bluuebunny/crossref_metadata_2025 huggingface dataset:
Life Cycle Environmental Impacts of Two Options for MSW Management in New York City: Modern Landfilling vs. Waste to Energy
Authors: Krishnan N. , Themelis N. J.
Published: November 2008

The U.S. generates about 370 million short tons of Municipal Solid Waste (MSW) each year. In 2002, an average of 26.9% of this material was either recycled or composted. Of the remainder, an estimated 242 million short tons were disposed of in landfills and about 29 million short tons were combusted in Waste to Energy (WTE) facilities to produce electricity and scrap metal. Effective management of MSW is becoming increasingly challenging, especially in densely populated regions, such as New York City, where there is little or no landfill capacity and the tipping fees have doubled and tripled in recent years. There is also a growing appreciation of the environmental implications of landfills. Even with modern landfill construction, impacts remain from the need for transfer stations to handle putrescible wastes, their transport to distant landfills, and finally landfill gas emissions and potential aqueous run-off. Environmental impacts of concern associated with disposal in WTEs include air emissions of metals, dioxins and greenhouse gases. In the U.S., there is also a strong negative public perception of WTE facilities. Decisions about waste management should be influenced by a consideration of the overall, quantified life-cycle environmental impacts of different options. In this paper we therefore develop a methodology to assess these impacts for landfilling and WTE waste management options. Specifically we attempt to compare these two options for New York City, a large urban area.
Prediction of Global Loads and Structural Response Analysis on a Multi-Purpose Semi-Submersible
Authors: Lee Yongwon , Incecik Atilla , Chan Hoi-Sang
Published: November 2008

This paper presents analysis procedures of a prototype semi-submersible which consists of rectangular pontoons and square columns. The proposed semi-submersible is based on standard cubic boxes constructed by stiffened flat panel line assembly techniques. The prediction of global loads and responses is of great importance to engineers for assessing the safety of marine structures. In this paper analysis methods to determine the global structural loads and to assess the viability of the multi-purpose semi-submersible are described. Static loads in the still water condition and wave induced dynamic loads of cylindrical members in different design conditions were determined to investigate the viability of the proposed semi-submersible. Further the assessment of the safety against failure due to excessive maximum loads was accomplished in ultimate limit states.
Application of DNV-RP-F204 for Determining Riser VIV Safety Factors
Authors: Chezhian Muthu , Mo̸rk Kim , Ronæss Marit , Meling Trond Stokka
Published: November 2008

Fatigue is often the governing criterion for deepwater riser design. Fatigue assessment methods based on SN curves typically use fatigue safety factors and there is a lack on consensus about the appropriate Design Fatigue Factor (DFF) for VIV that should be applied. A DFF of 20 is commonly used in project specifications to account for a larger uncertainty in prediction of fatigue damage due to VIV, i.e. fatigue life due to VIV should be at least 20 times more than the service life of the riser. Recent case studies and benchmarking assessments, have confirmed that the DFF of 20 for VIV is not always an optimal choice. Owing to the complexity of the VIV problem, often semi-empirical solutions are adopted in the riser VIV analysis. The implicit uncertainty and bias associated with the VIV analysis model, needs to be considered along with the VIV fatigue safety factor, in order to establish the adequate acceptance criterion for VIV induced fatigue. The stochastic variables governing the VIV and their associated uncertainties can vary widely from case to case and this in turn will influence the VIV safety factor. Different stochastic variables may be relevant based on the floater type, riser type, environmental modeling, analysis methodology etc. In addition to these stochastic variables, the uncertainty in the VIV specific variables, such as Strouhal number, bandwidth parameters, damping effects, lift coefficient, response models (Amplitude /Diameter ratio), etc also need to be considered in the evaluation of the VIV safety factor. In this paper, guidance is provided by means of case studies for establishing case specific VIV safety factors. By performing a set of dedicated analyses for the prevailing uncertain input parameters, the resulting uncertainty in the VIV fatigue damage is estimated. The enhanced risk based criterion presented in DNV Recommended Practice RP-F204 [7], developed as part of the Norwegian Deepwater Programme (NDP) is applied for these case studies to calculate the required VIV fatigue safety factors. This project was sponsored by NDP, whose contribution and support is gratefully acknowledged.
A Study on Reliability-Based Improvement of Reliquefaction System for LNG Carriers
Authors: Chang Daejun , Lee Taejin , Han Kihoon , Chang Kwangpil , Moon Kiho , Ha Jongpil , Liknes Atle
Published: November 2008

