bluuebunny/crossref_metadata_2025_split huggingface dataset:
Concentrations of Volatile Organic Compounds in the Megacity of São Paulo in 2006 and 2011/2012 - A Comparative Study
Authors: Alvim Debora Souza , Gatti Luciana Vanni , Corrêa Sergio Machado , Chiquetto Julio Barboza , Pendharkar Jayant , Pretto Angélica , Santos Guaciara Macedo , Rossati Carlos De Souza , Herdies Dirceu Luis , Figueroa Silvio Nilo , Nobre Paulo 
Published: December 2020

The focus of this study was to measure the Volatile Organic Compounds (VOCs) concentrations in the megacity – São Paulo Metropolitan Area (SPMA). The measurements analyzed in this study included 78 hydrocarbon (HC) samples collected during 2006, and 66 samples of HC, 62 of aldehydes and 42 of ethanol collected during 2011-2012. The observational results showed that the consumption of ethanol, gasoline and diesel from 2006 to 2012 increased by 64 %, 23 % and 25 %, respectively, with substantial changes in the atmospheric composition. The 10 most abundant VOCs in the atmosphere found during 2011/2012 at CETESB IPEN/USP air quality monitoring station were ethanol, acetaldehyde, formaldehyde, acetone, propane, ethene, ethane, butane, 1-ethyl-4-methyl benzene, and 1,2,4-trimethyl benzene. During the 2006 campaign, alkanes represented 54.8 % of the total HC concentration, alkenes 29.2 %, aromatics 13.6 %, and alkadienes 2.4 %. On the other hand, during the 2011-2012 campaign, aldehydes represented 35.3 % of the VOCs, ethanol 22.6 %, aromatics 15.5 %, alkanes 13.5 %, acetone 6.8 %, alkenes 6.0 %, and alkadienes with less than 0.1 %. An increase in VOCs concentrations in the SPMA atmosphere from 2006 to 2012, such as aldehydes and aromatics (which are important ozone precursors) was measured.
Determination of CR-39 and LR-115 Type II Mean Critical Angle of Etching Using a New Monte Carlo Code
Authors: Harrass H. , Talbi A. , Touti R. 
Published: December 2020

Abstract
CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) are used, in order to assess the concentration of nuclides belonging to 238U and 232Th series, and these ones can be also used to measure the contents of radon 222Rn and thoron 220Rn gases in different locations. In this paper, a Monte Carlo code was developed to calculate the mean critical angle for which alpha particles emitted from 238U and 232Th families in studied material samples reach CR-39 and LR-115 type II surfaces and bring about latent tracks on them. The dependence of the SSNTDs mean critical angle on the removed thickness and the initial alpha particle energy has been studied. A linear relationship between CR-39 mean critical angle and the initial alpha particle energy for different removed thicknesses has been found. This straightforward relationship allows determining quickly the mean critical angle of etching which corresponds to initial alpha particle energy for a given removed thickness. CR-39 mean critical angle ranged from 59 deg for an alpha particle emitted by 212Po to 71 deg for an alpha particle emitted by 232Th, for the value of removed thickness of 6 μm; whereas LR-115 type II mean critical angle does not depend on the initial alpha particle energy except for 232Th, 238U, 230Th, and 234Ra when the removed thickness ranged from 6 μm to 8 μm. Obtained data by using the current method and those obtained in the literature are in good agreement with each other.
Large Eddy Simulation of a Condensing Wet Steam Turbine Cascade
Authors: Post Pascal , Winhart Benjamin , di Mare Francesca 
Published: December 2020

Abstract
The influence of turbulence modeling approach by means of (U)RANS and large eddy simulation (LES) on the overall modeling of turbulent condensing wet steam flows is investigated using the example of a low-pressure steam turbine cascade. For an accurate numerical treatment of turbulence in the presence of shock waves, necessary for predictive scale-resolving computations, a hybrid flux treatment switches between a baseline nondissipative central flux in energy consistent split form and a shock-capturing upwind flux in shocked regions based on a shock sensor. Condensation is realized by a monodispersed Euler–Euler source term model, the equation of state by the highly efficient and accurate spline based table lookup method (SBTL). The numerical treatment is validated with a decay of homogeneous isotropic turbulence test case containing eddy shocklets. The measurement results of the condensing wet steam cascade are overall much better matched by LES compared to RANS and URANS. Analysis shows that the LES is much better able to account for the inherently unsteady nature of the spontaneous condensation process and its interaction with the trailing edge shock wave structure.
Development of Experimental and Numerical Methods for the Analysis of Active Clearance Control Systems1
Authors: Da Soghe Riccardo , Mazzei Lorenzo , Tarchi Lorenzo , Cocchi Lorenzo , Picchi Alessio , Facchini Bruno , Descamps Laurent , Girardeau Julian , Simon Matthieu 
Published: December 2020

