bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Simulation of Hydrodynamic Performance of Dolphin Fluke Motion
Authors: Li Rijie , Chen Jiajun , Huang Yushen , Liu Liwei , Wang Xianzhou 
Published: September 2018

The dolphins’ cruising, generally, with an extremely high thrust efficiency and low drag, which attracted many researchers’ wide attention. It is hoped that we can improve the hydrodynamic performance of underwater vehicle by studying the thrust characteristics of dolphin’s kick and the relationship between the formation of vortex and the thrust generation. However, previous work is mostly focused on investigation of hydrodynamic performance of dolphin fluke motion with a rigid tail which means that the locomotion of caudal fin is defined only by the oscillating motion, without the chordwise deformation. In this paper, the dolphin’s fluke motion is realized by a flexible caudal fin which is defined by a combination of oscillating motion and chordwise deformation.
The simulation of the dolphin fluke motion is achieved by STRA-CCM, and dynamic moving mesh is implemented for different stroke functions. This paper primarily analyzed the thrust characteristics and the formation of vortex of dolphin fluke motion, then compared with the available data from previous work with rigid tail. It can be found that the structure of the vortex generated by the dolphin fluke motion with flexible caudal fin is different from a rigid one. Finally, by analyzing the instantaneous flow condition behind the dolphin caudal fin, it can get the reason why the thrust generated by the flexible caudal fin is larger than rigid one.
Code Comparison of a NREL-FAST Model of the Levenmouth Wind Turbine With the GH Bladed Commissioning Results
Authors: Serret Jordi , Rodriguez Carlos , Tezdogan Tahsin , Stratford Tim , Thies Philipp 
Published: September 2018

This paper describes the process adopted to set up a FAST model to produce relevant design load cases (DLCs) for the Levenmouth (Samsung Heavy Industries - S7.0-171) demonstration foreshore wind turbine owned by the Offshore Renewable Energy Catapult (ORE Catapult). The paper does not take into account hydrodynamic forces.
Existing literature has carried out FAST studies predominantly using reference turbines (e.g. NREL-5MW, DTU-10MW) instead of real prototype or commercial turbines. This paper presents the results for the Levenmouth wind turbine, a real, operating demonstration wind turbine. The paper explores and simulates the critical loads for the turbine, which will be very valuable validation case for industrial and academic use. Moreover, the Levenmouth wind turbine exhibits a new generation of extremely flexible blades that conflict with the previous approaches used by most common aero-elastic codes and makes this simulation a challenge.
The study is divided into three steps. It starts with building the model and fine-tuning it until it matches the natural frequencies of the blades and tower. The second step encompasses the comparison of the commissioning results with the relevant NREL FAST simulations to match the dynamic behaviour of the turbine. The final step comprises a load comparison for the interface between the tower and transition piece, in order to validate the new aero-elastic model with the commissioning loads.
The results of the study show 98% agreement in the natural frequencies and dynamic performance, and a 78% agreement in the loads between the aero-servo-elastic model and the certification results.
The present study is framed into an engineering doctorate project and a more comprehensive turbine virtualisation project. We anticipate that our work to be the initial point for more sophisticated aero-elastic models adapted to the unique properties of the Levenmouth demonstration wind turbine.
Stress Intensity Factors in Fitness-for-Service Assessment of Cracks in Mooring Chains
Authors: Arredondo Alberto , Altuzarra Jorge , Mena Alex , Fernández Jonathan 
Published: September 2018

Chain corrosion-fatigue often governs the design of the mooring systems of floating production units, and it is assessed based on a stress-life or S-N approach. For integrity management along the lifetime of the assets, a Fracture Mechanics (FM) approach can be more appropriate, especially if cracks were detected during in-service inspections.
An essential parameter of FM is the Stress Intensity Factor (SIF), which becomes fundamental to evaluate the response of a cracked link. The aim of this paper is to present SIF results for chains under different combinations of cracks and loads. Analytic or handbook solutions exist and provide accurate SIFs for simple geometries and test specimens. However, the particular geometry of chain links makes the Finite Element Method (FEM) more appropriate.
The authors utilized the contour integral method together with the general purpose nonlinear FEM code Abaqus, to carry out a large amount of analyses to obtain SIFs for different chain sizes, material grades, crack shapes, crack depths and crack locations along the links. In addition to this, SIFs were derived in combination with other degradation phenomena such as large pitting or interlink wear.
As an outcome, empirical equations were developed to predict the SIFs of propagating cracks in mooring chains under a large variety of scenarios. This allows engineers to assess the criticality of fatigue cracks using suitable crack growth models, and hence evaluate their fitness-for-service or need to implement remedial actions.
Late Stages in the Development of Modulation Instability of Waves
Authors: Shugan Igor , Kuznetsov Sergey , Saprykina Yana , Chen Yang-Yih 
Published: September 2018

