• Earthquakes and Structures
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• v.22 no.3
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• pp.245-261
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• 2022

Key questions to researchers interested in nonlinear analysis of skeletal structures are whether the distributed plasticity approach - albeit computationally demanding - is more reliable than the concentrated plasticity to adequately capture the extent and severity of the inelastic response, and whether force-based formulation is more efficient than displacement-based formulation without compromising accuracy. The present research focusing on performance-based seismic response of mid-span concrete bridges provides a pilot holistic investigation opting for some hands-on answers. OpenSees software is considered adopting different modeling techniques, viz. distributed plasticity (through either displacement-based or force-based elements) and concentrated plasticity via beam-with-hinges elements. The pros and cons of each are discussed based on nonlinear pushover analysis results, and fragility curves generated for various performance levels relying on incremental dynamic analyses under real earthquake records. Among prime conclusions, distributed plasticity modeling albeit inherently not relying on prior knowledge of plastic hinge length still somewhat depends on such information to ensure accurate results. For instance, displacement-based and force-based approaches secure optimal accuracy when dividing, for the former, the member into sub-elements, and satisfying, for the latter, a distance between any two consecutive integration points, close to the expected plastic hinge length. On the other hand, using beam-with-hinges elements is computationally more efficient relative to the distributed plasticity, yet with acceptable accuracy provided the user has prior reasonable estimate of the anticipated plastic hinge length. Furthermore, when intrusive performance levels (viz. life safety or collapse) are of concern, concentrated plasticity via beam-with-hinges ensures conservative predicted capacity of investigated bridge systems.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.355-373
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• 2017

Tunnelling in urban areas, it is essential to understand existing structure-tunnel interactive behavior. Serviced structures in the city are supported by pile foundation, since they are certainly effected due to tunnelling. In this research, thus, pile load distribution and ground behavior due to tunnelling below grouped pile were investigated using laboratory model test. Grouped pile foundations were considered as 2, 3 row pile and offsets (between pile tip and tunnel crown: 0.5D, 1.0D and 1.5D for generalization to tunnel diameter, D means tunnel diameter). Soil in the tank for laboratory model test was formed by loose sand (relative density: Dr = 30%) and strain gauges were attached to the pile inner shaft to estimate distribution of axial force. Also, settlements of grouped pile and adjacent ground surface depending on the offsets were measured by LVDT and dial gauge, respectively. Tunnelling-induced deformation of underground was measured by close range photogrammetric technique. Numerical analysis was conducted to analyze and compare with results from laboratory model test and close range photogrammetry. For expression of tunnel excavation, the concept of volume loss was applied in this study, it was 1.5%. As a result from this study, far offset, the smaller reduction of pile axial load and was appeared trend of settlement was similar among them. Particulary, ratio of pile load and settlement reduction were larger when the offset is from 0.5D to 1.0D than from 1.0D to 1.5D.

• Health Policy and Management
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• v.29 no.4
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• pp.469-481
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• 2019

Background: As South Korea is becoming an aged society very rapidly, the increase in osteoarthritis prevalence raises various public health issues in this country. This study aimed to explore the socio-demographic factors associated with osteoarthritis in the current Korean elderlies. Methods: Using the National Survey of Korean Elderly data (2014, 2017), we analyzed 20,326 elderlies (males, 8,248; females, 12,078) and conducted multivariate logistic regression analyses by sex. The dependent variable is whether a participant was diagnosed with osteoarthritis or not. Independent variables of interest is socio-demographic factors such as age, marital status, household type, residential area, household income, religion, the longest job, the number of close relatives, the number of close friends, and survey year. Control variables are various health behavioral factors and disease-related factors. Results: Prevalence of osteoarthritis was 19.2% in male elderlies and 47.0% in female elderlies. According to the results of the multivariate logistic regression adjusted for all studied control variables, the odds ratio (OR) for having osteoarthritis of under-elementary school graduates (their counterpart was college graduate group) was 1.81 (95% confidence interval [CI], 1.29-2.52) in males and 1.67 (95% CI, 1.12-2.47) in females. The OR of those having a job in agriculture & forestry fishery as their longest job (their counterpart was those who had never participated in labor force during their lifetime) was 5.07 (95% CI, 1.46-17.58) in males and 1.49 (95% CI, 1.27-1.74) in females. In males, the second-low quartile group in household yearly income (their counterpart was the highest quartile group) had the OR of 1.22 (95% CI, 0.98-1.53). In females, the OR of those having a religion of Buddhism (their counterpart was those having no religion) was 1.20 (95% CI, 1.07-1.35) and the OR of those who had no relatives (their counterpart was those having more than 3 close relatives) was 1.31 (95% CI, 1.10-1.56). Conclusion: This study found that in Korean elderlies, education, the longest job, household income, religion, and the number of close relatives are associated with their suffering from osteoarthritis. Further study and designing appropriate interventions are needed to alleviate current and future individual and socioeconomic burdens of osteoarthritis in an aged society like South Korea.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 1993.09a
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• pp.13-20
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• 1993

