bluuebunny/crossref_metadata_2025 huggingface dataset:
Is fundoplication mandatory in children with neurological impairment undergoing gastrostomy?
Authors: Dreznik Yael , Baazov Artur , Dvir Nadav , Seguier‐Lipszyc Emmanuelle , Zevit Noam , Nica Adrianna , Samuk Inbal , Shamir Raanan , Dlugi Elena , Freud Enrique , Kravarusic Dragan
Published: October 2021

Aim

Percutaneous endoscopic gastrostomy (PEG) and surgical gastrostomy (SG) are common procedures in children with neurological impairment (NI) with swallowing difficulties. Pulmonary aspirations are a major concern and performing concomitant or delayed fundoplication is still controversial, especially among these patients. The aim of our study was to review our experience with fundoplication performed concomitantly with gastrostomy or later and to evaluate patient outcomes.

Methods

This is a retrospective, cohort study including all paediatric patients who underwent SG or PEG with or without Nissen fundoplication at Schneider Children's Medical Center of Israel between the years 2007 and 2018. Patients' clinical and surgical data were recorded and analysed.

Results

Between 2007 and 2018, 345 patients underwent SG or PEG. Of these, 89 patients underwent fundoplication. Of the patients who underwent PEG/SG, 158 (45.8%) were neurologically impaired. Most of the patients who underwent fundoplication (n = 69, 77.5%) were NI patients (P = 0.0001). NI patients with refractory seizures showed almost no improvement in terms of relief of gastro‐oesophageal reflux disease symptoms following fundoplication (P = 0.0001) compared to NI patients without refractory seizures.

Conclusion

Our findings suggest that in NI patients a concomitant fundoplication is not mandatory and is not efficacious in preventing gastro‐oesophageal reflux disease in patients with refractory seizures.
Private citizens, stakeholder groups, or governments? Perceived legitimacy and participation in water collaborative governance
Authors: Hui Iris , Smith Gemma
Published: October 2021

Collaborative governance (CG), involving partnership between governmental and non‐governmental actors, has emerged as an alternative to traditional government (TG). While CG may be seen as a strategy for increasing legitimacy, we know little about how the public evaluates inclusion of private citizens and stakeholder groups in decision‐making processes. Following the methodology of Cain et al. in their 2020 study of transportation and drawing on legitimacy theory, we develop a series of “components” of legitimacy. We then use these to test how respondents perceive the legitimacy of different institutional arrangements through a survey experiment on a nationally representative sample of U.S. adults. Our results reveal that regardless of board function, respondents perceived CG as more legitimate than TG. Among different types of CG, they prefer the inclusion of private citizens over stakeholder groups, adding empirical data to theoretical debate over how and under what conditions CG may increase the legitimacy of public governance.
Taking bell hooks on zoom: Embodying feminist pedagogy in a graduate theological classroom
Authors: Dhala Mahjabeen , Johnson Sheryl
Published: October 2021

What does feminist pedagogy look like online? Is it even possible? This article describes intentionally incorporated many aspects of embodied feminist pedagogy into the Women's Studies in Religion online learning community during the semester when the seminar was taught online due to the COVID‐19 pandemic. This essay shares techniques for and trials and triumphs in taking specific aspects of bell hooks's engaged critical pedagogy to an online classroom format. The authors assert that, despite the absence of physical bodies and a physical classroom, such feminist pedagogies can apply to and thrive in an online graduate theological classroom.
Remote liver injury following acute renal ischaemia–reperfusion: involvement of circulating exosomal miR‐687 and regulation by thymoquinone
Authors: Ashour Hend , Rashed Laila , Elkordy Miran Atif , Abdelwahed Omaima Mohammed
Published: October 2021

New Findings

What is the central question of this study?

What is the role of circulating exosomal miR‐687 in remote hepatic injury following renal ischaemia–reperfusion injury (IRI) and does thymoquinone have a modulatory impact?

What is the main finding and its importance?

Exosomal miR‐687 was expressed in renal IRI, entered the circulation and was deposited in the liver. Liver exosomal miR‐687 was correlated with liver inflammation and apoptosis. Thymoquinone aborted the renal production of exosomal miR‐687 and its further circulation to the liver.

