bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation for Vortex-Induced Vibrations of Steel-Lazy-Wave-Risers: Part I — CFD Validation Against Forced Oscillation Model Test
Authors: Jang Hyunchul , Kim Jang Whan
Published: November 2019

Vortex-Induced Vibration (VIV) is one of the main sources of fatigue damage for long slender risers. Typical VIV assessment of risers is conducted using semi-empirical software tools with the sectional hydrodynamic coefficients derived from forced-oscillation model tests on short rigid riser sections. The Steel Lazy Wave Riser (SLWR) with buoyancy sections is an attractive concept for improving fatigue performance in deep water developments, but there is limited model test data available for the hydrodynamic coefficients on SLWR’s. CFD simulation is an alternative VIV assessment tool, once it is validated for an existing model test. It can provide accurate estimates of VIV response and help to design configurations of SLWR’s without additional model tests. The present CFD simulations are performed to validate hydrodynamic coefficients of a SLWR section. The predicted drag and excitation (lift) coefficients on both bare riser and buoyancy sections are compared to the test data with respect to oscillation frequency and amplitude.
Improving the Productivity and Sustainability of Port Management Against High Tide and Tsunamis
Authors: Takahashi Koji
Published: November 2019

In 2011, the National Diet of Japan passed a law to implement the policy of “International Container Strategy Ports,” which would be applied to public-built private-management system and private company financing methods to container terminals at the main ports operated by Port Management Bodies which are local governments. It would also establish the port management corporation at each port in order to improve the productivity of container terminals throughout Japan. Port management corporations have already been established at several ports such as “Kobe-Osaka,” “Yokohama-Kawasaki” and “Nagoya-Yokkaichi.” The purpose of establishing these port management corporations for container terminals is to amend the rigid port management system by local governments, and to be prepared to provide a quick response to global economic changes and the wills of cargo owners and shipping companies. Current port management corporations, however, are facing various problems of management. On the other hand, as in the cases of the tidal inundation disaster at Kansai Airport and the port area due to heavy rain in 2018, port management needs to make new capital investment to cope with the issues such as the construction to protect ground structure against high tide and tsunamis. Therefore, the author would like to first analyze the issues that current port management face, and then propose solutions and possible scenarios for improving the productivity and sustainability of port management against high tide and tsunamis.
Improving the Hydrodynamic Performance of OWC Wave Energy Converter by Attaching a Step
Authors: Rezanejad Kourosh , Gadelho Jorge F. M. , López Ivan , Carballo Rodrigo , Guedes Soares C.
Published: November 2019

The influence of attaching a step to the conventional shore based Oscillating Water Column device on the hydrodynamic performance has been assessed by carrying out experimental investigations. The level of the efficiency improvement in various wave characteristics and Power Take-Off damping conditions were investigated. Three different Power Take-Off damping conditions have been applied to the system and experiments were carried out for both regular and irregular wave conditions. The results obtained from the experimental study prove that the Oscillating Water Column with the attached step has substantially improved hydrodynamic performance in all the Power Take-Off damping conditions compared to the Oscillating Water Column model in uniform water depth.
An Experimental Study of Snap Loads on a Vertical Hanging Cable System
Authors: Hsu Wei-Ting , Chuang Tzu-Ching , Hsu Wen-Yang , Sharman Krish , Yang Ray-Yeng
Published: November 2019

Sudden snap events on mooring lines and hanging cables can cause spikes in tension, resulting in reduced safety factors during extreme events. For example, the mooring system of a floating offshore wind turbine (FOWT) can be exposed to wave-induced motions making the former vulnerable to snap type impact. Suitable criteria to define snap events are still largely unclear, making current design practices overly conservative.

To understand the underlying physics of snap loads on a mooring line system, this paper presents a theoretical development and an experimental parametric study of snap events. The effects of the nonlinearity of bilinear line stiffness and hydrodynamic drag force, as well as the weight of payload on snap events are investigated using the vertical hanging cable model. This cable model includes two springs in series and a payload. The bilinear spring model is designed to create nonlinear dynamic tension. A total of 108 tests were conducted in the wave tank of Tainan Hydraulic Laboratory. The excitation amplitude ranges from 0.01 to 0.04m; excitation time period ranges from 0.5 to 2s; the weight of payload ranges from 6.13 to 18.95N. The tests carried out in water are compared to those conducted in air. It is seen that the hydrodynamic drag force together with the small pretension could result in larger normalized tension ranges.
Study on the Flow Field and the Shielding Effect of a Hemisphere Artificial Reef and Other Alike Sub-Sea Structures
Authors: Zhao Lin , Tan Junwei
Published: November 2019

