프로세스 데이터를 활용한 응답속도와 정확도의 관계 분석 : PISA 2015 미국과 한국의 사례를 중심으로

신효정(Hyo Jeong Shin) 한국교육평가학회 2021 교육평가연구 Vol.34 No.3

최근 PISA를 비롯한 국제학업성취도 평가가 컴퓨터 기반 검사로 전환되면서 단순 응답 결과뿐 아니라, 피험자가 문항에 응답하는 과정을 기록한 프로세스 데이터의 수집 및 활용이 가능해졌다. 프로세스 데이터 중에서도 응답시간은 가장 주목받고 있으며, 문항반응이론에 근거하여 응답속도와 정확도의 관계를 분석하는 다양한 심리측정모형이 개발되고 있다. 본 연구에서는 실험심리학에서 수립된 speed-accuracy tradeoff 개념과 van der Linden의 위계적 모형(2007)을 소개하고, 이를 응답속도가 문항 유형(구성형 또는 선다형)을 반영할 수 있도록 확장시켰다. 두 가지 심리측정 모형을 통해 한국과 미국의 PISA 2015 과학 영역 자료를 분석한 결과, 한국과 미국 모두 정확도가 높은 학생들이 더 천천히 응답하는 경향이 있는 것으로 나타났으며, 이러한 경향은 미국보다 한국에서 더욱 강하게 나타났다. 또한 선다형 문항보다 구성형 문항에서 천천히 응답할수록 정확도가 높아지는 경향성이 더 강하게 나타났다. The transition to computer-based assessment in international large-scale assessments, including PISA, enabled the collection of response processes, in addition to response outcomes. Recently, advanced psychometric models have been proposed to jointly model the response outcomes and processes. Response time, as one of the popular variables among process data, is receiving increased attention from researchers due to its accessibility. To deepen our understanding of Koreans’ extremely fast responses in PISA, I introduced and fitted van der Linden’s hierarchical model (van der Linden, 2007) and its extended version that accounts for the item types (multiple choice vs. constructed response items) to the PISA 2015 science data, collected in Korea and the United States. Negative accuracy-speed latent correlations were estimated between accuracy and speed dimensions, implying faster responses were associated with lower accuracy in both countries. Compared to the United States, Korea showed stronger negative accuracy-speed latent correlations. In addition, when the item types were considered, the model fit improved to some extent and showed stronger relationships between accuracy and speed on constructed-response items. Such a pattern was consistently observed on the technology-enhanced items, which were newly developed and administered in PISA 2015 both in Korea and the United States.

연료전지 하이브리드 차량의 효율적인 작동을 위한 배터리 충전 시기에 대한 연구

Wei Jin,권오정,조인수,현덕수,천승호,오병수 한국수소및신에너지학회 2009 한국수소 및 신에너지학회논문집 Vol.20 No.1

Recently, the research focused on fuel cell hybrid vehicles (FCHVs) is becoming an attractive solution due to environmental pollution generated by fossil fuel vehicles. The proper energy control strategy will result in extending the fuel cell lifetime, increasing of energy efficiency and an improvement of vehicle performance.1) Battery state of charge (SoC) is an important quantity and the estimation of the SoC is also the basis of the energy control strategy for hybrid electric vehicles. Estimating the battery's SoC is complicated by the fact that the SoC depends on many factors such as temperature, battery capacitance and internal resistance2). In this paper, battery charging time estimated by SoC is studied by using the speed response and current response. Hybrid system is consist of a fuel cell unit and a battery in series connection. For experiment, speed response of vehicle and current response of battery were determined under different state of charge. As the results, the optimal battery charging time can be estimated. Current response time was faster than RPM response time at low speed and vice versa at high speed.

