bluuebunny/crossref_metadata_2025 huggingface dataset:
Crashworthiness Assessment of Thin-Walled Bottom Structures During Powered-Hard Grounding Accidents
Authors: Prabowo Aditya Rio , Sohn Jung Min , Bae Dong Myung , Setiyawan Agus
Published: September 2018

Advance development in engineering and technology has been massively triggered by establishment of the free market memorandum between countries across the globe. Explicitly, this agreement affects ship and offshore industries, where stakeholder and investor demand a wide range of accidental damage assessment. Achievement of this objective is highly influenced by sustainable research on maritime accidents. Ship grounding is categorized in impact phenomena, and record has evidenced grounding as the most risky accident. Since it is capable to evoke massive losses, estimation of structural performance and limit under grounding is required.

This work aims to evaluate crashworthiness of a thin-walled tanker structures in encountering ship grounding. A series of benchmark simulations based on pioneer experimental test is re-performed as calibration of numerical configuration for grounding analysis. Several scenarios are designed in this stage by varying mesh sizes on the idealized test geometry. Preparation for the grounding analysis is presented in the next stage. Considering its characteristic as impact load, powered-hard scenario is taken into account as the worst possible damage on the structures. It is assumed that grounding happens suddenly when the tanker is in a voyage and interacts with a hard object. A medium-carbon steel is embedded with the Det Norske Veritas - Germanischer Lloyd (DNVGL) fracture criterion. In this study, an oceanic obstruction is defined as seabed reef geometry with the properties are adopted based on data of ocean crustal seismology. Varieties of location, angle and elevation are applied to accidental grounding scenarios. The assessment of structural crashworthiness brings an insight into the effect sensitivity of the parameters on the double bottom behavior. Brief recommendation for grounding simulation is provided in final conclusion to give adequate references in applying numerical input and configuration, especially using the finite element (FE) method.
Experimental Study of Wave Force Distribution on a Monopile Structure
Authors: Vested Malene H. , Carstensen Stefan , Damgaard Christensen Erik
Published: September 2018

As the demand for offshore wind energy continues to grow, the strive to understand the wave forces acting on the substructure of the wind turbines continues. In regard to wind turbine design, it is vital to consider not only the total wave force, but also the local wave forces. Local forces are particularly important for the design of secondary structures as e.g. mooring platforms. Typically, however, experimental studies mainly concern total forces or idealized local forces. We present here a rather simple way to measure local forces along a model monopile. The study is conducted in a wave flume of 28 m in length, in which waves are generated by a piston-type wave maker at a water depth of 0.515 m and shoal onto a bed of slope 1:25. A model monopile is installed and subjected to forcing from a series of both regular and irregular waves. In the experimental set-up, the model monopile is fixed at the bottom and the top and consists of seven independent cylindrical sections. The cylindrical sections are connected by force transducers which measure local shear, and so the associated local forces may be determined. The measured local forces are compared to the force distribution given by Morisons equation combined with linear theory and Wheeler stretching, which is a force estimate commonly used in the industry. This study shows that the total force is rather well captured by Morison’s equation. The force distribution estimated from Morison’s equation, however, shows larger discrepancies from the measured forces. This encourages for further measurements. In this study, we show that it is possible to measure force distribution on a model monopile in a simple and cost-effective manner. The aim is here to demonstrate the method and we will later present a larger body of work associated with the outcome of the measurements.
On Wave Diffraction of a Two-Dimensional Moonpool in a Two-Layer Fluid in Finite Water Depth
Authors: Song Xingyu , Xu Xin , Zhang Xinshu , You Yunxiang
Published: September 2018

This paper studies the wave diffraction of a two-dimensional moonpool in a two-layer fluid in finite water depth by using a domain decomposition scheme and an eigenfunction matching method. The formulae of the wave exciting forces, the free surface and internal wave elevations at zero-frequency are derived. Numerical convergence has been assessed by repeating the computations for increasing values of the truncation orders. The present model has been validated by comparing a limiting case with a single-layer fluid case and the comparisons are in general satisfactory. Although the wave exciting forces and free surface wave elevations around resonance frequency are overestimated, the piston mode resonance frequency is well predicted. Two typical configurations with different moonpool widths are selected for computations in both free surface and internal wave modes. It is found that, the wave exciting forces, free surface and internal wave elevations in internal wave mode are much smaller than those in free surface wave mode. In addition, the wave exciting forces in internal wave mode attenuate to zero quickly as incident wave frequency increases. For moonpool with small width, only piston mode resonance can be observed. The piston mode resonance frequencies identified in free surface and internal wave modes are the same. The characteristics of piston mode resonance can also be observed in the horizontal and vertical wave exciting forces. Around the piston mode resonance frequency, the wave exciting forces reach their local maximums. It is revealed that, as moonpool width increases, the piston mode resonance frequency decreases. Meanwhile, it shows that more asymmetric and symmetric sloshing mode resonances appear alternately and occur at higher frequencies than the piston mode resonance. Moreover, the predicted sloshing mode resonance frequencies are compared with those estimated by a simple approximate formula.
Improved Bend Over Sheave Durability of HMPE Ropes for Deep Sea Handling
Authors: Davies Peter , Lacotte Nicolas , Arhant Mael , Durville Damien , Belkhabbaz Abderrahim , François Michel , Khouri Fabien , Konate Kara , Mills Stephen , Philippe Jean-Robert , DeFrance Christophe , Smeets Paul , Sherman Dennis , Newboles Kurt , Ledoux Alain , Chazot Nicolas , Saillard Sebastien , Kante Ramesh , Cannell David , Chevallier Patrick , Lodeho Olivier
Published: September 2018

