bluuebunny/crossref_metadata_2025 huggingface dataset:
PERFORMANCE ANALYSIS OF ENERGY MANAGEMENT CONTROLLER FOR STAND ALONE SOLAR POWER GENERATION SYSTEM USING SOFT COMPUTING TECHNIQUES
Authors: V. Balaji, , K. Sekar, , V. Duraisamy, , S. Uma, , T. S. Raghavendran,
Published: October 2015

This paper presents a viability study of solar renewable power generation system for telecommunication tower applications. Rapid depletion of fossil fuel resources necessitated research on alternative energy sources. A solar power generation using photovoltaic system is one of the reliable alternative energy sources for conventional power generation system. Main objective of this paper is to supply uninterruptible power for telecommunication tower equipments from standalone solar power system with necessitate energy storage unit and a backup power system. The Energy Management Controller is developed using soft computing techniques which monitor the power generation from renewable source, SOC of battery bank continuously. The working rules of the monitoring system have been developed for all seasonal climatic weather conditions in India. It provides uninterrupted power during day time, improves life time of battery and minimized usage of diesel run generator. The whole system is analyzed using MATLAB / Simulink.
SELF-EVALUATION OF RTS TROOP’S PERFORMANCE
Authors: Kim On Chin , Kee Tong Chang , Teo Jason , Alfred Rayner , Cheng Wang , Tse Guan Tan
Published: October 2015

This paper demonstrates the research results obtained from a comparison of Evolutionary Programming (EP) and hybrid Differential Evolution (DE) and Feed Forward Neural Network (FFNN) algorithms in the Real Time Strategy (RTS) computer game, namely Warcraft III. The main aims of this research are to: test the feasibility of implementing EP and hybrid DE into RTS game, compare the performances of EP and hybrid DE, and generate gaming RTS controllers autonomously, an issue primarily of reinforcement/troops balancing. This micromanagement issue has been overlooked since last decade. Experimental results demonstrate success with all aims: both EP and hybrid DE could be implemented into the Warcraft III platform, and both algorithms used able to generate optimal solutions.
INFLUENTIAL VARIABLES INDUCING AERONAUTICAL REVENUES AT REGIONAL AIRPORTS
Authors: Wan Mohamed Wan Mazlina , Jaffar Ahmed , Shuib Adibah
Published: October 2015

Maximising revenues is one of the main objectives for regional airports to achieve in order to sustain their business, especially after the introduction of deregulation and privatisation of airports. Optimising aeronautical revenues has always been considered as a straightforward method and airport managers generally overlooked on the importance of daily operational factors that could influence the generation of aeronautical revenues. Thus, the objective of this paper is to validate whether the identified influential factors such as type of flight services offered, type of aircraft that airlines utilised, time of the day, day of the week the flights arrives or departs, and the number of passenger the airlines ferry in and out of the airport have an effect on the generation of aeronautical revenues.  This study has adopted a quantitative approach using regression analysis to investigate the influence of these selected variables on the generation of aeronautical revenues. The findings indicate that the selected variables have positive and negative significant influence on the generation of aeronautical revenues at regional airports
CONVERTING CONSTANT AMPLITUDE LOADING OF PRESTRESSED CONCRETE SLEEPER (PCS) FROM VARIABLE AMPLITUDE
Authors: I. Sharul Nizam , A.B. Afidah , H. Siti Hawa , Fazlan R. Mohd Ikmal
Published: October 2015

Prestressed Concrete Sleepers are structures that support railway system and absorb variable loading from the train that pass along the rail. In this study, variable amplitude loading from PCS taken from site measurement was converted into constant amplitude loading. Therefore the number of cycles and frequency are also important to be determined. There are various method for counting the number of cycles and the best adoptive method was Rainflow Cycle Counting. Once the number of cycles is obtained as well as the constant amplitude stress in a series of stress block, the prediction of fatigue life of PCS can be analyzed by further research in the laboratory work. However the limitation of this study is only to obtain the constant amplitude loading of PCS and also counting the number of cycles in various series of stress blocks.
EFFECTS OF ETHANOL BLENDS ON GASOLINE ENGINE PERFORMANCE AND EXHAUST EMISSIONS
Authors: Abdullah Nik Rosli , Zaharin M.S.M. , Mamat A.M.I. , Nawi M.R.M. , Sharudin Hazim
Published: October 2015

