bluuebunny/crossref_metadata_2025 huggingface dataset:
Verification of DP Safety Barriers for Offshore Well Intervention Vessels
Authors: Chen Haibo , Abrahamsen Bjo̸rn
Published: February 2010

DP safety barriers for a new-build Light Well Intervention vessel were verified in the design and construction stage. The verification was guided by a DP safety barrier model developed for DP well intervention units on the Norwegian Continental Shelf. The DP operational experience from a sister vessel was also taken into account in the verification process. The verified barrier elements are related to technical systems such as Differential GPS and DP control software, as well as the DP operator. The paper presents deficiencies found in the past operations and in the current design, as well as the recommendations to vessel owners and DP equipment vendors in order to increase the DP safety in operations. The barrier model demonstrates itself in this study as an effective and systematic tool to diagnose DP safety and facilitate experience transfer from operations back to design. The recommendations in this study are also considered valid for design and operations of DP well intervention vessels worldwide.
Extreme Response Statistics of Fixed Offshore Structures Subjected to Ringing Loads
Authors: Gaidai Oleg , Krokstad Jo̸rgen
Published: February 2010

Paper describes a method for prediction of extreme response statistics of fixed offshore structures subjected to random seas by Monte Carlo simulation. The nonlinear structural response know as “ringing” is studied, caused by the wave impact force on structural support units. Common challenge for design of such structures is a sound estimate of the hydrodynamic load inclusive diffraction effects. Structure is modeled as a multi-degree of freedom (MDOF) system and number of Monte Carlo simulations was performed to highlight extreme response in severe random seas. Since MDOF numerical simulation is costly, an efficient statistical technique was adopted, minimizing required computational effort. Environmental contour method was combined with accurate distribution tail extrapolation. The aim of the work was to develop specific methods which make it possible to extract the necessary information about the extreme response from relatively short time histories. The method proposed in this paper opens up the possibility to predict simply and efficiently both short-term and long-term extreme response statistics. The results presented are based on extensive simulation results for the large fixed platform operating on the Norwegian Continental Shelf. Measured response time histories were used to validate numerical results.
Concept Design of Two Permanently Coupled Floaters for Production and Storage of Oil and LNG
Authors: ter Brake Erik , Oma Narve , Rettedal Wenche
Published: February 2010

The combination of oil, LNG and LPG present at offshore fields may require a multi purpose production and storage facility that can produce the different hydrocarbons. In order to achieve feasibility, the required vessel size to handle multiple hydrocarbons is significant. HSE, technical and economical considerations led to the investigating of using two floaters to split the LNG / LPG storage from the production vessel. This paper deals with the intention to deploy two vessels in tandem: One producing unit that has storage capacity for produced oil and one barge that stores the LNG and LPG. Challenges to be met in the design of the tandem moored vessels relate to relative motions between the vessels: The relative motion is restricted by the transfer lines for products and the flexibility of a gangway that enables safe passage between the vessels. The mechanism that connects the two vessels should be capable of withstanding the forces to keep the vessels at the intended distance without growing into enormous proportions itself. This paper provides the technical background and the feasibility of the concept to connect two large barges in benign conditions. The concept has been developed based on existing tower mooring principles that is combined with a spread moored mooring arrangement. Additionally the paper discusses the sensitivity of the connector and mooring design on the overall performance.
Multi Vessel Interaction in Shallow Water
Authors: Hansen Hans Fabricius , Carstensen Stefan , Christensen Erik Damgaard , Kirkegaard Jens
Published: February 2010

A numerical package for simulating vessel motions in the time domain, WAMSIM, is extended to handle multiple moving bodies interconnected through a nonlinear mooring system. WAMSIM relies on the industry standard program WAMIT to calculate the hydrodynamic characteristics and interaction of multiple bodies in the frequency domain. The numerical code is used to simulate the motions and mooring line and fender forces of two LNG tankers moored side-by-side in shallow water. One of the gas tankers is moored to the sea floor through a turret with chain catenaries. Realistic short-crested irregular waves obtained from a Boussinesq wave model are used to force the model. Motion spectra of the simulated motions are compared to measured motions from physical scale model tests. The model shows good agreement with measured motions and mooring line forces.
Experimental Observations and Numerical Simulations of Wave Impact Forces on Recurved Parapets Mounted Above a Vertical Wall
Authors: Newborn David , Sultan Nels , Beynet Pierre , Maddux Tim , Shin Sungwon , Cox Dan
Published: February 2010

