bluuebunny/crossref_metadata_2025 huggingface dataset:
A Preliminary Study Unveiling the Concept of Hemispherical Hull Structure for FPSOs With Special Emphasis on Fatigue Damage
Authors: Kumar M. Ashok , Anbukumar S. , Srivastava Amit Kumar
Published: January 2011

FPSOs, moored permanently at deep seas, are more vulnerable to fatigue failures due to cyclic loads from environmental conditions and operating cycles. In welded structures, the fatigue crack initiation strongly depends on the structural geometry and the stress concentration. In this work, a parent conventional hull is taken and an equivalent hemispherical hull, which could be a refined shape hull structure with smooth transition joints, is created with equal volumes. In both the hulls, the common critical location selected for comparison is a stiffener on central girder of the hull structures and the fatigue damage at full load and ballast load conditions are calculated, for design life of 25 years, by using simplified fatigue assessment procedure and S-N curve. It is observed that the hemispherical hull structure components have higher fatigue capacity than the conventional hull structure.
Acoustic AUV Navigation Referring to the Position of a Surface Station With Acoustic Data Transmission
Authors: Watanabe Yoshitaka , Ochi Hiroshi , Shimura Takuya , Hattori Takehito
Published: January 2011

In this paper, a navigation method of autonomous underwater vehicle (AUV) is proposed. In the method, the continuous acoustic signal is transmitted from a surface station to the AUV. The acoustic signal includes information of the position and the velocity of the surface station measured by the global positioning system (GPS). The AUV receives the acoustic signal with receiver array equipped on the top surface of the body, and obtain the included information and perform the inverted ultra short baseline (IUSBL) computation using the same acoustic signal. Using the depth data by a depth sensor, the AUV is not needed to transmit any acoustic signal to measure the round-trip time of the acoustical propagation. The output of the inertial navigation system (INS) equipped on the AUV, the IUSBL result, and the transmitted information are integrated for the navigation of AUV. A simulation result was shown. The depth of the AUV was 3000 meters. In the simulation the used sensors had the typical error source respectively. The initial positional error of the INS output was about 100 meters. As the result, the error was converged within about 100 seconds and finally the error was around 1 meter. In this method the large random error of the acoustic navigation is rapidly converged because the output rate of the acoustic navigation is very fast.
Standing Wave-Induced Dynamic Response and Instability of Seabed Under a Caisson Breakwater
Authors: Ulker M. B. C. , Rahman M. S. , Guddati M. N.
Published: January 2011

The wave-induced dynamic response and instability of the porous seabed and the rubble mound foundation under a composite caisson-type breakwater is studied using finite elements. In this study the focus is on the effect of inertial terms on the dynamic response and instability of the foundation material underneath the breakwater. It is assumed that a fully standing wave condition occurs in front of the caisson under the cyclic wave action and the dynamic response of the seabed and rubble mound is presented in terms of pore pressures and stresses induced around the breakwater. A complete formulation of the fully dynamic (FD) response requires inclusion of the inertial terms associated with both the motion of solid skeleton and that of pore fluid. However, partly dynamic (PD) and quasi-static (QS) idealizations are also possible. The objective of this study is to investigate the standing wave induced dynamic response and instability of seabed-rubble-breakwater system.
Research and Development of Deep Sea Mining Technology in China
Authors: Liu Shaojun , Yang Ning , Han Qingjue
Published: January 2011

This paper discusses the state of the art of deep sea mining technology in China. The research and development of deep sea mining technology in China started from the polymetallic nodules mining. A pilot mining system, which consists of a self-propelled collector, hydraulic pipe lift and a surface vessel, has been developed. In 2001, a lake mining trial was conducted in the pilot system, through which artificial nodules lying on the floor of lake were collected by the collector and then transported up to the surface vessel by a flexible hose subsystem. The lake mining trial confirmed the maneuverability and controllability of the self-propelled collector, the efficiency of the hydraulic pick-up device, and the feasibility of lifting system with flexible hose. In addition, some research has been conducted on the cobalt-rich ferromanganese crusts mining techniques such as the methods of in situ fragmentation and separation of crusts from the substrate rock, and the technique of crust mining using the robotic seabed vehicles. During the past decade, China has enhanced the research on key techniques of deep sea mining system. Some new laboratories and facilities have been constructed, including a miner test laboratory with a 50 mx50 mx5 m basin, a lifting test setup which can carry out circular lifting test and one way transporting test, and a computer simulation research laboratory which can partially test some boundary conditions and demonstrate simulation results. China has further planned to investigate the techniques of deep sea mining for polymetallic sulphide, to develop the facilities for the application, and to assess the economic feasibility of the deep sea mining development. We will continue to explore the new deep sea mining methods and technologies.
The Wave Buoy Analogy: Analysis of Synthetic Data by Bayesian Modelling
Authors: Nielsen Ulrik D. , Iseki Toshio
Published: January 2011

