• 한국철도학회논문집
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• 제20권4호
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• pp.521-528
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• 2017

실제 체결장치는 들림하중이 작용할 때 압축하중이 작용할 때와 동일한 강성은 작은 하중범위 내에서 유지되고 어느 정도 들림하중이 커지면 매우 강한 비선형 거동특성을 보인다. 압상력 기준을 초과하는 개소들에서는 보통보다 매우 고가인 특수체결장치를 부설하여야하는데, 설계하고자하는 선로 전체구간에서 그 비용은 매우 크게 소요될 수 있다. 따라서 경제적 설계를 위하여 체결장치의 비선형 거동특성을 반영하여 압상력을 정확하게 평가할 필요가 있다. 본 연구에서는 현재 국내 콘크리트궤도에서 주로 사용되고 있는 일반 체결장치들(SFC와 System 300-1)을 대상으로 압상력 작용 시 거동특성을 파악하기 위하여 실내시험을 실시하였다. 시험결과를 토대로 수치해석에 적용하기 위한 체결장치의 비선형 하중-변위선도를 도출하였다. 기존의 선형모델과 더불어 도출된 비선형모델을 적용하여 교량단부의 변형에 따른 체결장치에 작용하는 압상력을 평가하였다. 또한 교량단부 체결장치 압상력에 미치는 영향요소인 침목간격, 교좌장치 중심으로부터 교량상판 최 끝단에 위치한 체결장치까지의 수평거리, 교량 거더높이 등에 대한 매개 변수연구를 통하여 이들 영향요소가 체결장치의 최대 압상력에 미치는 영향을 분석하였다. 평가결과 경제적인 궤도 설계를 위해서는 교량단부에 부설되는 체결장치의 사용성 검토 시에 체결장치의 비선형 특성이 반영될 필요가 있음을 알 수 있었다.

• 한국공간구조학회논문집
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• 제8권5호
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• pp.47-58
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• 2008

대공간 구조는 형태저항구조로서, 기둥-보로 구성되는 일반적인 건축골조구조가 설계외력에 대해 휨 및 전단으로 저항되는 것에 반해, 구조물의 내부에 기둥이 없는 공간을 내포하는 대공간 구조는 축력 및 면내 단면력에 의해 저항되는 경우가 대부분이다. 이러한 특성상 공간구조에는 일반적으로 장스팬이 사용되는 경우가 많으며, 그 결과 일반적인 골조와는 달리, 부재에 발생하는 변형도가 작은 경우에도 큰 변형이 발생하는, 즉 대변형 혹은 유한변형을 동반하게 된다. 일반적으로 수치해석에 있어 비선형 해석이란 기하학적 비선형 및 재료적 비선형, 또는 이 두 가지를 동시에 고려한 복합 비선형 해석을 들 수가 있다. 본 논문에서는 유한요소법으로 기하학적 비선형을 고려한 비선형 평형방정식을 적용하고, 부재의 응력-변형률 관계를 이용하여 재료적 비선형성도 함께 고려하였다. 사용된 수치해석 기법은 불안정 경로의 해를 찾아갈 수 있는 호장법을 적용하여 하중-변위 곡선을 추적하였다. 또한, 해석 결과는 범용 유한요소 프로그램인 ABAQUS를 이용하여 비교 검토하였다. 본 연구의 수치 해석결과 제시한 평면 및 공간 트러스의 비탄성 비선형 거동을 정확하고 효율적으로 예측 가능한 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1115-1123
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• 2008

When constructing projects such as road embankments, bridge approaches, dikes or buildings on soft, compressible soils, significant settlements may occur due to the consolidation of these soils under the superimposed loads. The compressibility of the soil skeleton of a soft clay is influenced by such factors as structure and fabric, stress path, temperature and loading rate. Although it is possible to determine appropriate relations and the corresponding material parameters in the laboratory, it is well known that sample disturbance due to stress release, temperature change and moisture content change can have a profound effect on the compressibility of a clay. The early research of Tezaghi and Casagrande has had a lasting influence on our interpretation of consolidation data. The 24 hour, incremental load, oedometer test has become, more or less, the standard procedure for determining the one-dimensional, stress-strain behavior of clays. An important notion relates to the interpretation of the data is the ore-consolidation pressure ${\sigma}_p$, which is located approximately at the break in the slope on the curve. From a practical point of view, this pressure is usually viewed as corresponding to the maximum past effective stress supported by the soil. Researchers have shown, however, that the value of ${\sigma}_p$ depends on the test procedure. furthermore, owing to sampling disturbance, the results of the laboratory consolidation test must be corrected to better capture the in-situ compressibility characteristics. The corrections apply, strictly speaking, to soils where the relation between strain and effective stress is time independent. An important assumption in Terzaghi's one-dimensional theory of consolidation is that the soil skeleton behaves elastically. On the other hand, Buisman recognized that creep deformations in settlement analysis can be important. this has led to extensions to Terzaghi's theory by various investigators, including the applicant and coworkers. The main object of this study is to suggestion the modified compression index value to predict settlements by back calculating the $C_c$ from different numerical models, which are giving best prediction settlements for multi layers including very thick soft clay.

