Applied Mechanics and Materials Vols. 130-134

Abstract: In order to extend engineering application of nonlinear ultrasonic nondestructive testing technique in wave structure, an experimental technique for excitation and reception directly of Rayleigh wave by fixing piezoelectric sensor on the edge of the specimen is presented. Using the experimental system and procedure, the surface fatigue damage of AZ31 magnesium thick plate is detected by nonlinear Rayleigh waves. Although the experimental results have some dispersion, the ultrasonic nonlinearity parameters overall increase apparently with the fatigue cycles increasing, which demonstrates the Rayleigh wave nonlinearity parameters are sensitive for the changes of microscopic defects in the materials internal, and the experimental system and procedure are reliable. The Rayleigh wave nonlinearity parameters for the thick plate structure fatigue life prediction have potential engineering applications.

Abstract: The paper intends to study the core losses of non-oriented electrical steel laminations under high frequency voltage excitations. The measurement of core losses of the electrical steel laminations in Epstein Frame is implemented step by step from 50 Hz to 5000Hz. The accuracy of results evaluated from Expanded GSE method is compared with those tested by Epstein Frame. The core loss database for three different kinds of medium, medium-high and high quality electrical steel laminations (50CS350, 50CS470, 50CS600) is completed in the paper. Also, 85 test points of core loss data are established in the flux density ranging from 0.3T to 1.8T and in the power supply frequency ranging from 50Hz to 5000Hz. Maximum core loss value is close to 443W/kg. The tested core loss data and the Expanded GSE models are useful and may cover for the applications of large-scale wind-driven generators and general motors. They also enough provide designers with the accurate information to minimize the core losses of wind turbine generators.

Abstract: Cables are used as critical structure components for suspended and cable-stayed bridges. It has been recently increased the need for inspection methods to assess the conditions of the cables due to owners concern about the operability and safety of such aging structures. An alternative technique is being developed in this paper. The magnetostrictive guided wave technology is used to test broken wires. The suitability of this method is studied through application tests on experimental setups, lab-made cables with simulated broken wires and field test. Test Results indicate that this technique can detect two broken wires away exceeding two meters and propagating over one hundred meters. It is a promising method for nondestructive testing of bridge cables.

Abstract: The sound sources positioning method based on time delay estimation is through the iteration of a group of nonlinear equation to solve the target position. Most of the existing methods is to solve under the hypothesis that the sound spread velocity in air is known. This paper puts forward several effective methods of source orientation and propagation velocity estimation. These methods are only using the time delay which comes from the received signal between sensors separated in space to deduce the solving method of sound source location and sound’s speed estimation based on least squares, total least squares, limited data not sure and constraint least squares method, and then compare the characteristics of these methods through the computer simulation.

Abstract: Taking the computer sound card instead of current acquisition card as hardware and Labview as software development platform, a kind of sound card data acquisition system with higher sampling precision, middling sampling frequency and better flexibility is designed, it is given an example of six-path analog input multiplexing．It has realized data acquisition of multi-path FDM(frequence division multiplexing) signal. The system has many advantages, for example, high cost performance, strong commonality, and good expansibility．It takes on wider foreground in the fields of engineering measure and laboratory application．

Abstract: Half-band filter is a linear phase FIR filter, which is symmetric-even and odd .Because the coefficient of half-band filter is symmetrical and nearly half of the coefficient are zero, it make the filters reduce the number of multiplication operations by almost 3 / 4, and the number of addition operations by nearly half . The memory used to store filter coefficients are also reduced by half, so it make the implementation of efficient real-time digital signal processing more conducive. The half-band filter has many characteristics: for instance, simple structure, easy to implement and excellent performance, it is widely used in multi-rate system. This paper first describes the principle of half-band FIR filter, the character and method for implementation, then puts forward the design and simulation process which is based on MATLAB and Xilinx's half-band filter, and at last analyses the result.

Abstract: based on factor analysis of multivariate statistical analysis, aim directly at Enginering Project management practice, establishment the index system of Engineering Project performance evaluation, and use the SPSS software make a factor analysis of the data of Engineering Project, the final order factor score make evaluation value of the Engineering Project performance. This article studies the performance of Engineering Project risk provides a reasonable, practical feasibility of approach.

Abstract: Fulgide is well-known as a thermally irreversible organic photochromic compound. The fulgide films can be applied as recording materials in ordinary holography and polarization holography, which were respectively based on the photochromic and photoinduced anisotropy properties. In this report, different kinds of multiplexing holographic storage, like angle multiplexing, circumrotation multiplexing and polarization multiplexing are realized in a 3-indoly-benzylfulgimide/ PMMA film for the first time, where 5 images, 18 images and 2 images are stored at the same position of the film, and diffracted without crosstalk with each other. It is proved that 3-indoly-benzylfulgimide film has spatial resolution of 6300lines/mm, sensitivity of 2.89 × 10^-3cm²/mJ at 632.8nm on the polarization direction of the exciting beam, fatigue resistance of 70 times, thermal stability of 14 months and has advantages like low cost, easy to used, rewritable, long life time at room temperature for both states, and high signal to noise ratio. Overall, 3-indoly-benzylfulgimide is a better rewritable holographic storage medium, but the fatigue resistance and thermal stability should be improved.

Abstract: The stepped-frequency radar can measure the velocity between radar and target as while as obtain high range resolution. The Doppler shift of moving target may make its high resolution range profile move away from high resolution imaging region of stationary target. Consequently stepped-frequency radar possesses the ability of detecting dim target in clutter, which is suitable for attacking low-altitude dim target with low velocity. In this paper, the distribution of clutter is analyzed in frequency domain firstly. Then the design method of signal parameters is put forward based on the analysis in frequency domain. Finally, the simulation results demonstrate the effectiveness of the method.

Abstract: SVM(Support Vector Machine) is a new artificial intelligence methodolgy, basing on structural risk mininization principle, which has better generalization than the traditional machine learning and SVM shows powerfulability in learning with limited samples. To solve the problem of lack of engine fault samples, FLS-SVM theory, an improved SVM, which is a method is applied. 10 common engine faults are trained and recognized in the paper.The simulated datas are generated from PW4000-94 engine influence coefficient matrix at cruise, and the results show that the diagnostic accuracy of FLS-SVM is better than LS-SVM.