• 제목/요약/키워드: Velocity variance

검색결과 142건 처리시간 0.027초

난류 파이프 유동 내 물질전달에 대한 레이놀즈 수 영향: Part II. 순간농도장, 고차 난류통계치 및 물질전달수지 (REYNOLDS NUMBER EFFECTS ON MASS TRANSFER IN TURBULENT PIPE FLOW: PART II. INSTANTANEOUS CONCENTRATION FIELD, HIGHER-ORDER STATISTICS AND MASS TRANSFER BUDGETS)

  • 강창우;양경수
    • 한국전산유체공학회지
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    • 제17권3호
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    • pp.59-67
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    • 2012
  • Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The effects of Reynolds number on the turbulent mass transfer are identified in the higher-order statistics(Skewness and Flatness factor) and instantaneous concentration fields. The budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effect of Reynolds number on turbulent mass transfer. Furthermore, to understand the correlation between near-wall turbulence structure and concentration fluctuation, we present an octant analysis in the vicinity of the pipe wall.

Study on the Dynamic Model and Simulation of a Flexible Mechanical Arm Considering its Random Parameters

  • He Bai-Yan;Wang Shu-Xin
    • Journal of Mechanical Science and Technology
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    • 제19권spc1호
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    • pp.265-271
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    • 2005
  • Randomness exists in engineering. Tolerance, assemble-error, environment temperature and wear make the parameters of a mechanical system uncertain. So the behavior or response of the mechanical system is uncertain. In this paper, the uncertain parameters are treated as random variables. So if the probability distribution of a random parameter is known, the simulation of mechanical multibody dynamics can be made by Monte-Carlo method. Thus multibody dynamics simulation results can be obtained in statistics. A new concept called functional reliability is put forward in this paper, which can be defined as the probability of the dynamic parameters(such as position, orientation, velocity, acceleration etc.) of the key parts of a mechanical multibody system belong to their tolerance values. A flexible mechanical arm with random parameters is studied in this paper. The length, width, thickness and density of the flexible arm are treated as random variables and Gaussian distribution is used with given mean and variance. Computer code is developed based on the dynamic model and Monte-Carlo method to simulate the dynamic behavior of the flexible arm. At the same time the end effector's locating reliability is calculated with circular tolerance area. The theory and method presented in this paper are applicable on the dynamics modeling of general multibody systems.

Performance assessment of nano-Silica incorporated recycled aggregate concrete

  • Mukharjee, Bibhuti Bhusan;Barai, Sudhirkumar V
    • Advances in concrete construction
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    • 제8권4호
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    • pp.321-333
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    • 2019
  • The present study targets to access the consequence of utilization of coarse aggregates retrieved from waste concrete as a substitution of coarse fraction of natural aggregates and silica nano-particles as partial substitution of cement using principles of factorial design. Furthermore, procedures of design of experiments are employed to examine the effect of use of recycled aggregates and nano-silica. In this investigation, compressive strength found after at 7, 28, 90 and 365 days, split and flexural tensile strength, ultrasonic pulse velocity and rebound number and are chosen as responses, whereas the percentages of recycled coarse aggregates (RCA%) and nano-silica (NS(%)) are selected as factors. Analysis of Variance has been conducted on the experimental results for the selected responses with consideration the both factors, which indicates that RCA (%) and NS (%) have substantial impact on the various responses. However, the present analysis depicts that interaction between factors has considerable effect on the chosen parameters of concrete. Furthermore, validation experiments are carried to validate these models for compressive and tensile strength for 100% RCA and 1% NS. The results of comparative study indicates that that the error of the estimation determined using the relevant models are found to be small (±5%) in comparison with the analogous experimental results, which authenticates the calculated models.

