• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.667-674
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• 2014

A ship's propulsion shafting system is subjected to varying magnitudes of intermittent loadings that pose great risks such as failure. Consequently, the dynamic characteristic of a propulsion shafting system must be designed to withstand the resonance that occurs during operation. This resonance results from hydrodynamic interaction between the propeller and fluid. For ice-class vessels, this interaction takes place between the propeller and ice. Producing load- and resonance-induced stresses, the propeller-ice interaction is the primary source of excitation, making it a major focus in the design requirements of propulsion shafting systems. This paper examines the transient torsional vibration response of the propulsion shafting system of an ice-class research vessel. The propulsion train is composed of an electric motor, flexible coupling, spherical gears, and a propeller configuration. In this paper, the theoretical analysis of transient torsional vibration and propeller-ice interaction loading is first discussed, followed by an explanation of the actual transient torsional vibration measurements. Measurement data for the analysis were compared with an applied estimation factor for the propulsion shafting design torque limit, and they were evaluated using an existing international standard. Addressing the transient torsional vibration of a propulsion shafting system with an electric motor, this paper also illustrates the influence of flexible coupling stiffness design on resulting resonance. Lastly, the paper concludes with a proposal to further study the existence of negative torque on a gear train and its overall effect on propulsion shafting systems.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.1
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• pp.43-52
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• 2006

Numerical model tests are done in order to evaluate impact zone of low salinity water on outer region of the developing Saemankeum reservoir. Also saline mixing processes are investigated f3r the inner reservoir with consideration of Mankyoung and Donjin riverine flood discharges when sea water is passing freely through gate. In these analyses 2-d ADCIRC, 3-d TIDED3D and CE-QUAL-ICM models are used. Through models tests, it is found that inner reservoir mixing process caused by inflow of outer sea water occurs gradually. It takes at least one month for complete mixing on Mankyoung part and 6 month on Dongjin part of the reservoir. When Sinsi or Garyeok gates are opened to control inner reservoir level, discharging velocities decrease exponentially from the gates, but show very strong currents of 0.5m/sec to the 10Km region apart. These results imply that hydrodynamic circulation and ecosystem of frontal region of the Saemankeum dike might be affected in amount by gate operations, since low saline inner waters are discharged periodically at ebb tide according to tidal level.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.537-543
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• 2017

Underwater glider is the long-term operating underwater robot that was developed with a purpose of continuous oceanographic observations and explorations. Torpedo-type underwater glider is not efficient from an aspect of maneuverability, because it uses a single buoyancy engine and motion controller for obtaining propulsive forces and moments. This paper introduces a ray-type underwater glider(RUG) with dual buoyancy engine, which improves the control performance of buoyancy and motion compared with torpedo-type underwater glider. Carrying out Computational Fluid Dynamics (CFD) analysis as static pitch drift test, the performance of fluid resistance for gliding motion was identified. Based on the calculated hydrodynamic coefficients, the dynamic simulation compared and analyzed the motion performance of torpedo-type and ray-type while controlling same volume of buoyancy engine. Small-sized model of RUG was developed to perform fundamental performance tests.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.4
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• pp.247-254
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• 2013

In this paper, dynamic response analysis of a heave compensation system is performed for offshore drilling operations based on multibody dynamics. With this simulation, the efficiency of the heave compensation system can be virtually confirmed before it is applied to drilling operations. The heave compensation system installed on a semi-submersible platform consists of a passive and an active heave compensator. The passive and active heave compensator are composed of several bodies that are connected to each other with various types of joints. Therefore, to carry out the dynamic response analysis, the dynamics kernel was developed based on mutibody dynamics. To construct the equations of motion of the multibody system and to determine the unknown accelerations and constraint forces, the recursive Newton-Euler formulation was adapted. Functions of the developed dynamics kernel were verified by comparing them with other commercial dynamics kernels. The hydrostatic force with nonlinear effects, the linearized hydrodynamic force, and the pneumatic and hydraulic control forces were considered as the external forces that act on the platform of the semi-submersible rig and the heave compensation system. The dynamic simulation of the heave compensation system of the semi-submersible rig, which is available for drilling operations with a 3,600m water depth, was carried out. From the results of the simulation, the efficiency of the heave compensation system were evaluated before they were applied to the offshore drilling operations. Moreover, the calculated constraint forces could serve as reference data for the design of the mechanical system.

• Journal of Korea Water Resources Association
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• v.48 no.1
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• pp.45-55
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• 2015

In this study, when seawall or harbor gate is installed for coastal disaster prevention, a two-dimensional water analysis in the bay is carried out to consider the flood amount of river inflow and effect of harbor gate. The Yeongsan river and the port Mokpo area are selcected for the study region. Then, by analyzing the hydraulic characteristics of flood flow of the Yeongsan river, we analysed the compatibility of the results in the two-dimensional hydrodynamic model. A tw-odimensional water analysis were conducted for the four cases considering whether a harbor gate is installed or not, and whether the inland water boundary condition is considered or not, also with open sea boundary condition. The results of the two-dimensional water analysis shows that water level change near the port Mokpo area is mainly caused by the discharge of the estuary barrage of the Yeongsan river because the harbor gate was installed. In addition, it is revealed that the volume of reservoir created by the harbor gate and the estuary barrage is too much small compared to the volume of the discharge from the Yeongsan river. Therefore, when the harbor gate is installed in the open sea, we concluded that a flexible management between the harbor gate and the estuary barrage of the Yeongsan river is required. A initial water level of the bay and outflow from the harbor gate are proposed for disaster prevention in the coastal area of port Mokpo.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4B
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• pp.343-352
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• 2011

