bluuebunny/crossref_metadata_2025 huggingface dataset:
Power Performance and Environmental Footprint of High-Speed Vessels in Calm Deep Water
Authors: Skejic Renato , Jullumstrø Egil
Published: August 2013

This paper reports a theoretical study of the power performance and environmental footprint of high-speed vessels in calm deep water, paying particular attention to a high-speed catamaran cargo vessel Faltinsen [1]. The power analysis uses a modified version of the method of Doctors and Day [2]. One modification to their approach is that the wave resistance and free surface wave profiles, have been numerically predicted using two different linear potential flow field theories; Michell thin-ship theory (Yeung and Wan [3]) and the 3D Rankine panel method (Hess and Smith [4]), respectively. We have based the latter method on the combination of the Dawson [5] upstream finite difference operator and the ‘staggered grid’ technique (Jensen et al. [6]). In addition, this paper shows how the viscosity effects modeled on the free surface layer influence the behavior of the wave resistance curves as predicted by Michell’s thin ship theory. This was done by adopting the approaches described by Tuck [7] and Lazauskas [8].

The wave resistance models were verified and validated using the examples of Wigley monohull (Lazauskas [8], Tarafder and Suzuki [9]) and catamaran (Yeung and Wan [3], Tarafder and Suzuki [10]) analytical forms, as well as on the Tuck parabolic strut (Tuck [7]). Furthermore, the resistance models were extended using free surface profile estimates at selected Froude numbers and applied to the case of a high-speed catamaran cargo vessel. The numerical results obtained were compared with published results and their accuracy and application feasibility is discussed from the perspective of preliminary high-speed vessel design.

Based on the discussion above, suitable wave resistance models were selected and combined with the modified Doctors and Day [2] method giving the total resistance of the high-speed catamaran cargo vessel in the interval of Froude numbers. Having the estimates of total resistance, enables the effective power to be found. The results were compared with known results and were found to be in good agreement. Through combination of the effective power and propulsion factors, the brake power of the generic propulsion system is predicted. Taking into account the type of vessel being analyzed, the most common type of the propulsion diesel engine was selected. Finally, knowing the indicative environmental footprint of the selected engine, emission levels of Green House Gases (GHG) and solid particles were obtained. The emission results are further discussed in an ecologically friendly high-speed vessel design perspective (IMO [11, 19]).
Comparative Study of Utilizing a New Type V-Shaped Tuned Liquid Column Damper and U-Shaped Tuned Liquid Column Damper in Floating Wind Turbines
Authors: Shadman Milad , Akbarpour Abbas
Published: August 2013

While utilizing TLCD (Tuned Liquid Column Damper), severe excitation circumstances may lead to empty one of the vertical sections and make the liquid column to lose its U-Shape which results in dramatic changes in mathematical formulation and physical behavior of the liquid column. In this work, the response of a floating wind turbine with a barge type support controlled by a new type V-Shaped Tuned Liquid Column Damper subjected to couple hydrodynamic and aerodynamic loads is investigated through using a modified version of the aero-elastic code FAST (Fatigue, Aerodynamics, Structures and Turbulence). A sequential method is applied to solve the multi degree of freedom floating wind turbine couple with a single degree of freedom V-Shaped Tuned Liquid Column Damper. Through this method, the nonlinear equation of motion of the damper is incorporated in a modified version of FAST while V-Shaped Tuned Liquid Column Damper damping force due to the fore-aft tower top acceleration on turbine’s tower is calculated in each time step. The results are compared to the floating wind turbine system with TLCD (Tuned Liquid Column Damper) as well as the baseline system. It is shown that utilizing V-Shaped Tuned Liquid Column Damper in comparison to U-Shaped one result in more reliable structural response specifically under severe wind conditions in floating wind turbine systems.
Influence of Incoming Flow Direction on Spacing Between Vertical Axis Marine Current Turbines Placed in a Row
Authors: Dyachuk Eduard , Goude Anders , Lalander Emilia , Bernhoff Hans
Published: August 2013

From the commercial point of view it may be beneficial to install a set of marine current turbines forming a park, by analogy with wind parks. Consequently, this motivates research on park configurations.

An array of ten vertical axis marine current turbines is simulated to study how the distance between the turbines affects the performance of the park for different flow directions. The simulations are performed using a two-dimensional vortex method. An array of identical turbines is created, where all turbines are on a single line. The turbines are operated at the tip speed ratio, which corresponds to the highest power coefficient for a single turbine. The distance between the turbines is varied and the total power from the array is compared to the turbine spacing for different flow directions.

