Elastic stability of shallow pin-ended parabolic arches subjected to step loads

Buckling could be induced when shallow arches were subjected to vertical step loads. In-plane static and dynamic buckling of shallow pin-ended parabolic arches with a horizontal cable was investigated. Based on the equations of motion derived from Hamilton's principle, nonlinear equilibrium equations and static buckling equilibrium equations were deduced. Through the pseudo-static analysis, approximate solutions to the lower and upper dynamic buckling loads under step loads were obtained, for shallow parabolic arches. The results show that dynamic buckling and snap-through buckling are impossible when modified slenderness ratio λ<λc and λ>λs, where λc and λs denote critical slenderness ratios of bucking and snap-through buckling, respectively; effects of the stiffness of the horizontal cable on the dynamic buckling are significant; and the dynamic buckling loads under a equivalent central concentrated step load are lower than the loads under a distributed load appreciably.

Bending Properties of GCr15 Steel Guide Rail under the Multi-step Loading

To analyze the bending properties of GCr15 steel guide rail based on the elastic-plastic theory, the novel bending loading method consisting of multi-step loading and corresponding unloading was applied in three specimens with different cross section shape and different heat treatment condition. According to the experimental results, using numerical calculation software program and the numerical simulation with finite element analysis （FEA）, the relationships among the maximal load and displacement on cross section shape with each step bend loading, the loading stroke with the heat treatment condition, and the loading stroke with cross section shape were gained, and also those curves were discussed qualitatively. Finally, the contrast results between the numerical simulation and experiment were carried out to study the influence about the multi-step loading on specimen. It is put forward that enlightenment for the straightening stroke in the precision linear guide rail manufacture process.

Reciprocating Engine Step Load Response in Islanded Power Generation

The step load response of reciprocating engines is one of the key characteristics when considering its application in medium to large scale stationary power generation especially with islanded generation. This paper discusses the impacts of power frequency deviation on the generators and electrical equipment in the network and presents the relationship between step load capabilities and generator operating parameters. For a power plant consisting of a number of generators both step load and power output requirements must be satisfied. An analysis method is proposed to facilitate the development of an operation strategy which can meet both step load and power demand requirements in the full load range.? Typical reciprocating engine step load curves are used to demonstrate the analysis method and the results are further optimised for lower operational cost. This analysis method provides a general approach to operation strategy of large reciprocating engines used in islanded power generation.

Step-Loading Characteristics of Gas Engine Cogeneration System Using Doubly-Fed Induction Generator in Stand-Alone Operation

Application of a DFIG （doubly-fed induction generator）, which is one of adjustable speed generators, to a gas engine cogeneration system has been investigated. To operate during a blackout as an emergency power supply is one of important roles for the gas engine eogeneration system. In the case of conventional constant speed of synchronous generator, the amount of the allowed step load is limited to around 30% of the rated power. On the other hand, DFIG is expected to increase the amount of step load during the stand-alone operation. In this paper, it has been demonstrated that an increase in the gas engine speed resulted in an increase in the maximum amount of step load using experimental equipment with a real gas engine. It has been concluded that the proposed system can improve the performance of an emergency power supply at step-loading.

Strength reduction and step-loading finite element approaches in geotechnical engineering

The finite element limit analysis method has the advantages of both numerical and traditional limit equilibrium techniques and it is particularly useful to geotechnical engineering.This method has been developed in China,following well-accepted international procedures,to enhance understanding of stability issues in a number of geotechnical settings.Great advancements have been made in basic theory,the improvement of computational precision,and the broadening of practical applications.This paper presents the results of research on（1） the efficient design of embedded anti-slide piles,（2） the stability analysis of reservoir slopes with strength reduction theory,and（3） the determination of the ultimate bearing capacity of foundations using step-loading FEM（overloading）.These three applications are evidence of the design improvements and benefits made possible in geotechnical engineering by finite element modeling.

RADIAL VIBRATIONS OF AXISYMMETRICALLY LOADED STEPPED PRESSURE VESSELS

Differential equations of free/forced radial vibrations of axisymmetrically loaded stepped pressure vessels are established by using singular functions. Furthermore, their general solutions are solved, the expression of vibration mode function and frequency equations on usual supports are derived with W operator and the forced response of such vessels are calculated.

