bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Investigation Regarding the Landing Manoeuvre of a Catamaran Vessel at an Offshore Wind Turbine in Waves
Authors: Ferreira González Daniel , Lemmerhirt Matthias , Abdel-Maksoud Moustafa , König Marcel , Düster Alexander
Published: October 2015

In this work, the landing manoeuvre of a catamaran vessel at a monopile foundation is investigated by experiments compared with numerical simulations. Therefore, a method is presented which allows simulating the described landing manoeuvre at offshore structures. The simulation in the time domain is based on potential theory using a boundary element method (BEM) and it computes the motions of the rigid body due to the hydrodynamic loads which consist of the incoming waves and the diffraction caused by the monopile. Further, a fender model is implemented, considering the reaction forces due to the friction and the deformation of the fender. The model is further able to distinguish between slip and non-slip condition of the fender. Apart from this, model tests of the landing manoeuvre were carried out with a catamaran model. During the tests the model pushed its fender against an equally scaled monopile. The motions of the vessel and the forces at the attachment of the fender were measured in regular and irregular waves. The obtained data which leads to a better understanding of the hydrodynamic effects during a landing manoeuvre is compared with the simulation results in order to improve the numerical method. The validation with experimental results shows that the method is applicable to quantify the risk of the fender suddenly slipping.
Extreme Response Prediction of Offshore Wind Turbine Using Inverse Reliability Technique
Authors: Karmakar D. , Guedes Soares C.
Published: October 2015

In the present study, the environmental contour method is applied for predicting out-of-plane bending moment loads at the blade root and tower base moment loads for 5MW offshore floating wind turbine of spar-type, DeepCWind and WindFloat semi-submersible floater configuration. FAST code is used to simulate the wind conditions for various return periods and a brief comparison on the design loads of the floating wind turbine for I-D, 2-D and 3-D environmental contour method is analyzed. In addition, a brief comparison of design loads with the spar-type, DeepCWind and WindFloat semi-submersible floater is discussed. The study is helpful to improve the turbine design load estimates and is useful in predicting accurate long-term design loads for wind turbines without requiring excessive computational effort.
Monitoring Hydrate Safety Margin Using Freezing Point Method
Authors: Kogo Bridget , Wang Bin
Published: October 2015

Feasibility of Peltier element device for monitoring hydrate safety margin was experimentally investigated; alongside, cooling capability of the Peltier device. Freezing point depressions of aqueous alcohol solutions were measured using the device. Results showed that device is able to freeze aqueous ethylene glycol and methanol solutions in a few minutes, up to 35 mass% of ethylene glycol, 30 mass% of methanol. Measured freezing point depressions well matched the predicted. Methane hydrate phase boundary was determined using the previously developed correlation based on the measured freezing point depressions, which is in line with the predicted one in an acceptable deviation range.
Spherical Indentation Tests on Confined Ice Specimens at Small Scales
Authors: O’Rourke Brian J. , Jordaan Ian J. , Taylor Rocky S. , Gürtner Arne
Published: October 2015

A recent series of small-scale ice indentation tests was conducted as a continuation of previous series, to cover additional strain rates and indentor sizes, and to test the effect of scaling. Tests using indentors 10, 20, 40 and 70 mm in diameter attached to a very stiff structure were carried out at indentation rates over three orders of magnitude, while scaling indentation rate with indentor diameter. Slow rates resulted in creep-like response and deep and wide damage zones. As indentation rate was increased, sawtooth loading and random failure activity were observed, together with a thin layer of microstructurally modified ice beneath the indentor.

This latest test series also included indentation tests with a flexible beam apparatus, with the aim of generating locked-in vibrations. It was determined from previous tests that indenting at much faster rates was necessary to produce lock-in with such an apparatus. For this series, two new beam apparatus of differing stiffness and variable natural frequency were fabricated; the beams were designed in a manner that enabled control and testing of the outcome of varying these factors independently. Tests were conducted with either one or two indentors attached. The typical sawtooth behaviour occurred at lower indentation rates, progressing at higher rates into lock-in activity, which occurred over a range of speeds for both beams. The frequency of lock-in vibrations was found to be lower than the structure’s natural frequency, and to increase with indentation speed over the lock-in range. The ice load on the indentor during lock-in activity appears more ‘cusp’ shaped, rather than the assumed sawtooth.
Seismic Design of Hebron Platform: An Integrated Soil-Structure-Interaction Approach
Authors: Younan Adel H. , Kaynia Amir M. , Loo Max M. , Widianto  , Khalifa Jameel
Published: October 2015