Abstract
The ever increasing performance requirements of modern aeroengines necessitate the development of effective ways to improve efficiency and reduce losses. Casing temperature control is particularly critical from this point of view, since thermal expansion directly affects the blade tip clearance and thus the associated leakages. To limit the turbine tip flows, active clearance control (ACC) systems have been implemented over the last decades. These systems are usually based upon impingement cooling, generated by a series of perforated manifolds enclosing the turbine casing. When dealing with aeroengine low pressure turbines, the current trend in increasing the engine bypass ratio, so as to enhance the system propulsive efficiency, pushes the limits of ACC traditional design performance. The reduction of the pressure head at the ACC system inlet requires lower nozzle-to-target distances as well as denser impingement arrays to compensate the reduction of the jets' Reynolds number. Literature correlations for the impingement heat transfer coefficient estimation are then out of their confidence range and also RANS numerical approaches appear not suitable for future ACC designs. In this work, methodologies for the development of accurate and reliable tools to determine the heat transfer characteristics of low pressure ACC systems are presented. More precisely, this paper describes a custom designed finite difference procedure capable of solving the inverse conduction problem on the target plate of a test sample. The methodology was successfully applied to an experimental setup for the measurement of the thermal loads on a target plate of a representative low pressure ACC impinging system. The experimental outcomes are then used to validate a suitable numerical approach. Results show that RANS model is not able to mimic the experimental trends, while scale-resolving turbulence models provide a good reconstruction of the experimental evidences, thus allowing to obtain a correct interpretation of flow and thermal phenomena for ACC systems.
Auto-Tuning Control of Proton Exchange Membrane Water Electrolyzer With Self-Assessment and Gain Scheduling
Authors: Keow Alicia Li Jen , Chen Zheng 
Published: December 2020

Abstract
Proton exchange membrane (PEM) electrolyzer can produce gases at the pressure suitable for direct storage into metal hydride cylinders, bypassing compressors, and other auxiliary components. For direct storage into metal hydride containers, hydrogen gas's pressure and flowrate must be well controlled. However, the PEM electrolyzer's time-variant and nonlinear dynamics call for an adaptive control to maintain its output performance. Therefore, in this paper, a model-free relay-feedback autotuning approach is proposed to tune a proportional-integral (PI) controller online. The controller determines the voltage supply to the electrolyzer to track a certain current setpoint, which corresponds to a constant hydrogen production rate. A gain scheduling approach is developed to pick up the right controller gain at different setpoints, minimizing the tuning frequency. A self-assessment algorithm is developed to determine the situations where the autotuner should activate to update the PI parameters, thus allowing the control system to be tuned autonomously. The autotuning PI control is successfully tested with a PEM electrolyzer setup. Experiment results showed that autotuner with gain scheduling could tune the controller parameters producing a desired transient behavior and is adaptive to the variations in setpoint and operating conditions.
Onset Criteria for Bulk-Mode Thermoacoustic Instabilities in Supercritical Hydrocarbon Fuels
Authors: Hunt Steven A. , Migliorino Mario Tindaro , Scalo Carlo , Heister Stephen D. 
Published: December 2020

