强夯双向土压力模型试验测试及加固效果分析

【目的】从土体应力分布特征的角度研究不同夯击方式对砂土强夯加固效果的影响。【方法】通过室外场地进行的强夯模型试验对夯击过程中土体内部的竖向与径向土压力以及落锤加速度进行监测,并结合数值模拟的方法对土体内部的位移进行分析。【结果】研究得出:在强夯法施工中竖向土压力存在冲击与震荡衰减两种波形,径向土压力则主要以冲击波形为主;在砂土强夯加固过程中存在两种加固模式,夯击点正下方土体主要以竖向压实为主,而斜下方土体同时兼有显著的径向挤密作用;在同能级强夯施工中,“重锤低落”组合适合对深层土体与径向土体进行加固,“轻锤高落”组合适合对浅层土体进行快速加固。【结论】研究成果对同能级强夯夯击方式的选用具有一定的指导意义。

基于扰动观测器的大挠性航天器姿态预见控制

针对航天器的大型挠性附件振动会严重影响其姿态控制的问题,设计了基于扰动观测器的信息融合姿态预见控制器。将挠性附件振动引起的不确定项视作对姿态的复合扰动,设计扰动观测器对该复合扰动进行实时估计。在此基础上,通过融合期望轨迹和系统动态方程等信息,依据信息融合理论,推导了大挠性航天器的姿态预见控制律,用以改善航天器姿态系统的控制性能。所设计的姿态控制算法具有设计过程简单及容易实现等优点。仿真结果表明,所设计的控制策略对挠性附件振动具有较好的抑制作用,航天器姿态角能快速达到期望指令,具有良好的控制特性。

大挠性航天器的模糊模型预测控制

针对带有大型挠性附件的航天器姿态控制系统,将自适应模糊控制和模型预测控制相结合,设计了大挠性航天器的模糊模型预测姿态控制策略。基于大挠性航天器的动力学模型,采用泰勒展开设计出了非线性模型预测控制律,避免了预测控制在线优化过程中繁琐的计算,有效降低了计算复杂度。针对大挠性附件振动导致的不确定性扰动对姿态控制的影响,使用自适应模糊控制来逼近不确定扰动。基于Lyapunov理论证明了控制系统的稳定性,并推导了模糊参数的自适应律。仿真结果表明所设计的控制策略对大挠性附件振动有很好的抑制作用,可以控制姿态角对期望值实现快速跟踪,具有较好的控制特性。

Dynamic response analysis of liquefiable ground due to sinusoidal waves of different frequencies of shield construction

Vibration induced by shield construction can lead to liquefaction of saturated sand.Based on FLAC3D software,a numerical model of tunnel excavation is established and sinusoidal velocity loads with different frequencies are applied to the excavation face.The pattern of the excess pore pressure ratio with frequency,as well as the dynamic response of soil mass under different frequency loads before excavation,is analyzed.When the velocity sinusoidal wave acts on the excavation surface of the shield tunnel with a single sand layer,soil liquefaction occurs.However,the ranges and locations of soil liquefaction are different at different frequencies,which proves that the vibration frequency influences the liquefaction location of the stratum.For sand-clay composite strata with liquefiable layers,the influence of frequency on the liquefaction range is different from that of a single stratum.In the frequency range of 5-30 Hz,the liquefaction area and surface subsidence decrease with an increase in vibration frequency.The research results in this study can be used as a reference in engineering practice for tunneling liquefiable strata with a shield tunneling machine.

加筋褥垫层在灰土挤密桩复合地基中的应用

通过对建筑条形地基下的灰土挤密桩复合地基加筋褥垫层的现场试验,对桩顶、桩间土应力、三向土工格栅应变等项目进行了测试,得到了在桩土应力比、三向土工格栅应变随建设高度的变化过程线。通过现场试验表明,建筑条形地基下加筋褥垫层灰土挤密桩复合地基中,在不同位置桩顶应力、桩间土应力有不同的变化趋势;桩间土的变化趋势也有不同,在柱下、条形基础交接处中心达到最大值。通过柔性位移计对土工格栅的变形进行量测,得到土工格栅在纵向、横向、斜向的应变变化过程线,试验表明:不同位置的土工格栅的应变变化过程线差异较大,在柱下、条形基础交接处中心达到最大值。同一位置的3个不同方向应变变化过程线也有差异,柱下条形基础交接中心处斜向肋条受力最大。

盾构下穿浅基础建筑的沉降规律分析

盾构施工会引起隧道周围土体变形,使地表已有建筑产生沉降和倾斜。针对太原地区汾河漫滩地层盾构下穿浅基础建筑物这一施工工况,比较FLAC3D模拟与现场监测两种方法得到的结果,分析建筑物存在与否以及建筑物刚度对于沉降规律的影响。结果表明:建筑物的存在对形成的横向沉降槽影响较小,但沉降过程与没有建筑物相比差别很大,建筑物的存在会约束周围土体,使建筑物及周围地层在沉降过程中表现出滞后性和整体性;建筑物刚度的改变对沉降滞后性的影响较小,刚度越大整体性越强。研究成果有助于盾构施工过程中建筑物及周围地层变形的预测。

