bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparing Dynamic and Static Push Over Analysis in Assessment: The Ultimate Capacity of Fixed Offshore Platforms
Authors: Memarpour Mohammad M. , Kimiaei Mehrdad , Shayanfar Mohsenali
Published: February 2010

Quasi static push over analysis is commonly used in assessing the Reserve Strength Ratio (RSR) of fixed offshore platforms. In this method, the lateral loads are proportionally increased until overall structural collapse is reached. In reality the forces imparted by the waves traversing the structure, are dynamic loads. If these lateral dynamic loads are to be used in push over analysis, they can provide a more precise estimation of the maximum load that can be resisted by the structure compared to the value derived using quasi static approach. The main objective of this study is to compare RSR of a sample fixed offshore platform in quasi static and a dynamic loading approaches. The extents of the effect of main input parameters in determination of static and dynamic RSR for offshore platforms are also investigated in this paper.
Life-Cycle Risk Evaluation for Offshore Platform Based-on Uncertain Grey-AHP Method
Authors: Liu Zhijun , Ji Zhuoshang , Lin Yan
Published: February 2010

Due to the complexity of real-world and the subjective nature of human judgments, an uncertain Grey-AHP method is developed to evaluate the life-cycle risk for offshore platform. According to the proposed method, interval numbers are introduced to express the values evaluating loss of risk indicators and the judgments of possibilities comparison of two indicators in a pairwise comparison matrix. In this paper, a life-cycle based risk evaluation criteria system for offshore platform can be built by risk identification in each stage of life-cycle. Then the values evaluating loss of risk indicators and interval comparison matrices are obtained by experts concerned. From the former, interval grey numbers is acquired by grey clustering analysis. Simultaneously, interval weight vectors are calculated from the later. With synthetic evaluation, the grade of risk is determined by the maximal subjection grade and its near degree. In the end, a practical case is provided to illustrate the validity and practicality of the proposed method.
Experimental Study of the Local Wave Velocity Field During a Wave Impact Occurrence
Authors: Muthanna Chittiappa , Stansberg Carl Trygve , Baarholm Rolf , Harendza Astrid , Priscic Mia
Published: February 2010

The velocity field in the wave crest zone during wave impact phenomena was successfully measured using a 2 component PIV technique with a simplified two dimensional box model in a wave tank. Measurements were made for two different regular wave conditions and of the undisturbed wave field for the two wave conditions in order to study the influence of the modeled platform deck. The measurements of the wave velocity field showed that for the higher amplitude wave condition, vertical velocity components were amplified in the wave run up region, and away from this region, were not as heavily influenced as the horizontal velocity component. For the smaller wave amplitude vertical velocity components were reduced slightly, whereas the horizontal velocity components did not seem to be influenced. The measurements showed that the PIV technique is a practical and feasible tool in which to study and measure the wave velocity field, but it does come with some limitations.
New Standard for Assessment of Structural Integrity for Existing Load-Bearing Structures-Norsok N-006
Authors: Solland Gunnar , Lotsberg Inge , Bjo̸rheim Lars G. , Ersdal Gerhard , Gjerstad Vidar-Andre´ , Smedley Philip
Published: February 2010

An increasing number of platforms in the Norwegian continental shelf are reaching their design life. For various reasons these platforms will require an assessment of their structural integrity. When performing these assessments the engineer is faced with tasks where little guidance is found in design standards, for several reasons. The two most important being: 1) The analyses that is performed in a typical assessment of existing structure is often applying very advanced techniques and methodology that seldom is used in design of new structures, as the cost of doing advanced analysis is relatively low compared to replacement of an existing structure, but relatively high compared to moderate additions of e.g. steel in the design of a new structure. 2) Design standards are based on theories, methods and experience for structures in a given design life (e.g. fatigue design and corrosion protection design). When this design life is extended, sound methods for ensuring that the structures are still sufficient safe is needed. Such methods will normally be “condition based design”, where inspection, maintenance and repairs are included in the assessment in integrated way. Such methods are not given in normal design standards. For these reasons a new NORSOK standard is developed that gives recommendation on how to deal with the specific aspects that engineers meet when performing assessments of structures in general, but also specifically for assessment for life extension. The standard is named “Standard for Assessment of Structural Integrity for Existing Load-bearing Structures” and is issued as a NORSOK standard and given the number N-006 [1]. The topics that are covered in the standard include: Shut down and unmanning criteria for platforms not meeting ordinary requirements, specific issues for determination of ultimate capacities by use of non-linear methods, cyclic capacity checks, fatigue life extension, requirements to in-service inspection etc. The paper describes the background and the content of the new standard and it presents examples of recommendations given. The role of the new standard in the Norwegian regulatory system is shown.
Analysis of the Tunnel Immersion for the Busan-Geoje Fixed Link Project Through Scale Model Tests and Computer Simulations
Authors: Cozijn Hans , Heo Jin Wook
Published: February 2010

