• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.733-739
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• 1999

A modified low-Re $k-\varepsilon$ model is used for the calculation of drag-reducing turbulent flow by polymer injection in a pipe. With the viscoelastic model, molecular viscosity in the definition of turbulent viscosity is related to elongations viscosity of the solution to account for the effects of drag reduction. Finite volume method is used for the discretization, and power-law scheme is used as a numerical scheme. Computed dimensionless velocity profiles are in good agreements with the experimental data in case of low drag reductions. However, in case of high drag reductions, they deviate largely from the measurements in the central zone of the flow field.

• ETRI Journal
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• v.44 no.3
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• pp.379-388
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• 2022

This study proposes a novel low-complexity algorithm for computing inverse fast Fourier transform (IFFT)/fast Fourier transform (FFT) operations in binary phase shift keying-modulated orthogonal frequency division multiplexing (OFDM) communication systems without requiring any twiddle factor multiplications. The peak-to-average power ratio (PAPR) reduction capacity of an efficient PAPR reduction technique, that is, H-SLM method, is evaluated using the proposed IFFT algorithm without any complex multiplications, and the impact of oversampling factor for the accurate calculation of PAPR is analyzed. The power spectral density of an OFDM signal generated using the proposed multiplierless IFFT algorithm is also examined. Moreover, the bit-error-rate performance of the H-SLM technique with the proposed IFFT/FFT algorithm is compared with the classical methods. Simulation results show that the proposed IFFT/FFT algorithm used in the H-SLM method requires no complex multiplications, thereby minimizing power consumption as well as the area of IFFT/FFT processors used in OFDM communication systems.

• Journal of Korean Society of Water and Wastewater
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• v.31 no.2
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• pp.177-186
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• 2017

This study concerned the analysis on the efficiency of the conversion of water tank type supply system to direct water supply system to examine the feasibility of the conversion, as well as the calculation of optimal conversion range that enables the supply of safe, high-quality water at stable pressure in accordance with the standards of water supply facility. The results of this research showed that when converting water supply system from water tank type supply system to direct water supply system, more nodal points could be properly converted and more reduction of electricity usage was expected in case water pressure rather than residence time was fixed. This means that higher efficacy can be obtained by fixing water pressure when converting water supply system. However, since the number of the locations that received on-spot inspection was small and the electricity usage measured was not exclusively by water supply facility, it is difficult to judge that such reduction of electricity usage accurately represents reduced electricity usage by water supply facility alone. therefore, after having secured on-spot information about a larger number of locations in apartment complexes that have converted water supply system, and utilizing information about electricity usage exclusively by water supply facility, the proposed method of this research could be applied to accurately deducing expected reduction of electricity usage by water supply facilities of various other apartment complexes. It is also considered possible to deduce an effective operation method of water supply system by finding out an area that shows low pressure or low residual chlorine concentration in the optimal conversion range of water supply, followed by estimating the proper location of pumping station or the proper chlorine dosage at the power purification plant that supply water to the target area.

• The Journal of the Acoustical Society of Korea
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• v.25 no.2
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• pp.61-71
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• 2006

An MP3 encoder chip has been designed and fabricated with the hardware and software co-design concepts. In the aspect of the software. the calculation cycles of the distortion control loop. which requires most of the calculation cycles in MP3 encoding procedure. have been reduced to $67\%$ of the original algorithm through the 'scale factor Pre-calculation'. By using a floating Point 32 bit DSP core and designing the FFT block with the hardware. we can get the additional reduction of the calculation cycles in addition to the software optimization. The designed chip has been verified using HW emulation and fabricated via 0.25um CMOS technology The fabricated chip has the size of $6.2{\time}6.2mm^2$ and operates normally on the test board in the qualitative and quantitative aspect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.11 s.102
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• pp.1147-1154
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• 2005

In this paper, we propose some PAPR(Peak to Average Power Ratio) reduction methods using WHT(Walsh Hadamard Transform) to reduce high PAPR generated in OFDM system because of multi carrier modulation. These proposed methods are the methods which has additional PAPR reduction performance without a loss of bandwidth efficiency and a large increment of calculation complexity than common PAPR reduction methods by combining the WHT with some common methods. In this paper, we propose two PAPR reduction methods made by combining a SLM(Selective Mapping) and DSI(Dummy Sequence Insertion) with a WHT. From simulation result, we can find that the PAPR reduction methods using a WHT can get about 1 dB additional PAPR reduction performance than common PAPR reduction methods; they are SLM and DSI. And, because our proposed methods have not only PAPR reduction effect, but also frequency diversity effect, more stabile data transmission is possible in nonlinear HPA and multipath fading channel.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.5
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• pp.1017-1022
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• 2011

