Browsing by Author "Chen, Yen-Ju"

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A drawdown solution for constant-flux pumping in a confined anticline aquifer
(2011-08-05)
Chen, Yen-Ju
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Yeh, Hund-Der
;
Kuo, Chia-Chen
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環境工程研究所
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Institute of Environmental Engineering
An An anticline, known as a convex-upward fold in layers of rock, commonly is formed during lateral compression, which may be elected as a potential site for carbon sequestration. A mathematical model is developed in this study for describing the steady-state drawdown distribution in an anticline aquifer in response to the constant-flux pumping. The topographical shape of the anticline is mimicked by three successive blocks. The solution is obtained by applying the infinite Fourier transform and the finite Fourier cosine transform in each blocks and acquiring the hydraulic continuities between the blocks. Simulated results reveal that the introduction of a thin-limbs or narrow-ridged anticline would produce a much greater head drop in the ridge zone. For a well of constant pumping rate, the dimensionless drawdown around the well increases with decreasing well screen length or/and aquifer anisotropy ratio. An examination of the effect of well location on the drawdown reveals that the partially penetrating well located at the top-middle of the ridge zone produces the largest drawdown. The simulation of the flow in an anticline aquifer based on MODFLOW results in slightly smaller drawdown values in most regions when compared with those predicted by the present solution. The present solution can also be used to simulate the flow in a slab-shaped aquifer or a hillslope aquifer. It can be applied to determine the aquifer parameters if coupled with an optimization scheme and to provide the basis for selecting a potential site for carbon sequestration in the future as well. (C) 2011 Elsevier B.V. All rights reserved.
A mathematical solution and analysis of contaminant transport in a radial two-zone confined aquifer
(2012-09-01)
Chen, Yen-Ju
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Yeh, Hund-Der
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Chang, Kai-Ju
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環境工程研究所
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Institute of Environmental Engineering
An aquifer with a wellbore surrounded by a finite-thickness skin, such as a gravel pack, can be regarded as a radial two-zone system. In this study, a mathematical model is developed to describe contaminant transport in a radial two-zone confined aquifer system. The solution of the model equations can be used to delineate contaminant transport in such a two-zone aquifer system and to investigate the skin effect on the temporal and spatial concentration distribution. The present solution is shown to reduce to an existing solution for transport in a homogeneous aquifer in the case when there is no wellbore skin. The results predicted from the solution indicate that the skin effect has a significant impact on the concentration distribution at early time. But an abrupt change in the spatial concentration distribution may occur at the interface of the skin zone and aquifer formation zone. The results from a sensitivity analysis reveal that dispersivity in the formation zone has a more significant effect on the concentration distribution than do the effects of skin thickness and dispersivity in the skin zone. (c) 2012 Elsevier B.V. All rights reserved.
Analytical Solutions for Constant-Flux and Constant-Head Tests at a Finite-Diameter Well in a Wedge-Shaped Aquifer
(2009-04-01)
Chen, Yen-Ju
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Yeh, Hund-Der
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Yang, Shaw-Yang
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環境工程研究所
;
Institute of Environmental Engineering
Neglecting the effect of well radius may lead to a significant error in the predicted drawdown distribution near the pumping well area. New analytical solutions describing aquifer responses to a constant pumping or a constant head maintained at a finite-diameter well in a wedge-shaped aquifer are derived based on the image-well method and applicable to an arbitrarily located well in the system. The solutions are useful for quantifying groundwater exploitation from a wedge-shaped aquifer and for determining the hydrogeological parameters of a wedge-shaped aquifer in inverse problems.
Approximate discharge for constant head test with recharging boundary Discussion
(2007-11-01)
Yeh, Hund-Der
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Yang, Shaw-Yang
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Chen, Yen-Ju
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環境工程研究所
;
Institute of Environmental Engineering
Aquifer Parameter Estimation for a Constant-Flux Test Performed in a Radial Two-Zone Aquifer
(2009-09-01)
Yeh, Hund-Der
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Chang, Chun-Hao
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Chen, Yen-Ju
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環境工程研究所
;
Institute of Environmental Engineering
A patchy aquifer or an aquifer with a finite thickness skin can be considered as a radial two-zone aquifer system, which can be characterized by five parameters, i.e., the thickness of the first zone and four aquifer parameters including the transmissivity and storage coefficient for each of the first and second zones. This paper proposes an approach based on an analytical solution of a constant-flux pumping in a confined two-zone aquifer and the simulated annealing algorithm to determine the five parameters simultaneously. The estimated results for the five parameters are fairly good even assuming the aquifer as a single-zone system at the beginning of the data analysis. The estimated results indicate that the first-zone parameters are much more difficult to accurately identify than the second-zone parameters due to insufficient early-time data and high correlation of the sensitivities among the first-zone parameters. However, the problem of inaccurate results obtained at the first-zone can be significantly improved if more densely temporal drawdown measurements are used.
