• Smart Structures and Systems
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• v.16 no.5
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• pp.961-980
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• 2015

Magnetorheological (MR) fluids are capable of changing their rheological properties under the application of external fields. When MR fluids operate in the so-called squeeze mode, in which displacement levels are limited to a few millimetres but there are large forces, they have many potential applications in vibration isolation. This paper presents an experimental and a numerical investigation of the performance of an MR fluid under tensile and compressive loads and oscillatory squeeze-flow. The performance of the fluid was found to depend dramatically on the strain direction. The shape of the stress-strain hysteresis loops was affected by the strength of the applied field, particularly when the fluid was under tensile loading. In addition, the yield force of the fluid under the oscillatory squeeze-flow mode changed almost linearly with the applied electric or magnetic field. Finally, in order to shed further light on the mechanism of the MR fluid under squeeze operation, computational fluid dynamics analyses of non-Newtonian fluid behaviour using the Bingham-plastic model were carried out. The results confirmed superior fluid performance under compressive inputs.

• Journal of Distribution Science
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• v.18 no.2
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• pp.5-15
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• 2020

Purpose : Today's retailers are integrating new VR technology into their new marketing strategies. Thus, this research aims to understand the role of virtual experiences in the circumstance of sales channels. Research design, data and methodology : Our model hypothesizes that five key factors determine the consumer experience of VR in the virtual retailing context: smartness, vividness, interactivity, playfulness, escape. Information access and flow are mediating variables that connect key drivers and VR satisfaction. Information access and flow then give influence to satisfaction towards VR. Satisfaction serves as a mediator that determines changes in consumer's dual intention: intention to revisit VR and intention to visit the real site. Results : According to the test results, every path except the relationship between information access and satisfaction of VR is accepted as expected at the significance level of 0.05. Conclusions : This research emphasizes the potential importance of VR and continue VR marketing research as an advent research area. Through the dual-path model, this study found that the primary function of VR is information access and flow experience. This result shows that most VR users value emotional benefits rather than rational benefits provided by VR. Finally, the satisfaction of VR can stimulate both the intention to use the VR and the intention to visit real mall.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.2
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• pp.159-167
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• 2019

In this paper the potential of the principal component analysis(PCA) technique for the application of detecting leaks in water pipe networks was evaluated. For this purpose the PCA was conducted to evaluate the relevance of the calculated outliers of a PCA model utilizing the recorded pipe flows and the recorded pipe leak incidents of a case study water distribution system. The PCA technique was enhanced by applying the computational algorithms developed in this study which were designed to extract a partial set of flow data from the original 24 hour flow data so that the effective outlier detection rate was maximized. The relevance of the calculated outliers of a PCA model and the recorded pipe leak incidents was analyzed. The developed algorithm may be applied in determining further leak detection field work for water distribution blocks that have more than 70% of the effective outlier detection rate. However, the analysis suggested that further development on the algorithm is needed to enhance the applicability of the PCA in detecting leaks by considering series of leak reports happening in a relatively short period.

• Journal of Korean Society of Transportation
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• v.17 no.1
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• pp.131-139
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• 1999

The quality of progression at signalized intersection has the largest potential effect. TRANSYT-7F is widely used to estimate the signal progression delay, but the progress of collecting and executing the compute program appears to be rather cumbersome. The research is to develop the analytical and progressing platoon delay model that is as simple as the methodology of HCM and familiar with the output of simulation model. The general approach to this research was conducted to examine the Rouphail and NCHRP 339 methodology together with the existing progression delay model (TRANSYT-7F. HCM). The scope is contained to be applicable only to cycles with no overflow queue and to obtain a comprehensive evaluation of the effects of changes in the quality of traffic signal progression on stopped delay and to be analyzed a simple mathematical method. The principle assumption for this model is that secondary flows is dispersed and partly mixed with average flow of the primary progressed flow. A second assumption is that through flow is consisted with the part of saturation flow at the front of it and the part of average flow at the rear of it. The delay equations vary for two arrival. The conclusion of this study could be summarized as 1)The evaluation of this model was consistently similar to that of TRANSYT-7F, 2) Platoon pattern has the real traffic flow characteristics. 3) The computing process of progression delay is made to have simple logic and easy calculation by integration, 4) This model could be estimated to be applied in almost all case.

• Korean Journal of Radiology
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• v.24 no.7
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• pp.647-659
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• 2023

Objective: The study was conducted to investigate the effect of correct occlusion of the left atrial appendage (LAA) on intracardiac blood flow and thrombus formation in patients with atrial fibrillation (AF) using four-dimensional (4D) flow magnetic resonance imaging (MRI) and three-dimensional (3D)-printed phantoms. Materials and Methods: Three life-sized 3D-printed left atrium (LA) phantoms, including a pre-occlusion (i.e., before the occlusion procedure) model and correctly and incorrectly occluded post-procedural models, were constructed based on cardiac computed tomography images from an 86-year-old male with long-standing persistent AF. A custom-made closed-loop flow circuit was set up, and pulsatile simulated pulmonary venous flow was delivered by a pump. 4D flow MRI was performed using a 3T scanner, and the images were analyzed using MATLAB-based software (R2020b; Mathworks). Flow metrics associated with blood stasis and thrombogenicity, such as the volume of stasis defined by the velocity threshold ($\left|\vec{V}\right|$ < 3 cm/s), surface-and-time-averaged wall shear stress (WSS), and endothelial cell activation potential (ECAP), were analyzed and compared among the three LA phantom models. Results: Different spatial distributions, orientations, and magnitudes of LA flow were directly visualized within the three LA phantoms using 4D flow MRI. The time-averaged volume and its ratio to the corresponding entire volume of LA flow stasis were consistently reduced in the correctly occluded model (70.82 mL and 39.0%, respectively), followed by the incorrectly occluded (73.17 mL and 39.0%, respectively) and pre-occlusion (79.11 mL and 39.7%, respectively) models. The surfaceand-time-averaged WSS and ECAP were also lowest in the correctly occluded model (0.048 Pa and 4.004 Pa^-1, respectively), followed by the incorrectly occluded (0.059 Pa and 4.792 Pa^-1, respectively) and pre-occlusion (0.072 Pa and 5.861 Pa^-1, respectively) models. Conclusion: These findings suggest that a correctly occluded LAA leads to the greatest reduction in LA flow stasis and thrombogenicity, presenting a tentative procedural goal to maximize clinical benefits in patients with AF.

