• Title/Summary/Keyword: fiber elements

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Nonlinear Vibration Analyses of Stiffened Composite Panels under Combined Thermal and Random Acoustic Loads (열-랜덤 음향 하중을 받는 보강된 복합재 패널의 비선형 진동 해석)

  • Choi, In-Jun;Lee, Hong-Beom;Park, Jae-Sang;Kim, In-Gul
    • Journal of the Korea Institute of Military Science and Technology
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    • v.23 no.6
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    • pp.533-541
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    • 2020
  • This study using ABAQUS investigates the nonlinear vibration responses when thermal and random acoustic loads are applied simultaneously to the stiffened composite panels. The nonlinear vibration analyses are performed with changing the number of stiffeners, and layup condition of the skin panel. The panel and stiffeners both are modeled using shell elements. Thermal load (ΔT) is assumed to have the temperature gradient through the thickness direction of the stiffened composite panel. The random acoustic load is represented as stationary white-Gaussian random pressure with zero mean and uniform magnitude over the panels. The thermal postbuckling analysis is conducted using RIKS method, and the nonlinear dynamic analysis is performed using Hilber-HughesTaylor time integration method. When ΔT = 25.18 ℃ and SPL = 105 dB are applied to the stiffened composite panel, the effect of the number of stiffener is investigated, and the snap-through responses are observed for composite panels without stiffeners and with 1 and 3 stiffeners. For investigation of the effect of layup condition of the skin panel, when ΔT = 38.53 ℃ and SPL = 110 dB are applied to the stiffened composite panel, the snap-through responses are shown when the fiber angle of the skin panel is 0°, 30°, and 60°.

The Dietary Behavior and Nutrient Intake Status of the Yooth in Rural Areas of Korea (중.고등학생의 식생활행동과 영양섭취 실태와의 관계 연구)

  • 이건순;유영상
    • Korean Journal of Community Nutrition
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    • v.2 no.3
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    • pp.294-304
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    • 1997
  • The purpose of this study was to explore the relationship between dietary behavior and the nutrient intake status in the youth of rural areas, based on their personal characters such as their sex, age, family type, number of family members, mother's age, occupation, and school career. This study was made by use of a self-administrated questionnaire with a 24-hour recall for 5days as an instrument with 439 randomly selected students. Statistical methods applied to analyze the data were frequency, percent, Willcoxon Rank-sum test, Kruskal-wallis test, x2-test by contingence table, and Spearman's correlation coefficient in non parametric statistical cases. Some of the interesting results are as follows : 1) The correlation between sex and breakfast is highly significant. That is, over 80% of male students had breakfast every day, whereas only about 60% of female students had breakfast every day. Bad table manners and some other problems are insignificant with respect to the personal characters in the relations between the personal characters and eating behaviors. However, the regularity of every meal, the frequency of having meals with other family members, and the frequency of meals eaten out and snacks show significant differences. 2) The mother's occupation does not have any influence on the nutrient intake of their students when the relationship between personal characters and nutrient intake was analysed. On the other hand sex, the mother's school career, the numbers of family members, the type of family, and the income of the family showed significant differences nutrient intakes. 3) The regularity and the frequency of having meals, meals eaten out with their family members, and the table manners during meals showed significant differences in the intake of nutrient elements such as calorie, protein, fat, fiber, calcium, iron, phosphorus, vitamin B1, vitamin B2, niacin and vitamin C. However some consideration during meals and problems in eating habit are insignificant with regard to nutrient intake.

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Evaluation of Forest Tree Leaves of Semi-hilly Arid Region as Livestock Feed

