bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of Wave-Structure Interaction of a Cylinder in Regular Sea Waves With Vessel Motions Using Coupled Transient CFD and Diffraction Methodology
Authors: Jia David , Schofield Paul , Shen Joanne , Malachowski Jim
Published: October 2015

This paper is a continuation of our previous paper [1] (OMAE2014-23225) where we did a parametric study for wave-structure interaction of a hollow cylinder in regular sea waves without vessel motions. The effect of waves and current on the motion of the cylinder and the associated forces were evaluated using a state-of-the-art methodology [2] (OMAE2013-11569) for predicting the motions and loads of subsea equipment and structures during offshore operations. In this paper, we extend the solution to include wave – structure interaction in regular sea waves and vessel motions. The 5th order Stokes regular waves in CFD and vessel motions are included in the modeling. This methodology couples the transient CFD with a hydrodynamic motion analysis after diffraction analyses, instead of relying on the traditional approach which uses simplified equations or empirical formulae to estimate hydrodynamic coefficients [3], or using steady-state CFD simulation on stationary equipment and structures to predict drag and added masses on submerged structures. The time domain diffraction simulation is coupled with a multiphase CFD simulation of subsea equipment and structures in waves. A transient CFD model with rigid body motions for the equipment and structures calculates added masses, forces and moments on the equipment and structures for the diffraction analysis, while the diffraction analysis calculates linear and angular velocities for the CFD simulation. In this paper, simulations are performed to investigate effect of the vessel motions on the motion of a hollow cylinder in regular sea waves. The results are compared with that from the traditional approach. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in waves during offshore operations. The results in this paper show wave-structure interaction of a hollow cylinder in regular sea waves, and the effect of vessel motions on the motion of the cylinder. The results provide better understanding of structure motion in regular waves with vessel motions using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations, or by using steady-state CFD analyses in traditional decoupled approaches. The results show that the coupled physics of regular sea waves, vessel motions and cylinder motion is captured by using this methodology. The coupled physics is not captured by the traditional approach.
Numerical Prediction of Scouring Depth Around Foundations of Offshore Structures
Authors: Hwang Jeongwoo , Lee Ja-Hoon , Cho Yong-Sik
Published: October 2015

The pile foundations of offshore structures are vulnerable to local ground loss by scouring. The vortex flow affected by the flow conditions, ground conditions, and the shape of the pile is the main cause of scouring. The decrease of an embedded depth of foundation pile by scouring may lead to an excessive displacement of the structure and a decrease of the bearing power, leading to a collapse of the offshore structure. In this work, a three-dimensional commercial code named STAR-CCM+ has been employed to predict the final depth of the scouring-hole around the foundation of offshore structures. Assuming the bed as a fluid having a high level of dynamic viscosity and density, the prediction has been accomplished by using the multi-phase flow model. The model solves the Reynolds Averaged Navier-Stokes (RANS) equations, and standard k-ε turbulence model to estimate the depth of the scouring-hole. To guarantee the reliability of the model, the results of the numerical model have been compared with available laboratory measurements. A reasonable agreement has been observed.
Real-Time Marine Vessel and Power Plant Simulation
Authors: Bø Torstein I. , Johansen Tor A. , Dahl Andreas R. , Miyazaki Michel R. , Pedersen Eilif , Rokseth Børge , Skjetne Roger , Sørensen Asgeir J. , Thorat Laxminarayan , Utne Ingrid B. , Yum Kevin K. , Mathiesen Eirik
Published: October 2015

In this paper, we present a system simulator of a marine vessel and power plant which contains the mechanical system with diesel engines, propellers, steering gear, and thrusters; the electrical system with generators, switchboards, breakers, and motors; and the plant level controllers with dynamic positioning controller, thrust control, and power management system. Interconnections are possible to simulate by using a multi domain simulator. This is important when evaluating system performance and fault handling. The simulator is implemented in Simulink and is modular, configurable and scalable. It can be extended to run on National Instruments’ cRIO embedded control and acquisition system, for real-time simulation.
A Voxel-Based Numerical Method for Computing and Visualising the Workspace of Offshore Cranes
Authors: Hatledal Lars I. , Sanfilippo Filippo , Chu Yingguang , Zhang Houxiang
Published: October 2015

Workspace computation and visualisation is one of the most important criteria in offshore crane design in terms of geometry dimensioning, installation feasibility and operational performance evaluation. This paper presents a numerical method for the computation and visualisation of the workspace of offshore cranes. The Working Load Limit (WLL) and the Safe Working Load (SWL) can be automatically determined. A three-dimensional (3D) rectangular grid of voxels is used to describe the properties of the workspace. Firstly, a number of joint configurations are generated by using the Monte Carlo method, which are then mapped from joint to Cartesian space using forward kinematics (FK). The bounding box of the workspace is then derived from these points, and the voxels are distributed on planes inside the box. The method distinguishes voxels by whether they are reachable and if they are on the workspace boundary. The output of the method is an approximation of the workspace volume and point clouds depicting both the reachable space and the boundary of the workspace. Using a third-party software that can work with point clouds, such like MeshLab, a 3D mesh of the workspace can be obtained. A more in-depth description and the pseudo-code of the presented method are presented. As a case study, the workspace of a common type of offshore crane, with three rotational joints, is computed with the proposed method.
Two-Dimensional Numerical Simulations of Wall Proximity Effect on Cylinders
Authors: Li Zhong , Jaiman Rajeev K. , Tham Mun Yew Daniel , Khoo Boo Cheong
Published: October 2015

