• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.4
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• pp.1330-1350
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• 2022

As a preprocessing operation of transmitter antennas, the hybrid precoding is restricted by the limited computing resources of the transmitter. Therefore, this paper proposes a novel hybrid precoding that guarantees the communication efficiency with low complexity and a fast computational speed. First, the analog and digital precoding matrix is derived from the maximum eigenvectors of the channel matrix in the sub-connected architecture to maximize the communication rate. Second, the extended power iteration (EPI) is utilized to obtain the maximum eigenvalues and their eigenvectors of the channel matrix, which reduces the computational complexity caused by the singular value decomposition (SVD). Third, the Aitken acceleration method is utilized to further improve the convergence rate of the EPI algorithm. Finally, the hybrid precoding based on the EPI method and the Aitken acceleration algorithm is evaluated in millimeter-wave (mmWave) massive multiple-input and multiple-output (MIMO) systems. The experimental results show that the proposed method can reduce the computational complexity with the high performance in mmWave massive MIMO systems. The method has the wide application prospect in future wireless communication systems.

• Journal of The Korean Astronomical Society
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• v.27 no.2
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• pp.191-201
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• 1994

We propose to use the entropy of power spectra defined in the frequency domain for the deconvolution of extended images. Spatial correlations requisite for extended sources may be insured by increasing the role of power entropy because the power is just a representation of spatial correlations in the frequency domain. We have derived a semi-analytical solution which is found to severely reduce computing time compared with other iteration schemes. Even though the solution is very similar to the well-known Wiener filter, the regularizingng term in the new expression is so insensitive to the noise characteristics as to assure a stable solution. Applications have been made to the IRAS $60{\mu}m\;and\;100{\mu}m$ images of the dark cloud B34 and the optical CCD image of a solar active region containing a circular sunspot and a small pore.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.91-99
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• 2012

The Fighter aircraft transmission system consists of a light weight, High Speed Flexible Coupling (HSFC) known as Power Take-Off shaft (PTO) for connecting Engine gearbox (EGB) with Accessory Gear Box (AGB). The HSFC transmits the power through series of specially contoured metallic annular thin flexible plates whose planes are normal to the torque axis. The HSFC operates at high speed ranging from 10,000 to 18,000 rpm. The HSFC is also catered for accommodating larger lateral and axial misalignment resulting from differential thermal expansion of the aircraft engine and mounting arrangement. The contoured titanium alloy flexible plates are designed with a thin cross sectional profile to accommodate axial and parallel misalignment by the elastic material flexure. This paper investigates the effect of misalignment on the transmission characteristics of the HSFC couplings. A mathematical model for the HSFC coupling with misalignment has been developed for analyzing the torque transmission and force interaction characteristics. An extensive testing has been conducted for validating characteristics of the designed coupling under various misalignment conditions. With this the suitability of the model adapted for the design iteration of HSFC development is validated. This method will reduce the design iteration cycles of HSFC and can be extended for the similar development of flexible couplings.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.308-312
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• 1999

Developed the model equations which calculate roll force, roll power during hot rolling in real time. The variables which mainly effect on the roll force, roll power are shape factor, reduction, roll diameter, roll velocity, strip inlet temperature, carbon content of strip and strip-roll contact friction coefficient. Among these variables roll diameter, roll velocity, inlet temperature, carbon content and friction coefficient can be excluded in interpolated model equation by introducing equation of die force(F'), power(p') of the frictionless uniform plane strain compression which can be calculated without iteration. At the case of coulomb friction coefficient of 0.3, we evaluated coefficient of polynomial equations of {{{{ { F} over {F' } }}}}, {{{{ { Pf} over {Pd }, { Pd} over {P' } }}}} from the result of finite element analysis using interpolation. It was found that the change of values of {{{{ { F} over {F' }, { P} over {P' } }}}} with the friction coefficient tend to straight line which slope depend only on shape factor. With these properties, developed model equations could be extended to other values of coulomb friction coefficient. To verify developed roll force, roll power model equation we compared the results from these model equation with the results from these model equation with the results from finite element analysis in factory process condition.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.34 no.8
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• pp.308-316
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• 1985

