bluuebunny/crossref_metadata_2025 huggingface dataset:
Technical Solutions of the Active Ice Protection of Offshore Structures for the Russian Arctic
Authors: Sabodash Olga A. , Tarasov Valerii V.
Published: October 2016

The device for active protection against ice loads using pneumatic soft shells (PSS) on offshore production platforms has been studied. For technical modeling of devices the Solid Works CAD system was applied. The calculation results of model of the main components of the device by contact with the ice field in the Sea of Okhotsk ice conditions have been obtained. Finally, recommendations on the future effective application of the structures ice protective equipment have been worked out.
Comparison of Bitumen’s Large Strain Viscoelastic Properties in Cables and Umbilicals to Small Strain Rheometer Measurements
Authors: Konradsen Bjørn
Published: October 2016

When a steel wire armored cable or umbilical is bent, the armor wires will move relative to the underneath layer if the wires are free to move. If this movement is restricted by friction or stiff bitumen, the bending will result in shear stress in the armor wires. In the case of bitumen, the bitumen will behave as a viscoelastic material dependent on temperature, frequency, and strain. Comparison of measurements of bitumen with small and large strain shows that the viscoelastic properties of bitumen are highly affected by the size of the strain. Therefore, the small strain rheometer measurements are not suitable for describing the viscoelastic properties of bitumen in the case of repeated bending of the cable or umbilical to a certain curvature.
A Novel Fatigue Stress Model of Power Phases and Coated Tubes in Deep-Water Power Cables, Umbilicals, and Power Umbilicals
Authors: Komperød Magnus
Published: October 2016

Short fatigue life is a significant challenge for power cables, umbilicals, and power umbilicals to be installed in ultra-deep and hyper-deep waters. This paper presents a novel model for calculating fatigue stresses in conductors of power phases and in tubes with coating. The novelty is that the axial displacement of the conductor within the electric insulation system, or the tube within the sheath, is taken into consideration. For a real-life power cable designed for 2 300 m water depth, the novel model gives a reduction in fatigue stress of 69% compared to the traditional resultant-based approach for oscillations smaller than the slip curvature. This corresponds to a reduction in fatigue damage of more than 99%.
On the Optimum Sizing of a Real WEC From a Techno-Economic Perspective
Authors: de Andres Adrian , Maillet Jéromine , Hals Todalshaug Jørgen , Möller Patrik , Jeffrey Henry
Published: October 2016

When designing “multi-MW arrays” of Wave Energy Converters (WECs), having a low number of converters with high individual power ratings can be beneficial as the Operation and Maintenance (O&M) costs may be reduced. However, having converters of small dimensions or small power ratings could also be beneficial as suggested by previous works due to a reduction in material costs as compared to power production, the use of small, inexpensive vessels.

In this work, a case study investigating the optimum size of WEC for a 20MW array is performed. Analysis is carried out based on the CorPower Ocean technology. In this case study, firstly a Levelized Cost of Energy (LCOE) model is created. This model incorporates the latest Capital Expenditure (CAPEX) estimates for CorPower Ocean’s 250 kW prototype. Using this techno-economic model, several sizes/ratings of WEC are tested for use in a 20 MW array.

Operational Expenditure (OPEX) is calculated using two different calculation approaches in order to check its influence on final indicators. OPEX is firstly calculated as a percentage of CAPEX, previous works, and secondly using a failure-repair model, taking into account individual failures of WECs in the array. Size/rating analysis is carried out for several European locations in order to establish any dependence between site location and optimal WEC size/rating.
Residual Torsional Strength of Cracked Stiffened Girders With a Large Deck Opening
Authors: Ao Lei , Wang Deyu
Published: October 2016

This paper studies the residual torsional strength of stiffened girders with large deck openings by using the software ABAQUS. The influence of cracks is considered. Potential parameters which may have effects on the torsional strength including the mesh refinement, initial deflection, geometric properties of crack are discussed. Two new concepts that play significant roles in the ultimate strength research of damaged box girders are introduced, one of which is the effective residual section (ERS), the other is the initial damage of the failure zone (IDFZ) for intact structures. New simple formulas for predicting the residual ultimate torsional strength of cracked stiffened girders are derived on the basis of the two new concepts. The formulas are verified to be reasonable which can be used as an reference.
A Numerical Study on the Load-Bearing Armored Cable Performance of an 11,000m ARV for the First Phase Sea Trial
Authors: Jiang Zhe , Hu Yong , Cui Weicheng , Zhang Tianyu , Liu Xiaoyan
Published: October 2016

To better study the biology and ecology of hadal trenches for the marine scientists, the hadal science and technology center (HAST) of Shanghai Ocean University has made a significant commitment to develop operational support for the promotion of hadal science. The first focus of HAST is to construct a movable laboratory for hadal trenches which includes a mothership, an full ocean depth (FOD) Human Occupied Vehicle (HOV), an FOD Autonomous and Remotely-operated Vehicle (ARV) and several FOD landers. All of them are named as Rainbowfish series.