The paper presents results of the wave buoy analogy applied to synthetic data including measurement noise (white noise). The wave buoy analogy is of particular interest in the context of on-site wave estimations to be used in onboard decision support systems. In the study, Bayesian modelling is introduced as the underlying methodology. The analysis concerns an LNG vessel with forward speed and estimations are made of a rather comprehensive set of wave excitations. In general, reasonable agreements with the true wave parameters are observed. The paper forms parts of the background of another paper, Nielsen and Iseki [17], submitted also to OMAE 2010.
Dynamic Model Development and Simulation Analysis of China’s Total Integrated Deep Ocean Mining Pilot System
Authors: Dai Yu , Liu Shaojun , Li Li , Li Yan , Wang Gang , Hu Xiaozhou
Published: January 2011

A typical and may be the most prospective deep ocean mining system is an integration of a mining ship system, a hoist pipeline system and a self-propelled seafloor miner system. According to this representative system configuration, China has designed and developed a deep ocean mining pilot system. In order to evaluate and improve the design of the pilot system, and further to provide technical references for the practical system operation, dynamic simulation models of the subsystems and the total integrated system are developed. For the seafloor miner, a multi-body model with the scale of 1:1 to the actual size of the pilot miner is built, which can be used effectively to perform detailed design, analysis and optimization of the miner system. Meanwhile, to make the integration of the total mining system possible, a simplified 3D single-body model with 6 DOF of the miner is also developed, which is capable of real-time simulation and can be easily integrated with other subsystems. For the pipeline system including the rigid lifting pipe, submerged pump, buffer storage and flexible hose, finite element method (FEM) and discrete element method (DEM) are all proposed and developed. With the FEM model, the towing mining operation process, as well as the launching and retrieval process, can be analyzed. Whereas, the DEM model is preferred to perform the dynamic analysis of the total integrated mining system due to its relative high computation efficiency compared with that of the FEM model. To realize the dynamic analysis of the total integrated mining system with relative high efficiency and accuracy, the single body model of the miner and the DEM model of the pipeline are chosen to be integrated to form the total system and perform dynamic analysis, which in a way can provide specific guidance and suggestions for the practical deep ocean mining system analysis, operation and control. For further researches, more attention will be focused on the analysis of the launching and retrieval operation process of the total mining system, including the water entry of the miner, the launching process of the pipeline system and the final seafloor-touchdown of the miner.
The Ship Lift Floating Dry-Dock System
Authors: Hudson W. R.
Published: January 2011

The paper describes an economical system that transfers vessels from a floating dry-dock to a raft for service or repair. The innovations lie in separating the docking process from the maintenance platform and ballast water displacement by low-pressure air instead of pumping. A 150 tonne lift capacity system has been designed.
Rotor-Floater-Mooring Coupled Dynamic Analysis of Mini TLP-Type Offshore Floating Wind Turbines
Authors: Bae Yoon Hyeok , Kim M. H. , Shin Young S.
Published: January 2011

An increasing number of floating offshore wind turbines are planned and designed these days due to their vast potential in massive generation of clean energy from ocean wind. In the present study, a numerical prediction tool has been developed for the fully coupled dynamic analysis of an offshore floating wind turbine system in time domain including blade-rotor dynamics and control, mooring dynamics, and platform motions. In the new computer program, the dynamic coupling between the rotating blades and the floater is considered in addition to the mooring-floater dynamic coupling so that the influence of rotor dynamics on the hull-mooring performance and vice versa can be assessed. Mono-column mini TLPs with 1.5MW units for two different water depths, 80m and 200m, are selected as an example. The TLP becomes stiffer both in horizontal- and vertical-plane modes as water depth decreases. As a result, wave-frequency motions and the resulting tendon tensions tend to increase in the 80-m case. However, the coupling effects with rotors are decreased in the shallower depth case. When compared with the uncoupled analysis, we can observe more pronounced rotor-dynamics effects at high frequencies in the coupled simulations, which may appreciably influence fatigue life in the case of larger blades. The developed technology and numerical tool are readily applicable to the design of new offshore floating wind farms in irregular waves, dynamic winds, and steady currents.
Study on Erodibility Change of the Yellow River Sediment Into the Sea in the Process of Consolidation
Authors: Meng Xiangmei , Jia Yonggang , Hou Wei , Liu Hui , Yang Zhongnian
Published: January 2011

The erodibility change of estuarine sediment in the process of consolidation directly determines the resuspension and secondary migration of sediment, which plays an important decisive role in estuarine and coastal stability. The rapid deposition of Yellow River sediment into the sea was simulated on the tidal flat of the modern Yellow River delta, and the erodibility and physical-mechanical properties of the sediment at different consolidation time were measured in situ. The results show that the anti-erodibility of Yellow River sediment into the sea rapidly increases with consolidation time, and the critical erosion shear stress has already exceeded the value of the undisturbed tidal flat surficial sediment when the consolidation time extends as long as 8 hours. The critical erosion shear stress of the newly deposited sediment has a good positive correlation with bulk density, penetration resistance and shear strength, a good negative correlation with water content. The rise rate of measured critical erosion flow velocity of the Yellow River sediment into the sea with consolidation time is higher than the rise rate of calculated value using different formulas, and the former is 1.5–4.1 times as high as the latter.
Straked Riser Design With VIVA
Authors: Deka Dhyanjyoti , Hays Paul R. , Raghavan Kamaldev , Campbell Mike
Published: January 2011

