• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.146-151
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• 2011

A method to evaluate and to reduce the source- and receiver- consistent noise in a cross-well travel time data was proposed. These systematic noises, which can cause some serious effects on the result of a travel time tomography, can be considered as the source and receiver statics. The method evaluates the statics through a curve-fitting of the first arrival travel times in the common source and common receiver gathers. Feasibility study was conducted on a synthetic data which simulates the cross-well travel time tomography to detect a small scale tunnel in a uniform background medium. First arrival travel times at a given source and receiver points are computed by a raytracing method, and the source consistent- and receiver consistent noises are added to the record. In case of the added noise with rms amounting to 25% of the maximum expected anomalous travel time delays, it is confirmed that the method successfully extracted the noise at the 7th step of iteration.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1063-1075
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• 2013

The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the degree of saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the degree of saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from $20^{\circ}C$ to $-10^{\circ}C$, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the degree of saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of $0^{\circ}C$. This study renders the basic information of elastic waves in frozen soils according the degree of saturation.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10c
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• pp.600-602
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• 1998

본 논문은 정면과 측면 얼굴 이미지의 특성을 살린 3차원 개인 아바타 합성에 관한 연구이다. 표준 얼굴 메쉬를 얼굴 이미지의 특징점에 맞추려는 힘을 특징점 이외의 점들까지의 거리에 대한 가우스 분포를 따라 부드럽게 전달시켜 매쉬를 탄성있게 변형하는 힘으로 작용시켜 메쉬를 얼굴 이미지의 윤곽선을 중심으로 매칭시키고, 매칭된 메쉬가 매칭 이전의 메쉬의 기하학적 특성을 유지할 수 있도록 메쉬에 동적 피부 모델을 적용한다. 이렇게 생성한 3차원 메쉬에 이미지를 텍스춰 매핑하여 개인 특성을 살린 3차원 개인 아바타를 생성한다.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• v.11 no.2
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• pp.406-413
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• 2006

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.689-697
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• 2002

The dynamic loads and load-point displacements of concrete three-point bend (TPB) specimens had been measured. The average crack velocities measured with strain gages were 0.16 ㎜/sec ∼ 66 m/sec. The fracture energy for crack extension was determined from the difference of the kinetic energy for the load-point velocity and the strain energy without permanent deformation from the measure external work. For all crack velocities, there were micro-cracking for 23 ㎜ crack extension, stable cracking for 61 ㎜ crack extension at the maximum strain energy, and then unstable cracking. The unstable crack extension was arrested at 80 ㎜ crack extension except the tests of 66 m/sec crack velocity. The tests less than 13 ㎜/sec crack velocity and faster than 1.9 m/sec showed static and dynamic fracture behaviors, respectively. In spite of much difference of the load and load-point displacement relations for the crack velocities, the crack velocities of dynamic tests did not affect on fracture energy rate during the stable crack extension due to the reciprocal action of kinetic force, crack extension and strain energy. During stable crack extension, the maximum fracture resistances of the dynamic tests was 147％ larger than that of the static tests.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.6
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• pp.455-462
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• 2013

The effects of earthquakes can be devastating especially to existing structures that are not based on earthquake resistant design. This study proposes a steel grid shear wall that can provide a sufficient lateral resistance and can be used as a seismic retrofit method. The pushover analysis was performed on RC structure with and without the proposed steel grid shear wall. Obtain the performance point that the target structure for seismic loads applied to evaluate the response and performance levels. The capacity spectrum at performance point is nearly elastic range, so satisfied the performance objectives(LS level). And response modification factor(R factor) were calculated from the pushover analysis. The R factor approach is currently implemented to reflect inelastic ductile behavior of the structures and to reduce elastic spectral demands from earthquakes to the design level. The R factor increases from 2.17 to 3.25 was higher than the design criteria. As a result, according to reinforcement by steel grid shear wall, strength, stiffness, and ductility of the low-rise RC structure has been appropriately improved.

• The Journal of Engineering Geology
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• v.11 no.2
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• pp.163-174
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• 2001

For quantitative evaluation of geotechnical engineering properties such as rippability and diggability, clear interpretation on the subsUJiace velocity structures should be preceded by figuring out top soil, weathered and soft rock layers, shape of basement, fracture zones, geologic boundary and etC. from the seismic refraction data. It is very important to set up suitable field parameters, which are the configuration of profile and its length, spacings of geophones and sources and topographic conditions, for increasing field data Quality. Geophone spacing of 3 to 5m is reconunended in the land slope area of house land development site. In refraction tomography technique, the number of source points should be more than a Cluarter of available channel number of instrument and the subsurface structure interpretation can be decreased the artifact of inversion by topographic effect. Compared with core logging data, it is shown that the velocity range of the soil is less than 700m/s, weathered rock 700~1,200m/s, soft rock 1,200~1,800m/s on the velocity tomogram section. And the upper limit of P-wave velocity for rippability is estimated 1,200 to 1,800m/s in land slope area of gneiss.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.2
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• pp.69-80
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• 2008

