Developed Hybrid Method Research Articles

Investigation of interphase effects in silica-polystyrene nanocomposites based on a hybrid molecular-dynamics-finite-element simulation framework.

A recently developed hybrid method is employed to study the mechanical behavior of silica-polystyrene nanocomposites (NCs) under uniaxial elongation. The hybrid method couples a particle domain to a continuum domain. The region of physical interest, i.e., the interphase around a nanoparticle (NP), is treated at molecular resolution, while the surrounding elastic continuum is handled with a finite-element approach. In the present paper we analyze the polymer behavior in the neighborhood of one or two nanoparticle(s) at molecular resolution. The coarse-grained hybrid method allows us to simulate a large polymer matrix region surrounding the nanoparticles. We consider NCs with dilute concentration of NPs embedded in an atactic polystyrene matrix formed by 300 chains with 200 monomer beads. The overall orientation of polymer segments relative to the deformation direction is determined in the neighborhood of the nanoparticle to investigate the polymer response to this perturbation. Calculations of strainlike quantities give insight into the deformation behavior of a system with two NPs and show that the applied strain and the nanoparticle distance have significant influence on the deformation behavior. Finally, we investigate to what extent a continuum-based description may account for the specific effects occurring in the interphase between the polymer matrix and the NPs.

A developed hybrid method for crack identification of beams

A developed hybrid method for crack identification of beams is presented. Based on the Euler-Bernouli beam theory and concepts of fracture mechanics, governing equation of the cracked beams is reformulated. Finite element (FE) method as a powerful numerical tool is used to discritize the equation in space domain. After transferring the equations from time domain to frequency domain, frequencies and mode shapes of the beam are obtained. Efficiency of the governed equation for free vibration analysis of the beams is shown by comparing the results with those available in literature and via ANSYS software. The used equation yields to move the influence of cracks from the stiffness matrix to the mass matrix. For crack identification measured data are produced by applying random error to the calculated frequencies and mode shapes. An objective function is prepared as root mean square error between measured and calculated data. To minimize the function, hybrid genetic algorithms (GAs) and particle swarm optimization (PSO) technique is introduced. Efficiency, Robustness, applicability and usefulness of the mixed optimization numerical tool in conjunction with the finite element method for identification of cracks locations and depths are shown via solving different examples.

Layout and configuration design for a satellite with variable mass using hybrid optimization method

This article deals with configuration design and layout optimization of a GEO communication satellite. Layout design optimization of satellite objects are performed based on two-stage algorithm. Finite Circle Method (FCM) is used to express geometric constraints mathematically, and provide a smooth design space. For mathematical expression of performance constraints such as electromagnetic and thermal requirements, the distance constraints between objects have been developed. Then a hybrid method is proposed to optimize layout design which is a combination of simulated annealing optimization and quasi-Newton methods. This approach provides global and deterministic optimal solutions. Developed hybrid method validation is performed on a sample test problem. Finally, the proposed algorithm has been implemented for configuration and optimal layout design of a communication satellite. The results show that considered constraints of communication satellite are satisfied.

Removal of phosphate and suspended solids by electrocoagulation coupled with woven fabric membrane at pilot plant

The objective of this study was to develop a rapid, economical, and eco-friendly process for the efficient removal of phosphate and suspended solids (SS) from the wastewater in the continuous mode at pilot plant scale. In this method, electrocoagulator (EC) was coupled with woven fabric membrane and the effluent was removed directly from the reactor through the membrane thus omitting the settling stage. The experiment was carried out for four months by maintaining an optimal current density of 0.8 mA/cm2 in the EC reactor. No chemical injection was made at any stage of the investigations and the membrane was operated at very high flux rates ranging from 25 to 75 LMH. The phosphate and SS removal efficiencies of the developed hybrid method were around 98 and 99%, respectively, while the removal efficiencies of these contaminants were between 78 and 61%, respectively, by providing only EC treatment. The final effluent phosphate and SS contents were less than 0.20 and 0.35 mg/L, respectively, in the treated wastewater. The removal rates were identical at all flux rates and the maximum increase in transmembrane pressure was 10 kPa at 75 LMH. SEM images showed that woven fabric membrane had excellent regeneration ability. It had high robustness, generated good quality effluent, and only needed physical cleaning.

Inspection method of aluminium extrusion process

The paper presents the method for the monitoring of aluminium extrusion processes. The developed hybrid method combines the advantages of computer based, simultaneous infrared and visible image analysis for surface inspection of the profile directly after leaving the die. Thermograms present the temperature distribution on the surface of the extruded profile and contain information about the extrusion process. The proposed inspection system can be applied in industry for on-line monitoring of aluminium extrusion processes and the inspection of defects arising in extruded products.

