Dynamic precipitation during multi-axial forging of an Mg-7Gd-5Y-1Nd-0.5Zr alloy

The dynamic precipitation behavior during multi-axial forging in an Mg-7Gd-5Y-1Nd-0.5Zr alloy has been investigated and compared with that in static precipitation treatment. The results indicated that dynamic precipitation does occur during multi-axial forging. The dynamic precipitate can be deduced as β phase with face-centered cubic crystal structure (a = 2.22 nm). Most of the β precipitates locate at the dynamic recrystallization grain boundaries. The morphology and orientation relationship is different from that of the β phase formed in the static precipitation treated alloys, although the crystal structure is the same. The precipitation temperature of β phase during MAF is higher than that in the static precipitation treatment.

Multi-axial strain-stiffening elastic potentials with energy bounds:explicit approach based on uniaxial data

According to the well-known models for rubberlike elasticity with strain- stii^ening effects, the unbounded strain energy is generated with the unlimitedly growing stress when the stretch approaches certain limits. Toward a solution to this issue, an explicit approach is proposed to derive the multi-axial elastic potentials directly from the uniaxial potentials. Then, a new multi-axial potential is presented to characterize the strain-stiffening effect by prescribing suitable forms of uniaxia] potentials so that the strain energy is always bounded as the stress grows to infinity. Numerical examples show good agreement with a number of test data.

An Adaptive Modal Discontinuous Galerkin Finite Element Parallel Method Using Unsplit Multi-Axial Perfectly Matched Layer for Seismic Wave Modeling

The discontinuous Galerkin finite element method(DG-FEM)is a highprecision numerical simulation method widely used in various disciplines.In this paper,we derive the auxiliary ordinary differential equation complex frequency-shifted multi-axial perfectlymatched layer(AODE CFS-MPML)in an unsplit format and combine it with any high-order adaptive DG-FEMbased on an unstructuredmesh to simulate seismicwave propagation.To improve the computational efficiency,we implement Message Passing Interface(MPI)parallelization for the simulation.Comparisons of the numerical simulation results with the analytical solutions verify the accuracy and effectiveness of our method.The results of numerical experiments also confirm the stability and effectiveness of the AODE CFS-MPML.

基于液压胀破测试方法的聚合物防水膜多轴拉伸性能表征

本研究设计了一种基于液压胀破的多轴拉伸测试装置和数据处理方法,以准确表征聚合物防水膜的拉伸性能。测试结果显示:随着防水膜厚度的增加,拉伸峰值应力降低;随着试件直径的增加,拉伸峰值应力增加;与单轴拉伸相比,多轴拉伸避免了“颈缩”效应,断裂伸长率降低;防水膜的应力-应变曲线符合线性应变强化弹塑性模型,并可通过多轴拉伸试验拟合得到相关参数。结论表明,多轴拉伸方法结果更接近实际工况下的应力-应变响应,可为合理评估防水膜在工程环境中的力学性能提供参考和借鉴。

多层连接结构的轴向应力分布的数值计算与试验

为了解多层连接结构的轴向应力分布,从双层法兰螺栓连接结构连接轴向载荷分布着手,建立了被连接件轴向应力分布的中空椭球体分布模型,推导出被连接件的轴向连接刚度理论表达式;并进行了连接结构扭矩与预紧力关系的试验及压力分布测试试验;将该模型应用于航空发动机多层法兰连接结构,采用数值模型和试验方法对中空椭球体模型进行验证。结果表明:测试试验件预紧力与力矩呈正相关,且拧紧系数约为0.2,可满足工程中无润滑条件下螺栓拧紧力矩系数的经验值;连接界面接触范围随扭矩的增大先增大到一定范围后保持不变;与被连接件轴向应力分布的试验测试结果相比,采用改进的中空椭球体模型和原中空圆锥体模型的计算结果的最大误差分别为9.42%和21.97%,证明了改进的中空椭球体分布模型的精度较高。

基于Kriging插值代理模型的轴流式止回阀多目标优化

基于Kriging插值代理模型,对轴流式止回阀的各项性能进行综合优化,具体的优化目标为:降低正向流阻;减小阀芯振动;提升止回性能。通过试验设计方案找到影响轴流式止回阀正向流阻的主要结构参数因素,并以其作为优化对象,通过Kriging插值法拟合主要结构参数对应的性能样本点,在保证拟合精度的情况下,使用NSGA-II遗传算法同时对3个主要结构参数进行多目标优化,得到了三目标Pareto前沿,经过权衡不同因素对性能指标的影响大小,最终得到了综合性能最优的结构参数为:阀瓣丰满度系数α_(1)=2.199,阀芯长度L=386.322 mm,阀芯半径R=113.997 mm。其对应的止回阀性能为:正向出口流量Q=161.839 kg/s,正向出口流速v=3.30235 m/s,止回阀进口压力p=97632.2287 Pa。相比优化之前,阀门正向流阻减小了1.2%,阀芯振动降低了0.24%,止回性能提升了2.3%。

