bluuebunny/crossref_metadata_2025 huggingface dataset:
‘Inverse’ Concept: Wave Energy Generation by Motion and Green Water Maximisation
Authors: Buchner Bas , Jaouen Frederick
Published: February 2010

This paper presents the initial investigations into the ‘Inverse’ concept for wave energy conversion, based on the maximisation of motions and green water. The ‘Inverse’ concept combines aspects of ‘overtopping’, ‘heaving’ and ‘pitching’ wave energy conversion concepts, but also adds specific aspects such as the use of green water. Instead of reducing the motions and green water as is done in normal offshore hydrodynamics, the ‘Inverse’ concepts tries to maximise the motions and green water to generate energy from the waves. Results are presented of frequency domain calculations for the motion (de-) optimisation. Improved Volume Of Fluid (iVOF) simulations are used to simulate the green water flow on the deck. It is concluded that the potential of the ‘Inverse’ concept is clear. As a result of the double connotation of the word ‘green’, this renewable energy concept could also be called the ‘green water’ concept. Further work needs to be carried out on the further optimisation of the concept.
Elastomeric Fender Systems Subject to Random Excitation
Authors: Ofoegbu James , Niedzwecki John M.
Published: February 2010

The current design process for fender systems is based upon a deterministic approach whereas it would appear that for many practical situations the combined wind, wave and current conditions involve some level of random excitation and response behavior. A two-body system consisting of a mini-TLP and tender barge excited by random seas was selected for analysis. This laboratory experiment provided measurements of the normal component of force response between the two vessels needed to design a fender system and was measured in the experiments for both head sea and beam sea conditions. In the original design concept a fender system consisting of cylindrical fender elements was envisioned and this idea was used as the basis to consider the elastomeric elements discussed in this study. This study identifies the key problem variables that can be used to characterize this two-body system and it discusses the development of the appropriate dimensionless parameters needed to compactly present design curve information on deflection/compression and energy absorption of the fender elements. An illustrative example that compares deterministic and random excitation predictions based upon some assumed geometries is presented and discussed. This includes the characterization of fender force time series in terms of statistical moments and its underlying probability distribution. Using parameter estimation techniques, coefficients of a best-fit two-parameter model were determined and the resulting model was used in the illustrative example.
Crack Detection in Offshore Structures Using Dynamic Characteristics and Wavelet Transform
Authors: Zhang Zhao-de , Xie Yong-he , Wang De-yu
Published: February 2010

Dynamic parameters of offshore structures, such as frequencies, modal shapes, modal strain energy (MSE) and frequency response functions (FRF) are numerically and experimentally studied to detect the crack in the structures. A 3-pile and a 4-pile platform are analyzed. And a model of the 3-pile platform has been constructed for the experimental verification. When a crack occurs, the parameters of the structure will change. The shift of these parameters may be applied to identify the crack, the location and even the crack magnitude. Wavelet transform can be employed to find the singularity of the signal, so as to predict the early crack. The dynamic parameters due to mass change are also evaluated.
Dynamic Response Research of Ship/Jacket Platform Collision
Authors: Gan Jin , Wu Weiguo , Pan Jin , Sun Huanxiang , Zhu Mengwei
Published: February 2010

In this paper, a new simplified finite element model is proposed for ship-jacket platform collision. This model can achieve all kinds of concerned parameters and time history curves through once calculation. This paper also discusses the effect of stain rate in ship-platform collision. On the basis of the above work, finite element numerical simulation of ship-platform collision is carried out. Some important results such as collision forces, stress, local deformations, distribution of various energies and displacement of platform are discussed. At last, some useful conclusions are achieved.
Statistics of Nonlinear Waves Simulated in a Wave Basin
Authors: Cherneva Zhivelina , Tayfun M. Aziz , Guedes Soares C.
Published: February 2010

Modulational instabilities induced by third-order nonlinear interactions among freely propagating waves can cause the statistics of various surface features to deviate significantly from the predictions based on the linear Gaussian and second-order models. This study analyzes deep-water waves simulated in a wave basin and characterized with such instabilities, and compares the statistics of the wave heights, crests and troughs amplitudes observed with a variety of theoretical approximations based on Gram-Charlier expansions. The results indicate that the theoretical approximations describe the empirical distributions observed reasonably well, for the most part. Further comparisons also show that the heights and crests of the largest waves do not exceed Miche-Stokes type upper limits.
Study on the Wave Loads and Strength Assessment Method on Semi-Submersible Platform
Authors: Li Hui , Ren Huilong , Wei Tao , Feng Guoqing
Published: February 2010

In this paper, the wave loads of a semi-submersible platform is calculated by the deterministic design wave method and the stochastic design wave method based on the rules established by ABS and DNV classification society respectively. Then, the yielding strength, buckling strength and fatigue strength of important members are assessed according to these different rules. Through the comprehensive comparison of the results of wave loads and strength assessment, the differences between these rules are summarized. Then some significant suggestions are given.
Turkstra Models of Current Profiles
Authors: Winterstein Steven R. , Haver Sverre , Nygaard Einar
Published: February 2010

