• Title/Summary/Keyword: Condition Number

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Design of Integrated-Mirror Etalons for Surface-Emitting Lasers and Photonic Switching (광스위칭과 표면 발진 레이저를 위한 집적 거울 Etalon의 설계)

  • 정종술;윤태훈;김재창
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.29A no.3
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    • pp.41-46
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    • 1992
  • In this paper we report how to design integrated-mirror etalons for surface-emitting lasers and photonic switching without time-consuming numerical calculation. It consists of the following two-step process (step 1) find the minimum reflectance to achieve the maximum allowable linewidth. (step 2) find the number of the quarter-wave layers in each mirror to realize the reflectance given by step 1. The condition for maximum transmission in an integrated- mirror etalon is also derived. Under this condition we can achieve the required linewidth with the minimum number of quarterwave layers.

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Development of Low-Reynolds-Number Ssecond Moment Turbulence Closure by DNS Data (DNS 자료에 의한 저레이놀즈수 2차 모멘트 난류모형의 개발)

  • Sin, Jong-Geun;Choe, Yeong-Don
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.8
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    • pp.2572-2592
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    • 1996
  • A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

An iterative method for damage identification of skeletal structures utilizing biconjugate gradient method and reduction of search space

  • Sotoudehnia, Ebrahim;Shahabian, Farzad;Sani, Ahmad Aftabi
    • Smart Structures and Systems
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    • v.23 no.1
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    • pp.45-60
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    • 2019
  • This paper is devoted to proposing a new approach for damage detection of structures. In this technique, the biconjugate gradient method (BCG) is employed. To remedy the noise effects, a new preconditioning algorithm is applied. The proposed preconditioner matrix significantly reduces the condition number of the system. Moreover, based on the characteristics of the damage vector, a new direct search algorithm is employed to increase the efficiency of the suggested damage detection scheme by reducing the number of unknowns. To corroborate the high efficiency and capability of the presented strategy, it is applied for estimating the severity and location of damage in the well-known 31-member and 52-member trusses. For damage detection of these trusses, the time history responses are measured by a limited number of sensors. The results of numerical examples reveal high accuracy and robustness of the proposed method.

Flowering Responses of Rice and Soybean to Nyctoperiod and Night Break (암기간과 야간조파에 따른 벼와 콩의 출수ㆍ개화 반응)

  • 김충국;서종호;최성호;최경진;이진모;변종영
    • Korean Journal of Agricultural and Forest Meteorology
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    • v.5 no.3
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    • pp.208-212
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    • 2003
  • Extended light illumination by street lamp and automobile light has provoked problem in farmland. Night break was imposed by incandescent lamp (50∼60 lux) for 10 minutes every three hours during 12 hours dark period increased culm length compared to continuous dark of 12 hours, and decreased the number of grains per spike in rice. However, these characters were increased by 12 hours dark period with and without night break as compared to 9 hours continuous dark condition. Compared to 12 hours continuous dark condition, night break delayed heading by 9 and 26 days and 9 hours continuous dark condition delayed it by 47 and 41 days in Ilpumbyeo and Hwaseongbyeo, respectively. Night break increased stem length and node number, while decreased pods of soybean cultivar Hwanggeumkong. The stem length and node number were increased by 9 hours continuous dark condition compared to 12 hours dark condition with and without night break. Compared to 12 hours continuous dark rendition, night break delayed flowering by 4 days and to 9 hours continuous dark condition by 19 days.

Effects of Number of Heating Walls on Heat Transfer in the Rough Square Channel with Twisted Tape (테이프가 있는 거친 사각채널에서 가열벽면의 수가 열전달에 미치는 효과)

  • Ahn, S.W.;Kim, M.H.;Bae, S.T.;Kang, H.K.
    • Journal of Power System Engineering
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    • v.10 no.3
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    • pp.17-22
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    • 2006
  • Surface modifications like rib-roughening and displaced insert devices like the twisted tape are commonly used in applications such as compact heat exchangers and cooling systems. In this paper, regionally averaged heat transfer distributions in square channels with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. Each wall of the square channel is composed of isolated aluminum sections. Regionally averaged Nusselt number and channel averaged Nusselt number in turbulent air flows are presented for Reynold numbers from 8,900 to 29,000. We have obtained the following conclusions from the experimental study: 1) The local Nusselt number in the two-sided heated case is higher than that in the four-sided heated condition. 2) In the 4 heating wall channel with twisted tape inserts, Nusselt number based on bottom wall temperature is enhanced by 1.2 - 1.6 times if adding the axial interrupted ribs on the bottom wall only. 3) The twisted tape with interrupted ribs under the two-sided heating condition produces the highest heat transfer coefficient.

