bluuebunny/crossref_metadata_2025 huggingface dataset:
Bilge Keel Loads and Hull Induced Pressures: Experimental Results and CFD Validation
Authors: van ‘t Veer Riaan , Schut Xavier , Pelerin Jean-Luc
Published: October 2015

This paper present results obtained in an experiment with a rotating cylinder to which a single bilge keel was fitted. Forced oscillations were performed leading to a KC range between 1 and 16. The loads acting on the bilge keel were measured as well as the vortex induced hull pressures in the vicinity of the bilge keel.

Computational Fluid Dynamic simulations were conducted with a 2D representation of the experiment. Good correlation in the bilge keel loads and vortex induced pressures is obtained.

Using Fourier analysis the first and first two higher harmonic (3ω and 5ω) drag and inertia coefficients of the bilge keel load were calculated. It is shown that the higher harmonic drag and inertia terms are essential to obtain a good load representation.

The vortex induced pressure in front of the moving bilge keel is found to be KC independent. The pressure jump over the bilge keel can be correlated to the instantaneous normal force on the bilge keel. In the wake of the moving bilge keel the pressure depend on KC. These findings are in agreement with the observations reported by Ikeda et al. [1].
Analyses of Current and Wave Forces on Velocity Caps
Authors: Christensen Erik Damgaard , Buhrkall Jeppe , Eskesen Mark C. D. , Jensen Bjarne
Published: October 2015

Velocity caps are often used in connection with for instance offshore intake sea water for the use of for cooling water for power plants or as a source for desalinization plants. The intakes can also be used for river intakes. The velocity cap is placed on top of a vertical pipe. The vertical pipe leads the water into another pipe or tunnel system. A pressure gradient generated by the water level difference between the sea and basin drives the flow through the tunnel system. The tunnel system is often in the order of a couple kilometers long. Based on CFD analyses (computational fluid dynamics) this paper investigates the current and wave forces on the velocity cap and the vertical cylinder. The Morison’s force model was used in the analyses of the extracted force time series in from the CFD model. Further the distribution of the inlet velocities around the velocity cap was also analyzed in detail in the wave case.
Validation of Ship Manoeuvring in Shallow Water Through Free-Running Tests
Authors: Eloot Katrien , Delefortrie Guillaume , Vantorre Marc , Quadvlieg Frans
Published: October 2015

The shallow water effect on ship manoeuvring cannot be neglected. Most sea-going ships become more course stable when they sail from deep to (very) shallow water. International collaborations such as SIMMAN intend to grade up the knowledge on ship manoeuvring prediction through model tests and system based and numerical methods. Free-running model tests executed with the very large crude carrier KVLCC2 at two laboratories have been compared with the results of simulated turning circles and zigzag manoeuvres from two different mathematical models. It was concluded that the type of mathematical model has an important influence on the simulated behaviour. Moreover, further research is necessary as simulations result into a more course stable behaviour compared to free-running tests at model scale.
Power Generation Potential of a VLFS Equipped With OWC Type WECs and Damper Effects on Elastic Motion
Authors: Ikoma Tomoki , Masuda Koichi , Watanabe Yuka , Eto Hiroaki , Rheem Chang-kyu , Kinoshita Takeshi
Published: October 2015

This paper describes potential of PTO (Power Take-Off) and the damper effect of motion in a large scale pontoon type floating structure on which lots of oscillating water column (OWC) type wave energy convertors (WEC) are installed. It is enable to use upper space for utilizing marine renewable energy such as wind power, tidal power, wave power generation farm using large pontoon structure. Due to the concept, it should reduce cost of maintenance as well.

For investigation of PTO and elastic motion behaviours of large floating structures, we calculated three types of models on which OWC devices were installed differently. We examined how much reduction was possible when including elastic motion effects and the fixed type which radiation wave was not taken into account. In this paper, a boundary condition in order to give effect of a free water surface with air pressure is theoretically modeled. We can directly consider influence of wave energy absorption to hydrodynamic forces and wave exciting forces on the floating structure with the Green’s function method based on the linear potential theory. In the modeling, a boundary condition on a free water surface and an equation of state within an air-chamber above OWC are mathematically and linearly formulated. Air-pressures and vertical displacement within OWC areas can be simultaneously and directly solved by setting both the variables and by solving the simultaneously equations of the air-pressure and the vertical displacement.