The pathophysiology of remote hepatic injury following acute renal ischaemia–reperfusion injury (IRI) is of particular clinical interest. Secreted small non‐coding microRNA (miRs) are thought to exist in exosome‐encapsulated form. Thymoquinone (TQ) is the main bioactive ingredient of Nigella sativa and has several renoprotective actions. We expected exosomal miR‐687 to be relevant as it could act as a humoral mediator, with possible modulation by TQ. Thirty adult male Wister albino rats were assigned to three groups (n = 10); (1) sham‐operated, (2) renal ischaemia–reperfusion injury (IRI), and (3) renal IRI pre‐treated with TQ 10 mg/kg/day i.v. (TQ‐IRI) for 10 days in addition to a dose administered at reperfusion onset. Following 24 h of reperfusion, the IRI group showed renal tissue hypoxia‐inducible factor upregulation (P < 0.001). Electron microscopy images of exosomes and analysis of miR‐687 revealed elevated levels, which appeared in the circulation. Large amounts of exosomal miR‐687 were transmitted to the liver tissue. In the IRI group, liver transaminases (alanine aminotransferase, aspartate aminotransferase) were markedly (P < 0.001) elevated. The hepatic tissue inflammatory markers (vascular cell adhesion molecule‐1, myeloperoxidase, monocyte chemotactic protein‐1 and nuclear factor‐κB) were upregulated (P < 0.001) accompanied with elevated caspase‐3. TQ suppressed (P < 0.001) the renal expression and release of exosomal miR‐687 into the circulation and its further deposition in the liver tissue; consequently, TQ diminished (P < 0.001) liver tissue inflammation and cellular apoptosis. The results were confirmed by histological tissue assessment. In conclusion, exosomal miR‐687 liberated from injured renal tissues into the circulation may be an important factor in inducing remote hepatic injury. Exosomal miR‐687 inhibition by TQ protected both renal and hepatic tissues from injury.
Arte e architettura, patrimonio e identità. Appunti per una storia del restauro in Colombia (1920-1970)
Authors: Botti Giaime
Published: October 2021

Este artículo propone una aproximación a la historia de la disciplina de la restauración arquitectónica en Colombia, desde los años Veinte del siglo XX –durante los cuales el debate sobre el patrimonio toma fuerza a raíz de las búsquedas de un arte y una arquitectura “propia”– hasta los Setenta, cuando la práctica de la restauración arquitectónica empieza a tener una fundamentación científica y ser desarrollada por profesionales específicamente entrenados al interior de centros universitarios de investigación. Este trabajo, basado en una amplia bibliografía secundaria y en unas fuentes primarias parcialmente inéditas, se desarrolla a partir de un enfoque de historia cultural, necesario para mostrar las conexiones subyacentes entre diferentes actividades, alejándose así de una mera historia disciplinar para en cambio abarcar los campos de la historia del arte, de la literatura y de la política, señalando las interrelaciones entre la elaboración de un discurso sobre el patrimonio y su tutela, las construcciones identitarias en el campo del arte y los procesos políticos.
Quebrada de Humahuaca, Patrimonio Mundial: valores, usos y apropiaciones en disputa
Authors: Salleras Lucila
Published: October 2021

El presente artículo aborda los valores, usos y apropiaciones en disputa alrededor del patrimonio cultural de la Quebrada de Humahuaca (Jujuy, Argentina), a partir de su inscripción como patrimonio mundial por la Organización de Naciones Unidas para la Educación, la Ciencia y la Cultura (UNESCO) en el año 2003, bajo la categoría de paisaje cultural en el año 2003.Buscamos mostrar las relaciones complejas y conflictivas que se evidencian a raíz de la articulación entre patrimonio y turismo en una región atravesada por la colonialidad del poder.Los aspectos trabajados en este artículo surgen de una investigación doctoral que se desarrolló entre los años 2009 y 2012 y cuya tesis fue defendida en junio del 2016. La misma se llevó a cabo a partir de una perspectiva socioantropológica y se recurrió a diferentes estrategias metodológicas de recolección, construcción y análisis de la información proveniente tanto de fuentes primarias como secundarias.
How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?
Authors: Masoumifar Mehran , Verma Suyash , Hemmati Arman
Published: October 2021

This study evaluates how Reynolds-averaged Navier–Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (1×104−1.58×105). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relation in the far downstream region, where the flow obtains a fully-developed state. The consistency of computationally predicted results and their similarities with experiments suggested that the Standard k−ε model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.
Impacts of Tandem Configurations on the Aerodynamic Performance of an Axial Supersonic Through-Flow Fan Cascade
Authors: Sun Shijun , Hao Jiaqi , Yang Jutao , Zhou Ling , Ji Lucheng
Published: October 2021

In the current study, the tandem blade technology is applied to an supersonic throughflow fan (STFF) tandem cascade for the first time and a 2D STFF tandem cascade is preliminarily designed. Through the modification design of the tandem airfoils and their configuration (axial overlap (AO) and percent pitch (PP)), the coefficients of total pressure loss and loading are reduced by 4% and 8.58%, respectively. Furthermore, the impact of tandem configurations on the performance is parametrically investigated by numerical simulations. The results indicate that compared with AO, the performance under design incidence is more sensitive to PP except for the cases with PP exceeding a threshold value (1.15). PP dominates the loss and load by controlling the evolution of the FB wake and the shock structure of FB and the rear one of the tandem blade (RB), while AO mainly adjusts the entire shock system structure through the change of virtual shape, resulting in the variation in load distribution between FB and RB. It is worth noting that the overall loading and the total loss remain unchanged with increasing AO except for the tandem configurations (PP = 1.05, AO ≤ −0.01), which make the flow structure in the gap region undergo a fundamental change. With the optimal tandem configuration (PP = 1.05, AO = −0.01) and the modified tandem blades (the ratios of chord length and camber for FB over RB are 0.67 and 0.5, respectively), the total pressure loss coefficient is further reduced by 19.7% in comparison with the preliminary tandem design.
Vortex Tracking of Purge-Mainstream Interactions in a Rotating Turbine Stage
Authors: Mesny Alex W. , Glozier Mark A. , Pountney Oliver J. , Scobie James A. , Li Yan Sheng , Cleaver David J. , Sangan Carl M.
Published: October 2021

