bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Analysis of In-Line Interaction of Closely Spaced Cylinder Arrays in Random Waves
Authors: Lu Jiangnan , Niedzwecki J. M.
Published: December 2020

Closely spaced cylinder arrays are widely used in offshore platform designs. When subject to random waves and currents, their interactive response behavior is very complicated and perhaps beyond the ability of direct analytical formulations to model their motions. In this study extremal statistics methods were utilized to analyze model basin data that investigated the response behavior of in-line paired and triple deep-water cylinder arrays. The cylinder models used in the model basin experiments were constructed with an ABS outer plastic shell that surrounded an inner steel wire core that could be pretensioned. The cylinder model diameter ratio of the outer shell to steel wire was 4.25 with a slenderness ratio of approximately 1300. The cylinder arrays were pretensioned on the top side and were tested varying pitch to diameter ratios of 3.0, 4.4, and 8.75. The random sea states were simulated using a JONSWAP spectrum. The response time series were investigated using generalized extreme value (GEV) distributions that were fitted to the block maxima that represented the maximum in-line relative displacement between two adjacent tendons. The most appropriate models were selected by comparing their goodness of fit via the Anderson-Darling (AD) test criterion with special attentions paid to their performance in fitting the upper tail of the distribution. The selected models were then used to predict threshold-crossing probabilities of the cylinder array relative response behavior. Both tabular and graphical interpretations of the findings are presented and discussed.
Flow-Induced Vibration Screening of a Thermoplastic Composite Pipe Water Injection Jumper
Authors: Pontaza Juan P. , Nadathur Varadarajan , Rosche John L.
Published: December 2020

An active subsea field in the Gulf of Mexico has adopted a thermoplastic composite pipe (TCP) water injection jumper for its waterflood upgrade. The TCP spool is lightweight and flexible — relative to the traditional steel-only spool segments used in subsea jumpers. As such, the flow-induced vibration (FIV) threat from internal fluid flow must be assessed for the intended service. A three-tiered approach is used to assess the level of FIV threat expected in this TCP subsea jumper application. A high-level screening based on widely used industry guidelines indicates a high susceptibility to FIV fatigue failure for the steel product in the jumper, with no applicability to the TCP material. A comprehensive screening based on structural finite element analysis and computational fluid dynamics shows that the vibration levels and stress cycling due to FIV will be acceptable for the intended water injection application and a 30-year design life, when adopting a factor of safety of 10 for subsea service.
An Efficient Method for Hydrate Plugging Prevention During Deep-Water Gas Well Testing
Authors: Zhang Jianbo , Wang Zhiyuan , Lou Wenqiang , Duan Wenguang , Fu Weiqi , Yin Bangtang , Sun Baojiang , Liu Jian
Published: December 2020

Hydrate plugging is an important factor affecting the safety and efficiency of flow assurance. Current prevention methods for hydrate plugging are costly or environmentally unfriendly or inefficient. In this work, an efficient method to prevent hydrate plugging during deep-water gas well testing was put forward, which is achieved by reasonably changing the testing orders of different gas production rates. The deposited hydrates in the tubing under low testing rates will be decomposed under high rates to reduce the risk of hydrate plugging without hydrate inhibitor injection. A case study is carried out to investigate the applicability of this method. The results show that the maximum dimensionless thickness of hydrate deposit reaches 68.14% under the conventional testing order, but decreases to 33.59% by using the proposed method. It is indicated that the proposed method can obviously decrease the risk of hydrate plugging without using hydrate inhibitor injection. Hence, the proposed method is a more economical and environmentally friendly method for hydrate plugging prevention, which can be applied as an alternative to the present prevention methods during deep-water gas well testing.
A Bayesian Machine Learning Approach for Efficient Integrity Management of Steel Lazy Wave Risers
Authors: Hejazi Rasoul , Grime Andrew , Randolph Mark , Efthymiou Mike
Published: December 2020

In-service integrity management (IM) of steel lazy wave risers (SLWRs) can benefit significantly from quantitative assessment of the overall risk of system failure as it can provide an effective tool for decision making. SLWRs are prone to fatigue failure within their touchdown zone (TDZ). This failure mode needs to be evaluated rigorously in riser IM processes because fatigue is an ongoing degradation mechanism threatening the structural integrity of risers throughout their service life. However, accurately evaluating the probability of fatigue failure for riser systems within a useful time frame is challenging due to the need to run a large number of nonlinear, dynamic numerical time domain simulations.

Applying the Bayesian framework for machine learning, through the use of Gaussian Processes (GP) for regression, offers an attractive solution to overcome the burden of prohibitive simulation run times. GPs are stochastic, data-driven predictive models which incorporate the underlying physics of the problem in the learning process, and facilitate rapid probabilistic assessments with limited loss in accuracy.

This paper proposes an efficient framework for practical implementation of a GP to create predictive models for the estimation of fatigue responses at SLWR hotspots. Such models are able to perform stochastic response prediction within a few milliseconds, thus enabling rapid prediction of the probability of SLWR fatigue failure.