In the oil and offshore industry, it is a common phenomenon that subsea pipelines placed on or in the proximity of the seabed are exposed to underwater waves and currents. Free spanning in sections along the length of pipeline frequently results from the erosion of sediments or the irregular terrain. This scenario can be modelled by a much more simplified set-up, where a circular cylinder situated near a plane wall is subjected to the oncoming flows. In this case, unlike the well-studied isolated cylinder, the hydrodynamic forces exerting on the near-wall cylinder will depend largely upon on the gap between the wall and the cylinder itself.

In this work, flows around a stationary and a freely vibrating two-dimensional circular cylinder near a plane boundary are numerically simulated using the Immersed Interface Method (IIM) and Finite Element Method (FEM) with Arbitrary Lagrangian-Eulerian (ALE) approach, respectively. In the case of a stationary cylinder, instead of a fixed wall, a moving wall with no-slip boundary is considered in order to avoid the complex involvement of the boundary layer and to focus only on the shear-free wall proximity effects in evaluating the lift and drag forces in the low Reynolds number regime (Re ≤ 200), with the aim of validating our IIM solver since it is the first time to apply IIM in solving flows past a near-wall cylinder. The gap ratio e/D is typically taken from 0.1 to 2.0 in this part of studies, where e denotes the gap between the cylinder and the wall and D denotes the diameter of the cylinder. The key findings are that the mean drag coefficient increases and peaks at e/D = 0.5 with the increase of e/D and keeps decreasing from e/D = 0.5 to e/D = 2.0, while the mean lift coefficient decreases monotonically with the increase of e/D. In the case of the freely vibrating cylinder in both transverse and in-line directions, the fixed wall is used to include the shear-layer effect from the bottom wall in considering the near-wall vortex-induced vibration (VIV) by using FEM with ALE approach. It can be concluded from our observations that when the cylinder is brought closer to the wall from e/D = 10.0 to e/D = 0.75, the peak transverse displacement amplitude decreases, while the peak in-line displacement amplitude increases, by greater than 20 times that of an isolated cylinder.
Response Based Design Metocean Conditions for an FPSO by the Extremum Search Within Joint Metocean PDF
Authors: Drobyshevski Y. , Wadhwa H. , Whelan J. R.
Published: October 2015

The response based analysis of a floating system aims at the prediction of extreme N-year return period responses by analysing their statistics in site-specific metocean conditions. After the extreme responses have been determined the inverse problem is solved: the most probable design metocean conditions (DMC) should be determined which cause these responses. The most probable DMC associated with a given response can be determined by using the joint probability density function (PDF) of metocean parameters. Mathematically, the most probable DMC is equivalent to a “design point”, at which the joint metocean PDF has a conditional maximum. This paper presents a method for finding the most probable DMC by the extremum search. Several numerical examples are presented to demonstrate finding the most probable DMCs for typical responses of an FPSO in North Sea environment, including global motions, wave loads, turret motions and relative wave motions. The most probable DMCs are found by the search process implemented in the space of physical metocean variables, which allows for easy interpretation of the results and exploring the response sensitivity to variability of metocean parameters.
Flow-Induced Vibrations of Single and Tandem Square Columns
Authors: Meng Zhao Guan , Pillalamarri Narasimha Rao , Mysa Ravi Chaithanya , Jaiman Rajeev K.
Published: October 2015

This work reports a set of numerical experiments to understand flow-induced vibrations of the square columns kept in a tandem arrangement. Results on the coupled force and response dynamics are presented for an isolated column and for a pair of square columns in the tandem configuration where downstream column is elastically mounted and free to oscillate in in-line and transverse directions. We assess the combined wake-induced and sharp-corner based galloping effects on the downstream column by comparing with the isolated square column counterpart. It is known that the circular cylinders undergo vortex-induced motion alone whereas motion of a square column is vortex-induced at low Re and galloping at high Re. The simulations are performed by means of a Petrov-Galerkin based finite-element solver using Arbitrary Lagrangian-Eulerian technique to account for the fluid mesh motion. The predicted results of the isolated column agree well with the available numerical results in the literature. The dimensions of the square columns and the domain are set in order to a have total blockage area of 5 %. The effects of reduced velocity on the fluid forces, wake contours, and the phase angles are analyzed. This work is also an attempt to enhance our understanding on the origin of wake-induced vibrations in a tandem arrangement of bluff bodies. In the case of tandem arrangement, upstream vortex shifts the stagnation point on the downstream column to the lower suction region. Thus a larger lift force is observed for the downstream column as compared to a vibrating isolated column. Phase difference between the transverse load and velocity of the downstream column determines the extent of upstream wake interaction with downstream column. When the column velocity is in-phase with the transverse pressure load component, interaction of wake vortex with the downstream column is minimum. For higher reduced velocities (Ur > 15), the wake downstream is very wide and irregular and the phase angle is consistently close to 180°.
An Experimental and Numerical Investigation of a Box-Shaped Object in Moonpool: A Three-Dimensional Study
Authors: Kristiansen Trygve , Ommani Babak , Berget Kjetil , Baarholm Rolf
Published: October 2015