• 한국지진공학회논문집
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• 제14권5호
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• pp.65-76
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• 2010

본 연구에서는 국내에서 널리 사용되고 있는 매설가스배관인 API X65에 대해 지진 취약도 해석을 수행하였다. 이를 위해, 15가지 경우의 배관 해석모델에 대해 12본 세트의 다양한 지진파를 0.1g 등간격으로 스케일링하여 비선형 시간이력해석을 수행한 후, 비선형 시간이력해석으로 얻어진 매설가스배관의 최대 변형률을 이용하여 지진취약도 해석을 수행하였다. 지진 취약도 해석을 위해 본 연구에서는 또한, 지반조건, 단부지점조건, 매립깊이 및 배관형태 등을 변수로 고려하여 지진 취약도 해석을 수행하였다. 지진 취약도 해석결과, 지반조건, 단부지점조건 및 매립깊이는 매설가스배관의 취약도 곡선에 영향을 끼치는 것으로 판단되었고, 특히 지반조건이 미치는 영향은 다른 두 변수에 비해 다소 큰 것을 확인할 수 있었다. 반면에, 배관형태가 취약도 곡선에 미치는 영향은 미미한 것을 알 수 있었다. 종합적으로, 매설가스배관의 지진 취약도 해석과 관련된 연구가 많지 않은 현실을 감안할 때, 본 연구결과는 매설가스배관의 지진 취약성 평가해석에 초석으로 고려되어질 수 있고, 추후 관련분야 연구에 좋은 참고자료가 될 것으로 사료된다.

• 한국수자원학회논문집
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• 제47권11호
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• pp.1007-1015
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• 2014

본 연구에서는 실내실험을 통하여 국내 중 소하천에 가장 많이 설치되고 있는 개량형 공압식 가동보를 대상으로 다양한 유량 변화에 대한 흐름특성을 분석하고, 유량계수산정식을 도출하였다. 실험결과, 가동보 기립각도에 따라 월류유량계수 ($C_d$)의 값은 0.613~0.634로 산정되었으며, 상류 Froude number ($F_{r1}$), 상대위어길이(${\xi}$), 전수두비($H_1/W$), 상류수심과 위어마루를 월류하는 수심의 비($y_c/y_1$)는 상류의 영향을 받으며 하류 Froude number ($F_{r2}$), 하류수심과 위어마루를 월류하는 수심의 비($y_c/y_2$)는 하류의 영향을받아 변화하였다. 상 하류수위차와 하류수심의 비(${\Delta}y/y_2$)는 상 하류의 영향을 모두 받아 변화되는 특성을 보여주었다. 주요 영향변수를 고려하여 다중회귀분석에 의한 유량계수산정식을 도출한 결과, 개량형 공압식 가동보의 월류유량계수는 상류흐름 조건이 상류일 때, 가동보의 높이 즉, 기립각도에 따른 물리적 제원과 상류 접근흐름수두의 조건에 의하여 결정되는 것으로 나타났다.

• Journal of Dental Anesthesia and Pain Medicine
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• 제20권5호
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• pp.293-301
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• 2020

Background: The success rate of intubation under direct laryngoscopy is greatly influenced by laryngoscopic grade using the Cormack-Lehane classification. However, it is not known whether grade under direct laryngoscopy can also affects the success rate of nasotracheal intubation using a fiberoptic bronchoscpe, so this study investigated the same. In addition, we investigated other factors that influence the success rate of fiberoptic nasotracheal intubation (FNI). Methods: FNI was performed by 18 anesthesiology residents under general anesthesia in patients over 15 years of age who underwent elective oral and maxillofacial operations. In all patients, the Mallampati grade was measured. Laryngeal view grade under direct laryngoscopy, and the degree of secretion and bleeding in the oral cavity was measured and divided into 3 grades. The time required for successful FNI was measured. If the intubation time was > 5 minutes, it was evaluated as a failure and the airway was managed by another method. The failure rate was evaluated using appropriate statistical method. Receiver operating characteristic (ROC) curves and area under the curve (AUC) were also measured. Results: A total of 650 patients were included in the study, and the failure rate of FNI was 4.5%. The patient's sex, age, height, weight, Mallampati, and laryngoscopic view grade did not affect the success rate of FNI (P > 0.05). BMI, the number of FNI performed by residents (P = 0.03), secretion (P < 0.001), and bleeding (P < 0.001) grades influenced the success rate. The AUCs of bleeding and secretion were 0.864 and 0.798, respectively, but the AUC of BMI, the number of FNI performed by residents, Mallampati, and laryngoscopic view grade were 0.527, 0.616, 0.614, and 0.544, respectively. Conclusion: Unlike in intubation under direct laryngoscopy, in the case of FNI, oral secretion and nasal bleeding had a significant effect on FNI difficulty than Mallampati grade or Laryngeal view grade.

