bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Slug Control Techniques in Pipeline Systems
Authors: Monteiro P. C. C. , Loureiro Silva L. , Vidal J. L. A. , Netto Theodoro A.
Published: September 2014

Severe slugging may occur at low flow rate conditions when a downward inclined pipeline is followed by a vertical riser. This phenomenon is undesirable for offshore oil and gas production due to large pressure and flow rate fluctuations. It is of great technological relevance to develop reliable and economical means of severe slugging mitigation. This study aims to develop an automated control system to detect and mitigate the formation of severe slugging through a choke valve and a series of sensors. As a first step, an overall flow map is generated to indicate the region within which severe slugging may occur based on Boe’s criterion [1] and Taitel’s model [2, 3]. It was possible to obtain different flow patterns by controlling the rate of water and gas injection.

The aim of this paper is, however, the formation of severe slugs and study of mitigation techniques. In the control part, we used a choke valve controlled by software which is in feedback with data from a system with pressure, temperature, flow, which are able to measure even small changes in the relevant parameters to the model. A two-phase flow loop was built for the study of severe slugging in pipeline-riser system with air and water as work fluids. The inner diameter of riser and flowline is 76.2 mm. The riser is 20 meters high and the flowline is 15 meters long and could be inclined upward or downward up to 8-degree. It has been shown by experiments how riser slugging can be controlled by automated control system.
Determination of Wave Impact Loads for the Hebron Gravity Based Structure (GBS)
Authors: Oberlies Robert , Khalifa Jameel , Huang Jerry , Hetland Steinar , Younan Adel , Overstake Meghan , Slocum Scott
Published: September 2014

ExxonMobil Canada Properties and its co-venturers are building a gravity based structure (GBS) in Newfoundland and Labrador to be installed on the Hebron Field offshore Eastern Canada. This area is characterized by harsh storms with large waves and high winds. The geometry of the Hebron GBS has an effect on the behavior of the incident waves with regards to their likelihood of breaking onto the shaft. Model tests of the structure in storm waves were executed to provide local wave impact load data on the shaft of the GBS. These tests required significant planning and design of the model, environment, and instrumentation in order to properly satisfy the test objectives. The results of the test showed that the measured wave impact loads on the structure were highly variable, requiring a long-term, response based method to quantify the design loads on an annual exceedance basis. In this paper, we discuss the salient aspects of the model testing effort and the long-term analysis approach which was utilized to define the wave impact loads that were incorporated into the Hebron GBS structural design.
Numerical and Experimental Study of Damaged Sandwich Pipe Under External Pressure
Authors: de Castilho João Fabrício Machado , Pasqualino Ilson Paranhos
Published: September 2014

Studies on sandwich pipes, which comprise two concentric high strength steel tubes and a suitable annular material have shown good results due to their improved strength under external pressure and therefore they have been indicated as a good alternative for application in brazilian pre-salt scenario as gas and oil exportation pipelines. After installation on seabed a sandwich pipe can undergo mechanical damage caused by possible impacts of an anchor or some dropped heavy objects. When this happens, its strength under external pressure can be significantly reduced. This paper presents a numerical and experimental study of the reduced strength under external pressure (initiation pressure) of a damaged sandwich pipe. To this end, small scale sandwich pipe models were manufactured using steel tubes and PVDF in the annular space. Mechanical damages were simulated on the external surface of the models to collapse them under external pressure. The test results were compared to a three dimensional FE model simulating both the initiation pressure and the propagation pressure of the tested samples. A parametric study was carried out to analyze the sandwich pipe performance under damaged conditions.
Revisiting the Dimensional Analysis of Pipeline Embedment During Installation
Authors: Carneiro Daniel
Published: September 2014

In deep water, pipelines are usually laid directly onto the seabed, in which they embed becoming partially buried. The depth a pipe will embed during installation depends on its weight and on the soil strength, but also on many other features of the lay process. The embedment along the pipeline length will govern many aspects of its behavior, for example the axial and lateral stiffness in thermo-mechanical expansion process. Despite its importance, foreseeing this penetration in design stage is still a difficult task, for which many models have been proposed over the years.

Verley & Sotberg [1] and Verley & Lund [2] have presented a thorough dimensional analysis of the pipe-soil interaction, as part of a broad study on the lateral stability of pipelines. Their equations for the initial embedment (in particular the last for embedment in undrained conditions) have been often used in design, but usually receiving additional correction factors to account for aspects not originally considered by the authors. Unlike the original dimensional analysis, the calibration of these correction factors has been done in trial and error basis, often leading to unreasonable results.

This paper revisits the dimensional analysis of the pipeline embedment during installation, aiming at widening the set of variables involved. The objective is to put together a dimensionally consistent framework in which additional aspects of the embedment process can be included in a rational way.