Presently, the construction of the ARV has been finished and the first phase sea trial has been conducted in South China Sea from September 26th to October 25th 2015. In the sea trial, the ARV was laid down to certain water depth and recovered back to water surface through a load-bearing armored cable. The reliability of the cable is critical to the safety of the ARV, as if the cable was broken, the ARV could hardly be retrieved. In such circumstances, this paper focuses on two important issues, i.e. the tensions of the cable and the ARV offset using numerical methods. Due to the change of the mothership in the final phase before the sea trial, the cable analyses with two different types of supporting vessels (a catamaran and a barge) were performed respectively and a comparison was made. In addition, a sensitivity study of submergence depths and winch hook positions was also conducted. Finally, the first phase sea trial of the ARV was described and discussed.
A Simplified Method of Water Impact on Elastic Plate in Early Stage
Authors: Sun Hua , Wang Deyu
Published: October 2016

For most flat-bottom marine structures, the impact loads are generated by complex transient coupling effects of solid, air and water. However, there are rare simplified forecasting methods to obtain the impact loads and dynamic response of the flat-bottom structures by considering both hydro elastic and air cushion effects. In the paper, a new simplified analysis method of water impact on the elastic plate is proposed referred to Verhagen’s model of the rigid plate. The analysis is focused on the initial stage during which the highest hydrodynamic loads are generated. The method simulates the interaction between the plate, the air and the water. Also, fluid-structure coupling results from the simplified method are compared to numerical results from Arbitrary Lagrangian–Eulerian method and experimental results to validate the feasibility and accuracy of this simplified method.
Contribution of Axial Soil Resistance in Buckle Initiation of the HPHT Pipelines on Sleepers
Authors: Vosooghi Navid , Ivanovic Ana , Sriramula Srinivas
Published: October 2016

The objective of this paper is to assess the impact of soil axial resistance on initiation of the buckles on sleepers. It also covers the effects of history of pressure and temperature increase on effective axial force as well as the incorporation of external pressure in the Finite Element (FE) models. This is carried out for 6″, 8″, 10″ and 12″ pipelines laying on sleepers with different heights for a range of axial soil frictions and mobilisations. Knowing the sensitivity of buckle initiation to soil parameters can help in simplifying engineering analysis by avoiding repetitive simulations for parameters with less importance.

To carry out the above, a series of FE models including normal and bi-linear axial contacts between pipeline and sleeper / seabed were built in Abaqus FE package and at the point of initiation of the buckles, the effective axial force was extracted by a Python script. FE models were validated by comparison of the simulation results with analytical solutions and experimental results from published literature.
Hydrodynamic Coefficients of Hexagonal Heave Plates for Floating Offshore Wind Turbine Platforms
Authors: Moreno Javier , Thiagarajan Krish P. , Cameron Matthew
Published: October 2016

Experiments were conducted on a 1:80 scaled column of the WindFloat semi-submersible floating offshore wind turbine platform. The structure was forced to oscillate at frequencies of up to 6 Hz and at various amplitudes to create a parameter space much larger than previously reported. The hydrodynamic coefficients of the column with a hexagonal heave plate were compared to the base case of a column with a circular heave plate. Results show remarkably similar behavior between the two cases over the range of parameters tested, but quite distinct from published data on square plates. At low Keulegan-Carpenter number, the hexagonal plate showed a slightly higher added mass, but the difference narrowed down with increasing KC. An opposite trend was noticed for the damping coefficients. Overall the maximum difference in damping was about 8%. The paper presents some of the challenges in experimenting over a large parameter range, and also analyzes the trends in data over the range. It is expected that the presented data will be of use with engineers attempting to use heave plates for stabilizing wind turbine platforms in range of wave and wind conditions to maximize wind energy generation efficiency.
Development and Verification of Measurement Equipment for Residual Gas Content of a Coal Sample
Authors: Seo Hyeongjun , Kwon Sunil , Lee Seungrok
Published: October 2016

This paper presents the development of measurement equipment for residual gas content consisting of a cylindrical canister, a grooved rod, and a crusher, as well as a test for verifying its efficiency and crushing ratio. The equipment was designed by considering factors such as crushing mode, material type and size, sealing, empty volume inside the canister, and portability to site. Particularly by designing a rod having grooves, unlike existing rod mills, the initial crushing time was shortened. Test results showed that an average of 83 min was consumed to achieve a 96% crushing ratio, which proved the developed equipment had excellent performance for use at coalbed methane sites.
Improvement of Rankine Panel Method for Seakeeping Prediction of a Ship in Low Frequency Region
Authors: Yasuda Eiji , Iwashita Hidetsugu , Kashiwagi Masashi
Published: October 2016

