• Journal of the Korea Concrete Institute
• /
• v.17 no.2 s.86
• /
• pp.303-309
• /
• 2005

This study aims the evaluation of the corrosion of steel bar embedded in antiwashout underwater concrete, which has rather been neglected to date. To that goal, accelerated steel bar corrosion tests have been performed on three series of steel bar-reinforced antiwashout underwater concrete specimens manufactured with different admixtures. The three series of antiwashout underwater concrete were: concrete constituted exclusively with ordinary portland cement (OPC), concrete composed of ordinary portland cement mixed with fly-ash in $20\%$ ratio (FA20), and concrete with ground granulated blast furnace slag mixed in $50\%$ ratio (BFS50). The environment of manufacture was in artificial seawater. Measurement results using half-cell potential surveyor showed that, among all the specimens, steel bar in OPC was the first one that exceeded the threshold value proposed by ASTM C 876 with a potential value below -350mv after 14 cycles. And, the corresponding corrosion current density and concentration of water soluble chloride were measured as $30{\mu}A/mm^2$ and $0.258\%$. On the other hand, for the other specimens that are FA20 and BFS50, potential values below -350mV were observed later at 18 and 20 cycles, respectively. Results confirmed the hypothesis that mineral admixtures may be more effective on delay the development of steel bar corrosion in antiwashout underwater concrete.

• Journal of the Korea Concrete Institute
• /
• v.12 no.1
• /
• pp.89-99
• /
• 2000

The objective of this study is to investigate the bond strength properties of antiwashout underwater concrete. The arrangement of bars (vertical bar, horizontal upper bar, horizontal lower bar), condition of casting and curing (fresh water, sea water), type of fine aggregate (river sand, blended sand(river sand : sea sand = 1:1), and proportioning strength of concrete (210, 240, 270, 300, 330kgf/$\textrm{cm}^2$)are chosen as the experimental parameters. The test results(ultimate bond stress) are compared with bond and development provisions of the ACI Building Code(ACI 318-89) and proposed equations from previous research(which was proposed by Orangun et. al). The experimental results show that ultimate bond stress of antiwashout underwater concrete which arranged bar on the horizontal lower, used the blend sand, and was cast and cured in the fresh water are higher that other conditions. The ultimate bond stress were increased in proportion to {{{{( SQRT {fcu }) }}3 2. From this study, rational analytic formula for the ultimate bond stress are to be from compressive strength of concrete.

• Korean Journal of Remote Sensing
• /
• v.11 no.2
• /
• pp.59-73
• /
• 1995

The study is focused on the analysis of geomorphological environment changes of alluvial bar in lower Kum river using satellite-based multitemporal/multisensor data. Landsat datas for environment changes analysis consists of Landset MSS(2 scenes) and Landset TM(7 scenes) acquired from 1979 to 1994. This study is to develop the analysis techniques for the environment change detection of using ratio, classification, false color composite etc, of Landsat data especially useful to the geomorphological study of tidal flats and river channels. The results of this study can be summarized as follows : 1. The lower Kum River alluvial bar have had rapid geomorphological changes after the construction of the temporary dam to block the river flowing in 1983. The most alluvial bar located in the river has both bankway growth, especially the allurival bar in the Lower Kum River had grown between 1983 to 1990. 2. After construction of the estuarine barrage, no remarkable geomorphological changes have been found in Kum River area but the growth and formation of new underwater bar has continued. The enormous materials was needed for the growth and formations of new underwater barrier oslands and bar would be supplied from the sea bottom and river sediment to diminish of stream velocity after construction of the estuarine barrage.

• Journal of the Korea Concrete Institute
• /
• v.16 no.2 s.80
• /
• pp.283-291
• /
• 2004

Recently, the construction of underwater structures has been gradually increased, but underwater concrete got some problems of quality deterioration and water contamination around cast-in-situ of construction. In addition, massive underwater structures such as LNG tank, underwater concrete structures of large and continuous high- strength subterranean wall under water are being demanded lower heat of hydration. In this paper, the mechanical properties of high-strength antiwashout underwater concrete (HAWC) containing with two kinds of mineral admixtures respectively were investigated. On the basis of these results, the pH value and suspended solids of HAWC manufactured in the mock-up test were 10.0$\Box$11.0 and 51 mg/${\iota}$ at 30 minutes later, respectively, initial and final setting time were about 30,37 hours, and the slump flow was 530$\pm$20Tm. In the placement at a speed of $27 m^3/hr$, there was no large difference in flowing velocity with or without reinforcing bar, and flowing slope was maintained at horizontal level. Compressive strength and elastic modulus of the cored specimen somewhat decreased as flowing distance was far; however, those of central area showed the highest value.

