Predicting Deformation and Relaxation Processes in Uniaxially Oriented Polymers

In modern distributed energy systems (DES), focus is shifting from the conventional centralized approach towards distributed architectures. However, modeling and analysis of these systems is more complex, as it involves the interface of multiple energy sources with many different type of loads through power electronics converters. The integration of power electronics converters allows distributed renewable energy sources to become part of modern electronics power distribution systems (EPDS). It will also facilitate the ongoing research towards DC-based DES which is mostly composed of commercial DC-DC converters whose internal structure and parameters are unknown. For the system level analysis, the behavioral modeling technique is the only choice. Since most power electronics converters are non-linear systems and linear models can’t model their dynamics to a desired level of accuracy, hence non-linear modeling is required for accurate modeling. The non-linear modeling approach presented here aims to develop behavioral models that can predict the response of the system over the entire operating range. In this work, either a lookup table or a polytopic structure-based modeling technique is used. The technique is further applied to cascade and parallel connected converters, being two DES scenarios. First the procedure is verified via application to switching models in a simulation and then validated for commercial converters via experiments. The results show that the developed behavioral models accurately predict both the transient and steady state response.

Modeling and analysis of ear dynamics with a round-window stimulating active middle ear implant

Training β relaxation to rejuvenate metallic glasses

This paper analyzes delamination of multilayered inhomogeneous beam structure by utilization a non-linear viscoelastic mechanical model. The non-linear time-dependent response is treated by a non-linear spring and a non-linear dashpot connected in series to a system of two linear springs and two linear dashpots. The model is under stress that is a linear function of time. The constitutive law of the model representing a non-linear dependence between stress, strain and time is derived. The main goal of the paper is to obtain a solution of the strain energy release rate for the delamination in the multilayered inhomogeneous beam by applying the non-linear viscoelastic model. Solutions are derived by using the complementary strain energy and by analyzing the balance of the energy with taking into account the non-linear viscoelastic behaviour. For this purpose, the constitutive law of the non-linear viscoelastic mechanical model is used. The solutions are applied to obtain results for multilayered beams with non-linear variation of material properties in longitudinal direction. The influence of different parameters on the time-dependent strain energy release rate is assessed. The study indicates the effectiveness of the viscoelastic mechanical models with non-linear springs and dashpots in time-dependent delamination analyses of multilayered inhomogeneous beam structures.

Polymers are widely used as dielectrics in microelectronics. As the thickness of polymer films decreases to the submicrometer or nanometer scale, abnormal relaxation deviations from the bulk matrix are expected. Evaluation of the relaxation dynamics in an efficient and quantitative manner is highly desired. Utilizing this patterned charge as an indicator, we demonstrate here that the polymer relaxation dynamics and glass transition temperature (Tg) of thin polymer films can be investigated by monitoring the charge decay behaviors. This approach of charge patterning combined with atomic force microscopy is more facile to evaluate polymer relaxation behavior with direct contrast between charged and electrically neutral domains versus conventional polymer Tg and relaxation dynamic measurements. This study also illuminates the coexisting processes of polymer relaxation and trapped charge decay in thin polymer film. This sheds light on the microscopic mechanism of charge storage and relaxation properties in th...

Nonlinear mechanical plane base-rotator models of DNA are considered. Various expressions for the potential energy of interaction between complementary bases are analyzed. Dissipative functions are introduced into these models: the external function describing the motion of the bases in a solvent and the function describing the internal friction in the molecule. Particle-like solutions of the model without dissipation are obtained and the influence of dissipation on these (soliton) excitations is studied.

When processing metals by pressure, various types of additional physical influence are used in the form of heating, mechanical shock, vibration, acoustic ultrasonic irradiation, and electric pulse influence. Such impacts, in particular, are associated with manifestations of the oscillatory motion of material particles, which can be considered as a trigger for the movement of dislocations and structural inhomogeneities of the material. Such inhomogeneities can be in conditions of a residual mechanical stress state, which, under oscillatory influence, leads to their movement and transition to a more stable state. Such processes are accompanied by improved mechanical properties and deformation processes with increased plasticity. The work examines some features of the manifestation of such oscillatory processes that arise under additional external influences, which can be used in the development of metal forming technologies in order to reduce resistance to deformation and improve the structure of materials.

