为探究圆钢管混凝土柱-钢梁结构体系中梁柱削弱式节点的抗震性能,建立翼缘犬骨削弱和腹板圆孔削弱两种形式的节点在水平往复荷载作用下的有限元计算模型,对两种节点的破坏模式、能量耗散性能和节点延性进行对比研究.计算结果表明,不同削弱形式的节点翼缘板均发生弯扭破坏,腹板区域发生屈曲破坏.两种削弱形式极限承载力和刚度退化规律相似,建议对梁翼缘犬骨削弱范围不大于0.25bf,梁腹板圆孔削弱范围不大于0.35 hb.相对于翼缘削弱节点,腹板削弱节点在水平往复荷载作用下易发生面外失稳,但其具有更好的耗能能力.实际工程中,对面外稳定性有更高要求时可采用翼缘削弱式节点,对于梁端约束且削弱区段可替换情况下可采用腹板削弱式节点,以满足不同的梁柱节点对抗震性能的要求.
采用热丝增强等离子体磁控溅射技术,在Ti6Al4V(TC4)基体表面沉积单相CrN涂层,并分别在温度为400、500、600、700、800℃下空气中退火.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)与能谱(EDS)、Raman光谱、原子力显微镜(AFM)、X射线荧光光谱仪(XRF)、划痕仪、纳米压痕仪、台阶仪和摩擦磨损仪分析涂层的物相组成、微观形貌、成分及力学性能.随着退火温度的升高,CrN所有取向的峰位均向右移动接近标准峰位,内应力得到释放.当退火温度达到600℃后,涂层表面氧化迹象明显,粗糙度升高,出现白色颗粒状Cr2O3.随退火温度升高,涂层与基体结合力提高,在800℃时临界失效载荷达到25.2 N;涂层硬度和弹性模量下降,硬度从未退火的24.86 GPa降至800℃的15.23 GPa,弹性模量从327 GPa降至260 GPa;涂层耐磨性小幅下降,磨损量从未退火的0.78×10-16 m3/(m·N)上升至11.74×10-16 m3/(m·N),但均远低于TC4基体的磨损量10371.61×10-16 m3/(m·N).划痕与摩擦磨损检测结果中,涂层均未出现分层及剥落现象.采用热丝增强等离子体磁控溅射技术在钛合金表面制备的CrN涂层,在高温环境下保持较高的耐磨损性能和与基体良好的结合力,提高了软质不耐磨的TC4基体在高温磨损环境的使用寿命.
在超大宽厚比钢锭铸造过程中,水口的数量和位置会影响钢液的流动轨迹和温度分布,水口设计不合理会导致钢液卷渣、钢锭内部缺陷增多等问题.本文基于ProCAST软件对超大宽厚比钢锭模铸过程进行模拟,研究单、双和三水口对超大宽厚比钢锭充型和凝固过程的影响.结果表明,多水口浇铸时钢液循环范围扩大,上升流股冲力小;三水口铸锭的疏松缩孔体积比单水口铸锭减少14.2％,比双水口铸锭减少36.9％,三水口浇铸工艺利于减少疏松缩孔缺陷.
为了分析立方准晶材料轴对称问题的应力和变形情况,首先从立方准晶材料的基本方程出发,获得声子场和相位子场的位移平衡方程,通过求解微分方程获得立方准晶材料平面轴对称位移的通解,再利用本构关系,获得立方准晶材料内的应力分布,最后利用通解和界面连续的边界条件,获得准晶材料圆筒置入无限大弹性体内的位移和应力状态,从而获得准晶材料对结构的影响:相同弹性常数情况下,准晶材料的刚度有所降低,抵抗变形能力变弱.
