bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of System Level Parameters on the Fatigue Life of Jacket Substructures for 10 MW and 20 MW Wind Turbines
Authors: Conti Davide , Natarajan Anand , Bech Abrahamsen Asger
Published: September 2018

This paper investigates the influence of system-level innovations on the fatigue life of jacket substructures for offshore wind turbines. The innovations consist of active control strategies as individual pitch control and individual flap control. Further the effect of a magnetic pseudo direct-drive generator (PDD) mounted upfront the rotor is investigated. Fully-coupled aeroelastic simulations are performed for 10 MW and 20 MW wind turbines, with the selected innovations, supported by jacket structures under specific met-ocean conditions at 50 m of water depth. Fatigue limit states at the jacket’ welded joints are evaluated based on S-N curves and Miner’s rule according to DNV-RP-C203 guideline. Results show the potential of advanced control systems to reduce stresses at jacket members. Few design challenges characterize PDD models, as increased tower base torsional loads and excitation of global bending modes may be critical for jacket’s members. Altogether, this study indicates the benefit of an integrated-iterative design approach for jacket substructures, where system-level parameters are iterated along with the jacket design parameters using fully-coupled models.
TELWIND: Numerical Analysis of a Floating Wind Turbine Supported by a Two Bodies Platform
Authors: Armesto José A. , Jurado Alfonso , Guanche Raúl , Couñago Bernardino , Urbano Joaquin , Serna José
Published: September 2018

This paper presents a numerical study of an innovative floating wind turbine developed by ESTEYCO S.A.P. as part of an intensive R&D roadmap initiated ten years ago. The concept is called TELWIND, an evolved spar concept composed by a telescopic tower and two independent concrete bodies: the upper tank (acting as buoyancy body) and lower tank (acting as ballasting body), connected by suspension tendons. An ad-hoc numerical model has been developed by IHCantabria, calibrated and validated, based on a set of large scale laboratory tests performed at the Cantabria Coastal and Ocean Basin (CCOB), located at IHCantabria, Santander, Spain.

The inhouse numerical model is a fully coupled model which comprehends three main modules: i) Hydrodynamic model that analyses the coupled hydrodynamics of floater and ballast. ii) Mooring and tendon module, and iii) Aerodynamic model. The full description of the numerical model is summarized, as well as the validation procedure followed. Finally, the validation of the numerical model is shown.
CFD Simulations of Spilling Breaking Waves and Steep Waves Past a Monopile Structure at Different KC Numbers
Authors: Liu Shengnan , Ong Muk Chen , Obhrai Charlotte
Published: September 2018

A 3D numerical two-phase flow model based on solving Unsteady Reynolds-averaged Navier-Stokes (URANS) equations has been used to simulate spilling breaking waves and steep waves past a monopile structure at a 1:10 slope. The volume of fluid (VOF) method is employed to capture the free surface and the k–ω Shear-Stress Transport (k–ω SST) turbulence model is used to simulate the turbulence effects. Mesh and time-step refinement studies have been conducted. The numerical results of wave forces on the structure are compared with the experimental data from Irschik et al. (2004) to validate the numerical model, and the numerical results are in good agreement with the measured data. The wave forces on the structure at different KC numbers are discussed in terms of the generation of the slamming force. The secondary load cycles are observed after the wave front past the structure. The pressure and velocity distribution, as well as the characteristics of the vortices around the structure at four important instants, are studied.
High Fidelity Simulation of Multi-MW Rotor Aerodynamics by Using a Multifan
Authors: Battistella Tommaso , Paradinas Daniel De Los Dolores , Urbán Albert Meseguer , Garcia Raul Guanche
Published: September 2018

During the last decades the offshore wind energy sector has experienced large developments. Despite bottom fixed wind turbines have been widely used, some their limitations have brought to scout and develop concepts based on floating support structures.

The behavior of such structures is affected by forces of different nature, so the analysis of these structural systems becomes complex and requires an accurate definition of their dynamics. This is one of the reasons for which the numerical simulations can be highly improved from experimental tests at reduced scale.

The interaction between hydrodynamic forces and the structure is investigated experimentally by means of wave tank tests. In these circumstances the correct representation of the aerodynamic forces is not trivial due to laboratory scale law conflicts. These issues can be eased by using hybrid systems.

This work aims to describe a hybrid system developed by IH Cantabria. The system is meant to define the most significant aerodynamic loads affecting the dynamic performance of a floating wind turbine by using an aerodynamic model (BEM), while their generation in the scaled model is obtained by using a multi-fan system.

This approach successfully satisfies issues related to the scalability of the aerodynamic forces and their variability due to the turbine controller and wind variability. Nevertheless, some shrewdness have to be taken in order to comply with the following matters.

The correct representation of the dynamic effects relative to the aerodynamic forces requires high frequency calculations. For this reason some simplifications on the aerodynamic model must be taken. This work explains the criteria used to define the simplifications to be adopted, showing the low impact they have on the tests results. On the present paper it will be demonstrated the capabilities of the multi-fan that was chosen to reproduce the rotor aerodynamics. Moreover, it will evidence the high fidelity of the forces developed by the multi-fan, both in terms of amplitude and reactiveness on the forces fluctuations.