As a result, performance of PTO and hydroelastic motion of the floating structure increased when including elastic motion effect. In addition, expected value of annual PTO was about 4.4MW with 146 OWCs.
Numerical Study of Bilge-Keel Effect on Parametric Roll and Water on Deck for an FPSO
Authors: Greco Marilena , Lugni Claudio , Colicchio Giuseppina , Faltinsen Odd M.
Published: October 2015

This research activity represents the logical continuation of the work documented in [1] and [2] on water on deck and parametric roll for an FPSO in regular waves. Here the same numerical method, based on a domain-decomposition strategy, is used to examine the platform with bilge keels, both without and with mooring-line system. It is found that bilge keels with length 40% of the ship length and with breadth the 3% of the ship breadth limit effectively the roll when instability is promoted by vertical bow motions in waves. In these conditions also the amount of the shipped water is substantially reduced. Large roll induced by the coupling with the lateral motions seems to be less well counteracted and remains close to 10° for steepness kA ≥ 0.2. This value is often set as maximum allowed amplitude for FPSOs in normal operational conditions. Also the effect on the shipped water is limited in this case. Increasing the bilge-keels breadth is confirmed to be beneficial but the combination of the mooring system with dynamic positioning appears needed for a proper control of the roll motion in the worst examined cases.
Practical Formula of the Shape Evolution of a Surface Crack Under Fatigue Loading
Authors: Anai Yosuke , Niwa Toshio , Gotoh Koji
Published: October 2015

Fatigue life estimation for planar cracks, e.g. part-through surface cracks or embedded cracks is very important because most of fatigue cracks found in welded built-up structures show planar crack morphologies. Although authors had proposed the estimation procedure of crack shape evolution for a planar crack based on the fracture mechanics approach, this method cannot apply if the values of stress intensity factor at the vertices of the surface crack approximated as an ellipse cannot calculated. Then, development of the shape evolution procedure of a planer crack under the stress field with arbitrary gradient, because fatigue cracks in welded built-up structures exist near the stress concentrated region. A Practical estimation formula the shape evolution of a surface crack under stress field with the gradient is proposed in this study. This formula is established by considering the stress field under no crack condition and some former proposed formulae under uniform and pure bending stress fields. The validity of the proposed formula are confirmed by comparing some measured surface crack shape evolutions under some stress gradient conditions.
Sensitivity of a Wave Energy Converter Dynamics Model to Nonlinear Hydrostatic Models
Authors: Coe Ryan G. , Bull Diana L.
Published: October 2015

A three dimensional time-domain model, based on Cummins equation, has been developed for an axisymmetric point absorbing wave energy converter (WEC) with an irregular cross section. This model incorporates a number of nonlinearities to accurately account for the dynamics of the device: hydrostatic restoring, motion constraints, saturation of the power-take-off force, and kinematic nonlinearities. Here, an interpolation model of the hydrostatic restoring reaction is developed and compared with a surface integral based method. The effects of these nonlinear hydrostatic models on device dynamics are explored by comparing predictions against those of a linear model. For the studied WEC, the interpolation model offers a large improvement over a linear model and is roughly two orders-of-magnitude less computationally expensive than the surface integral based method.
A True Transient Hydrodynamic Force Prediction Method on a Descending and Oscillating Buoy
Authors: Lee Sungho , Huang Zhenjia (Jerry)
Published: October 2015

Disconnectable turret-moored Floating Production, Storage and Offloading (FPSO) or Arctic Floating Drilling (AFD) units may operate in harsh environments for offshore oil and gas production. The turret buoy is designed to be disconnected from the FPSO or AFD to circumvent excessive loads on the mooring system in these harsh environments which could be driven by extreme waves or icebergs. Due to the large descending and oscillating motions after disconnect, the hydrodynamic force on the buoy is of transient nature (i.e. unsteady hydrodynamic force). To confidently predict the buoy motions during the disconnect event, it is necessary to understand and accurately predict the transient effects from the body’s instantaneous position and the water surface on the hydrodynamic force. However, no analytical or numerical methods have been successfully applied by current industry practice that accurately capture the forces on a descending buoy in this this transient phenomenon. In this work, we present a numerical analysis method developed by ExxonMobil Upstream Research Company (URC) to calculate the “true” transient hydrodynamic force on a descending buoy. A transient potential-flow mathematical model is developed in the time-domain through a transient free-surface Green’s Function by applying the instantaneous buoy position and velocity. The hydrodynamic force on the buoy is evaluated using a “fluid impulse” theory, which is computationally efficient. Computational results are presented and compared with model test results to illustrate the performance of the developed numerical approach on predicting the hydrodynamic force on a descending buoy for various disconnect scenarios.
Evaluation of the Dynamic-Response-Based Intact Stability Criterion for Floating Wind Turbines
Authors: Masciola Marco , Chen Xiaohong , Yu Qing
Published: October 2015

As an alternative to the conventional intact stability criterion for floating offshore structures, known as the area-ratio-based criterion, the dynamic-response-based intact stability criteria was initially developed in the 1980s for column-stabilized drilling units and later extended to the design of floating production installations (FPIs). Both the area-ratio-based and dynamic-response-based intact stability criteria have recently been adopted for floating offshore wind turbines (FOWTs).

In the traditional area-ratio-based criterion, the stability calculation is quasi-static in nature, with the contribution from external forces other than steady wind loads and FOWT dynamic responses captured through a safety factor. Furthermore, the peak wind overturning moment of FOWTs may not coincide with the extreme storm wind speed normally prescribed in the area-ratio-based criterion, but rather at the much smaller rated wind speed in the power production mode. With these two factors considered, the dynamic-response-based intact stability criterion is desirable for FOWTs to account for their unique dynamic responses and the impact of various operating conditions.

