• Journal of Power Electronics
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• 제15권5호
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• pp.1318-1328
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• 2015

The photovoltaic (PV) power conditioning system for small-scale applications has gained significant interest in the past few decades. However, the standalone mode of operation has been rarely approached. This paper presents a two-stage multi-level micro-inverter topology that considers the different operation modes. A multi-output flyback converter provides both the DC-Link voltage balancing for the multi-level inverter side and maximum power point tracking control in grid connection mode in the PV stage. A modified H-bridge multi-level inverter topology is included for the AC output stage. The multi-level inverter lowers the total harmonic distortion and overall ratings of the power semiconductor switches. The proposed micro-inverter topology can help to decrease the size and cost of the PV system. Transient analysis and controller design of this micro-inverter have been proposed for stand-alone and grid-connected modes. Finally, the system performance was verified using a 120 W hardware prototype.

• 한국항공우주학회지
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• 제34권10호
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• pp.71-79
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• 2006

액체로켓엔진에서 고주파 연소불안정을 제어하기 위하여 다단 접선 유입구를 갖는 스월 인젝터를 분석하였다. 음향흡수자로서 인젝터의 효과를 분석하기위하여 인젝터는 1/4 파장 공명기로 해석하였고, 상온에서 감쇠 효과의 적합성을 검증하였다. 이러한 인젝터는 모델 챔버의 고유주파수에 동조시킬 수 있는 고유주파수를 갖게 된다. 다단의 접선 유입구를 갖는 인젝터가 단일 유입구를 갖는 인젝터 보다 인젝터 내부의 air core가 안정되었다. 또한, 다단 접선 유입구를 갖는 인젝터를 사용하였을 때 불안정 모드에 동조되는 인젝터 길이가 계산된 길이와 잘 일치하였다. 이러한 실험 결과로부터 인젝터 내부의 air core가 안정되게 유지된다면, 동조된 스월 인젝터는 모델 챔버의 불안정 모드를 효과적으로 감소시킬 수 있고, 감쇠율을 증가시킬 수 있음을 확인하였다.

• 대한치과교정학회지
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• 제51권2호
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• pp.77-85
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• 2021

Objective: To evaluate the accuracy of a multi-stage convolutional neural network (CNN) model-based automated identification system for posteroanterior (PA) cephalometric landmarks. Methods: The multi-stage CNN model was implemented with a personal computer. A total of 430 PA-cephalograms synthesized from cone-beam computed tomography scans (CBCT-PA) were selected as samples. Twenty-three landmarks used for Tweemac analysis were manually identified on all CBCT-PA images by a single examiner. Intra-examiner reproducibility was confirmed by repeating the identification on 85 randomly selected images, which were subsequently set as test data, with a two-week interval before training. For initial learning stage of the multi-stage CNN model, the data from 345 of 430 CBCT-PA images were used, after which the multi-stage CNN model was tested with previous 85 images. The first manual identification on these 85 images was set as a truth ground. The mean radial error (MRE) and successful detection rate (SDR) were calculated to evaluate the errors in manual identification and artificial intelligence (AI) prediction. Results: The AI showed an average MRE of 2.23 ± 2.02 mm with an SDR of 60.88% for errors of 2 mm or lower. However, in a comparison of the repetitive task, the AI predicted landmarks at the same position, while the MRE for the repeated manual identification was 1.31 ± 0.94 mm. Conclusions: Automated identification for CBCT-synthesized PA cephalometric landmarks did not sufficiently achieve the clinically favorable error range of less than 2 mm. However, AI landmark identification on PA cephalograms showed better consistency than manual identification.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.489-502
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• 2022

This paper is aimed at developing an optimization-based Finite Element model updating approach for structural damage identification and quantification. A modal flexibility-based error function is introduced, which uses modal assurance criterion to formulate the updating problem as an optimization problem. Because of the inexplicit input/output relationship between the candidate solutions and the error function's output, a robust and efficient optimization algorithm should be employed to evaluate the solution domain and find the global extremum with high speed and accuracy. This paper proposes a new multi-stage Selective Particle Swarm Optimization (SPSO) algorithm to solve the optimization problem. The proposed multi-stage strategy not only fixes the premature convergence of the original Particle Swarm Optimization (PSO) algorithm, but also increases the speed of the search stage and reduces the corresponding computational costs, without changing or adding extra terms to the algorithm's formulation. Solving the introduced objective function with the proposed multi-stage SPSO leads to a smart feedback-wise and self-adjusting damage detection method, which can effectively assess the health of the structural systems. The performance and precision of the proposed method are verified and benchmarked against the original PSO and some of its most popular variants, including SPSO, DPSO, APSO, and MSPSO. For this purpose, two numerical examples of complex civil engineering structures under different damage patterns are studied. Comparative studies are also carried out to evaluate the performance of the proposed method in the presence of measurement errors. Moreover, the robustness and accuracy of the method are validated by assessing the health of a six-story shear-type building structure tested on a shake table. The obtained results introduced the proposed method as an effective and robust damage detection method even if the first few vibration modes are utilized to form the objective function.