This paper proposes an analytic tool for long-term generation expansion planning based on the maximum principle. Many research works have been performed in the field of generation expansion planning. But few works can be found with the maxinmum principle. A recently published one worked by professor Young Moon Park et al. shows remarkable improvements in modeling and computation. But this modeling allows only thermal units. This paper has extended Professor Park's model so that the optimal pumped-storage operation is taken into account. So the ability for practical application is enhanced. In addition, the analytic supply-shortage cost function is included. The maximum principle is solved by gradient search due to its simplicity. Every iteration is treated as if mathematical programming such that all controls from the initial to the terminal time are manipulated within the same plane. Proposed methodology is tested in a real scale power system and the simulation results are compared with other available package. Capability of proposed method is fully demonstrated. It is expected that the proposed method can be served as a powerful analytic tool for long-term generation expansion planning.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.13 no.4
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• pp.47-55
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• 1999

In this paper, we construct the controller for the heat exchanger system using iterative method. For awlying the linear quadratic control theory to the heat exchanger system which is represented by the bilinear system, we fomrulate the bilinear system to execute iteration We also propose Extended Kalman Filter to estimate bilinear system state for the purpose of state feedback controller design. We also awly the iterative controller to the thennal power plant superheater system temperature control, and computer simulation show that the estimated value follows the superheater steam temperature under the variation of the external inputs, and that the output steam temperature is properly maintained.tained.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.705-715
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• 2016

In this study, the cycle performance of an air conditioner with multi-indoor units is analyzed and simulated. The cycle performance could be predicted through the integration of mathematical formulation for these devices. The condenser pressure is obtained by an iteration process to match the mass flow rates of the compressor and the expansion valve and the evaporator pressure is determined by an iteration process, in which the suction super heat is tracing the targeted super heat. The required software was developed by system programming. the software algorithm is extended to predict the cycle performance of an air conditioner system with multi-indoor units, and then the numerical results are compared with experimental results. This mathematical model is validated from the result of experiments conducted on 8.3kW air conditioner. The errors in capacity, electronic power, and COP are found to be within 10% in general.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.2 s.119
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• pp.121-129
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• 2007

There has been much effort to find suitable methods for structural analysis in the mid-frequency region where traditional low frequency methods have increasing uncertainties whilst statistical energy analysis is not strictly applicable. Systems consisting of relatively stiff beams coupled to flexible plates have a particularly broad mid-frequency region where the beams support only a few modes whilst the plate has a high modal density and modal overlap. A system of two parallel beams coupled to a plate is investigated based on the wave method, which is an approximate method. Muller's method is utilised for obtaining complex roots of a dispersion wave equation, which does not converge in the conventional wave method based on a simple iteration. The wave model is extended from a single-beam-plate system, to a plate with two identical beams which is modelled using a symmetric-antisymmetric technique. The important hypothesis that the coupled beam wavenumber is sufficiently smaller than the plate free wavenumber is experimentally verified. Finally, experimental results such as powers and energy ratios show the validity of the analytical wave models.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.1
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• pp.101-110
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• 2002

A method to control the inverter output voltage lineally in over modulation mode of the third harmonics injected PWM inverter is proposed. The third harmonics injected PWM has a extended linear region compared with the sine PWM. But it still has a maximum voltage about 90% compared with the six step inverter. Therefore, to control the output voltage linearly in over modulation mode, analyzing the relationship between the modulation index and the peak of the fundamental component of the modified reference voltage, we can settle the problem in over modulation mode without iteration. Then we can increase the maximum fundamental component of the third harmonics injected PWM inverter comparative to six-step inverter continuously in over modulation mode. The simulation results of the inverter-induction motor system shows the validity of this method and experimental results prove it.

• Journal of KIISE:Databases
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• v.29 no.2
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• pp.138-147
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• 2002

The concept of the critical path in the workflow is important because it can be utilized In many issues in workflow systems, e.g., workflow resource management and workflow time management. However, the critical path in the contest of the workflow has not been much addressed in the past. This is because control flows in the workflow, generally including sequence, parallel, alternative, iteration and so on, are much more complex than those in the ordinary graph or network. In this paper we first describe our workflow model that has considerable work(low control constructs. They would provide the sufficient expressive power for modeling the growing complexities of today's most business processes. Then, we propose a method to systematically determine the critical path in a workflow schema built by the workflow control constructs described in our workflow model.