Academic literature on the topic 'High–Order Perturbation of Surfaces Methods'
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Journal articles on the topic "High–Order Perturbation of Surfaces Methods"
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Nicholls, David P., Fernando Reitich, Timothy W. Johnson, and Sang-Hyun Oh. "Fast high-order perturbation of surfaces methods for simulation of multilayer plasmonic devices and metamaterials." Journal of the Optical Society of America A 31, no. 8 (July 24, 2014): 1820. http://dx.doi.org/10.1364/josaa.31.001820.
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Klahn, Mathias, Per A. Madsen, and David R. Fuhrman. "On the accuracy and applicability of a new implicit Taylor method and the high-order spectral method on steady nonlinear waves." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, no. 2243 (November 2020): 20200436. http://dx.doi.org/10.1098/rspa.2020.0436.
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This paper presents an investigation and discussion of the accuracy and applicability of an implicit Taylor (IT) method versus the classical higher-order spectral (HOS) method when used to simulate two-dimensional regular waves. This comparison is relevant, because the HOS method is in fact an explicit perturbation solution of the IT formulation. First, we consider the Dirichlet–Neumann problem of determining the vertical velocity at the free surface given the surface elevation and the surface potential. For this problem, we conclude that the IT method is significantly more accurate than the HOS method when using the same truncation order, M , and spatial resolution, N , and is capable of dealing with steeper waves than the HOS method. Second, we focus on the problem of integrating the two methods in time. In this connection, it turns out that the IT method is less robust than the HOS method for similar truncation orders. We conclude that the IT method should be restricted to M = 4, while the HOS method can be used with M ≤ 8. We systematically compare these two options and finally establish the best achievable accuracy of the two methods as a function of the wave steepness and the water depth.
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Yan, Jun Xi, Fang Peng, and Yu Feng Peng. "Influence of Thermal Distortion of Mirrors in Laser Resonators on Laser Modes." Applied Mechanics and Materials 214 (November 2012): 223–26. http://dx.doi.org/10.4028/www.scientific.net/amm.214.223.
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Taking into account the thermal absorption of laser light on laser mirror surface, the thermal deformation of the mirror substrate was analyzed. Influence of the thermal distortions of the mirror substrate on the laser resonant modes was calculated. The expressions for the field distributions of transverse laser modes with perturbation methods were derived. By comparing them with the elegant Hermite-Gaussian modes where there were no thermal distortions, the intensity profiles of the transverse laser modes versus the amount of the thermal deformation were obtained. The results show that the larger the thermal distortions of mirrors are, the wider the intensity profiles of the fundamental mode become, and the smaller the peak intensity becomes. Meanwhile, the high-order modes will be induced.
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Machado, M. R., and J. M. C. Dos Santos. "Reliability Analysis of Damaged Beam Spectral Element with Parameter Uncertainties." Shock and Vibration 2015 (2015): 1–12. http://dx.doi.org/10.1155/2015/574846.
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The paper examines the influence of uncertainty parameters on the wave propagation responses at high frequencies for a damaged beam structure in the structural reliability context. The reliability analyses were performed using the perturbation method, First-Order Reliability Method (FORM), and response surface method (RSM) which were compared with Monte Carlo simulation (MCS) under the spectral element method environment. The simulated results were performed to investigate the effects of material property and geometric uncertainties on the response at high frequency modes, such as the computational efficiency of reliability methods. For the first time, the spectral element method is used in the context of reliability analysis at medium and high frequency bands applied to damage detection. It has shown the effects of parameters uncertainty on the dynamic beam response due on an impulsive load and the robustness of each method. Numerical examples in a bending vibrating beam with random parameters are performed to verify the computational efficiency of the present study.
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Karton, Amir, and Laura K. McKemmish. "Can Popular DFT Approximations and Truncated Coupled Cluster Theory Describe the Potential Energy Surface of the Beryllium Dimer?" Australian Journal of Chemistry 71, no. 10 (2018): 804. http://dx.doi.org/10.1071/ch18269.
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The potential energy surface (PES) of the ground state of the beryllium dimer poses a significant challenge for high-level ab initio electronic structure methods. Here, we present a systematic study of basis set effects over the entire PES of Be2 calculated at the full configuration interaction (FCI) level. The reference PES is calculated at the valence FCI/cc-pV{5,6}Z level of theory. We find that the FCI/cc-pV{T,Q}Z basis set extrapolation reproduces the shape of the FCI/cc-pV{5,6}Z PES as well as the binding energy and vibrational transition frequencies to within ~10 cm−1. We also use the FCI/cc-pV{5,6}Z PES to evaluate the performance of truncated coupled cluster methods (CCSD, CCSD(T), CCSDT, and CCSDT(Q)) and contemporary density functional theory methods (DFT) methods for the entire PES of Be2. Of the truncated coupled cluster methods, CCSDT(Q)/cc-pV{5,6}Z provides a good representation of the FCI/cc-pV{5,6}Z PES. The GGA functionals, as well as the HGGA and HMGGA functionals with low percentages of exact exchange tend to severely overbind the Be2 dimer, whereas BH&HLYP and M06-HF tend to underbind it. Range-separated DFT functionals tend to underbind the dimer. Double-hybrid DFT functionals show surprisingly good performance, with DSD-PBEP86 being the best performer. Møller–Plesset perturbation theory converges smoothly up to fourth order; however, fifth-order corrections have practically no effect on the PES.