This paper demonstrates the implementation of a FOWT intact stability assessment using the dynamic-response-based criterion. Performance-based criteria require observed behavior or quantifiable metrics as input for the method to be applied. This is demonstrated by defining the governing load cases for two conceptual FOWT semisubmersible designs at two sites. This work introduces benchmarks comparing the area-ratio-based and dynamic-response-based criteria, gaps with current methodologies, and frontier areas related to the wind overturning moment definition.
Observations on the Time-Dependent Fracture of Ice
Authors: Kavanagh Mark B. , O’Rourke Brian J. , Jordaan Ian J. , Taylor Rocky S.
Published: October 2015

The results of a recent ice indentation series, along with a 4-point beam bending series, are analysed in the present paper with regard to time-dependent fracture. The beam bending series used a a 4-point apparatus to test the effects of velocity on fracture toughness, and to study time delayed fracture at loading rates below the fracture strength of ice. The indentor series used different indentors (diameters ranging from 10 mm to 70 mm), and applied various velocities used to test the time-dependent fracturing of ice. For experiments with a low ratio of velocity to indentor showed damaged-enhanced creep behaviour, ending in large, global failure during some tests. For the highest velocity tests, the ice showed increasingly brittle failure. The loading curve in these tests displayed many smaller spalling events, or ice extrusion events, with cyclic ramp-up of loads between each event.
Some Issues in Ice Mechanics
Authors: Jordaan Ian
Published: October 2015

Ice mechanical behavior is time-dependent, as has been known for many decades. But in many references, the attempt is made to use time-independent plasticity theory. The relevant analytical approach that accounts for time is viscoelastic theory. The need for this approach is made quite essential by study of microstructural changes that occur in ice under high stresses. In no case does there appear to be a clear yield condition, with flow occurring after a certain threshold value. Furthermore, the microstructural changes occurring under stress result in a highly significant enhancement of the creep rates. This results in a spatially varying viscoelastic response that is a function of prior stress history. The ice response is then a function of position resulting in a microstucturally modified layer in the region where compressive stress is applied. This can be deep or highly localized, depending on the loading rate. The most promising approach is that based on damage mechanics combined with viscoelasticity, using the thermodynamics of irreversible processes.

Ice is also prone to fracture, especially at high loading rates and under high stresses. This is basic to the notion of scale effect. Fracture processes are also time-dependent in viscoelastic materials, a phenomenon that needs to be explored further. Furthermore, failure often will take place in a random fashion, depending on the distribution of flaws in ice. This indicates strongly that a theory based on “weakest-link” hypotheses and probability theory is appropriate.

Finally, some aspects relevant to practical data analysis are discussed. These include measurement uncertainties of Molikpaq data, and geometric approximations of ice features, e.g. ridges as uniform beams.
Finite Element Analysis of Flexible Pipes Under Compression: Influence of the Sample Length
Authors: Malta Eduardo Ribeiro , de Arruda Martins Clóvis
Published: October 2015

In order to study the compressive behavior of flexible pipes, a nonlinear tridimensional finite element model was developed. This model recreates a five layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape and a rigid inner nucleus. Using this model, several studies are being conducted to verify the influence of key parameters on the wire instability phenomenon. The pipe sample length can be considered one of these parameters and its variation causes significant change at the stability response of the tensile layers. This article includes a detailed description of the finite element model itself and a case study where the length of the pipe is changed. The procedure of this analysis is here described, along with the results.
Ultimate Strength of Damaged Stiffened Panels Subjected to Uniaxial Compressive Loads Accounting for Impact Induced Residual Stress and Deformation
Authors: Cai Jie , Jiang Xiaoli , Lodewijks Gabriel
Published: October 2015

In case of ship accidents, the ship’s hull will inevitably suffer from damages such as holes, cracks, dent etc., which will threaten the structural safety of ship. It is essential to study the ultimate strength of damaged ships in order to facilitate the decision-making process of ship salvage. There are considerable publications on the subject, however, the impact of the induced residual stress and deformation are normally excluded in those studies. This paper therefore aims at investigating the effect of the impact induced residual stress and deformation on the ultimate strength of a stiffened panel through application of a nonlinear Finite Element Analysis (FEA) method. Firstly, a literature review on ultimate strength of damaged ships is presented. Secondly, a nonlinear numerical simulation is adopted to investigate the ultimate strength of stiffened panels accounting for residual stress and deformation. this procedure consists of two stages: the impact stage and the static stage. The results of the numerical simulation of both stages are validated through the results of experiments and simulations available in literature. Afterwards, a series of case studies are performed deploying the validated numerical method. Finally, a closed form expression to predict the ultimate strength accounting for impact induced residual stress and deformation is proposed based on direct simulation. Results show that the combined effect of impact induced residual stress and deformation can significantly reduce structures’ load carrying capacity. The maximum reduction ratio reaches 37% in local stiffened panel. The method of removal of all the plastic deformation area is generally too conservative to predict the ultimate strength of a damaged local stiffened panel, which will underestimate the residual load carrying capacity of ships considerably.
Coupled Dynamic Analysis for Multi-Unit Floating Offshore Wind Turbine in Maximum Operational and Survival Conditions
Authors: Jang H. K. , Kim H. C. , Kim M. H. , Kim K. H.
Published: October 2015

