Browsing by Author "Lin, Cheng-Han"

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Discrete element simulation of the dynamic response of a dip slope under shaking table tests
(2018-09-04)
Lin, Cheng-Han
;
Li, Hung-Hui
;
Weng, Meng-Chia
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土木工程學系
;
Department of Civil Engineering
A dip slope contains weak planes in the same dip direction along the slope face. In this study, a discrete element simulation was implemented to investigate the behavior of a dip slope under shaking table tests. The simulated dip slope model was first verified by testing under different horizontal excitations. Then, the influence of the slope angle and dynamic force on the deformation characteristics of the dip slopes was explored. The simulations provide detailed descriptions of the deformation processes and potential sliding mechanisms associated with the dip slopes. The results of this study are summarized as follows: (1) Two types of slope sliding, namely differential and complete, were recognized. The model with a dip angle lower than 20 degrees was more stable, and differential sliding developed gradually during external excitation. In the model with a dip angle higher than 20 degrees, the external excitation easily triggered complete sliding. (2) For threshold slope angles higher than 20 degrees, the behavior of the dip slope model changed from deformation to sliding, and the displacement within the models increased with increasing slope angle. (3) An increase in frequency led to a decrease in the trigger time for slope sliding. In addition, the slope angle was negatively correlated with the triggering time for sliding. (4) The amplification factor of peak ground displacement (PGD) increased as the slope angle increased. The amplification factors corresponding to low excitation frequencies were considerably lower than those for high excitation frequencies. In contrast to the trends for PGD, the amplification factor of peak ground acceleration (PGA) decreased as the slope angle increased.
Dynamic response of a dip slope with multi-slip planes revealed by shaking table tests
(2018-09-01)
Li, Hung-Hui
;
Lin, Cheng-Han
;
Zu, Wei
;
Chen, Chi-Chieh
;
Weng, Meng-Chia
This study investigated the effect of internal discontinuity on the dynamic response of a dip slope and evaluated the performance of Newmark's theory on the sliding of a dip slope with multi-slip planes. A series of shaking table tests were performed under various geometric conditions to explore the dynamic behavior of a dip slope under different external excitations. The test results, including for deformation processes and critical accelerations, under various slope angles, slope sizes, and seismic intensities were examined and further compared with Newmark's theory. The results of this study are summarized as follows: (1) two types of slope sliding (differential and complete) were determined. (2) Increasing the slope angle and the height of sliding mass tended to shorten the duration of slope deformation. (3) Critical acceleration of the slope increased gradually with increasing peak ground accelerations of input excitations; when the slope height and dip angle increased, the critical acceleration decreased. (4) The triggering time became earlier as the frequency of input excitation increased; the magnitude of sliding mass greatly depended on the amplitude of the input excitation. (5) By comparing critical acceleration between the experimental and theoretical results, Newmark's theory was determined to overestimate critical acceleration during seismic-induced dip slope failure. This may cause unsafe evaluations, and sliding along existing discontinuities develops more easily in reality.
Evaluating failure mechanisms of dip slope using a multiscale investigation and discrete element modelling
(2019-12-20)
Weng, Meng-Chia
;
Lin, Ming-Lang
;
Lo, Chia-Ming
;
Lin, Hsi-Hung
;
Lin, Cheng-Han
This study proposed an in-depth multiscale analysis procedure to identify the dip slope area and assess dip slope stability and influencing area. The proposed analysis procedure comprised five stages: (1) identifying the potential area of a dip slope, (2) analyzing the possible failure types of the dip slope, (3) evaluating slope activity, (4) analyzing dip slope stability under the influence of possible triggering factors, and (5) assessment of the deformation and deposition area. To validate the proposed procedure, the Chaochouhu region of Taiwan was analyzed as a dip slope case. In stages (1) to (3), the scale of the utilized map and the precision of associated data were evaluated to identify the potential area of a dip slope, the possible failure types, and the activity of each slope unit. In stages (4) and (5), the processes of deformation and sliding in a high-activity slope unit were simulated using the discrete element method. The numerical model was first verified using in-situ monitoring data obtained from inclinometers. Subsequently, the model was used to predict the slope behavior under conditions of wetting deterioration of geomaterial. The multiscale analysis revealed comprehensive information regarding the dip slope. The application of the proposed approach would be useful to civil engineers for evaluating dip slope stability as well as to relevant authorities for planning hazard mitigation strategies.
Failure mechanism of a mudstone slope embedded with steep anti-dip layered sandstones: case of the 2016 Yanchao catastrophic landslide in Taiwan
(2019-11-01)
Lin, Cheng-Han
;
Hung, Ching
;
Weng, Meng-Chia
;
Lin, Ming-Lang
;
Uzuoka, Ryosuke
On September 28, 2016, the torrential rainfall carried by Typhoon Megi induced a catastrophic mudstone landslide in the Yanchao District of Kaohsiung City, Taiwan. The total volume of the sliding mass was approximately 8700 m(3), which blocked an industrial road and displaced a duplex house in the downslope, leading to three deaths. Unprecedentedly, the 2016 Yanchao land-slide was large and quickly raised public awareness regarding the possibility of large landslides that could occur in the nearby mudstone areas. Based on field surveys, topographic and geological maps, unmanned aerial vehicle (UAV) photography, and remote-sensing imagery, the failure mechanism of the 2016 Yanchao landslide is described in this study. The results revealed that steep anti-dip layered sandstones embedded with the mud-stones play a critical role in large, rainfall-induced landslides. In the case of Yanchao landslide, the bedding joint between two formations was associated with the runoff infiltrating the low permeability mudstone. The kinematic process of the landslide consisted of two phases: a circular failure in the lower formation (alternation of mudstone and sandstone) and the subsequent regressive failure in upper formation (thick sandstone interbedded with mudstone). This study discloses the role of steep anti-dip layered sandstone influencing mudstone slope failure behaviors and presents a preliminary guide for assessing large, rainfall-induced landslides in mudstones. The results could also provide useful information for calibrating the numerical modeling of large landslides that may occur in the mudstone area in the future.
