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Yongbin Zhang - One of the best experts on this subject based on the ideXlab platform.
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analytical solution to a mode of mixed elastohydrodynamic lubrication with mixed contact regimes part ii considering the contact adhering Layer effect in the inlet zone
Journal of Molecular Liquids, 2007Co-Authors: Yongbin ZhangAbstract:Abstract The present paper presents the researches succeeding the first part of the paper [Y.B. Zhang, Analytical Solution to A Mode of Mixed elastohydrodynamic lubrication with Mixed Contact Regimes: Part I—Without Consideration of Contact Adhering Layer in the Inlet Zone. Journal of Molecular Liquids, 2006, Vol.117, (10.1016/j.molliq.2006.04.006)], which analyzed one mode of mixed elastohydrodynamic lubrication with mixed contact regimes for the relatively heavy load and low rolling speed which make the conventional hydrodynamic lubrication occur in the inlet zone while make the physical adsorbed Layer Boundary lubrication occur in the Hertzian zone, based on the Newtonian fluid model. The present paper presents analysis to other two modes of mixed EHL with mixed contact regimes for relatively heavy loads, low rolling speeds and Newtonian fluids, where the conventional hydrodynamic lubrication, physical adsorbed Layer Boundary lubrication and oxidized chemical Layer Boundary lubrication can simultaneously occur in the inlet zone while the oxidized chemical Layer Boundary lubrication or the fresh metal-oxidized chemical Boundary Layer dry contact occur in the Hertzian zone, considering the contact adhering Layer effect in the inlet zone. The present analysis is also extended to the first mode of mixed EHL with mixed contact regimes as analyzed in Part I [Y.B. Zhang, Analytical Solution to A Mode of Mixed elastohydrodynamic lubrication with Mixed Contact Regimes: Part I—Without Consideration of Contact Adhering Layer in the Inlet Zone. Journal of Molecular Liquids, 2006, Vol.117, (10.1016/j.molliq.2006.04.006)] when the contact adhering Layer effect in the inlet zone is considered. Results of contact pressures, film thicknesses, load partitions in the contact and characteristic rolling speeds for approaching to zero averaged hydrodynamic film thickness in the Hertzian zone are obtained from this analysis respectively as functions of the contact adhering Layer thickness in the inlet zone. The results show that the contact adhering Layer effect in the inlet zone in the present EHL is reduced with the increase of load; At large loads, this effect may be negligible; At small loads, it may be very significant. The results also show that at low rolling speeds, when the contact adhering Layer effect in the inlet zone is considered, the load-carrying capacity of the present EHL contact is increased especially for small loads. This means that at low rolling speeds the contact adhering Layer effect in the inlet zone may reduce the elastohydrodynamic lubrication deviation from classical EHL theory predictions especially for small loads.
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analytical solution to a mode of mixed elastohydrodynamic lubrication with mixed contact regimes part i without consideration of contact adhering Layer in the inlet zone
Journal of Molecular Liquids, 2007Co-Authors: Yongbin ZhangAbstract:In 2005, Zhang presented a Grubin-like inlet zone analysis to the isothermal line contact elastohydrodynamic lubrication under relatively heavy loads when the hydrodynamic film thickness in the Hertzian zone approaches zero and the EHL fluid is Newtonian [Zhang, Y.B. A justification of the load-carrying capacity of elastohydrodynamic lubrication film based on the Newtonian fluid model. Industrial Lubrication and Tribology, 2005, Vol. 57, pp. 224–232]. His results showed that in this EHL, when the rolling speed is lower than the characteristic rolling speed (Uch =) 0.0372W1.50/G, the Hertzian zone is in physical adsorbed Layer Boundary lubrication while the inlet zone is in conventional hydrodynamic lubrication. This mode of EHL represents a mode of mixed EHL with mixed contact regimes, where hydrodynamic films with different rheological behaviors occur in different areas of the contact. The present paper presents an analysis to this mode of mixed EHL by using the Grubin type method when the contact adhering Layer in the inlet zone is neglected. Pressures, film thicknesses and load partition in the contact are obtained from this analysis. It is also found that the formula for the characteristic rolling speed Uch = 0.0372W1.50/G obtained by Zhang [Zhang, Y.B. A justification of the load-carrying capacity of elastohydrodynamic lubrication film based on the Newtonian fluid model. Industrial Lubrication and Tribology, 2005, Vol. 57, pp. 224–232] may be valid for the dimensionless load W > 1.0E−7, while it may be invalid for the dimensionless load W < 1.0E−8. In part II [Zhang, Y.B. Analytical solution to a mode of mixed elastohydrodynamic lubrication with mixed contact regimes: Part II. Considering the contact adhering Layer effect in the inlet zone. Journal of Molecular Liquids, 2006, Vol. 117. (doi:10.1016/j.molliq.2006.04.007)] will be presented an analysis to other two modes of mixed EHL with mixed contact regimes for relatively heavy loads, low rolling speeds and Newtonian fluids, where the conventional hydrodynamic lubrication, physical adsorbed Layer Boundary lubrication and oxidized chemical Layer Boundary lubrication can simultaneously occur in the inlet zone while the oxidized chemical Layer Boundary lubrication or the fresh metal-oxidized chemical Boundary Layer dry contact occur in the Hertzian zone, considering the contact adhering Layer effect in the inlet zone.