The final section will prove the ability of the hybrid system to reproduce with high fidelity and large flexibility the aerodynamic load conditions desired in lab scale wave tank tests.
PIV Analysis of Dynamic Velocity Profiles in Non-Newtonian Drilling Fluids Exposed to Oscillatory Motion
Authors: Amaratunga Maduranga , Nybø Roar , Time Rune W.
Published: September 2018

Drilling fluids experience a wide range of shear rates and oscillatory motion while circulating through the well and also during the operations for solids control. Therefore, it is important to investigate the influence of oscillatory fields on the velocity profiles, shear rate and resulting rheological condition of non-Newtonian polymers, which are additives in drilling fluids. In this paper, we present the dynamic velocity profiles within both Newtonian (deionized water) and non-Newtonian liquids (Polyanionic Cellulose – PAC) exposed to oscillatory motion. A 15 cm × 15 cm square cross-sectional liquid column was oscillated horizontally with very low frequencies (0.75–1.75 Hz) using a laboratory made oscillating table. The dynamic velocity profiles at the bulk of the oscillating liquid column were visualized by the Particle Image Velocimetry (PIV) method, where the motion of fluid is optically visualized using light scattering “seeding” particles. Increased frequency of oscillations lead to different dynamic patterns and ranges of velocity-shear magnitudes. The experiments are part of a comprehensive study aimed at investigating the influence of low frequency oscillations on particle settling in non-Newtonian drilling fluids. It is discussed, how such motion imposed on polymeric liquids influences both flow dynamics as well as local settling velocities of cuttings particles.
Using Lightweight or Low Viscosity Preflushes for Primary Cementing of Surface Casing
Authors: Maleki Amir , Frigaard Ian
Published: September 2018

Preflushes are often used as part of the sequence of fluids pumped in primary cementing. Usually two functions are served by preflushes: I) to wash the drilling fluid ahead, by a combination of turbulence and chemical reaction; II) to provide a chemically compatible spacer between the lead slurry and the drilling mud. In some cases a wash precedes a spacer, but often only a single preflush is used. We consider well parameters typical of surface casing cementing in North Eastern British Columbia. Using a two-dimensional model of annular displacement flows, we show that the wash concept is flawed. In particular, in a sequence of simulations varying from intermediate density to low density we show that the wash progressively advances ahead of the lead slurry, channeling rapidly up the wide side of the annulus. Even when fully turbulent, it is ineffective at displacing mud from around the annulus, invalidating the motivation of chemical cleaning through contact time. Furthermore, the advance along the wide side of the annulus drains the volume of fluid separating the cement from drilling mud. Thus, the idea that the wash provides a barrier between slurry and and mud is invalid.
Numerical and Experimental Study of Wave-Induced Load Effects on a Submerged Body Near the Surface
Authors: Jones L. M. , Klamo J. T. , Kwon Y. W. , Didoszak J. M.
Published: September 2018

Marine structures are subjected to wave forces whether they are stationary or moving. Such wave forces play a significant role in the design and operation of marine structures. The aim of this study is to understand and predict the unsteady hydrodynamic loads experienced by a submerged body near the surface. Both numerical and experimental studies were conducted. For the experimental work, a newly constructed wave maker inside a tow tank was utilized while a computational fluid dynamics model was developed for the numerical study. Both experimental and numerical studies can complement each other. First, the computational model was validated against experimental wave data so as to understand what parameters in numerical modeling influence the reliability of the numerical results. The second aim was to understand the force and moment that a submerged body would experience for different wave lengths.
Development of Cylinder Type Concrete FPSO With Tangerine-Shaped Cross-Section
Authors: Cho Jae-Young , Park Jong-Heon , Kim Jung J.
Published: September 2018

Concrete platforms have proven to be a viable offshore solution for deep-water projects according to the documented performance of over 40 years [1]. Since concrete has resistance to seawater corrosion, reduced maintenance costs and motions, concrete structures have become attractive to the offshore oil and gas industry [2, 3]. There are many floating concrete structures such as barge, ship, platform and LNG/LPG terminals. While most concrete offshore platforms are the fixed structures, floating concrete platforms have been used for drilling, extraction /storage and production units for oil and gas including heavy lifter. There are two representative floating concrete facilities on the Norwegian shelf, Troll B and Heidrun A [4, 5]. Troll B is the first concrete semi-submersible product unit and Heidrun A is the floating concrete tension leg platform. The concrete FPSO (Floating Production Storage and Offloading), however, was assessed to be inferior to the steel FPSO in respect of feasibility. In this study, an optimization design of the cross-section for cylinder shaped concrete platform is presented in order to promote the feasibility of a concrete hull for an FPSO. Optimal aspect ratio (depth to diameter) with economic analysis is examined and tangerine-shaped section which can utilize the excellent material properties of the concrete in compressive strength is developed. Exterior wall having a small curvature are applied to transmit the load to interior bulkhead. A parametric sensitivity study was conducted to find the optimal curvature of the exterior wall. Subsequently, an arch-shaped wall is applied to center wall in order to improve the upper and lower tension force caused by bending moment. The tendon was placed in the center of any cross-section, taking into account the tensile force that can be caused by additional asymmetric loads. The effect of tangerine shaped cross-section can be clearly identified by comparing the results with the circular shaped cross-section.
A Cost-Driven, High-Level Optimization of OSV Operations in the Flemish Pass
Authors: Gauthier Philippe , Molyneux David
Published: September 2018