Seismic analysis of an offshore platform requires an integral model combining all its elements: foundation, substructure, deck, modules, appurtenances, and even pipeline and riser tie-ins. With typical breakdown of project scope amongst several EPC contractors, the task of creating a seismic model and ensuring proper input, output and updates for EPC contractors’ design always rests with the operator’s engineering team. This model is complicated by the nature of dynamic soil-structure-interaction characterized by radiation of earthquake wave and energy to the far field. This radiation of energy is significant for short squatty gravity-base structures while most structural software lack this capability. This problem has been worked by the nuclear industry, but in this paper we summarize ExxonMobil practice for carrying this task in this scope breakdown environment. The need for this practice emerged during the engineering of Orlan (Sakhalin), was first used on the Adriatic LNG Terminal (Italy) and applied since on Berkut (Sakhalin) and Hebron (Canada).
Influence of the Rotor Characterization on the Motion of a Floating Wind Turbine
Authors: Gueydon Sébastien , Venet Guillaume , Fernandes Gerson
Published: October 2015

It is useful to complement model tests of a floating wind turbine with simulations mimicking the scaled-down turbine. Standard engineering tools have some short-comings to model a rotor at the very low Reynolds that Froude scaled wind and rotor’s rotation speed impose. The flow around an airfoil at the scale of a wave basin brings new distinct challenges than at full scale. The capacity of standard engineering tools for the design of wind turbines to capture this complexity may be questioned. Therefore, work-around solutions need to be proposed. This paper looks at a common solution that consists of optimizing the load coefficients of the rotor to reproduce the measured rotor loads. 3 variants of optimizations are applied to a semisubmersible floating wind turbine at scale 1/50th, the DeepCwind semisubmersible platform. The effects of the differences between these 3 methods on the motions of the floater in waves and wind are analyzed. In the absence of a controller for the rotor, no significant differences related to the induced aerodynamic damping was noticed, but an offset in the motion related to a thrust deficit was observed.
Hydrodynamic Performance of a FPSO in Highly Oblique Flow Conditions
Authors: Islam Mohammed , Jahra Fatima , Ryan Ron , Molyneux David , Hedd Lee
Published: October 2015

The capability of the viscous-flow solver Star-CCM+ to simulate the flow around a ship in steady oblique motion has been studied. To obtain insight into the reliability and accuracy of the results, grid dependency studies were conducted. Local flow quantities as well as integral variables were compared to measurement values. A FPSO hull form was considered for the simulations as well as experimental assessment of the resistance and flow field at multiple oblique flow conditions. The measurements and simulations have been completed at one draft, one Froude numbers and in 7 inflow conditions (0° to 180° with 30° increments).

The measurements and predictions were made for the resistance in the inflow direction, side force and yawing moment. Additionally, the pressure and velocity distributions around the hull at multiple cross-sections are presented derived from the RANS predictions. Qualitatively, promising results are obtained. For practical purposes however, the accuracy of the results may require further improvement. For the current calculations, the predicted yaw moment is close to the measurements but the side force is under-predicted. Reasons for these discrepancies might be the neglect of trim and sinkage for the FPSO and of the insufficient grid resolution at the bow and stern. This should be studied in future research.
New Methodology for Flexible Riser End-Fittings Fatigue Assessment Based on Remote S-N Curves
Authors: Borges Marcelo Favaro , Vardaro Eduardo , Campello George , Kwietniewski Carlos Eduardo Fortis
Published: October 2015

Production of oil and gas in the Brazilian pre-salt will face several technical challenges. One of them that is a major concern is the fatigue life of top risers end-fittings. The new ultra-deep water fields will require a complete new fatigue assessment methodology with higher accuracy. Besides that, the historical data of failure for this sort of equipment shows that the current methodology is not quite optimized for floating units operating in deep water fields. With this, even worst results are expected in ultra-deep water fields.

During its assembly inside the end-fitting, the tensile armor wires need to be folded, unfolded and set in position using epoxy resin. This assembly process involves localized plastic deformation and as consequence of this produces a complex residual stress field and also introduces an elastic stress to maintain the wires in position. Both stresses are not actually taken into account in the current fatigue assessment methodology.

Therefore, the aim of this work is to develop and evaluate a new fatigue assessment methodology for top risers end-fittings based on remote S-N curves. The proposed methodology takes into account both residual and assembly elastic stresses. The effect of stress concentration on the tensile armor wire at the region with localized plastic deformation is also evaluated. Basically, the objectives of this investigation will be achieved through the construction of remote S-N curves using a test box that contains the deformed wire embedded in resin representing a single wire physical 2D model of an end-fitting, the so called mid-scale testing. For this investigation, a six inches API end-fitting was selected because it is widely used and most available in the market.

