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Journal articles on the topic 'Tangential distortion'
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1
Peng, Fu Qiang, Qiang Chen, and Jun Wei Bao. "Distortion Correction for the Gun Barrel Bore Panoramic Image." Applied Mechanics and Materials 427-429 (September 2013): 680–85. http://dx.doi.org/10.4028/www.scientific.net/amm.427-429.680.
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Single Reflector Panoramic Imaging System (SRPIS) has been widely used because of its advantages such as simple structure, fast imaging, integration and miniaturization. It can observe objects around the reflector mirror, which fits for the quality inspection of gun barrel bore. However, its images often suffer from serious distortions in radial and tangential directions. Therefore, to ensure the accuracy of captured images, distortion must be eliminated. In this paper, a distortion correction method is proposed based on the imaging characteristics of SRPIS. Firstly the relationship between the height of a certain point on the gun barrel bore and the radius of image point is derived. Then the correction model is built based on the relationship. Aiming at the captured annular image, a new chessboard corner detection algorithm is proposed. The correction parameters are obtained by using the algorithm according to the labeled image. The real experiment results demonstrate that the correction effects of radial and tangential distortions are satisfactory. The error is controlled at sub-pixel level.
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Apriani, Atika, Rochan Rifai, Frida Agung Rakhmadi, and Khamidinal. "USB 2.0 Digital Camera Characterization for Optimizing the Making of High Power RGB-LED Fluorescence Imaging System." Proceeding International Conference on Science and Engineering 3 (April 30, 2020): 255–57. http://dx.doi.org/10.14421/icse.v3.508.
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This research aims to obtain the focal length and radial and tangential distortion of a USB 2.0 digital camera. This research was conducted in three stages namely preparation of tools and materials, camera characterization, and data processing. The tools used in this study include a USB 2.0 digital camera and MATLAB R2013a software, while the object is a collimator board. Characterization of digital cameras is done through data collection with a distance variation of 3 cm until 15 cm, then the data obtained is processed using MATLAB R2013a software to obtain the focal length and radial distortion and tangential distortion values. The USB camera that used has the characteristic focal length and radial distortion and certain tangential distortion for each distance.
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Ekpar, Frank, Masaaki Yoneda, and Hiroyuki Hase. "Correcting Distortions in Panoramic Images Using Constructive Neural Networks." International Journal of Neural Systems 13, no. 04 (August 2003): 239–50. http://dx.doi.org/10.1142/s0129065703001601.
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This paper presents a novel approach to the correction of panoramic (wide-angle) image distortions. Unlike traditional methods that separate the distortion of the panoramic image into radial and tangential components and then concentrate on the correction of one type of distortion at a time, the method presented in this paper uses an integrated approach that simultaneously corrects all non-linear distortions of the panoramic image. The system uses data obtained from carefully constructed calibration patterns to automatically build and train a constructive neural network of suitable complexity to approximate the characteristic distortion of the panoramic image. The trained neural network is then used to correct the distortions represented by the sample data. It is demonstrated that by applying the distortion correction method presented in this paper to panoramic images representing real world scenes, perspective-corrected views of the real world scene that are usable in a wide variety of applications can be generated.
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Liu, Yue, Dewen Cheng, Qiwei Wang, Qichao Hou, Luo Gu, Hailong Chen, Tong Yang, and YongTian Wang. "Optical distortion correction considering radial and tangential distortion rates defined by optical design." Results in Optics 3 (May 2021): 100072. http://dx.doi.org/10.1016/j.rio.2021.100072.
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Walker, Amy, Peter Metcalfe, Gary Liney, Vikneswary Batumalai, Kylie Dundas, Carri Glide-Hurst, Geoff P. Delaney, et al. "MRI geometric distortion: Impact on tangential whole-breast IMRT." Journal of Applied Clinical Medical Physics 17, no. 5 (September 2016): 7–19. http://dx.doi.org/10.1120/jacmp.v17i5.6242.
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Li, Yu Long, Peng Sun, and Ming Li Dong. "A Spatial Optimization for Camera Interior Orientation Parameters." Applied Mechanics and Materials 389 (August 2013): 941–47. http://dx.doi.org/10.4028/www.scientific.net/amm.389.941.
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A new calibration method for camera interior orientation parameters is proposed using the known spatial coordinates and the corresponding single photo. Firstly, principle point coordinates, principle distance and exterior orientation parameters are solved by the direct linear method without consideration of distortion parameters. Then, accurate interior and exterior orientation parameters are refined through the process of nonlinear optimization, during which the distance of spatial point to corresponding ray are minimized. Distortion factors of radial distortion, tangential distortion, affine distortion and non-orthogonal distortion are taken into consideration. This paper uses Levenberg-Marquardt optimization method to avoid inaccurate initial parameters influence upon the process of convergence.
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Peng, Hong Xing, Xiang Jun Zou, Jun Tao Xiong, Ding Zhong Wu, Jia Hui Shen, and Ze Xuan She. "Picking Robot Camera Calibration System Based on OpenCV." Advanced Materials Research 430-432 (January 2012): 1963–66. http://dx.doi.org/10.4028/www.scientific.net/amr.430-432.1963.
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Aim at the effect of the radial distortion and tangential distortion, the camera calibration principle, geometric model and complex equation solution were studied, in order to reduce the artificial participation in proofreading and error correction, then the camera’s software precise calibration module based on OpenCV was developed. The results showed that the system was quickly speed, high precision and could satisfy the requirements of robot vision navigation system and built the foundation for the next step research.
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Wu, Li Ming, Qi Li, and Si Cheng Chen. "Research of Multi-Touch Projection Camera Interaction Techniques Based on SOPC." Applied Mechanics and Materials 543-547 (March 2014): 784–87. http://dx.doi.org/10.4028/www.scientific.net/amm.543-547.784.
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Projection-camera interaction is a human-computer interaction technology which uses projector-camera as input-output devices, and combined with human movement as interactive mode. Introducting radial distortion and tangential distortion of lens to projection-geometric calibrate the camera system, the platform is used the Xilinx main processor Virtex-4 FX experimental box to building a projection-camera interactive implementation platform, and used the Baum-Welch algorithm which based on hidden Markov model for training gesture.
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Tian, Shan, Yu Li Liu, Gang Yao Zhao, and He Yang. "Experimental Research on Strain Distribution Characteristics of Thin-Walled Rectangular Tube in Rotary-Draw Bending." Advanced Materials Research 139-141 (October 2010): 502–5. http://dx.doi.org/10.4028/www.scientific.net/amr.139-141.502.
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The rotary-draw bending process of thin-walled rectangular tube is a complex process with large deformation, large displacement and finite strain which makes the defects, such as wrinkling, distortion and crack be easily produced. To study the complex plastic deformation characteristics of thin-walled rectangular 3A21 aluminum tube during rotary-draw bending, the distributions of tangential, circumferential and normal strain have been studied by experiment using grid method. The results show that the maximum value of three-direction strain appears in the ridges of rectangular tube and tangential strain is the maximum principal strain. The value of maximum tangential tensile strain is lager than the maximum tangential compressive strain; it is the reason why crake is prone to occur during rotary-draw bending. The strain distribution curve along bending direction is not completely symmetrical with middle cross-section. With the increase of bending angle, three-direction strain of tube also increases and circumferential strain increases relatively smaller.
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Hakkarainen, J. "DETERMINATION OF RADIAL AND TANGENTIAL DISTORTION OF AERIAL CAMERAS WITH A HORIZONTAL GONIOMETER." Photogrammetric Record 8, no. 44 (August 26, 2006): 180–87. http://dx.doi.org/10.1111/j.1477-9730.1974.tb00039.x.
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Ma, Shilun, Xueyi Zhang, Qinjun Du, Liwei Shi, and Xiangyu Meng. "Optimization Design of a New Type of Interior Permanent Magnet Generator for Electric Vehicle Range Extender." Journal of Electrical and Computer Engineering 2019 (May 2, 2019): 1–10. http://dx.doi.org/10.1155/2019/3108053.
