bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the Temperature Effect on the Viscoelastic Responses of Flexible Risers
Authors: Liu Junpeng , Ma Jinsheng , Vaz Murilo Augusto , Duan Menglan
Published: November 2019

Mechanical behavior of flexible risers can be challenging due largely to its complex design generating strong nonlinear problems. Nonlinear material properties, as one of them, from polymer layers dominate the overall viscoelastic responses of flexible risers which may play an inevitable role on the global analysis in deepwater application. An alternative to predict the viscoelastic behavior comprising of the time domain and the frequency domain has been proposed recently by the authors (Liu and Vaz, 2016). Given the fact that polymeric material properties are temperature-dependent and that the temperature profiles in flexile risers vary continuously in both axial and radial direction, the temperature of the internal hydrocarbons must affect the viscoelastic responses. However, such phenomenon dose not draw much attention in previous studies. This paper presents an improved model for overcoming some drawbacks in the proposed model involving assumption of steady temperature distribution in polymer layer and no gap appearance between the adjacent layers. The computing method of model is developed by using a step by step test approach. Consequently, some important parameters like equivalent axial stiffness, contact pressure or gap between the near layers, and force-deformation relationship can be observed. Parametric studies are conducted on the axisymmetric viscoelastic behavior of flexible risers to study the role of input temperature and loading frequency. Results show that equivalent axial stiffness given by the improved model is smaller than before. It can also be found that the gap between metal layer and polymer layer appear easily and increases as time goes on.
Numerical Modelling of Net Motion in Waves and Current Using CFD
Authors: Martin Tobias , Kamath Arun , Bihs Hans
Published: November 2019

The structural and environmental challenges in the operation of marine fish cage structures, in particular in the open sea, can accurately be determined if the fluid dynamics in and around the whole system is studied. An important part of the system represents the porous net which encloses the fish. In this paper, a numerical model for the determination of the deformed shape of nets under consideration of hydrodynamic loads and elastic twines is elaborated. It is a quasi-static approach based on force equilibria at the knots and geometrical constraints. The missing time step restriction leads to an overall less costly computation. The fluid around the net is calculated using a two-phase CFD model. The focus of the research is on the calculation of fluid forces on the net and the analyses of the nets motion in current and waves.
The Wave Climate of the Southern Ocean
Authors: Young Ian R.
Published: November 2019

An analysis of the wind and wave climate of the Southern Ocean is provided based on a combination of more than 30-years of satellite altimeter data plus insitu buoy measurements at 5 locations in the Southern Ocean. The analysis shows that the Southern Ocean is a unique environment where there are strong winds year-round which blow over exceptionally long distances. This unique situation results in spectral forms which are not seen in any other oceanic basin.
Estimation and Comparison of Accuracy in Various Data Resolutions on Optimal Ship Routing Across the North Pacific Ocean
Authors: Sasa Kenji , Fujimatsu Takuya , Chen Chen , Shoji Ruri
Published: November 2019

The amount of maritime cargo has been increasing for several decades. However, most seafarers have been shifting from lifetime employment to temporary employment. This may result in the ships lacking the adept techniques of seafarers, which significantly increases the reliance and importance of operational support systems. There are many studies on optimal ship routing, but its accuracy has not been discussed sufficiently. Especially, the grid point value on the weather database is the most important factor to discuss regarding its accuracy. In the field of meteorology, these databases have been improved to include global data in recent decades. In this study, the simulation results are compared to know the influence to the accuracy if the spatial and time resolutions vary in each condition. Optimal ship routing is computed using the isochrone method, which is one of the major methods of route analysis. Numerical simulations are conducted for a container ship between Tokyo and Los Angeles, with the weather databases of National Centers for Environmental Prediction (NCEP) and National Oceanic and Atmospheric Administration (NOAA). It is known that there are no significant differences between each resolution setting. However, the optimal voyage routes are different if the ship avoids high waves or strong winds in any direction. The accuracy is more influenced by the maneuverability in rough seas than the spatial and time resolutions of the weather databases. Accordingly, optimal ship routing must consider the actual maneuvering and speed loss theories, besides the development of a meteorological database.
A Study of Hydrate Inhibition for Deepwater Gas Field Development
Authors: Yi Hualei , Hao Yun , Zhou Xiaohong
Published: November 2019