The results produced here indicated that the localized plastic deformation imposed during the folding and unfolding process has a very important detrimental effect on the flexible risers end-fittings tensile armor wires fatigue life, which makes mandatory a revision of the current four-point bending fatigue assessment methodology.
Results From an Integrated Tool for Marine System Hydrodynamic and Control Modeling
Authors: Bretl James , Edwards Kathleen , Mekhiche Mike , Dufera Hizkyas
Published: October 2015

While wave energy converters (WECs) offer the potential of renewable energy from ocean waves, a central challenge for developers is the ability to investigate candidate geometries and control systems prior to expensive wave tank tests or field deployment. If WEC behavior and power output can be simulated numerically, results can be analyzed to determine if a candidate development direction should be pursued. This paper describes the validation of a tool used at Ocean Power Technologies (OPT) to refine the design of its PowerBuoy® product. The tool, Simulink Target for OrcaFlex Runtime Model (STORM), was developed by OPT with support from MathWorks. STORM takes advantage of the ability of (a) OrcaFlex to represent the interaction of complex geometries with a realistic marine environment and (b) Simulink to represent the behavior of the device’s Power Takeoff (PTO) under different control functions, including the digital nature of real-time control. Optimal control of WECs is an active area of research within the industry. STORM provides the tools necessary to implement and evaluate various control architectures while exposing them to realistic physical constraints and nonlinearities.
A Velocity Decomposition Approach for Unsteady External Flow
Authors: Chen Yang , Maki Kevin J. , Rosemurgy William J.
Published: October 2015

In this work we address the development of the velocity decomposition algorithm, a numerical flow solution method that incorporates both velocity potential and Navier-Stokes-based solution procedures. The motivation for this is so that the field discretization required by the Navier-Stokes solver can be reduced to the region of the flow domain in which the flow is vortical. Specific advantages are that the computational cost is reduced, it is easier to discretize the flow domain, and difficult problems such as the simulation of ships maneuvering in a seaway are closer to being within reach. The target applications are broad, ranging from vortex shedding on bluff objects such as risers, to the wave induced loads on a platform in a current and irregular seas. In previous work, the algorithm has been successfully applied to address steady flows of 3-D non-lifting bodies without water waves, or 2-D bodies that can have lift and be near a water surface. In this paper, the velocity decomposition approach is extended to numerically solve for the unsteady flow of single-phase viscous flows. The velocity vector is decomposed into irrotational and vortical components. A boundary element method is used to solve for the irrotational component (designated as the viscous potential) by applying a viscous boundary condition to the body boundary. A field method is used to solve for the total velocity on a reduced domain where the flow is vortical. The new algorithm investigates two approaches to solve the unsteady problem based on different types of time-dependence exhibited by the solution. The unsteady velocity decomposition method is demonstrated on two cases, and the solutions are compared to those generated by a conventional viscous flow solver. The results by the new algorithm agree well with the benchmark solutions and exhibit a reduction in time.
Integrity of Weld Overlay of Flexible Joints and Lined Pipe
Authors: Zumpano Petrônio , Garmbis Alexandre G. , Oazen Eduardo V. , Leite Luis Guilherme T. S. , Silva Rafael N.
Published: October 2015

This paper describes different alternatives to be adopted to assess the integrity of weld overlays of flexible joints and lined pipes in offshore pipeline and riser projects. Protective layers are adopted as an interesting alternative to full thickness corrosion resistant alloys due to the possibility to adopt carbon steel as base material in order to reduce overall material costs. UNS N06625 (alloy 625) is generally selected for internal layers, such as weld overlay steels, lined pipes or clad pipes because of its sulfide stress cracking (SSC) resistance and outstanding weldability. However, unless the long-term integrity of the cladding or overlay as a protective layer can be demonstrated under the intended service conditions, the base material shall also be resistant against sulfide stress corrosion cracking. Due to low resistance of carbon steel to corrosion fatigue in the presence of contaminants in fluid content, the rupture of thickness of CRA (Corrosion Resistant Alloy) layer becomes a failure mode. An Engineering Critical Assessment (ECA) shall be performed in order to assess if circumferential planar flaws in weld overlay regions will not propagate through the CRA layer, thus exposing the base material, when submitted to critical cyclic loads during the service life. Such analysis would involve fatigue crack growth simulation and surface interaction of full circumferential embedded defects to determine the maximum weld overlay pass height to be limited by machining. This limited height of machined layers should guarantee that a full circumferential flaw will withstand the operational fatigue life. However, this is a very time consuming manufacturing process and would implicate additional concerns for long extensions due to out of straightness and out of roundness. Alternatively, the ECA results may be used to determine the flaw acceptance criteria and required probability of detection of volumetric non-destructive testing. Recent developments in ultrasonic inspection were successfully adopted and represent a better solution for alloy 625 weld overlay in terms of project scheduling and manufacturing costs. Radiographic testing may also be used provided it meets the required sensitivity, in terms of image quality indicators (IQI). Anyway, validation tests shall be performed to demonstrate adequate reliability to detect the minimum required flaw height.
Post-Installed Fiber Optic Pressure Sensors on Subsea Production Risers for Severe Slugging Control
Authors: Eaton Ammon N. , Safdarnejad Seyed Mostafa , Hedengren John D. , Moffat Kristie , Hubbell Casey B. , Brower David V. , Brower Alexis D.
Published: October 2015

Fiber optic sensors have gained increasing use in monitoring offshore structures. The sensors have successfully monitored flowlines, umbilicals, wells, Tension Leg Platform (TLP) tendons, production and drilling risers, and mooring lines. Fiber optic sensors are capable of monitoring strain, temperature, pressure, and vibration. While the success of fiber optic monitoring has been clearly demonstrated, the sensors are now under consideration for automation applications. This paper details the plausibility of using pressure measurements from post-installed fiber Bragg grating (FBG) sensors with Model Predictive Control (MPC) to suppress severe slugging in subsea risers.