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.1-5
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• 2014

We calculated the resonance tunneling energy band in the BCS gap for Type-II superconductor in which periodic potential is generated by external magnetic flux. In this model, penetrating magnetic flux was assumed to be in a fixed lattice state which is not moving by an external force. We observed the existence of two subbands when we used the same parameters as for the $Nd_{1.85}Ce_{0.15}CuO_X$ thin film experiment. The voltages at which the regions of negative differential resistivity (NDR) started after the resonant tunneling ended were in a good agreement with the experimental data in the field region of 1 T - 2.2 T, but not in the high field regions. Discrepancy occurred in the high field region is considered to be caused by that the potential barrier could not be maintained because the current induced by resonant tunneling exceeds the superconducting critical current. In order to have better agreement in the low field region, more concrete designing of the potential rather than a simple square well used in the calculation might be needed. Based on this result, we can predict an occurrence of the electromagnetic radiation of as much difference of energy caused by the 2nd order resonant tunneling in which electrons transit from the 2nd band to the 1st band in the potential wells.

• Journal of Ocean Engineering and Technology
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• v.36 no.5
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• pp.303-312
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• 2022

A submarine is optimized to operate below the water surface because it spends most of its time in a submerged condition. However, the performance in free surface conditions is also important because it is unavoidable for port departure and arrival. Generally, potential flow theory is used for seakeeping analysis of a surface ship and is known for excellent numerical accuracy. In the case of a submarine, the accuracy of potential theory is high underwater but is low in free surface conditions because of the nonlinearity near the free surface area. In this study, the seakeeping performance of a Canadian Victoria Class submarine in regular waves was investigated to improve the numerical accuracy in free surface conditions by using computational fluid dynamics (CFD). The results were compared to those of model tests. In addition, the potential theory software Hydrostar developed by Bureau Veritas was also used for seakeeping performance to compare with CFD results. From the calculation results, it was found that the seakeeping analysis by using CFD gives good results compared with those of potential theory. In conclusion, seakeeping analysis based on CFD can be a good solution for estimating the seakeeping performance of submarines in free surface conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.789-794
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• 2017

Subthreshold current model is presented using analytical potential distribution of junctionless cylindrical surrounding-gate (CSG) MOSFET and threshold voltage shift is analyzed by this model. Junctionless CSG MOSFET is significantly outstanding for controllability of gate to carrier flow due to channel surrounded by gate. Poisson's equation is solved using parabolic potential distribution, and subthreshold current model is suggested by center potential distribution derived. Threshold voltage is defined as gate voltage corresponding to subthreshold current of $0.1{\mu}A$, and compared with result of two dimensional simulation. Since results between this model and 2D simulation are good agreement, threshold voltage shift is investigated for channel dimension and doping concentration of junctionless CSG MOSFET. As a result, threshold voltage shift increases for large channel radius and oxide thickness. It is resultingly shown that threshold voltage increases for the large difference of doping concentrations between source/drain and channel.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.245-258
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• 2020

In this study, a data-driven response surface method using the results acquired from the numerical simulation is developed to evaluate the potential storage capacity of groundwater due to the construction of a groundwater dam. The hydraulic conductivities of alluvium and basement rock, depth and slope of the channel are considered as the natural conditions of the location for groundwater dam construction. In particular, the probability models of the hydraulic conductivities and the various types of geometry of the channel are considered to ensure the reliability of the numerical simulation and the generality of the developed estimation model. As the results of multiple simulations, it can be seen that the hydraulic conductivity of basement rock and the depth of the channel greatly influence to the groundwater storage capacity. In contrast, the slope of the channel along the groundwater flow direction shows a relatively lower impact on the storage capacity. Based on the considered natural conditions and the corresponding numerical simulation results, the storage capacity estimation model is developed applying an artificial neural network as the nonlinear regression model for training. The developed estimation model shows a high correlation coefficient (>0.9) between the simulated and the estimated storage amount. This result indicates the superiority of the developed model in evaluating the storage capacity of the potential location for groundwater dam construction without the numerical simulation. Therefore, a more objective and efficient comparison for the storage capacity between the different potential locations can be possibly made based on the developed estimation model. In line with this, the proposed method can be an effective tool to assess the optimal location of groundwater dam construction across Korea.

• Journal of Environmental Impact Assessment
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• v.3 no.2
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• pp.47-56
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• 1994

AGNPS model is an event-based model to analyze nonpoint-source and to examine potential water quality problems from agricultural watershed. This model uses a square grid-cell system to represent the spatial variability of watershed conditions, and simulates runoff, sediment, and nutrient transport for each cell. AGNPS model was applied on Yeonwha watershed, and the test results were compared with the measured data for runoff volume, peak runoff rate, suspended solids, and phosphorus concentration. The watershed of 278.8 ha was divided into 278 cells, each of which was 1 ha in size. The coefficients of determination for runoff volume and peak flow were (0.893 and 0.801 respectively from regression of the estimated values on the measured values. The concentration of suspendid solid was increased but decreased that of phosphate with runoff volume.