• Steel and Composite Structures
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• v.52 no.5
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• pp.501-513
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• 2024

Two-directional functionally graded materials (2D-FGMs) show extraordinary physical properties which makes them ideal candidates for designing smart micro-switches. Pull-in instability is one of the most critical challenges in the design of electrostatically-actuated microswitches. The present research aims to bridge the gap in the static pull-in instability analysis of microswitches composed of 2D-FGM. Euler-Bernoulli beam theory with geometrical nonlinearity effect (i.e. von-Karman nonlinearity) in conjunction with the modified couple stress theory (MCST) are employed for mathematical formulation. The micro-switch is subjected to electrostatic actuation with fringing field effect and Casimir force. Hamilton's principle is utilized to derive the governing equations of the system and corresponding boundary conditions. Due to the extreme nonlinear coupling of the governing equations and boundary conditions as well as the existence of terms with variable coefficients, it was difficult to solve the obtained equations analytically. Therefore, differential quadrature method (DQM) is hired to discretize the obtained nonlinear coupled equations and non-classical boundary conditions. The result is a system of nonlinear coupled algebraic equations, which are solved via Newton-Raphson method. A parametric study is then implemented for clamped-clamped and cantilever switches to explore the static pull-in response of the system. The influences of the FG indexes in two directions, length scale parameter, and initial gap are discussed in detail.

• Hip & pelvis
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• v.34 no.2
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• pp.115-121
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• 2022

Purpose: The purpose of this study was to evaluate the wear and survival rates of third-generation ceramic heads on a conventional ultra-high molecular weight polyethylene liner. Materials and Methods: A total of 160 hips (147 patients with a mean age of 55.9 years) who underwent total hip arthroplasty using the third-generation ceramic head on a conventional polyethylene liner from March 1998 to August 2003 were reviewed retrospectively. Evaluation of the wear rate for 56 hips (49 patients) followed-up for at least 15 years was performed using the PolyWare program version 8 (Draftware Developers, USA). The Kaplan-Meier survivorship was also evaluated. Results: Linear wear and volumetric wear rates were 0.11±0.47 mm/year and 32.75±24.50 mm³/year, respectively. Nine revisions were performed during the follow-up period because of cup or stem loosening. The Kaplan-Meier survival rate, using cup revision or total revision total hip arthroplasty (THA) as the endpoint of analysis, was 93.7% at 15 years and 73.6% at 20 years. Conclusion: Because all revisions were performed between 15 and 20 years in our study, surgeons should pay greater attention to patients who underwent THA with ceramic-on-polyethylene bearing from 15 years postoperatively. Contemporary alumina ceramic on highly cross-linked polyethylene could certainly be a good alternative bearing couple providing better longevity.

• Korean System Dynamics Review
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• v.12 no.2
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• pp.69-94
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• 2011

Daejeon, encompassing Daedeok Science Town and Daedeok Innopolis, possesses the advantage of portraying relatively higher regional innovation capacity and facilitating network formation among regional professional research organizations. Applying the Social Network Analysis(SNA) techniques, this paper focuses on divulging structural and spatial characteristics of the Daejeon Information and Communication(ICT) industry network, analyzing co-research projects implemented by the Daejeon-based universities. For the analytical tool, it depends on NETMINER 3.0. Furthermore, based on the Systems Thinking approaches, this study suggests a couple of policy implications. Judging from the Korea Standard Industrial Classification principles, the existing ICT industry is subdivided into 11 sub-industries. The highest degree centralization value comes from the Mobile Communication sub-industry(188.668%), indicating that Mobile Communication sub-industry exerts the most significant impact on the regional innovation networking in Daejeon. Among various stakeholders, Korea Advanced Institute of Science and Technology(KAIST) records the top ranking in most categories, conspicuously leading the institute-industry linkage. In terms of the ICT spatial distribution, the intra-regional cooperation examples present the strongest linkage values, followed by Daejeon-the Capital Region ones. Finally, as well shown in a series of causal loop analyses, this study recommends that Daejeon should put top policy priority in strengthening the internal ICT network within Daejeon proper. Here, Daejeon should keep in mind the fact that there exist reinforcing loops between Daejeon's attractiveness and the entering of new ICT firms.

