• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.483-492
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• 2007

Pre-Engineering Building (PEB) system is one of the most economical structural systems. Tapered members can resist a maximum stress at a single location, whereas stresses of the rest of the members are considerably low. This results in appreciable savings both in terms of materials and construction costs. However, it was appreciated that special consideration would be required for certain aspects of this structural form. In particular, because of their slenderness, webs would buckle laterally and torsionally under the combined action of excessive axial, bending and shear forces. In this study, a total of four large-scale rafters with simple ends were tested. The main parameters were the width-thickness ratio of the web, the stiffener, and the flange brace. The purpose of this experiment is to evaluate the structural stability and to offer back-data on PEB design.

• Tribology and Lubricants
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• v.30 no.6
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• Journal of Korean Society on Water Environment
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• v.32 no.2
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• pp.135-141
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• 2016

This study investigated changes of hydrology, soil characteristics, riparian vegetation communities, and geomorphology in sandbars before and after sand-mining to determine the effect of sand-mining at upstream of Guemgang and Bochungcheon streams in Korea. Sand-mining events affected the mining area. They supplied organic matters and nutrients during flood. Sediment deposition caused soil texture change and expansion of vegetation area. However, riverbeds were stabilized after the disturbance. According to the analyses of aerial photographs, the vegetation area was significantly expanded in both dam-regulated streams and dam-unregulated streams after sand-mining. Willow shrubs advanced in disturbed area at an average of 10 years after sand-mining. It took willows trees 10.6 years to become dominant communities. Therefore, it took a total of 20.6 years for new riparian forest to form in sandbar after sand-mining. Our results confirmed that stream flow condition were dependent on vegetation recruitment in dam-regulated streams and dam-unregulated streams. For willow recruitment in unregulated streams, calculation of water level below dimensionless bed shear stress is important because low water level variation is a limiting factor of vegetation recruitment.

• Journal of Nutrition and Health
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• v.10 no.3
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• pp.1-6
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• 1977

Flow properties of heated edible oils, such as soybean, rapeseed, rice bran, corn and perilla oils, were measured with Maron-Belner type capillary viscometer. These oils were heated at $180{\pm}5^{\circ}C$ (general cooking temperature) for $5{\sim}20$ hours except soybean oils ($5{\sim}40$ hours). Fluidities of these heated oils except rice bran oil were decreased according to heating time and decreasing ratio of fluidity was outstanding after 15 hour heating in corn oil and 20 hours heating in soybean and perilla oils. All the oils examined in this experiments except rice bran oil showed non-Newtonian motion after 15 hour hinting at high shear stress and Newtonian motion at less than 10 hour heating. In the soybean oil non-Newtonian flow property was outstanding after 30 hour heating at $180{\pm}5^{\circ}C$. Rice bran oil exhibit characteristic flow property, that is, non heated rice bran oil has lowest fluidity but heated one has highest fluidity compared to other oils examined in this experiment. Change of fluidity with extension of heating time was not detected and non heated rice bran oil showed non-Newtonian motion.

• Journal of Korean Neurosurgical Society
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• v.60 no.5
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• pp.504-510
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• 2017

Objective : To investigate the morphological and hemodynamic parameters associated with middle cerebral artery (MCA) bifurcation aneurysm rupture. Methods : A retrospective study of 67 consecutive patients was carried out based on 3D digital subtraction angiography data. Morphological and hemodynamic parameters including aneurysm size parameters (dome width, height, and perpendicular height), longest dimension from the aneurysm neck to the dome tip, neck width, aneurysm area, aspect ratio, Longest dimension from the aneurysm neck to the dome tip (Dmax) to dome width, and height-width, Bottleneck factor, as well as wall shear stress (WSS), low WSS area (LSA), percentage of LSA (LSA%) and energy loss (EL) were estimated. Parameters between ruptured and un-ruptured groups were analyzed. Receiver operating characteristics were generated to check prediction performance of all significant variables. Results : Sixty-seven patients with MCA bifurcation aneurysm were included (31 unruptured, 36 ruptured). Dmax (p=0.008) was greater in ruptured group than that in un-ruptured group. D/W (p<0.001) and the percentage of the low WSS area ($0.09{\pm}0.13$ vs. $0.01{\pm}0.03$, p<0.001) were also greater in the ruptured group. Moreover, the EL in ruptured group was higher than that in unruptured group ($6.39{\pm}5.04$ vs. $1.53{\pm}0.86$, p<0.001). Multivariate regression analysis suggested D/W and EL were significant predictors of rupture of MCA bifurcation aneurysms. Correlation analyses revealed the D/W value was positively associated with the EL (R=0.442, p<0.01). Conclusion : D/W and EL might be the most two favorable factors to predict rupture risk of MCA bifurcation aneurysms.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.172-172
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• 2015