  • Bakshi, M.P.S.;Wadhwa, M.
    • Asian-Australasian Journal of Animal Sciences
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    • v.17 no.6
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    • pp.777-783
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    • 2004
  • Samples of 13 species of forest tree leaves fed to livestock in the semi-hilly arid zone of Punjab State in India were collected at 30 d interval for 12 months, in order to assess their nutritional worth for livestock. The ground samples were pooled for 4 different seasons viz. dry hot, hot humid, fall and winter. The chemical composition irrespective of the season revealed that CP content varied between 8.9 (Carrisa) to 22.0% (Leucaena). Globulin was the major protein fraction in most of the leaves. The lowest concentration of cell wall constituents was observed in Morus alba and Grewea. The leaves in general became fiberous and lignified during winter and fall as compared to summer season. The leaves of Grewea, Morus alba, Leucaena, Carrisa and Acacia were rich in Ca, P and most of the trace elements. The total phenolics ranged between 1.88% (Azardirachta) to 15.82% (Acacia). The leaves of Acacia had the highest concentration of hydrolysable tannins (14.6%) whereas that of Carrisa had that of condensed tannins (5.9%). The condensed tannins (more than 3%) were negatively correlated to the digestibility of dry matter (DM), neutral detergent fiber (NDF) and crude protein (CP). The digestion kinetic parameters for DM, NDF and CP revealed that leaves of Morus alba, Zizyphus and Ehretia had highest insoluble but potentially degradable fraction. The minimum rumen fill values also revealed that leaves of Grewea, Azardirachta, Morus, Ehretia and Leucaena had great potential for voluntary DM intake. The leaves of Ougeinia, Malha, Dodenia and Carrisa had significantly higher rumen fill value indicating poor potential for voluntary DM intake. Season did not have any significant impact on digestion kinetic parameters except that most of the leaves had low potentially degradable fraction, which was degraded at slow rate during winter. It was concluded that the leaves of Morus, Ehretia, Grewea and Leucaena had great potential as livestock feed, while feeding of Ougeinia, Malha and Dodonea leaves should be avoided.

Nonlinear Earthquake Analysis of a Steel Girder Bridge using Point Hinge Models (힌지모델을 이용한 강 거더 교량의 비선형 지진해석)

  • Lee, Do Hyung;Kim, Yong Il;Lee, Doo Ho;Jeon, Jeong Moon
    • Journal of Korean Society of Steel Construction
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    • v.21 no.4
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    • pp.403-411
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    • 2009
  • In the present study, nonlinear earthquake analysis was carried out for a steel girder bridge that had been damaged by the 1995 Kobe earthquake. For such analysis, the use of hysteretic models describing flexure-axial and shear-axial interaction was suggested. The models were incorporated into a structural analysis program in terms of the joint elements representing hinge models, and then a simplified analysis scheme using the hinge models was employed for bridge piers. The analytical predictions of the flexure-axial interactive hinge model show a good correlation with those of the detailed fiber element model. In addition, the analytical predictions of the flexure-shear-axial interactive hinge model enable a displacement component to be separately captured. It is thus recognized that the present study can be a useful scheme for the healthy evaluation of the global displacement performance of piers subjected to earthquake excitation.

Numerical Simulation of the Delamination Behavior of Polymeric Adhesive Tapes Using Cohesive Zone Element (응집 영역 요소를 이용한 고분자 접착 테이프의 박리거동 모사)

  • Jang, Jinhyeok;Sung, Minchang;Yu, Woong-Ryeol
    • Composites Research
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    • v.29 no.4
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    • pp.203-208
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    • 2016
  • Metal and polymer sandwich composites, which are made of sheet metal sheath and polymer or fiber reinforced plastic core, have been reconsidered as an alternative to sheet metal due to their lightness and multifunctional properties such as damping and sound-proof properties. For the successful applications of these composites, the delamination prediction based on the adhesion strength is important element. In this study, the numerical simulation of the delamination behavior of polymeric adhesive tapes with metallic surfaces was performed using cohesive zone elements and finite element software. The traction-separation law of the cohesive zone element was defined using the fracture energy derived from peel mechanics and experimental results from peel test and implemented in finite element software. The peel test of the polymeric adhesive film against steel surface was simulated and compared with experiments, demonstrating reasonable agreement between simulation and experiment.

