• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.786-791
• /
• 2005

This paper is concerned with the examination and evaluation concerning a tuning method of multivariable PID controllers based on partial model matching on frequency domain proposed by authors from practical view point. In this case, PID controller parameters are determined by minimizing the loss function defined by the difference between frequency response of ideal model transfer function and actual frequency response on several frequency points. The purpose of the paper is to examine and evaluate the performance of the method through actual experiments of MIMO liquid level experimental process control equipment.

• 대한기계학회논문집A
• /
• 제41권10호
• /
• pp.905-913
• /
• 2017

본 연구에서는 형상 정보가 주어지지 않은 부품과 형상 정보가 주어진 부품으로 구성된 봉의 고유 주파수를 최대화하는 치수 최적화 방법을 제시한다. 두 부품으로 구성된 봉의 진동 특성을, 각 부품의 형상 대신, 두 부품의 주파수 응답 함수들로부터 예측한다. 이를 위해, 실험 모달 해석 방법을 이용하여 각 부품의 등가 진동계를 구하고, 두 등가 진동계의 질량 행렬과 강성 행렬들로부터, 두 부품이 결합된 봉의 등가 질량 행렬과 강성 행렬을 도출한다. 몇 가지 수치 예제에서, 제시한 방법으로 얻어진 봉의 등가 진동계의 주파수 응답 함수를 실제 봉의 주파수 응답 함수와 비교하여, 등가 진동계를 이용한 고유 주파수 예측 방법의 유효성을 검증한다. 검증된 방법으로 얻어진 등가 진동계를 이용하여, 봉의 1차 고유 주파수를 최대화하기 위한 치수 최적화 문제를 정식화하고, 최적화 알고리즘을 사용하여 봉의 구조를 최적화한다.

• 대한전기학회논문지
• /
• 제31권8호
• /
• pp.33-38
• /
• 1982

This paper deals with the simplification of the transfer function in a frequency domain, viz. the integral of the squared errors between the original and the simplified model is minimized and the latter is estimated by the Walsh function. It tries to minimize the errors between the frequency responses of the two functions. This method is compared with the existing method by means of a numercal example. The frequency response of this simplified model approximates closely to that of the original model. The proposed method is simpler in analysis and easier in implementation than the existing methods. Though the Walsh function can be easily generated with the discrete values, it has errors because its zero crossings are not continuous. This method aims at the reduction of the errors in the real parts and the imaginary parts of the two functions by dividing into the more sub-intervals, and selecting the reduced-order model according to the response of the model. As a result, it can be applied for the simplification of higher order functions into lower order functions and for the design of control systems.

• 한국시뮬레이션학회논문지
• /
• 제10권4호
• /
• pp.1-10
• /
• 2001

For the simulation of piping vibrations in petrochemical plants, forcing functions mainly depend upon the equipment working mechanism and vibration resources in the piping systems. In general, harmonic function is used to simulate rotary equipment. Mechanical driving frequencies, wave functions, and response spectrum are used to simulate reciprocating compressors, surge vibration of long transfer piping, and seismic/wind vibration, respectively. In this study, the general suggestions for forcing functions were reviewed and proposed the forcing function to simulate the spray injection system inside the pipe in which two different fluids are distributed uniformly. To confirm the results, the scheme was applied for a real piping system. The vibration mode of the real system was consistent with the 4th mode (26.725 Hz) obtained by simulation using the forcing function presented in this study.

• 한국소음진동공학회논문집
• /
• 제12권10호
• /
• pp.792-798
• /
• 2002

The spectrum of impulse response signal from an impulse hammer testing is widely used to obtain frequency response function (FRF) of the structure. However the FRFs obtained from impact hammer testing have not only leakage errors but also finite record length errors when the record length for the signal processing is not sufficiently long. The errors cannot be removed with the conventional signal analyzer which treats the signals as if they are always steady and periodic. Since the response signals generated by the impact hammer are transient and have damping, they are undoubtedly non-periodic. It is inevitable that the signals be acquired for limited recording time, which causes the finite record length error and the leakage error. In this paper, the errors in the frequency response function of multi degree of freedom system are formulated theoretically. And the method to remove these errors is also suggested. This method is based on the optimization technique. A numerical example of 3-dof model shows the validity of the proposed method.

