• Title/Summary/Keyword: 잠수

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Experimental Performance Analysis of BCJR-Based Turbo Equalizer in Underwater Acoustic Communication (수중음향통신에서 BCJR 기반의 터보 등화기 실험 성능 분석)

  • Ahn, Tae-Seok;Jung, Ji-Won
    • Journal of Navigation and Port Research
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    • v.39 no.4
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    • pp.293-297
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    • 2015
  • Underwater acoustic communications has been limited use for military purposes in the past. However, the fields of underwater applications expend to detection, submarine and communication in recent. The excessive multipath encountered in underwater acoustic communication channel is creating inter symbol interference, which is limiting factor to achieve a high data rate and bit error rate performance. To improve the performance of a received signal in underwater communication, many researchers have been studied for channel coding scheme with excellent performance at low SNR. In this paper, we applied BCJR decoder based ( 2,1,7 ) convolution codes and to compensate for the distorted data induced by the multipath, we applying the turbo equalization method. Through the underwater experiment on the Gyeungcheun lake located in Mungyeng city, we confirmed that turbo equalization structure of BCJR has better performance than hard decision and soft decision of Viterbi decoding. We also confirmed that the error rate of decoder input is less than error rate of $10^{-1}$, all the data is decoded. We achieved sucess rate of 83% through the experiment.

A Study on the Wireless Ship Motion Measurement System Using AHRS (AHRS를 이용한 무선 선체 운동 측정 시스템에 관한 연구)

  • Kim, Dae-Hae;Lee, Sang-Min;Kong, Gil-Young
    • Journal of Navigation and Port Research
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    • v.37 no.6
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    • pp.575-580
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    • 2013
  • The IMU(Inertial Measurement Unit) which is the expensive equipment has been used as a special limited area, usually in measurement of posture of applying to the areas of ship, submarine, aircraft and military equipment application. However, in the current situation, MEMS AHRS technology can replace the high-priced IMU in MEMS AHRS selected application field. In this paper, wireless hull motion measurement system was suggested for measuring key elements of ship's movement such as rolling, pitching and yawing using gyro, acceleration and magnetic sensors of AHRS. In order to reduce the error such as instantaneous acceleration, effects and vibration of geomagnetic, we have adopted the sensors equipped with Kalman filtering. The Wireless hull motion measurement system using AHRS sensors was tested in actual ship and it could easily be applied in limited installation circumstances of the ship. In the future, this system can be useful in the navigation safety and marine accident analysis by using with ship equipment such as INS or VDR in the maritime.

A Research Review for Establishing Effective Management Practices of the Highly Invasive Cordgrass (Spartina spp.) (생태계 교란식물 cordgrass (Spartina spp.)의 효과적인 관리방안 수립을 위한 고찰)

  • Kim, Jin-Seog
    • Weed & Turfgrass Science
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    • v.5 no.3
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    • pp.111-125
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    • 2016
  • Cordgrass (Spartina spp.) is recognized as a highly invasive plant in estuaries throughout the world because of remarkable versatility and resiliency, significant reproduction, strong adaptability, rapid spreading, and vigorous growth. In this review, therefore, to provide insights on the effective management practices, the previous research works were summarized and discussed. Spartina spp. is a perennial halophyte, warm-season (C4) grass that reproduces both sexually through seeds and asexually by rhizomes. Management strategies for cordgrass have included various physical, biological, and chemical controls. Herbicides are usually the most cost-effective means of control. Currently, glyphosate, imazapyr, fluazifop and haloxyfop have been practically used. To improve the control efficacy, a combination of two more than methods (example, mowing-spraying) is needed to be applied consistently every year for at least 3 to 4 years and to be sprayed with enough dry time (>4-6 hr) at an early growth stage (before flowering). Consistently repeated application of same herbicide have to be avoided to prevent an unexpected emergence of herbicide-resistant lines. On the other hand, Spartina spp. have many positive functions for agricultural and eco-engineering purposes. Thus, we have to give more intensive research for effectively managing advantages and disadvantages of Spartina plantations.