Additionally, flow data from a real site is used to find an optimal orientation of the line of turbines. The performance of the array is estimated for the site as a function of turbine spacing.
DP Ice Model Test of Arctic Drillship and Polar Research Vessel
Authors: Hals Torbjørn , Jenssen Nils Albert
Published: August 2013

The paper presents the results from a series of ice model tests performed as part of the DYPIC (Dynamic Positioning in Ice Conditions) research program. DYPIC is a research and development project within the EU’s ERA NET MARTEC project. The major purpose of the DYPIC project is development of equipment and methods for DP Ice Model testing which allows the prediction of station keeping capability of different vessel types and offshore structures under various ice conditions.

The first DYPIC model tests performed in 2011 was conducted with two significantly different vessel sizes, a 68.0000 m3 volume displacement arctic drillship and an 8.600 m3 polar research vessel. The model scale was 1/30 for the arctic drillship and 1/18.6 for the Polar Research Vessel.

The model tests were performed in the ice model basin at HSVA using vessel models equipped with thruster capacity similar to full scale operation according to DP class 2 / 3 operations. The DP control system was also modified from normal open water DP operations in order to cope with the highly varying ice drift loads acting on the vessel.

The test program gave data supporting the development of numerical models of ice loads from managed ice, see reference [6]. The main focus in this paper is on the station keeping performance and associated thrust utilization as a function of varying ice drift loads.

The results and data collected in the first year of the DYPIC program demonstrates that DP ice model tests will be a valuable tool for evaluation of vessel performance prior to moving on to full scale arctic DP operations.
The Influence of Vortex Formation on the Damping of FPSOs With Large Width Bilge Keels
Authors: de Oliveira Allan C. , Fernandes Antonio Carlos , Guimarães Hélio Bailly
Published: August 2013

The roll damping of a FPSO assessment is a different subject than the ship case. The fact that the FPSO is not moving changes the flow hydrodynamics in such a way that the well established understanding is no longer applied. This is so at least for certain particularities such as flat bottom, no lift effect due to zero velocity, and so on. Recent researches have proven the strong effect of the vortex shedding on the roll damping of a FPSO mainly when large width bilge keel are present. Although these effects are known by a long time for ships, the increase of the vortex magnitude due the large width bilge keels on a FPSO has let to uncertainties about the behavior of the structures and the situation is challenging. It has been understood that the vortex can modify deeply the pressure distribution along the FPSO hull in such way that the final roll dissipation is higher. Surprisingly, under certain conditions the memory effects are small. The use of visualization techniques allied to the analysis of several decay tests for the same hull can help the understanding of several aspects such as the uncertainty in the measurements and the vortex behavior.
Pipeline Walking Interaction With Buckle Formations Along Routes With Significant Seabed Features
Authors: Wang Yunxiao Nick , Maschner Emil , McKinnon Colin
Published: August 2013

In the last few years some ‘long’ HPHT (high pressure high temperature) offshore pipelines have been required to be routed across challenging seabed terrains such as salt diapirs and deep trenches with relatively large OOS (out of straightness) and steep slopes. This has given rise to a combined design concern of lateral buckling with pipeline walking. Typically anchor points in the form of caisson piles as well as buckle sites in the form of sleepers or buoyancy modules maybe required in the vicinity of the seabed features to release the compressive forces associated with the high pressure and temperature loads in a controlled manner and to prevent the pipelines from migrating down slope during operation. The instigation of buckle sites can essentially divide any ‘long’ pipelines into a number of short sections with different walking behaviour due to varying seabed slopes and varying pressure and temperature gradients at locations along the route. In addition pipeline anchors influence the development of any planned buckle site and thus limit the extent of cyclic feed-in and/or pull-out. This integrated mechanism is termed buckling walking interaction within this paper.

The prevailing methodology and numerical modelling of pipeline walking usually evaluates ratcheting end expansions by means of ‘short’ and overall ‘long’ pipe lengths which ignore or consider the existence of buckle sites along any pipeline route respectively. This paper presents a general-purpose study on the phenomenon of buckling walking interaction considering a typical pipe route configuration with anchors and buckles along its length. Aspects such as the cyclic evolution of mode shapes of buckles and the effect of soil berm resistance on buckling walking interaction are explored. Finally the design application of buckling walking interaction for ‘long’ cyclically constrained pipelines with buckles and anchors is discussed.
Prediction of Roll Damping Using Viscous Flow Solvers
Authors: Manzke Manuel , Rung Thomas
Published: August 2013

This article illustrates the use of a RANSE solver coupled to a motion solver to predict the free roll decay and the associated damping coefficients of floating bodies. The necessary building blocks to perform such a prediction are described briefly. A sensitivity study for the convergence criterion, the time step, the domain size and the grid resolution is performed for a simple 2-dimensional barge. The results are compared to results from experiments. Furthermore a simulation for a free roll decay of a Navy Combatant is performed, considering the results of the parameter study for the Barge. Overall results indicate that the natural roll frequency can be well predicted, while the prediction of the roll damping coefficients is afflicted with some uncertainties.
Forces on Nets With Bending Stiffness: An Experimental Study on the Effects of Flow Speed and Angle of Attack
Authors: Gansel L. C. , Jensen Ø. , Lien E. , Endresen P. C.
Published: August 2013

