基于有效约束集法的混合梁斜拉桥合理成桥状态确定方法

 针对混合梁斜拉桥的结构特点,提出基于有效约束集法的混合梁斜拉桥合理成桥状态优化方法.以混合梁斜拉桥主梁、桥塔的弯曲及拉压能量之和为目标函数,以钢箱梁段竖向位移、桥塔水平位移、主梁上下缘及桥塔两侧应力、斜拉索索力及其均匀性为约束条件,建立混合梁斜拉桥合理成桥状态的二次规划数学模型,采用有效约束集算法进行合理成桥状态的优化.实例优化及比较结果显示,优化所得成桥状态,主梁竖向位移-22~8 mm,桥塔塔顶水平位移为向主跨侧偏20 mm,结构整体线形平顺;钢箱梁上下缘及钢桥塔两侧应力为-84.43~16.38 MPa,混凝土主梁上下缘及混凝土桥塔两侧应力为-16.31~-0.003 MPa,结构内力及应力均与无约束最小弯曲能量法计算结果相近;斜拉索索力为2061~2457 kN,其分布比无约束最小弯曲能量法的计算结果更均匀,且边墩具有更大的压力储备,表明该方法的有效性和优越性.     

用能量法求解分布载荷作用下的静不定梁

采用能量法求解了分布载荷作用下静不定梁的内力。算例计算表明,采用能量法求解分布载荷作用下静不定梁的内力,比积分法、力法、位移法等方法简洁。     

厚板弯曲问题的能量法

本文引入了Timoshenko梁振型函数,用能量法求解了厚板问题,得到了较为精确的结果。     

悬臂梁在横向荷载下的力学响应分析

从能量的角度出发,考虑弹性梁轴线伸长的基础上,建立Euler-Bernoulli梁在横向机械载荷作用下的几何非线性数学模型。结合Hamilton变分原理和Kantorovich时间平均法得到了梁的非线性自由振动的无量纲常微分控制方程组。采用打靶法,求得了悬臂梁的弯曲变形和自由振动的数值解,并对数值结果进行了分析。     

局域共振声子晶体失谐梁的减振特性研究

通过把声子晶体中的局域共振特性应用到梁上形成一种局域共振梁,在局域共振周期梁的基础上,引入晶格参数失谐,提出一种新型的局域共振失谐梁.对失谐梁和周期梁分别进行正弦激励响应和频率响应分析,并改进能量法,可得出结论:通过选择合适的失谐参数,可使失谐梁较传统周期梁具有更好的减振特性.     

考虑节点刚度的预制混合梁框架抗侧刚度研究

基于边界条件为两端刚接的钢-混凝土预制混合梁,推导了考虑连接半刚性影响的预制混合梁刚度矩阵.当螺旋弹簧转动刚度趋于无穷大时,刚度矩阵将退化为两端刚接的预制混合梁单元刚度矩阵.通过引入无量纲参数p、δ对刚度矩阵进行简化处理.其中预制混合梁刚度系数p介于0～1之间,其反映了预制混合梁的半刚性特性.当节点为铰接时,刚度系数p...     

用分区混合有限元法分析高梁和托墙梁

本文用[1]、[2][3]中提出的分区混合能量原理和分区混合有限元法分析高梁和托墙梁。在应力梯度大的区域用应力单元,在应力梯度小的区域采用位移单元。两种单元结合,各自发挥所长,能以较疏的网格取得较高的精度。     

用无网格局部Petrov-Galerkin法分析弹性地基上的梁

利用无网格局部彼得洛夫－伽辽金法求解了弹性地基上的浅梁。给出了简支梁和固支梁的位移和能量的索波列夫模及其相对误差。计算结果表明,这种方法具有稳定性好、收敛快且精度高的优点。     

大变形柔性梁系统的绝对坐标方法

研究了绝对坐标法在大变形柔性梁系统刚柔耦合动力学问题中的应用．考虑几何非线性,用绝对坐标法推导出有限元离散的平面梁系统的动力学方程．用能量守恒原理验证了绝对坐标法计算结果的正确性．比较大变形时的绝对坐标法与一次近似的混合坐标法的计算结果表明,文中绝对坐标法比一次近似的混合坐标法模型更精确,适合于大变形的情况．     

