Energy Minimization Method Research Articles

Influence of grid resolution, parcel size and drag models on bubbling fluidized bed simulation

In this paper, a bubbling fluidized bed is simulated with different numerical parameters, such as grid resolution and parcel size. We examined also the effect of using two homogeneous drag correlations and a heterogeneous drag based on the energy minimization method. A fast and reliable bubble detection algorithm was developed based on the connected component labeling. The radial and axial solids volume fraction profiles are compared with experiment data and previous simulation results. These results show a significant influence of drag models on bubble size and voidage distributions and a much less dependence on numerical parameters. With a heterogeneous drag model that accounts for sub-scale structures, the void fraction in the bubbling fluidized bed can be well captured with coarse grid and large computation parcels. Refining the CFD grid and reducing the parcel size can improve the simulation results but with a large increase in computation cost.

Weakly Supervised Part Proposal Segmentation From Multiple Images.

Weakly supervised local part segmentation is challenging, due to the difficulty of modeling multiple local parts from image level prior. In this paper, we propose a new weakly supervised local part proposal segmentation method based on the observation that local parts will keep fixed along the object pose variations. Hence, the local part can be segmented by capturing object pose variations. Based on such observation, a new local part proposal segmentation model is proposed. Three aspects, such as shape similarity-based cosegmentation, shape matching-based part detection and segmentation, and graph matching-based part assignment are considered. A part segmentation energy function is first proposed. Four terms, such as MRF-based single image segmentation term, shape feature-based foreground consistency term, NCuts-based part segmentation term, and two-order graphs matching based part consistency term, are contained. Then, a three sub-minimization-based energy minimization method is proposed to accomplish approximation solution. Finally, we verify our method based on three image data sets (PASCAL VOC 2008 Part data set, UCB Bird data set, and Cat-Dog data set), and one video data set (UCF Sports) data set. The experimental results demonstrate a better segmentation performance compared with the existing object cosegmentation and part proposal generation methods.

Thermodynamic equilibrium analysis of combined dry and steam reforming of propane for thermochemical waste-heat recuperation

The thermochemical waste-heat recuperation is one for perspective way of increasing the energy efficiency of the fuel-consuming equipment. In this paper, the thermochemical waste-heat recuperation (TCR) by combined steam-dry propane reforming is described. To understand the influence of technological parameter such as temperature and composition of inlet gas mixture on TCR efficiency, thermodynamic equilibrium analysis of combined steam-dry propane reforming was investigated by Gibbs free energy minimization method upon a wide range of temperature (600–1200 K) and different feed compositions at atmospheric pressure. The carbon and methane formation was also calculated and shown. From a thermodynamic perspective, the TCR can be used for increasing energy efficiency at temperatures above 950 K because in this range the maximum conversion rate is reached (from 1.22 to 1.30 for the different feed composition). Approximately 10 mol of synthesis gas can be generated per mole of propane at the temperatures greater than 1000 K. Furthermore, the propane conversion rate and yield of hydrogen are increased with the addition of extra steam to the feed stock. Also, undesirable carbon formation can be eliminated by adding steam to the feed. The thermodynamic equilibrium analysis was accomplished by IVTANTHERMO which is a process simulator for thermodynamic modeling of complex chemically reacting systems and several results were checked by Aspen-HYSYS.

Minimum Energy Method (MEM) microphone array back-propagation for measuring musical wind instruments sound hole radiation

Using a 128 microphone array, the sound source distribution of musical wind instruments from their blowing and finger holes are measured. The Japanese \emph{shakuhachi} flute, the Chinese \emph{dizi} transverse flute, the Balinese \emph{suling} bamboo flute and flue organ pipes are investigated. The sound radiation is measured by a rectangular microphone array in the near field, and back-propagated onto the flute radiation plane using the Minimum Energy Method (MEM). Here, the radiation is assumed to be composed of as many sound sources as there are microphones, where the source positions can be chosen arbitrarily in space. Using a regularization parameter $\alpha$ the virtual sound sources, which are monopoles for $\alpha = 0$ are narrowed for higher $\alpha$. Calculating the reconstruction energy on the radiation plane while using different $\alpha$, this energy becomes minimal for the correct $\alpha$. The ill-posedness of the solved Fredholm integral at the presence of measurement noise is met by easing $\alpha$ slightly, therefore stabilizing the solution in a robust way. This is especially necessary for problems like musical wind instruments, where the sound sources are the air itself and often a precise sound source position cannot be known in advance. The flutes show complex radiation behavior and sometimes even a coupling of the sound field between finger holes outside the flute. Coupling between organ pipes can also lead to synchronization between the pipes.

