Improved adaptive filter and its application in acoustic emission signals

In order to de-noise and filter the acoustic emission(AE) signal, the adaptive filtering technology is applied to AE signal processing in view of the special attenuation characteristics of burst AE signal. According to the contradiction between the convergence speed and steady-state error of the traditional least mean square(LMS) adaptive filter, an improved LMS adaptive filtering algorithm with variable iteration step is proposed on the basis of the existing algorithms. Based on the Sigmoid function, an expression with three parameters is constructed by function translation and symmetric transformation.As for the error mutation, e(k) and e(k-1) are combined to control the change of the iteration step. The selection and adjustment process of each parameter is described in detail, and the MSE is used to evaluate the performance. The simulation results show that the proposed algorithm significantly increases the convergence speed, reduces the steady-state error, and improves the performance of the adaptive filter. The improved algorithm is applied to the AE signal processing, and the experimental signal is demodulated by an empirical mode decomposition(EMD) envelope to obtain the upper and lower envelopes. Then, the expected function related to the AE signal is established. Finally, the improved algorithm is substituted into the adaptive filter to filter the AE signal. A good result is achieved, which proves the feasibility of adaptive filtering technology in AE signal processing.

Finite element reliability analysis of slope stability

The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.

A New Hybrid Reliability Index Definition and Its Application to the Structure Buckling Reliability Analysis of Supercavitating Projectiles

As structure buckling problems easily arise when supercavitating projectiles operate with high underwater velocity, it is necessary to perform structure buckling reliability analysis. Now it is widely known that probabilistic and non-probabilistic uncertain information exists in engineering analysis. Based on reliability comprehensive index of multi-ellipsoid convex set, probabilistic uncertain information is added and transferred into non-probabilistic interval variable. The hybrid reliability is calculated by a combined method of modified limit step length iteration algorithm(MLSLIA) and Monte-Carlo method. The results of engineering examples show that the convergence of MLSLIA is better than that of limit step length iteration algorithm(LSLIA). Structure buckling hybrid reliability increases with the increase of ratio of base diameter to cavitator diameter, and decreases with the increase of initial launch velocity. Also the changes of uncertain degree of projectile velocity and cavitator drag coefficient affect structure buckling hybrid reliability index obviously. Therefore, uncertain degree of projectile velocity and cavitator drag coefficient should be controlled in project for high structure buckling reliability.

Parallel algorithm and its convergence of spatial domain decomposition of discrete ordinates method for solving radiation heat transfer problem

To improve the computational efficiency and hold calculation accuracy at the same time,we study the parallel computation for radiation heat transfer. In this paper, the discrete ordinates method（DOM） and the spatial domain decomposition parallelization（DDP） are combined by message passing interface（MPI） language. The DDP–DOM computation of the radiation heat transfer within the rectangular furnace is described. When the result of DDP–DOM along one-dimensional direction is compared with that along multi-dimensional directions, it is found that the result of the latter one has higher precision without considering the medium scattering. Meanwhile, an in-depth study of the convergence of DDP–DOM for radiation heat transfer is made. Analyzing the cause of the weak convergence, we relate the total number of iteration steps when the convergence is obtained to the number of sub-domains. When we decompose the spatial domain along one-,two- and three-dimensional directions, different linear relationships between the number of total iteration steps and the number of sub-domains will be possessed separately, then several equations are developed to show the relationships. Using the equations, some phenomena in DDP–DOM can be made clear easily. At the same time, the correctness of the equations is verified.