A realistic North West Shelf (NWS) case study is used to demonstrate the framework, comprising a 20” SLWR connected to a representative floating facility located in 950 m water depth. A full hindcast metocean dataset with associated statistical distributions are used for the riser long-term fatigue loading conditions. Numerical simulation and sampling techniques are adopted to generate a simulation-based dataset for training the data-driven model. In addition, a recently developed dimensionality reduction technique is employed to improve efficiency and reduce complexity of the learning process.

The results show that the stochastic predictive models developed by the suggested framework can predict the long-term TDZ fatigue damage of SLWRs due to vessel motions with an acceptable level of accuracy for practical purposes.
Numerical Study on Torsional Behavior of Carbon Steel-Concrete-Stainless Steel Double-Skin Tube (DST)
Authors: Wang Fa-Cheng , Xie Wen-Qi , Han Lin-Hai
Published: December 2020

One type of submarine composite pipeline structure, with carbon steel-concrete-stainless steel (CCS) double-skin tube (DST), was introduced in this paper. This composite pipeline was expected to make optimal use of the three types of the materials, and provide significant structural and internal corrosion resistance. During installation and service stage, submarine pipelines may experience significant torsion effects. Global response of the system depends on both the behavior of each constituent part and interactions between them. In this paper, an interaction model considering the friction and the cohesive force between the steel tube and the concrete is introduced, and a finite element model of the submarine pipeline under torsion is established by using this interaction model. The developed finite element model was verified through the comparisons between the numerical and experimental determined results, in terms of torque rotation angle histories, stiffness and ultimate torque. The results show that the ultimate strength and stiffness of the model considering cohesive force are increased by 4.6% and 11.9% respectively compared with the model only considering friction force.
Finite Element Analysis of Trawl Pull-Over Behaviour of Pipe-in-Pipe With Residual Curvatures
Authors: Yu Yi , Norland Kristian
Published: December 2020

Subsea 7 is currently planning for the installation of PiP flowlines in the Norwegian Sea. A case study has been performed for a 8 × 12in PiP to be installed in a water depth between 320 m to 420 m. Fishing activities are frequent in this area. Therefore, the integrity of the pipeline in case of trawl pull-over must be checked. It is found that pipelines with residual curvatures could behave very differently from pipelines without residual curvatures when they are pulled over by trawl gear. However, the effect of residual curvature on pull-over resistance capacity of rigid pipelines has not been mentioned in DNVGL-RP-F111 [1]. Therefore, an optimised methodology involving FE analyses and Monte Carlo simulation has been used in this project to check the integrity of the pipe-in-pipe flowline for the trawl pull-over load case.

This paper focuses on the FE analyses of the pipe-in-pipe flowline pulled over by trawl gear. The related Monte Carlo simulation has been discussed elsewhere [2]. To understand in detail the behaviour of the pipeline with trawl pull-over loading, the pipeline was modelled using a combination of beam, shell and brick (solid) elements. The advantage of the model was demonstrated by comparing output from the model with corresponding output using beam elements. The effects of some result-sensitive parameters were studied, which include centralizer location, pressure, trawl contact area and wall thickness. Special attention was paid to these parameters because their effects are not able to be captured with the normal beam element. Finally, the impact of residual curvatures on the trawl pull-over behaviour was studied. It was found that the pipeline pull-over resistance capacity is sensitive to residual curvature direction and contact location, but not sensitive to RC spacing and RC shape. Based on the advantage of this analysis methodology, it is believed to be a good option for pipeline trawl pull-over analysis, especially with complex pipeline configuration.
Long-Term Analysis Applied to Mooring Systems Design
Authors: Seabra Pedro , Sagrilo Luis Volnei Sudati , Esperança Paulo
Published: December 2020

Nowadays, the most used methodology to predict line tensions is the short-term coupled analysis, where the mooring system responses are obtained by a time-domain analysis for only some specific design combinations of extreme environmental conditions. This mooring analysis demands certain considerations and it is not the best way to obtain the offshore structure responses. The advances in both quantity and quality of collected environmental data and the increase of the computers processing power has enabled to consider the approach of more accurate long-term methodologies for mooring systems design. This paper proposes a numerical/computational procedure to obtain the extreme loads (ULS) acting on offshore platforms’ mooring lines. The work is based on the methodology of long-term analysis, employing a 10-yr long short-term environmental dataset of 3-h sea-states, where each short-term environmental condition is composed of the simultaneously observed environmental parameters of wave (sea and swell), wind and current. The methodology is applied to the analysis of three different mooring systems: a) spread-moored FPSO, b) Semi-Submersible platform and c) turret-moored FPSO. The Bootstrap approach is employed in order to take into account the statistical uncertainty associated to the estimated long-term most probable extreme response due to the limited number of short-term environmental conditions. The work was carried out using Dynasim software [1] to generate the time domain tension time series, which were later post-processed by using computational codes developed with Python software. Longer short-term numerical simulations lengths than the short-term period (3-h) have been investigated in order to understand the influence of this parameter on the final extreme long-term top tensions.
Effect of Hydrophobic Iron Oxide Nanoparticles on the Properties of Oil Based Drilling Fluid
Authors: Alvi Muhammad Awais Ashfaq , Belayneh Mesfin , Fjelde Kjell Kåre , Saasen Arild , Bandyopadhyay Sulalit
Published: December 2020

In recent years, nanoparticles (NPs) have shown the potential to improve the performance of oil well fluids significantly. Several studies have reported the ability of NPs to produce improved properties of both water and oil-based drilling fluids.

