• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1033-1042
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• 1994

Dynamic behavior of flexible rectangular liquid containers is analyzed by a two-dimensional coupled boundary element-finite element method. The irrotational motion of inviscid and incompressible ideal fluid is modeled by boundary elements and the motion of structure by finite elements. A singularity free integral formulation is employed for the implementation of boundary element method. Coupling is performed by using compatibility and equilibrium conditions along the interface between the fluid and structure. The fluid-structure interaction effects are reflected into the coupled equation of motion as added fluid mass matrix and sloshing stiffness matrix. By solving the eigen-problem for the coupled equation of motion, natural frequencies and mode shapes of coupled system are obtained. The free surface sloshing motion and hydrodynamic pressure developed in a flexible rectangular container due to horizontal and vertical ground motions are computed in time domain.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.12
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• pp.71-79
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• 2013

This paper describes a 12.5 Gb/s low-power receiver design with equalizer adaptation. The receiver adapts to channel and chip process variation by adaptation circuit using sampler and serializer. The adaptation principle is explained. It describes technique receiving ground referenced differential signal of voltage-mode transmitter for low-power. The CTLE(Continuous Time Linear Equalizer) having 17.6 dB peaking gain to remove long tail ISI caused channel with -21 dB attenuation. The voltage margin is 210 mV and the timing margin is 0.75 UI in eye diagram. The receiver consumes 0.87 mW/Gb/s low power in 45 nm CMOS technology.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.1
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• pp.121-127
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• 2016

Satellite communication is a communication method using a satellite as a repeater communication on the air and have a communication range is wide and is possible to transmit high-speed data, so Satellite communication has been highlighted as the next generation communication. However, because the distance between the ground and the satellite is far away, there is a disadvantage that propagation delay time is very long and packet is damaged. Therefore, this study was applied to Link Relay H-ARQ system in order to complement the damage to the packet. Furthermore, we propose the Modified Link Relay H-ARQ scheme is a new scheme to supplementation the delay time. By applying the Markov channel for implementing a channel of satellite communications, the results of analyzing the performance, when applying the Link Relay HARQ scheme, BER and PER performance was improved, when applying the Modified Link Relay H-ARQ scheme, Throughput performance was confirmed improvement.

• Journal of the Korean Geotechnical Society
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• v.33 no.4
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• pp.5-15
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• 2017

Three-hinge failure occurs in a jointed rock slope with a joint set parallel with slope and a conjugate joint set. Limit Equilibrium Method (LEM) and Finite Element Method (FEM) which are commonly used for slope design, are not suitable for evaluating stability against three-hinge failure, and this study performed parametric study to analyze the failure mechanism and to find influence factors causing three-hinge failure using UDEC which is a commercial two-dimensional DEM based numerical program. Numerical analyses were performed for various joint structural conditions and joint properties as well as ground water conditions. It was found that pore water pressure is the main factor triggering the three-hinge failure and the mode of failure depends on friction angle of basal joint and bedding joint set. The results obtained from this study can be used for adequate and economic footwall slope reinforcement design and construction.

• Journal of the Korean GEO-environmental Society
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• v.14 no.2
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• pp.43-50
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• 2013

In this study, the tests were carried out for the behavior according to method of constrained nail head of slope reinforced with soil nail under dynamic loading, by using shaking table. Shaking table tests were carried out by applying Hachinohe seismic wave having the long-period characteristics and Ofunato seismic wave having short-period characteristics, as changing constrained and unconstrained condition of nail head, and so on. Failure mode, ground acceleration characteristics, vertical displacement and horizontal displacement of slope were compared and analyzed on the basis of results obtained from the test. Results of carrying out shaking table test showed that both short-period wave and long-period wave had large effects on slope, and constraint of nail head was found to have large shear resistance for dynamic load. And it was confirmed that stability of slope under seismic loading was largely improved by constrained head of soil nail.