The use of purge flow in gas turbines allows for high turbine entry temperatures, which are essential to produce high cycle efficiency. Purge air is bled from the compressor and reintroduced in the turbine to cool vulnerable components. Wheel-spaces are formed between adjacent rotating and stationary discs, with purge air supplied at low radius before exiting into the mainstream gas-path through a rim-seal at the disc periphery. An aerodynamic penalty is incurred as the purge flow egress interacts with the mainstream. This study presents unparalleled three-dimensional velocity data from a single-stage turbine test rig, specifically designed to investigate egress–mainstream interaction using optical measurement techniques. Volumetric velocimetry is applied to the rotating environment with phase-locked measurements used to identify and track the vortical secondary flow features through the blade passage. A baseline case without purge flow is compared to experiments with a 1.7% purge mass fraction; the latter was chosen to ensure a fully sealed wheel-space. A non-localized vortex tracking function is applied to the data to identify the position of the core centroids. The strength of the secondary flow vortices was determined using a circulation criterion on rotated planes aligned to the vortex filaments. The pressure-side leg of the horseshoe vortex and a second vortex associated with the egress flow were identified by the experimental campaign. In the absence of purge flow, the two vortices merged, forming the passage vortex (PV). With the addition of purge flow, the two cores remained independent to 40% of the blade axial chord, while also demonstrating an increased radial migration and intensification of the PV. The egress core was shown to remain closer to the suction-surface with purge flow. Importantly, where the vortex filaments demonstrated strong radial or tangential components of velocity, the circulation level calculated from axial planes underpredicted the true circulation by up to 50%.
Locomotion Identification Method of one-DOF Six-Bar for Jumping Robot
Authors: Shun Gui
Published: October 2021

Exploring the locomotion of creatures is a challenging task in bionic robots, and the existing iterative design methods are mainly based on one or two characteristics to optimize robots. However, it is hard to obtain other features. Here, we introduced the thinking of system identification theory to the bionic robots, averting the exploration of the dynamics and reducing the difficulty of design greatly. A one-DOF six-bar mechanism (Watt I) was designated as the model to be identified, and it was divided into two parts, i.e. a one-DOF four-bar linkage and a three-DOF series arm. Then we formed constraints and a loss function. The parameters of the model were identified based on the kinematic data of a marmoset jumping. As a result, we obtained the desired model. Then, a prototype derived from the model was fabricated, and the experiments verified the effectiveness of the method. Our method also can be applied to other motion simulation scenarios.
A Graph Partitioning Technique to Optimize the Physical Integration of Functional Requirements for Axiomatic Design
Authors: Green Emilyn , Estrada Spenser , Gopalakrishnan Praveen Kumare , Jahanbekam Sogol , Behdad Sara
Published: October 2021

According to the concept of physical integration as understood in axiomatic design, design parameters of a product should be integrated into a single physical part or a few parts with the aim of reducing the information content, while still satisfying the independence of functional requirement. However, no specific method is suggested in the literature for determining the optimal degree of physical integration in a given design. This is particularly important with the current advancement in technologies such as additive manufacturing. As new manufacturing technologies allow physical elements to be integrated in new ways, new methods are needed to help designers optimize physical integration given the specific constraints and conflicts of each design. This study proposes an algorithm that uses graph partitioning to allow a designer to optimize the integration of functional requirements into a target number of parts, with the goal of minimizing the co-allocation of incompatible functional requirements in the same part. The operation and viability of the algorithm are demonstrated via two numerical examples and a practical example of designing a pencil.
Multi-Material Integrated Three-Dimensional Printing of Cylindrical Li-Ion Battery
Authors: Zhou Weiping , Li Xiying , Duan Huiling , Lv Pengyu
Published: October 2021

A simple, low-cost and highly efficient method of fabrication has always been the goal of manufacturing technology. In order to improve the speed of fabrication and simplify the preparation steps, this work proposes a multi-material integrated 3D printing method, aiming to obtain the desired structure from the print head in one step. As a typical example, a cylindrical Li-ion battery (LIB) with core–shell structure was integrally fabricated using this one-step multi-material integrated printing method. A multi-material print head is designed based on the structure to be printed. The inks with the characteristics of non-Newtonian fluid are developed for battery printing. Anode, cathode, separator layer, and packaging layer are easily printed simultaneously by coaxial wrapping layer by layer. The parameters of ink viscosity, printing pressure, and printing speed are studied. Electrochemical performance of the printed battery is tested with the charge and discharge capacities of the printed battery up to 147 and 99 mAh g−1 at 0.1 C rate, respectively. Compared with the traditional step-by-step printing, the proposed multi-material integrated printing method realizes the one-step printing of the battery structure, which improves manufacturing efficiency. This system can be directly extended to fabricate other integrated devices such as supercapacitors. Based on this idea, it should also be possible to design different print heads to print other multi-material devices in one step.
Rigid Spool & Riser Slugging Induced Vibrations
Authors: Aljarah Raghid , Le Prin Kevin , Saunier Claire , Minguez Matthieu
Published: October 2021

The paper addresses response of subsea components subject to internal intermittent slug flows. The proposed work pursues experiments already published last year (OMAE2020-18620) and focuses on the way to numerically model such complex coupled physics for both rigid spool and steel lazy wave riser.

