Browsing by Author "Wang, Wei-Hsiang"

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An investigation of compressible forced convection in a three dimensional tapered chimney by CUDA computation platform
(2011-07-01)
Fu, Wu-Shung
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Wang, Wei-Hsiang
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Huang, Yun
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Li, Chung-Gang
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機械工程學系
Compressible forced convection in a three dimensional tapered chimney is investigated numerically. Schemes of Roe and preconditioning are adopted to resolve compressible flow problem under a low speed velocity situation. Coordinates transformation of algebraic grid generation and non-reflecting boundary condition is used to execute the coordinated transformation of the tapered duct and decrease the computation domain, respectively. Computing procedures are performed on the CUDA computation platform which is developed recently and is a very effective tool. Due to the variation of the geometry of three dimensional tapered chimney, the flow velocity increases in the central region and decreases near the corner region. Therefore, heat transfer rates are enhanced remarkably in the central region and become inferior abruptly near the corner region. The efficiency of CUDA computation platform is marvelous, and the possibility of capability of super computation of individualization may be realized by using the CUDA computation platform. (C) 2011 Elsevier Ltd. All rights reserved.
An investigation of effects of heights and a length on natural convection of three dimensional parallel plates with a heated bottom surface by a CUDA computation platform
(2013-12-01)
Fu, Wu-Shung
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Huang, Shang-Hao
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Wang, Wei-Hsiang
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機械工程學系
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Department of Mechanical Engineering
Effects of heights and a length on natural convection of three dimensional parallel plates with a heated bottom surface are investigated numerically. The compressibility of fluid induced by a high temperature difference is taken into consideration for simulating more realistic situations, and then the Boussinesq assumption is not necessary to be adopted. Methods of the Roe scheme, preconditioning and dual time stepping matching the method of LUSGS are simultaneously used to solve the compressible flow problem. Non-reflecting boundary conditions are held on apertures to prevent reflections from apertures induced by pressure waves. A CUDA computational platform is used to economize massive computing time. Under a low height case, the flow field is restricted by the shear force caused by the low height and displays a stable situation. Oppositely, under a high height case the flow field indicates active behaviors and an irregular situation is observed. (C) 2013 Elsevier Ltd. All rights reserved.
An investigation of natural convection in a three dimensional square wavy channel
(2015-08-01)
Fu, Wu-Shung
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Huang, Kun-Rong
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Lo, Chi-Xiu
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Wang, Wei-Hsiang
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機械工程學系
Natural convection in a three dimensional wavy channel, which is composed of numerous two dimensional cross sections, is investigated numerically. The method of elliptic partial differential equations grid generation is adopted to construct a distribution of grids on each cross section. The distributions of the whole cross sections are piled up in sequence from the inlet to outlet to form a three dimensional channel. In order to solve a low speed compressible flow problem, the compressibility and viscosity of the working fluid are taken into consideration, and the non-reflecting boundaries at the inlet and outlet of the channel are held. The Bossinesq assumption is then no longer necessary. As well, the methods of the Roe scheme, preconditioning and dual time stepping matching the implicit LUSGS algorithm (Implicit Lower Upper symmetric Gauss-Seidel algorithm) are simultaneously used to solve governing equations. Effects of the Rayleigh number and the ratio of the amplitude to wave length on heat transfer rates of the channel are examined. Results of both this study and existing studies have good agreements. (C) 2015 Elsevier Ltd. All rights reserved.
An investigation of natural convection in a three dimensional tapered chimney without Boussinesq assumption
(2012-04-01)
Fu, Wu-Shung
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Huang, Yun
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Wang, Wei-Hsiang
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機械工程學系
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Department of Mechanical Engineering
Natural convection in a three dimensional tapered chimney is investigated numerically. In order to investigate the natural convection under a high temperature difference situation. Boussinesq assumption is not adopted instead of consideration of the compressibility of fluid. Methods of Roe scheme, preconditioning and dual time stepping are used to solve governing equations for a low speed compressible flow. Coordinates transformation of algebraic grid generation and non-reflecting boundary condition are used to facilitate computation processes. The results reveal that in the expanding duct local Nusselt numbers distributed around the corner region are larger than those distributed around the central region. An available correlation equation is proposed and is well consistent with the numerical results. (C) 2012 Elsevier Ltd. All rights reserved.
