• Steel and Composite Structures
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• v.10 no.2
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• pp.129-149
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• 2010

The objective of this study is to formulate a general 3D material-structural analysis framework for the thermomechanical behavior of steel-concrete structures in a fire environment. The proposed analysis framework consists of three sequential modeling parts: fire dynamics simulation, heat transfer analysis, and a thermomechanical stress analysis of the structure. The first modeling part consists of applying the NIST (National Institute of Standards and Technology) Fire Dynamics Simulator (FDS) where coupled CFD (Computational Fluid Dynamics) with thermodynamics are combined to realistically model the fire progression within the steel-concrete structure. The goal is to generate the spatial-temporal (ST) solution variables (temperature, heat flux) on the surfaces of the structure. The FDS-ST solutions are generated in a discrete form. Continuous FDS-ST approximations are then developed to represent the temperature or heat-flux at any given time or point within the structure. An extensive numerical study is carried out to examine the best ST approximation functions that strike a balance between accuracy and simplicity. The second modeling part consists of a finite-element (FE) transient heat analysis of the structure using the continuous FDS-ST surface variables as prescribed thermal boundary conditions. The third modeling part is a thermomechanical FE structural analysis using both nonlinear material and geometry. The temperature history from the second modeling part is used at all nodal points. The ABAQUS (2003) FE code is used with external user subroutines for the second and third simulation parts in order to describe the specific heat temperature nonlinear dependency that drastically affects the transient thermal solution especially for concrete materials. User subroutines are also developed to apply the continuous FDS-ST surface nodal boundary conditions in the transient heat FE analysis. The proposed modeling framework is applied to predict the temperature and deflection of the well-documented third Cardington fire test.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.5
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• pp.775-782
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• 2022

In this paper, a novel small-diameter cylindrical post capacitor inserted into an evanescent-mode rectangular waveguide (EMRWG) is proposed for easier tuning. In order to feed the EMRWG, the proposed structure uses a single ridge rectangular waveguide with the same width and height as the waveguide at the input and output ends. The inserted post capacitor are made up a circular groove formed in the center of the lower part of the broad wall of the EMRWG, and a concentric cylindrical post inserted into the upper part. First, the equivalent circuit model for the proposed structure is presented. When the EMRWG and the single ridge waveguide are combined, the joint susceptance and the turns ratio of the ideal transformer are calculated by two simulations using HFSS (3d fullwave simulator, Ansoft Co.) respectively. The susceptance and resonance characteristics of the inserted post were analyzed by using the obtained parameters and the characteristics of the EMRWG. A 2-post filter with a center frequency of 4.5 GHz and a bandwidth of 170 MHz was designed using a WR-90 waveguide, and the simulation results by using the HFSS and CST, equivalent circuit model were in good agreement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.55-55
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• 2009

Silicon Carbide (SiC) is a material with a wide bandgap (3.26eV), a high critical electric field (~2.3MV/cm), a and a high bulk electron mobility (${\sim}900cm^2/Vs$). These electronic properties allow high breakdown voltage, high frequency, and high temperature operation compared to Silicon devices. Although various SiC DMOSFET structures have been reported so far for optimizing performances. the effect of channel dimension on the switching performance of SiC DMOSFETs has not been extensively examined. In this paper, we report the effect of the interface states ($Q_s$) on the transient characteristics of SiC DMOSFETs. The key design parameters for SiC DMOSFETs have been optimized and a physics-based two-dimensional (2-D) mixed device and circuit simulator by Silvaco Inc. has been used to understand the relationship with the switching characteristics. To investigate transient characteristic of the device, mixed-mode simulation has been performed, where the solution of the basic transport equations for the 2-D device structures is directly embedded into the solution procedure for the circuit equations. The result is a low-loss transient characteristic at low $Q_s$. Based on the simulation results, the DMOSFETs exhibit the turn-on time of 10ns at short channel and 9ns at without the interface charges. By reducing $SiO_2/SiC$ interface charge, power losses and switching time also decreases, primarily due to the lowered channel mobilities. As high density interface states can result in increased carrier trapping, or recombination centers or scattering sites. Therefore, the quality of $SiO_2/SiC$ interfaces is important for both static and transient properties of SiC MOSFET devices.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.168-185
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a large-scale high-temperature cavern thermal energy storage (CTES) at a shallow depth has been investigated, and the effects of hydrological conditions such as water table and rock permeability on the behavior have been examined. The liquid saturation of ground water around a storage cavern may have a small impact on the overall heat transfer and mechanical behavior of surrounding rock mass for a relatively low rock permeability of $10^{-17}m^2$. In terms of the distributions of temperature, stress and displacement of the surrounding rock mass, the results expected from the simulation with the cavern below the water table were almost identical to that obtained from the simulation with the cavern in the unsaturated zone. The heat transfer in the rock mass with reasonable permeability ${\leq}10^{-15}m^2$ was dominated by the conduction. In the simulation with rock permeability of $10^{-12}m^2$, however, the convective heat transfer by ground-water was dominant, accompanying the upward heat flow to near-ground surface. The temperature and pressure around a storage cavern showed different distributions according to the rock permeability, as a result of the complex coupled processes such as the heat transfer by multi-phase flow and the evaporation of ground-water.

