Analog simulation of magnetic hysteresis and its application

An analog simulation of hysteresis phenomena based on the magnetic domain theory is proposed. Hysteresis curves are simulated by superposition of a number of backlash elements which are followed by output limiters. The interaction of magnetization between domains is taken into account. This consideration makes it possible to simulate individual characteristics of various magnetic materials. A satisfactory performance of the simulator is obtained for an arbitrary form of the input; thus, the simulation of initial magnetizing curves, hysteresis loops and minor loops is found to agree with experimental observation. As an application of the simulator, the author applied this simulator to the analog computer setup and carried out a computer analysis of the series resonant circuit including a saturable core. The frequency response curves and the regions of initial conditions leading to the various oscillations which are obtained by the simulation found to agree with the experimental results.     

Identification of nonlinear hysteretic parameters by enhanced response sensitivity approach

Hysteresis is a ubiquitous phenomenon describing the special nonlinear memory-based relation between the input and the output in many physical systems. Identifying the hysteretic parameters is the first step towards practical application of hysteretic models. In this paper, a general framework for parameter identification of nonlinear hysteretic models is developed based on the enhanced response sensitivity approach. To do so, three typical hysteretic models—Bouc–Wen model, bilinear model with kinematic hardening and bilinear model with equal yielding force are analyzed at first and the general way to model a structure with such hysteretic components is established thereafter. Then, the enhanced response sensitivity approach is presented for inverse parameter identification where the key lies in the sensitivity analysis and the trust-region constraint. Particularly, smoothing procedure is introduced to overcome the non-differentiability of bilinear hysteretic functions for sensitivity analysis of bilinear models. Numerical examples are studied to testify the feasibility and performance of the proposed approach.     

Stability aspects of the Hayes delay differential equation with scalable hysteresis

Nonlinear Dynamics - Hysteresis models are strongly nonlinear, with slope discontinuities at every load reversal. Stability analysis of hysteretically damped systems is therefore challenging....     

Steady-state thermal waves in the free-stream flow of an ideal gas with a temperature-dependent thermal conductivity

The structure of the stationary transition layer in a cold ideal gas impinging on a heated permeable surface (lattice) is investigated. Hysteresis occurs in establishing the structure of the stationary transition layer.     

论迟滞与时滞

迟滞和时滞是自然科学、工程科学、乃至社会科学中常见的两种现象,但在我国学术界常被混淆. 从两种现象的定义和本质出发,阐述两者的共性、个性及其联系. 通过多个例子说明:迟滞现象反映两个相关参变过程周期变化时彼此间的相位滞后关系;而时滞现象则反映两个相关动态过程任意变化时彼此间的时间滞后关系.在某些特定的情况下, 它们可以等同; 但在一般情况下,它们是具有不同性质的两类现象, 尤其在描述记忆特性方面, 两者有本质的差异.      

Effects of Relative Permeability History Dependence on Two-Phase Flow in Porous Media

Hysteresis phenomena in multi-phase flow in porous media has been recognized by many researchers and widely believed to have significant effects on the flow. In an attempt to account for these effects, a theoretical model for history-dependent relative permeabilities is considered. This model is incorporated into 1-D two-phase nondiffusive flow system and the corresponding flow is predicted. Flow history is observed to have a notable impact on the saturation profile and fluids breakthrough.     

Statics of a magnetic fluid containing magnetic field concentrators

Various static surface shapes of a magnetic fluid containing bodies made of easily magnetizable materials (magnetic field concentrators) in a uniform applied magnetic field are numerically calculated with account for the gravity force, surface tension, and the dependence of the magnetic-fluid magnetization on the magnetic field strength. The possibility of a sudden change in surface shape is shown. Hysteresis in the surface shape with a cyclic increase and decrease in the applied field is predicted.     

Experimental investigation of three-dimensional supersonic flow past an axisymmetric body with an annular cavity

The results of an experimental investigation of supersonic Mach 2.5 flow past an axisymmetric cylindrical model body with a rectangular annular cut-out on its lateral surface are presented. The evolution of the structure of the flow over the cavity with continuous variation in the angle of attack is studied on the basis of the data of flow visualization and balance measurements on the range of the relative cavity lengths L/h from 8 to 16. Hysteresis phenomena are revealed and analyzed.     

A simple isothermal model for homogeneous-heterogeneous reactions in boundary-layer flow. I Equal diffusivities

A simple model for homogeneous-heterogeneous reactions in stagnation-point boundary-layer flow is constructed in which the homogeneous (bulk) reaction is assumed to be given by isothermal cubic autocatalator kinetics and the heterogeneous (surface) reaction by first order kinetics. The possible steady states of this system are analysed in detail in the case when the diffusion coefficients of both reactant and autocatalyst are equal. Hysteresis bifurcations leading to multiple solutions are found. The temporal stability of these steady states is then discussed.     

