bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Harmonic Decomposition of Sea Measured Data of Offshore Platforms
Authors: Liu Fushun , Cao Jinchao , Chen Jiefeng , Yang Wenlong , Li Wei
Published: October 2016

The measured data are often required and taken as the input of different kinds of algorithms for modal parameter identification, model updating and/or damage detection of offshore platforms. This paper investigates the application performance of the approach to offshore platforms, by using real measured data. Considering the fact of a recorded loading is always finite in duration, most likely aperiodic, and even damped because of the existence of damping of the structures, a recent developed complex exponential decomposition method [1] was employed to deal with real measured data. Therefore, in this article, three kinds of measured data will be used. The first one is a measured wave force that was collected through an experiment conducted in the lab of Ocean University of China, to investigate the feasibility of original external loading decomposition. To study the performance of the proposed method when applied to offshore structures, two sets of typical signals are used: one set was collected from the JZ20-2MUQ offshore platform when it was excited by ice, and the other was collected from the WZ11-4D platform when it was excited by waves. The results show that the approach can decompose the real measured data into a series of non-harmonic components, and a large model order is often suggested.
Instability of Mooring Cables in Presence of Ice-Load
Authors: Ghoshal Ritwik , Yenduri Anurag , Ahmed Aziz , Chen Zhuo , Wang Wenping , Hussain Anis , Jaiman Rajeev K. , Qian Xudong
Published: October 2016

Station keeping system for arctic floaters such as mooring cables requires an innovative engineering design coupled with a detailed investigation on its resistance against the impact loading. The ice-induced vibration, together with the wave and current actions, imposes a strong demand on the mooring cable design. However, in present industry practice, the mathematical models/software used in designing the mooring cables for offshore structures use linear strain theory. In this paper, an analytical modal based procedure for underwater submerged cable considering its geometric nonlinearity is presented. Introducing geometric nonlinearity into the modal procedure enables coupling between different modes, which is not included in the standard the linear analysis of integrated mooring system. In the present analysis, the second in-plane and first two out-of-plane modes are considered to highlight the effect of geometric nonlinearity near the 2:1 internal resonance phenomena of underwater mooring cables. The differential equation for cable is solved using a modal decomposition method considering second-order terms of the finite strain tensor. A simply supported boundary condition is assumed at both ends of the cable. A unidirectional wave loading is considered and thereby, the floater will have two translational motions, i.e., surge and heave. The floater motions will cause a support excitation at the pinned connection between the floater and mooring. This phenomenon is modelled as a base excitation at the top support point of the mooring cable. The support excitation frequency is chosen to be close to the natural frequency of the second in-plane mode. Therefore, the in-plane mode is excited directly. Ice load is applied at the support from an out-of-plane direction as a pulse load which may come from the ice impact and/or breaking. So, the out-of-plane mode is excited parametrically. It is observed that the out-of-plane mode responses show instability under certain base excitation amplitude, i.e., the responses due to the pulse load from the ice impact never decay. This instability in the responses may lead to the fatigue failure of the mooring cables. It is observed that this instability in the responses arises from the modal interaction between the different modes, i.e., autoparametric excitation, which the linear analysis is unable to capture. Numerous simulations are carried out to determine the stability boundary of different out-of-plane modes for various amplitude and excitation frequency. The stability boundaries are also determined using the harmonic balance method to verify the results obtained from the modal analysis. It can be concluded from this analysis that the nonlinear coupling terms play a significant role, close to the 2:1 resonance region which can lead to an unstable response of the mooring cables in the presence of ice loads.
Methodology for the Design of LNG Terminals in a Nearshore Environment
Authors: Jaouën Frédérick , Waals Olaf , de Jong Martijn , van der Hout Arne , Christou Marios
Published: October 2016

Nowadays, more and more nearshore LNG terminals are being built as it offers easy access to vessels coming from deep water and mitigates the risk by isolating regasification units from the cities. However, designing these terminals can be challenging in shallow water, as it is exposed to low-frequency waves which can excite the moored vessels at their natural periods. By lack of knowledge and adequate numerical simulation techniques, the effect of these low-frequency waves on the motions of moored vessels are unfortunately often ignored in the design. This is likely to result in an underestimation of the vessel motions and terminal downtime. In this paper, a methodology for the design of terminals in a nearshore wave climate is presented. The methodology consists of six steps which guide the engineer from the definition of the deep-water sea states to the calculation of the vessel motions and terminal downtime. In an initial stage, computational efficient tools are used, with the limitation that several approximations need to be made. In a later stage, more detailed but expensive methods are applied. The objective of this paper is to show how the developed methodology can give insight in the expected downtime due to the low-frequency waves in any nearshore mooring location. As an example, the methodology is applied on a fictive but realistic case, for which the motion response of a LNG carrier moored to a jetty on a sloping bottom is calculated. From seven years of deep-water sea states, the terminal downtime is estimated. The application of the methodology to the design case confirms that the terminal downtime can be significantly underestimated if shallow water effects are not taken into account. So the influence of the water depth, bathymetry, wave directionality and low-frequency waves on the vessel motions should be investigated with care. However, the results obtained in the design case also show that the spectral shape of the low-frequency waves predicted by the wave models are sensitive to the tuning of numerical parameters. Tuning the wave models against model tests or full scale data is therefore highly recommended, because the motion response of a low-damped moored vessel can be dominated by the amount of low-frequency free wave energy at its natural periods.
Breaking Load on Jacket Structure
Authors: Chandrasekar Sruthi , Venkatachalam Sriram
Published: October 2016