Automotive sector is one of the major contributors to air pollution and global warming due to the carbon residue and smoke opacity emission. Today, the trend of decreasing sources of petroleum fuel has led to innovation of other resources such as alternative fuel. Alternative fuel can be produced from biomass such as alcohol in which it is produced by fermentation of sugar, cane and corn. This experiment was conducted to investigate the effects of ethanol on gasoline engine performance and exhaust emissions. A four-stroke, single cylinder engine was tested by different range of ethanol volume percentages i.e. 10% (E10), 20% (E20) and 30% (E30) blended with fossil gasoline. The experiment was carried out at variations of engine speed and constant load. The engine speeds used for a constant load at 2 Nm were 2000rpm, 2500rpm and 3000rpm. From the results obtained, it shows that the brake specific fuel consumption for the blended fuel is better than gasoline fuel. Combustion efficiency of gasoline engine has improved with the use of ethanol-gasoline blends. Exhaust emissions such as CO and smoke opacity are decreased due to the presence of oxygenated properties of ethanol in blended fuel. However, emissions of CO2 are increased due to the high combustion temperature. In overall, the E20 shows the best results for all measured parameters at all engine test conditions.
Study on Friction Characteristics Between Ice and Various Rough Plates
Authors: Cho Seong-Rak , Ha Jung-Seok , Jeong Seong-Yeop , Kang Kuk-Jin
Published: October 2015

Ice is a very particular material that does not obey Amonton’s law of friction. Research on frictional phenomena between sea ice and ice-class vessels or platforms in arctic regions is still in its early stage, even though ships and platforms are greatly influenced and moved by the friction force of sea ice. In this paper, various friction tests were carried out, using freshwater ices and model ices in the Korea Research Institute of Ships and Ocean Engineering (KRISO) ice tank, to find the fundamental friction characteristics of ice and to estimate accurate ice friction force between ship and sea ice. As a result, we not only evaluated a painting method by using matting powders for ice-breaking ship models, but also found that the friction with an ice depends on the fundamental roughness and the supplemental roughness of material by measuring the roughness parameters of the plates. This study is intended to contribute to the understanding of the friction characteristics with ice.
Numerical Model of Flow Field Around a Horizontal Axis Tidal Stream Turbine With a Mono-Pile Foundation
Authors: Song Fan , Zheng Jinhai , Ding Cong , Zhang Jisheng , Peng Yuxuan
Published: October 2015

The horizontal axis tidal stream turbine with a mono-pile foundation is one of the most used devices for the exploitation of tidal stream energy, because of its convenience and low expense in construction and high efficiency in extracting energy. A 3D hydrodynamic model is developed to investigate flow field around the tidal stream turbine subjected to a steady current. After verified with the previous experimental works, the numerical model is used to study the complex flow motion around the horizontal axis tidal stream turbine with a mono-pile foundation. The numerical results show that the existence of tidal stream turbine may largely change the flow dynamics. A wake region with low velocity is formed behind the device. Water surface in front of the turbine fluctuates periodically. It is also found that the installing elevation of the turbine and the incoming flow speed have significant impacts on the mean kinetic energy and the resulting fluid force of the rotating turbine.
Smooth Redemption Policy of Port Facilities in Case of Ocean Space Utilization
Authors: Takahashi Koji , Kasugai Yasuo , Kondo Takeo
Published: October 2015

The ports of the world are operated by port authorities. The systems for establishing port facilities are roughly classified into two types depending on their sources of revenue. In the first type of system (used mainly for channels, breakwaters, berths, etc.), the national/local government and the port authority share the cost of construction. In the second type of system (used for cargo handling facilities, reclaimed lands, etc.), the port authority alone raises funds through a port-related bond-financed project and issues bonds. One characteristic of such bond-financed projects is that the costs of operating the facility and redeeming the bonds are funded through usage fees for the ground and profit from the sale of reclaimed land. Port authorities now require a smooth redemption policy for bonds issued in the past. However, port authorities have found it difficult to choose between having to raise usage fees and land prices high enough to enable smooth redemption in bond-financed projects on the one hand and having to reduce usage fees and land prices to reinforce international competitiveness in port logistics on the other. Unless a solution to this problem is found quickly, the finances of port authorities may become even more constrained, given the rising trend in port construction costs due to the risks of disasters such as earthquakes and due to growing interest rates. This is because prior investments are required for the construction of port facilities that takes a long time (between 5 and 10 years) and usage fees and profits from the sale of land must be suppressed to low levels because of political pressure. This will lead to larger bond issues and therefore a greater necessity for a smooth redemption policy of port facilities in the case of ocean space utilization. The authors first describe the structure of port management in the world, and analyze the financial situation of port authorities. Next, the authors point out that as the capital, maintenance, and management costs of port facilities grow in response to large-scale natural disasters, which exceed existing assumptions, and other factors, port authorities are being forced to take measures to address this. Lastly, the authors argue that public incentive assistance to shipping companies and logistics companies can effectively address the conflicting demands of reinforcing international competitiveness, strengthening disaster restoration capabilities, and enabling the smooth redemption of bonds in bond-financed projects.
Development and Application of a Global Satellite Database of Wind and Wave Conditions
Authors: Young I. R. , Zieger S. , Babanin A. V.
Published: October 2015

