• Journal of the Korean Society for Precision Engineering
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• v.30 no.12
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• pp.1341-1347
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• 2013

Energy harvesting is a clean technology to obtain energy from the surrounding environment such as wind, sun, vibration and so on. In particular, the current TPMS (Tire Pressure Monitoring Device) is very small and attached to the outside of a vehicle and power supply of the TPMS is limited. Therefore, energy harvesting using vibration energy of piezoelectric materials is important to the TPMS. In this paper, we analyzed several models using ANSYS which is one of the FEA (Finite Element Analysis) package and compared corresponding strain frequency response functions of the TPMS. In addition, we confirmed that dynamic characteristics variations according to geometry changes have effects on the performance of the TPMS.

• Journal of the Korean School Mathematics Society
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• v.20 no.3
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• pp.303-323
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• 2017

This is a multiple-case study of how preservice secondary mathematics teachers teach a particular mathematics using a technological tool. In a performance interview, the preservice teachers demonstrated how they would teach a specific mathematical topic using Geometer's Sketchpad. The results of this study showed that the preservice teachers designed diverse types of lesson plans and implemented different pedagogical and technological techniques in their teaching demonstrations. The findings suggest that preservice teachers' pedagogical content knowledge is an important factor in the integration of technology into their mathematics teaching. Thus, mathematics teacher educators should help preservice teachers gain a robust pedagogical content knowledge in order to effectively teach mathematics with technological tools.

• Structural Engineering and Mechanics
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• v.89 no.5
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• pp.437-452
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• 2024

Functionally graded materials (FGMs) have gained substantial attention from researchers due to their exceptional strength and thermal resistance. Their utilization in the aviation and automobile industries has significantly improved the efficiency of various structural components. Moreover, stiffened panels find wide applications in aerospace and automobile structures and these panels are frequently exposed to extreme environments. It is from this perspective that our research is focused on analysing the vibroacoustic response of stiffened functionally graded panels subjected to external dynamic excitations in a thermal environment. In the present research work, a finite element model is developed to conduct the dynamic analysis of functionally graded stiffened panels using the first-order shear deformation theory. Subsequently, a boundary element based model is also developed and coupled with the finite element model to investigate the sound radiation behaviour of those panels in a thermal environment. The material properties of FG stiffened panels are considered as temperature dependent, while the thermal environment is assumed to be acting as linearly varying through the panel's thickness. The present investigation aim to compare the vibroacoustic responses of different panels due to stiffener orientations, material compositions, power law indices and plate thicknesses at various temperatures. The research findings highlight the significant impact of addition of stiffeners, its orientation and material compositions on the sound radiation characteristics of these panels under thermal environments. The present numerical model can easily be employed for analysing the sound radiation behaviour of other types of flat or curved stiffened panels having arbitrary geometry and boundary conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.254-260
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• 2011

Telemetry link is dynamic communication link that antenna gain and polarization are varying with the movement of the airplane. In this paper we calculated the antenna gain, polarization mismatch using the flight trajectory, motion of the airplane and 3D antenna pattern. And we modeled the multipath environment to the 2-Ray spherical earth reflection geometry, estimated the received signal strength when the narrow beam antenna received the RF signal transmitted from the airplane. Also we performed the flight test and after comparing measured value with the estimated value, we confirmed to almost coincide with each other.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.51 no.3
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• pp.112-121
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• 2002

This paper describes a new bike system for the postural balance rehabilitation training. Virtual environment and three dimensional graphic model is designed with CAD tools such as 3D Studio Max and World Up. For the real time bike simulation, the optimized WorldToolKit graphic library is embedded with the dynamic geometry generation method, multi-thread method, and portal generation method. In this experiment, 20 normal adults were tested to investigate the influencing factors of balancing posture. We evaluated the system by measuring the parameters such as path deviation, driving velocity, COP(center for pressure), and average weight shift. Also, we investigated the usefulness of visual feedback information by weight shift. The results showed that continuous visual feedback by weight shift was more effective than no visual feedback in the postural balance control It is concluded this system might be applied to clinical use as a new postural balance training system.

• The Mathematical Education
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• v.42 no.2
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• pp.177-191
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• 2003

In this paper, we present the theory of computers and mathematics education based on the concept of microworlds for mathematics education. We lust look back some previous papers published in the journal of the Korea society of mathematical education series A and else where. Then we present the new view points regarding mircroworlds and mathematics curriculems, microworlds and mathematics teaching and teaming, microworld based problem centered teaming, and microworld based diagnostics and debuggings. We use JavaMAL microworld that is designed to make LOGO and dynamic geometry system in one microworld to give some examples to explain the necessary mathematics educational needs fur designing microworlds for mathematics education. The JavaMAL microworld is a web based microworld that is programmed using JAVA, and the user on use script language, menus, keyboard, and mouse interaction to use the environment.

