• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.71-76
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• 2017

The roll damping problem in the design of ships and offshore structures remains a challenge to many researchers due to the fluid viscosity and nonlinearity of the phenomenon itself. In this paper, the study on viscous roll damping of a circular cylinder was carried out using forced oscillations. The roll moment generated by forced oscillation using a torque sensor was measured for each forced oscillation period and compared with the empirical formula. Although the magnitude of the measured torque from the shear force was relatively small, the results were qualitatively similar to those obtained from the empirical formula, and showed good agreement with the quantitative results in some oscillation periods. In addition, the flow around the circular cylinder wall was observed closely through the PIV measurements. Owing to the fluid viscosity, a boundary layer was formed near the wall of the circular cylinder, and a minute wave was generated by periodical forced oscillations at the free surface through the PIV measurement. In this study, the suitability of the empirical formula for the roll moment caused by viscous roll damping was verified by model tests. The wave making phenomenon due to the fluid viscosity around the wall of a circular cylinder was testified by PIV measurements.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.688-696
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• 2023

In the present study, free roll decay and resistance performances of fishing vessels were evaluated with the combinations and variations of in the parameters of appendages which are attached to improve motion performance of fishing vessels. Computational Ffluid Ddynamics was used to perform free roll decay and resistance analysis. The roll period and decay coefficient were derived by the variations in the combination and dimensions of the primary appendages of the bilge keel and the under keel. It was observed thatThe variations of in the length of the under keel did not significantly impact to the roll damping coefficient. Conversely, for the bilge keel, an increase in the length and angle resulted in an increase in the roll damping coefficient. Comparison of resistance performance was additionally assessed among the selected hulls with the appendages and bare hull. The resistance of the hull with the appendages was higher than that of the bare hull due owing to the changes of in the pressure on the surface of the hull and trim angle. Throughout the present study, the impact of appendage parameter and arrangement on the free roll decay and resistance performance of fishing vessels were was assessed,. which This will be beneficial for the application of appendages to fishing vessels.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.53 no.4
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• pp.337-348
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• 2017

The tension of warp from trawler and sea-floor contact can generate tilt and wake turbulence around otter boards. Preliminary measurements of otter board tilt and 3-D flow velocity during bottom trawl operations were taken using a vector instrument to investigate the effects of wake turbulence at the trailing edge of the otter board. Tilt data (i.e., yaw, pitch, and roll) at 1 Hz and flow data (velocities in the towing, lateral, and vertical directions) at 16 Hz were analyzed to determine their periods and amplitudes using global wavelet and peak event analyses. The mean period (${\pm}standard$ deviation) of the tilt from the peak event analysis ($5{\pm}2s$) was longer or double than that of flow velocity ($3{\pm}2s$). The two periods also had a significant linear relationship. The turbulence rate of flow was 30-50% at the trailing edge and was closely related to roll deviation. The frequency of phase difference ratios (i.e., peak time differences between tilts and flow periods) was significantly different from random occurrence in two trials, possibly due to side tidal effects. However, in the other trials, flow peaks were random, as shown by the even peak times between tilts and flows. Future studies should focus on reducing tilt variation, wake turbulence, and bottom contact to stabilize otter board motion.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7377-7384
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• 2015

Agricultural tractors must have a function of ROPS to protect drivers under roll-over accident. In this study, finite element analyses and an optimal design were performed to reduce the cost and the production period of the cabin frame of a tractor to pass the ROPS strength test. To confirm the pass of ROPS strength test of an initial design model, the results of deformation and principal strain from the analyses were evaluated. To reduce the weight of the cabin frame, design of experiment of Taguchi was implemented, and an optimal design was obtained. The weight of the optimal design model was reduced by 7% comparing with the initial design model.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.7
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• pp.1068-1079
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• 2008

Tilt and heading angles information of a remotely operated vehicle (ROV) are very important in underwater navigation. This paper presents a low.cost tilt and heading estimation system. Three single.axis rate gyros, a tri-axis accelerometer, and a tri-axis magnetometer are used. Output signals coming from these sensors are fused by two Kalman filters. The first Kalman filter is used to estimate roll and pitch angles and the other is for heading angle estimation. By using this method, we have obtained tilt (roll and pitch angles) and heading information which are reliable over long period of time. Results from experiments have shown the performance of the presented system.

