bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dual Stiffness Approach for Polyester Mooring Line Analysis in Time Domain
Authors: Tahar Arcandra , Sidarta Djoni , Ran Alex 
Published: August 2013

Polyester mooring lines have been used in the offshore industry since the late ’90s. With increasing oil exploration and production in deeper waters, using polyester lines provides greater benefit than using traditional steel wires and chains. Some advantages of using polyester include a reduction of mooring line weight, a reduction in vessel offset and a reduction in the dynamics of the line tensions. However, unlike steel, polyester lines exhibit axial stiffness characteristics that are nonlinear and vary with time and loading history.
Tahar (2001) developed a comprehensive theory and numerical tool to capture this behavior. The formulas allow relatively large elongation and nonlinear stress-strain relationships, as typically observed in polyester fibers. The mooring line dynamics are based on a rod theory and finite element method (FEM), with the governing equations described in a generalized coordinate system.
Since this theory is computationally intensive, the benefits outweigh the costs less than they do for the practical approach recommended by API. Therefore, the fully coupled dynamic analysis tool CHARM3D has been modified to incorporate the API-recommended approach. Two axial stiffnesses (EA), post installation (static) stiffness and storm (dynamic) stiffness, have been convoluted into a dual stiffness to represent the total response of the floating platform in a single run. In the traditional method, the analyses are done twice, one run for each stiffness. Then, the extremes from each run are used as governing values for design. This paper presents the global performance comparison between the dual stiffness method and the traditional method. The effect of motions on SCR strength is also investigated using ABAQUS software.
Simulating Ice-Sloping Structure Interactions With the Cohesive Element Method
Authors: Lu Wenjun , Løset Sveinung , Lubbad Raed 
Published: August 2013

The major processes that occur when level ice interacts with sloping structures (especially wide structures) are the fracturing of ice and upcoming ice fragments accumulating around the structure. The cohesive zone method, which can simulate both fracture initiation and propagation, is a potential numerical method to simulate this process. In this paper, as one of the numerical methods based on the cohesive zone theory, the cohesive element-based approach was used to simulate both the fracturing and upcoming fragmentation of level ice.
However, simulating ice and sloping structure interactions with the cohesive element method poses several challenges. One often-highlighted challenge is its convergence issue. As an initial attempt, the mesh dependency of the cohesive element method was alleviated by both creating a mesh with a crossed triangle pattern and utilizing a penalty method to obtain the initial stiffness for the intrinsic cohesive elements. Furthermore, two potential methods (i.e., introduction of a random ice field and bulk energy dissipation considerations) to alleviate the mesh dependency problem were evaluated and discussed.
Based on a series of simulations with the different aforementioned methods and mesh sizes, the global ice load history is obtained. The horizontal load information is validated against the test results and previous simulation results. According to the comparison, the mesh objectivity alleviation with different approaches was discussed. As a preliminary demonstration, the results of one preliminary simulation are summarized, and the load contributions from different ice structure interaction phases are illustrated and discussed.
Uncertainty of Long Term Fatigue Load of Subsea Well Heads
Authors: Grytoyr Guttorm , Steinkjer Oddrun 
Published: August 2013

Well heads (WH) are exposed to dynamic loading from waves and floater motions through the marine drilling riser and the drill string. Risers are known to have a pronounced nonlinear response characteristic, this influences the dynamic loading of the well heads. Non-linear time-domain finite element analyses are in general required to give an adequate description of the non-linearities involved. Analyses of a large number of short-term environmental conditions considering stochastic wave loading are required to give a representative description of the long-term fatigue loading on the structure.
The objective of this paper is to give an assessment of the sufficient simulation time of each short term seastate in order to get a required level of the statistical uncertainty of the long term fatigue load of the well head and conductor. The analyst can actually influence this statistical uncertainty by selecting proper analysis methodology. A statistical uncertainty measure can be used to evaluate the robustness in the estimated fatigue life. Assessment of statistical uncertainty in fatigue damage estimate is demonstrated by a case study, using typical North Sea conditions, and for varying boundary conditions.
Short term fatigue damage is established by means of rainflow cycle (RFC) counting in each stationary short-term condition. It has been experienced that significant statistical uncertainties can be present in the short-term fatigue damage estimates. This is because the accumulated fatigue damage in a stationary condition normally has significant contribution from the largest stress cycles in the realization. Selection of sufficient simulation length is hence essential to obtain reliable fatigue life estimates.
Applicable codes and standards for risers provide Design Fatigue Factors (DFF) to secure adequate safety against failure due to wave induced fatigue. The total uncertainty in the calculated fatigue damage comes from various sources and the DFFs in e.g. DNV-OS-F201 “Dynamic Risers” and API-RP-2RD corresponds to a certain uncertainty level in the fatigue damage estimate. A recommended target value for the statistical uncertainty of the fatigue damage estimates is given with basis in these design codes. There are no similar target values for statistical uncertainty of long term fatigue damage given in the applicable design codes for well heads and drilling equipment, hence the values from the riser codes have been selected as a starting point.
The recommendations and methodologies presented in this paper, will be included in the upcoming DNV RP “Fatigue design and analysis of drilling and well equipment”, at present this is available only as a draft, ref. [1].
State-of-the-Art Review of Floating Platform Concepts for Offshore Wind Energy Generation
Authors: Thiagarajan K. P. , Dagher H. J. 
Published: August 2013