The use of synthetic fiber ropes for subsea installation is extending, as the offshore industry explores deeper waters, but there are few data available to evaluate the lifetime of these materials. In a previous OMAE presentation the authors described results from the first phase (2010–2013) of a JIP aiming to understand the mechanisms controlling the long term behavior of HMPE fibre ropes [1]. This presentation will describe the results from the second phase of this study (2014–2018) in which predictive models have been developed and applied to a range of improved braided rope materials. Two modeling approaches will be discussed, an empirical method based on residual strength after cycling, and a numerical approach using finite element software specifically adapted to fibre materials [2]. An extensive test program, which has generated a database of CBOS (cyclic bend over sheave) results for various grades of HMPE and different constructions, will be described. Comparisons have been made with steel wire handling lines in order to quantify the benefits of fibre ropes for these deepwater applications.
Novel Sensor Technology for Identifying Subsea Power Cables’ and Umbilicals’ Axial Stiffness
Authors: Jordal Lars , Slora Roger , Konradsen Bjørn , Karlsen Per Ivar
Published: September 2018

This paper presents how to establish the axial stiffness for subsea power cables and umbilicals based on multiple measurement points along the test object. The Cartesian coordinates of the measuring points are measured with use of a total station consisting of an electronic theodolite integrated with an electronic distance measurement unit. The advantage of the total station compared to other displacement measuring systems is that the sensors are not in physical contact with the test object. The measurement method, including calculation of elongation and axial stiffness, is evaluated through a full-scale test with a super duplex steel tube with known mechanical properties. The deviation between the theoretical axial stiffness of the steel tube and the measurement method is 1.2%.
Durability of Polymers and Composites: The Key to Reliable Marine Renewable Energy Production
Authors: Davies Peter , Le Gac Pierre-Yves , Le Gall Maelenn , Arhant Mael , Humeau Corentin
Published: September 2018

Recovery of marine energy is progressing from the prototype stage to arrays, and all of the systems currently being developed include critical elements manufactured from polymers and composites. Structural MRE (Marine Renewable Energy) components range from composite turbine blades, for floating wind and tidal turbines, to polymer fiber ropes for wave, tidal and floating wind mooring systems. Elastomeric components are also widely used for sealing and protection. In all cases it is essential to understand how seawater diffuses into these polymers and how it affects mechanical properties; this allows appropriate safety factors to be applied without excessive over-conservative design, and can result in significant cost reduction. This paper will present a methodology for evaluating the long term behavior of such components based on accelerated testing. Three examples will be shown to illustrate the approach; tidal turbine blade composites, synthetic fiber rope moorings, and rubber components. In each case the seawater diffusion kinetics will be described first, then the influence of water on mechanical behavior will be quantified for the particular loadings of interest, and finally results from fully coupled fatigue tests in seawater will be discussed.
Investigation on the Shooting Method Ability to Solve Different Mooring Lines Boundary Condition Types
Authors: Surmont Florian , Coache Damien
Published: September 2018

The study of undersea cables and mooring lines statics remains an unavoidable subject of simulation in offshore field for either steady-state analysis or dynamic simulation initialization. Whether the study concerns mooring systems pinned both at seabed and floating platform, cables towed by a moving underwater system or when special links such as stiffeners are needed, the ability to model every combination is a key point.

To do so the authors propose to investigate the use of the shooting method to solve the two point boundary value problem (TPBVP) associated with Dirichlet, Robin or mixed boundary conditions representing respectively, displacement, force and force/displacement boundary conditions.

