• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.286-292
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• 2011

In order to design a shear coaxial injector of solid particles for underwater propulsion system, basic experiments on gas-liquid shear coaxial injector are necessary. In the gas-liquid coaxial injector self-pulsation usually occurs with an intense scream. When self-pulsation occurs, mass flow rate oscillation and intense scream are detected by the interactions between the liquid and gas phase. Self-pulsation must be suppressed since this oscillation may cause combustion instabilities. Considerable research has been conducted on self-pulsation characteristics, but these researches are conducted in swirl coaxial injector. The main objective of this research is to understand the characteristics of self-pulsation in shear coaxial injector and reveal the mechanism of the phenomenon. Toward this object, self-pulsation frequency and spray patterns are measured by laser diagnostics and indirect photography. The self-pulsation characteristics of shear coaxial injector are studied with various injection conditions, such as the pressure drop of liquid and gas phase, and recess ratio. It was found that the frequency of the self-pulsation is proportional to the liquid and gas Reynolds number, and proportional to the L/d.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1243-1249
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• 2004

In this paper, the multipath effect on underwater acoustic channel bandwidth and BFSK and BPSK bit error dependancy on channel bandwidth are analyzed. The multipath is modeled as a discrete multipath and a continuous multipath and the channel bandwidth is expressed as a function of multipath delay spread constant. Bit error characteristics on the channel bandwidth and the criteria of the multipath delay spread constant are found through the numerical simulation. The transmission bit rate of less than 100bps in the water tank which has a channel bandwidth of 100Hz, is a consistent result with the numerical simulation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.34-39
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• 2002

A Semi-Autonomous Underwater Vehicle (SAUV) capable of simple work at sea bed is under development in KRISO-KORDI. A pressure vessel of SAUV which is composed of FRP was manufactured to load electronic equipments. The objective of this paper is to verify the safety of the pressure vessel through conducting the structural analysis and test in pressure tank. Strain and stress under unit load were obtained by using ANSYS in the linear structural analysis. And local buckling analysis was performed with NASTRAN for the middle cylindrical hull. For the pressure test, strains were measured at three point. We found that the results by linear structural analysis and experiment are coincide well at the points where buckling does not occur. Maximum depth was estimated to be 250m by the local buckling analysis.

• Nuclear Engineering and Technology
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• v.48 no.6
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• pp.1338-1348
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• 2016

A novel fully passive small modular superheated water reactor (SWR) for underwater deployment is designed to produce 160 MWe with steam at $500^{\circ}C$ to increase the thermodynamic efficiency compared with standard light water reactors. The SWR design is based on a conceptual 400-MWe integral SWR using the internally and externally cooled annular fuel (IXAF). The coolant boils in the external channels throughout the core to approximately the same quality as a conventional boiling water reactor and then the steam, instead of exiting the reactor pressure vessel, turns around and flows downward in the central channel of some IXAF fuel rods within each assembly and then flows upward through the rest of the IXAF pins in the assembly and exits the reactor pressure vessel as superheated steam. In this study, new cladding material to withstand high temperature steam in addition to the fuel mechanical and safety behavior is investigated. The steam temperature was found to depend on the thermal and mechanical characteristics of the fuel. The SWR showed a very different transient behavior compared with a boiling water reactor. The inter-play between the inner and outer channels of the IXAF was mainly beneficial except in the case of sudden reactivity insertion transients where additional control consideration is required.

• Korean Journal of Remote Sensing
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• v.11 no.2
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• pp.59-73
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• 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 Society of Naval Architects of Korea
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• v.55 no.6
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• pp.482-489
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• 2018

Most of the numerical and experimental studies on supercavitating flows are focused on the cavitator only. However, the partial cavity growing into the supercavity is affected by the shape of the body placed behind the cavitator. In this paper, we develope a numerical method which is based on the boundary element method to predict supercavitating flow around three-dimensional axisymmetric bodies. We estimate the influence of the body shape on the supercavity growth. Here, we consider various parameters of the body such as cavitator shape, shoulder length and body diameter, and compare the results with the case of the cavitator only. In summary, it is found that the body may impede the cavity growth, the shoulder mainly affects the cavity length, and the supercavity occurring in the cone type cavitator is strongly influenced rather than that of the disk type cavitator.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.617-635
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• 2020

