bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mode Selection for Offshore Platform Damage Identification Using CMSE Sensitivity
Authors: Xu Mingqiang , Liu Yuchi , Jiang Yufeng , Wang Shuqing 
Published: November 2019

Abstract
A sensitivity-based mode selection strategy for cross modal strain energy (CMSE) method is proposed to identify damage more effectively. The cross modal strain energy sensitivity is defined as the sensitivity index. For this purpose, the cross modal strain energy sensitivity to structural damage is deduced, and is used to select the preferable mode combinations that are sensitive to damage. By using the preferable mode combinations, the CMSE system is refined and the degree of ill-posedness of the CMSE system is reduced. A numerical study is conducted on an offshore platform structure to demonstrate the effectiveness of the proposed scheme. The performances of the CMSE method with and without using the mode selection strategy are compared in the presence of noise. Results show that: (1) the accuracy of damage localization is improved when only a few mode combinations are utilized; (2) On account of excluding substantial low-sensitivity mode combinations, the amount of computation is significantly reduced.
Experimental Study on a Relation Between Nonlinear Hydrodynamic Forces and Wave-Induced Ship Motions
Authors: Taguchi Masakazu , Kashiwagi Masashi 
Published: November 2019

Abstract
Nowadays, in maritime industries, container ships increase in size and they have large flares, which may induce nonlinear wave loads in large-amplitude waves. It is also well known that hydrodynamic forces acting on a ship and resulting ship motions show nonlinearities at some range of wave frequencies. Therefore, we should investigate not only correct estimation of wave loads and ship motions, but also nonlinear ship-motion characteristics in large-amplitude waves. However, it is not that clear which nonlinear hydrodynamic force terms are dominating for the nonlinearity in the ship motions. Although the linear equations of motion have been used, they should be modified to incorporate at least the most important nonlinear hydrodynamic forces and to establish a practical calculation method taking account of only the indispensable nonlinear terms. In this research, we did extensive experimental measurement of hydrodynamic forces and wave-induced ship motions, with which we aim to understand what are practically important nonlinear terms, and to derive practical nonlinear ship motion equations through numerical computation and comparison with experimental data.
Ship Manoeuvring Model Parameter Identification Using Intelligent Machine Learning Method and the Beetle Antennae Search Algorithm
Authors: Chen Changyuan , Tello Ruiz Manases , Lataire Evert , Delefortrie Guillaume , Mansuy Marc , Mei Tianlong , Vantorre Marc 
Published: November 2019

Abstract
In order to identify more accurately and efficiently the unknown parameters of a ship motions model, a novel Nonlinear Least Squares Support Vector Machine (NLSSVM) algorithm, whose penalty factor and Radial Basis Function (RBF) kernel parameters are optimised by the Beetle Antennae Search algorithm (BAS), is proposed and investigated. Aiming at validating the accuracy and applicability of the proposed method, the method is employed to identify the linear and nonlinear parameters of the first-order nonlinear Nomoto model with training samples from numerical simulation and experimental data. Subsequently, the identified parameters are applied in predicting the ship motion. The predicted results illustrate that the new NLSSVM-BAS algorithm can be applied in identifying ship motion’s model, and the effectiveness is verified. Compared among traditional identification approaches with the proposed method, the results display that the accuracy is improved. Moreover, the robust and stability of the NLSSVM-BAS are verified by adding noise in the training sample data.
Numerical Modelling of the Mooring Line Failure Induced Performance Changes of a Marine Fish Cage in Irregular Waves and Currents
Authors: Tang Hung-Jie , Yang Ray-Yeng , Huang Chai-Cheng 
Published: November 2019

