Consideration Of Dynamic Effects Research Articles

Equivalent Circuit Model of Magnetoelectric Composite Nanoparticles

This study presents an analysis of magnetoelectric nanoparticles (MENPs) through the development of equivalent circuits to predict the frequency-dependent magnetoelectric coefficient, with a focus on the widely utilized CoFe2O4@BaTiO3 core–shell configuration. This approach involves –derivation of phenomenological expressions that capture the dynamic behavior of MENPs under varying magnetic and electric fields. By integrating piezoelectric and magnetostrictive constitutive equations, along with consideration of dynamic effects and bio-load conjugation, a magneto-elasto-electric effect equivalent circuit has been constructed. This circuit model not only facilitates the investigation of longitudinal data in cube-shaped MENPs but also offers insights into fundamental biological processes. The versatility of this model is shown through translation to other core–shell nanoparticles, composite structures, and multiferroic nanostructures. This analysis provides quantitative predictions of the magnetoelectric coefficients, enhancing general understanding of MENP characteristics across a broad frequency range. Furthermore, the study highlights the framework for future refinement to incorporate intrinsic composition-specific resonances, such as ferromagnetic and ferroelectric resonances, to further significantly improve the nanoparticles’ performance. Overall, this work lays the groundwork for future technology to intelligently and wirelessly control biological processes using MENPs, thus paving a way for innovative biomedical applications. This quantitative approach may facilitate further interdisciplinary research and contribute to advancement of magnetoelectric materials and their applications.

Using static postures to estimate spinal loading during dynamic lifts with participant-specific thoracolumbar musculoskeletal models

Static biomechanical simulations are sometimes used to estimate in vivo kinetic demands because they can be solved efficiently, but this ignores any potential inertial effects. To date, comparisons between static and dynamic analyses of spinal demands have been limited to lumbar joint differences in young males performing sagittal lifts. Here we compare static and dynamic vertebral compressive and shear force estimates during axial, lateral, and sagittal lifting tasks across all thoracic and lumbar vertebrae in older men and women. Participant-specific thoracolumbar full-body musculoskeletal models estimated vertebral forces from recorded kinematics both with and without consideration of dynamic effects, at an identified frame of peak vertebral loading. Static analyses under-predicted dynamic compressive and resultant shear forces, by an average of about 16% for all three lifts across the thoracic and lumbar spine but were highly correlated with dynamic forces (average r2 > .95). The study outcomes have the potential to enable standard clinical and occupational estimates using static analyses.

Effects of dynamic fibre failure in unidirectional composites

The stress redistribution around a broken fibre is a substantial issue in longitudinal strength analysis of unidirectional (UD) composites. Most investigated models are based on a regular fibre packings and classical shear lag theory (static failure) that considers pre-broken fibers, where the dynamic aspects of brittle fiber failure are not considered. In the present work, Representative Volume Elements with random fibre packings were modeled by means of 3D finite element analysis, and simulated considering the event of dynamic fibre failure. Significant effects were observed on the stress concentration factor (SCF) and ineffective load length which are related to the fibre debonding length and the volume of matrix damage-plasticity zones. Hence, it can be concluded that an accurate representation of the stress redistribution after a fibre breakage event requires consideration of dynamic effects.

Adjoint-based fluid dynamic design optimization in quasi-periodic unsteady flow problems using a harmonic balance method

Shape optimization in unsteady flow problems enables the consideration of dynamic effects on design. The ability to treat unsteady effects is attractive, as it can provide performance gains when compared to steady-state design methods for a variety of applications in which time-varying flows are of paramount importance. This is the case, for example, in turbomachinery or rotorcraft design. Given the high computational cost involved in time-accurate design problems, adjoint-based shape optimization is a promising option. However, efficient sensitivity analysis should also be accompanied by a significant decrease in computational cost for the primal flow solution, as well. Reduced-order models, like those based on the harmonic balance concept, in combination with the calculation of gradients via adjoint methods, are proposed for the efficient solution of a certain class of aerodynamics optimization problems. The harmonic balance method is applicable if the flow is characterized by discrete finite dominant flow frequencies that do not need to be integer multiples of a fundamental harmonic. A fully-turbulent harmonic balance discrete adjoint formulation based on a duality-preserving approach is proposed. The method is implemented by leveraging algorithmic differentiation and is applied to two test cases: the constrained shape optimization of both a pitching airfoil and a turbine cascade. A key advantage of the current approach is the accurate computation of gradients as compared to second order finite differences without any approximation in the linearization of the turbulent viscosity. The shape optimization results show significant improvements for the selected time-dependent objective functions, demonstrating that design problems involving almost-periodic unsteady flows can be tackled with manageable computational effort.

