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The development of high‐precision, non‐destructive, and three‐dimensional (3D) in situ imaging of micro‐scale damage inside polymers is extremely challenging. Recent reports suggest that 3D imaging technology based on micro‐CT technology causes irreversible damage to materials and is ineffective for many elastomeric materials. In this study, it is discovered that electrical trees inside silicone gel induced by an applied electric field can induce a self‐excited fluorescence effect. Based on this, high‐precision, non‐destructive, and 3D in situ fluorescence imaging of polymer damages is successfully achieved. Compared with the current methods, the fluorescence microscopic imaging method enables slicing of the sample in vivo with high‐precision operation, realizing the precise positioning of the damaged area. This pioneering discovery paves the way for high‐precision, non‐destructive, and 3D in situ imaging of polymer internal damage, which can solve the problem of internal damage imaging in insulating materials and precision instruments. This study reports for the first time the characterization of electrical tree degradation in polymers through the detection of self‐excited fluorescence in the channel area of the tree. Furthermore, this high‐precision, in situ technique is developed without causing further damage to the polymer which is an issue that is present in currently used imaging techniques.

The moment when stability moves to instability and order moves to disorder constitutes a chaotic systems; such phenomena are characterized sensitively on the basis of initial conditions. In this manuscript, a fractal–fractionalized chaotic chameleon system is developed to portray random chaos and strange attractors. The mathematical modeling of the chaotic chameleon system is established through the Caputo–Fabrizio fractal–fractional differential operator versus the Atangana–Baleanu fractal–fractional differential operator. The fractal–fractional differential operators suggest random chaos and strange attractors with hidden oscillations and self-excitation. The limiting cases of fractal–fractional differential operators are invoked on the chaotic chameleon system, including variation of the fractal domain by fixing the fractional domain, variation of the fractional domain by fixing the fractal domain, and variation of the fractal domain as well as the fractional domain. Finally, a comparative analysis of chaotic chameleon systems based on singularity versus non-singularity and locality versus non-locality is depicted in terms of chaotic illustrations.

Low-voltage induction motors, which are widely used in industrial fields, have a large change in power factor from starting to reaching the rated speed when starting directly, and are used by installing an additional power factor compensation capacitor due to the low power factor at the rated speed. However, depending on the additional installation of this capacitor and the operating conditions of the induction motor, a self-excitation phenomenon in which the capacitor leading current becomes larger than the induction motor magnetizing current may occur, so detailed analysis and research on reduction measures are necessary. In this paper, the changes of parameters related to self-excitation during the starting in an analytical model including a 50 [hp] induction motor and a power factor correction capacitor is quantitatively analyzed using by electromagnetic transients program. In order to reduce the self-excitation phenomenon, the proper connection timing of capacitor was suggested based on the analysis results, and a method of implementing the capacitor switching controller was presented. In the analysis model to which this was applied, the application and feasibility of the switching controller is verified by the analysis and comparison of the magnetization current of the induction motor and the current of the capacitor.

An economical method for numerical simulation of self-excitation of gas oscillations in low-emission combustors of gas turbine plants is developed and tested. The method is based on using an SAS SST   turbulence model and a turbulent combustion model with a modified equation for a variable degree of combustion completion. Simulating the self-excitation of gas oscillations requires that a factor associated with gas pressure oscillations is introduced into the source term of this equation. Isolation of one of the gas oscillation modes prone to self-excitation is carried out using a resonant filter operating in each cell of the computational domain. The computational results obtained using the proposed method make it possible to study the effect of design measures and operating parameters of self-oscillations and to approach the choice of measures to suppress them.

This paper deals with the computation of the performance characteristics of the single-phase self-excited induction generator by field–circuit method. It presents and compares previously unpublished results—self-excitation and no-load characteristics of the generator for different rotor speeds, and complete load steady-state performance characteristics for various types of the core materials. The discrepancies between the performance characteristics of the generator for the catalog’s magnetization curves of different types of electrical sheets and for an actual magnetic core of the generator for self-excitation transients and load steady-state are presented. The results may be useful for designing new constructions of single-phase self-excited induction generators.

A previous study proposed an optimal vibration isolator for self-excitation, but the solution results showed a critical drawback for the basement input. Because the plant system is exposed to self-excitation and basement input, the vibration isolator characteristics must meet all the requirements of both excitation cases. Two performance indices of the vibration isolator were introduced to evaluate the vibration control capability over two excitation cases, self-excitation and basement input, using the theoretical linear model of the electric power generator. The compromise strategy was devoted to enhancing the vibration control capability over the basement input, owing to the acceptable margin for self-excitation. The modification of the mechanical properties of the vibration isolator focused on the isolator between the mass block and the surrounding building. Simulation results revealed that an increase in the spring coefficient and a decrease in the damping coefficient of the vibration isolator beneath the mass block could enhance the vibration reduction capability over the basement input.

