation of the ice load on the wall with 45 degrees slope in ANSYS with the boundary conditions of the structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4.1. Heave RAO for the two different hull shapes. . . . . . . . . . . . . . . 37 4.2. Pitch RAO for the two different hull shapes. . . . . . . . . . . . . . . 38 4.3. Surge RAO for the two different hull shapes. . . . . . . . . . . . . . . 38 4.4. Displacement in z-direction of FLNG model with a vertical wall for wave-period of Tp = 8s. Max: 0.063. . . . . . . . . . . . . . . . . . . 40 4.5. Displacement in z-direction of FLNG model with a sloped wall for wave-period of Tp = 8s. Max: 0.168. . . . . . . . . . . . . . . . . . . 40 4.6. Compared displacement in z-direction of FLNG with a vertical and a sloped wall for a wave period of 25 seconds. . . . . . . . . . . . . . . 42 4.7. Comparison of maximum hydrodynamic pressure on the different hulls for a wave direction of 45◦ . . . . . . . . . . . . . . . . . . . . . . 44 4.8. Resulting stress on the vertical wall of the SOTCON FLNG from the ice-ridge after the applied displacement. . . . . . . . . . . . . . . . . 46
  • 8. List of Figures vi 4.9. Resulting stress on the sloped wall of the SOTCON FLNG from the consolidated layer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 4.10. Moment of the dynamic simulation showing the stresses on in the structure after the impact of the ice ridge. . . . . . . . . . . . . . . . 49 4.11. Moment of the dynamic simulation showing the deformations on the structure after the impact of the ice sheet. . . . . . . . . . . . . . . . 50 A.1. CAD model of adopted SEVAN Marine Design [18]. . . . . . . . . . . 55 A.2. CAD model of the SOTCON FLNG Design. . . . . . . . . . . . . . . 55 B.1. Cylindrical hull shape: Hydrodynamic Load Distribution for Wave Period of 8 seconds for 45 degrees (Peak Period Case). . . . . . . . . 56 B.2. Cylindrical hull shape: Hydrodynamic Load Distribution for Wave Period of 9 seconds for 45 degrees. . . . . . . . . . . . . . . . . . . . . 56 B.3. Cylindrical hull shape: Hydrodynamic Load Distribution for Wave Period of 14 seconds for 45 degrees (Heave Resonance Case). . . . . . 57 B.4. Cylindrical hull shape: Hydrodynamic Load Distribution for Wave Period of 25 seconds for 0 degrees (Pitch Resonance Case). . . . . . . 57 B.5. Conical hull shape: Hydrodynamic Load Distribution for Wave Period of 8 seconds for 45 degrees (Peak Period Case). . . . . . . . . . . . . 58 B.6. Conical hull shape: Hydrodynamic Load Distribution for Wave Period of 9 seconds for 45 degrees. . . . . . . . . . . . . . . . . . . . . . . . . 58 B.7. Conical hull shape: Hydrodynamic Load Distribution for Wave Period of 13 seconds for 45 degrees (Heave Resonance Case). . . . . . . . . . 59 B.8. Conical hull shape: Hydrodynamic Load Distribution for Wave Period of 19 seconds for 45 degrees (Pitch Resonance Case). . . . . . . . . . 59
  • 9. List of Tables vii List of Tables 1.1. Main dimensions of SOTCON FLNG. . . . . . . . . . . . . . . . . . . 6 2.1. Total horizontal and vertical ice forces for different hull inclinations. . 18 2.2. Parameters of the mooring lines in the maximum load case. . . . . . . 24 3.1. Input Values for Environmental Data and Analysis Conditions . . . . 30 3.2. Scatter diagram of the Barents Sea [5]. . . . . . . . . . . . . . . . . . 30 4.1. Overview of maximum displacement for a set of representative periods. 39 4.2. Hydrodynamic pressures for vertical wall. . . . . . . . . . . . . . . . . 43 4.3. Hydrodynamic pressures for sloped wall. . . . . . . . . . . . . . . . . 43 4.4. Comparison of hydrodynamic pressures on cylindrical to conical hull shape. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