Large-scale hydraulic model tests and detail numerical model investigations were conducted on recurved wave deflecting structures to aid in the design of wave overtopping mitigation for vertical walls in shallow water. The incident wave and storm surge conditions were characteristic return period events for an offshore island on the North Slope of Alaska. During large storm events, despite depth-limited wave heights, a proposed vertical wall extension was susceptible to wave overtopping, which could potentially cause damage to equipment. Numeric calculations were conducted prior to the experimental tests and were used to establish the relative effectiveness of several recurved parapet concepts. The numerical simulations utilized the COrnell BReaking waves and Structures (COBRAS) fluid modeling program, which is a Volume-of-Fluid (VOF) model based on Reynolds Averaged Navier-Stokes equations [1] [2]. The experimental testing was conducted in the Large Wave Flume (LWF) at Oregon State University, O.H. Hinsdale Wave Research Laboratory. The experimental test directly measured the base shear force, vertical force, and overturning moment applied to the recurved parapets due to wave forcing. Wave impact pressure on the parapet and water particle velocities seaward of the wall were also measured. Results from the experimental testing include probability of exceedance curves for the base shear force, vertical force, and overturning moment for each storm condition. Qualitative comparisons between the experimental tests and the COBRAS simulations show that the numerical model provides realistic flow on and over the parapet.
Dynamic Analysis of Offshore Pile Launch
Authors: Yiu F. , Liu N. , Wang J. , Litton D.
Published: February 2010

Successful installation of offshore piles is often challenged by the constraints of cost, technical feasibility, availability of suitable installation vessels and the environment. A practical installation procedure is defined as one that utilizes the capacity of available equipment to operate in a wide allowable environmental window. To find such procedures there is a continuing need for research, use of new technologies, and the adoption of new ideas. This paper presents a feasibility study for side launching piles from a conventional cargo barge. Sophisticated nonlinear time domain dynamic simulations formed the basis of the evaluation. Two noted software packages with nonlinear time domain dynamic finite element analysis capabilities were used to predict the trajectory of the launched pile and the resulting impulsive load on the restraining cable/wire. Analytical results from the software programs were compared to provide a first level of validation. The numerical results were in good agreement. Cable/wire properties (size, length, and material) and tug vessel velocity were varied in an effort to minimize the cable loads during the highly dynamic launch event. The study concluded that side launch was feasible and design recommendations are provided.
Experimental and Numerical Study on Large Truncation of Deepwater Mooring Line
Authors: Su Yihua , Yang Jianmin , Xiao Longfei , Chen Gang
Published: February 2010

Modeling the deepwater mooring system in present available basin using standard Froude scaling at an acceptable scale presents new challenges. A prospective method is to truncate the full-depth mooring lines and find an equivalent truncated mooring system that can reproduce both static and dynamic response of the full-depth mooring system, but large truncation arise if the water depth where the deepwater platform located is very deep or the available water depth of the basin is shallow. A Cell-Truss Spar operated in 1500m water depth is calibrated in a wave basin with 4m water depth. Large truncation arises even though a small model scale 1:100 is chosen. A series of truncated mooring lines are designed and investigated through numerical simulations, single line model tests and coupled wave basin model tests. It is found that dynamic response of the truncated mooring line can be enlarged by using larger diameter and mass per unit length in air. Although the truncated mooring line with clump presents a “taut” shape, its dynamic characteristics is dominated by the geometry stiffness and it underestimates dynamic response of the full-depth mooring line, even induces high-frequency dynamic response. There are still two obstacles in realizing dynamic similarity for the largely truncated mooring system: lower mean value of the top tension of upstream mooring lines, and smaller low-frequency mooring-induced damping.
Plastic Buckling of Conical Shells
Authors: Blachut J. , Ifayefunmi O.
Published: February 2010

The buckling of unstiffened truncated conical shells subjected to axial compression and/or to external pressure is discussed. This work is both experimental and theoretical/numerical. Results of tests on four laboratory scale cones and the associated numerical estimations of buckling loads are provided. The models were machined from mild steel and they had integral top and bottom flanges in them. The bottom and top diameters of the cones were about 200 mm and 100 mm, respectively. Semi-vertex angle was about 27°, whilst the nominal wall thickness was 3mm. The numerical results are based on the finite element analyses.
Residual Strength of Damaged Jacket Type Offshore Platform and the Effects of Local Repair
Authors: Naderi Banafsheh , Aghakouchak A. A. , Mirzaei Madhi
Published: February 2010

In the design of offshore platforms, the aim is to have a characteristic capacity higher than the characteristic environmental loads with a return period of typically 100 years multiplied by some partial safety factors for loads and resistance. Simplified of the assumptions is inherent in the derivation of force components. In addition, any potential of the structure for yielding and load redistribution, giving the inherent “reserve capacity” is neglected in the design stage. Reserve strength is commonly defined as the ability of a structure to sustain loads in excess of the design value. The frame action and system redundancy are implicit sources of reserve strength which are not generally controlled or quantified in design. Reserve strength should not be solely considered as overdesigning of structures. However, there are situations where such reserve strength may be demonstrated, for example in case of reassessment of existing structures, e.g. improved exploitation methods or increased petroleum service may call for service life extension, the characteristic loads may increase due to installation of new modules. It is also important that a structure can sustain damage without collapse so that it has sufficient remaining or “residual” strength. Such damage may result from extreme overloading of structures as a whole, or from localized damage such as ship impact or dropped object. This paper is concerned with the reserve strength of a jacket evaluated by pushover analysis in intact and damaged conditions. The tested structure is a PP (Production Platform) jacket, a K-braced space frame, located in the Persian Gulf. The loading on the structure contains functional and environmental loads. The test is carried out under displacement control. The influence of damages including “Local Denting” and “Out of Straightness” on the critical members is investigated, and then reassessment and Probabilistic Collapse Analysis of the platform are considered to illustrate the mechanisms of failure caused by each damage The effects of some repair scenarios is investigated too.
Fatigue Life Prediction of Mooring Chains Subjected to Tension and Out of Plane Bending
Authors: Lassen Tom , Storvoll Eirik , Bech Arild
Published: February 2010

