Готові списки джерел за темами / Partial local Saha equilibrium

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Добірка наукової літератури з теми "Partial local Saha equilibrium"

Автор: Grafiati

Опубліковано: 10 грудня 2022

Оновлено: 28 січня 2023

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Статті в журналах з теми "Partial local Saha equilibrium"

Timmermans, C. J., R. J. Rosado, and D. C. Schram. "An Investigation of Non-Equilibrium Effects in Thermal Argon Plasmas." Zeitschrift für Naturforschung A 40, no. 8 (August 1, 1985): 810–25. http://dx.doi.org/10.1515/zna-1985-0804.

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The parameters and transport properties of a wall stabilized argon arc (40-200 A) at atmospheric pressure with diameters of 5 and 8 mm are studied by spectroscopy and interferometry. The plasma is assumed to be partial local thermal equilibrium and this assumption is verified with the aid of a collisional-radiative model. The departures from Saha-equilibrium of the argon neutral ground state are found to be associated with particle diffusion and the escape of recombination radiation. The measurement of the total excitation rate, from the ground level, including direct ionization, of neutral argon is in reasonable agreement with the literature value.

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Anders, A. "Plasma fluctuations, local partial Saha equilibrium, and the broadening of vacuum-arc ion charge state distributions." IEEE Transactions on Plasma Science 27, no. 4 (1999): 1060–67. http://dx.doi.org/10.1109/27.782282.

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Cherevko, A. S., and A. A. Morozova. "On the violation of local thermodynamic equilibrium in the plasma jet of an argon arc two-jet plasmatron." Industrial laboratory. Diagnostics of materials 85, no. 1II) (February 15, 2019): 145–50. http://dx.doi.org/10.26896/1028-6861-2019-85-1-ii-145-150.

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The degree and nature of the violation of local thermodynamic equilibrium (LTE) in the analytical zone of a plasma jet generated by an argon arc two-jet plasmatron (TJP) was estimated using an unconventional method based on determination of the nonequilibrium parameterbiequal to the ratio of the experimentally determined actual population of the energy level (ni) of the element to the population of the same level calculated from the Saha equation (nis). Partial ionizing deviation of plasma under study from the equilibrium state takes place only when low-lying atomic levels are overpopulated. The distinct dependence ofbion the ionization potential of the considered element (e.g., Ca, Mg, and Be) is shown. The results were interpreted in the light of the increasing role of radiation processes upon excitation of spectra in the argon arc two-jet plasmatron.

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RUBIANO, J. G., R. RODRÍGUEZ, J. M. GIL, P. MARTEL, and E. MÍNGUEZ. "Calculation of the ionization state for LTE plasmas using analytical potentials." Laser and Particle Beams 17, no. 4 (October 1999): 635–47. http://dx.doi.org/10.1017/s0263034699174081.

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In this work, the Saha equation is solved using atomic data provided by means of analytical potentials to calculate the ionization state and ion abundances for local thermodynamic equilibrium (LTE) plasmas of Al, Fe, and Au. The plasma effects are taking into account using an analytical potential which includes plasma effects. The problem of the cut off partition functions in the Saha equation is also analyzed using three different criteria. Finally, some opacity calculations are performed.

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Kochuev, D. A., A. F. Galkin, A. S. Chernikov, R. V. Chkalov, A. A. Voznesenskaya, K. S. Khorkov, and A. V. Egorova. "Local thermodynamic equilibrium in a laser-induced plasma channel formed by interaction of femtosecond laser radiation with argon." Journal of Physics: Conference Series 2131, no. 5 (December 1, 2021): 052090. http://dx.doi.org/10.1088/1742-6596/2131/5/052090.

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Abstract In this paper, we estimate the possibility of applying local thermodynamic equilibrium conditions for a laser-induced plasma channel formed by femtosecond laser radiation in an argon medium at different pressures. The presence of a local thermodynamic equilibrium was determined on the basis of the time of heat exchange of electrons with argon atoms. The Saha equation is used to estimate the concentration of free electrons, the temperature of the laser-induced plasma channel, and its conductivity. A necessary condition for using this ratio was the presence of a state of local thermodynamic equilibrium in the plasma under study.

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White, J. R., W. Johns, C. J. Fontes, N. M. Gill, N. R. Shaffer, and C. E. Starrett. "Charge state distributions in dense plasmas." Physics of Plasmas 29, no. 4 (April 2022): 043301. http://dx.doi.org/10.1063/5.0084109.