Prior control schemes demonstrate that slugging is mitigated using a topside choke valve. The most effective methods use a pressure measurement immediately upstream of the touchdown zone of the riser; however, the majority of production risers do not have pressure sensing at that location. With advances in subsea clamp design and bonding it is now possible to install a non-penetrating FBG sensor to monitor pressure near the touchdown zone without shutting down production. Stabilizing the two phase flow both reduces vibration-induced fatigue and has the potential to allow increased throughput with relaxed topside processing constraints.

MPC predicts and adjusts for disturbances to avoid pressure and flow instability. The performance of the controller is influenced by sensor location, choke valve response time, and riser geometry. This study demonstrates that severe riser slugging is effectively controlled with MPC and a post-installed, non-penetrating FBG sensor.
Appraisal of the IEC Technical Specification for Assessment of Wave Energy Resources
Authors: Piche Steffanie , Cornett Andrew , Baker Scott , Nistor Ioan
Published: October 2015

This article describes and presents results from research focused on appraising the new technical specification (TS) for the assessment of wave energy resources developed by technical committee 114 of the International Electro-technical Commission (IEC-TC-114). The new IEC TS is appraised through an extensive pilot application to the waters off the west coast of Vancouver Island, British Columbia, Canada. A series of wave models are developed and used to simulate the wave conditions and estimate the wave energy resource over the study area. The accuracy of the various resource estimates derived from the model outputs is assessed through comparison with measurements from a directional wave buoy. Furthermore, sensitivity analyses are conducted to determine the main sources of error and uncertainty impacting the precision of resource assessments obtained following the IEC methodology. Preliminary results indicate that the IEC TS can be applied to the estimation of wave energy resources with a reasonable level of effort and accuracy.
Large Scale Experimental Storm Impact on Nourished Beach Using Cobble-Gravel-Sand Mix
Authors: Frandsen Jannette B. , Xhardé Régis , Bérubé Francis , Tremblay Olivier Gauvin
Published: October 2015

We have investigated beach stability against storm waves. The studies are done in relation to eroded beaches. We are testing a cobble-sand-gravel mixture as a means of using a soft method for coastal protection on nourished beaches. A physical model of an existing beach was built at scale 1:3. The cobble/sand grain size is in 1:3 scale while the gravel is 1:1.5 scale. The large scale experimental flume tests have been set-up in the new outdoor 120 m long flume in Québec city, Canada. The tests were conducted over two test seasons (2013–14). While we in the first test season studied impact on the beach due to incoming regular plunging breakers, the last season contained tests with incoming irregular plunging breakers on the beach with/without tidal variation.

Herein, we primarily report on the wave impact due to irregular plunging breakers on constant and tidal varying water depths. The wave-tide interactions were conducted with a tidal range of 1 m in relation to beaches with steep beach slopes (1:10, 1:5, 1:1). The model inlet significant wave height was 1.1–1.5 m corresponding to equivalent prototype waves in the range of max. wave heights of 6–8.5 m with dominant periods of 12 s in water depth of about 15 m and tidal range of 3 m.

In general, the Equilibrium Beach Profile (EBP) was reached after exposure to about 10,000 plunging breakers or the equivalent of five storms assuming each lasting 3 hours. A cobble berm was formed rapidly on the top of the beach, protecting the backshore against wave action and flooding while finer sediment was transported “offshore”. Beach width reduction was observed when the initial slope of the beach fill material exceeded the equilibrium beach slope. Sediment grain size sorting along the beach profile is discussed and compared to existing beach models, and EBP was compared to several EBP equations.

From a coastal management perspective, in terms of durability, the mixed cobble-sand-gravel material is showing promise as a material to use for coastal protection. It is highly absorbent and the beach tends to maintain its shape over long time when exposed to several storms. However, storm surges in the combination with high tides can results in excessive run-up and potential flood risks. The stabilized beach typically had slopes of 1:7–1:9 independent of the initial slope. We found that irregular seas result in a less pronounced trough in the beach profile in the swash zone than incoming regular plunging breakers. The tidal interaction was further advantageous, naturally shifting the material back and forth. However, other materials and other sensitivity studies are necessary in order to provide firm conclusions about the usage of the cobble-gravel-sand mixture for coastal protection.
2D Numerical Viscous Predictions of Wave Impact Effects on an Idealized Seawall Rooted in Large Scale Experiments (1:4)
Authors: Tremblay Olivier G. , Frandsen Jannette
Published: October 2015

This study aims to investigate the free-surface flow involved in a wave impact and the vibrational characteristics of an idealized seawall to achieve an improved insight in the design of seawalls and coastal infrastructures subjected to moderate and storm wave conditions. This type of structure can be subjected to frequently occurring as well as high impact wave loadings. In addition to the structural concerns, it is also important to evaluate the importance of the coupling between both fluid and structure motion.

