bluuebunny/crossref_metadata_2025 huggingface dataset:
Chasing the Mirage: a grounded theory of the clinical reasoning processes that Registered Nurses use to recognize delirium
Authors: El Hussein Mohamed , Hirst Sandra
Published: October 2015

Aim

The aim of this study was to construct a grounded theory that explains the clinical reasoning processes that registered nurses use to recognize delirium in older adults in acute care hospitals.

Background

Delirium is under‐recognized in acute hospital settings, this may stem from underdeveloped clinical reasoning processes. Little is known about registered nurses’ (RNs) clinical reasoning processes in complex situations such as delirium recognition.

Design

A grounded theory approach was used to analyse interview data about the clinical reasoning processes of RNs in acute hospital settings.

Method

Seventeen RNs were recruited. Concurrent data collection and comparative analysis and theoretical sampling were conducted in 2013–2014.

Findings

The core category to emerge from the data was ‘chasing the mirage’, which describes RNs’ clinical reasoning processes to recognize delirium during their interaction with older adults.

Conclusion

Understanding the reasoning that contributes to delirium under‐recognition provides a strategy by which, this problem can be brought to the forefront of RNs’ awareness and intervention. Delirium recognition will contribute to quality care for older adults.
Fostering critical thinking and reflection through blog‐mediated peer feedback
Authors: Novakovich J.
Published: October 2015

The introduction of digital literacy practices has created a tension in academia, with many academics challenging the view that critical thinking can be fostered on social networks. A quasi‐experimental study was conducted on two sections of university‐level writing classrooms to determine if there were meaningful differences in the quality of writing and peer feedback generated through in‐class draft workshops using traditional methods as compared to draft workshops using a blogging platform. The results indicated that blogs produced a higher quality of writing as measured by grades, f(42) = 11.512, p < .002 and acceptance scores, f(42) = 8.364, p < .006. Furthermore, blog‐mediated peer workshops produced a statistically significantly higher number of critical comments, f(42) = 120.438, p < .000; and directive comments, f(42) = 33.861, p < .000. There were no statistically significant differences in the number of editing comments, f(42) = .001, p < .974, and traditional draft workshops produced a statistically significant higher number of naïve comments, f(42) = 14.119, p < .001. Within the study, critical comments were found to correlate positively with learning outcomes, b = 1.115, t(41) = 2.716, p < .01. The findings suggest that blogging software improved learner performance and fostered complex literacy skills.
A cross‐cultural study of the effect of a graph‐oriented computer‐assisted project‐based learning environment on middle school students' science knowledge and argumentation skills
Authors: Hsu P.‐S. , Van Dyke M. , Chen Y. , Smith T.J.
Published: October 2015

The purpose of this mixed‐methods study was to explore how seventh graders in a suburban school in the United States and sixth graders in an urban school in Taiwan developed argumentation skills and science knowledge in a project‐based learning environment that incorporated a graph‐oriented, computer‐assisted application (GOCAA). A total of 42 students comprised the treatment condition and were engaged in a project‐based learning environment that incorporated a GOCAA. Of these 42 students, 21 were located in the United States and 21 were located in Taiwan. A total of 26 students comprised the control condition and were engaged in a project‐based learning environment without the GOCAA. Of these 26 students, 15 were in the United States and 11 were in Taiwan. In each country, verbal collaborative argumentation was recorded and the students' post‐essays were collected. A one‐way analysis of variance (ANOVA) was conducted for each measure of science knowledge about alternative energies. The results showed a significant treatment effect for the outcome of scientific explanation among U.S. students, while among Taiwanese students, a significant treatment effect on scientific facts was observed. A one‐way ANOVA was additionally conducted for each measure of argumentation skills and a significant treatment effect on counterarguments and rebuttals was observed among the U.S. students, while in Taiwan, a significant treatment effect on reasoning and rebuttals was observed. A qualitative analysis was conducted to examine how the GOCAA supported students' development of argumentation skills in different countries. This study found distinct argumentation patterns between the U.S. and Taiwanese intervention teams. Additionally, a distinct gender difference in the use of evidence and division of labour was noted when the Taiwanese teams were compared with the U.S. teams, which may be explained by cultural differences. This study concluded that, in both the United States and Taiwan, a project‐based learning environment incorporating a GOCAA was effective in improving students' science knowledge and developing their scientific argumentation skills.
Binge Drinking and Risk Taking Behavior Among Adolescent Females in Israel
Authors: Isralowitz Richard , Reznik Alexander
Published: October 2015

Purpose

This prospective study examined binge drinking and alcohol‐related problem behavior among Israeli adolescent females attending public school or a residential facility for substance abuse treatment.

Problem

Scant information is known about adolescent females, especially those with high‐risk (e.g., school dropout and immigrant origin) characteristics.

Methods

The authors hypothesized that school, residential treatment, and mothers' country of origin status are associated with binge drinking and problem behavior.

