• 한국음향학회지
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• 제24권7호
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• pp.402-409
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• 2005

본 논문에서는 고대역 (4kHz-8kHz)의 주기적 성분이 강하게 나타나는 신호에 대해서 MP (Matching Pursuit) 알고리즘을 이용한 부호화 방법을 제안한다. 또한 분석된 스펙트럼 크기 파라미터와 위상 파라미터의 효율적인 양자화 방법을 제안한다. MP 알고리즘은 오류 상쇄 원리와 정현파 모델에 바탕을 두고 있기 때문에 정확한 피치 주기 예측이 필요하다. 고대역의 정확한 피치 주기 예측을 위해 저대역 (0kHz-4kHz) 신호에서 검출한 피치 주기를 이용함으로써 부호화와 비트할당의 효율을 높일 수 있다. 스펙트럼 크기 계수의 양자화를 위해 계수들에 대해 고정 차원 이산코사인 변환 (MDCT : Modified Discrete Cosine Transform) 및 다단계 (multi-stage) 구조를 결합시킨 양자화 기법을 사용하였고, 위상 값들은 스펙트럼 크기에 따른 가중치 필터와 위상의 $2{\pi}$ 순환 특성을 이용하여 양자화하였다. 또한 제안한 양자화 기법과 부호화 방법을 음성 분석-합성 (analysis-by-synthesis) 시스템에 적용하여, 목적 신호와의 비교를 통해 검증한다. 향후 대역 분할을 기본 구조로 하는 계층 구조의 광대역 음성부호화기에의 적용 가능성을 제시한다.

• Journal of Electrical Engineering and Technology
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• 제4권2호
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• pp.219-228
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• 2009

The growing application and the numerous qualities of induction motors (1M) in industrial processes that require high security and reliability levels has led to the development of multiple methods for early fault detection. However, various faults can occur, such as stator short-circuits and rotor failures. Traditionally the diagnosis machine is done through a sinusoidal power supply, in the present paper we study experimentally the effects of the rotor failures, such as broken rotor bars in function of the ac supplying, the load and show the impact of the converter from diagnosis of the machine. The technique diagnosis used is based on the spectral analysis of stator currents or stator voltages respectively according to the types of induction motor ac supplying. So, four different ac supplying are considered: ${\odot}$ the IM is directly by the balanced three-phase network voltage source, ${\odot}$ the IM is fed by a sinusoidal current source given the controlled by hysteresis, ${\odot}$ the IM is fed (in open loop) by a scalar control imposing through ratio V/f=constant, ${\odot}$ the IM is controlled through a vector control using space vector pulse width modulation (SVPWM) technique inverter with an outer speed loop.

• 한국해안해양공학회지
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• 제8권1호
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• pp.44-51
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• 1996

해안선에서 장파의 처오름높이의 정확한 산정은 공학적인 측면에서 매우 중요하다. 본 논문에서는 크노이드파 이론을 이용하여 장파의 처오름높이에 관한 연구를 하였다. 크노이드파는 파형이 복잡하여 발생과 처오름높이 산정이 매우 어렵다. 본 연구에서는 경계요소법을 이용하여 급경사 지형에서 크노이드파의 처오름높이를 계산한다. 일반적으로 크노이드파의 처오름높이는 동일한 파고를 갖는 고립파의 처오름높이보다는 작지만, 동일한 파고와 파장을 갖는 정현파의 것보다는 항상 크다. 크노이드파의 처오를높이는 또한 파장이 상대적으로 짧을 경우에는 파장에 따라 단순히 증가하지 않으며, 파장이 매우 커지면 고립파의 처오름높이에 점근적으로 접근한다. 경계요소법에 의해 계산된 크노이드파의 처오름높이는 기존의 수리실험 결과와 대체로 일치한다.

• Steel and Composite Structures
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• 재36권6호
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• pp.643-656
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• 2020

This article presents a comprehensive static analysis of simply supported cross-ply carbon nanotubes reinforced composite (CNTRC) laminated nanobeams under various loading profiles. The nonlocal strain gradient constitutive relation is exploited to present the size-dependence of nano-scale. New higher shear deformation beam theory with hyperbolic function is proposed to satisfy the zero-shear effect at boundaries and parabolic variation through the thickness. Carbon nanotubes (CNTs), as the reinforced elements, are distributed through the beam thickness with different distribution functions, which are, uniform distribution (UD-CNTRC), V- distribution (FG-V CNTRC), O- distribution (FG-O CNTRC) and X- distribution (FG-X CNTRC). The equilibrium equations are derived, and Fourier series function are used to solve the obtained differential equation and get the response of nanobeam under uniform, linear or sinusoidal mechanical loadings. Numerical results are obtained to present influences of CNTs reinforcement patterns, composite laminate structure, nonlocal parameter, length scale parameter, geometric parameters on center deflection ad stresses of CNTRC laminated nanobeams. The proposed model is effective in analysis and design of composite structure ranging from macro-scale to nano-scale.

• 한국전자통신학회논문지
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• 제11권9호
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• pp.893-900
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• 2016

극점의 위치와 제동비의 변화에 따른 출력응답을 해석하였다. RLC 회로의 시스템 모델링과 출력응답을 단위계단함수와 정현파 입력에 따라 해석하였다. 프로그램으로 확인한 내용들이 이론을 이해하는데 도움이 되었는지를 설문으로 평가하였다. 조사에서 시스템의 전달함수를 해석하는 능력은 이해도가 높게 나타났다. 또한 매개변수 변화에 따른 출력응답 파형을 이해하는 능력도 높게 나타났다. 시간영역의 출력응답을 계산할 수 있다는 응답이 다소 낮게 나왔으며, 이는 부분분수의 조합이 어려웠던 것으로 분석된다.