基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计

由于轴向柱塞泵的非对称结构特性,其输出压力和输出流量存在脉动特性,对液压系统的输出稳定性和可靠性造成影响,因此提出了一种基于多目标遗传算法的斜盘式轴向柱塞泵低脉动结构优化设计方法。首先,通过CFD(computational fluid dynamics,计算流体动力学)仿真分析方法,对轴向柱塞泵上/下死点位的压力-流量脉动的产生机理进行了分析;其次,对阻尼槽结构参数对轴向柱塞泵输出压力-流量脉动的影响规律进行了分析,构建了阻尼槽结构的多目标优化模型;最后,求解了低脉动阻尼槽结构。优化后的结构参数:阻尼槽半径为2.21 mm,阻尼槽长度为10.32 mm,阻尼槽错配角为16.54°。优化后压力脉动率为0.59%,相比于优化前的0.75%降低了0.16%,脉动幅值为0.25 MPa;优化后流量脉动率为12.02%,相比于优化前的5.61%降低了43.59%。研究结果为轴向柱塞泵低脉动结构的优化设计提供了有效的理论支持和实践指导。

多轴平稳非高斯随机振动试验控制方法

多轴向平稳非高斯随机振动控制试验能够对指定响应信号的时、频域特征进行同时控制。提出了一种快速生成具有指定功率谱密度、斜度和峭度的平稳非高斯随机振动信号的方法。通过频率采样方法将目标功率谱密度设计成滤波器,利用非线性变换方法获取非高斯随机信号,再将此信号经过设计的滤波器以获得满足要求的非高斯随机信号。该方法简单、快速并克服了传统非线性变换方法的缺点。进一步将此方法应用于三轴向平稳非高斯随机振动试验中,给出了三轴向非高斯随机振动控制的闭环均衡步骤,此方法能够同时对信号的功率谱自谱、相干系数、相位差以及斜度和峭度进行解耦控制。进行了三轴向平稳非高斯随机振动控制试验,三个方向上加速度信号的功率谱密度、斜度和峭度控制效果均令人满意,满足工程应用要求。

有限空间内电子芯片风冷系统的优化研究

芯片的冷却问题已经成为限制电子设备发展的技术瓶颈之一。本文通过数值模拟,对某人脸识别电子芯片在有限空间内的散热问题展开优化研究。研究芯片温升与轴流风扇流量、进风面积、芯片工作功率的关系,并通过多目标优化得到更加符合当前目标需求的芯片及风扇的工作参数。研究结果表明,轴流风扇流量从0增加到9CFM范围内,芯片温升下降约56%;风扇进风面积从0.031 m^(2)增大到0.196 m^(2),芯片温升上升13%;随着芯片功率增加,芯片稳定工作的温升呈线性提升。通过多目标优化设计,得到的芯片及风扇的工作参数为P=5.87 W,Q=1.056 CFM,A=0.041 m^(2)。

基于四配流轴向柱塞马达的制动能回收方法

针对大惯性回转机构在制动时,动能都以热能的方式损失的问题,提出一种四配流轴向柱塞马达和蓄能器结合的制动能回收方法。不同体积、初始压力的蓄能器对惯性负载的回转制动能的回收和再利用的效果不同,为寻求较合理的蓄能器参数以达到较高的能量回收效果,手动调整仿真参数较为繁琐,提出采用基于多核CPU的快速并行优化方法用于蓄能器参数优化。首先,大惯性负载的驱动机构采用四配流轴向柱塞马达,其能量系统回收模型在Simulation X搭建,进而导出成具有CVODE求解加速的可执行程序,脱离仿真软件平台,在Windows操作系统独立运行;然后,利用导出的可执行程序与VC++进行二次开发,以微粒群算法解决特定工况下蓄能器选型的问题,充分利用多核CPU实现并行优化以提高仿真速度。仿真结果表明,在特定负载下得到优化后的蓄能器的参数,蓄能器回收并释放的能量占惯性动能的24.5%,回收油液全部得到释放。采用基于多核CPU的并行优化方法,仿真效率提高了10倍以上,该方法对系列化液压产品的快速开发具有一定的借鉴价值。

