der-chang Lo - Academia.edu (original) (raw)
Papers by der-chang Lo
Water, Nov 22, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
2016 IEEE 18th International Conference on High Performance Computing and Communications; IEEE 14th International Conference on Smart City; IEEE 2nd International Conference on Data Science and Systems (HPCC/SmartCity/DSS), 2016
With the fast advance of GPS technology and mobile devices, the location-based queries that can p... more With the fast advance of GPS technology and mobile devices, the location-based queries that can provide useful location information for the user have attracted much attention in the database research community. In this paper, we focus on developing a location-based query system, called the QTWN, which provides various queries to retrieve points of interest (POI) on Taiwan maps. The provided queries are classified into the distance-based queries, the attribute-based queries, and the mixed distance/attribute queries. We dedicate to improve the usability of QTWN, design the user-friendly interface, and provide a consistent user experience for all cross-devices.
Water, 2015
This paper presents artificial neural network (ANN)-based models for forecasting precipitation, i... more This paper presents artificial neural network (ANN)-based models for forecasting precipitation, in which the training parameters are adjusted using a parameter automatic calibration (PAC) approach. A classical ANN-based model, the multilayer perceptron (MLP) neural network, was used to verify the utility of the proposed ANN-PAC approach. The MLP-based ANN used the learning rate, momentum, and number of neurons in the hidden layer as its major parameters. The Dawu gauge station in Taitung, Taiwan, was the study site, and observed typhoon characteristics and ground weather data were the study data. The traditional multiple linear regression model was selected as the benchmark for comparing the accuracy of the ANN-PAC model. In addition, two MLP ANN models based on a trial-and-error calibration method, ANN-TRI1 and ANN-TRI2, were realized by manually tuning the parameters. We found the results yielded by the ANN-PAC model were more reliable than those yielded by the ANN-TRI1, ANN-TRI2, and traditional regression models. In addition, the computing efficiency of the ANN-PAC model decreased with an increase in the number of increments within the parameter ranges because of the considerably increased computational time, whereas the prediction errors decreased because of the model's increased capability of identifying optimal solutions.
Journal of Mechanics, 2001
ABSTRACTIn this study, the motion of incompressible viscous fluid in a two-dimensional domain is ... more ABSTRACTIn this study, the motion of incompressible viscous fluid in a two-dimensional domain is solved by the finite element method using the velocity-vorticity formulation. To demonstrate the model feasibility, first of all the steady Stokes flow in a square cavity are computed. The results of square cavity flow are comparable with the numerical solutions of Burggraff (1966, FDM) [1]. Then the unsteady Navier-Stokes flow are computed and compared with other models [1∼4]. The results reveal that finite element analysis is a very powerful approach in the realm of computational fluid mechanics.
Water, 2020
In this study, the level set (LS) and immersed boundary (IB) methods were integrated into a Navie... more In this study, the level set (LS) and immersed boundary (IB) methods were integrated into a Navier–Stokes equation two-phase flow solver, to investigate wave-structure interactions and induced motions of floating bodies in two dimensions. The movement of an interfacial boundary of two fluids, even with severe free-surface deformation, is tracked by using the level set method, while an immersed object inside a fluid domain is treated by the IB method. Both approaches can be implemented by solving the Navier–Stokes equations for viscous laminar flows with embedded objects in fluids. For accurate treatment of the solid–liquid phase, appropriate source terms as forcing functions to take into account the hydrodynamic effects on the body boundaries are added into the governing equations. The integrated compact interfacial tracking techniques between the interfaces of gas–liquid phase and the solid–liquid phase allow the use of a combined Eulerian Cartesian and Lagrangian grid system. Prob...
As an attempt to improve the performances of multi-entry gullies with applications to drainage sy... more As an attempt to improve the performances of multi-entry gullies with applications to drainage system of a building, the hydrodynamic characteristics of air-water flows through the gullies with and without swirl generation vanes (SGV) are experimentally and numerically examined. With the aid of present Charge Coupled Device (CCD) image and optical systems for experimental study, the mechanism of air entrainment by vortex, the temporal variations of airflow pressure, the trajectories of drifting air bubbles and the self-depuration process for the gullies with and without SGV are disclosed. The numerical simulations adopt Flow-3D commercial code to attack the unsteady two-phase bubbly flows for resolving the transient fields of fluid velocity, vorticity and pressure in the gullies with and without SGV. In the twin-entry gully without SGV, air bubbles entrained by the entry vortex interact chaotically in the agitating bubbly flow region. With SGV to trip near-wall flows that stratify the drifting trajectories of the air bubbles, the air-bubble interactions are stabilized with the discharge rate increasing more than 7%. The reduction of the self-depuration period by increasing discharge rate is observed for the test gullies without and with SGV. Based on the experimental and numerical results, the characteristic hydrodynamic properties of the air-water flows through the test gullies with and without SGV are disclosed to assist the design applications of a modern drainage system in a building.