In Korea, the elderly support has been accomplished by the families in the extended family system with the influence of the transmigration and the confucianism thought. But in Korea the drastic changes of society such as, the growth of the elderly pollution, the urbanization, the decrease of the birth rate, the increase of the working women, the growth of the nuclear families, etc., make the family difficult to take care of the elderly. Therefore, some people insist on the construction of the elderly home as the way to solve the elderly problems and some of corporations including profit-organizations are ready to participate the construction of the elderly home. They force the change of the current social security law because it is impossible to carry out the plans uncer the law. At this point, the conditions of the elderly home in Japan which is geographically close to Korea and has facillicated the elderly home business were examined at the consumer perspectives. The purpose of this study were to consider the possible problems in the elderly home and to prevent from happening another elderly problems in the future.

• Tribology and Lubricants
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• v.17 no.5
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• pp.391-398
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• 2001

Two dimensional slow viscous flow around two counter-rotating equal cylinders is investigated based on Stokes'approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns around the cylinders are shown and the pressure distribution in the flow field is determined. By integrating the stress distributions on the cylinder, the force and the moment exerted on the cylinder are calculated. The flow rate through the gap between the two cylinders is also determined as the distance between two cylinders varies. Special attention is directed to the case of very small distance between two cylinders concerned with the lubrication theory and the minimum pressure is calculated to explain a possible cavitation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.142-149
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• 2000

Two dimensional slow viscous flow around two counter-rotating equal cylinders is Investigated based on Stokes' approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns around the cylinders are shown and the pressure distribution In the flow field is determined. By Integrating the stress distribution on the cylinder, the force and the moment exerted on the cylinder are calculated. The flow rate through the gap between the two cylinders is determined as the distance between two cylinders vary. It Is also revealed that the velocity at the far field has finite non-zero value. Special attention is directed to the case of very small distances between two cylinders by way of the lubrication theory.

• Smart Media Journal
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• v.4 no.2
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• pp.9-16
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• 2015

Fluids appear in innumerable phenomena; therefore, it is interesting to reproduce those phenomena by computer graphics techniques. However, this process is not trivial. We work with a fluid simulation that uses Navier-Stokes equations to model the fluid, a semi-Lagrangian approach to solve it and the level set method to track the surface of the fluid. Modified versions of the Navier-Stokes equations for computer graphics allow us to create a wide diversity of effects. In this paper, we propose a technique that allows us to integrate a force inspired by surface tension into the model. We describe which information we need and how to modify the model with this new approach. We end up with a modified simulation that has additional effects that might be suitable for computer graphics purposes. The effects that we are able to recreate are small waves and droplet-like formations close to the surface of the fluid. This model preserves the overall behavior governed by the Navier-Stokes equations.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.354-359
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• 2001

As the temperature of liquid under negative pressure approaches the absolute zero, the nucleation process due to thermal fluctuations hardly occurs. Instead of this mechanism, quantum fluctuations may lead the formation of nucleus for new phase in metastable state. In this study, the thermal as well as quantum nucleation bubble in liquid helium under negative pressure was investigated theoretically. The energy barrier against nucleation was estimated by molecular interaction due to the Londom dispersion force. It is shown that the phase transition from liquid to vapor in is possible due to the quantum tunneling below 0.2 K for Helium-4 and 0.1 K for Helium-3, at negative pressures close to the ideal tensile strength at which every liquid molecules become bubbles simultaneously.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.283-288
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• 2001

We have investigated aluminum cluster deposition using a classical molecular dynamics simulations. We studied the variations of the cluster momentum and the impulse force during collisions, and found that the close-packed cluster impact has some of properties of the single particle collision and the linear atomic chain collisions. We also simulated the series of energetic cluster deposition with energy Per atom. When energy Per atom in cluster has some eV rather than very low, the intermixing occurred easily in growth film and we can obtain a good film without subsequent annealing process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.704-713
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• 1998

The analysis of dynamic forces is essential to the design of systems, stress analysis, or life prediction of part of machine. Calculation of dynamic forces has very close relations with multibody dynamics algorithm. In this paper, an algorithm which calculates joint reaction force/moment of flexible multibody dynamic systems is proposed by using inverse dynamic algorithm and velocity transformation technique.