Thermal Behaviors and Their Correlations of Mg(BH4)2-Contained Explosives

ABSTRACTIn order to explore the effect of metal hydride on energetic materials’ thermal behaviors and their correlations, we studied the heats of combustion and detonation of RDX, TNT, and Mg(BH4)2-containing explosives both theoretically and experimentally. The results showed that Mg(BH4)2 can significantly improve the energy of explosive. As the mass fraction of Mg(BH4)2 increases, the combustion heat of composite explosives increases gradually, while the combustion efficiency decreases. When its mass fraction is about 30%, the theoretical heats of detonation of RDX/Mg(BH4)2 and TNT/Mg(BH4)2 reach maximum, which are 7418.47 and 7032.46 kJ/kg, respectively. When we compared the errors between calculation and experimental values, we found that L-C method is more accurate in calculating oxygen-enriched and oxygen-balanced explosives, and that minimum free energy method is more suitable for seriously negative oxygen-balanced explosive. For single explosive, there are three kinds of relationships between heat of combustion and detonation according to the oxygen balance. For Mg(BH4)2-containing explosives, the relationship is in accordance with Boltzmann function.

Study on Equilibrium Compositions of HTO/H2 Mixture in Purge Gas Flow in Tritium Breeding Blanket

The equilibrium chemical compositions of purge gas at the outlet of the Test Blanket Module in Helium Cooled Ceramic Reflector (HCCR) Test Blanket System are studied. Mole fractions of H, T, O, H2, HT, T2, H2O, HTO, and T2O in the equilibrium state are calculated by a Gibbs free energy minimization method starting from the initial state of H2/HTO mixture. The standard Gibbs free energy for tritium species obtained by the density functional theory is used in the calculations. The tritium recovery rates in the form of HT, T2, HTO and T2O are estimated from the equilibrium chemical compositions obtained in the calculations. The effects of H2 concentration in the purge gas on the tritium recovery process are also investigated by parametric study with variations of purge gas flow rate and volume ratio of hydrogen to helium in the purge gas.

Hydrogen production by catalytic gasification of petroleum residue

ABSTRACTThe liquid fuel gasification to obtain a clean flue gas for power generation and produce chemicals such as methanol is a most promising attempt to reduce the greenhouse gas emissions and air pollutants. In this paper, an equilibrium model of liquid fuel gasification was developed by the method of Gibbs free energy minimization. Two kinds of catalysts: Ni/CeO2/Al2O3 and Ni/Al2O3 were used to explore the influence of catalysts and operating conditions on hydrogen yield and char conversion. Over the ranges of operating conditions studied, the maximum hydrogen yield reached 52.47 vol%, whereas the char conversion varied between 45.2% and 98.5%. The results indicated that an appropriate reaction temperature is favorable for higher hydrogen production and char conversion. The model was validated with experimental data obtained from a fluidized bed gasifier.

The fabrication of Fe-W-mullite-based composite coatings inside a steel pipe by centrifugal-SHS process

Fe-W-mullite-based composite coatings were prepared on the inner-surface steel pipe from two reactions of Fe(Mn)WO4-Fe2O3-Al-Si and Fe(Mn)WO4-Fe2O3-B2O3-Al-Si mixture powder by centrifugal-SHS process. Standard Gibbs energy minimization method was used to compute the adiabatic temperature (Tad) and predict equilibrium composition of the products. The composite coatings consisted of two layers of alloy (α) and ceramic (β) which were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX). Surface roughness, hardness, and adhesive strength properties of the coating layer were investigated by profilometer, Vickers microhardness, and compression-shear test, respectively. In addition, the effects of adding Fe to the system was studied. It was found that the composite coating from the reaction of Fe(Mn)WO4-Fe2O3-Al-Si with 1.4 wt% Fe provided the smoothest surface, highest hardness, and adequate adhesive strength.

