• International Journal of Ocean System Engineering
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• v.3 no.1
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• pp.44-48
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• 2013

This paper describes the design and implementation of a practical underwater positioning system, which is applicable for shallow water depth conditions. In this paper, two strategies are used to enhance the navigation performance. First, a low-cost acoustic-ranging-based precise navigation solution for shallow water is designed. Then, the outlier rejection algorithm is introduced by designing a velocity gate. The acoustic-ranging-based navigation is implemented by modifying the long base line solution. To enhance the tracking precision, the outlier rejection algorithm is introduced. The performance of the developed approach is evaluated using experiments. The results demonstrate that precise shallow water depth navigation can be implemented using the suggested approaches.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.511-514
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• 2003

Nowadays, wells tapping the deep aquifers become general because water quality of the shallow groundwater has been gradually degraded over the last 30 years as a result of rapid industrialization and intensive agricultural activities. However, many of the deep wells also suffer problems of water-quality degradation in several years after the well installation, nevertheless those were properly completed and managed. It is believed that the heavy pumping from deep wells causes the doward movement of the contaminated, shallow groundwaters and introduces them into the deep aquifers. In this study, we introduces a shallow capture well system, which could effectively prevent the shallow groundwaters of poor water duality from moving into the deep aquifers by pumping of deep production wells. Even though additional costs are required to apply this system, we believe that this method could be appropriate for the deep wells that are important for the public health.

• Water Engineering Research
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• v.2 no.3
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• pp.151-160
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• 2001

A two-dimensional flow model is newly developed. Two-dimensional shallow-water equations are discretized by the finite volume method. A nonorthogonal coordinate system is then employed. The developed model is applied to simulations of flows in a 180 degree curved bend flow. Numerical prediction are compared to available laboratory measurement. A good agreement is observed.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.231-238
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• 2001

To investigate the underground structure of shallow water, Han-river near Yangsou-Ri, high resolution hydroacoustic measurements were carried out for the engineering design of railroad bridge. The acoustic source was a Boomer with an energy of 90 to 280J and in a frequency range up to about 16KHz. The reflected signals were received by using both traditional hydrophones(passive element) and a specially devised receiver unit(active element) mainly composed of piezofilms and preamplifier. They are connected to the "SUMMIT" data acquisition system(DMT-GeoTec company), where the sampling interval was set to 1/32㎳. The source position was continuously monitored by a precision DGPS system whose positioning accuracy was on the order of loom. For the quality control purposes, two different source-receiver geometries were taken. That is to say, the measurements were repeated along the profile everytime depending on the different source energy(175J, 280J), the receiving elements(passive, active) and two different source-receiver geometries. It was shown that the data resolution derived from a proper arrangement with the active hydrophone could be greatly enhanced and hence the corresponding profile section caused by the regular data processing system "FOCUS" accounted excellently for the underground formation below the shallow water.w the shallow water.

• Journal of Ocean Engineering and Technology
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• v.34 no.5
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• pp.342-350
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• 2020

In this study, a hydrate inhibition system is investigated for shallow water gas fields. Mono-ethylene glycol (MEG) injection has been used as a typical method for inhibiting hydrate formation in gas fields; therefore, most offshore platforms are equipped with MEG injection and regeneration processes. A recent application of a kinetic hydrate inhibitor (KHI) has reduced the total volume of MEG injection and hence reduce the operating cost. Experiments are designed and performed to evaluate and verify the KHI performance for inhibiting hydrate formation under shallow water conditions. However, the shut-in and restart operation may require the injection and regeneration of MEG. For this operation, the MEG concentration must be optimized while considering the cost of MEG regeneration. The obtained results suggest that decreasing MEG concentration from 80 wt% to 70 wt% can reduce the life cycle cost (LCC) of MEG regeneration process by approximately 5.98 million USD owing to reduced distillation column cost. These results suggest that the hydrate inhibition system must be evaluated through well-designed experiments and process simulations involving LCC analysis.