The paper is limited to the desktop study of selecting a new set of dimensionless groups. This might be later used for deriving a new, more accurate, model for foreseeing pipeline embedment levels in design stage. This would though require extensive testing. Which is beyond the scope of the current work.
Design of Hydrocyclone With Axial Inlet and its Performance Used in Wellbore
Authors: Zhang Yong , Wang Yang , Zhang Yan , Zhao Lixin , Li Feng , Wang Fengshan , Zheng Guoxing
Published: September 2014

With the increasing of the water ratio in produced fluid year by year, the cost of oil extraction will turn high gradually wherever in onshore oilfields or offshore oilfields. Downhole Oil/Water Separating System (DOWS) with hydrocyclone as the downhole separator is the key technology to separate most water from the produced fluid and reinject it into the suitable formation. This system can significantly reduce the oilfield produced water which is the universal puzzle all around the world. While how to decrease the diameter of the separator is a bottleneck problem to expand the flexibility of DOWS. There is a disk type inlet used for the conventional hydrocyclone which can bring fluid into the main body of hydrocyclone with the speed of rotation. The size of the disk type inlet will be bigger than the main body. And this is the main bottleneck for the miniaturization of hydrocyclone. So two new kinds of axial flow inlets were designed for the downhole separator in this paper. Helical structure was used as the unit of running fluid into hydrocyclone with the speed of rotation. It can make the diameter of the inlet and the main body of hydrocyclone to be equal. In the same time, it will simplify the arrangement of the flow path. The design, structure parameter optimization, the influence of separating efficiency of this inlet is discussed in this paper. And they show sharp separating capability as the downhole separators.
Microstructure Identification for X80 Plates/Pipes With Low Temperature Toughness and Enhanced Strain Capacity
Authors: Di Schino Andrea , Zheng Lei , Zhang Chuanguo , Porcu Giorgio
Published: September 2014

Due to the increasing demand for natural gas, the construction of long-distance pipelines through seismically active regions or arctic regions with ground movement caused by permafrost phenomena will become more and more necessary. To guarantee the safe operation of those pipelines, the pipe material has to fulfil strain-based design requirements. Hence in longitudinal direction low yield-to-tensile ratios, high uniform elongation values and a roundhouse shape of the stress-strain curve combined with sufficient strength values in transverse direction are essential. Moreover, a satisfactory low temperature toughness has to be guaranteed.

An adequate plate metallurgical design is fundamental for appropriate pipe properties achievement. As far as concerns the plate design the understanding and the control of microstructure are the key factors, achieved by an adequate steel chemical composition and proper process parameters.

In the framework of a co-operation between Baosteel and Centro Sviluppo Materiali (CSM), a project has been started aimed at manufacturing X80 strain based designed pipes. As a starting point pilot trials have been carried out at Baosteel Research Center in order to produce different microstructures. Besides the steel chemical composition, the cooling process has the most significant influence on the formation of the microstructure: in order to assess the effect of the cooling process, the same rolling schedule was adopted for producing the different test materials, obtained varying the start cooling and finish cooling temperatures.

The microstructure and mechanical properties of the different test materials were assessed and the best microstructure for the plates for X80 pipes with enhanced strain capacity has been identified.
A Review on Composite Materials for Offshore Structures
Authors: Razavi Setvati Mahdi , Mustaffa Zahiraniza , Shafiq Nasir , Syed Zubair Imam
Published: September 2014

Research into advanced composite materials for offshore structures is growing due to factors such as new challenges in extreme environments, contaminated contexts (chemical, biological) and increasing awareness of earthquake risks. Advances in theory and practice of composites technology have modified the general perception of offshore structures. This paper provided an introduction to composite material and reviewed the application of composites in offshore structures. This survey focused on (1) composites, especially FRP, for repairing offshore structures and also (2) fire protection of composites in offshore structures. Various national and international research projects on uses of composites for marine structures either ongoing or completed during last decades summarized. Future environmental issues considered and eco-friendly sustainable composite suggested and forecasted for new generation of offshore structures.
Load Response and Finite Element Modelling of Bonded Loading Hoses
Authors: Lassen Tom , Lem Andreas Istad , Imingen Geir
Published: September 2014

Steel reinforced bonded vulcanized rubber loading hoses are frequently used in offshore oil loading systems. The hoses are used as offloading system between platforms and shuttle tankers and represent a flexible economical feasible solution for hydrocarbon transfer. The reliability of these hoses throughout the service life is an important issue both with respect to operational availability and with respect to environmental safety. Hence, the load bearing capacity of these hoses and the fatigue endurance become matters of concern and important design topics. Due to the large deformation of these hoses and the complicated composite structure in the hose wall, the hoses are difficult to analyze with respect to the strain and stress response when subjected to the various load cases.