The forced heave motion of a dummy ship model with moonpool, including a fixed box-shaped object, was realized experimentally in the Towing tank at MARINTEK. The blockage effect caused by a large object was investigated. Regular and irregular forced heave motions were imposed. In the regular motion tests, four forcing amplitudes, and 11 forcing periods near the piston-mode resonance period were tested. PVC3D (Potential Viscous Code) was used to study the regular heave motion problem numerically. PVC3D is a code developed at MARINTEK, in collaboration with Statoil RDI, which couples a Naviér-Stokes solver with the linear potential flow theory for the free-surface waves. PVC3D has in previous studies proven to be fast, robust and accurate for marine resonance problems. It has not previously been validated for object in moonpool. Here, a validation study is presented. The moonpool response is well predicted by PVC3D both for the case of empty moonpool and moonpool with object. The studied object has a non-negligible blockage effect in resonant condition.
Uncertainty Analysis of Numerical Wave Modelling With Relevance to the Dynamics of Oil Booms
Authors: Silva Monica C. , Vitola Marcelo de A. , Esperança Paulo de Tarso T. , Sphaier Sergio H.
Published: October 2015

This paper presents the first attempt to estimate the numerical uncertainty in wave propagation studies. This work was motivated by a current project at LabOceano (COPPE/UFRJ) related to studying the dynamic behaviour of oil containment booms on waves and currents. To study the dynamics of an oil boom, the influence of the viscous effect needs to be taken into consideration due to the geometry of the boom. Numerically, this can be achieved using software that solves the Navier-Stokes equation. However, prior to evaluating the wave-structure interaction using a viscous model, it is important to evaluate how the numerical model represents the wave flow only, which is the focus of the present paper. Thus, a model based on the continuity and momentum equations available in the software package StarCCM+ is used to simulate the wave propagation. The computational domain is discretized using a trimmer mesh. The results obtained for a regular wave with a wave steepness (H/L) equal to 0.025 are presented. The numerical uncertainties in the mean wave height and in the mean wave period are estimated along the domain using the methodology proposed by [8]. The wave elevation is also compared with the second-order Stokes wave solution.
The Importance of Grid Convergence Studies in the Design of a Semi-Submersible Platform
Authors: Smith Clinton , Smith Tyler , Rahumathulla Lubeena
Published: October 2015

The design of semi-submersible platforms for offshore oil and gas operations requires an iterative process between early-stage design, numerical simulation, measurements, and full-scale design. Early stage designs are evaluated using numerical simulations, which are typically validated using measurements of a scaled model tested in a wave tank. Full-scale semi-submersibles present a unique challenge, because of the sheer size of the structure. Since VIV measurements of full scale structures are not possible, numerical simulation plays an important role for evaluating vortex-induced vibration (VIV) effects in the appropriate physical regime. The quantification of error in numerical simulation results is limited to verification-type studies, in which the error is reduced by converging the solution on the computational grid. The importance of grid convergence studies in this field cannot be understated, since it is the only way to judge solution accuracy in the absence of measurement data at the full scale. In this paper, a method for a grid convergence study of vortex-induced vibration (VIV) of a model scale semi-submersible platform is presented, in which solutions are obtained using the ANSYS Fluent CFD solver. Five levels of grid refinement are used, with the finest mesh acting as the reference solution for the coarser four levels. Qualitative results of vorticity, pressure and Q-criterion (vortex identification) are presented. Quantitative results such as the nominal amplitude (A/D) of the sway motion are used for judging the convergence of the solution as the grid is refined.
Vortex-Induced Motion of Deep-Draft Semisubmersibles: A CFD-Based Parametric Study
Authors: Vinayan Vimal , Antony Arun , Halkyard John , Kim Seung-Jun , Holmes Sam , Spernjak Dusan
Published: October 2015

Deep Draft Column Stabilized Floaters (DDCSFs) provide a viable dry-tree platform for ultra-deep water applications. A particular area of concern for this concept is its susceptibility to Vortex-Induced-Motions (VIM) due to its deeper draft that results in higher column slenderness ratios than conventional semisubmersibles. The VIM characteristics of platforms have traditionally been assessed through experimental measurements but in recent years Computational Fluid Dynamics (CFD) has been used alongside experiments to predict VIM. Besides solving problems that cannot be addressed by other analysis methods, CFD can be seamlessly integrated into the overall concept design cycle where different geometric parameters can be varied to optimize the performance of the platform. While tank experiments give little fluid flow information without extensive instrumentation, CFD solutions provide flow details that can be used to improve design. CFD also provides a cost-effective solution given the high cost of experiments and facility scheduling constraints. One such DDCSF concept is the Paired-Column semi-submersible (PC-Semi) and the design has a pair of columns instead of one at each of the four sides of the platform. Several design parameters of the columns, like the inter-column spacing, the cross-sectional areas, and the shape of the respective columns can be tuned to minimize the heave response. This study takes a detailed look at the effect of the change in the column-dependent parameters on the overall VIM characteristics of the PC semisubmersible. A two-step approach is presented in which the first step is to identify aspects of the physics that are unique to VIM and then formulate a methodology to predict it within the framework of a set of commercially available CFD tools. The methodology is verified further through a comparison with available experimental data. The second step is to apply the verified methodology and CFD tools to predict the VIM performance of a range of PC-Semi concepts obtained through a systematic variation of the column-dependent design parameters in model scale. Through this exercise the critical design parameters that can either improve or prove detrimental to the VIM performance of the PC-Semi design are identified.
Vortex-Induced Motion of Floating Structures: CFD Sensitivity Considerations of Turbulence Model and Mesh Refinement
Authors: Kim Seung Jun , Spernjak Dusan , Holmes Samuel , Vinayan Vimal , Antony Arun
Published: October 2015

