• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.5
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• pp.1325-1331
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• 1996

In this paper, a new current-memory circuit is proposed that reduces the clock feedthrough(CFT) error voltage causing total harmonic distortion(THD) increment in switched-current(SI) systems. Using PMOS transistor in CMOS complementary, the proposed one reduces output distortion current due to the CFT errorvoltage. A proposed current-memory is designed using a 1.2.mu.m CMOS process anda 1MHz sinusoidal signal having a 68.mu.A amplitude current is applied as input (sampling frequency:20MHz). It hasbeen shown from the simulation that the output distortion current effected by the CFT error voltage is reduced by approximately 10 times the error voltage of conventional one, THD is -57dB in case ofappling 1kHz frequency input signalwith 0.5 peak signal-to-bias current ratio.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.4
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• pp.357-364
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• 2011

In this study, ring-shaped acoustic resonators were proposed to be installed in a silencer to increase the acoustic performance of silencer in the low-frequency range. Evaluation of noise reduction performance of acoustic resonator arrays was carried out by measuring the random-incidence absorption coefficient. It was found that the absorption coefficient of resonator array was measured up to 1 at 125 Hz of 1/3-octave band center frequency. Insertion losses of silencers with ring-shaped acoustic resonator arrays were measured based on ISO 7235. The results were shown that the ring-shaped resonator could increase the insertion loss up to 13 dB without flow, whereas 7 dB when flow speed reached 15 m/s. As increasing the flow speed above 15 m/s, the effect of acoustic resonator decreased due to the effect of nonlinear air damping of the resonator. It was also found that the increment of pressure drop by the presence of resonator arrays was about 9 % at flow speed of 25 m/s.

• Journal of Advanced Navigation Technology
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• v.13 no.6
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• pp.950-956
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• 2009

Nowdays the mobile traffic have been greatly increasing. This traffic increment has been caused the lack of frequency. To solve this problem, many study to improve the frequency efficiency in the field of mobile communication has been performed in a variety angle. However this kind of study was focused to 1:1 traffic. This paper propose the allocation scheme of the receiving channel in 1:N group traffic. This method apply to the TRS(Trunk Radio System) that use for the emergency disaster telecommunications. The result of the study show the performance improvement in the call loss ratio and load distribution in the group channel.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1915-1920
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• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer impinging on a rigid surface. In this paper we present a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method. We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing a conventional FDLB model, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}=23^{\circ}$ . At a stand-off distance ${\omega}$ , the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.2
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• pp.372-379
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• 2015

The latest video compression standard (such as H.264/AVC and HEVC) utilizes quarter-pel accuracy motion estimation in order to retain detailed motion information. Many sub-pixel motion estimation algorithms used in the spatial domain usually encounters increment of computational complexity due to embedded interpolation algorithm. In this paper, an approach to measure sub-pixel accuracy motion estimation in frequency domain using shifting matrix is proposed. Complexity can be reduced utilizing shifting matrix algorithm in frequency domain and simulation results demonstrate not only higher PSNR but lower bit rates than spatial domain algorithms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.392-393
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• 2007

In this paper, we report the characteristics inorganic EL device with high dielectric constant materials of PMN, PZT. Fabricated EL device shows stable light emission even at 20kHz -400Volt without any break down failure. Brightness voltage curve of EL device is same with typical EL. As increasing applied voltage, the brightness increased linearly. From the results of Frequency and duty ratio variation, over 50% of brightness increment was seen. Luminous efficiency was increased upto 200V range and saturated over 200V by slow increasement of light emission. We got e bright stable emission of 1733 cd/m2 at the condition of Frequency 35 KHz, Duty 10%, 400V.

• ETRI Journal
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• v.43 no.1
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• pp.120-132
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• 2021

A frequency diverse array (FDA) multiple-input multiple-output (MIMO) radar employs a small frequency increment across transmit elements to produce an angle-range-dependent beampattern for target angle and range detection. The joint angle and range estimation problem is a trilinear model. The traditional trilinear alternating least square (TALS) algorithm involves high computational load due to excessive iterations. We propose a fast-convergence trilinear decomposition (FC-TD) algorithm to jointly estimate FDA-MIMO radar target angle and range. We first use a propagator method to obtain coarse angle and range estimates in the data domain. Next, the coarse estimates are used as initialized parameters instead of the traditional TALS algorithm random initialization to reduce iterations and accelerate convergence. Finally, fine angle and range estimates are derived and automatically paired. Compared to the traditional TALS algorithm, the proposed FC-TD algorithm has lower computational complexity with no estimation performance degradation. Moreover, Cramer-Rao bounds are presented and simulation results are provided to validate the proposed FC-TD algorithm effectiveness.

• Smart Structures and Systems
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• v.15 no.3
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• pp.627-643
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• 2015

Negative stiffness, previously emulated by active or semi-active control for cable vibration mitigation, is realized passively using a self-contained highly compressed spring, the negative stiffness device (NSD).The NSD installed in parallel with a viscous damper (VD) in the vicinity of cable anchorage, enables increment of damper deformation during cable vibrations and hence increases the attainable cable damping. Considering the small cable displacement at the damper location, even with the weakening device, the force provided by the NSD-VD assembly is approximately linear. Complex frequency analysis has thus been conducted to evaluate the damping effect of the assembly on the cable; the displacement-dependent negative stiffness is further accounted by numerical analysis, validating the accuracy of the linear approximation for practical ranges of cable and NSD configurations. The NSD is confirmed to be a practical and cost-effective solution to improve the modal damping of a cable provided by an external damper, especially for super-long cables where the damper location is particularly limited. Moreover, mathematically, a linear negative stiffness and viscous damping assembly has proven capability to represent active or semi-active control for simplified cable vibration analysis as reported in the literature, while in these studies only the assembly located near cable anchorage has been addressed. It is of considerable interest to understand the general characteristics of a cable with the assembly relieving the location restriction, since it is quite practical to have an active controller installed at arbitrary location along the cable span such as by hanging an active tuned mass damper. In this paper the cable frequency variations and damping evolutions with respect to the arbitrary assembly location are then evaluated and compared to those of a taut cable with a viscous damper at arbitrary location, and novel frequency shifts are observed. The characterized complex frequencies presented in this paper can be used for preliminary damping effect evaluation of an adaptive passive or semi-active or active device for cable vibration control.

• Transactions of the Korean hydrogen and new energy society
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• v.26 no.3
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• pp.241-246
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• 2015

The interest of New Renewable Energy is increasing globally because of the increment of the uncertainty for the energy's supply and demand, and the increment of the frequency in weather anomaly and its damages. One of the New Renewable Energies, Hydrogen receives attention as the future energy that can deal with global environment regulation. Fuel Cell Electric Vehicle (FCEV) is an environment-friendly vehicle that uses Hydrogen as fuel. The electric power for FCEV is generated by chemical reaction with Oxygen from the air and Hydrogen. Hyundai Motor Company (HMC) has developed a proprietary fuel cell system since 2005. In 2012, HMC is the first car maker that mass-produces the ix35 FCEV to the worldwide such as North America, Europe, etc. In order to develop and improve the FCEV technology, data acquisition and analysis of the driving vehicle information is essential. Therefore, the monitoring system is developed, which is consist of datalogger, Automatic Vehicle Location (AVL) server and main server. Especially, WCDMA technology is integrated into the system which enables the data analysis without any restriction of time and region. The main function of the system is the analysis of the driving pattern and the component durability, and the safety monitoring. As a result, ix35 FCEV has successfully developed by using the developed monitoring system. The system is going to take an advantage of development in the future FCEV technology.