• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.11-23
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• 2010

A sacrificial member with aluminum foam of excellent energy absorption capacity was proposed for the protection of significant structures. Parametric studies of explicit finite element analyses were performed to investigate the pressure mitigation of close-range air-blasts. The scaled distance of the blast had a range of Z=0.48~0.95 and an empirical blast load function was utilized. The analytical parameters of the aluminum foam were density, thickness and the existence of a cover sheet. Analytical results showed that the transmitted pressure can be controlled to have a similar level of yield values of the foam by using a foam with low density and higher thickness. As the blast load increased, the sacrificial member needed to have higher density and thickness. A cover sheet of the foam clearly showed its effect on the wider distribution of blast pressure. It is necessary to determine the design parameters of sacrificial foams considering different energy dissipation capacities according to the scaled distance.

• Journal of Energy Engineering
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• v.12 no.2
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• pp.84-92
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• 2003

A one-dimensional thermal-hydraulic analysis computer program is developed for thermal sizing of a copper bonded steam generator. It is assumed that the conduction heat transfer of copper region between the hot side and the cold side tube is one-dimensional and its thermal resistance is derived as a function of a tube pitch. The flow regions of the water/steam side are divided into four regions: subcooled, saturated, film boiling, and super-heated. The number of tube selected ranges from 250 to 3500 and the pitch to tube diameter (P/D) ratios are 1.4, 1.6 and 1.8 for the parametric study calculation. The calculation results showed that when the number of tube was 2500, the length of the heating tube was about 12 m and the outside diameter of the steam generator was about 3 m. If the P/D ratio increases, the thermal resistance of copper component also increases, however the length of the heating tube is not so much increased.

• Tribology and Lubricants
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• v.34 no.3
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• pp.75-83
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• 2018

Microturbomachinery (< 250 kW) using gas foil bearings can function without oil lubricants, simplify rotor-bearing systems, and demonstrate excellent rotordynamic stability at high speeds. State-of-the-art technologies generally use bump foil bearings or leaf foil bearings due to the specific advantages of each of the two types. Although these two types of bearings have been studied extensively, there are very few studies on leaf-bump foil bearings, which are a combination of the two aforementioned bearings. In this work, we illustrate a simple mathematical model of the leaf-bump foil bearing with leaf foils supported on bumps, and predict its static and dynamic performances. The analysis uses the simple elastic model for bumps that was previously developed and verified using experimental data, adds a leaf foil model, and solves the Reynolds equation for isothermal, isoviscous, and ideal gas fluid flow. The model predicts that the drag torques of the leaf-bump foil bearings are not affected significantly by static load and bearing clearance. Due to the preload effect of the leaf foils, rotor spinning, even under null static load, generates significant hydrodynamic pressure with its peak near the trailing edge of each leaf foil. A parametric study reveals that, while the journal eccentricity and minimum film thickness decrease, the drag torque, direct stiffness, and direct damping increase with increasing bump stiffness. The journal attitude angle and cross-coupled stiffness remain nearly constant with increasing bump stiffness. Interestingly, they are significantly smaller compared to the corresponding values obtained for bump foil bearings, thus, implying favorable rotor stability performance.

• The Korean Journal of Applied Statistics
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• v.32 no.5
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• pp.721-740
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• 2019

Noise reduction is an important field in image processing and requires a statistical approach. However, it is difficult to assume a specific distribution of noise, and a spatial filter that reflects regional characteristics is a small sample and cannot be accessed in a parametric manner. The first order image differential and the second order image differential show a clear difference according to the noise level included in the image and can be more clearly understood using the canyon edge detector. The Fligner-Killeen test was performed and the bootstrap method was used to statistically check the noise level. The estimated noise level was set between 0 and 1 using the cumulative distribution function of the beta distribution. In this paper, we propose a nonparametric noise reduction algorithm that accounts for the noise level included in the image.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.7 no.2
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• pp.301-315
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• 2000

The main purpose of this study was to evaluate the effect of a Rhythmical Exercise Program(REP) on physiological functions such as muscle strength, blood pressure, pulse, flexibility and body fat in the elderly. The research employed a non-equivalent control group pre-post test quasi experimental design. REP consisted of 45 minutes of dance, 3 times a week for 10 weeks. The formulated hypothesis were examined using the non-parametric statistics; Wilcoxon Signed rank sum test and Mann-Whitney test. The results are as follows; 1. The upper muscle strength and lower muscle strength of the experimental group were significantly higher than those of the control group following the REP(P<.0 5). And the Period of REP affected the muscle strength; the longer the exercise period, the stronger the muscle strength became. 2. The systolic blood pressure of the experimental group was significantly lower than that of the control group following the REP(p<.05). But there was no significant difference in the diastolic blood pressure between the experimental and control groups. The period of REP affected only systolic pressure; the longer the exercise period, the lower the systolic pressure became. 3. There was no significant difference in heart rate between the experimental and control groups, following the exercise period. 4. The flexibility of the experimental group was significantly higher than those of the control group following the REP(p<.01). And the period of REP affected flexibility; the longer the exercise period, the higher the flexibility(p<.05) became. 5. There was no significant difference of body fat between the experimental and control groups. The body fat of the experimental groups was significantly lower only 10 weeks after exercise(p<.01). Based on these results, it is suggested that rhythmical exercise program improves muscle strength, systolic pressure, and flexibility in the elderly.

