Machine learning in mechanics

Machine learning has attracted much attention in various fields of mechanics. It can represent high-dimensional complex nonlinear systems and has powerful optimization algorithms. So far, machine learning has achieved much success in various mechanical simulation problems, including reconstruction and reduced-order modeling of complex mechanical systems, turbulence modeling and simulation, aerodynamic optimization design for wings, flow control,etc.

苹果机械化采收发展历程、模式及其技术现状

经过近千年的进化发展,苹果伴随着品种及树形的改良,经历从自然熟落到人工采摘,从辅助工具、辅助收获平台、振动捡拾到智能机器人采收的发展历程及相应的不同的机械化作业模式。介绍苹果机械化采收的发展历程及技术现状、不同收获模式下所使用的机具设备以及不同收获模式所应用的场景与条件,为我国苹果主产区因地制宜地选择适合当地苹果收获作业模式提供借鉴。如人工或机器人采摘适用于苹果鲜售市场,非选择性振动捡拾收获方式适用于苹果的二次加工领域;而为提高机器人的作业效率,需要对苹果树的树形进行结构简化改良,需要考虑农机与栽培农艺的结合。

Effect of boundary conditions on shakedown analysis of heterogeneous materials

The determination of the ultimate load-bearing capacity of structures made of elastoplastic heterogeneous materials under varying loads is of great importance for engineering analysis and design. Therefore, it is necessary to accurately predict the shakedown domains of these materials. The static shakedown theorem, also known as Melan's theorem, is a fundamental method used to predict the shakedown domains of structures and materials. Within this method, a key aspect lies in the construction and application of an appropriate self-equilibrium stress field(SSF). In the structural shakedown analysis, the SSF is typically constructed by governing equations that satisfy no external force(NEF) boundary conditions. However, we discover that directly applying these governing equations is not suitable for the shakedown analysis of heterogeneous materials. Researchers must consider the requirements imposed by the Hill-Mandel condition for boundary conditions and the physical significance of representative volume elements(RVEs). This paper addresses this issue and demonstrates that the sizes of SSFs vary under different boundary conditions, such as uniform displacement boundary conditions(DBCs), uniform traction boundary conditions(TBCs), and periodic boundary conditions(PBCs). As a result, significant discrepancies arise in the predicted shakedown domain sizes of heterogeneous materials. Built on the demonstrated relationship between SSFs under different boundary conditions, this study explores the conservative relationships among different shakedown domains, and provides proof of the relationship between the elastic limit(EL) factors and the shakedown loading factors under the loading domain of two load vertices. By utilizing numerical examples, we highlight the conservatism present in certain results reported in the existing literature. Among the investigated boundary conditions, the obtained shakedown domain is the most conservative under TBCs.Conversely, utilizing PBCs to construct an SSF for the shakedown analysis leads to less conservative lower bounds, indicating that PBCs should be employed as the preferred boundary conditions for the shakedown analysis of heterogeneous materials.

A Measurement Study of the Ethereum Underlying P2P Network

This work carried out a measurement study of the Ethereum Peer-to-Peer(P2P)network to gain a better understanding of the underlying nodes.Ethereum was applied because it pioneered distributed applications,smart contracts,and Web3.Moreover,its application layer language“Solidity”is widely used in smart contracts across different public and private blockchains.To this end,we wrote a new Ethereum client based on Geth to collect Ethereum node information.Moreover,various web scrapers have been written to collect nodes’historical data fromthe Internet Archive and the Wayback Machine project.The collected data has been compared with two other services that harvest the number of Ethereumnodes.Ourmethod has collectedmore than 30% more than the other services.The data trained a neural network model regarding time series to predict the number of online nodes in the future.Our findings show that there are less than 20% of the same nodes daily,indicating thatmost nodes in the network change frequently.It poses a question of the stability of the network.Furthermore,historical data shows that the top ten countries with Ethereum clients have not changed since 2016.The popular operating system of the underlying nodes has shifted from Windows to Linux over time,increasing node security.The results have also shown that the number of Middle East and North Africa(MENA)Ethereum nodes is neglected compared with nodes recorded from other regions.It opens the door for developing new mechanisms to encourage users from these regions to contribute to this technology.Finally,the model has been trained and demonstrated an accuracy of 92% in predicting the future number of nodes in the Ethereum network.