In Korea a four lane motorway is constructed between the city of Busan and the island Geoje, reducing traveling times from 1 hour by ferry to just 10 minutes by car. The so-called Busan-Geoje Fixed Link consists of 2 cable-stayed girder bridges and a tunnel, crossing the bay of Jinhae. The submerged tunnel is built by transporting each of its 18 elements below 2 pontoons from a construction dock to their final positions and lowering them on the sea bed. The project is unique, because the tunnel elements are installed in a bay with direct access towards open sea. For this reason, the effects of incoming swells and wind seas were investigated in detail, so that the operational limits of the tunnel element immersion could be accurately determined. This was achieved by using an approach of combined hydrodynamic scale model tests and time-domain computer simulations. First, scale model tests were carried out in MARIN’s Shallow Water Basin. A detailed test set-up was constructed, including the trench in which the tunnel elements are placed, as is shown in the photograph. Models of a tunnel element, two pontoons, the mooring system, contraction lines and suspension wires were constructed at a scale of 1:50. The motions of the pontoons and the submerged tunnel element, as well as the tensions in the lines, were measured in a range of different wave conditions. Different stages of the tunnel immersion were investigated. Second, a simulation model of the pontoons and tunnel element was constructed in MARIN’s time-domain simulation tool aNySIM. The large number of mooring lines, contraction lines and suspension wires resulted in a relatively complex numerical model. The simulation model was calibrated such that the results from the model tests could be accurately reproduced. Subsequently, a sensitivity study was carried out, investigating the parameters most critical to the operation and the mooring system of the pontoons was further optimized. Finally, the operational limits of the tunnel immersion were evaluated by carrying out more than 6,500 time-domain simulations, investigating a large number of different combinations of wind sea and swell. The simulation results included motions, velocities and accelerations, as well as line tensions. The extreme values were used to perform a combined evaluation of more than 10 structural and operational criteria. The photograph below (copyright Peter de Haas, Royal Haskoning) shows the immersion of the first of 18 tunnel elements in the bay of Jinhae, in February 2008.
Calculation of Low-Frequency Waves in Shallow Water and Comparison to Common Practice in Diffraction Methods
Authors: de Jong Martijn P. C. , Borsboom Mart J. A. , Dekker Johan
Published: February 2010

The increasing interest in LNG terminals at nearshore locations has led to the recent Joint Industry Project (JIP) HAWAI (sHallow WAter Initiative, 2005–2008), a collaboration between MARIN, Single Buoy Moorings, Bureau Veritas, and Deltares (formerly Delft Hydraulics). In this JIP shallow-water wave conditions and their effect on moored vessels were studied. Part of the JIP involved the evaluation of knowledge and numerical models from coastal engineering with respect to their potential for determining shallow-water wave conditions. Operational Boussinesq-type wave models and a long-wave shallow-water model with primary-wave forcing were considered in detail. The former were found to be limited in application due to the limited depth range that can be covered accurately by such models. The latter is considered the most practical and versatile modelling approach that is presently available in coastal engineering for the application considered here. It was used for numerical simulations of a measurement site near the city of Duck (NC, USA). Computed low-frequency wave parameters compare favourably to measured values for three typical primary wave conditions. A comparison of these numerical results with low-frequency wave parameters obtained from the standard approach used in diffraction methods, originally developed for deep water applications, indicates that such a standard approach is not expected to be applicable at shallow-water locations. Detailed local measurements, site-specific numerical calculations and scale-model tests that include the local geometry and the effects of directional spreading, are required to determine the low-frequency wave conditions for design and workability limits at such locations with sufficient detail and accuracy.
Procedure to Define Loads on Stools of FPSO’s
Authors: de Souza Silva Rodrigo , de Souza Santos Mario Antonio , Videiro Paulo Mauri´cio
Published: February 2010

FPSO units require process plants that are usually structured in modules fitted to deck by means of a minimum discrete supports because of assembling difficulties. This structural arrangement imposes high local stress level to the hull and their supports due to large module weight. Reactions are even greater during the operation, because of inertial forces due to unit motion. Therefore, accuracy is required in order to obtain reactions and to develop a safe and optimized design of module connections and hull and module design, as well. Whereas, installation and operation phases could have different boundary conditions, which means: free rotation after module landing to deck supports and fixed after final hook up to deck, it is necessary to be performed a full assessment of those parameters variation (boundary conditions). The aim of this paper is to present a calculation procedure where each step produces results which must be combined to achieve the final result, providing more accurate results.
Hydrodynamic Interactions and Relative Motions Analysis for Installation of an Extendable Draft Platform
Authors: Koo Bonjun , Kim Jang Whan
Published: February 2010

