Three-Dimensional Isogeometric Analysis of Flexoelectricity with MATLAB Implementation

Flexoelectricity is a general electromechanical phenomenon where the electric polarization exhibits a linear dependency to the gradient of mechanical strain and vice versa.The truncated pyramid compression test is among the most common setups to estimate the flexoelectric effect.We present a three-dimensional isogeometric formulation of flexoelectricity with its MATLAB implementation for a truncated pyramid setup.Besides educational purposes,this paper presents a precise computational model to illustrate how the localization of strain gradients around pyramidal boundary shapes contributes in generation of electrical energy.The MATLAB code is supposed to help learners in the Isogeometric Analysis and Finite Elements Methods community to learn how to solve a fully coupled problem,which requires higher order approximations,numerically.The complete MATLAB code which is available as source code distributed under a BSD-style license,is provided in the part of Supplementary Materials of the paper.

Total Harmonic Distortion Minimization of Multilevel Converters Using Genetic Algorithms

This paper presents a genetic algorithm (GA) optimization technique to find the optimum switching angles of 11-level inverter with minimum number of dc sources and switches in comparison with the cascade multilevel inverter in order to minimize the total harmonic distortion (THD) of their output voltage waveform. Theoretical and simulation results for an 11-level converter show the efficiency of the proposed algorithm to determine the optimum angles in order to decrease the undesired harmonics and produce very high quality output voltage waveform.

Prediction of the Microstructural Variations of Cold-Worked Pure Aluminum during Annealing Process

The mechanical properties such as hardness and ultimate tensile strength of metals depend on the grain size, which have to be properly controlled and optimized to ensure the better economy and desirable mechanical characteristics of the metals. In order to study the microstructure evolution of AA1070, many experimental tests were conducted at different cold working and annealing conditions. Utilizing the experimental results, the static recrystallization and grain growth behavior of AA1070 have been investigated and the developed equations that can be used to the FEM of the annealing process have been obtained. The agreement between numerical modeling and experimental results is reasonably good for this material. The results showed that the recrystallization and grain growth behavior of AA1070 was evidently affected by both the annealing temperature and plastic strain.

不同成分铝/铜双金属复合材料的热变形行为及其本构模型

通过等温压缩实验,研究Al/Cu双金属复合材料在400~500℃、应变速率0.001~0.1 s^(-1)条件下的热变形行为,并考虑复合材料成分体积分数(Al含量为30%~51%)的影响。采用Arrhenius模型和混合定律(ROM)模型建立新的本构方程。流变应力(FS)实验表明,工艺参数和体积分数对复合材料的流变行为有影响,而Cu的体积分数对复合材料的高温流变行为影响更大。对于体积分数为51%、42%和30%Al的复合材料,建立的Arrhenius型本构方程和ROM模型的相关系数(R)分别为0.9826、0.9742和0.9718,其平均相对误差分别为0.18%、1.69%和-0.84%。结果表明,新建立的本构模型能较好地预测双金属复合材料的热加工行为。最后,研究不同工艺条件下复合材料的显微组织,确定三种不同成分Al/Cu复合材料在不同温度、应变和应变速率范围内的主要热变形机制。

析出硬化AA7022-T6铝合金高温流变行为的本构模型

在温度623~773 K和应变速率0.01~1 s^−1条件下,采用等温压缩试验研究析出硬化AA7022-T6铝合金的热力学行为。结果表明,动态再结晶是主要的热变形机制,特别是在高温和低应变速率下。采用改进的Johnson−Cook(J−C)模型和应变补偿Arrhenius模型预测不同变形条件下的热流变行为。这两种模型的线性相关系数分别为0.9914和0.9972,平均相对误差(ARE)分别为6.074%和4.465%,均方根误差(RMSE)分别为10.611和1.665 MPa。结果表明,应变补偿Arrhenius模型能准确预测AA7022-T6铝合金的热流变应力。

