• 대한인간공학회지
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• 제30권5호
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• pp.671-681
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• 2011

Objective: The purpose of this study is to compare the workload level at each lower limbs posture and suggest the ergonomic workstation guideline for working period by evaluating the imbalanced lower limbs postures from the physiological and psychophysical points of view. Background: Many workers like welders are working in various imbalanced lower limbs postures either due to the narrow working conditions or other environmental conditions. Method: Ten male subjects participated in this experiment. Subjects were asked to maintain 3 different lower limbs postures(standing, squatting and bending) with 3 different working conditions(balanced floor with no scaffold, imbalanced floor with 10cm height of scaffold, and imbalanced floor with 20cm height of scaffold). EMG data for the 4 muscle groups(Retus Femoris, Vastus Lateralis, Tibialis Anterior, Gastrocnemius) from each lower limbs posture were collected for 20 seconds every 2 minutes during the 8 minutes sustaining task. Subjects were also asked to report their discomfort ratings of body parts such as waist, upper legs, lower legs, and ankle. Results: The ANOVA results showed that the EMG root mean square(RMS) values and the discomfort ratings(CR-10 Rating Scale) were significantly affected by lower limbs postures and working time(p<0.05). The correlation was analyzed between the EMG data and the discomfort ratings. Also, prediction models for the discomfort rating for each posture were developed using physical condition, working time, and scaffold height. Conclusion: We strongly recommend that one should not work more than 6 minutes in a standing or squatting postures and should not work more than 4 minutes in a bending posture. Application: The results of this study could be used to design and assess working environments and methods. Furthermore, these results could be used to suggest ergonomic guidelines for the lower limbs postures such as squatting and bending in the working fields in order to prevent fatigue and pain in the lower limbs body.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
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• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
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• pp.34.1-34.1
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• 2008

Cosmic ray (CR)s are energetic particles that are found in space and filter through our atmosphere. They are classified with galactic cosmic ray (GCR)s and solar cosmic ray (SCR)s from their origins. The process of a CR particle colliding with particles in our atmosphere and disintegrating into smaller pions, muons, neutrons, and the like, is called a cosmic ray shower. These particles can be measured on the Earth's surface by neutron monitor (NM)s. Regarding with the space weather, there are common types of short term variation called a Forbush decrease (FD) and a Ground Level Enhancement (GLE). In this talk, we will briefly introduce our recent studies on CRs observed by NM: (1) simultaneity of FD depending on solar wind interaction, (2) an association between GLE and solar proton events, and (3) diurnal variation of the GCR depending on geomagnetic cutoff rigidity. NM will provide a crucial information for the Korea Space Weather Prediction Center (KSWPC).

• Journal of Welding and Joining
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• 제22권4호
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• pp.35-42
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• 2004

Contact tips are required to have a higher resistance to wear and thus to have an extended life time under the advanced GMAW welding process. Several requirements have been specified and employed by domestic industries for selecting their tips for such a purpose. However no attempt has been made to justify their requirements based on the experimental data of wear resistance or life time of contact tips. In this study, five different contact tips with three different compositions were employed for actual GMA welding up to 4 hours and were evaluated their wear resistance by measuring in every one hour the area of enlarged hole at the exit side. Experimental results clearly showed that the Cr-containing tips strengthened by precipitation hardening have much better resistance to wear than those made by work hardening. It was further noticed that Cr is an excellent alloying element for improving the wear resistance of contact tips only when it is in an properly aged condition. Initial hardness may play some role in the early stage of wear but not in the later stage of welding because the microstructure of tip changes significantly by the prolonged exposure to welding arc heat. Based on these results, critical review has been made on the current requirements employed by domestic industries. Of importance is that a new guideline has been confirmed to be more reasonable.