Abstract
This study aims to investigate the performance changes resulted from a mooring line failure of a marine fish cage exposed to irregular waves and current. A numerical model based on the lumped mass method and Morison equation was extended to simulate the mooring line failure scenario. In this study, the failed resulting changes were compared with its normal counterpart in both the time domain and the frequency domain. After one upstream anchor loss, the maximum tension on the remaining anchor has increased significantly, as well as the drift distance of the rearing part (net chamber, floating collar, and tube-sinker) of the fish cage. The resulting changes can also be seen in both the wave-frequency and the low-frequency region in the spectra, including mooring tensions and body motions.
Analysis of Fatigue Life of Ship Structure Under the Non-Linear Slamming Load
Authors: Ren Huilong , Ma He 
Published: November 2019

Abstract
As one of the hot topics in ship structures, hull structural fatigue has been widely studied by overseas and domestic scholars in recent years. And fatigue assessment methods can be divided into simplified calculation method and direct calculation method. However most of the calculation methods are based on liner wave load. Some high-speed ships, large external floats and larger ships may have frequent outflows and inflows during the voyage. These ships can be influenced by more serious wave attack. In this situation, the influence of nonlinear slamming load on ship structures cannot be ignored. In this paper, the author selected the deck longitudinal and the bottom longitudinal of the example ship midship section, then calculated the fatigue damage under the action of liner load and total fatigue damage under non-linear slamming load respectively.
And the effect of non-linear slamming load on the fatigue life of hull structure can be obtained: it is 49% larger than that without attack fatigue damage in the deck longitudinal, and 35% larger in the bottom longitudinal. Based on the results, the author got the influence coefficient of non-linear slamming load on the fatigue life of the ship. Finally, a nonlinear correction method of fatigue damage is proposed.
Statistical Analysis for the Duration and Time Intervals of Tropical Cyclones, Hong Kong
Authors: Tao Shanshan , Song Jialing , Wang Zhifeng , Liu Yong , Dong Sheng 
Published: November 2019

Abstract
Hong Kong is impacted by tropical cyclones from April to December each year. The duration of tropical cyclones is one key factor to impact the normal operation of port or coastal engineering, and longer time interval between two tropical cyclones can provide longer operation or construction time. Therefore, it is quite important to study on the long-term laws of the duration and time intervals of tropical cyclones which attacked Hong Kong. The Hong Kong Observatory issues the warning signals to warn the public of the threat of winds associated with a tropical cyclone. Choose the tropical cyclones with warning signal No. 3 or above as the research object. A statistical study was conducted on the duration of each tropical cyclone, the time interval between every two continuous tropical cyclones during the year, and the time interval between the last cyclone of each year and the first cyclone of the following year. Poisson compound extreme value distributions are constructed to calculate the return values, which can make people know how long a tropical cyclone with a fixed duration or time interval occurs once in statistical average sense. Based on bivariate copulas, the joint probability distribution of duration and time intervals of tropical cyclones are presented. Then when the duration of a tropical cyclone is known, the conditional probability that the time interval before the next tropical cyclone occurs is greater than a certain value can be calculated. The results provide corresponding conditional probability distributions. Similarly, for the sum of the duration of tropical cyclones each year, and the time interval between the last cyclone of each year and the first cyclone of the following year, their joint probability distribution and conditional probability distributions are also presented. The conditional probability can provide the probabilistic prediction of the length of the stationary period (with no impact of tropical cyclones).
Flexible Riser Top Connection Analysis With I-Tube Interface and Bending Hysteresis Effect
Authors: He Yangye , Lu Hailong , Vaz Murilo Augusto , Caire Marcelo 
Published: November 2019

