bluuebunny/crossref_metadata_2025_split huggingface dataset:
Central fatigue aetiology in prolonged trail running races
Authors: Espeit Loic , Brownstein Callum G , Royer Nicolas , Besson Thibault , Martin Vincent , Millet Guillaume Y , Lapole Thomas 
Published: January 2021

New Findings
What is the central question of this study?
Are spinal and/or supraspinal perturbations implicated in central fatigue induced in the plantar flexor muscles following prolonged trail running races?
What is the main finding and its importance?
The study confirmed the presence of central fatigue following various trail running distances from 40 to 170 km. The reduction in the V‐wave in conjunction with the lack of change in the H‐reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms in the plantar flexor muscles.
AbstractTrail running races are known to induce considerable impairments in neuromuscular function of which central mechanisms are a substantial component. However, the loci of this central fatigue (i.e. supraspinal and/or spinal) is not well identified. The aim of this study was to better understand central fatigue aetiology induced in the plantar flexor muscles by various trail running distances from 40 to 170 km. Eighteen runners participated in the study and neuromuscular function of their plantar flexors was tested before (PRE) and after (POST) various races during the Ultra‐Trail du Mont Blanc. Neuromuscular function was evaluated with voluntary and evoked contractions using electrical tibial nerve stimulation. H‐reflex and V‐wave responses were also measured during submaximal and maximal voluntary contraction, respectively. Reductions in maximal voluntary contraction torque (−29%; P < 0.001) and voluntary activation level (−12%; P < 0.001) were observed after trail running races. The V‐wave was reduced in soleus (−35%; P = 0.003) and gastrocnemius medialis (−28%; P = 0.031), with no changes for the H‐reflex in soleus (P = 0.577). The present study confirmed the presence of central fatigue following trail running exercise. The reduction in the V‐wave in conjunction with the lack of change in the H‐reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms.
Impact of pre‐exercise feeding status on metabolic adaptations to endurance‐type exercise training
Authors: Edinburgh Robert M. , Koumanov Francoise , Gonzalez Javier T. 
Published: January 2021

AbstractNutrition and exercise metabolism are vibrant physiological fields, yet at times it feels as if greater progress could be made by better integrating these disciplines. Exercise is advocated for improving metabolic health, in part by increasing peripheral insulin sensitivity and glycaemic control. However, when a modest‐to‐high carbohydrate load is consumed before and/or during each exercise bout within a training programme, increases in oral glucose insulin sensitivity can be blunted in both men of a healthy weight and those with overweight/obesity. Exercise training‐induced adaptation in the energy sensing AMP‐activated protein kinase (AMPK) and the insulin‐sensitive glucose transporter GLUT4 protein levels are sensitive to pre‐exercise feeding status in both healthy individuals and individuals classified as overweight or obese. Increased lipid oxidation may, in part, explain the enhanced adaptive responses to exercise training performed before (i.e. fasted‐state exercise) versus after nutrient ingestion. Evidence in individuals with type 2 diabetes currently shows no effect of altering nutrient–exercise timing for measured markers of metabolic health, or greater reductions in glycated haemoglobin (HbA1c) concentrations with exercise performed after versus before nutrient provision. Since the metabolic inflexibility associated with type 2 diabetes diminishes differences in lipid oxidation between the fasted and fed states, it is plausible that pre‐exercise feeding status does not alter adaptations to exercise when metabolic flexibility is already compromised. Current evidence suggests restricting carbohydrate intake before and during exercise can enhance some health benefits of exercise, but in order to establish clinical guidelines, further research is needed with hard outcomes and different populations.
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Enhancing Cavitation Intensity in Co-Flow Water Cavitation Peening With Organ Pipe Nozzles
Authors: Vidvans A. N. , Melkote S. N. , Sanders D. G. 
Published: January 2021

AbstractCo-flow water cavitating jets induce compressive residual stress through cavitation impacts produced by the collapse of the cavitation cloud. Co-flow water cavitation peening causes minimal surface alteration when compared with conventional processes such as shot peening, which is a major advantage. However, enhancement of cavitation intensity for co-flow water cavitation peening nozzles is required for practical applications requiring greater process capability. Scaling of co-flow cavitation peening nozzles to achieve greater cavitation intensity requires higher flowrates, thus requiring pumps of higher capacities. In contrast, organ pipe geometry nozzles can enhance cavitation intensity without a significant increase in pump capacity and have been used in deep-sea drilling applications. The objective of this work is to study the effects of organ pipe inner jet nozzle geometry on co-flow water cavitation intensity and peening performance relative to a standard (unexcited) inner jet nozzle geometry through experiments on aluminum alloy Al 7075-T651. Nozzle performance is characterized via extended mass loss and strip curvature tests, high-speed visualization of the cavitation cloud, analysis of impulse pressures, and through-thickness residual stress measurements. It is found that the optimum organ pipe inner jet nozzle geometry enhances the mass loss and peak strip curvature by 61% and 66%, respectively, when compared with the unexcited inner jet nozzle. Residual stress measurements show that the organ pipe inner jet nozzle produces deeper compressive residual stresses in the material than the unexcited inner jet nozzle.
Comparing Filtering Multifidelity Optimization Strategies With a Simulation-Based Multidisciplinary Aircraft Model
Authors: Chell Brian , Hoffenson Steven , Philippe Cory J. G. , Blackburn Mark R. 
Published: January 2021

