• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 추계학술대회 논문집
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• pp.799-805
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• 1996

In many cases, the magnetic farce model is linearized at the origin in designing the controller of a magnetic bearing system. However. this linear assumption is violated by the unmodeled nonlinear effect such as sensor dislocation and backup bearing dislocation. Therefore, a direct probe into the nonlinear magnetic force model in an active magnetic bearing system is necessary. To analyze the nonlinear magnetic force model of a magnetic bearing system, phase plot analysis which is to plot the numerical solution of the nonlinear equation in several initial points in the interested region is applied. Phase plot analysis is used to observe a nonlinear dynamic system qualitatively (not quantitatively). With this method, we can get much useful information of the nonlinear system. Among this information, a bifurcation graph that represents stability and locations of fixed points is essential. From the bifurcation graph, a stability criterion of magnetic bearing system is derived.

• 전기학회논문지
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• 제59권9호
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• pp.1605-1610
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• 2010

In this paper, the relative stability of magnetic bearing system for the flywheel energy storage is evaluated using both simulation and experimental analysis. We make the simulation model for the magnetic bearing flywheel system using the rigid body shaft model. According to international standard ISO 14839-3, We experimentally analyzed the relative stability of magnetic bearing system. Additionally using both the simulation model and experimental tests, Phase margin and Gain margin is acquired through Nyquist plot.

• Steel and Composite Structures
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• 제41권6호
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• pp.775-785
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• 2021

Analysis of nonlinear stability behaviors of composite magneto-electro-elastic (MEE) nano-scale shells have been represented in this reaserch. The shell is assumed to be under a transverse mechanical load. Composite MEE material has been produced form piezoelectric and magnetic ingradients in which the material charactristics may be varied according to the percentages of the ingradients. The governing equations including scale effects have been developed in the framework of nonlocal elasticity. It has been demonstrated that nonlinear stability behaviors of MEE nano-sized shells in electrical-magnetic fields rely on the percentages of the ingradients. Also, the efficacy of nonlocality parameter, magnetic intensities and electrical voltages on stability loads of the nanoshells have been researched.

• Smart Structures and Systems
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• 제25권6호
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• pp.707-717
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• 2020

In this paper, analysis of thermal post-buckling behaviors of sandwich nanobeams with two layers of multi-phase magneto-electro-thermo-elastic (METE) composites have been presented considering geometric imperfection effects. Multi-phase METE material is composed form piezoelectric and piezo-magnetic constituents for which the material properties can be controlled based on the percentages of the constituents. Nonlinear governing equations of sandwich nanobeam are derived based on nonlocal elasticity theory together with classic thin beam model and an analytical solution is provided. It will be shown that post-buckling behaviors of sandwich nanobeam in thermo-electro-magnetic field depend on the constituent's percentages. Buckling temperature of sandwich nanobeam is also affected by nonlocal scale factor, magnetic field intensity and electrical voltage.

• 동력기계공학회지
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• 제15권1호
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• pp.78-85
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• 2011

In order to design the control system of the magnetic bearing for the high speed 3 phase induction motor, the mathematical modeling was conducted and LQ regulator system was designed. When the plant is controllable and detectable, the nominal stability of LQ regulator could be guaranteed. However, LQ regulator doesn't ensure the robustness of stability and performance for the real system because LQ control is the mathematical optimal theory. In this paper to ensure the robustness of stability and performance for the real system, the control systems are designed by the simulation to the variation system parameters and this method was confirmed as an effective means.

• 한국자기학회지
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• 제5권5호
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• pp.543-547
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• 1995

A set of $Fe_{1-x}Ni_{x}$ (x=0.10, 0.25, 0.30, 0.35, 0.50, 0.60, 0.75, 0.85) fine particles prepared by the gas evaporation technique was studied by $M\"{o}ssbauer$, XRD and other techniques. The XRD and $M\"{o}ssbauer$ patterns of the sample with x=0.10 ($Fe_{90}Ni_{10}$) were found to be exceptionally different, showing an austenite phase stability when the particles are quenched. This phase stability is quite different from that of the corresponding bulk alloy. Using binomial distrbution fits of the $M\"{o}ssbauer$ spectra of the particles in terms of nearest and next nearest neighbour configurations around the Fe atoms, an analysis of this phase stability is given. The changes in the relative intensities of the resulting magnetic sextets are used to determine the increase in martensite following the austenite-martensite transformation process. The stable austenite can, therefore, be determined. This stability may be related to the oxide surface layer and the small number of atoms of these fine particles.

• 한국세라믹학회지
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• 제28권2호
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• pp.93-100
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• 1991

For determination the optimum manufacturing condition Fe4N powder for magnetic recording media, we have studied the following important conditions : the effect of particle size of metal powder on the nitridation, the condition of nitridation on the formation and magnetic properties of Fe4N, and stability of Fe4N powder against temperature and change on standing. The results can be summarized as : 1) Single phase Fe4N is formed at 50v/o of ammonia concentration during the nitridation reaction, 2) Single phase Fe4N is formed above 40$0^{\circ}C$, 15min regardless of the metal powder sizes, 3) Coercivity and saturation magnetization of Fe4N powder almost constant value until 20 day-passing from preparation date.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1171-1172
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• 2006

Addition of 2.0wt%$Dy_2O_3$ or 0.3wt%Sn proved to be very effective in improving the permanent magnetic properties of NdFeNbB magnets. $Dy_2O_3$ additions result in the increase in the Hci and temperature dependence due to formation of (NdDy)-rich phase and grain refinement of $\Phi$ phase. This improvement of the coercivity stability of the magnets from the addition of Sn is attributed to the smoothing effect of the Sn addition at the grain boundaries. The magnetic properties, the temperature dependence and Curie temperature of NdFeNbB with $Dy_2O_3$ and Sn combined addition were found to be considerably improved.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2015년도 자성 및 자성재료 국제학술대회
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• pp.72-72
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• 2015

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2013년도 임시총회 및 하계학술연구발표회
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• pp.15-16
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• 2013

Magnetization behavior of ultra thin $Fe_xCo_{1-x}$ alloy (where x varies from 0 to 100) has been investigated as functions of composition on Cr (100) substrate by using in situ surface magneto optical Kerr effect (SMOKE). It's always show in plane uniaxial magnetic anisotropy at room temperature (RT) & Low temperature (LT). It is observed that composition dependent coercive force maximum at about 30 at % Co and 70 at % Co atomic ratio and minimum near equiatomic site. The relative magnetic moments as composition variation also show magnetization collapse near equiatomic site. The magnetization behaviors of Fe-Co alloy on Cr (100) due to composition varies are supported the order-disordering as well as structural stability bcc (ferromagnetic)/fcc (anti-ferromagnetic) phase stability magnetism.