• Title, Summary, Keyword: Number of Excitations

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Experimental Study on Comparison of Buoyancy Driven and Lewis Number Induced Self-excitations in Laminar Lifted Coflow-jet Flames. (층류 동축류 제트 부상화염에서 부력에 의한 자기진동과 루이스 수에 의한 자기진동 비교에 관한 실험적 연구)

  • Ban, Gyu Ho;Lee, Won June;Park, Jeong;Keel, Sang-In;Yun, Jin-Han;Lim, In Gwon
    • 한국연소학회:학술대회논문집
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    • pp.367-369
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    • 2014
  • A study on laminar coflow jet flames diluted with helium and nitrogen has been conducted to investigate self-excitations. The stability map was provided with a function of nozzle exit velocity and fuel mole fractions of propane or methane. The results show that there exist three types of self-excitations; (1) buoyancy-driven self-excitation (BDSE), (2) Lewis number induced self-excitation coupled with buoyancy (LCB) and (3) Lewis number induced self-excitation (LISE).

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A study on Self-excitations in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 실험적 연구)

  • Ban, Gyu Ho;Lee, Won June;Park, Jeong;Keel, Sang-In;Yun, Jin-Han;Lim, In Gwon
    • 한국연소학회:학술대회논문집
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    • pp.129-132
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    • 2014
  • A study on laminar coflow jet flames diluted with helium and nitrogen has been conducted to investigate self-excitations. The stability map was provided with a function of nozzle exit velocity and fuel mole fractions of propane or methane. The results show that there exist three types of self-excitations; (1) buoyancy-driven self-excitation (BDSE), (2) Lewis number induced self-excitation coupled with buoyancy (LCB) and (3) Lewis number induced self-excitation (LISE).

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A two-stage and two-step algorithm for the identification of structural damage and unknown excitations: numerical and experimental studies

  • Lei, Ying;Chen, Feng;Zhou, Huan
    • Smart Structures and Systems
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    • v.15 no.1
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    • pp.57-80
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    • 2015
  • Extended Kalman Filter (EKF) has been widely used for structural identification and damage detection. However, conventional EKF approaches require that external excitations are measured. Also, in the conventional EKF, unknown structural parameters are included as an augmented vector in forming the extended state vector. Hence the sizes of extended state vector and state equation are quite large, which suffers from not only large computational effort but also convergence problem for the identification of a large number of unknown parameters. Moreover, such approaches are not suitable for intelligent structural damage detection due to the limited computational power and storage capacities of smart sensors. In this paper, a two-stage and two-step algorithm is proposed for the identification of structural damage as well as unknown external excitations. In stage-one, structural state vector and unknown structural parameters are recursively estimated in a two-step Kalman estimator approach. Then, the unknown external excitations are estimated sequentially by least-squares estimation in stage-two. Therefore, the number of unknown variables to be estimated in each step is reduced and the identification of structural system and unknown excitation are conducted sequentially, which simplify the identification problem and reduces computational efforts significantly. Both numerical simulation examples and lab experimental tests are used to validate the proposed algorithm for the identification of structural damage as well as unknown excitations for structural health monitoring.

A Study on Self-excitations in Laminar Coflow Jet Flames (층류 동축류 제트화염에서의 화염진동에 관한 실험적 연구)

  • Yoon, Sung Hwan;Park, Jeong;Yun, Jin Han;Keel, San In;Kwon, Oh Boong
    • 한국연소학회:학술대회논문집
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    • pp.83-85
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    • 2012
  • Experimental study in coflow jet flames has been conducted to investigate the effects of adding $N_2$, $CO_2$ and He to coflowing air-side in self-excitations. Differences in the behaviors between buoyancy-driven and diffusive-thermal self-excitations with similar frequency range are explored and discussed in laminar coflow jet flames.

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Experimental Study on Comparison between Buoyancy Driven and Lewis Number Induced Self-excitations in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서 부력에 의한 자기진동과 루이스 수에 의한 자기진동 비교에 관한 실험적 연구)

  • Lee, Won June;Park, Jeong;Kwon, Oh Boong;Yun, Jin Han;Keel, Sang In
    • Journal of the Korean Society of Combustion
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    • v.19 no.2
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    • pp.21-27
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    • 2014
  • Experimental study in laminar propane coflow jet flames has been conducted to investigate self-excitations. For various propane mole fractions and jet velocities, two types of self-excitation were observed: (1) buoyancydriven self-excitation (hereafter called BDSE) and (2) Lewis-number-induced self-excitation coupled with (1) (hereafter called LCB). The mechanism of Lewis-number-induced self-excitation (hereafter called LISE) is proposed. When the system $Damk\ddot{o}hler$ number was lowered, LISE was shown to be launched. The LISE is closely related to heat loss, such that it can be launched in even helium-diluted methane coflow-jet flame (Lewis number less than unity). Particularly, The LISE becomes significant as the $Damk\ddot{o}hler$ number decreases and heat-loss is excessively large.

