Earticle

Concrete cracks are early indicators of material performance degradation and defects, and concrete crack monitoring is an important technique that helps to reduce maintenance costs and improve the performance and safety of concrete structures. Existing techniques, including visual inspection, are based on the surface crack images or ultrasonic velocity differences and have limitations to find internal cracks (e.g., concrete delamination and flexural cracks). Therefore, in this study, a detection system was developed using wave attenuation of guided waves for detecting concrete internal cracks. The system was verified through finite element analysis and crack exploration experiments in concrete hume pipes. The surface cracks showed more wave energy attenuation than the internal cracks since the surface waves transmit higher energy than the body waves resulting in more energy reflection and scattering. On the other hand, in the case of internal cracks. As a result, it showed sufficient sensitivity to detect both surface and internal cracks and can be developed into a crack evaluation system with a damage index in the future.

This article uses radiosonde data of balloons in Hanoi to determine the radio refractive index and the conditions of radio wave propagation in the atmosphere. The research results in the three years 2016?2018 show the highest average radio refractivity, the maximum radio refractivity difference between the years. Secondly, radiosonde data are used to estimate the accuracy of global ITU models, and showed that the radio refractivity’s difference between the ITU-R model and the observed value by radiosonde method is up to 60 N-units at a lower altitude of atmosphere. In conclusion, it is recommended to use radiosonde data instead of the ITU model (where available) to obtain refractive index when studying wave propagation conditions in the atmosphere.

이 연구에서는 P파 속도와 밀도를 고려한 음향파 파동 전파 모델링을 위한 고차 셀 기반 유한 차분법을 제안하였다. 셀 기반 유한 차분법을 사용하면 불연속적인 매질 특성을 직접 미분하지 않고도파동 전파를 모델링할 수 있다. 그러나 기존의 2차 차분식을 사용하는 셀 기반 유한 차분법에서는정확한 결과를 얻기 위해 파장당 격자수가 커야 한다는 한계가 있었다. 이 연구에서는 임의의 고차차분식을 사용할 수 있도록 기존 기법을 개선하였다. 수치 예제에서 해석해와의 비교를 통해 고차셀 기반 유한 차분법을 이용하면 파장당 격자수가 작아도 정확한 결과를 얻을 수 있음을 보였다.

We propose high-order finite-difference methods for acoustic wave propagation modeling considering the P-wave velocity and density. We can simulate wave propagation without directly differentiating discontinuous medium parameters using the cell-based finite-difference method. However, a limitation of the conventional cell-based finite-difference method using the second-order scheme is that it requires a large number of grids per wavelength to obtain an accurate result. We improve the conventional cell-based method to exploit arbitrary high-order schemes. In a numerical example, we compare results of the proposed methods with that of the analytic solution, and show that we can obtain accurate results with small number of grids per wavelength using the high-order cell-based methods.

본 연구에서는 3차원 시간 영역 파동 전파 모델링을 이용하여 고성능 라이브러리를 이용한 파이썬과 C언어 의 성능 및 생산성을 비교하였다. 수치 모델링 결과 고성능 파이썬 라이브러리인 Numba 또는 Cython을 사용하는 경 우와 C 언어를 사용하는 경우 순수 파이썬에 비해 각각 1844배, 2049배, 2305배 빨라졌다. Numba와 Cython 라이브러 리를 사용한 모델링의 경우 C언어보다 각각 23.3%, 16.2% 느렸다. 그러나 소스 코드 줄 수는 C언어보다 각각 45.1%, 40.7% 적었다. SEG/EAGE 3차원 암염돔 모델에 적용한 결과, Numba와 Cython을 사용한 경우 C언어에 비해 계산 속 도가 각각 22.9%, 13.3% 느렸다. 따라서 20%의 성능 차이를 받아들일 수 있는 경우 C와 같은 정적 자료형 언어 대신 고성능 파이썬 라이브러리를 이용하는 것이 더욱 생산적일 것이다.

In this study, we compared performance and productivity of C and Python with high-performance libraries using 3D time-domain wave propagation modeling. As a result of numerical modeling, Numba, Cython and C attained speed-ups of 1884, 2049, and 2305 times, respectively, compared with a reference Python implementation. Python programs using Numba and Cython were slower than the C program by 23.3% and 16.2%, respectively. However, the numbers of source code lines for Python programs using Numba and Cython were 45.1% and 40.7% shorter than that of C, respectively. Modeling experiments using Numba and Cython for the SEG/EAGE 3D salt dome model were 22.9% and 13.3% slower than that of the C program. Therefore, if performance difference of 20% is acceptable, it will be more productive to use Python with high-performance libraries instead of static-typing languages such as C.

In order to achive effective system for wirless communication in tunnel, research on wave propagation in tunnel was accomplished.

