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Study of Dynamics in Metallic MEMS Cantilevers - Pull-In Voltage and Actuation Speed
(2023-01-13)
For different metals and varying geometries, this paper presents simulations of electrostatically actuated MEMS cantilevers regarding their influence on pull-in voltage and actuation speed. Three-dimensional electromechanical modeling including many non-linearities has been performed to study some static but mainly dynamic features. The results show that the involved parameters have different influences on the actuation speed and pull-in voltage: lower length, higher thickness as well as lower density and higher ...
Aufsatz
A monolithic approach toward coupled electrodynamic–thermomechanical problems with regard to weak formulations
(2021-11-11)
Weak formulations of boundary value problems are the basis of various numerical discretization schemes. They are classically derived applying the method of weighted residuals or a variational principle. For electrodynamical and caloric problems, variational approaches are not straightforwardly obtained from physical principles like in mechanics. Weak formulations of Maxwell’s equations and of energy or charge balances thus are frequently derived from the method of weighted residuals or tailored variational approaches. ...
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Potential of Fe-Mn-Al-Ni Shape Memory Alloys for Internal Prestressing of Ultra-High Performance Concrete
(2023-05-18)
Prestressing of concrete is a commonly used technique in civil engineering to achieve long spans, reduced structural thicknesses, and resource savings. However, in terms of application, complex tensioning devices are necessary, and prestress losses due to shrinkage and creep of the concrete are unfavourable in terms of sustainability. In this work, a prestressing method using novel Fe-Mn-Al-Ni shape memory alloy rebars as a tensioning system in UHPC is investigated. A generated stress of about 130 MPa was measured ...
Aufsatz
Flexible Electrochromic Device on Polycarbonate Substrate with PEDOT:PSS and Color-Neutral TiO2 as Ion Storage Layer
(2023-04-22)
Electrochromic (EC) windows on glass for thermal and glare protection in buildings, often referred to as smart (dimmable) windows, are commercially available, along with rearview mirrors or windows in aircraft cabins. Plastic-based applications, such as ski goggles, visors and car windows, that require lightweight, three-dimensional (3D) geometry and high-throughput manufacturing are still under development. To produce such EC devices (ECDs), a flexible EC film could be integrated into a back injection molding process, ...
Aufsatz
Structural and superelastic properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on industrial process routes by hot rolling
(2023-05-02)
In the present study the structural and functional properties of Fe–Mn–Al–Ni shape memory alloy sheets produced on an industrial process route focusing on hot rolling were investigated. The as-processed condition is characterized by a high fraction of the non-transforming γ-phase, which ensures good workability, but is associated with poor superelasticity. The alloy shows good structural properties with a yield strength of about 600 MPa, which is well above the usual transformation stress related to the martensitic ...
Aufsatz
Measurement and analysis of residual stresses and warpage in fiber reinforced plastic and hybrid components
(2021-02-16)
Glass/carbon fiber reinforced plastic (GFRP/CFRP) and hybrid components have attracted increasing attention in lightweight applications. However, residual stresses induced in the manufacturing process of these components can result in warpage and, eventually, negatively affect the mechanical performance of the composite structures. In the present work, GFRP, CFRP, GFRP/steel and CFRP/steel hybrid components were manufactured through the prepreg-press-technology always employing the same process parameters. The residual ...
Aufsatz
Multi-Task Autoencoders and Transfer Learning for Day-Ahead Wind and Photovoltaic Power Forecasts
(2022-10-30)
Integrating new renewable energy resources requires robust and reliable forecasts to ensure a stable electrical grid and avoid blackouts. Sophisticated representation learning techniques, such as autoencoders, play an essential role, as they allow for the extraction of latent features to forecast the expected generated wind and photovoltaic power for the next seconds up to days. Thereby, autoencoders reduce the required training time and the time spent in manual feature engineering and often improve the forecast ...
Aufsatz
New Distributed Optimization Method for TSO-DSO Coordinated Grid Operation Preserving Power System Operator Sovereignity
(2023-06-16)
Electrical power system operators (SOs) are free to realize grid operations according to their own strategies. However, because resulting power flows also depend on the actions of neighboring SOs, appropriate coordination is needed to improve the resulting system states from an overall perspective and from an individual SO perspective. In this paper, a new method is presented that preserves the data integrity of the SOs and their independent operation of their grids. This method is compared with a non-coordinated ...
Aufsatz
Probabilistic upscaling and aggregation of wind power forecasts
(2020-03-16)
Background
Wind power forecasts of the expected wind feed-in for the next hours or days are necessary to integrate the generated volatile wind energy into power systems. Most forecasting models predict in some sense the best value, but they ignore the other possible outcomes which may arise because of forecasting uncertainties. Probabilistic forecasts, on the other hand, also predict a distribution of possible outcomes with their respective probabilities that specific power values will occur and therefore have higher ...
Aufsatz
Metastable CrMnNi steels processed by laser powder bed fusion: experimental assessment of elementary mechanisms contributing to microstructure, properties and residual stress
(2022-12-18)
The complex thermal history imposed by the laser-based powder bed fusion of metals (PBF-LB/M) process is known to promote the evolution of unique microstructures. In the present study, metastable CrMnNi steels with different nickel contents and, thus, different phase stabilities are manufactured by PBF-LB/M. Results clearly reveal that an adequate choice of materials will allow to tailor mechanical properties as well as residual stress states in the as-built material to eventually redundantize any thermal post-treatment. ...