Papers by Keyword: Frequency

Abstract: This paper by taking the hypersonic speed wing surface as the research object, according to the basic theory of thermal mode analysis, calculates and analyzes the influence of temperature variation on model vibration characteristics. According to the analysis, the structural natural vibration characteristics can be influenced by different temperature loads obviously. As for the 7075 root fixed wing surface model under the temperature range of 150K~500K, the basic linearity of frequencies of different order modals decreases with the rise of temperature; The structural frequency decreases sharply with the rise of temperature when the temperature is higher than 500K.

Abstract: A difference in frequency of loading during the test may give a different number of cycles to failure, especially at a higher frequency. The difference becomes more evident when higher frequency was applied at the same stress value. The change of frequency should be analyzed to define its effect on the fatigue life of the Extended Hollobolt to concrete filled hollow section. A number of tests are conducted to determine this effect. Frequencies between 0.25 and 5.0 Hz were applied. Analysis of the result indicates that frequency below 3 Hz does not significantly affect the fatigue life of Extended Hollobolt.

Abstract: The main effort of each technological process is not only to reduce the costs, but also to reduce the impact on the environment. The technology of abrasive water jet is one of the methods of division and cutting materials with the lowest impact on the environment, since water is the cutting tool, in our case with the addition of an abrasive. The aim of the measurement was the observation (examination) and evaluation of the vibration impact on the technological head in the technology of abrasive water jet when changing the selected technological parameters, namely the feed rate of the technological head. The experiments were carried out on one kind of material - steel HARDOX 500 with a thickness of 10 mm. The impact of the change of the technological head’s feed rate (100, 50, mm/min) on the size of the vibration acceleration amplitude and its frequency were examined. A database was created from the measured vibration values on the technological head and from that database the data was evaluated in selected softwares (LabVIEW, SignalExpress a Microsoft Excel). Graphical dependencies, frequency spectra covers and covers comparison graph were created from which new findings and conclusions were formulated.

Abstract: This paper shows the groundwork of correct interval of lubrication the bearing and its impact on the operating and technical status. The method of monitoring vibration in frequency range from 0 to 200 Hz was selected for determining the technical state of bearing. The bearing was monitored and lubricated every month during the half an year except one month.

Abstract: Cantilevered shaft-rotor systems consisting of multi disks and multi profiled shafts are considered. In this paper the procedures for the determination of the deflection, slope, shear force and bending moment at the extremities of the shaft are employed. Critical speeds or whirling frequency conditions are computed using transfer matrix method (TMM). For particular shaft-lengths, rotating speeds and shaft-profiles, the response of the system is determined for the establishment of the dynamic characteristics. A built-in shaft-rotor system consisting of two disks and two different profiled shafts is investigated for illustration purposes. Step response of the multi profiled shaft-rotor system is also found out.

Abstract: Radio Frequency Identification (referred to as RFID) is an effective and contactless feature of identification and localization of the object of interest with specific system structure that includes defining the principle of operation of the primary components, which are the transponder and the reader. The range of applicability of RFID system is diverse, but its optimum usability is given primarily by the choice of appropriate frequency which will ensure the functionality of the whole system in terms of physical protection. The article therefore deals with the operation of RFID technology in various wavelengths of frequency band and influence of radio frequency signal with a focus on the action radius of physical protection of renewable resources (e.g. research centers, universities, power plant using energy from renewable resources) as a technical means destined for increasing the level of security and protection of persons, property or other assets.

Abstract: In this paper, a new approach for harmonic detection in power signals based on fast modified S-transform (FMST) is proposed, which combines the advantages of the incomplete S-transform and the modified S-transform. Initially, the Fast Fourier Transform was performed and dynamic measurement values were obtained from the envelope of power spectrum, then the valid harmonic frequency points were detected by selecting the dynamic measurement values which were larger than the set thresholds. Further, the FMST was specifically performed on these major frequency points and a complex matrix was generated. The row vectors of the matrix reflected the phase and the time location information of harmonic disturbances, while the column vectors reflected the amplitude-frequency characteristics. And the feature vectors extracted from the complex matrix were used to detect the harmonic amplitude, phase and transient information. Simulation results validate the high accuracy, strong noise immunity and rapidity of the proposed approach.

Abstract: Cross-linked polyethylene cables are widely used in power transmission system. In this work the effect of frequency and boost on the breakdown performance of XLPE cable with inserted needle defects was investigated by the frequency-tund resonant system with frequency ranging from 20Hz to 300Hz. The breakdown paths were observed by an optical microscope, and the fractal dimensions of the paths were estimated according to box-counting method. It was found that, with the increase of frequency, the variation of path fractal dimension as a function of frequency corresponded to that of breakdown voltage. Compared with the continuous boost method, the frequency, at which the fractal dimension of breakdown paths approached saturation and the breakdown voltage peaked, became lower under step test method. The increase of breakdown voltage is due to the increase of electrical power used for the initiation and development of dense discharge paths.

Abstract: This research performed dynamic tests on a 1/4 scale test model of a new-styled Korean traditional wooden house to study its dynamic characteristics. The dynamic tests were performed both by the impact hammer test and the shaking table test of an El-centro N-S seismic wave. Together with these dynamic tests, structural analysis was also performed and the results were compared. The natural frequency from the impact hammer test was slightly higher than that from the shaking table test. The natural frequency from the eigenvalue analysis was about 16~33% lower than that from both the impact hammer test and the shaking table test. It can be deduced that the rotational stiffness of joints of analysis model were somewhat underestimated than those of experiment model.

Abstract: The airborne omni-directional antenna must not only satisfy the indicators of omni-directional horizontal requirements, but also have conformal shape with the surface of airplane. The common monopole antenna and microstrip antenna can not meet the above requirements. Under the background of the airborne antenna miniaturization and conformal demand, this article designs a kind of airborne circular slot antenna. The structure of the antenna is simple, which meets pattern VSWR < 1.4 bandwidth of 350 MHz to 376 MHz and meets pattern VSWR < 2 bandwidth of 338 MHz to 438 MHz .Its maximum gain within the operating frequency range can be 4.205 dB .