• 한국소음진동공학회논문집
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• 제16권9호
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• pp.912-918
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• 2006

A modeling method for the vibration analysis of rotating multi-blade systems considering the coupling stiffness effect is presented in this paper. Blades are assumed as cantilever beams and the coupling stiffness effect originates from disc or shroud between blades. As the angular speed, hub radius ratio, and the coupling stiffness vary, the natural frequencies of the system vary. Numerical results show that the coupling stiffness is very important to estimate the natural frequencies. Along with the natural frequencies, associated mode shapes, critical angular speed, and critical hub radius ratio are obtained through the analysis.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1354-1359
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• 2006

A modeling method for the vibration analysis of rotating multi-blade systems considering the coupling stiffness effect is presented in this paper. Blades are assumed as cantilever beams and the coupling stiffness effect originates from disc or shroud between blades. As the angular speed, hub radius ratio, and the coupling stiffness vary, the natural frequencies of the system vary. Numerical results show that the coupling stiffness is very important to estimate the natural frequencies. Along with the natural frequencies, associated mode shapes, critical angular speed, and critical hub radius ratio are obtained through the analysis.

• 소음진동
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• 제10권6호
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• pp.1022-1028
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• 2000

This paper presents a modeling method for the vibration analysis of rotating cantilever beams considering the elastic foundation effect. Mass and stiffness matrices are derided explicitly by considering coupling effect between stretching and bonding motion. Numerical results show that the bending direction elastic foundation stiffness influences the vibration characteristics significantly in practical range of beam configuration. The ranges of elastic foundation stiffness to avoid the dynamic buckling are also presented. The method presented in this paper can be used to predict the variations of natural frequencies of rotating cantilever beams with elastically restrained root.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.393-399
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• 2008

A modeling method for the modal analysis of a pre-twisted multi-packet blade system undergoing rotational motion is presented in this paper. Blades are idealized as pre-twisted cantilever beams that are fixed to a rotating disc. The stiffness coupling effects between blades due to the flexibilities of the disc and the shroud are modeled with discrete springs. The coupling effect between chordwise and flapwise bending deflection is also considered. Hybrid deformation variables are employed to derive the equations of motion. To obtain more general information, the equations of motion are transformed into dimensionless forms in which dimensionless parameters are identified. The effects of the dimensionless parameters and the number of packets as well as blades on the modal characteristics of the rotating multi-packet pre-twisted blade system are investigated with some numerical examples.

• 한국유체기계학회 논문집
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• 제16권3호
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• pp.32-38
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• 2013

This paper deals with the study on the rotordynamic and experimental analysis of turbine-generator system connected with a magnetic coupling. Although magnetic coupling has been used to torque transmission of chemical processing pump rotating at under 3,600rpm, magnetic coupling in this study is applied to high-speed turbine-generator system using a working fluid that is refrigerant such as ammonia or R-124a. Results of rotordynamic design analysis are as follows. The first, shaft diameter nearest to outer hub of magnetic coupling has a big effect on the $1^{st}$ critical speed of generator rotor. The second, if the $1^{st}$ critical speeds of turbine rotor and generator rotor have enough to separation margin in comparison to rated speed, the $1^{st}$ critical speed of turbine-magnetic coupling-generator rotor train has enough to separation margin regardless of connection stiffness of magnetic coupling. The analytical FE model is guaranteed by impact test on the prototype and condition monitoring such as measurements of vibration and bearing temperature is also performed.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2108-2117
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• 1996

The purpose of this paper is to investigate the influence of the exciter attached for the measurement of natural frequencies when extracting the frequency response functions of the test structure in experimental modal analysis. The procedure is first to model the attached exciter as an additional degree of freedom system and next to verify the suggested model by experimentally extracting the natural frequencies of the test structure with various values of exciter mass, stinger stiffness and attachment position of the exciter on the test structure. It is concluded that as additional degree of freedom system which includes the natural frequency of the exciter itself and axial stiffness of stinger should be considered to quantatively define the coupling effects of structure-exciter interaction on the measured natural frequencies. It is not the mass of the exciter itself but the coupling effect of the additional degree of freedom mass-spring system consisting of exciter body and armature coil that characterizes the natural frequency deviation. Therefore, when the natural frequency of this additional mass-spring system is outside of the test frequency range, the coupling effect of structure-exciter interaction can be minimized.

• Coupled systems mechanics
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• 제9권2호
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• pp.183-200
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• 2020

Connection of adjacent buildings with stiff links is an efficient approach for seismic pounding mitigation. However, use of highly rigid links might alter the torsional response in asymmetric plans and although this was mentioned in the literature, no quantitative study has been done before to investigate the condition numerically. In this paper, the effect of rigid coupling on the elastic lateral-torsional response of two adjacent one-story column-type buildings has been studied by comparison to uncoupled structures. Three cases are considered, including two similar asymmetric structures, two adjacent asymmetric structures with different dynamic properties and a symmetric system adjacent to an adjacent asymmetric one. After an acceptable validation against the actual earthquake, the traditional random vibration method has been utilized for dynamic analysis under Ideal white noise input. Results demonstrate that rigid coupling may increase or decrease the rotational response, depending on eccentricities, torsional-to-lateral stiffness ratios and relative uncoupled lateral stiffness of adjacent buildings. Results are also discussed for the case of using identical cross section for all columns supporting eachplan. In contrast to symmetric systems, base shear increase in the stiffer building may be avoided when the buildings lateral stiffness ratio is less than 2. However, the eccentricity increases the rotation of the plans for high rotational stiffness of the buildings.

• Computers and Concrete
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• 제15권3호
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• pp.373-389
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• 2015

The development of a finite element model for the geometric and material nonlinear analysis of bonded prestressed concrete continuous beams is presented. The nonlinear geometric effect is introduced by the coupling of axial and flexural fields. A layered approach is applied so as to consider different material properties across the depth of a cross section. The proposed method of analysis is formulated based on the Euler-Bernoulli beam theory. According to the total Lagrangian description, the constructed stiffness matrix consists of three components, namely, the material stiffness matrix reflecting the nonlinear material effect, the geometric stiffness matrix reflecting the nonlinear geometric effect and the large displacement stiffness matrix reflecting the large displacement effect. The analysis is capable of predicting the nonlinear behaviour of bonded prestressed concrete continuous beams over the entire loading stage up to failure. Some numerical examples are presented to demonstrate the validity and applicability of the proposed model.

• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1244-1251
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• 2009

In this paper the vibrational behavior of a multi-packet blade system having a cracked blade is investigated. Each blade is assumed as a slender cantilever beam. The coupling stiffness effect that originates from either disc flexibility or shroud is considered in the modeling. Hybrid deformation variables are employed to derive the equations of motion. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. In the paper, the results of the change in modal parameters due to crack appearance are presented. The influence of the crack parameters, especially of the changing location of the crack is examined.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.407-413
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• 2001

A modeling method for the vibration analysis of rotating composite cantilever plates is presented. Explicit mass and stiffness matrices are derived by considering the coupling effects between extensional motions and the bending motion, To confirm the accuracy of the method presented in this study, numerical results are obtained and compared to those of a commercial program. Numerical results show that the coupling effect among the three motions becomes important for the accurate estimation of natural frequencies as laminates are stacked up unsymmetrically. Also, natural frequencies loci veering, loci crossing, and mode shape variations are observed.