bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Gap Flow on Vortex-Induced Vibration of Side-by-Side Cylinder Arrangement
Authors: Liu Bin , Jaiman Rajeev K.
Published: October 2016

A numerical investigation of vortex-induced vibration (VIV) of a pair of identical circular cylinders placed side by side in an uniform flow has been performed. One of the cylinder is elastically mounted and only vibrates in the transverse direction, while its counterpart remains stationary. When two cylinders are placed sufficiently close to each other, a flip-flopping phenomenon can be an additional time-dependent disturbance in the range of 0.2 ≲ g* ≲ 1.2. This phenomenon was well-reported by the experimental work of Bearman and Wadcock [1] in a side-by-side circular cylinder arrangement, in which the gap flow biased toward one of the cylinders and switched the sides intermittently. Albeit one of the two cylinders is free to vibrate, this flip-flopping during VIV dynamics can still be observed. In the side-by-side arrangement, the lock-in region shrinks due to the presence of its stationary counterpart and occurs prematurely compared to that of an isolated counterpart. Similar to the tandem cylinder arrangement, in the post lock-in region, the vibration amplitude is amplified compared to the isolated counterpart. For the vibrating cylinder in the side-by-side arrangement, the biased gap flow shows a quasi-stable flow regime within the lock-in region, instead of a bi-stable regime which is reported in the stationary side-by-side arrangement. When these factors take place simultaneously, the dynamics of freely vibrating cylinder becomes complex and such a side-by-side canonical arrangement is common in offshore engineering applications, for example a floating platform operating in the side of FPSO, arrays of riser and pipelines, ships travelling in rows within close proximity and many other side-by-side operations. The chaotic fluctuation and large vibration may occur when two bluff bodies are placed closely. It often causes inevitable damages and potential risks to the offshore structures and may leads to a collision or long-term fatigue failure associated with flow-induced vibrations.
DNVGL-ST-F101 Combined Loading Criterion: Range of Application and Comparison With Other Criteria
Authors: Fyrileiv Olav , Collberg Leif , Aamlid Olav
Published: October 2016

The most essential pipeline design criterion is, of course, the pressure containment or bursting criterion normally determining the pipe wall thickness. When the pressure containment is ensured, the concern is often towards the action of the combined loading; pressure, axial force and bending moment. The combined loading criterion typically governs the installation and also set up requirements for other design issues such as seabed intervention and global buckling.

The combined loading criterion of DNV GL submarine pipeline systems standard, DNV-OS-F101 or DNVGL-ST-F101 which is its new name [1], has been modified several times, and the current version was introduced in its present form in the 2007 revision of the offshore pipeline standard. This paper discusses the current criterion for combined loading, i.e. bending moment capacity, when the pipeline is under influence of axial force and internal over-pressure. The criterion is compared with several other similar criteria from previous revisions of the DNV GL pipeline and riser standards and from other offshore pipeline standards. In addition a comparison with physical and numerical tests is given, while the background and derivation of the criterion are given in an accompanying paper by Collberg and Levold [2].
Hydrodynamic Interaction of Ice Sheet and a Floating Platform
Authors: Ahmed Aziz , Hannan Mohammed Abdul , Qian Xudong , Wei Bai
Published: October 2016

Arctic is the one of the final frontiers in the field of oil and gas exploration. It is also a potential source of the vast amount of renewable energy using wind turbines and wave energy converters. Floating platforms hold certain advantages over fixed platforms for such harsh environment, as they allow disconnection and reconnection in the event of large icebergs or vast multi-year ice floes. They are also commercially attractive as they allow redeployment in other regions during the Arctic off-peak periods. However, such platforms will still need to encounter and withstand first-year level ice of varying sizes and from different directions. Such large ice floes will interfere with the hydrodynamic response of the floater. The hydrodynamic analysis of an isolated floater without accounting for the effect of the level ice is incomplete and may result in a un-conservative prediction of the floater’s response. The lack of any simple methodology to account for the effect of level ice on the hydrodynamic behavior of the floater is the motivation behind this study. This study aims to identify the most relevant parameters affecting the multi-body hydrodynamic behavior of level ice and a single floater. A standard semi-submersible represents the floater, and a range of geometric variations of the level ice simulates the varying nature of the ice environment encountered by the floaters in the Arctic. This study validates the hydrodynamic analysis procedure against model test on an ice floe and wave interaction. The calibration of the model test provides the damping coefficient required for the frequency domain, multi-body hydrodynamic model. This investigation varies the ice orientation and distance from the floater for a detailed parametric study employing the calibrated model.

