Energy Minimization Method Research Articles

Springback control and plastic deformation of metal plates with large curvature in heat-assisted incremental bending process

With the development of the shipbuilding, chemical engineering, and military industry, the demand for bending the metal plates with large curvature is increasing dramatically. Take the shipbuilding as an example, the line heating method is widely applied. However, this traditional method has significant disadvantages. In order to improve the manufacturing efficiency and precision, a novel method called incremental bending has been presented by our team, which is based on the minimum energy principle and model-less control method. However, due to the limited formability of the metal plates at room temperature, the bending curvature of the plates during the incremental bending process cannot meet the requirements of the shipbuilding industry. Researches show that heating can reduce springback and improve the metal formability effectively. So here in this paper, a new method called heat-assisted incremental bending is presented. In this method, the metal plate is supported by several supporting pillars and the punch moves according to the loading trajectory, which is calculated by minimum energy method. In addition, the induction heating system is applied to heat the plates at the punching positions. The bending process continues step by step until the metal plate achieves the designed shape finally. During this study, the springback behavior of the metal plates during the heat-assisted incremental bending process was investigated based on theory, numerical simulation, and experiment. Then, the metal plates with large single curvature and variable curvature were deformed based on the novel thermal-mechanical coupled metal forming process. The experimental results show this new forming process can better control the springback behavior of the metal plates and achieve the objective metal plates with lager curvature with higher processing efficiency and accuracy.

Micro-buckling of carbon fibers in shape memory polymer composites under bending in the glass transition temperature region

Abstract The influence of a wide temperature range in the glass transition region of a shape memory polymer (SMP) matrix on micro-buckling of the fiber reinforcements in shape memory polymer composites (SMPC) under large bending deformation is described. Analytical expressions to estimate the strain energy, neutral strain surface, critical buckling surface and half wavelength of the buckled fibers in the SMPC are presented based on the minimum energy method. This study considers the reinforced fibers as three-dimensional elastic bodies and the matrix as a temperature stimulated flat plate. A comprehensive study was performed to understand the dynamic temperature behavior of the micro-buckled fibers and corresponding results were validated by previous works in the literature. The effects of fiber volume fraction and thickness of the SMPC plates on the half wavelength are also discussed along with the simultaneous influence of temperature on the parameters computed in the minimum energy analysis.

Bayesian Constrained Energy Minimization for Hyperspectral Target Detection

For better performance of hyperspectral target detectors, the prior target spectrum is expected to be accurate and consistent with the target spectrum in the hyperspectral image to be detected. The existing hyperspectral target detection algorithms usually assume that the prior target spectrum is highly reliable. However, the label obtained is not always precise in practice, and pixels of the same object may have quite different spectra. Since it is hard to acquire a highly reliable prior target spectrum in some application scenarios, we propose a Bayesian constrained energy minimization (B-CEM) method for hyperspectral target detection. Instead of the point estimation of the target spectrum, we infer the posterior distribution of the true target spectrum based on the prior target spectrum. Specifically, considering the characteristics of hyperspectral image and target detection task, we adopt the Dirichlet distribution to approximate the true target spectrum. Experimental results on three datasets demonstrate the effectiveness of the proposed B-CEM when the known target spectrum is noisy or inconsistent with the true target spectrum. The necessity to approximate the true target spectrum is also proved. Generally, the distributional estimate achieves better performance than using the known target spectrum directly.

Porous SiOC/SiC ceramicsviaan active-filler-catalyzed polymer-derived method

Effects of Fe and POSS on the phase formation of SiOC between 1100 °C and 1500 °C were studied. Fe induces higher SiO2and SiC contents. Phase contents are calculated based on a modified Gibbs free energy minimization method.

Generic Tool path planning method of T-spline surface CNC milling

T-spline is a new surface modeling technology, which has superior advantages in complex shape representation over traditional NURBS and mesh surfaces. However, the research in CAM field is insufficient, which hinders the further promotion of this technology. To fit the complex topology of T-spline surface, a general tool path planning method of T-spline surface CNC milling is proposed based on the commonly used zig-zag or contour-parallel toolpath pattern. This method utilizes the 2-dimensional scallop height model to calculate side step, the iso-scallop height method to generate tool paths, the minimum energy method to smooth them, and Hermite curves to join them as one tool path, which can realize the milling of T-spline surface model with arbitrary topology. Finally, a T-spline CAM prototype system is successfully developed to implement simulation analysis and machining experiments to verify the algorithms above. And the results of simulations and experiments prove this method can generate a smooth tool path with uniform iso-scallop height distribution, short length, smooth corner transition, and one retraction, which can achieve better finish machining effect.