For deepwater subsea tie-back gas field development, hydrate tends to be formed in deepwater subsea production system and gas pipeline due to high pressure and low temperature. Based on the gas field A development, this paper studies the selection of hydrate inhibitors and injection points, i.e. different injection points with different inhibitors. Transient and steady flow simulations are performed using the OLGA software widely used for multiphase flow pipeline study in the world. The produced water flow rate affects the hydrate inhibition in case of well opening, including cases of different times with different water temperatures. This paper presents the calculation of the maximum inhibitor injection rate in the subsea pipeline by taking the whole production years into consideration. The measures on hydrate remediation are taken by quickly relieving the subsea pipeline pressure from wellheads and the platform according to different hydrate locations. Now more and more deepwater gas fields are developed in South China Sea and around the world. The experience obtained from the gas field A development will benefit the hydrate inhibition for future deepwater gas field development.
Experimental Study of Drillstring Dynamics Using a High-Speed Camera As a Non-Invasive Motion Sensor
Authors: Wiktorski Ekaterina , Khatibi Milad , Geekiyanage Suranga , Sui Dan , Time Rune W.
Published: November 2019

In the last decades, drilling industry has been developing solutions to overcome challenges that impede drilling of long directional wells as excessive friction, poor directional control, narrow drilling windows, etc. One of the problems that is identified, yet not solved is the drillstring vibrations. Drillstring vibrations result in low ROP, fatigue and failure of the drillstring elements and weakened wellbore integrity. They are often detected through surface symptoms, as large surface WOB fluctuations (axial vibrations), torque and RPM fluctuations (torsional vibrations), reduced ROP, pressure fluctuations, rig/top drive shaking, etc.

To control vibrations, a good understanding of basic mechanisms of vibrations initiation and propagation is required. Therefore, this paper aims at the experimental investigation of the drillstring dynamics using a small-scale drilling rig constructed at the University of Stavanger. The experimental drilling rig is equipped with a WOB surface sensor, which works as a strain gauge, as well as RPM and torque encoder and other sensors. For a small-scale system, measurements of the surface sensors represent the combined responses of the whole rig structure, not just the drillstring. Therefore, more information to show drillstring dynamics (displacements and frequencies) is desired, besides surface measurement.

This paper presents experiments designed to detect vibrations of the drillstring using a high-speed camera, which in this study serves as an along-the-pipe downhole sensor. The paper also provides the image-processing algorithm that was developed to extract the signal from the images, digitize and normalize it. The high-speed camera has proved to be an accurate and practically noise-free displacement sensor.

As a part of this study, analysis of the captured frequencies and decaying amplitudes (damping) was performed for both the high-speed camera and the load cells data. It helped to evaluate whether the surface sensors are able to provide sufficient information about the downhole vibrations. We have seen that in the case where the drillstring interacts with the wellbore, the downhole vibrations are reflected to the surface. However, when the string hangs freely, surface and downhole sensors measure responses from different parts of the system. These conclusions are mostly valid for small-scale vertical systems, however, can also be considered for drilling shallow vertical wells/top sections.
FIV Energy Harvesting From Sharp-Edge Oscillators
Authors: Tamimi Vahid , Armin Milad , Shahvaghar-Asl Selda , Naeeni Seyed Taghi Omid , Zeinoddini Mostafa
Published: November 2019

The relative incompetency of rectangular galloping excavators against conventional circular VIV harvesters is already known. In this experimental study, the hydroelastic energy performances of new right-angle isosceles triangular cylinder against circular, square and diamond cross-sections are investigated. The triangular cylinder displays VIV or galloping type of response in four different symmetrical and unsymmetrical configurations tested. The results show the distinct higher overall galloping energy performance of the triangular cylinder in Config. 2 among other VIV and galloping harvesters. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is employed to order the remaining tested cross-sections using the averaged and maximum values of the mechanical power and efficiency as criteria. The TOPSIS algorithm shows that the VIV diamond and circular harvesters stay at the second and third places of the energy performance, respectively. The preference value of the diamond and circular cross-sections are almost comparable but are less than half of that in Config. 2. In general, the sharp-edge cylinders display superior energy performance over circular cross-section. However, the axisymmetric circular cylinders, because of their omnidirectional performances, are more efficient in places with the varying flow direction.
Safe Operations of Bolted Connections in the Oil and Gas Industries
Authors: Langøy Morten A. , Hinderaker Rolf H. , Andersen Terje L.
Published: November 2019

The objective of this paper is to discuss the risk associated with fasteners used in the offshore industry. The intention is to suggest a way forward in establishing a robust system for management of fastener integrity on offshore installation, both topside and subsea, and thereby improve the safety level.

However, the large variation in design and use of bolted connections have to be analysed to identify the areas with the largest risk. Based on analysis of incidents reported to the Petroleum Safety Authority, Norway and analysis of industry standards and practices possible industry initiatives are identified.
Finite Element Analysis of the Effect of Twist on Chain Fatigue Performance
Authors: Jones Justin
Published: November 2019

Mooring chains may be installed with twist or become twisted during service. This paper describes an investigation of the effect of a range of twist angles on the fatigue life of studless chain through the use of detailed finite element analysis.