This paper presents a cost driven, high-level optimization of Offshore Supply Vessel (OSV) operations in the Flemish Pass sector. This is an area located in the offshore waters of Newfoundland where significant oil discoveries were made in recent years, but where oil extraction will pose logistical challenges due to the increased distance from shore bases. In the first part of this paper, a simple non-linear programming model is used to minimize the monthly costs to supply a hypothetical offshore oil installation located in the Flemish Pass and to assess whether hypothetical fast supply vessels make economic sense. The second part of this paper explores the application of Pareto frontiers to the non-linear system, to evaluate the impact of schedule slack on costs, but also to look at winter operations in the Flemish Pass area.
Dynamic Particle Transport in Horizontal Pipes Based on Three-Layer Modeling: Simulation and Experimental Study
Authors: Petersen Johnny , Khatibi Milad , Time Rune Wiggo , Siahaan Hardy
Published: September 2018

A new 1D dynamic model was developed to predict the liquid-particle flow behavior in a horizontal pipe. The dynamic model combines three effects: steady-state solutions, the Bernoulli effect (due to local accelerations), as well as the flow separation and re-circulation zone occurring at the lee-side of a dune. Experiments of liquid-particle flow were conducted in a medium-scale flow loop, and the results were compared with the dynamic model. Two high-speed cameras were used to measure the particle dune characteristics, mainly length and height of the dune, as well as the particles velocity. Particles were spherical glass beads with median diameter of 0.3 and 1.2 mm. Water was used as test fluid, and the flow was fully turbulent. It was found that the model captured the essential physics of particle transport for the measurements reported, such as prediction of pressure drop fluctuations, as a function of both space and time.
The Effect of Blade Pitch and Reynolds Number on the Performance of Cross-Flow Turbines
Authors: Somoano Miguel , Huera-Huarte Francisco J.
Published: September 2018

In this work we studied experimentally the performance of a three straight-bladed Cross-Flow Turbine (CFT) based on symmetric NACA-0015 profiles, with a chord to rotor diameter ratio c/D = 0.16. The fixed pitch angle of the blades of the CFT can be changed, so experiments were carried out with a β = 0° and with a β = 8° toe-out blade pitch. Tests were made in a wind tunnel facility at three different turbine diameter Reynolds numbers in the range ReD = 3 · 105 – 5 · 105. The Tip Speed Ratios (TSRs) covered in the experiments went up to 2.6.

Results showed how as the Reynolds number based on the diameter of the turbine, had practically no effects on the performance of the CFT for the experiments conducted with β = 0°, in the case of β = 8° toe-out, the range of ReD covered a transitional region in which the torque produced by the blades overtook the aerodynamic resistive torque imposed by the arms (blade supports) of the CFT yielding high performances for the case with ReD = 5 · 105.
Ice Pressure Prediction Based on the Probabilistic Method for Ice-Going Vessels in Inland Waterways
Authors: Zhang Meng , Cheemakurthy Harsha , Ehlers Sören , von Bock und Polach R. U. Franz , Garme Karl , Burman Magnus
Published: September 2018

With increasing need to utilize inland waterways (IWW), the design for IWW vessels gains attention both from a transport efficiency and an emission control point of view. The primarily issue is to estimate the ice pressure acting on the ship hull for inland waterways. Ice information for Lake Mälaren is extracted and analysed in this work. Since the ice properties have great influence on the impact load, they are studied based on empirical formulae and are calibrated by reference data. The ice impact is then predicted for an inland water barge. Probabilistic method is selected to derive the load based on available field test data. Several parent datasets are chosen, and different design strategies are implemented to evaluate the ice impact load and investigate the influences from exposure factors. The paper finds that the design curve of α = 0.265a−0.57 can be used for Lake Mälaren. The approach itself introduces a possible way to investigate loads on ice affected IWW.
New Insight on the Effects of Reynolds Number in Vortex Induced Vibration
Authors: Gu Jian , Fernandes Antonio Carlos , Sales Joel Sena
Published: September 2018

So far, the influence of Reynolds number is not sufficiently investigated and it is often implicitly involved in the response plot versus reduced velocity. In the present article, a new dimensionless parameter α (named as “inertial-viscosity ratio”) is introduced for coordinating reduced velocity and Reynolds number. It is shown that individual Reynolds number effects can be explicitly clarified on different branches, through the coordination of α. Besides, this parameter is preliminarily shown to be capable of coordinating two systems with different structural scale, which is believed to potentially reduce the uncertainty caused by large gaps in Reynolds number between reduced model tests and prototype tests.
Cooperation of the Ports at the Time of the Large-Scale Disaster Such As High Tide and Tsunamis
Authors: Takahashi Koji
Published: September 2018

The Great East Japan Earthquake in Japan paralyzed functions of Japanese ports operated by the local governments in 2011. If an anticipated Nankai Trough Earthquake occurs, port functions may be paralyzed just as in 2011 under the current port operation system conducted by the local governments. Today, horizontal/vertical division of work has been expanded in the global economy, and thus, paralysis of Japanese port functions may result in severe damage on the global economy. Using the sacrifice model, the variation in container logistics caused by earthquakes was analyzed for the Nankai Trough Earthquake.

