Energy Minimization Method Research Articles

Thermal-induced upheaval buckling of continuously-reinforced semi-infinite concrete pavements

In some configuration cases for concrete pavements, such as at the intersection of two road pavements or the connection of a road pavement to a bridge abutment, the pavement can be considered to be semi-infinite with one end adjoining a rigid structure. In addition, continuously reinforced concrete pavements may weaken over time as a result of corrosion, erosion, shrinkage, fatigue cracking or the like, and in these instances the weakened pavement can also be considered as being semi-infinite with a joint. This rotational joint constrains the end of the pavement, which has an effect on the potential upheaval buckling of the pavement when subjected to heatwaves. This paper presents an analytical solution for thermal-induced upheaval buckling of such a semiinfinite continuously reinforced concrete pavement when constrained by a rigid medium with a quantifiable rotational stiffness. The method of minimum total potential energy is invoked to derive the differential equations for the post-buckling response, and the equilibrium equations with variable parameters that govern the behaviour are solved analytically by considering both the deformation of the pavement and the rotational and translational restraints. Parametric investigations are conducted on the buckling response of the pavement when constrained at one end; the parameters considered being the rotational stiffness of the joint, the thickness of the pavement, the properties of the pavement subgrade base and the effective weight of the pavement. It is found that the constraint affects the buckling temperature considerably, and the so-called safe temperature increases with the rotational stiffness of the constraint the end of the pavement.

Controllable helical deformations on printed anisotropic composite soft actuators

Helical shapes are ubiquitous in both nature and engineering. However, the development of soft actuators and robots that mimic helical motions has been hindered primarily due to the lack of efficient modeling approaches that take into account the material anisotropy and the directional change of the external loading point. In this work, we present a theoretical framework for modeling controllable helical deformations of cable-driven, anisotropic, soft composite actuators. The framework is based on the minimum potential energy method, and its model predictions are validated by experiments, where the microarchitectures of the soft composite actuators can be precisely defined by 3D printing. We use the developed framework to investigate the effects of material and geometric parameters on helical deformations. The results show that material stiffness, volume fraction, layer thickness, and fiber orientation can be used to control the helical deformation of a soft actuator. In particular, we found that a critical fiber orientation angle exists at which the twist of the actuator changes the direction. Thus, this work can be of great importance for the design and fabrication of soft actuators with tailored deformation behavior.

Classical Optimal Control for Energy Minimization Based On Diffeomorphic Modulation under Observable-Response-Preserving Homotopy.

We introduce the so-called "Classical Optimal Control Optimization" (COCO) method for global energy minimization based on the implementation of the diffeomorphic modulation under observable-response-preserving homotopy (DMORPH) gradient algorithm. A probe particle with time-dependent mass m( t;β) and dipole μ( r, t;β) is evolved classically on the potential energy surface V( r) coupled to an electric field E( t;β), as described by the time-dependent density of states represented on a grid, or otherwise as a linear combination of Gaussians generated by the k-means clustering algorithm. Control parameters β defining m( t;β), μ( r, t;β), and E( t;β) are optimized by following the gradients of the energy with respect to β, adapting them to steer the particle toward the global minimum energy configuration. We find that the resulting COCO algorithm is capable of resolving near-degenerate states separated by large energy barriers and successfully locates the global minima of golf potentials on flat and rugged surfaces, previously explored for testing quantum annealing methodologies and the quantum optimal control optimization (QuOCO) method. Preliminary results show successful energy minimization of multidimensional Lennard-Jones clusters. Beyond the analysis of energy minimization in the specific model systems investigated, we anticipate COCO should be valuable for solving minimization problems in general, including optimization of parameters in applications to machine learning and molecular structure determination.

Generalized fusion moves for continuous label optimization

Energy-minimization methods are ubiquitous in computer vision and related fields. Low-level computer vision problems are typically defined on regular pixel lattices and seek to assign discrete or continuous values (or both) to each pixel such that a combined data term and a spatial smoothness prior are minimized. In this work we propose to minimize difficult, non-convex energies over continuous unknowns by repeated generalized fusion moves. In contrast to standard fusion moves, the fusion step jointly optimizes over binary and continuous sets of variables representing label ranges. Further, each fusion step can optimize over additional continuous unknowns appearing in the energy. We demonstrate the general method on a variational-inspired stereo approach, and optionally optimize over radiometric changes between the images as well.

