bluuebunny/crossref_metadata_2025 huggingface dataset:
Global Performance Analysis of Deep Draft Semi-Submersible Designed for Standard GOM Application
Authors: Yuck R. H. , Kang D. H. , Kim E. S. , Kim M. S. , Kim T. M. , Kim H. J. , Lee D. Y. , Park Y. C.
Published: November 2019

A deep draft semi-submersible hull has been developed by SHI (Samsung Heavy Industries) and Williams as a standardization concept which can support the topside structures up to the facility weight for the specific level of daily oil production in GOM (Gulf of Mexico). The designed hull has the optimized dimensions of pontoon and column which secure the sufficient level of GM for the stability and ballast capacity for coping with the weight change of topside structures. The hull form also has the good global motion in waves to be able to use the SCR (Steel Catenary Riser) as a deep draft semi-submersible concept.

Two hull forms are designed to have 4 columns with two different cross sections and the conventional ring pontoon. The compartmentation and basic hydrodynamic analysis are performed at the hull sizing stage to achieve the sufficient stability and the motion performance as well. The mooring systems are also designed for two different water depths of 1000m and 3000m as a standard design concept of hull including mooring lines.

To verify the feasibility of the proposed hull concept with regard to the hydrostatic/hydrodynamic characteristics and mooring line design, the numerical global performance analyses are carried out. Hydrostatic stability is investigated for intact and damage condition of operational loading condition and the proper tank compartments are verified under the given topside weight and the environment condition in GOM.

The global motion is validated for all the possible combinations of wave, wind, current for a site in central GOM. Through the frequency-domain analysis and quasi-static time-domain analysis as well, the essential items such as the maximum offset, mooring line tension/fatigue, air-gap and the extreme acceleration at topside are examined and confirms that the certain design criteria of Semi FPU (Floating Production Unit) operation are satisfied. The possibility of SCR usage is also investigated with the fully coupled time domain analysis using the preliminary design of risers and confirms that the designed hull form has the suitable hydrodynamic characteristics to permit the minimum motion performance for SCR in the sense of extreme load and fatigue life.
Fatigue Life Evaluation for the Repair Methods of High Pressure Gas Pipeline
Authors: Kim Woo Sik
Published: November 2019

High pressure gas pipeline must maintain structural integrity during the design life. To do this, periodic pipeline inspections are carried out, and fitness-for-service assessments are performed on defects found by inspection. Defects that do not meet the evaluation criteria should be repaired and replaced to ensure the integrity of the pipeline structure at the same level as before the defect. High pressure gas pipeline repair method is applied to repair of composite reinforced sleeve and repair of steel sleeve. Although there have been many studies on the short-term structural integrity evaluation of rupture pressure in these repair methods, there is insufficient research to verify whether the long-term operation of the repair pipeline maintains the long-term structural integrity of the repaired pipe.

In this study, an optimum process to improve structural integrity was established by investigating effect of the process variables on fatigue lifetime of steel-sleeve repair welds in buried gas pipeline. Residual stresses in the repair welds were derived through sequentially-coupled temperature-stress analysis using ABAQUS, which is a commercial finite element analysis program. In addition, variations of operating stresses were derived by finite element linear elastic stress analysis. Fatigue lifetimes of the steel-sleeve repair welds were evaluated by substituting the derived weld residual stresses and operating stress variations into the structural stress/fracture mechanics approach as input. Appling this method confirms long-term integrity over 200 years in terms of fatigue the abstract here in italics.
Dynamic Response of Monopile Wind Turbine in Large Waves
Authors: Seng Sopheak , Monroy Charles , Malenica Šime
Published: November 2019

A strongly coupled hydroelastic code based on OpenFOAM has been applied to evaluate dynamic responses of a bottom mounted monopile in regular waves at 3 different wave periods and 3 wave steepness. The code uses a free surface RANSE solver to determine accurately the hydrodynamic loads and a modal superposition approach to describe the dynamic structural responses. Numerical simulations include both rigid and elastic monopiles and the results are evaluated against publicly available model test experiments. The discussion includes a quality control of the numerically simulated incident wave fields, mesh dependency and the quality of the numerically predicted and experimentally measured third harmonic of the inline forces.
Lessons Learned From Operational Integrity of HP/HT Deepwater Pipelines
Authors: Cardoso Carlos O. , Solano Rafael F. , Antunes Bruno R.
Published: November 2019

This paper addresses the results from a monitoring inspection as part of Petrobras regular plane of inspection of rigid pipelines (PIDR) and numerical Finite Element analysis (FEA) of two parallel HP/HT subsea pipelines operating in Brazilian deepwater subjected to lateral buckling and walking behaviors. The results obtained from inspection and numerical reanalysis furnishes important feedback for the integrity management of the two pipelines, reducing potential risks and lessons learned for future projects.

