149544 research outputs found
Sort by
Complete CASSE acceleration data measured upon landing of Philae on comet 67P at Agilkia
No full textOn November 12th, 2014, the Rosetta lander Philae touched down at the site Agilkia on comet 67P. Here, we report unpublished data of the Comet Acoustic Surface Sounding Experiment (CASSE) which belonged to the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME). The CASSE signals were measured by the accelerometers built-in in the landing feet of Philae. Whereas the acceleration data in the direction perpendicular to the comet surface have been published earlier, the acceleration data measured parallel to the comet surface have been archived until now only on a server of the ESA Planetary Science Archive, and were not further evaluated. However, analyzing the acceleration data with the short-time Fourier-transform allows one to discern the time-sequence of the touch-down of the lander feet at the site Agilkia corroborating an earlier study by another group based on finite element calculations. In our analysis, the contact-resonances of the foot soles are exploited as a sign for surface contact. Because the acceleration data represent structure-borne sound in the foot soles in the audio range, they can be made audible in audio files which are attached to this publication
Optimizing Wind Turbine Load Reduction: Trade-offs Including Blade Angle Deviation in PID Individual Pitch Control and MPC Collective Pitch Control
Get PDFThis study investigates trade-offs in Individual Pitch Control (IPC) for wind turbines by optimizing proportional-integral-derivative (PID) controllers, introducing blade pitch angle deviation as a performance objective that has received little attention so far. Smaller deviation angles reduce IPC-induced actuator duty cycles and lower the risk of unintended increases in out-of-plane root moments caused by load sensor inaccuracies. Another drawback of larger blade deviations is that, during emergency shutdowns, blades can stop at different pitch angles, potentially causing temporary asymmetric aerodynamic braking forces and higher transient loads than collective pitch control. While often disregarded in proof-of-concept studies, keeping blade deviation within acceptable limits is crucial for implementing IPC in production. By quantifying blade deviations alongside damage equivalent loads (DEL), power output, and actuator energy, this study provides a comprehensive IPC assessment. Results reveal a trade-off between DEL reduction and blade deviation in IPC-PID controllers. Additionally, a comparison with Model Predictive Control (MPC)-based Collective Pitch Control (CPC) highlights that incorporating wind information and advanced algorithms can improve this trade-off by shifting the Pareto front
Parabolic Troughs in Process and District Heating
No full textA mix of different renewable energy technologies combined with efficiency measures is needed to ensure a secure, climate-friendly and cost-efficient heat supply in Germany. All scenarios for the future energy mix show a strong increase in the use of heat pumps, (deep) geothermal energy and solar thermal energy. The Pro-Sol-Netz project aims to make a significant contribution to the dissemination of knowledge about the many possible applications of concentrating solar thermal energy, including combined applications with other renewable energy technologies
Advancing Sulfur–Carbon Composite Production: Industrial and Lab-Scale Infiltration Techniques for Metal–Sulfur Batteries
No full textIn a metal-sulfur battery, the cathode consists of a composite material made from activated carbon and sulfur, which acts as the electrochemically active component. To fill the pores of the activated carbon with sulfur, both melt infiltration and gas infiltration techniques are employed. [1-3] However, the entire procedure, involving heating and cooling phases, is highly time- and energy-consuming. Moreover, the currently established methods allow only very small sample quantities to be processed in batch mode. The cost associated with processing larger volumes is prohibitively high, rendering these methods economically unviable.
To optimize the production of sulfur-carbon composites, infiltration techniques that increase material throughput while reducing processing time and energy consumption are essential. For this purpose, various infiltration methods have been tested and their performance thoroughly analyzed.
Sulfur is introduced into microporous carbon using different infiltration approaches based on both melt and gas infiltration. Continuous industrial-scale processes and rapid batch methods are evaluated and compared against laboratory-scale techniques.
The infiltration experiments were conducted using a carbon aerogel with a micropore volume ranging from 0.27 to 0.45 cm³/g. The findings demonstrate that the highest sulfur loadings were achieved through gas, extruder and melt infiltrations, with the sulfur predominantly present in the micropores. The composites produced with gas [4], spray-coating technique [5], and extruder infiltrations [3] exhibit good cycle stability and high discharge capacity. In contrast, open gas infiltration, microwave infiltration and solvent infiltration resulted in lower sulfur loading and inadequate performance in the cell. The results are summarized in our poster.
Depending on the specific battery requirements, the infiltration technique can be chosen between complex, non-scalable methods with outstanding performance and more economically efficient methods offering moderate performance
Development of Raney-type Electrodes for Alkaline Water Electrolysis via Atmospheric Plasma Spraying
No full textHydrogen (H2) is regarded as the most promising energy carrier for the future with the potential to substitute fossil fuels. Its flexibility as energy carrier allows it to produce electricity via direct electrochemical conversion in fuel cells and it can also be used to produce heat through combustion which can later be used to produce work. In addition, H2 can be readily used to produce other energy carriers such as synthetic fuels and it is also fundamental in key industries such as in metallurgy and ammonia production.
Even when H2 has been used industrially for decades, its current demand is met mainly through processing routes based on fossil fuels. For this reason, the development of cleaner and cost-effective routes for H2 production is one of the utmost active R&D topics around the world. The most promising of such routes is water electrolysis (WE).
