• Title/Summary/Keyword: step-up ratio

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Kinematic Analyses of Women's Pole Vault in IAAF World Championships, Daegu 2011 (2011 대구 세계육상선수권대회 여자 장대높이뛰기경기 기술의 운동학적 분석)

  • Choi, Kyoo-Jeong;Yi, Kyung-Ok;Kim, Nam-Hee;Kang, Ji-Eun;Kim, Hye-Lim
    • Korean Journal of Applied Biomechanics
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    • v.21 no.5
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    • pp.561-571
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    • 2011
  • The purpose of this study was to perform the kinematic analyses of the women's pole vault skills in IAAF World Championships Daegu 2011. Subjects were the 1st through 8th place finishers in the pole vault. The kinematic analyses were divided into four phases: two dimensional run up analysis, and three dimensional analyses for the remaining plant, swing up, and extension phases. Run-up variables consisted of run up distance, number of steps, average step length, ratio of step length to height, average velocity at the final 5~10 m, approach position. Three variables were analyzed during plant: pole angle, center of gravity (COG) velocity, and COG takeoff angle. Swing up phase variables included: pole flection angle, COG velocity (horizontal, vertical, resultant), COG trajectory and bar approach angle of COG. Compared to the 2009 World Championships in Berlin, the average vault height increased, while run up velocity and approach position were almost unchanged. However, horizontal velocity during the last two steps of the final approach decreased noticeably compared to speeds from 1990. These results reflect the change in both technique and physical fitness in pole vaulters. During extension, the peak height of COG surpassed the clearance height by an average of 0.11m. These specific results can help coaches and athletes modify training and improve performance.

A Basic Study on the Influence of an Understructure on the Seismic Response of a Spatial Structure (공간구조의 지진응답에 대한 연구 하부구조의 영향에 관한 기초적 연구)

  • Jung, Chan-Woo;Jung, Hwan-Mok
    • Proceeding of KASS Symposium
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    • 2005.05a
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    • pp.215-226
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    • 2005
  • To study the influence of an lower part on the seismic response of a spatial structure as the upper part of a structure, as a first step, authors subsititude the upper part and the lower part of a structure to single degree of freedom systems indivisually, and set up structural models connected by them. It is clarified that the mass ratio and the period ratio of an upper part to a lower part are important parameteres to find the amplification or reduction of the sesimic response of an upper part by considering of a lower part.

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Numerical Characteristics of Upwind Schemes for Preconditioned Compressible Navier-Stokes Equations (예조건화된 압축성유동 수치기법에서의 풍상차분법의 수치특성 검토)

  • Gill J. H.;Lee D. H.;Choi Y. H.;Kwon J. H.;Lee S. S.
    • 한국전산유체공학회:학술대회논문집
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    • 2002.10a
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    • pp.95-102
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    • 2002
  • Studies of the numerical characteristics of implicit upwind schemes, such as upwind ADI, Line Gauss-Seidel(LGS) and Point Gauss-Seidel(LU) algorithms, for preconditioned Navier-Stokes equations ate performed. All the algorithms are expressed in approximate factorization form and Von Neumann stability analysis and convergence studies are made. Preconditioning is applied for efficient convergence at low Mach numbers and low Reynolds numbers. For high aspect ratio computations, the ADI and LGS algorithms show efficient and uniform convergence up to moderate aspect ratio if we adopt viscous preconditioning based on min- CFL/max- VNN time-step definition. The LU algorithm, on the other hand, shows serious deterioration in convergence rate as the grid aspect ratio increases. Computations for practical applications also verify these results.

