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Mg-5wt%Al-0.6wt%Zr 합금의 용탕단조시 주조결함의 형성 및 방지
황영하,허승호,홍준표 ( Young Ha Hwang,Seung Ho Huh,Chun Pyo Hong ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.3
N/A The squeeze casting of a Mg-5wt%Al-0.6wt%Zr alloy was carried out to investigate the conditions for the formation and the prevention of macrodefects, such as macrosegregation and shrinkage defects. The effects of the process parameters, the applied pressure, the die temperature, and the pouring temperature on the formation of macrodefcts were investigated in correlation with the evolution of macrostructure. Three types of macrodefects were found; macrosegregation only, shrinkage defects only, both macrosegregation and shrinkage defects. It was found that the pouring temperature, the die temperature, and the applied pressure are closely related to the formation of macrodefects. Sound castings without macrosegregation and shrinkage defects can be obtained under the conditions of 80 MPa < P < 110 MPa, 730˚C < Tp < 760˚C, and 180˚C < Tp < 250˚C. (Received April 15, 1998)
센서용 Incremental cascade 델타-시그마 모듈레이터의 모델링과 capacitance non-linearity 효과 분석
황영하(Young-Ha Hwang),정덕균(Deog-Kyoon Jeong) 대한전자공학회 2016 대한전자공학회 학술대회 Vol.2016 No.6
Sensor applications, such as audio, touchscreen controller, biosensor, smart sensor, require delta-sigma ADCs(ΣΔ ADCs) with high accuracy and linearity as well as high resolution. ΣΔ ADCs can achieve high resolution in short time by utilizing oversampling and higher-order noise-shaping, so can get better energy-efficiency. For many applicaions, ΣΔ ADCs operate in incremental mode, in which they are first reset and then operate for a fixed number of cycles. In this paper, a method to model incremental cascaded ΣΔ modulator with SIMSIDES, MATLAB simulink-based tool, and consider non-linearity of capacitor is proposed.
A Low-Voltage, Low-Power Asynchronous SAR ADC With A Double-Biased Comparator
Young-Ha Hwang(황영하),Deog-Kyoon Jeong(정덕균) 대한전자공학회 2017 대한전자공학회 학술대회 Vol.2017 No.6
Successive-approximation-register analog-to-digital converters (SAR ADCs) are widely used in low-power applications, such as medical implant devices like a pacemaker, and Internet-of-Things (IoTs), which require the resolution from 8 to 10 bits and moderate sampling speed. Since these applications, powered by a battery or an energy-harvesting module, are power-hungry, SAR ADC is required to be scaled towards low-voltage operation. This paper presents a low-voltage, low-power asynchronous SAR ADC which is appropriate for the low-power applications.
저전력 125MS/s 256-point radix-2² SDF FFT 프로세서의 설계 및 구현
황영하(Young-Ha Hwang),정덕균(Deog-kyoon Jeong) 대한전자공학회 2015 대한전자공학회 학술대회 Vol.2015 No.6
FFT(Fast Fourier transform) algorithm is one of the most widely used DSP(Digital Signal Processing) algorithm, reducing the operations of DFT effectively by decomposing the sequence of length N to the smaller sequence. Often, a high performance FFT processor is the key component in the embedded applications like wireless sensor networks or wide band OFDM systems. In this paper, a low power 125M/s 256-point R2²S-DF FFT processor is proposed. The processor is synthesized using Samsung 65nm low power CMOS process with a core size of 0.194㎟ and 11.4mW power consumption.
한국형 전투기 개발을 위한 전투기 임무격렬도 모델 연구
김석호,황영하,신기수,Kim, Sug-Ho,Hwang, Young-Ha,Shin, Ki-Su 한국군사과학기술학회 2009 한국군사과학기술학회지 Vol.12 No.2
The aim of this paper is to propose fighter aircraft's mission severity model which can be used as one of key factors for designing a structure and determining design life of KF-X. The mission severity is a quantitative data of flight loads and expressed by Nz(Vertical Load Factor) exceedances or occurrences. The severities of the flight loads depended on the circumstances of the countries which operate fighter aircraft. In this paper we have studied on Nz occurrences/exceedances of ROKAF fighter aircraft to generate mission severity model for the KF-X. The analyses of flight data were accomplished by using the Matlab.