본 논문에서는 3차원 광선추적 기법을 이용한 실내 환경에서의 전파특성 분석을 위한 3D 시뮬레이터를 이용 한 분석 결과를 제시하였다. 지금까지 소개된 대부분의 전파특성 분석 결과들은 2차원 평면에서 거리에 따른 신호의 손실(Path Loss) 위주로 연구가 진행 되었다. 본 연구에서는 실내에서 전파특성을 분석하기 위해 다양한 ITU 모델을 사용하여 입체구조의 실내 환경에서 전파의 수신신호의 세기에 대한 분석을 수행하였다. 본 연구에서 개발된 시뮬레 이터를 이용해 150MHz와 2GHz대역의 손실 특성이 비교 되었고 예상한 결과를 얻을 수 있었다. 그리고 각 수신기의 위치에서 수신 신호는 전파경로상의 벽면에서 손실되는 전력에 따라 차이가 생기기 때문에 송신기의 출력이 중요한 요인으로 분석되었다.

In this study, we present the investigation results using a 3D radio wave propagation simulator in indoor environments. Previous studies treat only the path loss between the transmitter and receiver in 2D geometry. We provide the simulation results of indoor propagation prediction based on various ITU-R Recommendations. Simulation results compared here indicate that 150MHz and 2GHz frequency bands give quite different characteristics in presented indoor geometry. Since the field intensity is affected by the loss at the wall, the transmitting power level is one of the key factor for receiving power.

본 논문에서는 실내 환경에서 전파특성 분석에 유용한 마이크로 셀용 3D 시뮬레이터를 제시하였다. 지금까지 소개된 대부분의 전파특성 분석 결과들은 2차원 평면에서 거리에 따른 신호의 손실(Path Loss) 위주로 연구가 진행 되었다. 본 연구에서는 실내에서 전파특성을 분석하기 위해 다양한 ITU 모델을 사용하여 입체구조의 실내 환경에서 전파의 수신신호의 세기에 대한 분석을 수행하였다. 시뮬레이션에서 나타난 결과를 분석해보면 저 주파수(150MHz-400MHz) 대역과 고주파수 대역(2GHz-6GHz) 에서 전파특성이 많은 차이를 나타내고 있다. 그리고 각 수신기의 위치에서 수신 신호는 전파경로상의 벽면에서 손실되는 전력에 따라 차이가 생기기 때문에 송신기의 출력도 중요한 요인으로 분석되었다.

In this study, we introduce a 3D micro-cell simulator for radio wave propagation analysis in indoor environments. Previous studies treat only the path loss between the transmitter and receiver in 2D geometry. We provide the simulation results of indoor propagation prediction based on various ITU-R Recommendations. Simulation results described here indicate that the low and high frequency bands give quite different characteristics in presented indoor geometry. The propagation loss as a function of distance has two distinct regions. It is similar to that occurring in free space within 5–20m of the transmitter, however, increases significantly as the electromagnetic waves become obstructed by the walls at distances further away in the next region.

The main purpose of this study is to develope a dry-contact geophone sensing device that improves sensor coupling to structural members during elastic wave measurements without a need of coupling materials. Test results in the laboratory showed that the signal-to-noise ratio (SNR) of typical signals from the proposed sensing devise was about 48dB, which was comparable to that of a commercially available integrated circuit piezoelectric (ICP) accelerometer. Furthermore, the value was about 35 dB improved than using a conventional geophone using vacuum grease as a couplant material. In addition, typical signals from the proposed sensing devise had excellent coherence (about 99.6%) to the values from an ICP accelerometer, which was about 10% improved than using a conventional geophone. In addition, when applied to impulse response and multichannel analysis of surface waves, the proposed sensing devise resulted in equivalent or improved accuracy compared to the two conventional sensors and significantly improved test speed.

The sample researches the broadcasting power of empire Japan which boils the fact that in the goal. Drew the shape of the broadcasting power which becomes known from network formation process inside of namely empire Japan and, the radio wave’ propagation led and to observe features radio broadcast as the sending person of cultural shaking tried. Specially the cultural power the political events which confirm the overwhelming power of broadcasting, cultural (Berlin Olympic) makes the real value of radio broadcast confirm from event inside. The concept which is a cultural power the entity which is concrete is visible in the eye knows at is symbolic appears from culture and line of authority (Image) with to be bitter the person and the person, the group and the group, operates from the nation and national etc. various territory. By the way cultural power accommodating the masses is logical or refuses the reaction which is scientific and wants unconscious accommodating. The means of accommodating which is natural consequently rightly is to be a cultural medium. The electric wave of political event of domestic propagation trust of political power and believing in the citizens, as the zoom to do to make plant notification makes a political national ceremony, the electric wave of sports relay broadcasting propagation the citizen of empire Japan becoming, to stamp culturally. The citizen the manifestation of natural national ceremony is to be a state which the cultural power prefers most. In order to complete like this intention the cultural power of empire Japan broadcasting system (Media System) thoroughly, intervened. To the inside of course with intention of broadcasting power planning was entering.

