bluuebunny/crossref_metadata_2025 huggingface dataset:
Assisted reproductive technology and neonatal intensive care unit: A retrospective observational study from a single center
Authors: Ibi Kyosuke , Takahashi Naoto
Published: October 2022

Background

An increasing number of infants are being conceived using assisted reproductive technology (ART). The effects of infertility treatments (IFTs) on infant outcomes have been extensively debated; however, a consensus has not yet been reached. In the present study, we investigated the impact of IFTs on neonatal intensive care unit (NICU) managements using data collected at a single large NICU center.

Methods

We retrospectively investigated patients admitted to the University of Tokyo Hospital NICU during three different time periods (2010, 2015, and 2020). We included 131, 201, and 323 infants, respectively, and compared a number of factors among groups classified by the mode of conception: spontaneous pregnancy (SP), non‐ART (conceived with assisted ovulation or artificial insemination), and ART. We also compared the mode of conception among inborn singletons.

Results

The rate of admission of ART infants significantly increased from 2010 (9.1%) to 2015 (22.9%) and 2020 (25.7%) (p values of <0.05 and <0.01, respectively). When compared among inborn singletons, ART infants were more often admitted to NICU (p < 0.01). Congenital anomalies and surgical interventions were significantly more frequent in the SP group than in the ART group (p < 0.01). No significant differences were observed in neonatal outcomes among ART infants from 2010 to 2015/2020.

Conclusions

The rate of ART infants admitted to the NICU has significantly increased, with ART pregnancies now accounting for 25% of admissions to the perinatal medical center. ART procedure may be a risk factor for NICU admission. Neonatal intensive care is becoming increasingly indispensable for ART pregnancies.
Why and when does CFO ranking in top management team informal hierarchy affect entrepreneurial firm initial public offering fraud?
Authors: Zhang Zhe , Gong Mijia , Jia Ming , Zhu Qi
Published: October 2022

We build upon the approach/inhibition theory of power to explain why and when CFO ranking in top management team (TMT) informal hierarchy may be related to entrepreneurial firm initial public offering (IPO) fraud, a typical type of unethical behaviour with potential benefits and costs. Our theory explains why CFOs with high rankings in TMT informal hierarchy tend to have a high level of psychological sense of power and may pay more attention to potential benefits rather than costs of unethical behaviours, resulting in a high likelihood to engage in fraud during IPO process. We further suggest that the positive relationship between CFO ranking in TMT informal hierarchy and entrepreneurial firms IPO fraud is weakened by CEO narcissism (internal environment) and environmental dynamism (external environment), respectively. Based on a sample of Chinese entrepreneurial firms listed in growth enterprise market from 2010 to 2017, we find support for our theoretical predictions. By focusing on the ‘specialist’ executives – CFOs – the findings suggest the need to consider rankings in TMT informal hierarchy when analysing the antecedents of IPO fraud.
Periodontitis and edentulism as risk indicators for mortality: Results from a prospective cohort study with 20 years of follow‐up
Authors: Antonoglou Georgios N. , Romandini Mario , Meurman Jukka H. , Surakka Markku , Janket Sok‐Ja , Sanz Mariano
Published: October 2022

Aim

To investigate the association between periodontitis and edentulism with cardiovascular disease (CVD) and all‐cause mortality.

Methods

Baseline data of 506 subjects including 256 angiographically verified coronary artery disease patients and 250 matched participants in cardiovascular health from the Kuopio Oral Health and Heart study were collected from 1995–1996. Mortality data were accrued until May 31, 2015, and related to baseline periodontal health and edentulism, assessed as exposure and collected by means of clinical and radiographic examination by a single examiner. Cox proportional hazards regression models were fit using covariates such as age, gender, smoking, BMI, and education.

The final sample size for the periodontitis models ranged from 358 to 376, while the edentate models included 413 to 503 subjects for CVD and all‐cause mortality, respectively with no missing values in the predictor, confounders, and outcome.

Results

The strongest association was found between edentulism and CVD and all‐cause mortality (HR: 1.9 CVD, HR: 1.6all‐cause; p < .01).

Conclusions

Edentulism considered as a poor oral health marker was associated strongly with CVD mortality while periodontitis was not.
Visual comfort generative design framework based on parametric network in underground space
Authors: Gui Yingbin , Zhou Biao , Xie Xiongyao
Published: October 2022