Vortex-Induced-Motion (VIM) is an important issue in offshore engineering as it impacts the integrity of the mooring system for floating structures such as oil platforms and wind turbine platforms. Understanding and predicting VIM is a challenging task because of the inherent complexity of vortex structure shedding and fluid-structure interaction (FSI) in high Reynolds number flows. Computational Fluid Dynamics (CFD) is one of the key tools in VIM studies and optimization of the offshore systems design. We report a CFD sensitivity study with focus on turbulence model, mesh refinement, and time-step selection. Experimental measurements in a tow-tank facility are used to validate the CFD results. Three types of tank tests are modeled numerically: current drag, oscillating free decay, and VIM. The effect of turbulence model is evaluated by comparing Delayed Detached Eddy Simulation (DDES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS) models. The influence of mesh refinement and time step is investigated by using the grid convergence index (GCI). For present geometry and flow conditions (Re∼105), the DDES turbulence model demonstrates better agreement with experimental measurement in model scale VIM compared to the URANS model. In addition, DDES simulation captures the vortex structure more realistically, as evidenced by Q-criteria and turbulent eddy viscosity distribution. Finally, we show how the mesh refinement and time step selection affect simulation accuracy. Two viscous-flow commercial solvers are tested: the finite-volume solver ANSYS-Fluent™, and the finite-element solver Altair AcuSolve™. The results of this CFD Sensitivity study provide useful guidelines for CFD simulation of FSI and VIM problems for offshore engineering applications.
A Time-Domain Boundary Elements Method Applied to Multi-Body Simulations With Large Relative Displacements
Authors: Watai Rafael A. , Ruggeri Felipe , Simos Alexandre N.
Published: October 2015

This paper presents a time domain boundary elements method that accounts for relative displacements between two bodies subjected to incoming waves. The numerical method solves the boundary value problem together with a re-meshing scheme that defines new free surface panel meshes as the bodies displace from their original positions and a higher order interpolation algorithm used to determine the wave elevation and the velocity potential distribution on new free surface collocation points. Numerical solutions of exciting forces and wave elevations are compared to data obtained in a fundamental experimental text carried out with two identical circular section cylinders, in which one was attached to a load cell and the other was forced to move horizontally with a large amplitude oscillatory motion under different velocities. The comparison of numerical and experimental result presents a good agreement.
Development of Operational Limit Diagrams for Offshore Lifting Procedures
Authors: Roncetti Leonardo , Corrêa Fabrício Nogueira , Albrecht Carl Horst , Jacob Breno Pinheiro
Published: October 2015

Lifting operations with offshore cranes are fundamental for proper functioning of a platform. Despite the great technological development, offshore cranes load charts only consider the significant wave height as parameter of environmental load, neglecting wave period, which may lead to unsafe or overestimated lifting operations. This paper aims to develop a method to design offshore crane operational limit diagrams for lifting of personnel and usual loads, in function of significant wave height and wave peak period, using time domain dynamic analysis, for a crane installed on a floating unit. The lifting of personnel with crane to transfer between a floating unit and a support vessel is a very used option in offshore operations, and this is in many cases, the only alternative beyond the helicopter. Due to recent fatal accidents with lifting operations in offshore platforms, it is essential the study about this subject, contributing to the increase of safety. The sea states for analysis were chosen covering usual significant wave heights and peak periods limits for lifting operations. The methodology used the SITUA / Prosim software to obtain the dynamic responses of the personnel transfer basket lifting and container loads on a typical FPSO. Through program developed by the author, it was implemented the automatic generation of diagrams as a function of operational limits. It is concluded that using this methodology, it is possible to achieve greater efficiency in the design and execution of personnel and routine load lifting, increasing safety and a wider weather window available.
VIV Response and Drag Measurements of Circular Cylinders Fitted With Permeable Meshes
Authors: Cicolin Murilo M. , Assi Gustavo R. S.
Published: October 2015