Design of deep-water structures requires accurate models of currents versus water depth. Common models are N-year profiles, which conservatively assume the N-year extreme current speed occurs simultaneously at each depth. To address this conservatism, we introduce Turkstra models of current profiles here. These yield a set of current profiles, each of which coincides with the N-year profile at a single depth and is reduced elsewhere. The degree of reduction is a direct function of the spatial correlation structure of the current process. Results are shown for a deep-water North Sea site, and compared with time-domain prediction of extreme loads for linear and drag load mechanisms. Extensions are suggested to combine these methods with procedures such as Empirical Orthogonal Functions, permitting the data to define the most economical set of basis vectors upon which the Turkstra logic is applied.
Influence of Nonlinear Mooring Stiffness on Hydrodynamic Performance of Floating Bodies
Authors: Ren Huilong , Zhang Jian , Feng Guoqing , Li Hui , Li Chenfeng
Published: February 2010

Coupled dynamic analysis between floating marine structures and flexible members such as mooring lines and risers, is a challenging work in the ocean engineering field. Coupled analysis on mooring-buoy interactions has been paid more and more concern for recent years. For floating offshore structures at sea, the motions driven by environmental loads are inevitable. The movement of mooring lines occurs due to the excitation on the top by floating structures. Meanwhile the lines restrict the buoy’s motion by forces acting on the fareleads. Positioning is the main function of mooring system, its orientation effects can’t be ignored for floating structures such as semi-submersible, FPS, and TLP, especially when the buoy’s equilibrium position shifting to another place. Similar as hydrostatic restoring forces, mooring force related with the buoy’s displacement can be transformed into mooring stiffness and can be added in the differential equations of motion, which is calculated at its equilibrium point. For linear hydrodynamic analysis in frequency domain, any physical quantity should be linear or be linearized, however mooring stiffness is nonlinear in essence, so the tangent or differential stiffness is used. Steel chains are widely used in catenary mooring system. An explicit formulation of catenary mooring stiffness is derived in this article, which consists of coupled relations between horizontal and vertical mooring forces. The effects of changing stiffness due to the shift of equilibrium position on the buoy’s hydrodynamic performance are investigated.
A Robotic Concept for Remote Inspection and Maintenance on Oil Platforms
Authors: Kyrkjebo̸ Erik , Liljeba¨ck Pa˚l , Transeth Aksel A.
Published: February 2010

This paper presents a novel concept for remote inspection and maintenance operations on next generation normally-unmanned offshore oil platforms. The concept is presented through the design of a robotic lab facility for automated and teleoperated inspection and maintenance operations by robot manipulators — ranging from simple inspection tasks to advanced maintenance operations. The lab facility is built around two cooperating robot manipulators equipped with sensors measuring temperature, vibrations, gas concentration and sound, and that automatically changes between tools to operate valves, exchange batteries in wireless sensors and to manipulate objects and the integrated process equipment. A graphical interface allows users to start automated inspection rounds where sensor data are collected, analyzed and compared to normal operating conditions, and alarms are generated if deviations are detected. Users may also plan new operations in a virtual environment before executing them, or remotely control the robots through a number of control interfaces. Live video feeds and stereoscopic vision are available to aid the operator during remote operations. A model-based collision avoidance system ensures that both automated operations and unplanned operations are verified before and during execution, and ensures safe operation of the robots. The paper presents results from the lab facility to illustrate the functionality of the remote inspection and maintenance concept, and demonstrate how remote operators may start automatic inspection and maintenance operations, plan new operations in a virtual environment, or directly control the remote facility onshore.
A Truss Semisubmersible Optimized for the Post Katrina Environment in Gulf of Mexico Correlated With Model Test
Authors: Yang Chan K. , Murray John , Lee Hanseong , Choi Myoungkeun , Chen Cheng-Yo , Ding Yun
Published: February 2010

This paper presents a Truss Semisubmersible (Truss Semi) design optimized to meet the post-Katrina Gulf of Mexico (GoM) environment criteria, with global performance correlated in 1:50 scale model tests in a wave basin. A conventional semisubmersible with a ring pontoon is facilitated with heave plates supported by the truss structure to increase heave natural period. The size of the semisubmersible hull and the configuration of the heave plates are optimized through frequency domain analysis to minimize the vertical motion enough to allow the dry trees to accommodate top tensioned production risers. The system includes eight production top tension risers (TTRs) connected to the production deck and a single drilling riser connected to the drilling deck. All of the TTRs are connected through the hydro-pneumatic tensioner system. One gas export and one oil export steel catenary riser (SCR) export the oil and gas to the storage facility. Structures designed for this deepwater area (4,300 ft) of the central Gulf of Mexico (GoM) must be designed to meet newly proposed environmental criteria [1]. The optimized Truss Semi was tested in the Offshore Technology Research Center (OTRC) model basin, to confirm the global performance, such as motion, air gap and loads on the heave plates. The numerical predictions correlate well with the model test results.
Structural Response to Sloshing Excitation in Membrane LNG Tank
Authors: Graczyk Mateusz , Moan Torgeir
Published: February 2010

