• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.10
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• pp.80-87
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• 2021

Our study introduces an improved modular agricultural platform to provide convenience to agricultural workers. We upgrade the platform design in three parts, namely, by adding a 458 pattern tire, electricity control, and four-wheel steering function, to improve the platform performance. Results showed that the upgrades enhanced the platform performance and reduced its overall weight as compared with the existing platform. To demonstrate the performance of our improved platform, we conducted five types of experiments with respect to the climbing angle, variable width, attitude control, speed, and obstacle passing.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.24-29
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• 1997

Recently, Genetic Algorithm(GA), which is a stochastic direct search strategy that mimics the process of genetic evolution, is widely adapted into a search procedure for structural optimization. Contrast to traditional optimal design techniques which use design sensitivity analysis results, GA is very simple in their algorithms and there is no need of continuity of functions(or functionals) any more in GA. So, they can be easily applicable to wide area of design optimization problems. Also, owing to multi-point search procedure, they have higher porbability of convergence to global optimum compared to traditional techniques which take one-point search method. The methods consist of three genetics opera- tions named selection, crossover and mutation. In this study, a method of finding the omtimum size and topology of drilling machine is proposed by using the GA, For rapid converge to optimum, elitist survival model,roulette wheel selection with limited candidates, and multi-point shuffle cross-over method are adapted. And pseudo object function, which is the combined form of object function and penalty function, is used to include constraints into fitness function. GA shows good results of weight reducing effect and convergency in optimal design of drilling machine.

• International Journal of Highway Engineering
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• v.16 no.2
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• pp.25-34
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• 2014

PURPOSES : This paper numerically evaluates the contribution of transverse steel to the structural behavior of continuously reinforced concrete pavements to understand the role of transverse steel. METHODS : Two-lane continuously reinforced concrete pavements with and without transverse steel were analyzed through finite element analysis with the aid of commercial finite element analysis program DIANA; the difference in their structural behavior such as deflection, joint opening, and stress distribution was then evaluated. Twenty-node brick elements and three-node beam elements were used to model concrete and steel, respectively. Sub-layers were modeled with horizontal and vertical tensionless spring elements. The interactions between steel and surrounding concrete were considered by connecting their nodes with three orthogonal spring elements. Both wheel loading and environmental loading in addition to self-weight were considered. RESULTS : The use of transverse steel in continuously reinforced concrete pavements does not have significant effects on the structural behavior. The surface deflections change very little with the use of transverse steel. The joint opening decreases when transverse steel is used but the reduction is quite small. The transverse concrete stress, rather, increases when transverse steel is used due to the restraint exerted by the steel but the increase is quite small as well. CONCLUSIONS : The main role of transverse steel in continuously reinforced concrete pavements is supporting longitudinal steel and/or controlling unexpected longitudinal cracks rather than enhancing the structural capacity.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.397-397
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• 2016

Triboelectric nanogenerators (TENG) can produce power from ambient mechanical sources and have strong points of high output performance, light weight, low cost, and easy manufacturing process. It is expected that TENG can be utilized in the fields of wireless electronics and self-powered devices in the world which pays attention to healthcare and the IoT. In this work, we focus on scavenging ambient rotational energy by using a durably designed TENG. In previous studies regarding harvesting rotation mode energy, the devices were based on sliding mechanism and durability was not considered as a major issue. However friction by rotation causes reliability problems due to wear and tear. Therefore, in this study, we convert rotary motion to linear motion utilizing a cam by which we can then utilize contact-mode TENG and improve device reliability. In order to increase output performance, bumper springs were used below the TENG and the optimum value for the bumper spring constant was analyzed theoretically. Furthermore, the inserting a soft substrate was proposed and its effect on high output was determined to be due to an increase in the contact area. By increasing the number of cam noses, the output frequency was shown to increase linearly. For the purpose of maximum power transfer, the input impedance of the device was determined. Finally, to demonstrate the use of the C-TENG as a direct power source, it was installed on a commercial bicycle wheel and connected to 180 LEDs. In conclusion we present a rotational motion TENG energy scavenger system designed for enhanced durability and optimized output by appropriate choice of spring constants and substrate.

• Biomolecules & Therapeutics
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• v.12 no.4
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• pp.242-249
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• 2004

The main aim of this study was to investigate stress related activities of Sun-ginseng extract as a candidate for anti-stress-related functional supplement by comparing its effect to those of red ginseng, which is also known to alleviate stress. Normal group was not exposed to stress while the control group was exposed to stress. Rats were orally administered once a day with 200 mg red ginseng (RG) extract, 100 or 200 mg Sun-ginseng (SG) extract/kg body weight. Mice were given water containing 400 mg red ginseng extract, 200 or 400 mg SG/100 mL potable water. Rats were given supplements for 5 days without stress, and 5 days with restraint and electroshock stress. After final stress, stress-related behavioral changes of experimental animals were recorded and levels of blood corticosterone were measured. Mice were given supplements for 5 days through drinking water, and then fatigue related motor activity were recorded. SG-supplementation partially blocked stress effect on locomotion and elevated plus maze test in rats, and also partially blocked stress-induced behavioral changes such as freezing, burrowing, smelling, facewashing, grooming and rearing behavior in rats. SG-supplementation decreased blood corticosterone level which is increased by stress in rats. Effects of SG may not be modulated by GABAnergic nervous system. SG-supplementation prolonged swimming time and staying time on the wire and rotarod wheel in mice. These results suggest that SG partially protects living organisms from stress attack in some cases and thus has the potential to be used as a functional food to alleviate stress response.