The first part of the paper relies on the coupling approach already presented in OTC-29306 and OMAE2020-18620 mixing (i) Finite Element solver to predict the mechanical behavior of the system and (ii) a Unit Cell solver to recover the intermittent slug flow. It accounts for both (i) the complexity of the slug flow properties at the spool inlet and (ii) their variability along the system. This approach is successfully compared to the experimental (large scale) results already published. This preliminary step validates the ability of the proposed numerical model to recover real-life behavior and underlines some limitations resulting from the Industry Best Practices use.

The second part of the paper extends the applicability of the proposed coupling philosophy to a steel lazy wave riser where a classical Flow Assurance software (e.g. Olga) is considered for the characterization of the intermittent flow and then coupled with a mechanical solver. This one-way coupling accounts for the slugging variability along the riser length and consequently exhibits a finer granularity of the mechanical behavior of the riser. This modelling is then compared to the industry best practices to open a discussion on the observed differences.
Advanced Intelligent Control Strategy in Dynamic Positioning (DP) System Applied to a Semi-Submersible Drilling Platform in the North Sea
Authors: Alremeihi Mohamad , Norman Rosemary , Pazouki Kayvan , Dev Arun , Bashir Musa
Published: October 2021

Dynamic Positioning (DP) systems play a crucial role in oil and gas drilling and production floaters used globally for deep-water operations. Drilling operations need to maintain automatic positioning of the platform in the horizontal-plane within the safe zone. Operating DP systems typically require highly responsive control systems when encountering prevailing weather conditions. However, DP incident analysis demonstrates that control and thruster failures have been the leading causes of accidents for the past two decades, according to the International Marine Contractors Association (IMCA). In this paper, a Predictive Neural Network (PNN) strategy is proposed for thruster allocation on a platform; it has been developed by predicting the platform response and training the network to transform the required force commands from a nonlinear Proportional Integral Derivative (PID) motion controller for each thruster. The strategy is developed for increasing safety and zone keeping of DP-assisted-drilling operations in harsh weather. This is done by allowing the platform to recover the position more rapidly whilst decreasing the risk of losing the platform position and heading, which can lead to catastrophic damage. The operational performance of the DP system on a drilling platform subjected to the North Sea real environmental conditions of wind, currents and waves, is simulated with the model incorporating the PNN control algorithm, which deals with dynamic uncertainties, into the unstable conventional PID control system for a current drilling semi-submersible model. The simulation results demonstrate the improvement in DP accuracy and robustness for the semi-submersible drilling platform positioning and performance using the PNN strategy.
Nonlinear Behaviors of Three Dimensional Sloshing in the LNG Elastic Tank
Authors: Wang Zhongchang , Jiang Meirong , Yu Yang
Published: October 2021

Aiming at the nonlinear sloshing in the LNG tank, a three-dimensional elastic model is established to investigate the fluid structure interaction effect. For the transient flow and the tank motion, the direct coupling method is employed to calculate the interaction between the sloshing and the bulkhead. The finite element software ADINA is adopted to do the computation. The sloshing natural frequency is verified with the results of the theoretical formula. Different wall thicknesses, filling ratios and external excitations are considered and the structure natural frequency, surface elevation and sloshing pressure are obtained. The results of the elastic case are further compared with the rigid results and the nonlinear characteristics are extracted to see the hydro-elastic effect. The sloshing natural frequencies are agreed well with the theoretical results. Due to the influence of the fluid structure interaction, the couple frequencies are obviously less than those of the empty tank. With the increase of the wall thickness, the frequencies of the empty tank and the couple frequencies all increase gradually. For the surface elevation, the thinner the bulkhead thickness is, the more the high frequency component is. The free surface is relatively flat and stable in the rigid tank but tend to be chaotic for the elastic one. Due to the fluid structure interaction, the sloshing pressure of the elastic case presents obvious high-frequency fluctuation and the sloshing pressure in the elastic tank is smaller than that in the rigid tank. This model clearly shows the valuable ability to solve the three dimensional sloshing in the elastic tank.
Resistance Tests of an Articulated Pusher Barge System in Deep and Shallow Water
Authors: Zhang Li , Xing Lei , Dong Mingyu , Chen Weimin
Published: October 2021