Findings

Females in residential treatment reported higher levels of binge drinking and problem behavior as expected. However, country of origin was not a significant factor differentiating the female adolescents in school or a residential facility. Logistic regression points to current cigarette smoking, ease of purchasing alcohol, unsupervised night activity, low religiosity, and being physically threatened as predictors of binge drinking and problem behavior.

Conclusion

The lack of differences based on country of origin status points to acculturation as a possible reason for the homogeneity. Further research is needed to study the impact of acculturation as well as monitor the alcohol use patterns and problems of adolescents over time and across locations to address prevailing needs.
Oppositional defiant disorder dimensions and subtypes among detained male adolescent offenders
Authors: Aebi Marcel , Barra Steffen , Bessler Cornelia , Steinhausen Hans‐Christoph , Walitza Susanne , Plattner Belinda
Published: October 2015

Background

In adolescent offenders, oppositional defiant disorder (ODD) and its dimensions/subtypes have been frequently ignored due to the stronger focus on criminal behaviours. The revised criteria of the DSM‐5 now allow diagnosing ODD in older youths independent of conduct disorder (CD). This study aimed at analysing ODD dimensions/subtypes and their relation to suicidality, comorbid psychiatric disorders, and criminal behaviours after release from detention in a sample of detained male adolescents.

Methods

Suicidality and psychiatric disorders (including ODD symptoms) were assessed in a consecutive sample of 158 male adolescents (Mage = 16.89 years) from the Zurich Juvenile Detention Centre. Based on previous research findings, an irritable ODD dimension and a defiant/vindictive ODD dimension based on ODD symptoms were defined. Latent Class Analysis (LCA) was used to identify distinct subtypes of adolescent offenders according to their ODD symptom profiles. Logistic regression and Cox regression were used to analyse the relations of ODD dimensions/ODD subtypes to comorbid psychopathology and criminal reoffenses from official data.

Results

The ODD‐irritable dimension, but not the ODD defiant/vindictive dimension predicted comorbid anxiety, suicidality and violent reoffending. LCA identified four subtypes, namely, a no‐ODD subtype, a severe ODD subtype and two moderate ODD subtypes with either defiant or irritable symptoms. The irritable ODD subtype and the severe ODD subtype were related to suicidality and comorbid affective/anxiety disorders. The irritable ODD subtype was the strongest predictor of criminal (violent) reoffending even when controlling for CD.

Conclusions

The present findings confirm the presence of ODD dimensions/subtypes in a highly disturbed adolescent offender sample. Irritable youths were at risk of suicide and persistent criminal behaviours. Due to the severe consequences of irritability, a standardized assessment approach and a specific treatment is needed in prison to prevent suicide among the detainees and further harm to the society. As defined in the DSM‐5, the present findings confirm the validity of ODD and ODD dimensions/subtypes as a diagnostic category among older youths.
Early constraints in sexual dimorphism: survival benefits of feminized phenotypes
Authors: López‐Rull I. , Vergara P. , Martínez‐Padilla J. , Fargallo J. A.
Published: October 2015

Sexual dimorphism (SD) has evolved in response to selection pressures that differ between sexes. Since such pressures change across an individual's life,SDmay vary within age classes. Yet, little is known about how selection on early phenotypes may drive the finalSDobserved in adults. In many dimorphic species, juveniles resemble adult females rather than adult males, meaning that out of the selective pressures established by sexual selection feminized phenotypes may be adaptive. If true, fitness benefits of early female‐like phenotypes may constrain the expression of male phenotypes in adulthood. Using the common kestrelFalco tinnunculusas a study model, we evaluated the fitness advantages of expressing more feminized phenotypes at youth. Although more similar to adult females than to adult males, common kestrel fledglings are still sexually dimorphic in size and coloration. Integrating morphological and chromatic variables, we analysed the phenotypic divergence between sexes as a measure of how much each individual looks like the sex to which it belongs (phenotypic sexual resemblance,PSR). We then tested the fitness benefits associated withPSRby means of the probability of recruitment in the population. We found a significant interaction betweenPSRand sex, showing that in both sexes more feminized phenotypes recruited more into the population than less feminized phenotypes. Moreover, males showed lowerPSRthan females and a higher proportion of incorrect sex classifications. These findings suggest that the mechanisms in males devoted to resembling female phenotypes in youth, due to a trend to increase fitness through more feminized phenotypes, may provide a mechanism to constrain the SD in adulthood.
Impacts of historical records on extreme flood variations over the conterminous United States
Authors: Mei X. , Dai Z. , Tang Z. , van Gelder P.H.A.J.M.
Published: October 2015

