• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.258-259
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• 2009

Pipe wall thinning is one of severe problems on structural safety in nuclear power plants. A guided wave can be a proper tool for the fast evaluation or monitoring. As for gradual wall thinnings, however, low sensitivity caused by the low reflection coefficient limits the use of the guided wave. In this work, instead of the guided wave reflection at the wall thinning, the variation of dispersion characteristics is concerned. SH waves were employed due to several advantages and the magnetostrictive patch transducers were used for the excitation and sensing of the SH waves. The proposed method were verified with some experiments and showed the feasibility as an effective tool for the inspection of gradual wall thinning.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.28-36
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• 2000

Numerical simulation based on the superposition of ring waves generated by the linear periodic source distributions for the plunger type wave maker was accomplished. The characteristics of directional spreading function were investigated. Mirror images are also introduced to consider reflections of side-wall together with the reflection coefficient to account for the imperfect reflection from the real side wall in the long experimental towing tank. Unexpected spurious waves, resulting from the combined effect of finite breadth of segmented wave maker, wavelength and main wave maker, wavelength and main wave propagating direction, were observed in the line source method and also in the analysis of the directivity. The influence of spurious waves to the directional spreading function was also investigated.

• Journal of the Korean Society of Safety
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• v.36 no.2
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• pp.26-31
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• 2021

Buildings with glass curtain walls have become popular due to their appealing aesthetics and ability to let in natural light. However, light reflection from the glass surface is unavoidable in these buildings. In particular, the reflection of light from the glass envelope can create afterimage glare, a hazard to nearby drivers and pedestrians. Despite this potential danger, glare from buildings with curtain walls has not been well-studied. Hence, we analyzed the effect of light reflection on glare around a glass-enclosed skyscraper, depending on its surface reflectance. We investigated the potential hazard of glare to drivers using a commercially available software program. The results indicate that the direction of light reflection is distinctive when the incident angle of solar light increases. Moreover, this light reflection is high enough to induce an afterimage to drivers and pedestrians near the building. We found that keeping the reflectance of the building surface under 3% is required to minimize the afterimage hazard to drivers. Consequently, we recommend managing glass reflectance and installing additional traffic safety systems to reduce traffic accidents near curtain wall buildings.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.6
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• pp.343-351
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• 2014

The reflection and transmission coefficients of waves due to perforated wall are mainly determined by both the porosity and wall thickness of the perforated wall and the period and nonlinearity of incident waves. Among them the wall thickness is very important because it affects the head loss coefficient and the inertia length of the wall. However, by employing the head loss coefficient derived for sharp crested orifice, the previous researches have neglected, or incorrectly considered the effect of wall thickness on the head loss coefficient. Even though it is considered, the effect of the inertia length is neglected in some empirical formulae. Thus, the effect of wall thickness on the reflection and transmission coefficients of waves is not properly considered. In this study comprehensive experiments are conducted for the perforated walls with various thicknesses, and the results are compared with those predicted by the empirical formulae. As a result it is found that the existing formulae can not properly consider the effect of wall thickness, and it is confirmed that a new formula which can correctly consider the effect of wall thickness on the head loss coefficient is necessary.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1455-1462
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• 2013

This study examines the reflection of a partially perforated wall with single chamber by 2D and 3D hydraulic experiments. The effects of slit shape on the front wall, relative chamber width and wave steepness were discussed. For the normal incident wave condition, the reflections of horizontal slit case were lower than that of the vertical slit with the similar porosity, but the differences are not significant. When the wave steepness is relatively small, the reflection coefficients are large. In the oblique incidence, the normalized wave heights along a perforated wall with similar porosity are almost same for the vertical and horizontal slit walls and therefore the difference by slit shape can be ignored.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.143-150
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• 2003

Based on the eigenfunction expansion method, the interaction between monochromatic waves and a partially immersed slotted plate with a back wall has been investigated. Analytical results show that the reflection coefficients by a partially immersed slotted plate depend on the porosity, immersed depth, chamber width, incidence angle and wave frequency. It is found that the reflection coefficient has minimum value within entire frequency range when the porosity has optimal value 0.1. Comparison between the analytical results and the experimental results(Zhu,2001) of reflection coefficients is made for various chamber widths, immersed depths and wave periods with good agreement. The present analytic method can account adequately for energy dissipation caused by flow separation behind a slotted plate and provide the design informations for the construction of slit caisson breakwater.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.2141-2145
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• 2008

Three kind of system composed with buoyant flap hinged at the sea floor are modeled experimentally. The mechanically coupled system provides shelter by reflecting incident waves and by attenuating wave energy through structural and viscous damping. The characteristics of wave reflection, transmission and dynamic angle of the flap oscillation for various conditions were investigated. The structure can minimize wave transmission by attaching offshore wing wall.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.461-464
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• 2006

The caisson of the inner wall type has a weak point that reflecting wave is big. Therefore it has been studied that the research of the decreasing reflecting wave using installation the perforated wall in front of caisson to decrease of that weak point. In this study, we analyzed the characteristic of reflection horizontal and diamond style vertical slit caisson using hydraulic model test. According to the results of experiments, we could confirm that diamond style vertical caisson has a reflection coefficient which has lower than horizontal caisson of the reflection coefficient of 5~10%.

• Proceedings of the KOSOMBE Conference
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• v.1996 no.11
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• pp.103-106
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• 1996

In this paper, we proposed the design and algorithm of force reflection joystick which control mobile robot as a rehabilitation assistance system. The disabled persons are poor at joystick control because of hand vibration and clumsiness in operating it. These problems bring tasks which concerned with operator's safety So there is required technique which prevent collision with wall or obstacles. One of these solution is force reflection joystick which disturb that robot is closed to the wall. To confirm this way, we experimented and simulated with force reflection joystick which attached torque controller.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.19-26
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• 2009

This study is performed by method for the influx of natural light in underground space. to solve the several negative underground issues make the covered courtyard and high reflected wall toward the adjacent space. for illuminance level test of sunken garden space, the adjacent space size is $15M{\times}9M{\times}12M$ sunken Garden with space to install the ceiling on the size of the companion light performance analysis, and seasonal changes derived by the light of changes in performance. In addition, increase the distance of the wall and the adjacent space and estimate the average at true time P.M12. The resulting data indicate that the road was an average lux DESKTOP RADIANCE of the modeling and analysis was conducted.