Hysteresis losses in oscillatory systems

Hysteresis losses restrict the quality factors of oscillatory systems. We have considered the energy dissipation mechanism using as an example the contact spots of the ball supports of a pendulum tribometer with plane samples. The bending of a contact spot leads to a storage of the system׳s elastic energy. Measuring the quality factor of the pendulum at oscillations, owing to the inclination of the contact spot, makes it possible to determine the coefficient of hysteresis losses in materials and thin coatings without destroying their structures.     

Studies on heat transfer and flow characteristics in subcooled flow boiling—Part 1. Boiling characteristics

Measurement of wall temperature profile and photographic observation are performed for R-113 subcooled boiling flow in a channel with heat fluxes up to the CHF. The incipient boiling superheats measured are little affected by mass velocity and liquid subcooling. Hysteresis in boiling observed by increasing and decreasing heat flux seems to be ascribed to variation in size of active nucleation cavities on the wall. Increasing heat flux up to the CHF, the bubble density on the heated surface increases and remarkably large coalescent bubbles appear periodically near the heating section outlet.     

Influence of periodic disturbances on inception of cavitation in sharp-edged orifices

The influence of periodic flow disturbances on the onset of cavitation in sharp-edged orifices was determined through a series of experiments. Different amplitudes and frequencies of disturbance were introduced in the flow. The threshold value of cavitation parameter for which transition from attached to cavitating flow took place was shown to depend on the amplitude of the disturbance. Cavitating flow was initiated more spontaneously as the amplitude of disturbance increased. Hysteresis in the flow was, however, observed to decrease. Variations in the frequency of the disturbance did not bring about any significant change in the cavitation parameter at transition. The results are interpreted in terms of the available dwell time for cavitation and the characteristic residence time of the fluid in the sharp-edged orifice and in the pipeline upstream of the orifice.     

Codimension-two bifurcations induce hysteresis behavior and multistabilities in delay-coupled Kuramoto oscillators

Hysteresis phenomena and multistability play crucial roles in the dynamics of coupled oscillators, which are now interpreted from the point of view of codimension-two bifurcations. On the Ott–Antonsen’s manifold, two-parameter bifurcation sets of delay-coupled Kuramoto model are derived regarding coupling strength and delay as bifurcation parameters. It is rigorously proved that the system must undergo Bautin bifurcations for some critical values; thus, there always exists saddle-node bifurcation of periodic solutions inducing hysteresis loop. With the aid of center manifold reduction method and the MATLAB package DDE-BIFTOOL, the location of Bautin and double Hopf points and detailed dynamics are theoretically determined. We find that, near these critical points, four coherent states (two of which are stable) and a stable incoherent state may coexist and that the system undergoes Neimark–Sacker bifurcation of periodic solutions. Finally, the clear scenarios about the synchronous transition in delayed Kuramoto model are depicted.     

Numerical Simulation of a CT-Scanned Counter-Current Flow Experiment

Counter-current flow occurs in many reservoir processes and it is important to understand and model these processes in order to operate them effectively. Both drainage and imbibition processes exist simultaneously during counter-current flow. It has thus proven difficult to model this type of flow using conventional techniques because of the impossibility of assigning a single capillary pressure curve applicable over the entire sample. In the current paper, a new saturation-history-dependent approach has been developed to simulate a counter-current flow experiment done with an X-ray CT scanner. Hysteresis in both capillary pressure and relative permeabilities is considered during simulation. Capillary hysteresis loop and relative permeabilities are extracted through history matching and a family of scanning curves is constructed connecting the two branches of the capillary hysteresis loop. Each gridblock of the sample is assigned a different scanning curve according to the local saturation history. History-dependent modeling of the experiment reproduced two-dimensional saturation distributions over time with good accuracy, which cannot be obtained with traditional simulation using only one capillary pressure curve.     

Capillary Hysteresis in Neutrally Wettable Fibrous Media: A Pore Network Study of a Fuel Cell Electrode

Hysteresis in the saturation versus capillary pressure curves of neutrally wettable fibrous media was simulated with a random pore network model using a Voronoi diagram approach. The network was calibrated to fit experimental air-water capillary pressure data collected for carbon fibre paper commonly used as a gas diffusion layer in fuel cells. These materials exhibit unusually strong capillary hysteresis, to the extent that water injection and withdrawal occur at positive and negative capillary pressures, respectively. Without the need to invoke contact angle hysteresis, this capillary behaviour is re-produced when using a pore-scale model based on the curvature of a meniscus passing through the centre of a toroid. The classic Washburn relation was shown to produce erroneous results, and its use is not recommended when modelling fibrous media. The important effect of saturation distribution on the effective diffusivity of the medium was also investigated for both water injection and withdrawal cases. The findings have bearing on the understanding of both capillarity in fibrous media and fuel cell design.     