A hemisphere artificial reef is designed and numerically simulated in this paper. Investigations of this structure subject to various flow fields with different hole ratios and different diameter are carried out. Besides, the effect of the hemisphere structure to the surrounding flow field is discussed. Further studies are carried out for an array of hemisphere structures of this kind. Comparing to the traditional artificial structures like the trapezoidal reefs and square reefs, the hemisphere reef can not only produce a qualified ascending flow field, but his internal shadowing effect is not negligible.This area then can provide a better ocean ecological environment and living environment to attach and promote the marine life.
Cargo Liquefaction and Influence on Ship Stability
Authors: Chua Kie Hian , Zhang Yali , Konovessis Dimitrios
Published: November 2019

Fine grain solid bulk cargo with “sufficient” moisture content may undergo liquefaction during a voyage, posing a danger to the bulk carrier and the crew on-board due to its potential to shift and adversely affect the vessel’s stability. Between the years 2005 to 2017, it is believed that at least 21 bulk carriers have been lost due to cargo liquefaction. Most of these vessels are of 60,000 deadweight tonnes (DWT) and below, i.e. belonging to the “handysize” class. At the present moment, liquefaction is thought to occur through either conventional liquefaction or dynamic separation. In the former, wet granular cargo particles are rearranged through cyclic loads induced by the ship’s motions, resulting in overall compaction of the cargo and a corresponding increase in pore pressure between the particle grains. Shear resistance of the cargo pile decreases and movement of significant portions of the liquefied cargo material may occur, which in turn poses significant risks for the vessel. In dynamic separation, a pile of wet granular cargo particles undergo progressive transformation through intermediate stages, where the moisture separates from the cargo pile, forming fluid slurry comprising water and entrained particles that would be denser than water perched on top of a drier, compacted particle pile. The slurry will slosh with the vessel motion adversely influencing the stability of the vessel. Compared to conventional liquefaction, the compacted particle pile is drier and less susceptible to shift under vessel movement. In this study, a numerical modelling to assess the impact of the two cargo liquefaction mechanisms on a vessel’s stability is undertaken. The numerical models will be described and the results will be discussed.
Evaluation of Entropy Generation Methods in Wells Turbine
Authors: Licheri F. , Ghisu T. , Virdis I. , Puddu P. , Cambuli F.
Published: November 2019

Entropy generation analyses have been applied, in recent years, to a variety of systems, including Wells turbines. This can be a very powerful method, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. However, some of the simplifications used in recent studies raise more than a concern on the validity of the approach. This work proposes a method based on RANS equations to evaluate the entropy production in Wells turbines. An estimation of the second-law efficiency of different Wells turbine rotors is also presented, under conditions representative of the air flow inside an OWC device. The main sources of entropy generation are highlighted and compared for the different geometries.
Centrifuge Modelling of a Novel Skirted Spudcan for Penetration in Layered Soil
Authors: O’Loughlin Conleth , Gaudin Christophe , Quah Matthew , Perry Michael
Published: November 2019

This paper reports on a series of centrifuge tests to investigate the feasibility and performance of a novel spudcan foundation design featuring a peripheral skirt with side openings. The ‘skirted spudcan’, designed and patented by Keppel, is particularly beneficial in layered seabeds with a clay layer overlaying sand. The purpose of the side openings is to enable the clay trapped within the spudcan skirt to flow outside the skirt, so the skirt can penetrate into the sand and develop the required fixities against combined vertical, horizontal and moment loading. The centrifuge tests considered different skirted spudcan designs, each 10 m in diameter, but with a skirt length of either 1.38 m or 2.76 m, two spudcan invert shapes and various configurations of side and top openings. The model skirted spudcans were penetrated into a soil sample featuring a clay layer 6 m thick (in prototype scale) with an average undrained shear strength of about 15 kPa, overlaying a silica sand layer with a relative density of about 40%. The skirted spudcan embedded the sand layer by more than the skirt height at the maximum penetration resistance of about 4 MPa. However, examination of the model after retrieval demonstrated that a clay layer remained inside the skirt, despite the openings on the side of the skirt. The comparison between the eight tests demonstrated that the thickness of the clay plug reduces with the strength of the soil and with the size of the openings. Large horizontal openings located at the top of the skirt were shown to generate the lowest plug thickness and the largest skirt embedment into the sand. Somehow surprisingly, the addition of top openings (in addition of side openings) does not have beneficial effects. In general, the results demonstrated the efficiency of the skirted spudcan with side openings concept. Although the clay plug inside the skirt compartment was only partially expelled, significant skirt embedment into the sand layer (and hence high fixities) could be achieved. The high compressive stresses within the residual clay plug should limit concerns about potential rocking of the spudcan when clay remains trapped within the skirt compartment.
Realistic Adaptive DP Controller for Flotel Operating in Side-by-Side Configuration With FPSO
Authors: Yenduri A. , Magee A. R. , Liu J. , Xu W. , Choudhary A. , Hussain A. A.
Published: November 2019