土工格栅老化对双向复合地基性状影响的室内模型试验

为研究土工格栅老化时长对双向复合地基性状影响的规律,对土工格栅进行光氧、热氧老化,选用不同老化时长的土工格栅作为双向复合地基的横向增强体,建立双向复合地基室内模型,定时监测复合地基及其各组成部分(包括褥垫层、桩体加固区和桩底持力层)的沉降、土工格栅应变和土工格栅上下的土压力;分析经不同时长老化的土工格栅对双向复合地基及其各组成部分沉降、土工格栅应变和土工格栅上下桩土应力比的影响规律。试验发现:双向复合地基及其各组成部分沉降值和土工格栅应变量均随土工格栅老化时长增大而增大;土工格栅下侧桩土应力比和复合地基承载能力均随土工格栅老化时长增大而减小;土工格栅上侧桩土应力比与土工格栅老化时长无关。

深基坑水平封底在富水深厚砂层的加固效果

对于位处富水深厚砂层中的深基坑,在开挖过程中可能出现涌水涌砂等施工安全问题。采用基底封底配合降水减压是保证基坑安全开挖的常用措施。以太原某地铁车站区间明挖法施工工程为背景,采用有限元软件进行基坑开挖过程的流固耦合分析和对比,并结合现场监测数据,研究了不同封底形式和降水对基坑的变形影响。结果表明:封底加固能有效减小地连墙最大侧位移、地表最大沉降和基底最大隆起,相比未加固,变形量减少约50%;同一加固厚度,从基底开始加固效果更好;封底加固区与地连墙组成的新支护体系配合井点降水能很好地控制地下水渗流和基坑变形。

基于自触发的大挠性航天器模型预测姿态控制

针对大挠性航天器,考虑其控制量受限,设计了自触发模型预测姿态控制系统。在控制量更新时刻,基于模型求解优化问题推导出预测控制序列,取控制序列的前若干步来控制实际系统。不同于传统模型预测控制需要在每个采样时刻求解优化问题,该控制方法采用自触发策略确定控制量更新时刻和预测时域,以有效减少优化问题的求解次数,从而缩短了控制算法的在线计算时间,使系统状态能快速进入终端区域,然后采用状态反馈控制使姿态角迅速到达期望值,证明了控制算法的可行性及自触发预测姿态控制系统的稳定性。仿真结果表明,该姿态控制方法可使大挠性航天器姿态角快速跟踪姿态角期望值,有较好的动静态性能。

航天器太阳帆板伸展过程的自适应动态规划方法

运用自适应动态规划方法求解航天器太阳帆板伸展过程的最优控制问题。根据多体动力学理论,导出航天器太阳帆板伸展过程的姿态运动规划,并将其转化为最优控制问题。使用自适应动态规划算法,利用评价网络近似最优性能指标,执行网络逼近最优控制,用龙格库塔法求解状态向量。并进行了执行依赖启发式动态规划(ADHDP)控制器的设计,合理选择参数。数值仿真实验验证了该算法对航天器太阳帆板伸展过程运动规划最优控制问题的可行性。

OPTIMAL MOTION PLANNING FOR A RIGID SPACECRAFT WITH TWO MOMENTUM WHEELS USING QUASI-NEWTON METHOD

An optimal motion planning scheme based on the quasi-Newton method is proposed for a rigid spacecraft with two momentum wheels. A cost functional is introduced to incorporate the control energy, the final state errors and the constraints on states. The motion planning for determining control inputs to minimize the cost functional is formulated as a nonlinear optimal control problem. Using the control parametrization, one can transform the infinite dimensional optimal control problem to a finite dimensional one that is solved via the quasi-Newton methods for a feasible trajectory which satisfies the nonholonomic constraint. The optimal motion planning scheme was applied to a rigid spacecraft with two momentum wheels. The simulation results show the effectiveness of the proposed optimal motion planning scheme.

Numerical Simulation of Dynamic Response of Saturated Sand During Shield Construction

In order to study the disturbance of the liquefiable stratum caused by the vibration induced by construction of the shield machine,the construction process of the shield tunnel was simulated based on the finite difference software FLAC 3 D.A sinusoidal velocity boundary that simulates the vibration of shield construction is applied in the horizontal direction of the excavation surface,and dynamic response analysis is carried out to analyze the excess pore water pressure,acceleration,and vertical effective stress time-history curves.The research results show that in the liquefiable stratum,the vibration induced by shield construction will form a certain liquefaction area in the soil in front of the excavation face.The area has not developed to the ground.The area where the vibration induced by shield construction has a great influence on the excess pore water pressure of the soil is below the excavation surface.This area is vortex-shaped.The excess pore water pressure of the overlying soil layer on the excavation surface increases,and the vertical effective stress decreases.The horizontal vibration wave induced by shield construction has no obvious attenuation in the horizontal direction,but has obvious attenuation during the propagation to the ground surface.In the area where the peak value of soil acceleration is large,the soil liquefaction is serious.

