• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.329-334
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• 2017

The structures, which are made up with the huge number of degrees-of-freedom and the assembly of substructures, have a great complexity. In order to increase the computational efficiency, the analysis models have to be simplified. Many substructuring techniques have been developed to simplify large-scale engineering problems. The techniques are very powerful for solving nonlinear problems which require many iterative calculations. In this paper, a modal derivatives-based model order reduction method, which is able to capture the stretching-bending coupling behavior in geometrically nonlinear systems, is adopted and investigated for its performance evaluation. The quadratic terms in nonlinear beam theory, such as Green-Lagrange strains, can be explained by the modal derivatives. They can be obtained by taking the modal directional derivatives of eigenmodes and form the second order terms of modal reduction basis. The method proposed is then applied to a co-rotational finite element formulation that is well-suited for geometrically nonlinear problems. Numerical results reveal that the end-shortening effect is very important, in which a conventional modal reduction method does not work unless the full model is used. It is demonstrated that the modal derivative approach yields the best compromised result and is very promising for substructuring large-scale geometrically nonlinear problems.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.163-171
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• 2024

Structural health monitoring for ships and offshore structures is important in various aspects. Ships and offshore structures are continuously exposed to various environmental conditions, such as waves, wind, and currents. In the event of an accident, immense economic losses, environmental pollution, and safety problems can occur, so it is necessary to detect structural damage or defects early. In this study, structural response data of multi-linked floating offshore structures under various wave load conditions was calculated by performing fluid-structure coupled analysis. Furthermore, the order reduction method with distortion base mode was applied to the structures for predicting the structural response by using the results of numerical analysis. The distortion base mode order reduction method can predict the structural response of a desired area with high accuracy, but prediction performance is affected by sensor arrangement. Optimization based on a genetic algorithm was performed to search for optimal sensor arrangement and improve the prediction performance of the distortion base mode-based reduced-order model. Consequently, a sensor arrangement that predicted the structural response with an error of about 84.0% less than the initial sensor arrangement was derived based on the root mean squared error, which is a prediction performance evaluation index. The computational cost was reduced by about 8 times compared to evaluating the prediction performance of reduced-order models for a total of 43,758 sensor arrangement combinations. and the expected performance was overturned to approximately 84.0% based on sensor placement, including the largest square root error.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1757_1758
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• 2009

본 논문에서는 철도차량의 능동조향시스템 연구를 위한 축소 조향대차의 장애물 검지시스템 구축에 대여 연구하였다. 철도차량에서 능동조향이란 곡선부 주행 시 차륜/레일 접촉에 의한 승차감 저하 및 차륜/레일의 마모와 소음을 줄이고, 고속주행을 위한 조향성능 및 주행안정성을 확보하기 위한 휠셋의 제어기술이다. 따라서 논문에서는 조향제어전략 및 제어기법을 연구하기 위한 축소 차량모델(견인대차와 조향대차로 구성)의 개발과정으로서 자동운전을 위한 장애물 검지시스템에 대한 연구를 수행하였으며 주행실험을 통해 그 성능을 검증하였다.

• Journal of KIISE:Software and Applications
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• v.35 no.5
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• pp.313-324
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• 2008

A sentence reduction is the information compression process which removes extraneous words and phrases and retains basic meaning of the original sentence. Most researches in the sentence reduction have required a large number of lexical and syntactic resources and focused on extracting or removing extraneous constituents such as words, phrases and clauses of the sentence via the complicated parsing process. However, these researches have some problems. First, the lexical resource which can be obtained in loaming data is very limited. Second, it is difficult to reduce the sentence to languages that have no method for reliable syntactic parsing because of an ambiguity and exceptional expression of the sentence. In order to solve these problems, we propose the sentence reduction method which uses templates and POS(part of speech) information without a parsing process. In our proposed method, we create a new sentence using both Sentence Reduction Templates that decide the reduction sentence form and Grammatical POS-based Reduction Rules that compose the grammatical sentence structure. In addition, We use Viterbi algorithms at HMM(Hidden Markov Models) to avoid the exponential calculation problem which occurs under applying to Sentence Reduction Templates. Finally, our experiments show that the proposed method achieves acceptable results in comparison to the previous sentence reduction methods.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.2
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• pp.39-48
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• 1997