Articulated pusher barge vessel is a short-distance transport vessel with good economic performance and practicability, which is widely used in the Yangtze River of China. In this present work, the resistance performance of articulated pusher barge vessel in deep water and shallow water was studied by model tests in the towing tank and basin of Shanghai Ship and Shipping Research Institute. During the experimental investigation, the articulated pusher barge vessel was divided into three parts: the pusher, the barge and the articulated pusher barge system. Firstly, the deep water resistance performance of the articulated pusher barge system, barge and the pusher at design draught T was studied, then the water depth h was adjusted, and the shallow water resistance at h/T = 2.0, 1.5 and 1.2 was tested and studied respectively, and the difference between deep water resistance and shallow water resistance at design draught were compared. The results of model tests and analysis show that: 1) in the study of deep water resistance, the total resistance of the barge was larger than that of the articulated pusher barge system. 2) for the barge, the shallow water resistance increases about 0.4–0.7 times at h/T = 2.0, 0.5–1.1 times at h/T = 1.5, and 0.7–2.3 times at h/T = 1.2. 3) for the pusher, the shallow water resistance increases about 1.0–0.4 times at h/T = 2.7, 1.2–0.9 times at h/T = 2.0, and 1.7–2.4 times at h/T = 1.6. 4) for the articulated pusher barge system, the shallow water resistance increases about 0.2–0.3 times at h/T = 2.0, 0.5–1.3 times at h/T = 1.5, and 1.0–3.5 times at h/T = 1.2. Furthermore, the water depth Froude number Frh in shallow water was compared with the changing trend of resistance in shallow water.
Automated Iterative Gap Filling Method for Drilling Logs and Other Data Series
Authors: Tunkiel Andrzej T. , Sui Dan , Wiktorski Tomasz
Published: October 2021

Data scientists are facing multiple issues when working with real-life data. Logs are rarely devoid of incorrect values and one of the common categories of data problems is missing values. Gaps in logs are of various shapes, sizes, and quantities, with a plethora of techniques to infill, or restore missing values. No single algorithm will perform best for all scenarios, hence in pursuit of best results exploration of various options is necessary. Furthermore, gap filling in single step may be impossible for certain methods, where gaps exist for multiple attributes. This paper explores an automated iterative approach, where a selection of common algorithms and different input combinations are evaluated on existing data to select the best method based on R2 score. With the ability to perform iterative infilling, where previously imputed data is re-used as training data to patch other gaps, this represents the most automated and universal approach for gap filling in real-life data-series. This paper presents the methodologies and issues behind automated iterative approach to gap filling, and discusses what is necessary to achieve the final goal of high quality, one-click and optimal data infilling.
Scale and Configuration Effects of an Airchamber on PTO of Oscillating Water Column Type Wave Energy Converters
Authors: Ikoma Tomoki , Hirai Shota , Aida Yasuhiro , Masuda Koichi
Published: October 2021

Wave energy converters (WECs) have been extensively researched. The behaviour of the oscillating water column (OWC) in OWC WECs is extremely complex due to the interaction of waves, air, and turbines. Several problems must be overcome before such WECs can be put to practical use. One problem is that the effect of the difference in scale between a small-scale experimental model and a full-scale model is unclear. In this study, several OWC models with different scales and geometries were used in forced oscillation tests. The wave tank was 7.0 m wide, 24.0 m long, and 1.0 m deep. In the static water experiment, we measured the air pressure and water surface fluctuations in an air chamber. For the experiments, models with a box shape with an open bottom, a manifold shape with an open bottom, and a box shape with a front opening, respectively, were fabricated. Furthermore, 1/1, 1/2, and 1/4 scale models were fabricated for each shape to investigate the effects of scale and shape on the air chamber characteristics. Numerical calculations were carried out by applying linear potential theory and the results were compared with the experimental values. The results confirmed that the air chamber shape and scale affect the air pressure fluctuation and water surface fluctuation inside the OWC system.
Hydrodynamic Analysis of Tandem Flapping Hydrofoils
Authors: Joshi Vaibhav , Chaithanya Mysa Ravi
Published: October 2021

Flapping hydrofoils in tandem configuration find applications in wave gliders, dragonfly, dorsal-tail fin interaction in fishes, among others. The flapping motion consists of a combination of heaving and pitching motion. This type of motion involves complex interaction of the vortices shed from the upstream hydrofoil with the downstream hydrofoil, thus influencing the performance of the downstream hydrofoil. A two-dimensional stabilized finite element moving mesh framework is utilized for the current study. The important parameters which influence the flow interactions are the chord size ratio and the gap between the hydrofoils. The size ratio is defined as the ratio of the chord of the upstream hydrofoil to that of the downstream hydrofoil. The size ratio is varied from 0.25 to 1. The gap is varied from one chord length to 3 chord lengths of the downstream foil. The study focuses on the effect of the size ratio, gap and flapping kinematics based on sinusoidal heaving and pitching motion on the detailed flow dynamics of the tandem hydrofoils. The effect on the thrust coefficient and hydrodynamic efficiency is explored and compared with that of an isolated hydrofoil. The results obtained from the study can pave way for a better understanding with regard to engineering designs based on biomimetics.
Vibration Control of an Offshore Wind Turbine
Authors: Alkhoury Philip , Aït-Ahmed Mourad , Soubra Abdul-Hamid , Rey Valentine
Published: October 2021

In order to reduce their cost, offshore wind turbines (OWTs) must have a powerful generator and a minimum overall weight. This has the consequence of making the OWT structure sensitive to dynamic excitations even at low frequencies. Indeed, modern multi-megawatt OWTs are composed of slender flexible and lightly damped components. The excessive vibrations of the OWT structure can impact the wind energy conversion to electricity, decrease the fatigue lifetime and even result in a total collapse of the structure when exposed to harsh environmental conditions. It is therefore important to reduce the unwanted vibrations of an OWT by implementing an appropriate control device that enhances its structural safety.