Sloshing in LNG membrane tanks may cause large pressures on the tank structure. To keep the cargo at the required low temperature, the tank structure is covered with an insulation which has a much less strength than steel. The containment system is a very complex structure which consists of different materials and requires a careful analysis with due consideration of the load process and dynamic effects in the response. The structural response of the membrane tank wall is investigated in this paper by finite element analyses. First, a modal composition of the structural response is studied. It is shown that many modes contribute to the response, which makes it difficult to establish simplified DLF approach. Dynamic structural response to a typical sloshing impact is investigated in detail. An important observation is that although the containment system has traditionally been modeled with a rigid support, the steel plate that supports the insulation may be flexible under the relevant load conditions. It is shown that the flexibility of the steel plate causes significant stress variation in the insulation. Different response patterns of the Mark III containment system are presented and mechanisms that cause large stress concentrations and different response patterns in the static and dynamic case are discussed. Scaling issue in view of the response is also investigated. Various scaling formulations may apply in post-processing sloshing experiments. While the Froude law yields conservative scaling for pressure magnitude, its conservatism for scaling the time needs to be investigated in view of the relevant dynamic response. By analyzing the structural response to the differently scaled loads it is found that the Froude approach is conservative but the scatter of results may be very large.
Time Domain Methodology for Vortex-Induced Motion Analysis in Monocolumn Platform
Authors: Gonc¸alves de Lacerda Thiago Aˆngelo , Ellwanger Gilberto Bruno , Queija de Siqueira Marcos , Siqueira Elizabeth Frauches Netto
Published: February 2010

The offshore oil exploration in Brazil has been, traditionally, made by semi-submersible and moored ship-based units. The need for more restricted wave-induced motions has demanded new conceptions of floating structures, in which the mono-column concept distinguishes itself. Due to its cylindrical shape hull, this floating unit could present a significant low frequency vibratory movement caused by the vortex shedding phenomenon. This kind of phenomenon on huge structures like platforms is usually known as VIM (Vortex Induced Motions). The main objective of this work is to evaluate a time domain methodology applied in VIM problems. This methodology uses a Van der Pol equation to represent the vortex shedding phenomenon. The force calculation schemes presented in this work are applied in physical examples and its results will be compared to model test data. The analyses were performed in a non linear dynamic analysis program, using a six degree of freedom model, developed for this study.
Coupled Surge-Heave-Pitch Dynamic Modeling of Spar-Moonpool-Riser Interaction
Authors: Spanos Pol D. , Nava Vincenzo , Arena Felice
Published: February 2010

Due to the ongoing rather intense development of deep water gas and oil fields, the technical community has been increasingly focusing its attention to the dynamic behavior of Spar floating structures. Spar dynamics exhibits a highly nonlinear behavior due to the presence of various components such as mooring lines, moonpool, and risers (Spanos et al., 2005). In this regard Gupta et al, 2008a, have studied the reduction of the heave response in a single degree-of-freedom spar model due to the oscillations of water entrapped in the moonpool through the partially closed bottom plates. In this paper a novel coupled six-degree-of-freedom analytical model of a Spar system tensioned by TTR risers is proposed. The model accounts for the interactions among spar hull motions (heave, surge and pitch), the riser motion (heave and surge), and the moonpool. This model involves six coupled nonlinear differential equations comprising nonlinearity terms associated not only with stiffness and damping but also with inertia terms. A dynamic analysis is performed by subjecting the model to JONSWAP ocean wave spectrum compatible extreme forces (corresponding to the 100 yr wave); and to moments applied to the center of gravity computed by means of standard motion program. Both numerical and semi-analytical techniques (equivalent linearization including inertial terms) are used for the determination of the response of the proposed dynamic model both in the time and frequency domains. Some parameter study results are reported, including ones pertaining to the dependence of the spar motion on the open guide plates.
Study on the Standardized Nonlinear Finite Element Analysis of the Ultimate Strength of Ship Hull Girder
Authors: Feng Guoqing , Ren Huilong , Bai Baoqiang , Li Chenfeng , Liu Xiaobo
Published: February 2010

The ultimate strength of ship hull girder has been a study hot spot in ship mechanics. Caldwell method, Smith method, idealized structural unit method and nonlinear finite element method are usually used to predict the ultimate strength of ship hull girder. In the paper, a standardized procedure on the nonlinear finite element analysis of the ultimate strength of ship hull girder is presented. Firstly, the finite element modeling for the ultimate strength of ship hull girder is studied, which include material property, element type, mesh size, model length and boundary conditions. Then, the influence of welding residual stress and initial deflection are studied. For the validation of the method in this paper, a MST-3 model from the test of Nishihara is used as an example. Finally, the results from the nonlinear finite element analysis and Smith method are compared for the ultimate strength analysis of a container ship. The study shows the standardized procedure on the nonlinear finite element analysis of the ultimate strength of ship hull girder is satisfactory and suitable for engineering application.
Membrane and Bending Strain in Cylindrical Shell Vibrations
Authors: Alzahabi Basem , Kowalski Henry
Published: February 2010

