• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.7
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• pp.561-568
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• 2013

After we designed Bearingless rotor hub system for 7,000lb class helicopter, flexbeam fatigue analysis was conducted for validation of requirement life time 8,000 hours. sectional structural analysis method applying elastic beam model was used. Fatigue analysis for two sections of flexbeam which were expected to weak to fatigue damage from result of static analysis was conducted. Extension, bending and torsion stiffness of flexbeam section shape was calculated using VABS for structure analysis. S-N curve of two composite material which composed flexbeam was generated using wohler equation. Load analysis of bearingless rotor system was conducted using CAMRAD II and load analysis result was applied HELIX/FELIX standard load spectrum to generate bearingless rotor system load spectrum which was used flexbeam fatigue safe life analysis.

• Journal of Preventive Medicine and Public Health
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• v.46 no.6
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• pp.336-345
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• 2013

Objectives: Research has shown that obesity appears to spread through social ties. However, the association between other characteristics of social networks and obesity is unclear. This study aimed to identify the association between social network characteristics and body mass index (BMI, $kg/m^2$) in an elderly Korean population. Methods: This cross-sectional study analyzed data from 657 Koreans (273 men, 384 women) aged 60 years or older who participated in the Korean Social Life, Health, and Aging Project. Network size is a count of the number of friends. Density of communication network is the number of connections in the social network reported as a fraction of the total links possible in the personal (ego-centric) network. Average frequency of communication (or meeting) measures how often network members communicate (or meet) each other. The association of each social network measure with BMI was investigated by multiple linear regression analysis. Results: After adjusting for potential confounders, the men with lower density (<0.71) and higher network size (4-6) had the higher BMI (${\beta}$=1.089, p=0.037) compared to the men with higher density (>0.83) and lower size (1-2), but not in the women (p=0.393). The lowest tertile of communication frequency was associated with higher BMI in the women (${\beta}$=0.885, p=0.049), but not in the men (p=0.140). Conclusions: Our study suggests that social network structure (network size and density) and activation (communication frequency and meeting frequency) are associated with obesity among the elderly. There may also be gender differences in this association.

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.347-357
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• 2013

Recently, In recognition of outstanding structural performance the use of Concrete Filled steel Tube(CFT) columns has been increased. Research is ongoing that effective use of cross-sectional because steel strength development and rising prices. In this Lab, suggests new shape by Thin steel plates bent to be L-channel welded to form square steel tube to maximize efficiency of the cross section. In addition, since the rib placed at the center of the tube width acts as an anchor; higher load capacity of buckling is acceptable. we have developed New shape welded built-up square tube for broader usability which were bent to be L-shaped and thin Plate each unit member were welded. In order to apply the new shape built-up square columns, we predicted structure behavior, stress distribution with parameter Width thickness ratio. The experimental results presented in standards and even exceed the b/t of the rib anchors installed in the role due to exert enough strength and deformation to improve performance was favorable.

• Journal of Ecology and Environment
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• v.44 no.3
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• pp.143-154
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• 2020

Background: Korean wild boars (Sus scrofa coreanus Heude), because of their adaptability, are a widespread large mammal; however, they sometimes cause problems by invading farms and eating the crops, creating insufficiencies of some foods in South Korea. To understand the diet composition of Korean wild boars according to sex and body size, we collected their feces from Mt. Jeombongsan, Seoraksan National Park, South Korea. The sizes of fecal samples were measured, and genomic DNA was extracted from the samples. We amplified specific loci targeting plants (rbcL and trnL) and animals (COI) to detect the food sources of this omnivore and amplified the ZF and SRY regions to determine the sex. Results: In the wild boar feces, Rosaceae and Bryophyte were the most frequently detected plant food sources at the family level and Diptera and Haplotaxida were the most frequently detected animal food sources at the order level. As a result of sex determination, the sex ratio of wild boars collected in the Mt. Jeombongsan area was approximately 1:1. Our result suggested that there is no significant difference between the diet composition of male and female boars. Based on the average cross-sectional area of the feces, the top 25% were classified into the large body size group and the bottom 25% were classified into the small body size group. The large body size group mainly preferred Actinidiaceae, and the small body size group most frequently consumed Fagaceae. The diet of the large body size group was more diverse than the small body size group. Conclusions: Our results showed that the wild boars preferred Rosaceae, especially Sanguisorba and Filipendula, as plant food sources, and Diptera and Coleoptera of Insecta as animal food sources. Based on the results, the dietary preferences of wild boar appear to be distinguished by not their sex but their body size. Our study could help to elucidate the feeding ecology and population structure of wild boar, as well as address conservation and management issues.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.2
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• pp.674-680
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• 2013

