• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.3
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• pp.49-59
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• 2008

In this study, the design method of a 155 mm Solid Fuel Ramjet projectile is proposed and a flight performance analysis program through mathematical modelling is developed. Through flight performance analysis, ramjet performance during flight, which is comprised of thrust, specific impulse, pressure recovery ratio, location of shock waves, and magnitude of drag, was predicted. The results show that compared to Rocket Assisted Projectile(RAP), the range was increased by 90 %. Furthermore, how variations in nozzle exit area ratio and the intake area cause variations in range was observed. This research on modeling and simulation methodology will provide useful data for future development of solid fuel ramjet projectiles.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.4
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• pp.34-40
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• 2012

In wireless communication system, fading is an unavoidable problem. Hence, errors in form of BER are introduced with the transmitted signal. It is necessary to recognize the behavior of these errors in different fading channels. To obtain the mathematical solution for the average bit error rate(BER) of coherent MPSK, some techniques are presented. In this paper, the impact of diversity is also analyzed over slow and flat Rician fading channel. In here, the value of modulation index, M is varied and the effects of its variation are also depicted. So, these performance curves with different diversity values and fading parameter are useful to design and evaluate the radio channel for faithful communication system.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.1-12
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• 1990

Interactions between a propeller and vortex system contained in a ship stern flow is treated theoretically. A new formulation to determine the effective velocity distributions is developed, which may be immediately applicable to the design and analysis of compound propulsors under the influence of severe vortical cross-flows around ship stern. An axisymmetric shear flow is represented by a system of ring vortices and the axial variation of the stream lines due to the action of propeller is represented by a cubic function. The strengths of ring vortices, which are varying along the stream lines, are determined by the conservation of angular momentum. Two simplified effective velocity models are proposed to confirm the theory. Sample calculations using the simplified models are made to compare with the results by other investigators.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.211-216
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• 2008

In this study, we have developed a program which can calculate phase and group velocities, attenuation and wave structures of each mode in multi-layered plates. The wave structures of each mode are obtained, varying material properties and number of layers. The key in the success of guided wave NDE is how to optimize the mode selection scheme by minimizing energy loss when a structure is in contact with liquid. In this study, the normalized out-of-plane displacements at the surface of a free plate are used to predict the variation of modal attenuation and verily the correlation between attenuation and wave structure. It turns out that the guided wave attenuation can be efficiently obtain from the out-of-plane displacement variation of a free wave guide alleviating such mathematical difficulties in extracting complex roots for the eigenvalue problem of a liquid loaded wave guide. Through this study, the concert to optimize guided wave mode selection is accomplished to enhance sensitivity and efficiency in nondestructive evaluation for multi-layered structures.

• Convergence Security Journal
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• v.22 no.5
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• pp.135-143
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• 2022

The defense environment is rapidly changing, such as nuclear and missile threats of North Korea, changes in war patterns, and a decrease in military service resources due to low birth rate. In order to actively respond to these changes, the Korean military is promoting Defense Innovation 4.0 and is trying to foster an army armed with high technology such as artificial intelligence (AI), big data analysis, etc. In this regard, we analyze the effectiveness of the radar-based AI scientific guard system applied by high technology for guard operations using Analytic Hierarchy Process (AHP). We first select evaluation factors that can assess the effectiveness of the scientific guard system, and analyze its relative importance. Each evaluation factor was selected by deriving a significant concept from operating principle and how they work, and by consulting experts on the correlation between each factor and effectiveness of the scientific guard system. We examine the relative effects of the radar-based AI scientific guard system and existing scientific guard system based on the importance of the evaluation factors.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.7
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• pp.1419-1424
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• 2005

This paper suggests a new cipher mode of operation which can recover cryptographic synchronization. First, we study the typical cipher modes of operation, especially focused on cryptographic synchronization problems. Then, we suggest a statistical cipher-feedback mode of operation. We define the error sources mathmatically and simulate propagation errors caused by a bit insertion or bit deletion. In the simulation, we compare the effects of changing the synchronization pattern length and feedback key length. After that, we analyze the simulation results with the calculated propagation errors. finally. we evaluate the performance of the statistical cipher-feedback mode of operation and recommand the implementation considerations.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.2
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• pp.105-111
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• 2007

A finite element analysis scheme is proposed to assess the dynamic response due to impulse excitation of ocean mining pipe system. Transient dynamic response analysis based on the proposed scheme was carried out for various types of impulses, and the magnitude of cable tension induced by impulse was discussed by using a model of 'Segero', a special purpose ship of KT-Submarine as well as ROV carrier 'Onnuri' A qualitative, prospective guideline for the relevant marine operation is obtained.

• Journal for History of Mathematics
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• v.27 no.3
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• pp.197-210
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• 2014

Species like insects and fishes have, in many cases, non-overlapping time intervals of one generation and their descendant one. So the population dynamics of such species can be formulated as discrete models. In this paper various discrete population models are introduced in chronological order. The author's investigation starts with the Malthusian model suggested in 1798, and continues through Verhulst model(the discrete logistic model), Ricker model, the Beverton-Holt stock-recruitment model, Shep-herd model, Hassell model and Sigmoid type Beverton-Holt model. We discuss the mathematical and practical significance of each model and analyze its properties. Also the stability properties of stationary solutions of the models are studied analytically and illustratively using GSP, a computer software. The visual outputs generated by GSP are compared with the analytical stability results.

• Computational Structural Engineering
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• v.3 no.1
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• pp.83-95
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• 1990

Many structural optimization problems are solved by numerical algorithms since these are complicated and nonlinear. To provide a wider base and popular it to structual design optimization, reliable, accurate and superlinearly convergent nonlinear programming algorithm with active-set strategy have been developed. One of these is RQP(recursive quadratic programming method). This algorithm has several parameters and its performance is influenced by variations of these key parameters. Therefore, an RQP algorithm is selected to enhance its numerical performances by choosing proper parameters. The paper persents these influences on its numerical performance. For comparison of performances, a structural design software for minimum weight of truss subjected to displacement, stress, and lower and upper bounds on design variables is also implemented.

• Journal of Educational Research in Mathematics
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• v.25 no.4
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• pp.499-524
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• 2015

In the present study, we propose four participating $8^{th}$ grade students' genetic decomposition of congruent transformation and investigate the role of their dragging activities while understanding the concept of congruent transformation in GSP(Geometer's Sketchpad). The students began to use two major schema, 'single-point movement' and 'identification of transformation' simultaneously in their transformation activities, but they were inclined to rely on the single-point movement schema when dealing with relatively difficult tasks. Through dragging activities, they could expand the domain and range of transformation to every point on a plane, not confined to relevant geometric figures. Dragging activities also helped the students recognize the role of a vector, a center of rotation, and an axis of symmetry.