As power electronic converters become more widely used in aviation power systems, the associated capacitive loads in the harmonic filter circuits increase accordingly. The risk of self-excitation of aeronautical synchronous generators due to capacitive loads is thus increased. Compared with the self-excitation of a generator in a conventional fixed-frequency power system, this process is more complicated in a variable-frequency aviation power supply (360–800 Hz), as both the varied frequency and the loading conditions contribute to the self-excitation. To quantify this effect, in our study, a series-parallel model of simplified RLC loads under a variable-frequency power supply was built. The criterion of generator self-excitation, given in terms of the generator impedance and the load impedance, was then derived. To facilitate the load configuration design in the case of an aviation power system, a comprehensive analysis of the influences of the varied load power and system frequency on the load impedance was conducted. A graphical approach was proposed to determine self-excitation by comparing the series load reactance and resistor with three critical impedances corresponding to three self-excitation criteria, which is more intuitive and enables one to visualize the tendency of self-excitation with varied frequencies and loading conditions more effectively. Finally, the influence of variable frequency on the self-excitation of the aeronautical synchronous generator was verified by the simulation results.

Purpose The purpose of the paper is to present an analysis of an influence of shape and material of rotor bars on the process of self-excitation and performance characteristics of single-phase, self-excited induction generator (SP-SEIG). Design/methodology/approach The presented analysis is based on the results of transient simulations of SP-SEIG performed with the use of field-circuit model of the machine. Four various shapes of the rotor bars and two different conductor materials were investigated. The results for the base model with rounded trapezoidal rotor slots were validated by measurements. Findings An improvement of the performance characteristics – the extension of the stable operating range of the generator – was obtained for rectangular copper rotor bars. The improvement is the result of strong skin effect in the squirrel rotor cage. Application of round rotor slots results in shorter time of voltage build-up during the self-excitation of the generator caused by less apparent deep bar effect in round bars. Originality/value The originality of the paper is the application of the copper rotor cage in the single-phase, self-excited induction generator. Its use is beneficial, as it allows for extension of the range of stable operating range. The results may be used for designing new constructions of the single-phase, self-excited induction generators, as well as the constructions based on general purpose single-phase induction motors.

This work concerns the usage of the internal stiffness and damping nonlinearity for vibration suppression in a van der Pol–type mechanical self-excitation system. Changing the vertical or horizontal damping could limit the growth of the flow-induced instability. Applying harmonic balance method, the energy transfer for the self-excitation vibration is investigated through the limit circle. The steady amplitude of the limit circle is a key parameter that could be used to evaluate the effectiveness of the self-excitation oscillation suppressing. Increasing horizontal damping could reduce the rate of roll on for the steady amplitude curve of the limit circle, but the critical flow velocity for the limit circle occurring is minimally affected. Increasing vertical damping could increase the critical flow velocity, but the rate of the roll on is virtually unaffected when the parameters are properly chosen.

Today, improving the quality of the images acquired by the atomic force microscope (AFM) and obtaining the close properties of various samples are among the most important and challenging issues tackled by researchers. One of the key mechanisms of achieving these objectives is the excitation of higher modes, which raises the sensitivity of the AFM and consequently improves the resolution. To attain this goal, it is imperative to design or select a type of cantilever which is able to excite the second mode and produce maximum sensitivity in higher modes, especially the second mode. In this paper, an AFM cantilever with rectangular cross section has been investigated in air medium. The cantilever has been modeled by the Timoshenko beam model and the normal and tangential forces between cantilever tip and sample have been considered in the simulations. By changing the geometrical parameters of the AFM’s cantilever and tip including length, width, thickness of cantilever, the angle between cantilever and sample surface, mass of tip, length of tip and Radius of tip, the frequency ratio of the second mode to first mode varies. The geometrical parameters that produce the minimum frequency ratio can increase the self-excitation probability of the second mode due to the excitation of the first mode simultaneously. The optimum geometrical parameters are derived that can increase the chance of higher mode excitation. The results indicate that the sensitivity of the second mode to sample stiffness also increases optimal geometrical parameters that yield the minimum frequency ratio; and, as a result, a higher contrast is achieved and it leads users to utilize the cantilevers with optimum geometry for achieving best contrast in imaging and properties estimation of unknown samples.