The present paper presents extreme load capacity assessments and a fatigue life prediction methodology for bonded loading hoses subjected to high pressure, tension and bending in a catenary configuration and in repeated reeling under high hose tension. The load effects on the hose during the reeling operations and the fatigue life predictions methodology for both steel components and rubber are emphasized in the present work. A combination of advanced finite element modeling and full scale testing to corroborate the analyses results has been carried out to qualify the hoses to be fit for service and to fulfill the API17K requirements. The present paper presents results from advanced finite element models and full scale testing for a 20″ bonded hose with steel end fittings. The investigation brings new knowledge in the field of hose design methodology and the results are discussed in light of current requirements and regulations such as OCIMF and API 17K.

A consequence of the comprehensive testing and analysis work is that the requirement for testing in future projects is reduced, and calibrated analysis models can be used to predict hose capacities.
Wrinkling and Collapse of Girth-Welded Lined Pipe Under Bending
Authors: Yuan Lin , Kyriakides Stelios
Published: September 2014

Pipelines and flowlines that carry corrosive hydrocarbons are often protected by lining them internally with a thin layer of a corrosion resistant material. In the most economic method, the liner is brought in contact with a carbon steel carrier pipe by mechanical expansion. In applications involving severe plastic bending, such as reeling, such a liner can wrinkle and collapse while the carrier pipe remains intact. A numerical framework for establishing the extent to which lined pipe can be bent before liner collapse was presented in [1,2]. This framework, suitably extended is used here to examine the effect of girth welds on liner collapse. The modeling starts by simulating the expansion process that plastically deforms the two tubes bringing them into contact. Bending plastically the composite structure leads to differential ovalization of the two tubes and detachment of the liner. The girth weld locally prevents this detachment creating a periodic boundary effect in the liner. With increasing bending this local disturbance grows leading eventually to a diamond-shaped liner collapse mode. The problem is first investigated using a 12-inch carrier pipe base case followed by a parametric study of the factors that influence collapse.
Vortex-Induced Vibration of Steel Catenary Riser Under Vessel Motion
Authors: Wang Jungao , Fu Shixiao , Baarholm Rolf
Published: September 2014

A truncated steel catenary riser (SCR) model was experimentally tested in the ocean basin by oscillating the top end of the model to simulate the heave and surge vessel motion in order to investigate the vortex-induced vibration (VIV) features. Out-of-plane VIV responses were generally analyzed revealing that although the root mean square (RMS) strain distributed rather broadband, the displacement was quite consistent within a narrowband from 0.2D to 0.3D, and the touch-down point (TDP) area was found not to be the place suffering the maximum out-of-plane VIV response due to near wall effects. What’s more, strong wave propagations were firstly reported and summarized as a distinguished feature for VIV of a SCR under vessel motions, and further results reveal that wave propagation during the ‘lift up’ phase was quite different from that during ‘push down’ in terms of both wave speed and ‘power-in’ region location which is assumed to be caused by the tension variation along the model.
An Experimental Investigation on Cylinder VIV Trajectories Under Different Model Scale
Authors: Kang Zh. , Zhai Yunhe , Song Ruxin , Sun Liping
Published: September 2014

In this paper, model tests were carried out to investigate two degrees of freedom VIV of horizontally-laid cylinders with diameters of 5cm, 11cm, 20cm and length 120cm and compared their vibration trajectories. The test results showed that the in-line and cross-flow vibration frequency of different scale cylinders demonstrate “multi frequency” phenomenon, that is, the in-line vibration frequency is not only twice but also once or four times as much as the cross-flow vibration frequency in some scale, natural frequency and reduced velocity conditions. Also, the cross-flow multi-frequency vibration phenomenon occurred. The trajectory of the vibration cylinder differentiated from the traditional “8” shape accordingly. The vibration trajectory, especially of small-scale cylinder, changed in most conspicuous manner. Through the initial research and analysis, it was found that in addition to in-line and cross-flow natural vibration frequency and the flow velocity, the shape of cylinders was also one of the main causes leading to different vibration trajectory forms.
Increasing the Operation Window for Dynamic Positioned Vessels Using the Concept of Hybrid Control
Authors: Brodtkorb Astrid H. , Sørensen Asgeir J. , Teel Andrew R.
Published: September 2014

In order to extend the operational window of marine vessels, the high-level control of the dynamic positioning (DP) system is revised. Major contributions of this paper include the modeling of a hybrid controller for a DP vessel in a varying sea state using the hybrid dynamical systems framework proposed by [1], and establishing global asymptotic stability of the closed-loop hybrid system. Simulations in a sea state varying from calm to extreme are conducted with the hybrid controller, and a single controller with adaptive wave filtering for comparison. The single controller becomes unstable in extreme seas whereas the hybrid controller shows good performance. Switching is based on spectral analysis of the vessel wave frequency motions.
Integrity Assessment of Clad Pipe Girth Welds
Authors: Carlucci Antonio , Bonora Nicola , Ruggiero Andrew , Iannitti Gianluca , Testa Gabriel
Published: September 2014