With the growing demand for a high‐quality life, visual comfort (VC) is becoming increasingly important for improving the quality of underground spaces. The underground space landscape features can be defined by the spatial and material parameters of the components. This study proposes a novel parametric generative network (StepGN) for the 3D generative design of VC. It combines parametric modeling, VC evaluation, and a novel reinforcement learning (RL) model called encoded soft actor critic (ESAC) and simplifies the optimization of complex VC scenes into a parameter‐generating optimization process. Among them, parametric modeling is used to generate a 3D underground space scene with components and material properties through parameterization, and the optimization of parameters depends on the evaluation and RL model. The evaluation model provides reward value, and a new ESAC algorithm is developed. It combines the soft actor‐critic (SAC) algorithm with the encoder process and by setting the reward with a confidence threshold. In addition, the Swin cosine distance (SCD) is used to measure the diversity of the generated scenes. A comparison of the policy types and range conversion methods proves that the stochastic policy and Sigmoid function are more suitable for the generative design of VC. By comparing StepGN with a generative adversarial network‐based generative network (VCGN) and other RL processes, it shows that StepGN can generate discrete distributions of the VC levels and can realize a high‐comfort level scene, and the training speed and stability are considerably improved. Finally, StepGN is applied for the optimization of the Wujiaochang subway station scene in Shanghai, and it is proved that the VC of the generated results can provide a high comfort level.
Long‐lasting effects of harsh early‐life conditions on adult survival of a long‐lived vertebrate
Authors: Payo‐Payo Ana , Sanz‐Aguilar Ana , Oro Daniel
Published: October 2022

Early life conditions, especially in long‐lived organisms, can have both immediate and long‐lasting effects in vital traits generating demographic structure across cohorts. Multiple non‐exclusive hypotheses have been proposed to explore this question. For instance, the silver spoon, the viability selection or the predictive adaptive response hypothesis, predict that long lasting effects resulting from harsh early conditions could be negative, positive or vary with current environmental conditions, respectively. We use an 18‐year capture–mark–recapture dataset on adult Audouin's gulls Ichthyaetus audouinii to test for these different hypotheses while accounting for age, breeding experience and large‐scale dispersal. Audouin's gull cohorts experiencing harsh conditions during early life (i.e. nestling period and first winter) are known to experience lower first year survival. Here, we show that early life conditions also explained a large proportion (54%) of adult survival variation among cohorts. However, adulthood cohorts experiencing poor early life conditions had higher adult survival, in accordance with the viability selection hypothesis. Our results also show that apparent inexperienced breeders showed lower survival than experienced ones. Moreover, adult survival decreased with age. These results could suggest an increased cost of reproduction for deferred breeders, individual quality differences or survival senescence in this population. Overall, our study highlights the importance of early development, age and breeding experience as potential factors generating heterogeneity of survival between cohorts. Understanding the mechanisms driving responses to early life conditions at different life stages is fundamental to understanding the long‐term dynamics of wild populations.
Geomorphology shapes relationships between animal communities and ecosystem function in large rivers
Authors: Scholl Eric A. , Cross Wyatt F. , Guy Christopher S.
Published: October 2022

Understanding how the Earth's surface (i.e. ‘nature's stage') influences connections between biodiversity and ecosystem function (BEF) is a central objective in ecology. Despite recent calls to examine these connections at multiple trophic levels and at more complex and realistic scales, little is known about how landscape structure shapes BEF relationships among animal communities in nature. We coupled high‐resolution habitat mapping with extensive field sampling to quantify connections among the geophysical habitat templet, invertebrate assemblages and secondary production in two large North American riverscapes. Patterns of sediment size governed invertebrate assemblage structure, with particularly strong effects on composition, richness and taxonomic and functional diversity. These relationships propagated to drive positive relationships between biodiversity and secondary production that were modified by scale, context‐dependencies and anthropogenic modification. Finally, leveraging spatially‐explicit descriptions of geophysical and biological properties, we uncovered distinct and nested spatial scales of biodiversity and secondary production, and suggest that multiple geophysical processes simultaneously influence these patterns at different scales. Together, our findings advance our understanding of relationships between the physical templet and patterns of BEF, and help to predict how perturbations to the Earth's surface may propagate to influence biodiversity and energy flux through food webs.
Bone grafts in dentistry: A case report of migration of bone graft material
Authors: Thwaini Mustafa , Al‐Helou Noor , Lord Tim , McKernon Sarah
Published: October 2022

Bone graft materials are becoming more frequently utilised in dentistry. The evolution of materials means that practitioners need to understand the wide spectrum of graft materials used both previously and currently. We report a case of a patient who had graft material placed over 35 years ago which presented in a distant site.
What we know and what we don't know about the perioperative use of methadone in children and adolescents
Authors: Boisvert‐Plante Virginie , Poulin‐Harnois Christelle , Ingelmo Pablo , Einhorn Lisa M.
Published: October 2022