Experiments have been carried out on models of rigid circular cylinders fitted with three different types of permeable meshes to investigate their effectiveness in the suppression of vortex-induced vibrations (VIV). Measurements of amplitude of vibration and drag force are presented for models with low mass and damping which are free to respond in the cross-flow direction. Results for two meshes made of ropes and cylindrical tubes are compared with the VIV response of a bare cylinder and that of a known suppressor called the “ventilated trousers” (VT). All three meshes achieved an average 50% reduction of the peak response when compared with that of the bare cylinder. The sparse mesh configuration presented a similar behaviour to the VT, while the dense mesh produced considerable VIV response for an indefinitely long range of reduced velocity. All the three meshes have increased drag when compared with that of the bare cylinder. Reynolds number ranged from 5,000 to 25,000 and reduced velocity was varied between 2 and 15.
Modeling Transition for the Cylinder Flow With Verification and Validation
Authors: Rosetti Guilherme F. , Vaz Guilherme , Fujarra André L. C.
Published: October 2015

The widespread use of Computational Fluid Dynamics (CFD) tools for engineering applications is certainly positive. However, users must also be aware of the physics of the problems being modeled, as well as the shortcomings of turbulence models in use. New state-of-the-art turbulence models are currently being developed with the aim of enhancing the turbulent flow predictions but the laminar-turbulent transition is still out of the scope of most the models. Bearing upon those ideas, this paper investigates the performance of the Local Correlation Transition Model (LCTM) for the cylinder flow with Solution Verification and Validation at high Reynolds numbers. Furthermore, attention is paid to characteristics of the setup, numerics and physical conditions and we study how these features alter the results. We also bring recommendations on the use of the transition model regarding grid, setup and physical conditions. The results show much better comparison of numerical and experimental results regarding drag coefficients than seen with the SST turbulence model, even with the two-dimensional calculations done herein.
Strategies for Quantifying the Installation Reliability of Skirted Subsea Foundations
Authors: Bransby M. F. , White D. J. , Xie Y.
Published: October 2015

An increasing number of well-related and pipeline-related subsea structures (e.g. PLETs, ILTs, buckle initiators, etc.) are being placed on the seabed. Many of these structures are founded on unskirted and skirted mudmat foundations as a cost-effective, low risk solution.

Much attention has been placed in the literature on the geotechnical capacity of subsea mudmat foundations, but less attention on how these types of foundations are installed. In some soil conditions this can be a critical aspect of design: the requirement to add skirts to ensure sufficient foundation capacity comes with the penalty of increasing the necessary foundation weight to ensure that these skirts can be reliably installed. The addition of weight to a foundation increases its installation and fabrication cost and so requires careful treatment in design. As an example of this design optimization process, attention is given to dealing with uncertainty associated with variable soil conditions. It is shown how probabilistic geotechnical analysis can give a clearer perspective of cost and risk and how carefully targeted site investigation can also be used in this context.
Hydrodynamic Force Measurements on a Circular Cylinder Fitted With Peripheral Control Cylinders: Preliminary Results on the Development of VIV Suppressors
Authors: Silva-Ortega Mariana , Assi Gustavo R. S. , Cicolin Murilo M.
Published: October 2015

Recent achievements in controlling the boundary layer by moving surfaces have been encouraging the development and investigation of passive suppressors of vortex-induced vibration. Within this context, the main purpose of the present work is to evaluate the suppression of vortex shedding of a plain cylinder surrounded by two, four and eight smaller control cylinders. Experiments have been carried out on a fixed circular cylinder to investigate the effect of the control cylinders over drag reduction. Control cylinders with diameter of d/D = 0.06 were tested, where D is the diameter of the main cylinder. The gap between the main cylinder and the control cylinders varied between G/D = 0.05 and 0.15. Experiments with a plain cylinder in the Reynolds number range from 5,000 to 50,000 have been performed to serve as reference. It was found that a cylinder fitted with four control cylinders presented less drag and fluctuating lift than cylinders fitted with two or eight small cylinders.
The Impact of Multi-Body Operations on DP Capability
Authors: Giorgiutti Yann , Rezende Flávia C. , Boulland Julien , Araujo Rodrigo
Published: October 2015

As offshore activities are growing, the marine operations are becoming more complex involving the presence of few or several vessels in proximity to each other which increases the risk associated to those operations. Shuttle tankers, PSVs, floatels are often equipped with DP systems for maintaining position. The capability of these systems is defined during design phase by the DP manufacturer based on the assumption of standalone operation and considering environmental load cases prescribed in Industry standards (ex. wind, wave and current all aligned). During a realistic operational condition, however, the presence of other unities may significantly alter the loads acting on the DP vessel which will affect somehow its station keeping capacity. Furthermore, in some areas of the world, the misalignment between the environmental loads and the presence of several wave trains from different directions (ex. off-shore Brazil) shall be considered in the sake of safety of the operation. In order to provide the clients means to simulate these complex operations (including moored vessels), a DP module has been integrated to Bureau Veritas multi-body mooring software, ARIANE. In this paper, the case of a DP floatel vessel operating close to a turret moored FPSO in Brazilian waters is analyzed and the differences in the DP capacity under realistic conditions with respect to the original DP capability are presented and discussed.
Vortex-Induced Motions of a Model Scale Column Stabilized Floater With Round Columns in Calm Water and Random Waves
Authors: Pontaza Juan P. , Baar Job , Liu Nicole
Published: October 2015

When an offshore platform is exposed to a steady current, alternating vortices are shed from its aft at a regular period, creating oscillatory hydrodynamic forces. Under these forces, the platform experiences vortex-induced motions (VIM) close to its natural period. VIM still poses a design challenge for new deep-water platform moorings and risers. VIM imparts cyclic fatigue loads on the riser’s hang off and touchdown points and on the mooring chains — and an accurate prediction of VIM is important in estimating and allocating fatigue damage budgets to the risers and mooring chains.