Motivated by the potential of the structural control methods in suppressing OWTs vibration, this paper proposes the design of a controlled active tuned mass damper (ATMD) system to reduce the nacelle/tower out-of-plane vibration of a monopile-supported 10 MW DTU OWT subjected to combined wave and wind loads. Compared to previous works, the main originality of this paper is the inclusion of a state estimator, Linear Quadratic (LQ) observer, within an optimal control schema. The state observer aims to drastically reduce the number of required system states. Indeed, as some measurements are practically impossible, all system states cannot be obtained. In this study, a fully coupled multi-degree of freedom (MDOF) analytical model of a monopile-supported OWT developed in [4] is used for this purpose. The optimal control schema makes use of the robust LQR feedback controller to establish the ATMD actuator control force. The developed active control schema proved to efficiently reduce the nacelle/tower vibration.
Mean Wave Drift Force on a Barge-Type Floating Wind Turbine With Moonpools
Authors: Tan Lei , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi
Published: October 2021

The barge-type foundation with moonpool(s) is a promising type of platform for floating offshore wind turbines, since the moonpool(s) could improve the hydrodynamic performance at particular frequencies and reduce the costs of construction. In this paper, the horizontal mean drift force and yaw drift moment of a barge-type platform with four moonpools are numerically and experimentally investigated. Physical model tests are carried out in a wave tank, where a 2MW vertical-axis wind turbine is modelled in the 1:100 scale. By varying the rotating speed of the turbine and the mass of the blades, the gyroscopic effects due to turbine rotations on the mean drift forces are experimentally examined. The wave diffraction and radiation code WAMIT is used to carry out numerical analysis of wave drift force and moment. The experimental results indicate that the influence of the rotations of a vertical-axis wind turbine on the sway drift force is generally not very significant. The predictions by WAMIT are in reasonable agreement with the measured data. Numerical results demonstrate that the horizontal mean drift force and yaw drift moment at certain frequencies could be reduced by moonpool(s).
Hydrodynamic Behaviors of Aquaculture Net Cages After the Successive Mooring Lines Failure
Authors: Tang Hung-Jie , Yang Ray-Yeng
Published: October 2021

This paper aims to study the successive mooring line failure (also known as the domino effect) and the collision between floating collars for aquaculture net cages subjected to currents. The numerical model of this study is developed based on the Morison equation and the lumped-mass scheme in the time domain. This model is then applied to see if the domino effect of moorings will happen after releasing the anchor point #1 on the upstream side. In this study, we adopt four different current speeds (0.5, 1.0, 1.5, 2.0 m/s) and three different safety factors (SF, 1.0, 1.5, 2.0) settings to calculate the number of mooring failures, and to see whether it will cause floating collars collision. The results show that in the case of the SF is 2.0, the domino effect will not be triggered, and the floating collar collision will not occur. When the SF is 1.5, and the current speed is up to 1.0 m/s or higher, only the two anchor points on the upstream side will fail and no collision will occur. However, if the SF is not considered (that is, 1.0), the domino effect will occur under all the four current speeds, and the floating collar collision will all occur. Therefore, we suggest that in order to avoid the domino effect of the mooring system of aquaculture net cages from currents, the SF of the mooring system design must be at least 2 times.
Determination of the Welding Residual Stresses in Welded Joints and Their Effects on SIFs for Surface Cracks: A Review of Recent Progress
Authors: Qiang Bin , Wang Xin
Published: October 2021

In this paper, the recent progress on the determination of welding residual stresses in Q345qD steel welded structural components and their effects on stress intensity factors for semi-elliptical surface cracks has been reviewed. Two different welded structural components: butt-welded steel plate and orthotropic steel deck (OSD) are considered. First, we summarize the results from recent studies on the experimental measurements and numerical simulations of the surface and through-thickness residual stress in the welded plate and OSD; the complete longitudinal and transverse residual stress distributions are discussed. Then, the effects of the obtained welding residual stresses on the SIFs for surface cracks in the weldments are quantified. The loading conditions considered are the combinations of service loading and residual stresses on the butt-welded plate and OSD. Semi-elliptical surface cracks with a wide range of aspect ratios and relative depths are investigated. In particular, both 3D FEA and weight function method are used for the determination of SIFs for surface cracks. The effects of welding residual stresses on SIFs are illustrated thoroughly. The current results are very important for the appropriate fatigue life assessment for welded structural components.
Reconstruction of Ocean Surfaces From Randomly Distributed Measurements Using a Grid-Based Method
Authors: Desmars Nicolas , Hartmann Moritz , Behrendt Jasper , Klein Marco , Hoffmann Norbert
Published: October 2021