레이저빔 크기변화에 따른 광조형수지의 경화특성 (Cure Properties in Photopolymer for Stereolithography according to Variance of Laser Beam Size)

  • 이은덕;심재형;백인환
    • 한국정밀공학회지
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    • 제20권2호
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    • pp.76-84
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    • 2003
  • Stereolithography is the technique using a laser beam to cure a liquid resin, a photopolymer, with three dimensional computer-aided design (CAD) data. The build parameters of stereolithography such as beam size, scan velocity. hatch spacing, layer thickness and etc. are determined by the accuracy of prototype, the build time and the cured properties of the resin. In particular, beam size is important processing parameter fur the other parameters. Therefore, this study observed the cured property to beam size. For this purpose, according to hatch spacing and beam size, the cure width and depth were measured on single cured line. Also, the cure width and depth were measured at single cured layer As a result of experiments. cure depth which varied from 0.23mm to 0.34mm was directly proportioned to beam radius. on the other hand, cure width which varied from 0.42mm to 1.07mm was inversely proportioned to beam radius. Surface roughness varied from 1.12 to 2.23 m for the ratio of hatch spacing to beam radius.

간조직 센서를 이용한 dopamine의 정량 (Liver tissue sensor for the determination of dopamine)

  • 허문회;김기묘;김영학;백광진;최현영;안문규
    • 분석과학
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    • 제8권3호
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    • pp.365-370
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    • 1995
  • Dopamine 정량을 위한 조직 센서로 Sprague-Dawley계 숫쥐의 간조직을 암모니아 기체 감응 전극에 고정화하였다. 조직 센서가 가지고 있는 단점을 극복하기 위해 기존의 Nernst equation 대신, 감응 곡선의 최대 속도를 측정하여 Lineweauer-Burk equation에 적용함으로써 그 가능성을 살펴보았다. 기존의 방법으로는 조직마다 slope, linear range에 변화가 심하나 본 방법에 따른 경우 그 변화 정도가 적으며, 감응 시간은 7분~12분 정도로부터 2~3분으로 단축시킬 수 있었다.

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가스아토마이징된 $Al_{87.3}misch$ $metal_{8.3}Ni_{4.4}$ 분말의 냉각속도와 수지상 가지 가격에 관한 고찰 (A Study on Cooling Rate and Dendrite Arm Spacing of Gas Atomized $Al_{87.3}misch$ $metal_{8.3}Ni_{4.4}$ Powder)

  • 김지훈;예병준;김영환
    • 한국주조공학회지
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    • 제19권1호
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    • pp.54-65
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    • 1999
  • The present work is an attempt to evaluate the relationship between dendrite arm spacing and average cooling rate in gasatomized $Al_{87.3}misch$ $metal_{8.3}Ni_{4.4}$ powder by means of the following methods. One is calculation of heat transfer coefficient and average cooling rate, which are derived from estimated particle velocity during gas-atomization. The other is measurement of secondary dendrite arm spacing, which are observed on the particle surface. Then, we make experimental equation for this relationship in case of permanent mold casting and compare it with similar equation in case of rapidly solidified powder. Both average cooling rates and solidification rates are considered to represent the variance of dendrite arm spacings in two types soidification route. Even though there is a considerable difference in each average cooling rate, the dendrite arm spacing values are similar in two cases; particle diameter, $100\;{\mu}m$, and casting width, 2.05 mm. It is because that each solidification route has similar solidification rate.

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크로스홀 탄성파 시험을 이용한 쇄석다짐말뚝의 검측 (Logging for a Stone Column Using Crosshole Seismic Testing)

  • 김학성;박철수;이태희;목영진
    • 한국지반공학회:학술대회논문집
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    • 한국지반공학회 2009년도 춘계 학술발표회
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    • pp.84-90
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    • 2009
  • An integrity testing for stone columns was attempted using crosshole S-wave logging. The method is conceptionally quite similar to the crosshole sonic logging (CSL) for drilled piers. The critical difference in the logging is the use of s-wave rather than p-wave, which is used in CSL, because s-wave is the only wave sensing the stiffness of slower unbounded materials than water. An electro-mechanical source, which can generate reversed S-wave signals, was utilized in the logging. The stone column was delineated from the S-wave travel times across the stone column, and taking S-wave velocities of the crushed stone and surrounding soil into account. The volume calculated from the diametrical variance delineated is very close to the actual quantity of the stone filled.