Side-by-side operation of multiple floaters in the ocean environment is very challenging and the operators always prefer a maximum operable weather window, in order to minimise the cost incurred from the downtime. The safety of the gangway connecting the floaters is very crucial and its dynamic response in the ocean environment raises concerns during operations. Therefore, an efficient dynamic positioning system is essential to maintain the floater and ultimately, the gangway response within the desired limits. In this work, a novel dynamic positioning system for floater operating aside another vessel is presented. The system includes an adaptive controller combined an optimised thruster allocation law and with a sea state detector. The adaptive control is achieved by using the barrier Lyapunov function and a predictor-based method in combination with the neural network scheme. The limitations include the saturation of inputs and the forbidden zones due to thruster-thruster or thruster-hull interaction. An optimised allocation for lower fuel consumption, wear and tear of the thruster equipment and to ensure the resultant command in the respective direction of the azimuth thrusters is designed. The optimisation here is a non-convex problem and a locally convex reformulation of second order is implemented. The presence of unknown shielding effect due to nearby vessel in a side-by-side configuration and input time delay is also considered in the development of this thruster allocation law. In order to overcome these effects, a novel sea state detector is designed. The sea state detector can effectively monitor the variation of drift wave-induced force on the vessel and activate the neural network compensator in the controller when a large wave drift force is identified. Simulation studies are conducted to verify the efficiency of this dynamic position system and a demonstration of flotel in side-by-side configuration with a turret moored FPSO is presented for the non-collinear ocean environment.
Research on the Probability Distribution of the Underwater Moving of the Wrecked Targets
Authors: Duan Wenyang , Shi Zhang , Chen Yunsai , Huang Limin , Cao Guanzhou , Zhang Hongsen
Published: November 2019

There has a great challenge for deep-sea exploration and search because the underwater motion trajectories and sinking location of wrecked targets are uncertain under the influence of random factors such as currents. The traditional underwater motion model can’t know exactly the probability distribution of wrecked targets. This thesis introduces Monte-Carlo random function into the underwater non-dynamic motion equations and the targets sinking location probability model based on Monte-Carlo method is established as well. The purpose is to get the targets’ sinking probability distribution and to improve the successful probability of searching the wrecked targets. In this thesis, the motion reference frame is introduced firstly, and the motion model of underwater non-dynamic subsidence based on the motion reference frame is established then. The Monte-Carlo method of stochastic simulation is discussed at the same time. After that the drop point of the sandbag is taken as an example to verify the reliability of the model. Finally, the probability of targets dispersion underwater is simulated and analyzed, and the conclusion is drawn that the whole points are normally distributed.
Fundamental Engineering Characteristics of Cohesive Sediments in the Northern Region of South China Sea
Authors: Li Shuzhao , Jia Xu , Li Zhigang , Li Jiagang
Published: November 2019

The northern region of South China Sea is the important strategic region for the offshore oil and gas resources development in China. The main shallow sediment of the region is the cohesive soil with diverse engineering characteristics difficult to be determined. The paper collects the comprehensive geotechnical data obtained from the laboratory test and the in-situ Cone Penetration Test (CPT) for the offshore oil and gas projects in the northern region of South China Sea, and presents the fundamental engineering characteristics of the cohesive soil. Results indicate that the cohesive soil with the low plasticity index and the low clay particle content in shallow water is obviously different from that in deep water in the northern region of South China Sea. The physical properties of the clay soil with the high plasticity index and high clay particle content in the northern deep water region of South China Sea are similar to those found in the Gulf of Mexico and West Africa. Moreover, there are two different deposit modes for the sediment in the northern region of South China Sea, which are the fine-grained and coarse-grained govern deposit modes in deep and shallow water respectively. It is found that the sleeve friction ratio of the cohesive sediment is very low in shallow water. The normalized values of the clay soil in deep water are consistent with those from the Gulf of Mexico and West Africa.
Qualification of TMCP Pipe for Severe Sour Service: Mitigation of Local Hard Zones
Authors: Newbury B. D. , Fairchild D. P. , Prescott C. A. , Anderson T. D. , Wasson A. J.
Published: November 2019

C-Mn steels are extensively used as line pipe material for sour service oil and gas applications, i.e. in the presence of hydrogen sulfide (H2S), because of their ease of fabrication, weldability and significantly lower cost compared to Corrosion Resistant Alloys (CRAs). However, use of C-Mn steel in sour conditions can be limited by its susceptibility to various hydrogen damage mechanisms such as sulfide stress cracking (SSC) and hydrogen induced cracking (HIC). Presently, there are several industry standards which provide guidelines for materials selection and qualification testing to ensure the integrity of carbon steel pipelines in sour service. In recent years, examples of line pipe susceptibility to SSC have occurred due to undetected Local Hard Zones (LHZs) produced during steel plate manufacture. A companion paper (Fairchild, et al, [1]) describes historical and one newly recognized root causes for LHZs. Due to this newly recognized root cause, the adequacy of the current industry practice for specifying and qualifying C-Mn line pipe for severe sour service should be evaluated. In this work, a new approach to monitoring steel plate manufacture during Thermo Mechanical Controlled Processing (TMCP) in order to manage LHZs is explained. Results from implementing this qualification approach will be discussed. In addition, several gaps were identified in the current test methods and various potential modifications to address these gaps were identified. Based on the results of these studies, recommendations to the test methods are made to improve the robustness in the materials qualification process used for sour pipeline projects.
Hole Cleaning Related Stuck Pipe Analysis During Extended Reach Drilling by Using a Transient Cuttings Transport Model: A Case Study
Authors: Zeng Hao , Zeng Yijin , Zhang Feifei , Yang Guang , Wang Yuezhi , Wang Xi
Published: November 2019

