• Transactions of Materials Processing
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• v.29 no.3
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• pp.157-162
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• 2020

Blind rivet nuts are increasingly used in automotive for the joining of sheets. Their application, however, requires appropriate design guides to prevent catastrophic events arising from the failure of joints. In this study, the shaft shape of a frequently used M8 blind rivet nut is optimized based on 3D numerical analysis of the blind rivet nut considering the characteristics of thread. The thread needs to be modeled to suitably consider the fastening of the M8 bolt after the crimping process. FE analysis showed that while the friction in the contact between crimp flange and plate has no significant effect on the crimp geometry, shaft thickness (t) and shaft height (h) are the most significant design variables. The parameter study including various combinations of t and h reveals that they affect the gap (the distance between the crimped flange and the plate that develops through riveting) and the load acting on the plate. The gap is an indicator of the tightening force. It is found that t is inversely proportional to the gap, and proportional to the load, whereas h is proportional to the gap and inversely proportional to the load. Based on our FE analysis results, we propose the range 0.062 < t/h < 0.1 to ensure sufficient fastening (high clamping load, small gap) of the M8 blind rivet nut. The design guide for determining the t/h ratio proposed in this study can be used for general quantitative analysis of the size and the t/h ratio of blind rivet nuts.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.590-598
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• 2005

The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with $90^{\circ}-rib$ turbulators. The rib turbulator has a square cross section of 1.5 mm. The rib height-to-hydraulic diameter ratio $({e/D_{h})$ is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon, that is, the difference of heat transfer between the leading and the trailing surfaces is distinctly presented by rotation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.319-324
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• 2016

Soils with various particle sizes generally show good shear strength. Some soils have a relatively strong resistance to shear failure in spite of narrow particle distribution, such as gap grading. Based on this example, it can be inferred that appropriate arrangements of particle size in soils might result in an increase in shear strength. This study investigates the strength variation of soils with respect to the particle size distribution. Gap, well, and uniform graded soils were prepared with a desired ratio, and a wide range of direct shear tests were done using the prepared samples. The test results show that there is a strong relationship between the particle size ratio and internal frictional angle. Gap graded soil has a greater frictional angle than a well-graded sample, even when specimens have the same maximum particle size, which is also the case for the uniform grade specimen. The results have potential for developing a methodology for stronger soils through a simple manipulation of particle size distribution.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.799-812
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• 2017

Backfill grouting and realistic convergence distribution were not properly considered in previous studies on 2D numerical analysis of a shield TBM tunnel. In this study, a modeling method was suggested to cope with this problem by considering a realistic convergence distribution and proper properties of backfill grouting. To this end, the influence of gap parameter and depth of rock cover on volume loss and composed of ground volume loss around tunnel excavation and surface volume loss were analyzed with a single layer of weathered soil. As a result, most of surface settlements were occurred immediately after excavation. Additional, as depth of rock cover and gap parameter increased, the influence range of surface settlement curves obtained from 2D numerical analyses became broader than a suggested theoretical equation. Therefore, it is inferred that gap parameter should be applied based on load distribution ratio and the property of backfill grouting properly considered for the estimation of the precise behavior of a shield TBM tunnel in 2D numerical analysis.

• Applied Chemistry for Engineering
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• v.30 no.2
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• pp.205-211
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• 2019

Over the past several decades, the polymer dispersed liquid crystal (PDLC) has received particular attention as a material for developing smart window due to their electro-optical switchable properties. In this study, PDLC cells were fabricated using acrylate monomers, namely 2-hydroxyethyl acrylate (2-HEA) and ethylene glycol phenyl ether acrylate (EGPA), and the effect of the monomer composition on their electro-optical properties was investigated. The monomer mixture with a low viscosity (~10 cps) was easily filled between indium tin oxide (ITO) glasses by capillary action at room temperature. PDLC cells prepared using the mixture ratio of 1 : 9 (2-HEA : EGPA) did not show a complete opaque state at a 0 V condition but exhibited unstable electro-optical properties under an electric field. As the LC composition increased in the reaction mixture for PDLC cell preparation, the $V_{th}$ (threshold voltage) and $V_{sat}$ (saturation voltage) values as well as contrast ratio (CR) increased. $V_{th}$ and $V_{sat}$ values also increased with the cell gap thickness. PDLC cells with a $20{\mu}m$ cell gap thickness exhibited higher CR than those with 10 and $40{\mu}m$ cell gap thicknesses. Particularly, PDLC cells prepared using the mixture ratio of 7 : 3 (2-HEA : EGPA) showed excellent electro-optical properties such as a low driving voltage and high contrast ratio.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.2
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• pp.63-71
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• 2003