Abstract
Multifidelity optimization leverages the fast run times of low-fidelity models with the accuracy of high-fidelity models (HFMs), in order to conserve computing resources while still reaching optimal solutions. This work focuses on the multifidelity multidisciplinary optimization of an aircraft system model with finite element analysis and computational fluid dynamics simulations in the loop. A two-step filtering method is used where a lower fidelity model is optimized, and then the solution is used as a starting point for a higher-fidelity optimization routine. By starting the high-fidelity routine at a nearly optimal region of the design space, the computing resources required for optimization are expected to decrease when using local algorithms. Results show that, when using surrogates for the lower fidelity models, the multifidelity workflows save statistically significant amounts of time over optimizing the original HFM alone. However, the impact on solution quality varies depending on the model behavior and optimization algorithm.
Pressure Losses at Moderate Reynolds Numbers in Diamond-Shaped Cylinders Arrays: Application to Microregenerators
Authors: Sochinskii A. , Colombet D. , Medrano Muñoz M. , Ayela F. , Luchier N. 
Published: January 2021

Abstract
Cylinders with an elliptical, oblong, lenticular, sinus, or diamond transveral shape are very interesting geometries for the design of compact heat exchangers. This work investigates the role of the porosity and of the apex angle of diamond-shaped cylinders networks on the pressure losses, at moderate Reynolds numbers, inside microheat regenerators. The design of the geometry under test has been chosen so that the cross section of the flow remains almost constant along the path of the flow between cylinders. Experiments have been performed at 1 ⩽ Re ⩽ 30 and a porosity range 0.40&lt;ε&lt;0.90 for an apex angle of α=33deg. Numerical simulations have been conducted using the same Reynolds and porosity ranges but varying the apex angle 33deg ⩽ α ⩽ 90deg. Experimental measurements and dimensional analysis have shown that the friction factor can be affected by the porosity. Two-dimensional numerical simulations confirmed that the friction factor increases with the porosity but also with the apex angle. An analysis at the scale of a channel flanked by adjacent cylinders has provided an original correlation able to describe easily the evolution of the Poiseuille number and the collective effects on the drag coefficient as a function of α and ε. Such a diamond-shaped design is found to induce much lower Poiseuille numbers than those expected from conventional stacked spheres, woven wires, and circular cylinders arrays. The findings of this study can help for better understanding the optimization of low pressure drop regenerators and how to reduce associated hydraulic power.
Optimization of NARX Neural Models Using Particle Swarm Optimization and Genetic Algorithms Applied to Identification of Photovoltaic Systems
Authors: Silva Ronnyel Carlos Cunha , de Menezes Júnior José Maria Pires , de Araújo Júnior José Medeiros 
Published: January 2021

Abstract
In this study, genetic algorithms (GAs) and particle swarm optimization (PSO) are used to make an automated choice of hyperparameters of the multilayer perceptron (MLP)-NARX, extreme learning machine (ELM)-NARX, and echo state network (ESN)-NARX neural models applied to the identification of two photovoltaic systems: one installed in Teresina, in Brazil, and another in Hamburg, Germany. The automatic optimization process results showed that the PSO algorithm presents superior performance compared to the GA algorithm. Likewise, the identification carried out aimed to estimate the power generated by photovoltaic systems from two different approaches: linear mathematical models and neural identification models. Thus, the neural models implemented are more efficient and accurate than the linear mathematical models compared. From accuracy, the neural models ESN-NARX and MLP-NARX were considered the best in identifying Hamburg and Teresina’s photovoltaic systems, respectively.
Numerical Assessment of Density Ratio and Mainstream Turbulence Effects on Leading Edge Film Cooling: Heat and Mass Transfer Methods
Authors: Ravelli S. , Abdeh H. , Barigozzi G. 
Published: January 2021

