• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.3-11
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• 2003

We analysed phases recorded by the M$_{L}$ 3.6 Cheolwon, Korea, earthquake occurred on the 10th of December, 2002 and computed source parameters such as hypocenter, origin time, earthquake magnitude and focal solutions. We used PmP and SmS phases to increase the accuracy in determinations of the hypocenter and origin time in addition to the phases such as Pg, Pn, Sg and Sn which are generally used in routine processes. The epicenter, depth, and origin time of the Cheolwon earthquake determined based on data of 11 stations within 200 km from the epicenter are 38.8108$^{\circ}$N, N, 127.2214'E, 11.955 km, and on 7:42:51.436. The earthquake magnitude obtained from all the stations is 3.6 M$_{L}$. The fault plane solution calculated based on data from 19 stations indicates slip process of a normal fault including strike-slip motion. The direction of compressional stress field has a large vertical component and a ESE-WNW direction of horizontal component, which is different from the mainly horizontal direction of main compressional stress field in the Korean Peninsula (ENE-WSW) obtained by previous studies.ies.s.

• Smart Structures and Systems
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• v.28 no.6
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• pp.727-735
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• 2021

Recently, non-destructive health monitoring methods such as magnetic flux leakage (MFL) method, have become popular due to their advantages over destructive methods. Currently, numerical study on this field has been limited to simplified studies by only obtaining MFL instead of induced voltage inside coil sensor. In this study, it was proposed to perform a novel numerical simulation of MFL's coil sensor by considering vital parameters including specimen's motion with constant velocity and saturation status of specimen in time domain. A steel-rod specimen with two stepwise cross-sectional changes (i.e., 21% and 16%) was fabricated using low carbon steel. In order to evaluate the results of numerical simulation, an experimental test was also conducted using a magnetic probe, with same size specimen and test parameters, exclusively. According to comparative results of numerical simulation and experimental test, similar signal amplitude and signal pattern were observed. Thus, proposed numerical simulation method can be used as a reliable source to check efficiency of sensor probe when different size specimens with different defects should be inspected.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.10
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• pp.944-950
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• 2015

Recent studies on ankle-foot prostheses used for transtibial amputees have focused on the adaptation of the ankle angle of the prosthesis according to ground conditions. For adaptation to various ground conditions (e.g., incline, decline, and step conditions), ankle-foot prostheses should first recognize the ground conditions as well as the current human motion pattern. For this purpose, the ground reaction forces and orientation angle of the tibia provide fundamental information. The measurement of the orientation angle, however, creates a challenge in practice. Although various sensors, such as accelerometers and gyroscopes, can be utilized to measure the orientation angles of the prosthesis, none of these sensors can be solely used due to their intrinsic drawbacks. In this paper, a time-varying complementary filtering (TVCF) method is proposed to incorporate the measurements from an accelerometer and a gyroscope to obtain a precise orientation angle. The cut-off frequency of TVCF is adaptively determined according to the human gait phase detected by a fuzzy logic algorithm. The performance of the proposed method is verified through experiments.

• Korean Journal of Applied Biomechanics
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• v.34 no.2
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• pp.81-92
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• 2024

Objective: The purpose of this study was to analyze the impact acceleration, shock attenuation and biomechanical variables at various running speed. Method: 20 subjects (height: 176.15 ± 0.63 cm, weight: 70.95 ± 9.77 kg, age: 27.00 ± 4.65 yrs.) participated in this study. The subjects ran at four different speeds (2.5 m/s, 3.0 m/s, 3.5 m/s, 4.0 m/s). Three-dimensional accelerometers were attached to the distal tibia, sternum and head. Gait parameters, biomechanical variables (lower extremity joint angle, moment, power and ground reaction force) and acceleration variables (impact acceleration, shock attenuation) were calculated during the stance phase of the running. Repeated measures ANOVA was used with an alpha level of .05. Results: In gait parameters, decreased stance time, increasing stride length and stride frequency with increasing running speed. And at swing time 2.5 m/s and 4.0 m/s was decreased compared to 3.0 m/s and 3.5 m/s. Biomechanical variables statistically increased with increasing running speed except knee joint ROM, maximum ankle dorsiflexion moment, and maximum hip flexion moment. In acceleration variables as the running speed increased (2.5 m/s to 4.0 m/s), the impact acceleration on the distal tibia increased by more than twice, while the sternum and head increased by approximately 1.1 and 1.2 times, respectively. And shock attenuation (tibia to head) increased as the running speed increased. Conclusion: When running speed increases, the magnitude and increasing rate of sternum and head acceleration are lower compared to the proximal tibia, while shock attenuation increases. This suggests that limiting trunk movement and increasing lower limb movement effectively reduce impact from increased shock. However, to fully understand the body's mechanism for reducing shock, further studies are needed with accelerometers attached to more segments to examine their relationship with kinematic variables.