Grand canonical electronic density-functional theory: Algorithms and applications to electrochemistry.

First-principles calculations combining density-functional theory and continuum solvation models enable realistic theoretical modeling and design of electrochemical systems. When a reaction proceeds in such systems, the number of electrons in the portion of the system treated quantum mechanically changes continuously, with a balancing charge appearing in the continuum electrolyte. A grand-canonical ensemble of electrons at a chemical potential set by the electrode potential is therefore the ideal description of such systems that directly mimics the experimental condition. We present two distinct algorithms: a self-consistent field method and a direct variational free energy minimization method using auxiliary Hamiltonians (GC-AuxH), to solve the Kohn-Sham equations of electronic density-functional theory directly in the grand canonical ensemble at fixed potential. Both methods substantially improve performance compared to a sequence of conventional fixed-number calculations targeting the desired potential, with the GC-AuxH method additionally exhibiting reliable and smooth exponential convergence of the grand free energy. Finally, we apply grand-canonical density-functional theory to the under-potential deposition of copper on platinum from chloride-containing electrolytes and show that chloride desorption, not partial copper monolayer formation, is responsible for the second voltammetric peak.

Deflection of circular diaphragm-type piezoactuators coupling with gas compression in micropumps

An analytical solution is formulated to predict the deflection of circular piezoactuators for the sake of gas compression in micropumps. The solution is derived from the energy minimization method and Rayleigh–Ritz method based on the Kirchhoff thin plate theory. Energy associated with the micropump includes elastic potential energy of the deflecting actuator, electric potential energy in the piezodiscs and compression work to gas. The proposed analytical solution is validated via the finite element simulations and experimental data. Furthermore, the effects of dimensions and material properties of the piezoactuator on the static pressure rise are discussed; there exist optimal radius ratio of the PZT layer to passive layer, optimal thickness ratio of the PZT layer to passive layer, and optimal ratio of the passive layer thickness to its radius, however, these optimal values are related to pressure load as well. Finally, the static pressure rise and the deflection profile of the piezoactuator have been discussed under the optimal dimensions.

Effects of roughness on droplet apparent contact angles on a fiber

Abstract This paper reports on our investigation of the effects of surface roughness on the equilibrium shape and apparent contact angles of a droplet deposited on a fiber. In particular, the shape of a droplet on a roughened fiber is studied via the energy minimization method implemented in the surface evolver finite element code. Sinusoidal roughness varying in both the longitudinal and radial directions is considered in the simulations to study the effects of surface roughness on the most stable shape of a droplet on a fiber (corresponding a global minimum energy state). It is found that surface roughness delays droplet shape transition from a symmetric barrel to a clamshell or an asymmetric barrel profile. A phase diagram that includes the effects of fiber roughness on droplet configurations—symmetric barrel, clamshell, and asymmetric barrel—is presented for the first time. It is also found that droplet apparent contact angle tends to decrease on rough fibers. Likewise, roughness tends to increase the force required to detach a droplet from a fiber but the effect diminishes as droplet size increases relative to the size of surface roughness. The results presented in our study have been compared with experimental data or those from prior studies whenever possible, and good agreement has been observed.