Through the case of Japan, it was demonstrated that the powerful leadership of the national government could establish port operations resistant to large-scale natural disasters.

This paper has developed the author’s research [1]–[13].
Study on the Failure Mechanism of Flexible Pipes Under Large Torsion Considering the Layer Interaction
Authors: Wu Shanghua , Yang Zhixun , Chen Jinlong , Lu Qingzhen , Yue Qianjin , Yan Jun , Gao Bo
Published: September 2018

Flexible pipe is the typical multi-layer structure which is designed to resist different loads when it is utilized under the severe deep-water environment. However, there is not any structural layer to withstand the torsion specially. Tension armors are only arranged to bear the tension with consideration of the torque balance. Especially, when flexible pipe is loaded out from the cargo vessel to the installation vessel, twist angle could be accumulated at high level so that all of layers need to resist the torsion. So, the failure mechanism is very complicated due to the interaction effect between different layers. Firstly, the interaction mechanism between layers of flexible pipes is analyzed under large torsion and some potential failure modes are identified, namely the strength failure and buckling failure of tensile armor, collapse failure of the inner layers. The theoretical descriptions of involved failure behaviors are investigated and the governing physical effects of failure modes are discussed. In addition, some failure criteria for predicting the pipe capacity are introduced. Finally, the methodology can be used to predict the flexible pipe torsional capacity and to prevent the torsional failure in engineering.
Experimental and Numerical Investigations Into Wave Run-Up on Fixed Surface-Piercing Square Column
Authors: Fang Zhichao , Xiao Longfei , Guo Yinghao , Yang Lijun , Lu Wenyue
Published: September 2018

This paper concerns the estimation of wave run-ups on a fixed surface-piercing square column. Experiments and numerical simulations were carried out under waves of different scattering parameters and steepnesses. The results of the run-up height ratio, force coefficient, velocity field, and scattered wave profile were shown and discussed. The reasonable agreement with the experimental results indicates the capability and reliability of the numerical model in the wave run-up prediction. The nonlinearity under short waves is mainly due to the interaction between the scattered waves and the next incident wave crest, while the wave-induced flow around the column becomes more influential under long waves. These nonlinearities are further intensified under steeper waves, and the run-up height ratio increases consequently. A correction factor of 1.2–1.3 can be applied to estimate the run-up height based on the linear potential prediction, but a higher factor of 1.3–1.4 is necessary under long and steep incident waves.
Research on Influence of Horizontal Offsets of Underwater Equipment Based on Pendulous Installation Method
Authors: Wang Jingqian , Sun Liping , Deng Zhongchao , Ma Gang , Zhu Xiaomeng , Hou Zhicheng
Published: September 2018

Large underwater equipment used in deep-sea engineering, which needs mooring line in order to hang down while using pendulous installation method in 1500m deep-water installation. During the procession, the mooring line will suffer the vessel’s pull, large equipment’s traction, fluid force leading to elongation, bending and other deformation, so need to analyze its motion. Aiming at the numerical simulation problem of underwater equipment installed by pendulous installation method in deep-water environment, this paper combines lumped mass method, three-dimensional potential theory and Morison equation to establish the analysis model of the whole installation system. Under the different horizontal dropping offsets of the equipment, this paper computes not only tension of mooring line, but motion performance of underwater equipment and working vessel during the pendulous lowering phase.

The Pendulous Installation Method (PIM) puts a working vessel, a mooring line and a underwater equipment installed in succession, and there is a coupling interaction among them, so it is essential to do time-domain coupling analysis. So the Orcaflex Software is used to simulate the entire deep-water installation system. Using different horizontal dropping position as a variable, we can get the contrast about the different movement states of the mooring line and underwater equipment, and finally we will get the conclusion.
Research Regarding the Conceptual Change Observed in the Sea City Concept
Authors: Sugahara Ryo , Kuroyanagi Akio
Published: September 2018

From the 1960th to 1980th years in the second half of the 20th century, numerous “sea city concepts” were proposed as a new city image. Among these concepts, in Japan, the sea city concept reflecting the current urban development situation of that time, was drawn by the architects as an image of the ideal city.

During that period, in Japan for the purpose of the further economic development, the landfilled industrial zones were created in the surroundings of large metropolitan areas of Tokyo, Osaka and Nagoya. It led to the concentration of the population due to the people fleeing to the big cities from the provinces for employment, which created various problems of big cities such as population overcrowding, land shortage, traffic jams, air pollution, etc., so the different tasks became apparent.