Water, 2015
As an attempt to improve the performances of multi-entry gullies with applications to drainage sy... more As an attempt to improve the performances of multi-entry gullies with applications to drainage system of a building, the hydrodynamic characteristics of air-water flows through the gullies with and without swirl generation vanes (SGV) are experimentally and numerically examined. With the aid of present Charge Coupled Device (CCD) image and optical systems for experimental study, the mechanism of air entrainment by vortex, the temporal variations of airflow pressure, the trajectories of drifting air bubbles and the self-depuration process for the gullies with and without SGV are disclosed. The numerical simulations adopt Flow-3D commercial code to attack the unsteady two-phase bubbly flows for resolving the transient fields of fluid velocity, vorticity and pressure in the gullies with and without SGV. In the twin-entry gully without SGV, air bubbles entrained by the entry vortex interact chaotically in the agitating bubbly flow region. With SGV to trip near-wall flows that stratify the drifting trajectories of the air bubbles, the air-bubble interactions are stabilized with the discharge rate increasing more than 7%. The reduction of the self-depuration period by increasing discharge rate is observed for the test gullies without and with SGV. Based on the experimental and numerical results, the characteristic hydrodynamic properties of the air-water flows through the test gullies with and without SGV are disclosed to assist the design applications of a modern drainage system in a building.
本論文之主旨在於應用微分積分法和有限元素法，來求解二維和三維速度-渦度列式與原始變數法的奈維爾-史托克斯方程式。 首先，將奈維爾-史托克斯方程式表示成速度-渦度法的形式，接著利用微分積分法來求解... more 本論文之主旨在於應用微分積分法和有限元素法，來求解二維和三維速度-渦度列式與原始變數法的奈維爾-史托克斯方程式。 首先，將奈維爾-史托克斯方程式表示成速度-渦度法的形式，接著利用微分積分法來求解二維和三維自然對流的穴室流場。本模式的最大優點是將流場中的速度場、渦度場及溫度場的未知變數，使用一種偶合的方法來求解單一的矩陣系統，因此能精準的求解出流場中的未知變數。相較其他數值方法本文所採用少釭漁磏I數而能得到很好的精度，此外在邊界上的渦度值可利用微分積分法精準的計算出。 再者，本文亦採用有限元素法配合投影法的數值方法來求解三維原始變數法的奈維爾-史托克斯方程式。此法最主要的概念是使用一種分離的離散式、數值平衡擴散式、時間前進法及共軛梯度法來求解。三維穴室流和後向階梯流用來驗證模式的可行性與準確性，接著應用本模式來模擬二邊拖曳的混合對流的穴室流場。 最後，本研究提出一種創新的速度-渦度模式來模擬二維和三維自由液面之流場。使用速度-渦度法之模式，不管是計算內之區域或是在自由液面上皆能完全的消除壓力項，經由一些數值實驗的驗證例子顯示此模式具有很好的精確性，此外藉由計算觀點來述說本模式相較於原始變數法的優勢。The main topics of this dissertation are to apply the differential quadrature (DQ) method and finite element method (FEM) for modeling two- and three-dimensional Navier-Stokes equations in velocity-vorticity form and primitive variables. First of all, a novel velocity-vorticity formulation is used for 2D and 3D Navier-Stokes equations and its applications in natural convection cavity flow by using DQ method. The main advantages are that the velocity and vorticity as well as temperature ...
Water, 2020
The air-water two-phase flow model is developed to study the transformation of monochromatic wave... more The air-water two-phase flow model is developed to study the transformation of monochromatic waves passing over the submerged structure. The level set method is employed to describe the motion of the interface while the effect of the immersed object on the fluid is resolved using the ghost-cell immersed boundary method. The computational domain integrated with the air-water and fluid-solid phases allows the use of uniform Cartesian grids. The model simulates the wave generation, wave decomposition over a submerged trapezoidal breakwater, and the formation of the vortices as well as the drag and lift forces caused by the surface waves over three different configurations of the submerged structures. The numerical results show the capability of the present model to accurately track the deformation of the free surface. In addition, the variation of the drag and lift forces depend on the wavelength and wave induced vortices around the submerged object. Hence, the study observes that the ...