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The Characteristics of Piezoelectric Transformer for Driving CCFL (CCFL 구동용 압전 변압기의 특성)

  • Jeong, Su-Hyun;Lee, Jong-Sub;Hong, Jong-Kuk;Chae, Hong-In;Yoon, Man-Soon;Lim, Kee-Joe
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.49 no.5
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    • pp.259-264
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    • 2000
  • In this paper, the characteristics of piezoelectric transformer is studied for driving CCFL(Cold Cathode Fluorescent Lamp). In order to investigate the effects of geometrical dimensions, λvibration-mode type piezoelectric transformers with different sizes in the length(l), width$(\omega)$ and thickness(t) are made of ceramics with PZT-PMWS compositions. The increases in temperature and aging effect are also measured in the transformer of PT-3 sample under the condition of operation continuously for 10 hrs. As the results of dimensional effects, the output power and voltage step-up ratio are largely affected by the ratio of length to thickness(l/t) rather than that of length to $width(l/\omega)$. The output power and step-up ratio are increased with increasing l/t. On case of PT-3, the output voltages are 510[Vrms] at 36[Vrms] in input voltage, $100[k\Omega]$ in load resistance. Temperature increases and variation of output voltages are $10[^{\circ}C]$ and less than 5[%], respectively.

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A Study on the Optimum Treatment Criteria of the Leachate for Food Waste Composting (음식물 쓰레기 퇴비화를 위한 탈리액의 적정 처리 기준 설정 연구)

  • Kwon, Woo-Seok;Sin, Jin-Ho;Nam, Duk-Hyon;Park, Chul-Hwi
    • Journal of Korean Society of Water and Wastewater
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    • v.20 no.3
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    • pp.397-402
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    • 2006
  • The treatment characteristics of leachate produced from pretreatment facilities like composting and feeding were investigated in a mesophilic anaerobic treatment. Experiments were performed in two phase which were acidification and methane fermentation. The acidification step was optimized for OLR from 1 to $4.5kg\;COD/kg\;VS{\cdot}day$ without adding NaOH. As experiment dates became longer, the solubilization ratio of particles increased up to 30% over 70 days. TVA was generated up to maximum 9,970mg HAc/L at OLR of $2kg\;COD/kg\;VS{\cdot}day$. But TVA was generated to minimum 6,519mg HAc/L at OLR of $4.5kg\;COD/kg\;VS{\cdot}day$. The acidification ratio was analyzed from 10.9% to 3.8% at OLR of $2kg\;COD/kg\;VS{\cdot}day$ and $4.5kg\;COD/kg\;VS{\cdot}day$ respectively. After 55 days, salt contents in the acid fermenter were accumulated and stabilized at the concentration of 3,150mg/L. Sodium ion($Na^+$) concentration was stabilized at 1,300mg/L. At methane fermentation step, biogas was generated up to 750ml and 937.5ml at the feeding volume of 20ml and 25ml respectively for acid fermented liquid during 25 days. About 80% of total biogas was generated during early 15 days and 95% were generated during 18 days respectively. After 25 days of the BMP test, acetic acid was removed approximately 97% and 98%, in case of those two experimental conditions.

Kinematic Analyses of Men's Pole Vault in IAAF World Championships, Daegu 2011 (2011 대구 세계육상선수권대회 남자 장대높이뛰기경기 기술의 운동학적 분석)

  • Choi, Kyoo-Jeong;Yi, Kyung-Ok;Kim, Nam-Hee;Kang, Ji-Eun;Kim, Hye-Lim
    • Korean Journal of Applied Biomechanics
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    • v.21 no.5
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    • pp.551-560
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    • 2011
  • The purpose of this study was to perform the kinematic analyses of the men's pole vault skills in IAAF World Championships Daegu 2011. Subjects were the 1st through 8th place finishers in the pole vault. The kinematic analyses were divided into four phases: two dimensional run up analysis, and three dimensional analyses for the remaining plant, swing up, and extension phases. Run-up variables consisted of run up distance, number of steps, average step length, the ratio of step length to his height, average velocity at the final 6~11 m, approach position. Three variables were analyzed during plant: pole angle, center of gravity (COG) velocity, and takeoff angle of COG. Swing up phase variables included: pole flexion angle, COG velocity (horizontal, vertical, resultant), COG trajectory and bar approach angle of COG. Compared to the 2009 World Championships in Berlin, the average vault height, run up velocity and approach position increased. However, horizontal velocity during the last two steps of the final approach decreased dramatically compared to speeds from 1990. These results reflect the change in both technique and improved physical fitness in pole vaulters. During extension, the peak height of COG averaged 0.3m higher then COG height when the pole was released. These specific results can help coaches and athletes modify training and improve performance.

