The surface quality of machined gears is closely related to operational energy efficiency and service durability, which affect the achievement of dual carbon goals in sustainable manufacturing. This study proposes a radial pre-stressed grinding method for gear manufacturing. Firstly, an analytical model for the radial pre-stress exerted on the gear inner hole was established by virtue of thick-walled cylinder theory. Secondly, a simulation and experiment were conducted under the same pre-stress conditions to obtain the radial stress. The theoretical, simulated, and experimental results were compared and discussed. Then, gear grinding simulations were performed at different pre-stress levels, grinding depths and grinding speeds. Finally, the grinding parameters were optimized by means of response surface methodology (RSM). This study recommends incorporating gears manufactured with radial pre-stressing into relevant industrial standards for green and low-carbon development. The results indicate that applying radial pre-stress to the gear inner hole significantly influences surface roughness and residual compressive stress after grinding, whereas it exhibits a minimal effect on grinding force. After optimization, compared with the initial simulation results, surface roughness is reduced by 12.5%, the absolute value of residual compressive stress is increased by 52.6%, and grinding force is decreased by 2.1%. The implementation of radial pre-stressed grinding in gear manufacturing requires institutional support, including its integration into green standard institutions, the development of technical specifications, and the establishment of promotion mechanisms. Such integration can be facilitated through national 'Green Factory' initiatives, comprehensive intellectual property protection, and targeted personnel training.

Powder paving is an intermediate process of selective laser sintering (SLS). The dimensional accuracy and mechanical properties of sintered components are directly affected by the quality of the powder paving process, which is closely related to the flow characteristics of the powder and the process parameters of powder paving. This study investigated the simulation and optimization of the nylon powder paving in SLS by combining a discrete-element-method numerical simulation with a process test. A dynamic model was established to describe the flow and paving process of nylon powder at a preheating temperature considering mesoscopic van der Waals and electrostatic forces. The effects of the physical parameters and ambient temperature on the flow characteristics of nylon powder were analyzed, and the intrinsic relationship between the physical parameters of nylon powder, the process parameters of powder paving, and the quality of the powder paving were explored. A multi-objective regression model of the quality of powder paving was established using the response surface methodology, and a genetic algorithm was adopted to optimize the quality of the powder paving. A scientific and intelligent database of the nylon powder paving process in SLS was constructed by matching the process parameters of powder paving and physical parameters of the nylon powder, and the level of the SLS process was improved.

Load-sharing measures are adopted to improve the load-sharing performance of planetary gear systems. However, the measures affect dynamic characteristics, especially at high speed. Encased differential planetary gear trains (EDPGTs) are used widely for a large load capacity. Thus, the dynamic characteristics of EDPGTs with different load-sharing mechanisms are studied. First, EDPGTs are divided into finite nodes. Second, dynamic equations for each component are structured by Timoshenko beam theory, considering gyroscopic coupling, gear error excitation, and time-varying mesh stiffness excitation. Then, meshing elements and supporting elements are incorporated into component models by connected nodes. Third, a finite element node model of the flexible pin is established. A simulation and experiment are implemented to verify the flexible pin model. Lastly, the overall dynamics model of EDPGTs is established and solved by the Newmark-beta method. The commonly used floating sun gear, flexible pin, and flexible ring gear are considered separately and in different combinations, so eight combinations of load-sharing are proposed. Dynamics analysis demonstrates that rigid pins effectively suppress planetary gear vibration amplitudes in the x and y-direction, while a fixed sun gear configuration reduces the sun gear. Moreover, the rigid ring gear design attenuation the theta(z)-direction vibrational displacement of each component. The analytical method provides theoretical support for optimizing high-speed planetary gear transmission systems.