Postoperative pain control is essential to optimizing patient outcomes, improving satisfaction, and allowing patients to resume their baseline functional activities. Methadone, a synthetic mu‐opioid agonist, has multiple pharmacologic properties that may be optimal for perioperative use. Compared to other opioids, methadone has a longer duration of action, rapid onset, extended dosing intervals, high oral bioavailability, low cost, lack of active metabolites, and action on multiple receptors. The current literature examining the use of methadone in the perioperative care of children and adolescents is limited and most often reported within the context of spine or cardiothoracic surgery. Overall, these studies support the hypothesis that perioperative methadone in pediatric patients may decrease postoperative pain, opioid consumption, length‐of‐stay, and the incidence of some opioid‐related side effects, like constipation and urinary retention. A variety of protocols for the perioperative use of methadone have been described, including a single intraoperative dose as well as multiple small doses within multimodal pain protocols. The superiority of these protocols has not been established. Like all opioids, methadone has a side effect profile which includes nausea, vomiting, reduced GI motility, sedation, and respiratory depression at high doses. There is also a concern that it can cause QTc prolongation in patients. The primary aim of this educational review is to examine the pharmacologic data, published perioperative protocols, dosing considerations, and risks and benefits associated with inclusion of methadone in analgesic regimens for surgical patients. A secondary aim is to introduce opportunities for research around the perioperative use of methadone in children and adolescents. Based on our review, we would prioritize establishing optimal procedure‐specific methadone protocols, determining generalizability for use in routine pediatric surgeries, and investigating methadone safety and efficacy prospectively as the primary opioid for pain management in the postanesthesia care unit or postsurgical floors.
Redundancy allocation under state‐dependent distributional uncertainty of component lifetimes
Authors: Li Jun , Huang Yizhe , Li Yan‐Fu , Wang Shuming
Published: October 2022

In this paper, we consider a redundancy allocation problem in a series‐parallel system with uncertain component lifetimes of multiple states, which involves multitype components and mixed redundancy strategy. We develop a distributionally robust redundancy allocation model using state‐dependent ambiguity set, which describes the mean, expected cross‐deviation, and the support conditional on each state of the component lifetime distribution. Our structural analysis of the worst‐case system reliability function identifies a concave equivalent for the conditional worst‐case reliability function in each state and achieves an averaged finite piece‐wise affine representation for the overall worst‐case system reliability function, which enjoys valuable operational insights for reliability evaluation and scalable optimization of the redundancy designs. Furthermore, we analyze the reliability guarantees for the worst‐case reliability in optimality under possible misspecification of ambiguity‐set parameters, which admit the structure of “Reliability Target + Target Surplus + Estimated Elasticity,” and insightfully imply that the auxiliary dual variables obtained via solving the design problem can be regarded as the scale of elasticity. Computationally, the redundancy design problem can be linearized and reformulated as a mixed 0–1 second‐order cone program. Exploiting the above finite piece‐wise affine structure of the worst‐case reliability function, the design problem also admits a practical iterative decomposition scheme with finite convergence, which is more scalable especially for the possible situations of large number of states in practice. Finally, numerical experiments including a case with real‐life data of braking system components well justify the value of state information incorporated by our model in producing favorable cost‐effective redundancy designs for reliability operations.
Life event stress is associated with blunted cardiovascular responding to both personally salient and personally non‐salient laboratory tasks
Authors: Howard Siobhán , Gallagher Stephen , Ginty Annie T. , Whittaker Anna C.
Published: October 2022

Life event stress has been associated with blunted cardiovascular reactivity to acute psychological stress. However, recent studies have suggested that blunted reactivity to stress only arises when the laboratory tasks are not personally salient to the individual. We re‐analyzed data from 136 healthy young adults where we had previously reported a negative association between life event stress and cardiovascular reactivity to two combined stressors. Participants completed a mental arithmetic task and a personally salient speech task, following a formal baseline period with Finometer‐assessed cardiovascular parameters. The reanalyses examined reactivity to the verbal mental arithmetic (personally non‐salient) and speech (personally salient) tasks separately and found that life event stress was negatively associated with diastolic blood pressure reactivity, to both the personally non‐salient, β = −.20, p = .023, and personally salient stressors, β = −.24, p = .004. Life event stress was negatively associated with systolic blood pressure reactivity to the personally salient stressor only, β = −.20, p = .021, and was not associated with heart rate reactivity. This study provides evidence against the argument that blunted reactivity to stress emerges as a result of stressor context, with findings indicating that low reactors show lower reactivity to both personally salient and personally non‐salient stress.
Longitudinal stability and change in time–frequency measures from an oddball task during adolescence and early adulthood
Authors: Malone Stephen M. , Harper Jeremy , Iacono William G.
Published: October 2022