In the various steps to design proper wall deflector (wave guide) and to predict pressures and forces following a wave impact, we first present a comparison between numerical results from a CFD model and experimental recordings conducted in a large scale flume in the new Quebec Coastal Physics Laboratory, Canada. A CFD model performance is tested to investigate the more fundamental mechanisms of the underlying processes and to assess real conditions around seawalls to facilitate design process. The preliminary results are based on the assumption of treating the fluid-structure interaction physics as decoupled processes and the wall as a rigid plate. Modal analysis performed on the structure indicates that this approach is adequate, since loadings are of short duration (less than 1 ms) compared to the wall natural frequencies. A maximum local wall pressure of 3.5 MPa has been obtained from an air-pocket impact which generates an instantaneous horizontal force of 4.3×106 N/m.
Validation of a Modular Mathematical Model for Low-Speed Maneuvering Using Small Scale Tests With an Oceanographic Research Vessel
Authors: Masetti Felipe Ribolla , Tannuri Eduardo A. , de Mello Pedro Cardoso
Published: October 2015

This paper presents small scale low-speed maneuvering tests with an oceanographic research vessel model. The purpose of the tests is to validate the mathematical model of the real-time ship simulator for low-speed maneuvering developed by the University of São Paulo. The tests are intended to verify the behavior of the vessel and the model under transient and low-speed tests.
Mathematical Model for Efficient Prediction of Lifeboat Sailaway Performance in Calm Water and Waves
Authors: Quadvlieg Frans , Tonelli Roberto , Palermo Elia , Teigen Per
Published: October 2015

Free fall lifeboats have been developed for emergency evacuation from offshore installations, when conventional means of transportation cannot be applied. As a consequence, the ability of the lifeboats to perform safe drop- and sail away under all circumstances has to be demonstrated. This paper focuses on efficient and robust numerical simulation of these operations.

To predict the lifeboat behavior under a large variety of stochastic conditions, such as irregular waves, in combination with wind and current, calls for many individual simulations of the sailaway performance. The present paper presents a brand new mathematical model that is able to predict the behavior of a free fall lifeboat during drop-phase, the submerged phase, the surfacing phase and the “sailing in waves” phase (combined, not gluing time traces from different predictions together).

The proposed mathematical model is completely non-linear in nature and considers instantaneous submergence and attitude of the lifeboat. All forces and moments in 6 degrees of freedom are calculated instantaneously.

Consequently, accelerations, velocities and displacements, are calculated based on this. The paper describes the build-up of the mathematical model. This is based on a summation of forces due to impact forces, cross flow drag forces, generated lift, centrifugal forces, buoyancy forces, propulsion (propeller and nozzle), steering forces due to steering action and resistance. Obviously, also the instantaneous added masses play an important role. This results in a mathematical model for rigid body motions in 6 degrees of freedom, which can be used for predicting the motion response during drop- and sail away. This means a validity range in very extreme weather and in calm water. The paper will show basic validation and several applications.
Prospects of Linear Model Predictive Control on a 10 MW Floating Wind Turbine
Authors: Lemmer Frank , Raach Steffen , Schlipf David , Cheng Po Wen
Published: October 2015

The presented research has the objective of supporting the integrated conceptual design of floating offshore wind turbines (FOWT). The dynamics of the multidisciplinary coupled system with the aerodynamics, hydrodynamics, structural dynamics, the catenary mooring lines and the controller shall be represented in simulation models adapted to the current design stage. Here, a linear model-predictive controller (MPC) as an optimal multiple input-multiple output (MIMO) controller is designed for a novel concept of the floating foundation for a 10MW wind turbine. The performance of this controller is easily adjustable by a cost function with multiple objectives. Therefore, the MPC can be seen as a benchmark controller in the concept phase, based on a simplified coupled simulation model with only approximate model information. The linear model is verified against its nonlinear counterpart and the performance of the MPC compared to a SISO PI-controller, which is also designed in this work. The developed models show to be well suited and the linear MPC shows a reduction of the rotor speed overshoot and tower bending from a deterministic gust.
Quantifying Spatial Variability of As-Laid Embedment for Subsea Pipeline Design
Authors: Westgate Zack , White Dave
Published: October 2015

In deep water, the pre-service embedment of on-bottom pipelines is mainly controlled by the lay process and its effects on the soil strength. Predicted ranges in local pipeline embedment are often very wide due to uncertainties associated with the surface soil properties, the influence of the sea state and vessel motions on soil remolding, and the complexity of the large-deformation process of pipe-seabed penetration. Pipeline embedment has a significant impact on pipe-soil interaction resistance — commonly described by the ‘friction factors’ used for pipeline design. Most design checks, such as for controlled lateral buckling, need to be satisfied under both low and high extremes of pipe-soil resistance and therefore pipe embedment. A wide range in pipe embedment can create significant design challenges for pipeline engineers, for example where engineered buckle mitigation structures are required to alleviate potential high strains in the pipeline.

