• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.653-673
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• 2019

This work investigates a novel quasi-3D hyperbolic shear deformation theory is presented to discuss the buckling of new type of sandwich plates. This theory accounts for both shear deformation and thickness stretching effects by a hyperbolic variation of all displacements through the thickness. The enhancement of this formulation is due to the use of only five unknowns by including undetermined integral terms, contrary to other theories where we find six or more unknowns. It does not require shear correction factors and transverse shear stresses vary parabolically across the thickness. A new type of FGM sandwich plates, namely, both FGM face sheets and FGM hard core are considered. The governing equations and boundary conditions are derived using the principle of virtual displacements. Analytical solutions are obtained for a simply supported plate. The accuracy of the present theory is verified by comparing the obtained results with quasi-3D solutions and those predicted by higher-order shear deformation theories. The comparison studies show that the obtained results are not only more accurate than those obtained by higher-order shear deformation theories, but also comparable with those predicted by quasi-3D theories with a greater number of unknowns.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1981-1982
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• 2006

본 논문에서는 자율 이동 로봇에 대한 인터넷 기반의 가상실험실의 구현 방법을 제안한다. 제어공학 연구에서는 개발된 새로운 이론들을 적용하고 검증할 수 있는 적절한 실험장비의 확보가 필수적이나 매번 이를 위한 실험장비의 확보는 비경제적이다. 오늘날 인터넷의 보급은 보편화 되어있다. 또한 인터넷을 이용할 수 있는 기술들이 발전되고 장비들이 개발, 발전되고 있다. 이러한 흐름을 공학연구에 적용 할 수 있다. 인터넷 기반의 자율 이동 로봇의 가상실험실은 인터넷의 이용이 가능한 곳이면, 시간과 장소의 제한을 받지 않고 자율 이동 로봇에 대한 실험을 하고 결과를 얻을 수 있는 장점이 있다. 이러한 방법은 다른 실험장비에 대해서도 가능하게 할 수 있다. 자율 이동 로봇은 제어 컴퓨터의 탑재가 가능하여. 통신선에 의한 이동거리의 제약을 받지 않으나 무선인터넷이 가능한 공간에서만 실험이 가능하다. 본 논문에서 제안된 가상실험실은 자율 이동 로봇에 탑재한 컴퓨터(클라이언트)와 일반컴퓨터(서버) 구조를 가지며 다중제어 인터페이스로 구현된다.

• Steel and Composite Structures
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• v.22 no.5
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• pp.975-999
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• 2016

This work investigates a thermomechanical bending analysis of functionally graded sandwich plates by proposing a novel quasi-3D type higher order shear deformation theory (HSDT). The mathematical model introduces only 5 variables as the first order shear deformation theory (FSDT). Unlike the conventional HSDT, the present one presents a novel displacement field which includes undetermined integral variables. The mechanical properties of functionally graded layers of the plate are supposed to change in the thickness direction according to a power law distribution. The core layer is still homogeneous and made of an isotropic ceramic material. The governing equations for the thermomechanical bending investigation are obtained through the principle of virtual work and solved via Navier-type method. Interesting results are determined and compared with quasi-3D and 2D HSDTs. The influences of functionally graded material (FGM) layer thickness, power law index, layer thickness ratio, thickness ratio and aspect ratio on the deflections and stresses of functionally graded sandwich plates are discussed.

• Computers and Concrete
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• v.20 no.5
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• pp.617-625
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• 2017

Prestress force identification (PFI) is crucial to maintain the safety of prestressed concrete bridges. A synergic identification method has been proposed recently by the authors that can determine the prestress force (PF) and the excitation force simultaneously in prestressed concrete beams with good accuracy. In this paper, the ability of this method in the application with prestressed concrete box-girder bridges is demonstrated. A reasonable assumption is made to capture the similarity of the dynamic behavior of the prestressed concrete box-girder bridge and a beam under a certain loading scenario, and the feasibility of this method for application in a prestressed box-girder bridge is affirmed. A comprehensive laboratory test program is conducted, and the effects of PF, excitation, measuring time and uncertainties are studied. Results show that the proposed method can predict the PF and the excitation force in a prestressed concrete box-girder accurately and has a great robustness against uncertainties.

• Journal of Korea Multimedia Society
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• v.17 no.11
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• pp.1307-1312
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• 2014

Online games are virtual space where it connects individual users through network connection to offer enjoyment of play games and game developer who service online games have to develop new contents and provide them to users to extend life of their service. Typically, in order to update new contents, all service companies have maintenance schedule to stop the game service for a while to update both server and client applications. Usually this process takes quite amount of time and users do not have any other choice but disconnected from server and wait until it is over. The purpose of this thesis is to describe the advantages of new design system which will allows users to continue to play the game even during the update. The main focus of this design is to make users feel more convenience in online gaming experience by move client from previous server to new server while users are still playing. If they can to connect current client with new server without any certificate validation process while users information from the client can automatically pass through to the new server, users may not need to experience maintenance for new contents update.

