bluuebunny/crossref_metadata_2025 huggingface dataset:
A Curvature and Density‐based Generative Representation of Shapes
Authors: Ye Z. , Umetani N. , Igarashi T. , Hoffmann T.
Published: October 2020

This paper introduces a generative model for 3D surfaces based on a representation of shapes with mean curvature and metric, which are invariant under rigid transformation. Hence, compared with existing 3D machine learning frameworks, our model substantially reduces the influence of translation and rotation. In addition, the local structure of shapes will be more precisely captured, since the curvature is explicitly encoded in our model. Specifically, every surface is first conformally mapped to a canonical domain, such as a unit disk or a unit sphere. Then, it is represented by two functions: the mean curvature half‐density and the vertex density, over this canonical domain. Assuming that input shapes follow a certain distribution in a latent space, we use the variational autoencoder to learn the latent space representation. After the learning, we can generate variations of shapes by randomly sampling the distribution in the latent space. Surfaces with triangular meshes can be reconstructed from the generated data by applying isotropic remeshing and spin transformation, which is given by Dirac equation. We demonstrate the effectiveness of our model on datasets of man‐made and biological shapes and compare the results with other methods.
Adapting participatory processes to fine‐tune conservation approaches in multiactor decision settings
Authors: Buchs Arnaud , Hassenforder Emeline , Meinard Yves
Published: October 2020

Conservation decisions are typically made in complex, dynamic, and uncertain settings, where multiple actors raise diverse and potentially conflicting claims, champion different and sometimes contradictory values, and enjoy varying degrees of freedom and power to act and influence collective decisions. Therefore, effective conservation actions require conservation scientists and practitioners to take into account the complexity of multiactor settings. We devised a framework to help conservation biologists and practitioners in this task. Institutional economic theories, which are insufficiently cited in the conservation literature, contain useful insights for conservation. Among these theories, the economies of worth can significantly contribute to conservation because it can be used to classify the types of values peoples or groups refer to when they interact during the elaboration and implementation of conservation projects. Refining this approach, we designed a framework to help conservation professionals grasp the relevant differences among settings in which decisions related to conservation actions are to be made, so that they can adapt their approaches to the features of the settings they encounter. This framework distinguishes 6 types of agreements and disagreements that can occur between actors involved in a conservation project (harmony, stricto sensu arrangement, deliberated arrangement, unilateral and reciprocal compromise, and locked‐in), depending on whether they disagree on values or on their applications and on whether they can converge toward common values by working together. We identified key questions that conservationists should answer to adapt their strategy to the disagreements they encounter and identified relevant participatory processes to complete the adaptation.
The De Ritis ratio as prognostic biomarker of in‐hospital mortality in COVID‐19 patients
Authors: Zinellu Angelo , Arru Francesco , De Vito Andrea , Sassu Alessandro , Valdes Giovanni , Scano Valentina , Zinellu Elisabetta , Perra Roberto , Madeddu Giordano , Carru Ciriaco , Pirina Pietro , Mangoni Arduino A. , Babudieri Sergio , Fois Alessandro G.
Published: October 2020

Increased concentrations of serum aspartate transaminase (AST) and alanine transaminase (ALT) are common in COVID‐19 patients. However, their capacity to predict mortality, particularly the AST/ALT ratio, commonly referred to as the De Ritis ratio, is unknown. We investigated the association between the De Ritis ratio on admission and in‐hospital mortality in 105 consecutive patients with coronavirus disease of 2019 (COVID‐19) admitted to three COVID‐19 referral centres in Sardinia, Italy. The De Ritis ratio was significantly lower in survivors than nonsurvivors (median: 1.25; IQR: 0.91‐1.64 vs 1.67; IQR: 1.38‐1.97, P = .002) whilst there were no significant between‐group differences in ALT and AST concentrations. In ROC curve analysis, the AUC value of the De Ritis ratio was 0.701 (95% CI 0.603‐0.787, P = .0006) with sensitivity and specificity of 74% and 70%, respectively. Kaplan‐Meier survival curves showed a significant association between the De Ritis ratio and mortality (logrank test P = .014). By contrast, no associations were observed between the ALT and AST concentrations and mortality (logrank test P = .83 and P = .62, respectively). In multivariate Cox regression analysis, the HR in patients with De Ritis ratios ≥1.63 (upper tertile of this parameter) remained significant after adjusting for age, gender, smoking status, cardiovascular disease, intensity of care, diabetes, respiratory diseases, malignancies and kidney disease (HR: 2.46, 95% CI 1.05‐5.73, P = .037). Therefore, the De Ritis ratio on admission was significantly associated with in‐hospital mortality in COVID‐19 patients. Larger studies are required to confirm the capacity of this parameter to independently predict mortality in this group.
Incidence and treatment of arrhythmias secondary to coronavirus infection in humans: A systematic review
Authors: Malaty Michael , Kayes Tahrima , Amarasekera Anjalee T , Kodsi Matthew , MacIntyre C Raina , Tan Timothy C
Published: October 2020

Background

The coronavirus disease 2019 (COVID‐19) pandemic has affected millions of people worldwide resulting in significant morbidity and mortality. Arrhythmias are prevalent and reportedly, the second most common complication. Several mechanistic pathways are proposed to explain the pro‐arrhythmic effects of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. A number of treatment approaches have been trialled, each with its inherent unique challenges. This rapid systematic review aimed to examine the current incidence and available treatment of arrhythmias in COVID‐19, as well as barriers to implementation.