프로세스 대형 모터-발전기의 저어널 베어링 설계 개선

이안성(An Sung Lee) 한국트라이볼로지학회 2012 한국트라이볼로지학회지 (Tribol. Lubr.) Vol.28 No.6

In the preceding Part I study, for improving the unbalance response vibration of a large PRT motorgenerator rotor fundamentally by design, a series of design analyses were carried out for bearing improvement by retrofitting from original plain partial journal bearings, applied for operation at a rated speed of 1,800 rpm, to final tilting pad journal bearings. To satisfy evenly key basic lubrication performances such as the minimum lift-off speed and maximum oil-film temperature, a design solution of 5-pad tilting pad journal bearings and maximizing the direct stiffness by about two times has been achieved. In this Part II study, a detailed rotordynamic analysis of the large PRT motor-generator rotor-bearing system will be performed, applying both the original plain partial journal bearings and the retrofitted tilting pad journal bearings, to confirm the effect of rotordynamic vibration improvement after retrofitting. The results show that the rotor unbalance response vibrations with the tilting pad journal bearings are greatly reduced by as much as about one ninth of those with the plain partial journal bearings. In addition, for the tilting pad journal bearings there exist no critical speed up to the rated speed and just one instance of a concerned critical speed around the rated speed, whereas for the plain partial journal bearings there exist one instance of a critical speed up to the rated speed and two instances of concerned critical speeds around the rated speed.

100,000 rpm 운전용 원심분리기 로터-베어링 시스템의 회전체동역학 해석

이안성,김영철,박종권 한국소음진동공학회 1998 소음 진동 Vol.8 No.3

A rotordynamic analysis is performed with a centrifuge rotor-bearing system for the raing speed of 100,000 rpm. The system is composed of a centrifuge rotor(or simply the rotor), flexible shaft, motor rotor and shaft, and two support rolling element bearings of the motor shaft. Design goals are to achieve wide separation margins of critical speeds and favorable unbalance responses of the rotor at the associated critical speeds. The latter requirements are especially important as the system crosses multiple numbers of critical speeds and as the system may not have enough separaton margins around the rating speed. As the system adopts an extra-flexible shaft, it is shown that the rotor has satisfactory small unbalance responses over higher criticals while having an unsatisfactory large one at the first critical. To supress this a bumper ring or guide bearing needs to be installed at a suitable location of the flexible shaft. It is also shown that even with the flexible shaft the dynamics of the motor must be incoporated into the full system model to accurately identify the fourth critical speed, which is close to the rating speed, and higher ones. The analysis is based on the finite element method.

데스크탑 밀링머신의 고속 스핀들 설계 해석

장성현,황현영,정우영,홍정표,최영휴 한국공작기계학회 2009 한국공작기계학회 춘계학술대회논문집 Vol.2009 No.-

During a decade, there are many researches on microfactory which is the miniature, flexible, and efficient manufacturing system for the micro/meso scale machining device. Moreover many micro machine tool has developed in Japan, U.S., Europe, and Korea. Already we are developing a desktop milling machine with 380×450×450 ㎣ machine size for microfactory or BT (Bio technology) factory. In this study, we carried out the design analysis of a high speed spindle system for our desktop milling machine by using ADROS, which is our own developed S/W for dynamic design analysis of rotor systems. As the result, we obtained some analyzed dynamic characteristics of a spindle system, such as natural frequency, whirl frequency, critical speed, and harmonic response.

동 다이캐스팅 고속 유도전동기의 불평형 응답 해석

홍도관(Hong, Do-Kwan),정승욱(Jung, Seung-Wook),우병철(Woo, Byung-Chul),구대현(Koo, Dae-Hyun),안찬우(Ahn, Chan-Woo) 한국소음진동공학회 2012 한국소음진동공학회 논문집 Vol.22 No.7

This paper deals with a copper die casting induction motor which has several advantages of motor performance. The developed motor is used as spindle motor in machining center. The dynamic characteristic analysis of rotor is dealt with for precision machining. The critical speed of rotor considering rotation and gyroscopic effect should be above operating speed, 18,000 rpm, and have a 201 % sufficient separation margin. Also, the 3-D unbalance vibration response analysis is performed and enabled the prediction of the expected vibration amplitude by unbalance in high speed. The unbalance vibration responses of each position on the rotor are satisfied with allowable vibration displacement of API 611 standard according to balancing G grade(G 0.4, G 2.5, G 6.3). Copper die casting high speed induction motor is successfully developed and verified by experiment.

