• 조명전기설비학회논문지
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• 제24권4호
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• pp.177-184
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• 2010

본 논문에서는 유한요소법을 이용하여 2[MVA] 몰드변압기의 전계분포에 대한 기포의 영향을 분석하였다. 1차로 기포가 없을 때 전계해석을 하고, 다음으로 전계의 세기가 가장 큰 부분에 에폭시 절연물 내부에 기포가 발생한 경우 전계의 영향을 분석하고 전계분포를 해석하였다. 또한 기포에 의해 생기는 부분방전 개시전압에 대해서도 예측하였다. 해석 조건으로서 기포의 크기, 위치, 개수 및 형상에 대하여 해석하고, 해석 조건에 따른 전계의 영향에 대해 비교 검토하였다.

• Journal of Welding and Joining
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• 제29권5호
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• pp.82-89
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• 2011

The effect of welding condition on tensile properties of KS5J32 Al Alloy was investigated under various welding conditions. The 1.6 mm thick KS5J32 alloy sheets were joined by friction stir welding (FSW) technique with butt joint. The tool rotation speeds were 1000, 1250 and 1500 rpm, and the welding speeds were varied within the range from 100 to 600 mm/min. Voids mainly occurred at the advancing side of the tool probe, when the tool rotation speed was low, due to insufficient materials flow. When the weld pitch exceeded 0.4 mm/rev, voids were observed under all welding conditions and the area of voids increased with increasing weld pitch. For void-free specimens, fracture always occurred at base materials. However voids affected the location of fractures, base metal or welded zone, when the voids existed within the welds.

• Geomechanics and Engineering
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• 제18권6호
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• pp.605-614
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• 2019

The present paper seeks to investigate propagation and reflection of waves at free surfaces of homogeneous, anisotropic and rotating micropolar fibre-reinforced medium with voids. It has been observed that, in particular when P-wave is incident on the free surface, there exist four coupled reflected plane waves traveling in the medium; quasi-longitudinal displacement (qLD) wave, quasi-transverse displacement (qTD) wave, quasi-transverse microrotational wave and a wave due to voids. Normal mode Analysis usually called harmonic solution method is adopted in concomitant with Snell's laws and appropriate boundary conditions in determination of solution to the micropolar fibre reinforced modelled problem. Amplitude ratios which correspond to reflected waves in vertical and horizontal components are presented analytically. Also, the Reflection Coefficients are presented using numerical simulated results in graphical form for a particular chosen material by the help of Mathematica software. We observed that the micropolar fibre-reinforced, voids and rotational parameters have various degrees of effects to the modulation, propagation and reflection of waves in the medium. The study would have impact to micropolar fibre-reinforecd rotational-acoustic machination fields and future works about behavior of seismic waves.

• 천문학회보
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• 제45권1호
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• pp.48.2-48.2
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• 2020

We present a new void definition that connects voids with clusters, the high-density counterpart. We use a pair of ΛCDM simulations whose initial density fields are sign inverted versions to each other, and study the relation between the effective void volume and the corresponding cluster mass. Massive cluster halos (M ≥ 1013M⊙/h) are identified in one simulation at z=0 by linking dark matter particles. The corresponding void to each cluster is defined in the other simulation as the region occupied by the member particles of the cluster. We find a universal functional form of density profiles at z=0 and 1. We also find a power-law relation between the void effective radius and the corresponding cluster mass. Based on these findings, we identify cluster-counterpart voids directly from a density field without using the pair information by utilizing three parameters such as the smoothing scale, density threshold, and minimum core fraction. We identified voids corresponding to clusters more massive than M ≥ 3 × 1014M⊙/h at approximately 70-74 \% level of completeness and reliability. Our results suggest that we can detect voids comparable to clusters of a particular mass-scale.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 추계학술발표대회 논문집
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• pp.217-220
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• 2003

The effective thermoelastic properties of porous metals are discussed herein after each material forming process such as hot pressing or extrusion. The voids in metal matrix are assumed to be initially spherical in shape and to be distributed randomly. Once the porous material deforms plastically due to each material forming process, the voids change their shape from a sphere to an ellipsoid and align in one direction. Since the voids are compressible in nature, the void volume fraction is assumed to be decreasing during each material forming process.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1303-1308
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• 2000

Detection of square shape voids with size 30$\times$20$\times$5cm and 20$\times$20$\times$20cm in concrete were carried out by ultrasonic image processing technique. The advantages and limitations of this technique for non-destructive inspection of square shape voids in concrete are investigated. In this study, it has been verified that the semi-direct measurement method is more effective than the other methods for detecting the voids in concrete using ultrasonic image processing method.

• Steel and Composite Structures
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• 제50권2호
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• pp.123-133
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• 2024

The paper deals with the propagation of Rayleigh waves in a nonlocal thermoelastic isotropic layer which is lying over a nonlocal thermoelastic isotropic half-space under the purview of Green-Lindsay model and Eringen's nonlocal elasticity in the presence of voids. The normal mode analysis is employed to the considered equations to obtain vector matrix differential equation which is then solved by eigenvalue approach. The frequency equation of Rayleigh waves is derived and different particular cases are also deduced. The effects of voids and nonlocality on different characteristics of Rayleigh waves are presented graphically.

• Computers and Concrete
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• 제21권3호
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• pp.345-353
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• 2018

This paper approaches to improve the mechanical and durability properties of low calcium fly ash geopolymer concrete with the addition of Alccofine as a mineral admixture. The mechanical and durability performance of GPC was assessed by means of compressive strength, flexural strength, permeability, water absorption and permeable voids tests. The correlation between compressive strength and flexural strength, depth of water penetration and percentage permeable voids are also reported. Test results show that addition of Alccofine significantly improves the mechanical as well as permeation properties of low calcium fly ash geopolymer concrete. Very good correlations were noted between the depth of water penetration and compressive strength, percentage permeable voids and compressive strength as well as between compressive strength and flexural strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.783-788
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• 2001

Voids created with concrete construction or deterioration result in serious weakness from the aspects of both structural and durable function. Ultrasonic method using image processing technique was used for detecting pattern of voids in concrete in this study Experimental investigation was carried out for three types(patterns) of void in concrete. The effect of curing period of concrete and ultrasonic measurement method was also investigated. As a result it has been verified that the semi-direct measurement method is more effective than the other methods for detecting pattern of voids in concrete in ultrasonic method using image processing technique. The longer the curing period of concrete is, the better the detection accuracy of void pattern can be obtained.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.246-250
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• 2001

In resin transfer molding (RTM), resin is forced to flow through the fiber perform of inhomogeneous permeability. This inhomogeneity is responsible for the mismatch of resin velocity within and between the fiber tows. The capillary pressure of the fiber tows exacerbates the spatial variation of the resin velocity. The resulting microscopic perturbations of resin velocity at the flow front allow numerous air voids to form. In this study, a mathematical model was developed to predict the formation and migration of micro-voids during resin transfer molding. A transport equation was employed to account for the migration of voids between fiber tows. Incorporating the proposed model into a resin flow simulator, the volumetric content of micro-voids in the preform could be obtained during the simulation of resin impregnation.