• Title/Summary/Keyword: 물성 및 전단 특성

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램제트 엔진에서의 화염 전파와 비정상 연소 현상에 관한 수치해석

  • ;Vigor Yang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2000.04a
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    • pp.10-10
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    • 2000
  • 램제트 엔진은 비추력이 높고 추력 레벨은 낮으므로, 2단 추진기관에 적합한 추진 시스템이다. 1단-추진기관의 작동이 끝나고, 2단 램제트 엔진이 점화 후 안정된 연소에 도달되기까지 비행체의 속도는 항력에 의하여, 초당 약 마하수 0.1 정도씩 감소된다. 1단 연소 후 2단 램제트로 전환되는 지연시간이 길수록 1단에서 요구되는 종말 가속도는 증가되므로, 1단이 차지하게되는 부피는 증가되고 비행체의 크기 또한 늘어나게 된다. 따라서 1단에서 2단 램제트로 천이되는데 소요되는 시간을 가능한 짧게 하는 것이 효과적이다. 그러나 램제트 엔진의 특성상 선결되어야할 다음과 같은 여러 문제들이 있다. 첫째, 1단 작동 시 공기 흡입구와 연소실은 차단벽으로 분리되어 있다가, 1단 연소후 차단막이 제거되어 외부공기가 램제트 연소실로 흡입된다. 흡입되는 공기는 흡입구의 형상에 의하여 램 압축되지만 초음속으로 연소실을 통과하게된다. 연료 주입 구에서 공급되는 연료는 연소실에서 유동의 흐름방향(streamline)에 따라서 연소실로 확산되는데, 연소되기 전에는 유속이 빠르게 노즐로 빠져 나가므로 램제트 연료가 재순환 구역(recirculation zone)으로 침투하는데 쉽지가 않다. 둘째, 연소실 입구에서 발생되는 와류 (ring vortex)는 1단 연료의 고온 연소 가스를 연소실로 확산시키는데, 비 균일한 온도 분포를 유발하여 램제트 연료의 점화에너지가 공급되는 시간이 적당하지 않을 경우 균일한 화염 전파에 악영향을 준다. 셋째, 연소실에서의 빠른 유동 조건은 연료가 연소실에 머무를 수 있는 시간을 감소시키며, 연소실 입구에서 강한 전단 응력이 발생되어 화염이 안정화되는데 악 영향을 미치게된다. 본 논문은 공기 흡입구, 연소실 및 노즐을 통합하여 수치해석을 하였으며 열유동/점화/연소등의 미케니즘을 이해하고, 주요 인자들 중 와류의 영향에 초점을 맞추었다.다고 판단되며 배기 가스 자체에 대기 공기중에 함유되어 있던 습기가 얼어붙는(Icing화) 문제가 발생하기 때문에 배기가스의 Icing을 방지하기 위하여 압축기 끝단에서 공기를 추출하여 배기부분에 송출할 필요성이 있는 것으로 판단되었다. 출구가스의 기체 유동속도가 매우 빠르므로 (100-l10m.sec) 이를 완화하기 위한 디퓨저의 설계가 요구된다고 판단된다. 또 연소기 후방에 물을 주입하는 경우 열교환기 및 기타 부분품에 발생할 수 있는 부식 및 열교환 효율 저하도 간과할 수 없는 문제로 파악되었다. 이러한 기술적 문제가 적절히 해결되는 경우 비활성 가스 제너레이터는 민수용으로는 대형 빌딩, 산림, 유조선 등의 화재에 매우 적절히 사용되어 질 수 있을 뿐 아니라 군사적으로도 군사작전 중 및 공군 기지의 화재 그리고 지하벙커에 설치되어 있는 고급 첨단 군사 장비 등의 화재 뿐 아니라 대간첩작전 등에 효과적으로 활용될 수 있을 것으로 판단된다.가 작으며, 본 연소관에 충전된 RDX/AP계 추진제의 경우 추진제의 습기투과에 의한 추진제 물성 변화는 미미한 것으로 나타났다.의 향상으로, 음성개선에 효과적이라고 사료되었으며, 이 방법이 편측 성대마비 환자의 효과적인 음성개선의 치료방법의 하나로 응용될 수 있으리라 생각된다..7%), 혈액투석, 식도부분절제술 및 위루술·위회장문합술을 시행한 경우가 각 1례(2.9%)씩이었다. 13) 심각한 합병증은 9례(26.5%)에서 보였는데 그중 식도협착증이 6례(17.6%), 급성신부전증 1례(2.9%), 종격동기흉과 폐염이 병발한 경우와 폐염이 각 1례(2.9%)였다. 14) 식도경 시행회수는 1회가 17례(54.8%), 2회가 9례(29.0%), 3회 이상이 5례(16.1%)였다.EX>$IC_{50}$/ 값이 210 $\mu\textrm{g}$/$m\ell$로서 효과적