Current research finds that the presence of a comparably sized level ice floe near the floater significantly influences the hydrodynamic Response Amplitude Operator (RAO) of the floater. It can diminish the RAOs in some degree of freedom while enhancing the RAOs in other degree of freedoms. This study identifies the wave direction, ice floe distance, ice floe orientation as the most important parameters. Sway and pitch motion of the floater experienced the most enhancements due to the presence of level ice floe along the incoming wave direction. Additionally, this study proposes some initial upper bound values to account for the effect of level ice floes on the RAOs generated from a single body hydrodynamic analysis.
Finite Element Analysis of Longitudinal Bending Collapse of Container Ship Considering Bottom Local Loads
Authors: Tatsumi Akira , Fujikubo Masahiko
Published: October 2016

The purpose of this research is to clarify the effect of bottom local loads on the hull girder collapse behavior of large container ship (8000TEU class) A 1/2+1+1/2 hold model of container ship is analyzed using implicit finite element method. The results reveal two major causes of reduction of hull girder ultimate strength due to local loads. One is biaxial compressive stresses induced at outer bottom. Thus, smaller hogging moment can induce a collapse of bottom panels. The other is a reduction of effectiveness of inner bottom that is on the tension side of local bending. As a result, the container ship attains hull girder ultimate strength with smaller spread of collapse region compared to that under pure bending.
Prediction of Facies Distribution in a Clastic Reservoir Using a Hidden Markov Model Combined With an Expectation-Maximization Algorithm
Authors: Suk Hwasoo , Min Baehyun , Kang Joe M. , Jeong Cheolkyun
Published: October 2016

This study determines facies distribution in a clastic reservoir using a hidden Markov model combined with an Expectation-Maximization algorithm. Iterating expectation and maximization steps of the algorithm builds the hidden Markov model by tuning the model parameters including initial state distribution, state transition probability distribution, and observable symbol probability distribution. Optimized model parameters contribute to improving the predictability of facies distribution along the well trajectory using core and logging data.
Challenges for Under-Inhibition Strategies for Offshore Gas Fields With Low Production Rates Using OLGA
Authors: Seo Yutaek , Kim Jakyung , Chang Daejun
Published: October 2016

This study identifies challenges for under-inhibition strategies for offshore flowlines transporting gas-dominant fluids with low flow rates to determine the optimal concentration of hydrate inhibitor. The offshore gas fields considered in this study contains four wellheads, two manifolds, and one flexible riser. The distance between the offshore platform and the manifold is about 20 km with the maximum water depth of 250 m. The commercial multiphase flow simulation tool, OLGA, is used to simulate the operation conditions of the gas fields. The liquid holdup, temperature-pressure profiles, and the accumulated amounts of MEG (Mono-ethylene Glycol) with the distance along the pipeline are calculated during the steady state operation. The obtained results present that at least 44 wt% of MEG is required to completely avoid the hydrate formation when the shut-in condition of the flowline is assumed to be 3 °C and 90 bar. The production rate of base case is about 200 MMscfd and it may decrease to 40 MMscfd in the end of the design life. The accumulated amounts of MEG in the flowline is increased, mainly due to the increase in the accumulated liquid holdup in the pipeline when the production rate is decreased. The injected MEG aqueous solution from each wellhead which has relatively higher density than gas and condensates is stayed in the low spot of the pipeline due to the slower liquid velocity. This system is evaluated to identify the possibility of hydrate blockage formation. An experiment using high pressure autoclave is performed to validate the effect of under-inhibition system with MEG and the kinetic performance of MEG. The optimal concentration of THI (Thermodynamic Hydrate Inhibitor) considering the accumulated amounts in the flowline is calculated from the simulation and experimental results.
Analysis of Thermal Residual Stress on Large Thickness Polypropylene Joints as in a Reel-Lay System
Authors: Reaves Kristopher , Pascali Raresh , Rypien David
Published: October 2016

The purpose of this document is to be an initial study into the affects that increased insulation thickness requirements have on a typical field joint. An observed increase in joint failures has begun to occur with larger insulation thickness requirements which requires justification as to a possible and probable cause. The method of failure that is looked into in this document is the increase in comparative stress at the bonding joints caused by the increased stress of the comparatively increased thermal shrinkage and resultant residual thermal stress. This is analyzed through an ABAQUS simulation for current stress of the common 3in insulation thickness and the resultant stress of increasing the insulation to a 4 in thickness. The increase in stress upwards of 30% can be a cause of concern when paired with bending due to the requirements of reel lay installation methods.
Experimental and Numerical Investigation on the Effect of Varying Hull Shape Near the Water Plane on the Mathieu-Type Instability of Spar
Authors: Senthil Kumar N. , Nallayarasu S.
Published: October 2016

Spar platforms have been used for oil and gas exploration in deep water for the past two decades. Spar experience low heave and pitch motions in operating conditions with its deep draft and large inertia. The heave motions can be large when encountered by long period swells. These resonant response leads to unstable motions due to heave-pitch coupling in spar platforms when the heave/pitch natural period ratio is 0.5, 1.0, 1.5 and 2.0, referred to as Mathieu-type instability. This instability can be avoided by changing heave or pitch natural periods, so that the heave-pitch coupling can be avoided.