High-performance computing numerical simulation tools are used to simulate the VIM response of a 1:50 model scale semisubmersible with round columns. Computational fluid dynamics (CFD) coupled to a structural model is used to predict the VIM response for a range of flow conditions and headings, including wave action. The simulation results are compared side-by-side to the measured response from model scale physical measurements and good agreement instills confidence towards full-scale simulations. The simulation results confirm that inclusion of wave action, in the form of a background sea state, results in diminished VIM.
Nucleation and growth of ultrathin BaTiO3 films on single terminated Nb:SrTiO3 (100) substrates for ferroelectric tunnel junctions
Authors: Ambriz-Vargas Fabian , Velasco-Davalos Ivan , Thomas Reji , Ruediger Andreas
Published: October 2015

The authors report on a new table top radio frequency (RF)-magnetron sputtering unit and process for the sputter deposition of barium titanate thin films. Like silicon substrate in conventional electronics, strontium titanate (SrTiO3) is the substrate of choice in the emerging field of oxide electronics and hence Nb doped SrTiO3 n-type semiconducting substrates were considered. The authors observe substrate etching and nonstoichiometry in the film composition at high RF-power and low processing pressure, respectively. However, films deposited at 20 mTorr and 10 W of RF power resulted in stoichiometric BaTiO3. Layer by layer (two-dimensional) growth, prerequisite for epitaxial BaTiO3 on Nb:SrTiO3 (100) substrates, were realized at 600 °C. Hysteresis loops (phase angle versus applied voltage) in piezoresponse force microscopy confirm ferroelectricity of the films. Ultrathin epitaxial BaTiO3 on Nb:SrTiO3 (100) is of great interest as a ferroelectric tunnel junction with pronounced contrast between the ON/OFF tunnel resistance.
A novel approach to background subtraction in contrast‐enhanced dual‐energy digital mammography with commercially available mammography devices: Polychromaticity correction
Authors: Contillo Adriano , Di Domenico Giovanni , Cardarelli Paolo , Gambaccini Mauro , Taibi Angelo
Published: October 2015

Purpose:

Contrast‐enhanced digital mammography is an image subtraction technique that is able to improve the detectability of lesions in dense breasts. One of the main sources of error, when the technique is performed by means of commercial mammography devices, is represented by the intrinsic polychromaticity of the x‐ray beams. The aim of the work is to propose an iterative procedure, which only assumes the knowledge of a small set of universal quantities, to take into account the polychromaticity and correct the subtraction results accordingly.

Methods:

In order to verify the procedure, it has been applied to an analytical simulation of a target containing a contrast medium and to actual radiographs of a breast phantom containing cavities filled with a solution of the same medium.

Results:

The reconstructed densities of contrast medium were compared, showing very good agreement between the theoretical predictions and the experimental results already after the first iteration. Furthermore, the convergence of the iterative procedure was studied, showing that only a small number of iterations is necessary to reach limiting values.

Conclusions:

The proposed procedure represents an efficient solution to the polychromaticity issue, qualifying therefore as a viable alternative to inverse‐map functions.
Analytic image reconstruction from partial data for a single‐scan cone‐beam CT with scatter correction
Authors: Min Jonghwan , Pua Rizza , Kim Insoo , Han Bumsoo , Cho Seungryong
Published: October 2015

Purpose:

A beam‐blocker composed of multiple strips is a useful gadget for scatter correction and/or for dose reduction in cone‐beam CT (CBCT). However, the use of such a beam‐blocker would yield cone‐beam data that can be challenging for accurate image reconstruction from a single scan in the filtered‐backprojection framework. The focus of the work was to develop an analytic image reconstruction method for CBCT that can be directly applied to partially blocked cone‐beam data in conjunction with the scatter correction.

Methods:

The authors developed a rebinned backprojection‐filteration (BPF) algorithm for reconstructing images from the partially blocked cone‐beam data in a circular scan. The authors also proposed a beam‐blocking geometry considering data redundancy such that an efficient scatter estimate can be acquired and sufficient data for BPF image reconstruction can be secured at the same time from a single scan without using any blocker motion. Additionally, scatter correction method and noise reduction scheme have been developed. The authors have performed both simulation and experimental studies to validate the rebinned BPF algorithm for image reconstruction from partially blocked cone‐beam data. Quantitative evaluations of the reconstructed image quality were performed in the experimental studies.

Results:

The simulation study revealed that the developed reconstruction algorithm successfully reconstructs the images from the partial cone‐beam data. In the experimental study, the proposed method effectively corrected for the scatter in each projection and reconstructed scatter‐corrected images from a single scan. Reduction of cupping artifacts and an enhancement of the image contrast have been demonstrated. The image contrast has increased by a factor of about 2, and the image accuracy in terms of root‐mean‐square‐error with respect to the fan‐beam CT image has increased by more than 30%.