• Earthquakes and Structures
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• v.14 no.3
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• pp.215-227
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• 2018

Supplemental passive control devices are widely considered as an important tool to mitigate the dynamic response of a building under seismic excitation. Nevertheless, a systematic method for strategically placing dampers in the buildings is not prescribed in building codes and guidelines. Many deterministic and stochastic methods have been proposed by previous researchers to investigate the optimum distribution of the viscous dampers in the steel frames. However, the seismic performances of the retrofitted buildings that are under large earthquake intensity levels or near collapse state have not been evaluated by any seismic research. Recent years, an increasing number of studies utilize genetic algorithms (GA) to explore the complex engineering optimization problems. GA interfaced with nonlinear response history (NRH) analysis is considered as one of the most powerful and popular stochastic methods to deal with the nonlinear optimization problem of damper distribution. In this paper, the effectiveness and the efficiency of GA on optimizing damper distribution are first evaluated by strong ground motions associated with the collapse failure. A practical optimization framework using GA and NRH analysis is proposed for optimizing the distribution of the fluid viscous dampers within the moment resisting frames (MRF) regarding the improvements of large drifts under intensive seismic context. Both a 10-storey and a 20-storey building are involved to explore higher mode effect. A far-fault and a near-fault earthquake environment are also considered for the frames under different seismic intensity levels. To evaluate the improvements obtained from the GA optimization regarding the collapse performance of the buildings, Incremental Dynamic Analysis (IDA) is conducted and comparisons are made between the GA damper distribution and stiffness proportional damping distribution on the collapse probability of the retrofitted frames.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.10
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• pp.805-812
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• 2013

The operational flight program(OFP) which has the functions of I/O processing with avionics, flight control logic calculation, fault diagnosis and redundancy mode is embedded in the flight control computer of Smart UAV. The OFP was developed in the environment of PowerPC 755 processor and VxWorks 5.5 real-time operating system. The OFP consists of memory access module, device I/O signal processing module and flight control logic module, and each module was designed to hierarchical structure. Memory access and signal processing modules were verified from bench test, and flight control logic module was verified from hardware-in-the-loop simulation(HILS) test, ground integration test, tethered test and flight test. This paper describes development environment, software structure, verification and management method of the OFP.

• Journal of the Korean Society of Visualization
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• v.16 no.1
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• pp.30-36
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• 2018

In the present study, we investigate the flow characteristics of a quadrotor UAV in a hovering mode by measuring multiple two-dimensional velocity fields in the wake. The experiment is conducted at Re = 24,000 in a chamber large enough to neglect the ground effect, where Re is the Reynolds number based on the rotor chord length and the rotor tip speed. The rotational speed of the rotor is determined by an optical tachometer so that the lift force can be balanced with the weight of the UAV. The velocity field measured on the center plane of the rotor shows that the vortices are shedding from the tip of the rotor, inducing large fluctuations in the streamwise velocity along the wake shear layer. The strength of the rotor-tip vortex shedding is asymmetric with respect to the rotor axis due to the interaction between the rotor and the wake centerline of each rotor is inclined to the center of the UAV due to the pressure difference caused by the induced velocity. The wake from each rotor moves closer to each other while traveling in the streamwise direction, and then is merged together inducing large fluctuations in the transverse velocity. Due to the wake merging, on the center plane of the UAV, the velocity increases in the streamwise direction showing two-peak structure in the streamwise velocity contours.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.98-105
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• 2005

This paper presents the result of the aeroelastic stability test of the small-scaled hingeless hub system with composite paddle blades in hover and forward flight conditions. Excitation tests of hingeless hub system installed in GSRTS(General Small-scale Rotor Test System) at KARI(Korea Aerospace Research Institute) were carried out to get lead-lag damping ratio of blades with flexures as hub flexure. MBA(Moving Block Analysis) technique was used for the estimation of lead-lag damping ratio. First, blades with metal flexures, then with composite flexures of the same dynamic properties of rotor system as metal one were tested. Tests were done on the ground and in the wind tunnel according to the test conditions of hover and forward flight, respectively. Composite flexures were found to have better damping characteristics over metal ones in the non-rotating vibration test, and it was confirmed that the use of composite flexures would give observable improvement in aeroelastic stability compared to metal ones in all test conditions.

• The Journal of the Korea Contents Association
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• v.4 no.2
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• pp.21-27
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• 2004

In an urban area telecommunication using wireless system, the accurate prediction and analysis of wave propagation characteristics are very important to determine the service area optimized selection of base station, and eel design, etc. In the stage of these analyses, we have to present the propagation prediction mood which is varied with the type of antenna, directional angle, and configuration of the ground in our urban area in addition we need to perform an analysis of the conventional mode which is similar to ours and dig out the parameters to evaluate the wave environment before the cell design for the selected area. In this paper, we propose a wave propagation prediction model concerning the topography and obstacles in our urban area. We extract the parameters and apply them to the proposed wave environment for the simulation analyzing the propagation characteristics. Throughout these analyzing procedure, we extracted the essential parameters such as the position of the base station, the height of topography, and adequate type and height of the antenna with our preferable cuteness.