Rankine panel methods have been studied for solving 3D seakeeping problems of a ship with forward speed and oscillatory motions. Nevertheless, there is a drawback in the numerical method for satisfying the radiation condition of outgoing waves at low frequencies, because the waves generated ahead of a ship reflect from the outward computational boundary and smear the flow around the ship. The so-called panel shift technique has been adopted in the frequency-domain Rankine panel method, which is effective when the generated waves propagate downstream of a ship. In this paper, in addition to this conventional panel shift method, Rayleigh’s artificial friction is introduced in the free-surface boundary condition to suppress longer wave components in a computational region apart from the ship. With this practical new method, it is shown that there is no prominent wave reflection from the side and/or upstream computational boundaries even in the range of low frequencies. As a consequence, the unsteady pressure, hydrodynamic forces, wave-induced ship motions, added resistance are computed with reasonable accuracy even in following waves and in good agreement with measured results in the experiment using a bulk carrier model which is also conducted for the present study.
Prediction of Welding Deformation and Residual Stress in a Multiply-Stiffened Plate
Authors: Guo Min , Chen Zhen , Luo Yu
Published: October 2016

In this paper, welding induced deformation and residual stress of a multiply-stiffened plate is studied by means of sequentially coupled thermal elasto-plastic finite element method. For the purpose of enhancing calculation efficiency, the FE model combining shell and solid elements is employed in the analysis. A transient moving heat source is used in the numerical analysis to consider important welding parameters such as heat input, welding speed and welding sequences. The welding processes of three stiffeners being attached to a base plate by single-side welds are simulated according to assembly configurations. The influence of three welding sequences and the position of weld foot on distortions and residual stress are discussed. The results demonstrate the different characteristics of residual distortion and stress in the multiply-stiffened plate by different welding sequences. The position of weld foot affects the local distortion of panel between two adjacent stiffeners.
Image Based Method to Estimate Regular Wave Parameters
Authors: Lavieri Rodrigo S. , Tannuri Eduardo A.
Published: October 2016

Image based methods, particularly those applying stereoscopic approaches, have difficulty in measuring waves produced in laboratory facilities, mainly because, in such conditions, the water surface is smooth, translucent and highly specular. The present study introduces a method to estimate regular wave parameters (particularly the amplitude) that is capable of dealing with such characteristics of the surface. The method is based on image intensity and its relationship with the surface normal. Although the concepts behind the method are well known since the 1960 decade, we present a novel framework of algorithms and experimental setup which produces promising results even using cheap cameras and under regular laboratory illumination conditions. The specific set of results reported herein was obtained by a single camera; however, multiple cameras can be used both to improve the quality of calibration parameters and to reduce the overall estimation errors. To conclude, we present conjectures regarding the expansion of the method to measure irregular waves and to deal with more unrestricted illumination conditions.
Analysis of the Motion Response of Trimaran Based on Directional Spectrum
Authors: Sun Shuzheng , Sun Hui , Li Jide , Liu Xiyang , Du Wenlei
Published: October 2016

The seakeeping performance of trimaran is crucial to its design and development. A series of trimaran model tests for seakeeping performance are conducted in towing tank. Directional spectrum theory and long-crested wave theory are introduced to the spectrum analysis method so as to analyze the motion response of trimaran. The comparison of the results gaining from two theories and those achieving from the long-crested irregular wave tests is carried out. By statistical analysis, there is a big difference between the motion responses of trimaran according to different wave theories in several operating conditions. The characteristics of trimaran motion responses under different course angles are studied. Compared with long-crested wave theory, directional spectrum theory is introduced as a more accurate approach to research the seakeeping performance of trimaran.
The Improved Method of Risk Assessment for Falling Objects From the Crane of FPSO
Authors: Yu Bin , Sun Liping , Li Siqi , Zhang Xu
Published: October 2016

It is very frequent for a crane to lift cargoes on the marine structure. The accident of falling objects often occurs and causes great damages to the marine structure. In this paper, the improved risk assessment of FPSO’s structural damage caused by falling objects is carried out. ANSYS/LS-DYNA is used to simulate the impact on the deck structure of FPSO and submarine pipelines respectively for several times. To gain the relationship between the maximum impact force and parameters of falling objects, it is necessary to fit the data obtained by simulation, so as to construct the failure function in Monte Carlo sampling during the subsequent work. Based on the method of DNV’s recommendation, the calculation method of collision probability about submarine pipelines will be improved. According to probability statistics, failure probability theory and energy method, the Matlab GUI program can be compilied to simplify calculation. Through the input data, the failure probability of the different segments of the pipeline can be obtained, then comparing the failure probability with the acceptance criteria. If the calculated failure probability does not meet the DNV’s acceptance criteria, we should find out the larger risk and give it some protective measures. This process provides a scientific basis for reducing the damage of the marine structure and how to take reasonable protective measures.
Uncertainties of Crack Propagation Analysis in Ship Structures
Authors: Mao Wengang , Yue Jingxia , Wu Da , De Gracia Luis , Osawa Naoki
Published: October 2016