An investigation of natural convection in parallel square plates with a heated bottom surface by an absorbing boundary condition
(2013-01-01)
Fu, Wu-Shung
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Wang, Wei-Hsiang
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Li, Chung-Gang
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Huang, Shang-Hao
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機械工程學系
A study of natural convection in three dimensional square plates is investigated numerically. Several open boundaries co-exist in the physical domain, and a non-reflecting boundary condition applied at the aperture is no longer suitable for solving the problem of this study. An absorbing boundary condition is then adopted and modified in the solution processes. Methods of the Roe scheme, preconditioning and dual time stepping matching LSUGS scheme are used to solve a situation of a low speed compressible flow. The geometry of the physical model is the parallel square plates, and the parameter of Rayleigh number is not high, and then phenomena observed are almost symmetrical. The results of the work have good agreements with the experimental results of a previous paper. (c) 2012 Elsevier Ltd. All rights reserved.
An investigation of natural convection in parallel square plates with a heated top surface by a hybrid boundary condition
(2014-10-01)
Fu, Wu-Shung
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Wang, Wei-Hsiang
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Li, Chung-Gang
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機械工程學系
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Department of Mechanical Engineering
Natural convection in parallel squares plats with a heated top surface is investigated numerically. For solving a problem induced by different directions between the thermal diffusion and main flow streams, a hybrid boundary condition composed of the absorbing boundary condition and local one-dimensional inviscid relations (LODI) method is then adopted in artificial buffer zones. Methods of the Roe scheme, preconditioning and dual time stepping matching the Monotone Upstream-centered Schemes for Conservation Laws (MUSCL) are used to solve low speed compressible flows caused by natural convection. The results show that the hybrid boundary condition successfully prevents the rebound of heat energy from the artificial buffer zone back to the domain. The area-averaged Nusselt numbers of this study are slightly larger than those of existing experimental results, and the averaged deviation is about 10%. (C) 2014 Elsevier Masson SAS. All rights reserved.
An investigation of natural convection in parallel square plates with a heated top surface by a hybrid boundary condition
(2014-10-01)
Fu, Wu-Shung
;
Wang, Wei-Hsiang
;
Li, Chung-Gang
;
機械工程學系
;
Department of Mechanical Engineering
Natural convection in parallel squares plats with a heated top surface is investigated numerically. For solving a problem induced by different directions between the thermal diffusion and main flow streams, a hybrid boundary condition composed of the absorbing boundary condition and local one-dimensional inviscid relations (LODI) method is then adopted in artificial buffer zones. Methods of the Roe scheme, preconditioning and dual time stepping matching the Monotone Upstream-centered Schemes for Conservation Laws (MUSCL) are used to solve low speed compressible flows caused by natural convection. The results show that the hybrid boundary condition successfully prevents the rebound of heat energy from the artificial buffer zone back to the domain. The area-averaged Nusselt numbers of this study are slightly larger than those of existing experimental results, and the averaged deviation is about 10%. (C) 2014 Elsevier Masson SAS. All rights reserved.
An investigation of natural convection of three dimensional horizontal parallel plates from a steady to an unsteady situation by a CUDA computation platform
(2012-08-01)
Fu, Wu-Shung
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Wang, Wei-Hsiang
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Huang, Shang-Hao
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機械工程學系
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Department of Mechanical Engineering
"The heat transfer of natural convection in three dimensional horizontal parallel plates with a heated bottom surface is investigated numerically. For enlarging the application domain, the compressibility of the fluid is taken into consideration instead of the Boussinesq assumption. Numerical methods of the Roe scheme, preconditioning and dual time stepping are adopted for solving governing equations of a low speed compressible flow. A non-reflection condition is used at both apertures in order to decrease computational grids and a CUDA computational platform is developed to economize massive computing time. Variations of thermal and flow fields are examined in detail. The results show that accompanied with elongating the length of the heated bottom surface, both thermal and flow fields are changed from a steady to an unsteady situation. (C) 2012 Elsevier Ltd. All rights reserved."
