• Journal of the Korean Society for Precision Engineering
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• v.16 no.6
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• pp.166-175
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• 1999

This paper describes a design and performance evaluation of robust controller which overrides unstable motion and pulls out quickly after water entry of underwater vehicle dropped from aircraft or surface ship. We use 6-DOF equation for model of motions and assume parameter uncertainty to reflect the difference of real motion from modelled motion equation. we represent a nonlinear system with uncertainty as Takagi and Sugeno's(T-S) fuzzy models and design controller stabilizing them. The fuzzy controller utilizes the concept of so-called parallel distributed compensation (PDC). Finally, we confirm stability and performance of the controller through computer simulation and hardware in the loop simulation (HILS).

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.1
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• pp.3-10
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• 2003

Oil drop formation during the underwater oil discharge is investigated experimentally. The focus is placed on the size of the drops formed with the variation of discharge speed and nozzle diameter. As the Reynolds number based on the nozzle diameter increases, the droplet size decreases first and then increases until an explosive atomization occurs. The length of the jet attached to the nozzle Increases with the Reynolds number and then decreases. The transition occurs when the flow becomes asymmetry.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.77-89
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel that allows tunnel segments to float underwater by buoyancy, and is being actively studied in recent years. When the submerged floating tunnel is connected to the ground, the tunnel and the bored tunnel inside the ground must be connected. There is risk that the stress will be concentrated at the connection between the two tunnels due to the different constraints and behavior of the two tunnels. Therefore, special design and construction methods should be applied to ensure the stability around the connection. However, previous studies on the stability at the connection site have not been sufficiently carried out, so study on the basic stage of the stability at connection site are necessary. In this study, numerical analysis simulating the connection between submerged floating tunnel and the bored tunnel confirmed that the shear strain concentration occurred in the ground around the connection, and it was analyzed that the structural factors can be handled during construction to have effects on the stability of the ground around the connection. Numerical results show that the risks from disproportionate displacements in the two tunnels can be mitigated through the construction of grouting material and joint design. Although the results from this study are qualitative results, it is expected that it will contribute to the determination of structural factors and risk areas that should be considered in the design of connections between the submerged floating tunnel and bored tunnel in the future studies.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.243-250
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• 2014

Fiber-optic cables towed by underwater vehicles have an important role in enhancing the mission capability of a mother ship. In general, fiber optic cables are unwound in water for securing unwinding stability and preventing unwinding-related problems. Therefore, in this study, the numerically simulated result is verified against the experimental result in water, and the cable-unwinding motion is predicted based on the increase in unwinding velocity. The experimental apparatus is composed of a water tank and a winder, and a high-speed camera is used for photographing the cable-unwinding motion. The numerical result defined in the Cartesian coordinate system is solved using a transient-state unwinding equation of motion. The numerical result agrees well with the experimental result, and it can predict cable-unwinding behaviors in according to an increase in the unwinding velocity.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.1
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• pp.25-33
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• 2020

In this study, parametric analyses are performed using the coupled Eulerian-Lagrangian scheme for the collision behaviors of a vessel and an underwater slope that constitutes part of an artificial protective island. The vessel parameters considered in the analysis are bow angle, stem angle, draft, and impact velocity. The gradient of the slope, the friction coefficient between the bow and the slope, and soil strength are considered as parameters of the slope. For each parameter, the dissipated collision energy and the collision force are estimated from the behavior of the vessel, and the energy dissipation mechanism is identified in terms of the ground deformation. The collision force is assumed as an exponential function, and the effects of the parameters are estimated. As a result, only two parameters, the gradient of the slope and the friction coefficient between the vessel and the soil, can affect the exponential coefficient of the function. The dissipated energy by the soil can thus be estimated adequately. The relationship between the volume of the soil pushed out by the bow and the dissipated collision energy is estimated as a linear function. This relationship is independent of the magnitude of the collision energy, and affected more by the friction coefficient and the soil strength than by the parameters of the vessel.

• Journal of Conservation Science
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• v.29 no.4
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• pp.421-435
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• 2013

The purpose of this study is to suggest environmental guidelines for the conservation of ceramics excavated from underwater. Accordingly, the conditional change of the soluble salt on surface of the excavated ceramics was examined by changing the relative humidity. Examining the relative ratio [high humidity(RH70%+RH80%)/low humidity(RH20%+ RH40%)] for 24 weeks using accumulated conductivity(${\mu}s/cm$), the result showed that the amount of ion elution increased more in high humidity than in low humidity. In particular, the ion elution increased significantly within the celadon sample. In addition, comparing the accumulated conductivity and physical characteristics of the samples in high humidity, the results indicated that the amount of the ion elution is proportioned to the increased rate of the sample's absorption capacity and porosity. Ceramics excavated from underwater has risks of the secondary physical and chemical attacks from remaining salts. Therefore, it is suggested these ceramics be stored in a storage which maintains proper temperature and low humidity conditions. Also, the collections need to be pre-classified according to the properties of the materials.