Numerical comparative investigation on blade tip vortex cavitation and cavitation noise of underwater propeller with compressible and incompressible flow solvers (압축성과 비압축성 유동해석에 따른 수중 추진기 날개 끝 와류공동과 공동소음에 대한 수치비교 연구)

  • Ha, Junbeom;Ku, Garam;Cho, Junghoon;Cheong, Cheolung;Seol, Hanshin
    • The Journal of the Acoustical Society of Korea
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    • v.40 no.4
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    • pp.261-269
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    • 2021
  • Without any validation of the incompressible assumption, most of previous studies on cavitation flow and its noise have utilized numerical methods based on the incompressible Reynolds Average Navier-Stokes (RANS) equations because of advantage of its efficiency. In this study, to investigate the effects of the flow compressibility on the Tip Vortex Cavitation (TVC) flow and noise, both the incompressible and compressible simulations are performed to simulate the TVC flow, and the Ffowcs Williams and Hawkings (FW-H) integral equation is utilized to predict the TVC noise. The DARPA Suboff submarine body with an underwater propeller of a skew angle of 17 degree is targeted to account for the effects of upstream disturbance. The computation domain is set to be same as the test-section of the large cavitation tunnel in Korea Research Institute of Ships and Ocean Engineering to compare the prediction results with the measured ones. To predict the TVC accurately, the Delayed Detached Eddy Simulation (DDES) technique is used in combination with the adaptive grid techniques. The acoustic spectrum obtained using the compressible flow solver shows closer agreement with the measured one.

Numerical investigation on cavitation and non-cavitation flow noise on pumpjet propulsion (펌프젯 추진기의 공동 비공동 유동소음에 대한 수치적 연구)

  • Garam Ku;Cheolung Cheong;Hanshin Seol;Hongseok Jeong
    • The Journal of the Acoustical Society of Korea
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    • v.42 no.3
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    • pp.250-261
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    • 2023
  • In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.

Distribution of the Seagrass, Zostera spp. in Ulleungdo (울릉도 연안의 거머리말속 잘피 분포)

  • PARK, JUNG-IM;KIM, JAE HOON;SONG, HWI-JUNE;KIM, GU YEON
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.25 no.4
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    • pp.106-116
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    • 2020
  • To examine distribution of the Zostera species growing naturally in Ulleungdo, scuba diving surveys using ships were conducted along the coast and inside the harbors of the island at the end of September 2019. In areas of seagrass occurrence, environmental factors such as nutrient concentrations in water column and sediment pore water, salinity, and sediment organic content were also analyzed. Zostera caulescens meadows appeared in the relatively deep waters (14-24 m MSL) of Cheonbu-ri, Jeodong-ri, Sadong-ri, and Namyang-ri in Ulleungdo, and the total seagrass coverage was approximately 4.9 ha. Approximately 0.9 ha of Zostera marina meadow was found at the depths of 3-5 m MSL within Hyeonpo-hang in Hyeonpo-ri. The average shoot density and biomass of Z. caulescens were 121.9±9.7 shoot m-2 and 99.0±13.2 gDW m-2, respectively, with no significant differences by location. The average shoot density and biomass of Z. marina were 193.8±18.8 shoot m-2 and 102.6±6.8 gDW m-2, respectively. The nutrient concentrations in the sediment pore water and sediment organic content in the seagrass meadows in Ulleungdo were lower than those in eelgrass meadows on the southern and eastern coasts of Korea. These results will provide useful basic information for the marine protected species, Z. caulescens and Z. marina, and for the conservation of the waters of Ulleungdo, which has been designated as a marine protected area.

Ecological Characteristics and Their Implications for the Conservation in the Taehwagang River Estuarine Wetland, Ulsan, South Korea (울산 태화강하구습지의 생태적 특성 및 보전을 위한 제안)

  • Pyoungbeom Kim;Yeonhui Jang;Yeounsu Chu
    • Ecology and Resilient Infrastructure
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    • v.10 no.4
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    • pp.171-183
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    • 2023
  • Estuarine wetlands, which form a distinctive brackish water zone, serve as important habitats for organisms that have adapted to and thrive in this environment. Nonetheless, excessive development and utilization result in artificial disruptions that alter the distinctive functions and attributes of estuarine wetlands. To collect the basic data for the conservation of estuarine wetlands with excellent ecosystems, we investigated the vegetation distribution characteristics and biota status of the Taehwagang River Estuarine Wetland. Data from vegetation surveys have shown that 25 plant communities of six physiognomic vegetation types, including willow vegetation, lotic and lentic herbaceous vegetation, floating/submerged vegetation. In the upper reaches, where topographical diversity was high, various types of wetland vegetation were distributed. In terms of biodiversity, a total of 696 species, including 7 endangered wildlife species, were identified. Due to good ecological connectivity, tidal rivers are formed, brackish water species including various functional groups are distributed around this section. The inhabitation of various water birds, such as diving and dabbler ducks, were confirmed according to the aquatic environment of each river section. The collection of ecological information of the Taehwagang River Estuarine Wetland can be used as a framework for establishing the basis for conservation and management of the estuarine ecosystem and support policy establishment.

