Higher-order flow modes in turbulent Rayleigh–Bénard convection

2016 ◽  
Vol 805 ◽  
pp. 31-51 ◽  
Author(s):  
Heng-Dong Xi ◽  
Yi-Bao Zhang ◽  
Jian-Tao Hao ◽  
Ke-Qing Xia
Keyword(s):  
Large Scale ◽  
Experimental Studies ◽  
Higher Order ◽  
Working Fluid ◽  
Dynamical Process ◽  
Total Flow ◽  
Flow Energy ◽  
The Third ◽  
Higher Order Modes ◽  
Second Mode

We present experimental studies of higher-order modes of the flow in turbulent thermal convection in cells of aspect ratio ($\unicode[STIX]{x1D6E4}$) 1 and 0.5. The working fluid is water with the Prandtl number ($Pr$) kept at around 5.0. The Rayleigh number ($Ra$) ranges from $9\times 10^{8}$ to $6\times 10^{9}$ for $\unicode[STIX]{x1D6E4}=1$ and from $1.6\times 10^{10}$ to $7.2\times 10^{10}$ for $\unicode[STIX]{x1D6E4}=0.5$. We found that in $\unicode[STIX]{x1D6E4}=1$ cells, the first mode, which corresponds to the large-scale circulation (LSC), dominates the flow. The second mode (quadrupole mode), the third mode (sextupole mode) and the fourth mode (octupole mode) are very weak, on average these higher-order modes each contains less than 4 % of the total flow energy. In $\unicode[STIX]{x1D6E4}=0.5$ cells, the first mode is still the strongest but less dominant, the second mode becomes stronger which contains 13.7 % of the total flow energy and the third and the fourth modes are also stronger (containing 6.5 % and 1.1 % of the total flow energy respectively). It is found that during a reversal/cessation, the amplitude of the second mode and the remaining modes experiences a rapid increase followed by a decrease, which is opposite to the behaviour of the amplitude of the first mode – it decreases to almost zero then rebounds. In addition, it is found that during the cessation (reversal) of the LSC, the second mode dominates, containing 51.3 % (50.1 %) of the total flow energy, which reveals that the commonly called cessation event is not the cessation of the entire flow but only the cessation of the first mode (LSC). The experiment reveals that the second mode and the remaining higher-order modes play important roles in the dynamical process of the reversal/cessation of the LSC. We also show direct evidence that the first mode is more efficient for heat transfer. Furthermore, our study reveals that, during the cessation/reversal of the LSC, $Nu$ drops to its local minimum and the minimum of $Nu$ is ahead of the minimum of the amplitude of the LSC; and reversals can be distinguished from cessations in terms of global heat transport. A direct velocity measurement reveals the flow structure of the first- and higher-order modes.

Efficient and High-Quality Seeded Graph Matching: Employing Higher-order Structural Information

2021 ◽  
Vol 15 (3) ◽  
pp. 1-31
Author(s):  
Haida Zhang ◽  
Zengfeng Huang ◽  
Xuemin Lin ◽  
Zhe Lin ◽  
Wenjie Zhang ◽  
...  
Keyword(s):  
Large Scale ◽  
Graph Matching ◽  
Structural Information ◽  
Experimental Studies ◽  
Higher Order ◽  
Personalized Pagerank ◽  
Matching Accuracy ◽  
Approximation Techniques ◽  
Order Of Magnitude ◽  
Matching Score

Driven by many real applications, we study the problem of seeded graph matching. Given two graphs and , and a small set of pre-matched node pairs where and , the problem is to identify a matching between and growing from , such that each pair in the matching corresponds to the same underlying entity. Recent studies on efficient and effective seeded graph matching have drawn a great deal of attention and many popular methods are largely based on exploring the similarity between local structures to identify matching pairs. While these recent techniques work provably well on random graphs, their accuracy is low over many real networks. In this work, we propose to utilize higher-order neighboring information to improve the matching accuracy and efficiency. As a result, a new framework of seeded graph matching is proposed, which employs Personalized PageRank (PPR) to quantify the matching score of each node pair. To further boost the matching accuracy, we propose a novel postponing strategy, which postpones the selection of pairs that have competitors with similar matching scores. We show that the postpone strategy indeed significantly improves the matching accuracy. To improve the scalability of matching large graphs, we also propose efficient approximation techniques based on algorithms for computing PPR heavy hitters. Our comprehensive experimental studies on large-scale real datasets demonstrate that, compared with state-of-the-art approaches, our framework not only increases the precision and recall both by a significant margin but also achieves speed-up up to more than one order of magnitude.