In this paper, hydrophobic iron oxide NPs were synthesized by thermal decomposition of iron pentacarbonyl in an inert atmosphere, and its performance was tested in the oil-based drilling fluid with 90/10 oil to water ratio (base fluid). Oil-based drilling fluids treated with nanofluids were formulated by adding 0.5 wt. % and 1.0 wt. % iron oxide NPs in hexane solution to the base drilling fluid.

The base fluid and the nanofluid treated drilling fluids were evaluated by characterizing their rheological properties at different temperatures, viscoelastic properties, lubricity, filtrate loss, static & dynamic settling, and separation properties.

Results showed that 0.5 wt. % iron oxide dispersed in hexane reduced the HPHT filtrate loss by 70%, filter cake thickness by 55%, and the coefficient of friction by 39%. Moreover, the nanofluid based drilling fluid reduced the free oil layer caused by syneresis during aging at high temperature by 16.3% compared to the base fluid.

This study has shown that hydrophobic iron oxide NPs have the potential to improve the properties of oil-based drilling fluid.
Ship-Wave Impact Generated Sea Spray: Part 2 — Formulating Spray Frequency
Authors: Mintu Shafiul A. , Molyneux David , Colbourne Bruce
Published: December 2020

In certain, but not all, circumstances a cloud of spray forms after a wave impacts a ship. The frequency of spray events affects the icing process. Previous spray frequency formulas are derived empirically from field observations considering only the ship’s forward speed and oceanographic conditions. The significance of various degrees of ship motions on the spray frequency is ignored. However in reality, the interrelationships of heave and pitch motions under wave actions together with surge motion determine the number of spray events that a ship may experience in a given period of time.

This paper introduces a theoretical model for estimating the frequency of sea spray considering ship motions. Ship motions can be easily estimated by strip/panel methods. However, in this work, the aim was to develop a simple framework for a quick estimate of spray frequency. The model inputs are, therefore, restricted to ship’s principal particulars, its operating conditions, and the environmental conditions. The wave-induced motions are estimated by semi empirical analytical expressions. A novel spray threshold is developed to keep the deck wetness frequency separated from the spray frequency. The proposed spray frequency formula is validated against available full-scale field measurements from a Russian fishing vessel, MFV Narva, and reasonable agreement is found. Limitations of previous empirical formulas are also discussed.
A Comparative Study of Laminar-Turbulent Displacement in Eccentric Annulus Under Imposed Flow Rate Conditions
Authors: Foolad Yasaman , Bizhani Majid , Frigaard Ian
Published: December 2020

In this paper, we present and discuss an experimental study of fluid-fluid displacement in a fully eccentric horizontal annulus. Experiments were designed to simulate turbulent displacing flows, and the results are used to investigate the displacement processes in terms of interface dynamics and displacement efficiency. It is widely believed that turbulent flows are more efficient at displacement, but it is not always clear under what conditions this comparison is made. A set of experiments was conducted to investigate the role of flow regime under a constant imposed flow rate in the absence of any stabilizing buoyancy effect (i.e. iso-density fluids). Carbopol solutions are displaced with various concentrations of Xanthan gum, to simulate a drilling mud displaced by a spacer fluid. The flow regime of the displacing fluid spans from laminar to fully turbulent flow regimes. The displacement tests are all unsteady in a sense that wide-gap velocity is always faster than that of the narrow-gap. The displacement flows and interface dynamics are captured using optical techniques, and the images are post-processed to ascertain the displacement efficiency, interface velocity and elongation. We conclude with a discussion on the significance of outcomes achieved in this study, and also limitations of the experimental technique.
Numerical Simulation of the Domino Effect of Mooring System Failure for an Aquaculture Net Cage Under Waves and Currents
Authors: Tang Hung-Jie , Yang Ray-Yeng , Wen Tzu-Chieh , Yeh Po-Hung , Huang Chai-Cheng
Published: December 2020

Up to date, the mooring system failure of aquaculture net cage remains a continuing problem, especially the domino effect, which often leads to huge economic losses. Thus, this study aims to investigate the domino effect of a mooring system of a net cage under waves and currents. In this study, a time-domain numerical model based on the Morison equation and the lumped mass method is applied. A full-scale net cage system widely used in a local sea area is adopted. A 50 years return period waves with a strong following current is considered to be the design condition. It can be expected that the tension on the remaining upstream anchor increases dramatically when an upstream anchor is lost. Then, the domino effect occurs if the maximum tension on the remaining anchor exceeds its design condition. Therefore, in this simulation, the initial failure is considered to be a man-made event at a preset time, but the rest failures are resulted from exceeding the breaking strength of a rope. Both the current-only condition and the wave-current condition have been examined. The results including mooring line tension, volume reduction coefficient and rigid body motion are discussed. In addition, the results show that the failure sequence of anchor is different between the current-only condition and the wave-current condition.
Path Following Control of Autonomous Underwater Vehicle Using Nonlinear Model Predictive Control
Authors: Taniguchi Tomoki , Umeda Jun , Fujiwara Toshifumi , Kim Kangsoo , Sato Takumi , Inaba Shogo
Published: December 2020

