• 대한토목학회논문집
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• 제31권2C호
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• pp.83-92
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• 2011

암반에서의 탄성계수는 암반의 변형특성을 나타내는 매우 중요한 인자로서 암반에서의 터널굴착으로 인한 내공변위를 파악하는데 이용된다. 그럼에도 불구하고 현재까지는 암석종류 및 절리특성을 반영하여 탄성계수를 산정하는 연구는 미흡한 것으로 판단된다. 따라서, 본 연구는 다양한 암석 및 절리상태에서 암반의 탄성계수를 추정하는 방법과 그 결과를 제시하고자 한다. 이를 위해서 2차원 개별요소법에 근거한 수치해석이 수행될 것이며 이를 통해 암석과 절리상태가 고려된 터널굴착 유발 내공변위가 조사될 것이다. 조사된 변위결과는 암반에서의 원형터널에 대한 탄성이론을 역이용하여 암석종류 및 절리특성이 반영된 탄성계수를 추정하는데 사용될 것이다. 본 연구를 통해 암석종류 및 절리특성을 고려하여 추정된 탄성계수는 향후 실무에서 절리가 형성된 암반터널에서의 발생변위를 파악함에 있어서 그 활용도가 매우 클 것으로 기대된다.

• 한국운동역학회지
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• 제23권2호
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• pp.109-116
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• 2013

The purpose of this study was to provide fundamental information for the enhancement of performance through kinematic analysis of cornering according to the radius of curve course in short track speed skating. To perform this study, six skaters: three narrow radius players(N, body mass: $56.0{\pm}7.2$ kg, height: $163.7{\pm}5.1$ cm, age: $21.3{\pm}1.5$ yrs) and three wide radius players(W, body mass: $61.0{\pm}9.5$ kg, height: $169.0{\pm}4.4$ cm, age: $20.0{\pm}1.7$ yrs). Three-dimensional motion analysis was performed on the section from the forth block starting to show the change of radius to the sixth block using eight infrared cameras(sampling frequency of 100 Hz for N and W players). The time of push-off was greater for N than for W(p<.05) while the radius of center of mass was greater for W than for N(p<.05). The flexion and extension of knee and hip joint were greater for N than for W(p<.05). The external rotation of left knee joint was greater for N than for W(p<.05). Based on the findings, a small radius by increasing the range of the flexion and extension of knee and hip joint with greater external rotation of left knee joint would be related to more efficient run at curve. It is expected that these results will be useful in developing a training program for enhancing performance of short track speed skating athletes.

• Geomechanics and Engineering
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• 제33권1호
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• pp.101-112
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• 2023

When a submerged floating tunnel is connected to the ground, there is a risk of stress concentration at the shore connection owing to the displacement imbalance caused by low confinement pressures in water and high confinement pressures in the ground. Here, the effects of the boundary condition and stiffness of the joints installed at the shore connection on the behaviors of a submerged floating tunnel and its shore connection were analyzed using a numerical method. The analysis results obtained with fixed and ground boundaries were similar due to the high stiffness of the ground boundary. However, the stability of the shore connection was found to be improved with the ground boundary as a small displacement was allowed at the boundary. The effect of the joint stiffness was evaluated by investigating the dynamic behavior of the submerged floating tunnel, the magnitude of the load acting on the bored tunnel, and the stress distribution at the shore connection. A lower joint stiffness was found to correspond to more effective relief of the stress concentration at the shore connection. However, it was confirmed that joints with low stiffness also increase the submerged floating tunnel displacement and decrease the frequency of the dynamic behavior, causing a risk of increased resonance when wave loads with low frequency are applied. Therefore, it is necessary to derive the optimal joint stiffness that can achieve both stress concentration relief and resonance prevention during the design of shore connections to secure their dynamic stability.

• 한국공작기계학회논문집
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• 제16권1호
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• pp.26-32
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• 2007

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform(WFT or STFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform(WT) is used to decompose the acoustic emission(AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.342-348
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• 2005

This study was carried out fusion-welded butt joints in SWS 490A high strength steel subjected to tensile test that load-deflection curve. The windowed or short-time Fourier transform (WFT or SIFT) makes possible for the analysis of non-stationary or transient signals into a joint time-frequency domain and the wavelet transform (WT) is used to decompose the acoustic emission (AE) signal into various discrete series of sequences over different frequency bands. In this paper, for acoustic emission signal analysis to use a continuous wavelet transform, in which the Gabor wavelet base on a Gaussian window function is applied to the time-frequency domain. A wavelet transform is demonstrated and the plots are very powerful in the recognition of the acoustic emission features. As a result, the technique of acoustic emission is ideally suited to study variables which control time and stress dependent fracture or damage process in metallic materials.

