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Michael Davis Michael A. Demetriou David J. Olinger 《Flow, Turbulence and Combustion》2003,71(1-4):75-91
A highly efficient, low-order model for vortex-induced vibration of flexible cables at low Reynolds number has been developed. A coupled map lattice (CML) wake model, based on circle maps, is combined with a cable model (linear wave equation). With this model, both the self-excited response of the cable oscillation in the crossflow direction and the resulting wake structures are examined at Re = 100. This represents an improvement over earlier CML models capable of only modelling wakes behind externally forced cables. For comparison, spectral-element based numerical simulations, in addition to experiments on a freely vibrating cable flow, were conducted. The freely vibrating CML model predicted lace-like structures consistent with these numerical simulations and experimental results. Little difference was noted between the vortex shedding wake patterns determined for forced cables (from previous CML models) and freely vibrating cables. The freely vibrating CML matched experimental data for maximum cable amplitude reasonably well over a range of mass-damping parameter employed in offshore structural applications. 相似文献
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This paper deals with a comparison between experimental observations in a low-Reynolds-number wake behind an oscillating cylinder
and the universal properties of a sine circle map. When the limit cycle due to the natural vortex shedding in the wake is
modulated at a second frequency by oscillating the cylinder transversely, one obtains in phase space a flow on a two torus.
The nonlinear interaction between the two oscillators results in Arnol’d tongues due to phase locking, the devil’s staircase
along the critical line, and a transition from order to chaosvia the quasiperiodic route. The sine circle map describes these features adequately. A comparison between the experiment and
the theory is made in terms of multifractal formalism and trajectory scaling function. 相似文献
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van de Waal BW 《Physical review letters》1991,67(23):3263-3266
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Lindemuth IR Reinovsky RE Chrien RE Christian JM Ekdahl CA Goforth JH Haight RC Idzorek G King NS Kirkpatrick RC Larson RE Morgan GL Olinger BW Oona H Sheehey PT Shlachter JS Smith RC Veeser LR Warthen BJ Younger SM Chernyshev VK Mokhov VN Demin AN Dolin YN Garanin SF Ivanov VA Korchagin VP Mikhailov OD Morozov IV Pak SV Pavlovskii ES Seleznev NY Skobelev AN Volkov GI Yakubov VA 《Physical review letters》1995,75(10):1953-1956
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A coupled map lattice (CML) with self-learning features is developed to model flow over freely vibrating cables and stationary cylinders at low Reynolds numbers. Coupled map lattices that combine a series of low-dimensional circle maps with a diffusion model have been used previously to predict qualitative features of these flows. However, the simple nature of these CML models implies that there will be unmodeled wake features if a detailed, quantitative comparison is made with laboratory or simulated wake flows. Motivated by a desire to develop an improved CML model, we incorporate self-learning features into a new CML that is first trained to precisely estimate wake patterns from a target numerical simulation. A new convective-diffusive map that includes additional wake dynamics is developed. The new self-learning CML uses an adaptive estimation scheme (multivariable least-squares algorithm). Studies of this approach are conducted using wake patterns from a Navier-Stokes solution (spectral element-based NEKTAR simulation) of freely vibrating cable wakes at Reynolds numbers Re=100. It is shown that the self-learning model accurately and efficiently estimates the simulated wake patterns. The self-learning scheme is then successfully applied to vortex shedding patterns obtained from experiments on stationary cylinders. This constitutes a first step toward the use of the self-learning CML as a wake model in flow control studies of laboratory wake flows. 相似文献
7.
The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns,
vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and
are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist
of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex
wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML
models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control
methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method
used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller
was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex
dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved
for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional
and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially
varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order
CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle
map. 相似文献
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Wilson B. Lutz Craig R. Mcnamara Max R. Olinger David F. Schmidt Douglas E. Doster Mark D. Fiedler 《Journal of heterocyclic chemistry》1984,21(4):1183-1188
5,6-Carbonyldioxyindole ( 4 ), a melanogenic derivative of 5,6-dihydroxyindole ( 1 ), was synthesized by a procedure starting with 3,4-methylenedioxycinnamic acid ( 5 ). Compound 4 is a stable crystalline solid which is readily hydrolyzed to 1 , a key intermediate on the biosynthetic pathway from tyrosine to melanin. 相似文献
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