• Journal of Animal Science and Technology
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• 제57권5호
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• pp.18.1-18.8
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• 2015

Background: Quantitative real time reverse transcription PCR (qRT-PCR) is one of the most important techniques for gene-expression analysis in molecular based studies. Selecting a proper internal control gene for normalizing data is a crucial step in gene expression analysis via this method. The expression levels of reference genes should be remained constant among cells in different tissues. However, it seems that the location of cells in different tissues might influence their expression. The purpose of this study was to determine whether the source of mesenchymal stem cells (MSCs) has any effect on expression level of three common reference genes (GAPDH, ${\beta}$-actin and ${\beta}2$-microglobulin) in equine marrow- and adipose-derived undifferentiated MSCs and consequently their reliability for comparative qRT-PCR. Materials and methods: Adipose tissue (AT) and bone marrow (BM) samples were harvested from 3 mares. MSCs were isolated and cultured until passage 3 (P3). Total RNA of P3 cells was extracted for cDNA synthesis. The generated cDNAs were analyzed by quantitative real-time PCR. The PCR reactions were ended with a melting curve analysis to verify the specificity of amplicon. Results: The expression levels of GAPDH were significantly different between AT- and BM-derived MSCs (p < 0.05). Differences in expression level of ${\beta}$-actin (P < 0.001) and B2M (P < 0.006.) between MSCs derived from AT and BM were substantially higher than GAPDH. In addition, the fold change in expression levels of GAPDH, ${\beta}$-actin and B2M in AT-derived MSCs compared to BM-derived MSCs were 2.38, 6.76 and 7.76, respectively. Conclusion: This study demonstrated that GAPDH and especially ${\beta}$-actin and B2M express in different levels in equine AT- and BM-derived MSCs. Thus they cannot be considered as reliable reference genes for comparative quantitative gene expression analysis in MSCs derived from equine bone marrow and adipose tissue.

• 한국물환경학회지
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• 제23권4호
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• pp.474-481
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• 2007

With population growth, industrialization, and urbanization within the watershed, the hydrologic response changed dramatically, resulting in increases in peak flow with lesser time to peak and total runoff with shortened time of concentration. Infiltration is directly affected by initial soil moisture condition, which is a key element to determine runoff. Influence of the initial soil moisture condition on hydrograph analysis should be evaluated to assess land use change impacts on runoff and non-point source pollution characteristics. The Long-Term Hydrologic Impact Assessment (L-THIA) model has been widely used for the estimation of the direct runoff worldwide. The L-THIA model was applied to the Little Eagle Creek (LEC) watershed and Its estimated direct runoff values were compared with the BFLOW filtered direct runoff values by other researchers. The $R^2$ value Was 0.68 and the Nash-Sutcliffe coefficient value was 0.64. Also, the L-THIA estimates were compared with those separated using optimized $BFI_{max}$ value for the Eckhardt filter. The $R^2$ value and the Nash-Sutcliffe coefficient value were 0.66 and 0.63, respectively. Although these higher statistics could indicate that the L-THIA model is good in estimating the direct runoff reasonably well, the Antecedent Moisture Condition (AMC) was not adjusted in that study, which might be responsible for mismatches in peak flow between the L-THIA estimated and the measured peak values. In this study, the L-THIA model was run with AMC adjustment for direct runoff estimation. The $R^2$ value was 0.80 and the Nash-Sutcliffe coefficient value was 0.78 for the comparison of L-THIA simulated direct runoff with the filtered direct runoff. However there was 42.44% differences in the L-THIA estimated direct runoff and filtered direct runoff. This can be explained in that about 80% of the simulation period is classified as 'AMC I' condition, which caused lower CN values and lower direct runoff estimation. Thus, the coefficients of the equation to adjust CN II to CN I and CN III depending on AMC condition were modified to minimize adjustments impacts on runoff estimation. The $R^2$ and the Nash-Sutcliffe coefficient values increase, 0.80 and 0.80 respectively. The difference in the estimated and filtered direct runoff decreased from 42.44% to 7.99%. The results obtained in this study indicate the AMC needs to be considered for accurate direct runoff estimation using the L-THIA model. Also, more researches are needed for realistic adjustment of the AMC in the L-THIA model.