As a way to solve such problems, a sea city plan has been proposed. The oldest initiative was the Tokyo Bay concept of 1958 which proposed the creation of a new city by creating a new land by landfilling Tokyo Bay. However, that initiative only covered the expansion of the existing land, and didn’t make any advantage of “ocean” resources.

For that reason, the further proposals subsequently enabled taking advantage of the sea by creating the canals, artificial islands or pile-style structures which led to adoption of proposal to float up. After that, the sea city concepts basing on the floating type had increased, and the subjected water area transited from the shallow water to the offshore area.

Furthermore, the authors are planning to arrange the process of transition of the concept of the sea city by taking into account the changes the way oceans are treated and the structures relative to time.
A Simple Design Formula to Estimate the Ultimate Strength of Stiffened Panels Under Bi-Axial Compression Mainly in Transverse Direction
Authors: Komoriyama Yusuke , Yanagihara Daisuke
Published: September 2018

Most of stiffened panels subjected to bi-axial compression mainly in transverse direction collapse with the buckling deformation of one times one half-wave in a local panel between longitudinal stiffeners and transverse frames. The authors defined this collapse mode as “local panel buckling mode”. In this study, the collapse behavior of the stiffened panel with local panel buckling mode is investigated in detail. Then, a simple design formula to estimate ultimate strength of a stiffened panel with local panel buckling mode is derived based on the collapse behavior. This formula is composed of a formula to predict the ultimate strength of a rectangular unstiffened panel subjected to uniaxial transverse compression, and the effects of stiffeners, bi-axial compression and von Mises yield condition are added to the formula. The ultimate strength calculated by the proposed formula is in good agreement with FEA results. Finally, the proposed formula is compared with an existing method and formulae used in the CSR-OT, CSR-BC and H-CSR. As a result, it is confirmed that the proposed formula has sufficient accuracy and high availability.
Analysis of Numerical Errors of the Hess Smith Panel Method With Asymmetric Meshes
Authors: Ren Huilong , Xu Chen , Zhou Xueqian , Sutulo Serge , Guedes Soares Carlos , Li Chenfeng
Published: September 2018

Although less accurate in comparison with most of the existing high-order panel methods, the Class Hess Smith panel method is still popular for potential flow calculations due to its simplicity, robustness, and especially efficiency. In the application where the method is adopted for the problems in concern, the method is usually first validated and analyzed for numerical accuracy prior to the application. This is a common practice as also seen in almost all the literature. However, the objects chosen for validation and accuracy analysis are often geometrically symmetric (most typically, spheres) and discretized into symmetric meshes. However, such analysis with symmetric meshes does not actually reveal the numerical errors as the body involved in the problem in concern or the flow around the body may not be symmetrical. In this paper, the numerical errors of the Hess Smith method are systematically analyzed with asymmetrical meshes. The values of various quantities associated with isolated panels and also the entire body are obtained and compared with the Hess Smith panel method does exhibit a very different error pattern.
Modelling and Simulation of Moored-Floating Structures Using the Tension-Element-Method
Authors: Martin Tobias , Kamath Arun , Bihs Hans
Published: September 2018

The application of a discrete mooring model for floating structures is presented in this paper. The method predicts the steady-state solution for the shape of an elastic cable and the tension forces under consideration of static loads. It is based on a discretization of the cable in mass points connected with straight but elastic bars. The successive approximation is applied to the resulting system of equations which leads to a significant reduction of the matrix size in comparison to the matrix of a Newton-Raphson method. The mooring model is implemented in the open-source CFD model REEF3D. The solver has been used to study various problems in the field of wave hydrodynamics and fluid-structure interaction. It includes floating structures through a level set function and captures its motion using Newton and Euler equations in 6DOF. The fluid-structure interaction is solved explicitly using an immersed boundary method based on the ghost cell method. The applications show the accuracy of the solver and effects of mooring on the motion of floating structures.
Nonlinear Strain Estimation Based on Linear Parameters
Authors: Nabuco Bruna , Friis Tobias , Tarpø Marius , Amador Sandro , Katsanos Evangelos I. , Brincker Rune
Published: September 2018

This paper aims to demonstrate how to estimate strains of fixed structures considering cases with nonlinearities based on parameters determined from one linear case. Both simulated and experimental data have been evaluated. A finite element model was used to obtain the simulated responses. Accelerations and strains were measured along the application of random loading to a fixed structural model for the experimental data. Operational Modal Analysis has been considered in the time domain in order to identify the modal properties. Nonlinearities are included as friction is imposed on the models.
Simulation-Based Tracking of UOE Pipe Yield Strength Considering Various Thickness-to-Diameter Ratios
Authors: Yi Jiwoon , Kang Soo-Chang , Koh Hyun-Moo , Choo Jinkyo F.
Published: September 2018