A self-adaptive hybrid approach for wind speed forecasting

Wind power, as a promising renewable energy source, has environmental benefits, as well as economic and social ones. To evaluate wind energy properly and efficiently, this study proposes a hybrid forecasting approach that combines the Extreme Learning Machine (ELM), which rarely presents in literature on wind speed forecasting, the Ljung-Box Q-test (LBQ) and the Seasonal Auto-Regressive Integrated Moving Average (SARIMA) to enhance the accuracy of wind speed forecasting. The proposed hybrid method is examined by forecasting the mean daily and mean monthly wind speed of four wind speed observation sites located in northwestern China. The results confirm that, compared with other popular models (ARIMA，SARIMA，Back-Propagation neural network (BP) and ELM), the hybrid forecasting method improves the predictions of daily and monthly wind speed, which indicates that the developed hybrid method exhibits stronger forecasting ability. The forecasting results also suggest the hybrid approach has better generality and practicability in different wind farms.

Numerical simulation of gas–solid fluidized beds by coupling a fluid-dynamics model with the discrete element method

Gas–solid fluidization is not only an essential phenomenon in many areas of industry, but is also used to understand particle behavior in a number of research fields. For the safety analysis of core disruptive accidents in liquid-metal fast reactors, a hybrid method is developed by combining the discrete element method with a fluid-dynamics model of the reactor safety analysis code SIMMER-III to reasonably simulate particle transient behavior, as well as the occurring thermal-hydraulic phenomena. As a preliminary validation procedure, the developed hybrid method is applied to simulations of gas–solid two-phase flows. In this study, numerical simulations of two typical gas–solid fluidized bed systems are performed. The particles in the beds are porous alumina of 70μm diameter and glass of 530μm diameter, which belong to Geldart groups A and B, respectively. The reasonable agreement between our simulation results and experimental data from the literature demonstrates the fundamental validity of the present simulation method for multiphase flows with large amounts of solid particles.

Hybrid Analysis of Gas Annular Seals With Energy Equation

Annular seals are used in turbomachinery to reduce secondary flow between regions of high and low pressure. In a vibrating rotor system, the nonaxisymmetric pressure field developed in the small clearance between the rotor and the seal generate reactionary forces that can affect the stability of the entire rotor system. Traditionally, two analyses have been used to study the fluid flow in seals, bulk-flow analysis and computational fluid dynamics (CFD). Bulk-flow methods are computational inexpensive, but solve simplified equations that rely on empirically derived friction factor coefficients and are moderately accurate. CFD analyses generally provide more accurate results than bulk-flow codes, but solution time can vary between days and weeks. For gas damper seals, these analyses have been developed with the assumption that the flow can be treated as isothermal. However, some experimental studies have shown that the temperature change across the seal can be as much as 37%. Thus, a comprehensive analysis requires the solution of an energy equation. Recently, a new hybrid method that employs a CFD analysis for the zeroth-order flow and a bulk-flow analysis for the first-order, perturbed flow has been developed. This method has shown to compare well with full CFD analysis and experimental data while being computationally efficient. In this study, the previously developed hybrid method is extended to include the effects of nonisothermal flow. The hybrid method with energy equation is then compared with the isothermal hybrid method and experimental data for several test cases of hole-pattern seals and the importance of the use of energy equation is studied.

A Hybrid Pareto Frontier Generation Method for Trade‐Off Analysis in Transportation Asset Management

AbstractTrade‐off analysis, one of the key elements of transportation asset management (TAM), helps decision makers to not only quantify how different resource allocations affect system performance but also investigate the trade‐off relationships between cost and performance measures and between different performance measures. In the fast‐growing field of TAM, researchers are beginning to quantify the trade‐offs among the performance measures. A successful quantification of these trade‐offs is important for the practice because the highway agency decision makers responsible for project selection have long been stymied by a lack of knowledge of the extent to which different decisions lead to different performance trade‐offs. In a follow‐up to recent research efforts that have sought to address this issue, this article presents a further improved methodology to facilitate the analysis of trade‐offs in TAM. First, a general multiobjective optimization framework for TAM is established. Next, the developed hybrid method is presented, which is then shown to quicken the generation of Pareto frontiers for the purpose of conducting trade‐off analysis. Using a case study, the proposed hybrid method, which was implemented on a computer to generate Pareto frontiers, ultimately converged faster and generated better‐distributed Pareto frontiers compared to the NSGA II method of Pareto frontier generation in the TAM context. Using the generated Pareto frontiers, trade‐off analysis between cost and performance measures and between performance measures are demonstrated in this article.