Literature relating to offshore wind energy generation is produced at a significant rate, as research efforts are diverted to the emerging area of future clean energy. This paper presents an overview of recent research in the specific area of floating offshore structure design for wind energy. Earlier literature has broadly grouped these platforms into three categories based on their source of stability:
- Ballast stabilized (low center of gravity), e.g. spar
- Mooring stabilized, e.g. Tension Leg Platform
- Buoyancy or water-plane stabilized, e.g. semi-submersible.
These concepts were modifications of similar structures used in the offshore oil and gas industry. Recent papers have presented further improvements to these designs including active ballasting and control systems. These are examined for stability and global performance behavior and ease of operability and maintenance.
The paper also attempts to examine efforts to bring such concepts to fruition. Combined with this, the authors highlight activities that are ongoing in a consortium of industry and research institutions that is headed by the University of Maine. The origin of such a consortium is explained with reference to the future wind energy potential offshore Maine. This paper sets the stage for other papers in the Special Session on UMaine/ DeepCWind Consortium within the Offshore Renewable Energy Symposium at OMAE 2012.
An Integrated Methodology for the Design of Mooring Systems and Risers of Floating Production Platforms
Authors: Cruces Girón Aldo Roberto , Corrêa Fabricio Nogueira , Jacob Breno Pinheiro , Senra Stael Ferreira 
Published: August 2013

Nowadays, coupled analysis tools that allow the simultaneous modelling of the hydrodynamic behaviour of the hull and the structural behaviour of the lines of floating production platforms have been increasingly used.
The use of such tools is gradually allowing the introduction of some feedback between the design of risers and mooring systems. In the current practice, that comprises the so-called “hybrid” methodologies, mooring designers have been using these tools to consider the influence of the risers on the platform motions. On the other hand, riser designers can use motions that result from coupled simulations for the analysis of each riser. Such integration is already being implemented in the design practice of Petrobras; however, elsewhere the design of risers and mooring systems may still be performed separately, by different teams, therefore not fully exploiting the benefits that the coupled analysis tools can provide.
In this context, this work describes an innovative, fully integrated methodology for the design of mooring systems and risers of floating production systems (FPS). This methodology considers different design stages (from preliminary to advanced), integrating the design activities of mooring lines and risers in a single spiral, allowing gains in efficiency and cost reduction. The initial design stages already include a feedback between riser and mooring analyses. The integrity of the risers can be considered in the mooring design by determining their safe operational zones, and therefore, mooring line pretensions can be modified to improve its structural performance. Then, in advanced stages critical design cases for both mooring and risers systems can be identified and rigorously verified by using fully coupled models.
The application of the proposed methodology is illustrated with a case study of a typical FPS, representative of the platforms that have been recently considered for deepwater applications.
It should be stressed that the methodology described here does not reflect the current design practice of Petrobras. Presently it is merely a proposal that is being studied and assessed; this work comprises the first draft of the methodology, which will be enhanced and consolidated as the result of current and future studies.
A New Nonlinear Coupled Analysis Tool for Floating Structures
Authors: Li Zhiling , Llorente Carlos , Chen Cheng-Yo , Kang Chang Ho , Muehlner Edmund , Banumurthy Surya 
Published: August 2013