Oceanographic satellites have now been in operation for almost 30 years, collecting global data on oceanic winds and waves. During this period, a variety of satellites have been operational. These include altimeters (wind speed and wave height), SSMI radiometers (wind speed), scatterometers (wind speed and direction) and Synthetic Aperture Radar, SAR (full directional wave spectrum). Data from these instruments potentially represents an invaluable resource for offshore engineering design and facilities operation. This paper describes the development of a unique database containing data from all these instruments over their full periods of operation. The paper will describe the calibration and cross-validation of all instruments. This analysis shows the limitations of individual instruments and the relative accuracies. Instruments are calibrated against a very comprehensive buoy data set from the United States, Canada, UK, France, Spain, Australia and New Zealand. The extensive buoy dataset means that it is possible to have individual calibration buoys and independent validation sites. Further validation is provided by examining cross-over points between different satellite instruments where they image the same region of ocean at the same time.

The paper will also demonstrate the application of this database. These applications include the evaluation of seasonal wind and wave climate on a global scale, the determination of extreme value statistics (100 year return values) for wind speed and wave height, long term trends in wind speed and wave height and potential trends in extreme values.
Numerical Investigation on 3-D Two Collinear Cracks in Offshore Pipelines Under Bending
Authors: Zhang Yanmei , Xiao Zhongmin , Ariffin Mohammad Zaidi Bin , Zhang Wengang
Published: October 2015

Under complicated loading conditions, small yet closely located cracks can grow and coalesce into a large crack which may pose a significant threat to the reliability of marine structures. A lot of research work has been carried out for the investigation of multiple cracks’ stress intensity factors and estimation of fatigue growth of multiple cracks. However, there is a lack of information on nonlinear elastic plastic analysis on fracture behavior of ductile materials.

In this study, 3-D finite element analyses are conducted on offshore pipelines with two collinear cracks (a semi-elliptical surface crack and an elliptical embedded crack). The nonlinear elastic-plastic investigations are performed on fracture behaviors of these two interacting cracks subjected to large plastic strains. A comparison of fracture response (in terms of CTOD value) has been made between the current numerical results and the computational outcomes derived from BS7910: 2005. Last but not least, strain-based CTOD estimation formulas are proposed for assessing the fracture response of flawed pipelines with two collinear cracks under large plastic strain conditions.
Observations on Shallow Water Wave Distributions at an Ocean Energy Site
Authors: Vögler Arne , Venugopal Vengatesan
Published: October 2015

The paper analyses the changes in wave conditions during wave propagation between intermediate and shallow water depths at a potential wave energy deployment location.

The Outer Hebrides of Scotland in the United Kingdom are home to the world’s largest fully consented wave power project and hence a detailed understanding of the local resource is important to the developer to inform annual yield forecasting, technology refinements, and installation and operational plans. To support wave power projects and to reduce uncertainty and risk associated with yield production and performance estimates of energy developments, a sensor network was installed in the area from 2011–2013. Consisting of three floating buoys in intermediate depth and two combined acoustic and pressure sensors in the nearshore region, the data obtained from the different sensors at different locations in close proximity to each other have given a valuable insight in the hydrodynamic wave processes in the area.

Data of the two acoustic sensors and one wave buoy are analysed in this paper for a period covering the full range of sea states to be expected throughout a calendar year. Distributions of maximum and significant wave heights, wave steepness and wave direction during a range of different meteorological conditions are examined and a comparison between the different sensor locations is included. The analysis also considers different distributions of both wave power and period observed during the measurement campaign.
Monitoring and Dynamic Identification of VEGA-A Platform
Authors: Vignoli Andrea , Rizzo Michele
Published: October 2015

The Sicily Channel has been operating the VEGA-A offshore platform since 1988. The platform is equipped with a monitoring system both environmental and structural. This paper involves the collection and statistical interpretation of structural response data recorded. The acquired data are processed on the platform in order to establish their representativeness in relation to the structural control of the platform. The results of data processing, provided by the monitoring system, will be used for the spectral analysis and dynamic identifications, in particular, will be obtained the frequencies of oscillation in order to find a variation of them during the life of the platform. The variation of forms and periods of oscillation own may be related to damage to the structure or a variation of loads. Moreover, a dynamic identification will be performed for both important storms and for smaller events, the aim of detecting a non-linear behavior of the structure essentially linked to the foundation. Finally, the job includes a statistical analysis of the accelerometer signals in order to identify the warning thresholds and alarm. These results are then compared with data from the project in accordance with the storms that have affected the structural system.
Analytical Methodology for Wave Fatigue Analysis on Riser Suspended and Moored by Chains (RSAA) Configurations
Authors: Pereira Victor Milanez da Silva , Queija Marcos , Dantas Claudio Marcio Silva , Ellwanger Gilberto Bruno
Published: October 2015

As oil exploration moves into fields located in deep water, the need for developing new concepts of riser systems aiming at reducing the influence of environmental loads consequently increases. Therefore, a new riser configuration called RSAA (riser suspended and moored by chains - in Portuguese) is proposed. This structure consists on a rigid vertical riser connected on its top to a floating unit and on its bottom to flexible and mooring lines segments. This new configuration improves the structural response for some of the most critical points in riser design: top tensions and bending moments at the touch down zone.

