• International Journal of Highway Engineering
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• v.18 no.2
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• pp.51-60
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• 2016

PURPOSES : The applicability of the mechanics-based similarity concept (suggested by Feng et al.) for determining scaled variables, including length and load, via laboratory-scale tests and discrete element analysis, was evaluated. METHODS: Several studies on the similarity concept were reviewed. The exact scaling approach, a similarity concept described by Feng, was applied in order to determine an analytical solution of a free-falling ball. This solution can be considered one of the simplest conditions for discrete element analysis. RESULTS : The results revealed that 1) the exact scaling approach can be used to determine the scale of variables in laboratory tests and numerical analysis, 2) applying only a scale factor, via the exact scaling approach, is inadequate for the error-free replacement of small particles by large ones during discrete element analysis, 3) the level of continuity of flowable materials such as SCC and cement mortar seems to be an important criterion for evaluating the applicability of the similarity concept, and 4) additional conditions, such as the kinetics of particle, contact model, and geometry, must be taken into consideration to achieve the maximum radius of replacement particles during discrete element analysis. CONCLUSIONS : The concept of similarity is a convenient tool to evaluate the correspondence of scaled laboratory test or numerical analysis to physical condition. However, to achieve excellent correspondence, additional factors, such as the kinetics of particles, contact model, and geometry, must be taken into consideration.

• Journal of KSNVE
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• v.4 no.4
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• pp.435-442
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• 1994

Self-Compensating Dynamic Balancer (SCDB) is composed of a circular disk with a groove containing spherical balls and a low viscosity damping fluid. To investigate the stability of the motion equations these equations are perturbed and the resulting perturbation equations are analyzed further to determine whether the perturbations grow or decay with dimensionless time. Based on the results of stability investigation, ball positions that result in a balanced system are stable above the critical speed for .betha.' = 3.8. At critical speed the perturbed motion is said to be stable for .betha.' = 23. However, the system is unstable below critical speed in any case of .betha.'.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1166-1171
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• 2001

The method for output disturbance estimation is proposed. In this method, output disturbance is estimated from the closed loop system dynamics using the output and control input signals. In the closed-loop output-disturbance estimator, precise system identification is required to reduce estimation error. The realization of estimator was done by the DSP board (DSPl103), and disturbance estimation in various environments was performed： change of rotation speed, media feature and spindle motor with (or without) auto-ball balancing system (ABS). From these experiments, the disturbance characteristics of ODD under various conditions are analyzed, and the desirable servo loop configuration based these results is proposed.

• Korean Journal of Metals and Materials
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• v.46 no.8
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• pp.516-523
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• 2008

The effect of glass-frit size on microstructural evolution and electrical resistance of conductive silver paste was investigated. Silver paste was prepared by mixing 70 wt% commercial silver powder with $1.6{\mu}m$, 3 wt% Bi based glass-frit and 27 wt% organic vehicle. Two different sizes of glass-frit were obtained by ball-milling of commercial glass-frit ($3{\mu}m$) for 3 and 5 days, which had an average particle size of 1.0 and $0.5{\mu}m$. The smaller glass-frit was melt at low sintered temperature and rapidly spread between the silver particles, which is induced the dense networking among silver particles and strong adhesiveness to $Al_2O_3$ substrate. The silver film with smaller glass-frit sintered at $500^{\circ}C$ showed the small pore size and low porosity resulting in low electrical resistivity of $4{\mu}{\Omega}cm$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.8
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• pp.2718-2731
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• 2021

In the structural health monitoring of composite materials, in order to solve the ill-posed problem of impact force reconstruction, regularization techniques are often used to deal with it. Due to the poor convergence of the traditional Tikhonov regularization method, in order to accurately reconstruct the time history of the impact force, this paper improves Tikhonov regularization method and constructs homotopy function with strong convergence. Since the optimal regularization parameters need to be found in the homotopy function, the Newton downhill method is used to find the optimal parameters and the homotopy function can be calculated, which can accurately reconstruct the time history of the impact force. In order to verify the universality of the method in this paper, impact hammers of different materials were used in the experiment in this paper to study and compare the reconstruction effect of impact time history of different impact hammers.