3D nonlinear static string calculations are confronted to a semi-analytic formulation established from the catenary closed form equations. The comparisons are performed on various pairs of boundary conditions developed in five configurations.
A Field Monitoring System for Dynamic Positioning Floatover Installation
Authors: Wang Peng , Wu Xiao , Lu Wenyue , Tian Xinliang , Li Xin
Published: September 2018

Floatover method has been proven a competitive installation technology in last thirty years. However, floatover installation is subject to a variety of technical challenges. Apart from weather restrictions, motions and position of the topside and deck transport vessel (DTV) should be strictly controlled during the entire installation operations. Therefore, a field monitoring system is essential to guarantee the installation safety. In this paper, a comprehensive introduction to the monitoring system developed by Shanghai Jiao Tong University is presented. The subsystems, including environment monitoring system, motions and position monitoring system, deck support units (DSUs) separating monitoring system, closed-circuit-television (CCTV) monitoring system as well as the integrated monitoring system (IMS), are proposed. Besides, the pre-installation surveys are also presented.
Large Scale Physical Modelling for a Floating Concrete Caisson in Marine Works
Authors: Meneses Lucía , Sarmiento Javier , de los Dolores Daniel , Blanco David , Guanche Raúl , Losada Íñigo J. , Rodriguez de Segovia María F. , Ruiz Manuel J. , Martín Miguel A. , Conde María J. , Esteban Francisco
Published: September 2018

In the last years, the use of floating concrete caissons in coastal infrastructures has been generalized: docking structures, vertical breakwater and special floating structures. In this field, one of the most important and less analyzed stages of the marine works is the sinking process of the floating caissons.

The test campaign presented in this work is innovative in scale (1:12) and includes an analysis of the different stages of a floating caisson during its life cycle: detached concrete caisson, caisson positioning and sinking and berthed floating caisson, resulting in more than 130 tests performed. Movements and tensions have been analyzed for a wide array of sea states and different configurations of mooring systems and horizontal layouts.

A new tool for dynamic positioning control was designed and developed as part of the test campaign. The design of this tool has led to the development of a specific numerical model that reproduced the dynamic behavior during sinking. The dynamic positioning control was implemented in the physical model campaign, which has meant an important advance in the construction process of maritime infrastructures.

Moreover, the campaign carried out has allowed the validation and calibration of the tools developed, allowing all the work to reduce costs and increase the safety of these types of marine operations.
Verification of a Numerical Model of the Offshore Wind Turbine From the Alpha Ventus Wind Farm Within OC5 Phase III
Authors: Popko Wojciech , Huhn Matthias L. , Robertson Amy , Jonkman Jason , Wendt Fabian , Müller Kolja , Kretschmer Matthias , Vorpahl Fabian , Hagen Torbjørn Ruud , Galinos Christos , Le Dreff Jean-Baptiste , Gilbert Philippe , Auriac Bertrand , Víllora Francisco Navarro , Schünemann Paul , Bayati Ilmas , Belloli Marco , Oh Sho , Totsuka Yoshitaka , Qvist Jacob , Bachynski Erin , Sørum Stian Høegh , Thomassen Paul E. , Shin Hyunkyoung , Vittori Felipe , Galván Josean , Molins Climent , Bonnet Paul , van der Zee Tjeerd , Bergua Roger , Wang Kai , Fu Pengcheng , Cai Jifeng
Published: September 2018

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project, is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project analyzes the Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. This paper shows results of the verification of the OWT models (code-to-code comparison). A subsequent publication will focus on their validation (comparison of simulated results to measured physical system response data). Based on the available data, the participants of Phase III set up numerical models of the OWT in their simulation tools. It was necessary to verify and to tune these models. The verification and tuning were performed against an OWT model available at the University of Stuttgart – Stuttgart Wind Energy (SWE) and documentation provided by Senvion and OWEC Tower. A very good match was achieved between the results from the reference SWE model and models set up by OC5 Phase III participants.
Potential Changes in the Joint Probabilistic Description of the North Atlantic Wave Climate
Authors: Bitner-Gregersen Elzbieta M. , Gramstad Odin
Published: September 2018

Climate changes include natural climate variability and anthropogenic climate change. The latter is leading to global warming and causes changes in metocean conditions. For most marine structures waves represent the dominant environmental load. Therefore, projections of changes of wave characteristics in the 21st century are crucial with respect to design and marine operations. The study investigates potential changes in simultaneous occurrence of significant wave height and spectral wave period in twelve North Atlantic locations by comparing the past and future wave climate. Two IPCC emission scenarios, with radiative forcing of 4.5 and 8.5 W/m2 by the end of the 21st century, have been selected to project future wave conditions. The third generation (3G) wave model WAM with a resolution of 50 km is used to simulate waves. The model has been forced with winds obtained from six CMIP5 climate models for the historical period 1971–2000 and the future period 2071–2100 for the two emissions scenarios. Wave climate projections obtained from one climate model and one ensemble member are presented herein to indicate potential changes in extreme wave characteristics derived from the long-term joint probabilistic model of significant wave height and spectral wave period. Deviations between the past and future wave climate are shown, given attention to the shape of the joint distribution and wave steepness. Uncertainties associated with the presented results are discussed.
MAESTRALE: The Implementation of Blue Energy in the Mediterranean Sea
Authors: Abanades Javier , Torregrosa Juan Pablo
Published: September 2018

The project Maestrale is an European Project funded by the Interreg MED programme (2016–2019) that aims at establishing the basis for a Maritime Energy Deployment Strategy in the Mediterranean Sea. The project is formed by a consortium with partners around the South of Europe with the objective of determining a suite of pilot zones, which will become the pillars of future developments for the implementation of Blue Energy projects in the Mediterranean Sea.