VIVA is a vortex induced vibration (VIV) analysis software that to date has not been widely used as a design tool in the offshore oil and gas industry. VIVA employs a hydrodynamic database that has been benchmarked and calibrated against test data [1]. It offers relatively few input variables reducing the risk of user induced variability of results [2]. In addition to cross flow current induced standing wave vibration, VIVA has the capability of predicting traveling waves on a subsea riser, or a combination of standing and traveling waves. Riser boundary conditions including fixed, pinned, flex joint or SCR seabed interaction can be modeled using springs and dashpots. VIVA calculates riser natural frequencies and mode shapes and also has the flexibility to import external modal solutions. In this paper, the applicability of VIVA for the design of straked steel catenary risers (SCR) and top tensioned risers (TTR) is explored. The use of linear and rotational springs provided by VIVA to model SCR soil interaction and flex joint articulation is evaluated. Comparisons of the VIV fatigue damage output with internal and external modal solution is presented in this paper. This paper includes validation of the VIVA generated modal solution by comparing the modal frequencies and curvatures against a finite element (FE) model of the risers. Fatigue life is calculated using long term Gulf of Mexico (GoM) currents and is compared against the industry standard software SHEAR7. Three different lift curve selections in SHEAR7 are used for this comparison. The differences in riser response prediction by the two software tools are discussed in detail. The sensitivity of the VIVA predicted riser response to the absence of VIV suppression devices is presented in this paper. The riser VIV response with and without external FE generated modal input is compared and the relative merits of the two modeling approaches are discussed. Finally, the recommended approach for VIVA usage for SCR and TTR design is given.
The General Arrangement Study of Jack-Up Drilling Unit
Authors: Ren Xiangang , Bai Yong
Published: January 2011

In this paper, the general arrangement principal of offshore jack-up drilling unit and some latest generations are introduced. The key technical points including variable load, drilling system, drilling tool storage and engine rooms are analyzed. Then the general arrangement is illuminated synthetically. Finally, the general arrangement corresponding to China’s offshore characteristic and its most optimum capacity are presented.
Numerical Simulation and Analysis of Joint Multi-Line to Defend Storm Surges Due to a Super Typhoon
Authors: Li Lei-yan , Zhu Xi-bing , Huang Shi-chang , Shi Yan-hua , Wu Xing-long
Published: January 2011

This paper aims to the inundated conditions which probably occur in the macro-tidal estuary where the floodplains are lower than the high tidal level. A high Precision two-dimensional numerical model is developed to simulate the inundated degree introduced by storm surges taking the Qiantangjiang estuary coastal area as an example. Except for the sea area, both sides of the floodplains are included in the calculation scope. Meanwhile, the secondary dikes owing to the reclamation projects and some roads which have the effect on tide resistance are considered. In this article, the front dikes damaged scale is determined by Interior Wave Model Experiment[3], Safety Assessment of the Front Dikes’ Ultimate Defense Capability[11]. Using the model, this paper simulated inundated conditions under the typical super typhoon which takes Typhoon No.5612, the most intense typhoon landed in china since 1949, as the controlling conditions. According to the calculated results, this paper analyzed the effects of joint multi-line defense (the secondary dikes and roads) behind the front dikes and obtained action sphere and role of each defense. These results can be applied to direct the defense of storm surges over designed standard occurring in the macro-tidal estuary.
Observation of the Occurrence of Air Flow Separation Over Water Waves
Authors: Tian Zhigang , Perlin Marc , Choi Wooyoung
Published: January 2011

A preliminary study on the occurrence of air flow separation over mechanically generated water waves under following wind conditions is presented. Separated air flows over both non-breaking and breaking waves are observed in the flow visualization. A first attempt to identify an air flow separation criterion based on both wind speed and wave steepness is made. It was believed that, in the case of water waves propagating in the following wind condition, air flow separation will occur only in the presence of breaking waves. However, some laboratory experiments and field measurements suggested the occurrence of air flow separation over nonbreaking waves. Therefore, we conducted lab experiments to observe the air flow over mechanically generated waves. In the experiments, the air is seeded with water droplets generated with a high-pressure spray gun and is illuminated with a thin laser light sheet. A high-speed imaging system is used to record and observe the air flow over the mechanically generated wave waves. Our observations show that the separation of air flow occurs above both breaking and non-breaking wave crests, implying that wave breaking is sufficient, but not necessary for air flow separation. In addition, as compared to the separation over breaking waves, a higher wind speed is necessary for the separation over non-breaking ones, indicating that a robust air flow separation criterion likely depends on both the wave crest geometry and the wind speed above the crest. Our preliminary results support, to a certain degree, such a criterion. To the best of our knowledge, this criterion has not been reported previously in laboratory studies.
A Cohesive Element Framework for Dynamic Ice-Structure Interaction Problems: Part III—Case Studies
Authors: Konuk Ibrahim , Yu Shenkai
Published: January 2011