• Journal of the Korean Geosynthetics Society
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• v.16 no.3
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• pp.11-19
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• 2017

A series of pullout tests to compression type anchors is conducted. The test is carried out on a couple of steel cables installed in sandy soil with 60% of relative density. The test is performed with 6 different bonded lengths, which are 1, 2, 3, 4, 5, 6 times longer than the initial bonded length (Lc =30 mm). A numerical analysis with the same condition as the test is also performed to compare each other. Finally, those results are compared with theoretical result by Oosterbaan and Gifford (1972). The result shows that the ultimate pullout capacity appears to increase with an increase of bonded length, and that the results of test, numerical analysis and theoretical approach have a good agreement in the ultimate pullout capacity at failure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.973-978
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• 2010

In this paper, we studied the shimmy phenomena of an aircraft nose landing gear considering free-play. Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. This phenomena is caused by a couple of conditions such as low torsional stiffness of the strut, friction and free-play in the gear, wheel imbalance, or worn parts, and it may make an aircraft unstable. Free-play non-linearity is linearized by the described function for a stability analysis in a frequency domain, and time marching is performed using the fourth-order Runge-Kutta method. We performed the numerical simulation of the nose landing gear shimmy and investigated its linear and nonlinear characteristics. From the numerical results, we found limit-cycle-oscillations at the speed under linear shimmy speed for the case considering free-play and it can be concluded that the shimmy stability can be decreased by free-play.

• Journal of Biomedical Engineering Research
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• v.32 no.1
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• pp.7-14
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• 2011

This study suggested an optimized algorithm for detecting the loss of balance(LOB) in the seated position. And the sensitivity analysis was performed in order to identify the role of each design variable in the algorithm. The LOB algorithm consisted of data processing of measured signals, an internal model of the central nervous system and a control error anomaly(CEA) detector. This study optimized design variables of a CEA detector to obtain improved values of the success rate(SR) of detecting the LOB and the margin time(MT) provided for preventing the falling. Nine healthy adult volunteers were involved in the experiments. All the subjects were asked to balance their body in a predescribed seated posture with the rear legs of a four-legged wooden chair. The ground reaction force from the right leg was measured from the force plate while the accelerations of the chair and the head were measured from a couple of piezoelectric accelerometers. The measured data were processed to predict the LOB using a detection algorithm. Variables S2, h2 and hd are related to the detector: S2 represents a data selecting window, h2 a time shift and hd an operating period of the LOB detection algorithm. S2 was varied from 0.1 to 10 sec with an increment of 0.1 sec, and both h2 and hd were varied from 0.01 to 1.0 sec with an increment of 0.01 sec. It was found that the SR and MT were increased by up to 9.7% and 0.497 sec comparing with the previously published case when the values of S2, h2 and hd were set to 4.5, 0.3 and 0.2 sec, respectively. Also the results of sensitivity analysis showed that S2 and h2 had considerable influence on the SR while these variables were not so sensitive to the MT.

• Geotechnical Engineering
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• v.7 no.2
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• pp.51-66
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• 1991

In the stability analysis of hillside slopes, the roots of vegetation have been considered to act as a soil reinforcement. In order to predict the amount of increase in soil shear resistance, produced by tensile strength of roots that intersect a potential slip surface in hillside slopes, new soil -root interaction models are proposed in this paper. For this purpose, firstly, laboratary teats and in-situ tests wert performed on soil-root systems, and experimental results were compared with a couple of soil-root interaction models which had been proposed by Gray, Waldron, and Wu etc. Based on this comparison, a new soil-root interaction model is proposed. Secondly, a probabilistic soil-root model is proposed based on statistical analysis considering random nature of root distribution, root characteristics, and soil-root interactions. Finally, to examine the effect of this root reinforcement system on stability of hillside slopes, a simple three-dimensional stability analysis was performed, and it was shown that root reinforcement had a significant stabilizing influence on shallow slips rather than deep slips in hillside slopes.

