• Journal of the Korean Society for Precision Engineering
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• v.18 no.7
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• pp.98-105
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• 2001

The machining accuracy is affected by geometric, volumetric errors of the machine tools. To improve the product quality, we need to enhance the machining accuracy of the machine tools. To this point of view, measurement and inspection of finished part as error analysis of machine tools ahas been studied for last several decades. This paper suggests the enhancement method of machining accuracy for precision machining of high quality metal reflection mirror or optics lens, etc. In this paper, we study 1) the compensation of linear pitch error with NC controller compensation function using laser interferometer measurement, 2) the method for enhancing the accuracy of NC milling machining by modeling and compensation of volumetric error, 3) the spherical surface manufacturing by modeling and compensation of volumetric error of the machine tool, 4) the system development of OMM without detaching work piece from a bed of machine tool after working, 5) the generation of the finished part profile by OMM. Furthermore, the output of OMM is compared with that of CMM, and verified the feasibility of the measurement system.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.29 no.2
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• pp.76-82
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• 1997

In paper the evenness of planar distribution of mass in a small scale is called formation (orbetter:mass formation). Traditionally formation has been assessed visually, by looking the sheet of paper against transmitted light. Different kinds of optieal testers are being usd to obtain quantitative rankings htat would be independent of the observer but would well correspond to the visual assessment. However, various raw-material and process factors do influence light trans-mittance in paper and do impair the correspondence between basis weight and the optical formation measurement (or visual assessment). As the optical formation test methods do not incorporate an efficient calib ration routine, the formation of the sophisticated paper grades of today the is rather difficult to measure optically and may lead to erroneous results. It may be concluded that the optical measurement is not suitable for paper grades with high filler content. coating, heavy calendering or that are made of heavily beaten pulp, nordoes it apply for dyed or printed papers. For this reason, visual assessment and optical evaluation shoild be replaced with a measurement that gives reliable results independent on paper grode and manufacturing process. Formation measuremend based on beta radiation is suitable for all paper grades regardless to the material contents or process treatment. It is possible to measure even dyed or printed samples. Thonks to a sim ple and relioble calibration, the results are converted to real basis weight balues that remain reliable even with time. The only beta tester commercially available is the AMBERTEC Beta Formation Tester. Formation of paper does vary locally in the web. Typically there exists a formation profile, too similarly to other properties of paper. Therefore, formation should ？ ays be expressed as a mean of a sufficient amount of parallel determinations. All formation measurements should be calibrated against basis weight.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.599-603
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• 2003

This paper present an error compensation system and On-Machine Measurement(OMM) system for improving the machining accuracy of ultra-precision lathe. The Fast-Tool-Servo(FTS) driven by a piezoelectric actuator is applied for error compensation system. The controller is implemented on the 32bit DSP for feedback control of piezoelectric actuator. The control system is designed to compensates three kinds of machining errors such as the straightness error of X-axis slide, the thermal growth error of the spindle. and the squareness between spindle and X-axis slide. OMM is preposed to measure the finished profile of workpiece on the machine-tool using capacitive sensor with highly accurate ruby tip probe guided by air bearing. The data acquisition system is linked to the CNC controller to get the position of each axis in real-time. Through the experiments, it is founded that the thermal growth of spindle and tile squareness error between spindle and X-axis slide influenced to machining error more than straightness error of X-axis slide in small travel length. These errors were simulated as a sinusoidal signal which has very low frequency and the FTS could compensate the signal less than 30 m. The implemented OMM system has been tested by measuring flat surface of 50 mm diameter and shows measurement error less than 400 mm

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.245-250
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• 2010

The procedure for estimating the gas (rotational) temperature of an air discharge in supersonic flows is presented in detail. Since direct measurement of the temperature in a supersonic flow is difficult, a nonintrusive measurement was performed by optical emission spectroscopy based on the emission spectra of nitrogen molecular ions. A detailed explanation, including the equations for emission line intensity, is presented in order to understand the structure of the emission spectra of nitrogen molecular ions. Using the obtained representation for emission spectrum, a synthetic spectrum of the first negative system of $N_2^+$ is obtained, and it is compared with the experimentally measured spectrum. Within a relative error of approximately 6.8% for the overall band spectra, the synthetic and measured spectra agree well. In the case of a 25-mA DC air discharge in a supersonic (Mach 3) flow, the gas temperature profile shows an approximately linear variation and a peak temperature of approximately 350 K.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.2
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• pp.135-145
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• 2023

Developing high-fidelity Computational Fluid Dynamics (CFD) simulation methods used to evaluate the airwake characteristics along a flight deck of a large ship, the various kind of data such as actual ship measurement and wind tunnel results are required to verify the accuracy of CFD simulation. Inflow velocity profile at the bow, local unsteady flow field data around the flight deck, and highly reliable wind tunnel data which were measured after reviewing Atmospheric Boundary Layer (ABL) simulation and Reynolds Number effects were also used to determine the key parameters such as turbulence model, time resolution and accuracy, grid resolution and type, inflow condition, domain size, simulation length, and so on in STAR CCM⁺. Velocity ratio and turbulent intensity difference between Full-scale CFD and actual ship measurement at the measurement points show less than 2% and 1.7% respectively. And differences in velocity ratio and turbulence intensity between wind tunnel test and small-scale CFD are both less than 2.2%. Based upon this fact, the selected parameters in CFD simulation are highly reliable for a specific wind condition.

