• Steel and Composite Structures
• /
• v.44 no.3
• /
• pp.371-388
• /
• 2022

The present study tackles the problem of forced vibration of imperfect axially functionally graded shell structure with truncated conical geometry. The linear and nonlinear large-deflection of the structure are considered in the mathematical formulation using von-Kármán models. Modified coupled stress method and principle of minimum virtual work are employed in the modeling to obtain the final governing equations. In addition, formulations of classical elasticity theory are also presented. Different functions, including the linear, convex, and exponential cross-section shapes, are considered in the grading material modeling along the thickness direction. The grading properties of the material are a direct result of the porosity change in the thickness direction. Vibration responses of the structure are calculated using the semi-analytical method of a couple of homotopy perturbation methods (HPM) and the generalized differential quadrature method (GDQM). Contradicting effects of small-scale, porosity, and volume fraction parameters on the nonlinear amplitude, frequency ratio, dynamic deflection, resonance frequency, and natural frequency are observed for shell structure under various boundary conditions.

• East Asian mathematical journal
• /
• v.31 no.4
• /
• pp.505-525
• /
• 2015

The purpose of this study is to analyze teaching method of addition and subtraction of whole number in Korea and New Zealand lower grade textbook and to get some suggestive points to develop mathematics curriculum and for a qualitative improvement of textbook. To do this, we will analyze focusing on teaching material, type and method of teaching, cases of real teaching and in the case of New Zealand, we will analyze portfolios together to see what kind of things do they deal with related to addition and subtraction. From these analyzing, the results are as follows: First, the guideline of accomplishment of group of year are stated in 2009 revised curriculum in Korea but it is rough. On the other hand, the level of accomplishment from kindergarten to high school are stated divided by eight kinds of thing in New Zealand curriculum. Second, there were common and different points in the aspect of teaching material. The common points are that both of our Korea and New Zealand are using materials related to real life intimately and the diifferent points are to use technology such as calculator and computer. They are more widely used in New Zealand than our Korea. Third, Korea had used routine method mainly but New Zealand had used method to develop creativity of learner such as to write problem corresponding to expression, posing problem corresponding to information, to complete table and find pattern and to write word problem to explain pattern and so on. Fourth, we could see special calculation strategies in the case of teaching addition and subtraction such as concept of double, compensation, various strategy based on counting of number, addition of the same number, magic square, near-double which are not finding in our mathematics textbook. Fifth, in the New Zealand textbook they had used teaching methods inducing curiosity of learner such as finding message and puzzle problem than solving given problem simply.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.30 no.10
• /
• pp.656-664
• /
• 2017

This paper presents the design and fabrication of a high power piezoelectric ultrasonic surgery unit for multi-purpose dental implantation. A conventional piezoelectric ultrasonic surgery units consists of a transducer and a tip. However, the drawback of this simple structure is that the output performance of the transducer considerably changes with the change of the tips. An ultrasonic surgery unit that has an additional booster between the transducer and the tip can solve this problem to some extent; for this, an optimal structural design for the transducer is required. We used the Bolted Langevin Transducer (BLT) as the basic transducer; it consists of piezoelectric ceramics and a metal body. It's structure was optimized using mathematical methods to determine the length and radius of the tail and head masses. Additionally, the booster was also subjected to the same methods. Using these mathematical methods, optimal results in terms of the resonance frequency (24.96 kHz), displacement ($14.27{\mu}m$), and pressure (2.8 MPa), could be obtained. The validity of this proposed surgery unit was confirmed experimentally, exhibiting a cutting force of around 7% higher than that of a conventional surgery unit.

• Journal for History of Mathematics
• /
• v.22 no.3
• /
• pp.187-206
• /
• 2009

On this study, the historical flow of the notation was briefly examined and the direction of mathematical investigation activity of the content of notation by analogy was explored and teaching learning materials were developed. Diverse mathematical facts were investigated on the basis of decimal system and binary system which are learned in middle school. First, the way of progressing analytic activity with algebraic material was examined. Second, on the basis of the notation which are learned in the first grade of middle school, the definition of the scale of a -notation, -a -notation, $\frac{1}{a}$notation, $\sqrt{a}$-notation was extended by analogy. The result of this study will be expected to establish the curriculum of mathematics and provide teaching and learning with the meaningful current events.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.1
• /
• pp.21-28
• /
• 2008

Stress-strain curves based on Ramberg-Osgood and Hollomon relations are strongly dependent upon the regressed range of strain. This work investigates mathematical expressions of true stress-strain curves of metallic materials. We first observe the variation of yield strength, strain hardening exponent and stress-strain curve with regressed range of stain. Based on sectional regression and expression using one or two parameters, we propose an optimal strain range for which yield strength and nonlinear material behavior are quite appropriate.

