bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study on Vortex-Induced Motions of Semisubmersibles With Three Columns With Different Sections Types
Authors: Tian Chenling , Xiao Longfei , Liu Mingyue , Yang Lijun , Liu Jing 
Published: November 2019

Abstract
Vortex-induced motion (VIM) phenomenon is a great challenge for design and operation of offshore structures subjected to ocean flow. Semi-submersibles with three columns are often applied to the field of wind turbine, suffering VIM motions probably. In recent years, it is showed that many factors have more or less influence on VIM of platforms. A comparison of circular columns with square columns on VIM characteristics of three-column semisubmersibles is carried out using the detached eddy simulation (DES) method via Star-ccm+ software. This paper analyzes motions in the transverse direction and yaw, as well as fluid forces including drag force and fluctuating lift force. The results show that transverse amplitudes of semisubmersible with three square columns are much lower than those of semisubmersible with three circular columns at all incidences. Besides, the authors conclude that the semisubmersible with three square columns do not experience obvious resonance behavior, which is different from the semisubmersible with three circular columns. Besides, galloping phenomenon occurred at large reduced velocities at 0°-incidence for the semisubmersible with three square columns, which is likely not induced by lift force directly. Meanwhile, in these cases, yaw amplitudes are also larger than the others. This may be due to the galloping behavior, which is just a conjecture.
Numerical Study on the Dynamical Characteristic and Impact Force Between Vessel With Rake Bow and Bridge Pier
Authors: Xu Ming Cai , Zhang Zi Xuan , Zhang Xiao Qiang , Pan Jin , Huang Yi Fei 
Published: November 2019

Abstract
The possibility of collisions between vessels and bridges has an unavoidable increase, which may cause significant economic losses and sometimes even casualties. The finite element method is used to simulate the impact process between the vessel with raked bow and bridge pier. The influence of parameter on the structural response and impact force is discussed, including the impact velocity, angle, mass of vessel, and the shape of bridge. The relationship of collision force and energy of impact vessel is investigated. It is found that the collision energy shows a quadratic growth trend with the increase of vessel velocity.
Numerical Simulation of Container Stacks Dynamics Under Typical Motion Excitation
Authors: Li Chuntong , Wang Deyu , Liu Jiaqi 
Published: November 2019

Abstract
Present regulation and norms for securing equipment are calculated based on static strength analysis ignore the dynamic situations faced by containers during maritime transportation, and the event of container loss still occurs. This research aim to investigate the dynamic behavior of container stack under typical motion excitations simulating real ocean conditions. A two-tier scaled model of a 20-ft ISO freight container were built based on scaling law. The research process is divided into three stages. The first stage: establish a full-scale 20-ft container mode, and obtain characteristic information such as mass and stiffness through finite element analysis. In the second stage, the multi-objective optimization algorithm is used to establish the scale model of the container, and the scale model of the design is verified. In the third stage, the finite element method is used to further understand the influence of each design variables on the dynamic response of container stack. Under different motion excitations, the influence of each basic variables on the structural response and the load change on the critical points of the structure are determined. Meanwhile, the results of this study also show that the mathematical model constructed is effective and can reasonably predict the actual situation of container stacks stored on the ship’s deck.
Dynamic Response of Spar Wind Turbine Moored by Dynamic Catenaries Under Random Wind and Wave Loads
Authors: Li Yilun , Guo Shuangxi , Kong Yue , Chen Weimin , Li Min 
Published: November 2019