垭口微地形下档内线路不均匀覆冰研究

明确垭口地形因子对垭口输电线路覆冰的影响规律,对山区输电线路的差异化防冰非常关键。该文基于水文分析中反地形理论提出山腰垭口,建立垭口风场数值模型,并通过风洞实验验证该模型。依据垭口风场分布,选定3类垭口线路的架设路径,得出垭口线路的风速区间。将初始状态下导线单次覆冰冰层厚度不得超过线径的7%作为覆冰步长取值依据,循环计算流场、粒子传输模型、热力学方程得出线路风速区间内导线的覆冰情况,进而得出垭口线路的冰荷载曲线,山腰、山脉、双山垭口线路冰荷载曲线在弧垂区分别出现了弯折、下行、下凹的走势。通过野外垭口线路自然覆冰实验,验证了覆冰计算的有效性,证实横跨垭口线路的不均匀覆冰性,不均匀覆冰规律与计算冰荷载曲线类似。计算不同地形因子组合下3类垭口的冰荷载曲线,并提出最大应力比概念,作为评判覆冰所引起线路事故可能性的标准,量化了不同垭口地形因子与线路最大应力比之间的关系。

双路卷积神经网络和序列到序列的多步短期负荷预测

为提高多步短期电力负荷预测精度,满足实际应用中对于不同时间长度的预测需求,提出一种双路卷积神经网络和序列到序列相结合的多步预测方法。首先,构造双支路并行结构的特征提取网络双路卷积神经网络对负荷输入数据进行不同尺度的深层次特征提取;其次,分别以双向门控循环单元和长短期记忆网络作为编码器和解码器构建序列到序列网络,利用编码器对双路卷积神经网络的输出特征进行编码,并引入注意力机制完成输入数据到动态变化的中间向量的信息转换;最后通过解码器解码实现未来多个时刻的负荷序列输出。实验结果表明,所提方法较其他方法具有更优的多步预测性能。

需求响应激励下耦合电转气、碳捕集设备的综合能源系统优化

为了充分调动用户侧柔性负荷资源,发挥氢能的低碳特性,本文提出了一种需求响应激励下耦合两阶段电转气和碳捕集设备的综合能源系统优化方法。首先,构建两阶段电转气、碳捕集、氢燃料电池和储氢罐等设备组成的氢基综合能源系统。其次,结合负荷能源转换间耦合关系与调节特性,引入阶梯型需求响应激励机制并对补偿基价、区间长度、价格增长率3个参数进行自适应优化。最后,设置多种场景,用多目标灰狼算法对系统的供能侧、需求侧和阶梯型需求响应激励机制进行优化求解。结果表明,基于此方法系统运行的总成本和CO_(2)排放量都有所降低。

基于负荷台阶的工业需求响应用户优选方法

在未来高比例新能源渗透下,供需平衡不确定性逐步增加,需求响应是通过挖掘用户侧灵活性资源保障系统电力电量平衡的重要手段。在电力部门进行需求响应工作时,需要使用历史数据来初步评估负荷响应潜力,以便选择潜力高的用户并展开动员工作。面向表征工业用户用能特点的负荷台阶,对其进行了定义并给出了数学表达,进而提出了基于负荷台阶的工业需求响应用户优选方法。首先,构建了基于负荷台阶的工业用户多时间尺度需求响应潜力指标体系;然后,构建了需求响应用户优选模型,实现对不同用户响应潜力的初评估,并利用k-means算法和近邻传播算法进行群体划分,在不同时间尺度对用户进行优选;最后,基于水泥、造纸等4个行业的多个工业用户实际负荷数据进行算例分析,呈现了所提方法下工业需求响应的用户优选结果。

考虑柔性负荷和阶梯式碳交易的微电网鲁棒优化调度

针对低碳背景下微电网中可再生能源出力的不确定性以及碳排放问题,提出了一种考虑阶梯式碳交易机制同时柔性负荷参与调控的微电网两阶段鲁棒优化方法。在调度模型中引入阶梯式碳交易机制,限制系统的碳排放量;通过柔性负荷的调控作用弥补由于可再生能源出力波动造成的功率缺额,进一步减小了微电网的碳排放量和调度成本;模型中引入不确定参数调节系统的保守性,日前阶段基于预测数据并考虑系统日内可能遭受的最恶劣场景,制定预测数据下的日前调度方案,日内调控阶段则在日前调度方案的基础上进行二次优化,在最恶劣场景下给出系统的日内调控方案;模型利用嵌套C&CG算法对调度模型进行求解。算例仿真结果证明,鲁棒优化方法相较于确定性优化方法其总调度成本平均减少了3.1%;考虑阶梯式碳交易机制后,系统单日运行的碳排放量和总调度成本相较于未考虑碳交易机制时分别下降了17.7%和3.7%;考虑柔性负荷参与调度后,系统单日运行的碳排放量和总调度成本相较于未考虑柔性负荷时分别下降了26%和24.3%,验证了所提优化模型的有效性。

