bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Hydrodynamic Analysis of Dolphin Fluke Motion With a Flexible Tail
Authors: Chen Xi , Yang Wenjing , Yu Jiawei , Feng Dakui , Wu Yongfeng 
Published: November 2019

Abstract
This paper studies the effect of the the caudal fin superimposed chordwise deformation on the propulsion performance. The calculation results show that the appropriate chord deformation of the caudal fin can effectively increase the propulsion efficiency. It describes the shape change of dolphin tail by mathematical formula, and studies the propulsion performance of dolphin tail by numerical method combined with morphing mesh technology. The quasi-propulsive efficiency is used to evaluate the propulsive efficiency of self-propelled objects. The results show that the active deformation of the caudal fin can effectively increase the propulsive efficiency and provide a theoretical basis for the design of the flapping bionic propeller.
Analysis of the Momentum Transfer Operated by the Breaking in Modulated Wave Trains in Wind and No-Wind Conditions
Authors: Iafrati Alessandro , Falchi Massimo 
Published: November 2019

Abstract
An analysis of the flow and of the vertical transfer of the horizontal momentum induced by the breaking of modulated wave trains in wind and no-wind conditions is presented. The study is based on the results of two-dimensional numerical simulation of the Navier-Stokes equations for two-phase flow. The open source Gerris flow solver has been used, which employs a Volume of Fluid technique to capture the air-water interface.
The breaking is induced through the Benjamin-Feir instability mechanism. The numerical simulations cover the entire range from the initial development of the instability, the breaking phase and the post-breaking evolution. In order to investigate the role played by the wind, a uniform wind profile, twice the phase speed, is initialized in the air phase and it is left to evolve while interacting with the wave system.
Results in terms of averaged horizontal velocity and vertical flux of horizontal momentum are presented. It is shown that in the wind case the backward stresses induced at the wave troughs as a consequence of the flow separation at the crest influence significantly the flow in the upper water layer, particularly in the pre-breaking phase. No substantial differences are found between the wind and no-wind solutions in terms of the vertical transfer of horizontal momentum in the lower water layer. The vertical flux of horizontal momentum in air is consistent with the velocity reduction occurring in the wind case in the early stage.
Ice Model Tests for Semi-Submersible Platforms in Pack Ice Conditions
Authors: Luping Liu , Xin Li , Xiao Wu , Bo Wu 
Published: November 2019

Abstract
As development of the Arctic grows in intensity, semi-submersible platforms are one of promising type of offshore structures used for arctic oil exploitation. Generally a good ice management is equipped by a moored floating platform to reduce ice loads to manageable levels, thus the most common scenario for a polar operating semi-submersible platform is pack ice conditions. The resistance test of a 4-columns structure is performed in a normal towing tank in China using synthetic non-refrigerated material with similar density to model sea ice. Three component load cells on top of each column and a batch of single component load cells embedded in the surface of the columns near the waterline are used to measure indirect and direct ice loads on the structures. The effects of a series of parameters such as column shapes, orientations, column spacing ratios, ice floe shapes, ice drift speeds and ice concentrations are analyzed.
Mitigated Riser Response During Submerged BOP Move Through Use of Drillstring Active Heave Compensation System
Authors: Sevillano Lucas Cantinelli , Morooka Celso Kazuyuki , Sangesland Sigbjørn 
Published: November 2019

Abstract
Rig costs account for a substantial part of the total cost of an offshore field development project. Systems and methods that can reduce the non-productive time are therefore of interest to operators. In deep and ultra-deep waters, the duration of drilling campaigns with multiple, closely located wells may potentially be reduced by optimizing equipment-retrieving procedures between moving from one drilling location to another. This may be achieved by not retrieving the whole drilling riser and the BOP to the surface. Instead, retrieving just a few joints and navigating the drilling rig with the drilling riser and BOP suspended may save several days of rig time.
Previous works on this topic have investigated the riser response during the move and delineated under which environmental conditions (waves and current) this operation may be safely executed. The axial displacement of the riser column may be of concern, and it has been presented that the hang-off condition may substantially influence the response of the riser. Instead of looking at the riser hanging either from the spider-gimbal or from the tensioners, this work proposes to use the active heave compensation system of the drillstring to more efficiently decouple motions of the rig from the riser during the move. Thus, mitigating the riser response and enabling the navigation with the suspended riser and BOP to take place under broader environmental conditions.
A commercial program for computational simulations of the riser dynamic responses was used in the study presented in this paper. A representation of the active heave compensation drilling system and the tool used to achieve this purpose were added to the model. The responses of a typical riser used in deep water were determined under several environmental conditions, and the responses of different hanging systems were compared. Results indicate that the proposed approach for suspending the riser may decrease the dynamic forces and stresses during the rig move. The ability of the modeled rig equipment to withstand the move was also investigated.
Improvement on Toughness of Weld Heat Affected Zone of Cu-Containing Low Alloy Steel of Long Scale Forging for Offshore Applications by Optimizing Chemical Composition
Authors: Honma Yuta , Sasaki Gen , Hashi Kunihiko , Minami Fumiyoshi 
Published: November 2019