MIRIS 우주관측카메라 FM Dewar 설계

  • Cha, Sang-Mok;Mun, Bong-Gon;Jeong, Ung-Seop;Lee, Dae-Hui;Nam, Uk-Won;Park, Yeong-Sik;Lee, Chang-Hui;Park, Seong-Jun;Lee, Deok-Haeng;Ga, Neung-Hyeon;Han, Won-Yong;Park, Jang-Hyeon;Seon, Gwang-Il;Yang, Sun-Cheol;Park, Jong-O;Lee, Seung-U;Lee, Hyung-Mok;Matsumoto, Toshio
    • The Bulletin of The Korean Astronomical Society
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    • v.35 no.1
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    • pp.40.2-40.2
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    • 2010
  • MIRIS 우주관측카메라는 과학기술위성 3호의 주탑재체로서 $0.8{\sim}2.0{\mu}m$의 근적외선영역에서 우주배경복사와 우리은하 평면의 Pa-$\alpha$ survey 관측을 목적으로 한다. 이러한 임무를 수행하기 위해 MIRIS 우주관측카메라에는 MCT(HgCdTe) IR 검출기가 사용되고 6개의 필터를 장착할 수 있는 필터휠이 설계되었으며, 열잡음을 줄이고 원하는 SNR을 얻기 위해 모두 100K 이하로 냉각이 요구된다. 효과적인 냉각 및 저온유지를 위해서 외부의 열을 1차적으로 차단하는 Cryostat 외부용기와 100K 이하로 냉각되는 내부 Cold Box의 이중구조를 가지는 Dewar가 설계 되었다. 내부 Cold Box의 냉각은 소형 stirling cooler로 이루어지고 외부의 열 유입량이 Cooler의 냉각용량을 넘지 않도록 설계하였다. Cryostat 외부용기는 radiation cooling으로 냉각되어 200K 이하의 온도를 유지하며 내부 Cold Box로의 열유입을 최소화하기 위해 GFRP(Glass Fiber Reinforced Plastic) 단열 지지대와 MLI(Multi Layer Insulation)가 사용된다. 또한 100K으로 냉각시 필터고정부와 Cold Box 구조에서 일어날 수 있는 구조적인 피로도를 줄이고 열변형에 의한 문제를 방지하기 위한 고려가 설계에 포함되었다. FM(Flight Model)은 고진공 환경의 우주공간에서 문제가 발생하지 않도록 설계되었다. 또한 EQM 진동시험결과를 토대로 발사환경에서 발생하는 강한 진동을 견딜 수 있도록 FEM(Finite Elements Method) 구조해석을 통하여 필터고정부에 flexible structure 설계와 완충제를 추가하고 필터휠 구동부와 harness 고정부 및 cooler 지지부를 비롯한 전체 구조물에서 충분히 진동을 극복할 수 있도록 설계하였다.

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Manufacture and performance test of the composite cantilever arm for electrical discharge wire cutting machine (방전 가공기용 복합재료 외팔보의 제작 및 성능평가)

  • 최진호
    • Composites Research
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    • v.13 no.6
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    • pp.39-46
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    • 2000
  • Electrical discharge machining (EDM) cuts metal by discharging electric current across a thin gap between tool and workpiece. Electrical discharge wire cutting, a special form of EDM, uses a continuously moving conductive wire as an electrode, and is widely used for the manufacture of punches, dies and stripper plates. In the wire cutting process, the moving wire is usually supported by cantilever arm and wire guides. As the wire traveling speed has been increased in recent years to improve productivity, the vibration of the cantilever arm occurs, which reduces the positional accuracy of the machine. Therefore, the design and manufacture of the cantilever arm with high dynamic characteristics have become important as the machining speed increases. In this paper, the cantilever arm for guiding the moving wire was designed and manufactured using carbon fiber epoxy composite in order to improve the static and dynamic characteristics. Specimens for the composite cantilever arm were manufactured and tested to investigate the effect of the number of reinforcing plies and length fitted to steel flange on the load capacity. Also, the finite element analysis using layer and contact elements was performed to compare the calculated results with the experimental ones. From the results, the prototype of the composite cantilever arm for the electrical discharge wire cutting machine was manufactured and the static and dynamic characteristics were compared with those of the conventional steel cantilever arm.