The objectives of the study are to quantify the reliability of a boil-off gas (BOG) reliquefaction system for liquefied natural gas (LNG) carriers and to verify design improvements based on the reliability analysis. The system is broken into subsystems and then further into components. Failure rates are collected from generic references, primarily from the OREDA handbook. The reliabilities of the subsystems are estimated, and a reliability block diagram for the whole system is established. The subsystems are classified into three ranks according to their reliability: the high reliability rank comprises the subsystems ‘BOG preparation system,’ ‘Seawater intake system,’ and ‘Buffer N2 reservoir system’, the medium reliability rank the subsystem ‘BOG liquefaction system’, and the low reliability rank the subsystems ‘BOG compression system,’ ‘N2 cooling system’, and ‘Buffer N2 generation system.’ The reliability and availability are estimated for various process configurations where some of the low reliability category have a standby. The ‘bare’ system without any redundancy fails to attain an availability higher than 0.96. Addition of redundancy to one of the least reliable three commonly results in an increase in reliability improvement, to around 0.97. If all of the three subsystems have standby units, the system reliability improves to 0.99. It is recommended that maintenance efforts should be concentrated on the rotating machines that caused the subsystems to have a low reliability.
Fatigue Damage Assessment Using a Bandwidth Parameter for VIV Applied to the Foinaven Dynamic Umbilical
Authors: Trarieux F. , Lyons G. J.
Published: November 2008

The application of a method for fatigue damage assessment applied to the relative effects of mooring, wave, and Vortex Induced Vibration (VIV) is presented. It is a simpler procedure than rainflow counting and uses a bandwidth parameter with standard deviation applied to modify narrow band fatigue estimation. This bandwidth parameter has been successfully applied by the authors to investigate in detail the curvature (bending stress) response of the Foinaven lazy-wave umbilical for investigations into VIV. This parameter is valuable since as a single value it may be used to track the variation of bandwidth response with time and against other measures such as varying current speed. The method is conveniently based on a peak counting approach. Low values close to zero indicate a narrow band process whereas values near unity indicate a broad-band process. It is a much better measure than kurtosis for determining bandwidth. Curvature and environmental data were gathered by the Foinaven Umbilical Monitoring System installed on the Foinaven Petrojarl IV floating production unit located in the Altantic margin, West of Shetland. The VIV frequency range owing to current excitation considered is that which is considered as being above consequential wave frequencies (0.2 to 2Hz). This paper presents results of fatigue damage assessment for the periods where a strong variation of bandwidth was observed. 64 records (each lasting about 10 minutes) representing a daily acquisition of about 8 hours were processed showing the correlation between the bandwidth of curvature and the amount of fatigue experienced by the umbilical. Strong VIV regimes are often characterized by an intense activity around a particular frequency and the impact of such narrow-band events on the fatigue life of the structure is clearly demonstrated. This paper also presents the relative contributions of mooring, and waves/vessel motions, and VIV to fatigue damage. Although wave excitation remains the main source of fatigue, VIV appears to potentially contribute to a significant part of the overall fatigue damage.
Validation Study for Free-Surface Wave Flows Around Surface-Piercing Cylindrical Structures
Authors: Rhee Shin Hyung , Makarov Boris
Published: November 2008

The present study is concerned with the free-surface wave flows around surface-piercing cylindrical structures. The volume of fluid method implemented in a Navier-Stokes computational fluid dynamics code is employed for test cases that involve general ship waves, spilling breaking waves, bubbly free-surface in separated regions, and interaction between free-surface waves and underlying viscous flow. The computational results are validated against existing experimental data, showing good agreement. The validation results suggest that the present computational approach provides a tool that is flexible and accurate enough to capture the outstanding flow physics associated with the free-surface wave flows around surface-piercing cylindrical structures.
Dynamic Model of Pipeline During Pulling in Directionally Drilled Hole
Authors: Tikhonov Vadim S. , Safronov Alexander I. , Gelfgat Mikhail Ya. , Figarov Namik G.
Published: November 2008

The most important problem in pulling pipeline in the directionally drilled hole is overcoming of the soil resistance. This paper presents the 2-D model of contact interaction between the pipeline and soil as well as a numerical method of calculation of the pipeline vertical displacement and drag while pulling. The model is based on dynamic equation of lateral forces. Using this model it is quite easy to take into account nonlinear contact interaction of pipeline and soil in terms of both contact force and friction drag as well as a convective nature of the lateral load propagation at an axial motion of pipeline. Based on the suggested numerical model, a computer program was developed to improve an accuracy of pulling process analysis with moderate computer time needed. The developed program was applied to analyze and select parameters of the Lisichansk-Tikhoretsk oil pipeline in the tunnel under the river of Don. Calculations provided the updating of pulling process parameters and identification of those tunnel intervals, which might be challenging with pipelining.
Global Configuration Design of Umbilicals in Deepwater
Authors: Fleming Ray , Moros Thanos , Ghosh Rupak , Lambrakos Kostas , Robson Dave
Published: November 2008