• 대한의용생체공학회:의공학회지
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• 제24권4호
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• pp.363-367
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• 2003

인공무릎관절의 수명에 직접적인 영향을 주는 인자는 접촉면에 대한 접촉면적과 압력분포이다 따라서. 이에 대한 실험적인 평가가 필요하였고 knee simulator 혹은 K-scan sensor를 포함한 시스템과 같은 많은 연구가 진행되어 왔다. 그러나 지금까지 보행주기에 따른 연속적인 인공관절 운동에 대한 접촉면의 압력분포를 실시간으로 분석한 연구는 미흡하다 따라서 본 연구의 목적은 보행주기를 모사하는 simulator와 I-scan을 이용하여 연속적인 동작에 따른 접촉면의 압력분포를 분석함에 있다. 본 연구의 목적을 이루기 위해서 생체내 인공관절 환경을 정확히 표현할 수 있는 knee simulator를 제작하였다. 네 방향의 자유도를 갖고 있는 본 simulator는 soft tissue의 기능을 포함하고 있고 PC Program을 통하여 압축하중과 femoral component의 굴곡각을 조절할 수 있다. 본 시스템의 I-scan sensor는 보행주기에 따른 압력분포를 분석할 수 있다. 보행주기에 대한 압력분포는 압축하중곡선에 따라 주요하게 변화함을 알 수 있고 운동성에 영향을 쿠는 압력중심의 위치도 변한다는 것을 알 수 있다. 따라서 본 연구에서 제작한 knee simulator는 보행주기 같은 특정의 운동정보를 이용하여 접촉면의 압력분포 및 운동성 같은 기계적 성능을 평가할 수 있고 형상 설계를 위한 기초 자료를 제공할 수 있다.

• 대한조선학회지
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• 제6권1호
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• pp.25-34
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• 1969

From viewpoints of over-all ship economy the straight framed V-bottom hull forms with chines are considered to be attractive even for usual commercial vessels, because increments of resistance over that of round hull forms, if any, can be well compensated with reduction in construction cost.[1] To investigate the influences of both prismatic coefficient and chine elevation on resistance performance, three models of straight-framed V-bottom hull forms which are similar to Prof. C. Ridgely-Nevitt's W-18, W-8, and W-20[2],[3] in size and hull form coefficients were tested at the SNU Ship Model Towing Tank for resistance measurements. They are of Cp=0.60, 0.65 and 0.70 and of ${\Delta}/(0.01L)^3=300$. Influence of variation of chine elevation on resistance performance were observed with the test results obtained at normal condition, and at the trimed by the stern by 2% and 4% of $L_{bp}$ at normal condition under same displacement. The hull form characteristics are shown in Table 1, and in Fig. 1, 2, 3, 4 and 5. The test results are shown in Fig 8, 9 and 10 in the form of Cr vs. $V/\sqrt{L}$ curves taking Cp as a parameter for normal condition, trim by the stern in 2% and 4% $L_{bp}$ at normal condition , respectively. Cr vs. $V/\sqrt{L}$ curves taking trim condition as a parameter are also shown in Fig 11, 12 and 13 for Cp=0.60 and 0.70, respectively. The best and the worst trim condition at given $V/\sqrt{L}$ in viewpoint of Cr are plotted for each Cp-value as shown in Fig 14, 15 and 16. From the above results the following conclusions are derived: (1) In general, the resistance performance of the straight-framed V-bottom hull forms are not inferior to those of round hull forms. At a certain range of $V/\sqrt{L}$ the former gives less resistance than the latter. (2) Regarding influences of Cp on Cr, it is observed that, at $V/\sqrt{L}$ less than about 0.925, the greater Cp-value gives the more increment of Cr, and that, at $V/\sqrt{L}$ greater than about 0.925 the smaller Cp-value gives the more increment of Cr. It is also noteworthy that the model of Cp=0.70 has remarkable hump on Cr vs. $V/\sqrt{L}$ curve between $V/\sqrt{L}=0.80$ and 0.90. (3) For higher speed within the test range, the chine elevation having the steeper slope around bow and the easier slope around amidship and stern, refered to watering, give the better results in resistance performance. (4) Assuming the chine elevations adopted for the tested models were not of the best, we would expect further improvement of resistance performance for such form. Hence, a systematic study on chine elevation is very disirable to prepare design data of general purpose for the such hull forms.