Modeling dynamic non-equilibrium water flow observations under various boundary conditions

Summary Experimental evidence of variably-saturated flow in soils often shows a non-equilibrium between water content and water potential. Such phenomena, summarized by the term “dynamic effects” often occur in laboratory experiments specifically designed for the identification of soil hydraulic properties which are a mandatory input for water flow simulations at the field scale using the Richards equation. Depending on boundary conditions, dynamic non-equilibrium leads either to a relaxation of pressure head for constant water content or vice versa. Diamantopoulos et al. (2012) presented a model which describes dynamic effects in the case of multistep outflow experiments by assuming that the total water content is portioned into two fractions: one fraction which is in instantaneous equilibrium with the pressure head, and a second fraction for which the equilibration of the water content with the pressure is described by a first-order kinetics which leads to a temporal shift in water content at constant pressure head. In this work we applied this non-equilibrium model to four different observations of dynamic non-equilibrium effects presented in the literature and demonstrate that it successfully describes (1) non-equilibrium in water absorption experiments which results in a non-uniqueness of the diffusivity vs water content function, (2) the flow-rate dependence of soil hydraulic properties, (3) dynamic effects in multistep outflow and (4) dynamic effects in multistep flux experiments. We conclude the article by a discussion of possible macroscopic explanations, the consideration of dynamic effects for modeling water flow at the field scale, the uniqueness of the estimated non-equilibrium parameters among different experiments, and further theoretical considerations concerning dynamic effects.

Train loading on bridges since Stephenson's Rocket

Railway locomotives increased in weight from less than 10 tons in 1825 to more than 100 tons by the 1930s. Originally loading on bridges was assumed as an average weight per unit length ignoring axle concentration and generous factors of safety were used to compensate for the absence of any dynamic allowance. After the Dee Bridge collapse of 1847 Board of Trade rules were imposed. The comparatively few bridge failures under train loading are summarised. After several failures of flawed cast-iron girders these were gradually replaced after 1891. There was no rigorous consideration of dynamic effects until the 1900s. Civil engineers had been rejecting heavier new locomotives without comparing hammer blow characteristics. Dynamic effects were eventually investigated for the Bridge Stress Committee Report of 1928. With the elimination of steam traction, loading as developed for Europe was introduced and is now adopted in the Eurocodes. Comparisons are made between early and modern loadings taking account of the effect of increasing speeds.

A Simplified Approach for Predicting Bridge Pier Responses Subjected to Barge Impact Loading

Bridge piers are often designed to resist barge impact loads according to empirical equations given in various design codes based primarily on equivalent static analyses. Although these analyses can give useful guidance in design practice, they neglect dynamic effects which can have significant influence on barge-bridge structure interactions. It is necessary to develop an efficient and accurate method that takes into consideration of dynamic effect, material nonlinearity and structural damage in predicting impact loads and structural responses. In this study, empirical equations based on intensive numerical simulation results proposed in a previous study are used to estimate dynamic impact loads on bridge piers. The bridge structure is simplified as a nonlinear single degree of freedom system to calculate its dynamic response. As compared to detailed finite element simulation, this simplified approach is straightforward and gives reasonably accurate prediction of bridge responses. It can be used in the preliminary analysis and design of bridge structures against barge impact.