Current design standards and codes do not provide specific guidance how to perform engineering criticality assessment with bi-metallic girth weld in lined or clad pipe. Recently, Bonora et al. (Proc. ASME 2013 32nd OMAE conf.) proposed the equivalent material method (EMM) which allows one still to use current design assessment routes. The method consists in considering instead of three materials in the weld joint, a single “equivalent” material with a flow curve defined as the interpolated lower bound of the three weld joint material flow curves. In this work, the applicability of the EMM was verified considering the effect associated with inner pressure loading and weld residual stresses. To this purpose, two flaw geometry configurations have been investigated. Particular relevance was given to the multi-pass weld process simulation. Numerical results indicate that the EMM always provides conservative results in terms of applied J with respect to those estimated considering the effective multi-materials configuration in the weld joint.
Northern Sea Route: Modern State and Challenges
Authors: Marchenko Nataliya
Published: September 2014

It is well-known that navigating the waterway from the primary trade hubs in northern Europe to the Asia-Pacific ports and contrariwise along the Russian Arctic Coast (Northern Sea Route - NSR) is much shorter and faster, than southern ways via Suez or around Africa. The NSR can significantly save costs (through saving time and fuel) and avoids the risk of attack by pirates. In addition, an increase in oil and gas activity in the North, forecasts of global warming and an ice-free Arctic have stimulated interest in Arctic navigation. However, Arctic transportation poses significant challenges because of the heavy ice conditions that exist during both the winter and summer. The profitability of using the NSR is called into question if possible high tariffs are included in the cost estimates.

For many years, the NSR was principally used for internal Russian transport and since the end of the 1980s up until 2010, it was in stagnation with total amount of cargo transported annually stood at less than two million tons. Important political decisions in the 90s and increased economic feasibility intensified traffic and freight turnover. In 2013, the NSR Administration (NSRA) was established, new rules for navigation were approved and tariff policies were modified. In 2013, the NSRA issued 635 permits to sail in NSR waters, and 71 transit voyages have since been completed. The total amount of transit cargo was 1.36 million tons. More than 40% of the total number of permits were issued to vessels without ice class [1] according to the Russian Maritime Register of Shipping [2]. There are strong technical requirements for vessels attempting to sail the NSR; regardless, several accidents occurred in 2012–2013. Two vessels were dented by ice in the Chukchi Sea in 2012. A tanker was holed in September 2013 and created a real danger of an ecological disaster from fuel leakage for several days. Despite the expectation of an ice-free Arctic, the ice conditions in 2013 were rather difficult, and the Vilkitsky Strait (a key strait in the NSR between the Kara and Laptev seas) was closed by ice for almost the entire navigation period.

In this paper, we review the current situation in the Russian Arctic, including political and administrative actions, recent accidents and the associated conditions and lessons learned.
Study on a Six-Axis Sensor for Measuring the Loading Force of Large-Scale Equipment in Fatigue Test
Authors: Lu Yun , Li Weijia , Zhou Kai , Wang Xiao , Wu Yaozhong
Published: September 2014

Aiming at solving the problem of measuring six-axis heavy load and improving measuring accuracy in fatigue test of large structure, this study presents a new type of six-axis force sensor based on the heavy load division principle. The sensor is made with piezoelectric quartz which is used as force sensitive element. This study proposes a type of four point support structure and the spatial mechanical model is deducted for the sensor. Finally, the static calibration experiment is carried out in this study. Experimental results show that the six-axis force of heavy load equipment can be measured with this type of sensor. The basic performance of the sensor shows that it can meet the engineering requirements well.
Measurements of Tidal Current Velocities in the Folda Fjord, Norway, With the Use of a Vessel Mounted ADCP
Authors: Carpman Nicole , Leijon Mats
Published: September 2014

Measurements of tidal current water velocities is an important first step in evaluating the potential for a tidal site to be used as a renewable energy resource. For this reason, on site measurements are performed at the inlet of a fjord situated at the coast of Norway. The site has an average width of 580 m and a depth of 10–15 m which is narrow and shallow enough to give rise to water velocities that can be of use for energy conversion. With the use of an Acoustic Doppler Current Profiler (ADCP) cross-section measurements are conducted along four transects. The measurements covered flood and ebb currents around one tide and the data give a first approximation of the magnitude and distribution of the flow field. Depth averaged mean current velocities are calculated along the transects for horizontal bins with sizes in the order of 50 × 50 m. Maximum mean velocity for the flood currents were 1.31 m/s and 1.46 m/s for the ebb currents. The measurements show that even a small amount of data can give an indication of the potential and characteristics of the site.
Model Test of a 1:8 Scale Floating Wind Turbine Offshore in the Gulf of Maine
Authors: Viselli Anthony M. , Goupee Andrew J. , Dagher Habib J.
Published: September 2014