Global configuration design of subsea umbilical risers in deep water is a major challenge due to extreme environmental and operational requirements. The critical issues considered in design are the interference between umbilicals in the presence of strong loop and submerged current, and the on-bottom stability along with the strength and fatigue requirements. The vessel motion primarily controls the selection of the configuration, catenary or lazy wave, and the latter is an obvious choice in the presence of significant heave motion. The length and routing on the seabed ensures the on-bottom umbilical stability by dissipating the axial load through soil friction. However, the interference with other subsea components as well as the space availability can also be a governing criterion in the routing. Finally, all these design requirements must be satisfied economically from the perspective of overall cost of the project without compromising quality of the product and safety of design. This paper presents a brief outline of the global configuration design of umbilicals accounting for various design considerations. The host is a semi submersible in a water depth of 6050-ft in the Gulf of Mexico. The lazy wave configurations of the chemical injection and control umbilicals are considered for the study presented herein. The methodology of design for the global configuration is discussed considering different environmental loadings such as the 100-yr and 10-yr loop current, and 100-yr submerged current. The stability of the umbilical on the seabed is discussed on the basis of analysis results for the environmental loadings with dominant vessel motions. The phenomenon of “walking” under the influence of dynamic loading is investigated and the necessary considerations in design to prevent the umbilicals from “walking” are also discussed.
Experimental Optimization of Extreme Wave Sequences for the Deterministic Analysis of Wave/Structure Interaction
Authors: Clauss Gu¨nther F. , Schmittner Christian E.
Published: November 2008

For the deterministic analysis of wave/structure interaction in the sense of cause-reaction chains, and for analyzing structure responses due to special wave sequences (e.g. three sisters phenomenon or other rogue wave groups) methods for the precise generation of tailored wave sequences are required. Applying conventional wave generation methods, the creation of wave trains satisfying given local wave parameters and the generation of wave groups with predefined characteristics is often difficult or impossible, if sufficient accuracy is required. In this paper we present an optimization approach for the experimental generation of wave sequences with defined characteristics. The method is applied to generate scenarios with a single high wave superimposed to irregular seas. The optimization process is carried out in a small wave tank. The resulting control signal is then transferred to a large wave tank considering the electrical, hydraulic and hydrodynamical RAOs of the respective wave generator in order to investigate wave/structure interaction at a large scale.
An Overview of the Reassessment Studies of Fixed Offshore Platforms in the Bay of Campeche, Mexico
Authors: Chakrabarti Partha , Abu-Odeh Ibrahim , Mukkamala Adinarayana , Majumdar Bidyut , Havbro Faber Michael , Straub Daniel , de la O. Rami´rez Juan de Dios
Published: November 2008

Pemex Exploration Produccio´n owns and operates several fields in the Bay of Campeche, located in the south Gulf of Mexico, for oil and gas production. Many of these fixed offshore platforms were built during the 70s and 80s and have already exceeded their design service life. In order to meet the growing demand for oil and natural gas it is necessary to extend the service life of these platforms by at least another 15 to 30 years. To meet this extended service life, thorough and systematic reassessment studies need to be conducted leading to identification of any structural weakness and possible locations of fatigue problems. To extend the fatigue life of the welded joints, inspections are required to be performed according to a risk based inspection planning procedure. In the present paper, an overview of the reassessment study procedure is outlined and pertinent results are presented for more than twenty platforms which were studied in a recent project. The most important engineering considerations and various analyses involved in the study are discussed in detail. The platforms cover the categories of Drilling, Production, Gathering and Habitation. Depending on the category, Pemex specifications assign different levels of acceptable reliabilities and reserve strength ratios. The ultimate strength of the platforms is determined using a detailed finite element model of jacket, piles and deck structures and a state-of-the-art non-linear progressive collapse analysis technique commonly known as ‘pushover’ analysis. The analytical structural models include local joint flexibility of the jacket joints, soil-pile interaction, geometric non-linearity and material plasticity. They also include the information of damages and deterioration obtained from inspection reports, such as dents, bents, cracks etc. The joint strength modeling is performed using the latest available procedures that use non-linear load-deformation curves. Fatigue analyses are based on spectral analysis technique and include the dynamic response of the structure to wave loads. The structural models for fatigue analysis include the effects of local joint flexibility (LJF) and soil-pile interaction. Results for one typical platform are presented in complete detail to facilitate the understanding of the reassessment study procedure. A typical risk based inspection planning for extending fatigue service life is also presented. Finally, the summary of results for 28 platforms is presented to appreciate the importance of the various analytical parameters. It is hoped that this very wide database of results for platforms of different configurations can serve as a useful resource for the offshore industry in general.
Truss Spar VIM in Waves and Currents
Authors: Finnigan Tim , Irani Mehernosh , van Dijk Radboud
Published: November 2008