Data obtained from as-laid field surveys of subsea pipeline embedment have been analyzed to illustrate quantitatively how embedment varies along a pipeline route. This variation is linked to both anthropogenic influences, for example as a result of the stop-start pipeline construction process, as well as natural variability in (i) soil conditions along the route and (ii) sea state conditions during laying. Accounting for this variability through statistical analysis of as-laid embedment, and incorporation of appropriate length scales relevant to each design check, can have significant beneficial impacts on pipeline design through reductions in the ranges of pipe-soil friction factors. In some cases these may reduce or negate the need for expensive mitigation. The approaches illustrated in this paper have already found beneficial use on real projects.
Ductile Fracture Prediction for Marine Structures
Authors: Woelke Pawel B. , Hiriyur Badri , Benowitz Brett , Hutchinson John W.
Published: October 2015

Reliable modelling of fracture on a structural scale restricts the type of the finite elements used in the analyses to shell elements with in-plane dimension larger than the thickness. Thus, we consider a comprehensive constitutive formulation embedded in the shell mechanics framework. We propose a three-invariant plasticity model that accounts for dependence of the strain at fracture on both stress triaxiality and the third invariant of the deviatoric stress, which has a significant influence for shear-dominated stress states. This is achieved through a phenomenological damage evolution equation that includes both the dilatational term and plastic deviatoric energy term. The latter is dependent on the omega parameter, which can be considered a normalization of the Lode angle. A consistent calibration procedure is also developed based on a small number of carefully selected coupon-level experimental tests.
Benchmarking Experiments for Wave Absorption Modeling
Authors: Magee Allan R. , Nelko Varjola , Lim Kian Yew , Chew Lup Wai
Published: October 2015

Passive wave absorption is usually employed at the downstream end of a wave flume or basin to avoid the build-up of wave energy in the tank. However, absorption of waves is not perfect in physical tanks. A beach of different shape and/or composition can result in different absorption efficiency. Laboratory investigations of various passive beach configurations are costly and time-consuming. A more efficient approach is to perform studies using a numerical wave tank (NWT), which in turn requires empirical data to tune the dissipative effects.

This study attempts to better understand the quality of waves simulated in a laboratory flume with a uniformly inclined porous beach and a parabolic-shaped solid beach. The data will be used to validate a newly-developed NWT with passive wave absorption. Different incident wave properties are examined and the reflection coefficient is calculated primarily with the two-probe method proposed by Goda & Suzuki (1976) and compared with other methods. An overview of the experiments, absorption analysis and numerical simulation is presented and discussed.
An Experimental Study on Two-Phase Flow at Different Orientations
Authors: Brueckner T. M. , Rahman M. A. , Awad M. M.
Published: October 2015

In the current study, an experimental study on two-phase flow at different orientations is carried out at the Fluids Laboratory, Memorial University of Newfoundland (MUN). Three different orientations are used. They are horizontal, vertical and slanted orientation respectively. The experimental unit consists of pipes that are three inches (DN 80) in diameter and are capable of producing many various regimes of gasliquid flows. The experimental unit has sensors to measure the pressure, temperature and volume flow at numerous locations. Experiments are conducted for two-phase flow (bubble and slug flow). The new experimental data can provide valuable insights on the viscous effects with many flow regimes, phase compositions and direction of flow. The results of this research provide valuable new experimental data on two-phase flow characteristics for many flow regimes that can improve the safety and efficiency of wellstream flows.
Comparison of Numerical Simulations With Experimental Measurements for the Response of a Modified Submerged Horizontal Cylinder Moored in Waves
Authors: Roy André R. , Beatty Scott J. , Mishra Virag , Steinke Dean M. , Nicoll Ryan S. , Buckham Bradley J.
Published: October 2015

Ocean industries such as oil and gas, defence, and marine renewables, face the challenge of costly and risky deployments and operations due to their complex and capital intensive nature. Numerical simulation tools are valuable assets that can be used to anticipate motions and stresses and therefore inform structural and operational design before deployment. Simulation tools that can capture all pertinent hydrodynamic phenomena increase their value by reducing design time, uncertainty, risk and capital associated with a deployment.

