bluuebunny/crossref_metadata_2025 huggingface dataset:
Maintaining Technical Integrity of Petroleum Flowlines on Offshore Installations: A Decision Support System for Inspection Planning
Authors: Ratnayake R. M. Chandima , Markeset Tore
Published: January 2011

Oil and Gas (O&G) platforms in the North Sea are facing aging problems as many of the installations have matured and are approaching their design lifetime. Flowlines are used to transport oil and gas well stream from the wellhead to the production manifold. They are categorised as one of the most critical components on a production facility. Flowline degradation takes place due to corrosion and erosion. The deterioration of a flowline may increase the risk of leakages, ruptures, etc., which shall lead to serious HSE (health, safety and environmental) and financial consequences. Any such risks have a direct impact on the O&G installation’s technical integrity as well as the operator’s sustainability concerns. Conventionally, pipelines are designed with safety provisions to provide a theoretical minimum failure rate over the life span. Furthermore, to reduce the risk of failure various techniques are routinely used to monitor the status of pipelines during the operation phase. The existing methods of flowline health monitoring planning requires one to take into consideration the operator’s plant strategy, flowline degradation mechanisms, historical data, etc. A technical condition report is made based on findings’ reports and degradation trends. This report recommends the inspection of a number of points on the flowlines in a certain year using non-destructive evaluation methods such as visual inspection, ultrasonic testing, radiographic testing, etc. Based on the technical condition report, in general for a certain preventive maintenance shutdown, 10 to 15 flowline inspection openings are accommodated as finance, time and resource availability are taken into consideration. However, it is customary to plan to open more locations in a certain inspection package than can be inspected and minimization of such points is at present done on an ad hoc basis. This paper suggests a formal model and a framework to formally minimize the number of visual inspections by executing the plant strategy as well as HSE concerns. The model is derived using analytic hierarchy process (AHP) framework, which is a multi-criteria decision-making approach. The model is developed based on literature, industrial practice, experience as well as real inspection data from a mature offshore O&G installation located on the Norwegian Continental Shelf.
Static and Dynamic Ice Actions in the Light of New Design Codes
Authors: Bjerka˚s Morten , Albrektsen Arne , Gu¨rtner Arne
Published: January 2011

A case study on the lighthouse Norstro¨msgrund in the Gulf of Bothnia has been performed. Design ice load for the lighthouse is compared to existing code recommendations. It was found that the lighthouse was designed for a load level 110% higher than what is proposed by the recently issued ISO/DIS 19906 design code. By the fact that the structure has got damages by ice action, it is concluded that separate dynamic analyses should be performed instead of simply adding amplification factors to the static loads. The present work shows ones again that a sawtooth like time series gives lower responses in the structure than harmonic functions when both are applied at the fundamental frequency.
Sensitivity Study of Critical Parameters Influencing the Uncertainty of Fatigue Damage in Steel Catenary Risers
Authors: Li Feng Zi , Low Ying Min
Published: January 2011

The most challenging aspect of a deepwater development is the riser system, and a cost-effective choice is the Steel Catenary Riser (SCR). Fatigue is often a governing design consideration, and it is usually most critical at the touchdown point (TDP) where static and dynamic bending stresses are highest. Unfortunately, it is also at this region that uncertainty is the maximum. The increased uncertainty casts doubt on the applicability of generic safety factors recommended by design codes, and the most consistent way of ensuring the structural safety of the SCR is to employ a reliability-based approach, which has so far not received attention in SCR design. As the number of basic random variables affects the complexity of a reliability analysis, these variables should be selected with caution. To this end, the aim of this paper is to draw up a comprehensive list of design parameters that may contribute meaningfully to the uncertainty of the fatigue damage. From this list, several parameters are selected for sensitivity studies using the commercial package Orcaflex. It is found that variations in seabed parameters such as soil stiffness, soil suction and seabed trench can have a pronounced influence on the uncertainty of the fatigue damage at the touchdown point.
Probabilistic Assessment of the Clashing Between Flexible Marine Risers
Authors: He Jian Wen , Low Ying Min
Published: January 2011

Flexible marine risers are compliant to external forces from waves, current and platform motions, and clashing between risers is an important concern. In deepwater developments where the number of connected risers is large, it is not economical to space them too far apart. In this regard, it is necessary to establish the probability of riser clashing throughout the service life; however, at present there appears to be no systematic procedure for assessing this risk. This paper presents a novel procedure for estimating the probability of riser clashing based on post-processing results obtained from time domain simulations of flexible risers subjected to random wave loads. First, an efficient technique is employed to sieve out critical pairs among riser elements. From these element pairs, the time history of a normalized clearance parameter is derived from the nodal displacements of the elements. Subsequently, the mean up-crossing rate of this parameter is extracted and extrapolated to the threshold of clashing using extreme value theory. As this method is still in its early developmental stage, critical effects such as vortex-induced vibrations and wake interference will not be considered in the present work.
The Fatigue Crack Growth Under Compressive to Compressive Fluctuating Loading
Authors: Huang Xiaoping , Wang Anqing , Cui Weicheng , Bian Rugang
Published: January 2011