In order to study the creep characteristics of the coarse-grained soil as embankment filler under long-term vehicle loading, the creep test was performed on coarse-grained soil using the large scale dynamic and static triaxial instruments, and the creep process of the coarse-grained soil sample was simulated by PFC3D software, and the internal particle motion and energy change during the deformation process were studied. The research results show that the coarse-grained soil embankment filler has non-linear creep characteristics. At a low stress level, the coarse-grained soil is in the stage of elastic deformation. At a high stress level, the final creep deformation curve of the coarse-grained soil does not converge. The creep process is a process in which the particles are distorted and rotated, changing from an unstable state to a stable state. During this process, the particle energy is dissipated to the minimum, and the creep of the sample reaches a stable state. This understanding of particle motion and energy changes during the triaxial creep test of coarse-grained soil will help deepen the understanding of creep characteristics of coarse-grained soil and provide a reference for engineering practice.

According to the structural characteristics and static equilibrium of the joints, immersed tube tunnel three-dimensional nonlinear stiffness mechanical model is established. What's more, the harmonious relation for deformation and stress-strain relations of GINA and OMEGA gasket are analyzed. By using this model, the different operating modes of the joints can be divided and identified by the relative displacement of the shear key. In addition, the mechanical characteristics of joints and the nonlinear relation between the joint displacement and internal force has are further revealed.

The current work presents a parametric study, which involves different generalized nonlinear mechanical formulations with different damping characteristics to account for the interaction between a monopile‐supported offshore wind turbine and the surrounding soil. The novelty of the study lies in the fact that recently developed nonlinear mechanical models used so far for the simulation of high‐damping rubber isolators are introduced to describe the nonlinear hysteretic soil behavior. More specifically, the first generalized mechanical model consists of a combination of elastoplastic and trilinear elastic elements (labeled as model 3), while the second model consists of trilinear hysteretic models connected in parallel with trilinear elastic springs and hysteretic dampers used to ensure that the unloading stiffness will be as close as possible to the initial stiffness of the system (labeled as model 4). These newly developed models are compared with well‐known models within the industry, namely, a model that comprises elastoplastic elements (labeled as model 1) and a model that comprises trilinear elastic springs (labeled as model 2). All these models provide exactly the same effective stiffness, but on the other hand different levels of damping are involved in each one of them. The goal of the present work is 3‐fold, introducing novel mechanical models for the simulation of soil behavior, to investigate the effect of different soil damping levels in the response of offshore wind turbines and to highlight the limitations of the commonly used models within the industry. To this end, the differences between the response due to different levels of damping characteristics and modeling approaches are shown, highlighting the importance of soil damping in the overall response of the system.