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삼각형상 그루브 채널에서 맥동유동에 의한 열전달 향상에 관한 실험적 연구

  • 권오준;이대영;김서영;강병하;김용찬
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.13 no.10
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    • pp.1009-1016
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    • 2001
  • The heat transfer enhancement by pulsatile flow in a triangular grooved channel has been experimentally investigated in this study The experiment was performed in the ranges of the Reynolds number from 270 to 910, the pulsatile fraction from 0.125 to 0.75, and the Strouhal number from 0.084 to 0.665. It was measured that the heat transfer improves up to 350% compared with the steady flow case at Re=270,$\eta=0.5$, and St=0.335. The heat transfer enhancement was found to increase as the pulsatile fraction increases and the Reynolds number decreases. It was also found that the heat transfer enhancement is maximized at a specific pulsatile frequency satisfying the resonant condition. The nondimensional frequency, i.e., the Strouhal number at the resonant condition was found to increase as the Reynolds number decreases. The flow visualization revealed that the heat transfer enhancement results from the strong mixing caused by the repeating sequence of vortex formation, rotation and subsequent ejection from the grooves by the pulsatile flow.

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Impingement Heat Transfer Within a Row of Submerged Circular Water Jets (1열 원형 서브머지드 충돌수분류군에 의한 열전달의 실험적 연구)

  • Ohm, Ki-Chan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.8
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    • pp.538-544
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    • 2010
  • An experimental investigation is presented to study the effect nozzle spacing, jet to plate spacing and Reynolds number on the local heat transfer to normally upward impinging submerged circular water jets on a flat heated surface. Nozzle arrays are a single jet(nozzle dia. = 8 mm), a row of 3 jets(nozzle dia. = 4.6 mm, nozzle spacing = 37.5 mm) and a row of 5 jets(nozzle dia. = 3.6 mm, nozzle spacing = 25 mm), and jet to plate spacing ranging from 16∼80 mm(H/D = 2∼10) is tested. Reynolds number based on single jet exit condition is varied 30000∼70000($V_o$ = 3∼7 m/s). Except for the condition of H/D = 10, the average Nusselt number of multi-jet is higher than that of single jet. For H/D = 2, average Nusselt number is increased by 50.3∼82.5% for a row of 3 jets and by 52.9∼65.2% on a row of 5 jets when compared to the average Nusselt number on the single jet.

Optimization of monitoring methods for air-borne bacteria in the environmental conditions of pig facilities (무균 돈사 환경 모니터링을 위한 대기 중 미생물 탐지기법 확립)

  • Lee, Deok-Yong;Seo, Yeon-Soo;Kang, Sang-Gyun;Yoo, Han Sang
    • Korean Journal of Veterinary Research
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    • v.46 no.3
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    • pp.255-261
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    • 2006
  • Experimental animals have been used to biological and medical purposes and the animals must be, for these purposes, healthy and clean to microbial infection. However, the animals can be easily exposed to pathogenic microorganism via several routes. Of the routes, environmental conditions are the most important factors to keep the animals healthy and clean, especially air condition. Monitoring of air-condition has been required to keep the animal healthy and clean. However, any guideline is not available for experimental conditions with pigs. Therefore, the sampling times and points were compared in different conditions to establish an optimal protocol for monitoring of air borne bacteria. Tryptic soy agar(TSA), blood agar containing 5% defibrinated sheep blood and Sabraud dextrose agar(SDA) were used as media to capture total bacteria, pathogenic bacteria and fungi, respectively. Two methods, compulsive capture using an air-sampler and capturing fall-down bacteria were used to capture the microorganisms in the air. The points and time of capturing were different at each experiment. Air borne microorganisms were captured at three and five points in the open and closed equipments, respectively. Air was collected using an air-sampler for 1 min and 5 min and the agar plates as open status were left from 30 min to 2hr. At first, we monitored an experimental laboratory which dealt with several pathogenic bacteria and then, a protocol obtained from the investigation was applied to open or close experimental conditions with pigs. Number of bacteria was high from 10:00 to 15:00, especially on 13:30-15:30 but sharply decreased after 17:00. The tendency of the number of bacteria was similar between two methods even though the absolute number was higher with air sampler. Critical difference in the number of cells was observed at 5 min with air sampler and 2 hr with fall-down capturing method. However, 1 min with air sampler and 1 hr with fall-down capturing were the best condition to identify bacterial species collected from the air. Number of bacteria were different depending on the sampling points in closed condition but not in opened condition. Based on our results, a guide-line was suggested for screening air-borne microorganism in the experimental conditions with pigs.

