• Title/Summary/Keyword: Frequency drift

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Irregular frequency effects in the calculations of the drift forces

  • Liu, Yujie;Falzarano, Jeffrey M.
    • Ocean Systems Engineering
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    • v.9 no.1
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    • pp.97-109
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    • 2019
  • Accurate calculation of the mean drift forces and moments is necessary when studying the higher order excitations on the floater in waves. When taking the time average of the second order forces and moments, the second order potential and motion diminish with only the first order terms remained. However, in the results of the first order forces or motions, the irregular frequency effects are often observed in higher frequencies, which will affect the accuracy of the calculation of the second order forces and moments. Therefore, we need to pay close attention to the irregular frequency effects in the mean drift forces. This paper will discuss about the irregular frequency effects in the calculations of the mean drift forces and validate our in-house program MDL Multi DYN using some examples which are known to have irregular frequency effects. Finally, we prove that it is necessary to remove the effects and demonstrate that the effectiveness of the formula and methods adopted in the development of our program.

Analysis of vortex induced vibration frequency of super tall building based on wind tunnel tests of MDOF aero-elastic model

  • Wang, Lei;Liang, Shuguo;Song, Jie;Wang, Shuliang
    • Wind and Structures
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    • v.21 no.5
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    • pp.523-536
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    • 2015
  • To study the vibration frequency of super high-rise buildings in the process of vortex induced vibration (VIV), wind tunnel tests of multi-degree-of-freedom (MDOF) aero-elastic models were carried out to measure the vibration frequency of the system directly. The effects of structural damping, wind field category, mass density, reduced wind velocity ($V_r$), as well as VIV displacement on the VIV frequency were investigated systematically. It was found that the frequency drift phenomenon cannot be ignored when the building is very high and flexible. When $V_r$ is less than 8, the drift magnitude of the frequency is typically positive. When $V_r$ is close to the critical wind velocity of resonance, the frequency drift magnitude becomes negative and reaches a minimum at the critical wind velocity. When $V_r$ is larger than12, the frequency drift magnitude almost maintains a stable value that is slightly smaller than the fundamental frequency of the aero-elastic model. Furthermore, the vibration frequency does not lock in the vortex shedding frequency completely, and it can even be significantly modified by the vortex shedding frequency when the reduced wind velocity is close to 10.5.

Active Frequency Drift Positive Feedback Method for Anti-islanding applied Digital Phase-Locked-Loop (Digital PLL을 이용한 Active Frequency Drift Positive Feedback에 관한 연구)

  • Lee, K.O.;Choi, J.Y.;Choy, I.;Jung, Y.S.;Yu, G.Y.;Song, S.H.
    • 한국신재생에너지학회:학술대회논문집
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    • 2007.11a
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    • pp.250-254
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    • 2007
  • As photovoltaic(PV) power generation systems become more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive powers of the load and PV system are closely matched, islanding detection by passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.

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Using MZIs for Optical PSBT Transmissions: Requirements for Thermal Stabilization

  • Ducournau, Guillaume;Latry, Olivier;Ketata, Mohamed
    • ETRI Journal
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    • v.28 no.5
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    • pp.615-620
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    • 2006
  • In this paper, we discuss the quantification of Mach-Zehnder interferometer (MZI) thermal stabilization which is needed in optical phase shaped binary transmission (PSBT) links. Considering the thermo-optic and thermal expansion effects, we revisit the analytical expression for the thermal drift (GHz/$^{\circ}C$) of the MZI center frequency (denoted here by the 'MZI spectral drift'). An MZI is then used in an experimental transmission system using the optical PSBT format. We study the effect of spectral MZI drift by using a thermally stabilized interferometer and applying a frequency shift to the optical carrier. By using the thermal drift coefficient of the MZI, we find that to ensure low bit error rate fluctuations due to the MZI drift, the thermal stabilization of the device must have an accuracy of $0.5^{\circ}C$.

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Modeling and Analysis of Modified Active Frequency Drift Method (개선된 AFD기법의 모델링 및 분석)

  • An, Jin-Ung;Yu, Gwon-Jong;Choy, Ich;Choi, Ju-Yeop;Lee, Ki-Ok
    • The Transactions of the Korean Institute of Power Electronics
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    • v.16 no.2
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    • pp.145-151
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    • 2011
  • In this paper, among the active islanding detection techniques, the modified active frequency drift method was analyzed, which is relatively easy to apply to the single-phase grid-connected PV PCS. The existing designs for turbulences in these applications were empirically conducted, and do not have sufficient reliability and performance. Therefore, three application forms of the modified active frequency drift technique were modeled, based on which the proper magnitude of turbulence, which is the frequency acceleration component, was calculated. Using the results, the magnitude of and injection method for turbulence for ensuring the islanding detection performance and improving the output power quality were proposed, and they were verified via simulations and experiment to prove that the reliable islanding detection technique can be developed merely by measuring the basic output power quality, without the need for expensive islanding simulation equipment.