The rate of thermally activated transitions can generally be described by the Arrhenius law, as k=f0 exp(-ΔE/kBT). In the previous expression, ΔE is the internal energy barrier, and f0 is a prefactor that encompasses both dynamical and entropic contributions. In this work, we show how the activation entropy can play a crucial role in thermally activated magnetic transitions. To that end, we study two types of transitions involving solitons either as the stable state or the transition state, namely, skyrmion annihilation, and domain-wall mediated magnetization reversal in nanodisks.The aforementioned transitions pertain to the class of rare events, i.e., they are unlikely to arise in the course of a Langevin simulation, because the mean waiting time between events is much larger than the integration timestep. In this case, one possible approach is to use a form of reaction rate theory to calculate the energy barrier and the Arrhenius prefactor. To this end, we apply Langer’s theory [1], which is an extension of the Kramers method to many dimensions. Alternatively, one may use a path sampling method such as forward flux sampling [2] in order to sample the transition path ensemble from the system’s dynamics and extract a transition rate. In this work, we employ both methods in conjunction to study the thermal stability of magnetic skyrmions and nanodisks, for which the two methods show a good agreement.Magnetic skyrmions are particle-like, two-dimensional, non-collinear solitonic spin textures with a nontrivial topology. In ultrathin films and multilayers, small skyrmions are stabilized by an interfacial form of the Dzyaloshinskii-Moriya interaction (DMI). Skyrmion-based designs currently appear very promising for novel spintronics devices, e.g., for racetrack memories and logic gates, reservoir computing, or probabilistic computing [3]. Isolated skyrmions exist as metastable excitations of the collinear magnetic ground state and can be longed-lived. For applications, a stability of up to 10 years at room temperature is a technological requirement, and the ability to accurately predict that stability is therefore crucial. We find that skyrmions can be stabilized not only by an internal energy barrier, but also by a large activation entropy. This stems from the fact that the metastable skyrmion state possesses a large entropy compared to the transition state, because skyrmions exhibit stable internal modes of deformation [4]. When applying a destabilizing magnetic field perpendicular to the skyrmion core, the skyrmion lifetime decreases quickly with the field amplitude. This results from a shrinking of the skyrmion, which simultaneously reduces the the energy barrier, as well as the activation entropy through the suppression of the stable internal modes (Fig. 1) [5].Next, we compute the mean waiting times between thermally activated domain-wall mediated magnetization reversals in a perpendicularly magnetized nanodisk. We use parameters that resemble that of a free CoFeB layer, as typically used in magnetoresistive random access memories [6]. By varying the perpendicular anisotropy and the interfacial DMI, we find that the Arrhenius prefactor can take extreme, seemingly non-physical values up to 1021 Hz, which is orders of magnitude beyond the typically assumed value of 109 Hz, and vary drastically as a function of material parameters. We show that the prefactor behaves like an exponential of the energy barrier, which stems from a linear variation of the activation entropy with the energy barrier (Fig. 2) [7]. This phenomenon, known as the Meyer-Neldel rule, or entropy-enthalpy compensation, has been reported across diverse fields of the natural sciences for over a century—in semiconductors, chemical reactions, biological death rates, etc [8]. In magnetism, it was only recently observed in the decay of the skyrmion lattice [9]. This result implies that the transition state, which, in the case of the magnetization reversal, is a domain wall found in the center of the disk, tend to possess a very large entropy compared to the collinear ground state. This is verified by the existence of gapless, low energy modes propagating along domain walls [10].These findings suggest that the Arrhenius prefactor, which is typically taken as an attempt frequency within the characteristic timescale of a magnetic system's dynamics, may in some cases contain a very large entropic contribution which should not be neglected. This seems to be particularly true in magnetic transitions involving solitons. **

Water inrush in the working face caused by seepage instability of fault fracture zone is a major disaster which threatens the safety production in a coal mine. Based on the principle of fluid mechanics, a nonlinear mechanical model with three flow fields is established in this paper. Combining with the actual situation of a fault fracture zone in a coal mine, a multicoupled numerical model is built in COMSOL Multiphysics, in order to study the water pressure and flow velocity in the three flow fields and the flow state of fluids in the aquifer and fault under different ratios of fault permeability and aquifer permeability. The research results show that the permeability in the fault fracture zone is an essential factor affecting the danger of water inrush, and the pressure and flow velocity in the boundary zone of the adjacent flow field varies significantly. Besides, the water inrush in the fault fracture zone is a gradual dynamic process, and the fluid flow from the aquifer through the fault gradually changes from a linear flow state into a nonlinear flow state. Meanwhile, the non-Darcy effect increases and decreases with the growth and decrease of the permeability in the fault fracture zone.

METHOD OF JUDGING THE SELF-EXCITED VIBRATION OF ROLLING MAIN DRIVE SYSTEM IN ROLLING SLIPPAGE

A nonlinear mechanical model has been proposed for application to nonlinear viscoelastic elastomers. The model consists of four nonlinear elements similar to the Burgers model. Based on the theory of reaction rate proposed by Eyring and the statistic concept of entropy‐spring developed in rubber elasticity, four relevant nonlinear elements are used to construct the model. The deformation, or the time rate of deformation of each element is described by a nonlinear stretch parameter A. According to the model and the parameter A, two groups of equations are derived to describe the creep or relaxation behavior of solid‐filled and pure rubbers, respectively. In order to examine the applicability of the model as well as the nonlinear stretch parameter, a series of experiments for solid‐filled polybutadiene rubbers has been carried out, which include constant rate of tensile tests, creep and relaxation tests with and without aging effects. It is found that the nonlinear stretch parameter satisfies the Eyring equation and that the model agrees the experiments extremely well.

Non-linear modeling of seismic isolation systems made of recycled tire-rubber