Comment on "Utilization of Weibull Techniques for Short-Term Data Analysis in Environmental Engineering,'' by Isaiah A. Oke, 2008, 25, 1099-1106
(2009-08-01)
Yeh, Hund-Der
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Chen, Yen-Ju
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環境工程研究所
;
Institute of Environmental Engineering
The use of linear regression to obtain the parameter estimates for a nonlinear model could lead to imprecise results. This comment is to point out the problem of linearization in the parameter estimation for a nonlinear model. In Oke (2008), the reliability of ultimate BOD (L(0)) and BOD removal rate (k) were first calculated using the Weibull plotting position formula and then the L(0)-reliability and k-reliability data were fit to a nonlinear system-reliability model. Model parameters were estimated based on a linearized model and the linear regression. In this comment, we examine and compare the results of parameter estimation from the linear and nonlinear regressions. According to the residual plots, the nonlinear regression gives better estimates of the parameters than the linear one.
DESIGN OF MARINE VEHICLE POWERED BY MAGNETOHYDRODYNAMIC THRUSTER
(2020-01-01)
Chan, Cherng-Shyong
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Cheng, Jia-Hong
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Zeng, Cing-Hui
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Huang, Jen-Rung
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Chen, Yu-Hsuan
The present study outlines the design of a magnetohydrodynamic (MHD) thruster system which is capable to power a 3-meter ship model cruising at a speed of V = 0.5 m/s using the Lorentz force generated by the electric field and magnetic field in conducting seawater. Based on the computational fluid dynamics (CFD) simulation of a modified Delft 372 catamaran model, the thrust needed to achieve the targeted cruising speed is first estimated. To achieve the estimated magnitude of the thrust, dimensions of thruster modules are designed based on numerical simulations of magnetic field, for better distributions of the strength and uniformity of the magnetic field. Additional CFD simulations of the flows through the thruster module, coupled with magnetic and electric fields, are conducted to realize the hydrodynamics. Consequently, several configurations of thruster modules are manufactured and experimented. A particular configuration of a shielded two-unit module is chosen to power the ship model. Finally, a complete system of MHD-1 marine vehicle, including a ship model, multiple MHD thruster modules and power suppliers, is assembled and tested. The system is shown capable to cruise closely to the targeted speed.
Determination of skin and aquifer parameters for a slug test with wellbore-skin effect
(2007-09-01)
Yeh, Hund-Der
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Chen, Yen-Ju
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環境工程研究所
;
Institute of Environmental Engineering
Slug test is considered to reflect the hydraulic parameters in the vicinity of the test well. The aquifer parameters are usually identified by fitting an appropriate mathematical solution or graphical type curves with slug test data. In this paper, we developed an approach by combining [Moench, A.F., Hsieh, P.A., 1985. Analysis of slug test data in a well with finite-thickness skin. In: Memoirs of the 17th International Congress on the Hydrogeology of Rocks of Low Permeability, U.S.A. Members of the International Association of Hydrologists, Tucson, AZ, vol. 17, pp. 17-29] and simulated annealing (SA) approach to estimate five parameters, i.e., three skin parameters and two aquifer parameters. The three skin parameters are hydraulic conductivity, specific storage, and thickness of the wellbore-skin zone, white the two aquifer parameters are hydraulic conductivity and specific storage of the formation zone. It is worthy to note although the thickness of the wellbore-skin zone is usually taken as an input data for the data-analyzed software, it is actually an unknown parameter that cannot be measured directly. This paper proposes a methodology for estimating the thickness of the wellbore-skin zone with other hydraulic parameters at the same time. Eight sets of well water-level. (WWL) data of aquifers with both positive and negative skins are generated by Moench and Hsieh [Moench and Hsieh, 1985] and four sets of standard normally distributed noise are then added to each set of WWL data. The results indicate that the negative-skin cases generally give a better estimated result than that of the positive-skin cases. Sensitivity analysis is also employed to demonstrate the physical behavior when slug test was performed under positive-skin effect. For the case of an aquifer with a positive-skin, the use of a longer series of WWL data for analysis is strongly recommended for better estimation of aquifer hydraulic conductivity. Analyzing the WWL data of the test and observation wells simultaneously could significantly improve the estimations on specific storages. Impetuously presuming an arbitrary value for the thickness of the wellbore-skin zone may lead to poor estimation for the other four parameters. (C) 2007 Elsevier B.V. All rights reserved.
