• Journal of the Korean Society of Safety
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• v.18 no.4
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• pp.169-175
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• 2003

In this paper, and estimation method for estimating the states of underwater vehicle systems with external unknown disturbance is proposed. First, the dynamics of underwater vehicle are induced by Taylor series expansion in the vertical plane and horizontal plane, respectively. For constructing the system model, the external efforts, i.e., the sea surface disturbances, the current, wave and etc., are regarded as external unknown disturbances. Thus the disturbance is added as external input into state-space form of underwater vehicle system. To estimate the state of systems with unknown disturbance, a disturbance observer which does not effected the external unknown input is proposed, and the existence condition for the observer is given. Finally, the effectiveness of the proposed disturbance observer for robust control of underwater vehicle systems is verified by using numerical simulation.

• Tunnel and Underground Space
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• v.22 no.1
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• pp.69-76
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• 2012

Theoretical backgrounds on the experimental methods of explosive welding, explosive forming and shock consolidation of powders are introduced. Explosive welding experiments of titanium (Ti) and stainless steel (SUS 304) plate were carried out. It was revealed that a series of waves of metal jet are generated in the contact surface between both materials; and that the optimal collision velocity and collision angle is about 2,100~2,800 m/s and $15{\sim}20^{\circ}$, respectively. Also, explosive forming experiments of Al plate were performed and compared to a conventional press forming method. The results confirmed that the shock-loaded Al plate has a larger curvature deformation than those made using conventional press forming. For shock consolidation of powders, the propagation behaviors of a detonation wave and underwater shock wave generated by explosion of an explosive are investigated by means of numerical calculation. The results revealed that the generation and convergence of reflected waves occur at the wall and center position of water column, and also the peak pressure of the converged reflected waves was 20 GPa which exceeds the detonation pressure. As results from the consolidation experiments of metal/ceramic powders ($Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$), shock-consolidated $Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$ bulk without cracks was successfully obtained by adapting the suggested water container and strong bonding between powder particles was confirmed through microscopic observations.

• Ecology and Resilient Infrastructure
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• v.8 no.3
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• pp.143-153
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• 2021

The growth inhibition effects of M. aeruginosa were verified using large volume (7.2 L) of algae samples and ultrasonication (high frequency of 1.6 MHz vs. low frequency of 23 kHz) in lab-scale experiment. The chlorophyll-a (chl-a) and cell number decreased gradually after 6 hr sonication with high frequency of 1.6 MHz whereas both decreased sharply after 6 hr sonication with low frequency of 23 kHz. Additionally, the first order degradation coefficient (k) values after sonication were greater than those during sonication. These results indicate that relatively low sonication energy per volume may affect the cell membrane and internal organs of M. aeruginosa in a slow and retarded manner and resulted in gradual decrease of cell numbers of M. aeruginosa. Based on the comparison of chl-a and cell number of M. aeruginosa after sonication, low frequency of 23 kHz is superior for growth inhibition of M. aeruginosa, since low frequency of 23 kHz easily penetrates the cell membrane and ruptures the internal organs including gas vesicles. As is evident in SEM and TEM images, ruptured cell membranes were clearly observed for low frequency of 23 kHz. Finally, the microcystin-LR in water is not detected and considered to be harmless in aquaculture systems.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.387-390
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• 1999

누설탄성표면파(Leaky Surface Acoustic Wave : LSAW) 측정에 사용하는 것을 목적으로 PVBF 압전막을 이용하여 직선집속 초음파트랜스듀서를 제작하고 그 특성을 평가하였다. 제작은 한쪽 면이 원통형 구조를 갖는 구리, 알루미늄, 3mmPVC-에폭시 3가지 재료를 배면층으로 사용하여 각각에 PVDF를 부착시켜서 수중에 음파를 방사하도록 구성하였고, 특성평가는 임펄스응답 특성과 음장 특성으로 나누어서 평가하였다. 임펄스응답 특성은 제작한 3종류의 집속 초음파트랜스듀서에 대해 실험적으로 측정하고, Mason 등가회로1)를 이용한 이론적 해석결과와 비교하였다. 음장특성 측정실험은 구리를 배면체로 하여 제작한 집속 초음파트랜스듀서에 대해서 실시하였고, 그 이론적인 계산결과는 Raylelgh-Somme-rfeld 회 절이론2)을 도입하여 초점면에 형성되는 음압분포를 계산하는 것으로 얻어졌다. 실험은 펄스 초음파 송수기 및 $2{\mu}m/step$으로 이동하는 정밀 x-y-z 스테이지를 컴퓨터에 연결하여 자동 측정하는 것으로 수행되었는데, 그 결과는 이론 해석결과와 비교적 잘 일치하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.158-165
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• 2005

