• Smart Structures and Systems
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• 제22권4호
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• pp.481-493
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• 2018

Ultrasonic guided waves have attracted increasing attention for non-destructive testing (NDT) and structural health monitoring (SHM) of bridge cables. They offer advantages like single measurement, wide coverage of acoustical field, and long-range propagation capability. To design defect detection systems, it is essential to understand how guided waves propagate in cables and how to select the optimal excitation frequency and mode. However, certain cable characteristics such as multiple wires, anchorage, and polyethylene (PE) sheath increase the complexity in analyzing the guided wave propagation. In this study, guided wave modes for multi-wire bridge cables are identified by using a semi-analytical finite element (SAFE) technique to obtain relevant dispersion curves. Numerical results indicated that the number of guided wave modes increases, the length of the flat region with a low frequency of L(0,1) mode becomes shorter, and the cutoff frequency for high order longitudinal wave modes becomes lower, as the number of steel wires in a cable increases. These findings were used in design of transducers for defect detection and selection of the optimal wave mode and frequency for subsequent experiments. A magnetostrictive transducer system was used to excite and detect the guided waves. The applicability of the proposed approach for detecting and locating wire breakages was demonstrated for a cable with 37 wires. The present ultrasonic guided wave method has been found to be very responsive to the number of brokenwires and is thus capable of detecting defects with varying sizes.

• Korean Chemical Engineering Research
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• 제59권3호
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• pp.359-365
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• 2021

본 연구에서는 분진의 착화 특성 및 정전기 위험성 평가법을 실험적으로 조사하였다. 착화에너지 시험은 PE(HD), PE(LD), PMMA 분진에 대해 MIKE-3장치를 사용하여 실시하였다. PE (HD)의 경우 약 8 ms의 일정 시간 경과 후에 분진운의 착화 화염이 형성되고, 착화원 중심부에서는 화염 핵이 관찰되지 않았다. 분진의 분산 횟수가 증가함에 따라 정전압이 증가하고 분진 농도에 따른 정전압 발생 증가율은 PMMA, PE(LD), PE (HD) 순으로 가장 높았다. PE(HD) 분진의 분산 조건이 정전압에 미치는 영향을 조사하였으며, 분산 횟수가 많아질수록 정전압이 증가하였고 동일한 분산 횟수에서는 분진 농도가 높아질수록 정전압이 증가하였다. 정전기 착화에 의한 화재폭발사고 예방을 위한 안전 정전압은 PE(HD), PE(LD)-1, PE(LD)-2, PMMA에 있어서 각각 2.58, 44.72, 25.82, 8.16 kV로 추정되었다. 정전압 측정자료를 사용하여 정전기 착화 위험성을 효율적으로 조사하여 최소착화에너지를 추정하는 방법을 제안하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.97-106
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• 2004

Stability of laminar premixed planar flames inclined in gravitational field which generate vorticity is asymptotically examined. The flame structure is resolved by a large activation energy asymptotics and a long wave approximation. The coupling between hydrodynamics and diffusion processes is included and near-unity Lewis number is assumed. The results show that as the flame is more inclined from the horizontal plane it becomes more unstable due to not only the decrease of stabilizing effect of gravity but also the increase of destabilizing effect of rotational flow. The obtained dispersion relation involves the Prandtl number and shows the destabilizing effect of viscosity. The analysis predicts that the phase velocity of unstable flame wave depends on not only the flame angle but also the Lewis number. For relatively short wave disturbances, still much larger than flame thickness, the most unstable wavelength is nearly independent on the flame angle and the flame can be stabilized by gravity and diffusion mechanism.

• 한국연소학회지
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• 제9권4호
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• pp.9-21
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• 2004

Stability of laminar premixed planar flames inclined in the gravitational field is asymptotically examined. The flame structure is resolved by a large activation energy asymptotics and a long wave approximation. The coupling between hydrodynamics and diffusion processes is included and near-unity Lewis number is assumed. The results show that as the flame is more inclined from the horizontal plane it becomes more unstable due to not only the decrease of stabilizing effect of gravity but also the increase of destabilizing effect of rotational flow. The obtained dispersion relation involves the Prandtl number and shows the destabilizing effect of viscosity. The analysis predicts that the phase velocity of unstable flame wave depends on not only the flame angle but also the Lewis number. For relatively short wave disturbances, still much larger than flame thickness, the most unstable wavelength is nearly independent on the flame angle and the flame can be stabilized by gravity and diffusion mechanism.

• 한국안전학회지
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• 제30권2호
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• pp.70-76
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• 2015

This study deals with the traffic accident of circular intersections. The purpose of the study is to develop the accident models by traffic violation type. In pursuing the above, this study gives particular attention to analyzing various factors that influence traffic accident and developing such the optimal models as Poisson and Negative binomial regression models. The main results are the followings. First, 4 negative binomial models which were statistically significant were developed. This was because the over-dispersion coefficients had a value greater than 1.96. Second, the common variables in these models were not adopted. The specific variables by model were analyzed to be traffic volume, conflicting ratio, number of circulatory lane, width of circulatory lane, number of traffic island by access road, number of reduction facility, feature of central island and crosswalk.