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Aiming at the disadvantages of large leakage flux and low magnetic flux density of radial magnetic circuit and tangential magnetic circuit, a new type of permanent magnet (PM) rotor with parallel tangential and radial magnetic circuits is proposed. Based on Ohm’s law and Kirchhoff’s law of magnetic circuits, equivalent magnetic circuits for rotor poles are developed. The structure parameters of the generator are preliminarily determined. At the same time, by means of the Taguchi method and employing finite element analysis, the rotor poles of generator are optimized to improve air gap magnetic density, the cogging torque, and the distortion of back-EMF waveform. Finally, the validity of proposed design methods is validated by the analytical and experimental results.
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Zeller, N., C. A. Noury, F. Quint, C. Teulière, U. Stilla, and M. Dhome. "METRIC CALIBRATION OF A FOCUSED PLENOPTIC CAMERA BASED ON A 3D CALIBRATION TARGET." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences III-3 (June 6, 2016): 449–56. http://dx.doi.org/10.5194/isprsannals-iii-3-449-2016.
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In this paper we present a new calibration approach for focused plenoptic cameras. We derive a new mathematical projection model of a focused plenoptic camera which considers lateral as well as depth distortion. Therefore, we derive a new depth distortion model directly from the theory of depth estimation in a focused plenoptic camera. In total the model consists of five intrinsic parameters, the parameters for radial and tangential distortion in the image plane and two new depth distortion parameters. In the proposed calibration we perform a complete bundle adjustment based on a 3D calibration target. The residual of our optimization approach is three dimensional, where the depth residual is defined by a scaled version of the inverse virtual depth difference and thus conforms well to the measured data. Our method is evaluated based on different camera setups and shows good accuracy. For a better characterization of our approach we evaluate the accuracy of virtual image points projected back to 3D space.
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Zeller, N., C. A. Noury, F. Quint, C. Teulière, U. Stilla, and M. Dhome. "METRIC CALIBRATION OF A FOCUSED PLENOPTIC CAMERA BASED ON A 3D CALIBRATION TARGET." ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences III-3 (June 6, 2016): 449–56. http://dx.doi.org/10.5194/isprs-annals-iii-3-449-2016.
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In this paper we present a new calibration approach for focused plenoptic cameras. We derive a new mathematical projection model of a focused plenoptic camera which considers lateral as well as depth distortion. Therefore, we derive a new depth distortion model directly from the theory of depth estimation in a focused plenoptic camera. In total the model consists of five intrinsic parameters, the parameters for radial and tangential distortion in the image plane and two new depth distortion parameters. In the proposed calibration we perform a complete bundle adjustment based on a 3D calibration target. The residual of our optimization approach is three dimensional, where the depth residual is defined by a scaled version of the inverse virtual depth difference and thus conforms well to the measured data. Our method is evaluated based on different camera setups and shows good accuracy. For a better characterization of our approach we evaluate the accuracy of virtual image points projected back to 3D space.
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Spakovszky, Z. S. "Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors." Journal of Turbomachinery 122, no. 4 (February 1, 2000): 761–68. http://dx.doi.org/10.1115/1.1312801.
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A new analytical model to predict the aerodynamic forces in axial flow compressors due to asymmetric tip-clearance is introduced. The model captures the effects of tip-clearance induced distortion (i.e., forced shaft whirl), unsteady momentum-induced tangential blade forces, and pressure-induced forces on the spool. Pressure forces are shown to lag the tip-clearance asymmetry, resulting in a tangential (i.e., whirl-inducing) force due to spool pressure. This force can be of comparable magnitude to the classical Alford force. Prediction and elucidation of the Alford force is also presented. In particular, a new parameter denoted as the blade loading indicator is deduced. This parameter depends only on stage geometry and mean flow and determines the direction of whirl tendency due to tangential blade loading forces in both compressors and turbines. All findings are suitable for incorporation into an overall dynamic system analysis and integration into existing engine design tools. [S0889-504X(00)01604-4]
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Li, Jie, Xiao Yan Wang, and Zhi Yong Wang. "Study on Interaction Theory of Thermal Distortion Friction Pairs and Effect on Friction Coefficient." Applied Mechanics and Materials 713-715 (January 2015): 223–27. http://dx.doi.org/10.4028/www.scientific.net/amm.713-715.223.
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The thermal distortion of friction pair will be produced in high line speed frictioning. For solving interaction theory from this problem, thermal distortion micro-bulges model of two interaction friction surfaces is built by ways of micro-interaction dynamics, and equations of contact forces of micro-bulges are obtained. By using mathematic statistics and normalization, equations of macro-normal and tangential contact forces are obtained, and relation between friction coefficient and micro-parameters is found. Contact forces and friction coefficient characteristics expressed by parameters of dimensionless clearance and curvature are simulated. The results show that the interaction theory is important in deeper understanding friction and wear theory in high line speed running, and offers reliable proof for future finer structure design of friction pair and model design of clutch.
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Kliger, Robert, Charlotte Bengtsson, and Marie Johansson. "Comparison between HT-dried and LT-dried spruce timber in terms of shape and dimensional stability." Holzforschung 59, no. 6 (November 1, 2005): 647–53. http://dx.doi.org/10.1515/hf.2005.104.
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Abstract The performance of timber studs from Norway spruce (Picea abies) in terms of shape and dimensional stability was evaluated. The shape stability studied included three modes of distortion, i.e. twist, bow and spring. The dimensional stability was assessed by measuring longitudinal shrinkage and swelling properties. The study comprised 96 studs measuring 45 mm×70 mm×2500 mm from 15 butt logs. Half the studs from each log were dried using a high-temperature method (HT) at 115°C, while the other half were dried using a conventional low-temperature method (LT) at 70°C. Distortion in the studs was measured at moisture contents of 14% and 9%. The HT-dried timber had significantly lower distortion values than the LT-dried timber. As a result, 80% of the high-temperature-dried studs were able to pass the limits for distortion, while only 60% of the low-temperature-dried studs passed the same limit. Studs cut close to the pith displayed the largest twist, independent of the drying method. A simple model for predicting twist that was used in previous studies was also valid for HT-dried timber. The most important parameters in this model for both HT- and LT-dried timber were grain angle, annual ring curvature and tangential shrinkage.
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Wang, Xinzheng, Jing Yu, Bo Yang, Guijuan Li, and Xiongzhu Bu. "Corrected unwrapping method based on the tangential and radial distortion centre for the panoramic annular image." IET Image Processing 9, no. 2 (February 1, 2015): 127–33. http://dx.doi.org/10.1049/iet-ipr.2014.0301.
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Ozcinar, Cagri, and Aakanksha Rana. "Quality Assessment of Super-Resolved Omnidirectional Image Quality Using Tangential Views." Electronic Imaging 2021, no. 9 (January 18, 2021): 295–1. http://dx.doi.org/10.2352/issn.2470-1173.2021.9.iqsp-295.
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Omnidirectional images (ODIs), also known as 360-degree images, enable viewers to explore all directions of a given 360-degree scene from a fixed point. Designing an immersive imaging system with ODI is challenging as such systems require very large resolution coverage of the entire 360 viewing space to provide an enhanced quality of experience (QoE). Despite remarkable progress on single image super-resolution (SISR) methods with deep-learning techniques, no study for quality assessments of super-resolved ODIs exists to analyze the quality of such SISR techniques. This paper proposes an objective, full-reference quality assessment framework which studies quality measurement for ODIs generated by GAN-based and CNN-based SISR methods. The quality assessment framework offers to utilize tangential views to cope with the spherical nature of a given ODIs. The generated tangential views are distortion-free and can be efficiently scaled to high-resolution spherical data for SISR quality measurement. We extensively evaluate two state-of-the-art SISR methods using widely used full-reference SISR quality metrics adapted to our designed framework. In addition, our study reveals that most objective metric show high performance over CNN based SISR, while subjective tests favors GAN-based architectures.