大挠性航天器的自触发模型预测控制

针对大挠性附件的剧烈振动严重影响大型挠性航天器姿态精度的问题,设计了基于自触发机制的模型预测姿态控制策略。不同于传统模型预测控制策略需要在每个采样时刻求出最优控制序列,自触发模型预测控制仅在触发时刻求解优化问题算出最优控制序列。根据自触发算法计算下一个触发时刻和预测时域,在到达下一个触发时刻前,取最优控制序列中前几步控制量施加到实际系统中,从而降低优化问题的求解频率,缩短控制策略的在线计算时间。所设计的自触发控制可使系统状态快速进入终端集,而后切换为状态反馈控制姿态快速跟踪上期望值。最后,开展了仿真校验。仿真结果表明,所设计的控制算法能控制大挠性航天器迅速达到期望姿态,具有较好的控制特性。

内外套管组合沉管夯扩法在大厚度湿陷性黄土地基中的现场试验研究

由传统技术改进而来的内外套管组合沉管夯扩法,是一种利用内外套管组合沉管成孔,加大成孔深度,再由重锤二次夯扩挤密的新技术,地基处理深度可达60m。结合具体的工程,对在大厚度湿陷性黄土地基中使用该方法成桩的桩长26,32,35m的灰土挤密桩和桩长20,32,36m的水泥土挤密桩进行现场试验研究,测得两种桩间土挤密系数均不小于0.93,桩体压实系数均不小于0.97,湿陷系数均小于0.015,满足规范要求;同时承载力也满足设计要求。

大直径预应力高强混凝土管桩抗剪承载力数值模拟研究

针对预应力高强混凝土(PHC)管桩抗剪承载力的问题,现有规范和图集提出了不同的计算公式。为了探究大直径PHC管桩的极限抗剪承载力,在现行公式计算结果与前人试验结果的基础上,采用ABAQUS数值模拟软件,对工程中常用的大直径(600~1000 mm)PHC管桩的抗剪承载力进行数值分析。通过分析剪跨比为1.5~3.0的管桩在剪压破坏过程中破坏面混凝土和箍筋的抗剪承载力,得出以下主要结论:管桩抗剪承载力在下降过程中表现出波动下降的趋势;管桩达到最大抗剪承载力与管桩破坏不同步,在达到最大抗剪承载力时,管桩中性轴上部混凝土发生拉裂;随着位移加载的进行,在拉裂缝基本贯通时,桩身混凝土发生破坏,箍筋应力增大,且箍筋屈服,但未断裂。最后,在现有公式的基础上,基于45°破裂面假设,提出了PHC管桩抗剪承载力计算公式。

Optimal control of a spacecraft with deployable solar arrays using particle swarm optimization algorithm

The optimal control problem of the multibody dynamics of a spacecraft in space, modeled as a central body with one-sided connected deployable solar arrays, is investigated. The dynamical equations of motion of the spacecraft with solar arrays are derived using the multibody dynamics method. The control of the attitude motion of a spacecraft system can be transformed into the motion planning problem of nonholonomic system when the initial angular momentum is zero. These are then used to investigate the motion planning of the spacecraft during solar arrays deployment via particle swarm optimization (PSO) and results are obtained with the optimal control input and the optimal trajectory. The results of numerical simulation show that this approach is effective for the control problem of the attitude of a spacecraft during the deployment process of its solar arrays.

Nonholonomic motion planning for a free-falling cat using spline approximation

An optimal motion planning of a free-falling cat based on the spline approximation is investigated.Nonholonomicity arises in a free-falling cat subjected to nonintegrable velocity constraints or nonintegrable conservation laws.The equation of dynamics of a free-falling cat is obtained by using the model of two symmetric rigid bodies.The control of the system can be converted to the motion planning problem for a driftless system.A cost function is used to incorporate the final errors and control energy.The motion planning is to determine control inputs to minimize the cost function and is formulated as an infinite dimensional optimal control problem.By using the control parameterization,the infinite dimensional optimal control problem can be transformed to a finite dimensional one.The particle swarm optimization(PSO) algorithm with the cubic spline approximation is proposed to solve the finite dimension optimal control problem.The cubic spline approximation is introduced to realize the control parameterization.The resulting controls are smooth and the initial and terminal values of the control inputs are zeros,so they can be easily generated by experiment.Simulations are also performed for the nonholonomic motion planning of a free-falling cat.Simulated experimental results show that the proposed algorithm is more effective than the Newtoian algorithm.