The present paper describes the behaviour of chain segments that are subjected to pretension and a rotation angle at the segment end. The behaviour such segments has been investigated both experimentally and by finite element modelling. The purpose is to carry out fatigue life predictions. A full scale test with a studless chain segment with a diameter of 125 mm has been carried out to shed more light on the behaviour. The test corroborated the assumption that the chain segment behaves semi-rigidly under the given conditions due to locking of the inter-link hinge mechanism. The influence of various important parameters on the bending effect was studied. The chain segment has a significant flexural stiffness and an intra-link bending curvature for links that are in a flat position with respect to the inflicted end rotation. The associated Out of Plane Bending (OPB) stresses are significant for critical links close to the end hang-off. This effect must be taken into account when carrying out fatigue life predictions. There is still no guidance given in rules and regulations for this case. In the present work it is suggested that a hot spot method is applied for fatigue life predictions. Under a combined loading mode, defined by tension and OPB, the maximum principal stress range in the link bend area must be determined by refined finite element analysis. Subsequently, the fatigue life can be predicted by using an appropriate hot spot S-N curve. The paper points out how a good fatigue design of the hang-off area can reduce the effect of OPB. A Buoy Turret Loading (BTL) is used as a case study to demonstrate both the design proposal and the fatigue life prediction methodology.
A Comparative Study on the Impact Damage of Membrane Type LNGC Insulation System
Authors: Chun Min Sung , Seo Yong Suk , Hisasi Ito , Kim Wha Soo , Noh Byeong Jae , Kim Myung Hyun , Kim Min Soo , Yoon Jang Ho , Erm Hang Sub , Han Dae Suk , Lee Jae Myung
Published: February 2010

To verify the structural safety under impact load caused by sloshing of LNG is one of the main issues in the design of membrane type LNG cargo containment system of LNG carrier. In order to estimate structural response under sloshing impact load, many kinds of studies including experimental test and numerical simulation have been done by various research groups such as shipyards, oil companies, universities as well as classification societies. In spite of these efforts, many uncertainties still exist to predict the structural behavior of LNG insulation system under sloshing impact load. Therefore, it can be regarded as a challenge to investigate dynamic response of LNG cargo insulation system against sloshing load. In this paper, Cooperative research results obtained by SHI-HHI-PNU-Lloyd-ABS-DNV JDP focused on the impact damage or failure mode of membrane type LNG cargo insulation system are summarized. A systematic experimental research is carried out to find out failure mode of the insulation system under impact load and criteria which can be applied for the design of LNG carrier. A series of dry drop tests as well as static compressive tests are carried out. The structural behavior of the specimen under impact load is recorded using ultrahigh-speed camera and reaction force is measured using load cells which are installed under bottom of the test facility. By analyzing recorded video, deformation history of the specimen at impact moment is obtained. The numerical simulations are also carried out for the dry drop test for verification purpose, It is expected that the insights observed from the systematic experiments and numerical simulations for the structural response of the LNG cargo insulation system subjected to the impact load can be effectively used as design guide for evaluation of the integrity of structural components of LNG cargo hold system.
Comparative Wet Drop Experiments of Mark III and KC-1 for Membrane Type LNG Carriers
Authors: Noh Byeong Jae , Kim Wha Soo , Kwon Sun Hong , Chung Jang Young
Published: February 2010

The increasing demand for safe storage and transportation of LNG (Liquefied Natural Gas) in the global energy market initiated a trend for further development of the design technology for LNG tanks. An LNG tank in LNG carriers or FLNGs (LNG-FPSO, LNG-FSRU) of the membrane type is constituted with primary and secondary metal alloy membrane barriers incorporated in insulation panels. One of the key technical issues associated with LNG carriers or FLNGs is the ability of the cargo containment system to withstand sloshing loads induced by ship motion in harsh environment. To assess the safety of membrane LNG tanks with a newly proposed configuration of CCS (Cargo Containment System) against sloshing, usually a comparative approach is adopted through numerical simulations and/or testing. The aim of the comparative approach is to assess the relative sloshing load and structural capacity under the fundamental assumption that the current membrane systems are safe. Over the period 2004-08, a JDP (joint development project) for an LNG CCS was carried out by Korea Gas Corporation (KOGAS) in corporation with major Korean shipyards and Korean universities. The aim of the project was to develop “a new CCS for membrane Type LNG carriers” which could lead to the improved and updated CCS of the structural safety. In this paper, experimental research results for the evaluation of structural performance of GTT MARK III type and KC-1 (Korean Cargo Containment System) insulation system, which is currently under development by KOGAS in corporation with major Korean shipyards, under hydro impact loads are presented. Based on the results of wet drop tests, a comparative evaluation was carried out for the time history of the impact pressure on the primary barrier and damage characteristics and so on. It is expected that the state-of-the art of engineering research described in this work can be directly applicable for the design and the development of high-valued LNG carriers and FLNGs.
Dynamic Response Analysis of Harbor Caisson Structure Under Various Boundary Conditions
Authors: Kim Jeong-Tae , Lee So-Young , Hong Dong-Soo , Yi Jin-Hak , Kang Yoon-Koo
Published: February 2010