The buoy form Spar proposed in this study is a cylindrical hull with curved surface near the water plane. A classic Spar of 31 m diameter and deep draft buoy form Spars with 25 m and 20 m diameter at the water plane area have been considered. The moon pool diameter of 12.5 m and the displacement of 63000 tonnes are maintained for all Spars. The experimental investigations are conducted using 1:100 scale models in the wave flume. Numerical simulations have been carried out using panel method.

The classic Spar experiences Mathieu-type instability, since the heave/pitch natural period ratio is 0.5. The heave natural period of the buoy form Spar is higher than the classic Spar by 24% and 72%. The heave/pitch natural period ratio of the first buoy form Spar with 25 m diameter at the water plane area is 0.667; hence the heave-pitch coupling is avoided. The second buoy form Spar with 20 m diameter at the water plane area does not experience Mathieu-type instability, even though the heave/pitch natural period ratio is 1.0. Also the heave natural period of the second buoy form Spar is 36s (3.6 s in scale model) which is much above the design wave period. The possibility of Mathieu-type instability is avoided in the Spar by varying the hull shape near the water plane.
Numerical Simulation of a Tidal Turbine Based Hydrofoil With Leading-Edge Tubercles
Authors: Shi Weichao , Atlar Mehmet , Seo Kwangcheol , Norman Rosemary , Rosli Roslynna
Published: October 2016

The tubercles along the leading edges of the humpback whale flippers can provide these large mammals with an exceptional maneuverability. This is due to the fact that the leading-edge tubercles have largely a 3D benefit for the finite hydrofoils, which can maintain the lift, reduce the drag and delay the stall angle. Newcastle University launched a series study to improve a tidal turbine’s performance with the aid of this concept.

This paper presents a numerical simulation of the tested hydrofoil, which is representative of a tidal turbine blade, to investigate the flow around the foil and also to numerically model the experiment. This hydrofoil was designed based on an existing tidal turbine blade with the same chord length distribution but a constant pitch angle. The model tests have been conducted in the Emerson Cavitation Tunnel measuring the lift and drag. The results showed that the leading-edge tubercles can significantly improve the performance of the hydrofoil by improving the lift-to-drag ratio and delaying the stall.

By applying Shear Stress Transport (SST), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) via using the commercial CFD solver, Star-CCM+, the tested hydrofoil models were simulated and more detailed flow information has been achieved to complement the experiment. The numerical results show that the DES model is in close agreement with the experimental results. The flow separation pattern indicates the leading-edge tubercles can energize the flow around the hydrofoil to keep the flow more attached and also separate the flow into different channels through the tubercles.
An Experimental Study on Performance Verification of the New Type High Performance Anchor
Authors: Masuda Mitsuhiro , Minami Kiyokazu
Published: October 2016

In order to prevent the accident of the ships under anchorage, an anchor is a very important tool. The anchor with various types and performances has been developed over the centuries. For example, JIS types and AC-14 types are mostly applied to Japanese ships at present. However, marine accidents by dredging anchor are eliminated even now. As for it, there is a problem in the shape of an anchor. The purpose of this research is to develop a higher performance anchor. In this paper, new type high performance anchor is developed. And, anchor water tank experiment for performance verification of new type high performance anchor is carried out. As a result, the usefulness of the new type high performance anchor was confirmed.
Flow-Induced Motion of an Elastically Mounted Circular Cylinder With Roughness Strips at Different Angles of Attack
Authors: Zhang Li , Shangguan Qiyang , Ding Lin , Chen Yanrong , Ye Qianyun
Published: October 2016

Flow-induced motions (FIM) of an elastically mounted circular cylinder with roughness strips at different angles of attack are investigated by 2-D URANS simulations based on the open source CFD tool OpenFOAM. The cylinder is constrained to one degree of freedom motion in the transverse direction. Two selectively distributed roughness strips on cylinder surface are used to enhance the FIM of the cylinder. Simulations are conducted at Re = 60,000 and Re = 100,000 with the angle of attack, αattack, varies from 0° to 90°. Amplitude response, frequency response, and near-wake structures of the cylinder are discussed in numerical results. The simulation results indicate that both suppression and enhancement of FIM are observed for the cylinder as the angle of attack rises from 0° to 90°. For αattack≥ 55°, the near-wake region becomes quite slender and vortex shedding is suppressed. The FIM of the cylinder is greatly inhibited when αattack ≥55°. In addition, a complex vortex reattachment observed in the near-wake region intensifies the fluid-structure interactions and causes obviously higher amplitude.
Design Approach for CALM Buoy Moored Vessel in Squall Conditions
Authors: Brown Alison , Gorter Ward , Paalvast Mark , Kymmell Jelte
Published: October 2016