Jackets are structures used in the offshore industry as a bottom supported platform for oil and gas production. The jackets have to be built in order to withstand the harsh sea environment. Such designs demand in depth analysis to predict the loads acting on the structure and its response. Depending on the sea states in which the structure needs to be installed, breaking load can be important. Estimation of breaking load for single cylinder exists in literature, since the breaking load on the jacket structure needs a lot more clarity. The aim of this paper is to estimate the impact force on a model jacket using Duhamel integral, which was not explored before. The impact load so far analyzed was compared with theoretical explanations given by Goda, et al. (1966), Wienke and Oumeraci (2005). The scope of the study is limited to plunging type of breakers. Five loading cases include wave breaking at far-front of a structure, in front of structure, on the front leg, on the rear leg and a non-breaking case was considered.
Fatigue Algorithm for Modeling Many Weld Toe Cracks Propagating at Welded Joints
Authors: Tsang Kin Shun , Pang John H. L. , Hoh Hsin Jen
Published: October 2016

Fatigue crack growth at welded joints often propagates from as many as tens to hundreds of small weld toe cracks along the weld toe line in offshore welded structures. This paper will present a fatigue algorithm for modeling many small weld toe cracks propagating from a welded joint. Cracks usually initiate at the weld toe region of the structures and propagate as surface cracks at the stress concentration regions of the weld-toe line. The presence of such weld defects or crack-like flaws can have a severe detrimental effect on their fatigue life and fracture resistance. Currently, there is a lack of studies that considers the effects of multiple cracks and their distribution density in welded joints. This work focuses on the fatigue analysis and modeling of multiple weld toe cracks, specifically in T-butt joints.

Fatigue crack growth prediction is usually determined by the stress intensity factor range and crack propagation rate through Paris law. To predict the Stress Intensity Factor (SIF) of a weld toe crack, the magnification (Mk) factor was used. The Mk factor is influenced by the size of the welded attachment, as well as the size and depth of the weld toe crack. Simplified solutions for practical prediction of Mk factors were determined from 3D extended finite element method (XFEM) by modelling a semi-elliptical weld toe crack in a T-butt weld for cracks of different dimensions. The accuracy of the Mk factor solutions was verified by comparison to HSE fatigue data on 16 mm thick tubular joints.

The Mk factor solutions were used to predict the growth of fatigue cracks using a model based on Paris Law and SIF solutions by Newman and Raju with plastic zone size corrections. Fatigue life was predicted for plates with and without attachments. It could be seen that the predicted life of a weld toe crack was severely reduced with the addition of a welded attachment. The model was extended to the multiple surface cracks commonly observed at the weld toe, where each crack is treated as independent, following established code procedures. The multiple cracks will coalesce as they propagate, until a single dominant crack emerges and fracture occurs. In this paper, the relationship between the fatigue life and the number and density distribution of the initial cracks was investigated. Fatigue life was predicted for plates with attachments with 1, 2, 10 and 100 cracks initially. The results show that as the number of cracks increases, the predicted fatigue life decreases.
Fatigue Crack Propagation Characteristics of 3.5 to 9 wt% Nickel Steels for Low Temperature Applications
Authors: Park Jeong-Yeol , Kim Myung-Hyun
Published: October 2016

The Marine Environmental Protection Committee (MEPC) of the International Maritime Organization (IMO) agreed upon progressively stricter limitations for Nitrogen Oxide (NOx) emissions for vessels. This latest trend has led to increased demand for liquefied natural gas (LNG) and ethane gas carriers. One of the most important issues in the design of LNG and ethane carriers is structural integrity of storage tanks. Considering the operation temperature of LNG and ethane gas carriers, storage tanks are typically manufactured with low temperature materials, such as Al-5083, SUS 304, Invar and nickel steels. In particular, nickel steels are used in demanding good strength and heat-resistant applications. In this regard, this study evaluated fatigue crack propagation characteristics of nickel steels with various Ni contents between 3.5 wt% and 9 wt% both at room and cryogenic temperatures. Fatigue crack growth rate (FCGR) characteristics of 3.5 and 7% nickel steel are obtained by testing according to ASTM E647. Moreover, FCGR of nickel steels are compared with those of other low temperature materials. For room temperature, test results showed that fatigue crack propagation rate increased with the increase of nickel contents. The value m at cryogenic temperature is higher than that of room temperature. In addition, the value C at cryogenic temperature is lower than that of room temperature when the FCGR characteristics are presented by Paris’ law.
Influences of Fiber Types on the Scabbing of Concrete Slabs Subjected of Projectile Impact
Authors: Kim Gyuyong , Kim Hongseop , Nam Jeongsoo , Lee Sanggyu
Published: October 2016