The Extendable Draft Platform (EDP) is a deep draft, column stabilized platform with a deck box support for topsides and a single, deep draft heave plate that provides suitable motion characteristics to enable the use of dry tree top tensioned risers. The EDP can be fabricated with topsides installed on the deck box and commissioned quayside in a typical construction yard. With the columns in the retracted position, the EDP floats on its deck box and can be towed, in this configuration, to the location of interest. Once the EDP is transported to its final site, the columns and heave plate are lowered to their final operating draft. During the lowering sequence, the deck box and the lower hull become two relatively independent bodies, mechanically connected by chains that control the lowering of the columns and heave plate, and the guides between the deck box and the columns. This multi-body system is hydrodynamically coupled because of radiated and diffracted waves. The global performance analyses of the installation process (lowering of the lower hull) are carried out by three different methods. The first method is frequency-domain analysis by WAMIT and a frequency domain motion solver. In the frequency domain analysis, all the mechanical connections are modeled as linear springs. The second method is time-domain, partially coupled analysis using HARP/WINPOST. In this analysis, the off diagonal 6×6 hydrodynamic interactions are ignored. The last method is a time domain, fully coupled analysis using HARP/WINPOST. In this analysis, full 12×12 hydrodynamic interactions are considered. In the time domain analyses, the mechanical couplings between each column and deck box are modeled with linear springs and the chain connections are modeled with slender rods by using the nonlinear finite element method. This paper presents and compares analysis results based on the three methods for relative motions and loads between the deck box and the lower hull during the lowering of the columns and heave plate.
Whole Ship and Fatigue Analyses for Development of Ice Class LNGC
Authors: Jun Min-Jung , Park Jae-Hyung , Woo Je-Hyouk
Published: February 2010

This paper describes the whole ship and fatigue analyses of a 170 k Ice class LNGC, first ice class vessel of DSME. This paper includes determination of design load, global strength and fatigue strength. This subject vessel was designed to have more than 40 years’ fatigue life against given environmental conditions and fatigue damage was assessed based on stochastic method. Whole ship FE analysis was also carried out to verify the structural adequacy of global strength based on direct wave load analysis. In stochastic fatigue analysis, fatigue damage was calculated based on direct wave load analysis. D-SAFS, developed by DSME, was used in stress RAO generation and fatigue damage assessment. Stress RAOs were made based on ‘Component Based Method’. In this method, structural analyses were carried out for each unit load case and then resultant stress was combined with wave load analysis results to generate stress RAOs. D-SFAS defines unit load cases automatically and generated stress RAO from motion analysis results. Whole ship FE models having fine mesh in fatigue sensitive area were used in structural analysis. Different steel density was also assigned along ship length for mass adjustment within hull structure. Some hot spots were found not to satisfy the design fatigue life of 40 years in initial design stage. Through geometry modification, structural reinforcement or improving fabrication method such as grinding, all structural details could satisfy design fatigue life of 40 years. According to the results of whole ship analysis, there were some high stresses at local area. Conclusively, additional strengthening of the hull was required compared to standard class rule requirements, with respect to yield and buckling and fatigue strength, leading to a more robust vessel.
Dry Wellhead Completion for Mono-Column FPSO Units Operating in Ultradeep Waters
Authors: Reyes Marta C. T. , Alho Alexandre T. P. , Kaleff Peter , Masetti Isaias Q.
Published: February 2010

A floating structure is proposed to act as a dry wellhead completion support for a mono-column design developed by Petrobras: the MONOBR FPSO. After the discussion of the design issues involved, the MONOBR design is introduced and the peculiarities affecting the insertion of a floating structure into its moonpool are analyzed. In what follows, the main characteristics of the proposed floating structure layout are presented in the context of its purpose of allowing for the effortless vertical motion relatively to the housing mono-column unit, followed by the considerations pertinent to the ballast system devised to allowing for the adequate operation, by the characteristics of the roller mechanisms proposed to ensure the aligned motion desired and by the analysis of the structural issues and the proposed structural layout.
Time Domain Analysis for DP Simulations
Authors: Serraris Jorrit-Jan
Published: February 2010

As the offshore industry is developing into deeper and deeper waters Dynamic Positioning (DP) techniques are becoming more important to the industry. MARIN’s new multibody time domain simulation program aNySIM is recently extended with a module to simulate DP applications. The model is 6 degrees of freedom and includes a Kalman filter, PID controller and a Lagrange optimized allocation algorithm. Thruster interaction effects are taken into account in the model. The present paper focuses on the methods used in the numerical DP model. A typical case for a DP operated monohull drillship is presented and will be discussed in comparison with model test results.
The Equivalent Power Storm Model for Long-Term Predictions of Extreme Wave Events
Authors: Fedele Francesco , Arena Felice
Published: February 2010