The general framework for a cohesive finite element model for the analysis of ice-structure interaction problems incorporating plasticity and fracture was presented at OMAE 2009 as Parts I & II. This third paper presents the application of the framework to various ice-structure interaction problems. It investigates the important aspects of these scenarios and reveals their characteristics which may play a major role in the design of structures. The investigations include the geometry, size and velocity effects as well as the influence of the structure stiffness. The paper also studies the effects of ice characteristics, and interaction speeds.
Wave Spreading and Wave Drift Loads for a Standard LNG Carrier in Shallow Water
Authors: Sergent Emmanuel , Naciri Mamoun
Published: January 2011

The need for LNG export and import terminals is anticipated to grow as natural gas progressively accounts for a larger fraction of worldwide consumed energy. These terminals are preferably located nearshore i.e. in relatively shallow water. Design of floating structures is most of the time performed assuming long-crested waves. In shallow water, diffraction of waves by a variable bathymetry can result in wave spreading i.e. in short crested seas. The effect of short crested seas on the wave drift load spectral densities for a 135,000m3 storage capacity LNG Carrier in 15m water depth is investigated. It is shown that the impact of wave spreading on drift loads depends on the natural frequency of the moored vessel and thus on the stiffness of the mooring system under consideration. Although response calculations are not performed herein for reasons to be discussed, it is conceivable that wave spreading could adversely affect loading/offloading terminal availability for stiff moorings.
Model Tests for Floatover Installation of Spar Topsides
Authors: Koo Bonjun , Magee Allan , Lambrakos Kostas , Beyko Eleni , Sablok Anil
Published: January 2011

There are several substantial advantages to installing an integrated deck on a Spar using floatover installation, particularly for large topsides which exceed the single lift capacity of the available heavy lift derrick barge fleet. These advantages include schedule and cost savings for the integration and commissioning of modules on land rather than at sea. Uncoupling the deck fabrication schedules from the availability of heavy lift vessels is another advantage. The purpose of the model tests described in this paper was to generate data on motions and loads for the operational sea states in the Gulf of Mexico, and to define and validate different approaches of transferring the topsides to the Spar, using a catamaran configuration. The data are intended to (1) demonstrate the feasibility of the installation method for the GOM, and (2) validate Technip’s analysis tools. The model tests were performed at OTRC (Texas A&M) with a model set-up corresponding to a 1:60 model scale. The simulated topsides was about 18,000Te, and Jones Act compliant barges were modeled for the catamaran configuration. The paper will describe the catamaran and spar models, and the instrumentation to measure motions and loads for transportation and installation. It will also describe the shock cell configuration used for the mating operation, and several alternative methods for performing the mating. The environmental conditions tested included several random sea states, harmonic waves, and three headings (beam, head, and quartering seas). Selected data will be shown to demonstrate the range of motions and loads associated with the floatover installation in the GOM. Estimates of limiting sea states for the GOM will be discussed. The validation of the analysis tools is the subject of another paper in Ref [1].
Non-Resonant In-Line VIV and Its Implications on Model Tests
Authors: Jhingran Vikas , Vogiatzis Johnny , Pontaza Juan P. , Lee Li
Published: January 2011

Recently, small-scale experiments were conducted by [1] to study in-line VIV in pipe spans. The experiments were performed with six different pipes of varying stiffness and mass ratio, but with the same length-to-diameter ratio. The response of the pipe with the lowest mass and stiffness, made out of Acrylonitrile Butadiene Styrene (ABS), was surprising. The in-line RMS A/D response of the ABS pipe was larger and over a much wider reduced velocity range than shown in design codes like DnV F105. Since these codes are commonly used to design real pipelines, the authors were interested in understanding these observations. In the past, observations of VIV response over a wide reduced velocity range have been explained using added mass. This paper shows that though added mass could play an important role, observations of the in-line and cross-flow response mode and frequency content suggests that there could be other reasons for the response observed in the experiments. In particular, this paper investigates the observed large response away from the region of resonant VIV and proposes that this non-resonant in-line response could be different from what researchers typically call VIV. The paper also investigates when such a mechanism could contribute to substantial in-line VIV motion. The implications of this work could be significant, not just for pipe-span design but also for scaling pipes for in-line VIV model tests.
On High-Resolutive Analysis of Direction of Waves Generated by a Small High-Speed Boat
Authors: Shiotani Shigeaki
Published: January 2011