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Charge state distributions in hot, dense plasmas are a key ingredient in the calculation of spectral quantities like the opacity. However, they are challenging to calculate, as models like Saha–Boltzmann become unreliable for dense, quantum plasmas. Here, we present a new variational model for the charge state distribution, along with a simple model for the energy of the configurations that includes the orbital relaxation effect. Comparison with other methods reveals generally good agreement with average atom-based calculations, the breakdown of the Saha–Boltzmann method, and mixed agreement with a chemical model. We conclude that the new model gives a relatively inexpensive, but reasonably high fidelity method of calculating the charge state distribution in hot dense plasmas, in local thermodynamic equilibrium.

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Barthélemy, Olivier, Joëlle Margot, Stéphane Laville, François Vidal, Mohamed Chaker, Boris Le Drogoff, Tudor W. Johnston, and Mohamad Sabsabi. "Investigation of the State of Local Thermodynamic Equilibrium of a Laser-Produced Aluminum Plasma." Applied Spectroscopy 59, no. 4 (April 2005): 529–36. http://dx.doi.org/10.1366/0003702053641531.

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In this work, the assumption of local thermodynamic equilibrium (LTE) for a laser-induced plasma in ambient air is examined experimentally using two different laser systems, namely an infrared short-pulse Ti:Sapphire laser and an ultraviolet long-pulse XeCl excimer laser. The LTE assumption is investigated by examining the plasma produced at a laser fluence of 10 J/cm2 from aluminum targets containing iron and magnesium impurities. The excitation temperature is deduced from Boltzmann diagrams built from a large number of spatially integrated neutral iron lines distributed from 3.21 to 6.56 eV. It is shown that at any time after the end of the laser pulse, the neutral excited states are in excellent Boltzmann equilibrium. Detailed investigation of Boltzmann equilibrium further validates previous temperature measurements using less accurate diagrams. However, observations of ion lines provide some evidence that the ionized species do not obey Saha equilibrium, thereby indicating departure from LTE. This could be explained by the fact that the plasma cannot be considered as stationary for these species.

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Hey, J. D., C. C. Chu, and J. P. S. Rash. "Partial local thermal equilibrium in a low-temperature hydrogen plasma." Journal of Quantitative Spectroscopy and Radiative Transfer 62, no. 3 (June 1999): 371–87. http://dx.doi.org/10.1016/s0022-4073(98)00110-1.

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Novakovic, R. N. V., B. S. Milic, S. M. Stojilkovic, and Dragan Gajic. "Some transport properties in plasmas containing argon and fluorine." Facta universitatis - series: Physics, Chemistry and Technology 2, no. 5 (2003): 285–91. http://dx.doi.org/10.2298/fupct0305285n.

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In this paper some results of numerical evaluation of transport coefficients in plasmas in the mixtures of argon and fluorine are presented. These transport characteristics are given in the function of the temperature for low pressures ranging from 0,1 kPa to 1,0 kPa and for low temperatures between 500 K and 5 000 K in argon plasmas with 20% and 30% of the fluorine added. It is assumed that the system is kept under constant pressure and that a corresponding state of local thermodynamical equilibrium (LTE) is attained in it. The equilibrium plasma composition, necessary for the evaluations, was determined on the ground of the Saha equations for ionization processes and the law of mass action for the thermal dissociation of F2, combined with the charge conservation relation and the assumption that the pressure remained constant in the course of temperature variations. The ionization energy lowering, required in conjunction with the Saha equations, was obtained with the aid of a modified expression for the plasma Debye radius proposed previously. A previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas considered as weakly non-ideal in the whole temperature range, is used. The cut-off at the Landau length rather than of the smallest of ionic radii is introduced. This alteration in the evaluation procedure brings different considerable changes in the final numerical results for the all relevant quantities.

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Khater, Mohamed A. "Vacuum ultraviolet assessment of ionization temperature by space-resolved emission spectroscopy." Canadian Journal of Physics 91, no. 9 (September 2013): 733–36. http://dx.doi.org/10.1139/cjp-2012-0550.

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In this article, the electron ionization temperature in plasmas generated by 1064 nm laser pulses in the vacuum ultraviolet spectral range is evaluated as a function of the axial distance from a steel target surface using emission spectroscopy. The temperature was determined using the relative line intensities ratio of C II 90.41 nm and C III 97.7 nm spectral lines, applied to the Saha–Boltzmann equation. Ionization temperatures determined in this way changed from 33 900 K at the target surface to 26 800 K (2.92–2.31 eV) at 4.0 mm away from it. Large differences between the measured excitation and ionization temperatures suggest nonthermal equilibrium conditions between electrons and heavier ionic species. Based upon the results obtained from this and a previous study under the same operating conditions, the validity of the local thermal equilibrium condition in the plasmas investigated is presented and discussed.