Deepwater pipelines submitted to high pressures and temperatures (HP/HT) are susceptible to global buckling due to axial compressive load. To guarantee pipeline and equipment’s integrity frequently is necessary to relieve high stresses and strains at buckle apex as well as to mitigate end expansion. Thus, the two parallel HP/HT pipelines were designed with single and double sleepers to trigger buckles at pre-determined locations and an anchoring system to prevent pipeline walking. Another important design aspect was to avoid undesirable buckles at the several crossings along the pipeline route applying a special device with stoppers to lock lateral displacements.

During a programmed inspection as part of regular Petrobras pipeline integrity program of rigid pipelines (PIDR), it has been verified that some double sleepers didn’t work as foreseen in design. Otherwise, some unplanned buckles on soil have been formed along the two pipelines changing the buckle apex stress levels and end expansions foreseen in detailed design.

In order to understand buckle formation behavior and guarantee long-term integrity of the HP/HT pipelines a Multi-Beam Echosounder Survey (MBES) was conducted in 2016 to build a representative Finite Element (FE) model. The temperature and pressure gradients from steady state and transient conditions were obtained from flow assurance simulations based on monitored platform operational historic data. The FE model was calibrated with buckle shapes and end displacements to assess pipeline behavior and its long-term integrity for load scenarios different from original design.
Nonlinear Evolution of a Steep, Focusing Wave Group in Deep Water Simulated With OceanWave3D
Authors: Barratt Dylan , Bingham Harry B. , Adcock Thomas A. A.
Published: November 2019

Steep, focusing waves can experience fast and local nonlinear evolution of the spectrum due to wave-wave interactions resulting in energy transfer to both higher and lower wavenumber components. The shape and kinematics of a steep wave may, thus, differ substantially from the predictions of linear theory. We have investigated the role of nonlinear interactions on group-shape for a steep, narrow-banded, directionally-spread wave group focusing in deep water using the fully-nonlinear potential flow solver, OceanWave3D. Exact second-order correction of the initial conditions has been implemented together with a novel third-order approximate correction based on a Stokes-type formulation for surface elevation combined with a scaling-argument for the third-order velocity potential. Four-phase separation reveals that the third-order scheme provides a good estimate for the third-order superharmonics. A quantitative assessment of numerical error has also been performed for the spatial and temporal discretization, including energy conservation, a reversibility check and validation against previous simulations performed with a higher-order spectral (HOS) code. The initially narrow-banded amplitude spectrum exhibits the formation of sidelobes at angles of approximately ±35° to the spectral peak during the simulated extreme wave event, occurring in approximately 10 wave periods, with a preferential energy transfer to high-wavenumber components. The directional energy transfer is attributed to resonant third-order interactions with a discussion of the engineering implications.
Large Amplitude Time Domain Seakeeping Simulations of KVLCC2 in Head Seas Taking Into Account Forward Speed Effect
Authors: Pollalis Christos , Hizir Olgun , Boulougouris Evangelos , Turan Osman
Published: November 2019

Time-domain analysis is important for the development of performance-based criteria for the intact stability of ship (level 3 criteria in the 2nd Generation Intact Stability Criteria). It can be implemented to assess directly the vulnerability of ships against various modes of intact stability failure and ensure a sufficient level of safety. In this context, ELIGMOS, a novel time domain simulation code combining a maneuvering model and a seakeeping model, is under development. As the maneuvering model has been the subject of previous paper, the seakeeping part is presented herein and validated in terms of linear and nonlinear vertical motions in head seas. Heave and pitch motions are augmented near the resonant periods, testing the ability of the numerical tool to capture accurately the ship’s behaviour, as it plays a dominant role for her direct stability assessment afterwards. Surge motion is considered uncoupled and it is excluded from the system of equations, keeping the forward speed constant. Comparison regarding the seakeeping performance of KVLCC2 is presented against experimental results and results obtained by a 3D-potential flow, frequency domain software as well. Ship’s geometry is modelled by means of quadrilateral panels whilst radiation forces were incorporated by means of memory functions by adopting the well-known concept of convolution integrals. The ability of ELIGMOS to capture the effect of geometrical nonlinearities on the vertical motions is demonstrated through preliminary simulation of large amplitude motions of a C11-class containership.
QUAD Lift: Enabling Lifting of Larger Integrated Topsides
Authors: van Winsen Ivan , van Dijk Radboud R. T.
Published: November 2019

Over the past years Heerema Marine Contractors (HMC) has developed the QUAD lift method enabling the lift of single piece objects up to 30,000mT. This development is driven by the demand from our clients to install or remove larger topsides, both in size and weight. Lifting with two (or more) vessels simultaneously has been done before. Unique is that the QUAD lift operation is performed on DP. Two vessels lifting the topsides from opposite sides, instead of lifting the topsides from one side, creates the possibility for increasing dimensions and layouts of the topsides.