Numerical tools for a single floating offshore wind turbine (FOWT) have been developed by a number of researchers, while the investigation of multi-unit floating offshore wind turbines (MUFOWT) has rarely been performed. Recently, a numerical simulator was developed by TAMU to analyze the coupled dynamics of MUFOWT including multi-rotor-floater-mooring coupled effects.

In the present study, the behavior of MUFOWT in time domain is described through the comparison of two load cases in maximum operational and survival conditions. A semi-submersible floater with four 2MW wind turbines, moored by eight mooring lines is selected as an example. The combination of irregular random waves, steady currents and dynamic turbulent winds are applied as environmental loads. As a result, the global motion and kinetic responses of the system are assessed in time domain. Kane’s dynamic theory is employed to formulate the global coupled dynamic equation of the whole system. The coupling terms are carefully considered to address the interactions among multiple turbines. This newly developed tool will be helpful in the future to evaluate the performance of MUFOWT under diverse environmental scenarios.

In the present study, the aerodynamic interactions among multiple turbines including wake/array effect are not considered due to the complexity and uncertainty.
Wave Motion Control Over Submerged Horizontal Plates
Authors: Karmakar D. , Guedes Soares C.
Published: October 2015

The interaction of surface gravity waves with horizontal pitching plate for actively control waves is investigated based on the linearized theory of water waves. The two dimensional problem is formulated for the submerged plate pitching about its middle point and the other plate is considered to be floating above the submerged plate. The submerged plate’s thickness is considered negligible in comparison with the water depth and wavelength of the incident wave. The study is carried out using the matched eigenfunction expansion method and the analytical solution is developed for the interaction of the surface gravity waves with horizontal submerged structure. The numerical results for the reflection coefficient, transmission coefficient and free surface deflection are computed and analyzed. The study is carried to find the optimal value of the length and depth of the submerged plate at which the dissipation of the incident wave energy is observed. The reduction the wave transformation due to the pitching of the plate with the change in angle of incidence is also analyzed. The present study will be helpful in the analysis of proper functioning of submerged pitching plate to control wave motion for the protection of offshore structures.
Investigation of Compaction and Sand Migration Effect on Permeability and Non-Darcy Coefficient With Pore-Scale Simulations
Authors: Anbar Sultan , Tyagi Mayank , Thompson Karsten
Published: October 2015

Compaction and sand migration are some of the main problems for the loosely consolidated and unconsolidated high rate gas reservoirs. A reliable estimation of the well productivity depends on accurate modeling of permeability and inertial effects. Therefore, the key objective of this paper is to quantify the flow parameters change in the case of compaction and sand migration, and the development of permeability and the non-Darcy coefficient correlations that can be used in reservoir simulations. The compaction effects are simulated by increasing grains diameters with the same ratio. Permeability and the non-Darcy coefficients are calculated from lattice Boltzmann method (LBM). Results indicate that permeability decrease is not directional and the change in permeability can be estimated from porosity change with a Kozeny-Carman type relation with an exponent of 3.2. A Kozeny-Carman type relation between the non-Darcy coefficient and permeability is also found with an exponent −1.303. For high compressibility reservoirs, estimation of the inertial effects from the correlations developed as a function of permeability and porosity may also lead to underestimation of the inertial effects.

Sand migration causes pore-throat plugging that leads to significant reduction in permeability. Permeability impairment due to sand or fines migration is usually estimated from Kozeny-Carman type relation based on porosity. There is no study in the literature on how the inertial effects are changed with permeability impairment due to sand or fines migration. Sand particle plugging locations are found from the network simulations for different pore volume reduction, and corresponding permeability and the non-Darcy coefficient are calculated from LBM. It is found that permeability change with sand plugging is direction dependent: permeability reduction in the flow direction is twice compared to other directions. Porosity reduction does not depend on only pore-throat plugging, porosity can be decrease due to compaction and pore-surface deposition. Therefore, a correlation is developed to estimate permeability from pore-throat sand concentration. Even though permeability change is directional, the trend between permeability and the non-Darcy coefficient is similar and the magnitude of exponent in Kozeny-Carman type relation is larger, −1.803, compared to that of compaction.
Analysis and Design of an Oscillating Water Column Wave Energy Converter With Dielectric Elastomer Power Take-Off
Authors: Moretti Giacomo , Rosati Gastone Pietro Papini , Alves Marco , Grases Manuel , Vertechy Rocco , Fontana Marco
Published: October 2015

In this paper, we present a concept of near/off-shore Oscillating Water Column (OWC) Wave Energy Converter (WEC) that is equipped with a Power Take Off (PTO) unit based on Dielectric Elastomer Generators (DEGs). DEGs are soft/deformable generators with variable capacitance able to directly convert the mechanical energy that is employed for their deformation into electrostatic energy.