Abstract
We have investigated supercritical-p (p &gt; 1192 psi (8.22 MPa)) methanol at pressures up to 1645 psi (11.3 MPa) flowing through a heated tube at flow rates of 4–7 lb/h (1.8–3.2 kg/h). Tube heated lengths have been varied from 4 to 6 in (10 to 15 cm), internal diameters from 0.027 to 0.069 in (0.069 to 0.175 cm), and heat inputs between zero and 800 W. Fluid temperature at the tube inlet remained subcritical (T &lt; 464 °F (513 K)); outlet temperatures were transcritical or supercritical. Two phenomena were observed: system-wide bulk-mode oscillations and localized acoustic modes. In this study, predictive efforts are undertaken to characterize system-wide bulk-mode oscillations. The parameter space has been nondimensionalized, yielding four dimensionless variables. Stability criteria based on these dimensionless groups have been established for two separate test articles and fluids; both criteria suggest that the heat required for the onset of oscillations is proportional to the mass flow rate times the mean pressure and inversely proportional to the fuel density.
Wall-Shear-Stress-Based Conditional Sampling Analysis of Coherent Structures in a Turbulent Boundary Layer
Authors: Ryu Sangjin , Davis Ethan , Park Jae Sung , Zhang Haipeng , Yoo Jung Yul 
Published: December 2020

Abstract
Coherent structures are critical for controlling turbulent boundary layers due to their roles in momentum and heat transfer in the flow. Turbulent coherent structures can be detected by measuring wall shear stresses that are footprints of coherent structures. In this study, wall shear stress fluctuations were measured simultaneously in a zero pressure gradient turbulent boundary layer using two house-made wall shear stress probes aligned in the spanwise direction. The wall shear stress probe consisted of two hot-wires on the wall aligned in a V-shaped configuration for measuring streamwise and spanwise shear stresses, and their performance was validated in comparison with a direct numerical simulation result. Relationships between measured wall shear stress fluctuations and streamwise velocity fluctuations were analyzed using conditional sampling techniques. The peak detection method and the variable-interval time-averaging (VITA) method showed that quasi-streamwise vortices were inclined toward the streamwise direction. When events were simultaneously detected by the two probes, stronger fluctuations in streamwise velocity were detected, which suggests that stronger coherent structures were detected. In contrast to the former two methods, the hibernating event detection method detects events with lower wall shear stress fluctuations. The ensemble-averaged mean velocity profile of hibernating events was shifted upward compared to the law of the wall, which suggests low drag status of the coherent structures related with hibernating events. These methods suggest significant correlations between wall shear stress fluctuations and coherent structures, which could motivate flow control strategies to fully exploit these correlations.
Intermittency, Secondary Bifurcation and Mixed-Mode Oscillations in a Swirl-Stabilized Annular Combustor: Experiments and Modeling
Authors: Singh Samarjeet , Roy Amitesh , K. V. Reeja , Nair Asalatha , Chaudhuri Swetaprovo , Sujith R. I. 
Published: December 2020

Abstract
We experimentally study thermoacoustic transitions in an annular combustor consisting of sixteen premixed, swirl-stabilized turbulent flames. We show the changes in the characteristics of bifurcations leading to the state of longitudinal thermoacoustic instability (TAI) when equivalence ratio and bulk velocity are systematically varied. Depending upon the bulk velocity, we observe different states of combustor operation when the equivalence ratio is varied. These states include combustion noise, intermittency, low-amplitude TAI, mixed-mode oscillations (MMO), and high-amplitude TAI. We closely examine the special case of MMO that is encountered during the transition from low-amplitude TAI to high-amplitude TAI. We also discuss the global and local flame dynamics observed during the state of MMO. We find that during epochs of low-amplitude oscillations of MMO, all the flames are partially synchronized, while during epochs of high-amplitude oscillations, all the flames are perfectly synchronized. Finally, we replicate the criticalities of bifurcation of the annular combustor in a phenomenological model containing sixth-order nonlinearities.
Preliminary Design Framework for the Power Gearbox in a Contra-Rotating Open Rotor
Authors: San Benito Pastor Diana G. , Nalianda Devaiah , Sethi Vishal , Midgley Ron , Rolt Andrew , Block Novelo D. Alejandro 
Published: December 2020