Insufficient hole cleaning is one of the major challenges in drilling, particularly in extended-reach drilling (ERD). This paper presents a case study of a stuck pipe incident caused by cuttings pack off during drilling an extended-reach well. A generalized, transient, solid-transport model that can handle different flow patterns is used to replay the hole-cleaning process. Results show that, although cuttings beds in the deviated part of the wellbore are not significant while drilling ahead, cuttings can still cause problems during tripping. This study reinforces the facts that hole cleaning in wells with long deviated sections is complicated and a transient approach is required to fully understand the hole-cleaning condition. Effective hole cleaning does not only mean that the cuttings concentration is low or the cuttings transport ratio is high. In addition, the absence of additional cuttings being produced from the shale shaker during circulation does not necessarily indicate that the hole is clean. The cuttings accumulated behind the BHA can lead to tight spots and over-pull incidents during tripping. By conducting drill string reciprocations without circulation, the tight spots can be “worked through” but packed cuttings cannot be removed from the wellbore. This paper presents lessons learned from this incident, as well as recommendations for future operations.
Time-Varying Vector Field Guidance Law for Path Following and Obstacle Avoidance for Underactuated Autonomous Vehicles
Authors: Xu Haitong , Hinostroza M. A. , Guedes Soares C.
Published: November 2019

This paper presents a time-varying vector field guidance law for path-following control of underactuated autonomous vehicles. The proposed guidance law employs a time-varying equation to calculate the desired heading angle. A sliding mode controller is designed to track the desired heading angle, and it is proved to be globally exponentially stable (GES). With this controller, the stability proof for guidance system is presented and the equilibrium point of the guidance system is Uniform Global Asymptotic Stable (UGAS). In order to avoid the obstacle when ship approaching the predefined path, a combined Path-following and repelling field based obstacle avoidance system is proposed in this paper. Simulations are carried out to validate the performance of the combined path-following and collision avoidance system.
Extreme Wind and Wave Predictability From Operational Forecasts at the Drake Passage
Authors: Campos Ricardo Martins , D’Agostini Andressa , Machado Cruz Leandro , Reis Leite França Bruna , Guedes Soares C.
Published: November 2019

The Drake Passage is an ocean area between the South America and Antarctic with very extreme wind and wave climates. The forecast accuracy of surface winds and significant wave heights is analyzed in the present paper, in order to study the behavior and distribution of model uncertainties as a function of: forecast range, severity, location, and numerical model. The operational forecast considered is run twice a day by the Brazilian Navy, and a period of one year (2017) is selected for the assessment. Observations consist of four satellite missions: JASON2, JASON3, CRYOSAT, and SARAL. The numerical atmospheric models with 10-m winds are GFS (Global Forecast System) and ICON (Icosahedral Nonhydrostatic Model). They force wave simulations using the model WAVEWATCH III with a mosaic of two grids. The forecast horizon analyzed is five days, which is made publicly available by the Brazilian Navy. Results show that under calm to moderate conditions, within the first two days of forecast, the wind and wave model skill is very high. However, above the 90th percentile and beyond the third forecast day, the predictability drops significantly. It highlights specific contours of forecast range versus percentiles where the wind and wave modelers should focus, in order to anticipate and to improve the predictability of extreme events at the Drake Passage.
Buoyancy Induced Convection of Riser Gas in Deepwater Drilling Operations
Authors: Nahri Syed Y. , Chen Yuanhang , Williams Wesley , Santos Otto , Sun Ting
Published: November 2019

Riser gas migration has been an area of interest since the last three decades due to its importance in gas handling in deepwater drilling operations. A previously conducted full-scale test at LSU Petroleum Engineering Research & Technology Transfer (PERTT) well facility indicates, as contrary to traditional belief, significant migration of dissolved gas taking place even when circulation had ceased. In order to understand whether a reduction in density of the underlying contaminated mud resulting from gas absorption is the contributing factor to the above-mentioned phenomenon, a computational fluid dynamics (CFD) analysis was conducted to study the transport of the gas influx while in solution due to buoyancy induced convective mass transfer and simultaneous diffusion.