There are some components subjected to compressive and bending loading in ship and offshore structures and fatigue cracks were fond in compressive side of these components caused by fluctuation loadings, during their service. For better understanding the fatigue behavior of these components subjected to compressive to compressive loading, plate specimens with center crack (CCP) and plate specimens with double edge crack (DECP) have been designed for the experiment for examining the fatigue crack growth under axial compressive fluctuation loading. In this paper, a high strength steel plate was used as the test material. Fatigue test has been performed using MTS810 material testing system. Experimental results show that cracks can be propagated under compressive to compressive loading. It also shows that the cracks propagated to a certain length and then arrested completely. The experimental procedure and the phenomena are described. The stress-strain and the residual stress during a cycle were simulated by FEA. The stress intensity factor of the crack by residual stress and its propagation life were estimated and compared with the test data. The residual stress plays a very important role in crack growth under compression to compression fluctuation load.
General Recommendations From the Results of Reassessment of 21 Platforms in Bay of Campeche
Authors: Chakrabarti Partha , de la O. Juan de Dios
Published: January 2011

Pemex Explorac´ion y Produccio´n (Pemex) owns and operates several fields for oil and gas exploration in the Bay of Campeche located in the south Gulf of Mexico. In order to meet the growing demand for oil and natural gas it was necessary to extend the service life for many existing platforms by at least another 15 to 30 years. To ensure a safe operation throughout this period, thorough and systematic reassessment studies needed to be conducted leading to the identification of any structural weakness. Finally, to control the fatigue behavior of the welded joints, risk based inspection planning (RBI) was adopted to ensure extended service life. In these reassessment studies the ultimate strength of the platforms is evaluated through nonlinear pushover analyses as a part of condition assessment. Spectral fatigue analyses are performed to identify the fatigue sensitive joints. This is followed by redundancy analyses, assuming that one individual member at a time becomes ineffective given a weld fatigue failure at the joint. For the inspections aimed to control the development of predictable degradation such as fatigue crack growth, the inspection efforts can be targeted such that the risks implied by the degradation are kept within acceptable limits. This is done through a risk based inspection planning strategy. The analytical aspects for this approach were discussed in previous papers on the subject by the authors. The current paper presents the overall results of 21 platforms taken up for a recent study and discusses the trends in view of broad parameters such as water depth, loading, structural arrangement. These structures include drilling, production, gathering and living quarter platforms. The platforms are located in various assets in water depths ranging from 40 to 90m, have different configurations with 3, 4 and 8 legged jackets, they also support different deck weights. In the present paper overall results of the study performed for 21 platforms are presented. The platforms have been classified in terms of platform type, number of legs, framing pattern, leg diameter etc. The results for strength of the platforms obtained from pushover analyses, and fatigue life are analyzed in light of the classification parameters. The differences in the platform characteristics such as stiffness, wave loading and natural period are discussed along with their implications to strength and fatigue life. Inspection requirements are also interpreted in the light of these global parameters. Finally, some general recommendations are made for design of jackets keeping in view the overall behavior and inspection requirements. It is believed that if the recommendations are followed in the initial design there would be benefits in the future for inspection, maintenance, and repair and possible life extension increasing their economic return.
On the Use of Mode Shapes in the Identification of Structural Damage
Authors: Elshafey Ahmed , Haddara Mahmoud , Marzouk Hesham
Published: January 2011

The random decrement technique is an averaging technique that can be used to extract the free decay response of a structure from its stationary random vibratory response. The free decay response can then be used to identify the vibratory characteristics of the structure. The main advantage of the technique is that the identification of the parameters of the structure is achieved without previous knowledge of the excitation forces. This paper extends the random decrement technique to obtain the mode shapes of the structure using the concept of a multichannel random decrement technique (MCRD). This technique is based on extracting simultaneous random decrement records from measurements made at several points on the structure. The change in mode shapes as a result of occurrence of damage to the structure is then used to detect the presence and location of damage. The method is illustrated and validated using two case studies and finite element modeling. Excellent agreement between mode shapes obtained using the MCRD and those obtained from classical modal analysis techniques was found. The use of changes in the mode shapes of the structure to detect the presence and location of damage was successful.
Enlarging the Cargo Hold of a Multi Purpose Vessel by Structural Reinforcement Complying With the SOLAS Regulations
Authors: Uhlenbrock Santiago , Zhang Leshan
Published: January 2011

