• 한국염색가공학회지
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• 제33권4호
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• pp.202-209
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• 2021

Natural dyes are more expensive than synthetic dyes and the dyeing process, which is mainly immersion of dye, is complicated. For this reason, relatively small-scale production methods were predominant. However, awareness and interest in environmental sustainability is rising globally, and the use of synthetic dyes causes various environmental problems such as wastewater and CO₂ emission, so the consumption of natural dyes is increasing. In addition, interest in digital textile printing, an eco-friendly dyeing method that can produce products of various designs and uses less water, is growing. In this study, natural indigo dye (Indigofera tinctoria) was used as a raw material for Digital Textile Printing ink, and ¹⁴C (Biocarbon) present in it was measured to confirm whether it was derived from natural ingredients. The performance was confirmed by testing the pH, viscosity, electrical conductivity, surface tension, and particle size analysis of natural indigo ink. In addition, the performance of natural indigo DTP ink and printing fabric was evaluated by inspecting the change in color fastness and corresponding index substances before and after digital printing with natural indigo DTP ink on textiles. Through this, the possibility of commercialization of DTP ink and printing fabric using natural indigo was confirmed.

• 지질공학
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• 제20권2호
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• pp.213-220
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• 2010

현재 국내의 수리시험 장비는 적절한 장비가 갖추어지지 않은 상태로 시행되고 있기 때문에 투수성 해석 자료의 신뢰성은 그리 높다고 볼 수 없다. 본 연구는 고도의 정밀성을 요구하는 고준위폐기물의 처분기술 개발을 위해서는 무엇보다도 자연방벽에 대한 특성 평가가 중요하므로 현행 시험 장비의 기술적 문제들을 해결하기 위한 목적으로 장심도 (1,000 m) 시추공에서 정밀한 수리시험이 가능한 장비를 성공적으로 구축하였다. 본 장비에서 가장 중요하게 반영된 기술사항은 공내 저류효과를 최소화시키기 위하여 H-DHSIV를 장착하고, 시험 자료의 품질을 향상시키기 위하여 실시간으로 시험 구간을 포함한 3개 구간의 압력 변화자료를 취득할 수 있는 DAS를 구축한 것이다. 본 연구의 결과로 구축된 심부 시추공에서의 정밀 수리 시험 장비는 국내 현장조사 기술력의 획기적인 향상을 선도할 것이며, 방사성폐기물 처분기술 개발을 위한 연구와 부지 특성평가에 직접 적용될 것이다.

• Advances in aircraft and spacecraft science
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• 제2권2호
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• pp.217-232
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• 2015

To prevent over-testing of the test-item during random vibration testing Scharton proposed and discussed the force limited random vibration testing (FLVT) in a number of publications. Besides the random vibration specification, the total mass and the turn-over frequency of the load (test item), $C^2$ is a very important parameter for FLVT. A number of computational methods to estimate $C^2$ are described in the literature, i.e., the simple and the complex two degrees of freedom system, STDFS and CTDFS, respectively. The motivation of this work is to evaluate the method for the computation of a realistic value of $C^2$ to perform a representative random vibration test based on force limitation, when the adjacent structure (source) description is more or less unknown. Marchand discussed the formal description of getting $C^2$, using the maximum PSD of the acceleration and maximum PSD of the force, both at the interface between load and source. Stevens presented the coupled systems modal approach (CSMA), where simplified asparagus patch models (parallel-oscillator representation) of load and source are connected, consisting of modal effective masses and the spring stiffness's associated with the natural frequencies. When the random acceleration vibration specification is given the CSMA method is suitable to compute the value of the parameter $C^2$. When no mathematical model of the source can be made available, estimations of the value $C^2$ can be find in literature. In this paper a probabilistic mathematical representation of the unknown source is proposed, such that the asparagus patch model of the source can be approximated. The chosen probabilistic design parameters have a uniform distribution. The computation of the value $C^2$ can be done in conjunction with the CSMA method, knowing the apparent mass of the load and the random acceleration specification at the interface between load and source, respectively. Data of two cases available from literature have been analyzed and discussed to get more knowledge about the applicability of the probabilistic method.

• 한국산학기술학회논문지
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• 제12권1호
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• pp.1-6
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• 2011

유한요소해석을 통한 대상 구조물의 동특성 해석에 있어서 신뢰성 높은 실제 구조물의 동특성을 정확히 예측하는 해석결과는 얼마나 신뢰성이 높은 유한요소모델을 수립하는가하는 문제와 직결된다고 할 수 있다. 따라서 많은 경험과 노력을 통해 만들어진 모델을 대상으로 모달 테스팅을 통해 관심주파수대역에 걸쳐 모델을 검증하고, 이때 얻어진 데이터를 이용, 모델을 개선하는(Model updating) 작업을 거치게 된다. 본 연구에서는 이와 같이 중량과 크기의 제한으로 인하여 충격망치나 가진기로 가진하기 어려운 함정의 고유진동수 등을 얻기 위한 모달 테스팅 방법으로써 함정의 시운전 항목 중 하나인 주포 사격시험을 이용하여 그 결과와 가능성, 향후 진행방향에 대하여 고찰해 보았다.

• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.429-444
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• 2004

The ambient vibration measurement is a kind of output data-only dynamic testing where the traffics and winds are used as agents responsible for natural or environmental excitation. Therefore an experimental modal analysis procedure for ambient vibration testing will need to base itself on output-only data. The modal analysis involving output-only measurements presents a challenge that requires the use of special modal identification technique, which can deal with very small magnitude of ambient vibration contaminated by noise. Two complementary modal analysis methods are implemented. They are rather simple peak picking (PP) method in frequency domain and more advanced stochastic subspace identification (SSI) method in time domain. This paper presents the application of ambient vibration testing and experimental modal analysis on large civil engineering structures. A 15 storey reinforced concrete shear core building and a concrete filled steel tubular arch bridge have been chosen as two case studies. The results have shown that both techniques can identify the frequencies effectively. The stochastic subspace identification technique can detect frequencies that may possibly be missed by the peak picking method and gives a more reasonable mode shapes in most cases.

• 한국생산제조학회지
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• 제9권3호
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• pp.130-135
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• 2000

In this study the vibration behavior of the stiffened double cylinder was experimently analyzed. Due to the complex structure of the double cylinder the outside cylinder frequency responses to the exciting forces applied on various posi-tions were analyzed by using spectrum analyzer in conjunction with an accelerometer and the natural frequencies were obtained. The technique of time-averaged holographic interferometry is applied to study the vibration characteristics of outside cylinder with stiffening T frame. The experimental data showed that the T frame had salient effect of damping on the testing structure at most of resonances. however the experimental results also revealed interesting phenomenon. At some particular frequencies the T frame. The experimental data showed that the T frame had salient effect of damping on the testing structure at most of resonances. However the experimental results also revealed interesting phenomenon. At some particular frequencies the T frame seemed to behave as a transmitter. In addition it has been successfully demon-started that optical method such as holographic interferometry is well suited for the identification of mode shapes. They can give us a whole-field non-contact measurement instead of the point-wise measurement by accelerometer in classical modal testing.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.17-23
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• 2001

Measurements of the initial values lead to an inverse and mathematically unprecisely formulated problem. A precise definition of an inverse problem is possible. It is to state a mathematical model of a physical process with clearly defined initial and exit values for the system behind the process. One can grasp the idea of an inverse problem by considering the tire as a copy of the objects of nature in a room with observations. Interpretation of nature is generally a result of an inverse problem. On one hand, the tire may be represented through the sensory organs and the nervous system as well as the experiences of the developer's existing apparatus of the projection of reality. On the other hand, it may be represented by a physical law or a model that can be confirmed or is to be refuted with the help of suitable measurements. During reconstruction of a measuring signal and the identification of a black box that can be assumed to be linear and causal, the tire becomes a first type Volterra integral equation of the convolution type. But measurements of the initial values are always fuzzy, the errors grow and the system behavior can no longer be forecasted. Thus, we have to deal with a chaotic system. This chaos produces fractals in a natural way. These are self-similar geometric structures. This self-similarity is clearly visible in the design.

• 비파괴검사학회지
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• 제25권4호
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• pp.239-246
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• 2005

골다공증에 따른 쥐 대퇴골의 고유진동수의 변화를 예측하기 위하여 유한요소해석과 진동 시험을 수행하였다. 연구 대상으로 골다공증에 걸린 쥐 그룹, 골다공증을 치료한 쥐 그룹, 그리고 골다공증이 없는 정상 쥐 그룹을 구성하였다. 유한요소해석에서는 미세단층촬영(Micro-CT)에서 얻은 해면골 영상 데이터와 Voxel 요소 생성 알고리즘을 이용하여 3차원 미세 유한요소 모델을 생성한 다음 고유진동수 해석을 수행하였다. 진동 시험에서는 모빌리티 실험에 의한 주파수 응답함수로부터 고유진동수를 측정하였다 연구 결과로부터 골다공증에 걸린 쥐 그룹의 고유진동수가 가장 높고, 골다공증을 치료한 쥐의 그룹, 골다공증이 없는 정상 쥐의 그룹 순서로 낮아지는 경향을 볼 수 있었다. 모든 그룹에서 유한요소해석에 의한 고유진동수는 시험에서 측정한 결과보다 10-15% 오차 범위 내로 높은 값을 보였다. 본 연구로부터 개발된 미세단층촬영기 장치, Voxel 요소 생성 알고리즘, 진동시험 및 유한요소해석 방법을 이용하여 골다공증에 의한 생체 골조직의 구조적 변화 진단 및 치료 평가 등에 대한 응용가능성을 확인할 수 있었다.

• 항공우주시스템공학회지
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• 제4권2호
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• pp.21-25
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• 2010

Fatigue properties of composite materials are extremely important to design durable and reliable helicopter rotor blades. However, it is very difficult to apply conventional fatigue test loads in short period. Therefore, accelerating test speed and facilitating spectrum load realization are required. In this study, we have developed a fatigue testing method that uses a resonance of simply supported beam type blade specimen. This test consists in exciting the blade specimen with a frequency that corresponds to its natural frequency. In that case, the test specimen similar to a beam fixed between two pivot points starts vibrating and is significantly deformed. Resonant fatigue tests were performed by changing exciting vertical amplitude and frequency, and S-N curves of each composite materials were successfully obtained.

• 항공우주기술
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• 제9권2호
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• pp.1-7
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• 2010

Fatigue properties of composite materials are extremely important to design durable and reliable helicopter rotor blades. However, it is very difficult to apply conventional fatigue test loads in short period. Therefore, accelerating test speed and facilitating spectrum load realization are required. In this study, we have developed a fatigue testing method that uses a resonance of simply supported beam type blade specimen. This test consists in exciting the blade specimen with a frequency that corresponds to its natural frequency. In that case, the test specimen similar to a beam fixed between two pivot points starts vibrating and is significantly deformed. Resonant fatigue tests were performed by changing exciting vertical amplitude and frequency, and S-N curves of each composite materials were successfully obtained.