Simulation of Vortex-Induced Oscillations within a Shear Thinning Liquid

The present work discusses the impact of nonlinear shear thinning in a viscous fluid flow on the vibration behavior of an elastic bar. In the process numerical simulations have been performed concerning a well-known FSI benchmark geometry. In contrast to past investigations a non-Newtonian liquid of the Carreau-Yasuda type is used as fluid component. In order to accomplish the coupling between the liquid and the solid domain, an approach using quasi-Newton iterations is applied. In a parameter study material and geometrical parameters are changed. The solutions show distinct deviations compared to results obtained with a Newtonian liquid. These differences emphasize the nonlinearity of the shear thinning material model. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wavelength Tuning of Double-Cavity Micromachined Filter with Electrical and Thermal Actuations

We demonstrate double-cavity micromachined tunable filters with electrical actuations for both blue and red wavelength tuning. Electrical actuations for both shifts can be achieved by combining electrostatic and electro-thermal actuations below and above the breakdown voltage of p-n junctions in the micromachined cantilevers. The measured tuning range with the actuation is 8 nm for both tuning sides and the micromachined filter with a cantilever length of 80 μm exhibits a switching time of less than 115 μs for both turn-on and turn-off states. We also present the theoretical and measured temperature dependence of fabricated micromachined filters at various cantilever lengths, which experimentally gives us a temperature dependence of 0.14 nm/K for a cantilever length of 100 μm.     

Size Reduction of Tunable Micromachined Filters for High Speed Operations

The size reduction of tunable micromachined filters is carried out for high-speed wavelength tuning. We fabricated micromachined filters having a miniature structure with an air gap of 300 nm and a short cantilever of 45 μm, exhibiting fast response of below 3 μs.     

Numerical Investigation of the Free-Surface Flow within an Annulus

This study describes the free-surface flow of a highly viscous liquid between two concentric cylinders. In the process the morphology of the phase boundary is determined using a straight volume of fluid approach. Due to large differences in viscosity the gaseous phase is considered as vacuum. The numerical results of free-surface flow measures are compared to previous calculations and experimental values. The investigation shows that the used two-phase method is well-suited to predict the location and shape of the interface. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A microcrack-based continuum damage model with application towards refractories

The present work discusses numerical results of damage evolution due to thermoshock processes at refractory ceramics. Damage patterns have been generated using a two-scale approach for brittle materials, implemented into a finite element framework. For this purpose, a cell model has been employed, incorporating cracks on a microscopic level. The impact of these discontinuities on macroscopic material properties and damage evolution is determined with the help of analytical homogenization techniques. Finally, the potential of the numerical tool is demonstrated by means of refractory bricks, being imposed by thermomechanical loading. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)