• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.1197-1202
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• 2001

Near-field acoustic holography is a powerful tool to visualize sound sources. This method requires pressure measurement at many points for a good hologram. Thus one has to measure carefully so that errors due to the uncertainty of position, sensor mismatch, and so on are reduced. A method to solve this problem is to use a well-designed measurement system. This paper introduces a sound visualization system at center for noise and vibration control (NOVIC), KAIST, and addresses the advantages in terms of the error reduction. The system consists of array microphones, array jigs, a system to control the position and the velocity of the jigs, a data acquisition system, and a monitoring system. This paper also shows some sound visualization results when the system is applied to a speaker and a computer. The results verifies that the sound visualization system is useful for identifying sound sources.

• Journal of KSNVE
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• v.5 no.2
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• pp.197-206
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• 1995

Microphone array is designed to measure the equivalent source height of vehicle noise. The equivalent source position is defined for an arbirary distribution of acoustic sources above a perfectly reflecting plane and a microphone array for its measurement is developed. The normalized errors of the measured equivalent source heights are defined including the effects of background noise, the geometric near field, and source size. Normalized errors of the measured source heights obtained by a nemerical simulation for each parameter lead to optimization of the microphone spacing and to the design of an array which gives the equivalent source height as a function of frequency. The performance of the designed array is verified using the stationary loudspeaker experiments.

• Wind and Structures
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• v.30 no.1
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• pp.69-83
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• 2020

Modelling incompressible, neutrally stratified, barotropic, horizontally homogeneous and steady-state atmospheric boundary layer (ABL) is an important aspect in computational wind engineering (CWE) applications. The ABL flow can be viewed as a balance of the horizontal pressure gradient force, the Coriolis force and the turbulent stress divergence. While much research has focused on the increase of the wind velocity with height, the Ekman layer effects, entailing veering - the change of the wind velocity direction with height, are far less concerned in wind engineering. In this paper, a modified k-ε model is introduced for the ABL simulation considering wind veering. The self-sustainable method is discussed in detail including the precursor simulation, main simulation and near-ground physical quantities adjustment. Comparisons are presented among the simulation results, field measurement values and the wind profiles used in the conventional wind tunnel test. The studies show that the modified k-ε model simulation results are consistent with field measurement values. The self-sustainable method is effective to maintain the ABL physical quantities in an empty domain. The wind profiles used in the conventional wind tunnel test have deficiencies in the prediction of upper-level winds. The studies in this paper support future practical super high-rise buildings design in CWE.

• Journal of Korean Society on Water Environment
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• v.18 no.3
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• pp.283-290
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• 2002

In this study, home-made detection system by means of noble FIA is introduced on the measurement of toxic nitrite in the water samples collected from the area of Kwangju. As the standard calibration between 30 to 1000 ppb, the linearity has been shown more than 0.9999 as the correlation coefficient($R^2$) with the detection limit 1.5 ppb(S/N>2). The distribution of sample concentration was monitored as N.D. - 123 ppb which is wide span of concentrations in field water samples. The low level of nitrite is hardly detectable with other expensive sophisticated instruments including ion chromatography. Whereas the result of high concentration brings forth the necessity monitoring constantly our precious water resources. Successfully, the FIA system has played a very important role detecting wide span of nitrite in water sample. This technique can be adopted for controlling our environment in the near future.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.91-97
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• 2005

Class A evaporation pan has been used throughout the world to measure free water evaporation mainly by manual observation once a day. In this study, a new automatic water level measurement method is used for understanding of free water evaporation and numerical analysis. This new technique measures the weight of buoyancy bar in water, and does not need calibration because it is not affected by water density change with water temperature. Field observations of evaporation were made near Haenam Meteorological Station over paddy field located in southwestern Korea from 20 April to 30 May 2004 and the data from ten clear days (16 - 25 May) were used for this analysis. The observed total evaporation was about 50.7mm during this period whereas the estimated from an empirical equation was 50.4mm. As expected, the pan evaporation is well correlated with wind speed and the vapor pressure deficit between the water surface and the air.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.479-482
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• 2002