Abstract
Geared contra-rotating open rotors have the potential to further reduce fuel consumption relative to geared turbofans, but require a more-complex speed-reducing transmission system to drive the propellers. Hitherto, the preliminary design for such transmission systems has been reported independently of the overall engine modeling or has been limited by many predetermined engine constraints. This has restricted the feasible design space of the transmission systems. A simple transmissions preliminary design approach is needed that does not involve complicated mechanical assessments and can be integrated with engine preliminary design studies. This paper presents a novel design framework for sizing a double-helical differential planetary gearbox for a contra-rotating open rotor. An up-to-date methodology is proposed for the design of maximum load capacity gears for this application based on the power-transmitted, durability, and space envelope requirements. The methodology was validated with published data, demonstrating only very minor differences in geometry dimensions. Parametric analyses have been made to assess the impact of the design assumptions on gearbox dimensions. The framework also enables the identification of feasible torque ratios between the output shafts of the speed-reducer and the contra-rotating propellers driven by them. The impact of the torque ratio on the size of the gearbox has been analyzed for equal propeller rotational speeds and different speed ratios between the output shafts. This study shows that potential torque ratios lie between 1.1 and 1.33, with the higher ratios enabling more compact gearboxes having four or five planet gears.
A Review of Tubular Conical Transition Strength Design Equations
Authors: Ku Albert , Chen Jieyan , Cyprian Bernard 
Published: December 2020

Abstract
This paper consists of two parts. Part one presents a thin-shell analytical solution for calculating the conical transition junction loads. Design equations as contained in the current offshore standards are based on Boardman’s 1940s papers with beam-column type of solutions. Recently, Lotsberg presented a solution based on shell theory, in which both the tubular and the cone were treated with cylindrical shell equations. The new solution as presented in this paper is based on both cylindrical and conical shell theories. Accuracies of these various derivations will be compared and checked against FEM simulations.
Part 2 of this paper is concerned with the ultimate capacity equations of conical transitions. This is motivated by the authors’ desire to unify the apparent differences among the API 2A, ISO 19902 and NORSOK design standards. It will be shown that the NORSOK provisions are equivalent to the Tresca yield criterion as derived from shell plasticity theory. API 2A provisions are demonstrated to piecewise-linearly approximate this Tresca yield surface with reasonable consistency. The 2007 edition of ISO 19902 will be shown to be too conservative when compared to these other two design standards.
Experimental Study of the Effect of the Pontoon Dimensions on the Flow-Induced Motions (FIM) of a Semi-Submersible Platform With Four Square Columns
Authors: Gonçalves Rodolfo T. , Suzuki Hideyuki , Marques Matheus A. , Silva Leandro S. P. , Tian Chenling , Hirabayashi Shinichiro 
Published: December 2020

Abstract
The Flow-Induced Motions (FIM) is an essential topic on multi-column platforms due to the effect on the mooring line fatigue life. Vortex-Induced Motions (VIM) or galloping behavior can be observed for an array of four columns with square sections. The presence of pontoons showed to be important for changing the flow around the array and promoting different amplitude behaviors of the motions in the transverse direction mainly. This article aims to understand the effect of the presence of four pontoons on the FIM of a semi-submersible platform (SS) with four square section columns. Model tests of a floating system supported elastically utilizing four springs were performed in a towing tank. Five different pontoon ratios were tested, namely P/L = 0, 0.25, 0.50, 0.75, and 1.00; where P is the pontoon height (the dimension in the vertical direction), and L is the length of the square column face. The draft condition was kept constant as H/L = 1.5; where H is the draft of the platform. The spacing ratio of the columns was S/L = 4; where S is the distance between column centers. Two incidence angles of the current were carried out, namely 0 and 45 degrees. The amplitudes in the transverse direction (direction perpendicular to the incidence current) decreased by increasing the pontoon ratio for 0 and 45-deg incidences. The pontoons positioned aligned to the flow significantly reduced the amplitudes in the transverse direction since the pontoon presence in this position modified the incident wake in the downstream columns. The pontoon presence needs to be well investigated to choose the best condition to avoid raising the FIM or mitigating the FIM.
Analysis of Open-Source CFD Tools for Simulating Complex Hydrodynamic Problems
Authors: Siddiqui Mohd Atif , Xu Hui-li , Greco Marilena , Colicchio Giuseppina 
Published: December 2020