We present the Equivalent Power Storm (EPS) model as a generalization of the Equivalent Triangular Storm (ETS) model of Boccotti for the long-term statistics of extreme wave events. In the EPS model, each actual storm is modeled in time t by a power law ∼|t−t0|λ, where λ is a shape parameter and t0 is the time when the storm peak occurs. We then derive the general expression of the return period R(Hs > h) of a sea storm in which the maximum significant wave height Hs exceeds a fixed threshold h as function of λ. Further, given the largest wave height Hmax, we identify the most probable storm in which the largest wave occurs and derive an explicit expression for the return period R(Hmax >H) of a storm in which the maximum wave height exceeds a given threshold H. Finally, we analyze wave measurements retrieved from two of the NOAA-NODC buoys in the Atlantic and Pacific oceans and find that the EPS predictions are in good agreement with those from the ETS model.
Probability Distributions for Wave Runup on Offshore Platform Columns
Authors: Izadparast Amir H. , Niedzwecki John M.
Published: February 2010

For the design of offshore structures it is important to accurately predict wave runup and thus avoid topside inundation and minimize the wave impact on the underside of the deck structure. In this paper a three-parameter probability distribution function for nonlinear wave run-up amplitudes is presented. It builds upon previous studies and utilizes the quadratic transformation of incident waves. The parameters of this probability distribution are estimated from the data using method of L-moments and the explicit relation between the parameters and L-moments is presented. The L-moments themselves are linear combinations of ordered data and consequently they are less influenced by outliers and unexpectedly large values. Earlier theoretical models, based on simplified diffraction theory, are presented and compared with the L-moments model. A three-parameter Weibull distribution model that utilizes the method of L-moments is derived and discussed. Run-up measurements from a mini-TLP model test program are used as the basis for comparison of the three methods. This study demonstrates that the new empirical model and Weibull distribution are more robust in representing the probability distribution of nonlinear runup amplitudes especially for the weakly nonlinear cases with moderate steepness. Although the new empirical model and Weibull distribution have different probability structure their estimates are found to be fairly close.
Riser Top Loads on Turret Moored FPSO
Authors: de Arau´jo Castro Felipe , Magluta Carlos , Ellwanger Gilberto Bruno
Published: February 2010

In the Campos Basin, offshore Brazil, catenary flexible risers are extensively used in marine production systems. One of the most important design phases of these systems is the riser extreme top load analysis, which provides results for riser and accessory designs as well as input for structural analysis of platform supports. In addition to the riser’s characteristics (weight, diameter, structural damping, axial and bending stiffness), riser top loads depend on several other factors, such as platform static and dynamic behavior, including the collective effect of lines (mooring lines and risers) drag and damping, platform motion, connection support position and environmental loading cases. This study is based on the results from a model test and numerical analysis of a typical turret moored FPSO system, with catenary risers and mooring lines. This test was programmed to evaluate the consequence of each of the above mentioned parameters on flexible riser top loads. Model tests were performed in the MARIM (Maritime research Institute Netherlands) wave tank to represent the offshore system in 850 meter water depth and included loading case tests combining wind, waves and current in different relative directions (collinear, crossed and transversal). The analysis of the model tests results indicated significant variations in the platform behavior, when the drag and damping generated by the risers and mooring lines were taken into account. Additional analyses were performed, based on numerical simulations of the top load variations (axial, shear tension and moment), induced by movement changes (added drag and damping caused by risers and mooring lines) and to evaluate the influence of vessel heading on top load results.
An Idealization of Wave Scatter Diagram for Spectral Fatigue Analysis
Authors: Oh Min Han , Lee Ki Myung , Jang Young Sik
Published: February 2010

A spectral fatigue analysis method is most popularly applied for the detailed design of FPSOs. As the environmental loads at the installation site are directly calculated in the spectral analysis, this method gives the most reliable results although it needs much time-consuming works to fully reflect the environmental loads. As the technology of wave measurements advances, the measured wave data increase. Also their spectral models are very complicated because these include many wave components such as swells and wind seas. Since much time and effort are needed to treat these enormous and complicated wave data for the spectral fatigue analysis, a rational idealization of wave data is definitely required. In this paper, wave scatter diagram at Offshore Nigeria was reviewed and their idealization method was proposed. The influence level of each sea state of the wave scatter diagram was identified considering the fatigue damage levels estimated from the significant wave heights and dominant fatigue load RAOs. The sea states giving small fatigue damages were lumped symmetrically by merging or disregarding while those giving large fatigue damages were kept as original. For the validation of this method, the comparisons of dominant fatigue loads and representative fatigue damages were presented for the idealized wave scatter diagram and the original one. From these comparison works, it was confirmed that the idealized wave scatter diagram gives reliable results with reduced amount of calculation work.
An Experimental Study on Damping Effect of RPUF Under Compressive Load
Authors: Lee Tak Kee , Rim Chae Whan , Kim Myung Hyun , Chun Min Sung , Kil Yoon Pyo , Suh Yong Suk
Published: February 2010