The path following control of an AUV considering arrival times at waypoints is proposed in this paper. The temporal constraint is considered by adding the surge velocity and the nominal thrust force as reference trajectory in the objective function of the nonlinear model predictive control (NMPC). The proposed control strategy uses fewer reference variables than conventional trajectory tracking problems. The simulated results of the proposed control strategy are compared to the NMRI Cruising AUV#4 actual dive data. The simulated arrival times of waypoints were matched well to the measured data. Two guidance laws, the line of sight with lookahead-based steering law and the pure pursuit guidance law, are also applied to NMPC to determine reference yaw angle.
Numerical Study on the Slamming Impact of Stiffened Flat Panel Using ICFD Method: Effect of Structural Rigidity on the Slamming Impact
Authors: Yamada Yasuhira , Takamoto Kota , Nakanishi Toru , Chong Ma , Komoriyama Yusuke
Published: December 2020

In order to preliminary investigate structural response of stiffened panel due to slamming impact, two series of fluid structure coupling analysis is carried out using a new fluid structure interaction (FSI) methodology of Incompressible Fluid Dynamics (ICFD) [1]. ICFD is the method where structure and fluid are modeled as both Lagrange methods.

Firstly, slamming impact of a sphere is analyzed with ICFD and SPH methods respectively and compared with experimental and analytical results. Acceleration, slamming force and pressure are compared and discussed in detail.

Secondary a fixed stiffened flat panel of offshore structure subjected to slamming impact is investigated as a part of the ISSC II.1 benchmark study. Effect of mesh size is investigated. Analysis results are compared with existing ALE method [1] as well as other results within the framework of ISSC II.1 benchmark study.

In both studies, structure is modeled by elastic-plastic and by rigid respectively. By comparing these two results, effect of structural rigidity on the slamming pressure as well as slamming force is investigated.
Collapse Resistance Under Combined External Pressure and Bending Deformation of Coated Linepipe
Authors: Sakimoto Takahiro , Tajika Hisakazu , Handa Tsunehisa , Murakami Yoshiaki , Igi Satoshi , Kondo Joe
Published: December 2020

As offshore pipeline projects have expanded to deeper water regions with depths of more than 2 000 m, higher resistance against collapse by external pressure is now required in linepipe. Collapse resistance is mainly controlled by the pipe geometry and compressive yield strength. In UOE pipe, the compressive yield strength along the circumferential direction changes dramatically due to tensile pre-strain that occurs in pipe forming processes such as the expansion process. In order to improve the compressive yield strength of pipes, it is important to consider the Bauschinger effect caused by pipe expansion. As the mechanism of this effect, it is understood that internal stress is generated by the accumulation of dislocations, and this reduces reverse flow stress. Compressive yield strength is also changed by the thermal cycle associated with application of fusion-bond epoxy in pipe anti-corrosion coating by induction heating. In the typical thermal heat cycle of this coating process, the maximum heating temperature is from 200 °C to 250 °C. In this case, compressive yield strength increases as an effect of the thermal cycle, resulting in increased collapse resistance. Thus, for deep water application of UEO linepipe, it is important to clarify the conflicting effects of the Bauschinger effect and the thermal heat cycle on compressive yield strength. During installation of deep water pipelines by a method such as J-lay, curvature is imposed on the pipe axis, but the circumferential bending that leads to ovalization is determined by the interaction of the curvature of bending deformation. This bending deformation decreases collapse resistance. The interaction of external pressure and bending is also important when evaluating collapse.

Against this background, this study discusses the collapse criteria for coated linepipe and their bending interaction against collapse based on a full-scale collapse test under external pressure with and without bending loading. The effect of the thermal heat cycle on linepipe collapse criteria is also discussed based on the results of tensile pre-strain tests with simulation of the thermal cycle and a collapse calculation by FEA.
High-Fidelity Representation of Three-Hour Offshore Short-Crested Wave Field in the Fully Nonlinear Potential Flow Model REEF3D::FNPF
Authors: Wang Weizhi , Pakozdi Csaba , Kamath Arun , Bihs Hans
Published: December 2020