Masanori Koshiba - One of the best experts on this subject based on the ideXlab platform.
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finite element method using port truncation by perfectly matched Layer Boundary conditions for optical waveguide discontinuity problems
Journal of Lightwave Technology, 2002Co-Authors: Yasuhide Tsuji, Masanori KoshibaAbstract:A powerful algorithm based on a finite element method (FEM) is newly formulated for the analysis of waveguide discontinuities. In an earlier approach, FEM was applied to the finite region with discontinuities, and a mode expansion technique was applied to the uniform waveguides that are connected to the input and output ports of finite region. Although, in the present approach, the uniform waveguides are replaced by perfectly matched Layer (PML) Boundary conditions, it is possible to treat periodically varying waveguide structures such as photonic crystal (PC) waveguides. A combined method of beam propagation method (BPM) and FEM is also shown in such a form that a mode expansion technique is not required. To show the validity and usefulness of the present approach, numerical examples for optical gratings, circuit components based on PC waveguides and optical directional couplers are presented.
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guided mode and leaky mode analysis by imaginary distance beam propagation method based on finite element scheme
Journal of Lightwave Technology, 2000Co-Authors: Yasuhide Tsuji, Masanori KoshibaAbstract:As a simple analysis method to solve eigenmodes of optical waveguides, we present an imaginary distance beam propagation method (BPM) based on finite element scheme. The matrices used in the beam propagation analysis are essentially complex, so lossy optical waveguides can be easily treated. Moreover, employing the transparent Boundary condition or perfectly matched Layer Boundary condition, the validity of a which has been already confirmed in the real distance BPM, we can easily treat not only guided modes but leaky ones. To show the validity and usefulness of this approach, eigenmodes of twoand three-dimensional leaky waveguides, and optical fibers are calculated.
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time domain beam propagation method and its application to photonic crystal circuits
Journal of Lightwave Technology, 2000Co-Authors: Masanori Koshiba, Yasuhide Tsuji, M HikariAbstract:A time-domain beam propagation method (BPM) based on the finite-element scheme is described for the analysis of reflections of both transverse electric and transverse magnetic polarized pulses in waveguiding structures containing arbitrarily shaped discontinuities. In order to avoid nonphysical reflections from the computational window edges, the perfectly matched Layer Boundary condition is introduced. The present algorithm using the Pade approximation is, to our knowledge, the first time-domain beam propagation method which can treat wide-band optical pulses. After validating this method for an optical grating with modulated refractive indexes, various photonic crystal circuit components are simulated.
Yasuhide Tsuji - One of the best experts on this subject based on the ideXlab platform.
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complex modal analysis of curved optical waveguides using a full vectorial finite element method with perfectly matched Layer Boundary conditions
Electromagnetics, 2004Co-Authors: Yasuhide TsujiAbstract:A full-wave modal analysis of three-dimensional curved optical waveguides using the finite element method based on edge/nodal hybrid elements is presented. In order to calculate bending losses, an anisotropic perfectly matched Layer (PML) Boundary condition is employed, and to apply the PML concept to curved waveguides, the PML, which is applicable to inhomogeneous regions, is derived.
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finite element method using port truncation by perfectly matched Layer Boundary conditions for optical waveguide discontinuity problems
Journal of Lightwave Technology, 2002Co-Authors: Yasuhide Tsuji, Masanori KoshibaAbstract:A powerful algorithm based on a finite element method (FEM) is newly formulated for the analysis of waveguide discontinuities. In an earlier approach, FEM was applied to the finite region with discontinuities, and a mode expansion technique was applied to the uniform waveguides that are connected to the input and output ports of finite region. Although, in the present approach, the uniform waveguides are replaced by perfectly matched Layer (PML) Boundary conditions, it is possible to treat periodically varying waveguide structures such as photonic crystal (PC) waveguides. A combined method of beam propagation method (BPM) and FEM is also shown in such a form that a mode expansion technique is not required. To show the validity and usefulness of the present approach, numerical examples for optical gratings, circuit components based on PC waveguides and optical directional couplers are presented.