Cylindrical Shells are widely used in many structural designs, such as offshore structures, liquid storage tanks, submarine hulls, and airplane hulls. Most of these structures are required to operate in a dynamic environment. Therefore, investigating the dynamic characteristics of cylindrical shells is very critical in developing a strategy for modal vibration control for specific operating conditions. Reduction of vibration amplitudes and in sound radiation is most efficiently achieved at the design stage, and the acoustic signatures may be determined by considering operational scenarios, and modal characteristics. In cylindrical shells, mode shapes associated with each natural frequency are combination of Radial, Longitudinal, and Circumferential modes, and unlike those of beam structure, the lowest natural frequency does not necessarily correspond to the lowest wave index. In fact, the natural frequencies do not fall in ascending order of the wave index in cylindrical shells. The ratio of membrane strain energy to total strain energy is high for modes with simple modal patterns and decrease toward zero as the number of nodal (n) lines increase, while the ratio of bending energy to total strain energy is small for simple nodal patterns and increase with increase in complexity of it. Modes associated with membrane deformation require a lot of strain energy while modes associated with bending deformation require less strain energy. The lowest natural frequency occurs where the sum of the two energies are at minimum. Moreover, the natural frequencies that are controlled by membrane strain energy are approximately independent of the shell thickness change. In this paper, a scaled model of submarine hull segment under shear diaphragm boundary conditions is analyzed analytically and numerically. Then the experimental modal analysis of the scaled model utilizing strain gauges was performed to decouple the strain components. Designing a boundary condition that simulate a shear diaphragm is very challenging task by itself. The experimental data were correlated with those results obtained analytically and numerically using the finite element methods using MSC.NASTRAN software. The results were found to be in excellent agreement.
Cost Benefit Analysis of Inert Gas Systems for Chemical and Product Tankers
Authors: Thomas Martyn , Skjong Rolf
Published: February 2010

This paper details the work carried out to complete a Formal Safety Assessment (FSA) to assess the effectiveness of inert gas systems (IGS) in reducing the risk associated with cargo tank fire and explosions on chemical and oil tankers <20,000dwt. Two different IGSs are considered; N2 for chemical tankers and conventional oil burning type for oil tankers. N2 IGS is required on chemical tankers to preserve the quality of the chemicals transported on these ships. These IGS systems are evaluated with Cost Benefit Assessments (CBA) to ascertain their cost effectiveness with regards to reducing potential loss of life, potential loss of cargo, potential pollution and potential loss of property. In this respect, the Gross Cost of Averting a Fatality (GCAF) and Net Cost of Averting a Fatality (NCAF) are calculated using the standard FSA method recognized by the International Maritime Organization (IMO). Further, the Cost of Averting one Tonne of oil Spilled (CATS) (Skjong et al., 2005 & Vanem et al., 2008) is applied to understand the cost effectiveness of IGSs in preventing environmental pollution. The risk reduction is estimated from detailed considerations of the accident statistics for tankers >20,000dwt, where mandatory requirements for IGS was introduced in 1990. Comparison was made on risks resulting from accidents involving fire and/or explosion in the cargo tank of tankers of >20,000dwt for the period of 1978–1983, in which most such tankers were not provided with IGS; and for the period 1990–2005, in which all such tankers were provided with IGSs under the requirement of SOLAS Chapter II-2. The paper further assumes that tankers <20,000dwt that carry cargo with flashpoint <60°C should have IGS installed, whilst ships without IGS may continue carrying cargo with flashpoint >60°C. This way the question of requiring IGS is answered based on real risk of fire and explosion, and avoid introducing a rather arbitrary limit based on size of the ships.
Documentation of Operational Limits of Free-Fall Lifeboats by Combining Model Tests, Full-Scale Tests, and Computer Simulation
Authors: Kauczynski Wojciech E. , Werenskiold Per , Narten Frode
Published: February 2010

Historically, approval of lifeboats is based on a “calm water” philosophy through the SOLAS regulatory regime. In spring 2005 during offshore installation tests in calm water, unacceptable structural deflection of the roof for one type of free-fall lifeboat was revealed. Immediate actions were initiated by the Norwegian Oil Industry Association (OLF) and Statoil, including the goal of studying and documenting the main performance factors for free-fall lifeboats at up to a 100-year weather condition. In addition, OLF has request to develop relevant criteria for in depth classification of performance, and finally to upgrade urgently, when relevant, all free-fall lifeboats operating on the Norwegian continental shelf to the agreed standards. The basic performance criteria of free-fall lifeboat systems in emergency conditions are: structural strength, acceleration loads on passengers during water impact, boat forward speed immediately after water entry, and the manoeuvring away to a safe distance from the installation. Within the OLF-project, MARINTEK has performed an extensive model test program (over 25000 tests) with the 14 different types of free-fall lifeboats (launched by vertical drop or from a skid). Boat performances have been examined in different weather conditions, ranging from still water up to 11m wave height (regular waves and wind) or 7m (irregular significant wave height with corresponding wind). Calm water model test results have been compared to full-scale test results. In order to extend prognosis of the lifeboat performances up to 100-year storm condition (Hs = 15.7m), special extrapolation methods have been developed for studying the three basic performance areas, augmented by computer simulations applied for higher sea states. This paper presents example results and experiences gained from the model tests, full-scale tests and combined use of simulations and model test results. Experimental model test set-up and applied analysis and extrapolation methods are reviewed. Finally, the application of newly proposed performance and technical criteria is discussed.
Assessment of the Total Ship’s Hull Girder Bending Stresses When Unified Model of Sagging and Hogging Bending Moments is Used
Authors: Ivanov Lyuben D.
Published: February 2010