본 논문에서는 SHA-3 프로젝트 현황을 살펴보고 SHA-3 2 라운드에 선정된 알고리즘들을 공격 형태, 안전성 분석 결과, 전체 구조 유형별로 분류한다. 또한, 국내 표준 해쉬 함수인 HAS-160 과 구현 효율성을 비교하여 해쉬 함수의 객관적인 비교 지표로 활용할 수 있도록 한다.

The shortest routing problem is the key to the efficiency of routing in Wireless Sensor Network .This paper aimed at the problem of no obtaining the real-time shortest routing and the poor adaptability of the large-scale wireless sensor network, which is caused by considering adequately the network topology in those present shortest routing algorithms, simulating water diffusion, puts forward a shortest route algorithm of WSN. In the diffusion process, water waves gradually expand to the surrounding, and iterate over all the area, the region is treated as the network which consists of a large number of nodes and arcs. The algorithm simulates the spread of the wave movement through multiply operation, and emulates the single coverage of water wave through die operation, then simulates the motion law of the real water wave using the substitution operation, it can avoid the dead diffusion zone by overlapping operation, achieve full traversal and determine the shortest route according to the arrived wave information of each node recorded in a shortest period of time. Meanwhile, the algorithm's time complexity and space complexity are analyzed in the paper, and concluded that the time complexity of the algorithm is linear change along with the square of the node number, the space complexity is linear change along with the node number in the worst case. Experiments show that the performance of the algorithm is superior to existing shortest route algorithms in most application cases.

Tire noise is a major noise source at high speeds. One of the noise source is controlled by pattern and structure. Pattern noise is effected by the shape of tread. And the bending stiffness of tire is influenced to the resonance of tire‘s belt. But in high frequency region, FEA is not appropriated with application. So this paper discusses about wave propagation of tire. There has been much effort to verify the flexural wave velocity with structure design specification.

The objective of this study is to observe and optimize a typical ocean environment and reduce wave reflections in the wave flume. In order to generate ocean waves in the wave flume, a combination of a horizontal piston type wave generator and wave absorbers was installed in the channel. Two probes for measuring the wave heights, i.e., wave level gauges, were used to record the continuous variation of the wave surface, the phase difference, and the maximum (crest) and minimum (trough) points of the propagating waves. In order to optimize the shape and size of the propagating waves, several absorption methods were proposed. Apart from an active wave absorption method, we used methods that involved vertical porous plates, horizontal punching plates, and sloping-wall-type wave absorbers. To obtain the best propagating waves, a sloping-wall-type wave absorber was chosen and tested in terms of the constitutive filling materials and the location and shape of the plate. This study also focused on the theoretical prediction of the wave surface, separating them into the incident and reflective components. From the results, it is evident that the wave absorber comprising a hard filling material exhibits a better performance than the absorber comprising a soft material, i.e., the wave absorber can be a strong sink to control the energy of the incoming wave. In addition, larger wave absorbers correspond to lower reflectance because a larger volume can reduce the incoming wave energy. Therefore, at constant absorber conditions, the reflectance of the wave increases as the wave period increases. Finally, the reflectance of the wave was controlled to be less than 0.1 in this study so that the wave flume can be used to simulate an offshore environment.

As a new technical approach, wave energy converter by using vertical motion of water in the multiple water chambers were developed to realize actual wave power generation as eco-environmental renewable energy. And practical use of wave energy converter was actually to require the following conditions: (1) setting up of the relevant device and its application to wave power generation in case that severe wave loading is avoided; (2) workability in installation and maintenance operations; (3) high energy conversion potential; and (4) low cost. In this system, neither the wall(s) of the chambers nor the energy conversion device(s) are exposed to the impulsive load due to water wave. Also since this system is profitable when set along the jetty or along a long floating body, installation and maintenance are done without difficulty and the cost is reduced. In this paper, we describe the system which consists of a float, a shaft connected with another shaft, a rack and pinion arrangement, a ratchet mechanism, and rotary type generator(s). Then, we present the dynamics model for evaluating the output electric power, and the results of numerical calculation including the effect of the phase shift of up/down motion of the water in the array of water chambers aligned along the direction of wave propagation.