The strict regulations of the actual SOLAS regarding damage stability may sometimes interfere with the design wishes of the ship owners. A reason may be that the approach stated in the SOLAS regulation is merely a probabilistic method. In this study the application of an alternative approval procedure to the pure probabilistic SOLAS damage stability calculations is presented. The procedure differs from probabilistic SOLAS regulations in the form that it considers the structural strength characteristics of the vessel design within damage stability assessment. A multi purpose vessel (MPV) with one large cargo hold is analyzed. A reference design complying with SOLAS regulations with a double hull width of 2.2m is optimized based on the alternative approval procedure and it is shown that the optimized design with ice class reinforcement and a double hull width of 1.5m has an equivalent level of safety. Thus, the double hull width could be reduced by 40% and the cargo hold breadth could be enlarged by 10%. This latter fact may be of particular interest for ship owners and designers as the flexibility of utilization of the vessel could lead to an improved cost benefit.
A Numerical Investigation of the Response of an Elastically Mounted Rigid Cylinder With Two Degrees of Freedom
Authors: Ferreira Bruno C. , Vitola Marcelo A. , Wanderley Juan B. V. , Sphaier Sergio H. , Levi Carlos A.
Published: January 2011

The vortex induced vibration (VIV) on a circular cylinder is investigated by the numerical solution of the Reynolds average Navier-Stokes equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates and the k–ε turbulence model is used to simulate the turbulent flow in the wake of the body. The cylinder is supported by a spring and a damper and free to vibrate in the transverse and in-line directions. In previous work, numerical results for the amplitude of oscillation, vortex shedding frequency, and phase angle between lift and displacement were compared to experimental data obtained from Khalak and Williamson (1996) to validate the code for VIV simulations in the transverse direction. In the present work, results are obtained for phase angle, amplitude, frequency, and lift coefficient and compared to experimental data from Jauvtis and Williamson (2003) for an elastically mounted rigid cylinder with two degrees of freedom. Differences in the amplitude of oscillation between experimental and numerical data were observed for both direction. It seems that the fluid flow memory effect is an important aspect that should be taken in consideration on numerical simulation to reproduce the experimental results for VIV with 2DOF as pointed out by Moe and Wu [1].
Forced Oscillation of a Circular Cylinder
Authors: Camargo Bruno G. , Vitola Marcelo A. , Wanderley Juan B. V. , Sphaier Sergio H. , Levi Carlos A.
Published: January 2011

Circular structures are frequently found in offshore industrial application, such as risers, umbilicals, spars, and TLP platforms. Theses structures are frequently subjected to vortex induced vibration. Sometimes, they are also subjected to forced vibration. In the present paper, the forced vibration of a circular cylinder is investigated by the numerical solution of the Reynolds Average Navier-Stokes (RANS) equations. An upwind and Total Variation Diminishing (TVD) conservative scheme is used to solve the governing equations written in curvilinear coordinates. The k–ε turbulence model is used to simulate the turbulent flow in the wake of the body, when necessary. The cylinder is forced to oscillate only in the transverse direction of the mean flow with low Reynolds number and low amplitude ratio. The numerical results of the lift and drag coefficients were compared with numerical data obtained from Benevenutti and Silvestrini [1] and Meneghini and Bearman [2] to validate the code for forced vibration. The numerical results indicate that the implemented code is able to reproduce the experimental data capturing quite well the lock-in boundary, and results of practical interest are obtained, such as mean drag, RMS lift and lock-in range and.
Damping Coefficient Analyses for Floating Offshore Structures
Authors: Malta Edgard B. , Gonc¸alves Rodolfo T. , Matsumoto Fabio T. , Pereira Felipe R. , Fujarra Andre´ L. C. , Nishimoto Kazuo
Published: January 2011

The damping evaluation of floating offshore systems is based on the viscous effects that are not considered in numerical models using the potential theory. Usually, different techniques for different systems are used to evaluate these hydrodynamic coefficients. The total damping is separated by potential and viscous damping, the first one is evaluated numerically and the second through experiments at reduced scale model. Common techniques considering linear motion equations cannot be applied to all degrees of freedom. Some methods were compared for results of decay test, such as: exponential and quadratic fit. Fourier transform (FT) spectral analysis and Hilbert Huang transform (HHT) can be used to evaluate the signal natural frequency and with HHT this can be done during the time domain. Also, analysis through the Random Decrement Technique (RDT) is presented to demonstrate the damping evaluation for irregular waves. The method to obtain external damping was presented for the different techniques in an ITTC semi-submersible model. The linear method is not sufficient to predict the damping coefficient for all the cases, because in most of them, the viscous damping was better represented by a quadratic fit. The HHT showed to be a good alternative to evaluate damping in non-linear systems.
On the Mechanics of Pipewalking: Case of a Buried Pipeline
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Adelaja Adekunle O.
Published: January 2011