In this study, vibration responses of harbor caisson structures with various boundary conditions are experimentally examined as a fundamental study to develop a health assessment technique for harbor structures. To achieve the objective, four-step approach is implemented. Firstly, a target caisson structure is selected and a small-scale model of the caisson model is constructed in the laboratory. Secondly, a finite element model of the caisson model is generated to analyze dynamic responses of the structure. Thirdly, experimental tests are performed on the caisson model to obtain dynamic responses under various boundary conditions and impact locations. Four different boundary conditions, 1) ‘hanging by crane’, 2) ‘standing on styrofoam block’, 3) ‘standing on sand mat’, and 4) ‘standing on concrete floor’ are considered. Finally, variation of frequency response ratio assurance criterion and correlation coefficients of frequency response functions are analyzed.
FHS Semi: A Semisubmersible Design for Dry Tree Applications
Authors: Mansour Alaa M.
Published: February 2010

In this paper the performance of a new conceptual semisubmersible design that provides motion response similar to a Spar is investigated. The new invention introduces a new feature which is the Free-Hanging Solid Ballast Tank, hence the name FHS Semi. The use of the free-hanging Solid Ballast Tank (SBT) significantly increases the heave natural period while controlling the heave response in the wave frequency range and, therefore, enables the use of the FHS Semi in dry tree applications. The new design’s quayside integration technique and its interface with the top tensioned risers are presented in this paper. Case study for the new design to support a 32,000 ST payload including 15 Top Tensioned Risers (TTRs) in an ultra-deepwater of 8,000 ft water depth is considered. Frequency domain and fully coupled time-domain hydrodynamic analyses have been performed and numerical results are presented to illustrate the new semisubmersible design response in extreme Gulf of Mexico hurricane events.
New Approach for Analyzing Collision of Ships
Authors: Yoon B. S. , Cho S. R. , Isshiki H.
Published: February 2010

In order to avoid the loss of human lives due to a collision of ships, it is very important to have a correct understanding on the phenomena of collision of ships and collapse of ships due to collision. A more reasonable model describing collision of ships and whole structure analysis is proposed in the present paper. Present model employs lumped masses with elasto-plastic spring system to represent striking ship considering hydrodynamic effect during collision process. When the responses of the whole structures of a striking ship and a struck one are estimated properly, more exact local structure analysis would be possible. And this makes it possible to design more reliable shock absorbing structures, soft bow for example. Quite good results are shown for behavior and deformation of striking ship by very simple calculation based upon the model proposed in the present paper.
The Statistics of the Second Order Response of an FPSO in Spreading Seas
Authors: Zhang Yahui , Langley Robin S.
Published: February 2010

An expression for the probability density function of the second order response of a general FPSO in spreading seas is derived by using the Kac-Siegert approach. Various approximations of the second order force transfer functions are investigated for a ship-shaped FPSO. It is found that, when expressed in non-dimensional form, the probability density function of the response is not particularly sensitive to wave spreading, although the mean squared response and the resulting dimensional extreme values can be sensitive. The analysis is then applied to a Sevan FPSO, which is a large cylindrical buoy-like structure. The second order force transfer functions are derived by using an efficient semi-analytical hydrodynamic approach, and these are then employed to yield the extreme response. However, a significant effect of wave spreading on the statistics for a Sevan FPSO is found even in non-dimensional form. It implies that the exact statistics of a general ship-shaped FPSO may be sensitive to the wave direction, which needs to be verified in future work. It is also pointed out that the Newman’s approximation regarding the frequency dependency of force transfer function is acceptable even for the spreading seas. An improvement on the results may be attained when considering the angular dependency exactly.
Current Wake Effects on DP System of a Shuttle Tanker
Authors: Illuminati Cesar , Tannuri Eduardo A. , Matos Vini´cius L. F. , Simos Alexandre N.
Published: February 2010

