First application of large reactivity measurement through rod drop based on three-dimensional space–time dynamics

Abstract Reactivity measurement is an essential part of a zero-power physics test,which is critical to reactor design and development.The rod drop experimental technique is used to measure the control rod worth in a zero-power physics test.The conventional rod drop experimental technique is limited by the spatial effect and the difference between the calculated static reactivity and measured dynamic reactivity;thus,the method must be improved.In this study,a modified rod drop experimental technique that constrains the detector neutron flux shape function based on three-dimensional space–time dynamics to reduce the reactivity perturbation and a new method for calculating the detector neutron flux shape function are proposed.Correction factors were determined using Monte Carlo N-particle transport code and transient analysis code for a pressurized water reactor at the Ulsan National Institute of Science and Technology and Xi’an Jiaotong University,and a large reactivity of over 2000 pcm was measured using the modified technique.This research evaluated the modified technique accuracy,studied the influence of the correction factors on the modification,and investigated the effect of constraining the shape function on the reactivity perturbation reduction caused by the difference between the calculated neutron flux and true value,using the new method to calculate the shape function of the detector neutron flux and avoiding the neutron detector response function(weighting factor)calculation.

Multi-objective strategy to optimize dithering technique for high-quality three-dimensional shape measurement

Dithering optimization techniques can be divided into the phase-optimized technique and the intensity-optimized technique. The problem with the former is the poor sensitivity to various defocusing amounts, and the problem with the latter is that it cannot enhance phase quality directly nor efficiently. In this paper, we present a multi-objective optimization framework for three-dimensional(3D) measurement by utilizing binary defocusing technique. Moreover, a binary patch optimization technique is used to solve the time-consuming issue of genetic algorithm. It is demonstrated that the presented technique consistently obtains significant phase performance improvement under various defocusing amounts.

A method for phase reconstruction in optical three-dimensional shape measurement

In optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that lie in the x-axis direction of the phase domain are given. Partial derivatives of the phase function in the x- and y-axis directions are obtained with a phase-shifting mechanism, the origin of which is analysed. Furthermore, to avoid phase unwrapping in the phase reconstruction, we derive the gradient of the phase function and perform a two-dimensional integral along the x- and y-axis directions. The reconstructed phase can be obtained directly by performing numerical integration, and thus it is of great convenience for phase reconstruction. Finally, the results of numerical simulations and practical experiments verify the correctness of the proposed method.

A fast and precise three-dimensional measurement system based on multiple parallel line lasers

This paper conducts a trade-off between efficiency and accuracy of three-dimensional(3 D)shape measurement based on the triangulation principle,and introduces a flying and precise 3 D shape measurement method based on multiple parallel line lasers.Firstly,we establish the measurement model of the multiple parallel line lasers system,and introduce the concept that multiple base planes can help to deduce the unified formula of the measurement system and are used in simplifying the process of the calibration.Then,the constraint of the line spatial frequency,which maximizes the measurement efficiency while ensuring accuracy,is determined according to the height distribution of the object.Secondly,the simulation analyzing the variation of the systemic resolution quantitatively under the circumstance of a set of specific parameters is performed,which provides a fundamental thesis for option of the four system parameters.Thirdly,for the application of the precision measurement in the industrial field,additional profiles are acquired to improve the lateral resolution by applying a motor to scan the 3 D surface.Finally,compared with the line laser,the experimental study shows that the present method of obtaining 41220 points per frame improves the measurement efficiency.Furthermore,the accuracy and the process of the calibration are advanced in comparison with the existing multiple-line laser and the structured light makes an accuracy better than 0.22 mm at a distance of 956.02 mm.

Influence of sampling on three-dimensional surface shape measurement

In order to accurately measure an object’s three-dimensional surface shape,the influence of sampling on it was studied.First,on the basis of deriving spectra expressions through the Fourier transform,the generation of CCD pixels was analyzed,and its expression was given.Then,based on the discrete expression of deformation fringes obtained after sampling,its Fourier spectrum expression was derived,resulting in an infinitely repeated"spectra island"in the frequency domain.Finally,on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component,the inverse Fourier transform was used to reconstruct the signal strength.A method of reducing the sampling interval,i.e.,reducing the number of sampling points per fringe,was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating.This was done to reconstruct the object’s surface shape more accurately under the condition of m>4.The basic principle was verified through simulation and experiment.In the simulation,the sampling intervals were 8 pixels,4 pixels,2 pixels,and 1 pixel,the maximum absolute error values obtained in the last three situations were 88.80%,38.38%,and 31.50%in the first situation,respectively,and the corresponding average absolute error values are 71.84%,43.27%,and 32.26%.It is demonstrated that the smaller the sampling interval,the better the recovery effect.Taking the same four sampling intervals in the experiment as in the simulation can also lead to the same conclusions.The simulated and experimental results show that reducing the sampling interval can improve the accuracy of object surface shape measurement and achieve better reconstruction results.