Feasibility analyses have shown that the vertical riser is the most critical part of the proposed system due to the high level of vertical motions and dynamic tension. Therefore, a parametric study is vital in order to understand the system’s behavior as well as to establish the main parameters which influence its structural behavior. Analytical methods may require some slight simplifications of the problem to be applicable, but they generally lead to compact formulas that do explain which parameters influence the results and why and how it does so.

This work proposes an analytical model that evaluates the vertical motions and axial tension along the vertical riser subjected to wave loads applied to the floating unit. This procedure could enable parametric studies and the evaluation of the stress amplitudes and, consequently, the fatigue damage along the vertical riser of the RSAA configurations. Furthermore, this work aims to show that this methodology is a fast and effective pre-design tool by comparing it with a nonlinear time domain finite element method analysis.
Uncertainties in Extreme Value Analysis of Wave Climate Data and Wave Climate Projections
Authors: Vanem Erik
Published: October 2015

The extreme values of climate data are of interest in design of marine structures and the return values of certain met-ocean parameters such as significant wave height is of particular importance. However, there are various ways of analyzing the extremes and estimating the required return values, which introduce additional uncertainties. These are investigated in this paper by applying different methods to particular data sets of significant wave height, corresponding to the historic climate and two future projections of the climate assuming different forcing scenarios. In this way, the uncertainty due to the extreme value analysis can also be compared to the uncertainty due to a changing climate. The different approaches that will be considered is the initial distribution approach, the block maxima approach, the peak over threshold (POT) approach and the average conditional exceedance rate method (ACER). Furthermore, the effect of different modelling choices within each of the approaches will be explored. Thus, a range of different return value estimates for the different data sets is obtained. This exercise reveals that the uncertainty due to the extreme value analysis method is notable and, as expected, the variability of the estimates increases for higher return periods. Moreover, even though the variability due to the extreme value analysis is greater than the climate variability, a shift towards higher extremes in a future wave climate can clearly be discerned in the particular datasets that have been analysed.
Global Buckling Analysis of Stem Pipe During Side-Step in J-Lay Tower
Authors: van der Heijden Bob (H. E. J.) , Liu Richard , Perez Gabriel Vazquez , Smienk Henk
Published: October 2015

Within Heerema Marine Contractors’ (HMC) global installation analysis scope, the sidestep procedure of structures (e.g. in-line tee structure, 2nd end FLET structure or upper riser assembly structure) is identified that might require global buckling analysis. During a side-step procedure a structure is skidded out of the J-Lay tower while free-standing via the stem pipe on the hang off collar of the last hex-joint. While skidding the tower cannot support the structure vertically, only horizontally via a side step clamp higher up in the tower. Hence the stem pipe could buckle globally under the structure weight. The weight of the structure causes compression in the stem pipe and a center of gravity offset of the structure with respect to the pipe centerline causes a bending moment leading to potential global buckling.

A global buckling analysis must be performed to check this load case. The purpose of this paper is to provide validation for the use of Flexcom for performing global buckling analysis for the side-step procedure of structures in the J-Lay tower. In order to prove that Flexcom can indeed model global buckling behavior with sufficient accuracy, the critical buckling load obtained is validated using the FE packages Abaqus and Ansys. This comparison serves as validation, not only for the use of Flexcom, but also for the method used to determine the critical buckling load in Flexcom.

The analysis methodology used to assess a pipeline or riser for global buckling behavior is updated using the benefits of Flexcom. The use of Flexcom for global buckling analysis is more efficient, due to the ease and simplicity of modeling, and allows dynamic load cases, due to environmental loads and vessel motions, to be analyzed. Hence the potential benefit of performing global buckling analysis in Flexcom.
Metocean Design Criteria for Deep Water Offshore Systems
Authors: Drago Michele , Mattioli Matteo , Quondamatteo Federico
Published: October 2015

In the last decades the off-shore hydrocarbon extraction industry has extended its field of activities in very deep waters up to more than 2000 m. Extraction and production systems can vary between complete subsea development with export pipelines to on-shore treatment plants and surface development by means of surface units (SSFU) connected to subsea wells by risers and anchored by mooring systems which extend through the whole water column. For exclusively subsea developments, including sealines, the metocean design data and criteria to be developed and the applicable methodologies to derive them are well established. Univariate theory is usually applied in order to quantify the risk of failure due to (extreme) sea conditions.

The surface developments and the connections through the water column (e.g. risers, moorings) are newly challenging aspects. They could suffer from severe damages due to the occurrence of critical combinations of different variables during a single sea storm:: thus, it may be important to consider the joint occurrence of different forcing conditions (i.e. multivariate analysis).