This paper investigates the impact of liquidity constraints on investment expenditures of family and non-family firms. We analyze the ownership structure of family firms to determine whether family control alleviates or exacerbates investment-cash flow sensitivity in domestic firms. To examine the impact of liquidity constraints on investment expenditures of family and non-family firms, we used a financial data of 644 Korea Exchange traded companies over the 2000 - 2010 period. We estimated a time-series and cross-sectional regression model, using samples of family firms and non-family firms. The results show that cash flow is not associated with investment expenditure in family firms, whereas cash flow has a positive impact on investment in non-family firms. Our results show that lower or no investment-cash flow sensitivities in family-controlled firms are mainly attributable to lower agency costs through strong monitoring activities of family members. Higher investment-cash flow sensitivities are observed in non-family firms with more agency problems. This suggests that investment-cash flow sensitivities would be useful measures of liquidity constraints.

• Journal of the korean society of oceanography
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• v.39 no.1
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• pp.72-95
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• 2004

The Yellow Sea is characterized by relatively shallow water depth, varying range of tidal action and very complex coastal geometry such as islands, bays, peninsulas, tidal flats, shoals etc. The dynamic system is controlled by tides, regional winds, river discharge, and interaction with the Kuroshio. The circulation, water mass properties and their variability in the Yellow Sea are very complicated and still far from clear understanding. In this study, an effort to improve our understanding the dynamic feature of the Yellow Sea system was conducted using numerical simulation with the ROMS model, applying climatologic forcing such as winds, heat flux and fresh water precipitation. The inter-annual variability of general circulation and thermohaline structure throughout the year has been obtained, which has been compared with observational data sets. The simulated horizontal distribution and vertical cross-sectional structures of temperature and salinity show a good agreement with the observational data indicating significantly the water masses such as Yellow Sea Warm Water, Yellow Sea Bottom Cold Water, Changjiang River Diluted Water and other sporadically observed coastal waters around the Yellow Sea. The tidal effects on circulation and dynamic features such as coastal tidal fronts and coastal mixing are predominant in the Yellow Sea. Hence the tidal effects on those dynamic features are dealt in the accompanying paper (Kim et at., 2004). The ROMS model adopts curvilinear grid with horizontal resolution of 35 km and 20 vertical grid spacing confirming to relatively realistic bottom topography. The model was initialized with the LEVITUS climatologic data and forced by the monthly mean air-sea fluxes of momentum, heat and fresh water derived from COADS. On the open boundaries, climatological temperature and salinity are nudged every 20 days for data assimilation to stabilize the modeling implementation. This study demonstrates a Yellow Sea version of Atlantic Basin experiment conducted by Haidvogel et al. (2000) experiment that the ROMS simulates the dynamic variability of temperature, salinity, and velocity fields in the ocean. However the present study has been improved to deal with the large river system, open boundary nudging process and further with combination of the tidal forcing that is a significant feature in the Yellow Sea.

