bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determining Side-by-Side Current Loads Using CFD and Model Tests
Authors: Koop Arjen 
Published: October 2016

When two vessels are positioned close to each other in a current, significant shielding or interaction effects can be observed. In this paper the current loads are determined for a LNG carrier alone, a Shuttle tanker alone and both vessels in side-by-side configuration. The current loads are determined by means of tow tests in a water basin at scale 1:60 and by CFD calculations at model-scale and full-scale Reynolds number.
The objective of the measurements was to obtain reference data including shielding effects. CFD calculations at model-scale Reynolds number are carried out and compared with the model test results to determine the capability of CFD to predict the side-by-side current load coefficients. Furthermore, CFD calculations at full-scale Reynolds number are performed to determine the scale effects on current loads.
We estimate that the experimental uncertainty ranges between 3% and 5% for the force coefficients CY and CMZ and between 3% and 10% for CX. Based on a grid sensitivity study the numerical sensitivity is estimated to be below 5%. Considering the uncertainties mentioned above, we assume that a good agreement between experiments and CFD calculations is obtained when the difference is within 10%.
The best agreement between the model test results and the CFD results for model-scale Reynolds number is obtained for the CY coefficient with differences around 5%. For the CX coefficient the difference can be larger as this coefficient is mainly dominated by the friction component. In the model tests this force is small and therefore difficult to measure. In the CFD calculations the turbulence model used may not be suitable to capture transition from laminar to turbulent flow. A good agreement (around 5% difference) is obtained for the moment coefficient for headings without shielding effects. With shielding effects larger differences can be obtained as for these headings a slight deviation in the wake behind the upstream vessel may result in a large difference for the moment coefficient.
Comparing the CFD results at full-scale Reynolds number with the CFD results at model-scale Reynolds number significant differences are found for friction dominated forces. For the CX coefficient a reduction up to 50% can be observed at full-scale Reynolds number. The differences for pressure dominated forces are smaller. For the CY coefficient 5–10% lower values are obtained at full-scale Reynolds number. The moment coefficient CMZ is also dominated by the pressure force, but up to 30% lower values are found at full-scale Reynolds number. The shielding effects appear to be slightly smaller at full-scale Reynolds number as the wake from the upstream vessel is slightly smaller in size resulting in larger forces on the downstream vessel.
Modeling and Simulation of the Accumulator During Active Heave Compensation Operations
Authors: Chu Yingguang , Æsøy Vilmar , Bunes Øyvind , Pedersen Eilif 
Published: October 2016

The paper presents the modeling and simulation of the thermodynamics of the accumulator system of the heave compensation system. Heave compensators in offshore and subsea applications are used to reduce the relative vertical motion of the load caused by the vessel movement. The accumulator system is an integral part of the power system, which typically can be the hydraulic system of the crane cylinders or the winch motor. The accumulators are mainly used to reduce the power consumption during heave compensation through regenerating power. Hence, the working properties of the accumulator gas become important, and these properties are very dependent upon the temperature and pressure.
Modeling of the dynamics of the accumulator and the hydraulic system is complex due to the nonlinear characteristics of fluid dynamics and thermal processes. The derivation of the constitution formula for the accumulator dynamics is described, and the modeling is presented using the Bond Graph method. The implementation of the modeling and simulation is done in a software tool called 20-sim. The temperature and pressure variations of the accumulator during heave compensation were discussed considering the impacts of the heat transfer process and the pipe flow between the accumulator and the gas bank. Compared to the experimental testing data, the simulation results appear realistic and convincing. The simulation model provides useful information for system design and analysis.
Hydrostatic Stability and Global Performance Analysis for Set TLP
Authors: Yuck R. H. , Kim S. J. , Sung S. U. , Kim H. J. , Lee D. Y. , Kim B. K. 
Published: October 2016

SET (Samsung Enhanced hull for Tendon) TLP (Tension Leg Platform) has been designed as an innovative TLP hull form with optimized number of tendons compared to conventional TLP design. SHI (Samsung Heavy Industries) designed the SET TLP to have the minimized hull weight with narrow and thin pontoon which results in the less number of tendons without any outboard extension of column or pontoon.
The SET TLP has 8 tendons which are evenly attached along with the octagonal shaped-ring pontoon. The unique shape of octagonal ring pontoon distributes the wave load and concentrated tendon loads in larger areas, which can minimize the structural reinforcement.
To verify the feasibility of the proposed hull concept with regard to the hydrostatic/hydrodynamic characteristics and tendon design, the numerical analyses for the hydrostatic stability and global performance are carried out. Hydrostatic stability is investigated for all the possible loading cases such as float-off, wet transit, tendon installation and operational conditions, and the proper tank compartments are achieved for all the scenarios without using any temporary stability module.
The global performance is validated for all the possible combinations of wave, swell, wind, current and/or squall for a site in Western Africa. Through the frequency-domain analysis and nonlinear time-domain analysis as well, the essential items such as the maximum offset/set-down/top tendon tension, minimum bottom tendon tension are examined and confirms that the certain design criteria of TLP operation are satisfied.
A Study on the Simplified Calculation Method for the Residual Ultimate Strength of Damaged Hull Structures
Authors: Toh Kimihiro , Maeda Shunsuke , Yoshikawa Takao 
Published: October 2016

In order to obtain the non-linear average stress-average strain relationships (σ-ε curves) of damaged structural members under both tensile and compressive loads, the systematical calculations are performed using the non-linear FE analysis (FEA) code, LS-DYNA, and the idealized σ-ε curves of damaged structural members are estimated from FEA results.
In addition, by introducing the idealized σ-ε curves of damaged structural members to the simplified calculation program, which is developed by authors and based on the Smith’s method, the residual ultimate strength of damaged hull structures is calculated. The residual ultimate strength of damaged hull structures is also calculated utilizing FEA, the calculation results by the simplified calculation program are compared with the results obtained from FE analyses so as to examine the accuracy of simplified calculation method.
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.
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.
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.
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.
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.