• Journal of Institute of Control, Robotics and Systems
• /
• v.19 no.12
• /
• pp.1061-1066
• /
• 2013

In the steel industry, the detection of tiny defects including its 3D characteristics on steel surfaces is very important from the point of view of quality control. A multi-spectral photometric stereo method is an attractive scheme because the shape of the defect can be obtained based on the images which are acquired at the same time by using a multi-channel camera. Moreover, the calculation time required for this scheme can be greatly reduced for real-time application with the aid of a GPU (Graphic Processing Unit). Although a more reliable shape reconstruction of defects can be possible when the numbers of available images are increased, it is not an easy task to construct a camera system which has more than 3 channels in the visible light range. In this paper, a new 6-channel camera system, which can distinguish the vertical/horizontal linearly polarized lights of RGB light sources, was developed by adopting two 3-CCD cameras and two polarized lenses based on the fact that the polarized light is preserved on the steel surface. The photometric stereo scheme with 6 images was accelerated by using a GPU, and the performance of the proposed system was validated through experiments.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.7 no.6
• /
• pp.1056-1063
• /
• 2015

Waves can be expressed in terms of a spectrum; that is, the energy density distribution of a representative wave can be determined using statistical analysis. The JONSWAP, PM and BM spectra have been widely used for the specific target wave data set during storms. In this case, the extracted wave data are usually discontinuous and independent and cover a very short period of the total data-recording period. Previous studies on the continuous wave spectrum have focused on wave deformation in shallow water conditions and cannot be generalized for deep water conditions. In this study, the Generalized Extreme Value (GEV) function is proposed as a more-optimal function for the fitting of the continuous wave spectral shape based on long-term monitored point wave data in deep waters. The GEV function was found to be able to accurately reproduce the wave spectral shape, except for discontinuous waves of greater than 4 m in height.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.48.1-48.1
• /
• 2012

We present the ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) to investigate the properties of hot stellar populations responsible for the UV excess (UVX). The initial sample of ETGs is selected by the spectroscopic redshift and the morphology parameter from the SDSS DR 7, and then cross-matched with the GALEX far-UV (FUV) and near-UV (NUV) GR6 data. The cross-matched ETG sample is further classified by their emission line characteristics in the optical spectra into quiescent, star-forming, and active galactic nucleus categories. Contaminations from early-type spiral galaxies, mergers, and morphologically disturbed galaxies are removed by visual inspection. By drawing the FUV-NUV (as a measure of UV spectral shape) versus FUV-r (as a measure of UVX strength) diagram for the final sample of -3700 quiescent ETGs, we find that the "old and dead" ETGs consist of a well-defined sequence in UV colors, the "UV red sequence," so that the stronger UVX galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical stellar population models in which the UV flux is mainly controlled by age or metallicity parameters. Moreover, 2 mag of color spreads both in FUV-NUV and FUV-r appear to be ubiquitous among any subsets in distance or luminosity. This implies that the UVX in ETGs could be driven by yet another parameter which might be even more influential than age or metallicity.

• Korean Journal of Remote Sensing
• /
• v.20 no.5
• /
• pp.289-305
• /
• 2004

Atmospheric correction of Landsat Visible and Near Infrared imagery (VIS/NIR) over aquatic environment is more demanding than over land because the signal from the water column is small and it carries immense information about biogeochemical variables in the ocean. This paper introduces two methods, a modified dark-pixel substraction technique (path--extraction) and our spectral shape matching method (SSMM), for the correction of the atmospheric effects in the Landsat VIS/NIR imagery in relation to the retrieval of meaningful information about the ocean color, especially from Case-2 waters (Morel and Prieur, 1977) around Korean peninsula. The results of these methods are compared with the classical atmospheric correction approaches based on the 6S radiative transfer model and standard SeaWiFS atmospheric algorithm. The atmospheric correction scheme using 6S radiative transfer code assumes a standard atmosphere with constant aerosol loading and a uniform, Lambertian surface, while the path-extraction assumes that the total radiance (L/sub TOA/) of a pixel of the black ocean (referred by Antoine and Morel, 1999) in a given image is considered as the path signal, which remains constant over, at least, the sub scene of Landsat VIS/NIR imagery. The assumption of SSMM is nearly similar, but it extracts the path signal from the L/sub TOA/ by matching-up the in-situ data of water-leaving radiance, for typical clear and turbid waters, and extrapolate it to be the spatially homogeneous contribution of the scattered signal after complex interaction of light with atmospheric aerosols and Raleigh particles, and direct reflection of light on the sea surface. The overall shape and magnitude of radiance or reflectance spectra of the atmospherically corrected Landsat VIS/NIR imagery by SSMM appears to have good agreement with the in-situ spectra collected for clear and turbid waters, while path-extraction over turbid waters though often reproduces in-situ spectra, but yields significant errors for clear waters due to the invalid assumption of zero water-leaving radiance for the black ocean pixels. Because of the standard atmosphere with constant aerosols and models adopted in 6S radiative transfer code, a large error is possible between the retrieved and in-situ spectra. The efficiency of spectral shape matching has also been explored, using SeaWiFS imagery for turbid waters and compared with that of the standard SeaWiFS atmospheric correction algorithm, which falls in highly turbid waters, due to the assumption that values of water-leaving radiance in the two NIR bands are negligible to enable retrieval of aerosol reflectance in the correction of ocean color imagery. Validation suggests that accurate the retrieval of water-leaving radiance is not feasible with the invalid assumption of the classical algorithms, but is feasible with SSMM.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.1 no.2
• /
• pp.17-29
• /
• 1997

