Papers by Keyword: Frequency Response Analysis

Abstract: This study describes a practical and systematic procedure for identifying and modeling nonlinear systems based on the input-output analysis. Frequency domain data is used to obtain a reduced linear models of nonlinear systems. A coherence function is introduced to specify the identification accuracy. The procedure is applied to a small vertical take-off and landing air vehicle. Control compensators are then designed based on the identified models and autonomous hovering is successfully achieved. Simulation results demonstrate the effectiveness and superiority of this method in comparison with other classical approaches.

Abstract: Distribution transformer in Malaysian electricity network is categorized as major element on delivering electricity throughout the nation. Advanced diagnostic tools are used to monitor any technical problem of transformer to sustain its capability in the long run. One type of it which is currently being used in worldwide is Frequency Response Analysis (FRA). The reliability from this method is proven worldwide in diagnosing transformer condition especially a mechanical movement. FRA technique is done by comparing the response result in transformer initial condition to its current condition. The interpretation of transformer condition from the response is based on frequency sub-bands. Each frequency sub-bands are indicating any movement parts of transformer and electrical faults. Currently, there are three worldwide standards established for interpreting the FRA results but both of them are different in frequency sub-bands range. Up to now, there are no research papers comparing the fault detection capabilities from frequency sub-bands range for both standards. In this paper, comparative study is done to visualize and interpret the capabilities from three standards (IEEE Std C57.149 2012, DL/T911-2004 and Cigre WG A2/26); by focus on the frequency sub-bands range.

Abstract: The dynamic characteristics and dynamics parameters of rolling bearings is very important to dynamics and vibration response of rotate machine such as rotor systems, gear systems and Spindle systems. The frequencies of rotate machine are affected by dynamics parameters of rolling bearings at different places. The purpose in the work presented is to research a new approach and multibody model of Spindle systems with equivalent dynamics parameters of rolling bearings. The flexible Spindle body has been constructed by the fixed interface component mode method. The four different models of rolling bearings for Spindle systems have been developed using equivalent spring and damper elements. The experiments of Spindle body and Spindle system have been carried out. Experimental modal frequencies have been got by impulse vibration test and sweep frequency vibration test. The frequencies and vibration response of Spindle systems have been calculated by adjusting equivalent spring and damper elements to minimizing errors between the calculated and experiment frequencies. The results show the errors of frequencies of linear equal and unequal spring and damper models are large except the first frequency. However, the errors of nonlinear equal and unequal spring and damper models are small. The predicted frequencies of nonlinear unequal spring and damper model are the most accurate and agree well with the experiment results. The presented method can be applied to calculate the nonlinear equivalent stiffness parameters accurately for rolling bearings in multibody systems.

Abstract: Noise and vibration analysis has become thoroughly researched in vehicle engineering where is needed to keep the noise level low and affect the vehicle users. The analysis in the paper shows a frequency response study where we will determine the frequency response on a coupled structure-fluid model. The study will be made on a simplified “train wagon“ model to show in a better way the differences between a perfect coupled structure-fluid model and a non-conformal coupling. The analysis shows that the distribution of the nodes for the two cases influences the results.

Abstract: In order to discover the hidden trouble of the 10kV transformer, in this paper, on-line monitoring system based on LabVIEW is developed. The paper briefly introduces the basic concept of the virtual instrument and the frequency-response analysis (FRA), and then it expounds the development process of the hardware and software of this system. The hardware performs the main functions: signal injection, filtering, amplifying, signal conditioning, and storing the result in computer. The software includes four modules: user login, data acquisition, data analysis, data query. Finally, the monitoring system is validated by a corresponding experimental study.

Abstract: The frequency response analysis (FRA) is a effective diagnostic method in monitoring the deformation of transformer winding. This paper uses the current sweep-sequency source as the excitation to replace the voltage source in the traditional method.And the frequency response curves can be drawn from the current signal rather than the voltage signal.It can be judged whether there is deformation in the transform winding by comparing the frequency response curves.The method can realize the on-line monitoring and diagnosis for the transformers whose neutral points is grounded directly. The Research Background The safety of transform is the necessary condition for power system operation. As the increasing of power system capacity,the short-circuit current will be bigger than before.Therefore, transformer will take more risk of winding deformation.

Abstract: System Identification is a key technology for the development and integration of modern engineering systems including unconventional flying vehicles. These systems are highly parametric with complex dynamics and nonlinearities. Ducted fans are special class of these vehicles that can take off vertically, hover and cruise at very low speed. In this paper, an exact equivalent linear system is found from the non-linear dynamic model of a ducted fan by use of frequency response identification. Here, power spectral density analysis is performed, using CIFER software, to evaluate the input-output responses in hover and to derive the transfer functions based on the coherence criterion. Then, PID controllers are designed by utilizing the identified transfer functions and the performance characteristics of the controllers are evaluated in fully non-linear simulation of the system.

Abstract: Online testing system based on frequency response analysis is proposed for the deformation of transformer winding. The structure of testing system, the selection of sweep sequence and computer diagram of data acquisition system are developed in the course of design. In the process of analysis, the concept of correlation coefficient is introduced to judge the relationship between the deformation extent and correlation coefficient. With the proposed method, the location of deformation can be determined. The testing curves demonstrate the effectiveness of the presented system.

Abstract: Giant electromechanical coupling factor of k31 mode over 86% was found for (100) Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 and (110) Pb[(Mg1/3Nb2/3)0.74Ti0.26]O3 single-crystal plates poled in the [100] and [110] directions, respectively. The P-E hysteresis loops in the single-crystal plates with giant k31 became asymmetric. Furthermore, the frequency response of impedance in these plates with giant k31 consisted of a single vibration in the length direction. A mechanism to realize giant k31 can be explained by the relationship between the crystal plane and poling direction. In addition, the existence of giant piezoelectric d31 constant was proven by the strain measurement as well as by the impedance measurement.