Frequency Response Analysis

For past few decades the study about phononic crystals are getting more popular. Understanding and controlling the phononic properties of the phononic crystals provides opportunities to reduce environmental noise. In this thesis there is a brief introduction to phononic crystals.
My research topic of the thesis is about vibration reduction of beams connected to spring resonators with one degree of freedom, with the ultimate purpose to find bandgaps. In the bandgaps of the frequency ranges, flexural wave cannot propagate in the structures. I have done two analysis to find bandgaps. The first one is finding flexural bandgaps through Eigenfrequencies. And the second one is finding band gaps through frequency response analysis. Two methods also shows us the range of band gaps.
All the simulation works have been done in COMSOL Multiphysics. COMSOL Multiphysics is a very suitable tool for analysis of wave propagation in phononic crystals. In the thesis, I give the steps for two kind of simulations in COMSOL Multiphysics.

KEY WORDS：Phononic Crystals, FEM, Eigenfrequencies, Frequency Response Analysis, Band Gap, Euler-Bernoulli Beam, Spring Resonator.

The paper presents the description for diagnostic methods of induction motor's stator windings fault. The presented methods use Frequency Response Analysis (FRA) technique for detection of Winding Faults in Induction Motor. This method is previously reliable method for faults diagnosis and detection in many parts of transformers including transformer windings. In this paper, this method was used for motor windings faults detection. This paper presents the FRA response interpretation on internal short circuit (SC) fault at stator winding on three cases studies of different three-phase induction motors (TPIM), were analysed according to two status: healthy induction motor at normal winding status and same motor with windings shorted of main windings. A conclusion of this paper provides the interpretation of and validation the FRA response due to internal SC fault case by using NCEPRI algorithm, which is considered as one of certified statistical indicators. The proposed method in this paper had a useful result for detect and diagnosis of stator windings faults of TPIM. The applications of developed method can be used to detece the other machines types faults.

Monitoring and diagnosis of power transformer in power systems have been examined and debated significantly in last few decades. Recently, more researchers have expressed their interest in these issues as the utilities and network operators operating under a rising cost-effecting pressure. Especially, in studying to monitor winding faults which is found to be the most common fault within transformers. This paper addresses the issue of the effect of inter-windings short circuit fault in a Dyn11 connected transformer. The specific aim is to study the effect of fault at winding of other phases to the response of measured phase. Frequency Response Analysis (FRA) which is discovered to be a powerful and sensitive method to examine and evaluate the condition, including the mechanical reliability of the transformer windings is used.

One of the most important methods for transformers fault diagnosis (especially mechanical defects) is the frequency response analysis (FRA). The most important step in the FRA diagnostic process is to differentiate the faults and classify them in different classes. This paper uses the intelligent support vector machine (SVM) method to classify transformer faults. To this end, two groups of transformers were tested and necessary measurements were obtained; the transformers with healthy conditions and the ones with various fault conditions (axial displacement, radial deformation, disc space variation, short-circuits, and core deformation). Then, by dividing the frequency intervals of the measurements, a new feature based on the cross-correlation technique was proposed for SVM training and validation. After the training process, by applying the data obtained from actual transformers, the performance of SVM in different conditions was evaluated and compared. Finally, the most appropriate feature was presented.

Study and analysis the effect of variable applied voltage on SCIM performances based on FEA is presented. Three phase squirrel cage induction motor SCIM has been investigated and numerically simulated using finite element method (FEM) with the aid of ANSYS software (RMxprt and Maxwell 2D/3D). This research presents study and analysis of the effects of the voltage variation on performance and efficiency of the three-phase induction motor of the squirrel cage type. The Finite Elements Analysis Method FEA is used as one of the best methods for analysis and simulation of electrical motors in addition to the possibility of dealing with nonlinear equations, Since the induction motor is a complex electromagnetic reaction, the researchers used the ANSYS program to represent and analyze the performance of the motor under variable supply voltage. The case studied in this research is three phases, 380V, 50Hz, 2.2kW, induction motor that widely use in industrial application. The aim of this research is to study the effect of voltage variation on efficiency, current value, power factor and torque of SCIM. The RMxprt software has been used for modeling and simulating the induction motor and calculating the values of phases currents, input and output power in additional of overall efficiency at steady state condition. The next stage of the research is creating Maxwell 2-D design from the base model of RMxprt software, Maxwell 2-D model has the ability to computing the distribution of magnetic field and explaining the performance under steady-state operation. The obtained results show significant reduction of motor performance due to the effect of variation of apply voltage.

This paper presents an embedded frequency response analyzer (EFRA) for fuel cells (FC) based on a low-cost digital signal processor (DSP). Frequency response analysis technique provides valuable information of different electrochemical processes that occur inside the FC. The small size and low power consumption allows this special device to be embedded into the FC controller or the power conditioning stage. The system is capable of measuring automatically the frequency response of the FC at different operating points, even when the FC is operating with load. These measurements can be used to characterize the FC at design stage and to perform on-line monitoring of the FC state during continuous operation. The proposed instrument uses the lock-in amplification technique, which allows very accurate and precise measurements even in the presence of high noise levels. The proposed hardware and signal processing technique are described in this paper including experimental result of a 1.2 kW proton exchange membrane fuel cell (PEMFC) system

The major amount of worldwide transportation is done by using automobiles. In automotive industries truck chassis are designed as per the design standards but the bodies manufactured by various manufacturers are designed without standard design considerations. In India there is huge market of these manufacturers. These bodies are manufactured as per their loading capacity, there is no standardization of design considering engine vibrations and dynamic performance. Truck bodies manufactured without design standards are unsafe for dynamic performance. The body is excited by dynamic force induced by the engine. Under such dynamic excitations, the body tends to vibrate at some frequency, as truck engine operating rpm range is between 900rpm to 3000rpm. Because of engine, truck body undergoes vibration range between 15Hz to 50Hz. Whenever the natural frequency of vibration of a truck body structure coincides with the frequency of the external excitation induced by engine, there occurs a phenomenon known as resonance, at resonance drastic increase in deflection occurs which leads to excessive deflections and failure of the truck body structure. Hence there exists a need for the industry sector to modify the design of dump truck body structure which allows dump truck body to withstand safe between engine excitation frequencies and simultaneously improvising the strength, reducing weight, and prolonged operational life.

ABSTRACT Interturn winding faults are one of the most prevalent and potentially destructive electrical faults in power transformers. This contribution is an initiative to explore the potential of the sweep frequency response analysis (SFRA) method in detecting interturn winding faults and also identifying the most appropriate measurement configuration for making sensitive frequency response measurements. This application enables timely warning of the rising failure and so is of particular importance, as these kinds of defects, if left undetected, can propagate and lead to catastrophic phase–ground or phase–phase faults which can finally cause the breakdown of the whole transformer. In this paper contribution is made to a better understanding of the transformer performance and modification of the transformer winding frequency response in the presence of interturn faults. The paper includes a full description of the details of the SFRA method and measuring procedure, along with principal experiments conducted on a 100 kVA distribution transformer. A large number of measurements with different transfer functions, various terminal configurations and three categories of measurement types was conducted to identify the most appropriate configuration for making SFRA measurements. The experimental results proved that the identified measurement configuration is sensitive to detect unambiguously interturn faults even down to 0.2% shorted turns along the winding.