• Journal of the HCI Society of Korea
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• v.13 no.4
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• pp.5-14
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• 2018

The Empathy for Dementia using Virtual Reality (EDuVR) system, developed by the Jeju Provincial Dementia Center, is a 3D video system capturing the experience of dementia in a first-person perspective using 360 degree vritual reality (VR) technology. It was developed to create a greater understanding of dementia and to help people empathize with individuals with dementia through an immersive VR experience. The EDuVR shows how a dementia patient has impairments in memory, orientation, language, judgment and problem solving, as well as problems with activities of daily living. The present study reported the effectiveness of the EDuVR experience in changing public awareness of, and attitude toward, dementia. Sixty-six participants were assigned to the EDuVR (n = 34) or the conventional education (n = 32) groups, and two types of questionnaires - attitude and awareness questionnaires - were administered to the subjects before and after the EDuVR experience or education. The simulator sickness and presence questionnaires were administered to the EDuVR group to assess cybersickness and presence of the VR experience. As a results, the attitude and awareness toward dementia patients changed positively in both the EDuVR and the conventional education groups, and these changes did not differ between two groups. Only one person reported a significant level of cybersicness after experiencing the EDuVR system. These results suggest that the EDuVR enhances the level of understanding and empathy for dementia and would be a useful tool for improving awareness in the general public.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.246-258
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• 2006

A circuit model has been developed to analyze characteristics of the PSII(plasma source ion implantation) pulse system with dynamic plasma load. The plasma sheath in front of the immersed planar target biased with a negative-high voltage pulse is assumed to be governed by the dynamic Child-Langmuir sheath model. Target current is self-consistently varied with the applied voltage by using the voltage-controlled current source in the circuit model. Circuit simulations are conducted with Pspice circuit simulator, and simulated pulse currents and voltages on the target are compared and confirmed with experimental results for various voltage pulses and plasma conditions.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.1
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• pp.51-55
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• 2007

This paper investigates the subthreshold behavior of Fin Field Effect Transistor (FinFET). The FinFET is considered to be an alternate MOSFET structure for the deep sub-micron regime, having excellent device characteristics. As the channel length decreases, the study of subthreshold behavior of the device becomes critically important for successful design and implementation of digital circuits. An accurate analysis of subthreshold behavior of FinFET was done by simulating the device in a 3D process and device simulator, Taurus. The subthreshold behavior of FinFET, was measured using a parameter called S-factor which was obtained from the $In(I_{DS})\;-\;V_{GS}$ characteristics. The value of S-factor of devices of various fin dimensions with channel length $L_g$ in the range of 20 nm - 50 nm and with the fin width $T_{fin}$ in the range of 10 nm - 40 nm was calculated. It was observed that for devices with longer channel lengths, the value of S-factor was close to the ideal value of 60 m V/dec. The S-factor increases exponentially for channel lengths, $L_g\;<\;1.5\;T_{fin}$. Further, for a constant $L_g$, the S factor was observed to increase with $T_{fin}$. An empirical relationship between S, $L_g$ and $T_{fin}$ was developed based on the simulation results, which could be used as a rule of thumb for determining the S-factor of devices.

