• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.51-52
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• 2002

We report results on microtribological studies of chemically grafted nanoscale polymer layers of different architecture with thickness below 30 nm. We have fabricated the molecular lubrication coatings from elastomeric tri-block copolymers and tested two different designs of corresponding nanocomposite coatings. We observed a significant reduction of friction forces and an increase of the wear stability when a minute amount of oil was trapped within the grafted polymer layer. These polymer gel layers exhibited a very steady friction response and a small value of the coefficient of friction as compared to the initial polymer coating. A polymer 'triplex' coating has been formed by a multiple grafting technique. The unique design of this layer Includes a hard-soft-hard architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the elastic rubber interlayer.

• Smart Structures and Systems
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• 제19권2호
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• pp.225-236
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• 2017

Railroad bridges in North America are an integral but aging part of the railroad network and are typically only monitored using visual inspections. When quantitative information is required for assessment, railroads often monitor bridges using accelerometers. However without a sensor to directly measure displacements, it is difficult to interpret these results as they relate to bridge performance. Digital Image Correlation (DIC) is a non-contact sensor technology capable of directly measuring the displacement of any visible bridge component. In this research, a railroad bridge was monitored under load using DIC and accelerometers. DIC measurements are directly compared to serviceability limits and it is observed that the bridge is compliant. The accelerometer data is also used to calculate displacements which are compared to the DIC measurements to assess the accuracy of the accelerometer measurements. These measurements compared well for zero-mean lateral data, providing measurement redundancy and validation. The lateral displacements from both the accelerometers and DIC at the supports were then used to determine the source of lateral displacements within the support system.

• Structural Engineering and Mechanics
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• 제43권4호
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• pp.545-560
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• 2012

Design codes provide the minimum requirements for the design of code-compliant structures to ensure the safety of the life and property. As for code-exceeding buildings, the requirements for design are not sufficient and the approval of such structures is vague. In mainland China in recent years, a large number of code-exceeding tall buildings, whether their heights exceed the limit for the respective structure type or the extent of irregularity is violated, have been constructed. Performance-based seismic design (PBSD) approach has been highly recommended and become necessary to demonstrate the performance of code-exceeding tall buildings at least equivalent to code intent of safety. This paper proposes the general methodologies of performance-based seismic analysis and design of code-exceeding tall buildings in Mainland China. The PBSD approach proposed here includes selection of performance objectives, determination of design philosophy, establishment of design criteria for structural components and systems consistent with the desirable and transparent performance objectives, and seismic performance analysis and evaluation through extensive numerical analysis or further experimental study if necessary. The seismic analysis and design of 101-story Shanghai World Financial Center Tower is introduced as a typical engineering example where the PBSD approach is followed. The example demonstrates that the PBSD approach is an appropriate way to control efficiently the seismic damage on the structure and ensure the predictable and safe performance.

• Smart Structures and Systems
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• 제3권1호
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• pp.89-114
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• 2007

Two aspects of the design of a small-scale smart wing are addressed in this work, related to the ability of the wing to modify its cross section assuming the shape of two different airfoils and to the possibility of deflecting the profiles near the trailing edge in order to obtain hingeless control surfaces. The actuation is provided by one-way shape memory alloy wires eventually coupled to springs, Shape Memory Alloys (SMAs) being among the most promising materials for this kind of applications. The points to be actuated along the profiles and the displacements to be imposed are selecetd so that they satisfactorily approximate the change from an airfoil to the other and to result in an adequate deflection of the control surface; the actuators and their performances are designed so that an adequate wing stiffness is guaranteed, in order to prevent excessive deformations and undesired airfoil shape variations due to aerodynamic loads. The effect of the pressure distributions, calculated by way of the XFOIL software, and of the actuators loads, is estimated by FE analyses of the loaded wing. Two prototypes are then realised incorporating the variable airfoil and the hingeless aileron features respectively, and the verification of their shapes in both the actuated and non-actuated states, supported by image analysis techniques, confirms that interesting results are achievable with the proposed lay out and design considerations.

• 한국통신학회논문지
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• 제35권7A호
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• pp.682-687
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• 2010

The IEEE 802.15.4a specification targets the low-rate (LR) Impulse-radio (IR) ultra-wideband (UWB) system which is now widely applied in the WPANs considering rather short distance communications with low complexity and power consumption. The physical (PHY) layer uses concatenated coding with mixed binary phase-shift keying and binary pulse-position modulation (BPSK-BPPM), and direct sequence spreading with time hopping in order that both coherent and non-coherent receiver architectures are supported. In this paper, the performances of multiple access schemes compliant with IEEE 802.15.4a specification are investigated with energy detection receiver, which allow avoiding the complex channel estimation needed by a coherent receiver. However, the performance of energy detection receiver is severely degraded by multi-user interference (MUI), which largely diminishes one of the most fascinating advantages of UWB, namely robustness to MUI as well as the possibility to allow parallel transmissions. So as to improve the performance of multiple access schemes, we propose to apply the novel TH sequences as well as to increase the number of TH positions. The simulation results show that our novel multiple access schemes significantly improve the performance against MUI.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권1호
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• pp.523-549
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• 2018

The increasing number of subscribers and demand of multiplicity of services has turned Multi-Server Authentication (MSA) into an integral part of remote authentication paradigm. MSA not only offers an efficient mode to register the users by engaging a trusted third party (Registration Centre), but also a cost-effective architecture for service procurement, onwards. Recently, Lu et al.'s scheme demonstrated that Mishra et al.'s scheme is unguarded to perfect forward secrecy compromise, server masquerading, and forgery attacks, and presented a better scheme. However, we discovered that Lu et al.'s scheme is still susceptible to malicious insider attack and non-compliant to perfect forward secrecy. This study presents a critical review on Lu et al.'s scheme and then proposes a secure multi-server authentication scheme. The security properties of contributed work are validated with automated Proverif tool and proved under formal security analysis.