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Preparation and Properties of Autoxidation Drying Type Waterborne Coatings Containing Bentonite (벤토나이트가 포함된 자동산화 건조형 수성코팅제의 제조 및 특성)

  • 이석기;구광모;이병교
    • Journal of the Korean Ceramic Society
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    • v.38 no.11
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    • pp.1067-1074
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    • 2001
  • Four different composition of autoxidation drying type waterborne coatings (WBC-1, WBC-2, WBC-3, WBC-4) were prepared by the compounding of bentonite (BEN) as a water swellable clay and organometallic soaps as a drier with acrylic binder and coating additives. The solution viscosity, solid content, rheological properties and drying rate of WBCs were investigated. Also the thermal stability, the transmittance and the water-resistance of the films casted by WBCs were measured, and the surface topology of WBC films were investigated by the scanning probe microscopy. As WBC-2, WBC-3 and WBC-4 containing BEN showed the thixotropy with the shear rate, the storage stability of WBC was a excellent. When the driers was mixed in the ratio of Mn/Zn/Ba=1/2/3, the dry ability of WBCs showed maximum as 5.0 sec at 60$\^{C}$. The initial decomposition temperature and the transmittance of WBC films containing BEN increased in range of 32.2∼54.7$\^{C}$ and 5.1∼8.6% than the commercial WBC (MC-21W), respectively. The water resistance of WBC films increased in order of MC-21W

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Synthesis of Functional Copolyester, its Blend with PET, and Properties of Carbon Black Dry Color (기능성 폴리에스테르 공중합체의 합성, PET와의 블렌드 및 카본 블랙 Dry Color의 물성)

  • Park, Lee Soon;Lee, Dong Chan;Kim, Jin Kon;Huh, Wan Soo
    • Applied Chemistry for Engineering
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    • v.7 no.3
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    • pp.496-503
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    • 1996
  • Aromatic and aliphatic copolyesters for the dispersing agent were synthesized by two stage reaction, esterification and polycondensation. Copolyesters were blended with PET in the melt state and their thermal and rheological properties were investigated. From GPC analysis Mn's and Mw's of copolyesters were about 30000 and 65000g/mol, respectively. From DSC experiment copolyesters had melting range of $90{\sim}150^{\circ}C$. Copolymer composition was in good agreement with comonomer feed ratio from $^1H$-NMR analysis. Copolyesters and SPA (standard sample) were blended with PET in the melt state. From DSC experiment, copolyesters and SPA were miscible with PET. From the dynamic melt viscosity experiment, melt viscosity of blended sample was increased as the content of aromatic copolyester was increased, while it was decreased as the content of aliphatic and SPA were increased. As for volume resistivity of dry color containing carbon black and copolyesters with dispersing time, aromatic copolyester showed highest value. It was conferred from this result that aromatic copolyester was the best dispersing agent for carbon black in PET resin.