The present manuscript provides a simplified methodology in order to carry out a sensible multivariate analysis of the contemporary data such as wind, waves and current.

Three different cases are analyzed: i) the correlation of extremes of different variables (wind, wave and current), ii) the extreme profiles of current and iii) the current profile climate. A practical case study is illustrated throughout the paper.
Bitumen Shear Mechanics in a Dynamic Subsea Electrical Cable
Authors: Mullins Jonathan , Morin Daniel , Tyrberg Andreas , Sonesson Claes , Ekh Johan
Published: October 2015

The bending mechanics of dynamic subsea electrical cables are strongly influenced by the frictional shear interactions that exist between the armour wires and surrounding materials. In some cases the armour wires are clad with bitumen filler material so that the shear mechanics of bitumen are important to the overall bending mechanics of the cable. In this work the shear mechanics of bitumen are studied. Pull-out tests on bitumen-clad armour wires were conducted in-situ on a stub of a dynamic subsea electrical test cable. Test temperatures ranged from 0°C to room temperature and shear velocities ranged from 0.1mm/min to 40mm/min. A thermally activated model of the bitumen shear interaction, incorporating temperature, speed and displacement dependence was proposed and implemented into a finite element code. The testing and modelling was then extended to incorporate the effects of cyclic loading. The bitumen response was highly sensitive to test temperature, applied velocity and cyclic loading with the shear strength varying by approximately two orders of magnitude over the range of conditions studied. The experimental results and model predictions indicate that the shear mechanics of cables containing bitumen clad armour wires differ from the shear mechanics of cables that do not. The bending stiffness displays a velocity and temperature dependence and relaxation of cable stresses is expected during holding events. Because of this, it is recommended that modelling of bitumen clad armour wires be conducted using a suitable bitumen interaction model and not a classic friction model.
Risk Reduction for Floating Offshore Installations Through Barrier Management
Authors: Vinnem Jan-Erik , Utne Ingrid B.
Published: October 2015

Marine system accidents have a relatively high frequency worldwide. In Norwegian waters loss of installations has been avoided the last 20 years, but several near-misses and severe incidents confirm that the risk level is not insignificant. Barriers should prevent undesired events or reduce consequences should such events occur. The main purpose of barrier management is to establish and maintain the necessary barriers. It includes the processes, systems, solutions and measures needed to ensure implementation and follow-up of barriers. Petroleum Safety Authority has emphasized the need to develop barrier strategies during the last few years, and this has been particularly emphasized for topside systems and barrier functions to prevent and/or mitigate the consequences of hydrocarbon (HC) leaks. Insofar, the same focus on barrier management has not been put on marine systems and structural hazards. Risk associated with ballast systems, anchoring systems and dynamic positioning is at a level where further improvements should be made. Independent barrier elements and/or functions are required in order to provide substantial risk reduction. Some suggestions for independent barriers are discussed in this paper.
Establishing Operational Fatigue Limits for Short-Term Riser Operations
Authors: Sundararaman Shankar , Cerkovnik Mark , Ferreira Luiza , Ward Phil
Published: October 2015

Drilling and intervention risers are widely used for oil and gas production in deep as well as shallow waters in oil fields around the world for subsea operations. The risers come in a diverse array of configurations, some of which may be challenged by fatigue if operated in high currents or seastates. The suitability of the selected riser and the operating limits are assessed by conducting strength and fatigue analysis based on design codes such as API RP 2RD, [7], API RP 16Q, [9], and API RP 17G, [10].

Typically, drilling and intervention activities are conducted for short periods of time but used repetitively. The codes are clear about the return period of the design environmental event which must be checked to insure safe operation with respect to strength; however, assessment of fatigue integrity can be more difficult to determine. The allowable fatigue operating environment should account for the ability to disengage, the time required to disengage, the damage rates in particular seastates, prior accumulation of fatigue damage, and variations in soil, tension and internal fluid weights.

In this paper, an orderly method of establishing the allowable fatigue operation limits for drilling and intervention risers is presented based on Monte Carlo simulations along with a case study implementing the methodology in a shallow water environment. To illustrate this concept, a riser with wellhead and conductor system is assessed and is subjected to directional loading from several long-term seastates. The variation in effects is studied by doing fatigue analysis for different durations: 3 days, 1 week, 3 months, 1 year and 10,000 hours.
Integrating Structural Health and Condition Monitoring: A Cost Benefit Analysis for Offshore Wind Energy
Authors: May Allan , McMillan David , Thöns Sebastian
Published: October 2015

There is a large financial incentive to minimise operations and maintenance (O&M) costs for offshore wind power by optimising the maintenance plan. The integration of condition monitoring (CM) and structural health monitoring (SHM) may help realise this. There is limited work on the integration of both CM and SHM for offshore wind power or the use of imperfectly operating monitoring equipment. In order to investigate this, a dynamic Bayesian network and limit state equations are coupled with Monte Carlo simulations to deteriorate components in a wind farm.

