• Smart Structures and Systems
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• 제11권6호
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• pp.589-604
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• 2013

Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.

• 대한토목학회논문집
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• 제30권3A호
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• pp.309-316
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• 2010

이 논문에서는 인장과 압축하중에 놓은 무근 콘크리트와 철근콘크리트 구조물의 거동을 모사하기 위해 비국소화 이방성 손상모델을 제안하였다. 손상변수로써 대칭형의 이차 텐서을 사용한 연속체 손상모델에 기초한다. 콘크리트와 같은 준-취성재료에 있어 손상양상은 인장부와 압축부에서 다른 양상을 나타낸다. 이러한 두 개의 손상영역은 전체 변형률 텐서의 주변형률 성분을 손상텐서 속도에 비례하는 손상진전 법칙을 이용하여 모델링하였다. 제안된 모델의 유효성을 검토하기 위해 nooru-mohamed에 의해 실시된 이중 노치가 있는 시험체와 철근콘크리트 휨 시험체를 대상으로 해석을 수행하였다. 해석결과, 비국소화 이방성 모델은 혼합모드 파괴에 대한 균열진전을 적절히 모사할 수 있었으며 철근콘크리트 휨 시험체의 구조적 파괴에 있어서도 높은 수준의 콘크리트 손상 및 철근의 항복까지를 해석할 수 있었다.

• 한국응용곤충학회지
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• 제46권1호
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• pp.165-168
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• 2007

고구마 재배지에 발생하는 풍뎅이류 유충(굼벵이)의 종류 및 종별 피해양상을 조사하였다. 고구마 재배지 토양에 발생하는 풍뎅이류는 큰검정풍뎅이(Holotrichia parallela), 참검정풍뎅이(Holotrichia diomphalia), 애풍뎅이(Anomala rufocuprea) 3종이지만 주로 발생하는 풍뎅이류는 대부분 큰검정풍뎅이로 조사되었다. 굼벵이류에 의한 고구마 괴근 피해율은 지역에 따라 차이가 있었는데 평군 2-40%였고, 심한 경우는 80% 이상의 피해를 나타낸 포장도 있었다. 큰검정풍뎅이는 10월 하순부터 다음해 6월 하순까지 토양 속에서 3령의 노령유충으로 월동하였으며, 월동기간 동안 유충의 생존율은 92%로 매우 높았다. 고구마 포장에서 큰검정풍뎅이 유충은 7월 하순부터 8월 중순 사이에 발생하기 시작하였고, 고구마의 굼벵이 피해는 8월 하순부터 나타나기 시작하여 수확기까지 지속되었다.

• 한국해양환경ㆍ에너지학회지
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• 제9권4호
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• pp.187-192
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• 2006

조선소에서 배출되는 처리수, 혼합방류수 및 주변 하천수가 양식 생물에 미치는 생물 독성영향을 알아보기 위해 48시간 급성독성과 DNA 손상을 조사하였다. 조사대상 생물종으로는 조선소 주변에서 양식되고 있는 넙치, 조피볼락, 피조개, 멍게가 사용되었으며, 48 시간 노출 후 치사율을 파악하였고, DNA 손상 정도는 Comet assay을 이용하여 측정되었다. 급성독성 실험 결과, 넙치는 장평천에서 치사가 나타났고(26%), 조피볼락은 혼합방류수 1에서 치사가 나타났다(13%). 멍게는 고현천에서 10%의 치사율을 보였고, 피조개는 어느 시료에서도 치사가 나타나지 않았다. 본 연구에 사용되어진 어떠한 시료에서도 실험생물을 50%까지 치사시키는 독성이 나타나지 않아 $LC_{50}$은 계산될 수 없었다. 넙치는 장평천과 혼합방류수에서 대조구보다 유의하게 높은 DNA 손상을 보여주었고, 조피볼락은 장평천에서 유의하게 높은 DNA손상이 나타났다(p<0.05). 멍게는 세탁폐수에서 유의한 DNA손상이 나타났지만, 피조개에서는 모든 처리구에서 DNA 손상을 보이지 않았다. 치사율과 DNA 손상을 고려하였을 때 조선소의 처리수와 혼합방류수보다는 장평천에서 놀은 생물독성을 보여주는 것으로 나타났다.

• Geomechanics and Engineering
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• 제24권6호
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• pp.519-529
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• 2021

In coal mining activities, the abutment stress of the coal has to undergo cyclic loading and unloading, affecting the strength and seepage characteristics of coal; additionally, it can cause dynamic disasters, posing a major challenge for the safety of coal mine production. To improve the understanding of the dynamic disaster mechanism of gas outburst and rock burst coupling, triaxial devices are applied to axial pressure cyclic loading-unloading tests under different axial stress peaks and different pore pressures. The existing empirical formula is use to perform a non-linear regression fitting on the relationship between stress and permeability, and the damage rate of permeability is introduced to analyze the change in permeability. The results show that the permeability curve obtained had "memory", and the peak stress was lower than the conventional loading path. The permeability curve and the volume strain curve show a clear symmetrical relationship, being the former in the form of a negative power function. Owing to the influence of irreversible deformation, the permeability difference and the damage of permeability mainly occur in the initial stage of loading-unloading, and both decrease as the number of cycles of loading-unloading increase. At the end of the first cycle and the second cycle, the permeability decreased in the range of 5.777 - 8.421 % and 4.311-8.713 %, respectively. The permeability decreases with an increase in the axial stress peak, and the damage rate shows the opposite trend. Under the same conditions, the permeability of methane is always lower than that of helium, and it shows a V-shape change trend with increasing methane pressures, and the permeability of the specimen was 3 MPa > 1 MPa > 2 MPa.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.27-30
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• 2004

