• 제목/요약/키워드: Reduction of amplitude

검색결과 376건 처리시간 0.029초

평행식 진동탄환 암거 천공기의 연구(III)-견인력, 토크, 동력 및 모멘크에 관한 모형시험- (A Study on Balanced -type Oseillating Mole-Drainer(III)-Model Test for Draft Force, Torque, Power and Moment)

  • 김용환
    • Journal of Biosystems Engineering
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    • 제1권1호
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    • pp.1-6
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    • 1976
  • This paper is the third one of the study on balanced type oscillating mole-drainer, the first one was presented in No 9. Gyeongsang College Report and the second one in Vol. 17, No.4 of the KSAE. In the first part of this study, the characteristics of traction forces between the nonoscillating earth working equipments and oscillating ones was compared. A model of the balanced type oscillating mole-drainer, which composed of a mechanism that may reduce the machine vibration, was designed following the dimensional analysis and similitude technique. The model test was carried out to clarify the balancing mechanism of the oscillating parts and other parts of the machine. In the light of the results from the model tests, a prototype machine was made for experimental purpose. Results from the field test by a reported in the near future. In the second report, the model tests were carried out under the same soil conditions, i.e, . oscillating frequency, running velocity, and oscillating amplitude, etc. It was clear that use of balanced type oscillating model could substantially reduce the vibration of the whole system of the machine, when compared with the nonoscillating type model. In this paper(the third report), results of investigation on the traction force, power requirement, and moment. etc, is presented. Analysis of variance technique was used for analyzing the effect of the frequency, amplitude, and running velocity on the draft force, torque, power requirements, and moments. The results obtained from the model tests are as follows, 1) By practicing a balanced-type oscillating mole-drainer, it was possible to reduce the traction resistance by 55.1-61. 2 percent of traction resistance, however, was 1.75 - 1.95 times greater than the value of resistance which was induced by use of a mole-drainer with single bullet. The resistance of rear shank against soil was considered as a main causing factor of the above results. 2) As the oscillation frequency was increased, the traction resistance was decreased. Considering on the effect of oscillation the greater the amplitude, and the slower the running velocity was, the greater the reduction ratio of traction resistance was. 3) The ratio of the traction resistance of oscillating mole-drainer to that of non-oscillating one could be represented as a function of dimensionless variable (V/$Af$). The results from the tests were well agreed with the reported results from the experim ents on oscillation plow or hoe. 4) By taking a lower value of (V/$Af$), reducing the traction resistance was possible. This fact meant, however, that the efficiency of mole drain practice would be lower. 5) It was experimentally confirmed under the same condition of soil that the variable (R/$rD1^3$) could be represented as a function of a variable($V^2/gD$) when a non\ulcornerocillating mole-drainer was used. 6) When a oscillating mole-drainer was used, the variable(R/$rD_1^{3}$) could be represented as a function of two variables ($v^2/gD_1$) and (V^2/gD_1$). 7) The torque was not affected by a change of frequency. However, a relation of proportionality existed between torque and amplitude, running velocity, and ratio of bullet diameter. When a balanced type oscillating mole-drainer with two bullets was used, torque was increased by 52.8-78. 4 percent and total power requirement was also increased. 8) Total power requirement was increased linearly in accordance with the increasing frequency, 41.96 percent of total power was used for oscillating action. The magnitude of total power requirement was 1. 8-9. 4 times greater than that of a non-oscillating mechanism. In the view point of power requirement, it was not advisable to increase the frequency, amplitude, running velocity, and ratio of bullet diameter at the same time. 9) Only the positive moment occured in the rear shank. Change of the diameter of a rear bullet, could not affect the balancing against the soil resistance. It was necessary for rear bullet to have a large resistance against soil only when the rear bullet was in backward motion. 10) Within an extent of the experimental base, optimum limits for several design factors were A=0.5cm, $f$=22.5Hz, V=O. 05m/sec, and $\lambda$=1.0 By adapting these values traction resistance was reduced by 40 percent and vibration acceleration wa s reduced by 60 percent. Even though the total , power requirements for operating a balanced type oscillation mechanism was greater ~than that of non-oscillating one, using a oscillating mechanism would be more effective. Because a balanced type oscillating mechanism is used, tractive resistance will be reduced and then the lighter . tractive equipment could be used.