The plastic forming processes involved in the production of UOE pipes alter significantly the yield strength of the original steel plate. Numerous studies indicated that the work hardening and Bauschinger effect are the main factors influencing the alteration of the yield strength. Moreover, apart from the forming process itself, the flattening executed on strips sampled from the formed pipe appears to have also nonnegligible effect on the final yield strength that is used as quality index of the formed pipe. Therefore, this study tracks the yield strength of UOE pipe made of API-X70 steel with various thickness-to-diameter ratios by FE-simulation of the forming and flattening processes so as to identify the factors influencing the yield strength of the UOE pipe. The results show that the flattening process constitutes a critical phase in which steel experiences large loss of its tensile yield strength.
Comparisons Between the Typical Wind Shear and the Wind Shear Induced by Platform Pitch Motion for an Offshore Floating Wind Turbine
Authors: Wen Binrong , Zhang Qi , Wei Sha , Tian Xinliang , Dong Xingjian , Peng Zhike
Published: September 2018

The pitch motion of the Offshore Floating Wind Turbine (OFWT) introduces additional wind speed to the rotor. The additional wind speed distributes linearly along the vertical altitude, which is called as the platform-pitch-induced wind shear effect in this paper. Comparisons between the typical wind shear and the platform-pitch-induced wind shear are conducted with the Free Vortex Method (FVM) for the NREL 5MW baseline wind turbine. It is found that the platform-pitch-induced wind shear is the results of the rotor rotating and platform pitching, and its wind speed profile is time-varying. At the designed point of tip speed ratio of 7, the averaged power output is reduced slightly under the typical wind shear while it is increased by 4% under the platform-pitch-induced wind shear. The aerodynamic loads of the OFWT under the platform pitch-induced wind shear experience much more considerable variations than the typical wind shear, which introduce severer fatigue damages to the OFWT components. For the sake of the safety of the OFWT, advanced control strategy and superior design should be developed to mitigate the platform pitch motion.
Cargo-Flow-Oriented Design of Supply Vessel Operating in Ice Conditions
Authors: Kondratenko Aleksander A. , Tarovik Oleg V.
Published: September 2018

Due to the dynamic development of the oil and gas fields in the Arctic, the challenges of supply fleet sizing and composition in this region are becoming relevant. In most studies, the Arctic is mainly associated with ice conditions, but it is not the only factor that influences the design of platform supply vessels (PSV) and corresponding marine transport systems (MTS) for this region. The structure of cargo flow (i.e. its distribution by cargo types) affects the supply system significantly. It defines the level of utilization of vessel capacity that determines transport efficiency. At the same time, the literature represents this aspect poorly.

This paper describes an approach to optimize supply fleet configuration by the criterion of total cost considering both non-stationary ice conditions and structure of cargo flows. The cargo-flow-oriented design concept incorporates the detailed calculation model of PSV and the special tactical planning algorithm. PSV model allows considering the influence of cargo spaces on the main characteristics and operational parameters of the ship. It covers the main design aspects of PSVs: general arrangement; lines plan; resistance in open water and ice; engine and propeller characteristics; hydrostatics; capacity and mass calculation. The pseudo-optimal tactical planning algorithm is intended to build the plan of voyages and to set the size of fleet considering the structure of cargo flow.

As the test example, we examine a task of servicing the group of platforms in the Kara Sea. The case study shows that cargo flow structure has a high influence on the efficiency of PSVs in case of high-load operation; while a widespread “deck-cargo” approach is unable to consider this aspect because it ignores the vessel’s carrying capacity and payload. The conclusion about a higher efficiency of PSV compared to AHTS with the same displacement was drawn.
Wave Load Acting on Advanced Spar in Regular Waves
Authors: Hirai Takayuki , Sou Akira , Nihei Yasunori
Published: September 2018

Offshore wind turbines have been investigated and developed as one of the renewable energies. In Japan, the research and development of floating type offshore wind turbines have been carried out because the water around the country is too deep to settle the bottom mounted type.

In this paper, we investigate the effects of the diameter of the column floater of the advanced spar in regular wave by using open source computational fluid dynamics software OpenFOAM. We use olaFOAM which equipped with the functions to set the boundary conditions of wave generation at the inlet and wave absorption at the outlet. The forces acting on a spar obtained by the numerical simulation and Morison’s equation are compared to examine the validity of the numerical model. A good agreement between them confirms the validity of the numerical method. Then we simulate numerically the effects of the column diameter on the flow around the advanced spars and the wave load. The result clarifies that Morison’s equation overestimates the wave force, and the difference increases with the column diameter. For more detailed analysis we divide the advanced spar into three parts, the upper spar above the column, the column floater and the lower spar below the column. As a result, we find that the difference between the wave load acting on the column by Morison’s equation and that by numerical simulation is dominant due to the flow separation around the column. Finally we modify the load coefficients of Morison’s equation for the column so that the modified equation can accurately evaluate the wave load acting on the advanced spar.
Cuttings Bed Removal in Deviated Wells
Authors: Ytrehus Jan David , Lund Bjørnar , Taghipour Ali , Kosberg Birgitte Ruud , Carazza Luca , Gyland Knud Richard , Saasen Arild
Published: September 2018

A drilling fluid for drilling deviated wellbores must provide adequate hole cleaning efficiency for all well angles relevant to the operation. For angles near vertical, experience show that hole cleaning is straight forward. In wellbore angles larger than, say, 45 degrees hole cleaning is more difficult. Cuttings beds are formed and at some well angles these beds may avalanche during circulation stops etc.