预应力CFRP绞线和钢筋混合配筋混凝土梁的抗弯性能

为了探索碳纤维复材(CFRP)绞线在混凝土结构中的应用,采用CFRP绞线作为预应力筋,开展了预应力CFRP绞线和钢筋混合配筋混凝土梁的抗弯性能试验研究。试验结果表明:平截面假定适用于混合配筋的混凝土梁;配置预应力CFRP绞线可以显著提高混凝土梁的抗弯承载力,相比于普通钢筋混凝土梁,混合配筋混凝土梁的开裂荷载、屈服荷载和极限荷载分别提高了74%~146%、27%~48%和29%~50%,但混合配筋混凝土梁的延性明显降低;在混凝土压碎失效模式下,预应力水平和预应力CFRP绞线数量对延性影响并不明显;GB 50608—2020《纤维增强复合材料工程应用技术标准》中预应力纤维复材(FRP)筋混凝土梁的抗弯承载力计算公式可以应用于预应力CFRP绞线和钢筋混合配筋混凝土梁的抗弯承载力计算。     

有限能量Airy光束的自我修复特性研究

对有限能量Airy光束的自我修复特性做了深入研究，给出了畸变有限能量Airy光束的自我修复能力是弱衍射光束与衍射光束的竞争机制新的理论说明。文中采用对比实验、结合数值模拟得到自由传播下不同初始畸变的有限能量Airy光束的场分布演变过程，结果表明:初始光束的主瓣畸变是一个渐近修复过程，畸变越大修复速度越快；而初始光束的旁瓣畸变是一个光束能量波动修复过程，离主瓣越远的旁瓣被遮挡自我修复速度越快。     

Monoenergetic beams of relativistic electrons from intense laser-plasma interactions

High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 10(19) W cm(-2) at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and gamma-rays. Relativistic electrons are generated through the breaking of large-amplitude relativistic plasma waves created in the wake of the laser pulse as it propagates through a plasma, or through a direct interaction between the laser field and the electrons in the plasma. However, the electron beams produced from previous laser-plasma experiments have a large energy spread, limiting their use for potential applications. Here we report high-resolution energy measurements of the electron beams produced from intense laser-plasma interactions, showing that--under particular plasma conditions--it is possible to generate beams of relativistic electrons with low divergence and a small energy spread (less than three per cent). The monoenergetic features were observed in the electron energy spectrum for plasma densities just above a threshold required for breaking of the plasma wave. These features were observed consistently in the electron spectrum, although the energy of the beam was observed to vary from shot to shot. If the issue of energy reproducibility can be addressed, it should be possible to generate ultrashort monoenergetic electron bunches of tunable energy, holding great promise for the future development of 'table-top' particle accelerators.     

钢筋混凝土梁弯曲破坏时声发射信号能量特征及其辅助定位

为了得到钢筋混凝土梁在弯曲破坏时声发射能量特征,对钢筋混凝土梁进行了弯曲破坏实验,捕捉实时能量特征。加载方式分为直接加载至破坏和分段加载至破坏两种方式。通过分析捕获的实时声发射信号能量信息以及整个加载阶段钢筋混凝土梁的能量释放特征,对钢筋混凝土梁的损伤断裂进行了预示。加载之前进行了断铅实验,进行了能量辅助定位,并获得了较好的精度。     

燕尾榫样式对CFRP加固榫卯接长木梁抗弯性能影响试验

通过11根木梁的静力受弯试验,研究燕尾榫样式对榫卯接长木梁加固后的抗弯性能的影响.试验结果表明,未加固前榫卯接长木梁承载力较低,仅为完整木梁的1.00%~2.62%,经CFRP布加固后其抗弯承载力可提高至完整木梁的50%~83.33%;旋转90°后,传统燕尾榫进行榫卯接长和采用榫头带榫肩接长,其抗弯承载力和能量吸收能力提高.燕尾榫榫头斜率从0.1变化至0.3,木梁的抗弯承载力和能量吸收能力随之提高,其抗弯承载力分别可达完整木梁的71.43%~83.33%,能量吸收能力分别达完整木梁的43.01%~61.33%.当燕尾榫榫头长度超过传统燕尾榫榫头长度时,其抗弯承载力、能量吸收能力和刚度反而降低.     