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Performance Analysis of Multicarrier Code Select CDMA System for PAPR Reduction in Multipath Channels

  • Ryu, Kwan-Woong;Jin, Jiyu;Park, Yong-Wan;Choi, Jeong-Hee
    • Journal of Communications and Networks
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    • 제11권1호
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    • pp.11-19
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    • 2009
  • Multicarrier direct sequence code division multiple access (MC DS-CDMA) is an attractive technique for achieving high data rate transmission. This is valid regardless of whether or not the potentially large peak-to-average power ratio (PAPR) is an important factor for its application. On the other hand, code select CDMA (CS-CDMA) is an attractive technique with constant amplitude transmission of multicode signal regardless of subchannels. This is achieved by introducing a code select method. In this paper, we propose a new multiple access scheme based on the combination of MC DS-CDMA and CS-CDMA. The proposed scheme, which we call MC CS-CDMA, includes as special cases the subclasses of MC DS-CDMA and CS-CDMA. This paper investigates the performance of these systems over a multipath frequency selective fading channel using a RAKE receiver with maximal ratio combiner. In addition, the PAPR of the proposed system is compared with that of both MC DS-CDMA and CS-CDMA. Simulation results demonstrate that the proposed system provides better PAPR reduction than MC DS-CDMA, at the expense of the complexity of the receiver and the number of available users. The numerical result demonstrates that the proposed system has better performance than MC DS-CDMA due to the increased processing gain and time diversity gain.

Operational modal analysis of Canton Tower by a fast frequency domain Bayesian method

  • Zhang, Feng-Liang;Ni, Yi-Qing;Ni, Yan-Chun;Wang, You-Wu
    • Smart Structures and Systems
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    • 제17권2호
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    • pp.209-230
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    • 2016
  • The Canton Tower is a high-rise slender structure with a height of 610 m. A structural health monitoring system has been instrumented on the structure, by which data is continuously monitored. This paper presents an investigation on the identified modal properties of the Canton Tower using ambient vibration data collected during a whole day (24 hours). A recently developed Fast Bayesian FFT method is utilized for operational modal analysis on the basis of the measured acceleration data. The approach views modal identification as an inference problem where probability is used as a measure for the relative plausibility of outcomes given a model of the structure and measured data. Focusing on the first several modes, the modal properties of this supertall slender structure are identified on non-overlapping time windows during the whole day under normal wind speed. With the identified modal parameters and the associated posterior uncertainty, the distribution of the modal parameters in the future is predicted and assessed. By defining the modal root-mean-square value in terms of the power spectral density of modal force identified, the identified natural frequencies and damping ratios versus the vibration amplitude are investigated with the associated posterior uncertainty considered. Meanwhile, the correlations between modal parameters and temperature, modal parameters and wind speed are studied. For comparison purpose, the frequency domain decomposition (FDD) method is also utilized to identify the modal parameters. The identified results obtained by the Bayesian method, the FDD method and a finite element model are compared and discussed.

터널발파작업에 따른 방음시설의 설치시기와 방법에 대한 고찰. (A Study on the installation time and method of soundproofing facilities according to a Tunnel blasting work.)

  • 원연호;손영복;정재형
    • 대한화약발파공학회:학술대회논문집
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    • 대한화약발파공학회 2006년도 추계학술발표회 논문집
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    • pp.119-140
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    • 2006
  • 발파를 통한 암반 굴착작업은 폭약의 폭발 시 발생하는 충격압과 가스압을 이용하여 암석을 파괴하며, 폭원으로 부터 3차원적으로 전파되어온 충격압에 의한 충격파는 발파에 의한 에너지의 $0.5{\sim}20%$가 탄성파의 형태로 균열대 외부의 지반속으로 전파되면서 공기매체를 타고 전달되는 것이 발파소음이다. 발파소음은 공기의 진동에 의한 음파 가운데 가청범위 ($20{\sim}20000Hz$)의 주파수를 갖는 충격성 소음으로 인체 감응에 의해 영향이 제기되는 것으로, 정신적 고통에 의한 민원발생으로 공사정지, 발파규모 축소 등으로 발파작업에 지장을 주고 있다. 본 연구는 터널발파작업에 따른 발파소음 저감을 위해 현장마다 설치하고 있는 방음시설의 설치시기와 설치방법 그리고 재질에 대하여 현장시공 사례를 통하여 고찰하였다.