The analysis includes the local contact patch deformation and residual stress state that results from plasticity during the proof testing of the chain. The effect of high in-service tension resulting from storms that produces additional plasticity when the chain is loaded in the twisted state is also included. The change in fatigue life at the crown, inner bend and around the contact patch are assessed. Local to the contact patch the fatigue life calculation includes an assessment of the multiaxial stress state.

For small angles of twist the calculated fatigue life at the crown and around the contact increases and that at the inner bend sees a marginal reduction. At twist angles above 12 to 14 degrees per link the calculated inner bend and contact patch fatigue lives reduce markedly with increasing twist, but the crown fatigue life continues to increase.
Large Diameter Deepwater Gas Pipelines Subjected to Global Buckling Behavior
Authors: Antunes Bruno R. , Solano Rafael F. , Cardoso Carlos O.
Published: November 2019

In general, gas export pipeline designs have low restrictions concerning the flow assurance requirements, i. e., hydrate formation is not a great concern once processes in production platform facilities can significantly decrease the water content in the gas to be exported. Thus, these pipelines have only a small thickness of a single or multilayer anticorrosive coating and export gas at low temperatures. However, high pressures are required in order to overcome long distances and to increase the production flow rates.

Large diameter gas pipelines submitted to high pressures even with low associated temperatures can be susceptible to global buckling, mainly if the pipelines are simply rested on a seabed of low resistance. This scenario characterizes strictly the gas pipelines installed in Brazilian Pre-Salt fields, where currently a relevant amount of export lines is operating in these conditions. Post-installation and operating pipeline surveys have identified marks on seabed confirming the buckle formation in some gas pipelines. In addition, axial movements of end equipment (PLETs) have been also observed. These issues require at least a verification and confirmation of the assumptions and predictions made in detailed design phase.

This paper aims to present evaluations of the global buckling behavior of large diameter deepwater gas pipelines. Lateral buckles on very soft clayey seabed and displacements in ends and crossing locations are addressed in this work. Finally, numerical analyses confirm that gas pipelines structural integrity has not been jeopardized.
A Comparative Study of Mechanical Properties of Biodegradable PBSAT and PA Gillnets in Norwegian Coastal Waters
Authors: Su Biao , Moe Føre Heidi , Grimaldo Eduardo
Published: November 2019

This paper presents a comparative study of mechanical properties of biodegradable PBSAT (polybutylene succinate co-adipate-co-terephthalate) and conventional polyamide (PA) gillnets used in Norwegian fisheries. Field tests were performed to simulate abandoned, lost, or otherwise discarded fishing gear. Changes in mechanical properties of PBSAT and PA nets in two Norwegian coastal environments were studied. Samples of biodegradable PBSAT gillnets and PA gillnets were placed inside modified lobster pots at four different locations: two outside the island Hitra in the middle of Norway and two outside Tromsø in the north of Norway. For each pot, seawater temperature was logged each hour, and net samples were retrieved for analyses at 3 to 9 months intervals.

Tensile strength testing was performed to determine and compare mechanical properties of biodegradable and PA monofilaments and gillnets. Comparative analyses were conducted, aimed at investigating the different behaviors of biodegradable material and conventional PA material, and the possible influence of seawater temperature on the degradation process of biodegradable PBSAT gillnets. Reduced tensile strength and elongation at break, and a slight increase in stiffness was observed for both PA and PBSAT monofilaments after the field trial at Hitra, indicating degradation of both polymer materials. After 25 months immersion in seawater, the PBSAT gillnets exhibited a significant reduction of tensile strength due to seawater exposure (35%), and the tensile strength of PBSAT gillnets was then 26% lower than the average strength of the PA net samples.
Scaling of Pop-Ins During Brittle Fracture Testing
Authors: Coppejans O. J. , Walters C. L.
Published: November 2019

Measurement of the fracture toughness of steel is important for the assurance of the safety of ships and offshore structures, especially when these structures are made of thick sections and/or applied in cold environments. One key factor that will affect the determination of the fracture toughness is a pop-in, which is a short event in which unstable fracture is initiated and then self-arrests. If the pop-in is large enough, it will be used to calculate the fracture toughness. Pop-ins are believed to be the products of local brittle zones, which occur randomly at crack tips and have finite sizes. Fracture toughness testing codes have ways of determining whether a pop-in is critical (thus, identifying the maximum force and displacement to be used in the determination of the toughness of the material) or not important (thus, allowing for the test to proceed).