The main functions of containment boom for marine floating debris are to prevent spreading of the marine floating debris and to effectively collect the trash skimmer. The design characteristics of containment boom for marine floating debris in wave, current and wind are investigated. The response of a containment boom on the current is a function of a number of parameters, such as geometric characteristics, buoyance/weight ratio and towing velocity. To understand the relationship between these design parameters more clearly, a series of tests with three models with the variation of current speed and gap ratio was conducted. The model tests results are developed to new numerical equation that is tension prediction method of containment boom for marine floating debris. Also its is compared with open sea experimental results.

• Polymer(Korea)
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• v.35 no.6
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• pp.574-579
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• 2011

3-Roll coating process as a key application technology for manufacturing automotive pre-painted metal-sheets has been studied. The 3-Roll coating system for this study consists of pick-up roll for picking up and distributing coating liquid from the reservoir, metering roll to properly meter coating liquid in metering gap regime, and applicator roll for directly transferring liquid into metal-sheet surface. Flow dynamics and operable coating windows of a polymeric paint (primer) with shear-thinning rheological property have been correlated with processing parameters such as speed ratio and metering gap between pick-up and metering rolls. In the uniform coating regime, dry coating thickness increased with increasing metering gap or decreasing speed ratio. Ribbing and cascade instabilities were observed in low speed and high speed ratio conditions, respectively. It is revealed that lower speed ratio makes severity and wavelength of the ribbing increase, aggravating flow instability in coating systems.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.5
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• pp.492-502
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• 2021

In electronic warfare, source enumeration and direction-of-arrival estimation are important. The source enumeration method based on eigenvalues of covariance matrix from received is one of the most used methods. However, there are some drawbacks such as accuracy less than 100 % at high SNR, poor performance at low SNR and reduction of maximum number of estimating sources. We suggested new method based on eigenvalues gaps, which is named AREG(Accumulated Ratio of Eigenvalues Gaps). Meanwhile, FGML(Fast Gridless Maximum Likelihood) which reconstructs the covariance matrix was suggested by Wu et al., and it improves performance of the existing source enumeration methods without modification of algorithms. In this paper, first, we combine AREG with FGML to improve the performance. Second, we compare the performance of source enumeration and direction-of-arrival estimation methods in Rayleigh fading. Third, we suggest new method named REG(Ratio of Eigenvalues Gaps) to reduce performance degradation in Rayleigh Fading environment of AREG.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.49-62
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• 1999

The main functions of oil booms are to prevent spreading of the oil slick and to increase the recovering efficiency of oil skimmers. The oil-containment capability of a floating boom on an open sea is affected by environmental parameters such as waves, currents and winds, as well as the motion characteristics of a boom section. In this study, a series of tests were conducted for three kinds of booms (internal foam type, air inflatable type, self-expanded type) at the open sea off Yosu, and the results are presented. Motion characteristics and oversplashing phenomenon were observed for each boom in different environmental conditions. And the tension exerted on towing line of the boom was also measured with a systematic varitation of towing speeds and gap ratios.

• Journal of Aerospace System Engineering
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• v.10 no.4
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• pp.11-16
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• 2016

In this paper, an experimental study on the aerodynamic characteristics of a variable span wing flying inside a channel guideway is accomplished using wind tunnel testing. A variable span wing with a NACA 0012 airfoil section was fabricated and actuated using a linear servo motor. The aerodynamic effects of 1) wing aspect ratio, 2) ground effect, and 3) the gap between the wingtip and the wing fence were investigated. It was found that both ground effect and wing fence gap increased lift. Also, the wing fence gap does not significantly affect drag. Therefore, it was found that a variable span mechanism can be used as an effective high lift device when flap use is limited.