Non-harmonic resonance of viscoelastic structures subjected to time-dependent exponentially decreasing transverse distributed loads

In this paper,the non-harmonic resonance of Bernoulli viscoelastic beams,Kirchhoff viscoelastic plates,Timoshenko viscoelastic beams,and Mindlin viscoelastic plates subjected to time-dependent exponentially decreasing transverse distributed load is investigated for the first time.The constitutive equations are expressed utilizing Boltzmann integral law with a constant bulk modulus.The displacement vector is approximated by employing the separation of variables method.The Laplace transformation is used to transfer equations from the time domain to the Laplace domain and vice versa.The novel point of the proposed method is to express,prove and calculate the critical time in which the displacement will be several times the displacement at time zero.In addition,this new method calculates the maximum deflection at the critical time,explicitly and exactly,without any need to follow the time-displacement curve with a low computational cost.Additionally,the proposed method introduces the critical range of time so that the responses are greater than the responses at time zero.

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.

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.

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.

Time-dependent deviation of bridge pile foundations caused by adjacent large-area surcharge loads in soft soils and its preventive measures

Time-dependent characteristics(TDCs)have been neglected in most previous studies investigating the deviation mechanisms of bridge pile foundations and evaluating the effectiveness of preventive measures.In this study,the stress-strain-time characteristics of soft soils were illustrated by consolidation-creep tests based on a typical engineering case.An extended Koppejan model was developed and then embedded in a finite element(FE)model via a user-material subroutine(UMAT).Based on the validated FE model,the time-dependent deformation mechanism of the pile foundation was revealed,and the preventive effect of applying micropiles and stress-release holes to control the deviation was investigated.The results show that the calculated maximum lateral displacement of the cap differs from the measured one by 6.5%,indicating that the derived extended Koppejan model reproduced the deviation process of the bridge cap-pile foundation with time.The additional load acting on the pile side caused by soil lateral deformation was mainly concentrated within the soft soil layer and increased with the increase in load duration.Compared with t=3 d(where t is surcharge time),the maximum lateral additional pressure acting on Pile 2#increased by approximately 47.0%at t=224 d.For bridge pile foundation deviation in deep soft soils,stress-release holes can provide better prevention compared to micropiles and are therefore recommended.

A Finite-Difference Approach to the Time-Dependent Mild-Slope Equation

A finite-difference approach is used to develop a time-dependent mild-slope equation incorporating the effects of bottom dissipation and nonlinearity. The Enler predietor-corrector method and the three-point finite-difference method with varying spatial steps are adopted to discretize the time derivatives and the two-dimensional horizontal ones, respectively, thus leading both the time and spatial derivatives to the second-order accuracy. The boundary conditions for the present model are treated on the basis of the general conditions for open and fixed boundaries with an arbitrary reflection coefficient and phase shift. Both the linear and nonlinear versions of the numerical model are applied to the wave propagation and transformation over an elliptic shoal on a sloping beach, respectively, and the linear version is applied to the simulation of wave propagation in a fully open rectangular harbor. From comparison of numerical results with theoretical or experimental ones, it is found that they are in reasonable agreement.

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.

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.

Analytical solutions for consolidation of stone column composite foundations considering time-dependent boundary and loading

In response to the existing consolidation theory for stone column composite foundations which cannot consider the time-dependent loading and the well resistance effect of stone columns under time-dependent boundaries,a consolidation model that can reflect these characteristics is developed in this study,and the corresponding analytical solutions are obtained under permeable top surface with permeable bottom surface(PTPB)and permeable top surface with impermeable bottom surface(PTIB),respectively.In addition,the reliability of the proposed solutions is verified by comparing them with existing analytical solutions.Extensive calculations are then performed by the proposed solutions to analyze the consolidation behaviors of stone column composite foundations under time-dependent boundaries,the results show that the interface parameters have a large effect on the distribution of excess pore water pressure(EPWP)along the depth;for projects with longer construction time,the permeability of the top and bottom surfaces of the composite foundation has a smaller effect on the average consolidation rate.Finally,the proposed solution is applied to the settlement calculation in an actual engineering project,and the theoretical results show a general agreement with the measured data by considering the influence of the interface parameters.

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。

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。

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。

油气井斜承载台阶面强度研究——以万米超深井超重送入钻杆45°台阶面为例

为应对钻探深度增加带来的井口设备超重载荷挑战,解决超重载荷承载台阶设计校核缺乏统一标准等问题,开展对承载台阶强度的研究。首先,建立考虑摩擦力的斜面台阶力学模型,提出承载台阶剪切失效模型下的计算公式,并对不同设计准则、安全系数和标准下的结果进行对比分析。然后,以万米超深井超重尾管设计的新型带45°斜坡的送入钻杆为例,结合理论分析与弹塑性非线性有限元,进行多种方法求解极限载荷研究,得到轴向的许用载荷和极限载荷,并对钻杆台阶面进行局部应变等评价。研究结果表明:所提出剪切失效公式可用于斜面台阶承载极限载荷计算,建议采用ASME BPVCⅧ-3规定的弹塑性方法进行精细分析,载荷系数取1.8计算许用极限载荷。研究结果为油气井行业中井口设备承载的斜台阶设计与计算提供理论基础与参考。

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.

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.

迈步式吸能支架-巷道围岩系统动力响应数值分析

为防止吸能支架与冲击地压引起的围岩发生共振,提高巷道支护围岩体系的安全性。采用理论分析和数值模拟方法,建立吸能支架-巷道围岩系统模型,考虑初始应力条件,通过在巷道上方施加简谐激励以模拟动载作用,研究在不同动载频率下吸能支架动力响应规律。研究结果表明:当外界扰动频率接近系统固有频率时,会发生共振现象。动载作用下,吸能支架最大位移发生在顶梁,而顶梁位移分布呈中间大两端小趋势,应力分布呈中间高两边低趋势;靠近顶板和靠近动载源处的围岩的加速度幅值较大。动载频率为吸能支架固有频率时,立柱的振动频率与围岩振动频率相差较小。研究结果为动载作用下巷道围岩控制提供有益参考。

基于改进SVT的电力负荷数据恢复算法

针对传统奇异值阈值(Singular Value Thresholding,SVT)数据恢复算法在对电力负荷数据恢复中忽视数据先验信息以及大规模数据计算效率低等问题,提出一种基于相空间重构与自适应变步长的改进SVT的数据恢复算法.为解决传统SVT容易忽视数据先验信息的问题,引入相空间重构算法将原始缺失数据映射到高维空间,利用数据间的关联性和结构特征,为后续数据恢复算法提供先验知识;结合对数与Sigmoid函数构建变步长基础函数,并利用等比项提高前期步长,构建自适应变步长SVT算法,克服传统SVT在大规模数据情况下计算效率低的问题.结合多项公用电力负荷数据集及多种常用电力负荷数据恢复算法进行对比实验分析,结果表明,改进SVT算法可获得更好的数据恢复效果,收敛速度、精度以及稳定性得到提升,具有较强的工程实用性.