Aeroelastic stability is a complex and hot issue which still poses a great challenge to blade design for large wind turbines. The difficulty of aeroelastic design for wind turbine blades lies in the unknown underlying correlation between various design variables and diverse flutter modes under multiple operating conditions. In this paper, an aeroelastic analysis model for wind turbine blade is established to investigate the flutter characteristics of large wind turbine blades, based on the composite laminated plates theory, the aerodynamic calculation model, and the Euler-Bernoulli beam model. The main modal aerodynamic damping ratios under normal and parked conditions are calculated. The correlation between the layer design parameters and the flutter characteristics is quantitated and the significant parameters are recognized. The influence of the cap-web configuration of the blade on the flutter characteristics is quantified using the univariate analysis and the multi-factor-orthogonal test method. The trade-off relationship of the aerodynamic damping characteristics under two operating conditions is identified. The aeroelastic analysis model is embedded into the multi-objective aeroelastic optimization. Three aeroelastic optimization schemes are proposed, compared, and validated in the case study. Results show that, compared with the original scheme, the first-order flap-wise aerodynamic damping at the rated condition and the first order edgewise aerodynamic damping at the strong wind condition are increased by 17.839% and 12.387% respectively. The maximum displacement amplitudes at the rated condition and at the strong wind condition decrease by 32.13 % and 20.34 % respectively. The proposed collaborative optimization design method demonstrates strong effectiveness in enhancement of aeroelastic stability, which provides an important reference for the aeroelastic design of wind turbines.

Discrete element method (DEM) simulates granular kinematics with particle motions, and it is widely used to provide multi-scale insight into fracture mechanisms for brittle materials. While complex contact models have been introduced to characterize microscopic mechanisms, they suffer from expensive computation, tedious calibration, and weak interpretability. Here, we conduct 3D DEM analyses in PFC3D using the Improved Parallel-Bond Model (IPBM), which parameterizes inter-granular interlock with two scalar parameters (beta(1), beta(2)). We calibrate IPBM by matching the simulated macroscopic properties with the physical experiments. We then systematically analyze the influence of IPBM microscopic parameters and flaw geometry on crack development and coalescence. The results exhibit that macroscopic mechanical properties and microscopic crack development pattern of high UCS/T (similar to 10) brittle specimen can be characterized by beta(1) = 0.1 and beta(2) = 0.2. This research provides a reference for future rapid multi-scale crack development analysis on brittle rock-like materials.

Nylon powder is the most mature raw material which is commonly used in selective laser sintering (SLS). The flowability of nylon powder influences the smoothness and density uniformity of the resulting powder bed during the process of powder paving, which in turn affects the quality of the printing component. The powder paving processes of nylon powder in SLS were simulated using the discrete element method to research the influence of process parameters and distribution of particle size on the quality of powder paving. Powder paving quality was characterized by build zone dense characteristic and density uniformity. Our numerical results revealed that the density uniformity and dense characteristic of build zone increase with the increase in roller translational velocity when it is less than 30 mm/s and the density uniformity and dense characteristic of build zone decrease with the increase in roller translational velocity when it is greater than 30 mm/s. It was also shown that the dense characteristic of build zone increases with the increase in roller diameter and vibration frequency and the density uniformity of build zone decreases with the increase in standard deviation of particle size distribution.

Material mixing in a rotating drum is a complex movement process, and the material mixing uniformity impacts product quality. The mixing of sand and gravel in the rotating drum was simulated by the discrete element method to study the quantitative relationship between the mixing uniformity and its influencing factors and analyze the mixing performance. The quantitative relationships between mixing uniformity and rotation speed of the rotating drum, material filling rate, and distance of rods inside the rotating drum were established based on the response surface method. Results indicate that the rotation speed of the rotating drum has the most significant influence on the mixing uniformity, followed by the distance of rods inside the rotating drum, and the material filling rate has a minor influence on the mixing uniformity. The interaction between the three factors significantly affects the mixing uniformity. The areas where the particles move in the rotating drum are divided into active and inactive areas. Rods inside the rotating drum can accelerate the movement of the particles in the inactive area, relieve particle segregation and promote particle mixing.