The present article presents the tasks to be conducted for the study of the area in the Spanish Mediterranean Arc:

• Identification of recommendations and regulations

• A benchmark of the technologies installed worldwide will be carried out in order to identify their degree of adaptability to the conditions of the Med Area

• The analysis of the available resource: wind, wave and tidal

• The study of the area and its features: bathymetry, land cover, protected areas, etc.

• The identification of the stakeholders, as the project intends to strengthen cooperation between public authorities, research bodies, businesses and the civil society

• The formation of clusters with the stakeholders, either at the national or trans-national level, to increase connections in order to promote knowledge and technological transfer and generate the critical mass and environmental conditions needed to improve innovation capacities and competitiveness

The main outcomes of the project are the support of the future blue energy policies and concrete strategies for blue growth and a suite of pilot projects that will serve the purpose of raising awareness among local stakeholders, facilitating social acceptance, decreasing uncertainty and increasing feasibility of concrete interventions.
Motion Analysis of Flexible Hose Based on Water Tank Experiment
Authors: Zhou Xue , Mizukami Yoichi , Yoshida Takero , Kitazawa Daisuke
Published: September 2018

Set net fishery faces the problems of decrease in harvest, with lack of labor and aging of fishermen. These problems make it necessary to develop a new automatic harvesting way of set net fishery. An automatic net-hauling system is one of the promising ways, while the system using rubber tubes and polyethylene pipes are not prevailing because of the high maintenance cost and the difficulty in the operation. In the present study, the flexible hose net is proposed to harvest fish in the box chamber net of set net fishery. The flexible hose net is installed on the water bottom below the box chamber net. Compressed air is injected from one edge of the hose net to haul the box chamber net gradually, resulting in cornering fish in the other edge. In the preset study, the feasibility of the net-hauling system for set net fishery was examined by water tank experiment. The variation in the formation of the hose net and the time for sinking and floating were examined, changing the parameters such as air pressure and buoyancy balance. As a result, the hose net sank automatically if the weight attached to the hose net was 39% of the total buoyancy of the hose net with full of air. The time spent for sinking operation was about 160 s, which corresponds to about 10 min for actual hose net according to the similarity law. However, it should be noted that the similarity of water pressure could not be reproduced in the water tank experiment. To reduce the sinking time, the initial inner pressure of the hose net must be the atmospheric pressure before the beginning of the sinking operation. There is an inflection point between the flexible hoses with and without air. It is worried that air flow in the flexible hoses may be impeded. So the inside structure of the flexible hoses may have to be improved to secure the air flow in any condition. In relation to the difficulty in reproducing the water pressure condition in the water tank, the numerical analysis will be required to reproduce the motion of the hose net and its sinking time both for scaled and full-scale models. In the future, three-dimensional coupled model of fluid, structure, and air flow will be developed and validated by the experimental data, beginning with the simple two-dimensional modeling of the motion of the hose net.
Numerical Modeling of the Forced Motion Dynamics of Antiroll Tank With OpenFOAM
Authors: Bernal-Colio V. R. , Cercos-Pita J. L. , Calderon-Sanchez J. , Diaz-Ojeda H. R. , Abad Ricardo , Souto-Iglesias A.
Published: September 2018

The aim of this work is to approach the full design of an anti-roll tank through numerical simulation, looking for the way to minimize the computational cost. The results have been validated with experiments from a rectangular tank, a tank with a C-shaped section and a rectangular tank with baffles. These tests were performed for 3 and 6 degrees of roll, and for different levels of water inside. The Open Source Computational Fluid Dynamics (CFD) tool OpenFOAM has been used to carry out the simulations and to validate the numerical model. We have worked in 3D testing different turbulence models (laminar, k-ε, k-ω, k-ω SST) and different boundary conditions (fixed values or slip). Convergence analyses of different meshes have also been performed. After filtering the outcomes, it is shown that the model k-ω SST with slip boundary estimation is the most reliable model.
An Analysis on the Change of Ship Speed According to Ice Load Signal in Continuous Icebreaking and Ramming
Authors: Ahn Se-Jin , An Woo-Seong , Lee Tak-Kee , Choi Kyungsik
Published: September 2018

Recently, the research activities by domestic and overseas researchers using the Korean ice-breaking research vessel, ARAON have been actively conducted. The ARAON regularly operates for research activities in the Antarctic and the Arctic Ocean every year. She conducts many scientific and engineering tasks including ice load measurement, investigation of the properties of material strength for sea ice, and icebreaking performance test during her voyages. Such tests provide important data for studying icebreaker.