The influence of soil sedimentation on the pipe walking phenomenon is investigated analytically via a set of coupled nonlinear partial differential equations where the effects of operating variables such as internal fluid temperature variation, prestress and internal pressurization, Coriolis and axial accelerations of the internal fluid and cross sectional area change are fully captured. For this problem, a segment of an offshore pipeline resting on the ocean floor is idealized as elastic beam on an elastic foundation using recently refined Euler-Bernoulli beam theory. By invoking integral transforms, closed form analytical expressions for displacement of the fluid-pipe-soil interaction system associated with pipe walking is computed. Simulated results showed that pipe walking phenomenon is strongly dependent on sedimentation level, friction at the interface of pipe-ocean sub soil layer, temperature variation, fluctuations in internal fluid pressurisation and oscillatory strain of the pipe in both transverse and longitudinal modes.
Properties of a Novel Local Scour Protective Equipment Around Pile of Marine Bridge Under Wave Action
Authors: Li Qiang , Liu Chunhua , Sun Zhongjian , Dong Haiming , Qiu Jianying
Published: January 2011

Piles are widely used in practice to support marine bridge structures. However, scour around piles may reduce the stability of bridge structures. In the present paper, novel protective equipment is developed to reduce local scour around bridge piles under coastal environment. The equipment is composed by a collar on the top and a protective tube with rows and columns circle holes on the surface of tube. Series of wave flume model tests are performed on single pile to study the properties of the new equipment based on the principal of similarity. Wave flume experiments are carried out in a wave flume with a test section of 1.4 m wide, 1.0 m deep and 17.3 m long and a 4.8m long and 0.50m deep sand bed section is installed in the middle of the wave flume. The test system is comprised with wave monitors and an endoscope detector for scour depth. Regular waves are generated by the wave maker in wave flume. Properties of local scour around pile with or without the protective equipment are compared by means of experimental method. As a result, the maximum erosion depth around the pile is in direct proportion to the wave height, wave length, and pile diameter, but in inverse proportion to water depth and collar diameter. It is concluded that the protective equipment present here can reduce the depth of local scour around the pile effectively on basis of the experimental results. A moderate height of protective device is benefit for reduction of scour.
Use of Weight Elements to Improve the Dynamic Performance of Umbilicals
Authors: Rustad Anne Marthine , So̸dahl Nils , Kalleklev Arve Johan , Ottesen Torfinn , Nordal Rune , Wang Jan Butler , Aarum Truls
Published: January 2011

The development strategy in the North Sea has over the last years been towards tie in of smaller fields to existing infrastructure. Detailed engineering is required to obtain an optimal design for each application. This can be challenging for systems with multiple design constraints e.g. interference with adjacent structures combined with strict floater interface design requirements. Flexible risers and umbilicals are usually arranged in compliant configurations, where floater motions are absorbed by large changes of the configuration geometry in the 3D space. A vital design issue for such systems is to avoid overbending and fulfill fatigue life design criteria at floater supports. Another design challenge often encountered in design of such systems is to avoid/limit compressive effective tension in extreme load cases. In this paper it is proposed to introduce weight elements along parts of the riser/umbilical to improve the overall dynamic behavior and thereby address these design challenges. This principle was applied when designing the configuration for Morvin DEH riser. Morvin DEH riser is connected to A˚sgard B semi-submersible platform in the North Sea at 300m water depth. For this particular problem the design challenge was to limit the angle response in extreme load cases and fulfill fatigue design requirements in the bellmouth interface. Another constraint was at the same time to avoid interference between adjacent mooring lines and umbilicals. A feasible solution was found by introducing weight elements in the upper part of the umbilical. This had a minor impact on the cost schedule of the project. The Morvin DEH riser was installed successfully in the summer of 2009.
Predicting Loads on a LNG Carrier With CFD
Authors: Fathi Fahd , Klaij Christiaan , Koop Arjen
Published: January 2011

The Current Affairs Joint Industry Project was initiated to develop the understanding and tools for the assessment of current loads on offshore structures. CFD is one of these tools requiring a good understanding of the underlying physical and mathematical models. In order to assess its suitability for the prediction of current loads on monohulls, the flow around a LNG carrier for which model scale data is available was considered. The LNG carrier, including bilge–keels and rudder, was towed at scale 1/50 in Marin’s shallow water basin during the HAWAI JIP, for flow angles between 0 and 180 degrees. The measurements were shared with the Current Affairs JIP, for which the participants were invited to perform CFD computations reproducing the model test results. A number of these simulations are presented in this paper. The analysis of the results includes discussion on the grid generation as well as the numerical and physical parameters of the simulation. The comparison between experiments and computations shows that CFD can provide good qualitative predictions for the variation of force coefficients with inflow angle. The origin of the result variability between the participants is discussed and attention is drawn to the different factors influencing the quality of the simulation.
Effects of Soil Non-Linearity on the Dynamic Behavior and Fatigue Life of Pipeline Spans Subjected to Slug Flow
Authors: Casanova Euro , Blanco Armando
Published: January 2011

