Abstract: The motion of an axially moving beam with rotating prismatic joint with a tip mass on the end is analyzed to investigate the nonlinear vibration and dynamic stability of the beam. The beam is moving with a harmonic axially and rotating velocity about a constant mean velocity. A time-dependent partial differential equation and boundary conditions with the aid of the Hamilton principle are derived to describe the beam lateral deflection. After the partial differential equation is discretized by the Galerkin method, the method of multiple scales is applied to obtain analytical solutions. Frequency response curves are plotted for the super harmonic resonances of the first and the second modes. The effects of non-linear term and mean velocity are investigated on the steady state response of the axially moving beam. The results are validated with numerical simulations.
Abstract: In this paper, using the method of multiple scales, the second sub-harmonic resonance in vortex-induced vibrations (VIV) of a marine pipeline close to the seabed is investigated based on a developed wake oscillator model. The amplitude-frequency equations are also derived. It is found that the oscillation will increase all the time when both discriminants of the amplitude-frequency equations are positive while the oscillation will decay when the discriminants are negative.
Abstract: This paper presents an analysis study on the impacts
of the changes of the capacitor banks, the loss of a transformer, and
the installation of distributed generation on the voltage total harmonic
distortion and harmonic resonance. The study is applied in a real
system in Oman, Sohar Industrial Port–C Substation Network.
Frequency scan method and Fourier series analysis method are used
with the help of EDSA software. Moreover, the results are compared
with limits specified by national Oman distribution code.
Abstract: This paper presents the results of a comprehensive
investigation of five blackouts that occurred on 28 August to 8
September 2011 due to bushing failures of the 132/33 kV, 125 MVA
transformers at JBB Ali Grid station. The investigation aims to
explore the root causes of the bushing failures and come up with
recommendations that help in rectifying the problem and avoiding the
reoccurrence of similar type of incidents. The incident reports about
the failed bushings and the SCADA reports at this grid station were
examined and analyzed. Moreover, comprehensive power quality
field measurements at ten 33/11 kV substations (S/Ss) in JBB Ali
area were conducted, and frequency scans were performed to verify
any harmonic resonance frequencies due to power factor correction
capacitors. Furthermore, the daily operations of the on-load tap
changers (OLTCs) of both the 125 MVA and 20 MVA transformers
at JBB Ali Grid station have been analyzed. The investigation
showed that the five bushing failures were due to a local problem, i.e.
internal degradation of the bushing insulation. This has been
confirmed by analyzing the time interval between successive OLTC
operations of the faulty grid transformers. It was also found that
monitoring the number of OLTC operations can help in predicting
bushing failure.