하천에서 발생하는 소류력은 하상 변동을 발생시키기 때문에 주변 구조물이나 하천의 흐름특성 등을 변화시키게 되며, 유사이송, 침식 및 퇴적, 유동해석 등에 매우 중요한 하천 계수이다. 하천에서 소류력의 직접 측정은 매우 어려워 직접 측정 대신 하천경사 및 동수반경을 기반한 단면 평균소류력 산정 공식을 일반적으로 이용한다. 그러나, 이러한 방식은 상세한 유사이송, 세굴 등의 해석에는 한계가 있기 때문에 국부적인 소류력이 필요하다. 실내 실험에서는 프레스톤게이지를 활용한 직접 측정이나, 난류측정을 통한 레이놀즈 분포를 외삽하여 단면에서 국부적인 소류력을 측정하는 방식이 사용되어 왔다. 반면, 실제 하천에서는 국부 소류력 직접측정 및 난류 산정이 거의 불가능하거나 비효율적이므로 대안으로 하천의 연직유속분포에 대수분포를 적용하여 소류력을 추정하는 간접적인 방법이 제시되어 왔다. 일부 실내실험에서 대수법칙을 통한 소류력 산정 방식은 직접 측정을 통해 검증한 바가 있으나 실제 하천은 난류의 공간 시간적 스케일이 실내 규모와 상이하여 국부 소류력에 영향을 미칠 수 있어 이러한 검증결과를 현장 적용하기에는 한계가 있다. 본 연구에서는 실제 규모 하천에서 대수법칙을 활용한 국부 소류력 산정 결과와 레이놀즈 응력의 연직분포 측정을 통해 산정한 값과 비교하여 대수법칙 활용 소류력 산정 방식의 적용성을 검토하였다. 실험은 중소규모의 하천을 재현한 한국건설기술연구원 안동하천실험센터 직선(A1) 및 사행(A2) 하천의 유속측정을 수행하였으며, 유속 측정에는 정밀도가 높으나 실내에서 주로 사용된 초음파지점유속계(Micro ADV)를 현장에 설치하여 사용하였다. ADV의 관측 시간은 90초이며, 직선수로에서는 횡방향으로 25 cm 간격, 수심방향으로는 5 ~ 10 cm 간격으로 측정하였고, 사행수로는 횡방향으로 50 cm 간격, 수심방향 5 ~ 10 cm 간격으로 측정을 수행하였다. 실험결과 대수법칙과 레이놀즈 분포로부터 산정된 국부 소류력은 사행과 직선 모두 상당한 이격을 보였다.

• Structural Engineering and Mechanics
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• v.41 no.6
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• pp.711-734
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• 2012