Reinforced polyurethane foam (RPUF) is one of important materials of Mark III type insulation system used in LNG cargo containment system. But RPUF is the most difficult material to deal with in the numerical approach for the safety assessment, because there is little public and reliable data on its mechanical properties, and even some public data have relatively large difference between them. In this study, in order to investigate the structural response of the system under compressive loads such as sloshing action, time dependent characteristics of RPUF were examined by experiments. A series of compressive load tests of the insulation system including RPUF under various temperature conditions was carried out by using specimens with rectangular section. As the results, the relationship between deformation of RPUF and time is linear and dependent on the loading rate, so the concept of strain-rate could be applied to the analysis of the insulation system. Also, it was found that the spring constant tends to converge to a value as the loading rate increased, and the convergence level is dependent on temperature.
Progressive Mooring-Line Failure of a Deepwater MODU in Hurricane Conditions
Authors: Zhang Zhi , Kim M. H. , Ward E. G.
Published: February 2010

During 2004–2005, three consecutive category-5 storms hit the central region of Gulf of Mexico (GOM) and damaged numerous drilling and production platforms. Since then, a number of forensic studies have been conducted to better understand the failure causes and mechanism. In this study, a representative deepwater semi-submersible Mobile Offshore Drilling Unit (MODU) that suffered a mooring failure and went adrift during the hurricane Ivan was selected for numerical forensic study. The platform responses and progressive mooring-line failure are simulated in the time domain. A time-domain vessel-mooring coupled dynamic analysis computer program is used to simulate the sequence of progressive mooring-line failure of the MODU in the hindcast Ivan environment, in which the wind, wave, and currents were non-collinear. The case of non-collinear environment is also compared with that of collinear environment. The numerical prediction and simulated results are compared with the available field-analysis data.
Design of the PMXL-1 Platform
Authors: Maciel Vitor G. , Alves Luiz H. M.
Published: February 2010

This paper presents the design of the Mexilha˜o-1 Platform (PMXL-1), located at Brazilian Santos Basin, focusing in the concept development and design of the light weight optimized jacket. PXML-1 is a gas and condensate production hub platform with 525 MMscf/d processing capacity and 18350 metric tons (mton) topside design load. Installed in 172m water depth, is the deepest fixed production unit in Brazil. Jacket concept was developed aiming to structural and functional optimization, based on previous company work on Campos Basin. Due to height, top and base dimensions and expected weight, lift option was discarded and a 4-leg launched and self upended jacket was selected. To increase structural efficiency, bracing was provided by fewer but larger diameter and heavier walled members. Launch trusses, with conventional bay spans, form a central core that is used also to support risers, I-tubes and other appurtenances. Face bays are double spanned, X-braced, with central cross nodes stabilized by members connected to the central core. Horizontal levels have no peripheral members and are double X-braced. Top horizontal frame level is located above operational wave crest, reducing environmental loads, and bottom level is elevated about 6m from mudline. Topside modules are directly supported by jacket main legs and two additional dummy legs, eliminating a module support frame. Foundation is provided by eight large diameter vertical skirt piles. Comparison with PNA-2, a conventional 8-leg platform, installed about 20 years ago in Campos Basin, in similar environmental conditions, with analogous functional requirements, shows considerable advantages and savings. In comparison to PNA-2, PMXL-1 jacket weight is reduced by 32% and pile weight is reduced by 65%. Number of structural elements and tubular connections to be fabricated and erected is also drastically reduced.
VIM and Wave-Frequency Fatigue Damage Analysis for SCRs Connected to Monocolumn Platforms
Authors: Sagrilo Lui´s Volnei Sudati , Queija de Siqueira Marcos , Gonc¸alves de Lacerda Thiago Aˆngelo , Ellwanger Gilberto Bruno , Castro Prates de Lima Edison , Siqueira Elizabeth Frauches Netto
Published: February 2010

The large Vortex Induced Motion (VIM) due to current acting on a circular-shaped monocolumn platform induces low-frequency stress variations on the SCRs (Steel Catenary Risers) connected to it. These stresses together with stress variations associated to wave effects must be accounted for in the fatigue analysis of these risers. Normally, the joint statistics of waves and currents show that these environmental variables may be considered as statistically independent. Therefore, the number of global riser analyses necessary for the SCRs fatigue analysis becomes extremely high in order to consider a suitable number of combinations (including intensities and directions) of waves and currents. This paper describes a methodology for computing the fatigue damage in SCRs (Steel Catenary Risers) due to wave-frequency and VIM (Vortex Induced Motion) load effects based on a combination damage formula presented in DnV-OS-F204 [1]. The wave-frequency and VIM fatigue damages are calculated separately (by a time-domain rainflow approach) and the combined damage is evaluated by means of the DnV formula. This methodology reduces considerably the number of global riser analyses and consequently the computational burden associated to the fatigue analyses of SCRs connected to monocolumn-type platforms.
Study on Ultimate Strength Analysis Method for SWATH Ships
Authors: Liu Bin , Wu Weiguo
Published: February 2010