A simplified estimation of the height and period of waves generated by a small boat was proposed in previous papers. The estimated height and period of waves were in good agreement with field results using a small boat. In addition, a new method called MUSIC (Multiple Signal Classification) was proposed to analyze the direction of ship waves. The distribution of the directional spectrum of ship waves as estimated by MUSIC presented a sharp monotone peak, and the estimated results were supported by field results using a small boat. The proposed estimation of ship waves by MUSIC was confirmed to be very effective. In present study, the direction of waves generated by a small boat was determined using MUSIC. In the previous study, the triangular array was fixed to a stand on the quay, and the measurement of the ship waves was limited to the sea area near the pier. In the current study, a triangular array was made by three buoys in order to analyze the waves created by a ship offshore. The analytical results derived by MUSIC were analyzed and were confirmed to be highly effective.
On the Use of Main Hoist Tension Measurement for Feed Forward in DP Systems During Offshore Installations
Authors: Waals Olaf
Published: January 2011

DP systems are nowadays widely used on installation and crane vessels. In recent years a few cases have been reported where the DP system becomes instable during the installation. Two main reasons can cause these instabilities. First of all the predictor model that is used in the Kalman filter has to accommodate the difference in the mass that occurs when its weight shifts from the barge to the crane. The second and more important reason is the tension in the main hoist wire which acts as an additional spring in the horizontal plane. Some DP-systems have a special heavy lift mode, which is activated when instabilities occur. The present paper describes a different method that uses the actual tension measurement in the hoist wire to enhance the DP system and correct for the additional forces in the horizontal plane due to the hoisting wire. The proposed method is investigated in a series of model tests and results are presented. It is shown that the hoist feed forward improves the overall behavior significantly.
Corrosion Fatigue Performance of Duplex 2507 for Riser Applications
Authors: Gui Feng , Thodla Ramgopal , Evans Ken , Joia Carlos , Baptista Ilson Palmieri
Published: January 2011

Corrosion fatigue performance is of interest for high strength steels in riser applications. This work investigated the corrosion fatigue performance of 2507 duplex stainless steel for use as riser materials in environments containing high partial pressures of carbon dioxide (50–100 bar) and limited quantity of hydrogen sulfide (0–0.12 bar). The procedures developed for controlling oxygen and Fe2+ contamination as well as methods to evaluate the concentration of H2S in the autoclave are presented. The crack growth rates and ΔKth for these materials in the pressure environments were discussed along with procedures to obtain ΔKth, when they were below 5ksi√in. Low crack growth rates in the range of 1×10−8 in/cycle were measured and the effect of sour environments was quantified. The fatigue crack growth rate in sour environments on 2507 duplex stainless steel is a 10x higher than in air.
Numerical Simulation of Multi-Grade Separators for Multi-Phase Fluid Media Down Hole in Offshore Oilfield
Authors: Zhang Yong , Zhang Yan , Jiang Minghu
Published: January 2011

It’s an effective method to get higher oil production efficiency during offshore petroleum production by separating some water from produced fluid and re-injecting it in some given formation using down hole separators. However some kinds of oil, water, gas and sand will enter the separator in the down hole separating system as a mixture because of the complex environment down hole. In oilfield onshore multiphase separators will be a good answer to this puzzle. But it becomes almost impossible to use multi-phase separators down hole because of the complex condition and the limitation of diameter of well bore. However multi-grade separators can be arranged in bridge or in series and some path-breaking theoretical and experimental investigation related has been done which based on modular design. This not only gives the answer to the puzzle to arrange multi-grade separators, but also bring it to be possible to separate different separating media with different separator. And this takes role of multiphase separator limited by maximum diameter down hole. Some new results are introduced in this paper about the implement method of separating gas/oil/water in different grade of separators which are arrayed in series. It shows different conditions for down hole separators simulating by CFD technique which can be a perfect reference for design of separators and separating systems.
Collision Analysis of Stiffened Plates
Authors: Alali Amier , Abdel-Nasser Yehia , Swielm Swielm A.
Published: January 2011

Structural design of ships against collision requires prediction of the extent of damage to stiffened plates subjected to impact. Structural components such as stiffened plates, bulkheads are our concern. In ship structures stiffened plates are furnished with vertical or horizontal stiffeners to sustain conventional acting loads such as shearing, bending and local buckling. The consideration of collision in ship structural design is necessary for tankers where accidents may cause serious environmental pollution. In predicting the extent of collision damage, finite elements (FE) modeling of stiffened plates using ABAQUS software is applied to demonstrate collision scenario. Typical stiffened plates of tanker in service with different configurations of stiffeners are selected to examine absorbed energy for each one. The aim of this paper is to select the proper stiffener shape absorbing more deformed energy. These analyses of stiffened plates will guide ship designers to properly select effective stiffener absorbing higher deformed energy when simulate full scale ship against collision.
Mechanistic Study of Upper Ocean Turbulence Interacting With Surface Waves
Authors: Guo Xin , Yang Di , Liu Yi , Shen Lian
Published: January 2011

