基于正交函数的曲面拟合优化算法

最小二乘法在拟合曲面时通常需要提高拟合阶数以满足曲面重构精度,拟合阶数提高会造成曲面光顺性变差。为改善最小二乘法在曲面重建中的缺陷,利用正交函数进行曲面优化,通过局部内插曲面,使整体曲面具有较好的连续性。采用4×4阶拟合参数进行曲面重构,形成曲面的相邻面片符合G2连续,曲面-点云最大偏差为0.0943mm。曲面拟合实验表明,采用改进的曲面拟合算法,实现了曲面拟合阶数和曲面曲率、拟合精度的最优融合,提高了重建曲面的品质。     

G~2连续的A级曲面精确重构及光顺技术研究

A级曲面重构中拟合高精度曲面过程复杂繁琐,需要进行大量运算,且曲面拟合后没有保留参数特征,无法编辑修改,进而造成曲面逆向重构工作反复进行。针对上述问题提出一种高效准确的方法进行曲面重构。根据K-邻域搜索的离散点云,采用直线、圆弧等多方式分段插值拟合出曲率连续过渡的曲线,保留参数特征,方便修改;再利用NURBS理论拟合曲面,通过调整控制点、权因子和节点矢量等因素,确保曲面拟合精度和曲率连续过渡。经过实例分析,此方法拟合A级曲面快速准确,并保留了曲面形状参数,提高了曲面重构的精度和效率。     

基于实时重构的自由曲面自适应布点方法

针对现有的自适应算法计算量庞大、在工程中可应用性不强的缺陷,提出在等距法布点的基础上,对测量点进行实时重构来指导三坐标测量机根据曲面本身特性自动增加测量点的方法。测量过程中,当通过拟合五次B样条曲线、三次B样条曲面判断现有测量点不满足精度时,利用两侧测量点的曲率半径,计算出需增加测量点的准确位置,重新拟合包含新检测点的检测样本,直到满足精度要求。以曲面样件为例,辅以计算机图形可视化验证该算法,实验结果表明该方法测量精度及重构精度均可满足数字化检测要求,且在工程应用中相比曲率自适应算法其计算量大幅下降,有效提高了曲面检测效率。     

基于三坐标测量机自适应测量的自由曲面逆向

自由曲面的精确测量和重构是决定具有自由曲面特征的零部件复现精度的重要因素,传统逆向中测量与重构是相互独立又不能有效评估的。为提高自由曲面测量速度和重构精度,基于三坐标测量机(Coordinate measuring machine,CMM),提出自适应测量的曲面重构方法。测量过程中,通过不断拟合样件上已测点,预算待测点及其测量矢量,指导CMM自动采集曲面上数据。由点云拟合自由曲面模型后,检验拟合模型上点与样件上相应点的误差;若误差偏大,则在测量点云中加入检测点后重新拟合曲面,进一步检测重拟合实体模型直至满足精度要求,得到精准数据点和精致的自由曲面模型。辅以计算机图形可视化实例验证本法,测量精度及其重构精度可达μm级,具有自由曲面特征的零部件整个逆向周期呈数量级下降,算法鲁棒性强。     

基于自适应测量和实时重构的自由曲面特征产品的逆向研究

为提高自由曲面测量速度和重构精度,基于三坐标测量机CMM,提出自适应测量的曲面重构方法。测量过程中,通过不断拟合样件上已测点,预算待测点及其测量矢量,指导CMM自动采集曲面上数据。由点云拟合自由曲面模型后,检验拟合模型上点与样件上相应点的误差;若误差偏大,则在测量点云中加入检测点后重新拟合曲面,进一步检测重拟合实体模型直至满足精度要求,得到精准数据点和精致的自由曲面模型。辅以计算机图形可视化实例验证本法,测量精度及其重构精度可达μ级,具有自由曲面特征的零部件整个逆向周期呈数量级下降,算法鲁棒性强。     

基于B样条曲面的点云孔洞拟合填充

为了后续曲面重构的需要,针对有孔洞的点云数据,提出了一种孔洞拟合填充的自适应方法.由于孔洞与其周围离散点有一定的连续性,该算法首先从孔洞周围已有的点云数据中选取离散点,用新的参数化方法对得到的离散点参数化后,用最小二乘法进行自适应曲面拟合,对得到的拟合曲面通过迭代法逐步逼近优化,考虑曲率变化的影响在曲面上取点,实现了孔洞光滑填充.实例表明,改进的参数化方法使算法的复杂度减低,进一步迭代优化提高了曲面拟合精度,在面上取点时考虑了曲率变化,因此该方法可以应用于具有复杂曲面形状的点云中的孔洞填充.     

NURBS自由型曲面延展和过渡功能的开发

根据曲面的延展量进行曲面分割，对分割后曲面进行控制点的反射对称，得到满足G^2连续的延展曲面。给出了散乱控制点的有序化的方法，有效地防止了拓展曲面产生折叠、起皱，实现了曲面延展设计的算法。     

激光扫描数据重构曲面的优化技术研究

本文提出了一种利用激光扫描数据和曲面灰度图像重构曲面的方法和步骤 ,利用图像处理技术构造连续的 3D边界 ,采用最小二乘法拟合激光扫描数据构建参数化基曲面 ,通过对 3D边界曲线进行优化处理并作为约束条件 ,使实物反求过程中重构的曲面模型能真实地再现采样曲面的原貌     

基于B样条曲面的点云孔洞拟合填充

为了后续曲面重构的需要,针对有孔洞的点云数据,提出了一种孔洞拟合填充的自适应方法。由于孔洞与其周围离散点有一定的连续性,该算法首先从孔洞周围已有的点云数据中选取离散点,用新的参数化方法对得到的离散点参数化后,用最小二乘法进行自适应曲面拟合,对得到的拟合曲面通过迭代法逐步逼近优化,考虑曲率变化的影响在曲面上取点,实现了孔洞光滑填充。实例表明,改进的参数化方法使算法的复杂度减低,进一步迭代优化提高了曲面拟合精度,在面上取点时考虑了曲率变化,因此该方法可以应用于具有复杂曲面形状的点云中的孔洞填充。     

曲面重构算法的研究

提出了一种基于多层感知器网络的曲面重构算法 (ML PSR) ,建立了用于曲面重构的多层感知器网络模型。本文对基于二维拉格朗日局部插值的曲面重构算法 (2 DL L SR)与 ML PSR进行对比。为了更好地评估这两种算法的有效性 ,选择可用数学表达式表达的曲面作为重构对象。仿真实验结果表明 ,这两种算法在曲面重构上各有优点。当 2 DL L SR算法的阶次高于等于曲面本身的阶次时 ,曲面重构的效果很好。ML PSR算法在曲面重构的速度和精度上都比较好 ,尤其在曲面受到破坏或不完全时特别有效。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.