Ice-breaking mode is determined by conditions of sea ice and ice field, and it is divided into ramming and continuous icebreaking. When the icebreaker meets thick ice or icebergs, the ramming is conducted. At that time, the ship speed is generally slower than that of the continuous icebreaking. The ARAON conducted icebreaking performance tests at the Amundsen Sea in Antarctica in 2012. Many strain data were measured in the ramming and the continuous icebreaking.

This study was based on the strain gauge signals measured by the ARAON during the research voyage in 2012 in the Antarctic and 2010 in the Arctic. The signals measured from repetitive ramming under the heavy ice condition in 2012 in the Antarctic Ocean were classified into the five profiles. And the classified ice load signals were analyzed with a focus on raising time, half-decaying time and total time duration. Also, the signals measured from continuous icebreaking in 2010 in the Arctic Ocean were analyzed in the same way as the ramming data. Finally, the time histories of ice load signals were summarized from the viewpoint of speed change at the time of ice load, and two data sets were compared.
Application of GPGPU to Accelerate CFD Simulation
Authors: Mintu Shafiul A. , Molyneux David
Published: September 2018

Computational Fluid Dynamics (CFD) is widely used in industry and academic research to investigate complex fluid flow. The bottleneck of a realistic CFD simulation is its long simulation time. The simulation time is generally reduced by massively parallel Central Processing Unit (CPU) clusters, which are very expensive. In this paper, it is shown that the CFD simulation can be accelerated significantly by a novel hardware called General Purpose Computing on Graphical Processing Units (GPGPU). GPGPU is a cost-effective computing cluster, which uses the Compute Unified Device Architecture (CUDA) of NVIDIA devices to transform the GPU into a massively parallel processor.

The paper demonstrates the faster computing ability of GPU compared to a traditional multi-core CPU. Two scenarios are simulated; one is a 2-dimensional simulation of regular wave and another one is a 3-dimensional motion of a floating ship on a regular wave. A smoothed particle hydrodynamics (SPH) based CFD solver is used for simulating the complex free-surface flow. The performance of a single GPU is compared against a commonly used 16 core CPU. For a large simulation of 6 degrees of freedom (DOF) ship motion simulation, the comparative study exhibits a speedup of more than an order of magnitude, reducing simulation time from 30 hours to about 2 hours. This indicates a CUDA enabled GPU card can be used as a cost-effective computing tool for a reliable and accurate SPH-based CFD simulation. The cost-benefit analysis of GPU over a CPU cluster is also discussed.
Recent Developments in Experimental and Numerical Assessments of Welding-Induced Residual Stresses
Authors: Chen Bai-Qiao , Hashemzadeh Marzieh , Garbatov Yordan , Guedes Soares C.
Published: September 2018

The objective of this work is to present and review the recent developments in the experimental and numerical assessment and simulation techniques on the welding induced distortions and residual stresses. The temperature distribution, welding induced distortion and residual stresses in thin walled welded structures, originating from different experimental tests are reviewed and discussed. Different mathematical models and their numerical applications in representing the heat source are analysed and their advantages and drawbacks are discussed. Thermal stress analyses employing the three-dimensional nonlinear thermo-elasto-plastic approaches and finite element simulations with inherent deformation applicable to large-scale and complex welded structures are also revised and discussed. Discussions on the material properties of the base metal, heat affected zone (HAZ) and weld metal, the effect of the welding sequence, and the pattern of residual stress distribution presented are given a special attention.
Numerical Investigation on Weld Induced Imperfections in Aluminium Ship Plates
Authors: Chen Bai-Qiao , Guedes Soares C.
Published: September 2018

The present work aims at better understanding and predicting the thermal and structural responses of aluminium components subjected to welding, contributing to the design and fabrication of aluminium ships such as catamarans, lifesaving boats, tourist ships and fast ships used in transportation or in military applications. Taken into consideration the moving heat source in MIG welding, finite element models of plates made of aluminium alloy are established and validated against published experimental results. Considering the temperature-dependent thermal and mechanical properties of the aluminium alloy, thermo-elasto-plastic finite element analyses are performed to determine the size of the heat affected zone (HAZ), the temperature histories, the distortions and the distributions of residual stresses induced by the welding process. The effects of the material properties on the finite element analyses are discussed, and a simplified model is proposed to represent the material properties based on their values at room temperature.
Influence of Stiffness Ratio on Vortex-Induced Vibration of Cylinder With Low Aspect Ratio
Authors: Gambarine Dennis M. , Minioli Luiz E. B. , Gonçalves Rodolfo T. , Kogishi André M. , Fujarra André L. C.
Published: September 2018