A Frequency Domain Motion Response Analysis of Substructure of Floating Offshore Wind Turbine with Varying Trim (부유식 해상풍력발전기 하부구조물의 종경사각에 따른 주파수 영역 운동응답 분석)

  • In-hyuk Nam;Young-Myung Choi;Ikseung Han;Chaeog Lim;Jinuk Kim;Sung-chul Shin
    • Journal of Navigation and Port Research
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    • v.48 no.3
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    • pp.155-163
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    • 2024
  • As the demand for reducing carbon emissions increases, efforts to reduce the usage of fossil fuels and research on renewable energy are also increasing. Among the various renewable energy harvesting techniques, the floating offshore wind turbine has several advantages. Compared to other technologies, it has fewer installation limitations due to interference with human activity. Additionally, a large wind turbine farm can be constructed in the open ocean. Therefore, it is important to conduct motion analysis of floating offshore wind turbines in waves during the initial stage of conceptual design. In this study, a frequency motion analysis was conducted on a semi-submersible type floating offshore wind turbine. The analysis focused on the effects of varying trim on the motion characteristics. Specifically, motion response analysis was performed on heave, roll, and pitch. Natural period analysis confirmed that changing the trim angle did not significantly affect the heave and pitch motions, but it did have a regular impact on the roll motion.

Locates the Sunken Ship 'Dmitri Donskoi' using Marine Geophysical Survey Techniques in Deep Water (지구물리 탐사기법을 이용한 심해 Dmitri Donskoi호 확인)

  • Yoo, Hai-Soo;Kim, Su-Jeong;Park, Dong-Won
    • 한국지구물리탐사학회:학술대회논문집
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    • 2004.08a
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    • pp.104-117
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    • 2004
  • Dmitri Donskoi, which went down during the Russo-Japanese War occurred 100 years ago, was found by using geophysical exploration techniques at the 400 m water depth of submarine valley off Jeodong of Ulleung Island. In the submarine area with the rugged seabed topography and volcanic seamounts, in particular, the reliable seabed images were acquired by using the mid-to-shallow Multibeam exploration technique The strength of corrosion (causticity) of the sunken Donskoi, measured by the electrochemical method, decreased to 2/5 compared with the original strength.

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Effect of Duck Free-Ranging Density on Duck Behavior Patterns, and Rice Growth and Yield under a Rice-Duck Farming System in Paddy Field (논오리 방사밀도가 오리의 행동양상 및 벼 생육 ${\cdot}$ 수량에 미치는 영향)

  • Goh, Byeong-Dae;Song, Young-Han;Manda, Masaharu
    • Korean Journal of Environmental Agriculture
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    • v.20 no.2
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    • pp.86-92
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    • 2001
  • The current study was conducted to elucidate the optimum density of free-ranging ducks in a rice-duck farming system in terms of effects on duck behavior, and growth and yield of rice plants. Four paddy fields were used for this experiment, with 6, 9, 12 and 15 birds per plot, respectively. Ducklings at eight days of age were free ranged in experimental paddy plots (4.0 a each) on the 9th day after the transplantation of rice plants. Ducks were kept in the plot for seventy days, at which point rice plants reached the earing stage. Foraging, moving, working, resting, diving and pecking behaviors of the ducks were observed two times during the experimental period. Also, rice plant growth and yield according to the density of ducks per plot were examined. The foraging and moving behavior of free-ranging ducks in paddy fields for 12 hours during the daytime tended to be longer in the 12-bird plot, and working behavior was significantly (P<0.01) longer in the 12-bird plot than in the other three plots. The resting behavior was significantly (P<0.01) higher in the 9- and 15-bird plots than in the 12-bird plot. The frequency of moving behavior for 6 hours during the daytime in the 15-bird plot tended to be lower than that in the other three plots, but this difference was not significant. The amount of diving and pecking behavior in the 9-bird plot was significantly (P<0.05) higher than that in the other three plots, and the number of hills pecked tended to be higher with increasing of duck density. From thirty days after ducks were introduced to the paddy fields, the length of rice plants tended to be significantly (P<0.05) shorter in high free-ranging density plots as compared to low free-ranging density plots. The number of tillers per hill was not affected by the free-ranging density. The culm length of rice plants was significantly (P<0.05) shorter in the 12- and 15-bird plots than in the other two plots, however, the duck free-ranging density did not affect panicle length. The dry weight of the root of rice plants was increased with high free-ranging density, but there was no such increase in the top parts of the rice plants. The percent of rice plants badly damaged by free-ranging density tended to be lower in the order of 12-, 9-, 6- and 15-bird plots. The number of ears, ripening grains and crop yield per hill of rice plants in the 12-bird plot were significantly (P<0.05) higher than those of the other three plots. Therefore, the yield of each rice plant per 10 a was significantly increased in the 12-bird plot.

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