Nowadays, numerical calculation and structural model test are mainly applied in the ultimate strength analysis of ship structure. This paper presents the results of an ultimate strength test to determine the ultimate load-carrying capacity of an ocean-survey SWATH ship. A comparison between nonlinear FEA (finite element analysis) for test model and test results is presented. The FE-models of real ship and model ship as well as their relations are studied.
Operational Modal Analysis of Existing Floating Structure
Authors: Saito Keisuke , Naruta Shigeyuki , Eto Hiroaki , Saijo Osamu , Ohki Kiyotaka
Published: February 2010

The oceanic architectural buildings were designed in consideration of structural safety based on various structural calculations. However, there is not conclusive proof such as constructed buildings satisfy strength according to the expectation or the buildings built in 1970’s still satisfies specified concrete strength. Therefore, in this study, vibration characteristics of existing floating structure were measured by mode analysis. Generally mode analysis is performed by giving a measurement object a shock with the impulse hammer. But it is hard to be allowed to strike the existing oceanic architectural buildings with a big impulse hammer for a vibration experiment. Therefore, operational modal analysis (OMA) which does not give a shock to measurement object was adopted in this study. In the OMA, natural frequency, mode shape and damping ratio are calculated from the measurement results of ordinary vibration by ground vibration, winds and waves. OMA is used in a field of mechanical engineering. However, it is not easy to apply a vibration experiment by OMA to floating structure. It is because the mode peaks of rigid motions such as heaving and pitching motion in low frequency domain is prominent, and the mode peaks of elastic vibration are difficult to be confirmed. Firstly, we carried out a water tank experiment with floating elastic plate model. Concretely, elastic plate model in floating condition on the water was analyzed by OMA. Because mode peak of the elastic vibration in floating condition was detected by examining frequency response function carefully, it was confirmed that we could apply OMA to the vibration experiment of existing floating structure. Secondly, vibration characteristic of the floating lounge named “WATERLINE” in Tokyo Bay was investigated by OMA. Ordinary vibrations of the base and the building of “WATERLINE” were measured, and natural frequency, mode shape and damping ratio were calculated. And it was reported about vibration characteristic that is given by measurement of existing floating structure by OMA.
Virtual Prototype Based Virtual Test Technique for Fatigue Life of Ship Structure
Authors: Ren Huilong , Liu Xiaobo , Li Luodong , Feng Guoqing , Li Chenfeng
Published: February 2010

Virtual test (VT) technique is a new kind of test technique which takes computer simulation analysis as its core. It develops rapidly in aviation, automobile manufacturing as well as in electronic system, but it is at an initial stage in ship field. In this paper, the virtual prototype (VP) based virtual test technique for fatigue life of ship structure was studied, and a virtual test system for fatigue life of ship structure was developed.
Experimental Studies on Semi-Active Vibration Control of Jacket Platforms With Magnetorheological Damper
Authors: Ji Chunyan
Published: February 2010

Jacket platforms are inevitably undergoing the environmental loads such as wind, waves, current, ice and earthquake etc., which will induce continuous vibration of the platforms. The vibration, on one hand, will cause fatigue damage, decreasing the platform’s reliability; on the other hand, the excessive vibration can’t satisfy the basic psychological requirements of the personnel. In order to reduce the excessive vibration of jacket platforms effectively, many control strategy and control equipments are proposed and studied. In the present study, a model experiment is designed to investigate the effectiveness of semi-active vibration control system with Magnetorheological (MR) Damper. A typical jacket offshore platform in Mexico Gulf is selected as experimental prototype. The model of the jacket platform is designed based on dynamical similarity criterion by the scale of 1:50. Furthermore, the optimal semi-active system of MR damper is designed by fuzzy control theory. In order to investigate the control effect of MR damper on the jacket platform under regular and random wave state, several model experiment load cases are performed. The experimental results show that the MR system designed by fuzzy theory can reduce the vibration of the platform effectively and in the same time the control effect is stable.
Structural Safety Assessment of Existing Ice-Resistant Jacket Platforms in Ice Zone
Authors: Zhang Dayong , Yue Qianjin , Liu Yuan , Che Xiaofei
Published: February 2010

Until now dozens of offshore structures have been deployed in Bohai bay since the first drilling platform was erected in 1965. The oil and natural gas resources of Bohai Bay are mainly marginal oil fields. It is necessary to build both ice-resistant and economical offshore platforms. Full-scale measurement for many years shows the design of some ice-resistant platforms is not so sophisticated, the most significant is that ice induced vibration is the main which has caused harmful accidents in Liaodong bay of Bohai. In order to ensure security operation, structural safety assessment and life extension become key problems. In this paper, failure modes of ice resist jacket platforms, the related failure evaluation criteria, and risk grade are treated. Combined with monitoring data of ice loads, assessment strategy is presented. Lastly, as an application example, safety assessments of a practical platform in Bohai Bay are carried on.
Nonlinear Analysis of Offshore Platforms Subjected to Earthquake Loading Considering the Effects of Joint Flexibility
Authors: Samadani S. , Aghakouchak A. A. , Mirzadeh Niasar J.
Published: February 2010