• Structural Engineering and Mechanics
• /
• v.84 no.1
• /
• pp.17-33
• /
• 2022

An experimental study is carried out to investigate the performance of the cutting tool regarding the insert wear, surface roughness, cutting forces, cutting power and material removal rate of three coated carbides GC2015 (TiCN-Al₂O₃-TiN), GC4215 (Al₂O₃-Ti(C,N)) and GC1015 (TiN) during the dry turning of AISI4140 steel. For this purpose, a Taguchi design (L₉) was adopted for the planning of the experiments, the effects of cutting parameters on the surface roughness (R_a), tangential cutting force (F_z), the cutting power (P_c) and the material removal rate (MRR) were studied using analysis of variance (ANOVA), the response surface methodology (RSM) was used for mathematical modeling, with which linear mathematical models were developed for forecasting of R_a, F_z, P_c and MRR as a function of cutting parameters (V_c, f, and a_p). Then, Multi-Objective Ant Lion Optimizer (MOALO) has been implemented for multi-objective optimization which allows manufacturers to enhance the production performances of the machined parts. Furthermore, in order to characterize and quantify the flank wear of the tested tools, some machining experiments were performed for 5 minutes of turning under a depth of 0.5 mm, a feed rate of 0.08 mm/rev, and a cutting speed of 350 m/min. The wear results led to a ratio (V_B-GC4215/V_B-GC2015) of 2.03 and (V_B-GC1015/V_B-GC2015) of 4.43, thus demonstrating the efficiency of the cutting insert GC2015. Moreover, SEM analysis shows the main wear mechanisms represented by abrasion, adhesion and chipping.

• The Journal of the Korea Contents Association
• /
• v.16 no.8
• /
• pp.477-483
• /
• 2016

The effect of dose enhancement was evaluated using Snyder head phantom, dependence on size of gold nanoparticle and material concentration in megavoltage X, ${\gamma}$-ray. Monte Carlo simulation using MCNPX was used for 4, 6, 10, 15 MV and Co-60 ${\gamma}$-ray. Described the tumor in Snyder head phantom, gold nanoparticle of 25, 75, 125nm diameter was inserted inside tumor. Concentration of dose enhancement material was used for 5, 15, 25 mg/g and dose enhancement factor was calculated on the basis of the no dose enhancement material. The lower incident energy and the higher concentration of material were that high dose enhancement factor is indicated. The size of gold nanoparticle had relatively high dependence on lower incident energy and higher concentration of material. It will increase dose inside the tumor, and be additional effect of use of gold nanoparticles in radiation therapy.

• Computers and Concrete
• /
• v.26 no.3
• /
• pp.213-226
• /
• 2020

The present study covenants with the static and free vibration behavior of nanocomposite sandwich plates reinforced by carbon nanotubes resting on Pasternak elastic foundation. Uniformly distributed (UD-CNT) and functionally graded (FG-CNT) distributions of aligned carbon nanotube are considered for two types of sandwich plates such as, the face sheet reinforced and homogeneous core and the homogeneous face sheet and reinforced core. Based on the first shear deformation theory (FSDT), the Hamilton's principle is employed to derive the mathematical models. The obtained solutions are numerically validated by comparison with some available cases in the literature. The elastic foundation model is assumed as one parameter Winkler - Pasternak foundation. A parametric study is conducted to study the effects of aspect ratios, foundation parameters, carbon nanotube volume fraction, types of reinforcement, core-to-face sheet thickness ratio and types of loads acting on the bending and free vibration analyses. It is explicitly shown that the (FG-CNT) face sheet reinforced sandwich plate has a high resistance against deflections compared to other types of reinforcement. It is also revealed that the reduction in the dimensionless natural frequency is most pronounced in core reinforced sandwich plate.

• Proceedings of the Korean Institute Of Construction Engineering and Management
• /
• 2007.11a
• /
• pp.768-773
• /
• 2007

Standardization to information attribute of construction material is continuous demanded through the life cycle of a construction project, and the productivity elevation is derived of contribution effect in construction market. This study surveyed the means of acquisition and attribute of information to a staff in purchase, which are effected on the revitalization of information circulation to the construction material Proposed the standardization to information attribute of construction material that is based on improvement and application to the information attribute. And information attribute is classified with construction process through analysis on test list of quality certification. This study also suggested representative attribute of quality information, for the elevation of safety and quality in construction industry. Therefore, logicality of common information is based by analysis of mathematical statistics, systemicity of quality information is applied by MasterFormat(2004)

• Journal of Educational Research in Mathematics
• /
• v.23 no.2
• /
• pp.117-133
• /
• 2013

Mathematical misconception is one of the big obstacles of the underachieving students to learn mathematics correctly. This study aims to develop the instruction materials for secondary school students who are underachieving in mathematics to reduce the occurrence of the misconception and to help them to build the correct concept in the mathematical learning. Before developing the material, we tried to collect the misconception cases occurring in common mathematics lesson. This materials tries to provide key educational contents for mathematics teachers who is responsible for teaching underachieving student and help them to creative interesting ideas for lessons. The materials could be used not only as an teaching materials for underachieving students or students with the misconceptions, but also could be used as training materials for mathematics teachers.