bluuebunny/crossref_metadata_2025_split huggingface dataset:
Current Profile Data Sources for Engineering Design West of Shetlands
Authors: Jeans Gus , Fox Joe , Channelliere Claire 
Published: September 2014

Current profile data sources considered for derivation of engineering design criteria West of Shetland are described. The region is impacted by a variety of oceanographic processes that combine to produce a complex current regime. Reliable quantification of the resulting current profiles is required for safe and cost effective offshore exploration and field development.
A key challenge to all offshore developments is acquisition of appropriate data. Site specific measurement remains the primary current profile data source for engineering applications, with full water column coverage at sufficient resolution required for riser design. Such in-situ data are generally expensive and time consuming to collect, so there is an increasing tendency for numerical model current data to be considered.
Model data are often relatively quick and inexpensive to obtain, with the added benefit of a much longer duration, potentially allowing inter-annual variability and extreme events to be captured. However, the accuracy and reliability of numerical model data remains questionable, or unproven, in many deepwater development regions.
This paper describes a recent study in which in-situ data remained the primary source for derivation of current profile criteria for engineering design. Short duration proprietary data were supplemented by additional public domain data from nearby sites in a regional synthesis, with critical results. The performance and benefits of readily available model data are also considered.
Assessment of the Feasibility of the Arctic Sea Transportation by Using Ship Ice Transit Simulation
Authors: Valkonen Janne , Riska Kaj 
Published: September 2014

Arctic sea transportation has drawn a lot of attention in the recent years. The possibility of using a shorter route between Europe and Asia interests many actors in the shipping industry. Benefits from the shorter route may, at first, seem attractive. However, there might be factors affecting the feasibility of the route that are not obvious at first. The estimated transit speed along the Arctic route is not necessarily reached due to ice and other prevailing conditions. Simplified methods can underestimate the actual transit time, so the use of advanced methods is advisable. A thorough assessment of ship performance along the selected route can reveal factors that affect the feasibility of trans-Arctic shipping.
This paper presents how the ship transit along an Arctic route can be simulated and how the ship performance can be assessed based on the simulation results. In this paper comparative results of ship performance in different ice conditions are shown and the benefits and challenges of the ship ice transit simulations are discussed. The effect of the input ice conditions to the ship performance estimates and how the ice information from various sources can be used for the simulations are discussed.
Ship performance in the Arctic transit is tested using a probabilistic model called COSSARC for ship performance simulation in ice and open water. The tool can be used for assessing the economic feasibility of ship designs and transport concepts. One of the main benefits of the ship ice transit simulations compared to the simpler methods is that ice ridges are described in the realization of ice conditions statistically and the ship performance in ridges is modeled. A ship might get stuck in ridges and might be forced to wait for assistance from an icebreaker, or a double acting ship might travel slower than anticipated through ridge fields. This increases the transit time significantly, which is not necessarily revealed by simpler methods. The main outcome from the ship ice transit simulations described in this paper, is a more realistic estimate of transit time for a given route. This can be used as input for economic or other assessments. It is possible to estimate the probability of getting stuck in ice ridges from the ship ice transit simulation results, and thus the need for icebreaker assistance can be assessed. The probabilistic simulation of ship performance can be done in the design phase of the ship to assess various design concepts or while selecting what kind of ship or fleet of ships is the most suitable for the given transport task.
Review of Low-Constraint Fracture Resistance Testing With SENT Specimens
Authors: Zhu Xian-Kui , McGaughy Tom , Orth Fabian , Jennings Jon 
Published: September 2014

Fracture resistance is an important material property and characterized by a J-integral resistance curve (J-R curve) or a crack-tip opening displacement (CTOD) resistance curve. ASTM standard specimens with deep cracks are subject to bending dominant forces, leading to high crack-tip constraint conditions and conservative fracture resistance curves.
Actual cracks occurring in line pipes and welds are often shallow ones dominated by tensile forces, resulting in low constraint conditions. Shallow cracks have been shown to generate elevated fracture resistance curves in comparison to standard deep-crack results. To reduce the over-conservatism of standard resistance curves and to produce more realistic toughness properties to meet the needs of strain-based design approaches for pipelines, different procedures and technologies have been developed over the years to determine the low-constraint fracture resistance curves by use of the single edge-notched tension (SENT) specimens. This includes the multiple specimen method developed and standardized by DNV for J-R curve testing, the single specimen method developed by CanMet for J-R and CTOD-R curve testing, and the single-specimen method developed by ExxonMobil for CTOD-R curve testing. This paper delivers a technical review of existing fracture test methods using SENT specimens, and discusses the advantages and limitations of each method.
Wave Drift Forces and Resonance Analysis on Two Ships Arranged Side by Side
Authors: Zhang Yu , Yu Dapeng , Fu Shixiao , Guo Fei , Wei Wei 
Published: September 2014