This study investigates the effects of changes in flow speed and angle of attack on drag and lift forces on nets with bending stiffness. Today most fish cage nets are made from nylon, but new cage materials are proposed in order to improve the stability of cages in currents and waves, to reduce biofouling, prevent escapes, and to secure fish from predator attacks. The use of some of these materials leads to nets with bending stiffness in at least one direction. However, not much is known about the performance of such nets in currents and waves. In this study three different nets with bending stiffness were tested together with nylon nets. Net panels were subjected to different flow speeds at different angles between flow direction and net plane, and the forces on the nets were measured with a multi-axis force/torque sensor system. Based on the experiments, drag and lift coefficients were determined for the different net materials and compared to existing theory [1,2]. The results are in reasonably good agreement with the existing theory for the nets with low solidity, however, for nets with higher solidity the results are significantly lower than the drag and lift coefficients provided by Aarsnes [1] and Løland [2].
Actuator Saturation Control of Floating Wind Turbines
Authors: Ramos Roberto
Published: August 2013

A state feedback aerodynamic controller is proposed for the stabilization and reduction of platform/tower pitch vibrations of a spar-type floating wind turbine, considering blade pitch saturation effects. The controller is synthesized from a linearized rigid body model developed for a NREL 5-MW offshore wind turbine operating at the above rated condition (region 3). Wind turbulence and wave induced loads are obtained from the blade element momentum (BEM) aerodynamic theory and Morison’s equation, respectively. The simulation results show that the proposed nonlinear control system yields significant vibration reduction in comparison to a proportional-integral controller.
Are Basin Waves Different From Field Waves?: First Investigations During the ‘CresT’ JIP
Authors: Buchner Bas , Forristall George
Published: August 2013

The possible differences between basin waves and field waves were investigated, comparing long crested and short crested waves, short crested waves at different scales and the high frequency spectra of field and basin waves. It was observed that short crested basin waves and field waves show very similar behavior. We conclude that, beside simulations and field data, basin testing is an important tool to study extreme waves and their statistics.
Design and Aero-Elastic Simulation of a 5MW Floating Vertical Axis Wind Turbine
Authors: Vita Luca , Paulsen Uwe S. , Madsen Helge A. , Nielsen Per H. , Berthelsen Petter A. , Carstensen Stefan
Published: August 2013

This paper deals with the design of a 5MW floating offshore Vertical Axis Wind Turbine (VAWT). The design is based on a new offshore wind turbine concept (DeepWind concept), consisting of a Darrieus rotor mounted on a spar buoy support structure, which is anchored to the sea bed with mooring lines [1]. The design is carried out in an iterative process, involving the different sub-components and addressing several conflicting constraints. The present design does not aim to be the final optimum solution for this concept. Instead, the goal is to have a baseline model, based on the present technology, which can be improved in the future with new dedicated technological solutions. The rotor uses curved blades, which are designed in order to minimize the gravitational loads and to be produced by the pultrusion process. The floating platform is a slender cylindrical structure rotating along with the rotor, whose stability is achieved by adding ballast at the bottom. The platform is connected to the mooring lines with some rigid arms, which are necessary to absorb the torque transmitted by the rotor. The aero-elastic simulations are carried out with Hawc2, a numerical solver developed at Risø-DTU. The numerical simulations take into account the fully coupled aerodynamic and hydrodynamic loads on the structure, due to wind, waves and currents. The turbine is tested in operative conditions, at different sea states, selected according to the international offshore standards. The research is part of the European project DeepWind (2010–2014), which has been financed by the European Union (FP7-Future Emerging Technologies).
Numerical-Analytical Prediction of the Collapse of Flexible Pipes Under Bending and External Pressure
Authors: Loureiro Walter C. , Pasqualino Ilson P.
Published: August 2013

This work gathers the phenomena indicated through the available literature and industry standards as determinant in the evaluation of the collapse of flexible pipes under combined bending and external pressure. It also proposes a complete analytical formulation to assess the collapse strength. The effects of dimensional variations and added ovalization due to bending are combined to evaluate the final collapse pressure. Numerical models are generated for comparison purposes and experimental results are used to validate the formulation proposed. The good agreement obtained between numerical and analytical predictions show that is possible to determine the curve collapse of flexible pipes through analytical approaches.
Effect of Polyester Mooring Stiffness on SCR Design for Semi Applications
Authors: Cao Peimin , Thompson Hugh , Kwan Tom
Published: August 2013

Polyester rope mooring system has been widely accepted as a reliable and cost effective choice for deepwater mobile offshore drilling and floating production units in recent years. Polyester rope is made of a visco-elastic material and its stiffness is affected by mean tension, tension amplitude, loading period, and loading history. This creates complexity and uncertainty in the design of hull, mooring and riser systems.