Time–frequency representations of electroencephalographic signals lend themselves to a granular analysis of cognitive and psychological processes. Characterizing developmental trajectories of time–frequency measures can thus inform us about the development of the processes involved as well as correlated traits and behaviors. We decomposed electroencephalographic (EEG) activity in a large sample of individuals (N = 1692; 917 females), assessed at approximately 3‐year intervals from the age of 11 to their mid‐20s. Participants completed an oddball task that elicits a robust P3 response. Principal component analysis served to identify the primary dimensions of time–frequency energy. Component loadings were virtually identical across assessment waves. A common and stable set of time–frequency dynamics thus characterized EEG activity throughout this age range. Trajectories of changes in component scores suggest that aspects of brain development reflected in these components comprise two distinct phases, with marked decreases in component amplitude throughout much of adolescence followed by smaller yet significant rates of decreases into early adulthood. Although the structure of time–frequency activity was stable throughout adolescence and early adulthood, we observed subtle change in component loadings as well. Our findings suggest that striking developmental change in event‐related potentials emerges through a gradual change in the magnitude and timing of a stable set of dimensions of time–frequency activity, illustrating the usefulness of time–frequency representations of EEG signals and longitudinal designs for understanding brain development. In addition, we provide proof of concept that trajectories of time‐frequency activity can serve as potential endophenotypes for childhood externalizing psychopathology and alcohol use in adolescence and early adulthood.
Benefits of and strategies to update premium rates in the US National Flood Insurance Program under climate change
Authors: Zhang Fang , Lin Ning , Kunreuther Howard
Published: October 2022

The United States’ National Flood Insurance Program (NFIP) has accumulated over $20 billion in debt to the US Treasury since 2005, partly due to discounted premiums on homes in flood‐prone areas. To address this issue, FEMA introduced Risk Rating 2.0 in October 2021, which is able to assess and charge more accurate and equitable rates to homeowners. However, rates must be continually updated to account for increasing flood damage caused by sea level rise and more intense hurricanes due to climate change. This study proposes a strategy to adopt updated premium rates that account for climate change effects and address affordability and risk mitigation issues with a means‐tested voucher program. The strategy is tested in a coastal community, Ortley Beach, NJ, by projecting its future flood risk under sea level rise and storm intensification. Compared with using static rates for all the properties in Ortley Beach, the proposed strategy is shown to reduce the NFIP's potential losses to the community from 2020 to 2050 by half (from $4.6 million to $2.3 million), improve the community's flood resistance, and address affordability concerns. Sensitivity analysis of varying incomes, loan interest rates, and conditions for a voucher indicates that the strategy is feasible and effective under a wide range of scenarios. Thus, the proposed strategy can be applied to various communities along the US coastline as an effective way of updating risk‐based premiums while addressing affordability and resilience concerns.
Differences in kinetic variables between injured and uninjured rearfoot runners: A hierarchical cluster analysis
Authors: Senevirathna Angela M. , Pohl Andrew J. , Jordan Matthew J. , Edwards William Brent , Ferber Reed
Published: October 2022

Running is a popular form of physical activity with a high incidence of running‐related injuries. However, the etiology of running‐related injuries remains elusive, possibly due to the heterogeneity of movement patterns. The purpose of this study was to investigate whether different clusters existed within a large group of injured and uninjured runners based on their kinetic gait patterns. A sample of 134 injured and uninjured runners were acquired from an existing database and 12 discrete kinetic and spatiotemporal variables which are commonly associated with running injuries were extracted from the ground reaction force waveforms. A principal components analysis followed by an unsupervised hierarchical cluster analysis was performed. The results revealed two distinct clusters of runners which were not associated with injury status (OR = 1.14 [0.57, 2.30], χ2 = 0.143, p = 0.706) or sex (OR = 1.72 [0.85, 3.49], χ2 = 2.3258, p = 0.127). These results suggest that while there appeared to be evidence for two distinct clusters within a large sample of injured and uninjured runners, there is no association between the kinetic variables and running related injuries.
A Fluid-Structure Interaction Model on the Hydroelastic Analysis of a Container Ship Using preCICE
Authors: Wei Yujia , Tezdogan Tahsin
Published: October 2022

Commercial vessels have recently shown a common trend in increasing their sizes to meet the growing demand for transportation and operations. This trend may however result in more flexible or ‘softer’ hulls. The flexible hull structure reduces the ship natural frequency close to the wave encounter frequency, increasing the probability of resonance or high-frequency vibrations. Meanwhile, the resulting structural deformations from flexible hull could significantly affect the flow field and the hydrodynamic loads cannot be estimated accurately. Hence, it is important to treat a flexible hull and its surrounding flow field as an interacting system to predict a ship’s dynamic behaviour based on the hydroelastic theory. In this study, a novel fluid-structure interactions coupling scheme using the “preCICE” library to communicate with the fluid solver “OpenFOAM” and structure solver “calculiX” was first proposed to study the hydroelastic behavior of a container ship with a forward speed in regular waves. With the advantage of this numerical model, the flexible behaviour of this ship, such as its vertical bending displacement and corresponding bending moment can be quantified, and the “springing” and “whipping” responses can be calculated. It is believed that the present FSI model will exhibit more advantages over the traditional rigid-body methods currently used in the ship seakeeping field.
Simulation of a Vertical Riser System Composed of Two Pipes for Deep Sea Mining
Authors: Yamamoto Marcio , Yamamoto Joji , Masanobu Sotaro
Published: October 2022

The Deep Sea Mining will require a vertical riser system to convey a slurry composed of the ore and seawater from the seafloor up to the floating platform. Then a second pipe shall be necessary to return this seawater to be discharged above the seafloor.

