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In this paper, we propose a second-order adaptive DLN algorithm with different subdomain variable time steps for the 3D closed-loop geothermal system. Theoretically, the stability and convergence of the algorithm in the case of variable time steps are analyzed. In numerical experiments, the DLN algorithm is combined with an adaptive algorithm to verify not only its effectiveness and second-order convergence under any arbitrary sequence of time steps but also to improve computational efficiency. We overcome the difficulty of 3D programming, and verify the applicability and accuracy of the proposed algorithm by simulating the flow characteristics and heat transfer of the closed-loop geothermal system with 3D convection. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes a second-order decoupled Backward Euler method plus time filter for the evolutionary Stokes/Darcy model, which allows different variable time steps in the free fluid flow region and the porous media flow region. Furthermore, this algorithm, which is a combination of first order Backward Euler method and time filter scheme, uncouples the Stokes/Darcy model into the Stokes and Darcy problems per time step. In particular, adaptive algorithm is constructed to improve the computational efficiency. Moreover, we mainly deduce the stability and error estimation in theoretical analysis. In addition, numerical experiments are used to verify the effectiveness, second order convergence and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we propose and analyze a second-order partitioned method with multiple-time-step technique for the nonstationary Stokes-Darcy model. This method allows different time steps in different subdomains and improves the accuracy by the time filters. Besides, by designing new error estimate and time step adjustment strategy, we extend this method to variable timestep and develop single and double adaptive algorithms. Constant and variable time step tests are given to confirm the theoretical analysis and illustrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, the variable time-stepping decoupled algorithm proposed by Dahlquist, Liniger, and Nevanlinna (DLN algorithm) is used to discretize the coupled Stokes-Darcy model in time. In theory, we prove the stability and second-order convergence of DLN algorithm. Further, we combine DLN algorithm with the time adaptive algorithm to improve the computational efficiency. Numerical experiments verify the stability and second-order convergence of the DLN algorithm at any arbitrary sequence of time steps. [ABSTRACT FROM AUTHOR]

The key of bearing fault feature extraction is to select the optimal resonant frequency band (ORFB) containing fault information with an appropriate index. However, the background noise and cyclostationary impulsive noise will seriously affect the location of ORFB. Moreover, traditional indexes may be ineffective for compound faults. Thus, a novel fault feature method for rolling bearings is explored to solve these problems. First, by evaluating the potential fault types with the designed relative local threshold, an adaptive harmonic kurtosis (AHK) is first proposed to locate the ORFB for an arbitrary fault or compound fault. Then, according to the index of AHK, an improved bat algorithm (IBA) is proposed to find the ORFB unlike fast kurtogram (FK). The proposed rolling bearing fault diagnosis method based on an adaptive harmonic kurtosis and IBA has been applied to two single faults and a compound fault. The comparative results indicate that the proposed method can more accurately extract the fault feature compared with the FK method, the method based on the ratio of cyclic content, discrete wavelet transform based on kurtosis, and ensemble empirical mode decomposition based on kurtosis. [ABSTRACT FROM AUTHOR]

Rule mechanism has been widely used in many areas, such as databases, artificial intelligent and pervasive computing. In a rule mechanism, rule activation decides which rules are activated, when the rules are activated, and which tuples can be generated through the activation. Rule activation determines the efficiency of rule mechanism. In this article, we define the semantic constraints, constant constraint and variable constraint, of the rule according to the semantics of Datalog rules. Based on the constraints, we propose an index structure, named Yield index, to support the rule activation effectively. Yield index consists of the data index and semantic index, and records the complete information of a rule, including the matching relationship among the tuples of different relations in rule body. The index integrates tuple insertion and rule activation to directly determine whether the matching tuples of new inserted tuple exist. Due to this character, we perform effective rule activation only, avoiding ineffective rule activation that cannot generate new tuples, so that the efficiency of rule activation is improved. The article describes the structure of Yield index, the construction and maintenance algorithms, and the rule activation algorithm based on Yield index. The experimental results show that Yield index has better performance and improves activation efficiency of one order of magnitude, comparing with other index structures. In addition, we also discuss the possible extensions of Yield index in other applications. [ABSTRACT FROM AUTHOR]

Signal decomposition is a widely-used approach for multicomponent signal processing. To improve the accuracy and anti-noise performance of multicomponent decomposition, this paper proposes a novel multicomponent signal decomposition method based on wavelet ridge extraction, called the Wavelet ridge signal decomposition (WRSD). A wavelet ridge extraction algorithm is introduced. We find that this algorithm can obtain the wavelet ridge of one component in a multicomponent signal and the initial scale will determine the wavelet ridge of which component is extracted. Since the instantaneous frequency obtained by wavelet ridge has small frequency fluctuation, low-pass filtering is used to increase the accuracy of instantaneous frequency estimation. With the improved instantaneous frequency, the synchronous demodulation method is used to separate the corresponding component from the signal composition. By repeating this process, all components can be adaptively and automatically obtained. This method is employed to analyze three typical simulated vibration signals and compared with Hilbet vibration decomposition and empirical mode decomposition. The comparison results demonstrate its superiority in decomposition accuracy and noise insensitivity. Finally, the proposed WRSD method is successfully applied to the diagnosis of a shaft misalignment fault and a gearbox wear fault. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel multiple-image encryption method is proposed by lateral shift multiplexing of phase-only mask. Multiple images are encrypted into three phase-only masks, one of which is generated in computer and saved as the secret key, and the other two can be obtained with a simple non-iterative algorithm. The optical scheme for decryption is quite simple, and different original images could be successfully retrieved at the output plane while the secret key is laterally shifted continuously with predefined intervals. In addition, the silhouette problem, which persecuted the previous interference-based encryption scheme, is simultaneously eliminated. The feasibility and effectiveness of the proposed method are demonstrated by numerical results. [Copyright &y& Elsevier]

