1,721,026 research outputs found
Natural convection phenomena affected by radiation in concentric and eccentric horizontal cylindrical annuli
No full textA numerical investigation has been performed to study the radiation-affected steady-laminar natural convection induced by a hot inner cylinder under a large temperature difference in the cylindrical annuli filled with a gray gas. Ib examine the effects of thermal radiation on thermofluid dynamics behavior in the eccentric geometry, the generalized body-fitted coordinate system is introduced while the finite volume method is used for solving the radiative transport equation. After validating numerical results for the case without radiation, the detailed radiation effect is discussed. Based on the results of this study, when there exists a large temperature difference between two cylinders, the existence of a radiatively participating medium is found to incur a distinct difference in fluid dynamics as well as thermal behavior
Radiation affected ignition and flame propagation for solid fuel in a cylindrical enclosure
No full textIgnition and flame propagation for pyrolysing fuel in a cylindrical enclosure has been examined in this study. The pyrolysing fuel of cylindrical shape was located both eccentrically and concentrically inside an outer cylinder that was sustained at high temperature. Due to gravity, buoyancy motion was inevitably incurred in the enclosure, and this was found to affect the flame initiation and propagation behaviour. Radiative heat transfer also played an important role in the thermo-fluid mechanical behaviour because of the high temperature involved in the problem. Numerical studies have been performed for various parameters such as the Grashof number, overheat ratio, gas absorption coefficient and vertical fuel eccentricity. The flame behaviour and initiation were observed to be totally different depending on the Grashof number. Due to absorbed radiant energy, the radiative gas played a significant role in flame evolution. The location of flame onset was also affected by both the vertical eccentricity of the inner pyrolysing fuel and the thermal conditions applied. The heating process and the flow field development were found to govern flame initiation and propagation.The present work was supported by the Combustion Engineering Research Center in the Department of Mechanical Engineering, KAIST
The effects of radiation on natural convection in a rectangular enclosure divided by two partitions
No full textThe phenomena of radiation-affected steady-laminar natural convection in a rectangular enclosure with two incomplete partitions are numerically examined under a large temperature difference. Tare convection, convection with surface radiation, and convection with surface/gas radiation are considered and compared. To examine the effects of two incomplete partitions on thermofluid dynamics behavior, they are assumed to be very thin and adiabatic. The finite-volume method (FVM) is used for solving the radiative transport equation, assuming that partitions are radiatively opaque. After validating the numerical procedures, the detailed radiation effects were sought. Based on the results of this study, it,vas found that the radiation played a significant role in developing the fluid dynamic and thermal distributions compared with eases without radiation. Once radiation was involved, the surface radiation was dominant over the gas radiation. The baffle configuration was also found to affect the results of radiation
Radiative ignition of volatile gases on a vertical fuel plate
No full textThe ignition phenomena of a solid fuel plate of polymethyl-methacrylate (PMMA), which is vertically positioned and exposed to a thermal radiation source, is numerically studied here. A two-dimensional transient model includes such various aspects as thermal decomposition of PMMA, gas phase radiation absorption, chemical reaction and air entrainment by natural convection. Whereas the previous studies consider the problem approximately in a one-dimensional geometry by neglecting the natural convection, the present model takes account of two-dimensional effect of radiation and air entrainment. The inert heating of the solid fuel is also taken into consideration. Radiative heat transfer is incorporated by the Discrete Ordinates Method (DOM) with local absorption coefficient evaluated with corresponding gas species concentrations. The thermal history of solid fuel plate shows a good agreement compared with experimental results. Despite of induced natural convective flow that takes away heat from the fuel surface, the locally absorbed radiant energy, which is eventually converted to the internal energy, is found to play an important role in the onset of gas phase ignition. The ignition is considered to occur when the rate of variation of gas phase reaction rate reaches its maximum value. Once the ignition takes place, the flame propagates downward. Then the effects of incident radiant intensity and gas phase absorption coefficient on the ignition are discussed.
A low-power array multiplier using separated multiplication technique
No full textIEEE Transactions on Circuits and Systems II : Analog and Digital Signal Processing. Sep. 2001.This brief proposes a separated multiplication technique that can be used in digital image signal processing such as finite impulse response (FIR) filters to reduce the power dissipation. Since the 2-D image data have high spatial redundancy, such that the higher bits of input pixels are hardly changed, the redundant multiplication of higher bits is avoided by separating multiplication into higher and lower parts. The calculated values of the higher bits are stored in memory cells, caches, such that they can be reused when a cache hit occurs. Therefore, the dynamic power is reduced by about 14 % in multipliers by using the proposed separated multiplication technique (SMT) and in a 1-D 4-tap FTR filter by about 10%
Geometry engine architecture with early backface culling hardware
No full textMost graphics accelerators waste valuable performance on transforming invisible vertices. To solve this problem, we have performed backface culling (BFC) earlier than transform and lighting (TnL). This paper proposes a survived vertex decision (SVD) algorithm to remove invisible vertices, and also suggests a geometry engine architecture that performs the early BFC with the SVD algorithm. This approach requires less hardware overhead. The SVD algorithm discards a vertex only if all triangles sharing that vertex are invisible in the mesh representing triangle lists or strips. The dedicated hardware performing the early BFC guarantees better performance in our approach, since it runs with the vertex engines in parallel. Particularly for a standalone engine, we introduce a unified architecture named the VP-Engine, which can perform the same tasks of the vertex engine and also handle the early BFC. Our architecture is designed using an instruction set simulator with a C + + library for cycle-accurate simulations. The early BFC removes half of the vertices that are transformed in the conventional approach, and as such the performance of our proposed architecture is twice as fast at maximum. Even with the sequential operations of early BFC and typical TnL, the VP-Engine is faster while the length of a vertex program is larger than 24. (c) 2005 Elsevier Ltd. All rights reserved
A method to generate soft shadows using a layered depth image and warping
No full textWe present an image-based method for propagating area light illumination through a Layered Depth Image (LDI) to generate soft shadows from opaque and nonrefractive transparent objects. In our approach, using the depth peeling technique, we render an LDI from a reference light sample on a planar light source. Light illumination of all pixels in an LDI is then determined for all the other sample points via warping, an image-based rendering technique, which approximates ray tracing in our method. We use an image-warping equation and McMillan's warp ordering algorithm to find the intersections between rays and polygons and to find the order of intersections. Experiments for opaque and nonrefractive transparent objects are presented. Results indicate our approach generates soft shadows fast and effectively. Advantages and disadvantages of the proposed method are also discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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