Fatigue cracks can be observed quite frequently on today’s ocean crossing vessels. To ensure the safety of ship structures sailing in the sea, it is important to know the residual fatigue life of these damaged ship structures. In this case, the fracture mechanics theory is often employed to estimate how fast these cracks can propagate along ship structures. However, large uncertainties are always associated with the crack prediction and residual fatigue life analysis. In this study, two uncertainties sources will be investigated, i.e. the reliability of encountered wave environments connected with shipload determinations and different fracture estimation methods for crack propagation analysis. Firstly, different available codes based on fracture mechanic theory are used to compute the stress intensity factor related parameters for crack propagation analysis. The analysis is carried out for both 2D and 3D cases of some typical ship structural details. The comparison is presented to illustrate the uncertainties of crack propagation analysis related with different codes. Furthermore, it is assumed that the structural details will undertake dynamic loading from a containership operated in the North Atlantic. A statistical wave model is used to generate wave environments along recorded ship routes for different years. The uncertainties of crack growth analysis related with encountered weather environments is also investigated in the study. The comparison of these two uncertainties indicated the requirement of further development for the fracture mechanics theory and associated numerical codes, as well as the reliable life-cycle encountered weather environments.
Evaluation of CTOD Resistance Curve Test Methods Using SENT Specimens
Authors: Zhu Xian-Kui , Zelenak Paul , McGaughy Tom
Published: October 2016

Single edge-notched tension (SENT) specimens in clamped end conditions are widely adopted in the oil/gas industry to measure fracture resistance curves in terms of the J-integral or crack-tip opening displacement (CTOD) for the strain-based design and crack assessment of onshore and offshore pipelines. Typical CTOD-R curve test methods developed for SENT specimens include CanMet, ExxonMobil, and BS 8571 methods. While CanMet determines CTOD using the J-integral conversion method via one clip gage measurement, the other two infer CTOD directly from double clip gage measurements. ExxonMobil simply uses the total measured displacements to calculate CTOD, but BS 8571 separates CTOD into elastic and plastic parts to be determined, respectively, from the elastic K factor and the plastic component of measured displacements. It is unknown if these CTOD test methods determine comparable R-curves for a same SENT test, and what are the differences between these CTOD test methods.

To answer those questions, this paper performs an experimental evaluation of the SENT CTOD test methods. A set of clamped SENT specimens are tested for pipeline steel X80 and structural steel A36. For each SENT test, the unloading compliance method and the double clip gage arrangement are used, and then CTOD-R curves obtained by different methods are evaluated. Evaluation results and conclusions are given for those SENT CTOD test methods.
Subsea Pipeline UHB Design: An Improved Analysis Approach
Authors: Liu M. , Cross C.
Published: October 2016

A subsea pipeline operating at temperature and pressure may buckle both vertically and laterally. For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analysing post pipelay OOS survey data incorporating appropriate safety factors based on a structural reliability analysis. The normal approach is to examine the pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation is typically performed a priori based on the assumed imperfections using the methodology outlined in ref [1]. The additional rockdump schedule is derived from the crown of the pipeline imperfections regardless of adjacent profiles and overall backfill data.

A new pseudo energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis.

The approach takes into account the effects of varying effective axial force, trench imperfections and vertical uplift resistance, by combining both axial friction and lateral resistance methods into a unified model. A new concept, effective uplift resistance and associated load is also introduced to deal with non-uniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. An FE model is developed to consist of 3-noded quadratic pipe elements using ABAQUS Ver 6.12 and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.
Asset Integrity Assessment and Management Program for Life Preservation of a Purpose Built FPSO and Associated Subsea System Facilities
Authors: Nezamian Abe , Nicolson Robert J.
Published: October 2016

Floating facilities for production, storage and offtake (FPSO) and other offshore production facilities have been used safely and reliably throughout the oil industry for many years. Asset Integrity is increasingly important to optimising safety and operational life and asset performance efficiency. Operators need to comply with Corporate, Regulatory and Certification requirements but recognise that developing and managing an effective and compliant Asset Integrity Management System is both time consuming and costly.