We carried out numerical simulation in the time domain, assuming a 4,000 m riser system composed of two rigid pipes with the same diameter and thickness. The numerical model has two separate pipes in side-by-side and tandem configurations regarding the platform’s forward motion. These two pipes are attached in the way they shall bend together. We assumed a current profile, irregular waves, and floating platform motion as external loads. Besides, we considered the three different boundary conditions for the bottom end of the riser, namely, (i) no equipment, (ii) 300-ton submerged pump, and (iii) 500-ton submerged pump attached to the bottom end.

We observed the Mathieu Instability in both configurations with no pump. For the cases with pumps attached to the bottom end, the Mathieu Instability did not occur because the pump’s wet weight kept the pipes tensioned throughout the whole simulation. Finally, the set of pipes in tandem configuration with a 300-ton pump had the best dynamic response among the cases studied in this article.
Numerical Simulations of Static Rudder Tests Based on Two Propeller Modeling Methods
Authors: Chen Changzhe , Liu Jinzhou , Zou Lu , Zou Zaojian
Published: October 2022

Simulating the captive model tests using Computational Fluid Dynamics (CFD) technique to obtain the hydrodynamic derivatives and hull-propeller-rudder interaction coefficients has been proved to be an effective method for establishing the mathematical model of ship maneuvering motion. To simulate the captive model tests for a fully appended ship model, the key issue is to choose a suitable modeling method for the propeller to calculate the hydrodynamic force on the ship with high efficiency and enough accuracy. In this paper, the Reynolds-averaged Navier-Stokes (RANS) equations are solved by using CFD method to simulate the static rudder tests of the fully appended KRISO ship KVLCC2 model, with the propeller being treated by the Multiple Reference Frames (MRF) method and the Sliding Mesh (SM) method and the sinkage and trim being taken into consideration. The reliability of the numerical method is verified by comparing the computed hydrodynamic results with the available benchmark data. The flow field information obtained from the numerical simulations is used to analyze the hydrodynamic phenomena related to the different propeller modeling methods. Comparing the results of the two methods for dealing with the propeller shows that the SM method’s accuracy is slightly higher than that of the MRF method for the computed force/moment on the hull/rudder, while the MRF method under-estimates the thrust of the propeller.
Two-Phase Flow Induced Vibrations With CO2 Multiphase Flow
Authors: Belfroid Stefan , Orre Steinar , Bazuin Rens , Lunde Knud
Published: October 2022

In CO2 storage plants, internal multiphase flow of CO2 may occur in piping elements in various parts of the process. From the energy and process industries, it is known that multiphase flow can induce high amplitude vibrations, especially in flexible piping. In the last decade, experimental data sets and results from excitation spectrum modelling have become available for fluid systems involving oil, gas, water, and steam. Multiphase flow-induced vibrations are affected by fluid properties, and the properties of CO2 are quite different from those of water and oil. To address this uncertainty a multiphase CO2 test campaign was performed in the same flow loop that high pressure gas/water/oil experiments had been performed previously. The vibrations measured in the CO2 tests were in line with those measured in the high pressure gas/water and gas/oil cases. Although multiphase flow of CO2 tends to be more mixed and with less slip than typical of the other fluid systems, the measured vibrations are still a factor of 2–3 higher than for single-phase liquid CO2 flows. A conclusion is that CO2 multiphase induced forces can be modelled in line with the high pressure gas/water systems.
An Implicit Time-Domain Rankine Panel Method for Ship Motions in a Non-Inertial Body-Fixed Frame of Reference
Authors: Liang Hui , Shao Yanlin , Chua Kie Hian , Magee Allan
Published: October 2022

Evaluation of wave loads on a ship translating in water waves is of practical importance in ship hydrodynamics, because it is paramount to the design of ship hull structures and provides essential inputs for ship maneuvering analysis. The linear radiation and diffraction of water waves by a translating ship is studied in this paper. A time-domain Rankine panel method is developed in a non-inertial body-fixed coordinate system, which is able to consider large-amplitude horizontal motions consistently. The double-body flow is used as the basic steady flow model. To ensure numerical stability, an implicit Euler scheme is adopted for time marching, and horizontal derivatives on the free surface are calculated using an upwind-biased finite difference scheme. Numerical examples in comparison with experimental measurements are exhibited to demonstrate the validity of the developed solver.
Numerical Simulation of the Wave-Induced Drift of Floating Marine Plastic Debris Modeled as Discrete Particles
Authors: Sainte-Rose Bruno , Rakotonirina Andriarimina Daniel , van den Bremer Ton , Pham Yannick
Published: October 2022

