• Structural Engineering and Mechanics
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• 제44권4호
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• pp.431-448
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• 2012

In this paper, the first-order shear deformation theory (FSDT) (Mindlin) for continuum incorporating surface energy is exploited to study the static behavior of ultra-thin functionally graded (FG) plates. The size-dependent mechanical response is very important while the plate thickness reduces to micro/nano scales. Bulk stresses on the surfaces are required to satisfy the surface balance conditions involving surface stresses. Unlike the classical continuum plate models, the bulk transverse normal stress is preserved here. By incorporating the surface energies into the principle of minimum potential energy, a series of continuum governing differential equations which include intrinsic length scales are derived. The modifications over the classical continuum stiffness are also obtained. To illustrate the application of the theory, simply supported micro/nano scaled rectangular films subjected to a transverse mechanical load are investigated. Numerical examples are presented to present the effects of surface energies on the behavior of functionally graded (FG) film, whose effective elastic moduli of its bulk material are represented by the simple power law. The proposed model is then used for a comparison between the continuum analysis of FG ultra-thin plates with and without incorporating surface effects. Also, the transverse shear strain effect is studied by a comparison between the FG plate behavior based on Kirchhoff and Mindlin assumptions. In our analysis the residual surface tension under unstrained conditions and the surface Lame constants are expected to be the same for the upper and lower surfaces of the FG plate. The proposed model is verified by previous work.

• 대한족부족관절학회지
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• 제18권4호
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• pp.183-188
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• 2014

Purpose: The accepted general management principle after ankle arthrodesis is to maintain non-weight bearing for 6 to 8 weeks. The aim of this study was to report clinical outcome of patients allowed early weight bearing after arthroscopic arthrodesis. Materials and Methods: We analyzed medical records and radiographs to determine fusion rate and complication risk of 22 sequential patients allowed to walk under short leg cast within 3 days after arthroscopic ankle arthrodesis using 2 screws from January 2008 to June 2012. The minimum follow-up period was 18 months, and the mean age of the patients was 67 years. Results: The mean visual analog scale was decreased from 8.9 points preoperatively to 2.3 points after 12 months. Complete ankle fusion was achieved in 19 patients (86.4%) at 3-month follow-up. There were 2 cases of delayed union and one case of nonunion at 12-month follow-up. There was no other complication such as wound problem, persistent swelling of the ankle. Conclusion: Bony union may not be interfered even though patients were allowed to walk under cast within a few days after arthroscopic ankle arthrodesis.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2007년도 정기학술발표대회 논문집
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• pp.643-646
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• 2007

도심지 지가가 높아짐에 따라 건축물의 공간 활용도에 대한 기대치가 높아지게 되었고, 건축물은 더 크고, 더 깊고, 더 높게 지어지는 방향으로 나아가고 있다. 이에 따라, 공사의 첫 단계이자 전체 건물의 기초가 되는 지하 공사는 그 중요성이 날로 더해가고 있다. 최소한의 비용으로 최단기간에 터파기 공사를 완료해야 하는 도심지 공사의 특성상 공사 관계자들은 지하 공사를 계획, 설계, 시공, 설계하는 과정에서 심혈을 기울이고 있다. 그럼에도 불구하고 지하 공사 전번에 걸쳐 있는 불확실성과 위험 요소 때문에 공사 실패 사례가 발생하고 있다. 더욱이 이러한 사고가 어느 정도의 경제적 피해를 끼쳤는지에 대한 보고나 연구없이 사고 사례만 알려지기 때문에 지하 공사의 위험성에 대한 경각심이 부족한 것이 우리나라 건축의 현실이다. 이런 사고를 타산지석으로 삼아 터파기 공사 공법을 선정하고 지하 공사를 이행하는데 있어서 하나의 지침이 되기를 바라면서 지하 공사 실패 사례가 과연 어느 정도의 경제적 피해를 발생시키는지를 개산견적 기법을 도입하여 추정해 보았다.