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Більше джерел

Дисертації з теми "Partial local Saha equilibrium"

Balcon, Nicolas, and nicolas balcon@gmail com. "Atmospheric pressure Radio Frequency discharges, diagnostic and numerical modeling." The Australian National University. Research School of Physical Sciences and Engineering, 2008. http://thesis.anu.edu.au./public/adt-ANU20080318.234936.

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The aim of this thesis is to investigate the properties of a Radio Frequency capacitive discharge at atmospheric pressure in argon. In these conditions where the pressure x distance product is around 150 Torr.cm, the discharge usually consists of several locally hot filaments. By pulsing the RF generator with an appropriate width and period, it was found possible to control the filament to glow transition in order to obtain a diffused and stable plasma.¶ The 2 mm gap between the electrodes is open to the ambient air and fed with argon via one hundred submillimetric holes regularly spread on the surface of the top electrode. This configuration allows on-line surface treatment of polymer films without having to turn the discharge off between successive samples. An important and lasting improvement of the polymer wettability is quickly obtained without risk of damage. The plasma diagnostic methods are emission spectroscopy and electric measurements. The Stark broadening of the Balmer β transition line of atomic hydrogen is measured to determine a plasma density of 10^15/cm3 in the filamentary mode. The glow mode density estimation was based on power balance yielding a density of 5×10^11/cm3. Emission line ratios between neutrals and Ar+ ions are used in the Saha equation to calculate the electron temperature. It results in an approximation of 1.3 eV for the glow mode and 1.7 eV for the filaments.¶ A unidimensional self-consistent fluid model is developed to gain insight into the homogeneous discharge behaviour. Poissons equation for the electric field is coupled to the first moments of the Boltzmann equation (continuity equation, drift-diffusion equation and energy equation). Transport and reaction coefficients are obtained from the mean energy of the electrons.¶ The model is applied to a reduced argon kinetic with the main ionization and excitation processes. Simulation results are in agreement with experimental measurements. The atmospheric pressure RF discharge is similar to a lower pressure RF discharge for which the ionization occurs mainly inside the oscillating sheaths where electrons are the most energetic

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Balcon, Nicolas. "Atmospheric pressure Radio Frequency discharges, diagnostic and numerical modeling." Phd thesis, 2007. http://hdl.handle.net/1885/49282.

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Книги з теми "Partial local Saha equilibrium"

Levy, Brian, Robert Cameron, Ursula Hoadley, and Vinothan Naidoo, eds. The Politics and Governance of Basic Education. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198824053.001.0001.

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This book brings together scholars from multiple disciplines to explore how political and institutional context influences the governance of basic education in South Africa at national, provincial, and school levels. A specific goal is to contribute to the crucial, ongoing challenge of improving educational outcomes in South Africa. A broader goal is to illustrate the value of an approach to the analysis of public bureaucracies, and of participatory approaches to service provision which puts politics and institutions at centre stage. Stark differences between the Eastern Cape and Western Cape provinces offer something of a natural experiment for exploring the influence of context. The Eastern Cape’s socio-economic, political, and institutional legacy resulted in a low-level equilibrium trap in which incentives transmitted from the political to the bureaucratic levels reinforced factionalized loyalty within multiple patronage networks, and which is difficult to escape. The Western Cape, by contrast, enjoyed a more supportive environment for the operation of public bureaucracy. However, bureaucracy need not be destiny. The research also shows that strong hierarchy can result in ‘isomorphic mimicry’—a combination of formal compliance and a low-level equilibrium of mediocrity. Participatory school-level governance potentially can improve outcomes—as a complement to strong bureaucracies, or as a partial institutional substitute where bureaucracies are weak. Whether this potential is realized depends on the relative strength of developmentally oriented and predatory actors, with the outcomes not fore-ordained by local context, but contingent and cumulative—with individual agency by stakeholders playing a significant role.

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Частини книг з теми "Partial local Saha equilibrium"

Cosmi, C., S. Di Leo, S. Loperte, F. Pietrapertosa, M. Salvia, M. Macchiato, and V. Cuomo. "Comprehensive Energy Systems Analysis Support Tools for Decision Making." In Green Technologies, 493–514. IGI Global, 2011. http://dx.doi.org/10.4018/978-1-60960-472-1.ch307.