Noise source reconstruction using ANN and hybrid methods in VVER-1000 reactor core

The present paper consists of two separate sections. In the first section, the neutron noise source is reconstructed using Artificial Neural Network (ANN) in a typical VVER-1000 reactor core. In the first stage of this section, the neutron noise calculations are performed based on Galerkin Finite Element Method (GFEM). To this end, two types of noise sources including absorber of variable strength and vibrating absorber are considered. As the results of noise calculations, the neutron noise is obtained in the location of detectors. In the second stage, the multilayer perception neural network is developed for reconstruction of the noise source. Complex neutron noises (real and imaginary parts) in the location of detectors are considered as the inputs of ANN. The developed artificial neural network consists of two hidden layers of type hyperbolic tangent sigmoid transfer function and a linear transfer function in the output layer. Noise source characteristics including strength, frequency and the location (X and Y coordinates) are identified with high accuracy. The developed hybrid method which comprises scanning method and multilayer perception neural network is employed for reconstruction of two coincidence noise sources. The number, type and location of noise source are exactly reconstructed using the hybrid method. The strength and frequency of noise source(s) are also identified with high accuracy using the developed method. A sensitivity analysis of the reconstructed noise source to some ANN parameters like the number of hidden layers, neurons in each hidden layer and the applied transfer functions is performed. Variation of accuracy of reconstructed noise source versus number of detectors and their arrangement in the reactor core are investigated as well.In the second section of present work, neutron flux variations (neutron noise) due to absorber of variable strength and vibrating absorber noise sources are studied in both frequency and time domains. Time dependency of neutron noise was obtained using inverse Fourier transform.

A new hybrid bonding technique: Adhesive-soft soldered joints

Joining of components is usually accomplished by mechanical fastening, welding, or adhesive bonding. Apart from the classical methods, various hybrid methods applied with adhesives are widely used in industry to bond mechanical parts. This study describes a new hybrid bonding method as an alternative to currently used hybrid methods: adhesive-soft soldered joints. In this new hybrid technique, joints are made by adding various (5 wt%, 15 wt%, 25 wt%, and 50 wt%) amounts of soft soldering alloy powder into the adhesive at two different temperatures (180℃ and 200℃). The strength of the joints is measured by tensile shear tests. The mechanical strength of adhesive joints carried out by adding soft soldering powder melted at 200℃ is higher than that of joints with only adhesives and unmelted soft soldering powders. The developed hybrid method is applied to attach the insert to cutting tools used in the machining industry and the feasibility of the method is investigated with experiments.

Espacio literario relevante sobre el problema del vendedor viajero (TSP): contenido, clasificación, métodos y campos de inspiración

Se describe y se analiza un espacio literario relevante sobre el Problema del Vendedor Viajero (TSP) en términos de contenido, clases de TSP, métodos y campos de inspiración. Los datos empleados provinieron de los trabajos más citados en Scopus sobre el TSP, tanto a través de la historia como en el período 2006-2010. Se encontró que el TSP prevalece en las investigaciones, con enfoques tanto en el problema original como en sus variantes, entre las cuales se identificaron el TSP Múltiple y el TSP Probabilístico. Entre los principales campos de inspiración para resolver el TSP están la evolución biológica y su base genético-molecular, el comportamiento de hormigas reales, la termodinámica, las estrategias sistemáticas para combinar reglas de decisión y la búsqueda de vecindades. Hoy día se tiende a desarrollar métodos híbridos, especialmente integrando enfoques globales con búsquedas locales, y se identifica la necesidad de introducir nuevos campos de inspiración.

Development of a Particle–Particle Hybrid Scheme to Simulate Multiscale Transitional Flows

In the present work, a new particle–particle hybrid method that combines the statistical ellipsoidal-statistical Bhatnagar–Gross–Krook and direct simulation Monte Carlo methods is developed. The switching criterion between the two methods is based on the deviation of the cumulative velocity distribution function from Maxwellian as measured by the Kolmogorov–Smirnov statistical test. Unlike other hybrid approaches that use switching criteria based on macroscopic properties, the selection of a particular particle method in a cell is determined by the local Kolmogorov–Smirnov parameter value with respect to a preset global switching criterion. A numerically efficient technique to compute the Kolmogorov–Smirnov parameter was developed to enable the efficient calculation of the degree of nonequilibrium. Two well-known fluid-flow problems, expanding argon flow through a nozzle and hypersonic flow over a blunt body, were studied. The Kolmogorov–Smirnov parameter is shown to demarcate the regions of nonequilibrium from the near-equilibrium regions, and the solutions obtained by the hybrid method are shown to agree well with the benchmark direct simulation Monte Carlo solutions for both case studies. The newly developed hybrid method is also shown to be numerically more efficient than either of the component methods.