Methods

Our search of scientific databases identified relevant published studies from 1 January 2000 until 1 June 2020. We also searched Google Scholar for grey literature. We identified 1729 publications of which 1704 were excluded.

Results

The incidence and nature of arrhythmias in the setting of COVID‐19 were poorly documented across studies. The cumulative incidence of arrhythmia across studies of hospitalised patients was 6.9%. Drug‐induced long QT syndrome secondary to antimalarial and antimicrobial therapy was a significant contributor to arrhythmia formation, with an incidence of 14.15%. Torsades de pointes (TdP) and sudden cardiac death (SCD) were reported. Treatment strategies aim to minimise this through risk stratification and regular monitoring of corrected QT interval (QTc).

Conclusion

Patients with SARS‐CoV‐2 are at an increased risk of arrhythmias. Drug therapy is pro‐arrhythmogenic and may result in TdP and SCD in these patients. Risk assessment and regular QTc monitoring are imperative for safety during the treatment course. Further studies are needed to guide future decision‐making.
Lithium minerals
Authors: Brooks Kent
Published: October 2020

Lithium is a critical element in modern technology, and lithium minerals will play a key role in the fight against climate change. However, the demand for lithium‐ion batteries is dependent on an expanding supply of primary resources. Lithium occurs in limited amounts on the Earth in a surprising diversity of mineral species, from pyroxenes to amphiboles, phyllosilicates to phosphates. This article examines the principal mineral groups likely to be a target for future exploitation.
Headache and Left Ventricular Efficiency After Transcatheter Closure of Atrial Septal Defect
Authors: Matsuoka Ryohei , Muneuchi Jun , Nagatomo Yusaku , Sugitani Yuichiro , Ezaki Hiroki , Doi Hirohito , Watanabe Mamie
Published: October 2020

Objective/Background

This study aimed to clarify the relationship between migraine‐like headache and ventriculo‐arterial coupling after transcatheter closure of the atrial septal defect in children. We hypothesized that migraine headache after defect closure would be related to an abnormal hemodynamic response against an increased left ventricular filling.

Design

A retrospective cohort study.

Methods

We calculated the end‐ventricular systolic elastance (Ees), effective arterial elastance (Ea), and ventricular energy efficiency approximated based on echocardiography before and after defect closure, and compared these parameters between the subjects with and without headache after defect closure.

Results

A total of 167 subjects were studied. Age at the procedure, defect diameter, and pulmonary to systemic blood flow ratio were 11 (9‐17) years, 12.8 (9.2‐16.0) mm, and 1.8 (1.6‐2.3), respectively. We identified 47 (28%) subjects with migraine headache after defect closure. Although there was no significant difference in the Ees, Ea, and ventricular energy efficiency before defect closure between the groups, the Ees (4.0 [3.4‐4.9] vs 4.8 [3.7‐6.1], P = .014) and ventricular energy efficiency (0.79 [0.76‐0.82] vs 0.83 [0.79‐0.85], P = .001) after defect closure in subjects with headache were significantly lower than those in subjects without headache. Migraine headache after defect closure was significantly associated with age (odds ratio: 0.97, 95% confidential interval: 0.94‐1.00, P = .036) and a decrease in the ventricular energy efficiency after defect closure (odds ratio: 6.42, 95% confidential interval: 2.76‐14.90, P < .001).

Conclusion

A loss of ventricular energy efficiency was common in pediatric subjects with migraine‐like headache after transcatheter closure of the atrial septal defect, which suggested that the left ventricular function maladaptation was related to headache development after defect closure. We advocate that an impaired ventriculo‐arterial coupling may be one of the mechanisms for developing attacks in not only this population but also in other patients with migraine.
Intermediate Units in Multinational Corporations: Advancing Theory on their Co‐parenting Role, Dynamics and Outcomes
Authors: Pla‐Barber José , Botella‐Andreu Ana , Villar Cristina
Published: October 2020

Due to the dispersion of headquarters’ activities across organizational and geographical boundaries, intermediate units (IUs) are emerging as a key actor in international business. These units are intermediate structural layers between headquarters (HQ) and local subsidiaries with specific HQ responsibilities. Through a systematic review of 68 studies published between 1996 and 2020, we develop a conceptual framework that integrates complementary streams of theoretical and empirical research with IUs as the focal unit of analysis. Our aims are to disentangle how the main theories in this field address the antecedents of IU creation, and explain the dynamism in the roles and functions of IUs and their outcomes. We also propose a conceptualization of IUs as co‐parents in a dynamic system in which parenting functions are shared by IUs and headquarters. Finally, we highlight avenues for future research, emphasizing opportunities to advance the understanding of IUs using different theoretical lenses that may help scholars position their work within the broader stream of literature.
First record of Gorgona guitarfish (Pseudobatos prahli) off the Baja California peninsula with updated key to the guitarfishes of the North Eastern Pacific
Authors: Rutledge Kelsi M.
Published: October 2020