In recent years, with the development of new ships and further utilization of marine resources, multi-body floating systems are widely used in practice. Compared with the single floating body, the movement in multi-body floating system is not only affected by the external environment, but the interaction between the bodies cannot be neglected. So analysis of hydrodynamic performance of a multi-body floating system is of great importance.
In this paper, a multi-body system consisting of two side-by-side ships is studied. The code AQWA® is used for its hydrodynamic performance analysis in frequency domain. Its hydrodynamic parameters are compared with those of the related single-ship system and the difference is obvious. The two-ship system shows a peak in motion different from single-ship system at some frequencies and its wave exciting forces have period effects. Also, negative values appear in added masses, which never occur for a single-body floating system. When the gap between the two ships is changed, there is a significant trend that the wave frequency of the peak value decreases with the gap size between the two ships.
In addition, this paper also discussed the length of wave and distance of ships ratio that the motion resonance usually happens. Through the analysis of this dimensionless parameter, a conclusion about resonance between two parallel ships is deducted.
The Identification of Power-In Region in Vortex-Induced Vibration of Flexible Cylinders
Authors: Rao Zhibiao , Resvanis Themistocles L. , Vandiver J. Kim 
Published: September 2014

This paper proposes a novel method to identify the power-in regions of long flexible cylinders subjected to vortex-induced vibration (VIV). It also attempts to address a practical problem: “Will a secondary power-in region appear after the primary power-in region is covered with suppression devices?” The source of data is a recent model test on a 38 meter long flexible cylinder, densely instrumented with fiber optic strain gauges and accelerometers.
For pipes with partial coverage of suppression devices in uniform flow, the bare region would be expected to be a power-in region and the section with suppression devices is expected to be a power-out region. Experimental data from these types of tests are used to benchmark the proposed power-in zone identification method. The method is then used to identify the power-in zones on a bare cylinder in a sheared flow.
This paper also explores the occurrence of secondary power-in regions that may exist, when suppression devices are placed in the primary power-in zone. Secondary power-in regions were observed. Lessons learned from the power-in region identification in sheared flows will be a useful tool for designer/engineers choosing where to place suppression devices.
Pipeline Roll During Reel-Lay Installation due to Piggyback DEH Cable and Local Residual Curvature
Authors: Endal Geir , Rao Venu , Ragupathy P. , Sriskandarajah T. 
Published: September 2014

Offshore pipelines may require a Direct Electric Heating (DEH) cable for auxiliary heating purposes which will be strapped as close to the pipe wall as possible at pre-determined intervals for efficient thermal performance particularly during start-up and shut-down conditions. The straps are provided with tension to maintain the orientation of the DEH cable intact. The positioning of DEH cable causes differential buoyancy and gravity loads and the associated positioning vectors giving a tendency to rotate the pipeline in the catenary.
If the pipeline inplace buckling design by residual curvature method for controlled thermal expansion during operation is adopted for the pipeline with a DEH cable, the additional imperfection in the pipeline will contribute to the pipeline’s tendency of rotation together with the imbalance in buoyancy and weight. This paper discusses the analytical approach used based on the Stiffened Catenary Calculations Method and Simplified Energy Balance Approach Method to determine the roll, the pipeline may experience to reach stable equilibrium in combination with the residual imperfection. The total work required to bend and twist the pipe from surface to seabed is estimated for twist angles at touch down between 0 and 180 degrees and in water depth of 360m.
The paper further discusses the numerical finite element analyses performed to estimate the amount of twist in the pipeline as the pipe is paid from the vessel. The analytical and numerical approaches support the view that the pipeline will have restoring moment to lay the pipeline with DEH cable in the sideways for pipe laid on seabed. Comparisons are made with the post lay test data from other projects to confirm the findings from the assessment are in agreement. The unlikely scenario of pipeline being laid with residual curvature section in a position other than in the horizontal plane and its effect on the lateral buckling behaviour on application of steady state temperature and pressure was also investigated and the results are presented in the paper.
Stochastic Analysis of a Nonlinear Energy Harvester Model
Authors: Spanos P. D. , Richichi A. , Arena F. 
Published: September 2014