• Magazine of the Korean Society of Agricultural Engineers
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• v.45 no.4
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• pp.55-65
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• 2003

Pilot study was conducted to examine the effects of ponded-water depth and reclaimed wastewater irrigation on paddy rice culture. For the ponded-water depth effect, three treatments of shallow, traditional, and deep water depths were applied, and each treatment was triplicated. The irrigation water for the treatment pots was an effluent from constructed wetland system for sewage treatment, while the control pot was irrigated with tap water kept traditional ponded-water depth. Irrigation water quantity varied with ponded-water depth as expected and drainage water quantity also varied similarly, which implies that shallow irrigation might save irrigation water and also reduce environmental impacts on downstream water quality. Rice growth and production were not significantly affected by ponded-water depth within the experimental condition, instead there was an indication of increased production in shallow and deep ponded-water depths compared to the traditional practice. Raising drainage outlet to the adequate height in paddy dike might be beneficial to save water resources within the paddy field. There was no adverse effect observed in reclaimed wastewater irrigation on the rice production, and mean yield was even greater than the control pots with tap water irrigation although statistically not significant. Water-saving irrigation by shallow ponded-water depth, raising the outlet height in diked rice paddy fields, minimizing forced surface drainage by well-planned irrigation, and reclaimed wastewater irrigation are suggested to save water and protect water quality. However, deviation from traditional farming practices might affect rice growth in long term, and therefore, further investigations are recommended before full scale application.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.13-22
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• 1989

Underwater channels can be regarded as time-varying systems in view of the acoustical characteristics due to the fact that the characteristics of the channel are affected by the environmental and geometrical conditions. Especially in shallow water case, the surface and bottom conduct as a waveguide so echo effect due tu the multipath reflections are severe. Therefore in shallow water communications, it is very important to equalize the transmitted signals distorted by the underwater channels with time-varying multipath fading. In this paper an equalizer system which employs the frequency domain adaptive filter to equalize the channels using inverse modeling technique is introduced.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.7-14
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• 2005

In this study, the shallow water equations on the sphere is simulated by the proposed method which has high spatial resolution and is based on the CIP(Cubic Interpolated Pseudoparticle) method. The governing equations are approximated on the longitude-latitudinal coordinate system. To avoid the problems resulting from the convergence of the meridians toward high-latitude and singularities on the poles, the semi-Lagrangian and finite volume method are employed. in addition, the CIP method is employed to solve the advection equations and is extended to apply on the equations in the polar coordinate system. The mathematical formulation and numerical results are also described. To verify of the efficiency, accuracy and capability of proposed algorithm, the standard test cases proposed bv Williamson et. al are simulated and the results are compared with other results. As a result, it is found that the present scheme gives a good properties in preserving shapes of solution and settles the pole problems in solving the shallow water equations on the sphere.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.494-500
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• 2015

It has been reported that a ship sailing in shallow water possesses better straight-line stability due to the change of fluid flow around the ship. This tendency affects manoeuvring characteristics of the ship. To investigate this phenomenon, indoor free running model test(FRMT) on KVLCC2 was carried out in three water depth conditions(H/T = 1.2, 1.5 & 2.0). Turning circle tests(± 35° ) and zigzag tests(± 20° /5° and ± 20° /10° ) were conducted with newly developed indoor FRMT system, and the manoeuvring results were compared with test results from other institutes. As the water depth decreased, the yaw rate of the ship decreased, and the distances of circular trajectories at the same heading angle increased in the turning circle tests. The first overshoot angles of the zigzag tests decreased. From both tests, the time for course change increased as the water depth decreased. These manoeuvring characteristics show that KVLCC2 in shallow water becomes more stable in terms of straight-line stability.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.204-209
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• 2004

It is well known fact that acoustic positioning systems are absolutely needed for various underwater operations. According to the distances between their sensors they are classified into three parts: long baseline(LBL), short baseline(SBL), and ultra-short baseline(USBL). Among them the USBL system is widely used because of its simplicity, although it is the most inaccurate. Recently, in order to increase the positioning accuracy, various USBL systems using broadband signal such as MFSK(Multiple Frequency Shift Keying) are produced. However, their positioning accuracy is still limited by background noise and reflected waves. Therefore, there is difficulty in applying the USBL system using MFSK signal in a shallow water with noisy conditions. In order to examine the effect of the noise and wave reflections this paper analyze position errors for various conditions using numerical simulations. The simulation results say that tile SNR must be greater than 20dB and errors in the vertical direction are slightly increased by wave reflections by upper and lower boundaries.