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101.
Beam structures undergoing finite deflections and rotations in space have extensive application in the subsea industry particularly for the analysis of holistic systems with larger numbers of mooring and riser components. In using the finite element analysis approach, there is an increasing requirement for large element sizes which preserve accuracy with regard to the coupling of axial, bending and torsion response.The authors outline a method for improving the current state of practice for the analysis of riser systems. The approach draws on the convected coordinates method, Euler–Bernoulli beam theory, the principle of virtual work and the finite element method. Two quasi-rotation measures are developed including a quasi-material rotation definition for rotational deformation relative to the convected axis of a beam and a quasi-space rotation definition to deal with the path dependent nature of rotations in three dimensions.The novel aspect of this work is to relate the rate of change of the quasi-material rotation vector along the beam axis to a linear transformation of the beam axis rate-of-rotation vector through utilising the convected coordinates axes system. In this way, incremental values of quasi-material rotation are directly linked to incremental values of nodal quasi-space rotation and a global Newton–Raphson solution technique for interconnecting beam elements is straightforward to assemble.Furthermore, this leads to accurate definitions of coupled axial, bending and torque response for beams with significant deflection. The approach has particular advantages in the analysis of subsea riser sections. Also, the accuracy of the solution is preserved for a fewer number of elements compared to alternative solutions for computationally sensitive load cases with highly non-linear loading regimes. 相似文献
102.
Hesam Makki Koen N. S. Adema Elias A. J. F. Peters Jozua Laven Leendert G. J. van der Ven Rolf A. T. M. van Benthem Gijsbertus de With 《Journal of Polymer Science.Polymer Physics》2016,54(6):659-671
In this article we studied the evolution of thermomechanical properties of a polyester‐urethane coating during degradation under different degradation conditions, i.e., aerobic and anaerobic conditions with and without dry/wet cycling during degradation. Dynamic mechanical and thermal analyses show that under aerobic conditions the coatings become stiffer and more brittle in the glassy state. This stiffening is probably due to the increase in the amount of hydrogen bonding and the formation of oxidized groups which increase the polarity of the material and enhance the interactions of the polymer segments. However, oxidation reactions result in a considerable decrease in cross‐link density and stiffness in the rubbery state. Both changes, in the glassy and rubbery states, give rise to development of internal stresses. These stresses increase as the degradation process proceeds. Nevertheless, for samples exposed to anaerobic conditions, the stiffness remains constant in the glassy state and the cross‐link density slightly increases as a result of degradation. This reconfirms the dominance of the effect of oxidation reactions on the mechanical failure of the coatings. Oxygen permeation measurements show a more‐or‐less time‐independent diffusion coefficient and a gradual decrease in solubility of oxygen as a function of exposure time. This results in a slight decrease in oxygen permeation (mainly in the early stage of the degradation) as degradation proceeds. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 659–671 相似文献
103.
Natasha Samko 《Mathematical Methods in the Applied Sciences》2020,43(16):9416-9434
We find conditions for the boundedness of integral operators commuting with dilations and rotations in a local generalized Morrey space. We also show that under the same conditions, these operators preserve the subspace of such Morrey space, known as vanishing Morrey space. We also give necessary conditions for the boundedness when the kernel is non-negative. In the case of classical Morrey spaces, the obtained sufficient and necessary conditions coincide with each other. In the one-dimensional case, we also obtain similar results for global Morrey spaces. In the case of radial kernels, we also obtain stronger estimates of via spherical means of . We demonstrate the efficiency of the obtained conditions for a variety of examples such as weighted Hardy operators, weighted Hilbert operator, their multidimensional versions, and others. 相似文献
104.
105.
A novel inorganic-organic hybrid supramolecular compound,[(3-nitroanilinium~+)(18-crown-6)][IO_4](CH_3OH)(1),was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH_3OH,whereas the space grouping of the crystal remains unchanged. 相似文献
106.
107.
In this paper, we introduced a method to measure grain rotation of nanomaterials under external stress using a high pressure diamond anvil cell and the Laue microdiffraction technique at a synchrotron facility. We used tungsten carbide marker crystals to investigate grain rotation activities of 3 and 500?nm nickel media. Our results show that the grain rotation of 3 and 500?nm nickel nanocrystals increase with pressure and finally rotation of 500?nm nickel tends to stop at a lower pressure/stress level than 3?nm nickel. 3?nm nickel nanocrystals show a higher rotation magnitude than 500?nm nickel nanocrystals. Our measurements show an effective method to study the grain rotation of nanomaterials especially in ultrafine nanocrystals. 相似文献
108.
Nobumasa Kamigata 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):667-678
Abstract The synthesis and stereochemistry of tricoordinated optically active selenium and tellurium compounds are described. Telluronium salts, telluronium imides, and seleninic acids were prepared and optically resolved by fractional recrystallization of diastereomeric mixtures or by chromatography using a chiral column of racemic mixtures. Diphenyl dichalcogenides also were optically resolved by chiral crystallization. Their absolute configurations were determined or estimated based on X-ray crystallographic analysis, specific rotations, and circular dichroism spectra. The kinetic studies and the mechanism for the racemization were also studied. 相似文献
109.
Xiao-Bo Ma Jing-Lin Zhang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):233-237
Abstract 1,3,2-Diazaphosphetidin-4-one derivatives were synthesized. Their 1H NMR signals at ambient temperature displaed a broad doublet which eventually coalesced before becoming sharp upon warming, and the 13C NMR spectra also showed that the α-and β-carbons of the dialkylamino group were non-equivalent. The phenomena were ascribed to restricted rotation about the exocyclic P—N bond. 相似文献
110.
Conjugated polymers (CPs) have long been recognized as an important class of materials. The highly conjugated backbone of the CPs will facilitate the rapid exciton migration and result in amplification of fluorescence signals. However, CPs are likely to aggregate and form excimers in solid states, directly leading to the fluorescence quenching, namely aggregation-caused quenching (ACQ), hence inhibiting their prospective utilizations in a large degree. Since the effect of aggregation-induced emission (AIE) is opposite to that of notorious ACQ, the AIE has raised great attention from scientists. CPs with AIE or aggregation-enhanced emission (AEE) features may help to solve the ACQ problem and meanwhile impart polymers with new properties and practical applications. In this review, we summarize the recent progress on the preparation of CPs with AIE or AEE characteristics, where AIE-active luminogens are located at polymer backbones or pendants. Their potential applications including fluorescent sensors, biological probes, and active layers for the fabrication of light-emitting diodes are also described. 相似文献