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guided mode and leaky mode analysis by imaginary distance beam propagation method based on finite element scheme
Journal of Lightwave Technology, 2000Co-Authors: Yasuhide Tsuji, Masanori KoshibaAbstract:As a simple analysis method to solve eigenmodes of optical waveguides, we present an imaginary distance beam propagation method (BPM) based on finite element scheme. The matrices used in the beam propagation analysis are essentially complex, so lossy optical waveguides can be easily treated. Moreover, employing the transparent Boundary condition or perfectly matched Layer Boundary condition, the validity of a which has been already confirmed in the real distance BPM, we can easily treat not only guided modes but leaky ones. To show the validity and usefulness of this approach, eigenmodes of twoand three-dimensional leaky waveguides, and optical fibers are calculated.
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time domain beam propagation method and its application to photonic crystal circuits
Journal of Lightwave Technology, 2000Co-Authors: Masanori Koshiba, Yasuhide Tsuji, M HikariAbstract:A time-domain beam propagation method (BPM) based on the finite-element scheme is described for the analysis of reflections of both transverse electric and transverse magnetic polarized pulses in waveguiding structures containing arbitrarily shaped discontinuities. In order to avoid nonphysical reflections from the computational window edges, the perfectly matched Layer Boundary condition is introduced. The present algorithm using the Pade approximation is, to our knowledge, the first time-domain beam propagation method which can treat wide-band optical pulses. After validating this method for an optical grating with modulated refractive indexes, various photonic crystal circuit components are simulated.
Malvin C Teich - One of the best experts on this subject based on the ideXlab platform.
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breakdown probabilities for thin heterostructure avalanche photodiodes
IEEE Journal of Quantum Electronics, 2003Co-Authors: Majeed M Hayat, Unal Sakoglu, Ohhyun Kwon, Shuling Wang, J C Campbell, Bahaa E A Saleh, Malvin C TeichAbstract:The recurrence theory for the breakdown probability in avalanche photodiodes (APDs) is generalized to heterostructure APDs that may have multiple multiplication Layers. The generalization addresses Layer-Boundary effects such as the initial energy of injected carriers as well as the Layer-dependent profile of the dead space in the multiplication region. Reducing the width of the multiplication Layer serves to both downshift and sharpen the breakdown probability curve as a function of the applied reverse-bias voltage. In structures where the injected carriers have an initial energy that is comparable to the ionization threshold energy, the transition from linear mode to Geiger-mode is more abrupt than in structures in which such initial energy is negligible. The theory is applied to two recently fabricated Al/sub 0.6/Ga/sub 0.4/As-GaAs heterostructure APDs and to other homostructure thin GaAs APDs and the predictions of the breakdown-voltage thresholds are verified.
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Boundary effects on multiplication noise in thin heterostructure avalanche photodiodes theory and experiment al sub 0 6 ga sub 0 4 as gaas
IEEE Transactions on Electron Devices, 2002Co-Authors: Majeed M Hayat, Ohhyun Kwon, Shuling Wang, J C Campbell, Bahaa E A Saleh, Malvin C TeichAbstract:The history-dependent recurrence theory for multiplication noise in avalanche photodiodes (APDs), developed by Hayat et al., is generalized to include inter-Layer Boundary effects in heterostructure APDs with multiLayer multiplication regions. These Boundary effects include the initial energy of injected carriers as well as bandgap-transition effects within a multiLayer multiplication region. It is shown that the excess noise factor can be significantly reduced if the avalanche process is initiated with an energetic carrier, in which case the initial energy serves to reduce the initial dead space associated with the injected carrier. An excess noise factor reduction up to 40% below the traditional thin-APD limit is predicted for GaAs, depending on the operational gain and the multiplication-region's width. The generalized model also thoroughly characterizes the behavior of dead space as a function of position across Layers. This simultaneously captures the effect of the nonuniform electric field as well as the anticipatory nature of inter-Layer bandgap-Boundary effects.
B Chen - One of the best experts on this subject based on the ideXlab platform.
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the perfectly matched Layer Boundary condition for scalar finite difference time domain method
IEEE Photonics Technology Letters, 2001Co-Authors: Dong Zhou, Weiping Huang, D G Fang, B ChenAbstract:The perfectly matched Layer (PML) Boundary condition for the scalar finite-difference time-domain (FDTD) method is developed in this letter. It is demonstrated that the PML is suitable and effective in computation of optical waveguides. The results also show how to optimize the parameters of PML.