Concern over the Vortex-induced Motions (VIM) acting on offshore structures, with special focus on monocolumn and spar platforms, mooring systems have crucial importance on system movements; the system has thus been transformed into a concept study herein. A floating and rigid circular cylinder with low aspect ratio (L/D = 2) was used in the experiments carried out to investigate the influence of stiffness ratio (kx/ky) on Vortex-Induced Vibration (VIV). The cylinder was mounted in an elastic base composed of four springs with differences in in-line and transverse stiffness, defining: kx/ky ≅ 0.3, 0.5, 1.0, 2.0 and 3.0. The Reynolds number analysed belongs to a range between 0.2 · 104 and 2 · 104. Some good qualitative and quantitative agreements are found for in-line amplitudes, and higher kx/ky systems demonstrate significant oscillation for low relative velocities. This variation can be seen and justified when the XY-plane trajectories were plotted. When kx/ky is defined as 2 and 3, the traditional VIV 8-shape is illustrated for reduced velocities between 3 and 6. In contrast, the other stiffness systems do not show significant movements and, consequently, a negligible XY shape. Roll and pitch degrees of freedom have shown the motions coupled with the transverse and the in-line motions respectively. Moreover, the yaw motion did not present considerable angles. kx/ky = 2 has presented the highest lift force coefficients, without a great difference from the other aspects ratios, though. The drag force coefficient showed constant values for kx/ky = 2 and 3, the smallest results were observed for the system kx/ky = 3.
Autonomous Ship Navigation Under Deep Learning and the Challenges in COLREGs
Authors: Perera Lokukaluge P.
Published: September 2018

A general framework to support the navigation side of autonomous ships is discussed in this study. That consists of various maritime technologies to achieve the required level of ocean autonomy. Decision-making processes in autonomous vessels will play an important role under such ocean autonomy, therefore the same technologies should consist of adequate system intelligence. Each onboard application in autonomous vessels may require localized decision-making modules, therefore that will introduce a distributed intelligence type strategy. Hence, future ships will be agent-based systems with distributed intelligence throughout vessels. The main core of this agent should consist of deep learning type technology that has presented promising results in other transportation systems, i.e. self-driving cars. Deep learning can capture helmsman behavior, therefore that type system intelligence can be used to navigate autonomous vessels. Furthermore, an additional decision support layer should also be developed to facilitate deep learning type technology including situation awareness and collision avoidance. Ship collision avoidance is regulated by the Convention on the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs) under open sea areas. Hence, a general overview of the COLREGs and its implementation challenges, i.e. regulatory failures and violations, under autonomous ships are also discussed with the possible solutions as the main contribution of this study. Furthermore, additional considerations, i.e. performance standards with the applicable limits of liability, terms, expectations and conditions, towards evaluating ship behavior as an agent-based system on collision avoidance situations are also illustrated in this study.
Modeling of a Semisubmersible Floating Wind Platform in Severe Waves
Authors: Rivera-Arreba I. , Bruinsma N. , Bachynski E. E. , Viré A. , Paulsen B. T. , Jacobsen N. G.
Published: September 2018

Floating offshore wind platforms may be subjected to severe sea states, which include both steep and long waves. The hydrodynamic models used in the offshore industry are typically based on potential-flow theory, and/or Morison’s equation. These methods are computationally efficient, and can be applied in global dynamic analysis considering wind loads and mooring system dynamics. However, they may not capture important nonlinearities in extreme situations. The present work compares a fully nonlinear wave tank (NWT), based on the viscous Navier-Stokes equations, and a second-order potential-flow model for such situations.

A validation of the NWT is first completed for a moored vertical floating cylinder. The OC5-semisubmersible floating platform is then modelled numerically both in this nonlinear NWT and using a second-order potential-flow based solver. To validate both models, they are subjected to non-steep waves and the response in heave and pitch is compared to experimental data.

More extreme conditions are examined with both models. Their comparison shows that if the structure is excited at its heave natural frequency, the dependence of the response in heave on the wave height and the viscous effects cannot be captured by the adjusted potential-flow based model. However, closer to the inertia-dominated region, the two models yield similar responses in pitch and heave.
Study of a Hybrid Renewable Energy Platform: W2Power
Authors: Legaz María J. , Coronil Daniel , Mayorga Pedro , Fernández Javier
Published: September 2018

