• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.191-196
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• 1998

A two-dimensional airfoil flying over a wavy wall is calculated by solving the unsteady Euler equation. Unsteady Transonic flow over an NACA00012 airfoil in pitching motion has been computed for code validation. Some numerical results for NACA6409 airfoil under different wave number, wave length, fly height are presented. The numerical results show the variation of lift and pitching moment coefficients are increased as wave length decrease.

• Kyungpook Mathematical Journal
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• v.18 no.2
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• pp.311-319
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• 1978

This paper deals with the evaluation of two definite integrals involving spheroidal wave function, H-function of two variables, and the generalized hypergeometric function. Also, an expansion formula for the product of generalized hypergeometric function and the H-function of two variables has been obtained. Since the H-function of two variables, spheroidal wave functions, and the generalized hypergeometric function may be transformed into a number of higher transcendental functions and polynomials, the results obtained in this paper include some known results as their particular cases. As an application of such results, a problem of heat conduction in a non-homogenous bar has been solved by using the generalized Legendre transform [9].

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.5 no.1
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• pp.14-21
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• 2002

In the present paper, the hydrodynamic properties of a Rahmen-type, flexible, porous breakwater interacting with obliquely or normal- incident small amplitude waves are numerically investigated. This system is composed of dual vertical porous membranes, hinged at the side edges of a submerged horizontal membrane. The dual vertical membranes are extended downward and hinged at seabed. The effects of permeability, Rahmen-type membrane breakwater geometry, pre-tensions on membranes, relative dimensionless wave number, and incident wave headings are thoroughly examined.

• The Journal of the Acoustical Society of Korea
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• v.3 no.2
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• pp.23-29
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• 1984

In this paper surface acoustic wave beam track changers using symmetric multistrip coupler are designed on the basis of the perturbation theory, and its characteristics are studied. SAW beam track changers, which have the configuratio of the periodic array of metal strips, are designed with the following specifications ; the number of strips : 140, the strip period: 0.25λ, the ratios of the strip width to the period a/p: 0.5, 0.375, 0.25, respectively, and approximately consistent with the theoretical values, and also the bulk wave mode and the 2nd-order effects are suppressed by these track changers.

• Journal of Power Electronics
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• v.5 no.4
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• pp.257-263
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• 2005

This paper describes the development and testing results of a high density High Voltage Power Supply (HVPS) that drives microwave Traveling Wave Tubes (TWTs) of phased array transmitters for airborne EW systems. The HVPS is designed to consist of a number of modules connected in series. Among them, especially, the high-density pulse transformer module including the resonant circuit is newly designed to make the HVPS much more reliable. In addition, this paper describes the development of high voltage solid-state modulation using fast switching devices (FETs) and also represents the test results of a modulator module.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.265-277
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• 2019

Using the measured data of waves and shore-line, we reviewed the grand circulation process and seasonal variation of beach cusp at the Mang-Bang beach from the perspective of trapped mode Edge waves known as the driving mechanism of beach cusp. In order to track the temporal and spatial variation trends of beach cusp, we quantify the beach cusp in terms of its wave length and amplitude detected by threshold crossing method. In doing so, we also utilize the spectral analysis method and its associated spectral mean sand wave number. From repeated period of convergence and ensuing splitting of sand waves detected from the yearly time series of spectral mean sand wave number of beach cusp, it is shown that the grand circulation process of beach cusp at Mang-Bang beach are occurring twice from 2017. 4. 26 to 2018. 4. 20. For the case of beach area, it increased by $14,142m^2$ during this period, and the shore-line advanced by 18 m at the northen and southern parts of the Mang-Bang beach whereas the shore-line advanced by 2.4 m at the central parts of Mang-Bang beach. It is also worthy of note that the beach area rapidly increased by $30,345m^2$ from 2017.11.26. to 2017.12.22. which can be attributed to the nature of coming waves. During this period, mild swells of long period were prevailing, and their angle of attack were next to zero. These characteristics of waves imply that the main transport mode of sediment would be the cross-shore. Considering the facts that self-healing capacity of natural beaches is realized via the cross-shore sediment once temporarily eroded. it can be easily deduced that the sediment carried by the boundary layer streaming toward the shore under mild swells which normally incident toward the Mang-Bang beach makes the beach area rapidly increase from 2017.11.26. to 2017.12.22.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.644-653
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• 1991