In a conventional method of structural analysis, for modeling and analysis of jacket type offshore platforms, member connections are assumed to be rigid. In this method, members are rigidly connected which means there is no axial or rotational deformation at the end of brace member relative to chord axis. However in reality local deformations occur at chord surface due to applied loads from braces, which mean tubular joints are considerably flexible especially in non linear range of deformations. Therefore results of analysis based on rigid connections assumption differ from real behavior of the structure. Various research works have been carried out in the past on tubular joints and different methods have been presented in order to include the effect of joint flexibility in structural analysis. Most of these methods are just valid in elastic range but some non-linear methods have also been developed for simple tubular joints. In order to carry out a nonlinear analysis on a 3-D model of an offshore platform with multi-brace / multi-planar tubular joints, none of these simplified methods is applicable. In this case a complete model of tubular joints by non-linear shell elements is the most accurate one which is not only valid for non-linear analyses but also covers all type of tubular joints. In this paper two samples of offshore platforms are studied. These platforms are modeled using the following approaches: 1. No modeling of joints as structural elements (rigid connections). 2. Modeling of joint can with nonlinear shell elements (flexible connection). Different types of static non-linear analysis (Push over) are carried out and results are compared. In order to evaluate the results and compare this type of modeling with simplified methods included in professional software for the analysis of offshore structures, aforementioned platforms are also analyzed using the Fessler and MSL models to include effects of joint flexibility. The results of these types of modeling are also compared with the previous ones.
The Influence of Middle Frames on the Ultimate Strength of Pressure Cylinder Shell
Authors: Wang Lin , Li Feng
Published: February 2010

The influence of middle frames on the ultimate strength of pressure cylindrical shell is studied in this paper, the relationship between the critical stiffness of middle frames and the value of α is discussed, and the criterion of the necessity of adding middle frames on the issue of elastoplastic stabilities is specified.
The Structural Design Developments of Riser I-Tube Support in an FPSO
Authors: Park Sung Hwan , Lee Myung Ki , Kim Jin Tae
Published: February 2010

This paper deals with the optimized load case selection and the design developments for constructability and fatigue criteria of the Riser I-tube support structural design in an FPSO. Many risers including umbilical lines are arranged longitudinally in the outside of FPSO. Also Riser Pull-in System (RPS) is disposed for covering all risers. All risers have different loads in several environmental conditions and need different I-tube diameters. Accordingly their support structures have also different geometrical shape. In fact, it is quite a challenging task to consider all loads and load combination, i.e. Riser loads, environmental loads, the reaction load from RPS, internal tank load, etc. In this paper, the optimized load cases including its back-up descriptions are represented. During the structural design many options and alternative design approaches were explored in order to consider several problems, i.e. the structural arrangement, appropriate connections, constructability issues, the fatigue life, etc. Among these, the constructability and fatigue critically influenced the Riser I-tube support design. So together with the optimized load cases, the design developments on account of them also are represented in this paper.
The Prediction Method of Typhoon Induced Extreme Sea Level in Southeast Coast of China
Authors: Liu Defu , Jiang Hao , Pang Liang , Liu Junna , Xie Botao
Published: February 2010

With the trend of global warming, sea level rising and the frequency and intensity of typhoon increasing, how to deal with the typhoon induced storm tide has increasingly becoming a question that people pay more attention. This paper takes Hangzhou Bay as an example, according to the grey-markov chain model and compound extreme value distribution, proposes a method to predict typhoon induced extreme sea level. This method can predict correct trend, and can make sure the rationality of design extreme sea level because of using typhoon process data sampling.
Simulation Techniques for Ship Onboard Fire Safety
Authors: Dutta Bhargab B. , Kar Apurba R.
Published: February 2010

Unlike land based transportation/industry, ships sail in mid-ocean with very little or no access to external helps and supports to deal with fire accident on board. Fire is a significant threat to safety of ship, lives of the personnel onboard and cargo she carries. Fire on ships can also cause heavy damage to the marine environment. In case of fire initiation if the containment of fire is not efficient then it will not provide adequate time to make use of internal appliances or any possible external support to extinguish fire and result in a severe damage. So, it is important to predict the growth of fire and associated smoke propagation for all possible types and sources of fire. The prediction of fire growth and smoke propagation may be achieved by exercising simulation techniques. The provision of the prevention of fire propagation as prescribed in the presently applicable rules and regulations need investigation from the first principle. Also, the present rules are not explicit about the fire scenarios which have or have not been considered in the development of the rules. For the analysis of fire growth and smoke propagation in order to develop efficient evacuation process onboard a ship, there is a need to study the scenarios with the help of fire simulation techniques. As an ongoing research work, in this paper, the applicability of fire modeling techniques — Field Modeling and Zone Modeling, are investigated and a comparative study is made between both the techniques. The results are explained wherever necessary and future scope of the work is identified. An attempt has been made to define the accuracy level needed for fire simulation tools, considering present state of the art and limitations.
Evaluation of a Model for Estimating Infragravity Waves in Shallow Water: Accuracy and Suitability for Long-Term Climatologies
Authors: Bijl Matthijs , Reniers Ad , Ewans Kevin , Masterton Stephen , Huijsmans Rene´
Published: February 2010