The Ocean Cleanup Foundation is developing floating barrier systems to concentrate and extract buoyant plastics from the global accumulation regions located in the subtropical convergence zones in the world’s oceans. In this context, it is important to understand the transport and accumulation of these floating marine debris. Since marine litter transport is a multi-scale problem, it is important to know the transport of these objects at their very own scale. For this end, two Discrete Particle Models have been implemented in the open-source two-phase Navier-Stokes flow solver Basilisk to study their wave-induced drift: i) using a simple linear interpolation and ii) using the high-order WENO interpolation scheme (Jiang and Wu [1999]) combined with reference frame intrinsic to the particle and its time-dependent submergence. It is shown that in longtime trajectory along the free surface, the two models differ drastically and the sophisticated one shows the best performance. A performance that is highlighted through a wave-induced drift factor defined as the ratio between the wavelength averaged plastic velocity and the wavelength averaged water particle Stokes drift.
VIV Responses of a Drilling Riser Subjected to Current and Top Motions
Authors: Wu Jie , Yin Decao , Jin Jingzhe , Lie Halvor , Passano Elizabeth , Sævik Svein , Tognarelli Michael A. , Grytoyr Guttorm , Igland Ragnar , Karunakaran Daniel , Anderson Torgrim , Gaskill Collin
Published: October 2022

Vortex induced vibrations (VIV) have been subjected to extensive studies, but most of the research focuses on VIV in a constant flow. However, slender marine structures are often experiencing complex environmental conditions. As an example, the drilling riser may be subjected to vessel motions at the top end of the riser, wave loads, in addition to ocean currents. The consequence of the top motions is that the relative flow speed field is changed especially close to the top end of the riser. VIV responses can be significantly affected if the relative flow speed induced by top motions is in the same order as the current speed, which are further affected by the direction of the top motion relative to the current direction. The influence of top motions on VIV responses is less understood. Such effects are also neglected in the present design practice based on frequency domain prediction tools, which can not combine two simultaneously acting load processes. This has been investigated in the present work based on the analysis of laboratory test data and numerical case studies with a time domain VIV prediction tool. The results showed the importance of including top motions in a time domain VIV analysis.
Modelling Aerodynamics of a Floating Offshore Wind Turbine Using the Overset Mesh Solver In OpenFOAM
Authors: Lin Zaibin , Qian Ling , Campobasso Michele Sergio , Bai Wei , Zhou Yang , Ma Zhihua
Published: October 2022

An accurate prediction of aerodynamic and hydrodynamic loads on an offshore floating wind turbine plays a critical role in determining its operational stability, fatigue life and survivability, as well as optimising its power control system. Therefore, it is essential to develop an integrated aerodynamics and hydrodynamics model, which is capable of capturing both loading on and dynamic response of an entire offshore wind turbine system with high accuracy and reliability. Prior to developing such an integrated model, aerodynamics and hydrodynamics models need to be systematically examined, individually. In this study, the performance of the overset mesh solver in OpenFOAM for modelling aerodynamics of a floating offshore wind turbine rotor is evaluated. A benchmark test on the rotor of the National Renewable Energy Laboratory (NREL) 5MW turbine, which is designed to be mounted on a semi-submersible platform is performed. The predicted power and thrust for cases of the rotor with its centre fixed and undergoing pitching motion are compared between the overset mesh solver, a frequency-domain Naiver-Stokes Computational Fluid Dynamics code and the open-source Blade Element Momentum theory code.
Hybrid Multiphase CFD Model for Bubbly, Slug, Churn and Annular Flow Regimes in Vertical Pipes
Authors: Agrawal Madhusuden , Khanna Samir , Kopliku Ardjan , Lockett Timothy
Published: October 2022

Prediction of erosion rate or flow-induced vibrations and fatigue assessment depends strongly on the way multiphase flow occurs through the fitting such as bend, tee, manifolds, etc. Therefore, it is important to have a better understanding of multiphase behavior to improve confidence in erosion and fatigue prediction. Multiphase flow behavior is more complex in vertical pipe compared to horizontal pipe because of the phenomena generated when the gravity vector aligns with the axis of the pipe. Transport mechanisms for gas-liquid multiphase flow in vertical pipe broadly consist of (i) entrance effects due to short unstable liquid slugs which form at the entrance, (ii) a flooding effect as liquid film drains downward along the wall, (iii) a wake effect from one slug that can destroy neighboring slugs and, (iv) coalescence of gas phase entrained in liquid slugs. This paper presents a hybrid multiphase modelling approach, which combines the Eulerian-Eulerian model and the Volume of Fluid (VOF) model to effectively capture all these transport mechanisms. A hybrid multiphase model allows selective use of surface tension and interface sharpening schemes in a Eulerian framework for any flow regimes.

