• 제목/요약/키워드: foam layer

검색결과 156건 처리시간 0.027초

Comparison of the Impact of an Optimized Ice Cooling Vest and a Paraffin Cooling Vest on Physiological and Perceptual Strain

  • zare, Mansoor;dehghan, Habibollah;yazdanirad, Saeid;khoshakhlagh, Amir hossein
    • Safety and Health at Work
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    • 제10권2호
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    • pp.219-223
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    • 2019
  • Background: Ice cooling vests can cause tissue damage and have no flexibility. Therefore, these two undesirable properties of ice cooling vest were optimized, and the present study was aimed to compare the impact of the optimized ice cooling vest and a commercial paraffin cooling vest on physiological and perceptual strain under controlled conditions. Methods: For optimizing, hydrogel was used to increase the flexibility and a layer of the ethylene vinyl acetate foam was placed into the inside layer of packs to prevent tissue damage. Then, 15 men with an optimized ice cooling vest, with a commercial paraffin cooling vest, and without a cooling vest performed tests including exercise on a treadmill (speed of 2.8 km/hr and slope of %0) under hot ($40^{\circ}C$) and dry (40 %) condition for 60 min. The physiological strain index and skin temperature were measured every 5 and 15 minutes, respectively. The heat strain score index and perceptual strain index were also assessed every 15 minutes. Results: The mean values of the physiological and perceptual indices differed significantly between exercise with and without cooling vests (P < 0.05). However, the difference of the mean values of the indices except the value of the skin temperature during the exercises with the commercial paraffin cooling vest and the optimized ice cooling vest was not significant (P > 0.05). Conclusions: The optimized ice cooling vest was as effective as the commercial paraffin cooling vest to control the thermal strain. However, ice has a greater latent heat and less production cost.

Computational simulations of transitional flows around turbulence stimulators at low speeds

  • Lee, Sang Bong;Seok, Woochan;Rhee, Shin Hyung
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제13권1호
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    • pp.236-245
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    • 2021
  • In this study, direct numerical and large eddy simulations of transitional flows around studs were conducted to investigate the effectiveness of turbulence stimulators at very low speeds for the minimum propulsion power condition of four knots. For simplicity, the studs were assumed to be installed on a flat plate, while the wake was observed up to 0.23 m downstream behind the second stud. For applicability to a model ship, we also studied the flow characteristics behind the first and second studs installed on a curved plate, which was designed to describe the geometry of a bulbous bow. A laminar-to-turbulent transition was observed in the wake at ReD ≥ 921 (U≥0.290 m/s), and the wall shear stress at ReD = 1162 (U = 0.366 m/s) in the second wake was similar to that of the fully developed turbulent boundary layer after a laminar-to-turbulent transition in the first wake. At ReD = 581 (U = 0.183 m/s), no turbulence was stimulated in the wake behind the first and second studs on the flat plate, while a cluster of vortical structures was observed in the first wake over the curved plate. However, a cluster of vortical structures was revealed to be generated by the reattachment process of the separated shear layer, which was disturbed by the first stud rather than directly initiated by the first stud. It was quite different from a typical process of transition, which was observed at relatively high ReD that the spanwise scope of the turbulent vortical structures expanded gradually as it went downstream.

5㎓ 대역에서 동작하는 다중 U-슬롯 모양의 마이크로스트립 안테나의 설계 및 제작 (Design and Fabrication of Mulitiple U-shaped slot Microstrip Antenna on 5㎓ Application)

  • 윤중한;정계택;이상목;안규철;곽경섭
    • 대한전자공학회논문지TC
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    • 제40권11호
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    • pp.85-92
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    • 2003
  • 본 논문에서는 5㎓ 대역에서 동작하는 다중 V-슬롯 모양의 마이크로스트립 안테나를 설계하고 제작하였다. 단일 U-슬롯 모양 위에 두 개의 작은 역 U-슬롯 모양을 갖도록 하였으며 접지면과 기판사이에 공기층을 삽입하여 충분한 대역을 얻고자 하였다. 여러 파라메타, 큰 U 슬롯모양 가로 길이, 세로 길이, 너비, 위치 그리고 두 개의 역 U 슬롯 모양 간격, 급전 위치 그리고 공기갭의 두께를 최적화시킨 후에 다중 U-슬롯 모양의 마이크로스트립 안테나가 제작되었으며 제작된 안테나의 측정결과는 다음과 같다. VSWR<2.0에서 20.4%의 대역폭과 5.5㏈i의 이득과 방사패턴을 얻었다.