The CM system has a ‘deterioration window’ allowing for the possible detection of faults up to 6 months in advance. The SHM system model uses a reduction in the probability of failure factor to account for lower modelling uncertainties.

A case study is produced that shows a reduction in operating costs and also a reduction in risk. The lifetime levelised costs are reduced by approximately 6%.
Investigation Into Stability and Accuracy in Predicting Slender Bodies’ Hydroelasticity Using Loose Coupling Methods
Authors: Ma Leixin , Fu Shixiao , Hu Ke , Shi Qian , Li Runpei
Published: October 2015

Problems concerning fluid-structure-interaction are often encountered in aquaculture engineering. For a moving slender structure like fishing net or floater in currents and waves, modified Morison Equation is a widely employed formula to estimate its hydrodynamic loads. The hydrodynamic forces are closely dependent on the structures’ velocity and acceleration, and quadratic relative velocity in the equation even adds nonlinearity in the forces. To study the hydroelastic response, two time-saving loosely coupling methods, calculating the hydrodynamic forces based on the structure’s response in the previous time step without iteration, are proposed in this paper. The loose coupling methods were proved to affect the traditional stability criteria for time integration. Based on the two loose coupling methods, the stability and accuracy of a slender beam’s hydroelasticity undergoing large deformation were studied. The calculated responses were compared against strong coupling results. It was found that if loose coupling is assumed in added mass force, unconditional instability is likely to occur. On the other hand, the accuracy of numerical results can be improved with smaller time increments set if loose coupling is only assumed in the quadratic relative drag force.
Comparison of Weathervane Performance Between Two Types of FOWT Systems Moored to SPM
Authors: Iijima Kazuhiro , Kuroda Yuiko , Nihei Yasunori , Murai Motohiko
Published: October 2015

This paper addresses the weathervane performance of Floating Offshore Wind Turbines (FOWTs) moored to single-point mooring (SPM) systems. A system of equations of motion to describe the motions in horizontal plane around the mooring point in the combined environmental conditions is derived. Wind, wave and current loads are considered. Two types of SPM-FOWT systems proposed by the present authors are considered for comparison. It is found out that the weathervane performance of the SPM-FOWT systems is acceptable in a point that the power generation efficiency does not reduce significantly. The stability is also checked based on the eigenvalue analysis for the linearized equations of motion around the equilibrium point. The stability and the responsivity are discussed in comparison between the two systems. Sensitivity of the stability and responsivity to design parameters such as length between the buoy and the main floater to the turning motion performance is discussed, too.
The Coupling Effects Between the Underwater High-Pressure Bubble and the Marine Structure
Authors: Huang Xiao , Liu Yunlong , Wang Shiping , Yao Xiongliang
Published: October 2015

When underwater explosion breaks out, usually the bubble with a radius of meters is generated. The bubble’s oscillation may cause the damage of the floating structure thereabout. In the present paper, a 3-D Boundary Element Method (BEM) model based on the potential theory is implemented to simulate the strong non-linear interaction process. The focusing problem is to track the movement of the contact line between the structure and the free surface with some degree of robustness. Although the negative mirror image model could take the free surface’s effect into consideration without catching the contact line, its assumption that the free surface be motionless wasn’t tally with the real situation to some extent. Non-linear free surface effect is simulated in this paper. By splitting the nodes, both the Direchlet and the Neumann boundary conditions will be satisfied of the nodes on the contact line. Therefore, the moving boundaries’ deformation can consistent with the actual situation well. In this paper, the authors firstly introduce a 3-D BEM model for bubble dynamics, and present a way to deal with the strongly integral for the open boundary. Then the accuracy of the model is examined in comparison with the negative mirror image model. By using the numerical model, bubble dynamics near a marine structure with varying increment’s position and weight are studied respectively. We find out that the depth and the weight of charge will affect the bubble’s shape. This paper has its implication to offer ideas on multiphase fluid interaction and the damage mechanism induced by high-pressure bubble on floating structures.
Dynamic Analysis of Buoyant Leg Storage and Regasification Platform Under Regular Waves
Authors: Chandrasekaran Srinivasan , Sreeramulu Lognath Radhakrishnan , Jain Arvind
Published: October 2015