Abstract
As offshore wind turbine is developed toward larger water depth, the dynamics coming from structural and fluid inertia and damping effects of the mooring-line gets more obvious, that makes the response analysis of the large floating wind turbine under wind&wave load more challenging. In this study, the dynamic response of a spar floating wind turbine under random wind and wave loads is examined by the modified FEM simulations. Here an integrated system including flexible multi-bodies such as blades, tower, spar and mooring-lines is considered while the catenary dynamics is involved.
The dynamic restoring performance of the catenary mooring-line is analyzed based on the vector equations of 3D curved flexible beam and its numerical simulations. Then the structural responses, e.g. the top tension, structural displacements and stress of the tower and the blade, undergoing random wind&wave loads, are examined. Morevoer, the influences of the catenary dynamics on its restoring performance and the hysteresis behavior are presented. Our numerical results show: the dynamics of mooring-line may significantly increase the top tension, and, particularly, the snap tension could be more than 3 times larger than the quasi-static one. Moreover, the structural response under random wind&wave load gets smaller mainly because of the hysteresis effect coming from the mooring-line dynamics. The floating body displacement at surge frequency is around 20% smaller, and the tower root stress at bending frequency is about 30% smaller than the quasi-static values respectively.
Second-Order Responses of a 10 MW Floating Wind Turbine, Considering the Full QTF
Authors: Cao Qun , Xiao Longfei , Guo Xiaoxian , Liu Mingyue 
Published: November 2019

Abstract
Second-order components of wave loads acting on the floating foundation for wind turbines may induce severe resonance and lead to fatigue damage at natural frequencies of structures. In this study, the INNWIND.EU Triple-Spar and the DTU 10 MW Reference Wind Turbine were simulated by utilizing software FAST to obtain the second-order responses of the floating wind turbine under selected steady winds with collinear random waves. Low-frequency responses at surge and pitch natural frequencies dominated the response spectra, which were underestimated by the first-order numerical model. A response peak appeared in tower-top motion spectrum in vicinity of the first-order fore-aft vibration frequency of the tower when the sum-frequency wave effects were considered. The second-order high-frequency responses arose when the full QTF was utilized, compared to results with Newman approximation. Different operating conditions with varying wind speeds, wave periods, significant wave heights and wave directions were selected to conduct the sensitivity study of the second-order responses.
Numerical Simulation of Water Wave Propagation Over Porous Slope Bottom by Using Two-Domain Method
Authors: Min Eun-Hong , Koo Weoncheol 
Published: November 2019

Abstract
This study aims at the numerical analysis of wave characteristics when a wave propagates on the porous slope seabed. Numerical wave tank technique was developed using boundary element method with constant panels on the boundary. The fluid was satisfied with potential flow conditions and Darcy’s law was applied for porous intersection. Two computational domain method, which consists of fluid and porous domains, was used to simulate the propagating waves over a sloped seabed having a permeability. To consider fluid-porous boundary interaction, three-step boundary value problems were calculated. The wave amplitude decreased along the free surface as the wave propagated over a sloped bottom. The wave reflection and transmission by subsea structures were also analyzed.
Experimental Study on the Motion of a Flexible Hose Net Used in Automated Net-Hauling System
Authors: Li Yue , Mizukami Yoichi , Yoshida Takero , Li Qiao , Han Jialin , Kitazawa Daisuke 
Published: November 2019

Abstract
In the set-net fishery, large amount of manpower is needed for hauling the box chamber to harvest fish. With aging problem and labor insufficiency, the labor-intensive net-hauling method faces the problems of lower production, lower efficiency and higher operational risk. An automated net-hauling system using the flexible hose net which is installed in the box chamber is being developed to solve such problems. With air injected from one edge of the hose net, the hoses are inflated and the buoyancy force increases, the net floats up gradually, cornering the fish in the other edge. To corner and harvest the fish efficiently and safely, the deformation and the motion parameters of the hose net are of significance. This paper presents the results of the water tank experiment using 1/6 scale model, which was conducted to analyze the deformation of the hose net with different volumes of air in, the time spent for floating up and sinking down and the average velocities of sinking and floating processes. The results showed that when the attached weight reached 42.5% of the maximum buoyancy force of the hose net, the net could float up gradually in an ideal form and sink down smoothly through natural exhaust and stretched on the bottom of the water tank. The time spent and average velocities in floating up and sinking down processes varied with air pressure and air flow rate, making it possible to control the motion of the hose net by adjusting the air flow in practical operation.
Three-Dimensional Physical Environment Modelling for Integrated Multi-Trophic Aquaculture (IMTA) Implementation in Onagawa Bay, Japan
Authors: Zhou Jinxin , Yoshida Takero , Zhang Junbo , Park Sanggyu , Kitazawa Daisuke 
Published: November 2019