A method is proposed for calculating the hull girder bending stresses following the procedure in the class rules but in probabilistic terms, i.e. the still water and the wave-induced bending moments; the total hull girder bending moment; the hull girder section modulus and the hull girder bending stresses are treated as random variables with corresponding probabilistic distributions. The still water and wave-induced hull girder hogging and sagging loads are presented in probabilistic format as one phenomenon, i.e. using bi-modal probability density functions. The probabilistic distribution of the total hull girder load is calculated using the rules of the composition of the distribution laws of the constituent variables. After that, the hull girder geometric properties are presented in probabilistic format as annual distributions and distributions for any given life-span. Thus, it becomes possible to calculate both the annual probabilistic distributions and the probabilistic distribution for any given ship’s life span of the hull girder stresses. Individual amplitudes statistical analysis and extreme value statistics are used. Then, the probability of exceeding the permissible hull girder bending stresses in the class rules is calculated. An example is given for 25K DWT bulk carrier.
Validation of a New Hydroelastic Code for Flexible Floating Structures Moored in Waves
Authors: van Kessel J. L. F.
Published: February 2010

Natural periods of elastic modes can be in the range of the wave spectrum for relatively long and slender floating bodies. As a result elastic body deformations such as vertical bending, horizontal bending and torsion may be significant and need to be taken into account in the hydrodynamic analysis of very large floating structures. The behavior of flexible floating bodies in waves has been studied at Delft University of Technology. For this purpose the existing linear three dimensional diffraction code DELFRAC was modified to take into account the fluid-structure interaction of deformable bodies at zero forward speed in waves. This paper focuses on the validation of the new hydroelastic code for flexible floating structures moored in waves. Numerical results are validated by model experiments of a flexible barge in waves from different headings. In addition, the obtained results are compared with results from other existing hydroelastic programs. In general it is shown that numerical results show good agreement with experimental values.
A Robust and Efficient Computational Method for Fatigue Reliability Update Using Inspected Data
Authors: Wu Y.-T. , Ku A. P. , Serratella C. M.
Published: February 2010

This paper presents a new methodology for reliability-based inspection planning focusing on robust and accurate computational strategies for fatigue-reliability updating using inspection results. The core of the proposed strategy is a conditioned sampling-based method, implemented by a Fast Probability Analyzer (FPA) software where efficiency is achieved by using the importance sampling principal. For a single component or limit state, FPA first generates Markov-Chain Monte Carlo (MCMC) samples in the failure domain, then applies an adaptive stratified importance sampling (ASIS) method to compute probability of failure (PoF) with error control. Once the MCMC samples have been created, solving a reliability updating problem is fairly straightforward and computationally robust relative to the conventional system reliability methods that rely on linearization of the limit states. The new approach is demonstrated using examples including stiffened panels of a ship-shaped vessel where reliability is updated using inspection results from 100 panel connections.
Estimation of Long Term Extreme Waves From Storm Statistics and Initial Distribution Approach
Authors: Hagen O̸istein
Published: February 2010

Extreme wave heights and extreme crest heights are estimated by the initial distribution approach and by Peak Over Threshold (POT) analysis for storm events. The analysis applies the Ekofisk Reference Data Set (ERDS), which is a high quality data set covering a time span of 26 years from the Ekofisk Area in the North Sea. The paper addresses methodology issues that influence the predicted extreme value statistics for metocean variables. These issues include plotting position, minimization procedures for least squares regression, and threshold selection for the POT analysis. Furthermore, directional statistics, sampling variability and combination of wave crests and sea level variability. Uncertainties and sensitivity to assumptions are discussed.
Extreme Weather Warning Criteria
Authors: Hagen O̸istein , Solland Gunnar
Published: February 2010

