• Title/Summary/Keyword: Effective ratio

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Dynamic characteristics of structures with multiple tuned mass dampers

  • Jangid, R.S.
    • Structural Engineering and Mechanics
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    • v.3 no.5
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    • pp.497-509
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    • 1995
  • Effectiveness of multiple tuned mass dampers (MTMD) in suppressing the dynamic response of base excited structure for first mode vibration is investigated. The effectiveness of the MTMD is expressed by the ratio of the root mean square (RMS) displacement of the structure with MTMD to corresponding displacement without MTMD. The frequency content of base excitation is modelled as a broad-band stationary random process. The MTMD's with uniformly distributed natural frequencies are considered for this purpose. A parametric study is conducted to investigate the fundamental characteristics of the MTMD's and the effect of important parameters on the effectiveness of the MTMD's. The parameters include: the fundamental characteristics of the MTMD system such as damping, mass ratio, total number of MTMD, tuning frequency ratio, frequency spacing of the dampers and frequency content of the base excitation. It has been shown that MTMD can be more effective and more robust than a single TMD with equal mass and damping ratio.

Strength Prediction and Optimum Design of Internally Ring-Stiffened Tubular X-and T-Joints (내부 환보강 X형 및 T형 관이음부의 강도산정과 최적설계)

  • Cho, Hyun-Man;Ryu, Yeon-Sun;Lee, Hyun-Jin
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2007.04a
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    • pp.315-320
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    • 2007
  • An effective reinforcement method for steel tubular joints having a large chord diameter is the use of internal ring stiffeners. This paper presents the results of a numerical study on the static strength of internally ring-stiffened tubular X- and T-joints subjected to brace axial compression loading. Nonlinear finite element analyses are used to compute the joint strength. The influence of geometrical parameters has been studied and the maximum reinforcement effect of a ring stiffener has been evaluated. A strength ratio is defined. by the ratio of ring-stiffened joint strength to unstiffened joint strength, and an equation for this strength ratio is derived by regression analysis. Design optimization for ring stiffener of tubular joints is carried out using metropolis genetic algorithm.

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Evaluation of the Device Temperature and Optical Characteristics in High Power White LED Lamp by Driving Condition (고출력 백색 LED 램프의 구동조건에 따른 온도 및 광 특성 평가)

  • Yun, Jang-Hee;Ryeom, Jeong-Duk
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.25 no.11
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    • pp.33-38
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    • 2011
  • In this paper, the effect of pulse current and generated heat on characteristics of the LED is measured and evaluated. For experiments, the LED driving circuit and digital logic which determines period and duty ratio of lighting are designed. At rated current, the temperature and optical characteristics of the LED with change in duty ratio and period are compared, and those of the LED with change in duty ratio and existence of cooling fan are also compared at constant average current. As a result, frequency does not affect device temperature and optical characteristic of the LED but duty ratio does. Also, the cooling fan is less effective on those of the LED at rated current.

Study on development of Solar Collector using Oscillating Capillary Tube Heat Pipe (진동세관형 히트파이프를 이용한 태양열 집열기 개발에 관한 기초연구(I);작동유체의 내부 충진율과 경사각도의 영향)

  • Kim, Tae-Hoon;Kim, Jong-Soo;Ha, Soo-Jung;Im, Yong-Bin
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.1394-1399
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    • 2004
  • Recently solar energy is representative in the technology development and spread of alternative energy. Specially in condition of solar collectors, they have had very various shape. This paper reports experimental study about the application of Oscillating Capillary Tube Heat Pipe to flat-plate solar collector. In conclusion, overall temperature distribution of OCHP was investigated by charging ratio and inclination angle. Respective charging ratio is 15%, 20%, 40% and respective inclination angle is horizontal, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, perpendicular. As a result of experiment, charging ratio 20% heat pipe has shown the most uniform temperature distribution and also performance of heat transfer has been the best.

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A Study on the Proper Pore pressure ratio in Continuous Loading Consolidation tests (연속재하 압밀시험에서 적정 간극수압비에 관한 연구)

  • Chae, Sum-Sik;Lee, Song
    • Proceedings of the KSR Conference
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    • 2002.05a
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    • pp.271-276
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    • 2002
  • Continuous loading is applied the sample has been developed to overcome some of the problems associated with the incremental loading consolidation test. Therefore, it is able to reduce the test time and provide a well defined the curve of effective stress versus strain due to continuous stress-strain points. Also, the constant rate of strain consolidation(CRSC) test has been accepted widely as a standard method in foreign countries because of its many advantages. However, in Korea the CRSC test has not been used in engineering practice and experimentally verified. Because there is not a precise criterion of testing despite consolidation characteristics are influenced on strain rate and Pore pressure ratio. Consequently, it is difficult to apply in engineering practice. In this study, artificial neural networks are applied to the estimation of th proper strain rate and pore pressure ratio of the CRSC test. This study shows the possibility of utilizing the artificial neural networks model of estimation of the strain rate and pore pressure ratio in the CRSC test.