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Peng, Ming Kai, Ying Hei Chui, Yi Chiech Ho, Wei Chung Wang, and Yao Tang Zhou. "Investigation of Shrinkage in Softwood Using Digital Image Correlation Method." Applied Mechanics and Materials 83 (July 2011): 157–61. http://dx.doi.org/10.4028/www.scientific.net/amm.83.157.
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Distortion in lumber, such as twist, cup, spring and bow, can cause serious problems for its use in service. Lumber distortion is largely a result of differential shrinkage in wood in different directions and the presence of different types of wood (i.e. juvenile and mature wood) in a single piece. Shrinkage varies within tree because of different types of wood. In this paper, the digital image correlation (DIC) method was used to investigate shrinkage variation within tree. The DIC method is an image-based, non-contact and full-field displacement and strain measurement method. Two softwood species grown in Eastern Canada, jack pine and white spruce, were used in this study. In this paper, average full-field shrinkage over each growth ring was measured, and the growth ring position in relation to pith of the tree was recorded. The shrinkage variations in the radial, tangential and longitudinal directions in a tree stem are presented. The work described in this paper is part of a larger study to develop a modeling technique to predict distortion of lumber based on its position in a tree stem.
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Jou, Ben Jong-Dao, Wen-Chau Lee, Su-Ping Liu, and Yu-Cheng Kao. "Generalized VTD Retrieval of Atmospheric Vortex Kinematic Structure. Part I: Formulation and Error Analysis." Monthly Weather Review 136, no. 3 (March 1, 2008): 995–1012. http://dx.doi.org/10.1175/2007mwr2116.1.
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Abstract The primary circulation of atmospheric vortices, such as tropical cyclones and tornadoes, can be estimated from single-Doppler radar observations using the ground-based velocity track display (GBVTD) algorithm. The GBVTD algorithm has limitations in the following four areas: 1) distortion in the retrieved asymmetric wind fields, 2) a limited analysis domain, 3) the inability to resolve the cross-beam component of the mean wind, and 4) the inability to separate the asymmetric tangential and radial winds. This paper presents the generalized velocity track display (GVTD) algorithm, which eliminates the first two limitations inherent in the GBVTD technique and demonstrates the possibility of subjectively estimating the mean wind vector when its signature is visible beyond the influence of the vortex circulation. In this new paradigm, the GVTD algorithm fits the atmospheric vortex circulation to a new variable VdD/RT in a linear azimuth angle (θ′), rather than the Doppler velocity Vd in a nonlinear angle (ψ), which is used in GBVTD. Key vortex kinematic structures (e.g., mean wind, axisymmetric tangential wind, etc.) in the VdD/RT space simplify the interpretation of the radar signature and eliminate the geometric distortion inherent in the Vd display. This is a significant improvement in diagnosing vortex structures in both operations and research. The advantages of using VdD/RT are illustrated using analytical atmospheric vortices, and the properties are compared with GBVTD. The characteristics of the VdD/RT display of Typhoon Gladys (1994) can be approximated by a constant mean wind plus an axisymmetric vortex.
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Liu, Y., C. Tian, and Y. Huang. "CRITICAL ASSESSMENT OF CORRECTION METHODS FOR FISHEYE LENS DISTORTION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B1 (June 3, 2016): 221–28. http://dx.doi.org/10.5194/isprsarchives-xli-b1-221-2016.
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A fisheye lens is widely used to create a wide panoramic or hemispherical image. It is an ultra wide-angle lens that produces strong visual distortion. The distortion modeling and estimation of the fisheye lens are the crucial step for fisheye lens calibration and image rectification in computer vision and close-range photography. There are two kinds of distortion: radial and tangential distortion. Radial distortion is large for fisheye imaging and critical for the subsequent image processing. Although many researchers have developed calibration algorithms of radial distortion of fisheye lens, quantitative evaluation of the correction performance has remained a challenge. This is the first paper that intuitively and objectively evaluates the performance of five different calibration algorithms. Upto- date research on fisheye lens calibration is comprehensively reviewed to identify the research need. To differentiate their performance in terms of precision and ease-using, five methods are then tested using a diverse set of actual images of the checkerboard that are taken at Wuhan University, China under varying lighting conditions, shadows, and shooting angles. The method of rational function model, which was generally used for wide-angle lens correction, outperforms the other methods. However, the one parameter division model is easy for practical use without compromising too much the precision. The reason is that it depends on the linear structure in the image and requires no preceding calibration. It is a tradeoff between correction precision and ease-using. By critically assessing the strengths and limitations of the existing algorithms, the paper provides valuable insight and guideline for future practice and algorithm development that are important for fisheye lens calibration. It is promising for the optimal design of lens correction models that are suitable for the millions of portable imaging devices.
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Liu, Y., C. Tian, and Y. Huang. "CRITICAL ASSESSMENT OF CORRECTION METHODS FOR FISHEYE LENS DISTORTION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLI-B1 (June 3, 2016): 221–28. http://dx.doi.org/10.5194/isprs-archives-xli-b1-221-2016.
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A fisheye lens is widely used to create a wide panoramic or hemispherical image. It is an ultra wide-angle lens that produces strong visual distortion. The distortion modeling and estimation of the fisheye lens are the crucial step for fisheye lens calibration and image rectification in computer vision and close-range photography. There are two kinds of distortion: radial and tangential distortion. Radial distortion is large for fisheye imaging and critical for the subsequent image processing. Although many researchers have developed calibration algorithms of radial distortion of fisheye lens, quantitative evaluation of the correction performance has remained a challenge. This is the first paper that intuitively and objectively evaluates the performance of five different calibration algorithms. Upto- date research on fisheye lens calibration is comprehensively reviewed to identify the research need. To differentiate their performance in terms of precision and ease-using, five methods are then tested using a diverse set of actual images of the checkerboard that are taken at Wuhan University, China under varying lighting conditions, shadows, and shooting angles. The method of rational function model, which was generally used for wide-angle lens correction, outperforms the other methods. However, the one parameter division model is easy for practical use without compromising too much the precision. The reason is that it depends on the linear structure in the image and requires no preceding calibration. It is a tradeoff between correction precision and ease-using. By critically assessing the strengths and limitations of the existing algorithms, the paper provides valuable insight and guideline for future practice and algorithm development that are important for fisheye lens calibration. It is promising for the optimal design of lens correction models that are suitable for the millions of portable imaging devices.
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Chmielewski, Szymon. "Chaos in Motion: Measuring Visual Pollution with Tangential View Landscape Metrics." Land 9, no. 12 (December 12, 2020): 515. http://dx.doi.org/10.3390/land9120515.
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Visual pollution (VP) in the form of outdoor advertisements (OA) is a threat to landscape physiognomy. Despite their proven usefulness in landscape aesthetic studies, landscape metrics have not yet been applied to address the phenomenon of VP. To fill this knowledge gap, a methodological framework for the measurement of VP using tangential view landscape metrics is proposed, which is accompanied by statistically significant proofs. Raster products derived from aerial laser scanning data were used to characterize two study areas with different topographic conditions in the city of Lublin, East Poland. The visibility of the cityscape in motion was simulated through viewshed measurements taken at equal intervals in the forwards and backwards directions along pedestrian walkways. The scrutinized tangential view landscape metrics (visible area, maximum visible distance, skyline, Shannon depth, view depth line) was the object of a two-fold interpretation wherein the spatial occurrence of VP as well as its impacts on the visual landscape character (VLC) were examined. The visible area metrics were found to be highly sensitive VP indicators. The maximum visible distance metrics provided evidence for the destructive effect of OA on view corridors. The Shannon depth and depth line metrics were not found to be statistically significant indicators of VP. Results from directional viewshed modelling indicate that distortion in the analyzed cityscape physiognomy depends on the view direction. The findings allow for particular recommendations with practical implementations in land use planning, which are discussed along with limitations to our proposed methods.