액체로켓 터보펌프의 임계 속도 해석

전성민(Seong Min Jeon),곽현덕(Hyun Duck Kwak),윤석환(Suk Hwan Yoon),김진한(Jin han Kim) 한국항공우주학회 2005 韓國航空宇宙學會誌 Vol.33 No.6

30톤 추력급 터보펌프에 대한 회전체 동역학 해석이 수행되었다. 연료펌프와 터빈에 의해서 유발되는 공력 및 수력 하중이 볼 베어링과 비접촉식 실의 강성 및 감쇠 예측을 위하여 고려되었다. 임계 속도의 분리 안전 여유와 회전체 부품의 팁 변위를 예측하기 위하여 임계 속도 해석과 질량 불평형 응답 해석이 수행되었다. 정확한 해석을 위하여 3차원 유한요소법을 사용하였고 1차원 전달함수 행렬법의 결과와 비교하였다. 탄성 링을 추가적으로 장착함으로써 베어링 지지부의 강성 제어를 통하여 충분한 공진 분리 여유의 확보가 가능함을 확인하였다. Numerical analyses of critical speed and mass unbalance response are performed for a 30 ton thrust turbopump. The stiffness and damping of ball bearings and non-contact seals are quantified under aerodynamic and hydrodynamic loads induced by a fuel pump and turbine. Critical speed margin and tip displacements of the rotating parts are evaluated using a three-dimensional finite element method. The results are used to ensure the soundness of the rotordynamic design using an one-dimensional transfer matrix method. A further study shows that sufficient resonance margin may be assured via controlling the stiffness of the rotor support by employing an additional elastic ring to the bearing support.

물 분사 펌프의 동특성 분석

이종명(Jong Myeong Lee),이정훈(Jeong Hoon Lee),하정민(Jeong Min Ha),안병현(Byung Hyun Ahn),김원철(Won Cheol Kim),최병근(Byeong Keun Choi) 대한기계학회 2013 大韓機械學會論文集A Vol.37 No.12

물 분사 펌프는 심해 유정의 시추작업 후 유정 내 높은 압력으로 인하여 원유를 1 차 생산하고 이후 유정 내 압력이 낮아져 유정 자체의 압력 만으로 생산이 어려울 때 고압의 해수를 유정에 주입해 회수율을 높이는 해양플랜트에서 사용되는 핵심 기자재이며, 여러 기업에서 개발 중이다. 본 논문은 회전체의 동특성 을 분석하여 베어링 강성에 따른 고유진동수 변화분석, 운전속도 변화에 따른 고유진동수의 변화와 위험속도 분석, 안정성 평가, 불평형 응답을 통하여 변위와 틈새 관계 분석 등의 수학적 해석을 통하여 개발 중의 제품의 신뢰성에 기여하였다. Water injection pump outputs oil with high pressure during this process, seawater is injected into the well to recover the well pressure and maintain high productivity. A water injection pump has high productivity, and therefore, it serves as a key piece of equipment in marine plants. In this light, water injection pumps are being studied widely in industry. In this study, the rotor dynamics is analyzed to determine the natural frequency according to the bearing stiffness and operation speed change. This study aims to establish the pump reliability through critical speed, stability, and unbalance response analysis.

물 분사 펌프 동특성의 해석적 평가

이종명(JongMyeong Lee),이정훈(JeongHoon Lee),하정민(JeongMin Ha),안병현(ByungHyun Ahn),구동식(DongSik Gu),최병근(ByeongKeun Choi) 한국소음진동공학회 2013 한국소음진동공학회 학술대회논문집 Vol.2013 No.4

Water injection pump produced the 1st oil well through the high pressure after the Deep water oil well drilling. After finish the work it is hard to produce only using itself pressure due to low pressure. Therefore it can be increased recovery factor through the injection seawater of high pressure. Is the key equipment used in the marine plant and it is developing at many industries. In this paper, Analyze changes in the natural frequency due to the stiffness of the bearing. Analyze the critical speed of the natural frequency due to the change of operation speed. And evaluate the Stability. And then analyze the displacement and clearance through the unbalance response this way has contributed to the reliability of the developing product. Through a mathematical analysis.

고정 커플링의 오프셋을 갖는 발전용 가스터빈-발전기의 동적 응답해석

하진웅(Jin Woong Ha),정대석(Dae Seok Jung) 한국유체기계학회 2014 한국유체기계학회 논문집 Vol.17 No.4