Experimental dataset on 67mm and 127mm diameter vertical pipe from Abdulahi ([1], [14], [15]) and Azzopardi ([16], [17], [18]) were used to benchmark CFD modelling for bubbly, slug, churn, and annular flow regimes in vertical straight pipe. These data contain multiphase flow characteristic for air-water and air-oil at both atmospheric pressure and elevated pressure. The predicted results obtained with our model show good agreement with the experimental work and clearly highlight the benefits of applying the hybrid multiphase modelling to predict the flow regimes and to get better understanding of complex flow behavior in gas-liquid vertical flows. Furthermore, sensitivity studies were performed to understand the effect of drag models, inlet boundary treatment, solution initialization, mesh resolution, and time step size on CFD predictions for multiphase flow in vertical pipes.
Life-Cycle Cost Analysis on a Marine Engine Innovation for Retrofit: A Comparative Study
Authors: Bui Khanh Q. , Perera Lokukaluge P. , Emblemsvåg Jan , Schøyen Halvor
Published: October 2022

Stricter regulations and ambitious targets regarding air emissions from ships have led the shipping industry to a tipping point necessitating disruptive technologies for green and ecological operation. This study introduces a dual-fuel engine innovation with ultra-high energy conversion efficiency, thereby reducing exhaust gas emissions. However, the total cost performance of such an innovation throughout its long lifespan can be a matter of concern for decision makers (i.e. ship owners) if they decide to retrofit their existing fleet. The purpose of this study is to provide insights into the economic performance of such an innovative dual-fuel engine when it is utilized as the main propulsion system. From a cradle-to-grave perspective ranging from construction, operation, maintenance to end-of-life, the life-cycle costing (LCC) framework is proposed to evaluate the long-term cost performance of the dual-fuel engine with that of a conventional diesel engine. By using the net present cost (NPC) as an evaluation indicator, the research results reveal that the dual-fuel engine is considered as a cost-effective option except for the high fuel price differential scenario, meaning that fuel prices are the most critical factor for ship owners. In addition, the environmental impact of these engines is included in the evaluation to show that 33% reduction in emissions of carbon dioxide (CO2) can be achieved when running the dual-fuel engine, compared to the diesel engine. The proposed framework could conceivably be beneficial in selecting marine engine innovation that takes not only the environmental impact but also the economic performance into consideration.
Two-Dimensional Numerical Analysis of Mean Wave Drift Loads on Two Fixed Boxes
Authors: Tan Lei , Ikoma Tomoki , Hu Changhong
Published: October 2022

Wave drift forces on two barges in side-by-side arrangement are of engineering significance for control of the distance between the vessels. Hence the influence of resonant behaviors between the two barges on drift forces is worthy to investigating. In this paper, a two-dimensional numerical model is developed to evaluate the time-averaged drift forces on two floating bodies. The near-field and far-field methods have been implemented in an in-house program code for computations. First, numerical validations were conducted against published data in literatures. Then, the influence of the gap width and edge shapes of two fixed floating boxes were investigated numerically. It is found that the total mean surge drift force in wave direction was substantially reduced by the piston mode resonance in the gap, whereas considerable drift forces were observed on two respective boxes in opposite directions. Further examinations indicate that the effect of resonant wave behaviors on drift force is dependent on viscous damping of gap resonance.
On the Calibration of Metocean Time Series Using Machine Learning
Authors: Enet François , Podrazka Olga , Renac Laury
Published: October 2022

Nowadays, numerical model data is one of the primary inputs to all metocean studies, whether for deep-water locations or coastal applications. This paper presents the use of machine learning to calibrate long term metocean time series of wind and wave parameters obtained from numerical models against measurement records, usually covering shorter periods. We present the added value of machine learning compared to standard calibration methods to improve data used as primary input to both operability studies and engineering design studies. Time series of wind and wave parameters obtained from global numerical hindcast data sets are compared to oceanographic buoy measurements. We investigate the improvement brought by machine learning methods on the quality of the calibrated populations for the bulk of the distributions, but also the agreement between the calibrated data and the measurements for extreme events, not only for peak values but also for storm profiles. We evaluate the reliability of the method by comparing the results over different periods at 1 location and with varying length of training, validation and test sets.
Dynamic Analysis of Blade Mating Process Using Jack-Up Crane Vessel: A Code-to-Code Comparison
Authors: Bhaskaran Saravanan , Verma Amrit Shankar , Yuan Shuai , Halse Karl Henning
Published: October 2022

Offshore wind turbine blade installation is a challenging task. Jack-up crane vessels are commonly used for blade installation in shallow waters. The motion of the blade root is mainly due to wind loads on the lifting arrangement and wave loads on the jack-up legs. The relative motion between the blade and the hub should be minimal during the blade mating process to avoid structural damage. Thus, it becomes crucial to reliably estimate the motion of the blade installation system. Currently, there are several software and tools that are used to perform such an analysis, however there are no experiment results available for validation. Hence, a comparison exercise of their results is necessary for a reliable prediction of dynamic responses. This study aims to numerically model the blade mating process using a jack-up crane vessel in Orcaflex, and perform a code-to-code comparison with SIMA using the published results. The comparison was performed at different levels — (1) modal analyses of the jack-up vessel and the blade lifting arrangement, and (2) time-domain analysis for fully coupled model of installation system. The results of the study show that there is good agreement between the results from SIMA and OrcaFlex.
Accurate WEC Power Estimation for Multi-Modal Wave Spectra
Authors: Parsa Kourosh , Kim Mark , Williams Neil
Published: October 2022

