800 publications from this institution
This paper presents an algorithm structure for an active noise control (ANC) system based on an improved equation error (EE) model that employs the offline secondary path modeling method. The noise of a compressor in a gas station is taken as an example to verify the performance of the proposed ANC system. The results show that the proposed ANC system improves the noise reduction performance and convergence speed compared with other typical ANC systems. In particular, it achieves 28 dBA noise attenuation at a frequency of about 250 Hz and a mean square error (MSE) of about −20 dB.
Damage of shear connectors in slab-on-girder structures will result in shear slippage between slab and girder, which significantly reduces the load-carrying capacity of the bridge. This paper proposes a dynamic damage detection approach to identify the damage of shear connectors in slab-on-girder bridges with power spectral density transmissibility (PSDT). PSDT formulates the relationship between the auto-spectral density functions of two responses. Measured impact force and acceleration responses from hammer tests are analyzed to obtain the frequency response functions at the slab and girder sensor locations by experimental modal analysis. When measurement data from the undamaged structure are available, PSDT from the slab response to the girder response is derived with the obtained frequency response functions. PSDT matrices in the undamaged and damaged states are directly compared to identify the damage of shear connectors. When the measurement data from the undamaged structure are not available, PSDT matrices from measured response at a reference sensor response to those of the slab and girder in the damaged state can also be used to detect the damage of shear connectors. Experimental studies with a concrete slab supported by two steel girders are conducted to investigate the accuracy and efficiency of the proposed approach. Identification results demonstrated that damage of shear connectors can be identified accurately and efficiently with and without measurement data from the undamaged structure.
Due to the complexity of surface texture,the images obtained from the existing online detection system cannot show the strip surface defects exactly,which becomes one of the important problems to be solved for the detection of surface defects of cold-rolled strip.A novel wavelet-based image filtering algorithm by virtue of anisotropic diffusion is therefore proposed.It decomposes the original image into the low and high-frequency components by wavelet transform,then the high-frequency components are regularized by wavelet diffusion coefficients and,finally,the filtered image is reconstructed by inverse wavelet transform. To achieve a satisfactory filtering result,the wavelet-based anisotropic diffusion is often performed iteratively.Experimental results indicated that this new algorithm could not only filter off the unnecessary texture background but also preserve the valuable information in detail effectively.With more favorable combinability in filtering,this algorithm will lay a solid foundation for the subsequent image processing,e.g.image edge detection,image auto-segment,etc.
This paper analyzed and summarized the NM force correlation curves of eccentrically pressed and steel reinforced concrete parts with rectangular cross section in all occasions and then found out the different MuNu combinatory interrelation of eccentrically pressed steelconcrete parts which had a certain section area,reinforcing steel and strength and reached their maximal load capacity,and worked out the methods to determine the most disadvantageous one of differently combined internal NM force groups endured by the same rectangular cross section and to draw diagrams for the section design of eccengrically pressed members.All the analyzed results provided basis to design calcuation and simplified the calculation.
Motorcycle chain wheel is important bolt which join Rear wheel and Chain wheel.It must endure great shearing force and radial stress. The analysis of binding bolt were made by means of SEM, optical microscope and chemical analysis. It is shown that the failure of binding bolt caused by brittle fracture. This paper introduced characters and main reason of the defect, such as extending acid wash time. In addtion fold defect, insufficiency of getting rid of Hydrogen, etc. also influence binding bolt quality. In the same time, the conditions causing brittle fracture and the measure to prevent the crack are also discussed.
This paper proposes a damage-identification and optimal sensor-placement approach for structures under unknown traffic-induced vibrations. Response reconstruction is performed for structures under traffic-induced vibrations to formulate the relationship between different sets of time-domain responses. Measured acceleration responses from a structure under traffic-induced ground motions are used for damage identification with a sensitivity-based iterative model updating method. Numerical simulations on a seven-story planar frame structure are conducted to verify the performance of the proposed approach. Damage identification is conducted based on the initial finite-element model of the structure and the measured responses from the damaged state under traffic-induced vibrations. Structural elemental stiffness factors are iteratively updated until the reconstructed responses match the measured ones as closely as possible. A two-phase optimal sensor-placement scheme is proposed for better response reconstruction and subsequent damage identification. Optimal sensor placement is investigated to identify the best locations for response reconstruction and sensitivity-based damage identification. With the use of optimal sensor locations, the introduced damages can be identified effectively and accurately with nearly exact damage severity estimation and very small false positives and false negatives under a 5% noise effect.