The connection of the two crane vessels to the lifted object means that all actions taken on one ship influences not only the lifted object but also the second crane vessel. This requires a clear communication plan and full understanding of the complete system such as the DP behaviour, stability, ballast operations and crane operations. During a QUAD lift operation the Dynamic Positioning (DP) system plays an important role. Therefore in the development process the DP-system was modified to ensure stability of the DP system throughout the entire operation. A systematic series of tests was performed to gain insight in the DP behaviour of both vessels with the goal to ensure a synchronous move with two vessels connected in a QUAD lift configuration.

In 2018 a demonstration QUAD lift is performed using Balder and Thialf to show HMCs commitment to perform this kind of operations in the future. The QUAD lift demonstration lift was prepared and executed in the Heerema Simulation Center (HSC) with the offshore crew in preparation of the actual offshore execution.

This paper will address the steps followed to prepare for the offshore execution, describing DP behaviour, vessel coupled dynamics and human factor aspects. Based on the offshore experience validation was performed on the numerical tools used in the preparation.
Research and Development of a Self-Walking Vertical Mining System Using DTH Drilling Unit and the Scale Model Test
Authors: Watanabe Yoshiyasu , Watanabe Keisuke , Suzuki Hideyuki , Ooshima Teruo , Tsukamoto Yoshiaki
Published: November 2019

Traditional subsea mining systems use a heavy subsea crawler, which has a big drill and scrapes the mineral deposit horizontally and have limitations of seafloor inclination, roughness and softness. Those traditional systems also have issues from operational and economical points of view. Furthermore, traditional on-board drilling machines and seabed drilling machines are used for core sampling by drilling to analyze mineral contents of seafloor deposits at the stage of mineral resource estimation before the production but operational and economical efficiencies are required to those traditional systems as well.

The objective of this research is to develop an innovative Self-Walking Vertical Mining System (SW-VMS) that overcomes these issues. The system is a fully submerged eight-legged jack up platform and is able to walk autonomously on a rough, soft and inclined seafloor. The SW-VMS can be used both as the mining system to mine seafloor deposits and as the sample drilling system to analyze mineral contents in-situ and on-land efficiently before the mining with a DTH drilling unit.

This paper introduces the detail of the SW-VMS as the mining system at first and then introduces the concept of the SW-VMS as the sample drilling system and finally the results of the scale model test of the SW-VMS on-land are shown. The scale model test has been carried out to confirm the walking ability of the SW-VMS from the structural and autonomous control points of view. The scale of the test model is approximately 1/40 of the preliminary design of the SW-VMS which has been already completed. The test consists of test cases of walking on a flat foundation, on a flat foundation including partially soft foundations and on inclined foundations of up to 45 degrees.
Weathervane Performance and Stability of Single Point Moored FOWTs Under Wind-Current Coexisting Field
Authors: Srinivasamurthy Sharath , Hashimoto Kazuki , Iijima Kazuhiro , Nihei Yasunori
Published: November 2019

The objective of this study is to understand the weathervane performance and stability of FOWTs moored to SPM systems under wind and current coexisting field. Two types of FOWT systems, a semi-submersible and a spar (1/200 scale) are designed and manufactured based on Froude’s scaling law. A series of scaled model experiments are conducted and compared during wind-current coexisting field in a circulating water tank at Osaka Prefecture University, Osaka, Japan. Weathervane performance is evaluated under various conditions of wind and current. It is found during experiments that the weathervane performance of the SPM-FOWT systems is acceptable in rated wind and slow current condition. However, in the rated wind and high speed current condition, the weathervane performance is found to be not acceptable and unstable oscillation is observed. A numerical program is also developed to understand the behavior using the maneuvering equations. Further, attempts are made to understand the stability of SPM-FOWT systems based on Eigenvalue analysis.
Investigation on Mechanical Properties of Fiberglass Reinforced Flexible Pipes Under Bending
Authors: Gao Yifan , Jin Shan , Cheng Peng , Han Peihua , Bai Yong
Published: November 2019

Fiberglass reinforced flexible pipe (FRFP) is a kind of composite thermoplastic pipe, which has many advantages compared to boned flexible pipes. This paper describes an analysis of the mechanical behavior of FRFP under bending. The bending behavior of FRFP was investigated by experimental, analytical and numerical methods. Firstly, this paper presents experimental studies of three 10-layer FRFP in a typical four-point bending test. Curvature-bending moment relations were recorded during the test. Then, based on the nonlinear ring theory and the principle of virtual work, a simplified method was proposed to study the mechanical behavior of FRFP. In addition, a finite element model (FEM) including reinforced layers and high density polyethylene (HDPE) layers was established to simulate the HDPE layers and reinforced layers, respectively. The result of Curvature-bending moment relations obtained from three methods agree well with each other, which proves that the simplified analytical model and FEM are accurate and reliable. The conclusions of this paper could be useful to manufacturing engineers.
Three-Dimensional Direct Numerical Simulations of Flows Past an Inclined Cylinder Near a Plane Boundary
Authors: Ji Chunning , Zhang Zhimeng , Xu Dong , Srinil Narakorn
Published: November 2019

