Hybrid Two-step Method Research Articles

A hybrid two-step method for direct solutions of general second order initial value problem

The study is concerned with the development of a two-step hybrid linear multi-step method for direct solution of general second order initial value problem. Power series is adopted as the basis function, and the differential system arising from it are collocated at all grid and off-grid points, while the approximate solution is interpolated at the selected points. The scheme developed is tested for consistency and zero stability, and it was found to be convergent.The scheme is expanded term by term by Taylor series approach, also the efficiency of the methods is tested on some test problems, and the accuracy is compared with some existing result in literature.

Numerical prediction of asymmetrical ship slamming loads based on a hybrid two-step method

Slamming load is one of fundamental importance in the design of ship structures. However, the prediction of ship slamming load largely focuses on the head sea due to the more complex physics mechanism in oblique waves. In this paper, asymmetrical slamming loads of ship in oblique waves had been numerically predicted, where one hybrid two-step solution was applied through combining seakeeping theory and CFD method. Firstly, asymmetrical ship motions (vertical, horizontal and roll motions) were obtained through the seakeeping analysis. Then, slamming loads of two typical bow-flare sections were predicted through applying the CFD method, where the complicated flow forms (flow separation and air pocket) were included. The characteristics of impact hydrodynamics including free surface, pressure distribution and pressure time history were analyzed systematically showing that the slamming load in oblique wave has obvious asymmetry and is much larger than the head sea. These findings clarify the complicated impact phenomenon in oblique wave cases, which could improve our understanding on the asymmetrical impact of bow-flare sections.

Determining an accurate fault location in electrical energy distribution networks in the presence of DGs using transient analysis

Distributed generation resources are becoming more popular in electric energy distribution networks. As more Distributed generation are integrated into the grid, the system performance is challenged by issues such as manifold power injection to the network or nonlinear behavior when a fault occurs. To address this, fault location in electric energy distribution networks in the presence of distributed generation needs particular attention. This is important to reduce the loss of generated energy, reduce interruptions time, increase the reliability of the network and consequently improve the security of electricity supply. In this paper, a novel fault location method is presented applied to distributed networks with distributed generation. The proposed method is a hybrid two-step method which identifies accurate fault location using information stored in the network at pre- and post-fault time. The proposed method employs voltage and current information at the beginning of the feeder to estimate fault distance in the first step. The estimated distance will be associated with several similar sections considering the topology of the distributed networks. In the second step, the proposed method determines accurate fault location through transient analysis based on the frequency component. In this step, the exact fault location is identified. In order to investigate its performance, a standard IEEE-11 network is simulated in MATLAB. Furthermore, experiments are carried out in a network power simulator, showing good results.

New hybrid two-step method with optimized phase and stability characteristics

In this paper and for the first time in the literature, we develop a new Runge–Kutta type symmetric two-step finite difference pair with the following characteristics: For the new developed algorithm we present a detailed numerical analysis (local truncation error and stability analysis). The effectiveness of the new developed algorithm is evaluated with the approximate solution of coupled differential equations arising from the Schrodinger type.

Use of Er Burnable Absorber for Improvement of CANDU6 Safety Parameters

This paper reports on the improvement of the power coefficient of reactivity (PCR) and minimization of the coolant void reactivity (CVR) of a CANDU6 reactor. A burnable absorber of Er2O3 (erbia) was mixed homogeneously with UO2 fuel in the central fuel element to maximize the Doppler broadening and minimize the CVR of the CANDU6 reactor. In this study, recovered uranium (RU) with 0.9 wt% 235U enrichment was utilized in the advanced CANFLEX fuel bundle instead of natural uranium (NU). First, the optimal loading of erbia was investigated through lattice-based analysis, and its impact on the lattice characteristics was examined. In particular, both the fuel Doppler effect and CVR were evaluated for the RU-loaded lattice. For a more reliable analysis, a three-dimensional (3-D) equilibrium core was determined based on the standard time-average methods for erbia-loaded CANDU6 cores using the Serpent-COREDAX/CANDU code system. The core analysis was based on a hybrid two-step method in which the lattice analysis was performed by the Serpent Monte Carlo code, and the 3-D whole-core analysis was done using a diffusion theory–based nodal code named COREDAX. For the derived equilibrium cores, the core performances were evaluated in terms of the fuel burnup and power profile. Additionally, the safety parameters, including the PCR and CVR, were evaluated for the equilibrium core conditions. The safety parameters of the 3-D whole core were compared with those obtained with simple lattice-based analysis. It was observed in the analysis that Er-loaded CANFLEX-RU fuel provides a 60% more negative fuel temperature coefficient than standard CANDU-NU fuel.