• 한국항공우주학회지
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• 제50권5호
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• pp.317-323
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• 2022

본 논문에서는 c-스파 단면을 갖는 복합재 로터 블레이드에 대해 co-rotational(CR) 이론 기반 비선형 쉘 요소를 사용하는 In-house code를 통해 고유진동수를 구하고, 이를 이용하여 블레이드의 진동특성을 예측하는 심층신경망 모델을 개발하였다. 심층신경망 모델은 무작위 두께 분포를 갖는 데이터와 스팬 방향으로 두께 감소 경향성을 보이는 데이터를 통해 심층신경망 모델의 정확성을 평가하였다.

• Geomechanics and Engineering
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• 제30권5호
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• pp.437-448
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• 2022

Alluvial soil is challenging to work with due to its high compressibility. Thus, consolidation settlement of this type of soil should be accurately estimated. Accurate estimation of the consolidation settlement of alluvial soil requires accurate prediction of compressibility parameters. Geotechnical engineers usually use empirical correlations to estimate these compressibility parameters. However, no attempts have been made to develop correlations to estimate compressibility parameters of alluvial soil. Thus, this paper aims to develop new models to predict the compression and recompression indices (Cc and Cr) of alluvial soils. As part of the study, geotechnical laboratory tests have been conducted on large number of undisturbed samples of local alluvial soil. The obtained results from these tests in addition to available results from the literature from different parts in the world have been compiled to form the database of this study. This database is then employed to examine the accuracy of the available empirical correlations of the compressibility parameters and to develop the new models to estimate the compressibility parameters using the nonlinear regression analysis. The accuracy of the new models has been accessed using mean absolute error, root mean square error, mean, percentage of predictions with error range of ±20%, percentage of predictions with error range of ±30%, and coefficient of determination. It was found that the new models outperform the available correlations. Thus, these models can be used by geotechnical engineers with more confidence to predict Cc and Cr.

• 대한기계학회논문집
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• 제16권1호
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• pp.53-62
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• 1992

본 연구에서는 약 10년 정도 사용하여 경년 열화가 되었다고 예상되는 실구조 물의 일부를 입수하였으며 열화재의 특성과 비교하기 위하여 열처리에 의해 충격치를 회복시킨 재료를 회복재로 하여 두가지 재료에 대해 시험편을 제작하였따.열확현상 을 파악하기 위하여 평활재로 피로과정, 즉 미소 균열의 발생, 진전 및 복수 균열이 간섭합체하여 파단에 달하는 과정에 대하여 파괴역학적 견지에서 열화재와 회복재를 해석하고 이결과로 부터 확율변수를 추정하여 통계학적인 수명예측방법의 하나를 제시 하여 실구조물에 적용하는 방법에 대해 시도해 보았다.

• 한국전산구조공학회논문집
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• 제30권1호
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• pp.1-6
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• 2017

본 논문에서는 비교적 최근 정립된 co-rotational 이론을 기반으로 한 4절점 평면요소 정식화를 확장하여 9절점 평면 요소에 적합한 CR 정식화를 제시하고자 한다. 그리고 등방성 재료의 소성 해석을 위해, 선형 경과 규칙(bi-linear hardening rule)을 바탕으로 하는 Newton-Raphson return-mapping 알고리즘을 적용하였다. 이때, von Mises 기준을 적용하여 소성 변형 상태를 예측하였다. Lagrange 승수를 도입하여 2차원 접촉에 대한 구속조건을 부여하였다. 개발한 요소는 상용프로그램인 ABAQUS 해석결과와 비교 검증하였다.

• 열처리공학회지
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• 제18권4호
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• pp.247-255
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• 2005

Although heat treatment is a process of great technological importance in order to obtain desired mechanical properties such as hardness, the process was required a tedious and expensive experimentation to specify the process parameters. Consequently, the availability of reliable and efficient numerical simulation program would enable easy specification of process parameters to achieve desired microstructure and mechanical properties without defects like crack and distortion. In present work, the developed numerical simulation program could predict distributions of microstructure and thermal stress in steels under different cooling conditions. The computer program is based on the finite difference method for temperature analysis and microstructural changes and the finite element method for thermal stress analysis. Multi-phase decomposition model was used for description of diffusional austenite decompositions in low alloy steels during cooling after austenitization. The model predicts the progress of ferrite, pearlite, and bainite transformations simultaneously during quenching and estimates the amount of martensite also by using Koistinen and Marburger equation. To verify the developed program, the calculated results are compared with experimental ones of casting product. Based on these results, newly designed heat treatment process is proposed and it was proved to be effective for industry.