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Gerwe, Brian S., Ehsan Nasr Esfahani, Jiangyu Li, and Stuart B. Adler. "Detecting Dynamic Manipulation of the Space Charge Region in Doped Ceria with Scanning Thermo-Ionic Microscopy." ECS Meeting Abstracts MA2018-01, no. 32 (April 13, 2018): 1939. http://dx.doi.org/10.1149/ma2018-01/32/1939.
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A new generation of high performance energy storage and conversion devices is instrumental to commercial adoption of renewable, but intermittent, energy sources. Developing new materials for these devices often relies on bulk characterization techniques, such as electrochemical impedance spectroscopy, which are inherently unable to spatially resolve electrochemical phenomena and material properties. Conversely, scanning probe methods (SPM) have long been employed to probe local electrochemistry and material properties; however, relating these measurements to macroscopic performance can be challenging. We aim to bridge this gap by using SPM as a localized in operando witness during macroscopic measurements. Workers have recently employed Scanning Thermo-Ionic Microscopy (STIM), a strain-based SPM that leverages mechano-thermo-chemical coupled effects to detect local ionic concentrations. Briefly, STIM operates by inducing thermal stresses in the material from a periodic temperature perturbation at the scanning probe tip. The strain related to these thermal stresses drives ionic motion and is detected by deflection of the probe tip at a higher order harmonic of the temperature perturbation. This allows the ionic response to be distinguished from electrostatic and electromechanical responses, which occur at the temperature perturbation frequency. Previous ex-situ measurements demonstrated the potential of STIM to image grain boundary effects in doped ceria, possibly due to space charge regions. More recently, STIM was implemented point-wise to study manipulation of the space charge region under static polarization. Though promising, intensive hardware demands prevented imaging with STIM, thus ultimately reducing the impact of s-SPM implementation. Herein we demonstrate the use of data science enhanced SPM to overcome hardware limitations and extend our work to in operando, dynamic polarization studies. Furthermore, the effect of adsorbed surface species on STIM response is examined by controlling temperature, gas environment, and relative humidity.
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Hou, Thomas Y. "Numerical Solutions to Free Boundary Problems." Acta Numerica 4 (January 1995): 335–415. http://dx.doi.org/10.1017/s0962492900002567.
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Many physically interesting problems involve propagation of free surfaces. Vortex-sheet roll-up in hydrodynamic instability, wave interactions on the ocean's free surface, the solidification problem for crystal growth and Hele-Shaw cells for pattern formation are some of the significant examples. These problems present a great challenge to physicists and applied mathematicians because the underlying problem is very singular. The physical solution is sensitive to small perturbations. Naïve discretisations may lead to numerical instabilities. Other numerical difficulties include singularity formation and possible change of topology in the moving free surfaces, and the severe time-stepping stability constraint due to the stiffness of high-order regularisation effects, such as surface tension.This paper reviews some of the recent advances in developing stable and efficient numerical algorithms for solving free boundary-value problems arising from fluid dynamics and materials science. In particular, we will consider boundary integral methods and the level-set approach for water waves, general multi-fluid interfaces, Hele–Shaw cells, crystal growth and solidification. We will also consider the stabilising effect of surface tension and curvature regularisation. The issue of numerical stability and convergence will be discussed, and the related theoretical results for the continuum equations will be addressed. This paper is not intended to be a detailed survey and the discussion is limited by both the taste and expertise of the author.
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Stewart, James A., Joseph D. Olles, and Mitchell A. Wood. "Elucidating size effects on the yield strength of single-crystal Cu via the Richtmyer–Meshkov instability." Journal of Applied Physics 131, no. 11 (March 21, 2022): 114901. http://dx.doi.org/10.1063/5.0082495.