An investigation of the unstable phenomena of natural convection in parallel square plates by multi-GPU implementation
(2017)
Fu, Wu-Shung
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Wang, Wei-Hsiang
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Li, Chung-Gang
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Tsubokura, Makoto
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機械工程學系
Unstable phenomena induced by natural convection of parallel square plates are investigated numerically. The geometry belongs to the open boundary problem, and the compressibility of fluids is taken into consideration. The absorbing boundary condition and modified local one-dimensional inviscid relation method are adopted for open boundaries. Numerical methods of the Roe scheme, preconditioning, and dual time stepping matching the data-parallel lower-upper relaxation method are coordinated with multi-GPU implementation. Unstable phenomena of natural convection caused by the buoyancy force can be observed. Present results have good agreement with the experimental results in the overlap range of the existing study.
Applying Compute Unified Device Architecture to Investigate Gaseous Discharge from High-Pressure Vessel
(2016-01)
Fu, Wu-Shung
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Huang, Kun-Rong
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Wang, Wei-Hsiang
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Li, Chung-Gang
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機械工程學系
The aim of this study is to investigate gases discharged from a high-pressure vessel numerically. To simulate this subject more realistically, the viscosity and compressibility of the gas are taken into consideration simultaneously. The methods of the Roe scheme, preconditioning, and dual time-stepping matching the lower-upper symmetric-Gauss-Seidel method are adopted to solve compressible flow problems during gaseous discharge processes. The nonreflecting boundary condition is used to prevent flowfields from being polluted by the reflection of the pressure wave induced by the compressible flow at the boundary. Computing procedures are performed on the compute unified device architecture computation platform, which was recently developed and is a highly effective technology for accelerating computational speed. Results show that the mass flow rate of this work is consistent with the existing experimental work. Because of a sudden expansion at a small opening, the phenomena of an alternating variation of the pressures of gases, rapid decrements of the temperature of gases, and a quick acceleration of the velocities of gases are remarkably observed in the mainstream direction. The ratio of the thrust caused by the gases released to the reaction force is less than 1 because of the dissipation of entropy generation.
Competing weak localization and weak antilocalization in amorphous indium-gallium-zinc-oxide thin-film transistors
(2017-01-09)
Wang, Wei-Hsiang
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Lyu, Syue-Ru
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Heredia, Elica
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Liu, Shu-Hao
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Jiang, Pei-Hsun
We have investigated the gate-voltage dependence and the temperature dependence of the magneto-conductivity of amorphous indium-gallium-zinc-oxide thin-film transistors. A weak-localization feature is observed at small magnetic fields on top of an overall negative magnetoconductivity at higher fields. An intriguing controllable competition between weak localization and weak antilocalization is observed by tuning the gate voltage or by varying the temperature. Our findings reflect controllable quantum interference competition in the electron systems in amorphous indium-gallium-zinc-oxide thin-film transistors. Published by AIP Publishing.
Compressible direct numerical simulation with a hybrid boundary condition of transitional phenomena in natural convection
(2015-11-01)
Li, Chung-Gang
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Tsubokura, Makoto
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Fu, Wu-Shung
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Jansson, Niclas
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Wang, Wei-Hsiang
We investigate the phenomena involved in the transition from laminar to turbulent flow in natural convection through a channel using compressible direct numerical simulation (DNS). The Roe numerical scheme with preconditioning and dual time stepping is employed to handle slow natural convection flows with large temperature differences and variable densities. A hybrid boundary condition that combines absorbing and non-reflecting boundary conditions is applied at the inlet and outlet, which does not require a priori knowledge of the flow rate. No empirically derived turbulence parameters are required in the DNS code. The numerical predictions are qualitatively consistent with published experimental data and the transition point can be accurately captured. Our results show that the transitional phenomena can be naturally induced by the interactions between the buoyancy force and shear stress without prescribing any fluctuations at the inlet. We submit that the numerical scheme and model configuration developed in this study has the potential to be a benchmark case for evaluating the accuracy of other turbulence models. (C) 2015 Elsevier Ltd. All rights reserved.