We perform direct numerical simulations to simulate the interaction between surface waves and the turbulence underneath. The Navier–Stokes equations are simulated using a pseudo-spectral method in horizontal directions and a finite-difference method in vertical direction, with fully nonlinear viscous free-surface kinematic and dynamic boundary conditions at the free surface. We set up the turbulence and the waves by a random forcing method in the bulk flow and a pressure forcing method at the surface, which were recently developed by [1]. It is found that there are surface waves generated on the free surface due to the excitation by the turbulence. The surface elevation is sensitive to the effect of gravity and surface tension. In the presence of progressive waves at the free surface, the turbulent vortical structure is turned, stretched, and compressed periodically by the strain field of waves.
Real Time Prediction of Second Order Wave Drift Forces for Wave Force Feed Forward in DP
Authors: Naaijen P. , Huijsmans R. H. M.
Published: January 2011

The presented research is an extension of the development of an onboard wave and motion estimation system that aims to predict wave elevation and wave frequent vessel motions some 60–120 s ahead, using remote measurements of short crested waves. The main aim is to provide decision support during motion critical offshore operations. As an addition to this, an attempt is made to predict second order wave drift forces. This can be useful for condition monitoring of a Dynamic Positioning (DP) system [18] or for feed forward of wave drift forces into the control of DP systems. The paper describes the techniques used to predict second order wave drift forces real time from remote wave measurements. For validation, measurement data is used from model experiments during which wave elevation in irregular short crested seas was recorded by a large number of probes simultaneously. A method is described to obtain a 3D representation of a wave field in such a way that it can be used to predict both first order waves and motions and second order forces. The second order forces resulting from the wave field description as obtained from remote probe measurements can be compared to those that have been derived from the probes in the proximity of the prediction location, thus providing insight in the sensitivity of the 2nd order wave force prediction error with respect to the first order wave prediction error. In a full scale field situation, remote wave sensing can be provided by X-band radar. Possibilities for application of the developed method with the WAMOS II X-band radar system is considered.
Experimental and Numerical Study of the Slow-Drift Motion of a Rectangular Barge Moored at an Inclined Beach
Authors: Molin Bernard , Remy Fabien , Liu Yanan , Rouault Marie-Christine
Published: January 2011

An experimental campaign is reported on the slow-drift motion of a rectangular barge moored in irregular beam seas. The 24 m long false bottom of the basin is raised and inclined at a slope of 5%, from 1.05 m below the free surface to 0.15 m above. The barge is moored successively at 4 different locations, in water-depths ranging from 54 to 21 cm. The measured slow-drift component of the sway motion is compared with state-of-the-art calculations based on Newman approximation. At 54 cm depth good agreement is obtained between calculations and measurements. At 21 cm depth the Newman calculation exceeds the measured value. When the flat bottom setdown contribution is added up, the calculated value is 2 to 3 times larger than the measured one. A second-order model is proposed to account for the shoaling of a bichromatic sea-state propagating in decreasing water-depth. Application of this numerical model to the scale-model tests shows that in shoaling conditions the setdown contribution to the slow-drift excitation can counteract and not necessarily add up to the Newman component.
A Wave Resistance Formulation for Slender Bodies With Fine Bow Shapes
Authors: Taravella Brandon M. , Vorus William S. , Givan Daniel R.
Published: January 2011

Ogilvie (1972) investigated a Green’s function method for calculating the wave profile of slender ships with fine bows. He recognized that near a slender ship’s bow, rates of change of flow variables axially should be greater than those typically assumed in slender body theory. Ogilvie’s (1972) result is still a slender body theory in that the rates of change in the near field are different transversely (a half-order) than axially; however, the difference in order of magnitude between them is less than in the usual slender body theory. Typical of slender body theory, this formulation results in a downstream stepping solution (along the ship’s length) in which downstream effects are not reflected upstream. Ogilvie (1972), however, only developed a solution for wedge-shaped bodies. In this paper, a general solution for arbitrary slender ships has been developed based on Ogilvie’s (1972) formulation. The results for wave resistance have been calculated and are compared to previously published model test data and calculated results. The free surface profile has also been calculated.
System Identification of Jack-Up Platform by Spectral Analysis
Authors: Wang X. M. , Koh C. G. , Thanh T. N. , Zhang J.
Published: January 2011

