Surrogate-based Analysis and Optimization

A hybrid RANS-LES approach with delayed-DES and wall-modelled LES capabilities

This paper addresses the solution of bound-constrained optimization problems using algorithms that require only the availability of objective function values but no derivative information. We refer to these algorithms as derivative-free algorithms. Fueled by a growing number of applications in science and engineering, the development of derivative-free optimization algorithms has long been studied, and it has found renewed interest in recent time. Along with many derivative-free algorithms, many software implementations have also appeared. The paper presents a review of derivative-free algorithms, followed by a systematic comparison of 22 related implementations using a test set of 502 problems. The test bed includes convex and nonconvex problems, smooth as well as nonsmooth problems. The algorithms were tested under the same conditions and ranked under several criteria, including their ability to find near-global solutions for nonconvex problems, improve a given starting point, and refine a near-optimal solution. A total of 112,448 problem instances were solved. We find that the ability of all these solvers to obtain good solutions diminishes with increasing problem size. For the problems used in this study, TOMLAB/MULTIMIN, TOMLAB/GLCCLUSTER, MCS and TOMLAB/LGO are better, on average, than other derivative-free solvers in terms of solution quality within 2,500 function evaluations. These global solvers outperform local solvers even for convex problems. Finally, TOMLAB/OQNLP, NEWUOA, and TOMLAB/MULTIMIN show superior performance in terms of refining a near-optimal solution.

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Derivative-free optimization: a review of algorithms and comparison of software implementations

The numerical simulation of high Reynolds number flows is hampered by model accuracy if the Reynolds-averaged Navier–Stokes (RANS) equations are used, and by computational cost if direct or large-eddy simulations (LES) that resolve the near-wall layer are employed. The cost of a calculation scales like the Reynolds number to the power 3 for direct numerical simulations, or 2.4 for LES, making the resolution of the wall layer at high Reynolds number infeasible even with the most advanced computers. In LES, an attractive alternative to compute high-Re flows is the use of wall-layer models, in which only the outer layer is resolved, while the near-wall region is modeled. Three broad classes of approaches are presently used: bypassing this region altogether using wall functions, solving a separate set of equations in the near-wall region, weakly coupled to the outer flow, or simulating the near-wall region in a global, Reynolds-averaged, sense. These approaches are discussed and their ranges of applicability are highlighted. Various unresolved issues in wall-layer modeling are presented.

Wall-layer models for large-eddy simulations

A versatile sharp interface immersed boundary method for incompressible flows with complex boundaries

Yb3+/Al3+-doped and Yb3+/Al3+/P5+-doped silica fibers with almost identical Yb3+ doping concentrations were prepared using modified chemical vapor deposition methods. A harsh experimental environment for simultaneous photo-darkening (PD) and radio-darkening (RD) of an ytterbium-doped silica fiber (YDF) was established. The RD, PD, and photo-radio-darkening (PRD) of the YDF were characterized at two dose rates of 0.1 rad(Si)/s and 1 rad(Si)/s. The laser performances before and after the darkening process were tested under 974-nm pumping. The results demonstrated that the PD largely dominated the PRD kinetics of the YDF at a low dose rate (e.g., that in space) and that the PRD was not a superposition of RD and PD owing to the pump light bleaching if the induced loss was larger than the PD equilibrium level. The induced loss and defect types were investigated through absorption spectra and electron paramagnetic resonance. The results revealed that the P doping could enhance the PD, RD, and PRD resistances by inhibiting the formation of aluminum–oxygen hole centers.

Research on Photo-Radiation Darkening Performance of Ytterbium-Doped Silica Fibers for Space Applications

Large-eddy simulation (LES) with wall-modeling is evaluated for applications to aerooptical predictions at practical Reynolds numbers. Turbulent boundary layers and flow over a cylindrical turret are considered. The results of boundary-layer flows at both subsonic and supersonic speeds show accurate predictions of mean velocity profiles and velocity fluctuations. The density fluctuations and hence wavefront distortions are found to be more demanding in terms of grid resolution. The subsonic separated shear layer over a cylindrical turret is computed at the same Reynolds number as in the experiment conducted by Gordeyev et al. [1]. Both flow and optical results show good agreement with the experimental measurements and the previous wall-resolved LES results of Wang et al. [2] at a reduced Reynolds number.

http://www3.nd.edu/~mkamel/publications/MKamel-AIAA-Paper-2016-1462.pdf

Predictions of Aero-Optical Distortions Using LES with Wall Modeling

Effect of electron-hole spatial correlation on spin relaxation dynamics in InAs submonolayer

The preparation and characteristics of a new transparent glass ceramic were described. Crystal phase particles with nanometer size were successfully precipitated in glass matrix, which was confirmed to be one of indium aluminum zinc oxide compounds (InxAlyZnzO). The presence of aluminum (Al) and indium (In) impurities in the zinc oxides (ZnO) crystal lattice leads to some changes of the carrier concentration in the material and then promote the sharply changes of transmission spectra in IR range wavelength. And subsequently, the IR cut-off edge blue shifted from 5.5 μm in base glass to 3 μm in transparent glass ceramic sample. Furthermore, passive Q switched 1.54 μm Er glass laser pulses with pulse energy of 10 mJ and pulse width of 800 ns were successfully obtained by using the cobalt doped transparent glass ceramic as a saturable absorber.

Transmission properties of a new glass ceramic and doped with Co2+ as saturable absorber for 1.54 µm Er glass short pulse laser

Large-eddy simulation of turbulent flow interaction with a ten-bladed rotor is performed to investigate the turbulence ingestion noise. The turbulent inflow is homogeneous and isotropic, mimicking grid-generated turbulence in a previous experiment. The acoustic response of the rotor is computed at low Mach numbers using the Ffowcs Williams-Hawkings extension to the Lighthill theory. Results show that turbulence ingestion noise is broadband with small spectral peaks at the blade passing frequency and its harmonics. It is much stronger than the rotor self noise generated by vortex shedding. The computed sound pressure spectrum exhibits a similar shape to the experimental spectrum but the level is lower by 2–5 dB, which is likely due to a mismatch in the incident flow condition and is under further investigation. The effects of different levels of acoustic compactness assumptions on the sound prediction are evaluated and discussed.

Meng Wang

Papers

Research on Photo-Radiation Darkening Performance of Ytterbium-Doped Silica Fibers for Space Applications

Predictions of Aero-Optical Distortions Using LES with Wall Modeling

Effect of electron-hole spatial correlation on spin relaxation dynamics in InAs submonolayer

Transmission properties of a new glass ceramic and doped with Co2+ as saturable absorber for 1.54 µm Er glass short pulse laser

Computation of Rotor Noise Generation in Grid Turbulence Using Large-Eddy Simulation