• Journal of Advanced Research in Ocean Engineering
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• 제2권4호
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• pp.202-208
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• 2016

In this paper, we propose novel seabed sediment classification algorithm using feature obtained by continuous wavelet transform (CWT). Contrast to previous researches using direct reflection coefficient of seabed which is function of frequency and is highly influenced by sediment types, we develop an algorithm using both direct reflection signal and backscattering signal. In order to obtain feature vector, we employ CWT of the signal and obtain histograms extracted from local binary patterns of the scalogram. The proposed algorithm also adopts principal component analysis (PCA) to reduce dimension of the feature vector so that it requires low computational cost to classify seabed sediment. For training and classification, we adopts K-means clustering algorithm which can be done with low computational cost and does not require prior information of the sediment. To verify the proposed algorithm, we obtain field data measured at near Jeju island and show that the proposed classification algorithm has reliable discrimination performance by comparing the classification results with actual physical properties of the sediments.

• 로봇학회논문지
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• 제16권2호
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• pp.94-102
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• 2021

This study addresses a method for 3D reconstruction using acoustic data with heterogeneous sonar devices: Forward-Looking Multibeam Sonar (FLMS) and Profiling Sonar (PS). The challenges in sonar image processing are perceptual ambiguity, the loss of elevation information, and low signal to noise ratio, which are caused by the ranging and intensity-based image generation mechanism of sonars. The conventional approaches utilize additional constraints such as Lambertian reflection and redundant data at various positions, but they are vulnerable to environmental conditions. Our approach is to use two sonars that have a complementary data type. Typically, the sonars provide reliable information in the horizontal but, the loss of elevation information degrades the quality of data in the vertical. To overcome the characteristic of sonar devices, we adopt the crossed installation in such a way that the PS is laid down on its side and mounted on the top of FLMS. From the installation, FLMS scans horizontal information and PS obtains a vertical profile of the front area of AUV. For the fusion of the two sonar data, we propose the probabilistic approach. A likelihood map using geometric constraints between two sonar devices is built and a monte-carlo experiment using a derived model is conducted to extract 3D points. To verify the proposed method, we conducted a simulation and field test. As a result, a consistent seabed map was obtained. This method can be utilized for 3D seabed mapping with an AUV.

• 한국지반환경공학회 논문집
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• 제12권5호
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• pp.21-28
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• 2011

연약지반의 효율적이고 경제적인 설계와 시공을 위하여 사전에 물리적, 역학적 특성을 상세히 파악하는 것이 중요하다. 본 연구는 대심도 해저지층의 연약점토에 대하여 함수비, 초기간극비, 액 소성한계, 압축지수 등의 물리적 역학적 특성을 파악하고 토질정수간의 상관성을 규명하여 국내 외 학자들이 발표한 식과 비교 분석하였다. 또한 이를 비교하여 높은 상관성을 가질 수 있는 대표적인 관계식을 산정하였다.

• 제어로봇시스템학회논문지
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• 제19권8호
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• pp.709-717
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• 2013

This paper presents the development of a specialized underwater leg with a manipulator function(convertible-to-arm leg) for the seabed walking robot named CRABSTER200(CR200). The objective functions of the convertible-to-arm leg are to walk on the seabed and to work in underwater for precise seabed exploration and underwater tasks under coastal area with strong tidal current. In order to develop the leg, important design elements including the degree of freedom, dimensions, mass, motion range, joint structure/torque/angular-speed, pressure-resistance, watertight capability and cable protection are considered. The key elements of the convertible-to-arm leg are realized through concept/specific/mechanical design and implementation process with a suitable joint actuator/gear/controller selection procedure. In order to verify the performance of the manufactured convertible-to-arm leg, a 25bar pressure-resistant and watertight test using a high-pressure chamber and a joints operating test with posture control of the CR200 are performed. This paper describes the whole design, realization and verification process for implementation of the underwater convertible-to-arm leg.

• Ocean and Polar Research
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• 제36권4호
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• pp.423-435
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• 2014

Verifying the similarity of environmental characteristics between an artificial impact site and a preserved or reference site is necessary to quantitatively and qualitatively evaluate the environmental impact of mining activity. Although an impact site (BIS station) and a preserved site (called KOMO station) that have been selected in the Korea manganese nodule contract area may share similar environmental characteristics, similarities in terms of the water column environment between both sites has not been investigated. In this study, we compared the chemical properties of the water columns and sinking particle fluxes between BIS and KOMO stations through two observations (August 2011 and September 2012). Additionally, we observed particle fluxes at the KOMO station for five years (July 2003~July 2008) to understand long-term natural variability. Vertical distributions of water column properties such as dissolved oxygen, inorganic nutrients (N, P, Si), total organic carbon below surface layer (within the depth range of 200 m) were not considerably different between the two sites. Especially, values of water column parameters in the abyssopelagic zone from 4000 m to bottom layer (~5000 m) were very similar between the BIS and KOMO sites. Sinking particle fluxes from the two sites also showed similar seasonality. However, natural variation of particle flux at the KOMO site varied from 3.5 to $129.9mg\;m^{-2}day^{-1}$, with a distinct temporal variation originating from ENSO events (almost forty times higher than a minimum value). These results could provide valuable information to more exactly evaluate the environmental impact of mining activity on water columns.