This paper summarizes the results of a JIP study investigating the effect of polyester rope stiffness on the SCR design of a semi-submersible FPU at two water depths in the Gulf of Mexico (GoM). A two-slope static-dynamic stiffness model proposed in the recently issued ABS “Guidance Notes on The Application of Fiber Rope for Offshore Mooring”[1] is used in the global motion analysis to provide input for the riser analysis. Parametric studies of SCR extreme analysis, wave fatigue analysis, and VIM fatigue analysis have been performed. Based on the results, recommendations on the impact of rope stiffness to the riser design are presented.
Statistical Design of Experiments Applied to the Design of Compliant Vertical Access Risers
Authors: Martins Michele A. L. , Silveira Eduardo S. S. , Lages Eduardo N.
Published: August 2013

This paper applies design of experiments (DOE) methodology to the design of Compliant Vertical Access Risers (CVAR). This relatively new riser configuration is characterized by its differentiated geometry, achieved by the use of syntactic buoyancy at the lower section of the riser and additional weight at its upper section. The characteristic compliance of the CVAR system is obtained by providing an excessive length of pipe and a horizontal offset between the riser top and end connections. Thus, this system provides vertical access to dispersed subsea wells and its compliance can also compensate for vessel motion. CVAR, being vertical access to the wells, brings the advantage of using dry trees, and also allows the completion and workover operations to be performed from the FPU, offering significantly economic and operational benefits to deepwater oil field development. To guarantee such benefits, some operational and structural constraints must be satisfied. The design of the CVAR system is dependent upon several parameters. This study can provide a better understanding about the behavior of the CVAR in terms of its design parameters by the use of the DOE methodology. DOE is a statistical technique that provides an objective measure of how design parameters are correlated and the effective contribution of each at the riser performance. Consideration of the main effects as well as interaction effects coupled with sensitivity analysis is essential for insightful interpretation of model results and effective decision-making. Thus, this study contributes with the design of Compliant Vertical Access Risers as well as with a methodology that can lead to efficient riser design, being a first step in the optimization design process.
Combination of Multiple Extreme Bending Moment Components
Authors: Leira Bernt J.
Published: August 2013

A procedure for estimating the combined load effect for processes with different zero-crossing periods is described. The procedure is illustrated by application to the combination of wave-induced bending moments. The basic formulations related to the distribution of maxima and extremes for a scalar Gaussian process are first reviewed. Subsequently, an outline of the procedure for multi-component processes is given. The developed formulation is then applied for analysis of the combined bending moment load effect.

Two cases of such combinations are addressed (i) A case with widely different velocity variances (ii) A case involving a non-linear combination of the bending moments. A geometric approach to the interpretation and derivation of associated load effect combination factors is also demonstrated.
Surveillance Models of Large-Scale ESP With High Viscosity Fluids and Gas
Authors: Barrios Lissett , Scott Stuart , Deuel Charles
Published: August 2013

The paper reports on developmental research on the effects of viscosity and two phases, liquid–gas fluids on ESPs which are multi stage centrifugal pumps for deep bore holes.

Multiphase viscous performance in a full-scale Electrical Submersible Pump (ESP) system at Shell’s Gasmer facility has been studied experimentally and theoretically. The main objectives is to predict the operational conditions that cause degradations for high viscosity fluids when operating in high Gas Liquid Radio (GLR) wells to support operation in Shell major Projects. The system studied was a 1025 series tandem WJE 1000.

The test was performed using this configuration with ten or more pump stages moving fluids with viscosity from 2 to 200 cP at various speed, intake pressure and Gas Void Fractions (GVF). For safety considerations the injected gas was restricted to nitrogen or air.

The ESP system is a central artificial lift method commonly used for medium to high flow rate wells. Multiphase flow and viscous fluids causes problems in pump applications. Viscous fluids and free gas inside an ESP can cause head degradation and gas locking. Substantial attempts have been made to model centrifugal pump performance under gas-liquid viscous applications, however due to the complexity this is still a uncertain problem. The determination of the two-phase flow performance in these harmful conditions in the ESP is fundamental aspects in the surveillance operation.

The testing at Shell’s Gasmer facility revealed that the ESP system performed as theoretical over the range of single flowrates and light viscosity oils up to Gas Volume Fractions (GVF) around 25%. The developed correlations predict GVF at the pump intake based on the operational parameters. ESP performance degrades at viscosity higher than 100cp as compared to light oil applications, gas lock condition is observed at gas fraction higher than 45%. Pump flowrate can be obtained from electrical current and boost for all range of GVF and speed.