Numerical investigation of a novel device for bubble generation to reduce ship drag

  • Zhang, Jun;Yang, Shuo;Liu, Jing
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제10권5호
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    • pp.629-643
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    • 2018
  • For a sailing ship, the frictional resistance exerted on the hull of ship is due to viscous effect of the fluid flow, which is proportional to the wetted area of the hull and moving speed of ship. This resistance can be reduced through air bubble lubrication to the hull. The traditional way of introducing air to the wetted hull consumes extra energy to retain stability of air layer or bubbles. It leads to lower reduction rate of the net frictional resistance. In the present paper, a novel air bubble lubrication technique proposed by Kumagai et al. (2014), the Winged Air Induction Pipe (WAIP) device with opening hole on the upper surface of the hydrofoil is numerically investigated. This device is able to naturally introduce air to be sandwiched between the wetted hull and water. Propulsion system efficiency can be therefore increased by employing the WAIP device to reduce frictional drag. In order to maximize the device performance and explore the underlying physics, parametric study is carried out numerically. Effects of submerged depth of the hydrofoil and properties of the opening holes on the upper surface of the hydrofoil are investigated. The results show that more holes are favourable to reduce frictional drag. 62.85% can be achieved by applying 4 number of holes.

SAR를 위한 X-band 광대역 배열 안테나의 설계 및 제작 (Design and Fabrication of X-band Broadband Array Antenna for SAR Applications)

  • 원영진;이영주;공영균;김영수
    • 한국전자파학회:학술대회논문집
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    • 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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    • pp.317-322
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    • 2005
  • Synthetic Aperture Radars(SAR) are used mainly for high-resolution imaging of the terrain. This paper describes the 16$\times$16 array antenna designed for an X-band, automobile-based SAR(AutoSAR) system. This antenna has the structure of several layers such as radome, radiators, slots, feed network, and honeycomb cores. Each layer is adhesively bonded to meet different combination of structural and electrical design requirements. Using the Strip-Slot-Foam-Inverted-Patch(SSFIP) structure and dogbone slots, a wide bandwidth and a structural hardness were achieved. Measurement results were compared with simulation results. It was observed that the SAR antenna had a bandwidth of 1.7 GHz, side-lobe levels of less than -20 dB, half-power beamwidth of 5$^{\circ}$, and gains of 25.0 dBi. The observed results show that the designed array antenna is suitable for the broadband AutoSAR system.

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VLM-S용 선형열선절단기의 회전각 계산 (Calculation of Rotation Angle of the Linear Hotwire Cutting System for VLM-s)

  • 이상호;안동규;양동열
    • 한국정밀공학회지
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    • 제19권2호
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    • pp.87-94
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    • 2002
  • Most of Rapid Prototyping (RP) process adopt a solid Computer Aided Design (CAD) model, slicing into thin layers of uniform, but not necessarily constant, thickness in the building direction. Each cross-sectional layer is successive1y deposited and at the same time, bonded onto the previous layers; the stacked layers form a physical part of the model. The objective of this study is to develop a method for calculating the rotation angle ($$\theta$_x, $\theta$_y$) of hotwire of the cutting system in the three-dimensional space for the Variable Lamination Manufacturing process using expandable polystyrene foam sheet (VLM-S). In order to examine the applicability of the developed method to VLM-S, various three-dimensional shapes. such as a screw, an extruded cross, and free surface bodies such as miniatures of the monkey(a figure of Sonokong), were made using the data obtained form the method.