The water quantity by intake station as well as the tributary flow discharge acting as sink or source were added to the main flow rate in the present study and RMA-2 and RMA-4 models were applied to the reach from Pal-dang dam to Jam-sil submerged weir to investigate the influence of water supply withdrawal on the river flow and water quality. The numerical results revealed that the water supply withdrawal from 5 intake stations located upstream of Jam-sil submerged weir changed the total flow rate and therby induced different hydraulic characteristics in terms of water surface elevation and velocity. The changed flow field by the inclusion of water intake quantity led to the variation of water quality. By the consideration of the water supply withdrawal, the velocity structure was significantly disturbed by the outflowing flow condition nearby Gu-ui, Ja-yang, and Pung-nap intake stations. Furthermore, the mean velocity was lowered by 25% and the stage upstream of Gu-ui station rose upto 1.5 cm compared with the result by exclusion of water intake. In case of no water withdrawal, the distribution of BOD concentration was parallel throughout the domain. However, when the water withdrawal is considered, the distribution of BOD concentration nearby the Gu-ui, Am-sa, and Ja-yang station was signifiantly changed. In addition, the BOD concentration including the intake stations showed higher value at the downstream of the reach due to the loss of the discharge by water withdrawal effect. It is concluded that both the inflow and outflow discharges from tributaries and water intake stations should be included in the numerical simulation to analyze the hydrodynamic behaviors and mixing characteristics more accurately.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.2
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• pp.151-158
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• 2016

Tidal farm is a multi-arrayed turbine system for utilizing tidal stream energy. For horizontal-axis turbine(HAT) system, it is recommended that each unit has to be deployed far apart in order to avoid hydrodynamic interference among turbines, as proposed by the European Marine Energy Centre(EMEC). But there is no rule for the arrangement of vertical-axis turbine(VAT) yet. Moreover it has been reported that a proper arrangement of adjacent turbines can enhance the overall efficiency even greater than an arrangement without mutual interference effect. This paper suggests the layout of VATs showing the better performances, which turned out to be quite different from HATs' arrangement. Numerical calculations were performed to investigate the performance variation in terms of the rotational direction as well as the distance between turbines. It has been shown that the best combination of rotational direction and distance between turbines can increase its performance higher about 9.2% than that of two independently operated turbines. It is likely that such improvement is due to the increased velocity between adjacent turbines. For diagonally arranged turbines, the maximum normalized mean power coefficient was obtained to be higher about 5.6% than that of two independent turbines. It is expected that the present results can be utilized for conceptual design of tidal farm to harness the tidal stream energy.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.4
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• pp.345-354
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• 2007

A sedimentation analysis has been attempted to figure out sedimentation environment due to construction of coastal jetties, such as fish harbor dike, flow guided dike and jetty in shallow Kusipo area, in which tidal range marks up to 6.6 meters in spring tide. As an initial approach of understanding field measurement were done on several stations along reference lines with total station and photo analysis taken by remote controlled small air craft far one and half years. Also numerical tests were done by 2-D ADCIRC model considering dry-wet treatment to evaluate flow and bottom shear stress variations. According to direct measurement, deposition seems to be dominant on Kusipo beach. Model results show bottom shear stress lessens to $0.10{\sim}0.15\;N/m^2$ on most shadow zone of jetties and the inner zone is suffering sedimentation as a result of dike construction. However this is the first approach with limited analysis, thus it should be dealt further considering physical characteristics of bottom sediments in a complete sediment model on upcoming study.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.5
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• pp.455-463
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• 2012

In this study, we calculate dynamic constrained force of tower top and blade root of a floating offshore wind turbine. The floating offshore wind turbine is multibody system which consists of a floating platform, a tower, a nacelle, and a hub and three blades. All of these parts are regarded as a rigid body with six degree-of-freedom(DOF). The platform and the tower are connected with fixed joint, and the tower, the nacelle, and the hub are successively connected with revolute joint. The hub and three blades are connected with fixed joint. The recursive formulation is adopted for constructing the equations of motion for the floating wind turbine. The non-linear hydrostatic force, the linear hydrodynamic force, the aerodynamic force, the mooring force, and gravitational forces are considered as external forces. The dynamic load at the tower top, rotor shaft, and blade root of the floating wind turbine are simulated in time domain by solving the equations of motion numerically. From the simulation results, the mutual effects of the dynamic response between the each part of the floating wind turbine are discussed and can be used as input data for the structural analysis of the floating offshore wind turbine.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.3
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• pp.151-164
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• 2013

Multidimensional dynamic water quality model of organic matter and trophic state was applied to the Han River system. The model was calibrated using field measurement data obtained during the year of 2007. The model results showed reasonable performance in predicting temporal variations of TN, TP, Chl-a and BOD concentrations. The applied integrated modeling system can be effectively used to simulate water quality as well as hydrodynamic and water temperature for river-lake continuous system in the Han River. Utilizing the calibrated model, we analyzed the spatial and temporal distributions of TN, TP, Chl-a and BOD concentrations in the Han River system. The temporal variations of water quality at each river reach and lake were effectively simulated with the developed model and spatial distribution of water qualities in the Han River system could be compared. The multidimensional dynamic modeling system can simulate the water qualities of entire waterbody where Lake Paldang and the incoming flows are included using single modeling system. So it can be effectively used for integrated water quality management of the Han River system.