Abstract
Continually increasing demands on aquaculture products drive the current monoculture to upgrade and upscale because of not only economic but environmental sustainability reasons. Over the past decade, open water integrated multi-trophic aquaculture (IMTA) practiced as a potential alternative has been demonstratively illustrated from both scientific and public attention. Basing on previous studies of this synergistic aquaculture system, we, here, studied the physical environment in Onagawa Bay as the cornerstone for further IMTA implementation. Onagawa Bay locates in Miyagi Prefecture, Japan, and because of its mature practice on polyculture, it is recognized as a suitable site for IMTA. Unfortunately, the earthquake and tsunami in 2011 caused a huge uncertainty on physical environment changes. Still insufficient researches have been conducted on physical environment study, especially through modelling method. Here, adopting the three-dimensional Marine Environmental Committee (MEC) ocean model, we described the setup and validation for Onagawa Bay in this research. At the present stage, simulation results can best fit observation data on the tidal elevation with the correlation coefficient between observed and simulated tidal elevation reaching 0.96, captured the main characteristic of flow velocity, and exhibited homogenous tendency towards water temperature. Furthermore, through the plot of the residual velocity field and statistical seasonal velocity distribution, potential aquaculture configuration has been discussed spatio-temporally on the hypothesis that high current speeds contribute to the further implementation.
A Simulation Program for Load-Out Operation Using Self-Propelled Modular Transporters
Authors: Du Zunfeng , Zhu Haiming , Xu Dong 
Published: November 2019

Abstract
Self-propelled modular transporters (SPMTs) are special vehicles designed for transporting massive objects. It is becoming popular to transport offshore structure modules onboard using SPMTs in recent years. The operation is a high-risk task which needs to be carefully planned. This paper aimed at developing a load-out simulation program that can be utilized to improve the existing planning method. To achieve this goal, the risks in load-outs were addressed, and an analysis procedure was established based on the principle of SPMT hydraulic system and ship hydrostatics. We built the simulation program on the basis of the analysis procedure. It enables users to practice load-out operations in a virtual environment. By using the program, engineers can obtain an overview of the load-out process and a clear knowledge of the risks that will arise. The load-out plan can be made, verified, and optimized beforehand, which is quite beneficial to minimize the risks and get well prepared for the operation.
New Spar Design for Floating Offshore Wind Turbine With Damping Plates
Authors: Ishida Shigesuke , Imai Yasutaka 
Published: November 2019

Abstract
Spar is one of the promising floating structures which support wind turbine at sea. In general, some lower part of spar is used as a ballast tank. It is possible to replace this part with other shapes without water-tightness because this part does not contribute to buoyancy nor stability to support the weight or heeling moment of wind turbine. In the field of oil and gas production, truss spar has been developed with this concept and the lower part consists of heave plates. However, for wind turbine, pitching motion is more important than heaving. The authors changed this part to four vertical damping plates to reduce this motion. The effect of the central gap and holes in the damping plates were investigated because these parameters have effects on flow separation and hydrodynamic forces. The motions in waves of the new spars were compared with a classic spar of the same dimensions and stability. The proposed vertical damping plates, with central gap or holes, work to reduce the pitching motion in wide range of wave frequency. Considering the expected cost reduction and some motion reduction, the promising nature of the proposed spar revealed.
Validation of Pack Ice Resistance in Oblique Condition by the Comparison With Ice Model Test Results
Authors: Kim HyunSoo , Ozden Erinc , Lee Jae-bin 
Published: November 2019