The main technical contributions are the analysis of pump head degradation under two important variables, high viscosity and two-phase flow inside the ESP.
Finite Element Analysis of Nonlinear Water Wave-Body Interaction: Computational Issues
Authors: Vendhan C. P. , Sunny Kumar P. , Krishnankutty P.
Published: August 2013

Design of floating structures exposed to water waves often requires nonlinear analysis because of high wave steepness and large body motion. In this context, Mixed Eulerian-Lagrangian (MEL) methods for nonlinear water wave problems based on the potential flow theory have been studied extensively. Here, the Laplace equation with Dirichlet boundary condition on the free surface is solved using the boundary integral method, and a time integration method is used to find the particle displacements and velocity potential on the free surface. Finite element methods based on the MEL formulation have been developed in the 90s. Several researchers have pursued this approach, addressing the various challenges thrown open, such as velocity computation, pressure computation on moving surfaces, remeshing of the computational domain, smoothing and imposition of radiation condition. Apart from these, the implementation of the FE model in particular involves several computational issues such as element property computation, solution of large banded matrix equations, and efficient organization of computer storage, all of which are crucial for the computational tool to become successful. A study of these aspects constitutes the primary focus of the present work.

The authors have recently developed a 3-D FE model employing the MEL formulation, which has been applied to predict waves in a flume and basin. The fluid domain is discretized using 20-node hexahedral elements. The free surface equations are solved in the time domain employing the three-point Adams-Bashforth method. Validation of the numerical model and relative computation times for salient steps in the FE model are discussed in the paper.
Hydroelastic Response of a Ship Structural Detail to Seakeeping Loads Using a Top-Down Scheme
Authors: Sireta François-Xavier , Derbanne Quentin , Bigot Fabien , Malenica Šime , Baudin Eric
Published: August 2013

In order to investigate the local response of a ship structure, it is necessary to transfer the seakeeping loading to a 3DFEM model of the structure. A common approach is to transfer the seakeeping loads calculated by a BEM method to the FEM model. Following the need to take into account the dynamic response of the ship to the wave excitation, some methods based on a modal approach have been recently developed that include the dry structural modes in the hydro-structure coupling procedure and allow to compute the springing and whipping response of the ship structure to the seakeeping loads.

In the context of the fatigue life assessment of a structural detail, a very fine FE model is required. A very large number of seakeeping loading cases also need to be considered to account for all the conditions encountered by the ship through its life. It becomes then clear that because of the CPU time issue, the whole FE model can not be very fine. This is why a hierarchical top-down analysis procedure is commonly used, in which the global ship structure is modelled in a coarse manner using one finite element between web frames. The structural details are modelled separately using a fine meshing. Such top-down methods are commonly used for the estimation of the quasi-static response of structural details to the seakeeping loads.

This paper presents a methodology in which a top-down method is used to estimate the springing response of a ship structural detail loaded with wave pressure, and its fatigue life. The global dry structural modes are transferred to the detail fine model using the shape functions of the finite elements of the global model. The hydrodynamic pressures are computed directly on the fine mesh model, avoiding any interpolation error. The imposed displacements at the fine mesh boundary are computed using the same method that is used to transfer the structural mode shapes, and the local pressure induced loads and inertia loads are applied on the fine mesh nodes.

This method is applied for the calculation of the elongation of a strain gauge which is installed in the passage way of an ultra large container ship.
Study of the Reliability of the Ship Transportation by Applying the Historical Hindcast Weather Data
Authors: Kauczynski Wojciech E.
Published: August 2013

Regularity of ship transportation depends strongly on environmental conditions, on the ship’s route and on the seakeeping characteristics of a vessel. The ship’s route property selected and the ship characteristics designed appropriately to a region of the ship operation can assure a higher regularity of the transportation.

In the presented paper an exemplifying analysis of the ship transportation on a selected typical ship’s route has been performed. The principal purpose of such an analysis was to determine the magnitude and distribution of speed losses in a realistic operational environment to serve as a basis for estimation of reliability of the sea transportation.

The aim of the analysis precludes the use of long term statistics as this would not give a correct representation of the extreme value tail of the probability distribution of sailing time. Instead of this, the ship performances on the considered sea routes were simulated in roundabout trips by applying time series of historical (hindcast) weather data (waves, swell, wind, and ocean current). The applied data cover three complete years starting from February 2003 and they are specified with the 6 hour time interval at about 3000 grid points covering almost the whole world ocean area.