Evaluation of flood variations over time, especially for floods with large return periods, is of great significance to flood risk assessment. ‘Historical’ data that have been recorded before the construction of a gauging station provide an effective way to analyse the temporal changes of extreme floods. Here, comparison of maximum likelihood method, L‐moment method and Bayesian theory are made to calculate the Gumbel distribution parameters via Monte Carlo simulation experiment. The best option is applied to 37 unregulated rivers over the conterminous United States to analyse their 100‐year flood variations. The Monte Carlo simulation results indicate that L‐moment method is substantially better than the other two estimators for both systematic and unsystematic series. Over 70% of studied river catchments detect 100‐year flood decrease when the historical data are considered. The impacts of historical records on 100‐year flood variation estimations are closely related to censoring threshold and historical period length.
Wax Lining in an Impression Tray and Accuracy in Gypsum Cast Fabrication
Authors: Hansen Paul , Franco Raul , Beatty Mark
Published: October 2015

Purpose

Controversy exists as to whether lining a metal‐perforated impression tray with wax will yield a distorted irreversible hydrocolloid impression. Two current textbooks have completely different recommendations, but there is no evidence to support either theory. This project evaluates distortion in gypsum casts that have been prepared from wax‐lined and unlined metal impression trays. The purpose of this study was to assess the influence of wax on the border and in the palate of metal‐perforated impression trays on the dimensional stability of the resulting irreversible hydrocolloid impression.

Materials and Methods

A dentaform was prepared with marks on the cusp tips of teeth 6 and 11 and distobuccal cusps of teeth 2 and 15. Using a standard maxillary rim lock impression tray, alginate impressions were made using a dentaform with no wax lining, wax lining the border of the tray, and wax lining the border and the palate (n = 10). Casts were randomized. Six measurements were taken using a stereographic measuring microscope, from tooth #6 to #11, #11 to #15, #15 to #2, #2 to #6, #6 to #15, and #2 to #11. An acrylic template was used to position the cast in a reproducible position on the microscope.

Results

Trays lined with wax on the border and the palate yielded casts with significantly different dimensions when compared to those poured from unlined or border‐lined trays (p < 0.05). Casts produced from unlined and border‐lined trays were not significantly different in dimension from the dentaform (p > 0.05).

Conclusion

There is no difference between the metal tray with no wax, the metal tray with a wax around the border, and the dentaform. The clinician can make irreversible hydrocolloid impressions using wax on the periphery or without wax on the periphery and feel confident that the impression has not been compromised in its ability to accurately reproduce the maxillary arch when used. Caution should be exercised when adding wax to the palate of the impression tray.
In Vivo Comparison of the Masticatory Efficiency of Artificial Teeth with Two Different Cusp Heights in Complete Dentures: A Preliminary Study
Authors: Barbosa Wallace Ferreira , Iegami Carolina Mayumi , Uehara Priscila Nakasone , Furuyama Ricardo Jun , Tamaki Regina
Published: October 2015

Purpose

The goal of complete denture rehabilitation is to restore facial esthetics and masticatory function to edentulous patients. Several types of artificial teeth with different occlusal anatomy are available. Theoretically, teeth with a higher cusp height provide improved masticatory efficiency. The aim of this study was to compare the masticatory efficiency of complete denture wearers using artificial teeth with two cusp heights.

Materials and Methods

Sixteen complete denture wearers were given complete dentures with Heraeus Premium teeth. Fifteen days after denture installation, a first masticatory efficiency test was performed with Optocal. A new pair of complete dentures with Dentsply Biotone teeth was then given to each participant to replace the first set. This second set was fabricated by duplicating the same models used to fabricate the first set of dentures. Fifteen days after installation of the dentures with Biotone teeth, a second masticatory efficiency test was performed with Optocal. On both tests, the comminuted material was treated and sieved through a stack of sieves under vibration. The content of each sieve was weighed, and the obtained data were tabulated. Statistical analysis was performed using the Kolmogorov‐Smirnov and Wilcoxon tests.

Results

Mean and standard deviation of participants’ masticatory efficiency, as measured by X50 particle size (mm), were 8.39 and 5.59 for dentures with Premium teeth, and 8.56 and 5.84 for dentures with Biotone teeth.

Conclusion

According to the results, there were no differences (p < 0.05) in the masticatory efficiency of the complete denture sets using teeth with the two cusp heights.
HYPOTHETICAL SURVEYS AND EXPERIMENTAL STUDIES OF INSURANCE DEMAND: A REVIEW
Authors: Jaspersen Johannes G.
Published: October 2015

We offer a structured literature survey of experimental studies involving insurance demand choices and their experimental methodology. With this, we aim to fulfill two goals. First, we want to give an overview of the status of the literature as is. Second, the overview of the methodology provides researchers with an idea of how insurance demand experiments can be designed and what the advantages and disadvantages of the different design aspects are. We thus offer a resource for the design of future experiments.
Impact of mobile apps to combat obesity in children and adolescents: A systematic literature review
Authors: Quelly Susan B. , Norris Anne E. , DiPietro Jessica L.
Published: October 2015

Purpose

This review examines the impact of mobile app technology on obesity‐related anthropometric, psychosocial, and behavioral outcomes in children and adolescents.