In an ongoing project on the use of small-scale fracture specimens to predict standard fracture toughness test results, we would like to know how pop-in acceptance criteria should be scaled for specimen size. It is expected that the physical size of the brittle zones that cause pop-ins is invariant of specimen size, meaning that the contribution of the pop-in will be proportionally more important for smaller specimens. An analytical method for relating the pop-ins on one specimen size to another specimen size is developed. This method is partially verified by observations on the size of a local brittle zone observed on a fracture surface and the effect of that pop-in on the force-displacement curve during a CTOD test. The analytical method showed that an equivalent pop-in for a small-scale specimen is indeed larger, but that the effect was subtle.
On the Use of Consumer-Grade Remotely Piloted Aircraft Systems for Monitoring Shallow Coral Reefs in Colombia: Case Old Providence Island
Authors: Lopera-Gil Manuela , Vásquez Rafael E. , Zuluaga Carlos A. , Zapata-Ramírez Paula A.
Published: November 2019

This work addresses the initiative to use consumer-grade Remotely Piloted Aircraft Systems (RPAS), known as Unmanned Aerial Vehicles (UAVs) or drones, as potential instruments for the evaluation and monitoring of shallow coral reefs in Colombia. This initiative started with the construction of an interdisciplinary team that includes institutions from academia, the Ministry of Defense, the Ministry of Environment and Sustainable Development, a marine surveying private company, and a German research center. The test was conducted inside the Marine Protected Area (MPA) of Old Providence; an island that is located at the Archipelago of San Andrs, Providencia and Santa Catalina, which includes the Seaflower Biosphere Reserve (the third largest true barrier reef in the world). Field data were acquired by using two DJI RPAS: Phantom 4 Pro and Mavic Air, and geo-referenced diving. In this work, we show the potential for using such technologies with a geometrically corrected mosaic of images of Crab Cay, a small cay located inside the MPA. This project is the first of its kind within the Seaflower Reserve and may support technology-based data collection, increasing the quality of information that can be useful to make important decisions regarding ocean space utilization. Additionally, obtained images will be shared for the benefit of local communities, other stakeholders, and visitors, in a manner that opens up science to broader society, promoting outreach activities and educational tool via photos and videos.
Estimating Extreme Waves in the Gulf of Mexico Using a Simple Spatial Extremes Model
Authors: Wada Ryota , Jonathan Philip , Waseda Takuji , Fan Shejun
Published: November 2019

We seek to characterize the behavior of extreme waves in the Gulf of Mexico, using a 109 year-long wave hindcast (GOMOS). The largest waves in this region are driven by strong winds from hurricanes. Design of offshore production systems requires the estimation of extreme metocean conditions corresponding to return periods from 1 year to 10,000 years and beyond. For extrapolation to long return periods, estimation using data for around 100 years from a single location will incur large uncertainties. Approaches such as spatial pooling, cyclone track-shifting and explicit track modeling have been proposed to alleviate this problem. The underlying problem in spatial pooling is the aggregation of dependent data and hence underestimation of uncertainty using naïve analysis; techniques such as block-bootstrapping can be used to inflate uncertainties to more realistic levels. The usefulness of cyclone track-shifting or explicit track modeling is dependent on the appropriateness of the physical assumptions underpinning such a model.

In this paper, we utilize a simple spatial statistical model for extreme value estimation of significant wave height under tropical cyclones, known as STM-E, proposed in Wada et al. (2018). The STM-E model was developed to characterize extreme waves offshore Japan, also dominated by tropical cyclones. The method relies on the estimation of two distributions from a sample of data, namely the distribution of spatio-temporal maximum (STM) and the exposure (E). In the current work, we apply STM-E to extreme wave analysis in Gulf of Mexico. The STM-E estimate provides a parsimonious spatially-smooth distribution of extreme waves, with smaller uncertainties per location compared to estimates using data from a single location. We also discuss the estimated characteristics of extreme wave environments in this region.
Pipeline Rockberm Design Principles for UHB Mitigation
Authors: Liu M. , Cross C.
Published: November 2019

Rockdumping may be necessary for pipeline UHB mitigation, crossings for separation, protection and stability. It is imperative that the structural reliability analysis for UHB is assessed with all aspects and factors taken into account to predict accurately the amount of rock and download required to ensure the integrity of pipelines. For UHB mitigation design, there are a number of analytical models available for download calculations to determine rockdump schedule.

This paper examines and highlights some fundamental issues and pitfalls for rockberm design with respect to UHB download assessment. The lateral breakout has been previously addressed by some engineers and researchers. The potential risk for pipe to breakout from the rockberm is studied herein focusing on the vertical direction due to upheaval load.

