bluuebunny/crossref_metadata_2025_split huggingface dataset:
CFD Simulations of Breaking Stokes Waves
Authors: Hino Takanori , Ikenoue Harushi , Takagi Youhei 
Published: November 2019

Abstract
Free surface flow simulations using CFD (Computational Fluid Dynamics) can be categorized into two approaches in terms of free surface modeling. One is a two-phase flow model which solves both water and air. The other is a single-phase approach in which only the water region is solved with free surface boundary conditions. Breaking waves have been simulated by many researchers using CFD techniques with two-phase flow models in the most cases. In ship flow CFD applications, however, a single-phase approach is often used since this is considered to be more effective and efficient. However, when a single-phase method is applied to flows with bow wave breaking of a blunt ship, it is observed in some cases that numerical solutions fail to reproduce wave breaking well. This may be due to the differences of the air-water interface treatment between two-phase and single-phase approaches. To investigate these differences, breaking of Stokes waves is simulated by using both single-phase and two-phase flow models. The comparisons of single-phase and two-phase approaches are made in wave profiles, pressure and vorticity distributions. The velocity distributions near the free surface boundaries are also compared. Through these comparisons, impact of free surface boundary conditions in a single-phase approach to wave breaking phenomena is discussed.
CFD Analysis on Similarity Criteria of Hydrodynamic Characteristics for Gravity-Installed Anchors
Authors: Gao Jiancai , Liu Haixiao 
Published: November 2019

Abstract
For reduced-scale model tests of gravity-installed anchors (GIAs), it is of great significance to extrapolate the testing results to prototype. This highlights the necessity of investigation of similarity criteria. The present work aims to find the similarity criteria of three prioritized hydrodynamic characteristics including VT, HP, and Cd for GIAs during installation in water through CFD simulations. In the present study, free falling processes of different reduced-scale T98 anchor models and prototype anchor is simulated, from which VT, HP, and Cd are extracted and analyzed to get the fitting curves for these three characteristics over reduced-scale λ. Based on these curves, hydrodynamic characteristics for prototype and other reduced-scale model can be extrapolated from model testing results. And, the researching procedure in this paper sets an example and reference to study about similarity criteria for other hydrodynamic characteristics.
The Design and Installation of Wet Park Configuration for Dynamic Umbilicals in Ultra-Deep Environment
Authors: Reagan Perdinan , Lovie Graeme 
Published: November 2019

Abstract
Two dynamic umbilicals in a tethered lazy wave configuration were required to be wet parked in an ultra-deep environment with a water depth in excess of 2900m.
The close proximity to the pre-installed mooring lines, along with the in-place configuration requirements (seabed connection location, short seabed tether length, quantity of distribution buoyancy modules) made the design of a viable wet park configuration particularly challenging.
Strong current was also a major driving factor. The speed and dominant directionality influences the umbilical hump excursion, the stability of the umbilical and potential interference between the umbilicals and mooring lines. Several different routes were assessed to overcome the key problems as part of the wet park engineering solutions.
The installation of these umbilicals into their wet park configurations similarly presents a significant engineering undertaking.
An innovative and unconventional solution was chosen for the design of the wet park. The configuration utilises an umbilical ‘cross-over’, which allowed both umbilicals to be laid perpendicular to the dominant current direction and clear of any interference risks. An installation methodology was developed to successfully hook up the tether and lay down the umbilicals. Custom components and installation aids were designed for this purpose.
An Experimental and Numerical Study of Added Mass and Damping for Side by Side Plates in Oscillating Flow
Authors: Solaas Frøydis , Mentzoni Fredrik , Abrahamsen-Prsic Mia , Kristiansen Trygve 
Published: November 2019

Abstract
Forced harmonic oscillations of seven configurations consisting of horizontal side by side plate elements are performed experimentally and numerically. The configurations are oscillated in vertical direction and represent generalized mudmats of subsea structures. The tests are performed for Keulegan-Carpenter (KC) numbers relevant for force estimation during lifting operations. Hydrodynamic added mass and damping coefficients are presented. The coefficients are found to be amplitude dependent for all configurations tested. The interaction effects between the plates increase with increasing amplitude and decreasing distance between the plates. For oscillation amplitudes small compared with the gap between the plates, the plates behave approximately like individual plates. A study of the relation between the damping force and the added mass force for the tested structures illustrates the importance of applying representative damping coefficients in numerical analysis of marine operations.
Numerical results are obtained using a potential flow solver (BEM) and a viscous flow solver (CFD). Low-KC added mass coefficients predicted with the BEM are in accordance with the experiments. There is acceptable agreement between the CFD and the experiments. Best agreement is obtained for small KC numbers. For increasing KC numbers, the differences are, in general, larger. This is possibly due to the CFD being based on two-dimensional laminar flow.
Bore Pressure on Horizontal and Vertical Surfaces
Authors: Liu Jiaqi , Hayatdavoodi Masoud , Ertekin R. Cengiz 
Published: November 2019