Utilization of acetone-butanol-ethanol-water mixture obtained from biomass fermentation as renewable feedstock for hydrogen production via steam reforming: Thermodynamic and energy analyses

A thermodynamic equilibrium analysis on steam reforming process to utilize acetone-butanol-ethanol-water mixture obtained from biomass fermentation as biorenewable fuel has been performed to produce clean energy carrier H2 via non-stoichiometric approach namely Gibbs free energy minimization method. The effect of process variables such as temperature (573–1473 K), pressure (1–10 atm), and steam/fuel molar feed ratio (FABE = 5.5–12) have been investigated on equilibrium compositions of products, H2, CO, CO2, CH4 and solid carbon. The best suitable conditions for maximization of desired product H2, suppression of CH4, and inhibition of solid carbon are 973 K, 1 atm, steam/fuel molar feed ratio = 12. Under these conditions, the maximum molar production of hydrogen is 8.35 with negligible formation of carbon and methane. Furthermore, the energy requirement per mol of H2 (48.96 kJ), thermal efficiency (69.13%), exergy efficiency (55.09%), exergy destruction (85.36 kJ/mol), and generated entropy (0.29 kJ/mol.K) have been achieved at same operating conditions.

Design Improvement of a Staggered YBCO Undulator

A strong field and short period undulator can be a desirable light source device in a storage ring or a free-electron laser. Bulk YBCO can be used to construct a high-temperature-superconducting undulator in a staggered array structure. The YBCO material in form of 32 mm diameter and 2.5 mm thick was used to assemble a staggered magnet array. The period length is 5 mm and the magnet gap is 4 mm. To estimate the strength of a sinusoidal field and to optimize the end-pole design to minimize the first (i.e., electron angle) and second field integral (electron position), an energy-minimization method (EM-method) based on Bean's model to simulate the field trapped in the HTS-Block is introduced. In this paper, we focus on promoting the practical value of the EM-method simulation. Combining the experimental experience of a YBCO staggered undulator and the simulation experience based on the EM-method, we address some issues to enhance the efficacy of this undulator design.

Supercritical water gasification of a heavy fuel oil

ABSTRACTIn this research, the supercritical water gasification for a sort of heavy fuel oil, Mazut, has been investigated. Mazut was modeled with a 33-pseudo-component using the corresponding distillation curve. In a reactor, the equilibrium reactions were simulated using the Gibbs free energy minimization method. A parametric study was performed on this system. The parameters were included mass fraction of fuel and pressure and temperature of the gasifier. Two approaches were investigated, one with constant pressure (P = 22.1 MPa) and the other with constant temperature (T = 600°C), varying the other two parameters. H2 production efficiency reaches a maximum at fuel mass fraction about 30 percent and gasifier temperature in the range of 500°C to 700°C.

Plasma Spraying of Solution Precursor in Pulsed Mode: In-Flight Phenomena and Coating Deposition

In the field of plasma spray technologies, new processes were developed in order to obtain coatings with nanostructured architectures. Among them, solution precursor plasma spraying is a promising technique. However, to be industrially viable, efforts must be made to understand and control the steps of the process. In alternative to instabilities attenuations, the time-modulation of current–voltage characteristics of a low-powered arc plasma jet was proposed, resulting in time-modulation of plasma properties. This modulation was synchronized with a drop-on-demand printhead for injection to improve the control of plasma/material interaction. An aluminum nitrate ink was formulated to be compatible with a drop-on-demand printhead dispenser. Plasma composition was calculated by the Gibbs free energy minimization method. Moreover, in-flight diagnostics coupled with coating characterization were carried out. Results showed that the controlled injection system leads to the formation of vapors of aluminum oxide that leaded to the deposition of nanostructured cauliflowers-like structures. Amorphous alumina coatings with inclusions of γ-alumina micro-sized particles were obtained and a description of main in-flight mechanisms was proposed.