For the purpose of structural health monitoring (SHM), it is beneficial to develop a robust and accurate numerical strategy so as to identify key parameters of offshore structures. In this regard, it is difficult to use time-domain methods as the time history of wave load is not available unless output-only methods can be developed. Alternatively, spectral analysis widely used in offshore engineering to predict structural responses due to random wave conditions can be used. Thus the power spectral density (PSD) of structural response may be more appropriate than time history of structural responses in defining the objective (fitness) function for system identification of offshore structures. By minimizing PSD differences between measurements and simulations, the proposed numerical strategy is completely carried out in frequency domain, which can avoid inherent problems rising from random phase angles and unknown initial conditions in time domain. A jack-up platform is studied in the numerical study. A search space reduction method (SSRM) incorporating the use of genetic algorithms (GA) as well as a substructure approach are adopted to improve the accuracy and efficiency of identification. As a result, the stiffness parameters of jack-up legs can be well identified even under fairly noisy conditions.
Pipeline Free Spans: Influence of Internal Pressure
Authors: Fyrileiv Olav , Aamlid Olav , Andreassen Erik
Published: January 2011

The trend the last decades has been to develop the offshore fields by use of Subsea templates and flowline tie-backs rather than traditional platforms and topside processing. The exploitation of new offshore fields has moved towards deep waters, rougher seabed and reservoirs with high temperatures and high pressures. As flowlines are not necessarily trenched and buried, an uneven seabed may cause significant free spans. Then, if the current and wave induced flow velocities are sufficient, the free spans may be exposed to cyclic loading and associated fatigue failure. One of the governing parameters to ensure the structural integrity of free spans is the natural frequency of the span. As such it is in many cases of vital importance to estimate a realistic value of this frequency. The natural frequency is mainly determined by the bending stiffness and the span length but also operational parameters like the internal pressure and the fluid temperature. Recently some papers have been published that claim to prove that the effect of the internal pressure is the opposite of what has been the understanding in the industry and given by various codes. This paper tries to give an overview of the effect of the internal pressure and hopefully clarify what is believed to be misinterpretations of some experimental data.
Wave Impacts on the Column of a Gravity Based Structure
Authors: Roos Jannicke , Swan Chris , Haver Sverre
Published: January 2011

An accurate prediction of the wave loading on the columns of any offshore structure is an integral part of the design / re-assessment process. Earlier studies have investigated the nonlinear loads on single columns covering a wide range of diameters (expressed as a ratio of the incident wave length) and addressing a variety of incident wave steepness. As a result, it is generally accepted that wave-structure interaction effects can be important even outside the diffraction regime and may be one possible cause of structural dynamic response. The importance of wave-structure and wave-wave interaction effects will again be highlighted in the present study; the emphasis of the work being the occurrence of wave impacts on the columns of a gravity-based structure in random seas involving very large, steep waves. This paper presents the results of an experimental study of a gravity based structure in a severe wave climate. The structure comprises an arrangement of storage caissons located on the sea bed in relatively shallow water, with four large diameter surface-piercing columns. The primary purpose of the present paper is to provide a comparison between the incident waves and the measured loads. This shows that robust predictions of the slamming load cannot be made without taking into account the geometry of the structure, including that of the underlying caissons. It is also shown that the largest loads frequently do not correspond to the tallest or steepest incident waves. This emphasizes the importance of correctly incorporating the nonlinear wave-wave interactions and hence the need to undertake long random wave tests in offshore engineering design.
Ice Collision Forces Considering Structural Deformation
Authors: Daley Claude , Kim Hyunwook
Published: January 2011

With increasing interest in resource exploitation and shipping in the Arctic, the focus on ice class ships and offshore structures is growing every year. In Arctic waters collision with ice is a major concern. The standard analytical ship-ice collision load model is based on the assumption that the ship structure is perfectly rigid body and the crushing energy of ice is equated to the available kinetic energy to calculate the ice load. This paper extends the standard approach by including the local plastic deformation. By considering the plastic work done to the structure in the balance of energy, a model is developed that can be used to help specify the levels of structural damage that may occur at various speeds. A simple unit side shell of ship structure is modeled to evaluate the absorbed energy and permanent deformation, with elasto-plastic response including linear strain hardening. A simple patch load is used. The purpose of this model is to provide a practical evaluation method of ice loads with the consideration of ship structure’s deformation. While there have been similar issues tackled numerically by several researchers, this work takes a more analytical approach, and will hopefully enable designers to more rapidly assess potential designs. Furthermore, this approach may provide a tool for regulation that is more related to actual risk levels and consequences. To illustrate the issues and practical application, the paper presents an assessment of the bow structure of a high ice class 150kT arctic tanker involved in an iceberg collision.
Properties of North Atlantic Abyssal Plain Sediments From High-Quality Long Piston Cores
Authors: Brandes Horst G.
Published: January 2011

Two abyssal plain sites on either side of the North Atlantic Ocean are characterized by sequences of distal turbidites and pelagic clays. At the Great Meteor East location, turbidites are quite thick and geotechnical properties such as water content and shear strength can be correlated to the observed stratigraphy. At the Southern Nares Abyssal Plain site, turbidites are much thinner, harder to identify, and less distinct from the pelagic clays. Geotechnical properties there can not easily be correlated to the type of sediment.
Hydroelastic Response of VLFS With a Hinge or Semi-Rigid Line Connection
Authors: Wang Chien Ming , Tay Zhi Yung , Gao Rui Ping , Koh Chan Ghee
Published: January 2011