Two vessels which represent typical classes of ships (a tanker and a container ship) were used in this analysis. The ships voyages were simulated with different departure time and with the time interval of 6 hours providing high sailing frequency and the considerable large amount of results. Results of the calculations were analyzed with respect to the seasonal variations, alternative routes, and different power settings. The purpose of these numerical exercises was to illustrate how to perform the analysis and to present a scope of the obtained results.
An Overset Grid Approach to Linear Wave-Structure Interaction
Authors: Read Robert W. , Bingham Harry B.
Published: August 2013

A finite-difference based approach to wave-structure interaction is reported that employs the overset approach to grid generation. A two-dimensional code that utilizes the Overture C++ library has been developed to solve the linear radiation problem for a floating body of arbitrary form. This software implementation has been validated by performing time-domain simulations to evaluate the dynamic forces applied to a half-submerged cylinder and a rectangular barge in response to a prescribed motion. A Gaussian displacement is used to introduce a range of wave frequencies, thereby allowing the measurement of the body response over the frequency range of interest. The radiation added-mass and damping coefficients of both bodies have been evaluated and compared to exact analytical solutions. The numerical and analytical results show good agreement when the modes of excitation and response are the same. The cross-coupled results are in qualitative agreement, but show some quantitative variations that may be related to slight differences in the fluid domain geometry. For both the cylinder and the barge, the effects of bottom slope on the coefficients are found to be minimal.
A Nonlinear Extension for Linear Boundary Element Methods in Wave Energy Device Modelling
Authors: Merigaud Alexis , Gilloteaux Jean-Christophe , Ringwood John V.
Published: August 2013

To date, mathematical models for wave energy devices typically follow Cummins equation, with hydrodynamic parameters determined using boundary element methods. The resulting models are, for the vast majority of cases, linear, which has advantages for ease of computation and a basis for control design to maximise energy capture. While these linear models have attractive properties, the assumptions under which linearity is valid are restrictive. In particular, the assumption of small movements about an equilibrium point, so that higher order terms are not significant, needs some scrutiny. While this assumption is reasonable in many applications, in wave energy the main objective is to exaggerate the movement of the device through resonance, so that energy capture can be maximised. This paper examines the value of adding specific nonlinear terms to hydrodynamic models for wave energy devices, to improve the validity of such models across the full operational spectrum.
Limit Strength of New Sandwich Pipes With Strain Hardening Cementitious Composites (SHCC) Core: Finite Element Modelling
Authors: An Chen , Castello Xavier , Oliveira Andrielli M. , Duan Menglan , Toledo Filho Romildo D. , Estefen Segen F.
Published: August 2013

Sandwich Pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation. Besides polymer, strain hardening cementitious composites (SHCC), a micromechanically designed material with the characteristic of high tensile ductility, can be another choice for the annular material. The purpose of this work is to investigate numerically the limit strength of SP with SHCC under external pressure and longitudinal bending. The mechanical behaviour of SHCC is simulated using a Concrete Damaged Plasticity (CDP) model provided by Abaqus/Standard. The finite element (FE) model is employed to better understand the structural behaviour of SP in different conditions of geometry, adhesion and loading. The pressure-curvature (P – K) failure envelopes for SP with unbonded and fully bonded interface conditions are presented. The results show that the resistance of the annulus layer has a great contribution for the overall structural behaviour. The interface condition and the thickness of the annulus are important influence factors on the overall structural behaviour. Besides, the lateral confinement effect on SHCC caused by the inner and outer steel tubes and the ultra high ductility of the SHCC have strong influence on the results for the pressure-curvature collapse envelopes.
Interaction of Boundary Layer and Blade Vibration at Ultra-Low Advance Ratios and Low Reynolds Numbers in a Novel Flapping and Spinning Propulsor
Authors: Bandyopadhyay Promode R. , Fredette Albert R. , Hansen Joshua C.
Published: August 2013

The nonlinear thrust properties of a small, near-hovering, conventional-looking propulsor are examined. When the propulsive power versus displacement of large and small manmade underwater vehicles is compared against that of large and small fish (distinguishing their red and white muscle distributions), universal trends are observed for cruising and maneuvering irrespective of size. While there is an overlap in the low displacement range of 0.1 to 1 m3, manmade propulsors have rotating blades that are fixed, but animals use flapping pectoral fins. With this cue, a small and novel propulsor has been built where the fins/blades can both flap and spin. The blade pitch can also be varied, allowing the production of reverse thrust. The nondimensional parameter range of thrust production in both the flapping and spinning modes is determined. When the advance ratio (J) and Reynolds number (Rec) are ultra-low in the spinning mode, the blade boundary layer couples with small pitch oscillations, and a bimodal behavior ensues. Boundary layer fence and rough blade surfaces shift the behavior to higher effective pitch angles, but the bi-modal behavior persists. A quasi-steady thrust modeling is carried out of the spin mode when the boundary layer couples with the inadvertent small pitch oscillation and when it does not. Temporal modeling indicates that, at ultra-low values of J and Rec, the boundary layer and blade vibration interaction can be described as a Lienard (nonlinear) oscillator. The potential mechanism of interaction between blade vibration and rotation, and of their modeling, is discussed.
Dynamic Analysis and Configuration Design of a Two-Component Wave-Energy Absorber
Authors: Cochet Christophe , Yeung Ronald W.
Published: August 2013