针对NPSVR训练速度和预测精度问题,提出一 种基于L1范数损失的非平行支持向量回归机L1NPS-VR模型,用于预测数值输出.L1NPSVR通过求解两个较小规模的凸规划问题,建立一 个ε1-不敏感的下界函数和一 个ε2-不敏感的上界函数.在L1NPSVR模型中,每个优化问题同时最小化训练样本的L1范数损失和铰链损失,以保证模型的稳定性,减轻噪声和异常值的影响.L1NPSVR通过求解一 对更小的优化问题来提高模型的运行效率.仿真结果验证了所提出方法的可行性及有效性.
四旋翼无人机在飞行时的初始状态极易受到未知的外界干扰,影响其飞行稳定性.本文采用一 种与初始跟踪条件无关的预设性能控制设计方法,解决四旋翼无人机在初始跟踪状态未知时的预设性能控制器设计问题.基于该方法,将自抗扰技术、预设性能控制和有限时间控制等在设计过程中有机结合,设计无人机的自抗扰预设性能有限时间跟踪控制器,同时保证四旋翼无人机在未知初始跟踪状态下的暂态、稳态和抗干扰性能.仿真结果验证了控制方法的有效性.
将LEACH协议应用于环境复杂的煤矿巷道中存在不足,为了使LEACH协议更适用于煤矿巷道,对LEACH协议进行改进.首先,本文对选择簇头的阈值函数进行调整,加入节点剩余能量、位置信息以及邻节点数量因素;其次,改进建簇算法,节点通过计算与簇头节点和汇聚节点之间的距离来判断加入簇头还是与汇聚节点直接通信;最后,改进簇间通信机制,簇头之间通过多跳方式进行数据传输,并根据能量和距离信息选择下一跳簇头节点,提高簇间数据传输的可靠性.仿真实验表明,改进后的LEACH协议可以有效降低煤矿巷道无线传感器网络能耗,延长网络生命周期.
以旅行商问题(TSP)为研究对象,提出一 种基于差分(DE)算法的改进蚁群算法(ACO&DE).ACO算法具有快速构造机制,DE算法可以扩展ACO算法的搜索范围,避免蚁群算法陷入局部最优.为了使DE算法适合求解离散TSP问题,对变异算子和交叉算子的策略进行重新设计.同时,在ACO算法中嵌入DE算法来改进解的质量.仿真结果验证了ACO&DE算法在求解TSP问题时的有效性,可以扩展应用到TSP的变型和其他物流运输领域.
为了使航天器在部分执行器发生失效故障的情况下更好地跟踪期望姿态,本文研究了航天器有限时间自适应容错姿态跟踪控制问题.通过配置冗余的执行器,确保提供足够的控制力矩用以完成姿态跟踪.控制器采用自适应控制、容错控制及有限时间控制,兼顾系统的鲁棒性、可靠性及快速性.数值仿真示例验证了所提出的自适应容错控制器的有效性.
采用氟硅烷链对有序介孔SiO2光学减反射薄膜进行表面改性,有效提高其在潮湿环境中的稳定性.以三嵌段共聚物F127为模板剂,以正硅酸四乙酯为前驱物,在酸催化的醇体系中制备SiO2溶胶.采用提拉法在石英基底上镀制薄膜,经350℃热处理后得到有序介孔SiO2薄膜,薄膜对中心波长的透射率达到99.83％.通过嫁接氟硅烷链对薄膜表面进行改性,以有效阻止羟基和微孔开口对水蒸气的吸附.薄膜耐湿性测试在相对湿度80％、温度40℃的可控环境中进行,每隔15天进行一 次薄膜透射光谱测试,采用光谱拟合方法分析薄膜的光学常数随测试时间的变化.结果表明,在湿度环境下,薄膜结构沿厚度方向具有非均匀性,薄膜折射率由靠近基底的边界到薄膜-空气界面呈非线性下降趋势.
人工生态系统优化算法是一 种模拟生态系统中生物生产、消耗和分解的一 种元启发式算法,具有简单、可调节参数少等优点,但容易早熟收敛或陷入局部最优.为了进一 步提高人工生态系统优化算法的性能,本文提出一 种改进的人工生态系统优化算法,记作IIAEO.通过模拟光的折射进行种群初始化,提高初始解的质量,将Lévy飞行和布朗运动相结合,更好地平衡探索和开采能力;同时,加入余弦算子和Cauchy算子,避免陷入局部最优.将IIAEO算法与其他四种算法在5个基准函数上进行对比实验,统计分析结果表明,该算法具有良好的性能,明显优于原始的人工生态系统优化算法.
