Forced convection across a single tube was investigated numerically for various Reynolds numbers using various numerical models to identify suitable ranges for each model. Direct numericalsimulations (DNS), large edd...
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Forced convection across a single tube was investigated numerically for various Reynolds numbers using various numerical models to identify suitable ranges for each model. Direct numericalsimulations (DNS), large eddy simulations (LES), and a Reynolds averaged model using the Reynolds stress model (RSM) were compared with experimental date. The calculations used unsteady two-dimensional models with air as the working fluid. For the mesh used here, for Re < 10,000, the DNS method gave good results. For 10,000 < Re < 100,000, the LES is preferred while for Re > 100,000, the RSM is better. Nonlinear phenomena were found for various Reynolds numbers. For Re < 100, the average Nusselt number did not change with time while for 100 < Re < 1000, the average Nusselt number oscillated with time. The local Nusselt numbers along the entire tube are also discussed. (C) 2017 Published by Elsevier Ltd.
This paper presents a subsea DC collection grid with robust control and protection scheme and flexible expansion capability. By virtue of the DC/DC converter, different sections of the subsea grid are functionally int...
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ISBN:
(纸本)9781479977208
This paper presents a subsea DC collection grid with robust control and protection scheme and flexible expansion capability. By virtue of the DC/DC converter, different sections of the subsea grid are functionally interconnected and in the meantime decoupled in the event of DC faults. The faults are selectively isolated and system recovery from the faulty DC intertie branch is achieved by a coordinated operation on DCDC converters and DC disconnectors (or standard AC circuit breakers). A test system is presented which consists of two 100MW renewable energy sources and DC collection/transmission grids. The simulation results confirm the N-1 security of the presented topology and good control performance over DC faults.
As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. This paper develops and compares four average models for high frequency converters l...
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ISBN:
(纸本)9781479964154
As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. This paper develops and compares four average models for high frequency converters like DC/DC or DC hubs: the average model in the ABC frame using Dommel's method (Model 1), the average model in the dq frame using Dommel's method (Model 2), the average model in the ABC frame using Runge-Kutta method (Model 3) and the average model in the dq frame using Runge-Kutta method (Model 4). Schematics and principles of the numerical algorithms for the four models are presented. Detailed switching model of a 500MW, 2kHz, +/- 200kV/+/- 400kV DC/DC converter is taken as benchmark for comparing the four average models. It is found that Model2 is numerically unstable. Model 1 and Model3 need the same small solution time step as the detailed switching model to give accurate results. Model 4 is the recommended average model for high frequency (1-3kHz) converter. It gives accurate result as the detailed switching model at the benefit of 100 times faster simulation speed.
Traditional numerical analyses of laser beam transmission through "active" nonlinear materials have involved many assumptions that narrow their general applicability. As more complex optical phenomena are wi...
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ISBN:
(纸本)9780819498939
Traditional numerical analyses of laser beam transmission through "active" nonlinear materials have involved many assumptions that narrow their general applicability. As more complex optical phenomena are widely employed in research and industry, it is necessary to expand the use of numerical simulation methods. Historically, laser-matter interactions have involved calculations of "classical" wave propagation by Maxwell's equations and photon absorption through rate equations using numerous approximations. We describe a novel numerical modeling framework that adapts itself for simulation of different types of active materials provided by a simple graphical input. Our framework combines classical electric field propagation with "active" photon absorption kinetics using computational active photonic building blocks (APBB). It allows investigating a plane electromagnetic wave propagating through generic organic or inorganic photoactive materials;while, "active" photo-transitions are implemented using the APBB algorithm on the user interface. To date we have used the method in multiphoton absorbers, upconversion, semiconductor quantum dots, rare earth ions, organic chromophores, singlet oxygen formation, energy transfer, and optically-induced chemical reactions. We will demonstrate the method with applications of amplification in rare-earth ions and multiple two-photon absorbers materials in tandem.
As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. This paper develops and compares four average models for high frequency converters l...
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ISBN:
(纸本)9781479964161
As the future DC grids will involve numerous converter systems, the accuracy and speed of their modeling becomes of high importance. This paper develops and compares four average models for high frequency converters like DC/DC or DC hubs: the average model in the ABC frame using Dommel's method (Model 1), the average model in the dq frame using Dommel's method (Model 2), the average model in the ABC frame using Runge-Kutta method (Model 3) and the average model in the dq frame using Runge-Kutta method (Model 4). Schematics and principles of the numerical algorithms for the four models are presented. Detailed switching model of a 500MW, 2kHz, ±200kV/±400kV DC/DC converter is taken as benchmark for comparing the four average models. It is found that Model2 is numerically unstable. Model 1 and Model3 need the same small solution time step as the detailed switching model to give accurate results. Model 4 is the recommended average model for high frequency (1-3kHz) converter. It gives accurate result as the detailed switching model at the benefit of 100 times faster simulation speed.
In this work we study optical response of noble metal nanoparticles and report how it may be controllably varied over a wide range of wavelengths. Altering the particle shape and materials we investigate the surface p...
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ISBN:
(纸本)9780819483560
In this work we study optical response of noble metal nanoparticles and report how it may be controllably varied over a wide range of wavelengths. Altering the particle shape and materials we investigate the surface plasmon resonances of nanostars. To design novel nanostructures possessing diverse optical properties we assemble several plasmonic materials into a single nanoparticle. With numericalsimulation tool based on the spectral boundary integral equation method we investigate far-field and near-field characteristics of a variety of metal, metal-dielectric and bimetal nanostructures to be used in a range of applications from disease diagnostics through to the identification of contraband.
Behavior of the elastic-viscous-plastic (EVP) model for sea ice dynamics is explored, with particular attention to a necessary numerical Linearization of the internal ice stress term in the momentum equation. Improvem...
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Behavior of the elastic-viscous-plastic (EVP) model for sea ice dynamics is explored, with particular attention to a necessary numerical Linearization of the internal ice stress term in the momentum equation. Improvements to both the mathematical and numerical formulations of the model have moderated the impact of linearizing the stress term;simulations with the original EVP formulation and the improved version are used to explain the consequences of using different numerical approaches. In particular,, we discuss the model behavior in two regimes, low ice concentration such as occurs in the marginal ice zone, and very high ice concentration, where the ice is nearly rigid. Most of these results are highly relevant to the viscous-plastic (VP) ice dynamics model on which the EVP model is based. We provide examples of certain pathologies that the VP model and its numerical formulations exhibit at steady state. (C) 2001 Academic Press.
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