The proposed WEC is based on an existing tubular collector chamber of an OWC system designed by the company Sendekia, that is combined with an Inflatable Circular Diaphragm (ICD) DEG. This simplified design presents a very reduced number of moving parts showing potentially high efficiency, reliability and noise-free operation.

A multi-physics dynamic model of the system is built using time domain linear hydrodynamics coupled with an analytical non-linear electro-hyperelastic model for the DEG-based PTO. The power matrix of the system is calculated for both regular and irregular waves. Some design issues are introduced showing that the electro-elastic response of the DEG provides the system with an additional stiffness that adds up to the hydrostatic stiffness and affects the resonance of the WEC. As a consequence, the geometric shape/dimensions of the OWC chamber and the layout of the DEG diaphragm should be chosen using an integrated procedure aimed at tuning the overall response of the WEC to the spectra a reference wave climate.
Analysis of Iceberg Frequency in Labrador Sea Using Aerial Reconnaissance Flight Surveys and Satellite Radar Data
Authors: Habib Kashfi B. , Cuff Andrew , King Tony
Published: October 2015

Recently Nalcor announced the discovery of three newly defined hydrocarbon basins located primarily in deep water in the Labrador Sea, off the east coast of Newfoundland and Labrador, Canada. The basins are Henley, Chidley and Holton Basins and expanded the extent of the Hawke Basin. On behalf of Nalcor Energy, C-CORE recently completed the Offshore Newfoundland and Labrador Metocean Study which summarizes environmental conditions of these regions to support offshore petroleum exploration and development in the Labrador Sea and to outline the resource potential to the global oil and gas industry. Defining iceberg densities was one of the required tasks for the study. Among various environmental conditions, iceberg density is one of the most challenging parameter to define accurately both spatially and temporally. Aerial iceberg reconnaissance flight surveys provided by IIP (International Ice Patrol) and CIS (Canadian Ice Service) were studied, classified and analyzed to compute iceberg density (number of icebergs per square km). Only open water icebergs were considered for analysis because of the difficulty associated with reliably identifying icebergs in pack ice, which may lead to an underestimation of iceberg occurrence. Therefore, aerial reconnaissance data were compared with CIS pack ice charts to eliminate any possibility of iceberg sightings in pack ice being included in the analysis. Satellite radar data acquired using Envisat wide swath mode (WSM) imagery was also used for iceberg detections in order to provide full coverage of the study area. Again, sea ice was outlined in the imagery to ensure no targets in sea ice were counted. The WSM imagery provided a 400 km wide swath with an approximate radar resolution of 150 m, meaning smaller targets were not detected. In order to combine satellite radar data with aerial reconnaissance surveys a non-detection factor was calculated using a comparison of concurrent Envisat and aerial coverage to compensate for missed targets due to the coarser radar resolution. The resulting map of open water iceberg densities will provide a baseline for the region which shall be further refined through an on-going program using high-resolution Sentinel satellite data. Detailed descriptions of the analysis, procedures and results are presented in this paper. Areal density results of the newly defined basins are compared to the other frontier regions, where iceberg risks are higher.
An Integrated Numerical Approach to Design Offshore Pipelines Susceptible to Lateral Buckling
Authors: Van den Abeele F. , Boël F. , Hayes D. , Scales D.
Published: October 2015

Lateral buckling is a global response to excessive compressive axial force due to thermal and internal pressure loads which when combined, exceeds the initiating Euler Buckling force and overcomes the lateral friction force reacting against a pipeline laid on the seabed.

According to DNV-RP-F110, the integrity of a pipeline susceptible to buckling can be assured by either restraining the pipeline, thus sustaining large axial compressive forces, or releasing them through a combination of pipeline displacements; lateral buckles. Buckling may be rogue in nature or engineered at predetermined locations, either of which must demonstrate compliance to DNV OS F101. Engineered lateral buckles are a cost effective way to manage for example HP/HT pipelines as opposed to the construction of restraint designs. However, uncertainty in the initial buckle formation process and buckle behaviour may reduce design reliability; resulting in an increased level of redundancy in a buckle management system.