Conclusions:

The authors have successfully demonstrated that the proposed scanning method and image reconstruction algorithm can effectively estimate the scatter in cone‐beam projections and produce tomographic images of nearly scatter‐free quality. The authors believe that the proposed method would provide a fast and efficient CBCT scanning option to various applications particularly including head‐and‐neck scan.
Finite element modelling of elastic wave scattering within a polycrystalline material in two and three dimensions
Authors: Van Pamel Anton , Brett Colin R. , Huthwaite Peter , Lowe Michael J. S.
Published: October 2015

Finite element modelling is a promising tool for further progressing the development of ultrasonic non-destructive evaluation of polycrystalline materials. Yet its widespread adoption has been held back due to a high computational cost, which has restricted current works to relatively small models and to two dimensions. However, the emergence of sufficiently powerful computing, such as highly efficient solutions on graphics processors, is enabling a step improvement in possibilities. This article aims to realise those capabilities to simulate ultrasonic scattering of longitudinal waves in an equiaxed polycrystalline material in both two (2D) and three dimensions (3D). The modelling relies on an established Voronoi approach to randomly generate a representative grain morphology. It is shown that both 2D and 3D numerical data show good agreement across a range of scattering regimes in comparison to well-established theoretical predictions for attenuation and phase velocity. In addition, 2D parametric studies illustrate the mesh sampling requirements for two different types of mesh to ensure modelling accuracy and present useful guidelines for future works. Modelling limitations are also shown. It is found that 2D models reduce the scattering mechanism in the Rayleigh regime.
Twisted logic
Authors: Clery Daniel
Published: October 2015

Germany completes the epic construction of the reactor designed in hell. Its tortuous shape may point the way forward for fusion.
Methane metabolism in the archaeal phylum Bathyarchaeota revealed by genome-centric metagenomics
Authors: Evans Paul N. , Parks Donovan H. , Chadwick Grayson L. , Robbins Steven J. , Orphan Victoria J. , Golding Suzanne D. , Tyson Gene W.
Published: October 2015

Methane cycling gets more diverse

The production and consumption of methane by microorganisms play a major role in the global carbon cycle. Although these processes can occur in a range of environments, from animal guts to the deep ocean, these metabolisms are confined to the Archaea. Evans
et al.
used metagenomics to assemble two nearly complete archaeal genomes from deep groundwater methanogens (see the Perspective by Lloyd). The two reconstructed genomes are members of the recently described Bathyarchaeota and not the phylum to which all previously known methane-metabolizing archaea belonged.

Science
, this issue p.
434
, see also p.
384
Reduced grid-cell–like representations in adults at genetic risk for Alzheimer’s disease
Authors: Kunz Lukas , Schröder Tobias Navarro , Lee Hweeling , Montag Christian , Lachmann Bernd , Sariyska Rayna , Reuter Martin , Stirnberg Rüdiger , Stöcker Tony , Messing-Floeter Paul Christian , Fell Juergen , Doeller Christian F. , Axmacher Nikolai
Published: October 2015

Early signs of dementia

There is currently no cure for Alzheimer's disease. One of the reasons could be that interventions start too late, when there is already irreversible damage to the brain. Developing a biomarker that would help to effectively start therapy at very early stages of the disease is thus of high interest. Kunz
et al.
studied neural correlates of spatial navigation in the entorhinal cortex in control study participants and individuals at risk of developing Alzheimer's. The at-risk group showed a different brain signal many decades before the onset of the disease, and they navigated differently in a virtual environment.

Science
, this issue p.
430
How safe are nanomaterials?
Authors: Valsami-Jones Eugenia , Lynch Iseult
Published: October 2015

There is still no consensus on the toxicity of nanomaterials
Assembling the wheel of death
Authors: Liu Zhonghua , Xiao Tsan Sam
Published: October 2015

A single ligand-activated protein triggers the assembly of an entire inflammasome

[Also see Research Article by

Hu
et al.

and Report by

Zhang
et al.

]
Genome Sequences of Five Additional Brevibacillus laterosporus Bacteriophages
Authors: Merrill Bryan D. , Berg Jordan A. , Graves Kiel A. , Ward Andy T. , Hilton Jared A. , Wake Braden N. , Grose Julianne H. , Breakwell Donald P. , Burnett Sandra H.
Published: October 2015

Brevibacillus laterosporus
has been isolated from many different environments, including beehives, and produces compounds that are toxic to many organisms. Five
B. laterosporus
phages have been isolated previously. Here, we announce five additional phages that infect this bacterium, including the first
B. laterosporus
siphoviruses to be discovered.
Complete Genome Sequence of Streptococcus agalactiae Serotype III, Multilocus Sequence Type 283 Strain SG-M1
Authors: Mehershahi Kurosh S. , Hsu Li Yang , Koh Tse Hsien , Chen Swaine L.
Published: October 2015