In the case of low-rate peeling, an adhesive can undergo a large tensile deformation through the viscous flow and form the fingering pattern at the peeling interface, resulting in homogeneous stripes on the peeled surface. In the case of high-rate peeling, no larger viscous deformation occurs, and no surface patterns will be generated. However, it is still unclear how the surface pattern evolves when an adhesive is peeled from a relatively low rate to a high rate. Here, by peeling an adhesive tape at 180° over a wide range of rates, we find that the adhesive tape can undergo a steady peeling. As the peeling rate increases, it is observed that the surface pattern in the peeled adhesive tape tends to evolve from the initial striped pattern to a crescent pattern, then to a spotted pattern. Even in the case of the stick-slip peeling at a small angle, the patterned region also presents the same evolutionary trend. By exploiting a high-speed camera to track the deformation process of the adhesive, it is found that this evolution is actually driven by the cohesive failure of the peeling adhesive. We describe the failure process, revealing the formation mechanism of the crescent pattern. We also discuss the effect of the peeling rate on the interface instability morphology by combining the finite element simulations, elucidating how the surface pattern evolves with the peeling rate.

This paper proposes a hybrid identification method of material parameters based on genetic algorithm and improved homotopy algorithm. In this method, genetic algorithm is first used to perform a preliminary identification of the model parameters. Then, the results of the preliminary identification are used as the initial values for more precise parameter identification using the improved homotopy algorithm. Based on the Euler prediction-Newton correction homotopy algorithm, a curve prediction-Newton correction homotopy algorithm is proposed to improve the calculation accuracy and efficiency. The effectiveness and accuracy of the hybrid identification method are verified by numerical examples. The hybrid identification method is applied successfully to determine material characteristic parameters of FGH97. The results indicate that based on experimental data and numerical simulations, the hybrid identification method can rapidly obtain effective and reliable material parameters. This method reduces the calculation amount, avoids dependence on the selection of the initial population, and has a high calculation accuracy and efficiency for the inverse problem of parameter identification. It provides an effective method to accurately identify material parameters and can also be applied to parameter identification of other materials.

Apart from presenting peptides to T cells, class I HLA molecules serve as ligands for killer cell immunoglobulin-like receptor (KIRs) and regulate the response of natural killer (NK) cells. The role played by HLA and KIR in the acute rejection (AR) following liver transplantation has been controversial. In this retrospective study, we assessed the influence of class I HLA alleles, HLA matching between donor-recipient pairs, recipient KIR and donor HLA ligands on AR following liver transplantation in southern Chinese. In total, 143 recipients and 78 donors obtained from a single transplant center were included in the study cohort. Thirty-three recipients with histologically confirmed AR were observed. We found that the incidence of AR did not correlate with donor or recipient class I HLA alleles and HLA matching. Neither recipient KIR gene nor the KIR genotype was associated with AR, moreover, high-resolution genotyping of 14 functional KIR genes of recipients showed that no KIR allele was independently associated with AR. However, the frequency of HLA-C2(+) donor significantly increased in AR group compared with NAR group (52.9% vs. 24.6%, p = 0.03). In the presence of HLA-C2 by the donor allograft, AR was more frequently observed in recipients with normal expressed KIR2DS4 (43.8% vs. 15.0%, p = 0.03). Donor with HLA-C2 is therefore a major determinant of AR, which can confer risk effect in liver transplantation. Our findings can provide valuable clues for better understanding pathogenesis of AR and have important clinical implications in liver transplantation for Chinese.

The discrete element method (DEM) [...]