The paper addresses determination of the weather criteria that should apply for platforms that are assumed to be unmanned during storms. The methodology ensures that the safety of personnel on these platforms is at least as good as for personnel on platforms that satisfy current structural requirements for manned platforms. A probability based procedure is defined to achieve this goal. In this paper the requirements in the NORSOK standards are used as the reference standard for the structural reliability. The forecasted environmental conditions that require unmanning are determined by a stepwise procedure: First, adopting the principles of the structural code, we determine the maximum environmental action (described by crest elevation Clim) the structure can resist. If Clim is lower than the crest corresponding to the requirements for manned structures, unmanning criteria are established. By integration over all sea states below the threshold significant wave height Hs,thr, the required Hs,thr is determined such that the probability that the annual maximum crest exceeds Clim, complies with the acceptance criterion. The forecasted environmental conditions at which shut-down and unmanning shall be completed are for Hs ≥ Hs,thr. The target probability for the governing failure mode is distributed between the directional sectors such that the frequency of unmanning the platform is minimized. Because forecasted wave directions are uncertain, the decision process is made more robust by a smoothing technique that retains the exceedance probabilities for the directional sectors.
Discussion on the Defence Criterion of Disaster Prevention Engineering in Coastal Region
Authors: Xie Botao , Liu Defu , Jiang Hao , Wang Fengqing , Huang Shichang , Liu Junna
Published: February 2010

In recent years, the frequency and intensity of the typhoon is gradually increasing on account of the global warming and sea level rise. The disasters induced by typhoon are complex, such as strong wind, huge waves, storm surge, heavy rain, floods, and so on. In consideration of the lessons from disasters and complexity of typhoon, a statistical and numerical model based the on Double-Layer Nested Multi-objective Probability Model (DLNMPM) and numerical model was established to calculate the probable maximum storm surge with different combinations of typhoon characteristics. In this model, the long term probability characteristics of typhoon factors such as the typhoon occurring frequency (λ), drop of central pressure (ΔP), radius of maximum wind speed (Rmax), typhoon moving speed (S), minimum distance between typhoon center and certain area (δ) are considered, and the storm surge of Hangzhou Bay in Zhejiang Province is carried out as example. The results predicted by this model can offer a useful reference for the defence criterion of the coastal regions for its probabilistic meaning.
Innovative Harsh Environment Dry-Tree Support Semi-Submersible for Ultra Deepwater Applications
Authors: Srinivasan Nagan , Sundaravadivelu R. , Selvakumar R. , Kanotra Rahul
Published: February 2010

Natural heave period exceeding over 21 sec is not the only important design criteria for the design of an ultra deepwater semi-submersible for dry-tree support application. The key design features that would enhance the applications of the semi-submersible design for ultra deepwater are vessel motion characteristic, heave natural period, high air-gap, large deck-area, large deck pay-load, reduced mooring load, large riser pull-down load, feasible for dynamic positioning, feasible for dry-tow, feasible for wet-tow, feasible for self-installation, feasible for quay-side top side integration, feasible for float-over installation. This paper presents the design innovations of the semi-submersible that has reached the above listed desired key factors. The designed vessel supports dry-tree with large riser loads resulted from ultra deepwater which is decoupled and is also independent of the designed top side pay load. The design is streamlined to withstand harsh environment. The vessel is designed to favor both options with quay-side deck integration or float-over deck installation. Extreme low accelerations in extreme wave environment on top of the above desired features make this semi-submersible suitable for harsh environment and ultra deepwater applications. A brief summary of hydrodynamic response of the vessel is added in this paper.
Development of a Multi-Body Vessel Dynamics Simulation Tool
Authors: Yu Xiaochuan , Lakhotia Chandan , Falzarano Jeffrey M.
Published: February 2010

Multi-body dynamics is important in many fields of engineering. For the at-sea transfer of cargo between ships multi-body dynamics is particularly important. There are several methods of transferring solid cargo between vessels and these include by crane or by ramp. Each method is extremely sensitive to the relative motions between the various vessels. An accurate modeling of the vessels’ motions is critical in determining limiting sea state conditions and in suggesting how to improve the given system. There are various levels of approximation which are commonly employed to model vessel hydrodynamics and we hope to eventually determine what level of approximation is appropriate for a given situation. In this paper, we will compare the effects of considering as well as ignoring the multi-body hydrodynamic interactions using a constant coefficients approximation to the time domain radiated wave force.
Nonlinear Seismic Soil-Pile-Structure Interaction Analysis of Fixed Offshore Platforms
Authors: Zargar Ehssan , Aghakouchak Ali Akbar , Gholami Maziar
Published: February 2010

A nonlinear seismic soil-pile-structure interaction (SSPSI) analysis of fixed offshore platforms constructed on pile foundations including both vertical and battered piles is presented. The analysis is carried out in time domain and the effects of soil nonlinearity, discontinuity at pile soil interfaces, energy dissipation through soil radiation damping, formation of soil layers on bed rock, structural material nonlinearity and geometrical nonlinearity are considered. A combination of FEM approach and BNWF approach is used in modeling pile (substructure), platform structure (superstructure) and soil media. Gapping in clay is modeled by a special connector configuration. To find out the ground motion of soil layers caused by earthquake excitations at bed rock, a nonlinear site response analysis is performed. The effects of soil-pile-structure interaction on nonlinear seismic analysis of offshore platforms are discussed. A comparison of SSPSI model and pile stub modeling is investigated and it is generally concluded that considering soil-pile-structure interaction causes higher deflections and lower stresses in the platform elements due to soil flexibility, nonlinearity and radiation damping and leads to a more feasible and realistic platform design. The sequence of generation of plastic zones in the structure and their distribution are also investigated. Results show that this nonlinear behavior is started at brace elements and then propagated to leg elements as earthquake last.
Wave Elevation Between Elliptical Structures
Authors: Chatjigeorgiou Ioannis K. , Mavrakos Spyros A.
Published: February 2010