• Journal of Navigation and Port Research
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• v.30 no.1 s.107
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• pp.105-111
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• 2006

A LMTT (Linear Motor-based Transfer Technology) is a horizontal transfer system for the yard automation This system is based on PMLSM (Permanent Magnetic Linear Synchronous Motor) that consists of stator modules on the rail and shuttle car. In this research, the kriging interpolation method using sequential sampling is utilized to find the optimum design of a mover in LMTT. The design variables are considered as the transverse, longitudinal and wheel beam's thicknesses. The objective function is set up as weight, while the constant functions are set up as the stresses generated by four loading conditions. The optimum results obtained by the suggested method are compared with those determined by the GENESIS.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.799-807
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• 2014

This paper describes the development of an indoor locomotion assistive robot, Ball-Chair, comprising a novel drive system. This robot facilitates locomotion assistive operation in narrow spaces, in which common wheelchairs cannot move easily. The Ball-Chair has two main features: its structural feature and driving mechanism. The exoskeleton frames of the Ball-Chair have been designed with octagonal shapes resembling a circle, for minimizing its volume and weight. Additionally, all its driving parts (including the ball) are mounted within of the robot to enhance its safety. The Ball-Chair features a reverse ball-mouse driving mechanism comprising two driving omni-wheels in the x- and y-axes. By controlling the speed of each omni-wheel, a holonomic driving system that can facilitate omnidirectional locomotion has been achieved using only two wheels. The effective movement of the Ball-Chair in any direction within narrow indoor spaces was experimentally verified. The paper outlines the development procedure in detail.

• Plant Journal
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• v.4 no.3
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• pp.66-72
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• 2008

The vibration of steam turbine is caused by Mass unbalance, Shaft misalignment, Oil whip and rubbing etc. But in turbine which is normally operated and maintained, the Mass unbalance component possesses the greatest portion. Our power plant has two steam turbines in capacity of 200 MW and 135 MW respectively and each turbine is supported by 6 journal bearings. However, we had many difficulties because the vibration amplitude of #3 and #4 Bearings was high during the start-up and operation mode change of steam turbine. But, with this study, we completely solved the vibration problem caused by the mass unbalance of #1 steam turbine. Until a recent date, #3 and #4 bearings which support high pressure turbine for #1 steam turbine had shown about $135{\mu}m$ in vibration amplitude (sometimes it increased to $221{\mu}m$ maximum. alarm: 6 mils, trip: 9 mils) at base load. After applying the study, they decreased to about $45{\mu}m$ maximum. It is a result from that we did not change the setting value of bearing alignment and only changed the assembly position of internal parts in Synchro clutch coupling rachet wheel which links between high pressure turbine and low pressure turbine, and increased the internal gap and machining of the Pawl cage surface. In the operation of steam turbine, if the vibration value increases by 1X, we should reduce the vibration of bearing by weight balancing. However, unless the vibration of bearing is declined by the balancing, we will have to disassemble and check the component and find the cause. In this study, we researched the way to lower mass unbalance that is 1X vibration component which has the greatest portion of vibration generated by steam turbine and we got good result by applying the findings of this study.

• Design & Manufacturing
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• v.1 no.1
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• pp.7-11
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• 2007

The fabrication of precision optical components by deterministic CNC grinding is an area of great current interest. Replacement of the traditional, craftsman driven, optical fabrication process is essential to reduce costs and increase process flexibility and reliability. Moreover, CNC grinding is well suited to the fabrication of complex shapes such as aspheres, making it possible to design optical systems with fewer components and reduced weight. Current technology is capable of producing surfaces with less than 2 microns peak to valley error, 50 nm rms surface roughness, and less than 1 micron subsurface damage. Bound abrasive tools, in which the abrasive particles are fixed in a second (matrix) material, play an important part in achieving this performance. In this paper, the factors affecting the ultra-fine surface roughness and profile accuracy of machined surfaces of aspheric parts has been analyzed experimentally and theoretically and on ultra-precision aspheric grinding system and precise adjusting mechanism have been designed and manufactured. In the paper we report the results of experiments and modeling performed to examine the effects of machinability, occurring during grinding of optical surfaces, on the tool surface profile. Profiles of machined surface were measured by using SEM. In order to optimize grinding conditions of aspheric lens processing, we performed experiments by design of experiments.

• International Journal of Highway Engineering
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• v.14 no.6
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• pp.25-35
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• 2012

PURPOSES : Hollows are easily made, and bearing capacity can be lowered near underground structures because sublayers of pavement settle for a long time due to difficult compaction at the position. If loadings are applied in this condition, distresses may occur in pavement and, as the result, its lifespan can decrease due to the stress larger than that expected in design phase. Although reinforced slab is installed on side of box culvert to minimize the distresses, length of the reinforced slab is fixed as 6m in Korea without any theoretical consideration. The purpose of this paper is investigating the behavior of concrete pavement according to the cover depth of the box culvert ad the length of the reinforced slab. METHODS : The distresses of concrete pavement slabs were investigated and cover depth was surveyed at position where the box culverts were located in expressways. The concrete pavements including the box culverts were modeled by finite element method and their behaviors according to the soil cover depth were analyzed. Wheel loading was applied after considering self weight of the pavement and temperature gradient of the concrete pavement slab at Yeojoo, Gyeonggi where a test road was located. After installing pavement joint at various positions, behavior of the pavement was analyzed by changing the soil cover depth and length of the reinforced slab. RESULTS : As the result, the tensile stress developed in the pavement slab according to the joint position, cover depth, and reinforced slab length was figured out. CONCLUSIONS : More reasonable and economic design of the concrete pavement including the box culvert is expected by the research results.