利用晶粒尺寸构建本构方程模拟AA1070铝的热变形行为

对原有Johnson−Cook本构模型中的项进行修正,提出一种新的现象学的、基于经验的本构模型。该模型可用于描述和预测具有不同初始晶粒尺寸的AA1070铝在热加工过程中的流变应力。该模型考虑热软化、应变速率硬化、应变硬化、初始晶粒尺寸及其相互影响,能够正确模拟具有不同应变、应变速率和初始晶粒尺寸AA1070铝的高温行为。通过压缩试验测试的AA1070铝的热流变行为,温度范围为623~773 K,应变速率为0.005~0.5 s−1,初始晶粒尺寸为50~450μm。结果表明,初始晶粒尺寸对AA1070铝的流变行为有显著影响。通过相关系数(R)、平均绝对相对误差(AARE)、相对误差评估模型的可预测性。结果表明,新模型预测的具有不同初始晶粒尺寸材料的流变应力与实验值完全一致,平均相对误差为1.19%,证实新修正的Johnson−Cook关系能准确估计考虑初始晶粒尺寸时AA1070铝的热流变应力。

Computational Machine Learning Representation for the Flexoelectricity Effect in Truncated Pyramid Structures

In this study,machine learning representation is introduced to evaluate the flexoelectricity effect in truncated pyramid nanostructure under compression.A Non-Uniform Rational B-spline(NURBS)based IGA formulation is employed to model the flexoelectricity.We investigate 2D system with an isotropic linear elastic material under plane strain conditions discretized by 45×30 grid of B-spline elements.Six input parameters are selected to construct a deep neural network(DNN)model.They are the Young's modulus,two dielectric permittivity constants,the longitudinal and transversal flexoelectric coefficients and the order of the shape function.The outputs of interest are the strain in the stress direction and the electric potential due flexoelectricity.The dataset are generated from the forward analysis of the flexoelectric model.80%of the dataset is used for training purpose while the remaining is used for validation by checking the mean squared error.In addition to the input and output layers,the developed DNN model is composed of four hidden layers.The results showed high predictions capabilities of the proposed method with much lower computational time in comparison to the numerical model.

Resilient Fault Diagnosis Under Imperfect Observations–A Need for Industry 4.0 Era

In smart industrial systems,in many cases,a fault can be captured as an event to represent the distinct nature of subsequent changes.Event-based fault diagnosis techniques are capable model-based methods for diagnosing faults from a sequence of observable events executed by the system under diagnosis.Most event-based diagnosis techniques rely on perfect observations of observable events.However,in practice,it is common to miss an observable event due to a problem in sensorreadings or communication/transmission channels.This paper develops a fault diagnosis tool,referred to as diagnoser,which can robustly detect,locate,and isolate occurred faults.The developed diagnoser is resilient against missed observations.A missed observation is detected from its successive sequence of events.Upon detecting a missed observation,the developed diagnoser automatically resets and then,asynchronously resumes the diagnosis process.This is achieved solely based on postreset/activation observations and without interrupting the performance of the system under diagnosis.New concepts of asynchronous detectability and asynchronous diagnosability are introduced.It is shown that if asynchronous detectability and asynchronous diagnosability hold,the proposed diagnoser is capable of diagnosing occurred faults under imperfect observations.The proposed technique is applied to diagnose faults in a manufacturing process.Illustrative examples are provided to explain the details of the proposed algorithm.The result paves the way towards fostering resilient cyber-physical systems in Industry4.0 context.