Abstract
Bores generated by dam-break and initial mound of water and their propagation over horizontal and inclined surfaces are studied by use of theoretical approaches. Calculations are carried out in two and three dimensions and particular attention is given to the bore impact on horizontal and vertical surfaces. Downstream of the initial mound of water may be wet or dry. Discussion is provided on the influence of the downstream water on the bore behaviour and impact. Three methods are used in this study, namely the Reynolds-Averaged Navier-Stokes equations (RANS), the Green-Naghdi (GN) equations and Saint Venant equations (SV). The governing equations subject to appropriate boundary conditions are solved with various numerical techniques. Results of these models are compared with each other, and with laboratory experiments when available. Discussion is given on the limitations and applicability of these models to study the bore generation, propagation and pressure on horizontal and vertical surfaces. It is found that the GN equations compare well with the RANS equations, while the SV equations have substantially simplified the solution.
Effective Harmonic Analysis With Spectrum Filtering Technique
Authors: Peng Zhong , Grant Hazel , Sproson Richard 
Published: November 2019

Abstract
A spectrum filtering technique has been introduced to improve harmonic analysis in this study. The impact of site characterization and physical processes have been examined to justify the necessity of applying the spectrum filtering technique following classic harmonic analysis. Investigations show that the imperfection of the harmonic toolbox, e.g. T_Tide, could be attributed to significant contributions to the long period energy of density gradient and background currents, the greater variability of current amplitude energy, and the larger energy surrounding the clustering diurnal and semi-diurnal tidal constituents. From applications on hydrodynamic model data, this study supports the argument that harmonic analysis with the spectrum filtering technique could significantly improve the accuracy of tidal energy and residuals separation.
Numerical Investigation on the Rogue Wave Occurrence in Crossing Wave Fields
Authors: Liu Shuai , Zhang Xinshu , Song Xingyu , Chen Ke 
Published: November 2019

Abstract
A series of directly numerical simulations of potential Euler equation have been performed using high-order spectral (HOS) method, to investigate the nonlinear wave statistics and the probability of rogue wave occurrence in crossing sea states. Several typical crossing sea states in deep water with different wave steepness are chosen for the computations. The ensemble statistical properties for those crossing waves are measured, including the temporal evolution of directional and omnidirectional wave spectra, exceedance probability of wave crest amplitude, as well as the kurtosis and skewness of free surface elevations. Particular attention is paid to the correlation between kurtosis and rogue wave occurrence. Our numerical results suggest that the global wave steepness plays a significant role in the statistical properties of crossing seas. Results also show the dependence of rogue wave occurrence probability on the kurtosis of free surface elevations.
Numerical Methods for Interlink Stiffness Formulations and Parameters Sensitivity of Out-of-Plane Bending in Mooring Chains
Authors: Edward Ceasar , Dev Arun Kr. 
Published: November 2019

Abstract
Mooring components used for offshore floaters are conventionally designed only to resist axial loads with minimum resistance to bending loads. However, the unprecedented failure of four mooring lines of the Girassol Buoy followed by new modifications of similar buoys exposed the gaps in the existing methodology for failure assessment. The root cause of this failure was attributed to the critical role of out-of-plane (OPB) bending induced fatigue which reduced the fatigue life by 95%. The methodology to incorporate OPB fatigue for failure assessments involves a complex process due to numerous parameters required in the formulations and variability of mooring configurations. One of the most critical steps required to simplify methodology is the formulation of the interlink stiffness, contact stiffness and global stiffness of the chain segment. Currently, the interlink stiffness is derived from full-scale laboratory testing which is expensive and has limitations in generating data for a range of configurations.
This paper focuses on producing the interlink stiffness using numerical simulations based on non-linear FE analysis to capture the complex interlink contacts mechanism at the mating surface, elastic-plastic material properties considering non-linear isotropic and non-linear kinematic behaviors during OPB response modes, and compare the numerical models based on available experimental data. The numerical model developed for this research are designed to replicate real case OPB scenarios which induces both rotation and vertical displacements at the mooring connection points. This is different from models studied so far that induces only vertical displacements to study OPB responses which produces conservative results.
Further to this, an exhaustive analysis of the key OPB inducing parameters like chain diameter, types, pre-tension, instantaneous tensions, proof loading, residual stress, material properties, boundary condition etc. are required for understanding the underlying failure mechanism. This research also investigates the key OPB parameters and analyze their inter-dependencies, proportionalities and relative sensitivities to understand their overall contribution to OPB failures. This paper presents the first part of this research work which focuses on some of these key aspects to generate the simplified methodology using numerical methods.
The findings of this research can be used to generate a database of interlink stiffness for application to a range of mooring configurations and develop mathematical formulations for carrying out a direct assessment of OPB fatigue in combination with tension-tension fatigue failures and proposes potential mechanisms for improving the fatigue life.
Investigation of Focused Wave Impact on Floating Platform for Offshore Floating Wind Turbine: A CFD Study
Authors: Zhou Yang , Xiao Qing , Liu Yuanchuan , Incecik Atilla , Peyrard Christophe 
Published: November 2019