• Journal of the Ergonomics Society of Korea
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• v.30 no.4
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• pp.563-569
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• 2011

Objective: This study focuses on the effects of pre-cues informing the location of upcoming visual stimulus on finger movement response in the context of control-on-display interfaces. Background: Previous research on pre-cues focus on attention allocation and motion studies were limited to indirect control conditions. The design of this study aimed to collect data on the exact landing point for finger-tap responses to a given visual stimulus. Method: Controlled visual stimuli and tasks were presented on a UI evaluation system built using mobile web standards; response accuracy and response time were measured and collected as appropriate. Among the 16 recruited participants, 11 completed the experiment. Results: Providing pre-cue on the location of stimulus affected response time and response accuracy. The response bias, which is a distance from the center of stimulus to the finger-tap location, was larger when the pre-cue was given during a one-handed operation. Conclusion: Given a pre-cue, response time decreases, but with accuracy penalized. Application: In designing touch-screen UI's - more strictly, visual components also acting as controllers - designers would do well to balance human perceptual and cognitive characteristics strategically.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.713-722
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• 2020

This article aims to illustrate the damped dynamic responses of layered functionally graded (FG) thick 2D beam under dynamic pulse sinusoidal load by using finite element method, for the first time. To investigate the response of thick beam accurately, two-dimensional plane stress problem is assumed to describe the constitutive behavior of thick beam structure. The material is distributed gradually through the thickness of each layer by generalized power law function. The Kelvin-Voigt viscoelastic constitutive model is exploited to include the material internal damping effect. The governing equations are obtained by using Lagrange's equations and solved by using finite element method with twelve -node 2D plane element. The dynamic equation of motion is solved numerically by Newmark implicit time integration procedure. Numerical studies are presented to illustrate stacking sequence and material gradation index on the displacement-time response of cantilever beam structure. It is found that, the number of waves increases by increasing the graduation distribution parameter. The presented mathematical model is useful in analysis and design of nuclear, marine, vehicle and aerospace structures those manufactured from functionally graded materials (FGM).

• Journal of Power System Engineering
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• v.11 no.1
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• pp.98-106
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• 2007

This paper presents a statistical prediction procedure for the propeller racing of ships with twin screw propellers sailing in ocean waves. The propeller racing is one of the most important factors of seakeeping qualities in relation to the safety of main engine and shafting system. It is especially significant key word for designing the twin-screw-propeller-type ship in view of allowable maximum propeller diameter etc.. In former studies, the propeller racing generally means the situation (propeller exposed) in which the relative motion amplitude between ship hull and wave surface would exceed a depth of point in rotary disk propeller. Therefore, it seems that the magnitude of the amplitude and its exceeding frequency have been examined as a principal subject of study as usual. However, the time during which the amplitude exceeds a depth of point must be also one of most important factor affecting the trend of propeller racing. This paper proposes a simply practical method for estimating the time lasting of exposed propeller related to twin screw propeller racing in rough confused seas on the basis of the statistics. Then, it is confirmed that the practical method is useful and convenience for considering the propeller racing in the stage of the basic design.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.965-968
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• 2005