Liquid chemical looping gasification of biomass: Thermodynamic analysis on cellulose

Liquid chemical looping technology is an innovation of chemical looping conversion technology. Using liquid metal oxide as the oxygen carrier during gasification process could prolong the service life of oxygen carrier and improve the process efficiency. In this paper, based on Gibbs minimum free energy method, the thermodynamic characteristics of biomass liquid chemical looping gasification were studied. Cellulose and lignin, the main components of biomass, were taken as the research objects. Bismuth oxide and antimony oxide were selected as liquid oxygen carriers. The results showed that when the temperature increased from 600 °C to 900 °C, the output of H 2 and CO in the products of cellulose gasification increased from 0.5 and 0.3 kmol to 1.3 and 2.6 kmol respectively. Different ratios of oxygen carriers to gasification raw materials had the best molar ratio. The addition of steam in the system was beneficial to the increase of H 2 content and the increase of H 2 /CO molar ratio. Bi 2 O 3 and Sb 2 O 3 with different mass ratios were used as mixed oxygen carriers. The simulation results showed that the gasification temperature of biomass with different mixed oxygen carriers had the same equilibrium trend products. It could be seen from the results of product distribution that the influence of the mixing ratio of Bi 2 O 3 and Sb 2 O 3 on gas product distribution could be neglected. These results could provide simulation reference and data basis for subsequent research on liquid chemical looping gasification.

Micro buckling of carbon fiber in triple shape memory polymer composites under bending in glass transition regions

Abstract Micro buckling of carbon fiber reinforced in triple shape memory shape polymer composites subjected to large bending strain is presented in the two distinct thermal regions through the minimum energy method. The properties of triple shape memory polymers are formulated by Boltzmann superposition principle, which are substituted in the formulation to obtain micro buckling behavior of carbon fiber in temperature dependent soft matrix. Total strain energy and half buckling wavelength of fiber are presented for the wide range of temperature encompassing the two thermal transitions. Temperature significantly regulate the behavior the volatile modulus property of the matrix in the glass transition regions. Parametric study is also presented to understand the effect of thickness and volume fraction along with the temperature. The maximum half wavelength of the fiber is obtained at the values of thickness and volume fraction as 1.75 mm and 0.4 respectively for all the thermal conditions.

Alkali-activated slag supplemented with waste glass powder: Laboratory characterization, thermodynamic modelling and sustainability analysis

Finding new aluminosilicate wastes to make sustainable alkali-activated materials (AAMs) has gained increasing attention in cement industry. In this work, the ground granulated blast-furnace slag (SG) was incorporated by waste glass powder (GP) as the raw materials for the production of AAMs. Laboratory tests were conducted to analyze the compressive strength and phase assemblages of hardened pastes at increasing ages. Analytical modelling based on Gibbs free energy minimization method (GEM) was implemented to compare with the experimental results and assist in the analysis of relationship between phase assemblage and compressive strength. The results show that GP had a lower reaction rate compared with SG, and about 28 days of curing was required to show its delayed contribution on the mechanical properties. The incorporation of up to 50% of GP into SG did not cause the significant detrimental effect on the late-age strength of AAMs, and the final strength ranged between 33.5 and 33.1 MPa. X-ray diffraction (XRD), thermogravimetric analysis (TG) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-DES) showed the presence of calcium (sodium) aluminosilicate (C-(N-)A-S-H) gels and hydrotalcite phases in the reaction products. In addition, it was found that a higher amount of C-(N-)A-S-H and lower porosity in AAMs generally contributed to a higher compressive strength. The sustainability and cost analysis also confirmed the environmental friendliness and the economic feasibility of incorporating GP in the traditional alkali-activated slag cement, paving the path for the value-added utilization of waste glass in cement industry.

Critical point of jamming transition in two-dimensional monodisperse systems.

