Advances in Deepwater Steel Catenary Riser Technology State-of-the-Art: Part II—Analysis

2009 ◽  
Author(s):  
Ruxin Song ◽  
Paul Stanton
Keyword(s):  
Gulf Of Mexico ◽  
Time Domain ◽  
State Of The Art ◽  
Wave Theory ◽  
Frequency Domain Analysis ◽  
Strength Analysis ◽  
Response Analysis ◽  
Random Wave ◽  
Steel Catenary Riser ◽  
Induced Motion

The Steel Catenary Riser (SCR) concept offers advantages over other riser concepts and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (Spars, TLPs, SEMIs, and FPSOs) in the deepwater fields of West of Africa, the Gulf of Mexico (GoM), and Offshore Brazil. As the second of two companion papers, this paper presents the state-of-the-art of key analysis techniques of deepwater SCRs while the first paper addresses the design methodology [R. Song, P. Stanton, Ref. 4]. First of all, the procedure for analysis of deepwater SCRs is discussed and presented in more detail than given in the first paper and is also illustrated in an analysis flowchart. Wave theory applicable to deepwater SCR analysis and time domain vs. frequency domain analysis approaches are described and discussed. More focus is given to the strength analysis including discussion and comparison of regular wave and random wave approaches. Attention is paid to the vortex induced vibration (VIV) analysis including discussion of modal response analysis and VIV parameter selections. For SCRs on semisubmersibles and FPSOs, vessel heave-induced VIV needs to be taken into account, and a corresponding time-domain approach is presented. Similarly, for Spars and deep draft semisubmersibles, vortex-induced motion (VIM) fatigue damage of SCRs is discussed in more detail. Particular attention is also given to the analysis of SCR compression in the touch-down zone (TDZ) and corresponding acceptance criteria are presented. The application of fracture mechanics to engineering criticality assessment (ECA) is explored. Two examples of deepwater SCRs corresponding to a semi and a Spar are given to illustrate the presented methodology.

Advances in Deepwater Steel Catenary Riser Technology State-of-the-Art: Part I — Design

2007 ◽  
Author(s):  
Ruxin Song ◽  
Paul Stanton
Keyword(s):  
Gulf Of Mexico ◽  
Design Methodology ◽  
Fatigue Testing ◽  
State Of The Art ◽  
Material Selection ◽  
Design Procedure ◽  
Design Guideline ◽  
Joint Stress ◽  
Steel Catenary Riser ◽  
Global Configuration

Steel Catenary Riser (SCR) concept offers great advantages over others and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (SPAR, TLP, SEMI, and FPSO) in the deepwater fields of West of Africa, Gulf of Mexico, and Offshore Brazil. This paper presents the state-of-the-art of the design methodology of deepwater SCRs. First of all, the design procedure is discussed and is also illustrated in a flowchart. Material selection is discussed in terms of weldability, corrosion resistance, and effect on riser performance. Different wall thickness sizing criteria and design codes are compared. The three most commonly used types of SCR hang off system (flex joint, stress joint, and pull tube) are presented and their application limitations are discussed. Strakes and fairings are discussed and compared as the vortex induced vibration (VIV) suppression devices. Focus is given to the design of SCR global configuration and riser routing. Effect of different floaters on the global configuration design is discussed and illustrated through examples. Thermal performance requirements versus riser global response are traded off. Corrosion, thermal insulation, and anti-abrasion coating materials available for deepwater SCRs are summarized. SCR cathodic protection design methodology is summarized and a design guideline is given. The number one challenge of deepwater SCR design is fatigue. Selection of SN curve, effect of sweet and sour service on fatigue performance, stress concentration factor (SCF) calculation, full scale fatigue testing requirements, application of fracture mechanics to engineering criticality assessment (ECA) is discussed. Fatigue mitigation design is also explored supported by examples. Design of the SCR subsea interface to flowline and pipeline is presented.

Robustness of an SCR in Gulf of Mexico Hurricane Conditions

2010 ◽  
Author(s):  
Partha Sharma ◽  
Kim Mo̸rk ◽  
Vigleik Hansen ◽  
Celso Raposo ◽  
Srinivas Vishnubhotla
Keyword(s):  
Gulf Of Mexico ◽  
Time Domain ◽  
Offshore Structures ◽  
Coupled Analysis ◽  
Floating Structure ◽  
Steel Catenary Riser ◽  
Strength Capacity ◽  
Critical Components ◽  
Robustness Check ◽  
Robustness Assessment

Recent hurricanes in Gulf of Mexico, most notably Ivan (2004), Katrina & Rita (2005), Ike (2008), were more severe than the local 100 year extremes in the Gulf of Mexico (GoM). As a result API has issued an interim metocean bulletin, API Bulletin 2INT-MET [1]. Concurrently, API also issued API Bulletin 2INT-EX [2] for assessment of existing offshore structures for hurricane conditions. API Bulletin 2INT-EX recommends a robustness check to evaluate floating structure critical components including production and export risers. The robustness check for risers as a minimum should consider the capacity and ductility of the key riser components. This paper investigates the robustness of a steel catenary riser (SCR) suspended from a deepwater tension leg platform (TLP) unit in Central GoM. The robustness assessment is performed for the 1000 year Central GoM hurricane conditions provided in API 2INT-MET. Time domain coupled analysis using the program DeepC is performed to determine the TLP motions and the associated loading on the SCR. SCR strength capacity checks are performed as per the methods outlined in new ISO 13628-12 [3].