Riblets with longitudinal grooves along the streamwise direction have been used as an effective flow control technique for drag reduction. A flexible micro-riblet with v-grooves of peak-to-peak spacing of $300{\mu}m$ was made using a MEMS fabrication process of PDMS replica. The flexible micro-riblet was attached on the whole surface of a NACA0012 airfoil with which grooves are aligned with the streamwise direction. The riblet surface reduces drag coefficient about $7.9{\%}\;at\;U_o=3.3m/s$, however, it increases drag about $8{\%}\;at\;U_o=7.0m/s$, compared with the smooth airfoil without riblets. The near wake has been investigated experimentally far the cases of drag reduction ($U_o\;=\;3.3 m/s$) and drag increase ($U_o\;=\;7 m/s$). Five hundred instantaneous velocity fields were measured for each experimental condition using the cross-correlation PIV velocity field measurement technique. The instantaneous velocity fields were ensemble averaged to get spatial distribution of turbulent statistics such as turbulent kinetic energy. The experimental results were compared with those of a smooth airfoil under the same flow condition. The micro-riblet surface influences the near wake flow structure largely, especially in the region near the body surface

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.154-161
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• 2009

Recently, as many functional blocks are integrated on a small area the high speed integrated circuits emerge as a critical electromagnetic interferer which causes mal-function of adjacent circuitries and lowers the sensitivity of the wireless receivers. Therefore, it is necessary to devise an precise analyzing tool to pinpoint the major electromagnetic noise contributor among the internal circuit blocks of high speed IC's. This paper presents the design, fabrication, and measurement results of the high resolution magnetic field probe which can measure the current density on the IC surface. In order to achieve the high resolution, the magnetic field probe is fabricated using 3-metal semiconductor process so that its thickness is reduced by 10% than that of conventional works. Through the magnetostatic analysis and EM simulation, spatial resolution and sensitivity to the nonmagnetic field components are analyzed. Experimentally, it is found that the fabricated probe can measure the current density on the IC surface with $210{\mu}m$-spatial-resolution.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.13-18
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• 2004

It is important to estimate the distribution of intensity of a magnetic field for application of magnetic method to industrial nondestructive evaluation. Magnetic camera provides the distribution of a quantitative magnetic field with homogeneous lift-off and same spatial resolution. Leakage magnetic flux near the crack on the specimen could be amplified by 3-dimensional magnetic fluid and zoom in and out of measurement area. This study introduces the experimental consideration of the effects of lens for concentrating of magnetic flux. The experimental results showed that the magnetic fluid has sufficient lens effect for magnetic camera and effect of improvement in probability of detection.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.401-406
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• 1998

This study aimed at the technique for the construction control in braced excavation works. Selecting a case of Kwangju subway works, field observational values were compared with prediction using Plaxis's. Maximum observational values relevant to both horizontal and vertical proved satisfactory in that they were within the criteria. Numerical results by used Plaxis were overestimated greater than observational values, which meant the prediction were safe tendency. .It must be emphasized that displacement measurement for neighboring important structures should be carried out in order to take countermeasure charge for construction methods, in case that the risk or failure was previewed.

• Journal of KSNVE
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• v.11 no.2
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• pp.354-364
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• 2001

The vibration induced by high speed train running on rail is dealt with as an environmental problem. The train induced vibration is characterized by moving loads at specific frequencies and soil conditions. In fact, it is predicted that the vibration sources are involved the wheel distance, number of cars, speed of operation, drift of rails, structural born vibration, etc. In this paper the characteristics of transferring vibration induced by the high-speed train in operation is discussed. Field measurements was conducted at region from Chungnam Yungj So-jung-myan to Chungbuk Chungwon hyun-do-myun. In the near future. these data will be used as the fundamental data for establishment of the countermeasure for vibrational reduction of high speed train using the results of the field measurements and quantitative prediction of the vibration level