Application configuration selection for energy-efficient execution on multicore systems

Modern computer systems are designed to balance performance and energy consumption. Several run-time factors, such as concurrency levels, thread mapping strategies, and dynamic voltage and frequency scaling (DVFS) should be considered in order to achieve optimal energy efficiency for a workload. Selecting appropriate run-time factors, however, is one of the most challenging tasks because the run-time factors are architecture-specific and workload-specific.While most existing works concentrate on either static analysis of the workload or run-time prediction results, in this paper, we present a hybrid two-step method that utilizes concurrency levels and DVFS settings to achieve the energy efficiency configuration for a workload. The experimental results based on a Xeon E5620 server with NPB and PARSEC benchmark suites show that the model is able to predict the energy efficient configuration accurately. On average, an additional 10% EDP (Energy Delay Product) saving is obtained by using run-time DVFS for the entire system. An off-line optimal solution is used to compare with the proposed scheme. The experimental results show that the average extra EDP saved by the optimal solution is within 5% on selective parallel benchmarks.

Hybrid two-step method of damage detection for plate-like structures

This paper develops a two-step approach for structural damage detection. In the first step, the two-dimensional generalized local entropy (2D-GLE) is proposed to identify the damage location and number for plates. Based on the 2D-GLE, singularities in plates are revealed with the aid of mode shapes; hence, damages are localized, and the number of which is estimated. Besides, the statistical analysis is applied in the analysis of 2D-GLE damage maps to overcome the difficulty in damage detection methods without baseline data. In the second step, the damage severities at the identified locations are evaluated via the optimization using artificial bee colony (ABC) with the designed frequency object function. The advantages of the present method are as follows: (1) No-baseline in the measurement of mode shapes. Damage localization via the 2D-GLE avoids using healthy mode shapes serving as baselines in damage detection, and then only damaged mode shapes are required. (2) No down-sampling. Compared with the wavelet-based methods, no down-sampling enhances the algorithmic robustness and accuracy. (3) Efficiency. This hybrid two-step method shrinks the solving parameter domain sharply in optimization via the first step. Hence, only the severity parameters need to be investigated in ABC. (4) Robustness. ABC ensures the robustness of the proposed method. Different damage cases are investigated in simulations, single-damage/multiple-damage cases, and noise immunity tests demonstrate that the proposed method is effective and accurate in damage detection. At last, a simple experiment is given to verify the present algorithm. Copyright © 2015 John Wiley & Sons, Ltd.

A low computational cost eight algebraic order hybrid method with vanished phase-lag and its first, second, third and fourth derivatives for the approximate solution of the Schrödinger equation

A low computational cost eighth algebraic order hybrid two-step method with vanished phase-lag and its first, second, third and fourth derivatives is developed in this paper. We also investigate the local truncation error, the stability and the result of the elimination of the phase-lag and its derivatives on the effectiveness of the produced method.

A new hybrid two-step method with vanished phase-lag and its first and second derivatives for the numerical solution of the Schrödinger equation and related problems

The maximization of the efficiency of a hybrid two-step method for the numerical solution of the radial Schrodinger equation and related problems with periodic or oscillating solutions via the procedure of vanishing of the phase-lag and its derivatives is studied in this paper. More specifically, we investigate the vanishing of the phase-lag and its first and second derivatives and how this disappearance maximizes the efficiency of the hybrid two-step method.

Hybrid modeling of P-SV seismic motion at inhomogeneous viscoelastic topographic structures

Abstract A new hybrid two-step method for computation of P-SV seismic motion at inhomogeneous viscoelastic topographic structure is presented. The method is based on a combination of the discrete-wavenumber (DW), finite-difference (FD), and finite-element (FE) methods. In the first step, the DW method is used to calculate the source radiation and wave propagation in the background 1D medium. In the second step, the FD-FE algorithm is used to compute the wave propagation along the topographic structure. The accuracy of the method has been separately tested for inclusion of the attenuation and for inclusion of the free-surface topography through numerical comparisons with analytical and independent numerical methods. The method is a generalization of the hybrid DW-FD method of Zahradník and Moczo (1996) for localized structures with a flat free surface. Numerical computations for a ridge, sediment valley, and the ridge neighboring the sediment valley show that a ridge can considerably influence the response of the neighboring sediment valley. This means that the neighboring topographic feature should be taken into account even when we are only interested in the valley response.