Improving accuracy of XRII image distortion correction using a new hybrid image processing method: Performance assessment

Improving accuracy in x-ray image intensifier (XRII) image distortion correction has clinical impact in order to apply XRII images in a variety of clinical applications more reliably. This study aimed to develop and evaluate a new hybrid mathematic approximation method to correct geometric distortions of XRII images. The proposed hybrid method integrated an MLS (moving least-squares method) and an MBA (multilevel B-spline approximation) approach (MLSMBA). In the hybrid method, MLS is used to generate denser "virtual" data points on the basis of sparse original data points; MBA is applied to approximate an ultimate mapping function based on the generated and original data points. Using both computer-simulated and real XRII images, the authors compared the image distortion correction accuracy of the proposed method with those yielded using a number of previously developed and currently routinely used methods. The comparison methods include the traditional local and global approximation methods, an approach combining both local and global approximation methods, and an author's previously developed hybrid method by integrating MLS followed by another traditional least-square approximation (MLSILS). The image distortion correction accuracy was evaluated using mean-squared residual errors measured at control and intermediate points. In addition, the impact of pincushion distortion, sigmoidal distortion, local distortion, and control point localization errors on these methods was tested using computer-simulated image data. The experimental results using the computer-simulated data showed that unlike the traditional local and global approximation methods that are quite sensitive to pincushion and∕or sigmoidal distortion, the MLSMBA method was insensitive to these two types of common distortion depicted in XRII images. Similar to the MLSILS method, sensitivity of MLSMBA to local distortion was lower than or comparable with that of the traditional global approximation method. Although sensitivity of MLSMBA to control point localization errors was higher than that of the global approximation method, as long as the standard deviation of pixel displacement errors was smaller than 0.1 pixels, the overall distortion correction accuracy of MLSMBA remains higher than that of the other methods. By selecting a proper cutoff radius, accuracy of MLSMBA is also higher than that of the other methods (including MLSILS). Experiments on real XRII images yielded similar results. For example, processing results using one XRII image showed that residual error (0.248 ± 0.236 pixels) of MLSMBA was smallest as compared to that of the other methods, including two local approximation methods (0.456 ± 0.352 pixels and 0.370 ± 0.402 pixels), a global approximation method (0.422 ± 0.388 pixels), an approach combining local and global methods (0.389 ± 0.386 pixels), and MLSILS (0.255 ± 0.248 pixels). The MLSMBA method could be a better choice to correct geometric distortion of raw XRII images in the following conditions: (1) pincushion distortion, sigmoidal distortion, and local distortion exist simultaneously in the XRII images, (2) the number of original control points (landmarks) is limited, and (3) reusability of the correction mapping function is required.

A MULTI-DOMAIN HYBRID METHOD FOR HEAD-ON COLLISION OF BLACK HOLES IN PARTICLE LIMIT

A hybrid method is developed based on the spectral and finite-difference methods for solving the inhomogeneous Zerilli equation in time-domain. The developed hybrid method decomposes the domain into the spectral and finite-difference domains. The singular source term is located in the spectral domain while the solution in the region without the singular term is approximated by the higher-order finite-difference method. The spectral domain is also split into multi-domains and the finite-difference domain is placed as the boundary domain. Due to the global nature of the spectral method, a multi-domain method composed of the spectral domain only does not yield the proper power-law decay unless the range of the computational domain is large. The finite-difference domain helps reduce boundary effects due to the truncation of the computational domain. The multi-domain approach with the finite-difference boundary domain method reduces the computational cost significantly and also yields the proper power-law decay. Stable and accurate interface conditions between the finite-difference and spectral domains and the spectral and spectral domains are derived. For the singular source term, we use both the Gaussian model with various values of full width at half-maximum and a localized discrete δ-function. The discrete δ-function was generalized to adopt the Gauss–Lobatto collocation points of the spectral domain. The gravitational waveforms are measured. Numerical results show that the developed hybrid method accurately yields the quasi-normal modes and the power-law decay profile. The numerical results also show that the power-law decay profile is less sensitive to the shape of the regularized δ-function for the Gaussian model than expected. The Gaussian model also yields better results than the localized discrete δ-function.