Train Loads on Bridges 1825 to 2010

Weights of railway locomotives increased from less than 10 tons in 1825 to more than 100 tons at the zenith of steam power in the 1930s. With the elimination of steam traction, wagon loading became more critical. Early bridges of timber and cast iron became unsuitable as loadings increased, but on secondary lines some early bridge types have survived. In the early years, the criterion for bridge loading was taken as the quotient of the weight of a vehicle divided by its length (an average tons per foot run), ignoring axle concentration. Generous factors of safety were used to compensate for the absence of any dynamic allowance. There were no formal rules until the Dee Bridge disaster of 1847 led to those of the Board of Trade. The comparatively few bridge failures under train loading are summarised. After several failures due to casting flaws culminating in the 1891 Norwood Junction collapse, cast iron girders were gradually replaced. There was no rigorous consideration of dynamic effects until the twentieth century. Civil engineers had been rejecting new locomotives with heavier axle loading without considering comparative hammer blow characteristics. Dynamic effects were investigated for the Bridge Stress Committee Report of 1928. With the elimination of steam traction in 1968, European standards (Eurocodes) have been introduced. Comparisons are made between early and modern loadings taking account of the effect of increasing speeds.

Design bending moment of RC slabs in consideration of dynamic effect passing expantion joint

Design bending moment of RC slabs in consideration of dynamic effect passing expantion joint

NONLINEAR TRANSIENT ANALYSIS OF A RAILWAY CONCRETE SLEEPER IN A TRACK SYSTEM

Railway sleepers in a track system are usually subjected to a wide range of loading conditions. A critical type of loading condition that causes cracking in the railway concrete sleepers is the dynamic transient wheel force. The transient wheel forces are often due to wheel or rail abnormalities. This paper presents a dynamic finite element model of a railway concrete sleeper in a track system, aimed at raising the consideration of dynamic effects in sleeper design. The railway concrete sleeper is modeled using the beam-on-elastic-foundation theory. Since in the actual tracks the ballast underneath does not provide any tensile resistance, the finite beam elements employed in this investigation take into account the bending and shear deformations, together with the tensionless nature of the elastic support. This paper places emphasis on the effect of the transient periods on the flexural responses of railway sleepers in track systems. Using the robust finite element software STRAND7, the finite element model of the railway concrete sleeper was previously established and validated against experimental data by the authors. The numerical analyses present the ratio between the dynamic and the static bending moment resultants, the dynamic magnification factor, of the railway concrete sleeper under different sinusoidal pulse durations.

Dynamic limit analysis formulation for impact simulation of structural members

This paper introduces an extended concept of limit analysis to deal with the dynamic equilibrium condition considering the inertia and strain-rate effect for dynamic behavior of structures. The conventional limit analysis method has been applied to only static collapse analysis of structures without consideration of dynamic effects in the structural behavior. A dynamic formulation for the limit analysis has been derived for incremental analysis dealing with time integration, strain and stress evaluation, strain hardening, strain-rate hardening and thermal softening. The time dependent term in the governing equation is integrated with the WBZ- α method. The dynamic material behavior is described by the Johnson–Cook model in order to consider strain-rate hardening and thermal softening as well as strain hardening. Simulations have been carried out for impact analysis of a Taylor bar and an S-rail and their numerical results are compared with elasto-plastic explicit analysis results by LS-DYNA3D. Comparison demonstrates that the dynamic finite element limit analysis can predict the crashworthiness of structural members effectively with less effort and computing time than the commercial code compared. The crashworthiness of a structure with the rate-dependent constitutive model is also compared to that with the quasi-static constitutive relation in order to investigate the dynamic effect on deformation of structures.

Promotions, Demotions, Halo Effects, and the Earnings Dynamics of American Executives

This paper explores the determinants of earnings growth in corporate hierarchies using static and dynamic panel data techniques. The novelty derives from the distinction between base pay and bonus, the asymmetric effects of promotion and demotion, and the consideration of dynamic effects. We find that the convexity of pay structures is robust to the allowance for unobserved individual heterogeneity. Demotion has a stronger effect on compensation growth in absolute value than promotion. Dynamic models indicate that the causal effect of past promotion is positive on the growth in base and total pay but has no significant effect on bonus growth.

"Concerted" transition state, stepwise mechanism. Dynamics effects in C2-C6 enyne allene cyclizations.