Conclusions

Nine research articles retrieved from a systematic review of the literature met criteria. Evidence is limited and mixed, but argues for an impact of mobile app use on motivation and goal‐setting behavior, and supports further study of the impact on childhood obesity‐related outcomes such as attitudes, perceptions, physical activity, and dietary habits.

Practice Implications

Nurses can use this evidence to discuss potential benefits of health promotion mobile apps with parents, children, and adolescents to combat childhood obesity.
Incumbency Effects under Proportional Representation: Leaders and Backbenchers in the Postwar Italian Chamber of Deputies
Authors: Golden Miriam A. , Picci Lucio
Published: October 2015

We study incumbency effects for individual legislators from two political parties (Christian Democracy and the Italian Socialist Party) in Italy's lower house of representatives over 10 legislatures (1948–92) elected using open‐list proportional representation. Our analysis finds no reelection advantage for the average incumbent legislator. Only a tiny elite in each party successfully creates an incumbency advantage. We find incumbents advantaged for reselection by their political party. We interpret reselection advantage as a party loyalty premium. Our study depicts a political environment monopolized by party leaders who reward party loyalty but hamper legislators in appealing directly to voters.
The Impact of District Magnitude on Voter Drop‐Off and Roll‐Off in American Elections
Authors: Herrnson Paul S. , Taylor Jeffrey A. , Curry James M.
Published: October 2015

This study demonstrates that multimember districts (MMDs) complicate ballots, reduce voter information, and increase incentives for strategic voting in ways that reduce voter participation. Using data from three states that elect members of at least one legislative chamber from both single‐member districts (SMDs) and MMDs, we test hypotheses about the impact on MMDs on ballot drop‐off (selecting fewer candidates for an office than permissible) and roll‐off (not voting in down‐ballot races). We find support for both sets of hypotheses, with the strongest results related to ballot drop‐off. The results have broad implications for voter participation, representation, and election administration in the many states and localities that use MMDs to elect public officials.
Disordered Eating/Eating Disorder: Hidden Perils of the Nation's Fight against Fat
Authors: Greenhalgh Susan
Published: October 2015

The nation's fight against fat has not reduced obesity, but it has had other worrying effects. Mental health researchers have raised the possibility that the intense pressures to lose weight have heightened the risks of developing eating disorders, especially among the young. Medical anthropology can help connect the dots between the war on fat and disordered eating, identifying specific mechanisms, pathways, and contextual forces that may lie beyond the scope of biomedical and psychiatric research. This article develops a biocitizenship approach that focuses on the pathologization of heaviness, the necessity of having a thin, fit body to belonging to the category of worthy citizen, and the work of pervasive fat‐talk in defining who can belong. Ethnographic narratives from California illuminate the dynamics in individual lives, while lending powerful support to the idea that the battle against fat is worsening disordered eating and eating disorders among vulnerable young people.
Oscillations of Skin Microvascular Blood Flow in Patients with Asthma
Authors: Tikhonova Irina V. , Kosyakova Ninel I. , Tankanag Arina V. , Chemeris Nikolai K.
Published: October 2015

Objective

This research is aimed at studying the features of skin blood flow oscillations in patients with severe persistent atopic BA during a period of fine control over symptoms.

Methods

The study of microcirculation was carried out by LDF at rest and in response to a transient ischemia in 20 patients. The time‐amplitude adaptive wavelet analysis of the blood flow oscillations was conducted to elucidate the peculiarities of microcirculatory regulation system functioning.

Results

No significant changes were revealed for SBP and the oscillation amplitudes in the cardiac (0.6–2 Hz) and respiratory (0.145–0.6 Hz) intervals, both at rest and in response to transient ischemia, in patients compared to the control group. A consistent twofold decrease in the oscillation amplitudes was found in the neurogenic (0.021–0.052 Hz) interval at rest, as well as in the myogenic (0.052–0.145 Hz) and NO‐dependent endothelial (0.0095–0.021 Hz) intervals both at rest and during the postocclusive reactive hyperemia in patients with lung obstruction (FEV1 < 80%) in comparison with a control group.

Conclusions

The amplitudes of skin blood flow oscillations in the myogenic, neurogenic and NO‐dependent endothelial intervals in patients with obstruction are different from those in patients without obstruction.
Soil losses due to potato harvesting: a case study in western Turkey
Authors: Parlak M. , Blanco‐Canqui H.
Published: October 2015

Harvesting of potato (Solanum tuberosum L.) may cause soil losses, but the magnitude of such losses has not been widely documented. We quantified the amount of soil lost with the mechanical harvesting of potatoes in 39 fields in western Turkey in 2013. The amount of soil lost was 1.81 Mg/ha/harvest and increased with increased gravimetric water content and plant density. The cost to replace nutrients lost with soil was about US$3 per hectare. Overall, soil loss due to potato harvesting is an important component of total erosion in the study region.
Carbon Deposition Simulation in Porous SOFC Anodes: A Detailed Numerical Analysis of Major Carbon Precursors
Authors: Schluckner C. , Subotić V. , Lawlor V. , Hochenauer C.
Published: October 2015

