• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.631-638
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• 2018

In this paper, we propose a method to improve the performance by guidance technique and applying it to the precision guided ammunition. The proposed method is a technique designed to reduce the target error of ammunition by reducing the projectile error without analyzing the motion characteristics of the shot. This technique is applied to the moving average filter technique which is widely used as signal processing technique to reduce the fluctuation of the output of the inboard mounting inertial sensor caused by the rotation and the coning motion of the ammunition. In order to compare the performance of the applied technique including the simple 3D guided control technique and the proposed improvement technique. It is confirmed that the application of this technique improves the accuracy of impact of the cannon - launched ammunition with severe environmental conditions and irregular motion characteristics unlike the missile.

• Tribology and Lubricants
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• v.34 no.4
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• pp.125-131
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• 2018

A precision tribometer consisting of a cantilever was designed to measure frictional forces in the micro-Newton range. As frictional forces are measured based on the bending of the cantilever, vibration of the cantilever is the most significant factor affecting the quality of the friction measurement. Therefore, improved design of the tribometer with double cantilevers and a connecting plate that united the two cantilevers mechanically was suggested. For the verification of the modified design of the tribometer, numerical analysis and experiments were conducted. Examination using the finite element method revealed that the tribometer with a double cantilever and a connecting plate exhibited faster damping characteristics than the tribometer with a single cantilever. In the experiment, effectiveness of the double cantilever and connecting plate for vibration reduction was also confirmed. Vibration of the tribometer with double cantilever decreased eight times faster than that of the tribometer with a single cantilever. The faster damping of the double cantilever design is attributed to the mechanical interaction at the contacting surfaces between the cantilever and the connecting plate. Tribotesting using the tribometer with a single cantilever resulted in random fluctuation of frictional forces due to the stick-slip behavior. However, using the tribometer with a double cantilever and connecting plate for the tribotest gave relatively uniform and steady measurement of frictional forces. Increased stiffness owing to using a double cantilever and mechanical damping of the connecting plate were responsible for the stable friction signal.

• Journal of Biosystems Engineering
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• v.16 no.2
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• pp.124-132
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• 1991

This study was carried out to obtain the information needed in the development of forward speed control system and the improvement of combine performance. The effects of variety, grain moisture content and forward speed on the combine load characteristics were investigated through experiments. The results of this study are summarized as follows. 1. A data acquisition system was developed to measure the engine speed and the torques and speeds of the threshing cylinder, dean-grain auger and tailings-return auger. The system consisted of transducers, signal conditioner, interface board and microcomputer. The system accuracy is better than ${\pm}2.3%$ full scale. 2. Linear regression equations were obtained for the torque, speed and power requirement of threshing cylinder for different paddy varieties, grain moisture contents and feed rates. 3. The maximum value of relative frequency for threshing cylinder torque decreased as the increase in feed rate and moisture content. The range of torque fluctuation was 1.2~3.7 and 1.2~1.9 times the average and maximum torque, respectively. The maximum value of power spectrum density (PSD) appeared to be about 11 Hz regardless of paddy variety, grain moisture content and feed rate. 4. The speed of tailings return thrower decreased rapidly at below 900rpm, and it fell to near zero about 3 seconds after that time. When the travelling of combine harvester was stopped immediately after sensing the overload, it took about 7 seconds for a full recovery of the no-load speed of tailings return thrower.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.419-427
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• 1996

Thermally-stabilized fiber-optic current sensors are proposed and demonstrated. The sensor head is made of two coil formers combined perpendicularly. In this sensor head, bending-induced birefringences can be reduced to the level much smaller than those of the single former type because the eigen-axes of the two perpendicular coil formers are made orthogonal to each other. Moreover, thermal variation of the birefringence is also expected to be minimized by the orthogonality of the two polarization eigen-axes. We changed the temperature slowly in the range of 20~45$^{\circ}C$ during 100 minutes. The overall linearity of the sensor is better than 1.2% in the range of 0~1000A. The long-term fluctuation of the sensor is less than 1% when measured for 3 hours at 500A and room temperature. Two orthogonally-polarized laser diodes are combined together to make the incident beam unpolarized. In the signal processing, the signals are separated by two parts and normalized respectively, which minimize the efects of optical fluctuations coming from sources, connectors, etc.

• Spatial Information Research
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• v.21 no.1
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• pp.87-100
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• 2013

Recently, the use of locational information is growing rapidly. GPS technology has been adopted generally for obtaining locational information in outdoor spaces. In the other hand, the researches on indoor positioning have been carried out applying WLAN, RFID or Bluetooth technology because of the multi-path interference of GPS signal caused by the physical obstacles such as walls or columns in buildings. However, such technologies for indoor positioning cost too much to build sensing infrastructure and compute-intensive processes are involved. Furthermore, the accuracy of location estimation is variable caused by interior structures in buildings. In this study, to make up for the limitations, descriptive data such as phone number, unique room numbers, or business names readily available in mixed-use buildings is used for extracting location information. Furthermore, during the process, a geocoding method using character matching is applied to this study enabling prompt location estimation and sublating the fluctuation of accuracy caused by interior structures. Based on the proposed method in this study, an architecture is designed, and three-dimensional viewer program is developed for the implementation of this study. Also, this research is quantitatively analyzed through match rate and processing time of proposed method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.1
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• pp.79-87
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• 2013