This paper reports the main results of an investigation on the effects of hydrodynamic interactions on current forces on a typical shuttle tanker, when offloading a FPSO moored in SMS configuration. In this situation, large angles between the direction of environmental agents and the platform centerline may exist and cause intense disturbance on the wind, waves and current fields that reach the shuttle tanker. A procedure for incorporating the FPSO wake on the current forces was proposed and validated by means of a series of towing-tank tests. In this article, the methodology is applied to evaluate how the disturbances in the incoming flow may affect the DP thrust allocation and power consumption during typical offloading operations. Wake effects on the tanker behavior after DP failures are also investigated. It is shown that current wake effects may contribute to an increase in power demand even for typical distances between ships, usually adopted for the safety reasons. They might also influence the ship course after a drive-off failure, with consequences on maneuvering decisions.
Comparing the Results of a Simplified Numerical Model With DNV Guidelines for Installation of Subsea Platforms
Authors: Kimiaei Mehrdad , Xu JiaJing , Yu He
Published: February 2010

Installation engineering of subsea platforms has always been one of the major areas of concerns in subsea engineering. These days, conventional installation method, on which subsea modules are lowered directly toward seabed through a lifting wire, is being used widely by offshore operators. Accurate prediction of hydrodynamic forces on subsea structures, particularly when they are passing through water surface zone, is a challenging task in installation engineering of subsea platforms. DNV Rules for Marine Operations are used around the world for prediction of hydrodynamic loads during subsea lifting, checking structural strength and verifying the capacity of the lifting equipments. This paper presents a simplified numerical model for more accurate estimating of characteristic hydrodynamic forces on subsea platforms. Series of different conventional installation analyses are performed in this study to compare the results of the numerical models with DNV guidelines. The main purpose of this study is to figure out the sensitivity of the numerical and DNV results to main input parameters in installation of subsea platforms.
Fatigue and Fracture Reliability of Articulated Tower Joint Under Random Loading
Authors: Zaheer Mohd Moonis , Islam Nazrul
Published: February 2010

An articulated tower is one of the compliant offshore structures connected to the sea bed through a universal joint. In the random sea environment, this joint is subjected to reversal of shear stresses, which makes it susceptible to fatigue damage. In this study, fatigue damage accumulation in articulated joint under random loading is studied. The dynamic analysis of the tower has been carried out for twelve simulated sea states under random wave alone and random wave with wind. Nonlinearities due variable submergence, instantaneous position of the tower and hydrodynamic loading have been taken into account in the derivation of equation of motion. Fatigue life of the joint has been determined by S-N curve and fracture mechanics (F-M) approaches. Advanced First Order Reliability Method (FORM) and Monte Carlo Simulation method have been used for the reliability estimation. The results of the analyses are presented in terms of probability of failure and reliability indices. Sensitivity analysis is carried out to study the effect and participation of various random variables on the joint reliability. Most probable point (MPP) or design points have been located on the failure surface. Important parametric studies have been carried out which yield important information for reliability based design. The results of the study indicate that Miner’s rule, which is generally used in the design against fatigue in steel structures, yields a conservative estimate of probability of failure as compared to the fracture mechanics approach.
Vortex-Induced Motion of a Monocolumn Platform: New Analysis and Comparative Study
Authors: Gonc¸alves Rodolfo T. , Fujarra Andre´ L. C. , Rosetti Guilherme F. , Nishimoto Kazuo , Cueva Marcos , Siqueira Elizabeth F. N.
Published: February 2010

This paper presents a new analysis and a comparison of results obtained from Vortex-Induced Motion (VIM) model tests of the MonoGoM platform, a floating unit designed for the Gulf of Mexico. The choice of scale between the model and the platform in which the tests took place was a very important issue that took into account the basin dimensions and mooring design. The tests were performed in three different basins: the IPT Towing Tank in Brazil (September 2005), the NMRI Model Ship Experimental Towing Tank in Japan (March 2007) and the NMRI Experimental Tank in Japan (June 2008. The objective of this work is to discuss the most relevant issues regarding the concept, execution and procedures to analyze comparatively the results obtained from model tests. The approach employed in the tests was designed to build a reliable data set for comparison with theoretical and numerical models for VIM prediction, especially that of Monocolumn platforms.
Mitigation of Vortex-Induced Motions in a Monocolumn Platform
Authors: Fujarra Andre´ L. C. , Gonc¸alves Rodolfo T. , Faria Fernando , Cueva Marcos , Nishimoto Kazuo , Siqueira Elizabeth F. N.
Published: February 2010

A great deal of works has been developed on the Spar VIM issue. There are, however, very few published works concerning VIM of monocolumn platforms, partly due to the fact that the concept is fairly recent and the first unit was only installed last year. In this context, the present paper presents a meticulous study on VIM for this type of platform concept. Model test experiments were performed to check the influence of many factors on VIM, such as different headings, wave/current coexistence, different drafts, suppression elements, and the presence of risers. The results of the experiments presented here are inline and cross-flow motion amplitudes, ratios of actual oscillation and natural periods, and motions in the XY plane. This is, therefore, a very extensive and important data set for comparisons and validations of theoretical and numerical models for VIM prediction.
Fatigue Analysis of an FPSO Under Operational Sea States With Multimodal Spectra
Authors: Gue´de´ Z. , Olagnon M. , Pineau H. , Franc¸ois M. , Quiniou V.
Published: February 2010