The amount of power generated by a wave energy converters (WECs) is generally dependent on the wave height and period. When the power performance of a WEC is analyzed via simulations, idealized wave spectra are commonly used to estimate the power output under a range of sea states. Then, from those results, a power characteristic matrix is formed, which is then used to estimate the WEC’s generation capability at any site of interest. However, the power performance of a WEC is also dependent upon the shape of the spectra, especially if the sea state is a combination of wind-generated (short) and swell (long) components, each with its own spectra. Under such a circumstance, considering only the wave height and period can lead to erroneous results. In this paper, we propose decomposing each wave spectrum into its components. The power-generation capability corresponding to each component can then be estimated, and the largest value can be taken as the power number associated with that sea state. The efficacy of this approach was assessed via conducting a simulation study on the power performance of the OPT PB3 PowerBuoy® at a point offshore Chile. The results show that the annual and maximum monthly mean relative errors incurred are under 0.6% and 2.5%, respectively, thus validating the efficacy of the method. This approach should be applied in mixed sea conditions to any WEC whose power generation characteristic exhibits strong period dependency.
Modelling Green Water Impact Load on a Single Circular Cylinder
Authors: Gao Min , Draper Scott , McCauley Guy , Chen Lifen , Zhang Xiantao , Wolgamot Hugh , Taylor Paul H.
Published: October 2022

This paper investigates the ability of physical and numerical models to simulate green water impact loads on a circular cylinder located on top of a fixed box. A focused wave group was used to overtop the box and generate the green water event, which resembled a plunging wave with air entrainment. The plunger collapsed and ran across the deck before impacting the cylinder and scattering. With respect to the physical modelling, identical experiments were conducted in two different laboratories, in different countries. The numerical modelling comprised computational fluid dynamics (CFD) simulations performed using OpenFOAM. The flow features, the force on the cylinder and the surface elevation on top of the box are compared in detail across the two physical models and the CFD. Good agreement in the load measurements from the two physical model tests implies very repeatable results despite the complex flow-structure interaction observed. Comparison of the physical and numerical models indicate the flow measured on top of the box and the green water load are sensitive to experimental precision, but agreement is generally satisfactory. This agreement between experiment and CFD serves as an example of the reliability of CFD for modelling green water impact loads.
CFDwavemaker: An Open-Source Library for Efficient Generation of Higher Order Wave Kinematics
Authors: Lande Øystein , Helmers Jens Bloch
Published: October 2022

Computational fluid dynamics (CFD) for propagation of waves have become an important tool for the calculation of wave loading on offshore structures for such problems as run-up, wave slamming and other load related problems where nonlinear breaking wave kinematics is of importance.

There are multiple CFD codes, both commercial and open source which today supports features related to wave propagation. Examples are OpenFOAM, ComFLOW, Basilisk, StarCCM+ and more. All of these codes require the either initialization of the domain or propagation of waves from the boundaries, with a known theoretical solution or with the use of wave paddles. In terms of higher order theoretical wave descriptions, the most frequent implementations are often limited to uni-directional regular waves, which is well defined and efficient to calculate. However, ocean waves are neither regular nor long crested.

CFDwavemaker is a cross-platform open-source library which provides higher order non-linear wave kinematics for irregular and short-crested waves, purpose built for initialization and generation of waves at the domain boundary of CFD domains. The library is written in C++ and may be compiled and linked into most CFD codes.

The library has built-in second order irregular wave theory and supports the use of Higher-order Spectral methods (HoS) as input through the extension Spectral Wave Data (SWD). The code is designed to utilize multiprocessing and advanced interpolation schemes which are favorable for efficient generation of higher-order wave kinematics generation.
Stress Analysis for Three-Dimensional Structures Considering the Global Hydroelasticity by Beam Connected Discrete Modules Method
Authors: Zhang Shiyuan , Li Shuai , Fu Shixiao , Moan Torgeir , Pan Zhiyuan , Xu Yuwang , Song Bin
Published: October 2022

This paper proposes a stress analysis method for three-dimensional structures, with the consideration of the global hydroelasticity which is calculated through the beam connected discrete modules method. First, the continuous structure is discretized into rigid modules connected by elastically equivalent beams. The hydroelastic responses are solved by the coupling of the hydrodynamics of rigid modules and the structural stiffness of elastic beams. Then, according to six degrees of freedom motions of each module extracted from the hydroelasticity, the pressure distributions of rigid modules can be obtained based on the three-dimensional potential theory. Finally, the inertia force and the pressure distributions are statically loaded on three-dimensional finite element model. The process is applied to a barge under the regular wave. In rigid condition, the local stress using the proposed method is verified against the result from the Quasi-static method. Furthermore, the springing effect on the local stress is investigated. In the test model, the result shows that the springing effect induces an obvious difference.