• ETRI Journal
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• v.32 no.3
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• pp.362-369
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• 2010

While the elliptic curve cryptosystem (ECC) is getting more popular in securing numerous systems, implementations without consideration for side-channel attacks are susceptible to critical information leakage. This paper proposes new power attack countermeasures for ECC over Koblitz curves. Based on some special properties of Koblitz curves, the proposed methods randomize the involved elliptic curve points in a highly regular manner so the resulting scalar multiplication algorithms can defeat the simple power analysis attack and the differential power analysis attack simultaneously. Compared with the previous countermeasures, the new methods are also noticeable in terms of computational cost.

• Transactions of the Korean Society of Mechanical Engineers
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• v.1 no.2
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• pp.65-72
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• 1977

Major problems in the design and use of refief valve are (a) chattering because of instability, (b) excessive pressure differential which makes the valves crack far below maximum pressure diminishing useful flow in the system. In this study, A magnet-coupled relief valve is investigated theoretically and experimentally in order to improve the performance of a conventional direct type reliefvalve. A theory is developed to predict the performance, response, and stability of the magnet-coupled valve taking into account the delivery line response. In the experiment, a typical magnet-coupled relief valve is designed on the basis of the analytical results; the discharge rates are measured varying the supply pressure, and both the pressure-time curves and valve displacament-time curves are recorded providing the supply pressures greater than the setting pressure. The measured override characteristic curves are then compared with those of conventional pilot type and direct type releif valves. It is showm that the excessive pressure differential of a magnet-coupled relief valve becomes less than that of a conventional direct type valve. It is also shown that the most important chatacteristic of a magnet-coupled relief valve is to eliminate valve chattering due to instability regardless of the magnitude of setting pressures and discharge rates, which suggests wide applications of the idea of the use of a magnet in the design of hydraulic valves.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.9
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• pp.86-94
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• 2008

A total stroke of an opening or closing motion of a hinge mechanism in a folder-type mobile phone is composed of two portions. In the first portion, human fingers act a force to open or close the folder. In this portion, the rotating folder compresses the coil spring installed in the mechanism. In the last portion, this compressed coil spring generates a torque to rotate the folder. The main merit of this study is that we have designed a hinge mechanism to be operated by a uniform torque in the first portion of the total stroke. The uniform torque means that it is constant along the folder's swing angle. This mechanism will give softer feeling to human fingers. A pair of contours in the mechanism plays an important role. It transforms rotation into translation in the first portion; on the other hand, it transforms translation into rotation in the last portion. In this study, we have developed an algorithm to obtain the pair of contour curves. We divided the total contour curves into finite sub-intervals. Assuming that the curves in every sub-interval are parabolas, we have obtained the coefficients of them by solving systems of nonlinear equations recursively.

• Korean Journal of Computational Design and Engineering
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• v.5 no.2
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• pp.144-154
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• 2000

We propose an algorithm for obtaining a triangular approximation of a trimmed NLRBS surface. Triangular approximation is used in the pre-processing step of many applications such as RP(Rapid Prototyping), NC(Numerical Control) and FEA(Finite Element Analysis), etc. The algorithm minimizes the number of triangular elements within tolerance and generates a valid triangular mesh for STL file and NC tool path generation. In the algorithm, a subdivision method is used. Since a patch is a basic element of triangular mesh creation, boundary curves of a patch are divided into line segments and the division of curves is applied for the interior of the surface. That is, boundary curves are subdivided into line segments and two end points of each line segment are propagated to the interior of the surface. For the case of a trimmed surface, triangulation is carried out using a model space information. The algorithm is superior because the number of elements can be controlled as the curvature of the surface varies and it generates the triangular mesh in a trimmed region efficiently. To verify the efficiency, the algorithm was implemented and tested for several 3D objects bounded by NURBS surfaces.

• Journal of the Korea Furniture Society
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• v.25 no.1
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• pp.28-35
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• 2014

The most widely used material in furniture is wood. It is not only because it has good machinability and can be easily accessed, but also it is eco-friendly and human-friendly. Such material has been continuously being used for furniture and its machining method has been being actively researched and developed. Lumber has and has developed its own machining method. The conventional lumber machining method is difficult to make various types of furniture because it focuses on solving lumber's own modification problem due to the swelling and shrinking, and durability. Considering such characteristic of the material, a method to make it light and durable has been being researched and possibilities were found in wooden ships. Wooden ships are ships made of lumber, and are light and strong to be used in water. Also, in order to reduce the water resistance, it has streamlined curves so is formatively beautiful. The elegant curves and light and strong structure showed sufficient possibility to be used in furniture. Thus, the purpose of this study is to find a method to make various shapes of lumber lightly and strongly, using the production method of wooden ships, and to use this production method in designing furniture to propose a new form and structure of bench design, differentiating from conventional monotypic furniture.

