• Structural Engineering and Mechanics
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• v.74 no.2
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• pp.227-241
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• 2020

The bi-axial and shear buckling behavior of laminated hypar shells having rhombic planforms are studied for various boundary conditions using the present mathematical model. In the present mathematical model, the variation of transverse shear stresses is represented by a second-order function across the thickness and the cross curvature effect in hypar shells is also included via strain relations. The transverse shear stresses free condition at the shell top and bottom surfaces are also satisfied. In this mathematical model having a realistic second-order distribution of transverse shear strains across the thickness of the shell requires unknown parameters only at the reference plane. For generality in the present analysis, nine nodes curved isoparametric element is used. So far, there exists no solution for the bi-axial and shear buckling problem of laminated composite rhombic (skew) hypar shells. As no result is available for the present problem, the present model is compared with suitable published results (experimental, FEM, analytical and 3D elasticity) and then it is extended to analyze bi-axial and shear buckling of laminated composite rhombic hypar shells. A C⁰ finite element (FE) coding in FORTRAN is developed to generate many new results for different boundary conditions, skew angles, lamination schemes, etc. It is seen that the dimensionless buckling load of rhombic hypar increases with an increase in c/a ratio (curvature). Between symmetric and anti-symmetric laminations, the symmetric laminates have a relatively higher value of dimensionless buckling load. The dimensionless buckling load of the hypar shell increases with an increase in skew angle.

• Advances in nano research
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• v.16 no.5
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• pp.509-519
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• 2024

In this study, the static analysis of carbon nanotube-reinforced composites (CNTRC) beams resting on a Winkler-Pasternak elastic foundation is presented. The developed theories account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. To study the effect of carbon nanotubes distribution in functionally graded (FG-CNT), we introduce in the equation of CNT volume fraction a new exponent equation. The SWCNTs are assumed to be aligned and distributed in the polymeric matrix with different patterns of reinforcement. The rule of mixture is used to describe the material properties of the CNTRC beams. The governing equations were derived by employing Hamilton's principle. The models presented in this work are numerically provided to verify the accuracy of the present theory. The analytical solutions are presented, and the obtained results are compared with the existing solutions to verify the validity of the developed theories. Many parameters are investigated, such as the Pasternak shear modulus parameter, the Winkler modulus parameter, the volume fraction, and the order of the exponent in the volume fraction equation. New results obtained from bending and stresses are presented and discussed in detail. From the obtained results, it became clear the influence of the exponential CNTs distribution and Winkler-Pasternak model improved the mechanical properties of the CNTRC beams.

• Communications of Mathematical Education
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• v.32 no.3
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• pp.275-296
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• 2018

The purpose of this study is to investigate the change of gaze and the change of the proof learning achievement after learning the analytic method for proof to mathematical gifted students using eye tracking technique. In order to complete the purpose of this study, a mixed method research was used, that is a combination of quantitative and qualitative research methods. Quantitative analysis was conducted based on the data obtained through the eye tracker, and qualitative analysis was also done using post interview data to make up for the quantitative analysis. The subjects of this study were 8 mathematical gifted 3rd grade middle school students in the gifted education center. The conclusions of this study are as follows. First, the learning of analysis leads to a change of gaze in the proof learning of students. The students, after learning the analysis, moved their gaze from the bottom to the top when solving the proof problem, and the occupancy rate of the gaze to the bottom of the proof was higher than the higher part. Second, the change of gaze caused by the learning of the analysis have a correlation with the achievement of the proof learning and it can be seen that the method learning improves the achievement of the proof learning of the students.

• Ocean and Polar Research
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• v.27 no.3
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• pp.341-349
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• 2005

Temporal variation of the natural planktonic community in the Southern Sea of Korea was investigated by using low floating enclosed bags (3.2m deep and 2,500 liter) in order to understand the effect of enriched nitrate on the planktonic community in the spring (March-April) of 2002. Prior to beginning the incubation, the bags were placed in two different concentrations of nitrate, which consisted of control (ambient water) and experimental mesocosms (final concentration of $12{\mu}M$). The nitrate concentration in the experimental mesocosms remained significantly higher than those in control mesocosms throughout the study period (ANOYA, p<0.001). Following the addition of nitrate, abundance and chi-a concentration of phytoplankton peaked on Day 1, when diatoms established the peak in the experimental mesocosms. Diatoms consisted mainly of Thalasxiosira decipiens, Pseudo-nitzschia pungem, Leptocylindrus danicu, Thalassionema nitzschioides, Chaetoceros pseudocrinitus and Actinoptychus senariu. However, the peak did not lead to the difference in abundance and composition of phytoplankton between control and experimental mesocosms during the study period. The dinoflagellates began to increase soon after the diatoms decreased in all mesocosms. Copepods, as a dominant group in the rnosozooplankton community, showed no immediate peak in relation to the nitrate addition, but only their own developmental process from the eggs to adult stage during the study period. The bottom-up control from enriched nitrate via phytoplankton to adult copepods was not distinguished in terms of the abundance of the planktonic community. This might stem from the relatively low nitrate availability of phytoplankton at no N-limited seawater and the weak coupling between rapidly sunken diatoms and copepods through the water column.