Abstract
The flexible riser top connection to the floating production platform is a critical region for fatigue lifetime (re)assessment. The interface with the I-tube and its curved sleeve combined with the gap between the riser and bend stiffener may lead to different curvature distribution when compared to the traditional modeling approach that considers the bend stiffener attached to the pipe. For a more accurate top connection assessment, the flexible riser bending hysteresis can also be directly incorporated in the global dynamic analysis helping to reduce curvature amplitude and lifetime prediction conservatism. This work investigates a 7” flexible riser-bend stiffener top connection with I-tube interface by performing irregular wave global dynamic analyses with the OrcaFlex package and considering a nonlinear bending moment vs curvature riser behavior obtained from a detailed cross sectional model developed in Abaqus. OrcaFlex curvature distribution results are also compared with a quasi-static finite element model that uses an elasto-plastic formulation with kinematic hardening to represent riser hysteresis through an equivalent beam model. A good curvature distribution correlation is observed for both top connection models (OrcaFlex x Abaqus) in the bend stiffener area with reduced amplitudes when riser bending hysteresis is considered.
The Tentative Case Study of Annulus Build Up Pressure in the Deepwater Gas Production Well in South China Sea
Authors: Feng Ming 
Published: November 2019

Abstract
As China’s offshore drilling and production projects gradually march into the deep water, the requirements for scientific and technological progress are imminent. The occurrence of the 2010 Macondo disaster has presented a serious challenge to the safety of deepwater in technology. The deepwater wellbore consists of several layers/channel barriers, which constitute the wellbore barrier system and have a complicated structure. With the increase of water depth and well depth, the temperature of oil and gas produced at the wellhead is getting higher and higher, and the fluid in the annulus of the casing is heated by the conduction and convection of fluids such as oil and gas produced in the high temperature formation. Up to 60 degrees Celsius, the thermal expansion of the annulus fluid can cause the casing to burst, which can cause significant loss of personnel and property. Therefore, accurate temperature calculation of deep water wellbore is the key to the calculation of trap pressure prediction. The calculation of the wellbore temperature is affected by the oil casing and the thermophysical parameters such as the size of the wellbore, fluid composition, flow regime, casing and cementing sheave. By appropriately simplifying the model and sensitivity analysis, it is found out the dominant factors which affect the temperature profile.
System Based Prediction of Ship’s Manoeuverability in Varying Water Depth Area
Authors: He Shi , Incecik Atilla , Yuan Zhiming , Kellett Paula 
Published: November 2019

Abstract
In this study, numerical prediction of a ship maneuvering in calm water area with varying water depth are carried out to investigate the shallow water effect on ship’s maneuverability. The system based prediction approach is adopted by establishing a 3 degrees of freedom (DOF) mathematical model based on the modular concept. The lateral added mass and added moment of inertia are obtained by a strip theory method. Other coefficients including the longitudinal added mass, the maneuvering derivatives and the coefficients for estimating the resistance on the hull in straight moving, the propulsive force by the propeller, steering force by the rudder, and the interaction between hull-propeller-rudder are obtained by commonly used empirical and semi-empirical formulae, or directly from published data. The MOERI KVLCC2 tanker vessel is selected as the sample ship. The free running manoeuvers in deep and shallow water at different water depths are simulated and compared with available experimental results for validation. A special simulation case of stepped bottom varying from deep water to shallow water which resembles the real situation in harbor area is also carried out. The shallow water effects on ship’s maneuverability are discussed and recommendations on steering operations in shallow water are given.
Modal Interactions in Drillstring Borehole Interactions
Authors: Kartheek A. , Vijayan K. , Friswell M. I. 
Published: November 2019

Abstract
Understanding the vibration of drillstrings is important for the economical and efficient extraction of oil. Vibrations involve bending, axial, and torsional vibration. Drillstring interaction with the borehole during whirling involves nonlinearities. For the present work the whirling interaction of the drillstring and borehole is studied using an equivalent conceptual experimental test rig and a theoretical model of the drillstring. The drillstring is modeled as an Euler Bernoulli beam with multiple discs considering damping and gyroscopic effects. The finite element method is used as a numerical technique and the eigenvalue problem is solved using a state space formulation. The forward whirling frequency obtained from the experiments was used to update the bearing stiffness of the theoretical model. The contact is modeled experimentally using a tube for the stator with added roughness to aggravate the friction effect. A run up analysis was carried out within the safe operating regime of the test rig and the frequencies were analyzed using a time frequency plot. The effect of typical system parameters was considered such as the location of the contact, the mode excited and the clearance. The results from the study indicated the possibility of interaction between the forward and backward whirling modes which increased the bandwidth of acceleration response.
Comparison of Dynamic Response in a 2MW Floating Offshore Wind Turbine During Typhoon Approaches
Authors: Tanaka Koji , Sato Iku , Utsunomiya Tomoaki , Kakuya Hiromu 
Published: November 2019