Flows past an inclined cylinder in the vicinity of a plane boundary are numerically investigated using direct numerical simulations. Parametric studies are carried out at the normal Reynolds number of 500, a fixed gap ratio of 0.8 and five inclination angles (α) ranging from 0° to 60° with an increment of 15°. Two distinct vortex-shedding modes are observed: parallel (α ≤ 15°) and oblique (α ≥ 30°) vortex shedding modes. The occurrence of the oblique vortex shedding is accompanied by the base pressure gradient along the cylinder span and the resultant axial flows near the cylinder’s base. The drag and lift coefficients decrease from the parallel mode to the oblique mode, owing to the intensified three-dimensionality of the wake flows and the phase difference in the vortex-shedding along the span. The Independent Principle (IP) is valid in predicting the hydrodynamic forces and the wake patterns when α ≤ 15°, and IP might produce unacceptable errors when α ≥ 30°. Compared to the mean drag force, the fluctuating lift force is more sensitive to the inclination angle. The IP validity range is substantially smaller than that for flows past a wall-free cylinder.
Visualization Study on Plugging Mechanism of Fibers and Particles in Rough and Tortuous Fracture
Authors: Fan Fan , Zhou Fujian , Yuan Lishan , Yang Xuda
Published: November 2019

Temporary plugging technology are widely used in unconventional exploitation, for it can produce more fracture thus to enhance oil recovery, however, it is still unclear how the plugging is formed and the diverters migrate in the hydraulic fracture. In this work, a self-developed visualization fracture system is set up. And the plugging mechanism of guar-based fracturing fluid with temporary plugging materials is visualized in a rough laboratory-scale fracture. Impacts of parameters on plugging process like particle concentration,fibre concentration, and fracture width are systematically investigated.Through a series of comparative experiments, it is found that the plugging process was triggered by fibre, they form nets to capture particles, then the nets with particles roll bigger and bigger like snowballs,while the nets can not capture particles will be broken in higher pressure. Comparative results indicate that the sealing effect of the same forum for wider fracture will be worse, replacing with the larger particles is more effective than increasing the amount of diverter; Increasing particles can increase sealing strength while increaing fibres can shorten the sealing formation time; Using 1% fiber only, the 3mm-wide fracture can be plugged but it cost much time and the sealing is not so firm. While using 1% particles only, a particle dump forms instead of a sealing layer. For field operation, it is suggested that (1) For wider fracture, use bigger particle is more effective than add more fibre and particles; (2) Particle should be added later than fibre; (3) To increase sealing pressure and enhance efficiency, the ratio of fibre and particles should be around 2:1.
CFD Simulation of a Twin-Screw Ship Self-Propulsion Using DDES-Overset Method
Authors: Wang Jianhua , Wan Decheng
Published: November 2019

Rotating propellers and moving rudders are necessary for the simulation of free running ship with the purpose of resolving detailed flow interaction. In the present work, CFD method is used to numerically investigate self-propulsion behavior for a twin-screw fully appended ship. The simulation conditions are following the experiment performed at IIHR. The benchmark ship model ONR Tumblehome is used for all the numerical computations. Overset grids are used to fully discretize the ship hull, twin propellers and rudders. Self-propulsion simulation is carried out using a PI controller to achieve target ship speed of Fr = 0.20 in calm water and the ship model is free to trim and sinkage. All the numerical calculations are carried out by the in-house CFD solver naoe-FOAM-SJTU. Unlike most previous studies based on RANS method, the present self-propulsion simulations adopt the Delayed Detached-Eddy-Simulation (DDES) approach to resolve the complex flow around ship hull, propeller and rudder. The main parameters of the self-propulsion as well as flow visualizations are presented. The predicted results are compared with previous RANS data and the available experimental data. The comparison with the experiment is satisfactory and the flow field shows that the present DDES-overset method can give more flow details for the self-propulsion condition.
Extending Integrability of Nonlinear Water Wave Equations: Nonlinear Fourier Analysis of Breather Packets and Rogue Waves at Higher Order
Authors: Osborne Alfred R.
Published: November 2019