This study evaluates the influences of fiber types on the scabbing of concrete slabs subjected of projectile impact. The scabbing on the rear side occurred by tensile stress and strain which caused by shock wave that transmitted to the rear side. In order to reduce the fracture of concrete on the rear side, the study of impact resistance of fiber reinforced concrete was performed. Fiber-reinforced concrete has been improved flexural and tensile performance by the cross-linking action of the fiber, and the scabbing on the rear side by the projectile impact was inhibited. However, there is a difference in flexural and tensile performance and impact performance improvement by the type of reinforcing fiber. If the type of the reinforcing fibers are different, it is necessary to consider the flexural and tensile performance of the concrete with form and mechanical properties of fibers or the number of fiber.
Prediction of Distortion Produced in Welded Structures During Straightening Process Using the Inherent Strain Method
Authors: Ruiz Valdes Hector Olmedo , Osawa Naoki , Murakawa Hidekazu , Rashed Sherif
Published: October 2016

In order to optimize the straightening process, it is necessary to predict the deformation due to local heating. Numerical simulation is an advantageous way to do this. In this study, Osaka University’s inherent strain based welding simulation code JWRIAN is modified so that inherent strain’s equivalent nodal forces are calculated in cases where the inherent strain confines within narrow region whose size is smaller than element size. In the developed code, the initial strain force vector and element stiffness matrix’s non-linear term which includes stress components are integrated using higher order (e.g. 20 × 20 × 6 for 4-nodes shell elements) Gauss-Legendre quadrature while other quantities are evaluated by using ordinary order (2 × 2 × 2) quadrature. The validity of the developed software is examined by comparing rectangular plate’s angular distortion due to gas line heating calculated by three-dimensional thermal-elastic-plastic analysis and that calculated by the developed system.
Application of the Most Likely Extreme Response Method for Wave Energy Converters
Authors: Quon Eliot , Platt Andrew , Yu Yi-Hsiang , Lawson Michael
Published: October 2016

Extreme loads are often a key cost driver for wave energy converters (WECs). As an alternative to exhaustive Monte Carlo or long-term simulations, the most likely extreme response (MLER) method allows mid- and high-fidelity simulations to be used more efficiently in evaluating WEC response to events at the edges of the design envelope, and is therefore applicable to system design analysis. The study discussed in this paper applies the MLER method to investigate the maximum heave, pitch, and surge force of a point absorber WEC. Most likely extreme waves were obtained from a set of wave statistics data based on spectral analysis and the response amplitude operators (RAOs) of the floating body; the RAOs were computed from a simple radiation-and-diffraction-theory-based numerical model. A weakly nonlinear numerical method and a computational fluid dynamics (CFD) method were then applied to compute the short-term response to the MLER wave. Effects of nonlinear wave and floating body interaction on the WEC under the anticipated 100-year waves were examined by comparing the results from the linearly superimposed RAOs, the weakly nonlinear model, and CFD simulations. Overall, the MLER method was successfully applied. In particular, when coupled to a high-fidelity CFD analysis, the nonlinear fluid dynamics can be readily captured.
CFD Simulation of the Effect of Different Oils on Water Wetting and Internal Corrosion of Oil Pipelines
Authors: Pouraria Hassan , Seo Jung Kwan , Paik Jeom Kee
Published: October 2016

Internal corrosion of subsea flow-lines and pipelines is one of the major challenges in flow assurance. Although the crude oil itself is not corrosive the presence of water and dissolved gasses such as CO2 and H2S can potentially result in internal corrosion. It is well known that the corrosion occurs if a continuous layer of corrosive water wet the pipe. However, past experiences revealed that the probability of water wetting critically depends on the oil properties. Due to the complex nature of oil-water flows predicting the phase behavior under different conditions is a challenging task. Hence, any progress in developing a reliable method for predicting the onset of water wetting and the characteristics of corrosive water layer can significantly increase the accuracy of corrosion prediction as well as the confidence regarding the integrity of the pipelines. The present study is an attempt toward using computational fluid dynamics for studying the effect of oil properties on the sweet corrosion. To this end, an Eulerian-Eulerian approach along with population balance model is employed. Furthermore, the capability of model in predicting the main features of oil water flow and the effect of different crude oils on water wetting and corrosion rate are investigated.
A Novel Electrical Based Breach Detection System for Flexible Pipe
Authors: Nott Phil , Shepherd William , McNab John , Harley Phil , Ahmed Syed Zakir
Published: October 2016