Abstract
In this paper, we describe the analysis of the dynamic response of a 2 MW floating offshore wind turbine (FOWT) at the time of typhoon attack in the actual sea area. In order to introduce floating offshore wind turbine in Asia, it is essential to evaluate the influence of typhoon attack accurately. This FOWT, named HAENKAZE is the only FOWT to operate commercially in areas where typhoons occur. On July 3rd, 2018, the strongest typhoon (Prapiroon) at the installed area of the FOWT since its installation approached the HAENKAZE. The central atmospheric pressure of the typhoon at the closest time was 965 hPa, the maximum instantaneous wind speed at the hub height was 52.2 m/s, and the maximum wave height was 7.1 m. In this paper, the dynamic response of the floating body at the time of typhoon attack is compared for the measured and the simulated values. As a result of the comparison, basically a good agreement has been obtained between the measured and the simulated values except for yaw response, for which the simulated values considerably overestimate the measured values.
Next Generation Well Design and Integrity Digital Tools: Boosting Drilling Systems Automation (DSA)
Authors: Brechan B. , Dale S. , Sangesland S. 
Published: November 2019

Abstract
The first of the next generation applications for well planning and operational support is under development. All aspects of construction, integrity, intervention and final plugging of wells are supported and fully automated into digital programs and procedures. Expanding the scope of software support entails a change from current practice of simulating all activity upfront to keep the model active and updated to supply all integrity data through production and final plugging of the well.
The software is built to carry executable experience. These “digital experiences” range from the single event type often noted during operations, to complex sets of instructions in governing documentation. Experiences act as rules for how the software select methods outlined in activity plans and how these plans are executed by the equipment on drill floor. Any activity plan, e.g. drilling, completion, intervention or plug and abandonment (P&A), will be established using the entire company portfolio of experience regardless of the capacity and experience of the planning team.
Engineers working with the next generation software will focus on ensuring the quality of the produced digital procedures. The software will handle administrative routines, such as invoicing and logistics, which will free up capacity for engineers. The user threshold of the next generation software will be low for any person familiar with the daily operational reporting system.
Feasibility Study of Mooring Lines Design for a Floating Tidal Turbine Platform Using Double Hull Structure
Authors: Arini Nu Rhahida , Thies Philipp R. , Johanning Lars , Ransley Edward , Brown Scott , Xie Nan , Greaves Deborah 
Published: November 2019

Abstract
The aim of this paper is to study the mooring tension characteristics on a tidal energy converter (TIC) platform considering i) a horizontal and ii) a vertical tidal turbine. The study examines numerically the feasibility of a catenary mooring line for a modular tidal energy platform. A modular platform is designed and modelled with two floating hulls and anchored by studlink catenary mooring chains on the seabed. Vertical and horizontal axis turbines which have similar Cp are selected and modelled separately. The effect of those turbines on the mooring system are compared and the results informs lifetime of the mooring component for each turbine connection. The hydrodynamic model with no turbine is firstly developed and validated against an experiment with 1:12 scale ratio. The starboard fore mooring line tension, platform surge and pitch displacements are validated against the experiment. The model results show identical signal frequency with slightly different magnitude from the experiment. The mooring tension under vertical and horizontal tidal turbine operations in the particular environment is further examined. The result shows that the mooring line using selected vertical axis turbine experiences higher tension. For platform motions, the horizontal turbine generates slightly larger displacement in surge. However the pitch motion record shows equal displacement under both turbine operations. The selected vertical axis tidal turbine also produces longer lifetime mooring components.
Studies About Design of Rear Stator of Ducted Propeller Using CFD
Authors: Feng Dakui , Zhang Hang , Sun Yue , Wang Qing , Hu Xiaofei 
Published: November 2019