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Interfacial and Surface Energies Evaluation of Modified Jute and Hemp Fibers/Polypropylene (PP)-Maleic Anhydride Polypropylene Copolymers (PP-MAPP) Composites using Micromechanical Technique and Contact Angle Measurement (미세역학시험법과 접촉각 측정을 통한 변형된 Jute와 Hemp섬유 강화 Polypropylene (PP)-Maleic Anhydride Polypropylene Copolymers (PP-MAPP) 복합재료의 계면 및 표면에너지 평가)

  • Park, Joung-Man;Son, Tran Quang;Jung, Jin-Gyu;Kim, Sung-Ju;Hwang, Byung-Sun
    • Journal of Adhesion and Interface
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    • v.7 no.2
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    • pp.1-11
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    • 2006
  • Interfacial evaluation of the untreated and treated Jute and Hemp fibers reinforced different matrix polypropylene-maleic anhydride polypropylene copolymer (PP-MAPP) composites were investigated by micromechanical technique and dynamic contact angle measurement. For the statistical tensile strength of Jute and Hemp fibers, bimodal Weibull distribution was fitted better than the unimodal distribution. The acid-base parameter on the interfacial shear strength (IFSS) of the natural fiber composites was characterized by calculating the work adhesion, $W_a$. The effect of alkaline, silane coupling agent on natural fibers were obtained with changing MAPP content in PP-MAPP matrices. Alkaline treated fibers made the surface energy to be higher due to removing the weak boundary layers and thus increasing surface area, whereas surface energy of silane treated Jute and Hemp fibers decreased due to blocked high energy sites. MAPP in the PP-MAPP matrix caused the surface energy to increase due to introduced acid-base sites. Microfailure modes of two natural fiber composites were observed clearly differently due to different tensile strength of natural fibers.

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A Study on Physical Properties About Velvet Antler of the Elk(Cerus canadensis) (엘크 녹용의 물성 특성에 관한 연구)

  • Sung, S.H.;Han, J.H.;Kim, Y.M.;Kim, B.K.
    • Journal of Animal Environmental Science
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    • v.13 no.3
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    • pp.201-210
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    • 2007
  • In this study, physical properties of Elk antler was investigated to develop the optimum drying and packaging methods for improving the antler quality as well as deal with diversify of demand. After the antler was sliced with 5 mm thickness, and the compressive, shear, and tensile stresses were measured at the center and velvet parts of pre-dried and dried antlers after the contained water rate of the dried antlers was maintained below 10%. The results are as follows. 1. Considering the center of pre-dried antlers, the compressive stresses were $60.73\;g/mm^2$, $145.65\;g/mm^2$, and $260.97\;g/mm^2$, respectively at the upper, middle, and lower parts while $70.67\;g/mm^2$, $811.90\;g/mm^2$, $3,235.52\;g/mm^2$, respectively for velvet layer. Considering the center of dried antlers, the compressive stresses were $190.43\;g/mm^2$, $445.81\;g/mm^2$, and $705.86\;g/mm^2$, respectively at the upper, middle, and lower parts while $734.01\;g/mm^2$, $1,238.40\;g/mm^2$, $4,134.03\;g/mm^2$, respectively for velvet layer. 2. For the pre-dried, the shear stresses were $50.24\;g/mm^2$, $294.44\;g/mm^2$, and $423.47\;g/mm^2$, respectively, and $124.14\;g/mm^2$, $367.69\;g/mm^2$, and $425.86\;g/mm^2$, respectively for the dried antlers. 3. The tensile stresses were $13.59\;g/mm^2$, $62.85\;g/mm^2$, and $112.07\;g/mm^2$, respectively for the pre-dried and $77.24\;g/mm^2$, $175.87\;g/mm^2$, and $184.06\;g/mm^2$, respectively for the dried antlers. 4. In the case of drying antlers, the physical characteristics of the antlers was. changed such as moisture evaporation, contraction, and surface hardening. For the center part, the changes of the physical characteristics were more significant at the lower part while at the upper part for the velvet layer. 5. The stress changes of Elk antlers was shown very remarkably according to growth point. Moreover, the stress was clearly higher at velvet layer part to the center part, base parts compared to the upper parts.