This paper focuses on examining the response of a vessel moored to a Catenary Anchor Leg Mooring (CALM) buoy in squall conditions. This type of mooring arrangement is typically a temporary mooring used for loading and offloading product or a temporary arrangement used during construction and typically selected for shallow water locations, often in tropical environments when conditions are otherwise relatively benign. Squalls are mesoscale convective systems that cause rapid increases in wind speed and are often associated with large changes in wind direction and also occur mostly in tropical environments. Hence for some locations squall events are the design drivers for this mooring arrangement and are particularly important due to the imperfect squall forecasts available to the industry. To understand the risks in a squall environment the vessel-CALM buoy system is modelled for a range of both squall conditions and associated environmental conditions, covering typical associated wave and current conditions by season and direction. A response-based approach is used to determine the design parameters for the extreme loads, extrapolated using a peak over threshold (POT) approach and using a Generalized Pareto Distribution (GPD), for the vessel-CALM buoy system. The method for this approach is described in detail and contrasted with previous industry approaches.
Numerical Simulation of Extremely Nonlinear Interaction Between Solitary Wave and Flat Plate
Authors: Wang Jiadong , He Guanghua , Zhang Dehe
Published: October 2016

A numerical wave tank that specialized to Navier-Stokes equation was established by a CIP (Constrained Interpolation Profile) method in present study. The numerical model is used to simulate the strongly nonlinear interaction between the solitary wave and a horizontal two-dimensional plate. Most of all, hydrodynamic forces acting on the plate due to solitary wave are investigated in both submerged cases and elevated cases. Sufficient numerical simulations with parameters varied, including different water depths, submergence depths, elevations above the still water level and wave amplitudes are carried out. The time series for hydrodynamic forces and the extremum of horizontal and vertical force are presented in this paper for some significant conclusions. The numerical results are compared with experimental data is in good agreement.
The EXWAVE JIP: Improved Procedures to Calculate Slowly Varying Wave Drift Forces on Floating Units in Extreme Seas
Authors: Fonseca Nuno , Stansberg Carl Trygve , Nestegård Arne , Bøckmann Arne , Baarholm Rolf
Published: October 2016

The EXWAVE Joint Industry Project (JIP) was initiated with the aim of improving methods and standard industry practice in design prediction of nonlinear wave loadings on Mobile Offshore Drilling Units (MODUs) induced by severe and steep seastates. The focus is on slowly varying wave excitation, including wave-current interaction effects. The present paper describes the technical background which led to the EXWAVE JIP, the project objectives, the planned work program and initial results.

An important part of the work program consists on performing model tests with representative floating structures. Two floating structures have been selected for investigation, namely a semi-submersible drilling rig and a floating production storage and offloading vessel (FPSO). Comparisons between experimental results and standard numerical calculations are presented for the semi-submersible. Computational fluid dynamics (CFD) is applied for detailed analysis and interpretation of complex physical phenomena.
Power Performance Assessment of the Tidal Turbine Sabella D10 Following IEC62600-200
Authors: Paboeuf Stéphane , Yen Kai Sun Pascal , Macadré Laura-Mae , Malgorn Gaël
Published: October 2016

Recently, the tidal turbine Sabella D10 has been installed in the Fromveur Passage, off Ushant Island, in France. Sabella D10 is a 1 MW tidal turbine fully submerged and laid on the seabed with a horizontal axis and 6 blades. It is the first French tidal turbine producing electricity and connected to the electrical network. As tidal turbines are emerging technologies, the demonstration of the power performance in real conditions is vital for designers. Currently, few full scale prototypes have been tested at sea and even less have been integrated into the electricity grid. Due to this context, the standard IEC62600-200 Electricity producing tidal energy converter - power performance assessment has been applied only on a limited number of turbines and, as a consequence, industrials have a limited feedback on the use of the IEC62600-200.

The aim of this paper is to detail the IEC62600-200 requirements for the power performance assessment, and the application case on the tidal turbine Sabella D10. The technical specification IEC62600-200 was issued in 2013 and describes the procedure for the power performance assessment of the tidal converters. This technical specification gives requirements for the site and test conditions, the measurement procedures and their exploitation to obtain the power curves. Finally, the reporting format of the results, is detailed to provide a complete document to the certification body. In the framework of the project Sabella D10, funded by ADEME, the power curves of the tidal turbine prototype D10 of Sabella have been established in cooperation with Sabella and Bureau Veritas according to IEC62600-200. They worked together for the interpretation of the technical specification, the exploitation of the measurements and the presentation of the results.