Abstract
Copper-containing low alloy steel based on ASTM A707 5L grade is widely used for structural parts of offshore wells. Applications of the steel for Ultra-deepwater development require excellent low temperature toughness from the viewpoint of marine accident prevention. However it is difficult to stably obtain good weld joint toughness because the welding condition is inevitably scattering. With those backgrounds, this paper focuses on metallurgical factors controlling the HAZ toughness of A707 modified steel. Potential factors considered are the grain size, M-A and precipitates. A challenge is demonstrated to improve the HAZ toughness by optimizing the Cu and Mn contents.
In this study, we investigated mechanical properties including crack tip opening displacement (CTOD) and we observed microstructure using welding tests or various weld heat cycle specimens. The weld heat affected zone (HAZ) of a conventional material had good toughness for the low heat input condition. However it was remarkably decreased for the high heat input condition due to the precipitating martensite-austenite constituent (M-A) in local brittle zones (LBZ).
The weld test results indicated the importance of suppressing the formation of M-A in order to improve toughness in the HAZ of the steel. Thereby, we challenged the optimization of chemical composition for HAZ toughness improvement. Cu had no bad influence on the HAZ toughness. It was demonstrated that the HAZ toughness is recovered by good use of Cu precipitates in SC cycle. Moreover the area fraction of M-A is decreased in keeping with Mn content, which leads to the improvement of the ICCG HAZ toughness. Based on our study, the recommended amounts of Cu and Mn are more than 1.0 mass% and less than 0.6 mass%, respectively, to ensure the HAZ toughness, especially ICCG HAZ toughness.
Multi-Focused Wave Groups in Wave Flume
Authors: Fang Qinghe , Zhao Cunbao , Guo Anxin 
Published: November 2019

Abstract
People can simulate extreme hydrodynamic conditions in a laboratory facility by interfering a numbers of regular waves at a certain point in space and time, which is focused wave. It is obviously higher and steeper than any other wave, e.g. regular or irregular waves, within the propagating wave group. The focused wave occurs at a designed point both in space and time. It represents an event with a large return period which would take a long time to reproduce within a random wave sequence. The focused wave, representing of a large wave occurring in a random sea, is quite frequently used to investigate wave loading on marine or coastal structures. However, most research only employ one single focused wave group. Taking the randomness of the wave-structure interaction, repeated tests would be suggested by some textbooks or codes to eliminate the odd results. However, it would take more time to conduct those tests no matter in the laboratory or in the numerical simulations.
In our present work, we use a novel method to experimentally generate several focused wave group with different focus time but same focus point at the same time to obtain multi-focused wave groups. The wave elevation and water particle kinematics are measured. The influence of peak frequency, frequency resolution and period of focused wave group are checked and discussed. The results show that present method can generate stable and repeatable focused wave groups in the wave flume.
Analysis of Heat Transfer Performance for Deepwater Phase Change Material Sandwich Pipes
Authors: An Chen , Wang Hui , Duan Menglan 
Published: November 2019

Abstract
As the exploitation of oil and gas gradually enters the deep sea, the low-temperature and high-pressure deep-sea environment poses a huge challenge to the flow protection of pipelines (2014a). In this paper, the phase change material sandwich pipeline which uses phase change heat storage and exothermic to maintain the pipeline temperature is taken as the research object, the heat transfer characteristics of the deep-water phase change material sandwich pipe are studied through the combination of theoretical analysis and numerical simulation (2014b). The main contents include: Firstly, through the establishment of two-dimensional and three-dimensional pipe models, analyzed the temperature distribution along the pipeline and the radial temperature distribution of the pipeline under steady oil flow conditions. Secondly, by using transient heat transfer, the effects of phase change material parameters, the proportion of phase change material in the insulation layer, and the difference in the ratio of phase change materials in the insulation layer on the insulation performance are analyzed to obtain the best results. Insulation material and optimal insulation layer layout; finally, the thermal storage and the phase change conditions of the phase-change material sandwich pipe is studied under the re-starting condition. The results show that the effective holding time of the phase change material insulation layer is close to 1.4 times that the non-phase change material insulation layer, and the melting point size has little effect on the insulation material. The closer the phase change material is to the inner tube, the better the insulation effect. This study provide guidance for the design and utilization of phase change material sandwich pipe.
Effect of the Wind Drag Estimation Methods on Numerical Storm Surge Modeling
Authors: Shankar C. Gowri , Behera Manasa Ranjan 
Published: November 2019