Simulations performed in this study include the hydrodynamics of the upward moving gas cut mud and simultaneous mass transfer of natural gas into the under-saturated drilling fluid. The parameters studied here are the distance traveled of the gas cut mud and saturation levels in the drilling fluid along the length of the riser. The dense phase behavior was shown to have considerable effects on gas loading capacities which in turn affected the density of the gas cut mud, and at pressures upwards of 5,000 psi, the solubility of a natural gas influx can be seen to be infinite in certain synthetic and oil-based drilling fluids. The rate and extent of mass transfer are dependent on drilling fluid density gradients, which in turn are based on gas influx saturation level. Results obtained from this study can help better comprehend migration phenomena of a dissolved influx in oil-based muds in a riser with the BOP shut in and when circulation has ceased.
Anti-Icing and De-Icing of Pipe Structures on Marine Vessels Using Waste Heat Recovery
Authors: Æsøy Lene , Piehl Henry , Bjørnøy Palmar
Published: November 2019

One of the major challenges for a ship sailing in Arctic waters is ice aggregation. Atmospheric water or sea spray that comes into contact with the cold railing, equipment and superstructure deposits ice on the exposed surfaces. This ice can build up over time to such an extend, that the weight of the ice can severely impair the ships stability, even lead to capsizing. To prevent such accidents, the IMO Polar Code for ships operating in Arctic areas requires countermeasures against icing. Ulmatec Pyro has developed a “double pipe system” that makes use of waste heat, recovered from the ships propulsion and energy system.

The main objective of this research project has been to investigate the behavior of anti-icing and de-icing for pipe structures to provide design rules and operational guidelines for such systems.

Pipe systems have been studied using both numerical and experimental methods. First a simple 1D pipe system, simulating the steady heat transfer with a finite difference method, was implemented. The purpose of this model is was to be able to quickly study design variations. Next, a more advanced 3D axis-symmetric heat flow model was simulated, using a commercial transient finite element solver. The results of the advanced model was used to evaluate the simple model. Subsequently these simulation tools were used to support the design decisions for the experimental setup. To get the IMO approval for the double pipe system, the experiments were conducted at the site of the classification society. The experimental setup was used to validate the simulation model, and furthermore as a design verification lab for Ulmatec Pyro.

A comparison of the results between both numerical simulation models and experiments show a good correlation. In addition, the experiments provide a valuable insight into the icing- and anti-icing processes. Specifically, a better understanding of the complex ice melting process.
Non-Repeatability, Scale- and Model Effects in Laboratory Measurement of Impact Loads Induced by an Overtopped Bore on a Dike Mounted Wall
Authors: Streicher Maximilian , Kortenhaus Andreas , Altomare Corrado , Hughes Steven , Marinov Krasimir , Hofland Bas , Chen Xuexue , Suzuki Tomohiro , Cappietti Lorenzo
Published: November 2019

Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects were studied, by comparing the up-scaled force measurements from both models in prototype. It was noted that if a minimum layer thickness, velocity of the overtopping flow and water depth at the dike toe were maintained in the small-scale model, the resulting differences in impact force due to scale effects are within the range of differences due to non-repeatability and model effects.
Study on Desulfurization and Decarbonization Technology of Natural Gas on Bohai Offshore Platform
Authors: Lu Ping , Qu Zhaoguang , Gao Guoqiang , Huang Yan , Qian Xin , Cheng Lin
Published: November 2019

Based on the latest developments of desulfurization and decarbonization technologies of acidic natural gas, the process characteristics, product purity, consumptions, occupied area, advantages and disadvantages of various desulfurization and decarbonization methods are analyzed and compared, and the adaptability of the methods on offshore platform is fully considered. According to the actual situation of a Bohai offshore gas field, the low temperature separation method is adopted and the desulfurization and decarbonization process is simulated by using HYSYS software, and then the technical scheme is put forward to meet the requirements of the gas turbines on surrounding platforms and the transportation quality index of the southwest Bohai gas supply pipeline network. This research has a certain reference value for technical programs of natural gas desulfurization and decarbonization on similar offshore projects.
Well Control Simulation With Non-Aqueous Drilling Fluids
Authors: Chagas Felipe , Ribeiro Paulo R. , Santos Otto L. A.
Published: November 2019

The demand for energy has increased recently worldwide, requiring new oilfield discoveries in order to supply this need. Following this demand increase, challenges grow in all areas of the petroleum industry especially those related drilling operations. Due to hard operational conditions found when drilling complex scenarios such as high pressure/high temperature zones, deep and ultradeep waters and other challenging ones, the use non-aqueous drilling fluids became a must. The reason for that is because this kind of drilling fluid is capable to tolerate these extreme drilling conditions found in those scenarios. However, it can experience changes in its properties as results of pressure and temperature variations, requiring special attention during some drilling operations, such as the well control. The well control is a critical issue since it involves safety, social, economic and environmental aspects. To support well control operations and preserve the well integrity, well control simulators are very useful to verify operational parameters and to assist drilling engineers in the decision making process during well control operations and kick situations. Well control simulators are also important computational tools for rig personnel training. This work presents well control research and development contributions, as well as the results of a computational well control simulator that applies the Driller’s Method and allows the understanding the thermodynamic behavior of synthetic drilling fluids, such as n-paraffin and ester base fluids. The simulator employed mathematical correlations for the drilling fluids PVT properties obtained from experimental data.The simulator results were compared to a test well data set, as well to published results from other kick simulators.
Capturing Two Consecutive Green Water Events by Convolution
Authors: Hernández-Fontes Jassiel V. , Silva-Casarín Rodolfo , Mendoza Edgar
Published: November 2019