A wave instability problem is formulated for natural convection flows adjacent to a inclined isothermal surface in pure water near the density extremum. It accounts for the nonparallelism of the basic flow and temperature fields. Numerical solutions of the hydrodynamic stability equations constitute a two-point boundary value problem which are accurately solved using a computer code COLSYS. Neutral stability results for Prandtl number of 11.6 are obtained for various angles of inclination of a surface in the range from-10 to 30 deg. The neutral stability curves are systematically shifted toward modified Grashof number G=0 as one proceeds from downward-facing inclined plate(.gamma.<0.deg.) to upward-facing inclined plate (.gamma.>0.deg.). Namely, an increase in the positive angle of inclination always cause the flows to be significantly more unstable. The present results are compared with the results for the parallel flow model. The nonparallel flow model has, in general, a higher critical Grashof number than does the parallel flow model. But the neutral stability curves retain their characteristic shapes.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.695-705
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• 2014

In this paper, two types of techniques for the prediction of radiated sound pressure due to vibration of a structure are investigated. The prediction performance using wave-number sensing technique is compared to that of conventional prediction method, such as Rayleigh's integral method, for the prediction of far-field radiated sound pressure. For a coupled plate, wave-number components are predicted by the vibration response of plate and the prediction performance of far-field sound is verified. In addition, the applicability of distributed sensors that are not allowable to Rayleigh's integral method is considered and these can replace point sensors. Experimental implementation verified the prediction accuracy of far-field sound radiation by the wave-number sensing technique. Prediction results from the technique are as good as those of Rayleigh's integral method and with distributed sensors, more reduced computation time is expected. To predict the radiated sound by the efficient configuration of structural sensors, composed(synthesized) mode considering sound power contribution is determined and from this size and location of sensors are chosen. Four types of sensor configuration are suggested, simulated and compared.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.38-47
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• 2017

This paper presents experimental data on water droplet breakup in high-speed air flows. Exact-time-dependent evolution of wave and droplet interaction as well as breakup processes were optically visualized using a shadowgraph technique. Droplet experiments were conducted in a shock tube. Five flow conditions were used with an incident shock wave Mach number from 1.40 to 2.19 with Weber number based on the droplet initial diameter from 2300 to 38000, respectively. This corresponds to post-shock flow speeds varying from subsonic to supersonic. The considered droplet diameters were 2.0 mm to 3.6 mm. Some interesting wave patterns in the near wake were found. The present data shows that with an increase in the Weber number the droplet acceleration coefficient decreases and the level of decrease was weaker for the case of higher Mach numbers. This state of affair is different to the existing data in literature. Possible reasons are discussed.

• Advances in concrete construction
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• v.13 no.4
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• pp.327-337
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• 2022

This paper is concerned with the vibration analysis of middle layer cylindrical shell made of functionally graded material. The outer layers and inner layer are composed of functionally graded and isotropic material respectively. The Rayleigh Ritz method is applied to solve the presented shell dynamics equations. Two configurations are constructed with layers distributions. Fundamental natural frequencies of the three layered cylindrical shell is plotted against the circumferential wave number with different power law exponents. The frequency decreases with the increase of power law exponent. The fundamental natural frequencies first decreases and fall down to its minimum value, after frequencies increases with circumferential wave number. This is due to change in the magnitude of extensional and bending energies of the cylindrical shells. The computer software MATLAB has been employed for the computation of presented frequencies and tested the results obtained in order to assess the accuracy and validity of the cylindrical shell model for predicting the vibration frequencies of cylindrical shell.