Direct numerical simulation of film cooling with a fan-shaped hole under low Reynolds number conditions
(2018-08-01)
Fu, Wu-Shung
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Chao, Wei-Siang
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Tsubokura, Makoto
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Li, Chung-Gang
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Wang, Wei-Hsiang
Shaped film cooling holes have several features that can greatly improve film cooling effectiveness, and it has been studied and utilized in gas turbine engines for decades. Few studies, however, have reported the effects of low mainstream Reynolds number on shaped film cooling holes. In this study, the effects of mainstream Reynolds number on film cooling with a fan shaped hole are studied by utilizing direct numerical simulation (DNS). In addition, the compressibility and the viscosity of the working fluid are simultaneously considered, and the non-reflecting and absorbing boundary conditions are adopted at the exit of the main channel. The methods of the Roe scheme, preconditioning, and dual time stepping are employed together to solve the governing equations of a low-speed compressible flow problem. This study considers the mainstream Reynolds numbers of Re-D = 480 and 3200 with 0% and 5% turbulence intensity in the mainstream. Results reveal that the coolant jet penetrates into the mainstream with a mainstream Reynolds number of 480. However, at the higher Reynolds number, the coolant jet develops along the wall and results in better film cooling effectiveness. In addition, special attention is paid to the structures of the vortices developed from the crossflow. Hairpin vortices become smaller at higher mainstream Reynolds numbers. On the contrary, horseshoe vortices appear when the mainstream Reynolds number is increased. A detailed comparison of the vortices is presented in this study. (C) 2018 Elsevier Ltd. All rights reserved.
Highly graphitized laterally interconnected SWCNT network synthesis via a sandwich-grown method
(2011-04-13)
Teng, I-Ju
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Chen, Kai-Ling
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Wang, Li-Chun
We present a sandwich-grown method for growing laterally interconnected single-walled carbon nanotube (SWCNT) networks with a high degree of graphitization by microwave plasma chemical vapour deposition (MPCVD). An Al(2)O(3)-supported Fe catalyst precursor layer deposited on an oxidized Si substrate with an upper Si cover is first pretreated in pure hydrogen, and then exposed to a gas mixture of methane/hydrogen for growth process at a lower growth temperature and a faster rate. The effects of various parameters, such as catalyst film thickness, gas flow rate, working pressure, growth time and plasma power, on the morphologies and structural characteristics of the SWCNT networks are investigated, and therefore provide the essential conditions for direct growth of laterally interconnected SWCNT networks. Analytical results demonstrate that the SWCNT-based lateral architecture comprises a mixture of graphene-sheet-wrapped catalyst particles and laterally interconnected nanotubes, isolated or branched or assembled into bundles. The results also show that the formation of the laterally interconnected SWCNT networks is related to the sandwich-like stack approach and the addition of an Al(2)O(3) layer in the MPCVD process. The successful growth of lateral SWCNT networks provides new experimental information for simply and efficiently preparing lateral SWCNTs on unpatterned substrates, and opens a pathway to create network-structured nanotube-based devices.
Investigation of boundary layer thickness and turbulence intensity on film cooling with a fan-shaped hole by direct numerical simulation
(2018-08-01)
Fu, Wu-Shung
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Chao, Wei-Siang
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Tsubokura, Makoto
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Li, Chung-Gang
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Wang, Wei-Hsiang
Effects of the mainstream boundary layer thickness and the turbulence intensity on film cooling under low Reynolds number conditions are studied in this work by the direct numerical simulation (DNS). In other to solve low-speed compressible flow problems, several methods of Roe scheme, preconditioning, dual time stepping, and LUSGS are adopted to solve governing equations. Results reveal that a horseshoe vortex appears with a thicker mainstream boundary layer, and thus the lateral coverage of the coolant fluid has increased significantly. In addition, the existence of turbulence intensity eliminates the blow-off phenomenon, which happens in a thin mainstream boundary layer condition and enhances the film cooling effectiveness.
Laser, buffer layer and CoCrPtO(x)-assisted low temperature fabrication process of a small-sized-CNT pattern by MPCVD
(2010-10-01)
Teng, I-Ju
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Hong, Tsai-Hau
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Wang, Wei-Hsiang
For improving compatibility with IC processes, this work presents a low temperature process (<400 degrees C) to fabricate a small-sized-carbon nanotube (CNT) (<6 graphene layers) pattern by buffer layer (AlN) and CoCrPtO(x) catalyst precursor-assisted microwave plasma chemical vapor deposition (MPCVD). Without high temperature heating on the whole specimen, the low temperature process mainly results from selective local activation laser heating (>= 600 degrees C) to form the catalyst nanostructures, which are beneficial to low temperature H-plasma treatment to form catalyst nanoparticles for CNT growth. The functions of the buffer layer and the catalyst precursor are to help the heat dissipation and the small-sized CNT formation. (C) 2010 Elsevier B.V. All rights reserved.
