• 정보교육학회논문지
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• 제26권4호
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• pp.285-293
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• 2022

예상보다 길어진 코로나19 사태는 학생들의 수학 교과 기초학력에 적지 않은 손상을 끼쳤다. 본 논문에서는 학생들의 기초 곱셈 연산 능력 개선에 도움을 줄 수 있는 곱셈구구 연습 애플리케이션을 클라우드에 기반하여 개발하였으며, 학생 개별 맞춤형 지도를 위해 데이터 시각화 기술을 접목시켜 교사의 피드백을 돕고자 하였다. 구글에서 개발한 Flutter framework, Google Cloud, Google Sheets를 통합적으로 활용하여 애플리케이션의 성능을 높였다. K광역시 소재 초등학교 6학년 72명의 학생들이 본 애플리케이션을 일주일간 곱셈구구 활동에 활용한 결과, 학생들의 곱셈구구 소요 시간이 초기에 비해 28%이상 감소한 가운데, 학생들의 학습 데이터가 오류없이 정교하게 수집된 것을 확인할 수 있었다. 본 연구에서 Flutter framework를 통해 진행한 개발 사례가 다른 교육용 학습 애플리케이션 개발로 이어질 수 있기를 희망한다.

• Wind and Structures
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• 제17권3호
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• pp.275-298
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• 2013

This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg's empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of ($H_1^*$, $A_2^*$) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

• International Journal of Aeronautical and Space Sciences
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• 제13권2호
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• pp.199-209
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• 2012

An advanced aeroelastic formulation for flutter analyses is presented in this paper. Refined 1D structural models were coupled with the doublet lattice method, and the g-method was used for flutter analyses. Structural models were developed in the framework of the Carrera Unified Formulation (CUF). Higher-order 1D structural models were obtained by using Taylor-like expansions of the cross-section displacement field of the structure. The order (N) of the expansion was considered as a free parameter since it can be arbitrarily chosen as an input of the analysis. Convergence studies on the order of the structural model can be straightforwardly conducted in order to establish the proper 1D structural model for a given problem. Flutter analyses were conducted on several wing configurations and the results were compared to those from literature. Results show the enhanced capabilities of CUF 1D in dealing with the flutter analysis of typical wing structures with high accuracy and low computational costs.

• Wind and Structures
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• 제14권4호
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• pp.359-381
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• 2011

This paper deals with the flutter instability problem of flexible bridge decks in the framework of bimodal-coupled aeroelastic bridge system analysis. Based on the analysis of coefficients of the polynomials deduced from the singularity conditions of an integral wind-structure impedance matrix, a set of simplified formulations for calculating the critical wind velocity and coupled frequency are presented. Several case studies are discussed and comparisons with available approximated approaches are made and presented, along with a conventional complex eigenvalue analysis and numerical results. From the results, it is found that the formulas that are presented in this study are applicable to a variety of bridge cross sections that are not only prone to coupled-mode but also to single-mode-dominated flutter.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.446-451
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• 2003

This paper presents some examples of active control of flow-induced vibration using piezoelectric actuators. The flutter phenomenon, which is the dynamic instability of structure due to mutual interaction among inertia, stiffness, and aerodynamic forces, may cause catastrophic structural failure, and therefore the active flutter suppression is one of the main objectives of the aeroelastic control. Active flutter control has been numerically and experimentally studied for swept-back lifting surfaces using piezoelectric actuation. A finite element method, a panel aerodynamic method, and the minimum state space realization are involved in the development of the governing equation, which is efficiently used for the analysis of the system and design of control laws with modern control framework. The active control suppressed flow-induced vibrations and extended the flutter speed around by 10%. Another representative flow-induced vibration phenomenon is the oscillation of blunt bodies due to the vortex shedding. In general, it is quite difficult to set up the numerical model because of the strong non-linearity of the vortex shedding structure. Therefore, we applied adaptive positive position feedback controller, which requires no pre-determined model of the plant, and successfully suppressed the flow-induced vibration.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2024년도 춘계학술발표대회
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• pp.53-56
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• 2024

Though lots of approaches to develop mobile apps are suggested up to now, developers have difficulties selecting a right one. This study compares native and cross-platform application development approaches, particularly focusing on the shift in preference from Java to Kotlin and the increasing use of Flutter. This research offers practical insights into factors influencing developers' choice of programming languages and frameworks in mobile application development by creating identical applications using Java, Kotlin, and Dart (Flutter). Furthermore, this study explores the best practices for development by examining the quality of code in 45 open-source GitHub repositories. The study evaluates LOC and code smells using semi-automated SonarQube assessments to determine the effects of selecting a specific language or framework on code maintainability and development efficiency. Preliminary findings show differences in the quality of the code produced by the two approaches, offering developers useful information on how to best optimize language and framework selection to reduce code smells and improve project maintainability.

• Wind and Structures
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• 제13권3호
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• pp.235-256
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• 2010

The aeroelastic stability of bridge decks equipped with multiple tuned mass dampers is studied. The problem is attacked in the time domain, by representing self-excited loads with the aid of aerodynamic indicial functions approximated by truncated series of exponential filters. This approach allows to reduce the aeroelastic stability analysis in the form of a direct eigenvalue problem, by introducing an additional state variable for each exponential term adopted in the approximation of indicial functions. A general probabilistic framework for the optimal robust design of multiple tuned mass dampers is proposed, in which all possible sources of uncertainties can be accounted for. For the purposes of this study, the method is also simplified in a form which requires a lower computational effort and it is then applied to a general case study in order to analyze the control effectiveness of regular and irregular multiple tuned mass dampers. A special care is devoted to mistuning effects caused by random variations of the target frequency. Regular multiple tuned mass dampers are seen to improve both control effectiveness and robustness with respect to single tuned mass dampers. However, those devices exhibit an asymmetric behavior with respect to frequency mistuning, which may weaken their feasibility for technical applications. In order to overcome this drawback, an irregular multiple tuned mass damper is conceived which is based on unequal mass distribution. The optimal design of this device is finally pursued via a full domain search, which evidences a remarkable robustness against frequency mistuning, in the sense of the simplified design approach.