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Capturing the dynamic response of a material under high strain-rate deformation often demands challenging and time consuming experimental effort. While shock hydrodynamic simulation methods can aid in this area, a priori characterizations of the material strength under shock loading and spall failure are needed in order to parameterize constitutive models needed for these computational tools. Moreover, parameterizations of strain-rate-dependent strength models are needed to capture the full suite of Richtmyer–Meshkov instability (RMI) behavior of shock compressed metals, creating an unrealistic demand for these training data solely on experiments. Herein, we sweep a large range of geometric, crystallographic, and shock conditions within molecular dynamics (MD) simulations and demonstrate the breadth of RMI in Cu that can be captured from the atomic scale. Yield strength measurements from jetted and arrested material from a sinusoidal surface perturbation were quantified as [Formula: see text] GPa, higher than strain-rate-independent models used in experimentally matched hydrodynamic simulations. Defect-free, single-crystal Cu samples used in MD will overestimate [Formula: see text], but the drastic scale difference between experiment and MD is highlighted by high confidence neighborhood clustering predictions of RMI characterizations, yielding incorrect classifications.
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Veerappan, Anbu, and Vijayalakshmi Karattadipalayam Arumugam. "Quantum Chemical Studies on the Spectroscopic, Electronic Structural and Nonlinear Properties of an Organic N-Methyl-N- (2,4,6-Trinitrophenyl) Nitramide Energetic Molecule." Current Physical Chemistry 9, no. 1 (June 3, 2019): 5–21. http://dx.doi.org/10.2174/1877946809666190218154806.
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Background: Earlier studies on the energetic molecule MTNPN show a small HOMO-LUMO energy gap. In general, the material which acquires small energy gap exhibits NLO response and identical counterparts in both IR and Raman spectra. Hence, the combined experimental and theoretical studies were performed to explore the fundamental properties of the molecule. Objective: The objective of this study was to explore the fundamental structural properties of an energetic molecule MTNPN in addition to its application as a nonlinear optical material. Methods: FT-IR technique and quantum chemical methods were used to analyze the vibrational normal modes and structural properties of the molecule. Kurtz and Perry technique is used to find second harmonic generation efficiency in comparison to the standard NLO reference material. Results: The potential energy distribution was used to assign the vibrational normal modes of the molecule. The second order perturbation energies between the lone pair and anti-bonding species were predicted to understand the driving forces of molecular stability. The chemical reactivity of the molecule was determined from the molecular electrostatic potential surface and global reactivity descriptor results. The second-order hyperpolarizability of MTNPN and SHG efficiency of MTNPN were studied to find its NLO response and it was found from the results that MTNPN exhibits high NLO response than the standard NLO reference material. Conclusion: The vibrational degrees of freedom of MTNPN molecule were assigned and the experimental FT-IR spectra were compared with the scaled harmonic frequencies. The predicted second-order hyperpolarizability of MTNPN was about 6.46 times greater than the standard NLO reference urea. The interacting species between the lone pair orbitals and antibonding orbitals such as n3O8→ π*(N7-O9), n3O11→ π*(N10-O12) and n3O14→ π*(N13-O15) stabilized the molecule to a greater extent.
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Isabel B. LOBO, L., and David C. WILTON. "Effect of lipid composition on lipoprotein lipase activity measured by a continuous fluorescence assay: effect of cholesterol supports an interfacial surface penetration model." Biochemical Journal 321, no. 3 (February 1, 1997): 829–36. http://dx.doi.org/10.1042/bj3210829.
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The breakdown of normal substrates by lipases requires an interfacial binding step prior to hydrolysis. Interfacial binding and subsequent hydrolysis will be affected by the lipid components and hence physical properties of the substrate surface. In order to investigate in detail the effect of lipid structure on the activity of lipoprotein lipase (LPL), triolein-containing emulsion particles of defined composition have been used as substrates. In addition, lipase activity has been measured using a continuous fluorescence displacement assay that monitors the release of long-chain fatty acids as an alternative to normal radiochemical assays. Using this fluorescence assay, rates of hydrolysis of triolein were the same as when using a standard radiochemical assay under identical conditions. Activation by apolipoprotein CII was very similar by both methods; however, the extent of activation (2Ő3-fold) was less than has been reported previously using different assay conditions. In order to investigate the effect of cholesterol on LPL activity, emulsion particles were prepared in which the cholesterol/egg-phosphatidylcholine ratio was increased up to a 1:1 molar ratio. A pronounced stimulatory effect of cholesterol was observed under these assay conditions, with up to a 5-fold increase in rate compared with emulsion particles without cholesterol. Since high molar ratios of cholesterol are reported to exclude triacylglycerol from the phospholipid surface [Spooner and Small (1987) Biochemistry 26, 5820Ő5825], these results are not consistent with a mechanism involving LPL hydrolysis of surface triacylglycerol. Instead, they support an interfacial penetration model, allowing the enzyme's active site direct access to triacylglycerol in the lipoprotein core. Perturbation of the surface phospholipid monolayer of the emulsion particle as a result of hydrolysis by Naja naja phospholipase A2 resulted in a 10-fold activation of LPL, providing further support for an interfacial penetration model. The stimulatory effect of apolipoprotein CII was not modulated by modification of the interface with cholesterol.