• 한국음향학회지
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• 제22권7호
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• pp.554-561
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• 2003

음원과 수신기 사이의 거리가 고정된 상태에서 측정한 광대역 천이 신호의 스펙트럼에 나타나는 간섭 패턴으로부터 모드차단 주파수를 인식하고 이로부터 해저면 음속을 추정하기 위해 수치 모의 및 실험 결과 분석을 통해 고찰하였다. Pekeris 도파관 환경에 대한 수치 모의 결과는 주파수 변화에 따른 전달 손실 및 간섭 패턴 변화가 모드 차단 주파수와 밀접한 관련이 있으며 간섭 패턴의 변화로부터 모드 차단 주파수를 인식하는 것이 가능할 수 있음을 보여주었다. 수치 모의를 통해 고찰한 개념을 해상 실험을 통해 획득한 신호에 적용하여 모드 차단 주파수를 인식하고 해저면 음속을 추정하였다. 추정된 음속을 모델 입력 인자로 이용하여 예측한 전달 손실은 손실 수준 린 간섭 패턴에서 실험 결과 분석을 통해 산출한 것과 매우 유사한 결과를 나타내었다.

• Ocean and Polar Research
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• 제37권2호
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• pp.119-125
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• 2015

This paper focuses on the efficient arrangement plan of buoyancy modules, which plan is used to secure the safe operation and structural stability of a marine riser. The marine riser is connected between a vessel and seabed devices. The movement of the vessel and the seabed devices are affected by the motion of the riser. The riser of a deep-seabed integrated mining system exerts a strong influence on the healthy transfer of minerals. So, buoyancy modules must be equipped to compensate for the problem which is the structure stability and the dynamic motion. Installation locations and quantities of the buoyancy modules are determined by real sea experiments. But this is not easy to do because in real sea experimental conditions the cost is expensive as well as being, time-consuming and dangerous. Therefore, the locations and quantities should be determined by numerical simulation. This method is called simulation-based design. The dynamic analysis models of the riser and the buoyancy modules are built into the commercial software of DAFUL.

• Ocean and Polar Research
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• 제36권2호
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• pp.179-187
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• 2014

Directly searching for undiscovered hydrothermal vent sites is inefficient due to the practical difficulty of comprehensively imaging vent fields. Thus, most searches for hydrothermal vent sites rely on the detection of hydrothermal plumes from water column observation. Detecting and measuring the hydrothermal plumes are the most efficient way to infer the presence and distribution of hydrothermal vents. Both the array of vertical casting and lateral towing are the most common methods to discover hydrothermal plumes. In this study, we compared results of cast and tow-yo operations along the same section of a spreading center with a distance of 20.5 km in the North Fiji Basin for mapping hydrothermal plumes. Operation of CTD tow-yo provides a detailed pattern of plumes which enable us to locate the hydrothermal vents. On the other hand, identification of hydrothermal activity can be determined effectively by CTD cast with additional analysis of geochemical tracers. Reduction in the operating time is another advantage of CTD cast operation, especially for regional-scale survey. Our results show that the combination of CTD cast and tow-yo would improve the efficiency of the hydrothermal plume survey to locate new hydrothermal vent sites.

• 한국해양공학회지
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• 제30권4호
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• pp.310-319
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• 2016

If a spoiler was attached to the pipeline investigated in a previous study, a strong flow and vortex at the lower part caused scouring and thus an asymmetric pressure distribution, which assisted in the analysis of the self-burial structure where a down force was applied to the pipe. However, only the fluid-pipe interaction was considered, excluding the medium (seabed), when practically burying the pipeline. Thus, this study applied a numerical model (LES-WASS-2D) to directly analyze the non-linear interactions among the fluid, pipe, and seabed in order to perform numerical simulations of a pipeline with a spoiler installed on the seabed. This allowed the self-burial mechanism of a pipeline with a spoiler to be analyzed in the same context as the previous study that considered only the fluid-pipe interaction. However, when a pipeline was installed on the seabed, a strong flow and vortex were found at the front of the bottom, and a spoiler accelerated the fluid resistances. This hydraulic phenomenon will reinforce the scouring and down force on the pipeline. In the general consideration of the numerical analysis results by the specifications and arrangements of the spoiler, a pipeline with a spoiler was found to be the most effective for the self-burial function.

• 한국해안·해양공학회논문집
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• 제33권4호
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• pp.160-167
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• 2021

단층파괴에 의한 해저지형변화는 공간적으로 시간차를 가진다. 특정 지점에서 파괴가 발생하면 이웃지점으로 단층파괴가 전파하면서 시간차에 따른 단층파괴가 발생하며, 단층파괴시 연직방향으로 상승하면서 지진해일을 야기한다. 해저 지형의 상승속도는 지진해일 초기파형에 영향을 주며 결과적으로 지진해일의 도달시간 및 크기에 영향을 준다. 본 연구에서는 단층파괴에 의한 해저 지형의 수평적 및 수직적 변화를 능동적 및 동적으로 고려하여 지진해일의 생성 및 전파를 모의할 수 있는 수치모형을 개발하였다. 모델의 검증을 위하여 2011년 동일본대지진에 대해 적용하였으며 기존의 수동적 및 정적 모형에 비해 정확성이 개선되는 것을 확인하였다.