A Study on the Wave Drift Damping of a Moored Ship in Waves (파랑중 계류된 선박의 표류감쇠에 관한 연구)

  • 이호영;박홍식;신현경
    • Journal of Ocean Engineering and Technology
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    • v.14 no.4
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    • pp.17-22
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    • 2000
  • As the offshore oil fields are moved to the deep ocean, the oil production system of FPSO(Floating Production Storage and Offloading System) Type are constructed frequently these days. So, it is very important to estimate the drift motion and damping effects due to the drift motion simultaneously. The components of slow drift motion damping consist of viscous, wave radiation effect and wave drift damping. It is needed to estimate the wave drift damping more accurately than others. The wave drift damping signifies the time-rate of mean wave drift force on oscillating ship or ocean structure which constant speed. In order to calculate this, the 3-Dimensional panel method is employed with the translating and pulsating Green function in the frequency domain. The calculation is carried out for a Series 60 ($C_B$/=0.7) and the results are compared with other numerical ones.

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Implementation of Frequency Bandwidth Expander using VCO Drift Canceller and Comb generator (VCO 표류 성분 상쇄기와 빗쌀 하모닉 발생기를 이용한 주파수 대역 확장기의 구현)

  • 강승민
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.9B
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    • pp.1683-1689
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    • 1999
  • We have implemented Frequency bandwidth expander with frequency upconverting by VCO drift canceller and comb generator. Te output of the low frequency synthesizer which the output frequency is 220~280MHz(Resolution : 5MHz) is expanded to 1660~2140MHz by this system. The phase noise of this system only depends on the phase noise of comb generator and low frequency synthesizer. The phase noise of VCO don’t influence at the frequency expander because the drift of VCO cancel out. When we control the output of VCO, the output frequency of this system is varied by 60MHz x N as filter banker. The switching time and the spurious of the frequency expander is below 3usec, -55dBc respectively. This system easily expands bandwidth additively by expanding the output bandwidth of the VCO. We can apply the frequency expander to very wide band microwave synthesizer which has fast switching time.

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A Study of Non-Detection Zone using AFD Method applied to Grid-Connected Photovoltaic Inverter for a variety of Loads (계통연계형 태양광발전 인버터에 사용된 AFD기법의 다양한 부하에 따른 단독운전 불검출영역에 대한 고찰)

  • Ko, Moon-Ju;Choy, Ick;Choi, Ju-Yeop
    • Journal of the Korean Solar Energy Society
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    • v.26 no.1
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    • pp.91-98
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    • 2006
  • Islanding phenomenon of utility-connected photovoltaic power conditioning systems(PV PCS) can cause a variety of problems and must be prevented. If the real and reactive power supplied by PV PCS are closely matched to those of load, islanding detection by passive methods becomes difficult. The active frequency drift(AFD) method, called the frequency bias method, enables islanding detection by forcing the frequency of the voltage in the islanding to drift up or down. In this paper, non-detection zone(NDZ) of AFD is analyzed for the islanding detection method of utility-connected PV PCS by the simulation software tool PSIM.

Analysis of Anti-Islanding Schemes using Frequency Drift in Distributed Generation System (분산전원 시스템의 주파수 변동을 통한 단독운전 방지기법 분석)

  • Jo, Yeong-Min;Cho, Sang-Yoon;Song, Seung-Ho;Choy, Ick;Choi, Ju-Yeop;Lee, Young-Kwoun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.3
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    • pp.247-254
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    • 2015
  • Unintentional islanding results in safety hazards, power quality degradation, and many other issues. Thus, islanding detection of grid-connected distributed generation system is a key function for standards compliance. Many anti-islanding schemes are currently being studied; however, existing anti-islanding schemes used in inverters have power quality degradation and non-detection zone issues. Therefore, this paper analyzes existing anti-islanding schemes by using frequency drift in accordance with both islanding detection performance and power quality. This paper also proposes a new anti-islanding scheme by using frequency drift. Both simulation and experimental results show that the proposed scheme has negligible power quality degradation and no non-detection zones compared with other existing schemes.

Active Frequency Drift Positive Feedback Method for Anti-islanding using Digital Phase-Locked-Loop (디지털 위상검출기법을 적용한 능동적 주파수 변화 정궤환기법)

  • Lee, Ki-Ok;Young, Young-Seok;Choi, Ju-Yeop;Choy, Ick;Song, Seung-Ho;Ko, Moon-Ju
    • Journal of the Korean Solar Energy Society
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    • v.27 no.2
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    • pp.37-44
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    • 2007
  • As photovoltaic(PV) power generation system becomes more common, it will be necessary to investigate islanding detection method for PV systems. Islanding of PV systems can cause a variety of problems and must be prevented. However, if the real and reactive power of the load and PV system are closely matched, islanding detection by Passive methods becomes difficult. Also, most active methods lose effectiveness when there are several PV systems feeding the same island. The active frequency drift positive feedback method(AFDPF) enables islanding detection by forcing the frequency of the voltage in the island to drift up or down. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF considering output power quality and islanding prevention performance are performed by simulation and experiment according to IEEE Std 929-2000 islanding test.