Streptococcus agalactiae
(group B
Streptococcus
) is a common commensal strain in the human gastrointestinal tract that can also cause invasive disease in humans and other animals. We report here the complete genome sequence of
S. agalactiae
SG-M1, a serotype III, multilocus sequence type 283 strain, isolated from a Singaporean patient suffering from meningitis.
Whole-Genome Sequence of Staphylococcus aureus S54F9 Isolated from a Chronic Disseminated Porcine Lung Abscess and Used in Human Infection Models
Authors: Aalbæk Bent , Jensen Louise Kruse , Jensen Henrik Elvang , Olsen John Elmerdahl , Christensen Henrik
Published: October 2015

We obtained a draft genome sequence of
Staphylococcus aureus
strain S54F9, which was isolated from a chronic disseminated porcine lung abscess and used in porcine infection models. Genes coding for a number of toxins, including enterotoxins and superantigen, were demonstrated in this strain.
Draft Genome Sequence of the Polychlorinated Biphenyl-Degrading Bacterium Pseudomonas stutzeri KF716 (NBRC 110668)
Authors: Hirose Jun , Yamazoe Atsushi , Hosoyama Akira , Kimura Nobutada , Suenaga Hikaru , Watanabe Takahito , Fujihara Hidehiko , Futagami Taiki , Goto Masatoshi , Furukawa Kensuke
Published: October 2015

Pseudomonas
stutzeri KF716 (NBRC 110668) utilizes biphenyl as a sole source of carbon and energy and degrades polychlorinated biphenyls. Here, we report the first draft genome sequence of a biphenyl-degrading strain of the species
P. stutzeri
.
Draft Genome Sequence of Yellow Pigmented Jeotgalibacillus alimentarius JY-13
T
, the First Halophile Strain of the Genus
Jeotgalibacillus
Authors: Yaakop Amira Suriaty , Chan Kok-Gan , Gan Han Ming , Goh Kian Mau
Published: October 2015

Jeotgalibacillus alimentarius
JY-13
T
(=KCCM 80002
T
= JCM 10872
T
) is a moderate halophile. In 2001, this was the first strain of the newly proposed
Jeotgalibacillus
genus. The draft genome of
J. alimentarius
was found to consist of 32 contigs (
N
50
, 315,125 bp) with a total size of 3,364,745 bp. This genome information will be helpful for studies on pigmentation as well as applications for this bacterium.
Draft Genome Sequence of Burkholderia cordobensis Type Strain LMG 27620, Isolated from Agricultural Soils in Argentina
Authors: Draghi Walter Omar , Mancini Villagra Ulises M. , Wall Luis Gabriel , Zorreguieta Angeles
Published: October 2015

Bacteria of the genus
Burkholderia
are commonly found in diverse ecological niches in nature. We report here the draft genome sequence of
Burkholderia cordobensis
type strain LMG 27620, isolated from agricultural soil in Córdoba, Argentina. This strain harbors several genes involved in chitin utilization and phenol degradation, which make it an interesting candidate for biocontrol purposes and xenobiotic degradation in polluted environments.
Draft Whole-Genome Sequence of
Xenorhabdus
sp. Strain GDc328, Isolated from the Indigenous South African Nematode Host
Steinernema khoisanae
Authors: Soobramoney Lee-Anne O. , Featherston Jonathan , Gray Vincent M.
Published: October 2015

Here, we describe the draft genome sequence of
Xenorhabdus
sp. GDc328, an endosymbiont of the native South African entomopathogenic nematode host,
Steinernema khoisanae
. The total genome size of the bacteria is 4.09 Mb. The genome comprises a total of 3,608 genes with a molecular G+C content of 44.64%.
Draft Genome Sequence of Aeromonas caviae Strain 429865 INP, Isolated from a Mexican Patient
Authors: Padilla Juan Carlos A. , Bustos Patricia , Castro-Escarpulli Graciela , Sánchez-Varela Alejandro , Palma-Martinez Ingrid , Arzate-Barbosa Patricia , García-Pérez Carlos A. , López-López María de Jesús , González Víctor , Guo Xianwu
Published: October 2015

Aeromonas caviae
is an emerging human pathogen. Here, we report the draft genome sequence of
Aeromonas caviae
strain 429865 INP which shows the presence of various putative virulence-related genes.
Moraxella catarrhalisbacteraemia and prosthetic valve endocarditis
Authors: Shahani Lokesh , Tavakoli Tabasi Shahriar
Published: October 2015

Moraxella catarrhalis, once considered a non-pathogenic coloniser of the oropharynx, has now been recognised as a true pathogen and is reported in cases of bacteraemia. A 63-year-old man with an aortic bioprosthetic valve was brought to the emergency room with altered mental status. Initial blood cultures revealed Gram-negative diplococci on Gram stain; echocardiogram showed a 5 mm vegetation on the aortic bioprosthetic valve. The blood cultures grewM. catarrhalisand the patient was treated medically for prosthetic valve endocarditis with 6 weeks of ceftriaxone and had a favourable clinical outcome.M. catarrhalishas a high prevalence of β-lactamase production and hence the patient was treated with ceftriaxone. This case highlights the importance of consideringM. catarrhalisas a pathogen in cases of invasive disease.