• Journal of Korean Society of Steel Construction
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• v.13 no.6
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• pp.651-659
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• 2001

The main purpose of this paper is to present an analytical method for free vibration of stepped horizontally curved members on two-parameter elastic foundation. The ordinary differential equations governing the free vibration of such beams are derived as non-dimensional forms including the effects of rotatory inertia and shear deformation. The governing equations are solved numerically for the circular, parabolic, sinusoidal and elliptic curved beams with hinged-hinged, hinged-clamped and clamped-clamped end constraints. As the numerical results, the lowest four natural frequency parameters are presented as the functions of various non-dimensional system parameters. Also the typical mode shapes are presented.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.673-682
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• 1997

The main purpose of this paper is to investigate the effects of rotatory inertia and shear deformation on the natural frequencies of arches with variable curvature. The differential equations are derived for the in-plane free vibration of linearly elastic arches of uniform stiffness and constant mass per unit length. The governing equations are solved numerically for parabolic, circular and elliptic geometries with hinged-hinged, hinged-clamped and clamped-clamped end constraints. For each cases, the four lowest frequency parameters are presented as functions of the two dimensionless system parameters; the arch rise to span length ratio, and the slenderness ratio.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.3
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• pp.478-491
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• 2013

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.5
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• pp.614-620
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• 1998

In this paper, we analyze theoritically the propagation and radiation characteristics for elliptical corrugated waveguides. The solutions of wave equations in an elliptic cylinder system are obtained in terms of Mathieu functions of 1st and 2nd kind. The electromagnetic fields in the elliptical corrugated waveguide can be represented by series and products of angular and radial Mathieu functions. By using impedence matching at the boundary between the inner region and the slot region, characteristic equations are derived. Then the characteristic equation is solved for $HE_{11}$ mode which is dominant mode in the elliptical corrugated waveguide and the fields in the aperture is calculated. And the propagation pattern for the elliptical corrugated waveguides is calculated through the field equivalence principle.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.991-998
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• 1989

This investigation was carried out for the purpose of studying the turbulent flow and mixing characteristics after collision of two jets depending upon the cross angle variations. For effectuating this experimental study, a subsonic wind tunnel and a constant temperature type two channel hot-wire anemometer system have been utilized. The jets issuing from two nozzles have same Reynolds numbers and their cross angle was variable. After collision of two jets, the cross section of the mixing flow, mean and fluctuating velocities and Reynolds stresses have been measured, and analyzed comparing them with semi-empirical equations. It was found that the nondirectional contour of the cross section agreed well with an elliptic formula and the mean velocities along the centerline had a good similarity independent of cross angle variations. The distributions of U over bar-components measured in the Y direction have a good similarity and agree well with semi-empirical equations of Hinze and Gortler. The Reynolds stresses of u'v' over bar on the Y axis show a similar distributions and their agreement with the theoretical curve is remarkable but those of u'w' over bar measured along the Z axis are randomly scattered.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.4
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• pp.19-30
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• 2000

A finite-volume method is developed to solve turbulent flows around modern commercial hull forms with bow and stern bulbs. The RANS equations are solved. The cell-centered finite-volume method employs QUICK and central difference scheme for convective and diffusive flux discretization, respectively. The SIMPLEC method is adopted for the velocity-pressure coupling. The developed numerical methods are applied to calculate turbulent flow around KRISO 3600TEU container ship. Surface meshes are generated into five blocks: bow and stern bulbs, overhang, fore and afterbody. 3-D field grid system with O-H topology is generated using elliptic grid generation method. Surface friction lines and wake distribution at propeller plane is compared with experiment. The calculated results show that the present method can be used to predict flow around a modern commercial hull forms with bulbs.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.23 no.2
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• pp.65-92
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• 2019

