关键词： wind turbine   dynamic modeling   grey-box parameter identification   subspace identification   recursive least squares   optimal identification  

摘要： With increasing size and flexibility of modern grid-connected wind turbines, advanced control algorithms are urgently needed, especially for multi-degree-of-freedom control of blade pitches and sizable rotor. However, complex dynamics of wind turbines are difficult to be modeled in a simplified state-space form for advanced control design considering stability. In this paper, grey-box parameter identification of critical mechanical models is systematically studied without excitation experiment, and applicabilities of different methods are compared from views of control design. Firstly, through mechanism analysis, the Hammerstein structure is adopted for mechanical-side modeling of wind turbines. Under closed-loop control across the whole wind speed range, structural identifiability of the drive-train model is analyzed in qualitation. Then, mutual information calculation among identified variables is used to quantitatively reveal the relationship between identification accuracy and variables' relevance. Then, the methods such as subspace identification, recursive least square identification and optimal identification are compared for a two-mass model and tower model. At last, through the high-fidelity simulation demo of a 2 MW wind turbine in the GH Bladed software, multivariable datasets are produced for studying. The results show that the Hammerstein structure is effective for simplify the modeling process where closed-loop identification of a two-mass model without excitation experiment is feasible. Meanwhile, it is found that variables' relevance has obvious influence on identification accuracy where mutual information is a good indicator. Higher mutual information often yields better accuracy. Additionally, three identification methods have diverse performance levels, showing their application potentials for different control design algorithms. In contrast, grey-box optimal parameter identification is the most promising for advanced control design considering st

关键词： nano-SiO2   poly (urea-formaldehyde)   molecular dynamics simulation   mechanical properties   hydrogen bonds  

摘要： Self-healing materials can promote the sustainable reuse of resources. Poly (urea-formaldehyde) (PUF) microcapsules can be incorporated into dielectric materials for self-healing. However, the mechanical properties of PUF microcapsules need to be improved due to insufficient hardness. In this paper, PUF models incorporated with nano-SiO2 of different filler concentrations (0, 2.6, 3.7, 5.3, 6.7, 7.9 wt.%) were designed. The density, the fractional free volume, and the mechanical properties of the PUF-SiO2 models were analyzed at an atomic level based on molecular dynamics simulation. The interfacial interaction model of PUF on the SiO2 surface was also constructed to further investigate the interaction mechanisms. The results showed that the incorporation of nano-SiO2 had a significant effect on the mechanical properties of PUF. Density increased, fractional free volume decreased, and mechanical properties of the PUF materials were gradually enhanced with the increase of nano-SiO2 concentration. This trend was also confirmed by experimental tests. By analyzing the internal mechanism of the PUF-SiO2 interfacial interaction, it was found that hydrogen bonds play a major role in the interaction between PUF and nano-SiO2. Moreover, hydrogen bonds can be formed between the polar atoms of the PUF chain and the hydroxyl groups (-OH) as well as O atoms on the surface of SiO2. Hydrogen bonds interactions are involved in adsorption of PUF chains on the SiO2 surface, reducing the distance between PUF chains and making the system denser, thus enhancing the mechanical properties of PUF materials.

关键词： interleukin 15   IL-15 interfaces   molecular dynamics simulations   protein protein interactions  

摘要： Interleukin 15 (IL-15), a four-helix bundle cytokine, is involved in a plethora of different cellular functions and, particularly, plays a key role in the development and activation of immune responses. IL-15 forms receptor complexes by binding with IL-2R beta- and common gamma (gamma c)-signaling subunits, which are shared with other members of the cytokines family (IL-2 for IL-2R beta- and all other gamma c- cytokines for gamma c). The specificity of IL-15 is brought by the non-signaling alpha-subunit, IL-15R alpha. Here we present the results of molecular dynamics simulations carried out on four relevant forms of IL-15: its monomer, IL-15 interacting individually with IL-15R alpha (IL-15/IL-15R alpha), with IL-2R beta/gamma c subunits (IL-15/IL-2R beta/gamma c) or with its three receptors simultaneously (IL-15/IL-15R alpha/IL-2R beta/gamma c). Through the analyses of the various trajectories, new insights on the structural features of the interfaces are highlighted, according to the considered form. The comparison of the results with the experimental data, available from X-ray crystallography, allows, in particular, the rationalization of the importance of IL-15 key residues (e.g., Asp8, Lys10, Glu64). Furthermore, the pivotal role of water molecules in the stabilization of the various protein-protein interfaces and their H-bonds networks are underlined for each of the considered complexes.