This paper presents the vision of an engineering tool aimed at providing an integrated single model environment which enables straightforward engineering analysis, with application to all phases of design, and providing support to operations. Verification of buckling forces and post-buckling configurations is undertaken through comparison with Hobbs and Kerr analytical models and validated against ABAQUS.
Evaluation of Response of a Floating Cryogenic Hose in Offloading Operation Between FLNG Unit and LNG Carrier in Tandem
Authors: Ferreira André Luís F. , Morooka Celso K.
Published: October 2015

Static and dynamic response of a floating cryogenic hose is analyzed in offshore offloading of LNG, taking into account FLNG unit and LNG carrier in tandem. Response of the hose in the operation depends on several parameters involved. Among them, hose overall length, span, buoyancy and position of the hose ends (terminations at the vessels) relative to the sea surface are considered important, and they are investigated. Environmental loads as well as vessels motions are considered in the computational simulations achieved to evaluate the response of the hose in operation. Parametric variation is conducted in order to observe sensitivity of the hose to parameters aforementioned. Forces and moments at hose terminations (hose ends) as well as effective tension and curvature along hose length are observed. Critical zones of the hose (as its sections close to sea surface) are analyzed with details and main remarks are addressed.
Hydrodynamic Modelling Competition: Overview and Approaches
Authors: Garcia-Rosa Paula B. , Costello Ronan , Dias Frederic , Ringwood John V.
Published: October 2015

This work describes the overall aspects of the Competition on Hydrodynamic Modelling of a Rigid Body, a competition outlined to evaluate different ways to model and simulate the motions of a rigid body in waves. The main objective is to determine a hydrodynamic model for a submerged horizontal cylinder which best predicts a recorded motion to a specific excitation in panchromatic waves. A blind study was performed by the competition participants, i.e., the simulation results were obtained without knowledge of the actual recorded motion of the cylinder. Only the geometry of the cylinder in solid model and the time series of the incoming waves were issued to the participants. The proposed approaches by the participants for modelling the rigid body and the fluid motions are based on the boundary-integral equation methods (potential flow theory) with additional viscous damping forces, where the drag terms are calculated either empirically or via the Navier-Stokes equation method. This paper describes the details about rationale for choice of the rigid body, the experimental tests, the competition criteria and an overview of all modelling approaches proposed by the competition participants.
Economic Effects of Multiple Disasters in the Gulf of Mexico
Authors: Dahi-Taleghani Negar , Tyagi Mayank
Published: October 2015

With the recent exploration/discovery of deep-water reservoirs andcontinued developments of drilling and production, it remains very important to have a comprehensive and quantitative risk assessment ofthe drilling/production processes including effective response to deal with such disasters. What measures must be taken to recover from the disaster scenario of a hurricane impacting the same region in the aftermath of an oil spill? The Deepwater Horizon oil spill, the largest marine oil spill in history, was caused by an explosion on a semi-submersible drilling rig about 50 miles southeast of the Mississippi River delta on April 20, 2010. Catastrophic events such as oil spills have enormous impact for the local economy of the area and even for the local labor markets. Another regional disaster, Hurricane Katrina impacted Louisiana, Mississippi, and Alabama, as it ripped over the core of the Gulf of Mexico (GoM) producing zone, one of the important oil and gas production areas of the worldin 2005. Also, if acatastrophic disaster occurs and the emergency response supply chain is not adequately prepared, then the economic consequences of sucheventcan be huge. Whenever a disaster happens, another reaction to this event that should be considered is resiliency. It is the ability to reduce or remove potential losses due to disaster events.

The impact of different shocks on various aspects of a state’s economic performance is estimated using a Vector Autoregressive model (VAR). In this study, the dynamic response of a variety of industrial sectors in Louisiana to each of these disasters is considered. The responses of different impulses in this model are shown to demonstrate the interdependence of various time series data.
A Control Strategy for PTO Systems in a U-OWC Device
Authors: Strati Federica Maria , Malara Giovanni , Laface Valentina , Romolo Alessandra , Arena Felice
Published: October 2015

This paper deals with the implementation of a control algorithm for a turbine equipped into a U-Oscillating water column (U-OWC) plant. The open literature has largely ignored the problem of coupling the U-OWC behaviour to the turbine behaviour with the objective of maximizing the energy harvesting. Therefore, this paper has the objective of assessing the reliability of a Maximum Power Point Tracking (MPPT) algorithm.

The paper uses a numerical algorithm for estimating the energy produced by a U-OWC in real seas. In this regard, the computations rely on long time domain analyses that allow testing a variety of environmental conditions.

The MPPT is proved adequate for controlling the turbine behavior in conjunction with U-OWCs. In this context, it is shown that a reference parameter, used for determining the reference rotational speed, can be the significant wave height.
A Numerical Study of Fluid Structure Interaction of a Flexible Submerged Cylinder Mounted on an Experimental Rig
Authors: Cakir Erkan , Akinturk Ayhan , Allievi Alejandro
Published: October 2015

The aim of the study is to investigate VIV effects, not only on a test cylinder but also on the experimental rig being towed under water at a prescribed depth and operating speeds. For this purpose, a numerical Multi-Physics model was created using one way coupled analysis simultaneously between the Mechanical and Fluent solvers of ANSYS software package. A system coupling was developed in order to communicate force data alternately between the solvers with the help of automatic mapping algorithms within millesimal time periods of a second. Numerical investigation into the dynamic characteristics of pressure and velocity fields for turbulent viscous fluid flow along with structural responses of the system, stressed the significance of time and space scales for convergence and accuracy of our Finite Volume (FV) CFD calculations.
Post Well Vibration Analysis in the North Sea: A Tool to Understand Drilling Performance
Authors: Al Dushaishi M. F. , Nygaard R. , Hoel E. , Hellvik S. , Andersen M.
Published: October 2015

