• 한국재료학회지
• /
• 제24권10호
• /
• pp.538-542
• /
• 2014

Microstructural and mechanical characteristics of Al-6Si-2Cu alloy for lightweight automotive parts were investigated. The test specimens were prepared by gravity casting process. Solution heat treatments were applied to as-cast alloys to improve mechanical properties. The microstructure of the gravity casting specimen presents a typical dendrite structure, having a secondary dendrite arm spacing (SDAS) of $37{\mu}m$. In addition to the Al matrix, a large amount of coarsened eutectic Si, $Al_2Cu$ intermetallic phase, and Fe-rich phases were identified. After solution heat treatment, single-step solution heat treatments were found to considerably improve the spheroidization of the eutectic Si phase. Two-step solution treatments gave rise to a much improved spheroidization. The mechanical properties of the two-step solution heat treated alloy have been shown to lead to higher values of properties such as tensile strength and microhardness. Consequentially, the microstructural and mechanical characteristics of Al alloy have been successfully characterized and are available for use with other basic data for the development of lightweight automotive parts.

• Structural Engineering and Mechanics
• /
• 제63권1호
• /
• pp.77-88
• /
• 2017

Correction Factor Method (CFM) is one of the earliest methods for simulating the actual behavior of structure according to construction sequences and practical implementation steps of the construction process which corrects the results of the conventional analysis just by the application of correction factors. The most important advantages of CFM are the simplicity and time-efficiency of the computations in estimating the final modified forces of the beams. However, considerable inaccuracy in evaluating the internal forces of the other structural members obtained by the moment equilibrium equation in the connection joints is the biggest disadvantage of the method. This paper proposes a novel method to eliminate the aforementioned defect of CFM by using the column shortening correction factors of the CFM to modify the axial stiffness of columns. In this method, the effects of construction sequences are considered by performing a single step analysis which is more time-efficient when compared to the staged analysis especially in tall buildings with higher number of elements. In order to validate the proposed method, three structures with different properties are chosen and their behaviors are investigated by application of all four methods of: conventional one-step analysis, sequential construction analysis (SCA), CFM, and currently proposed method.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
• /
• pp.464-469
• /
• 1999

Recently, the need for designing multi-stage gear drive has been increased as the hear drives are used more in the applications with high-speed and small volume. The design of multi-stage gear drives includes not only dimensional design but also configuration design of various machine elements. Until now, however, the researches on the design of gear drives are mainly focused on the single-stage gear drives and the design practices for multi-stage gear drives, especially in configuration design activity, mainly depend on the experiences and 'sense' of the designer by trial and error. We propose a design algorithm to automate the dimension design and the configuration design of multi-stage gear drives. The design process consists of four steps. The number of stage should be determined in the first step. In second step, the gear ratios of each reduction stage are determined using random search, and the ratios are basic input for the dimension design of gears, which is performed by the exhaustive search in third step. The designs of gears are guaranteed by the pitting resistance and bending strength rating practices by AGMA rating formulas. In configuration design, the positions of gears are determined to minimize the volume of gearbox using simulated annealing algorithm. The effectiveness of the algorithm is assured by the design example of a 4-stage gear drive.

• 한국공간구조학회논문집
• /
• 제22권2호
• /
• pp.39-46
• /
• 2022

Recently, machine learning is widely used to solve optimization problems in various engineering fields. In this study, machine learning is applied to development of a control algorithm for a smart control device for reduction of seismic responses. For this purpose, Deep Q-network (DQN) out of reinforcement learning algorithms was employed to develop control algorithm. A single degree of freedom (SDOF) structure with a smart tuned mass damper (TMD) was used as an example structure. A smart TMD system was composed of MR (magnetorheological) damper instead of passive damper. Reward design of reinforcement learning mainly affects the control performance of the smart TMD. Various hyper-parameters were investigated to optimize the control performance of DQN-based control algorithm. Usually, decrease of the time step for numerical simulation is desirable to increase the accuracy of simulation results. However, the numerical simulation results presented that decrease of the time step for reward calculation might decrease the control performance of DQN-based control algorithm. Therefore, a proper time step for reward calculation should be selected in a DQN training process.

• Journal of Microbiology
• /
• 제44권5호
• /
• pp.508-514
• /
• 2006

In this study, the double-stranded DNA-dependent activities of Deinococcus radiodurans RecA protein (Dr RecA) were characterized. The interactions of the Dr RecA protein with double-stranded DNA were determined, especially dsDNA-dependent ATP hydrolysis by the Dr RecA protein and the DNA strand exchange reaction, in which multiple branch points exist on a single RecA protein-DNA complex. A nucleotide cofactor (ATP or dATP ) was required for the Dr RecA protein binding to duplex DNA. In the presence of dATP, the nucleation step in the binding process occurred more rapidly than in the presence of ATP. Salts inhibited the binding of the Dr RecA protein to double-stranded DNA. Double-stranded DNA-dependent ATPase activities showed a different sensitivity to anion species. Glutamate had only a minimal effect on the double-stranded DNA-dependent ATPase activities, up to a concentration of 0.7 M. In the competition experiment for Dr RecA protein binding, the Dr RecA protein manifested a higher affinity to double-stranded DNA than was observed for single-stranded DNA.