Reactive Transport Modelling of Dolomitisation Using the New CSMP++GEM Coupled Code: Governing Equations, Solution Method and Benchmarking Results

Reactive transport modelling (RTM) is a powerful tool for understanding subsurface systems where fluid flow and chemical reactions occur simultaneously. RTM has been widely used to understand the formation of dolomite by replacement of calcite, which can be an important control on carbonate reservoir quality. Dolomitisation is a reactive transport process governed by slow dolomite precipitation and cannot be correctly simulated without a kinetic rate model. The new CSMP++GEM coupled RTM code uses the GEMS3K kernel for solving geochemical equilibria by the Gibbs energy minimisation method with the CSMP++ framework that implements a hybrid finite element–finite volume method to solve partial differential equations. The unique feature of the new coupling is the mineral reaction kinetics, implemented via additional metastability constraints. CSMP++GEM is able to simulate single-phase flow and solute transport in porous media together with chemical reactions at different pressure, temperature, and water salinity conditions. This RTM assures mass conservation which is crucial when simulating transport of solutes with low concentrations over geological time. A full feedback of mineral dissolution/precipitation on the fluid flow is provided via corresponding porosity/permeability evolution and two source terms in the pressure equation. First, the mass source term accounts for the mass of solutes released during mineral dissolution or taken from the solution by mineral precipitation. The second source term attributes to the fact that the solution density is affected by mineral dissolution/precipitation, too. This effect is included through the equivalent water salinity, which is calculated from the total amount of dissolved solutes and is used to update the properties of saline water from the H $$_2$$ O–NaCl equation of state. This paper puts emphasis on the thorough mathematical derivation of the governing equations and a detailed description of the numerical solution procedure. Two sets of benchmarking results are presented. The first benchmark is a well-known 1D model of dolomitisation by MgCl $$_2$$ solution with thermodynamic reactions. In the second benchmark, CSMP++GEM is compared with TOUGHREACT on a 1D model of dolomitisation by sea water taking into account mineral reaction kinetics. The results presented in this paper demonstrate the ability of the CSMP++GEM code to correctly reproduce dolomitisation effects.

Monte Carlo replica-exchange based ensemble docking of protein conformations.

A replica-exchange Monte Carlo (REMC) ensemble docking approach has been developed that allows efficient exploration of protein-protein docking geometries. In addition to Monte Carlo steps in translation and orientation of binding partners, possible conformational changes upon binding are included based on Monte Carlo selection of protein conformations stored as ordered pregenerated conformational ensembles. The conformational ensembles of each binding partner protein were generated by three different approaches starting from the unbound partner protein structure with a range spanning a root mean square deviation of 1-2.5 Å with respect to the unbound structure. Because MC sampling is performed to select appropriate partner conformations on the fly the approach is not limited by the number of conformations in the ensemble compared to ensemble docking of each conformer pair in ensemble cross docking. Although only a fraction of generated conformers was in closer agreement with the bound structure the REMC ensemble docking approach achieved improved docking results compared to REMC docking with only the unbound partner structures or using docking energy minimization methods. The approach has significant potential for further improvement in combination with more realistic structural ensembles and better docking scoring functions. Proteins 2017; 85:924-937. © 2016 Wiley Periodicals, Inc.

Simulation of magnetization and levitation properties of arrays of ring-shaped type-II superconductors

This paper presents an analysis of the magnetic and mechanical properties of arrays of superconducting rings arranged in axial, radial, and matrix configurations under different magnetic fields. In terms of the Bean's critical state model and the minimum magnetic energy method, the dependences of the magnetization and levitation behaviors on the geometry, number, and gap of the superconducting rings are obtained. The results show that when the applied field is spatially uniform, the magnetic property of the superconducting array is associated with the gaps between the rings. For the case of small gaps, the entire array becomes not easy to be fully penetrated by the induced currents, and the magnetic field profiles of which are almost the same as ones in a single large ring. If the superconducting array is fully penetrated, its saturation magnetization value is affected by the radial interval and, however, is almost independent of the vertical separation. When the applied field produced by a cylindrical permanent magnet is nonuniform, the superconducting array will be subjected to a levitation force. The levitation force increases monotonically and finally reaches a saturation value with increasing height or thickness of the rings, and such saturation value is closely related to the inner radius of the array.