Abstract
Tropical cyclones have always proved the extent of its catastrophe on several occurrences over the years. In particular, the Bay of Bengal (BoB) basin in the Northern Indian Ocean has produced such historic devastating events, thereby mandating accurate real-time predictions. Numerical modeling of storm surge has always been an arduous task, as it is integrated with various uncertain factors. Among those, the major governing component being the wind forcing or the wind stress — that signifies, the computational accuracy of simulated surge and wave parameters. The present study is aimed at analysing the most suited wind drag evaluation method for real-time predictions of storm surge along the BoB. Cyclone Phailin (2013) was considered for the numerical simulations. To evaluate the wind drag coefficient, three most extensively used linear empirical relations along with the enhanced Wave Boundary Layer Model (e_WBLM) were used. The surge was subsequently simulated (using the coupled hydrodynamic circulation and wave model: ADCIRC and SWAN, respectively), individually for each of the above wind stress methods to obtain the corresponding storm surge (residual) and the storm wave features. The modeled values were further validated with the in-situ data obtained from tide gauge station and buoys respectively. It was quite intuitively observed that, e_WBLM based results correlated well with the in-situ values than its linear counterparts since, the former pragmatically includes the effects of air-sea interaction at high wind speeds in the model. The e_WBLM-based computation of significant wave heights (Hs) in deep as well as shallow water, nevertheless enabled efficient and reasonably-reliable estimations of the peak incidents.
Power Spectrum for Surface Description of Corroded Ship Structure From Laser Scan
Authors: Neumann Karoline M. , Ehlers Sören 
Published: November 2019

Abstract
Strength of corroded marine structures is in the industry traditionally assessed using average thickness reduction together with the assumption of a uniform surface. In academia it is however realised that the surface texture will influence the strength where the effect of the irregular surface is considered through various parameters such as reduced material properties, roughness, geometrical ratios and thickness distributions. In this paper, the objective is to present a power spectrum which describes the corroded surface topography. Therefore, power spectra of surface and thickness are produced from 3D laser scan of real corroded mild steel specimens from a 30 year old ship using Fast Fourier Transform (FFT). The frequency distribution describes the spatial variability, wherefrom the autocorrelation function (ACF) is deduced. A log-log fit is made to the power spectrum, where the interception with the ordinate axis describes the corrosion severity. This way of describing the surface pattern of the corrosion deterioration may serve as input to novel ways of calculating corroded strength and fatigue initiation as well as simulation of corroded surfaces.
Fatigue Life Estimation for HFMI Treated Weldments Considering Weld Toe Magnification Factor
Authors: Kim Dong Yub , Kim Myung Hyun 
Published: November 2019

Abstract
HFMI (High-Frequency Mechanical Impact) post-treatment is a statistically proven method to significantly improve fatigue life of welded structures. Positive effects of improved fatigue life by the HFMI treatment are attributed to the weld toe geometry and the compressive residual stress. This study investigates the effect of geometric and mechanical effects by HFMI treatment on fatigue life with an explicit consideration of the weld magnification factor Mk.
The conventional fatigue life estimation method to assess the effect of HFMI treatment by an experiment and analysis involves significant expense and time. In this regard, this study suggests an improved method by using Mk weld magnification factor and the stress ratio to assess the effect of HFMI post-treatment in more efficient manner. First step of this method is to calculate Mk weld magnification factor in HFMI treated condition to consider the geometrical effect by HFMI treatment at weld toe region. Second, the stress ratio model is introduced to consider the compressive residual stress by HFMI treatment based on Paris equation. The result is obtained by Paris-Erdogan equation for a S355 material. The result from this study is validated by a comparison with a previous fatigue test of HFMI treated welded specimen.
A Basic Study on Influence of Airchamber Volume on OWC Models to Power Conversion Performance
Authors: Ikoma Tomoki , Kihara Yoshiyuki , Hirai Shota , Aida Yasuhiro , Masuda Koichi , Eto Hiroaki 
Published: November 2019

Abstract
Oscillating water column (OWC) types of wave energy converters have still several issues to be studied because system including wave-air-turbine interaction is complex. Besides, scale effects between small scale models and full scale models have not been definite. Although the effect in initial design of OWC devices might been able to be ignored, it is important to understand its characteristics exactly. The present study carried out forced oscillation tests in a water tank corresponding to the radiation problem. Three models whose scale are 1/1, 1/2 and 1/4 were used. In the forced oscillation test, we measured mean water elevation in an airchamber to predict the air flow rate and air pressure inside of the airchamber. From the mean water elevation and the air pressure, the primary power conversion was calculated. As a result, the pressure and the elevation were affected by not only the scale reduction but also the difference of airchamber volume. Variation of the volume of an airchamber affected on hydrodynamic performance sensitively.
The Design and Simulation of Hull Segmentation Docking and Correcting Hydraulic System
Authors: Zeng Yuhao , Yu Zuyao , Xu Tang 
Published: November 2019

