bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue Analysis for Mooring System of a Spar-Type Floating Offshore Wind Turbine
Authors: Xue Xutian , Liu Xiaoyong , Chen Nian-Zhong , Gao Xifeng 
Published: December 2020

Abstract
This paper aims to perform a time-domain mooring fatigue analysis for a Spar-type floating offshore wind turbine operated in the South China Sea. Tension ranges of mooring lines are achieved from a hydrodynamic analysis where the effects of wind, wave and current are considered. A rainflow counting method is used to calculate the number of mooring tension cycles with corresponding ranges. The fatigue lives of mooring lines are then predicted by Palmgren-Miner’s rule according to T-N & S-N curves. A comparison of fatigue lives predicted by T-N & S-N curves-based approaches with/without considering safety factors is made. The results show that the T-N curves-based approach is more conservative than the S-N curves-based approach if safety factors are not considered in the two approaches, while the fatigue lives predicted by both approaches are in general comparable when the safety factors suggested by API and DNVGL are applied in the two approaches. A comparative study of three kinds of R4 grade studless mooring chains with different diameters (2.5-inch, 4-inch, 5-inch) is also conducted and the results show that the design with the 2.5-inch chain does not meet the fatigue requirements.
Influence of Torpedo Piles Parameters When Assessing Final Penetration Depths
Authors: Sant’Anna do Nascimento Leonardo 
Published: December 2020

Abstract
This paper has been influenced by a basic question: assuming a torpedo pile launching in a base case scenario, which parameters, when not well controlled, would affect more the pile final penetration depth? Aiming to provide an answer to this question, the methodology adopted in this study assumes the application of numerical simulations and statistical analyses in order to quantify the influence of the uncertainties of such parameters in the final penetration depth. From the assessment, one may expect responses in terms of which parameters shall be better controlled during a launching procedure in order to reduce the uncertainties associated to the target depth.
For the development of the study, a simplified approach for the dynamic numerical analyses has been adopted in order to allow a massive data generation for the statistical treatment. The main parameters associated to the torpedo pile and the launching scenario have been generated taking into account their uncertainties. The Monte Carlo method has been considered and statistical treatment has been applied to quantify the influence of the parameters in the final penetration depth.
The results demonstrate that apply the simplified method described in the paper is adequate to simulate both the subsea free fall and the pile driving phases to obtain the final penetration depths. The torpedo mass has been found as the physical parameter which influences more the final penetration depth. However, the study demonstrates that, given a standard launching procedure assessed by numerical simulations, uncertainties on physical parameters are much less significant for the final penetration depth than the uncertainties inherent to the assumptions and data applied to simulate the soil damping.
Nonlinear Analysis of an Oscillating Wave Surge Converter in Frequency Domain via Statistical Linearization
Authors: da Silva Leandro S. P. , Sergiienko Nataliia Y. , Cazzolato Benjamin S. , Ding Boyin , Pesce Celso P. , Morishita Helio M. 
Published: December 2020

Abstract
Wave energy devices operate in resonant conditions to optimize power absorption, which leads to large displacements. As a result, nonlinearities play an important role in the system dynamics and must be accounted for in the numerical models for realistic prediction of the power generated. In general, time domain (TD) simulations are employed to capture the effects of the nonlinearities. However, the computational cost associated with these simulations is considerably higher compared to linear frequency domain (FD) methods. In this regard, the following work deals with the nonlinear analysis of an oscillating wave surge converter (OWSC) in the FD via the statistical linearization (SL) technique. Four nonlinearities for the proposed device are addressed: Coulomb-like torque regulated by the direction of motion, viscous drag torque, nonlinear buoyant net torque, and parametric excitation torque modulated by the flap angle. The reliability of the SL technique is compared with nonlinear TD simulations in terms of response probability distribution and power spectrum density (PSD) of the response and torque; and mean power produced. The results have demonstrated a good agreement between TD simulations and SL, while the computation time of the SL model is approximately 3 orders of magnitude faster. As a result, SL is a valuable tool to assess the OWSC performance under various wave scenarios over a range of design parameters, and can assist the development of such wave energy converters (WECs).
Column Interference Effect of Multi-Column Floating Structures on Vortex-Induced Motion Using Numerical Prediction Model
Authors: Toyoda Yosuke , Hirabayashi Shinichiro , Gonçalves Rodolfo T. , Suzuki Hideyuki 
Published: December 2020