Abstract
Within the context of leading edge film cooling in a high-pressure turbine vane, the present study is a step forward towards modelling showerhead performance for a baseline geometry (namely 4 staggered rows of cylindrical holes) at engine like conditions, starting from a previous investigation, at low speed flow (exit isentropic Mach number of Ma2is = 0.2), low inlet turbulence intensity of Tu1 = 1.6% and density ratio of DR ∼ 1. Those operating conditions, dictated by experimental constraints, were essential to validate results from delayed detached-eddy simulation (DDES) against off-the-wall measurements of velocity, vorticity and turbulent fluctuations, for the coolant-to-mainstream blowing ratio of BR = 3 (momentum flux ratio of I = 9). Here, the potential of DDES is exploited to predict the aero-thermal features of the flow in the leading edge region in the presence of larger density ratio (DR ∼ 1.5) and turbulent mainstream (Tu1 = 13%), while matching either BR or I. The experimental database contains surface measurements of film cooling adiabatic effectiveness (η), obtained by using the pressure sensitive paint (PSP) technique. DDES predictions of η were computed by means of the species transport model (i.e. mass transfer), for comparison against the conventional thermal method, based on creating a temperature differential between the mainstream and the coolant (i.e. heat transfer). The simulated film cooling performance was found to depend on the method used, thus suggesting that other parameters than DR, BR, I and Tu1 should be taken into account when the goal is matching engine-like conditions.
Acoustically Testing Stock and Modified UAS Propellers in Both the Near and Far Field
Authors: Van Treuren Kenneth , Sanchez Ricardo , Wisniewski Charles , Leitch Paul 
Published: January 2021

Abstract
In an urban setting, the sound level of a drone must be acceptable. This paper compares a stock DJI Phantom 2 propeller to a stock propeller modified with a Trailing Edge (TE) notch. The purpose was to determine the extent of the near and far field noise signature of the propellers. Measurements were taken in an anechoic chamber at measurement distances of 1 ft to 24 ft. Upstream of propeller, the sound decay follows the standard decay rate (6 dB decrease for a doubling of the distance) from a location of approximately 4 ft. Downstream the sound decay does not follow standard decay rates until 22 ft. A comparison of the two propellers shows that the TE notch and stock propellers have similar Sound Pressure Level (SPL) values at all distances measured. Traverse measurements downstream of the two propellers in the wind tunnel confirms that the magnitudes of the SPL values are similar after a distance of one foot, however, there does seem to be an influence of the TE notch on the frequency spectrum, shifting frequencies slightly higher.
In addition to the single propeller tests, a DJI F550 Flame Wheel hexacopter was used to compare the stock and TE notch propellers. While the hexacopter was overall 20 dBA nosier, no discernable difference in SPL between the two propellers was measured.
Managing the Pressure to Increase the H2 Capacity Through a Natural Gas Transmission Network
Authors: Bainier Francis , Kurz Rainer , Bass Philippe 
Published: January 2021

Abstract
Gas Transmission System Operators (TSO1) are considering injecting hydrogen gas into their networks. Blending hydrogen into the existing natural gas pipeline network appears to be a strategy for storing and delivering renewable energy to markets [1], [2], [3].
In the paper GT2019-90348 [4], the authors have explored the efficiency of H2-blending in a natural gas pipeline network. The conclusion of the paper is: the energy transmission capacity and the efficiency decrease with the introduction of H2, nevertheless, the authors conclude that it is not an obstacle, but the way of using transmission natural gas networks should be closely studied to find an economic optimum, based both on capital and operating expenses. To establish the comparison, the paper did not take into account the limits of the equipment; all equipment was considered as compatible with any load of hydrogen blending.
In the current paper, the idea is to consider the hypothesis that the only factor which has impact on the infrastructure is the partial pressure of H2. The idea is not new, in 1802, Dalton published a law called Dalton’s Law of Partial Pressures [5]. Dalton established empirically that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual component gases. The partial pressure is the pressure that each gas would exert when it alone occupied the volume of the mixture at the same temperature.
Independent of the limits of the equipment, the authors explore the relationships between a network capacity and its associated pressures in regards to the H2 partial pressure. Within the partial pressure constraint, the goal is to find the maximum H2 flowrate. This flowrate is then compared with a flowrate which is a function of % H2.
Nevertheless, steel is subjected to hydrogen invasion while being exposed to hydrogen containing environments during mechanical loading: resulting in hydrogen embrittlement (HE). HE also depends on the textured microstructure. In the final results [6] [7], the measured fatigue data reveals that the fatigue life of steel pipeline is degraded by the added hydrogen. The H2 has an effect on the steel fatigue which is not simply due to the partial pressure.
The idea of the authors through the results of their 2 papers is to give the key points to help to find the optimum points for introducing H2 into a natural gas network, because, for them, the idea is that partial pressure is a factor in the equilibrium between H2 capacity and the remaining lifetime of the equipment.
This paper shows the interest of the pressure management. With this management, it is possible to reach a constant H2 injection flow independently of the natural gas flow in the pipeline.
In conclusion, to optimize the H2 capacity in their current network, a proposal to the TSOs is to adjust their dispatching methodology and their Pipeline Integrity Management (PIM) [8] [9].
Coupled Mode Flutter Analysis of Turbomachinery Blades Using an Adaptation of the P-K Method
Authors: Schuff Matthias , Chenaux Virginie Anne 
Published: January 2021