Based on the theoretical analysis and numerical FEA modelling, it is demonstrated that the common practice for rockbern design is not consistent resulting in unconservative rockdumping for UHB stability. Further design optimization can be compromised by lack of understanding of the failure mechanisms. Uplift resistance for stratified and layered soil types applicable for rock enhancement is also discussed and formulated. The design principle and rationale for selecting an appropriate rockberm profile and its sizing is proposed. Its effect on the UHB is illustrated by a detailed theoretical analysis and a series of numerical simulations with respect to pipeline dimensions.
Hydrodynamic Analysis of a Suspended Cylinder Under Regular Wave Loading Based on Computational Fluid Dynamics
Authors: Mucha Philipp , Robertson Amy , Jonkman Jason , Wendt Fabian
Published: November 2019

An investigation into the computation of hydrodynamic loads on a suspended cylinder in regular waves is presented. The primary goal was to perform a three-way validation of the loads between experimental measurements and simulations from two computational methods. Experimental measurements of the longitudinal in-line force on a cylinder suspended at a fixed position were available from the Offshore Code Comparison Collaboration, Continued, with Correlation (OC5) project, Phase Ia. These measurements were compared to computational fluid dynamics (CFD) simulations based on the solution of Reynolds-averaged Navier-Stokes (RANS) equations, as implemented in STAR-CCM+. The study encompassed a sensitivity analysis of the loads computed in STAR-CCM+ based on wave modeling, boundary conditions, turbulence modeling, and spatial and temporal discretization. The analysis was supplemented by results generated with the offshore wind turbine engineering software OpenFAST, based on a hybrid combination of second-order potential flow and viscous drag from Morison’s equation. The focus of the investigation was on the assessment of the accuracy of the computation of first- and higher-order hydrodynamic loads. Substantial differences were observed in the numerical prediction of the second and third harmonic force contribution. Local flow field analysis with CFD was applied to study the physics of wave run-up and diffraction dynamics to identify the causes.
Nonlinear Fourier Analysis Algorithm and Models for Water Waves in Terms of Surface Elevation, Amplitude Modulations
Authors: Osborne Alfred R.
Published: November 2019

This paper addresses two issues with regard to nonlinear ocean waves. (1) The first issue relates to the often-confused differences between the coordinates used for the measurement and characterization of ocean surface waves: The surface elevation and the complex modulation of a wave field. (2) The second issue relates to the very different kinds of physical wave behavior that occur in shallow and deep water. Both issues come from the known, very different behaviors of deep and shallow water waves. In shallow water one often uses the Korteweg-deVries that describes the wave surface elevation in terms of cnoidal waves and solitons. In deep water one uses the nonlinear Schrödinger equation whose solutions correspond to the complex envelope of a wave field that has Stokes wave and breather solutions. Here I make clear the relationships between the two ways of characterizing surface waves. Furthermore, and more importantly, I address the issues of matching the two types of wave behavior as the wave motion passes from deep to shallow water, or vice versa. For wave measurements we normally obtain the surface elevation with a wave staff, resistance gauge or pressure recorder for getting time series. Remote sensing applications relate to the use of lidar, radar or synthetic aperture radar for obtaining space series. The two types of wave behavior can therefore crucially depend on where the instrument is placed on the “ground track” or “field” over which the lidar or radar measurements are made. Thus the matching problem from deep to shallow water is not only important for wave measurements, but also for wave modeling. Modern wave models [Osborne, 2010, 2018, 2019a, 2019b] that maintain the coherent structures of wave dynamics (solitons, Stokes waves, breathers, superbreathers, vortices, etc.) must naturally pass from deep to shallow water where the nature of the nonlinear physics, and the form of the coherent structures, change. I address these issues and more herein. This paper is directed towards the development of methods for the real time measurement of waves by shipboard radar and for wave measurements by airplane and helicopter using lidar and synthetic aperture radar. Wave modeling efforts are also underway.
Evolution of the Stress-Induced Magnetic Field of Pipeline Steel due to Fatigue Loading
Authors: Bao Sheng , Zhao Zhengye , Luo Qiang , Gu Yibin
Published: November 2019

The objective of this research is to explore the correlation between piezomagnetic fields and cyclic loading in X80 pipeline steel. A series of stress-controlled fatigue tests were carried out, and the magnetic field variations were recorded simultaneously during the whole loading process. The results demonstrate that the fatigue life of the investigated steel can be divided into three stages. The reversal points that appear during the loading and unloading processes can be used as new parameters to reflect the fatigue state and estimate the fatigue life.
Impact of a Plate on an Asymmetric Water Wedge
Authors: Wen Xueliang , Liu Peiqing , Qu Qiulin , Liu Qingchuan
Published: November 2019

The impacts of a plate on an asymmetric water wedge with a constant speed and with varying speed are studied in this paper by considering the fluid to be incompressible, inviscid, weightless and with negligible surface tension effect and the flow to be irrotational. We derive the analytical solution for the impact with a constant speed with the help of Wagner’s function and Schwarz-Christophel mapping technique, and then proceed the numerical process given by following an iterative method. The verification is conducted by comparing the profile of free surface and the pressure distribution predicted by the present method and the published data. The impact with varying speed is first studied by VOF method and compared with the impact with a constant speed. An approximate solution is provided for the impact with speed that satisfies a power law of time based on the CFD results from VOF method. The approximate solution can provide an explicit expression for the pressure that is acting on the plate, which can describe the effects of the changing impact speed and the acceleration of plate.
Situation Awareness of Autonomous Ship Navigation in a Mixed Environment Under Advanced Ship Predictor
Authors: Perera Lokukaluge P. , Murray Brian
Published: November 2019