• Radiation Oncology Journal
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• v.19 no.1
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• pp.53-65
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• 2001

Purpose : To improve the local control of patients with nasopharyngeal cancer, we have implemented 3-D conformal radiotherapy and forward intensity modulated radiation therapy (IMRT) to used of compensating filters. Three dimension conformal radiotherapy with intensity modulation is a new modality for cancer treatments. We designed 3-D treatment planning with 3-D RTP (radiation treatment planning system) and evaluation dose distribution with tumor control probability (TCP) and normal tissue complication probability (NTCP). Material and Methods : We have developed a treatment plan consisting four intensity modulated photon fields that are delivered through the compensating tilters and block transmission for critical organs. We get a full size CT imaging including head and neck as 3 mm slices, and delineating PTV (planning target volume) and surrounding critical organs, and reconstructed 3D imaging on the computer windows. In the planning stage, the planner specifies the number of beams and their directions including non-coplanar, and the prescribed doses for the target volume and the permissible dose of normal organs and the overlap regions. We designed compensating filter according to tissue deficit and PTV volume shape also dose weighting for each field to obtain adequate dose distribution, and shielding blocks weighting for transmission. Therapeutic gains were evaluated by numerical equation of tumor control probability and normal tissue complication probability. The TCP and NTCP by DVH (dose volume histogram) were compared with the 3-D conformal radiotherapy and forward intensity modulated conformal radiotherapy by compensator and blocks weighting. Optimization for the weight distribution was peformed iteration with initial guess weight or the even weight distribution. The TCP and NTCP by DVH were compared with the 3-D conformal radiotherapy and intensitiy modulated conformal radiotherapy by compensator and blocks weighting. Results : Using a four field IMRT plan, we have customized dose distribution to conform and deliver sufficient dose to the PTV. In addition, in the overlap regions between the PTV and the normal organs (spinal cord, salivary grand, pituitary, optic nerves), the dose is kept within the tolerance of the respective organs. We evaluated to obtain sufficient TCP value and acceptable NTCP using compensating filters. Quality assurance checks show acceptable agreement between the planned and the implemented MLC(multi-leaf collimator). Conclusion : IMRT provides a powerful and efficient solution for complex planning problems where the surrounding normal tissues place severe constraints on the prescription dose. The intensity modulated fields can be efficaciously and accurately delivered using compensating filters.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.5
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• pp.35-47
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• 2011

Dynamic characteristics of a flow control valve, which plays an important role in thrust and O/F control of liquid rocket engines, have been analyzed by the AMESim simulator modeling. The speed control method was proposed for the control of the flow valve equipped with a BLDC motor. The experimental results demonstrated the feasibility of systematical application as well as the performance of the speed control method. Moreover, the speed control method for BLDC motor is much simpler than the P control method in complex flow systems. With the speed control method, the control flow characteristics were evaluated according to plunger shapes. Consequently, same plunger shape proved to be more efficient in the mixture ratio control operated by two flow valves. It was also shown that the appropriate modification of plunger shapes could reduce the mixture ratio perturbation by 0.5%.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2577-2596
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• 2013

In this paper, we present an Energy-Aware Self-Stabilizing Distributed Clustering protocol based on message-passing model for Ad Hoc networks. The latter does not require any initialization. Starting from an arbitrary configuration, the network converges to a stable state in a finite time. Our contribution is twofold. We firstly give the formal proof that the stabilization is reached after at most n+2 transitions and requires at most $n{\times}log(2n+{\kappa}+3)$ memory space, where n is the number of network nodes and ${\kappa}$ represents the maximum hops number in the clusters. Furthermore, using the OMNeT++ simulator, we perform an evaluation of our approach. Secondly, we propose an adaptation of our solution in the context of Wireless Sensor Networks (WSNs) with energy constraint. We notably show that our protocol can be easily used for constructing clusters according to multiple criteria in the election of cluster-heads, such as nodes' identity, residual energy or degree. We give a comparison under the different election metrics by evaluating their communication cost and energy consumption. Simulation results show that in terms of number of exchanged messages and energy consumption, it is better to use the Highest-ID metric for electing CHs.