Non-Dimensional Parameters Governing the Onset of Wake-Induced Marine Riser Collision

2003 ◽  
Author(s):  
Shan Huang ◽  
Wusheng Wu
Keyword(s):  
Critical Current ◽  
Large Amplitude ◽  
Low Frequency ◽  
Critical Value ◽  
Current Speed ◽  
Loss Of Stability ◽  
Marine Riser ◽  
Dimensional Parameters ◽  
Stationary Bifurcation

Wake-induced riser oscillation can lead to riser clashing. Furthermore, the onset of the wake-induced riser oscillation, which is typified by its large amplitude and low frequency, is attributed to the loss of stability of the downstream riser in the wake once the current exceeds a critical value. The loss of stability is mathematically characterised by a stationary bifurcation. Based upon our previous work, further results are presented in the paper on the non-dimensional parameters which govern the critical current speed. These non-dimensional parameters, once computed, can then be used by riser designers to assess potential riser clashing and/or ascertain the minimum riser spacing and top tension required in order to avoid riser clashing.

Wake-Induced Large-Amplitude Low-Frequency Motions of a Vertical Riser in the Wake of an Upstream Riser

2002 ◽  
Author(s):  
Wusheng Wu ◽  
Shan Huang ◽  
Nigel Barltrop
Keyword(s):  
Numerical Method ◽  
Impact Velocity ◽  
Current Velocity ◽  
Large Amplitude ◽  
Significant Contribution ◽  
Structural Model ◽  
Low Frequency ◽  
Critical Value ◽  
Irregular Motion ◽  
Induced Motion

It is concluded from our previous work that a vertical riser situated in the wake of an upstream riser can lose its stability when the current velocity exceeds a critical value. The ensuing irregular motion of the downstream riser is characterised by its large amplitude and low frequency. A numerical method is further developed in this paper to simulate the wake-induced large-amplitude low-frequency motions of the downstream riser as it wanders about in the wake. While an accurate structural model for riser clashing is still yet to be developed, the preliminary results presented here do indicate that in considering the riser impact velocity it is inadequate to use the VIV velocity alone as the wake-induced motion can have a significant contribution to the riser impact velocity.

scholarly journals Strong Waves from Pulsars and Morphologies in SNRs

1983 ◽  
Vol 101 ◽  
pp. 499-501
Author(s):  
Gregory Benford ◽  
Attilio Ferrari ◽  
Silvano Massaglia
Keyword(s):  
Large Amplitude ◽  
Crab Nebula ◽  
Surrounding Medium ◽  
Low Frequency ◽  
Optical Emission ◽  
Amplitude Wave ◽  
Surface Magnetic Field ◽  
Plasma Absorption ◽  
The Crab Nebula ◽  
Large Amplitude Wave

Canonical models for pulsars predict the emission of low–frequency waves of large amplitudes, produced by the rotation of a neutron star possessing a strong surface magnetic field. Pacini (1968) proposed this as the basic drain which yields to the pulsar slowing–down rate. The main relevance of the large amplitude wave (LAW) is the energetic link it provides between the pulsar and the surrounding medium. This role has been differently emphasized (Rees and Gunn, 1974; Ferrari, 1974), referring to absorption effects by relativistic particle acceleration and thermal heating, either close to the pulsar magnetosphere or in the nebula. It has been analyzed in the special case of the Crab Nebula, where observations are especially rich (Rees, 1971). As the Crab Nebula displays a cavity around the pulsar of dimension ∼1017cm, the function of the wave in sweeping dense gas away from the circumpulsar region is widely accepted. Absorption probably occurs at the inner edges of the nebula; i.e., where the wave pressure and the nebular pressure come into balance. Ferrari (1974) interpreted the wisps of the Crab Nebula as the region where plasma absorption occurs, damping the large amplitude wave and driving “parametric” plasma turbulence, thus trasferring energy to optical radiation powering the nebula. The mechanism has been extended to interpret the specific features of the “wisps” emission (Benford et al., 1978). Possibly the wave fills the nebula completely, permeating the space outside filaments with electromagnetic energy, continuously accelerating electrons for the extended radio and optical emission (Rees, 1971).

