Digital twin-based analysis of volumetric error mapping procedures

The evaluation of the volumetric accuracy of a machine tool is an open challenge in the industry, and a wide variety of technical solutions are available in the market and at research level. All solutions have advantages and disadvantages concerning which errors can be measured, the achievable uncertainty, the ease of implementation, possibility of machine integration and automation, the equipment cost and the machine occupation time, and it is not always straightforward which option to choose for each application. The need to ensure accuracy during the whole lifetime of the machine and the availability of monitoring systems developed following the Industry 4.0 trend are pushing the development of measurement systems that can be integrated in the machine to perform semi-automatic verification procedures that can be performed frequently by the machine user to monitor the condition of the machine. Calibrated artefact based calibration and verification solutions have an advantage in this field over laser based solutions in terms of cost and feasibility of machine integration, but they need to be optimized for each machine and customer requirements to achieve the required calibration uncertainty and minimize machine occupation time.This paper introduces a digital twin-based methodology to simulate all relevant effects in an artefact-based machine tool calibration procedure, from the machine itself with its expected error ranges, to the artefact geometry and uncertainty, artefact positions in the workspace, probe uncertainty, compensation model, etc. By parameterizing all relevant variables in the design of the calibration procedure, this simulation methodology can be used to analyse the effect of each design variable on the error mapping uncertainty, which is of great help in adapting the procedure to each specific machine and user requirements. The simulation methodology and the analysis possibilities are illustrated by applying it on a 3-axis milling machine tool.     

用硫酸铁铵容量法测定钛精矿中二氧化钛含量

样品在过氧化钠熔融、水浸取及盐酸酸化后，在盐酸和硫酸介质中，隔绝空气，用金属铝将钛(Ⅳ)还原至钛(Ⅲ)，以硫氰酸盐为指示剂，用硫酸铁铵标准溶液滴定。     

Towards an Unbiased Comparison of CC,BCC, and FCC Lattices in Terms of Prealiasing

In the literature on optimal regular volume sampling, the Body‐Centered Cubic (BCC) lattice has been proven to be optimal for sampling spherically band‐limited signals above the Nyquist limit. On the other hand, if the sampling frequency is below the Nyquist limit, the Face‐Centered Cubic (FCC) lattice was demonstrated to be optimal in reducing the prealiasing effect. In this paper, we confirm that the FCC lattice is indeed optimal in this sense in a certain interval of the sampling frequency. By theoretically estimating the prealiasing error in a realistic range of the sampling frequency, we show that in other frequency intervals, the BCC lattice and even the traditional Cartesian Cubic (CC) lattice are expected to minimize the prealiasing. The BCC lattice is superior over the FCC lattice if the sampling frequency is not significantly below the Nyquist limit. Interestingly, if the original signal is drastically undersampled, the CC lattice is expected to provide the lowest prealiasing error. Additionally, we give a comprehensible clarification that the sampling efficiency of the FCC lattice is lower than that of the BCC lattice. Although this is a well‐known fact, the exact percentage has been erroneously reported in the literature. Furthermore, for the sake of an unbiased comparison, we propose to rotate the Marschner‐Lobb test signal such that an undue advantage is not given to either lattice.     

Interfacial area and volumetric mass transfer coefficient in a bubble reactor at elevated pressures

The present study deals with the pressure effects on mass transfer parameters within a bubble reactor operating at pressures up to . The gas-liquid systems are N₂/CO₂-aqueous solution of Na₂CO₃-NaHCO₃ and N₂/CO₂-aqueous solution of NaOH. A sintered powder plate is used as a gas distributor. Three parameters characterizing the mass transfer are identified and investigated with respect to pressure: the gas-liquid interfacial area a, the volumetric liquid side mass transfer coefficient k_La and the volumetric gas side mass transfer coefficient k_Ga. The gas-liquid absorption with chemical reaction is used and the mass transfer parameters are determined by using the model reaction between CO₂ and the aqueous solutions of Na₂CO₃-NaHCO₃ and NaOH. For a given gas mass flow rate, the interfacial area as well as the volumetric liquid mass transfer coefficient decrease with increasing operating pressure. However, for a given pressure, a and k_La increase with increasing gas mass flow rates. The mass transfer coefficient k_L is independent of pressure. Furthermore, the pressure increase results in a decrease of k_G and k_Ga for a given gas mass flow rate. The values of the interfacial area, which are obtained from both chemical systems are found to be different. These discrepancies are attributed to the choice of the liquid system in the absorption reaction model.     