• 대한물리의학회지
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• 제13권3호
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• pp.113-120
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• 2018

PURPOSE: This study was conducted to investigate the characteristics of a specific functional shoe in terms of the range of motion (ROM) of ankle and foot joints during walking when compared to a standardized shoe. METHODS: Kinematic ROM data pertaining to ankle, tarsometatarsal, and metatarsophalangeal joints were collected from twenty-six healthy individuals during walking using a ten-camera motion analysis system. Kinematic ROM of each joint in three planes was obtained over ten walking trials consisting of two different shoe conditions. Visual3D motion analysis was finally used to coordinate the kinematic data. All kinematic ROM data were interpolated using a cubic spline algorithm and low-pass filtered with a cutoff frequency of 6 Hz for smoothing. RESULTS: The overall ROM of the ankle joint in the sagittal and coronal planes when wearing the specific functional shoe was significantly decreased in both ankles during walking when compared to wearing a standard shoe (p<.05). Significantly more flexibility was observed when wearing the specific functional shoe in the tarsometatarsal and metatarsophalangeal joints compared to a standard shoe (p<.05). CONCLUSION: Although clinical application of the specific functional shoe has shown clear positive effects on knee and ankle moments, the results of this study provide important background information regarding the kinematic mechanisms of these effects.

• 로봇학회논문지
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• 제6권3호
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• pp.274-283
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• 2011

A simplified linearized dynamic equation for the propulsion force generation of an Ostraciiform fish robot with elastically jointed double caudal fins is derived in this paper. The caudal fin is divided into two segments and connected using an elastic joint. The second part of the caudal fin is actuated passively via the elastic joint connection by the actuation of the first part of it. It is demonstrated that the derived equation can be utilized for the design of effective caudal fins because the equation is given as an explicit form with several physical parameters. A simple Ostraciiform fish robot was designed and fabricated using a microprocessor, a servo motor, and acrylic plastics. Through the experiment with the fish robot, it is demonstrated that the propulsion force generated in the experiment matches well with the proposed equation, and the propulsion speed can be greatly improved using the elastically jointed double fins, improving the average speed more than 80%. Through numerical simulation and frequency domain analysis of the derived dynamic equations, it is concluded that the main reason of the performance improvement is resonance between two parts of the caudal fins.

• 한국수자원학회논문집
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• 제50권11호
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• pp.745-758
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• 2017

Copula 함수 기반의 모형들은 가뭄빈도해석 및 수문시계열분석 등 수문학적 모델링을 위해 다각적으로 활용되고 있다. 그러나 기존 연구에서는 Copula 함수 및 주변확률분포 매개변수에 대한 불확실성을 정량적으로 평가할 수 있는 모형의 개발 사례는 국내외적으로 미진한 실정이다. 이러한 점에서 본 연구에서는 기존 Copula 모형에 Bayesian 기법을 도입하여 매개변수의 불확실성을 평가할 수 있는 이변량 가뭄빈도해석 기법을 개발하였다. 본 연구에서는 우선적으로 모의자료를 대상으로 모형의 적합성을 평가하였으며, 모형 적용결과 가정한 매개변수를 정확하게 재추정하는 것을 확인할 수 있다. 최종적으로 기 개발된 Bayesian Copula 함수 기반의 이변량 가뭄빈도해석 모형을 한강유역에 적용하여 최근 2013~2015년에 가뭄 사상을 평가하였다. 서울, 경기 및 강원 지역에서 특히 가뭄이 심한 것으로 나타났으며, 대부분의 지역에서 결합재현기간이 100년을 상회하는 것으로 평가되었다. 본 연구를 통해 제안된 모형의 검증과정과 도출된 결과를 기준으로 판단해보면 가뭄자료의 분포특성 및 자료간의 상관성을 효과적으로 재현하는데 유리할 뿐만 아니라 매개변수의 불확실성을 평가할 수 있는 장점을 확인할 수 있었다.

• ETRI Journal
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• 제26권6호
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• pp.622-634
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• 2004

In this paper, we discuss the design problem and the robustness of space-frequency trellis codes (SFTCs) for multiple input multiple output, orthogonal frequency division multiplexing (MIMO-OFDM) systems. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with the regular correlation function of the number and time delay of the multipaths. By introducing the first-order auto-regressive model, we decompose the correlated fading channel into two independent components: a slow fading channel and a fast fading channel. Therefore, the design problem of SFTCs is converted into the joint design in both slow fading and fast fading channels. We present an improved design criterion for SFTCs. We also show that the SFTCs designed according to our criterion are robust against the multipath time delays. Simulation results are provided to confirm our theoretic analysis.

• 대한기계학회논문집A
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• 제40권5호
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• pp.483-488
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• 2016

플러그인 디지털 프레임웍은 계의 구성요소가 블랙박스 형태로 구성되어 있을 때 계의 응답을 해석하는 도구이다. 일반적으로 구성요소를 연결하는 동역학계의 연결부는 계의 응답에 크게 영향을 미치게 되고, 많은 경우 연결부의 특성은 변위와 주파수에 따라 달라지는 특성을 보인다. 그러므로 연결부의 특성에 대한 민감도의 계산은 전역적으로 수행되어야 한다. 본 연구에서는 플러그인 디지털 프레임웍에서 연결부의 전역민감도를 계산하는 방법을 주파수응답함수 기반의 부분구조합성법을 기반으로 제시한다. 일차 전역민감도는 무작위균형설계법을 이용하여 적은 수의 샘플링으로 각 인자영향을 계산할 수 있다. 이 방법은 승용차의 실내소음에 대한 각 연결부 강성의 민감도를 계산하는 예에 적용함으로써 그 효용성을 검증하였다.