Review of operational history of existing large FPSOs around the world indicated low confidence in operational life expectancy and to achieve the design life without possible dry docking or major repair. FPSOs have certain loading characteristics and damage consequences that make them different to other offshore installations and conventional ships, and often more challenging to maintain and operate. Maintenance and inspection campaigns are important inputs in the Asset Integrity Management (AIM) system of FPSOs and other floating offshore facilities. Considering that the unit shall stay on site during the whole life of the field, where disconnection or the removal of the mooring system is not planned, a comprehensive methodology for the asset integrity management, survey, inspection, testing, maintenance and repair of the unit during this period needs to be developed and subject to review based on the results of the scheduled inspections and audits. So as well as class and statutory requirements, inspection and survey, maintenance and repair plans should reflect the required availability, functionality, survivability and durability of the unit, giving due regard to its field life, as part of the safety management of the facility. Risk Based Integrity management methodology has been adopted in several projects and is an important tool to establish a rational inspection campaign for structural components, mainly for those located in areas where access is critical and operational constraints are an important parameter. This paper gives an overview of the challenges and discusses various aspects of ageing related to FPSO facilities, represented risk to the integrity of a facility and the required procedures and reassessment criteria for maintaining the structural integrity. This paper also provides an overall view on the regulatory requirements, documentation and calibrations/validations of the original design values to maintain the safety level by means of a maintenance and inspection programs balancing the ageing mechanisms and improving the reliability of assessment results. A brief summary of an example project of an asset integrity assessment and management program for life preservation of a purpose built FPSO and associated subsea system facilities is presented.
Computational Fluid Dynamics Study of a Flexible Flapping Hydrofoil Propulsor
Authors: Vijayakumaran Harikrishnan , Krishnankutty Parameswaran
Published: October 2016

A CFD study to understand the hydrodynamics and fluid flow around a chordwise flexible hydrofoil with combined sway and yaw motion which imitates the caudal fin flapping in thunniforms, is presented. The dependency of motion parameters of the flexible flapping hydrofoil to its propulsive performance is studied by carrying out the analyses over a Strouhal number range of 0.1 to 0.4 in steps of 0.025 at three maximum angle of attacks viz. 10°,15°,20°. Qualitative observations of the wake field and trailing jet is presented using velocity magnitude contours and vorticity contours. The analyses carried out at 40,000 Reynolds number and sway amplitude of 0.75 chordlength, revealed that the average thrust coefficient increases with increase in Strouhal number and maximum angle of attacks. The highest efficiency is achieved when the maximum angle of attack is 15° and Strouhal number is 0.225.
Fuel Optimized Thrust Allocation Algorithm Development Using Penalty-Method for the Dynamic Positioning FPSO
Authors: Kim S. W. , Kim Joseph Moo-Hyun , Choi J. W. , You Y. J.
Published: October 2016

In this paper, a thrust allocation algorithm is proposed to minimize the fuel consumption and the gas emission of the offshore platform dynamic positioning system. The thrust allocation algorithm generates thruster commands that keep the position of offshore platform while physical limitation. Generally, the offshore platform control system is an over-actuated system. Thus, a thrust allocation problem of the offshore platform can be determined as an optimization problem. In this research, a thrust allocation problem is designed to minimize the fuel-consumption and the gas emission. Fuel-optimal thrust allocation was newly formulated and solved based on penalty-method based optimization. Developed thrust allocation method was evaluated by comparing to conventional pseudo-inverse based thrust allocation. The proposed thrust allocation method was validated with comparison with an offshore support vessel static allocation cases. A fully coupled dynamics of hull, mooring, riser, and dynamic positioning system were simulated in time domain. The proposed thrust allocation method that uses penalty-method achieved a 3% accumulated fuel consumption reduction compared to the conventional pseudo-inverse method based thrust allocation algorithm in GOM 1-yr storm condition.
The Effect of Mooring Line Pre-Tension on FDPSO’s Motion
Authors: Sun Yanlong , Ren Huilong , Liu Zhendong , Yan Liu , Guo Zepeng
Published: October 2016

As a multifunction floating platform, Floating Drilling, Production, Storage and Offloading (FDPSO) combining the well-known Floating Production, Storage and Offloading (FPSO) with a drilling unit. For the environment condition of deep-water oilfield is very severe, the motion response and mooring line tension of FDPSO is a worthy topic of studying. In this study, the numerical time-domain coupled prediction method for the mooring line tension and motion response of FDPSO system is constructed by ANSYS AQWA software. Furthermore, the results of a model test conducted in Harbin Engimeering University are used to investigate the feasibility and validity of the commercial simulation. The effect of mooring line pre-tension on the response of FDPSO is studied by varying the pre-tension of mooring line during the calculation. The time series curve of the mooring line tension and motion response, and the comparison of motion spectrum and mooring line tension spectrum are provided in this article.
A Study on the Wave Drift Forces Calculation on Two Floating Bodies Based on the Boundary Element Method: Attempt for Improvement of the Constant Panel Method
Authors: Li Qiao , Tsubogo Takashi , Ikeda Yoshiho , Nihei Yasunori
Published: October 2016