A Study on the Utility Interactive Photovoltaic System using a Chopper and a PWM Inverter (쵸퍼와 PWM 전압형 인버터를 이용한 계통연계형 태양광발전시스템에 관한 연구)

  • 유택빈;성낙규;이승환;김성남;이훈구;한경희
    • The Transactions of the Korean Institute of Power Electronics
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    • v.3 no.2
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    • pp.131-137
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    • 1998
  • The solar cells should be operated at the maximum power point because its output characteristics are greatly fluctuated on the variation of insolation, temperature and load. Photovoltaic system needs an inverter which can interface the dc output power of solar cell with the residential ac load. The inverter has to supply a sinusoidal current and voltage to the load and the utility line with a high power factor. This paper proposes an utility interactive photovoltaic system designed with a step-up chopper and a PWM voltage source inverter. The step-up chopper operates in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power points of solar cell without any influence on the variation of insolation and temperature. The voltage source inverter operates in a manner that its output voltage is in phase with the utility voltage. The inverter supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

Characteristics of Piezoelectric Transformer Using PMS-PZT, PMN-PZT Ceramics (PMS-PZT, PMN-PZT계 세라믹스를 이용한 압전변압기의 특성)

  • 이동균;안형근;한득영;윤석진;김현재
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.13 no.3
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    • pp.220-226
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    • 2000
  • The piezoelectric material for piezoelectric transformer needs the high electromechanical coupling factor( $k_{p}$) the piezoelectric constant( $d_{33}$) and the mechanical quality factor( $Q_{m}$)in order to obtain high voltage step-up ratio and low temperature rising. In this study the piezoelectric transformers were fabricated using Pb[$Zr_{0.45}$/ $Ti_{0}$48//L $u_{0.02}$(M $n_{1}$3//S $b_{2}$3/)$_{0.05}$$O_3$(PMS-PZT) and Pb[Z $r_{0.25}$/ $Ti_{0.375}$(M $g_{1}$3//N $b_{2}$3/)$_{0.375}$$O_3$+0.5wt%Mn $O_2$(PMN-PZT) ceramics. The piezoelectric properties of PMS-PZT and PMN-PZT were measured. The voltage set-up ratios of the piezoelectric transformers using PMS-PZT and PMN-PZT were the value of 15, 20 respectively under 100$_{KΩ}$ in Rosen type transformer.r.ormer.r.r.r.r.r.r.

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Effect of Anodizing Current Density on Anti-Corrosion Characteristics for Al2O3 Oxide Film (Al2O3 산화 피막의 내식성에 미치는 양극산화 전류밀도의 영향)

  • Lee, Seung-Jun;Jang, Seok-Gi;Kim, Seong-Jong
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2016.11a
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    • pp.153-153
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    • 2016
  • Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the sea water upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Afterward, the irregular oxide film that was created in the first step surface modification was removed. For the second step surface modification process (identical to the step 1), etching was performed using mixture of chromic acid (1.8 wt.%) and phosphoric acid (6 wt.%) at $60^{\circ}C$ temperature for 30 minutes. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification presented a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

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Analysis of Folded Dipole Antenna by Moment Methods (모멘트법에 의한 접힌 안테나의 특성해석)

  • 이상설
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.15 no.2
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    • pp.15-18
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    • 1978
  • The impedance step up ratio and variations of input admittances of the folded dipole antenna are calculated by the moment method. The results are compared with those calculated by Guertler's formula. The input admittance of the folded dipole antenna has the maximum value at the frequency somewhat lower than the resonance frequency and its susceptance which has periodic properly is null lot several different frequencies if radius ratio of two elements is not very large. Frequency characteristic of folded dipole antenna is improved when its radius ratio is increased.

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