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Sound Propagation
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
where the height is above a horizontal reference plane and the corrected definition of D is the horizontal distance between the two points at which the sound ray arc strikes the horizontal reference plane, as shown in Figure 5.5. For the purposes of the following analysis, the ‘reference plane’ is defined as a horizontal plane of height equal to the source height when the source is higher than the receiver and a horizontal plane equal to the receiver height when the receiver is higher than the source. The quantity, hmax, is the maximum height of the sound ray above this plane. This differs from the definitions used in Harmonoise documentation and in the book by Salomons where hmax is defined as the maximum height of the sound ray above the ground and it is assumed that the source and receiver heights are small compared to hmax. This latter definition results in the analysis being invalid for very high sound sources such as wind turbines. However, the new definition of the reference plane described above allows for high sources and receivers in the model and will be the one used here to enable the Harmonoise model to be applied to sound propagation from high sound sources such as wind turbines.
A combinatorial optimisation approach for recognising interacting machining features in mill-turn parts
Published in International Journal of Production Research, 2018
Wenbo Wu, Zhengdong Huang, Qinghua Liu, Lianhua Liu
Since a mill-turn part may have various 2.5D milling features with different TADs, a reference plane is selected for each TAD at first. One of the part planar faces manufactured by milling operations is selected as reference plane. Since the machined surface is always perpendicular to TAD in 2.5D milling operation, the reference plane is chosen as a plane perpendicular to the TAD. The surface, which has the farthest distance away from the reference axis, is manually selected as the reference plane. In Figure 7(a), in the cross-section view perpendicular to the axis, the reference planes are classified into three categories: (1) planar feature; (2) step feature; (3) slot feature. They are, respectively, related to TAD1, TAD2 and TAD3 in the figure. In addition, the three kinds of reference planes may interact with each other. Figure 7(b) shows such interactions between reference planes with different TADs; although they are adjacent through a shared edge, they should still be machined in separate TADs.
Terrestrial laser scanning for structural inspection with Kriging interpolation
Published in Structure and Infrastructure Engineering, 2022
Thomas Sanchez, David Conciatori, Mahdi Ben-Ftima, Bruno Massicotte
Finally, several suggestions are given to facilitate the implementation of this measurement system:A good physical knowledge of reference plane parameters permits to define the grid and its refinement easily. For most structures, the choice of a reference plane is a flat surface. The parameters and may be chosen to form two orthogonal unitary vectors in a local reference coordinate in the reference plane. One or both vectors can be aligned with one or two edges of the current surface. If the choice of the reference plane is a surface of revolution, the parameters and represent the distance from the rotation axis and the rotation angle. The accuracy of the Kriging interpolation model must also be calibrated after the first inspection with a sufficiently refined grid. This refinement depends on what the user wishes to observe: a general tendency (with low precision) or finest degradations like micro-cracks (with very high precision).The pre-treatment of laser scanning coordinates must be performed after each structural inspection and can be done with specialized software from inspectors. It permits to clean outside points of the studied field. Keeping in mind that this step requires great care because it is important to remove sharp edges from surfaces, otherwise, the Kriging interpolation model gives locally erroneous results. If the requested accuracy is high, or if the number of grid nodes is important, it is possible to divide the surface into several parts, treating each one separately and finally juxtaposing the results.
Full-field phase error compensation method based on relationship between unwrapped phase and phase error
Published in Journal of Modern Optics, 2018
Cheng Chen, Yiping Cao, Yingying Wan, Guangkai Fu, Yapin Wang, Chengmeng Li
A typical PMP system is illustrated in Figure 1. The plane coinciding with the x–y plane is regarded as the reference plane. Sinusoidal fringe patterns with phase shifting are projected by a digital-light-processing (DLP) projector onto the measured object on the reference plane, and the deformed fringe patterns are captured by a camera.