导流板倾斜角度对Π型叠合梁涡振性能的影响研究

型叠合梁被广泛应用于大跨度斜拉桥建设中,但该类断面较差的涡振性能严重影响了其应用前景。以某主跨为530 m的Π型叠合梁双塔斜拉桥为工程背景,通过风洞试验对Π型主梁的涡振性能及气动优化措施进行研究。试验结果表明,原设计Π型断面在各风攻角下均存在显著涡激振动,通过在断面工字梁下缘处设置导流板与下中央稳定板可降低梁体的涡振振幅,且导流板倾斜角度的改变对该组合气动措施的制振效果影响显著,其中30°倾角导流板组合气动措施的制振效果最优,可在规范要求阻尼比1.0%下显著抑制甚至消除梁体的涡激振动。通过CFD数值模拟对该组合气动措施的制振机理与导流板倾斜角度的变化对组合气动措施制振性能的影响机理进行了研究,计算结果表明,30°倾角导流板组合气动措施中的迎风侧导流板可显著改善上游断面的气体绕流状态,并配合下中央稳定板削弱Π型断面尾流的卡门涡脱,从而起到抑制主梁涡振的效果,改变导流板倾斜角度会在影响导流板自身附近旋涡生成的同时,影响下中央稳定板对断面下侧旋涡脱落状态的改善作用,从而对该组合气动措施的制振性能产生显著影响。

多拱肋异型系杆钢拱桥动载试验分析

通过现场实际对多拱肋异型系杆钢拱桥进行动载试验,详细介绍了异型拱桥动载试验的主要工作内容、试验方法、试验结果分析等。通过现场测试与理论计算分析,桥梁结构各阶自振频率的实测值均比理论计算值大,表明桥梁实际结构刚度好于理论刚度,桥梁实测阻尼比0.145%~0.390%之间,属于正常范围,桥梁主要振型为主梁一阶扭转,拱肋横向一阶侧弯,拱肋的横向刚度相对较弱。桥梁在各行车工况下的实测冲击系数在1.04~1.20,与设计所用冲击系数1+μ=1.05较为接近,满足规范要求。

大跨悬索桥Π形加劲梁处风参数实测与风攻角修正

以一座已建的大跨悬索桥为工程依托,基于现场实测与计算流体动力学(Computational Fluid Dynamics,CFD)方法研究Π形加劲梁断面气动外形对桥面高度处实测风参数的影响,并提出实测风攻角的修正方法.进行为期5个月的桥面高度处风速和风攻角现场实测,分析风参数沿桥轴线的分布规律,并比较了桥面高度处迎风侧与背风侧风速仪实测的风速和风攻角;采用计算流体动力学方法模拟气流流经静止加劲梁断面的流场,研究来流风攻角和风速对风速仪安装在加劲梁不同位置处风参数的影响;结合数值模拟结果,通过函数拟合得到Π形加劲梁断面风速仪实测风攻角的修正公式.结果表明:实测风速在大桥主跨范围内较为接近,且边跨风速相较于主跨风速偏小;现场实测得到的迎风侧风攻角明显大于背风侧,两侧风速基本一致;迎风侧与背风侧的风参数数值模拟结果与现场实测具有一致性,主梁绕流对距主梁20 m范围内的风攻角监测结果均存在一定影响.通过本文建立的风攻角修正方法,可以根据迎风侧风攻角的实测值得到较为合理的风攻角修正结果.

基于单色条纹投影的高动态范围物体表面形貌三维测量

条纹投影轮廓术以其高速、高精度的优点在机械零件自动在线检测、汽车制造、文化遗产保护等领域得到了广泛的应用。然而,传统的条纹投影采用单一曝光时间或单一投影强度来测量高动态范围的物体,在反射率较大的区域会发生过度曝光,超过相机传感器的最大亮度范围,导致无法获得真实的强度和准确的三维数据。为解决此问题,利用彩色相机对单色条纹投影的不同颜色通道响应,提出了一种基于单色条纹投影的高动态范围物体表面三维测量方法。该方法投影蓝色条纹图到被测物体表面,彩色相机从另一个视角采集彩色条纹图像。从采集的彩色条纹图像中分离蓝绿通道对应的两个条纹图像。从蓝绿通道条纹图像中选择不饱和且调制度最大的一组像素生成蓝绿通道的掩膜图像,利用蓝绿通道的掩膜图像和蓝绿通道条纹图像合成高动态图像。然后应用相位解算方法和系统标定,实现高动态范围物体表面形貌的三维测量。实验验证了该方法的有效性。所提方法一方面减少了投影图像的数量,避免了复杂的计算问题,提高了测量效率;另一方面,不需要额外的硬件设施。