This paper describes the improvement of the calculation by using $6{\sigma}$ method on steam turbine simulator in a nuclear power plant. The simulator is essential to not only verification and validation of control logic but also making sure of control constants in upgrading the long time used control system into the new one. And the dynamic model is a key point in that simulator. The model used during the retrofit period of the turbine controller in Kori Nuclear Power Plant makes difference in calculating generator output and control valve positions. That is because such operating data as the main steam pressure, the main steam temperature and control valve positions of Yongkwang #3 are different from those of Kori #4. Therefore, the model parameters must be tuned by using actual operating data for the high fidelity of simulator in calculating the dynamic characteristic of the model. This paper describes that the $6{\sigma}$ method is used in improvement of precision of generator output calculation in the steam turbine model of the simulator.

• Structural Engineering and Mechanics
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• v.74 no.4
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• pp.533-545
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• 2020

An optimal design method for a spoke double-layer cable-net structure (SDLC) is proposed in this study. Simplified calculation models of the SDLC are put forward to reveal the static responses under vertical loads and wind loads. Next, based on an energy principle, the relationship among the initial prestress level, cross-sectional areas of the components, rise height, sag height, overall displacement, and relative deformation is proposed. Moreover, a calculation model of the Foshan Center SDLC is built and optimized. Given the limited loading cases, material properties of the components, and variation ranges of the rise height and sag height, the self-weight and initial prestress level of the entire structure can be obtained. Because the self-weight of the cables decreases with increasing of the rise height and sag height, while the self-weight of the inner strut increases, the total weight of the entire structure successively exhibits a sharp reduction, a gradual decrease, a slow increase, and a sharp increase during the optimization process. For the simplified model, the optimal design corresponds to the combination of rise height and sag height that results in an appropriate prestress level of the entire structure with the minimum total weight.

• Journal of the Korea Institute of Building Construction
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• v.9 no.1
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• pp.65-73
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• 2009

Looking at current construction costs estimations of publicly declared public works, there are many instances where estimation criteria are ambiguous and doesn't imply the reality. Up to date, estimation criteria for calculating construction cost estimations are simply by unit area multiplication and stochastic construction cost estimation. However, possibility of making errors are high due to using uniform data that excludes each public work's specifications and environmental conditions. Further, on the aspect of cost management, there is certain limitation in the efficiency of cost management in order-placing stage and commencing-work stage; while efficient cost management and reduction of expenses are highly possible during initial stages of the project. In this respect, the paper adopts positive approach with regards to construction cost estimations of public works and draws common elements from calculation tables of the construction cost estimations from 3 completed domestic construction works; after which, the paper analyzes whether business exposition, construction guide and publicly-declared estimated construction costs that the orderer issued are calculated economically and properly; deducing problems in the process, the paper seeks to recommend rational calculation method on this.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.53-59
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• 2011

In this paper, the implementation of a production control system has been studied in order to obtain Realtime Cost Calculation using an exact Machine Factor and Man Factor based on RFID reader data transferred through network. For the study, microprocessor built in the controller of production facilities is used and also RFID reader is built additionally. Control part, card reader used for check the beginning and ending working time of workers, and Machine Factor and Man Factor calculated are transferred to server via PLC transmission port, serial transmission port, or Ethernet transmission port. By using the system, the production cost or the production efficiency is calculated exactly. Therefore it is possible to improve production rate and cost reduction by the use of the proposed production control system.

• Steel and Composite Structures
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• v.17 no.2
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• pp.173-184
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• 2014

This study aimed to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites. The analytical solution of residual stress field distribution was obtained by using coaxial cylinder model, and the numerical solution was obtained by using finite element model (FEM). Both of the above models were compared and the thermal residual stress was analyzed in the axial, hoop, radial direction. The results indicated that both the two models were feasible to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites, because the deviations between the theoretical calculation results and the test results were less than 8%. In the titanium matrix composites, along with the increment of the SiC fiber volume fraction, the longitudinal property was improved, while the equivalent residual stress was not significantly changed, keeping the intensity around 600 MPa. There was a pronounced reduction of the radial residual stress in the titanium matrix composites when there was carbon coating on the surface of the SiC fiber, because carbon coating could effectively reduce the coefficient of thermal expansion mismatch between the fiber and the titanium matrix, meanwhile, the consumption of carbon coating could protect SiC fibers effectively, so as to ensure the high-performance of the composites. The support of design and optimization of composites was provided though theoretical calculation and analysis of residual stress.