The boundary element method (BEM) which can solve the boundary integral equations is used to calculate the velocity potential on the floating bodies. The equation is discretized by the higher order BEM or the constant panel method. The constant panel method is relatively easy to compute the velocity potential. However the near field method cannot evaluate the wave drift forces and moment accurately, when the velocity potential is computed by the constant panel method.

In the article, a new numerical technic of the constant panel method is proposed. Then it is easy to take advantage of the near field method to calculate the wave drift forces and moment, especially considering two floating system. In addition, the results of the fluid forces calculated by new method are compared to the other methods results. At last the hydrodynamic interaction between two floating bodies is assessed in the calculation of the wave exciting forces and the wave drift forces.
A Method to Estimate Inherent Deformation in Thin-Plate Welded Joint With Buckling Distortion
Authors: Liang Wei , Murakawa Hidekazu
Published: October 2016

It has been recognized that the elastic finite element method based on inherent strain theory is an effective tool to estimate the total welding deformation of large and complex welded structures. When this computational approach is employed to predict welding deformation in a welded structure, one prerequisite is that the inherent deformation of each welded joint should be known beforehand. The inverse analysis method based on the combination of measuring technology and finite element method has been proposed to obtain the inherent deformations for various welded joints. However, if buckling distortion occurs in a welded joint, it will be difficult for this method to accurately obtain the inherent deformation especially in thin-plate joints. To overcome this difficulty, an improved inverse analysis method with the help of cutting technique was developed in the current study. The effectiveness of the proposed method was demonstrated through obtaining the inherent deformations in an Al-alloy thin-plate joint with buckling distortion.
Retracted: “Numerical Investigation Into the Effects of Top Water-Bearing Zone on Steam and Gas Push” [ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology, Busan, South Korea, June 19–24, 2016, Conference Sponsors: Ocean, Offshore and Arctic Engineering Division, ISBN: 978-0-7918-4999-6. Paper No. OMAE2016-54268, pp. V008T11A010; 6 pages; doi:10.1115/OMAE2016-54268]
Authors: ASME
Published: October 2016

This paper was not presented at the conference. ASME does not hold the copyright. December 21, 2018.

Copyright © 2018 by ASME
Simulation and Development of a Wind-Wave Facility for Scale Testing of Offshore Floating Wind Turbines
Authors: McElman Sarah , Koop Arjen , de Ridder Erik-Jan , Goupee Andrew
Published: October 2016

The development of a new wind-wave facility for offshore floating wind turbine testing can be complex; outfitting existing basins with wind generation capacity can be even more of a challenge. We present the simulation, design, and construction of a wind generation system for use in a modified existing basin at MARIN for the purpose of new concept testing for floating offshore wind turbines. Computational fluid dynamics simulations using MARIN’s ReFRESCO software are carried out for wind generator design and flow characterization within the basin. Modifications to improve the wind flow quality from the designed configuration, with the aid of CFD simulations, are discussed for the constructed system. Measurements on the completed wind generation system show reasonable spatial uniformity of the flow and turbulence intensities similar to atmospheric wind flows. Finally, suggestions for the construction of similar testing facilities are provided based on lessons learned from this retrofit project.
Directional Analysis and Potential for Spectral Modelling of Infragravity Waves
Authors: Nose Takehiko , Babanin Alexander , Ewans Kevin
Published: October 2016

In this paper, we interrogated wave data collected by US Army Corps of Engineers at their well-known Field Research Facility, Duck, North Carolina and SHELL Corporation at Lagos, Nigeria. Both measurements were designed to collect wind waves with a conventional wave sampling configuration and not a dedicated infragravity wave sampling regime. Here, we developed a new approach to obtain directional information of and explored the potential to model infragravity waves in the spectral domain. It was found that infragravity wave heights had a strong dynamic relationship with an inverse relative depth parameter and that directional spreadings were moderately correlated with wind wave spreadings and wave energy. Further, infragravity directional spreadings were typically broader compared to their wind wave directional spreading counterparts.
Study on the Piezomagnetic Response to Low-Cycle Fatigue of X80 Pipeline Steel
Authors: Bao Sheng , Hu Shengnan , Fu Meili , Lou Huangjie
Published: October 2016