This paper presents results from laboratory tests with injected cuttings using a low viscosity oil based drilling fluid with micronized grained barite as weight material. The fluid is designed for highly deviated wells with low ECD requirements and the cuttings transport performance through relevant wellbore inclinations was investigated.

The experiments have been performed under realistic conditions. The flow loop includes a 10 meters long test section with 2” OD freely rotating steel drill string inside a 4” ID wellbore made of steel, representing a cased wellbore. Sand particles were injected while circulating the drilling fluid through the test section. Experiments were performed in three wellbore inclinations: 48, 60 and 90 degrees from vertical.

Results show that hole cleaning in absence of drill pipe rotation is significantly improved if the well angle is less than a critical angle. This critical angle appears to be less than 60 degrees from vertical. Further result show that this critical inclination angle is dependent to the drill string rotation rate and the annular flow velocity.
Design Analysis and Fatigue Testing of the Typical Structural Details of Aluminium Ships
Authors: Ren Huilong , Ma Kaikai , Li Chenfeng , Zhang Zhichao , Xu Weijun , Feng Guoqing
Published: September 2018

Aluminium alloy is widely used structural design in light-weighting design. Due to the material strength loss in welding, fatigue strength of typical joints fabricated by aluminium alloy is more sensitive than steel joints. The aim of this study is to investigate one aluminium detail of the longitudinal through the transverse, with high-performance of fatigue strength compared to the original design. The alloy of longitudinal is AA6082-T6 and the other components (including plate and transverse) is AA5083-H2. Firstly, eight schemes of structural details with various configurations of bracket and / or stiffener are designed. Based on the finite element analyses, the stress distribution of panels with eight designed details is obtained under typical loading condition respectively. According to the principle of hot spot stress being minimum, the optimal detail is determined, which using stiffener reinforced on both sides of transverse. Secondly, the fatigue tests of the optimal detail were designed and carried out. The testing panels consist of 2-span and 3 longitudinal stiffeners, and the frame with optimal joints is located in the middle of the panels. The test panels were simply supported at two ends with applied cyclic loading in the middle panel. According to the designed loading scheme (loading level, frequency, etc.), the fatigue tests of the panels with typical detail were carried out. The hot stress and the cycle times of the typical detail under different load levels were obtained. Based on the test data, the S-N curve of the typical detail in aluminium alloy is established. Finally, the fatigue strength assessment of the typical detail in target ship is performed based on the Miner’s linear cumulative damage theory and established S-N curve. The results show that the fatigue life of proposed optimal detail meets the design requirements of the target ship. The S-N curve of the typical detail made of AA6082-T6 obtained in this study can be also used for other aluminium ships with similar structural details.
Survey Research on Legal System of Floating Residence and on Management of Water Utilization in the United States: Case Study on Seattle, Washington and Sausalito, California
Authors: Dobashi Daisuke , Kuroyanagi Akio , Sugahara Ryo
Published: September 2018

Effective utilization of oceanic space in Japan is just recent compared to U.S. Since the end of 19th century, water utilization and management for residence constructed on lake was promoted in U.S.

It is then the aim of this paper to comprehend the laws and regulations for floating residence as well as water utilization and management of United States.

Through web survey, each State in United States will be searched if there are existing laws and regulation on floating residence.

After searching and reading all conditions of the U.S. States regarding laws and regulation as well as legal positions on floating residence, two states in the west coast of U.S: Seattle in Washington and Sausalito, California are chosen for this study. Floating residence in U.S. are divided into two; the Floating Homes and Houseboats. Floating Homes are handled by law the same with homes built in land while Houseboats are treated as type of ship. The State managing the water will lease it to the private sector, then, building of Floating Home will be carried out. Furthermore, design and construction of Floating Homes follow the building standards of the counties and cities where it will be built.
Steady and Unsteady Hydrodynamics of Different Shapes of Slender Drift Anchors With a Lattice Boltzmann Approach
Authors: Dommergues Bénédicte , Sainte-Rose Bruno , Abiza Zaki
Published: September 2018

The Ocean Cleanup designs floating systems to intercept and accumulate plastic marine debris by having a relative velocity towards the plastic drifting with the sea-surface current of the oceans. One of the solutions to create such a velocity difference is by the mean of drift anchors located in a deeper and slower water layer therefore slowing down the system. As a basic design, two main shapes are being investigated: a punctured cylindrical pipe and a cross shape.