I suggest a formulation to give approximate spectral solutions of nonintegrable, nonlinear wave equations in 2+1 dimensions. Nonintegrable systems such as the 2+1 NLS, Dysthe and extended Dysthe equations can be approximately integrated by selecting a nearby theta function formulation. I study the subclass of wave equations that are in the form of nonlinear envelope equations for which all members can be reduced to a particular Hirota bilinear form. To find the approximately integrable formulation associated with a nonintegrable equation, I first study the one and two soliton solutions and subsequently extend these to larger numbers of solitons to obtain the Hirota N-soliton solution (for infinite-plane boundary conditions). Subsequently, I address the one and two periodic solutions from the bilinear form, so that I can develop the associated Riemann theta function solution to a nearby integrable case. I discuss how to obtain the higher order breather packets from the point of view of the theta functions. This work is being developed for real time analysis of shipboard radar analysis of ocean waves. Further applications include real time analysis of lidar and synthetic aperture radar (SAR) data taken by airplanes flying over high sea states.
Numerical Simulations of KCS Parametric Rolling in Head Waves
Authors: Wang Shuang , Wei Junkai , Chen Xuanshu , Liu Liwei , Zhang Zhiguo
Published: November 2019

As a type of the ship stability failure modes, parametric rolling has attracted more attention from many researchers in recent years because of a series of accidents due to ship instability, especially the instability of container ship. Parametric rolling is a complex nonlinear stochastic dynamic problem, which is often accompanied by large amplitude vertical motions of ships. At present, there are many difficulties in the research of ship parameter rolling, mainly including the nonlinearity of parameter rolling motion, the random variation of wetted area of the hull surface up to the incident wave waterline and the coupling effect of rolling, pitching and heaving. Nowadays, the potential flow theory is a common method to predict parametric rolling, but this method may generate results with low accuracy in some conditions. This paper describes a numerical simulation method based on in-house CFD code HUST-Ship to analyze parametric rolling motion of KCS (KRISO Container Ship) container ship model. The paper studies the occurring conditions of parametric rolling motion of KCS model and reveals the mechanism of parametric rolling.
Analyzing the Effect of Shaft and End-Plates of a Newly Developed Elliptical-Bladed Savonius Rotor From Wind Tunnel Tests
Authors: Alom Nur , Kumar Nitish , Saha Ujjwal K.
Published: November 2019

In recent times, drag-based vertical-axis wind turbine rotors have gained increasing interests in offshore applications because of their performance potential and reliability. Their advantages like simplicity, easier manufacture and lower maintenance cost have attracted the researcher’s attention toward improving their design further. However, this type of rotor is still suffering from lower efficiency than the lift-based Darrius and the horizontal-axis wind turbine rotors. A recently developed elliptical-bladed Savonius rotor has shown its potential to harvest wind energy more efficiently. However, the geometric parameters of this rotor such as aspect ratio, overlap ratio, number of blades, shaft and end plates, the aerodynamic parameters such as Reynolds number, lift and drag coefficients are needed to be optimized for further improvement of its performance. In the present investigation, the wind tunnel tests have been conducted to analyze the effect of shaft and end-plates of a newly developed elliptical-bladed vertical-axis Savonius wind turbine rotor. Experiments have been conducted over a range of tip speed ratios to find the torque and power coefficients of a two-bladed rotor system for two individual cases viz., the rotor with a shaft and the rotor with end-plates. In order to have a direct comparison, the experimental data are also obtained for the same rotor without the shaft and without the end-plates. The wind tunnel tests have demonstrated an improvement of power coefficient by 26.31% for the rotor with the end plates.
A Fluid-Structure Interaction Study on a Passively Deformed Fish Fin
Authors: Luo Yang , Xiao Qing , Shi Guangyu , Yuan Zhiming , Wen Li
Published: November 2019

In this paper, the propulsive performance of a caudal peduncle-fin swimmer mimicking a bio-inspired robotic fish model is numerically studied using a fully coupled FSI solver. The model consists of a rigid peduncle and a flexible fin which pitches in a uniform flow. The flexible fin is modeled as a thin plate assigned with non-uniformly distributed stiffness. A finite volume method based in-house Navier-Stokes solver is used to solve the fluid equations while the fin deformation is resolved using a finite element code. The effect of the fin flexibility on the propulsive performance is investigated. The numerical results indicate that the compliance has a significant influence on the performance. Under the parameters studied in this paper, the medium flexible fin exhibits remarkable efficiency improvement as well as thrust augment, while the least flexible fin shows no obvious difference from the rigid one. However, for the most flexible fin, although the thrust production decreases sharply, the efficiency reaches the maximum value. It should be noted that by non-uniformly distributing the rigidity across the caudal fin, our model is able to replicate some fin deformation patterns observed in both the live fish and the experimental robotic fish.
Numerical Investigation of Steady Flow-Induced Rotary Response of Circular Cylinder With Splitter Plate
Authors: Pang Dan , Xi Huili , Zhou Zhong-bing , Tang Guo-qiang , Lu Lin
Published: November 2019