Offshore production fields require long submarine pipelines for transporting production fluids that are inherently multiphase. This condition and hydraulic sizing of pipelines lead often to the development of slug flow patterns in which condensate slugs traveling in the pipeline, act as moving gravity loads for the piping structure, therefore producing a dynamic response especially important for the free spans. Recently some authors have shown that this phenomenon may produce a cyclic damage that could reduce in a significant way the fatigue life of the pipelines, thus constituting a governing mechanism in their design. On the other hand, pipe-soil interaction has also been identified as an important factor in pipeline design and fatigue life; in particular it is important for determination of the static equilibrium configurations and the vibration response of free spanning pipelines. In this work a previously presented numerical model which combines fluid equations for predicting slug characteristics and a structural finite element model for the pipelines transporting slugs, is improved by introducing non linear characteristics of seabed supports. Different seabed supports (linear, perfectly plastic, and non linear with tension cut-off) and different properties of soil-pipe interaction (stiffness, damping and length of soil-pipe interaction) are considered, and their effects on vibration response and fatigue life are compared. Results show that soil pipe interaction is an important parameter in vibration response and fatigue life for pipeline spans subjected to slug flow.
A Conceptual Overtopping Wave Energy Convertor Suitable for Small Waves
Authors: Imamura John T. , Mansour Alaa
Published: January 2011

This paper proposes a design concept in the area of overtopping ocean wave energy devices. Current models of overtopping devices are limited to locations which experience large wave activity. The high energy associated with large waves enables the ocean water waves to overtop the device ramp into the collection reservoir which discharges through a power generating turbine. The ramp height is necessarily large to establish a sufficient collection reservoir head. The proposed design concept can utilize small waves by implementing a gearing system which can transfer water to the collection reservoir. This allows for greater access to the wave energy resource at more locations than currently possible. A simplified model of this design concept is presented and applied to varying wave conditions off the coast of California.
Super Duplex/Duplex Stainless Steel Umbilical Tube Resistance to HISC
Authors: An X. , Dobson A. , Probyn I. , Fellow P.
Published: January 2011

Super duplex/duplex stainless steel is susceptible to Hydrogen Induced Stress Cracking (HISC) whilst under the influence of Cathodic Protection (CP) systems. Field failure experiences have been reported on super duplex stainless steel components in subsea applications. However, HISC is a non ductile mode of failure caused by combinations of particular conditions associated with hydrogen charging, metallurgical factors of the alloy, stress/strain level and service conditions. DNV RP F112 [4] has been introduced recently and is a guideline for the design of duplex stainless steel components for offshore applications operating under CP systems. Super duplex/duplex stainless steel tubes have been used as components in DUCO umbilical systems for more than 15 years without any failure feedback. A combination of controlling the material microstructure, welding operation design, component stress design, and surface condition design have contributed to this record. This paper describes the design methodology applied by DUCO for the super duplex/duplex umbilical tubes for optimum mitigation against HISC. The influences of the microstructure, stress/strain condition, surface condition and cathodic potential on the seamless super duplex stainless steel (UNS 32750) umbilical tubes resistance to HISC are discussed. Results of laboratory tests using Slow Strain Rate Testing (SSRT), stepwise uni-axial and constant load methods, with reference to offshore oil field application best practice, are presented.
Seasonal Downtime Analysis of DP and Non-DP Offloading Operation in Brazilian Waters
Authors: Tannuri Eduardo A. , Pesce Celso P. , de Azevedo Paulo Cesar , Fucatu Carlos H. , Simos Alexandre N.
Published: January 2011

Oil offloading from Spread Mooring System (SMS) FPSO is usually done by means of a shuttle tanker (ST) in tandem configuration. The ST receives the oil pumped by the FPSO from a bow or stern offloading station, and the operation may take up to 3 days. In order to minimize the risks associated with the operation, the shuttle tanker (ST) should be kept within a safety zone with respect to the FPSO, which is usually given as a minimum distance between the two ships and an aperture angle from the FPSO centerline. In order to guarantee the tanker position during the whole operation, the operation is usually assisted by tug boats or performed with tankers provided with DP (dynamic positioning) systems. Since SMS FPSOs may be not aligned to the environmental forces, keeping the shuttle tanker in position may be a hard task either for the DP system or for the tug boats, depending on the environmental conditions. There are non-rare situations in which the ST must be disconnected and the operation interrupted. The present paper presents a methodology based on fully-nonlinear dynamic simulations for evaluating the downtime of such offloading operations, considering both DP and conventional non-DP tankers, in the later case assisted by a tugboat. Typical Brazilian waters environmental conditions (current, wind and waves) are considered for each seasonal period of the year. The main objective is to provide a quantitative comparison between both cases in each season. The results may also be used for strategic definition concerning logistics of oil production. The procedure is based on exhaustive dynamic simulations, and a statistical analysis of the oceanographic data was used to generate a representative set of environmental conditions together with the corresponding probability of occurrence for each season. A full time-domain dynamic simulation is then carried out for each case, considering detailed models for the dynamics of each floating structure, mooring lines and DP system. The vessel excursion, hawser tension and other operational parameters are then evaluated for each case, and the occurrence of unsafe conditions may be properly evaluated. A statistical procedure is finally applied to compute the associated downtime. Illustrative results for two different classes of ST (Aframax and Suezmax) are presented and discussed, and the advantages of employing DP assisted vessels become clear.
Parametric Comfort Analysis of a Standard Swath Vessel
Authors: Prata Vieira Daniel , Matsumoto Fabio Tadao , Malta Edgard Borges , Nishimoto Kazuo , Vilamea Eduardo Marc¸al
Published: January 2011

