Influence Of Dynamic Effects Research Articles

A Tribo‐Dynamic Model of a Helical Gear Pair Based on the Finite Line Contact Theory

In this article, a finite line contact tribo‐dynamics model of helical gears is established by coupling the tooth surface friction, friction moment, and vibration velocity. To obtain convergent results, a cycle iteration strategy is adopted to solve the two submodels, the dynamic model and the thermal elastohydrodynamic lubrication model. The parameters obtained from the dynamic model such as the dynamic load, dynamic transmission error, and instantaneous speed of the teeth surfaces are used as the boundary conditions for solving the lubrication model. Meanwhile, the friction force and friction moment obtained by the lubrication model are used as parametric excitations of the dynamic model. Based on the proposed model, the influence of dynamic effect, thermal effect, rotational speed, and tooth surface roughness on the tribological and dynamic properties of helical gears are discussed. The results show that the tribological and dynamic parameters deviate significantly from the quasistatic values, especially at the characteristic speed. The vibration along the off‐line‐of‐action direction is obviously affected by the friction excitation. As the rotational speed increases, the friction coefficient and friction force decrease as well as the vibration of the gear pair along the off‐line‐of‐action direction weakens. In addition, the surface roughness has the greatest influence on the vibration of the off‐line‐of‐action direction in all directions of gear vibrations.

Dynamical effects in the integrated X-ray scattering intensity from imperfect crystals in Bragg diffraction geometry. II. Dynamical theory.

The analytical expressions for coherent and diffuse components of the integrated reflection coefficient are considered in the case of Bragg diffraction geometry for single crystals containing randomly distributed microdefects. These expressions are analyzed numerically for the cases when the instrumental integration of the diffracted X-ray intensity is performed on one, two or three dimensions in the reciprocal-lattice space. The influence of dynamical effects, i.e. primary extinction and anomalously weak and strong absorption, on the integrated intensities of X-ray scattering is investigated in relation to the crystal structure imperfections.

Non-Newtonian flow effects in supercooled water

The viscosity of supercooled water has been a subject of intense study, in particular with respect to its temperature dependence. Much less is known, however, about the influence of dynamical effects on the viscosity in its supercooled state. Here we address this issue for the first time, using molecular dynamics simulations to investigate the shear-rate dependence of the viscosity of supercooled water as described by the TIP4P/Ice model. We show the existence of a distinct cross-over from Newtonian to non-Newtonian behavior characterized by a power-law shear-thinning regime. The viscosity reduction is due to the decrease in the connectivity of the hydrogen-bond network. Moreover, the shear thinning intensifies as the degree of supercooling increases, whereas the cross-over flow rate is approximately inversely proportional to the Newtonian viscosity. These results stimulate further investigation into possible fundamental relations between these nonequilibrium effects and the quasi-static Newtonian viscosity behavior of supercooled water.

Failure of hybrid composites under longitudinal tension: Influence of dynamic effects and thermal residual stresses

A progressive failure model including dynamic effects and thermal residual stresses able to simulate the failure and damage development of hybrid unidirectional polymer composites under fibre tensile loading is presented. The model is used to study the influence dynamic effects and thermal residual stresses have on the development of clusters of fibre breaks and the failure process of different hybrid composites. The results obtained show that while the dynamic effects change cluster formation, nonetheless they do not significantly alter the final failure of the material. Overall, the influence is greater for the more brittle materials. Although the thermal residual stresses do not affect the formation of clusters, they can delay damage initiation and final failure by inducing compressive stresses into the fibres.

On the influence of dynamical effects on reactivity descriptors

In this paper, we investigate the role of structural dynamical effects on reactivity properties of selected Michael acceptors. To this aim, quantum molecular dynamics simulations were performed. Conceptual density functional theory descriptors were then evaluated on selected snapshots, providing statistical indicators suitable to assess the discrepancies between static and dynamical approaches. The implications of these results for building a predictive model correlated to Mayr’s electrophilicity index are then discussed, paving the way towards a more realistic account of experimental results.

