• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.247-255
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• 2016

The purpose of this study is to investigate unsteady-state characteristics of a pintle thruster with various pintle speed. Based on steady state experimental results, non-linear pintle stroke equation is obtained and applied to the unsteady state experimental system. For the unsteady state experiments, three different pintle speeds are used: 3.10 mm/s, 5.65 mm/s, 10.83 mm/s, respectively. Results show that backward pintle stroke results in faster convergence time because of high chamber pressure during backward pintle stroke sequence. During the forward and backward process, thrust curve shows singular points. These phenomenons is caused by variation of mass flow rate, which is mainly due to changes of both chamber pressures and nozzle throat area. This behavior becomes distinctive for a faster pintle speed case.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.6
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• pp.827-832
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• 2013

In this study, curve responsiveness was assessed based on the lateral force and running safety was evaluated based on the wheel unloading ratio and derailment coefficient, which is the ratio of the wheel load and the lateral force. The evaluation of the curving performance and running safety of the new high-power electric locomotive showed that the derailment coefficient appeared higher when the wheel-set was set to the front of the train instead of being placed backward, and the maximum value of the derailment coefficient was recorded as 0.572 on the Gyeongbu line. Furthermore, the lateral force increased in curved sections, and it appeared to be proportional to the curve radius. Meanwhile, a maximum axis lateral force of 77.6 kN was recorded on the Taebaek line, and the wheel unloading ratio was 47.6% on the Yeongdong line. Finally, the running safety at the maximum speed as well as the through-curve performance of the curve radius satisfied the required standards.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.2 s.95
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• pp.206-212
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• 2005

In many machines handling lightweight and flexible media, such as magnetic tape drives, xerographic copiers and sewing machines, the media must transit an open space. It is important to predict the static and dynamic behavior of the sheets with a high degree of reliability. The nonlinear theory of the dynamic elastica has often been used to a nonlinear dynamic deflection model. In this paper, the governing equation is derived and simulated by the finite difference method. The parametric cubic curve is applied for defining the guide shape. The dynamic contact conditions suggested by Klarbring is used to predict the direction of the flexible media according to the initial velocity and the friction coefficient. The analysis is also compared to the conventional model, showing that after contacting a $45^{\circ}$ wall, the directions of flexible media of two models are different.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.47-54
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• 2011

In this paper, longitudinal behaviors of a tunnel with respect to various conditions are analyzed, and a new equation of longitudinal deformation curve during tunnel expansion is proposed. Finally, the range of protection by a protector is investigated using the proposed equation. To achieve the objectives, numerical analysis according to the ground and expansion conditions is performed. The results show that the range of protection, when a 2 traffic lane tunnel is expanded to 4 traffic lanes, should cover at least 24m to backward and 35m forward.

• Journal of Korean Academy of Nursing
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• v.44 no.4
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• pp.398-406
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• 2014

Purpose: This study was done to develop and test the validity and reliability of the Korean version of the Pain Assessment Checklist for Seniors with Limited Ability to Communicate (PACSLAC-K) in assessing pain of elders with dementia living in long-term care facilities. Methods: The PACSLAC-K was developed through forward-backward translation techniques. Survey data were collected from 307 elders with dementia living in 5 long-term care facilities in Korea. Data were analyzed using descriptive statistics, Pearson correlation, Spearman's rho, paired t-test, ROC (receiver operation characteristic) curve with the SPSS/WIN (20.0) program. Results: The PACSLAC-K showed high internal consistency (.90), interrater reliability (.86), intrarater reliability (.93), and high concurrent validity (.74) in paired t-test with PAINAD. Discriminant validity also showed a significant difference compared with no pain. The PACSLAC-K showed a sensitivity of .93, specificity of .88, and Area Under the Curve of .95 in the ROC curve. Conclusion: The findings of this study demonstrate that PACSLAC-K is useful in assessing pain for elders with dementia living in long-term care facilities.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.529-534
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• 2002

