Characterization of Electromagnetic Device by Means of Spice Models

— In this paper, the lumped parameter circuital approach devoted to the simulation of massive, conductive, and ferromagnetic cores including eddy currents and nonlinearity is presented. In the first part of the paper, the circuit analogies devoted to the simulation of magnetic structure coupled with external electrical and eventually mechanical equations are summarised. The two techniques are known in the literature as reluctance-resistance and permeancecapacitance analogies. In particular, it is put in evidence the exploitation of the gyrator component in the modelling of the coupling among magnetic and electrical quantities. The originality of this paper consists in demonstrating for the first time that the rotator-capacitor approach is very suitable for simulations in spice environment and the solution is validated on real applications. Following the circuital approach, the effect of the conductivity and nonlinear magnetic behaviour of the magnetic branches is formalized and introduced in the model. The simulation of the conductivity behaviour, which introduces in massive cores significant eddy current effects, is modelled according to the two possible analogies: the reluctance and the permeance-capacitor model. Under sinusoidal steady-state behaviour, energy aspects related to the two models are then presented and discussed. The nonlinearity is taken into account through the fixed-point technique which is suitable for a lumped circuit representation. The full circuital approach is then adopted for the simulation of the real electromechanical actuator under transient and sinusoidal steady-state behaviour conditions. The simulated result is then compared with numerical finite element and experimental result

Modeling the impedance response and steady state behaviour of porous CGO-based MIEC anodes

The SOFC MIEC anode model enables an appropriate understanding of the complex physico-chemical processes and microstructure effects and thus provides a basis for a systematic materials optimization.

TIME DOMAIN METHOD FOR THE DETERMINATION OF THE STEADY STATE BEHAVIOUR OF NONLINEAR CIRCUITS DRIVEN BY MULTI-TONE SIGNALS

Time domain methods, while well suited to compute the steady state behaviour of strongly nonlinear non-autonomous electrical circuits, are inefficient if the periods of the forcing signals have a very large minimum common multiple. The solution of the periodicity constraint requires to integrate the differential algebraic equation (DAE) describing the circuit along the T period and this can be a CPU time consuming task. Literature reports several attempts to extend the SH method to simulate circuits driven by multi-tone signals [2] [4] [5]. However, as far as we know, all they suffer of limitations and it is our opinion that an efficient and general extension has not been found, yet. In this paper we present a possible extension that takes its origin from the previous approach reported in [2]. In this paper a modification of the conventional shooting method is presented that tries to overcome the above drawback.

Computational analysis of the steady state performance of an adjustable/controllable multi-pad bearing profile under LBP orientations

A theoretical model of a four-pad bearing profile with unique adjustable or controllable features is simulated in the present study by considering load directed between the pads. Radial and tilt adjustable mechanism of the four bearing pads can effectively control and modify the rotor operating behaviour. Inward and outward motions of the bearing pads result in the generation of narrow and broader convergent regions, which directly influences the fluid film pressures. In the theoretical analysis, load-between-pad (LBP) orientations and pad adjustment configurations are taken account of by employing a modified film thickness equation. The effect of load position in influencing the steady state behaviour of the four-pad adjustable bearing under varied pad displaced conditions is analysed in this study. The outcome of the analysis highlighted the effectiveness of four-pad adjustable bearing in improving the steady state performance by operating under negative adjustment conditions and with load acting on the bearing pads.

BioSwitch: a tool for the detection of bistability and multi-steady state behaviour in signalling and gene regulatory networks

Motivation Multi-steady state behaviour, and in particular multi-stability, provides biological systems with the capacity to take reliable decisions (such as cell fate determination). A problem arising frequently in systems biology is to elucidate whether a signal transduction mechanism or a gene regulatory network has the capacity for multi-steady state behaviour, and consequently for a switch-like response to stimuli. Bifurcation diagrams are a powerful instrument in non-linear analysis to study the qualitative and quantitative behaviour of equilibria including bifurcation into different equilibrium branches and bistability. However, in the context of signalling pathways, the inherent large parametric uncertainty hampers the (direct) use of standard bifurcation tools. Results We present BioSwitch, a toolbox to detect multi-steady state behaviour in signalling pathways and gene regulatory networks. The tool combines results from chemical reaction network theory with global optimization to efficiently detect whether a signalling pathway has the capacity to undergo a saddle node bifurcation, and in case of multi-stationarity, provides the exact coordinates of the bifurcation where to start a numerical continuation analysis with standard bifurcation tools, leading to two different branches of equilibria. Bistability detection in the G1/S transition pathway of Saccharomyces cerevisiae is included as an illustrative example. Availability and implementation BioSwitch runs under the popular MATLAB computational environment, and is available at https://sites.google.com/view/bioswitch.

Some Facts We Can Learn from Analytical Modeling of DDRX in Pure Metals and Solid Solutions

Modeling and simulation of discontinuous dynamic recrystallization (DDRX) are now commonly carried out by numerical methods, most often finite element computation. It is also possible to use simple analytical approaches on the grain scale to get relevant information about the basic mechanisms involved in DDRX, in particular regarding the large strain steady state behaviour. This is illustrated in the present paper on the basis of a model previously proposed by the author and co-workers, which is first briefly presented. The macroscopic constitutive parameters associated with DDRX are then derived and three distinct “Derby exponents” are introduced for describing the relationship between steady state grain size and flow stress. Finally, it is shown, with the example of grain sizes, that not only can average quantities be predicted analytically, but also their distributions.