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The nonlinear dynamic characteristics of giant magnetostrictive ultrasonic transducer (GMUT) are researched in this paper, and the optimal control strategy is proposed. New nonlinear differential terms are introduced to explain the hysteretic phenomena of giant magnetostrictive materials (GMM), and the nonlinear dynamic model of a giant magnetostrictive ultrasonic transducer subjected to harmonic magnetic field and stochastic disturbance is developed. The system's nonlinear dynamic responses are discussed, and the optimal control strategy is proposed to improve the system's accuracy. Numerical simulation and experiment results show that there are abundant nonlinear dynamic behaviors in the system; the stability of the system varies with the parameters, which causes stochastic bifurcation; the system's accuracy is improved through stochastic optimal control. The results of this study are helpful for the application of giant magnetostrictive ultrasonic transducer in engineering fields. [ABSTRACT FROM AUTHOR]

The nonlinear dynamic characteristics of Fe-Ga cantilever nanobeam subjected to stochastic excitation are studied in this paper where the nonlocal effect is considered. Nonlinear differential terms are introduced to explain the hysteretic phenomena of the Fe-Ga alloy's strain-magnetic field intensity curves, and the nonlinear dynamic model of Fe-Ga cantilever composite nanobeam subjected to stochastic excitation is developed. The system's nonlinear dynamic characteristics are discussed, and the optimal control strategy is proposed to enhance the system's reliability. Numerical simulations show that the nonlocal effect can influence the system's stochastic Hopf bifurcation; the boundary of the system's safe basin has fractal characteristics, the area of safe basin decreases when the intensity of the noise increases, and it increases again through stochastic optimal control. The results of this study are helpful for the application of Fe-Ga composite nanobeam in engineering fields. [ABSTRACT FROM AUTHOR]

Nonlinear dynamic characteristics and optimal control of magnetic shape memory alloy (MSMA) cantilever beam subjected to axial stochastic excitation is studied in this paper. Nonlinear difference item is introduced to interpret the hysteretic phenomena of MSMA, and the nonlinear dynamic model of MSMA cantilever beam subjected to axial stochastic excitation is developed. The steady-state probability density function of the dynamic response of the system is obtained, and the conditions of stochastic Hopf bifurcation are analyzed. The reliability function of the system is solved, and then the probability density of the first-passage time is obtained. Finally, the optimal control strategy is proposed in stochastic dynamic programming method. Numerical simulations show that the stability of the trivial solution varies with bifurcation parameter, and stochastic Hopf bifurcation appears in the process; the reliability of the system is proved by stochastic optimal control, and the first-passage time is delayed. The results are helpful to engineering application of MSMA cantilever beam. [ABSTRACT FROM AUTHOR]

In this paper, nonlinear dynamic characteristics and optimal control of giant magnetostrictive laminated plate (GMLP) subjected to in-plane stochastic excitation were studied. Von del Pol nonlinear item was introduced to interpret the hysteresis phenomenon of the strain-magnetic field intensity curve of giant magnetostrictive material, and the nonlinear dynamic model of GMLP subjected to in-plane stochastic excitation was developed. Local and global stochastic stabilities were analyzed according to largest Lyapunov exponent theory and singular boundary theory. The functions of steady-state probability density and joint probability density were obtained, and the condition of stochastic Hopf bifurcation was analyzed. The reliability function was solved from backward Kolmogorov equation, and the probability density of the first-passage time was obtained. Finally, the optimal control strategy was proposed in stochastic dynamic programming method. Numerical simulation shows that the stability of the solution varies with parameter, and stochastic Hopf bifurcation appears in the process; the reliability of the system was improved by optimal control, and the first-passage time was delayed. The result is helpful to engineering applications of GMLP. [ABSTRACT FROM AUTHOR]

