• 한국해양공학회지
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• 제35권3호
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• pp.183-190
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• 2021

Tomographic particle image velocimetry (PIV) is a widely used method that measures a three-dimensional (3D) flow field by reconstructing camera images into voxel images. In 3D measurements, the setting and calibration of the camera's mapping function significantly impact the obtained results. In this study, a camera self-calibration technique is applied to tomographic PIV to reduce the occurrence of errors arising from such functions. The measured 3D particles are superimposed on the image to create a disparity map. Camera self-calibration is performed by reflecting the error of the disparity map to the center value of the particles. Vortex ring synthetic images are generated and the developed algorithm is applied. The optimal result is obtained by applying self-calibration once when the center error is less than 1 pixel and by applying self-calibration 2-3 times when it was more than 1 pixel; the maximum recovery ratio is 96%. Further self-correlation did not improve the results. The algorithm is evaluated by performing an actual rotational flow experiment, and the optimal result was obtained when self-calibration was applied once, as shown in the virtual image result. Therefore, the developed algorithm is expected to be utilized for the performance improvement of 3D flow measurements.

• 대한기계학회논문집B
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• 제41권4호
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• pp.293-301
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• 2017

초임계 이산화탄소 발전사이클의 다양한 특성을 분석하기 위하여 Sub-kWe급의 소형 실험장치를 설계, 제작하였으며, 터보발전기를 개발하였다. 초임계 이산화탄소 발전용 터빈에서는 팽창비가 작고, 유량이 작기 때문에 터보발전기의 회전수가 높아지게 되고, 이에 따라 회전 부품의 선정, 터빈 공력설계, 축력 및 회전체 동역학 설계가 어려워지게 된다. 이에 터보발전기의 회전수를 줄이기 위하여 노즐의 여러 채널 중 1개의 노즐만 사용하는 부분유입 방법을 세계 최초로 초임계 이산화탄소 발전용 터보발전기에 적용하였으며, 회전체의 진동을 측정하여 부분유입 노즐을 적용함에도 회전체 안정성은 허용 범위내에 있음을 확인하였다.

• 한국지열·수열에너지학회논문집
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• 제17권1호
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• pp.14-22
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• 2021

Drilling equipment is an essential part used in various fields such as construction, mining, etc., and it has drawn increasing attention in recent years. The drilling method is generally divided into three types. There are a top hammer method that strikes on the ground, a DTH (Down-The-Hole) method that directly strikes a bit in an underground area, and a rotary method that drills by using rotational force. Among them, the DTH method is most commonly used because it enables efficient drilling compared to other drilling methods. In the conventional DTH hammer, the valve between the piston and the bit is opened and closed using a face to face method. In order to improve the power of the DTH hammer, a DTH hammer with foot valve which is capable of instantaneous opening and closing is used in the drilling field. In this study, we designed a lab-scale DTH hammer with the foot valve, and manufactured an evaluation device for the experiment of the DTH hammer. In addition, we analyzed the performance of the DTH hammer adopted with foot valve according to the pressure range of 3-10 bar. As a result, the internal pressure distribution in the DTH hammer was experimentally analyzed, and then, the movement of the piston according to the pressure was predicted. We believe that this study provides the useful results to explain the performance characteristics of the DTH hammer with the foot valve.

• 센서학회지
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• 제15권3호
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• pp.153-157
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• 2006

This paper presents the method for three-dimensional micro structure with photoresist spray coating system. The system consists of a high temperature rotational chuck, ultrasonic spray nozzle module, angle control module and nozzle moving module. Spray coating system is effected by several parameters such as the solid contents, the dispensed volume, the scanning speed of the spray nozzle and the wafer of dimension. The photoresist (AZ 1512) has been coated on the three-dimensional micro structure by spray coating system and the characteristics have been evaluated.

• Carbon letters
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• 제7권2호
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• pp.87-96
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• 2006

This paper describes the physical properties of filled Nylon6 composites resin with nano-sized carbon black particle and graphite nanofibers prepared by melt extrusion method. In improving adhesions between resin and fillers, the surface of the carbon filler materials were chemically modified by thermo-oxidative treatments and followed by treatments of silane coupling agent. Crystallization temperature and rate of crystallization increased with increases in filler concentration which would act as nuclei for crystallization. The silane treatments on the filler materials showed effect of reduction in crystallization temperature, possibly from enhancement in wetting property of the surface of the filler materials. Percolation transition phenomenon at which the volume resistivity was sharply decreased was observed above 9 wt% of carbon black and above 6 wt% of graphite nanofiber. The graphite nanofibers contributed to more effectively in an increase in electrical conductivity than carbon black did, on the other hand, the silane coupling agent negatively affected to the electrical conductivity due to the insulating property of the silane. Positive temperature coefficient (PTC) phenomenon, was observed as usual in other composites, that is, temperature increase results conductivity increase. The dispersity of the fillers were excellently approached by melt extrusion of co-rotational twin screw type and it could be illustrated by X-ray diffraction and SEM.

