• Proceedings of the KSME Conference
• /
• 2008.11a
• /
• pp.1623-1628
• /
• 2008

A temperature gradient focusing (TGF) via Joule heating phenomenon was numerically studied. The governing transport equations are implemented into a quasi-1D numerical model to predict the resulting temperature, velocity, and concentration profiles along a microchannel of varying width under an applied electric field. The model is used to analyze the effects of varying certain geometrical parameters of a microchannel on the focusing performance of the device. We show the effects of varying width of the microchannel having a fixed length, and propose the optimal geometry of the device. This method can be easily implemented into lab-on-a-chip (LOC) applications where focusing is required based on its simple design.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.4C no.6
• /
• pp.276-281
• /
• 2004

In this paper, the optimal design of a novel microstrip directional coupler with a grooved housing for high directivity characteristic is presented. It will be shown that the high directivity of the microstrip coupler can be achieved simply by attaching an optimized housing structure. over the microstrip, which is much easier to fabricate than other conventional types. The dimensions of the proposed structure are maximized by using (1+1) evolution strategy (ES) combined with the deterministic algorithm. To improve the effectiveness of the results, efficient optimization procedures suitable for the model are proposed. From these results, it is determined that the proposed structure indicates an improved directivity. The optimized results are verified by full wave analysis at the center frequency of 850MHz.

• Proceedings of the KIEE Conference
• /
• 2002.11d
• /
• pp.118-120
• /
• 2002

In this paper, a multi-object optimization based on a progressive quadratic response surface method (PQRSM) and a time stepping finite element method (FEM) is proposed. The new PQRSM and FEM are able to decide optimal geometric and electric variables of the switched reluctance motor (SRM) with two objective functions: torque ripple minimization and average torque maximization. The result of the optimum design for SRM show an improved performance of motor and a relationship between torque ripple and average torque.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.559-560
• /
• 2006

Fiber optic connector, ferrule, is a device to connect and align fiber optics cable on fiber-optic communication system. In general $ZrO_2$ ceramic ferrule is manufactured by grinding process because the demands precision is very high. For the precision grinding machining, it is very important that structure of co-axial ferrule grinding system is optimized. In this paper, Structural analysis was performed to analyze bed and frame structure of co-axial grinding machine. Deformation and modal analysis for natural frequency was performed using ANSYS design space program to analyze structural characteristics. New improved model of bed and frame structure was proposed based on initial basic model. Therefore, we estimated the structural characteristics precision co-axial grinding machining system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2000.10a
• /
• pp.242-248
• /
• 2000

This paper has focused on the optimization of the cutting parameters for turning operation based on the Taguchi method. Four cutting parameters, namely, cutting speed, feed, depth of cut and nose radius are optimized with consideration of the surface roughness. The design and analysis of experiments are conducted to study the performance characteristic. The effects of these parameters on the surface roughness have been investigated using the signal-to-noise (S/N) ratio, analysis of variance (ANOVA). The experiments have been peformed using coated tungsten carbide inserts without any cutting fluid. Experimental results illustrate the effectiveness of this approach.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.2
• /
• pp.86-93
• /
• 2010

The tilting index table has attached to CNC machining center with 3axes, it can be improvement of its performance and its machining efficiency. The tilting index table is a key unit in order to manufacture some non-rotational and 3-dimensional parts, using the conventional machining center. In this study, structural analysis is carried out by FEM simulation using the commercial software ANSYS Workbench 11 to develop tilting index table using direct drive motor. The shape of the tilting index table obtained from the optimization was analyzed and compared with the initial model. Also, the initial model was modified based on the optimization model and the result was verified to have the acceptable improvement.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.9 no.8
• /
• pp.2840-2853
• /
• 2015

A major challenge in network service providers is to provide adequate resources in service level agreements based on forecasts of future demands. In this paper, we address the problem of capacity provisioning in a network subject to demand uncertainty such that a network coded multicast is applied as the data delivery mechanism with limited budget to purchase extra capacity. We address some particular type of uncertainty sets that obtain a tractable constrained capacity provisioning problem. For this reason, we first formulate a mathematical model for the problem under uncertain demand. Then, a robust optimization model is proposed for the problem to optimize the worst-case system performance. The robustness and effectiveness of the developed model are demonstrated by numerical results. The robust solution achieves more than 10% reduction and is better than the deterministic solution in the worst case.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.9
• /
• pp.2153-2169
• /
• 2012

Femtocells provide high quality indoor communications with low transmit power. However, when femtocells are applied in cellular systems, a co-channel interference problem between macrocells and femtocells occurs because femtocells use the same spectrum as do the macrocells. To solve the co-channel interference problem, a previous study suggested a resource allocation scheme in LTE cellular systems using FFR. However, this conventional resource allocation scheme still has interference problems between macrocells and femtocells near the boundary of the sub-areas. In this paper, we define an optimization problem for resource allocation to femtocells and propose a femtocell resource allocation scheme to solve the optimization problem and the interference problems of the conventional scheme. The evaluation of the proposed scheme is conducted by System Level Simulation while varying the simulation environments. The simulation results show that the proposed scheme is superior to the conventional scheme and that it improves the overall performance of cellular systems.

• Transactions of the Society of Information Storage Systems
• /
• v.1 no.2
• /
• pp.137-142
• /
• 2005

In this paper, we propose a new servo system design strategy to reduce the position error signal(PES) and track mis-registration(TMR) in magnetic disk drive systems. The proposed method provides a systematic design procedure based on the plant model and an optimal solution via an optimization with a 'Robust Random Neighborhood Search(RRNS)' algorithm. In addition, it guarantees the minimum PES level as well as stability to parametric uncertainties. Furthermore, the proposed method can be used to estimate the performance at the design stage and thus can reduce the cost and time for the design of the next generation product. The reduction of PES as well as robust stability is demonstrated by simulation and experiments.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.1
• /
• pp.110-122
• /
• 1996

The objective of this study is to understand the dynamic characterictics of OHV type valve trains and to design and optimal cam profile which will improve engine performance. A numerical model for valve train dynamics is presented, which aims at both accuracy and computational efficiency. The lumped mass model and distributed parameter model were used to describe the valve train dynamics. Nonlinear characterictics in the valve spring behavior were included in the model. Comprehensive experiments were carried out concerning the valve train dynamics, and the model was tuned based on the test results. The dynamic model was used in designing an optimal cam profile. Because the objective function has many local minima, a conventional local optimizer cannot be used to find an optimal solution. A modified adaptive random search method is successfully employed to solve the problem. Cam lobe area could be increased up to 7.3% without any penalties in kinematic and dynamic behaviors of the valve train.