Abstract
Ducted propeller designs are becoming more popular because of their high efficiency, resistance to cavitation and low radiated noise. In this paper, unsteady RANS simulations are carried out for the design of rear stators for ducted propeller to improve its hydrodynamic performance. The design of rear stator is carried out based on the wake field behind propellers. The two-dimensional airfoil modified from NACA4603 is studied to obtain the angle of attack that makes thrust on stators maximum. The analyses are performed at different angles of attack, using commercial computational fluid dynamics (CFD) solver STAR-CCM+ to solve URANS equations. URANS equations are discretized by finite volume method and solved by PISO algorithm. Simulations have been made using unstructured grid with mesh moving technique. The simulation results indicate that the total thrust coefficient and efficiency of modified ducted propeller have been improved by 7.32% and 5.72% respectively compared with the parent one. The simulation results show that the design method is reasonable and feasible.
Wave Impact Loads Prediction With Compressible Air Effects Using CFD
Authors: Gatin I. , Liu S. , Vladimir N. , Jasak H. 
Published: November 2019

Abstract
A computational method for predicting wave impact loads where compressible air effects might be present is presented in this paper. The method is a Finite Volume based Computational Fluid Dynamics method where air is modelled as a compressible ideal gas while water is treated as incompressible. Special numerical treatment of the interface based on the Ghost Fluid Method enables capturing the sharp transition in compressible properties of air and water across the free surface, making the method accurate for predicting trapped air pockets during wave impacts or slamming. The approach enables predicting impacts where trapped air pockets play an important role in the loading of the structure due to the capacity to absorb and redistribute wave impact energy. The present approach is validated on a falling water slamming case where trapped air compression is present. Next, a full scale wave breaking impact on a vertical wall is simulated and the results compared to experimental measurements, with trapped air compression effects. Finally, the method is applied on a breakwater green water loading calculation of an Ultra Large Container Ship in an extreme focused wave impact based on the Response Conditioned Wave theory. Motion of the container vessel is calculated directly during the simulation. The calculation is shown to be computed with limited computer resources in reasonable amount of time. Overall the approach proved to be accurate, robust and efficient, providing a tool for assessing wave impact loads with or without compressible air effects.
A Validation of a Pivoted Point Absorber Type Wave Energy Converter Using CFD
Authors: Yang Injun , Tezdogan Tahsin , Incecik Atilla 
Published: November 2019

Abstract
Wave energy is sustainable and clean energy, so it has great potential to be an eco-friendly and lasting renewable energy resource in the future. Recently, a number of researchers have investigated different types of wave energy converters (WECs) using numerical models such as potential theory and Computational Fluid Dynamics (CFD) to enhance the efficiency of such devices. In this paper, a validation of a point absorber type WECs is investigated to capture the movement of the WEC system and to measure the moment on the WEC system. The WEC consists of a lever and a buoy. The geometry is the same as the existing experimental geometry of the reference in order to validate the present numerical simulation. The buoy is connected to the lever and has a hinge on the connection point. Besides, another hinge is installed in the middle of the lever, and the WEC system rotates in the pitch direction. The commercial CFD package Star-CCM+, which solves Reynolds-Averaged Navier-Stokes equations, is employed in this study. In the initial stages of this research, a validation study against published experimental results was conducted. The rotational displacement and the moment on the buoy were compared with the existing experimental data of the reference. The result shows good agreement. In the near future, a study on a new pivoted point absorber WEC device regarding the buoy shape of the WEC device and an operation principle will be performed based on this numerical study.