A new floating wind turbine platform design called VolturnUS developed by the University of Maine uses innovations in materials, construction, and deployment technologies such as a concrete semi-submersible hull and a composite tower to reduce the costs of offshore wind. These novel characteristics require research and development prior to full-scale construction. This paper presents a unique offshore model testing effort aimed at de-risking full-scale commercial projects by providing properly scaled global motion data, allowing for implementation of full-scale structural materials, and demonstrating full-scale construction and deployment methods. The model is a 1:8-scale model of a 6MW semi-submersible floating wind turbine and was deployed offshore Castine, Maine, USA in June, 2013. The model uses a fully operational turbine and was the first grid connected offshore wind turbine in the Americas.

The testing effort includes careful treatment of the offshore test site, scaling methods, model design, and construction. A suitable test site was identified that provides the correct proportions of wind and wave loading in order to simulate design load cases prescribed by the American Bureau of Shipping Standard for Building and Classing Floating Offshore Wind Turbines.

Sample model test data is provided. Model test data is directly compared to full-scale design predictions made using coupled aeroelastic/ hydrodynamic software. VolturnUS performance data from scaled extreme sea states show excellent agreement with predictive models. Model test data are also compared to a numerical representation of the physical model for the purposes of numerical code validation. The numerical model results compare very favorably with data collected from the physical model.
Design of Novel Solution of Flexible Pipe for Offshore Oil Offloading Transfer
Authors: Do A. T. , Legeay S. , Charliac D. , Pere J. M. , Roques J. P. , Karnikian A.
Published: September 2014

Spread moored FPSO (Floating Production and Storage Offloading) vessels are generally used for the large West African oil fields. The oil is transferred from the FPSO to shuttle tankers via an Oil Loading Terminal (OLT). 2 to 3 large diameter flexible lines are connecting the FPSO to the OLT. The final connection between the OLT and the shuttle tanker is made by floating hoses.

The single length of each flexible pipe can be typically 2,300 meters or higher, and the internal diameter is generally very large in the order of 15_23″ to minimize the pressure drop and the offloading time.

Conventional flexible pipe is the most suitable solution for this application. However, its long length and large diameter require a large number of buoyancy modules which are necessary to support the substantial weight generated by the steel armor wires.

An alternative to steel is Carbon Fiber Composite (CFC). This material is not only twice as strong and five times lighter than a high strength steel but it is also characterized by its exceptional performance in fatigue. As the weight of the composite armor flexible pipe is significantly reduced, the use of buoyancy is no longer necessary. The pipe can also be manufactured in a single length without intermediate connection.

A qualification program based on a 19″ internal diameter prototype has been launched. This is the first time that a large internal prototype with Carbon Fiber Composite Armor (CFA) and end-fittings have been designed and manufactured. The main goals are to confirm the suitability of the CFA flexible pipe for oil offloading application in accordance with the design tools. The mechanical behavior responses of the CFA are monitored by strain gages when the flexible pipe is in straight and curved positions under internal pressure and bending cycles.

The paper will present the main mechanical properties and the overall performance of the flexible pipe designed and tested.

The economic viability will be demonstrated by showing how the CFC material cost is positively offset by the removal of the buoyancy modules and a faster offshore installation.
Analysis of the Geometric Tunability of a WEC From a Worldwide Perspective
Authors: de Andrés Adrián D. , Guanche Raúl , Vidal César , Losada Íñigo J.
Published: September 2014

Nowadays the goal of WEC developers is to reduce the price of the harvested energy for its own technology, via either decreasing the cost of WECs or increasing the power production. In order to increase the power production of a particular WEC, usually the WECs are tuned with the wave climate at the target location. However, in order to achieve the maximum profitability, the WECs must be able to be deployed in a bunch of locations with different wave climates. Therefore WECs must be flexible to be adapted to different kind of locations.

The matchability of a device could be achieved via the PTO control or changing the geometric characteristics of a particular device. In this study, an analysis about how the geometric tuning of a generic wave energy converter affects to different climate scenarios is performed.

Firstly, a generic wave energy converter is assumed to be formed by an array of floating cylinders that absorb in heave. Three options are proposed in the present study, a cylinder with its natural period on 4 s, typical of enclosed seas, another option with a natural period of 8 s (mean Atlantic swell) and an option that is tunable as a function of the location in order to evaluate the influence of tuning on the power performance.

