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Accurately characterizing the surface topography of parts is crucial to improve the surface measurement accuracy and analyze the surface contact performance. A method is proposed to separate the morphological characteristics of the actual machined surface based on the layer-by-layer error reconstruction method and the signal-to-noise ratio method during the wavelet transform process, so as to evaluate the contact performance of the different joint surfaces. First, the actual machined surface morphological features are separated by using the wavelet transform method, the layer-by-layer error reconstruction method, and the signal-to-noise ratio method. Second, the reconstructed three-dimensional surface contact model is established by the reverse modeling engineering method. Third, the finite element method is used to analyze the impact of processing methods and surface roughness on contact surface parameters. The result demonstrates that the simplified and efficient three-dimensional reconstructed surface is achieved based on the real machining surface in contrast to other existing approaches. The surface roughness has a more significant influence on contact performance. The contact deformation increases with the increase of surface roughness, while the curves of average contact stress, contact stiffness, and contact area have the opposite trend. [ABSTRACT FROM AUTHOR]

Fretting wear is a kind of material damage in contact surfaces caused by microrelative displacement between two bodies. It can change the profile of contact surfaces, resulting in loosening of fasteners or fatigue cracks. Finite element method is an effective method to simulate the evolution of fretting wear process. In most studies of fretting wear, the coefficient of friction was assumed to be constant to simplify model and reduce the difficulty of solving. However, fretting wear test showed that the coefficient of friction was a variable related to the number of fretting cycles. Therefore, this paper introduces the coefficient of friction as a function of the number of fretting cycles in numerical simulation. A wear model considering variable coefficient of friction is established by combining energy consumption model and adaptive grid technique. The nodes of contact surfaces are updated through the UMESHMOTION subroutine. The effects of constant coefficient of friction and variable coefficient of friction on fretting wear are analyzed by comparing the wear amount under different loading conditions. The results show that when compared with coefficient of friction model, fretting wear is obviously affected by variable coefficient of friction and the variable coefficient of friction model has a larger wear volume when the fretting is in partial slip condition and mixed slip condition. In gross slip condition, the difference of wear volume between variable coefficient of friction model and coefficient of friction model decreases with the increase in the displacement amplitudes. [ABSTRACT FROM AUTHOR]

Crown volume is an important tree factor used in forest surveys as a prerequisite for estimating biomass and carbon stocks. This study developed a method for accurately calculating the crown volume of individual trees from vehicle-borne laser scanning (VLS) data using a concave hull by slices method. CloudCompare, an open-source three-dimensional (3D) point cloud and mesh processing software package, was used with VLS data to segment individual trees from which single tree crowns were extracted by identifying the first branch point of the tree. The slice thickness and number to be fitted to the canopy point cloud were adaptively determined based on the change rate in area with height, with the area of each slice calculated using the concave hull algorithm with portions of the crown regarded as truncated cones. The overall volume was then calculated as the sum of all sub-volumes. The proposed method was experimentally validated on 30 urban trees by comparing the crown volumes calculated using the proposed method with those calculated using five existing methods (manual measurement, 3D convex hull, 3D alpha shape, convex hull by slices, and voxel-based). The proposed method produced the smallest average crown volume. Gaps and holes in the point cloud were regarded as part of the crown by the manual measurement, 3D convex hull, and convex hull by slices method, resulting in the calculated volume being higher than the true value; the proposed method reduced this effect. These results indicate that the concave hull by slices method can more effectively calculate the crown volume of a single tree from VLS data. [ABSTRACT FROM AUTHOR]

Solar energy utilization will play an increasingly important role in sustainable urban development because it will help motivate low-carbon development. This study proposed a framework that calculates the solar irradiance on roofs and façades of city-scale buildings, as well as the potential reductions in energy consumption and CO 2 emissions that can be derived from solar energy utilization. This framework consolidates data acquired using 3D remote sensing techniques (e.g., light detection and ranging (LiDAR) data and digital photogrammetry) with existing 3D building vector models from urban planning and building design. To further the economical use of solar energy, the framework provides a new strategy based on three aspects (threshold, structure, and orientation), for a more realistic analysis of the available area of roofs and façades, by combining street view images and point clouds. Nanjing, China, was selected as a study area for validating and analyzing the proposed framework. The experimental area covers approximately 30 km 2 and 5216 buildings. The reliability of the proposed method was validated by comparing the results with the computation modules of mainstream commercial programs and previous international studies. The following conclusions were drawn from the experimental area. (1) Annual solar energy on the roofs of all buildings was 9647.89 GWh, corresponding to a PV yield of 1447.18 GWh, which equates to reductions of 584.66 kt in standard coal consumption and 1261.94 kt in CO 2 emissions. The annual solar energy on the façades was 5364.63 GWh, corresponding to a PV yield of 804.69 GWh, which equates to reductions of 325.10 kt in standard coal consumption and 701.69 kt in CO 2 emissions. (2) Based on the calculated potential solar energy utilization of the building envelopes, it was shown that the utilization of solar radiation on roofs and façades would promote low-carbon urban development. The utilization of solar energy on the façades of high buildings will contribute to the supply of energy for these buildings and help balance their energy consumption. (3) As the solar incidence angle changes over time, the reductions in energy consumption and CO 2 emissions related to PV power generation are maximal in summer for building roofs, whereas no significant seasonal differences were observed for façades. (4) Incorporating the available area translates the utilization of solar energy and potential CO 2 reductions from theory to practical application by reducing inefficient and invalid areas. The percentages of available area of roof and façade were estimated at 47% and 16% by comprehensive calculations considering three aspects (threshold, structure, and orientation). The corresponding potential of solar energy on the roofs and façades in the validation area B are 167.18 GWh and 53.63 GWh, respectively, compared to the original theoretic values of 316.97 GWh and 237.98 GWh. [ABSTRACT FROM AUTHOR]

Abstract: Hollow europium-doped yttrium orthovanadate (YVO4:Eu3+) microspheres were fabricated via a sodium dodecyl sulfate (SDS)–polyethylene glycol (PEG)-assisted hydrothermal technique. The as-synthesized hollow YVO4:Eu3+ microspheres were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy (PL). The obtained results showed that the morphology and size of the hollow microspheres have a strong dependence on the hydrothermal reaction time of the YVO4:Eu3+ powders. It is believed that the SDS–PEG clusters perform a function of dual soft-template that results in a unique template-induced secondary assembly in the one-pot synthesis of hollow YVO4:Eu3+ microspheres. The photoluminescence measurement revealed that the YVO4:Eu3+ powders with a spherical hollow shape have better red luminescence compared to the YVO4:Eu3+ solid microspheres. As a result, the controlled synthesis of hollow YVO4:Eu3+ microspheres not only has a great theoretical significance in studying the three-dimensional control and selective synthesis of inorganic materials but also benefits the potential applications based on hollow YVO4:Eu3+ microspheres owing to reducing the usage of expensive rare-earth elements. [Copyright &y& Elsevier]