Stochastic wave properties are crucial for the design of offshore structures. Short-crested seas are commonly seen at the sites of offshore structures, especially during storm events. A long time duration is required in order to obtain the statistical properties, which is challenging for numerical simulations because of the high demand of computational resources. In this scenario, a potential flow solver is ideal due to its computational efficiency. A procedure of producing accurate representation of short-crested sea states using the open-source fully nonlinear potential flow model REEF3D::FNPF is presented in the paper. The procedure examines the sensitivity of the resolutions in space and time as well as the arrangements of wave gauge arrays. A narrow band power spectrum and a mildly spreading directional spreading function are simulated, and an equal energy method is used to generate input waves to avoid phase-locking. REEF3D::FNPF solves the Laplace equation together with the boundary conditions using a finite difference method. A sigma grid is used in the vertical direction and the vertical grid clustering follows the principle of constant truncation error. High-order discretisation methods are implemented in space and time. Message passing interface is used for high performance computation using multiple processors. Three-hour simulations are performed in full-scale at a hypothetic offshore site with constant water depth. The significant wave height, peak period, kurtosis, skewness and ergodicity are examined in the numerically generated wave field. The stochastic wave properties in the numerical wave tank (NWT) using REEF3D::FNPF match the input wave conditions with high fidelity.
Cost-Optimal Planning of Inspections and Maintenance of Production Tubings Subject to Scale Deterioration
Authors: Akinsanya Akinyemi O. , Qin Jianjun , Sørensen John D. , Faber Michael H.
Published: December 2020

Integrity tests, inspections (caliper log) and maintenance activities are critical to the integrity management of the production tubing and are important to ensure that loss of production — due to e.g. excessive reduction in the wells cross-section and numerous unplanned shut-ins, is reduced over the service life while maintaining safety and availability. The progressive loss of integrity of production resulting from deterioration processes such as scaling, are time variant with large uncertainties. The time variability together with large uncertainties is one main driver of increasing need of rational tools for cost-optimal planning of inspections and maintenance. Optimal planning of inspections and maintenance is therefore necessary to achieve timely and risk-efficient management of the production wells by finding a trade-off between the cost of inspection and maintenance, and the benefit of increased production amongst others.

This paper presents a framework for identifying cost-optimal planning of inspections and maintenance of the production tubing of sub-surface oil and gas wells subject to time dependent scale degradation. The proposed framework is based on a risk-based approach, which allows uncertainties to be accounted for. By adopting this approach, the strategies which give the minimum expected value of the total cost of inspection and maintenance are identified. In this paper, the approach uses categorization of the sizes of scale thickness characterized by damage sizes, and inspection results into damage states, and takes into account imperfection in the inspection results in terms of the probability of detection and damage sizing accuracy. For each of the damage states, a certain damage cost and maintenance decision rules, stating the next line of action, are established. The inspection and maintenance decision problems are therefore modeled based on the pre-defined decision rules while the optimization parameters are the intervals of inspections and the maintenance alternatives. The probabilistic model, accounting for uncertainties, scale propagation proposed by Guan et. al. (2019) is used to describe the scale growth or damage evolution. Bayesian pre-posterior decision theory is the basis for the decision making. All costs — including damage, inspections and maintenance costs, through the lifetime of the production tubing are evaluated and included in the decision model and the expected value of the life cycle costs are estimated and compared for different maintenance alternatives. An example in the paper demonstrates the framework and the implementation of the decision rules for one sub-surface production well subject to calcite scales.
Aerodynamic Roll-Yaw Instabilities of Floating Offshore Wind Turbines
Authors: Haslum Herbjørn , Marley Mathias , Navalkar Sachin Tejwant , Skaare Bjørn , Maljaars Nico , Andersen Håkon
Published: December 2020

This paper presents an investigation of a newly discovered motion instability phenomenon for floating wind turbines. The instability is due to anti-symmetric coupling terms in roll and yaw caused by the turbine thrust force. For floaters with small separation between the uncoupled roll and yaw natural periods these coupling forces may result in rigid body roll and yaw oscillations. The paper explains the theory and the physics of the instability phenomenon, and analytical expressions for these stiffness coupling terms (K46 and K64) are derived.

The instability phenomenon is demonstrated using several points of attack, by using time domain simulations, conservation of energy flow and eigenvalue stability analysis. The problem is stripped down to a simplified two degree of freedom roll-yaw model where analytical stability criteria are developed. The instability is also demonstrated in tailor made six degree of freedom time domain simulations, and in simulations using a fully coupled aero-hydro-servo elastic simulation tool including a BEM model.

An important finding is that damping forces are needed to fully understand the observed instability. It is demonstrated, quite counter-intuitively, that damping reduces the stability margin. This is explained by considering the effect damping forces has on roll-yaw phasing, for the typical damping values relevant for a floating offshore wind turbine.
Distributed Potential Theory and its Application for Spar-Type Floating Offshore Wind Turbines
Authors: Engebretsen Espen , Haslum Herbjørn , Aagaard Olav
Published: December 2020

Coupled aero-hydro-servo-elastic time-domain analysis is required for robust design and engineering of Floating Offshore Wind Turbines (FOWTs). For spar-type FOWTs, it is convenient to adopt a nonlinear beam finite element formulation in order to capture the coupled structural response of substructure, tower, blades and mooring lines accurately.