Solid oxide fuel cells (SOFCs) can be operated on a wide range of fuels, including hydrocarbons. Such a fuel supply includes the risk of carbon formation on the catalytically active nickel centers within the porous anodic substrate. Coking is very critical for the reliability and durability of the SOFCs. Thus, within this study, coking propensity of the most prominent carbon containing fuels was analyzed by thermodynamic equilibrium calculations for two fundamentally different types of carbon and detailed transient numerical simulations based on heterogeneous reforming kinetics. This approach is new to the literature and reveals the strengths and weaknesses of both fundamentally different approaches. It was shown that in thermodynamic equilibrium calculations, carbon formation is most likely due to pure methane. Carbon monoxide will form the least amounts of carbon in typical SOFC temperature ranges. Furthermore, based on a validated computational fluid dynamics (CFD) simulation model, detailed heterogeneous reaction kinetics were used to directly simulate elementary carbon adsorbed to the reactive substrate surface. The amounts, spatial and temporal distribution, of carbon atoms within the porous structure were identified between 600 °C and 1000 °C for a broad steam-to-carbon ratio range of 0.5–2. It was shown that most carbon is formed at the beginning of the substrate. A key finding was that steady-state results differ greatly from results within the first few seconds of fuel supply. An increment in temperature causes a significant increase in the amount of carbon formed, making the highest temperatures the most critical for the SOFC operation. Moreover, it was shown that mixtures of pure methane deliver the highest amounts of adsorbed elementary carbon. Equimolar mixtures of CH4/CO cause second highest surface coverages. Pure carbon monoxide blends led to least significant carbon formations. This work has shown the important contribution that thermodynamic equilibrium calculation results, as well as the outcomes of the detailed CFD simulations, allow to identify suitable operating conditions for the SOFC systems and to minimize the risk of coking on porous anodes.
Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage
Authors: Besem Fanny M. , Kielb Robert E. , Key Nicole L.
Published: October 2015

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades has been shown to significantly affect the flutter and forced response behavior of a blade row. While tuned computational fluid dynamics (CFD) analyses are now an integral part of the design process, designers need a fast method to evaluate the localized high blade responses due to mistuning. In this research, steady and unsteady analyses are conducted on the second-stage rotor of an axial compressor, excited at the first torsion vibratory mode. A deterministic mistuning analysis is conducted using the numerical modal forces and the individual blade frequencies obtained experimentally by tip timing data. The mistuned blade responses are compared in the physical and traveling wave coordinates to the experimental data. The individual and combined impacts of frequency, aerodynamic, and forcing function perturbations on the predictions are assessed, highlighting the need to study mistuned systems probabilistically.
Full Coverage Shaped-Hole Film Cooling in an Accelerating Boundary Layer With High Freestream Turbulence
Authors: Kingery J. E. , Ames F. E.
Published: October 2015

Full coverage shaped-hole film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over a large cylindrical leading edge test surface. The shaped holes had an 8 deg lateral expansion angled at 30 deg to the surface with spanwise and streamwise spacings of 3 diameters. Measurements were conducted at four blowing ratios, two Reynolds numbers, and six well documented turbulence conditions. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds number. The film cooling measurements were acquired at a coolant to free-stream density ratio of approximately 1.04. The flows were subjected to a low turbulence (LT) condition (Tu = 0.7%), two levels of turbulence for a smaller sized grid (Tu = 3.5% and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aerocombustor (AC) (Tu = 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the AC turbulence condition are reduced to as low as 20% of LT values by the furthest downstream region. The film cooling discharge is located close to the leading edge with very thin and accelerating upstream boundary layers. Film cooling data at the lower Reynolds number show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. Downstream effectiveness levels are very similar to slot film cooling data taken at the same coolant flow rates over the same cylindrical test surface. However, slots perform significantly better in the near discharge region. These data are expected to be very useful in grounding computational predictions of full coverage shaped-hole film cooling with elevated turbulence levels and acceleration. Infrared (IR) measurements were performed for the two lowest turbulence levels to document the spanwise variation in film cooling effectiveness and heat transfer.
Helideck Turbulence Study on Offshore Platforms by Anisotropic Turbulence Model
Authors: Venkatraman Marutha Muthu , Nyiredy Robert
Published: October 2015