Multiple-S-Shaped Critical Manifold and Jump Phenomena in Low Frequency Forced Vibration with Amplitude Modulation

2019 ◽  
Vol 29 (05) ◽  
pp. 1930012 ◽  
Author(s):  
Yue Yu ◽  
Qianqian Wang ◽  
Qinsheng Bi ◽  
C. W. Lim
Keyword(s):  
Amplitude Modulation ◽  
Large Amplitude ◽  
Low Frequency ◽  
Slow Variable ◽  
Critical Manifold ◽  
Singular Orbit ◽  
Modulation Control ◽  
Cycle Oscillation ◽  
Tuning Frequency ◽  
Complex Mechanical Systems

Motivated by the forced harmonic vibration of complex mechanical systems, we analyze the dynamics involving different waves in a double-well potential oscillator coupling amplitude modulation control of low frequency. The combination of amplitude modulation factor significantly enriches the dynamical behaviors on the formation of multiple-S-shaped manifold and multiple jumping phenomena that alternate between epochs of slow and fast motion. We can conduct bifurcation analysis to identify two harmonic vibrations. One is that the singular orbit makes multiple jumps to a fast trajectory segment from one attracting equilibrium to another as the expression of slow variable by using the DeMoivre formula. With the increase of tuning frequency, the system exhibits relaxation-type oscillations whose small amplitude oscillations are produced by nonlinear local cycles together with a distinct large amplitude cycle oscillation accounting for the Melnikov threshold values. The tuning frequency may not only affect the asymptotic expressions for the solution curves near fold singularities but also allow for the large amplitude orbit vibrations near fold-cycle singularities. Numerical analysis for computing critical manifolds and their intersections is used to detect the dynamical features in this paper.

Low-frequency critical current noise in Josephson junctions induced by temperature fluctuations

2012 ◽  
Vol 101 (9) ◽  
pp. 092601 ◽  
Author(s):  
S. M. Anton ◽  
C. D. Nugroho ◽  
J. S. Birenbaum ◽  
S. R. O’Kelley ◽  
V. Orlyanchik ◽  
...  
Keyword(s):  
Critical Current ◽  
Josephson Junctions ◽  
Low Frequency ◽  
Temperature Fluctuations ◽  
Current Noise

Infrared imaging of large-amplitude, low-frequency disturbances on a planar jet

AIAA Journal ◽  
1994 ◽  
Vol 32 (2) ◽  
pp. 317-323 ◽  
Author(s):  
Robert B. Farrington ◽  
Scott D. Claunch
Keyword(s):  
Large Amplitude ◽  
Infrared Imaging ◽  
Low Frequency ◽  
Planar Jet

scholarly journals Transition Between Type I and Type III Bursts in Closed or Open Magnetic Field Lines

1980 ◽  
Vol 86 ◽  
pp. 363-368
Author(s):  
Monique G. Aubier
Keyword(s):  
Magnetic Field ◽  
Velocity Component ◽  
Low Frequency ◽  
Critical Value ◽  
Type I ◽  
Accelerated Electrons ◽  
Type Iii ◽  
Field Lines ◽  
Parallel Momentum ◽  
Open Magnetic Field

When studying the propagation of accelerated electrons outwards in the corona, we have shown that the perpendicular momentum of the electrons remaining after the type I process is transformed into parallel momentum during the propagation along the decreasing magnetic field, and that type III emission can occur when the parallel velocity component reaches a critical value. With this model we explain in particular the low frequency cut-off of type I emission, the characteristics of the type III bursts near their starting frequency and the transition between type III- and type I-like decameter emission observed in few cases.

Wear Properties of Oil Palm Cellulose Fibre Reinforced Polymer Composites

2013 ◽  
Vol 845 ◽  
pp. 81-85
Author(s):  
D. Sujan ◽  
C.W. Nguong ◽  
S.N.B. Lee ◽  
Mesfin G. Zewge
Keyword(s):  
Drill Pipe ◽  
Low Frequency ◽  
Cellulose Fibre ◽  
Major Effect ◽  
Drill String ◽  
Drilling Process ◽  
Marine Riser ◽  
Wear Properties ◽  
Maximum Displacement ◽  
Drilling Tools

This paper attempts to explain the motion behaviour of the marine riser coupled to a drill string when the vortex induced vibration (VIV) is involved. Vibrations have been reported to have a major effect on the drilling performance, affecting the rate of penetration (ROP), causing severe damages to the drilling tools and also reduces the efficiency of the drilling process. There are two major components of drilling tools that are subjected to vibration, namely the marine riser and the drilling string. Analysis of vibration in the marine riser and drill string are two topical areas that have individually received considerable attention by researchers in the past. Though these two subjects are interrelated, borne by the fact that the marine riser encapsulates and protects the drill pipe, there have been few attempts to investigate them together as a unity. Due to the complexities of the models, simplified assumptions were made in order to undertake the investigation by using staggered approach. The results were compared with the experimental and simulation data from the open literature. It was found that the maximum displacement with negative damping occurs at low frequency and rotation speed.

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