Roll drafting operation causes variations in the linear density of bundles because the bundle flow cannot be controlled completely by roll pairs. Defects occurring in this operation bring about many problems successively in the next processes. In this paper, we attempt to analyze the draft dynamics and the linear density irregularity based on the governing equation of a bundle motion that has been suggested in our previous studies. For analyzing the dynamic characteristics of the roll drafting operation, it is indispensable to investigate a transient state in time domain before the bundle flux reaches a steady state. However, since governing equations of bundle flow consisting of continuity and motion equations turn out to be nonlinear, and coupled between variables, the solutions for a transient state cannot be obtained by an analytical method. Therefore, we use the Finite Difference Method(FDM), particularly, the FTBS(Forward-Time Backward-Space) difference method. Then, the total equations system yields to an algebraic equations system and is solved under given initial and boundary conditions in an iterative fashion. From the simulation results, we confirm that state variables show different behavior in the transient state; e.g., the velocity distribution in the flow field changes more quickly the linear density distribution. During a transient flow in a drafting zone, the output irregularity is influenced differently by the disturbances, e.g., the variation in input bundle thickness, the drafting speed, and the draft ratio.

• Investigative Magnetic Resonance Imaging
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• v.23 no.3
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• pp.202-209
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• 2019

Purpose: To investigate the temperature-based differences of cortical bone ultrashort echo time MRI (UTE-MRI) biomarkers between body and room temperatures. Investigations of ex vivo UTE-MRI techniques were performed mostly at room temperature however, it is noted that the MRI properties of cortical bone may differ in vivo due to the higher temperature which exists as a condition in the live body. Materials and Methods: Cortical bone specimens from fourteen donors ($63{\pm}21$ years old, 6 females and 8 males) were scanned on a 3T clinical scanner at body and room temperatures to perform T1, $T2^*$, inversion recovery UTE (IR-UTE) $T2^*$ measurements, and two-pool magnetization transfer (MT) modeling. Results: Single-component $T2^*$, $IR-T2^*$, short and long component $T2^*s$ from bi-component analysis, and T1 showed significantly higher values while the noted macromolecular fraction (MMF) from MT modeling showed significantly lower values at body temperature, as compared with room temperature. However, it is noted that the short component fraction (Frac1) showed higher values at body temperature. Conclusion: This study highlights the need for careful consideration of the temperature effects on MRI measurements, before extending a conclusion from ex vivo studies on cortical bone specimens to clinical in vivo studies. It is noted that the increased relaxation times at higher temperature was most likely due to an increased molecular motion. The T1 increase for the studied human bone specimens was noted as being significantly higher than the previously reported values for bovine cortical bone. The prevailing discipline notes that the increased relaxation times of the bound water likely resulted in a lower signal loss during data acquisition, which led to the incidence of a higher Frac1 at body temperature.

• Earthquakes and Structures
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• v.14 no.2
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• pp.129-142
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• 2018

The current paper introduces a new approach for development of damage index to obtain the maximum damage in the reinforced concrete frames caused by as-recorded single and consecutive earthquakes. To do so, two sets of strong ground motions are selected based on maximum and approximately maximum peak ground acceleration (PGA) from "PEER" and "USGS" centers. Consecutive earthquakes in the first and second groups, not only occurred in similar directions and same stations, but also their real time gaps between successive shocks are less than 10 minutes and 10 days, respectively. In the following, a suite of six concrete moment resisting frames, including 3, 5, 7, 10, 12 and 15 stories, are designed in OpenSees software and analyzed for more than 850 times under two groups of as-recorded strong ground motion records with/without seismic sequences phenomena. The idealized multilayer artificial neural networks, with the least value of Mean Square Error (MSE) and maximum value of regression (R) between outputs and targets were then employed to generate the empirical charts and several correction equations for design utilization. To investigate the effectiveness of the proposed damage index, calibration of the new approach to existing real data (the result of Park-Ang damage index 1985), were conducted. The obtained results show good precision of the developed ANNs-based model in predicting the maximum damage of regular reinforced concrete frames.