The Gorgona guitarfish is a poorly documented ray found in the Eastern Pacific. It can be distinguished from its congeners due to its distinctive coloration and rostral cartilages. Here I document an extensive northern range expansion of almost 2000 km based on a juvenile specimen caught off the Baja California Peninsula. This specimen also represents the smallest documented individual of this species, along with the first quantitative morphometric data reported since the 1995 description. Additionally, an updated key to the guitarfishes of the North Eastern Pacific is included.
Can an advanced audiology‐led service reduce waiting times for paediatric ear nose and throat outpatient services?
Authors: Pokorny Michelle A , Thorne Peter R , Whitfield Bernard CS , Lee Arier C , Wilson Wayne J
Published: October 2020

Aim

Children with middle ear disease often experience lengthy delays waiting for outpatient paediatric ear nose and throat (ENT) services. This study aimed to investigate whether an alternative service delivery model using audiologists working in an expanded scope of practice reduced waiting times for children to access such services.

Methods

A total of 131 children consecutively referred to a large ENT outpatient service in Queensland, Australia, for middle ear and hearing concerns were prospectively allocated to either a standard ENT service or an advanced audiology (AA)‐led service. Waiting times and attendance rates were collected and compared between the two patient groups.

Results

The median waiting time from referral to first offered appointment was 96 days for children in the AA‐led service versus 417.5 days for children in the standard ENT service. Seventy‐nine percent of children in the AA‐led service attended their first offered appointment versus 61% in the standard ENT service. For children receiving grommets, the median waiting time from initial referral to grommet insertion was 226 days for children in the AA‐led service versus 627 days for children in the standard ENT service.

Conclusion

The AA‐led service was an effective alternative pathway to reduce waiting times for children referred to ENT services with middle ear and hearing concerns.
Trends in pediatric hospitalizations for ambulatory care sensitive respiratory diseases in Brazil
Authors: Carneiro Viviane Santos Mendes , Vila Vanessa Carvalho da Silva , Vieira Maria Aparecida da Silva
Published: October 2020

Objective

To analyze the trend in hospitalization rates for ambulatory care sensitive respiratory diseases (ACSRD) of children under five years of age in Brazil.

Design

Time series study of hospitalization rates using secondary information from the Hospital Information System of the Brazil's Unified Health System.

Sample

Hospitalizations of children under five years of age living in Brazilian regions. Hospitalizations were separated according to cause: nose and throat infections, asthma, bacterial pneumonias, and lung diseases.

Measurements

Rates were calculated for total hospitalizations for ACSRD, and by cause, age group, and region. Trends were analyzed by using means of simple linear regression and were classified into stationary (p ≥ .05), ascending (β positive and p < .05) or declining (β negative and p < .05) trends.

Results

All regions showed stationary trends in total hospitalization rates for ACSRDs, except in the Southeast, where trends were ascending. Asthma was the only cause that showed a declining trend. Bacterial pneumonias showed stationary trends, while lung diseases and nose and throat infections had predominantly ascending trends.

Conclusion

Brazil's hospitalization rates for ACSRDs are high. Investigations into primary health care organization and work processes, as well as socioeconomic, cultural, and geographical factors are necessary.
BT or MAb: That is the question!
Authors: Wechsler Michael E.
Published: October 2020

See related article
fusionImage: An R package for pan‐sharpening images in open source software
Authors: Cánovas‐García Fulgencio , Pesántez‐Cobos Paúl , Alonso‐Sarría Francisco
Published: October 2020

The objective of this article is to evaluate the performance of three pan‐sharpening algorithms (high‐pass filter, principal component analysis and Gram–Schmidt) to increase the spatial resolution of five types of multispectral images and to evaluate the results in terms of color, coherence and spatial sharpness, both qualitatively and quantitatively. A secondary objective is to present an implementation of the aforementioned pan‐sharpening techniques within the open source software R. From a qualitative point of view, pan‐sharpening of images with a high spatial resolution ratio give better results than those whose spatial resolution ratio is 2. According to the quantitative evaluation, there is no pan‐sharpening methodology that obtains optimal results simultaneously for all types of images used. The results of the spectral and spatial ERGAS index vary for four out of the five types of images analyzed. The results show that none of the methods implemented in this work can be considered a priori better than the others. At the same time, this work indicates the importance of both qualitative and quantitative assessment.
Nebulization of epinephrine to reduce the severity of brachycephalic obstructive airway syndrome in dogs
Authors: Franklin Phil H. , Liu Nai‐Chieh , Ladlow Jane F.
Published: October 2020

Objective

To determine the preoperative and postoperative effect of nebulized epinephrine on brachycephalic obstructive airway syndrome (BOAS) severity in dogs.

Study design

Prospective clinical study.

Sample population

Thirty‐one client‐owned pugs, French bulldogs, and English bulldogs with moderate to severe BOAS.

Methods

Whole body barometric plethysmography was used to determine BOAS severity (BOAS index; 0%–100%) prior to and after nebulization with 0.05 mg/kg epinephrine diluted in 0.9% saline preoperatively. The same protocol was repeated postoperatively (within 24 hours of surgery).