The C2-C6 (Schmittel)/ene cyclization of enyne-allenes is studied by a combination of kinetic isotope effects, theoretical calculations, and dynamics trajectories. For the cyclization of allenol acetate 9, the isotope effect (k(CH3)/k(CD3) is approximately 1.43. The isotope effect is interpreted in terms of a highly asynchronous transition state near the concerted/stepwise boundary. This is supported by density functional theory calculations that locate a highly asynchronous transition structure for the concerted ene reaction. However, calculations of both the experimental system and a model reaction were unable to locate a transition structure for formation of the diradical intermediate of a stepwise mechanism. The stepwise mechanism and the asynchronous concerted mechanism start out geometrically similar, and the two pathways appear to have merged as far as the initial transition structure. For the model reaction, quasiclassical direct dynamics trajectories emanating from the initial transition structure afforded the diradical intermediate in 29 out of 101 trajectories. A large portion of the remaining trajectories completes hydrogen transfer before carbon-carbon bond formation, despite the advanced carbon-carbon bond formation in the asynchronous transition structure. Overall, the single minimum-energy path from starting material to product is inadequate to describe the reaction, and a consideration of dynamic effects is necessary to understand the mechanism. The implications of these observations toward questions of concert in other reactions are discussed.

Isotope Effects, Dynamics, and the Mechanism of Solvolysis of Aryldiazonium Cations in Water

The mechanism of the heterolytic solvolysis of p-tolyldiazonium cation in water was studied by a combination of kinetic isotope effects, theoretical calculations, and dynamics trajectories. Significant (13)C kinetic isotope effects were observed at the ipso (k(12)C/k(13)C = 1.024), ortho (1.017), and meta (1.013) carbons, indicative of substantial weakening of the C(2)-C(3) and C(5)-C(6) bonds at the transition state. This is qualitatively consistent with a transition state forming an aryl cation, but on a quantitative basis, simple S(N)1 heterolysis does not account best for the isotope effects. Theoretical S(N)2Ar transition structures for concerted displacement of N(2) by a single water molecule lead to poor predictions of the experimental isotope effects. The best predictions of the (13)C isotope effects arose from transition structures for the heterolytic process solvated by clusters of water molecules. These structures, formally saddle points for concerted displacements on the potential energy surface, may be described as transition structures for solvent reorganization around the aryl cation. Quasiclassical dynamics trajectories starting from these transition structures afforded products very slowly, compared to a similar S(N)2 displacement, and the trajectories often afforded long-lived aryl cation intermediates. Critical prior evidence for aryl cation intermediates is reconsidered with the aid of DFT calculations. Overall, the nucleophilic displacement process for aryldiazonium ions in water is at the boundary between S(N)2Ar and S(N)1 mechanisms, and an accurate view of the reaction mechanism requires consideration of dynamic effects.

Vibration and Stability of Frictional Sliding of Two Elastic Bodies With a Wavy Contact Interface

Abstract The stability of steady sliding, with Amontons-Coulomb friction, of two elastic bodies with a rough contact interface is analyzed. The bodies are modeled as elastic half-spaces, one of which has a periodic wavy surface. The steady-state solution yields a periodic set of contact and separation zones, but the stability analysis requires consideration of dynamic effects. By considering a spatial Fourier decomposition of the vibration modes, the dynamic problem is reduced to a singular integral equation for determining the eigenvectors (modes) and eigenvalues (frequencies). A pure imaginary root for an eigenvalue corresponds to a standing wave confined to the interface, while a positive/negative real part of the eigenvalue indicates instability/dissipation. A complex eigenvector indicates a complex mode of vibration. Two types of modes are considered—periodic symmetric modes with period equal to the surface waviness period and periodic antisymmetric modes with the period equal to twice the surface waviness. The singular integral equation is solved by reducing it to a system of linear algebraic equations using a Jacobi polynomial series and a collocation method. For the limit of zero friction it can be demonstrated analytically that the problem is self-adjoint and the eigenvalues, if they exist, are pure imaginary (no energy dissipation). These roots are found for a wide range of material properties and ratios of separation to contact zones lengths. For the limiting case of complete contact, the solution found corresponds to a superposition of two slip waves (generalized Rayleigh waves) traveling in opposite directions and forming a standing wave. With increasing separation zone length, the vibration frequency decreases from the slip wave frequency to the smaller surface wave frequency of the two bodies. With a nonzero separation zone, solutions can exist for material combinations which do not allow slip waves. For nonzero friction and sliding velocities, unstable solutions are found. The degree of instability is proportional to the product of the friction coefficient and the sliding velocity. These instabilities may contribute to the formation of friction-induced vibrations at high sliding speeds.

