• Tribology and Lubricants
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• 제34권1호
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• pp.9-15
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• 2018

Modern high-performance automotive turbochargers (TCs) implement ceramic hybrid angular contact ball bearings in series with squeeze film dampers (SFDs) to enhance transient responses, thereby reducing the overall emission levels. The current study predicts the rotordynamic responses of the commercial automotive TCs (compressor wheel diameter = ~53 mm, turbine wheel diameter = ~43 mm, and shaft diameter at the bearing locations = ~7 mm) supported on ball bearings and SFDs for various design parameters of SFDs, including radial clearance, axial length, lubricant viscosity, and rotor imbalance conditions (i.e., amplitudes and phase angles) while increasing rotor speed up to 150 krpm. This study validates the predictive rotor finite element model against measurements of mass, polar and transverse moments of inertia, and free-free mode natural frequencies and mode shapes. A nonlinear rotordynamic model integrates nonlinear force coefficients of SFDs to calculate the transient responses of the TC rotor-bearing system. The predicted results show that SFD radial clearances, as well as phase angles of rotor imbalances, have the paramount effect on the dynamic responses of TC shaft motions.

• 한국공작기계학회논문집
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• 제15권1호
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• pp.95-101
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• 2006

Minimum weight design of laminated composite panel under combined loading was studied using linear and nonlinear deformation theories and by closed-form analysis and finite difference energy methods. Various buckling load factors are obatined for laminated composite panels with rectangular type longitudinal stiffeners and various longitudinal length to radius ratios, which are made from Carbon/Epoxy USNl25 prepreg and are simply-supported on four edges under combined loading, and then for them, minimum weight design analyses are carried out by the nonlinear search optimizer, ADS. This minimum weight design analyses are constructed with various process such as the simple design process, test simulation process and sensitivity analysis. Subseguently, the buckling mode shapes are obtained by buckling and minimum weight analyses.

• 한국정밀공학회지
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• 제17권9호
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• pp.109-121
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• 2000

A simplified modeling approach of free vibration for occupied car seats was demonstrated to be feasible. The model consisting of interconnected masses springs and dampers was initially broken down into subsystems and experiments conducted to determine approximate values for model parameters. Which were each stiffness and damping value. Nonlinear equations of motion were derived and model parameters obtained in experiments were applied to these equations. A mathematical model of free vibration for car seat and mannequin system was built with 7 degrees of freedom. in order to calculate natural frequencies and the corresponding mode shapes. linear equations of motion were obtained through linearization. In order to explore the effects of each model parameter free vibration analysis were preformed.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.263-269
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• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

• 콘크리트학회지
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• 제6권3호
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• pp.180-189
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• 1994

모드좌표를 이용한 R/C 골조구조물의 근사적인 비선형 동적해석법을 제안하였다. 과거에도 비선형 문제를 푸는데 있어서 모드좌표에서의 해석이 부분적으로 이용되어 왔으나 각 하중증분에 따른 구조물의 강성변화로 인하여 고유치를 재계산하여야 하기 때문에 그리 널리 사용되지 못하였다. 여기서 제안된 방법은 동적해석 수행중에 산정된 제한된 수만의 고유치를 산정하였다. 그리하여 일정한 수의 고유치만으로 동적해석에서 반복하여 사용하였다. 부재의 소성힌지영역에서의 강성변화 및 핀치효과등을 부재의 이력모델에 의해서 표현되었으며 이러한 알고리즘은 휨변형이 지배하는 R/C 골조구조물의 예비해석에 유용하게 사용될 수 있다. 본 연구에서는 철근콘크리트 부재의 비선형 구조모델의 구성방법 및 그 특성 그리고 모드해석법의 알고리즘을 제안하고 그 효율성을 입증하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.812-817
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• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

• Wind and Structures
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• 제12권3호
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• pp.259-279
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• 2009

The paper is concerned with the numerical study of the cross-wind response of the 295 m-tall six-flue industrial chimney, located in the power station of Belchatow, Poland. The response of the chimney due to turbulent wind flow is caused by the lateral turbulence component and vortex excitation with taking into account motion-induced wind forces. The cross-wind response has been estimated by means of the random vibration approach. Three power spectral density functions suggested by Kaimal, Tieleman and Solari for the evaluation of the lateral turbulence component response are taken into account. The vortex excitation response has been calculated by means of the Vickery and Basu's model including some complements. Motion-induced wind forces acting on a vibrating chimney have been modeled as a nonlinear aerodynamic damping force. The influence of three components mentioned above on the total cross-wind response of the chimney has been investigated. Moreover, the influence of damping ratios, evaluated by Multi-mode Random Decrement Technique, and number of mode shapes of the chimney have been examined. Computer programmes have been developed to obtain responses of the chimney. The numerical results and their comparison are presented.

• 한국기계가공학회지
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• 제9권2호
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• pp.12-19
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• 2010

The characteristics of the torsional systems are generally examined with the nonlinearities such as the several staged clutch damper springs, gear backlashes and drag torques. Generally speaking, the system's characteristics can be found out by the eigensolutions which can show the system natural frequencies and the mode shapes. However, these factors can not give the complete solutions to avoid the noise and vibration problems related to the nonlinear effects. Therefore, several assumptions should be made for solving the real physical system problems under the linear analysis which can reflect the nonlinear effects in the torsional system. This means that the several modified linear factors such as the modified clutch damper spring constants can be used to examine and avoid the natural frequency zones related to the noise and vibration problems. Under the linear analysis with the assumed and modified values, the system can be investigated with the more reliable ways for the realistic phenomena.

• Smart Structures and Systems
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• 제26권2호
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• pp.213-226
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• 2020

In this manuscript, static and dynamic behaviors of geometrically imperfect carbon nanotubes (CNTs) subject to different types of end conditions are investigated. The Doublet Mechanics (DM) theory, which is length scale dependent theory, is used in the analysis. The Euler-Bernoulli kinematic and nonlinear mid-plane stretching effect are considered through analysis. The governing equation of imperfect CNTs is a sixth order nonlinear integro-partial-differential equation. The buckling problem is discretized via the differential-integral-quadrature method (DIQM) and then it is solved using Newton's method. The equation of linear vibration problem is discretized using DIQM and then solved as a linear eigenvalue problem to get natural frequencies and corresponding mode shapes. The DIQM results are compared with analytical ones available in the literature and excellent agreement is obtained. The numerical results are depicted to illustrate the influence of length scale parameter, imperfection amplitude and shear foundation constant on critical buckling load, post-buckling configuration and linear vibration behavior. The current model is effective in designing of NEMS, nano-sensor and nano-actuator manufactured by CNTs.

• 한국해양공학회지
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• 제22권3호
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• pp.41-46
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• 2008

It is a recent trend for advanced ships and submarines to incorporate composite structures with viscoelastically damping material. Much research has been done on curve-fitting techniquesto identify vibration characteristic parameters such as natural frequencies, modal damping ratios, and mode shapes of the composite structure. In this study, an advanced technique for accurately determining vibration characteristic of a circular cylindrical shell-attached viscoelastically damping material is used, based on a multi-degree of freedom (MDOF) curve-fitting method. First, an initial value is obtained by using a linear least square method. Next, using the initial value, the exact modal parameters of the composite circular cylindrical shell are obtained by using a nonlinear least square method. Results show computation time is greatly decreased and accurate results are obtained by the MDOF curve-fitting method.