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A Research on the Chinese Color through the Costume of Qing Dynasty (중국 청대 복식에 사용된 색채에 관한 연구)

  • Geum, Key-Sook;Jung, Hyun
    • Journal of the Korean Society of Costume
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    • v.54 no.4
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    • pp.41-53
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    • 2004
  • The significant role of colors in fashion design is not enough to emphasize in terms of one of the important design elements and its influences on the behaviors of the people. The purpose of this research is to examine the traditional Chinese colors and its ways of color combinations to appreciate the Chinese culture and its people. The Chinese traditional costume of Ching Dynasty were investigated through historic records, historic nobles, costume accessories and so on. The results of the study were summarized as follows: (1) The Blue was the most favoured color for clothing among men and women during Ching dynasty and various blues in terms of hue, value and intensities were used. (2) The bright Yellow which had been a symbol of Emperor were prohibited being used among people. Though, the late period of Dynasty, the regulation became not to strict and various shades of yellow families were adapted among People. (3) The Red which had been preferred during Ming Dynasty were constantly favoured for the formal wears of auspicious events such as weddings. (4) Dark color groups were loved for the clothing which were used as a ground colors against the flamboyant patterns revealing strong visual effects through value contrast or primary color combinations. (5) The White had a symbol of mourning and there were some intentions to adopt pale color groups such as mint, jade, gray, moon whit,. silver white to make up for white. (6) Contrast color combinations were one of the basic ways of color combination in Chinese traditional costume. Therefore Chinese color combinations has a strong visual effect and easy to draw attention of people by the contrast of the hue, value or intensity of color. (7) Multi-color combinations were another characteristics of Chinese costume in the formal wears which bears many surface designs. The surface decorated with full of motifs, were appreciated by the people expressing their longings and hopes through the auspicious meanings of patterns and striking visual effects of color combinations.

Seasonal Changes in Chemical Components of the Leaves of Dendropanax morbifera Lev. (채취시기(採取時期)에 따른 황칠(黃漆)나무 잎의 화학성분(化學性分) 변화(變化))

  • Kim, Hyung-Ryang;Chung, Hee-Jong
    • Journal of Korean Society of Forest Science
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    • v.88 no.4
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    • pp.562-567
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    • 1999
  • Dendropanax morbifera Lev. leaves were collected during different seasons to analyze the chemical components. In proximate composition the leaves collected in spring had the highest moisture content and in winter had the lowest. Lipid, ash and fiber contents gradually increased from spring to winter and in winter had the highest. Protein content decreased until summer and then it increased. All of free sugars detected have gradually increased during the growing season. Unsaturated fatty acids content was higher than that of the saturated fatty acids and the major saturated and unsaturated fatty acids were arachidic acid and cis-13,16-docosadienoic acid. respectively. Fifteen free amino acids detected with arginine content being the highest regardless of season and amino acid content gradually decreased during the seasons. The highest content of mineral elements was potassium in leaves collected in spring, with calcium was the highest in leaves picked in other seasons. Vitamin C content was gradually decreased over the growing season and soluble tannin content increased notably.

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Aeroelastic Stability Analysis of Bearingless Rotors with Composite Flexbeam in Hover (복합재 유연보를 갖는 무베어링 로우터 시스템의 정지 비행시 공탄성 안정성 해석)

  • Lim, In-Gyu;Choi, Ji-Hoon;Lee, In;Han, Jae-Hung
    • Composites Research
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    • v.17 no.3
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    • pp.29-37
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    • 2004
  • The aeroelastic stability analysis of composite bearingless rotors is investigated using a large deflection beam theory in hover. The bearingless rotor configuration consists of a single flexbeam with a wrap-around type torque tube and the pitch links located at the leading edge and trailing edge of the torque tube. The outboard main blade, flexbeam and torque tube are all assumed to be an elastic beam undergoing flap bending, lead-lag bending, elastic twist and axial deflections, which are discretized into beam finite elements. For the analysis of composite bearingless rotors, flexbeam is assumed to be a rectangular section made of laminate. Two-dimensional quasi-steady strip theory is used for aerodynamic computation. The finite element equations of motion for beams are obtained from Hamilton's principle. The p-k method is used to determine aeroelastic stability boundary. Numerical results are presented for selected bearingless rotor configurations based on the lay-up of laminae in the flexbeam and pitch links location. A systematic study is made to identify the importance of the stiffness coupling terms on aeroelastic stability for various fiber orientation and for different configuration.