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Search Results: 1 - 10 of 25284 matches for " Changgil Lee "
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Flaw Imaging Technique for Plate-Like Structures Using Scanning Laser Source Actuation
Changgil Lee,Seunghee Park
Shock and Vibration , 2014, DOI: 10.1155/2014/725030
Abstract: Recently, the longitudinal, shear, and surface waves have been very widely used as ultrasonic wave-based exploration methods to identify internal defects of host structures. In this context, a noncontact nondestructive testing (NDT) method is proposed to detect the damage of plate-like structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND:YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using 3-dimensional Fourier transformation (3D FT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a plate-like structure are conducted using the damage-sensitive features. Finally, the plates with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach. 1. Introduction Recently, there have been increasing demands on structural 2 health monitoring (SHM) and nondestructive testing (NDT) in the fields of civil, mechanical, and aerospace engineering and so on to prevent losses of life and property by continuously monitoring the systems. Especially, local monitoring methodologies have been studied to overcome the limitation of global monitoring techniques [1–4]. Effective SHM/NDT methods must be intuitive so that inspection results can be easily understandable and must have high throughput [5]. To tackle this issue, a lot of researches based on acoustic and ultrasonic technologies have been proposed using laser interferometry, laser vibrometer, pulsed laser, and so on because the ultrasonic waves are sensitive to the mechanical properties of structures, while the wave responses are hardly affected by radiation [5]. Holography based imaging technique, one of the full-field ultrasonic wave imaging techniques, requires highly diffusive target surface. Also, holographic images can be obtained clearly in dark environments, and hence this method is not suitable to remote automatic inspection although this has noncontact inspection capability [6]. Dynamic responses can be collected by laser Doppler vibrometry which measures vibrational velocity of target structures. Although the performance of the laser Doppler vibrometry is improved in terms of scan angles and automatic focusing [7], it has still disadvantage that retroreflective film should be attached on target surfaces to
Magnetic Flux Leakage Sensing-Based Steel Cable NDE Technique
Seunghee Park,Ju-Won Kim,Changgil Lee,Jong-Jae Lee
Shock and Vibration , 2014, DOI: 10.1155/2014/929341
Abstract: Nondestructive evaluation (NDE) of steel cables in long span bridges is necessary to prevent structural failure. Thus, an automated cable monitoring system is proposed that uses a suitable NDE technique and a cable-climbing robot. A magnetic flux leakage- (MFL-) based inspection system was applied to monitor the condition of cables. This inspection system measures magnetic flux to detect the local faults (LF) of steel cable. To verify the feasibility of the proposed damage detection technique, an 8-channel MFL sensor head prototype was designed and fabricated. A steel cable bunch specimen with several types of damage was fabricated and scanned by the MFL sensor head to measure the magnetic flux density of the specimen. To interpret the condition of the steel cable, magnetic flux signals were used to determine the locations of the flaws and the levels of damage. Measured signals from the damaged specimen were compared with thresholds that were set for objective decision-making. In addition, the measured magnetic flux signals were visualized as a 3D MFL map for intuitive cable monitoring. Finally, the results were compared with information on actual inflicted damages, to confirm the accuracy and effectiveness of the proposed cable monitoring method. 1. Introduction Recently, there have been increasing demands on structural health monitoring (SHM) and nondestructive testing (NDT) in the fields of civil, mechanical, and aerospace engineering. Especially, local monitoring methodologies for specific critical members have been studied to overcome the limitation of global monitoring techniques for whole structures [1–4]. Steel cables in long span bridges are also critical members that suspend almost all of the dead load of the structure. However, cross-sectional damage can occur in a steel cable due to corrosion and fracture, which can lead to stress concentrations. Cross-sectional damage can be a direct cause of structural failure. Therefore, nondestructive evaluation (NDE) is necessary to detect the initial stages of cross-sectional damage in a cable. However, it is difficult to monitor the condition of most cables, as the damage can be invisible and inaccessibly located. To overcome these drawbacks, we propose an automated cable monitoring system, which uses a suitable NDE technique and a cable-climbing robot that can approach the damaged point, which is shown in Figure 1. Figure 1: The cable-climbing robot with suitable NDE equipment. Meanwhile, NDE techniques available for incorporation into cable-climbing robots have been widely researched. In this study,
The Relationship between Visual Satisfaction and Water Clarity and Quality Management in Tourism Fishing Ports  [PDF]
Lee-Hsueh Lee
Journal of Water Resource and Protection (JWARP) , 2016, DOI: 10.4236/jwarp.2016.88064
Abstract: Visual satisfaction of the tourists with a water body is strongly influenced by water clarity, which is in turn influenced by a number of water quality parameters. Visual satisfaction thus stands to benefit from having a water quality management tool that results in better water clarity. A Clarity Suitability Index of Water Quality (CSIWQ), derived from clarity suitability curves of selected water quality parameters, can allow estimation of optimal values for these parameters, while ensuring high visual satisfaction among tourists. The present study used sampling and survey methodologies to investigate water clarity and quality at five tourism fishing ports; simultaneously, tourists’ visual satisfaction with a water body was assessed through a questionnaire based on their perceptions. The relationship between tourists’ visual satisfaction and water clarity was found to be positive and strong, with water clarity having predictive power of 74.2%. The study showed that DO, BOD, TP, and SS were the most critical parameters for water clarity. A continued product approach of CSIWQ was found to be most appropriate for describing the relationship between water clarity and these four parameters. This enabled a CSIWQ Index value to be calculated. With a CSIWQ value of 0.6, water clarity would be more than 2.08 m, and tourists would experience very high satisfaction. CSI curves showed that DO would preferably be 9.0 mg/L, and BOD, TP, and SS less than 0.5 mg/L, 0.12 mg/L, and 45.0 mg/L, respectively. The model thus produced valuable insights for assessing and improving water quality and ensuring high levels of visual satisfaction among tourists in tourism fishing ports. This model identified only four parameters but could be improved by ensuring that other water quality parameters were included, to encourage an increase in the number of tourists and to include monitoring of more pollutant sources.