The wave-energy absorber being developed at UC Berkeley is modeled as a moored compound cylinder, with an outer cylinder sliding along a tension-tethered inner cylinder. With rigid-body dynamics, it is first shown that the surge and pitch degrees of freedom are decoupled from the heave motion. The heaving motion of the outer cylinder is analyzed and its geometric proportions (radii and drafts ratios) are optimized for wave-energy extraction. Earlier works of Yeung [1] and Chau and Yeung [2,3] are used in the present heave-motion study. The coupled surge-pitch motion can be solved and can provide the contact forces between the cylinders. The concept of capture width is used to characterize the energy extraction: its maximization leads to optimal energy extraction. The methodology presented provides the optimal geometry in terms of non-dimensional proportions of the device. It is found that a smaller radius and deeper draft for the outer cylinder will lead to a larger capture width and larger resulting motion.
A Small-Scale Field Experiment on Random Froude-Krylov Force on a Rectangular Structure
Authors: Arena Felice , Malara Giovanni
Published: August 2013

This paper investigates random Froude-Krylov (FK) force on a rectangular structure. It is a key parameter in the design process of some maritime structures. Indeed, the exciting force on a large floating body is commonly determined by a contribution due to the incident wave field (FK) and by a contribution due to the diffraction of sea waves.

The work is based on results of a small-scale field experiment at NOEL (Natural Ocean Engineering Laboratory) in Reggio Calabria, Italy. First, field experiment is described, with characteristics of the selected sea states. Then, FK forces are analytically derived in the context of linear random waves. Frequency spectrum of the FK force is derived and it is discussed the occurrence of zeros in frequency domain.

Extreme FK forces are determined by Quasi-Determinism theory. The theory enables to derive the analytical expression of the FK force when a large wave (either a large crest height or a large crest-to-trough wave height) occurs at any given point of the wave field, in a fixed time instant. Time domain representation allows investigating the wave force and extreme wave pressure. It is shown that the wave force is highly width dependent in time domain. Further, time histories are not quasi-impulsive. This characteristic is well-rendered in large structures (large with respect to the dominant wave length), where the wave group crossing gives rise to a time history “protraction” in time domain.

In the last part of the paper theoretical results are supplemented by comparison with experimental data.
The Wake Flow Behind Azimuthing Thrusters: Measurements in Open Water, Under a Plate and Under a Barge
Authors: Cozijn J. L. , Hallmann R.
Published: August 2013

The wake flow behind a ducted azimuthing thruster was investigated. The thruster wake is an important factor in thruster interaction effects. Model tests were carried out for 3 different configurations; a thruster in open water conditions, a thruster under a flat plate and a thruster built into a barge. Two different thrusters were considered, a ‘normal’ thruster with a horizontal propeller axis and a ‘tilted’ thruster with a propeller axis and nozzle oriented 7 deg down-wards. In the tests the propeller thrust and torque were recorded, as well as the nozzle thrust and unit thrust. The velocities in the wake of the thruster were measured using a PIV (particle image velocimetry) system, for down-stream locations up to x/D = 19. The influence of the thruster tilt, the plate above the thruster and bilge radius on the thruster wake flow were investigated.

Detailed PIV measurements were carried out on the wake flow behind the thruster in open water conditions. The PIV system used can measure 3D velocities in large set of points in a 2D plane, which is illuminated by a laser light beam. The flow velocities were measured in a large number of cross sections at different distances from the thruster. The PIV measurements provide a detailed image of the flow velocities in the thruster wake, showing the axial velocities, as well as the rotation and divergence of the wake.

Subsequently, PIV measurements were carried out for the thruster under a flat plate and the thruster under a barge. The measurement results show a thruster wake that is deformed by the presence of the plate and the barge. The plate and the bottom of the barge form a flat plane above the thruster, clearly flattening the cross section of the thruster wake. Furthermore, the wake flow at the side of the barge, near the bilge radius, results in a low pressure region, causing the wake flow to diverge up as it flows from under the barge into the open water. This phenomenon is known as the Coanda effect and is strongly dependent on the bilge radius and the distance between the thruster and the side of the barge. The effect of both these parameters was confirmed in the model test results presented. The typical flow patterns observed as a result of the Coanda effect are illustrated in Figure 1 below.

The results of the present model test research are used to further improve the understanding of the physics of thruster interaction effects. Furthermore, the results will serve as validation material for CFD calculations.
Response-Based Analysis of FPSO Systems for Squall Loadings
Authors: Minnebo Joerik , Izadparast Amir H. , Duggal Arun , Huijsmans René H. M.
Published: August 2013

Squalls can be the major design driver for FPSO systems in offshore West Africa where other environmental loadings are relatively benign. The measured squall time series indicate a transient change in the wind speed, starting with a sudden increase to a peak wind speed followed by a rapid decay, all within a total duration of about an hour. In the design of FPSOs for squall loadings, careful attention needs to be given to the transient characteristics of squalls.