Severe drill stem vibrations could leads to excessive damage to the bottom hole assembly causing an increase in nonproductive time. Different drill stem vibrations models are used to predict and avoid resonance regions by optimizing the selection of bottom hole assembly components and operating parameters such as weight on bit, and surface RPM. In addition to avoid the resonance regions, specialized tools have been developed to reduce vibrations. However a complete understanding on how to mitigate vibration and its effect on drilling performance is still lacking. This study investigates the cause of drill stem vibrations, its effect on drilling performance, and the effect of including vibration reductions tools in the bottom hole assembly design in several recent drilled wells in the North Sea.

Vibration damping tools used in this study were able to reduce both lateral and torsional drill stem vibration compared to a well with no vibration damping tool. Torsional drill stem vibrations tend to increase through rich sand zones causing an increase in lateral vibrations. The impact drill stem vibrations have on drilling performance was identified through rate of penetration. As lateral vibration intensity increases, instantaneous rate of penetration decreases.
Optimization of Rock Berms for Pipeline Stabilization Subject to Intense Hydrodynamic Forcing
Authors: Cornett Andrew , Baker Scott , Riedel Peter , Knox Paul
Published: October 2015

This article describes a comprehensive study in which 2D and 3D physical modelling at 1:40 scale was used to optimize the design and validate the performance of dynamically stable rock berms to be used for stabilizing several large pipelines traversing water depths from 5m to 65m and potentially exposed to large waves and strong currents generated by intense tropical cyclones. For added realism, all of the model rock berms were constructed using a scaled simulation of rock installation by fall pipe vessel to be used in the field. Special attention was also given to simulating the self-stability of the model pipeline segments, including special end constraints designed to mimic the behaviour of a continuous pipeline. A large data set concerning the behaviour of dynamically reshaping rock berms in a range of water depths under intense hydrodynamic forcing due to three-dimensional waves and currents was produced and used to develop efficient and cost-effective rock berm designs for all depth zones.
New Benchmark Data for Manoeuvring in Shallow Water Based on Free Running Manoeuvring Tests Including Uncertainty of the Results
Authors: Tonelli Roberto , Quadvlieg Frans
Published: October 2015

This paper gives the results of free running model tests for the KVLCC2 in shallow water. The paper describes how free running model tests in shallow water are carried out, and gives the results of free running model tests at two shallow water depths, corresponding to a water depth to draught ratio h/T of 1.2 and 1.5. Free running (partly) turning circle tests and zigzag tests are carried out in shallow water in a dedicated shallow water basin where the water depth is lowered to sail above a concrete floor, while measuring the level of flatness of the concrete floor.

The ITTC issued a brand new approach to perform uncertainty analysis for free running manoeuvring tests. For a proper comparison of simulations to model tests, it is of prime importance to not just know the results of a free running manoeuvre, but also to know the uncertainty of the results. This paper addresses also the uncertainty of the results. The combination of the results of the model tests and the uncertainty analysis allows the use of this data as benchmark data.
Demonstration of the Recent Additions in Modeling Capabilities for the WEC-Sim Wave Energy Converter Design Tool
Authors: Tom Nathan , Lawson Michael , Yu Yi-Hsiang
Published: October 2015

WEC-Sim is a midfidelity numerical tool for modeling wave energy conversion devices. The code uses the MATLAB SimMechanics package to solve multibody dynamics and models wave interactions using hydrodynamic coefficients derived from frequency domain boundary element methods. This paper presents the new modeling features introduced in the latest release of WEC-Sim. The first feature discussed is the conversion of the fluid memory kernel to a state-space approximation that provides significant gains in computational speed. The benefit of the state-space calculation becomes even greater after the hydrodynamic body-to-body coefficients are introduced as the number of interactions increases exponentially with the number of floating bodies. The final feature discussed is the capability to add Morison elements to provide additional hydrodynamic damping and inertia. This is generally used as a tuning feature, because performance is highly dependent on the chosen coefficients. In this paper, a review of the hydrodynamic theory for each of the features is provided and successful implementation is verified using test cases.
Isothermal and Non-Isothermal Transient Gas Flow in Submarine Pipeline
Authors: Nalin Augusto F. , Tsukada Raphael I. , Shiguemoto Denis A. , Mendes Jose R. P. , Serapiao Adriane B. S.
Published: October 2015

