• Journal of the Korean Institute of Intelligent Systems
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• v.12 no.1
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• pp.39-43
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• 2002

In the frequency response analysis using a modal method, it is very important to determine the number of modes involved with the formulation of a frequency response function. Most engineers are inclined to determine mode truncation with their experience. But it is difficult for non-experts to decide the mode truncation reasonably in many problems of dynamic analyses. In this study, fuzzy theory is used to standardize the empirical determination of mode truncation so that not only the experts but also non-experts can decide a Proper mode truncation easily. Fuzzy rule base is based on the simulation results using finite element method. Numerical simulations show that the developed mode truncation method is a very effective method to choose the number of the considered modes.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05a
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• pp.484-488
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• 1997

Fission product release (FPR) assessment for 100% reactor outlet header (ROH) break in CANDU reactor loaded with CANFLEX-NU fuel bundles has been performed. The predicted results are compared with those for the reactor loaded with standard 37-element bundles. The fuel failure thresholds for the CANFLEX and standard bundle elements are very similar. All the sheaths at the corresponding fuel failure thresholds for the CANFLEX and standard bundles fail due to the significant cracks in the surface oxide, except those for the CANFLEX inner element at burnups of 220 to 240 MW.h/kg(U), which fail due to the excessive diametral strain. The fuel failure analysis predicts that the number of failed fuel elements for the CANFLEX bundle case is none, while that for the standard bundle case is 1827. The total (gap plus bound) I-131 releases for the CANFLEX and standard bundles are none and 5889 TBq, respectively The significant reduction of the number of failed fuel elements and FPR for the CABFKEX fuel bundle is attributed to the lower linear power of the CANFLEX fuel bundle compared with the standard fuel bundle.

• Communications of Mathematical Education
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• v.25 no.4
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• pp.693-734
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• 2011

The purpose of this research is to analyze the pedagogical content knowledge on the natural number concepts of Korean Elementary School Teachers. Shulman(1986b) had developed a tool in order to understand teachers' knowledge, as he defined three types of knowledge in teaching ; Subject Matter Knowledge, Curricular Knowledge, and Pedagogical Content Knowledge. Pang(2002) defined two types of elements including in the ways of teaching ; individual element, and sociocultural element. Two research questions are addressed; (1) What is the pedagogical content knowledge of Natural number Concepts for Korean Elementary School Teachers? ; (2) What factors are included in the pedagogical content knowledge of Natural number Concepts for Korean Elementary School Teachers? Findings reveal that (1) the Korean Elementary School Teachers had three types of the pedagogical content knowledge on the natural number concepts; (2) Teacher Factors were more included than Social-Cultural Factors in the pedagogical content knowledge on the natural number concepts of the Korean Elementary School Teachers. Further suggestions were made for future researches to include (1) a comparative study on teachers between ordinary teachers and those who majored mathematics education in the graduate school. (2) an analysis on the classroom activities about the natural number concepts.

• Steel and Composite Structures
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• v.46 no.4
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• pp.451-469
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• 2023

The use of precast hollow-core slabs (PCHCS) in civil construction has been increasing due to the speed of execution and reduction in the weight of flooring systems. However, in the literature there are no studies that present a finite element model (FEM) to predict the load-slip relationship behavior of pushout tests, considering headed stud shear connector and PCHCS placed at the upper flange of the downstand steel profile. Thus, the present paper aims to develop a FEM, which is based on tests to fill this gap. For this task, geometrical non-linear analyses are carried out in the ABAQUS software. The FEM is calibrated by sensitivity analyses, considering different types of analysis, the friction coefficient at the steel-concrete interface, as well as the constitutive model of the headed stud shear connector. Subsequently, a parametric study is performed to assess the influence of the number of connector lines, type of filling and height of the PCHCS. The results are compared with analytical models that predict the headed stud resistance. In total, 158 finite element models are processed. It was concluded that the dynamic implicit analysis (quasi-static) showed better convergence of the equilibrium trajectory when compared to the static analysis, such as arc-length method. The friction coefficient value of 0.5 was indicated to predict the load-slip relationship behavior of all models investigated. The headed stud shear connector rupture was verified for the constitutive model capable of representing the fracture in the stress-strain relationship. Regarding the number of connector lines, there was an average increase of 108% in the resistance of the structure for models with two lines of connectors compared to the use of only one. The type of filling of the hollow core slab that presented the best results was the partial filling. Finally, the greater the height of the PCHCS, the greater the resistance of the headed stud.