Results

Five dogs were excluded because they did not tolerate nebulization, and postoperative data were available for 13 dogs. Epinephrine nebulization resulted in a decreased BOAS index across all breeds of dog both before (9.6% [3.1% to −30.2%], n = 26) and after surgery (14.3% [0.9% to −24.3%], n = 13). The preoperative reduction in BOAS index was greater (17.3% [1.8% to −27.4%]) in dogs with a baseline BOAS index >70% (P = .006) and in pugs (16.9% [0.8% to −27.4%]) compared with French bulldogs (5.2% [3.1% to −30.2%], P = .03). Simple linear regression was used to identify a positive relationship between baseline BOAS index and reduction in BOAS index for pugs (n = 10, P = .001). Nausea was noted as a side effect in four dogs.

Conclusion

Nebulized epinephrine reduced the BOAS index of dogs in this study. This effect was clinically significant in preoperative dogs with a BOAS index >70% and in dogs recovering from surgery.

Clinical significance

This study provides evidence to support the use of nebulized epinephrine in the perioperative management of BOAS‐affected dogs.
Between Worlds: Exploring the Links Between the Tangible and Intangible Costs of Prototypes
Authors: Nelson Jacob , Menold Jessica
Published: October 2020

Prototyping is an important part of the design process, but researchers currently have a limited understanding of how the resources invested in a prototype or designer teams’ intent for a prototype influence decision-making and perceptions of a prototype’s value. Prior work has shown that significant investment of time or money in design tasks can lead to design fixation, but little work has explored how these factors might impact design teams’ perceived value of prototypes with respect to the design process. Likewise, it is unclear how resource allocation and prototype intention effects the evolution of design team knowledge and subsequent design actions. To explore these relationships, an in situ study of prototyping tendencies was performed across two mechanical engineering design courses. Results suggest that effective design teams leveraged prototypes to uncover new design knowledge and limit uncertainty early in the design process. Importantly, this study did not find any significant relationships between the cost of a prototype in terms of money and time, and the perceived value of that prototype. Nor were any significant relationships found between costs and final design outcomes. Findings suggest that the true cost and value of a prototype with respect to design outcomes are challenging to explicitly quantify.
Verification of Manual Digitization Methods During Experimental Simulation of Knee Motion
Authors: Hargett Zachary , Gutierrez Manuel , Harman Melinda
Published: October 2020

Cadaveric testing is a common approach for verifying mathematical algorithms in computational modeling. In models of total knee replacement (TKR) motion, model inputs commonly include rigid body motions defined using the Grood–Suntay spatial linkage between tibial and femoral components. This approach requires definition of coordinate systems for each rigid TKR component based on fiducial points, manual digitization of a point cloud within the experimental setup, and registration of the orientation relative to bone marker arrays. This study compared variability between two different manual point digitization methods (hand-held stylus and pivot tool each registered in an optical tracking system). This was accomplished by verifying the mathematical algorithm used to calculate the coordinate system from digitized points and quantifying the variability of the digitization methods in a simulated cadaver limb experimental setup. For the hand-held stylus method, the standard deviation was 0.50 mm for the origin and 1.31, 0.51, and 0.62 deg for the x–y–z axes, respectively. Required digitization of each rigid marker array created additional errors of 0.54 mm for the origin and 1.70, 1.66, and 0.98 deg for the x–y–z axes, respectively. For the pivot tool method, the standard deviation was 0.35 mm for the origin and 0.37, 1.27, and 1.24 deg for the x–y–z axes, respectively. In this experimental setup, the pivot tool was the better option for minimizing error while providing repeatable manual digitization of fiducial points and point clouds.
Reliability Assessment Based on Multisource Information Fusion Method for High Pressure Natural Gas Compressors
Authors: Zhou Dengji , Wei Tingting , Huang Dawen , Liang Maozong , Zhang Huisheng , Weng Shilie , Jiang Ping
Published: October 2020

Compressor units used for long-distance transportation natural gas pipeline pressurization have high-pressure and high-risk characteristics. Hence, the scientific reliability assessment is important for high-pressure compressor units, to evaluate the reliability standard, find the performance deficiency, and provide references for operation and maintenance. The classical reliability assessment method is not suitable for the complex and high-reliability equipment, like high-pressure compressor units and pipelines. The reliability assessment of the high-reliability equipment is faced with the challenge of the multisource information. A reliability assessment method based on the multisource information fusion is proposed in this work. The fusion resources consist of design information, component test information, and trial operation information. The reliability of high-pressure compressor units can be assessed by fusing the characteristic parameters, from component-based assessment, function-based assessment, quality evaluation, and life model, by D–S evidence theory. A case study is conducted to verify the proposed reliability assessment method in a 20 MW-class high-pressure compressor. There are four information resources in the case, i.e., component test data, design information, operation data, and simulation data. The compressor reliability is assessed as 99.32%, validated by the statistical assessment result based on long-term shutdown reports. This application points out the existing weakness in the high-pressure compressor units and indicates the directions for improving the design, analysis, operation, and failure prevention technologies. It reveals that the reliability assessment based on multisource information can provide a guarantee for the operation and maintenance of high-pressure compressor units. Meanwhile, the proposed method has good expansibility, which may be used in more fields.
Pressurized Water Reactor Mixed Oxide/UO2 Transient Benchmark Calculations Using Monte Carlo Serpent 2 Code and Open Nodal Core Simulator ADPRES
Authors: Imron Muhammad , Hartanto Donny
Published: October 2020