• 한국국방경영분석학회지
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• 제26권2호
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• pp.101-119
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• 2000

US DoD designated the High LEvel Architecture (HLA) as the standard technical architecture for all military simulation since 1996. HLA will supercede the current Distributed Interactive Simulation(DIS) and Aggregated LEvel Simulation Protocol(ALSP) methods by no funds for developing/modifying non-HLA compliant simulations. The new architecture specifies Rules which define relationships among federation components, an Objects Model Template which species the form which simulation elements are described, and an Interface Specification which describes the way simulations interact during operations. HLA is named as standard architecture in NATO, Australia and many other militaries. Also, it will be IEEE standard in the near future. It goes without saying that ROK military whose simulation models are almost from US must be prepared in areas such as ROK-US combined exercise, training, weapon system acquisition, interface models with C4I system, OPLAN analysis, operations, and os on. In this paper, we propose several effective alternatives and issues for ROK Defense Modeling and Simulation under the transition of new HLA architecture. Those include secure the kernel of new simulation technology and develop our own conceptual model, RTI software, prototype federation for each service and aggregated one. In order to challenge the new simulation architecture effectively, we should innovate our current defense modeling and simulation infrastructure such s manpower, organization, budget, research environment, relationships among academia and industry, and many others.

• 로봇학회논문지
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• 제6권3호
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• pp.220-229
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• 2011

This paper focuses on a development of an anthropomorphic robot hand. Human hand is able to dexterously grasp and manipulate various objects with not accurate and sufficient, but inaccurate and scarce information of target objects. In order to realize the ability of human hand, we develop a robot hand and introduce a control scheme for stable grasping by using only kinematic information. The developed anthropomorphic robot hand, KITECH Hand, has one thumb and three fingers. Each of them has 4 DOF and a soft hemispherical finger tip for flexible opposition and rolling on object surfaces. In addition to a thumb and finger, it has a palm module composed the non-slip pad to prevent slip phenomena between the object and palm. The introduced control scheme is a quitely simple based on the principle of virtual work, which consists of transposed Jacobian, joint angular position, and velocity obtained by joint angle measurements. During interaction between the robot hand and an object, the developed robot hand shows compliant grasping motions by the back-drivable characteristics of equipped actuator modules. To validate the feasibility of the developed robot hand and introduced control scheme, collective experiments are carried out with the developed robot hand, KITECH Hand.

• Earthquakes and Structures
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• 제17권1호
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• pp.75-89
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• 2019

The paper presents experimental and numerical studies carried out on low-rise RC frames, typically found in developing countries. Shake table tests were conducted on 1:3 reduced scaled two-story RC frames that included a code conforming SMRF model and another non-compliant model. The later was similar to the code conforming model, except, it was prepared in concrete having strength 33% lower than the design specified, which is commonly found in the region. The models were tested on shake table, through multiple excitations, using acceleration time history of 1994 Northridge earthquake, which was linearly scaled for multi-levels excitations in order to study the structures' damage mechanism and measure the structural response. A representative numerical model was prepared in finite element based program SeismoStruct, simulating the observed local damage mechanisms (bar-slip and joint shear hinging), for seismic analysis of RC frames having weaker beam-column joints. A suite of spectrum compatible acceleration records was obtained from PEER for incremental dynamic analysis of considered RC frames. The seismic performance of considered RC frames was quantified in terms of seismic response parameters (seismic response modification, overstrength and displacement amplification factors), for critical comparison.

• 한국인터넷방송통신학회논문지
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• 제19권1호
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• pp.103-109
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• 2019

자동차 전장 시스템에는 여러 개의 전자 제어 장치에 시간 제약성을 갖는 다수의 응용프로그램들이 탑재되어 안전하게 수행될 수 있는 방법이 제공 되어야 한다. 본 논문은 자동차 전장용 실시간 운영체제 규격인 AUTOSAR에서 실시간성 태스크의 스케줄링시에 각 태스크의 마감시간을 준수할 수 있는 효율적인 스케줄링 기법은 제시하고, 타이밍 보호 메커니즘을 적용하는 방안을 제안한다. 고정 우선 순위나 동적 우선순위 태스크의 유연한 마감 시간 보장하기 위한 동적 비선점 알고리즘과, 오류 발생에 대한 실행 시간 모니터링 가능 위치를 제시하고, AUTOSAR 타임 보호 매커니즘 구현 방안을 제시하였다.