• Journal of the Society of Naval Architects of Korea
• /
• v.32 no.4
• /
• pp.48-54
• /
• 1995

A new propeller open water testing device is developed and tested in a tow tank. The devised dynamometer consists of a torque measuring part, a thrust measuring part and a driving motor with an RPM counter. Torque is designed to be measured directly from the torsion of the structure holding the motor by using strain gauges and, consequently, conventional slip ring is removed. Also, in order to make the device fit in relatively small model ships, the weight and the size of the whole integrated structure are reduced in various ways. The developed tester is proved to be easily utilized in small circulating water channel experiments and is believed to have provided us with essential information for future design of various types of conventional or object oriented force measuring device.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.2 s.140
• /
• pp.136-141
• /
• 2005

An experiment method has been developed to analyse the vibration characteristics of marine propeller blades, and vibration tests have been carried out on the model scale propeller in air and in water. The driving point transfer function(acceleration/excitation force) has been measured and modified by compensating the attachment effect of the impedance head. The measured natural frequencies in air have been compared with the theoretical results by an in-house FEM code PROSTEC. The added masses have been derived by comparing the measured natural frequencies in air and in water, and the results have been compared to the results using existing formula based on experience.

• Journal of the Society of Naval Architects of Korea
• /
• v.57 no.6
• /
• pp.345-352
• /
• 2020

This study aims to investigate the crabbing motion of the research vessel "NARA" by full-scale maneuvering trials. The crabbing test method refers to ITTC recommended procedures and guidelines. In order to minimize the fluctuation of the heading angle due to the external force acting on the hull during the pure lateral motion, the tests are conducted using the dynamic positioning system applied to the ship. The test results are analyzed by applying a low-pass filter to remove the noise included in the measurement data. Three conditions are set to define the steady state of crabbing motion. The index to be derived from the crabbing test is quantitatively presented. The ship is confirmed to be capable of the lateral motion of up to 0.844m/s in Beaufort 3.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.58 no.1
• /
• pp.68-74
• /
• 2022

This study analyzed the wake characteristics of the rim-driven propeller (RDP) used in an underwater robot. For underwater robots to perform specific missions, not only propulsion characteristics but also wake characteristics must be considered. In this study, a blade was designed based on NAC 0012 with a symmetrical cross-section. The RDP was hubless with three or four blades. The influence of both the free water surface and the bottom was considered, and the wake was measured using a particle image velocimetry in the advance ratio of 0.2 to 1. Model 1 showed symmetrical wakes in the entire advance ratio section. Model 2 showed asymmetric wakes due to the influence of the free water surface and the bottom at low advance ratio.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.59 no.1
• /
• pp.65-73
• /
• 2023

This study analyzed the duct characteristics of hubless rim-driven propeller (RDP) used in underwater robots. In the previous study, flow visualization experiments were performed with an advancing ratio of 0.2 to 1. The vortex at the front of the duct increased in strength while maintaining its size as the advancing ratio decreased. Therefore, it is necessary to study the optimization of the duct shape. Conventional propeller thrusters use acceleration/deceleration ducts to increase their efficiency. However, unlike conventional propellers, it is impossible to apply to airfoil acceleration/deceleration ducts due to the RDP structure. In this study, duct wake flow characteristics, thrust force, and efficiency according to the duct shape of RDP were analyzed using numerical analysis techniques. Duct design is limited and six duct shapes were designed. As a result, an optimized duct shape was designed considering duct wake flow characteristics, thrust force, and efficiency. The shape that the outlet width of the RDP was kept constant until the end of the duct showed higher thrust force and efficiency.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.60 no.1
• /
• pp.80-86
• /
• 2024

We analyzed the performance of hubless rim propellers based on the number of blades, maintaining a fixed pitch ratio and expanded area ratio, using computational fluid dynamics (CFD). Thrust coefficient, torque coefficient and efficiency according to the number of blades were analyzed. In addition, the pressure distribution on the discharge and suction sides of the blade was analyzed. As the advance ratio increases, the thrust coefficient decreases. The highest thrust was shown when the advance ratio was lowest. For the three, four, five and six-blades, the torque coefficient tended to decrease as the advance ratio increased. In the case of seven and eight-blades, the torque coefficient tended to increase as the advance ratio increased. The maximum efficiency was found when the advance ratio was 0.8. When the three-blade, it showed high efficiency at all advance ratios. A high pressure distribution was observed at the leading edge of the discharge blade, and a low pressure distribution was observed at the trailing edge. Applying a hubless rim-driven thruster with the three-blade can generate higher thrust and increase work efficiency.