Thermodynamic Analysis of Chemical and Phase Equilibria in CO2 Hydrogenation to Methanol, Dimethyl Ether, and Higher Alcohols

CO2 hydrogenation can lead to the formation of various products, of which methanol, dimethyl ether (DME) and ethanol have received great attention. In this study, a comprehensive thermodynamic analysis of CO2 hydrogenation in binary (methanol/CO) and ternary product systems (methanol/CO with DME or ethanol) is conducted in Aspen Plus by the Gibbs free energy minimization method combined with phase equilibrium calculations. It is demonstrated that product condensation can be utilized to circumvent thermodynamic restrictions on product yield. Significant improvements in CO2 conversion can be achieved by operating at conditions favorable for product condensation, whereas the selectivity is mildly affected. The relevance of the results herein is discussed with regards to recent advances in catalysis and process design for CO2 hydrogenation. Our study highlights the importance of obtaining a thorough understanding of the thermodynamics of CO2 hydrogenation processes, which will be critical for developing poten...

Thermodynamic analysis of H2 production by oxidative steam reforming of butanol-ethanol-water mixture recovered from Acetone:Butanol:Ethanol fermentation

Thermodynamic equilibrium analysis has been adopted for oxidative steam reforming of butanol-ethanol mixture (B-E) as renewable source obtained from Acetone:Butanol:Ethanol (ABE) fermentation to produce H2 by using Gibbs free energy minimization method. The effects of pressure (1–10 atm), temperature (573–1473 K), steam/fuel molar feed ratio (fO1 = 9 and 12), O2/fuel molar feed ratio (fO2 = 0–3), and B-E mixture compositions (50–90%B) on equilibrium compositions of H2, CO, CO2, CH4, and carbon are performed. The maximum H2 yield (65.456% for fO2 = 0 and 58% for fO2 = 0.75) has been achieved at fO1 = 9, 90% B mixture, 1 atm, and 973 K. The yields of CO, CO2, and CH4 with respect to maximum H2 are 53.390%, 44.384%, and 2.225% for fO2 = 0, and 45.677%, 53.269%, and 1.053% for fO2 = 0.75, respectively. Energy required per mol of H2, thermal and exergy efficiencies for the process are also evaluated to utilize the potential of B–E mixture for H2 production.

Experimental and numerical study on one flexible incremental bending process

In the shipbuilding industry, the traditional manufacturing method for the complicated ship hull metal plates is line heating method, which is not only labor intensive but also inefficient. Considerable efforts have been taken to develop the new automated manufacturing processes at a reasonable quality, efficiency and price during the last few decades. This paper presents a novel flexible forming process called incremental bending to achieve complicated plates. In this method, the initial metal plate is supported by some rotatable hydraulic cylinders and the punches move according to the given path, which is decided by minimum energy method and springback compensation method, to achieve the final plate. Taking one variable curved metal plate as one example, this paper investigates the formability of this novel process based on experiment and numerical simulation. During the numerical simulation, the implicit method is used and the gravity of the plate is considered mainly for the automatic positioning of the plate during each springback process. Results show that the incremental bending process can achieve variable curved metal plates with good accuracy, high efficiency, and relatively small punch load. In comparison with the existing methods, the new process has greater potentiality in the ship hull manufacturing industry.

Large-scale atomistic simulations of CNT-reinforced thermoplastic polymers

Different multiscale techniques were developed over the past two decades for modeling CNT-reinforced composites. However, these techniques contained numerous approximations to allow scaling up the properties from nanoscale to bulk levels. These approximations were partly responsible for the anomaly between model predictions and experiments. In this study, we overcame this problem by modeling large (up to one million atoms) representative volume elements (RVEs) reinforced by CNTs with different lengths (aspect ratio up to 500), curvatures (ranging from straight to severely curved) and bundle sizes to simulate actual nanocomposites. The RVE dimensions were carefully selected to ensure that the molecular structure of the nanocomposite is successfully represented and the obtained elastic properties are independent of the RVE size. A series of extensive MD simulations were conducted to determine the elastic moduli of the nanocomposite using the constant-strain energy minimization method. The developed models were verified by comparing their predictions with the reported experimental results. The developed MD models were further used to study the effect of CNT morphology and the state of dispersion on the elastic moduli of CNT-polyethylene composite. The current model can be integrated with electrical and thermal models to predict the multifunctional properties of CNT-reinforced composites.