碳纤维多轴向织物的特点及其发展趋势

阐述了碳纤维织物的分类及其制备工艺。重点介绍了碳纤维多轴向织物的性能特点及其在航空航天、风力发电、民用等领域的广泛应用,分析了未来碳纤维多轴向织物的发展趋势和市场前景。

车载耦合工况下波纹管加速寿命载荷谱编制

以某商用车排气系统波纹管为研究对象,通过样车道路试验对其多维耦合随机载荷激励进行测试,并对其解耦算法进行了探讨。对波纹管结构多轴疲劳寿命进行预测,进而采用时域损伤保留法对波纹管加速寿命载荷谱编辑方法进行了探讨,将加速寿命载荷谱缩短至原始谱的17.86%,为波纹管加速寿命试验设计提供了依据。

基于细粒度特征提取的轻量骨龄评估级联方法

针对现有骨龄自动评估模型细节特征提取能力较弱且没有兼顾手骨发育特点的问题,提出了一种基于轻量级网络的两阶段骨龄评估级联模型。首先,定位提取手掌区域进行背景去噪。其次,提出了一种新型的轴向空间注意力与多尺度并行空洞卷积相结合,融入模型中,从而提升模型细节特征提取能力。同时,将每个骨龄标签转化为两点分布向量,充分利用个体手骨发育的信息。实验结果表明,模型预测结果的平均绝对误差为4.80且评估误差在±0.5、±1、±2岁以内的准确率分别为69.26%、95.60%、99.80%。本研究提出的模型不仅能快速准确的评估骨龄,且充分考虑了手骨发育过程中所包含的信息,同时,基于轻量化的架构为其后续推广应用提供了基础,具有良好的临床应用前景。

基于两点模型的堆芯功率多目标保性能控制

现阶段能源产业需要核电站能够根据实际功率需求对输出功率进行调整,因此压水堆堆芯负荷跟踪运行是现阶段压水堆商业化运行的重要需求之一.为了避免运行过程中由于堆芯功率分布不均匀导致的氙震荡、热点等问题,对堆芯运行过程中产生的轴向功率偏差进行控制也是压水堆安全运行的关键.基于中子动力学方程、反应性反馈方程和热工水力学方程,结合堆芯功率空间耦合构建了压水堆堆芯功率两节点模型,并在这一模型的基础上增加负荷跟踪和轴向功率偏差跟踪量.根据这一模型设计了能够实现负荷跟踪控制和轴向功率分布控制并且具有抗时变性的LPV-LQR多目标控制器.在经典的多个瞬态工况下进行仿真的结果表明,LPV-LQR控制器具有良好的负荷跟踪控制和轴向功率分布控制能力,并且能够更好适应堆芯功率系统的时变性.

轴向预制破片战斗部飞散特性数值模拟

为分析轴向预制破片战斗部的飞散特性,利用LS-DYNA软件模拟轴向预制破片战斗部中心单点起爆方式和多点起爆方式下破片速度及飞散角特征参数并进行试验验证,得到了中心单点起爆和多点起爆方式对破片速度及飞散角特征参数的影响规律。研究表明:相较于中心单点起爆方式,多点起爆方式可以提升轴向预制破片速度,且随着起爆点数增加,破片速度先增加后趋于稳定,起爆点数从2点增加到6点,破片初速提升了21.1%,当起爆点数继续增加,则破片速度不再增益,而起爆点数对飞散角影响较小。

Three-dimensional Tool Radius Compensation for Multi-axis Peripheral Milling

Few function about 3D tool radius compensation is applied to generating executable motion control commands in the existing computer numerical control (CNC) systems. Once the tool radius is changed, especially in the case of tool size changing with tool wear in machining, a new NC program has to be recreated. A generic 3D tool radius compensation method for multi-axis peripheral milling in CNC systems is presented. The offset path is calculated by offsetting the tool path along the direction of the offset vector with a given distance. The offset vector is perpendicular to both the tangent vector of the tool path and the orientation vector of the tool axis relative to the workpiece. The orientation vector equations of the tool axis relative to the workpiece are obtained through homogeneous coordinate transformation matrix and forward kinematics of generalized kinematics model of multi-axis machine tools. To avoid cutting into the corner formed by the two adjacent tool paths, the coordinates of offset path at the intersection point have been calculated according to the transition type that is determined by the angle between the two tool path tangent vectors at the corner. Through the verification by the solid cutting simulation software VERICUTwith different tool radiuses on a table-tilting type five-axis machine tool, and by the real machining experiment of machining a soup spoon on a five-axis machine tool with the developed CNC system, the effectiveness of the proposed 3D tool radius compensation method is confirmed. The proposed compensation method can be suitable for all kinds of threeto five-axis machine tools as a general form.