In view of deterministic ocean wave prediction, we introduce and investigate a new method to reconstruct ocean surfaces based on randomly distributed wave measurements. Instead of looking for the optimal parameters of a wave model through the minimization of a cost function, our approach directly solves the free surface dynamics — coupled with an interpolation operator — for the quantities of interest (i.e., surface elevation and velocity potential) at grid points that are used to compute the relevant operators. This method allows a high flexibility in terms of desired accuracy and ensures the physical consistency of the solution. Using the linear wave theory and unidirectional wave fields, we validate the applicability of the proposed method. In particular, we show that our grid-based method is able to reach similar accuracy than the wave-model parameterization method at a reasonable cost.
Abandonment Solution for Wells With Gauge Cables: An Engineered Self-Sealing Cement System
Authors: Rublevskyi Anton , Johnson Carl , Tay Chuang Hwee , Main Darren , Herrera Axle
Published: October 2021

With an increasing number of wells transitioning to their abandonment stages, associated operational efficiency and cost cutting have become a major focus in the industry. An operator had an objective to permanently abandon an offshore well that was suspended in 2016. The key challenge was to develop a long-term well abandonment solution leaving the completion tubing and gauge cables in the well. All the associated operations had to be completed utilizing a lightweight well intervention vessel.

Traditionally, retrieving the entire 5 ½-in. production tubing during plug and abandonment operations has added operational complexity and costs, which increases the risk of exposure to health, safety, and environment (HSE) hazards. Alternatively, a sealant technique placing cement through and around the completion tubing with gauge cables in situ exists. However, this technique is associated with a heightened risk of leak path development over time. Ongoing experimental work suggested that enhancements to the conventional cement sealant systems are beneficial to improve long-term sealing; thus, an active self-sealing cement (SSC) system that would seal microannuli or small fissures around the tubing and gauge cables was designed. The set cement sealant characteristics include low Young’s modulus to resist failure from wellbore stresses and the ability to regenerate the original seal upon contact with any hydrocarbons that may seep through any isolation defects through the life of the abandoned well. To achieve proper cement placement, advanced fluid simulation software and carefully tailored fluid density and rheology profiles were used.

During the operation, a plug of the SSC sealant was pumped through the production tubing and squeezed into the perforations to create a permanent barrier across the reservoir section. Next, a mechanical plug was set inside the production tubing to isolate the lower section, and the tubing was perforated to provide access to the A-annulus above; subsequently, a balanced plug of SSC system was spotted above. After 30 hours, the plug passed a 3.4-MPa [500-psi] verification pressure test. The operator estimated the operation saved 2 to 3 days of rig time, valued at approximately GBP 400,000 to 600,000. The operator also avoided the risk of leaving the well on long-term suspension with mechanical plugs while waiting for a rig to complete the isolation, and the operation minimized the number of intervention steps required for abandonment, thereby limiting scope growth.

Operators are constantly looking for ways to increase reliability, improve efficiency, and minimize risks; and therefore, abandonment techniques are evolving. The developed solution is a novel and robust alternative to conventional well abandonment using an advanced cement sealant technology for the first time and an innovative placement technique.
Transitions in Charpy Energy and Splitting for X80 Pipe Steel
Authors: Mohr William , Birchfield Neal , McGaughy Tom
Published: October 2021

Using data obtained for a recent production 48-inch diameter X80 PSL2 pipe, the transition in fracture behavior between fully brittle and fully ductile modes was examined to assess any effects of transverse splits or delaminations. The additional surface area formed at the splits can increase and decrease the Charpy energy by expending energy to form more fracture surface and reduce constraint on the propagating crack as it extends through the unnotched Charpy ligament. Fitting of full Charpy energy transition curves for the tested material with standard hyperbolic tangent functions does not represent the behavior well. An important transition is noted in the behavior between splitting that initiates at the initial notch tip and splitting that occurs further down in the ligament. Spitting across the notch tip increases Charpy energy by releasing constraint on crack initiation behavior at the machined notch and occurs at temperatures just above the lower shelf temperature where brittle fracture dominates. The splitting behavior can also be correlated to effects on fracture toughness in the same orientation for CTOD specimens in the base material and for correlated effects on CTOD behavior in the weld heat affected zone when the crack advance is in the through thickness direction.
Visual Flooding Experiment of Hot Water, Steam and Solvent Under SAGD and VAPEX Conditions
Authors: Li Songyan , Han Rui , Wang Qun , Wei Xuemei
Published: October 2021