Capturing the propagation of green water events on in ships and other marine structures is of importance when studying the hydrodynamic effects on their motion and the structure’s behavior. Analytical models used to predict green water elevations, such as dam-break models, have been considered to represent time series of water elevations of single green water events. This paper presents the use of a convolution approach to represent the time series of water elevations of two consecutive green water events on deck of a fixed structure. The procedure is described considering green water events, generated with regular waves, on a barge-type fixed structure. Its application is compared with results available elsewhere in the literature. With the assumptions related with the selection of input parameters of the convolution model, and considering only the first green water event, the results show that this methodology allows two consecutive green water events to be captured acceptably. It is hoped that this methodology will be useful in further time-domain applications which study the dynamic behavior of structures subjected to green water.
Quantitative Wear Estimation for Mooring Chain of Floating Structures and its Validation
Authors: Takeuchi Takaaki , Utsunomiya Tomoaki , Gotoh Koji , Sato Iku
Published: November 2019

For reducing maintenance cost of floating offshore wind turbine structures, it is necessary to establish quantitative wear estimation method for the mooring chains. In this paper, attempts have been made to improve the accuracy and applicability of the estimation method in the following steps.

By using the wear analysis method between the links of mooring chain that Gotoh et al. investigated with the finite element analysis software (MSC. Marc), the expression of the wear amount was obtained, which was a proportional functional form associated with sliding angle and tension.

The relative sliding angle and tension between links were analyzed by using a multibody dynamics software (MSC. Adams). A spar-type floater moored with three catenary mooring lines at Goto, Nagasaki prefecture, Japan was analyzed. Here, the floating body was modelled as a rigid body and mooring chains were modelled by mass-spring (lumped mass) model.

From these results, the wear amounts calculated by using the estimation formula and relative sliding angle and tension between links were compared with the measured wear amounts for mooring chain of the floater which was deployed for about one-year at Goto. The cases with only waves and those with wind and waves were analyzed.

From the comparison between the simulation results and the measured ones, it was found that the proposed method can fairly predict the wear amount of mooring chains. However, it was also found that the proposed method has a tendency to overestimate the measured results. These reasons were discussed in the paper.
Computations of Hydrodynamic Forces on Vessels Advancing in Waves by Four-Node Higher-Order Boundary Element Method
Authors: Yang Yuntao , Zhu Renchuan , Huang Shan
Published: November 2019

A higher-order boundary element method (HOBEM) using three dimensional translating-pulsating (3DTP) Green’s function is developed and applied to calculate the hydrodynamic forces on vessels advancing in waves in the present study. In this HOBEM, geometrical and physical variables are expressed by the shape functions defined by four nodal values; and Green’s function in Havelock form is adopted in the numerical implementation. The Gauss-Legendre quadrature is first adopted for the integral of 3DTP Green’s function over panel. However, due to the highly oscillating characteristic of Green’s function near the free surface, numerical instability is observed in the final results. To avoid this unstable problem, an improved algorithm for the integral of Green’s function is proposed. We discretize the panel into a series of horizontal line segments and derive an integral expression of 3DTP Green’s function distributing on the line segment. By accumulating a series of 3DTP Green’s function distributing on various horizontal line segments, the panel integral of Green’s function is obtained. To validate the performance of the improved algorithm, hydrodynamic forces on a mathematical ship model Wigley III are first calculated. The results are compared with those of the former algorithm and experimental data, which shows that improved algorithm is more stable and accurate. The present HOBEM is then applied to analyse the radiation and diffraction problems for a Series 60 hull and a catamaran hull. The computed hydrodynamic coefficients and wave forces are found to be in good agreement with experimental data.
Flange Neck Creep Damage Below API 579-1/ASME FFS-1 Creep Damage Threshold Triggered by Ring Joint Dissimilar Flanges
Authors: Ishizaki Yoichi , Yonekawa Futoshi , Suzuki Teppei , Hase Akira
Published: November 2019

Reduced flange design is commonly used for fixed bed reactor top nozzles due to the easier provision of manway access for down time maintenance. In this design, a dissimilar flange design is often opted for a material break point of the unit to avoid a dissimilar weld in the piping system.