• 문화기술의 융합
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• 제9권5호
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• pp.557-562
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• 2023

본 연구는 순환자원을 대량 활용한 지반안정재를 터널공사 시 보조공법으로 이용하는 강관다단공법의 주입재로 활용을 검토하기 위해 다양한 주입재 배합비에 따른 겔타임, 호모겔 강도를 비교하였다. 강관다단공법은 터널의 보조공법으로써 시공 후 초기강도의 발현이 중요한 요인으로, 초기에 강도발현이 우수할수록 강관다단공법에 적합한 주입재로 활용이 가능하다. 실내시험 결과, 순환자원을 활용하는 주입재의 호모겔타임은 시멘트를 주입재로 활용하는 배합비에 비해 많은 시간이 필요한 것으로 나타났으며, 2.0MPa를 만족하는 초기강도 양생시간은 24시간 이상이 필요한 것으로 확인되었다. 따라서 순환자원 활용 주입재는 동일 배합비의 시멘트에 비해 긴 초기경화 시간이 필요한 것으로 나타났다.

• Asia pacific journal of information systems
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• 제30권2호
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• pp.397-419
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• 2020

Business analytics is a management tool for achieving significant business performance improvements. Many organizations fail to or only partially achieve their business objectives and goals from business analytics. Business analytics adoption is a multi-stage complex activity consisting of evaluation, adoption, and assimilation stages. Several research papers have been published in the field of business analytics, but the research on multi-stage BA adoption is fewer in number. This study contributes to the scant literature on the multi-stage adoption model by identifying the critical themes for evaluation, adoption, and assimilation stages of business analytics. This study uses the thematic content analysis of peer-reviewed published academic papers as a research technique to explore the key themes of business analytics adoption. This study links the critical themes with the popular theoretical foundations: Resource-Based View (RBV), Dynamic Capabilities, Diffusion of Innovations, and Technology-Organizational-Environmental (TOE) framework. The study identifies twelve major factors categorized into three key themes: organizational characteristics, innovation characteristics, and environmental characteristics. The main organizational factors are top management support, organization data environment, centralized analytics structure, perceived cost, employee skills, and data-based decision making culture. The major innovation characteristics are perceived benefits, complexity, and compatibility, and information technology assets. The environmental factors influencing BA adoption stages are competition and industry pressure. A conceptual framework for the multi-stage BA adoption model is proposed in this study. The findings of this study can assist the practicing managers in developing a stage-wise operational strategy for business analytics adoption. Future research can also attempt to validate the conceptual model proposed in this study.

• 한국자동차공학회논문집
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• 제11권6호
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• pp.108-117
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• 2003

Development of advanced restraint system challenges both restraint and automobile manufacturers to come up with proper airbag design to reduce occupant out-of-position related injury. The important component of the advanced restraint system is the multi stage inflator. The multi stage inflator can independently control two or more airbag inflation stages to maximize occupant protection. The objective of this research is to develop relationship between airbag inflation characteristics, the occupant positions and the airbag design variables. The tests are conducted using five kinds of inflators, two kinds of airbag cushion folding methods and two kinds of tear lines. In the case of inflator, the out-of-position tests are performed with a traditional inflator, a depowered inflator and a dual stage inflator. And the efficiency and injury mechanism are evaluated by analyzing the injury pulses and values. Using this relationship, airbag design guideline is established for airbag aggressivity thresholds and the risk of injury is identified according to occupant positions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.525-528
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• 2008

The dynamic range of MR damper is the most important characteristics for the usage of semi-active control system. The damping force can be increased by simply decresing the orifice gap in the traditional oil damper, but it deteriorate the dynamic range in MR damper. In this paper, the multi-stage electro-magnetic core is suggested to maintain the performance of MR damper with a large damping force. The MR damper with 3 stage core is designed and manufactured for testing and analysis.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.111-118
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• 1995

A method of determining an optimum blank shape for the non circular deep drawing process is more investigated and applied to the balnk design for multi-stage deep drawn product. The forming procedure of two-stage deep drawing process is looked over and the method of determining a blank shape is proposed. In experimental research, a optimum blank and a optional rectangular blank were considered and we measured thickness strain distributions. We could predict a strain distribution and compare with a experimental strain distribution. Also, the strain distributions for the blank shapes, optimum and rectangular, were compared.

• 소성∙가공
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• 제5권4호
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• pp.288-296
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• 1996

A method of determining an optimum blank shape for non-circular deep drawing process is extended to the multi-stage deep drawing process. As an example concentric two-stage square deep drawing process is considered and the ideal blank shape with uniform cup height and without flange part after the process is constructed by the backward tracing of rigid plastic FEM. The conventional square blank shapes are also adopted for the comparison of two cases. As a result it is confirmed that the drawn products with better thickness strain distribution and deeper cup depth could be obtained by the suggested ideal blank shapes.