An outer shield breach is the most common form of damage that can occur to a subsea flexible pipe during both installation and operation. Definitive and accurate detection and location of such damage is imperative in triggering the appropriate repair response. The overall aim is to minimise corrosion damage to the carbon steel strength elements in the pipe annulus, which occurs from the resulting ingress of seawater. GE Oil & Gas, in collaboration with Photon Fire Ltd have developed a new method of detecting seawater in a subsea flexible pipe annulus. This paper describes a novel breach detection system developed to monitor pipes using very low energy electrical signals appropriate for use in hazardous areas. The technique provides an enduring record of the occurrence of a breach and the extent of the subsequent flooding. A brief outline of the development programme is presented. The work involved determining the sensing technique used, development of appropriate electronic instrumentation, the optimised method for installing the sensor into the riser, and bespoke connection to the instrumentation. A prototype system, approved for use in Hazardous Area ATEX zone zero has been implemented on midscale pipe samples and the transient and steady state ‘scans’ of the pipe have been investigated. A summary of the test results and a proposed testing regime is presented. Results show that using this technique can accurately determine that a breach has occurred in the wall of the riser and the extent of the flooding.
A Rubber Bag for Liquid Cargo to Improve Ship Collision Safety
Authors: Kubiczek Jan M. , Liang Boyuan , Molter Lars , Ehlers Sören
Published: October 2016

Collisions and grounding accidents of ships, but also the failure of the hull-integrity, can lead to oil leakage. Examples are the Rena in 2011, the Hebei Spirit in 2007 and the much known accident of the Prestige in 2002.

Consequently research regarding the enhancement of the structural design to increase the safety-level of ships in case of accidents is important. In this paper the use of a rubber bag as a second barrier is presented as an alternative concept to prevent oil leakage in case of accidents.

The influence of the rubber bag is investigated using the example of a ship collision. A simplified tanker side structure as well as a box shaped rubber bag are analyzed with the finite element method. The material model for the rubber bag is calibrated with tensile tests to obtain the required material parameters.

The reaction forces and the associated penetration depth are analyzed. The comparison is done between the structure with and without the rubber bag. For the latter, the general behavior is compared with large-scale experimental results. Furthermore an additional increase of the survivability of the ship due to the rubber bag without changing the common structural design is discussed.
Sea Ice Distribution in the Barents Sea
Authors: Fritzner Sindre M. , Sagerup Trond
Published: October 2016

This paper provides a statistical description of the sea ice occurrence in the Barents Sea, using yearly maximum sea ice data for the last 36 years from the European Centre for Medium-Range Weather Forecasts (ECMWF). A set of four distribution functions have been estimated with the maximum likelihood method. The distribution functions used were Extreme Value distribution, Gumbel distribution, Normal distribution and kernel density estimation. The normal distribution was found to fit the data best and provide the most likely result. Our results verify dependency of the North Atlantic current on the sea ice edge. Warm water northwards prevents the ice from extending south; this makes the extreme value distribution unlikely since this will prevent long tailed distributions. The results for sea ice occurrence are compared to the boundaries given in the proposed revision to NORSOK N-003. These boundaries were found to be too simplistic and not necessarily conservative. Here we have proposed new and more accurate boundaries for the sea ice occurrence. We have found trends indicating northwards movement of the sea ice edge in the Norwegian Sea and eastern parts of the Barents Sea. These trends are mostly due to less ice in the last ten years and not trends for the whole period. In the south-western parts of the Barents Sea where oil and gas operations are imminent no trends have been discovered. The lack of trend is related to the islands in the western Barents Sea.
Identify Modal Parameters of a Real Offshore Platform From the Response Excited by Natural Ice Loading
Authors: Yang Wenlong , Li Lei , Fu Qiang , Teng Yao , Wang Shuqing , Liu Fushun
Published: October 2016