This design concept is also adopted our fixed bed reactors. The vessel is made of 2.25Cr steel including 40inch top nozzle. On the 2.25Cr top nozzle, 347SS dissimilar reduced flange was provided for manway access purpose in conjunction with top nozzle. It had been operated for 54,000Hrs until the reduced flange neck experienced minor cracks. As the total operating hours reached 140,000Hrs, cracks were propagated and leaked. According to their inspection record of those cracks, a creep damage like pattern was observed while its operating temperature was 520Deg. C, that was below the 550Deg.C of ASME Sec II Part D[1] allowable stress table time dependent allowable stress range, and also below the 537Deg.C of potential creep damage threshold indicated in API 579-1 / ASME FFS-1[2] Table 4.1 which is the same with API 571 Table 4.3[3]. As we conducted FEM analysis using an isochronous curve based on API 579/ASME FFS-1 Omega Method[2], the results well explained the actual damage and life, and confirmed a creep damage could happen below the creep damage threshold of API 579-1 / ASME FFS-1[2] and API 571[3], depending on the multiaxial stress state.

In this paper, the detail of the inspection findings and isochronous model FEM analysis including remaining life assessment as well as comparison between the damage and analysis will be discussed.
Effect of Interference on Stress and Strain Distribution on the Spherical Sealing Cup of a PIG in Dented Pipeline
Authors: Zhang Hang , Dong Jinhui , Cui Can , Liao Ningsheng
Published: November 2019

Regular pigging operation of the pipeline inspection gauges (PIGs) is crucial for pipeline transportation. However, the PIG is often stuck when it runs in the oil and gas pipeline due to the interaction between spherical sealing cup and dent inside the pipe. The stress and strain distribution of the outer edge of the spherical sealing cup can provide a reference to the problem of understanding the blockage. In this study, numerical simulation of a PIG with spherical sealing cups runs through a pipe with dented wall is presented using MSC Marc 2016. Effects of the interference (δ) of the spherical sealing cup on the stress and strain distribution on the outer edge of the cup were discussed based on the model. Simulation results indicate that the smaller the thickness of the spherical sealing cup, the greater the effect of the interference of the cup on the stress. And the thickness of the cup should not be too small, an example of the failure of pigging due to the small thickness of the cup and the increase in the interference is given. The conclusions obtained in this study can contribute to the optimization design of the PIGs.
Influence of Quenching-Tempering on the Carbide Precipitation of 2.25Cr-1Mo-0.25V Steel Used in Reactor Pressure Vessels
Authors: Wang Yafei , Hu Songyan , Cheng Guangxu , Zhang Zaoxiao , Zhang Jianxiao
Published: November 2019

The carbide precipitation of 2.25Cr-1Mo-0.25V steel is studied during the head-fabrication heat treatment process using gold replica technique, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Shapes, structures and sizes of carbides before and after heat treatment are analyzed. The dissolution of strip-shaped carbides and the precipitation of granular carbides are confirmed. Amorphous films at the boundaries of carbides are observed by high-resolution transmission electron microscope (HRTEM), which is formed due to the electron irradiation under TEM.
Thermal Analysis of the 9977 Package Used for Nuclear Material Storage
Authors: Tamburello David , Kesterson Matthew , Hensel Steven
Published: November 2019

The 9977 is a US Department of Energy (DOE) shipping package used to transport plutonium bearing materials. The package utilizes a single 6 inch diameter containment vessel and a foam overpack to protect against fire and impact events. A storage facility fire, hotter and longer than the regulatory transportation fire, is evaluated to ensure radioactive material containment is maintained. A sensitivity analysis of foam degradation is also considered to conservatively simulate potential aging effects of the foam during storage. A minimum foam thickness needed to maintain containment during the hypothetical facility fire is determine.
A Framework for Underground Gas Storage System Reliability Assessment Considering Functional Failure of Repairable Components
Authors: He Lei , Wen Kai , Gong Jing , Wu Changchun
Published: November 2019

As one of the most important means of nature gas peak shaving and energy strategic reserving, the reliability assessment of underground gas storage (UGS) system is necessary. Although many methods have been proposed for system reliability assessment, the functional heterogeneity of components and the influence of hydrothermal parameters on system reliability are neglected. To overcome these problems, we propose and apply a framework to assess UGS system reliability. Combining two-layer Monte Carlo simulation (MCS) technique with hydrothermal calculation, the framework integrates dynamic functional reliability of components into system reliability evaluation. To reflect the state transition process of repairable components and their impact on system reliability, the Markov model is introduced at system level. In order to improve the calculation speed, artificial neural network model based on off-line MCS is established to replace the on-line MCS at components level. The proposed framework is applied to the reliability assessment and operation optimization of an UGS under different operation conditions. Compared with the traditional single-layer MCS method, the proposed method can not only reflect the variation of UGS reliability with hydrothermal parameters and operation time, but also can improve evaluation efficiency significantly.
Tuning of the Acoustical Analysis Model for Hypercompressors Through Strain Gage Pulsation Measurements
Authors: Fusi Andrea , Cappelli Leonardo , Carcasci Cosimo , Sacco Marco
Published: November 2019

Reciprocating compressor plants are typically exposed to vibrations, resulting from the discontinuity of the flow (pressure pulsations) and from external mechanical loads (compressor motion). To minimize the impact of pressure pulsations on vibration issues, a robust acoustical study is needed in the early design stage. Reliable standards and guidelines concerning vibration and pulsation are available for common applications (up to 350 bar) [1][2]. Within this pressure range it is possible to meet the standards by introducing pulsation suppression devices such as volume bottles or orifices. The Low-Density Polyethylene (LDPE) process requires very high pressures obtained with dedicated machines (Hypercompressors). There are no specific pulsation guidelines for these extreme pressures; in addiction reactive pulsation suppression devices like volume bottles are ineffective due to the high speed of sound in real gas (and related long wavelengths) at such pressures.