Abstract
Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study.
Oscillating Water Column Motion Inside Circular Cylindrical Structures
Authors: de Oliveira Costa Daniel , Sales Junior Joel Sena , Fernandes Antonio Carlos 
Published: November 2019

Abstract
A non-linear mathematical model is presented for the Equation of Motion of the Water Column inside circular cylindrical structures in different cases, comparing to previous models in literature. Experimental model tests were carried out investigating the water column decay under given initial conditions, and an analysis is performed for each cycle showing the dynamic behaviour of OWC evolving in time. The results show asymmetric pattern in the time series acquired in the decay tests as a consequence of variations of the Added Length and quadratic viscous damping as the direction of the flow changes, as observed in previous studies.
A general procedure is proposed to assess the unknown parameters including the quadratic damping viscous coefficients through the concept of “equivalent linear harmonic” as a linearisation of such terms, enlightening its dependence on the motion amplitude as well as the water column draft.
Experimental data for the OWC response under a set of incoming regular waves is also presented, comparing the results to numerical simulation through a solver based on the estimation of the damping coefficients obtained in the decay tests.
Study on the Effect of Impact Load Generated From Pile Driving on Adjacent Berthing Structure
Authors: John Jeena Mary , Saha Nilanjan , Sundaravadivelu R. 
Published: November 2019

Abstract
The extension of ports and offshore structures has increased due to feasible marine transportation with more cargoes pouring into the ports across the world. In many ports, there is limited availability of favourable conditions to berth and lack of space for an extension. This leads to the construction of new berthing structures at very close vicinity to existing structures which are aged but significant. One prime concern in such berths is the vibration that will be transmitted to the existing old structure during the construction of the new one. Therefore there is a requirement to keep vibration effects under control to ensure that existing structures remain serviceable.
One of the scenarios that determine the intensity of vibration that will be transmitted to soil and adjacent structure is the impact load applied on the pile. In the paper, the study is chosen at a specific port which needs reconstruction and extension due to the change in nature of the cargo to be handled and its requirements and also due to deterioration of aged berthing structure. Therefore, this study aims to find out the effect of impact load that is applied on pile casing during the pile driving process, so that the adjacent structure and machinery can be kept serviceable. The structure, soil medium and pile driving process are modelled in PLAXIS 3D. A damping ratio of 5 percent is assumed for both structure and soil throughout the modelling. A parametric study is done by varying the load on the pile casing while pile driving. The study gives the response of the structure to dynamic loading and influence of load on peak particle velocity during pile driving that gives economical piling and also ensures the safety of the adjacent berthing structure.
CFD Analysis of a Captive Bullet Entry in Calm Water With and Without Turbulence
Authors: Rauffus René Bettencourt , Maximiano António , Eça Luís , Vaz Guilherme 
Published: November 2019