This paper presents a validation of theoretical formulas for the assessment of fatigue damage induced by a multimodal wave spectrum. Those formulas, denoted Iterative Component Addition (ICA), were set up to provide a conservative estimate and use the individual damages of the components of the spectrum. Their objective and main interest is a drastic reduction of computation time, especially for complex (multimodal) wave loading conditions. They are validated on an actual application, which is the assessment of the fatigue damage induced by the wave bending moment of an FPSO hull girder subjected to wave loading in a West Africa area. That damage is computed according to two different procedures, one with the conventional method, taken as a reference, and the other using the ICAs formulas. The results are compared and discussed. They show that the use of ICA formulas provides a reasonably conservative estimate and allows significant savings of computational time.
Experimental Study and Modelling of Thermal Protection in Liferafts Using a Thermal Manikin and Human Subjects
Authors: Mak Lawrence , Kuczora Andrew , DuCharme Michel B. , Farnworth Brian , Boone James , Brown Rob , Cheung Stephen , Evely Kerri-Ann , Basset Fabien A. , MacKinnon Scott
Published: February 2010

Experiments were conducted in cold conditions (5°C water temperature and 5°C air temperature) to assess the thermal protection of a 16-person, SOLAS approved, commercially available liferaft using a thermal manikin and human subjects. The comparison tests included four cases — 1. Inflated raft floor; dry clothing (Idry); 2. Inflated raft floor; wet clothing (Iwet); 3. Uninflated raft floor; dry clothing (Udry); 4. Uninflated raft floor; wet clothing (Uwet). The results demonstrated equivalence in insulation between human subjects and a thermal manikin for all cases of comparison (Idry: Manikin 0.236 (m2°C)/W versus Human 0.224 (m2°C)/W; Iwet: Manikin 0.146 (m2°C)/W versus Human 0.145 (m2°C)/W; Udry: Manikin 0.174 (m2°C)/W versus Human 0.185 (m2°C)/W; Uwet: Manikin 0.101 (m2°C)/W versus Human 0.116 (m2°C)/W). The results also showed the repeatability of the thermal manikin tests (0.177 (m2°C)/W versus 0.171 (m2°C)/W in Udry baseline case; and 0.101 (m2°C)/W versus 0.104 (m2°C)/W in Uwet baseline case). The results indicated that the insulation of a closed cell foam floor is comparable to an inflated floor (0.236 (m2°C)/W compared to 0.221 (m2°C)/W and 0.236 (m2°C)/W for closed foam floor from manufacturer A and B respectively). TPA provided considerable additional insulation than all baseline cases. A test with a human subject wearing a TPA in the Uwet case showed an improved insulation of 48% over the baseline case. TPA provided more additional insulation than a wet suit in all test cases except Udry case. In Uwet case, the worst test condition, the insulation obtained by sitting on a lifejacket (0.149 (m2°C)/W) is less than wearing a TPA (0.158 (m2°C)/W). Both of these are better than sitting directly on an uninflated floor (0.104 (m2°C)/W) or a closed cell foam floor (0.129 (m2°C)/W). There is a significant decrease in insulation value sitting in 10 cm of water (0.05 (m2°C)/W). Two human subject tests show an insulation value of 0.079 (m2°C)/W and 0.081 (m2°C)/W respectively. A liferaft occupant heat loss model was developed and integrated with Defense R&D Canada’s Cold Exposure Survival Model to predict survival time. For Uwet case, the worst test condition, the survival time is 32 hours and functional time is 24 hours for the experimental conditions.
Comparison of Design Criteria for Externally Pressurized Vessels
Authors: Kahlen Franz-Josef , Curry Richard
Published: February 2010

The design of an underwater chemical species concentration probe using optical diagnostics for depths of up to 1000m is presented. An initial investigation into the most appropriate spectroscopic techniques and the required geometries is followed by an investigation into the application of current externally loaded pressure vessel theory and a comparison with a finite element model. The probe geometry can be approximated as a cylindrical object with a center tube which is open to the ambient. The ultimate goal being to propose a housing which will be able to operate safely and reliably. The finite element program ABAQUS is used to analyze the different configurations using a static analysis across the different models as a comparison. As most externally loaded pressure vessels initially fail in an elastic buckling mode it is also necessary to investigate the modes of failure and to improve the design. The buckling modes are analyzed by means of an eigenvalue investigation on each model, which are then imposed on a perfect model as an imperfection to induce a failure. A static analysis is used to simulate the loading conditions experienced in operation and the external pressure and arc length are solved simultaneously to find a failure point.
Motion Behaviour of a New Offshore LNG Transfer System at Harsh Operational Conditions
Authors: Clauss Gu¨nther F. , Sprenger Florian , Testa Daniel , Hoog Sven , Huhn Roland
Published: February 2010