• 한국결정성장학회지
• /
• 제26권5호
• /
• pp.171-174
• /
• 2016

The diamond wire sawing method to produce silicon wafers for the photovoltaic application is still a new and highly investigated wafering technology. This technology, featured as the higher productivity, lower wear of the wire, and easier recycling of the coolant, is expected to become the mainstream technique for slicing the silicon crystals. However, the saw marks on the wafer surface have to be investigated and improved. This paper discusses the removal of saw marks on diamond wire-sawn single crystalline silicon wafer. With a pretreatment step using tetramethyl ammonium hydroxide ($(CH_3)_4NOH$, TMAH) and conventional texturing process with KOH solution (1 % KOH, 8 % IPA, and DI water), the saw marks on the surface of the diamond wire-sawn silicon wafers can be effectively removed and they are invisible to naked eyes completely.

• Nuclear Engineering and Technology
• /
• 제39권1호
• /
• pp.51-62
• /
• 2007

To efficiently design safety-critical systems such as nuclear power plants, with the requirement of high reliability, methodologies allowing for rigorous interactions between the synthesis and analysis processes have been proposed. This paper attempts to develop a reliability-centered design framework through an interactive process between Axiomatic Design (AD) and Fault Tree Analysis (FTA). Integrating AD and FTA into a single framework appears to be a viable solution, as they compliment each other with their unique advantages. AD provides a systematic synthesis tool while FTA is commonly used as a safety analysis tool. These methodologies build a design process that is less subjective, and they enable designers to develop insights that lead to solutions with improved reliability. Due to the nature of the two methodologies, the information involved in each process is complementary: a success tree versus a fault tree. Thus, at each step a system using AD is synthesized, and its reliability is then quantified using the FT derived from the AD synthesis process. The converted FT provides an opportunity to examine the completeness of the outcome from the synthesis process. This study presents an example of the design of a Containment Heat Removal System (CHRS). A case study illustrates the process of designing the CHRS with an interactive design framework focusing on the conversion of the AD process to FTA.

• 조명전기설비학회논문지
• /
• 제20권2호
• /
• pp.45-49
• /
• 2006

본 논문은 마이크로 전극 시스템에 의하여 연료전지 및 Ni-MH 전지로의 응용을 가정한 $AB_5$계 수소저장합금인 $MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3}$의 단일 입자에 대하여 전기화학적인 평가를 수행하였다. 즉 Carbon fiber 마이크로 전극을 합금 입자 한개 위에 전기적인 접촉을 이루도록 조정하고, 합금 입자 내에서 수소원자의 겉보기 화학적 확산계수를 계산하기 위하여 Potential-Step 실험을 실시하였다. 여기에서 사용되는 합금입자는 치밀하고 전도성이 있는 구형이므로 데이터 해석을 위해 구형확산 모델을 적용하였다. 실험결과로서 겉보기 확산계수($D_{app}$)는 수소 흡장 및 방출되는 전 과정에서 $10^{-9}$과 $10^{-10}[cm^2/s]$ 수준인 것으로 확인되었다. 마이크로 전극 측정 시스템에 의한 단일 입자의 전기화학적 평가는 기존의 Composite Film 전극에 비해 수소저장합금에 대해 보다 상세하고 정확한 정보를 쉽게 얻을 수 있었다.

• 한국압력기기공학회 논문집
• /
• 제9권1호
• /
• pp.1-7
• /
• 2013

In around 2000, the U.S. NPPs have developed the various advanced engineering processes based on the INPO AP-913(Equipment Reliability Process Description) and showed the high performance in availability. With these benchmarking cases, the Korean NPPs have introduced the advanced engineering technology since 2005. The first step of the advanced engineering is to analyze and determine component importance for all components of a plant. This process is called Functional Importance Determination(FID). These results are basically utilized to determine the priority with limited resources in various areas. However, because the consistency of FID results is insufficient despite applying the same criteria in the existing operating NPPs, the degree of application is low. Therefore, this paper presents the improved methodology for FID interfacing system functions of Maintenance Rule Program and results of Single Point Vulnerability(SPV). This improved methodology is expected to contribute to enhance the reliability of FID data.

• 전자공학회논문지C
• /
• 제35C권10호
• /
• pp.22-29
• /
• 1998

본 논문에서는 휴대용 영상신호처리 시스템에 집적화할 수 있는 전류예측기와 모듈형 기준전류원을 이용한 10비트 저전력 전류구동 CMOS A/D 변환기를 설계하였다. 전류예측기와 모듈형 기준 전류원을 사용함으로써 2단 플래시구조를 갖는 A/D 변환기에 비해 비교기와 기준전류원의 개수를 줄일 수 있게 되었고, 따라서 설계된 A/D변환기의 저전력 동작이 가능하였다. 설계된 10비트 저전력 전류구동 CMOS A/D 변환기는 0.6㎛ n-well single-poly triple metal CMOS 공정을 사용하여 제작되었다. +5V 단일 공급전압하에서 동작할 때 측정된 전력소모는 94.4mW이며, 아날로그 입력 전류범위는 16㎂에서 528㎂로 측정되었으며, INL과 DNL은 각각 ±1LSB, ±0.5LSB이하로 나타났다. 또한 10MSamples/s의 변환속도를 나타내었고, 제작된 10비트 전류구동 CMOS 4/D 변환기의 유효 칩면적은 1.8㎜ x 2.4㎜이다.