• Structural Engineering and Mechanics
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• 제48권3호
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• pp.367-382
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• 2013

Different types of long slender pile shall buckle with weak soil and liquefied stratum surrounded. Different from considering single side earth pressure, it was suggested that the lateral earth pressure can be divided into two categories while buckling: the earth pressure that prevent and promotes the lateral movement. Active and passive earth pressure calculation model was proposed supposing earth pressure changed linearly with displacement considering overlying load, shaft resistance, earth pressure at both sides of the pile. Critical buckling load calculation method was proposed based on the principle of minimum potential energy quoting the earth pressure calculation model. The calculation result was contrasted with the field test result of small diameter TC pile (Plastic Tube Cast-in-place pile). The fix form could be fixed-hinged in the actual calculation assuring the accuracy and certain safety factor. The contributions of pile fix form depend on the pile length for the same geological conditions. There exists critical friction value in specific geological conditions that the side friction has larger impact on the critical buckling load while it is less than the value and has less impact with larger value. The buckling load was not simply changed linearly with friction. The buckling load decreases with increased limit active displacement and the load tend to be constant with larger active displacement value; the critical buckling load will be the same for different fix form for the small values.

• Journal of Electrical Engineering and Technology
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• 제9권5호
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• pp.1471-1481
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• 2014

This paper presents the new power dissipation model of individual switching device in a high-level modular multilevel converter (MMC), which can be mostly used in voltage sourced converter (VSC) based high-voltage direct current (HVDC) system and flexible AC transmission system (FACTS). Also, the voltage balancing method based on sorting algorithm is newly proposed to advance the MMC functionalities by effectively adjusting switching variations of the sub-module (SM). The proposed power dissipation model does not fully calculate the average power dissipation for numerous switching devices in an arm module. Instead, it estimates the power dissipation of every switching element based on the inherent operational principle of SM in MMC. In other words, the power dissipation is computed in every single switching event by using the polynomial curve fitting model with minimum computational efforts and high accuracy, which are required to manage the large number of SMs. After estimating the value of power dissipation, the thermal condition of every switching element is considered in the case of external disturbance. Then, the arm modeling for high-level MMC and its control scheme is implemented with the electromagnetic transient simulation program. Finally, the case study for applying to the MMC based HVDC system is carried out to select the appropriate insulated-gate bipolar transistor (IGBT) module in a steady-state, as well as to estimate the proper thermal condition of every switching element in a transient state.

• 대한원격탐사학회지
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• 제21권2호
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• pp.163-171
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• 2005

합성구경레이더(Synthetic Aperture Radar) 원시 자료(raw data)를 range-Doppler 알고리듬을 이용하여 처리하는 교육용 공개 프로그램을 개발하였다 이 프로그램은 SAR 시스템에 따라 자료처리에 필요한 변수를 자유롭게 조절함으로써, 특정 SAR 시스템에 치우치지 않고 다양한 자료를 처리할 수 있도록 일반화된 알고리듬을 구현하였다. 저가 사양의 컴퓨터에서도 최소 단위의 영상을 선택적으로 처리할 수 있고 자료 처리 중간 단계별로 영상 출력이 가능하기 때문에, 프로그램 작동 상태와 SAR의 원리를 직접 확인할 수 있도록 하였다. 특히 Doppler 변수를 자료 처리 중간 단계의 영상을 보고 직접 구할 수 있도록 고안하여 교육적 효과를 높였다. 또한 자료 처리 알고리듬과 원시프로그램을 모두 공개함으로써, SAR 시스템 원리를 이해하고 응용하는데 도움을 주고자 한다. 이 논문에서는 프로그램의 원리와 작동 환경을 소개하고, ERS-1 원시 자료를 이용한 자료 처리의 예를 보였다.

• Steel and Composite Structures
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• 제33권4호
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• pp.509-523
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• 2019

In the present work, the buckling analysis of micro sandwich plate with an isotropic/orthotropic cores and piezoelectric/polymeric nanocomposite face sheets is studied. In this research, two cases for core of micro sandwich plate is considered that involve five isotropic Devineycell materials (H30, H45, H60, H100 and H200) and an orthotropic material also two cases for facesheets of micro sandwich plate is illustrated that include piezoelectric layers reinforced by carbon and boron-nitride nanotubes and polymeric matrix reinforced by carbon nanotubes under temperature-dependent and hydro material properties on the elastic foundations. The first order shear deformation theory (FSDT) is adopted to model micro sandwich plate and to apply size dependent effects from modified strain gradient theory. The governing equations are derived using the minimum total potential energy principle and then solved by analytical method. Also, the effects of different parameters such as size dependent, side ratio, volume fraction, various material properties for cores and facesheets and temperature and humidity changes on the dimensionless critical buckling load are investigated. It is shown from the results that the dimensionless critical buckling load for boron nitride nanotube is lower than that of for carbon nanotube. It is illustrated that the dimensionless critical buckling load for Devineycell H200 is highest and lowest for H30. Also, the obtained results for micro sandwich plate with piezoelectric facesheets reinforced by carbon nanotubes (case b) is higher than other states (cases a and c).The results of this research can be used in aircraft, automotive, shipbuilding industries and biomedicine.