The exciting force induced by vortex shedding on the hull of bluff body floaters, such as Spars, may cause response near the resonant period of any of the 6 rigid body modes of response of the floater [1]. Usually the sway vortex induced motion (VIM) is of particular concern for mooring and riser integrity. Most efforts to study this phenomenon to-date have focused on uniform current loading over the depth of the platform, such as one would find in the eddy/loop currents in the Gulf of Mexico. Under these conditions, tow tests with the model mounted horizontally or vertically and restrained with a spring system have been sufficient to characterize the VIM behavior [2, 3]. VIM responses of a Classic Spar measured in the field after the passage of a hurricane in what is referred to as the “hurricane inertial current” event has raised the awareness of the possibility of platform VIM response in sheared currents and in the presence of waves. In order to evaluate this condition, model scale Truss Spar VIM tests were conducted at the MARIN Offshore Basin in the summer of 2004. Uniform current, “shear” or two-layer current, and wave plus current conditions were simulated and compared with benchmark uniform current tow test results. The tests were done in current alone, in waves alone, and with waves in-line with the current, and, waves transverse and oblique to the current. Comparisons are made of VIM response in uniform and shear current conditions, and, response with and without waves. One of the key findings is that with waves in-line with the current, VIM is generally reduced; however, at some headings the response in waves plus current in transverse waves is larger than in current alone.
Change of Mechanical Properties of High Strength Line Pipe by Thermal Coating Treatment
Authors: Shinohara Yasuhiro , Hara Takuya , Tsuru Eiji , Asahi Hitoshi , Terada Yoshio , Doi Naoki
Published: November 2008

In strain-based design, the overmatch condition in the girth weld portion primarily must be maintained. The pipes may also be required to have a low yield to tensile (Y/T) ratio and a high uniform elongation (U.EL) in the longitudinal direction to achieve a high compressive buckling strain. However, change in the mechanical properties by heating during coating treatment has not been paid attention so much. Furthermore, how much the mechanical properties change is affected by production conditions is unclear. This study aims to clarify firstly the relation between the mechanical properties (Y/T ratio, U.EL etc.) and the microstructure and secondly the change in mechanical properties by thermal coating treatment. The Y/T ratio and U.EL are affected by the volume fraction of ferrite and the secondary phase, which are changed by thermomechanical control processing (TMCP) conditions. For example, use of dual phase microstructure is very effective for decreasing the Y/T ratio and increasing the U.EL as the pipe. On the other hand, yield strength (YS) rises and the U.EL does not change after coating. The increase in the YS after coating is influenced by the microstructure and TMCP conditions. Resultantly, dependence of the Y/T ratio on the microstructure and TMCP conditions is reduced for line pipes after thermal coating treatment.
Three-Dimensional Analysis of Hydroelastic Behaviors of an Aircushion Type Large Floating Structure
Authors: Ikoma Tomoki , Masuda Koichi , Rheem Chang-Kyu , Maeda Hisaaki
Published: November 2008

This paper describes theoretical formulations for a prediction of hydrodynamic forces on the aircushion type large floating structure and shows corresponding results. Therefore, a new program code is developed. The structure is supported by large mono-aircushion. The present theory is based on the three-dimensional singular point distribution method. Effect of the aircushion is considered in this. Then, a processing of a singular integral of the boundary integral method is shown and its validity is confirmed. In conclusion, the draft effect to the pressure within the aircushion is discussed. As a result, when width of the skirt is thin, the draft effect is little. However, in case that the width is large, the draft effect is enlarged.
Burst Tests on Pipeline Containing Interacting Corrosion Defects
Authors: Benjamin Adilson C. , Freire Jose Luiz F. , Vieira Ronaldo D. , Diniz Jorge L. C. , de Andrade Edmundo Q.
Published: November 2008

In this paper the burst tests of seven tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from longitudinal welded tubes made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The specimen IDTS 1 is a defect-free pipe. The specimen IDTS 2 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other five specimens contain groups of interacting defects constituted by the combination of two or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by six assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method, the RSTRENG Effective Area method and the DNV RP-F101 method for interacting defects.
A Simplified Model for the Study of Dynamic Coupling Effects in Deepwater Floating Structures
Authors: Low Ying Min , Langley Robin S.
Published: November 2008

As the exploitation of hydrocarbon moves towards deeper waters, the global dynamic response of a floating production system needs to be predicted with coupled analysis methods to ensure accuracy and reliability. Two types of coupling can be identified: one is between the floating platform and the mooring lines/risers, while the other is between the mean offset, the wave frequency and the low frequency motions of the system. At present, it is unfeasible to employ fully coupled time domain analysis on a routine basis due to prohibitive computational time. This has spurred the development of more efficient methods that account for the various couplings, including frequency domain approaches. It is paramount for the complex coupling mechanisms to be well understood before appropriate simplifications and assumptions can be made. In this paper, a simplified two degree-of-freedom system representing the surge motion of a vessel and the fundamental vibration mode of the lines is examined which captures the important underlying physics. Within this framework, the frequency domain equations are rigorously formulated, and the nonlinearities in the restoring forces and drag are stochastically linearized. The model allows key coupling effects to be identified: among other things, the equations demonstrate how the wave frequency dynamics of the mooring lines are coupled to the low frequency motions of the vessel. Subsequently, the effects of making certain simplifications are investigated through a series of frequency domain spectral analyses, and comparisons are made to simulations in the time domain. The work highlights the effect of certain common approximations, and recommendations are made regarding the development of efficient modeling techniques.
Coupled CFD Simulation of the Response of a Calm Buoy in Waves
Authors: Woodburn Peter , Gallagher Paul , Naciri Mamoun , Borleteau Jean-Paul
Published: November 2008