关键词： Evolutionary biomechanics   many-to-one mapping   trait evolution  

摘要： Animals use a diverse array of motion to feed, escape predators, and reproduce. Linking morphology, performance, and fitness is a foundational paradigm in organismal biology and evolution. Yet, the influence of mechanical relationships on evolutionary diversity remains unresolved. Here, I focus on the many-to-one mapping of form to function, a widespread, emergent property of many mechanical systems in nature, and discuss how mechanical redundancy influences the tempo and mode of phenotypic evolution. By supplying many possible morphological pathways for functional adaptation, many-to-one mapping can release morphology from selection on performance. Consequently, many-to-one mapping decouples morphological and functional diversification. In fish, for example, parallel morphological evolution is weaker for traits that contribute to mechanically redundant motions, like suction feeding performance, than for systems with one-to-one form-function relationships, like lower jaw lever ratios. As mechanical complexity increases, historical factors play a stronger role in shaping evolutionary trajectories. Many-to-one mapping, however, does not always result in equal freedom of morphological evolution. The kinematics of complex systems can often be reduced to variation in a few traits of high mechanical effect. In various different four-bar linkage systems, for example, mechanical output (kinematic transmission) is highly sensitive to size variation in one or two links, and insensitive to variation in the others. In four-bar linkage systems, faster rates of evolution are biased to traits of high mechanical effect. Mechanical sensitivity also results in stronger parallel evolution-evolutionary transitions in mechanical output are coupled with transition in linkages of high mechanical effect. In other words, the evolutionary dynamics of complex systems can actually approximate that of simpler, one-to-one systems when mechanical sensitivity is strong. When examined in a macroevo

关键词： Difficult-to-cut materials   H-SEAM   Water-based dielectric   Material removal rate  

摘要： A sustainable and advanced manufacturing method named high-speed electric arc milling (H-SEAM) was presented in this research to solve the problems where of environmental pollution and low machining efficiency for difficult-to-cut materials in the traditional electrical discharge machining (EDM)EDM process. This method can achieve high material removal efficiency with arc breaking via a coupling of mechanical and hydrodynamic forces in H-SEAM. Firstly, the material removal mechanisms of H-SEAM and theoretical arc breaking conditions are analysed. Then, comparative experiments on machining titanium alloy Ti6Al4V by different arc breaking methods are conducted to study the material removal rate (MRR), tool electrode wear rate, and machined surface quality of the workpiece. Our experiment results showed that the MRR can reach 780 mm(3)/min when using a mechanical-hydrodynamic coupling method to break arcs, which is almost five times and nearly twice that when using independent mechanical or hydrodynamic methods to break arcs. Moreover, experimental results showed the machined grooves via mechanical-hydrodynamic coupling forces to break arcs in H-SEAM exhibited higher dimensional accuracy, lower tool electrode wear, lower surface roughness, thinner recast layers, and smaller heat-affected areas than those in arc breaking by independent mechanical or hydrodynamic methods. This can be attributed to the higher removal efficiency of molten metal material and the uniform distribution of energy when using mechanical-hydrodynamic coupling forces to break arcs.

关键词： Silicon carbide  

摘要： Bulk ultrafine-grained (UFG) AA6063/4wt pct SiC composites with varying reinforcement sizes [12 mu m (coarse), 1 mu m (fine), and 45 nm (nano)] have been developed by a hybrid route of stir-casting and cryorolling. In the current study, the influence of annealing temperatures (423K to 573K) on the precipitation evolution, particle-stimulated nucleation (PSN), recrystallization, grain growth kinetics, and thermal stability of developed bulk UFG composites have been studied, and the resultant effect of microstructural evolution is correlated with mechanical properties. UFG coarse and UFG fine composites have shown evidence of recrystallized grains via PSN and retained their UFG microstructure up to 473K and 523K, respectively. Superior microstructural stability with retained UFG microstructure up to 573K was observed in the UFG nanocomposite due to the effective pinning of nano-SiC particles and precipitates along grain boundaries. This ultimately resulted in the increased grain growth activation energy and strength of the UFG nanocomposite. However, the overall increase in strength is maximum in the UFG nanocomposite due to the dominant effect of dislocation strengthening, grain boundary strengthening, and precipitation strengthening mechanisms. A thorough examination of the microstructural evolution of UFG composites at different annealing temperatures along with their mechanical behavior is presented in this paper.

