• Journal of Korean Tunnelling and Underground Space Association
• /
• v.11 no.4
• /
• pp.327-351
• /
• 2009

Laboratory tests are performed in this paper to investigate the brittle failure characteristics of over-stressed rocks taken in deep depth. Also, numerical simulation performed using that the so-called CWFS(Cohesion Weakening Frictional Strengthening) model is known to predict brittle failure phenomenon reasonably well. The most typical rock types of Korean peninsula - granite and gneiss - were used for testing. Results of uniaxial compression tests showed that the crack initiation stress was about 41 % to 42% of the uniaxial compressive strength regardless of rock types, where as, the crack damage stress of granite was about 75%, and that of gneiss was about 97%. Through the damage-controlled test, strength parameters of each rock were obtained as a function of damage degree. After the peak, the crack damage stress and the maximum stress were decreased, The cohesion was decreased and the friction angle was increased with increase of rock damage. Before reaching the peak, the elastic modulus was slightly increased, while decreased after the peak. Poisson's ratio was increased as the damage of rock proceeds. Comparison of uniaxial compression tests and damage-controlled tests shows the crack initiation stress estimated from the damage-controlled test fluctuated within the range of crack initiation stress obtained from the uniaxial compression test; the crack damage stress was less than that estimated from the uniaxial compression test. In order to predict the critical depth that brittle failure occurs, numerical simulations using the CWFS model were performed for an example site. Material parameters obtained from the laboratory tests mentioned above were used for CWFS simulation. Comparison between the critical depth predicted from the numerical simulation using the CWFS model and that predicted by using the damage index proposed by Martin et al.(l999), showed that critical depth cannot be reasonably predicted by the currently used damage index except for circular tunnels. A modified damage index was proposed by the author which takes the shape of tunnels other than circular into account.

• Journal of the Korean Society of Visualization
• /
• v.12 no.3
• /
• pp.9-14
• /
• 2014

Two-photon microscopy (TPM) has been used in plant research as a high-resolution high-depth 3D imaging modality. However, TPM is known to induce photo-damage to the plant in case of long time exposure, and optimal excitation wavelength for plant imaging has not been investigated. Longer excitation wavelength may be appropriate for in vivo two-photon imaging of Arabidopsis thaliana leaves, and effects of longer excitation wavelength were investigated in terms of imaging depth, emission spectrum. Changes of emission spectrum as a function of exposure time at longer excitation wavelength were measured for in vivo longitudinal imaging. Imaging depth was not changed much probably because photon scattering at the cell wall was a limiting factor. Chloroplast emission spectrum showed its intensity peak shift by 20 nm with transition of excitation wavelength from 849 nm or below to 850 nm or higher. Emission spectrum showed different change patterns with excitation wavelengths in longitudinal imaging. Longer excitation wavelengths appeared to interact with chloroplasts differently in comparison with 780 nm excitation wavelength, and may be good for in vivo imaging.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1992.10a
• /
• pp.101-105
• /
• 1992

Machined graphite/epoxy composite surfaces were studied by using SEM(Scanning Electron Microscopy). surface profilometry and its analysis to determine suitable surface describing parameters for machined unidirectional and laminate composite surface. The surface roughness and profile are found to be highly dependent on the fiber layup direction and the measurement direction. Machined unidirectional and 0.deg. 45 .deg. 90 .deg. plies in laminate composite surface profiles are found to be Gaussian in the direction of machining. Since there exist bare fibers without matrix smearing in 0 .deg. ply, higher surface roughness values were found in this orientation. It was possible to machine 90 .deg. and -45 .deg. plies due to the adjacent plies, which were holding those plies. It was found that the microgeometrical variations in terms of roughness parameters Ra without Dy (maximum Damage Depth) region and Dy are better descriptors of the machined laminate composite surface than commonly used roughness parameters Ra and Ra. The characteristics of surface profiles in laminate composite are well represented in CHD (Cumulative Height Distribution) plot and PPD (Percentage Probability Density) plot. Also, the power spectral density function is shown to be capable of identifying the wavelength distribution of the machining damage.

• Structural Engineering and Mechanics
• /
• v.77 no.1
• /
• pp.47-56
• /
• 2021

This paper deals with damage detection using a Gapped Smoothing Method (GSM) combined with deep learning. Convolutional Neural Network (CNN) is a model of deep learning. CNN has an input layer, an output layer, and a number of hidden layers that consist of convolutional layers. The input layer is a tensor with shape (number of images) × (image width) × (image height) × (image depth). An activation function is applied each time to this tensor passing through a hidden layer and the last layer is the fully connected layer. After the fully connected layer, the output layer, which is the final layer, is predicted by CNN. In this paper, a complete machine learning system is introduced. The training data was taken from a Finite Element (FE) model. The input images are the contour plots of curvature gapped smooth damage index. A free-free beam is used as a case study. In the first step, the FE model of the beam was used to generate data. The collected data were then divided into two parts, i.e. 70% for training and 30% for validation. In the second step, the proposed CNN was trained using training data and then validated using available data. Furthermore, a vibration experiment on steel damaged beam in free-free support condition was carried out in the laboratory to test the method. A total number of 15 accelerometers were set up to measure the mode shapes and calculate the curvature gapped smooth of the damaged beam. Two scenarios were introduced with different severities of the damage. The results showed that the trained CNN was successful in detecting the location as well as the severity of the damage in the experimental damaged beam.