A Frequency Domain Approach for Random Fatigue Analysis of Steel Catenary Risers at Brazil’s Deep Waters

2004 ◽  
Author(s):  
Claudio Marcio Silva Dantas ◽  
Marcos Queija de Siqueira ◽  
Gilberto Bruno Ellwanger ◽  
Ana Lu´cia F. Lima Torres ◽  
Marcio Martins Mourelle
Keyword(s):  
Frequency Domain ◽  
Fatigue Damage ◽  
Time Domain ◽  
Oil And Gas ◽  
Large Diameter ◽  
Water Injection ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Fatigue Analysis ◽  
Steel Catenary Riser

The steel catenary riser was adopted by Petrobras as a cost-effective alternative for oil and gas export and for water injection lines on deepwater fields, where large diameter flexible risers present technical and economic limitations. The installation of the P-18 SCR was a pioneer project of a free-hanging steel catenary riser linked to a semi-submersible [1] and demonstrated the technical feasibility of the concept. Fatigue damage verification is an important issue in SCR design, demanding a high number of loading cases to be analyzed. The random time domain nonlinear analysis is considered an attractive and reliable tool for fatigue analysis as nonlinearities are properly modeled and the random behaviour of environmental loadings is considered. As time domain analysis is high computer time consuming, the frequency domain analysis has been considered as an alternative tool for the initial phases of riser design to be used mainly for fatigue damage verification. This paper presents a methodology developed to perform a linearized frequency domain analysis aiming at fatigue damage verification. Two drilling risers were analyzed with the frequency domain procedure developed. The model of a steel lazy-wave riser was analyzed both in frequency and time domain in order to compare fatigue damage results. The analyses were performed using the Petrobras’s in-house computer codes ANFLEX, ALFREQ and POSFAL developed and implemented as part of projects from CENPES/PETROBRAS with “COPPE/UFRJ -The Engineering Post-Graduating Coordination of the Federal University of Rio de Janeiro”.

Blades Forced Response Analysis With Friction Dampers

1998 ◽  
Vol 120 (2) ◽  
pp. 468-474 ◽  
Author(s):  
M. Berthillier ◽  
C. Dupont ◽  
R. Mondal ◽  
J. J. Barrau
Keyword(s):  
Time Domain ◽  
Dry Friction ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Forced Response ◽  
Response Analysis ◽  
Friction Damper ◽  
Friction Dampers ◽  
Fan Blade

A multiharmonic frequency domain analysis combined with a Craig-Bampton component mode synthesis is presented to compute the dry friction damped forced response of blades. The accuracy of the analysis is established, for a cantilever beam with a dry friction damper attached, by comparison with experimental results and time domain analysis. The method has then been applied to a model fan blade damped by a blade to ground damper.

Summary and Recommendations for Safe Mooring System Design in ULS and ALS

2017 ◽  
Author(s):  
Siril Okkenhaug ◽  
Torfinn Hørte ◽  
Øivind Paulshus
Keyword(s):  
Gulf Of Mexico ◽  
Frequency Domain ◽  
Time Domain ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Mooring Line ◽  
Safety Factors ◽  
Design Code ◽  
Oil Companies ◽  
Reliability Level

DNV GL is currently running a Joint Industry Project, “NorMoor JIP”, with participants from oil companies, engineering companies, rig-owners, manufacturers and marine authorities. It is a global study covering Gulf of Mexico, Northern Europe and Brazil waters. Our motivation for initiating a study on mooring line reliability was that all the global standards (API, ISO, DNV GL, others) are mostly based on work from late 1990s, when frequency domain analysis was prevalent. The reliability level implied by these regulations is not known, and we also see that the mooring standards are interpreted and applied differently. Thus, there is a need for a mooring design code with a consistent analysis methodology and with safety factors that are in line with this methodology and calibrated at an appropriate target reliability level. This is achieved through reliability-based calibration for a range of different units, mooring systems, water depths and geographical locations. The focus in the present paper is the calibration of safety factors and selection of target reliability level. The underlying probabilistic analysis results used for the calibration are reported in two accompanying papers at OMAE 2017, [1] and [2], dealing with structural reliability analyses for the ULS and ALS respectively. For mobile units frequency domain analyses are common, and although the main attention in the JIP is towards time domain analyses, it is part of the JIP to calibrate safety factors for frequency domain analyses as well. The annual extreme value distribution of line tension for all cases is calculated in time domain and is applied both in the calibration of safety factors for time domain and frequency domain analyses. It is seen that characteristic tensions from time domain analyses are likely to be higher than those from frequency domain analyses. The dilemma of not being penalized when using more refined time domain analyses is discussed, and different safety factors have been suggested for use with time domain and frequency domain analyses. A discussion about target reliability level is included, and the target levels are proposed with basis in the existing mooring design practice for mobile units, where frequency domain analysis is prevalent. Different targets are proposed depending on consequences of failure. Calibration for different design formats are carried out. The current format using a single safety factor is challenged with a format with two safety factors. The objective is to arrive as close as possible to the target reliability for all cases analyzed. A different design philosophy is needed in the Gulf of Mexico in order to achieve acceptable risk, and options are discussed. The present work provides a unique and comprehensive set of results, where advanced reliability methods are used to calibrate a mooring design code where the mooring line tensions are calculated in the time domain. The results provide a basis for regulators, such as ISO, to update their rules. ULS and ALS are covered here, and a potential phase 3 of the JIP will cover the fatigue limit state. When the NorMoor JIP is completed the plan is to implement the results into DNVGL-OS-E301, [5].