• Structural Engineering and Mechanics
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• v.61 no.4
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• pp.527-538
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• 2017

The evaluation of the loss-of-support conditions of frictional beam-to-column connections using simplified numerical models describing the transverse response of a portal-like structure is presented in this paper considering the effects of the seismic-hazard disaggregation. Real earthquake time histories selected from European Strong-motion Database (ESD) are used to show the effects of the seismic-hazard disaggregation on the beam loss-of-support conditions. Seismic events are classified according to different values of magnitudes, epicentral distances and soil conditions (stiff or soft soil) highlighting the importance of considering the characteristics of the seismic input in the assessment of the loss-of-support conditions of frictional beam-to-column connections. A rigid and an elastic model of a frame of a precast industrial building (2-DoF portal-like model) are presented and adopted to find the minimum required friction coefficient to avoid sliding. Then, the mean value of the minimum required friction coefficient with an epicentral distance bin of 10 km is calculated and fitted with a linear function depending on the logarithm of the epicentral distance. A complete parametric analysis varying the horizontal and vertical period of vibration of the structure is performed. Results show that the loss-of-support condition is strongly influenced by magnitude, epicentral distance and soil conditions determining the frequency content of the earthquake time histories and the correlation between the maxima of the horizontal and vertical components. Moreover, as expected, dynamic characteristics of the structure have also a strong influence. Finally, the effect of the column nonlinear behavior (i.e. formation of plastic hinges at the base) is analyzed showing that the connection and the column are a series system where the maximum force is limited by the element having the minimum strength. Two different longitudinal reinforcement ratios are analyzed demonstrating that the column strength variation changes the system response.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.2
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• pp.45-51
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• 2006

In this paper, we propose a new architecture of Information Granulation based genetically optimized Self-Organizing Fuzzy Polynomial Neural Networks (IG_gSOFPNN) that is based on a genetically optimized multilayer perceptron with fuzzy polynomial neurons (FPNs) and discuss its comprehensive design methodology involving mechanisms of genetic optimization, especially information granulation and genetic algorithms. The proposed IG_gSOFPNN gives rise to a structurally optimized structure and comes with a substantial level of flexibility in comparison to the one we encounter in conventional SOFPNNs. The design procedure applied in the construction of each layer of a SOFPNN deals with its structural optimization involving the selection of preferred nodes (or FPNs) with specific local characteristics (such as the number of input variables, the order of the polynomial of the consequent part of fuzzy rules, and a collection of the specific subset of input variables) and addresses specific aspects of parametric optimization. In addition, the fuzzy rules used in the networks exploit the notion of information granules defined over system's variables and formed through the process of information granulation. That is, we determine the initial location (apexes) of membership functions and initial values of polynomial function being used in the premised and consequence part of the fuzzy rules respectively. This granulation is realized with the aid of the hard c-menas clustering method (HCM). To evaluate the performance of the IG_gSOFPNN, the model is experimented with using two time series data(gas furnace process and NOx process data).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.1
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• pp.62-66
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• 2017

The interest on the potential earthquake magnitude and the request on the earthquake-resistant design examination for coastal structures are emerged because of the recently occurred magnitude 5.8 earthquake in Gyeoung-Ju, Korea. In this study, the magnitude and its confidence intervals with the return periods are estimated using the KMA earthquake magnitude data (over 3.5 and 4.0 in magnitude) by the non-parametric extreme value analysis. In case of using the "over 4.0" data set, the estimated magnitudes on the 50- and 100-years return periods are 5.81 and 5.94, respectively. Their 90% confidence intervals are estimated to be 5.52-6.11, 5.62-6.29, respectively. Even though the estimated magnitudes have limitations not considering the spatial distribution, it can be used to check the stability of the diverse coastal structures in the perspective of the life design because the potential magnitude and its confidence intervals in Korea are estimated based on the available 38-years data by the extreme value analysis.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.1-8
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• 2014

The present study proposes a simple equation to straightforwardly determine the potential plastic hinge length in boundary element of reinforced concrete shear walls. From the idealized curvature distribution along the shear wall length, a basic formula was derived as a function of yielding moment, maximum moment, and additional moment owing to diagonal tensile crack. Yielding moment and maximum moment capacities of shear wall were calculated on the basis of compatability of strain and equilibrium equation of internal forces. The development of a diagonal tensile crack at web was examined from the shear transfer capacity of concrete specified in ACI 318-11 provision and then the additional moment was calculated using the truss mechanism along the crack proposed by Park and Paulay. The moment capacities were simplified from an extensive parametric study; as a result, the equivalent plastic hinge length of shear walls could be formulated using indices of longitudinal tensile reinforcement at the boundary element, vertical reinforcement at web, and applied axial load. The proposed equation predicted accurately the measured plastic hinge length, providing that the mean and standard deviation of ratios between predictions and experiments are 1.019 and 0.102, respectively.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.87-93
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• 2008

The large scale shaker can be employed to measure linear and nonlinear shear moduli of soils in situ as a function of shear strain. The method involves applying dynamic loads on a surface foundation measuring the dynamic response of the soil mass beneath the foundation with embedded instrumentation. This paper focuses on the development of a framework of the inverse analysis for the interpretation of test data to estimate linear and nonlinear shear moduli of soils along with the necessity of the inverse analysis. The suggested framework is based on the nonlinear least squares but it uses two iterative loops to account for the nonlinear behavior of soil that sensors are not located. The validity of the suggested inversion framework is tested through a series of numerical parametric studies. An example use of the suggested inversion framework is also shown. Because the field condition may affect the accuracy of suggested method, it is important to conduct a preliminary inverse analysis to quantify the discrepancy between the estimated modulus and the baseline.