The objective of this paper is to investigate the predictive capabilities of an anisotropic turbulence model for Helideck turbulence studies on offshore platforms and also to discuss the challenges in fulfilling the regulations and demands from the authorities for ensuring a safe helideck design. A Computational Fluid Dynamics (CFD) study is performed on a Front End Engineering Design (FEED) phase offshore platform geometry using unsteady Reynolds Stress model (RSM) [1] and the mean flow conditions for safe helideck operations are evaluated. The results are compared with an isotropic turbulence model using the realizable-kEpsilon (RKE) model [2] to establish if there is any gain or added merits in using computationally intensive RSM versus RKE model. The result comparison shows that for the skewed wind angles, flow separation from the platform outer edges will develop a swirl that starts to rise towards the helideck areas. This is well captured in the RSM model when compared to RKE model. In addition to numerical prediction, operational experience from pilots and their reactions to turbulence has also been documented in this paper. An open source software tool OpenFOAM is used in this study for the numerical analysis. As a part of this study, OpenFOAM has also been tested for canonical flows and the results are compared with experimental studies. Guidelines for evaluating helideck flow conditions and potential design modifications for safe helideck operations are also discussed in this paper.
Simulation of Wave Impact With Compressible Air Entrainment Based on Consistent Particle Method
Authors: Koh C. G. , Luo M. , Bai W. , Gao M.
Published: October 2015

A numerical strategy for incompressible-compressible two-phase flows with large density difference is presented. The incompressible phase is modeled by the recently developed 2-phase Consistent Particle Method (2P-CPM) for incompressible flows. For the compressible phase, a thermodynamically-consistent compressible solver is developed by using the ideal gas equation of state (EOS). Since sound speed is not explicitly involved, this compressible solver can overcome the issues in the determination of numerical sound speed. In addition, the compressible solver can be integrated with the incompressible 2P-CPM seamlessly because they both use a predictor-corrector scheme to solve the governing equation of primitive form. The benchmark example of dam break with entrapped air pocket is studied to demonstrate the accuracy of the proposed method.
CFD Simulations on the Vortex-Induced Vibrations of a Flexible Cylinder With Wake Interference
Authors: González Leo M. , Rodriguez Alvaro , Garrido Carlos A. , Suarez Juan C. , Huera-Huarte Francisco
Published: October 2015

In this work, CFD computations showing the dynamic response of a long flexible cylinder subject to a stepped current immersed in the wake of another cylinder are presented. These two cylinders are placed upstream in tandem configuration, where the flexible cylinder is excited by vortex shedding mechanisms. This work completes from the computational point of view, the research started 2 years ago with experiments conducted at the E.T.S.I. Navales towing tank of the Technical University of Madrid. The flexible cylinder studied is 3 m long having an external diameter of 16 mm. A combination of two codes that simulate the fluid-structure interaction phenomenon was used to obtain the velocity and pressure fields and also to measure the deformation of the cylinder at the same points where the strain gauges where placed during the experiment. This code communicates a finite volume (FV) software that solves the Navier-Stokes equations and reports the shear and pressure fields on the flexible cylinder to a second finite element (FEM) code that is able to compute stresses and deformations. Deformations are reported back to the first fluid solver in order to compute the next time step. In the experiments, only the 65% length of the cylinders were under the water surface, consequently a VOF technique was used to simulate the free surface separation between air and water. The numerical stability of these two combined codes is one of the most delicate aspects of the simulation. Taking into account that the upstream cylinder was orders of magnitude more rigid than the downstream one, we considered the upstream cylinder as stationary and consequently having no role during the FEM calculation. Boundary conditions for the flexible cylinder where such that they should imitate the universal joints used in the experiments. The fundamental natural frequencies of oscillation were monitored and compared to the towing tank experiments.
Nonlinear Analysis of Dynamic Responses of a MOSES TLP in Extreme Conditions
Authors: Yan Fasuo , Yang Hui , Sun Liping , Zhang Dagang
Published: October 2015

The configuration of MOSES TLP is quite different from conventional types. A compact central columns group and extended tendon support structure provides better deck support and hydrodynamic efficiency. A fully-coupled time domain analysis was adopted to evaluate effects of first and second order wave forces, motions and tendon tensions in hurricane conditions. The nonlinear responses due to the environmental load and interaction between the hull and tendons that includes large surge-heave motion in the low frequency and resonant heave/pitch responses with the spring loads in the high frequency are focused on in the paper. Results from numerical simulation are compared with data in full scale measurement.
CFD Study on Free-Surface Influence on Tidal Turbines in Hydraulic Structures
Authors: Tralli Aldo , Bijlsma Arnout C. , te Velde Wilbert , de Haas Pieter
Published: October 2015

In order to estimate the impact on energy production and environment of tidal turbines placed in or near hydraulic structures like discharge sluices or storm surge barriers, a Computational Fluid Dynamics (CFD) study has been carried out on the relation between (head) loss induced by the turbines and their gross power production.

CFD computations have been performed for Tocardo T2 turbines, using STAR-CCM+.

Simulations of a single turbine in free flow conditions compare favorably with results of Blade Element Momentum (BEM) computations, in terms of torque and thrust. This BEM method model had been previously validated against both CFD data and field measurements.

Then, a series of tests has been performed in a “virtual tow tank”, including the effect of the free surface and the blockage by side and bottom walls.