Water, Nov 22, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
2016 IEEE 18th International Conference on High Performance Computing and Communications; IEEE 14th International Conference on Smart City; IEEE 2nd International Conference on Data Science and Systems (HPCC/SmartCity/DSS), 2016
With the fast advance of GPS technology and mobile devices, the location-based queries that can p... more With the fast advance of GPS technology and mobile devices, the location-based queries that can provide useful location information for the user have attracted much attention in the database research community. In this paper, we focus on developing a location-based query system, called the QTWN, which provides various queries to retrieve points of interest (POI) on Taiwan maps. The provided queries are classified into the distance-based queries, the attribute-based queries, and the mixed distance/attribute queries. We dedicate to improve the usability of QTWN, design the user-friendly interface, and provide a consistent user experience for all cross-devices.
Water, 2015
This paper presents artificial neural network (ANN)-based models for forecasting precipitation, i... more This paper presents artificial neural network (ANN)-based models for forecasting precipitation, in which the training parameters are adjusted using a parameter automatic calibration (PAC) approach. A classical ANN-based model, the multilayer perceptron (MLP) neural network, was used to verify the utility of the proposed ANN-PAC approach. The MLP-based ANN used the learning rate, momentum, and number of neurons in the hidden layer as its major parameters. The Dawu gauge station in Taitung, Taiwan, was the study site, and observed typhoon characteristics and ground weather data were the study data. The traditional multiple linear regression model was selected as the benchmark for comparing the accuracy of the ANN-PAC model. In addition, two MLP ANN models based on a trial-and-error calibration method, ANN-TRI1 and ANN-TRI2, were realized by manually tuning the parameters. We found the results yielded by the ANN-PAC model were more reliable than those yielded by the ANN-TRI1, ANN-TRI2, and traditional regression models. In addition, the computing efficiency of the ANN-PAC model decreased with an increase in the number of increments within the parameter ranges because of the considerably increased computational time, whereas the prediction errors decreased because of the model's increased capability of identifying optimal solutions.
Journal of Mechanics, 2001
ABSTRACTIn this study, the motion of incompressible viscous fluid in a two-dimensional domain is ... more ABSTRACTIn this study, the motion of incompressible viscous fluid in a two-dimensional domain is solved by the finite element method using the velocity-vorticity formulation. To demonstrate the model feasibility, first of all the steady Stokes flow in a square cavity are computed. The results of square cavity flow are comparable with the numerical solutions of Burggraff (1966, FDM) [1]. Then the unsteady Navier-Stokes flow are computed and compared with other models [1∼4]. The results reveal that finite element analysis is a very powerful approach in the realm of computational fluid mechanics.
Water, 2020
In this study, the level set (LS) and immersed boundary (IB) methods were integrated into a Navie... more In this study, the level set (LS) and immersed boundary (IB) methods were integrated into a Navier–Stokes equation two-phase flow solver, to investigate wave-structure interactions and induced motions of floating bodies in two dimensions. The movement of an interfacial boundary of two fluids, even with severe free-surface deformation, is tracked by using the level set method, while an immersed object inside a fluid domain is treated by the IB method. Both approaches can be implemented by solving the Navier–Stokes equations for viscous laminar flows with embedded objects in fluids. For accurate treatment of the solid–liquid phase, appropriate source terms as forcing functions to take into account the hydrodynamic effects on the body boundaries are added into the governing equations. The integrated compact interfacial tracking techniques between the interfaces of gas–liquid phase and the solid–liquid phase allow the use of a combined Eulerian Cartesian and Lagrangian grid system. Prob...
As an attempt to improve the performances of multi-entry gullies with applications to drainage sy... more As an attempt to improve the performances of multi-entry gullies with applications to drainage system of a building, the hydrodynamic characteristics of air-water flows through the gullies with and without swirl generation vanes (SGV) are experimentally and numerically examined. With the aid of present Charge Coupled Device (CCD) image and optical systems for experimental study, the mechanism of air entrainment by vortex, the temporal variations of airflow pressure, the trajectories of drifting air bubbles and the self-depuration process for the gullies with and without SGV are disclosed. The numerical simulations adopt Flow-3D commercial code to attack the unsteady two-phase bubbly flows for resolving the transient fields of fluid velocity, vorticity and pressure in the gullies with and without SGV. In the twin-entry gully without SGV, air bubbles entrained by the entry vortex interact chaotically in the agitating bubbly flow region. With SGV to trip near-wall flows that stratify the drifting trajectories of the air bubbles, the air-bubble interactions are stabilized with the discharge rate increasing more than 7%. The reduction of the self-depuration period by increasing discharge rate is observed for the test gullies without and with SGV. Based on the experimental and numerical results, the characteristic hydrodynamic properties of the air-water flows through the test gullies with and without SGV are disclosed to assist the design applications of a modern drainage system in a building.