A new modulation technique - correlative encoded FSK (CEFSK) - for use in power and bandwidth limited digital communication system is proposed. CEFSK is free of ISI and generates output signals which have a smooth and continuous phase transition and a reduced envelope fluctuation by keeping correlation between amplitude and phases of two subsequent symbols. In comparison to conventional one-bit differential detected (1DD) GFSK, the performance of the 1DD-CEFSK in a non-linearly amplified (NLA) channel impaired by additive white Gaussian noise (AWGN), ISI and IM, is analyzed via computer simulation. The simulation result shows that, in an NLA single-channel, 1DD-CEFSK provides a signal-to-noise ratio (SNR) advantage of up to 1.2dB and 0.8dB at BER of $1{\times}10^{-4}$ when input back-off (IBO) of HPA is -1.0dB and -3.0dB, respectively. For the same channel environment with multi-channel, 1DD-CEFSK outperforms 1DD-GFSK by 1.1dB in SNR, regardless of the value of IBO.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.7
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• pp.765-773
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• 2016

The vehicle interior noise caused by exterior fluid flow field is one of critical issues for product developers in a design stage. Especially, turbulence and vortex flow around A-pillar and side mirror affect vehicle interior noise through a side window. The reliable numerical prediction of the noise in a vehicle cabin due to exterior flow requires distinguishing between the aerodynamic (incompressible) and the acoustic (compressible) surface pressures as well as accurate computation of surface pressure due to this flow, since the transmission characteristics of incompressible and compressible pressure waves are quite different from each other. In this paper, effective signal processing technique is proposed to separate them. First, the exterior flow field is computed by applying computational aeroacoustics techniques based on the Lattice Boltzmann method. Then, the wavenumber-frequency analysis is performed for the time-space pressure signals in order to characterize pressure fluctuations on the surface of a vehicle side window. The wavenumber-frequency diagrams of the power spectral density shows clearly two distinct regions corresponding to the hydrodynamic and the acoustic components of the surface pressure fluctuations. Lastly, decomposition of surface pressure fluctuation into incompressible and compressible ones is successfully accomplished by taking the inverse Fourier transform on the wavenumber-frequency diagrams.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.348-353
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• 2012

This paper presents the HRTF based experimental approach to figure out why the human auditory perception on the interior noise source including the directional tonal components does not well match with the dominant features extracted from recorded acoustic signals in terms of psycho-acoustics. Since the general objective evaluation models for tonalness among various sound attributes are a function of width, frequency, excessive level of tonal components respectively, the directional tonal components cannot be properly evaluated without considering the effects of head-related transfer function on the binaural auditory perception. Thus, the directivity of source is additionally considered to prevent the erroneous conclusions from the same sound source in the process of source identification. The signal synthesis technique is used to solve a little difficulty in measuring all of desired acoustic signals for jury evaluation. The sound attributes of synthetic acoustics signals are analyzed to roughly predict the results of jury evaluation in advance by using sound quality factors such as loudness, sharpness, roughness, fluctuation strength and tonality. The jury evaluation is carefully conducted based on the recommended guideline suggested by N. Ottoet al. Each sound is respectively evaluated by selecting a value between -2 and 2 in intervals of 0.2 point. Through above procedure, based on the results of jury evaluation, it is confirmed that serious problems can be caused in the process of analyzing the dominant sound attributes in terms of psycho-acoustics according to the type of a microphone and a playback system.

• 한국연소학회:학술대회논문집
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• 2003.12a
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• pp.103-108
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• 2003

The effect of equivalence ratio and fuel/air mixing quality on the phase-resolved gas temperatures at different phases of the oscillating pressure cycle was experimentally investigated. An atmospheric pressure, optically accessible and laboratory-scale dump combustor operating on methane with heat release rate of 1.59kW was used. Temperature measurements were made using coherent anti-Stokes Raman spectroscopy (CARS) at several spatial locations for typical unstable combustion conditions. Analysis was conducted using parameters such as phase-resolved averaged temperature, normalized standard deviation and temperature probability distribution functions (PDFs). Also the probability on the occurrence of high temperature (over 1900K) was investigated to get the information on the perturbation of equivalence ratio and NOx emission characteristics. It was shown that most of temperature histograms exhibit Gaussian profile which has short breadth of temperature fluctuation at equivalence ratio of 0.6, while beta profile was predominant for the cases of other equivalence ratios (${\Phi}$=0.55, 0.50). The characteristics on the occurrence of high temperature also displayed periodic wave form which is very similar to the pressure signal. And the amplitude of this profile goes larger as the fuel/air mixing quality become poorer. These also provided additional information on the perturbation of equivalence ratio at flame as well as NOx emission characteristics.

• Fire Science and Engineering
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• v.32 no.4
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• pp.1-6
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• 2018

As a preliminary study to quantify the measurement uncertainty of the Schmidt-Boelter type heat flux gauge, the present study has been conducted to evaluate the measurement error due to the calibration constant supported by manufacturer. Calibrations of heat flux gauges are performed at NIST Fire Research Division using a calibration facility with heat source of a 2000 W halogen-tungsten filament lamp and the calibration constant is obtained by comparing the response of the reference and a standard heat flux gauge at the same irradiance conditions. Calibration for heat flux gauges made by three different manufacturers is compared with their factory calibration constant. Relative error due to fluctuation of output signal from heat flux gauges does not exceed 1% of the mean value and the relative error between calibration of this study and factory calibration constant ranged from 1.5% to 14.3%. The present study shows that a continuous and periodic calibration is necessary for accurate heat flux measurement.