• International Journal of Aeronautical and Space Sciences
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• v.14 no.1
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• pp.19-29
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• 2013

This paper deals with the study of buckling, vibration, and parametric instability characteristics in a damaged cross-ply and angle-ply laminated plate like beam under in-plane harmonic loading, using the finite element approach. Damage is modelled using an anisotropic damage formulation, based on the concept of reduction in stiffness. The effect of damage on free vibration and buckling characteristics of a thin plate like beam has been studied. It has been observed that damage shows a strong orthogonality and in general deteriorates the static and dynamic characteristics. For the harmonic type of loading, analysis was carried out on a thin plate like beam by solving the governing differential equation which is of Mathieu-Hill type, using the method of multiple scales (MMS). The effects of damage and its location on dynamic stability characteristics have been presented. The results indicate that, compared to the undamaged plate like beam, heavily damaged beams show steeper deviations in simple and combination resonance characteristics.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.192-194
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• 1997

This paper propose an efficient space harmonic analysis method for magnetic field. Permanent magnet and primary core considered slot are replaced by EMC(equivalent magnetizing current). And the resultant air gap flux density is calculated by superposition due to the permanent magnet and EMC. We analyze the harmonic distribution of air gap flux density taking into account slot for PMLSM.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.732-739
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• 2005

The determination of sound pressure radiated from periodic plate structures is fundamental in the estimation of noise level in aircraft fuselages or ship hull structures. As a robust approach to this problem, here a very general and comprehensive analytical model is developed for predicting the sound radiated by a vibrating plate stiffened by periodically spaced orthogonal symmetrical beams subjected to a sinusoidally time varying point load. In this these, we experiment with the numerical analysis using the space harmonic series and the SYSNOISE for measuring the vibration mode and character of response caused by sound radiation with adding the harmonic point force in the thin isotropic plate supported by the rectangular lattice reinforcement. We used the reinforcements, beams of open type section like the style of 'ㄷ' letter; the space of the beams were chosen to be 0.2m, 0.3m, 0.4m. We studied the behavior of sound pressure levels, analysis of vibration mode between support points, connection between frequency function and sound pressure levels, and connection between position function and sound pressure levels.

• Proceedings of the KIPE Conference
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• 2002.11a
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• pp.171-174
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• 2002

This paper deals with a novel method in order to analyze the harmonic characteristics in the multi-level inverter. Generally, the magnitude of harmonic components is different according to the carrier PWM techniques, modulation Index(Mi), and the level of multi-level inverter The previous papers analyzed the harmonic characteristics from the viewpoint of the space vector. Hence, the calculation of the harmonic vector becomes difficult and complex in 4-level or more than S-level. However, the proposed method of this paper reduced an amount of calculation and simplified the process of calculation by using the relationship between reference voltage and output phase voltage to load neutral. This paper analyzed the harmonic and it is applied to the multi-carrier PWM techniques in 5- level and other-level of cascaded inverter system.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.2
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• pp.69-78
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• 1995

Nonlinear analysis methods are developed which will enable the reliable prediction of the dynamic behavior of the space shuttle main engine(SSME) turbopumps in the presence of bearing clearances and other local nonlinearities. A computationally efficient convolution method, based on discretized Duhamel and transition matrix integral formulations, is developed for the transient analysis. In the formulation, the coupling forces due to the onlinearities are treated as external forces acting on the coupled subsystems. Iteration is utilized to determine their magnitudes at each time increament. The method is applied to a nonlinear generic model of the high pressure oxygen turthods, the convolution approach proved to be more accurate and highly more efficient. For determining the nonlinear, steady-state periodic responses, an incremental harmonic balance(IHB) method was also developed. The method was successfully used to determine dominantly harmonic and subharmonic(subsynchronous) responses of the HPOTP generic model with bearing clearances. A reduction method similar to the impedance formulation utilized with linear systems is used to reduce the housing-totor models to their coordinates at the bearing clearances.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.615-619
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• 1998

Active power filter is a kind of device used for compensating instantaneous reactive and harmonic current in three-phase circuits. An essential technology that determines the behavior of an active power filter is the method of detecting the distorted current. Using three-dimensional space vectors, this paper describes a simple method for detecting the distorted current without any coordinate transformation. The effectiveness of the novel method is verified by the theoretical analysis and simulation.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1945-1954
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• 2017

In recent years, several LCL filter design methods for different converter topologies have been published, many of which use analytical expressions to calculate the ideal converter AC voltage harmonic spectrum. This paper presents the LCL filter design methodology but the focus is on presentation and validation of the non-iterative filter design method for a grid-connected three-phase two-level PWM-VSC. The developed method can be adapted for different converter topologies and PWM algorithms. Furthermore, as a starting point for the design procedure, only the range of PWM carrier frequencies is required instead of an exact value. System nonlinearities, usually omitted from analysis have a significant influence on VSC AC voltage harmonic spectrum. In order to achieve better accuracy of the proposed procedure, the system nonlinear model is incorporated into the method. Optimal filter parameters are determined using the novel cost function based on higher frequency losses of the filter. An example of LCL filter design for a 40 kVA grid-connected PWM-VSC has been presented. Obtained results have been used to construct the corresponding laboratory setup and measurements have been performed to verify the proposed method.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.67.5-67
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• 2001

A closed loop system with a linear plant and nonlinearity in the feedback connection is analyzed for its quasi-static orbital stability by a state-space approach. First a periodic orbit is assumed to exist in the loop which is determined by describing function method for the given nonlinearity. This is possible by selecting a proper nonlinearity and a rigorous justification of the describing function method.[1-3, 18, 20]. Then by introducing residual operator, a linear perturbed model can be formulated. Using various transformations like a modified eigenstructure decomposition, periodic-averaging, charge of variables and coordinate transformation, the stability of the periodic orbit, as a solution of harmonic balance, can be shown by investigating a simple scalar function and result of linear algebra. This is ...

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.649-660
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• 2021

Through analytical method based on S-76 model, the level of rotor hub vibration reduction was analyzed according to higher harmonic actuating by individual blade control. The higher harmonic actuating method for individual blades was divided into a method of generating an additional actuating force from the pitch-link in the rotating part and generating actuating force through the active trailing edge flap control of the blade. In the 100kts forward flight conditions, the hub load analysis was performed by changing the phase angle of 15 degree for the 2P/3P/4P/5P harmonic actuation for individual blades. Through the harmonic actuation results, the sensitivity of the rotor system according to the actuating conditions was analyzed, and the T-matrix representing the characteristics of the rotor system was derived based on this analysis result. And through this T-matrix, optimal higher harmonic actuating condition was derived to minimize hub vibration level for flight condition. In addition, the effect on the performance of the rotor system and the pitch-link load under minimum hub vibration condition, as well as the noise influence through the noise analysis were confirmed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.8
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• pp.1115-1122
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• 2012

This paper analyzes eddy-current loss induced in magnets of surface-mounted permanent magnet (SPM) machines by using an analytical method such as a space harmonic method. First, on the basis of a two-dimensional (2D) polar coordinate system and a magnetic vector potential, the analytical solutions for the flux density produced by armature winding current are obtained. By using derived field solutions, the analytical solutions for eddy current density distribution are also obtained. Finally, analytical solutions for eddy current loss induced in rotor magnets are derived by using equivalent electrical resistance calculated from magnet volume and analytical solutions for eddy-current density distribution. In particular, the influence of time harmonics in armature current on the eddy current loss is fully investigated and discussed. All analytical results are validated extensively by finite element analysis (FEA).