The Sodium Ion Binding Region at the Focus of P1 Helices Attracts both Charged and Electroneutral Ligands of Sodium Channels

The inner pore of eukaryotic voltage-gated sodium channels is targeted by ligands of dramatically different chemical structures. These include organic cations such as a local anesthetic lidocaine and electroneutral drugs such as an anticonvulsant carbamazepine. Mutations of the critical phenylalanine residue in helix IVS6 and some other inner pore-facing residues are known to affect action of both charged and neutral ligands. The structural cause of this ligand-binding promiscuity of sodium channels is unclear. Here we used the X-ray structure of a prokaryotic sodium channel NavMs to model the pore domain of the Nav1.x channels. We further employed the Monte Carlo energy-minimization method to perform intensive docking of lidocaine and carbamazepine from thousands starting points in the inner-pore region. The sodium ion NaIII, which is located between the four backbone carbonyls at the C-ends of P1 helices and does not make direct contacts with the channel protein, attracted carbamazepine, but repelled lidocaine. Therefore we further docked electroneutral ligands (lamotrigine, carbamazepine, phenytoin, lacosamide and bisphenol A) and cationic ligands (lidocaine, QX-314, cocaine, quinidine, and sipatrigine) in the channel models, respectively, with and without NaIII. In our models all the ligands interacted with the phenylalanine residue in IVS6 and most of the ligands also interacted with the tyrosine residue in IVS6. Some ligands extended their moieties in the III/IV sidewalk (fenestration). The electroneutral ligands bound the sodium ion with their electronegative groups and lacosamide chelated this ion. The ligand-bound ion remained close to the NaIII position due to attraction to the pore-facing backbone carbonyls. The same region attracted the charged group of the cationic ligands. In the predicted binding modes even small-size ligands would block the ion permeation by the electrostatic and steric mechanisms. Our study proposes a common pharmacophore for the diverse ligands. It includes a cation (the ligand's ammonium group or the ligand-bound sodium ion) and an aromatic moiety, which are usually linked by four bonds. Supported by NSERC and RFBR.

SplitRacer: MATLAB Code and GUI for Semiautomated Analysis and Interpretation of Teleseismic Shear‐Wave Splitting

We present a graphical user interface in the MATLAB environment for teleseismic shear‐wave splitting analysis. In view of increasingly large seismological experiments, SplitRacer is designed to process large data sets quickly for which it integrates automatic and user‐active steps. This enables a straightforward analysis based on the user’s own quality criteria. SplitRacer offers a number of features designed to ensure precise measurements as well as user‐friendliness. Data can be downloaded directly from all data centers that are part of the International Federation of Digital Seismograph Networks Web Services. Existing data can easily be used when cut into 1‐hr three‐component seismograms. A first automatic data check is followed by visual assessment of the phases in question. We account for a possible misalignment of the sensor by analyzing the particle motions and comparison with the theoretical back azimuths of the events recorded at a station. The shear‐wave splitting analysis is based on the minimum (transverse) energy method (Silver and Chan, 1991), which constrains the fast‐polarization direction and the delay time. Measurements can be repeated for a number of time windows to enable a statistical error analysis. SplitRacer provides an overview of single‐phase splitting measurements per station that can be used to detect azimuthal dependencies. To infer the anisotropic properties beneath a station, SplitRacer offers the possibility to fit models of one or two anisotropic layers or a model of smoothly varying anisotropy to the observed data. Furthermore, SplitRacer also offers a multiphase joint‐splitting analysis for one and two hypothetical layers in which all events at a given station are used simultaneously to constrain the anisotropic model. This significantly reduces the influence of noise and makes the measurement more robust. As an example, we apply SplitRacer to constrain seismic anisotropy beneath the permanent station BKS of the Berkeley Digital Seismic Network.