The existence of amorphous packings in two-dimensional monodisperse system is a classical unsolved problem. We get the energy minimum state by the energy minimization method of enthalpy under constant pressure conditions. Firstly, we find that there are two peaks in the experiment, which demonstrate the interesting features of the coexistence of crystals and amorphous crystals. And then, we confirm the critical point of jamming transition of the two-dimensional monodisperse is [Formula: see text]. Finally, we prove that the jamming scaling is still satisfied in two-dimensional monodispersed system: [Formula: see text] and vanishes as [Formula: see text], and the boson peak shifts to lower frequencies for less compressed systems.

Weierstrass’ variational theory for analysing meniscus stability in ribbon growth processes

We use the method of free energy minimization to analyse static meniscus shapes for crystal ribbon growth systems. To account for the possibility of multivalued curves as solutions to the minimization problem, we choose a parametric representation of the meniscus geometry. Using Weierstrass’ form of the Euler–Lagrange equation we derive analytical solutions that provide explicit knowledge on the behavior of the meniscus shapes. Young’s contact angle and Gibbs pinning conditions are analysed and shown to be a consequence of the energy minimization problem with variable end-points. For a given ribbon growth configuration, we find that there can exist multiple static menisci that satisfy the boundary conditions. The stability of these solutions is analysed using second order variations and are found to exhibit saddle node bifurcations. We show that the arc length is a natural representation of a meniscus geometry and provides the complete solution space, not accessible through the classical variational formulation. We provide a range of operating conditions for hydro-statically feasible menisci and illustrate the transition from a stable to spill-over configuration using a simple proof of concept experiment.

Research on the simulation of a new compensation strategy for dynamic voltage correction device

A new detection and compensation method for voltage sag is proposed. Dynamic voltage correction device(DVCD) is the most effective device to solve voltage sag. Based on the shortcomings of the traditional compensation strategy, the compensation characteristics of the compensation strategy are analyzed systematically. This paper proposes a new compensation method based on the traditional minimum energy compensation method, which uses different minimum energy methods for different sags, namely zero active power exchange and minimum energy exchange. Through Simulink to establish the simulation model of minimum energy method, and make simulation analysis. The simulation results show that the method can achieve the minimum output active power while ensuring the compensation effect, which proves the feasibility and effectiveness of the method. This method can make full use of energy storage of equipment and has high economic benefits.

Thermodynamic analysis of steam reforming of glycerol for hydrogen production at atmospheric pressure

Thermodynamic chemical equilibrium analysis of steam reforming of glycerol (SRG) for selective hydrogen production was performed based on the Gibbs free energy minimisation method. The ideal SRG reaction (C3H8O3+ 3H2O → 3CO2+7H2) and a comprehensive set of side reactions during SRG are considered for the formation of a wide range of products. Specifically, this work focused on the analysis of formation of CO2, CO and CH4 in the gas phase and determination of the carbon free region in SRG under the conditions at atmospheric pressure, 600 K–1100 K and 1.013 × 105–1.013 × 106 Pa with the steam-to-glycerol feed ratios (SGFR) of 1:5–10. The reaction conditions which favoured SRG for H2 production with minimum coke formation were identifies as: atmospheric pressure, temperatures of 900 K–1050 K and SGFR of 10:1. The influence of using the inert carrier gas (i.e., N2) in SRG was studied as well at atmospheric pressure. Although the presence of N2 in the stream decreased the partial pressure of reactants, it was beneficial to improve the equilibrium yield of H2. Under both conditions of SRG (with/without inert gas), the CH4 production is minimised, and carbon formation was thermodynamically unfavoured at steam rich conditions of SGFR > 5:1.

Stress Distributions of Rectangular Thin-Film Superconductor with a Centric Hole

In this paper, the stress distributions of rectangular thin-film superconductors with a centric rectangular or elliptical hole are investigated. The bean critical current density model is adopted. In the present work, the influence of the existing hole on both the current density and magnetic field in the rectangular thin film is considered. By virtue of the minimum magnetic energy method, the principal stresses are calculated. Finally, the numerical examples about stress analysis along hole edge are examined and discussed in detail. Some important phenomena are found, which should be helpful for the analysis and design of superconducting film structure.

