• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.10
• /
• pp.42-50
• /
• 2005

Based upon the derived analytical model and equation of motion for the general rotor system with anisotropic stator and asymmetric rotor treated as a periodically time-varying system, the series of equations are structured by associating with the time modulated coefficients. The frequency response functions (FRFs) expressed by physical parameters are derived in such a convenient way from the direct inverse matrices of the Fourier transformation of those series of equations, from which the characteristics are analyzed and the properties are suggested.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.137-141
• /
• 1995

회전기계에서 발생하는 진동 원인 중 약 60% 이상이 불평형(unbalance)에 의한 진동이다. 불평형은 기계의 과도한 진동을 유발시킬 뿐 아니라 베어링의 수명 단축 및 소음을 발생시킨다. 따라서, 기게의 수명을 연장시키고, 기계의 성능을 향상시키며 부드럽고 진동이 없는 운전을 위하여 평형잡이(balancing)는 절대적으로 중요하다. 불평형은 축 중심선에 대하여 회전체의 질량 분포가 비대칭이기 때문에 발생하는데 그 원인으로는 부품 자체가 비대칭에서 오는 설계 또는 제도 오차, 주물의 기포 및 용접의 불균일 등에 의한 재질상의 결함, 그리고 부품조립시 형상누적공차 등에 의한 가공.조립오차 등이 있다. ISO의 정의에 따르면 평형잡이는 회전체의 질량 분포를 조사하고 필요하다면 저널의 진동과 베어링의 작용력들이 운전속도에 대응하는 주파수에서 특정한 한계내에 있도록 보증하게 하기 위한 조정을 하는 과정이다. 불평형 상태에 대한 조사도 평형잡이로 표현된다. 그러나 수정이 필요하다고 간주된다면 수행된다. 모든 회전체는 초기 불평형(initial unbalance)이라 불리는 임의의 불평형을 가지고 출발한다. 완벽하게 평형이 잡힌 회전체를 달성하는 것이 평형잡이 작업의 목적은 아니다. 임의의 잔류 불평형(residual unbalance)은 항상 허용된다. 경제적인 이유에서 회전체는 일반적으로 요구되는 적절한 허용치보다 더 이상 평형잡이를 하지 않는다. 현장에서 현장 평형잡이를 수행하게 될 경우, 가끔 계산된 수정질량이 매우 클 경우가 있다. 이때 기게의 조건상 큰 수정질량을 부착하기가 곤란한 경우가 자주 발생한다. 작은 수정질량으로 평형잡이를 할 수 있다면 기계의 안정성 면에서 매우 유리하다. 따라서 본 연구에서는 영향계수법(Influence Coefficient Method : ICM)의 기본 개념과 유전 알고리즘(Genetic Algorithm : GA)을 이용하여 회전기계의 안정성을 보장할 수 있는 허용진동 내에서의 최적 수정질량 계산법을 제시한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.11a
• /
• pp.304-309
• /
• 2003

A new modal analysis method for rotor systems with periodically time-varying parameters is proposed. The essence of method is to introduce modulated coordinates to derive the equivalent time-invariant equation. This paper presents a modal analysis method using modulated coordinates fur general rotors, of which rotating and stationary parts both possess asymmetric properties. The equation of motion with time-varying parameters is transformed to an infinite order matrix equation with the time-invariant parameters. A theory of modal analysis for the system is presented with the infinite order equation and a couple of reduced order equations. A numerical example with simple asymmetric rotor is provided to demonstrate the effectiveness of the proposed method

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2004.05a
• /
• pp.681-686
• /
• 2004

Identification of asymmetry and anisotropy of rotor system is important for diagnosis of rotating machinery. Directional frequency response functions (dFRFs) are known to be powerful tool in effectively detecting the presence of asymmetry or anisotropy. In this paper, an estimation method of dFRFs for rotors is newly developed, when both asymmetry and anisotropy are present. The method transforms the finite degrees-of-freedom time-varying linear differential equation of motion to an infinite degree-of-freedom time-invariant linear one, employing the modulated coordinates. The validity of the method is demonstrated by numerical simulation with a simple rotor model.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.6
• /
• pp.463-469
• /
• 2004

In order to improve the instability of journal bearings, the leaf spring dampers (LSD) are introduced. The effects of LSD on the stability of journal bearings are investigated theoretically The stability of the journal bearing with LSD are compared with the results of the journal bearing without LSD. And the effects of the asymmetry of the stiffness of the leaf spring damper on the stability of rotors are also investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.05a
• /
• pp.941-944
• /
• 2005

Asymmetry of rotor systems is an important factor for identification of dynamic characteristics including the stability and response of rotors and for condition monitoring. In this work, asymmetry of rotors is identified by applying curve-fitting method to the directional frequency response functions (dFRFs), which are known as a powerful tool for detecting the presence and degree of asymmetry. This method minimizes least square error between analytical and measured dFRFs by iteratively updating physical parameters associated with rotor asymmetry. The effectiveness of the identification method is demonstrated by experiments with a laboratory test rotor.

• Journal of KSNVE
• /
• v.3 no.3
• /
• pp.279-283
• /
• 1993

A diagnostic method of anisotropy and asymmetry in rotor systems utilizing the two-sided directional spectra of the operating responses has been presented and tested with a laboratory flexible rotor-bearing system. The experimental results show that the directional spectra can be effectively used for the diagnosis of anisotropy and/or asymmetry in rotor systmes by the investigation of -1X and +2X components in the directional spectrum of unbalance and gravity responses.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.4 s.247
• /
• pp.442-450
• /
• 2006

This paper describes the new modal analysis method to detect the presence of the breathing crack in a general rotor system with disk asymmetry and stator anisotropy. It is proposed that the modal analysis using directional frequency response functions (dFRFs), which, accounting for the directivity in modes, clears the heavily over-lapping of other harmonics occurring from non-isotropic properties in addition to those due to crack, can provide an effective method to detect the modes by a crack. The simulations from the simple general rotor model show that the r-dFRFs (reverse dFRFs) for asymmetry confirms a good indicator of the presence of the breathing crack and the instability is primarily influenced by the shaft asymmetry than the breathing crack.

• The Journal of the Acoustical Society of Korea
• /
• v.26 no.7
• /
• pp.361-365
• /
• 2007

Aero-pulsation noise, generally caused by geometric asymmetry of a rotating device, is one of considerable sources of annoyance in passenger cars using the turbocharged diesel engine. Main source of this noise is the compressor wheel in the turbocharger system, and can be reduced by after-treatment devices such as silencers, but which may increase the manufacturing cost. More effective solution is to improve the geometric symmetry over all, or to control the quality of components by sorting out inferior ones. The latter is more simple and reasonable than the former in view of manufacturing. Thus, an appropriate discrimination method should be needed to evaluate aero-pulsation noise level at the production line. In this paper, we introduce the accurate method which can measure the noise level of aero-pulsation and also present its evaluation criteria. Besides verifying the reliability of a measurement system - a rig test system-, we analyze the correlation between the results from rig tests and those from vehicle tests. The gage R&R method is carried out to check the repeatability of measurements over 25 samples. From the result, we propose the standard specification which can discriminate inferior products from superior ones on the basis of aero-pulsation noise level.