• 한국정보통신학회논문지
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• 제23권3호
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• pp.311-317
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• 2019

먼저 광학 신호를 이용한 다양한 응용 분야에서의 핵심 요소인 광학 빔 조향 성능 향상을 위하여 실리콘 기반 격자 구조의 특성을 해석하였다. 이를 기반으로 높은 방사 효율과 좁은 빔 폭을 얻기 위해서 기존의 격자 구조 방사기에 분배 브래그 반사기(Distributed Bragg Reflector, DBR)를 집적한 구조를 제안한다. 분배 브래그 반사기의 위치에 따른 방사 효율과 방사 각도의 전치 반폭을 분석하고 이를 토대로 최적화 구조를 제안한다. 제안한 격자 구조는 상보형 금속산화 반도체(complementary metal-oxide semiconductor, CMOS) 공정과 호환 가능하며, 최대 방사 효율 87.1% 및 최소 방사 각도의 반치 전폭 $4.68^{\circ}$를 가진다.

• Steel and Composite Structures
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• 제29권6호
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• pp.785-802
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• 2018

In this paper, two different computational methods, called Rayleigh-Ritz and collocation are developed to estimate the ultimate strength of composite plates. Progressive damage behavior of moderately thick composite laminated plates is studied under in-plane compressive load and uniform lateral pressure. The formulations of both methods are based on the concept of the principle of minimum potential energy. First order shear deformation theory and the assumption of large deflections are used to develop the equilibrium equations of laminated plates. Therefore, Newton-Raphson technique will be used to solve the obtained system of nonlinear algebraic equations. In Rayleigh-Ritz method, two degradation models called complete and region degradation models are used to estimate the degradation zone around the failure location. In the second method, a new energy based collocation technique is introduced in which the domain of the plate is discretized into the Legendre-Gauss-Lobatto points. In this new method, in addition to the two previous models, the new model named node degradation model will also be used in which the material properties of the area just around the failed node are reduced. To predict the failure location, Hashin failure criteria have been used and the corresponding material properties of the failed zone are reduced instantaneously. Approximation of the displacement fields is performed by suitable harmonic functions in the Rayleigh-Ritz method and by Legendre basis functions (LBFs) in the second method. Finally, the results will be calculated and discussions will be conducted on the methods.

• 사물인터넷융복합논문지
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• 제9권2호
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• pp.55-60
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• 2023

최근 클라우드 컴퓨팅의 수요가 증가하고 자택근무 및 외부 업무로 인한 원격접속의 증가했다. 또한 외부 공격자의 접근뿐만이 아니라 내부 직원의 업무 접속과 같은 내부에서의 접근을 경계해야 할 필요성이 증가함과 동시에 다양한 공격 기법들이 고도화되는 현 상황에서 그에 맞는 새로운 보안 패러다임이 요구된다. 이로 인해 모든 것을 의심하고 신뢰하지 않는다는 핵심 원칙을 가진 제로 트러스트(Zero-Trust)를 적용한 네트워크 보안 모델이 보안업계에서 주목받기 시작했다. 제로 트러스트 보안은 모든 네트워크를 감시하고 접근을 허용 받기 위해선 먼저 인증을 받아야 하며 접근 요청자에 대한 최소한의 접근 권한을 부여함으로써 보안성을 높인다. 본 논문에서는 제로 트러스트와 제로 트러스트 아키텍처에 대해 설명하고, 제로 트러스트와 블록체인을 이용하여 기존 보안 시스템의 한계점을 극복하고 다양한 기업에서 활용할 수 있고 접근제어 강화를 위한 새로운 클라우드 보안 체계를 제안하고자 한다.