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플라즈마 디스플레이 패널(Plasma Display Panel) 텔레비전에서의 냉각 소음 저감

  • 김규영;최민구;이덕주
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2003년도 춘계학술대회논문집
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    • pp.719-724
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    • 2003
  • The present experimental study deals with noise reduction and improvements in cooling performance in a plasma display panel(PDP) television (TV). To reduce the noise, the effects of installation parameters are studied. The experimental parameters under investigation are the distance between the fan and the rear case of a PDP TV, position of the strut on the fan, and the fan RPM. The variance of RPM is the most significant facto., and a 250 RPM decrease from 910 RPM causes about 4㏈(A) reduction in the system noise. To increase performance, flow characteristics are investigated by using a visualization technique and measuring the volume flow rate. The visualized results show that a radial direction flow due to large system resistance is significant, and an axial velocity oscillation is observed from the measurement of the volume flow rate. To prevent both a radial direction flow and an axial velocity oscillation, sponges are inserted in the space between f3n and the rear case. Inserted sponges improve the volume flow rate of cooling fans up to 32% since they convert a radial direction flow to an axial direction flow. Also an axial velocity oscillation with large amplitude and low RPM disappears. Increasing volume flow rate causes the PDP TV to improve its cooling performance. Additionally the same volume flow rate can be obtained with a decreased fan speed due to the inserted sponge. Noise reductions of 4.2 ㏈(A) at the rear and 1.1 ㏈(A) at the front of the TV are obtained by the decreased RPM. An increase of 10% of the volume flow rate is also achieved by inserting sponges.

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주기적으로 회전진동하는 원주 후류의 유동구조에 관한 실험적 연구 (Experimental Study on Flow Structure of Wake Behind a Rotationally Oscillating Circular Cylinder)

  • 이정엽;이상준
    • 대한기계학회논문집B
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    • 제30권4호
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    • pp.298-305
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    • 2006
  • The flow around a circular cylinder which oscillates rotationally with a relatively high forcing frequency has been investigated experimentally using flow visualization and hot-wire measurements. Dominant parameters are Reynolds number (Re), oscillation amplitude $({\theta}_A)$, and frequency ratio $F_R=f_f/f_n$, where $f_f$ is the forcing frequency and $f_n$ is the natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\theta}_A={\pi}/6$, and $0{\leq}F_R{\leq}2$. The effect of frequency ratio $F_R$ on the flow structure of wake was evaluated by measuring wake velocity profile and spectral analysis of hot-wire signal. Depending on the frequency ratio $F_R$, the cylinder wake has 5 different flow regimes. The vortex formation length and vortex shedding frequency are changed significantly before and after the lock-on regime. The drag coefficient was reduced under the condition of $F_R<1.0$ and the maximum drag reduction is about 33% at $F_R=0.8$. However, the drag is increased as $F_R$ increases beyond $F_R=1.0$. This active flow control method can be effective in aerodynamic applications, if the forcing parameters are selected optimally.

천수만 방조제 건설로 인한 조석현상 변화 (Numerical Modeling of Changes in Tides and Tidal Currents Caused by Embankment at Chonsu Bay)

  • 소재귀;정경태;채장원
    • 한국해안해양공학회지
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    • 제10권4호
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    • pp.151-164
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    • 1998
  • 서산 A·B지구 간척사업에 따른 방조제 축조에 따라 야기되는 천수만 내 조석현상 변화를 파악하기 위하여 수심적분 2차원 해수유동 수치모형실험을 실시하였다. 외해 개방경계조건을 확보하기 위하여 3개 지점에서 조석관측을 실시하였고 수치모형의 검증을 위하여 천수만 내 2개 지점에서 조류관측을 실시하였다. 수치모형 실험결과는 관측된 조류를 기준으로 할 때, 북부해역, 백사수도, 중부해역, 남부해역의 순으로 유속의 감소가 크게 나타났다. 방조제 건설 후 천수만 북부에서 조간대 노출이 발생하는 시각은 약 51분 정도 빨라졌으며, 노출시간은 23분 정도 길어진 것으로 나타났다. 고조 발생 시각은 1시간 정도 앞당겨졌으며, 고조 수위는 15 cm 정도 낮아졌다.

