• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.601-606
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• 2004

This paper deals with friction-induced vibration of disc brake system under constant friction coefficient. A linear, lumped and distributed parameter model to represent the floating caliper disc brake system is proposed. The complex eigenvalues are used to investigate the dynamic stability and in order to verify simulations which are based on the theoretical model, the experimental modal test and the dynamometer test are performed. The comparison of experimental and theoretical results shows a good agreement and the analysis indicates that mode coupling due to friction force is responsible for disc brake squeal. And squeal type instability is investigated by using the parametric analysis. This indicates parameters which have influence on the propensity of brake squeal. This helped to validate the analysis model and establish confidence in the analysis results. Also they may be useful during system development or diagnostic analysis.

• 소음진동
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• 제9권6호
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• pp.1210-1217
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• 1999

This paper presents schematic process of identifying the principal cause to make the vibration problem of rotating circular saws. In the tandem pencil slat saw lines, feeding of cedar blocks is often stopped because excessive motro current is required in a saw motor. These events are called "kick-offs" in technical reports. Research on saw behavior at kick-offs is required to understand are reduce the frequency and severity of kick-offs events. This research aims at finding out the principal cause of kick-offs, and evloving design improvements for high cutting performance with fewer and less severe kick-offs. Measurements of critical speed, cutting force, cutting temeprature and dynamic displacements are carried out to observe the instability mechanism and also to obtain saw design parameters for the numerical analyses. And the numerical analyses involving FEM and multiple scale method are utilized to show the possibility of the principal cause.pal cause.

• 한국소음진동공학회논문집
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• 제14권8호
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• pp.702-708
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• 2004

This paper deals with friction-induced vibration of disc brake system under constant friction coefficient. A linear, lumped and distributed parameter model to represent the floating caliper disc brake system is proposed. The complex eigenvalues are used to investigate the dynamic stability and in order to verify simulations which are based on the theoretical model, the experimental modal test and the dynamometer test are performed. The comparison of experimental and theoretical results shows a good agreement and the analysis indicates that mode coupling due to friction force is responsible for disc brake squeal. And squeal type Instability is Investigated by using the parametric analysis. This indicates parameters which have influence on the propensity of brake squeal. This helped to validate the analysis model and establish confidence in the analysis results. Also they may be useful during system development or diagnostic analysis.

• KIEE International Transactions on Power Engineering
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• 제12A권1호
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• pp.6-14
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• 2002

In this paper, an EMM(Equivalent Mechanical Model) Is developed to explain the voltage collapse mechanism by reflecting the effects of reactive powers. The proposed EMM exactly represents the voltage instability mechanism described by the system equations. By the use of the EMM model, the voltage collapse mechanism has been illustrated by showing the exactness of the results. The stable region has been investigated with a reactive-power-controlled two-bus system, which shows that special alerts are required when the system operates with leading power factor. It is also discussed a system transform technique to eliminate the resistance component of the Thevenin equivalent impedance for practical applications. Finally, the results adopting the proposed method fur sample systems which were transformed are listed

• 한국추진공학회지
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• 제2권1호
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• pp.41-49
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• 1998

램제트 혹은 오그멘터에서 발생하는 길이방향 비선형 연소불안정성 해석을 위하여 모달해석법을 사용하여 수학적 모델을 만들었다. 이 모델은 2-모드 공식에 국한되며, 지배 방정식을 분석적으로 또한 수치적으로 풀었다. 이 2-모드 비선형 모델은 비선형 속도 민감 연소 반응의 특징인 부트스트래핑 효과를 예측할 수 있다. 또한, 파라미터 연구를 수행하였다.

• Structural Engineering and Mechanics
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• 제67권6호
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• pp.629-641
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• 2018

The paper describes the development of a two-dimensional (2D) co-rotational nonlinear beam finite element that includes advanced path-following capabilities for detecting bifurcation instability in elasto-plasticity of steel elements subjected to fire without introducing imperfections. The advantage is twofold: i) no need to assume the magnitude of the imperfections and consequent reduction of the model complexity; ii) the presence of possible critical points is checked at each converged time step based on the actual load and stiffness distribution in the structure that is affected by the temperature field in the elements. In this way, the buckling modes at elevated temperature, that may be different from the ones at ambient temperature, can be properly taken into account. Moreover, an improved displacement predictor for estimating the displacement field allowed significant reduction of the computational cost. A co-rotational framework was exploited for describing the beam kinematic. In order to highlight the potential practical implications of the developed finite element, a parametric analysis was performed to investigate how the beam element compares both with the EN1993-1-2 buckling curve and with experimental tests on axially compressed steel members. Validation against experimental data and numerical outcomes obtained with commercial software is thoroughly described.