The Distributed Potential Theory (DPT) approach applies first-order frequency-dependent added mass, radiation damping and excitation loads distributed over all submerged beam elements in the coupled time-domain simulation, as obtained from diffraction/radiation analysis. This approach therefore includes frequency-dependent diffraction effects for all wavelengths, while keeping the substructure flexible, thus enabling hydro-elastic coupling and extraction of internal sectional loads along the substructure.

This paper demonstrates the use of DPT in coupled aero-hydro-servo-elastic time-domain analysis of a spar-type FOWT and illustrates the effect on tower and substructure fatigue life compared to using the classical Morison approach.
Cabin Noise Prediction and Acoustic Optimization Design of a Cruise Ship
Authors: Ni Yue , Li Xiaobin
Published: December 2020

The cabin noise level is an important criterion in high-performance ships, and the noise prediction is the premise of the ship noise control and low noise design. Taking a cruise ship as the research object, a comprehensive application of the statistical energy analysis (SEA) and the finite element-statistical energy analysis hybrid method (FE-SEA) is used to predict the full-frequency noise of typical cabins. The structure-borne noise and air-borne noise, caused by the external excitation from the main engine, propellers and auxiliary machinery, are obtained with the empirical formula. The primary noise sources of typical cabins are analyzed. The noise reduction scheme of sound package is adopted and optimized for the cabin with excessive noise.
Study on Vertical Bearing Capacity of the Wide-Shallow Bucket Foundation in Two Layered Sand
Authors: Sun Guodong , Liu Run , Lian Jijian , Cai Runbo , Yang Xu , Fu Dengfeng , Chen Guangsi
Published: December 2020

The wide-shallow bucket foundation proposed by Tianjin University of China is a new type of offshore wind turbine foundation. In this paper, the vertical bearing capacity of wide-shallow bucket foundation embedded in two layered sand that contains an underlying medium strength sand layer and a weaker or stronger overlaying sand layer is studied. A parametric study for bearing capacity is carried out with the ratio of unit weight γ1/γ2 (where γ1 and γ2 are the unit weight of the upper and lower sand layers respectively), the ratio of internal friction angle φ1/φ2 (where φ1 and φ2 are the internal friction angle of the upper and lower sand layers respectively) and relative thickness of the top sand layer H1/B (where H1 and B are the thickness of the top sand layer and the bucket foundation diameter). All of the presents were performed by the Finite Element Method and the results show that the thickness of the top layer has a great influence on the vertical bearing capacity of the foundation. Specifically, the upper sand layer is stronger, the bearing capacity ascends with the increase of the thickness of the top layer, and on the contrary, the upper layer is weaker, and the bearing capacity decreases with the increase of the top layer thickness. In addition, the bearing capacity of the foundation also increases with the ratios of the effective unit weight and the internal friction angle.
Validation of Numerical Wave Tank Simulations Using REEF3D With JONSWAP Spectra in Intermediate Water Depth
Authors: Pakozdi Csaba , Fouques Sebastien , Thys Maxime , Kamath Arun , Wang Weizhi , Dadmarzi Fatemeh Hoseini , Bachynski Erin , Bihs Hans
Published: December 2020

As offshore wind turbines increase in size and output, the support structures are also growing. More sophisticated assessment of the hydrodynamic loads is needed, particularly for the ultimate limit state design. For higher-order phenomena related to rare steep wave events such as ringing, a better understanding of the stochastic loads is needed. As an innovative step forward to reduce the cost of extensive model tests with irregular waves, a larger number of investigations can be carried out using high-performance high-fidelity numerical simulations after an initial stochastic validation with model test data.

In this paper, the open-source hydrodynamic model REEF3D::FNPF (Fully Nonlinear Potential Flow) is used to carry out three-hour long simulations with the JONSWAP spectrum in intermediate water depth conditions. Statistical properties of the free surface elevation in the numerical wave tank are validated using the available data from model tests carried out at SINTEF Ocean/NTNU. The spectral shape, significant wave height, peak period, skewness, kurtosis, and wave crest height statistics are compared. The results are analyzed and it is found that the numerical model provides reasonably good agreement with the model test data.
A KNN Based Collapse Methodology and Recent Qualification of Flexible Pipes in Deepwater Application
Authors: Zhu Linfa , Nogueira Victor Pinheiro Pupo , Tan Zhimin
Published: December 2020

As the flexible pipe industry targets more on deepwater applications, collapse performance of flexible pipes becomes a key challenge due to the huge hydrostatic pressure during installation and service. The collapse strength of flexible pipes largely depends on the structural characteristics of carcass, pressure sheath and pressure armor layers. Therefore, the collapse prediction methodology involving a sound modeling of these layers is essential. Over the years, Baker Hughes have collected a large amount of collapse testing data. The prediction tool needs to be validated and calibrated against all the collapse tests for best accuracy. In this paper, the latest progress of the collapse prediction methodology and qualification tests are presented. A generalized collapse model was developed to predict the collapse pressure of flexible pipes. This model incorporates the advantages of both the weighted kNN regression technique and an analytical collapse model. It is able to reproduce the exact collapse pressure on the pipes tested and can predict the collapse pressure of other pipe designs not tested. As part of the qualification process, the capacity to prevent collapse must be demonstrated. Several flexible pipes were designed based on this generalized prediction methodology for deep water application, and pipe samples were manufactured using industrial production facilities for collapse tests. The results show that flexible pipes following current design guidelines are suitable for deepwater applications.
Reliability Analysis of Mooring Lines of Floating Structures Under Corrosion and Material Degradation
Authors: Soares Gomes Junior Ricardo , Videiro Paulo Mauricio , Esperança Paulo de Tarso Themistocles , Volnei Sudati Sagrilo Luis
Published: December 2020