• Steel and Composite Structures
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• v.31 no.6
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• pp.629-640
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• 2019

The investigation of retaining wall structures behavior under dynamic loads is considered as one of important parts for designing such structures. Generally, the performance of these structures is under the influence of the environment conditions and their geometry. The aim of this research is to design retaining wall structures based on smart and optimal systems. The use of accuracy and speed to assess the structures under different conditions is one of the important parts sought by designers. Therefore, optimal and smart systems are able to have better addressing these problems. Using numerical and coding methods, this research investigates the retaining wall structure design under different dynamic conditions. More than 9500 models were constructed and considered for modelling design. These designs include height and thickness of the wall, soil density, rock density, soil friction angle, and peak ground acceleration (PGA) variables. Accordingly, a neural network system was developed to establish an appropriate relationship between data to obtain safety factor (SF) of retaining walls under different seismic conditions. Different parameters were analyzed and the effect of each parameter was assessed separately. According to these analyses, the structure optimization was performed to increase the SF values. The optimal and smart design showed that under different PGA conditions, the structure performance can be appropriately improved while utilization of the initial (or basic) parameters leads to the structure failure. Therefore, by increasing accuracy and speed, smart methods could improve the retaining structure performance in controlling the wall failure. The intelligent design process of this study can be applied to some other civil engineering applications such as slope stability.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.201-209
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• 2003

Virtual human models are widely used to save time and expense in vehicle safety studies. A human model is an essential tool to visualize and simulate a vehicle driver in virtual environments. This research is focused on creation and application of a human model fer virtual reality. The Korean anthropometric data published are selected to determine basic human model dimensions. These data are applied to GEBOD, a human body data generation program, which computes the body segment geometry, mass properties, joints locations and mechanical properties. The human model was constituted using MADYMO based on data from GEBOD. Frontal crash and bump passing test were simulated and the driver's motion data calculated were transmitted into the virtual environment. The human model was organized into scene graphs and its motion was visualized by virtual reality techniques including OpenGL Performer. The human model can be controlled by an arm master to test driver's behavior in the virtual environment.

• KIEAE Journal
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• v.12 no.2
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• pp.25-32
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• 2012

This paper focused on the daylighting performance of residential high-rise buildings in South-Korea. the purpose of this study is to estimate the visual environment of sunlight coming into opening according to sky conditions, orientation of windows and each space of Apartment buildings. Season of the year, weather, and time of day combine with predictable movement patterns of the sun to create highly variable and dynamic daylighting conditions. Daylighting design is usually based on the dominant sky condition and the micro-climate for the building site. There are three common sky conditions: clear sky, overcast sky, and partly cloudy sky. The clear sky includes sunshine and is intense and brighter at the horizon than at the zenith, except in the area around the sun. Daylight received within a building is directly dependent upon the sun's position and the atmospheric conditions. Easily used charts, diagrams, and software programs allow study of solar geometry for any geographic location and time of day. on the other hand, the overcast sky is characterized by diffuse and variable levels of light and has dense cloud cover over 90% of the sky. This paper was calculated by a Desktop Radiance program. The space dimensions were based on a unit module of real constructed apartment having divided into five sections such as living room, room1, room2, room3 and kitchen.

• Journal of Environmental Health Sciences
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• v.35 no.6
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• pp.500-509
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• 2009

Passive samplers have been used for many years for the sampling of organic vapors in work environment atmospheres. Currently, all passive samplers used in domestic occupational monitoring are foreign products. This study was performed to evaluate variable parameters for the development of passive organic samplers, which include the geometry of the device and diffusive length for the sampler design. Four prototype diffusive lengths; A-1(4.5 mm), A-2(7.0 mm), A-3(9.5 mm), A-4(12.0 mm) were tested for adsorption performances to a chemical mixture (benzene, toluene, trichloroethylene, and n-hexane) according to the US-OSHA's evaluation protocol. A dynamic vapor exposure chamber developed and verified by related research was used for this study. The results of study are as follows. The results in terms of sampling rate and recommended sampling time test indicate that the most suitable model was A-3 (9.5 mm diffusive lengths on both sides) for passive sampler design in time weighted average (TWA) assessment. Sampling rates of this A-3 model were 45.8, 41.5, 41.4, and 40.3 ml/min for benzene, toluene, trichloroethylene, and n-hexane, respectively. The A-3 models were tested on reverse diffusion and conditions of low humidity air (35% RH) and low concentrations (0.2 times of TLV). These conditions had no affect on the diffusion capacity of samplers. In conclusion, the most suitable design parameters of passive sampler are: 1) Geometry and structure - 25 mm diameter and 490 $mm^2$ cross sectional area of diffusion face with cylindrical form of two-sided opposite diffusion direction; 2) Diffusive length - 9.5 mm in both faces; 3) Amount of adsorbent - 300 mg of coconut shell charcoal; 4) Wind screen - using nylon net filters (11 ${\mu}m$ pore size).