The objective of this work is to explore the relationship between the progressive material degradation process of fatigue and the evolution of the piezomagnetic field surrounding a ferromagnetic sample. The continuous examination of changes in the magnetomechanical behavior during a series of strain-controlled fatigue tests was performed on X80 pipeline steel samples. Analysis of the data obtained allowed the division of the fatigue life of the investigated steel into three stages: incipient stage, steady stage and terminal stage. Furthermore, the piezomagnetic field evolution demonstrates conspicuous changes in the initial stage of fatigue loading, then reverts to a relatively stable phase, and finally, drastic variations appear again before terminal failure. The progressive degradation of the steel under cyclic loading can therefore be tracked by following the evolution of the piezomagnetic field. The characteristics of the evolution of the piezomagnetic responses are also discussed in terms of the mechanical and microstructural condition of the steel during the fatigue process.
A Transient Model for Hydraulic Simulation of Bullheading and Pressurized Mud Cap Drilling
Authors: Ghauri Abrar Akram , Fjelde Kjell Kåre , Frøyen Johnny
Published: October 2016

Bullheading is the process of pumping fluids into the well without circulating back to surface. This operation can be carried out for several reasons. In well control, this can be an alternative well kill approach in situations where conventional kill methods do not apply. When considering the pressurized mud cap drilling technique, bullheading is used for controlling pressures when drilling highly fractured and vugular carbonate formations. Bullheading is also carried out for killing production wells prior to workover operations.

For a bullheading operation to be successful one need to ensure that the correct flow rate is chosen to overcome gas migration. This countercurrent to downward flow situation is best described using transient flow simulators to correctly predict what kind of rates and fluid volumes that are required. In addition, a transient flow model can also predict what kind of pressures that will be experienced during the operation to ensure that equipment and fracture pressure limitations are not exceeded.

This paper aims at giving an overview of the application and challenges associated with bullheading operations for different type of well operations including the pressurized mud cap drilling technique. Then a mathematical model and a numerical scheme (AUSMV) that can be used for simulating the transient dynamics of a bullheading operation will be described. The drift flux model combined with a slip law will be used.

Here special emphasize will be given on describing how we made the numerical scheme second order to reduce effects associated with numerical diffusion. The numerical boundary treatment and handling of flow regime transitions will also be described since one will here alternate between different conditions like cocurrent, countercurrent and downward flow.

Two simulation scenarios will be considered. In the first example, a kick scenario will be considered and it will be shown how the transient model can be used to predict the effect of using different bullheading rates when trying to kill the well. Both time and depth variables will be visualized. The model can also predict how large volumes are required for a successful bullheading operation for a given rate.

In the second example, it will be shown how the model can be used for simulating the alternating conditions experienced in a pressurized mud cap drilling operation. Here one will have a situation where surface pressure will build up if a kick is migrating in the closed annulus and if the pressure reaches a certain level, the kick has to be bullheaded back into the formation. This process can be repeated several times.

The paper will show that the transient model proposed can provide good insight into the dynamics of bullheading and pressurized mud cap drilling. The model seems to be robust in handling the alternating flow conditions. Finally, some words will be said with respect to what is considered as important with respect to improving the modelling.
URANS Prediction of Ship Hydrodynamics in Head Sea Waves at Zero Forward Speed With Model Testing Validation
Authors: Jin Yuting , Chai Shuhong , Duffy Jonathan , Chin Christopher , Bose Neil , Sun Liping
Published: October 2016

The paper presents computations on predicting the hydrodynamics of a generic floating liquefied natural gas (FLNG) hull form in regular head sea waves using unsteady Reynolds-Averaged Navier-Stokes (URANS) solver StarCCM+. Initially, model scale simulations were conducted at model test basin water depth (d = 0.8m), with detailed verification and validation study performed to estimate numerical uncertainties. The simulation results were compared with potential flow solutions and validated against experimental studies. Using the verified numerical setup, ship hydrodynamics including wave induced loads, moments as well as ship motion responses in deep water waves (d = 8.0m) have been studied. The computed time history results were decomposed by Fourier series to obtain force/moment and motion transfer functions on the frequency domain. From the obtained results, the presented URANS approach demonstrates slightly better accuracy compared with potential flow (PF) solutions. It is also found that water depth has great influences on the computed wave force and ship motion transfer functions for certain range of wave frequencies.
Numerical Investigation of Wave Period Influence on Long Wave Run-Up on Slope With Rigid Vegetation
Authors: Tang Jun , Shen Yongming
Published: October 2016