A parametric analysis which investigates the effects of the hull main dimensions on the seakeeping comfort was proposed to improve a standard SWATH vessel. This study was numerically carried out involving some comfort parameters and worldwide sea conditions. Some types of SWATH and their non-dimensional ratios were considered. The main dimensions of a standard SWATH vessel are: length (L), beam (B), pontoons radius (R), draft (T) and strut thickness (t). Some secondary dimensions were assumed so that a parametric model of wet surface could be designed using MULTISURF, which later was used on WAMIT to evaluate the hydrodynamics coefficients. The TPN receives these coefficients as a basic tool to provide the dynamic response of each SWATH case. The parametric comfort analysis was performed using three usual methodologies applied to evaluate the ship behavior: The ISO2631/3 Severe Discomfort, the MSI (Motion Sickness Incidence) and the VI (Vomiting Incidence).
Cylinder Bore Wear Damage Analysis of a Heaving-Buoy Wave Energy Converter With Hydraulic Power Take-Off
Authors: Yang Limin , Moan Torgeir
Published: January 2011

Wave energy is a non-polluting and renewable source of energy. Among several wave energy converters (WEC), an oscillating body with a hydraulic power take-off (PTO) is commonly used for energy conversion. For such a hydraulic system, the piston ring and cylinder play very important roles in achieving desired energy converting performance and durability. Among the failure modes of the ring-bore components, wear is a prevailing one. Compared with the ring wear, cylinder wear is more important to the manufacturer and user, because cylinders are more expensive to replace than the rings. Since the floating body is exposed to irregular incident waves, the dynamic response of the PTO is also random. The position of maximum accumulated wear damage along the cylinder bore cannot be as easily determined as the engine bores where the maximum wear occurs near the Top Dead Centre (TDC). It is controlled by the characteristic dynamics of the system together with the lubrication of the interface which can be modelled by the well-known Stribeck curve. The purpose of this paper is to establish and apply a method for estimating the wear damage along the cylinder bore. The dynamic response of the WEC system is based on the nonlinear mathematical model established by Yang et al [1]. A particular issue in this research is to calculate the dimensionless film thickness λ (the ratio between the oil film thickness h and the composite surface roughness σ) in the lubricated contacts and then determine the lubrication regime according to the Stribeck curve. Combining the wear coefficient which is related to the lubrication regime and the contact pressure, the bore wear damage along the cylinder wall is predicted. In this paper, the bore wear damage is estimated on the basis of time domain simulations. The results show that the bore wear distribution is affected by two main factors: sea state condition and the nonlinearity of the PTO system. The position of the bore where the maximum accumulated wear occurs is predicted. Finally, the relative contribution of wear damage from different sea states is obtained.
Utilization of Adaptive Management Technique for Restoration of Large-Scale Tidal Flat in Tokyo Bay
Authors: Ohmura Tetsuo , Arai Yoichi , Kondo Takeo , Hosokawa Yasushi
Published: January 2011

This paper proposes that the pilot field be created to apply the Adaptive Management Technique in order to promote the policy of large-scale restoration of the tidal flat/shallow sea. It will be a case study in Tokyo Bay, a major enclosed urban sea in Japan. The motif and background of the study are stated in the beginning. Creation of the symbiotic structure with marine life, of which the artificial tidal flat is a representative example, is more and more in need as a new direction of port environmental policymaking. This paper discusses that the creation of large-scale tidal flat will be especially effective in Tokyo Bay, a highly reclaimed and enclosed sea and that an innovative technical approach is necessary in view of the long-term efforts. First, an artificial tidal flat built in the past, Itsukaichi Area Artificial Tidal Flat in Hiroshima Prefecture, was analyzed to identify its technical problems. Based on what occurred in this case, the need for a new technical approach to practice the Adaptive Management Technique is discussed. Secondly, Tokyo Bay is taken up as a case study. With the ultimate goal of restoring the tidal flat/shallow sea on a large-scale, it is proposed that small pilot fields be created in the Bay and that the Adaptive Management Technique be applied. Technical and social problems will be addressed step by step in the pilot field, which will be gradually expanded. They are open experimental fields, where systematic observation will be conducted. Technically appropriate structure of the tidal flat will be assessed. The pilot field will also be a forum where consent and support of those concerned including citizens and non-specialists is sought. Furthermore, “Shiosai no Nagisa,” an artificial tidal flat with a reinforced seawall in Port of Yokohama is examined from the viewpoint of the Adaptive Management Technique. It was built by Kanto Regional Bureau of Ministry of Land, Infrastructure, Transport & Tourism in 2008.
Reinforced Design of an Unbonded Flexible Flowline for Shallow Water
Authors: Lu Qing-zhen , Yue Qian-jin , Tang Ming-gang , Zheng Jie-xin , Yan Jun
Published: January 2011