The trend in our days seems to drive to hybrid renewable offshore platforms. Several European projects have advanced in this sense. One of these hybrid configurations is obtained by combination of wind and wave energy which allows higher production of electric power. W2Power platform combines offshore wind and wave energy in a semi-submersible floating platform. In this work we present a preliminary study of platform W2Power carried by UCA and collaboration with EnerOcean. A first step of the study, is presented, in this first step the platform and the wave converter are separately studied. A model of these components is created in the software SeaFEM and they are calibrated in the software using previous experimental test tank results. Taking into account this preliminary work, a study of a complete fully coupled model of the W2Power including wind and WECs under different control laws [11] platform will be made in future works.
Experimental Study on Model Predictive Control for a Point Absorber Type Wave Energy Converter With a Linear Generator
Authors: Umeda Jun , Goto Hiroki , Fujiwara Toshifumi , Taniguchi Tomoki , Inoue Shunji
Published: September 2018

This paper presents the experimental evaluation results of power production efficiency of model predictive control (MPC) on a wave energy converter (WEC) with a linear generator in regular and irregular waves. A bottom-fixed WEC of point absorber type was subjected to the WEC model in this paper. To compare the power production efficiency, the power production efficiency of the approximate complex-conjugate control with considering the copper loss (ACL) was also evaluated. In regular waves, the MPC performance was comparable to the ACL one in the power-production amount reasonably. In irregular waves which have narrow band spectral distribution, a same trend as the trend in regular waves was obtained. On the other hand, in irregular waves which have broadband spectral distribution, the MPC was more effective than the ACL. Moreover, Experiments in regular and irregular waves were carried out in the MPC under the constraint of the small heave displacement. The constraint of the displacement was approximately satisfied by the MPC. This is useful in practical operation. It is also investigated experimentally how time horizon affects the performance of the MPC. When the time horizon is short, the power production amount of the MPC increases.
Large Eddy Simulation of Cross Flow in Pipe Junction
Authors: Chen Jiajun , Sun Yue , Zhang Hang , Feng Dakui , Zhang Zhiguo
Published: September 2018

Mixing in pipe junctions can play an important role in exciting force and distribution of flow in pipe network. This paper investigated the cross pipe junction and proposed an improved plan, Y-shaped pipe junction. The numerical study of a three-dimensional pipe junction was performed for calculation and improved understanding of flow feature in pipe. The filtered Navier–Stokes equations were used to perform the large-eddy simulation of the unsteady incompressible flow in pipe. From the analysis of these results, it clearly appears that the vortex strength and velocity non-uniformity of centerline, can be reduced by Y-shaped junction. The Y-shaped junction not only has better flow characteristic, but also reduces head loss and exciting force. The results of the three-dimensional improvement analysis of junction can be used in the design of pipe network for industry.
Numerical Simulation of Focused Wave Based on Fourth Order Compact Finite Volume Scheme
Authors: Bai Junli , Ma Ning , Gu Xiechong
Published: September 2018

Freak wave is an unexpectedly large wave in ocean with extreme height and abnormal shape. The viscous effect is important in prediction of the flow patterns of the freak wave due to its strong nonlinearity. Thus, compared with the potential theory, more accurate information of flow field of the freak wave can be obtained by using the computational fluid dynamics (CFD) method. In laboratory test and numerical study, the focused wave is often adopted to substitute the freak wave in real sea. In this paper, we present a high accurate numerical model for large eddy simulation of the focused wave. In this model, the space filtered Navier-Stokes equations are solved on non-staggered grids by the finite volume. The fourth order compact scheme is adopted for discretization of both convection and diffusion terms of the governing equations. The standard fourth-order Runge-Kutta method is used for time advancement. The velocity-pressure coupling is ensured at each stage and the discretized equations are solved by strongly implicit procedure (SIP) method. The turbulence is simulated by the Smagorinsky model while the free surface is captured by using of the volume of fluid (VOF) method. The model is firstly validated by simulation of the cavity flow and linear wave. The simulation results are compared with theoretical values and published results, respectively. Finally, large eddy simulation of focused wave is presented. The comparison of the numerical results and measured data reveals that the proposed model is capable of reproducing the propagation and evolution of the focused wave.
Comparison of Wave-Induced Loads on a Near Surface Slender Body From Inviscid Flow Linear Solution and an Experimental Model Test
Authors: Turner Travis M. , Klamo Joseph T. , Kwon Young W.
Published: September 2018

The wave-induced loads experienced by a fully-submerged vehicle, but operating near the surface, play an important role in the design and operation of the vehicle. For an inviscid fluid with a monochromatic wave field, the first-order loads on a slender body of revolution can be solved for analytically using the method of singularities. The solution involves an integral expression dependent on the cross-sectional geometry of the body. For the canonical shape of a circular cylinder with hemispheric end caps, the integrals can be directly evaluated piecewise and a closed-form solution determined. This allows the rapid and easy calculation of wave-induced loads in any simple wave environment and at any operating depth. However, the use of potential flow ignores any viscous effects and effects due to changes to the wave as it passes over the vehicle. These effects may be important for smaller man-portable unmanned underwater vehicles. To determine the usefulness of this closed-form solution for small diameter bodies, an experimental model test was conducted to measure the loads where both potential and viscous effects are present. Experiments were performed for various wavelengths, at two model depths, and for one wave height while measuring the drag and vertical force along with the pitch moment on a 4.5 inch diameter model. These experimental loads are then compared to predicted loads from the analytic solution to assess their accuracy. This allows the determination of the importance of viscous effects and passing wave modification for wave-induced loads of small diameter underwater vehicles.
Structural Reliability of Oil Tanker in the Adriatic Sea Damaged in Collision and Exposed to Combined Bending Moments
Authors: Ćorak Maro , Parunov Joško
Published: September 2018