聚乙烯醇纤维钢筋复合梁抗弯性能试验研究

掺入聚乙烯醇纤维(简称“PVA纤维”)的钢筋混凝土梁具有优良的抵抗变形能力和抗裂性能,在工程结构中具有良好的应用前景。为研究PVA纤维的掺入对PVA纤维钢筋复合梁(简称“PRC梁”)抗弯性能的影响,进行了4根PVA纤维体积掺量不同的PRC梁的静态三点弯曲加载试验。结果表明：PVA纤维的掺入并没有改变PRC梁的破坏形态,且破坏过程相似;但是掺入PVA纤维极大增强了PRC梁的抗裂性,延缓了裂缝的出现。相比于普通RC梁,0.75%(体积分数)掺量下的PRC梁开裂荷载提高了2.1倍;同时,掺入PVA纤维能够小幅增加PRC梁的抗弯承载力,在加载过程中,PVA纤维混凝土与钢筋能够更好地协同工作,从而增强了PRC梁的持荷变形能力;荷载位移曲线的积分面积表明(利用Origin曲线积分发现)PRC梁在加载过程中吸收的能量更多,因此,掺入PVA纤维能够有效增强PRC梁的延性。     

梁振动控制中压电作动器的位置优化准则

以输入的控制信号能量最小为目标,提出了梁结构振动控制中压电作动器的位置优化准则,基于压电片层合简支弹性梁的模态振动方程,给出了反映各压电作动器上控制电压与模态控制力之间关系的控制电压影响系数的表达式;详细推导了控制信号能量的表达式,并根据控制能量最小的准则对压电作动器的位置进行优化,数值分析中,对梁结构的振动控制过程进行系统仿真,比较了相同衰减时间下压电作动器位于梁表面不同位置时系统输入能量的大小,数值模拟所得的最优位置与理论结果非常吻合,验证了该准则的正确性。     

纤维布加固混凝土连续梁弯矩重分布特征分析

通过延性系数指标来研究纤维布加固矩形截面混凝土连续梁的弯矩重分布能力,采用数值分析方法模拟纤维布加固矩形截面混凝土连续梁的弯矩重分布系数。研究发现,能量法计算的能量比可考虑纤维布加固T形截面混凝土连续梁的实际弯矩重分布能力,可利用弯曲刚度法分析纤维布加固T形截面混凝土连续梁截面弯矩重分布系数的演变过程。     

Calculation of depth-dose distribution of intermediate energy heavy-ion beams

Based on the characteristics of the interactions between intermediate energy heavy-ion beam and target matter, a method to calculate the depth-dose distribution of heavy-ion beams with intermediate energy (10 -100 MeV/u) is presented. By comparing high energy beams where projectile fragmentation is overwhelm ing with lowenergies where energy straggling is the sole factor instead, a crescent energy spread with increasing depth and a simple fragmentation assumption were included for the depth-dose calculation of the intermediate energy beam. Rel ative depth-dose curves of carbon and oxygen ion beams with intermediate energie s were computed according to the method here. Comparisons between the calculated relative doses and measurements are shown. The calculated Bragg curves, especially the upstream and downstream Bragg peaks, agree with the measured data. Differences between the two results appear only around the peak regions because of th e limitations of the calculation and experimental conditions, but the calculated curves generally reproduce the measured data within the experimental errors. Th e reasons for the divergences were analyzed carefully and the magnitudes of the deviations are given.     

Morphology of polar ionospheric O^＋ ion upflow： FAST observations during quiet time

With energetic ion measurements on FAST satellite, the morphologic features of quiet-time ionospheric O ion upflowing at altitudes of 2000 to 4000 km are drawn out for the first time. The pre-noon cusp/cleft is the predominant region of upflowing occurrence for O with lower energy. Meanwhile the pre-dawn sector near the equatorward edge of the plasma convection dominates the occurrence for the higher energy O ions. No matter whether the energy is lower or higher, the upflows occur often over a wide MLT range of lower latitudes outside the auroral oval. The upflowing within the pre-midnight (21:00― 22:00 MLT) auroral oval carrys larger energy fluxes, with extremely large fluxes for higher energy O appearing near the polar cap boundary. For altitudes of 2000―4200 km under observation, the ion conics occur much more frequently than ion beams. Ion beams are rarely found below 3000 km, while the conics occur uniformly over the observed altitudes.