Springback law study and application in incremental bending process

One incremental bending process has been proposed for manufacturing the complex and thick ship-hull plates. The accuracy and efficiency for this novel process is mainly dependent on the loading path and thus the unavoidable springback behavior should be considered in the loading path determination. In this paper, firstly, the numerical simulation method is verified by the corresponding experiment, and then the springback law during the incremental bending process is investigated based on numerical simulation, and later the loading path based on the springback law and the minimum energy method is achieved for specific machining shape. Comparison between the designed curve based on springback law and the new simulation results verifies that the springback law obtained by numerical simulation is believable, so this study provides a new perspective for the further research on incremental bending process.

Experimental study of springback behavior in incremental bending process

Manufacturing complicated and thick ship-hull plates at reasonable price and efficiency has always been a challenge in shipbuilding industry. One widely used method is line heating process, which is not only labor intensive but also ineffective. Recently many flexible forming processes have been developed while they all have avoidable disadvantages. In order to reduce the forming force, our group proposed one flexible incremental bending technology, during which the flat blank was bended into the required shape by gradually stamping at various positions. During the incremental bending process, the minimum energy method is used to determine the proper loading path. However, there is huge springback phenomenon after each bending. The shape change after each springback process should be considered in the loading path determination to make sure the accurate shape can be obtained.Here in this paper, the springback behavior of the carbon steel Q235 during the incremental bending process was investigated by experiments. In the first stage, the flat plates were bended several times at the same position while the final bending depth is the same, the final bending shapes after springback were compared to each other to investigate the influence of loading path on the springback behavior of the material. In the second stage, the flat plates were bended once at various positions and bending depths to study the springback behavior in one step bending process. It was found that loading path has little influence on the springback behavior, so during the incremental bending process, the springback law obtained from each single bending process can be used to combine with the minimum energy method to obtain the proper punch moving trajectory.

SDF-2-SDF Registration for Real-Time 3D Reconstruction from RGB-D Data

We tackle the task of dense 3D reconstruction from RGB-D data. Contrary to the majority of existing methods, we focus not only on trajectory estimation accuracy, but also on reconstruction precision. The key technique is SDF-2-SDF registration, which is a correspondence-free, symmetric, dense energy minimization method, performed via the direct voxel-wise difference between a pair of signed distance fields. It has a wider convergence basin than traditional point cloud registration and cloud-to-volume alignment techniques. Furthermore, its formulation allows for straightforward incorporation of photometric and additional geometric constraints. We employ SDF-2-SDF registration in two applications. First, we perform small-to-medium scale object reconstruction entirely on the CPU. To this end, the camera is tracked frame-to-frame in real time. Then, the initial pose estimates are refined globally in a lightweight optimization framework, which does not involve a pose graph. We combine these procedures into our second, fully real-time application for larger-scale object reconstruction and SLAM. It is implemented as a hybrid system, whereby tracking is done on the GPU, while refinement runs concurrently over batches on the CPU. To bound memory and runtime footprints, registration is done over a fixed number of limited-extent volumes, anchored at geometry-rich locations. Extensive qualitative and quantitative evaluation of both trajectory accuracy and model fidelity on several public RGB-D datasets, acquired with various quality sensors, demonstrates higher precision than related techniques.

The Buckling Analysis of Conical Sandwich Shells with Temperature Dependent Properties and an Improved Higher-Order Theory

In this research paper, an improved theory is used for buckling analysis of sandwich truncated conical shells with thick core and thin functionally graded material face sheets and homogeny core and with temperature-dependent properties. Section displacements of the conical core are assumed by cubic functions, and displacements of the functionally graded material face sheets are assumed by first-order shear displacements theory. The linear variations of temperature are assumed in the through thick. According to a power-law and exponential distribution the volume fractions of the constituents of the functionally graded material face sheets are assumed to be temp-dependent by a third-order and vary continuously through the thickness. In other words to get the strain components, the nonlinear Von-Karman method and his relation is used. The equilibrium equations are obtained via minimum potential energy method. Analytical solution for simply supported sandwich conical shells under axial compressive loads and thermal conditions is used by Galerkin’s solution method. Analysing the results show that the critical dimensionless axial loads are affected by the configurations of the constituent materials, compositional profile variations, thermal condition, semi-vertex angle and the variation of the sandwich geometry. Numerical modeling is made by ABAQUS finite element software. The comparisons show that the present results are in the good and better agreement with the results in the literature and the present finite element modelling.