A gated recurrent unit model to predict Poisson’s ratio using deep learning

Static Poisson’s ratio(vs)is crucial for determining geomechanical properties in petroleum applications,namely sand production.Some models have been used to predict vs;however,the published models were limited to specific data ranges with an average absolute percentage relative error(AAPRE)of more than 10%.The published gated recurrent unit(GRU)models do not consider trend analysis to show physical behaviors.In this study,we aim to develop a GRU model using trend analysis and three inputs for predicting n s based on a broad range of data,n s(value of 0.1627-0.4492),bulk formation density(RHOB)(0.315-2.994 g/mL),compressional time(DTc)(44.43-186.9 μs/ft),and shear time(DTs)(72.9-341.2μ s/ft).The GRU model was evaluated using different approaches,including statistical error an-alyses.The GRU model showed the proper trends,and the model data ranges were wider than previous ones.The GRU model has the largest correlation coefficient(R)of 0.967 and the lowest AAPRE,average percent relative error(APRE),root mean square error(RMSE),and standard deviation(SD)of 3.228%,1.054%,4.389,and 0.013,respectively,compared to other models.The GRU model has a high accuracy for the different datasets:training,validation,testing,and the whole datasets with R and AAPRE values were 0.981 and 2.601%,0.966 and 3.274%,0.967 and 3.228%,and 0.977 and 2.861%,respectively.The group error analyses of all inputs show that the GRU model has less than 5% AAPRE for all input ranges,which is superior to other models that have different AAPRE values of more than 10% at various ranges of inputs.

Effects of friction stir processing and nano-hydroxyapatite on the microstructure,hardness,degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications

Nowadays,magnesium alloys are emerging in biomedical implants for their similar properties to natural bones.However,the rapid degradation of magnesium alloys in biological media hinders successful implantation.Refinement of microstructure,as well as reinforcement particles can significantly improve the degradation rate.In this work,multi-pass friction stir processing(FSP)was proposed to synthesize WE43/nano-hydroxyapatite(n HA)surface composite,the microstructure,reinforced particle distribution,micro-hardness,corrosion behavior and in-vitro bioactivity were studied.The subsequent FSP passes of WE43 alloy and WE43/n HA composite refined the grain size which was reduced by 94.29%and 95.92%(2.63 and 1.88μm,respectively)compared to base metal after three passes.This resulted in increasing the microhardness by 120%(90.86 HV0.1)and 135%(105.59 HV0.1)for the WE43 and WE43-n HA,respectively.It is found that increasing FSP passes improved the uniform distribution of n HA particles within the composite matrix which led to improved corrosion resistance and less degradation rate.The corrosion rate of the FSPed WE43/n HA composite after three passes was reduced by 38.2%(4.13 mm/year)and the degradation rate was reduced by 69.7%(2.87 mm/y).This is attributed to secondary phase(Mg24Y5and Mg41Nd5)particle fragmentation and redistribution,as well as a homogeneous distribution of n HA.Additionally,the growing Ca-P and Mg(OH)2layer formed on the surface represented a protective layer that reduced the degradation rate.The wettability test revealed a relatively hydrophilic surface with water contact angle of 49.1±2.2°compared to 71.2±2.1°for base metal.Also,biomineralization test showed that apatite layer grew after immersion 7d in simulated body fluid with atomic ratio of Ca/P 1.60 approaching the stoichiometric ratio(1.67)indicating superior bioactivity of FSPed WE43/n HA composite after three passes.These results raise that the grain refinement by FSP and introduction of n HA particles significantly improved the degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications.

Optimizing a Transportation System Using Metaheuristics Approaches (EGD/GA/ACO): A Forest Vehicle Routing Case Study

The large-scale optimization problem requires some optimization techniques, and the Metaheuristics approach is highly useful for solving difficult optimization problems in practice. The purpose of the research is to optimize the transportation system with the help of this approach. We selected forest vehicle routing data as the case study to minimize the total cost and the distance of the forest transportation system. Matlab software helps us find the best solution for this case by applying three algorithms of Metaheuristics: Genetic Algorithm (GA), Ant Colony Optimization (ACO), and Extended Great Deluge (EGD). The results show that GA, compared to ACO and EGD, provides the best solution for the cost and the length of our case study. EGD is the second preferred approach, and ACO offers the last solution.