The power matrix is computed with a frequency domain model and then, the converters are evaluated worldwide, taking the met-ocean data from a global reanalysis database (GOW) from Reguero et al (2012). The results are presented in terms of two main indicators, on one hand, the capture width ratio, that evaluates the efficiency of the converter on each location, and the kW/Ton parameter that evaluates the efficiency of the converter on “economic” terms.

Finally, tuning a converter for each location of deployment resulted positive in terms of capture width ratio, however regarding the kW/Ton indicator tuning resulted useless due to the heaviness of the structures needed to tune the converter with high peak periods. The number of suitable locations (in terms of an acceptable kW/Ton indicator) was higher as the mass of the structure is reduced, regardless of the natural period of the converter, thanks to a good performance of high natural periods converters.
Ageing Accidents: Suggestion for a Definition and Examples From Damaged Platforms
Authors: Ersdal Gerhard , Sharp John , Galbraith David
Published: September 2014

An increasing number of offshore installations are in the life extension stage of life, resulting in a growing concern among structural engineers about ageing related issues. However, structural engineers are often asked if there is experience of any ageing accidents or if there are examples of such. A safety conscious person would then reply that theory points towards a growing failure rate and hence that ageing accidents will eventually occur. Good engineering practice would then imply that there is no point in waiting for the accident to occur. As responsible engineers we should investigate the hazards and avoid accidents without having to wait for a potentially fatal accident to lead to action. The other possible answer is to question the term “ageing accident”. What is the definition of an “ageing accident”? This paper will investigate into the term “ageing accident” and will propose a definition of this term. Further, this paper will describe some examples of ageing accidents, in particular the many structural failures that have occurred in the Gulf of Mexico hurricanes.
The Design Limitations of a Circular Wave Pool
Authors: Schmied Steven A. , Binns Jonathan R. , Renilson Martin R. , Thomas Giles A. , Macfarlane Gregor J. , Huijsmans Rene
Published: September 2014

In this paper, the design of a circular wave pool that produces continuously breaking waves is discussed, whereby a pressure source is rotated within an annular wave pool. The concept was that the pressure source generates non-breaking waves that propagate inward to the inner ring of the annulus, where a sloping bathymetry (beach) triggers wave breaking. In order to refine the technique, research was conducted to better understand the mechanics of waves generated by moving pressure sources in a constrained waterway, the transformation of these waves as they travel across the channel and the effect of the sloping beach on the wave quality for surfing.

The quality of the waves was defined in terms of wave height, speed and shape, with the aim to create plunging waves, known as “barrels”, that are highly desired by surfers.

A predominantly experimental approach was undertaken to determine the required design parameter values and their limitations. Scale model experimental results were previously presented at OMAE 2011 and OMAE2013.

This paper presents the steps to design the pool using the empirical analysis and experimental results are presented. The effect of the pressure source and pool bathymetry on the currents formed in the pool, are also presented. Through this design process, high quality continuous breaking waves with the desired plunging shape were able to be generated.

Finally, the authors are planning to use the facilities and techniques developed to investigate the complexities of predefined wave fields, including the three dimensional (3D) details of the velocity, pressure and turbulence fields beneath. Understanding these complexities within multidimensional wave patterns is the key to analysing a number of different fields, including wave resistance of ships; wave disturbances to other maritime users; bank erosion; wave signal tracking; and wave structure interaction.
Lessons Learned From Auditing Structural Integrity Management
Authors: Ersdal Gerhard , Galbraith David , Sharp John
Published: September 2014

As part of its regulatory duties the Norwegian Petroleum Safety Authority (PSA) periodically undertakes audits of the Structural Integrity Management (SIM) functions of the operators of facilities within the Norwegian offshore jurisdiction; typically one or two audits of reasonable detail are undertaken each year, but in addition PSA have also tried a series of mini-audits based purely on interviews without examination of evidence.

In many cases certain aspects of the SIM cause the auditors some concern and there is a degree of consistency about those aspects of SIM causing such concern, and on occasion become formal “findings” of the audits. In general the actual execution of SIM activities are performed adequately, but the full understanding of the purpose of SIM and realistic intent and expectation are missing. A particular concern of the auditors is the anticipation of structural form-specific accidental and abnormal events and their incorporation into the SIM.