New form of base isolators made of steel spring coated with both natural and artficial rubber were manufactured and tested for material properties. Shaking table experiments were performed using a model structure attached with the bearings. The model structure used in the test is a 1/4 scaled steel structure, and earthquake records were used to check the lateral and vertical stability and effectiveness of the isolators. According to the results all three types of isolators turned out to be effective in reducing the acceleration induced by the earthquake vibration.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.4
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• pp.11-18
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• 2006

Compound flow by confluence of two parallel flows through a convergent channel and its choking phenomenon are calculated by one-dimensional isentropic model and completely mixing model. Optical observations and pressure measurements for subsonic/subsonic compound flows are carried out and compared with the results of one-dimensional calculations. As a result, it is found that inlet conditions of one flow influence the behavior of the other flow as well as the choking condition and present experimental data agree well with the results of one-dimensional calculations.

• New & Renewable Energy
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• v.3 no.2 s.10
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• pp.53-59
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• 2007

NREL Phase VI 12% 축소모델을 사용한 표준풍력터빈 풍동시험은 2006년에 1차 시험이 수행되었다. 1차 풍동시험은 복합재블레이드를 사용하여 표준조건(설치각 3도)에 대해 수행되었으며 블레이드 표면상태에 따라 측정값이 영향을 받는 것을 파악하였다. 2007년 4월에 수행된 2차 풍동시험은 표면상태의 영향을 보다 정확히 파악하기 위해 알루미늄 블레이드를 사용하여 시험을 수행하였으며, 블레이드 제작 정밀도에 따른 영향을 파악하였다. 낮은 레이놀즈 수 영역(저속영역)에서는 블레이드 표면상태 따라 토크 값 다르게 나타나며, 블레이드 끝단 부근의 제작 정밀도는 최대 토크 이후의 영역에 영향을 미치는 것으로 나타났다. 0.1mm 이내의 정밀도로 제작된 모델의 경우 NREL 시험결과와 전체적인 형상이 유사하게 나타나며, 축소효과에 의한 영향으로 최대토크는 약 25% 정도 감소현상을 보이고 있다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.69-72
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• 2011

Hot-firing tests were performed on the third sub-scale gas generator for development of a 75 ton-class liquid rocket engine. This paper deals with the analysis results of low-frequency combustion instabilities that were encountered during combustion tests of the gas generator. The low-frequency pressure fluctuations seem to be related to chamber pressure and pressure drops through oxidizer/fuel injectors.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.591-597
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• 2013

Because most existing non-Newtonian models are not suitable for application to the lattice Boltzmann method, theoretical and numerical studies in this regard remain challenging. In this study, the hydrokinetic (HK) model was modified and applied to a 3D sudden contraction-expansion channel flow, and the characteristics of the HK model flow were evaluated to generate non-trivial predictions in three-dimensional strong shear flows. The HK model is very efficient for application to the lattice Boltzmann method because it utilizes the shear rate and relaxation time. However, the simulation would be unstable in a high shear flow field because the local relaxation time sharply decreases with an increase in the shear rate in a strong shear flow field. In the HK model, it may become necessary to truncate the relaxation time and non-dimensional parameter to obtain stable numerical results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.6
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• pp.83-88
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• 2010

In this paper, to propose a valid method solving a problem relevant to grounding from actual field data, the experimental results relevant to touch and step voltages and surface potential profiles measured around the real-sized and small-sized grounding electrode models were described. The ground surface potential profiles and dangerous voltages around the concrete pedestals employed in street facilities such as street lamps, traffic signal lamp and controllers as a case study were measured and discussed. The hemispherical cell with a diameter of 1,160[mm] was employed to simulate uniform soil. As a result, the results measured with the small-sized model were in reasonably agreement with the data obtained from the real-sized installation. It was found that the small-sized model test could be employed as a useful means evaluating the dangerous voltages around grounding electrodes installed at the inaccessible areas such as mountains, underground, underwater, and so on.