• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.37-46
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• 2016

This study describes the spatio-temporal distributions in phytoplankton community such as species composition, standing crops and dominant species from April to November 2008 in the Uljin Marine Ranching Area (UMRA). A total of 123 species of phytoplankton belonging to 67 genera was identified. In particular, diatoms and dinoflagellates were occupied more than 60.5% and 34.6% of total species, respectively. The annual dominant species were Thalassiosira sp., Pseudo-nitzschia pungens in spring, Leptocylindrus danicus, Guinardia striata in early summer, Cheatoceros cirvisetus, Ch. decipiens in early autumn and Skeletonema costatum -ls (like species), Pn. pungens in autumn. Phytoplankton cell density fluctuated with an annual mean of $48cells{\cdot}mL^{-1}$ between the lowest value of $1.8cells{\cdot}mL^{-1}$ in early autumn and the highest value of $240cells{\cdot}mL^{-1}$ in spring. According to the cluster analysis, the phytoplankton community of the UMRA was characterized by the nutrient supply from land side and water movement as current.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.145-152
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• 2012

As the problems of global warming are brought up recently, many skillful solutions for developing new renewable energy are suggested. One of the most remarkable things is ocean energy. Korea has abundant ocean energy resources owing to geographical characteristics surrounded by sea on three sides, thus the technology of commercialization about tidal current power, wave power is demanded. Especially, Tidal energy conversion system is a means of maintaining environment naturally. Tidal current generation is a form to produce electricity by installing rotors, generators to convert a horizontal flow generated by tidal current into rotating movement. According to rotor direction, a tidal current turbine is largely distinguished between horizontal and vertical axis shape. Power capacity depends on the section size crossing a rotor and tidal current speed. We therefore investigated three dimensional flow analysis and performance evaluation using commercial ANSYS-CFX code for an 100 kW class horizontal axis turbine for low water level. Then We also studied three dimensional flow characteristics of a rotating rotor and blade surface streamlines around a rotor. As a result, We found that torque increased with TSR, the maximum torque occurred at TSR 3.77 and torque decreased even though TSR increased. Moreover we could get power coefficient 0.38 at designed flow velocity.

• The Journal of the Acoustical Society of Korea
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• v.32 no.2
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• pp.104-115
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• 2013

In a shallow water waveguide, reverberation signals and their Doppler effects form the primary limitation on sonar system performance. Therefore, in the reverberation-limited environment, it is necessary to estimate the reverberation level to be encountered under the conditions in which the sonar system is operated. In this paper, high-frequency reverberation model capable of simulating the reverberation signals received by a high-speed moving source in a range independent waveguide is suggested. In this model, eigenray information from the source to each boundary is calculated using the ray-based approach and the optimizing method for the launch angles. And the source receiving position changed by the moving source is found by a scattering path-finding algorithm, which considers the speed and direction of source and sound speed to find the path of source movement. The scattering effects from sea surface and bottom boundaries are considered by APL-UW scattering models. The model suggested in this paper is verified by a comparison to the measurements made in August 2010. Lastly, this model reflects well statistical properties of the reverberation signals.

• Korean Journal of Environment and Ecology
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• v.23 no.5
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• pp.431-438
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• 2009

The main purpose of this research is to prepare and provide basic materials for the propagational strategy of eelgrass by investigating on the morphological adaptation of Korean Zostera marina to ocean currents. An eelgrass plant mainly consists of rhizome, leaf sheath, leaves and roots. The rhizome is the horizontal stem of the plant that serves as the backbone from which the leaves and roots emerge. The leaf sheath is the bundle at the base of the leaves that holds the leaves together, protecting the meristem, the primary growth point of the shoot. Leaves originate from a meristem which is protected by a sheath at the actively growing end of the rhizome. As the shoot grows, the rhizome elongates, moving across or within the sediment, forming roots as it progresses. The aggregated leaves from the leaf sheath are found to have two cell layers on one side and multiple layers of airy tissues called aerenchyma on the other. The aerenchyma tissues are developed in multi-layered cell structures surrounding the veins which are formed in the leaf sheath. Generative shoots are made of rhizomes, which are circular or ovoidal, stem, and spathe and spadix. The transverse section of rhizome and the stem and central floral axis is found to be circular, ovoid and in the shape of convex respectively, and the vascular bundle, which is a part of transport system, has one large tube in the center and two small tubes on both sides. The layers of collenchyma cells numbered from 12 to 15 in the stem, and from 7 to 12 in the rhizome. The seed coat is composed of sclereids, small bundles of sclerenchyma tissues, which prevent the influx of sea water from the outside and help endure the environmental stress. In conclusion, alternative multi-layer structure in circular, convex type aggregated leaf base are interpreted to morphological adaption as doing tolerable elastic structure through movement of seawater. The generative shoots develop long slim stem and branches in circular or ovoidal shapes to minimize the adverse impacts of sea current, which can be interpreted as the plant's morphological adaptation to its environment.