Appearance’s Aesthetic Appreciation to Inform Water Quality Management of Waterscapes  [PDF]
Lee-Hsueh Lee
Journal of Water Resource and Protection (JWARP) , 2017, DOI: 10.4236/jwarp.2017.913103
The appearance of the water is just one aspect of a waterscape that can be appreciated aesthetically. Water appearance is affected by water clarity and water colour. Here, an aesthetic assessment model of waterscape was suggested. In the model, water clarity and colour have direct effects, whereas water quality and phytoplankton biomass have indirect effects, on tourists’ aesthetic assessment of water bodies. The preferred water colour is aquamarine to blue, regardless of depth of clarity. Water colour ranges from pastel yellow to yellow-green are not favoured by tourists. Four water-quality parameters were correlated with water clarity and phytoplankton biomass. The coefficient of indirect effect of river pollution index on tourists’ aesthetic valuation of aquamarine to blue water colour was -0.457, and for pastel yellow to yellowgreen, it was -0.209. The research results showed observation of water colour could not only reflect waterscape aesthetic value, but also serve as a guide of judging water quality, and the status of phytoplankton benefited to simplify the process of water-quality management for waterscape.
Abdominal Fat Reduction through Cryolipolysis  [PDF]
Doyeop Lee, Kyurae Lee
Journal of Biosciences and Medicines (JBM) , 2018, DOI: 10.4236/jbm.2018.69005
Abstract: Although several studies showed the efficacy and safety from this procedure, the comparative assessment of adipose tissue by cryolipolysis has not been studied until now. Therefore we investigated the quantitative change of cross sectional areas of abdominal SAT (subcutaneous adipose tissue) and VAT (visceral adipose tissue) following cryolipolysis. A prospective study for twelve subjects with a single session of cryolipolysis on abdomen was performed. We assessed for their height, weight, and waist circumferences, body contours by photographs, and the cross sectional areas of visceral and subcutaneous adipose tissues were measured at umbilicus level by computerized tomography for 2 months. The cross sectional areas in SAT reduced from 243.3 ± 24.7 to 238.5 ± 40.7 cm2 at 2 months post-treatment. Those of VAT reduced from 141.3 ± 46.4 to 125.1 ± 42.8 cm2 at 2 months post-treatment. Cross sectional areas of VAT, and waist circumferences were significantly reduced by 16.2 cm2, 4.1 cm respectively. Additionally visual improvement without unexpected adverse events was noted. In conclusion a single session cryolipolysis demonstrated to reduce visceral adipose tissue as well as waist circumferences tissue for 2 months. Further controlled study would be needed to evaluate for reduction of visceral adipose tissue by cryolipolysis.
Exponential Ergodicity and β-Mixing Property for Generalized Ornstein-Uhlenbeck Processes  [PDF]
Oesook Lee
Theoretical Economics Letters (TEL) , 2012, DOI: 10.4236/tel.2012.21004
Abstract: The generalized Ornstein-Uhlenbeck process is derived from a bivariate Lévy process and is suggested as a continuous time version of a stochastic recurrence equation [1]. In this paper we consider the generalized Ornstein-Uhlenbeck process and provide sufficient conditions under which the process is exponentially ergodic and hence holds the expo-nentially β-mixing property. Our results can cover a wide variety of areas by selecting suitable Lévy processes and be used as fundamental tools for statistical analysis concerning the processes. Well known stochastic volatility models in finance such as Lévy-driven Ornstein-Uhlenbeck process is examined as a special case.