The discoveries of the Pre-salt oilfields have driven the development of new technologies to enable the production of the deepwater reservoirs. In this scenario, subsea pipelines play an important role. Analysis of the steady and transient flow inside the pipes should be addressed in the design, considering the variation of the fluid properties. In this context, a pipe flow simulator project has been developed to attend gas flow analysis for petroleum industry. In this project, the fluid compressibility factor (Z-factor) and the viscosity are considered function of the pressure, temperature and gas composition. The non-isothermal transient gas flow were calculated using the Method of Characteristics (MOC). The results shown the difference of the isothermal and non-isothermal steady state and transient flow.
Long-Term Wave Measurement by an Onboard Radar Wave Meter and Prediction of Ship Motions Based on the Onboard Wave Measurements
Authors: Yoshida Hisafumi , Orihara Hideo , Yamasaki Keiichi
Published: October 2015

Continuous measurement of waves, ship motions (roll and pitch), and so on has been carried out for about five years by onboard monitoring system installed ocean-going vessel. Measured wave data, including wave height, wave period and wave direction, are thoroughly evaluated with corresponding onboard weather observation data by comparing directly in terms of time series and statistical values.

Then, short term prediction of ship motions (roll and pitch) based on the measured wave data are compared with onboard motion data measured by vertical gyro.

From the results described, good accuracy and effectiveness of wave measurements by an onboard radar wave meter for safe navigation are demonstrated.
Freak Wave Generation in a Wave Basin With HOSM-WG Method
Authors: Houtani Hidetaka , Waseda Takuji , Fujimoto Wataru , Kiyomatsu Keiji , Tanizawa Katsuji
Published: October 2015

A method to produce freak waves with arbitrary spectrum in a fully directional wave basin is presented here. This is an extension of Waseda, Houtani and Tanizawa at OMAE 2013[1], which used “HOSM-WG” based on the higher-order spectral method (HOSM). We used the following three methods to improve the HOSM-WG in [1]: “separation of free waves from bound waves,” “using Biesel’s transfer function in wavenumber space” and “using Schaffer’s 2nd-order wave maker control method.” Modulational wave trains, freak waves in unidirectional irregular waves and freak waves in short-crested irregular waves were generated in a wave basin. The experimental results using the improved HOSM-WG were compared to the HOSM simulation, and good agreements were found. The effectiveness of the improved HOSM-WG was ascertained. We showed that the difference between HOSM-WG and HOSM simulations became larger as wave steepness, frequency bandwidth of the spectrum or directional spreading became larger.
Investigation of Ship Impact Scenarios and Mitigation Measures
Authors: Woelke Pawel , Hansen Eric , McArthur Chad , Abboud Najib , Tennant Darren , Wesevich James
Published: October 2015

Ship impact is an important loading scenario for analysis and design of bridges, oil platforms, and other marine structures. Ships collision is also a very important design consideration for ship hulls. Designing structures to resist both accidental and intentional ship impact requires characterization of the impact loading history. Standard design practice relies on simplified methods to determine the impact loads, which typically consider only speed and mass of the vessel. However, ship impact is a complicated non-linear structural dynamic event that depends not just on the size and mass of the vessel, but also local stiffening pattern, location and function of the bulkheads, possible ice-strengthening classification, draft, presence of the bulbous bow, and many other factors. Neglecting these factors can lead to overestimation or underestimation of the loads, depending on a specific scenario. The discrepancies between simplified load estimates and detailed finite element analyses are investigated in this paper.
3D Stereo Imaging of Abnormal Waves in a Wave Basin
Authors: Mozumi Kento , Waseda Takuji , Chabchoub Amin
Published: October 2015

This paper proposes a new method to measure the wave surface elevation in a wave basin. The Direct Linear Transformation (DLT) method is employed in the 3D reconstruction of the free surface marked by an array of floats attached to a flexible net. The method is coined the Marker-Net method (MNM). Experiments were conducted in a large basin to validate the proposed method. Regular wave records are compared against wave wire measurements to quantify the accuracy of the estimation based on the MNM. To demonstrate the advantage of the MNM over conventional techniques used in the tank, a set of experiments based on analytical solutions of the 2D+T nonlinear Schrodinger equations were conducted. The MNM reconstruction of the free surface revealed propagation of an oblique structure, which is difficult to visualize otherwise.
Laboratory Visualization of Gravity Fluid Displacement in Well Annulus Affected by Sustained Casing Pressure
Authors: Demirci Efecan , Wojtanowicz Andrew K.
Published: October 2015

Sustained Casing Pressure (SCP) in petroleum wells poses environmental risk and needs to be removed using either downhole intervention or annular intervention methods. The latter method involves displacing the annular fluid above the top of the gas-leaking well cement with a heavy fluid to increase the hydrostatic pressure and stop the gas leak. Past field applications of the method failed — most likely due to incompatibility of the two fluids. In this study, a see-through scaled-down hydraulic analog of the well’s annulus was designed and used for video-taped displacement experiments with clear synthetic-clay muds and heavy (kill) fluids. The results show that only immiscible hydrophobic kill fluids provide effective displacement. The study demonstrates importance of controlled injection of the kill fluid to set out efficient buoyant settling and prevent initial dispersion. A side- (versus top-) injection geometry and the injection rate data are analyzed to develop empirical correlation of maximum injection rate for a given properties of the two fluids.