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Robson, S., L. MacDonald, S. A. Kyle, and M. R. Shortis. "Multispectral calibration to enhance the metrology performance of C-mount camera systems." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-5 (June 6, 2014): 517–21. http://dx.doi.org/10.5194/isprsarchives-xl-5-517-2014.
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Low cost monochrome camera systems based on CMOS sensors and C-mount lenses have been successfully applied to a wide variety of metrology tasks. For high accuracy work such cameras are typically equipped with ring lights to image retro-reflective targets as high contrast image features. Whilst algorithms for target image measurement and lens modelling are highly advanced, including separate RGB channel lens distortion correction, target image circularity compensation and a wide variety of detection and centroiding approaches, less effort has been directed towards optimising physical target image quality by considering optical performance in narrow wavelength bands. This paper describes an initial investigation to assess the effect of wavelength on camera calibration parameters for two different camera bodies and the same ‘C-mount’ wide angle lens. Results demonstrate the expected strong influence on principal distance, radial and tangential distortion, and also highlight possible trends in principal point, orthogonality and affinity parameters which are close to the parameter estimation noise level from the strong convergent self-calibrating image networks.
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Broszeit, E., and O. Zwirlein. "Internal Stresses and Their Influence on Material Stresses in Hertzian Contacts—Calculations With Different Stress Hypotheses." Journal of Tribology 108, no. 3 (July 1, 1986): 387–93. http://dx.doi.org/10.1115/1.3261212.
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Using idealized assumptions, the stress condition in the semi-infinite body of the Hertzian contact region can be calculated for various geometries as a function of the surface pressure (normal force), the friction (tangential force at the surface), and the residual stresses in the material. Equivalent stresses can be formed from the coordinate stresses using various stress hypotheses (distortion energy hypothesis, shear stress hypothesis, and alternating shear stress hypothesis). The effects of friction, residual stresses, and contact geometry on the location and magnitude of the equivalent stresses appearing in the material have been investigated, the stress hypotheses being evaluated in terms of the extent to which they take account of these effects in an appropriate form. These investigations show clearly that the distortion energy hypothesis is the best representation of the extent of material stress in the case of dynamically loaded rolling elements. The shear stress hypothesis can be considered as a good approximation whereas the alternating shear stress hypothesis is only capable of providing useful conclusions to a limited extent.
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TEIXEIRA, M. A. C., and S. E. BELCHER. "Dissipation of shear-free turbulence near boundaries." Journal of Fluid Mechanics 422 (November 3, 2000): 167–91. http://dx.doi.org/10.1017/s002211200000149x.
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The rapid-distortion model of Hunt & Graham (1978) for the initial distortion of turbulence by a flat boundary is extended to account fully for viscous processes. Two types of boundary are considered: a solid wall and a free surface. The model is shown to be formally valid provided two conditions are satisfied. The first condition is that time is short compared with the decorrelation time of the energy-containing eddies, so that nonlinear processes can be neglected. The second condition is that the viscous layer near the boundary, where tangential motions adjust to the boundary condition, is thin compared with the scales of the smallest eddies. The viscous layer can then be treated using thin-boundary-layer methods. Given these conditions, the distorted turbulence near the boundary is related to the undistorted turbulence, and thence profiles of turbulence dissipation rate near the two types of boundary are calculated and shown to agree extremely well with profiles obtained by Perot & Moin (1993) by direct numerical simulation. The dissipation rates are higher near a solid wall than in the bulk of the flow because the no-slip boundary condition leads to large velocity gradients across the viscous layer. In contrast, the weaker constraint of no stress at a free surface leads to the dissipation rate close to a free surface actually being smaller than in the bulk of the flow. This explains why tangential velocity fluctuations parallel to a free surface are so large. In addition we show that it is the adjustment of the large energy-containing eddies across the viscous layer that controls the dissipation rate, which explains why rapid-distortion theory can give quantitatively accurate values for the dissipation rate. We also find that the dissipation rate obtained from the model evaluated at the time when the model is expected to fail actually yields useful estimates of the dissipation obtained from the direct numerical simulation at times when the nonlinear processes are significant. We conclude that the main role of nonlinear processes is to arrest growth by linear processes of the viscous layer after about one large-eddy turnover time.
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Peng, Mingkai, John A. Kershaw, Ying Hei Chui, and Meng Gong. "Modelling of tangential, radial, and longitudinal shrinkage after drying in jack pine and white spruce." Canadian Journal of Forest Research 43, no. 8 (August 2013): 742–49. http://dx.doi.org/10.1139/cjfr-2013-0127.
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The purpose of this study was to develop an understanding of the pattern of variation in longitudinal, radial, and tangential shrinkage in two commercially important Canadian wood species using multivariate nonlinear mixed-effects models. Shrinkage data were measured in each growth ring at different heights on trees harvested from a mixed-species Nelder tree-spacing plot located in New Brunswick, Canada. Live crown base was reconstructed based on stem analysis. Cambial age, sampling height, crown characteristics (crown length, crown ratio, and distance to live crown base), and ring width at time of wood formation were used as prediction variables. The results indicated that shrinkage magnitude and pattern were closely related to crown dimensions and stem position at time of wood formation. Trees from wider tree spacings with larger crown lengths and ratios tended to have smaller tangential and radial shrinkage. Longitudinal shrinkage decreased nonlinearly from pith outwards with slower rate changes near the bottom of the trees. The model fixed effects accounted for more variation in jack pine (Pinus banksiana Lamb.) than in white spruce (Picea glauca (Moench) Voss) for shrinkage in the same anatomical direction. After further validation, the model developed can be used to provide shrinkage predictions for lumber distortion models within the framework of an individual tree growth model.
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Gapare, W. J., M. Ivković, M. B. Powell, T. A. McRae, and H. X. Wu. "Genetics of Shrinkage in Juvenile Trees of Pinus radiata D. Don From Two Test Sites in Australia." Silvae Genetica 57, no. 1-6 (December 1, 2008): 145–51. http://dx.doi.org/10.1515/sg-2008-0022.
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Abstract To examine the genetic control of wood shrinkage (radial, tangential and longitudinal) in juvenile wood of radiata pine (Pinus radiata D. Don), we assessed samples collected at breast height in two related progeny tests of age 8 and 9 years, established at two different sites in Australia. Green to oven-dry tangential and radial shrinkage for the outer-rings was similar at both sites. Similarly, mean longitudinal shrinkage for the outer-rings was similar at both sites (0.3%, ranging from 0.1 to 1.9 at Flynn and 0.4%, ranging from 0.02 to 1.6, at Kromelite). Mean longitudinal shrinkage for the inner-rings was 4 times greater than that of the outerrings at both sites. The magnitude of the gradient of longitudinal shrinkage from pith to bark (0.001 to 2.9%) is large enough to cause distortion problems including twist and warp, during drying of sawn boards. These values also suggest that shrinkage in the juvenile core of radiata pine is of major economic importance and therefore should be improved either through genetics or silviculture. Individual-tree narrow-sense individual heritability for tangential and radial shrinkage in the outer-rings (4-6) was moderate at Flynn (0.24 ± 0.09 and 0.26±0.07, respectively). There was a lack of significant genetic variation for longitudinal shrinkage in the outer-rings but significant genetic control for the inner-rings (1-2) (h2 = 0.26 ± 0.07). More samples per family are required to detect significant genetic variation for shrinkage traits than other traits due to higher background variation in sampling and measuring shrinkage traits relative to other wood quality traits such as density, microfibril angle (MfA), spiral grain and modulus of elasticity (MoE).