Abstract
A hydraulic system for large cylindrical hull segmentation docking and correcting is developed. This system measures the roundness error of the hull before the welding phase and then corrects it by cold-pressed deformation and hydraulically locked until the end of the welding. The automation of the hull docking and correcting is implemented, the work efficiency and the accuracy of the hull manufacturing are improved. The design of the hydraulic system for docking and correcting and the simulation of it in AMESim are mainly introduced in this paper.
An Improved Methodology to Assess Weldability of Line Pipe Steels
Authors: Alleva Laura , Monti Mauro , Paravicini Bagliani Emanuele , Paggi Alessandro , Darcis Philippe 
Published: November 2019

Abstract
The exploration of oil & gas fields towards more demanding environments require the continuous development of line pipe steels capable to withstand severe working conditions (high pressure, high temperature, sour environment, large deformations) maintaining good weldability in terms of hardness control in the Heat Affected Zone (HAZ). Therefore, the response to welding thermal cycles needs to be taken into account since the first steps of the product development. This paper describes a methodology to ascertain the weldability of new line pipe steels.
A matrix of welding trials, based on different welding technologies, was designed; the manufactured welds were assessed in terms of hardness and microstructure using standard and non-standard approach.
Gas Tungsten Arc Welding (GTAW) cold wire technique with anthropomorphic robot was selected as principal process, being extremely robust, accurate and repeatable and able to reproduce with good accuracy the thermal field of different arc welding operations. Furthermore, GTAW process permits to manage separately the so called “Arc Energy” (Volt*Ampere) and wire feeding: this additional degree of freedom gives the possibility to produce different combinations of Heat Inputs and Diluting Ratios. Single and multi-pass bead on plates (WT∼40mm) with no pre-heating were used to promote high restrained configurations and high residual stresses to reproduce the worst welding condition. Furthermore bead on plate have been performed by Nd:YAG laser to generate fastest cooling rates and narrowest welding pools.
The investigation activity was performed according to the API RP 2Z for what concerns the characterization of the main Heat Affected Zone both for single and multi-pass. For the individuation and investigation of the HAZ sub-zones a thermal model has been selected, validated by dedicated instrumented welding activity and used to predict the thermal cycle in selected points/zones of the HAZ (e.g. CGHAZ, FGHAZ...).
In depth metallographic/hardness analysis was performed on the welded samples using non-standard methods: low, medium and high magnification optical microscope analysis to generate a complete morphological map, suitable hardness paths with low and standard loads along the main direction of heat propagation in the bead and “tint etching” to better individuate the phase fractions of the different sub-zones of the HAZ.
Finally, proprietary and commercial predictive tools, using different input parameters (e.g. heat input, cooling rate, composition...) were used to calculate hardness and phase fractions under the experimental operative conditions. Results were compared to those obtained by the experimental activity.
A Hybrid Power Generation Platform Combining Floating Wind Turbine and Oscillating Water Column Wave Energy Converters
Authors: Chen Zheng , Zeng Weijian , Tan Ming , Zhang Dahai , Si Yulin 
Published: November 2019

Abstract
Recent years have seen rapid development in offshore wind technology. Particularly, floating offshore wind turbines possess great potential in deep water coastal places around the world, though they are now still in the demonstration phase. At the same time, the unused wave energy is also abundant at the sites of offshore wind farms, especially those in deep sea regions. Collecting wave energy in offshore wind farms might benefit both total energy production and reduce maintenance cost. Therefore, integrating offshore wind turbine with wave energy conversion devices could be a good idea to achieve higher efficiency and lower cost.
In this paper, we report a combined wind and wave energy power generation concept called WindOWC, which constits of a 5MW wind turbine and three oscillating-water-column (OWC) wave energy converters (WECs). The wind turbine is mounted on a semi-submersible floating platform, which is similar to OC4-semibsubmersible, and the OWCs are located in its three offset columns. In this design, the wind turbine and WECs share the same supporting platform and the power transmission system, thus is expected to reduce the cost of energy. Also, it is possible the OWCs may improve the platform dynamic performance by providing positive damping through controlling the air turbine rotational speed. In this work, we describe the geometry properties of the proposed WindOWC concept and conduct preliminary hydrodynamic analysis using potential flow theory. The ANSYS AQWA is used to obtain the system dynamic responses in frequency and time domain, respectively. The OWC dynamics and expected positive damping from them will be investigated in the future.