Optimization and application of multiple tuned mass dampers in the vibration control of pedestrian bridges

  • Lu, Zheng;Chen, Xiaoyi;Li, Xiaowei;Li, Peizhen
    • Structural Engineering and Mechanics
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    • v.62 no.1
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    • pp.55-64
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    • 2017
  • An effective design approach for Multiple Tuned Mass Dampers (MTMDs) in pedestrian bridges was proposed by utilizing the transfer function to obtain each TMD's optimum stiffness and damping. A systematic simulation of pedestrian excitations was described. The motion equation of a typical MTMD system attached to a Multi-degree-of-freedom (MDOF) system was presented, and the transfer function from the input pedestrian excitations to the output acceleration responses was defined. By solving the minimum norm of the transfer function, the parameters of the MTMD which resulted in the minimum overall responses can be obtained. Two applications of lightly damped pedestrian bridges attached with MTMD showed that MTMDs designed through this method can significantly reduce the structural responses when subjected to pedestrian excitations, and the vibration control effects were better than the MTMD when it was considered as being composed of equal number and mass ratios of TMDs designed by classical Den Hartog method.

A Study on Self-excitation in Laminar Lifted Coflow-jet Flames (층류 동축류 제트 부상화염에서의 자기진동에 관한 연구)

  • Van, Kyu Ho;Lee, Won June;Park, Jeong;Kim, Tae Hyung;Park, Jong Ho
    • Journal of the Korean Society of Combustion
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    • v.20 no.1
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    • pp.43-51
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    • 2015
  • A study on laminar jet flames in coflow air diluted with helium has been conducted to investigate self-excitations for various propane mole fractions and nozzle exit velocities. The stability map was represented as a function of nozzle exit velocity and fuel mole fraction for propane. The results show that two types of self-excitation were observed : (1) buoyancy-driven self-excitation (hereafter called BDSE) and (2) Lewis-number induced-self-excitation coupled with (1) (hereafter called LCB) near extinction limit for 9.4 mm nozzle diameter. It was shown that with 0.95 mm nozzle diameter, Lewis-number-induced self-excitation (hereafter LISE) and BDSE could be separated. The differences between the two self-excitations were shown and discussed.

Self-excitation of Edge Flame (에지화염의 자기 진동)

  • Park, Jeong;Youn, Sung Hwan;Chung, Yong Ho;Lee, Won June;Kwon, Oh Boong
    • 한국연소학회:학술대회논문집
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    • pp.167-170
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    • 2012
  • Self-excitations of edge flame were studied in laminar lifted free- and coflow-jet as well as counterflow flames diluted with nitrogen and helium. The self-excitations, originated from variation of edge flame speed and found in the above-mentioned configurations, are discussed. A newly found self-excitation and flame blowout, caused by the conductive heat loss from premixed wings to trailing diffusion flame are described and characterized in laminar lifted jet flames. Some trials to distinguish Lewis-number-induced self-excitation from buoyancy-driven one with O(1.0 Hz) are introduced, and then the differences are discussed. In counterflow configuration, important role of the outermost edge flame in flame extinction is also suggested and discussed.

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Diffusion Weighted Imaging in Musculoskeletal MRI: Analysis on Optimal Number of Excitations Providing better Differentiation of Maglignant Tumor (악성종양의 감별진단을 위한 근골격의 확산강조영상 검사 시 최적의 여기횟수)

  • Choi, Kwan-Woo
    • The Journal of the Korea Contents Association
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    • v.18 no.8
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    • pp.338-344
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    • 2018
  • The purpose of this study was to determine the optimal number of excitations(NEX) of diffusion weighted imaging(DWI) which is clinically useful in patients with musculoskeletal diseases while the scan time is relatively long. In this study, 30 patients underwent knee MRI using diffusion weighted image sequence using b values targeted on the bone and muscle. The NEX were varied from 1 to 5 and the ADC values were measured and analyzed. As a result of the study, 4 NEX and 2 NEX showed an statistically identical effect with the existing NEX on the bone and muscle diffusion weighted images, respectively. Also, it proved that the scan time could be significantly reduced by 21.2 % and 59.6 % compared to the established NEX which meant the optimal NEX could replace the existing NEX. In conclusion, applying the optimal NEX on the musculoskeletal bone and soft tissue DWI could improve the problems caused by the long scan time.