Floating oscillating-bodies are a kind of wave energy converter developed for harvesting the great amount of energy related to water waves (see Falcão [1] for a review).
Although the assumptions of small-wave and linear behavior of oscillating system are reasonable for most of the time during which a floating point harvester is in operation, nonlinear effects may be significant in extreme sea states situations.
In this paper a nonlinear dynamic analysis of a point harvester wave energy converter is conducted. The model involves a tightly moored single-body floating device; it captures motion in the horizontal and vertical directions. The stiffness and damping forces, being functions of the displacement and velocity components, make the system nonlinear and coupled.
For the input forces, the erratic nature of the waves is modeled by a stochastic process. Specifically, wind-generated waves are modeled by means of the JONSWAP spectrum.
The method of statistical linearization [2] is used to determine iteratively the effective linear stiffness and damping matrices and response statistics of the system and to proceed to conducting a dynamic analysis of the harvester model.
The reliability of the linearization based approach is demonstrated by comparison with time domain integration, Monte Carlo simulation, data. This approach offers the appealing feature of conducting efficiently a variety of parameter studies which can expedite preliminary evaluations, inter alia, of competing design scenarios for the energy converter in a stochastic environmental setting.
Nonlinear Wave Amplification Around Column-Based Platforms in Steep Waves
Authors: Stansberg Carl Trygve 
Published: September 2014

The wave diffraction and upwelling around vertical columns such as platform legs and offshore wind turbine foundations is studied. Nonlinear contributions in steep wave conditions are particularly addressed. Data and analyses from a previous experiment with fixed cylinders in deep water regular and random waves are reviewed, and essential findings are highlighted. Measured extreme crests are clearly higher than linear predictions, connected with an increase in basic harmonics as well as with second-order components. Improved results are obtained with fully second-order modeling, while this is still incomplete, and such analyses can be computationally demanding as well as non-robust.
An alternative, simplified empirical nonlinear correction approach based on these findings, previously suggested for engineering design prediction of extreme crests in random waves, is validated against a re-analysis of the fixed column data. In addition, validation is also made against model test data for two floating production semis. The method agrees well with the data, taking into account the simplicity of the method and the complexity of the problem, and is a tool for early design phases. Detailed studies will still require model tests and CFD development.
Experimental and Numerical Investigation of Ship Roll Damping With and Without Bilge Keels
Authors: Kristiansen Trygve , Ruth Eivind , Firoozkoohi Reza , Borgen Henning , Berge Bjørn Ola 
Published: September 2014

This paper describes an experimental and numerical study on the effect of bilge keels on a specific offshore vessel. Forced roll and free decay experiments were carried out at MARINTEK in a joint project between VARD, DNV GL and MARINTEK during Nov. 2012. The 1:25 ship model was tested both with and without bilge keels. 19 forced roll periods were tested at 4 roll angles (2, 4, 6 and 10deg). Free decay tests were performed for initial roll angles 2, 4, 6, 10 and 15deg. Damping was extracted and compared with numerical simulations from a potential flow strip theory program (VERES) and a commercial CFD tool (StarCCM+).
Both qualitative and quantitative agreement between the experimentally and numerically obtained damping parameters was documented. Discrepancies were identified and discussed. The three different methods of investigation gave together a basis for discussing the effect of bilge keels. From the present study, it is recommended that both experimental and numerical work in combination, for both forced roll and free decay tests, should be performed to assess the damping efficiency of bilge keels.
On the Torsional Friction of Freely Rotating Short Fairing
Authors: Lie Halvor , Yin Decao , Liapis Stergios 
Published: September 2014

Vortex-induced vibrations (VIV) model tests were carried out by Shell on a 38 m flexible pipe at the MARINTEK Ocean Basin in March 2011, Trondheim. As part of the model test campaign, the pipe with short fairings under two different torsional friction conditions between riser and fairings was tested in uniform currents. Test with ‘high’ friction show small responses, tests with ‘low’ friction show distinct large responses, even though, the spectra analysis shows that the responses seem to be dominated by vortex induced forces.
Decay tests were carried out on a riser section with fairings to further investigate the torsional friction effect. Friction coefficients were calculated by ‘Coulomb damping model’, which is proved to be a suitable model for fairing-riser friction. The friction coefficients could be directly used to determine the damping ratio and implemented in numerical models. Such decay tests are especially useful to design, manufacture and install fairings in order to achieve a proper friction level and avoid unstable responses such as galloping.
Evaluation of the Stress Magnification Factor in Angled Discontinuities of Longitudinal Stiffeners
Authors: Yamatoki Shuichi , Hamamoto Yoshitaka , Gotoh Koji 
Published: September 2014