Laser, buffer layer and CoCrPtOx-assisted low temperature fabrication process of a small-sized-CNT pattern by MPCVD
(2010-10-01)
Teng, I-Ju
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Hong, Tsai-Hau
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Wang, Wei-Hsiang
For improving compatibility with IC processes, this work presents a low temperature process (<400 degrees C) to fabricate a small-sized-carbon nanotube (CNT) (<6 graphene layers) pattern by buffer layer (AlN) and CoCrPtOx catalyst precursor-assisted microwave plasma chemical vapor deposition (MPCVD). Without high temperature heating on the whole specimen, the low temperature process mainly results from selective local activation laser heating (>= 600 degrees C) to form the catalyst nanostructures, which are beneficial to low temperature H-plasma treatment to form catalyst nanoparticles for CNT growth. The functions of the buffer layer and the catalyst precursor are to help the heat dissipation and the small-sized CNT formation. (C) 2010 Elsevier B.V. All rights reserved.
Metal Oxide Film for Growing Vertically Aligned Single-Walled Carbon Nanotubes
(2009-08-01)
Tseng, Wen-Shou
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Wang, Wei-Hsiang
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Hong, Tasi-Hau
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Kuo, Cheng-Tzu
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材料科學與工程學系
In the present study, we use a method that uses the oxidation state of platinum in Co-Cr-Pt oxide films to cause a volume expansion to form isolated nanoparticles through exposure to H(2) microwave plasma. The generated nanoparticles are then used to grow single-walled carbon nanotubes (SWCNTs) at similar to 600 degrees C without the application of a buffer layer using a microwave plasma chemical vapor deposition system. The effects of metal oxide film thickness on the growth of SWCNTs are investigated. The characterization techniques including X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy are carried out, with the results showing that this method used is highly efficient in generating very small and dense catalytic nanoparticles. The results also show that, when the metal oxide film thickness is no more than 2nm, the nanoparticles produced with diameters ranging from 2 to 3nm can be effective for growing vertically and densely aligned SWCNTs. (C) 2009 The Japan Society of Applied Physics
Temperature-dependent electrical and photo-sensing properties of horizontally-oriented carbon nanotube networks synthesized by sandwich-growth microwave plasma chemical vapor deposition
(2013-02-01)
Teng, I-Ju
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Hsu, Hui-Lin
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Jian, Sheng-Rui
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Wang, Li-Chun
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Chen, Kai-Ling
The electrical and photo-sensing properties of horizontally-oriented interconnected carbon nanotube networks (CNT-NWs) prepared by means of a microwave plasma chemical vapor deposition sandwich-growth process are investigated. The temperature-dependent dark and illuminated current-voltage and transfer characteristics of CNT-NW-assisted devices are measured. Results show that the current-voltage characteristics of the devices exhibit nonlinear behavior, and the current can be further modulated by a gate voltage, revealing p-type semiconducting behavior with a device mobility of similar to 14.5 cm(2)/V.s and an on-off current ratio of -10(3). Moreover, when the CNT-NW-assisted devices are irradiated with 1.25-25 mu m infrared (IR) from 300 to 11 K, the photo currents increase approximately 1.1- to 2.7-fold compared to the dark currents at +/- 2 V bias voltage. Such results demonstrate that the presented CNT-NWs have high potential for IR photo-sensor applications. (C) 2012 Elsevier B.V. All rights reserved.
Using Repetitive Control for THD Reduction over Wide Load Range for Boost Digital PFC Converters
(2012)
Wang, Wei-Hsiang
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Tzou, Ying-Yu
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電控工程研究所
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Institute of Electrical and Control Engineering
This paper proposes a control scheme for the reduction of the line current total harmonic distortion (THD) over wide load variation range. A new current sensing scheme is used to detect the average current under fixed or variable switching frequency condition. A repetitive controller is designed to minimize periodic errors within the current loop bandwidth. A design procedure is given for synthesizing the current loop controller to achieve good current tracking under wide input voltage variation range. A single-phase boost PFC converter with single-chip DSP controller has been constructed for the verification of the proposed control scheme. Simulation and experimental results confirm the feasibility and performances of the proposed control scheme.