These computations provide a base for a first estimate of the effect of turbines on the discharge capacity of a generic structure. This is considered to be the first step in a more general approach in which ultimately the effect of tidal turbines in the Eastern Scheldt Storm Surge Barrier will be assessed.
Investigation on the VIM Mitigation of the HVS Semisubmersible
Authors: Kyoung Johyun , Kim Jang Whan , Jang Hyunchul , Lambrakos Kostas , O’Sullivan Jim
Published: October 2015

The mitigation of Vortex Induced Motion (VIM) of the HVS (Heave and VIM Suppressed) semisubmersible is investigated through extensive comparisons between CFD analysis and VIM model test results. It is shown that the lower VIM response of the HVS semisubmersible results from the break in coherence of vortex shedding along the length of column due to the column step. The present CFD application was carried out on the basis of in-house best practices for VIM analysis of multi-column floaters. The analysis results show excellent comparison with the model test results. The present findings and methodology can be applied to optimize semisubmersible hull designs for suppressed VIM response.
Flow Past a Circular Cylinder: A Comparison Between RANS and Hybrid Turbulence Models for a Low Reynolds Number
Authors: Pereira Filipe S. , Vaz Guilherme , Eça Luís
Published: October 2015

Several offshore applications deal with highly unsteady and detached flows, dominated by three dimensional effects. On such conditions, the usage of scale-resolving simulation (SRS) turbulence models has increased due to the well-known limitations of common RANS models. However, some of these offshore applications, such as flows past cylinders or raisers, present highly complex non-turbulent phenomena which, if not properly resolved, may pollute the outcome of any turbulence model. Therefore, it is crucial to mimic the flow conditions of the problem, the physical settings, and fulfil the numerical requirements of such problems to obtain reliable and accurate predictions. This paper assesses RANS and hybrid turbulence models, focusing on the dependence of the numerical predictions on the physical settings. To this end, the flow past a circular cylinder at a Reynolds number of 3900 is simulated using RANS, DDES and XLES models. The obtained results reveal a large dependence on the grid spatial resolution and physical settings, in particular on the computational domain width and boundary conditions. A substantial improvement of RANS predictions is found when a 3D computational domain is used. As expected, the hybrid models, DDES and XLES, lead to a better agreement with the experiments.
Nonlinear Foundation Spring and Calibration Using Measured Dynamic Response of Structure
Authors: Kaynia Amir M. , Norén-Cosgriff Karin , Andersen Knut H. , Tuen Kjell Arvid
Published: October 2015

Some offshore platforms need modifications or addition of new modules that require re-assessment of their design. An economical way of allowing for changes without major strengthening of the platform is by reducing the safety margin used in the original design by use of measured data during the operation. This paper presents application of this concept to Troll A platform in which the measured changes in the platform’s natural periods due to the nonlinear soil behavior under different storm conditions were used to calibrate the soil-foundation spring adopted in the design.
Basic Mechanics of Vortex-Induced Vibrations in Marine Risers
Authors: Zueck Robert F.
Published: October 2015

Vortex-Induced Vibrations (VIV) are three-dimensional (3D) oscillations of slender structures that are induced by fluid vortices shedding off the moving structure. VIV is intriguing because the largest magnitude of the oscillations is generally perpendicular to the incident fluid flow. Much of the historical research in VIV has focused on the inducing hydraulics of this fluid/structure interaction. We instead focus on the structural mechanics for valuable insights as to why and how VIV physically occurs. We first review the basic mechanics of a suspended pipeline that is horizontally-oriented and then explore the same for a marine riser that is vertically-oriented. In particular, we will investigate the following:

• How gravity and fluid drag curves the slender structures

• How this global curvature locally promotes VIV

• How period doubling is a natural consequence of geometry

• How changes in boundary conditions, shedding periodicity, fluid drag, and fluid velocity affect VIV
The Vertical Distribution and Evolution of Slam Pressure on an Oscillating Wave Surge Converter
Authors: Henry Alan , Abadie Thomas , Nicholson Jonathan , McKinley Alan , Kimmoun Olivier , Dias Frederic
Published: October 2015

The accurate definition of the extreme wave loads which act on offshore structures represents a significant challenge for design engineers and even with decades of empirical data to base designs upon there are still failures attributed to wave loading. The environmental conditions which cause these loads are infrequent and highly non-linear which means that they are not well understood or simple to describe. If the structure is large enough to affect the incident wave significantly further non-linear effects can influence the loading. Moreover if the structure is floating and excited by the wave field then its responses, which are also likely to be highly non-linear, must be included in the analysis. This makes the description of the loading on such a structure difficult to determine and the design codes will often suggest employing various tools including small scale experiments, numerical and analytical methods, as well as empirical data if available.

Wave Energy Converters (WECs) are a new class of offshore structure which pose new design challenges, lacking the design codes and empirical data found in other industries. These machines are located in highly exposed and energetic sites, designed to be excited by the waves and will be expected to withstand extreme conditions over their 25 year design life. One such WEC is being developed by Aquamarine Power Ltd and is called Oyster. Oyster is a buoyant flap which is hinged close to the seabed, in water depths of 10 to 15m, piercing the water surface. The flap is driven back and forth by the action of the waves and this mechanical energy is then converted to electricity.