전투기 J85GE21 터보제트 엔진 후기 연소기 연료펌프의 내부피스톤 패킹 연료 누출 원인
김익식 ( Ik Sik Kim ),황영하 ( Young Ha Hwang ),손경숙 ( Kyung Suk Sohn ),이중훈 ( Jung Hun Lee ),김성욱 ( Sung Uk Kim ) 한국고무학회 2014 엘라스토머 및 콤포지트 Vol.49 No.4
대부분 군사용 초음속 전투기는 후기 연소기를 사용한다. 후기 연소기는 초음속 비행, 이륙, 전투 상황에 대해비상 임무 수행을 가능하게 하는 중요한 역할을 한다. 최근 전투기 J85-GE-21 터보제트 엔진 후기 연소기 연료펌프의 내부 피스톤 패킹고무에서 반복적인 연료 누출 결함이 발생하였다. 이러한 결함은 두 제조사 중 한 제조사의부품에서만 발생하였다. 따라서, 결함발생 원인을 제조사가 상이한 정상품 및 결함품에 대하여 다양한 비교 분석방법을통하여 조사하였다. 결함분석에는 팽윤 또는 팽윤도, 총 황함량, 폴리머 확인, 카본블랙 함량 및 표면적, 경도와 같은분석방법이 적용되었다. 결론적으로, 반복적인 연료 누출 결함의 주요 원인은 보강제 카본블랙의 함량 미달로 확인되었으며, 더불어 표면적이 작은 카본블랙과 함량이 낮은 황 적용이 결함원인에 부가적인 영향을 준 것으로 확인되었다. Most of military supersonic aircraft use an afterburner. It plays an important role in performing unusual duties for supersonic flight, takeoff, and combat situations. Recently, repetitive fuel leakage from the inner piston packing rubber of afterburner fuel pump in an aircraft J85-GE-21 turbojet engine has happened. These failures have only happenedin one manufacturer`s parts of two manufacturers. Thus, the cause of these failures was investigated through the comparative analysis for both the failed and the un failed with two different manufacturers using various analysis methods. The failure analysis was performed using analysis methods such as swelling or swelling ratio, total sulfur content, polymer identification, loading and surface area of carbon black, and hardness. Consequently, the main cause of this failure was identified tobe insufficient loading of carbon black as a reinforcing agent, together with small surface area of carbon black and somewhat low sulfur content.
오상섭(Sang Sub Oh),황영하(Young Ha Hwang),김도향(Do Hyang Kim),홍준표(Chun Pyo Hong),박익민(Ik Min Park) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.1
N/A Microstructural characteristics and strengthening behavior in Mg-5wt%Zn-0.6wtZr alloys have been investigated by a combination of optical, secondary electron and transmission electron microscopy, differential thermal analysis, and hardness and tensile, creep property measurements. The result have been compared with those of Mg-5wt%Zn alloys. The as-squeeze cast microstructure consisted of dendrite α-Mg, interdendrite or intergranular Mg_7Zn₃ and fine dispersoids of ZnZr₂. The size of secondary solidification phases in Mg-5wt%Zn-0.6wtZr alloys was significantly smaller than that of the Mg-5wt%Zn alloys due to the existence of fine dispersoid of ZnZr₂ which also effected the refinement of grain size. TEM study showed that the main cause of age hardening is formation of fine rodlike β₁` precipitates as well as fine ZnZr₂ dispersoids. Due to the observed microstructural characteristics mechanical propeties of Mg-5wt%Zn-0.6wtZr alloys was found to be superior to those of Mg-5wt%Zn alloys. (Received June 22, 1998)