• Geomechanics and Engineering
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• v.18 no.2
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• pp.111-119
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• 2019

Due to certain geological characteristics (high thickness, rocky properties), some underground coal mines require the use of explosives. This paper explores the effects of fragmentation of different decks detonated simultaneously in a single borehole with the use of numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include an erosion criterion to simulate the cracks generated by the explosion. As expected, the near-borehole area was damaged by compression stresses, while far zones and the free surface of the boundary were subjected to tensile damage. With the increase of the number of decks in the borehole, different changes in the fracture pattern were observed, and the superposition effects of the stress wave became evident, affecting the fragmentation results. The superposition effect is more evident in close distances to the borehole, and its effect attenuates when the distance to the borehole increase.

• Geotechnical Engineering
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• v.5 no.2
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• pp.33-44
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• 1989

In this paper, uncertainties in dynamic soil structure interaction (SSI) of nuclear poi.or plants subjected to seismic loading are studied considering the random characteristics of soils surround- ing the structure. Firstly sensitivity analysis is performed to study the effect of uncertain dynamic soil properties on the response of the structure. Secondly, to take into account the non-neterministic characteristics in analysis caused by random characteristics of the soil properties, Perturbation method and Rosenblueth's Two point estimates were used for this studu. The procedure is based on the comptex response method which is constituted by a combined usage of conventional finite elements for the near field and infinite elements for the far field. Results of the sensitivity analysis show that dynamic soil properties greatly affect the response of the sol.uc- lure. Results of the probabilistic analysis show that the Two-point estimate method produces good agreements with the Perturbation method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.4
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• pp.307-314
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• 2008

Loading noise generated by steady aerodynamic force exerted on the rotating body surface is theoretically analyzed and its radiation characteristics is examined as a fundamental research of helicopter rotor noise. For simplicity, the force exerted on each blade is not distributed but concentrated at one point and the noise is evaluated by using Lowson' exact formula with a discussion of the physical meaning of each term in the formula. For a single point force rotating with various angular frequencies, we investigated the radiation characteristics and theoretically explained the physical behavior at near and far-field. By investigating the amplitude of acoustic pressure with various distances, we observed the different decreasing ratio at near- and far-field with the discussion of the effect of acceleration of angular frequency. Finally, the phenomenon that the noise level is reduced everywhere as the number of blade increases is explained with the suggestion of a noise reduction idea, the limitations of this study, and the future research topics.

• Journal of Distribution Science
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• v.18 no.3
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• pp.99-106
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• 2020

Purpose: The purpose of this study is to investigate the influence of perceived risk and psychological distance on purchase intention when purchasing a gift. It focuses on social distances and temporal distances, and aims to identify the interactions between these psychological distances and perceived risk. Data were collected through experiments. Research design, data and methodology: The experiment was carried out through the design of 2 (perceived risk: high/low) × 2 (social distance: far / near) × 2 (temporal distance: far / near) between-subjects design. Participants were 241 undergraduates from two universities in Chungnam and Gangwon, and randomly assigned to one of eight groups. Results: It was confirmed that there is a difference in purchase intention according to the risk perceived by consumers when purchasing a gift. In particular, the difference in purchase intention based on the risk perceived by the buyer was found to be greater as the social distance between the gift giver and the recipient is shorter. In addition, it was confirmed that the intention to purchase a gift was simultaneously influenced by three factors: social distance, perceived risk, and time remaining to purchase a gift. In other words, when both temporal distance and social distance were short, the difference in purchase intention according to perceived risk was greatest. Conclusions: The purpose of this study was to examine how the relationship between perceived risk and purchase intention when purchasing a gift varies with psychological distance. This study found that the closer the relationship between the gift purchaser and the beneficiary and the shorter the time remaining before the gift purchase, the greater the difference in the willingness to purchase due to the perceptual risk. In practice, the results of this study can be used to establish sales promotion strategies for various gift products. Above all, the closer the relationship between the gift buyer and the person receiving the gift, the more differentially there should be a guarantee program that can reduce or eliminate the risk perceived by the buyer. There is also a need to use step-by-step product recommendation programs that can reduce perceptual risk depending on the time remaining until a particular season, such as graduation or Christmas.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.1
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• pp.1-10
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• 2013

In order to predict inelastic displacement response without nonlinear dynamic analysis, the equal displacement rule can be used for the structures with longer natural periods than the characteristic period, $T_g$, of earthquake record. In the period range longer than $T_g$, peak displacement responses of elastic systems are equal or larger than those of inelastic systems. In the period range shorter than $T_g$, opposite trend occurs. In the equal displacement rule, it is assumed that peak displacement of inelastic system with longer natural period than $T_g$ equals to that of elastic system with same natural period. The equal displacement rule is very useful for seismic design purpose of structures with longer natural period than $T_g$. In the period range shorter than $T_g$, the peak displacement of inelastic system can be simply evaluated from the peak displacement of elastic system by using the inelastic displacement ratio, which is defined as the ratio of the peak inelastic displacement to the peak elastic displacement. Smooth hysteretic behavior is more similar to actual response of real structural system than a piece-wise linear hysteretic behavior such as bilinear or stiffness degrading behaviors. In this paper, the inelastic displacement ratios of the smooth hysteretic behavior system are evaluated for far-fault and near-fault earthquakes. The simple formula of inelastic displacement ratio considering the effect of $T_g$ is proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3B
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• pp.472-486
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• 2000