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Peng, Mingkai, Yi-Chieh Ho, Wei-Chung Wang, Ying Hei Chui, and Meng Gong. "Measurement of wood shrinkage in jack pine using three dimensional digital image correlation (DIC)." Holzforschung 66, no. 5 (July 1, 2012): 639–43. http://dx.doi.org/10.1515/hf-2011-0124.
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Abstract Dimensional stability is one of the most important properties of lumber. Shrinkage is especially critical in this regard. In this study, longitudinal, radial and tangential shrinkages in jack pine (Pinus banksiana) have been found to be 0.4, 3.3 and 5.7%, respectively, by means of three dimensional digital image correlation (3D DIC). Full field shrinkage data were extracted from two types of specimen. It was demonstrated that the 3D DIC method is a suitable method of providing localized shrinkage values. The shrinkages in the three anatomical dimensions exhibit different variation patterns from pith to bark. Detailed shrinkage measurements provided data for a better understanding and modeling of shrinkage within a tree stem, which could be useful for lumber distortion simulation.
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Koné, Gbah, Christophe Volat, Claude Hudon, and Simon Bernier. "Experimental Investigation of the Spatial and Temporal Evolution of the Tangential and Normal E-Field Components along the Stress Grading System of a Real Stator Bar." Energies 13, no. 3 (January 21, 2020): 534. http://dx.doi.org/10.3390/en13030534.
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This paper presents results based on direct experimental measurements of tangential (Et) and normal (En) E-field components along the stress grading system (SGS) of a real stator bar (Roebel type) for different AC 60 Hz applied voltages. These measurements were made with a new electro-optic system allowing for the study of both spatial distributions of two E-field components along the bar and their temporal evolution at critical points. The results obtained allowed us to calculate the correlation between the distribution of En and Et along the SGS. In particular, it was demonstrated that the En distribution presents a characteristic minimum, which can be used to identify the zone of partial discharge inception. Moreover, it was possible to observe an enlargement of the Et component distribution followed by a saturation in magnitude with the applied voltage increase. Moreover, the results have demonstrated that the waveform of the En component is mostly affected by the SG material used, producing a greater distortion in its waveform than those obtained for the Et component. The more significant distortion was obtained at the end of the outer corona protection (OCP) material, corresponding to the first maximum of the En component and characterized by the appearance of a third harmonic of large amplitude.
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Klimova, L. G. "Effects of residual stresses on the bending stiffness of shafts strengthened by enveloping de-formation." Proceedings of Irkutsk State Technical University 25, no. 4 (September 1, 2021): 412–20. http://dx.doi.org/10.21285/1814-3520-2021-4-412-420.
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The aim was to study the effects of technological residual stresses on the bending stiffness of cylindrical parts of shafts and axes. Experiments were conducted for elongated cylindrical specimens made of steel grade 35 with a diameter of 30 mm using boring and turning methods. Specimens were annealed in a protective medium to remove initial residual stresses. Experiments were carried out using an Amsler laboratory hydraulic testing machine and VK8 grade hard-alloy matrices. The experiments showed that, for an extremely low degree of relative crimping of 0.1 to 0.5%, the size of the layer with tangential residual compression stresses gradually decreases. The stiffness of such cylindrical workpieces remains almost unchanged. An increase in relative crimping (from 0.5 to 1.2%) leads to a decrease in resi dual compression stresses on the part surface. The layer thickness with tangential residual compression stresses starts to increase. This leads to a decreased residual buckling and an increased bending stiffness. It was found that the degree of relative crimping has no effect on the variation of distribution depth of axial residual stresses. Optimal distribution of tangential residual compression stresses can be reached by increasing their depth. A linear relationship was found for relative crimping of 0.1 to 1.0%. The highest bending resistance was recorded for specimens strengthened by residual crimping of about 1.0%. By processing workpieces using enveloping deformation with crimping of 0.1% and loading them with a transverse force of 0.6 kN, bending distortion can be decreased and the strength of parts can be increased by 5 times. It was found that the bending stiffness of cylindrical shafts is greatly affected by residual compression stresses. The bedding depth of residual stresses has various effects on the stiffness of cylindrical parts. Thus, correct use of strengthening enveloping deformation can form a high-quality surface layer on parts with the pre-defined distribution of residual stresses.
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Zhang, Jun, Long Ye, Qin Zhang, and Jing Ling Wang. "Three-Dimensional Object Surface Reconstruction Based on Camera Calibration and SIFT." Applied Mechanics and Materials 719-720 (January 2015): 1191–97. http://dx.doi.org/10.4028/www.scientific.net/amm.719-720.1191.
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This paper is focused on camera calibration, image matching, both of which are the key issues in three-dimensional (3D) reconstruction. In terms of camera calibration firstly, we adopt the method based on the method proposed by Zhengyou Zhang. In addition to this, it is selective for us to deal with tangential distortion. In respect of image matching, we use the SIFT algorithm, which is invariant to image translation, scaling, rotation, and partially invariant to illumination changes and to affine or 3D projections. It performs well in the follow-up matching the corresponding points. Lastly, we perform 3D reconstruction of the surface of the target object. A Graphical User Interface is designed to help us to realize the key function of binocular stereo vision, with better visualization. Apparently, the entire GUI brings convenience to the follow-up work.
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Qiao, Zhaowei, and Yutian Sun. "Analysis of Electromagnetic Force on Rotor End Windings of a 300 MW Variable-Speed Generator Motor for Pumped Storage." Mathematical Problems in Engineering 2020 (May 5, 2020): 1–6. http://dx.doi.org/10.1155/2020/6493581.
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The variable-speed generator motor (VSGM) for pumped storage has a cylindrical rotor with three-phase lap or wave windings distributed in slots evenly and fed by a converter. For a large-scale VSGM, the electromagnetic force (EMF) on rotor end windings is an important contributor to distortion, vibration, and even damage of rotor end windings. A 3D finite element model of rotor end region of a 300 MW VSGM is set up. The distribution map of EMF density on involute and nose parts of rotor end windings, under rated load and three-phase short circuit at supersynchronous and subsynchronous speed, is drawn. Furthermore, the amplitude of EMF is calculated, and the radial, tangential, and axial components of EMF are analyzed. The results in this paper will lay a foundation for design of rotor end windings and their support structure.
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Garg, Manish, B. S. Salaria, and V. K. Gupta. "Modeling creep in a variable thickness rotating FGM disc under varying thermal gradient." Engineering Computations 32, no. 5 (July 6, 2015): 1230–50. http://dx.doi.org/10.1108/ec-02-2014-0028.
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Purpose – The purpose of this paper is to investigate steady state creep behavior of a functionally graded rotating disc under varying thermal gradient (TG). Design/methodology/approach – The steady state creep in a rotating FGM disc with linearly varying thickness has been investigated by using von-Mises yield criterion. The disc under investigation is assumed to be made of FGM containing non-linear distribution of silicon carbide particle (SiCp) in a matrix of pure aluminum along the radial distance. The creep behavior of the FGM composite disc is described by threshold stress-based law. The stresses and strain rates in the FGM disc have been estimated for different kinds of TG. Findings – The results indicate that when the FGM disc is subjected to a radial TG, with temperature increasing with increasing radius, the radial stress in the disc increases over the entire disc but the tangential and effective stresses increase near the inner radius and decrease toward the outer radius. The imposition of such a radial TG in the FGM disc leads to significant reduction in the radial and tangential strain rates. With the increase in magnitude of TG in the FGM disc, the inhomogeneity in creep stresses increases but the inhomogeneity in strain rates decreases significantly, thereby reducing the chances of distortion in the FGM disc. Originality/value – The creep strain rates in rotating FGM disc could be significantly reduced when the disc is subjected to a radial TG, with temperature increasing with increasing radius.