Recent progresses in dry gas polymeric filters

Filtration and membrane separation are popular methods in gas separation since they are cost and energy efficient. Despite to air filters, there are comparatively few studies on dry gas filters, particularly at industrial scale. In fact, major unsolved challenges such as high efficiency, low pressure drop, long-term stability, high-thermal and chemical stability and advanced physiochemical properties, are still remained. The aim of this review is to scrutinize the advanced scientific and technological practices (such as selection of appropriate polymeric materials and additives, nanotechnology, modification techniques and preparation methods) towards design and fabrication of an efficient filter media for solid particles removal from the natural gas flow. Recent progresses in solid particle separation mechanisms, modeling and simulation techniques and the effect of membrane fabrication methods on its performance, strategies for modification of filter media, current challenges and future perspective are discussed.

Nd:YAG激光微型焊接超薄FeCo-V磁性合金焊接强度的优化（英文）

为了优化激光焊接FeCo-V合金拉伸强度,建立数学关系,结合工艺参数如荧光灯电流、焊接速度、脉冲时间和位置,以预测激光束焊FeCo-V薄片拉伸强度。建立程序以提高焊接强度和增大产率。结果表明,脉冲时间和焊接速度对拉伸强度影响很大,焊接接头的拉伸强度随脉冲时间的延长而增大,并在2.25 ms时达到最大。而且,接头的拉伸强度随着焊接速度的减小而增大,并在125 mm/min时达到最大。脉冲时间的延长和焊接速度的减小导致有效峰能量密度减小,因此更耐焊。在较高的脉冲时间和较低的焊接速度时,因为在熔合区形成了凝固微裂纹而使得焊接接头的拉伸强度增大。

Alleviation of spike stall in axial compressors utilizing grooved casing treatment

Abstract This article deals with application of grooved type casing treatment for suppression of spike stall in an isolated axial compressor rotor blade row. The continuous grooved casing treatment covering the whole compressor circumference is of 1.8 mm in depth and located between 90% and 108% chord of the blade tip as measured from leading edge. The method of investigation is based on time-accurate three-dimensional full annulus numerical simulations for cases with and without casing treatment. Discretization of the Navier Stokes equations has been carried out based on an upwind second-order scheme and k-a-SST （Shear Stress Transport） turbulence modeling has been used for estimation of eddy viscosity. Time-dependent flow structure results for the smooth casing reveal that there are two criteria for spike stall inception known as leading edge spillage and trailing edge backftow, which occur at specific mass flow rates in near-stall conditions. In this case, two dominant stall cells of different sizes could be observed. The larger one is caused by the spike stall covering roughly two blade passages in the circumferential direction and about 25% span in the radial direction. Spike stall disturbances are accompanied by lower frequencies and higher amplitudes of the pressure signals. Casing treatment causes flow blockages to reduce due to allevi- ation of backflow regions, which in turn reduces the total pressure loss and increases the axial veloc- ity in the blade tip gap region, as well as tip leakage flow fluctuation at higher frequencies and lower amplitudes. Eventually, it can be concluded that the casing treatment of the stepped tip gap type could increase the stall margin of the compressor. This fact is basically due to retarding the movement of the interface region between incoming and tip leakage flows towards the rotor leading edge Diane and suttressing the reversed flow around the blade trailing edee.

Multiscale RBF-based central high resolution schemes for simulation of generalized thermoelasticity problems

In this study, average-interpolating radial basis functions (RBFs) are successfully integrated with central high-resolution schemes to achieve a higher-order central method. This proposed method is used for simulation of generalized coupled thermoelasticity problems including shock (singular) waves in their solutions. The thermoelasticity problems include the LS (systems with one relaxation parameter) and GN (systems without energy dissipation) theories with constant and variable coefficients. In the central high resolution formulation, RBFs lead to a reconstruction with the optimum recovery with minimized roughness on each cell: this is essential for oscillation-free reconstructions. To guarantee monotonic reconstructions at cell-edges, the nonlinear scaling limiters are used. Such reconstructions, finally, lead to the total variation bounded (TVB) feature. As RBFs work satisfactory on non-unifdrm cells/grids, the proposed central scheme can handle adapted cells/grids. To have cost effective and accurate simulations, the multiresolution-based grid adaptation approach is then integrated with the RBF-based central scheme. Effects of condition numbers of RBFs, computational complexity and cost of the proposed scheme are studied. Finally, different 1-D coupled thermoelasticity benchmarks are presented. There, perfonnance of the adaptive RBF-based formulation is compared with that of the adaptive Kurganov-Tadmor (KT) second-order central high-resolution scheme with the total variation diminishing (TVD) property.