The foundation of a tall building frame resting on settable soil mass undergoes differential settlements which alter the forces in the structural members significantly. For tall buildings it is essential to consider seismic forces in analysis. The building frame, foundation and soil mass are considered to act as single integral compatible structural unit. The stress-strain characteristics of the supporting soil play a vital role in the interaction analysis. The resulting differential settlements of the soil mass are responsible for the redistribution of forces in the superstructure. In the present work, the nonlinear interaction analysis of a two-bay ten-storey plane building frame- layered soil system under seismic loading has been carried out using the coupled finite-infinite elements. The frame has been considered to act in linear elastic manner while the soil mass to act as nonlinear elastic manner. The subsoil in reality exists in layered formation and consists of various soil layers having different properties. Each individual soil layer in reality can be considered to behave in nonlinear manner. The nonlinear layered system as a whole will undergo differential settlements. Thus, it becomes essential to study the structural behaviour of a structure resting on such nonlinear composite layered soil system. The nonlinear constitutive hyperbolic soil model available in the literature is adopted to model the nonlinear behaviour of the soil mass. The structural behaviour of the interaction system is investigated as the shear forces and bending moments in superstructure get significantly altered due to differential settlements of the soil mass.

• Computers and Concrete
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• v.10 no.1
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• pp.1-18
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• 2012

This paper presents the details of studies conducted on hollow concrete block masonry (HCBM) units and wall panels. This study includes, compressive strength of unit block, ungrouted and grouted HCB prisms, flexural strength evaluation, testing of HCBM panels with and without opening. Non-linear finite element (FE) analysis of HCBM panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and then lateral load is applied in incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response reduction factors have been evaluated based on experimental results. From the study, it is observed that fully grouted and partially reinforced HCBM panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved towards the compression toe of the wall. The force reduction factor of a wall panel with opening is much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by non-linear FE analysis are found to be in good agreement with the corresponding experimental values. The influence of mortar joint has been included in the stress-strain behaviour as a monolith with HCBM and not considered separately. The derived response reduction factors will be useful for the design of reinforced HCBM wall panels subjected to lateral forces generated due to earthquakes.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.5
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• pp.647-655
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• 2010

In this paper, a numerical study is carried out for super-pipe, flat plate and axisymmetric body flows to investigate a validity of using wall function and high $y_1^+$ in calculation of high Reynolds number flow. The velocity profiles in boundary layer agree well with the law of the wall. And it is found that the range of $y^+$��which validated the logarithmic law of the wall grows with increasing Reynolds number. From the result, an equation is suggested that can be used to estimate a maximum $y^+$ value of validity of the log law. And the slope(1/$\kappa$) of the log region of the numerical result is larger than that of experimental data. On the other hand, as $y_1^+$ is increasing, both the friction and the pressure resistances tend to increase finely. When using $y_1^+$ value beyond the range of log law, the surface shear stress shows a significant error and the pressure resistance increases rapidly. However, when using $y_1^+$ value in the range, the computational result is reasonable. From this study, the use of the wall function with high value of $y_1^+$ can be justified for a full scale Reynolds number ship flow.

• Geomechanics and Engineering
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• v.13 no.3
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• pp.459-474
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• 2017

To investigate the mechanical properties of Expanded Polystyrene (EPS) Beads Stabilized Lightweight Soil (EBSLS), Laboratory studies were conducted. Totally 20 sets of specimens according to the complete test design were prepared and tested with unconfined compressive test and consolidated drained triaxial test. Results showed that dry density of EBSLS ($0.67-1.62g/cm^3$) decreases dramatically with the increase of EPS beads volumetric content, while increase slightly with the increase of cement content. Unconfined compressive strength (10-2580 kPa) increases dramatically in parabolic relationship with the increase of cement content, while decreases with the increase of EPS beads volumetric content in hyperbolic relationship. Cohesion (31.1-257.5 kPa) increases with the increase of cement content because it is mainly caused by the bonding function of hydration products of cement. The more EPS beads volumetric content is, the less dramatically the increase is, which is a result of the cohesion between hydration products of cement and EPS beads is less than that between hydration products of cement and sand particles. Friction angle ($14.92-47.42^{\circ}$) decreases with the increase of EPS beads volumetric content, which is caused by the smoother surfaces of EPS beads than sand grains. The stress strain curves of EBSLS tend to be more softening with the increase of EPS beads content or the decrease of cement content. The shear contraction of EBSLS increases with the increase of $c_e$ or the decrease of $c_c$. The results provided quantitative relationships between physico-mechanical properties of EBSLS and material proportion, and design process for engineering application of EBSLS.