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NEFF, PATRIZIO, KRZYSZTOF CHEŁMIŃSKI, and HANS-DIETER ALBER. "NOTES ON STRAIN GRADIENT PLASTICITY: FINITE STRAIN COVARIANT MODELLING AND GLOBAL EXISTENCE IN THE INFINITESIMAL RATE-INDEPENDENT CASE." Mathematical Models and Methods in Applied Sciences 19, no. 02 (February 2009): 307–46. http://dx.doi.org/10.1142/s0218202509003449.
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We propose a model of finite strain gradient plasticity including phenomenological Prager type linear kinematical hardening and nonlocal kinematical hardening due to dislocation interaction. Based on the multiplicative decomposition, a thermodynamically admissible flow rule for Fp is described involving as plastic gradient Curl Fp. The formulation is covariant w.r.t. superposed rigid rotations of the reference, intermediate and spatial configuration but the model is not spin-free due to the nonlocal dislocation interaction and cannot be reduced to a dependence on the plastic metric [Formula: see text]. The linearization leads to a thermodynamically admissible model of infinitesimal plasticity involving only the Curl of the nonsymmetric plastic distortion p. Linearized spatial and material covariance under constant infinitesimal rotations is satisfied. Uniqueness of strong solutions of the infinitesimal model is obtained if two non-classical boundary conditions on the plastic distortion p are introduced: [Formula: see text] on the microscopically hard boundary ΓD ⊂ ∂Ω and [ Curl p] · τ = 0 on the microscopically free boundary ∂Ω\ΓD, where τ are the tangential vectors at the boundary ∂Ω. A weak reformulation of the infinitesimal model allows for a global in-time solution of the rate-independent initial boundary value problem. The method is based on a mixed variational inequality with symmetric and coercive bilinear form. We use a new Hilbert-space suitable for dislocation density dependent plasticity.
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Yanze, Long, Zhang Ke, Shi Huaitao, Li Songhua, and Zhang Xiaochen. "Theoretical and Experimental Analysis of Thin-Walled Curved Rectangular Box Beam under In-Plane Bending." Scanning 2021 (April 30, 2021): 1–19. http://dx.doi.org/10.1155/2021/8867142.
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Thin-walled curved box beam structures especially rectangular members are widely used in mechanical and architectural structures and other engineering fields because of their high strength-to-weight ratios. In this paper, we present experimental and theoretical analysis methods for the static analysis of thin-walled curved rectangular-box beams under in-plane bending based on 11 feature deformation modes. As to the numerical investigations, we explored the convergence and accuracy analysis by normal finite element analysis, higher-order assumed strain plane element, deep collocation method element, and inverse finite element method, respectively. The out-of-plane and in-plane characteristic deformation vector modes derived by the theoretical formula are superimposed by transforming the axial, tangential, and the normal deformation values into scalar tensile and compression amounts. A one-dimensional deformation experimental test theory is first proposed, formulating the specific contributions of various deformation modes. In this way, the magnitude and trend of the influence of each low-order deformation mode on the distortion and warping in the actual deformation are determined, and the significance of distortion and warping in the actual curved beams subjected to the in-plane loads is verified. This study strengthens the deformation theory of rectangular box-type thin-walled curved beams under in-plane bending, thus providing a reference for analyzing the mechanical properties of curved-beam structures.
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Chen, Juntao, Yang Yang, Chao Ye, Ying Yang, and Ming Xiao. "Three-Dimensional Numerical Analysis of Compound Lining in Complex Underground Surge-Shaft Structure." Mathematical Problems in Engineering 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/387379.
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The mechanical behavior of lining structure of deep-embedded cylinder surge shaft with multifork tunnel is analyzed using three-dimensional nonlinear FEM. With the elastic-plastic constitutive relations of rock mass imported and the implicit bolt element and distributed concrete cracking model adopted, a computing method of complex surge shaft is presented for the simulation of underground excavations and concrete lining cracks. In order to reflect the interaction and initial gap between rock mass and concrete lining, a three-dimensional nonlinear interface element is adopted, which can take into account both the normal and tangential characteristics. By an actual engineering computation, the distortion characteristics and stress distribution rules of the dimensional multifork surge-shaft lining structure under different behavior are revealed. The results verify the rationality and feasibility of this computation model and method and provide a new idea and reference for the complex surge-shaft design and construction.
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Garg, Manish, B. S. Salaria, and V. K. Gupta. "Effect of Disc Geometry on the Steady State Creep in a Rotating Disc Made of Functionally Graded Materials." Materials Science Forum 736 (December 2012): 183–91. http://dx.doi.org/10.4028/www.scientific.net/msf.736.183.
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The steady state creep behaviour of a rotating FGM disc having linearly varying thickness has been investigated. The disc is assumed to be made of functionally graded composite containing non-linearly varying radial distribution of silicon carbide particles in a matrix of pure aluminum. The creep behaviour of the composite has been described by threshold stress based law. The effect of varying the disc thickness gradient has been analyzed on the stresses and strain rates in the FGM disc. It is observed that the radial and tangential stresses induced in the FGM disc decrease throughout with the increase in thickness gradient of the disc. The strain rates also decrease with the increase in thickness gradient of the FGM disc, with a relatively higher decrease near the inner radius. The increase in disc thickness gradient results in relatively uniform distribution of strain rates and hence reduces the chances of distortion in the disc.
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Guérin, S., and A. Holewa. "Fan tonal noise from aircraft aeroengines with short intake: A study at approach." International Journal of Aeroacoustics 17, no. 6-8 (August 7, 2018): 600–623. http://dx.doi.org/10.1177/1475472x18789001.
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This work assesses the risks of increased fan noise for high bypass ratio aeroengines with short intakes. The close proximity between the fan and inlet contributes to the increase in radiation of the rotor-alone tones and reinforces the interaction of the inflow distortion with the fan. Thus, the closer the fan is to the inlet, the higher the risk for noise generation. This article discusses the results of Harmonic Balance simulations performed on a conceptual turbofan operated at the approach condition. The inflow distortion created by the nacelle incidence is dominated by the circumferential component [Formula: see text] = 1. Its presence is visible throughout the nacelle. A thorough analysis of the unsteady pressure and velocity fields shows that the new acoustic source created by the periodic unsteady loading of the rotor cutting the inflow distortion is negligible compared to the rotor–stator interaction. But the amplitude of the rotor–stator interaction tones is affected by the unsteadiness of the rotor wake shape, particularly in the tip region where a pronounced flow separation on the rotor blade is created at a certain range of azimuthal position. The variations of the flow incidence at the rotor leading edge, due to the axial and tangential components of the mean velocity, cannot explain that flow separation. Instead, the origin is attributed to the azimuthal variations of the radial component of the mean flow velocity near the casing which slightly points inward to the spinner, i.e. in the opposite direction of the casing contour line. The flow separation induces a pronounced scattering of the wake azimuthal components mw = hB into [Formula: see text] in the tip region, whereas the same effect is rather limited on the rest of the blade height. This leads to a moderate increase of the tonal sound power level compared to the case with clean inflow. The azimuthal scattering due to the propagation of the sound waves through the distortion is found to be weak in the bypass duct. However, this effect is very important in the inlet lip vicinity, where the strong asymmetry of the flow modifies the path of the sound waves up to the far field.
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Teixeira, M. A. C., and C. B. da Silva. "Turbulence dynamics near a turbulent/non-turbulent interface." Journal of Fluid Mechanics 695 (February 13, 2012): 257–87. http://dx.doi.org/10.1017/jfm.2012.17.
