• 산업기술연구
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• 제21권A호
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• pp.263-271
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• 2001

Blast-vibration tests were carried out to determine the effects of the number of free face on the level of blast vibration. Frequency chatacteristics were also examined by using FFT analysis. To check the effects of the number of free face, charge weight per delay, drilling length, burden and space were applied uniformly and the number of free face was only changed from one to four. The results from tests were checked by regression analysis and K-value.

• Structural Engineering and Mechanics
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• 제65권6호
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• pp.657-678
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• 2018

Sandwich structures are well known for their use in aircraft, naval and automobile industries due to their high strength resistance with light weight and high energy absorption capability. Sandwich beams with soft core are very common and simple structures that are employed in day to day general use appliances. Modeling and analysis of sandwich structures is not straight forward due to the interactions between core and face sheets. In this paper, formulation of Super Convergent finite elements for analysis of the sandwich beams with soft core based on Euler Bernoulli beam theory are presented. Two elements, Eul4d with 4 degrees of freedom assuming rigid core in transverse direction and Eul10d with 10 degrees of freedom assuming the flexible core were developed are presented. The formulation considers the top, bottom face sheets and core as separate entities and are coupled by beam kinematics. The performance of these elements are validated by results available in the published literature. Number of studies are performed using the formulated elements in static, free vibration and wave propagation analysis involving various boundary and loading conditions. The paper highlights the advantages of the elements developed over the traditional elements for modeling of sandwich beams and, in particular wave propagation analysis.

• 대한기계학회논문집B
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• 제23권10호
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• pp.1254-1264
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• 1999

A three-dimensional coupled turbulent fluid flow and solidification process were analyzed in a continuous casting process of a steel slab with Electromagnetic Brake(EMBR). A revised low-Reynolds number $k-{\varepsilon}$ turbulence model was used to consider the turbulent effects. The enthalpy-porosity relation was employed to suppress the velocity within a mushy region. The electromagnetic field was described by Maxwell equations. Tile application of EMBR to the mold region results in the decrease of the transfer of superheat to the narrow face, the increase of temperature in free surface region and most liquid of submold region, and the higher temperature gradient near the solidifying shell. The increasing magnetic flux density effects mainly to the surface temperature of the solidifying shell of narrow face, hardly to the one of wide face. It is seen that in the presence of EMBR a thicker solidifying shell is obtained at the narrow face of the slab.

• 한국IT서비스학회지
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• 제16권2호
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• pp.97-110
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• 2017

Due to development of IT, various Internet services via the non-face-to-face are increasing rapidly. In the past, the resident registration numbers (RRN) was used a mean of personal identification, but the use of RRN is prohibited by the relevant laws, and the personal identification services using alternative means are activated. According to the prohibition policy of RRN, i-PIN service appeared as an alternative means to identify a person. However, the user's knowledge-based i-PIN service continues to cause fraudulent issuance, account hijacking, and fraud attempts due to hacking accidents. Due to these problems, the usage rate of i-PIN service which performs a nationwide free personal identification service, is rapidly decreasing. Therefore, this paper proposes a technical safety enhancement method for security enhancement in the i-PIN-based personal identification service. In order to strengthen the security of i-PIN, this paper analyzes the encryption key exposure, key exchange and i-PIN authentication model problems of i-PIN and suggests countermeasures. Through the proposed paper, the i-PIN can be expected to be used more effectively as a substitution of RRN by suggesting measures to enhance the safety of personal identification information. Secured personal identification services will enable safer online non-face-to-face transactions. By securing the technical, institutional, and administrative safety of the i-PIN service, the usage rate will gradually increase.

• 한국정보시스템학회지:정보시스템연구
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• 제23권1호
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• pp.53-71
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• 2014

The center of networking is moving toward mobile from PC based computing environment. The number of smartphone users are increasing rapidly today. One of the most popular smart phone applications is mobile SNS such as Kakao Story, Facebook, Twitter, Mobile Cyworld, etc. Mobile SNS means social network services based on mobile communication technology. This research focused on mobile SNS usage of married women who have not enough time for face-to-face communication with their friends to enhance their friendship. Married women in their 30s and 40s have lots of things to do like housework and caring their children. Mobile SNS would help their communication in aspect such of free of space and time. Through Mobile SNS married women can reinforce their personal relationship and self-esteem. Social Information Processing Theory (SIP) is an interpersonal communication theory developed by Walther(1992). Once established, online personal relationships may demonstrate the same relational dimensions and qualities as face-to-face relationships. The theory explains how people get to know one another online, without nonverbal cues, and how they develop and manage relationships in the computer-mediated environment. The result of empirical analysis indicates that marred women's Mobile SNS activities reinforce their personal relationship and self-esteem.