This article presents numerical results of flow-induced rotary oscillation of a circular cylinder with rigid splitter plate in steady flow. Different from the previous examinations with freely rotatable assembly which mainly considered linear restoring force, the rotary oscillation of the structure in this work is modelled by a Duffing oscillator with both linear and nonlinear restoring force, denoted by dimensional k and ε, respectively. Numerical simulations were carried out for various reduced velocities Ur ∈ [9 to 15] and ε ∈ [0 to 20] at a relatively low Reynolds number. Our previous investigations of a purely linear oscillator (i.e., ε = 0) show that the equilibrium position of the rotary oscillation is not parallel to the free stream as the reduced velocity exceeds a critical value, that is, bifurcation occurs. The present numerical studies suggest that, for a specific reduced velocity Ur, the increase in the nonlinear stiffness ε can eliminate the undesirable bifurcation. The numerical results also suggest that both odd and even-number lift frequency components appear for bifurcate cases, while only odd-number lift frequencies are observed for non-bifurcate cases. The dynamic mode decompositions for the wake flow corresponding to each lift frequency are presented.
The Influence of Piping Arrangement on the Response of Vibration Isolation System Under Underwater Explosion Loading
Authors: Pan Chen , Qiang Wei , Zhizhong Liu , Guan Wang
Published: November 2019

The response of ship equipment under non-contact underwater explosion shock loading was one of the main loadings of equipment. In order to cut down mechanical noise caused by mechanical equipment, vibration isolation measures, such as floating raft, vibration isolation, were widely used on noise mechanical equipments in acoustical stealth of ship, vibration isolation can reduce the vibration transfer to install base effectively, while the anti-shock resistance of vibration isolation and the equipment was important synchronously, as for the response of the equipment on vibration isolation, especially the actual response of the vibration isolation with piping system under shock loading. In this paper, the research on the response of vibration isolation, equipment, flexible piping and piping under underwater explosion shock loading were considered together, and the response of vibration isolation under shock load was analyzed with different piping arrangement. Found that the piping system has a significant impact on the response of the equipment under horizontal impact, but almost all equipments were assessed in experiment without considering the piping system. With the precondition of the effect of vibration isolation, a more rigid flexible pipe can be taken was benefit to the anti-shock resistance of vibration isolation.
The Investigation of a Circular Cylinder With a Detached Flexible Plate Using Immersed Smoothed Point Interpolation Method
Authors: Yan Boqian , Wang Shuangqiang , Zhang Guiyong , Xiao Qihang , Wang Peng
Published: November 2019

Flow control is an attractive topic in consideration of its significance associated with drag reduction or vibration suppression in fluid-structure interaction (FSI) system. A circular cylinder with a flexible plate in the wake region has been investigated numerically. An immersed smoothed point interpolation method (IS-PIM) has been employed to solve this FSI system. The splitter plate with the same length as the cylinder diameter is placed horizontally in the wake region. The drag variation of the circular cylinder and the behavior of the vorticities have been studied with regard to different locations of the detached plate. A comparative study of the rigid plate control has been presented. It shows that the effect of the flexible plate control is inferior to the rigid plate control because the flow field of the former is more complicated than the latter. When the flexible plate is far from the cylinder relatively, it would produce an opposite effect.
Study on the Design Method of Deepwater Steel Lazy Wave Riser
Authors: Wang Zhao , Qin Wei , Zhang Xiaojie , Zhao Jiannan , Bai Yong
Published: November 2019

The steel lazy wave riser has been used in deep-water oil and gas field development because it has good adaption to the movement of the upper platform and economic efficiency. The typical design criterion and design flow of steel lazy wave riser are introduced in this paper. The design method and the equivalence principle of distributed buoyancy modules are given. The formulas of equivalent hydrodynamic parameters are derived in this paper. The influences of distributed buoyancy modules (DBM) and the buoyancy factor on the configuration of the riser, the top tension, and the bending moment distribution are discussed and summarized. The distribution law of effective stress response along the pipe can be analyzed by dynamic analysis, and it provides reference for the global design of steel lazy wave riser.
Study on a Wave Energy Converter With Tension Leg Mooring Under Optimal Control
Authors: Umeda Jun , Taniguchi Tomoki , Fujiwara Toshifumi
Published: November 2019

A safety assessment for wave energy converters (WECs) in model scale is necessary before a demonstration test. WECs have various control conditions such as a maintenance and power generation mode etc. Although the safety assessment is required to carry out while considering the control conditions, the motion and load characteristics of the moored WEC to which applies various control conditions remains unclear. This study investigated the motion and load characteristics of the WEC including a mooring system when each control conditions was used. In experiments, the motion and load characteristics of the WEC without control were revealed. In the simulation, the motion and load characteristics were compared between two control methods which are the resistive loading control (RLC) and the approximate complex-conjugate control with considering the copper loss (ACL). The control methods have little effects on the surging, pitching and bending moment of the WEC. Mooring tension increased with increasing wave period when the RLC was used. When the ACL was applied, mooring tension reached the peak value near the natural period and decreased with increasing the wave period. The difference in the trends leads to that the control method maximizing mooring tension is not necessarily the same in each wave period. The select of the operating condition based on the wave period is required when the mooring tension of the WEC is assessed in the model-scale test stage.
Numerical Analysis of GBS Float-Over Deck Installation at Docking and Undocking Stages Based on a Coupled Heave-Roll-Pitch Impact Model
Authors: Chen Mingsheng , Zou Meiyan , Zhu Ling , Sun Liang
Published: November 2019