The global procedure of IEC has been followed however some adaptations have been made to take into account the Sabella D10 specifics and site characteristics. Indeed, the Sabella D10 project started before the IEC62600-200 publication and some requirements have not been anticipated at the beginning of the project. The first objective of this analysis is to challenge the IEC methodology with an analysis of a real set of production data and to demonstrate the applicability of the technical specification. Additionally, the assumptions and the deviation with the IEC will be presented and some improvements of the standard will be proposed in conclusion.
Effect of Reeling on Pipeline Structural Performance
Authors: Liu Yafei , Kyriakides Stelios
Published: October 2016

The winding and unwinding of a pipeline in the reeling installation process involves repeated excursions into the plastic range of the material, which induce ovality and changes to the mechanical properties. We present two modeling schemes for simulating reeling/unreeling capable of capturing these changes and can be used to assess their impact on the structural performance of the pipeline in deeper waters. In the first model, the complete 3-D reeling process is simulated through a finite element model that includes proper treatment of contact and nonlinear kinematic hardening for plasticity. The second model includes the pipe geometric cross sectional nonlinearities, contact, and nonlinear kinematic hardening, but variations along the length of the line are neglected. Instead, an axially uniform curvature/tension loading history is applied that corresponds to that experienced by a point of the line during the process. The two models are used to simulate a set of experiments in which tubes were wound and unwound on a model reel at different values of tension. Both models are shown to reproduce the induced ovality and elongation very well. Several of the reeled tubes were subsequently tested under external pressure demonstrating the effect of the reeling cycle on structural performance. The two models are shown to also reproduce the decrease in collapse pressure as a function of the applied back tension. Comparison of the results of such simulations highlight when a fully 3-D model is required and when the simpler 2-D model is adequate for evaluating the structural performance of a reeled pipe.
Hydro-Elastoplastic Analysis for Predicting Collapse Behavior of VLFS Under Large Waves
Authors: Iijima Kazuhiro , Sakai Megumi , Fujikubo Masahiko , Tatsumi Akira
Published: October 2016

This paper addresses collapse behavior of Very Large Floating Structure (VLFS) under large wave loads, as part of risk analysis. In predicting the consequence of collapse, the deformation of VLFS consisting of elastic and plastic ones under the large load event must be addressed. The deformation interacts with the fluid around it. Therefore, hydro-elastoplastic analysis needs to be developed. The whole VLFS structure is modeled as two elastic beams with an elasto-plastic hinge embedded at the connection. The deformation behavior is formulated by using finite element method (FEM). The hydrodynamic behavior is modeled by using Rankine source panel method based on two-dimensional and time-domain potential theory. The two domains are coupled. A series of simulation and tank test results for the basic collapse behavior of VLFS is presented.
Modulation Instability and Extreme Events Beyond Initial Three Wave Systems
Authors: Chabchoub Amin , Waseda Takuji
Published: October 2016

One possible mechanism that models the dynamics of extreme events in the ocean is the modulation instability (MI). The latter has been discovered in the 60s and significant progress in understanding the physics of modulationally unstable deep-water waves has been achieved since then. The MI instability starts its dynamics from a minor periodic perturbation of a regular Stokes wave, which enhances in amplitude, generating therefore periodic large waves, within the specific range of modulation period. In the spectral domain the same process starts from in amplitude very small symmetric side-band pair, lying in the unstable range from the main carrier frequency peak, which then starts to grow while generating by their own a side-band cascade. We report a new type of periodically modulated and unstable Stokes waves which initial dynamics starts from more that one unique unstable side-band pair. Laboratory experiments have been conducted in a large water wave basin, while numerical simulations have been performed using the modified nonlinear Schrödinger equation and the boundary element method. Both, experiments and numerical simulations are in reasonable agreement. Furthermore, the validity, limitations and applicability of such models will be discussed in detail.
Proposed Methodology for Extending the Lives of Steel Catenary Risers Connected to Floating Production Systems
Authors: Mekha Basim
Published: October 2016

Extending the life of steel catenary risers is becoming one of the main subjects of interest nowadays as many steel catenary risers (SCRs) are approaching their design lives. Many of the risers in this situation are export risers, which may require extended design lives due to development of new production fields being tied back to the floating facilities they service.

There have been no specific methodologies or defined approaches for dealing with this subject. The conservatism of the design methodology, which is usually adopted for the detailed design of new risers, will have to be adjusted when evaluating existing risers with known environmental and operational history as well as fabrication and installation data.

This paper will describe a proposed methodology and potential approach for extending the lives of existing steel catenary risers (SCRs) connected to floating structures in the Gulf of Mexico. It will highlight the essential steps that should be taken to evaluate the risers’ current status and to determine their already consumed fatigue lives. The proposed methodology for calculating the riser consumed fatigue damage will be discussed and compared with the typical but conservative approach that is usually taken during the detailed design of new risers.

The next step will then be the calculation of the riser remaining life including the treatment of its already consumed fatigue damage. The proposed methodology will also cover the relationship between the safety factors and availability of actual data during the life of the risers. Fracture mechanics assessment for riser welds and their flaws is another step that needs to be performed to support the fatigue analysis calculation.