This paper is concerned with the hydroelastic response of pontoon-type, very large floating structures (VLFS) with a hinge or semi-rigid line connection. For the hydroelastic analysis, water is modeled as an ideal fluid and its motion is assumed to be irrotational so that a velocity potential exists. The VLFS is modeled by a plate according to the Mindlin plate theory. In order to decouple the fluid-structure interaction problem, the modal expansion method is adopted for the hydroelastic analysis that is carried out in the frequency domain. The boundary element method is used to solve the Laplace equation together with the fluid boundary conditions for the velocity potential, whereas the finite element method is adopted for solving the deflection of the floating plate. This study examines the effect of the rotational stiffness and the location of such a semi-rigid line connection on the hydroelastic response. Hinge and semi-rigid line connections are found to be effective in reducing hydroelastic response of VLFS, depending on the wavelength.
Unsteady Buoyant Jet Simulations Using Dynamic Connection Scheme of Hydrostatic and Non-Hydrostatic Zone
Authors: Hasebe Masanobu , Tabeta Shigeru
Published: January 2011

Most of ocean models employ hydrostatic approximation because the horizontal scale is usually much larger than the vertical scale in oceanic phenomena. In hydrostatic approximation, dynamic pressure is neglected and the momentum equation in vertical direction needs not to be solved. But for the phenomena of buoyant jet from the sea bottom such as submarine groundwater discharge, hydrothermal plume and so on, hydrodynamic pressure cannot be neglected and the momentum equation of vertical direction must to be taken into account. Non-hydrostatic analysis requires so much computation time that it is usually difficult to calculate the current field in the wide ocean area by this approach. On the other hand, analysis assuming the hydrostatic approximation needs less computational time and usually gives reasonable results for large scale ocean phenomena such as tidal current. In the present study, the authors developed a new type of ocean model for multi-scale analysis, which conducts hydrostatic analysis for phenomena in wide area and non-hydrostatic analysis for the detail flow around the buoyant jet simultaneously. The application limit of hydrostatic approximation for ocean model was investigated, and a dynamic connection method of hydrostatic zone with non-hydrostatic zone was developed. By theoretical consideration employing parameter δ and ε which represent the ratio of grid size Δz to Δx and the ratio of vertical velocity to horizontal velocity, it was found that hydrostatic approximation can be applied if δε and ε2 are minute. To examine the developed method, simulations for lock-exchange problem and vertical jet under oscillating current were conducted. The result by the present model was similar to that of non-hydrostatic model in the case that hydrostatic approximation was applied on the area of δε<0.005 and ε2<0.005.
The State of Transfer Systems: An Analytical Study With Respect to Human Information Recognition—An Approach From a Smooth Transfer System in Marine Transportation
Authors: Oikawa Tomoe , Koga Takahiro , Kondo Takeo , Yamamoto Kazukiyo , Miyazaki Wataru , Idoji Atsushi
Published: January 2011

The purpose of this research is to examine in detail provision of signs for ensuring smooth movement, conducted by transportation companies at traffic nodes, and to identify future issues to be solved for maintenance of marine-based traffic nodes. To this end, as the study site, we selected the City of Hiroshima in Japan, where a wide variety of traffic nodes, such as railroads, streetcars, buses, and ferries, are available. In particular, as main facilities to be studied, we focused on Ujina Terminal, which is a marine traffic node, and Hiroshima Station, which is an onshore traffic node. We examined the current status of and problems with facility plans and sign plans at traffic nodes through field exploration of the City of Hiroshima and questionnaires with tourists. As a result, it was found that in order to formulate a sign plan that can ensure security, cooperation with not only land traffic nodes but also marine traffic nodes will be an important issue in future when providing signs at marine traffic nodes for ensuring smooth movement.
Slewing Motion Characteristics of a Towed Ship in Steady Wind
Authors: Fitriadhy Ahmad , Yasukawa Hironori
Published: January 2011

An excessive slewing motion of a towed ship intrudes on sea traffic ways and may lead to the hazardous responses, such as crashing to other vessels or fixed offshore structures. In the presence of wind disturbances, which exerted on an exposed windage areas of a towed ship, her slewing motion behaviour was clearly different as compared with calm water condition. This paper presents a nonlinear analysis of the slewing motion characteristics of towed ship in the steady wind condition. Two different towed ships, one of them equipped with skegs, were towed by a tow ship at the various velocities and the angles of winds. The results revealed that the slewing motion of towed ship (no skeg) was reduced significantly at the angle of wind (θw = 120°) in proportion with the increase of wind velocities (Uw). Concurrently, the towed ship has been drift, then preserved its course steadily with a certain heading angle. In addition, the slewing motion of towed ship was also reduced as the increase of ratios of tow point position (lB/L2). However, the slewing motions of towed ship raised gradually due to the increase of heading and following wind velocities, which finally led to the course instability.