• Journal of Ship and Ocean Technology
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• v.8 no.1
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• pp.31-41
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• 2004

A ducted marine propulsor has been widely used for the thruster of underwater vehicles for protecting collision damage, increasing propulsive efficiency, and reducing cavitation. Since a single-stage ducted propulsor contains a set of rotor and stator inside an annular duct, the numerical analysis becomes extremely complex and computationally expensive. However, the accurate prediction of viscous flow past a ducted marine propulsor is essential for determining hydrodynamic forces and the propulsive performances. To analyze a ducted propulsor having rotor-stator Interaction, the present work has solved 3D incompressible RANS equations on the sliding multiblocked grid. The flow of a single stage turbine flow was simulated for code validation and time averaged pressure coefficients were compared with experiments. Good agreement was obtained. The hydrodynamic performance coefficients were also computed.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.139-143
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• 2001

Ring-stiffened cylinders are widely used as the pressure hull of submarines and underwater vehicles. For large ring-stiffened cylinders cylindrical shells are fbricated by cold rolling of flat plates and then welding of curved shells. After forming cylinders ring-stiffeners are welded on th the cylinders. Due to these cold roiling and welding initial shape imperfections and residual stresses exists in fabricated ring-stiffened cylinders. It is well known that the initial shape and material imperfections affect the ultimate strength of ring-stiffened cylinders significantly. In this paper previous researches on the effects of initial shape imperfections and residual stresses are briefly reviewed Recently a numerical analysis computer program was developed to predict the ultimate strength of ring-stiffened cylinders subjected to hydrostatic pressure, which is based on the Dynamic Relaxation technique. This program was employed to numerically investigate those effects. The numerical predictions were substantiated with relevant experimental results.

• Journal of Ocean Engineering and Technology
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• v.21 no.1 s.74
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• pp.69-74
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• 2007

This paper is concerned about the dynamic analysis of an underwater test miner, which operates on cohesive soil. The test miner consists of tracked vehicles and a pick-up device. The motion of the pick-up device, relative to the vehicle chassis, is controlled by two pairs of hydraulic cylinders. The test miner is modeled by means of commercial software. A terramechanics model of cohesive soft soil is implemented with the software and applied to a dynamic analysis of the test miner model. The dynamic responses of the test miner are studied with respect to four different types of terrain conditions.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1994.11a
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• pp.14-16
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• 1994

The development of proton exchange membrane fuel cells(PEMFCs) with high energy efficiencies and high power densities is gaining momentum because their performance characteristics are attractive for terrestrial(power sources for electrical vehicles, stand-by power), space and underwater application[1]. Fuel cells are capable of running on non-petroleum fuels such as methanol, natural gas or hydrogen and also have major impact on improving air quality. They virtually eliminate particulates, NO$_{x}$, SO$_{x}$, and significant reduce hydrocarbons and carbon monoxide. Especially, fuel cell-battery hybrid power sources appear to be well suited to overcome both the so-called battery problem(low energy density) and the fuel cell problem(low power density)[2].[2].

• IEMEK Journal of Embedded Systems and Applications
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• v.6 no.3
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• pp.124-131
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• 2011

There are many researches in unmanned vehicles such as UGV(Unmanned Ground Vehicle), AUV(Autonomous Underwater Vehicle). In these researches, differential wheeled mobile robots are mainly used to develop the experimental stage algorithm because of the simplicity of modeling and control. Usually a commercial product used in the study, but in order to operate a commercial product to the restrictions because there would need to use a fixed protocol. Using the microprocessor makes the internal sensors(encoder and INS) and external sensors(ultrasonic sensors, infrared sensors) operate and to determine commands for robot operation. This paper propose a mobile robot design for suitable purpose.

• The Journal of Korea Robotics Society
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• v.17 no.2
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• pp.110-117
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• 2022

This paper describes a localization algorithm utilizing relative observations for multiple autonomous underwater vehicles (Multiple-AUVs). In order to maximize the efficiency of operation and mission accomplishment and to prevent problems such as collision and interference, the locations and directions of Multiple-AUVs must be precisely estimated. To estimate the locations and directions, we designed a localization algorithm utilizing relative observations and verified it with simulations based on sensor data sets acquired through real sea experiments. Also, an optimal combination of relative observation information for efficient localization is figured out through combining various relative observations. The proposed method shows improved localization results compared to those only using the navigation algorithm. The performance of localization is improved up to 58% depending on the combination of relative observations.

• The Journal of the Acoustical Society of Korea
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• v.32 no.4
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• pp.317-328
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• 2013

In this paper, the optimization has been performed to design a multi-layer structure that is used as a structure for noise reduction of acoustic sonar sensors in underwater vehicles. Two design goals are considered to reduce self-noise from own machineries and to enhance acoustic signals detected from outside. Both distinct and continuous design parameters have been used such as selection of material properties of each layer and thickness of each layer, respectively. The sensitivity of design parameters has been analyzed and the evolutionary algorithm has been implemented for design optimization. For design optimization process, each of the design goals and the two combined design goals have been considered to analyze the achievement of those design goals.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.53-59
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• 2018

In this study, a new design method is developed to optimize the structure of an underwater sparse array sensor. The purpose of this research is to design the structure of a sparse array that has the performance equivalent to a fully sampled array. The directional factor of a sparse planar array is derived as a function of the structural parameters of the array. With the derived equation, the structure of the sparse array sensor is designed to have the performance equivalent to that of the fully array sensor through structural optimization of the number and location of transmitting and receiving elements in the array. The designed sparse array sensor shows beam patterns very close to those of the fully array sensor in terms of PSLL (Peak Side Lobe Level) and MLBW (Main Lobe Beam Width), which confirms the effectiveness of the present optimal design method. Further, the validity of the analytic beam patterns is verified by comparing them with those from the FEA (Finite Element Analysis) of the optimized sparse array structure.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1575-1580
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• 2010

Recently, the development of bio-mimetic underwater vehicles that can emulate the characteristic movements of marine fish and mammals has attracted considerable attention. In this study, the motion of the batoid (i.e., cownose ray) fin that facilitates excellent cruising and maneuvering during underwater movement has been studied. The velocity achieved and distance covered with each fin movement are numerically studied. A fluid-structure interaction method is used to perform 3D time-dependent numerical analysis, wherein an adaptive mesh is employed to account for the large deformation of a fin interacting with a fluid. The results of a preliminary study show that the thrust of a ray fin is highly dependent on the frequency. Further, once the fin amplitude required for generating a given thrust is evaluated for the conditions experienced by an actual ray, the frequency and amplitude values for achieving better thrust are determined.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.352-360
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• 2019

This paper proposes a docking assessment algorithm for an autonomous underwater vehicles (AUVs) with sensor uncertainties. The proposed algorithm consists of two assessments, state assessment and probability assessment. The state assessment verifies the reachability by comparing forward distance to the docking station with expected distance to reach same depth as the docking station and necessity for correcting its route by comparing calculated inaccessible areas based on turning radius of the AUV to position of the docking station. When the AUV and the docking station is close enough and the state assessment is satisfied, the probability assessment is conducted by computing success probability of docking based on the direction angle, relative position to the docking station, and sensor uncertainties of the AUV. The final output of the algorithm is decided by comparing the success probability to threshold whether to try docking or to correct its route. To verify the validation of the suggested algorithm, the scenario that the AUV approaches to the docking station is implemented through Matlab simulation.