Influence of dynamic effects on surface roughness for face milling process

In face milling processes, the surface roughness of the machined part reflects the cutting performance of face milling cutter. Surface roughness depends on different factors including feed direction, axial and radial run-out errors, and cutting tool geometry. In this paper, an algorithm considering the effects of static and dynamic factors on surface roughness for predicting the surface roughness is proposed. This work is focusing on straight-edged square insert. The dynamic characteristics of the milling process are also introduced. An electronic impact hammer is used to identify the dynamic parameters of the cutting system. Milling experiments are conducted to validate the prediction model. Results show that the prediction model can estimate the surface roughness of the machined parts after face milling. This paper provides an in-depth understanding of the relationship between machined surface roughness and process conditions especially for axial and radial run-out errors induced by static deformation and Z-axial relative displacement induced by forced vibration. The outcome of this research will lead to methodologies for cost-effective monitoring and surface roughness control.

Distortion of a Unit Cell versus Phase Transition to Nonbulk Morphology in Frustrated Films of Cylinder-Forming Polystyrene-b-polybutadiene Diblock Copolymers

Dimensions of cylindrical domains and microphase separation behavior in thin films of polystyrene-b-polybutadiene diblock copolymer (SB) are analyzed under fine variation of the surface fields, polymer–polymer interactions, film thickness, and the symmetry of the wetting conditions. In thermally and in solvent annealed films the dimensions of the closest to the substrate cylinders are smaller than both in thicker films and in bulk due to the confinement effect. The related excess of the stretching energy favors a transition to nonbulk perforated lamella morphology in a narrow window of the film thickness, solvent concentration, and annealing temperature. The discussion of the apparent stability/instability of thin film morphologies includes the analysis of molecular architecture, interfacial tensions, and possible influence of dynamic effects.

微通道内台阶阀截止过程中的毛细流动动态效应

The relationship between the dynamic effect of a capillary and the length of microchannel in front of a step valve was researched,then the influence of dynamic effect in the process of stopping the capillary in microchannel formed by hydrophobic and hydrophilic walls on the step valve was analyzed. According to the working principle of the passive valve of capillary and energy conservation law,the critical length in front of the step valve was calculated when the step valve stoped the capillary. The calculated length corresponding to the critical length was obtained by numerical simulation.It shows that when the actual length in front of the step valve is greater than or equal to the calculated length,the valve can stop the capillary effectively.The step valves were fabricated by bonding polydimethylsiloxane(PDMS) to glass.Experiments of stopping the capillary by the step valve were performed in a rectangular microchannel formed by three hydrophobic PDMS walls and one hydrophilic glass wall.For the series of microchannel with a depth of 40 μm and widths from 200 μm to 400 μm,the calculated length in front of the step valve is from 4.531 6 μm to 10.081 μm.In the experiments,the actual length before the step valves for effectively stopping the capillary is in the interval from 10 μm to 2 000 μm.The results show that even if the actual length in front of the step valve is 10 μm,the step valve can also stop the capillary.Therefore,the dynamic effect of the capillary can be ignored in stopping the step valves in the microchannel.

Influence of dynamic effects in nuclear resonant Bragg scattering on the accuracy of determination of self-diffusion coefficient in 56Fe/57Fe periodic multilayers

The angular dependences of nuclear resonant scattering are considerably different from respective X-ray reflectometry curves because of some special features of their detection and nuclear decay acceleration (speedup effect) in the conditions of coherent scattering. Model calculations show that the kinematic formula relating the intensity of the nuclear Bragg reflection maximum at different stages of annealing to the diffusion coefficient is inapplicable when the Bragg peak falls near the critical angle.

