Browsing by Author "Liou, Jin-Cheng"

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Beach Erosion and Preventive Countermeasure at Kangnan Coast, Taiwan
(2009-03-01)
Liou, Jin-Cheng
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Chang, Hsien-Kuo
;
Chen, Wei-Wei
;
Liaw, Shyne-Ruey
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土木工程學系
Kangnan Coast has suffered from beach erosion since the extension of breakwaters and two groins of Hsinchu Fishing Harbor was completed. This is a typical example of human impact on coastal erosion in Taiwan. The aim of this article is to explore the erosion at Kangnan Coast using several analyses, such as shoreline revolution detected from satellite images, planform description of depth variation, volumetric change of bathymetry, and variations in the trends of volumetric changes of the sea bottom. Beach erosion at Kangnan Coast in response to structural effects was quantitatively determined. A suggested countermeasure using submerged detached breakwaters, developed through a 3-year study, is proposed to mitigate beach erosion.
Long wave reflection from submerged trapezoidal breakwaters
(2007-01-01)
Chang, Hsien-Kuo
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Liou, Jin-Cheng
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土木工程學系
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Department of Civil Engineering
This study addresses the reflection and transmission of long waves from a trapezoidal breakwater and a series of trapezoidal breakwaters, using the matching method. A systematic shape transfer is derived to determine wave reflection and transmission. The peak Bragg reflection of long waves from a series of trapezoidal breakwaters is shifted toward low frequency. In spite of the spacing between any pair of breakwaters, the top plane width and the arrangement of the series of breakwaters are found to be the two major parameters in designing multiply composite Bragg breakwaters. (C) 2006 Elsevier Ltd. All rights reserved.
Particle trajectories of nonlinear gravity waves in deep water
(2009-04-01)
Chang, Hsien-Kuo
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Chen, Yang-Yi
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Liou, Jin-Cheng
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土木工程學系
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Department of Civil Engineering
The paper presents a numerical method for calculating the particle trajectories of nonlinear gravity waves in deep water. Particle trajectories, mass-transport velocity and Lagrangian wave period can be accurately determined by the proposed method. The high success rate of the proposed method is examined by comparing the present results with those of(a) Longuet-Higgins, M.S., 1986,1987. Eulerian and Lagrangian aspects of surface waves. journal of Fluid Mechanics 173, 683-707 and (b) Lagrangian moments and mass transport in Stokes waves. Journal of Fluid Mechanics 179,547-555. It is shown that the dimensionless mass-transport velocity can exceed 10% for large waves, and the Lagrangian wave period is much larger than the Eulerian wave period for large waves. (C) 2009 Elsevier Ltd. All rights reserved.
Particle trajectory and mass transport of finite-amplitude waves in water of uniform depth
(2007-05-01)
Chang, Hsien-Kuo
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Liou, Jin-Cheng
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Su, Ming-Yang
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土木工程學系
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Department of Civil Engineering
A set of governing equations in Lagrangian form is derived for propagating gravity waves in water of uniform depth. The Lindstedt-Poincare perturbation method is used to obtain approximations up to fifth order. Recognizing the Lagrangian frequency to be a position function for all particles is a key to find these higher-order approximations. The present solution has zero pressure at the free surface and satisfies exactly the dynamic boundary condition. Under the present approximations, the Lagrangian frequency is composed of two parts. The first part is constant for all particles and equivalent to the term in the fifth-order Stokes' wave theory [J.D. Fenton, A fifth-order Stokes theory for steady waves, J. Waterway, Port, Coastal Ocean Eng. 111 (1985) 216-234]. The second part is a function of the depth. All the particles move as open (nonclosed) loops and have mean drift displacements that decrease exponentially with the water depth. Thus, a new fourth-order mass transport velocity is found. (c) 2006 Elsevier Masson SAS. All rights reserved.
Protection Priority in the Coastal Environment Using a Hybrid AHP-TOPSIS Method on the Miaoli Coast, Taiwan
(2012-03-01)
Chang, Hsien-Kuo
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Liou, Jin-Cheng
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Chen, Wei-Wei
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土木工程學系
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Department of Civil Engineering
CHANG, H.-K.; LIOU, J.-C., and CHEN, W.-W., 2012. Protection priority in the coastal environment using a hybrid AHP-TOPSIS method on the Miaoli Coast, Taiwan. Journal of Coastal Research, 28(2), 369-374. West Palm Beach (Florida), ISSN 0749-0208. Coastal erosion often happens around the island of Taiwan because of strong waves from typhoons in the summer. The problem of beach erosion cannot be completely solved at this time due to insufficient government budgets. Prioritization of coastal protection should be made yearly to match engineering requirements and annual official budgets. This paper proposes both analytic hierarchy process (AHP) and technique for order preference by similarity to ideal solution (TOPSIS) methods to prioritize the protection of the coastal environment on the Miaoli Coast of Taiwan. The weights of three main criteria (engineering safety, ecology, and coastal landscape) and their subcriteria are determined through the AHP method. Twenty-two segments of the Miaoli Coast are ranked according protection priority by the TOPSIS method. This multipart methodology can help decision makers prioritize coastal engineering and environmental efforts. This procedure also enables researchers to put more expert knowledge together, allowing more precise decisions and moderating personal judgments.
Shifting the waterlines of satellite images to the mean water shorelines considering wave runup, setup, and tidal variation
(2015-09-25)
Chang, Hsien-Kuo
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Chen, Wei-Wei
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Liou, Jin-Cheng
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土木工程學系
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Department of Civil Engineering
Shoreline evolution is a simple and common method to illustrate beach erosion or accretion in coastal engineering. Extracted waterlines on different satellite images are sometimes used for shoreline evolution. However, time-varying waterlines for tidal variation and wave runup are different from the shoreline at the mean water level. Waterline evolution may bring about misunderstanding of beach erosion or accretion. In a former study, the one-line shift method was proposed to determine the waterlines on a satellite image and to shift the water-lines to shorelines while only considering the tidal variation. The upward shift extension of the waterline due to wave runup and wave setup is considered. Some acceptable equations of wave runup were examined to correct the waterlines on three satellite images in one month when the foreshore beach slopes were specified. The suggested equation for wave runup includes both wave conditions and an average beachface slope at two points located shoreward and seaward away from mean water level by an equal distance of 62.5 m. When on-site shore bathymetrical measurement is sometimes unavailable, a method of minimizing the difference between the initially guessed and estimated foreshore beach slopes by the one-line shift method is proposed. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Simulated wave-driven ANN model for typhoon waves
(2011-01-01)
Chang, Hsien-Kuo
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Liou, Jin-Cheng
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Liu, Shen-Jung
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Liaw, Shyne-Ruey
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土木工程學系
This paper investigates an artificial neural network (ANN) model for typhoon waves used to modify poor calculations of the numerical model in special cases. Two key factors, local winds and simulated waves produced by the numerical model, were used as input parameters of the proposed ANN model. The waves were simulated by the numerical model from a wave action equation indicating the physical processes of energy transfer and wave propagation. Simulated wave input is a very important parameter for the proposed ANN model, allowing for the accurate calculation of water waves in the sea. The applicable Mike21_SW model was chosen to provide an accurate calculation. Through model verification, the proposed ANN model has a particularly accurate calculation at the peak of each typhoon and at its occurrence time. The computed waves of each typhoon were examined to be consistent with the observed waves. (C) 2010 Elsevier Ltd. All rights reserved.