Autonomous ship navigation in a mixed environment, where remote-controlled, autonomous and manned vessels are interacting, is considered. Since these vessels can have various encounter situations, adequate knowledge on such situations should be acquired to take appropriate navigation actions. That has often been categorized as situation awareness in a mixed environment, where appropriate tools and techniques to extract the respective knowledge on ship encounter situations should be developed. The collision risk assessment procedure has an important role in the same knowledge and that can eventually be used towards the respective collision avoidance actions. Hence, possible ship collision and near-miss situations can be avoided by both humans as well as systems due to their actions. Ship collision avoidance actions are regulated by the International Regulations for Preventing Collisions at Sea 1972 (COLREGs) in open sea areas and additional local navigation rules and regulations can also enforce especially in confined waters and maritime traffic lanes. It is expected that the COLREGs and other navigation rules and regulations will be interpreted by both humans as well as systems in future vessels and those interpretations will be executed as collision avoidance actions by the respective vessels in a mixed environment. Adequate understanding on situation awareness should be achieved to overcome possible regulatory failure due to human and system decisions in these situations. Hence, this study focuses on identifying such challenges in future ship encounters with possible solutions to improve situation awareness in a mixed environment as the main contribution.
Application of the MCC Model on 2-D Finite Element Analyses for the Assessment of Pipe-Soil Lateral Response
Authors: Thomaz Tianna Bloise , Carneiro Daniel , Bruno Ellwanger Gilberto , Sant’Anna do Nascimento Leonardo
Published: November 2019

The assessment of the pipe-soil interaction is an area of continuous research, either by the application of small- and full-scale tests in the attempt to reproduce accurately the interaction of the pipelines and the soil, or by the development of sophisticated numerical simulation models accounting for different sources of nonlinearities.

Motivated to investigate the interaction between subsea pipelines and the soil, with focus in the response under lateral loading, 2-D finite element numerical simulations have been developed applying soil plasticity mechanisms through the extended maximum distortion strain energy criteria [1] and critical state concept [2]. The modified-cam-clay MCC model has been adopted to simulate the soil behavior in large deformations, aiming to numerically reproduce site conditions for selected pipelines ranging from 12 in to 18 in.

The results are presented in terms of the lateral force-displacement curves for numerically representative drained and undrained cases. For the simulations investigated in this work, the agreement of the numerical results with the analytical breakout lateral resistances obtained from the SAFEBUCK guideline [3] formulations have been confirmed for cases where the ratio of initial pipe embedment and pipe diameter is below 0.4.
Enhanced Cement Composition for Preventing Annular Gas Migration
Authors: Kwatia George , Al Ramadan Mustafa , Salehi Saeed , Teodoriu Catalin
Published: November 2019

Cementing operations in deepwater exhibit many challenges worldwide due to shallow flows. Cement sheath integrity and durability play key roles in the oil and gas industry, particularly during drilling and completion stages. Cement sealability serves in maintaining the well integrity by preventing fluid migration to surface and adjacent formations. Failure of cement to seal the annulus can lead to serious dilemmas that may result in loss of well integrity.

Gas migration through cemented annulus has been a major issue in the oil and gas industry for decades. Anti-gas migration additives are usually mixed with the cement slurry to combat and prevent gas migration. In fact, these additives enhance and improve the cement sealability, bonding, and serve in preventing microannuli evolution. Cement sealability can be assessed and evaluated by their ability to seal and prevent any leakage through and around the cemented annulus. Few laboratory studies have been conducted to evaluate the sealability of oil well cement.

In this study, a setup was built to simulate the gas migration through and around the cement. A series of experiments were conducted on these setups to examine the cement sealability of neat Class H cement and also to evaluate the effect of anti-gas migration additives on the cement sealability. Different additives were used in this setup such as microsilica, fly ash, nanomaterials and latex.