This paper presents a procedure for reliability analysis of mooring lines of floating units for oil and gas production considering corrosion and material degradation over time. The proposed procedure is limited to the ultimate limit state (ULS) and considers mooring lines made up of chain and polyester rope segments, although the same methodology can be applied to cases with steel wire segments. The proposed procedure can also be applied for mooring lines connected to any other type of floating offshore structure.

For reliability assessments, it is necessary to consider the distributions and the probabilistic aspects of the random variables involved in the process. The weakest link system is used to model the strength of a mooring line segment. Simplified time-dependent probabilistic models for chain corrosion and polyester degradation are adopted to predict the strength degradation over time. The annual failure probability for different years is estimated by approximating the degraded strength by a piecewise constant model in order to perform a time variant reliability analysis. Monte Carlo simulations are used to determine the failure probability.

A study case is also presented, where annual extreme top tension is obtained from long-term statistics considering Brazilian offshore environmental conditions acting on a turret moored floating, production, storage and offloading unit (FPSO).
Frequency Domain Fatigue Analysis for a Unbonded Flexible Riser: Damage Induced by Dynamic Bending
Authors: Yuan Jiabei , Hou Yucheng , Tan Zhimin
Published: December 2020

The service life of flexible risers is a vital design parameter in offshore field development. The standard approach to calculate fatigue life is the nonlinear time-domain analysis. The approach uses time history of riser responses in local structure assessment to get the fatigue damage of tensile layers. Another approach is the linearized frequency-domain analysis. Instead of using time history of stress and rainflow counting technique, the approach uses stress spectrum and empirical mathematical terms to estimate the fatigue damage. The frequency domain approach is significantly faster. However, due to the whole system being linearized, the latter usually produces different results and is considered to be less accurate than the time domain approach. To address this issue, Baker Hughes previously developed an approach which uses the frequency domain technique as base solution and calibration factors from limited time domain cases. The approach is limited to tensile wires at the end fitting entrance where tension and tensile stress is directly linked. In this paper, a similar approach is proposed to be applied for tensile fatigue at all regions, whose tensile stress are induced by a combination of tension, pressure, bending and friction between layers. Since tensile stress is not directly related to any single riser response, the stress spectrum is predicted by using a transfer function. With the predicted stress spectrum, the fatigue damage of each case is calculated with Dirlik’s method and SN curves.

The paper summarizes the development of the hybrid frequency domain approach. The fatigue damage of risers from several projects are acquired with both time domain and frequency domain approaches. The approach is significantly faster than traditional time domain approach and produces conservative results. Furthermore, discussions are made on options to improve the approach and reduce the conservatism in the frequency domain fatigue analysis.
Development Study on Sea Water Intake Riser Using High Density Polyethylene Pipe for Floating Production Unit Application
Authors: Xiang Sherry , Bian Sean , Li Richard , Shi Merry , Cao Peimin
Published: December 2020

A development study on the integrated High Density Polyethylene (HDPE) Sea Water Intake Riser (SWIR) system for Floating Production Unit (FPU) is described in this paper. An integrated HDPE SWIR system configuration for a gas production semisubmersible operated in the harsh environment has been developed and analyzed through topsides optimization, hydraulic study for a sump tank design and global performance of HDPE pipe. The offshore installation methodology of this integrated HDPE SWIR system with FPU is also discussed and value assessment is presented.
From Peak Force Quantitative Nanomechanical Mapping Measurements to Triaxial Testing: A Comparative Study of Geomechanical Properties of Clay-Rich Carbonates
Authors: Mews Kim S. , Alhubail Mustafa M. , Hansen Luka , Motra Hem B. , Wuttke Frank , Ye Qiang , Misra Anil , Barati Ghahfarokhi Reza
Published: December 2020