This paper presents static and transient solutions for the pressurized water reactor (PWR) MOX/UO2 transient benchmark by Serpent 2 Monte Carlo (MC) code and open nodal core simulator called Abu Dhabi Polytechnic Reactor Simulator (ADPRES). The presence of mixed oxide (MOX) fuels and burn-up variation in the benchmark pose challenges for reactor simulators due to severe flux gradient across fuel assemblies. In this work, the two-step method was used, in which the assembly level two-group constants were generated from single assembly calculations with zero net current boundary conditions using Serpent 2 Monte Carlo code, and later the core calculation was performed using ADPRES open nodal core simulator. Two types of diffusion coefficients were generated: the conventional B1 leakage corrected and the cumulative migration method (CMM). Finally, the solutions of Serpent 2/ADPRES, including multiplication factor, power distribution, control rod (CR) worth, and critical boron concentration (CBC) using both diffusion coefficients, were compared against solutions from heterogeneous Serpent 2 calculations where the fuel and cladding are explicitly modeled. The reactor power during transients was also compared qualitatively against other nodal core simulators. The results showed that Serpent 2/ADPRES were able to predict the heterogeneous Monte Carlo solutions very well with reasonable differences. The transient solutions were also quite accurate compared to other nodal core simulators. For the diffusion coefficients comparison, it was found that the CMM diffusion coefficient provides more accurate solutions for the benchmark compared to the B1 leakage corrected diffusion coefficients.
Thermodynamic Analysis of a Highly Pressurized CO2 Cycle for Renewable Energy Applications
Authors: Kemmerer Geoffrey R. , Gross Thomas , Anderson Kevin R.
Published: October 2020

Refrigerated gases have been used to store energy with limited success. This paper presents the results of an exploratory study of how the behavior of fluids compressed to high pressures can be used to increase the efficiency of refrigeration cycles and one possible application for renewable energy. This research presents the results of thermodynamic modeling and analysis of a novel Carbon Dioxide (CO2) cycle to be used for alternative energy production. The thermodynamic computational simulations are carried out in MATLAB and use the NIST REFPROP database for modeling the high pressure (on the order of 1000 MPa) CO2 state points. Preliminary results show that the maximum energy that can be recovered using the proposed high pressure cycle in on the order of 11,043 J, for each mole of CO2 flowing in the cycle. Thus the Coefficient of Performance is COP = 2.22, and the efficiency of the cycle is estimated as η = 35%. Future work will focus on the development of equipment such as the cryogenic turbo-expander that can operate at the ultra-high pressures studied.
Four-Phase Flow of Oil, Gas, Water, and Sand Mixtures in Subsea Pipelines
Authors: Odan Mohamed , Ben Rajeb Faraj , Rahman Mohammad Azizur , Aborig Amer , Imtiaz Syed , Zhang Yan , Awad Mohamed M.
Published: October 2020

This paper investigates issues around four-phase (Oil/CO2/water/sand) flows occurring within subsea pipelines. Multi-phase flows are the norm, as production fluid from reservoirs typically include sand with water. However, these multi-phase flow mixtures, whether three- or four-phase, are at risk of forming slug flows. The inclusion of sand in this mixture is concerning, as it not only leads to increased levels of pipeline erosion but it also has the potential, to accumulate sand at the bottom of the pipe, blocking the pipe or at the very least hindering the flow. This latter impact can prove problematic, as a minimum fluid velocity must be maintained to ensure the safe and regulated flow of particles along a pipeline. The presence of low amounts of sand particles in oil/gas/water flow mixtures can serve to reduce the pressure exerted on bends. The sand volume fraction must in this case, be relatively low such that the particles’ resistance causes only a moderate loss in pressure. Therefore, the study aims to gauge the impact of oil/gas/water/sand mixtures on various pipeline structures as well as to further investigate the phenomenon of flow-induced vibration to determine the optimal flow variables which can be applied predicting the structural responses of subsea pipelines.
The Influence of Connecting Pipe on Surge Water Level and Water Hammer Pressure in Surge Tank
Authors: Li Gaohui , Zhang Lin , Zhou Tianchi
Published: October 2020

In the calculation of the traditional large fluctuation transition process, the influence of the connecting pipe at the bottom of the surge tank is often considered as the impedance hole. When the connecting pipe is long, the elasticity of the connecting pipe is neglected, which is liable to cause a large error. The surge joint have been mathematically modelized in two ways: with and without its connection to the pipe. Then these models have been used with the Gardel’s formula to treat the impulse coefficient of the surge tank. This study have been combined with concrete examples in order to figure out the influence of the connecting pipe’s diameter and length on the surge tank pressure, inlet pressure and unit speed of the surge tank. If the length of the linking pipe is too long, it would be necessary to consider its role. If the area of the linking pipe is too small, the surge tank will not be able to operate properly, causing water hammer waves.
Effect of Active and Passive Curvature on the Hydrodynamic Performance of Flapping Fins
Authors: Fernández-Gutiérrez David , van Rees Wim M.
Published: October 2020

