• 한국산업융합학회 논문집
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• 제25권1호
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• pp.131-139
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• 2022

The exchange of goods over the sea is a situation in which the amount of trade between countries is gradually increasing. In order to maintain the optimal operating condition, the ship maintains stability and optimal operating conditions by inserting or withdrawing ballast water from the ballast tank according to the loading condition of cargo capacity is also increasing. Control valves play an important role in controlling fluid flow in these pipes. When the flow rate is controlled using a control valve, problems such as cavitation, flashing, and suffocating flow may occur due to high differential pressure, and in particular, damage to valves and pipes due to cavitation is a major problem. Therefore, in this study, the cavitation phenomenon is reduced by installing orifices at the front and rear ends of the high differential pressure control butterfly valve to reduce the sudden pressure drop at the limiting part of the butterfly valve step by step. The flow coefficient according to the shape of the orifice, the degree of cavitation occurrence, and the correlation were analyzed using a CFD(Cumputational Fluid Dynamics), and an optimal orifice design for reducing cavitation is derived.

• 한국정밀공학회지
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• 제23권6호
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• pp.64-71
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• 2006

A target of this paper is to study on the usefulness of the adaptive piezoelectric energy harvesting device as a wireless electrical power supply when it is driven by mechanical vibrations of low frequency. For this purpose, an adaptive control technique and a step-down converter are used. A THUNDER series a piezoelectric material (TH7-R), which has been developed by a NASA engineer is selected for this study. In order to provide a mechanical energy to the piezoelectric material, a mechanical motion vibrator is designed. The adaptive controller is implemented using a dSPACE DS1104 controller board. The do-dc converter with an adaptive control technique harvests energy at over five times the rate of direct charging without a converter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.287-289
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• 1995

In this paper, We applied the $\mu$-stepping method on the Phase Excitation Sequence of Hybrid type LPM. Linear Pulse Motor can opeate in an open loop control as an effective positioning actuator. PWM driver was used for low power loss and automatically adjusted voltage at rate current. Finally we find that through the position-velocity for timing Triangular and Trapezoidal Profile are very affected by velocity and acceleration parameter.

• Journal of Power Electronics
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• 제15권4호
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• pp.886-898
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• 2015

The design feasibility of a micro unidirectional DC transmission system based on an input-parallel output-parallel (IPOP) converter is analyzed in this paper. The system consists of two subsystems: an input-parallel output-series (IPOS) subsystem to step up the DC link voltage, and an input-series output-parallel (ISOP) subsystem to step down the output voltage. The two systems are connected through a transmission line. The challenge of the delay caused by the communication in the control system is addressed by introducing a ring communication structure, and its influence on the control system is analyzed to ensure the feasibility and required performance of the converter system under practical circumstances. Simulation and experiment results are presented to verify the effectiveness of the proposed design.

• 경영과학
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• 제26권3호
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• pp.11-21
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• 2009

In this paper, we proposed some valuable analysis results of cultivation campaign marketing in A mobile telephone company. The cultivation campaign marketing is a new outbound TM campaign strategy composed of 4 steps for new subscribers. During the analyses, attrition rate of A mobile company, outbound TM rejection rate, contact rate/call success rate and additional service attrition rate after subscription are measured as an effect of cultivation campaign. The results showed that there were no statistical significance in improving retention rate between customers experienced 4 step cultivation campaign and control group. However, the cultivation campaign had a better effect on improving response rate and success of selling additional service product of mobile company compared to general selling campaign. This is because cultivation campaign group had been taking care of from subscription time. It is suggested that cultivation campaign had better confined customers more likely to buy additional service to outbound TM for the sake of financial efficiency.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.276-280
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• 1992

In the paper, an optimal tuning algorithm is presented to automatically improve the performance of a hybrid controller, using the simplified reasoning method and the proposed complex method. The method estimates automatically the optimal values of the parameters of a hybrid controller, according to the change rate and limitation condition of output, The controller is applied to plants with time-delay. Then, computer simulations are conducted at step input and the performances are evaluated in the ITAE.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1854-1857
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• 1991

A numerically efficient modification of a variable step size LMS (Least Mean Squares) algorithm is proposed. This proposed algorithm is very simple in calculation and has a variable step size adjusted by the filter output error. Its additional computational burden with respect to the conventional LMS algorithm is only two multiplications, two substraction, an addition and some bit operations. In a simulation example, it is shown that the proposed algorithm has not only the faster convergence rate but also less misadjustments in the environment of highly nonstationary and correlated data.

