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Multiaxial fatigue reliability assessment using a differential ant-stigmergy algorithm
유용훈,이보라,조용주 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5
This study presents a process of establishing a multiaxial Weibull model to assess S45C steel reliability and high-cycle fatigue. The proposed model includes multiaxial stress state, stress gradient and component size factors, and the probability of failure. The model was based on multiaxial fatigue theory, where the expressed damage parameter is a single value for one cycle of the multiaxial stress state, combined with the weakest link concept. Through the maximum likelihood method (MLE), a probabilistic stress-life (P-S-N) curve that reflects both failure and right-censored data was plotted; whereas optimal Weibull parameters were estimated via the differential ant-stigmergy algorithm (DASA). The completed multiaxial Weibull model was then applied to S45C steel tensioncompression (TC) and zero-tension (ZT) fatigue test data, both of which agreed well. Afterward, the model was cross-checked with torsion fatigue test data results for validity.
곡률 커플링 접촉각에 따른 접촉 강성 및 굽힘 강성해석
유용훈,조용주,이동현,김영철 한국트라이볼로지학회 2018 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.34 No.1
Coupling is a mechanical component that transmits rotational force by connecting two shafts. Curvic coupling is widely used in high-performance systems because of its excellent power transmission efficiency and easy machining. However, coupling applications change dynamic behavior by reducing the stiffness of an entire system. Contact surface stiffness is an important parameter that determines the dynamic behavior of a system. In addition, the roughness profile of a contact surface is the most important parameter for obtaining contact stiffness. In this study, we theoretically establish the process of contact and bending stiffness analysis by considering the rough surface contact at Curvic coupling. Surface roughness parameters are obtained from Nayak's random process, and the normal contact stiffness of a contact surface is calculated using the Greenwood and Williamson model in the elastic region and the Jackson and Green model in the elastic–plastic region. The shape of the Curvic coupling contact surface is obtained by modeling a machined shape through an actual machining tool. Based on this modeling, we find the maximum number of gear teeth that can be machined according to the contact angle. Curvic coupling stiffness is calculated by considering the contact angle, and the calculation process is divided into stick and slip conditions. Based on this process, we investigate the stiffness characteristics according to the contact angle.
유용훈(Yong Hoon Yoo),장두환(Doo Hwan Jang),박훈철(Hoon Cheol Park),변영환(Yong Hwan Byun),변도영(Doyoung Byun) 한국항공우주학회 2008 韓國航空宇宙學會誌 Vol.36 No.1
본 연구에서는 딱정벌레목 곤충의 비행특성을 알아보기 위해 유동가시화가 수행되었고, 겉날개의 날갯짓의 영향에 대해 고찰하였다. 또한 고속 카메라를 이용하여 겉날개와 속날개의 움직임을 분석하였다. 실험 결과 날갯짓 하는 곤충의 세 가지 양력발생 원리를 확인 할 수 있었다. 그리고 겉날개의 미세한 날갯짓을 확인할 수 있었으며, 겉날개의 효과를 예상할 수 있었다. A flow visualization is conducted to investigate a flight characteristics of a Coleoptera and an effect of flapping elytra was considered in this study. Also the movements of outer wing(elytra) and inner wing is analyzed using High Speed Camera. As a result of this experiment, in case of flapping insect, three mechanisms to generate lift is confirmed. A small movement of outer wing(elytra) is confirmed and the effect of outer wing(elytra) is estimated.
효율적인 메모리 관리 구조를 갖는 H.264용 고성능 디블록킹 필터 설계
유용훈(Yonghoon Yu),이찬호(Chanho Lee) 대한전자공학회 2008 電子工學會論文誌-SD (Semiconductor and devices) Vol.45 No.1
고성능 영상 압축 알고리즘으로서 널리 사용되고 있는 H.264 디코더의 디블록킹(Deblocking) 필터는 복호된 영상의 블록화 현상을 제거함으로써 영상의 질을 높이는 역할을 하는데 연산량이 많은 유닛중 하나이다. 본 논문에서는 효율적인 디블록킹 필터 설계를 위해 파이프라인 구조 및 1-D 필터를 사용하고 효율적인 메모리 관리를 통해 하드웨어 면적과 연산 사이클수를 줄이고 H.264 디코더의 성능을 향상시킬 수 있는 하드웨어 구조를 제안한다. 제안된 구조에서는 픽셀의 재배치를 통해 동일한 1-D 필터를 이용하여 수직방향의 필터연산과 수평방향의 필터연산을 모두 지원한다. 또한 4 개의 메모리 블록 구조를 이용하여 현재 매크로블록의 픽셀과 인접한 다른 매크로블록의 픽셀의 접근 및 저장을 효율적으로 할 뿐만 아니라 필터연산중에 움직임 보상기의 출력 픽셀을 저장하여 디블록킹 필터와 움직임 보상기 사이의 병목현상을 제거하였다. 이를 통해 디블록킹 필터에 관련된 메모리의 크기를 최소화하고 H.264 디코더의 성능을 향상시키는 이점을 얻을 수 있다. 제안된 디블록킹 필터는 Verilog-HDL을 이용하여 설계하고 FPGA를 통해 검증하였다. 합성 결과 77 ㎑에서 HD 영상 디코딩이 가능함을 확인하였다. The H.264 standard is widely used due to the high compression rate and quality. The deblocking filter of the H.264 standard improves the quality of images by eliminating blocking artifacts of pictures, and it requires a lot of computation. We propose a new hardware architecture for the deblocking filter with pipelined architecture, 1-D filters which support both horizontal and vertical filtering and efficient memory management. Four memory blocks are configured for the efficient storage and access of the current macroblock and adjacent referenced sub-macroblocks, and the pixel data from the motion compensation unit can be transferred without waiting during the computation cycles of the deblocking filter. The number of computation cycles and the hardware area are reduced using the proposed architecture, and the performance of the H.264 decoder is improved. We design the deblocking filter using Verilog-HDL and implement using an FPGA. The designed deblocking filter can be used for decoding HD quality images at 77 ㎑.