Dissertations / Theses on the topic "High–Order Perturbation of Surfaces Methods"
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Sayi, Mbani T. "High Accuracy Fitted Operator Methods for Solving Interior Layer Problems." University of the Western Cape, 2020. http://hdl.handle.net/11394/7320.
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Philosophiae Doctor - PhDFitted operator finite difference methods (FOFDMs) for singularly perturbed problems have been explored for the last three decades. The construction of these numerical schemes is based on introducing a fitting factor along with the diffusion coefficient or by using principles of the non-standard finite difference methods. The FOFDMs based on the latter idea, are easy to construct and they are extendible to solve partial differential equations (PDEs) and their systems. Noting this flexible feature of the FOFDMs, this thesis deals with extension of these methods to solve interior layer problems, something that was still outstanding. The idea is then extended to solve singularly perturbed time-dependent PDEs whose solutions possess interior layers. The second aspect of this work is to improve accuracy of these approximation methods via methods like Richardson extrapolation. Having met these three objectives, we then extended our approach to solve singularly perturbed two-point boundary value problems with variable diffusion coefficients and analogous time-dependent PDEs. Careful analyses followed by extensive numerical simulations supporting theoretical findings are presented where necessary.
Books on the topic "High–Order Perturbation of Surfaces Methods"
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Ohlupin, Dmitriy, Al'bert Korolev, and Il'ya Sinev. Mechanochemical method of polishing a polycrystalline diamond coating. ru: INFRA-M Academic Publishing LLC., 2021. http://dx.doi.org/10.12737/1141765.
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The monograph presents a solution to the technological problem of polishing a polycrystalline diamond coating by a mechanochemical method in order to ensure the required surface roughness and high processing performance. The analysis of existing schemes and methods of polishing diamonds and diamond coatings is carried out. A technology for polishing diamond coatings with a metal brush is proposed, which provides brittle destruction of the vertices of large micro-roughnesses and graphitization of small micro-roughnesses. For researchers, postgraduates and specialists of industrial enterprises involved in the technology of polishing the surfaces of parts.
Book chapters on the topic "High–Order Perturbation of Surfaces Methods"
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Lehrenfeld, Christoph, and Arnold Reusken. "High Order Unfitted Finite Element Methods for Interface Problems and PDEs on Surfaces." In Transport Processes at Fluidic Interfaces, 33–63. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-56602-3_2.
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Bruno, Oscar P., and Fernando Reitich. "3. High-Order Boundary Perturbation Methods." In Mathematical Modeling in Optical Science, 71–109. Society for Industrial and Applied Mathematics, 2001. http://dx.doi.org/10.1137/1.9780898717594.ch3.
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"High-order accurate numerical methods for singularly perturbed problems." In Difference Methods for Singular Perturbation Problems, 274–303. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9780203492413-17.
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"High-order accurate numerical methods for singularly perturbed problems." In Difference Methods for Singular Perturbation Problems, 259–88. Chapman and Hall/CRC, 2008. http://dx.doi.org/10.1201/9780203492413.ch10.
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Nesterov, Sergei. "Perturbation Method in Eigenvalue Problems for Fourth-Order Equations." In High-Precision Methods in Eigenvalue Problems and Their Applications, 121–31. Chapman and Hall/CRC, 2004. http://dx.doi.org/10.1201/9780203401286.ch8.
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N. Hattori, Azusa, and Ken Hattori. "Creation and Evaluation of Atomically Ordered Side- and Facet-Surface Structures of Three-Dimensional Silicon Nano-Architectures." In 21st Century Surface Science - a Handbook. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.92860.
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The realization of three-dimensional (3D)-architected nanostructures, that is, the transformation from novel two-dimensional (2D) film-based devices to 3D complex nanodevices, is of crucial importance with the progress of scaling down devices to nanometer order. However, little attention has been devoted to controlling the atomic ordering and structures of side-surfaces on 3D structures, while techniques for controlling and investigating 2D surfaces, namely, surface science, have been established only for planar 2D surfaces. We have established an original methodology that enables atomic orderings and arrangements of surfaces with arbitrary directions to be observed on 3D figured structures by developing diffraction and microscopy techniques. An original technique, namely, directly and quantitatively viewing the side- and facet-surfaces at the atomic scale by reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED), can be used to determine process parameters in etching. This chapter introduces methods of evaluation by RHEED and LEED based on a reciprocal space map and methods of creating various atomically flat 111 and {100} side-surfaces of 3D Si nano-architectures and tilted 111 facet-surfaces fabricated by lithography dry and wet etching processes, followed by annealing treatment in vacuum.