• Structural Engineering and Mechanics
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• v.85 no.5
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• pp.593-605
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• 2023

This work presents a comparison between analytical and finite element analysis for bending of porous sandwich functionally graded material (FGM) plates. The plate is rectangular and simply supported under static sinusoidal loading. Material properties of FGM are assumed to vary continuously across the face sheets thickness according to a power-law function in terms of the volume fractions of the constituents while the core is homogeneous. Four types of porosity are considered. A refined higher-order shear with normal deformation theory is used. The number of unknowns in this theory is five, as against six or more in other shear and normal deformation theories. This theory assumes the nonlinear variation of transverse shear stresses and satisfies its nullity in the top and bottom surfaces of the plate without the use of a shear correction factor. The governing equations of equilibrium are derived from the virtual work principle. The Navier approach is used to solve equilibrium equations. The constitutive law of the porous FGM sandwich plate is implemented for a 3D finite element through a subroutine in FORTRAN (UMAT) in Abaqus software. Results show good agreement between the finite element model and the analytical method for some results, but the analytical method keeps giving symmetric results even with the thickness stretching effect and load applied to the top surface of the sandwich.

• Fire Science and Engineering
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• v.20 no.2 s.62
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• pp.44-53
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• 2006

We have conducted a numerical simulation under two-dimensional unsteady conditions in order to analyze the effect according to the injection angle and velocity of the $CO_2$ agent nozzle which is one of the elements for the fixed type $CO_2$ fire extinguishing system installed in a ship on the characteristics of flow and $CO_2$ concentration distribution. The flow fields and concentration fields were measured and analyzed. We can found that the difference of flow patterns according to the conditions of $CO_2$ agent injection nozzle, and in all the conditions of $CO_2$ agent injection nozzle, the iso-concentration line was expanded from the region at which vortex was generated to the surroundings. We can expected that the intensity of the wall jet on the bottom floor was generated differently and the iso-concentration lines were expanded or shrunk according to the angle of $CO_2$ agent injection nozzle. In case of increasing $CO_2$ agent injection velocity maintaining the flow quantity of the $CO_2$ agent injection equally, the iso-concentration line of $CO_2$ agent on bottom floor can be formed more higher than in case of decreasing $CO_2$ agent injection velocity.

• The Journal of Korean Physical Therapy
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• v.6 no.1
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• pp.23-35
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• 1994

In this research, the mentally-handicapped children being able to be trained were investigated the actual condition of train function making 40 mentally-handicapped children in Kummi Hyedang Spacial Education School, to exmine the effect of physical exercise function when training the mentally-handicapped children who can be trained as applying exercise education programs, and trains for 10 weeks by assigning to both experiment group and control group according to children who are similar to training functions from pre-examination. The results are in following: First, the results of test in the exercise ability of mentally-handicapped children with the degree of being able to trained are very delayed in comparison with normal mental children through the both top and bottom examination. The developments of 5 exercise functions classified by domain, have the order of eyesight exercise, softness, physical strength, quickness, parallelism, the interaction of both eye and hand, and, have the exercise function being equal to the level of between 6 and 12 years old. In 13 bottom test, throwing bean-bag is equal to the nomal 12 years old boy. the board jump, sitting position / bending forward / closing are equal to the level of 12 years old boy. standing with only leg is the level of 9 years old, threading pearls is 7 years old, transfering the wood building, picking the upper body up, walking board, balancing one leg with opened, eye, fist / opening palm / palm, bending and opening arm with postrating on chair, are the exercise functions of below 6 years old. Second, there are great effects in carrying out the exercise education program to the mentally-handicapped children with the level of being able to trained. In experiment group, it is elevated to the middle level of 12 years old nomal children. Classified by domain of test the board jump, training, the bean-bag are far higher level than 12 years old normal children, and are elevated the level of 11 years old boy. Balancing only leg with closed eye is below the level of 10 years old boys, fist / opening palm / palm are the level of 9 years old boys. There and back running, picking the upper body is the level of 9 years old girls. Walking board is the level of 8 years old boys. Bending and opening arm with postrating on chair is the level of 7 rears old boy. Balancing one leg with opened eye is elevated to the level of f years old girls. These functions have the more balanced exercise function rather than pre-examination. In control group, they have little change by classified the bottom test, but have the exercise function on the time of pre-examination, go backward in physical strength. quickness. Third, the exercise function being learned by exercise education program on the mentally-handicapped children of the level with being able to train is appeared to maintain continuately. Softness, physical strength, quickness, eyesight training are maintained the learned exercise function, the interaction of both eye and hands, parallelism are delayed a little. Classified by the bottom test. threading pearls, transfering the wood building, throwing the bean-bag, sitting position / rolling forward / reaching, the broad jump and picking upper body up, there and bark running, picking upper body up, balancing with only leg as opened eye, bending and opening arm with postrating on chair, etc. are maintained. Fist / opening palm / palm, balancing with only leg as opened eye are delayed a little. The change of body position is elevated. Seeing these results, it is appeared to the mentally-handicapped children that the exercise education programs, which is suitable their actual condition and acomplishes in voluntary participation, have very positive effect. So, to develop the function of body exercise in mentally-handicapped children with the level of being to able to be trained, the measures must be groped so that the exercise education programs can be practiced positively, and the ,body exercise can be experienced more.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.143-156
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• 2015