The hydrodynamic interaction of waves with arrays of vertical elliptical cylinders is considered. The present paper aims at developing of an efficient calculation method for predicting the extreme elevation of the free surface, in the fluid domain between ship-shaped structures in close proximity. Linear potential theory is employed and the solution method is based on the semi-analytical formulation of the various velocity potentials in elliptical coordinates, using series expansions of Mathieu functions and the so-called addition theorem for Mathieu functions.
Fatigue Yield of Ship Structures
Authors: Zˇiha Kalman , Blagojevic´ Branko
Published: February 2010

The paper on the first place summarizes the fatigue yield approach as a cause-effect interaction between fatigue damage progression and fatigue endurance. Secondly it investigates the fatigue strength worsening on experimental S-N data and the load variability effects in shipbuilding. Next it applies the Classification Society’s rule-based procedure for fatigue analysis of ship’s structure that uses a simplified fatigue strength assessment method. The example elaborates fatigue yield effect on the seagoing operation of a double hull 47400 tdw tanker. At the end the paper recommends the procedure for assessment of ship lifetime shortening due to the fatigue yielding under constant and variable amplitude block loadings.
A State of Art FPSO With Dry Tree System
Authors: Ji Chunqun
Published: February 2010

This paper provides a state of art dry tree floating system by using a moored column-buoy connected to a ship shaped vessel. The Buoy Moored Floating Production Storage and Offloading system (BMFPSO) uses a column-buoy instead of the turret in a conventional FPSO design. Similar to the turret, the column-buoy allows the vessel to weather vane about the column-buoy. In addition, the vessel can move in vertical direction relative to the column-buoy. Thus vertical motion of the column-buoy is de-coupled from the FPSO hull motion. The buoy will have relatively small heave motion allowing the use of proven top tensioned riser technology. The motion characteristics of the system make it operable in a wide range of environmental conditions.
FPSO Risk Assessment and Acceptance Criteria With Application to FPSO Mooring Systems
Authors: Faber Michael H. , Straub Daniel , Montes-Iturrizaga Roberto , Heredia-Zavoni Ernesto
Published: February 2010

Risk based design code safety format calibration for FPSO installations is addressed based on the results of a recent industrial project performed for IMP by the authors. Generic risk models for general engineering systems are introduced taking basis in recent work by the Joint Committee on Structural Safety (JCSS). Thereafter, the scenarios considered for the risk based calibration of a design code safety format for the design of FPSO facilities in the Gulf of Mexico are outlined in some detail. Furthermore, it is shown how these scenarios may be represented in a generic risk assessment model greatly enhanced by the utilization of hierarchical risk modeling procedures such as Bayesian Probabilistic Nets (BPN’s). A short outline of the Life Quality Index (LQI) principle is then introduced as a practically applicable means to determine how much should be invested into life saving activities. Finally, an example is given where the introduced concepts are used for the purpose of determining the target reliability index for individual mooring lines taking into account the direct and indirect consequences of failure of the mooring system for a considered generic FPSO installation.
Unique Host Iron Utilization Mechanisms of
Helicobacter pylori
Revealed with Iron-Deficient Chemically Defined Media
Authors: Senkovich Olga , Ceaser Shantelle , McGee David J. , Testerman Traci L.
Published: February 2010

Helicobacter pylori
chronically infects the gastric mucosa, where it can be found free in mucus, attached to cells, and intracellularly.
H. pylori
requires iron for growth, but the sources of iron used
in vivo
are unclear. In previous studies, the inability to culture
H. pylori
without serum made it difficult to determine which host iron sources might be used by
H. pylori
. Using iron-deficient, chemically defined medium, we determined that
H. pylori
can bind and extract iron from hemoglobin, transferrin, and lactoferrin.
H. pylori
can use both bovine and human versions of both lactoferrin and transferrin, contrary to previous reports. Unlike other pathogens,
H. pylori
preferentially binds the iron-free forms of transferrin and lactoferrin, which limits its ability to extract iron from normal serum, which is not iron saturated. This novel strategy may have evolved to permit limited growth in host tissue during persistent colonization while excessive injury or iron depletion is prevented.
A HYBRID ARTIFICIAL BEE COLONY OPTIMIZATION AND QUANTUM EVOLUTIONARY ALGORITHM FOR CONTINUOUS OPTIMIZATION PROBLEMS
Authors: DUAN HAI-BIN , XU CHUN-FANG , XING ZHI-HUI
Published: February 2010