钢管混凝土加劲混合结构轴心受压工作机理及可靠性分析

钢管混凝土加劲混合结构是由内置钢管混凝土部分和外包钢筋混凝土部分混合而成的结构,由于其在承载力、刚度和延性上的优势,已在工程结构中得到应用。国家标准《钢管混凝土混合结构技术标准》(GB/T 51446—2021)给出其轴压承载力和刚度计算方法。但以往研究主要针对单一参数,尚缺少多参数耦合作用下受力机理研究;且亟需验证承载力计算方法的可靠性,为各行业下的安全性设计提供依据。该文首先建立了轴心受压试验数据库,分析了影响该类结构轴压性能的关键参数;之后,运用验证后的精细化有限元模型开展多参数耦合作用分析,明晰多参数耦合作用对结构刚度、承载力的影响规律,弥补试验研究的局限性,并进一步揭示结构在短期、长期荷载下的内力分布规律,为长期服役下安全性分析提供依据。在参数分析的基础上,开展可靠性分析,确定该类结构在房屋建筑、铁路桥涵、公路桥涵和港口工程中的可靠度指标,验证国家标准中轴压承载力设计方法的可靠性。

宽轴比波束双频带北斗导航天线设计

[目的]为了有效拓宽北斗天线3 dB轴比波束宽度,提出一种加载寄生单元的开槽叠层微带贴片天线。[方法]通过叠层基板结构实现北斗双频带特性,并通过开槽拓宽双频段带宽,在贴片边缘切角实现双频带圆极化;同时在贴片周围加载L形寄生单元来拓宽天线的3 dB轴比波束宽度。[结果]实测和仿真结果吻合度较高,在北斗B1和B2频段的相对带宽为3%和7.5%;3 dB轴比波束宽度可达到180°和176°;增益最高可达6 dBi。在北斗接收机试验中,天线搜星数量能达到17颗以上,定位精度在米级以内。[结论]所设计的双频带北斗导航天线具有宽轴比波束宽度和高定位精度,研究结果可为小型北斗导航天线的设计提供参考。

Anisotropic Force Ellipsoid Based Multi-axis Motion Optimization of Machine Tools

The existing research of the motion optimization of multi-axis machine tools is mainly based on geometric and kinematic constraints, which aim at obtaining minimum-time trajectories and finding obstacle-free paths. In motion optimization, the stiffness characteristics of the whole machining system, including machine tool and cutter, are not considered. The paper presents a new method to establish a general stiffness model of multi-axis machining system. An analytical stiffness model is established by Jacobi and point transformation matrix method. Based on the stiffness model, feed-direction stiffness index is calculated by the intersection of force ellipsoid and the cutting feed direction at the cutter tip. The stiffness index can help analyze the stiffness performance of the whole machining system in the available workspace. Based on the analysis of the stiffness performance, multi-axis motion optimization along tool paths is accomplished by mixed programming using Matlab and Visual C＋＋. The effectiveness of the motion optimization method is verified by the experimental research about the machining performance of a 7-axis 5-linkage machine tool. The proposed research showed that machining stability and production efficiency can be improved by multi-axis motion optimization based on the anisotropic force ellipsoid of the whole machining system.

Design of a Multi-axis Motion Control Platform Based on LabVIEW’s Fuzzy Control Algorithm

This paper presents a fuzzy control algorithm applied to the position control of a multi-axis motion platform to achieve high precision motion control of the multi-axis motion platform.A LabVIEW-based multi-axis motion control system is designed.This system controls stepper motors using trapezoidal acceleration/deceleration pulse types and fuzzy control algorithms,which effectively avoids mechanical jitter and loss of step in the process of multi-angle motion of the stepper motor,and achieves accurate control of the stepper motor.The TCP/IP(transmission control protocol/internet protocol)communication protocol is used,so that data are output stably and not lost in the process of transmission and communication,achieving the purpose of interconnection of different systems and remote control of equipment.This control system has been tested to maintain a high level of stability and repeatability during actual operation.