Seismic wave propagation in laterally inhomogeneous geological region via a new hybrid approach

2D seismic wave propagation in a local multilayered geological region rested in an inhomogeneous half-space with a seismic source is studied. Plane strain state is suggested. The vertical variation of the soil properties in the half-space is modelled by a set of horizontal flat isotropic, elastic and homogeneous layers. The finite local region is with non-parallel layers and free surface relief. Efficient hybrid wavenumber integration-boundary integral equation method (WNI-BIEM) is proposed, validated and applied for synthesis of seismic signals in the finite soil stratum. The numerical simulation reveals that the developed hybrid method is able to demonstrate the sensitivity of the obtained synthetic signals to the seismic source properties, to the heterogeneous character of the wave path and to the relief peculiarities of the local stratified geological deposit. The advantages and disadvantages of the proposed method are discussed.

Vibro‐acoustic analysis of aerospace structures and issues with the available commercial prediction tools.

The results of vibro‐acoustic modeling using the boundary element method (BEM) that predicts the acceleration responses at critical locations and at the interfaces of selected test articles are discussed. High fidelity acoustic tests were performed in a couple of cases and the results are used to validate the BEM predictions. The accuracy of the BEM and its ability to correctly predict the acceleration responses of lightweight structures are discussed in some detail. Also a combined system level BEM, consisting of structures very responsive to acoustic pressures, and force‐limited base shake random vibration analysis was performed. We will discuss how these results may be used to derive random vibration specifications for the purpose of qualifying large and lightweight structures for flight. In this paper, we also discuss the commercially available vibro‐acoustic tools that are used to predict the acoustic transmission losses and vibration responses of flight structures for lift‐off (assumed to be diffuse) and transonic (turbulent boundary layer) acoustic fields. The pros and cons of using the statistical energy analysis, finite element analysis, BEM, and newly developed hybrid methods within these vibro‐acoustic tools are discussed in some detail.

A lattice Boltzmann coupled to finite volumes method for solving phase change problems

A numerical scheme coupling lattice Boltzmann and finite volumes approaches has been developed and qualified for test cases of phase change problems. In this work, the coupled partial differential equations of momentum conservation equations are solved with a non uniform lattice Boltzmann method. The energy equation is discretized by using a finite volume method. Simulations show the ability of this developed hybrid method to model the effects of convection, and to predict transfers. Benchmarking is operated both for conductive and convective situation dominating solid/liquid transition. Comparisons are achieved with respect to available analytical solutions and experimental results.

Validation of a temperature emissivity separation hybrid method from airborne hyperspectral scanner data and ground measurements in the SEN2FLEX field campaign

This paper presents an assessment of the performance of a hybrid method that allows a simultaneous retrieval of land‐surface temperature (LST) and emissivity (LSE) from remotely‐sensed data. The proposed method is based on a synergistic usage of the split‐window (SW) algorithm and the two‐temperature method (TTM) and combines the advantages of both procedures while mitigating their drawbacks. The method was implemented for thermal channels 76 (10.56 µm) and 78 (11.72 µm) of the Airborne Hyperspectral Scanner (AHS), which was flown over the Barrax test site (Albacete, Spain) in the second week of July 2005, within the framework of the Sentinel‐2 and Fluorescence Experiment (SEN2FLEX) field campaign. A set of radiometric measurements was performed in the thermal infrared region in coincidence with aircraft overpasses for different surface types, e.g. bare soil, water body, corn, wheat, grass. The hybrid method was tested and compared with a standard SW algorithm and the results obtained show that the hybrid method is able to provide better estimates of LST, with values of bias (RMSE) of the order of 0.8 K (1.9 K), i.e. about one third (one half) of the corresponding values of 2.7 K (3.4 K) that were obtained for bias (RMSE) when using the SW algorithm. These figures provide a sound indication that the developed hybrid method is particularly useful for surface and atmospheric conditions where SW algorithms cannot be accurately applied.

Ray Optical Electromagnetic Far-Field Scattering Computations Using Planar Near-Field Scanning Techniques

For accurate scattering computations in the far-field of flat finite objects, field based ray optical methods cannot be used directly, since the finiteness of the objects is not considered in the formulations. In this paper, planar near-field scanning techniques are used to overcome this problem. In particular, scattered ray optical fields are first computed in a scanning plane in the near-field region of the involved objects and are transformed into the far-field afterwards using field expansions in terms of spectrum density functions of outgoing waves. Since evanescent waves are avoided in the scanning plane, sampling rates less than lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /2 can be used for restricted angle range around the normal direction to the scanning plane. Reduced accuracy at grazing directions of observation is overcome by combining solutions provided by several scanning planes. The proposed approach is applied in the postprocessing stage of the recently developed hybrid method combining the uniform geometrical theory of diffraction with the finite element boundary integral technique and with the multilevel fast multipole method.