Simulation of Steel Reinforcement on the Nonlinear Behaviour of Slender Glulam Beam Columns by Using the Newton-Raphson Method

The current theory in NF EN 1995-1-1/NA of Eurocode 5, which is based on maximum deflection, has been investigated on softwoods. Therefore, this theory is not adapted for slender glulam beam columns made of tropical hardwood species from the Congo Basin. This maximum deflection is caused by a set of loads applied to the structure. However, Eurocode 5 doesn’t provide how to predict this deflection in case of long-term load for such structures. This can be done by studying load-displacement (P-Δ) behaviour of these structures while taking into account second order effects. To reach this goal, a nonlinear analysis has been performed on a three-dimensional beam column embedded on both ends. Since conducting experimental investigations on large span structural products is time-consuming and expensive especially in developing countries, a numerical model has been implemented using the Newton-Raphson method to predict load-displacement (P-Δ) curve on a slender glulam beam column made of tropical hardwood species. On one hand, the beam has been analyzed without wood connection. On the other hand, the beam has been analyzed with a bolted wood connection and a slotted-in steel plate. The load cases considered include self-weight and a uniformly applied long-term load. Combinations of serviceability limit states (SLS) and ultimate limit states (ULS) have also been considered, among other factors. A finite-element software RFEM 5 has been used to implement the model. The results showed that the use of steel can reduce displacement by 20.96%. Additionally, compared to the maximum deflection provided by Eurocode 5 for softwoods, hardwoods can exhibit an increasing rate of 85.63%. By harnessing the plastic resistance of steel, the bending resistance of wood can be increased by 32.94%.

Overall Assessment of Heat Transfer for a Rarefied Flow in a Microchannel with Obstacles Using Lattice Boltzmann Method

The objective of this investigation is to assess the effect of obstacles on numerical heat transfer and fluid flow momentum in a rectangular microchannel(MC).Two distinct configurations were studied:one without obstacles and the other with alternating obstacles placed on the upper and lower walls.The research utilized the thermal lattice Boltzmann method(LBM),which solves the energy and momentum equations of fluids with the BGK approximation,implemented in a Python coding environment.Temperature jump and slip velocity conditions were utilized in the simulation for the MC and extended to all obstacle boundaries.The study aims to analyze the rarefaction effect,with Knudsen numbers(Kn)of 0.012,0.02,and 0.05.The outcomes indicate that rarefaction has a significant impact on the velocity and temperature distribution.The presence of nine obstacles led to slower fluid movement inside the microchannel MC,resulting in faster cooling at the outlet.In MCs with obstacles,the rarefaction effect plays a crucial role in decreasing the Nusselt number(Nu)and skin friction coefficient(Cf).Furthermore,the study demonstrated that the obstacles played a crucial role in boosting fluid flow and heat transfer in the MC.The findings suggest that the examined configurations could have potential applications as cooling technologies in micro-electro-mechanical systems and microdevice applications.

Development Program of Chemical Industry Based Computer Assisted Instruction for Students of Industrial Engineering Department in Indonesia

This study aims to improve the competence of students of the Department of Industrial Engineering in Indonesia in the subject of Chemical Industry, in particular through the model-based teaching materials CAI (Computer Assisted Instruction) in the form of an interactive CD. In particular, the study was carried out for the purposes of: 1) designing and developing models of devices based learning CAI (Computer Assisted Instruction) systematically in prototype form, 2) producing an interactive CD as a model learning devices Chemical Industry based CAI (Computer Assisted Instruction) to improve the competence of students of the Department of Industrial Engineering in Industrial chemistry courses. The benefits of this research are: 1) for the government, the results of this study can be used as a reference in implementing educational policies, especially to enhance the nation’s competitiveness in the era of informatics;and 2) for the Department of Industrial Engineering in Indonesia, the results of this research can be used to enhance learning that can improve the competence of students in the subject of Chemical Industry, which in turn can be passed with high achievement. Products produced in the first year are a design-based teaching materials CAI (Computer Assisted Instruction) in prototype form, with the following steps: 1) pre- production which includes needs analysis, identifying and analyzing the needs based on the content of curriculum and learning model based CAI (Computer Assisted Instruction), the development of a concept related to Chemical Industry, the development of multimedia content that includes developing materials, animation, and evaluation related to industrial chemicals, gathering material to make the recording sound, shooting, and editing with regard to the development of teaching materials chemical Industry based CAI (Computer Assisted Instruction), as well as developing the storyboard as the layout of the multimedia contents by involving experts multimedia;2) production process that includes design/design and conduct of programming a prototype which means at this stage of the design and development of teaching materials based CAI (Computer Assisted Instruction);and 3) post-production which includes the evaluation justification experts, conducted trials on stakeholders, being revised based on input from experts, and doing packing and labeling.