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Sustainability of energy systems is a common priority that involves key issues such as security of energy supply, mitigation of environmental impacts - the energy sector is currently responsible for 80% of all EU greenhouse gas emissions (European Environment Agency, 2007), contributing heavily to the overall emissions of local air pollutants - and energy affordability. In this framework, energy planning and decision making processes can be supported at different stages and spatial scales (regional, national, pan-European, etc.) by the use of comprehensive models in order to manage the large complexity of energy systems and to define multi-objective strategies on the medium-long term. This Chapter is aimed to outline the value of model-based decision support systems in addressing current challenges aimed to carry out sustainable energy systems and to diffuse the use of strategic energy-environmental planning methods based on the use of partial equilibrium models. The proposed methodology, aimed to derive cost-effective strategies for a sustainable resource management, is based on the experiences gathered in the framework of the IEA-ETSAP program and under several national and international projects.

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Тези доповідей конференцій з теми "Partial local Saha equilibrium"

GORBUNKOV, V. I., V. V. SHALAY, and N. V. PUSTOVOI. "THE SUPERSONIC ARGON FLOW PARAMETERS IN AN ARCJET THRUSTER." In 12TH INTERNATIONAL COLLOQUIUM ON PULSED AND CONTINUOUS DETONATIONS. TORUS PRESS, 2020. http://dx.doi.org/10.30826/icpcd12a29.

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A small closed volume occupied by the gas plasma is a specific feature of the propulsion systems for orbit correction of spacecraft (PSSC). We found the temperature of argon in the PSSC chamber using emission spectroscopy methods in the approximation of partial local thermal equilibrium.

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Gao, G., L. Pershin, and J. Mostaghimi. "Optical Emission Spectroscopic Diagnostics of Atmospheric Argon Radio Frequency Inductively Coupled Plasma." In ITSC2003, edited by Basil R. Marple and Christian Moreau. ASM International, 2003. http://dx.doi.org/10.31399/asm.cp.itsc2003p1337.

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Abstract An experimental study is conducted to determine the property fields of 40 MHz argon radio frequency inductively coupled plasma using optical emission spectroscopy. The pure argon plasma was operated at the input power of 0.3 kW and under atmospheric pressure. 29 atomic argon lines with upper level energies ranging from 12.9 to 15.5 eV, continuum emission and line width are used to evaluate plasma parameters such as temperature and electron number density. Since 40 MHz plasma is in almost complete nonequilibrium, the validaty and accuracy of most usual spectroscopic methods are questioned. Analysis based on the Boltzmann diagram, line-to-continuum intensity ratio, population of continuum extrapolated level, and continuum intensity reveals the departure from thermodynamic equilibrium in the plasma. Among these methods, the Boltzmann diagram method is shown to provide reliable plasma excitation temperature as long as the Boltzmann plot is drawn based on enough spectra lines covering from infrared to ultraviolet regions. The continuum emission at wavelengths within visible region can give good estimation of the electron density by using excitation temperature in the continuum relation. The line-to-continuum is not a reliable method for the temperature measurement of nonequilibrim plasma. The electron density obtained from the Saha plot can provide rough estimation of the electron density. It is shown that the electron-atom interaction contribution to the continuum radiation is more important than being expected before for the argon plasma in our study. The non-axisymmetric distribution of the emission was found to exist within the coil zone of the plasma, which may affect the estimation of the local emission coefficient, and consequently the measured plasma fields.

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Xiao, Bin, and Yuwen Zhang. "Partial Melting and Resolidification of Single-Component Metal Powder With a Moving Laser Beam." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72161.

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Partial melting and resolidification of single-component metal powders with a moving laser beam is investigated numerically. Since laser processing of metal powder is a very rapid process, the liquid layer and solid core of a partially molten powder particle may not at thermal equilibrium and have different temperatures: the temperature of the liquid part is higher than the melting point, and the temperature of the solid core is below the melting point. Therefore, the local temperature of regions with partial molten particles is within a range of temperature adjacent to the melting point, instead of at the melting point. The partial melting of the metal powder is also accompanied by shrinkage that drives out the gas in the powder bed and the powder structure is supported by the solid core of the partially melted powder particles. Melting with shrinkage and resolidification are described using a temperature transforming model. The convection driven by capillary and gravity forces in the melting liquid pool is formulated by using Darcy’s law. The effects of laser beam intensity and scanning velocity on the shape and size of the heat affected zone and molten pool are investigated.

