• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1996.11a
• /
• pp.799-805
• /
• 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.

• Journal of Power System Engineering
• /
• v.1 no.1
• /
• pp.106-123
• /
• 1997

In this study, vehicle directional stability is investigated for limit driving for crash avoidance maneuver using a full vehicle dynamic model. The model was analytically validated using typical step steering and lane change simulation. Limit driving condition for the vehicle model was quoted from research results of references. It was demonstrated that instable vehicle motion was caused by not only road conditions but also driving conditions. Also, the simulation showed that braking combined with steering caused very hazardous situation in crash avoidance maneuver. Finally, phase plane plot approach was used to evaluate the dynamic instability.

• Journal of Astronomy and Space Sciences
• /
• v.7 no.1
• /
• pp.23-35
• /
• 1990

Resonance effect on the orbital elements of geosynchronous artificial satellite due to the non-zonal geopotential has been calculated. For the perturbation of a artificial satellite, perturbation effects due to the non-zonal geopotential is less than due to the $J_2$ or Luni-Solar perturbation, but non-zonal harmonics resonance exist. So, we calculate the perturbation of geosynchronous artificial satellite orbit due to the non-zonal harmonics resonance. The effect on the orbit eccentricity of non-zonal harmonics resonance is represented by a phase plane plot of ec. The effect on the orbit eccentricity of non-zonal harmonics resonance is represented by a phase plane plot of $e_c$ verse $e_s$. The evolution of mean longitude and semi-major axis are obtained.

• Korean Journal of Applied Biomechanics
• /
• v.17 no.3
• /
• pp.133-145
• /
• 2007

The purpose of this paper was to compare of difference between energy walking and normal walking. Subjects were selected 8 male undergraduates. The kinematic variables of a pelvis and a thorax were analysed at the take off and contact with 3d cinematography. In addition to the variables, the phase plot angle was calculated in order to definite characteristics in the phase space. The pelvic angle and angular velocity showed significant differences in the flexion/extension between two walking patterns. The pelvic angle and angular velocity were increasing when walking speed was increasing and magnitude of the variables of energy walking was larger than corresponding values for normal walking. On the other hand, the thoracic angle demonstrated significant differences in the flexion/extension and rotation between two walking patterns. The angles of energy walking were smaller in the flexion/extension and were larger in the rotation than the angle of normal walking. The kinematic characteristics of energy walking were also showed clearly significant differences in the range of motion and the relative angle of the trunk. The angle of phase plot only showed demonstrated a significant difference in the rotation at contact between the two walking patterns.

• Journal of Mechanical Science and Technology
• /
• v.17 no.12
• /
• pp.1994-2003
• /
• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experimental and theoretical analysis. These kinds of studies have been performed to find the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and the coefficient of viscoelastic damping are discussed. The parameters are investigated by means of system identification so that comparisons are made between numerical analysis using the design parameters and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits, bifurcation diagram and Lyapunov exponent so that one can define optimal parameters for system design.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.495-500
• /
• 2003

The vibration of a flexible cantilever tube with nonlinear constraints when it is subjected to flow internally with fluids is examined by experiment and theoretical analysis. These kind of studies have often been performed that finds the existence of chaotic motion. In this paper, the important parameters of the system leading to such a chaotic motion such as Young's modulus and coefficient of viscoelasticity in tube material are discussed. The parameters are investigated by means of a system identification so that comparisons are made between numerical analysis using the parameters of a handbook and the experimental results. The chaotic region led by several period-doubling bifurcations beyond the Hopf bifurcation is also re-established with phase portraits and bifurcation diagram so that one can define optimal parameters for system design.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.178-178
• /
• 2008

ZnO 바리스터는 인가되는 전압에 따라 저항이 변하는 전압 의존형 저항체이며 각종 전기 전자 정보통신용 제품에 정전기(ESD) 대책용 소자로 폭 넓게 사용되는 전자 세라믹스 부품이다. 특별히 Bi-based ZnO 바리스터는 다양한 상(phase)으로 구성되어 있으며 그 입계의 전기적 특성은 소량 첨가되는 dopant의 종류에 따라 다양하게 변하는 것으로 알려져 있다. 본 연구에서는 Bi-based ZnO 바리스터 (ZnO-$Bi_2O_3$, ZnO-$Bi_2O_3-Mn_3O_4$)에서 각종 유전함수$(Z^*,M^*,\varepsilon^*,Y^*,tan{\delta})$를 이용하여 입계의 주파수-온도에 대한 특성을 살펴 보았다. 일반적인 ZnO 바리스터 제조법으로 시편을 제작하여 78K~800K 온도 범위에서 각종 유전함수를 이용하여 복소 평면도(complex plane plot)와 주파수 응답도(frequency explicit plot)의 방법으로 defect level과 입계 특성(활성화 에너지, 정전용량, 저항, 입계 안정성 등)에 대하여 고찰하였다. ZnO-$Bi_2O_3$(ZB)계와 ZnO-$Bi_2O_3-Mn_3O_4$(ZBM)계 모두 상온 이하의 온도에서 $Zn_i$와 $V_o$의 결함이 나타났으며, 이들의 결함 준위는 각 유전함수에 따라 다소 차이가 났다. 입계 특성으로 ZB계는 이상구간(560~660K)을 전후로 1.15 eV $\rightarrow$ 1.49 eV의 활성화 에너지의 변화가 나타났지만, ZBM계는 이러한 현상이 나타나지 않았다. 또한 입계 전위 장벽의 온도 안정성에 대해서는 Cole-Cole model을 적용하여 분포 파라미터 (distribution parameter; $\alpha$)를 구하여 고찰하였다. ZB계의 입계 안정성은 온도에 따라 불안정해 졌지만, ZBM계는 안정하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.5
• /
• pp.471-482
• /
• 2015