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PWM 인버터로 구동된 유도전동기의 누설전류 억제에 관한 연구(II) -능동형 커먼 모드 전압 감쇄기를 이용한 고주파 누설전류 억제- (A Study on the Reduction of high frequency leakage current in PWM inverter fed Induction Motor)

  • 성병모;류도형;박성준;김철우
    • 전력전자학회논문지
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    • 제5권5호
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    • pp.443-450
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    • 2000
  • PWM 인버터에 의하여 구동되는 유도전동기는 뛰어난 동작특성을 가지고 있지만, 커먼 모드 전압과 고주파 누설전류를 야기한다. 이 고주파 누설 전류는 여러가지 문제점을 일으킨다. 본 논문에서는 이러한 문제점을 일으키는 고주파 누설 전류와 커먼 모드 진압을 감쇄하기 위하여 커먼 모드 전압과 크기가 같고 반대극성을 가진 전압을 4 level half bridge 인버터를 이용하여 생성하고, 이것을 커먼 모드 transformer에 인가하여 고주파 누설 전류 역시 감쇄시킬 수 있는 새로운 형태의 능동형 커먼 모드 전압 감쇄기를 제안한다. 그리고 제안한 감쇄기의 동작 성능을 시뮬레이션과 실험을 통하여 검증하였다.

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Ku 대역 위성 중계기용 입력 멀티플렉서에 관한 연구 (A Study on Input Multiplexer for Ku-Band Satellite Transponder)

  • 이주섭;엄만석;염인복;이성팔
    • 한국전자파학회논문지
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    • 제14권4호
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    • pp.393-400
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    • 2003
  • 본 논문에서는 EQM(Engineering Qualification Model)급 Ku 대역 위성 중계기용 입력 멀티플렉서 설계 및 결과에 대하여 언급하였다. 각 채널은 Circulator Chain구조를 이용하여 분리되었으며, 채널 대역내에서의 진폭 변화와 군지연 변화를 최소화하기 위하여 각각의 채널은 채널필터 외부에 등화기를 사용하였다. 위성중계기의 무게와 부피를 최소화하기 위하여 채널필터와 등화기 모두 이중모드로 설계하였다. 채널별 주파수 선택도를 높이기 위하여 채널 필터는 8차 타원 응답형으로 설계하였으며, 등화기는 2차 반사형으로 설계하였다. 온도 변화에 따른 특성 변화를 최소화하기 위하여 필터와 등화기의 공동(cavity), 슬롯, 튜닝나사는 INVAR36을 사용하여 제작하였다. 제작한 입력 멀티플렉서는 진동 시험, 열진공 시험, EMC 시험을 실시하였으며 시험결과 Ku 대역 위성 중계기에 적용 가능한 성능을 나타내었다.

운동방정식에 기초한 공진주 실험의 자료분석 및 해석 (Data Reduction and Analysis of the Resonant Column Testing Based on the Equation of Motion)

  • 조성호;강태호
    • 한국지반공학회논문집
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    • 제19권4호
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    • pp.133-144
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    • 2003
  • 공진주 실험은 흙의 전단탄성계수, 재료감쇠비 등을 결정하는 실험으로, 최근 내진해석의 중요성과 더불어 그 사용빈도와 중요성이 증가하고 있다. 공진주 실험은 1960년 이후 널리 활용되어 왔으나, 현재까지의 공진주 실험은 측정장비의 제한성 때문에, 주로 선형스펙트럼 (linear spectrum)의 진폭성분만을 측정하여 왔다. 이는 공진주 실험 시스템의 동적거동을 규명하는 이론에 있어서도 시료의 점성이 고려되지 않았던 것과 동적거동에 대한 이해가 부족했기 때문이기도하다. 최근 조성호 등은 이러한 한계성을 극복할 수 있는 이론적 근거를 제시하였다. 즉, 공진주 실험 시스템의 동적거동에 대한 운동방정식과 그 일반해를 제시함으로써, 이론에 부합하는 공진주 실험의 자료분석 및 해석기법의 기초를 정립하였다. 본 연구에서는 발전된 계측장비와 공진주 실험 시스템의 동적거동에 대한 이론적 모델링을 이용하여 신뢰도가 향상된 공진주 실험의 자료분석 및 해석기법을 제안하였다. 그리고, 유한요소해석에 의한 공진주 실험의 수치실험을 통하여 본 연구에서 제안한 해석기법의 신뢰성과 타당성을 확인하였다. 또한, 주문진 표준사에 대한 공진주 실험을 통하여, 본 연구에서 제안한 자료분석 및 해석방법의 적용성을 확인하였으며, 기존 해석방법과의 비교를 통하여 기존 방법의 한계성과 문제점을 살펴보았다.