Internal and external inspection of the risers, including pipe welds, pipe corrosion and possible pitting, is a work in progress at this stage and would probably be essential part of any riser life extension program. Some discussion will also be provided for the risers’ special components (e.g. strakes, coating, cathodic protection, and top termination units) to ensure all aspects are covered in the evaluation of the riser life extension.
Seismic Soil-Structure Interaction Design Considerations for Offshore Platforms
Authors: Chen Jiun-Yih , Litton Richard , Ku Albert , Fraser Ramsay , Jeanjean Philippe
Published: October 2016

Offshore platforms for oil and gas production in seismic regions around the world are often required to be designed for seismic hazards according to International Standards (e.g., ISO 19901-2 [1] and ISO 19902 [2]). This paper discusses three important aspects of the nonlinear dynamic time history analysis commonly used to design for Abnormal Level Earthquakes (ALE) in light of findings from recent centrifuge modeling and numerical simulation of the response of offshore structures under earthquake excitations. First, greater-than-expected ground motion de-amplification has been observed in a recent seismic soil-structure interaction centrifuge program for typical “soft” marine clays with undrained shear strength up to 100 kPa per API RP 2GEO [3]. Second, the current industry practice of using uniform down-pile ground motions in the time history analysis tends to underestimate pile bending moments. Use of depth-varying ground motions is strongly recommended to better characterize pile bending moments. Alternatively, a simplified design approach is proposed to account for the higher bending moments from the use of more realistic depth-varying ground motions. This approach is illustrated with a design example. Lastly, hysteretic and radiation damping in soil-structure interaction is discussed. Modeling of hysteretic damping is achieved using nonlinear elasto-plastic soil springs with unload-reload behavior following Masing’s rule, whereas modeling of radiation damping is achieved using viscous dashpots in a parallel or series arrangement with the axial and lateral soil springs and with dashpot coefficients based on O’Rourke and Dobry [4]. The centrifuge data show that proper modeling of radiation damping is important to accurately predict pile load and settlement.
Performance of Two-Phase Flow Models on the Prediction of Oscillatory Flow Conditions
Authors: Posada Catalina , Waltrich Paulo
Published: October 2016

The present investigation presents a comparative study between two-phase flow models and experimental data. Experimental data was obtained using a 42 m long, 0.05 m ID tube system. The experimental data include conditions for pressures ranging from 1.2 to 2.8 bara, superficial liquid velocities 0.02–0.3 m/s, and superficial gas velocity ranges 0.17–26 m/s.

The experimental data was used to evaluate the performance of steady-state empirical and mechanistic models while estimating liquid holdup and pressure gradient under steady-state and oscillatory conditions. The purpose of this analysis is first to evaluate the accuracy of the models predicting the liquid holdup and pressure gradient under steady-state conditions. Then, after evaluating the models under state-steady conditions, the same models are used to predict the same parameters for oscillatory and periodic conditions for similar gas and liquid velocities. The transient multiphase flow simulator OLGA, which has been widely used in the oil and gas industry, was implemented to model one oscillatory case to evaluate the prediction improvement while using a transient instead of a steady-state model to predict oscillatory flows.

For the model with best performance for steady-state pressure gradient prediction, the absolute percentage error is 12% for Uls = 0.02 m/s and 5% for Uls = 0.3. For oscillatory conditions, the absolute percentage error is 30% for Uls = 0.02 m/s and 4% for Uls = 0.3. OLGA results underpredict the experimental pressure gradient under oscillatory conditions with errors up to 30%. Therefore, it was possible to conclude that the models can predict the average of the oscillatory data almost as well as for steady-state conditions.
Response of a CALM Buoy Moored Vessel in Squall Condition
Authors: Paalvast Mark , Kymmell Jelte , Gorter Ward , Brown Alison
Published: October 2016

This paper reviews the response of a hawser moored vessel to squalls and addresses a novel method for obtaining statistically reliable design loads. Industry paradigms related to squall selection for analysis input are reviewed and renewed.

A benchmark database consisting of more than 15,000 unique squall-wave-current induced extreme values enables the validation of a range of less computationally demanding analysis and squall selection methods.

Extreme values are extrapolated to a design value using a Peak Over Threshold (POT) method to fit a Generalized Pareto Distribution (GPD). The influence of associated metocean conditions and squall characteristics on the vessel response is presented. By means of bootstrapping a satisfactory population size for design purposes is studied. The findings challenge common design practices currently employed throughout the industry.
Waste Rejection on Seafloor by Hydrocyclone for Economic Seafloor Massive Sulfide Mining
Authors: Takeda Yosuke , Yamazaki Tetsuo , Arai Rei , Nakatani Naoki
Published: October 2016

Many seafloor massive sulfide (SMS) deposits have been discovered in Japan’s exclusive economic zones (EEZ). They have some useful metals and are expected to become future metal resources. In Japan, because of an expensive waste disposal cost, it seems to be difficult to realize the SMS mining. Adding a function of primary waste separation from metal-rich parts of SMS ore on seafloor by a hyrocyclone is proposed to overcome the problem. The water flow structure in a model hydrocyclone is observed in the study at first. Secondly, the performance of separation using differences in specific gravities of particles by the hydrocyclone is experimentally examined. Finally, the application of hydrocyclone in the actual sea area is examined. The result shows that 67% of larger specific gravity are collected and 67% of smaller one are rejected. From the separation efficiency, the hydrocyclone method is recognized to have a high possibility of application in the actual sea area.
Numerical Simulation of Submarine Surfacing With Six Degrees of Freedom in Regular Waves
Authors: Jiang Weijian , Wang Zhilin , He Ran , Wang Xianzhou , Feng Dakui
Published: October 2016