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P. Singh, Akhlash. "Genomic Techniques Used to Investigate the Human Gut Microbiota." In Human Microbiome. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.91808.
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The human gut is the complex microbial ecosystem comprises more than 100 trillion microbes also known as microbiota. The gut microbiota does not only include about 400–500 types of bacterial strains, but it also contains archaea, bacteriophage, fungi, and protozoa species. In order to complete the characterization of the gut microbial community, we need the help of many culture-dependent and culture-independent genomic technologies. Recently, next-generation sequencing (NGS), mediated metagenomics that rely on 16S rRNA gene amplification, and whole-genome sequencing (WGS) have provided us deep knowledge related to important interactions such as host-microbiota and microbe-microbe interactions under various perturbation inside the gut. But, we still lack complete knowledge related to unique gene products encoded by gut meta-genome. Hence, it required the application of high-throughput “omics-based” methods to support metagenomics. Currently, a combination of high-throughput culturing and microfluidics assays is providing a new method to characterize non-amenable bacterial strains from the gut environment. The recent additions of artificial intelligence and deep learning to the area of microbiome studies have enhanced the capability of identification of thousand microbes simultaneously. Given above, it is necessary to apply new genome editing tools that can be used to design the personalized microflora which can be used to cure lifestyle-related diseases.
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Kataieva, Mariia, and Alina Yurchuk. "Intellectual Measuring Complex for Control of Geometrical Parameters of Aviation Details." In Handbook of Research on Artificial Intelligence Applications in the Aviation and Aerospace Industries, 352–71. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-7998-1415-3.ch015.
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This chapter proposes a new automated method of measuring complex three-dimensional surfaces of aircraft parts in static and dynamic modes. The method allows conducting measurements in closed conditions and at the site of the aircraft disposition. The method consists in the continuous determination of the coordinates of the points of the surface of the detail and their representation in a three-dimensional graphic depiction. New methods of measuring the geometric parameters of parts with the complex spatial surface are suggested. This opens the prospect for the development of new ways of measuring geometric parameters of parts in real-time with high metrological characteristics and computer simulation of the measurement process. The differential-digital method is based on the suggested zero-coordinate principle of the measurement process which involves simultaneous parts availability check, and connects measurement result obtained which provided a reduction in the order of measurement error.
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Chemin, Jean-Yves, Benoit Desjardins, Isabelle Gallagher, and Emmanuel Grenier. "Other Systems." In Mathematical Geophysics. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198571339.003.0017.
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The methods developed in this book can be applied to various physical systems. We will not detail all the possible applications and will only quote three systems arising in magnetohydrodynamics (MHD) and meteorology, namely conducting fluids in a strong external “large scale” magnetic field, a classical MHD system with high rotation, and the quasigeostrophic limit. The main theorems of this book can be extended to these situations. The theory of rotating fluids is very close to the theory of conducting fluids in a strong magnetic field. Namely the Lorenz force and the Coriolis force have almost the same form, up to Ohm’s law. The common feature is that these phenomena appear as singular perturbation skew-symmetric operators. The simplest equations in MHD are Navier–Stokes equations coupled with Ohm’s law and the Lorenz force where ∇φ is the electric field, j the current, and e the direction of the imposed magnetic field. In this case ε is called the Hartmann number. In physical situations, like the geodynamo (study of the magnetic field of the Earth), it is really small, of order 10−5–10−10, much smaller than the Rossby number. These equations are the simplest model in geomagnetism and in particular in the geodynamo. As ε→0 the flow tends to become independent of x3. This is not valid near boundaries. For horizontal boundaries, Hartmann layers play the role of Ekman layers and in the layer the velocity is given by The critical Reynolds number for linear instability is very high, of order Rec ∼ 104. The main reason is that there is no inflexion point in the boundary layer profile (10.1.2), therefore it is harder to destabilize than the Ekman layer since the Hartmann profile is linearly stable for the inviscid model associated with (10.1.1). As for Ekman layers, Hartmann layers are stable for Re<Rec and unstable for Re>Rec. There is also something similar to Ekman pumping, which is responsible for friction and energy dissipation. Vertical layers are simpler than for rotating fluids since there is only one layer, of size (εν)1/4. We refer to for physical studies.
Conference papers on the topic "High–Order Perturbation of Surfaces Methods"
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Nihei, Yasunori, Weiguang Bao, and Takeshi Kinoshita. "New Methods to Solve High Order Potential Used in Calculating Non-Linear Wave Loads." In 25th International Conference on Offshore Mechanics and Arctic Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/omae2006-92438.