Buoyant Leg Storage and Regasification Platform (BLSRP) is the recent innovation in offshore structural engineering, which is essentially designed as storage and processing platform. The platform rests on six buoyant legs, which supports the deck through hinged joints. This is new hybrid conceptual design that restrains transfer of both rotational and translational responses from the BLS to the deck and vice-versa. BLSs are connected to the sea bed through taut mooring system. Numerical studies are carried out on the BLSRP at 600 m water depth, highlighting its dynamic response behavior under regular waves. Based on the studies conducted, it is seen that response of the deck is not influenced by wave action due to the presence of hinged joints. The proposed structural form proves to be effective in controlling the deck response in all active degrees-of-freedom. This improves the operational safety and shows high recentering capabilities even under large surge displacements.
Hurricane Risk Considerations for Offshore Wind Turbines on the Atlantic Coast
Authors: Valamanesh V. , Wei K. , Myers A. T. , Arwade S. R. , Pang W.
Published: October 2015

The development of renewable energy sources is a critical global need. The Atlantic coast and Gulf of Mexico of the U.S., with large wind resources and proximity to major population centers, are natural places for such development; however, these regions are also at considerable risk from severe hurricanes or tropical cyclones. Current international guidelines for the design of offshore wind turbines (OWTs) do not explicitly consider loading under hurricane conditions, however subsequent editions are anticipated to include language specific to hurricanes. Variability in extreme loads is greater in areas where hurricanes are likely and the design loads and risk profile of offshore structures installed in such areas are expected to be strongly influenced by hurricanes. For many offshore structures, environmental conditions at design recurrence periods and beyond are often estimated through extrapolation of long-term (i.e. multiple decades) wind and wave measurements from buoys, however, for offshore structures located at areas exposed to hurricanes, it is accepted practice to use physics-based models to augment the historical record of Atlantic hurricane activity and generate a stochastic catalog of synthetic hurricanes that provides tens of thousands of realizations for one year of potential hurricane activity. Once a stochastic catalog has been established, appropriate hazard intensity measures (e.g. the one-minute sustained wind speed, the significant wave height, and the peak spectral wave period) can be estimated for each storm at any site using well-known wind and wave parametric models. In this study, we consider several sites along the Atlantic coast and quantify the impact of estimating hazard for design recurrence periods and beyond for three different methods. The first is based on an extrapolation of wind and wave measurements from buoys, and the second and third are based on a stochastic catalog of synthetic hurricanes with wind and wave intensities estimated based on deterministic and probabilistic relationships.
Effect of Short-Crestedness on Extreme Wave Impact: A Summary of Findings From the Joint Industry Project “ShorTCresT”
Authors: Hennig Janou , Scharnke Jule , Swan Chris , Hagen Øistein , Ewans Kevin , Tromans Peter , Forristall George
Published: October 2015

Long-crested waves are typically used in the design of offshore structures. However, the corresponding statistics, kinematics and loading are significantly different in short-crested waves and up to date, there is no state-of-the-art methodology to apply short-crested models instead. The objective of the “ShortCresT” Joint Industry Project was to take into account short-crestedness in the design of offshore structures against extreme waves based on a good description of their spectral characteristics, statistics, kinematics, breaking and loading and to deliver (empirical) design recommendations and methods. This paper gives an overview of the findings of ShorTCresT regarding wave crest and height distributions, a comparison of basin and field data, the role of wave breaking, the most realistic directional model, hindcast models as well as the related platform loading.
On the Effect of Work Hardening on Strain-Localization and Fracture Initiation in Collision Simulations
Authors: Storheim Martin , Amdahl Jørgen
Published: October 2015

The exact material behavior is not known a priori in a collision event involving ships or offshore structures due to the vast number of ships with different materials and the variation in material properties from manufacturer to manufacturer and from material batch to batch. Hence, assumptions are necessary when calculating the resistance to a collision event.

A common starting point can be the requirements to the material quality set by regulatory bodies, often giving a range of allowable yield stress, ultimate stress and elongation at ultimate stress. This leaves the actual hardening response to the engineer.

This paper investigates the consequences of different choices of plastic work hardening calibrated to the same assumption of yield stress, ultimate stress and elongation at failure. Non-linear finite element analysis of ship collision is utilized. The findings are discussed, and some recommendations given.

The simulations shows that the collision response is highly sensitive to the actual material response; initial yield stress, tensile strength, strain at tensile strength and the rate of work hardening are all essential in this context.
Review of Steel Lazy Wave Riser Concepts for North Sea
Authors: Felisita Airindy , Gudmestad O. T. , Karunakaran Daniel , Martinsen Lars Olav
Published: October 2015

The Steel Catenary Riser (SCR) is considered a favorable solution for deepwater development. However, the application of SCRs in harsh environments is challenging, mainly due to fatigue at the touch down zone. One of the solutions to improve SCRs’ fatigue performance is the application of buoyancy modules in order to achieve a Steel Lazy Wave Riser (SLWR) configuration.

This paper presents a parametric study of a SLWR system for application in deepwater and harsh environments. The selected harsh environment is the seas within the Norwegian Continental Shelf. The main geometric variations are the length of the buoyancy section and the dimension of the buoyancy modules. These variations result in riser configurations with different riser’s wave heights. The term ‘riser’s wave height’ refers to the vertical distance between the lowest point at sagbend and the highest point at hogbend of a riser. The analysis works are performed using Orcaflex.