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Kharaghani, Abdolreza, Xiang Lu, and Evangelos Tsotsas. "Dependency of continuum model parameters on the spatially correlated pore structure studied by pore-network drying simulations." In 21st International Drying Symposium. Valencia: Universitat Politècnica València, 2018. http://dx.doi.org/10.4995/ids2018.2018.7417.

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Pore-network simulations are carried out for monomodal and bimodal pore structures with spatially correlated pore-size distributions. The internal and surface relationships between the partial vapor pressure and saturation as well as the moisture transport coefficient for these model porous structures are identified from the post-processing of the corresponding pore-network model solutions. The simulation results show that the deviation of the partial vapor pressure from the saturation vapor pressure in the presence of liquid – which is referred to as non-local equilibrium effect – in the bimodal pore structures is less pronounced than in the monomodal pore structures. For the monomodal pore structures the moisture transport coefficient profile is not unique over the entire drying process, whereas this profile depends marginally on the drying history of the bimodal pore structures. Finally the ability of the continuum model to predict the results of the pore-network simulations for multiple realizations of the pore space is assessed. Keywords: Scale transition, Moisture transport coefficient, Pore structure, Discrete model, Continuum model

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Hetzel, Ryan W., Shao Wang, Jonathon R. Lawry, and Ahmed H. Alsafwani. "Evolution of Transferred Lubricant Distributions on the Slider Surface Under Ambient and Laser-Heating Conditions." In ASME 2019 28th Conference on Information Storage and Processing Systems. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/isps2019-7458.

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Abstract The dynamic equilibrium among the condensation, evaporation and shear flow of the lubricant on a slider has been modeled by solving a continuum-based partial differential equation, with temperatures obtained from a finite element model. Zero-flux and specified-flux boundary conditions were used to study the trailing pad of a slider. The results show that the average lubricant thickness on the trailing pad gradually approaches a steady state, and the steady-state value increases with increasing disk lubricant thickness. A reduction of the flying height leads to a reduced steady-state slider lubricant thickness. The temperature rise of the disk surface tends to promote the lubricant transfer to the slider in a region close to the trailing edge. However, this effect may be locally suppressed by the laser-induced local thinning of the lubricant film on the disk.

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Franco, Fermin, and Yasuhide Fukumoto. "Mathematical models for turbulent round jets based on “ideal” and “lossy” conservation of mass and energy." In ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems. Valencia: Universitat Politècnica València, 2017. http://dx.doi.org/10.4995/ilass2017.2017.4778.

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We propose mathematical models for turbulent round atomized liquid jets that describe its dynamics in a simplebut comprehensive manner with the apex angle of the cone being the main disposable parameter. The basic assumptions are that (i) the jet is statistically stationary and that (ii) it can be approximated by a mixture of two fluids with the phases in local dynamic equilibrium, or so-called locally homogeneous flow (LHF). The models differ in their particular balance of explanatory capability and precision. To derive them we impose partial conservation of the initial mass and energy fluxes, introducing loss factors again as disposable parameters. Depending on each model, the equations admit explicit or implicit analytical solutions or a numerical solution in the discretized model case. The described variables are the the two-phase fluid’s composite density and velocity, both as functions of thedistance from the nozzle, from which the dynamic pressure is calculated.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4778

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Wickert, Jonathan. "Modeling and Free Vibration of Flex Circuits in Hard Disk Drives." In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/vib-48583.

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A flex circuit connects the stationary electronic components in a hard disk drive to the rotating arm that carries the read/write heads and positions them above data tracks on the disk. Flex circuits are conventionally formed as a laminate of polyimide substrate, adhesive, and copper conductors. Deformation of a flex circuit is discussed in the context of the following stages: the initial unstressed shape, configurations in which stresses set and relax in response to elevated temperature, equilibrium, and small amplitude vibration. The model involves displacements of the flex circuit in the directions tangent and normal to the local equilibrium shape, and those motions couple with the arm’s dynamics. Nonlinearity associated with finite curvature, partial elastic springback, and the arm’s geometry and inertia properties are incorporated within the vibration model to predict system-level natural frequencies, mode shapes, and coupling factors between the circuit and the arm. Laboratory measurements using noncontact laser interferometry validate the model with respect to the circuit’s shape, stiffness, restoring moment, and natural frequencies. The primary degrees of freedom for optimizing flex circuit design are the thicknesses of the individual layers within the circuit, free length, and the locations and slopes of the circuit’s attachment points to the arm and electronics block. The model’s predictions and trends developed from a case study in free length are discussed with a view toward reducing coupling between the circuit and arm in certain vibration modes.