Water, 2015
As an attempt to improve the performances of multi-entry gullies with applications to drainage sy... more As an attempt to improve the performances of multi-entry gullies with applications to drainage system of a building, the hydrodynamic characteristics of air-water flows through the gullies with and without swirl generation vanes (SGV) are experimentally and numerically examined. With the aid of present Charge Coupled Device (CCD) image and optical systems for experimental study, the mechanism of air entrainment by vortex, the temporal variations of airflow pressure, the trajectories of drifting air bubbles and the self-depuration process for the gullies with and without SGV are disclosed. The numerical simulations adopt Flow-3D commercial code to attack the unsteady two-phase bubbly flows for resolving the transient fields of fluid velocity, vorticity and pressure in the gullies with and without SGV. In the twin-entry gully without SGV, air bubbles entrained by the entry vortex interact chaotically in the agitating bubbly flow region. With SGV to trip near-wall flows that stratify the drifting trajectories of the air bubbles, the air-bubble interactions are stabilized with the discharge rate increasing more than 7%. The reduction of the self-depuration period by increasing discharge rate is observed for the test gullies without and with SGV. Based on the experimental and numerical results, the characteristic hydrodynamic properties of the air-water flows through the test gullies with and without SGV are disclosed to assist the design applications of a modern drainage system in a building.
本論文之主旨在於應用微分積分法和有限元素法，來求解二維和三維速度-渦度列式與原始變數法的奈維爾-史托克斯方程式。 首先，將奈維爾-史托克斯方程式表示成速度-渦度法的形式，接著利用微分積分法來求解... more 本論文之主旨在於應用微分積分法和有限元素法，來求解二維和三維速度-渦度列式與原始變數法的奈維爾-史托克斯方程式。 首先，將奈維爾-史托克斯方程式表示成速度-渦度法的形式，接著利用微分積分法來求解二維和三維自然對流的穴室流場。本模式的最大優點是將流場中的速度場、渦度場及溫度場的未知變數，使用一種偶合的方法來求解單一的矩陣系統，因此能精準的求解出流場中的未知變數。相較其他數值方法本文所採用少釭漁磏I數而能得到很好的精度，此外在邊界上的渦度值可利用微分積分法精準的計算出。 再者，本文亦採用有限元素法配合投影法的數值方法來求解三維原始變數法的奈維爾-史托克斯方程式。此法最主要的概念是使用一種分離的離散式、數值平衡擴散式、時間前進法及共軛梯度法來求解。三維穴室流和後向階梯流用來驗證模式的可行性與準確性，接著應用本模式來模擬二邊拖曳的混合對流的穴室流場。 最後，本研究提出一種創新的速度-渦度模式來模擬二維和三維自由液面之流場。使用速度-渦度法之模式，不管是計算內之區域或是在自由液面上皆能完全的消除壓力項，經由一些數值實驗的驗證例子顯示此模式具有很好的精確性，此外藉由計算觀點來述說本模式相較於原始變數法的優勢。The main topics of this dissertation are to apply the differential quadrature (DQ) method and finite element method (FEM) for modeling two- and three-dimensional Navier-Stokes equations in velocity-vorticity form and primitive variables. First of all, a novel velocity-vorticity formulation is used for 2D and 3D Navier-Stokes equations and its applications in natural convection cavity flow by using DQ method. The main advantages are that the velocity and vorticity as well as temperature ...
Water, 2020
The air-water two-phase flow model is developed to study the transformation of monochromatic wave... more The air-water two-phase flow model is developed to study the transformation of monochromatic waves passing over the submerged structure. The level set method is employed to describe the motion of the interface while the effect of the immersed object on the fluid is resolved using the ghost-cell immersed boundary method. The computational domain integrated with the air-water and fluid-solid phases allows the use of uniform Cartesian grids. The model simulates the wave generation, wave decomposition over a submerged trapezoidal breakwater, and the formation of the vortices as well as the drag and lift forces caused by the surface waves over three different configurations of the submerged structures. The numerical results show the capability of the present model to accurately track the deformation of the free surface. In addition, the variation of the drag and lift forces depend on the wavelength and wave induced vortices around the submerged object. Hence, the study observes that the ...