Abstract
In this study, a numerical prediction model for vortex-induced motions (VIM) of 4-circular-column floater was developed from a database of hydrodynamic forces acquired from the forced oscillation tests. A set of combinations of oscillation frequencies and amplitudes in the transverse direction (1 degree of freedom) were carried out. The numerical results were validated with experimental results of VIM performed in a towing tank. The effect of column interference was discussed by analyzing the hydrodynamic forces on each column separately and also the motion behavior of the floater for spacing ratios between columns, S/D = 2, and 3, where S is the distance between column centers and D is the column diameter.
Experimental Study on Fish-Harvest Performance of the Flexible Hose Net
Authors: Li Qiao , Li Yue , Mizukami Yoichi , Dong Shuchuang , Yoshida Takero , Kitazawa Daisuke 
Published: December 2020

Abstract
Set net fishery is one of the efficient fishery methods and has a history of several centuries in Japan. In 2017, fish harvest amount of set net fishery was 326,200 tons, about 10.2% of the total amount in Japan. The traditional method for harvesting fish is to use two fishing vessels to haul up the box chamber and obtain the fish in it, which requires supplementary equipment and human power. For reducing human power and safety, the automated net-hauling system has been developed. This system used a flexible hose net, with air injected from one side of the hose net, then the net could float up gradually and harvest the fishes. A new hose net was developed by reducing the number of air injection tubes from seven to two in comparison to the previous hose net. The paper presents the results of the animal experiment using 1/60 model of the flexible hose net. The fish-harvest effect in the flow are experimented by the Horizontal Circulating Water Channel. The fish-harvest effect was observed directly. The floating up velocity of the hose net can affect the fish-harvest rate. If the floating up velocity is too fast, the fish are easy to be stuck on the net and cannot swim forward to arrive at the catching spot (trap net). Therefore, the floating up velocity of the hose net not only determines the operational efficiency, but also affects the fish-harvest rate to some extent. Additionally, the deformation of flexible hose net was considered not only during the air injection, but also during the water intrusion.
Characteristic Analysis for Spectrum of Swell Dominated Seas With In-Situ Measurements
Authors: Gao Xiang , Ma Xiaozhou , Ma Yuxiang , Dong Guohai , Gao Junliang 
Published: December 2020

Abstract
The characteristics of wave spectrum in the swell dominated seas (i.e., the Chancay Bay on the western coast of Peru) are studied based on directional wave spectra measured using the technique of acoustic Doppler current profiler (ADCP). According to the wave rose diagram and the measured wave spectra, this sea area is mainly affected by the swell of the southwest direction and the significant wave height is between 0.7m-2.6m. Moreover, the wave spectra feature the single-peaked spectra and the double-peaked spectra. The JONSWAP spectrum model is adopted to fit single-peaked swell spectra. A close agreement could be found between the observed and fitted spectrum parameters. Hence, the JONSWAP model can be used to describe the single-peaked swell spectra in the sea area studied in this work. As for the double-peaked spectrum, Ochi-Hubble double peak spectrum model and simplified Torsethaugen double peak spectrum model are adopted to fit the wave spectra, respectively. Comparing the fitting results of two double-peaked spectrum modal, it’s possible to conclude that the measured double-peaked spectra can be well represented by the Ochi-Hubble double peak spectrum model.
Numerical Prediction of Cavitation Performance of Controllable Pitch Propellers With Different Pitch Adjustment Velocities
Authors: Xue Ying , Dong Xiao-Qian , Yang Chen-Jun 
Published: December 2020

Abstract
The turbulent flow around a cavitating controllable pitch propeller (CPP) is simulated by solving the Reynolds-Averaged Navier-Stokes (RANS) equations, to investigate the dynamic effects on cavitation when the pitch of propeller blades is changed at different pitch adjustment velocities (PAVs). The process of changing the pitch at prescribed PAVs is controlled by a user-defined function (UDF) in the software FLUENT, and during the process, the time-dependent flow domain is re-discretized at each time step with dynamic meshes. The SST k-ω turbulence model and the cavitation model proposed by Schnerr and Sauer are employed in the simulation. The numerical simulation approach is first validated against model experiments for a fixed pitch propeller (FPP) working in the open water. A grid dependence study is carried out to determine a proper mesh resolution for the simulation of such cavitating flows; then the hydrodynamic performance as well as the extent and volume of the sheet cavities obtained from the RANS simulations are compared with experimental data. Then influences of the PAV on the hydrodynamic performance and cavity geometry are investigated. The CPP blades are rotated around the spindle axes to change the pitch, and the movement is controlled by a UDF. The PAV is prescribed and kept constant in the process of adjusting the pitch. At different PAVs, the unsteady thrust and torque, pressure distributions on blade surfaces and propeller disk, cavity geometry, as well as cavitation volume of the cavitating flow are compared with each other to assess the dynamic effects of the PAV.
State Estimator for Floating Offshore Wind Turbines and Performance Evaluation
Authors: Tanabe Hiroki , Hara Naoyuki , Konishi Keiji 
Published: December 2020