In order to understand the dynamic characteristics of water column environments in the Western Pacific seamount area (approximately $150.2^{\circ}E$, $20^{\circ}N$), we investigated the water mass and the behavior of water column parameters such as dissolved oxygen, inorganic nutrients (N, P), and chlorophyll-a. Physico-chemical properties of water column were obtained by CTD system at the nine stations which were selected along the east-west and south-north direction around the seamount (OSM14-2) in October 2014. From the temperature-salinity diagram, the main water masses were separated into North Pacific Tropical Water and Thermocline Water in the surface layer, North Pacific Intermediate Water in the intermediate layer, and North Pacific Deep Water in the bottom layer, respectively. Oxygen minimum zone (OMZ, mean $O_2$ $73.26{\mu}M$), known as dysoxic condition ($O_2<90{\mu}M$), was distributed in the depth range of 700~1,200 m throughout the study area. Inorganic nutrients typified by nitrite + nitrate and phosphate showed the lowest concentration in the surface mixed layer and then gradually increased downward with representing the maximum concentration in the OMZ, with lower N:P ratio (13.7), indicating that the nitrogen is regarded as limiting factor for primary production. Vertical distribution of water column parameters along the east-west and south-north station line around the seamount showed the effect of bottom water inflowing at around 500 m deep in the western and southern region, and concentrations of water column parameters in the bottom layer (below 2,500 m deep) of the western and southern region were differently distributed comparing to those of the other side regions (eastern and northern). The value of Excess N calculated from Redfield ratio (N:P=16:1) represented the negative value throughout the study area, which indicated the nitrogen sink dominant environments, and relative higher value of Excess N observed in the bottom layer of western and southern region. These observations suggest that the topographic features of a seamount influence the circulation of bottom current and its effects play a significant role in determining the behavior of water column environmental parameters.

• Journal of Internet Computing and Services
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• v.11 no.5
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• pp.81-94
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• 2010

The purpose of the study is to suggest a standardized teaching-learning model as a method for strengthening the practical effect of the information ethic education for the adolescent, which is practiced in schools as the inter-disciplinary way. A survey was put to teachers and their needs are analyzed. At the same time, in order to draw the practical teaching-learning model, the teaching examples were collected for contesting. Through this process, a bottom-up approach which tries to analyze the actual class examples and generalizes them, the teaching-learning model has been suggested. As a result, another survey was conducted for the investigation of the efficacy of the model between beneficiary group and comparison group. The results are as followings; the experiment group showed a higher index in regard with such items as Information Culture Index, Lesson Satisfaction Degree, and Practice Will than Comparison Group, and the differences are statistically significant. According to the results of the analysis.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.264-269
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• 2016

This paper reports a fundamental study of temperature characteristics of a solar pond with an insulation layer. Further, these characteristics were compared with those of a solar pond without the insulation layer. The governing equation was discretized via finite difference method. The governing equations are two-dimensional unsteady-state second-order partial differential equations. The conclusions of the study are as follows: 1) If the depth of the solar pond was increased, the desired effect of increase in temperature was not produced because the amount of solar insolation received by the bottom of the solar pond decreased. 2) As the temperature of the soil during winter is higher than the temperature of the water in a solar pond, heat was transferred from the soil to the solar pond. 3) For the case of the solar pond with insulation layer, it was estimated that the dependence rate of solar energy was 83.3% and that of the boiler was 16.7%.