Sparse Weighted Constrained Energy Minimization for Accurate Remote Sensing Image Target Detection

Target detection is an important task for remote sensing images, while it is still difficult to obtain satisfied performance when some images possess complex and confusion spectrum information, for example, the high similarity between target and background spectrum under some circumstance. Traditional detectors always detect target without any preprocessing procedure, which can increase the difference between target spectrum and background spectrum. Therefore, these methods could not discriminate the target from complex or similar background effectively. In this paper, sparse representation was introduced to weight each pixel for further increasing the difference between target and background spectrum. According to sparse reconstruction error matrix of pixels on images, adaptive weights will be assigned to each pixel for improving the difference between target and background spectrum. Furthermore, the sparse weighted-based constrained energy minimization method only needs to construct target dictionary, which is easier to acquire. Then, according to more distinct spectrum characteristic, the detectors can distinguish target from background more effectively and efficiency. Comparing with state-of-the-arts of target detection on remote sensing images, the proposed method can obtain more sensitive and accurate detection performance. In addition, the method is more robust to complex background than the other methods.

Precipitation of silica from zinc process solution

Precipitation of silica in concentrated sulfuric acid solutions was studied with laboratory-scale batch experiments. The effects of initial silicic acid concentration, temperature, and sulfuric acid concentration were studied. It was observed also in this work that the high ionic strength of the leaching solution drastically decreased the solubility of silica. The solubility was also studied using Gibbs energy minimization method and Pitzer model using the ChemSheet program. Good agreement was obtained between the model and experimental results. The precipitation reaction of silica was observed to follow a pseudo-first-order rate law. Based on the rate law used, an activation energy of 61.7 kJ mol−1 was estimated. This implies a reaction-controlled mechanism of precipitation.

Methanol synthesis from biogas: A thermodynamic analysis

Abstract A new approach for the direct conversion of syngas into methanol has been proposed as alternative to the conventional process requiring WGS and/or PSA clean-up steps for syngas upgrading. A comparative thermodynamic equilibrium analysis of biogas reforming processes (dry reforming, steam reforming and oxy-steam reforming) has been performed using the Gibbs free energy minimization method. The calculations have been carried out under different biogas composition (CH4/CO2 = 1–2.3), reaction temperature (400–900 °C), S/CH4 (0.0–3.0) and O2/CH4 (0.0–0.2) molar ratios. The effects of process variables on the reforming performances as well as on the syngas quality, in term of CH4 and CO2 conversion, H2/CO and H2/CO2 ratios, coke deposition and energetic consumption, has been examined. Subsequently, methanol synthesis has been studied using the same mathematical approach, with the aim to identify the most adequate operating conditions for the direct conversion of the syngas obtained from reforming process into methanol. The simulations suggested that steam reforming of biogas, with high methane content, is the most appropriate route to produce a syngas quality suitable for the new proposed approach.

An analytical model for the response of carbon/epoxy-aluminum honeycomb core sandwich structures under quasi-static indentation loading

An analytical model is developed to predict the loading and unloading response, as well as the residual dent diameter and dent depth, of carbon/epoxy-aluminum honeycomb core composite sandwich structures undergoing quasi-static indentation loading. The model considers damage created using spherical indenters and is valid up to the barely visible external damage threshold. The initial low load regime (until the onset of core crushing) is modeled using a combination of local Hertzian indentation of an elastic half-space and small deflection plate theory of a circular plate on an elastic foundation. For loads above those required to cause core crushing, the model uses the Rayleigh-Ritz method of energy minimization with the total system energy determined using a combination of face sheet bending energy, face sheet membrane energy and work done to the core during both elastic deformation and crushing. Degraded face sheet properties are used in the model beyond the onset of face sheet delamination, which is predicted using Griffith’s energy criterion. The model is validated using experimental results for sandwich structures consisting of quasi-isotropic 8- (thin) and 16- (thick) ply carbon/epoxy face sheets and aluminum honeycomb cores. The results show that the overall mechanics of the model are fundamentally correct and reflective of physical behavior. Thus, in its present form the model shows promise as a preliminary design tool.