A prototype of a Superconducting Electromagnet Iron Remover (SEIR) system with a 3 tesla (T) central field has been designed and manufactured at the Institute of High Energy Physics (IHEP) of China. The SEIR system is deliberately designed to separate small pieces of hazardous ferromagnetic materials, such as detonators, from coal to achieve high purity and good yield. The SEIR system consists of a NbTi superconducting magnet, a LHe recondensation type cryostat with two GM cryocoolers (31 W/40 K, 1 W/4.2 K), and a pair of binary current leads (CLs), etc. This paper presents the thermal analysis and experimental results of the SEIR system. A three-dimensional (3D) model of calculation for the magnet system was built. The heat load and the temperature distribution of the magnet system were analyzed using a finite element method. With regard to the heat load of the system, the finite element analysis (FEA) simulation results were quite close to the experimental results. [ABSTRACT FROM AUTHOR]

With the increasing of wind energy, it is necessary to develop an energy storage system to level the wave of wind power, and to develop a fault current limiter for improvement of the LVRT capability of the wind farm. An innovative idea to deal with the above problem is to develop a superconducting fault current limiter-magnetic energy storage system (SFCL-MES). In this paper, we report the progress of the superconducting coil for a 1-MJ/0.5-MVA FCL-SMES system. The coil consisted of 46 double pancakes, in which 8 pancakes were made of YBCO tapes and the others were made of Bi2223 tapes; the inductance of the coil was 13.3 H, and its rated current was 388 A while the maximum magnetic field was 3.5 T. This coil had been used for a FCL-SMES system, which was installed and tested at a wind farm connected to the live power grid. [ABSTRACT FROM AUTHOR]

Stochastic resonance of a giant magnetostrictive film-shape memory alloy (GMF-SMA) composite cantilever plate subjected to in-plane stochastic magnetic excitation is studied in the paper. Van der Pol terms are developed to explain the hysteretic phenomena of both GMF and SMA, and the nonlinear dynamic model of GMF-SMA composite cantilever plate subjected to in-plane stochastic magnetic excitation is established. The probability density function of the system's dynamic response is obtained, and the conditions of stochastic bifurcation are analyzed. Numerical simulation and experimental results show that the stochastic noise intensity plays an important role in the system's vibration; the system's response is little when the stochastic noise intensity is weak, and then the system's response increases with the stochastic noise, and finally decreases when the stochastic noise reaches a certain value; the stochastic resonance phenomenon occurs with the stochastic noise varying. The results of this paper are helpful for the application of GMF-SMA composite cantilever plate in vibration reduction fields. [ABSTRACT FROM AUTHOR]

There are many irreplaceable advantages of high temperature superconducting (HTS) fault current limiter, applying in electric utilities. It is expected to be able to solve excessive fault current problems and to enhance safety and stability of power systems. In this paper, the R and D of an improved bridge-type 10.5 kV three-phase superconducting fault current limiter (SFCL) was present. Each phase adopted a HTS coil with inductance of 6.2 mH. The three coils wound with 8,571 m Bi2223/Ag tapes totally. After installation at a 110 kV/10.5 kV substation in Hunan Province of China, the performances of the whole SFCL were tested, including a three-phase-to-ground short circuit experiment at the pre-setup short circuit point. And then, the SFCL was put into operations in the 10.5 kV power grids for more than 11000 h. About 3 years later, the SFCL was moved, reinstalled, and put into operation again since February 16 of 2011 at a 10.5-kV superconducting power substation located in Baiyin, Gansu Province of China. In this paper, the redesigned and manufactured cryostats with nonmagnetic stainless steel, tests, and long-term operations of the SFCL in 10.5 kV power grids were also described in detail. [ABSTRACT FROM AUTHOR]

7 T experiment system, which was designed for a MRI superconducting switch test, has been developed at the Institute of High Energy Physics (IHEP) of China. The system mainly consists of a 7 T background superconducting coil, two pairs of 800 A vapor cooled current leads, a data acquisition system and more. The NbTi superconducting coil, with an operating current of 376 A, has a central field of 7 T and clear bore of 80 mm. The no-impregnation technique was adopted to fabricate this coil. The coil reached 96% of its short sample performance after three times quench. The system detailed experiments are presented in this paper. [ABSTRACT FROM AUTHOR]