The purpose of this study is to discuss how to improve the maneuverability of lifting and diving for underwater vehicle's vertical motion. Therefore, to solve these problems, applied the 3-D numerical simulation, Taguchi's Design of Experiment (DOE), and intelligent parameter design methods, etc. We planned four steps as follows: firstly, we applied the 2-D flow simulation with NACA series, and then through the Taguchi's dynamic method to analyze the sensitivity (β). Secondly, take the data of pitching torque and total resistance from the Taguchi orthogonal array (L9), the ignal-to-noise ratio (SNR), and analysis each factorial contribution by ANOVA. Thirdly, used Radial Basis Function Network (RBFN) method to train the non-linear meta-modeling and found out the best factorial combination by Particle Swarm Optimization (PSO) and Weighted Percentage Reduction of Quality Loss (WPRQL). Finally, the application of the above methods gives the global optimum for multi-quality characteristics and the robust design configuration, including L/D is 9.4:1, the foreplane on the hull (Bow-2), and position of the sail is 0.25 Ls from the bow. The result shows that the total quality is improved by 86.03% in comparison with the original design.

• Journal of Ocean Engineering and Technology
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• v.36 no.3
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• pp.161-167
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• 2022

Three-dimensional finite element analysis (3D-FEA) models have been used to evaluate the shock-resistance responses of various equipments, including armaments mounted on a warship caused by underwater explosion (UNDEX). This paper aims to check the possibility of using one-dimensional (1D) FEA models for the shock-resistance responses. A frigate was chosen for the evaluation of the shock-resistance responses by the UNDEX. The frigate was divided into the thirteen discrete segments along the length of the ship. The 1D Timoshenko beam elements were used to model the frigate. The explosive charge mass and the stand-off distance were determined based on the ship length and the keel shock factor (KSF), respectively. The UNDEX pressure fields were generated using the Geers-Hunter doubly asymptotic model. The pseudo-velocity shock response spectrum (PVSS) for the 1D-FEA model (1D-PVSS) was calculated using the acceleration history at a concerned equipment position where the digital recursive filtering algorithm was used. The 1D-PVSS was compared with the 3D-PVSS that was taken from a reference, and a relatively good agreement was found. In addition, the 1D-PVSS was compared with the design criteria specified by the German Federal Armed forces, which is called the BV043. The 1D-PVSS was proven to be relatively reasonable, reducing the computing cost dramatically.

• Journal of the Korean Geotechnical Society
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• v.26 no.3
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• pp.25-34
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• 2010

In the present paper, a numerical study was carried out to simulate ground expansion induced by an application of pulse discharge technology. Based on laboratory pulse discharge tests, the characteristics of shockwave were investigated, and then the laboratory tests were numerical1y simulated using underwater explosion model implemented in a coupled acoustic-structural finite element analysis. In addition, for clayey soils, the expansion of ground was also studied using soil properties obtained from empirical correlations with SPT N values. It was found that the calculation results well agreed with the field test results.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.45-50
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• 1997

Four different wedge angle absorptive tiles were designed and made, and the magnitudes of the reflected acoustic fields by the wedge shaped underwater sound absorptive tiles were measured. The minimum magnitude was found at the angle of 30$^{\circ}$ and the maximum of it was found at the wedge angle of 120$^{\circ}$ from measured the reflected acoustic fields at the front sides of the tiles. The fact that as wedge angle of the absorptive tile increases, the reflection coefficient is increasing is verified. The measured reflected acoustic fields were not dependent on the frequency in the range of 10kHz~30kHz used in this experiment for the same wedge angle tile. The measured reflected acoustic fields at the back sides of the tiles show that they are independent from both type of the absorptive tiles and the frequencies used in the experiments. The measured values and the computed values by the numerical model for the reflected acoustic fields of the wedge shaped absorptive tiles are fairly well comparable with one another.