Abstract
Countries around the world are increasingly interested in resource development in the Arctic due to global warming. Recently, Arctic coastal states (Russia, USA, Canada, etc.) are pursuing infrastructure construction projects for resource development in the Arctic region. Because the offshore structures in the Arctic are exposed to the sea ice, in order to ensure the safety of the structures, the calculation of the ice resistance is of paramount importance for offshore structures. In general, studies on the ice resistance have been carried out for the breaking and clearing performance of icebreakers. However, in the case of fpu (floating production unit) for resource development in the Arctic region, it is necessary to estimate the ice resistance in the oblique condition to ensure safety. Thus, despite estimation of the ice resistance in the oblique condition is significant, there has not been enough research until recently. In this paper, we suggest algorithms for estimating the ice resistance in the oblique condition. For the estimation process, an in-house code software program is used and an ice resistance estimation module is implemented for the oblique condition using empirical formula. This paper shows results of the ice resistance which was calculated in the oblique condition, and the change of the ice resistance is shown according to various oblique angles in pack ice. In addition, the results are compared to the model test result of a fpu in pack ice of 80% concentration.
Mechanical Analysis of Fiber Glass Reinforced Bonded Flexible Pipe Under External Pressure
Authors: Zhang Xiaojie , Bai Yong , Liu Chang , Wang Zhao , Zhao Jiannan 
Published: November 2019

Abstract
Fiber glass reinforced bonded flexible pipe (FGRFP) is one kind of new type composite pipe. However, the mechanical properties of FGRFP are not so clearly at present. Therefore, this article aims at studying the buckling pressure of FGRFP under external pressure by using external pressure test, numerical method and finite element method. Three kinds of buckling pressure have been obtained by using three methods as aforesaid. According to compare the buckling pressure of three methods, the relative error of the numerical method and the finite element method relative to external pressure test ranges from 4.09% to 14.51%. According to the result of finite element method, the first layer’s stress at the topside of FGRFP’s cross section and the final layer’s stress at the horizontal position of FGRFP’s cross section is the max stress. The numerical method and finite element method came up with in this article can be used to analyze the buckling pressure of FGRFP. These methods can also provide a guidance to pipeline engineers to design and production of FGRFP.
Numerical Manoeuvrable Tank on Wave Based Moving Domain
Authors: Feng Dakui , Cai Xiao , Sun Yue , Zhang Zhiguo , Huang XiaoWei 
Published: November 2019

Abstract
The maneuvering motion simulation of ship in waves needs large space, the simulation based static domain requires a large amount of mesh. On the contrary, the moving domain can reduce the grid amount and improve the simulation speed. This paper studies the establishment of numerical wave tank based moving domain. The wave-generation method of defining inlet boundary conditions is proposed. The level set method is used to solve the free surface. The URANS equation is solved by finite difference method and the projection algorithm. For the wave-generation method of defining inlet boundary conditions, the velocity inlet direction is always fixed because the direction of incident wave is always fixed. Specifically, the yaw should be turned off avoid the disturbance of wave in the y direction. Comparing the simulated wave with the target wave, the numerical results show that the simulated value is coincident with the theoretical value in the moving domain, and there are no obvious signs of dissipation over time. The established moving domain can produce a continuous and qualified wave, which provides a theoretical basis for the study of maneuvering simulation of ship in waves.
Numerical Investigation of an Optimised Horizontal Axis Tidal Stream Turbine
Authors: El Sheshtawy Hassan , el Moctar Ould , Schellin Thomas E. , Natarajan Satish 
Published: November 2019

Abstract
A tidal stream turbine was designed using one of the optimised hydrofoils, whose lift-to-drag ratio at an angle of attack of 5.2 degrees was 4.5% higher than that of the reference hydrofoil. The incompressible Reynolds-averaged Navier Stokes equations in steady state were solved using k-ω (SST) turbulence model for the reference and optimised tidal stream turbines. The discretisation errors and the effect of different y+ values on the solution were analysed. Thrust and power coefficients of the modelled reference turbine were validated against experimental measurements. Output power and thrust of the reference and the optimised tidal turbines were compared. For a tip speed ratio of 3.0, the output power of the optimised tidal turbine was 8.27% higher than that of the reference turbine of the same thrust.
Effect of Spectrum Tail Length on Modulational Instability and Freak Wave Occurrence in JONSWAP Sea States
Authors: Kirezci Cagil , Babanin Alexander V. 
Published: November 2019