This paper describes work done within the EU FP5 Project EXPRO-CFD to develop a system to couple commercial CFD software to existing hydromechanics tools to allow prediction of the response of floating structures in waves and currents, including viscous effects. Its focus is the use of this system to improve the prediction of CALM buoy response in waves. The Atkins EXPRO-CFD system is made up from the CFD code CFX, coupled to the AQWA-LINE and AQWA-NAUT hydromechanics codes. In this system, CFD provides the complete set of hydrodynamic forces and moments at each time step in the motions simulation, with the dynamics of the floating structure, its moorings and riser/export lines modeled in the AQWA-NAUT software. AQWA-NAUT returns the structure’s displacements and velocities to the CFD model and a moving grid algorithm uses these to couple motions and fluid flow in an accurate and stable manner. The motions of a CALM buoy were studied to test the capabilities of the system. The CALM buoy geometry (based on current designs by SBM) is 23m in diameter with a 2m wide skirt attached 1m above the keel; the effects of flow separation off this skirt and the associated viscous damping on the motions of the buoy were expected to be significant, especially around its natural period. A series of 1:40 model scale tests were carried out by Sirenha using a simplified mooring system with no risers. The results from the model tests, from AQWA-NAUT alone (carried out by SBM), and from the coupled EXPRO model were compared directly at model scale. The same AQWA-NAUT model was used in both the AQWA-NAUT-only simulations and the coupled simulations, allowing direct comparison between the results. The EXPRO-system simulations were carried out ‘blind’, i.e. without access to the experimental data. The three sets of RAOs showed reasonable agreement in long or short waves (within the limits of the specification of the mooring system). However, around the natural period, the AQWA-NAUT-only model significantly over-predicted the response in heave, and in particular in pitch. Although the EXPRO-CFD system slightly over predicted the heave and pitch responses, the results were close to the experimental measurements throughout. Further tests indicate that the weakness in the potential flow approach appears to be in the formulation of added viscous damping rather than the choice of model values for drag coefficients.
Combined Loading of a Wave and Surface Current on a Fixed Vertical Slender Cylinder
Authors: Zaman M. H. , Baddour R. E.
Published: November 2008

A study on the loading of an oblique surface wave and a surface current field on a fixed vertical slender cylinder in a 3D flow frame is illustrated in the present paper. The three dimensional expressions describing the characteristics of the combined wave-current field in terms of mass, momentum and energy flux conservation equations are formulated. The parameters before the interaction of the oblique wave-free uniform current and current-free wave are used to formulate the kinematics of the flow field. These expressions are also employed to formulate and calculate the loads imparted by the wave-current fluid flow on a bottom mounted slender vertical cylinder. The surface current considered in this report, is assumed uniform and acting over a layer of fluid that extends from the free surface to a specified finite depth. Prior work assumes that uniform currents existed over the total depth of the fluid domain. In this paper we extend the approach considered in Zaman and Baddour (2004) for the wave-current analysis. Morison et al equation is deployed for the load computations in all cases. The above model is utilized to compute the loads on a slender cylinder for a wave with varying range of incidence current field. Computations of the moments are also done for the case when current is existed over the whole water depth of the domain.
The Effect of Plenum Chamber Volume and Air Turbine Hysteresis on the Optimal Performance of Oscillating Water Columns
Authors: Folley Matt , Whittaker Trevor
Published: November 2008

It is well known that air compressibility is likely to influence the performance of oscillating water columns (OWC’s) and this has previously been modelled and estimated using linear aero-hydrodynamic lump-mass models. In addition, the optimum performance of specific OWC’s has been determined, with the effect of air compressibility included within the optimisation. This paper extends this work to determine the optimum performance of any OWC, defined by its hydrodynamic coefficients and serves as a reminder to experimentalists of the importance of considering air compressibility in their models. Moreover, the optimisation is analytical and so produces explicit expressions for maximum power capture, optimum damping, etc. The results indicate that for the majority of OWC’s the maximum power capture decreases with increasing plenum chamber volume, accompanied by a reduction in the optimum turbine damping and an increase in optimum water column motion. However, the results also show that air compressibility will increase maximum power capture for OWC’s when the incident wave period is shorter than the natural period of the water column. To date, air turbine hysteresis has been studied as a purely aerodynamic phenomenon and its effect on the optimum hydrodynamic performance of OWC’s has not been investigated. This paper uses a linearised phase shift to model an approximation of turbine hysteresis that shows that turbine hysteresis will have a small but significant influence on hydrodynamic performance, where the magnitude of influence is similar to the effect of subtle blade profile and blade sweep angle modifications on aerodynamic performance. The results indicate that hysteresis should be considered in turbine design, especially if a turbine modification improves aerodynamic performance whilst reducing hydrodynamic performance due to a change in the turbine hysteresis.
Effect of Turbulence Modeling on VIV Numerical Simulation
Authors: Wanderley Juan B. V. , Souza Gisele H. B. , Levi Carlos
Published: November 2008

