Numerical Results of an Integral Formulation of Transient Radiative Transfer

1999 ◽  
Author(s):  
Z.-M. Tan ◽  
P.-F. Hsu
Keyword(s):  
Steady State ◽  
Radiative Transfer ◽  
Incident Radiation ◽  
Integral Formulation ◽  
Time Step ◽  
Incident Intensity ◽  
Participating Media ◽  
Upwind Difference Scheme ◽  
The One ◽  
Reflecting Surface

Abstract Numerical computations are performed for the transient radiative transfer equation within the one-dimensional parallel plate geometry using an integral formulation obtained in a prior work. The medium under consideration is absorbing and isotropically scattering. One boundary is a black emitting surface or a transparent surface subjected to the collimated incident radiation. The incident intensity is applied at the start of the transient. The other boundary is a cold and black or specularly reflecting surface. The spatial and temporal incident radiation and radiative flux distributions are presented for different boundary conditions and for uniform and nonuniform property distribution. The transient results at large time step are compared with steady-state solutions by the finite volume and quadrature methods and show excellent agreement. The solutions of reflecting boundary condition exhibit distinctive behavior from that of the non-reflecting boundary. The integral formulation is extended to handle the transient transfer within the nonhomogeneous participating media. The integral formulation has several advantages over the differential treatment of the hyperbolic wave of the radiative transport; among others: (1) The avoidance of using a high order upwind difference scheme in resolving the wave front; (2) Providing a sound basis for physical interpretation as the radiative transfer is a volumetric process; and (3) Many integral equation numerical methods that have previously been developed for the steady state integral formulation can be re-applied to treat the transient problem.

An Integral Formulation of Transient Radiative Transfer

2000 ◽  
Vol 123 (3) ◽  
pp. 466-475 ◽  
Author(s):  
Z.-M. Tan ◽  
P.-F. Hsu
Keyword(s):  
Radiative Transfer ◽  
Incident Radiation ◽  
Integral Formulation ◽  
Time Dependent ◽  
Slab Geometry ◽  
Time Step ◽  
Participating Media ◽  
Quadrature Methods ◽  
Time Dependent Domain ◽  
Large Time Step

A time-dependent integral formulation is developed for modeling transient radiative transfer. The development is based on a rigorous analysis of the wave propagation process inside the participating media. The physical significance of the present integral formulation is the consideration of the time-dependent domain of computation, which is different from the domain disturbed by radiation (i.e., the wave front envelope). Numerical computations are performed for the medium that is an absorbing and isotropically scattering one-dimensional plane slab geometry. The spatial and temporal incident radiation and radiative flux distributions are presented for different boundary conditions and for uniform and nonuniform property distribution. The transient results at large time step are compared with steady-state solutions by the finite volume and quadrature methods and show excellent agreement. The solutions of reflecting boundary condition exhibit distinctive behavior from that of the non-reflecting boundary.

Transient Radiation Coupled With Conduction Heat Transfer in a One Dimensional Slab

2014 ◽  
Vol 619 ◽  
pp. 94-98
Author(s):  
Prerana Nashine ◽  
Ashok Kumar Satapathy
Keyword(s):  
Radiative Transfer ◽  
Radiation Effects ◽  
Research Work ◽  
Incident Radiation ◽  
Time Step ◽  
Participating Media ◽  
Transient Radiation ◽  
Transfer Equations ◽  
Volume Method ◽  
Radiative Transfer Equations

The present research work views over a solution of radiative transport problem along with conduction in one perspective piece and in the existence of participating media. The radiative transfer equations are developed for anisotropically scattering, absorbing, emitting medium and the equation is being discretized using finite volume method. Heat flux and the incident radiation effects have been computed at three different time step. Transient radiation along with transient conduction is solved and the radiative effect has been measured using radiative transfer equation while the conduction term has been measured using conduction equation.