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수중로봇 위치추정을 위한 베이시안 필터 방법의 실현과 거리 측정 특성 분석 (Implementation of Bayesian Filter Method and Range Measurement Analysis for Underwater Robot Localization)

  • 노성우;고낙용;김태균
    • 로봇학회논문지
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    • 제9권1호
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    • pp.28-38
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    • 2014
  • This paper verifies the performance of Extended Kalman Filter(EKF) and MCL(Monte Carlo Localization) approach to localization of an underwater vehicle through experiments. Especially, the experiments use acoustic range sensor whose measurement accuracy and uncertainty is not yet proved. Along with localization, the experiment also discloses the uncertainty features of the range measurement such as bias and variance. The proposed localization method rejects outlier range data and the experiment shows that outlier rejection improves localization performance. It is as expected that the proposed method doesn't yield as precise location as those methods which use high priced DVL(Doppler Velocity Log), IMU(Inertial Measurement Unit), and high accuracy range sensors. However, it is noticeable that the proposed method can achieve the accuracy which is affordable for correction of accumulated dead reckoning error, even though it uses only range data of low reliability and accuracy.

자동신경 냉각장치를 이용한 흡식반사와 호식반사의 온도특성 측정 (Measurements of Temperature Characteristics of The Lung Inflation and Deflation Reflexes Using Automated Vagal Cooling System in Anesthetized Dogs)

  • 송영진;차은종
    • 대한의용생체공학회:의공학회지
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    • 제12권3호
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    • pp.177-184
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    • 1991
  • Characteristics of the lung inflation and deflation reflexes were measured at various temperatrues on the cervical vagi in five anesthetized mongrel dogs. Nerve temperature was maintained at the body temperature, and $2-14^{\circ}C$ with $2^{\circ}C$ apart using a specially designed automated vagal cooling apparatus with an accuracy to within ${\pm}0.1^{\circ}C$ at each temperature. The inflation reflex was blocked abruptly at $8-10^{\circ}C$. The deflation reflex started weakened at $14^{\circ}C$, thereafter showed a gradual blockade with the temperature decreased with a substantial variance among the animals. It was approximately 75% blocked at $2-6^{\circ}C$. These differences in temperature characteristics made it hard to differentiate the deflation reflex from the inflation reflex. In one animal, however, the inflation reflex was completely blocked with the deflation reflex almost alive at $6-8^{\circ}C$. This suegests that differential cold blockade of the vagal reflexes can be done only in selected subjects. Fur- thermore, the fact that these two reflexes were blocked at different temperatures may be due to the differences in the nerve fiber size and the changes in the conduction velocity with temperature.

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Stationary and nonstationary analysis on the wind characteristics of a tropical storm

  • Tao, Tianyou;Wang, Hao;Li, Aiqun
    • Smart Structures and Systems
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    • 제17권6호
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    • pp.1067-1085
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    • 2016
  • Nonstationary features existing in tropical storms have been frequently captured in recent field measurements, and the applicability of the stationary theory to the analysis of wind characteristics needs to be discussed. In this study, a tropical storm called Nakri measured at Taizhou Bridge site based on structural health monitoring (SHM) system in 2014 is analyzed to give a comparison of the stationary and nonstationary characteristics. The stationarity of the wind records in the view of mean and variance is first evaluated with the run test method. Then the wind data are respectively analyzed with the traditional stationary model and the wavelet-based nonstationary model. The obtained wind characteristics such as the mean wind velocity, turbulence intensity, turbulence integral scale and power spectral density (PSD) are compared accordingly. Also, the stationary and nonstationary PSDs are fitted to present the turbulence energy distribution in frequency domain, among which a modulating function is included in the nonstationary PSD to revise the non-monotonicity. The modulated nonstationary PSD can be utilized to unconditionally simulate the turbulence presented by the nonstationary wind model. The results of this study recommend a transition from stationarity to nonstationarity in the analysis of wind characteristics, and further in the accurate prediction of wind-induced vibrations for engineering structures.