The main objective of this investigation is to characterize the response of FPSO systems subjected to squalls and develop a robust approach for estimating the design value. For this purpose, first, the dynamic behavior of an FPSO in squalls is studied and then the significant squall parameters that affect the dynamic response of the FPSO are identified. The results of this study are utilized to define the upper bound of the dynamic amplification factor and the upper limit of the extreme response of the FPSO. Next, three different response-based approaches: a) based on the long-term statistical analysis of the response, b) based on the long-term statistical analysis of the squall parameters and c) based upon the dynamic amplification limitations, are utilized to estimate the design values. Finally, the design value estimates obtained from the response-based approaches are compared with those estimated from scaling squall time traces to the 100-year peak wind speed. The study is mainly focused on spread moored systems; however, the proposed methods are also tested on turret moored FPSOs, and their application for these dynamically complicated systems is evaluated.
The Wind Tunnel Experiment Study of Wind Load on Jack-Up Drilling Unit
Authors: Yi Lin , Hu An-kang , Wei Jiang , Fei Xiong
Published: August 2013

Owing to the characteristics of the Jack-up drilling unit, the environment loads are important factors to the structure safety of jack-up. The wind load takes up a much larger proportion in structure analysis, and it has been now paid more and more attention in the field of offshore engineering. According to the MODU rule, the projected area method is used to calculate wind load. The height coefficient Ch and shape coefficient Cs are chosen by experience listed in MODU rule. However, the aerodynamic interference between platform components, such as wind shielding effects and acceleration flow effects are ignored. So the calculation results in accordance with MODU rule are conservative, and not good for structure optimization designing to some degree. Therefore, the wind tunnel experiment is very important and necessary. In this paper, a 400ft jack-up, which is developed by CIMC, is studied as an example. Considering the Reynolds number effects, the wind loads of jack-up both in normal drilling condition and severe storm condition are obtained in the experiment. Compared with the results, which are calculated according to MODU rule, it indicates that the experiment results are less, and the effect of aerodynamic interference and updraft can’t be ignored.
Fatigue Life Improvement of Welded Doubling Plates
Authors: Lotsberg Inge , Fjeldstad Arne , Helsem Morten Ro , Oma Narve
Published: August 2013

Fatigue life assessment is important for all floating offshore structures related to the new building stage but also related to lifetime extensions. Fatigue cracking occurs normally due to uncertainties in estimated fatigue life and this is a well-known problem for floaters.

In this paper the aim has been to look deeper into the effects of improvement methods for improvement of the fatigue life of structural connections.

Fatigue testing of full size fillet welded doubling plates has been performed of a specimen in as welded condition for comparison with two specimens improved by grinding. The paper also presents an alternative S-N curve for grinded details.

The primary goal is to assess the possibility for fatigue life improvement of fillet welded doubling plates where fatigue cracking may initiate from the weld root. The information gained in this project is considered to be important for the offshore floater industry, as well as for development of new fatigue assessment procedures and requirements in standardization.
Verification of Fracture and Fatigue Performance of Titanium Gr. 29 Welds in Tapered Stress Joints
Authors: Buitrago Jaime , Nissley Nathan A. , Rombado Gabriel
Published: August 2013

Design of a Steel Catenary Riser (SCR) requires the use of connection hardware to accommodate the bending moment that arises from the abrupt change in stiffness at the floater hang-off. Reliability of this connection hardware is of paramount importance in ultra deepwater applications (up to 3000m), especially those involving high pressure and temperature fluids. One type of such connection hardware is a metallic tapered stress joint. Because of its inherent density, strength, and stiffness, steel is not well suited for these applications due to the length and weight constraints. Titanium Gr. 29 (Ti), which is as strong as steel but lighter and more flexible, has been identified as a good material candidate for a tapered stress joint.

The required length (∼40ft) and thickness (∼3.5in.) of the Titanium Stress Joint (TSJ) cannot be fabricated as a single piece due to forging size limitations. Thus, an intermediate girth weld becomes necessary. The fracture and fatigue performances in the presence of the external seawater and cathodic protection (CP) and the internal sour production with galvanic effects between the Ti and steel must be assessed to verify the service life of the stress joint. ExxonMobil has developed and initiated a Joint Industry Project to fully address the fracture and fatigue qualification of titanium welds. In particular, the project plans to establish a robust methodology for the future qualification of TSJs that parallels, to the extent possible, the qualification process currently used for SCRs.

This paper discusses the primary aspects of the titanium weld qualification: (1) selection of test specimens, (2) load frequency effects on initiation and propagation lives, (3) environmental assisted cracking due to hydride formation under cathodic and galvanic conditions, (4) full-thickness small-scale fatigue, (5) size effect on fatigue, and (6) weld inspection.