Ray-finned fish swim by flapping their fins, which are composed of bony rays connected by an inextensible membrane. Throughout the flapping cycle, the fins typically undergo both ‘passive’ deformation due to hydrodynamic loading, and ‘active’ deformation arising from internal musculature deforming the fin against the flow. To systematically analyze the impact of fin shape on hydrodynamic performance, a parametric definition of the fin geometry and its modes of deformation is required, consistent with the fin’s material and mechanical properties. In this paper we present a model and algorithm to determine the fin shape corresponding to an arbitrary out-of-plane curvature distribution for each ray. The shape is computed by iteratively enforcing constraints corresponding to membrane inextensibility, and negligible torsional stiffness of the rays. Based on this model, we present a low-order parametrization of fin shapes that capture the predominant deformation modes due to combined hydrodynamic loading and intrinsic actuation, as compared to experimental observations. To demonstrate the model’s ability to provide insight into the effect of curvature on hydrodynamic fin performance, we integrate our algorithm into a 3D Navier-Stokes solver Using this framework, we present initial results on the cycle-averaged thrust coefficient of a passively and actively deforming generalized trapezoidal caudal fin model at Reynolds number 1500 and Strouhal number 0.3. The results demonstrate that our model, algorithm, and integration with the flow solver form a useful framework to understand the effect of 3D curvature on hydrodynamic performance of flapping fins.
Flow Measurement With a Helical Strake Type Thermowell in Flow Measurement Standard Systems
Authors: Kim Kisung , Lee Sibok , Chun Sejong
Published: October 2020

Helical strake type thermowells are replacing standard thermowells according to ASME PTC 19.3 TW-2016 in various industrial sectors. It is because the helical strakes can suppress the flow-induced vibration by Kármán vortex street over a thermowell. However, the ASME PTC 19.3 TW-2016 does not regulate the helical strakes because their design rules are too complicated to be specified.

This study attempts to characterize the effect of helical strakes on the thermowell vibrations by measuring pressure and strain signals at the same time. The pressure signal is expected to give information on the Kármán vortex street while the strain signal gives the flow-induced vibration on the thermowells. Relative vibration energy or relative vibration amplitude is defined to calculate the efficiency of suppressing the Kármán vortex street around the thermowells.
CFD Evaluation of Blood Flow in an Improved Blalock-Taussig Shunt Using Patient Specific Geometries
Authors: Lin Zhenghao , Agarwal Ramesh K. , Govindarajan Vijay , Schultz Noah , Hoganson David , Hammer Peter
Published: October 2020

Blalock-Taussig (BT) Shunt is a palliative surgical procedure used during a Norwood surgery on a newborn baby suffering from cyanotic heart defects. The BT Shunt can increase blood flow in patients’ pulmonary artery which can ease the “Blue Baby Syndrome.” Currently used BT Shunts do not produce a balanced flow distribution to the pulmonary arteries (PAs) which can cause high wall shear stress (WSS) and blood flow separation resulting in blood clots. A modified BT Shunt was designed to partially solve this problem. In our previous work [1], the modified BT Shunt was shown by numerical simulations to have the ability to better control the flow distribution between Innominate Artery (IA) and PA with lower and gradually varying WSS and with improved flow balance to the pulmonary artery at the T-junction of the shunt.

The goal of this paper is to computationally evaluate the flow in the modified BT shunt model between innominate and pulmonary artery using a patient specific aorta model. The simulations are performed using the commercial CFD software ANSYS Fluent. The improved modified BT shunt is connected between IA and PA. A change in the length of the shunt can be made to fit it under different conditions of actual patients. In numerical simulations, a full geometry of patient’s aorta is considered. Results for different lengths of the shunt are compared to determine the length that generates the lowest WSS and improved flow distribution to the PAs. It was found that the length of nearly 26mm creates lower WSS and flow rate difference between the two sides of PA at the T-junction attachment of the shunt. A sophisticated computational model was created using SolidWorks and Blender software to create the realistic geometry which included the IA, PA and modified BT shunt. The numerical simulations provide details of the flow field including velocity and pressure field, WSS, and blood damage. Several parameters in shunt design weigh heavily in reducing the thrombosis. This study demonstrates how CFD can be effectively utilized in the design of a medical device such as BT shunt to improve the clinical outcomes in patients.
Bubbling Flow in a Multi-Jet Fluidized Bed
Authors: Wang Liwu , Zhang Sijun
Published: October 2020