Flexible pipeline has been widely used in offshore engineering. Comparing to steel pipe, flexible subsea pipeline has some merits such as anti-corrosive, easy laying and recycling. So it is suitable to be used as flowline in shallow water. Especially there are lots of marginal oil fields in shallow water of China. Different from deepwater dynamic riser, flexible pipe for shallow water applications has a low requirement of resisting external pressure. On the other hand, Flexible pipe need to satisfy the requirement of tensile property during installation. Therefore, a kind of simple and economical flexible pipe can be developed to meet the requirement of shallow water application. This paper presents an economical unbonded flexible pipeline, which is helically wound by steel wires. In order to guarantee the safety of the economical flexible pipeline under the laying, installation and working loads, a reinforced design of tensile property is necessary. A helically wounded flat-steel layer is introduced to constrain the steel wire radial deformation and strengthen the axial tensile stiffness of the pipeline. A theoretical model is established to analyze the tension behavior of the flexible pipes and some suggestions are proposed to strengthen the flexible pipe design. Additionally, tensile experiments are carried out for the original and reinforced flexible pipes, which verify the theoretical model and the effectiveness of the reinforced design. The results show that the reinforced pipeline not only meets the tensile requirement during installation for shallow-water applications, but also meets requirements of the minimum bend radius as well as hydrostatic collapse (resistance of the external pressure) with low cost.
Flow Assurance for Deepwater Mining
Authors: Parenteau Thomas
Published: January 2011

The flow assurance aspects of all subsea projects have a major contribution to the pipe design, field layout, choice of lifting equipment (subsea-pump or air lift), power requirement and system topside as well as subsea operability. In the context of deepwater mining, the main task is to estimate the pressure drop in the flowline and riser as well as the liquid-solid or gas-liquid-solid flow regime. These are needed to guarantee the production target at steady state and to guarantee the system operability in transient mode at shut-down and system start-up cycles. Current knowledge of solid transport has successfully characterized pneumatic and hydraulic transport of fine particles that are close to powders, sand, or small gravel. Semi-empirical theories based on concepts such as isolated or hindered slip velocities, mixture properties, and in-situ concentration have emerged to analytically resolve the flow behavior in vertical, horizontal, and inclined pipe. The context of deepwater mining pushes these theories beyond the existing application cases due to the significantly larger particle size combined with the riser configuration. The riser configuration includes a wave shape to accommodate vessel motions due to environmental loads and excursion requirements to follow the subsea excavation tool. This paper starts with the state-of-the art papers review on hydraulic lifting fundamentals to the need of using computational fluid dynamics (CFD) for understanding transient behavior and pressure and power prediction for the wave shaped riser. This paper further proposes coupling of CFD and the discrete element method (DEM) for improving computational efficiency and accuracy of the computational results.
Extreme Waves of Sea Storms
Authors: Fedele Francesco , Arena Felice , Tayfun M. Aziz
Published: January 2011

We present a stochastic model of sea storms for describing long-term statistics of extreme wave events. The formulation generalizes Boccotti’s equivalent triangular storm model (Boccotti 2000) by describing an actual storm history in the form of a generic power law. The latter permits the derivation of analytical solutions for the return periods of extreme wave events and associated statistical properties. Finally, we assess the relative validity of the new model and its predictions by analyzing wave measurements retrieved from two NOAA-NODC buoys in the Atlantic and Pacific Oceans.
Environment Load Model of Platform Ice-Induced Fatigue Based on Ice-Induced Vibration Form
Authors: Yang Dongping , Chen Guoming
Published: January 2011