Submarine surfacing in waves is three dimensional unsteady motion and includes complex coupling between force and motion. This paper uses computational fluid dynamics (CFD) to solve RANS equation with coupled six degrees of freedom solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface. Computations were performed for the standard DARPA SUBOFF model. The structured dynamic overset grid is applied to the numerical simulation of submarine surfacing (no forward speed) in regular waves and computation cases include surfacing in the calm water, transverse regular waves with different ratio of wave height and submarine length (h/L = 0.01, 0.02, 0.03, 0.04) and transverse regular waves with different ratio of wave length and submarine length (λ/L = 0.5, 1, 1.5). The asymmetric vortices in the process of submarine surfacing can be captured. It proves that roll instability is caused by the destabilizing hydrodynamic rolling moment overcoming the static righting moment both under the water and in regular waves. Relations among maximum roll angle, surfacing velocity fluctuation and wave parameters are concluded by comparison with variation trend of submarine motion attitude and velocity of surfacing in different wave conditions. Simulation results confirm that wave height h/L = 0.04 and wave length λ/L = 1.5 lead to surfacing velocity fluctuation significantly. Maximum roll angle increases with the increase of wave height and wave length. Especially the law presents approximate linear relationship. Maximum roll angle with wave height (h/L = 0.04) can reach to 7.29° while maximum roll angle with wave length (λ/L = 1.5) can reach to 5.79° by contrast with 0.85° in calm water. According to the above conclusions, maneuverability can be guided in the process of submarine surfacing in waves in order to avoid potential safety hazard.
Stochastic Linearization and its Application in Motion Analysis of Cylindrical Floating Structure With Bilge Boxes
Authors: Shao Yan-Lin , You Jikun , Glomnes Einar Bernt
Published: October 2016

To account for the viscous effects of damping devices, for instance, bilge keels or bilge boxes, on the motions of ships and offshore structures, Morison’s equation is often adopted as an empirical but practical approach in the design process. In order to combine the standard engineering panel method with the drag term in Morison’s equation, and remain in the frequency domain, the drag term has to be linearized based on, for instance, stochastic linearization. In this paper, the stochastic linearization scheme is implemented in an in-house code and verified through the comparison with the DNV GL software WADAM.

The model test results of a large cylindrical FPSO with bilge box are used to calibrate the drag coefficients in the Morison’s equation. When the linearized drag forces are included, heave motion RAOs correspond better to the model test results. However, the predicted natural periods of heave motions are seen to be smaller than those obtained from model tests. It is suspected that the viscous flow separation around the bilge box increases the added mass of the unit beyond what is predicted by potential flow alone. Discussions are made on the effect of viscous added mass on the heave natural period.

It is quite common to only include the damping effects in the motion analysis for large offshore structures and ignore the contribution of the viscous effects on the excitation force. For the considered cylindrical FPSO, this paper demonstrates that the viscous excitation force can be important in survival conditions.
The Design Development on the Mooring System of a Floating Barge Positioned in the Shallow Water Zone
Authors: Kim YoungBok
Published: October 2016

This study is aimed to develop the dynamic analysis technique for a floating aquaculture in a shallow water region under the harsh sea condition. In case of the installation region to transform from a coastal area to the offshore area, the influence of sea bed with sea waves on the mooring lines was announced to be significant by other authors. In this study, the numerical tool was developed to solve dynamic behavior of the floating barge coupled with mooring lines in a shallow zone of the sea considering the influence of sea bed on the floating system.
Non-Linear 3D Hydrodynamics of Floating Wind Turbine Compared Against Wave Tank Tests
Authors: Heilskov Nicolai F. , Petersen Ole Svenstrup
Published: October 2016

Assessment of wave-structure interaction in terms of combined hydrodynamic stability and structural survivability is paramount in extreme wave conditions. Components of CFD methodologies needed for accurately capturing the detailed motion of a floating wind turbine (FWT) in survival sea-state is the focus of the study. Physical wave tank tests of a Tension Leg Platform (TLP) concept with four moorings are applied as a first validation, due to its simplicity from a CFD point of view. Two different codes have been objects of study, namely the open source code OpenFOAM® with a flexible mesh approach and the commercial CFD code StarCCM+ with the overset mesh method. The influence of the surface capturing algorithm (VOF method) and the two-way coupling of the six degrees-of-freedom body motion solver and the hydrodynamic solver have been identified as the crucial components in CFD simulation of the FWT. A major advantage of StarCCM+ was that it does not suffer from the same sensitivity as OpenFOAM to the fact that motion of the floating body is strongly coupled to the solution of the hydrodynamics (a stiff FSI problem) which led to instability of the numerical solution. The results obtained with StarCCM+ are comparable with the measured motion of and tension forces on the TLP in both in regular waves and irregular waves.
A Comparative Study of Different Grid Models for an Oil Spill Under Water
Authors: Jiang Meirong , Li Zhigang , Yu Jianxing , Yin Hanjun , Jiang Ying
Published: October 2016