• Computers and Concrete
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• v.28 no.5
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• pp.521-532
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• 2021

Present paper focuses on the modeling of size effect on the compressive strength of normal concrete with the application of Discrete Element Method (DEM). Test specimens with different size and shape were cast and uniaxial compressive strength test was performed on each sample. Five different concrete mixes were used, all belonging to a different normal strength concrete class (C20/25, C30/37, C35/45, C45/55, and C50/60). The numerical simulations were carried out by using the PFC 5 software, which applies rigid spheres and contacts between them to model the material. DEM modeling of size effect could be advantageous because the development of micro-cracks in the material can be observed and the failure mode can be visualized. The series of experiments were repeated with the model after calibration. The relationship of the parallel bond strength of the contacts and the laboratory compressive strength test was analyzed by aiming to determine a relation between the compressive strength and the bond strength of different sized models. An equation was derived based on Bazant's size effect law to estimate the parallel bond strength of differently sized specimens. The parameters of the equation were optimized based on measurement data using nonlinear least-squares method with SSE (sum of squared errors) objective function. The laboratory test results showed a good agreement with the literature data (compressive strength is decreasing with the increase of the size of the specimen regardless of the shape). The derived estimation models showed strong correlation with the measurement data. The results indicated that the size effect is stronger on concretes with lower strength class due to the higher level of inhomogeneity of the material. It was observed that size effect is more significant on cube specimens than on cylinder samples, which can be caused by the side ratios of the specimens and the size of the purely compressed zone. A limit value for the minimum size of DE model for cubes and cylinder was determined, above which the size effect on compressive strength can be neglected within the investigated size range. The relationship of model size (particle number) and computational time was analyzed and a method to decrease the computational time (number of iterations) of material genesis is proposed.

• Journal of Biomedical Engineering Research
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• v.31 no.1
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• pp.56-66
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• 2010

The various total replacement artificial discs have developed because spinal fusion has shown a lesser mobility of an operated segment and an accelerated degeneration at adjacent discs. But almost artificial discs have not yet been reached on the substitute surgery of fusion because many problems such as those clinical success rates were not more than them of fusion have not solved. In this paper, vertically inserted assemble-screw fixture in vertebrae was proposed to improve the fixed capability of artificial disc. And also, to evaluate the design suitability of newly designed screw-type, including fixtures of commercial discs such as wedge and plate type, the 1/4 finite element model with a vertebra and various implanted fixtures were generated, and next, 3 bending motions such as flexion, bending and twisting under the moment of 10Nm and compression under the force of 1000N were considered, respectively and finally, FE analyses were performed. Results of three fixture types were compared, such as Range of Motion and maximal stress, and so on. For ROM, the screw type was average 58% less than the wedge type and was average 42% less than the plate type under all loading conditions. For average stress ratio at closer nodes between vertebra and each fixture, the wedge type was the lowest as minimum 0.02 in twisting, screw types were the highest as maximum 0.28 in compression. As the results of using cement material, it was predicted that the instability problem of the wedge type was better solved. The screw type which could be increased by implanting depth according to the number of assembling mid screws, showed that the decreased tendency of ROMs and maximal cancellous bone stresses. In further study, controlling the number of assembling screws that was suitable for a patient's bone quality, development of surgical tools and keeping on design supplementations, which will be able to develop the competitive artificial disc.

• Journal of the Korean Institute of Landscape Architecture
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• v.33 no.4 s.111
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• pp.11-21
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• 2005

The purpose of this study was to analyze and evaluate landscape characteristics by classification of landscapes in Chuncheon. A system was developed to convert images taken with a fish-eye lens to panoramic pictures. Landscape characteristics were analyzed by appearance rate and area distribution rate of landscape elements on panorama picture. Landscape characteristics were analyzed according to the number of times landscape elements appeared and the amount of area that each element occupied in the panoramic picture. Each panoramic picture was classified into five types based on these landscape element factors. Landscape evaluation was carried out using dynamic images converted from picture by fish-eye lens. The results of this study can be summarized as follows. The urban landscape can be characterized by four essential factors: interconnectedness, nature, urban centrality and landscape scale. Five types of landscapes were determined: detached residential building landscape (type 1), street landscape with various elements (type 2), street landscape in the center of a city (type 3), landscape of housing complex (type 4), and landscape of green space (type 5). Type 5 had the highest degree of landscape satisfaction and the landscape satisfaction increased with the number of appearances of natural elements. The amount of peen space had a high relation with a landscape satisfaction.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.141-151
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• 2020