This paper analysis the performance of joint receiving structure consisting of the decorrelating multiuser detection and beamfromenr-RAKE receive for DS-CDMA communication systems. In asynchronous transmission as the number of simultaneous users increase. the capacity of CDMA system becomes severly reduced due to the nonideal orthogonality between user-assigned PN sequences and improper power control. Accordingly, the CDMA receiving system becomes vulnerable to the multiple access interferences and the near-far problem under multipath fading channel environment. To withstand these undesired performance degradations, this paper proposes the new type of multiuser detection which has a form of the hybrid structure of concatenating beamformer-RAKE receiver and decorrelating multiuser detection. the beam former-RAKE receiver performs temporal and spatial diversity combining with alleviating fading effect and suppressing undesired interferences, and the multiuser detection plays a role of making the receiver robust to the near-far problem. Regarding the individual merit on the usage of either multiuser detection or beamformer-RAKE receiver, the hybrid one is expected to produce the enhanced performance in multipath fading CDMA channel. However major drawback of using decorrelating multiuser detection for practical deployment is arised from its computational complexity , which is exponentially increased as more number of users and transmitted symbols involve. To diminish the computational complexity, this paper exploits an efficient block Toeplitz inversion technique using matrix Levinson polynomial will be introduced. And this paper provided the mathematical analysis to show the efficiency of the proposed joint structure under the multipath propagation environment. And results of a series of exhaustive computer simulations are presented in order to demonstrate the overall performance of the proposed hybrid structure in multipath fading CDMA channel.

• Journal of Digital Convergence
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• v.19 no.6
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• pp.91-101
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• 2021

As many CSR activities grow steadily, how charitable giving messages affect donation attitude is received attention. In the current research, temporal orientation and donation recipients is presented an effective variables to judge a organization activities. This article based on CLT theory, we establish the experimental condition focused on interaction effects between two variables: time orientation in charitable activities outcomes(near future: a week vs. far future: a year); and based on the recognizability of recipients(a individual child vs. collective group). Result from study, charitable activities outcomes generated in near future orientation(far future orientation) increase donation attitude and affective when messages are used in a specific(general group) context. Furthermore, empathy of CSR organization is a mediator on donation attitude and affective. We expect that these findings have important implication for charitable giving strategy.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.423-430
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• 2005

In this paper. a microphone array beamforming algorithm that reduces the signal distortion caused by reverberation and near-field effect in car environment is proposed. When reverberation or near-field effect is present, an optimum beamformer should be constructed with a steering vector consisting of transfer functions between source and microphones, but it is generally difficult to estimate transfer functions on-line without knowledge of the source signal. Instead, a sub-optimal beamforming algorithm that reduces signal distortion is proposed. It is constructed with steering vectors consisting of relative transfer functions between reference sensor and other sensors. In order to evaluate the performance of the proposed algorithm. we had recorded noisy speech database in a car, and performed speech recognition experiments with HMM Toolkit (HTK) released by Cambridge University. The recognition rate of the proposed algorithm was 15 percents higher than that of the conventional far-field beamformers in best case.

• Earthquakes and Structures
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• v.19 no.6
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• pp.427-444
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• 2020

The performance of an isolated horizontally curved continuous bridge with High Damping Rubber (HDR) Bearings has been investigated under seismic loading conditions. The effectiveness of response controls of the bridge by HDR bearings for various aspects viz. variation in ground motion characteristics, multi-directional effect, level of earthquake shaking, varying incidence angle, have been determined. Three recorded ground motions, representative of historical earthquakes along with near-field, far-field and forward directivity effects, have been considered in the study. The efficacy of the bearings with bidirectional effect considering interaction behavior of bearing and pier has also been investigated. Modeling and analysis of the bridge have been done by finite element approach. Sensitivity studies of the bridge response with respect to design parameters of the bearings for the considered ground motions have been performed. The importance of the nonlinearity of HDR bearings along with crucial design parameters has been identified. It has been observed that the HDR bearings performed well in different variations of ground motions, especially for controlling torsional moment. However, the deck displacement has been found to be increased significantly in case of Turkey ground motions, considering forward directivity effect, which needs to be paid more attention from designer point of view.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.815-818
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• 2002

The elliptic relaxation model(ERM) with the inhomogeneous correction intermediate between near wall with and far from the wall. The source of the ERM usually was appled quasi-homogeneous pressure-strain correlation in homogeneous situations. This formulation was easily applied to the linear model or non-linear pressure-strain model. It is observed that the boundary conditions of the relaxation operator dominate the homogeneous pressure-strain model in the near wall region. While looking at high-Reynolds number flows, it was found necessary to modify the effect of the relaxation operator throughout the log region by accounting for gradients of the flatness variable and turbulent length scales. These effects are kinematic blocking of the wall normal velocity fluctuation and pressure reflections from the surface. This model is wall distances and unit vectors which make the model applicable to flows boundary by a complex geometry. Inhomogeneous correction model is computed inertial and non-inertial channel flow These are compared DNS(Kim et at., Kristofffrsen & Andersson) for channel flow. The present model could be predicted well for rotating flows.