• Journal of Navigation and Port Research
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• v.48 no.3
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• pp.155-163
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• 2024

As the demand for reducing carbon emissions increases, efforts to reduce the usage of fossil fuels and research on renewable energy are also increasing. Among the various renewable energy harvesting techniques, the floating offshore wind turbine has several advantages. Compared to other technologies, it has fewer installation limitations due to interference with human activity. Additionally, a large wind turbine farm can be constructed in the open ocean. Therefore, it is important to conduct motion analysis of floating offshore wind turbines in waves during the initial stage of conceptual design. In this study, a frequency motion analysis was conducted on a semi-submersible type floating offshore wind turbine. The analysis focused on the effects of varying trim on the motion characteristics. Specifically, motion response analysis was performed on heave, roll, and pitch. Natural period analysis confirmed that changing the trim angle did not significantly affect the heave and pitch motions, but it did have a regular impact on the roll motion.

• Journal of Fisheries and Marine Sciences Education
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• v.12 no.2
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• pp.199-212
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• 2000

It is very important to investigate the hull response of a fishing vessel in the sea to ensure the safe navigation and fishing operation in rough sea by preserving excellent sea keeping qualities. For this purpose, the author measured various responses of three stem trawlers in waves using real sea experimental measuring system. The author analyzed the experimental data using the statistical and spectral analyzing method to get the characteristics of the motion responses of the vessels according to the wave height and the ship's speed. The results obtained can be summarized as follows ; (1) Rather higher response of the pitch motion due to the wave height appeared in the head sea and the bow sea than any other wave direction without relevance to ship's size. In case of the roll motion, the beam sea and the quartering sea have a high response value. The period of peak of the pitch motion and the roll motion according to the wave height in each vessel has almost same value respectively. (2) The change of response of the pitch motions deeply depend on the ship's speed in the head sea and the bow sea, but not in the other wave direction. (3) The change of response of the roll motions in the beam sea, the quartering sea and the following sea are affected by the influence of the ship's speed in 5k't to 8k't, but not related to the ship's speed in out of that range.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.196-201
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• 2017

A cylindrical structure has a very long period of heave and pitch motion response in ocean waves. To obtain the dynamic stability of a cylindrical structure, it is necessary to obtain the suitable metacentric height (GM). However, in a structure with sufficient metacentric height, Mathieu instability can occur if the natural frequency of the heave motion is double the natural frequency of the roll and pitch motion. This study carried out numerical calculations and experiments for vertical-axis wind turbines with cylindrical floaters, which had three different centers of gravity. In the regular wave experiment, the divergence of the structure motion without yaw was observed when the natural frequency of the heave motion was double the natural frequency of the roll and pitch motion. In the irregular wave experiment, the motion spectra of the structures with the different centers of gravity were compared, and one was very high when the natural frequency of the heave motion was double the natural frequency of the roll and pitch motion.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.3
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• pp.116-127
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• 2024

The floating pier is a representative type of floating structure installed along the coast, primarily used as a facility for berthing and mooring ships. Additionally, ongoing attempts have been made to utilize it for various purposes, such as wave control and wave energy conversion structures. In this study, we experimentally investigated the reflection and motion characteristics of a pile-moored floating pier, which allows heave and limited roll motion, with respect to the presence of perforated structures and the attachment of submerged plates. The hydraulic experiment results indicated that the reflection and motion characteristics of the pile-moored floating pier were significantly influenced by the presence and installation depth of the submerged plates, rather than the presence of perforated structures on the floating body. In particular, the installation of submerged plates increased the reflection coefficient in short-period waves and effectively reduced the heave and roll motions of the floating body.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.26 no.2
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• pp.76-82
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• 2018

A test simulator is needed to develop a fuel quantity measurement system that takes into account the roll and pitch motion of the aircraft. In this paper, we develop a test simulator that consists of attitude simulation equipment, fueling equipment, and data storage equipment. The attitude simulation equipment simulates the aircraft attitude. It is manufactured to operate pitch angle and roll angle movement. The fueling equipment supplies fuel to the supplementary fuel tank. The data storage equipment collects and stores the measured data. We also develop an automation software that operates the test simulator and collects data automatically. The test simulator has been automated to prevent testers from being exposed to toxic fuel. Through automation software, the collection period is reduced by one quarter compared to manual collection. The developed fuel quantity measurement system is verified through the test simulator.