• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.1 s.53
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• pp.69-77
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• 2009

An underwater structure is made to put with serious damage state by special environmental factors. If this damage phenomena persist, as for the structure, it is generated a structural serious problem because of the corrosion of a reinforcing bar and the loss of the concrete cut end. Repair work of an underwater structure is very harder than repair work in land, and it is actual that certification about a maintenance effect is uncertain. And the existing repair method is applied to a structure damaged with you without verification of a repair effect by a foreign reward and experience. In this study, a repair method about an underwater structure was proposed and observed a behavior characteristic and interface failure of an specimens. and comparison analyzed an effect of a proposed maintenance method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.10
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• pp.770-779
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• 2014

In this study, a numerical estimation method for 3D underwater radiated noise pattern using hull vibration and total acoustic power of the vibrating structure in the far-field is proposed. The underwater radiated noise pattern is known to be predicted using the vibration signals and radiation efficiency of each surface patch. But it is very difficult to know radiation efficiency of each surface patch which is one of important factors to calculate the 3D underwater radiated noise pattern. Instead of using radiation efficiency of each patch, the underwater radiated noise level is modified with the total acoustic power of the vibrating structure. The suggested estimation method for underwater radiated noise pattern is discussed with numerical model.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.451-454
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• 2000

Recently, the antiwashout underwater concrete has been increasingly used for underwater structure such as high strength massive concrete structures. However, Concrete has poor quality ad durability due to dilution with separating cementitious material. In this study, specimens were made with antiwashout underwater concrete replaced with mineral admixtures to improve their properties and were placed in air, water, and salt water. To estimation the chloride ion permeation in concrete, ASTM C 1202 Test was performed. The experimental results demonstrate that the increase of the admixtures improved the properties of antiwashout underwater concrete.

• The Journal of Korea Robotics Society
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• v.11 no.4
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• pp.226-234
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• 2016

In this study, a model-referenced underwater navigation algorithm is proposed for high-precise underwater navigation using monocular vision near underwater structures. The main idea of this navigation algorithm is that a 3D model-based pose estimation is combined with the inertial navigation using an extended Kalman filter (EKF). The spatial information obtained from the navigation algorithm is utilized for enabling the underwater robot to navigate near underwater structures whose geometric models are known a priori. For investigating the performance of the proposed approach the model-referenced navigation algorithm was applied to an underwater robot and a set of experiments was carried out in a water tank.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.3
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• pp.263-269
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• 1983

Underwater welding by a gravity arc welding process was investigated by using six types of coated electrodes and SM41A steel plates of 10 mm thickness as base metal and it was ascertained that this process may be put to practical use. Main results obtained are summarized as follows: 1. Angle of electrode affects no influence on bead appearance and the proper range of welding current and diameter of electrode for the high titanium oxide type is relatively wider than that for the ilmenite type. And the lime titania type, high titanium oxide type and ilmenite type of domestic coated arc welding electrodes of .phi.4 mm could attain the soundest underwater welded joints which contain no welding imperfection. 2. According to macro-structure, micro-structure and hardness distribution inspectionson underwater welded joint, the area between the HAZ and the surface of the weld in neighbourhood of the bond has the maximum hardness value. The structure of these parts is martensite and bainite. Other parts contain mocro-ferrite, micro-pearlite structure, which contain soundness of welded joint free from weld imperfection. 3. On consideration of both tensile strength of more than 100% joint efficiency and sufficient impact value, the welding condition which can get optimal welding strength is heat input of 1,400-1,500 J/mm, current of 200-215 ampere (voltage of 32-33 volts) in the case of lime titania type electrode. 4. Underwater welding strength (tensile strength, impact strength) depends on heat input (or current) quantitatively and they have the relationship of parabolic function. Each experimental equation has a high reliability and its percent of mean error is 4.14%. 5. It is suggested that the optimal design of weld strength by welding condition (current, heat input) could be utilized for a quality control of underwater welding.

• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.324-332
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• 2018

It is known that damages to the subsea cables used for electric power transmission between islands and countries, including renewable energy from offshore wind power, current, tides, etc., cost much to restore, which causes social and economic losses. Various types of fishing rigs and anchors have been reported to be the greatest hazards to subsea cables. It is possible to design and construct a suitable protection facility for a subsea cable by precisely estimating the underwater behavior of such hazardous apparatuses. In this study, numerical simulations of the underwater behaviors of various hazardous apparatuses were carried out using fluid-structure interaction (FSI) analysis as a basic study to simulate the actual behavior phenomena of hazardous apparatuses in relation to a subsea cable. In addition, the underwater drop characteristics according to the types of hazardous apparatuses were compared. In order to verify the accuracy of the FSI analysis method used in this study, we compared the test results for underwater drops of a steel ball bearing. Stock anchors, stockless anchors, and rocket piles, which were actually reported to be the cases of damage to subsea cables along the southwest coast of Korea, were considered as the hazardous apparatuses for the numerical simulations. Each hazardous apparatus was generated by a Lagrangian model and coupled with the fluid domain idealized by the Eulerian equation to construct the three-dimensional FSI analysis model. The accuracy of the numerical simulation results was verified by comparing them with the analytical solutions, and the underwater drop characteristics according to the types of hazard apparatuses were compared.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.907-918
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• 2014

In this study for the prediction of 3D underwater radiated noise pattern, a comparison between the proposed method(DHIE, Discrete Helmholtz Integral Equation) and the 3D underwater radiated noise calculation results using the measurement of near-field acoustic pressure data is performed. The near-field acoustic pressure in water is measured for the calculation of the far-field radiated noise pattern and the far-field acoustic power. Also the vibration field of the underwater structure is measured in simultaneously. Using the total far-field acoustic power and the vibration field on the surface of the structure, the proposed method(DHIE) can predict the underwater radiated noise pattern of the far-field The predicted results show the reasonable agreement within about 5dB comparing with the experiment result.

• Journal of the Korea Concrete Institute
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• v.12 no.5
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• pp.25-34
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• 2000

When concrete is placed underwater, it is diluted with separating cementitious material and as a result the quality of concrete becomes poor. To solve this problem, antiwashout underwater concrete is increasingly used for the construction and repair of the concrete structure underwater. The objective of this study is to investigate the characteristics of antiwashout underwater concrete as to the mix proportion, casting and curing water through experimental researches. The unit weight of water and cement, water-cement ratio, fine aggregate ratio, unit weight of antiwashout underwater agent and superplasticizer, and casting and curing water were chosen to measure the suspended solids, pH, air contents, slump flow, unit weight of hardened concrete, and compressive strength. From this study, the incremental modulus at mix proportion design and unit weight of antiwashout underwater agent were increased more than fresh water, and it is a optimum mix proportion that the unit weight of water(and cement) is 230kg/$\textrm{m}^3$(460kg/$\textrm{m}^3$), waterOcement ratio is 50%, fine aggregate ratio is 40%, unit weight of antiwashout underwater agent is 1.2% of water contents per unit weight of concrete, and unit weight of supeplasticizer is 2.5% of cement contents per unit weight of concrete when the antiwashout underwater concrete is used for the underwater work of ocean.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.4
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• pp.373-381
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• 2017

A Collaborative Optimization (CO) methodology for ring-stiffened composite material pressure hull of underwater vehicle is proposed. Structural stability and material strength are both examined. Lamination parameters of laminated plates are introduced to improve the optimization efficiency. Approximation models are established based on the Ellipsoidal Basis Function (EBF) neural network to replace the finite element analysis in layout optimizers. On the basis of a two-level optimization, the simultaneous structure material collaborative optimization for the pressure vessel is implemented. The optimal configuration of metal liner and frames and composite material is obtained with the comprehensive consideration of structure and material performances. The weight of the composite pressure hull decreases by 30.3% after optimization and the validation is carried out. Collaborative optimization based on the lamination parameters can optimize the composite pressure hull effectively, as well as provide a solution for low efficiency and non-convergence of direct optimization with design variables.

• Journal of Ocean Engineering and Technology
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• v.30 no.3
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• pp.227-233
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• 2016

This paper presents an underwater structure 3D reconstruction method using a 2D multibeam imaging sonar. Compared with other underwater environmental recognition sensors, the 2D multibeam imaging sonar offers high resolution images in water with a high turbidity level by showing the reflection intensity data in real-time. With such advantages, almost all underwater applications, including ROVs, have applied this 2D multibeam imaging sonar. However, the elevation data are missing in sonar images, which causes difficulties with correctly understanding the underwater topography. To solve this problem, this paper concentrates on the physical relationship between the sonar image and the scene topography to find the elevation information. First, the modeling of the sonar reflection intensity data is studied using the distances and angles of the sonar beams and underwater objects. Second, the elevation data are determined based on parameters like the reflection intensity and shadow length. Then, the elevation information is applied to the 3D underwater reconstruction. This paper evaluates the presented real-time 3D reconstruction method using real underwater environments. Experimental results are shown to appraise the performance of the method. Additionally, with the utilization of ROVs, the contour and texture image mapping results from the obtained 3D reconstruction results are presented as applications.