• Advances in aircraft and spacecraft science
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• 제4권5호
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• pp.543-553
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• 2017

Vibration is a source of performance degradation in all optical imaging systems. Performance of high resolution remote sensing payloads is often limited due to satellite platform vibrations. Effects of Linear and high frequency sinusoidal vibrations on the system MTF are known exactly in closed form but the low frequency vibration effects is a random process and must be considered statistically. Usually the vibration MTF budget is defined based on the mission requirements and the overall MTF limitations. For analyzing low frequency effects, designer must know all the systems specifications and parameters. With a good understanding of harmful vibration frequencies and amplitudes in the system preliminary design phase, their effects could be removed totally or partially. This procedure is cost effective and let the designer to eliminate just harmful vibrations and avoids over-designing. In this paper we have analyzed the effects of low-frequency platform vibrations on the payload's modulation transfer function. We have used a statistical analysis to find the probability of imaging with a MTF equal or greater than a pre-defined budget for different missions. The worst and average cases have been discussed and finally we have proposed "look-up figures". Using these look-up figures, designer can choose the electro-optical parameters in such a way that vibration effects be less than its pre-defined budget. Furthermore, using the results, we can propose a damping profile based on which vibration frequencies and amplitudes must be eliminated to stabilize the payload system.

• Journal of Power Electronics
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• 제14권6호
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• pp.1119-1129
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• 2014

This study proposes a novel five-level three-phase hybrid-clamped converter composed of only six switches and one flying capacitor (FC) per phase. The capacitor-voltage-drift phenomenon of the converter under the classical sinusoidal pulse width modulation (SPWM) strategy is comprehensively analyzed. The average current, which flows into the FC, is a function of power factor and modulation index and does not remain at zero. Thus, a specific modulation strategy based on space vector modulation (SVM) is developed to balance the voltage of DC-link and FCs by injecting a common-mode voltage. This strategy applies the five-segment method to synthesize the voltage vector, such that switching losses are reduced while optional vector sequences are increased. The best vector sequence is then selected on the basis of the minimized cost function to suppress the divergence of the capacitor voltage. This study further proposes a startup method that charges the DC-link and FCs without any additional circuits. Simulation and experimental results verify the validity of the proposed converter, modulation strategy, and precharge method.

• Geomechanics and Engineering
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• 제11권5호
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• pp.671-690
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• 2016

This work presents a static flexure analysis of laminated composite plates by utilizing a higher order shear deformation theory in which the stretching effect is incorporated. The axial displacement field utilizes sinusoidal function in terms of thickness coordinate to consider the transverse shear deformation influence. The cosine function in thickness coordinate is employed in transverse displacement to introduce the influence of transverse normal strain. The highlight of the present method is that, in addition to incorporating the thickness stretching effect (${\varepsilon}_z{\neq}0$), the displacement field is constructed with only 5 unknowns, as against 6 or more in other higher order shear and normal deformation theory. Governing equations of the present theory are determined by employing the principle of virtual work. The closed-form solutions of simply supported cross-ply and angle-ply laminated composite plates have been obtained using Navier solution. The numerical results of present method are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy, higher order shear and normal deformation theory (HSNDT) and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory. It can be concluded that the proposed method is accurate and simple in solving the static bending response of laminated composite plates.

• Structural Engineering and Mechanics
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• 제51권5호
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• pp.867-891
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• 2014

An equivalent single layer trigonometric shear deformation theory taking into account transverse shear deformation effect as well as transverse normal strain effect is presented for static flexure of cross-ply laminated composite and sandwich plates. The inplane displacement field uses sinusoidal function in terms of thickness coordinate to include the transverse shear deformation effect. The cosine function in thickness coordinate is used in transverse displacement to include the effect of transverse normal strain. The kinematics of the present theory is much richer than those of the other higher order shear deformation theories, because if the trigonometric term (involving thickness coordinate z) is expanded in power series, the kinematics of higher order theories (which are usually obtained by power series in thickness coordinate z) are implicitly taken into account to good deal of extent. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. The closed-form solutions of simply supported cross-ply laminated composite and sandwich plates have been obtained. The results of present theory are compared with those of the classical plate theory (CPT), first order shear deformation theory (FSDT), higher order shear deformation theory (HSDT) of Reddy and exact three dimensional elasticity theory wherever applicable. The results predicted by present theory are in good agreement with those of higher order shear deformation theory and the elasticity theory.

• Structural Engineering and Mechanics
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• 제28권6호
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• pp.749-765
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• 2008

Free axisymmetric vibrations of layered cylindrical shells of variable thickness are studied using spline function approximation techniques. Three different types of thickness variations are considered namely linear, exponential and sinusoidal. The equations of axisymmetric motion of layered cylindrical shells, on the longitudinal and transverse displacement components are obtained using Love's first approximation theory. A system of coupled differential equations on displacement functions are obtained by assuming the displacements in a separable form. Then the displacements are approximated using Bickley-spline approximation. The vibrations of two-layered cylindrical shells, made up of several types of layered materials and different boundary conditions are considered. Parametric studies have been made on the variation of frequency parameter with respect to the relative layer thickness, length ratio and type of thickness variation parameter.