• Wind and Structures
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• v.37 no.1
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• pp.25-38
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• 2023

Due to the complexity and difficulty in meeting the multiphase flow complexity, similarity, and multiscale characteristics, the mechanism of snow drift is so complicated that the snow deposition prediction is still inaccurate and needs to be far improved. Meanwhile, the validation of prediction methods is also limited due to a lack of field-measured data about snow deposition. To this end, a field measurement activity about snow deposition around a cube with time was carried out, and the snow accumulation process was measured under blowing snow conditions in northwest China. The maximum snow depth, snow profile, and variation in snow depth around the cube were discussed and analyzed. The measured results indicated three stages of snow accumulation around the cube. First, snow is deposited in windward, lateral and leeward regions, and then the snow depth in windward and lateral regions increases. Secondly, when the snow in the windward region reaches its maximum, the downwash flow erodes the snow against the front wall. Meanwhile, snow range and depth in lateral regions have a significant increase. Thirdly, a narrow road in the leeward region is formed with the increase in snow range and depth, which results in higher wind speed and reforming snow deposition there. The field measurement study in this paper not only furthers understanding of the snow accumulation process instead of final deposition under complex conditions but also provides an important benchmark for validating prediction methods.

• Journal of Korean Society of Rural Planning
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• v.30 no.3
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• pp.75-84
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• 2024

This study developed the procedure and method for the accuracy assessment of unmanned boat survey data, based on the reservoir water depth data of Misan Reservoir, measured by the manned and unmanned boats in 2009 by Korea Rural Community Corporation. In the first step, this study devised the method to extract the contour map of NGIS data in AutoCAD to generate easily the reservoir boundary map used to set the survey range of reservoir water depth and to test the survey accuracy. The surveyed data coordinate systems of the manned and the unmanned boat were also unified by using ArcGIS for the standards of accuracy assessment. In the accuracy assessment, the spatial correlation coefficient of the grid maps of the two measurement results was 0.95, showing high pattern similarity, although the average error was high at 78cm. To analyze in more detail assessment, this study generated randomly the 3,250m transverse profile route (PR), and then extracted grid values of water depth on the PR. In the results of analysis to the extracted depth data on PR, the error average difference of the unmanned boat measurements was 73.18cm and the standard deviation of the error was 55cm compared to the manned boat. This study set these values as the standard for the correction value by average shift and noise removal of the unmanned boat measurement data. By correcting the unmanned boat measurements with these values, this study has high accuracy results, the reservoir water depth and surface area curve with R² = 0.97 and the water depth and storage volume curve with R² = 0.999.

• Journal of Korea Water Resources Association
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• v.38 no.10 s.159
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• pp.811-824
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• 2005

The ADCP is an instrument based on Doppler effect, which measures discharge of a river in a short time while crossing it. In this study we aim to make a comparison of the discharge results from a moving-vessel ADCP with those measured by velocity-area method at the same cross-section, and to investigate the characteristics of velocity and discharge data using ADCP. Bathymetry measured by ADCP almost coincides with that by direct depth measurements. Because velocity data from ADCP are essentially instantaneous, individual velocity profiles obtained by ADCP are rather different from time-averaged velocity profiles. But spatially averaged velocity profiles of the individual ADCP data near the comparable verticals have similar vertical velocity pattern with the time-averaged ones. The average velocity profile from repeatedly crossed data is also similar with the time-averaged one. In case of the velocity distribution, individual and spatially averaged data for the sub-width of mid-section method Have good agreement with those by velocity-area method. Discharge data determined by averaging several ADCP measurement transects have $0.1\%{\~}9.3\%$ of difference with those from velocity-area method, and as the number of measurement increases, the relative difference to the velocity-area method decreases.

• Korean Journal of Optics and Photonics
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• v.19 no.5
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• pp.376-380
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• 2008

This paper presents the Projection Moire method using a line scan camera. The high resolution feature of a line scan camera makes it possible to scan an image quickly, thus enabling a much quicker 3D profile. This method uses a high resolution line scan camera making it possible to scan an image at high speed simultaneously measuring the 3D profile of a large FOV. When using a high resolution scan camera, a full FOV is scanned, thus requiring just one movement of a projection grating. As a result, the number of grating movements is reduced drastically. The end result is a faster and more accurate 3D measurement. Moving the grating too quickly causes vibration in the imaging system, which will normally be required to apply a stitching technique when using an area scan camera. However the technique is not required when using a line scan camera. Compared with the previous techniques, it has the advantages of simple hardware without moving mechanical parts - single exposure for obtaining three-dimensional information. A method using a high resolution line scan camera can be used in mass production to measure the bump height of wafers or the bump height of package substrates.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.132-139
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• 2016

This study was carried out near the waters of Jango port, Dangjin-gun, Chungcheongnam-do by utilizing 10kHz carrier frequency, for the purpose of measurement and analysis of underwater channel environment of the Western sea. For the measurement of horizontal channel environment, the separation distance between transmitter and receiver is made differently in the range between 10m and 4000m. Meanwhile, for the measurement of vertical channel environment, transmission and receiving side ships are fixed as contacted each other and measured differently depending on their depth of submergence. In this study, the Coherence Bandwidth and the Coherence Time were estimated by analyzing the Power delay profile of the real sea based on the measured data, and analyzing the doppler frequency through frequency conversion of received tone-signal, respectively. This study is expected to become a base study in carrying out the frame design for underwater communication to improve the communication and secure the reliability of communication in future underwater channel environment.