3,473 research outputs found
Optimal control-based inverse determination of electrode distribution for electroosmotic micromixer
This paper presents an optimal control-based inverse method used to determine
the distribution of the electrodes for the electroosmotic micromixers with
external driven flow from the inlet. Based on the optimal control method, one
Dirichlet boundary control problem is constructed to inversely find the optimal
distribution of the electrodes on the sidewalls of electroosmotic micromixers
and achieve the acceptable mixing performance. After solving the boundary
control problem, the step-shaped distribution of the external electric
potential imposed on the sidewalls can be obtained and the distribution of
electrodes can be inversely determined according to the obtained external
electric potential. Numerical results are also provided to demonstrate the
effectivity of the proposed method
State-of-the-art in aerodynamic shape optimisation methods
Aerodynamic optimisation has become an indispensable component for any aerodynamic design over the past 60 years, with applications to aircraft, cars, trains, bridges, wind turbines, internal pipe flows, and cavities, among others, and is thus relevant in many facets of technology. With advancements in computational power, automated design optimisation procedures have become more competent, however, there is an ambiguity and bias throughout the literature with regards to relative performance of optimisation architectures and employed algorithms. This paper provides a well-balanced critical review of the dominant optimisation approaches that have been integrated with aerodynamic theory for the purpose of shape optimisation. A total of 229 papers, published in more than 120 journals and conference proceedings, have been classified into 6 different optimisation algorithm approaches. The material cited includes some of the most well-established authors and publications in the field of aerodynamic optimisation. This paper aims to eliminate bias toward certain algorithms by analysing the limitations, drawbacks, and the benefits of the most utilised optimisation approaches. This review provides comprehensive but straightforward insight for non-specialists and reference detailing the current state for specialist practitioners
A novel convergence enhancement method based on Online Dimension Reduction Optimization
Iterative steady-state solvers are widely used in computational fluid
dynamics. Unfortunately, it is difficult to obtain steady-state solution for
unstable problem caused by physical instability and numerical instability.
Optimization is a better choice for solving unstable problem because
steady-state solution is always the extreme point of optimization regardless of
whether the problem is unstable or ill-conditioned, but it is difficult to
solve partial differential equations (PDEs) due to too many optimization
variables. In this study, we propose an Online Dimension Reduction Optimization
(ODRO) method to enhance the convergence of the traditional iterative method to
obtain the steady-state solution of unstable problem. This method performs
proper orthogonal decomposition (POD) on the snapshots collected from a few
iteration steps, optimizes PDE residual in the POD subspace to get a solution
with lower residual, and then continues to iterate with the optimized solution
as the initial value, repeating the above three steps until the residual
converges. Several typical cases show that the proposed method can efficiently
calculate the steady-state solution of unstable problem with both the high
efficiency and robustness of the iterative method and the good convergence of
the optimization method. In addition, this method is easy to implement in
almost any iterative solver with minimal code modification
Dynamo effect in parity-invariant flow with large and moderate separation of scales
It is shown that non-helical (more precisely, parity-invariant) flows capable
of sustaining a large-scale dynamo by the negative magnetic eddy diffusivity
effect are quite common. This conclusion is based on numerical examination of a
large number of randomly selected flows. Few outliers with strongly negative
eddy diffusivities are also found, and they are interpreted in terms of the
closeness of the control parameter to a critical value for generation of a
small-scale magnetic field. Furthermore, it is shown that, for parity-invariant
flows, a moderate separation of scales between the basic flow and the magnetic
field often significantly reduces the critical magnetic Reynolds number for the
onset of dynamo action.Comment: 44 pages,11 figures, significantly revised versio
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