Experimental modal analysis (EMA) is widely implemented to obtain the modal parameters of an offshore platform, which is crucial to many practical engineering issues, such as vibration control, finite element model updating and structural health monitoring. Traditionally, modal parameters are identified from the information of both the input excitation and output response. However, as the size of offshore platforms becomes huger, imposing artificial excitation is usually time-consuming, expensive, sophisticated and even impossible. To address this problem, a preferred solution is operational modal analysis (OMA), which means the modal testing and analysis for a structure is in its operational condition subjected to natural excitation with output-only measurements. This paper investigate the applicability of utilizing response from natural ice loading for operational modal analysis of real offshore platforms. The test platform is the JZ20-2MUQ Jacket platform located in the Bohai Bay, China. A field experiment is carried out in winter season, when the platform is excited by floating ices. An accelerometer is installed on a leg and two segments of acceleration response are employed for identifying the modal parameters. In the modal parameter identification, specifically applied is the data-driven stochastic sub-space identification (SSI-data) method. It is one of the most advanced methods based on the first-order stochastic model and the QR algorithm for computing the structural eigenvalues. To distinguish the structural modal information, stability diagrams are constructed by identifying parametric models of increasing order. Observing the stability diagrams, the modal frequencies and damping ratios of four structural modes can be successfully identified from both segments. The estimated information from both segments are almost identical, which demonstrates the identification is trustworthy. Besides, the stability diagrams from SSI-data method are very clean, and the poles associated with structural modes can become stabilized at very low model order. The research in this paper is meaningful for the platforms serving in cold regions, where the ices could be widespread. Utilizing the response from natural ice loading for modal parameter identification would be efficient and cost-effective.
Correlation Allowances in Model Tests Results: A Delicate Balance Between Performance, Accuracy and Commercial Interests?
Authors: Hagesteijn Gerco , Hooijmans Patrick , van der Meij Karola
Published: October 2016

Model tests at ballast and design draught are used to convert the sea trial results from the ballast trial draught to the contractual design draught. Correlation allowances in model test results and their effect on the trial performance prediction are of major importance. Nowadays it is not only typical to verify the contract speed but also the EEDI certification requires a verification of the speed power performance of the vessel. The use of a to favorable CA-value may lead to attractive performance figures, but also leads to higher fuel consumption figures than expected. Furthermore the design point of the propeller is affected, which leads to a too low light running margin and in some cases to erosive cavitation.

During a study, large spreading in the values of the correlation allowances for design draughts have been found for merchant vessels tested at different model test institutes, but at ballast trial draught the spreading is much less. Can it happen that some institutes select favorable correlations allowances on the basis of inaccurate trial data of shipyards? Or should we accept a large spreading in correlation allowances and have these indeed been confirmed by sea trials at design draught? This paper will present a discussion using the experience of a large full scale trial database as well as the accuracy of model and full scale tests.
Aframax in Numerical Wave Tank: From Classic Decay Test to the Ship Moored in Irregular Waves
Authors: Barcarolo Daniel , Thilleul Olivia , le Touzé David , Jacquin Erwan , de Vries Igor , Naciri Mamoun
Published: October 2016

The prediction of ship motions in extreme seastates is very complex as it involves strong nonlinearities. It deals with high motions of the ship and implies strong mooring system loads. These seastates are usually modeled in tank tests but an alternative in the near future could be CFD computations.

In this article, all required steps to setup and verify the hydrodynamic and numerical model are performed. The setup of the hydrodynamic and numerical model enable us to show that CFD computations of motion RAOS and pitch decay tests provide results in agreement with diffraction-radiation results.

Wave only simulations enable us to verify that irregular waves are accurately modelled in the CFD domain. Since the wavemaker motion used in tank tests to generate irregular waves is not available, a process of linear back propagation is set up from the wave elevation on a wave probe in tank tests. High Order Spectral (HOS) simulations are performed to reproduce the seastate measured in tank tests.

Finally, a test was performed to model the ship motions in irregular extreme waves with ICARE solver coupled to the computed HOS wave field through Spectral Wave Explicit Navier Stokes Equations (SWENSE).
A Numerical Study on Correlation Between the Bow Design Parameters and Added Resistance Using the Design of Experiments
Authors: Kim Gwan Hoon , Shin Hyun Joon , Seo Jeonghwa , Rhee Shin Hyung
Published: October 2016

In this study, numerical computation was carried out for evaluating the effects of the design parameter variations on the added resistance of Aframax tanker in head seas. The design of experiments (DOE) was used to efficiently conduct the numerical simulations with the hull form variations and save computational resources. A computational fluid dynamics (CFD) code based on the continuity and Reynolds averaged Navier-Stokes (RANS) equation was used for the numerical simulation. The simulation was performed in a short wave condition where the wave length was half of the ship length, which is expected to be most frequent in the vessel operation. Five design parameters of fore-body hull form were selected for the variations: design waterline length (DWL), bulbous bow height (BBH), bulbous bow volume (BBV), bow flare angle (BFA) and bow entrance angle (BEA). Each parameter had two levels in the variations, thus total 32 cases were designed initially. The results of the numerical simulations were analyzed statistically to determine the main effects and correlations in the five design parameters variations. Among them, the most significant parameter that influences on the added resistance in waves was DWL, followed by BBV and BEA. The other parameters had little effects on the added resistance in waves. By the computations, it was revealed that Extending DWL and decreasing BEA promoted the reflection of waves more toward the side than forward. In addition, there existed two-way interactions for the following two-factor combinations: DWL-BFA, DWL-BEA, DWL-BBV, BBH-BBV.
Establishment of a Validation and Benchmark Database for the Assessment of Ship Operation in Adverse Conditions
Authors: Sprenger Florian , Hassani Vahid , Maron Adolfo , Delefortrie Guillaume , Van Zwijnsvoorde Thibaut , Cura-Hochbaum Andrés , Lengwinat Antonio
Published: October 2016