Abstract
In this study, probability of freak wave occurrence due to modulational instability in JONSWAP sea states are investigated. This investigation has been conducted based on the quantitative indicators of instability in wave spectrum, which are two Benjamin-Feir index (BFI) [1,2] with different spectral bandwidth definitions and Π number [3]. Evolution of wave field are simulated using fully nonlinear phase-resolving Chalikov-Sheinin (CS) numerical model [4,5]. Initial sea surface is controlled with JONSWAP shape parameters (α and γ) and random initial phases. Effect of high frequency end of spectrum on modulational instability and freak wave evolution are discussed by considering 4 different tail lengths.
According to simulation results, all parameters that are considered here perform as an indicator for the occurrence of extreme events which makes it possible to define a certain interval for indicators, where freak wave occurrence probability is the highest and potentially dangerous, to be possibly used in extreme wave forecasting. Another key finding is that, modulational instability increases when high frequency part of spectrum is present (longer tail) as expected. Nevertheless, after certain nonlinearity, modulational instability is more prone to result in breaking which significantly decreases the probability of occurrence of freak events. Therefore, spectra with shorter tail length result in more dangerous sea states.
Vortex-Induced-Vibration of Jack-Ups With Cylindrical Legs in Regular Waves
Authors: Ramadasan Sudheesh , Tao Longbin , Dev Arun Kr 
Published: November 2019

Abstract
A simple mathematical model is developed based on the single-degree-of-freedom analogy and principle of conservation of energy evaluating various modes of Vortex-Induced-Vibration (VIV) of a jack-up with cylindrical legs in regular waves. Similar to uniform current, mass ratio, damping ratio and mode factor are found to be the important parameters controlling the cross-flow VIV and radius of gyration also for the yaw VIV. Criteria for the initiation of the mentioned VIV modes are developed for the cases of a single 2D cylinder experiencing planar oscillatory flow, four rigidly coupled 2D cylinders in rectangular configuration experiencing planar oscillatory flow and jack-up experiencing regular waves. The newly developed VIV model is validated by a set of experiments conducted in a wind, wave and current flume. The importance of mass damping parameter is further demonstrated in suppressing VIV in regular waves. The mathematical method will equip engineers to consider the effect of VIV due to regular waves in jack-up designs.
Implementation of Tidal Stream Turbines and Tidal Barrage Structures in DG-SWEM
Authors: Schnabl Andrea M. , Moreira Tulio Marcondes , Wood Dylan , Kubatko Ethan J. , Houlsby Guy T. , McAdam Ross A. , Adcock Thomas A. A. 
Published: November 2019

Abstract
There are two approaches to extracting power from tides — either turbines are placed in areas of strong flows or turbines are placed in barrages enabling the two sides of the barrage to be closed off and a head to build up across the barrage. Both of these energy extraction approaches will have a significant back effect on the flow, and it is vital that this is correctly modelled in any numerical simulation of tidal hydrodynamics. This paper presents the inclusion of both tidal stream turbines and tidal barrages in the depth-averaged shallow water equation model DG-SWEM. We represent the head loss due to tidal stream turbines as a line discontinuity — thus we consider the turbines, and the energy lost in local wake-mixing behind the turbines, to be a sub-grid scale processes. Our code allows the inclusion of turbine power and thrust coefficients which are dependent on Froude number, turbine blockage, and velocity, but can be obtained from analytical or numerical models as well as experimental data. The barrage model modifies the existing culvert model within the code, replacing the original cross-barrier pipe equations. At the location of this boundary, velocities through sluice gates are calculated according to the orifice equation. For simulating the turbines, a Hill Chart for low head bulb turbines provided by Andritz Hydro is used.
We demonstrate the implementations on both idealised geometries where it is straightforward to compare against other models and numerical simulations of real candidate sites for tidal energy in Malaysia and the Bristol Channel.