• Journal of Biosystems Engineering
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• v.29 no.3
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• pp.243-250
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• 2004

본 연구에서는 국내 미곡도정공장의 도정기계 작동상태와 가공된 발 품질의 원격감시를 위해서 인터넷기반 감시시스템을 개발하고자 하였다. 인터넷 감시시스템은 Laboratory Virtual Instrument Engineering Workbench(Lab VIEW)를 이용하여 개발되었으며 Hypertext Transfer Protocol(HTTP)을 제공할 수 있는 중앙서버, 현장제어용 Programmable logic controller (PLC) 및 각종 센서 등으로 구성되었다. 비상상태를 대비하기 위하여 도정기계를 원격으로 제어(ON/OFF)할 수 있도록 제어알고리즘을 설계하였다. 개발된 인터넷기반 감시시스템은 미곡 도정공장에 설치한 모든 도정기계의 작동상태, 백미 탱크내의 백미 무게와 백미의 온도 및 평형상대습도를 실시간으로 감시할 수 있었으며, 원격으로 측정한 백미탱크내의 평형온도 및 평형상대습도를 이용하여 백미의 함수율도 예측할 수 있었다. 거리 및 인터넷속도에 의해 발생된 시간지연의 측정과 원격으로 수집된 자료의 검증을 통해 인터넷 감시시스템의 성능을 평가하였다. 인터넷상의 시간지연(서울-광주간)은 약 1.2$\pm$0.2s 이었다.

• Proceedings of the KAIS Fall Conference
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• 2009.05a
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• pp.393-396
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• 2009

본 연구의 목적은 3D 가상공간인 세컨드라이프에서 예비교사의 성공적인 수업연습을 위한 물리적 환경 및 절차적 모형을 개발하는 것이다. 이를 위해 본 연구에서 수행한 내용은 다음과 같다. 첫째, 수업 연습 관련 이론 탐색 및 문헌 연구를 통해 성공적인 수업연습을 위한 필수조건들을 탐색하였으며, 이 조건들로부터 수업연습을 위한 절차적 모형의 시안을 개발하였다. 둘째, 세컨드라이프에서 수업연습을 위해 필요한 교실의 물리적 구성요소를 개발하였다. 개발된 교실의 물리적 구성요소는 교실공간, 칠판, 교사용 책걸상, 학생용 책걸상, 출입문, 창문, 게시판, 프리젠테이션 도구 등이었다. 셋째, 세컨드라이프에서 수업연습을 위해 필요한 의사소통 도구를 탐색하였다. 탐색 결과, 텍스트 대화 도구, 음성 대화 도구, 노트카드 사용 도구, 공지사항 사용 도구 등이 의사소통을 위해 필요한 요소로 결정되었다. 마지막으로, 세컨드라이프내의 교실 안에서 의사소통 도구를 활용하여 예비교사의 수업연습을 수행하였다. 이 수행결과에 기반하여 세컨드라이프에서의 예비교사의 수업연습을 위한 절차적 모형을 완성하였다. 이 연구는 예비교사들에게 실제적 수업연습(field-based teaching practice)에 앞서, 3D 가상공간인 세컨드라이프에서 실험적 수업연습(laboratory-based teaching practice) 경험을 가능하게 하였다는 점에서 의미가 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.8
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• pp.3769-3789
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• 2018

Social pedestrian groups are the basic elements that constitute a crowd; therefore, detection of such groups is scientifically important for modeling social behavior, as well as practically useful for crowd video understanding. A social group refers to a cluster of members who tend to keep similar motion state for a sustained period of time. One of the main challenges of social group detection arises from the complex dynamic variations of crowd patterns. Therefore, most works model dynamic groups to analysis the crowd behavior, ignoring the existence of stationary groups in crowd scene. However, in this paper, we propose a novel unified framework for detecting social pedestrian groups in crowd videos, including dynamic and stationary pedestrian groups, based on spatiotemporal-oriented energy measurements. Dynamic pedestrian groups are hierarchically clustered based on energy flow similarities and trajectory motion correlations between the atomic groups extracted from principal spatiotemporal-oriented energies. Furthermore, the probability distribution of static spatiotemporal-oriented energies is modeled to detect stationary pedestrian groups. Extensive experiments on challenging datasets demonstrate that our method can achieve superior results for social pedestrian group detection and crowd video classification.

• Advances in materials Research
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• v.8 no.3
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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.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.970-979
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• 2019

Compliant Vertical Access Risers (CVARs) are compliant systems that incorporate a differentiated geometric configuration that allows the exploitation of oil and gas in deepwater fields and enables a number of operational advantages in the offshore system. One of the main features of CVAR systems is that they allow direct intervention procedures to be applied to the well bore, enabling workover operations to be performed directly from the production platform. Based on the principles of virtual work and variation, a static geometric nonlinear equation of CVARs is derived and applied in this study. The results of this study show that the two ends of the riser as well as the transition region are subject to high stress, while the positions of the floating platform exert significant effects on the geometry of the riser configuration. Compliance and buoyancy factors should be set moderately to reduce the CVAR stress. In addition, the buoyancy modules should be placed in the lower region, in order to maximize the operation advantages of CVAR.