• 한국정밀공학회지
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• 제33권10호
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• pp.851-856
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• 2016

Planetary gear systems have several advantages over traditional gearboxes with parallel axis gear shafts. The planetary gearbox arrangement also creates greater stability due to the even distribution of mass and increased rotational stiffness. However, gears in planetary gear systems occasionally have a short-life due to wear and breakage by repetitive load during operation time. In this study, we evaluated variables of the strength design for each part and conducted structural analysis of seven cases of the planetary gear system. The result of structural analysis was applied to shape optimization method and obtaining the weight lightening designed value. Subsequently, the planetary gear system was performed to ensure the durability of gears during operation time with miner's rule.

• 센서학회지
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• 제29권3호
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• pp.205-210
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• 2020

The aim of this study is to develop a vertical vibration compensator that attenuates the vertical vibration of ships. The vibration compensator was designed according to the principle of generating vertical excitation forces by rotating two eccentric bodies of the same mass in opposite directions at the same rotational speed. In addition, the structural stability was analyzed using the finite element method. The maximum stress in the drive shaft was 95.6 MPa, which was approximately 35% of the allowable stress of the shaft material (SM45C, 270 MPa). The acceleration signals of the vibrator compensator body and the testbed were determined to evaluate the efficiency of the vibration compensator and the designed excitation forces. Subsequently, the excitation forces were estimated based on the relationship between force and acceleration. The estimated results were very close to the theoretical values with an error of less than 3%.

• 한국기계가공학회지
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• 제20권1호
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• pp.57-65
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• 2021

With the increased utilization of CAM programs, end-mill processing is most commonly used for machining and metal processing. In particular, hole or shaft machining has high assembly precision, which inevitably leads to high utilization of end mills. However, the analysis of quality characteristics according to the process conditions of end mills is not performed systematically at the site, causing poor quality and productivity. The most influential factor of quality is the runout of the end mill. In this paper, the number of turns of the end mill, number of tool blades, cutting direction, and artificial runout volume were determined to identify the correlation between the epicenter, cylindricality, and surface roughness. Two types of end mills, three levels of runout, three levels of rotational speed, and two cutting directions were considered and 36 rounds of hole processing were conducted. For the analysis of shape characteristics according to the set process variables, the experimental planning method was applied to the measured specimen and the processing characteristics were analyzed according to the runout of the end mill through correlation analysis.

• 로봇학회논문지
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• 제18권3호
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• pp.299-307
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• 2023

In the midst of accelerating wars around the world, unmanned robot technology that can guarantee the safety of human life is emerging. ERP-42 is a modular platform that can be used according to the application. In the field of defense, it can be used for transporting supplies, reconnaissance and surveillance, and medical evacuation in conflict areas. Due to the nature of the military environment, atypical environments are predominant, and in such environments, the platform's path followability is an important part of mission performance. This paper focuses on reducing the minimum turning radius in terms of improving path followability. The minimum turning radius of the existing 2WS/2WD in-wheel platform was reduced by increasing the torque of the independent driving in-wheel motor on the rear wheel to generate oversteer. To determine the degree of oversteer, two GPS were attached to the center of the front and rear wheelbases and measured. A closed-loop speed control method was used to maintain a constant rotational speed of each wheel despite changes in load or torque.

• 콘크리트학회논문집
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• 제15권5호
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• pp.759-767
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• 2003

This paper presents the simplified but more rational analysis method for the prediction of additional internal forces induced in integral abutment bridges. These internal forces depend upon the degree of restraint provided tc the deck by the backfill soil adjacent to the abutments and piles. In addition, effect of the relative flexural stiffness ratio among pile foundations, abutment, and superstructure on the structural behavior is also an important factor. The first part of the paper develops the stiffness matrices, written in terms of the soil stiffness, for the lateral and rotational restraints provided by the backfill soil adjacent to the abutment. The finite difference analysis is conducted and it is confirmed that the results are agreed well with the predictions obtained by the proposed method. The simplified spring model is used in the parametric study on the behavior of simple span and multi-span continuous integral abutment PSC beam bridges in which the abutment height and the flexural rigidity of piles are varied. These results are compared with those obtained by loading Rankine passive earth pressure according to the conventional method. From the results of parametric study, it was shown that the abutment height, the relative flexural rigidity of superstructure and piles, and the earth pressure induced by temperature change greatly affect the overall structural response of the bridge system. It may be possible to obtain more rational and economical designs for integral abutment bridges by the proposed method.