Validation of numerical tools is critical to ensure accuracy and reliability. The following paper reviews a framework for simulation of moored, multi-body, floating systems, including the component models employed, the results of a model verification study, and the challenges encountered in the project. Tank test data of a moored horizontal cylinder was provided for the purposes of numerical tool validation.
Envelope of Power Harvested by a Single-Cylinder VIVACE Converter
Authors: Liu Jianhui , Bernitsas Michael M.
Published: October 2015

Flow Induced Motions (FIM) of a single-cylinder VIVACE Converter is investigated using two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the Spalart-Allmaras turbulence model at Reynolds numbers (30,000 ≤Re≤120,000, 5.50≤U*≤9.85) in the TrSL3 flow regime. Computational results compare very well with experimental data. With implementation of Passive Turbulence Control (PTC), the VIVACE Converter can harness hydrokinetic energy from currents or tides over an expanded range of FIM synchronization, including Vortex Induced Vibrations (VIV) and galloping. The General Grid Interface (GGI) with topological mesh changes is proved to be an effective method for handling high-amplitude FIM response. Within the test Reynolds number range, five regions are clearly observed, including the no-FIM range, the VIV initial branch, the VIV upper branch, transition from VIV to galloping, and galloping. The power envelope calculated based on the CDF simulations for FIM agrees very well with the corresponding power envelope generated based on experiments. The range between VIV and galloping can be eliminated by adjusting the spring-stiffness and the harnessing damping-ratio. This is verified by both experiments and numerical simulation.
Large Scale Experimental Wave Impact on Walls in the Québec Coastal Physics Laboratory
Authors: Frandsen Jannette B. , Bérubé Francis
Published: October 2015

The present tests are conducted in the new Québec Coastal Physics Laboratory, Canada. The flume has a depth and a width of 5 m and is 120 m long.

This paper presents large scale experiments of water wave impact on a vertical wall following wave runup on a mixed sand-gravel-cobble beach. This present study is concerned with advancing knowledge on rapidly varying pressure magnitude and distributions on different types of sea/river/harbor walls. Protection against extreme events and subsequent coastal erosion is a key theme of application. Herein is presented preliminary test series which has focus on forces on vertical walls. Specifically, 27 pressure sensors are mounted on the vertical wall with a total test area of 1.2 m wide and 2.4 m high and is a stiffened aluminum plate. The outer regions of the wall are made of steel to span the entire width of the tank. The wall is designed to behave as a rigid plate. The geometric model to full scale is about 1:4.

The incoming waves evolve on a flat bed to climb the final 25 m on a beach with slope with constant slope of 1:10. A small regular wave train forms the basis for investigations of force patterns on the wall. Herein, our preliminary findings reported are based on selected 6 test series (18 impacts out of 150 impacts). In general, wall pressures greater than 1 MPa and 10 m run-up are easily developed even with moderate amplitude waves at the inlet. We will discuss some details of the underlying mechanism of various types of breaking and impact on the wall. The peak pressure identified on the wall with the mixed gravel beach surface was 1.23 million N/m2 occurring in 0.2 milli seconds. It was cuased by a plunging breaker with a relatively large air pocket (∼0.11 m2). It was further identified that the maximum pressure on the wall does not necessarily give the maximum jet velocity (equivalent to vertical force considered in design of on parapets). They are independent quantities in these very random rapid processes. The maximum jet velocity was in the order of 35 m/s but could higher on a different beach surface. Further, it was found that the maximum waves are not necessarily the most critical ones as the waves break and therefore dissipates its energy before reaching the wall. A plunging breaker with a relatively large airpocket with a crest tip located at the top part of the wall resulted in max. peak wall pressure. One impact case caused a near simultaneous double peak pressure generated by a plunging breaker with two relatively small airpockets (0.003 m2 and 0.01 m2). This was the impact case responsible for the max. vertical jet velocity. We further found that the max. peak water pressure of the plunging breakers had a similar order of magnitude as the max. pressure within an air pocket.
Assessment of Weld Fatigue by Effective Notch Stress Approach
Authors: Anvari Majid , Fagnastøl Øyvind , Leira Bernt J.
Published: October 2015

Applicability of different approaches, i.e. nominal stress-, structural hot spot- and effective notch stress approach, for fatigue assessment of welded structures has been discussed.

The effective notch stress approach was validated for a cruciform fillet welded and fully penetration welded joint, according to DNV guideline [1]. The same fillet welded joint was further investigated for varying weld sizes. The results show that with changing weld size, there are considerable differences between calculated stresses, and specially calculated fatigue lives, when comparing with nominal stress approach. Further investigations revealed that there is a nonlinear relation between effective notch stress and weld sizes, while comparison of the notch stress and nominal stress approaches indicate that a linear relation is to be expected. Based on the established methodology for the cruciform joint, another joint, i.e. a knee plate located in a horizontal brace of a drilling vessel, was assessed for weld root fatigue. Based on the proposed equations and the linear relation found between the nominal- and the notch stress S-N curves, a weld size providing a longer fatigue life at the weld root, rather than that at the toe, was proposed.
Transient Analysis of Coupled Longitudinal and Transverse Vibration of Large Container Ship Propulsion Shafting
Authors: Huang Qianwen , Zhang Cong , Liu Jia , Yan Xinping
Published: October 2015