Fragile Watermarking-based Authentication Scheme for Demosaicked Images
(2015)
Lin, Chia-Chen
;
Liu, Xiao-Long
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Lin, Cheng-Han
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Yuan, Shyan-Ming
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資訊工程學系
This paper presents a reversible fragile watermarking scheme for the authentication of demosaicked images. Each authentication code is embedded into the two rebuilt components of each color pixel by using a designed authentication table (ACT). The utilization of ACT secures the watermarking procedure and the watermarked image can be recovered back to the original demosaicked image by the proposed scheme. The proposed scheme is compared with some existing image authentication schemes, and the experimental results demonstrate that our scheme can preserve better image quality and provides superior tamper detection performance.
Measuring Foliation Tensile Strength of Metamorphic Rock by Using Pull-Off Test
(2018-01-01)
Weng, Meng-Chia
;
Li, Jin-Hong
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Lin, Cheng-Han
;
Liao, Chu-Tsen
;
土木工程學系
The tensile strength of rock is an important property of rock engineering. However, the measurement of the tensile strength of rock is often overlooked due to difficulties of specimen preparation and the accuracy of testing results. This study adopted the pull-off test to measure the foliation tensile strength of metamorphic rock such as slate, green schist, and black schist. Compared with contemporary tensile tests, this method is relatively simple and effective, with easy specimen preparation. Additionally, this approach can be conducted not only in the laboratory but also in the field, which is quite useful for evaluating the rock slope stability. This study recommends procedures for sample preparation and testing as well. The test results indicate that the black schist exhibited the greatest tensile strength and that the slate had the lowest strength. Besides this, the slate exhibited significant wetting deterioration. Examination of the failure patterns revealed that the failure planes of all specimens occurred on the foliation planes, indicating reasonable failure patterns. Finally, this study investigated the factors potentially affecting the validity of tensile strength measurement, including the failures occurring at (1) the preexisting joint during sample preparation and (2) the interface of rock and epoxy resin. Procedures for mitigating this effect were also suggested.
Temporal focusing-based widefield multiphoton microscopy with spatially modulated illumination for biotissue imaging
(2018-01-01)
Chang, Chia-Yuan
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Lin, Cheng-Han
;
Lin, Chun-Yu
;
Sie, Yong-Da
;
Hu, Yvonne Yuling
A developed temporal focusing-based multiphoton excitation microscope (TFMPEM) has a digital micromirror device (DMD) which is adopted not only as a blazed grating for light spatial dispersion but also for patterned illumination simultaneously. Herein, the TFMPEM has been extended to implement spatially modulated illumination at structured frequency and orientation to increase the beam coverage at the back-focal aperture of the objective lens. The axial excitation confinement (AEC) of TFMPEM can be condensed from 3.0 mm to 1.5 mm for a 50% improvement. By using the TFMPEM with HiLo technique as two structured illuminations at the same spatial frequency but different orientation, reconstructed biotissue images according to the condensed AEC structured illumination are shown obviously superior in contrast and better scattering suppression. Picture: TPEF images of the eosin-stained mouse cerebellar cortex by conventional TFMPEM (left), and the TFMPEM with HiLo technique as 1.09 mm(-1) spatially modulated illumination at 908 (center) and 08 (right) orientations. [GRAPHICS] .
The effect of hydrogen on programmed threshold-voltage distribution in NAND flash memories
(2019-08-01)
Chiu, Yung-Yueh
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Lin, Cheng-Han
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Yang, Jhih-Siang
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Yang, Bo-Jun
;
Aoki, Minoru
This paper, for the first time, presents a comprehensive study into the effect of hydrogen concentration in the forming gas on the reliability of NAND Flash memories. It is newly observed that a higher hydrogen concentration leads to broaden the threshold-voltage (V-T) distribution after programming. This suggests that a higher hydrogen concentration makes a larger amount of ionized hydrogens (H+) exist in the shallow trench isolation (STI), which results in the fluctuation of the Fowler-Nordheim tunneling current during programming. It is also found that the V-T distribution width difference between higher and lower hydrogen concentration turns out to be smaller after the program/erase cycling. This could be explained by the neutralization of H+ due to the capture of the tunneling electrons at the STI edge. On the other hand, the higher hydrogen concentration proves to be able to provide better retention characteristics. Thus, the programming and retention characteristics are the tradeoff relationship. Therefore, optimization of the hydrogen concentration is crucial for the NAND Flash process integration. (C) 2019 The Japan Society of Applied Physics