基于条纹投影的三维形貌与形变测量技术研究进展

基于条纹投影的三维形貌测量技术,已经在提升测量精度、提高测量速度、扩大测量景深、增加测量场景适应性等方面被进行了大量研究。但由于条纹投影技术本身的原理限制,仅利用传统条纹投影方法难于实现准确的对应点匹配。而依赖于对应点追踪的形变测量和应变分析可以进一步分析物体的运动状态、材料特性以及结构力学参数,在运动仿生学、材料力学、结构力学等诸多领域中起着不可或缺的作用。本文回顾了近年来新发展出的一系列基于条纹投影的三维形貌与形变测量技术,论述了学者们如何在条纹投影系统上一步步实现从简单刚体位移的测量到复杂、精细结构的形变测量和应变分析。分析了此类技术在测量完整度、分辨率以及计算效率上相比于已有形变测量技术的优势,给出了此技术所面临的挑战和潜在发展动向。

多元时间序列的相似性匹配

常用多元时间序列相似性匹配方法难以在高效刻画局部形态特征的同时考虑各变量间的相关信息.针对此问题,提出一种动态窗口内多维拟合分段方法.基于序列的局部形态特征抽象出各变量维度上拟合线段的倾斜角及持续时间,组成模式表示矩阵,并借助一种多元模式距离实现序列的相似性模式匹配.与主成分分析法、基于点分布特征的匹配法对不同数据规模的数据集进行对比,验证了该方法的有效性,特别对于多变量、不等时间跨度的中等规模多元时间序列相似性匹配具有较好的效果.

高反光表面三维形貌测量技术

陶瓷、古文物以及金属工件等高反光物体表面的三维形貌测量在各个领域有大量的需求和应用。由于表面反射率变化范围较大以及相机灰度范围有限等问题,传统的条纹投影方法不能正确地测量高反光表面的三维形貌。综述了高反光表面三维形貌测量技术的国内外研究现状、应用领域和未来发展方向。首先,根据所采用原理和测量方法的不同,将现有的高动态范围三维形貌测量技术分为下述六类进行详细的介绍:多重曝光法、投影图案强度法、偏振滤光片法、颜色不变量法、光度立体技术以及其他技术。然后,详细的比较了各种技术的优缺点并归纳其适应性分析。最后,总结了高反光表面三维形貌测量技术的应用领域并展望了该技术的未来研究方向。基于文中综述的内容,使用者可根据不同的应用需求和测量条件选择相应的最佳三维测量方法,进而更精确的重建高反光表面的三维形貌。

基于傅里叶变换去隔行图像的动态3维面形测量

为了解决动态面形测量中隔行扫描CCD相机记录动态物体表面变形条纹图像存在缺陷的问题,提出了傅里叶变换去隔行算法,即把隔行扫描CCD获取动态物体的错位模糊帧图像分成两个单场图像,分别对每一单场图像进行傅里叶变换去隔行处理,再利用条纹分析法重建对应时刻的3维面形。理论分析得出单场傅里叶变换去隔行图像与对应的准确满帧图像相同的结论。结果表明,该方法可以很好地恢复条纹和重建物体,且简单实用,可用于基于空间相位检测、相位测量轮廓术、傅里叶变换轮廓术等条纹分析方法的动态物体3维测量中。

基于稀疏增强动态解耦的电力系统振荡模式与模态辨识方法

提出一种基于稀疏增强动态解耦(SPDMD)的电力系统主导振荡模式及模态评估方法。该方法首先从电力系统的多通道广域量测信息中辨识出可表征系统关键动态振荡特征信息的低阶状态矩阵;然后,基于该低阶状态矩阵,借助交替方向乘子(ADMM)和拉格朗日乘子(LM)估计各振荡模式的最优振幅系数,根据系统主导振荡模式的最优振幅系数不为0这一特点,从低价状态矩阵中精确筛选出系统的主导振荡模式及模态;最后,将该文所提方法应用到16机68节点测试系统和中国南方电网进行分析,有效验证了所提方法的正确性与实用性。

摊铺机熨平板动态特性分析与测试

为了提升摊铺机熨平板的振动响应效果,改善其动态特性,首先建立了熨平板的动力学模型,根据拉格朗日定理对运动微分方程进行了求解,并通过虚拟样机仿真技术研究了熨平板箱体振幅响应与振动器频率的关系.然后提出了利用薄膜压力传感器测量振捣锤对地压力的方法,研究振捣锤对沥青料的压力与振捣频率的关系.最后在模态叠加理论的基础上,提出熨平板振动形态的测试方法,绘制出不同工作条件下的熨平板振动形态.结果表明,振动器工作频率在30-40Hz范围时,熨平板箱体振幅响应较明显;振捣机构工作频率在15-20 Hz范围时,振捣锤对沥青混合料的压力较小;振捣频率为15 Hz、振动频率为40 Hz的工作条件下,熨平板振动形态最平整,从而可以提升沥青层的平整度和密实度.