Due to the serious results of an oil leakage of a subsea pipeline, the prediction of the numerical simulation must be modeled accurately and quickly. To select a proper numerical model to simulate the complex flow, a comparative study with different grid models is carried out. A two dimensional oil diffusion model under the ocean current is established using the finite volume method. Based on the structured grid, the volume of fluid method is employed to track the interface of the multiphase flow. Two kinds of grid models, the sparse and the dense grid, are simulated under the same conditions. Three cases are selected from the typical experiments in Fan (1967). The available experimental data in the oil spill test of Fan (1967) are employed as a criterion for the comparison between different grid models. According to the calculation results, a comparative analysis of the oil diffusing form, the arriving time to the surface, and the lateral drifting distance is studied between the two grid models, respectively. The surface diffusion range and the simulated time are also introduced to do the comparison for the grid density.
Investigating routes toward atomic layer deposition of silicon carbide: Ab initio screening of potential silicon and carbon precursors
Authors: Filatova Ekaterina A. , Hausmann Dennis , Elliott Simon D.
Published: October 2016

Silicon carbide (SiC) is a promising material for electronics due to its hardness, and ability to carry high currents and high operating temperature. SiC films are currently deposited using chemical vapor deposition (CVD) at high temperatures 1500–1600 °C. However, there is a need to deposit SiC-based films on the surface of high aspect ratio features at low temperatures. One of the most precise thin film deposition techniques on high-aspect-ratio surfaces that operates at low temperatures is atomic layer deposition (ALD). However, there are currently no known methods for ALD of SiC. Herein, the authors present a first-principles thermodynamic analysis so as to screen different precursor combinations for SiC thin films. The authors do this by calculating the Gibbs energy ΔG of the reaction using density functional theory and including the effects of pressure and temperature. This theoretical model was validated for existing chemical reactions in CVD of SiC at 1000 °C. The precursors disilane (Si2H6), silane (SiH4), or monochlorosilane (SiH3Cl) with ethyne (C2H2), carbontetrachloride (CCl4), or trichloromethane (CHCl3) were predicted to be the most promising for ALD of SiC at 400 °C.
Factors influencing the performance of patient specific quality assurance for pencil beam scanning IMPT fields
Authors: Trnková P. , Bolsi A. , Albertini F. , Weber D. C. , Lomax A. J.
Published: October 2016

Purpose

A detailed analysis of 2728 intensity modulated proton therapy (IMPT) fields that were clinically delivered to patients between 2007 and 2013 at Paul Scherrer Institute (PSI) was performed. The aim of this study was to analyze the results of patient specific dosimetric verifications and to assess possible correlation between the quality assurance (QA) results and specific field metrics.

Methods

Dosimetric verifications were performed for every IMPT field prior to patient treatment. For every field, a steering file was generated containing all the treatment unit information necessary for treatment delivery: beam energy, beam angle, dose, size of air gap, nuclear interaction (NI) correction factor, number of range shifter plates, number of Bragg peaks (BPs) with their position and weight. This information was extracted and correlated to the results of dosimetric verification of each field which was a measurement of two orthogonal profiles using an orthogonal ionization chamber array in a movable water column.

Results

The data analysis has shown more than 94% of all verified plans were within defined clinical tolerances. The differences between measured and calculated dose depend critically on the number of BPs, total thickness of all range shifter plates inserted in the beam path, and maximal range. An increase of the dose difference was observed with smaller number of BPs (i.e., smaller tumor) and smaller ranges (i.e., superficial tumors). The results of the verification do not depend, however, on the prescribed dose, NI correction, or the size of the air gap. There is no dependency of the transversal and longitudinal spot position precision on the beam angle. The value of NI correction depends on the number of spots and number of range shifter plates.

Conclusions

The presented study has shown that the verification method used at Centre for Proton Therapy at Paul Scherrer Institute is accurate and reproducible for performing patient specific QA. The results confirmed that the dose discrepancy is dependent on the size and location of the tumor.
Just noticeable differences of spatial cues in echoic and anechoic acoustical environments
Authors: Klockgether Stefan , van de Par Steven
Published: October 2016

The perceptual limits for detecting changes in binaural cues also define the boundaries for the perception of differences in spatial impression. This study reports just noticeable differences for interaural time delays (ITDs) and interaural level differences (ILDs) of the early part and for the interaural cross-correlation (IACC) of the early and diffuse part of binaural room impulse responses. The results show that ITDs only allow a high accuracy in localization in anechoic environments, whereas ILDs show a higher robustness against reverberation. Subjects are rather insensitive to changes in IACC, only changes that bring the IACC close to one are detectable.