• 품질경영학회지
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• 제47권4호
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• pp.895-910
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• 2019

Purpose: The purpose of this study is to lighten the APU (Auxiliary Power Unit) structure of the KAAV (Korea Assault Amphibious Vehicle) through structural analysis. Methods: Commercially-available program (MIDAS.NFX) was used for finite element analysis. Frequency response analysis was performed through linear static and mode analyses to verify the structural stability according to the change of the structural materials. Results: Numerical simulation (linear static, mode and frequency response analyses) results showed that the safety factor of the APU was over 1.5 even under the worst case conditions. The APU made by aluminum structures was expected to be available in the military field, since every requirements in the KDS (Korean Defense Specifications) was fulfilled during the various tests and evaluations. Conclusion: The structural analysis was verified that the structural stability of the APU structure of the KAAV after change of the structural material.

• Structural Engineering and Mechanics
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• 제54권6호
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• pp.1045-1059
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• 2015

Form-finding for cable-membrane structures is a delicate operation. During the last decades, the force density method (FDM) was considered to be an efficient method to address the problem. Many researchers were devoted to improving this method and proposed many methods such as natural force density method (NFDM), improved nonlinear force density method (INFDM), et al. In this paper, a modified nonlinear force density method (MNFDM) is proposed. In this method, the stresses of membrane elements were transformed to the force-densities of cable nets by an equivalent relationship, and then they can be used as initial conditions. By comparing with the forming finding results by using the FDM, NFDM, INFDM and MNFDM, it had demonstrated that the MNFDM presented in this paper is the most efficient and precise.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.292-295
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• 2006

The terrorist attack of September $11^{th}$ 2001 has enforced a new examination of the response of modern steel structures, such as those found in large warehouses, auditoriums and airport terminals, to terrorist bomb attack. The effort described in this paper assesses the potential damage to such a newly designed structure form a medium-size car bomb. The structure is mostly composed of a lightweight complex beam structure with large windows and skylights piercing through a corrugated roof. The structural response to the terrorist attack requires the modelling of various physics phenomena including bomb detonation, blast wave propagation, reflections, and refractions and resulting blast impact on the structure. Hence, a fluid/structure coupled methodology is used to perform the assessment.

• The Plant Pathology Journal
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• 제23권3호
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• pp.203-209
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• 2007

Infection structures were observed using a fluorescence microscope at the penetration sites on the leaves of potato plants pre-inoculated with the bacterial strains Pseudomonas putida TRL2-3, Micrococcus luteus TRK2-2, and Flexibacteraceae bacterium MRL412, which mediated an induced systemic resistance on potato plants against late blight disease caused by Phytophthora infestans. In order to compare the infection structures on the leaves expressing systemic acquired resistance, the leaves of potato plants pre-treated with DL-3-amino butyric acid (BABA) were also observed after challenge inoculation with the same pathogen. The infection structures were investigated. The total number of germination and appressorium formation of P. infestans were counted. Furthermore, the frequencies of fluorescent epidermal cells at the penetration sites, which indicate a defense response of plant cell, were estimated. There were no differences on the germination rates of the fungal cysts among the untreated control, BABA pre-treated, and bacterial strains pre-inoculated plants. However, appressorium formation was slightly decreased on the leaves of BABA pre-treated plants compared to those of untreated as well as bacterial strains pre-inoculated plants. Furthermore, the frequencies of fluorescent cells of BABA pre-treated and bacterial strains pre-inoculated were higher than that of untreated plants, indicating an active defense reaction of the host cells against the fungal attack. On the other hand, the pre-treatment with BABA caused a stronger fluorescent of epidermal cells at the penetration sites compared to the pre-inoculation with the bacterial strains. Interestingly, the frequency of fluorescent cells by BABA, however, was lower than that by the bacterial strains. Based on the results it is suggested that the infection structures showing resistance reaction on the leaves of potato plants were different between by pre-inoculation with bacterial strains and by pre-treatment with BABA against the late blight pathogen.

• 대한조선학회논문집
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• 제49권6호
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• pp.498-503
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• 2012

Independent component analysis (ICA) technique based on statistical independency of the signals is known as suitable to identify the source signals by measuring and separating mixed signals through transfer paths and has successfully applied in the field of medical care, communications and so forth. In this study, the ICA technique is introduced for the identification of excitation sources from measured vibration signals of structures, which can be done by evaluating negentropy of centered and whitened vibration signals and correlation of separated signals. To validate the method, numerical analyses are carried out for a plate and a cylinder structure. The results show that the method can be applied efficiently to source identification of complex structures. Nevertheless, additional studies would be required to complement problems of occasional inaccuracy.