Within WE itself, different techniques have emerged, such as proton-exchange membrane water electrolysis (PEMWE), anion-exchange membrane water electrolysis (AEMWE), and alkaline water electrolysis (AWE). Among them, AWE exhibits higher potential for wide industrial deployment in short- to medium-term due to its maturity level and cost-effectiveness compared to AEMWE and PEMWE. However, more research is required to develop materials and processing methods to achieve higher durability and performance along with cost reductions. One strategy is the development of plasma spraying process for the fabrication of electrodes for AWE. Plasma spraying under atmospheric conditions (APS) has proven to be a low-cost, flexible technique suitable for the fabrication of Raney-type electrodes for AWE [1]. Its scalability capabilities also make it a great option for full research developments starting from lab-sized specimens, to full scale industrial electrodes.
In this work, the development of AlNiMo Raney-type electrodes for the hydrogen evolution reaction (HER) in AWE produced via APS is presented.
Electrodes are optimized through the control of different processing parameters and characteristics in order to reach the specific overpotential (oV) target of 75 mV at 0.5 A/cm2.
For this, a first rough processing parameter window is sought to stablish a base line for next improvements. As shown in panel a) of figure 1, a reduction from 136 to 100 mV is reached through this rough approximation.
Further studies include the effect of particle size distribution, where it was observed that the interlamellar porosity is an important feature of the performance of produced electrodes. Through the analysis of particle size distribution an oV value of 74 mV was obtained, thus fulfilling the initial target. Additional studies regarding the substrate type, the development of catalyst powders and the use of other special powder feedstock, allowed additional reductions to up to an oV value of -63 mV at 0.5 A/cm2, as depicted in panel b).
Results demonstrate the feasibility of developing and optimizing electrodes for the HER in AWE via APS to values which are attractive for commercialization. Also, the observations made during this research, lead the way to future developments for these and other components used in WE
Design Of A Morphing Winglet Trailing Edge With Fluid Actuation : Design Process And Experimental Results
No full textIntegrating active control surface technology into aircraft wings with confined spaces is challenging. It would be beneficially to do so to enable more efficient wing designs fore.g. load alleviation. This paper details a winglet trailing edge surface composed of fluid actuated morphing unit structures (FAMoUS) that enable control surface deflections under the corresponding aerodynamic hinge moments. The design of the FAMoUS actuators is comprised of elastomer and metallic stiffeners, which under internal pressure from a fluid exert displacement and force and thus output work. Combining these unit structures in a bimorph setup a trailing edge control surface is build, which is structural and actuating part at the same time.
The structural dimensioning of a demonstrator with 1 m span-width is shown, based on a finite element analyses consisting of detailed tuned material parameters obtained from testing on the individual unit structure tests as well as the inclusion of hydrostatic fluid elements to determine effective stiffnesses from the pressure-volume relationship between the housing structure
and internal fluid. The process of choosing a suitable actuating system including the feedback control and hydraulic systems is presented. Finally experimental results of tests are presented, starting with calibration of the feedback
system with an external measurement, also clarifying deflection uniformity along the span of the demonstrator. Deflection performance and deflection rate are discussed and compared with the predictions from the finite element analyses. The findings are discussed and contextualized. A summary of the results is given and an outlook on the way forward is presented
A Novel Method for Creating Complete, Gapless Lines From Fragmented 2D Data of Antarctic Grounding Line Measurements
Get PDFInSAR grounding line retrieval has resulted in numerous datasets that cover most of the ice shelves that fringe Antarctica. With the wealth of data the Sentinel-1 mission collects over the Antarctic grounding zone, it has become feasible to process nearly 60 grounding lines per year for some locations. While the interferometric pipelines are well established and operational, the need for manual delineation of the landward side of the dense fringe belt detected in double difference interferograms prevented the efficient processing of dense time series. Most Antarctic-wide products contain manually traced individual grounding lines at low temporal resolution and are focused on spatial completeness. However, recent advances in automatic detection with deep neural networks now offer the possibility to create long time series [Ramanath Tarekere et al. 2024].
Neither manually nor automatically delineated grounding lines are complete, as they often contain gaps due to variations in interferometric coherence, tidal states, and the generally intricate geometry of the grounding line. Furthermore, these limitations result in a time series of fragmented 2D line segments that cannot be directly used to trace the perimeter of an entire ice shelf or even form a single circum-Antarctic grounding line. However, applications in ice shelf modelling, calculation of ice export in the mass-budget method, and retreat measurements all benefit from simple continuous grounding line geometries, which surround entire ice shelves. Currently, a widely used product that fulfills these requirements but lacks annotation and timeliness is the MEaSUREs Antarctic Boundaries dataset [Mouginot et al. 2017].
Here, we present a novel method that is able to create single gapless and complete grounding lines for individual ice shelves for targeted time periods (annual, bi-annual, monthly). The fragmented grounding lines are stacked in time to distinguish grounded from floating ice. We then apply a median threshold to detect regions grounded in at least 50% of the measurements. In order to create the gapless perimeter of an ice shelf, we prioritize grounding lines according to their acquisition time and fill the remaining gaps with measurements from other periods or other sensors. Combined with ice shelf calving front data, we can produce time-annotated ice shelf perimeter, area, and area change.
References:
Mouginot, J., Scheuchl, Bernd and Rignot, Eric (2017). MEaSUREs Antarctic Boundaries for IPY 2007-2009 from Satellite Radar. (NSIDC-0709, Version 2). Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. (Visited on 11/19/2024).
Ramanath Tarekere, S. et al. (Mar. 11, 2024). "Deep Learning Based Automatic Grounding Line Delineation in DInSAR Interferograms". In: EGUsphere, pp. 1-35. (Visited on 04/16/2024)