• Journal of Hydrogen and New Energy
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• v.29 no.4
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• pp.307-316
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• 2018

In this study, the failure mode and effect analysis (FMEA) of hydrogen production process by using the Thermococcus onnurineus NA1 was conducted and advanced methodology to compensate the weakness of previous FMEA methodology was applied. To bring out more quantitative and precise FMEA result for bio-hydrogen production process, fuzzy logic and potential loss cost estimated from ASPEN Capital Cost Estimator (ACCE) was introduced. Consequently, risk for releasing the flammable gases via internal leakage of steam tube which to control the operating temperature of main reactor was caution status in FMEA result without applying the fuzzification and ACCE. Moreover, probability of the steam tube plugging caused by solid property like medium was still caution status. As to apply the fuzzy logic and potential loss cost estimated from ACCE, a couple of caution status was unexpectedly upgraded to high dangerous status since the potential loss cost of steam tube for main reactor and decrease in product gases are higher than expected.

• The Korean Journal of Ecology
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• v.21 no.2
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• pp.169-174
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• 1998

This is the review of vegetational history of the post-glacial period in Korea. most of studies for vegetational changes are located in the lowland alluvial plain, especially below the hilly zone of western and eastern coastal regions of Korea. A couple of methods, pollen analysis and radiocarbon dating, have been employed in these studies. These results lead us to establish the pollen zonation in Korea as the followings. Yasuda et al.(1980) classified six period in Yongrang lake of sokcho. These are as follow I. 17,000-15,000yr B.P.: Picea, Abies, Pinus(Haploxylon), Larix stage, II.15,000-10,000yr B.P:Herb, Pteridophyta stage, III.10.000-6,700yr BP.:Quercus stage, IV.6,700-4,500yr B.P.:Pinus, Quercus, Carpinus stage, V.4,500-1,400yr B.P.:Quercus. Pinus stage, VI.1,400yr B.P.-present: Pinus, Herbs stage. Jo(1979) also divided the period into two stages from the outcomes of analysis done in Jumoonjin and other sites I.10,000-6,000yr B.P.:Quercus stage, II.6,000-present: Pinus-Quercus stage, and three substages: IIa.6,000-3,400 yr B.P.:lower Pinus stage, IIb.3,400-2,000yr B.P.:Pinus-Quercus stage, IIc.2,000-present: Pinus stage. Choi(1993, 1996) divided the period into three stages: I.6,000-5,000yr B.P.:Alnus, Quercus stage, II.5,000-4,000yr B.P.: Alnus, Quercus, Pinus stage, III.4,500-2,600yr B.P.: Alnus, Pinus stage. In the period around 6,000yr B.P. distinct dominant species clearly occupied the lowland of the eastern and western coasts. Thus, this strongly supports the fact that even if Korea experienced its warm and wet climate after the lateglacial, it underwent a different environmental change, dry climate, compared to the regions of Japan.

• Smart Structures and Systems
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• v.13 no.4
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• pp.587-614
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• 2014

In recent years the interest in online monitoring of lightweight structures with ultrasonic guided waves is steadily growing. Especially the aircraft industry is a driving force in the development of structural health monitoring (SHM) systems. In order to optimally design SHM systems powerful and efficient numerical simulation tools to predict the behaviour of ultrasonic elastic waves in thin-walled structures are required. It has been shown that in real industrial applications, such as airplane wings or fuselages, conventional linear and quadratic pure displacement finite elements commonly used to model ultrasonic elastic waves quickly reach their limits. The required mesh density, to obtain good quality solutions, results in enormous computational costs when solving the wave propagation problem in the time domain. To resolve this problem different possibilities are available. Analytical methods and higher order finite element method approaches (HO-FEM), like p-FEM, spectral elements, spectral analysis and isogeometric analysis, are among them. Although analytical approaches offer fast and accurate results, they are limited to rather simple geometries. On the other hand, the application of higher order finite element schemes is a computationally demanding task. The drawbacks of both methods can be circumvented if regions of complex geometry are modelled using a HO-FEM approach while the response of the remaining structure is computed utilizing an analytical approach. The objective of the paper is to present an efficient method to couple different HO-FEM schemes with an analytical description of an undisturbed region. Using this hybrid formulation the numerical effort can be drastically reduced. The functionality of the proposed scheme is demonstrated by studying the propagation of ultrasonic guided waves in plates, excited by a piezoelectric patch actuator. The actuator is modelled utilizing higher order coupled field finite elements, whereas the homogenous, isotropic plate is described analytically. The results of this "semi-analytical" approach highlight the opportunities to reduce the numerical effort if closed-form solutions are partially available.