This paper will provide a summary of the more important lessons learnt over several years of auditing, in an attempt to provide industry with a better understanding of the regulator’s expectations of SIM, particularly for installations that are ageing or have unique features.
Use of FMECA Method for Leakage Analysis of LNG Fueled Vessels
Authors: Fu Shanshan , Yan Xinping , Zhang Di , Shi Jing , Wan Chengpeng , Song Zhanbing
Published: September 2014

Liquefied natural gas (LNG), a cleaner energy resource compared to heavy fuel oil (HFO), has been utilized as an energy source by vessels of various types, e.g., ferries, cargo vessels and platform supply vessels (PSV), notably after the release of International Maritime Organization (IMO) interim guideline MSC. 285(86) which officially authorized the natural gas as a marine fuel for merchant vessels in June 2009. LNG fuel is expected to have a promising prospect in green shipping industry with advantages in decreasing the emissions of NOX, SOX, and particulate material. However, as an inflammable and explosive energy source, safety issues of LNG should also be taken into account, especially under the circumstances of fuel leakage during a long voyage. In this paper, failure mode, effects and criticality analysis (FMECA) is conducted for the study on leakage failure modes of LNG fueled vessels. The criticalities of LNG leakage modes are calculated and ranked by taking failure rate, causes and effects (consequence probability and associated severity) of each failure mode into consideration. Event tree analysis (ETA) approach is utilized to identify possible failure consequences and estimate associated probabilities of occurrence, while computational fluid dynamics (CFD) modeling and simulation are applied for the consequence analysis of each failure mode. A typical Chinese LNG powered cargo ship in the Yangtze River is studied for critical leakage modes identification and risk control options (RCOs) provision so as to provide recommendations on the daily operations and safety managements of LNG fueled vessels.
Optimization of MEG Injection and Regeneration System for Offshore Gas Fields Using Multiphase Simulation and Synergistic Inhibition Strategies
Authors: Seo Yutaek , Kim Jakyung , Shin Kyuchul , Chae Heemoon , Ko Minsu
Published: September 2014

Industry has been relying on the injection of considerable amount of Mono Ethylene Glycol (MEG) for hydrate inhibition in petroleum production systems, especially in offshore gas wells. However current design of MEG injection and regeneration systems is used to be over-sized as it consider the worst operation conditions such as shut-in pressure, ambient seawater temperature, and maximum water production rate. Recently, multiphase simulation tools have been widely used to estimate the temperature and pressure profiles of offshore flowlines for both steady-state and transient operations, which would be useful to better estimate the worst operation conditions of offshore flowlines. Moreover, recent research [1] results on synergistic inhibition suggest that MEG injection rate might be reduced below the required concentration by adding small amount of Kinetic Hydrate Inhibitors (KHI). Here we carried out an experiment to validate the effect of using synergistic inhibition with MEG and KHI on the design of MEG injection and regeneration systems for offshore gas wells. The studied concentration range of MEG is up to 30 wt% and PVCap concentration is between 0.1 and 1.0 wt%. Synthetic natural gas composed of C1 90 mol%, C2 6 mol%, C3 3 mol%, and nC4 1 mol% is used for all experiments. High pressure autoclave system mounted with overhead stirrer is used with constant cooling method. Furthermore, multiphase simulation tool, OLGA, is used to simulate the operation conditions of offshore gas fields. The amount of condensed water and temperature-pressure profiles during extended shut-in period are calculated for 10 km offshore flowlines. The obtained results suggest that the injection rate of MEG can be reduced about 50% by adopting synergistic inhibition and multiphase flow simulation, which would reduce the CAPEX and OPEX for MEG. Moreover the reduced size of MEG regeneration unit would improve weight and space management on platform topside.
Analysis of the Loads on and Dynamic Response of a Floating Flexible Tube in Waves and Currents
Authors: Genzman Grant N. , Fredriksson David W. , Schultz Michael P. , Trent Jonathan D.
Published: September 2014

Recently proposed offshore structure designs for wastewater treatment and algae biomass production may incorporate floating flexible tubes. In one configuration, the tubes float at the surface and contain a fluid and algae mixture. The purpose of this study is to analyze the loads on and dynamic response of such tubes in varying environmental conditions, specifically waves and currents.

The approach includes both physical and numerical modeling techniques. Physical models at a scale of 1:4.21 (model to prototype) and two fill levels (50% and 95%) were tested in wave and towing tank facilities in the Hydromechanics Laboratory at the United States Naval Academy. The models were towed at a range of scaled speeds to represent currents and subjected to scaled wave conditions in one of the tanks. During these tests, attachment loads were measured and dynamic response was evaluated.

In addition to the physical modeling approach, Computational Fluid Dynamics (CFD) simulations were performed to assess steady drag measurements at the 1:4.21 scale and the results were compared to the experimental tests. The CFD modeling results were comparable to those obtained from the physical modeling tests, at least at the higher fill levels that were analyzed.

The results indicated that the model response tended to follow the wave forcing more at the middle wave frequencies. For both fill levels, the response of the forward end of model increased with wave frequency while the response of the rear end of the model remained rather consistent across the frequencies tested. The results did not indicate a significant difference in dynamic response when the model was tested in both waves and current. The average attachment loads, however, were higher when the model was tested in waves and a current than in waves only. The attachment loads were also higher in wave and current conditions that included a faster current or lower-frequency (larger) waves.

