• Journal of Navigation and Port Research
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• v.39 no.5
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• pp.385-391
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• 2015

In offshore, various external forces such as wind force, tidal current and impulsive breaking wave force act on offshore wind tower. Among these forces, impulsive breaking wave force is especially more powerful than other forces. Therefore, various studies on impulsive breaking wave forces have been carried out, but the soil reaction are incomplete. In this study, the p-y curve is used to calculate the soil reaction acting on the offshore wind tower when an impulsive breaking wave force occurs by typhoon. The calculation of offshore wind tower against impulsive breaking wave force is applied for the multi-layered soil. The results obtained in this study show that although the same wave height is applied, the soil reaction generated by impulsive breaking wave force is greater than the soil reaction generated by wave force.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.317-322
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• 2001

This study depicts an experimental work of the impulsive wave discharged from the open end of several kinds of right-angle bend pipes, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1.03 to 1.20 is employed to obtain the impulsive wave propagating outside the open end of the bend pipes. The experimental data of the magnitude of the impulsive wave and its propagation directivity are analyzed to characterize the impulsive waves discharged from the right-angle bend pipes and compared with those from a straight pipe. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulsive wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right angle miter bend pipe can playa role of passive control against the impulsive wave.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.355-360
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• 2001

This study addresses a computational work of the impulsive wave which is discharged from the open end of a pipe. An initial compression wave inside the pipe is assumed to propagate toward atmosphere. The over pressure and wave-length of the initial compression wave are changed to investigate the characteristic values of the impulsive wave. The second order total variation diminishing (TVD) scheme is employed to solve the axisymmetric, compressible, unsteady Euler equations. The relationship between the initial compression wave form and impulsive wave is characterized in terms of the peak pressure of the impulsive wave and its directivity. The results obtained show that for the initial compression wave of a large wave-length the peak pressure of the impulsive wave does not depend on the over pressure of the initial compression wave, but for the initial compression wave of a very short wave-length, like a shock wave, the peak pressure of the impulsive wave is increased with an increase in the over pressure of the initial compression wave. The directivity of the impulsive wave to the pipe axis becomes significant with a decrease in the wave-length of the initial compression wave.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.9
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• pp.406-413
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• 2001

The current study depicts and experimental work of the impulsive wave discharged from the exit of several kinds of right-angle bend pipes, which are attached to the open end of a simple shock tube. The weak normal shock wave with Mach number from 1.02 to 1.20 is employed to obtain the impulsive wave propagating outside the exit of the pipe bends. The experimental data of the magnitude of the impulsive wave and its propagation directivity are analyzed to characterize the impulsive waves discharged from the right-angle bend pipes and compared with those from a straight pipe. The impulsive waves are visualized by a Schlieren optical system. A computation work using the two-dimensional, unsteady, compressible Euler equation is also carried out to represent the experimented impulsive waves. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulsive wave and its directivity toward to the pipe axis, compared with the straight pipe. It is believed that the right angle miter bend pipe can play a role of passive control agianst the impulsive wave.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.06a
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• pp.253-254
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• 2014

In offshore, various external forces such as wind force, wave force and impulsive breaking wave force act on offshore structures. Many researches about this forces are published. Kim and Cao(2008) published researche on wave force of vertical cylinder. Kim and Go(2013) performed research on the subgrade reaction by external forces. Among this forces, impulsive breaking force is more massive than other forces, especially. Therefore, the studies about impulsive breaking wave forces have been carried out. Chun and Shim(1999) analyzed dynamic behavior of cylindrical pile subjected to impulsive breaking wave force. In this study, when the impulsive breaking wave force acts on the offshore wind turbine, the subgrade reaction acting on the mono-pile of the offshore wind turbine is calculated by p-y curve. The calculation is carried out to the multi-layered.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1595-1600
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• 2004

When a shock wave arrives at a duct, an impulsive wave is discharged from the duct exit and causes serious noise and vibration problems. In the current study, the characteristics of the impulsive wave discharged from a partial closed duct exit is numerically investigated using a CFD method. The Yee-Roe- Davis's total variation diminishing(TVD) scheme is used to solve the axisymmetric, unsteady, compressible Euler equations. With several partial closed duct exits, the Mach number of the incident shock wave $M_s$ and the distance L/D between the duct exit and a flat plate are varied in the range of $M_s$ = 1.01 ${\sim}$ 1.50 and L/D = 1.0 ${\sim}$ 4.0, respectively. The results obtained show that the magnitude of the impulsive wave impinging upon the flat plate strongly depends upon $M_s$, L/D and the partial closure of duct exit. The impulsive wave on the flat plate can be considerably alleviated by the partial closure of duct exit and, thus, the present method can be a passive control for the impulsive wave.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1095-1104
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• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.7
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• pp.850-856
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• 2004

When a shock wave arrives at the open end of a tube, an impulsive wave is discharged from the tube exit and causes serious noise and vibration problems. In the current study, the effect of the cross-sectional area of a circular tube on the impulsive wave is investigated using computational methods. Marten-Yee's TVD scheme was employed to solve axisymmetric, unsteady, compressible Euler equations. With a change in the cross-sectional area of the tube, the Mach number of an incident shock wave is varied between 1.01 and 1.50. The results obtained show that the magnitude of the impulsive wave strongly depends upon the Mach number of the incident shock wave and the cross-sectional area of the tube. It is also found that for a given cross-sectional area of the tube, the impulse wave has strong directivity to the tube axis.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.3
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• pp.175-181
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• 2015

In this study, two dimensional wave overtopping tests for vertical wall were performed and overtopping formulas were suggested for impulsive and non-impulsive wave conditions. The test results from this study were compared with those from EurOtop(2007). The wave overtopping formulas were derived and suggested considering the recent research trends, while the existing method used the diagram. The wave overtopping formulas have the form of exponential and power functions using non-dimensional variables for wave overtopping and freeboard heights for non-impulsive and impulsive condition, respectively. The wave overtopping formula and effective parameters for inclined superstructure were also suggested. It is analyzed that the locations of inclined superstructure do not have the significant effects on wave overtopping, that is, the wave overtopping rate were almost same for each locations.

• Journal of Mechanical Science and Technology
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• v.19 no.2
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• pp.605-617
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• 2005

A sudden discharge of mass flow from the exit of a duct can generate an impulsive wave, generally leading to undesirable noise and vibration problems. The present study develops an understanding of unsteady flow physics with regard to the impulsive wave discharged from a duct, using a numerical method. A second order total variation diminishing scheme is employed to solve three-dimensional, unsteady, compressible Euler equations. Computations are performed for several exit conditions with and without ground and wall effects under a change in the Mach number of an initial shock wave from 1.1 to 1.5. The results obtained show that the directivity and magnitude of the impulsive wave discharged from the duct are significantly influenced by the initial shock Mach number and by the presence of the ground and walls.