In this paper, design and implementation of the 94 GHz Gunn oscillator and the evaluation of the maximum power of the Gunn diode used in the oscillator are presented. The 94 GHz Gunn oscillator is used InP Gunn diode and designed employing a WR-10 waveguide. The designed oscillator is fabricated through machining and its performance is measured. The fabricated oscillator shows an oscillation frequency of 95 GHz, output power of 12.64 dBm, and phase noise of -92.7 dBc/Hz at 1 MHz offset frequency. To evaluation the maximum power of the InP Gunn diode used in oscillator, the oscillator structure is modified to a structure having a diaphram. The height of thick diaphram which is used in the oscillator is varied. As a result, an oscillator has several different load impedances, which makes it possible to plot $G_L-V^2$ plot at the post plane. Using the $G_L-V^2$ plot, the maximum power of used Gunn diode including post is computed to be 16.8 dBm. Furthermore using the shorted and zero bias Gunn diode, the post loss used for DC biasing can be computed. Using the two losses, The maximum power of a InP Gunn diode is computed to be 18.55 dBm at 95 GHz. This result is close to a datasheet.

• Restorative Dentistry and Endodontics
• /
• v.25 no.3
• /
• pp.359-370
• /
• 2000

The purpose of this investigation was to observe the viscoelastic properties of five commercial flowable(Aeliteflo, Flow it, Revolution, Tetric flow, Compoglass flow), three conventional hybrid(Z-100, Z-250, P-60) and two condensable(Synergy compact, SureFil) resin composites. A dynamic oscillatory shear test was done to evaluate the storage shear modulus (G'), loss shear modulus(G"), loss tangent(tan ${\delta}$) and complex viscosity(${\eta}^*$) of the resin composites as a function of frequency - dynamic frequency sweep test from 0.01 to 100 rad/s at $25^{\circ}C$ - by using Advanced Rheometric Expansion System(ARES). To investigate the effect on the viscosity of resin composites of filler volume fraction, the filler weight % and volume % were measured by means of Archimedes' principle using a pyknometer. The results were as follows 1. The complex viscosity ${\eta}^*$ of flowable resins was lower than that of hybrid resins and significant differences were observed between brands. The complex viscosity ${\eta}^*$ of condensable resins was higher than that of hybrid resins. The order of complex viscosity ${\eta}^*$ at ${\omega}$=10 rad/s was as follows, Surefil, Synergy compact, P-60, Z-250, Z-100, Aeliteflo, Tetric flow, Compoglass flow, Flow it, Revolution. The relative complex viscosity of flowable resins compared to Z-100 was 0.04~0.56 but Surefil was 30.4 times higher than that of Z-100. 2. The storage shear modulus G' and the loss shear modulus G" of flowable resins were lower than those of hybrid resins but those of condensable resins were higher. The patterns of the change of loss tangent, tan ${\delta}$, of resin composites with increasing frequency were significantly different between brands. The phase angles, ${\delta}$, ranged from $30.2{\sim}78.1^{\circ}$ at ${\omega}$=10 rad/s. 3. All composite resins represent pseudoplastic nature with increasing shear rate. 4. The complex shear modulus $G^*$ and the phase angle ${\delta}$ was represented by the frequency domain phasor form, $G^*({\omega})=G^*e^{i{\delta}}=G^*{\angle}{\delta}$. The locus of frequency domain phasor plots in a complex plane was a valuable method that represent the viscoelastic properties of composite resins. 5. There was no direct linear correlationship but a weak positive relation was observed between filler volume % or weight % and the viscosity of the resin composites.

• Restorative Dentistry and Endodontics
• /
• v.29 no.6
• /
• pp.489-497
• /
• 2004

Objective: The purpose of this study was to investigate the viscoelastic properties related to handling characteristics of composite resins, Methods: A custom designed vertical oscillation rheometer (VOR) was used for rheological measurements of composites. The VOR consists of three parts: (1) a measuring unit, (2) a deformation induction unit and (3) a force detecting unit, Two medium viscous composites, Z100 and Z250 and two packable composites, P60 and SureFil were tested. The viscoelastic material function, including complex modulus $E^{*}$ and phase angle ${\delta}$, were measured. A dynamic oscillatory test was used to evaluate the storage modulus (E'), loss modulus (E") and loss tangent ($tan{\delta}$) of the composites as a function of frequency ($\omega$) from 0.1 to 20 Hz at $23^{\circ}C$. Results: The E' and E" increased with increasing frequency and showed differences in magnitude between brands. The $E^{*}s$ of composites at ${\omega}{\;}={\;}2{\;}Hz$, normalized to that of Z100, were 2.16 (Z250), 4,80 (P60) and 25.21 (SureFil). The magnitudes and patterns of the change of $tan{\delta}$ of composites with increasing frequency were significantly different between brands. The relationships between the complex modulus $E^{*}$, the phase angle ${\delta}$ and the frequency \omega were represented by frequency domain phasor form, $E^{*}{\;}(\omega){\;}={\;}E^{*}e^{i{\delta}}{\;}={\;}E^{*}{\angle}{\delta}$. Conclusions: The viscoelasticity of composites that influences handling characteristics is significant different between brands, The VOR is a relatively simple device for dynamic, mechanical analysis of high viscous dental composites. The locus of frequency domain phasor plots in a complex plane is a valuable method of representing the viscoelastic properties of composites.