In order to analyze incompressible two-phase flow, Level Set method was applied on pseudo-compressibility formulation. Level Set function is defined as a signed distance function from the phase interface, and gives the information of the each phase location and the geometric data to the flow. In this study, Level Set function transport equation was coupled with flow conservation equations, and owing to pseudo-compressibility technique we could solve the resultant vector equation iteratively. Two-phase flow analysis code was developed on general curvilinear coordinate, and numerical tests of bubble dynamics and surging wave problems demonstrate its capability successfully.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.61-61
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• 2018

본 연구에서는 전자 플로터 시스템의 관한 것으로, 특히 수표면 위에서 작용하는 바람, 파도 등의 영향을 거의 받지 않으면서 물의 흐름방향에 순응하여 이동할 수 있도록 함으로써 정확한 유속 측정이 가능하도록 한 연직 다 지점 GPS 전자 플로터 시스템 및 이를 이용한 유속 측정방법을 제시하였다. 일반적으로 대기나 해양, 하천 등에서 유동 유체의 유동상태를 파악하기 위하여 다양한 연구가 진행되고 있다. 이 같은 연구에서 유체의 유동 특성을 파악하기 위해 시뮬레이션을 통한 모델링을 하는 것이 한 방법이나, 이는 실제 유체가 유동하는 환경에서 발생되는 요인들을 나타내기 위해서는 한계가 있기 때문에 실제 측정을 통한 검증만큼 실제적이진 못하였다. 본 연구의 유속 측정 장치는 GPS 수신기를 탑재한 GPS 전자플로터가 수표면에 부유하고 라인으로 연결된 수중 추진부인 가이드볼, 중량보강부재로 구성되어져 있다. 기존 연구의 GPS 전자플로터는 1구형으로 표면유속만 측정 할 수 있었고 바람, 파도와 같은 외부영향에 대한 단점이 있었다. 이를 보완하기 위해 연직 다 지점 GPS 전자 플로터를 개발하였으며 이는 수표면 위에서 가해지는 바람, 파도 등의 영향을 거의 받지 않고, 하측에서 지지해주는 가이드볼이 물의 흐름에 의해 자연스럽게 자전할 수 있도록 구성되어져 보다 원활하게 물의 흐름에 순응하여 이동하고 수심에 따라 가이드볼 개수를 조절할 수 있기 때문에 대하천에서 운용이 가능하다. 이러한 유속 측정 장치 개발은 접근의 위험성과 안정성이라는 장점을 가지고 있으며 대하천 및 중소하천에서도 다양하게 운용이 가능하다. 또한 화학유출사고와 같은 문제가 많이 발생하는 요즘 화학사고와 관련된 연구들에 많은 도움이 될 것으로 사료된다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.3
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• pp.19-32
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• 2003

In the conventional photorefractive joint transform correlator(PRJTC), the intensity ration of input signal-to-pump beam should be large enough to saturate two-beam coupling transfer function to obtain a desired correlation result. As a result, the signal-to-noise ratio(SNR) of correlation result is decreased in a noisy input image. In this paper, we propose the improved method for increasing the SNR of the PRJTC by using the characteristics of BaTiO$_3$. We stop the energy transfer saturating by low intensity ratio of input beam and realize a short length of effective interaction in BaTiO$_3$ by making large incident angle of the signal beam. So the gain in high frequency area is decreased and the gain in low frequency area comes up to the saturation gain of the beam coupling transfer function. Therefore the SNR is improved in noisy input image and the PRJTC can be easily realized by low intensity ratio of input beam.