This work concerns with numerical simulation of dense gas-particle two-phase flow in a fluidized bed in the framework of two-fluid model, where attention is given to the bubble formation in a single-jet and multi-jet fluidized beds. The kinetic theory is implemented in the model to avoid empirically determined model parameters. The validity of the approach is confirmed through the comparison between the computed results and the measurements in the literature. The results show that increasing the number of jets results in different behavior in bubble formation and the flow pattern in a multi-jet bed is much more complex than that in a single-jet bed.
Analysis of Blood Flow Patterns to Estimate Atherosclerosis Formation in the Left Carotid Artery by CFD Simulation
Authors: Momin Marzia , Ara Nusrat , Arafat M. Tarik
Published: October 2020

The purpose of this computational fluid dynamics (CFD) study is to simulate left carotid artery models to evaluate the influence of hematocrit (Hct) level and angle of bifurcation on the formation of atherosclerosis. Bifurcation angle can vary from person to person based on sex, age or diseased condition which has an impact on hemo-dynamic parameters. From the anatomical study, it is seen that the carotid artery bifurcation is the preferential region for atherosclerosis formation. The combination of bifurcation, curvature and diameter change in this bifurcation region causes the blood flow to be complex with recirculation regions and secondary flows which influence hemodynamic changes and the formation of atherosclerosis. Along with the bifurcation angle, the Hct level also influences on changing hemodynamic parameters. As the viscosity of blood is mainly controlled by the Hct level, the hemodynamic parameters of blood are changed on the basis of change in percentage of the Hct level. Therefore, the Hct percentage can act as a risk factor for atherosclerosis formation. We have assessed the probability of vulnerable atherosclerosis formation based on the change of both bifurcation angle and hematocrit level. In this study, three different carotid artery geometries with 40 degree, 48.5 degree, and 63.6 degree angles were simulated at a varying percentage of the Hct level. We discerned these models by using CFD simulation to calculate wall shear stress (WSS), time-averaged wall shear stress (TAWSS) and velocity. The effects of angulation and Hct percentage on the velocity of blood were studied on the plane of the bifurcation region. The carotid artery with 63.6 degree angulation faces more recirculation areas and peak recirculation areas are observed at 25% Hct level. This justifies the reason behind atherosclerosis formation in the artery. We observed low WSS at wider angled models and a high WSS at narrow angled models. WSS value is also affected by the percentage of Hct. In this study, we noticed a lower value of WSS at a lower percentage of Hct which is responsible for atherosclerosis formation. The WSS value of 0.4 Pa was considered as the critical point for the atherosclerosis formation. We also calculated time-averaged wall shear stress (TAWSS) which is similar to the WSS contour plot. Overall, after analyzing the results of velocity, WSS and TAWSS, we concluded that low Hct (around 25% or lower) along with higher bifurcation angle (around 63.6 degree or higher) are more accountable for atherosclerosis formation.
Computational Study of Pump Turbine: Partial Load Operations
Authors: Altimemy Muhannad , Caspar Justin , Oztekin Alparslan
Published: October 2020

The performance of a pump-turbine under partial flow rates, 85%, 75%, and 65%, is studied using the LES model. The power signal, velocity, vorticity, and pressure field is presented over the blades and throughout the draft tube. Pressure fluctuations are probed at various locations over the wall of the draft tube. Examining the flow field in the blade region can provide further insights into the system performance. Flow-induced pressure fluctuations can disrupt system stability.

For this turbine, a strong swirling region is observed around the draft tube walls, causing pressure fluctuations. The size and intensity of this region decrease with the flow rate. A vortex rope is present in all cases. At the design point, the strength is constant throughout the draft tube. However, at partial load, the rope is weakened along the draft tube. Between the region dominated by the vortex rope and the wall, there is a swirling shear layer, which moves closer to the wall as the flow rate decreases.

Both the magnitude of pressure fluctuations at the wall and the pressure difference over the blade decrease with the flow rate. The decreased pressure differences over the blade represent less power produced, and the decline in fluctuation magnitude at the wall represents more system stability. For this turbine, there appears to be a trade-off between power and strength of pressure fluctuations.
Feasibility Study for Flow-Induced Vibration in Stud Pipe Using Computational Fluid Dynamics
Authors: Nguyen Khac-Ha , Kim Won-Tae , Hong Seung-Pyo , Lee Haein , Lee Ahram
Published: October 2020

Piping systems in a nuclear plant can be damaged by high-cycle fatigue due to acoustic-induced vibration. Moreover, if the frequency of the vibration in the piping system is overlapped with a natural frequency of the piping, the magnitude of the amplitude will be increased resulting in many problems. For example, the damage is considered as flow-induced acoustic resonance at the branch pipes of the safety relief valve in the main steam lines. This study has investigated the Computational Fluid Dynamics (CFD) analysis methodology to predict and quantify the vortex shedding frequencies and the pressure pulsation magnitude in the dead-end piping system. In order to estimate the vortex shedding vibration, a high level turbulent model should be applied. Such a turbulent model, however, requires a substantial amount of computing time. Therefore, the purpose of the study is to investigate the effects of the main pipe length and the sublayer inflation rate on the vortex shedding frequency and pressure pulsation magnitude. The results for the effects will be able to reduce the size of the fluid domain so that the computing time can be significantly decreased in using the high resolution turbulent models.
Investigation on the Pump Suction Performance and Thermodynamic Effects
Authors: Jeong Eunhwan , Kang Byung Yun , Hong Soon Sam , Kim Dae Jin , Choi Chang Ho
Published: October 2020