• Tribology and Lubricants
• /
• 제39권6호
• /
• pp.221-227
• /
• 2023

A rotordynamic system consists of components that undergo rotational motion. These components include shafts, impellers, thrust collars, and components that support rotation, such as bearings and seals. The motion of this type of rotating system can be modeled as two-dimensional motion and, accordingly, the equation of motion for the rotordynamic system can be represented using complex coordinates. The directional frequency response function (dFRF) can be derived from this complex coordinate system and used as an effective analytical tool for rotating machinery. However, the dFRF is not widely used in the field because most previous studies and commercial software are based on real coordinate systems. The objective of the current study is to introduce the dFRF and show that it can be an effective tool in rotordynamic analysis. In this study, the normal frequency response function (nFRF) and dFRF are compared under rotordynamic analysis for isotropic and unisotropic rotors. Results show that in the nFRF, the magnitude of the response is the same for both positive and negative frequencies, and the response is similar under all modes. Consequently, the severity of the mode cannot be identified. However, in the dFRF, the forward and backward modes are clearly distinguishable in the frequency domain of the isotropic rotor, and the severity of the mode can be identified for the unisotropic rotor.

• 대한기계학회논문집A
• /
• 제22권2호
• /
• pp.458-466
• /
• 1998

In this work, a frequency domain method is tested numerically and experimentally to improve nonlinear model parameters using the frequency response function at the nonlinear element connected point of structure. This method extends the force-state mapping technique, which fits the nonlinear element forces with time domain response data, into frequency domain manipulations. The force-state mapping method in the time domain has limitations when applying to complex real structures because it needd a time domain lumped parameter model. On the other hand, the frequency domain method is relatively easily applicable to a complex real structure having nonlinear elements since it uses the frequency response function of each substurcture. Since this mehtod is performed in frequency domain, the number of equations required to identify the unknown parameters can be easily increased as many as it needed, just by not only varying excitation amplitude bot also selecting excitation frequency domain method has some advantages over the classical force-state mapping technique in the number of data points needed in curve fit and the sensitivity to response noise.

• 조명전기설비학회논문지
• /
• 제28권3호
• /
• pp.63-71
• /
• 2014

A single-inverted-pendulum model is presented to simulate and predict the passive response of human balance control. This simplified biomechanical model was comprised of a torsional spring and damper, and a lump mass. An estimation of frequency response function was conducted to parameterize the complexity. The frequency domain identification method is used to identify the parameters of the model. The equivalent viscoelastic parameters of standing body were obtained and there was good conformity between the simulation and experimental result.

• Journal of Mechanical Science and Technology
• /
• 제19권2호
• /
• pp.625-633
• /
• 2005

A finite element vibration analysis of thin-walled cylindrical shells conveying fluid with uniform velocity is presented. The dynamic behavior of thin-walled shell is based on the Sanders' theory and the fluid in cylindrical shell is considered as inviscid and incompressible so that it satisfies the Laplace's equation. A beam-like shell element is used to reduce the number of degrees-of-freedom by restricting to the circumferential modes of cylindrical shell. An estimation of frequency response function of the pipe considering of the coupled effects of the internal fluid is presented. A dynamic coupling condition of the interface between the fluid and the structure is used. The effective thickness of fluid according to circumferential modes is also discussed. The influence of fluid velocity on the frequency response function is illustrated and discussed. The results by this method are compared with published results and those by commercial tools.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.517-522
• /
• 2002

The frequency response function(FRF) of each substructure is used for the transfer function synthesis method(TFS). The dynamic characteristics of the full system are obtained by synthesizing FRFs of each substructure. The validation of TFS depends on accuracy for FRF of each substructure. Impact hammer testing is widely used to obtain the modal characteristics of structures. However, the FRF obtained from impact hammer testing contains several errors, such as finite record length error and leakage error of which characteristic depends on data acquisition time which we call record length. In this paper, a method to remove these errors is proposed so as to enhance results of TFS. Numerical examples show that the FRF of full structure can be predicted exactly by the method proposed in this paper.