A Multi-threaded Method to Assemble a Sparse Stiffness Matrix for Quasi-static Solutions of Linearized Bond-Based Peridynamics

Peridynamics is generally applied to obtain dynamic solutions of crack propagation problems where crack initiation, crack branching and usually fast fracture are involved. A fairly straightforward explicit time-stepping scheme is most commonly used. Quasi-static solutions can be obtained using an adaptive dynamic relaxation method or an energy minimization method applied to the dynamic equations of motion or by solving a linear system of equations in the case of linearized peridynamics for an implicit solution. A direct solution approach by forming a linear system of equations is advantageous as the implementation is fairly straightforward and does not require multiple iterations. However, memory requirements for storing full stiffness matrices scale quadratically with the number of degrees of freedom. For example, in 2D, a grid of nominal size, say 104 particles, would require memory of nearly 3 gigabytes when using double precision. This work presents detailed algorithms that use coordinate and neighbor information to directly generate the sparse matrices required to solve a peridynamic system of equations for quasi-static simulations. The algorithms are first prototyped in MATLAB®; and the stiffness matrix and solutions are verified by comparing with their counterparts obtained by assembling the full stiffness matrix. The algorithms are also implemented in a C++ code that is run on multiple threads and the performance is evaluated as a function of parameters such as problem size, horizon, and the number of threads used. The performance and solutions of two problems with a static crack and a propagating crack are compared with solutions obtained using more traditional methods. It is found that a massive computational gain can be achieved in terms of both memory and performance by taking advantage of multi-threading and sparse implementation simultaneously.

Thermodynamic Study on Reduction of Iron Oxides by H2 + CO + CH4 + N2 Mixture at 900 °C

The reduction gas used in the gas-based direct reduction iron-making process contains CH4 in different concentrations, which has an important effect on the gas and heat needed for the reduction of iron oxide. To investigate the influence of CH4 on gas utilization rate and heat needed at 900 °C, the initial conditions are set as H2% + CO% = 90, CH4% + N2% = 10, gas pressure 1–9 atm, and 0.5 mol Fe2O3, and the equilibrium state composition is calculated using the minimum free energy method. The utilization rate of total gas can be improved, and gas demand can be decreased by increasing CH4 concentration or H2 concentration or reducing gas pressure. For the production of per ton of Fe from 25 °C to 900 °C, 6.08–7.29 m3 of reduction gas, and 7.338–8.952 MJ of gas sensible heat can be saved by increasing 1 m3 CH4, while 10.959–11.189 MJ of reaction heat is increased. Compared with 3390.828–3865.760 MJ of the total heat of per ton of Fe for the reduction by H2 + CO, 2.174–3.703 MJ of total heat is increased by increasing 1 m3 CH4, and the increase ratio is 0.065–0.096%. This study is helpful to improve the gas efficiency and lower the pursuit of higher concentration of H2 + CO in reduction gas.

Simultaneous prediction of steam production and reduction efficiency in recovery boilers of pulping process

The role of the recovery boiler in the process of pulping is vital as it renders the industrial plant environmentally and economically viable. This boiler reduces the environmental impact of directly disposing liquor. Moreover, the equipment produces “green” steam without the use of fossil fuels as it burns the byproduct (black liquor). The reduction efficiency is the most important variable used to verify the completeness of black liquor combustion. However, because of the need to ensure green steam production, vapor generation in recovery boilers has become an important variable for evaluation. In the literature, only one of the cited variables (reduction efficiency and vapor generation) is found at a time. In this study, a recovery boiler is simulated using Aspen Plus® commercial software to determine the effect of airflows on both the reduction efficiency and green steam production simultaneously. The free energy minimization method is used to predict the composition and production of smelt and the composition of exhaust gas. The results are compared with industrial and literature data, and the model predictions are found to agree with the measurements. Furthermore, a sensitivity analysis is performed on the airflow rates to verify the possibility of increasing steam production without impairing the reduction efficiency. The observations indicated a feasibility of increasing steam by 1 t/h, resulting in a reduction of 675,840 Nm³/year of natural gas usage in conventional boilers. Reduction of CO, SOX, and NOX emissions by 57, 76, and 22%, respectively, can also be achieved owing to these improved airflow rates.