近β型钛合金线性摩擦焊接头变形行为及组织演变的热物理模拟

为了更好地理解近β型钛合金线性摩擦焊(LFW)接头的界面连接行为,采用热压缩物理模拟的方法,以TB2近β型钛合金为研究材料,设计符合LFW工艺特点的帽形热压缩试样,在不同下压量、变形温度及应变速率条件下进行热压缩试验,研究热压缩接头的变形行为及组织演变。结果表明,热压缩过程中热压缩接头连接区(BZ)的峰值剪切应力随变形温度的降低及应变速率的增加而增大,接头BZ的宽度随变形温度和应变速率的增加而减小。接头BZ边缘由沿剪切方向变形的晶粒组成,接头BZ中心由细小的等轴再结晶晶粒组成。接头的动态再结晶机制为连续动态再结晶(CDRX),且CDRX的程度随下压量、变形温度及应变速率的增加而增大。此外,在界面剪切力的作用下接头BZ边缘形成{112}[111]织构,接头BZ中心形成{110}[001]织构。

Improved Staggered Algorithm for Phase-Field Brittle Fracture with the Local Arc-Length Method

The local arc-length method is employed to control the incremental loading procedure for phase-field brittle fracture modeling.An improved staggered algorithm with energy and damage iterative tolerance convergence criteria is developed based on the residuals of displacement and phase-field.The improved staggered solution scheme is implemented in the commercial software ABAQUS with user-defined element subroutines.The layered system of finite elements is utilized to solve the coupled elastic displacement and phase-field fracture problem.A one-element benchmark test compared with the analytical solution was conducted to validate the feasibility and accuracy of the developed method.Our study shows that the result calculated with the developed method does not depend on the selected size of loading increments.The results of several numerical experiments show that the improved staggered algorithm is efficient for solving the more complex brittle fracture problems.

Pre-research on Enhanced Heat Transfer Method for Special Vehicles at High Altitude Based on Machine Learning

The performance of an integrated thermal management system signi?cantly in?uences the stability of special-purpose vehicles;thus,enhancing the heat transfer of the radiator is of great signi?cance.Common research methods for radiators include?uid mechanics numerical simulations and experimental measurements,both of which are time-consuming and expensive.Applying the surrogate model to the analysis of the?ow and heat transfer in louvered?ns can effectively reduce the computational cost and obtain more data.A simpli?ed louvered-?n heat transfer unit was established,and computational?uid dynamics(CFD)simulations were conducted to obtain the?ow and heat transfer characteristics of the geometric structure.A three-factor and six-level orthogonal design was established with three structural parameters:angleθ,length a,and pitch L_p of the louvered?ns.The results of the orthogonal design were subjected to a range analysis,and the effects of the three parametersθ,a,and L_p on the j,f,and JF factors were obtained.Accordingly,a proxy model of the heat transfer performance for louvered?ns was established based onthe arti?cial neural network algorithm,and the model was trained with the data obtained by the orthogonal design.Finally,the?n structure with the largest JF factor was realized.Compared with the original model,the optimizedmodel improved the heat transfer factor j by 2.87%,decreased the friction factor f by 30.4%,and increased the comprehensive factor JF by 15.7%.