Specifics in Weed Competition and Herbicide Response of Korean Lawngrass(Zoysia japonica) under Foggy Condition (안개에 기인하는 한국(韓國)들잔디(Zoysia japonica)의 잡초경합(雜草競合) 및 제초제반응(除草劑反應) 특이성(特異性))

  • Guh, J.O.;Lee, B.R.;Chon, S.U.;Han, S.U.
    • Korean Journal of Weed Science
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    • v.15 no.4
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    • pp.262-269
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    • 1995
  • The reseach was conducted to find out if there are any difference in growth, specific pattern in weed competition, and herbicide response of Korean lawngrass(Zoysia japonica Steud.) in a green house equipped with auto-foggy system. Plant height and leaf stage of Korean lowngrass under foggy condition were increased through all growing stages, whereas the number of tillers and shoot fresh weight harvested at 100 days after seeding were reduced by 24% and 29%, respectively, comparing with non-foggy condition. Weed emergence(total fresh weight) under foggy condition was much greater than that under non-foggy condition. Plant height, number of tillers, number of plant and shoot fresh weight of lawngrass under foggy condition were severely reduced with increasing the duration of competition(above 40 day-competition). Among the herbicides treated, oxyfluorfen completely inhibited plant height of lawngrass regardless of foggy condition, and bensulide considerably inhibited plant height of lawngrass under foggy condition. On the other hand, flazasulfuron did not affect the growth of lawngrass under both foggy and non-foggy conditions. At 40 days after herbicides application, weeding efficacy of bensulide and mecoprop under foggy condition were reduced by 6% and 13%, respectively, comparing with non-foggy condition.

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A Study on the Statistical Distribution of Rebound Number and Ultrasonic Pulse Velocity in RC and PSC Concrete Structures (RC 및 PSC 콘크리트에서 반발도 및 초음파 속도의 변화에 대한 연구)

  • Sa, Min-Hyung;Yoon, Young-Geun;Lee, In-Bok;Woo, In-Sung;Oh, Tae Keun
    • Journal of the Korean Society of Safety
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    • v.32 no.4
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    • pp.53-58
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    • 2017
  • The rebound hammer test and the measurement of ultrasonic pulse velocity(UPV) have been widely used for the physical properties & condition evaluation of reinforced & prestressed concrete structures for a long time, but the acoustoelastic effects by the prestressing in the prestressed concrete structures on the rebound number and ultrasonic pulse velocity have not been studied clearly. Therefore, this study investigated the data distribution of the rebound numbers and ultrasonic pulse velocities in reinforced and prestressed concrete slabs of $3000{\times}3000mm$ with a thickness of 250 mm. Also, the Kolmogorov-Smirnov goodness-of-fit test was done in order to identify statistical consistency and reliability. The statistical analysis results show that the rebound number and ultrasonic pulse velocities increased about 1.9% and 2.5%, respectively when prestressing was applied. As expected, the UPV shows better statistical reliability and potential for in situ evaluation than the RB because the RB are more sensitive to testing posture, surface condition, temperature and humidity so on. The experimental data in this study can be used for the condition assessment of reinforced and prestressed concrete structures by the rebound number and ultrasonic pulse velocity.