The intent of the project, through both modeling methods, was to increase the understanding of the loads on and the response of a floating tube in waves and currents. Future work could include an increase number of replicates for better accuracy, additional test frequencies and tow speeds, alternate attachment techniques, and testing at larger scales for comparison.
Experimental Verification of HFMI Treatment of Large Structures
Authors: Yildirim Halid Can , Marquis Gary B. , Haagensen Per J.
Published: September 2014

Design recommendations for high frequency mechanical impact (HFMI)-treated welds have been proposed based on available experimental fatigue data of axially-loaded high strength steel specimens which include longitudinal, cruciform and butt welds. Test specimens were of a size appropriate for laboratory study. However, in reality, structures in civil, offshore and ship industries generally include large-scale and more complicated components, such as bridges, cranes, platforms, excavators etc. This paper presents a further validation of the design proposals by considering fatigue data sets which are obtained from large-scale components. The extracted fatigue data from the available literature includes bridge, crane and beam like components. In total, 65 published test results of weld details with various yield strengths (250 ≤ fy ≤ 725 MPa) and stress ratios (−1 ≤ R ≤ 0.56) are presented. All the data are found to be in good agreement with the previously-shown design curves.
Mechanical Properties of Newly Developed API X80 Grade HFW Linepipe for Long-Term Exposure at Elevated Temperature
Authors: Toyoda Shunsuke , Goto Sota , Okabe Takatoshi , Kato Yasushi , Igi Satoshi , Inoue Tomohiro , Egi Motoharu
Published: September 2014

API X80 grade UOE double submerged arc-welded pipe has been applied to steam injection oil sand recovery systems to increase the volume of steam to be injected and decrease the installation cost. The pipes for the systems are subjected to high temperature for a long period, such as 350 °C for 20 years. Therefore, it is important to ensure the reliability of the pipes during and after long-term operation. In this study, based on the recent development of high-frequency electric-resistance-welded (HFW) linepipe with a high-quality weld seam, the durability of newly developed API X80 grade HFW linepipe for long-term high-temperature operation was investigated. The change in the microstructure of the pipe body and weld seam was small after exposure to 400 °C and lower temperatures. The tensile strength of the base metal and weld seam after heat treatment with temperatures as high as 400 °C can be determined using the Larson-Miller parameter, which depends on the temperature and holding time of the heat treatment. The newly developed API X80 grade HFW linepipe was considered to have sufficient tensile strength during and after long-term operation at 350 °C for 20 years, similar to API X80 grade UOE pipe. No significant change in the Charpy absorbed energy during long-term heating was observed. Creep tests indicated that the time to rupture at 400 °C or lower exceeded 106 hours, and the creep effect was considered almost negligible at temperatures less than 400 °C. The rupture stress at approximately 350 °C was estimated to be far higher than the typical hoop stress of approximately 200 MPa on the steam distribution system. High-temperature fatigue properties were also measured to ensure reliability under varying stress conditions.
Failure Prediction of Low-Temperature High-Strength Steel on Average Stress Triaxiality Using Abaqus User-Subroutine
Authors: Choung Joonmo , Yoon Sung-Won , Park Sung-Ju , Nam Woongshik
Published: September 2014

This study deals with failure strain prediction according to stress triaxiality of a typical polar class steel EH36. Choung et al. [1, 2] have formulated failure strain curve of EH36 steel by carrying out a number of tensile tests for round and flat specimens with various notches. Extra tests for notched flat specimens which machined in transverse direction are conducted to formulate the failure strain curve. In order to verify the validity of failure strain curve, we develop user-subroutine (VUSDFLD) of a commercial finite element code, Abaqus/Explicit. Fracture simulation with user-subroutine shows that two results are closely coincident by comparison of force-elongation curves.
Experimental Data on the Systematic Variation of the Internal Damping Inside a U-Shaped Anti-Roll Tank
Authors: Gunsing Michiel , Carette Nicolas , Kapsenberg Geert
Published: September 2014

Anti-Roll Tanks (ARTs) can be a successful device to reduce ship roll motion (Figure 1), but the tank has to be properly designed. A good design includes an appropriate number of damping devices in the tank to reduce the water motions at resonance and to increase the frequency range over which the tank works efficiently. It is difficult to accurately predict the effect of different damping devices on the roll damping moment of the tank; usually tests on a rotating table, so called bench tests, are performed for each individual design.

Nowadays, CFD (see e.g. [1]) calculations solving the URANS equations can predict the effect of damping devices on the roll motion of the tank. In order to validate such codes a series of experiments with a U-type ART on a rotating table have been carried out where the interior arrangement in the duct of the tank has been varied. The set-up of the experiment, the measurement system and the results of the experiments are presented and discussed in this publication; the raw data of the experiments are also made available.