Marine propulsion shafting connects between the host and the propellers to promote the movement of ship, varieties of Different coupled vibrations forms produce different kinds of coupled vibrations, the coupled vibration of propulsion shafting poses serious threat to the safety and reliability of the sailing of ship. Considering the uncertainty of the experimental test for propulsion shafting, the simulation technology of coupling dynamics becomes particularly significant. This paper introduces a finite element method in numerical modeling and simulation technology of coupled dynamics for propulsion shafting. Combined with the theory of coupled mechanics, the coupled longitudinal and transverse dynamic response of propulsion shafting under the condition of no-coupling and the coupled are compared. The structural dynamic characteristics of longitudinal and lateral loads are discussed respectively. Analysis shows that different forms of excitation have certain effects on the performance of coupled longitudinal and transverse vibration for propulsion shafting. The research aims to reveal the basic principle of coupled longitudinal and transverse vibration for marine propulsion shafting to improve the safety and reliability of the sailing performance of the ships.
Dynamic Responses of Ship Propulsion Shaft Under Hull Excitations at Bearings
Authors: Zhang Cong , Tian Zhe , Yan Xinping
Published: October 2015

With the development of ship enlargement and economization, dynamic interaction of a propulsion shaft and ship hull is more and more evident, especially when it is travelling in rough seas. Bearings, as the connection between propulsion shaft and ship hull, transmit the forces from ship hull to propulsion shaft. Thus, the model of shaft with the excitations at bearings can be seen as a simplified propulsion shaft-ship hull system to analyze the effect of hull deformation.

Based on the theory of vibration of shaft, in this paper, equations of shaft motion and boundary conditions are presented. Moreover, in the continuity conditions equations at each support, harmonic forces from hull is included. Dynamic responses of propulsion shaft under hull deformation excitations are gained by analytical method. The effects of supports stiffness, locations of hull deformation excitations, the amplitude of excitations and shaft size are discussed by comparing the response displacements of observed points. At the same time, numerical calculation is set to validate the accuracy and feasibility of analytical method. The conclusions could apply the accordance for design and optimization of the ship propulsion shaft, when the hull deformation excitations at bearings are considered.
Calculation of Vertical Bending Moment Acting on an Ultra Large Containership in Large Amplitude Waves
Authors: Rajendran Suresh , Fonseca Nuno , Guedes Soares C.
Published: October 2015

The time domain method is further extended here in order to calculate the hydroelastic response of an ultra large containership in regular waves. Based on strip theory, the hydrodynamic and the hydrostatic forces are calculated for the instantaneous wetted surface area. Slamming forces are calculated using a Von Karman approach in which the water pile up during slamming is neglected. Timoshenko beam which takes into account the shear deformation and rotary inertia is used to model the structural dynamic characteristics of the hull. The beam is discretized using the finite element method and the ship vibration is solved using the modal analysis. The method is used to calculate the vertical bending moment acting on an ultra large containership in large amplitude regular waves. The results are compared with the experimental results measured in wave tank.
Improving Reliability of Mechanical Equipment in Dredgers Based on Wear Control Methods
Authors: Xu Xiaojian , Yan Xinping , Sheng Chenxing , Zhou Xincong
Published: October 2015

As the main equipment of channel and port construction, the reliability of dredgers has a significant effect on providing the frequent and regular maintenance for the marine transport systems. However, the dredger is prone to damage extremely especially the wear fault due to its complex structure with various mechanical equipment and harsh working environment such as the silt-carrying conditions. In this paper, the tribological systems of dredgers were analyzed in detail based on AHP and based on the analysis, the framework of wear control methods for dredgers was proposed. A series of wear control methods were taken including online wear condition monitoring and wear self-repairing to ensure the reliable operation of the dredger. The effects of the wear control measures for dredgers were evaluated and it proved that all the measures taken in this paper are effective to improve the reliability of the mechanical equipment in dredgers.
Wind noise within and across behind-the-ear and miniature behind-the-ear hearing aids
Authors: Zakis Justin A. , Hawkins Daniel J.
Published: October 2015

Previous studies investigated wind noise with Behind-The-Ear (BTE) hearing aids, but not the more common mini-BTE style of device, which typically has a smaller shell and microphones located more deeply behind the pinna. The current study investigated wind-noise levels across one BTE and two mini-BTE devices, and between the front and rear omni-directional microphones within devices. Levels were measured at two wind speeds (3 and 6 m/s) and 36 wind azimuths (10° increments). The pattern of wind-noise level versus azimuth was similar across mini-BTE devices, and differed for the BTE device. However, mean levels were markedly different across mini-BTE devices, and could be higher, lower, or similar to those of the BTE device. For within-device level differences, the pattern and mean across azimuth were similar across mini-BTE devices, and differed for the BTE device. Wind noise had the potential to slightly or severely reduce speech intelligibility at 3 or 6 m/s, respectively, across all devices.