钴钒水滑石纳米片用于电催化尿素氧化

电解水是一种常用的制氢方法,但高能耗的阳极析氧反应(OER)阻碍了其应用。尿素氧化反应(UOR)具有较低的热力学电势,是最有前景的OER替代反应之一。过渡金属基水滑石具有独特的层状结构和层间阴离子可交换等优点,被认为是性能优异的UOR催化剂,然而目前大多数研究主要聚焦于后过渡金属元素。该研究通过一步法制备了具有前/后过渡金属的CoV-LDHs纳米片。与相同方法制备的Co(OH)_(2)相比,CoV-LDHs纳米片具有以下优点:1)纳米片结构有利于暴露更多的活性位点。2)V的引入增强了CoV-LDHs的亲水性,提高了其本征电催化动力学。3)Co(3d^(7)4s^(2))和V(3d^(3)4s^(2))之间的d-电子补偿效应有利于促进尿素的吸附。因此,CoV-LDHs仅需要1.52 V(vs.RHE)就可以达到10 mA·cm^(−2)的电流密度,比Co(OH)_(2)低了70 mV,同时CoV-LDHs较低的塔菲尔斜率表明了其较快的反应动力学。此外,CoV-LDHs在连续反应10 h后,驱动电位几乎没有增加,表明其具有良好的稳定性。该研究结果不仅证明了前/后过渡金属之间的d-电子补偿效应可以提高UOR催化性能,还为设计高效的UOR催化剂提供了可行的途径。

Tribological Performance of Different Concentrations of Al_(2)O_(3)Nanofluids on Minimum Quantity Lubrication Milling

Nanofluid minimum quantity lubrication(NMQL)is a green processing technology.Cottonseed oil is suitable as base oil because of excellent lubrication performance,low freezing temperature,and high yield.Al_(2)O_(3)nanoparticles improve not only the heat transfer capacity but also the lubrication performance.The physical and chemical proper-ties of nanofluid change when Al_(2)O_(3)nanoparticles are added.However,the effects of the concentration of nanofluid on lubrication performance remain unknown.Furthermore,the mechanisms of interaction between Al_(2)O_(3)nanoparti-cles and cottonseed oil are unclear.In this research,nanofluid is prepared by adding different mass concentrations of Al_(2)O_(3)nanoparticles(0,0.2%,0.5%,1%,1.5%,and 2%wt)to cottonseed oil during minimum quantity lubrication(MQL)milling 45 steel.The tribological properties of nanofluid with different concentrations at the tool/workpiece interface are studied through macro-evaluation parameters(milling force,specific energy)and micro-evaluation parameters(surface roughness,micro morphology,contact angle).The result show that the specific energy is at the minimum(114 J/mm^(3)),and the roughness value is the lowest(1.63μm)when the concentration is 0.5 wt%.The surfaces of the chip and workpiece are the smoothest,and the contact angle is the lowest,indicating that the tribological proper-ties are the best under 0.5 wt%.This research investigates the intercoupling mechanisms of Al_(2)O_(3)nanoparticles and cottonseed base oil,and acquires the optimal Al_(2)O_(3)nanofluid concentration to receive satisfactory tribological properties.

工业负荷可持续并网太阳能光伏的可行性评价

可再生能源发电因其间歇性而具有多变性,对发展中国家来说,可再生能源发电的成本很高。由于电价定价和机制设计不合理,上网电价和净计量等支持性政策和方案对消费者也没有太大吸引力。屋顶太阳能光伏系统自用技术可以避免这些方案的缺点,因为这种技术比公用电网的发电成本更低。因此,产消者可以以最低价格使用大部分电力,更具吸引力。本文分析了并网工业太阳能光伏发电系统的成本和可行性。结果发现,基于储能并网的光伏系统成本为0.0086$/(kW·h),公用电网将以0.062$/(kW·h)的价格出售给产消者,与使用时间评级模型相比,年能源成本将降低35.23%。此外,所提出的方案可满足96%的年能源需求,保证了供应的安全性,所提出的模型可用于其他发展中国家。

Novel Analysis of Two Kinds Hybrid Models in Ferro Martial Inserting Variable Lorentz Force Past a Heated Disk:An Implementation of Finite Element Method