Experiments conducted in this work revealed that the cement (without anti-gas migration additive) lack the ability to seal the annulus. Cement slurries prepared with latex improved the cement sealability and mitigated gas migration for a longer time compared to the other slurries. The cement slurry formulated with a commercial additive completely prevented gas migration and proved to be a gas tight. Also, it was found that slurries with short gas transit times have a decent potential to mitigate gas migration, and this depends on the additives used to prepare the cement slurry.
Environmental Regeneration for a Small-Scale Beach “Heda-Mihama Project”
Authors: Tabeta Shigeru , Okamoto Ken , Kato Takayoshi , Hisamatsu Rikito , Muto Hiroaki , Hino Akinori , Murai Motohiko , Ito Sho , Kitazawa Daisuke , Kinoshita Takeshi
Published: November 2019

In 1950’s and 1960’s, Mihama beach in Heda Bay located on western coast of Izu peninsular had been famous for the richness in shell fauna, for example, about 400 species including rare ones were collected. In 2000’s, however, the impoverishment of ecosystem function has become considerable, which led us to project the investigation on the origin and restoration. The authors carried out field survey in 2007–2008 and found that the impoverishment of Mihama is derived not from surface water but from the benthic environment. The measured water current at the site was quite small, which indicated the water exchange was very weak. It must be one of the main causes of unfavorable benthic environment. Thus environmental regeneration plans for Mihama was proposed in which the pears blocking the water current be removed. In order to assess the effect of proposed plans, simulation-based habitat evaluation was conducted. A three-dimensional hydrodynamic and sediment transport models were developed to reproduce the characteristics of currents and predict the sediment size around Mihama. For the assessment of the ecological status, HEP (Habitat Evaluation Procedure) was employed, in which one of the typical species of bivalves is chosen as a target species. Water depth, sediment size, friction velocity at the bottom, etc. were considered as the environmental factors for the target species. The suitability indices (SI) for each environmental factors were calculated by using the results of hydrodynamic and sediment transport simulations. By using the developed scheme, total habitat unit was evaluated for the proposed regeneration plans and compared to that without countermeasures. It was predicted that the removal of the piers will improve the habitat condition in the target site. Based on the proposal by the authors, a water pathway under the pier was built in 2009. The authors conducted field survey again in 2014 and confirmed that the benthic environment has been improved.
Numerical Study on Vortex-Induced Motions of Semisubmersibles With Three Columns With Different Sections Types
Authors: Tian Chenling , Xiao Longfei , Liu Mingyue , Yang Lijun , Liu Jing
Published: November 2019

Vortex-induced motion (VIM) phenomenon is a great challenge for design and operation of offshore structures subjected to ocean flow. Semi-submersibles with three columns are often applied to the field of wind turbine, suffering VIM motions probably. In recent years, it is showed that many factors have more or less influence on VIM of platforms. A comparison of circular columns with square columns on VIM characteristics of three-column semisubmersibles is carried out using the detached eddy simulation (DES) method via Star-ccm+ software. This paper analyzes motions in the transverse direction and yaw, as well as fluid forces including drag force and fluctuating lift force. The results show that transverse amplitudes of semisubmersible with three square columns are much lower than those of semisubmersible with three circular columns at all incidences. Besides, the authors conclude that the semisubmersible with three square columns do not experience obvious resonance behavior, which is different from the semisubmersible with three circular columns. Besides, galloping phenomenon occurred at large reduced velocities at 0°-incidence for the semisubmersible with three square columns, which is likely not induced by lift force directly. Meanwhile, in these cases, yaw amplitudes are also larger than the others. This may be due to the galloping behavior, which is just a conjecture.
Numerical Study on the Dynamical Characteristic and Impact Force Between Vessel With Rake Bow and Bridge Pier
Authors: Xu Ming Cai , Zhang Zi Xuan , Zhang Xiao Qiang , Pan Jin , Huang Yi Fei
Published: November 2019

The possibility of collisions between vessels and bridges has an unavoidable increase, which may cause significant economic losses and sometimes even casualties. The finite element method is used to simulate the impact process between the vessel with raked bow and bridge pier. The influence of parameter on the structural response and impact force is discussed, including the impact velocity, angle, mass of vessel, and the shape of bridge. The relationship of collision force and energy of impact vessel is investigated. It is found that the collision energy shows a quadratic growth trend with the increase of vessel velocity.
Numerical Simulation of Container Stacks Dynamics Under Typical Motion Excitation
Authors: Li Chuntong , Wang Deyu , Liu Jiaqi
Published: November 2019

Present regulation and norms for securing equipment are calculated based on static strength analysis ignore the dynamic situations faced by containers during maritime transportation, and the event of container loss still occurs. This research aim to investigate the dynamic behavior of container stack under typical motion excitations simulating real ocean conditions. A two-tier scaled model of a 20-ft ISO freight container were built based on scaling law. The research process is divided into three stages. The first stage: establish a full-scale 20-ft container mode, and obtain characteristic information such as mass and stiffness through finite element analysis. In the second stage, the multi-objective optimization algorithm is used to establish the scale model of the container, and the scale model of the design is verified. In the third stage, the finite element method is used to further understand the influence of each design variables on the dynamic response of container stack. Under different motion excitations, the influence of each basic variables on the structural response and the load change on the critical points of the structure are determined. Meanwhile, the results of this study also show that the mathematical model constructed is effective and can reasonably predict the actual situation of container stacks stored on the ship’s deck.
Dynamic Response of Spar Wind Turbine Moored by Dynamic Catenaries Under Random Wind and Wave Loads
Authors: Li Yilun , Guo Shuangxi , Kong Yue , Chen Weimin , Li Min
Published: November 2019