Effect of Initial Grain Size on the Hot Deformation Behavior and Microstructural Evolution of Pure Copper

The influences of initial grain size(IGS)with 20μm and 50μm on the hot flow behavior and microstructural changes of pure copper were investigated using hot compression tests at a temperature range of 623–1073 K and strain rate range of 0.001–0.1 s^(-1).The effects of critical stress and corresponding critical strain were studied based on the internal and external processing parameters.The critical stress and strain decreased with increasing temperature and decreasing strain rate.The investigation results of the microstructure and true strain–stress diagrams showed that dynamic recovery,dynamic recrystallization(DRX),and twinning mechanisms were caused during the hot deformation of pure copper.Microstructure evolution indicated some DRXed fine-grain took place around grain boundary of hot deformed samples with IGS of 20μm whereas DRXed fine-grain took place in interior grains for samples with larger IGS.The results also showed that grain growth is also dependent on IGS as the grain growth rate for samples with the larger IGS is greater than the smaller IGS.The critical strain rate and the temperature were obtained at 0.01 s^(-1) and 973 K,respectively,for the sudden change in the grain growth rate.Also,twinning highly depended on IGS which almost did not happen in fine grain size while the volume fraction of twinning increased with increasing grain size.

A multiscale material model for heterogeneous liquid droplets in solid soft composites

Liquid droplets in solid soft composites have been attracting increasing attention in biological applications.In contrary with conventional composites,which are made of solid elastic inclusions,available material models for composites including liquid droplets are for highly idealized configurations and do not include all material real parameters.They are also all deterministic and do not address the uncertainties arising from droplet radius,volume fraction,dispersion and agglomeration.This research revisits the available models for liquid droplets in solid soft composites and presents a multiscale computational material model to determine their elastic moduli,considering nearly all relevant uncertainties and heterogeneities at different length scales.The effects of surface tension at droplets interface,their volume fraction,size,size polydispersity and agglomeration on elastic modulus,are considered.Different micromechanical material models are incorporated into the presented computational framework.The results clearly indicate both softening and stiffening effects of liquid droplets and show that the model can precisely predict the effective properties of liquid droplets in solid soft composites.

Regenerative energy management of electric drive based on Lyapunov stability theorem

In recent years, urban rail systems have developed drastically. In these systems, when induction electrical machine suddenly brakes, a great package of energy is produced. This package of energy can be stored in energy storage devices such as battery, ultra-capacitor and flywheel. In this paper, an electrical topology is proposed to absorb regenerative braking energy and to store it in ultracapacitor and battery.Ultra-capacitor can deliver the stored energy to DC grid and charge the battery for auxiliary applications such as lighting and cooling systems The proposed system is modeled based on large signal averaged modeling, which leads to the simplicity of calculations. The control system is based on Lyapunov stability theorem which guarantees system stability. Also, an energy management algorithm is proposed to control energy under braking and steady-state conditions. Finally,the simulation results validate the effectiveness of the proposed control and energy management system.