Abstract
Simulations are carried out for a simplified lifeboat drop test case, which consists of a captive axisymmetric generic lifeboat shape (bullet), that penetrates the water surface at a constant velocity and angle of attack. The quantities of interest are the body fixed longitudinal force FX, vertical force FZ, and pitch moment MYY.This case was previously used in a verification and validation exercise [1]. Here, a step forward in complexity is taken, as the previous numerical model is now supplemented with the eddy-viscosity based turbulence model k–ω SST. Both approaches are then used to simulate two different cases: Case 1 with minimal wake effects; and Case 3 with flow separation and significant wake. The results are compared with the experimental data. The numerical uncertainty is estimated for both models. It is seen that for Case 1 the difference between both models is mostly within the comparison uncertainty, except for the longitudinal force FX, where the turbulent flow predicts a larger force, improving the comparison with the experiments. The loads predicted with turbulent flow stayed mostly within 6 % of the laminar flow. For Case 3 small differences between both models are found during/after the wake collapse stage. However, this difference is often within the comparison uncertainty. A reasonable agreement is found with the experimental data, except for FZ after the bow wake collapse. The turbulent flow improves slightly on the laminar approach regarding the agreement with the experiments, however it can be argued if this difference justifies the increased computational cost of the turbulence model.
Subsea Spare Parts Analysis Optimisation
Authors: Coffey Tiarnan , Rai Christopher , Greene John , O’Brien Bromley Stephen 
Published: November 2019

Abstract
The main objective of this paper is to present a fully quantitative methodology combining reliability, availability and maintainability (RAM) analysis and cost-benefit analysis (CBA) approaches to determine the optimum sparing strategy for subsea components considering reliability data, lead times, availability and cost. This methodology can be utilized at any stage of an asset lifecycle, from design to operation and can be adjusted to reflect modifications throughout the life of field.
Using commercially available RAM analysis software, Maros [2], a reliability block diagram (RBD) is constructed to represent the reliability structure and logic of the system being analyzed. Retrievable components, for which spares would be suitable, are then identified within the model to review and update the failure modes and reliability information for each component. Reliability information can be based on project specific data or from industry-wide sources such as OREDA. The RAM analysis software uses the Monte-Carlo simulation technique to determine availability. A sensitivity analysis is then performed to determine maximum availability while holding the minimum required stock level of spare components.
A sparing priority factor (SPF) analysis is then performed in addition to the RAM sensitivity analysis to support those results and consider spare purchase, storage and preservation costs. The SPF gives a weighting to the storage cost against the potential impact on production. The SPF is a number used to determine a component’s need to have a spare. A high SPF indicates an increased requirement to hold a spare.
Fatigue of Mooring Chains Connected to Offshore Floating Structures Considering Out of Plane Bending Effects
Authors: Hellum Vidar , Ding Songxiong , Lassen Tom 
Published: November 2019

Abstract
Reliability against fatigue fracture is an issue of major concern in the design of offshore mooring systems with chain segments. The present paper describes the investigation of the effect of OPB (out of plane bending) and IPB (in plane bending) loading modes on the fatigue performance of chain links in critical positions. The hang-off design at the floater is based on long rods with bearings at the connection points to the floating structure. The purpose of the paper is to shed some light on possible design improvements on the connection design when using the available design guidelines for calculation of combined Tension-Bending fatigue in the mooring line.
A challenge when using the existing design guidelines is that they often predict very short fatigue lives for what used to be a conventional hang-off design. A possible method for mitigating this is to improve the connection design so that the interlink angles could be reduced due to the slip in the bearings in the end of the rod. This would lower the bending stress to be occurred in those critical links. The present paper investigates the optimum length connecting rods and friction in the bearing on the fatigue lives of top mooring chains.
A case study for 125 mm mooring chain and a pretension of 1200 kN is included. A non-linear beam model established according to the BV guidelines showed good ability to model the behavior of the 125 mm chain observed during the test. It is however a challenge to select the right interlink rotational stiffness and the correct bearing friction coefficient. An optimization analyses demonstrated that a rod length should be minimum 3 meters and the friction coefficient should be down to 0.15.
A Fundamental Study on Tsunami Protection Measures for a Vessel Moored at a Wharf Considering the Backwash Influence
Authors: Masuda Mitsuhiro , Minami Kiyokazu , Masuda Koichi 
Published: November 2019

Abstract
When a tsunami attacks in harbors, a vessel moored at a wharf is occurred a serious damage. The first wave of the tsunami has two forms and those are called the leading wave and the backwash. And, it is difficult to predict the form of the first wave of tsunamis. Authors have been studying about damage protection measures against the leading wave of vessels moored at wharves. However, it is also necessary that a damage protection measure against the backwash of vessels moored at wharves is considered. In this study, it is examined the damage status of a vessel at a wharf due to the backwash. Then, it is examined the influence of the backwash to the author’s proposal tsunami protection measures. The three dimensional MPS (Moving Particle Semi-implicit) method is used. The Backwash is simulated as the dam break phenomenon. Outflow angles, flow velocities, mooring conditions and with and without of tsunami protection measures are considered.