• Resources Recycling
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• v.14 no.6 s.68
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• pp.60-63
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• 2005

It was possible to understand the adsorption characteristics of ions in aqueous environment based on the variations of PZC and IEP of particles when adsorption of ions on particle surface occurred. The specific adsorption of $Cu^{2+}$ ion upon chalcopyrite surface provoked a lowered PZC, which was considered to be due to increased adsorption of OH- ion via the electrostatic attraction between the two ions. On the contrary, IEP of chalcopyrite was observed to rise when Cu2+ was specifically adsorbed on its surface. The reason for this could be explained by the necessity of the increase of pH to offset the positively increased surface potential of chalcopyrite for the reestablishment of IEP. Neither PZC or IEP of chalcopyrite was observed to change when non-specific adsorption occurred since no change in the surface potential of chalcopyrite was invoked under this condition.

• Korean Chemical Engineering Research
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• v.44 no.2
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• pp.172-178
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• 2006

Mesoporous silicate materials have been used as adsorbents for the removal of heavy metals from water by introducing functional groups such as thiol and amine. In this research, it was investigated whether surfactants used as templating agents in synthetic processes can act as adsorption sites for heavy metals. Three mesoporous silicates-SBA-15, MCM-41, and HMS were synthesized using, respectively, block copolymer, hexadecyltrimethylammoniumbromide (HDTMA), and dodecyamine as surfactants. X-ray diffraction and $N_2$ gas adsorption analysis confirmed that the mesoporous silicates were well prepared and FT-IR spectra resulted in the existence of the surfactants in as-synthesized mesoporous silicates and the removal of surfactants after calcination. The interactions between $Pb^{2+}$ ions and the mesoporous silicate materials with/without surfactants were observed. In adsorption kinetic experiments, it revealed that the calcined mesoporous silicates and the surfactant-loaded SBA-15 almost had no adsorption capacity for $Pb^{2+}$ ions. In contrast, the surfactant-loaded MCM-41 and HMS showed, respectively, the adsorption capacities of 26.60 and 115.16 mg/g which were acquired through the fits of adsorption kinetic data to the pseudo second order kinetic model. The adsorption capacities were comparable to those of other mesoporous adsorbents for heavy metals.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.9
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• pp.763-771
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• 2014

As a preliminary study on the spray behavior characteristics of emulsified fuel, the fuel properties (viscosity, surface tension, and density) and evaporation characteristics of a fuel droplet were investigated. The emulsified fuel was made by mixing diesel and $H_2O_2$. In addition, the macroscopic spray behavior characteristics such as the spray penetrations and spray angles of the emulsified and diesel fuels were compared. The stirring condition of the emulsified fuel was a 9:1 mixture of the diesel fuel and the surfactant span 80. The mixing ratios for the hydrogen peroxide were set at EF2, EF12, EF22, EF32, EF42, EF52, EF62, EF72, EF82, and EF92. The injection pressures were set at 400, 600, 800, and 1000 bar. We found that as the mixing ratio of the hydrogen peroxide was increased from EF2 to EF52, the viscosity of the emulsified fuel increased. However, afterward, the viscosity of the emulsified fuel gradually decreased and approached the viscosity value of the diesel fuel. Therefore, generally oil-in-water emulsions were used for the hydrogen peroxide mixing ratios up to 52 (EF52), and water-in-oil emulsions were used for the hydrogen peroxide mixing ratios above 52. Finally, the spray behavior characteristics (spray penetration and spray angle) of the emulsified fuel were found to be almost independent of the mixing ratio.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1999.06a
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• pp.287-292
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• 1999

도시화 및 산업화가 급속히 진행되어감에 따라 하천에는 수중구조물이 상당수 설치되어 있어서 교량에서의 세굴에 대한 안전성 여부 및 그에 대한 대책 수립이 매우 절실한 실정이다. 국내의 경우 성수대교 및 행주대교 붕괴사고 이후 특히 하천의 교각에 대한 세굴의 영향은 많은 학자들의 관심이 되어 왔다. 연구의 주된 관점은 세굴에 영향을 미치는 인자들의 역학적 거동에 대한 것으로써 세굴을 일으키는 인자들의 최대 영향 및 최대 세굴심도를 예측하고 세굴로부터 보호하는 공법에 주력하고 있다. 그동안의 조사결과에 의하면 교각이나 교대의 하부구조가 세굴로 인한 위험성이 상당히 내재되어 있는 것으로 알려지고 있다. (중략)