Instabilities of micellar systems under homogeneous and non-homogeneous flow conditions

The rheological behavior of a cetylpyridinium chloride 100 mmol l^–1/sodium salicylate 60 mmol l^–1 aqueous solution was studied in this work under homogeneous (cone and plate) and non-homogeneous flow conditions (vane-bob and capillary rheometers), respectively. Instabilities consistent with non-monotonic flow curves were observed in all cases and the solution exhibited similar behavior under the different flow conditions. Hysteresis and the sigmoidal flow curve suggested as characteristic of systems that show constitutive instabilities were observed when running cycles of increasing and decreasing stress or shear rate, respectively. This information, together with a detailed determination of steady states at shear stresses close to the onset of the instabilities, allowed one to show unequivocally that "top and bottom jumping" are the mechanisms to trigger the instabilities in this micellar system. It is shown in addition that there is not a true plateau region in between the "top and bottom jumping". Finally, the flow behavior beyond the upturn seemed to be unstable and was found accompanied by an apparent violation of the no-slip boundary condition.     

Stabilized interface methods for mechanical joints: Physics-based models and variationally consistent embedding

This paper presents the application of a new method for interfacial modeling utilizing a merger of continuous Galerkin and discontinuous Galerkin concepts to simulate the behavior of mechanical joints. The interfacial flux terms arising naturally from the discontinuous Galerkin treatment provide a mechanism to embed friction models in a variationally consistent fashion. Due to the unbiased implementation of the interface, facilitated by avoiding the master–slave concept, the deformation of the two interacting surfaces conforms to the local material and geometric attributes of the surfaces. This results in a better preservation of physics in interface mechanics. Additionally, the method is incorporated into a Variational Multiscale framework that comes equipped with a built-in error estimation module, providing numerical estimation of convergence and distinguishing discretization errors from modeling errors. A series of quasi-static numerical simulations of a lap joint under fretting conditions are conducted to compare the performance of two friction models: (i) classical Coulomb friction model and (ii) physics-based multiscale model. Hysteresis study of a three-dimensional double-bolted lap joint for the two friction models is also presented and the computed results are shown to be consistent between conforming and nonconforming meshes.     

基于贝叶斯理论的恢复力模型参数识别方法

提出了基于贝叶斯理论的恢复力模型参数识别方法,该方法考虑了模型误差的影响,结合实测滞回曲线数据,不仅可以得到模型参数的最有可能值,而且可以得到模型参数的定量的不确定性。以密肋复合墙体在低周反复荷载作用下所得滞回曲线为例,提出了可考虑刚度降低、捏拢滑移及极限荷载后强度降低现象的恢复力模型,建立了基于贝叶斯理论的恢复力模型参数识别计算框架,推导得到了模型参数的负对数似然函数,据此可得到模型参数的最有可能值及协方差矩阵。对标准密肋复合墙体预制试件和现浇试件的恢复力模型参数进行了识别,将根据模型参数最有可能值得到的滞回曲线及根据模型参数最有可能值及协方差矩阵得到的骨架曲线,与相应的实测值进行了对比,验证了所提方法的可行性及识别结果的合理性,更新的模型参数概率分布可用于后续的抗震风险评估。     

Characteristics of ventilating flow generated by a rotating swirler in a vortex vent

A vortex ventilation system with a rotating annular disk installed coaxially with the exhaust inlet is a very effective local ventilator. A swirling flow generated by a rotating swirler makes the ventilation flow concentrated around the axis of rotation, which can increase the ventilation depth by a factor of five compared to a conventional exhaust hood. Despite the well-documented excellent ventilation performance of such a system, detailed flow characteristics are not well understood. In this study, the swirling flow field in the vortex vent was tested, and a number of peculiar flow characteristics were observed. When the rotational speed was varied, a series of different flow patterns appeared, and the changes in the flow pattern showed rapid transition, hysteresis, and flow instability similar to the vortex. The transition of the flow pattern could be explained based on the ratio of the centrifugal force to exhaust pressure. Hysteresis of the flow transition occurred in an unstable equilibrium mode between the two forces, and an unstable flow pattern occurred when the secondary recirculating flow was located beneath the swirler. A formula for the critical rotational speed was derived, which showed satisfactory agreement with experimental observation.     

Modeling the elasto-acoustic hysteretic nonlinearity of dry Berea sandstone

By means of the dynamic acousto-elastic technique the instantaneous state of a material is probed by a high-frequency pulse while an external, low-frequency dynamic source modulates it in time. When it is applied to rocks, a remarkable variety of responses in the form of hysteresis of the material’s modulus defect is obtained. Among them, the response by Berea sandstone is perhaps the most investigated. Hysteresis of the modulus defect in dry Berea sandstone shows intriguing features which have not yet been interpreted in terms of specific mechanisms occurring at atomic or meso-scale. In the present communication, three rheological models providing simplified representations of realistic mechanisms are considered. They involve dislocations interacting with point defects, and microcracks with finite stiffness in compression. Constitutive relations linking macroscopic anelastic strain and stress are derived from them together with the modulus defect associated to each model. These relationships are employed to construct a composite model capable of reproducing several of the main features observed in the experimental data. The limitations of the present approach, the validity of its physical interpretation, and, possibly, of the current implementation of the dynamic acousto-elastic technique are also discussed.