In order to compare the general hydrodynamic behavior and the influence of the holes pattern of the different anchor designs, a CFD study is carried out using a Lattice Boltzmann approach in order to characterize the in-line and cross-flow hydrodynamic coefficients.
Dynamic Response Analysis on Flexible Riser With Different Configurations in Deep-Water Based on FEM Simulation
Authors: Guo Shuangxi , Li Yilun , Li Min , Chen Weimin , Kong Yue
Published: September 2018

For case of oil/gas exploitation and mining in deep water, the length of riser is pretty large and, consequently, it brings huge challenges in both offshore installation and production operations and results in significant cost elevation due to the factors such as extreme tension loads induced from riser suspended self-weight and large structural flexibility. Therefore, there are several alternative riser configurations, e.g. lazy wave, hybrid tower and lazy-wave riser beside free hanging catenary, which have been proposed. In this paper, the dynamic characteristics and responses of several risers with typical configurations are considered and compared with each other based on our numerical simulations. Firstly, the nonlinear dynamic model of the riser systems are developed based on our 3d dynamic riser equations along with the modified FEM simulations. Then the dynamic response is analyzed based on our 3d curved flexible beam approach where the structural curvature changes with its spatial position and time in terms of vector equations. Compared with the linear approach, the nonlinear FEM method is used so as to consider large displacement/deformation, configuration geometry and structural stiffness changing with body motion. Moreover, the hydrodynamic force is considered as being related to body motion too.

Based on the FEM numerical simulations, the influences of the amplitude/frequency of the top vessel motion along with the buoyancy modules/tower distribution along structural length on riser’s dynamic responses, in terms of the temporal-spatial evolution of displacement, curvature/bending stress and dynamic tension, are studied for different riser’s configurations. Our results show that the dynamic responses, particularly the maximum top tension, of different riser systems significantly change. Among the examined riser configurations, the response of the riser with more buoyancy modules may have lower value, and buoyancy distribution along structural length can influence the top tension and curvature.
A Comparison of Response-Based Analysis and Environmental Contour Methods for FPSO Green Water Assessment
Authors: Wang Shuo , Wang Xin , Woo Wai Lok
Published: September 2018

Response-based green water analysis is carried out on an FPSO model with complicated effects of appendages and attachments. An efficient numerical approach developed and validated in our previous work is adopted in this study to evaluate the green water on FPSO, considering effects from bilge keel, spread mooring and portside risers in frequency domain. To accelerate the numerical study, an artificial neural network (ANN) is developed for nonlinear interpolation. Comparisons are made between relative wave elevation results from response-based analysis and traditional contour line approach using DNV and HDC methods. The response-based analysis using nonlinear model and simplified linear model are also compared to examine if nonlinear effect due to appendages and attachments on FPSO would affect the accuracy of response based analysis.
Stability of Compressive Residual Stress Introduced by HFMI Technique
Authors: Ruiz Valdes Hector Olmedo , Osawa Naoki , Murakawa Hidekazu , Rashed Sherif
Published: September 2018

Fatigue strength of welded structures is affected by welding residual stresses, which influence crack propagation at weld toe or root, considerably reducing the effectiveness of the structure and increasing its construction and maintenance costs. A mechanical post-weld treatment such as HFMI (High-Frequency Mechanical Impact) has been found to exhibit a significant fatigue life enhancement of welded joints.

The effectiveness of this mechanical impact treatment is primarily based on the combination of three effects: improvement of the local work hardening, introduction of compressive residual stresses and closing of notches at the weld toe. However, several aspects of this treatment need to be clarified or further investigated. Many researchers are focused on HFMI-treatment, simulating the impact of the peening tool at the weld toe. The present study focuses on the stability of compressive residual stresses introduced by HFMI-treatment when a cyclic load is applied on a gusset welded joint. Peening response of a flat stress-free-plate, under different peening process parameters is also investigated. Furthermore, comparisons of HFMI with other peening techniques are carried out to clarify which technique is the most reliable.

The validity of the present study is demonstrated by comparison with experimental residual stress measurements.
A Study on the Stochastic Aspects of the Whipping Vibrations in a Container Ship
Authors: De Gracia Luis , Osawa Naoki , Iijima Kazuhiro , Fukasawa Toichi , Tamaru Hitoi
Published: September 2018

The container carriers represent a challenge in the design process, where an important role play the estimation of design loads and their response. The wave-induced vibrations are often referred to as whipping as a transient phenomenon due to wave impacts and springing as a resonance phenomenon due to oscillating loads. These hydro-elastic vibratory phenomena’s are the most important consequences of the continuous increase in the ship length and low stiffness of the hull girder. While this is a concern in the marine industry, this phenomenon is not clearly considered in the design. Therefore, there are uncertainties associated with the wave-induced vibration intensity and the probability of occurrence of whipping to the sea state that needs to be clarified.

This paper address the effect of the relationship of the characteristics of whipping vibration to the sea state, evaluating the results of a series of time-domain computational simulations. A numerical method that combines a three-dimensional panel method and FEA proposed by one of the co-authors is employed for evaluating the load effects. The calculations are performed for the respective short-term sea states. This study presents the probability of occurrence and vibration intensity of the whipping vibration experienced by a 6500 TEU container carrier in a North Atlantic Ocean route.