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AbstractThe characteristics of the boundary layer separating a turbulence region from an irrotational (or non-turbulent) flow region are investigated using rapid distortion theory (RDT). The turbulence region is approximated as homogeneous and isotropic far away from the bounding turbulent/non-turbulent (T/NT) interface, which is assumed to remain approximately flat. Inviscid effects resulting from the continuity of the normal velocity and pressure at the interface, in addition to viscous effects resulting from the continuity of the tangential velocity and shear stress, are taken into account by considering a sudden insertion of the T/NT interface, in the absence of mean shear. Profiles of the velocity variances, turbulent kinetic energy (TKE), viscous dissipation rate ($\varepsilon $), turbulence length scales, and pressure statistics are derived, showing an excellent agreement with results from direct numerical simulations (DNS). Interestingly, the normalized inviscid flow statistics at the T/NT interface do not depend on the form of the assumed TKE spectrum. Outside the turbulent region, where the flow is irrotational (except inside a thin viscous boundary layer),$\varepsilon $decays as${z}^{\ensuremath{-} 6} $, where$z$is the distance from the T/NT interface. The mean pressure distribution is calculated using RDT, and exhibits a decrease towards the turbulence region due to the associated velocity fluctuations, consistent with the generation of a mean entrainment velocity. The vorticity variance and$\varepsilon $display large maxima at the T/NT interface due to the inviscid discontinuities of the tangential velocity variances existing there, and these maxima are quantitatively related to the thickness$\delta $of the viscous boundary layer (VBL). For an equilibrium VBL, the RDT analysis suggests that$\delta \ensuremath{\sim} \eta $(where$\eta $is the Kolmogorov microscale), which is consistent with the scaling law identified in a very recent DNS study for shear-free T/NT interfaces.
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Moorthy, V. "Unique correlation between non-linear distortion of tangential magnetic field and magnetic excitation voltage – Unexplored ferromagnetic phenomena and their application for ferromagnetic materials evaluation." Journal of Magnetism and Magnetic Materials 398 (January 2016): 101–8. http://dx.doi.org/10.1016/j.jmmm.2015.09.029.
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Filipenco, V. G., S. Deniz, J. M. Johnston, E. M. Greitzer, and N. A. Cumpsty. "Effects of Inlet Flow Field Conditions on the Performance of Centrifugal Compressor Diffusers: Part 1—Discrete-Passage Diffuser." Journal of Turbomachinery 122, no. 1 (February 1, 1998): 1–10. http://dx.doi.org/10.1115/1.555418.
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This is Part 1 of a two-part paper considering the performance of radial diffusers for use in a high-performance centrifugal compressor. Part 1 reports on discrete-passage diffusers (shown in Fig. 1) while Part 2 describes a test of a straight-channel diffuser designed for equivalent duty. Two builds of discrete-passage diffuser were tested, with 30 and 38 separate passages. Both the 30 and 38 passage diffusers investigated showed comparable range of unstalled operation and similar level of overall diffuser pressure recovery. The paper concentrates on the influence of inlet flow conditions on the pressure recovery and operating range of radial diffusers for centrifugal compressor stages. The flow conditions examined include diffuser inlet Mach number, flow angle, blockage, and axial flow nonuniformity. The investigation was carried out in a specially built test facility, designed to provide a controlled inlet flow field to the test diffusers. The facility can provide a wide range of diffuser inlet velocity profile distortion and skew with Mach numbers up to unity and flow angles of 63 to 75 deg from the radial direction. The consequences of different averaging methods for the inlet total pressure distributions, which are needed in the definition of diffuser pressure recovery coefficient for nonuniform diffuser inlet conditions, were also assessed. The overall diffuser pressure recovery coefficient, based on suitably averaged inlet total pressure, was found to correlate well with the momentum-averaged flow angle into the diffuser. Furthermore, the pressure recovery coefficient was found to be essentially independent of the axial distortion at diffuser inlet, and the Mach number, over the wide flow range (from maximum flow to the beginning of flow instabilities) investigated. It is thus shown that the generally accepted sensitivity of diffuser pressure recovery performance to inlet flow distortion and boundary layer blockage can be largely attributed to inappropriate quantification of the average dynamic pressure at diffuser inlet. Use of an inlet dynamic pressure based on availability or mass-averaging in combination with definition of inlet flow angle based on mass average of the radial and tangential velocity at diffuser inlet removes this sensitivity. [S0889-504X(00)00101-X]
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Pearson, Hamish, Brian Gabbitas, and Sigurdur Ormarsson. "Tensile behaviour of radiata pine with different moisture contents at elevated temperatures." Holzforschung 66, no. 5 (July 1, 2012): 659–65. http://dx.doi.org/10.1515/hf-2011-0185.
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Abstract The aim of this study was to obtain tensile elastic modulus (EM) information for radiata pine (Pinus radiata D. Don) sapwood in tangential grain direction, over a temperature range of 70°C to 150°C for a wide range of moisture contents. Such information is scarce, probably because of difficulties with research equipment design and process control strategies to perform accurate tests. As expected, EM dramatically decreased with increasing temperature and moisture content. The results were modelled to yield a relationship between stress and strain. The results were also successfully transposed into a mastercurve based on temperature-moisture equivalence through a modified form of the Williams, Landel, and Ferry equation for amorphous polymers. This result is consistent with the view that wood is visco-plastic around the glass transition zone of the ligno-hemicellulosic matrix. It is demonstrated that moisture and temperature can play a significant role in reducing stress during drying, regardless of the drying time. Properties of wood, such as tensile elastic information at elevated temperatures, are important for mechanical design, distortion modelling and understanding the fundamental behaviour of wood in general.
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Ogata, Yoshiyuki, and Minoru Fujita. "Z-Axis Calibration in Optical Sectioning from Xylem Cross Sections for Grain Angle Measurement." IAWA Journal 26, no. 4 (2005): 427–41. http://dx.doi.org/10.1163/22941932-90000125.
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Optical sectioning using confocal microscopy may be problematic under some conditions due to contamination with light from outside the focal plane and resulting z-axis compression. These problems can affect quantitative wood anatomy, such as grain angle measurement. In the present report, the exact surface of xylem sections, z-axis scaling, and available scanning depth with confocal microscopy were determined in xylem transverse sections of Japanese cedar (Cryptomeria japonica D. Don). The optical section containing the sample surface was determined using power spectral analysis to find the sharpest image. Image cross-correlation analysis in serial transverse optical sections revealed that the optical sections above the sample surface showed no tangential shift with that of the surface, indicating the non-focal cell wall information. Optical sections using an oil immersion lens with oil and a dry lens without oil were compared. Optical sections with an oil lens were relatively precise while those with a dry lens showed a z-axis distortion of about ×1.5 due to the mismatch of refractive index. Therefore, the exact cell orientation angle without oil can be obtained by the two-thirds multiplication. Adequate cell wall information was available up to c. 80 μm deep.
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Huang, He, Yizhou Xue, and Dean Luo. "Camera Rapid Calibration Method for Mobile Road Measurement System." Journal of Imaging Science and Technology 64, no. 4 (July 1, 2020): 40406–1. http://dx.doi.org/10.2352/j.imagingsci.technol.2020.64.4.040406.
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Abstract In recent years, a variety of mobile road measurement equipment has emerged and become an important means of collecting spatial information. As an important part of the mobile road measurement system, a camera’s function implementation and data accuracy largely depend on its internal parameters and the rotation and translation parameters corresponding to the world coordinate system. Based on this and on the traditional camera calibration method, radial and tangential distortion for monocular camera calibration is introduced in this article to establish a calibration model, and the nonlinear least-squares Levenberg‐Marquardt optimization algorithm is used in iterative calculation. The parameters provide a solution to the problem of rapid calibration of camera modules in mobile road measurement systems. The camera parameters obtained by the calibration algorithm in this study are used for visual reconstruction. Compared with two Zhang Zhengyou calibration methods optimized by the Gauss‐Newton method, the former has an average pixel offset of 0.28 pixel and the latter has deviations of 0.66 and 0.38 pixel. Using a monocular camera to collect data on geometric targets on a road, the average relative error does not exceed 2.16%. Experiments show that this method can obtain calibration results quickly and accurately.