Author’s previous work Wanderley [1] presented an efficient numerical method to investigate VIV phenomenon on circular cylinders. The numerical model solves the unsteady Reynolds Average Navier–Stokes equations for slightly compressible flows using the Beam–Warming implicit factored scheme. In the present work, the effect of the turbulence model on the results is evaluated for both Baldwin Lomax and k-ε models. To demonstrate the quality of the numerical method, results for the transversal oscillation of a cylinder laterally supported by spring and damper are compared with experimental data. The application of the turbulence models showed the much better agreement of the k-ε model with the experimental results.
Dynamic Simulation for a Fish Cage System
Authors: Lee Chun-Woo , Kim Hyung-Seok , Lee Gun-Ho , Koo Kwi-Yeon
Published: November 2008

This paper presents a physically based calculation model to simulate the behavior of a cage system considered as moored flexible structures. The flexible structure described is composed of a network of mass points and springs, the behavior of which is calculated using the implicit integration method of the fundamental law of dynamics. Also, to increase the accuracy of calculations, the reduction ratio of flow speed due to shielding effects is acquired by using the flume tank experiments. By applying the reduction ratio of flow speed to the numerical calculation, the calculation accuracy was increased, and it was found that the result of the simulated cage movements was very close to that of the model cage. In addition, the dynamic behavior of an actual fish cage system under the current and waves was simulated.
Experimental and Numerical Investigation of the Stabilizing Effects of a Water-Entrapment Plate on a Deepwater Minimal Floating Platform
Authors: Cermelli Christian A. , Roddier Dominique G.
Published: November 2008

The stabilizing effects of a water-entrapment plate at the keel of a small three-legged semi-submersible platform are determined using laboratory experiments and time-domain simulations. Motion predictions were carried out in the time-domain using coupled-analysis between the vessel and its mooring, linear diffraction-radiation theory, and an empirical wave-viscous interaction model. Model tests were conducted at the U.C. Berkeley Ship Model Testing Facility to determine the validity of the numerical model.
Pipeline Collapse Methodology for Ultra-Deepwater
Authors: Choi Han S. , Ayers Thomas R.
Published: November 2008

The objective of this paper is to summarize current ultra-deepwater (i.e. up to 3,500 meters water depth) pipeline mechanical design methodologies in the Gulf of Mexico (GOM), and the rest of the world. The standard mechanical design for ultra-deepwater pipelines in the GOM is based on API RP 1111. API code also has been used for deepwater projects in west Africa. DNV code OS-F101 was mostly used for deepwater projects in offshore Brazil and Europe. Some pipeline designs in the GOM have started to incorporate parts of the DNV design methodology. A discussion of collapse only design and combined loading (i.e. pressure + bending) design will be presented. The buckle arrestors shall be designed along with the ultra-deepwater pipeline mechanical design. The best design criteria are obtained from physical full-scale collapse testing. The comparison of the physical test data and collapse calculations using the DNV and API codes will be presented. It was found that the conservatism still exists within collapse prediction for ultra-deepwater pipeline using modern design codes such as DNV OS-F101 and API RP 1111. Recommendations of the mechanical design methodologies for the ultra-deepwater pipeline are presented.
TLP Reliability Study Based on the Limit State of Tendon Unlatching
Authors: Li Guang , Banon Hugh , Perego Ron
Published: November 2008

The tendons of a tension leg platform are critical structural components in maintaining the system integrity. A common tendon design limit is associated with the minimum tendon tension. Most TLP reliability studies in the past defined the minimum-tension limit state as the loss of tendon tension. However, studies have shown that temporary tension loss at a corner of a TLP will not necessarily jeopardize the system integrity if the tendon is allowed to stroke down during a loss of tension event. Hence, we define the limit state associated with minimum tension event as the down-stroke where the tendon unlatches itself. An approximate method is proposed in this study to evaluate the probability of tendon unlatching. Sensitivities to the key assumptions are also investigated.
Finite-Element Method for the Hydroelastic Response of Very Large Floating Structure in Water of Variable Depth
Authors: Kyoung J. H. , Hong S. Y. , Kim B. W. , Cho S. K. , Bai K. J.
Published: November 2008