Degenerate K–Rb Fermi–Bose gas mixtures with large particle numbers

We present experimental investigations on the mutual influence of fermionic 40K and bosonic 87Rb atoms during the various trapping and cooling stages needed to reach quantum degeneracy of the sample. In particular we present particle number optimization strategies, which have led to large 40K–87Rb mixtures in the quantum degenerate regime. In fact the achievable particle numbers are only limited by a collapse due to an attractive overall mean-field interaction for the mixture. We discuss the influence of dynamical effects on the collapse parameters and find our critical particle numbers consistent with predictions based on recent Feshbach resonance measurements. We also investigate loss mechanisms of the mixture where we have identified three-body K–Rb–Rb losses as the dominant loss process and have measured the loss coefficient to be .

Design Assessment for Transport and Storage Casks

The design assessment concerning the mechanical behaviour of transport and storage casks for radioactive material to fulfil nuclear safety criteria has to be based on two essential considerations: (1) Effective analysis of the stress–strain state of the cask components under both normal operational and test conditions including hypothetical accident scenarios with suitable accepted methods. (2) Economic estimation of the required properties and the structural state of the cask components with sufficient exactness. In an overview of the codes which are available at GNS/GNB for cask impact strength analyses (ANSYS, ADINA, VDI Codes), procedures and aspects of benchmarking and validation of calculation codes are described. The results of experimental full size cask drop test programs (CASTOR, POLLUX) and corresponding pre-test calculational analyses show the suitability of the codes used. The influence of dynamic effects on the mechanical properties of material (ductile cast iron, wood) has been investigated experimentally. By consideration of these dynamic values in strength analyses of casks at impact a good agreement between experimental and calculational results has been achieved.

Presence of Two Molecular Dynamic Processes in a Narrow Temperature Range: Cis–Trans Isomerization across Nineteen Chemical Bonds and Rotation about the CN Bond

We report the basis for the presence of two molecular dynamic processes, in enamino spiro-ketal-type compounds (structure in Fig. 1), that occur in a 330-350 K temperature range. Nuclear magnetic resonance (NMR) is a powerful tool for investigating such molecular dynamic processes in small and large molecules. This capability is a result of the pronounced influence of dynamic effects on NMR spectra. Analysis of experimental NMR data suggests that one of the two molecular processes is cis-trans isomerization across nineteen chemical bonds. To the best of our knowledge, this is the first example of monitoring cis-trans isomerization involving this many chemical bonds by NMR.

Comparison of dynamic initiation toughness measured by strain gauges and the shadow optical method

AbstractThe deformation and fracture behaviour in dynamically loaded Charpy specimens of BS11 rail steel were studied by two different measuring techniques. The transient records obtained from straingauges were compared with results obtained simultaneously by the shadowoptical method. Good agreement was obtained when measuring and comparing the stress intensity factor K in the initial stages of deformation behaviour prior to crack initiation. During fast fracture, the shadow optical method indicated the influence of dynamic effects on crack propagation.

Determination of atomic positions of point defects in solids by ENDOR

The experimental results which are obtained from electron nuclear double resonance (ENDOR) of point defects in solids are briefly reviewed. From the relation between the experimental superhyperfine and quadrupole interaction tensors and the spin density distribution and charge density distribution, the details of the microscopic structure and thus the positions of atoms can in principle be obtained. For this, in general, a precise theory of the defect wave function is required. However, there are many cases in which simple approximations to the wave function can be used to determine atomic positions rather well. This is illustrated with several examples, mainly from ionic solids. The particular difficulties encountered in semiconductors and the influence of dynamical effects are also discussed.