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Effect of Pole to Slot Ratio on Cogging Torque and EMF Waveform in Permanent Magnet Motor with Fractional-Slot (분수슬롯을 가진 영구자석 전동기에서 극당 슬롯 비율이 코깅토크와 역기전력에 미치는 영향)

  • Lee, Kab-Jae;Lee, Ju
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.52 no.9
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    • pp.454-459
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    • 2003
  • Conventional integral-slot design in permanent magnet(PM) motor tends to have a high cogging torque and large end turns, which contribute to copper losses. The fractional-slot design is effective compared to integral-slot design in the cogging torque and electromotive force(EMF) waveform. The effectiveness of fractional slot can be maximized by selecting optimal pole to slot ratio. This paper presents the effect of pole to slot ratio on the cogging torque and EMF waveform in the PM motor with fractional-slot. The effectiveness of the proposed designs has been confirmed by comparing waveform of EMF. cogging torque and torque ripple between conventional and new models.

Converter Utilization Ratio Enhancement in the THD Optimization of Cascaded H-Bridge 7-level Inverters

  • Khamooshi, Reza;Namadmalan, Alireza;Moghani, Javad Shokrollahi
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.173-181
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    • 2016
  • In this paper, a new technique for harmonic optimization in cascaded H-bridge 7-level inverters is proposed. The suggested strategy is based on minimizing an objective function which simultaneously optimizes the converter utilization and Total Harmonic Distortion (THD). The Switch Utilization Ratio (SUR) is formulized for both the phase and line-line voltages of a 7-level inverter and is considered in the final objective functions. Based upon the SUR formula, utilization ratio enhancement will reduce the value of feeding DC links, which improves the efficiency and lifetime of the circuit components due to lower voltage stresses and losses. In order to achieve more effective solution in different modulation indices, it is assumed that the DC sources can be altered. Experimental validation is presented based on a three-phase 7-level inverter prototype.

Thickening of Bulking Sludge using DAF (Dissolved Air Flotation) (DAF(Dissolved Air Flotation)를 이용한 팽화 슬러지 농축)

  • Kim Dong-Seog;Park Young-Seek
    • Journal of Environmental Science International
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    • v.15 no.1
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    • pp.77-84
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    • 2006
  • An effective technique of sludge separation is required for excess sludge of sewage or wastewater plant. The separation of bulking sludge of paper manufacturing plant was studied using DAF(Dissolved Air Flotation) system. The effects of parameters such as nozzle type, A/S(air/solid) ratio. pressure, injection time of pressured water and saturation time were examined. The results showed that the best nozzle type was flat which had small orifice hole, The optimum A/S ratio and pressure were $7.070\times10^{-3}$(recycle ratio of pressured water $20\%$) and 5atm, respectively. Injection times of pressurized water around 20-25 sesc and flotation time of 30 min appeared to be optimal for the DAF operation. The order of performance of packing was 18 mm > 22 mm > 32 mm.

Dynamic Characteristics and Responses of Tall Building Structures with Double Negative Stiffness Damped Outriggers

  • Sun, Feifei;Duan, Ningling;Wang, Meng;Yang, Jiaqi
    • International Journal of High-Rise Buildings
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    • v.10 no.3
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    • pp.229-242
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    • 2021
  • Dynamic characteristics of tall building structures with double negative stiffness damped outriggers (2NSDO) are parametrically studied using the theoretical formula. Compared with one negative stiffness damped outrigger (1NSDO), 2NSDO can achieve a similar maximal modal damping ratio with a smaller negative stiffness ratio. Besides, the 2NSDO can improve the maximum achievable damping ratio to about 30% with less consumption of an outrigger damping coefficient compared with the double conventional damped outriggers (2CDO). Besides, the responses of structures with 2NSDO under fluctuating wind load are investigated by time-history analysis. Numerical results show that the 2NSDO is effective in reducing structural acceleration under fluctuating wind load, being more efficient than 1NSDO.

A Study on Evaluation of Crack Opening Point in Al 2024-T3 Material (Al 2024-T3재의 Crack Opening Point의 평가에 관한 연구)

  • 최병기;국중민
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 2002.04a
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    • pp.53-58
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    • 2002
  • This paper aims to synthesize the research on fatigue mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents. To measure the data of crack opening ratio, the same materials and methods are used for evaluating the fatigue crack propagation rate as an effective stress intensity factor. But, many researchers have brought different results. An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propagation rate.

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