• Journal of Magnetics
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• v.20 no.1
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• pp.91-96
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• 2015

As many researchers are relentlessly trying to improve the power generation schemes from the power grid, to meet the constantly increasing electricity demand. In this paper, the results of a finite element analysis are carried out to study on a design optimization of an asymmetric air-gap structure in 3-phase Permanent Magnet Brushless DC Motors. To achieve a high efficiency for a 3-phase PM BLDC motor, the asymmetric air-gap structure is proposed considering the rotation direction of a motor. Generally, a single-phase BLDC motor is applied asymmetric air-gap structure for starting. This is because the asymmetric air-gap structure causes reluctance variation so the motor can utilize reluctance torque toward a rotation direction. In this paper, the asymmetric air-gap is applied to 3-phase BLDC SPM motor so it utilizes reluctance torque with alignment torque. A proposed model is designed by 2-D FE analysis and the results are verified by experimental test.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.505-530
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• 2008

This paper proposes the application of active multiple tuned mass dampers (AMTMD) for translational and torsional response control of a simplified two-degree-of-freedom (2DOF) structure, able to represent the dynamic characteristics of general asymmetric structures, under the ground acceleration. This 2DOF structure is a generalized 2DOF system of an asymmetric structure with predominant translational and torsional responses under earthquake excitations using the mode reduced-order method. Depending on the ratio of the torsional to the translational eigenfrequency, i.e. the torsional to translational frequency ratio (TTFR), of asymmetric structures, the following three cases can be distinguished: (1) torsionally flexible structures (TTFR < 1.0), (2) torsionally intermediate stiff structures (TTFR = 1.0), and (3) torsionally stiff structures (TTFR > 1.0). The even distribution of the AMTMD within the whole width and half width of the asymmetric structure, thus leading to three cases of installing the AMTMD (referred to as the AMTMD of case 1, AMTMD of case 2, AMTMD of case 3, respectively), is taken into account. In the present study, the criterion for searching the optimum parameters of the AMTMD is defined as the minimization of the minimum values of the maximum translational and torsional displacement dynamic magnification factors (DMF) of an asymmetric structure with the AMTMD. The criterion used for assessing the effectiveness of the AMTMD is selected as the ratio of the minimization of the minimum values of the maximum translational and torsional displacement DMF of the asymmetric structure with the AMTMD to the maximum translational and torsional displacement DMF of the asymmetric structure without the AMTMD. By resorting to these two criteria, a careful examination of the effects of the normalized eccentricity ratio (NER) on the effectiveness and robustness of the AMTMD are carried out in the mitigation of both the translational and torsional responses of the asymmetric structure. Likewise, the effectiveness of a single ATMD with the optimum positions is presented and compared with that of the AMTMD.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.837-843
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• 2001

Conventional reverberation chamber has a rectangular structure including mode stirrers or mode-turned stirrers to obtain the field uniformity inside the chamber. This paper explained the way to improve the field uniformity in an asymmetric structure instead of conventional rectangular structure with right-angled planes. Two types of asymmetric structure were considered. One was an asymmetric reverberation chamber using Quadratic Residue Diffuser and the other was an asymmetric chamber with oblique enclosure including fixed Randomly Made Diffusers. The FDTD simulation method was used to analyze the field homogeneous characteristics of these asymmetric reverberation chambers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.2
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• pp.83-87
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• 2020

In this letter, we propose and analyze a new asymmetric structure that can be used for next-generation power semiconductor devices. We compare and analyze the electrical characteristics of the proposed device with respect to those of symmetric devices. The proposed device has a p-emitter on the right side of the cell. The peak electric field is reduced by the shielding effect caused by the p-emitter structure. Consequently, the breakdown voltage is increased. The proposed asymmetric structure has an approximately 100% higher Baliga's figure of merit (~94.22 MW/㎠) than the symmetric structure (~46.93 MW/㎠), and the breakdown voltage of the device increases by approximately 70%.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.417-422
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• 2015

In this study, we investigate the effect of porous $Al_2O_3$ substrate on the strengths of asymmetric structures after we prepare such a structure consisting of a dense $Li_2ZrO_3$ top layer and porous $Al_2O_3$ substrate layer. The porosity and elastic modulus of the substrate layer are controlled by sintering temperature, which has three values of 1150, 1250 and $1350^{\circ}C$. The porosity is controlled in the range of ~ 30-50 vol%, elastic modulus is ~80-120 GPa and elastic mismatch $E_s/E_c$ is ~ 0.6-1.0. Indentation stress-strain curves are obtained and analyzed to evaluate the yield stress of the asymmetric structure by concentrated local loading of WC balls. Conventional flexural strengths are also obtained to evaluate the strength of the asymmetric structure. The results indicate that the local yield strength of the asymmetric structure has mid-values between the top and the substrate layer; however, the flexural strength of the asymmetric structure are mainly influenced by elastic modulus and strength of the substrate.