유도초음파는 얇은 판재와 다층재료를 평가하는데 널리 사용되는데, 이를 정량적으로 이용하기 위해서는 위상 및 군속도의 분산선도는 필수적이다. 본 연구에서는 후방복사 리키 램파를 이용하여 위상속도 분산곡선과 군속도를 측정하였다. 물에 잠긴 판재에 입사각을 변화 시키면서 판재에서 발생하는 후방복사 초음파 신호를 측정하였고, 후방복사된 초음파 신호는 유도초음파의 분산특성을 지님을 보였다. 입사각도와 수신된 파형의 주파수 분석을 통하여 램파의 위상속도 분산선도를 구하였다. 또한, 특정한 입사각에서 입사점을 변화시키면 서 론 파형의 시간대역 이동으로부터 군속도를 측정하였다.

• Journal of Power Electronics
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• v.10 no.6
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• pp.643-646
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• 2010

An interactive web-based teaching tool for a power semiconductor course at the University of Central Florida is presented in this paper. A novel approach is introduced using Technology Aided Design Tools (TCAD) to generate time-lapsed 2D semiconductor device cross-section embedded in a webpage using $Adobe^{(R)}$ Flash (web design tool) platform to create interactive movies that demonstrate complex device physical phenomenon. Students can step through the interactive movies forward, backward, pausing, or looping. Each step represents a giving bias condition. Current-voltage plots are represented along with the semiconductor device and a visual point is placed on the IV curve to indicate the current bias conditions. The changes are then reflected in the 2D cross-section movie area and the IV plot. This tool was implemented in a classroom setting to augment the lectures or for discovery learning.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.1
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• pp.55-62
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• 2023

Internal erosion is one of the main causes of levee damage and collapse, and representative of this is backward erosion piping. This type of internal erosion accounts for one-third of the damage to levees, meaning it is important to predict and prevent it. In this work, experiments were conducted with the aim of detecting piping in advance by using a tracer. Experiments were undertaken by changing the head difference, soil diameter, and the installation of the cutoff wall. A tracer was injected twice, once at the beginning of the experiment and once after the piping occurred. A key finding was that the piping process significantly affectedthe concentration variation of the tracer in a soil layer. Hence, a tracer concentration curve monitored at downstream could provide information about piping occurrence. It is expected that the results of this study can be used to prevent levee damage and collapse caused by piping.

• The Journal of the Acoustical Society of Korea
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• v.40 no.6
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• pp.555-565
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• 2021

The goal of this study is to improve flow and noise performances of existing backward-curved blade centrifugal fan system used for circulating cold air in a refrigerator freezer by optimally designing airfoil shape. The unique characteristics of the system is to drive cold airflow with two volute tongues in combination with duct system in a back side of a refrigerator without scroll housing generally used in a typical centrifugal fan system. First, flow and noise performances of existing fan system were evaluated experimentally. A P-Q curve was obtained using a fan performance tester in the flow experiment, and noise spectrum was measured in an anechoic chamber in the noise experiment. Then, flow characteristics were numerically analyzed by solving the three-dimensional unsteady Navier-Stokes equations and noise analysis was performed by solving the Ffowcs Williams and Hawkins equation with input from the flow simulation results. The validity of numerical results was confirmed by comparing them with the measured ones. Based on the verified numerical method, blade inlet and outlet angles were optimized for maximum flow rate using the two-factor central composite design of the response surface method. Finally, the flow and noise performances of a prototype manufactured with the optimum design were experimentally evaluated, which showed the improvement in flow and noise performance.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.4
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• pp.753-773
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• 2019

CV(Connected Vehicle) technology provides safety-related services and user convenience-related services to vehicle. Safety-related services can cause privacy problem by continuously transmitting vehicle information to nearby vehicles or base stations. Therefore, safety-related services should provide vehicle anonymity for privacy protection. However, if convenience-related services such as payment services fail to provide vehicle anonymity, driver information related to safety-related services may also be leaked. In this paper, we design a payment protocol based on ECQV(Elliptic Curve Qu-Vanstone) impicit certificate and group signature that provides BU-anonymity and traceability. The proposed payment protocol makes it impossible to track vehicles from payment transactions history by separating roles of payment system components. Moreover, we define the security requirements that the vehicle payment protocol must satisfy and show that the protocol satisfies the requirements.