The Energy Efficiency Design Index (EEDI), introduced by the IMO [1] is applicable for various types of new-built ships since January 2013. Despite the release of an interim guideline [2], concerns regarding the sufficiency of propulsion power and steering devices to maintain manoeuvrability of ships in adverse conditions were raised. This was the motivation for the EU research project SHOPERA (Energy Efficient Safe SHip OPERAtion, 2013–2016 [3–6]). The aim of the project is the development of suitable methods, tools and guidelines to effectively address these concerns and to enable safe and green shipping. Within the framework of SHOPERA, a comprehensive test program consisting of more than 1,300 different model tests for three ship hulls of different geometry and hydrodynamic characteristics has been conducted by four of the leading European maritime experimental research institutes: MARINTEK, CEHIPAR, Flanders Hydraulics Research and Technische Universität Berlin. The hull types encompass two public domain designs, namely the KVLCC2 tanker (KRISO VLCC, developed by KRISO) and the DTC container ship (Duisburg Test Case, developed by Universität Duisburg-Essen) as well as a RoPax ferry design, which is a proprietary hull design of a member of the SHOPERA consortium. The tests have been distributed among the four research institutes to benefit from the unique possibilities of each facility and to gain added value by establishing data sets for the same hull model and test type at different under keel clearances (ukc). This publication presents the scope of the SHOPERA model test program for the two public domain hull models — the KVLCC2 and the DTC. The main particulars and loading conditions for the two vessels as well as the experimental setup is provided to support the interpretation of the examples of experimental data that are discussed. The focus lies on added resistance at moderate speed and drift force tests in high and steep regular head, following and oblique waves. These climates have been selected to check the applicability of numerical models in adverse wave conditions and to cover possible non-linear effects. The obtained test results with the KVLCC2 model in deep water at CEHIPAR are discussed and compared against the results obtained in shallow water at Flanders Hydraulics Research. The DTC model has been tested at MARINTEK in deep water and at Technische Universität Berlin and Flanders Hydraulics Research in intermediate/shallow water in different set-ups. Added resistance and drift force measurements from these facilities are discussed and compared. Examples of experimental data is also presented for manoeuvring in waves. At MARINTEK, turning circle and zig-zag tests have been performed with the DTC in regular waves. Parameters of variation are the initial heading, the wave period and height.
An Experimental Assessment on Umbilical Cable Crushing Using Digital Image Correlation
Authors: Santos Caio C. P. , Pesce Celso P. , Franzini Guilherme R. , Otte Filho Olaf O.
Published: October 2016

Focusing on the integrity of umbilical cable components during the laying operation, particularly on hoses integrity, this paper assesses displacement fields on umbilical cable cross-sections by means of a special crushing test setup. Using a high resolution Digital Image Correlation system (DIC), experiments with two umbilical cables are carried out in a 250 kN mechanical tests rig. Besides measuring the components displacements, applied crushing forces and shoes displacements are acquired. The experimental samples are taken from two HCR-hoses umbilical cables, which have been cases of study of a finite element analysis methodology, recently proposed and presented in OMAE2015, [12]. Experimental analysis and a theoretical-experimental correlation are presented, for both umbilical cables.
Numerical Analysis of Combined VIV and Slug Flow in Time Domain
Authors: Huse Knudsen Tor , Sævik Svein , Thorsen Mats Jørgen
Published: October 2016

Vortex induced vibrations (VIV) and slug flow are two important aspects for marine risers conveying a multiphase flow, and should be carefully examined due to the influence on the fatigue life of the structure. This article examines a truncated riser exposed to VIV with an internal two-phase slug flow. The main focus of the article was to examine the effect of internal slug flow on the VIV of a riser. The VIV were simulated in time domain with a linear structural model with constant pretension. Approximately 150 vortex shedding periods were simulated after the response reached steady state. An internal two-fluid flow was introduced, with constant internal velocity, pressure and uniform slug lengths. From the numerical study it was apparent that the slug velocity and slug length had an influence on the response pattern, amplitude and frequency. An analytical model that predicts additional response frequencies due to slug flow was also compared to the numerical studies. The analytical study produced similar additional response frequencies as the numerical study.