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Brainerd, Tereasa G., Roger D. Blandford, and Ian Smail. "Weak Lensing By Individual Galaxies." Symposium - International Astronomical Union 173 (1996): 183–88. http://dx.doi.org/10.1017/s0074180900231252.
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In this paper we report on an investigation of statistical weak gravitational lensing of cosmologically distant faint galaxies by foreground galaxies. The signal we seek is a distortion of the images of faint galaxies resulting in a weakly preferred tangential alignment of faint galaxies around brighter galaxies. That is, if the faint galaxies have been gravitationally lensed by the brighter systems, the major axes of their images will tend to lie perpendicular to the radius vectors joining the centroids of the faint and bright galaxies (Fig. 1). Modeling a lens galaxy as a singular isothermal sphere with circular velocity Vc, an ellipticity of ∼ 2πVc2 /c2θ is induced in the image of a source galaxy at an angular separation θ from the lens. This is of order a few percent for faint–bright galaxy pairs with separations θ ∼ 30″ where the lens is a typical bright spiral. Over 1000 pairs must be measured in order to detect such a signal in the presence of the noise associated with the intrinsic galaxy shapes. Given a sufficiently large number of pairs, it may be possible to use the variation of the induced ellipticity with θ to study the angular extent of the halos of the lens galaxies.
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Sun, Cong, Haibo Liu, Mengna Jia, and Shengyi Chen. "Review of Calibration Methods for Scheimpflug Camera." Journal of Sensors 2018 (2018): 1–15. http://dx.doi.org/10.1155/2018/3901431.
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The Scheimpflug camera offers a wide range of applications in the field of typical close-range photogrammetry, particle image velocity, and digital image correlation due to the fact that the depth-of-view of Scheimpflug camera can be greatly extended according to the Scheimpflug condition. Yet, the conventional calibration methods are not applicable in this case because the assumptions used by classical calibration methodologies are not valid anymore for cameras undergoing Scheimpflug condition. Therefore, various methods have been investigated to solve the problem over the last few years. However, no comprehensive review exists that provides an insight into recent calibration methods of Scheimpflug cameras. This paper presents a survey of recent calibration methods of Scheimpflug cameras with perspective lens, including the general nonparametric imaging model, and analyzes in detail the advantages and drawbacks of the mainstream calibration models with respect to each other. Real data experiments including calibrations, reconstructions, and measurements are performed to assess the performance of the models. The results reveal that the accuracies of the RMM, PLVM, PCIM, and GNIM are basically equal, while the accuracy of GNIM is slightly lower compared with the other three parametric models. Moreover, the experimental results reveal that the parameters of the tangential distortion are likely coupled with the tilt angle of the sensor in Scheimpflug calibration models. The work of this paper lays the foundation of further research of Scheimpflug cameras.
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Xiong, Shangmin, Seung-Yub Lee, and Ismail Cevdet Noyan. "Average and local strain fields in nanocrystals." Journal of Applied Crystallography 52, no. 2 (February 26, 2019): 262–73. http://dx.doi.org/10.1107/s1600576719000372.
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This article presents a rigorous and self-consistent comparison of lattice distortion and deformation fields existing in energy-optimized pseudo-spherical gold nanoparticles obtained from real-space and powder diffraction strain analysis techniques. The changes in atomic positions resulting from energy optimization (relaxation) of ideally perfect gold nanoparticles were obtained using molecular dynamics modeling. The relaxed atomic coordinates were then used to compute the displacement, rotation and strain components in all unit cells within the energy-optimized (relaxed) particles. It was seen that all of these terms were distributed heterogeneously along the radial and tangential directions within the nanospheroids. The heterogeneity was largest in the first few atomic shells adjacent to the nanoparticle surface, where the continuity of crystal lattice vectors originating from the interior layers was broken because of local lattice rotations. These layers also exhibited maximum shear and normal strains. These (real-space) strain values were then compared with the average lattice strains obtained by refining the computed diffraction patterns of such particles. The results show that (i) relying solely on full-pattern refinement techniques for lattice strain analysis might lead to erroneous conclusions about the dimensionality and symmetry of deformation within relaxed nanoparticles; (ii) the lattice strains within such relaxed particles should be considered `eigenstrains' (`inherent strains') as defined by Mura [Micromechanics of Defects in Solids, (1991), 2nd ed., Springer]; and (iii) the stress/strain state within relaxed nanoparticles cannot be analyzed rigorously using the constitutive equations of linear elasticity.
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Prasad, Anil. "Evolution of Upstream Propagating Shock Waves From a Transonic Compressor Rotor." Journal of Turbomachinery 125, no. 1 (January 1, 2003): 133–40. http://dx.doi.org/10.1115/1.1516813.
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The evolution of upstream propagating shock waves from the isolated transonic compressor designated NASA Rotor-35 is examined numerically. Results from the numerical simulations are compared with those from a semi-analytical two-dimensional model based on the nonlinear acoustic interaction of shock waves in the axial-tangential plane upstream of the rotor. The evolution determined from a two-dimensional viscous computational solution is found to agree well with the semi-analytical prediction and confirms that shock wave evolution is a primarily inviscid phenomenon. Radial variations are found to increase the rate of decay of the shock wave amplitude in comparison to the prediction from the semi-analytical two-dimensional model. The velocity field from the three-dimensional viscous solution compares well with experimental measurements, indicating that the initial shock strength and shock wave evolution immediately upstream of the rotor blade leading edge are accurately captured. The upstream-propagating shock system is found responsible for nearly 20% of the total loss attributable to the rotor, and is consistent with earlier transonic airfoil cascade studies. The axial decay rate of the upstream induced circumferential static pressure distortion is found to be an order of magnitude slower at spanwise locations with supersonic relative inlet Mach numbers than those at which it is subsonic. As a consequence of this slower decay rate, it is found that the axial gap to the upstream stator would need to be about twice that used for subsonic blade sections.
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Ebner, Florian H., Maximilian Kleiter, Sören Danz, Ulrike Ernemann, Bernhard Hirt, Hubert Löwenheim, Florian Roser, and Marcos Tatagiba. "Topographic Changes in Petrous Bone Anatomy in the Presence of a Vestibular Schwannoma and Implications for the Retrosigmoid Transmeatal Approach." Operative Neurosurgery 10, no. 3 (September 1, 2014): 481–86. http://dx.doi.org/10.1227/neu.0000000000000454.
Full textAbstract:
AbstractBACKGROUND:The maneuver of transmeatal drilling carries the risk of injuring inner ear structures, which may cause immediate or delayed hearing loss.OBJECTIVE:To describe the changes in petrous bone anatomy caused by the tumor and to analyze both the incidence and the risk pattern for violation of the endolymphatic system in a surgical series.METHODS:One hundred patients operated on for vestibular schwannoma were included in this prospective study. Thin-slice computed tomography was performed before and after surgery. We assessed topographic measurements on both the pathological and healthy sides. Postoperatively, we evaluated anatomic and functional values.RESULTS:The diameter of the internal auditory canal was significantly larger (P < .001) in the petrous bones of the affected sides than in the contralateral healthy sides. An average of 5.6 ± 1.8 mm of the internal auditory canal was drilled, and the distance from the medial border of the sigmoid sinus to the drilling line (tangential to the drilled surface of the posterior lip of the internal auditory canal) was 9.8 ± 2.9 mm. A postoperative violation of the vestibular aqueduct (VA) was detected in 41 cases; the VA was intact in 55 cases; and the VA could not be clearly defined in 4 cases. The incidence of VA injury increased with increasing tumor size. In the patient group with good preoperative and postoperative hearing function, a VA injury occurred in 26% of cases, whereas the incidence increased to 67% in preoperatively deaf patients.CONCLUSION:Vestibular schwannomas cause significant distortion of the petrous bone anatomy. Detailed preoperative knowledge of the topography is necessary for the preservation of function.