• 천문학회지
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• 제42권5호
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• pp.107-123
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• 2009

We investigate the wave properties for isothermal plasma state around to the de Sitter black hole's horizon using 3+1 split of spacetime. The corresponding Fourier analyzed perturbed perfect GRMHD equations are used to obtain the complex dispersion relations. We obtain the real values of the wave number k, from these relations, which are used to evaluate the quantities like phase and group velocities etc. These have been analyzed graphically in the neighborhood of the horizon.

• 한국미생물생명공학회:학술대회논문집
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• 한국미생물생명공학회 1978년도 추계학술대회
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• pp.206.1-206
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• 1978

발효공업에 있어서 오염에 영향을 주는 미생물의 열살균 속도를 $120~130^{\circ}C$ 범위에서 조사하였다. 살균속도에 대한 온도의 영향은 Arrhenius식으로 다음과 같이 표시되었다. K=3.47$\times$$10^{28}$ EXP(-52.3 Kcal/RT)원형 반응기의 비이상혼합효과를 보기 위하여 난류영역에서 methylene blue 용액을 사용하여 계단압력을 주어 그 과도응답을 측정한 결과 체류시간 분포는 dispersion 모형에 잘 부합되었고 peclet number 100 을 얻었다. 당밀을 열분해시키면 hydroxymethl furfural이 생성되는 것을 확인하였고 온도와 pH에 따라 검토한 결과 고온의 산성용액에서 반응은 촉진되었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.491-492
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• 2009

이 논문에서는 이미지 프로세싱 기법을 이용하여 ECC 배합에 따라 섬유 분산성, 단위 면적당 섬유 개수, 섬유 방향성을 평가하고, 이 결과로 섬유 가교 응력을 예측한 결과를 제시하고자 한다.

• 환경영향평가
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• 제22권6호
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• pp.547-556
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• 2013

Recently, golf courses have increased over the years because golf became popular leisure sport. Various environmental problems have been then issued by a golf course during constructing and running them. A problem of pesticide, which is serious among various environmental problems, from golf course has harmful effect on surrounding area and makes human suffer from acute and chronic diseases. Pesticides are used for the cost-effective managing of golf course and the amount of pesticides also increases as the number of golf course increase. Since the assessment of pesticides on near-by surrounding has been focused on water and soil media, studies related to atmospheric dispersion have been hardly attempted. The method to assess an impact of pesticide nearby agricultural production by the atmospheric dispersion using AGDISP(AGricultural DISPersal) model was developed and applied to the actual planned golf course located in Hongcheon, Gangwon. For implementing AGDISP, parameters were investigated from the golf course's land use planning map, pesticide spray device, Hong-Cheon weather station and etc. First of all, a kind of pesticide, a form of spraying pesticide, geographical features, weather data, and distance(golf course to plantation) were investigated to understand how to work these parameters in AGDISP. Restricted data(slope angle, droplet size distribution and solar insolation) sensitivity analysis of these parameters to estimate effect of pesticide nearby a plantation and a high relative contribution data of analyzed data was selected for input data. Ethoprophos was chosen as the pesticide used in the golf course and the amounts of pesticide deposition per annual agricultural productions were predicted. The results show that maximum amount of pesticide deposition through atmospheric dispersion was predicted $2.32{\mu}/m^2$ at 96 m where the nearest organic plantation exists. The residues of pesticide were also estimated based on the annul production of the organic and the deposition amount of the pesticide. Consequently, buckwheat, wheat and millet were likely to exceed maximum residue limits for pesticides in foods(MRL) and sorghum, corn and peanut were likely to exceed MRL by organic farming as well.

• 대기
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• 제29권2호
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• pp.227-239
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• 2019

This paper reviews various bulk-type cloud microphysics parameterizations (BCMPs). BCMP, predicting the moments of size distribution of hydrometeors, parameterizes the grid-resolved cloud and precipitation processes in atmospheric models. The generalized gamma distribution is mainly applied to represent the hydrometeors size distribution in BCMPs. BCMP can be divided in three different methods such as single-moment, double-moment, and triple-moment approaches depending on the number of prognostic variables. Single-moment approach only predicts the hydrometeors mixing ratio. Double-moment approach predicts not only the hydrometeors mixing ratio but also the hydrometeors number concentration. Triple-moment approach predicts the dispersion parameter of hydrometeors size distribution through the prognostic reflectivity, together with the number concentrations and mixing ratios of hydrometeors. Triple-moment approach is the most time expensive method because it has the most number of prognostic variables. However, this approach can allow more flexibility in representing hydrometeors size distribution relative to single-moment and double-moment approaches. At the early stage of the development of BMCPs, warm rain processes were only included. Ice-phase categories such as cloud ice, snow, graupel, and hail were included in BCMPs with prescribed properties for densities and sedimentation velocities of ice-phase hydrometeors since 1980s. Recently, to avoid fixed properties for ice-phase hydrometeors and ad-hoc category conversion, the new approach was proposed in which rimed ice and deposition ice mixing ratios are predicted with total ice number concentration and volume.