• 한국산학기술학회논문지
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• 제22권5호
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• pp.251-256
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• 2021

일반적인 카메라와 다르게 초당 매우 많은 개수의 프레임을 캡처할 수 있는 기능을 가진 고속의 카메라는 그동안 제한적이었던 일부의 영상 처리 기술들의 고도화를 가능하게 할 수 있다. 본 논문에서는 입력되는 초고속의 컬러 영상으로부터 잡음을 제거한 다음, 잡음이 제거된 영상으로부터 사람의 얼굴 영역을 검출하는 방법을 제시한다. 본 논문에서는 우선 입력되는 초고속의 영상 안에 포함된 잡음 화소들을 양방향의 필터를 적용하여 효과적으로 제거한다. 그런 다음, 레티나 얼굴 모델을 사용하여 잡음이 제거된 영상으로부터 사람의 개인 정보를 대표적으로 나타내는 얼굴 영역을 강인하게 검출한다. 실험 결과에서는 본 논문에서 제시한 알고리즘이 입력되는 컬러 영상으로부터 잡음을 제거한 다음, 생성된 모델을 사용하여 사람의 얼굴 영역을 강인하게 검출한다는 것을 보여준다. 본 논문에서 제시된 모델 기반의 얼굴 영역검출 방법은 실내외 건물의 모니터링, 출입문 개폐 관리, 그리고 모바일 생체 인증과 같은 영상처리 및 패턴 인식과 관련된 실제적인 많은 응용 분야의 기초 기술로 사용될 것으로 예상된다.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.1-14
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• 2023

The use of functionally graded materials in applications involving severe thermal gradients is quickly gaining acceptance in the composite mechanics community, the aerospace and aircraft industry. In the present study, a refined sandwich plate model is applied to study the free vibration analysis of porous functionally graded material (FGM) sandwich plates with various distribution rate of porosity. Two types of common FG sandwich plates are considered. The first sandwich plate is composed of two FG material (FGM) face sheets and a homogeneous ceramic or metal core. The second one consists of two homogeneous fully metal and ceramic face sheets at the top and bottom, respectively, and a FGM core. The displacement field of the present theory is chosen based on nonlinear variations in the in-plane displacements through the thickness of the sandwich plate. The number of unknowns and equations of motion of the present theory is reduced and hence makes them simple to use. In the analysis, the equation of motion for simply supported sandwich plates is obtained using Hamilton's principle. In order to present the effect of the variation of the porosity distribution on the dynamic behavior of the FGM sandwich plates, new mixtures are proposed which take into account different rate of porosity distribution between the ceramic and the metal. The present method is applicable to study the dynamic behavior of FGM plates and sandwich plates. The frequencies of two kinds of FGM sandwich structures are analyzed and discussed. Several numerical results have been compared with the ones available in the literature.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2003년도 ISIS 2003
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• pp.640-643
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• 2003

A Walsh function based associative memory is capable of storing m patterns in a single pattern storage space with Walsh encoding of each pattern. Furthermore, each stored pattern can be matched against the stored patterns extremely fast using algorithmic parallel processing. As such, this special type of memory is ideal for real-time processing of large scale information. However this incredible efficiency generates large amount of crosstalk between stored patterns that incurs mis-recognition. This crosstalk is a function of the set of different sequencies [number of zero crossings] of the Walsh function associated with each pattern to be stored. This sequency set is thus optimized in this paper to minimize mis-recognition, as well as to maximize memory saying. In this paper, this Walsh memory has been applied to the problem of face recognition, where PCA is applied to dimensionality reduction. The maximum Walsh spectral component and genetic algorithm (GA) are applied to determine the optimal Walsh function set to be associated with the data to be stored. The experimental results indicate that the proposed methods provide a novel and robust technology to achieve an error-free, real-time, and memory-saving recognition of large scale patterns.

• Advances in materials Research
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• 제8권3호
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• pp.155-177
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• 2019

In this paper, a new displacement based high-order shear deformation theory is introduced for the static response of functionally graded sandwich plate with new definition of porosity distribution taking into account composition and the scheme of the sandwich plate. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, has strong similarity with classical plate theory in many aspects, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. Material properties of FGM layers are assumed to vary continuously across the plate thickness according to either power-law or sigmoid function in terms of the volume fractions of the constituents. The face layers are considered to be FG across each face thickness while the core is made of a ceramic homogeneous layer. Governing equations are derived from the principle of virtual displacements. The closed-form solution of a simply supported rectangular plate subjected to sinusoidal loading has been obtained by using the Navier method. Numerical results are presented to show the effect of the material distribution, the sandwich plate geometry and the porosity on the deflections and stresses of FG sandwich plates. The validity of the present theory is investigated by comparing some of the present results with other published results.

• Earthquakes and Structures
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• 제14권2호
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• pp.103-115
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• 2018

In this work, a simple but accurate hyperbolic plate theory for the free vibration analysis of functionally graded material (FGM) sandwich plates is developed. The significant feature of this formulation is that, in addition to including the shear deformation effect, it deals with only 3 unknowns as the classical plate theory (CPT), instead of 5 as in the well-known first shear deformation theory (FSDT) and higher-order shear deformation theory (HSDT). A shear correction factor is, therefore, not required. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM face sheet and the homogeneous core and the sandwich with the homogeneous face sheet and the FGM core. The equation of motion for the FGM sandwich plates is obtained based on Hamilton's principle. The closed form solutions are obtained by using the Navier technique. The fundamental frequencies are found by solving the eigenvalue problems. Numerical results of the present theory are compared with the CPT, FSDT, order shear deformation theories (HSDTs), and 3D solutions. Verification studies show that the proposed theory is not only accurate and simple in solving the free vibration behaviour of FGM sandwich plates, but also comparable with the higher-order shear deformation theories which contain more number of unknowns.