We conducted experimental and theoretical studies on Benjamin-Feir (BF) instability and revealed a number of new features of the development of instability on the late stages of wave’s evolution. We employ the reduced (truncated) version of Zakharov equations — the multi-wave near-neighbor resonance model (NN model), which takes into account the most effective quasi-resonances with minimum detuning from exact resonance conditions.
We show that near-neighbor model for wave interactions can adequately describe the number of new prominent features of BF instability observed in experiments and it is much simpler than Zakharov equation for computation and analysis. Numerical simulations of the full Zakharov equations confirm the main predictions obtained by the NN modeling and both reasonably correspond to the results of available physical experiments.
Strong permanent downshifting of spectral maximum for gentle waves without wave breaking is revealed for twice as narrow side band spectral width in comparison with the most unstable case. Regime of multiple downshifting accompanied by wave breaking is discovered for steep waves. Discrete energy flow to higher spectral components takes a place in breaking and no breaking regimes. Results of numerical simulations of Zakharov and NN models reasonably correspond to each other and to our experimental and field observations on wave modulation.
Experimental and Numerical Modelling of an Offshore Aquaculture Cage for Open Ocean Waters
Authors: Jurado Alfonso , Sánchez Patricia , Armesto Jose A. , Guanche Raúl , Ondiviela Bárbara , Juanes Jose A. 
Published: September 2018

An innovative offshore aquaculture cage design and its hydrodynamic behavior for different environmental conditions is presented. The work involves the following blocks: (i) design of the aquaculture cage, (ii) experimental tests performed at IHCantabria facilities (Cantabria Coastal and Ocean Basin, CCOB), (iii) brief description of the ad-hoc time domain numerical model developed, and (iv) calibration of decay tests and sea states cases, in order to be able to simulate different locations of interest for aquaculture stakeholders.
The offshore aquaculture cage is a floating cylindrical structure, designed according to different requirements from standards and needs of contacted aquaculture stakeholders. The cage is focused on the growing and farming of fish species in open ocean conditions. It has been specially designed to be able to withstand different environmental conditions, even waves of more than 5m height.
Through numerical and physical modeling, it has been shown that it has a good seakeeping and accessibility, to reduce O&M costs. Motions and loads have been registered during the tank testing to calibrate and validate a specific coupled time domain numerical model developed for multi-body structures to simulate the behavior of the assembled structure (cage and sinker connected by tendons), including non-linear damping forces and a FEM approach to model the mooring and the tendon system.
Development of New Methodologies to Assess the Structural Integrity of the Grouted Joint of a 10 MW Wind Turbine Substructure
Authors: Santos Benjamin , Rodriguez Alvaro , Fernandez David , Gintautas Tomas , Sorensen John , Natarajan Anand , Njomo Wilfried 
Published: September 2018

Monopiles are currently the most commonly used substructure in the offshore wind market due to their ease of installation in shallow to medium waters. The monopile and the transition piece are connected by a grouted joint.
Fatigue and corrosion are two of the most important degradation mechanisms in this type of support structures. These mechanisms increase the costs and compromise the reliability of the structures. The development of new models and methodologies for the analysis of these degradation mechanisms is crucial. For this reason, a deterministic methodology to analyze the behavior of grouted joints has been developed considering the effect of corrosion on the steel parts of the grouted joints and the reliability of the joint under fatigue. Also, a probabilistic model for concrete grout fatigue strength and two probabilistic models for fatigue reliability assessment of steel components of the grouted connection have been developed.
Mooring System Design Approach: A Case Study for MARMOK-A Floating OWC Wave Energy Converter
Authors: Touzon Imanol , de Miguel Borja , Nava Vincenzo , Petuya Victor , Mendikoa Iñigo , Boscolo Francesco 
Published: September 2018