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In the present study, non-linear wave loads such as the wave-drift force, wave-drift damping and wave-drift added mass, acting on the body is considered based on the potential theory. To investigate non-linear wave loads, consistent perturbation expansion by means of two small parameters, i.e. the incident wave slope and the low frequency body motion, is performed on a moving frame (body-fixed) coordinate system. To avoid complicated free surface integrals as much as possible, new approach for the higher order potential in the interaction problem of low frequency motion and waves is suggested in the present work. Instead of integrals, derivative operators are defined to obtain special solutions efficiently.
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Birknes, Jørn, Øistein Hagen, Thomas B. Johannessen, Øystein Lande, and Arne Nestegård. "Second-Order Kinematics Underneath Irregular Waves." In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-11629.
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The present paper is concerned with the prediction of horizontal velocities underneath measured irregular wave surface elevations. The simple case of unidirectional waves in deep water is considered. The main challenge in calculating accurately the kinematics in the crest region is related to the treatment of the contribution from wave components with frequencies much higher than the frequencies near the spectral peak. When using linear or weakly nonlinear perturbation methods, the wave components are superimposed at the still water level and it is necessary to truncate the tail of the spectrum in order to calculate accurately the velocity in the crest region. In the present paper, results from three methods of calculating the crest kinematics are compared with the model test results of Skjelbreia et al. [1]: • The second-order model of Stansberg et al. [5] which truncates consistently the high frequency part of the spectrum. • The second-order model of Johannessen [13] which calculates the velocity directly at the instantaneous free surface. • The Wheeler [3] stretching method which stretches the linear velocity profile from the still water level to the instantaneous free surface. In addition to comparing the horizontal velocity profiles underneath the crest, time traces of horizontal velocity is compared at the free surface in the vicinity of a large crest. The latter comparison highlights the differences between the models and the challenge of accurate predictions close to top of crest. All three models show a reasonable agreement with model test results although it is clear that the first two methods are superior to the Wheeler method.
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Shao, Yan-Lin. "Numerical Analysis of Second-Order Mean Wave Forces by a Stabilized Higher Order Boundary Element Method." In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/omae2018-78350.
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A stabilized Higher-Order Boundary Element Method (HOBEM) based on cubic shape functions is presented to solve the linear wave-structure interaction with the presence of steady or slowly varying velocities. The m-terms which involves second derivatives of local steady flow are difficult to calculate accurately on structure surfaces with high curvatures. They are also not integrable at the sharp corners. A formulation of the Boundary Value Problem (BVP) in a body-fixed coordinate system is thus adopted, which avoids the calculation of the m-terms. The use of body-fixed coordinate system also avoid the inconsistency in the traditional perturbation method when 2nd order slowly-vary motions are larger than the linear motions. The stabilized numerical method presented in this paper is based on streamline integration and biased differencing scheme along the streamlines. The presence of convective terms in the kinematic and dynamic free surface conditions will lead to instable solution if the explicit method is used. Thus a fully implicit scheme is used in this paper for the time integration of kinematic and dynamic free surface conditions. In an implicit scheme, solution of an additional matrix equation is normally required due to the fact that the presence of convective terms are approximated using the variables at current time step rather than the previous time steps only. A method that avoids solving such matrix equation is presented in this paper, which will reduce the computational efforts in the implicit method. The methodology is applicable on unstructured meshes. It can also be used in general second order wave-structure interaction analysis with presence of steady or slowly-varying velocities.
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Tang, Weihan, Seunghun Baek, and Bogdan I. Epureanu. "Reduced Order Models for Blisks With Small and Large Mistuning and Friction Dampers." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57850.
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In operation, rotating bladed disks (blisks) are often subject to high levels of dynamic loading, resulting in large amplitudes of forced vibrations especially at resonance. Moreover, variations in structural properties of individual sectors, referred to as mistuning, can lead to strain energy localization and can amplify forced responses. To prevent damages caused by high cycle fatigue, various frictional damping sources are introduced to dissipate vibration energy. Due to the nonlinear behavior of frictional contacts, conventional methods to study the dynamics of the blisk-damper systems are based often on numerical time integration, which is time-consuming and can be computationally prohibitive due to the large sizes of commercial blisk models. Existing techniques for model reduction either rely heavily on cyclic symmetry of the blisk-damper system, or are based on component mode synthesis (CMS). However, in the presence of mistuning, cyclic symmetry no longer exists. Also, mistuning is random and best studied statistically. Repetitive CMS condensation for a large amount of random mistuning patterns can lead to a computationally formidable task. This paper presents a reduced-order modeling technique to efficiently capture the nonlinear dynamic responses of blisk-damper systems with both small perturbations in blade material properties (small mistuning), and significant changes in the blisk geometries (large mistuning). The reduced-order models (ROMs) are formed by projecting the blisk-damper systems onto a novel mode basis that mimics the contact behavior. This mode basis contains normal mode shapes of the mistuned blisk-damper systems with either sliding or sticking conditions enforced on the contact surfaces. These mode shapes are computed through the N-PRIME method, a technique recently developed by the authors to efficiently obtain mode shapes for blisks with simultaneous large and small mistuning. The resulting modal nonlinear equations of motion are solved by a hybrid frequency/time (HFT) domain method with continuation. In the HFT method, the contact status and friction forces are determined in the time domain by a quasi-two-dimensional contact model at each contact point, whereas the modal equations of motion are solved in the frequency domain according to a harmonic balance formulation. The forced responses computed by the proposed ROMs are validated for two systems with distinct mistuning patterns. A statistical analysis is performed to study the effectiveness of the frictional dampers under random mistuning patterns.