For the global performance analysis of a floater, the traditional semi-coupled method models mooring lines/risers as nonlinear massless springs and ignores 1) the inertial effects from mooring lines/risers, 2) the current and wave load effects on mooring lines/risers, and 3) the dynamic interaction between mooring lines/risers and the floater. However, these effects are deemed critical for deepwater and ultra deepwater floating structures as they may have a significant impact on the floaters’ motions and mooring line/riser tensions.
This paper presents the development and verification of a time-domain nonlinear coupled analysis tool, MLTSIM-ROD, which is an integration of a recently developed 3D rod dynamic program, ROD3D, with the well-calibrated floater global performance analysis program, MULTISIM (Ref [9]). The ROD3D was developed based on a nonlinear finite element method and merged with MULTISIM by matching the forces and displacements of mooring lines/risers with the floater at their connections. MLTSIM-ROD can thus predict the floater’s large displacement/rotation motions and mooring line/riser tensions including all the coupled effects between the floater and mooring lines/risers. In this paper, global performance predictions for a SPAR in the Gulf of Mexico in deepwater were carried out using MLTSIM-ROD. The results were then verified with those from other coupled analysis programs.
The paper also presents the results of motions and mooring line/riser tensions of the SPAR using both the coupled and semi-coupled methods. The results from the coupled and semi-coupled analyses indicate that the floater’s motions and mooring line/riser tensions could be significantly influenced by the dynamic interactions between the floater and mooring lines/risers. Hence, the coupled method needs to be considered for deepwater floating structures.
DP Cooperative Control for Subsea Installation With Multiple Vessels: An Illustrative Case Study Based on Numerical Simulations
Authors: Oshiro Anderson T. , Tannuri Eduardo A. , Fucatu Carlos H. , Neves Cassiano R. , dos Santos Melquisedec F. 
Published: August 2013

This paper presents the development of cooperative control technique applied to vessels equipped with dynamic positioning (DP) system. An illustrative case study is suggested: the launching of subsea equipment using two DP vessels. In this example, the cooperative system controls the relative distance between the DP vessels. One of the advantages of this method is the increase of operation’s safety and operational window, since, among other factors, the tension in the launching cable is reduced by half.
Initially, it was proposed the control of vessels relative positions, trying to keep the movements at the top of the A-frames in counter-phase. This avoids the slackening of the launching cable. For this, an algorithm based on phase estimator (Hilbert transform) associated with a PD control was implemented. The results showed that for regular waves this strategy was effective.
A dynamic mapping was then obtained using simplified 2D simulator, previously validated by comparison with experimental tests. In these maps, two regions are defined — occurrence or non-occurrence of cable slackening — as a function of the distance of the vessels and the depth of the subsea equipment. This map defines the proper set-point for the DP systems for each depth of the subsea equipment. This map is used to define the best relative position for the vessels.
In addition, the hoisting control receives the measurements of the vertical motion at the top of the A-frame, and compensates its motion, trying to maintain a constant lowering velocity. This control was implemented considering errors of 10% and delay of 0.5s in the measurements. The results confirmed that the control is able to eliminate the tension peaks and the occurrence of slackening in the launching cable.
The conclusion is that the appropriate control strategy, considering regular waves, is to combine the control of both position of the vessels and hoisting of the cable. Therefore the position control, coupled with dynamic mapping, defines the “optimal path” to be followed during the line hoisting, trying to keep the vessels as close as possible to the “no slackening” region.
Impacts of Waterway Regulation Engineering on Saltwater Intrusion in the Modaomen Estuary
Authors: Zhu Yuliang , Xu Chencheng , Wei Xiaoyan 
Published: August 2013

A large-scale waterway regulation project, which is the main approach for people to manage coastal and estuary area will be imperative due to the high-speed economic development in Guangdong Province. The project will change the topography in the estuary region and influence the hydrodynamic conditions there. The Modaomen waterway, as the main access to the sea of Xijiang River, plays a key role in connecting outer sea. During recent years, a remarkable deterioration of tide intrusion occurred resulting in negative effect on water resource utilization in industry, agriculture and local people’s lives and therefore it is of great significance to study on the tide intrusion caused by dredging project.
This paper analyses measured Modaomen hydrological data and exhibits the temporal and spatial distribution of salinity and characteristics of fresh and salinity water mixing, as well as the correlation between salinity, water level and suspended sediment concentration in the Modaomen region. Based on the establishment of high-precision three-dimensional salinity mathematical model in Modaomen region, this paper calculates various engineering plans and examines the changes of flow field and tidal saltwater intrusion, which provides elementary base for implementation of the waterway regulation engineering. During the process of calculation, the terrain, the border and validation data that adopted in this paper is relatively new and have high reliability.
The study indicates that the salinity degree has a merely minor increase after projects indeed in the estuary to provide situation for tide intrusion. However, the influence is little and it fails to be the chief reasons responsible for the depravation of tide intrusion in the Modaomen estuary recent years.
A Surrogate Model for Evaluation of Maximum Normalized Dynamic Load Factor in Moving Load Model for Pipeline Spanning due to Slug Flow
Authors: Sultan Ibrahim A. , Reda Ahmed M. , Forbes Gareth L. 
Published: August 2013