• Journal of Intelligence and Information Systems
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• v.26 no.4
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• pp.87-109
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• 2020

Currently, thanks to the major stride made in developing wired and wireless communication technology, a variety of IT services are available on land. This trend is leading to an increasing demand for IT services to vessels on the water as well. And it is expected that the request for various IT services such as two-way digital data transmission, Web, APP, etc. is on the rise to the extent that they are available on land. However, while a high-speed information communication network is easily accessible on land because it is based upon a fixed infrastructure like an AP and a base station, it is not the case on the water. As a result, a radio communication network-based voice communication service is usually used at sea. To solve this problem, an additional frequency for digital data exchange was allocated, and a ship ad-hoc network (SANET) was proposed that can be utilized by using this frequency. Instead of satellite communication that costs a lot in installation and usage, SANET was developed to provide various IT services to ships based on IP in the sea. Connectivity between land base stations and ships is important in the SANET. To have this connection, a ship must be a member of the network with its IP address assigned. This paper proposes a SANET-CC protocol that allows ships to be assigned their own IP address. SANET-CC propagates several non-overlapping IP addresses through the entire network from land base stations to ships in the form of the tree. Ships allocate their own IP addresses through the exchange of simple requests and response messages with land base stations or M-ships that can allocate IP addresses. Therefore, SANET-CC can eliminate the IP collision prevention (Duplicate Address Detection) process and the process of network separation or integration caused by the movement of the ship. Various simulations were performed to verify the applicability of this protocol to SANET. The outcome of such simulations shows us the following. First, using SANET-CC, about 91% of the ships in the network were able to receive IP addresses under any circumstances. It is 6% higher than the existing studies. And it suggests that if variables are adjusted to each port's environment, it may show further improved results. Second, this work shows us that it takes all vessels an average of 10 seconds to receive IP addresses regardless of conditions. It represents a 50% decrease in time compared to the average of 20 seconds in the previous study. Also Besides, taking it into account that when existing studies were on 50 to 200 vessels, this study on 100 to 400 vessels, the efficiency can be much higher. Third, existing studies have not been able to derive optimal values according to variables. This is because it does not have a consistent pattern depending on the variable. This means that optimal variables values cannot be set for each port under diverse environments. This paper, however, shows us that the result values from the variables exhibit a consistent pattern. This is significant in that it can be applied to each port by adjusting the variable values. It was also confirmed that regardless of the number of ships, the IP allocation ratio was the most efficient at about 96 percent if the waiting time after the IP request was 75ms, and that the tree structure could maintain a stable network configuration when the number of IPs was over 30000. Fourth, this study can be used to design a network for supporting intelligent maritime control systems and services offshore, instead of satellite communication. And if LTE-M is set up, it is possible to use it for various intelligent services.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.2 no.1
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• pp.47-62
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• 1969

A goby, Synechogobius hasta (Temminck et Schlegel) was studied to investigate the food consumed and the biological change of the food organisms, and the fish were sampled from the closed tributary and the lower Part of the Naktong River, near Pusan, during the period from November of 1967 to December of 1968. The fish were sampled from four stations (Fig. 1), the total number of fish being 1,295 and they were grouped and analysed monthly. The content of the alimentary canal was analysed in three categories according to modified Nilsson's method (Dahl 1962) with a slight alteration: 1) The number of each item of stomach contents was counted and the percentage of each item in proportion to the total number of food organisms is indicated by the letter 'N' representing numerical percentage in Table 2. 2) The percentage of fish which contained any items of food organisms in proportion to the total number of fish caught in a given season is indicated by the letter 'O' representing frequency of occurrence. 3) Dominant groups of food items were selected and the percentage of the number of each dominant item in proportion to the number of the food organisms belonging to the dominant groups is indicated by the letter 'D' representing dominance. All food organisms were classified in 50 food item categories and then they were grouped in 13 main groups (Fig. 2-1), and they were further divided into 1) obligatory bottom animals, 2) organic drifts and 3) actively swimming forms; according to the conditions of the animal communities within the habitat. Since the majority of its food was composed of the obligatory bottom animals ($94.6\%$), the fish appeard to be a typical bottom feeder. And the dominant food organisms of the fish is generally determined by the local composition of the benthic fauna within the fish habitat. And their seasonal rhythm occurs among the food organisms in the stomach by the biological interaction. Locality variation in the population of the same food organism occurs due to the difference of food organisms in the habitat of the fish at Seonam and Garak, and at Seongsan and Hadan the condition of the niche for the fish in the both regions seems to be the same since the composition and the seasonal variation of the organisms were the same. The results may be summarized as follows: 1) The goby mainly feed on the animals of bottom fauna, and the food organisms are deter-mined by the food compositions within the habitat. 2) Seasonal variation of the stomach content shows the seasonal rhythm due to the biological variation of the population and their interaction. 3) The goby shows no preference on specific food, and the food is composed of a variety of animals. 4) Major food items of the goby are Polychaeta, Palaemon modestus, Isopoda, Gammaridea, Insecta (nymphs and larvae), Ilyoplax deschampsi, and Paratye compressa. 5) Logitudinal succession oil the population of the food organisms is apparently recognized within the community of Seongsan, Garak and Seonam. 6) The goby begins to descend toward the estuary and sea around April when the water temperature reaches $20^{\circ}C$, and they begin to return to river waters in September.