• Smart Structures and Systems
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• v.24 no.1
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• pp.15-26
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• 2019

Over the past decades, a great variety of dampers have been developed and applied to mechanical, aerospace, and civil structures to control structural vibrations. This study is focused on two emerging damper types, namely, eddy current dampers (ECDs) and electromagnetic damper (EMDs), both of which are regarded as promising alternatives to commonly-applied viscous fluid dampers (VFDs) because of their similar mechanical behavior. This study aims to enhance the damping densities of ECDs and EMDs, which are typically lower than those of VFDs, by proposing new designs with multiple improvement measures. The design configurations, mechanisms, and experimental results of the new ECDs and EMDs are presented in this paper. The further comparison based on the experimental results revealed that the damping densities of the proposed ECD and EMD designs are comparable to those of market-available VFDs. Considering ECDs and EMDs are solid-state dampers without fluid leakage problems, the results obtained in this study demonstrate a great prospect of replacing conventional VFDs with the improved ECDs and EMDs in future large-scale applications.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2019.05a
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• pp.382-384
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• 2019

In this study, we analyzed the angle of shooting based on the footage of shooting training of basketball student athletes taken by the basketball team leaders. In the shooting video, the shot height of the player and the trajectory of the ball were drawn through a solid line, and the player was shown to guide the player to adjust the angle of projection to a situation where the success rate was higher. Through this study, the video shows that efficient guidance can be made available to basketball players.

• Journal of the Korea Society of Computer and Information
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• v.24 no.1
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• pp.41-47
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• 2019

In this paper, we propose a new batter evaluation model that reflects the skill of the opponent pitcher in Korean professional baseball. The model consists of evaluation factors such as Run Value, Contribution Score and Ball Consumption considering the pitcher grade. These evaluation factors are calculated as different data. In order to include the evaluation factors having different characteristics into one model, each evaluation factor is weighted and added. The genetic algorithms were used to calculate the weights, and the data were based on the 2016 records of Korea Professional Baseball and the salary data of the players of 2017. As a result of calculation of the weight, the weight of the Run Value was high and the weight of the Contribution Score was very low. This means that when calculating the annual salary, it reflects much of the expected score according to the batting result of the batter. On the other hand, the contribution score indicating the degree to which the batting result contributed to the victory of the team according to the state of the economy is not reflected in the salary or point system.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.955-959
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• 2012

To increase the hydrogen storage capacity of Mg-based materials, a sample with a composition of 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ was prepared by planetary ball milling under hydrogen. The absorption and desorption properties of unmilled $MgH_2$, unmilled $LiBH_4$, and 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ were examined. At 648 K the unmilled $MgH_2$ desorbed 5.70 wt% for 60 min. The unmilled $LiBH_4$ desorbed 6.40 wt% H for 780 min at 673 K. The 69.7 wt% $MgH_2$ + 30.3 wt% $LiBH_4$ sample desorbed 3.10 wt% H for 50 min, and 3.32 wt% H for 300 min at 623 K at the second cycle.

• Advances in materials Research
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• v.13 no.1
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• pp.55-62
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• 2024

Cu-based sulfides have recently emerged as promising thermoelectric (TE) materials due to their low cost, non-toxicity, and abundance. In this research, point defect structure of Cu_2-xZnSnS₄ (x=0.1, 0.2, 0.3) samples were synthesized by the mechanical alloying method. Mixed powders of Cu, Zn, Sn and S were milled using high energy ball milling at a rotation speed of 300 rpm in Ar atmosphere. The milled Cu_2-xZnSnS₄ powders were heat-treated at 723 K for 24 h, and subsequently consolidated using spark plasma sintering (SPS) under an applied pressure of 60 MPa for 15 min. The thermal conductivity of the sintered Cu_2-xZnSnS₄ samples was evaluated. A well-defined Cu_2-xZnSnS₄ powders were successfully formed after milling for 16 h, with the particle sizes mostly distributed in the range of 60-100 nm. The lattice constants of aand cdecreased with increasing composition value x. The thermal conductivity of sintered x=0.1 sample exhibited the lowest value and attained 0.93 W/m K at 673 K.