基于试验的大跨异形钢连廊连体结构地震易损性分析

为研究大跨异形钢连廊连体结构的地震易损性,以某实际工程为研究背景,首先分别定义连体结构中的框架剪力墙结构、橡胶支座端和预埋锚固端的极限状态与损伤指标,并采用有限元软件SAP2000建立分析模型。其次,根据结构所在的场地条件,选取了24条地震动记录,并对结构进行三向地震激励下的增量动力分析。在此基础上,以最大层间位移角、橡胶支座的剪切应变和预埋锚固端的损伤因子作为结构地震需求参数,以地面峰值加速度作为地震动强度参数,根据增量动力分析的结果,得到大跨异形钢连廊连体结构的地震易损性曲线。最后,采用振动台试验对易损性分析结果进行验证。结果表明:在8度罕遇地震时,主楼、附楼I、橡胶支座端及角钢预埋锚固端发生毁坏的超越概率分别为0.8%、0.3%、0及47.7%,整体结构发生毁坏的超越概率上界为48.4%,下界为47.7%。这说明用局部结构的地震易损性来评价整体结构的地震易损性是偏于不安全的。易损性分析结果也显示连体结构易发生损坏的部位依次是预埋锚固端、主楼、附楼I和橡胶支座端,这与振动台试验结果相同。建议在设计中加强连体结构的锚固端,保证其可靠连接。

气动板形仪动态标定及系统圆周误差鉴相补偿

针对气动板形检测辊内表面存在机械加工误差而产生系统圆周误差,从而导致静态标定曲线偏差的问题,设计了一套动态标定装置,采用光纤传感器对检测辊进行鉴相定位,实现对系统圆周误差的补偿,并采用虚拟仪器LabVIEW技术开发了气动板形检测辊动态标定软件系统。实验表明,该方法有效消除了系统圆周误差,由动态标定方法所得出的检测辊特性曲线更加准确,且实验过程更加接近实际的板带轧制过程。

增量动力分析地震动强度参数研究综述

增量动力分析是目前基于性能的地震工程中最具有发展前景的方法之一。增量动力分析结果通过地震动强度参数与工程需求参数关系表示,地震动强度参数是影响增量动力分析方法评估结果的关键因素。从地震动强度参数的性质出发,在总结近年来标量型和向量型地震动强度参数研究现状和存在问题的基础上,指出基于反应谱谱形的地震动强度参数在有效性方面具有优势,仍为今后研究工作的主流方向。向量型地震动强度参数可提供更多信息,充分性、有效性优于标量型地震动强度参数,将是未来的发展趋势。基于多向地震动输入的地震动强度参数更能符合工程需求,也将成为研究的重点。

舰载导弹发射架状态动态测量系统设计

舰载导弹发射架状态信息是影响舰载导弹制导精度的重要因素,目前舰载导弹发射架状态信息的检测只能在静态条件下进行,缺乏动基座条件下导弹发射架状态动态实时检测手段;针对此问题,提出了舰载导弹发射架状态动态测量系统设计方案,实现动基座条件下导弹发射架发射导轨平行度精度和垂直度精度的实时检测;从总体方案设计、硬件设计、软件设计、关键技术方案等方面对舰载导弹发射架状态动态测量系统设计进行了论述,并对初始对准、持续测量、自标定、时间同步等关键技术方案和基于"旋转调制+Kalman滤波器"的对准和测量技术进行了详细阐述。

FTP动态测量航空发动机叶片三维型面

针对高速旋转状态下航空发动机叶片每个时刻形变量的研究,提出一种利用主动结构光,基于动态傅里叶变换轮廓术对不同速度下每个时刻三维型面及形变量的测量方法。利用对射激光传感器与AVR单片机设计同步控制装置,结合千兆网相机完成对高速旋转中航空发动机同一叶片的瞬态图像采集,再利用傅里叶变换轮廓术计算出每个时刻下该叶片的三维型面,通过分析,计算出每个时刻下旋转航空发动机叶片的形变量。实验结果表明该方法可行且满足准确度要求,相对于传统的叶片形变测量方法,具有实时、快速的优势。