• Journal of the Society of Naval Architects of Korea
• /
• v.61 no.4
• /
• pp.236-246
• /
• 2024

The present study aims to identify the effects of the oblique inflow and vertical acceleration on a marine propeller's hydrodynamic force and moment. Computational Fluid Dynamics analysis is performed for a rotating propeller in open water conditions with heave motion after performing validation against experiment in straightforward conditions. The oblique inflow results in a linear increase of the off-axial component of the hydrodynamic force and moment rather than the axial one. Pitch and yaw moments due to the hull motion are dominated by the heave force and the moment arm of the propeller location. Additionally, the vertical acceleration leads to a linear augmentation of off-axial hydrodynamic force and moment, implying the added mass and moment of inertia. Notably, it is found that the off-axial hydrodynamic force and moment are dominated by the oblique inflow velocity rather than the acceleration.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.4
• /
• pp.881-895
• /
• 2012

Micro-robots are utilized as useful tools in diagnosis and treatment of various human diseases. At present, lots of countries are developing and making many micro-robots. Government of S. Korea are trying to push ahead with the plan as technology policy, for the same reason. So this study examined about micro-robot technology development and trend of S. Korea, by using the method of SWOT(Strength-Weakness-Opportunity-Threat) analysis. As a result, the future policy for micro-robot of S. Korea is to further spur the development of new micro-robot technology and more improvement of the technology level of micro-robots registered by patent as 'micro-robot of bacterium base for lesion treatment' and 'micro-robot moved by compressive fluid'. Finally, It was already confirmed as high level, technology of 'micro-robot of bacterium base for lesion treatment' and 'micro-robot moved by compressive fluid' invented at S. Korea.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.6
• /
• pp.644-652
• /
• 2013

This paper describes the development and field experiments of Manta-type Unmanned Underwater Vehicle (UUV). Various simulations for Manta UUV are performed by using the nonlinear 6-DOF motion of equations. Through this simulation we verified the motion performances of Manta UUV. To acquire the blueprint of Manta UUV, it was designed with the simulation results. The Manta UUV uses a Doppler Velocity Log (DVL), gyrocompass, GPS, pressure sensor and other minor sensors, applied to measure the motion, position and path of Manta UUV. For its propulsion and changing a direction in the underwater, one vertical fin and four horizontal fins are installed at the hull of UUV. The Manta UUV system was verified with motion and autonomous navigation test at field.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.44 no.3
• /
• pp.239-249
• /
• 2008

Trawlers have to a sufficient towing force due to it's characteristics of the high performance. The newly constructed trawler with the conventional propellers shows the sufficient towing force, so that the propeller and engine are optimized. In the 1970s, many trawlers were imported from overseas by Korean fisheries industries. But the engine output degradation with year by year caused the trawlers to decrease the towing speed of the vessels. On the previous studies, the nozzle propeller had not so good efficiency with increasing of resistance in high-speed cruising operation over 15knots. But the trawling operation is just required the higher thrust and towing force, so that the nozzle propeller is very profitable for the it's effectiveness. A new nozzle propeller was designed for the 4,462G/T trawler, Dong-San, operated by Dongwon Industries Co., Ltd. to improve the towing speed, and the model tests were performed. The model ship and model propeller are preciously manufactured and used model tests in basin. The resistance test and propeller open water test were performed for the cases of the half and full loads. The required engine horse power and RPM were evaluated analytically by the speed-power curve, when the trawler was equipped with the nozzle propeller. The results of tests showed that the towing speed 4.85knots on the design load waterline requires the 200 engine RPM and 2,567ps in the delivered horsepower.