Influence of defects on the thickness dependence of integral reflectivity of dislocation-free silicon crystals

The influence of large dislocation loops and clusters (with radius rd of the order of extinction length Λ) in dislocation-free silicon crystals grown by the Czochralsky-method on the thickness dependence of the total integral reflectivity Ri as well as on its Bragg's RB and diffuse RD components is investigated by variation of the X-ray wavelength (MoK, CuK-radiation) and of the order of Laue diffraction. For such defects diffuse scattering is concentrated near the reciprocal lattice point (RLP). Integral intensities are measured by means of the Bragg-Laue double crystal spectrometer in the positions (n, −n) and (n, −2n). The components RB and RD are determined using the formula of the dynamical theory of X-ray scattering in crystals with homogeneously distributed defects and the values of diffraction parameters i.e. the static Debye-Waller's factor L, and coefficient absorption due to diffuse scattering μds measured under conditions of weak absorption where the interfere influence of dynamical effects is negligible. The sensitivity of Ri to large defects is shown to increase at the expence of growing of the relative contribution of the RD component by transition to reflection of higher orders as well as by using of harder short-wavelength radiation. The ratio RD/Ri does not depend on the crystal thickness under conditions of strong absorption what conforms the arising of the dynamical regime for the diffuse component. This effect is absent for small (rd ≫ Λ) defects. The parameter L is shown to be more sensitive to the presence of large defects than μds. [Russian Text Ignored].

Influence of dynamic effects, sample thickness and absorption on a fine structure in an electron microscope pole figure

Abstract A fine structure has been observed in electron microscope images of ⟨111⟩ pole figures of cubic dysprosium sesquioxide. The observed lines are shown to be due to upper-Laue-zone reflections, but the measured voltage values for which they cross at the centre of the figure pole do not correspond to a situation in which the involved reflections are on the Ewald sphere. This shift between the measured crossing-voltage value and the kinematic value can arise for several reasons. Calculations have been made to ascertain the respective influences of dynamic interactions, absorption or crystal thickness on this shift. We show that, for our specimens, the influence of thickness or absorption is rather weak. The shift in crossing values is mainly due to interactions between diffracted beams, not only from the zero-order zone but also from the upper Laue zone.

Optical bistability and dynamical hysteresis in CdS

We investigate the transmission of pulses of 20 ns duration from a tunable dye-laser through CdS platelets at low temperature. We observe optical bistability based on induced absorption due to a broadening of the free-exciton resonance and due to the formation of an electron-hole plasma. Model calculations show that there is optical bistability, however, with some influence of dynamic effects on the shape and width of the hysteresis loop. Thermal effects are found to play only a minor role in our experiments. Dispersive optical bistability is observed with switching times as short as 300 ps in transmission and reflection, especially for samples covered with low-loss dielectric reflecting coatings.

NUMERICAL ANALYSIS OF UNCOUPLED DYNAMIC PROBLEM OF THERMOELASTICITY

Abstract This paper deals with the use of the finite element method in an uncoupled dynamic problem of thermoelasticity. An effective method of choosing different schemes and corresponding time step that insures computational stability is suggested. A numerical example is included to illustrate the usefulness of the present method. The influence of dynamic effect is briefly discussed.

Apparent Temperature Factor Due to Dynamical Scattering in Electron Diffraction of Protein Crystals

The failure of the kinematic scattering approximation, and also of the “weak phase object” approximation, may represent one of the most serious problems in the interpretation of high resolution electron diffraction data and electron microscope images. The existence and behavior of dynamical diffraction effects are well characterized in materials science applications, but the possible influence of dynamical effects is still not completely understood in applications involving unstained biological materials, which are characterized by low atomic number and large unit cells. We have previously reported numerical calculations in which we have explored the conditions under which the kinematic approximation would be valid, to an acceptable level of accuracy, for complex biological structures. The known structure of a protein, cytochrome b5, was used as a test object, and the Cowley-Moodie multislice method was used to calculate the “exact” dynamical diffracted waves. For 100 keV electrons it has been found that the kinematic approximation is acceptable up to a specimen thickness of about 150 Å, as judged by the crystallographic “R-value”, by the appearance of the difference Patterson function (for heavy atom derivatives), and by the number of wrong phases that are derived from the dynamical diffraction intensities.

The Influence of Dynamical Effects on the Two‐Particle States (Excitons) in the Electron‐Hole Plasma

The Influence of Dynamical Effects on the Two‐Particle States (Excitons) in the Electron‐Hole Plasma