Comparison of finite element techniques for 2D and 3D crack analysis under impact loading

For several technical applications the dynamic aspect in fracture mechanics cannot be neglected. When the reliability of components with macroscopic cracks has to be assessed, the consideration of dynamic effects may lead to much higher stress intensity factors than under static conditions. In this paper three different methods to calculate the dynamic stress intensity factor for the mode-I loading of stationary cracks are compared. Based on two- and three-dimensional finite element simulations, the dynamic stress intensity factor is computed with the dynamic J-integral, the modified crack closure integral and the displacement interpretation method. The theoretical fundamentals of all three methods are summarized in the paper and the numerical implementation is explained briefly. Results for different models are shown and compared to findings in the literature.

Analysis of the sub-barrier fusion ofO16+Sm148,150,152,154

Recent measurements of the sub-barrier fusion of $^{16}\mathrm{O}$ with isotopes of Sm, which span the transition region from spherical to deformed equilibrium shapes, are analyzed in terms of static and dynamic reaction models. The classical equivalent-spheres method of incorporating the effect of nuclear deformation on heavy-ion fusion is shown to overpredict the experimentally observed differences in the fusion cross sections. An approximate, classical estimate of dynamic effects connected with the rotation of the target before fusion removes part, but not all, of this discrepancy. Coupled-channels calculations, which treat dynamic effects through the excitation of the ${2}^{+}$ and ${4}^{+}$ levels, are also presented. An estimate is given of the effects one may expect to observe for fusion with a polarized deformed target.NUCLEAR REACTIONS Barrier-penetration analysis of ${\ensuremath{\sigma}}_{\mathrm{fusion}}$ for $^{16}\mathrm{O}$+$^{148,\phantom{\rule{0ex}{0ex}}150,\phantom{\rule{0ex}{0ex}}152,\phantom{\rule{0ex}{0ex}}154}\mathrm{Sm}$, ${E}_{\mathrm{lab}}=60\ensuremath{-}75$ MeV, including effects of static deformation. Consideration of dynamic effects. Coupled-channels analysis.

On the Consideration of Dynamic Effect in Folding Deformation of a Layered Viscoelastic Medium in Compression

Previous works on folding deformation of a layered viscoelastic medium in compression preclude the consideration of dynamic effect as the contribution due to this effect is assumed to be negligibly small because of sufficiently slow deformation rate. In this discussion the dynamic effect is included in finding a modified expression for the dominant wavelength and the analysis is carried through to deduce criteria for the existence of the dominant wavelength under known prestress conditions. A workable estimate to detect the circumstances within the framework of classical linear theory of elasticity under which the results obtained by quasi-static and dynamic considerations differ significantly is constructed in later part. The presence of such significant deviation of values indicates the deformation rate is not sufficiently slow and therefore the inertia term characterizing the dynamic effect can not be neglected. To elucidate further a graph giving the values of the ratio of the dominant wavelengths in two considerations is provided in the end.

Synthesis of a slider-crank mechanism with consideration of dynamic effects

A method of dynamic synthesis of a slider-crank mechanism to meet specified velocity conditions at three design points including the inertia effects of the masses of the main links is presented. Velocity specifications are developed assuming a constant velocity of the input crank. The dynamic velocity error due to inertial effects is calculated by numerical solution of the differential equations of motion including the torque-speed relation for a typical three-phase electrical motor drive. An iterative dynamic-kinematic redesign of the mechanism is used to minimize the velocity error at three design points.