主轴划痕对轴承系统抵御多种载荷冲击的动态性能影响

建立了1个考虑主轴划痕、轴瓦变形和沟槽结构的水润滑橡胶轴承混合润滑瞬态模型,研究了划痕对水润滑橡胶轴承在周期性载荷及非周期性载荷作用下的动态行为影响.结果表明:在偏心载荷下,划痕的存在会使得主轴与轴承出现“高温布朗运动”般的反复碰撞现象,且划痕深度及宽度的增大均会延长启动过程中的微凸体接触时间,严重降低水润滑轴承寿命;在受到脉冲载荷后,划痕会使轴心的运动范围变大,导致轴承与主轴更容易发生碰摩,降低轴承抵抗脉冲载荷冲击的能力;深划痕及宽划痕时,水润滑轴承受到阶跃载荷干扰会从弹流润滑状态进入混合润滑状态.主轴表面出现划痕使轴承系统遭遇外载荷干扰时的自动抵御能力退化.

液体动静压球轴承轴心运动轨迹研究

为研究外载荷对轴承转子系统稳定性的影响,以小孔节流的液体动静压球轴承转子系统为研究对象,建立液体动静压球轴承转子系统动力学模型。通过求解轴承润滑数学模型获得非线性油膜力,分析转子所受到的外载荷,采用欧拉算法预测出轴心下一个时刻位移、速度和加速度,并分析转子系统质量、不平衡载荷和阶跃载荷对转子回转精度的影响。结果表明:随着转子系统质量的增加,所需平衡的油膜力增加,轴心振动幅度增加,从而导致转子回转精度降低;相对于不考虑不平衡载荷,考虑不平衡载荷后其振动形态为椭圆且振动幅值增大,减小不平衡值将减小振幅并提高旋转精度;随着阶跃载荷的增加,达到平衡所需的时间也增加。

海上风电高桩承台基础结构的受力特性

为研究海上风电高桩承台基础结构在风电机组大弯矩荷载及复杂海洋环境荷载作用下的受力及传力机理,采用在数值模型中逐级加载的方式,模拟不同荷载量级情况下基础受力特性,获得了高桩承台组合结构的关键承载部位,分析了混凝土承台及斜向钢管桩受力特性.研究结果表明,随着风电机组荷载和环境荷载的增大,混凝土承台承载模式将由轴压承载向偏压转变;钢管桩顶部与混凝土承台接触部位是承载及荷载传递的关键部位,混凝土受拉损伤首先从此处开始;随着荷载的增大,斜向钢管桩群桩应力最大部位将从波流荷载作用点向泥面处转变.研究明晰了海上风电高桩承台基础的荷载传递规律及关键部位,为基础结构的安全设计提供了指导.

基于阶跃阻抗谐振器的四阶频率可调滤波器设计

提出一种基于阶跃阻抗谐振器的紧凑型四阶四零点频率可调滤波器设计。滤波器使用变容二极管加载的阶跃阻抗谐振器(VL-SIR),有效拓宽了滤波器的调谐范围。在VL-SIR之间引入交叉耦合,从而在滤波器通带近端产生一对传输零点,显著提高了滤波器的选择性。同时,引入源和负载端的交叉耦合,在通带远端生成一对传输零点,以提高带外抑制。此外,采用基于VL-SIR的频变耦合结构来实现恒定绝对带宽。仿真结果与实测结果吻合良好。测量结果显示,可调滤波器频率调谐范围为0.78~1.15 GHz,3 dB绝对带宽约为55±3 MHz,滤波器的回波损耗大于10 dB,插入损耗约为2.8~3.3 dB。

煤蠕变过程电磁辐射频谱特征实验研究

为了研究煤在单轴蠕变加载条件下,电磁辐射频谱变化的响应规律,分别测试了不同煤种在单轴载荷下,垂直层理方向上短时蠕变过程中全阶段的电磁辐射频谱的变化特征,并讨论了其变化规律。研究结果表明,在单轴蠕变分级加载的过程中,煤体的电磁辐射频率及其振幅总体趋势出现了相似的变化规律,并且各个阶段的频率及其振幅也有各自相似的变化规律。在整个蠕变过程中煤体的电磁辐射信号频率整体处在低频阶段,主要集中于0~0.5 MHz,且加速蠕变变形阶段的电磁辐射频带范围大于减速和等速蠕变变形阶段。在减速和等速蠕变变形期,煤体的电磁辐射频率的振幅变化均处在低振幅阶段;在加速蠕变变形期,可能由于煤体损伤的加剧,使得电磁辐射频率的振幅变化出现较大幅度的波动;在加速蠕变变形末期直到样品临近断裂前,煤体的电磁辐射频率的振幅值会出现增大减小增大的趋势。研究结果可为煤岩流变突变过程中损伤破坏信息的准确感知及煤岩动力灾害的智能监测与预警提供一定的实验和理论依据。