Understanding the problem of slug-flow-induced fatigue damage is of particular importance to the reliable operation of pipelines. Slug flow, across unsupported pipeline spans, produces dynamic vibrations in the pipeline resulting in cyclical fatigue stresses. These dynamic effects will cause the pipeline to fail at a point of stress concentration if proper design procedure is not followed.
The response of a pipeline span, under the passage of slug flow, can be represented by dynamic load factors that are functions of the speed ratio and damping characteristics of the span. The aspects of these functional relationships are investigated, in this paper by conducting multiple simulations at different speed ratios and damping factors. The data obtained from the steady state Fourier expansion will, consequently, be used to produce a surrogate model with a level of accuracy that adequately qualifies it for use in determining dynamic loading of pipelines.
The closed-form surrogate model can be used to eliminate the need to employ costly mathematical procedures or finite element packages for the analysis. The model will also provide a solid ground for optimization studies and help designers gain an insight into how various model parameters impact the system response. This paper will demonstrate the aspects of a proposed surrogate model and endeavor to obtain parameter domains within which the model’s reliability is ensured. A numerical example will be demonstrated to prove the concepts presented in the paper and confirm the validity of the proposed model.
The Application of a “Giant” Floating Wave Barrier for Offshore Installation Work
Authors: Billingy Sean S. , Vermeulen Kees-Jan , Kortekaas Peter 
Published: August 2013

When focusing on offshore installation work, it can be seen that there has been a shift from one-off installations for the oil and gas industry to repetitive installations of, for instance, offshore renewables. An important aspect, which plays a large part in the success rate of these repetitive installations, is the workability of the installation vessels.
SMIT understands the importance of workability and is looking into ways to increase the workability of their sheerlegs crane barges in an offshore environment. A proposed method to increase the workability is the use of a floating wave barrier (FWB). This FWB can be a specific structure designed for this purpose, or, as in this case, a barge used for the transportation of the structures that will then be installed by the sheerlegs crane barge.
This paper discusses the effects of a FWB on the first-order motions of the sheerlegs crane barge. Dependent on the environmental conditions, the use of a FWB can decrease the first-order motions of the vessel and increase its workability on that particular phase in the total installation sequence. When applied on the phase with the lowest workability in the installation process, this can result in a higher overall workability. The limits of the use of a FWB are also discussed, particularly with respect to wave height and period.
Application of Deterministic and Probabilistic Methods in Pipeline Lateral Buckling Design
Authors: Zeitoun Hammam , Branković Maša , Shim Edwin , Chin EuJeen , Anderson Benjamin 
Published: August 2013

Subsea pipelines lateral buckling design has significantly evolved over the last years as more pipeline projects have moved into more challenging environments and into high temperature / high pressure (HT/HP) design application. Knowledge and understanding of pipeline lateral buckling has improved with design application resulting in refined and enhanced design approaches. Using current design approaches, it is now quite acceptable to control lateral buckle formation along the pipeline by using buckle triggers or to allow uncontrolled lateral buckles, provided that the various design limit states are satisfied.
A number of design methodologies can be used to check the acceptability of uncontrolled buckling or to design for controlled buckling including deterministic, probabilistic buckle formation and full Structural Reliability Assessment (SRA) methods. Using SRA or probabilistic methods is usually an attractive design option as lateral buckling design involves dealing with a large number of uncertainties and variation in design parameters. These methods help to ensure the reliability of the proposed buckle initiation scheme. However, the use of these methods is also associated with a number of challenges such as the need to identify key parameters influencing the design and quantifying their uncertainties. Deterministic design approaches on the other hand are simpler to apply. However, they do not provide means to quantify the reliability of the proposed buckling scheme or the design risks. The choice of input parameters in a deterministic design is also relatively subjective which can possibly result in an overly conservative or unconservative design solution depending on the adopted design approach, selected design parameters and pipeline system being considered.
Design guidelines and recommended practices such as SAFEBUCK (20) offer comprehensive guidelines to design for lateral buckling. However when faced with a range of complex variables, the designer needs to be aware of the effect of these parameters on the overall design.
This paper describes the application of Deterministic and Probabilistic design approaches in lateral buckling design. The paper starts by describing these approaches, their advantages and limitations. The paper then explores a number of key uncertainties and variation in design parameters that the designer is faced with and its effect on the pipeline response.