• Journal of the Korean Ceramic Society
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• v.54 no.1
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• pp.33-37
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• 2017

Single phase niobium nitride (NbN) coatings were deposited using asymmetric bipolar pulsed dc sputtering by varying pulse frequency and duty cycle of pulsed plasmas. Crystal structure, microstructure, morphology and mechanical properties were examined using XRD, FE-SEM, AFM and nanoindentation. Upon increasing pulse frequencies and decreasing duty cycles, the coating morphology was changed from a pyramidal-shaped columnar structure to a round-shaped dense structure with finer grains. Asymmetric bipolar pulsed dc sputtered NbN coatings deposited at pulse frequency of 25 kHz is characterized by higher hardness up to 17.4 GPa, elastic modulus up to 193.9 GPa, residual compressive stress and a smaller grain size down to 27.5 nm compared with dc sputtered NbN coatings at pulse frequency of 0 kHz. The results suggest that the asymmetric bipolar pulsed dc sputtering technique is very beneficial to reactive deposition of transition-metal nitrides such as NbN coatings.

• Journal of Magnetics
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• v.22 no.2
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• pp.266-274
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• 2017

In this paper, torques of two motors are compared by Finite Element Analysis (FEA). One has a symmetric rotor structure and the other has an asymmetric rotor structure. The comparison shows that the asymmetric rotor structured motor has reduced torque ripple compared to the symmetric. The torque of the compared motor models was analyzed by separating into magnetic torque and reluctance torque. Through the analysis of torque component separated, it is shown that the magnetic torque and the reluctance torque compensate each other in the motor with the asymmetric structure rotor. Here "compensate" means decrementing the effect of one or more harmonics. It is shown how this compensation appears between the magnetic torque and the reluctance torque by looking into back electro motive force (emf) and the relative permeability distribution of rotor core.

• Nuclear Engineering and Technology
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• v.55 no.12
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• pp.4307-4316
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• 2023

In this paper, modal effective mass for asymmetric fluid-structure interaction system is defined and equations for its calculation is derived. To establish consistency, modal effective mass in symmetric structure only system is briefly reviewed, followed by a definition of the modal effective mass in asymmetric system. The equations for calculating modal effective mass in asymmetric system are derived by utilizing the properties of left and right eigenvectors. To simplify the equations, the assumption is made that the mass matrix is only affected by the fluid. The simplified equation is then compared to the equation already used in ANSYS. Finally, the validity of the modal effective mass definition and derivation in this paper is demonstrated through a simple example.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.461-466
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• 2016

Nanocrystalline vanadium nitride (VN) coatings were deposited using asymmetric bipolar pulsed dc sputtering to further understand the influence of the pulsed plasmas on the crystal structure, microstructure and mechanical properties. Properties of VN coatings were investigated with FE-SEM, XRD and nanoindentation. The results show that, with the increasing pulse frequency and decreasing duty cycle, the coating morphology changed from a porous columnar to a dense structure, with finer grains. Asymmetric bipolar pulsed dc sputtered VN coatings showed higher hardness, elastic modulus and residual compressive stress than dc sputtered VN coatings. The results suggest that asymmetric bipolar pulsed dc sputtering technique is very beneficial for the reactive sputtering deposition of VN coatings.

• Journal of the Ergonomics Society of Korea
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• v.28 no.1
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• pp.1-7
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• 2009

As products are getting more diverse and new products are entering the market faster, customers have trouble learning how to use them. User-oriented menu structures may solve this problem. In order to design user-oriented menu structures, spreading activation theory has been studied. The spreading activation test shows that the strong associative relationship between words has shorter response times. Based on the spreading activation test, asymmetric spreading activation was introduced and a hypothesis that in a well-designed menu structure, association between upper-low menu pairs is not affected by an activation direction was tested for this study. In this study the menu of a cellular phone (Model: SPH-w2900) was extracted, and underwent 1st spreading activation tests. Then, on each menu pair, response time differences (asymmetric transition) by accuracy and directions were analyzed to find out problems in labels and improve menu structures and vocabulary. Second spreading activation tests were conducted to check whether asymmetric transitions decreased. The results showed that response time differences (asymmetric transition) for activation directions were found to be dropped significantly. Asymmetric transitions in spreading activation presented in this study will be helpful to define user-oriented menu structures.