Abstract
OpenFOAM (OF) represents an attractive and widely used open-source environment for simulating complex hydrodynamic scenarios with several implemented numerical methods and wide variety of problems it can be applied to. For commercial and open-source solvers, though, expertise and experience are required to get physical and reliable results. Here, without pretending to be exhaustive, we aim to contribute in highlighting advantages and challenges of some key computational fluid dynamics (CFD)-simulation tools, with focus on the OF platform. We examine the effect of grid type, grid size and time-evolution scheme. Dynamic-mesh techniques and their influence on local and global numerical results are discussed, as well as the use of an overset grid versus a deforming mesh. Lastly, possible error sources in CFD simulations are discussed. These numerical studies are performed investigating two complex hydrodynamic problems: 1. a fully-immersed flapping hydrofoil aimed to generate thrust, 2. a damaged and an intact ship section fixed in beam-sea waves, in forced heave and roll motion in calm water. In the first case, vortex-shedding and wake features are crucial; in the second case, free-surface flow effects play the key role while the importance of vortex-shedding and viscous-flow effects depends on the scenario. The first problem is solved with OF and validated with results from benchmark experiments. The second problem is solved using (A) OF, (B) an in-house CFD solver and (C) a fully-nonlinear potential-flow code. A and B assume laminar-flow conditions and use, respectively, a volume-of-fluid and a level-set technique to handle the free-surface evolution. C is considered to examine importance of nonlinear versus viscous effects for the examined problems. The results are compared against in-house experiments.
Simulation of Ship-Ice Interaction in Level Ice
Authors: Erceg Sandro , Ehlers Sören , von Bock und Polach Franz 
Published: December 2020

Abstract
This paper presents the capabilities of a ship-ice interaction simulator developed at the Hamburg University of Technology for the ship operation in level ice. Besides a brief introduction of the fundamentals of the simulator and the full availability of the source code, the capabilities of the simulator in terms of the following are presented: simulation of the local ice load distribution along the hull, simulation of the resistance in ice, simulation of the cusp size and form. In addition, and most importantly, it will be shown how these results are changing with changing geometries of the hull shape. Thus, the sensitivity to various geometric changes of the hull to the simulation results will be presented and thereby the capabilities of the simulator. In other words, this paper seeks to introduce and present a robust simulator for the ship performance in ice suitable for hull design evaluations. By doing so, the sensitivity of the simulator results will be shown for various geometric hull shapes and the results will be discussed. The findings indicate that the simulator is well suited for early and detailed design assessment of the hull shape and for general optimization of the hull for ship-ice interaction in level ice.
Experimental Study on Conductivity of Regional Sand and its Field Application
Authors: Li Minghui , Zhou Fujian , Wang Jin , Liang Tianbo , Wang Yuechun , Zhang Lufeng 
Published: December 2020

Abstract
Hydraulic fracturing is the most commonly used stimulation method at present. The improvement effect and validity period mainly depend on the fracture conductivity. Carbo proppant is widely used worldwide for its excellent performance in increasing the conductivity of fracture support. The proppant used in the fracturing development of the Karamay oilfield in Xinjiang is also mainly Carbo proppant, but Karamay has abundant regional sand resources due to its special geographical location and geological conditions. Compared with the high cost and transportation cost of the Carbo proppant, the available regional sand becomes cheaper and reduces the development cost. According to the evaluation standard of flow conductivity of proppant in petroleum and natural gas industry, Firstly, the basic physical properties of the regional sand in Xinjiang were evaluated through the laboratory experiment system, and compared with the Carbo proppant. Secondly, the effect of sand placement concentration (8kg, 10kg, 16kg) and mesh number of proppant (30/50, 40/70) on regional sand conductivity was studied based on the conductivity evaluation system. Finally, the effect of the combination of regional sand and Carbo proppant on the conductivity was studied, under the same sand placement concentration and mesh number of proppant. The results of laboratory experiments show that the hardness and density of regional sand are higher than that of Carbo proppant, but the sphericity of regional sand is smaller than that of Carbo proppant. Under the same sand placement concentration, the regional sand conductivity of 30/50 meshes was higher than that of 40/70 meshes. As the concentration of sand placement increases, the ability of regional sand conductivity increases. The conductivity of a 1:1 mixture of regional sand and Carbo quartz is comparable to that of all Carbo quartz. According to the application examples of adjacent Wells A and B in block X of Xinjiang oilfield, the project that the ratio of regional sand to Carbo proppant is 1:1 can guarantee stable and effective flow conductivity and save fracturing cost.