• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.68-78
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• 2013

In this paper, we propose an early spectrum sensing(ESS) as an advance preparation for radio-access trial, which enables multi-mode terminals to access the most appropriate radio-access system in a cloud-conceptual base station system where multiple radio access technologies(RATs) coexist. Prior to a random access to one of RATs, a multi-mode terminal conducts a spectrum sensing over entire frequency bands of whole RATs, then select the RAT with the lowest sensing power, that is likely to have the most available spectrum. Thus, an access failure caused by that the selected RAT has no available radio spectrum could be avoidable in advance. In computer simulation, we consider as various RATs as possible. First, circuit and packet systems are taken into consideration. In addition, the packet systems are classified according to the feasibility of carrier aggregation(CA). In case of terminal, three modes are considered with circuit-only, packet-only, and multi-mode. Subsequently, packet traffic is classified into real-time and non-real-time traffic with three different tolerable delay levels. The simulation includes a call process starting with a call generation and ending up with a resource allocation reflecting individual user's QoS requirements and evaluates the proposed scheme in terms of the successful access probability, system access time, system balancing factor and packet loss probability.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.3
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• pp.393-402
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• 2018

While interacting with a sloping structure, an ice floe may fracture in different patterns. For example, it can be local bending failure or global splitting failure depending on the contact properties, geometry and confinement of the ice floe. Modelling these different fracture patterns as a natural outcome of numerical simulations is rather challenging. This is mainly because the effects of crack propagation, crack branching, multi fracturing modes and eventual fragmentation within a solid material are still questions to be answered by the on-going research in the Computational Mechanic community. In order to simulate the fracturing of ice floes with arbitrary geometries and confinement; and also to simulate the fracturing events at such a large scale yet with sufficient efficiency, we propose a semi-analytical/empirical and semi-numerical approach; but with focus on the global splitting failure mode in this paper. The simulation method is validated against data we collected during the Oden Arctic Technology Research Cruise 2015 (OATRC2015). The data include: 1) camera images based on which we specify the exact geometry of ice floes before and after an impact and fracturing event; 2) IMU data based on which the global dynamic force encountered by the icebreaker is extracted for the impact event. It was found that this method presents reasonably accurate results and realistic fracturing patterns upon given ice floes.

• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.375-387
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• 2018

This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

• Earthquakes and Structures
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• v.11 no.3
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• pp.461-481
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• 2016

The research described in this paper investigates the seismic behaviour of lightly reinforced concrete (RC) bearing sandwich panels, heavily conditioned by shear deformation. A numerical model has been prepared, within an open source finite element (FE) platform, to simulate the experimental response of this emerging structural system, whose squat-type geometry affects performance and failure mode. Calibration of this equivalent mechanical model, consisting of a group of regularly spaced vertical elements in combination with a layer of nonlinear springs, which represent the cyclic behaviour of concrete and steel, has been conducted by means of a series of pseudo-static cyclic tests performed on single full-scale prototypes with or without openings. Both cantilevered and fixed-end shear walls have been analyzed. After validation, this numerical procedure, including cyclic-related mechanisms, such as buckling and subsequent slippage of reinforcing re-bars, as well as concrete crushing at the base of the wall, has been used to assess the capacity of two- and three-dimensional low- to mid-rise box-type buildings and, hence, to estimate their strength reduction factors, on the basis of conventional pushover analyses.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.452-455
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• 2004

MSC (Multi-Spectral Camera) system is a remote sensing instrument to obtain high resolution ground image. EOS (Electro-Optic System) for MSC mainly consists of PMA (Primary Mirror Assembly), SMA (Secondary Mirror Assembly), HSTS (High Stability Telescope Structure) and DFPA (Detector Focal Plane Assembly). High performance of EOS makes it possible for MSC system to provide high resolution and high quality ground images. Temperature of the EOS needs to be controlled to be in a specific range in order not to have any thermal distortion which can cause performance degradation. It is controlled by full redundant CPU based electronics. The validity of thermistor readings can be checked because a few thermistors are installed on each control point on EOS. Various kinds of thermal control logics are used to prevent 'Single Point Failure'. Control logic has a few set of database in order not to be corrupted by SEU (Single Event Upset). Even though the thermal control logic is working automatically, it can also be monitored and controlled by ground-station operator. In this paper, various ways of thermal control logic for EOS in MSC will be presented, which include thermal control mode and logic, redundancy design and status monitoring and reporting scheme.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.103-114
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• 1992