关键词： Methionine   assemblies   Gene Expression Regulation   Mutation   Dehydrogenases   Flexibility   nuclear factor   Lysine   dynamic structural analysis  

摘要： NPAC is a cytokine-like nuclear factor involved in chromatin modification and regulation of gene expression. In humans, the C-terminal domain of NPAC has the conserved structure of the beta-hydroxyacid dehydrogenases (beta-HAD) protein superfamily, which forms a stable tetrameric core scaffold for demethylase enzymes and organizes multiple sites for chromatin interactions. In spite of the close structural resemblance to other beta-HAD family members, the human NPAC dehydrogenase domain lacks a highly conserved catalytic lysine, substituted by a methionine. The reintroduction of the catalytic lysine by M437 K mutation results in a significant decrease of stability of the tetramer. Here, we have computationally investigated the molecular determinants of the functional differences between methionine and lysine-containing NPAC proteins. We find that the single mutation can determine strong consequences in terms of dynamics, stability, and ultimately ability to assemble in supramolecular complexes: the higher stability and lower flexibility of the methionine variant structurally preorganizes the monomer for tetramerization, whereas lysine increases flexibility and favors conformations that, while catalytically active, are not optimal for tetrameric assembly. We combine structure-dynamics analysis to an evolutionary study of NPAC sequences, showing that the methionine mutation occurs in a specifically flexible region of the lysine-containing protein, flanked by two domains that concentrate most of the stabilizing interactions. In our model, such separation of stability nuclei and flexible regions appears to favor the functional innovability of the protein.

关键词： Polymer mechanics   Force-extension   Finite-element   Brownian dynamics   Bayesian framework  

摘要： The micromechanical behavior of single polymer chains determines the macroscopic mechanics of a large number of synthetic and biological materials. An important tool for the study of polymers are Brownian dynamics simulations, classically based on bead-rod models. In a recent work by Cyron and Wall (2009), an advantageous approach in the finite-element framework was presented, where Brownian polymer dynamics have been described by a white noise driven stochastic partial differential equation (SPDE). In the present contribution, the SPDE is solved using a geometrically-exact Kirchhoff-Love beam element and a piecewise constant white noise approximation in time and space. The resulting numerical method is used to obtain mean force-extension data, to set up a surrogate model based on a Gaussian process, and to identify parameters through a fit to experimental data in a Bayesian framework. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Molecular dynamics   Al2O3   Phase transition   Fcc   Hcp   Deformation  

摘要： Molecular dynamics simulations of Al2O3 model have been carried out to study the structural evolution of Al2O3 model under the cooling process and the high-pressure of 45 GPa. The phase transition occurs in the temperature range of 2530 K down to 2280 K. Not only almost AlO4 and AlO5 units transform to AlO6 units but also almost OAl3 linkages transform to OAl4 linkages below the temperature of 2280 K. Both hcp and fcc oxygen clusters are detected during the cooling process. The formations of hcp and fcc oxygen clusters in Al2O3 model is in accordance to Ostwald's rule of stages. Firstly, both the gamma- and kappa-Al2O3 are formed at high temperature. Then, the gamma-Al2O3 transforms to the delta-Al2O3 and the kappa-Al2O3 transforms to the alpha-Al2O3 with decreasing temperate to 300 K. The mechanical behavior of Al2O3 model at 300 K, consisting of dominant alpha-Al2O3 and minor delta-Al2O3, has been investigated by the uniaxial tension test. Young modulus of this Al2O3 model is 396 GPa. That the hcp and fcc oxygen clusters are maintained at the large strain, at which these dusters are embedded by the poly-cluster of disordered atoms, indicates the plastic deformation in this Al2O3 model is inhomogeneous.

关键词： Batteries - Lithium   Energy Storage   composite cathode   interface   molecular dynamics  

摘要： The study explores the use of a composite, graphitic carbon (GC) - sulfur (S) based cathode in laminated structural batteries. Specifically, failure by delamination is studied with regards to the applicability of a double-walled tube architecture obtained by coating the inner surfaces of hollow carbon nanofibers with sulfur. Differences between the material responses of various Li-X S (X is an element of (0, 2)) compounds under bulk-like and interface confined conditions are discussed in terms of the shear response of physically and chemically bonded interfaces, formed with non-functionalized and H/OH/O-functionalized GC surfaces. The study indicates that only a chemically bonded interface with non-functionalized GC yields bulk-compatible mechanical behavior, with the exception of concentrations of X is an element of (0.8, 1.1). To strengthen the interface at low Li concentrations, at which a pronounced inhomogeneity in mass density in terms of interface debonding occurs, a modified transition layer was tested. The results indicate a distinct improvement in terms of homogeneity of mass density and plastic strain localization. The effect of delithiation at high rates on the interface structural stability is investigated at different concentrations of Li in structures of initially uniform Li distribution. According to the results, delamination failure is likely to occur. (C) 2019 The Electrochemical Society.