Finite element method is applied to investigate the influence of varying sea-bottom topography on the hydroelastic response of the Very Large Floating Structures (VLFS). A floating structure is modeled as a thin plate with uniform stiffness. The hydroelastic responses of a pontoon-type VLFS are analyzed by the mode superposition method. To enhance the satisfaction of free edge condition a set of orthogonal function is adopted as the mode function instead of well-known free-free beam mode. An influence on the hydroelastic response by the sea-bottom is observed in the numerical computations and the experimental measurements.
Optimization of a Semi-Submersible Type Mega-Float Using a Risk Based Objective Function
Authors: Suzuki Hideyuki , Nakada Satoshi
Published: November 2008

Design requirements for a Semi-submersible Type Mega-float are safety and functionality, and it has been shown that solutions which satisfy the requirements exist. In this paper, in order to find the optimal configuration of a semi-submersible type mega-float, an efficient optimization procedure and an objective function based on concept of risk were proposed. This function unifies the structural weight and the requirements of safety and functionality such as motion and elastic response. To reduce heavy computational load, a simplified analysis model with sufficient precision and short computational time was developed and used for the optimization. The simplified analysis model was developed based on the theory of plate. Using this modeling and the objective function, the structure was optimized and more efficient configuration of a semi-submersible type mega-float was obtained.
Investigation Into Float-Over Installations of Minimal Platforms by Hydrodynamic Model Testing
Authors: Xia J. , Hayne S. , Macfarlane G. , Field D. , Drobyshevski Y.
Published: November 2008

The idea of using float-over installations for minimal facilities platforms was shown to offer significant advantages, especially when coupled with a substructure installed by a jack-up rig. Recently, float-over installations of minimal facilities have been conducted by the cantilevered method by ICON Engineering Pty Ltd (ICON). The operation involves the platform topsides being loaded and transported to site on a barge, skidded over the barge bow, and lowered onto the jacket. The paper presents results of a research project undertaken by the Australian Maritime College (AMC) in conjunction with ICON, with the objective to investigate motions of a barge and loads exerted on the jacket when the two are docked together for a smooth load transfer operation. The model of an installation barge has been tested in the AMC wave basin and response amplitude operators of the barge motions have been determined for both the free floating and docked conditions. A range of wave periods and heights has been investigated. Model test results have been used to verify numerical predictions used in the design, and to get insight into uncertainties, which may otherwise be difficult to assess using standard software.
A Simple Numerical Method for Evaluation of Water Impact Loads on Decks of Large-Volume Offshore Platforms
Authors: Baarholm Rolf
Published: November 2008

A simple method for solving water impact loads underneath decks of offshore structures is developed. In the present paper the emphasis is on the vertical loads, but in principle the suggested method can also be applied to horizontal loading. The suggested method is three-dimensional and valid for general deck geometries and arbitrary incoming wave direction. First and second order wave amplification due to the large-volume structure is included in the analysis. An important feature of the present approach is that added mass of the instantaneous wetted deck area is approximated by the added mass of thin rectangular or elliptical plates. A numerical tool for solving the impact loads is implemented. This tool uses the results from an a priori second order diffraction analysis of the platform hull. In particular the wave-in-deck simulation program applies linear and quadratic transfer functions from the diffraction analysis as input. Since pre-computed hydrodynamic quantities are used in the simulations, very fast computations can be performed. The method is validated against experiments. Results from scaled model tests of the Statfjord A gravity-based structure (GBS) have been compared to numerical results. The comparisons are limited to regular waves. Satisfactory results are obtained from the numerical simulations. The theoretical results compare well with the experiments for the most severe cases. The vertical loads on the deck are well reproduced both during the water entry phase and the water exit phase. Moreover, the duration of the wave-in-deck event is satisfactorily predicted.
Experimental Investigation of Dual Riser Interaction
Authors: Baarholm Rolf , Kristiansen Trygve , Lie Halvor , Herfjord Kjell
Published: November 2008

Hydrodynamic interaction and clashing of two long flexible cylinders in uniform steady current have been studied. Model tests have been performed in the towing tank at Marintek in Trondheim. The riser models were free to move in vortex induced vibrations (VIV) and wake induced vibrations (WIO). The main objectives of the experimental campaign were to acquire high quality data that can be used to enhance the understanding of the mechanisms that drives riser clashing and to provide benchmark data for riser clashing code validation. Model tests were performed both for straked and naked risers, and for risers with and without bumper elements attached. Riser spacing, inflow angle, riser pretension and current velocity were systematically varied. The analysis of the recorded data has emphasized on assessing the spatial distribution of clashing, the relative impact velocities, WIO and VIV.
On the Numerical Accuracy of Wave Induced Structural Stresses of VLFs for Various Hydroelastic Analysis Methods
Authors: Hong S. Y. , Kyoung J. H. , Kim B. W. , Cho S. K.
Published: November 2008