Abstract
Floating offshore wind turbines (FOWTs) are considered as a promising technology for installing turbines in deeper sea sites. One of the difficulties is that the maintenance cost tends to be high because of the limited accessibility to the site. Therefore remote monitoring and estimation of various physical variables of a wind turbine in real-time is important for health assessment and fault diagnosis before a critical failure occurs. One promising way to do this is to have a wind turbine model in computer and estimate the various physical variables of the turbine in real-time by using the available noisy sensor measurements. In this paper, we consider a 5MW FOWT and design a Kalman filter to deal with the estimation problem of the turbine state variables and effective wind speed. A blade pitch controller that uses the estimated state feedback and wind feedforward is also designed. The proposed estimation and control scheme is evaluated using the turbine simulation code, FAST, and results show that the state variables are well estimated except for the blade flapwise moment.
Heave Motion Performance of Multiple Wave Energy Converters Arrayed in a Water Channel Resonator
Authors: Kim Jeongrok , Cho Il-Hyoung 
Published: December 2020

Abstract
The performance of multiple wave energy converters (WECs) arranged in a Y-shaped water channel resonator (WCR) for amplifying the wave energy with low density was investigated. The WCR consists of a long channel and waveguide installed at the entrance. If the period of the incident wave coincides with the natural period of the fluid in the WCR, then resonance occurs, and the internal fluid is greatly amplified in the form of standing waves. The WECs were positioned at the anti-nodes of standing waves formed in the WCR to maximize energy extraction. We dealt with the heave motion, time-averaged power, and capture width ratio (CWR) of WECs, which are composed of a heaving cylinder and a linear generator. For this purpose, we used the boundary element method and WAMIT commercial code. In parallel, systematic model tests were conducted at the 2D wave tank in Jeju National University to validate the numerical solution. Both results were in good agreement. WECs with a short draft are efficient in energy extraction compared with WECs with a long draft. Numerical and experimental results reveal that the WECs arranged in a WCR have higher efficiency over a wide band of periods than a single WEC without a WCR. Therefore, the wave energy with low density can be amplified by the resonance of the internal fluid in the WCR.
Feasible Numerical Technique for Analysis of Offshore Pipelines and Risers
Authors: Trapper Pavel A. 
Published: December 2020

Abstract
A simple 2D numerical model for pipeline and riser configuration analyses is presented. The model considers large deformations of the pipe, pipe-seabed contact detection, pipe’s interaction with uneven inelastic seabed, environmental loading such as drag forces applied by the ocean currents, water surface level variations and incorporation of buoyancy modules.
The solution technique is based on a consistent minimization of the total potential energy of the deformed pipe discretized as a Riemann sum, which results in a system of nonlinear algebraic finite difference equations that is solved in an incremental/iterative manner. At each increment, the total potential energy is being updated, thus accounting for energy dissipation due to irrecoverable plastic deformation of the seabed and according to hydrodynamic drag forces. The whole pipe is treated as a single continuous segment.
To demonstrate the method, examples with several riser configurations and pipe-lay scenarios are presented. It is shown how on-bottom unevenness, including pits and hills, incorporation of buoyancy modules and tidal effects can affect pipeline or riser configurations and their internal forces. Results are compared to those obtained with Abaqus and appear to be in an excellent agreement.
The model presents simple and time-efficient way to analyze the pipe-lay or riser configurations with various boundary and loading conditions. The proposed model, contrary to commercial packages, which impose using time-consuming Graphical User Interface (GUI), allows for performing the series of analyses for varying geometric and/or material properties, and processing the results in reasonable time by single click.
Retracted: “Dynamic Analysis of a Subsea Spool Under Dropped Container Impact Loads” [Proceedings of the ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering, Volume 4: Pipelines, Risers, and Subsea Systems, Virtual, Online, August 3–7, 2020, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-8435-5, Copyright © 2020 by ASME. Paper No. OMAE2020-18578, V004T04A037; 8 pages; doi: 10.1115/OMAE2020-18578]
Authors: ASME  
Published: December 2020

Abstract
This paper was removed from publication at the author’s request, August 30, 2021.
Copyright © 2021 by ASME
Measurements of Low Frequency Vibration in Subsea Piping Using ROV Video Analysis
Authors: van Wijhe Andries , Buijs Lennert , Stachyra Leszek , Macchion Olivier 
Published: December 2020