Radiative Characteristics of High-Porosity Media Containing Randomly Oriented Fibers in Space

2017 ◽  
Vol 9 (2) ◽  
Author(s):  
Herve Thierry Tagne Kamdem
Keyword(s):  
Diffraction Theory ◽  
Incident Radiation ◽  
Spherical Particles ◽  
High Porosity ◽  
Fibrous Media ◽  
Participating Media ◽  
Hemispherical Reflectance ◽  
Scattering Phase Function ◽  
The One ◽  
Radiative Characteristics

This paper proposed radiative characteristics' expressions for media containing randomly oriented fibers in space. In deriving these simple radiative characteristics' expressions, the fibrous medium effective extinction coefficient is defined to match with the one of large particle obtained by combining geometric optics and Fraunhofer diffraction theory. Fibrous media radiative characteristics are then derived as an average over all incident radiation angles of single fiber radiative characteristics. Theoretical hemispherical reflectance and normal transmittance predictions using the proposed fibrous media radiative characteristics based on the Mie theory agreed well with literature experiments. Therefore, media containing fiber randomly oriented in space can be scaled to a suitable equivalent media such that scattering mechanisms behave similarly to that occurring in a participating media containing spherical particles. Numerical investigations show that a theoretical model which assumes Henyey–Greenstein (HG) scattering phase function can conveniently be used for the estimation of equivalent fibrous media radiative characteristics using hemispherical reflectance measurements. On the other hand, the estimated equivalent fibrous media radiative characteristics from hemispherical measurements and using a two-flux model with isotropic scaling radiative characteristics may be subjected to serious errors in the case of semitransparent media for which the absorption is significant.

scholarly journals A New Discrete Implicit Monte Carlo Scheme for Simulating Radiative Transfer Problems

2022 ◽  
Vol 258 (1) ◽  
pp. 14
Author(s):  
Elad Steinberg ◽  
Shay I. Heizler
Keyword(s):  
Monte Carlo ◽  
Radiative Transfer ◽  
Monte Carlo Algorithm ◽  
Basic Algorithm ◽  
Time Step ◽  
Radiative Shock ◽  
Continuous Absorption ◽  
Discrete Nature ◽  
The One ◽  
Transfer Problems

Abstract We present a new algorithm for radiative transfer—based on a statistical Monte Carlo approach—that does not suffer from teleportation effects, on the one hand, and yields smooth results, on the other hand. Implicit Monte Carlo (IMC) techniques for modeling radiative transfer have existed from the 1970s. When they are used for optically thick problems, however, the basic algorithm suffers from “teleportation” errors, where the photons propagate faster than the exact physical behavior, due to the absorption-blackbody emission processes. One possible solution is to use semianalog Monte Carlo, in its new implicit form (ISMC), which uses two kinds of particles, photons and discrete material particles. This algorithm yields excellent teleportation-free results, but it also produces noisier solutions (relative to classic IMC), due to its discrete nature. Here, we derive a new Monte Carlo algorithm, Discrete Implicit Monte Carlo (DIMC), which also uses the idea of two kinds of discrete particles, and thus does not suffer from teleportation errors. DIMC implements the IMC discretization and creates new radiation photons for each time step, unlike ISMC. Using the continuous absorption technique, DIMC yields smooth results like classic IMC. One of the main elements of the algorithm is the avoidance of the explosion of the particle population, by using particle merging. We test the new algorithm on 1D and 2D cylindrical problems, and show that it yields smooth, teleportation-free results. We finish by demonstrating the power of the new algorithm on a classic radiative hydrodynamic problem—an opaque radiative shock wave. This demonstrates the power of the new algorithm for astrophysical scenarios.