Human natural killer (NK) cells are essential for controlling infection, cancer and fetal development. NK cell functions are modulated by interactions between polymorphic inhibitory killer cell immunoglobulin-like receptors (KIR) and polymorphic HLA-A, -B and -C ligands expressed on tissue cells. All HLA-C alleles encode a KIR ligand and contribute to reproduction and immunity. In contrast, only some HLA-A and -B alleles encode KIR ligands and they focus on immunity. By high-resolution analysis of KIR and HLA-A , -B and -C genes, we show that the Chinese Southern Han are significantly enriched for interactions between inhibitory KIR and HLA-A and -B. This enrichment has had substantial input through population admixture with neighboring populations, who contributed HLA class I haplotypes expressing the KIR ligands B*46:01 and B*58:01, which subsequently rose to high frequency by natural selection. Consequently, over 80% of Southern Han HLA haplotypes encode more than one KIR ligand. Complementing the high number of KIR ligands, the Chinese Southern Han KIR locus combines a high frequency of genes expressing potent inhibitory KIR, with a low frequency of those expressing activating KIR. The Southern Han centromeric KIR region encodes strong, conserved, inhibitory HLA-C specific receptors, and the telomeric region provides a high number and diversity of inhibitory HLA-A and -B specific receptors. In all these characteristics, the Southern Han represent other East Asians, whose NK cell repertoires are thus enhanced in quantity, diversity and effector strength, likely through natural selection for resistance to endemic viral infections.

During the cutting process of superalloy, intense heat will be generated. Traditional external flood cooling methods require a large amount of coolant, bringing high cutting costs, serious environmental pollution, and other adverse effects. In this paper, a method combining minimum quantity lubrication (MQL) and internal cooling is proposed to accurately spray the cutting fluid into the cutting area in turning nickel-based superalloy. The heat source model for micro-lubrication cutting was established, and the heat transfer coefficient and friction coefficient under different cooling methods were calculated. Hereafter, a two-dimensional cutting finite element model was established to analyze the nickel-based superalloy turning process under different cooling conditions. Subsequently, the turning experiment of nickel-based superalloy GH4169 was carried out on the self-built turning experimental platform. The influence of different cooling methods and cutting parameters on cutting force, cutting temperature, surface roughness, chip morphology, and surface morphology of the processed workpiece was systematically studied. Furthermore, the surface roughness prediction model is obtained through the experiment results. The simulation and experiment results show that under the same cutting parameters, the cutting temperature of MQL with internal cooling is significantly lower than that of dry cutting, indicating a better cooling effect of MQL with internal cooling. Moreover, the surface morphology quality of micro-lubrication cutting is prominent compared with dry cutting. Also, the larger the cutting fluid flow, the better the surface quality. Therefore, the proposed MQL turning with internal cooling method is an environmental-friendly technology with promising application prospects.

This paper provides a design-based framework in collapse assessment of multi-storey steel framed-structures. A simple approach for different column-removal scenarios of the structure is proposed, wherein the three-dimensional effects of the floor system, boundary restraints of the affected substructure and potential vierendeel actions in multi-storey framed-structures are incorporated. The effectiveness of the approach proposed is verified against numerical analyses on a full-scale steel frame with six-storey. Extensive discussions are also made from the comparisons between the results from the simplified approach and numerical simulations with finite element method (FEM). The proposed approach is found to sometimes give conservative evaluations for the column destabilizing-induced collapse of the structure, which ensures sufficient security in the robustness assessment of the structure. For the beam/connection failure-induced collapse, the proposed approach can obtain more reliable assessment conclusions.

Large open-ended cylinder piles have been widely used for engineering foundation of port. The penetration process of the large-diameter steel cylinder exhibit complex behaviors, which is difficult to be measured by test and reproduced in numerical models. This study presents a friction analysis of large diameter steel penetration process by using the discrete element method (DEM), which can simulate large deformation and nonlinearity well. Centrifugal model and full-scale model were developed to analyze the sliding friction of the cylinder during installation and the contact force chain of soil particles. The validity of the DEM model was examined by comparing with theoretical values and published studies. Parametric studies were carried out to study the effects of contact parameters on side friction. Simulation results showed that, unlike pile penetration, there is no obvious soil-plug effect during the penetration process of large-diameter steel cylinder. Besides, the inside friction is smaller than the outside friction for large-diameter steel cylinder. What’s more, the computational cost of full-scale model based on the upscale theory was less than the centrifugal model. There is a close relationship between the side friction and micro contact parameters, which provides a reference for the follow-up study of cylinder or pile penetration using DEM.