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Joint Diversion Analysis Using the Dispersion Characteristics of Love Wave and Rayleigh Wave (I) - Constitution of Joint Diversion Analysis Technique - (러브파와 레일리파의 분산특성을 이용한 동시역산해석(I) - 동시역산해석기법의 구성 -)

  • Lee Il-Wha;Joh Sung-Ho
    • Journal of the Korean Geotechnical Society
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    • v.21 no.4
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    • pp.145-154
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    • 2005
  • Love wave and Rayleigh wave are the major elastic waves belonging to the category of the surface wave. Those waves are used to determine the ground stiffness profile using their dispersion characteristics. The fact that Love wave is not contaminated by P-wave makes Love wave superior to Rayleigh wave and other body waves. Therefore, the information that Love wave carries is more distinct and clearer than that of others. Based on theoretical research, the joint inversion analysis that uses the dispersion information of both Love and Rayleigh wave was proposed. This analysis consists of the forward modeling using transfer matrix, the sensitivity matrix for evaluating the ground system and DLSS (Damped Least Square Solution) as an inversion technique. The technique of joint inversion uses the dispersion characteristics of Love wave and Rayleigh wave simultaneously making the sensitivity matrix. The sensitivity matrix was used for inversion analysis repeatedly to find the approximate ground stiffness profile. The purpose of the joint inversion analysis is to improve accuracy and convergency of inversion results by utilizing that frequency contribution of each wave is different.

Polygonal Grain-Based Distinct Element Modelling of Mechanical Characteristics and Transverse Isotropy of Rock (다각형 입자 기반 개별요소모델을 통한 암석의 역학적 특성과 횡등방성 모사)

  • Park, Jung-Wook;Park, Chan;Ryu, Dongwoo;Choi, Byung-Hee;Park, Eui-Seob
    • Tunnel and Underground Space
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    • v.26 no.3
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    • pp.235-252
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    • 2016
  • This study presents a methodology to reproduce the mechanical behavior of isotropic or transversely isotropic rock using the polygonal grain-based distinct element model. A numerical technique to monitor the evolution of micro-cracks during the simulation was developed in the present study, which enabled us to examine the contribution of tensile cracking and shear cracking to the progressive process of the failure. The numerical results demonstrated good agreement with general observations from rock specimens in terms of the behavior and the evolution of micro-cracks, suggesting the capability of the model to represent the mechanical behavior of rock. We also carried out a parametric study as a fundamental work to examine the relationships between the microscopic properties of the constituents and the macroscopic behavior of the model. Depending on the micro-properties, the model exhibited a variety of responses to the external load in terms of the strength and deformation characteristics. In addition, a numerical technique to reproduce the transversely isotropic rock was suggested and applied to Asan gneiss from Korea. The behavior of the numerical model was in good agreement with the results obtained in the laboratory-scale experiments of the rock.

Effects of Feed Containing Citrus Byproducts on the Physio-chemical Characteristics and Palatability of Korean Native Chickens (토종닭 고기의 이화학적 특성 및 기호성에 미치는 감귤 부산물 급여의 영향)

  • Jung, In-Chul;Yang, Jong-Beom;Moon, Yoon-Hee
    • Journal of the East Asian Society of Dietary Life
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    • v.18 no.4
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    • pp.524-530
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    • 2008
  • In this study, the effects of feed containing citrus byproducts on the physicochemical characteristics and palatability of Korean native chickens were investigated. The Korean native chickens used in this study were divided into two groups: T0 (chickens that were not fed citrus byproducts until they were 39 weeks old) and T1 (chickens that were fed citrus byproducts). The feed given to the T1 chickens was the same as that given to the T0 chickens for the first 16 weeks. Between weeks $17{\sim}39$, the feed given to the T1 chickens was prepared by adding 4% of the citrus byproducts to the feed given to the T0 chickens. The chickens used in the experiment were chilled for 2 days after being sacrificed. The feed containing citrus byproducts did not cause any statistically significant differences in the breast and thigh characteristics of lightness ($L^*$ value), redness ($a^*$ value), yellowness ($b^*$ value), water-holding capacity, frozen loss, thawing loss and boiling loss. As for the rheological properties, there was no statistically meaningful difference in the breast/thigh characteristics of springiness, cohesiveness, gumminess, and chewiness between the T0 and T1 chickens. However, hardness and shear force were significantly lower in the T1 chickens than in the T0 chickens (p<0.05). The acid and peroxide values were also lower in the T1 chickens than in the T0 chickens, but the difference was not statistically significant. Antioxidant activity was better in the T1 chickens than in the T0 chickens. Thus, the results of the present study show that consumption of citrus byproducts did not affect the color and smell of raw meat. The palatability of boiled meat was significantly better in the T1 chickens than in the T0 chickens.