  • 10. 1. Introduction and Field Information 1 1 Introduction and Field Information This report is the final outcome of the MSc group project module at Strathclyde University performed from January 2014 until May 2014. The aim of the group, consisting of five members, is to perform an analysis and design of structural systems in the Arctic region. Therefore a critical and state-of-the art review of current developments of the oil and gas industry in Arctic waters was performed. Based on this review, the Shtokman field in the Russian Barents Sea was chosen for further investigations and outline of new development opportunities. For the chosen field the environmental conditions and reservoir characteristics are reviewed and will be used for analysis purpose in this project. Furthermore the current field development concept of the Shtokman Development AG is presented and the alternative production approach, based on a floating liquefaction of natural gas concept, is introduced. The proposed FLNG design is based on the SEVAN Marine design and is conical shaped. For this chosen FLNG concept in the challenging region, the environmental loads due to ice and wave loads are estimated. Analytical and numerical approaches are used to determine the loads for the original cylindrical shaped hull form and for a modified conical configuration. A comparison of the two cases is performed in order to quantify the most suitable solution of the chosen field. Moreover an analytical mooring lines analysis was performed. The mooring system consists of a detachable buoy and two symmetrically stationed mooring lines with three segments. 1.1. Field Information The Shtokman field, also known as Shtockmanovskoye field, is a gas and gas con- densate field in the Russian part of the Barents Sea and was discovered in 1988 [7]. The field location is at 73◦ N and 43◦ , which is 600 km NE of Murmansk and 300 km W of Novaya Zemlya [23]. In figure 1.1 the seabed area around the Shtokmans field is shown. The water depth around the field is between 50 and 400 m and the seabed is uneven, which will in- fluence the pipeline design. The specific field water depth is between 320 and 340 m [6]. The reservoir is dome-shaped and spreads over 48 times 35 squarekilometers [32]. 1.1.1. Reservoir Capacities The reservoir contains huge amounts of gas and gas condensate. The exact number of capacity varies from 3.205 trillion cubic meter of gas and 226 million barrels of gas condensate [7] to 3.9 trillion cubic meters of gas and 56 million tons of gas con- densate [6]. The gas quality of the reservoir is good and contains no significant H2S or CO2. The reservoir pressure of 210 bar Wellhead Shut-In Pressure (WHSIP) as well as very low liquid content and a moderate reservoir temperature are positive factors for the production [3].
  • 11. 1.1. Field Information 2 Figure 1.1.: The seabed at the Shtokmans field. The shown area is 35x48 kilometer according to [32]. 1.1.2. Environment The Stokman field is located in an area with harsh environment. According to Potapov et. al. (2001) [23] waves can reach 17.5 meter and the wind speed can get up to 38 meter per second. Furthermore during winter months ice occurs with an average thickness of 1.2 meter. According to the Shtokman Development AG (2010) [3] ice occurs once in 2.6 years and stays in average for up to 3 month (average: 3.3 weeks). Therefore only first-year ice can occur with, according to them, an average thickness of 0.85 m (max. 2.0 m). Furthermore iceberg danger exists with ice ridges keel up to 21 m depth [3]. 1.1.3. Water Masses and Water Flow The Barents Sea is influenced by different water masses and current flows. The three main water masses are Coastal Water (CW), (North-) Atlantic Water (NAW), and Arctic Water (AW) and the locally formed water masses are Melt Water (MW), Bottom Water (BW), and Barents Sea Water (BSW) [17]. Figure 1.2b and 1.2a show the different water masses, currents and characteristics of the water masses. A combination of BSW and BW forms the water masses at the Shtokman field and has the characteristics of low temperature and high salinity [17]. The current velocity at the field is around 1.46m s [22]. During winter time, the upper 150 m of the water column is occupied by Arctic Water. During this time ice can build-up and the formations (and also icebergs) can drift south. During summer time the upper part of the water column of Arctic Water is covered with Melt Water (5 to 20 meter thickness) [17]. Due to the char- acteristics of BSW, the ice development is limited to the winter month and the time of ice occurrence is limited due to Atlantic Water in this area.
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