• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.310-319
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• 2017

This paper introduces the method how to measure the thrust in impulse facility. In a Facility having such a short duration time of steady flow, there's no time to reach a steady state of the forces acting on model so that the test model vibrates until the end of the flow. The forces exerted on an engine exist with vibration so that the usual force balance can not be used. SWFB(Stress Wave Force Balance) technique is utilized in a shock tunnel to get the thrust. As an example, a model force balance has been calculated its strain against impulse force by using FEM(Finite Element Method). A transfer function between the impulse force and strain has been obtained by the way of de-convolution.

• Journal of Ocean Engineering and Technology
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• v.18 no.6 s.61
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• pp.16-21
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• 2004

This study presents the wave forces for spar platforms. The advantage of a spar platform is that it is easy to manufacture and has excellent to motion characteristics. It is important to precisely determine the wave force acting on spar platforms for their basic design of them. We measur the wave exciting force for both the classic spar and truss spar models, and accomplish the numerical calculation using diffraction theory. The results show that experimental values have good agreement with theoretical values. However it is difficult to accurately estimate the value considering the heave plate of truss spar due to the viscosity.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.261-266
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• 2002

This study presents the wave forces for spar platforms. The advantage of spar platform is that it is easy to manufacture and excellency to motion characteristics. It is important to estimate exactly wave force acting spar platforms for basic design of them. We measured the wave exciting force for classic spar and truss spar model, and accomplished the numerical calculation using diffraction theory. The results show that experimental values are good agreement with theoretical values. But it is difficult to estimate accurate value considering the heave plate of truss spar due to the viscosity.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.377-381
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• 2006

Recently, as economy grow and population increase we need to develop our coastal area and make good use of it for various purposes. That's why large structures are being installed on the sea. Some samples are petroleum storage tanks, pier of sea bridges. These are large structures which have been installed at coastal area. When we design such vertical cylinder, we should avoid too much construction expense caused by excessive designing or by lack of sufficient design. In order to prevent excessive expenditure, it is important to correctly calculate the force of waves acting on structures and predict the wave transformation. In this study, apply to VOF method based on Navier-Stokes equation and then discussed that nonlinear wave force and wave transformation. A comparison between the numerical model and existing experimental results showed nice agreement among them.

• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1067-1076
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• 2014

In this study, a series of hydraulic experiments are conducted to measure wave pressure on vertical structures with incident solitary waves that well represent characteristics of tsunamis. The pressure transducers measure time histories of wave pressure according to wave height to see pressure distribution. The force of incident solitary wave is estimated from integrated pressure distributions and represented with square and cylindrical columns. Experimental measurements are compared with the predictions of existing empirical formulas frequently used to design of coastal structures.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.530-541
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• 2019

To improve our current understanding of tsunami-like solitary waves interacting with a row of vertical slotted piles on a sloping beach, a 3D numerical wave tank based on the CFD tool $OpenFOAM^{(R)}$ was developed in this study. The Navier-Stokes equations were employed to solve the two-phase incompressible flow, combining with an improved VOF method to track the free surface and a LES model to resolve the turbulence. The numerical model was firstly validated by our laboratory measurements of wave, flow and dynamic pressure around both a row of piles and a single pile on a slope subjected to solitary waves. Subsequently, a series of numerical experiments were conducted to analyze the breaking wave force in view of varying incident wave heights, offshore water depths, spaces between adjacent piles and beach slopes. Finally, a slamming coefficient was discussed to account for the breaking wave force impacting on the piles.

• Journal of Ocean Engineering and Technology
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• v.21 no.1 s.74
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• pp.18-24
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• 2007

When the wind blows strong, most waves are breaking at sea. Breaking waves occur by exceeding the limitation of wave steepness (wave height/wave length = 1/7). Because a wave of single angular frequency couldn't generate the breaking phenomena at a two-dimensional ocean engineering basin, the breaking wave can be generated by the superposition of waves with various angular frequencies based on dispersion relation. This study investigates the particle kinematics in the breaking wave and the magnitude of the breaking wave exciting force at the breaking point and breaking region. We compare the regular wave load in a regular wave, which has same specifications (wave height, period and length), with the breaking waveload. Also, the experimental results of wave exciting force and particle velocity are investigated, by comparison with the analytic results using the potential theory.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.2
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• pp.292-301
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• 1994

The resultant cutting force during machining with a worn tool is viewed as a decomposition of the cutting force into a cutting force component related to chip removal from the workpiece and into a component dependent on the contact force between the tool flank's wear land and the workpiece. The shear line method, in which the cutting force is considered proportional to the length of the shear line, is used to calculate the cutting force component for the removal of the chip, while the elastic effect of the workmaterial on the tool is taken into consideration to analyze the effect of tool flank wear. The predicted resultant cutting force, expressed as the sum of both components, is compared to experimental data obtained during wave-on-wave cutting.

• Journal of Ocean Engineering and Technology
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• v.35 no.5
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• pp.347-359
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• 2021

This study aims to evaluate the dynamic responses of the jacket-type offshore wind turbine using FAST software (Fatigue, Aerodynamics, Structures, and Turbulence). A systematic series of simulation cases of a 5 MW jacket-type offshore wind turbine, including wind-only, wave-only, wind & wave load cases are conducted. The dynamic responses of the wind turbine structure are obtained, including the structure displacement, rotor speed, thrust force, nacelle acceleration, bending moment at the tower bottom, and shear force on the jacket leg. The calculated time-domain results are transformed to frequency domain results using FFT and the environmental load with more impact on each dynamic response is identified. It is confirmed that the dynamic displacements of the wind turbine are dominant in the wave frequency under the incident wave alone condition, and the rotor thrust, nacelle acceleration, and bending moment at the bottom of the tower exhibit high responses in the natural frequency band of the wind turbine. In the wind only condition, all responses except the vertical displacement of the wind turbine are dominant at three times the rotor rotation frequency (considering the number of blades) generated by the wind. In a combined external force with wind and waves, it was observed that the horizontal displacement is dominant by the wind load. Additionally, the bending moment on the tower base is highly affected by the wind. The shear force of the jacket leg is basically influenced by the wave loads, but it can be affected by both the wind and wave loads especially under the turbulent wind and irregular wave conditions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.613-619
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• 2017

Recently, the size of container ships has been progressively increasing, and much attention is required for safe navigation in shallow areas such as coastal waters and ports due to increases in draft. It is necessary to understand the characteristics of ship motion not only in still waters but also with waves. Especially in shallow regions, squat due to the vertical movement of the ship can be an important evaluation factor for the safe navigation, and wave drift force acting in the horizontal direction can have a great influence on the maneuverability of a ship. In this study, a numerical simulation using computational fluid dynamics has been performed for the wave exciting force acting in the vertical direction and the wave drift force acting in the horizontal direction for a very large container vessel sailing in shallow zone. As a result, it was found that total resistance in still waters greatly increased in shallow water. Wave drift force was shown to decrease given longer wavelengths regardless of water depth. It was observed that the wave exciting force in shallow water was considerably larger than at other water depths. As wave height against the central part of the ship lowered, the aft side rose.