• Journal of Environmental Policy
• /
• v.11 no.4
• /
• pp.107-130
• /
• 2012

Economic analysis of climate change in the Korean peninsula has been conducted in the four major river basins. Although climate change impacts can vary in many terms, typically flood damages from the increase of precipitation and drought from rainless, this research only focused on effects of altering precipitation due to the lack of information and depth-damage functional form in Korea. This research also considered a gamma function of 5 % failure to deal with uncertainty issues in water resources. For the detailed analysis, time different discount rates have been used for short, mid, and long period, viz., 2.76%, 1.45%, and 0.62%, respectively. Over all effects of climate change on four major riverbasins can be summarized as no short period damage except the Han river basin. In the Han river basin, rapid increases of residential water use lead short term water shortage.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.3
• /
• pp.263-272
• /
• 2019

The aim of this study is to develop a rapid calculation technique of the residual strength in order to prevent sequential events under grounding accidents. Very Large Crude-Oil Carrier (VLCC), Suezmax, and Aframax double hull oil tankers carrying large quantities of crude oil were selected for target structures. The rock geometries are chosen from the published regulation by Marine Pollution Treaty (MARPOL) of the International Maritime Organization (IMO). Oceanic rocks as the most frequently encountered obstruction with ships are applied in this work. Damage condition was predicted using ALPS/HULL program based on grounding scenario with selected parameters, i.e. depth of penetration, damage location and tanker type. The results of the scenarios are quantified to form an empirical formula which can evaluate the residual strength. The proposed formula is validated by applying a series of random grounding scenarios.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.28 no.12
• /
• pp.1011-1014
• /
• 2017

Additional metal shielding is installed in the water pipes used in septic tanks to protect against damage from electromagnetic pulse (EMP) events. This shielding prevents EMP damage, but impurities present in water cannot pass through the shielding structure. Thus, the original function of the water pipes is lost as the pipes are blocked, and an additional maintenance workforce is needed to manage this blockage. To solve this problem, we propose a water pipe without an additional shielding structure; the proposed pipe was designed with consideration of the attenuation characteristics of water. The immersed depth was varied from 400 mm to 800 mm, while the diameter of the pipe was fixed at 100 mm. The shielding effectiveness increased from 70 dB to 100 dB around 2 GHz. Through the verification process, we propose an effective design guideline that can maintain the function of the water pipe and provide protection from EMP damages without additional shielding structure.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 1998.10a
• /
• pp.311-317
• /
• 1998

Recently irrigation reservoir has been developed to perform multipurpose function. To get a maximum effect it requires to establish optimal management system for irrigation reservoir in drought and flood season. Especially we dealt with optimal flood control system for irrigation reservoir in this study. This system consists of real-time rainfall data via online system, real-time flood forecasted by SCS method in hourly basis, storage volume by water balance equation, optimal releasing discharge from the gate, the water level in right downstream, and calculation of innundated area, depth, and time using GIS, and amount of flood damages. If we consider the relation of these sub module reasonably, we can reach the optimal flood control to minimize flood damage

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.225-228
• /
• 2008

There are many studies about submerged structures or porous wave absorbers to decrease damage of coast and structures. Submerged structures and porous wave absorber are decreasing energy of incoming wave by reflecting or dissipation with changing depth or with porous rubble mound. This study addresses the reflection and transmission of long wave from a trapezoidal breakwater and a vertical porous wave absorber at the same time. A systematic shape transfer is derived to determine wave reflection and transmission. And periodic solutions are matched at the slope and the front face of the absorber by assuming continuity of pressure and mass. The transmission coefficient is determined as a function of parameters describing the incoming waves, transmitting waves through the trapezoidal breakwater and the absorber characteristics.

• Journal of Multimedia Information System
• /
• v.9 no.3
• /
• pp.227-232
• /
• 2022

Disasters are now becoming commonplace and especially the vulnerable group such as the disabled, the elderly, children and foreigners are in a state of overlapping disasters. In this situation, ATSC 3.0-based UHDTV disaster information service for the visually and hearing impaired has been developing. This study focuses on the demand data collected through in-depth interview with the impaired. The demand analysis data is very important to development process of technology. The results of the interview show that it is essential to link the UHDTV disaster signals with home-network, IoT, wearable devices, and various assistive devices for the impaired (hearing aid, smart light bulbs, warning light, etc.). In outdoor space, UHDTV disaster information must be connected to public display media, digital signage, kiosk, screens in bus or taxi. If communication aids for the visually and hearing impaired are equipped with a function that can transmit and receive disaster information, it will help to minimize disaster damage.