The assessment of geomechanical properties of unconventional reservoirs is significant as they assist in placement as well as understanding of the geometry and properties of multi-stage hydraulic fractures in horizontal wells. Severe heterogeneities at micro-scale in addition to possibility of having non-intact samples provide opportunities for using micro-mechanics techniques on drill cutting size samples. This will lead to not only have a continuous log of geomechanical properties on heterogeneous formations but also be able to measure the mechanical properties of non-intact samples accurately. This study presents a multi-scale comparison of the elastic properties such as Young’s modulus and Poisson’s ratio on the Eagle Ford Formation. Peak Force Quantitative Nano-mechanical (PF-QNM) AFM-based technique has been performed and compared with true triaxial testing. A new model for AFM evaluation that corrects Young’s modulus in dependency of Poisson’s ratio has been developed. The results indicate that the distribution of Young’s modulus is separated into two regions, one dominated by brittle minerals indicating higher values and one dominated by ductile rock components resulting in lower values. The findings are significant as PF-QNM testing can be performed where only drill cutting-size samples are available, as it shows strong agreement with the triaxial testing result.
Fracture Toughness Characterization of LSAW UOE Pipes in Sour Media and Implications on Burst Pressure
Authors: Turkalj T. , Cravero S. , Valdez M. , Arroyo F. , Darcis Ph.
Published: December 2020

Large diameter Sour Service Pipelines are designed for the safe and efficient transportation of production fluids containing H2S. This service condition exposes the pipe to hydrogen embrittlement mechanisms and demands a material with high Sulfide Stress Cracking (SSC) resistance, and thus, a high fracture toughness in a representative sour environment.

Engineering Critical Assessment (ECA) procedures are usually employed to determine the suitability of a pipeline design, These procedures require the correct determination of the material fracture mechanical properties.

Although Method D of NACE TM0177_16 [1] using DCB specimens is the currently recognized testing methodology to evaluate SSC pipe performance, other type of tests could be employed for the purpose of an ECA.

In the present paper, a fracture mechanics experimental program in sour environment is presented. Parent Pipe and Weld Material of Longitudinal Submerged Arc Welded (LSAW) large diameter pipes in H2S were studied. Fracture Toughness Parameters, such K-limit from standard DCB tests and K-threshold from Single Edge Notch Tension (SENT) specimens under constant loading, are compared and discussed. Furthermore, the fracture toughness values obtained from SENT specimens in sour environment are used to estimate the burst pressure using an ECA procedure.
Fluid Drag With and Without Vortex-Induced Vibrations
Authors: Zueck Robert F.
Published: December 2020

Fluid drag is an integrated force that depends on the velocity of the fluid flow relative to the motion of a structure. In previous OMAE papers, we used nonlinear physics-based time-domain simulations to show how fluid drag evolves geometric changes in slender (long and thin) structures. We then showed how these changes physically determine the specific dynamic nature of the vibrations that the fluid can induce in the structure.

Induced vibrations are four-dimensional oscillations in a marine riser, suspended pipe or other slender structure, whereby the maximum amplitude of deflection is generally perpendicular to the sustained action. The sustained action is often fluid drag.

In this paper, we study the physical relationship between fluid drag and induced vibrations. By focusing on the nonlinear interaction between fluid and structure, we revisit a longstanding belief that vortex-induced vibrations amplify fluid drag.

Using nonlinear physics-based simulations of a slender structure interacting with flowing fluid, we show how amplification depends on the type of vibration (imposed or free). In other words, drag amplification can occur when we impose a vibration on the structure, but does not occur when we allow sufficient geometric freedom so that the fluid merely induces the structure to vibrate. Using simple visual experiments, we confirm that Vortex-Induced Vibrations (VIV) do not amplify fluid drag. This result is consistent with basic energy conservation principles.
Viscosity and Density Sweeps in Directional Wells
Authors: Ozbayoglu Evren M. , Rodrigues Flavio , Ettehadi Reza , May Roland , Clapper Dennis
Published: December 2020

As explorations advance and drilling techniques become more innovative, complex and challenging trajectories arise. In consequence, cuttings transport has continued to be a subject of interest because, if the drilled cuttings cannot be removed from the wellbore, drilling cannot proceed for long. Therefore, efficient cleaning of highly inclined and horizontal wellbores is still among the most important problems to solve, because these types of wells require specialized fluid formulations and/or specific hole cleaning techniques.

There are numerous studies and methods that focus in cuttings transportation in highly inclined and horizontal wells. One of them is the use of viscosity and density sweeps. Sweep pills have been used in the drilling industry as a tool to improve hole cleaning. This report presents the analysis of the performance of different sweeps pills working independently and in tandem in polymeric, oil and synthetic based systems and the comparison between them.

The main objective of this project is to provide experimental evidence on which types of fluids perform better under certain conditions by studying the effect of viscosity and density in the bed erosion process in highly inclined and horizontal wells. In order to achieve that, several fluid formulations were tested at different inclination angles (90, 75, 60 degrees) in the Small Indoor Flow Loop property of The University of Tulsa’s Drilling Research Projects. The results of the tests are presented in terms of volume of drilled cuttings removed from the test section and measured differential pressures. All the tests were conducted under atmospheric pressure and ambient temperature. Moreover, a 2-Layer model is used for estimating the erosion performance of sweeps for design purposes, and the model estimations are compared with experimental results.

From the experiments, it was identified that polymeric, oil and synthetic based muds with similar density and rheological properties eroded and transported the drilled cuttings similarly under similar test conditions. Furthermore, pumping the sweep pills in tandem demonstrated higher cuttings transport efficiency when compared with the sweep pills applied independently.