Today, the demand of natural gas from offshore fields is on a high level and still increasing. Floating turret moored terminals receive gas directly from the field via risers and liquefaction is achieved by on-board processing plants. The LNG (liquefied natural gas) is transferred to periodically operating shuttle carriers for onshore supply. This paper presents an innovative offshore LNG transfer system, based on newly developed flexible cryogenic pipes of 16″ inner diameter, which allow fast loading/offloading procedures in tandem configuration (see Fig. 1), even in harsh environmental conditions. The motion characteristics of the proposed concept are investigated in detail by the potential theory programmes WAMIT and ANSYS AQWA, respectively, with the focus on the dynamic behaviour of the multi-body system in waves. Each vessel is generating its own radiation and diffraction wave field affecting the motions of the adjacent vessels and vice versa. Results from calculations in the frequency and time domain are compared and show good agreement. Tolerable relative motions between terminal and carrier are limited by maximum torsion and bending of the flexible transfer pipe. Based on given limiting parameters, the operational range of the system and the annual expected downtime is exemplarily calculated for a location in the north sea. Finally, second-order forces — induced by drift motions — on the mooring lines between carrier and terminal are presented as time series for a three-hour sea state.
On the Application of Advanced Wave Analysis in Shallow Water Model Testing (Wave Splitting)
Authors: Waals Olaf J.
Published: February 2010

The HAWAI JIP originated from the observed differences between model tests and numerical simulations in shallow water. These differences were identified as being caused by spurious free waves and reflected waves in the model basin. Identifying these waves and incorporating them in the numerical simulations greatly improved the agreement between the model test results and the simulation results. Although the effect of spurious waves is also present in deep water, the effect is most profound in shallow water. The research therefore focused on shallow water, further refinement of wave identification, the background and theory behind spurious free waves, the effect of these waves on the motions of a LNG carrier and the occurrence of free waves in reality. In order to identify the different types of wave systems in a model basin a wave splitting (or separation) technique has been developed. This paper describes the current state-of-the-art of wave splitting and its limitations. Results are presented in the form of motion statistics of an LNG carrier that is moored in 15 m and 30 m water depth. The model tests results are compared with simulation results with and without the wave splitting methodology.
Bias and Uncertainty in the Estimation of Extreme Wave Heights and Crests
Authors: Gibson Richard , Grant Colin , Forristall George Z. , Smyth Rory , Owrid Peter , Hagen Oistein , Leggett Ian
Published: February 2010

The accurate prediction of extreme wave heights and crests is important to the design of offshore structures. For example, knowledge of the extreme crest elevation is required to set the deck elevation of the topside of a jacket structure. However, methods of extreme value analysis have an inherent bias, and the manner in which they are applied affects this bias. Furthermore, there is uncertainty in the design parameters at the time of design and the possibility that the predictions will change during the life of the structure. This paper is concerned with the accurate prediction of design values that incorporate uncertainty. In the first part of this paper the details of commonly applied extreme value analysis techniques are examined. This is achieved through analysis of simulated data of known distribution. In particular it is the application of least squares minimisation routines that is investigated; however, comparisons are made with maximum likelihood estimation. From this, preferred approaches to the analysis are recommended and their advantages and disadvantages discussed. The methods are applied to the analysis of a North Sea data set and the implications for the design values ascertained. In the second part of the paper Bayesian inference is used to consider the effect of uncertainty in the predicted wave heights and crest elevations. The practical implications are determined by the analysis of a measured North Sea data set.
Dynamic Effect of a Stabilizing Tank on a FPSO
Authors: de Souza Silva Rodrigo , Fernandes Antonio Carlos , Meneses Fa´bio , Silva Severino Fonseca
Published: February 2010

It is becoming clear that roll response of a FPSO may be hazardous if the resonance exits for certain incoming wave field. In several parts of the world this is happening. One manner to control the response is to use stabilizing tanks which is a dynamic absorber. The paper addresses the design of a stabilizing tank on board of a FPSO to control the roll response. It is shown how to use existing storage tanks for that matter. The existing tanks are constantly partially filled and tuned to the natural frequency. This is done by controlling the internal height. The sizing of the stabilizer tank was studied to check the responses and evaluated how sensitive the system is considering the stabilizer tanks. Results from a fully non linear CFD code are compared with frequency domain potential theory one. Subsequently the structural consequences of having a stabilizing tank on board are verified via numerical computations.
Offshore Platform Turn Around Using the Critical Chain Project Management Method (CCPM)
Authors: Finocchio Junior Jose , Martins Marcelo Ramos
Published: February 2010