二羟基苯异构体,如对苯二酚(HQ)和邻苯二酚(CC),具有高毒性且难降解,对环境造成很大污染.本文以黄铜矿和纳米铜为基底原料,通过熔融盐法制备黄铁矿/纳米铜复合材料,并制备电化学传感器,用于同时检测邻苯二酚及对苯二酚.通过对形貌表征及性能测试,优化黄铁矿和纳米铜掺杂比例、制备温度、电解质溶液pH值等参数,制备出性能优良的电化学传感器.利用定电位方法确定邻苯二酚和对苯二酚检测的线性范围分别为10～800 μmol/L和3～800 μmol/L,检测限分别为0.5μmol/L和1.0μmol/L.所制备的黄铜矿/纳米铜电化学传感器响应速度快,使用寿命较长.既为酚类物质电化学传感器提供性能优良的基础材料,又为黄铜矿的高附加值应用提供新的研究领域.
为了提高镁合金的表面硬度和耐蚀性,采用等离子体增强化学沉积技术在AZ31镁合金表面制备含氟DLC膜.研究了氟掺杂量对含氟DLC薄膜表面形貌、耐腐蚀性、疏水性和sp2键含量的影响,并探讨了相应的影响机理.结果表明,氟掺杂对AZ31镁合金表面DLC膜的组织和性能有显著影响.随着四氟化碳沉积时间增加,类金刚石薄膜的粗糙度减小,表面光滑;薄膜中的sp2杂化键逐渐增多;类金刚石薄膜的疏水性先增大后减小;当四氟化碳沉积时间为40 min时,类金刚石薄膜表现出优异的耐人体体液腐蚀特性.
The effect of copper on hot-rolled 301 austenitic stainless steel was studied by observing the microstructure and testing the electrochemical corrosion resistance property. The results showed that the number of small bands composed of chromium carbides（（Fe,Cr） 7 C 3 ） was obviously reduced and more twins appear in Cu-bearing hot-rolled 301 stainless steel,which implied that the addition of copper promoted the solid solution of Cu,Cr and other elements,and copper decreased the stacking fault energy in the hot rolling process.As a result,the corrosion resistance was steadily improved,because the solid solution of Cr and Cu in stainless steel was conductive to the formation of Cu-and Cr-rich passivation film. However,adding 1.8 wt% copper did not improve the pitting corrosion resistance of stainless steel.
CaCu3Ti4O12(CCTO)具有较大的介电常数,在储能领域具有巨大的应用潜力,但高介电损耗却限制了其应用.本文采用固态法共掺杂Mg和Al元素,研究Al掺杂量对CCTO的介电常数、介电损耗和阻抗等物理性能的影响.实验结果表明,Mg和Al元素共掺杂,CCTO的晶格常数减小,衍射峰位向高角度偏移;随Al含量的增加,CCTO的介电常数明显减小,而介电损耗随频率、温度的提高先减小后增大,阻抗显著增大;在中低频、低温时,掺杂可有效降低介电损耗.
The connection method of lengthening the steel tube of concrete filled circular steel tubes by inner lining tube and threaded connection is proposed. Taking the length, depth, and position of the thread as the basic parameters, 12 concrete filled circular steel tubes connected by thread through inner lining tube were designed and manufactured, and an axial compressive test was carried out. The axial compressive loading-longitudinal compressive displacement curves, axial compressive loading-strain of steel tube curves, and failure mode of the specimens were analyzed, and the effects of different parameters on the axial compressive bearing capacity and stiffness of the specimens were studied. The results show that the axial compressive loading-longitudinal compressive displacement curves of the specimen can be divided into the elastic stage, elasto-plastic stage, and plastic reinforcement stage in the range of parameters studied in this paper. The bearing capacity and stiffness of the specimens connected by thread through inner lining tube are no worse than those of the unconnected specimen or the specimen connected by weld. Bearing capacity and stiffness of the specimen increase with the increase of thread length. The calculation method of the axial compressive bearing capacity of concrete filled circular steel tubes connected by thread through inner lining tube are suggested.