Abstract
Vibrations in Subsea Production Systems are well recognized as a concern in the subsea industry. To identify the severity of the vibrations and potential accumulated fatigue damage, subsea vibrations need to be measured with great accuracy. Currently, accurate detection and subsea measurements are often performed by utilizing accelerometers, which have to be connected to the structure by ROV or a diver.
ROV video analysis provides an alternative solution. Video analyses are widely utilized across different applications. With the increased quality of a HD camera on ROV, the accessibility of such measurements is an attractive substitute to other techniques.
As a part of on-shore mechanical testing on a full assembled XT in St John’s Canada, a flowloop on a water injection XT was subjected to free vibrations. The vibrations were filmed using a commercial HD camera placed on a tripod.
This test was done to validate data generated using video processing in which pipe vibration of an operating subsea XT was filmed using an ROV camera.
A study that aimed to quantify the video processing accuracy, limitations and provide general guidance was conducted. For the onshore test filmed with a tripod the results of video analyses were compared with the measurements obtained by means of accelerometers. For the video of an operating subsea XT filmed by an ROV, the obtained vibration frequency and direction was compared with the free mechanical vibration obtained by a FEM model.
The results obtained by means of the video analysis matched well with the accelerometer data. A high accuracy was reached, as vibration displacements as low as 20% of the pixel were accurately determined in the video analysis. With respect to detection frequencies, the upper cut-off frequency was around 15 Hz determined by the video framerate. The video analysis utilizing ROV videos was found to be applicable for low frequency vibration measurements, opening the opportunity for easier and more cost effective vibration detection and monitoring. The method is also reliable for subsea application in which the camera is placed on an ROV and is thus not affected by ROV movements, subsea lighting condition and moving ocean debris.
Effect of Wave-Current Interaction on Structural Responses of a Very Long and Side-Anchored Floating Bridge
Authors: Dai Jian , Abrahamsen Bjørn Christian , Leira Bernt Johan 
Published: December 2020

Abstract
This paper is concerned with a computational study on the hydroelastic response of a long, straight and side-anchored fjord-crossing floating bridge accounting for the wave-current interaction. The effect of this interaction on a single bridge pontoon is investigated by using the three-dimensional potential solver VERES3D. The frequency-dependent hydrodynamic coefficients and excitation force transfer functions are presented and compared with WAMIT results where the current effect is ignored. Based on the frequency domain results, an approach to account for the wave-current interaction in time domain analysis is proposed. Next, a generic straight and side-anchored floating bridge model is put forward to examine the stochastic structural responses in the time domain. For the purpose of comparison, the bridge responses under waves and current without interaction are also investigated. This study attempts to quantify the wave-current interaction effect on the structural responses of a floating bridge and provide useful recommendations and suggestions to researchers and engineers for their study of similar structures.
Numerical Modelling of the Interaction of Moving Fish Nets and Fluid
Authors: Martin Tobias , Wang Gang , Bihs Hans 
Published: December 2020

Abstract
The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.
Elevated Pipelay Initiation and Cost Optimized Lowering of Subsea Rigid Pipeline
Authors: Vadassery Ittyarachan , George Gregory , Sudevan Hariraj 
Published: December 2020

Abstract
S-lay installation methodology is an industry accepted method for the installation of subsea rigid pipelines. Pipeline initiation is a major operation during the start of S-lay and its selection is dependent on various factors including project requirements, field layout and strength of holdback.
The beachpull initiation method is utilized in shallow water regions where a barge or vessel is unable to access the initiation point due to keel clearance. For most applications, however, the dead man anchor initiation method is utilized irrespective of the water depth. For the dead man anchor methodology, the type of anchor needs to be selected based on the in-situ conditions. Near the jacket, conventional dead-man anchor initiation is not feasible due to the presence of subsea assets. The holdback method provides an acceptable alternative in such cases. There are several variations of this method such as elevated holdback, vertical bow string and horizontal bow string initiation which are chosen based on operational requirements.
During a project undertaken recently in the Middle East region, several initiation challenges were encountered due to congested fields owing to subsea assets and the best suitable methodology was determined which included dead man and elevated holdback initiation. It was observed that optimizing the initiation, reduced risk associated with subsea asset clashes and accelerate the schedule. For another fast track project in Asia Pacific region at deeper water depths, vertical bow string initiation was used to override challenges in reducing loads on the jacket. On the same project a modified initiation method was adopted to avoid a davit lift operation, shorten the target box distance and avoid saturation diving which helped the project avoid mobilization of a large anchored or DP barge and utilize available diving support vessel with a single crane or davit.
The paper explains different challenges in pipelay initiation operations of subsea rigid pipelines and the selection of the appropriate type of initiation. It also presents recent case studies of different initiation operations with the associated challenges and benefits.