Clad wire , which has the advantages of the high strength of a steel core and the electro-conductivity, corrosion resistance of a copper layer, is widely being used the telecommunications, electric-electronic and military technology industries, among others. It is important to obtain uniform coated rate when producing clad wires. Clad wire drawing process can be influenced on damage and coated rate of core and sleeve by process variables as semi-die angle and reduction in area. Therefore, in this study, the finite-element results established in previous study is used to analyze the effect of the various forming parameters, which included the semi-die angle, reduction in area etc. The coated rate will be predicted with observation copper coated rate variation according to total reduction in area and the optimal pass schedule will be set up through proper reduction in area and semi-die angle variation.

• 한국해양공학회지
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• 제32권3호
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• pp.151-157
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• 2018

Offshore structures are exposed to low- and high-frequency responses due to environmental loads, and fatigue damage models are used to calculate the fatigue damage from these. In this study, we tried to optimize the main parameters used in fatigue damage calculation to derive a new fatigue damage model. A total of 162 bi-modal spectra using the elliptic equation were defined to describe the response of offshore structures. To calculate the fatigue damage from the spectra, time series were generated from the spectra using the inverse Fourier transform, and the rain-flow counting method was applied. The considered optimization variables were the size of the frequency increments, ratio of the time increment, and number of repetitions of the time series. In order to obtain optimized values, the fatigue damage was calculated using the parameter values proposed in previous work, and the fatigue damage was calculated by increasing or decreasing the proposed values. The results were compared, and the error rate was checked. Based on the test results, new values were found for the size of the frequency increment and number of time series iterations. As a validation, the fatigue damage of an actual tension spectrum found using the new proposed values and fatigue damage found using the previously proposed method were compared. In conclusion, we propose a new optimized calculation process that is faster and more accurate than the existed method.

• 한국응용곤충학회지
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• 제44권4호
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• pp.317-323
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• 2005

우리나라 더덕의 주 재배지인 전라남북도, 경상북도, 경기도, 강원도, 제주도, 울릉도 등 15지역 116개 재배포장을 대상으로 한 식물기생선충의 분포와 피해를 조사하였다. 분포가 확인된 9속의 선충 중 Ditylenchus citri, Meloidogyne hapla, M. incognita, Pratylenchus neglectus, Tylenchorynchus claytoni 등 5종이 동정되었다. 이들 중 M. hapla의 포장검출률이 61.9%로 가장 높았고, Tylenchu spp. 16.1%, Pratylenchus neglecrus 7.8%, Ditylenchus citri 5.1%, Helicotylenchus sp. 5.1%순이었다. 더덕 2년생을 대상으로 한 지역별 당근뿌리혹선충에 의한 피해는 포장감염률과 감염주율이 각각 67.0%, 60.2%였으며 평균 감수율은 10%였다. 전북지역 더덕 재배지에서 당근뿌리혹선충에 의한 피해는 재배년수가 길어질수록 많았고, 평야지가 산간지나 중산간지보다 많은 경향이었다.

• 한국유기농업학회지
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• 제21권4호
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• pp.523-538
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• 2013

To help improve the current government practice of direct damage-compensation policies, resulting from the loss of profit, sustained by Hanwoo farmers, as a result of the recent Korea-U. S. Free Trade Agreement (FTA), this research aims to examine any problems or issues caused by said policies. To accomplish this task, we have established Hanwoo-SIMO model and estimated the damage of Hanwoo farmers, one without the implementation of the FTA and another with the FTA, to compare and contrast the two. We then analyzed the efficacy of the current government policies. According to our analysis, the current direct compensation policies for the loss of profit on the part of Hanwoo farmers are insufficient. To address this problem, we recommend the government enact a new direct damagecompensation law to address the following issues. First, as the base formula of damage-compensation, the government should use current price of the beef rather than the annually changing flexible price. Second, the flexible control index should remain fixed at 1.0 rate while the government prepares the adequate amount of the damage compensating direct payment resulting from the FTA. Third, the direct government compensation policy should extend beyond the current 15 years (2013-2026) as the profit loss is expected to increase after the midpoint of the FTA.

• Computers and Concrete
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• 제21권5호
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• pp.547-557
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• 2018

This paper measures the mechanical response of precast pavement joints under moving axle loads using the finite-element method, and the models were validated with results of field tests. In order to increase the ability to use the non-linear FE analysis for design and assessment of precast pavement subjected to moving axle load, this paper investigated the effects of different load transfer between the slabs using the ABAQUS finite-element package to solve the nonlinear explicit model equations. The assembly of the panels using dowels and groove-tongue keys has been studied to assess the efficiency of keyway joint system. Concrete damage plasticity model was used to calculate the effects of permanent damages related to the failure mechanisms. With aggregate interlock as the only load transferring system, Load transfer efficiency (LTE) is not acceptable when the axle load reaches to slab joints. The Finite-element modelling (FEM) results showed that keyway joints significantly reduced tensile stresses developed at the mid-slab. Increasing the thickness of the tongue the LTE was improved but with increasing the height of the tongue the LTE was decreased. Stresses are transferred to the adjacent slab efficiently when dowels are embedded within the model. When the axle load approaches joints, tensile damage occurs sooner than compressive damage, but the damage rate remains constant, then compressive damage increases significantly and become the major form of distress under the dowels.