• Journal of Korean Society of Steel Construction
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• v.16 no.1 s.68
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• pp.123-134
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• 2004

In this research, a multilevel decomposition technique to enhance the efficiency of the configuration optimization of truss structures was proposed. On the first level, the nonlinear programming problem was formulated considering cross-sectional areas as design variables, weight, or volume as objective function and behavior under multiloading condition as design constraint. Said nonlinear programming problem was transformed into a sequential linear programming problem. which was effective in calculation through the approximation of member forces using behavior space approach. Such approach has proven to be efficient in sensitivity analysis and different form existing shape optimization studies. The modified method of feasible direction (MMFD) was used for the optimization process. On the second level, by treating only shape design variables, the optimum problem was transformed into and unconstrained optimal design problem. A unidirectional search technique was used. As numerical examples, some truss structures were applied to illustrate the applicability. and validity of the formulated algorithm.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.2
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• pp.25-36
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• 2018

Drip irrigation system is a low energy cost method which can efficiently save and supply water by dropping water slowly on the crop's root zone during crop growth. In the drip irrigation system, disk filters take an important role to physically remove impurity (inorganic and suspended organic) particles present in agricultural water which can cause emitter clogging. For the purpose, both top-and-bottom surfaces of the disk are grooved in micron size flowing from outside to inside. However, many congested flow paths in disk filter media incur higher head loss of inflow water resulting in relatively decreasing velocities depending on operation time than sand and mesh filters. Therefore, it is important to optimize the structure of disk filter in micro irrigation system. The head loss of disk filter media takes also charge of more than 60 % of total head loss in whole disk filter. This study is to find the appropriate cross-sectional shape of the disk groove to minimize the head loss by executing the experiment. The experiment used three disk filters that have similar filter body but have a half-elliptic and two kinds of triangular cross sections. The experimental results showed that the disk filter with half-elliptic cross sections of disk grooves have less head loss than the disk filter with regular triangular one.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.1
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• pp.11-18
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• 2017

In the present study, the low speed (4 km/h) crash behaviour of an aluminium bumper system was characterised by FE analyses based on the FMVSS 581, which regulates automotive bumpers. Two types of cross-sectional designs, i.e., Model 1, which contains a single rib and Model 2, double ribs, have been considered along with Al7021, 6082 and 6060 for the aluminium bumper back beam. Variations in thickness starting from 2 to 4 mm of the bumper system cross-section in the FE model was implemented in order to investigate the thickness effect on the bumper's crash behaviour.. Three kinds of design variables, namely, number of ribs, material and thickness, are considered. The FE analysis results are summarised with the maximum load and the Specific Energy Absorption (SEA) since they are the key factors in determining the crashworthiness of automotive structures. The results may also be able to indicate how to achieve lightweight structure of the automotive bumper system either directly or indirectly.

• Structural Engineering and Mechanics
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• v.65 no.6
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• pp.679-687
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• 2018

In composite materials technology, the fiber-reinforced polymers (FRP) have opened up new horizons in infrastructural engineering field for strengthening existing structures and components of structure. The Carbon fiber reinforced polymer (CFRP) sheets are well suited for RC columns to this application because of their high strength to weight ratio, good fatigue properties and excellent resistance to corrosion. The main focus of present experimental work is to investigate effect of shapes on axial behavior of CFRP wrapped RC columns having same cross-sectional area and slenderness ratio. The CFRP volumetric ratio and percentage of steel are also adopted constant for all the test specimens. A total of 18 RC columns with slenderness ratio four were cast. Nine columns were control and the rest of nine columns were strengthened with one layer of CFRP wrap having 35 mm of corner radius. Columns confined with CFRP wrap were designed using IS: 456:2000 and ACI 440.2R.08 provisions. All the test specimens were loaded for axial compression up to failure and failure pattern for each shaped column was investigated. All the experimental results were compared with analytical values calculated as per the ACI-440.2R-08 code. The test results clearly demonstrated that the axial behavior of CFRP confined RC columns is affected with the change in shapes. The axial deformation is higher in CFRP wrapped RC circular column as compared to square and rectangular columns. Stress-strain behaviour revealed that the yield strength gained from CFRP confinement was significant for circular columns as compare to square and rectangular columns. This behaviour may be credited due to effect of shape on lateral deformation in case of CFRP wrapped circular columns at effective confinement action.