We survey a recently developed immersed finite element method (IFEM) for the interface problems. The IFEM uses structured grids such as uniform grids, even if the interface is a smooth curve. Instead of fitting the curved interface, the bases are modified so that they satisfy the jump conditions along the interface. The early versions of IFEM [1, 2] were suboptimal in convergence order [3]. Later, the consistency terms were added to the bilinear forms [4, 5], thus the scheme became optimal and the error estimates were proven. For elasticity problems with interfaces, we modify the Crouzeix-Raviart based element to satisfy the traction conditions along the interface [6], but the consistency terms are not needed. To satisfy the Korn's inequality, we add the stabilizing terms to the bilinear form. The optimal error estimate was shown for a triangular grid. Lastly, we describe the multigrid algorithms for the discretized system arising from IFEM. The prolongation operators are designed so that the prolongated function satisfy the flux continuity condition along the interface. The W-cycle convergence was proved, and the number of V-cycle is independent of the mesh size.

• Journal of Yeungnam Medical Science
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• v.39 no.2
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• pp.98-107
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• 2022

Background: Stroke patients usually experience damage to multiple functions and a long rehabilitation period. Hence, there is a large volume of patient clinical information. It thus takes a long time for clinicians to identify the patient's information and essential pieces of information may be overlooked. To solve this, we stored the essential clinical information of stroke patients in a blockchain and implemented the blockchain technology using the Java programming language. Methods: We created a mini blockchain to store the medical information of patients using the Java programming language. Results: After generating a unique pair of public/private keys for identity verification, a patient's identity is verified by applying the Elliptic Curve Digital Signature Algorithm based on the generated keys. When the identity verification is complete, new medical data are stored in the transaction list and the generated transaction is verified. When verification is completed normally, the block hash value is derived using the transaction value and the hash value of the previous block. The hash value of the previous block is then stored in the generated block to interconnect the blocks. Conclusion: We demonstrated that blockchain can be used to store and deliver the patient information of stroke patients. It may be difficult to directly implement the code that we developed in the medical field, but it can serve as a starting point for the creation of a blockchain system to be used in the field.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.5
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• pp.1687-1707
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• 2022

With the development of multiuser online meetings, more group-oriented technologies and applications for instance collaborative work are becoming increasingly important. Authenticated Group Key Agreement (AGKA) schemes provide a shared group key for users with after their identities are confirmed to guarantee the confidentiality and integrity of group communications. On the basis of the Public Key Cryptography (PKC) system used, AGKA can be classified as Public Key Infrastructure-based, Identity-based, and Certificateless. Because the latter type can solve the certificate management overhead and the key escrow problems of the first two types, Certificateless-AGKA (CL-AGKA) protocols have become a popular area of research. However, most CL-AGKA protocols are vulnerable to Public Key Replacement Attacks (PKRA) due to the lack of public key authentication. In the present work, we present a CL-AGKA scheme that can resist PKRA in order to solve impersonation attacks caused by those attacks. Beyond security, improving scheme efficiency is another direction for AGKA research. To reduce the communication and computation cost, we present a scheme with only one round of information interaction and construct a CL-AGKA scheme replacing the bilinear pairing with elliptic curve cryptography. Therefore, our scheme has good applicability to communication environments with limited bandwidth and computing capabilities.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.1 no.1
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• pp.22-30
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• 1989

Wave propagation is changed by the effect of shoaling, current-depth refraction and shelter-ing etc. To solve these problems. numerous models have been developed. In the present study, a coordinate system is proposed based on the wave ray equation with the wave number equation including diffraction effects . The governing equation for the study was derived from the mild slope wave equation in non-steady state, including current effects (Kirby, 1986a) and trans-formed into an orthogonal curvilinear coordinate system on the basis of the wave ray equation. To obtain a numerical solution, an explicit finite difference scheme was used, and solved by the relaxation method. This model was tested for various cases: Firstly a submersed circular shoal and a constant unit depth. Secondly a submerged elliptic shoal on a slope, and finally a breakwater harbour with obliquely incident waves on a slope. The model was found to simulate the experimental results and other theoretical results in wave height and wave angle fairy well, and the applicability of the model around an arbitrary shaped coastal structure was also verified. To demonstrate the general usefullness of the present approach , the model is to be applied to a field situation with a complex bed topography.