scholarly journals Analysis of Three-Phase Wye-Delta Connected LLC

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3606
Author(s):  
Jing-Yuan Lin ◽  
Chuan-Ting Chen ◽  
Kuan-Hung Chen ◽  
Yi-Feng Lin
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Operation Time ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Complete Analysis ◽  
Plane Analysis ◽  
Analysis Methods ◽  
Three Phase

Three-phase wye–delta LLC topology is suitable for voltage step down and high output current, and has been used in the industry for some time, e.g., for server power and EV charger. However, no comprehensive circuit analysis has been performed for three-phase wye–delta LLC. This paper provides complete analysis methods for three-phase wye–delta LLC. The analysis methods include circuit operation, time domain analysis, frequency domain analysis, and state–plane analysis. Circuit operation helps determine the circuit composition and operation sequence. Time domain analysis helps understand the detail operation, equivalent circuit model, and circuit equation. Frequency domain analysis helps obtain the curve of the transfer function and assists in circuit design. State–plane analysis is used for optimal trajectory control (OTC). These analyses not only can calculate the voltage/current stress, but can also help design three-phase wye-delta connected LLC and provide the OTC control reference. In addition, this paper uses PSIM simulation to verify the correctness of analysis. At the end, a 5-kW three-phase wye–delta LLC prototype is realized. The specification of the prototype is a DC input voltage of 380 V and output voltage/current of 48 V/105 A. The peak efficiency is 96.57%.

Time-Domain Analysis of SOFAR Propagation in Low-Latitude Sea Area by Wave Theory and Ray Theory

1995 ◽  
Vol 34 (Part 1, No. 5B) ◽  
pp. 2940-2942
Author(s):  
Shinichi Imayoshi ◽  
Toshio Tsuchiya ◽  
Toshiaki Kikuchi ◽  
Akio Hasegawa
Keyword(s):  
Time Domain ◽  
Wave Theory ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Ray Theory ◽  
Low Latitude ◽  
Sea Area

Development of a Stepped Line Tensioning Solution for Mitigating VIM Effects in Loop Eddy Currents for the Genesis Spar

2004 ◽  
Author(s):  
T. Kokkinis ◽  
R. E. Sandstro¨m ◽  
H. T. Jones ◽  
H. M. Thompson ◽  
W. L. Greiner
Keyword(s):  
Gulf Of Mexico ◽  
Eddy Current ◽  
Eddy Currents ◽  
Comprehensive Evaluation ◽  
Design Solution ◽  
Loop Current ◽  
Mooring Lines ◽  
Test Methodology ◽  
Induced Motion ◽  
High Reynolds

A number of spars are being installed in deepwater areas in the Gulf of Mexico (GoM), which are subject to loop / eddy current conditions and must be designed for Vortex-Induced Motion (VIM). This paper shows how recent advances in VIM prediction enabled an efficient and effective mooring design solution for the existing Genesis classic spar, which is installed in Green Canyon Block 205 in the GOM. The solution may also be applicable to new spar designs. During the Gulf of Mexico Millennium Eddy Current event in April 2001, the Genesis spar platform underwent vortex induced motions (VIM) which were greater than anticipated during the design of the mooring & riser systems. Analysis showed that if such large motions were to occur in higher currents in the range of the 100-year event, they could cause significant fatigue damage, and could lead to peak tensions in excess of design allowables. After a comprehensive evaluation of potential solutions, Stepped Line Tensioning (SLT) was determined to be the best approach for restoring the platform’s original mooring capacity on technical, cost and schedule grounds. SLT did not require extensive redesign of the existing mooring system of the spar. Furthermore, SLT provided a means to improve mooring integrity on an interim basis, while completing details for permanent implementation. Under SLT, the pretensions of the mooring lines are adjusted based on forecast currents in order to keep the platform below the VIM lock-in threshold at all times and for all eddy/loop current conditions up to and including the 100-year condition. High Reynolds number model tests conducted with a new test methodology were used to get a reliable prediction of the spar’s VIM response for this evaluation.

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