Papers by Keyword: Time 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: This paper proposes an innovative method of converting digital signal to time-domain analog signal, which fully enjoys robustness and digital circuit friendliness. This technique utilizes a digital delta-sigma ( ) modulator following a digital-to-time converter (DTC) circuit with various modulation methods. As an application of the proposed method, novel spreadspectrum clock generation (SSCG) algorithms (such as for DC-DC converters) have been investigated which can select the noise spectrum spread bands; e.g., they can exclude the noisespectrum spread in AM, FM radio bands. The proposed circuit takes advantage of digital technology, which is simple, fast (reachable at high clock frequency) and flexible (programmable).

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: A inverse identification method is proposed to deal with the nonlinear boundary parameter identification problem. The boundary condition is modeled as unknown equivalent substructure applied on the initial linear structure and the parameter identification inverse problem is translated into a linear-model based equivalent force identification problem. Based on a given multi-point approximations method, the time history of the equivalent force is identified using the measured dynamic response. The unknown dynamic forces due to substructure are parameterized by combination the base functions on a series of space-time points. Using the moving least squares method, a matrix is derived to extract the force time history from the measured dynamic response. Then, the boundary stiffness and damping are identified using the input-output data of the equivalent substructure. The proposed approach has been demonstrated by some numerical examples and the boundary parameters are successfully identified.

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.

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.

Abstract: In the present work, an attempt has been made to monitor the tool condition status during microturning of aluminium alloy (AA 6061) using multiple sensors such as cutting force dynamometer, acoustic emission (AE) and accelerometer. The tool wear (nose wear) is correlated with surface roughness (R_a), chip width, thrust force (F_x), tangential force (F_y), feed force (F_z), AE_RMS and vibration signals. It is observed that R_a, chip width and cutting forces are increased with increase in the tool wear. Among the cutting forces, the tangential force (F_y) is found to be more sensitive to the tool wear status compared to that of the thrust force (F_x) and feed force (F_z). From the signal analysis, it is observed that during machining with good tool condition, the dominant frequency of the AE_RMS and vibration signals are found to be 81 kHz-110 kHz and 2.07 kHz-3.84 kHz respectively, whereas with the worn out tool the dominant frequencies are shifted to higher levels. Chip morphological studies indicated that favourable type of chips are formed upto 40^th minute and unfavourable chips are observed from 41^st minute to 60^th minute.

Abstract: There are advantages such as real time, quick, multi-constituents simultaneous measurement, green and no pollution, and so on, of using near infrared spectral method to detect concentration information of dairy products constituents. From time domain and frequency domain, near infrared spectral data mining methods based on orthogonality were separately researched to realize noise filtering and useful information extracting. For milk spectrum, methods in the time domain including Orthogonal Signal Correction and Direct Orthogonalization, Wavelet Transform de-noising method in the frequency domain, were separately explored and used in spectral preprocessing, PLS method was used to build calibration model, and processing effect of different data mining methods was compared with and analyzed. It is showed that in the time domain, using the orthogonality methods to make data mining for milk spectrum, the complex interfering signal and noise information uncorrelated with the measured constituents can be can reduced effectively, and the correlated information with the measured constituents is reserved in maximal limitation, prediction capability of calibration model is improved, furthermore, the Orthogonal Signal Correction method is better than the Direct Orthogonalization method, moreover, in the frequency domain, wavelet de-noising is better than the orthogonality methods within the time domain.

Abstract: In order to satisfy the need of automatic decision-making while shipboard-gun oppressive fire to the shore, This paper research the problem of shipboard-gun temporal fire distribution .This paper put forward the elements of oppressive fire distribution and solve out the calculation of every oppressive fire distribution elements(such as quick-firing’s quantity, surveillance firing’s quantity, every quick-firing’s ammunition wastage, every surveillance firing’s ammunition wastage and firing occasion). It could provide technical support for the realization of automatic decision-making while shipboard-gun suppression firing anti-shore.

Abstract: Engine is as a power machine, the operating status is good or bad, directly affects the working status of equipment. The status monitoring and fault diagnosis is very necessary to ensure that the equipment runs in its best, and improves equipment maintenance quality and efficiency. The engine failure shows the complexity and diversity of the interaction and complex relationship between the various subsystems of the engine, that is the fault of complexity, ambiguity, correlation, relativity and multiple faults coexistence. The available information are much in the engine diagnosis, for example, the vibration signal from bearings, cylinder head or cylinder block surface; oil, cooling water, pressure of intake, exhaust and fuel; temperature signal; noise, speed or oil-sample signals. In this paper, an engine as an example, engine fault diagnosis experimental system is built, the normal state, left one and right six cylinders off the oil, air filter blockage (inlet wood blockage is 30%, the inlet has screen cloth.) in the load of 2565Nm, and the speeds of 1500r/min, 1800r/min, 2200r/min are studied. The experimental results analysis, feature extraction and fault diagnosis are finished based on the time domain and frequency domain. Keywords: engine, fault diagnosis, time domain, frequency domain.