The slug length and internal velocity can influence the response of the riser, and should be considered for marine risers conveying multiphase flow.
Near Field Expression of Ship Wave Resistance by Green’s Theorem
Authors: Tsubogo Takashi
Published: October 2016

The ship wave resistance can be estimated by two alternative methods after solving the boundary integral equation. One is the far field method e.g. Havelock’s formula based on momentum conservation in fluid domain, and another is the near field method based on direct pressure integration over the wetted body surface. Nakos and Sclavounos (1994) had shown a new near field expression of ship wave resistance from the momentum conservation law in the fluid domain with linearized free surface condition. Their new expression differs slightly from the traditional near field form. This problem of near field expression is reconsidered in terms of Green’s second identity. After linearization of the free suface condition and some transformation of equations, the present paper will agree with the Nakos and Sclavounos’ near field expression for the ship wave resistance. Some numerical calculations of wave resistance from the far field method and from the near field method are shown using the classical Kelvin sources distributed on the centerplane of thin ship but solving the different boundary integral equation. Numerical results suggest that the problematic run-up square integration along the waterline is to be omitted as a higher order small quantity. If this run-up term is omitted in each method except for far field, the traditional direct pressure integrtaion is equal to the Nakos and Sclavounos’ near field expression.
Hull Deformation Effect on Membrane-Type LNG Containment Systems
Authors: Wang Bo , Shin Yung-Sup , Norris Eric
Published: October 2016

The objective of this study is to investigate the relationship between the maximum allowable hull deformation, which includes global elongation and local deflection, and the capacity of the CCS in membrane-type LNG vessels. The LNG CCS mainly consists of the primary barrier (e.g. a corrugated membrane for GTT MK III system and an invar membrane for GTT NO 96 system) and the insulation panel which is attached to the inner hull through mastics or couplers. The excessive hull elongation due to dynamic wave loads may cause fatigue damage of the primary barrier. Thus, the maximum allowable hull elongation (global deformation) can be determined based on the fatigue strength of the primary barrier. On the other hand, the excessive hull deflection due to cargo or ballast water pressure may cause failure of the insulation panel and the mastic. Therefore, the maximum allowable hull deflection (local deformation) in the hull design can be determined based on the strength of the insulation panel and the mastic. In the present paper, the determination of fatigue life vs. strain curves of materials has been summarized for the primary barrier. Fatigue curves based on either structural fatigue tests or standard specimen tests can be applied in fatigue assessment of a primary barrier. As an example, the finite element (FE) analysis has been conducted on the MK III CCS with the hull structure under pressure loads. Two different load cases including full load and ballast load conditions have been considered to evaluate the structural integrity of the insulation system in numerical simulations. FE results show that the mechanical behavior of the insulation system and the mastic under the maximum allowable hull deflection has been examined based on the yielding strength of each individual component. Finally, the complete procedure to determine the maximum allowable hull elongation and the maximum allowable hull deflection has been developed for meeting the requirements of containment system design for membrane-type LNG carriers.
Friction Behavior Between Epoxy and Flexible Pipes Armor Wires
Authors: Lorio Diego A. , Wedekamper Facundo J. , Bertoni Fabiano , Lopéz Facundo S. , Campello George C. , Strohaecker Telmo
Published: October 2016

The offshore industry has presented an increasing demand over the last few decades, requiring the production in deep water fields. The end fittings (EF) are critical points within the production system. Therefore, structural and fatigue analyses are essential in the EF design, making it necessary to know the stress distribution experienced by the armor wires along the EF. Numerical and analytical models are often used in order to assess the stress state. However, characteristics like geometries, materials and interactions must be previously known in order to apply these models.

The purpose of this work was to analyze the arithmetic mean surface roughness (Ra) and to determine the friction coefficient (μ) for two types of armor wires when in contact with resin used to fill the EF. The resin used in the interaction with the armor wires was an epoxy filled with metallic particles. For the experimental analysis straight carbon steel armor wires with different cross-sections, typically used in 2.5″ and 8″ flexible pipes were used. Surface profile was obtained for each wire by repeated measurements along two lines over each surface. A total of three repetitions were performed in each measure line. Longitudinal roughness was determined through these profiles. Finally, friction coefficients were obtained experimentally by means of a device that allows to simulate the wire pullout and sliding process. In this device, two epoxy pads were put in contact with the surface of the analyzed wire sample, and rigid bodies in contact with the pads were used to ensure that the normal load applied is transmitted uniformly through the contact surface. The displacement rate, contact pressure between the surface of the wire and the epoxy resin pads, and axial force were recorded.