Endosomal escape and transfection efficiency of PEGylated cationic liposome-DNA complexes prepared with an acid-labile PEG-lipid
(2012-06-01)
Chan, Chia-Ling
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Majzoub, Ramsey N.
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Shirazi, Rahau S.
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Ewert, Kai K.
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Chen, Yen-Ju
Cationic liposome-DNA (CL-DNA) complexes are being pursued as nonviral gene delivery systems for use in applications that include clinic trials. However, to compete with viral vectors for systemic delivery in vivo, their efficiencies and pharmacokinetics need to be improved. The addition of poly (ethylene glycol)-lipids (PEGylation) prolongs circulation lifetimes of liposomes, but inhibits cellular uptake and endosomal escape of CL-DNA complexes. We show that this limits their transfection efficiency (TE) in a manner dependent on the amount of PEG-lipid, the lipid/DNA charge ratio, and the lipid membrane charge density. To improve endosomal escape of PEGylated CL-DNA complexes, we prepared an acid-labile PEG-lipid (HPEG2K-lipid, PEG MW 2000) which is designed to lose its PEG chains at the pH of late endosomes. The HPEG2K-lipid and a similar but acid-stable PEG-lipid were used to prepare PEGylated CL-DNA complexes. TLC and dynamic light scattering showed that HPEG2K-CL-DNA complexes are stable at pH 7.4 for more than 24 h, but the PEG chains are cleaved at pH 5 within 1 h, leading to complex aggregation. The acid-labile HPEG2K-CL-DNA complexes showed enhanced TE over complexes stabilized with the acid-stable PEG-lipid. Live-cell imaging showed that both types of complexes were internalized to quantitatively similar particle distributions within the first 2 h of incubation with cells. Thus, we attribute the increased TE of the HPEG2K-CL-DNA complexes to efficient endosomal escape, enabled by the acid-labile HPEG2K-lipid which sheds its PEG chains in the low pH environment of late endosomes, effectively switching on the electrostatic interactions that promote fusion of the membranes of complex and endosome. (c) 2012 Elsevier Ltd. All rights reserved.
Parameter Estimation/Sensitivity Analysis for an Aquifer Test with Skin Effect
(2009-03-01)
Chen, Yen-Ju
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Yeh, Hund-Der
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環境工程研究所
;
Institute of Environmental Engineering
Aquifer information carried by aquifer test data may be affected by the presence of a finite thickness skin around the wellbore. The mathematical treatment for an aquifer accounting for the skin zone can be characterized by five parameters, that is, the outer radius of the skin zone and the transmissivity and storativity for each of the skin and aquifer zones. Sensitivity analysis was performed to examine the ground water flow behavior in the skin and aquifer zones in terms of the constant-head test (CHT) data. The simulated annealing procedure was applied to simultaneously determine the skin and aquifer parameters from the analysis of CHT data. Toward the previously mentioned goals, four suites of CHT data were analyzed in this article. The analyses of wellbore flow rate at the test well and the specific drawdown at the observation well gave accurate estimates for the skin and aquifer parameters, respectively. Only the skin thickness and both the skin and the aquifer diffusivities could be accurately estimated from the analysis of drawdown data in the observation well. The estimates for all skin and aquifer parameters from the composite analysis of flow rate and drawdown data were the most accurate. The results of sensitivity analyses and parameter estimations provide instructive references in the analysis of the skin-affected CHT data.
Semi-analytical solution for a slug test in partially penetrating wells including the effect of finite-thickness skin
(2008-08-30)
Yeh, Hund-Der
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Chen, Yen-Ju
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Yang, Shaw-Yang
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環境工程研究所
;
Institute of Environmental Engineering
This paper presents a new semi-analytical solution for a slug test in a well partially penetrating a confined aquifer, accounting for the skin effect. This solution is developed based on the solution for a constant-flux pumping test and a formula given by Peres and co-workers in 1989. The Solution agrees with that of Cooper and co-workers and the KGS model when the well is fully penetrating. The present Solution can be applied to simulate the temporal and spatial head distributions in both the skin and formation zones. It can also be used to demonstrate the influences of skin type or skin thickness on the well water level and to estimate the hydraulic parameters of the skin and formation zones using a least-squares approach. The results of this study indicate that the determination of hydraulic conductivity using a conventional slug-test data analysis that neglects the presence of a skin zone will give an incorrect result if the aquifer has a skin zone. Copyright (C) 2008 John Wiley &, Sons. Ltd.