Steam-assisted gravity drainage (SAGD) is an important method of heavy oil production, and the solvent vapor extraction (VAPEX) process is also an economically feasible, technically reliable, and environmentally friendly in situ heavy oil recovery method. In this paper, a microscopic visual flooding device was used to conduct seven groups of visual flooding experiments, including hot water, steam, liquid solvent and vapor solvent, at different temperatures. It can be directly observed that the residual oil in the hot water swept area is generally distributed in “spots”, “strips” and “clusters” of varying sizes. The residual oil after steam flooding generally has a “cluster” distribution, the residual oil after liquid solvent flooding has a “film” distribution, and there is only a little “spot” residual oil distributed after solvent vapor flooding. Additionally, we found that the sweep efficiency and displacement efficiency of hot water, steam and solvent increase with increasing temperature, and the sweep efficiency of hot water is higher than that of steam and liquid solvent. Vapor solvent has the greatest recovery factor, reaching approximately 90%. The experimental results hint at the future development trend of solvent injection and support the foundation of more general applications pertaining to the sustainable production of unconventional petroleum resources.
A Numerical Simulation of Non-Linear Air-Gap for Deepwater Semi-Submersible Platform
Authors: Kang Zhuang , Zhang Yansong , Sui Haibo , Chang Rui
Published: October 2021

Air gap is pivotal to the hydrodynamic performance for the semi-submersible platform as a key characteristic for the strength assessment and safety evaluation. Considering the metocean conditions of the Norse Sea, the hydrodynamic performance of a semi-submersible platform has been analyzed. Based on the three-dimensional potential flow theory, and combined with the full QTF matrix and the second-order difference frequency loads, the nonlinear motion characteristics and the prediction for air gap have been simulated. The wave frequency motion response, the second-order nonlinear air gap response and nonlinear motion response of the platform have been analyzed. By comparing the simulation results, the air gap response of the platform considering the nonlinear motion is more intense than the results simulated by the first-order motion without considering the second-order difference frequency loads. Under the heavy metocean conditions, for the heave and pitch motion of the platform, the non-linear simulation values for some air gap points and areas are negative which means the wave slam has been occurred, but the calculation results of linear motion response indicate that the air gap above has not appeared the wave slamming areas. The simulation results present that the influence of the second-order wave loads is a critical part in the air gap prediction for the semi-submersible platform.
Parametric Evaluation of Forces Due to a Passing Ship on a Moored Ship Using CFD Simulation
Authors: Radhakrishnan Sreedevi , Nallayarasu S.
Published: October 2021

Over the years, with advancements in the shipping industry, there has been considerable increase in size, numbers and speed of ships. Ports and harbours have to handle these larger ships and increased ship traffic within the limited space especially in matured ports. Due to the above mentioned issues at the ports and harbours, passing ship interactions with a moored ship is eventual. Pressure variations around the passing ship may cause additional forces and moments on the ship moored in the vicinity. Though there is literature from past research available on the subject, only few parameters have been investigated. The passing ship forces on a moored ship has been evaluated using Computational Fluid Dynamics (CFD), based on a double-body flow model. Simulations were carried out for three-dimensional, unsteady, inviscid flow using overset meshing technique to facilitate the movement of the vessel. The results obtained from CFD simulations were compared with the existing results obtained by experiments (Remery, 1974) for the validation of the CFD model. Detailed parametric studies were carried out for parameters such as velocity ratio and displacement ratio, spacing ratio, and water depth ratio. Empirical equations for force and moment coefficients are derived based on the present study and recommendations for passing vessel distances from moored vessel has been made in the article.
Impact of Various Nanoparticles on the Viscous Properties of Water Based Drilling Fluids
Authors: Alvi Muhammad Awais Ashfaq , Belayneh Mesfin , Saasen Arild , Bandyopadhyay Sulalit
Published: October 2021

Properly designed drilling fluid is a key element in achieving safe and effective drilling operations. Rheological parameters of drilling fluid determine the equivalent circulation density, the pump pressure, and hole cleaning efficiency. Also, they have a significant role in predicting the stability of drilling fluid under static and low shear rates. The chemical composition of the drilling fluid controls the rheological parameters. Recently, studies have shown that a small concentration of nanosized materials in the drilling fluid can substantially impact the rheological parameters of the drilling fluids.

In this study, various nanoparticles (NPs) with different shapes, sizes, and surface charges were used to investigate their impact on the viscous properties of water-based drilling fluid. Bentonite and KCl water-based drilling fluids were used as the base fluids. NPs such as Iron oxide, Silica (SiO2), and multi-walled carbon nanotubes (MWCNT) were added to these base fluids. Also, surface functionalization of the NPs with polymer and functional groups such as -OH and -COOH groups was done to compare the effect of bare NPs with surface functionalized NPs. Hershel-Buckley model with dimensionless shear rates was used to calculate the low and high shear curvature exponents, surplus stress, and yield stress of the samples.

Results indicate that NPs alter drilling fluid’s viscous properties based on their sizes, shapes, and surface charges. Moreover, the functionalization of NPs also modifies the properties based on the functional group attached to the NPs surface. This work shows that changing the size, shape, and surface charge of NPs has impact on viscous parameters, and NPs with different properties can fine-tune the fluid’s viscous properties based on the requirement for drilling fluid.