Sorption enhanced steam reforming of ethanol over Ni-based catalyst coupling with high-performance CaO pellets

Coupling with the conventional Ni/Al2O3 catalyst, novel CaO-based porous spherical sorbents (made by a new molding technique) were examined in the sorption enhanced steam reforming of ethanol process (SESRE) to improve the H2 quality. The cyclic H2 quality was monitored, and the catalytic properties of the catalyst for steam reforming of ethanol as well as the CO2 capture capacity of the modeled sorbents were studied in details. Besides, thermodynamic modelling has been done by Gibbs free energy minimization method to simulate the sorption enhancing effect and screen the optimized reaction conditions to yield high-quality H2; furthermore, the relative H2O consumption versus ethanol during the reforming process was further discussed. The results showed that the sorption enhanced steam reforming process was an effective and flexible way to produce high-quality H2 around 600 °C, and subsequently the simulated sorption enhanced process was validated experimentally. In addition, the properties of the catalyst and modeled sorbents were analyzed by N2 physisorption, SEM, EDS-Mapping, H2-TPR, XRD, Raman, In-situ DRIFTS and so on. A high purity H2 was yielded during the pre-breakthrough stages, in especial that process enhanced by the modeled sorbents templated by cellules (CaOS-C5 pellets), which illustrated a good prospect of SESRE process. With the CaOS-C5 pellets, during the 10th SESRE process, H2 could be constantly produced with purity above 90% within at least 15 min of SESRE process. The modeled CaO spheres greatly boosted the concentration and output of H2. Over the repeated cycles, the Ni/Al2O3 catalyst and the modeled sorbents displayed well stability over the long-term reactions, which illustrated a good prospect of SESRE process enhanced by these new spherical sorbents.

Electronic, Structural, and Optical Properties of Zinc Blende and Wurtzite Cadmium Sulfide (CdS) Using Density Functional Theory

Zinc blende (zb) and wurtzite (wz) structure of cadmium sulfide (CdS) are analyzed using density functional theory within local density approximation (LDA), generalized gradient approximation (GGA), Hubbard correction (GGA + U), and hybrid functional approximation (PBE0 or HSE06). To assure the accuracy of calculation, the convergence test of total energy with respect to energy cutoff and k-point sampling is performed. The relaxed atomic position for the CdS in zb and wz structure is obtained by using total energy and force minimization method following the Hellmann–Feynman approach. The structural optimization and electronic band structure properties of CdS are investigated. Analysis of the results shows that LDA and GGA underestimate the bandgap due to their poor approximation of exchange-correlation functional. However, the Hubbard correction to GGA and the hybrid functional approximation give a good bandgap value which is comparable to the experimental result. Moreover, the optical properties such as real and imaginary parts of the dielectric function, the absorption coefficient, and the energy loss function of CdS are determined.

Analytical Modeling and Design of Generalized Pneu-Net Soft Actuators with Three-Dimensional Deformations.

Pneu-net soft actuators, consisting of pneumatic networks of small chambers embedded in elastomeric structures, are particularly promising candidates in the society of soft robotics. However, there are few studies on the analytical modeling of pneu-net soft actuators, especially in the three-dimensional space. In this article, based on the minimum potential energy method and the continuum rod theory, we propose an analytical model and corresponding design approach for a class of generalized pneu-net soft actuators (gPNSAs) with both bending and twisting deformations by combining the geometric complexity and material elasticity. We experimentally verify our modeling approach and finally investigate the effects of geometric parameters, material properties, and external force on the deformations of gPNSAs, which can be used as a tool for the design of gPNSAs. We further demonstrate that our developed model can predict the deformations of gPNSAs made of multiple materials.

Optimization of bio-oil steam reforming process by thermodynamic analysis

A straightforward thermodynamic analysis of bio-oil steam reforming was carried out in the context of hydrogen and syngas production, employing Gibbs energy minimization method to determine equilibrium composition and global reaction heat. The bio-oil model compound was a mixture of acetic acid, phenol, and acetone. The effects of process variables, such as temperature and inlet S/C molar ratio, were investigated over a wide range of conditions. Thermodynamic analysis was performed using the software Aspen Plus v.11. It was identified the best operational conditions that could maximize syngas and further hydrogen production considering energy efficiency. The optimum production of hydrogen is 2.28 mol per carbon mole at S/C = 10 and 850 K, and syngas is 2.37 mol per carbon mole at S/C = 10 and 900 K. It has been demonstrated that the equilibrium calculations can be used to simulate these steam reforming reactions, given the catalyst's behavior.