Papers by Keyword: Frequency Domain

Abstract: Solar Array Drive Assembly (SADA) induces micro vibrations in satellite that have pronounced effect on precision of pointing direction and its imaging quality. The present study analyses amplitude of these disturbances both in time and frequency domain using theoretical methods and experimental techniques. SADA used for investigation is a four beat and two phase hybrid stepper motor driven in 32 & 64 subdivision (SD) numbers. The formulation for frequency of active vibration disturbance and electromagnetic coupling are calculated first leading to disturbance model for 32 & 64 subdivisions SADA running with dead load. A rigid force / moment test platform consisting of piezoelectric sensors is used to validate the theoretical results that give amplitude of disturbance moments produced by SADA. A gravity unload device is added in experimental setup to simulate the working environment in space (zero gravity conditions). 0G test setup not only confirms the presence of electromagnetic stiffness but also supplies comparison for disturbance amplitude of various subdivisions SADA running with & without gravity of load. Results acquired in time and frequency domain verify that increase of subdivisions cause reduction in micro vibrations generated by SADA. Moreover, addition of gravity unload device reduces the amplitude of vibrations in the structure and smoothen the operation. The work lays a firm foundation for study on vibration damping, design of drive circuit and SADA disturbance analysis during in orbit operation.

Abstract: Magnetorheological finishing (MRF) is an advanced polishing technique capable of rapidly converging to the required surface figure. In this article, dual-rotation MRF tool is used to generate centrosymmetric removal function that can be W-shaped or Gaussian-shaped. Using W-shaped removal function and Gaussian-shaped removal function respectively, this article compares the convergence of surface error by simulating the finishing process through iterative calculations. Furthermore, it compares mid-spatial-frequency surface error caused by the two removal functions, through 2D FFT and PSD estimation in the frequency domain. From simulation, this article proves that Gaussian-shaped removal function is more advantageous than W-shaped removal function. To solve the problem that the removal function obtained in dual-rotation MRF is W-shaped, this paper presents the method of adjusting the distance between the axes of self-rotation and co-rotation to secure Gaussian-shaped removal function. Finally, experiments have been conducted to demonstrate validity of the method.

Abstract: This study presents a methodology of frequency domain for analysis the output signal of the sensor device in order to enhancing the performance and resolution in measurement of a sensor module. However, in this case used the new sensor module namely 4-crossing Hall sensor, which was designed by the assembling of four permanent magnets with four Hall generators as a sensor device. An analysis of frequency domain in this study aims to develop a new non-destructive measurement using a new sensor module as a sensor device in order to measure the imperfection of metal materials using, in some cases, the methodology of non-destructive inspection. This process was performed by transforming the values in the pattern of the output voltage from sensor device, which was amplified by the instrumentation amplifier into the time domain by the voltage to frequency converter and then transformed into the frequency domain based on the principle of Fourier transform. It was found that an analysis by frequency domain is the methodology which can be explicitly applied to detect the dimension of holes on a metal surface. In an experiment, the principle of frequency domain can precisely determine and distinguish the depth of drilled holes with 1 mm difference.

Abstract: Dynamic stability parameters (dynamic derivatives) are important indicators for the control system design, orbit design and longitudinal and horizontal dynamic stability analysis of aircrafts. Methods that evaluate the quality and dynamics of an aircraft typically include flight experiment, wind tunnel testing and theoretical calculation, with one of the most important part of them being the obtainment of dynamic derivatives. Project estimation method derivative action is not considered suitable for boundary layer transition, flow separation and re-attached and the complex situation leeward area vortex small angle of attack linear range. Frequency domain is a dynamic non-scheduled periodic invariant system to get moving derivative calculation method, but the accuracy of the unsteady flow is much lower than the time-domain calculations. Currently, unsteady CFD approach represents a time-domain nonlinear aerodynamic characteristics predicted the most advanced level. Derivative prediction efficiency and adaptability under conditions of high angle of attack of the development trend of nonlinear dynamic derivatives were analyzed. As a global trend, obtaining dynamic parameters through numerical calculation is becoming a prevailing approach to dynamic parameter research.

Abstract: Based on the multi-degree of freedom in series model, structural displacement amplitude formula is derived in the frequency domain under the translation-rotation input situation, this formula indicates that the soil - structure interaction (SSI) could be considered as adding a correction term M˜ to the mass matrix of the structure with the hypothesis of Rigid foundation. This corrected mass matrix is actually a complex matrix, which related to the input frequency and damping. Equivalent translation-rotation input is coupled with two translation input components U* and Θ*. Besides, we uses case analysis to explain the characteristics of soil - structure interaction (SSI) in frequency domain by the end of this paper.

Abstract: This paper proposes a new damage warning process for structural health monitoring (SHM) system, which utilizes probability analysis on information of frequency abnormal development. This process was introduced to analyze information collected in frequency domain from a steel structure, and it achieves damage warning for the structure.

Abstract: Beam forming technology is an important content in the study of underwater target positioning, can directly use beam forming technology to identify the target direction, but can be by beam forming of target signal enhancement, and then to deal with the enhanced signal. No matter how to apply, beam forming technique can be regarded as a weighted sum of signal delay processing, its purpose is to form a beam and the scan to a specific direction. Based on uniform linear array as the example, this paper first of all, the simulation analysis of conventional beam forming technology direction scanning accuracy and array element spacing, number of array element, the relationship between the signal frequency; Then by analyzing grid scanning beam spatial distribution of power spectrum and the quantitative relationship between linear arrays, studying a selection method is suitable for the engineering application of fast beam domain, high precision and fast direction to estimate.

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Abstract: In some special fields such as precision optics, the part surface has strict requirements on the frequency domain errors, besides the conventional spatial domain errors such as surface roughness error. In light of the available works lacking of the frequency domain error analysis in ultra-precision flycutting, this paper therefore presents its frequency domain error analysis. A case study of KDP crystal flycutting is carried out to show its detailed processes, where the processing parameters, tool geometry, motion dynamic error of the machine guideway and tool-work vibration induced dynamic error are considered. A surface profile generation method is put forward. Two cases with different tool-work vibration frequencies are carried out. The spatial frequency spectrum is obtained based on the FFT analysis of the generated profile in the specified direction. After the in-depth analysis, the inherent correlation of the generated spatial frequency components with feed spatial frequency and machine dynamic errors induced spatial frequency under certain machining conditions are found, which is very meaningful for the frequency domain error prediction in the real application. The proposed analysis method can also be applied into other types of surface machining.

Abstract: In this work, an online acoustic emission (AE) monitoring system is developed, to investigate the effect of tool wear during the microturning of titanium alloy with a tungsten carbide insert of nose radius 0.1 mm. The AE signal parameters were analyzed in time domain, frequency domain and discrete wavelet transformation (DWT) techniques to correlate with the tool wear status. The root mean square (AE_RMS) and specific AE energies are also computed for the decomposed AE signals, using the DWT. The results demonstrated that dominant frequency and DWT techniques are found to be most suitable for online tool condition monitoring, using AE sensors in the microturning of titanium alloy.