With interest in developing shallow-water facilities on the increase, primarily for offloading LNG, there is also growing interest in infragravity waves. In particular, it is recognized that infragravity waves can have an important influence on the motions of tankers in shallow-water regions exposed to the open ocean, and therefore they need to be considered in the design and operation of the moorings and offloading facilities. Accordingly, there is a need to model infragravity waves both for design calculations and to be able to estimate the design criteria themselves. This paper is concerned with the later — setting infragravity wave design criteria, or more precisely on details involved in establishing an appropriate infragravity wave database from which design criteria can be estimated. The focus is on the accuracy of using the 1D linear Surf Beat model (IDSB) for estimating nearshore infragravity wave heights. The study has focused on field measurements made by U.S. Corp of Army Engineers Field Research Facility location at Duck on the east coast of the United States, and another location at Baja on the north west coast of Mexico. At the Duck location, the study involved data recorded in shallow water (8 meters water depth) with a pressure transducer array, while at the Baja location, data from a directional Waverider buoy with GPS are used. The “short wave” directional spectra from the measured data are used as input to the IDSB model, to compute the total infragravity response generated by the transformation of the grouped short waves through the surf zone including bound long waves, leaky waves and edge waves. The computed root mean square infragravity wave heights have been compared with measured infragravity waves at the respective sites, and assessment has been made of the accuracy of the predictions. The computed results show good agreement with the measured infragravity waves and provide confidence that the IDSB is a suitable tool for developing a long-term infragravity data set for developing design criteria.
Shear Strength of Plate Girders in Ship Structures
Authors: Dong Gang , Moan Torgeir
Published: February 2010

Analysis of 5 transversely stiffened and 12 longitudinally stiffened plate girder panels and 3 box girder web panels using ABAQUS [1] software package is conducted to validate the FEM for prediction of ultimate shear capacity of plate and box girders. Good agreement between ultimate strength obtained by calculations and experiments was achieved. Because the existing design procedure does not allow to account for the influence of the post critical behaviour of webs for ships, the results obtained by the application of JTP approach [2] have been demonstrated to be extremely conservative. The applicability of EC3-1-5 [3] to assess the shear capacity of plate girders in ship structures was investigated. The design procedure of EC3-1-5 by neglecting the contribution from the flanges has been proposed for design of plate girders in ship structures.
Condition Evaluation of Safety Critical Shut-Down Valves
Authors: Meland Erlend
Published: February 2010

This article gives an overview on how safety critical shutdown valves can be monitored and condition evaluated. These types of valves are the last barrier in maintaining the safety of personnel and environment, hence they must always function as required. Safety critical valves can be found throughout the whole petro-chemical industry, offshore topside, sub-sea and onshore, in a wide variety of sizes. To detect internal leaks in a closed valve, the operator can choose between remote monitoring, do intrusive manual inspection or non-intrusive inspection. Some methods can even be done without shutting down the system, and there are several other advantages and disadvantages that must be considered. The person in charge of the plant valves needs to have an overview to help make sure the reliability of the valves is as good as possible, but without inflicting too much down-time and inspection cost related to maintenance. Furthermore, methods for valve internal leak quantification estimation are reviewed. And finally, the presented maintenance methods are compared and discussed so that recommendations for the best possible scheme can be made.
Theoretical Study of the Water Entry of a Body in Waves: Application to Safety of Occupants in Free-Fall Lifeboats
Authors: Sauder Thomas , Fouques Se´bastien
Published: February 2010

The safety of occupants in free-fall lifeboats (FFL) during water impact is addressed. The first part of the paper describes a theoretical method developed to predict the trajectory in six degrees of freedom of a body entering water waves. Slamming forces and moments are computed, based on momentum conservation, long wave approximation and a von Karman type of approach. The added mass matrix of the body is evaluated for impact conditions by a boundary element method. The second part of the paper focuses on the application of the method to free-fall lifeboats, which are used for emergency evacuation of oil platforms or ships. Acceleration loads on FFL occupants during water impact are dependent on numerous parameters, especially the hull shape, the mass distribution, the wave heading relative to the lifeboat, and the impact point on the wave surface. Assessing operational limits of FFL by means of model tests only has therefore been costly and time consuming. This issue is addressed here by applying the theoretical method described in the first part. The model has been validated for FFL through extensive model testing in calm water and regular waves, and statistical estimates of acceleration levels for lifeboat occupants, as well as acceleration time series were obtained that can be used as inputs to numerical human response models.