At present, it is immature to precisely evaluate the ice-induced fatigue life of platform. One of the key problems for accurate estimation of the ice-induced fatigue life is to establish the rational ice load model. A new method of establishing the environment load model to evaluate the ice-induced fatigue life is put forward based on the two basic vibration forms that are structure resonance and non-resonance existing in the ice-induced platform. Compared with the traditional classification method for ice-induced conditions, not only the ice thickness and the ice velocity of corresponding ice zone will be thought as the important influencing factors, but also the platform natural vibration characteristics will be considered in this method. Finally, based on this method, the environment load model of ice zone No.4 in China’s Bohai Sea is established to do the simulation test of node’s fatigue stress of one platform in this sea area. The results show that the bending stress can’t be ignored in the vulnerability analysis of the dynamic response of the ice-induced platform; the relation between the natural vibration frequency and the period of the ice broken must be considered to classify the work condition in the estimation of the platform ice-induced fatigue; the result can’t be guaranteed determinately more secure when the ice-induced fatigue analysis is conducted by simple amplifying the ice thickness or the ice velocity under the condition that ignores the nature frequency of the platform.
Evaluation of Seismic Displacement of Quay Walls for the Passive Case Under Earthquake and Tsunami
Authors: Lin Yongliang , Zhang Mengxi , Li Xinxing
Published: January 2011

Prediction of the seismic rotational displacements of retaining wall under passive condition is an important aspect of design in earthquake prone region. In this paper, a rotating block method is developed to calculate the rotational displacements of quay walls based on rigid foundations under seismic loading and tsunami for the passive earth pressure condition. The proposed method considers the combined effect of the seismic forces, hydrostatic and hydrodynamic forces and tsunami force acting on the quay wall. Variations of different parameters involved in the analysis suggest sensitiveness of the rotational displacement and provides a better guideline for design.
Numerical Investigation on Bearing Capacity of a Pipeline on Clayey Soils
Authors: Zhao Bo , Gao Fu-Ping , Kang Rong-Yu
Published: January 2011

The bearing capacity of a pipeline foundation is crucial for the pipeline stability design. It is usually inappropriate to analyze the bearing capacity for the pipeline with special circular section directly by employing the theory for conventional rectangular strip footings. In this study, the ultimate loads of the pipeline on clayey soils are investigated numerically. A plane-strain finite element model is proposed to simulate the quasi-static process of the pipeline penetrating into the soil, in which the adaptive-grid technique and the ‘contact-pair’ algorithm are employed, and the Drucker-Prager constitutive model is used for modeling the soil plasticity. Based on the proposed numerical model, the development of soil plastic zone and the incremental-displacement vector field beneath the pipeline are examined numerically. It is indicated that, according to the obtained pipeline vertical load-displacement curves, concurrently referring to the plastic strain field and/or the soil incremental-displacement vector field, the shear failure type (e.g., general shear failure, punching shear failure) and the collapse loads can be thereby determined. The present numerical results match well with the analytical solutions of slip-line theory in plasticity mechanics.
Numerical Evaluation of Wind Loads on Semi-Submersible Platform by CFD
Authors: Zhang Shen , Wang Lei , Yang Shi-Zhi , Yang Huan
Published: January 2011

A numerical study of wind loads on a semisubmersible platform is presented on this paper. The techniques of Computational Fluid Dynamics (CFD), such as Reynolds Averaged Navier-Stokes Equations (RANS) model and Large Eddy Simulation (LES), etc., were adopted in this study to predict wind loads on and wind flows around the platform. The main objective of this study is to explore an effective and reliable approach for evaluation of wind loads on offshore structures by CFD methods. The computed results were compared with experimental data which obtained at wind tunnel test. It was found through the comparison that the LES with a dynamic sub grid-scale (SGS) model can give satisfactory predictions for mean and dynamic wind loads on the tall structures. Therefore, it is necessary to correctly simulate both the incident wind velocity profile and turbulence intensity profile in CFD computations to accurately predict wind effects on huge structures. The recommend CFD techniques and associated numerical treatments provide an effective way for designers to assess wind effects on offshore platforms and the need for a detailed wind tunnel test.
A New Device for Controlling the Position of Marine Seismic Streamer Cables
Authors: Duan Lei , Zhang Weijing , Liu Tao
Published: January 2011

The technology of marine seismic prospecting is an important method for exploration of offshore petroleum and natural gas resource. It can improve the precision of prospecting, otherwise reduce the number of prospecting by controlling the position of marine seismic streamer cables accurately. A new device for controlling the position (both vertical position and horizontal position) of the cables is designed. The device includes three parts, the main body, the rotating body and two wings. The main body is installed between two parts of the cable, and its front end and tail end are connected to the cable water-tightly. The rotating body is installed on the main body, and it is driven by a motor to rotate about the axial line of the main body. Two wings are installed on the rotating body, and they are driven by another motor to rotate about the wing axial line together. When water flows past the wings, the wings will generate a controllable force which is perpendicular to them. The controllable force whose direction and strength can be changed by rotating the rotating body and the wings is used for controlling the position of the cable. The specific mechanical structure of the device is supplied. And the operation processes are proposed. The test and simulation data are also presented. A conclusion is drawn that the designed position control device is effective on controlling the position of the marine seismic streamer cables.