In this article,the rheology of Ferro-fluid over an axisymmetric heated disc with a variable magnetic field by considering the dispersion of hybrid nanoparticles is considered.The flow is assumed to be produced by the stretching of a rotating heated disc.The contribution of variable thermophysical properties is taken to explore themomentum,mass and thermal transportation.The concept of boundary layermechanismis engaged to reduce the complex problem into a simpler one in the form of coupled partial differential equations system.The complex coupled PDEs are converted into highly nonlinear coupled ordinary differential equations system(ODEs)and the resulting nonlinear flow problem is handled numerically.The solution is obtained via finite element procedure(FEP)and convergence is established by conducting the grid-independent survey.The solution of converted dimensionless problem containing fluid velocity,temperature and concentration field is plotted against numerous involved emerging parameters and their impact is noted.From the obtained solution,it is monitored that higher values of magnetic parameter retard the fluid flow and escalating values of Eckert number results in to enhance temperature profile.Ferro-fluid flow and heat energy for the case of the Yamada Ota hybrid model are higher than for the case of the Hamilton Crosser hybrid model.Developing a model is applicable to the printing process,electronic devices,temperature measurements,engineering process and food-making process.The amount of mass species is reduced vs.incline impacts of chemical reaction and Schmidt parameter.

熔融和辐射对垂直多孔嵌入微通道MHD混合对流换热的影响

研究了导电和非导电两种壁型多孔微通道的熔融和滑移效应对混合对流换热的影响。采用高阶常微分非线性耦合模型,研究了横向磁场作用下流体在微通道内注入和喷出的流动力学。这些都是在通过相似变换完成的。采用解析解的同伦摄动方法对控制热流体输运的力学模型进行了分析,并利用已有文献在简单条件下进行了验证并得到满意的结果。研究了流体输送过程中传热流变参数的影响,以提高系统运行效率,降低能耗,从而最大限度地降低成本。结果表明,熔体和辐射对热边界层的共同作用使热边界层的厚度逐渐减小。当辐射参数(R)在1<R<5范围内增加时,微通道中板处的热廓线从−0.4804减小到−1.3081。该研究为磁流体动力学熔融金属和熔盐泵以及其他实应用提供参考。

Vegetable Oil-Based Nanolubricants in Machining:From Physicochemical Properties to Application

Cutting fluid is crucial in ensuring surface quality and machining accuracy during machining.However,traditional mineral oil-based cutting fluids no longer meet modern machining’s health and environmental protection require-ments.As a renewable,pollution-free alternative with excellent processing characteristics,vegetable oil has become an inevitable replacement.However,vegetable oil lacks oxidation stability,extreme pressure,and antiwear proper-ties,which are essential for machining requirements.The physicochemical characteristics of vegetable oils and the improved methods’application mechanism are not fully understood.This study aims to investigate the effects of viscosity,surface tension,and molecular structure of vegetable oil on cooling and lubricating properties.The mechanisms of autoxidation and high-temperature oxidation based on the molecular structure of vegetable oil are also discussed.The study further investigates the application mechanism and performance of chemical modification and antioxidant additives.The study shows that the propionic ester of methyl hydroxy-oleate obtained by epoxidation has an initial oxidation temperature of 175℃.The application mechanism and extreme pressure performance of conventional extreme pressure additives and nanoparticle additives were also investigated to solve the problem of insufficient oxidation resistance and extreme pressure performance of nanobiological lubricants.Finally,the study discusses the future prospects of vegetable oil for chemical modification and nanoparticle addition.The study provides theoretical guidance and technical support for the industrial application and scientific research of vegetable oil in the field of lubrication and cooling.It is expected to promote sustainable development in the manufacturing industry.

选择性激光熔化17-4 PH不锈钢零件的参数化研究和表征

本文对选择性激光熔化的17-4 PH不锈钢进行了参数化研究和表征。通过改变工艺参数包括激光功率和扫描速度以及扫描方式(设计参数)来研究试样的相对密度和显微硬度的变化。当使用中等能量密度和内外六角扫描方式时,试样的相对密和显微硬度最大;当使用低能量密度和交替带状扫描方式时,试样的相对密和显微硬度最小。在光学和扫描电子显微组织中,试样侧面有奥氏体、铁素体和小熔池。能量色散光谱分析表明,试样的化学成分变化导致相对密度和显微硬度发生变化。X射线衍射结果表明,中等能量密度试样的奥氏体相和铁素体峰强度最高。背散射电子衍射结果表明,随着能量密度的增加,奥氏体相增加,导致试样的显微硬度变化。相比于中等能密度试样,低能量密度试样易诱发更多的残余应力。采用不同能量密度得到的样品都具有较强的耐蚀性(0.05 mm/a),未出现明显的腐蚀裂纹。