• Journal of Advanced Navigation Technology
• /
• v.26 no.6
• /
• pp.464-473
• /
• 2022

In this paper, about a lightweight design that satisfies the performance of UHF-GPS Antenna used in autonomous underwater vehicle is proposed. Structural analysis, watertight external pressure test and non-destructive testing used in the design process are decided in consideration of structural safety for operating external forces in the underwater environment. First, the material of radome is selected for the performance of the UHF-GPS Antenna for communication with the carrier on the underwater operation in consideration of the 20 bar pressure generated. And the material of radome as PA-GF is selected by conducting electromagnetic field analysis and structural analysis and by considering high strength, rigidity and high dielectric constant. Electromagnetic field analysis and structural analysis by the thickness of radome are additionally performed in order to satisfy the required weight of UHF-GPS antenna. After selecting the final model, its structural safety is verified through watertight external pressure test and non-destructive testing.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10a
• /
• pp.447-450
• /
• 2000

Recently, antiwashout underwater concrete has used for underwater structure such as high strength massive concrete structures. When, concrete is placed in seawater the quality and durability of concrete could be doubt to especcially because the amount of cement placed in the concrete can be diminished by flowing seawater. In this study, antiwashout underwater concrete mixed with mineral admixtures for improvement of properties was placed in air, water, and salt water. Half-cell potential and current density was of specimens which made under different conditions measured for estimating corrosion degree. The experimental results demostrate that corrosion resistantce in saltwater was little and mineral admixtures improved properties of concrete.

• Journal of the Korean Society for Precision Engineering
• /
• v.30 no.9
• /
• pp.961-968
• /
• 2013

In this paper, we propose an optimal design for starfish capturing manipulator module with four-bar linkage mechanism. A tool link with compliance is attached on the four-bar linkage, and the tool repeats detaching starfish from the ground and putting it into the storage box. Since the tool is not rigid and the manipulator is operating underwater, the trajectory of the tool tip is determined by its dynamics as well as kinematics. We analyzed the trajectory of the manipulator tool tip by quasi-static analysis considering both kinematics and dynamics. In optimization, the lengths of each link and the tool stiffness are considered as control variables. To maximize the capturing ability, capturing stroke of the four-bar manipulator trajectory is maximized. Reaction force and reaction moment, and other kinematic constraints were considered as inequality constraints.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.54 no.4
• /
• pp.271-278
• /
• 2018

In this study, the conventional cylinder-shaped lower bar on the canvas was modified and its performance was tested to improve the opening force of the stow net on anchor. The improved new lower bar used in the test is consisted of 13 flat bars with a length of 1.8 m, a width of 0.075 m and a thickness of 4 mm, and a pipe with a length of 2.0 m and a diameter of 50 mm. A stow net with the improved lower bar and a stow net with an existing lower bar were installed underwater and their trajectories for 21 hours were examined. To confirm their trajectories, GPS loggers were attached to the buoys on the left and right canvases and the buoy of the hauling rope. As a result of the test, the rotation of the gear with the improved bar was smoother than that with the existing bar. As a result of comparing the changes in the interval of the buoys attached to the canvas after the low and high tide, the buoy spacing of the gear with the improved bar is wider than that of the conventional gear; moreover, the larger the interval, the smoother the rotation of the fishing gear was. Therefore, it is considered that using the improved lower bar can enhance the performance of the stow net.

• Journal of Institute of Control, Robotics and Systems
• /
• v.19 no.8
• /
• pp.709-717
• /
• 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.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.1
• /
• pp.7-13
• /
• 2006

Fisheries policy change from catching to farming requires more intensive consideration for aquaculture industry. The oceanic farm is a desirable cost effective aquaculture method. However. in odor to gather fish in the oceanic farm, eating sound or any attracting sound should be radiated through underwater loudspeaker. In this Paper, it has been found in literature that the frequency range responding to fish is about 16Hz to 13kHz but sensitive frequency range is about 150Hz to 2kHz and sound pressure level is about 100dB to 150dB reference $1{\mu}Pa$. Therefore, frequency range and output sound level of designed underwater loudspeaker has been specified as 150Hz to 3kHz and 100dB to 145dB reference $1{\mu}bar$. respectively To verify the stability and the endurance to the pressure of 40m water depth, manufactured underwater loudspeaker was examined before sea trial in manufactured water pressure tank which gives a maximum of 10 atmospheric Pressure. We experimented on acoustic characteristic with manufactured underwater loudspeaker under water depth of 10m.