In this paper, a novel hybrid Artificial Bee Colony (ABC) and Quantum Evolutionary Algorithm (QEA) is proposed for solving continuous optimization problems. ABC is adopted to increase the local search capacity as well as the randomness of the populations. In this way, the improved QEA can jump out of the premature convergence and find the optimal value. To show the performance of our proposed hybrid QEA with ABC, a number of experiments are carried out on a set of well-known Benchmark continuous optimization problems and the related results are compared with two other QEAs: the QEA with classical crossover operation, and the QEA with 2-crossover strategy. The experimental comparison results demonstrate that the proposed hybrid ABC and QEA approach is feasible and effective in solving complex continuous optimization problems.
CALLER BEHAVIOUR CLASSIFICATION USING COMPUTATIONAL INTELLIGENCE METHODS
Authors: PATEL PRETESH B. , MARWALA TSHILIDZI
Published: February 2010

A classification system that accurately categorizes caller interaction within Interactive Voice Response systems is essential in determining caller behaviour. Field and call performance classifier for pay beneficiary application are developed. Genetic Algorithms, Multi-Layer Perceptron neural network, Radial Basis Function neural network, Fuzzy Inference Systems and Support Vector Machine computational intelligent techniques were considered in this research. Exceptional results were achieved. Classifiers with accuracy values greater than 90% were developed. The preferred models for field 'Say amount', 'Say confirmation' and call performance classification are the ensemble of classifiers. However, the Multi-Layer Perceptron classifiers performed the best in field 'Say account' and 'Select beneficiary' classification.
GLOBAL ROBUST STABILITY ANALYSIS FOR NEURAL NETWORKS WITH CONSTANT OR VARIABLE DELAYS
Authors: WANG HUI , LI CHUANDONG , XU HONGBING
Published: February 2010

In this paper, some criteria are derived for global robust asymptotic stability of a class of interval neural networks with multiple constant or time-varying delays via the Lyapunov–Krasovskii stability theory for functional differential equations and the linear matrix inequality (LMI) approach. The main results are applied to the uncertain systems with single delay, and several new criteria to determine the asymptotical convergence of these systems are obtained. Numerical examples are also given to show the effectiveness of our results.
MEDICAL IMAGE SEGMENTATION USING FUZZY C-MEAN (FCM) AND USER SPECIFIED DATA
Authors: BALAFAR M. A. , RAHMAN RAMLI A. B. D. , SARIPAN M. IQBAL , MASHOHOR SYAMSIAH , MAHMUD ROZI
Published: February 2010

Image segmentation is one of the most important parts of clinical diagnostic tools. Medical images mostly contain noise and inhomogeneity. Therefore, accurate segmentation of medical images is a very difficult task. However, the process of accurate segmentation of these images is very important and crucial for a correct diagnosis by clinical tools. We proposed a new clustering method based on Fuzzy C-Mean (FCM) and user specified data. In the postulated method, the color image is converted to grey level image and anisotropic filter is applied to decrease noise; User selects training data for each target class, afterwards, the image is clustered using ordinary FCM. Due to inhomogeneity and unknown noise some clusters contain training data for more than one target class. These clusters are partitioned again. This process continues until there are no such clusters. Then, the clusters contain training data for a target class assigned to that target class; mean of intensity in each class is considered as feature for that class, afterwards, feature distance of each unsigned cluster from different class is found then unsigned clusters are signed to target class with least distance from. Experimental result is demonstrated to show effectiveness of new method.
NONCOST SENSITIVE SVM TRAINING USING MULTIPLE MODEL SELECTION
Authors: CHATELAIN CLEMENT , ADAM SEBASTIEN , LECOURTIER YVES , HEUTTE LAURENT , PAQUET THIERRY
Published: February 2010

In this paper, we propose a multi-objective optimization framework for SVM hyperparameters tuning. The key idea is to manage a population of classifiers optimizing both False Positive and True Positive rates rather than a single classifier optimizing a scalar criterion. Hence, each classifier in the population optimizes a particular trade-off between the objectives. Within the context of two-class classification problems, our work introduces "the receiver operating characteristics (ROC) front concept" depicting a population of SVM classifiers as an alternative to the receiver operating characteristics (ROC) curve representation. The proposed framework leads to a noncost sensitive SVM training relying on the pool of classifiers. The comparison with a traditional scalar optimization technique based on an AUC criterion shows promising results on UCI datasets.
USING NEURAL NETWORKS TO MINIMIZE THE DURATION OF AUTOMATED NEGOTIATION THREADS FOR HYBRID OPPONENTS
Authors: PAPAIOANNOU IOANNIS , ROUSSAKI IOANNA , ANAGNOSTOU MILTIADES
Published: February 2010

Neural networks (NNs) provide an efficient tool that can be trained to estimate the value of output parameters given certain metrics. In this paper, NNs are used to enhance intelligent agents that negotiate on behalf of their owners aiming to maximize their utility. More specifically, NNs are exploited in order to predict the hybrid negotiation behavior of the agents' opponents, thus achieving more profitable results for the parties these agents represent. The NNs provide the means so that the agents can early detect the cases where agreements are not achievable, thus supporting their decision to withdraw or not from the negotiation threads. The designed NN-assisted negotiation strategies have been evaluated via extensive experiments and are proven to be very useful, as they manage to significantly reduce the average duration of the negotiation threads.