A study result of buckling reliability is presented for the axially compressed imperfect elastic cylinder. Multi-mode analysis program is developed from Karman-Donnell Equation for the calculation of the buckling load of the cylindrical she1l. Geometric intial imperfection is approximated by double Fourier series of which coefficients are assumed random variables with jointly normal distribution characteristics. Crude Monte Carlo simulation technique is used to calculate the probabilistic failure properties of several cases with various imperfection Conditions.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.5 s.170
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• pp.152-158
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• 2005

Inner structured and bonded panel, or ISB Panel, as a kind of sandwich type panel, has metallic inner structures which have low relative density, due to their dimensional shape of metal between a pair of metal skin sheets or face sheets. Previous works showed that ISB panels containing inner structures formed as repeated pyramidal shapes saved weight up to $60\%$ in condition of same stiffness comparing with solid sheet. In this work, woven metal is adapted to inner structures replacing pyramidal structures. The test specimens of ISB panel containing woven metal made by multi-point electric resistance welding and 3-point bending test have been carried out. The results of experiments and comparisons of process parameters, stiffness and failure mode are discussed.

• Journal of Drive and Control
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• v.14 no.4
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• pp.71-78
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• 2017

The power train of hydro-mechanical continuously variable transmission (HMCVT) for 8-ton class forklift includes hydro-static units, hydraulic multi-wet disc brake & clutches and complex helical & planetary gears. The helical & planetary gears are key components of HMCVT's power train wherein strength problems are the main concerns including gear bending stress, gear compressive stress, and scoring failure. Many failures in power train gears of HMCVT are due to the insufficient gear strength and resonance problems caused by major excitation forces, such as gear transmission error of mating gear fair in the transmission. In this study, wherein excitation frequencies are the gear tooth passing frequencies of the mating gears, a Campbell diagram is used to calculate the power train gears' critical speeds. Mode shapes and natural frequencies of the power train gears are calculated by CATIA V5. These are used to predict resonance failures by comparing the actual working speed range with the critical speeds due to the gear transmission errors of HMCVT's power train gears.

• The Journal of Society for e-Business Studies
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• v.15 no.4
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• pp.49-58
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• 2010

The wireless sensor network technology becomes one of core technologies to make it possible to implement various e-business applications. Energy efficiency is an important issue in wireless sensor networks. IEEE 802.15.4, a representative international standard for wireless sensor networks, provides the beacon enabled mode for energy-efficient communication. However, the beacons may conflict each other when the network is of multi-hop topology such as mesh or cluster-tree topology with beacon-enabled mode. The beacon conflict causes the failure of synchronization between sensor nodes, and affects other nodes in the network in that unsynchronized nodes cannot participate in communication. In this paper, we suggest an energy-efficient beacon scheduling for the wireless sensor networks. Nodes can save their energy duringperiod and prevent beacon conflict using beacon scheduling. We implement the scheduling using QualNet, and evaluate the performance under mesh topology networks. It turns out that the proposed scheduling may improve the energy efficiency in the networks.

• Restorative Dentistry and Endodontics
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• v.30 no.1
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• pp.49-57
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• 2005

The purpose of this study was to evaluate the effect of multiple application of all-in-one dentin adhesive system on microtensile bond strength to caries-affected dentin. Twenty one extracted human molars with occlusal caries extending into mid-dentin were prepared by grinding the occlusal surface flat. The carious lesions were excavated with the aid of caries detector dye. The following adhesives were applied to caries-affected dentin according to manufacturer's directions; $Scotchbond^{TM}$ Multi-Purpose in SM group, Adper Prompt $L-Pop^{TM}$ 1 coat in LP1 group, 2 coats in LP2 group, 3 coats in LP3 group, $Xeno^{(R)}$ III 1 coat in XN1 group, 2 coats in XN2 group. and 3 coats in XN3 group. After application of the adhesives, a cylinder of resin-based composite was built up on the occlusal surface. Each tooth was sectioned vertically to obtain the $1{\times}1\;mm^2$ sticks. The microtensile bond strength was determined. Each specimen was observed under SEM to examine the failure mode. Data were analyzed with one-way ANOVA. The results of this study were as follows; 1. The microtensile bond strength values were; SM ($14.38{\pm}2.01$ MPa), LP1 ($9.15{\pm}1.81$ MPa), LP2(14.08{\pm}1.75$ MPa), LP3 ($14.06{\pm}1.45$ MPa). XN1 (13.65{\pm}1.95$ MPa). XN2 ($13.98{\pm}1.60$) MPa, XN3 ($13.88{\pm}1.66$) MPa, LP1 was significantly lower than the other groups in bond strength (p < 0.05). All groups except LP1 were not significantly different in bond strength (p > 0.05). 2. In LP1, there were a higher number of specimens showing adhesive failure. Most specimens of all groups except LP1 showed mixed failure.