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Chen, Li Hua, Shou Jie Cui, Xiao Zhi Zhang, and Wei Zhang. "Study on Large Deformation of Laminated Piezoelectric Rectangular Plate." In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-88599.

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For the laminated piezoelectric rectangular plate with large deflection and large rotation, the nonlinear equilibrium differential equations are derived and solved. Firstly, the global Cartesian coordinate system to describe the undeformed geometry and the local orthogonal curvilinear coordinate system to describe the deformed geometry are established respectively on the mid-plane of the plate before and after the deformation, and the relationship between the two coordinates is expressed by transformation matrix. For the convenience of calculation, the expressions of the nonlinear curvatures and inplane strains are obtained by Taylor series expansion. Considering the piezoelectric effect, three equilibrium partial differential equations describing nonlinear bending problems are obtained by the principle of virtual work. Furthermore, in order to simplify the solution process, the stress function is introduced to automatically satisfy the first two equations for the large deformation of the cantilever plate, and the relationship between stress function, the mid-plane internal force and shear force is also given for the first time. Therefore, the stress function and the transversal displacement are the main unknowns of the governing equation and compatibility equation. Additionally, the approximate deflection function and stress function are given which can satisfy all the displacement boundary conditions and only part of the force boundary conditions. Thereby, the generalized Galerkin method is used to obtain the approximate solution of the nonlinear bending problem. Finally, the results in the study are verified by comparison with the results obtained from the finite element method. It also provides a theoretical basis for the engineering application of the large deformation of the piezoelectric cantilever plate.

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Fossi, Alain, Alain deChamplain, Bernard Paquet, Smail Kalla, and Jeffrey M. Bergthorson. "Scale-Adaptive and Large Eddy Simulations of a Turbulent Spray Flame in a Scaled Swirl-Stabilized Gas Turbine Combustor Using Strained Flamelets." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42535.

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In this paper, the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor is numerically investigated using the commercial CFD software ANSYS FLUENT™-v14. The first scope of this study aims to explicitly compare the predictive capabilities of two turbulence models namely Scale-Adaptive Simulation (SAS) and Large Eddy Simulation (LES) for a reasonable compromise between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium effects caused by turbulent strain. Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases respectively. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane + toluene) are used as jet-A1 surrogates. The combustion model is based on the first and second moments of the mixture fraction, and a presumed-probability density function (PDF) is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the partial equilibrium assumption (PEQ) and thereafter, the detailed non-equilibrium (NEQ) calculations through the laminar flamelet concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1 045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0. Numerical results are compared with a set of published data for a steady spray flame. Firstly, it is observed that, by coupling the two turbulence models with a combustion model incorporating a representative chemistry to account for non-equilibrium effects with realistic fuel properties, the models predict reasonably well the main combustion trends, with a superior performance for LES in terms of trade-off between accuracy and computing time. Secondly, because of some assumptions with the combustion model, some discrepancies are found in the prediction of species slowly produced or consumed such as CO and H2. Finally, the study emphasizes the dominant advantage of an adequate resolution of the mixing characteristics especially with the more demanding simulation of a swirl-stabilized spray flame.

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Tirkey, J. V., H. N. Gupta, and S. K. Shukla. "Integrated Gas Dynamic and Thermodynamic Computational Modeling of Multicylinder 4-Stroke Spark Ignition Engine Using Gasoline as Fuel." In ASME 2008 Heat Transfer Summer Conference collocated with the Fluids Engineering, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/ht2008-56497.

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This paper presents a computational tool for the evaluation of engine performance and exhaust emissions for four stroke multi-cylinder spark ignition engine which uses gasoline as fuel. Gas dynamics flow in multi-cylinder intake and exhaust systems are modeled by using one dimensional unsteady compressible flow equations. The hyperbolic partial differential equations are transferred into a set of ordinary differential equations by using method of characteristics and solved by finite difference method. Compatibility relationships between local fluid velocity (U) and sonic velocity (a) are expressed in terms of Riemann variables, which are constant along the position characteristics. The equations are solved numerically by using rectangular grid in the flow direction (x) and time (t). In this model Nitric Oxide concentration is predicted by using the rate kinetic model in the power cycle and along the exhaust pipes. Carbon Monoxide is computed under chemical equilibrium condition and then empirical adjustment is made for kinetic behaviors based upon experimental results. A good agreement is obtained in the comparison of computed and experimental results of instantaneous cylinder pressure, manifold pressure and temperature, and NO, CO emissions level.

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