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An assessment of the elastic-plastic buckling limit state for multi-strake wind turbine support towers poses a particular challenge for the modern finite element analyst, who must competently navigate numerous modelling choices related to the tug-of-war between meshing and computational cost, the use of solvers that are robust to highly nonlinear behaviour, the potential for multiple near-simultaneously critical failure locations, the complex issue of imperfection sensitivity and finally the interpretation of the data into a safe and economic design.
This paper reports on an international ‘round-robin’ exercise conducted in 2022 aiming to take stock of the computational shell buckling expertise around the world which attracted 29 submissions. Participants were asked to perform analyses of increasing complexity on a standardised benchmark of an 8-MW multi-strake steel wind turbine support tower segment, from a linear elastic stress analysis to a linear bifurcation analysis to a geometrically and materially nonlinear buckling analysis with imperfections. The results are a showcase of the significant shell buckling expertise now available in both industry and academia.
This paper is the first of a pair. The second paper presents a detailed reference solution to the benchmark, including an illustration of the Eurocode-compliant calibration of two important imperfection forms.
Poly(butadiene)-b-poly(ethylene oxide) vesicles were successfully loaded with hydrophilic dye Phloxine B. Dye addition during vesicle formation leads to Phloxine B encapsulated inside the water filled vesicle core as well as to freely diffusing dye molecules. The removal of uncapsulated substrate involves time consuming methods like dialysis or harsher methods like ultra filtration or selective precipitation, posing the risk of irreversible sample manipulation. Here used Phloxine B as pH sensitive fluorescence indicator allows the characterization of hydrophilic loading without separation procedure by adjusting the pH value. Additionally membrane blocking efficiency can be studied by time dependent fluorescence measurements. Cryogenic TEM studies showed that the self-assembled structure remained unchanged when the hydrophilic dye was incorporated within the vesicles. Fluorescence microscopy imaging proved the encapsulation of the hydrophilic dye inside the core volume. The combination of fluorescence correlation spectroscopy (FCS) and dynamic light scattering (DLS) measurements as ensemble methods confirmed those results additionally.
Electrical and optical applications based on micro- and nanoparticles have specific demands on their interfacial properties. These properties are strongly related to atmospheric conditions to which the particles were exposed during their formation. In this study, metallic In microparticles are synthesized by solidification of In droplets on an amorphous Mo substrate at normal pressure and under vacuum conditions. The influence of ambient pressure on the interface and surface shape is investigated. While solidification at atmospheric pressure leads to collapsed particles with undisturbed contact to the substrate, low pressures result in smooth spherical particles but with cavities inside. Numerical simulations with COMSOL Multiphysics reveal different temperature profiles and heat flux in particles during solidification for both cases. This indicates different starting conditions of the solidification, which leads to the described phenomenon eventually. The investigation of the varying process conditions on the particle shape in combination with the calculated and measured temperature curves over time gives valuable insights into new approaches to synthesize micro- and nanoparticles with defined interfacial properties. Both ambient pressure and cooling rate provide well-controllable and reliable parameters for the realization of different interfacial shapes.
The synthesis of the polymorphic cocrystal caffeine:anthranilic acid was investigated to obtain a better understanding of the processes leading to the formation of different polymorphic forms. In the case of these cocrystal polymorphs synthesized by liquid-assisted grinding a distinct influence of the dipole moment of the solvent was found. A pre-coordination between the solvent molecules and the caffeine:anthranilic acid cocrystal could be identified in the formation of form II. In the case of form II the solvent can be regarded as a catalyst. The formation pathway of each polymorph was evaluated using synchrotron X-ray diffraction.
Mechanochemical reactions often result in 100% yields of single products, making purifying procedures obsolete. Mechanochemistry is also a sustainable and eco-friendly method. The ever increasing interest in this method is contrasted by a lack in mechanistic understanding of the mechanochemical reactivity and selectivity. Recent in situ investigations provided direct insight into formation pathways. However, the currently available theories do not predict temperature T as an influential factor. Here, we report the first determination of an apparent activation energy for a mechanochemical reaction. In a temperaturedependent in situ study the cocrystallisation of ibuprofen and nicotinamide was investigated as a model system. These experiments provide a pivotal step towards a comprehensive understanding of milling reaction mechanisms.
The stability of different theophylline cocrystals under milling conditions was investigated by competitive cocrystal reactions. To determine the most stable cocrystal form under milling conditions, the active pharmaceutical ingredient theophylline was either ground with two similar coformers (benzoic acid, benzamide, or isonicotinamide), or the existing theophylline cocrystals were ground together with a competitive coformer. All competitive reactions were investigated by in situ powder X-ray diffraction disclosing the formation pathway of the milling processes. On the basis of these milling reactions, a stability order (least to most stable) was derived: tp/bs < tp/ba < tp/ina < bs/ina.
The driving forces triggering the formation of co-crystals under milling conditions were investigated by using a set of multicomponent competitive milling reactions. In these reactions, different active pharmaceutical ingredients were ground together with a further compound acting as coformer. The study was based on new co-crystals including the coformer anthranilic acid. The results of the competitive milling reactions indicate that the formation of co-crystals driven by intermolecular recognition are influenced and inhibited by kinetic aspects including the formation of intermediates and the stability of the reactants.
Benzamide has been known for its polymorphism for almost 200 years.Three polymorphic forms are described. To date,itwas only possible to crystallizeametastable form in amixture together with the thermodynamically most stable form I. Acomplete transformation of form Iinto the metastable form III by mechanochemical treatment has been achieved. Catalytic amounts of nicotinamide seeds were used to activate the conversion by mechanochemical seeding. NMR experiments indicated that the nicotinamide molecules were incorporated statistically in the crystal lattice of benzamide form III during the conversion. The transformation pathway was evaluated using in situ powder X-ray diffraction.
Proline has been widely used for various cocrystallization applications, including pharmaceutical cocrystals. Combining enantiopure and racemic flurbiprofen and proline, we discovered 18 new crystal structures. Liquid-assisted grinding proved highly efficient to explore all the variety of crystal forms. A unique combination of stateof-the-art characterization techniques, comprising variable temperature in situ X-ray diffraction and in situ ball-milling, along with other physicochemical methods and density functional theory calculations, was indispensable for identifying all the phases. Analyzing the results of in situ ball-milling, we established a stepwise mechanism for the formation of several 1:1 cocrystals via an intermediate 2:1 phase. The nature of the solvent in liquidassisted grinding was found to significantly affect the reaction rate and, in some cases, the reaction pathway.