• 한국시뮬레이션학회논문지
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• 제30권3호
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• pp.31-39
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• 2021

포 사격 시에는 폭풍파 형태로 전파되는 과도한 수준의 충격소음이 발생한다. 포 사격 충격음은 주위 구조물의 안정성에도 영향을 미치게 되므로 아군의 포 사격으로 피해를 받지 않으려면 포와 구조물은 적정거리를 이격시켜야 한다. 그러나 이미 적정거리 이하로 건축되어 있는 경우에는 포와 구조물 사이에 방음벽을 세워 피해를 방지할 수 있다. 본 연구에서는 포와 구조물의 적정 이격거리를 산출하였으며, 경계요소법(Boundary Element Method)을 활용하여 방음벽의 다양한 높이와 형태에 의한 삽입손실을 시뮬레이션하였고 최적의 방음벽을 선정하였다.

• 한국정밀공학회지
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• 제33권10호
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• pp.821-828
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• 2016

Recently, the use of composite materials in the defense system has grown dramatically. The strength/weight and stiffness/weight ratios of composite structures are normally higher than of metals. Woven composites, especially, are increasingly considered for a variety of applications, because they offer good workability for complicated structures. HPW193/RS1222 is one of the most famous woven composites and has been used in many types of Korean military equipment, such as antenna pedestals and radar systems. In this study, we predicted the elastic modulus of HPW193/RS1222 using the principles of unidirectional composite stiffness predictions, such as ROM (Rule of Mixture), HSR (Hart Smith 10% Rule), CLA (Classical Laminate Analysis) and LAP (Laminate Analysis Program). We compared the dynamic characteristics with the experimental predictions and finite-element analysis (FEA). From our results we concluded that transversely isotropic materials are similar to isotropic materials when the shape of the composite structure is complicated.

• 한국항공우주학회지
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• 제41권8호
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• pp.619-624
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• 2013

확률론적 수명예측은 파라미터들의 불확실성에 대하여 확률론적인 요소를 적용한다. 따라서 기존의 결정론적 수명해석 기법에 확률론적 기법을 적용하기 위해서는 파손확률을 이용한 위험도 평가가 필요하다. 본 연구에서는 항공기 구조물의 확률론적 위험도평가를 수행하기 위하여 파손확률 추정 모델링 기법을 연구하였다. 이를 위해 파라미터들의 확률론적 불확실성을 효과적으로 반영할 수 있는 베이지안 기법을 이용하여 파손확률을 모델링하고 실험 데이터를 이용하여 검증하였다. 연구결과 베이지안 기반의 파손확률 추정 모델링은 정량적인 파손확률을 계산하고 확률론적 위험도평가를 효과적으로 수행할 수 있음을 입증하였다.

• 한국전자파학회논문지
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• 제25권7호
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• pp.709-720
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• 2014

본 논문에서는 VHF 및 UHF 대역에서 사용되는 LPDA(Log-Periodic Dipole Array) 안테나를 소형화 하는 연구를 하였다. LPDA 안테나를 소형화하기 위해, 본 연구에서는 LPDA 안테나의 저주파 대역 방사 소자를 급전 부분의 전류 상쇄 효과가 적은 삼각형 미앤더 구조로 변형시켰다. 삼각형 미앤더 구조는 이등변 삼각형 미앤더 구조와 직각 삼각형 미앤더 구조를 제안하였으며, 두 가지 미앤더 구조를 적용하여 LPDA 안테나를 소형화 하였다. 또한, 소형화된 LPDA 안테나에 대해서 시뮬레이션과 측정 결과를 비교하였다. 그 결과, 이등변 삼각형 미앤더 구조 적용 LPDA 안테나와 직각삼각형 미앤더 구조 적용 LPDA 안테나는 기본형 LPDA 안테나에 비해서 각각 60.5 %, 72.4 %로 소형화되었다. 따라서 제안된 삼각형 미앤더 구조가 LPDA 안테나의 소형화에 적합함을 확인할 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권1호
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• pp.128-141
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• 2015

Independent Component Analysis (ICA), one of the blind source separation methods, can be applied for extracting unknown source signals only from received signals. This is accomplished by finding statistical independence of signal mixtures and has been successfully applied to myriad fields such as medical science, image processing, and numerous others. Nevertheless, there are inherent problems that have been reported when using this technique: instability and invalid ordering of separated signals, particularly when using a conventional ICA technique in vibratory source signal identification of complex structures. In this study, a simple iterative algorithm of the conventional ICA has been proposed to mitigate these problems. The proposed method to extract more stable source signals having valid order includes an iterative and reordering process of extracted mixing matrix to reconstruct finally converged source signals, referring to the magnitudes of correlation coefficients between the intermediately separated signals and the signals measured on or nearby sources. In order to review the problems of the conventional ICA technique and to validate the proposed method, numerical analyses have been carried out for a virtual response model and a 30 m class submarine model. Moreover, in order to investigate applicability of the proposed method to real problem of complex structure, an experiment has been carried out for a scaled submarine mockup. The results show that the proposed method could resolve the inherent problems of a conventional ICA technique.