为满足电网运行风险“实时分析、预先调控”的安全性要求,提出计及安全稳定二、三道防线的电网运行风险评估方案,解决安全自动装置(安自装置)执行效果与电网实时运行缺乏互动的问题.该方案基于可扩展标记语言XML描述安自装置当值控制策略及定值,在线实时传送至在线动态安全评估系统.在线动态安全评估系统按启动逻辑、动作逻辑和控制设备三元素建立安自装置控制策略模型后,结合电网实时运行数据,评估安自装置当值控制策略在电网预想故障场景下能否保证电网安全稳定运行.进一步根据599号令等有关条款,统计安自装置动作切除设备所造成的电力安全事故事件等级,实现安自装置动作后果的风险评估.该方案首次在广东电网实际应用,效果表明该方案能够计及二、三道防线安自装置当值控制策略的影响,提升在线动态安全评估结果的实时性和准确性.

In this study, a combined finite element method (FEM) and discrete element method (DEM) numerical simulation is proposed to investigate the tool wear evolution in machining superalloy. Firstly, a finite element model for cutting is conducted to obtain the contact stress, the temperature distribution of the cutting tool, and the speed of chip flow. Based on the boundary conditions, a discrete element model is established to display the tool-chip abrasion behavior. The micro-crack number, detached particle number, and wear rate of the ceramic tool are predicted and analyzed by discrete element simulations. Moreover, the effects of cutting speed and depth of cut on tool abrasion are numerically investigated. Subsequently, a cutting experiment is designed to compare simulated results with experimental data. The high consistency of the predicted tool wear and experiments validates that the combined FEM-DEM method is feasible to study the tool wear behavior in machining superalloy. Furthermore, process optimization guidelines are also proposed for improving machining efficiency and tool life in the actual processing. Within a certain range, higher cutting speed notably leads to slighter tool wear. The larger depth of cut causes more severe wear of Sialon ceramic tools.

Security and stability control system (SSC) is an important guarantee for the safe operation of power grid, and for HVDC system modulation function is an important kind of stability control measures. Combined with Tianshengqiao-Guangzhou HVDC safety strategy transformation, RTDS simulation test is conducted. In allusion to the exposed defects about SSC handling with multiple DC power modulation orders and sequence coordination between SSC and pole control system, the handling way for the stability control device of Mawo converter station and control characteristics of DC power modulation for pole control system are analyzed in detail. An optimization method of control sequence coordination for stability control system and pole control system is proposed, and tested on the SSC test platform. Test results show the effectiveness of the proposed method, and meanwhile the significance for the design and implementation of SSC scheme of HVDC project with similar techniques.

An inverse method for parameters identification of discrete element model combined with experiment is proposed. The inverse problem of parameter identification is transmitted to solve an optimization problem by minimizing the distance between the numerical calculations and experiment responses. In this method, the discrete element method is employed as numerical calculator for the forward problem. Then, the orthogonal experiment design with range analysis was used to carry out parameters sensitivity analysis. In addition, to improve the computational efficiency, the approximate model technique is used to replace the actual computational model. The intergeneration projection genetic algorithm (IP-GA) is employed as the optimization algorithm. Consequently, the parameters of the discrete element model are determined. To verify the effectiveness and accuracy of the inverse results, the comparisons of shape deviation experiments with discrete element simulations are provided. It indicates that the effective and reliable discrete element model parameters can be quickly obtained through several sets of experimental data. Hence, this inverse method can be applied more widely to determine the parameters of discrete element model for other materials.