In this study, improved capacity spectrum method (CSM) is proposed. The method can account for higher mode contribution to the seismic response of MDOF systems. The CSM has been conveniently used for determining maximum roof displacement using both demand spectrum and capacity curve of equivalent SDOF system. Unlike the conventional CSM, the maximum roof displacement is determined without iteration using inelastic displacement ratio and R factor calculated from demand spectrum and capacity curve. Three moment resisting steel frames of 3-, 9- and 20-stories are considered to test the accuracy of the proposed method. Nonlinear response history analysis (NL-RHA) for three frames is also conducted, which is considered as an exact solution. SAC LA 10/50 and 2/50 sets of ground motions are used. Moreover, this study estimates maximum story drift ratios (IDR) using ATC-40 CSM and N2-method and compared with those from the proposed method and NL-RHA. It shows that the proposed CSM estimates the maximum IDR accurately better than the previous methods.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.2
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• pp.101-106
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• 2007

The optical performance of the mirror for satellite camera is highly dependent on the adhesive properties between the mirror and its support. Therefore, in order to design a mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this paper, the mechanical properties of three kinds of space adhesives are studied. Elastic moduli of the adhesives are determined by tensile tests. Stress-strain relation is obtained by using exponential curve fitting for the adhesive which shows non-linear behavior. In case of the linear behavior material, elastic modulus is calculated through linear curve fitting. For the tensile tests, several points have been selected in the operating temperature range of the adhesive. The elastic modulus of each adhesive is expressed as a function of temperature. Characteristics of the adhesives are discussed regarding their temperature sensitivity.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.40-40
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• 2011

현재 일반적으로 활용되고 있는 원통형 쉘구조로 이루어진 타워구조의 대형화가 추진되면서 제작, 운반 편의성, 단면효율성, 경제성 제고를 위해 다각형단면 기둥구조물의 활용이 대두되고 있다. 하지만 다각형 단면 기둥구조의 극한강도에 대한 자료가 충분치 않고 관련 기준이나 지침이 명확히 제시되고 있지 않은 실정이다. 본 연구에서는 원통형 쉘구조물을 다각형구조물로 대체하여 제작될 경우 축방향 압축에 대한 내하력 향상 효과를 수치해석적으로 검토해 보고자 한다. 해석모델은 지름 2m, 두께 20mm인 원형강관 프로토타입 풍력타워 구조를 참고로 하여 이에 내접하도록 결정한 6~12각형 단면 형상으로써 높이 10,000mm인 3차원 기둥모델을 구현하였고 유한요소프로그램인 ABAQUS를 이용하여 해석하였다. 각 subpanel의 중앙에 종방향 보강재를 설치하였을 때 국부좌굴에 대한 내하력 변화를 비교하기 위해 종방향보강재로 보강한 모델을 구성하여 비교 해석을 수행하였다. 종방향 보강재의 제원은 미국 SSRC 제안식을 기준으로 삼았다. 탄성좌굴해석을 통해 탄성좌굴모드 형상을, 비선형비탄성해석을 통해 최종파괴모드 및 극한강도를 얻었다. 보강 전 후의 탄성좌굴 해석 결과로부터 최소모드의 고유치 값을 비교하였다. 각 subpanel 단면 중심부에 한 개의 보강재를 설치한 경우 탄성좌굴강도가 4배 가량 증가하였다. 이로부터, 보강재(n=1) 설치에 따라 유효 폭두께비가 1/2로 감소하는 효과를 확인 할 수 있다. 비선형해석결과로부터 subpanel의 단면중심에 보강재를 설치한 경우 보강재가 위치한 곳에 고정점이 형성되어 이를 중심으로 국부 좌굴모드에 변화가 생기는 것이 확인되었다. 이러한 변화는 다각형 단면 기둥구조의 내하력 성능, 즉 국부좌굴강도에 영향을 준다. 충분한 강성을 갖는 종방향 보강재가 설치된 경우, 극한상태에서도 유효폭두께비가 줄어드는 것과 같은 강도 향상 효과를 확인할 수 있다. 이러한 사실은 각 해석결과 극한강도를 DIN code, Migita와 Fukumoto의 제안식, SSRC 설계제안식 등과의 비교를 통해 확인할 수 있었다.