scholarly journals Study on a Novel High-Efficiency Bridgeless PFC Converter

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Cao Taiqiang ◽  
Chen Zhangyong ◽  
Wang Jun ◽  
Sun Zhang ◽  
Luo Qian ◽  
...  
Keyword(s):  
Steady State ◽  
High Efficiency ◽  
Control Policy ◽  
Switching Frequency ◽  
Fast Recovery ◽  
Zero Current Switching ◽  
Zero Current ◽  
The One ◽  
Gain Characteristic ◽  
Conduction Mode

In order to implement a high-efficiency bridgeless power factor correction converter, a new topology and operation principles of continuous conduction mode (CCM) and DC steady-state character of the converter are analyzed, which show that the converter not only has bipolar-gain characteristic but also has the same characteristic as the traditional Boost converter, while the voltage transfer ratio is not related with the resonant branch parameters and switching frequency. Based on the above topology, a novel bridgeless Bipolar-Gain Pseudo-Boost PFC converter is proposed. With this converter, the diode rectifier bridge of traditional AC-DC converter is eliminated, and zero-current switching of fast recovery diode is achieved. Thus, the efficiency is improved. Next, we also propose the one-cycle control policy of this converter. Finally, experiments are provided to verify the accuracy and feasibility of the proposed converter.

Two-Frequency Oscillation With Combined Coulomb and Viscous Frictions

2002 ◽  
Vol 124 (4) ◽  
pp. 537-544 ◽  
Author(s):  
Gong Cheng ◽  
Jean W. Zu
Keyword(s):  
Steady State ◽  
Dry Friction ◽  
Single Frequency ◽  
Friction Oscillator ◽  
One Stop ◽  
Frequency Excitation ◽  
Stop Motion ◽  
The One ◽  
Coulomb Dry Friction ◽  
Mass Spring

In this paper, a mass-spring-friction oscillator subjected to two harmonic disturbing forces with different frequencies is studied for the first time. The friction in the system has combined Coulomb dry friction and viscous damping. Two kinds of steady-state vibrations of the system—non-stop and one-stop motions—are considered. The existence conditions for each steady-state motion are provided. Using analytical analysis, the steady-state responses are derived for the two-frequency oscillating system undergoing both the non-stop and one-stop motions. The focus of the paper is to study the influence of the Coulomb dry friction in combination with the two frequency excitations on the dynamic behavior of the system. From the numerical simulations, it is found that near the resonance, the dynamic response due to the two-frequency excitation demonstrates characteristics significantly different from those due to a single frequency excitation. Furthermore, the one-stop motion demonstrates peculiar characteristics, different from those in the non-stop motion.

Fluid turbulence simulations of divertor heat load for ITER hybrid scenario using BOUT++

2021 ◽  
Author(s):  
Xueyun Wang ◽  
Xueqiao Xu ◽  
Philip B Snyder ◽  
Zeyu Li
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Energy Loss ◽  
Heat Load ◽  
Type I ◽  
Fluid Turbulence ◽  
Drift Model ◽  
Steady State Operation ◽  
Different Types ◽  
The One

Abstract The BOUT++ six-field turbulence code is used to simulate the ITER 11.5MA hybrid scenario and a brief comparison is made among ITER baseline, hybrid and steady-state operation (SSO) scenarios. Peeling-ballooning instabilities with different toroidal mode numbers dominate in different scenarios and consequently yield different types of ELMs. The energy loss fractions (ΔWped/Wped) caused by unmitigated ELMs in the baseline and hybrid scenarios are large (~2%) while the one in the SSO scenario is dramatically smaller (~1%), which are consistent with the features of type-I ELMs and grassy ELMs respectively. The intra ELM divertor heat flux width in the three scenarios given by the simulations is larger than the estimations for inter ELM phase based on Goldston’s heuristic drift model. The toroidal gap edge melting limit of tungsten monoblocks of divertor targets imposes constraints on ELM energy loss, giving that the ELM energy loss fraction should be smaller than 0.4%, 1.0%, and 1.2% for ITER baseline, hybrid and SSO scenarios, correspondingly. The simulation shows that only the SSO scenario with grassy ELMs may satisfy the constraint.