It has been identified in previous experiments that Oyster is not only subject to wave impacts but it occasionally slams into the water surface with high angular velocity. This slamming effect has been identified as an extreme load case and work is ongoing to describe it in terms of the pressure exerted on the outer skin and the transfer of this short duration impulsive load through various parts of the structure.

This paper describes a series of 40th scale experiments undertaken to investigate the pressure on the face of the flap during the slamming event. A vertical array of pressure sensors is used to measure the pressure exerted on the flap. Characteristics of the slam pressure such as the rise time, magnitude, spatial distribution and temporal evolution are revealed. Similarities are drawn between this slamming phenomenon and the classical water entry problems, such as ship hull slamming. With this similitude identified, common analytical tools are used to predict the slam pressure which is compared to that measured in the experiment.
An Investigation on Two-Dimensional Nonlinear Sloshing in Rectangular Tank
Authors: Zhao Dongya , Hu Zhiqiang , Chen Gang
Published: October 2015

Two-dimensional liquid sloshing in rectangular tank of FLNG system is investigated both numerically and experimentally. In numerical simulation, a time-domain scheme has been developed based on potential flow theory in boundary element method. Tank movement is defined by wall boundary condition to produce a reciprocating oscillation. Nonlinear free surface condition is adopted to capture free surface elevation. Energy dissipation caused by viscous effects is considered by applying artificial damping term to the dynamic free surface condition, which is also vital to achieve a steady-state solution. For comparison, experiments of a rectangular tank filled with water subjected to specified oscillation are carried out. As coupling effects between sloshing and tank motion is not included in this research, the testing apparatus is required to produce consistent oscillation movement and not affected by the change of filling condition and sloshing load. Liquid surface elevations in several typical places of the tank were measured. Sloshing related parameters including oscillation amplitude, frequency and filling level are analyzed systematically. It’s found that numerical simulation results have good agreement with phenomenon observed under small amplitude excitation, and this nonlinear analysis method is proved to be effective in capturing liquid surface elevation. It is found that sloshing in tank is sensitive to filling level as well as excitation frequency, especially in the crucial combination cases of them. For given filling level, sloshing tends to be violent near corresponding natural frequencies, and viscous damping has limited contribution to sloshing amplitude when resonance occurs. This fundamental investigation also paves path for the study of more complicated sloshing problems.
Effect of Damping on VIV Response in Umbilicals and Flexible Risers
Authors: Hansen-Zahl Kay , Henøen Veronica , Baarholm Rolf , Parsinejad Farzan , Constantinides Yiannis
Published: October 2015

The fatigue life assessment of umbilicals and flexible risers due to vortex-induced vibrations (VIV) require special attention to the structural properties of the flexible bundle due to stick/slip behavior of helical elements in bending. The VIV response on umbilicals and flexible risers is complex, and it is controlled by several parameters. Structural damping is one of these parameters, but this is typically calculated based on the material damping of the structure. Similar to flexible risers and umbilicals, hysteresis damping due to the stick/slip behavior in the helical layers may be significant for cable structures. The purpose of this study is to evaluate the effect of the hysteresis damping on VIV response, and to demonstrate a procedure for consistent VIV fatigue analysis of flexible risers and umbilicals.

The stick/slip hysteresis varies with varying contact force, and the contact force is dependent on internal pressure and effective tension. The effect of varying these parameters is included in the study. Furthermore, the study includes different riser system configurations and current profiles.

In this paper, the stick/slip hysteresis has been established for two umbilicals and two flexible risers, with varying internal pressure and effective tension. Combined with five different configurations (both shallow and deep water) and 16 different current profiles, the VIV modes have been calculated and the corresponding stick/slip modal damping ratio has been established.

Finally, using fatigue current profiles, fatigue life estimates have been made based on different damping ratios, including the estimated stick/slip damping ratio.

The study presented in this paper has been carried out as part of the Norwegian Deepwater Programme (NDP).
Mooring Analysis of a Turret Moored FPSO in a Squall Environment
Authors: Oberlies Robert , Guha Amitava , Slocum Scott
Published: October 2015

The transient dynamic response of a FPSO in a squall environment is dependent on several input parameters. Because the response’s dependence on these input parameters is unclear prior to performing the analysis, a large number of parameter combinations need to be considered to find the combination that gives a worst-case load or response as required by reference [1]. Because the required time-domain simulations are computationally intensive, there is often a practical need to limit the number of simulations that are performed, raising questions about how many are necessary to meet the analysis objectives.

This study investigates the effect of different squall scenarios on a turret moored FPSO in the West African offshore environment. A large number of cases with selected vessel headings, squall types, squall approach directions and vessel drafts are studied and parameters affecting the critical mooring loads and turret positions are identified. Possible reductions in the load case matrix along with a sensitivity study of a few parameters affecting the results are also discussed.