This paper presents a methodology and a flowchart of steps to take for a, consistent and rapidly convergent design of catenary mooring systems. It is subsequently applied for a floating Oscillating Water Column WEC MARMOK-A developed by Oceantec Energías Marinas, in order to fulfill the technical requirements of such dynamic systems. The approach, based on the catenary equations, considers the water depth as a design scale factor for the mooring system, leading to an equivalent static mooring performance. In general, a mooring system configuration is described by the number and distribution of lines; thus, as a preprocess in the herein described procedure, a database is built for different line lengths. The main advantage of the procedure is that once that, after characterizing a mooring system configuration at a specific water depth with a specific line mass and axial stiffness, the database built can be used for any other water depth with any line mass and axial stiffness, accelerating the design optimization process. Mooring static properties are derived for a given material elastic modulus, lines’ mass and water depth. The mean offset and horizontal stiffness are afterwards derived with lines pretension and steady environmental forces (mean wave drift, current and wind) as well as maximum offset and characteristic line tensions. Finally, the process is applied for different lines pretensions to achieve an objective horizontal stiffness of the structure.
The introduced procedure is presented through its application to the MARMOK-A device at a 90m depth site moored by means of a Karratu named mooring configuration. Results are presented in terms of total lines mass, device maximum expected excursion and required footprint for different horizontal stiffness and lines mass in order to give an insight of the impact on total plant cost indicators.
Economic Potential of Industrializing Floating Wind Turbine Foundations
Authors: Andersen Morten Thøtt , Tetu Amelie , Stiesdal Henrik 
Published: September 2018

The potential of offshore wind is enormous. It could meet Europes electric energy demand seven times over, and the United States energy demand four times over. However, much of the offshore potential is at water depths that can only be served by floating systems. In order to truly enable floating offshore wind, the cost of energy needs to reach the level of fixed-bottom offshore wind. At the present time, a number of suppliers are offering floating offshore wind foundations, but at cost levels that are prohibitive for large-scale application. The root cause of the high cost levels is that existing designs have emerged from the offshore oil and gas sector; they are manufactured using conventional, non-industrialized methods, weights are measured in thousands of tons and manufacturing times are measured in months.
In contrast, the TetraSpar concept is based on the application of proven design and manufacturing technologies from the highly competitive wind industry. As a result, the weight is only a fraction of the weight of other floating wind turbine foundations, manufacturing takes place in factories using industrialized methods, and assembly and installation is measured in days or weeks, not months. The foundation and wind turbine can be installed in any port of a reasonable size using a standard, land-based crane, and the complete assembly can be towed to site and hooked up to the moorings and the electrical cable using standard tugs.
This paper presents how these desirable economic traits of the TetraSpar design are achievable, and how the near future feasibility of offshore floating wind turbines may develop as a consequence of this radical change in cost levels.
Numerical and Experimental Modelling of Mooring Systems: Effects of Wave Groupiness on Extreme Loads
Authors: Barrera Sánchez Carlos , Guanche Raúl , Losada Iñigo J. , Armesto José A. , de los Dolores Daniel 
Published: September 2018

Mooring systems constitute an important element to secure the stability and survival of floating structures. In the last years, its use has increased potentially linked to the growth of marine renewable energies, about all, offshore wind and waves. Traditionally, fixed foundations such as gravity, monopiles or jackets have been installed. However, new alternatives have been developed based on floating structures looking to take advantage of the potential resource in deep waters.
This paper involves an exhaustive mooring system study based on catenary configuration from different points of view. Physical modelling was performed by means of different experimental tests under different loading conditions including prescribed movements and natural forcing (waves and currents) considering two different types of seabed: a rigid seabed using the glass of the flume simulating a rocky bottom and a deformable seabed through sandy seabed. Different types of numerical approaches were implemented and they were validated with laboratory tests. Quasi-static and dynamic models were included. Also, a commercial software called SESAM was used to verify the results. Finally, the effect of wave groupiness on extreme loads was analysed using a Floating Offshore Wind Turbine (FOWT).
Mechanical Behavior After Stress Relaxation in PVDF
Authors: Menezes Freitas Rafael Luis , Costa Celio , Chaves Erica Gervasoni , Teixeira Sylvia 
Published: September 2018

This study presents the mechanical properties evaluation of two commercial grades of PVDFs, which were extruded with the same parameters but with different cooling temperatures. After processing, stress relaxation with 7% strain was imposed and tensile properties were measured.
The cooling temperature after extrusion were 4°C, 23°C and 80°C. Then, the PVDFs were submitted to stress relaxation at 23°C and 7% strain. The as processed and after relaxation samples were characterized by FTIR, XRD, DSC and tensile tests at 23°C.
The stress relaxation at 23 °C resulted in no change in volume fraction of crystallinity for PVDF A and B. The XRD and FTIR, for both PVDFs, showed that the crystalline phases were the same, for all cooling conditions and did not change after the stress relaxation. The tensile properties at room temperature showed that the yield stress was a little affect by the cooling temperature, while Young’s Modulus and yield strain were insensible to the cooling temperature. After the stress relaxation, these three tensile properties were slightly affected for both grades.
On the Handling of Moonpool Resonances by Green’s Function Methods
Authors: Vada Torgeir , Pan Zhi Yuan 
Published: September 2018