The results show that the application of buoyancy modules help to improve the performance of a steel catenary riser for application in a harsh environment. The dimension of a riser’s wave shape proves to be an important factor that controls strength and fatigue performance of a riser. Lazy wave riser configurations with larger and better defined wave shapes have lower stress utilizations and lower fatigue damage, while riser configurations with smaller wave shapes have higher stress utilizations and higher fatigue damage. This is due to lazy wave configurations with higher wave shape have better capability to absorb the dynamic loads.
Experimental Investigation on Mechanical Property of Hybrid Steel-to-Lattice Joint With Pyramidal Carbon Fiber Truss
Authors: Yao Xiongliang , Wang Wei , Yang Nana , Guo Zhanyi
Published: October 2015

As a novel type of composite sandwich structure in recent years lattice structure with carbon fiber pyramidal truss core is applied to warship’s superstructure because of its high specific stiffness and specific strength, but it is difficult to design joint between superstructure and hull and there are few researches about the mechanical property of hybrid steel-to-lattice joint. Two kinds of hybrid joint specimens are designed and their compressive and flexural properties are investigated. The experimental results show that in compression test lattice sandwich is weakest and that debonding resulted from core macro-shear and face sheet wrinkling can lead to overall instability; bearing reaction can result in resin base fracture in lattice core and face sheet delamination is the main damage mode of joint structure in three-point bending test, which happens where stiffness mutation appears.
Simulation of Added Resistance in High Waves
Authors: Ruth Eivind , Berge Bjørn Ola , Borgen Henning
Published: October 2015

A vessel traveling across the sea experiences waves. The waves produce forces on the vessel resulting in added resistance. The forces are caused by the combination of wave and vessel motion. A variety of methods for prediction of added resistance in waves exists. The complexity and accuracy varies significantly. This paper focuses on numerical solution of the problem when the waves are high compared to the vessel size. The commercial software Star-CCM+ is used to solve the Navier-Stokes equations by use of Reynolds averaging and a VOF model. This implies that all kind of nonlinearities are accounted for. Accurate numerical propagation of a 5th order Stokes wave is achieved. A study on the mesh and time step sensitivity of the added resistance is presented. The numerical results are validated by custom made model test. A numerical comparison of two alternative surge restrictions (constant speed or constant force) shows insignificant differences in results.
On Probabilistic Fracture Assessment of Defective Pipeline Based on Target Failure Probabilities
Authors: Lee Jae-Bin , Kim Ki-Seok , Cho Woo-Yeon , Shim Sang-Hoon , Huh Nam-Su
Published: October 2015

This paper investigates the priorities as well as the safety factors of each assessment variable for a defective pipeline based on a partial safety factor concept considering the target failure probabilities during operating period of components of interest.

For this, firstly wall-thinned pipeline under internal pressure is considered, which is important in fitness-for-service assessment of corroded pipeline. For the analysis, scatters in the applied pressure, mechanical properties and geometries of wall-thinned pipeline are considered using normal and log-normal distributions. In addition, partial safety factors of a circumferential through-wall cracked pipeline subjected to global bending moment are also evaluated based on the elastic-plastic fracture mechanics. In this case, scatters in the applied bending moment, mechanical and fracture properties are considered based on normal and log-normal distributions.

More importantly, two different deterministic integrity assessment methods are applied to wall-thinned pipeline and two different estimation methods of elastic-plastic J-integral are applied to circumferential through-wall cracked pipeline to evaluate the partial safety factors. Resulting values of partial safety factors are calculated using both the advanced first-order second moment method (AFOSM) and the second-order reliability method (SORM). Moreover, the effects of statistical distributions and variations of standard deviations of assessment variables on the partial safety factors are also demonstrated.
Roll Center of a FPSO in Regular Beam Seas for All Frequencies
Authors: Fernandes Antonio Carlos , Asgari Peyman , Seddigh Mohammadsharif
Published: October 2015

The so-called roll center is not a concept well defined for a rolling ship or platform when submitted to a wave field. The present paper discusses and proposes a clear definition. The paper shows a methodology to assess this point and shows that, for regular beam wave incidence on a symmetric body, the roll center is not necessarily located at the line of symmetry of the symmetric bodies. Also shows that the locus of the roll center is frequency dependent. Finally, the paper discusses the limits for low and high frequencies. This investigation uses basic equations of the rigid body kinematics and information for better understanding the complicated roll center. To validate the proposed methodology the paper reports model tests and frequency domain calculations regarding the behavior of the vessel in regular beam wave. A closed form equation for the calculation of the roll center is also proposed. All these results match very well. This is so, despite the very complicated phase behavior with frequency. The paper also addresses the question whether the bilge keels at each board should always be symmetric for a platform that will always operate in beams seas.