This paper describes the case history of a plant which exhibited high piping vibration from the first machine start-up. A survey was made to measure vibrations and pressure pulsations by means of strain gages: internal pressure was derived from external deformation through pressure vessel theory. Strain gages were chosen because they can be easily installed without positioning restrictions, while dynamic pressure sensors require pressure taps and must be limited to specific points.

Pulsation measurements were compared with an acoustic analysis, showing some discrepancy, especially at relatively high harmonics, mainly due to incorrect evaluation of the thermodynamic properties of high-pressure ethylene. In fact, in the LDPE process pressure range, isentropic exponent kv and compressibility factor Z can reach very high values, consequently affecting the calculation of the speed of sound.

A new acoustic modelling was developed to achieve better consistency with the measurements. Pressure-dependent kv and Z were taken into account and a sensitivity analysis of the most relevant valve parameters was performed.

Comparing the vibrations and pulsations spectra, once the MNF, compressor manifold arrangement and external loads are known, is fundamental to detect the origin of vibrations and how they are affected by pulsations.
Impact of Using ASME Section XI Code Case N-830 on Plant Heatup and Cooldown Pressure-Temperature Limit Curves for Pressurized Water Reactors
Authors: Carolan Alexandria , Mays Benjamin , Udyawar Anees , Hall J. Brian
Published: November 2019

Nuclear plant reactor pressure vessel heat-up and cool-down pressure temperature (P-T) limit curves are determined using ASME Section XI, Appendix G. ASME has adopted into ASME Section XI Appendix G the allowable use of the ASTM E1921 master curve fracture toughness based reference temperature (T0) to index the KIc curve. ASME Section XI Code Case N-830 allows the use of the KJc 95% lower bound master curve indexed using T0 directly. In ASME Section XI Appendix G, the equation RTT0 = T0 + 19.4°C, as an alternate RTNDT, shifts the KIc curve to approximate the KJc 95% lower bound master curve, however, the KIc exponential curve parameters are different. Thus, this paper evaluates the impact on plant heatup and cooldown pressure-temperature limit curves between the two ASME approved methods for typical pressurized water reactors (PWR). Different degrees of embrittlement are assessed to determine differences in the two approaches on reactor pressure vessel (RPV) beltline operating curves. Furthermore, in the proposed Revision 19 of Regulatory Guide 1.147, the US NRC has included a condition on the use of Code Case N-830 that prohibits the use of the current KIc equation in ASME Section XI Appendix G when these values are above the KJc lower bound 95% curve at temperatures below T0 − 64°C. This paper briefly discusses this NRC condition on the P-T limit curves.
The Influence of Multiaxial Stress Relaxation on Component Creep Damage Accumulation
Authors: Matev Nayden , Ainsworth Robert A. , Su Meini , Stevens Mark , Jappy Alan
Published: November 2019

Unless detailed inelastic analysis is utilised, high temperature codes base creep relaxation during a dwell period within a cycle on the start-of-dwell equivalent stress. The relaxation of the equivalent stress is then taken to be governed by a uniaxial creep law for the material being considered. Elastic follow-up is also included in such calculations. With this approach, only equivalent values of stress and creep strain rate are obtained and the stress multiaxiality is therefore assumed to remain at its initial value as the stress relaxes. Codes suggest that the stress drop is limited to a small fraction (typically 20%) of the initial equivalent stress to ensure that this assumption does not lead to significant inaccuracy. This paper reports creep relaxation results for a cruciform plate subjected to displacement-controlled biaxial loading. The initial biaxial loading ratio, the geometry of the cruciform plate and the value of the power in a power-law creep model are varied and these lead to variations in the elastic follow-up describing the creep relaxation. The biaxial stress ratio is generally found to change as relaxation occurs and a multiaxial ductility approach is used to evaluate the associated effect on creep damage accumulation. This is compared with the creep damage estimated by assuming relaxation is simply controlled by the equivalent stress with no change in multiaxial stress state during relaxation. For biaxial plane stress with one principal stress initially being negative, it is found that significant equivalent stress drops (up to about 40% of the initial value) can be allowed without the simplified equivalent stress approach becoming inaccurate. More care is required for positive stress biaxiality and the influence of multiaxial stress changes is found to depend on the initial stress biaxiality and the degree of elastic follow-up. The results will be used to propose improved guidance for simplified inelastic calculations.