As offshore wind turbine is developed toward larger water depth, the dynamics coming from structural and fluid inertia and damping effects of the mooring-line gets more obvious, that makes the response analysis of the large floating wind turbine under wind&wave load more challenging. In this study, the dynamic response of a spar floating wind turbine under random wind and wave loads is examined by the modified FEM simulations. Here an integrated system including flexible multi-bodies such as blades, tower, spar and mooring-lines is considered while the catenary dynamics is involved.

The dynamic restoring performance of the catenary mooring-line is analyzed based on the vector equations of 3D curved flexible beam and its numerical simulations. Then the structural responses, e.g. the top tension, structural displacements and stress of the tower and the blade, undergoing random wind&wave loads, are examined. Morevoer, the influences of the catenary dynamics on its restoring performance and the hysteresis behavior are presented. Our numerical results show: the dynamics of mooring-line may significantly increase the top tension, and, particularly, the snap tension could be more than 3 times larger than the quasi-static one. Moreover, the structural response under random wind&wave load gets smaller mainly because of the hysteresis effect coming from the mooring-line dynamics. The floating body displacement at surge frequency is around 20% smaller, and the tower root stress at bending frequency is about 30% smaller than the quasi-static values respectively.
Second-Order Responses of a 10 MW Floating Wind Turbine, Considering the Full QTF
Authors: Cao Qun , Xiao Longfei , Guo Xiaoxian , Liu Mingyue
Published: November 2019

Second-order components of wave loads acting on the floating foundation for wind turbines may induce severe resonance and lead to fatigue damage at natural frequencies of structures. In this study, the INNWIND.EU Triple-Spar and the DTU 10 MW Reference Wind Turbine were simulated by utilizing software FAST to obtain the second-order responses of the floating wind turbine under selected steady winds with collinear random waves. Low-frequency responses at surge and pitch natural frequencies dominated the response spectra, which were underestimated by the first-order numerical model. A response peak appeared in tower-top motion spectrum in vicinity of the first-order fore-aft vibration frequency of the tower when the sum-frequency wave effects were considered. The second-order high-frequency responses arose when the full QTF was utilized, compared to results with Newman approximation. Different operating conditions with varying wind speeds, wave periods, significant wave heights and wave directions were selected to conduct the sensitivity study of the second-order responses.
Numerical Simulation of Water Wave Propagation Over Porous Slope Bottom by Using Two-Domain Method
Authors: Min Eun-Hong , Koo Weoncheol
Published: November 2019

This study aims at the numerical analysis of wave characteristics when a wave propagates on the porous slope seabed. Numerical wave tank technique was developed using boundary element method with constant panels on the boundary. The fluid was satisfied with potential flow conditions and Darcy’s law was applied for porous intersection. Two computational domain method, which consists of fluid and porous domains, was used to simulate the propagating waves over a sloped seabed having a permeability. To consider fluid-porous boundary interaction, three-step boundary value problems were calculated. The wave amplitude decreased along the free surface as the wave propagated over a sloped bottom. The wave reflection and transmission by subsea structures were also analyzed.
Experimental Study on the Motion of a Flexible Hose Net Used in Automated Net-Hauling System
Authors: Li Yue , Mizukami Yoichi , Yoshida Takero , Li Qiao , Han Jialin , Kitazawa Daisuke
Published: November 2019

In the set-net fishery, large amount of manpower is needed for hauling the box chamber to harvest fish. With aging problem and labor insufficiency, the labor-intensive net-hauling method faces the problems of lower production, lower efficiency and higher operational risk. An automated net-hauling system using the flexible hose net which is installed in the box chamber is being developed to solve such problems. With air injected from one edge of the hose net, the hoses are inflated and the buoyancy force increases, the net floats up gradually, cornering the fish in the other edge. To corner and harvest the fish efficiently and safely, the deformation and the motion parameters of the hose net are of significance. This paper presents the results of the water tank experiment using 1/6 scale model, which was conducted to analyze the deformation of the hose net with different volumes of air in, the time spent for floating up and sinking down and the average velocities of sinking and floating processes. The results showed that when the attached weight reached 42.5% of the maximum buoyancy force of the hose net, the net could float up gradually in an ideal form and sink down smoothly through natural exhaust and stretched on the bottom of the water tank. The time spent and average velocities in floating up and sinking down processes varied with air pressure and air flow rate, making it possible to control the motion of the hose net by adjusting the air flow in practical operation.