보강재를 가진 평판 구조로 이루어진 많은 구조물의 진동 현상을 해석하기 위해서는 평판 요소에 대한 진동 특성을 이해하는 것이 필요하다. 이 연구에서는 폭이 유한하고 길이가 무한한 띠 평판의 진동 특성을 이론 해석과 수치 해석을 통해 알아보고자 한다. 수치 해석 기법으로는 단면의 형상이 길이 방향으로 일정한 도파관 구조물의 진동 해석에 효과적인 도파관유한요소법(waveguide finite element method)을 사용한다. 도파관유한요소법은 구조물의 2차원 단면만을 유한요소 모델링하고, 길이 방향으로는 파동이 조화 진동하면서 전파한다고 가정한다. 이 논문에서는 먼저 띠 평판의 분산 선도와 가진점 모빌리티에 대한 수치 해석 결과를 이론 해석 결과와 비교하여 수치 해법의 타당성을 검증한다. 그리고 수치 해석을 이용해 보강재가 부착된 평판에 대한 분산 선도와 가진점 모빌리티를 구하고, 보강재가 띠 평판의 파동 전파 및 진동에 미치는 영향을 검토한다. 마지막으로 보강재가 부착된 이중 평판(double plate)에 대해 분산 선도를 구하고, 이로부터 파동 전파 특성을 살펴본다.

It is important to understand the vibrating behavior of plate structures for its many engineering applications. In this study, the vibration characteristics of strip plates that have finite width and infinite length are investigated theoretically and numerically. The waveguide finite element(WFE) approach, which is an effective tool for studying waveguide structures, is used in this study. The WFE method requires only a cross-sectional finite element model, and uses theoretical harmonic solutions to assess wave propagation along the longitudinal direction. First, WFE results for a simple strip plate are compared with the theoretical results(i.e., dispersion diagrams and point mobilities) to validate the numerical model. Then, in the numerical analysis, different numbers of longitudinal stiffeners are included in the plate model to investigate the effects of stiffeners in terms of the dispersion curves and mobilities. Finally, the dispersion curves of a stiffened double plate are obtained to examine the characteristics of its wave propagation.

콘크리트 포장의 품질관리 항목 중에서 압축 강도는 매우 중요한 인자로 여겨져 왔다. 압축 강도 값을 얻기 위해 현장에서 코아를 채취하여 이를 품질관리의 기준으로 사용하였다. 그렇지만, 코아를 채취하는 것은 많은 인력과 시간을 필요로 하며 실제로 현장의 품질관리를 정확히 추정하는데 많은 어려움이 있다. 또한 포장의 설계 방법도 탄성계수에 근거한 역학적-경험적 방법이 도입되고 있다. 이러한 현장의 품질관리 문제점을 해결하고, 포장설계와의 연계를 위해 비파괴 실험방법이 도입되고 있다. 다양한 비파괴 실험 방법 중에서 이론적으로 탄성계수를 추정할 수 있는 방법은 Wave Propagation방법이므로 본 연구에서는 Wave Propagation 방법을 도입하였다. 본 연구에서는 현장의 품질관리를 수행하는 방법 중의 일환으로 실내에서 제작한시편의 압축 강도와 비파괴 방법으로 얻은 탄성 계수와의 상관성을 검토하였으며, 비파괴 방법으로 얻은 탄성 계수로부터 압축 강도를 추정 할 때 배합별 특성에 대한 분석을 실시하였다. 비파괴 실험에서 구한 탄성계수와 압축강도와의 상관성은 매우 우수한 것으로 판명되었으며, 골재의 종류별로 상관성이 서로 상이하게 나타남을 알 수 있었다.

For many years, the compressive strength of concrete has been regarded as an important index in determining concrete pavement quality. The compressive strength of the sample cores from the field has been used as quality index of concrete pavement. However, this process is time consuming and requires a lot of labor. Recently, the M-E Design Methodology in the pavement design based on the elastic modulus has been adopted. Therefore, several NDT methodologies have been adopted for QA/QC in the field and for the pavement design. Among various NDT methods, the wave propagation method can be used to measure the elastic modulus of concrete because the wave velocity is directly related to the elastic modulus. Therefore, in this study the wave propagation method was used for estimating the concrete modulus. The relationship between the compressive strength measured in he laboratory and the elastic modulus measured by the wave propagation method was analyzed, and the compressive strength was estimated from the elastic modulus for various mix types. The results showed that the relationship between the elastic modulus and the compressive strength was observed and the relationship varied depending on the aggregate types.

Transient acoustic and elastic wave propagation in inhomogeneous media are studied by using the Fourier method. It is known that the fourier method has advantages in memory requirements and computing speed over conventional methods such as FDM and FEM, because the Fourier method needs less grid points for achieving the same accuracy. To verify the proposed numerical scheme, several examples having analytic solutions are considered, where two different semi-infinite media are in contact along a plane boundary. The comparisons of numerical results by the Fourier method and analytic solutions show good agreements. In addition, the fourier method is applied to a layered half-plane, in which an elastic semi-infinite medium is covered by an elastic layer of finite thickness. It is showed how to derive the analytic solutions by using the Cagniard-de Hoop method. The numerical solutions are in excellent agreements with analytic results.