Abstract: Since the empirical mode decomposition (EMD) lacks strict orthogonality, a new method for multicomponent signal decomposition, orthogonal empirical mode decomposition (OEMD), is proposed by this paper. The essential principle of this method is to obtain the intrinsic mode functions (IMFs) and the residue by self-adaptive band-pass filtering. Firstly, the feasibility of OEMD is theoretically analyzed, then its strict orthogonality and completeness is proved, and the orthogonal basis used in OEMD is generated. Secondly, the method of analytical band-pass filtering which preserves perfect band-pass feature in the frequency domain is presented, then two fast algorithms to implement OEMD are proposed, i.e. IMF sequential searching (ISS) algorithm and IMF binary searching (IBS) algorithm. The speed of IBS is faster than that of ISS, whereas IBS algorithm may obtain much more false IMFs than ISS when signals are of complex spectral constitutions. Finally, OEMD is applied to both synthetic signals and mechanical vibration signals, the results show that compared with EMD, OEMD better solves mode aliasing, avoids the occurrence of false mode, is free of end extension, and can be effectively applied to mechanical fault diagnosis. [Copyright &y& Elsevier]

Abstract: In this paper, we propose a cosh-based smoothing function for nonlinear complementarity problems. We investigate the boundedness of the iteration sequence generated by smoothing methods under the assumption. Based on the new smoothing function, we design a nonmonotone Newton algorithm for solving the NCP problem and obtain the global convergence of the proposed algorithm. The numerical tests show our method works quite well. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a higher-density dyadic wavelet transform with two generators, whose corresponding wavelet filters are band-pass and high-pass. The wavelet coefficients at each scale in this case have the same length as the signal. This leads to a new redundant dyadic wavelet transform, which is strictly shift invariant and further increases the sampling in the time dimension. We describe the definition of higher-density dyadic wavelet transform, and discuss the condition of perfect reconstruction of the signal from its wavelet coefficients. The fast implementation algorithm for the proposed transform is given as well. Compared with the higher-density discrete wavelet transform, the proposed transform is shift invariant. Applications into signal denoising indicate that the proposed wavelet transform has better denoising performance than other commonly used wavelet transforms. In the end, various typical wavelet transforms are applied to analyze the vibration signals of two faulty roller bearings, the results show that the proposed wavelet transform can more effectively extract the fault characteristics of the roller bearings than the other wavelet transforms. [Copyright &y& Elsevier]

This report considers a variable time-stepping algorithm proposed by Dahlquist, Liniger and Nevanlinna and discusses its application to the unsteady Stokes/Darcy model. Although long-time forgotten and little explored, the algorithm performs advantages in variable time-stepping analysis of various fluid flow systems, including the coupled Stokes/Darcy model. We first prove that the approximate solutions to the unsteady Stokes/Darcy model are unconditionally stable due to the G -stability of the method. Then variable time-stepping error analysis follows from the combination of G -stability and consistency of the method. Numerical experiments verify the theoretical results, demonstrating both accuracy and stability of the algorithm. [ABSTRACT FROM AUTHOR]

Abstract: Phase cancellation in ultrasound due to large receiver size has been proposed as a contributing factor to the inaccuracy of estimating broadband ultrasound attenuation (BUA), which is used to characterize bone quality. Transducers with aperture size ranging from 2 to 5 mm have been used in previous attempts to study the effect of phase cancellation. However, these receivers themselves are susceptible to phase cancellation because aperture size is close to one center wavelength (about 3 mm at 500 KHz in water). This study uses an ultra small receiver (aperture size: 0.2 mm) in conjunction with a newly developed two-dimensional (2-D) synthetic array system to investigate the effects of phase cancellation and receiver aperture size on BUA estimations of bone tissue. In vitro ultrasound measurements were conducted on 54 trabecular bone samples (harvested from sheep femurs) in a confocal configuration with a focused transmitter and synthesized focused receivers of different aperture sizes. Phase sensitive (PS) and phase insensitive (PI) detections were performed. The results show that phase cancellation does have a significant effect on BUA. The normalized BUA (nBUA) with PS is 8.1% higher than PI nBUA while PI BUA is well correlated with PS BUA. Receiver aperture size also influences the BUA reading for both PI and PS detection and smaller receiver aperture tends to result in higher BUA readings. The results also indicate that the receiver aperture size used in the confocal configuration with PI detection should at least equal the aperture of the transmitter to capture most of the energy redistributed by the interference and diffraction from the trabecular bone. [Copyright &y& Elsevier]

Abstract: An adaptive generalized predictive control (GPC) system is presented for the management of output power of solid oxide fuel cells (SOFCs). The dynamics of SOFC output power are characterized by a fractional order model, which is more accurate than an integer order model to depict the dynamics; the fractional order dynamic model is taken as the controlled plant of the GPC system. The GPC algorithm adopts a linear approximation method that uses a linear predictive model to approximate locally and dynamically the nonlinear dynamics of SOFC output power at each sampling period. Moreover, the parameters of the predictive model are identified online to overcome the time-varying dynamics of SOFC output power via introducing a forgetting factor recursive least squares (FFRLS) algorithm. Finally, according to the future power outputs predicted by the predictive model, an optimal current control sequence is obtained by solving a multistage cost function. The results demonstrate that the dynamic responses of the GPC system are quick and smooth, and the change of the current control sequence is slow and smooth. The quick and smooth dynamics are important for satisfying the rapid load following of SOFC generating systems and for prolonging the lifetime of SOFC stack. [ABSTRACT FROM AUTHOR]