In ship hull design, longitudinal stiffeners may be twisted or knuckled to keep the continuity of strength along the vessel. This occurs at angled discontinuities such as discontinuous connections at the transverse web between two longitudinal stiffeners having different angles, e.g., a side shell longitudinal stiffener in the rounded part of the ship’s hull. Although the criteria for selection of “twist”, “knuckle”, or “angled discontinuity” as it is should be strength criteria, there are no generalized criteria or published systematic studies, and ship hull designers usually depend on experimental rules.
In this study we evaluate and compare the stress magnification factors and define the relative ratio between the stresses in the discontinuity and continuity structures by using finite element analysis from a strength-of-materials point of view. Our results show that under lateral load conditions the stress factor is larger in the twist structure than in the angled discontinuity structure, although under axial load conditions the stress factor in the knuckle and angle discontinuity structures is larger than in the twist structure. Additionally, we propose a formula that estimates the factor in the knuckle structure based on the strength-of-materials approach.
A New Ballasted Floating Support for Offshore Wind Turbine
Authors: Poirette Yann , Perdrizet Timothée , Gilloteaux Jean Christophe , Pourtier Alice , Mabile Claude 
Published: September 2014

In the framework of the developments of renewable marine energy and especially offshore wind energy, different design options of floating support have already been presented in the community such as barge-type, spar-type or semi-submersible-type floating structures. In the present paper, a study conducted by IFPEN is presented in order to design of a new floating platform concept dedicated to a multi-megawatt wind turbine. The design of the concept consists in a circular platform ballasted with water and concrete, anchored to the sea bed through a spread mooring system and designed to accommodate a multi-megawatt (in the range of 5 to 8 MW) offshore wind turbine.
The paper focuses on the methodology used in the conceptual and preliminary design phases and then on the major results obtained on the performance of the concept for a wide range of design load cases. The results, at current level, show that the concept is viable and interesting, and that the design can be improved further while requiring some additional validation.
An Experiment of Acoustic Navigation System Using Inverse Super Short Baseline for Underwater Vehicle
Authors: Watanabe Yoshitaka , Ochi Hiroshi , Shimura Takuya 
Published: September 2014

Recently underwater vehicles are typically navigated with an inertial navigation system (INS), a Doppler velocity log (DVL), and an acoustic positioning system (APS). APS are necessary, especially in deep sea observation, because it is absolute positioning method. Super short baseline (SSBL) is frequently used because it is easy to operate. In SSBL, the position of vehicle is obtained on the mother ship. In order to use the positioning result to navigate the vehicle, the result is transmitted to the vehicle with a certain amount of delay.
Authors are developing a test system of new type APS using inverse SSBL (ISSBL) method. In this method, the vehicle is equipped with a receiver array. Arrival direction of acoustic signal from mother ship is detected, and relative position between the mother ship and the vehicle is calculated with the obtained direction and the depth. Information of ship’s position is included in the transmitted acoustic signal, then absolute position of the vehicle can be calculated with the relative position and the included information. The vehicle position can be obtained in the vehicle in real-time and be used directly to navigate. No reply from the vehicle is necessary.
An ocean experiment of this method was conducted in Sagami Bay in Japan. Experimental device was moored on the seabed and the ship cruised with acoustic signal transmission. As a result, this method was available in deep sea area. Demodulation of information in the method was feasible, and positioning of the experimental device was achieved. High rate positioning is useful suppress random error with filtering.
Low Frequency Vibration Control of the Offshore Fixed Platforms by Using Tuned Liquid Column Damper
Authors: Lee Chan Hui , Kim Heui Won , Joo Won Ho 
Published: September 2014

The offshore fixed platforms are confronted with greater wind and wave forces as their installation site moves toward the deep sea, so it is definitely necessary to reduce the low frequency vibration of structures for the safety and comfort of crews.
The dynamic dampers are generally used to reduce vibration of structures. Especially, the tuned liquid column damper (TLCD) has been applied to reduce the low frequency vibration of onshore tall buildings.
In this paper, the design procedure of TLCD is proposed to control the low frequency vibration of fixed platforms through the simulation and experiment with a small-scale model. The vibration control target is the surge motion of fixed platforms and the major design variables of TLCD are mass and damping ratios.
The optimized design variables of TLCD are determined from the calculation of the amplification factor. In the experiment, the effects of mass and damping ratios are considered by changing the breadth of column, the opening ratio and number of the orifices. The results of experiment are found to well agree with the simulation. The 83% of structure vibration level can be reduced by applying the optimized TLCD.
Model Testing of Fish Farms for Validation of Analysis Programs
Authors: Berstad Are Johan , Heimstad Line Fludal , Walaunet Jørgen 
Published: September 2014

This paper presents a case study where results from numerical analysis have been compared to model experiments, performed on a 1/16 scale model. The tested model is a circular cage system with a polyethylene cage. The system is tested both in waves and current.
Numerical analysis to document the structural integrity of the fish farms are now a requirement. The state of the art analysis tool used in the aquaculture industry is AquaSim [1].
Results from model experiments are compared to numerical analysis carried out in AquaSim. Uncertainties in the model experiments are investigated and discussed. The differences between the experimental and numerical results are in the same range as the uncertainties.