The present study discusses the adequacy of the Critical Chain Project Management Method (CCPM) — also known as the Critical Chain Method — for scheduling projects involving shutdowns on oil platforms, as such projects involve decision-making processes under risk conditions. The CCPM is based on the Theory of Constraints and aims at providing more precise and more clearly focused control instruments than those traditionally used in the Critical Path Method (CPM). The CCPM also indicates the best moments to act and where and how the action should be directed. The hypothesis underlying the research is that the CCPM portrays, more adequately than the CPM, the uncertainty that exists in a platform shutdown. This characteristic also makes it possible to draw up a schedule that is both more realistic and more challenging, as it addresses the goal of causing less interruption of production. On the basis of this hypothesis, the two main questions that oriented the entire investigation were: 1) Is the CCPM suitable for scheduling the shutdown of an offshore oil platform and, 2) What advantages might it have over the traditional methods in use? To answer these questions the authors reviewed the existing bibliography on the topic and made direct on-site observations during an actual shutdown. In addition, interviews were held with a number of specialists in the area using qualitative approaches, namely, semi-structured interviews, focus groups, and action research.
Slowly Varying Wave Drift Forces Analyzed From Model Test Data on a Moored Ship in Shallow Water
Authors: Stansberg Carl Trygve , Paˆkozdi Csaba
Published: February 2010

Model test estimation of quadratic transfer functions (QTFs) is investigated for slowly varying wave drift excitation on a large moored ship in shallow water. Cross-bi-spectral analysis in irregular waves is used. A numerical study is run first, with a known, synthetical QTF model characterized by a strong off-diagonal variation, combined with a very lightly damped linear slow-drift dynamical system. The purpose is to check the accuracy of the analysis. For this simple model, a good accuracy is obtained in the estimated QTF. This is because of a refined noise reduction method which works well in this case. The wave frequency range of valid estimates is where the wave spectrum S(f) is higher than 7% of the spectral peak. Without the refinement, the useful range is reduced to where S(f) is higher than 15% of the spectral peak, based on a 3-hour sea state simulation. The method is then applied on experimental surge motion records from 1:50 scaled model tests carried out in an offshore basin, simulating 15m water depth. It is found that the QTF estimation procedure works reasonably well, but the accuracy is lower than that in the numerical study because the refined noise reduction could not be used due to the particular characteristics of the QTF. Therefore a basic version without the refinement had to be used. Still, results appear to be fairly reliable in the reduced wave frequency range with S(f) > 15% of the spectral peak, i.e. from 0.07Hz to 0.10Hz in this case.
Real and Virtual Convergence With Augmented Reality for Supporting Offshore Structure Management
Authors: Lee Kyung-Ho , Lee Jung-Min , Han Young-soo , Lee Jea-Joon , Lee Byung-Hak , Kim Sang-Kyum
Published: February 2010

As the demands of offshore structures are increasing, human’s error on the offshore structure is considered as important problems to prevent accident. Augmented reality technology is able to display the specific information to user in front of our eyes. Effect of augmented reality that is could provide high perception was reported already, so in this paper, we suggest augmented reality technology for the offshore structure’s management to reduce human’s error on the offshore structure and we will present a simple prototype which is able to display the specific knowledge/data on the PDA considering high usability on site.
On the Dynamics and Application of Sandwich Hydroelastic Foundation for Offshore Structures and Systems
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Damisa Olatunde
Published: February 2010

Subsea systems and structures are constantly being redesigned, reshaped and reconstructed to enhance offshore exploration, production and exploitation activities. Their structural stability and integrity are strongly dependent on the ability of their foundation footings to dissipate vibration energy arising from external influences such as hydrodynamic forces and propagation of seismic waves through a moving seabed or ocean floor. In this paper, the dynamic behavior, suitability and application of sandwich hydroelastic foundation system for vibration control and enhancement of structural stability in subsea structures is investigated analytically. By employing mechanics of contact and laminated thin plate theory, a well posed boundary value partial differential equation is formulated for a fluid-structure-soil interaction model of slip damping mechanism. For this problem, the proposed sandwich foundation footing is assumed to be partially buried on a moving seabed and is idealized as two sandwich homogenous hydroelastic plate layers in a moving elastic subsoil layer. By assuming linear pressure profiles across the plate axes, the effects of varying pressure gradients and subsoil layer sliding velocities, across the foundation axes, on the energy dissipation mechanism are computed for design analysis and applications.
Multiple Criteria Decision Making (MCDM) Process in Selecting Location for Floating Storage and Regasification Unit (FSRU): A Case Study of Bali Island Project
Authors: Artana Ketut Buda
Published: February 2010

This paper presents a case study in selecting the best location for a Floating Storage and Regasification Unit (FSRU) in Bali. FSRU is an alternative to replace a conventional shore LNG terminal. The selection involves several criteria/attributes that can be grouped into two general attributes, namely qualitative and quantitative attribute. Multiple Criteria Decision Making (MCDM) approach is utilized to solve the selection problem, considering the capability of this method in solving multi-criteria problem with mutual conflict. Qualitative criteria is evaluated using AHP method to calculate weight of each criteria, and decision matrix algorithm is then utilized to convert preference of stakeholders into, consecutively, probability assignment, total probability assignment and preference degree. Quantitative criteria are also converted into preference degree and after combining with the preference degree of qualitative attribute, entropy method is then used to rank the alternatives. Selected location would be the alternative having the highest entropy. Four alternatives are under consideration; Benoa, Celukan Bawang, Pemaron and Gilimanuk. This research found that Celukan Bawang is the best location for the FSRU.