P. R. China needs to develop its own method and experimental facility for assessing pressure distortion of a certain turbofan engine. Section-1 describes the features of the facility, among which we mention fluid-driven movable flashboard distortion generator and the pressure transducers that can make transient-state measurements. Section-2 explains the four steps of our experimental procedure. By changed the depth of movable flashboard and engine speed, the distortion of complicated inlet flow field and distortion index were investigated. The results show that the circumferential turbulence level is an axial symmetry distribution with center of the flashboard, the distribution curve almost likes the letter ‘M’. The turbulence level of each testing point is in direct proportion to flashboard depth, so is the radial turbulence level. And the distribution curve just likes the letter ‘V’ for single harrow. By way of analysis above, we then gained several testing point positions with high amplitude and sensitive to un-stability state from 30 testing points in air inlet duct. Section-3 discusses how to identify the inlet pressure distortion signal based on wavelet and neural network. While the surge was happening, the dynamic pressure signals firstly jumped then dived, and surge signals were not lasting more than 0.5s. In order to surveillance watch engine’s running, we first applied wavelet theory to process distortion signal’s de-noising and extracted the frequency characterization of distortion signal. Because of only processing a certain frequency bands, calculation workload is little with anti-jamming and convenient to process data in real time. Then we designed and trained a perceptron as neural network to identify the distortion signal automatically to help operators detect surge in time.
Software test is a reliable technological means of guaranteeing software quality. General testing methods divide testing input values into a number of sectors according to certain rules, and then they choose a figure from each sector as testing data. However, if inappropriately divided, the probability of at least one error is lower than that of random testing which uses the equivalent number of cases. In light of the problem, the article puts forward a measurement method of describing ideal testing division via testing interdependency. By means of reasonable testing division, the testing effect on software models can get improved.
Based on the principle of the fiber Bragg grating strain sensor as well as the volume expansion of the reinforcing steel due to corrosion, an optical fiber grating sensor for monitoring corrosion of reinforcing steel and the method of temperature compensation were studied in the present paper. The sensor construction is that one Bragg grating is stuck on the inner center of two bars against each other, and the reinforcement volume as well as the diameter will expand due to corrosion. Based upon sensing mechanism, monitoring will be carried out by transforming the diameter increase to the fiber strain, and as a result the degree and rate of reinforcement corrosion can be obtained. The principle of corrosion monitoring is that the strain induced by corrosion and temperature fluctuation is measured by a reinforcing steel fiber grating sensor. At the same time, the strain induced by temperature fluctuation is also measured by an individual stainless fiber grating sensor. Therefore by two independent fiber grating sensors, the volume changed by corrosion can be separated. By the concrete encapsulating and embedding method of FBG corrosion sensor, the degree of corrosion of reinforcing reinforcement will be measured directly, which is not affected by corrosion factors and can be used in the early corrosion monitoring of reinforcement in concrete structures. Finally the relationship between corrosion rate and shift in center wavelength was calibrated by experiment.
The method of long range network RTK is the main means to improve the accuracy of real-time kinematic positioning of GPS/BDS. The fast fixing of carrier phase integer ambiguity with GPS/BDS between long range reference stations was significant. The algorithm of multi-frequency carrier phase integer ambiguity resolution with GPS/BDS between long range network RTK reference stations was studied in this paper. The GPS wide-lane ambiguities were fixed by the double frequency observation data of reference station network. And the extra-wide-lane ambiguities of B2 and B3 frequency were fixed by using B2 and B3 frequency observation data at the same time. Then the solution model including GPS double difference carrier phase integer ambiguities and atmospheric errors can be established, the carrier phase integer ambiguity can be fixed by this solution model and the constraint of wide-lane ambiguities. Then the spatial correlation model of atmospheric delay error was established. And the computation model of BDS double difference carrier phase integer ambiguity including atmospheric delay error was established by the extra-wide-lane ambiguities of B2 and B3 frequency. The BDS carrier phase integer ambiguity resolution was constrained by the spatial correlation model of atmospheric errors. Therefore the influence of ambiguities fixing by using ionosphere free observation can be eliminated. The test of the algorithm was carried out by the GPS/BDS data with long range reference station network. The results of experiment indicate that the rapidly fixing of carrier phase integer ambiguity with GPS/BDS between long range reference stations was achieved by this algorithm.
A new time-varying system identification approach is proposed in this paper by using variational mode decomposition. The newly developed variational mode decomposition technique can decompose the measured responses into a limited number of intrinsic mode functions, and the instantaneous frequencies of time-varying systems are identified by the Hilbert transform of each intrinsic mode function. Numerical and experimental verifications are conducted to demonstrate the effectiveness and accuracy of using the proposed approach for time-varying system identification, that is, to obtain the instantaneous frequency. Numerical studies on a structural system with time-varying stiffness are conducted. Experimental validations on analyzing the measured vibration data in the laboratory from a steel frame structure and a time-varying bridge–vehicle system are also conducted. The results from the presented technique are compared with those from empirical mode decomposition-based methods, which verify that the developed approach can identify the instantaneous frequencies with a better accuracy.
A method for structural damage identification based on a modified Artificial Bee Colony algorithm is presented. A new formula is introduced to the onlooker bee phase to improve the convergence rate and the Tournament Selection Strategy is adopted instead of roulette to enhance global search ability of the algorithm. Test functions are introduced as benchmarks to verify the proposed algorithm. And then two numerical examples, including a supported beam and a plate, are conducted to investigate the efficiency and correctness of the proposed method. Final estimated results show that the present technique can produce more accurate damage identification results, comparing with other evolutionary algorithms, even with a few noise contaminated measurements.