Coastal vegetation can not only provide shade to coastal structures but also reduce wave run-up. Study of long water wave climb on vegetation beach is fundamental to understanding that how wave run-up may be reduced by planted vegetation along coastline. The present study investigates wave period influence on long wave run-up on a partially-vegetated plane slope via numerical simulation. The numerical model is based on an implementation of Morison’s formulation for rigid structures induced inertia and drag stresses in the nonlinear shallow water equations. The numerical scheme is validated by comparison with experiment results. The model is then applied to investigate long wave with diverse periods propagating and run-up on a partially-vegetated 1:20 plane slope, and the sensitivity of run-up to wave period is investigated based on the numerical results.
Probabilistic Analysis of the Collapse Pressure of Corroded Pipelines
Authors: Oliveira Nara , Bisaggio Helio , Netto Theodoro
Published: October 2016

Oil and gas offshore pipelines are one of the main components of a subsea system. A major accident can have a great economic impact due to loss of revenue and the expenses involving actions to mitigate damages to the environment. Therefore, investment in accident prevention through a carefully designed inspection and maintenance plan is necessary. In this scenario, many companies have changed their procedures to ensure the structural integrity of their pipelines — from a model that incorporates empirical safety factors and periodic inspections to another, based on methods that consider concepts of structural reliability to establish risk based inspections.

The collapse pressure of pipelines containing corrosion defects is usually predicted by deterministic methods, either numerically or through empirical formulations. The severity of each individual corrosion defect can be determined by comparing the differential pressure during operation with the estimated collapse pressure.

However, loads and resistance parameters have uncertainties which define the basic reliability problem. These uncertainties are related to the geometric and material parameters of the pipe and the operational conditions. In recent years, many studies have been developed using reliability concepts in order to predict the probability of failure of a corroded pipeline at any given time. The main problem in assuring the integrity and safe operation of pipelines lies in obtaining the necessary accurate prediction of their future condition.

A simple deterministic procedure for estimating the collapse pressure of pipes with narrow and long defects has been recently proposed by Netto (2010). This formulation was based on a combined small-scale experimental program and nonlinear numerical analyses accounting for different materials and defect geometries.

Probabilistic failure analyses of pipelines considering different failure mechanisms have been performed by different authors over the last decade. Limit state functions similar to the mentioned above, coupled with reliability algorithms such as the first-order second-moment (FOSM) iterative method, the Monte Carlo integration method, and the first-order and second-order reliability methods (FORM/SORM) are generally used. The analyses take into account the natural spread of material properties, geometric and operational parameters, and the uncertainties associated with the sizing of eventual corrosion defects. In this paper, Netto’s deterministic formulation and the crude Monte Carlo method were used to obtain the reliability of corroded pipelines under external hydrostatic pressure.

This approach provides a method to predict the probability of collapse of a corroded pipeline along its operational life. It applies concepts of structural reliability to evaluate the detrimental effect of corrosion damages, giving the basis to develop a risk based maintenance strategy.
VIM Simulation Method on a Cylindrical Floating Structure
Authors: Fujiwara Toshifumi
Published: October 2016

A cylindrical floating structure can basically experience Vortex-induced Motion (VIM) in strong current. Since the VIM on the structure with long term low-frequency motion causes fatigue damage of the structure’s mooring lines and risers, precise VIM assessment is needed for the safety evaluation of them. In the standard of the International Organization for Standardization ISO19901-7, ‘Specific requirements on stationkeeping systems for floating offshore structures and mobile offshore units’, for instance, a concrete method of assessing VIM displacement is not represented in the standard document, though the requirement on the VIM demands to do the assessment on the basis of proper ways.

Then in this paper, a VIM simulation method on a floating structure with circular cylinder form, that is, for example a Spar, a MPSO (Mono-column type floating Production Storage and Offloading) and so on, is shown using the wake-oscillator model. Transverse VIM is only treated since it is dominant factor on the fatigue damage of the mooring lines and risers. The assessment quality of the simulation method on the transverse VIM of floaters in current is confirmed by model test data.
Nonlinear Computational Welding Mechanics for Large Structures
Authors: Ikushima Kazuki , Shibahara Masakazu
Published: October 2016

Large-scale thin-plate structures including ships are constructed by welding, and distortion can occur after welding. Welding deformation can increase cost and work time, and so it is important to investigate welding deformation before construction. In this research, to predict welding deformation on the construction of a large thin-plate structure, Idealized Explicit FEM (IEFEM) was applied to the analysis of welding deformation on the construction of a ship hull block. In addition, to efficiently analyze deformation of the whole structure of a large-scale structure, an algebraic multigrid (AMG) method was introduced into the IEFEM. Then, this multigrid IEFEM (MGIEFEM) was applied to the analysis of welding deformation on the construction of a ship hull block. The ship hull block consisted of 10 million degrees of freedom and the MGIEFEM analysis was finished within the practical computing time of a week. Thus, it can be said that MGIEFEM is an effective tool for analyzing the welding deformation of real products.