This paper aims to compare the impact responses in float-over installation for a gravity-based platform under two different simplifications of shock absorbers. A coupled heave-roll-pitch impact model based on the Cummins equation has been established to analyze the dynamic behaviors of installation system, in which the time-consuming convolution integral is replaced by a state-space model, resulting in a constant parameter time-domain model. In present dynamic model, the Leg Mating Units (LMUs) and the Deck Support Units (DSUs), known as shock absorbers, are simplified as vertical gap springs (compression only) with appropriate damping properties since the heave motion of the float-over installation system is the main contribution to the impact loads. Linear and nonlinear springs are assumed to evaluate how the properties of LMUs/DSUs will affect the heave impact response at docking stage and undocking stage. The influence of characteristics of LMU and DSU on the dynamic responses at docking stage is also addressed through the Poincare map and phase portraits.
Dynamic Load Inversion Method of Ship Body Based on Influence Coefficient Matrix
Authors: Ren Huilong , Feng Guoqing , Liu Hao , Hu Xuecong , Zou Jian
Published: November 2019

Ships sail in complex marine environments, the load is complex and uncertain. In the actual hull strength analysis, hull health monitoring and diagnosis, structural optimization design and other issues, it is very important to determine or estimate the dynamic load which applied on the hull structure. Due to the complexity and uncertainty of the working environment of the ship, many dynamic loads such as slamming loads applied on the bow of the hull are impossible or difficult to be measured directly. However, the structural response (strain, displacement, acceleration, etc.) of the corresponding part and other system characteristic parameters such as natural frequency, vibration mode, damping ratio, etc. can be obtained by installing sensors. Using the dynamic response of the structure, combined with the load identification model, the dynamic load on the hull can be calculated reversely. The time domain method and the frequency domain method are currently the most commonly used methods on load inversion. The time domain method is very suitable for the inversion identification problem of non-stationary loads and impact loads. The solution is intuitive and easy to use. In this paper, on based the time domain method, for the non-transient dynamic load, the displacement and time orthogonal function basis functions are loaded on the structure as the load function, and the response of the structure is obtained. The influence coefficient matrix is established by the response, and then the inversion load function is fitted; For transient dynamic loads such as slamming load, unit pulse load is applied on the structure to obtain the response of the structure. Then the corresponding data are filtered to overcome the ill-conditioned matrix problem. The matrix of the influence coefficient is established by the response, and the dynamic load is obtained. The two methods of dynamic load inversion based on the influence coefficient matrix are verified by numerical examples. The error is within a reasonable range, which proves that the inversion method is feasible.
Improved Model for Tubular Burst
Authors: Brechan B. , Sangesland S. , Dale S.
Published: November 2019

Modern casing design can reduce significant amounts of CO2 and considerable cost per well [1]. Collapse design was modernized by ISO/API Technical committee 67, Sub Committee 5, Work Group 2b (ISO/API TC67/SC5/WG2b). Modernization of burst design has so far not had the same focus and only minor changes have been made. A new burst design model has been developed to add to the collapse prediction for a complete environmental and cost effective well design tool. It is based on the theories of Lubinski [2] (1975) and presents designs using “exact von Mises ellipsis” together with the Klever and Stewart ductile rupture model [3].

This paper presents the model developed for burst design and the improvement compared to current industry practice. Inspired by the current most accurate collapse prediction model [4], the modified burst model (prototype) is the first to consider actual wall thickness to predict a more accurate internal yield of OCTG (Oil Country Tubular Goods). Investigations show that the standard 12.5% wall thickness reduction for manufacturing tolerances may be obsolete. ISO 10400 offers physical measurements and statistics of tubular properties. Following the principals by WG2b applied with the Klever & Tamano collapse prediction, there is a set of data to be used for a specific batch of tubulars or they are deducted through large quantum of measurements; ensemble Probability Density Function (PDF). The value proposed as “ensemble PDF” for wall thickness is based on more than 10 000 measurements of tubulars from 11 vendors distributed over Electrical Weld (EW) and quenched and tempered (Q&T) qualities of miscellaneous sizes and grades. The batch specific value proposed is based on more modest numbers of specimens from 4 sources but offers “minimum measured wall thickness” for all the samples. Adding to the confidence of the final design is the automated ductile burst calculation, which is one of the latest contributions to burst modeling in the industry [4] [5] [6]. It is a useful aid for the design engineer to know the potential failure mode and the limit before loss of integrity. However, burst is limited to yield because exceeding this limit may lead to loss of the pipe’s effective diameter and eventually loss of integrity. Therefore, the ductile burst prediction is proposed as a visual aid only.
Wear Performance of Mooring Chain in Wet Environment With Substitute Ocean Water
Authors: Gotoh Koji , Ueda Tetsuya , Murakami Koji , Utsunomiya Tomoaki
Published: November 2019

Floating wind turbine facilities installed in deep sea areas play an essential role in the promotion of green energy. One of the problems associated with the commercialization of facilities installed in the deep sea is the maintenance cost of mooring chains, because they are expensive and wear between links leads to chain breakage. Therefore, it is necessary to establish a quantitative wear evaluation method for mooring chains.

