• 소음진동
• /
• 제8권3호
• /
• pp.477-484
• /
• 1998

An analytical procedure on the base of the substructure synthesis and assumed modes method is developed to investigate the flexibility effect of bladed disk assembly on vibrational modes of flexible rotor system. In modeling the system, Coriolis forces, gyroscopic moments, and centrifugal stiffening effects are taken into account. The coupled vibrations between the shaft and bladed disk are then extensively investigated through the numerical simulation of simplified models, with varying the shaft rotational speed and the prewist and stagger angles of the blade. It is found that the Coriolis and inertia forces and the inertia torque, which are induced by the one nodal diameter modes of the bladed disk and vary depending upon the stagger and prewist angles, lead to the coupled motions of the shaft and the bladed disk.

• 소음진동
• /
• 제9권5호
• /
• pp.1012-1018
• /
• 1999

This paper deals with the coupled flexural-torsional vibrations of Timoshenko beams with monosymmetric cross-section. The governing differtial equations for free vibration of such beams are derived and solved numerically to obtain frequencies and mode shapes. Numerical results are calculated for three specific examples of beams with free-free, clamped-free, hinged-hinged, clamped-hinged and clamped-clamped end constraints. The effect of warping stiffess on the natural frequencies and mode shapes is discussed and it is concluded that substantial error can be incurred if the effect is ignored.

• Wind and Structures
• /
• 제14권4호
• /
• pp.359-381
• /
• 2011

This paper deals with the flutter instability problem of flexible bridge decks in the framework of bimodal-coupled aeroelastic bridge system analysis. Based on the analysis of coefficients of the polynomials deduced from the singularity conditions of an integral wind-structure impedance matrix, a set of simplified formulations for calculating the critical wind velocity and coupled frequency are presented. Several case studies are discussed and comparisons with available approximated approaches are made and presented, along with a conventional complex eigenvalue analysis and numerical results. From the results, it is found that the formulas that are presented in this study are applicable to a variety of bridge cross sections that are not only prone to coupled-mode but also to single-mode-dominated flutter.

• Current Applied Physics
• /
• 제18권11호
• /
• pp.1275-1279
• /
• 2018

We investigate the change of the Fano effect by considering one Majorana zero mode to couple laterally to the single-dot Fano interferometer. It is found that the Majorana zero mode quenches the Fano effect thoroughly and causes the conductance to be independent of the dot level, the dot-lead coupling, and the increase of the Majorana-dot coupling. As a result, the linear conductance becomes only related to the interlead coupling and the magnetic-flux phase factor. These results can be helpful for the detection of Majorana zero mode.

• 한국항공우주학회지
• /
• 제32권6호
• /
• pp.34-48
• /
• 2004

본 연구에서는 대형 구조물의 최적설계에서 문제되는 많은 계산시간과 컴퓨터의 계산능력을 최소화할 수 있도록 부분구조합성법의 하나인 구속모드법을 이용한 연성하중해석 모델 및 모달과도해석을 포함한 최적화 절차를 제시하였다. 제안된 방법의 수치모사를 위한 프로그램을 개발하여 위성체 주요 구조부재인 플랫폼에 대한 최적화를 수행함으로써 그 타당성을 검증하였다. 제안된 기법을 통해 초기설계 단계에서 정확성을 유지하면서 계산시간을 단축할 수 있었고 위성체 구조부재에 대한 최적화를 수행하여 각각의 구조부재에 대한 특성을 파악함으로써 설계 활용방안을 제시하였다.

• Coupled systems mechanics
• /
• 제4권4호
• /
• pp.337-364
• /
• 2015

In this paper we present methodology for parameters identification of constitutive model which is able to present behavior of a connection between two members in a structure. Such a constitutive model for frame connections can be cast in the most general form of the Timoshenko beam, which can present three failure modes. The first failure mode pertains to the bending in connection, which is defined as coupled plasticity-damage model with nonlinear softening. The second failure mode is seeking to capture the shearing of connection, which is defined as plasticity with linear hardening and nonlinear softening. The third failure mode pertains to the diffuse failure in the members; excluding it leads to linear elastic constitutive law. Theoretical formulation of this Timoshenko beam model and its finite element implementation are presented in the second section. The parameter identification procedure that will allow us to define eighteen unknown parameters is given in Section 3. The proposed methodology splits identification in three phases, with all details presented in Section 4 through three different examples. We also present the real experimental results. The conclusions are stated in the last section of the paper.