The thermodynamic effects on the suction performance of a liquid oxygen (LOX) pump, observed during liquid rocket engine combustion tests, were investigated. Owing to the pump rotational speed and inlet pressure variation in the short duration of the engine starting, LOX pump head drops occurred occasionally depending on the initial pump inlet condition. Because the engine tests were performed at various inlet temperature and pressure settings of the LOX pump, the resulting suction performance behaviors of the LOX pump were varied. The critical cavitation number, at which the pump head drops 3%, was considered as the main parameter for representing the pump suction performance. The suction performance behaviors shown in the engine tests were investigated based on the classical theory of thermodynamic effects on cavitation. The LOX pump component test results in water, the LOX pump assembly suction performance test results in liquid nitrogen, and the J-2 LOX pump test results available in the open literature were used in the analysis and comparison. It was found that the critical cavitation number ratio of a pump could be expressed as a function of the thermodynamic parameter Σ*. For a given LOX pump flow condition, Stepanoff’s B-factor was almost constant at the specified head drop condition; as a result, Brennen’s time scale ratio βwas not constant but varying with Σ*. The argument of the geometrical similarity of pump cavitation at the critical condition of the pump head drop was addressed in conjunction with the constancy of Stepanoff B-factor.
Stereo-PIV Measurements of Turbulent Swirling Flow Inside a Pipe
Authors: Almheiri Ayesha , Khezzar Lyes , Alshehhi Mohamed , Salam Saqib , Goharzadeh Afshin
Published: October 2020

Stereo-PIV is used to map turbulent strongly swirling flow inside a pipe connected to a closed recirculating system with a transparent test section of 0.6 m in length and a pipe diameter of 0.041 m. The Perspex pipe was immersed inside a water trough to reduce the effects of refraction. The working fluid was water and the Reynolds number based on the bulk average velocity inside the pipe and pipe diameter was equal to 14,450. The turbulent flow proceeds in the downstream direction and interacts with a circular disk. The measurements include instantaneous velocity vector fields and radial profiles of the mean axial, radial and tangential components of the velocity in the regions between the swirler exit and circular disk and around this later. The results for mean axial velocity show a symmetric behavior with a minimum reverse flow velocity along the centerline. As the flow developed along the pipe’s length, the intensity of the reversed flow was reduced and the intensity of the swirl decays. The mean tangential velocity exhibits a Rankine-vortex distribution and reached its maximum around half of the pipe’s radius. As the flow approaches the disk, the flow reaches stagnation and a complex flow pattern of vortices is formed. The PIV results are contrasted with LDV measurements of mean axial and tangential velocity. Good agreement is shown over the mean velocity profiles.
Deformation of Erythrocyte in Couette Type of Pulsatile Shear Field
Authors: Hashimoto Shigehiro
Published: October 2020

The experimental methodology has been designed for evaluation of the cyclic deformation of an erythrocyte in the pulsatile shear field in vitro. To observe the deformation of the suspended erythrocytes in the Couette type of the shear flow, a rheoscope system has been manufactured. The system consists of a pair of counter-rotating parallel disks and an inverted phase-contrast microscope. The human erythrocytes were suspended in the dextran aqueous solution of high viscosity. The rotating speed varies sinusoidally to make the pulsatile shear field. The deformation of each erythrocyte was measured at the video image of the rheoscope. The experimental results show that the system is available to measure the following behavior of an erythrocyte. The ellipsoidal shape of each erythrocyte varies cyclically to follow the pulsatile cyclic shear field. The delay of deformation phase of each erythrocyte in the cycle is related to the frequency of the cyclic variation of the shear field. The delay is also related to deformability of the erythrocyte.
Sand Particle Concentration Distribution Inside Vertical Pipes: A CFD and Experimental Analysis
Authors: Sedrez Thiana A. , Shirazi Siamack A.
Published: October 2020

The concentration of the sand inside the flowlines can directly affect the magnitude of erosion in various pipelines and pipe fittings components. The erosion models available in the literature suggest that the relationship between erosion and sand concentration is linear. Furthermore, some authors believe that for a volume concentration of sand approximately below 0.75% by volume (corresponding to about 2% by mass in liquid), the effects of sand concentration on the rate of erosion are minimal. However, one could ask how this limitation on the amount of sand concentration varies in various geometries as the local concentration at the location where the sand particles are impacting can change within a flow geometry and how this can affect the maximum local erosion rates. Therefore, the sand concentration distributions inside a vertical pipe and two elbows in series for liquid-solid and liquid-gas-solid flows are examined in this investigation by CFD simulations and experimentally. Experiments are performed in a facility with two vertical pipe sections (101.6 mm reducing to a 50.8 mm inner pipe diameters) and immediately after the first and second elbows (50.8 mm inner pipe diameter) from the inner to the outer diameter of the elbows. The concentration distributions are associated with erosion measurement results in both the first and the second elbows. Finally, the CFD simulations of the corresponding experiments in liquid-sand and liquid-gas-sand flows are conducted and compared with the experimental erosion patterns and magnitude as well as various concentration distributions.