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Hydro-Mechanical Modelling of Fault Slip Induced by Water Injection: DECOVALEX-2019 TASK B (Step 1) (유체 주입에 의한 단층의 수리역학적 거동 해석: 국제공동연구 DECOVALEX-2019 Task B 연구 현황(Step 1))

  • Park, Jung-Wook;Park, Eui-Seob;Kim, Taehyun;Lee, Changsoo;Lee, Jaewon
    • Tunnel and Underground Space
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    • v.28 no.5
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    • pp.400-425
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    • 2018
  • This study presents the research results and current status of the DECOVALEX-2019 project Task B. Task B named 'Fault slip modelling' is aiming at developing a numerical method to simulate the coupled hydro-mechanical behavior of fault, including slip or reactivation, induced by water injection. The first research step of Task B is a benchmark simulation which is designed for the modelling teams to familiarize themselves with the problem and to set up their own codes to reproduce the hydro-mechanical coupling between the fault hydraulic transmissivity and the mechanically-induced displacement. We reproduced the coupled hydro-mechanical process of fault slip using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. A methodology to formulate the hydro-mechanical coupling relations of two different hydraulic aperture models and link the solid element of TOUGH2 and the interface element of FLAC3D was suggested. In addition, we developed a coupling module to update the changes in geometric features (mesh) and hydrological properties of fault caused by water injection at every calculation step for TOUGH-FLAC simulator. Then, the transient responses of the fault, including elastic deformation, reactivation, progressive evolutions of pathway, pressure distribution and water injection rate, to stepwise pressurization were examined during the simulations. The results of the simulations suggest that the developed model can provide a reasonable prediction of the hydro-mechanical behavior related to fault reactivation. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOLVAEX-2019 Task B and validated using the field data from fault activation experiments in a further study.

Effect of Autoclave and Microwave Treatments on Quality of Bread (반죽에 가압가열 및 Microwave 처리가 빵의 품질에 미치는 영향)

  • Kim, Koth-Bong-Woo-Ri;Choi, Jung-Su;Kim, Dong-Hyun;SunWoo, Chan;Jung, Seul-A;Kim, Hyun-Jee;Jeong, Da-Hyun;Jeong, Hee-Ye;Choi, Ho-Duk;Ahn, Dong-Hyun
    • Journal of the Korean Society of Food Science and Nutrition
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    • v.41 no.5
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    • pp.681-686
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    • 2012
  • This study conducted autoclave and microwave treatments on dough to determine if there were any changes in quality after the dough was cooked into bread. Wheat dough after secondary fermentation was treated with a microwave (1 min), an autoclave (30 min), and both an autoclave and microwave (30 min/1 min). We then measured the pH, moisture content, color, texture, and sensory evaluation. The results showed that pH was slightly decreased when it was treated in an autoclave (baking and no baking) and autoclave/microwave (baking and no baking). When microwaved and baked, the moisture content most decreased compared to the control. In crust color, there were no considerable differences in lightness, redness, or yellowness compared to the control, except when microwaved (no baking). The lightness of the crumb color decreased, while redness and yellowness increased, when dough was treated with an autoclave (baking and no baking) and autoclave/microwave (baking and no baking). Hardness, gumminess, chewiness and shear force were significantly increased when dough was treated with an autoclave (baking and no baking) and autoclave/microwave (baking and no baking) compared to the control. In the sensory evaluation, there were no considerable differences in color, aroma, taste, or overall preference when microwaved and baked. Color, aroma, shape, and overall preference were the worst when the dough was treated with autoclave/microwave (baking and no baking). These results suggest that autoclaving and microwaving may reduce the quality of bread, and countermeasures to this problem are necessary.