The aim of the paper is the assessment of structural reliability of oil tanker which may be damaged in collision accident in the Adriatic Sea and exposed to combined, horizontal and vertical bending moments. Damage size is assumed based on the direct numerical simulation of the ship-ship collision. This is justified for some specific sea environments, as the Adriatic Sea, where ship sailing routes and representative ship types involved in accidents are known, so possible collision scenarios may be reasonably predicted. Residual bending moment capacity under combined bending moment is calculated using regression equations developed based on non-linear finite element analysis. Still water vertical bending moments are obtained by damage stability analysis. Vertical and horizontal wave bending moments are determined by short-term response analysis of damaged ship in the Adriatic Sea, using transfer functions obtained by 3D panel hydrodynamic method. Limit state function is defined using interaction equation for damaged ship exposed to combined bending moments. Safety indices are calculated by FORM for different collision scenarios that are generated by MC simulations. Such approach enables to determine the safety indices for the most frequent damages and also to reveal the most critical situations resulting in the lowest safety indices.
Path Following of a Ship Sailing in Restricted Waters Based on an Extended Updated-Gain High-Gain Observer
Authors: Wang Jianqin , Zou Zaojian , Wang Tao
Published: September 2018

The paper studies the path following of a ship sailing in restricted waters based on an output feedback control, which consists of a state feedback control law and an extended updated-gain high-gain observer. According to the separation principle, the state feedback control and the extended updated-gain high-gain observer are designed separately. The state feedback control law is designed based on a robust guaranteed cost control method assuming that system states are measurable. Sufficient conditions are given for the control based on a linear uncertain system. The extended updated-gain high-gain observer, whose gains are updated according to the nonlinear functions of available evaluation errors, is used to reconstruct system states. Then the output feedback control is obtained by replacing states value in the state feedback control law with its estimation yielded by the state observer. Numerical simulations confirm the effectiveness of the proposed control method for the path following of a ship sailing in restricted waters.
New Generation of Heavy Wall Thicknesses Line Pipes for HPHT and Ultra-Deep Water Applications
Authors: Crippa Stefano , Motta Lorenzo , Paggi Alessandro , Bagliani Emanuele Paravicini , Elitropi Alessandro , Darcis Philippe
Published: September 2018

Oil and Gas industry in the last decades has increased the use and need of heavy wall thickness line pipes, in particular for onshore / offshore high pressures and high temperatures (HP/HT) and offshore deep water / ultra-deep water applications.

The paper presents the results achieved by Tenaris on seamless line pipes in grades X65/X70, according to API 5L / ISO 3183, with wall thickness in a range from 40 to 60 mm and diameter between 6 5/8” and 16”, produced by hot rolling process followed by quenching and tempering. Such line pipes are able to withstand very demanding conditions, like sour environment, very high pressure and wide temperature range.

In this publication, the main outcomes of laboratory testing activities on the mentioned materials will be presented as part of heavy wall line pipe qualification. For this purpose, a special testing program, including mechanical and corrosion tests, has been executed. Material demonstrated an excellent behaviour, exhibiting both mechanical, toughness and stress corrosion properties suitable for the envisaged harsh applications.
Numerical Method to Estimate Fluid-Structure Interaction Effect of Ships Under Severe Wave Condition
Authors: Takami Tomoki , Iijima Kazuhiro
Published: September 2018

In this study, for the sake of evaluating the structural response taking account of the fluid-structure interaction effect of a ship under severe wave condition, a method for coupling the CFD and 3D FEA in a sequentially staggered manner, is developed. The elastic deformation of the ship is taken over, not only to the following FEA stages but also to the following CFD stages. In order to validate the developed two-way coupling method, and to investigate into the fluid-structure interaction effect on the ship, the comparisons among the straightforward (one-way) coupling method, the experimental results and the developed two-way coupling method are carried out, in terms of the wave-induced loads exerted on the ship, and the hydroelastic response. Both the weakly and strongly coupled methods are investigated. The fluid-structure interaction effect is found as a decrease of the natural frequency of vertical vibration mode of the ship; the natural frequency predicted from the developed two-way coupling method is slightly lower than that from the one-way coupling method.