圈闭资源量计算中体积法的软件实现

从体积法的数据、原理到功能实现,提出了一个完整的体积法计算圈闭资源量的计算机软件功能实现方案。重点探讨了软件在实现过程中所涉及的确定性和不确定性两种方法,并介绍了不确定方法参数概率分布设置的4种方法:利用分布模型库、端值法、等值线法和面积-深度图版法。通过某构造圈闭资源量计算实例应用,表明该软件系统能满足计算过程中各种功能的需求,在实际工作中能够较好地应用到具体的资源量预测和评价中。     

Retailoring Box Splines to Lattices for Highly Isotropic Volume Representations

3D box splines are defined by convolving a 1D box function with itself along different directions. In volume visualization, box splines are mainly used as reconstruction kernels that are easy to adapt to various sampling lattices, such as the Cartesian Cubic (CC), Body‐Centered Cubic (BCC), and Face‐Centered Cubic (FCC) lattices. The usual way of tailoring a box spline to a specific lattice is to span the box spline by exactly those principal directions that span the lattice itself. However, in this case, the preferred directions of the box spline and the lattice are the same, amplifying the anisotropic effects of each other. This leads to an anisotropic volume representation with strongly preferred directions. Therefore, in this paper, we retailor box splines to lattices such that the sets of vectors that span the box spline and the lattice are disjoint sets. As the preferred directions of the box spline and the lattice compensate each other, a more isotropic volume representation can be achieved. We demonstrate this by comparing different combinations of box splines and lattices concerning their anisotropic behavior in tomographic reconstruction and volume visualization.     

Importance sampling for volumetric illumination of flames

Physically based rendering of scenes with volumetric illumination of flames remains a challenging problem due to the complexity of their heterogeneous radiative properties. Current bidirectional importance sampling strategies have been focusing on emissive light sources without anisotropic extinction. In this paper, we present an efficient importance sampling method for volumetric light sources with anisotropic extinction. According to the radiative properties of flames, we separate the computation of anisotropic extinction from the evaluation of illumination inside flames and utilize cluster-based hierarchies to rapidly estimate them. To exploit the coherence of radiative voxels, we also propose a new similarity metric to aggregate voxels into clusters. For each pixel to be shaded, we use these clusters to rapidly approximate the importance function of voxels, and draw final illumination samples from clusters. Our results show that this approach substantially reduces the variance of images when rendering scenes with flames.     

一种新的基于平面检测器的锥形束体积重建算法

由于锥形束体积重建算法具有较高的获取投影数据的速度、较大的 X射线利用率及能保持重建物体的空间和密度各向同性等方面的优点 ,因而引起了人们的广泛关注 .针对锥顶轨迹为单圆的锥形束体积重建问题 ,提出了一种基于平面检测器的 T- FDK算法 (简称 FT- FDK算法 ) .该算法首先将锥形束投影数据重排为倾斜平行投影数据 ,然后再经过加权滤波和反投影重建来得到待测物体的三维结构 .实验结果表明 ,该算法不仅与传统的 FDK算法有相同的计算复杂度 ,且重建图象的质量有了明显的提高 ,因而该算法在医学成像和无损探伤等领域具有重要的实用价值 .     

Development of a void ratio-moisture ratio-net stress framework for the prediction of the volumetric behavior of unsaturated granular materials

Despite extensive research on the behavior of unsaturated fine-grained materials, there is still a lack of understanding of the volumetric behavior of unsaturated granular materials. In this research, a model has been developed to predict the fundamental volumetric behavior of unsaturated granular materials through loading and wetting state paths. In this regard, a loading-wetting surface was developed in a space of void ratio-moisture ratio-net stress. A distinctive feature of the proposed model is the relative simplicity in obtaining the model parameters using conventional geotechnical testing equipment. Two types of recycled granular materials, commonly applied in unbound pavements were used, namely, recycled crushed brick (CB) and excavation waste rock (WR). The uniqueness of the developed surface was evaluated by employing a number of loading and wetting state paths. The results indicate that the developed surface is unique in its loading state paths; however, it only shows uniqueness in its wetting state paths for stress levels greater than 2000 kPa. The proposed model seeks to introduce the application of the unsaturated soil mechanics theory, for predicting the behavior of granular materials in the field, by providing a practical and cost-effective methodology.     

High-density oxygen-enriched graphene hydrogels for symmetric supercapacitors with ultrahigh gravimetric and volumetric performance

The contradiction between the porous structure and density of graphene materials makes it unable to meet the dual requirements of the next generation supercapacitors for gravimetric capacitance and volumetric capacitance. Herein, we successfully synthesized high-density oxygen-enriched graphene hydrogels (HOGHs) by a one-step hydrothermal method using high concentration graphene oxide (GO) solution and trometamol as precursors. The as-prepared HOGHs samples present a dense 3D network structure and moderate specific surface areas, which leads to a high packing density. In addition, the HOGHs samples also contain abundant oxygen-containing functional groups and some nitrogen-containing functional groups. These heteroatomic functional groups can provide pseudocapacitance for the electrode materials. Therefore, the HOGH-140 based symmetric supercapacitor shows ultrahigh gravimetric and volumetric specific capacitance (325.7 F g⁻¹, 377.8 F cm⁻³), excellent rate performance and cycling stability. Simultaneously, the symmetric binder-free supercapacitor exhibits high gravimetric specific energy density (11.3 Wh kg⁻¹) and volumetric specific energy density (13.1 Wh L⁻¹) in 6 M KOH, respectively. These outstanding properties make the material have a good application prospect in the field of compact energy storage devices.