Aeroacoustic Analysis of a UAV Propeller Operable at Various Altitudes

2021 ◽  
Author(s):  
Ji-Hun Song ◽  
Seungsoo Jang ◽  
Youn-Jea Kim
Keyword(s):  
Steady State ◽  
Turbulence Model ◽  
Technological Development ◽  
Basic Research ◽  
Noise Pollution ◽  
Maximum Error ◽  
Unmanned Aircraft ◽  
Time Step ◽  
Application Range ◽  
Noise Characteristics

Abstract With technological development and the wide application range of unmanned aerial vehicles (UAVs), the regulation of UAV altitude limits in many countries is further alleviated, and the problem of UAV noise pollution has emerged with the recent advent of urban air mobility (UAM) and personal air vehicle (PAV) markets. In this study, one typical propeller, the T-motor 15 × 5 propeller, was analyzed by use of the commercial CFD software, ANSYS FLUENT V19.3. The effects of gravity and convection were analyzed to determine the noise characteristics at altitude using the FW-H equation. A high-altitude drone, which operates at heights from 0 to 10 km with 1,000 to 5,000 revolutions per minute, was analyzed using the steady-state k-ω SST turbulence model. And using the steady-state data to initialize values, an unsteady analysis was performed with the LES turbulence model. The time step was divided based on the 1-degree rotational time, and the velocity residual on each axis was calculated until a value of 10−7 or less was achieved and there was no fluctuation of thrust, at which point it was considered converged. The CFD results were validated with the experimental results for thrust and their results show that the maximum error was 8.64%. The overall sound pressure level was calculated, and noise characteristics in the audible frequency range according to receiver points were also compared. Through this study, thrust and noise data according to altitude were provided. The aerodynamic and aeroacoustic characteristics at high-altitudes, which are generally difficult to measure by experiment, are also presented. Therefore, the appropriate operating altitudes and rotational speeds will be presented through the aeroacoustics analysis corresponding to operational altitude, and the basic research data can then be applied to upcoming unmanned aircraft system (UAS) market.

scholarly journals Comparison of numerical schemes of river flood routing with an inertial approximation of the Saint Venant equations

RBRH ◽  
2018 ◽  
Vol 23 (0) ◽  
Author(s):  
Alice César Fassoni-Andrade ◽  
Fernando Mainardi Fan ◽  
Walter Collischonn ◽  
Artur César Fassoni ◽  
Rodrigo Cauduro Dias de Paiva
Keyword(s):  
Numerical Stability ◽  
Flood Routing ◽  
Computational Time ◽  
Numerical Schemes ◽  
Time Step ◽  
Simple Formulation ◽  
One Dimensional ◽  
Saint Venant Equations ◽  
Original Scheme ◽  
The One

ABSTRACT The one-dimensional flow routing inertial model, formulated as an explicit solution, has advantages over other explicit models used in hydrological models that simplify the Saint-Venant equations. The main advantage is a simple formulation with good results. However, the inertial model is restricted to a small time step to avoid numerical instability. This paper proposes six numerical schemes that modify the one-dimensional inertial model in order to increase the numerical stability of the solution. The proposed numerical schemes were compared to the original scheme in four situations of river’s slope (normal, low, high and very high) and in two situations where the river is subject to downstream effects (dam backwater and tides). The results are discussed in terms of stability, peak flow, processing time, volume conservation error and RMSE (Root Mean Square Error). In general, the schemes showed improvement relative to each type of application. In particular, the numerical scheme here called Prog Q(k+1)xQ(k+1) stood out presenting advantages with greater numerical stability in relation to the original scheme. However, this scheme was not successful in the tide simulation situation. In addition, it was observed that the inclusion of the hydraulic radius calculation without simplification in the numerical schemes improved the results without increasing the computational time.

Sign in / Sign up

Export Citation Format

Share Document