Coastal Planning Strategies for Adaptation to Sea Level Rise: A Case Study of Mokpo, Korea  [PDF]
Yumi Lee
Journal of Building Construction and Planning Research (JBCPR) , 2014, DOI: 10.4236/jbcpr.2014.21007
Abstract: Climate change and sea level rise necessitate adaptation strategies for coastal areas. This paper showcases five strategies for sea level rise adaptation: hard protection, soft protection, accommodation, retreat, and attack. This study proposes adaptation measures and a phased development strategy for coastal areas of Mokpo, an old port city on the southwestern tip of the Korean Peninsula that has been expanded by land reclamation. Mokpo presently experiences frequent flooding during high-water and storm events; due to their low elevation and land subsidence, most of the reclaimed areas are susceptible to future inundation via sea level rise. The fundamental adaptation strategies for the impact areas are: hard protection of important infrastructures via multi-tiered terraces; the retreat of coastal developments accompanied by green buffer zones such as wetlands and parks to accommodate temporary inundation; and up-leveling the ground for new development and phased relocation of existing development. Through the case study of Mokpo, the paper emphasizes the importance of resilient planning strategies for urban development, and highlights both the challenges and opportunities for sea level rise adaptation.
Study on the Classification of Speech Anxiety Using Q-Methodology Analysis  [PDF]
SeoYoung Lee
Advances in Journalism and Communication (AJC) , 2014, DOI: 10.4236/ajc.2014.23008
Abstract: Public speaking is one of the cornerstones of mass communication, the influence of which has only been enhanced with the advent of the modern era. Yet despite its importance, up to 40% of the world’s population feels anxious when faced with the prospect of presenting in front of an audience (Wilbur, 1981). However, public speaking anxiety is human condition that can be understood and with effort, overcome by sufferers. Based on theoretical research, this study presents an empirical investigation of speech anxiety. The research uses Q-methodology to generate categories of speakers and then draws on the PQ-method program to suggest ways for speakers to improve their speaking confidence based on these categories. This research is of a value to those who are interested in speech anxiety for therapeutic or pedagogical practice.
Protecting the Coastline from the Effects of Climate Change: Adaptive Design for the Coastal Areas of Gangneung, Korea  [PDF]
Yumi Lee
Journal of Building Construction and Planning Research (JBCPR) , 2015, DOI: 10.4236/jbcpr.2015.32011
Abstract: The purpose of this research is to present design strategies to enable coastal areas to adapt to climate change and maintain the coastlines by addressing the environmental and urban issues. Gangneung is a tourist attraction situated on South Korea’s east coast, and there is an urgent need for integrated research on strategies to prevent the loss of sandy beaches and the damage caused by storm surges and high swell. This research has two objectives: The first is to offer an overview and describe the characteristics of exemplary projects carried out to manage the storm damage while maintaining the coastlines. The second is to propose a design model that can be applied to coastal areas susceptible to climate change by analyzing the design strategies and the current conditions of the Gangneung coastal area. In the case of Gangneung, the damage caused by the storm surges and high swells are more severe compared to inundation caused by sea level rise because of the steep slope and deep water. Therefore, adaptive design strategies are mainly focused on accommodation and retreat strategies that consider these characteristics by moving the coastal roads behind the pine forest and raising the coastal buildings to connect the coast to the forest and to prevent coastal erosion. This research has the potential to be used as an exemplary design adaptation for coastal erosion as well as a basis for regulating the land use policy in areas susceptible to flood by establishing guidelines for publicly funded developments, and preparing long-term relocation plans for the existing coastal developments to create a sustainable and resilient future for the coastal areas.
A Theoretical Solution for the Reynolds Stress: Validations in Canonical Flow Geometries  [PDF]
Taewoo Lee
Open Journal of Fluid Dynamics (OJFD) , 2016, DOI: 10.4236/ojfd.2016.64021
Abstract: A theoretical approach is developed for solving for the Reynolds stress in turbulent flows, and is validated for canonical flow geometries (flow over a flat plate, rectangular channel flow, and free turbulent jet). The theory is based on the turbulence momentum equation cast in a coordinate frame moving with the mean flow. The formulation leads to an ordinary differential equation for the Reynolds stress, which can either be integrated to provide parameterization in terms of turbulence parameters or can be solved numerically for closure in simple geometries. Results thus far indicate that the good agreement between the current theoretical and experimental/DNS (direct numerical simulation) data is not a fortuitous coincidence, and in the least it works quite well in sensible ways in canonical flow geometries. A closed-form solution for the Reynolds stress is found in terms of the root variables, such as the mean velocity, velocity gradient, turbulence kinetic energy and a viscous term. The form of the solution also provides radically new insight on how the Reynolds stress is generated and distributed.
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