• Nuclear Engineering and Technology
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• 제31권6호
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• pp.572-585
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• 1999

The characteristics of two-phase flow instability in a vertical boiling channel connecting with an unheated riser are investigated through the linear stability analysis model. Various two-phase flow models, including thermal non-equilibrium effects, are taken into account for establishing a physical model in the time domain. A classical approach to the frequency response method is adopted for the stability analysis by employing the D-partition method. The adequacy of the linear model is verified by evaluating experimental data at high quality conditions. It reveals that the flow-pattern-dependent drift velocity model enhances the prediction accuracy while the homogeneous equilibrium model shows the most conservative predictions. The characteristics of density wave oscillations under low-power and low-quality conditions are investigated by devising a simple model which accounts for the gravitational and frictional pressure losses along the channel. The necessary conditions for the occurrences of type-I instability and flow excursion are deduced from the one-dimensional D-partition analysis. The parametric effects of some design variables on low quality oscillations are also investigated.

• Steel and Composite Structures
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• 제24권4호
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• pp.499-512
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• 2017

This paper deals with nonlinear dynamic stability of embedded piezoelectric nano-composite separators conveying pulsating fluid. For presenting a realistic model, the material properties of structure are assumed viscoelastic based on Kelvin-Voigt model. The separator is reinforced with single-walled carbon nanotubes (SWCNTs) which the equivalent material properties are obtained by mixture rule. The separator is surrounded by elastic medium modeled by nonlinear orthotropic visco Pasternak foundation. The separator is subjected to 3D electric and 2D magnetic fields. For mathematical modeling of structure, three theories of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT) are applied. The differential quadrature method (DQM) in conjunction with Bolotin method is employed for calculating the dynamic instability region (DIR). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the dynamic instability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that the magnetic and electric fields as well as SWCNTs as reinforcer are very important in dynamic instability analysis of structure.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.271-298
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• 2016

In this paper, we study a problem of passive suppression of helicopter Ground Resonance (GR) using a single degree freedom Nonlinear Energy Sink (NES), GR is a dynamic instability involving the coupling of the blades motion in the rotational plane (i.e. the lag motion) and the helicopter fuselage motion. A reduced linear system reproducing GR instability is used. It is obtained using successively Coleman transformation and binormal transformation. The analysis of the steadystate responses of this model is performed when a NES is attached on the helicopter fuselage. The NES involves an essential cubic restoring force and a linear damping force. The analysis is achieved applying complexification-averaging method. The resulting slow-flow model is finally analyzed using multiple scale approach. Four steady-state responses corresponding to complete suppression, partial suppression through strongly modulated response, partial suppression through periodic response and no suppression of the GR are highlighted. An algorithm based on simple criterions is developed to predict these steady-state response regimes. Numerical simulations of the complete system confirm this analysis of the slow-flow dynamics. A parametric analysis of the influence of the NES damping coefficient and the rotor speed on the response regime is finally proposed.

• KIEE International Transactions on Power Engineering
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• 제5A권2호
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• pp.152-158
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• 2005

This paper describes a reactive optimal power flow incorporating margin enhancement constraints. Margin sensitivity at a steady-state voltage instability point is calculated using invariant space parametric sensitivity, and it can provide valuable information for selection of effective control parameters. However, the weakest buses in neighboring regions have high margin sensitivities within a certain range. Hence, the control determination using only the sensitivity information might cause violation of operational limits of the base operating point, at which the control is applied to enhance voltage stability margin in the direction of parameter increase. This paper applies an interior point method (IPM) to solve the optimal power flow formulation with the margin enhancement constraints, and shunt capacitances are mainly considered as control variables. In addition, nonlinearity of margin enhancement with respect to control of shunt capacitance is considered for speed-up control determination in the numerical example using the IEEE 118-bus test system.