Single-mode spectral analysis method is usually applied to a small-scale bridges with the simple geometric shape and uses only fundamental period to estimate the elastic earthquake forces and the displacements of the substructure. On the other hand, multi-mode spectral analysis method may be used instead if the possibilities of potential damage are developed when considering significance, scale, and geometric shape of briages. Since the dynamic responses of bridge can be significantly different depending on the modeling techniques for the restraint and support conditions etc, it may be misled to the unexpected results. In this study the dynamic analysis program which can model and analyze the bridge as a two- or three-dimensional framed structure is developed and verified with the results of other reliable program. Using this program together with the post processor, the designer can easily and readily obtain the reponses(moments, base shears, and displacements)of bridges necessary to design purpose. And further from the analysis results according to the variations of type, scale, and restraint and supprot conditions of bridges including sectional properties, applications of the effective and desirable seismic design are presented.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.25 no.5
• /
• pp.362-367
• /
• 2005

Ultrasonic backward radiation profile is frequency-dependent when the incident region has deptional gradient of acoustical properties or multi-layers. Until now, we have measured the profiles of principal frequencies of an used transducers so that it was not easy to characterize the frequency dependence of the SAW(surface acoustic wave) from the backward radiation profile. We tried to measure the spectral backward radiation profiles using DFP(digital filer package) in a Lecroy DSO(digital storage oscilloscope). The measured spectral profiles showed that the steel specimen of #1200 surface treatment have 2% SAW velocity dispersion of the loaded case and the severly rusty steel specimen have the very big changes in the shape and pattern of the spectral profile. It is concluded that the spectral backward radiation profiles could be very effective tool to evaluate the frequency dependence of surface area.

• Nuclear Engineering and Technology
• /
• v.2 no.2
• /
• pp.85-95
• /
• 1970

An attempt has been made to do interpretation of the fast neutron dose with two threshold detectors incorporated with the Harwell criticality locket. This method is based on the assumption that the spectral distribution of fission neutrons in criticality accidents may be governed by one spectral parameter. The surface-absorbed dose for a unit fission neutron fluence seems to be insensitive to spectral shifts of the fission neutron spectrum. The average cross-sections for the activation detectors, however, are considerably changed with the neutron spectral shape, which may lead to a large error in calculating the dose from the reaction rate if one uses a fixed value for the average cross sections regardless of the neutron spectral distribution. Besides, the doses calculated from three representative formulae for fission neutron spectra have been compared : these formulae are Watt, Cranberg at al. and Maxwellian forms. The results obtained front the Maxwellian formula show a departure from the Watt and Cranberg's, both being similarly close.

• Korean Journal of Materials Research
• /
• v.9 no.12
• /
• pp.1205-1210
• /
• 1999

Far infrared ceramic/aluminum composite powders for thermal spray were fabricated by spray drying method and investigated the characteristics of the plasma sprayed coating layers, I.e. microstructure, phases, thermal shock resistance and spectral emissivity. The shape of the spray dried composite powder was spherical and the particle size distribution was 34~105${\mu}m $. Aluminum was distributed homogeneously in the spray dried composite powder. Spectral emissivity of the plasma sprayed coating layer ranges from 3 to 14${\mu}m $ whereas spectral emissivity of the raw ceramic powder ranges from 8 to 14${\mu}m $. And then spectral emissivity of the coatings was better than that of the raw powder but spectral emissivity was decreased with increasing aluminum content. It was found that aluminum content ranging from 20 to 30wt% was suitable for fabricating far-infrared radiator by plasma spraying method.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.11
• /
• pp.1157-1169
• /
• 2008

This paper presents spectral element formulation which approximates Lamb wave propagation by PZT transducers bonded on a thin plate. A two layer beam model under 2-D plane strain condition is introduced to simulate high-frequency dynamic responses induced by a piezoelectric (PZT) layer rigidly bonded on a base plate. Mindlin-Herrmann and Timoshenko beam theories are employed to represent the first symmetric and anti-symmetric Lamb wave modes on a base plate, respectively. The Euler-Bernoulli beam theory and 1-D linear piezoelectricity are used to model the electro-mechanical behavior of a PZT layer. The equations of motions of a two layer beam model are derived through Hamilton's principle. The necessary boundary conditions associated with the electro-mechanical properties of a PZT layer are formulated in the context of dual functions of a PZT layer as an actuator and a sensor. General spectral shape functions of response field and the associated boundary conditions are obtained through equations of motions converted into frequency domain. Detailed spectrum element formulation for composing the dynamic stiffness matrix of a two layer beam model is presented as well. The validity of the proposed spectral element is demonstrated through numerical examples.

• Steel and Composite Structures
• /
• v.23 no.1
• /
• pp.95-105
• /
• 2017

The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. Because of different mechanical properties of SMAs compared to the regular steel bars, the use of SMAs as reinforcement in the concrete may change the response of structures under seismic loads. In this study, the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3-, 6- and 8-story reinforced concrete (RC) buildings. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel) only, (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Incremental Dynamic Analyses (IDA) are performed using ten different ground motion records to determine the seismic performance of Steel, Steel-SMA and SMA RC buildings. Then fragility curves for each type of RC building by using IDA results for IO, LS and CP performance levels are calculated. Results obtained from the analyses indicate that 3-story frames have approximately the same spectral acceleration corresponding with failure of frames, but in the cases of 6 and 8-story frames, the spectral acceleration is higher in frames equipped with steel reinforcements. Furthermore, the probability of fragility in all frames increases by the building height for all performance levels. Finally, economic evaluation of the three systems are compared.