Cu 용 슬러리 환경에서의 보호성 코팅이 융착 CMP 패드 컨니셔너에 미치는 영향 (Effect on protective coating of vacuum brazed CMP pad conditioner using in Cu-slurry)

  • 송민석;지원호
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2005년도 춘계학술대회 논문집
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    • pp.434-437
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    • 2005
  • Chemical Mechanical Polishing (CMP) has become an essential step in the overall semiconductor wafer fabrication technology. In general, CMP is a surface planarization method in which a silicon wafer is rotated against a polishing pad in the presence of slurry under pressure. The polishing pad, generally a polyurethane-based material, consists of polymeric foam cell walls, which aid in removal of the reaction products at the wafer interface. It has been found that the material removal rate of any polishing pad decreases due to the so-called 'pad glazing' after several wafer lots have been processed. Therefore, the pad restoration and conditioning has become essential in CMP processes to keep the urethane polishing pad at the proper friction coefficient and to allow effective slurry transport to the wafer surface. Diamond pad conditioner employs a single layer of brazed bonded diamond crystals. Due to the corrosive nature of the polishing slurry required in low pH metal CMP such as copper, it is essential to minimize the possibility of chemical interaction between very low pH slurry (pH <2) and the bond alloy. In this paper, we report an exceptional protective coated conditioner for in-situ pad conditioning in low pH Cu CMP process. The protective Cr-coated conditioner has been tested in slurry with pH levels as low as 1.5 without bond degradation.

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3차원 트랜지션을 이용한 광대역 마이크로스트립 패치 안테나의 설계 (A Design of the Wideband Microstrip Patch Antenna Using Three-dimensional Transition)

  • 정창권;강치운;윤서용;이봉석;김우수;이문수
    • 한국정보통신학회논문지
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    • 제3권2호
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    • pp.305-311
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    • 1999
  • 본 논문에서는 유전율 1.06, 두께 $\lambda$/4인 발포체 기판상의 얇은 필름에 인쇄한 새로운 형태의 단일층 마이크로스트립 패치 안테나를 설계했다. 안테나의 대역폭이 광대역 임피던스정합을 얻기 위하여 3차원 트랜지션을 사용한다. 안테나의 방사패턴 및 반사손실, 전압정재파비는 "IE3D" 시뮬레이션 패키지를 사용하여 계산하여 측정결과와 비교했다. 측정 결과 전압정재파비 $\le$ 2:1 인 대역폭이 중심주파수 6.8 GHz에서 약 65%로 광대역 안테나임을 입증하였다. 그리고 반사손실 및 전압정재파비는 계산치와 실험치가 거의 일치하였다. 거의 일치하였다.

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소스공개 라이브러리를 활용한 선박 저항계산 CFD 코드 개발 (CFD CODE DEVELOPMENT FOR THE PREDICTION OF THE SHIP RESISTANCE USING OPEN SOURCE LIBRARIES)

  • 박선호;박세완;이신형;이상봉;최정은;강선형
    • 한국전산유체공학회지
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    • 제17권2호
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    • pp.21-27
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    • 2012
  • Reynolds-averaged Navier-Stokes equations solver based on a pressure-based cell-centered finite volume method was developed using OpenFOAM libraries, which was an open source and providing computational continuum mechanics libraries. For the reasonable development of the turbulent boundary layer on the bow of the ship, specified library was developed. Grid sensitivities, such as skewness and aspect ratio of a cell, were tested for the solution convergence. Pressure, turbulent kinetic energy, turbulent dissipation rate contours on the ship surface computed by the developed CFD code were compared with those computed by the commercial CFD code, Fluent.

지오그리드 혼합 보강경량토의 강도특성 연구 (Characteristics of Compressive Strength of Geogrid Mixing Reinforced Lightweight Soil)

  • 김윤태;권용규;김홍주
    • 한국지반공학회:학술대회논문집
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    • 한국지반공학회 2006년도 춘계 학술발표회 논문집
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    • pp.383-393
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    • 2006
  • This paper investigates strength characteristics and stress-strain behaviors of geogrid mixing reinforced lightweight soil. The lightweight soil was reinforced with geogrid in order to increase its compressive strength. Test specimens were fabricated by various mixing conditions including cement content, initial water content, air content and geogrid layer and then unconfined compression tests were carried out. From the experimental results, it was found that unconfined compressive strength as well as stress-strain behavior of lightweight soil were strongly influenced by mixing conditions. The more cement content that is added to the mixture, the greater its unconfined compressive strength. However, the more initial water content or the more air foam content, the less its unconfined compressive strength. It was observed that the strength of geogrid reinforced lightweight soil was increased due to reinforcing effect by the geogrid for most cases except cement content less than 20%. In reinforced lightweight soil, secant modulus $(E_{50})$ was increased as the strength increased due to the inclusion of geogrid.

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