Abstract
Current trends in turbomachinery design significantly reduce the mass ratio of structure to air, making them prone to flutter by aerodynamic coupling between mode shapes, also called coupled-mode flutter. The p-k method, which solves an aeroelastic eigenvalue problem for frequency and damping respectively excitation of the aerodynamically coupled system, was adapted for turbomachinery application using aerodynamic responses computed in the frequency domain.
A two-dimensional test case is validated against time-marching fluid-structure coupled simulations for subsonic and transonic conditions. A span of mass ratios is investigated showing that the adapted p-k method is able to predict the transition between aeroelastically stable and unstable cascades depending on the mass ratio.
Finally, the p-k method is applied to a low mass ratio fan showing that the flutter-free operating range is significantly reduced when aerodynamic coupling effects are taken into account.
Laminar Flame Characteristics of Sequential Two-Stage Combustion of Premixed Methane/Air Flames
Authors: Duva Berk Can , Wang Yen-Cheng , Chance Lauren Elizabeth , Toulson Elisa 
Published: January 2021

Abstract
Due to their high load flexibility and air-quality benefits, axial (sequential) stage combustion systems have become more popular among ground-based power gas turbine combustors. However, inert combustion residuals passing from the initial stage onto the secondary stage affects the reactivity and stability of the flame in the second stage of the combustor. The present study investigates laminar flame characteristics of the combustion within the second stage of a sequential combustor. The method of constant pressure for spherically expanding flames was employed to obtain laminar burning velocities (LBV) and burned gas Markstein lengths (Lb) of premixed methane/air mixtures diluted using flue gas at 3 bar and 423 K. Combustion residuals were imitated using a 19.01% H2O + 9.50% CO2 + 71.49% N2 mixture by volume, while tested dilution ratios were 0%, 5%, 10%, and 15%. Experimental results showed that the LBV was decreased by 18–23%, 36–42%, and 50–52% with additions of 5%, 10%, and 15% combustion products, respectively. As the dilution and equivalence ratios increased, the Lb values increased slightly, suggesting that the stability and stretch of the CH4/air flames increased at these conditions. Numerical results were obtained from CHEMKIN using the GRI-Mech 3.0, USC Mech II, San Diego, HP-Mech, NUI Galway, and AramcoMech 1.3 mechanisms. The GRI-Mech 3.0 and HP-Mech performed best, with an average of 2% and 3% difference between numerical and experimental LBVs, respectively. The thermal-diffusion (TD), dilution (D), and the chemical (C) effects of inert post-combustion gases on the LBV were found using numerical results. The dilution effect was primarily responsible, accounting for 79–84% of the LBV reduction.
Effects of Combustor Enclosure Flow Path on Combustor Design
Authors: Briones Alejandro M. , Thomas Nathan , Rankin Brent A. 
Published: January 2021

Abstract
A design optimization procedure was implemented to resize the holes of a combustor liner for practical applications. A combustor geometry evaluated without an enclosure was to be reformulated within an enclosure. The objective functions of the combustor with enclosure involved targeting the flow splits of the combustor without enclosure. Latin Hypercube Sampling (LHS) design of experiments (DOE) was utilized to obtain at least a pure quadratic response surface (RS). These were computed using Genetic Aggregate (GA). These RS were, in turn, evaluated by a multiple objective genetic algorithm (MOGA) optimizer. The focus of this study was a small-scale cavity-stabilized combustor. Steady, compressible three-dimensional simulations are performed using a multi-phase Realizable k-ε Reynolds-averaged Navier-Stokes (RANS) approach. Combustion-turbulence interaction is modeled with flamelet progress variable (FPV) and β-presumed probability density function (PDF). There are eleven input and output parameters corresponding to the combustor hole sizes and associated mass flow rates. The RS obtained with GA were principally of the Kriging kind (with constant and linear trends and damped sinusoid and Gaussian kernels). A combustor hole mass flow rate was mainly determined by its hole size but was also influenced by the other holes. The combustor flow split non-linearity shows that increasing a hole size increases its mass flow rate, but simultaneously decreases another hole flow rate. This was also verified by sensitivity analysis. Due to this non-linearity, matching flow splits between geometry without and with enclosure is challenging and may not be possible for some situations. Thus, it is concluded that optimization of the combustor geometry without the enclosure is not the best route. Rather, it would be better for the geometry to be optimized with the enclosure included in order to account for flow separation and non-linear influence of the combustor holes on the flow field.