Computational Methods for Approximation of Large-Scale Dynamical Systems

This study is an evaluation of the computational methods in reproducing experimental data for a generic sports utility vehicle (SUV) geometry and an assessment on the influence of fixed and rotating wheels for this geometry. Initially, comparisons are made in the wake structure and base pressures between several CFD codes and experimental data. It was shown that steady-state RANS methods are unsuitable for this geometry due to a large scale unsteadiness in the wake caused by separation at the sharp trailing edge and rear wheel wake interactions. unsteady RANS (URANS) offered no improvements in wake prediction despite a significant increase in computational cost. The detached-eddy simulation (DES) and Lattice–Boltzmann methods showed the best agreement with the experimental results in both the wake structure and base pressure, with LBM running in approximately a fifth of the time for DES. The study then continues by analysing the influence of rotating wheels and a moving ground plane over a fixed wheel and ground plane arrangement. The introduction of wheel rotation and a moving ground was shown to increase the base pressure and reduce the drag acting on the vehicle when compared to the fixed case. However, when compared to the experimental standoff case, variations in drag and lift coefficients were minimal but misleading, as significant variations to the surface pressures were present.

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ON THE LOCATION AND CONTINUATION OF HOPF BIFURCATIONS IN LARGE-SCALE PROBLEMS

International Journal of Bifurcation and Chaos ◽

10.1142/s0218127408021208 ◽

2008 ◽

Vol 18 (05) ◽

pp. 1589-1597 ◽

Cited By ~ 2

Author(s):

M. FRIEDMAN ◽

W. QIU

Keyword(s):

Dynamical Systems ◽

Large Scale ◽

Orthonormal Basis ◽

Invariant Subspaces ◽

Hopf Bifurcations ◽

Augmented System ◽

Large Scale Problems ◽

System Technique ◽

Matlab Package ◽

Parameter Dependent

CL_MATCONT is a MATLAB package for the study of dynamical systems and their bifurcations. It uses a minimally augmented system for continuation of the Hopf curve. The Continuation of Invariant Subspaces (CIS) algorithm produces a smooth orthonormal basis for an invariant subspace [Formula: see text] of a parameter-dependent matrix A(s). We extend a minimally augmented system technique for location and continuation of Hopf bifurcations to large-scale problems using the CIS algorithm, which has been incorporated into CL_MATCONT. We compare this approach with using a standard augmented system and show that a minimally augmented system technique is more suitable for large-scale problems. We also suggest an improvement of a minimally augmented system technique for the case of the torus continuation.

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How public perceptions of social distancing evolved over a critical time period: communication lessons learnt from the American state of Wisconsin

Journal of Science Communication ◽

10.22323/2.19050211 ◽

2020 ◽

Vol 19 (05) ◽

pp. A11

Author(s):

Kaiping Chen ◽

Luye Bao ◽

Anqi Shao ◽

Pauline Ho ◽

Shiyu Yang ◽

...

Keyword(s):

Public Health ◽

Computational Methods ◽

Large Scale ◽

Critical Time ◽

Effective Communication ◽

Public Perceptions ◽

Social Distancing ◽

Time Period ◽

Large Scale Survey ◽

Main Barrier

Understanding how individuals perceive the barriers and benefits of precautionary actions is key for effective communication about public health crises, such as the COVID-19 outbreak. This study used innovative computational methods to analyze 30,000 open-ended responses from a large-scale survey to track how Wisconsin (U.S.A.) residents' perceptions of the benefits of and barriers to performing social distancing evolved over a critical time period (March 19th to April 1st, 2020). Initially, the main barrier was practical related, however, individuals later perceived more multifaceted barriers to social distancing. Communication about COVID-19 should be dynamic and evolve to address people's experiences and needs overtime.

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Large-Scale Uncertain Systems Under Insufficient Decentralized Controllers

Journal of Dynamic Systems Measurement and Control ◽

10.1115/1.3153061 ◽

1989 ◽

Vol 111 (3) ◽

pp. 359-363 ◽

Cited By ~ 1

Author(s):

Y. H. Chen

Keyword(s):

Dynamical Systems ◽

Uncertain Systems ◽

Large Scale ◽

Large Scale System ◽

Uncertain Dynamical Systems ◽

Partial Stability ◽

Decentralized Controllers ◽

Total Stability ◽

The Stability

We consider a class of large-scale uncertain dynamical systems under decentralized controllers. The system is composed of N interconnected subsystems which possess uncertainty. Moreover, there are uncertainties in the interconnections. If the subsystems are under sufficient decentralized controllers, the large-scale system is practically stable. As certain controllers fail, study on the conditions for total stability of partial stability to be preserved is made. It can be shown that the stability is only related to bound of uncertainty and the structure of the large-scale system. Moreover, the conditions can be utilized to determine the importance of some controllers for stability.

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