Importance of hydroelastic analysis in design of VLFS is well recognized since considering deformation of the structures is very important for such a huge structure. The ultimate goal of hydroelastic analysis is to insure structural integrity as well as operational effectiveness, so it is necessary to predict wave loads and induced structural stresses accurately. In the present paper, accuracy of hydroelastic analysis up to shear stress is investigated by comparing various hydroelastic analysis models.
Wave Run-Up and Second-Order Wave Forces on a Truncated Circular Cylinder Due to Monochromatic Waves
Authors: Mavrakos Spyridon A. , Chatjigeorgiou Ioannis K. , Lentziou Dimitra M.
Published: November 2008

The second-order diffraction potential around a truncated cylinder is considered. The solution method is based on a semi-analytical formulation for the double frequency diffraction potential. The later is properly decomposed into three components in order to satisfy all boundary conditions involved in the problem. The solution process results in a Sturm-Liouville problem for the ring-shaped outer fluid region, which is defined by the geometry of the structure. The matching of the potentials along the boundaries of neighborhood fluid regions is established with the aid of the ‘free’ wave component. The calculation of integral of the pressure distribution on the free surface is carried out using an appropriate Gauss-Legendre numerical technique. The efficiency of the method described in the present is validated through comparative numerical results.
Passive Disconnection of an SPM-Moored LNG Carrier in Waves
Authors: Naciri Mamoun , Maurel Walter , Que´au Jean-Pierre
Published: November 2008

The Soft Yoke Mooring and Offloading system (SYMO®) has been developed in SBM to allow the tandem mooring of an LNG carrier to the stern of an LNG FPSO or a Floating, Storage & Regasification Unit in harsh environments. The SYMO® system consists of two mooring legs supported by a crane. A yoke structure is suspended at the bottom of the two mooring legs by uni-joints. The tip of the yoke is connected to the bow of the LNG carrier via roll, pitch and yaw articulations. When connected the yoke structure is horizontal. Upon disconnection, the yoke settles at an equilibrium position characterized by a pitch angle of 35° to 40° with respect to the horizontal. Owing to the low friction articulations, the yoke oscillations decay very slowly and the yoke may come too close to the LNG carrier bow. A passive system has been developed to improve the SYMO® dynamics at disconnection whereby a small proportion of the overall yoke weight is replaced by water. This water is allowed to move in a suitably designed tank network thus shifting around the overall centre of gravity and yoke equilibrium angle as pitch oscillations take place. The above principle has first been investigated using a kinematics program before being model tested at a large scale of 1:16. A large matrix of tests has been performed to investigate the effect of the water ballast volume and the layout of the tank network. Once the principle was confirmed experimentally, CFD computations were performed in a blind fashion and compared to the experiments.
A Numerical Investigation Into the Value of Added Mass Coefficient for Circular Cylinders
Authors: Karadeniz H.
Published: November 2008

This paper presents a general axi-symmetrical solid element to be used mainly for the calculation of added masses of water surrounding members of offshore structures, and in general, for multi-purposes such as analyses of shells of revolution, circular beams and plates, axi-symmetrical structures and soils, plane stress/strain problems. Since one element type is used for modeling of different media such as structures, soil and water, the element is very suitable to solve interaction problems. The element is derived parametrically so that changing values of parameters can generate flexible geometrical shapes in exact forms. In the element formulation, a constant shear locking is used to solve bending problems of beam like structures. A similar fluid element is also formulated to analyze fluid-structure interactions and to determine added masses of co-vibrating water. The added mass is calculated from hydrodynamic pressures, which are produced by fluid-structure interactions. In the paper, a special solution algorithm is presented for the coupled eigenvalue problem of the interaction. An analytic calculation of the added mass is also presented for members along which a constant variation of hydrodynamic pressure occurs. A couple of examples are provided to demonstrate applications of the elements explained. Added mass coefficients of offshore structural members (tubular members) are investigated for practical uses.
LNG Floating Regasification Unit (FRU) Side-by-Side Mooring Analysis
Authors: Ye Wei , Luo Yong , Pollack Jack
Published: November 2008

This paper presents a newly developed Floating Regasification Unit (FRU) concept for LNG import in the US Golf of Mexico (GOM) region. The FRU can be converted from a Suezmax tanker and has a turret mooring system. One of the key technologies of the FRU concept is the Side-By-Side (SBS) mooring between the FRU and the LNG Carrier (LNGC) for offloading. The mooring lines and pneumatic fenders between the two vessels should be able to restrain the relative motions to ensure the safe transfer of LNG. Advanced hydrodynamics modeling techniques have been applied, which include full hydrodynamic interactions between the FRU and the LNGC with full QTFs considering the shallow water effect. The anchor legs are modeled as dynamically, fully coupled to the turret and the FRU. The feasibility of the FRU concept is established for LNG import in the GOM, with a variety of workable water depths ranging from 40 meters to more than 100 meters with an uptime exceeding 98%. Analysis results demonstrate the significance of hydrodynamic interactions between the two vessels in close proximity arrangement.