The roughness in the longitudinal direction of the wires was analyzed through descriptive statistic and compared by Student’s “t” test. The highest values were obtained on wires with larger sections. This behavior is exposed on the results obtained for the friction coefficient as a function of the contact pressure. Friction coefficient for both wires was analyzed and compared using a Mann-Whitney U test. Both friction coefficients have a positive slope, indicating a small increase as the contact pressure raise. The significance value obtained for the means comparisons was p = 0.0001 and confirms that the average friction coefficient of the two wires are really different. Because of that, we conclude that is necessary to treat the EF project for different flexible pipes differentially.
Effect of Combined Shear Stresses on the Ultimate Axial Response of the Double Bottom of a Containership
Authors: Gaiotti Marco , Bacoccoli Riccardo , Fujikubo Masahiko , Rizzo Cesare Mario
Published: October 2016

Ultimate strength of the hull girder of containerships became a significant issue in the last years in view of recent accidents and related investigations. Actually, larger and larger ships were put into service and still are designed and built. Recognizing such an issue, investigations were carried out and led to the issuance of a specific longitudinal strength standard for containerships by the International Association of Classification Societies [1]. Loading conditions become more and more challenging and especially combinations of various actions were found to impair the hull girder ultimate strength. In the attempt to better understand the influence of load combinations onto the ultimate strength of the hull girder, investigations were carried out. In this paper, the effects of the shear is considered using rather refined and accurate finite element models of a typical containership double bottom.
Evaluation of Upstream Logistics System Concepts for Offshore Operations in Remote Areas
Authors: Gribkovskaia Victoria , Johnsen Trond , Lindstad Haakon , Uthaug Eirik
Published: October 2016

As oil and gas (O&G) activities are moving north in the Arctic region new challenges for the offshore logistics have arisen. These challenges impose more stringent requirements for the logistics system setup, especially on the design and operation of vessels. We propose a methodology for quick evaluation of the feasibility and cost of the logistics system in the early stages of offshore supply planning. This methodology allows for testing the effects of using alternative ship designs and the overall supply fleet composition on system’s cost and performance while satisfying prospective campaign requirements. Safety standards and requirements for emergency preparedness and environmental performance are taken into account while cost effectiveness of the logistics system as a whole is the main quantifiable measure. The presented methodology is also very relevant for evaluation and planning of the logistics supply system for O&G activities in other areas around the world that are considered remote either due to physical distance or other characteristics that impact the complexity and cost of operations. The proposed methodology is tested on a real-life case for offshore supply planning of a drilling campaign in a remote area for one of the major international O&G operators.
Motion-Based Wave Inference: Monitoring Campaign on a Turret FPSO
Authors: da Silva Bispo Iuri Baldaconi , Queiroz Filho Asdrubal N. , Tannuri Eduardo A. , Simos Alexandre N.
Published: October 2016

In recent years, considerable effort has been made in order to validate different methods that aim at estimating the wave spectra from the motions recorded on a ship or on an offshore platform. For more than ten years now, the University of São Paulo has been working on a wave inference method for moored oceanic systems, such as Floating Production Storage and Offloading (FPSO) vessels.

This paper brings the first results from an ongoing field campaign, started in December 2014, for the estimation of wave statistics by means of this system, which is based on a Bayesian inference approach. The performance of the motion-based method is checked against the wave estimations provided by a commercial marine radar system. The radar is installed in a fixed platform close to the FPSO that is being monitored, which is moored in a turret configuration. Comparison between both systems allows one not only to evaluate the performance of the method but also to evaluate the inherent limitations that exist when the estimations are based on a very large vessel, especially one whose heading may be subjected to fast variations.

In this work, a new algorithm for the partition of the wave spectrum is used, differing from the previous works. This technique allows the identification and combination of energy peaks of the directional spectrum into wave systems, providing better modal wave statistics and less noise in the final spectrum.

Previously validation of the wave inference method was made through numerical and small-scale experimental analysis. Also, in previous studies, a 9-month field campaign was also used to validate the Bayesian method using a spread-moored FPSO, but no comparison to other measurement technique was made, instead, numerical forecasts were adopted. In this work this objective is achieved: so far, 10 months of estimates from the Bayesian inference algorithm have already been compared to data supplied by a radar system.

Comparisons with the marine radar readings attest an adequate identification of mean wave directions, with the Bayesian model estimating mean wave directions that are in close agreement to those provided by the radar system most of the time. There are, however, a few cases when the discrepancy is large and the reasons for this are still under investigation.

The comparison between both sources of data provides some insightful results, which are discussed in this paper. First, they confirm and quantify the main biases of the applied method, which are related to the filtering of the energy from high-frequency waves. On the other hand, they attest that the performance of the method for more severe sea states is good overall, showing that the method is able to provide good estimates of wave height and direction and also to capture situations when wave conditions are changing fast, such as the ones that occur with the incoming of cold fronts from South.