Using high sulfur petroleum coke as raw material and KOH as activator,the electrode material of petroleum coke based electrochemical capacitor was prepared by changing the ratio of material to agent at 800 ℃. The structure of activated carbon was characterized by XRD,and the electrochemical properties of the obtained materials were characterized by constant current charge-discharge,cyclic voltammetry,AC impedance,etc. The influence of the amount of KOH on the electrochemical properties was mainly investigated.The experimental results show that the electrochemical performance of the prepared activated carbon was the best when the amount of KOH was 3.5 times of the mass of high sulfur petroleum coke. At the current density of 1 A/g,the specific capacitance of the sample reached 191.45 F/g. After the current density was expanded by 6 times,the capacity retention rate still reached 82.16%,and the internal resistance of the material was only 0.3 Ω. As an electrode material for supercapacitor,it lays a foundation for withstanding high power discharge. After 2000 cycles,the mass specific capacitance remained at 191.13 F/g,and the coulomb efficiency was as high as 99.88%.
The adaptive bounded-H ∞ tracking control problem based on the event-triggered mechanism is investigated for a class of incommensurate fractional order strict feedback nonlinear systems with unknown external disturbances,input saturation and unknown control directions. By combining event-triggered strategy,bounded-H ∞ control method with Nussbaum-gain technique,an adaptive neural network bounded-H ∞ eventtriggered tracking control method is proposed. The designed controller can guarantee that the tracking error and all the signals in the closed-loop system are bounded,and the system has a good suppression effect on external disturbances. Furthermore,the proposed control strategy not only avoids the overlarge output value of the controller in H ∞ control method of nonlinear systems,but also makes the control input of the system no longer update frequently,so as to achieve the saving purpose of communication resources. Finally,the simulation results demonstrate the feasibility and effectiveness of the proposed method.
With the rapid development of the automotive industry,the demand for high-strength bolt steel as a base material for automotive connectors is increasing day by day. The oxide scale generated during the hot rolling process is an important factor affecting the quality of high-strength bolt steel products. In this paper,the influence of carbon content and rolling temperature on the oxidation behavior of SCM435 steel were studied,using detection methods such as scanning electron microscopy,XRD,and tensile experiments. The research results show that when the carbon content is low,the oxide scale is evenly distributed and mainly composed of Fe 2 O 3 ;when the carbon content is high,the oxide scale is mainly composed of Fe 3 O 4 ,and the distribution is uneven,and even band breaks and cracks may occur. High-carbon bolt steel is more likely to produce thinner oxide scale. During the heating process,the thickness of the oxide scale decreases with the increase of heating temperature. For bolt steel with a carbon content of 0.1%,there is a critical temperature at which the thickness of the oxide scale increases first and then decreases with the increase of temperature.
In order to relieve the pressure brought about by the continuous reduction of the fertility rate in China in recent years,some policies have been issued one after another. However,there are few studies on the mechanisms and impacts on the trend of population development. In this paper,according to the population age and the fertility character,a dynamic model of multi-stage population growth is established firstly. Taking the transfer rate between different stages as control variables,an optimal control model is built and solved with particle swarm algorithm. Secondly,the reliability of the model is verified by error analysis. Finally,the fertility intention parameter is introduced into the fertility rate of each stage,and the population growth trend is predicted by adjusting the fertility intention parameter. The result shows,improving the fertility intention of the first,second and third child all can significantly increase the total population and delay the arrival time of the peak population to different degrees; and the effect of improving the fertility intention of one child is significantly better than that of the second and third child.