scholarly journals Effect of Slam Force Duration on the Vibratory Response of a Lightweight High-Speed Wave-Piercing Catamaran

2015 ◽  
Vol 59 (02) ◽  
pp. 69-84
Author(s):  
Jason John McVicar ◽  
Jason Lavroff ◽  
Michael Richard Davis ◽  
Giles Thomas
Keyword(s):  
High Speed ◽  
Bending Strength ◽  
Experimental Studies ◽  
Bending Moment ◽  
Higher Order ◽  
Acute Angle ◽  
Beam Model ◽  
Higher Order Modes ◽  
Hull Structure ◽  
Vertical Bending Moment

When the surface of a ship meets the water surface at an acute angle with a high relative velocity, significant short-duration forces can act on the hull plating. Such an event is referred to as a slam. Slam loads imparted on ships are generally considered to be of an impulsive nature. As such, slam loads induce vibration in the global hull structure that has implications for both hull girder bending strength and fatigue life of a vessel. A modal method is often used for structural analysis whereby higher order modes are neglected to reduce computational effort. The effect of the slam load temporal distribution on the whipping response and vertical bending moment are investigated here by using a continuous beam model with application to a 112 m INCAT wave-piercing catamaran and correlation to full-scale and model-scale experimental data. Experimental studies have indicated that the vertical bending moment is dominated by the fundamental longitudinal bending mode of the structure. However, it is shown here that although the fundamental mode is dominant in the global structural response, the higher order modes play a significant role in the early stages of the response and may not be readily identifiable if measurements are not taken sufficiently close to the slam location. A relationship between the slam duration and the relative modal response magnitudes is found, which is useful in determining the appropriate truncation of a modal solution.

Nonlinear behaviour of contained inertia waves

1996 ◽  
Vol 315 ◽  
pp. 151-173 ◽  
Author(s):  
Richard Manasseh
Keyword(s):  
Fundamental Mode ◽  
Experimental Studies ◽  
Higher Order ◽  
Time Dependent ◽  
Linear Wave ◽  
Wave System ◽  
Nonlinear Behaviour ◽  
Rotating Fluid ◽  
Weakly Nonlinear ◽  
Higher Order Modes

Rotating fluid-filled containers are systems which admit inertial oscillations, which at appropriate frequencies can be represented as inertia wave modes. When forced by a time-dependent perturbation, systems of contained inertia waves have been shown, in a number of experimental studies, to exhibit complex and varied breakdown phenomena. It is particularly hard to determine a forcing amplitude below which breakdowns do not occur but at which linear wave behaviour is still measurable. In this paper, experiments are presented where modes of higher order than the fundamental are forced. These modes exhibit more complex departures from linear inviscid behaviour than the fundamental mode. However, the experiments on higher-order modes show that instabilities begin at nodal planes. It is shown that even a weakly nonlinear contained inertia-wave system is one in which unexpectedly efficient interactions with higher-order modes can occur, leading to ubiquitous breakdowns. An experiment with the fundamental mode illustrates the system's preference for complex transitions to chaos.

Instabilities in the slit-jet flow field

1983 ◽  
Vol 132 ◽  
pp. 79-86 ◽  
Author(s):  
J. F. Foss ◽  
D. Korschelt
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Large Scale ◽  
Jet Flow ◽  
Instability Mode ◽  
Regular Pattern ◽  
Additional Information ◽  
The Third ◽  
Second Mode ◽  
Convection Speed

Three modes of instabilities in the slit-jet flow field are recognized. Additional evidence for the universality of the Strouhal number for the second mode ST = fw/U0 ≈ 0.43 and additional information on the wavelength (λ) between, and convection speed uc of the symmetrically placed, large-scale motions that result from this instability are presented. Specifically λ/w ≈ 1.2 and uc/U0 ≈ 0.51. The third instability mode is initiated at a Reynolds number U0w/v of approximately 1600; this instability results in a loss of the regular pattern associated with the large-scale motions.

scholarly journals Performance of distributed multiscale simulations

2014 ◽  
Vol 372 (2021) ◽  
pp. 20130407 ◽  
Author(s):  
J. Borgdorff ◽  
M. Ben Belgacem ◽  
C. Bona-Casas ◽  
L. Fazendeiro ◽  
D. Groen ◽  
...  
Keyword(s):  
Load Distribution ◽  
Large Scale ◽  
Multiscale Simulations ◽  
Distributed Resources ◽  
Multiple Resources ◽  
The Third ◽  
Simulation Speed ◽  
Local Resources ◽  
Second Mode ◽  
Different Characteristics

Multiscale simulations model phenomena across natural scales using monolithic or component-based code, running on local or distributed resources. In this work, we investigate the performance of distributed multiscale computing of component-based models, guided by six multiscale applications with different characteristics and from several disciplines. Three modes of distributed multiscale computing are identified: supplementing local dependencies with large-scale resources, load distribution over multiple resources, and load balancing of small- and large-scale resources. We find that the first mode has the apparent benefit of increasing simulation speed, and the second mode can increase simulation speed if local resources are limited. Depending on resource reservation and model coupling topology, the third mode may result in a reduction of resource consumption.