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Fouques, Sébastien, and Csaba Pákozdi. "A Numerical Investigation of Steep Irregular Wave Properties With a Mixed-Eulerian Lagrangian HOS Method." In ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/omae2020-18216.
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Abstract The design of structures at sea requires knowledge on how large and steep waves can be. Although extreme waves are very rare, their consequences in terms of structural loads, such as wave impact or ringing, are critical. However, modelling the physical properties of steep waves along with their probability of occurrence in given sea states has remained a challenge. On the one hand, standard linear and weakly nonlinear wave theories are computationally efficient, but since they assume that the steepness parameter is small, they are unable to capture extreme waves. On the other hand, recent simulation methods based on CFD or fully nonlinear potential solvers are able to capture the physics of steep waves up to the onset on breaking, but their large computational cost makes it difficult to investigate rare events. Between these two extremes, the High-Order Spectral (HOS) method, which solves surface equations, is both efficient and able to capture highly nonlinear effects. It may then represent a good compromise for long simulations of steep waves. Unfortunately, it is based on a perturbation expansion where the small parameter is the wave steepness, and consequently, simulations tend to become unstable when steep wave events occur. In this work, we investigate the properties of irregular waves simulated with a modified HOS method, in which the sea surface is described with a Lagrangian representation, i.e. by computing the position and the velocity potential of individual surface particles. By doing so, nonlinear properties of the surface elevation are simply captured by the modulation of the horizontal and vertical particle motion. The same steep wave is then described more linearly with a Lagrangian representation, which reduces the instabilities of the HOS method. The paper focuses on bi-chromatic waves and irregular waves simulated from a JONSWAP spectrum. We compare simulations performed with the standard HOS and the modified Lagrangian methods for various HOS-orders.
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Zamboni, Giulio, Gabriel Banks, and Simon Bather. "Gradient-Based Adjoint and Design of Experiment CFD Methodologies to Improve the Manufacturability of High Pressure Turbine Blades." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56042.
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The tolerance of a turbine blade aerofoil is determined by the requirements to achieve an aerodynamic performance in operation. In fact, the manufacturing tolerance applied to the profile is driven by the effects of geometrical non-conformances on the efficiency and flow capacity of the aerofoil. However, this tolerance also has an impact on the ease with which the aerofoil can be manufactured, with tighter tolerance leading to lower manufacturing conformity. This paper details the application of an adjoint RANS solver and the according series of Design of Experiments (DoE) CFD calculations for a high pressure turbine blade to the above problem. There are two aims of this work; the first is to show that simpler linear CFD perturbation can be used to evaluate the effect of the geometric non-conformance. The second is to validate the spatial geometric correlation factor of the control points used in the manufacturing process on the performance evaluation with DoE techniques. This also verified the applicability of the adjoint CFD techniques; in fact the adjoint CFD calculation is an order of magnitude less computationally expensive than a large series of DoE RANS CFD calculations. The results confirm that the peak suction area is the most critical control region for the effect on the efficiency and flow capacity. Moreover, the CFD investigations show that a significant level of correlation exists between the influence factors at different control points. This suggests that not only the amount of geometric deviation but also the stream surface variation of profile tolerance significantly influence the final aerodynamic performance. The results from this calculation allow the creation of a 3D sensitivity map which will be used during the manufacturing of the aerofoil to optimise the control of the spatial distribution of the geometric non-conformance and to directly assess the expected performance effect during the manufacturing quality inspection. The methodology detailed in this paper shows how the CFD adjoint methods could be used for improved manufacturability of turbine blades ensuring that the critical characteristic features are controlled on the surface, relaxing the profile tolerance on those surface areas where the impact on the aerodynamic performance is predicted to be lower.
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Bianchi, Gian Marco, Piero Pelloni, Stefano Toninel, Ruben Scardovelli, Anthony Leboissetier, and Stephan Zaleski. "A Quasi-Direct 3D Simulation of the Atomization of High-Speed Liquid Jets." In ASME 2005 Internal Combustion Engine Division Spring Technical Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/ices2005-1067.