多工况下的直齿轮接触疲劳寿命仿真研究

基于直齿轮静力学分析的应力特征和瞬态动力学的应力时间子步历程,结合弹流润滑理论下的齿面摩擦因数,使用Workbench建立直齿轮接触疲劳寿命模型。通过弹性力学赫兹接触理论对静力学有限元仿真结果进行校核,确定应力历程输入中的放缩系数,估计材料的S-N曲线,并在Palmgren-Miner线性损伤理论框架下,利用nCode计算直齿轮接触疲劳寿命,得到寿命云图和危险节点位置。结果表明:齿轮接触疲劳的危险节点多出现在齿面沿齿宽方向线接触的两端位置,输入转速、负载转矩与接触疲劳寿命呈负相关,摩擦因数与接触疲劳寿命呈正相关,负载转矩对接触疲劳寿命的影响幅度最大。

分步负载金属法制备铁钴双金属位点高效氧还原电催化剂

过渡金属和氮掺杂的碳(M-N-C)由于优异的电催化活性以及较低的生产成本,成为铂基催化剂的替代。然而,目前的M-N-C催化剂通常涉及金属盐、含氮物质和碳载体的结合,在经过热处理和酸洗过程后得到的催化剂在活性位点密度和传质能力上性能不足。采用分步负载金属法制备了Fe、Co双金属掺杂的M-N-C催化剂。利用Zn2+和Co2+的竞争效应,成功合成了小尺寸且均匀的Zn-Co-ZIFs双金属沸石咪唑骨架。随后,在不形成金属团簇的前提下将最大量的Fe原子嵌入C-Zn-Co-ZIFs-H+前体结构中,使其在热解后能产生大量的FeCo—Nx活性位点。这种改进显著增加了FeCo-N-C-2催化剂中Fe活性位点的含量(1.9%,质量分数),并深度优化了其微孔和介孔结构(860 m^(2)·g^(-1))。该催化剂在0.1 mol·L^(-1) HClO_(4)和0.1 mol·L^(-1) KOH溶液中,氧还原反应(ORR)活性展现出了0.806 V和0.921 V的半波电位,并分别在50000、45000 s恒定电位测试后保持了91.21%和95.32%的活性。将其组装于质子交换膜燃料电池(PEMFCs)和碱性锌-空气液流电池(ZAFBs)中,峰值功率密度分别达到了746、164 mW·cm^(-2),显示出优越的性能。

立式物料反应釜出料闸阀密封特性研究

针对D-3400立式物料反应釜出料闸阀在设计阶段密封无法准确分析问题,建立出料闸阀有限元模型,通过多载荷步方式对出料闸阀密封圈的预应力及其工作过程进行动态仿真,分析其在装配后的预应力及负载工况下的变形规律,并利用结构强度及密封比压理论,验证了密封圈的结构强度及密封可靠性。分析结果表明,出料闸阀密封圈的最大等效应力小于材料的许用应力,满足强度要求;密封圈与闸阀阀座之间的关键接触对,其实际密封比压小于密封许用比压且大于密封必需比压,密封可靠;通过中试机构在设计工况下的保压试验证明,D-3400立式物料反应釜出料闸阀密封结构满足设计要求。

基于需求侧响应的“光储直柔”能源系统仿真研究

“光储直柔”技术是实现我国能源转型的重要途径,当前该技术仍面临电网负荷峰谷差所带来的用电风险,需求侧响应可以有效平抑峰谷差,但与此同时也给“光储直柔”能源系统带来了不稳定性因素。为了探究不同需求侧响应的柔性用电策略对于“光储直柔”能源系统的稳定性影响,通过Matlab/Simulink仿真平台建立了“光储直柔”能源系统动态仿真模型,以某办公建筑的用能需求为实例,对该能源系统模型在不同阶跃负荷的扰动下母线电压的偏差变化进行了研究。结果表明,基于Simulink的仿真系统可以很好地适用于“光储直柔”能源系统性能预测,在余电上网以及电网供电两种状态下,负荷阶跃变化量的极限值分别为13.5 kW和13.7 kW。