• Journal of Power Electronics
• /
• 제19권1호
• /
• pp.11-23
• /
• 2019

In this study, a novel zero voltage zero current transition (ZVZCT) bidirectional DC-DC converter is proposed by employing coupled inductors. This converter can turn the main switch on at ZVZCT and it can turn it off with zero voltage switching (ZVS) for both the boost and buck modes. These characteristics are obtained by using a simple auxiliary sub-circuit regardless of the power flow direction. In the boost mode, the auxiliary switch achieves zero current switching (ZCS) turn-on and ZVS turn off. Due to the coupling inductors, this converter can make further efficiency improvements because the resonant energy in the capacitor or inductor can be transferred to the load. The main diode operates with ZVT turn-on and ZCS turn-off in the boost mode. For the buck mode, there is a releasing circuit to conduct the currents generated by the magnetic flux leakage to the output. The auxiliary switch turns on with ZCS and it turns off with ZVT. The main diode also turns on with ZVT and turns off with ZCS. The design method and operation principles of the converter are discussed. A 500 W experimental prototype has been built and verified by experimental results.

• 한국음향학회지
• /
• 제41권4호
• /
• pp.397-409
• /
• 2022

본 논문에서는 거리 종속환경에서 해수면에 의한 배경소음 모델링을 수행하였다. 모델링 환경에서 음원은 해수면 근처에서 수평 방향의 전 영역에서 위치하고, 수신기 배열은 거리 종속환경의 해양 도파관 내에 위치하였다. 거리 종속환경에서의 소음원과 수신기 간의 음파전달은 연성모드법을 사용하여 계산되었으며, 이를 이용하여 수신기 간 상호 스펙트럴 밀도행렬 식을 유도하였다. 계산된 상호 스펙트럴 밀도행렬은 소음 인텐시티, 빔형성 결과, 코히런스 함수를 계산하는 데 사용되었으며, 그 결과를 거리 독립환경에서의 결과와 비교하였다. 이를 통해 해저면 특성에 의한 수직 방향성과 거리 종속환경에 의한 수평면상의 비대칭성 특성이 모델링 결과에 반영됨을 확인하였다.

• International Journal of Aeronautical and Space Sciences
• /
• 제15권2호
• /
• pp.113-122
• /
• 2014

The objective of the paper is to clarify a methodology based on the use of the existing component mode synthesis methods for the case of two damped substructures which are coupled through a linking viscoelastic flexible substructure and for which the structural modes with free geometrical interface are used for each main substructure. The proposed methodology corresponds to a convenient alternative to the direct use either of the Craig-Bampton method applied to the three substructures (using the fixed geometric interface modes) or of the flexibility residual approaches initiated by MacNeal (using the free geometric interface modes). In opposite to a geometrical interface which is a topological interface on which there is a direct linkage between the degrees of freedom of substructures, we consider a physical flexible interface which exists in certain present technologies and for which the general framework linear viscoelasticity is used and yields a frequency-dependent damping and stiffness matrices of the physical flexible interface.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2006년도 춘계 학술대회 개요집
• /
• pp.307-309
• /
• 2006

For efficient NDE of pipes, essential components of power plant facilities, ultrasonic guided waves were generated and received applying an air-coupled transducer and comb one as non-contact technology, Mode generation and selection were predicted based on theoretical dispersive curve and the element spaceof a comb transducer. In addition, a receiving angle of the air-coupled transducer was determined to acquire the predicted modes by theoretical phase velocity of each mode. Theoretical dispersive curve was compared with the results of the time-frequency spectroscopes based on the wavelet transform and 2D-FFT to identify the characteristics of the received mode. The received modes show a good agreement with the predicted ones.