• Coupled systems mechanics
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• v.4 no.4
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• pp.297-316
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• 2015

The use of fragility curves in the design of bridges is becoming common these days. In this study, experimental data have been used to develop fragility curves for the potential of girder unseating of a three-segment bridge and a bridge-abutment system including the influence of spatially varying ground motions, pounding, and abutment movement. The ground excitations were simulated based on the design spectra for different soil conditions. The Newmarket Viaduct replacement bridge in Auckland was used as the prototype bridge. These fragility curves were also applied to the 2010 Darfield and 2011 Christchurch earthquakes. The study showed that for bridges with similar characteristics as the chosen prototype and with similar fundamental frequencies, pounding could increase the probability of girder unseating by up to 35% and 30% based on the AASHTO and NZTA seating length requirements, respectively. The assumption of uniform ground excitations in many design practices, such as the NZTA requirements, could potentially be disastrous as girders might have a very good chance of unseating (as much as 53% higher chances when considering spatial variation of ground motions) even when they are designed not to. In the case of superstructures with dissimilar frequencies, the assumption of fixed abutments could significantly overestimate the girder unseating potential when pounding was ignored and underestimate the chances when pounding was considered. Bridges subjected to spatially varying ground excitations simulated based on the New Zealand design spectra for soft soil conditions with weak correlation shows the highest chances of girders falling off, of up to 65% greater than for shallow soil excitations.

• Structural Engineering and Mechanics
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• v.24 no.4
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• pp.395-410
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• 2006

This paper reports the result of an investigation into wave propagation in orthotropic laminated piezoelectric cylindrical shells in hydrothermal environment. A dynamic model of laminated piezoelectric cylindrical shell is derived based on Cooper-Naghdi shell theory considering the effects of transverse shear and rotary inertia. The wave characteristics curves are obtained by solving an eigenvalue problem. The effects of layer numbers, thickness of piezoelectric layers, thermal loads and humid loads on the wave characteristics curves are discussed through numerical results. The solving method presented in the paper is validated by the solution of a classical elastic shell non-containing the effects of transverse shear and rotary inertia. The new features of the wave propagation in laminated piezoelectric cylindrical shells with various laminated material, layer numbers and thickness in hydrothermal environment and some meaningful and interesting results in this paper are helpful for the application and the design of the ultrasonic inspection techniques and structural health monitoring.

• Proceedings of the Society of Korea Industrial and System Engineering Conference
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• 2002.05a
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• pp.461-466
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• 2002

In many applications of computer aided geometric design and computer graphics, B-spline is one of the most popular representation for curves and surfaces, and the evaluation of B-spline curves and surfaces is the most frequently used operation. For the evaluation and others, the power form representation of the curves and surfaces is preferred because it is possible to speed-up the operation using Horner's rule. In this paper, we present a new algorithm for the above-mentioned conversion focusing on a dynamic case. Experiment shows that the proposed algorithm significantly outperforms the conventional approach when one or more control points of a B-spline curve and surface are dynamically moving.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.1
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• pp.85-91
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• 1996

In the elM construction of naval architecture industry, ship hull surface modeling is critical process of design/manufacture process. This paper describes a fairing process of ship waterlines to represent boundary curves which are input data of surface modeling. Among the fairing methods, Sapidis's method and Rong's method are used in sequential to fair the boundary curves. Also it proposed four methods of determining the magnitude of end tangent vector. Among the four end tangents the best one is chosen by comparing with the shape of near curves. An application to the actual ship hull is given as an example.

• Proceedings of the KIEE Conference
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• 2004.07e
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• pp.123-125
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• 2004

Tilting train has been developed to increase the operational speed of the trains on conventional lines which have many curves. This train are tilted at curves to compensate for unbalanced carbody centrifugal acceleration to a greater extent than compensation produced by the track cant, so that passengers do not feel centrifugal acceleration and thus trains can run at higher speed at curves. This paper developed 3 Dimensional Digital Mock-UP using PDM(product data managemnet) to make a system engineering of TTX(tilting train express) wiht maximum operation speed 180 km/h.