Kinematics effect on honeycomb sandwich beams vibration

Composite structures are used in aerospace, aeronautics, and automotive industries, especially composite sandwich panels which are exposed to vibration, noise, and unusual loads. They are often considered to support vibrations due to their important resistance to fatigue. The aim of this work is to study the influence of displacement fields on the vibration of honeycomb sandwich beams, considering two materials: Nomex paper and Aluminum alloy. For this purpose, the minimum energy method is used to derive the natural frequencies and modal shapes equations of a cantilever honeycomb sandwich beam. The kinetic and potential energies of skins are derived using the classical laminate theory, and several polynomial displacement fields are tested. The effect of core rotational inertia and bending energy on the sandwich beam vibration is also studied. The modal shapes are then examined. Besides, an experimental study is done on the cantilever honeycomb sandwich beam, using an impact hammer for excitation and a laser vibrometer for measurement. The natural frequencies are then obtained by modal analysis. In addition, a numerical simulation is conducted on the cantilever honeycomb sandwich beam to complete this work, and the natural frequencies obtained analytically, numerically, and experimentally are compared. Future steps to enhance this work are finally advanced.

Investigation of the Ring Vibration Isolator, the Characteristics of which are Regulated by Changing the Radius of Curvature and Angle of Coverage

All-metal vibration isolators made from ribbons and ropes widely distributed and effectively reduce the harmful effects of the vibrations in mechanical systems. However, in modern literature is poorly understood issue of regulation of such vibration isolators taking into account the non-linearity of its characteristics. The paper established the method for calculating the load characteristics of controlled all-metal vibration isolators with adjustable change in the radius of curvature and angle of coverage. The calculation method is based on the joint use of Mora method, the finite element method and the method of minimum strain energy. Created full-size model of the design, which shows the possibility of significant regulation of stiffness and damping characteristics, which allows you to create adaptive systems of protection against vibration. The method allows to precisely determine the parameters of vibration isolator, thus reducing the time and cost of designing.

Effect of vacuum oxy-nitrocarburizing on the microstructure of tool steels: an experimental and modeling study

The thermochemical treatments of tool steels improve the performance of the components with respect to surface hardness, wear and tribological performance as well as corrosion resistance. Compared to the conventional gas ferritic nitrocarburizing process, the original vacuum oxy-nitrocarburizing is a time-, cost-effective and environmentally-friendly gas process. Because of the oxidizing nature of the gas atmosphere, there is no need to perform subsequent post-oxidation.In this study, a vacuum oxynitrocarburizing process was carried out onto four tool steels (AISI H10, H11, H21 and D2) at 570 °C, after hardening and single tempering. The structural analysis of the compound and diffusion layers was performed by optical and electron microscopy, X-ray diffraction and glow discharge optical emission spectrometry (GDOES) methods. A largely monophase e- layer is formed with a carbon accumulation at the substrate adjacent area. The overlaying oxides adjacent to the e-carbonitride phase contained Fe 3 O 4 (magnetite) as a main constituent. A thermodynamic modelling approach was also performed to understand and optimize the process. The “Equilib module” of FactSage software which uses Gibbs energy minimization method, was used to estimate the possible products during vacuum oxynitrocarburising process.

Energy-efficient biogas reforming process to produce syngas: The enhanced methane conversion by O2

We report an energy-efficient biogas reforming process with high and stable methane conversions by O2 presence. During this biogas reforming process, the effects of various O2 concentrations in biogas on initial conversions and stability at various temperatures on a Ni/SiO2 catalyst were detailed investigated. In addition, theoretical energy consumption and conversions were calculated based on the Gibbs energy minimization method to compare with experimental results. Carbon formation and sintering during the reforming process were characterized by thermal gravity analysis, the Brunauer-Emmett-Teller method, X-ray diffraction, and high-resolution transmission electron microscopy to investigate the feasibility of applying this process to an inexpensive nickel catalyst. The results showed that 5% O2 in biogas improved the CH4 conversion and stability of biogas reforming. The enhancement of stability was attributed to the inhibited sintering, our first finding, and the reduced carbon deposition at the same time, which sustained a stable conversion of CH4, and proved the applicability of base Ni catalyst to this process. Higher O2 concentrations (⩾10%) in biogas resulted in severe decrease in CO2 conversion and greater H2O productivity. Our proposed biogas reforming process, with a high and stable conversion of CH4, reduced energy input, and the applicability to inexpensive base metal catalyst, offers a good choice for biogas reforming with low O2 concentrations (⩽5%) to produce syngas with high energy efficiency.