In this paper, we will investigate the numerical treatment of irregular frequencies and moonpool resonance by using a Green’s function method. We will look at the interaction of these two resonances and how much the moonpool resonance will influence other results. We will also look at the importance of the meshing including the addition of a mesh in the moonpool. Such a mesh is normally only used when we want to include damping of the moonpool resonance, but it will be shown that including this mesh may be beneficial also without damping.
In addition to the wave elevation in the moonpool we will also investigate the effect of the moonpool resonance on the motions, sectional loads and mean drift forces.
Viscous Drift Forces on a Semi-Submersible in Combined Wave and Current
Authors: Kim Joo-Sung , Kim Hyun Joe , Lee Dong Yeon 
Published: September 2018

A time domain simulation tool is used to setup a numerical simulation model in which the wave loads of the potential flow are combined with the viscous drag force computed by the Morison equation. The drag coefficients in the Morison equation are determined to provide the best numerical results compared to model test data.
The numerical simulations and analytic solutions have been used to examine the characteristics of mean viscous drift force on the semi-submersible for fixed condition. The results show that the mean viscous drift force is mainly produced by the column. The column is divided into splash zone and submerged zone because they give much different mean viscous drift force. In high waves, the splash zone leads to mean drift force much larger than the submerged zone for both wave-only and wave-current coexisting flow fields.
The present results clearly show that the drag coefficients can be expressed as a function of the Keulegan-Carpenter number, especially for high waves. There is strong correlation between regular and irregular waves for both wave-only and wave-current coexisting flow fields. If current is present, the drag coefficient decreases significantly.
Pipeline and Cable Stability: Updated State of the Art
Authors: Griffiths Terry , Draper Scott , White David , Cheng Liang , An Hongwei , Tong Feifei , Fogliani Antonino 
Published: September 2018

At OMAE in 2008 the ‘state of the art’ in pipeline on-bottom stability engineering was summarized, providing an overview of the current available knowledge for addressing pipeline stability. The aim of that work was to summarise key aspects of the pipeline stability design process and to include some historical perspective. The paper discusses the advantage and shortfalls of the different design approaches with a view to consolidate understanding, rather than to provide a ready-made solution to a complex design problem [1].
Since that time, a decade of research and further methodology refinement has extended the boundaries of the industry’s knowledge and understanding of the behaviour of subsea pipelines and cables, including geotechnics, hydrodynamics, oceanography and structural response modelling. In particular, progress has been made in:
• The response of pipelines to sediment transport and scour;
• Understanding the behaviour of small diameter pipelines and cables within wave and current boundary layers; and
• The behaviour of cables on rocky seabeds in high energy marine environments.
This paper summarises these innovations to enable the application of new paradigms in engineering practice and improved outcomes for initial project capital cost, reliability and operational integrity, as well as better models to predict the long-term behaviour where pipes are decommissioned in-situ.
While a relatively widely studied field of engineering, there remain areas of active ongoing research to improve our understanding and ability to model and predict subsea pipeline on-bottom behavior, with a summary of the anticipated future opportunities proposed.
Uncertainty of Environmental Contours due to Sampling Variability
Authors: Gramstad Odin , Vanem Erik , Bitner-Gregersen Elzbieta 
Published: September 2018

Environmental contours are commonly applied in design of marine structures to identify extreme environmental conditions that may give rise to extreme loads and responses. Recently, there has been some focus on the fact that different methods exist for establishing such contours, and that in some cases significant differences may be obtained from the different methods.
In this study, we address another uncertainty related to the calculation of environmental contours, namely the uncertainty due to sampling variability when constructing environmental contours based on metocean data of finite sample size. The uncertainty of environmental contours for joint distribution of significant wave height and wave period for different sample sizes (10, 20, 30 and 100 years of data) are investigated considering different underlying datasets. Both cases where samples are drawn from a known joint distribution of wave height and periods and cases where samples are drawn from a real hindcast dataset and fitted to the joint distribution are considered. The uncertainty of the estimated contours is quantified and discussed in light of differences that can be anticipated from the different methods used to calculate the contours.