A Study on Flame Forming of Bowl Shaped Surface with Various Spiral Irradiating Schemes

In this paper, various strategies of spiral irradiating scheme for the flame forming of a bowl shaped surface are investigated experimentally and numerically. Experimental work is performed using a flame torch integrated with a 2-axis CNC workstation. The ABAQUS implicit solver is used in the numerical simulation. Three different strategies of the spiral irradiating scheme are investigated for the flame forming of a bowl shaped surface. The first strategy is the Simple spi- ral irradiating scheme, the second is the Rotational spiral irradiating scheme, and the third is the Symmetrical-Rotational spiral irradiating scheme. The results show that using the Symmetrical- Rotational spiral irradiating scheme, a bowl shaped surface with the maximum deformation can be produced, followed by using the Rotational scheme, and the Simple spiral scheme. It is also concluded from the results that the spiral irradiating scheme with Symmetrical-Rotational, Rota- tional and Simple spiral schemes lead to the maximum symmetries in the produced bowl shaped surface, respectively. All the numerical results are in good agreement with the experimental ob- servations.

Response of a spherical cavity in a fully-coupled thermo-poro-elastodynamic medium by cell-adaptive second-order central high resolution schemes

In this study,fully coupled thermo-poroelastic saturated media are simulated by a grid/cell adaptive central high resolution scheme.The central method corresponds to the second order Kurganov-Tadmor(KT)scheme working on adapted cells with the total variation diminishing(TVD)stability condition.The coupled equations include motion,fluid flow,heat flow,continuity condition,and a constitutive equation.The grid/cell adaptation is performed by the interpolating wavelet transform in the multiresolution framework to capture fine scale responses and to obtain a computationally effective solver.With respect to the use of central schemes,the coupled equations should be re-expressed as a system of coupled first-order hyperbolic-parabolic partial differential equations(PDEs)with possible source(load)terms.The system is initially derived in the Cartesian coordinate system,and it is subsequently modified to consider a spherical cavity in isotropic,symmetric,and saturated media in the spherical coordinate system.It is assumed that the cavity boundary is subjected to sudden time-dependent thermal/mechanical sources.Discontinuous propagating fronts develop in the media due to the aforementioned loading.It is challenging to handle these solutions with numerical methods,and special attention is required to prevent/control numerical dispersion and dissipation.Hence,as previously mentioned,adaptive central high resolution schemes are employed in the present study.

Probabilistic day-ahead simultaneous active/reactive power management in active distribution systems

Distributed generations(DGs)are main components for active distribution networks(ADNs).Owing to the large number of DGs integrated into distribution levels,it will be essential to schedule active and reactive power resources in ADNs.Generally,energy and reactive power scheduling problems are separately managed in ADNs.However,the separate scheduling cannot attain a global optimum scheme in the operation of ADNs.In this paper,a probabilistic simultaneous active/reactive scheduling framework is presented for ADNs.In order to handle the uncertainties of power generations of renewable-based DGs and upstream grid prices in an efficient framework,a stochastic programming technique is proposed.The stochastic programming can help distribution system operators(DSOs)make operation decisions in front of existing uncertainties.The proposed coordinated model considers the minimization of the energy and reactive power costs of all distributed resources along with the upstream grid.Meanwhile,a new payment index as loss profit value for DG units is introduced and embedded in the model.Numerical results based on the 22-bus and IEEE33-bus ADNs validate the effectiveness of the proposed method.The obtained results verify that through the proposed stochastic-based power management system,the DSO can effectively schedule all DGs along with its economic targets while considering severe uncertainties.

A Sliding Mode Controller Based on Robust Model Reference Adaptive Proportional-integral Control for Stand-alone Three-phase Inverter

This paper proposes a sliding mode controller based on robust model reference adaptive proportional-integral(RMRA-PI)control for a stand-alone voltage source inverter(SA-VSI).The proposed controller has two control loops where the coefficients of PI controller are regulated by the adaptive sliding law.This method is used to regulate the output voltage of the inverter under different load conditions and uncertainty,and adapts the output to the reference model to reduce the total harmonic distortion(THD).In this paper,the stability of the proposed controller is proven by using Lyapunov's theory and Barbalet’s lemma.The proposed controller performs well in voltage regulation such as low THD under sudden load change and uncertainty.Also,the results of the proposed controller are compared with PI controller to show the effectiveness of the presented control system.