An experimental facility to reproduce the wear caused by sliding between links at the scale of an actual floating wind turbine was developed to investigate the wear performance in seawater conditions, and wear tests were conducted. Substitute ocean water was applied to the experiment instead of seawater. In addition, a procedure for nonlinear finite element analysis was improved to estimate the behaviour of wear between links. Measured stress versus strain relations of the links was considered in the finite element analysis.

The experiments and numerical analysis confirmed that the amount of wear in the substitute ocean water was less than that obtained in dry air and that the tensile force between links is an important factor for the degree of wear between links.
A Parameterization of DNV GL Storm Profile for Long-Term Analysis of Ocean Storms: Trapezoidal Storm Model
Authors: Laface Valentina , Bitner-Gregersen Elzbieta M. , Arena Felice , Romolo Alessandra
Published: November 2019

The paper introduces a parameterization of the DNV GL storm profile for developing an analytical model for calculations of the return period of a storm whose peak exceeds a given threshold. The DNV GL storm evolution is represented via an isosceles trapezoidal shape in which the minor base represents the storm peak duration, the major base the total storm duration and the height is half of the highest significant wave height in the actual storm. In this representation, the storm duration is not related to the storm intensity and it is fixed constant and equal to 42 hours, while the peak duration is assumed to be 6 hours. The parameterization proposed in the paper consists in expressing the peak duration as a fraction of the total storm duration allowing to investigate the effects of storm peak duration on long term estimates. The analytical solution for the return period is derived by following the classical approach of Equivalent Storm Models that is referring to the equivalent storm sequence, with the only difference that all the Trapezoidal Storm durations are identical whatever the storm intensity is. This assumption leads to significant simplification on the model development and potential employment as well. Further, a closed form solution is achieved for the return period which is also a generalization of the triangular shape. Finally, data analysis with NDBC buoys data is carried out for validating the model and elucidating analogies and differences with respect to classical Equivalent Storm approach. Results have shown that the Trapezoidal Model can be thought as a triangular one with a prudential factor on the storm peak duration which results in a reasonable overestimation of maximum expected wave height and return values.
Seismic RTDT: Real-Time Digital Twin for Boosting Performance of Seismic Operations
Authors: Sadjina Severin , Skjong Stian , Pobitzer Armin , Kyllingstad Lars T. , Fiskerstrand Roy-Jostein , Torben Sverre , Granholt Jason D. D. A.
Published: November 2019

Here, we present the R&D project Real-Time Digital Twin for Boosting Performance of Seismic Operations, which aims at increasing the overall operational efficiency of seismic vessels through digitisation and automation. The cornerstone in this project is the development of a real-time digital twin (RTDT) — a sophisticated mathematical model and state estimator of all the in-sea seismic equipment, augmented with real-time measurements from the actual equipment. This provides users and systems on-board the vessel with a live digital representation of the state of the equipment during operations. By combining the RTDT with state-of-the-art methods in machine learning and control theory, the project will develop new advisory and automation systems that improve the efficiency of seismic survey operations, reduce the risk of equipment damage, improve health monitoring and fault detection systems, and improve the quality of the seismic data. This will lead to less unproductive time, reduced costs, reduced fuel consumption and reduced emissions for a given operational scope.

The main focus in this paper is the presentation of today’s challenges in offshore seismic surveys, and how state-of-the-art technology can be adopted to improve various operations. We discuss how simulation technology, machine learning and live sensor measurements can be integrated in on-board decision support and automation systems, and highlight the importance of such systems for designing the complex, autonomous offshore vessels of the future. Finally, we present some early results from the project in the form of two brief case studies.
Wave Interaction With a Shallowly Submerged Step in 2D
Authors: McCauley Guy J. , Wolgamot Hugh , Draper Scott , Orszaghova Jana
Published: November 2019

Water wave propagation over shallowly submerged structures is of much interest in the context of submerged wave energy devices, breakwaters or barrier reefs. This work examines waves passing over a two-dimensional shallowly submerged fixed step extending to the seabed. The problem has been modelled in CFD using the open source toolbox OpenFoam utilising the Reynolds Averaged Navier-Stokes Equations. These simulations are compared to experimental work from a previous study as means of validation and extended to larger amplitude waves for a single incident wave frequency. The flow over the step is characterised and examined in the context of developing an efficient hybrid numerical model for the problem.