This manuscript tends to investigate influences of nanoscale and surface energy on a static bending and free vibration of piezoelectric perforated nanobeam structural element, for the first time. Nonlocal differential elasticity theory of Eringen is manipulated to depict the long-range atoms interactions, by imposing length scale parameter. Surface energy dominated in nanoscale structure, is included in the proposed model by using Gurtin-Murdoch model. The coupling effect between nonlocal elasticity and surface energy is included in the proposed model. Constitutive and governing equations of nonlocal-surface perforated Euler-Bernoulli nanobeam are derived by Hamilton's principle. The distribution of electric potential for the piezoelectric nanobeam model is assumed to vary as a combination of a cosine and linear variation, which satisfies the Maxwell's equation. The proposed model is solved numerically by using the finite-element method (FEM). The present model is validated by comparing the obtained results with previously published works. The detailed parametric study is presented to examine effects of the number of holes, perforation size, nonlocal parameter, surface energy, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric perforated nanobeams. It is found that the effect of surface stresses becomes more significant as the thickness decreases in the range of nanometers. The effect of number of holes becomes significant in the region 0.2 ≤ α ≤ 0.8. The current model can be used in design of perforated nano-electro-mechanical systems (PNEMS).

• Steel and Composite Structures
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• v.16 no.6
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• pp.611-637
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• 2014

A single plate shear connection, or shear tab, is a very popular shear connection due to its merit in ease of construction and material economy. However, problems in understanding the connection behavior, both in terms of strength and ductility, have been well-documented. Suggestions or design model for single plate connections in AISC Design Manual have been altered several times, with the latest edition settling down to giving designers pre-calculated design strength tables if the connection details agree with given configurations. Results from many full-scale tests and finite element models in the past suggest that shear strength of a bolt group in single plate shear connections might be affected by yield strength of plate material; therefore, this research was aimed to investigate and clarify effects of plate yield strength and thickness on shear strength of the bolt group in the connections, including the validity of using a plate thickness/bolt diameter ratio ($t_p/d_b$) in design, by using finite element models. More than 20 models have been created by using ABAQUS program with 19.0- and 22.2-mm A325N bolts and A36 and Gr.50 plates with various thicknesses. Results demonstrated that increase of plate thickness or plate yield strength, with the $t_p/d_b$ ratio remained intact, could significantly reduce shear strength of the bolt group in the connection as much as 15 percent. Results also confirmed that the $t_p/d_b$ ratio is a valid indicator to be used for guaranteeing strength sufficiency. Because the actual ratio recommended by AISC Design Manual is $t_p/d_b$ + 1.6 (mm) for connections with a number of bolts less than six and plate yield strength in construction is normally higher than the nominal value used in design, it is proposed that shear strength of a bolt group in single plate connections with a number of bolts equal or greater than seven be reduced by 15 percent and the $t_p/d_b$ ratio be limited to 0.500.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.859-864
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• 2011

An operation temperature of $Pb(Zr,Ti)O_3$ based piezoelectric ultrasonic flowmeter was generally restricted to below 200$^{\circ}C$ due to a low depoling temperature of its ceramic material. Thus, a new designed piezoelectric ultrasonic flowmeter was fabricated in order to protect from the extremely hot fluid. Its structure is optimized by a finite element method to effectively stop heat flowing along a waveguide. Various materials such as Cu, Al, SUS were examined as a multi-plate radiation shield to enhance the performance of piezoelectric ultrasonic flowmeter. The SUS was evaluated as the most effective material to enhance the performance of piezoelectric ultrasonic flowmeter. As the number of plates of the radiation shield increased, the temperature at piezoelectric transducer away from the hot fluid was constantly decreased with a ratio of 3.12$^{\circ}C$ per the plate number.