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In this paper a quasi-direct solution of transient three-dimensional CFD calculations based on a finite volume approach has been adopted to simulate the atomization process of high velocity liquid jets issuing an injector-like nozzle. An accurate Volume-of-Fluid (VOF) method is used to reconstruct and advect the interface between the liquid and gas phases. An extended mesh which includes the injector nozzle and the upstream plenum has been considered in order to investigate accurately the effect of nozzle flow conditions on the liquid jet atomization. Cavitation modeling has not been included in the present computations. Two different mean injection velocities, 150 m/s and 270 m/s, respectively, have been considered in the calculations as representative of semi-turbulent and fully-turbulent nozzle flow conditions. The liquid-to-gas density ratio is kept fixed at 57. The calculations show that atomisation is directly linked to the temporally and spatially correlated turbulence of the liquid jet. The bulk flow perturbation and the relaxation of the boundary layer have been found to be the basic mechanisms that generate surface perturbations of the liquid jet.
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Liu, Yu, Pooya Ghaderi, and Andrew J. Dick. "High Fidelity Methods for Modeling Nonlinear Wave Propagation in One-Dimensional Waveguides." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-88162.
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In this paper, two new methods are proposed to study wave propagation in materials with constitutive law that have nonlinear terms. In the first method, the gauge transformation is used to derive the dynamic shape function. A perturbation method is then applied in order to derive an equation for the wavenumber. The influence of the nonlinearity takes the form of a dependence of the wavenumber on the magnitude of the corresponding frequency component. Under the small amplitude and weak nonlinearity assumptions of the perturbation method, the wavenumber is incorporated into the spectral finite element method (SFEM). The second approach is a numerical method based on alternating frequency-time (AFT) iterations. The nonlinear term represented as a residual nonlinear force term is reduced through the alternating iterations between the time-domain and the frequency-domain. Finally, response behaviors under impact loading predicted with these methods are studied and compared to equivalent linear response behavior.
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Wang, Feng, and Luca di Mare. "Analysis of Transonic Bladerows With Non-Uniform Geometry Using Spectral Method." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-15161.
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Abstract Turbomachinery blade rows can have non-uniform geometries due to design intent, manufacture errors or wear. When predictions are sought for the effect of such non-uniformities, it is generally the case that whole assembly calculations are needed. A spectral method is used in this paper to approximate the flow fields of the whole assembly but with significantly less computation cost. The method projects the flow perturbations due to the geometry non-uniformity in an assembly in Fourier space, and only one passage is required to compute the flow perturbations corresponding to a certain wave-number of geometry variation. The performance of this method on transonic blade rows is demonstrated on a modern fan assembly. Low engine order and high engine order geometry non-uniformity (e.g. “saw-tooth” pattern) are examined. The non-linear coupling between the flow perturbations and the passage-averaged flow field is also demonstrated. Pressure variations on the blade surface and the potential flow field upstream of the leading edge from the proposed spectral method and the direct whole assembly solutions are compared. Good agreement is observed on both quasi-3D and full 3D cases. A lumped approach to compute deterministic fluxes is also proposed to further reduce the computational cost of the spectral method. The spectral method is formulated in such a way that it can be easily implemented into an existing harmonic flow solver by adding an extra source term, and can be potentially used as an efficient tool for aeromechanical and aeroacoustics design of turbomachinery blade rows.
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Li, Nanxi, and Amy Rachel Betz. "Design and Fabrication of an Experimental Facility for High-Pressure Pool Boiling." In ASME 2014 Power Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/power2014-32107.
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In this work, we present the design and fabrication a high-pressure pool boiling facility to conduct pool boiling experiments on horizontal heated surfaces under elevated pressures, up to 20 bar. Previous research has shown that micro- and/or nano-structured surfaces and coated surfaces will increase heat transfer coefficients up to one order of magnitude at atmospheric pressure. However, most boiling applications are subjected to high pressure, especially in the power industry. Pressure inside a boiling water reactor in a nuclear power plant will reach as high as 75 atm (75.99 bar). In order to determine how heat transfer is enhanced at increased pressures, with deionized water and refrigerants, on modified surfaces, a special experimental setup needs to be designed and fabricated. Difficulties in making such an experimental setup come from stabilizing the system pressure, sealing the test setup and visualizing the boiling conditions in the vessel. Both advantages and disadvantages of this design will be discussed and possible methods for improvements will be proposed. Preliminary test results on a plane copper surface are also included. Future research will be focusing on boiling of water and refrigerants on micro-structured copper surfaces, graphene coated, and Teflon© coated surfaces under high pressure.