• 한국해양공학회지
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• 제11권4호
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• pp.213-220
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• 1997

In this study, a design for a shape of centrifugal pump impeller has been performed using a p.c. under a Windows environment. Interaction between a user and a computer has been easily established using the Visual Basic. In determining an outer diameter of an impeller, steps are divided into two, a basic computational step and a refinment step. In this way user can enter his/her experience at the refinment step and hence can expect to lessen the nonlinear nature inherent to the design. In determining a shape of a side view of an impeller, the Bezier cubic curve has been used, and it can be seen that the Bezier cubic curves are well suited in the shape design under a Windows environment. By simply manipulating the four control points, one can generate various cubic curves among which one is selected. Also, a simple method, which can determine the curved position of an impeller vane, has been developed. These data can be used for final CAD drawings.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.309-309
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• 2000

The main objective of this study is to understand the regeneration step of the PTSA(Pressure and thermal swing adsorption) process below the atmospheric pressure by rigorous dynamic simulation. This target process is to recover toluene using activated carbon as an adsorbent. To do this, the dynamic simulations for the regeneration step are performed at 360, 490, 590mmHg and at high temperature after the simulation of the adsorption step at latm and 298K. A mathematical model was developed to simulate the column dynamics of the adsorption systems. This model is based on non-equilibrium, non-isothermal and non-adiabatic conditions, and axial dispersion and heat conduction are also considered. Heat transfer resistances are considered in gas-solid, gas-column wall and column wall-outside air. The LDF(Linear Driving Force) approximation model describes the mass transfer rate between the gas and solid phase. This study shows that the recovery of toluene by PTSA is more preferable than that by general TSA.

• 대한통합의학회지
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• 제10권1호
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• pp.49-60
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• 2022

Purpose : The purpose of this study was to identify whether gym-ball exercise in standing position was an effective intervention for improving muscle strength, balance, gait, and fall efficacy in stroke patients. Methods : Twenty-four stroke patients were randomized into three groups: experimental group 1 (n=8), experimental group 2 (n=8), and control group (n=8). Experimental groups 1, 2 and the control group performed the gym-ball exercise in standing position, same exercise without a gym-ball, and general physical therapy for 4 weeks, five times a week in 30-minute sessions. Muscle strength, balance, gait, and fall efficacy were assessed using a handheld dynamometer, the Berg Balance Scale (BBS), the wearable BTS G-WALK® sensor, and the Korean version of the Falls Efficacy Scale (K-FES), before and after training, respectively. Comparisons within and between groups were analyzed using the Wilcoxon signed rank test, Kruskal Wallis H test, and Mann-Whitney U test. Bonferroni correction was performed when significant differences between groups were identified (p<.017, .05/3). Results : Regarding muscle strength, BBS score, cadence and FES-K were significantly improved after intervention in all three groups. The weight bearing rate, gait speed and step length in experimental group 1 and 2 were significantly improved after the intervention. The stride length in experimental group 1 were significantly improved after the intervention. Experimental group 1 had significantly improved BBS score and stride length after intervention than experimental group 2 and control group. Experimental group 1 and 2 improved muscle strength, weight bearing rate, and FES-K score more than the control group. Experimental group 1 showed significant improvement in cadence, gait speed, and step length after the intervention than control group. Conclusion : This study showed that exercise with gym-ball in standing position can be an effective intervention to improve balance and gait in stroke patients than the same exercise without gym-ball.