• 대한전자공학회논문지SP
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• 제47권6호
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• pp.127-136
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• 2010

다시점 비디오는 카메라간의 다른 위치와 불완전한 카메라 보정(calibration)으로 인접한 시점의 영상 내에 존재하는 동일물체 간에 색상 차이가 발생할 수 있다. 이러한 색상 불일치(color mismatch)는 시점 간 움직임 예측(inter-view prediction) 수행 시, 오정합을 발생시켜 다시점 비디오 부호화(Multi-view Video Coding : MVC) 성능을 저하시키는 원인이 된다. 본 논문에서는 이웃하는 영상 간에 존재하는 휘도 및 색차 성분 불일치를 보상하여 다시점 비디오 부호화의 압축률을 향상시키는 전처리 기법을 제안한다. 제안된 기법에서는 모든 시점의 영상을 히스토그램 매칭 기법에 의해 정해진 참조 시점 영상의 색상을 기준으로 보정된다. 또한 히스토그램 매칭 수행 전에 YCbCr 색상공간 변경 시에 색차 성분의 대표 값 추출(chrominance subsampling)에 사용되는 Cosited filter를 영상의 각 색상성분에 적용하여 성능을 더욱 높일 수 있다. 히스토그램 매칭은 YCbCr 색상공간에서 RGB 색상공간으로 변환하여 각 색상성분에 적용한다. 이 과정에서 영상에 존재하는 에지의 방향성과 화소 값의 존재 범위를 고려한 효과적인 색상 변환 기법이 사용된다. 실험을 통해 제안하는 전처리 기법이 다른 기법들에 비해 향상된 부호화 효율을 가지는 것을 확인하였다.

• Korean Chemical Engineering Research
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• 제44권6호
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• pp.623-630
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• 2006

분류층 가스화기에서 슬래그의 점도 변화는 가스화기 운전 온도을 결정하는 중요한 요소이다. 본 논문에서는 국내 가스화 대상탄 중 결정슬래그의 거동을 보여주는 5개 탄 슬래그의 $T_{cv}$를 문헌의 경험식과 Factsage를 이용한 평형계산으로 예측하고, 각 방법의 실용성을 조사하였다. 경험식으로는 두개의 모델이 사용되었는데 각각 회분용융시험의 $T_h$와 슬래그의 5개 주성분 농도를 이용하였다. $T_h$를 이용한 모델은 $20{\sim}100^{\circ}C$ 높은 $T_{cv}$를, 5개 주성분을 이용한 모델은 $80{\sim}120^{\circ}C$ 낮은 $T_{cv}$를 예측하였다. 평형계산에서는 액상선 온도로 $T_{cv}$를 구하였다. 평형계산에 주 4 성분만을 사용하였을 경우 측정된 $T_{cv}$보다 높은 온도가 예측되었다. 액상선 온도는 부 성분의 농도에 매우 민감하여 MgO와 $Na_2O$의 추가는 액상선 온도를 낮추어 주었다. 평형계산에서 석탄의 주성분뿐만 아니라 부성분을 모두 포함시켰을 때 측정된 $T_{cv}$에 가장 근접한 결과를 얻을 수 있었다. 또한 $Cr_2O_3$ 계열의 내화재가 사용되었을 경우, $T_{cv}$의 좀 더 정확한 예측을 위하여 용해 내화재의 농도도 평형계산에 포함시켜야함이 확인되었다.