Pèlerinages barrésiens

2013 ◽  
pp. 116-123
Author(s):  
Claire Bompaire-Evesque
Keyword(s):  
Large Scale ◽  
The Self ◽  
Joan Of Arc ◽  
The Third ◽  
National Importance ◽  
The Earth ◽  
Third Stage ◽  
The Dead

This article is a inquiry about how Barrès (1862-1923) handles the religious rite of pilgrimage. Barrès stages in his writings three successive forms of pilgrimage, revealing what is sacred to him at different times. The pilgrimage to a museum or to the birthplace of an artist is typical for the egotism and the humanism of the young Barrès, expressed in the Cult of the Self (1888-1891). After his conversion to nationalism, Barrès tries to unite the sons of France and to instill in them a solemn reverence for “the earth and the dead” ; for that purpose he encourages in French Amities (1903) pilgrimages to historical places of national importance (battlefields; birthplace of Joan of Arc), building what Nora later called the Realms of Memory. The third stage of Barrès’ intellectual evolution is exemplified by The Sacred Hill (1913). In this book the writer celebrates the places where “the Spirit blows”, and proves open to a large scale of spiritual forces, reaching back to paganism and forward to integrative syncretism, which aims at unifying “the entire realm of the sacred”.

scholarly journals Leisure Time Sports Activities and Life Satisfaction: Deeper Insights Based on a Representative Survey from Germany

2020 ◽  
Author(s):  
Michael Mutz ◽  
Anne K. Reimers ◽  
Yolanda Demetriou
Keyword(s):  
Life Satisfaction ◽  
Large Scale ◽  
Leisure Time ◽  
Organizational Context ◽  
Experimental Studies ◽  
Well Being ◽  
Activity Level ◽  
Leisure Satisfaction ◽  
General Life Satisfaction ◽  
Sports Activities

Abstract Observational and experimental studies show that leisure time sporting activity (LTSA) is associated with higher well-being. However, scholars often seem to assume that 1) LTSA fosters “general” life satisfaction, thereby ignoring effects on domain satisfaction; 2) the effect of LTSA on well-being is linear and independent of a person’s general activity level; 3) the amount of LTSA is more important than the repertoire of LTSA, i.e. the number of different activities; 4) all kinds of LTSA are equal in their effects, irrespective of spatial and organisational context conditions. Using data from the German SALLSA-Study (“Sport, Active Lifestyle and Life Satisfaction”), a large-scale CAWI-Survey (N = 1008) representing the population ≥ 14 years, the paper takes a closer look on these assumptions. Findings demonstrate that LTSA is associated with general life satisfaction and domain-specific satisfaction (concerning relationships, appearance, leisure, work and health), but that the relationship is most pronounced for leisure satisfaction. Associations of sport with life satisfaction, leisure satisfaction and subjective health are non-linear, approaching an injection point from which on additional LTSA is no longer beneficial. Moreover, findings lend support to the notion that diversity in LTSA matters, as individuals with higher variation in sports activities are more satisfied. Finally, results with regard to spatial and organizational context suggest that outdoor sports and club-organized sports have additional benefits.

scholarly journals Electrical characterisation of higher order spin wave modes in vortex-based magnetic tunnel junctions

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Alex. S. Jenkins ◽  
Lara San Emeterio Alvarez ◽  
Samh Memshawy ◽  
Paolo Bortolotti ◽  
Vincent Cros ◽  
...  
Keyword(s):  
Spin Wave ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Higher Order ◽  
Spin Torque ◽  
Micromagnetic Simulations ◽  
Higher Order Modes ◽  
Spin Diode ◽  
Super High Frequency ◽  
Wave Modes

AbstractNiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz. In this report, we present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz). This is achieved via micromagnetic simulations and electrical characterisation in magnetic tunnel junctions, both directly via the spin-diode effect and indirectly via the measurement of the coupling with the gyrotropic critical current. The excitation mechanism and spatial profile of the modes are shown to have a complex dependence on the vortex core position. Additionally, the inter-mode coupling between the fundamental gyrotropic mode and the higher order modes is shown to reduce or enhance the effective damping depending upon the sense of propagation of the confined spin wave.

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